Symposium MT05—Emerging Prospects and Capabilities in Focused Ion Beam Technologies and Applications

The key to advancing energy materials and biological systems is to understand and control the structure and chemistry at interfaces. While much of the dynamic chemistry can be studied on macro-scale systems, there is a lack of means to localize chemical measurements and correlate them to nanoscale structure of the material. Through a unique merger of advanced scanning probe and ion microscopy with mass spectrometry techniques rooted in innovative data processing and control algorithms, we are now able to understand the interplay between chemical and physical functionality at the fundamental length scales using multimodal chemical imaging. This multimodal imaging transcends existing techniques by providing nanoscale structural imaging with simultaneous chemical analysis. Here, I will discuss how we have developed and used this capability to visualize dynamic material transformations at interfaces, to correlate these changes with chemical composition, and to distil key performance-centric material parameters. One exciting capability is to drive materials away from equilibrium at the nanoscale with highly localized fields. This allows field confinement effects on localized chemistry in materials to be locally probed, especially at interfaces. This in turn yields direct information on key energy related questions such as electron and ion motion distribution and transport at and between interfaces. Overall, I will focus on ways to unlock the mystery of active interface formation through intertwining data analytics, nanoscale elemental and molecular characterization, with imaging; to better grasp the physical properties of materials and the mechanistic physics-chemistry interplay behind their properties

In the past decade, focused ion beam scanning electron microscopy (FIB-SEM) has transformed from a niche technique for semiconductor and materials science research into a broadly useful processing, analysis and characterization technique of choice for many disciplines. Although, Ga+ FIB-SEM instruments are the most commonly used FIB-SEMs, plasma FIB-SEMs have enabled routine 3D structural analysis of (relatively) large volumes. And the availability of multiple ion species is enabling application specific uses of different FIB instruments and renewing interests in techniques such as FIB-SIMS (Secondary Ion Mass Spectrometry). Additionally, advances in the instrument hardware and software have resulted in increased system stability and robustness, as well as ease of use and maintenance that have significantly lowered the barrier to entry into FIB-SEM techniques. However, as the FIB-SEM instrumentation becomes increasingly automated and complex, the challenges associated with the resulting data volume and complexity are increasing. The current trend towards open and re-usable data also requires added effort to provide necessary meta data and curate the research data into a consumable format.
In this presentation, examples of materials characterization applications that are uniquely enabled by FIB-SEM are described, and how the resulting data fits into various overlapping research data ecosystems is explored [1]. For example, a material characterizations study such as carbon fiber ultrastructure analysis can generate a large number of images. These image data sets can be used and re-used by materials scientists to explore structure property relationships while the same set of data, with an appropriate meta data, can be re-purposed as test data sets by computational imaging scientists for their algorithm development. We will explore some of the currently available data infrastructures supporting the findable, accessible, interchangeable, and reusable (FAIR)[2] data ecosystems and how the FIB-SEM community can effectively adapt these.
[1] Oliveira and Lóscio, 2018, ACM ISBN 978-1-4503-6526-0/18/05, doi:10.1145/3209281.3209335.
[2] Wilkinson et al., 2016, Scientific Data. p. 160018. doi:10.1038/sdata.2016.18.

An emerging paradigm in engineering is the design of materials to act as simple building blocks in order to achieve complex functionality at multiple scales. The discovery of new nanomaterials such as low-dimensional nanomaterials, new metal alloys and functional polymers, has been leading these developments, and more material and engineering design options have been given to scientific and engineering societies, with demands to overcome the challenges of the current existing technologies. However, challenges persist in integration of nanomaterials to device architectures, control of material properties, and realization of functional devices, for practical applications. To tackle these challenges, it is crucial to develop multidisciplinary, integrated approaches, to enable precise manipulation of these materials compatible with integrating them into existing engineering systems as well as for the development of new concepts of device architectures.
Developments of cutting edge technologies in manufacturing enabled to programmatically transform materials into real engineering components by ‘direct digital printing’ with high degree of controls, making it possible manufacture complex multi-dimensional components on demand in micro- and macro-scales. As the similar concept of manufacturing, directing matter on atomic-to-nanoscales, termed as ‘focused electron or ion beam induced processing’, is being developed to achieve atomically precise manufacturing of nanomaterials and 3D structures in solids, liquids and at interfaces. Focused electron or ion beam induced processing is a resist-free advanced nanomanufacturing technique for ‘direct-write’ processing of a wide range of structural and functional nanomaterials. Focused charged particle beam-based techniques involve in electron-matter or ion-matter interaction, enabling additive/subtractive nanofabrication as well as doping and functionalization of nanomaterials, along with the in-situ nanoscale imaging in the scanning or transmission electron/ion microscope environments. Thus, these techniques provide unique opportunities in materials design to address many challenges in nanoengineered systems.
In this research presentation, recent advancements of energetic focused ion beam technologies will be introduced, especially for their applications to direct manipulation of 2D nanomaterials such as graphene and molybdenum disulfide (MoS₂). Among the several technological developments, the synergistic theoretical and experimental research work will be presented to introduce the promise of the focused helium ion beam and argon molecular cluster ion beam technologies in atomic manipulation, multi-mode nanofabrication, defect engineering and chemical imaging as a next-generation nanofabrication tool.

Focused Ion Beam (FIB) processing has been developed into a well established and still promising technique for direct patterning and proto-typing on the nm scale, high resolution imaging or high resolution ion lithography¹. Exploring the Liquid Metal Alloy Ion Sources (LMAIS) potential represents a promising alternative to expand the global FIB application fields. Thanks to this, nearly half of the elements of the periodic table are made available in the FIB technology as a result of continuous research in this area during the last fifty years². Recent developments could make these sources to an alternative technology feasible for nanopatterning challenges.
Concerning ion beam resolution and minimization of unwanted damage, light ions like He or Li are preferred candidates. Liquid metal alloy ion sources (LMAIS) with a life time of more than 1000 µAh on the basis of Ga₃₅Bi₆₀Li₅ and Sn₉₅Li₅ alloys were developed, characterized and tested in a commercial mass-separated VELION FIB-SEM system (Raith GmbH) ³. In the case of Li ions from the mass separated FIB a lateral resolution of 5.6 nm could be obtained in first experiments and the sputter yield was determined to 0.4 for 35 keV Li ions on Au. For reference, the helium ion microscope (HIM) has a lateral resolution of about 0.5 nm and 1.8 nm, for He and Ne respectively, He has a sputter yield of 0.1⁴. For sub-10 nm focused ion beam nanofabrication and microscopy, the GaBiLi-FIB or the SnLi-FIB could therefore be considered as alternatives to the HIM with the benefit of providing additional ion species in a mass separated FIB without changing the ion source.
In this contribution the operation principle, the preparation and testing process as well as prospective domains for modern FIB applications will be presented^1,5. As an example we will introduce a GaBiLi LMAIS in detail. It enables high resolution imaging with light Li ions and sample modification with Ga or heavy polyatomic Bi clusters, all coming from one ion source. Moreover we will discuss the main properties of a modern LMAIS like long life-time, high brightness and stable ion current. The physical basics and experimental results of LMAIS, their physical properties (I-V characteristics, energy spread) and questions of the preparation technology using elementary as well as binary and ternary alloys as source material will be covered.

¹ L. Bruchhaus et al. Appl. Phys. Rev. 4, 011302 (2017).
² L. Bischoff et al. Appl. Phys. Rev. 3, 021101 (2016).
³ W. Pilz et al. J. Vac. Sci. Technol. B 37, 021802 (2019).
⁴ G. Hlawacek et al. J. Vac. Sci. Technol. B 32, 020801 (2014).
⁵ J. Gierak et al. J. Vac. Sci. Technol. B 36, 06J101(2018).

Initially launched in 2011 by Orsay Physics, Xe Plasma FIB-SEM is currently used to save operation time for many applications which were up to now realized by Ga FIB. Ga FIB and Xe FIB instruments are the go-to tools for chip material analysis in the semiconductor industry for applications like TEM lamella preparation, circuit editing, and physical inspection by sample preparation.
With the downscaling of the technologies, delayering, which consists of perfect layers by layer de-processing, is one particular very demanding application which was developed using the plasma FIB. The goal is to localize a failure in a fully integrated circuit included in a few hundreds of nanometers thick area. The demand for suitable and nano-accurate polishing technics are in growing demand to reveal buried interest areas with the assurance of matching to the reference sample with no modification due to the preparation technic used. Many trials have been attempted to use a FIB to remove homogeneously different metal/insulator layers. A solution is to work on ion species, ion energies, spot size, scanning strategy… But ion beam etching alone is not able to achieve planar surface on interconnect technologies. The milling rate of different materials is too unequal and their architecture is too tricky to reach deep layers with the minimum roughness on the sample. Thus, due to a constant evolution of the material used in the semiconductors and their intrinsic tangle at the nanometric level, it becomes an increasingly pressing demand to reach, without alteration, a specific area in such complex structures. To overcome these artifacts, a solution is to control FIB milling rates of all the different as-constitutive elements of the SC’s surface by adding a specific chemistry near the area of interest during operation. In this perspective, we developed a new reliable, fast and accurate Gas Injection System (OptiGIS) and its devoted precursors.
The chemistry used for homogeneous milling needs also to overcome the production of residues and particulates which are undesirable for electrical characterization and are caused by milling of surface materials such as the case of plasma FIB delayering. Conductive residues can redeposit on sample surface, shorting metal lines to one another and creating false electrical signals, while non-conductive residues may cover metal lines and result in bad electrical contact. To mitigate this issue, gases etchant are used in delayering process to produce volatile by-products when reacting with the surface easily removed by the vacuum pump instead of redepositing on sample surface.
A successful Xe FIB delayering on sub-14 nm technology from metal 8 to transistor contacts in combination with special gas chemistry will first be presented.
In a second part, this case will be compared to the performance of this process with a Ga FIB. The differences between the two use cases will then be exposed for comparison.
Experimentally, top-down delayering of sub-14 nm technology nodes were performed with both Ga and Xe FIBs using special gas precursor. GIS was inserted to inject gas on to the area of interest. Suitable current density, beam shape and gas delivery was prepared to conduce planarity and the process was monitored using end point detection based on the SE signal being generated during the etching process. The parameters will be discussed.
In a third part the focus will be on the end pointing. This end pointing recognizes each peak as the metal layer and the trough as via layer which gives full control to the operator to start and stop the process in any layer of interest. A final fine polishing is performed once the specific layer is entered to get rid of residual precursor or carbonated compounds before the final analysis such as probing.

Microscale and nanoscale structuring are important processing steps for prototyping advanced semiconductor devices from III-V materials such as GaAs and GaN. For example, the self-assembly of group III metallic nanodots and other nanostructures of III-V compound semiconductors has become a topic of much interest [1]. Also, the controlled growth of III-V materials shows interesting optical qualities with the prospect of negative index of refraction materials [2]. Traditionally, ion beam milling with a gallium focused ion beam instrument (Ga-FIB) has been used to structure these materials. The same Ga-FIB is also routinely used for sample preparation for subsequent transmission electron microscopy (TEM) imaging or analysis steps. However, the use of the Ga-FIB can significantly alter these materials through ion beam induced damage effects, including the implantation of gallium. In some cases, there is evidence of Ga-rich “droplets” that seem to form on the surface of these materials.

The ZEISS ORION NanoFab serves as a useful platform for the prototyping of advanced III-V materials for semiconductor, optical, and other device researches. This instrument provides a traditional Ga-FIB, but helium and neon focused ion beams with 0.5 and 2.0 nm probe sizes (respectively). Together these ion beams can offer sub-nanometer imaging resolution, as well as device fabrication with no artifacts associated with gallium residue. The same platform also offers secondary ion mass spectrometry (SIMS) based elemental analysis with a magnetic mass spectrometer, and a lateral resolution on the order of 15 nm.

In this talk, we compare the effects of Ga and Ne ion beam milling into a GaAs substrate. These two ion beams are used over a range of areal dosages (ions/cm²) to explore the milling rate, milling artifacts, and pattern formation. On the same platform, the helium focused ion beam is used to assess the milling rate, and for detailed examination of the milled patterns and surface morphology. As expected, experimental results show that the milling rate with a 30 keV Ga-FIB is much faster than that with a Ne ion beam. However, the gallium beam tends to induce a progressive formation of Ga-rich nanodots or nanodroplets on the bottom and sidewalls of the milled pits. In contrast, when using a Ne beam with the same 30 keV energy, the bottom surfaces of the milled pits show a porous texture. With a lower Ne ion beam energy, such as 10 keV, the bottom surface appears to be much less porous without any significant decrease of milling rate. The neon beam with its small probe size and easy operation at low probe currents, enables high fidelity patterning of the GaAs. We further examine the milled samples using TEM to assess damage, implantation, and structural changes below the surface. Further investigations include the effects of an etchant gas (XeF₂) for material removal using both the Ga and Ne beams. Additional experimental results include the milling of GaN substrates with both Ga and Ne ion beams.
[1] K. A. Grossklaus and J. M. Millunchick, J. Appl. Phys. 109, 014319 (2011).
[2] P. C. Wu, A. S. Brown, M. Losurdo, G. Bruno and H. D. Everitt, Appl. Phys. Lett. 90, 103119 (2007).

Focused ion beam (FIB) milling using gallium ions is routinely used for the site-specific preparation of sharp tips for Atom Probe Tomography (APT), in which atoms are evaporated from the tip and detected using a mass spectrometer to enable 3D reconstruction of the needle-shaped volume atom by atom. Artifacts from the Ga-FIB milling process include near-surface implantation of gallium and the accumulation of gallium along grain boundaries and between phases. With the advent of novel FIB sources, alternative ion species for precision milling are now available. For example, Ne-FIB-milling as the final polishing step in the preparation of electron-transparent samples for Transmission Electron Microscopy (TEM) has been demonstrated as an alternative approach for samples in which contamination effects from gallium cannot be tolerated [1].

Here we use the neon beam generated by the gas field-ionization source of a Helium/Neon Ion Microscope (HIM/NIM) for the final trimming of APT tips that have been extracted from bulk samples by Ga-FIB lift-out. Materials investigated include a titanium alloy and a sample comprising aluminum/aluminum oxide layers on a silicon substrate. High-resolution TEM analysis of Ne-FIB-milled tips reveals that implanted gallium from the pre-milling steps is successfully removed. A thin amorphous layer of < 5 nm is observed, beneath which the crystallinity of the tip is well-preserved. The experimental workflows for the Ne-FIB technique will be discussed and the 3D reconstructions from the APT measurements presented.

[1] T. C. Pekin, F. I. Allen, and A. M. Minor, J. Microscopy, 264 (2016) 59-63
P.T.B. present affiliation: Honeywell, Broomfield, CO, United States

In this talk we will review and detail the current status of EHD ion sources, also commonly referred as Liquid Metal Ion Sources, their development perspectives and their ever present expanding applicative domains. We will review the roots of this technology born in the early 70’s, deriving from space propulsion research, when physicists applied EHD phenomena onto liquid metal meniscus to create high brightness ion sources. Since then the LMIS qualities based on a remarkable brightness, excellent emission stabilities (current emission and emitting area invariance), ease of operation, lifespan and compactness small size were at the origin of the focused ion beam (FIB).
As a deeply involved team in the pursuing quest aiming at investigating the full applied potential of the direct-write Focused Ion Beams technology since the mid-80’s, we will analyze and comment the never interrupted major effort invested around the world aiming at developing alternative ion sources. As a complement to the development of high current sources or atomic-sized emitters, we will show that high performance Liquid Metal Ion Sources and Liquid Metal Alloys Ion Sources exhibit definitive advantages at the prototyping level.
We will analyze, quantify and describe the potential gains still to be expected from the widely used gallium LMIS and other alloy ion sources, that add a large number of ion species and patterning schemes.
In conclusion we will summarize our vision on the future of FIB technology based on electro-Hydro Dynamically (EHD) driven emitters operating in the cone-jet mode, both in terms of performances, versatility and on the science frontiers these might help to push. My presentation will be an attempt to provide an overview on this FIB continuous evolution and future capabilities.

L. Bischoff, P. Mazarov, L. Bruchhaus, and J. Gierak, Liquid Metal Alloy Ion Sources - An Alternative for Focused Ion Beam Technology, Appl. Phys. Rev. 3 (2016) 021101-1 – 021101-3

Focused Ion Beam (FIB) machining has emerged as a transformational tool for microscopy, making it possible to extract samples of particular features of interest with high spatial specificity. A challenge in this context is the damage FIB inevitably causes and the consequences this damage has for subsequent microscopy. Multi-reflection Bragg Coherent Diffraction Imaging (MBCDI) is an exciting, new coherent X-ray diffraction technique that allows the imaging of 3D structure and lattice strain in crystalline materials with 10s of nanometers 3D spatial resolution. However, to function, MBCDI requires samples less than one micron in size. This constraint has thus far limited MBCDI to materials that naturally form isolated micro-crystals of this size. The vast majority of technologically important materials have thus remained out of reach.

Here we present a new FIB-based fabrication approach that allows the manufacture of micron-sized strain microscopy samples for MBCDI. Importantly these can be manufactured with high spatial specificity, such that they contain specific defects or microstructural features of interest. A very important challenge is how to manage the damage cause by FIB milling. Our previous MBCDI work on initially pristine gold micro-crystals showed that milling with 30 keV Ga ions can cause large lattice strains that extend up to hundreds of nanometers into the sample. While these strains can be reliably probed using MBCDI, they obscure the subtle strain fields associated e.g. with crystal defects of interest. Using MBCDI we demonstrate that the strains from high energy FIB milling can be reliably removed by low energy FIB polishing. This is a key aspect of the new FIB-based strain microscopy sample preparation.

Several examples of strain-microscopy sample preparation using FIB will be presented, concentrating on materials not normally suited to coherent X-ray diffraction imaging. We show that, using the new approach, the full, 3D resolved strain fields of specific, pre-selected dislocation structures can be probed. We can also study in detail irradiation-induced lattice strains in samples extracted from macroscopic armor for future fusion reactors, or local strains in a nickel superalloy. These examples highlight the general applicability of the new FIB preparation routine, transforming MBCDI to a nano-scale microscopy tool for real-world engineering materials.

Quantitative in situ TEM small-scale mechanical testing has attracted broad interest over the past 20 years. Through these techniques, one can not only directly visualize the microstructure/defects evolution during mechanical deformation, but also measure the mechanical properties of nanostructured materials. Typically, the small-scale coupons for these tests are fabricated by Gallium focused gallium ion beam (Ga-FIB). It is well-known that Ga-FIB may introduce radiation damage and gallium contamination at the sample surface. Although these artifacts may only exist at the surface layer which is usually less than 30 nm, their effects on the mechanical behavior may be significant. In addition, the sample geometry may also impact the measured mechanical properties. For example, it is difficult to control the length of the cylinder-shape pillar; thus, measuring strain accurately can be difficult. In this presentation, we will systematically compare several focused ion beam fabrication methods for quantitative in-situ small-scale mechanical testing, with an emphasis on the ion type (Ga, Ne, or Ar) and sample geometry (round-/square- shaped cross-section). We hope to provide insights into choosing appropriate FIB fabrication methods that enable more reliable quantitative in-situ small-scale mechanical testing.

The modern technology demands the miniaturization of devices and the discovery of novel materials, both requiring matching characterization methods possessing nanoscale resolution and able to the three-dimensional physical properties of these devices and structures. Scanning Probe Microscopies (SPM), could allow the nanoscale mapping of the sample morphology, as well as local mechanical, electrical and thermal properties being a relatively easy to use and efficient tool for exploration of inorganic surfaces. However, studying 3D structures in SPM provides significant challenge, with mechanical sectioning of the samples ruled out as it creates too rough surface, focused ion beam (FIB) creates cuts that are usually too narrow for the SPM probing tip, as well as implanting Ga ions strongly modify the properties of the materials studied and damage the surface, with mechanical cleavage can only be applied to the narrow subset of epitaxial layers with minimal defects.
Here, we present the novel Beam Exit Cross-sectional Polishing (BEXP) approach, creating nanoscale near-atomically flat sections of layers from few nm to the surface down to several micrometres deep, and minimal damage to the sections device or material. BEXP uses triple broad 1 mm wide Ar-ion beams intersecting in the cut area and shaped by the edge mask to define a cut plane. This plane oriented in such a way that it intersects the sample surface at small negative angle, with beam exiting the sample (hence the BEXP name) keeping intact the sample surface. The glancing angle and inert nature of Ar results in minimal Ar-ions implantation and modification of the sample as well as fairly flat surfaces (roughness ~1nm RMS) ¹, providing optimal geometry for accessed via the material sensitive SPM ^{2, 3}.
The BEXP has been implemented in the nanomechanical and electrical studies of III-V compound semiconductor structures commonly employed in the manufacturing of optoelectronic devices – photovoltaics, LED and lasers.⁴ Due to the shallow angle of the BEXP section, the projection of the multi-layered structures increases approximately 1 to 10 the thickness of the layers, facilitating the visualization of the material defects, such as, the propagation of the antiphase domains across the structure, creating a charge separation in multiple quantum wells - one of the key problems in the efficiency of the devices. SPM maps of nanoscale sections of GaN NWs on Si revealed the electron affinity dependence with the material thickness and unexpected domain reversal in individual NW. In summary, tandem of BEXP with materials sensitive SPM provide a very efficient tool for exploring 3D structure and physical properties of solid state materials with true nanoscale resolution.

1. A. J. Robson, I. Grishin, R. J. Young, A. M. Sanchez, O. V. Kolosov and M. Hayne, Acs Applied Materials & Interfaces 5 (8), 3241-3245 (2013).
2. J. L. Bosse, P. D. Tovee, B. D. Huey and O. V. Kolosov, Journal of Applied Physics 115 (14), 144304 (2014).
3. B. J. Robinson, C. E. Giusca, Y. T. Gonzalez, N. D. Kay, O. Kazakova and O. V. Kolosov, 2D Materials 2 (1) (2015).
4. J. D. Ralston, S. Weisser, I. Esquivias, E. C. Larkins, J. Rosenzweig, P. J. Tasker and J. Fleissner, IEEE Journal of quantum electronics 29 (6), 1648-1659 (1993).

While focused ion beams (FIB) of light ion species such as He⁺ and Ne⁺ are often pursued for high-resolution, direct-etch patterning, their low sputtering rates – relative to heavier ion species like Ga⁺, Xe⁺ and Cs⁺ – limit such uses to low-volume-removal applications. In this work, we present two light ion FIB techniques that are useful for etched patterning on orders-of-magnitude larger scales than typical, while still maintaing the high-resolution capability (e.g. sub-10 nm for He-FIB and sub-20 nm for Ne-FIB) that is most attractive about them. In the first, helium ion beam lithography (HIBL) is used to create structures as small as 6 nm wide and 20 nm tall in silicon, spaced less than 20 nm apart, which represents a new lowest published benchmark for creating Si fins for e.g. FinFET technology. This is done by exposing a novel, metal–organic resist material with 35 keV HIBL, then transferring the pattern to the substrate with a pseudo-Bosch reactive-ion etch (RIE). Requsite exposure times are on the same order of magnitude as those needed in conventional 100 keV electron beam lithography (EBL), which makes producing sub-10 nm structures as scalable with HIBL as any other process is with EBL. The second technique involves the use of He- or Ne-FIB to create nanowires as thin as 20 nm, 60 nm tall, and as long as several millimeters. To do so, a sub-10 nm thick atomic layer deposition (ALD) hard mask is patterned by direct-etch FIB, followed by the transfer of the pattern through the underlying, thicker substrate material via RIE. Patterning times by this technique can be two orders of magniture lower than are necessary to remove the same volume of material by direct-etch only. The benefits and drawbacks to these two nanofabrication techniques are discussed, as are their underlying mechanisms and potential applications.

Ferroic materials including oxide ferroelectrics, magnets, and multiferroics are of great interest for a range of modern applications. What’s more, these materials stand poised to revolutionize next-generation applications, if we can determine ways to overcome inherent limitations in their function. Because of their complex chemistry, propensity for defect formation, etc. these materials – especially in the thin-film form required for many advanced applications – often have performance that lags behind that of their bulk counterparts. In turn, researchers working on advanced thin-film synthesis approaches have attempted to treat these ternary, quaternary, and more complex systems more-and-more like semiconductor systems. Efforts to make cleaner, more precise versions of these materials were envisioned to produce ever better properties – but alas, these efforts have not always play out as desired.

In recent years, however, it has been seen that we can borrow other lessons from the semiconductor community to control and improve the properties of these complex, functional materials. Namely, ion bombardment approaches are seeing a renewed interest as researchers better understand how ion beams can be used to manipulate the electronic and defect structures of materials and, in turn, how this affects the evolution of the physical properties. In this talk, we will explore recent efforts focused on the use of both low- (~30 keV) and high- (~3 MeV) energy ion beams can enable control of the concentration and type of defects in ferroic oxides and, in turn, how these beams can be used to enhance material properties. Using systems like helium-ion microscopes and pelletron accelerators, we are afforded access to a range of species and bombardment conditions. Specifically we will highlight examples of work done on materials such as the canonical ferroelectrics PbTiO₃ and PbZr_1-xTi_xO₃, relaxor ferroelectrics such as (1-x)PbMg_1/3Mg_2/3O₃-(x)PbTiO₃, and the multiferroic BiFeO₃. Here, among other things, we will show how the controlled introduction of ion-beam-induced knock-damage creates intrinsic defects that can, in surprising fashion, improve the electrical resistance (by orders of magnitudes) of these materials, how implantation and ion-beam-induced damage can provide a pathway to control local switching enabling emergent function like multi-state functionality, and how ion-beam-induced damage can even tune the competition of energies such that one can alter the ferroic nature of these materials. To end, we will discus where these ideas could lead us next in using ion beams to manipulate properties in materials.

We will present our results on the fabricate of single atom devices via direct write nanofabrication using Sandia National Laboratories nanoImplanter. This focused ion beam (FIB) implantation capability is part of Sandia’s Ion Beam Laboratory and is a multi-species 10-100 kV FIB system with a minimum spot size of 10 nm with both mass resolution using an ExB filter and single ion implantation capability using fast blanking and chopping. The combination of high spatial resolution, variable energy and the ability to implant a range of elements from the periodic table makes this a versatile machine for a range of topics from deterministic seeding of TaOx memristor devices, high resolution ion beam induced charge collection (IBIC) for probing the structure of defect cascades, deterministic single donor devices for quantum computing research, to the formation of individual defect centers in wide bandgap substrates including diamond, SiC, hBN, etc… using in-situ detectors. Here we concentrate on FIB implantation into diamond nano-structures for the creation of color centers.

Color centers in diamond including NV, SiV and GeV are used for a range of applications from metrology to single photon sources. We demonstrate the ability to deterministically implant ions into diamond photonic nanostructures with high spatial resolution, <40 nm. This enables high resolution arrays for yield testing as well as the development of strong coupling between the resulting color center and the nanophotonic cavities. Separately, we have demonstrated single ion detection using an in-situ diamond detector with signal-to-noise-ratio approaching 10.

This work was performed, in part, at the Center for Integrated Nanotechnologies, an Office of Science User Facility operated for the U.S. Department of Energy (DOE) Office of Science. Sandia National Laboratories is a multi-mission laboratory managed and operated by National Technology and Engineering Solutions of Sandia, LLC., a wholly owned subsidiary of Honeywell International, Inc., for the U.S. Department of Energy's National Nuclear Security Administration under contract DE-NA-0003525.

Two-dimensional layered semiconductors have recently emerged as attractive building blocks for next-generation low-power non-volatile memories. However, challenges remain in the controllable sub-micron fabrication of bipolar resistively switching circuit components from these novel materials. In this work, we demonstrate lateral on-dielectric memtransistors from monolayer single-crystal molybdenum disulfide (MoS₂) utilizing a focused helium ion beam. The site-specific irradiation with the probe of a helium ion microscope (HIM) allows for the creation of charged defects in the MoS₂ lattice. The reversible drift of these locally seeded defects in the applied electric field modulates the resistance of the semiconducting channel, enabling versatile memristive functionality on the nanoscale. The asymmetric nature of the ion irradiation plays a crucial role in controlling the resistive switching behaviour and hence optimising the device performance. This work has potential to advance the down-scaling of memristive devices with low power consumption and applicability for synaptic emulation in next-generation flexible electronic applications.

We have fabricated a variety of high-transition temperature superconducting (HTS) Josephson devices with properties that exceed prior-art devices using a focused helium ion beam (FHIB). These FHIB Josephson junctions have exceptional qualities such as resistance greater than 1k ohms as well as superconducting quantum interference devices with voltage close to 1 mV. These high figures of merit make HTS devices appealing for many applications. Unfortunately, these demonstrations are small scale devices with few junctions contained in small 100 micron areas due to the field of view of the FHIB at high resolution. To bring this technology to the next level, innovations are needed for large area patterning such as those implemented in commercial electron beam lithography equipment. We present our efforts in bringing this to fruition using our Orion plus microscope equipped with a Raith ELPHY pattern generator system. We developed an automated direct-write Josephson junction process where large-scale areas are broken into smaller write fields that are compatible with the field of view of the FHIB. The smaller areas are individually written and stitched together. Since the FHIB is not equipped with a laser interferometer stage, it is necessary to account for stage backlash and other sources of stitching error using auto-alignment marks in the circuit design. Using the Raith ELPHY pattern generator we maintain a small field of view for high resolution patterning and control the stage to stitch the device with errors less than a few micrometers per movement. Additionally, while setting up the coordinate system to match the design and the patterned device, a focal plan is fitted in the coordinate system to keep the beam in focus even after long stage movements. This further reduces the action needed by a human operator. To test the automation process, we designed a large area wide-bandwidth, high-dynamic range sensor which consists of a large number of long Josephson junctions in an array. The array, typically several millimeters long, is much larger than common lithography write fields (typically a hundred micrometers) making the fabrication process excessively long and tedious. The signal voltage output scales with the number of junctions contained in the series array which is an important metric for determining the device performance. Previous designs were limited to a few hundred junctions with output voltage of less than 5 mV. By automating the process, we are now capable of making arrays with over 2600 junctions in series with voltage output over 100 mV! This circuit was installed into a prototype receiver for signals intelligence research and is one of the first FHIB Josephson circuits to be transferred out of the university.

A helium gas field ion source has been demonstrated to be capable of realizing higher milling resolution relative to liquid gallium ion sources. One drawback, however, is that the helium ion mass is prohibitively low for reasonable sputtering rates of bulk materials, requiring a dosage that may lead to significant subsurface damage. Manipulation of suspended graphene is, therefore, a logical application for He⁺ milling. We demonstrate that competitive ion beam-induced deposition from residual carbonaceous contamination can be thermally mitigated via a pulsed laser-assisted He⁺ milling. By optimizing pulsed laser power density, frequency, and pulse width, we reduce the carbonaceous byproducts and mill graphene gaps down to sub 10 nm in highly complex kiragami patterns. The experimental observation is qualitatively in line with the Finite Element Method simulation results. This technique enables complex features to be direct written on suspended membranes, opening the gate to a variety of applications such as fabricating heterostructure carbon-based devices.

The metal-insulator transformation in vanadium dioxide (VO₂) at ~340K is accompanied by a spontaneous strain of ~1%, which can be used to create nano-scale sensors and actuators. The ability to grow homogeneous single-crystal nanostructures, the large change in lattice parameters (orders of magnitude greater than typical thermal expansion), and low transition temperature are advantageous in applications, and highly sensitive nano-thermometers and microscale solid engines have been previously demonstrated. In this work, we demonstrate nano-scale local patterning of the transition temperature of 100 nm thick VO₂ nanowires by 30 kV He⁺ focused ion beam irradiation. Doses in the range of 10¹⁵-10¹⁶ ions/cm² do not evidently disturb the VO₂ lattice, but rather are believed to introduce oxygen vacancies that modify the transformation behavior. Spatially resolved measurement of the transition temperature is accomplished using four-dimensional scanning transmission electron microscopy (4D-STEM), a technique where a convergent electron probe is rastered across an electron-transparent sample and the full diffraction pattern is acquired at every probe position. In each of the diffraction patterns we find the position of the Bragg scattered electrons, which are used to determine the local lattice parameters.

We performed 4D-STEM scans of VO₂ nanowires with different patterned He⁺ doses using an in situ heating stage to reveal the monoclinic-rutile transformation as a function of space and temperature. We found that the transition temperatures measured by the structural distortion match those separately measured by electrical resistivity on homogenously irradiated nanowires with the same He⁺ doses. We also observe sharp interfaces between the rutile and monoclinic phases at the boundaries between different He⁺ doses. These results demonstrate the possibility of fine-tuning of the transformation temperature for precisely controlled actuation, as well as graded structures that allow for smooth onset of the actuation or sensing signal, by local irradiation with the He⁺ FIB.

The interactions of 25 keV helium ions with a tungsten (100) single crystal target at room temperature for doses ranging from 1x10 ¹⁷ to 1x10¹⁸ ions/cm² are investigated using a helium Focused Ion Beam (FIB) microscope to perform the irradiations in a site-specific dose-controlled manner. The swelling and surface topographic changes of the exposed surfaces are initially observed using Helium Ion Microscopy (HIM) and Atomic Force Microscopy (AFM). At a dose of about 5x10¹⁷ ions/cm², blisters abruptly appear and randomly rupture. Channeling phenomena along 110 orientations becomes evident on W(100) blisters in the HIM micrographs. Blisters are found to grow to a maximum of 1 micron in diameter before rupture. Cross-sections through blisters prepared by gallium FIB milling and imaged by Transmission Electron Microscopy (TEM) reveal the formation of a blister cavity with helium nanobubbles of around 1 nm in diameter found in the material above and below the cavity. The formation of nano-cracks connecting nanobubbles is also observed, in agreement with the mechanism of blister formation involving the inter-bubble fracture of highly over-pressurized helium bubbles proposed decades ago by Evans [1], which until now, to the best of our knowledge, had not been experimentally verified. We also apply nanoindentation to measure the reduced modulus and hardness values versus indentation depth for areas implanted to different doses and propose a phenomenological equation to describe the experimentally-determined hardness and swelling values.
[1] J. H. Evans, J. Nuclear Materials 68 (1977) 129-140

Focused helium ion beam (FHIB) fabrication of high transition temperature superconductor (high-T_C) Josephson junctions has opened up new opportunities in both basic science and applications due to the much smaller critical dimensions afforded by the process. The displacement of critical element atoms such as oxygen or amorphization of the polycrystalline film directly introduced by FHIB can change the electrical property of high-T_C superconductor to normal metal, even insulator at low temperature. The controllable changes of the electrical properties within nanometers provides the basis to investigate the quasiparticle tunneling density of states at different angles, which is highly related to the cooper pairing mechanism where scientist are expecting breakthrough for decades. Versatile nanoscale quantum devices by combining the nanoscale functional features, such as very narrow barrier (at the order of the coherence length in a-b plane, ~2 nm), sub-10 nm insulating lines and area have also been designed and made. Scaling down the size of the features of basic also benefits the superconducting electronics technology for higher detector sensitivity, higher circuit integration density, and higher circuit performance. In this presentation, we show how helium ion junctions can be used for spectroscopic studies of the superconducting energy gap and its anisotropy in the a-b plane. In addition, we demonstrate applications of nanojunctions in high-frequency applications, digital circuits, and quantum sensing.

We present an alternative approach to creating nanowires through local damage by a focused He ion beam (HIM). Motivated by the successful realization of Josephson junctions (JJ) after the introduction of dislocations into an otherwise orderly atomic arrangement [1], we have fabricated nanoscale detectors on superconducting films using He⁺ ion beam irradiation < 0.5 nm diameter. The ion beam propagates through the thin film and leaves a very narrow damage track. It benefits from a reduced interaction volume compared to that of an electron beam of similar energy and archives higher resolution without needing resist. Furthermore, this He⁺ beam technique allows for control of the atomic layer in three dimensions due to low dose and high collimation. We have performed an analysis of critical dose for different materials and have characterized patterned nanostructures. Our results suggest HIM may have advantages over e-beam lithography for some applications.

[1] C. Cybart et al., Nature Nanotechnology 10, 598–602 (2015)

Josephson junctions (JJs) are widely used in many superconducting circuits. Focused He⁺ ion beam irradiation has the potential of direct writing JJ multi-junction circuits. We have used 30 KeV He⁺ focused ion beam (He-FIB) with beam diameter of less than 0.5 nm to create nano-scale “normal” barriers, fabricating planar Josephson junctions in superconducting MgB₂ [1,2] and Co-doped Ba(FeAs)₂ (Ba122) thin films. Results show excellent device-to-device reproducibility. Accurate descriptions of the ion beam created normal state are critical to the development of beam created JJs and superconducting devices. By exploiting TRIM, TEM, and channeling RBS analysis, we have explored several means to obtain experimental information of the final state of the irradiated materials, so as to correlate these structural results with the electronic properties of the resulting film.
1] L. Kasaei et al. AIP Advances 8, 075020 (2018); https://doi.org/10.1063/1.5030751
[2] L.Kasaei et al. IEEE Transactions on Applied Superconductivity, 29 (2019); https://doi.org/10.1109/TASC.2019.2903418

Recent advances in focused ion beam (FIB) techniques have opened new opportunities for nanoscale milling and local modification of thin film superconductors. We present various FIB-based approaches to produce devices in thin films of the cuprate superconductor YBa₂Cu₃O₇ (YBCO). By Ga FIB milling, we fabricated YBCO nanoSQUIDs on bicrystal substrates with ultra-low flux noise in the thermal white noise limit [1]. Such devices offer detection of magnetization reversal processes in individual magnetic nanoparticles or nanowires [1-3]. By He FIB irradiation, it is possible to locally drive YBCO from the superconducting to the insulating state, with high spatial resolution, and hence to “write” Josephson barriers into thin films [4]. We present here a comprehensive analysis of the electric transport properties at 4.2 K of He-FIB produced YBCO Josephson junctions [5]. The critical current density j_c can be adjusted by irradiation dose D, with an exponential decay of j_c(D). For Josephson devices we find an approximate scaling of the characteristic voltage V_c ∝ j_c^1/2, and current-voltage characteristics that are well described by the resistively and capacitively shunted junction model, without excess currents for V_c < 1 mV. The He-FIB technique provides the possibility to place junctions at arbitrary location, with different orientation and shape, and even with different j_c on the same chip. Moreover, He-FIB irradiation with high dose produces highly resistive walls or areas. We used this feature to produce dc SQUIDs with sub-µm loop sizes and very low flux noise. As a further He-FIB application, we demonstrate the creation of ultradense tailored periodic pinning arrays for Abrikosov vortices in YBCO thin films, with lattice spacing down to 70 nm. By electric transport measurements and molecular dynamics simulations, we study unconventional commensurability effects of the vortex lattice with the fabricated quasi-Kagomé pinning lattices. Altogether, the He-FIB technique provides a promising tool for nanoscale patterning of advanced devices, e.g. Josephson junction arrays, in YBCO thin films.

References
[1] T. Schwarz et al., Phys. Rev. Applied 3, 044011(2015)
[2] M. J. Martínez-Pérez et al., Supercond. Sci. Technol. 30, 024003 (2017)
[3] M. J. Martínez-Pérez et al., Nano Lett. 18, 7674-7682 (2018)
[4] S. A. Cybart et al., Nature Nanotechnol. 10, 589-602 (2015)
[5] B. Müller et al., Phys. Rev. Applied 11, 044082(2019)
[6] B. Aichner et al., arXiv:1905.09070

Nanometer-scale metallic clusters of Ag and Au can be formed via implantation of 0.785 MeV Ag and 1.450 MeV Au ions into high-purity optical quality fused quartz silica (Infrasil), followed by thermal annealing at temperatures from 500-700C (Ag nanocluster formation) or 900-1100C (Au nanocluster formation). The optical properties of the resulting material – specifically, the intensity and wavelength of the plasmonic absorption bands from 400-530 nm, as well as the off-resonance absorption – are strongly affected by the total ion fluence, the particular metallic ion(s) implanted, and the details of the annealing process (temperature, time, and implantation/annealing processing order).
In past studies, we have shown that ion beams focused to a 2mm diameter and stepped slowly in 0.5mm increments laterally across a silica surface results in significantly different nanocluster formation than when ion beams are rastered across a much larger area in a conventional way. We have speculated that the increased ionization and/or localized thermal load in a moderately-focused process can lead to the acceleration of metal atom diffusion and nucleation of metallic nanoclusters, even at relatively low overall sample temperatures.
In this work, we will extend these studies to more tightly focused beams using an electrostatic quadrupole lens recently installed on a National Electrostatics 5SDH-2 accelerator. Focusing Ag and Au beams down to less than 100 micrometers in diameter, we will explore the limits of MeV ion implantation into such small areas without unacceptable damage to the silica host. The implanted surfaces will be examined with 3D wide area microscopy and 3D laser microscopy and optical absorption photo spectrometry, as well as Rutherford Backscattering Spectrometry (RBS) to confirm the implantation dose. To reach the implantation fluences needed for nanocluster formation (10¹⁶ atoms/cm² to 10¹⁷ atoms/cm²) in reasonable times, it is likely that the current density in the microscopic area will be very high, which may lead to damage via melting, plastic flow, electric microdischarges, or even ablation. If, however, we can form nanoclusters with tailored optical properties in these small areas, this technique could be used to create regimented structures with interesting and useful optical properties.

FIB/SEM tools have become commonplace in many university, industry, and research labs and are employed for a wide range of applications in a variety of research and industrial fields. From preparing samples for Transmission Electron Microscopy (TEM) and Atom Probe Tomography (APT), to milling specific test structures for further analysis or mechanical/electrical characterization, to failure analysis and circuit edit tasks in semiconductors - FIB/SEMs are an integral part of many problem-solving and research workflows.
Injecting process gases is an important part of many FIB/SEM processes. Precursor materials are introduced into the microscope's vacuum chamber and are decomposed by either the ion or electron beam. This results in material deposition, enhanced etching of specific materials, or the generation of very smooth surfaces on mixed-material substrates. A compact, flexible gas injection system will be introduced. In addition, injecting liquids (at high chamber pressures) can also be of interest for specific research topics.
Another important topic is sample agility. For one, when milling into samples with the goal of preparing cross sections or large TEM lamella, so-called curtaining effects can be very bothersome. An approach for mitigating these effects will be discussed. In addition, some sample analysis methods require the ability to tilt and rotate samples to specific angles - beyond what the microscopes' stages allow by default. One such analysis is Electron Channeling Contrast Imaging (ECCI), which will be introduced briefly. Finally, there are assembly tasks which require a high degree of sample motion, not accessible with standard microscope stages. An example of such an assembly task will be provided.
In addition, FIB/SEMs are often used in materials characterization. Tensile and compression tests can be performed on FIB-milled structures. Or, the FIB can be a tool that allows preparing/retrieving micro- or nano-sized objects and mounting them to specific substrates for mechanical or electrical characterization. A number of examples will be discussed.
Atomic Force Microscopy is popular among a wide range of research fields as it provides 3D topography information. Combining AFM with FIB/SEM tools yields the ability for multi-modal tests e.g. by combining the AFM technique with electron-based analysis methods (e.g. EDX).

For about 20 years gallium FIB systems have been used to produce precise serial section datasets for the purpose of 3D analysis and reconstruction [1,2,3,4]. In this technique, volume pixels (voxels) with dimensions on the nanometer scale in x, y and z are acquired by "slicing" with a "machining beam" and detecting signals stimulated by an "imaging beam", resulting in datasets that can readily span one hundred micrometers or more in at least one dimension. In our lab, we have demonstrated 1,000,000 cubic micrometers of aluminum alloy can be analyzed (with 40 nm voxels) in about 48 hours.

While the initial published efforts typically achieved slice thicknesses on the order of 100 to 500 nm, across just a few dozen slices, more recent efforts have accomplished thicknesses (and voxels) below 5 nm in size [5] and many thousand slices in a dataset. Achieving precision, accuracy and information fidelity under these conditions has become a complex task. This presentation will outline our experiences performing precision sectioning with gallium ions and imaging with either low energy electrons (in our ZEISS Crossbeam 550) or helium ions (in our ZEISS Orion NanoFab), coupled with precise beam control and dynamic measurements of slice thickness and beam position to achieve these goals.

Recent advancements towards the goal of 1 nm³ voxels will be demonstrated in the analysis of a range of materials systems. Multi-resolution analysis encompassing high voxel resolution imaging coupled with intermediate resolution analytics using EDS and EBSD will also be presented. The trade-offs necessary between various instrument parameters in order to enable successful implementation, the challenges of the existing technologies, and the requirements for future instrumentation and analysis development will also be discussed.

[1] “Three-Dimensional Microanalysis of Solid Materials using Ion and Electron Dual Focused Beam Apparatus”, Sakamoto T, Cheng Z, Takahashi M, Kuramoto Y, Owari M and Nihei Y.
J. Surface Analysis 5(1): 150-153, Jan. 1999.
[2] “FIB Techniques for Analysis of Metallurgical Specimens”, Phaneuf MW, and Li J.
Microsc. Microanal. 6(Suppl 2:Proceedings), 524-525, Aug. 2000.
[3] “3D Determination of Grain Shape in a FeAl-Based Nanocomposite by 3D FIB Tomography”, Inkson BJ, Mulvihill M and Möbus G.
Scripta Materialia 45(7):753-758, Oct. 2001.
[4] “Three-dimensional analysis of porous BaTiO3 ceramics using FIB nanotomography”, Holzer L, Indutnyi F, Gasser PH, Münch B and Wegmann M.
J. Microscopy, 216(1): 84–95, Sept. 2004.
[5] “Multi-resolution correlative focused ion beam scanning electron microscopy: applications to cell biology”, Narayan K, Danielson CM, Lagarec K, Lowekamp BC, Coffman P, Laquerre A, Phaneuf MW, Hope TJ, Subramaniam S.
J. Structural Biology 185(3):278-284, Dec. 2013.

During the last decade the combination of different microscopic and spectroscopic methods into one instrument gained increasing importance due to the simultaneous acquisition of complementary information. Especially highly localized probing of mechanical, electrical, magnetic, chemical and crystallographic properties on the nanoscale represents a key success factor for gaining new insights in the micro and nano world.

We present a unique atomic force microscope (AFM) – the AFSEM™ - designed for seamless integration into scanning electron microscopes (SEM) or FIB systems. Its open design and the use of self-sensing cantilevers with electrical readout allows for simultaneous operation of SEM, FIB and AFM inside the vacuum chamber to perform correlative in-situ AFM/SEM/FIB analysis of ion-beam treated nanostructured materials. We present correlative AFM/EBSD data of a FIB polished ZrO₂ ceramic of phase transformed regions. While EBSD allows for locally identifying areas where the phase transformation has occurred, in-situ AFM can now be utilized to analyze phase-transformation-induced topographic changes with sub-nm resolution.

In a further step, we demonstrate how in-situ correlative analysis with the AFM in an SEM and dual-beam system can be extended into the third dimension to measure nanomechanical properties of soft material. To achieve this, FIB slicing and mapping of nanomechanical properties using the AFSEM™ is performed in repetitive steps to build up a 3-dimensional elasticity map. Finally, we present, for the first time, in-situ correlative AFM results of helium treated surfaces inside the Zeiss ORION Nanofab. These experiments include the detailed study of a broad variety of samples. The dose-dependent creation of helium bubbles is shown on silicon, copper and steel surfaces. In addition, in-situ correlative MFM analysis of helium treated samples are shown. We observed the creation of magnetic domains on helium treated steel surfaces as well as the modification of multi-layered magnetic structures by ion-beam treatment.

Based on the broad variety of applications regarding the characterization of different materials and devices we anticipate the AFSEM to be one of the driving characterization tools for correlative SEM/FIB/AFM analysis in the future.

In this study, strategical nanostructuring, patterning and characterization routes were applied to determine morphological, chemical and structural features of biomaterials, ranging from nanocomposite biocompatible ceramics and biodegradable polymer coatings to soft neural tissues. Studies concerning serial sectioning which is followed by high resolution imaging/EDS mapping were performed at Focused Ion Beam - Scanning Electron Microscope (FIB-SEM) platforms for revealing biomaterials’ inner structures (morphological and chemical distribution data e.g. porosity, dopant/matrix, networking) in three dimensions down to the nanoscale. Novel biodegradable and biocompatible polymer nanocomposites were developed by doping silver nanowires (AgNWs) and boron nitride (BN) nanoparticles inside biopolymer (e.g. PLA, PCL) matrices, and three-dimensional characteristics of these samples were investigated at the micro/nano-scale by the use of proper processing methodologies and instrumental parameters. In addition, different natural tissues and synthetic biocomposites; such as human tooth, human brain and ceramic bone-graft materials were processed and analyzed by using serial ion slicing applications provided by FIB-SEM platforms. This study showed the versatility of using case-specific strategies for instant and simple processing of a variety of both hard and soft biological samples, which can be coupled with simultaneous imaging and chemical analysis procedures.

Ion irradiation has successfully been used for introducing impurities and creating defects in two-dimensional (2D) materials in a controllable manner. Moreover, focused ion beams, especially when combined with in-situ or post-irradiation chemical treatments, can be employed for patterning and even cutting 2D systems with a high spatial resolution. The optimization of this process requires the complete microscopic understanding of the interaction of energetic ions with the low-dimensional targets. In my presentation, I will dwell upon the multi-scale atomistic computer simulations of the impacts of ions onto free-standing (e.g., suspended on a TEM grid) and supported (deposited on various substrates) 2D materials, including graphene and transition metal dichalcogenides (TMDs), such as MoS₂ and WS₂. The theoretical results will be augmented by the experimental data obtained by the coworkers. Finally, I will touch upon the interaction of highly-charged [3] and swift heavy ions [4] with 2D systems and overview recent progress in modelling this using non-adiabatic approaches including time-dependent density functional theory and Ehrenfest dynamics [5].

1. M. Ghorbani-Asl, S. Kretschmer, D.E. Spearot, and A. V. Krasheninnikov, 2D Materials 4 (2017) 025078.

2. S. Kretschmer, M. Maslov, S. Ghaderzadeh, M. Ghorbani-Asl, G. Hlawacek, and A. V. Krasheninnikov, ACS Applied Materials & Interfaces 10 (2018) 30827.

3. R. A. Wilhelm, E. Gruber, J. Schwestka, R. Kozubek, T.I. Madeira, J.P. Marques, J. Kobus, A. V. Krasheninnikov, M. Schleberger, and F. Aumayr, Phys. Rev. Lett. 119 (2017) 103401.

4. R. Kozubek, M. Tripathi, M. Ghorbani-Asl, S. Kretschmer, L. Madauß, E. Pollmann, M. O’Brien, N. McEvoy, U. Ludacka, T. Susi, G.S. Duesberg, R.A. Wilhelm, A. V. Krasheninnikov, J. Kotakoski, and M. Schleberger J. Phys. Chem. Lett. 10 (2019) 904.

5. A. Ojanperä, A. V. Krasheninnikov, and M. Puska, Phys. Rev. B 89 (2014) 035120.

Charged energetic particle radiation has technological interest in applications including nuclear energy, outer space, medicine, and fundamental research. As a result of irradiation, damage, including point defects, forms and ultimately determines the material properties. Therefore, understanding the underlying interactions between charged particles and a material is important. When using the semi-empirical SRIM model to describe the interaction of charged ions with target materials as well as defect formation, one particularly severe drawback is that the model assumes an equilibrium charge state for the projectile. However, the Lindhard-Winter model predicts that the charge state of the projectile strongly affects electronic stopping and recent experimental results show that channeling U⁺⁹¹ in Si indeed experiences larger stopping power than off-channeling U ion. The underlying mechanism is not fully understood.

We use first-principles simulations, based on real-time time-dependent density functional theory, to study charge equilibration and electronic stopping for projectiles in multiple initial charge states. Our simulations for heavy (silicon) projectiles traversing crystalline bulk silicon indeed showed a pronounced dependence of electronic stopping on the initial projectile charge state. This effect was not observed in computational data for light projectiles impacting metal or semiconductor targets, but is qualitatively similar to the experimental results of channeling U⁺⁹¹ in Si.

To provide detailed understanding, we analyze the dynamics of charge equilibration, influence of the impact parameter, and contributions of core and valence electrons to electronic stopping. We observe that the equilibrium charge state of the Si projectile primarily depends on the impact parameter and ultimately dominates electronic stopping. Our results provide insights for future application of multi-charge ion source and can be integrated with multi-scale models, e.g. two-temperature molecular dynamics, to more accurately predict the defect formation during primary knock-on events.

Nanoscale ion implantation represents an expanding, interdisciplinary field that combines radiation effects with nano-engineering to control matter on the atomic level. In so doing, it offers the potential to create novel nano-devices such as quantum computers, magnetometers, nanowire pn junctions, etc. In particular, ion implantation enables more precise control of the spatial distribution and concentration of dopants/defects, making it highly desirable to fabricate nano-devices reproducibly. However, confidently taking advantage of it hinges upon the accurate and precise knowledge of the spatial distribution of dopants and defects created by ion implantation. Widely used, modern 1D simulations, such as SRIM (the Stopping Range of Ions in Matter) for example, may fail to predict this distribution because of the breakdown of key assumptions, including a large ion beam and target homogeneity in at least one dimension. Full three dimensional (3D) simulations of ion implantation are necessary in a wide range of nanoscience and nanotechnology applications to capture the increasing effect of ion leakage out of surfaces [Handbook of Materials Modeling. https://doi.org/10.1007/978-3-319-50257-1_115-2].

Using a recently developed 3D Monte Carlo simulation code IM3D [Scientific Reports 5 (2015) 18130], we first quantify the relative error of the 1D approach in three applications of nano-scale ion implantation: (1) nanobeam for nitrogen-vacancy (NV) center creation, (2) implantation of nanowires to fabricate p–n junctions, and (3) irradiation of nano-pillars for small-scale mechanical testing of irradiated materials. Because the 1D approach fails to consider the exchange and leakage of ions from boundaries, its relative error increases dramatically as the beam/target size shrinks. Lastly, the “Bragg peak” phenomenon, where the maximum radiation dose occurs at a finite depth away from the surface, relies on the assumption of broad beams. We discovered a topological transition of the point-defect or defect-cluster distribution isosurface when one varies the beam width, in agreement with a previous focused helium ion beam irradiation experiment. We conclude that full 3D simulations are necessary if either the beam or the target size is comparable or below the SRIM longitudinal ion range [Nanoscale 10 (2018) 1598].

Secondary ion mass spectrometry (SIMS) is a well-known technique for 3D chemical mapping at the nanoscale, with detection sensitivity in the range of ppm or even ppb. Energy dispersive X-ray spectroscopy (EDS) is the standard chemical analysis and imaging technique in modern scanning electron microscopes (SEM), and related dual-beam focused ion beam (FIB/SEM) instruments. Contrary to the use of an electron beam, in the past the ion beam in FIB/SEMs analytical instruments has predominantly been used for local milling or deposition of material. In this talk we will review the emerging FIB-SIMS technique which exploits the focused ion beam as an analytical probe, providing the capability to perform secondary ion mass spectrometry measurements within FIB/SEM instruments: secondary ions, sputtered by FIB, are collected and selected according to their mass by a mass spectrometer. In this way a complete 3D chemical analysis with high lateral resolution < 50 nm and a depth resolution < 10 nm is attainable. We first report on the historical developments of both SIMS and FIB techniques and review recent developments in both instruments. Next, the components of modern FIB-SIMS instruments, from the primary ion generation in the liquid metal source in the FIB column, the focussing optics, the sputtered ion extraction optics, to the different mass spectrometer types are all detailed. The advantages and disadvantages of parallel and serial mass selection in terms of data acquisition and interpretation are highlighted, while the effects of pressure in the FIB/SEM, acceleration voltage, ion take-off angles and charge compensation techniques on the analysis results are then discussed. The capabilities of FIB-SIMS in terms of sensitivity, lateral resolution, depth resolution and mass resolution are reviewed including measurements conducted on standard calibration samples such as BAM and VCSEL samples and also metallic nanoparticles incorporated into an inorganic matrix. Different data acquisition strategies related to dwell time, binning and beam control strategies as well as roughness and edge effects are discussed. Application examples are then presented for the fields of thin films, polycrystalline metals, batteries, solar cells, metallic multilayers, and biological samples. These are followed by studies towards enhancing secondary ion yields, and therefore TOF-SIMS signal quality, using supplementary gases. Two approaches are presented – one using a novel Cs evaporator prototype and the other based on supplying water vapour and fluorine gas using a commercial in-situ Gas Injection System (GIS). The potential of fluorine gas for increasing the spatial resolution of TOF-SIMS data (elemental distribution images and depth profiles) and de-coupling mass interference is demontrated. Finally, FIB-SIMS is compared to EDS, and the potential of the technique for correlative microscopy with other FIB/SEM based imaging techniques is discussed.

The rapid development and evolution of the nanotechnology market has triggered an increased demand for advanced characterization techniques at the nanoscale level. As of today, nanofeatures characterization requires the use of multiple ex-situ correlative techniques. For instance, Transmission Electron Microscopy (TEM) or Scanning Electron Microscopy (SEM) is often combined with Secondary Ion Mass Spectrometry (SIMS). SEM/TEM can uniquely reveal the nanofeature’s morphology, size and specific location on a sample (sub-organelles of a cell for example) while SIMS, a well-established sensitive surface analytical technique, will provide the chemical information. Although essential, ex-situ correlative techniques comes with the caveat of requiring adaptative sample preparation and the non-trivial task of identifying features of interest for the subsequent elemental characterization technique. TEM combined with Energy-Dispersive X-ray spectroscopy (EDX), on the other hand, offers in-situ characterization; but unlike SIMS, EDX cannot provide chemical information at sub-micrometric resolution and lacks the ability to detect light elements (H and Li).

A promising new technology for the characterization of nanofeatures has emerged with the configuration of the NanoFab with a SIMS detector. The ORION NanoFab is an ion microscope that allows high resolution secondary electron (SE) imaging with a He⁺ focused ion beam which can be focused to a 0.5 nm probe size. This same instrument also provides a Ne⁺ ion beam with a focused probe sizes of 2 nm. Recently, this platform has been configured with a custom-designed magnetic sector spectrometer equipped with four Channel Electron Multipliers (CEMs) positioned in the same focal plane The accessible mass range is 1 to 250 amu and the mass resolution M/DM exceeds 400. Importantly, SIMS with neon provides elemental imaging with spatial resolution smaller than 15 nm. The combination of high resolution He⁺ secondary electrimaging (0.5 nm) with Ne⁺ SIMS elemental mapping yields a direct correlative technique particularly attractive for exploring nanoparticles, as well as nanofeatures in general, in their macroscopic environment.

The NanoFab-SIMS has demonstrated recent success for the characterization of nanofeatures in the fields of perovskite materials, CIGS solar cells, nanotoxicology, batteries and nano-analytics in life science. We will present novel applications of this technology to research in the fields of nanomedicine, photonics and biology. More specifically we will show results on the characterization of biogenic nanoparticles (size in the 20 to 200 nm range) whose properties provide alternative treatment for bacterial resistance to antibiotics. We also investigated the elemental composition of doped phase-separated dielectric nano-particles in optical fibers and demonstrated that their composition varies with the particle size (size range 30-700 nm). Biology examples will include visualization of cells sub-organelles tagged with osmium antibodies.

Recently, the ZEISS ORION NanoFab has been equipped with a double focusing magnetic sector secondary ion mass spectrometer (SIMS) capable of chemically mapping features on the order of 10 nm[1-3] using a highly focused neon ion beam produced from a tuned gas field ion source. Initial results are extremely promising, already demonstrating usefulness in applications ranging from defect localization for semiconductor chips, chemical endpointing, and depth profiling to nanotoxicology[4], battery research[5], and characterizing solar cells[6, 7] and optoelectronics[8].

However, the utility of such an instrument is limited by its ability to detect trace elements which at small dimensions can be comprised of a limited number of atoms. Ultimately, the sensitivity of the SIMS is determined by the secondary ion (SI) current produced via the primary ion beam sputtering away the target material. This SI current is dependent on the sputter yield of the material, the collection efficiency of the detector, and, importantly, the ionization cross section of the species of interest.

In this study, we present a method for increasing the ionization cross section of different materials via the introduction of an in-chamber oxygen co-flow on a prototype tool, demonstrating in some cases a more than 2 order of magnitude increase in the SI useful yield. It is shown that oxygen can significantly enhance the positive ion yield of neighboring ions due to the readily forming oxide bond. When this bond is broken by the incoming primary ion, the oxygen tends to accept electrons due to its high electron affinity leaving the ion of interest more likely to be positively charged. Evidence shows that the ion yield enhancement is directly related to the surface coverage of the oxygen.

To study mechanistic effects and dependencies, we present data showing the effect of varied oxygen partial pressure, pixel dwell time, refresh time, beam current, and material type. The effect of the gas co-flow on sputter rate is also noted and presented.
Finally, we demonstrate the effect on the ultimate resolution that results from enhanced sensitivity with metallic nanoparticle contaminants on a silicon surface as well as on the BAM L200 standard. The future implications and challenges of increased sensitivity are also discussed.

[1] B Lewis, F Khanom and J Notte, Microscopy and Microanalysis 24 (2018), p. 850.
[2] T Wirtz et al., Annual Review of Analytical Chemistry 12 (2019), p. null.
[3] T Wirtz, D Dowsett and P Philipp in “Helium Ion Microscopy”, Springer (2016), p. 297.
[4] I Fizesan et al., Particle and Fibre Toxicology 16 (2019), p. 14.
[5] F Khanom et al., Microscopy and Microanalysis 25 (2019), p. 866.
[6] I Zimmermann et al., Journal of Materials Chemistry A 7 (2019), p. 8073.
[7] P Gratia et al., ACS Energy Letters 2 (2017), p. 2686.
[8] Y Liu et al., Nature Materials, 17(11) (2018), p. 1013.

The Low Temperature Ion Source (LoTIS) produces a beam of Cs+ ions that can be focused to nanometer spotsizes. This capability enables LoTIS to provide value in FIB applications where excellent machining acuity is required, such as circuit edit, as well as analytical applications where a high yield of secondary ions is desirable, as in secondary ion mass spectrometry (SIMS). The combination in a single beam will enable process control of nanomachining applications using simultaneous FIB machining and SIMS analysis.

We present the latest results from a prototype Cs+ Low Temperature Ion Source (LoTIS) retrofitted to a commercial FIB platform. Spot sizes as small as (2.1 ± 0.2) nm (one standard deviation) are observed with a 10 keV, 1.0 pA beam. Brightness values as high as (2.4 ± 0.1) × 107 A m-2 sr-1 eV-1 are observed near 8 pA [1]. We will also discuss plans for a new FIB+SIMS platform and examples of applications that are enabled by this unique combination.

Compared with the gallium liquid metal ion source (LMIS) utilized in most FIB systems today, LoTIS can provide a similar range of currents (pA to several nA), smaller spot sizes, and a reduced subsurface affected volume. These benefits have been utilized in the prototype system to perform circuit edits on 10 nm node chips. When compared with the standard Cs ion source used in commercial SIMS systems, LoTIS can deliver 100x more current into an equivalent spot. Additionally, LoTIS can deliver a few pA into few nm spot sizes, enabling SIMS material analysis at the ~4nm fundamental physical limits of the technique. This also enables the use of SIMS in problem domains where x-ray dispersive spectroscopy has been used traditionally.

[1] A. V. Steele, A. Schwarzkopf, J. J. McClelland, and B. Knuffman. Nano Futures. 1, 015005 (2017).

Secondary Ion Mass Spectrometry (SIMS) is an extremely powerful technique for analyzing surfaces, owing in particular to its ability to detect all elements from H to U and to differentiate between isotopes, its excellent sensitivity and its high dynamic range. SIMS analyses can be performed in different analysis modes: acquisition of mass spectra, depth profiling, 2D and 3D imaging. Adding SIMS capability to FIB instruments offers a number of interesting possibilities, including highly sensitive analytics, in-situ process control during patterning and milling, highest resolution SIMS imaging (~10 nm), and direct correlation of SIMS data with data obtained with other analytical or imaging techniques on the same instrument, such as high resolution SE images or EDS spectra [1,2].

Past attempts of performing SIMS on FIB instruments were rather unsuccessful due to unattractive detection limits, which were due to (i) low ionization yields of sputtered particles, (ii) extraction optics with limited collection efficiency of secondary ions and (iii) mass spectrometers having low duty cycles and/or low transmission. In order to overcome these limitations, we have investigated the use of different primary ion species and of reactive gas flooding during FIB-SIMS and we have developed compact high-performance magnetic sector mass spectrometers operating in the DC mode with dedicated high-efficiency extraction optics. We installed such SIMS systems on different FIB based instruments, including the Helium Ion Microscope [3-5], a FIB-SEM DualBeam instrument and the npSCOPE instrument, which is an integrated Gas Field Ion Source enabled instrument combining SE, SIMS and STIM imaging with capabilities to analyse the sample under cryo-conditions [6].

Here, we will review the performance of the different instruments with a focus on new developments such as cryo-capabilities and new detectors allowing parallel detection of all masses, showcase methodologies for high-resolution 3D chemical imaging, present a number of examples from various fields of applications (nanoparticles, battery materials, photovoltaics, micro-electronics, tissue and sub-cellular imaging in biology, geology,…) and give an outlook on new trends and prospects.

[1] T. Wirtz, P. Philipp, J.-N. Audinot, D. Dowsett, S. Eswara, Nanotechnology 26 (2015) 434001
[2] F. Vollnhals, J.-N. Audinot, T. Wirtz, M. Mercier-Bonin, I. Fourquaux, B. Schroeppel, U. Kraushaar, V. Lev-Ram, M. H. Ellisman, S. Eswara, Anal. Chem. 89 (2017) 10702
[3] D. Dowsett, T. Wirtz, Anal. Chem. 89 (2017) 8957
[4] T. Wirtz, D. Dowsett, P. Philipp, Helium Ion Microscopy, ed. by G. Hlawacek, A. Gölzhäuser, Springer, 2017
[5] T. Wirtz, O. De Castro, J.-N. Audinot, P. Philipp, Ann. Rev. Anal. Chem. 12 (2019)
[6] This project has received funding from the European Union’s Horizon 2020 Research and Innovation Programme under grant agreement No. 720964.

Nowadays many consumer products contain nanoparticles in order for them to have certain desired properties. However, with the addition of nanoparticles these products can have potentially unknown health risks to humans, animal and plant species, and to the environment in general. The nanomaterial risk identification involves their physico-chemical characterization currently employing a variety of techniques and separate instruments. This makes the characterization an expensive and time-consuming process.
In the framework of the Horizon2020 project npSCOPE, we are developing a new integrated instrument for the characterization of nanoparticles. The aim is to improve the efficiency of the nanomaterial characterization workflow by integrating several techniques in one single instrument. The npSCOPE instrument is equipped with the ultra-high resolution Gas Field Ion Source (GFIS) technology [1] allowing the sample to be irradiated with very finely focused He+ and Ne+ ion beams at the nano-scale. Furthermore, the instrument incorporates detectors for secondary electron imaging, a secondary ion mass spectrometer (SIMS) for chemical analysis [2-4] and a detector allowing the detection of transmitted ions/atoms to obtain in-situ structural/3D visualisation data. The instrument will allow the characterization of nanoparticles in their native state as well as embedded in complex matrices (e.g. biological tissue, liquid, etc.). A further key feature of the instrument is cryo-capability, including a 5 axis cryo-stage, in order to perform analyses of biological samples in a frozen-hydrated state and thus avoid artefacts caused by classical sample preparation (e.g. chemical fixation) used for HV or UHV imaging of biological specimens at room temperature.
Beside analyses of nano-toxicological samples we are planning to use this instrument in different material science fields as well as other life science domains that require high resolution imaging in cryo-conditions (e.g. lipid research) [5].

(For further information please visit www.npscope.eu)
[1] B. W. Ward, J. A. Notte, N. P. Economou; Helium ion microscope: a new tool for nanoscale microscopy and metrology; J. Vac. Sci. Technol. B 24/6 (2006), 2871.
[2] T. Wirtz, D. Dowsett, P. Philipp; SIMS on the helium ion microscope: a powerful tool for high-resolution high sensitivity nano-analytics; Helium Ion Microscopy (2016), ed. G. Hlawacek, A. Golzhäuser, 297.
[3] D. Dowsett, T. Wirtz, Anal. Chem. 89 (2017) 8957.
[4] T. Wirtz, O. De Castro, J.-N. Audinot, P. Philipp, Ann. Rev. Anal. Chem. 12 (2019).

[5] This project has received funding from the European Union’s Horizon 2020 Research and Innovation Programme under grant agreement No. 720964.

Hybrid organic-inorganic perovskites (HOIPs) have attracted extensive interest due to its diverse and unique optoelectronic and sensing functionalities. At the same time, these materials are characterized by the presence of the mobile and highly dynamic ionic subsystem, coupling both to the ionic mobility and lattice dynamics. Therefore, the development of HOIPs based devices and understanding of fundamental physics of these materials both necessitate understanding the interplay between ionic dynamics and the photoelectric processes. Here, we show direct observation of time-dependent methylammonium (CH₃NH₃⁺) redistribution induced by light illumination or electric bias in methylammonium lead iodide (CH₃NH₃PbI₃) and methylammonium lead bromide (CH₃NH₃PbBr₃) using time-resolved time-of-flight secondary ion mass spectrometry (tr-ToF-SIMS). We reveal that the photoexcitation in HOIPs is accompanied by large ion-redistribution. With the assistance of machine learning analysis approach, we unveil a distinctive change in temporal dynamics of ions induced by light for the first time. Moreover, we show the importance of photoexcitation energy on ion dynamics by illuminating the HOIPs samples using various wavelength light. In addition, combining with the time-resolved Kelvin probe force microscopy (tr-KPFM), we observed the photoexcited potential dynamics that are opposite to the ion dynamics, implying the screening effects of ion dynamics. Thus, KPFM only detects the small remainder of the photoinduced field, suggesting that the large photoinduced chemical changes are shielded as such less visible in traditional indirect measurements like KPFM. These pieces of knowledge—which are critical for further developments of HOIPs optoelectronics—were unknown previously, suggesting the importance of the direct observation of ion dynamics in HOIPs using tr-ToF-SIMS.

In situ cryo-electron tomography (cryo-ET) has become a central technique in structural biology over the last decade, facilitating studies of molecular structures directly within the native cellular environment. This progress was to a large extent driven by ground-breaking developments in sample preparation of frozen-hydrated specimen by cryo-focused-ion-beam microscopy (cryo-FIB) [1-4]. Standard FIB millings routines for homogeneously thick, electron-transparent lamellas from plunge-frozen specimen are nowadays well established and regularly carried out [5]. Lamellas are created directly on the frozen TEM grid by completely removing all material on both sides of the volume of interest.

However, this technique is limited to samples which can be vitrified in toto by plunge-freezing TEM grids, preventing a wide range of biological questions from being addressed by cryo-ET. Large specimens such as tissue samples from multicellular organisms require vitrification by high-pressure-freezing (HPF) to prevent the formation of crystalline ice. These samples are then too thick for the standard cryo-FIB lamella milling.

Overcoming this limitation is thus the next milestone for in situ cryo-ET. Several FIB techniques from materials science have been proposed for adaptation to cryo-preparation of thick biological samples, and proof of principle studies showing the feasibility of the FIB milling at cryogenic temperatures have been published. However, due to the stringent sample quality requirements of cryo-ET at molecular resolution, successful application of these techniques has so far not been demonstrated.

In this presentation we will show our recent cryo-FIB sample preparation development which enabled the first molecular resolution cryo-ET studies of HPF vitrified tissue [6]. Utilizing a cryo-adapted micromanipulator ‘gripping’ tool developed especially for this application, this novel cryo-FIB lift-out technique completely avoids localized material deposition and associated contamination issues. Fluorescently-labelled volumes of interest are selectively extracted from large HPF bulk samples and transferred onto special customized TEM grids for final thinning and subsequent use in the cryo TEM. We will discuss the optimization steps of each part of the complete workflow from HPF freezing to final cryo-ET experiment which were required to obtain meaningful tomographic data at molecular resolution.

References:
[1] M Marko et al, Nat Methods 4 (2007), p. 215.
[2] A Rigort et al, PNAS 109 (2012), p. 4449.
[3] M Schaffer et al, J Struct Biol. 197 (2017), p. 73.
[4] J Mahamid et al, Science 351 (2016), p. 969.
[5] M Schaffer et al, Bio Protocol 5 (2015), e1575.
[6] M Schaffer et al, Nat. Methods, in press

In ageing societies all over the globe, the number of people suffering from bone disease, e.g. osteoporosis (OP) in the first place, has increased dramatically. OP considerably impairs patients' life quality, and results in high societal costs. However, current understanding of bone disease is still insufficient due to the lack of appropriate high resolution tools that permit a thorough analysis of scale bridging bone architectures from macro to nano with statistical significance to support the development of better treatments by drugs or surgical intervention.

Cutting-edge correlative workflows starting from X-ray microscopy (XRM) volume analysis, with voxel sizes of <1µm, over light sheet fluorescence microscopy (LSFM) and large scale scanning electron microscopy data acquisition, to dual beam microscope analysis (focused electron- and ion beams) permit the scale bridging investigation of bone architectures and thus merging the “big picture” and the underlying ultrastructure with statistical significance. Together with advanced data analysis even including machine learning approaches permit reaching the next, so far unprecedented level of understanding.

I will show an examplary correlative workflow from sample collection over sample preparation and the acquisition of bone fine structures, composed of trabecular-, vascular-networks as well as a three-dimensional arrangement of osteo-lacunae (OL) that host osteocytes and the interosteocyte lacuno-canalicular network (LCN).
Blood vessel and OL volume can be assessed quantitatively with statistical significance in a new generation of lab-based XRM and LSFM. For investigation of the more delicate LCN we conduct dual beam microscope analysis (focused electron- and ion beams) in combination with additional analytical add-ons and demonstrate how this correlatation of various image modalities utilizing correlated data from electron-, ion-beam imaging and analytics, probes and focused laser light will permit to advance the current understanding of scale bridging bone architectures and their function. [ref1, ref2, ref3].
References:
[ref1] P. Milovanovic et al., bone 110, 187 (2018)
[ref2] A. Grüneboom et al., A network of trans-cortical capillaries forms the mainstay for blood circulation in long bones, Nature Metab. Published online (02/2019)
[ref3] P. Milovanovic et al., The Formation of Calcified Nanospherites during Micropetrosis Represents a Unique Mineralization Mechanism in Aged Human Bone, small 13(3), 1602215 (2017)

Precise 3D electron/ion nanoprinting is best achieved by accounting for deposition artifacts during the computer-aided design (CAD) phase. Otherwise, deposition is relegated to a tedious trial-and-error approach to replicate the desired geometry. Empirical corrections can be used to account for deposition errors or artifacts, but such solutions usually apply over a limited range of deposition conditions. Ideally, a general mathematical correction is the best solution because the identification of rate limiting factors related to deposition, such as mass-transport or reaction-rate limitations, leads to a more robust correction method which can be applied over a much larger range of deposition conditions. A comprehensive 3D electron beam nanoprinting capability consisting of experiments, simulations and design will be demonstrated which enables precise 3D nanoprinting. In addition, a mathematical-based scheme will be presented that makes it possible to compensate for heat induced deposit distortions. If left uncorrected, this type of artifact/error prevents CAD replication during deposition when using a typical organometallic precursor for deposition. The compensation strategy will be demonstrated for electron-based nanoprinting using both simulations and experiments. However, the CAD capability that will be presented is also compatiable with the use of an ion beam for deposition. Select applications of functional 3D nanoprinted structures will also be presented.

Nowadays, superconductors are commonly utilized in several applications such as energy generators and storage due to their unique capability of transferring electricity without energy losses. In some applications, their nanoscale patterning enhances their performance and gives rise to new physical phenomena.
Innovative schemes have taken advantage of the third dimension (3D) for the development of advanced superconducting electronics. Thus, 3D nanosuperconductors could promote a change in the next generation of electronic components. Nevertheless, their fabrication and characterization are still challenging and only a few works addressing the growth of real 3D nanosuperconductors have been reported so far ^1–4.
In this contribution, we introduce a template-free nano-lithography method to fabricate in a single-step 3D nano-elements on-demand with arbitrary geometry. The fabrication of complex 3D nano-architectures opens fascinating novel routes in the fields of material science, physics and nanotechnology. This specific technique called focused ion beam induced deposition (FIBID) is based on chemical vapour deposition process assisted by a charged particle beam focused to a few nanometers.
Particularly, by using tungsten hexacarbonyl molecules with a He⁺ ion beam focused to 0.3 nm, complex 3D W-C nanostructures have been fabricated ⁵. As a proof of concept, we report for the first time the fabrication and characterization of 3D superconducting crystalline WC hollow nanowires with outer diameters down to 32 nm and inner ones down to 6 nm⁵⁶. In addition, by modifying the ion beam current, hollow nanowires with controllable inner and outer diameters have been achieved ⁷. The growth of the vertical WC nanowire occurs around the ion beam spot, mainly due to the interaction of secondary electrons with the adsorbed precursor molecules, whereas a cavity at the center of the nanowire is created due to the He⁺ beam milling effect on the growing material. As shown by transmission electron microscopy, nanowires microstructure displays grains of large size fitting with face-centered cubic WC_1-x phase. By studying their magnetotransport properties, we have found that nanowires exhibit 1.5 times higher superconducting critical temperatures (6.4 K) as well as 1.5 times higher upper critical magnetic fields (≈14 T) (Fig. 1(c)) when compared to nanowires grown by a Ga⁺ FIBID.
The fabrication of such nanomaterials with excellent properties makes this technique at the cutting edge of nanofabrication methods based on focused beams of charged particles.

Acknowledgement:
“This project has received funding from the EU-H2020 research and innovation programme under grant agreement No 654360 NFFA-Europe.”


References
1. Li, W., Gu, C. & Warburton, P. A. Superconductivity of Freestanding Tungsten Nanofeatures Grown by Focused-Ion-Beam. J. Nanosci. Nanotechnol. 10, 7436–7438 (2010).
2. Romans, E. J., Osley, E. J., Young, L., Warburton, P. A. & Li, W. Three-dimensional nanoscale superconducting quantum interference device pickup loops. Appl. Phys. Lett. 97, 222506 (2010).
3. Li, W. et al. Felling of individual freestanding nanoobjects using focused-ion-beam milling for investigations of structural and transport properties. Nanotechnology 23, 105301 (2012).
4. Porrati, F. et al. Crystalline Niobium Carbide Superconducting Nanowires Prepared by Focused Ion Beam Direct Writing. ACS Nano acsnano.9b00059 (2019). doi:10.1021/acsnano.9b00059
5. Córdoba, R. et al., manuscript in preparation.
6. Córdoba, R., Ibarra, A., Mailly, D. & De Teresa, J. M. Vertical Growth of Superconducting Crystalline Hollow Nanowires by He + Focused Ion Beam Induced Deposition. Nano Lett. 18, 1379–1386 (2018).
7. Córdoba, R., Ibarra, A., Mailly, D. & De Teresa, J. M., manuscript in preparation.

A Focused Ion Beam (FIB) can be combined with precursor materials to grow deposits, the technique being referred to as Focused Ion Beam Induced Deposition (FIBID). In the standard FIBID configuration, a gas injection system delivers a precursor material in the gas phase, which becomes adsorbed to the substrate surface. The FIB irradiation decomposes the precursor molecules, creating a local deposit. The primary application of FIBID is the growth of metal lines, used to perform electrical connections during circuit edit [1] or utilized to contact nano-objects such as nanowires [2]. More recently, FIBID has found applications for the direct growth of functional materials in the fields of magnetism [3], superconductivity [4] and nano-optics [5]. Typical disadvantages when using FIBID include the long processing times and the appearance of side effects in the deposit and in the substrate: ion-induced defects, implantation, amorphization and milling [6]. New advances in FIBID aiming to lower the required ion doses would have a beneficial impact by decreasing the processing time and by minimizing the detrimental side effects caused by the ion irradiation.
In the present contribution, we will introduce FIBID under cryogenic conditions (Cryo-FIBID), which has been found to be an ultra-fast method to grow metal layers, nanowires and contacts [7]. Cryo-FIBID relies on FIB irradiation of a condensed layer of a precursor material formed on the substrate under cryogenic conditions. The technique implies cooling the substrate below the condensation temperature of the gaseous precursor material, subsequently irradiating with ions according to the wanted pattern, and posteriorly heating the substrate above the condensation temperature.
It will be shown that by using W(CO)₆ as the precursor material, a Ga⁺ FIB, and a substrate temperature of -100 °C, W-C metal layers and nanowires with resolution down to 38 nm can be grown by Cryo-FIBID [8]. The most important advantages of Cryo-FIBID are the fast growth rate (about 600 times higher than conventional FIBID with the precursor material in gas phase) and the low ion irradiation dose required (~ 50 μC/cm²), which gives rise to very low Ga concentrations in the grown material and in the substrate (≤ 0.2 %). This approach gives solution to the typical problems of the FIB technique: ion implantation, ion milling, ion-induced creation of defects and amorphization. Electrical measurements indicate that W-C layers and nanowires grown by Cryo-FIBID exhibit metallic resistivity. These features pave the way for the use of Cryo-FIBID in circuit editing and photomask repair in the semiconductor industry and, more generally, for the local growth of metal layers, nanowires and contacts, with various applications in nanotechnology.

[1] Y. Drezner et al., J. Vac. Sci. Technol. B, Nanotechnol. Microelectron. Mater. Process. Meas. Phenom. 2011, 29 (1), 011026
[2] S. B. Cronin et al., Nanotechnology 2002, 13 (5), 653-658
[3] H. Wu et al., J. Mater. Sci. Mater. Electron. 2014, 25 (2), 587–595
[4] R. Córdoba et al., Nano Lett. 2018, 18 (2), 1379–1386
[5] M. Esposito et al., ACS Photonics 2015, 2 (1), 105–114
[6] A. V. Krasheninnikov and K. Nordlund, J. Appl. Phys. 2010, 107 (7), 071301
[7] J. M. De Teresa et al., patent ES201830757, submitted
[8] R. Córdoba et al., manuscript submitted

Focused Ion Beams (FIB) are versatile tools with cross-disciplinary applications from the physical and life sciences to archaeology. Nevertheless, the nanoscale patterning precision of FIB is often accompanied by defect formation and sample deformation, which brings opportunities in fabricating nanostructures with complicated three-dimensional geometries, as well as challenges in controlling the degree of deformation. In this study, we revealed the fundamental mechanisms governing the self-folding of nanostructures undergoing FIB processes by a series of GPU-accelerated, large-scale molecular dynamic simulations. We revealed that the primary mechanism leading to nanostructure deformation during FIB processes is the mass transport to the free surface of nanostructures induced by energetic ion bombardment. We revealed a surprisingly simple linear correlation between atomic volume removed from the film interior and film deflection angle, regardless of incident ion energies and currents, by quantitatively analyzing the amount of volume removed from film interior. Hence, the present study demonstrates that it is possible to control the self-folding of nanostructures by controlling the direction of mass transport via carefully manipulating incident ion energy, and direction, thereby allowing fabricating nanostructures with complex three-dimensional geometries.