Symposium Organizers
Santiago Solares, The George Washington University
Laura Fumagalli, University of Manchester
Ricardo Garcia, Consejo Superior de Investigaciones Científicas
Jason Killgore, National Institute of Standards and Technology
TC01.01: Mechanical Properties
Session Chairs
Ricardo Garcia
Jason Killgore
Monday PM, November 27, 2017
Hynes, Level 2, Room 208
8:15 AM - *TC01.01.01
Modeling and Measuring Viscoelastic Surface Forces with Intermodulation AFM
David Haviland 1 , Riccardo Borgani 1 , Per Anders Thorén 1 , Daniel Forchheimer 2
1 , KTH, Stockholm Sweden, 2 , Intermodulation Products AB, Segersta Sweden
Show AbstractDynamic AFM allows for understanding of not only the elastic character of the surface, but also its viscous nature. To measure both viscous and elastic forces we use a phase-coherent multifrequency excitation and measurement technique which locks-in on high-order intermodulation generated by the nonlinear tip-surface force and multiple drive tones. From this response in the frequency domain, we are able to subtract any linear background force, acting on the cantilever body, thus revealing only the tip-surface force [1]. We extract both quadratures of the tip-surface force, showing the conservative or elastic force (in phase with motion) and dissipative or viscous force (in phase with velocity). Both quantities are measured as a function of oscillation amplitude, at each image pixel. We can explain our measurements on soft polymers using a new type of model that treats the cantilever and surface as a two-body dynamical system, with an interaction that depends on their separation. Adhesive forces give rise to large surface motion on soft materials, with dissipation resulting from the viscous character of the material and interface. The model allows us to extract a local relaxation time on heterogeneous surfaces of crystalline and non-crystalline polymers [2].
[1] Background force compensation in dynamic atomic force microscopy. R. Borgani, P-A. Thoren, D. Forchheimer, I. Dobryden,2 S.M. Sah, P.M. Claesson, and D.B. Haviland, https://arxiv.org/abs/1701.04638
[2] Probing viscoelastic response of sot material surfaces at the nanoscale. D. B. Haviland, C.A. Van Eysden, D. Forchheimer, D. Platz, H.G. Kassa and P. Leclère. Soft Matter (2015), DOI: 10.1039/c5sm02154e
8:45 AM - TC01.01.02
Advances in Bimodal Viscoelastic Nanomechanical Mapping
Aleksander Labuda 1 , Marta Kocun 1 , Roger Proksch 1
1 , Asylum Research, Santa Barbara, California, United States
Show AbstractSimultaneous topography and mechanical property measurements have been a long-standing goal of AFM, especially obtaining complementary mechanical information during gentle tapping mode imaging. Bimodal force microscopy is a dynamic atomic force microscopy (AFM) method that excites two eigenmodes of a cantilever simultaneously [1]. The additional information provided by a second eigenmode allows the separation of topographic from mechanical properties. Combined with the benefits of operating the cantilever on resonance, bimodal force microscopy enables high-speed quantitative nanomechanical mapping across six orders of magnitude in modulus.
We present a new mathematical framework [2] for the extraction of indentation depth and Young’s modulus from bimodal AFM observables that avoids the use of fractional calculus, Laplace transforms, Gamma functions and Bessel functions, which are used by existing theories [3]. The simplicity of our proposed mathematical framework leads to an intuitive interpretation of bimodal AFM data in the context of Hertzian contact mechanics and is more transparent to the approximations required to reach analytical solutions. The proposed framework can be applied to any combination of amplitude modulation (AM) and frequency modulation (FM) for driving both eigenmodes, as in AM-AM, AM-FM, FM-AM, and FM-FM. The pros and cons of these variations will be discussed with respect to different imaging conditions.
Data acquired with the AM-FM technique, which offers robust and stable imaging while maintaining accurate nanomechanical mapping, will be presented. Furthermore, these AM-FM measurements, ranging from soft polymers to stiff metals, will be compared to bimodal cantilever dynamic simulations that were performed to provide insight into data interpretation and better understanding of the sources of variability. The benefits of using photothermal excitation [4] to drive the cantilever as well as recent efforts in accurately calibrating the stiffness and amplitude of the second eigenmode [5] will be presented, and their impact on AM-FM accuracy will be discussed.
[1] R. Garcia, R. Proksch, European Polymer Journal 49, 1897-1906 (2013)
[2] A. Labuda et al, Beilstein J. Nanotechnol. 7, 970–982 (2016)
[3] E.T. Herruzo, R. Garcia, Beilstein J Nanotechnology 3, 198-206 (2012)
[4] A. Labuda et al, Rev. Sci. Instrum. 83, 053702 (2012)
[5] A. Labuda et al, Rev. Sci. Instrum. 87, 073705 (2016)
9:00 AM - TC01.01.03
Closed-Form Solutions for the Boundary Value Problem of a Flat Punch AFM Tip Tapping on a Viscoelastic Surface with Multiple Characteristic Times
Enrique López-Guerra 1 , Santiago Solares 1
1 Mechanical Engineering, George Washington University, Washington, District of Columbia, United States
Show AbstractThe many AFM methods available offer multiple possibilities for exploring the nanomechanical properties of surfaces, including history-dependent (viscoelastic) surfaces, which are relevant in fields such as alternative energy and healthcare. Tapping-mode AFM has a privileged place due to its simplicity, stability and versatility in providing simultaneous topographical and compositional (phase) contrast. The phase contrast is relatively well understood, especially for high-Q environments, where its relation to dissipated energy and virial has been successfully established. Nevertheless, linking those energy quantities to unambiguous viscoelastic properties (e.g., relaxation times, loss modulus, storage modulus, etc.) is still a challenging open problem. Boundary value problems in linear viscoelasticity have been extensively treated since the 1960’s and generic expressions have been derived in terms of hereditary integrals, common in viscoelasticity. The challenges in using those expressions to derive closed-form solutions stem from the complexity of the viscoelastic material function and the required history conditions for the controlled parameter (force or displacement). In polymer rheology the material function has been represented through intricate models, such as spring-dashpot models with multiple characteristic times, spectral representations, and ladder models, which describe real materials well. Derivation of closed-form solutions has been generally reserved for static AFM or nanoindentation, where the deformation history is fairly controllable, such that acquisition of force-displacement quantities enables retrieval of meaningful material properties. In contrast, in tapping-mode AFM the problem is much more complex because deformation history is not measured and force is not an observable. However, through widely accepted assumptions in deformation history, and using the generalized Maxwell model with multiple relaxation times, we have developed a closed-form analytical relation between force and displacement, in addition to expressions relating the experimentally available dissipated energy and virial to real viscoelastic properties. This rigorous approach, based on the Laplace transform, allowed us to reach the counterintuitive conclusion that energy dissipation is not exclusively proportional to the loss modulus, as in the well-established dynamic mechanical analysis (DMA), but is also related to force transients arising from the intermittent-contact nature of the tip-sample interaction, and to the storage and relaxation moduli. This implies that it is not proper to conclude from phase contrast alone regarding the qualitative relation between the viscoelastic properties of different samples. This also highlights the complexities of tapping-mode AFM, where single harmonic assumptions of force and material deformation are no longer valid as they are in DMA. Our analytical developments are supported by numerical simulations.
9:15 AM - TC01.01.04
Improving the Accuracy of Atomic Force Microscope Based Nanomechanical Measurements
Bede Pittenger 1 , Shuiqing Hu 1 , Judy Mosley 1 , Lin Huang 1 , Peter De Wolf 1
1 , Bruker, Goleta, California, United States
Show AbstractThe mechanical properties and morphology of sub-micron features in materials are of interest due to their influence on macroscopic material performance and function. Atomic Force Microscopy has the resolution and force control to probe the mechanical properties of a wide range of these materials at the length scales of interest. Over the past two decades, several AFM based methods have evolved to provide mechanical mapping, each with specific strengths. These methods can be roughly divided into resonant modes (like TappingMode and Contact Resonance) and non-resonant modes (like Force Volume and PeakForce Tapping). An appropriate choice of method(s) can allow better understanding of the sample through improved accuracy, resolution or more details regarding the contact mechanics.
Although qualitative maps have long been available, accurate maps of mechanical properties have proven to be more elusive. Recently, new modes, improved modeling, better calibration, and more optimal probe design have become available, expanding the capabilities of AFM for nanomechanics. While there is still room for improvement, this has resulted in significantly improved ease-of-use and accuracy.
This presentation will review this recent progress, providing examples that demonstrate the dynamic range of the measurements, their repeatability, and the speed and resolution with which they were obtained. Examples cover the range from very soft biomaterials and cells, through polymer blends and composites, to metals and ceramics.
9:30 AM - TC01.01.05
Fundamental High Speed Limits in Single—Molecule and Nanoscale Force Spectroscopies
Carlos Amo 1 , Manuel Uhlig 1 , Ricardo Garcia 1
1 , ICMM-CSIC, Madrid Spain
Show AbstractForce spectroscopy (FS) is enhancing our understanding of single-molecule, single-cell, and nanoscale biophysical and mechanical properties1-3. FS postulates the proportionality between the interaction force and the instantaneous probe deflection, the well-known Hooke’s law. By studying the probe dynamics through numerical simulations4, we show that the total force probed by the tip has two additional contributions: the hydrodynamic (tip’s speed – dependent) and the inertial (acceleration – dependent). The amplitudes of these terms depend on the inverse of the ratio ω between the resonance frequency of the cantilever and the frequency at which the interaction is measured. As a consequence, the force−distance curve provides a faithful measurement of the interaction force between two molecules only when the inertial and hydrodynamic components are negligible, i. e, the frequency ratio ω>>1. Otherwise, FS measurements will underestimate the value of unbinding forces unless this effect is taken into account. We also developed a simple but accurate equation to succesfully correct this effect.
10:15 AM - *TC01.01.06
Beyond NanoIndentation—Å-Indentation to Investigate Interlayer Interactions and Phase Transitions in 2D Van der Waals Materials
Elisa Riedo 1 2 , Angelo Bongiorno 3 2 , Yang Gao 1 2
1 CCNY and ASRC, The City University of New York, New York, New York, United States, 2 Physics, Georgia Institute of Technology, Atlanta, Georgia, United States, 3 CSI and Graduate Center, The City University of New York, New York, New York, United States
Show AbstractTwo-dimensional (2D) materials, such as graphene and MoS2, are a few-atomic-layer thick films with strong in-plane bonds and weak interactions between the layers. The in-plane elasticity has been widely studied in bending experiments where a suspended film is deformed substantially; however, little is known about the films’ elastic modulus perpendicular to the planes, as the measurement of the out-of-plane elasticity of supported 2D films requires indentation depths smaller than the films’ interlayer distance.
Here, we present a new method to perform sub-Å-resolution indentations to measure the perpendicular-to-the-plane elasticity in 2D materials and nanotubes [1], and its implications for graphene and graphene oxide films. This method, called Å-indentation goes beyond the standard nanoindentation approach and allows for high resolution elasticity measurements of films that are atomically thin and extremely stiff.
Our indentation data, combined with semi-analytical models and density functional theory are then used to study the perpendicular elasticity of a few-layers thick graphene and graphene oxide films. We find that the perpendicular Young’s modulus of graphene oxide films reaches a maximum when one complete water layer is intercalated between the graphitic planes. This non-destructive methodology can map interlayer coupling and intercalation in 2D films. Furthermore, this method is proven to be a powerful tool to measure the elastic moduli of stiff materials, up to diamond films, with much higher resolution (both vertically and horizontally) than any other indentation method.
Finally, Å-indentation experiments revealed new phase transitions occurring in bilayer graphene on SiC.
[1] Elastic coupling between layers in two-dimensional materials, Nature Materials 14 (7), 714-720 (2015)
10:45 AM - TC01.01.07
Multidimensional Chemical Characterization of Material Properties Using Advanced, Two-Dimensional Atomic Force Spectroscopy
Jaime Colchero 1 , Jesus Sánchez-Lacasa 1
1 , Univ de Murcia, Murcia Spain
Show Abstract
Chemical sensitivity has been a target for Atomic Force Microscopy (AFM) from the beginning, unfortunately quantitative results are difficult to obtain [1]. In our opinion, one of the reasons for this difficulty is that tip-sample interaction in AFM is determined by tip-sample distance, by the tip-radius and by the material properties of the tip-sample system. In fact, according to the Derjaguin Approximation, the tip-sample force is F(d)=2π R wAB(d), where R is the tip radius, wAB(d) is the surface energy of two semi-infinite bodies of materials A and B (“chemistry”) and d is the distance between these semi-infinite bodies (“topography”). Note that experimentally a one dimensional parameter (the normal force F) is measured, which is determined by (at least) three different properties of the tip-sample system (R, w, and d). Disentangling tip radius, tip-sample distance and material properties from typical AFM spectroscopy curves is an extremely demanding task.
In this work we intend to characterize metallic and semiconductor surfaces using two parameters, the Hamaker Constant and the Contact Potential, which are related to the material properties of the tip-sample system.
Quantitative characterization of tip-sample interaction in a Atomic Force Microscopy setup is fundamental for optimum data acquisition as well as data interpretation. We use a 2dimenional spectroscopy technique (“interaction images”) to acquire AFM data I(U,d) as a function of tip sample distance d and tip sample Voltage U. Using advanced data processing of these “interaction images” allows precise separation of contact and (true) non-contact regimes; and precise separation of the Van der Waals and the electrostatic contributions to the total tip sample force. From this data, on the one hand the Hamaker constant of the tip-sample system is determined, and on the other hand the Contact Potential. A two dimensional Histogram of Hamaker constant vs. Contact Potential allows to characterize the chemical nature of the sample (more precisely the tip-sample system). Because our method is not affected by the tip radius, and because it is based on two properties that do not depend on tip-sample distance, it should exceed the performance of other AFM based techniques proposed so far for material characterization.
[1] S. Santos, C.Y. Lai, CA Amadei, K.R. Gadelrab, T.C. Tang, A. Verdaguer, V. Barcons, J. Font, J. Colchero and M. Chiesa. “The Mendeleev-Meyer force project”. Nanoscale, 8 17400-17406 (2016).
[2] E. Palacios-Lidón y J. Colchero, “Quantitative analysis of tip–sample interaction in non-contact scanning force spectroscopy”, Nanotechnology 17( 21), 5491 (2006).
11:00 AM - TC01.01.08
Are We There Yet? The Quest for Accurate and Quantitative Nanomechanical Measurements with AFM
Dalia Yablon 1
1 , SurfaceChar LLC, Sharon, Massachusetts, United States
Show AbstractAtomic force microscopy provides an inherently mechanical contact between tip and substrate. It is thus primed to measure elastic mechanical properties of materials such as modulus, adhesion, and dynamic moduli on the nanoscale. But are we there yet? Can we say today that AFM can truly perform accurate, quantitative nanomechanical measurements?
There has been significant progress since the early nanomechanical measurement days of contact mode, force volume, and phase imaging. Progress will be reviewed in force spectroscopy and contact resonance, two popular types of nanomechanical measurements that have been the focus of recent significant developments in both hardware and software in commercially available systems. These improvements include acquisition speed, calibration methods, modeling capabilities, and flexibility to collect and analyze multiple eigenmodes in the case of contact resonance. Results from application of these recently improved methods to soft materials will be discussed in the context of remaining challenges that still need to be addressed such as problems with frequency comparisons, inherent uncertainties in cantilever parameters, and modeling limitations.
11:15 AM - TC01.01.09
Temperature Dependent Mechanical Properties Using Contact Resonance Atomic Force Microscopy with Heated Cantilevers
Matthew Rosenberger 1 , Sihan Chen 1 , William King 1
1 , University of Illinois at Urbana-Champaign, Urbana, Illinois, United States
Show AbstractContact resonance atomic force microscopy (CR-AFM) is a useful technique for measuring mechanical properties at the nanometer-scale due to the high sensitivity of the contact resonance frequency to local sample mechanical properties. Temperature dependent CR-AFM would be particularly useful for the study of fundamental polymer physics and understanding the behavior of polymer composites. One obstacle to obtaining temperature dependent CR-AFM measurements is that, generally, the entire sample is heated to achieve different temperatures. Sample heating causes unwanted thermal drift and long equilibration times which prohibit rapid sweeps of temperature. A solution to this problem is to use a heated cantilever which is able to heat the sample locally. In this case, only a small volume of material heats up, so thermal drift and equilibration times are significantly reduced. Researchers have demonstrated temperature dependent measurements using heated cantilevers in the past, but these measurements have suffered from two problems: 1) the relationship between resonance frequency and contact stiffness is generally unknown and 2) the cantilever tip plastically deforms the polymer at elevated temperature, leading to unknown contact area and plastic deformation of the surface. We have recently address the first problem by developing a calibration sample which presents the cantilever tip with a series of known contact stiffnesses over which the cantilever resonant frequency can be calibrated. In this work, we present a calibration sample with contact stiffness ranging from 4 – 80 N/m, which covers the range relevant for polymer elastic moduli. To address the second problem, we track the resonance frequency while performing force curves which limits the contact time between the cantilever and sample and reduces plastic deformation. Using our cantilever calibration, we determine the contact stiffness corresponding to each measured resonance frequency. For each force curve, we obtain the contact stiffness as a function of force, which we fit with the DMT contact mechanics model to obtain the elastic modulus. We perform multiple force curves with different cantilever temperatures in order to obtain the elastic modulus as a function of temperature. In our CR-AFM measurements, we found that the elastic modulus of PTFE changes from 1.7 GPa at 23 °C to 1.1 GPa at 174 °C. From bulk sample dynamic mechanical analysis, we found that PTFE elastic modulus changed from 1.1 – 1.8 GPa over the frequency range of 0.1 – 100,000 Hz at room temperature. This result agrees with the concept of time-temperature superposition in viscoelastic materials, which states that (high temperature, high frequency) is equivalent to (low temperature, low frequency). We also measured polystyrene and PMMA and saw very little temperature dependence in polystyrene and a small temperature dependence in PMMA.
11:30 AM - TC01.01.10
Unexplored Features of the AFM Force Curve Contains Nanomechanics Information
Li Li 1 , Steven Eppell 1 , Fredy Zypman 2
1 , Case Western Reserve University, Cleveland, Ohio, United States, 2 , Yeshiva University, New York, New York, United States
Show AbstractAtomic force microscopy (AFM) is used to study the mechanical properties of materials. The snap to contact event is of particular interest as it can be used to obtain physically significant measurements in the near-surface region. Here, we report on a noise-hidden damped oscillating feature that appears just after the AFM tip comes in contact with the sample surface. This feature becomes clearly visible when we use the contact point as a reference and de-noise by auto-correlating at least 20 force-distance measurements. We demonstrate that the amplitude of this feature is independent of the absolute speed of the sample, proving that the impulse that generates the signal comes primarily from the snap to contact event. The snap to contact event causes a sharp tap on the sample surface, which induces a series of decaying rings. The amplitude and phase of these rings are determined by a combination of the cantilever and the surface mechanics. As a proof of concept, we use a damped simple harmonic oscillator to model the AFM experiment data. We are able to generate contrast images using the stiffness and viscosity parameters obtained from a polystyrene/polyethylene blend sample by using this feature.
11:45 AM - TC01.01.11
Nanotribology of 2D Materials
Clara Almeida 1 , Felipe Ptak 2 , Rodrigo Menezes 2
1 , Inmetro, Duque de Caxias Brazil, 2 , PUC-Rio, Rio de Janeiro Brazil
Show AbstractFriction is one of the oldest phenomenon known by the humanity. Friction is used in our
favor since the Stone Age ancestors, passing through the knowledge of the Egyptians and
explored for us in many areas of our daily life. Despite its use for a long time, even today,
there are fundamental open questions about this phenomenon. What are the mechanisms
responsible for energy dissipation during friction at nanoscale? What is the influence of the
crystalline orientation of the materials in the processes of friction? How can we correlate
the results obtained at the nanoscale with the phenomena that occur in the macroscopic
world?
With the current development of 2-D it is necessary to understand how such materials
behave when in contact, especially in the atomic scale. The tribological behavior of
materials at the nanoscale may present completely novel and unexpected features as
compared to their bulk counterparts. Particularly in the process of understanding and
controlling friction at the nanoscale one faces new challenges and paradigm shifts.
The nanoscale friction interaction between a sharp tip and graphene along different
crystallographic directions were investigated with friction force microscopy. Huge friction
anisotropy according to the crystallographic direction scanned is observed. That anisotropy
in graphene is tunable by the normal force and can reach values as high as 80% (the friction
is higher along the armchair direction), which represent a giant enhancement with respect to
graphite. This behavior is quite unexpected, since the linear elastic properties of graphene
(elastic constants, sound velocities, etc.) are isotropic, as expected from symmetry
considerations. These results represent a novel mechanism of energy dissipation in 2D
systems, opening new possibilities for the design and control of nano-mechanical systems
involving single layer materials.
TC01.02: Mechanical Properties and Multifrequency AFM
Session Chairs
David Haviland
Santiago Solares
Monday PM, November 27, 2017
Hynes, Level 2, Room 208
1:30 PM - *TC01.02.01
Multi-Frequency Atomic Force Microscopy for Functional Studies of Soft Materials
Laurene Tetard 1
1 NanoScience Technology Center, University of Central Florida, Orlando, Florida, United States
Show AbstractThe emergence of tools based on functional atomic force microscopy (AFM), at the forefront of nanoscale metrology, offers new means to bolster fundamental studies of previously unattainable structures in heterogeneous materials and living systems. The developments taking advantage of multi-frequency AFM for increasingly sensitive detection of a sample’s response to external stimuli have shown great promise for soft materials in materials, life and plant sciences.
In this talk, we will review the developments of our multi-frequency AFM platform for subsurface and for localized infrared spectroscopy measurements. We will discuss how the nonlinear nature of the tip-sample interaction in AFM can be utilized to synthesize new imaging modes that constitute the basis of our approach. We will illustrate the mechanisms of image formation on selected model samples and on soft heterogeneous materials. Furthermore, the potential of our multifaceted approach to obtain structural, mechanical and chemical mapping will be illustrated by our results on plant cell walls. Based on our findings, we will highlight the importance of multiscale measurements from conventional IR spectroscopy to nanoscale infrared spectroscopy as well as the significance of statistical analyses to grasp the complexity of the systems.
2:00 PM - TC01.02.02
Determination of Indentation Modulus of Thin Films of Porous Organosilicate Glass with Help of Atomic Force Acoustic Microscopy
Malgorzata Kopycinska-Mueller 1 , Andre Clausner 1 , Ehrenfried Zschech 1 , Bernd Köhler 1
1 , IKTS, Dresden Germany
Show AbstractAtomic force acoustic microscopy (AFAM) method was used to measure the indentation modulus M of thin films of porous organosilicate glass. The AFAM method utilizes the resonance frequencies of a rectangular AFM cantilever. The resonance frequencies of bending modes are determined in air and in contact with the samples surface. The shift in the resonance frequencies is caused by tip-sample interactions modeled as a spring coupling the tip to the sample surface. The stiffness of the spring is the so-called tip-sample contact stiffness k* that depends on the diameter of the contact area and the mechanical properties of the tip and the sample and can be calculated from the contact resonance frequencies. We determined the values of k* as a function of the increasing and decreasing load to ensure the elastic tip-sample interaction and asses the substrate influence.
Two sets of samples were investigated. The first set consisted of three films with thickness t ranging from 600 nm to 700 nm and porosities of 27%, 30%, and 40 %. The indentation modulus decreased with the increasing porosity from 6.8 GPa to 3.8 GPa. The results obtained by the AFAM method were in excellent agreement with these provided by nanoindentation and thus proved the reliability of the protocols established for the measurement and data analysis.
The second set of samples consisted of three samples of nominal porosity of 30 % and t of 350 nm, 200 nm, and 47 nm. The indentation moduli determined for the 350 nm and 200 nm films were 6.3 nm GPa and 7.2 GP, respectively. Taking into account the lack of dependence of M on the applied load we concluded that the results were free on the substrate influence. To determine the indentation modulus of the thinnest film, we tested it in four independent measurement series. We applied tips of relatively large radii of about 150 nm as well as standard ones with radii of less than 50 nm in different ranges of the applied load. Detailed data comparison showed that only one tip with radius < 50 nm applied within loads < 200 nN yielded results independent on the applied load. The mean M value calculated for this data set was 8.3 GPa.
The decrease of the indentation modulus with increasing porosity fit well within the expectations and previously published results. However, the increase of the indentation modulus with decreasing film thickness for the films of the same nominal porosity was surprising. In our data analysis we considered the influence of the tip radius and the resulting sample deformation in relation to the film thickness. We compared the data obtained from different measurement sets and were able to classify them into three categories, namely strongly dominated by, influenced by, and free of the substrate influence. The results of our analysis indicated that the stiffening observed for the porous films could be explained by evolution of the pore topology as a function of the film thickness.
2:15 PM - TC01.02.03
Mapping Buried Nanostructures Using SubSurface Ultrasonic Resonance Force Microscopy
Maarten van Es 1 , Abbas Mohtashami 1 , Paul van Neer 1 , Hamed Sadeghian 1
1 , TNO, Delft Netherlands
Show AbstractImaging of nanoscale structures buried in a covering material is an extremely challenging task, but is also considered extremely important in a wide variety of fields. From fundamental research into the way living cells are built up and how they react to external stimuli to process control in semiconductor manufacturing would all benefit from the capability to image nanoscale structures through arbitrary covering layers. Combining Atomic Force Microscopy (AFM) with ultrasound has been shown a promising technology to enable such imaging in various configurations. Here we report the development of an alternative method of combining AFM with ultrasound which we call SubSurface Ultrasonic Resonance Force Microscopy (SSURFM) and which is based on a combination of the two most common variants described in literature, which each have their specific strong points: Ultrasonic Force Microscopy (UFM) and Contact Resonance AFM (CR-AFM). We show the excellent performance of this combination on a number of samples designed specifically to mimic relevant conditions for the application as an in-line inspection technique in the semiconductor manufacturing process. We also discuss the physics of the contrast mechanism which is based on sensing visco-elastic properties of the sample through generating large indentations into the surface. Understanding the contrast mechanism allows us to optimize the image contrast and depth sensitivity of our method. In summary, the experimental results presented here provide possible new industrial metrology and inspection solutions for nanostructures buried below arbitrary covering layers with excellent resolution and depth sensitivity.
2:30 PM - TC01.02.04
Off-Resonance Intermittent Contact Mode AFM Using Multiple Harmonics
Marcos Penedo Garcia 1 , Hans Hug 1 2
1 , Empa-Swiss Federal Laboratories for Materials Science and Technology, Dubendorf Switzerland, 2 , University of Basel, Basel Switzerland
Show AbstractThe atomic force microscope (AFM) is a well-established tool for measuring the topography of a sample and its mechanical properties at the nanometer scale. For the latter, the tip must be brought into contact with the sample surface with a well-defined force. PeakForce Tapping is a convenient operation mode providing an excellent control of the maximal force even for very small forces. The method relies on a modulation of the sample z-position typically at a few kHz, such that the tip makes intermittent contact with the sample. The deflection of the cantilever versus time is then recorded. From the time-trace different properties such as the snap-to-contact point, sample modulus, adhesion force, dissipated energy and the peak force are extracted in real-time.
However, the PeakForce Method requires a control-system capable of real-time analysis of the cantilever deflection versus time curve, and is thus not trivial to implement. Moreover, the data rates and thus the recorded amount of data can become difficult to handle if higher modulation frequencies above 100 kHz were used.
Here we present an alternative off-resonance intermittent contact AFM operation mode that overcomes these limitations and can be implemented in any AFM system, operated under ambient conditions, in liquids, or in vacuum. Like the former method, the sample z-position is modulated at a frequency different from that of the cantilever resonance. However, instead of mapping the time trace of the cantilever deflection signal, a real-time data reduction method is employed by recording the amplitude and phase at the modulation frequency and those at several higher harmonics, i.e. only the periodic part of the signal is measured. For the distance feedback either the amplitude at the modulation frequency or a linear combination of amplitudes are used. The force-distance curve can then be reconstructed from the amplitudes and phases measured at the different harmonics. Thus, even high z-modulation frequencies of several MHz can be used provided the bandwidth of the AFM deflection sensor is sufficiently large to measure the higher harmonics. Sample mechanical properties can be extracted from the force curves at each point of the recorded topography image.
Here we studied a PS/LDPE polymer blend sample. An analysis of the recorded data allows the reconstruction of the topography of the sample, the tip-induced compression of the sample (the deviation of the as-measured topography from the real one), the adhesion map, and the local Young’s modulus. We also demonstrate this mode can be used under vacuum conditions providing an AFM operation mode capable of imaging the topography of micro-structured samples over tens of microns. Note that in vacuum, standard intermittent contact mode cannot be used, and conventional non-contact AFM operation modes are not convenient for scan ranges of several microns on samples with topographical features with heights of several hundreds of nanometers.
3:15 PM - TC01.02.05
Quantitative AM-FM Mode for Measurement of Elastic Modulus of Materials and Video-Rate AFM
Marta Kocun 1 , Aleksander Labuda 2 , Hiroaki Sugasawa 1 , Irene Revenko 1 , Ted Limpoco 1 , Mario Viani 1 , Roger Proksch 1
1 , Asylum Research Oxford Instruments, Santa Barbara, California, United States, 2 , Asylum Research Oxford Instruments, Santa Barbara, California, United States
Show AbstractAtomic Force Microscopy (AFM) is a unique and powerful tool for measuring structural, mechanical, and electrical properties of materials at the nanometer scale. Tapping mode AFM imaging, also known as amplitude modulated-atomic force microscopy, is one of the most well-known and reliable surface characterization AFM techniques. It is fast, provides high topographic resolution and is non-destructive. However, until recently, tapping mode was limited to only qualitative results. The work presented here will focus on AM-FM dual frequency technique where the first resonant mode of the cantilever is amplitude modulated (AM) and a higher resonant mode is frequency modulated (FM). This “bimodal” technique is capable of delivering topographical information, as expected from regular tapping mode, in addition to quantitative stiffness and, with appropriate models, elastic modulus of materials. We will present quantitative AM-FM imaging results on various samples such as polymers, composites and metals. Additionally, we will introduce practical video-rate AFM with improved imaging speeds that make it possible to capture movies with a temporal resolution better than a second. Examples of dynamic processes studied by video-rate AFM will include the real-time self-assembly of collagen into fibrils, the enzymatic cleaving of DNA, and the migration of surfactant micelles on graphite. Finally, we will discuss future research opportunities that might be enabled by the combination of video-rate AFM together with AM-FM dual frequency technique.
3:30 PM - TC01.02.06
Nanomechanical Characterization of Organic Self-Assembled Monolayers Using Bimodal Atomic Force Microscopy
Evangelia-Nefeli Athanasopoulou 1 , Francesco Stellacci 1
1 , EPFL, Lausanne Switzerland
Show AbstractAs technology advances, thin multilayer materials are becoming more and more attractive for a wide range of industrial applications. These complex and versatile products exhibit inhomogeneous properties, which often need to be spatially or surface resolved. The mechanical properties of such materials, generally considered an important quality indicator, are of particular interest. With the currently employed characterization techniques, nanomechanical characterization of soft matter with small indentation depths (<2nm) and small loads (<20nN) is not possible. Those are however the conditions required for the characterization of organic self-assembled monolayers (SAMs) on hard surfaces. Furthermore, direct correlation between topographical and mechanical features on a surface cannot be readily achieved. A sensitive, fast and non-destructive technique providing a local accurate description of the first few atomic layers of a surface is therefore imperative. In the presented research we investigate the applicability of bimodal Atomic Force Microscopy [1], known to yield good results in the characterization of thin polymer films, to molecularly thin soft films. The technique allows for the simultaneous topographical and nanomechanical characterization of the probed surface, giving information on surface elasticity and loss tangent.
Thiol SAMs on Au (111) have been synthesized as a model system. Surface elasticity has been reliably determined and found to be ligand-length dependent. This variation can be related to a change in the molecular ordering within the monolayer. [2] Moreover, thiolated mixed-ligand SAMs show phase separation, evident in ~10nm domain formation, that can be resolved in the mechanical images of the surface. A similar investigation has been extended to the characterization of octadecylphosphonic acid SAMs on Al2O3 [3], where surface ordering as a function of monolayer formation time was explored. The evolution of surface elasticity allows distinguishing between the consecutive steps of ligand adsorption, monolayer ordering and multilayer formation. The AFM results are in good agreement with XPS and static Contact Angle data.
Bimodal AFM can combine the high lateral resolution of conventional AFM with additional observables, from which information on nanomechanical properties can be extracted. Topographical features and nanomechanical properties can be directly correlated. Our results demonstrate that the technique allows for accurate characterization of surface nanomechanical properties in SAMs, as well as the way those scale with varying ligand length, monolayer formation time and monolayer ordering.
[1] R. Garcia and R. Proksch, Eur. Polym. J., vol. 49, no. 8, pp. 1897–1906, 2013
[2] F. W. Delrio, C. Jaye, D. A. Fischer, and R. F. Cook, Appl. Phys. Lett., vol. 94, no. 13, pp. 10–13, 2009
[3] T. Bauer, T. Schmaltz, T. Lenz, M. Halik, B. Meyer, and T. Clark, ACS Appl. Mater. Interfaces, vol. 5, no. 13, pp. 6073–80, 2013
3:45 PM - TC01.02.07
Multifrequency and the Unified Path Forward for AFM
Matteo Chiesa 1 , Sergio Santos 1 , Chia-Yun Lai 1 , Harry Apostoleris 1 , Tuza Olukan 1 , Mariam Almahri 1
1 , Khalifa University of Science and Technology, Abu Dhabi United Arab Emirates
Show AbstractThrough its ability to image in a variety of environments with very high resolution, the AFM has risen to prominence as a versatile tool to provide precise and detailed characterization of materials at the nanoscale. The rise of multifrequency AFM has been key to its value, providing a wealth of potentially useful parameters. In response to this abundance of information, AFM has come to increasingly rely on advanced computational and big data methodologies extract meaning from the “zoo of observables.” The development of these methodologies has been a major focus of research over the past several years in our group and others. In this presentation we cast this work in its broader historical and scientific context to project a pathway into the future of nanoscale materials science that makes full use of AFM’s capabilities as a measurement technique to more fully unlock the mysteries of the nanoscale world.
4:00 PM - TC01.02.08
Nanomechanical Spectroscopy of Soft-Matter with Angstrom-Scale Resolution
Ricardo Garcia 1
1 Instituto Ciencia de Materiales de Madrid, CSIC, Madrid Spain
Show AbstractA method that combines high spatial resolution, quantitative and non-destructive mapping of surfaces and interfaces is a long standing goal in nanoscale microscopy. The method would facilitate the development of hybrid devices and materials made up of nanostructures of different properties. Here we demonstrate that bimodal atomic force microscopy enables the accurate measurement of the elastic modulus of surfaces in liquid with a spatial resolution of 3 angstroms. It provides Young modulus, the peak force and the indentation. The method does not limit the data acquisition speed nor the spatial resolution of the force microscope. It is non-invasive and minimizes the influence of the tip radius on the measurements. The Young’s modulus can be determined with a relative error below 5% over a five order of magnitude range (1 MPa-100 GPa). Less than one minute is required to get a Young’s modulus map with subnanometer spatial resolution
E. T. Herruzo, A.P. Perrino and R.Garcia. Nat. Comm. 3, 3126 (2014)
R. Garcia and R. Proksch. Eur. Polym. J. 49, 1897-1906 (2013)
R. Garcia, E.T. Herruzo. Nat.Nanotech. 7, 217-226 (2012).
TC01.03: Magnetic Properties
Session Chairs
David Haviland
Santiago Solares
Monday PM, November 27, 2017
Hynes, Level 2, Room 208
4:15 PM - *TC01.03.01
Smart Magnetic Probes with Controllable States for Quantitative MFM
Olga Kazakova 1 , Vishal Panchal 1 , Hector Corte-Leon 1 , Luis Alfredo Rodríguez 2 , Volker Neu 3
1 , NPL, Teddington United Kingdom, 2 , CEMES-CNRS , Toulouse France, 3 , IFW, Dresden Germany
Show AbstractWe present a novel method for quantitative magnetic force microscopy (MFM) using smart functional magnetic probes with controllable states. A comprehensive method for visualisation and quantification of the magnetic stray field is applied to the particular cases of smart custom-made multi-layered (ML) and domain wall (DW) based probes with high/low magnetic moment states. The ML probes comprise two decoupled magnetic layers separated by a non-magnetic interlayer. V-shaped DW-probes were modified out of commercial magnetic probes using focused ion beam lithography. Both types of probes can controllably produce 4 stable magnetic states, i.e. 2 high (±ferromagnetic or DW) and 2 low (±antiferromagnetic or curl) moment states for ML and DW-probes, respectively. Direct visualisation of the stray field surrounding the probe apex using electron holography demonstrates a striking difference in the spatial distribution and strength of the magnetic flux in high/low moment states. In situ MFM studies of reference samples are used to define the probe switching fields and magnetization spatial resolution. Quantitative values of the probe magnetic moments are obtained by determining their real space tip transfer function. We also map the local Hall voltage in graphene Hall nanosensors induced by the probes in different states. The outcomes of the methods are introduced as inputs into a numerical model of Hall devices. The modelling results fully match the experimental measurements, outlining an all-inclusive method for the calibration of complex magnetic probes with a controllable low/high magnetic moment. Furthermore, a smart probe in the low moment state provide complementary information about the in-plane component of the sample’s magnetization, which is not achievable by standard methods, thus allowing for 3D reconstruction of the sample’s magnetisation.
4:45 PM - TC01.03.02
Skyrmion Spin Profiles and Supporting Dzyaloshinskii-Moriya Interaction by Quantitative Magnetic Force Microscopy
Hans Hug 1 2 , Marcos Penedo Garcia 1 , Mirko Bacani 1 , Xue Zhao 1 2 , Andrada-Oana Mandru 1 , Miguel Marioni 1
1 , Empa, Duebendorf Switzerland, 2 Department of Physics, University of Basel, Basel Switzerland
Show AbstractHigh resolution magnetic force microscopy (MFM) is an excellent tool to image the native domain state and skyrmions embedded in seed- and oxidation-protection layers such as a sample of Si/Pt/[Ir1nm/Co0.6nm /Pt1nm]×5/Pt with a superior signal-to-noise ratio and a lateral resolution below 10nm.
The average Dzyaloshinskii-Moriya (DM) interaction D, and the exchange stiffness A can be extracted from MFM data of the domain structure obtained after different demagnetization procedures. Calibrating the response of the MFM tip allows to extract all vector components of the stray field of the skyrmion from the measured MFM frequency shift image. Comparison of the field distribution obtained in this fashion for a measured skyrmion with calculated field distributions for various values of the Dzyaloshinskii-Moriya (DM) interaction D, anisotropy values Ku and exchange stiffnesses A allows the determination of local values at the position of the skyrmions.
We find that the local values of D are substantially larger than the average value, indicating that in our system skyrmions are strongly pinned. Apart from the domains and skyrmions the MFM can also record small field variations arising from a local variation of the areal magnetic moment density that can be attributed to a corresponding variation of the Co layer thickness. High-resolution and quantitative MFM is thus a powerful experimental method to assess local magnetic sample properties relevant for the development of future skyrmionic devices.
Symposium Organizers
Santiago Solares, The George Washington University
Laura Fumagalli, University of Manchester
Ricardo Garcia, Consejo Superior de Investigaciones Científicas
Jason Killgore, National Institute of Standards and Technology
TC01.04: Electrical Measurements I
Session Chairs
Laura Fumagalli
David Ginger
Tuesday AM, November 28, 2017
Hynes, Level 2, Room 208
8:30 AM - *TC01.04.01
Multimodal Microscopy for Probing Ion Motion in Soft and Hybrid Materials—From Bioelectronics to Perovskite Solar Cells
David Ginger 1
1 , University of Washington, Seattle, Washington, United States
Show AbstractIon transport in nanostructured materials underpins behaviors ranging from hysteresis in perovskite solar cells, to the efficiency of battery membranes, to the performance of bioelectronic transistors. In this talk we use correlated multimodal scanning probe microscopy methods to study structure/function relationships in ion-transporting materials, with a special emphasis on polymeric materials. In stiffer polymers, we combine electrochemical strain microscopy (ESM) in contact mode with local stiffness measurements using AM-FM AFM. These data indicate that nanoscale variations in ion uptake are associated with local changes in polymer packing that may impede ion transport to different extents within the same macroscopic film. In softer polymers, we apply combinations of non-contact time-resolved electrostatic force microscopy (trEFM) to measure ionic conductivity as a function of position, and showing that the measured local ion conductivity is well-correlated with chemical function as measured by super-resolution infrared spectroscopy. Finally, we show that combinations of these methods can be applied to a wide range of materials systems, and, by correlating them with electrical measurements probe the motion of ions in the model soft/hard inorganic hybrid perovskite methylammonium lead triiodide to better understand the origins of hysteresis and degradation in perovskite solar cells.
9:00 AM - TC01.04.02
Functional Imaging of Photovoltaics at the Nanoscale—From Perovskites to Polycrystalline Materials
Elizabeth Tennyson 1 2 , Marina Leite 1 2
1 Department of Materials Science and Engineering, University of Maryland, College Park, Maryland, United States, 2 Institute for Research in Electronics and Applied Physics, University of Maryland, College Park, Maryland, United States
Show AbstractHybrid organic-inorganic perovskites and thin-film polycrystalline solar cell materials, such as CdTe and Cu(In,Ga)Se2 (CIGS), have low fabrication costs while maintaining a high power-conversion efficiency of >22%. However, this promising performance could be improved further if the electrical properties, such as the short-circuit current (Jsc) or open-circuit voltage (Voc), primary figures-of-merit in photovoltaics (PV), were further increased. At present, the Voc of perovskites, CdTe, and CIGS devices is still >10% below the theoretical limit, and it has previously been shown that the voltage response in CIGS solar cells can vary spatially by more than 20% [1]. These thin-film materials are composed of grains and grain boundaries on the order of micro- and nanometers, respectively. The nanoscale interfaces can cause electrical charge carriers to become trapped and recombine non-radiatively, reducing the Voc locally. To understand and quantify the contribution each boundary has on the overall performance, an imaging platform that can resolve features at the nanoscale and collect its respective electrical response must be implemented [2]. Here, we probe perovskite, CdTe, and CIGS PV materials using Kelvin probe force microscopy (KPFM). In KPFM the work function difference between the sample surface and the scanning probe tip is measured. Upon illumination, the work function of the solar cell changes, due to the quasi-Fermi level splitting (Δµ) at the p-n junction. Since the Voc is proportional to Δµ we can directly map this figure-of-merit with nanoscale resolution 5 orders of magnitude better than previous results [3]. In perovskites, we discover Voc local variations >300 mV under 1-sun illumination and a residual voltage behavior that remains ~9 min post-illumination. Such observations are only obtained through utilizing fast-KPFM, where we show rapid imaging, 16 s/scan, 100x faster than conventional modes [4]. Within CdTe, we distinguish two grain boundaries with different electrical responses; one in which the boundary reduces the Voc by 60 mV, and another that behaves benign [3]. This indicates that only some CdTe grain interfaces are sources of non-radiative recombination, and fabrication parameters must be adjusted to suppress these sites. Further, we observe voltage variations >250 mV in a CIGS solar cell, never measured before. Overall, we demonstrate that KPFM is a non-destructive, universal functional imaging tool that can be realized to map any photovoltaic or optoelectronic material. We anticipate our imaging method to be widely implemented as a diagnostic tool for the rational design of photovoltaics with improved electrical performance and, thus, performance.
[1] E.M. Tennyson et al., ACS Energy Lett., 1, 899 (2016)
[2] E.M. Tennyson et al., ACS Energy Letters, 2, 1825 (2017) Invited Perspective
[3] E.M. Tennyson et al., Adv. Eng. Mat., 5, 1501142 (2015) Front Cover
[4] J.L. Garrett, E.M. Tennyson, et al., Nano Lett., 17, 2554 (2017)
9:15 AM - TC01.04.03
Achieving Sub-Cycle Measurements of Capacitance and Photocapacitance in a Scanning Probe Microscope Experiment by Using a Microcantilever as a Gated Mechanical Integrator
Ryan Dwyer 1 , Sarah Nathan 1 , John Marohn 1
1 , Cornell University, Ithaca, New York, United States
Show AbstractElectric force microscopy (EFM) and Kelvin probe force microscopy have revealed an enormous amount of useful information about organic semiconductor materials by enabling measurements of charge generation, injection, transport, and trapping with high spatial resolution. To test theories of charge generation and recombination, however, one also needs to follow sample properties with high temporal resolution. Light-induced charge generation and recombination is typically studied using nanosecond-resolution time-resolved microwave conductivity, but the technique has no spatial resolution [1]. Ginger and coworkers introduced time-resolved EFM (tr-EFM), in which transient photocapacitance is followed by observing the cantilever’s oscillation frequency with microsecond temporal resolution, and showed that the photocapacitance charging rate measured by tr-EFM was proportional to the external quantum efficiency in benchmark organic photovoltaic systems [2]. For charging rates faster than half a cantilever oscillation period (e.g., 1.5 microseconds), however, the demodulated cantilever frequency cannot be clearly interpreted because the cantilever’s oscillation spectrum violates the requirements of Bedrosian’s product theorem for analytic signals [3].
We introduce a new method for measuring photocapacitance transients with a scanning-probe microscope that sidesteps this seemingly fundamental limit. In our experiment [4], a voltage pulse is applied to charge the cantilever while a light pulse is applied to generate free charges in the sample. These sample charges shift the cantilever’s frequency and phase of oscillation. Snapshots of the sample’s evolving photocapacitance are obtained by recording the net change in cantilever phase as a function of the time delay between the light and voltage pulses. The cantilever in this experiment is essentially acting as a gated mechanical integrator. We demonstrate the method by using it to reveal a biexponential photocapacitance buildup in a polymer-blend solar-cell film, PFB:F8BT on ITO, with the fast component having a risetime of 40 microseconds at high light intensity. We demonstrate the superior signal-to-noise and time resolution of the new method by using it to record the 10’s of nanoseconds probe-wiring time constant of our apparatus in ca. 100 ms of total acquisition time.
[1] (a) Coffey, D. C.; et al. & Rumbles, G. J. Phys. Chem. C, 2012, 116:8916; (b) Ward, A. J.; et al. & Samuel, I. D. W. Adv. Mater., 2015, 27:2496; and (c) Ihly, R.; et al.; Rumbles G. & Blackburn, J. L. Nature Chem., 2016, 8:603.
[2] (a) Coffey, D. C. & Ginger, D. S Nat. Mater., 2006, 5:735; (b) Giridharagopal, R.; et al. & Ginger, D. S Nano Lett., 2012, 12:893; and (c) Karatay, D.U; et al. & Ginger, D.S. Rev. Sci. Instrum., 2016, 87:053702.
[3] (a) Boashash, B. Proc. IEEE, 1992, 80:520 and (b) Rihaczek, A. & Bedrosian, E. Proc. IEEE, 1966, 54:434.
[4] Dwyer, R. P.; Nathan, S. R. & Marohn, J. A. Sci. Adv., 2017, 3:e1602951.
10:00 AM - *TC01.04.04
Nanoscale Dielectric Microscopy in Materials and Life Sciences
Gabriel Gomila 1 2 , Laura Fumagalli 3
1 , Universitat de Barcelona, Barcelona Spain, 2 , Institute for Bioengineering of Catalonia, Barcelona Spain, 3 , University of Manchester, Manchester United Kingdom
Show AbstractI will present recent advances on the measurement of the dielectric properties of materials at the nanoscale by means of electrostatic force microscopy. I will first show some methodological improvements reached recently, including a method to get rid of topographic effects in the quantification of the dielectric properties of highly non-planar samples and a procedure to select the best measuring frequency when imaging the dielectric properties under liquid conditions. Then I will show some general applications of the technique including the imaging of buried nanostructures or the monitoring of the hydration properties of biological samples like bacterial cells and bacterial endospores.
10:30 AM - TC01.04.05
An Improved Treatment of the Scanning Kelvin Probe Microscopy Experiment to Track Coupled Slow and Fast Dynamics in Cesium Lead Bromide Perovskite
Ali Moeed Tirmzi 1 , Ryan Dwyer 1 , Tobias Hanrath 1 , John Marohn 1
1 , Cornell University, Ithaca, New York, United States
Show Abstract
To interpret Scanning Kelvin Probe Microscopy (SKPM) and Electric Force Microscopy (EFM) measurements, it is standard to assume that the tip-sample charge adjusts instantaneously, i.e. on a timescale fast compared to cantilever period, to changes in the applied tip voltage and the cantilever position. While this assumption holds for most organic and inorganic samples, the breakdown of this assumption can have a profound effect on the interpretation of experimental observations. Here we show the breakdown of this assumption on a technologically relevant photovoltaic sample, cesium lead bromide perovskite.
In our experiment we applied light to the sample. As we increased the light intensity, the apparent capacitance increased nonlinearly while the sample induced dissipation increased nonlinearly, reached a maximum, and then decreased. To understand these extremely puzzling observations, we developed a more rigorous treatment of the SKPM experiment in which Lagrangian mechanics was used to model the coupled motion of the cantilever tip and charges in the cantilever and the sample. In this treatment, the measured frequency shift and sample-induced dissipation depend explicitly on the complex sample impedance.2 This treatment revealed that the apparently puzzling photocapacitance increase and dissipation had a common origin -- a monotonic decrease in the sample RC time with light intensity, from sub-millisecond in the dark to sub-microsecond at high intensity. We independently validated this sample-RC finding by performing a variant of Broadband Local Dielectric Spectroscopy (BDLS) as a function of illumination intensity. The resulting data confirmed that we were indeed causing a transition from the fast-response limit to slow-response limit by increasing the background light intensity applied to the sample.1
Surprisingly, we found that sample’s RC time constant relaxed on the seconds time scale (at room temperature) when the light was turned off. We measured this relaxation time versus temperature and obtained an activation energy for the relaxation process. To explain the anomalously slow relaxation, we propose a picture in which ion-associated trapping centers cause this slow relaxation. This slow relaxation of sample conductivity in the dark provides direct evidence for coupled slow and fast dynamics in cesium lead bromide perovskite.
1) Tirmzi, A. M.; Dwyer, R. P.; Hanrath, T.; Marohn, J. A. Coupled Slow and Fast Charge Dynamics in Cesium Lead Bromide Perovskite. ACS Energy Lett. 2017, 2, 488−496
2) Dwyer, R. P , Tirmzi, A. M. , Harrell, L. E.; Marohn, J. A. (unpublished)
10:45 AM - TC01.04.06
Local Carrier Concentration in Semiconductors Measured by Dissipation Modulated Kelvin Probe Force Microscopy
Yoichi Miyahara 1 , Peter Grutter 1
1 , McGill University, Montreal, Quebec, Canada
Show AbstractMeasuring the local carrier and dopant concentrations with high spatial resolution is of fundamental importance for developing various electronic/optoelectronic devices such as field effect transistors and photovoltaic cells. Kelvin probe force microscopy (KPFM) is one of the promising techniques which can achieve such measurements nondestructively. Although various KPFM implementations have already been applied for various materials and devices, quantitative determination of carrier concentration has yet to be achieved.
We have recently developed a new KPFM implementation (D-KPFM) in which the electrically induced dissipation signal of the frequency modulation atomic force microscopy (FM-AFM) is used for the KPFM voltage feedback [1-3]. The D-KPFM can be operated in two operating modes, electrostatic force sensitive (1ωD-KPFM) and electrostatic force-gradient sensitive modes (2ωD-KPFM) which can be switched easily. In particular, the 1ωD-KPFM mode enables the use of a small ac modulation voltage amplitude (less than 100 mV) and can thus minimize the effect of the ac modulation voltage on the measured KPFM voltage which can be important for semiconductor samples due to the possible ac voltage induced band bending. We apply 1ωD-KPFM, 2ωD-KPFM and FM-KPFM to a calibration sample with a known doping profile and compare their results. We will discuss the effect of the ac modulation voltage amplitude and the prospect of the quantitative dopant profiling by KPFM.
[1] Y. Miyahara, J. Topple, Z. Schumacher, and P. Grutter, Phys. Rev. Applied 4, 054011 (2015).
[2] Y. Miyahara, and P. Grutter, Appl. Phys. Lett. 110, 163103 (2017).
[3] Y. Miyahara, and P. Grutter, arXiv:1704.06330.
11:00 AM - TC01.04.07
Energy Level Alignment of a Bimolecular Heterojunction
Katherine Cochrane 1 2 , Tanya Roussy 3 , Bingkai Yuan 2 , Erik Mårsell 2 , Sarah Burke 3 1 2
1 Chemistry, University of British Columbia, Vancouver, British Columbia, Canada, 2 , Stewart Blusson Quantum Matter Institute, Vancouver, British Columbia, Canada, 3 Physics & Astronomy, University of British Columbia, Vancouver, British Columbia, Canada
Show AbstractOrganic semiconductors are a promising class of materials for many applications such as photovoltaics, light emitting diodes, and field-effect transistors. As understanding energy level alignment at these boundaries is essential to device performance, these devices rely on the movement of charge at and near interfaces. As soft inter- and intra-molecular interactions permit a wide range of possible structures and conformations, these interfaces have the potential to be highly inhomogeneous on the molecular scale. Differences in the local environment and surrounding molecular geometry have the potential to cause significant energy level shifts occurring on single molecule length scales that will impact device properties.
In order to investigate the influence of interface geometry, we use pixel- by-pixel Scanning Tunneling Microscopy and Spectroscopy (STM/STS) to probe small clusters the acceptor-donor materials CuPc and PTCDA decoupled from the substrate by an insulating film. Previous SPM studies on closed monolayer systems of mixed donor-acceptor prototypical organic semiconductors have shown shifts in the energy levels of both components of the mixed domains. Here, by investigating small islands and utilizing molecular manipulation, we were able to probe numerous geometries that cannot be isolated within monolayer systems. We observe shifting of the donor and acceptor states in opposite directions, indicating at an equilibrium charge transfer between the two and narrowing of the gap dependent on the differing electrostatic environments. Further, we find that the location of electronic states of both acceptor and donor are strongly dependent on the positioning of both molecules in larger clusters. The observation of these strong shifts illustrates a crucial issue: interfacial energy level alignment can differ substantially from the bulk electronic structure in organic materials. This has significant implications for device design, where level alignment strongly correlates to device performance.
11:15 AM - TC01.04.08
Measuring Slow Ionic Processes in Perovskite Solar Cells with Time-Resolved Kelvin Probe Force Microscopy
Stefan Weber 1 2 , Ilka Hermes 1 , Victor Bergmann 1 , Wolfgang Tress 3 , Michael Graetzel 3 , Ruediger Berger 1
1 , MPI for Polymer Research, Mainz Germany, 2 Department of Physics, Johannes Gutenberg University, Mainz Germany, 3 , École Polytechnique Fédérale de Lausanne, Lausanne Switzerland
Show AbstractEfficient charge extraction within solar cells requires the optimization of the internal interfaces. Here, potential barriers, unbalanced charge extraction or interfacial trap states can prevent cells from reaching high power conversion efficiencies. In the case of perovskite solar cells, slow processes happening on timescales of seconds cause hysteresis in the current-voltage characteristics. Although hysteresis can nowadays be mostly avoided by selection of suitable selective electrode materials, its origin is not yet fully understood.
Here, we report on local and time-resolved potential measurements with Kelvin probe force microscopy (KPFM) [1,2] on cross sections of planar perovskite solar cells. By implementing a pointwise frequency modulated KPFM measurement approach, full quantitative potential maps with a spatial resolution of 20-50 nm and a time resolution of 0.5 ms could be obtained. Our experiments revealed a strong reverse electric field in the active layer for 100-200 ms after switching off of the illumination. Such effects cannot be observed by conventional scanning KPFM. The reverse field is caused by space charge regions close to the interfaces that contain slowly moving charged species. The timescales suggest that the charges are caused by ionic vacancies in the perovskite.
[1] Bergmann, V.W., et al., Nat. Commun., 2014. 5.
[2] Bergmann, V.W., et al., ACS Appl. Mater. Interf., 2016.
11:30 AM - TC01.04.09
Rapid I-V Acquisition in Scanning Probe Microscopy with Bayesian Methods
Suhas Somnath 1 , Kody Law 1 , Richard Archiblad 1 , Petro Maksymovych 1 , Sergei Kalinin 1 , Rama Vasudevan 1 , Stephen Jesse 1
1 , Oak Ridge National Laboratory, Oak Ridge, Tennessee, United States
Show AbstractElectronic structure characterization in materials by conductive atomic force and scanning tunneling microscopy (AFM and STM) dates back three decades, yet the traditional method of acquiring current-voltage (I-V) curves has not changed in the intervening time-frame. The collection of large numbers of I-V curves in a spectroscopic grid of points in both STM and AFM remains an extremely slow process, largely due to the imposition of a delay time after the applied voltage is altered, and an averaging time for enhancing signal to noise ratios. Here, we utilize Bayesian inference methods, and AC voltage excitation to the scanning tip, to capture I-V curves in both AFM and STM at extremely fast (hundreds of Hz) rates using the general-mode I-V acquisition (g-IV). The developed Bayesian inference methods are used to subtract the parasitic capacitance contributions to the current and reconstruct the resistance. We apply the technique in scanning mode in AFM for a ferroelectric material, and map the polarization values and dielectric constants via analysis of the I-V curves acquired over nanocapacitors. We further show the utility and generality of the technique by measurements on an Au sample in UHV at 4K in a commercially available STM system. This technique allows rapid acquisition of I-V curves at rates hundreds of times faster than the current state of the art, allows greatly increased spatial resolution, facilitates adaptive signal-noise filtering, and potentially expands the range of samples on which electronic property characterization is feasible. Thus, the g-IV mode overturns a three-decade paradigm in nanoscale electronic property characterization, using modern Bayesian inversion and full information capture techniques. This research was sponsored by the Division of Materials Sciences and Engineering, BES, DOE (RKV, SVK, PM, SS). This research was conducted at and partially supported (SJ) the Center for Nanophase Materials Sciences, which is a US DOE Office of Science User Facility. This research was also sponsored by the Applied Mathematics Division of ASCR, DOE; in particular under the ACUMEN project (KL, RA).
TC01.05: Electrical Measurements II
Session Chairs
Laura Fumagalli
Santiago Solares
Tuesday PM, November 28, 2017
Hynes, Level 2, Room 208
1:30 PM - TC01.05.01
Machine Detection of Enhanced Electromechanical Energy Conversion in PbZr0.2Ti0.8O3 Thin Films
Joshua Agar 1 , Ye Cao 2 , Brett Naul 1 , Shishir Pandya 1 , Stefan van der Walt 1 , Aileen Luo 1 , Joshua Maher 1 , Nina Balke 2 , Stephen Jesse 2 , Sergei Kalinin 2 , Rama Vasudevan 2 , Lane Martin 1
1 , University of California, Berkeley, Berkeley, California, United States, 2 , Oak Ridge National Laboratory, Oak Ridge, Tennessee, United States
Show AbstractUtilizing ferroic materials for nanoscale energy harvesting and sensing hinges on the ability to drive structural reconfiguration under external stimuli. Until recently, however, metrology tools capable of probing material responses at the appropriate length and time scales were not available. Instead, the stimuli-driven response of these materials has been inferred from static studies combined with computational simulations. The advent of in situ probes now allows for the imaging of material response under external stimuli at relevant length and time scales, leading to experimental data with a volume, variety, veracity, and velocity untenable for classical analysis such as fitting functions. Such fitting-based approaches are only possible when the spectra are well-behaved, and of a simple form failing to identify or even misrepresenting results when the data has an unknown variety (mathematical forms), veracity (uncertainty), and/or requires analysis of high-velocity data streams. Furthermore, these approaches are unsuitable when the mechanisms of response are unknown, and/or the response has fine-features. Alternatively, machine learning can be employed to identify correlations, trends, clusters, and anomalies which simplify the visualization and extraction of scientific insight.
Here, using band-excitation PFM and machine learning we develop a scalable computational approach to detect and classify switching events in ferroelectrics. We evaluate our machine learning model by conducting supervised learning on PbZr0.2Ti0.8O3 thin films with c/a/c/a domain structures where the structure and switching mechanisms are well-established. We then apply this model in an unsupervised learning task to PbZr0.2Ti0.8O3 thin films with complex hierarchical domain structures where the switching mechanisms are uncertain. Using this approach, we discover features and highlight the role of domain geometry in ferroelastic switching. In particular, we show that certain boundaries between c/a/c/a and a1/a2/a1/a2 domain bands have increased ferroelastic behavior under bias, giving rise to locally-enhanced electromechanical response, allowing an optimal domain geometry wherein maximum electromechanical energy conversion is possible. The ability to build a supervised learning model on a simple system, and apply it in an unsupervised fashion to another system with unknown response to derive new scientific insight demonstrates the applicability of this machine learning approach. Finally, we will conclude with a discussion of how unsupervised methods of feature generation can be used within a machine learning framework to identify mechanisms of response in hyperspectral experimental data. Such generalized unsupervised featurization methods can be used to analyze hyperspectral and hyper-imagery (image-per-pixel) data obtained from a variety of experimental techniques. We will provide access to a GitHub repository containing all data, codes, and analysis.
1:45 PM - TC01.05.02
Direct Probing of Polarization Charge at the Nanoscale
Owoong Kwon 1 , Daehee Seol 1 , Dongkyu Lee 2 , Hee Han 3 , Ionela Lindfors-Vrejoiu 4 , Woo Lee 3 , Stephen Jesse 5 , Ho Nyung Lee 2 , Sergei Kalinin 5 , Marin Alexe 6 , Yunseok Kim 1
1 School of Advanced Materials and Engineering, Sungkyunkwan University (SKKU), Suwon Korea (the Republic of), 2 Materials Science and Technology Division, Oak Ridge National Laboratory, Oak Ridge, Tennessee, United States, 3 , Korea Research Institute of Standards and Science (KRISS), Daejeon Korea (the Republic of), 4 , University of Cologne, Köln Germany, 5 The Center for Nanophase Materials Sciences, Oak Ridge National Laboratory, Oak Ridge, Tennessee, United States, 6 Department of Physics, University of Warwick, Coventry United Kingdom
Show AbstractFerroelectric materials possess spontaneous polarization that can be applied for non-volatile memory devices due to its electric-field switchable characteristics. A prerequisite for practical applications of ferroelectric materials is an evaluation of the ferroelectricity. In general, the existence of the ferroelectricity has been macroscopically examined by measuring polarization charges based on the detection of polarization switching current. However, owing to recent trend for reducing dimension of the electronic devices, preparation of nano-sized ferroelectric materials such as thin films and nanostructures has been of significant interest over the last decade. Even though piezoresponse force microscopy (PFM) has been used extensively for exploring nanoscale ferroelectricity over the past two decades, it was recently revealed that several non-ferroelectric effects can induce additional contributions to the PFM response, which often lead to a misinterpretation of the measured PFM response. Accordingly, an alternative approach is necessary to examine the existence of the ferroelectricity at the nanoscale. In this presentation, we will demonstrate direct probing of polarization charge at the nanoscale using conventional current atomic force microscopy (CAFM). The polarization charges in both thin films, here an epitaxial Pb(Zr,Ti)O3 thin film, and nanostructures, here BiFeO3 nanocapacitors, were directly measured through the Positive-Up-Negative-Down method based on the CAFM approach. These results could provide guidelines for evaluating the ferroelectricity at nanoscale based on the AFM approaches.
2:00 PM - TC01.05.03
Distinguishing Electromechanical from Electrostatic Phenomena Using Contact Kelvin Probe Force Microscopy
Sabine Neumayer 1 , Liam Collins 2 , Rama Vasudevan 2 , Mahshid Ahmadi 5 , Alp Sehirlioglu 4 , Nina Balke 2 , Stephen Jesse 2 , Andrei Kholkin 3 , Sergei Kalinin 2 , Brian Rodriguez 1
1 , University College Dublin, Dublin Ireland, 2 , Oak Ridge National Laboratory, Oak Ridge, Tennessee, United States, 5 , University of Tennessee, Knoxville, Knoxville, Tennessee, United States, 4 , Case Western Reserve University, Cleveland, Ohio, United States, 3 , University of Aveiro, Aveiro Portugal
Show AbstractDifferentiating ferroelectric from non-ferroelectric phenomena such as electrostatic interactions and electrochemical surface states is crucial for functional applications of ferroelectric and relaxor materials. However, in conventional piezoresponse force microscopy (PFM) based switching spectroscopy techniques it is often impossible to distinguish between electrostatic and electromechanical signal origins. Contact Kelvin probe force microscopy (cKPFM) can be used to detect bias-induced changes in junction contact potential difference between sample surface and tip and to obtain information on the impact of charge injection. Moreover, the ionic density of states and its evolution with bias is probed, which allows to differentiate electrochemical and ferroelectric dipoles. In cKPFM, a low direct current read voltage is applied between high direct current write pulses and varied in multiple cycles. Simultaneously, periodic displacement emanating from sample deformation (piezoelectric or other mechanisms) and/or electrostatic forces upon additional alternating current excitation across a range of frequencies is detected. From the response signal as function of read bias, capacitive, dielectric and ferroelectric material properties can be inferred. In this work, band excitation cKPFM and switching spectroscopy is used to investigate electromechanical, electrostatic and electrochemical coupling in ferroelectric and non-ferroelectric material systems comprising perovskite single crystals and thin films, semiconductors as well as relaxors under different ambient conditions. The studies highlight the impact of non-ferroelectric effects on response measured in atomic force microscopy techniques that involve applying voltage pulses and aid understanding of nanoscale functional behavior, which is key to device design in the fields of energy and information storage.
This research was conducted at and partially supported (RKV, LC, NB, SJ, SVK) by the Center for Nanophase Materials Sciences, which is a US DOE Office of Science User Facility. Support by Science Foundation Ireland (14/US/I3113) is acknowledged.
TC01.06: Functionalization and High Resolution
Session Chairs
Ricardo Garcia
Laurene Tetard
Tuesday PM, November 28, 2017
Hynes, Level 2, Room 208
2:15 PM - *TC01.06.01
Twenty Years of Atomic Force Microscopy Using the qPlus Sensor—What is in Store for the Future?
Franz Giessibl 1
1 , Univ of Regensburg, Regensburg Germany
Show AbstractThe atomic force microscope celebrated its thirtiest anniversary last year and continues to be of high value to materials science. The force sensor is key to this microscope and has evolved from a cantilever made from a gold foil with a diamond tip to sophisticated microfabricated silicon cantilevers with integrated tips. The invention of the qPlus sensor was a response to the basic principles that govern minimal noise in frequency-modulation atomic force microscopy (FM-AFM) as well as to the desire of a facile operation in challenging environments such as ultrahigh vacuum and low temperatures. The physical principles in maximizing the signal-to-noise ratio in FM-AFM ask for oscillation amplitudes that are on the order of the interaction lengths of the forces at play, requiring a stiffness of about 1 kN/m to prevent instabilities. The qPlus sensors were made of quartz, ensuring high frequency stability with temperature and an elegant piezoelectric deflection readout as well as a high quality factor. Today, the qPlus sensor is employed in most low-temperature AFMs and has enabled exciting images of matter on the atomic and subatomic scale. In 2009, L. Gross et al. discovered that attaching a CO molecule on the tip allows spectacular resolution of organic molecules. Since then, this tip termination that is often used and other tip terminations are investigated heavily today. While the qPlus sensor has been mainly used in vacuum, atomic resolution in ambient conditions has been achieved with it recently and has the potential to image materials at very high resolution into ambient conditions with relatively little effort.
2:45 PM - TC01.06.02
Atomic Resolution qPlus AFM at Ambient Conditions
Nikola Pascher 1 , Marcin Kisiel 2 , Claudio Alter 2 , Alessia Buehler 2 , Yemliha Bilal Kalyoncu 2 , Andreas Baumgartner 2 , Urs Gysin 2 , Korbinian Pürckhauer 3 , Dominik Kirpal 3 , Franz Giessibl 3 , Ernst Meyer 2
1 , Nanosurf AG, Liestal, BL, Switzerland, 2 Physics, University of Basel, Basel Switzerland, 3 Physics, University of Regensburg, Regensburg Germany
Show AbstractThe race for maximum performance in AFM currently aims at two goals: Some instruments allow scanning at increased speed, others offer highest resolution. While cryogenic- or UHV-instruments can routinely image single atoms and atomic defects, this still remains a challenging task at ambient conditions. Being forced to immerse the sample into an unsuitable environment greatly limits the benefit of the instrument, as it cannot be used in a standard device-fabrication workflow. The few AFMs, which allow atomically precise measurements in ambient conditions to date, rely on optical force detection and user-control intensive operation schemes.
We achieve atomic resolution with AFM, by combining a robust and environment-insensitive instrument with the qPlus sensor [1]. It consists of a stiff quartz oscillator and has proven to be much better suited to achieve atomic resolution at ambient conditions than conventional AFM techniques [2, 3]. This can be directly explained by considering that for resolving structures on the atomic scale, stability and vibration amplitudes on the same scale are necessary [4]. The stiff oscillator in combination with frequency modulation feedback allows stable operation with atomic-scale vibration amplitudes. Because the sensor is read out and excited all-electrically, a majority of the optimum feedback parameters can be calculated using simple algorithms.
For operation at ambient conditions there are further challenges: Soft cantilevers are disturbed from condensed water and have problems resolving the atomic structure of the sample-surface. Due to its high stiffness, the qPlus sensor can penetrate the water layer and resolve the structures underneath. Any tip can be attached, allowing a free choice of different hydrophilic or hydrophobic materials. With metallic tips, we can combine AFM and STM.
Here, we show that atomic resolution is routinely achieved on ionic crystals like KBr. The atomic lattice can be imaged despite the presence of a water layer. The formation and healing of tip-induced defects can be observed.
We use our instrument for characterization of graphene. If graphene or related 2D materials are used as sheets on top of a substrate, its electric-, optical-, mechanic- and structural properties greatly depend on the crystal structure, the cleanliness of the surface and the density of atomic defects. We start from a multilayer flake, which is exfoliated on a Si-SiO2 substrate. Exposure to a H2-plasma leads to the formation of hexagonal pits [5]. We image the atomic lattice of the top layer and see indications of the influence of the underlying layer and the substrate. We find that the edges of the hexagonal pits are influenced by the presence of amorphous carbon, accumulated charges and processing residues.
[1] US Patent 6240771, US Patent 8393009
[2] D. Wastl et al, ACS Nano 5, 5233 (2014)
[3] D. Wastl et al, PRB 87, 245415 (2013)
[4] F. Giessibl, Materials Today 8, 32 (2005)
[5] D. Hug et al, arXiv:1703.04762 (2017)
3:30 PM - *TC01.06.03
Quantitative Force Measurements with a Functionalized Tip of High-Resolution Atomic Force Microscopy at Low Temperature
Shigeki Kawai 1
1 , National Institute for Materials Science, Tsukuba Japan
Show AbstractA local probe of an atomic force microscope allows us to study the atomic-scale point contact. At room temperature, the thermal energy usually induces stochastic atom movements in the junction, leading formation and rupture of the atomic-scale neck and interchanges of atoms between tip and sample. These phenomena relate to the energy dissipation in dynamic mode atomic force microscopy. In contrast, the stability of the tip apex drastically improves at low temperature and hence a systematic force measurement becomes possible. Especially, terminating the metal tip with priori measured molecules or atoms, the so-called functionalized tip, is very beneficial to control the front-most atom. Furthermore, inner structures of molecules were successfully resolved with such the tip [1].
We used this technique to conduct quantitative force measurements. Rare gas atoms (Ar, Kr, and Xe) were stabilized at nodal sites of two-dimensional molecular organic framework on Cu(111). By taking force curves on the rare gas sites as well as the empty nodal sites with a Xe-tip, pair-wise van der Waals forces were measured [2]. Furthermore, we observed three-dimensional hydrocarbons (propellane) with a CO-tip. Due to the unique structure, C-H bonds are always point outward if the molecule adsorbs on a surface. In this way, very week C=O…H-C hydrogen bonding was quantitatively measured [3].
References
[1] L. Gross, F. Mohn, N. Moll, P. Liljeroth, and G. Meyer, Science 325, 1110 (2009).
[2] S. Kawai, A. S. Foster, T. Björkman, S. Nowakowska, J. Björk, F. Federici Canova, L. H. Gade, T. A. Jung, and E. Meyer, Nat. Commun. 7, 11559 (2016).
[3] S. Kawai, T. Nishiuchi, T. Kodama, P. Spijker, R. Pawlak, T. Meier, J. Tracey, T. Kubo, E. Meyer, and A. S. Foster, Sci. Adv. 3, e1603258 (2017).
4:00 PM - TC01.06.04
Chemical Phenomena of Contact Mode Atomic Force Microscopy Scanning
Chance Brown 1 2 , Anton Ievlev 2 , Petro Maksymovych 2 , Matthew Burch 2 , Sergei Kalinin 2 , Olga Ovchinnikova 2
1 , University of Tennessee - Knoxville, Knoxville, Tennessee, United States, 2 , Oak Ridge National Laboratory, Oak Ridge, Tennessee, United States
Show AbstractOver the past 20 years, atomic force microscopy (AFM) has been paramount in surface characterization. Electrical and mechanical properties of materials are easily obtained and manipulated via the AFM and are important to a variety of fields, such as medical and semiconductor industries. However, chemical phenomena of the tip/surface interaction during the AFM scanning are mostly ignored due to the lack of investigative techniques allowing local chemical imaging inside scanned areas. In this work, we used an approach combining AFM with Time-of-Flight Secondary Ion Mass Spectrometer (ToF-SIMS) to understand the chemical effects at the tip-surface junction while scanning in the contact AFM mode. The combined ToF-SIMS/AFM system can give insight and observation of important electrochemical processes such as polarization in ferroelectric materials [2]. Previous studies have shown induced surface chemistry changes through manipulation of ferroelectric surfaces with an SPM probe [3].
Systematic changes in tip parameters (contact force, scanning velocity, and applied electrical bias) were employed while scanning lead zirconate titanate (PZT) and strontium titanate (STO) films. The samples were cleaned in-situ using an oxygen ion sputtering gun to eliminate adsorption surface layer influences. After scanning, local changes of surface chemistry were inspected using ToF-SIMS. These investigations of the surface revealed no changes in the underlying sample chemistry, however multivariate analysis of data show layer of Si+ deposited inside scanned region, which is confirmed using a high resolution mass spectra. Tip parameters were varied while scanning 10 µm lines and show that scanning speed is the primary parameter controlling silicon deposition. Tip velocity being the major contributor shows chemical interaction at the tip-surface junction drives this phenomenon. An inverse relationship of velocity was developed showing dwell time to be the guiding factor, meaning the process is likely a diffusive process of surface contamination of the tips.
This work was conducted at the Center for Nanophase Materials Sciences, which is a Department of Energy (DOE) Office of Science User Facility.
[1] Binning G.K, Phys. Scr., T19A (1987), p. 53
[2] Kalinin S.V., et.al. , Rep. Prog Phys, 73 (2010), p. 056502.
[3] Ievlev, A.V., et.al, ACS Applied Materials & Interfaces 8 (43), 2016, p. 29588
4:15 PM - TC01.06.05
Surface Characterization of Oil-Carbonate Rocks Interaction for Enhanced Oil Recovery
Jehad Abed 1 , Cyril Aubry 1 , Mouna Zaidani 1 , Nabil El Hadri 1 , Rajakumar Devarapalli 1 , Mustapha Jouiad 1
1 , Masdar Institute of Science and Technology, Abu Dhabi United Arab Emirates
Show AbstractOnly one-third of the crude oil stored in underground reservoirs is successfully recovered by conventional recovery methods. An in-depth investigation of the interaction between crude oil and the rock surface of the reservoir is essential to develop innovative methods for optimum oil recovery. In this work, a novel in-situ atomic force microscopy technique (PeakForce QNMTM) is used to map the adhesion forces between oil and carbonate rocks rich with natural Calcite and Dolomite content in water. The samples are placed in a fluid cell filled with water to compromise for the surrounding environment, while the AFM tip is functionalized with oil. Wettability contact angle measurements are performed both in-situ and ex-situ using static contact angle technique and environmental electron microscope (ESEM). These measurements are carried out with respect to both water and oil at various roughness induced by sample surface modification. The microstructure of the carbonate rocks is assessed by scanning electron microscope (SEM) and the content of the phases is determined using energy dispersive spectroscopy (EDS) technique. The obtained force curves combined with wettability contact angle measurements and microstructure analysis of the rock surface are used to develop an empirical model that governs surface tension, wettability and mineralogy. The results demonstrate that the contact angle depends on both surface roughness and mineralogy of the rock samples, the increased roughness at the Calcite-rich regions induces an oleophobic nature where in contrast the contact angle at Dolomite-rich regions remained relatively unchanged with a slight variation of the roughness. Force curves results show different adhesion behavior of Calcite-rich and Dolomite-rich regions. While no adhesion between oil and Calcite was measured, however, some adhesion forces were observed for dolomite phase, in water.
TC01.07: Liquid and Biology I
Session Chairs
Ricardo Garcia
Laurene Tetard
Tuesday PM, November 28, 2017
Hynes, Level 2, Room 208
4:30 PM - TC01.07.01
Developing Multifunctional AFM Methods for Lubricious Coatings Research
Greg Haugstad 1 , Connor Colling 1 , Alon McCormick 1 , Klaus Wormuth 2 , Maggie Zeng 3
1 , University of Minnesota, Minneapolis, Minnesota, United States, 2 , Sartorius, Gottingen Germany, 3 , Boston Scientific Corporation, Maple Grove, Minnesota, United States
Show AbstractWe discuss atomic force microscopy modalities applied to lubricious polyvinyl pyrrolidone gel coatings. The character of this work is methods development, wherein different AFM surface imaging modes and property sensitive measurements are explored and utilized.
In much of our work under aqueous immersion, particularly on kPa-regime modulus gels (cases of none-to-low crosslinking), the sharp AFM tip is replaced with a colloid microprobe (radius 3.3 um); whereas we find that gels with moduli on the order of 10’s of kPa and higher can be mechanically probed, and even topographically imaged in (sliding) contact mode, using standard sharp AFM tips (radius ~10 nm). We explore differences in spatial resolution on these latter gels with both types of probe. In the process we discover that an array of defect structures seen in the initial dry state on sponge-deposited / UV-cured coatings – dubbed craters, pinholes, fissures and cheetah spots – tend to “anneal” upon hydration, and dramatically more so for lesser crosslinking.
Beyond these rich coating morphologies unveiled in topographic images, normal and shear force AFM perturbations yield variable coating responses. Shear perturbations reveal crosslinking-dependent viscoplastic response in the initial dry state. We further explore sliding friction, force-distance, and shear-modulation measurements in the (immersed) gel state. In all cases these spatially mapped measurements – up to several tens of microns in lateral scale – reveal crosslinking-dependent mechanical responses, as well as spatial correlations between these responses and the complex topography. Gel moduli are found to vary by 2-3 orders of magnitude per degree of crosslinking, but also by a factor of 2-4 across a given coating, with lower values corresponding to more swollen domains. A caveat is that vendor-provided algorithms for point-by-point calculation of elastic modulus must be generalized to account for local surface curvature, instead of assuming an (initial) sphere-flat contact geometry, given a large radius of curvature probe along with strong local curvatures due to heterogeneous swelling. We also find interesting differences in frictional responses between uncrosslinked and heavily crosslinked gels, mainly a presence of “stick-snap” macromolecular responses on light-to-non crosslinked gels.
Given an emerging appreciation of the importance of nano- to micro-scale structures and behavior to the interaction between medical device coatings and the body, we believe that the insights afforded by mechano/tribo AFM methods, as well as topographic imaging (variable swelling), merit an increasing role in understanding and predicting the performance of lubricious coatings.
4:45 PM - TC01.07.02
Scanning Probe Microscopies as Tools to Assess the Impact of Resin Embedding on the Physicochemical Properties of Plant Fibres—A Nanoscale Study
Raphael Coste 1 2 3 , Véronique Aguié-Béghin 2 , Laurene Tetard 3 , Brigitte Chabbert 2 , Michael Molinari 1
1 , Universite de Reims Champagne Ardenne, Reims France, 2 , INRA UMR FARE, Reims France, 3 Nanosciences Center, University of Central Florida, Orlando, Florida, United States
Show AbstractLignocellulosic biomass (LC) represents the most promising renewable resource for a sustainable production of energy, chemical, paper, textiles and materials. The physicochemical properties of plant fibers depend on their botanic origin and involve multiscale levels from macroscopic to supramolecular architecture of the plant cell walls [1, 2]. To characterize their properties, plant fibers generally need resin embedding and microtome cutting that allow to obtain flat surface with fixed cell walls. Nevertheless, there is a lack of information regarding the impact of the resin on the physicochemical properties of plant cell walls at nanoscale [3]. This study aims to understand the influence of the preparation of the sample and more specifically the resin embedding on their nanomechanical as well as chemical properties of poplar fibres. To this end, mapping of the local physical properties of cell wall at micro and nanoscale was assessed using atomic force microscopy (AFM) in PeakForce Quantitative Nanomechanical Mapping mode (PF QNM) that allow access to mechanical properties [4]. Then the nanomechanical properties were correlated to the nanochemical composition nano infrared microscopy technique (AFM-IR) [5].
1. Salmen L., Burgert I. Cell Wall Features with Regard to Mechanical Performance. A Review. Holzforschung, 63 (2009) 121-129.
DJ. Cosgrove, MC Jarvis, M.C. Comparative structure and biomechanics of plant primary and secondary cell walls. Frontiers in Plant Science. 3 (2012)
2. Wagner L, Bader T.K, De Borst K, Nanoindentation of wood cell walls: effects of sample preparation and indentation protocol, J Mater Sci (2014) 49:94–102.
3. A.Slade, B. Pittenger. Investigating cell mechanics with atomic force microscopy, Microscopy and Analysis 28 (2014) 6-9.
4. L. Muraille, V. Aguié-Béghin, B. Chabbert, M. Molinari. Bioinspired lignocellulosic films to understand the mechanical properties of lignified plant cell walls at nanoscale, Scientific Reports, 2017; 7: 44065.
5. A. Dazzi, C.B. Prater, Q. Hu, D. B. Chase, J. F. Rabolt, C. Marcott, AFM–IR: Combining Atomic Force Microscopy and Infrared Spectroscopy for Nanoscale Chemical Characterization, Applied spectroscopy, Volume 66, Number 12, 2012.
TC01.08: Poster Session I
Session Chairs
Ricardo Garcia
Jason Killgore
Wednesday AM, November 29, 2017
Hynes, Level 1, Hall B
8:00 PM - TC01.08.01
Atomic Force Microscopy Study of Graphite Surfaces
Lenore Miller 1 , Chibu Umerah 1 , Weigang Lu 1 , John Demaree 2 , Daryush Ila 1
1 , Fayetteville State University, Fayetteville, North Carolina, United States, 2 , U.S. Army Research Laboratory, Aberdeen Proving Ground,, Maryland, United States
Show AbstractAtomic Force Microscopy (AFM) was used to study the surface topology of graphite, and the obtained AFM images were correlated to the hexagonal carbon ring surface structure of graphene sheets. In order to understand the composition of the material under investigation, we are also using Rutherford Backscattering Spectrometry (RBS) in conjunction with x-ray photoelectron spectroscopy (XPS) to identify the impurities in the material, the concentration of such impurities at the surface, and their potential impact on graphite properties. RBS techniques are selected because impurities are heavier than carbon; therefore can be easily detected and quantified without any need for substrate background subtraction. XPS will confirm the RBS findings, and identify any differences in the distribution of impurities in the bulk and at the surface of the material.
8:00 PM - TC01.08.02
Determining Graphene Film Continuity from Direct Chemistry Mapping with Multifrequency AFM
Sohail Shah 1 , Harry Apostoleris 1 , Chia-Yun Lai 1 , Sergio Santos 1 , Matteo Chiesa 1 , Tuza Olukan 1 , Yu-Cheng Chiou 1 , Ibraheem Almansouri 1
1 , Khalifa University of Science and Technology, Abu Dhabi United Arab Emirates
Show AbstractGraphene is sought after for many applications due to its unique physical properties. The optimization of graphene fabrication for commercial use relies on the availability of characterization techniques that allow straightforward observation of the properties relevant for the desired application. For nanotechnology applications, standard spectroscopy techniques, while they offer significant information, are often insufficient for spatially-resolved measurements as they are optical techniques that are inherently diffraction limited. Here we present measurements of the continuity and uniformity of CVD-grown graphene films based on direct mapping of the Hamaker coefficient, with higher resolution than is possible with conventional spectroscopy, from multifrequency AM-AFM data. These measurements provide valuable information for improving graphene manufacturing and also point to the broader value of AFM-based techniques for high-resolution measurement and mapping of chemical characteristics of nanomaterials.
8:00 PM - TC01.08.03
Shape Formation of Electromechanical Hysteresis in Dynamic Contact Atomic Force Microscopy
Owoong Kwon 1 , Seunghun Kang 1 , Daehee Seol 1 , Yunseok Kim 1
1 , Sungkyunkwan University, Suwon-si Korea (the Republic of)
Show AbstractIn dynamic contact atomic force microscopy (DC-AFM), various physical properties, such as ferro/piezoelectric, electrochemical, mechanical and electrostatic properties, can be obtained by monitoring cantilever dynamics caused by voltage application, i.e. electromechanical (EM) response. The dominant origin of the EM response in DC-AFM can be dependent on the experimental conditions, e.g. target material, voltage conditions, and cantilever. Generally, EM response in the oxides can be primarily originated from piezoresponse and/or electrochemical strain. In such a case, DC-AFM can be called as piezoresponse force microscopy or electrochemical strain microscopy, depending on the origins of the main contribution. In both cases, hysteric behavior can be observed by application of bipolar dc triangular waveform. If the material is a mixed ferroelectric and an ionic system or new types of ferroelectrics, it is hard to know the main contribution of the EM hysteric behavior. In this work, we present the shape formation of the EM hysteresis loop in DC-AFM, depending on ac voltage conditions and materials. In case of the ferroelectric Pb(Zr,Ti)O3 thin film, the hysteresis loop shows irregular shape variation with increasing magnitude of ac voltage, whereas that observed in Li ionic conductor shows the gradual decrease of the hysteresis loop. Additionally, ac modulation hysteresis measurement was performed in HfO2 and TiO2, which might have piezoresponse and/or electrochemical strain. Our observation indicates that these results can provide fundamental understanding on the EM hysteric behavior varied by ac modulation voltage and target materials and, further, it can be effectively applied for distinguishing different mechanisms of the EM response in DC-AFM approach.
8:00 PM - TC01.08.04
Direct Observation of Lateral Joule Expansion in Monolayer Graphene Using Atomic Force Microscopy
Seunghun Kang 1 , Daehee Seol 1 , Hamza Gul 2 , Wonkil Sakong 2 3 , Seong Chu Lim 2 3 , Yunseok Kim 1
1 School of Advanced Materials Science and Engineering, Sungkyunkwan University (SKKU), Suwon Korea (the Republic of), 2 Department of Energy Science, Sungkyunkwan University (SKKU), Suwon Korea (the Republic of), 3 Center for Integrated Nanostructure Physics, Institute for Basic Science (IBS), Sungkyunkwan University (SKKU), Suwon Korea (the Republic of)
Show AbstractIn graphene based devices, understanding of the coupled electrical and thermal properties such as Joule heating and corresponding expansion is very important because they can affect directly device performance and reliability during device operation. Recently, scanning Joule expansion microscopy (SJEM) based on atomic force microscopy was suggested as a tool for investigating Joule expansion of monolayer graphene. However, even though exploring lateral expansion is a key for understanding the coupled electrical and thermal properties in terms of the in-plane current flow during device operation, lateral Joule expansion of the monolayer graphene was not directly observed in the most of the previous SJEM studies. In this presentation, we directly observed lateral Joule expansion as a function of input power and frequency in the monolayer graphene device through lateral SJEM. We further studied locally different thermal expansion as well as vertical Joule expansion for understanding Joule heating induced thermal expansion of graphene. Our finding can provide the information on Joule expansion in the graphene and locally varied thermal properties.
8:00 PM - TC01.08.05
To Deal or Not to Deal with the Emerging Zoo of Maps in Atomic Force Microscopy?
Chia-Yun Lai 1 , Tuza Olukan 1 , Mariam Almahri 1 , Sohail Shah 1 , Harry Apostoleris 1 , Matteo Chiesa 1 , Sergio Santos 1
1 , Khalifa University of Science and Technology, Abu Dhabi United Arab Emirates
Show AbstractIt could be argued that the atomic force microscopy community has reached a point reminiscent to what physicists lived when facing the emerging zoo of particles in particle physics. At this point, we face a growing set of contrast maps emerging from multiple observables, signals, expressions, and contrast channels, in a myriad of driving scenarios, that currently allow imaging with small and large amplitudes in liquid, air and vacuum environments. Here we discuss the use of both suitable raw data transformations that lead to physically intuitive maps and model free transforms general enough to be recognized by the broader community, always aiming at tractable forms of AFM maps. We further propose a more radical form of data analysis where AFM data is directly transformed into abstract machine learning features. The process consists of three steps: (1) acquiring nanoscale force data from materials, (2) parameterizing the raw data into standardized input features to generate a library, (3) feeding the standardized library into standard machine learning libraries for prediction and quantification. The concept is encapsulated in the Mendeleev-Meyer Force Project (MMFP) where data should be tabulated in a manner reminiscent of the construction of the periodic table. Overall, we predict that the merging of terminology and analysis of AFM data with data science and advanced forms of computation might provide be a key step for the advance of the field.
8:00 PM - TC01.08.06
Signal Distortion in Atomic Force Microscopes Due to Photodetector Limit
Steven Eppell 1 , Li Li 1 , Brandon White 1 , Fredy Zypman 2
1 Biomedical Engineering, Case Western Reserve University, Cleveland, Ohio, United States, 2 Physics, Yeshiva University, New York, New York, United States
Show AbstractIt is often assumed that the instrument response functions of our
atomic force microscopes have higher bandwidth than any signal of interest. However, as video rate imaging, multi-frequency detection, and experiments focusing on high-speed events like the snap-to-contact instability become more common, this assumption is challenged. To quantify this situation, we solved the inverse problem that inputs experimentally measured forces and outputs forces that would have been collected with a hypothetical perfectly flat-frequency-response photodetector. To apply this inverse method, the frequency-dependent complex impedance of the atomic force microscope photodetector is needed. We measured this impedance for our Veeco Multimode AFM. Finally, we studied the distortion that the true input signal undergoes as it passes through the photodetector on the way to becoming the experimentally measured output signal. We found that signals with features of interest faster than 10 microseconds render noticeable differences between the true and measured forces. Signals with features faster than 1 microsecond produce experimentally measured force curves that deviate so substantially from the true force curves that a classic spoon-shaped surface force becomes an experimentally measured monotonically decreasing force as a function of tip-sample separation. We provide a straightforward method for recovering the true force from the measured signal.
8:00 PM - TC01.08.07
Calibration of an AFM Tip for Quantitative Measurements of the Indentation Modulus—Comparison of Traditional and Novel Approaches
Malgorzata Kopycinska-Mueller 1 , Ute Rabe 2 , Bernd Koehler 1
1 , IKTS, Dresden Germany, 2 , IZFP, Saarbruecken Germany
Show AbstractUsing a method based on an atomic force microscope (AFM) to measure either Young’s or indentation modulus quantitatively can be very frustrating. There are numerous studies showing that the AFM methods are sensitive to the changes in the elastic properties of materials, yet every time the quantitative numbers are published they must be validated by reference measurements or literature values. These powerful AFM methods are often hampered by lack of comprehensive procedure for tip calibration allowing for determination of the tip-sample contact radius. There are two main trends to win information on the tip geometry. The first one concentrates on imaging the tip apex either by use of special calibration structures and shape reconstruction algorithms, or electron microscopes. The other approach is used by users of indentation methods, where the tip-indenter shape is characterized with help of calibration measurements performed on a reference sample with known elastic properties. The first approach assumes that the geometry information gained on a scale of few hundreds nm is valid at the very last nanometers where the tip-sample interaction happens. The other approach tries to describe the tip-sample interaction occurring at the scale of single nanometers with help of macroscopic models assuming a perfect tip geometry.
The contact resonance (CR) methods such as atomic force acoustic microscopy (AFAM), CR-AFM, or CR-force microscopy (FM) are capable of determination of the indentation modulus of materials in the range from 3 GPa to 300 GPa and yet their use is still limited due to absence of consistent, universally used, and certified method for the tip calibration. Different groups use different tip calibration approaches and this fact alone signalizes the fundamental problems arising from adaptation of the macroscopic models to a nanoscale object. Based on set of experimental data obtained on different reference materials with both silicon and diamond tips we will compare the effectiveness and limits of the available tip calibration procedures starting from macroscopic Hertz and flat punch models and ending on Batog’s approach. We will also present results obtained when a novel and comprehensive model for calibration of tip geometry is used. The results include values of the tip-sample contact radius independent on the choice of the reference samples, as well as values of the indentation modulus determined in the range from 6 GPa to 200 GPa with accuracy of about 10 %.
8:00 PM - TC01.08.08
Evaluation of Atomic Force Microscopy Probes and Instruments with Dynamic Cantilever Calibrator
John Alexander 1 , Sergey Belikov 1 , Sergei Magonov 1 , Mark Smith 2
1 , SPM Labs LLC, Tempe, Arizona, United States, 2 , AFM Services LLC, Goleta, California, United States
Show AbstractQuantitative measurements of mechanical and electric properties of samples in Atomic Force Microscopy (AFM) are essentially based on the knowledge of probe properties: resonant frequencies of different flexural and torsional modes, spring constant, Q-factor; and the microscope characteristics: inverse optical sensitivity (IOS) and noise of optical beam deflection (OBD). To assist a researcher in optimal measurements we have developed a dynamic cantilever calibrator (DCC), which is currently used with MultiMode and Dimension microscopes that dominate the market of scanning probe microscopes. The probe calibration is based on the Thermal Tune spectra, in which an optical deflection signal of a resting AFM probe on a photodetector is collected by DCC with up to 16 MHz sample rate. After real-time analysis of this signal in the frequency domain, it is presented as Power Spectral Density (PSD) or Noise Spectrum in the frequency range up to 8 MHz range. This range covers first and higher flexural resonances of AFM probes, which are used in multi-frequency operations. A part of this spectrum around the 1st flexural mode is fitted by Lorentz model to obtain the probe resonance frequency and Q-factor. These data combined with geometrical probe parameters are used for calculation of the probe spring constant by Sader method. DCC is particularly important for operation of AFM oscillatory modes in liquid, where parasitic oscillations complicate finding of the probe main resonance using a piezo-drive. Besides the cantilever parameters, the analysis of PSD spectrum provides the estimations of IOS and noise of OBD. The latter parameter serves as the indicator of the microscope performance, and it helps to figure out different contributions to the instrument noise thus helping their elimination. This facilitates the microscope use in advanced applications that require high sensitivity and use of sub-nanometer oscillatory amplitudes. Finding of IOS is invaluable for reliable AFM nanomechanical studies, and its direct measurement using deflection-versus-distance (DvZ) curves on hard surface might lead to probe damage. In alternative non-invasive approach IOS value can be extracted from Thermal Tune PSD once Sader method is used for getting the spring constant from the same PSD. We have performed a comparative analysis of IOS values, which were obtained using DvZ curves and Thermal Tune, for variety of AFM probes. It was found that the most reliable IOS data can be obtained for soft probes with spring constant below 5 N/m. For stiffer probes the IOS measurements should be performed when the probes are less coupled to the optical head and microscope as the latter often bring unwanted perturbations of the cantilever motion.
Symposium Organizers
Santiago Solares, The George Washington University
Laura Fumagalli, University of Manchester
Ricardo Garcia, Consejo Superior de Investigaciones Científicas
Jason Killgore, National Institute of Standards and Technology
TC01.09: Liquid and Biology II
Session Chairs
Georg Fantner
Laura Fumagalli
Wednesday AM, November 29, 2017
Hynes, Level 2, Room 208
8:30 AM - TC01.09.01
Functional High-Speed AFM Imaging Using Photothermal Off-Resonance Tapping
Adrian Nievergelt 1 , Niccolo Banterle 2 , Santiago Andany 1 , Pierre Gönczy 2 , Georg Fantner 1
1 Laboratory for Bio- and Nano-Instrumentation, Institute of Bioengineering, EPFL, Lausanne Switzerland, 2 Swiss Institute for Experimental Cancer Research, EPFL, Lausanne Switzerland
Show AbstractSelf-assembly of protein complexes is at the core of many fundamental biological processes. To reach a comprehensive understanding of the underlying protein self-assembly reactions, high spatial and temporal resolution must be attained. This is complicated by the need to not interfere with the reaction during the measurement. Since self-assemblies are often governed by weak interactions, they are especially difficult to monitor with high-speed atomic force microscopy[1] due to the non-negligible tip-sample interaction forces involved in current methods[2]. Here we develop a high-speed atomic force microscopy technique, photothermal off-resonance tapping (PORT), which is gentle enough to monitor self-assembly reactions driven by weak interactions. Using photothermal actuation on ultra-small HS-AFM cantilevers[3] we perform force-distance curves at two orders of magnitude higher rates than in conventional off-resonance methods. Because only the very small mass of the cantilever is moved, (rather than the whole chip-body, cantilever holder or even sample) we can do this at > 250 kHz (compared to the standard 2kHz). From the time-domain tip sample interaction we extract tip-sample force curves which can be used for measuring functional properties of the sample during HS-AFM imaging. An extensive multi-parameter experimental characterization of tip-sample forces in HS-AM-AFM and PORT revealed that imaging forces in PORT are less than 1/5th of those exerted in conventional HS-AFM.
We apply PORT to dissect the self-assembly reaction of SAS-6 proteins[4], which form a nine-fold radially symmetric ring-containing structure that seeds formation of the centriole organelle. Due to the high temporal and force resolution provided by PORT, we found that, contrary to the current belief, more than one assembly route exists to reach the nine fold symmetry. This observation resets our current thinking about the assembly kinetics of this crucial step in cell replication.
References
[1] N. Kodera, D. Yamamoto, R. Ishikawa, and T. Ando, Nature, 468, 72–6 (2010).
[2] X. Xu, C. Carrasco, P.J. de Pablo, J. Gomez-Herrero, and A. Raman, Biophys. J., 95, 2520–8 (2008).
[3] A.P. Nievergelt, J.D. Adams, P.D. Odermatt, and G.E. Fantner, Beilstein J. Nanotechnol., 5, 2459–2467 (2014).
[4] M. Hilbert, A. Noga, D. Frey, V. Hamel, P. Guichard, S.H.W. Kraatz, M. Pfreundschuh, S. Hosner, I. Flückiger, R. Jaussi, M.M. Wieser, K.M. Thieltges, X. Deupi, D.J. Müller, R.A. Kammerer, P. Gönczy, M. Hirono, and M.O. Steinmetz, Nat. Cell Biol., 18, 393–403 (2016).
8:45 AM - TC01.09.02
Force-Induced Strengthening of the Interaction between Staphylococcus Aureus Clumping Factor B and Loricrin
Pauline Vitry 1 , Claire Valotteau 1 , Cécile Feuillie 1 , Simon Bernard 1 , David Alsteens 1 , Joan Geoghegan 2 , Yves Dufrene 1
1 , Université Catholique de Louvain, Louvain la Neuve Belgium, 2 , Trinity College Dublin, Dublin Ireland
Show AbstractBacterial pathogens that colonize host surfaces are subjected to physical stresses, such as fluid flow and cell-surface contacts. How bacteria respond to such mechanical cues is an important yet poorly understood issue. Staphylococcus aureus uses a repertoire of surface proteins to resist shear stress during the colonization of host tissues, but whether their adhesive functions can be modulated by physical forces is not known. Here we use force nanoscopy to show that the interaction of S. aureus clumping factor B (ClfB) with the squamous epithelial cell envelope protein loricrin is enhanced by mechanical force. We find that ClfB mediates S. aureus adhesion to loricrin through weak and strong molecular interactions, both in a laboratory strain and in a clinical isolate. Strong forces, by far the strongest receptor-ligand interactions measured so far, are consistent with a high-affinity “dock, lock and latch” binding mechanism involving dynamic conformational changes of the adhesin. We demonstrate that the strength of the ClfB-loricrin bond increases as mechanical force is applied. These findings favour a two-state model whereby bacterial adhesion to loricrin is enhanced through force-induced conformational changes in the ClfB molecule, from a weak-binding folded state, to a strong-binding extended state. This newly described force-sensitive mechanism may provide S. aureus with a means to finely tune its adhesive properties during colonization of host surfaces, helping cells to attach firmly under high shear stress and, to detach and spread under low shear stress.
9:00 AM - TC01.09.03
Machine-Learning Multidimensional Analysis of Peakforce Images of Cells Collected from Urine for Noninvasive Detection of Bladder Cancer
Igor Sokolov 1 , Maxim Dokukin 1 , Vivekanand Kalaparthi 1 , Milos Miljkovic 1 , Eugene Demidenko 2 , Andrew Wang 1 3 , John Seigne 2
1 , Tufts University, Medford, Massachusetts, United States, 2 , Geisel School of Medicine at Dartmouth, Hanover, New Hampshire, United States, 3 , Present address: Phillips Academy , Andover, Massachusetts, United States
Show AbstractMorbidity and mortality of any cancer is substantially decreased if cancer is detected early. Bladder cancer demonstrates 95% five-year survival rate when detected in the early stage). Costly and painful cystoscopy exams required when monitoring cancer patients. Here we report a novel non-invasive method of detection of bladder cancer based on the analysis of individual cells extracted from urine, and imaged with an advanced modality of atomic force microscopy (AFM), sub-resonant tapping modes, e.g., PeakForce tapping. Such modalities allow simultaneous collection of several digital maps of physical parameters of the cell surface. Analysis of these maps can bring up as many as 80 surface parameters, which can be used for classification purposes. A large number of possible parameter combinations that can be used for identification of cancer (up to 1024) requires the big data mining analysis to classify cells as benign or malignant. We demonstrate the use of machine learning methods to segregate cancer from normal tests. Random Forest methods were adopted for the hierarchical data structure collected from the cells. We analyzed urine samples from 20 healthy controls and 15 subjects with pathologically confirmed bladder cancer When analyzing a single cell, the sensitivity was 93% and the specificity 87%. When analyzing two cells and defining the presence of malignancy as being at least one cell classified as malignant the, sensitivity and specificity reaches 99 and 93%, respectively. This is substantially better than the efficiency of any existing non-invasive methods such as biochemical evaluation of the urine (NMP22, BTA) or cellular analysis (urine cytology, FISH). We anticipate that the use of advanced modality atomic force microscopy can be expanded to improve the diagnosis and follow up of other tumor types where tissue or body fluid is available for analysis without the need the need for an invasive procedure or biopsy. This method can easily be extended to other cancers in which cells can be extracted without biopsy.
9:15 AM - TC01.09.04
High-Speed Imaging of Surface Compositional Properties of Cells and Soft Materials with “Ringing Mode” of Atomic Force Microscopy
Maxim Dokukin 1 , Igor Sokolov 1
1 , Tufts University, Medford, Massachusetts, United States
Show AbstractHere we present a novel extension to recently introduced sub-resonant tapping imaging modes (Digital Pulse, Peak Force Tapping, HybriD, etc.), “ringing mode”. This mode is a combination of the oscillatory sub-resonant mode and a resonant one. It utilizes the information from the free resonance oscillation (ringing) signal of the cantilever which occurs after detaching the probe from a sample surface. This part of the signal is currently treated as useless and typically filtered out in the existing modes.
The ringing mode can simultaneously record multiple additional unique compositional parameters related to adhesive and viscoelastic properties of the sample surface (up to 8) such as the restored (averaged) adhesion, adhesion height, adhesion neck height, detachment distance, and detachment energy losses. Furthermore, it can be up to 20 times faster and showing fewer artifacts compared to the existing sub-resonance tapping modes. We demonstrate that the ringing mode allows recording robust and unique information on fixed human epithelial cells, corneocyte skin flakes, and polymers used for bio-implants.
10:00 AM - *TC01.09.05
Recent Progress in Liquid-Environment FM-AFM and Its Related Techniques
Takeshi Fukuma 1 2
1 , Kanazawa University, Kanazawa Japan, 2 ACT-C, JST, Kawaguchi Japan
Show AbstractLiquid-environment frequency modulation AFM (FM-AFM) [1] has been a powerful tool for investigating subnanometer-scale surface structures of various materials including minerals [2], functional molecules [3] and biological systems [4, 5]. Combined with a three-dimensional (3D) tip scanning technique, FM-AFM has also been successfully used for visualizing 3D distributions of water (i.e. hydration structures) [6] and flexible molecular chains [7] at solid-liquid interfaces with subnanometer resolution.
After the establishment of these basic functions of the present in-liquid FM-AFM system, we continued to make efforts in improving its fundamental performance [8] and expanding its functionality [9]. So far, we improved the imaging speed of FM-AFM from 1 min/frame to 1 sec/frame and achieved direct imaging of calcite dissolution process with atomic resolution. We also applied the 3D imaging technique to study complicated non-uniform 3D adsorption structures of lubricants and surfactants used in various industrial applications. Furthermore, we combined FM-AFM with an in-liquid surface potential measurement technique referred to as open-loop electric potential microscopy (OL-EPM) [9] and applied it to visualize nanoscale distribution of electrochemical activity of corrosion [10] and photocatalytic reactions.
In this paper, we present these recent achievements in the instrumentation and applications of in-liquid FM-AFM and its related techniques.
[1] T. Fukuma, M. Kimura, K. Kobayashi, K. Matsushige, H. Yamada, Rev. Sci. Instrum. 76 (2005) 053704.
[2] T. Fukuma, K. Kobayashi, K. Matsushige, H. Yamada, Appl. Phys. Lett. 87 (2005) 034101.
[3] N. Inada, H. Asakawa, Y. Matsumoto, T. Fukuma, Nanotechnology 25 (2014) 305602.
[4] T. Fukuma, M. J. Higgins, S. P. Jarvis, Biophys. J. 92 (2007) 3603-3609.
[5] T. Fukuma, M. J. Higgins, S. P. Jarvis, Phys. Rev. Lett. 98 (2007) 106101.
[6] T. Fukuma, Y. Ueda, S. Yoshioka, H. Asakawa, Phys. Rev. Lett. 104 (2010) 016101.
[7] H. Asakawa, S. Yoshioka, K. Nishimura, T. Fukuma, ACS Nano 6 (2012) 9013-9020.
[8] T. Fukuma, K. Onishi, N. Kobayashi, A. Matsuki, H. Asakawa, Nanotechnology 23 (2012) 135706.
[9] N. Kobayashi, H. Asakawa, T. Fukuma, Rev. Sci. Instrum. 81 (2010) 123705.
[10] K. Honbo, S. Ogata, T. Kitagawa, T. Okamoto, N. Kobayashi, I. Sugimoto, S. Shima, A. Fukunaga, C. Takatoh, T. Fukuma, ACS Nano 10 (2016) 2575-2583.
10:30 AM - TC01.09.06
High-Speed 3D-SFM Imaging of Hydration Structures Formed at Calcite-Water Interfaces
Kazuki Miyata 1 2 , John Tracey 3 , Adam Foster 2 3 , Takeshi Fukuma 1 2 4
1 Bio-AFM Frontier Research Center, Kanazawa University, Kanazawa Japan, 2 Division of Electrical Engineering and Computer Science, Kanazawa University, Kanazawa Japan, 3 COMP Centre of Excellence, Aalto University, Helsinki Finland, 4 ACT-C, Japan Science and Technology Agency, Kawaguchi Japan
Show AbstractHydration is related to various phenomena at solid/liquid interface such as crystal growth and dissolution processes, catalytic reaction and metal corrosion. Thus, for understanding the mechanisms of these phenomena, direct imaging of dynamic behavior of hydration structures is demanded. Recently, in-liquid frequency modulation atomic force microscopy (FM-AFM) has shown rapid progress in its instrumentation and true atomic-resolution imaging in liquid have been achieved by several research groups. However, a standard FM-AFM imaging provides only a 2D topographic image that has no vertical extent. To solve this problem, we previously developed 3D scanning force microscopy (3D-SFM), where the tip is scanned vertically as well as laterally at the 3D interfacial space. During the scan, the variation in the force applied to the tip is recorded to produce a 3D force image. The obtained 3D force images provide subnanometer-scale information on the 3D hydration structures at solid/liquid interfaces. However, scanning speed of the present 3D-SFM is limited to ~1 min per 3D image, which is often insufficient for visualizing dynamic changes in the hydration structures caused by interfacial phenomena.
In this study, we have developed high-speed atomic-resolution 3D-SFM by combining our recently developed high-speed FM-AFM and 3D-SFM technologies. For enhancing the operation speed of FM-AFM, we needed to improve both the minimum detectable force (Fmin) and the feedback bandwidth (BFB). We previously showed that Fmin can be improved by ~7.3 times using a small cantilever (f0 of ~3.5 MHz). This implies that we can improve BFB by ~50 times without deteriorating Fmin. To achieve this BFB, we have improved the bandwidth and latency of various components such as scanner, cantilever deflection sensor, excitation unit and frequency shift detector. With these components, we have succeeded in atomic-resolution imaging of calcite crystal dissolution process in water at 1 s/frame. To combine these technologies with 3D-SFM, we implemented additional functions for modulating the Z tip position and recording the force variation in the field programmable gate array (FPGA) used for high-speed FM-AFM. With the developed system, we achieved 3D-SFM imaging at an interface between calcite and its supersaturated solution at 5 sec per 3D image. In spite of the fast imaging speed, the subnanometer-scale hydration structure was clearly visualized. We plan to apply this new technique to investigate calcite dissolution process. Our previous high-speed FM-AFM studies revealed that a transition region with a few nanometer width is formed at the step edges on the calcite surface as an intermediate state during its dissolution. By visualizing dynamic changes in the 3D hydration structures near the step edges, we aim to achieve detailed understanding of the origin for the transition region and eventually the atomistic dissolution processes at the step edges.
10:45 AM - TC01.09.07
Visualizing Inhomogeneous Molecular Adsorption Structures of a Lubricant Layer on a Magnetic Hard Disk by 3D-SFM
Keisuke Miyazawa 1 , Naoki Nakajima 1 , Mariko Toyoda 1 , Ryosuke Sagata 2 , Tsuyoshi Shimizu 2 , Takeshi Fukuma 1 3
1 , Kanazawa University, Kanazawa Japan, 2 , MORESCO Corporation, Kobe Japan, 3 , ACT-C, Kawaguchi Japan
Show AbstractThree-dimensional scanning force microscopy (3D-SFM) was developed based on frequency modulation atomic force microscopy (FM-AFM). In this method, an AFM tip is three-dimensionally scanned at a solid-liquid interface, and we record a 3D distribution of the force applied to an AFM tip with subnanometer-scale spatial resolution. Recent studies suggested that 3D-SFM is able to visualize averaged conformations of flexible molecular structures as well as hydration structures. Such unique capability of 3D-SFM is ideally suited for satisfying requirements from many industrial fields, where molecular adsorption layers are used for controlling surface properties. For example, a magnetic hard disk (HD) in a hard disk drive (HDD) is coated with an approximately 1 nm lubricant layer made of perfluoropolyether (PFPE) for protecting the HD from mechanical damage, corrosion and contamination. Recently, the thickness of lubricant layer is reduced to less than 1 nm to improve the memory density of a HD. To satisfy this demand, the real-space model of molecular-adsorption structure of lubricant layer should be understood. However, due to the lack of a direct imaging tool for molecular adsorption layer, real adsorption structure of lubricant layer has not been well understood.
In this study, we have performed 3D-SFM measurements of the lubricant layer on the HD, and investigated the possibility of 3D-SFM imaging of the molecular adsorption structures with molecular-scale resolution. The measured 3D force image clearly shows molecular-scale fibrillar contrasts, which show strong correlation with the expected molecular adsorption model of PFPE lubricant. In addition, the result visualizes complicated and inhomogeneous arrangements of the fibrillar contrasts in the 3D space. This result suggests that the adsorption structures of the lubricant molecules are more complicated than expected from the molecular conformation obtained by simple energy minimization. Although the relationship between the fibrillar contrasts and the intrinsic molecular adsorption structures may not be simple, the obtained images provide the real-space information that cannot be obtained by spectroscopic methods, and improve our understanding on the adsorption structure of the lubricant layer. This result opens up a wide range of new application fields of 3D-SFM in various industrial fields.
TC01.10: Novel Probes
Session Chairs
Shigeki Kawai
Jason Killgore
Wednesday PM, November 29, 2017
Hynes, Level 2, Room 208
11:00 AM - *TC01.10.01
New AFM Probe to Characterize Mechanical and Functional Material Properties
Sajith Dharmasena 1 , Randi Potekin 2 , Seok Kim 2 , Lawrence Bergman 2 , Alexander Vakakis 2 , Hanna Cho 1
1 , Ohio State University, Columbus, Ohio, United States, 2 , University of Illinois at Urbana-Champaign, Urbana, Illinois, United States
Show AbstractSince its introduction in 1986, atomic force microscopy (AFM) has been studied in depth to extend its capability as an advanced metrological tool at the atomic scale. Compared to other microscopy techniques ‘seeing’ a surface via photon or electron, AFM is unique in that it employs a mechanical transducer (i.e., a micro-cantilever with a nanoscale tip) to touch a surface and then transduce its ‘feeling.’ While AFM is widely used to image a sample with nanometer scale resolution, recent research efforts focus on expanding the capability of AFM for various material characterizations by better interpreting the feeling encoded in the cantilever’s dynamic motion.
We developed a new AFM probe design that can better deliver the information into the cantilever motion. This new cantilever system consists of a base cantilever incoportating an inner paddle in the form of a silicon nano-membrane. This two-field microcantilever design enables either to utilize multi-harmonics during tapping mode operations or to maintain an invariable frequency during contact resonance mode operations as in Piezoresponse Force Microscopy (PFM). For the tapping mode operation, the inner paddle is carefully designed to achieve a rational (1:n) eigenfrequency ratio to significantly enhance the nth higher harmonic via internal resonance triggered by nonlinear tip-sample interactions. This higher harmonic is demonstrated to be sensitive to the mechanical property of a sample by directly measuring the averaged tip-sample force at every cycle. For the contact resonance mode utilized to characterize functional material properties (e.g., PFM, contact Kelvin Probe Force Microscopy, and AFM-IR), a typical cantilever system suffers from the topographic crosstalk due to the change of contact resonance frequency depending on the contact stiffness. In the aforementioned cantilever system, however, the inner paddle can freely oscillate independent of the local contact conditions, providing a stable and invariable frequency reference to amplify the functional response of the material to mitigate the crosstalk issue.
11:30 AM - TC01.10.02
Nanophotonic AFM Transducers Enable Nanoscale Chemical Composition and Thermal Conductivity Measurements at the Nanoscale
Jungseok Chae 1 , Georg Ramer 1 , Sangmin An 1 , Vladimir Aksyuk 1 , Andrea Centrone 1
1 , National Institute of Standards and Technology, Gaithersburg, Maryland, United States
Show AbstractThe use of atomic force microscopy (AFM) and related techniques is pervasive in nanoscience and biology because, in addition to the sample topography, they provide maps of many sample properties with high spatial resolution. For example, photothermal induced resonance (PTIR) is an emergent technique that combines the spatial resolution of AFM with the specificity of absorption spectroscopy, enabling material identification, molecular conformational analysis, mapping of composition and electronic bandgap at the nanoscale. In PTIR, the absorption of a laser pulse induces a rapid thermal expansion of the sample. Conventional cantilevers are too slow to track the thermal expansion dynamics of the sample; however, the fast sample expansion kicks the cantilever in oscillation (like a struck tuning fork), with amplitude proportional to the absorbed energy.
Here, we revolutionize AFM signal transduction by integrating cavity-optomechanics for sensing the motion of fast, nanosized/picogram scale AFM probes with unprecedented precision and bandwidth, thereby breaking the trade-off between AFM measurement precision and ability to capture transient events. Applied in PTIR, the probe near-field ultralow detection noise and wide bandwidth improves the time resolution, signal-to-noise ratio and throughput by a few orders of magnitude each. Remarkably, this synergy enables a new PTIR measurement modality: capturing the previously inaccessible fast thermal-expansion response of the sample to nanosecond laser pulses, thus allowing concurrent measurement of the chemical composition and thermal conductivity, at the nanoscale, for the first time.
As first demonstration, we validate these new capabilities using polymer films and measure the intrinsic thermal conductivity (η) of metal-organic framework (MOF) individual microcrystals, a property not measurable by conventional techniques. MOFs are a class of nanoporous materials promising for catalysis, gas storage, sensing and thermoelectric applications where accurate knowledge of η is critically important.
Additionally, the improved sensitivity enable measurement of nanoscale IR spectra of monolayer this sample with high signal to noise ratio (≈ 170).
We strongly believe that the radical AFM innovation enabled by nanofabrication, nanophotonics and cavity-optomechanics is broadly-applicable and will benefit a wide range of dynamic observations in nanoscience and biology and it greatly improve the impact of the PTIR technique in those fields.
11:45 AM - TC01.10.03
Single Crystal Doped Diamond Tips for Enhanced Nanoelectrical Characterization
Peter De Wolf 3 , Jason Kilpatrick 1 2 , Colm McManamon 2 , Hector Cavazos 2
3 , Bruker Nano Surfaces, Santa Barbara, California, United States, 1 , University College Dublin, Dublin Ireland, 2 , Adama Innovations, Dublin Ireland
Show AbstractAFM provides powerful techniques for nanometer scale characterization of electrical properties such as charge, potential, conductivity, capacitance, and piezo-electric response. The availability of a wear resistant, highly conductive, high-resolution probe is a critical component for successful & reliable measurements. Traditionally, Si probes coated with a conductive layer (metal or doped diamond) or solid metal probes are used. These probes however demonstrate poor spatial resolution, limited by the relative large tip radii of these probes, and sensitivity to tip wear, the thin (and relatively soft) metal coatings often lead to low repeatability and degradation of signal/noise ratio and/or spatial resolution. The limitations are exacerbated for electrical modes requiring constant tip-sample contact (contact-mode), as this results in relatively high lateral and normal forces.
Here we report on the fabrication and performance of single crystal doped diamond tips for high resolution electrical and electromechanical applications. We demonstrate that single crystal diamond probes with < 10nm tip radius with superior electrical and mechanical properties. This unique combination of strength, conductivity and high-resolution in a wafer scale fabricated probe enables unique access to a parameter space previously unobtainable using traditional AFM probes. Contact based modes - Tunneling-AFM (TUNA), Piezo Force Microscopy (PFM), Scanning Capacitance Microscopy (SCM) and Scanning Spreading Resistance Microscopy (SSRM) - are demonstrated with samples which are known to be challenging. Tests indicate a drastic increase in tip lifetime (> 10x) and significant improvements in spatial resolution, while providing similar sensitivity as compared to conventional probes.
The relatively high normal & lateral forces in contact-mode based electrical modes, also prohibit high-resolution and repeatable nanoscale electrical characterization on soft & fragile samples. This additional limitation can be overcome by Peak Force Tapping - which eliminates lateral forces and provides normal force control to below 50pN. We demonstrate that Peakforce based electrical modes such as Peakforce TUNA, Peakforce SSRM and Peakforce KPFM can also benefit from single crystal doped diamond probes due to their unique combination of strength, conductivity and resolution. These properties combine to deliver an unsurpassed ability to probe nanomechanical and electrical properties simultaneously at high-resolution without compromise.
TC01.11: Equipment and Calibration
Session Chairs
Wednesday PM, November 29, 2017
Hynes, Level 2, Room 208
1:45 PM - TC01.11.01
Tuning Dynamic Spring Constants to Minimize Electrostatic Artifacts in Piezoresponse Force Microscopy
Gordon MacDonald 1 , Frank DelRio 1 , Jason Killgore 1
1 , National Institute of Standards and Technology, Boulder, Colorado, United States
Show AbstractIt is well established that compared to low spring constant cantilevers, cantilevers with higher spring constant are less susceptible to body electrostatic forces that arise due to the capacitance between the sample and cantilever body during an AC bias-induced strain measurement such as piezoresponse force microscopy (PFM). This has forced the user to make a tradeoff between precise DC force control (i.e. choosing a low stiffness cantilever) and electrostatic artifact minimization (i.e. choosing a high-stiffness cantilever). Here, we demonstrate that it is the dynamic spring constant of the cantilever, rather than the quasistatic spring constant, that is responsible for the body electrostatic artifact. Thus, by tailoring the dynamic stiffness with higher cantilever eigenmodes or the addition of precisely placed mass, it is possible to reduce the electrostatic contribution to negligible levels. PFM results with varying dynamic stiffness are demonstrated on a periodically poled lithium niobate (PPLN) sample. The fabrication of the sample should result in domains exhibiting 180° phase shift and minimal amplitude contrast. For the 1st eigenmode of a 0.3 N/m camtilever, the PFM results indicate only a 1° to 2° phase shift, correlating with an amplitude signal wherein only 10 % of the magnitude arises from the desired surface strain response, and 90 % of the amplitude is from the electrostatic artifact. For the 4th eigenmode, the result dramatically improves, with near perfect 180 degree phase shift between domains, and a factor of 5 reduction in amplitude contrast. Using this approach, the piezo contribution dominates the observed amplitude, with the piezo contribution estimated to be greater than 90% of the measured signal. Similar gains in dynamic stiffness have also been achieved with added mass on the end of the cantilever. Overall, these data indicate that reliable PFM results can be obtained with a much broader range of cantilever types than previously thought possible, enabling characterization of more delicate materials at higher spatial resolutions.
2:00 PM - TC01.11.02
Electrical Transport Measurements with Atomic Precision by 4-Probe SPM
Markus Maier 1
1 , Scienta Omicron GmbH, Taunusstein Germany
Show AbstractA major challenge in the development of novel devices in molecular and atomic scale electronics is their interconnection with larger scaled electrical circuits. Local electrical probing by multiple probes with atomic precision can significantly improve efficiency in analyzing electrical properties of individual structures without the need of a full electrical integration.
The LT NANOPROBE merges the requirements of a SEM navigated 4-probe system and an ultimate stability SPM, with each probe suitable for STM, nc-AFM (QPlus), spectroscopy and atom manipulation. The system is operated near thermal equilibrium at T< 5K and has been developed towards an extremely low thermal drift, which is the most important ingredient to allow for enough measurement time on atomic structures.
We will present measurements that prove the performance level of the instrument, specifically low thermal drift and pm stability and present atomic scale lateral transport measurement on dangling bond dimer rows created on hydrogenated Ge(001).
2:15 PM - TC01.11.03
Forces from Voltages in AFM
Fredy Zypman 1 , Matthew Feinstein 1 , David Friedenberg 1 , Steven Eppell 2 , Li Li 2 , Loren Picco 3 , Oliver Payton 3
1 , Yeshiva University, New York, New York, United States, 2 , Case Western Reserve University, Cleveland, Ohio, United States, 3 , University of Bristol, Bristol United Kingdom
Show AbstractForce is the quintessential quantity in AFM. Knowledge of tip-sample forces opens up a plethora of topographic and spectroscopic possibilities at the nanoscale. Yet, in no implementation does the AFM measure forces directly. For instance, in its most common setup, the AFM provides voltages that are proportional to angular bends and twists of the cantilever. This voltage signal is the only information available for the determination of forces. In this context the core question is, how do we turn AFM voltages into physical forces?
In static and quasi-static situations, the answer to the question is simple; the voltages are proportional to the forces. The cantilever can be properly modeled as a single spring whose constant is obtained by standard methods developed in the AFM community. This approach is pervasive in the AFM community.
Another common approach incorporates inertia by modeling the cantilever as a mass-spring system. In this case cantilever displacement is considered to be proportional to the voltage and, from its time dependence, cantilever acceleration can be obtained and used (when multiplied by cantilever mass) as a putative measure of the force. This analysis assumes a single mode of cantilever excitation.
However, higher modes of oscillation are routinely excited in AFM scans. To analyze the problem completely, one can resort to use of the Euler-Bernoulli equation valid for slender beams undergoing small perturbations. In cases like the snap-to-contact event where the boundary conditions are time dependent, this problem is not amenable to solution by standard frequency transform techniques. On the other hand, any practical solution to the problem requires a blind reconstruction. That is, the full shape of the cantilever needs to be reconstructed from voltage information coming only from its hanging extreme. We recently presented a method to compute the full shape from the available information. However, lack of nanoscale calibration standard, made it difficult to directly evaluate the limitations of the approach. For example: when is the cantilever not slender enough? And, how small do the displacements need to be to give forces to within a prescribed maximum uncertainty?
Using a special experimental arrangement, we measured cantilever displacement at multiple locations along its long axis. The experimental results are compared with the theoretical blind reconstruction using inputs only from the free end of the cantilever. We show the comparison between the two and use the theory to set limits on the usability of simpler models such as the spring or spring-mass simple harmonic oscillator.
3:30 PM - TC01.11.04
Development of High Speed AFM Operating at 1,000 Lines/s & 15x15x3µm XYZ Scan Range
Umit Celik 2 3 , Ihsan Kehribar 2 , Yigit Uysalli 1 , Kubra Celik 3 , Hakan Ozgur Ozer 4 , Ahmet Oral 1 2
2 , NanoMagnetics Instruments, Ankara Turkey, 3 Materials Science and Engineering, Istanbul Technical University, Istanbul Turkey, 1 Physics Department, Middle East Technical University, Ankara Turkey, 4 Physics Engineering Department, Istanbul Technical University , Istanbul Turkey
Show AbstractAtomic Force Microscopy (AFM) is a member of scanning probe microscopy family that allows characterizing the surfaces in 3D at nanoscale. Atomic Force Microscopes are widely used in many fields such as material science, biophysics, nanotechnology and industrial process control. However, AFM scanning speed limits the usability and application areas. The surface imaging for a given area with standard AFMs takes at least a few minutes. The dynamic phenomena occurring on the surfaces occur much faster than this speed. High-speed Atomic Force Microscopes (HS-AFM) enables the investigation of structural changes of materials and dynamic phenomena occurring on the surfaces. We developed a HS-AFM that can take the images at 8 frames/sec (f/s) of a 15μm2 scan area. A flexure based HS-AFM scanner with 15μmx15μmx3μm scanning area was developed and manufactured. The XY scanner resonance frequency was measured to be approximately 7kHz. We developed a dual Z scanner to increase the bandwidth of Z scanner. First flexure guided Z scanner resonance frequency was about 155kHz. We used a high bandwidth stack piezo actuator for the first stage. Second Z scanner resonance frequency measured to be around 1.6MHz. We used single crystal PMN-PT piezo layer to have larger displacement and higher resonance frequency. FPGA-based high-speed control electronics was developed. A novel multistage dynamic PID controller was developed. It allows scanning faster even the rough surfaces without any damage. A single cycle AC signal amplitude detector was developed to measure the cantilever oscillation amplitude. A novel direct digital synthesizer (DDS) based scan signal generator and data capture system was developed. It allows manipulating the scan signal waveform and data acquisition points. In addition, DDS based scan signal generator allows very sensitive scanning speed control as an advantage. The scanner is driven by sinusoidal waveform and data is acquired at equidistant positions. This allows the scanner to scan at high speed without stimulating the resonance frequency. A high bandwidth USB 2.0 data transfer was implemented that allows 40Mb/sec to transfer the image data in real-time. A high bandwidth HS-AFM piezo driver was developed to drive the HS-AFM scanner. Piezo driver is capable of driving a piezo with 1800nF at 1000Hz from -30 to 130V swing. In addition, Z channel piezo driver was optimized for 150 kHz bandwidth. We also worked on a tip-scan HS-AFM system to scan larger samples at high speed. Beam tracking lens method is simulated to measure the beam tracking errors. A laser beam tracking system was developed to compensate the laser beam tracking errors. We imaged calibration test sample, blu-ray disc, FeS oxidation and gold electroplating on an aluminum surface at high speeds.
3:45 PM - TC01.11.05
Expanding Functionality of Atomic Force Microscopy with Environmental Studies
Shijie Wu 2 , Sergei Magonov 1
2 , Keysight Technologies, Santa Clara, California, United States, 1 , SPM Labs LLC, Tempe, Arizona, United States
Show AbstractAtomic force microscopy (AFM) is broadly applied at ambient conditions for high-resolution visualization of surface structures and quantitative studies of their mechanical and electric properties. The use of this technique in various environments, which uniquely differentiates AFM in family of microscopic methods, is rather limited with majority of measurements being performed in water. The studies of materials in vapors of non-solvents and solvents are less common. We will demonstrate that such applications are invaluable for studies of variety of surface phenomena (wetting/dewetting, swelling, hydration, etc) and for visualization of vapor-induced structural and conformational changes. The environmental studies were done with Keysight 9500 scanning probe microscope in air of different humidity and in organic vapors of methanol, chloroform, and ethyl acetate. The measurements were performed in oscillatory amplitude modulation (AM) mode and Quick Sense (QS) mode on variety of polymers including brush macromolecules, which are formed of poly(methacrylate) backbone with grafted side chains of poly(butyl acrylate), liquid crystalline oligomer and multicomponent materials. Changes of surface morphology of polymers observed in different environments were related to their recrystallization, structural transformations, selective swelling and dewetting process. Selective swelling has helped in identification of the constituents of polymer blends and complex compounds. Imaging of cholesteric liquid crystalline material in chloroform vapor has revealed structural transition with substantial increase of the pitch charactering its surface order. This transition is directly related to selective optical reflectivity of this material. A partial swelling of side chains of the brush macromolecules in ethyl acetate and methanol vapors facilitates high-resolution visualization of the backbones’ conformations and a corona of side chains. Slow aggregation of the individual macromolecules into large domains was monitored in methanol vapor, and this process has accelerated in humid air.
4:00 PM - TC01.11.06
Surface Topography across Length Scales—The Experimental Characterization of Ultrananocrystalline Diamond from Angstroms to Centimetres
Abhijeet Gujrati 1 , Subarna Khanal 1 , Tevis Jacobs 1
1 , University of Pittsburgh, Pittsburgh, Pennsylvania, United States
Show AbstractWhile scanning probe microscopy has enabled unprecedented advances in the multi-functional characterization of surfaces at nanometer length scales, these insights cannot always be scaled up to describe the component scale properties of the same surfaces. One reason for this is that surfaces have multi-scale surface roughness, which affects functional properties such as adhesion, friction, and electrical and thermal transport. While SPM can, of course, measure surface topography, its range of scales is limited: by scan size on the large end, and by tip artifacts on the small end. While the height resolution may be on the Ångström-scale, the lateral resolution of rough-surface topography is frequently limited to tens of nanometers at best. For this reason, it is difficult to experimentally apply the many analytical and numerical models that predict the mechanical and functional behaviour of rough surfaces, and thus that predict their functional properties on a component-scale.
To fill this gap, the topography of ultrananocrystalline diamond (UNCD) surfaces has been characterised across an unprecedented 9 orders of magnitude – using scanning probe microscopy for the μm-nm-scale and combining it with stylus profilometry for the large scale (μm-cm) and transmission electron microscopy for the small-scale (nm-Å). By using spectral analysis of the surfaces, these multi-scale measurements can be combined into a single statistical description of the surface. It is shown that SPM-based measurements of roughness parameters can differ by more than an order of magnitude from the same measurements computed with the multi-resolution measurements. Further, the resultant predictions for surface-scale adhesion, friction, and interfacial transport can be off by just as much. Finally, estimation techniques will be discussed for extracting a more accurate description of multi-scale surface topography using only SPM-based measurements.
4:15 PM - TC01.11.07
Electrochemical Atomic Force Microscopy—Pushing the Limits of Speed, Environmental Control and Imaging Resolution
Nathan Kirchhofer 1 , Marta Kocun 1 , Aleksander Labuda 1 , Roger Proksch 1
1 , Oxford Instruments Asylum Research, Goleta, California, United States
Show AbstractWe present the high-resolution, fast-scanning electrochemical atomic force microscopy (EC-AFM) achieved with the Cypher ES Electrochemical Cell (EC Cell). The EC Cell utilizes blueDriveTM photothermal cantilever excitation, and maintains Cypher’s atomic resolution in numerous electrolyte solvents—from aqueous to ionic liquids to organic carbonates—while allowing surface potential control with an external potentiostat. The probe holder design allows for simultaneous liquid and gas perfusion, providing precise environmental control, and all components are manufactured from chemically inert materials. The entire EC Cell may be assembled inside the glovebox and transferred air-free to the scanner, where stringent O2-free conditions are maintained. These features enable high-resolution images to be acquired (atomic step edge widths < 3 nm) at scan rates up to 120 lines/s, enabling detailed spatiotemporal monitoring of electrochemical processes. Results demonstrate high-resolution electrochemically-controlled topographical features of metal deposition and stripping, Li-ion battery electrode operation, electroactive semiconductor surfaces, electron-transfer kinetics, and more. These EC-AFM results will be discussed in relation to electrochemical scanning tunneling microscopy (EC-STM), scanning electrochemical microscopy (SECM), electrochemical strain microscopy (ESM), and other advanced EC techniques
TC01.12: Other Novel Force Spectroscopy
Session Chairs
Wednesday PM, November 29, 2017
Hynes, Level 2, Room 208
4:30 PM - TC01.12.01
Quantifying Local Surface Forces Accurately Using Scanned Probes—Strategies, Challenges and Solutions
Omur Dagdeviren 1 , Chao Zhou 1 , Eric Altman 1 , Udo Schwarz 1
1 , Yale Univ, New Haven, Connecticut, United States
Show AbstractAtomic force microscopy is an analytical surface characterization method that is able to map topography along with a variety of different sample properties in real-space at high resolution. One example for such properties is the local tip-sample interaction potential, which is accessible by performing force spectroscopy experiments where the frequency shift or oscillation amplitude and phase data are recorded as a function of tip-sample distance. In this presentation, we theoretically and experimentally show that the interaction potentials obtained from such data using the most commonly applied methods deviate noticeably from the actual interaction potentials when the oscillation amplitude of the probe is of the order of the decay length of the interaction potential. Caused by the neglect of higher harmonics in the mathematical reconstruction procedures, the related inaccuracies can be effectively suppressed by using oscillation amplitudes sufficiently larger than the decay length of the interaction potential. To facilitate efficient data acquisition, we propose a novel technique that includes sweeping the drive amplitude at a constant height from the surface while monitoring the oscillation amplitude and phase. Ultimately, such amplitude sweep-based spectroscopy enables shorter data acquisition times and increased accuracy for quantitative chemical characterization compared to standard approaches that modulate the tip-sample distance. An additional advantage is that since no feedback loop is active while executing the amplitude sweep, the potential can be consistently recovered deep into the repulsive regime.
4:45 PM - TC01.12.02
Fast Free Force Reconstruction (F3R) in Non-Contact SPM Using the G-Mode Platform—Breaking the Time Barrier in Kelvin Probe Force Microscopy
Liam Collins 1 , Sergei Kalinin 1 , Stephen Jesse 1
1 , Oak Ridge National Laboratory, Oak Ridge, Tennessee, United States
Show AbstractSince its inception, the atomic force microscope (AFM) has offered unparalleled insight into both nanoscale structure and surface functionality across all fields of science. At the same time, compared to other common microscopy techniques (e.g. optical, scanning electron microscopy etc.), the spatial resolution afforded by AFM is counterpoised by the slow detection speeds. This ultimately limits AFM based measurements to equilibrium or quasi-static processes. For example, while Kelvin probe force microscopy (KPFM) is useful for quantifying “static” electronic, ionic or electrochemical functionalities across sub-micron length scales, it cannot be used to describe electroactive materials involving fast (<< ms) response times. In this presentation, I will outline a novel time resolved AFM imaging approach, referred to as Fast free force recovery (F3R) utilizing big data capture and analytics. F3R-AFM is based on the G-mode acquisition platform [1] allowing direct reconstruction of the tip-sample forces with much higher temporal resolution (~µs) than is possible using classical homodyne/heterodyne detection methods (~ms). I will describe how fast data acquisition, coupled with multivariate statistical denoising methods, can be harnessed to overcome the widely viewed temporal bottleneck in AFM, the mechanical bandwidth of the cantilever. Further, I will demonstrate quantitative recovery of electrostatic forces with <20 µs time resolution, free from influences of the cantilever ring-down. Finally, I will demonstrate one immediate application of this approach by demonstrating high speed F3R - KPFM for exploring electric field induced ion migration in solar cell devices.
[1] Belianinov, Alexei, Sergei V. Kalinin, and Stephen Jesse. "Complete information acquisition in dynamic force microscopy." Nature communications 6 (2015).
This research was conducted at the Center for Nanophase Materials Sciences, which is a DOE Office of Science User Facility.
TC01.13: Poster Session II
Session Chairs
Laura Fumagalli
Santiago Solares
Thursday AM, November 30, 2017
Hynes, Level 1, Hall B
8:00 PM - TC01.13.01
Circles—A Novel Scheme to Interpret Linear, Nonlinear and Dissipative Interactions in Scanning Force Microscopy
Pablo Contreras Velez 1 , Juan Francisco Gonzalez Martinez 2 1 , Jaime Colchero 1
1 , Univ de Murcia, Murcia Spain, 2 Biomedical Sciences Department, Faculty of Health and Society, Malmö University, Malmö Norway
Show AbstractIn this work a new scheme to interpret and unify linear, nonlinear as well as dissipative interactions is proposed. Using the classical model for the driven damped harmonic oscillator, its response is described by means of a complex number and it is shown how the processing of the deflection signal (normal force) by a typical “Tapping Box” (using essentially a Lock-In technique) allows visualizing the state of the SFM system on an oscilloscope. That is, the complex gain of the tip-sample system can be visualised directly and in real time as a point on the oscilloscope.
Using the Virial Theorem and essentially using the work of [1] as starting point, we show how a linear SFM system can be easily interpreted in terms of “Circles”. Essentially, as the drive frequency is tuned through the resonance frequency the outputs of a typical “Tapping Box” describe to a very good approximation a “Circle” when visualised in xy-mode on an oscilloscope. Interestingly, our model shows that this “Circle” remains essentially invariant when including the non-linearity of typical tip-sample interactions. As will be shown, these “Circles” are distorted only by dissipation which varies with tip-sample distance. We therefore propose that this representation scheme allows a very sensitive method to separate the effect of conservative interactions (linear as well as non-linear) from the effect of dissipative interactions.
Summarising, the polar plot of the complex amplitude relation from the driven damped harmonic oscillator (“circles”) establishes on the one hand a very visual representation of linear, nonlinear and dissipative interactions, and on the other hand a very direct interpretation of experimental data (a data point on an oscilloscope) with the fundamental parameters describing the oscillation state of the SFM system. Despite the simplicity of the scheme, experimental results show its effectiveness.
[1] Álvaro San Paulo y R. García. “Unifying theory of tapping-mode atomic-force microscopy”. Physical Review B, 66, 041406, 2002.
8:00 PM - TC01.13.02
Combining Machine Learning and Physical Modeling for Analysis of Multifrequency AFM Data
Daniel Forchheimer 2 1 , Per Anders Thorén 2 , Riccardo Borgani 2 , David Haviland 2
2 Nanostructure Physics, The Royal Institute of Technology (KTH), Stockholm Sweden, 1 , Intermodulation Products AB, Stockholm Sweden
Show AbstractModern SPM techniques often provide a large amount of measured data at each image pixel, such as amplitude and phase at multiple frequencies in multifrequency dynamic AFM. These very large data sets can be quite useful for measuring physical properties of the surface or enhancing image contrast. The analysis of this “big data” can be divided in to two distinct categories: either physical modeling or "black box" modeling. The former sometime also called "white box" modeling to contrast it with the later, starts with a physical model of the SPM apparatus and surface under investigation. The system is described with as much detail as needed using as much a priori knowledge as possible, so that one may deduce the results of the measurement from either analytic or numerical analysis of the model.. Successful modeling requires a good understanding of the physical principles involved as well as careful calibration of each sub-component, such as cantilever stiffness and its resonance frequency etc. When the data is fit to a carefully stated and well-calibrated white box model, one is rewarded with quantiatitive measurement of a physical property of the surface. In contrast, the black-box approach uses a minimal amount of a priori knowledge of the physical apparatus, rather making use of machine learning algorithms and the large number of ‘features’ in the multi-dimensional data set, where statistical measures and correlations reveal qualitative changes in physical properties of the surface, or enhance contrast in an image.
We have studied a complex multi-component polymer surface using Intermodulation AFM. The cantilever is driven at two frequencies near a single resonance frequency and multiple intermodulation products are recorded at each image pixel, resulting from the nonlinear tip-surface interaction [1]. We analysed the multi-frequency data set using both white-box and black-box methodologies and our conclusion is that a combination of both approaches is especially useful. The surface had a highly inhomogeneous mechanical response, containing very soft and rubbery-like regions that we know from experience are well described by physical model that takes motion of the surface into account [2]. However, this model is numerically demanding to evaluate at each pixel (several seconds per pixel) and thus not feasible to apply to each pixel. By first applying a black-box method, in this case the K-means algorithm, we could rapidly group together all pixels having similar properties and identify a small set of "key pixels" that characterize the larger group. The physical modeling is then performed on these key pixels to reveal quantitative physical properties representative of that group.
[1] Platz, D. et al. Appl. Phys. Lett. 92, 153106 (2008).
[2] Haviland, D. et al. Soft Matter (2015). doi:10.1039/C5SM02154E
8:00 PM - TC01.13.03
Pycroscopy—A Community-Driven Software Package for Analyzing Microscopy Data
Suhas Somnath 1 , Chris Smith 1 , Stephen Jesse 1 , Rama Vasudevan 1 , Nouamane Laanait 1 , Sergei Kalinin 1
1 , Oak Ridge National Laboratory, Oak Ridge, Tennessee, United States
Show AbstractSince the past fifteen years, microscopy has been undergoing profound changes, driven by experimental data that are rapidly growing in dimensionality and size, increased accessibility to high-performance computing (HPC) resources, and more sophisticated computer algorithms than ever before. These changes are especially pronounced in the imaging of functional materials. However, the software supplied with scanning probe microscopes are typically very expensive, do not provide access to advanced or user-defined data analysis routines. Furthermore, by storing data in proprietary formats, these proprietary software and data formats not only impede data analysis but also hinder continued research and instrument development, especially in the age of “big data”. Therefore, moving to the forefront of data-intensive materials research requires general and unified data curation and analysis platforms that are HPC-ready and open source.
To address these challenges, we have developed a software package called Pycroscopy, that uses an open-source approach for analyzing and storing data. Pycroscopy is freely available via popular software repositories, and therefore lifts any financial burden for handling data. We use an instrument-independent data structure that allows us to reuse the same analysis routines regardless of the instrument of origin, greatly simplifies the correlation of data acquired from multiple microscopes, which is necessary for comprehensive studies of materials. The data is stored in hierarchical data format (HDF) files that can be accessed and modified using any programming language, scale well from kilobyte to terabyte sized datasets, and can readily be used in HPC environments unlike proprietary data formats. More crucially, such formatting choices ensure that the data is curation-ready and therefore both meet the guidelines for data sharing issued to federally funded agencies and satisfies the implementation of digital data management as outlined by the United States Department of Energy. Unlike many other software packages that focus on analytical routines specific to an instrument, the general definition of Pycroscopy can be readily adopted for different characterization techniques. Scientific workflows in Pycroscopy are readily accessible as dynamic Jupyter notebooks that contain text, images, code snippets, and resultant plots that make the traceability and reproducibility of results fully transparent. Furthermore, the generality of Pycroscopy provides material scientists access to a vast and growing library of community-driven data processing and analysis routines that far exceed those provided by instrument manufacturers and are desperately needed in the age of big data. In summary, Pycroscopy can greatly accelerate materials research and discovery through the realms of big, deep, and smart data.
8:00 PM - TC01.13.04
Exploring Polarization Dependent Absorption in Plasmonic Structure with Photothermal Nanomechanical Detection
Negar Otrooshi 3 1 , Abraham Vasquez-Guardado 2 1 , Debashis Chanda 2 1 , Laurene Tetard 3 1
3 Physics, University of Central Florida, Orlando, Florida, United States, 1 Nanoscience Technology Center, University of Central Florida, Orlando, Florida, United States, 2 The College of Optics and Photonics, University of Central Florida, Orlando, Florida, United States
Show Abstract
Scanning probe microscopy has emerged, in recent years, as a powerful platform to explore light-matter interactions at the nanoscale. By exploiting the high sensitivity of Atomic Force Microscopy (AFM) to local height variations or vibrations of the sample, it is possible to monitor the photothermal expansion resulting from electronic energy transitions taking place as a result of the energy of the incoming infrared laser light excitation of the material probed. This integration of light and AFM paves the way to subwavelength spatial resolution when monitoring the sample’s response. Furthermore, it is possible to use the cantilever to detect the local changes in photothermal expansion, without the need for costly infrared detectors.
Here we study the behavior of cavity coupled plasmonic structures and the effect of polarization of light on the local response of the metamaterial. The plasmonic structure is irradiated by a tunable IR pulsed laser covering the range of absorption of the sample. Upon absorption, energy is transferred to the lattice and heat is generated, leading to thermal expansion. The spatial distribution of the thermal expansion is studied for cavity coupled plasmonic structure and compared to the same plasmonic structure without cavity. In addition, we investigate the effect of polarization with respect to structures orientation on the thermal expansion. The results suggest that using the “hot spots” of the cavity coupled plasmonic structures are significant and offer great potential for single molecule detection and sensing.
8:00 PM - TC01.13.05
Functional Atomic Force Microscopy to Characterize Individual Bacteria with Nanoscale Resolution
Briana Lee 1 , Laurene Tetard 1 2
1 NanoScience Technology Center, University of Central Florida, Orlando, Florida, United States, 2 Physics, University of Central Florida, Orlando, Florida, United States
Show AbstractSingular bacterium rarely pose a significant threat of virulence. However, as the cell undergoes an irreversible process of adhesion to form biofilms, infections and diseases can develop. Such processes have been observed in humans and in plants. As a result, evaluating adhesion and surface properties of individual bacterium with atomic force microscopy has been gaining a lot of interest, particularly for life science. Meanwhile, variations in stiffness, adhesion, or binding interactions within bacterial cells responsible for plant diseases as they interact with pesticides has received limited interest.
This study focuses on developing a novel protocol to explore and understand the behavior of bacteria and biofilm exposed to pesticide treatments in plants. By exploring these properties, we will identify attributes that can potentially serve as markers to develop more potent and targeted treatments. This approach will also offer some insight on the mode of actions of these treatments. Chemical and composition maps of the systems obtained with nanoscale infrared spectroscopy will be presented. These characteristics will be analyzed to assess variability in the populations using principle component analysis. By exploring these bacterial properties and relating the results to conventional bioassays and established literature, we propose a new approach with exciting implications, such as potential clues for the development of more potent treatments for resistant bacteria in medicine or agriculture.
8:00 PM - TC01.13.06
The Role of Room Temperature Ionic Liquids on Substrate Supported Lipid Bilayer Structure and Rupture Force
Chiara Rotella 1 , Antonio Benedetto 1 3 , Pietro Ballone 2 , Brian Rodriguez 1 , Suzanne Jarvis 1
1 School of Physics, University College Dublin, Dublin Ireland, 3 Laboratory for Neutron Scattering, Paul Scherrer Institut, Villigen Switzerland, 2 Department of Physics, Norwegian University of Science and Technology, Trondheim Norway
Show AbstractIonic liquids have garnered significant attention in part due to their potential use in, e.g., energy, pharmaceutical, and antimicrobial applications. Understanding the interaction between room temperature ionic liquids (RTILs) and substrate supported lipid bilayers as a model of the cell membrane is key to using RTILs in pharmaceutical and antimicrobial applications and to identifying the potential health effects of RTILs. Here, we investigate the interaction between 1-palmitoyl-2-oleoyl-sn-glycero-3-phosphocholine (POPC) lipid bilayers, abundant in mammalian cells, and the RTIL 1-butyl-3-methylimidazolium chloride (bmimCl) by atomic force microscopy (AFM) as a function of time after exposing the bilayer to the RTIL. Previous neutron reflectometry studies and molecular dynamic simulations identified irreversible adsorption of [bmim]+ into POPC bilayers and corresponding structural changes. Here, using AFM, the introduction of bmimCl is found to change the mechanical properties of the POPC bilayer, increasing the rupture force (by ~50%), and the thickness of the system due to its penetration into the bilayer. Correspondingly, localized defects in the bilayer are found to reduce in size. The introduction of bmimCl therefore increases the energetic cost of bilayer pore formation by an AFM tip. The observed increased order and rigidity resembles a transition from fluid to gel-like phase.
8:00 PM - TC01.13.07
Photo-Induced Changes in Nanoscale Surface Potential Distribution of Photocatalyst Electrodes Visualized by Open-Loop Electric Potential Microscopy in Electrolyte
Kaito Hirata 1 , Takuya Kitagawa 1 , Takumi Igarashi 1 , Sunao Kamimura 2 , Teruhisa Ohno 2 3 , Takeshi Fukuma 1 3
1 , Kanazawa University, Kanazawa Japan, 2 , Kyushu Institute of Technology, Kitakyushu Japan, 3 , ACT-C, Kawaguchi Japan
Show AbstractPhotocatalytic reactions in electrolyte have attracted much attention due to their importance in energy science. However, nano-level understanding of their mechanisms is often elusive because of the lack of a method able to visualize nanoscale distribution of reaction sites at solid-liquid interfaces. To solve this problem, we recently developed an in-liquid surface potential measurement technique referred to as open-loop electric potential microscopy (OL-EPM). In the previous studies, we demonstrated that OL-EPM can be used for visualizing nanoscale distribution of corrosion reaction sites (i.e. corrosion cells) in electrolyte. In this study, we use this technique to investigate nanoscale distribution of photocatalytic reaction sites on a bismuth vanadate (BiVO4) electrode in electrolyte.
The BiVO4 electrode was prepared by depositing BiVO4 particles with a diameter of 100-200 nm on an FTO/glass substrate. The OL-EPM measurements were performed in 1 mM KCl solution containing 10 wt.% ethanol with the electrochemical potential of the electrode controlled to 0.6 V vs. Ag/AgCl. A cantilever (AC55, Olympos) with Au coating on both front and back sides was used. The 365 nm light emitted from a LED was transmitted through an optical fiber and irradiated onto the sample surface just under the tip. Light intensity at the fiber end was approximately 2 mW.
We measured photo-induced changes in the surface structure and potential distribution by OL-EPM. After a long irradiation of the light, the electrode surface showed relatively uniform potential distribution yet some local sites showed higher or lower potentials than that of the majority of the surface area. Such local sites are mostly located around the grain boundaries, indicating that the grain boundaries can serve as a special reaction site. When we turned off the light, the average potential of the electrode was suddenly decreased. In addition, many local areas showing a lower potential appeared and non-uniform potential distribution was presented. In the potential image obtained by OL-EPM, a higher potential area corresponds to an anodic area, i.e. an active oxidation site. Therefore, these results show that there are some local sites that are inactive under dark condition but they can be activated by the photo-irradiation. These results demonstrate the effectiveness of OL-EPM for studying the local distribution of the photocatalytic reactivity.
8:00 PM - TC01.13.08
Quantitative Conductivity Measurements of Semiconducting Nanostructures with Infrared Near-Field Optical Microscopy
Earl Ritchie 1 , Tucker Mastin 1 , Joanna Atkin 1
1 Chemistry, University of North Carolina at Chapel Hill, Chapel Hill, North Carolina, United States
Show AbstractBy modifying the conductivity with dopants, semiconducting structures can be used for a wide range of optoelectronic applications. However, performance depends on nanometer-scale electronic and structural properties, including surface roughness, mobility, or dopant density. We report the use of mid-infrared scattering-type scanning near-field optical microscopy (s-SNOM) as a non-destructive optical method to extract nanoscale conductivity maps in semiconductors. Combining electrical atomic force microscope (AFM) characterization with mid-infrared spectroscopic analysis, we can extract quantitative local dielectric properties. This capability will enable the use of s-SNOM as an advanced platform for exploratory research and practical characterization of semiconducting structures.
Symposium Organizers
Santiago Solares, The George Washington University
Laura Fumagalli, University of Manchester
Ricardo Garcia, Consejo Superior de Investigaciones Científicas
Jason Killgore, National Institute of Standards and Technology
TC01.14: Hybrid Methods
Session Chairs
Laura Fumagalli
Olga Kazakova
Thursday AM, November 30, 2017
Hynes, Level 2, Room 208
8:30 AM - *TC01.14.01
Infrared and Terahertz Nanospectroscopy—An Emerging Analytical Tool for Science and Technology
Rainer Hillenbrand 1
1 , CIC nanoGUNE, San Sebastian Spain
Show AbstractWith the development of scattering-type scanning near-field optical microscopy (s-SNOM) [1], the analytical power of visible, IR and THz imaging has been brought to the nanometer scale. The spatial resolution of about 10 - 20 nm opens a new era for modern nano-analytical applications. We demonstrated chemical identification [2-4], free-carrier profiling [5] and mapping of plasmon polaritons in 2D materials such as graphene [6-8].
s-SNOM is based on elastic light scattering from atomic force microscope tips. Acting as an optical antenna, the tips convert the illuminating light into strongly concentrated near fields at the tip apex (nanofocus), which provides a means for localized excitation of molecule vibrations, plasmons or phonons in the sample surface. Recording the tip-scattered IR and THz radiation as a function of sample position yields nanoscale resolved images. Using broadband IR illumination and Fourier-transform spectroscopy of the tip-scattered light (nano-FTIR spectroscopy), IR spectra and IR hyperspectral images with 20 nm spatial resolution can be acquired.
In this talk, our recent instrumental advances and applications in materials sciences and nanophotonics will be discussed.
[1] F. Keilmann, R. Hillenbrand, Phil. Trans. R. Soc. Lond. A 362, 787 (2004)
[2] F. Huth et al., Nano Lett. 12, 3973 (2012)
[3] I. Amenabar et al., Nat. Commun. 4:2890 doi: 10.1038/ncomms3890 (2013)
[4] I. Amenabar et al., Nat. Commun. 8:14402 doi: 10.1038/ncomms14402 (2017)
[5] J. M. Stiegler, et al., Nano Lett. 10, 1387 (2010)
[6] J. Chen et al., Nature, 487, 77 (2012)
[7] A. Y. Nikitin et al., Nat. Photon. 10, 239 (2016)
[8] P. Alonso-González et al., Nat. Nanotechnol. 12, 31 (2017)
9:00 AM - TC01.14.02
Exploring the Effect of Heterogeneities and Their Properties on Image Formation for Nanoscale Subsurface Imaging
Mikhael Soliman 1 2 , Fernand Davilla 1 3 , Marcy Yi 1 , Cristian Lacera 1 , Angela Corrigan 1 , Laurene Tetard 1 2 3
1 Nanoscience Technology Center, University of Central Florida, Orlando, Florida, United States, 2 Materials Science and Engineering, University of Central Florida, Orlando, Florida, United States, 3 Physics, University of Central Florida, Orlando, Florida, United States
Show AbstractThe ability to non-destructively probe subsurface features and their properties at the nanoscale implies the development of broad ranging imaging functionalities. The rising interest in subsurface imaging capabilities has been motivated by the needs in fields including semiconductors and life sciences. The versatility of multi-frequency atomic force microscopy, demonstrated in recent years, has also been exploited to subsurface imaging. However, quantitative interpretation of the cantilever dynamics remains challenging.
Here, we compare the variations detected when the samples is actuated with acoustic waves and compare the signals with Atomic Force Acoustic Microscopy to those collected when the tip is actuated to excite its contact resonance with Lorentz Contact Resonance. The comparison is carried out on a set of engineered samples consisting of a buried layer of Nickel in a thicker layer of Gold. Mean contact resonances and standard deviations suggest a sensitivity of ~50-100nm in depth. Our results are expanded to determine the behavior of the material for polymers. Further, we apply these measurements to study the structural and mechanical properties of plant cell walls. Our results indicate amplitude and phase variations within cell layers, suggesting a complex organization of the different biopolymers constitutive of the cell wall.
9:15 AM - TC01.14.03
Dynamic Scanning Probe Microscopies for Mechanical and Chemical Properties Measurements at the Nanoscale
Gheorghe Stan 1 , Richard Gates 1 , Qichi Hu 2 , Kelvin Kjoller 2 , Craig Prater 2 , Alan Myers 3 , Kanwal Jit-Singh 3 , Ebony Mays 3 , Hui Yoo 3 , Sean King 3
1 , National Institute of Standards and Technology, Gaithersburg, Maryland, United States, 2 , Anasys Instruments Incorporated, Santa Barbara, California, United States, 3 , Intel Corporation, Hillsboro, Oregon, United States
Show AbstractVarious dynamic scanning probe microscopies (SPM) have been developed over the last decades to provide nanoscale material properties characterizations. Although in many cases they resemble microscale adaptations of some macroscale measurement counterparts, these techniques distinctively incorporate and take advantage of specific nanoscale interactions. It is therefore suitable to recognize the utility of retrieving different types of nanoscale interactions by combining or correlating various scanning probe microscopies that share the same basic operational mode (e.g. characterization methods operating in the contact mode of atomic force microscopy). In this work, we have combined two SPM-based techniques, namely atomic force microscopy infrared (AFM-IR) for chemical structure and contact resonance atomic force microscopy (CR-AFM) for mechanical properties, to track the effects of processing on the nanoscale structure-property relationship of nanoporous organosilicate patterns with lateral sizes from 20 nm to 500 nm. These patterns are one type of the so-called low-k dielectric materials that provide separation and structural support for the conductive Cu lines in the upper layers of integrated microchips.
In our CR-AFM and AFM-IR measurements, we found that both mechanical and chemical nanoscale properties correlate with feature size and fabrication processes. We observed the change in mechanical and chemical properties due to the selective removal and reinsertion of organic components in 500 nm, 90 nm, and 20 nm wide organosilicate patterns during processing (plasma etching, plasma ashing, wet cleans, metallization). Moreover, from the depth-dependence of the contact stiffness measured by intermittent CR-AFM (ICR-AFM is a newly introduced version of CR-AFM) it was concluded that about 20 nm of the top and sidewalls of the 90 nm fins consist of a thin "crust" layer with increased stiffness relative to the remaining bulk portion of the fins. The investigation also showed that this stiffened "crust" expands over the entire volume of the 20 nm fins. On the other hand, as shown by AFM-IR, this stiffening comes with a pronounced demethylation of the fins that are narrower than 20 nm and this carbon depletion is associated with an undesirable increase in the dielectric constant. A higher dielectric constant will increase the capacitance coupling and the electrical leakage between the Cu lines, reducing the electrical performance of the device. In a similar way, such unique combination of near-subsurface mechanical and chemical characterization can shed new light on understanding the nanoscale structure-property relationship of other materials and structures.
9:30 AM - TC01.14.04
Cross-Correlation of SPM and TERS- Powerful Method for Nanoscale Characterization of 2D Materials
Andrey Krayev 1
1 , AIST-NT Incorporated, Novato, California, United States
Show AbstractRaman spectroscopy proved to be an extremely useful tool for characterization of 2D materials, but its spatial resolution is limited to few hundreds of nanometers, which in many cases is insufficient for resolution of heterogeneities in materials of interest. Tip enhanced Raman spectroscopy (TERS) dramatically improves the resolution of Raman imaging bringing it down to the same scale as conventional scanning probe microscopy (SPM) techniques.
Two-dimensional semiconductors, specifically the broad class of transition metal dichalcogenides (TMDs) attract significant attention of research community in recent years due to the wealth of interesting and potentially applicable phenomena observed in these materials. In order to control the performance of devices based on TMDs, they must be characterized at the scale relevant to the corresponding application, which in most cases today corresponds to a few tens of nanometers.
Cross-correlation of various channels provided by SPM with TERS data allow not only identification of various defects and inhomogeneities in 2D semiconductors, but also provides otherwise unachievable basis for interpretation of observed contrast in these multiple channels.
To illustrate the power of this method, we’ll discuss unexpected increase of the conductivity and TERS response in the wrinkles and folds in flakes of graphene oxide (GO) deposited on gold, significant increase of the intensity of Raman peaks over the nanoscale patterns imprinted in GO with ultrasharp diamond probe as well as cross- correlation of the TERS and tip enhanced photoluminescence mapping that revealed nanoscale heterogeneity in as-grown flakes of monolayers of WS2.
10:15 AM - TC01.14.05
Recent Advancements in Nanoscale IR Spectroscopy (AFM-IR)
Anirban Roy 1 , Eoghan Dillon 1 , Kelvin Kjoller 1 , Craig Prater 1
1 , Anasys Instruments Corp., Santa Barbara, California, United States
Show AbstractFor the last few decades the rapid growth in the field of nanoscience and technology has led to the development of new characterization tools for nanoscale materials. Atomic Force Microscopy (AFM) is one of the primary techniques that provides high spatial resolution topography images as well as insight into a range of material properties, such as, electrical and thermal conductivity, viscoelastic properties etc. However, providing simultaneous chemical information with similar spatial resolution has always been challenging. Nanoscale IR spectroscopy is a proven technique that combines the high spatial resolution of an AFM with the reliable chemical analysis of IR spectro/microscopy (AFM-IR) to characterize nanoscale materials beyond the optical diffraction limit [1-3].
Recent developments in AFM-IR technology have significantly augmented the speed and spatial resolution for chemical analysis. One of the new developments, Tapping AFM-IR imaging, allows IR images at a specific absorption band to be acquired simultaneously with standard tapping mode topography and phase images. The IR signal detection scheme exploits the method used in heterodyne force microscopy by mixing the tapping frequency with the laser pulse repetition rate. By carefully tuning the laser pulse rate, a resonance enhancement is achieved to increase sensitivity down to a few nm thickness. Tapping AFM-IR mode operation also offers superior applicability to a wider range of samples ranging from particulates to thin films and spatial resolution to 10 nm or better.
One of the major applications of AFM-IR focuses on identifying individual components in a multicomponent/mixed system. This often requires numerous measurements followed by rigorous statistical analysis. New hyperspectral AFM-IR technology offers high speed spectral acquisition (50-100x times faster than previous generation) to acquire high quality spectral data over the whole imaging area. Subsequent statistical analysis yields spectra of individual components and generates chemical composition maps to successfully identify components and their spatial distribution.
We will discuss these techniques as well as demonstrate the application of Tapping AFM-IR and Hyperspectral imaging to yield high spatial resolution chemical and compositional mapping for nanoscale composites.
References:
[1] A. Dazzi, R. Prazeres, F. Glotin, and J. M. Ortega, Opt. Lett., 30, 2388-2390 (2005).
[2] F. Lu, M. Jin and M.A. Belkin, Nature Photon., 8, 307 (2014).
[3] A. Dazzi and C.B. Prater, Chem. Rev., 117, 5146-5173 (2016)
10:30 AM - TC01.14.06
Simultaneous Topographical, Electrical and Optical Microscopy of Optoelectronic Devices at the Nanoscale
Naresh Kumar 1 , Alina Zoladek-Lemanczyk 1 , Anne Guilbert 2 , Jenny Nelson 2 , Fernando Castro 1
1 , National Physical Lab, Teddington United Kingdom, 2 , Imperial College London, London United Kingdom
Show AbstractThe parallel non-destructive chemical and physical characterisation of materials at the nanoscale is a highly sought-after capability. However, the lack of analytical techniques that can directly probe these structure property relationships presents a major obstacle to device development. In this work, we demonstrate how the optimisation of the tip and the measurement procedure allows for the simultaneous, non-destructive mapping of the morphology, chemical composition and photoelectrical properties with < 20 nm spatial resolution by combining plasmonic optical signal enhancement with photocurrent atomic force microscopy [1]. We demonstrate that this approach offers subsurface sensitivity that can be exploited to provide molecular information with nanoscale resolution in all three spatial dimensions. Results are corroborated by simulation of the enhanced plasmonic near field and combined analysis of multiple measurement parameters. Such simultaneous measurements allows to directly identify the impact of film nanostructure on optoelectronic function and avoids the challenge associated with post processing image registration, sample contamination or degradation when measurements are performed separately. We apply this method to an organic solar cell and show that we are able to correlate local nanoscale composition to photocurrent generation, including the direct identification of impurities within nanoscopic domains of operating solar cells. The multi-parameter measurement approach demonstrated here is expected to play a significant role in guiding the design of nanomaterial-based optoelectronic devices, by opening new possibilities for advanced investigation via the combination of nanoscale optical spectroscopy with a range of scanning probe microscopy modes.
[1] Kumar et al., Nanoscale, 2017,9, 2723-2731
10:45 AM - TC01.14.07
Photoinduced Thermal Desorption Coupled with Atmospheric Pressure Chemical Ionization Mass Spectrometry for Multimodal Imaging
Matthias Lorenz 1 2 , Chance Brown 1 2 , Roger Proksch 3 , Mario Viani 3 , Aleksander Labuda 3 , Stephen Jesse 2 , Olga Ovchinnikova 2
1 , University of Tennessee, Knoxville, Tennessee, United States, 2 , Oak Ridge National Laboratory, Oak Ridge, Tennessee, United States, 3 , Oxford Instruments, Santa Barbara, California, United States
Show AbstractThe key to advancing materials is to understand and control their structure and chemistry. However, thorough chemical characterization is challenging since existing techniques characterize only a few properties of the specimen, thereby requiring multiple measurement platforms to acquire the necessary information. The multimodal combination of atomic force microscopy (AFM) and mass spectrometry (MS) transcends existing analytical capabilities for nanometer scale spatially resolved correlation of the chemical and physical properties of a sample surface. The combination of AFM and MS using resistively heated cantilever tips for thermal desorption has been demonstrated as a promising pathway for multimodal imaging. However, the nano thermal analysis (nano-TA) heated probes limit the ability to carry out more standard AFM measurements such as PFM, KPFM and cAFM.
To enable a more general application of chemical imaging into an AFM platform, we have developed a novel closed cell sampling on an Oxford Instruments Cypher ES for in situ surface sampling/imaging analysis using photothermal heating of the AFM tip for thermal desorption coupled to a Thermo Orbitrap Velos Pro with inline ionization by atmospheric pressure chemical ionization (APCI). This approach takes advantage of the blueTherm cantilever heating technology developed by Oxford Instruments for localized thermal desorption, and demonstrates its applicability to multimodal chemical imaging using mass spectrometry. The ability to use photothermal heating of an AFM probe versus conventional resistive heating nano-TA technology opens up the possibility for carrying out multiple AFM measurement approaches on a single AFM cantilever, for a true multimodal imaging approach to link chemical composition with material functionality. Additionally, the ability to introduce fast heating rates for the thermal desorption through ps laser pulsing reduces the melting of sample material and improves the access to intact molecules.
We show the use of photothermal heating as a means for thermal desorption surface sampling mass spectrometry. We illustrate the application of the AFM-MS coupling for the analysis of small molecules, i.e. pigment yellow 74 as a test substrate to show 500 nm achievable lateral resolution, as well as show the application to pharmaceuticals and polymer films.