Symposium Organizers
Stephen M. Kuebler University of Central Florida
Paul V. Braun University of Illinois, Urbana-Champaign
Valeria T. Milam Georgia Institute of Technology
Raymond C. Rumpf Prime Research, LC
Francesco Stellacci Massachusetts Institute of Technology
BB1: Direct Laser Writing
Session Chairs
Tuesday PM, April 14, 2009
Room 3005 (Moscone West)
9:30 AM - **BB1.1
Multiphoton Absorption Polymerization: 3D Fabrication and Replication from the Nanoscale to the Macroscale.
John Fourkas 1 2 3
1 Chemistry and Biochemistry, University of Maryland, College Park, Maryland, United States, 2 Institute for Physical Science and Technology, University of Maryland, College Park, Maryland, United States, 3 Maryland NanoCenter, University of Maryland, College Park, Maryland, United States
Show AbstractMultiphoton absorption polymerization (MAP) has become a widely-used method for fabricating 3D microstructures of arbitrary complexity. Due to chemical nonlinearity in the fabrication process, the transverse feature size can be as small as about one tenth of the wavelength of light employed, although the longitudinal feature size is usually a factor of three or more greater than this. We will discuss a new, nonlinear optical approach that gives us broad control over the aspect ratio of the feature size and allows us to create features smaller than one twentieth of the wavelength of light employed. We will also discuss fabrication of larger, 3D devices over centimeter scales for applications such as microfluidics. Finally, we will discuss new approaches for replicating complex 3D structures using soft lithography.
10:00 AM - BB1.2
Three-dimensional Lithography to Micropattern Hydrogels for Biomedical Applications.
Christopher Ober 1 , Shalin Jhaveri 1 , Ji-Hyun Jang 2 , Jing Sha 1 , Zhaoli Zhou 1 , Edwin Thomas 2 , William Shain 3
1 Materials Science & Engineering, Cornell University, Ithaca, New York, United States, 2 Materials Science and Engineering, Massachusetts Institute of Technology, Cambridge, Massachusetts, United States, 3 Wadsworth Center, NYS Department of Health, Albany, New York, United States
Show AbstractMicrofabricated neural prosthetic devices are in the early stages of design and development for chronic recording and stimulation of nervous system function. Interfacing the nervous system with electronic devices for recording and/or stimulation purposes holds great promise for acquiring new understanding of nervous system function as well as for treatment following injury or disease. However, the long-term performance of these devices is, in many cases, compromised by neuron loss and reactive cell responses. One approach to improve the device performance is to release neurotrophins from the device. Neurotrophin release can enhance neuronal survival near the site of the insertion of the device and promote neuronal sprouting towards the device, thereby improving the neuronal connection and enhancing the device performance.Hydrogels, crosslinked polymers that swell in aqueous solution, can be used to deliver neurotrophins from the device. Since, the dimension of the neural device is on the order of microns, microfabrication strategies have to be utilized to produce hydrogel structures on these devices.To that end, a one-step method to microfabricate hydrogels in three-dimensions using two-photon lithography (TPL) was developed. 2-Hydroxyethyl methacrylate and poly(ethylene glycol) diacrylate were used as monomers and Irgacure 651 was used as an initiator. The microfabrication was possible using Air Force chromophores (AFX) having high effective 2-photon absorption cross-section. The swelling ratio of the hydrogels could be varied between 0.03-0.30 by changing the size and shape of the microstructure, as well as by changing the laser power used to microfabricate the hydrogels. One of the drawbacks of using the high two-photon sensitive chromophores is the use of cytotoxic solvents such as toluene to dissolve the hydrophobic chromophores. This severely limits the use of this technique for encapsulation of for example, neurotrophin secreting cells. To overcome this limitation, non-ionic surfactant was used to disperse the AFX chromophores in water. As a result, hydrogels could be directly microfabricated in water via TPL. Hence, hydrogels could be microfabricated directly in any solvent and in any shape and size via TPL, having customized swelling properties. TPL due to its pixel-by-pixel microfabrication process takes a relatively a long-time to pattern a large area. Hence, to overcome that limitation of TPL, a relatively new technique known as phase-mask interference lithography (PMIL) was also employed. By flood exposing a photoresist with a collimated beam through a suitably designed phase mask, one can make complex 3D structures over a large area through this technique. In just seconds, hydrogels could be patterned via PMIL on the entire neural device having open micron sized pores. Neurotrophins could also be delivered from these patterns.
10:15 AM - BB1.3
Investigation of Inorganic Polymers as Thermally Stable Photoresists for Three-Dimensional Microfabrication
Prashant Nagpal 1 , Yoonho Jun 1 , David Norris 1
1 Chemical Engineering and Material Science, University of Minnesota, Minneapolis, Minnesota, United States
Show AbstractInvestigation of Inorganic Polymers as Thermally Stable Photoresists for Three-Dimensional MicrofabricationPrashant Nagpal, Yoonho Jun, and David J. NorrisDepartment of Chemical Engineering & Material Science, University of Minnesota, Minneapolis, MN 55455Multiphoton lithography is a valuable tool for fabrication of three dimensional (3D) microstructures with high fidelity. However, because this process typically utilizes an organic-based photoresist, the resulting structures suffer from poor thermal stability. This can be problematic if further high-temperature processing is required (e.g., coating with refractory metals) or for certain applications (e.g., thermophotovoltaics). Previously, we have developed methylsilsesquioxane prepolymers to use as thermally stable negative-tone photoresists for multiphoton lithography. Here we investigate a variety of silsesquioxane-based oligomers to improve the sensitivity and resolution of these materials. Specifically, we systematically modified the structure, molecular weight, and organic moieties of the prepolymers. Low molecular weight polymer chains were synthesized with different cross-linking groups to use both cationic and free radical polymerization. We then examined the impact of these modifications on the thermal stability of the photoresist by probing the resulting chemical changes via thermal gravimetric analysis (TGA), differential thermal analysis (DTA), and Fourier transform infrared spectroscopy (FTIR). We also tested our photoresists with direct laser writing to generate high fidelity 3D microstructures. The highest contrast and thermal stability (>750 °C) was achieved with methylsilsesquioxane-based oligomers that were polymerized with a photoacid. The polydispersity of the prepolymer was critical for obtaining high resolution. This work demonstrates that detailed chemical understanding of these materials can lead to improved resolution and thermal stability.
10:30 AM - BB1.4
Structure-Reactivity Relationship in D-π-A-π-D-based Photoinitiators for the Two-Photon Induced Photopolymerization Process.
Niklas Pucher 1 , Valentin Satzinger , Arnulf Rosspeintner , Christian Heller , Georg Gescheidt , Volker Schmidt , Juergen Stampfl , Robert Liska
1 Institute of Applied Synthetic Chemistry (Division: Macromolecular Chemistry), TU Vienna, Vienna, Vienna, Austria
Show AbstractThe development of new optimized photoinitiators for the two-photon induced photopolymerization (TPIP) is essential in order to obtain high resolutions in this solid freeform fabrication process for various applications. Herein, we present the syntheses and characterizations of a series of efficient photoinitiators, comprising of a cross conjugated D π A π D system. The different donor- ( H, OMe, SMe, NMe2, NPh2, NBu2) and acceptor (ketone, pyridine, pyridinium iodide) functionalities of the investigated photoinitiators as well as the synthesis of targeted derivatives containing double and triple bonds in the conjugated backbone allowed the evaluation of structure-activity relationships. UV-Vis measurements showed that especially the ketone based initiators have a high absorption at 400 nm and none or vanishingly small emission quantum yields. The activity and ideal processing window under TPIP conditions were investigated using equimolar amounts for each initiator. A typical commercially available one photon initiator (Irgacure 369) and two highly potential initiators well known from literature were used as reference. These tests figured out that the new chromophores are highly reactive even at concentrations down to 0.05 wt% although a low theoretical TPA-cross-section was calculated. Initiator B3K, with a n-butylamino-, triple bond, and ketone functionality, turned out to be the best performing initiator in our tests having a very good solubility in the resin and the broadest ideal processing window at laser intensities as low as 5 µW. By using optimized parameters, more complicated structures with a wall thickness of about 250 nm were obtained.
11:15 AM - **BB1.5
3D Nanoengineering for Photonics and Biology.
Georg von Freymann 1 2 , Michael Thiel 2 , Sean Wong 1 , Thomas Striebel 2 , Joachim Fischer 2 , Franziska Klein 3 , Martin Bastmeyer 3 , Martin Wegener 1 2
1 Institut of Nanotechnology, Forschungszentrum Karlsruhe, Karlsruhe Germany, 2 Institut für Angewandte Physik, Universität Karlsruhe (TH), Karlsruhe Germany, 3 Zoologisches Institut I, Universität Karlsruhe (TH), Karlsruhe Germany
Show AbstractDirect laser writing has become a versatile and widespread technique for the fabrication of almost arbitrarily complex three-dimensional nano- and microstructures and is already commercially available (www.nanoscribe.de). Together with a proper choice of materials this technique is utilized for fields as diverse as nanophotonics and cell-biology. In this talk I want to give an overview over our recent progress in two of our research fields, namely chalcogenide glasses for nanophotonics and flexible structures for cell-growth studies.In the field of nanophotonics we present a novel high-index-of-refraction (2.45) photoresist material based on erbium doped arsenic trisulfide. It shows room temperature photoluminescence at 1.5 microns wavelength, and can directly be used for direct laser writing (DLW) [1,2]. From the materials perspective, recent advances in photoresist chemistry have also allowed the high-refractive index material As2S3 (refractive index n = 2.45) to be used with 3-D DLW [2,3]. Due to the high refractive index, resulting 3-D photonic crystal structures can immediately possess a full photonic band-gap directly after fabrication. Nevertheless, this inorganic photoresist system lacks an important criterion for fabricating active structures, i.e., it does not exhibit an intrinsic room-temperature photoluminescence.Our new photoresist exhibits an intrinsic room-temperature photoluminescence at 1.55 µm wavelength. Er doping of As2S3 is achieved through a unique gas-phase direct doping technique. This method allows for facile and precise control of the Er doping concentration. Furthermore, sequences of active and passive layers have also been realized by us.The purity as well as the stochiometry can be better controlled compared to samples grown with previously known methods. Furthermore, the doped material exhibits photosensitivity, a property not realized in, e.g., ion-implanted thin films. Minimum lateral feature sizes that are routinely accessible in this Er:As2S3 photoresist system are on the order of 180 nm.For cell-growth studies direct laser writing is utilized for the reproducible and reliable fabrication of three-dimensional micron-sized templates in which by design and choice of material the local stiffness can be varied. This is achieved by combining two different materials (SU-8 and Ormocers) or, alternatively, by geometrical design of the structures in one material (Ormocer).[1] M. Deubel, G. von Freymann, M. Wegener, S. Pereira, K. Busch, and C.M Soukoulis, Nature Mater. 3, 444 (2004).[2] S. Wong, M. Deubel, F. Pérez-Willard, S. John, G.A. Ozin, M. Wegener, and G. von Freymann, Adv. Mater. 18, 265-269, (2006).[3] S. Wong, M. Thiel, P. Brodersen, D. Fenske, G.A. Ozin, M. Wegener, and G. von Freymann, Chem. Mater. 19, 4213-4221, (2007).
11:45 AM - BB1.6
Electrodeposition of 3D Titania Photonic Crystals.
Yongan Xu 1 , Xuelian Zhu 1 , Yaping Dan 2 , Jun Hyuk Moon 1 , Vincent Chen 3 , Alan Johnson 4 , Joseph Perry 3 , Shu Yang 1
1 Materials Science and Engineering, University of Pennsylvania, Philadelphia, Pennsylvania, United States, 2 Department of Electrical and Systems Engineering, University of Pennsylvania, Philadelphia, Pennsylvania, United States, 3 School of Chemistry and Biochemistry and Center for Organic Photonics and Electronics, Georgia Institute of Technology, Atlanta, Georgia, United States, 4 Department of Physics and Astronomy, University of Pennsylvania, Philadelphia, Pennsylvania, United States
Show AbstractTo fabricate a photonic crystal with large and complete photonic bandgap, it often requires backfilling of high index inorganic materials into a 3D polymer template. However, pore network may become disconnected before the template is completely filled in a conformal coating process, which, therefore, limits the achievable maximum bandgap in the 3D photonic crystals. Here, we demonstrate nearly complete filling of the holographically patterned, diamond-like polymer templates with titania sol-gel through electrodeposition method. The deposition proceeded in two stages: a thin titania seed layer (~ 55 nm thick) was conformally coated on the surface of the polymer template at the early stage of electrodeposition, after which the deposition occurred preferentially from the template bottom layer at a rate of ~ 0.4 μm/min. This bottom-up mechanism could be attributed to the diffusion-controlled hydroxyl ion concentration and a pH gradient within the template. SEM images suggested there was no pinch-off of the pore network after the backfilling. After calcination at 500 degree C to remove the polymer template, a nearly completely filled inverse 3D titania structure was obtained. We showed that a combination of pre-annealing step and a slow heating rate was important to form a dense 3D anatase titania crystal without pattern collapse. The optical properties of the 3D photonic crystals were measured at various processing steps and compared with the PBG calculation. The nearly perfect agreement of the experimental reflectance spectra with the simulated ones, and thus the obtained volume fraction at each step strongly supported the SEM observation: i.e., the polymer template was nearly completely filled with titania by the bottom-up process.
12:00 PM - BB1.7
3D-structuring of Optical Waveguides with Two Photon Polymerization.
Jurgen Stampfl 1 , Robert Infuehr 1 , Robert Liska 1 , Helga Lichtenegger 1 , Stefan Krivec 1 , Valentin Satzinger 3 , Volker Schmidt 3 , Nadejda Matsko 2 , Werner Grogger 2
1 , TU Wien, Vienna Austria, 3 , Joanneum Research, Weiz Austria, 2 , TU Graz, Graz Austria
Show AbstractTwo photon photopolymerization (2PP) is a new and modern method in solid freeform fabrication. 2PP allows the fabrication of sub-micron structures from a photopolymerizable resin. By the use of near-infrared (NIR) lasers it is possible to produce 3D structures with a spatial feature resolution as good as 200 nm. This technique can be used in polymer-based photonic and microelectromechanical systems (MEMS), for 3D optical data storage or for the inscription of optical waveguides into materials based on a local refractive index change upon laser exposure. Since the 2PP only takes place inside the focus of the laser beam, complex 3D-structures can be inscribed into a suitable matrix material. In the presented work, 2PP is used to write optical waveguides into a prefabricated mechanically flexible polydimethylsiloxane matrix. The waveguides were structured by selectively irradiating a polymer network, which was swollen by a monomer mixture. The monomer was polymerized by two photon photopolymerization and the uncured monomer was removed by evaporation at elevated temperatures. This treatment led to a local change in refractive index in the order of Δn = 0.02, which was significantly above the industrial requirement of Δn = 0.003. The measured optical losses were around 2.3dB/cm. Since all unreacted monomers were removed by evaporation, the final waveguide was stable up to temperatures of more than 200°C.In a second approach highly porous sol-gel materials (based on tetramethoxysilane (TMOS) as precursor and the surfactant cetylpyridinium chloride monohydrate as structural template) were utilized as matrix materials. The precursor was organically modified with poly(ethylene glycol) spacers in order to increase the toughness and thus facilitate the fabrication of transparent porous monoliths and flexible films. The pores of the sol-gel-derived matrix were filled with acrylate-based monomers of high refractive index and after selective irradiation using 2PP waveguides (Δn = 0.015) could be written into the material.
12:15 PM - BB1.8
Fast Laser-direct-write Creation of Free-standing Stable 3-dimensional Metallic and Ceramic Microstructures: Electro-magnetic High Frequency Devices and Applications.
Michael Stuke 1 , Kurt Mueller 1 , Magnus Jaeger 2 4 , Guenter Fuhr 3 4
1 Laser Chemical Processing, MPI f. biphys. Chemie, Göttingen, Niedersachsen, Germany, 2 , Universität Saarbrücken, Saarbrücken, Saarland, Germany, 4 , FhIBMT, Golm/Potsdam, Brandenburg, Germany, 3 , FhIBMT, St. Ingbert, Saarland, Germany
Show AbstractCompact, free-standing and stable 3-dimensional metallic and ceramic micro-structures are generated by laser-direct-write using suitable volatile gaseous precursor mixtures1. This talk will describe important details of the reliable, fast and perfectly reproducible generation process with special emphasis on key examples of various applications in the creation of materials combinations, including aluminum and aluminum-oxide, focussing on small electro-magnetic cages for precise handling/manipulation of polarizable objects in solution. This will be shown by short video sequences demonstrating the great potential of this process.1M. Stuke, K. Müller, T. Müller, K. Williams, R. Oliver, D.A.A. Ohlberg, G. Fuhr, R.S. Williams, MRS Bulletin 32 (Jan 2007) 32-39
Symposium Organizers
Stephen M. Kuebler University of Central Florida
Paul V. Braun University of Illinois, Urbana-Champaign
Valeria T. Milam Georgia Institute of Technology
Raymond C. Rumpf Prime Research, LC
Francesco Stellacci Massachusetts Institute of Technology
BB11: Surface-Tension, Evaporation, and Phase-Transition Driven Assembly.
Session Chairs
Thursday PM, April 16, 2009
Room 3005 (Moscone West)
4:30 PM - **BB11.1
3-Dimensional Assembly of Polymers.
Robert Miller 1
1 , IBM Almaden Research Center, San Jose , California, United States
Show AbstractPolymers offer a unique opportunity for exploring nanotechnology which relys on improved and novel functionality augmented by the development of well-controlled nanoscopic architectures. The self-assembly of polymer molecules is a facile route to functional nanostructures. A key factor for controlling the assembly of polymers is the molecular architecture. In this talk, we will discuss the assembly of polymer molecules with unique molecular architectures such as block copolymers and star polymers. The star systems are functionalized and are generated using an arm-first synthetic approach. The arms can be either homo or copolymers and can be biocompatible, biodegradable or neither. The self assembly of block copolymers can provide nanostructures with length scales ranging from 10 – 50 nm using simplified procedures and potentially low cost. While numerous approaches have been explored for the application of block copolymers to the formation of nanostructures, their use for fabricating 3-dimensional nanostructures still remains a challenge. By using hybrid block copolymers (organic block copolymers and block selective organosilicates), we can create well organized, multi-level, 3-dimensional nanostructures by self-assembly. We will present recent results on directed and multi-level assembly of lamellar microdomains utilizing self-assembly methods. We will also discuss the applications of star polymers for layer-by-layer assembly of both soft and hard colloidal particles monitored by surface plasmon resonance (SPR) and quartz crystal microbalance(QCM).
5:00 PM - **BB11.2
Fabrication of Anisotropic Assemblies from Microspheres and Nanoparticles inside Suspended or Sessile Droplets.
Orlin Velev 1
1 Chemical and Biomolecular Engineering, North Carolina State University, Raleigh, North Carolina, United States
Show AbstractThe controlled drying of liquid suspension droplets is one of the simplest and most efficient ways to assemble and shape particles in three dimensions. In this talk we will overview a few different geometries and processes, leading to the formation of a rich variety of organized structures. First, we will discuss the assembly of "supraparticles" inside water or hydrocarbon droplets that are suspended on the surface of a denser liquid and are driven by electric fields. The levitated droplets-on-a-chip could serve as self-contained templates and reactors with controlled on-chip mixing, drying and polymerization. When the droplets contain nanoparticle mixtures the evaporation of the liquid leads to microseparation of the components. On-chip fabrication inside droplets allowed making various types of anisotropic supraparticles and polymer capsules. In the second part of this talk we will discuss the factors leading to the assembly of self-contained supraparticles in drying sessile suspension droplets on solid surfaces. The organization of the particles is a result of a complex combination of convective transport and capillary forces at the liquid/air interface. The dynamic shape of the liquid surface guiding the assembly is a function of the contact angle on the substrate, liquid interfacial tension, droplet volume, particle size and volume fraction. We will demonstrate how, depending on the combination of these parameters, the droplet drying process can result in the formation of particle crystals in the form of disks, hemispheres, "doughnuts", ellipsoids or spheres. One simple and promising modification of this method is the guided assembly inside droplets deposited on superhydrophobic surfaces. The supraparticle assemblies formed could be anisotropic, "Janus," layered, patchy, magnetic or biologically active. The method is inexpensive and scalable and the complex supraparticles may find applications in various technologies.
5:30 PM - BB11.3
3-Dimensional Assembly of Block Copolymers.
Sang-Min Park 1 , Robert Miller 1 , Ho-Cheol Kim 1
1 , IBM Almaden Research Center, San Jose, California, United States
Show AbstractThe self-assembly of block copolymers has been studied extensively due to its potential uses as a building block for nanostructures. Some of examples include to use the microdomains of block copolymers for surface patterning (often denoted as block copolymer lithography), to use as a structure directing agent for functional materials, and to use for fabrication of nanoscopic templates for further building nanostructures. One of remaining challenges is, however, to use the block copolymers for fabricating 3-dimensional nanostructures. In this presentation, we report a route to 3-dimensional nanostructures from block copolymer self-assembly. We used a block copolymer hybrid, which is a mixture of an amphiphilic block copolymer and a low molecular weight polymethylsiloxane resin, to created multi-level structures. The hybrid shows two-phase morphology similar to the morphology of organic diblock copolymers. A lamellar morphology was obtained by controlling the length of each blocks of the block copolymer [i.e. poly(styrene-b-ethylene oxide), PS-b-PEO] and the mixing composition of their mixture with the polymethylsiloxane resin. The organic parts of the hybrid were removed by a thermal treatment at 450C after forming the lamellar structure on substrates, hence line patterns from the thermosetting polymethylsiloxane remained. 3-dimensional structures were fabricated by repeating the film deposition (spin-coating) and thermal treatment. By using a known directed self-assembly method for block copolymer lithography, we could create well organized 3-dimensional nanostructures from block copolymer self-assembly on substrates. This approach opens an opportunity to build well defined nanostructures of 10 – 50 nm length scales with great simplicity and low cost.
5:45 PM - BB11.4
Evaporative Self-Assembly of Highly Ordered Complex Structures: Learning from Coffee Rings.
Zhiqun Lin 1 , Myunghwan Byun 1 , Suck Won Hong 1
1 , Iowa State University, Ames, Iowa, United States
Show AbstractDrying of a sessile drop containing nonvolatile solutes readily self-assembles into a number of concentric “coffee rings” by repetitive “stick-slip” motion of the three-phase contact line. However, due mainly to lack of control over the evaporation process of the drop, the challenge remains to use evaporative self-assembly to rationally “synthesize” “coffee rings” of different shapes and sizes of high regularity and fidelity. Here, we report a facile, robust, and one-step evaporation method for producing in a precisely controllable manner versatile microstructures possessing high regularity, dispensing with the need for lithographic techniques and externally applied fields. Polymer or nanocrystal solutions are confined in a simple geometry comprised of a curved surface placed upon a flat substrate. By changing the shape of the upper surface of the imposed geometry, the controlled, evaporative self-assembly of polymer or nanocrystal solutions yields a variety of complex, intriguing, and well-ordered structures over large areas. As such, this method represents a significant advance in creating regularly organized, complex structures with potential applications in microelectronics, optoelectronics, and biotechnology, among other areas.