Focused Ion Beam System Research Articles

Rubidium and Cesium Ion-Induced Electron and Ion Signals for Scanning Ion Microscopy Applications.

Scanning ion microscopy applications of novel focused ion beam (FIB) systems based on ultracold rubidium (Rb) and cesium (Cs) atoms were investigated via ion-induced electron and ion yields. Results measured on the Rb+ and Cs+ FIB systems were compared with results from commercially available gallium (Ga+) FIB systems to verify the merits of applying Rb+ and Cs+ for imaging. The comparison shows that Rb+ and Cs+ have higher secondary electron (SE) yields on a variety of pure element targets than Ga+, which implies a higher signal-to-noise ratio can be achieved for the same dose in SE imaging using Rb+/Cs+ than Ga+. In addition, analysis of the ion-induced ion signals reveals that secondary ions dominate Cs+ induced ion signals while the Rb+/Ga+ induced signals contain more backscattered ions.

Artifact-free sample preparation of metal thin films using Xe plasma-focused ion beam milling for atomic resolution and in situ biasing analyses

The focused ion beam (FIB) technique using Ga ion beams is generally employed for transmission electron microscopy (TEM) sampling owing to its location-specific beam controllability on materials. However, Ga ion beam bombardment-induced damage hinders reliable structural analysis. Furthermore, Ga ions implanted in the damaged surface layer substantially lower the chemical stability of the samples, such as metal thin films. Here, aiming for atomic-level interface structural analysis, we propose a useful approach for the TEM sample preparation of heteroepitaxial Ag/Cu metal films without physical damage or chemical instabilities using the Xe plasma FIB (PFIB) system. Xe plasma-assisted sampling ensured that the interface structure of the Ag/Cu metal film remained intact; in contrast, the sample prepared using the focused Ga ion beam was damaged by elemental mixing. Furthermore, the sample prepared by Xe plasma milling exhibited robust structural stability over time after exposure to air in contrast to the sample prepared by Ga-ion milling, which induced structural decomposition owing to oxidation. In addition to the static structural analysis, the Cu thin film sample prepared by Xe PFIB exclusively exhibited pristine structural properties under in situ electrical biasing experiments, thus confirming the feasibility of conducting a fundamental study of Cu electromigration without artifacts.

Nanoporous Gold Thin Films as Substrates to Analyze Liquids by Cryo-atom Probe Tomography.

Cryogenic atom probe tomography (cryo-APT) is being developed to enable nanoscale compositional analyses of frozen liquids. Yet, the availability of readily available substrates that allow for the fixation of liquids while providing sufficient strength to their interface is still an issue. Here, we propose the use of 1-2-µm-thick binary alloy film of gold-silver sputtered onto flat silicon, with sufficient adhesion without an additional layer. Through chemical dealloying, we successfully fabricate a nanoporous substrate, with an open-pore structure, which is mounted on a microarray of Si posts by lift-out in the focused-ion beam system, allowing for cryogenic fixation of liquids. We present cryo-APT results obtained after cryogenic sharpening, vacuum cryo-transfer, and analysis of pure water on the top and inside the nanoporous film. We demonstrate that this new substrate has the requisite characteristics for facilitating cryo-APT of frozen liquids, with a relatively lower volume of precious metals. This complete workflow represents an improved approach for frozen liquid analysis, from preparation of the films to the successful fixation of the liquid in the porous network, to cryo-APT.

Large-area (50 cm × 50 cm) optically transparent electromagnetic interference (EMI) shielding of ZTO/Ag/ZTO: an analytical/numerical and experimental study of optoelectrical and EMI shielding properties

Transparent conducting oxides (TCOs), exhibiting both high optical transparency and low electrical resistivity, are commonly employed in optoelectronic devices. However, acquiring a balance between these optical and electrical properties in a uniform way over large areas has been a pending challenge, which is essential to achieving optically transparent electromagnetic interference (EMI) shielding surfaces. In this study, we propose and demonstrate a stratified thin film structure consisting of zinc-doped tin oxide (Zn2SnO4, ZTO) as TCO along with a metal layer of silver (Ag) deposited on a large area of 50 cm × 50 cm polycarbonate (PC) substrate enabled by a scanning magnetron sputtering gun. We achieved high EMI shielding of 99.9% at the optical transparency of 68% in the visible spectrum by engineering the stratified architecture of ZTO/Ag/ZTO. The Ag layer of 18 nm in thickness with a sheet resistance of 10 Ω/sq yields shielding effectiveness (SE) of 27 dB in a wide frequency range of 2–20 GHz. The bottom and top ZTO layers, 20 and 40 nm thick, respectively, provide the lowest optical loss of 13% across 400–700 nm. The structure’s EMI shielding, optical and structural performances were systematically characterized through a free-space focused-beam system, UV–Vis spectrophotometer, ellipsometry, focused ion-beam cross-sectional sampling and imaging, transmission electron microscopy, atomic force microscopy and secondary ion mass spectroscopy. EMI shielding and optical performances were validated by CST Microwave Studio and the transfer matrix method, respectively. These findings indicate that the proposed multi-layer architecture holds great promise for large-area EMI shielding and other optoelectronic applications.

Effects of the strain rate in compression of electrodeposited gold micro-pillars toward the design of MEMS components

In this study, the strain rate dependence in yield strengths of electrodeposited gold micro-pillars is evaluated for the design of movable components in MEMS devices. The micro-pillars are fabricated from electrodeposited gold by focused ion beam system. The strain rate dependence is quantified by the strain rate sensitivity, and the strain rate sensitivity is calculated from the yield strength obtained from compression tests of the gold micro-pillars having different sizes at different strain rates. An increase in the yield strength following a reduction in the pillar size is observed, which is the sample size effect. Also, weakening of the yield strength is observed following a decrease in the strain rate, which is the strain rate dependence, and the strain rate sensitivity of the gold micro-pillars is found be at roughly 0.03.

Crystallographic faceting of bulk tungsten surfaces observed during in situ heating in an environmental scanning electron microscope

The surface faceting of metals has been studied for several decades, typically using experimental methods such as low-energy electron diffraction. In the current paper, surface faceting of tungsten pellets was studied during in situ heating inside an environmental scanning electron microscope (ESEM), which allowed for direct, high-fidelity observation of morphological changes in response to high-temperature annealing under a moderate vacuum (0.8 Torr). Additionally, a second set of tungsten samples was annealed in an ultrahigh vacuum chamber (10−8 Torr), albeit without direct observation via ESEM. This study revealed that oxygen plays a crucial role in tungsten surface faceting and in a morphological transition to vertex rounding. Furthermore, this paper discusses relevant techniques for identifying the crystallographic indices of surface facets. It is demonstrated that a combination of electron backscatter diffraction, tilted-sample imaging from multiple angles, and serial sectioning in a focused ion beam system can be effectively deployed to determine the geometry of faceting, which in turn can be verified with the aid of software for generating Wulff shapes. The influence of processing environment on tungsten surface faceting enables the possibility of designing and controlling the morphology and crystallographic facets of tungsten surfaces.

Novel Method for the Preparation of Lamellas From Porous and Brittle Materials for In Situ TEM Heating/Biasing.

A novel method for the preparation of lamellas made from porous and brittle compressed green powder using a focused ion beam (FIB) is described. One of the main purposes for the development of this methodology is to use this type of samples in micro-electromechanical systems (MEMS) chips for in situ transmission electron microscopy heating/biasing experiments, concomitant with maintaining the mechanical integrity and the absence of contamination of samples. This is accomplished through a modification of the standard FIB procedure for the preparation of lamellas, the adaptation of conventional chips, as well as the specific transfer of the lamella onto the chips. This method is versatile enough to be implemented in most commercially available FIB systems and MEMS chips.

A High‐Resolution Versatile Focused Ion Implantation Platform for Nanoscale Engineering

The ability to spatially control and modify material properties on the nanoscale, including within nanoscale objects themselves, is a fundamental requirement for the development of advanced nanotechnologies. The development of a platform for nanoscale advanced materials engineering (P‐NAME) designed to meet this demand is demonstrated. P‐NAME delivers a high‐resolution focused ion beam system with a coincident scanning electron microscope and secondary electron detection of single‐ion implantation events. The isotopic mass‐resolution capability of the P‐NAME system for a wide range of ion species is demonstrated, offering access to the implantation of isotopes that are vital for nanomaterials engineering and nanofunctionalization. The performance of the isotopic mass selection is independently validated using secondary ion mass spectrometry (SIMS) for a number of species implanted into intrinsic silicon. The SIMS results are shown to be in good agreement with dynamic ion implantation simulations, demonstrating the validity of this simulation approach. The wider performance capabilities of P‐NAME, including sub‐10 nm ion beam imaging resolution and the ability to perform direct‐write ion beam doping and nanoscale ion lithography, are also demonstrated.

Interfacial reaction behavior of titanium/steel composite plate formed by cold-hot rolling

Titanium/steel composite plate was prepared by cold-hot rolling method. The influence of temperature on the interfacial reaction behavior of titanium/steel composite plate was studied by double beam focused ion beam system and spherical aberration correction transmission electron microscopy. The results show that the interfacial reaction of the cold-rolled titanium/steel composite plate mainly occurs in the heating stage, and the continuous intermetallic compounds layer formed at the interface during heating fractures during hot rolling. An interfacial layer composed of submicron TiC layer and α-Ti/α-Fe is formed when the hot rolling temperature is not higher than 850 °C, and the interfacial bonding strength increases with the increase of rolling temperature. An interface layer composed of micro (FeTi+TiC)/Fe2Ti layer, nano FeTi/Fe2Ti layer and micro pores is formed when the hot rolling temperature exceeds 900 °C. The interfacial micro (FeTi+TiC)/Fe2Ti layer and micro pores will seriously damage the interfacial bonding quality.

Specimen size effect on the strength of nickel-boron alloys

Nickel-boron alloys are prepared by an electrodeposition method. The as-deposited nickel-boron alloy is then annealed at 250 °C and 400 °C for 4 h. Their mechanical strengths and specimen size effects on the strength are evaluated by micro-compression test using pillar-type micro-specimens fabricated by focused ion beam system. In all as-deposited and annealed specimens, a smaller-is-stronger specimen size effect is confirmed. The compressive strength of the nickel-boron alloys reaches a maximum of 5.79 GPa with the smallest specimen size in this work.

Ion irradiation-induced nano pore/fiber formation and areal-vacancy distribution in semiconductor materials

In this study, the formation of nano-porous/fibrous structures was investigated by spot-ion irradiation on Ge and GaSb substrates to consider the formation range of nanostructures and point defects. Spot-ion irradiation was performed in a focused ion beam system with a beam diameter of 35.1 nm, which is determined by the system. The fluence and ion beam current ranged within 5 × 1019–1 × 1022 ions/m2 and 500–520 pA, respectively. All the irradiated ions were Ga+ with incident energy adjusted at 30 keV, and the angle of incidence to the surface normal was 0°. The interval of the irradiated spot ranged from 100 to 1000 nm. For line-patterned irradiations, these spots overlapped with one another at an overlap ratio of 50%, producing a 35.1 nm × 10 μm irradiated region. Result shows that nanostructured regions followed a spot interval. When an interval was shorter than 200 nm, each nanostructured spot coalesced with neighbors to form large and uniform structures. Furthermore, line-patterned irradiation indicated that the migration distance of vacancy was ∼300 nm at maximum, which is consistent with the coalescence phenomenon.

Correlation of sample geometry and grain size in micro-bending of electrodeposited polycrystalline gold

In this study, micro-cantilevers are fabricated from electrodeposited gold by focus ion beam system, and correlations of the sample geometry effect and average grain size on the bending characteristics are evaluated. The average grain size of all as-fabricated micro-cantilevers is measured to identify contributions of each of the sample geometry effect and average grain size to the micro-mechanical strength. The micro-cantilever with a finer average grain size shows a higher yield stress as a result of the grain boundary strengthening mechanism. The sample geometry effect is confirmed when varying the width and thickness of the micro-cantilever, which the yield stress is more dependent on the thickness than that on the width.

Single-Layer Transmissive Chiral Plasma Metasurface with High Circular Polarization Extinction Ratio in Visible Wavelength.

Chiral metamaterials are extensively applied in the fields of photoelectric detection, biomedical diagnostics and micro-nano polarization imaging. Currently, single-layer chiral metamaterials are unfortunately limited by several issues, such as a weaker circular polarization extinction ratio and circular polarization transmittance difference. To tackle these issues, a single-layer transmissive chiral plasma metasurface (SCPMs) suitable for visible wavelength is proposed in this paper. Its basic unit is composed of double orthogonal rectangular slots and a spatial π/4 inclined arrangement of the rectangular slot to constitute a chiral structure. Each rectangular slot structure has characteristics that enable the SCPMs to easily achieve a high circular polarization extinction ratio and strong circular polarization transmittance difference. Both the circular polarization extinction ratio and circular polarization transmittance difference of the SCPMs reach over 1000 and 0.28 at a wavelength of 532 nm, respectively. In addition, the SCPMs is fabricated via the thermally evaporated deposition technique and focused ion beam system. This compact structure coupled with a simple process and excellent properties enhances its applicability for the control and detection of polarization, especially during integration with linear polarizers, to achieve the fabrication of a division-of-focal-plane full-Stokes polarimeter.

Robotic Fabrication of High-quality Lamellae for Aberration-corrected Transmission Electron Microscopy

Aberration-corrected scanning transmission electron microscopy (STEM) is widely used for atomic-level imaging of materials. To accelerate the discovery of new materials based on atomic-level investigations, the throughput of aberration-corrected STEM experiments becomes more and more important. However, the throughput of the full workflow of aberration-corrected STEM is still quite low. A fundamental problem is that the preparation of high-quality thin STEM samples (lamellae) depends on manual operation. Here, inspired by the recent successes of robot scientists, we demonstrate robotic fabrication of high-quality lamellae by focused-ion-beam (FIB) with full automation software. First, we show that robotic FIB can prepare lamellae with a high success rate, where the robotic FIB controls rough-milling, lift-out, and final-thinning processes. Then, we optimize the FIB parameters of the final-thinning process for single crystal Si. Aberration-corrected STEM imaging of these Si lamellae shows atomic-level images with 55 pm resolution. We also demonstrate robotic fabrication of high-quality lamellae of SrTiO3 and sapphire. The robotic FIB system will resolve the current bottleneck of the full workflow of aberration-corrected STEM analysis and accelerate materials discovery based on atomic-level imaging.

FIB and Wedge Polishing Sample Preparation for TEM Analysis of Sol-Gel Derived Perovskite Thin Films

In ceramic thin films, choosing an appropriate sample preparation method for transmission electron microscopy (TEM) analyses is of paramount importance to avoid preparation-induced damage and retain nanoscale features that require investigation. Here we compare two methods of TEM thin film sample preparation, namely conventional wedge polishing and focused ion beam (FIB) based lift out preparation applied to ferroelectric barium titanate (BaTiO3, BT) thin films made by chemical solution deposition (CSD). The aim of the work is to determine the pros and cons of each method considering not only the quality of the TEM specimen, but also aspects such as availability, ease of use, and affordability. Besides some limitations on the selection of visualized area due to thickness constraints on the FIB-made sample, both methods offer the capability to prepare samples with very comparable quality, as indicated by achieving the same thickness, a largely agreeing microstructure, no secondary phases on the diffraction pattern, and good atomic resolution. This last observation is especially important in the current context of material science, where more nanoscale phenomena are becoming the subject of study. The wedge polishing method, however, is deemed more affordable in terms of instrumentation, as it only requires a tripod polisher, a polishing wheel, and a precision ion polishing system, whereas the lift out method requires a scanning electron microscope (SEM) equipped with an FIB system. We believe that this work serves groups working on ferroelectric thin films in preparing TEM samples in a more effective and uncomplicated manner, facilitating progress in understanding this fascinating class of materials.

Investigation of Rb+ milling rates using an ultracold focused ion beam

Several ion source alternatives for current focused ion beam (FIB) systems have been studied to achieve higher brightness, including cold atom ion sources. However, a study of ultracold ions interacting with often used materials is seldom reported. Here, we investigate milling on several typical samples in a prototype ultracold Rb FIB system at 8.5 keV beam energy. For polycrystalline metallic substrates, such as Cu and Au, patterns milled by Rb+ ions are observed to have reduced surface roughness but still high milling rates compared with those milled by Ga+ ions. Rb+ also shows similar sputter rates as 30 keV Ga+ on semiconductor substrates GaAs and InP. Special cases for Rb+ milling show that the Rb+ ion beam has a 2.6× faster sputter rate on diamond but a 3× slower sputter rate on Al compared with a normal 30 keV Ga+ ion beam. In general, an Rb+ ion beam is shown to be suitable for nanostructuring of several basic materials.

Sample size effect in Ni-TiO2 composites fabricated by supercritical CO2 emulsified CO-electroplating for miniaturized device

This study reports the micro-mechanical property and sample size effect in Ni-TiO 2 composites (NTO) fabricated by supercritical CO 2 emulsified co-electroplating (SCNTO). NTO by conventional co-electroplating (CVNTO) is also prepared as a comparison. The micro-mechanical property is evaluated by micro-compression test of micro-pillars prepared from the NTO by focus ion beam system. Cross-sections of the micro-pillars are 5 μm × 5 μm, 7.5 μm × 7.5 μm and 10 μm × 10 μm, and the height is kept twice of one side of the cross-section. The yield strength of a SCNTO micro-pillar with the dimensions of 7.5 μm × 7.5 μm × 15 μm is 3.37 GPa, which is three times higher than that of the CVNTO. The sample size effect is not observed in the SCNTO micro-pillars, while a smaller-is-weaker effect is observed in the CVNTO micro-pillars. The ultrafine (<10 nm) average grain size of the Ni in the SCNTO is suggested to cause the weakening in the sample size effect. The average grain size of the CVNTO is 23.6 nm, which is in the region of grain boundary-mediated mechanism that leads to the smaller-is-weaker effect. • Sample size effect in Ni-TiO 2 composites is investigated by micro-compression tests • Co-electroplating with supercritical CO 2 is used in preparation of the composite • Square-top pillars of 5 μm ~ 10 μm sample size are fabricated by FIB milling • 3-fold enhancement in the mechanical strength of the composite is observed • Mechanical strength of the composite is independent of the sample size

Electrodeposition and Micro-Mechanical Property Characterization of Nickel–Cobalt Alloys toward Design of MEMS Components

Nickel–cobalt alloys were prepared by alloy electrodeposition with a sulfamate bath, and the mechanical properties on the micro-scale were evaluated for the application as micro-components in miniaturized electronic devices. Nickel bromide and a commercially available surface brightener were used as the additives. The cobalt content increased from 21.5 to 60.1 at.% after addition of nickel bromide into the bath, and the grain size refined from 21.1 to 13.2 nm when the surface brightener was used. The mechanical properties on the micro-scale were evaluated by micro-compression test using micro-pillar type specimens fabricated by a focused ion beam system to take the sample size effect into consideration. The yield strength of the nickel–cobalt alloy having an average grain size at 13.9 nm and cobalt content of 66.6 at.% reached 2.37 GPa, revealing influences from the sample size, grain boundary strengthening, and solid solution strengthening effects.

Use of Thermal Boron Technique to Determine Optimum Synthesis Parameters for Zirconium and Hafnium Diborides

Zirconium and hafnium diborides were synthesized. The process of obtaining zirconium and hafnium diborides was carried out by reduction of zirconium and hafnium dioxides with amorphous boron at high temperature in a vacuum furnace with a residual pressure of 10 Pa. The synthesis of metal diborides included the following stages: preparation of charge, pressing, annealing of tablets, milling, and classification. The initial components were mixed in a drum-type apparatus; an aqueous solution of polyvinyl alcohol was used as a plasticizer. Tableting was performed on an OYSTAR Manesty FlexiTab tablet press with a punch diameter of 13 mm at a pressure of 218.7 MPa. The thickness of the obtained tablets was 3 mm. The obtained tablets were annealed in a Nabertherm VHT/GR vacuum furnace. A graphite crucible with zirconium oxide or hafnium oxide backfill, respectively, was used for annealing. The furnace was vacuumized with a forevacuum pump to a residual pressure of 10 Pa. The morphology of ZrB2 and HfB2 particles was investigated using the QUANTA 200 3D electron and focused-beam system. The phase composition and structural parameters of the samples were investigated on a Shimadzu XRD-6000 diffractometer with Cu K&alpha; radiation. We determined the optimal parameters for the synthesis of zirconia and hafnium diborides: the optimal temperature for the synthesis of zirconia diboride was 1800 оС, for the synthesis of hafnium diboride &mdash; 1850 оС, the heating rate was 8.5 оС/min. The highest yield of zirconium and hafnium diborides was achieved in samples with a molar ratio of MeO2:B = = 1:6 at a synthesis time of 60 minutes. The yield of metal diborides was 99%.The authors who contributed to this paper include V. I. Sachkov, R. A. Nefedov,&nbsp;R. O. Medvedev, A. S. Sachkova, D. A. Biryukov.The authors would like to thank the Tomsk Regional Centre of Shared Knowledge&nbsp;for their support of this research work. This research was funded by the&nbsp;Ministry of Education and Science of the Russian Federation under the Governmental&nbsp;Assignment no. FSWM-2020-0028.

Effect of Synthesis Time on Synthesis and Photoluminescence Properties of ZnO Nanorods

With the hydrothermal method, the p-type silicon &lt;100&gt; wafer was used as the substrate to synthesize ZnO nanorods in different synthesis times. To prepare the ZnO seed layer on the p-type silicon &lt;100&gt; wafer, a prepared ZnO gel was deposited as the seed layer using the spin coating method. A 0.2 M solution of zinc acetate dihydrate (Zn(CH3COO)2-2H2O) and hexamethylenetetramine ((CH2)6N4) were used as the source materials at a synthesis temperature of 90 °C. The synthesis time was changed from 10 to 60 min as the synthesis parameter. X-ray diffraction patterns, scanning electron microscopy, and a focused ion beam system were used to analyze and compare the crystal characteristics and the heights and widths of synthesized ZnO nanorods. We found that the crystal characteristics, the heights and widths, and the photoluminescence properties of synthesized ZnO nanorods were dependent on the synthesis time.