Ga Focused Ion Beam Research Articles

Characteristics of [formula omitted]-gallium oxide sputtering etching by focused gallium ion beam in the micro-nano scale fabrication

β−Gallium oxide (β−Ga2O3) is an ultra-wide bandgap (UWBG) semiconductor that is widely recognized as an ideal material for the fabrication of optoelectronic and high-voltage devices. As an advanced sputtering etching technology, focused ion beam (FIB) is increasingly used in the micron and nanoscale processing of semiconductor materials. In this paper, the influence of Ga FIB on β−Ga2O3 sputtering etching is systematically investigated from three parts, namely, the calibration of sputtering yield, the influence of process parameters on etched profiles and the effect of redeposition. Firstly, sputtering etching of β−Ga2O3 substrate was carried out under typical processing conditions with different incident angles, and the key parameter of sputtering yield was precisely calibrated. Further, Yamamura’s model is applied to fit the curve of sputtering yield as a function of incident angle. In addition, the sputtering yield of β−Ga2O3 is compared with those of GaNand Si under the same conditions, revealing the differences between them. Next, through line scan etching and trench structure etching experiments, this study analyzed the maximum etched depth, width, and etched volume variation with ion dose. The evolution of β−Ga2O3 trench structure is described and compared with GaN and GaAs, and from the perspective of redeposition effects, the reasons for the differences between the three in the sputtering etching process are analyzed. Lastly, the study investigated the impact of FIB process parameters on the redeposition effects of β−Ga2O3. Experimental results indicated that significant redeposition effect occurs when etching β−Ga2O3 with large single dwell time. Further analysis identified a specific range of single dwell times under different beam currents that reduce redeposition and prevents the formation of sidewall angles. These findings provide important data support for the high-resolution etching process of β−Ga2O3-based micro-nano devices using FIB technology, and also establish a reliable data foundation for related simulation studies.

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.

Automation and optimization of stopping and range of ions in matter simulation runtime

Prior to every ion implantation experiment a simulation of the ion range and other relevant parameters is performed using Monte-Carlo based codes. Although increasing computing power has improved the speed of these calculations, the demands on Monte-Carlo codes are also increasing, requiring evaluation of the optimal number of simulations while ensuring accuracy within threshold bounds. We evaluate the “Stopping and Range of Ions in Matter” (SRIM) code due to its widespread usage. We show how dividing simulations into multiple parallel simulations with different random seeds can lead to calculation speedup and find lower bounds for the required number of ion traces simulated based on an exemplar system of a Ga focused ion beam and a high energy C beam as used in high linear energy transfer testing. Our results indicate simulations can yield results within the underlying data accuracy of SRIM at 10X and 100X shorter simulation time than the SRIM default values.

Systematic study of FIB-induced damage for the high-quality TEM sample preparation

Nowadays, a focused Ga ion beam (FIB) with a scanning electron microscopy (SEM) system has been widely used to prepare the thin-foil sample for transmission electron microscopy (TEM) or scanning TEM (STEM) observation. An establishment of a solid strategy for a reproducible high-quality sample preparation process is essential to carry out high-quality (S)TEM analysis. In this work, the FIB damages introduced by Ga+ beam were investigated both experimentally and stopping and range of ions in matter (SRIM) simulation for silicon (Si), gallium nitride (GaN), indium phosphide (InP), and gallium arsenide (GaAs) semiconductors. It has been revealed that experimental investigations of the FIB-induced damage are in good agreement with SRIM simulation by defining the damage as not only “amorphization” but also “crystal distortion”. The systematic evaluation of FIB damages shown in this paper should be indispensable guidance for reliable (S)TEM sample preparation.

Allotropic transition of Dirac semimetal α-Sn to superconductor β-Sn induced by focused-ion-beam irradiation

Diamond-type structure allotrope α-Sn is attracting much attention as a topological Dirac semimetal (TDS). In this study, we demonstrate that α-Sn undergoes a phase transition to another allotrope β-Sn with superconductivity at low temperature by irradiating with a focused Ga ion beam (FIB). To clarify the transition mechanism, we performed x-ray photoemission spectroscopy (XPS) measurements on an α-Sn thin film irradiated with FIB and an as-grown α-Sn thin film. The XPS results suggest that the local annealing, which is one of the side effects of FIB, causes the transformation from α-Sn into β-Sn. Furthermore, the difference in the chemical states between α-Sn and β-Sn can be quantitatively explained by the crystal structures rather than the degree of metallicity reflecting the conductivity. These results propose a way of fabricating TDS/superconductor in-plane heterostructures based on α-Sn and β-Sn.

Unexpected modulation revealed by electron diffraction in Ni-Mn-Ga-Co-Cu tetragonal martensite exhibiting giant magnetic field-induced strain

Although the modulation of martensite structure has been considered as a precondition for highly mobile twin boundary and thus a giant magnetic field induced strain, the largest strain to date has been reported in non-modulated tetragonal martensite of Ni-Mn-Ga-Co-Cu. Using high-resolution transmission electron microscopy (HRTEM), we found that nominally non-modulated tetragonal Ni46Mn24Ga22Co4Cu4 single crystal possesses a modulation. The modulation was observed in thin lamellae containing b/c twins prepared by a focused Ga-ion beam and on a sample prepared by a conventional wedge thinning method. The modulation vector q* = (0, 0.2554, 0.4642), was determined by 3D electron diffraction. The simulated HRTEM image of such a structure agrees with the HRTEM micrograph. The presence of modulation in the thin lamellae and not in bulk suggests that Ni-Mn-Ga-Co-Cu martensite is on the edge of the shear instability enabling the high mobility of twin boundaries.

Modulation of GaAs nanowire growth by pre-treatment of Si substrate using a Ga focused ion beam

We reveal a novel phenomenon observed after self-catalytic growth of GaAs nanowires (NWs) on Si(111) substrates treated with a Ga focused ion beam (FIB). Depending on the ion dose, NW arrays with various geometrical parameters can be obtained. A minor treatment of the substrate enables a slight increase in the surface density of NWs relative to an unmodified substrate area. As the ion dose is increased up to ∼0.1 pC μm−2, the growth of GaAs NWs and nanocrystals is suppressed. However, a further increase in the ion dose stimulates the crystal growth leading to the formation of extremely thin NWs (39 ± 5 nm) with a remarkably high surface density of up to 15 μm−2. Resting upon an analysis of the surface structure before and after stages of ion-beam treatment, ultra-high vacuum annealing and NW growth, we propose a mechanism underlying the phenomenon observed. We assume that the chemical interaction between embedded Ga ions and a native Si oxide layer leads either to the enhancement of the passivation properties of the oxide layer within FIB-modified areas (at low and middle ion doses), or to the etching of the passivating oxide layer by excess Ga atoms, resulting in the formation of pores (at high ion doses). Due to this behavior, local fabrication of GaAs NW arrays with a diverse range of characteristics can be implemented on the same substrate. This approach opens a new way for self-catalytic growth of GaAs NWs.

Fabrication and Evaluation of YBa2Cu3O7-δ Probe for Scanning Probe Microscopy

We proposed, fabricated, and evaluated a high-temperature superconducting probe made of YBa <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">2</sub> Cu <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">3</sub> O <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">7-δ</sub> (YBCO) for scanning probe microscopy. A c-axis-oriented bulk was cut into a rectangular solid rod (0.5 × 0.5 × 10 mm <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">3</sup> ) using a fine cutter machine. The transition temperature of the rod was approximately 90 K, which was almost the same as that of the original bulk, indicating no critical damage to the superconductivity owing to the cutting process. One end of the rod was polished to a pyramid shape with <100-μm radius of curvature, and the apex was further sharpened to ∼1 μm using a focused Ga ion beam. The penetration depth of Ga ions from the YBCO surface was much less than 1 μm at an acceleration voltage of 40 kV, suggesting that the chemical composition was conserved inside the rod. An YBCO probe was installed in an atomic force microscope (AFM), where the probe temperature was set at 300 K at the time. Depending on the tip radius, a clear AFM image was obtained by gluing the probe to a quartz-tuning fork.

Nonlinear Photoluminescence from Patterned ITO Thin Films

ITO is a transparent conductive material commonly used in everyday life and for its potential in material research. In nonlinear optics for instance, ITO has shown great capabilities for harmonic generation in its epsilon-near-zero configuration. In this article, we demonstrate a completely new nonlinear behaviour from ITO thin layers. After a Ga-Focused Ion Beam (FIB) milling of the thin film, we observe nonlinear photoluminescence produced for tightly focused femtosecond pulses. The signal shares strong similarities with that commonly detected from noble metals. We show that the arising of this nonlinear photoluminescence originates from the radiative decay of metal-like hot electron distribution in the material and is associated to a modification of the optical properties by the Ga ions.

Effect of Si(111) Surface Modification by Ga Focused Ion Beam at 30 kV on GaAs Nanowire Growth

This paper presents the results of experimental studies of the effect of Si(111) surface modification by Ga-focused ion beam (FIB) at 30 kV accelerating voltage on the features of the epitaxial GaAs nanowire (NW) growth processes. We experimentally established the regularities of the Ga ions' dose effect during surface modification on the structural characteristics of GaAs NW arrays. Depending on the Ga ion dose value, there is one of three modes on the surface for subsequent GaAs NW growth. At low doses, the NW growth is almost completely suppressed. The growth mode of high-density (up to 6.56 µm-2) GaAs NW arrays with a maximum fraction (up to 70%) of nanowires normally oriented to the substrate is realized in the medium ion doses range. A continuous polycrystalline base with a dense array of misoriented short (up to 0.9 µm) and thin (up to 27 nm) GaAs NWs is formed at high doses. We assume that the key role is played by the interaction of the implanted Ga ions with the surface at various process stages and its influence on the surface structure in the modification region and on GaAs NW growth conditions.

Pore Ordering in Anodic Aluminum Oxide: Interplay between the Pattern of Pore Nuclei and the Crystallographic Orientation of Aluminum.

Anodization of aluminum with a pre-patterned surface is a promising approach for preparing anodic aluminum oxide (AAO) films with defect-free pore arrangement. Although pronounced effects of crystallographic orientation of Al on the AAO structure have been demonstrated, all current studies on the anodization of pre-patterned aluminum consider the substrate as an isotropic medium and, thus, do not consider the azimuthal orientation of the pattern relative to the basis vectors of the Al unit cell. Here, we investigate the interplay between the azimuthal alignment of the pore nuclei array and the crystallographic orientation of aluminum. Al(100) and Al(111) single-crystal substrates were pre-patterned by a Ga focused ion beam and then anodized under self-ordering conditions. The thickness-dependent degree of pore ordering in AAO was quantified using statistical analysis of scanning electron microscopy images. The observed trends demonstrate that the preferred azimuthal orientation of pore nuclei rows coincides with the <110> directions in the Al unit cell, which is favorable for creating AAO with a high degree of pore ordering. In the case of an unspecified azimuthal orientation of the pore nuclei array, crystallography-affected disorder within the AAO structure occurs with increasing film thickness. Our findings have important implications for preparing defect-free porous films over 100 µm in thickness that are crucial for a variety of AAO applications, e.g., creating metamaterials and 2D/3D photonic crystals.

Microstructure deformation and near-pore environment of resolidified tungsten in high heat flux conditions

Tungsten is a candidate divertor material for many tokamak reactors and has potential to be durable to high heat flux conditions. However, plasma-materials interaction and edge localized modes (1–10 GW/m2) can cause significant hardening and melting damage. Tungsten in a high heat flux (46.3 GW/m2) and helium plasma environment was investigated. We studied possible residual helium and microstructure deformation in resolidified tungsten. Following this, a 1–30 keV Ga focused ion beam was used for TEM sample milling. In as-received tungsten, dark spots of possible lattice strain and defects were in the grains. After high heat exposure under plasma pressure, intergranular features, dark spots in TEM, diffraction patterns, and elongated FIB induced pore-artifact structures (second phase) formed. Helium appears to be absent from the resolidified tungsten matrix due to erosive melting damage and high temperature conditions. A simple four-step microstructure deformation process from the elastic bulk side to the near-pore environment is proposed. The presence of defects in TEM images, grain size reduction, and microstructure deformation affected hardening. The near-pore environment likely experienced grain refinement, and further disordered nanophases are possible under severe deformation conditions.

Using Xe Plasma FIB for High-Quality TEM Sample Preparation.

A direct comparison between electron transparent transmission electron microscope (TEM) samples prepared with gallium (Ga) and xenon (Xe) focused ion beams (FIBs) is performed to determine if equivalent quality samples can be prepared with both ion species. We prepared samples using Ga FIB and Xe plasma focused ion beam (PFIB) while altering a variety of different deposition and milling parameters. The samples’ final thicknesses were evaluated using STEM-EELS t/λ data. Using the Ga FIB sample as a standard, we compared the Xe PFIB samples to the standard and to each other. We show that although the Xe PFIB sample preparation technique is quite different from the Ga FIB technique, it is possible to produce high-quality, large area TEM samples with Xe PFIB. We also describe best practices for a Xe PFIB TEM sample preparation workflow to enable consistent success for any thoughtful FIB operator. For Xe PFIB, we show that a decision must be made between the ultimate sample thickness and the size of the electron transparent region.

Is the Ne operation of the helium ion microscope suitable for electron backscatter diffraction sample preparation?

Electron backscatter diffraction (EBSD) is a powerful characterization technique which allows the study of microstructure, grain size, and orientation as well as strain of a crystallographic sample. In addition, the technique can be used for phase analysis. A mirror-flat sample surface is required for this analysis technique and different polishing approaches have been used over the years. A commonly used approach is the focused ion beam (FIB) polishing. Unfortunately, artefacts that can be easily induced by Ga FIB polishing approaches are seldom published. This work aims to provide a better understanding of the underlying causes for artefact formation and to assess if the helium ion microscope is better suited to achieve the required mirror-flat sample surface when operating the ion source with Ne instead of He. Copper was chosen as a test material and polished using Ga and Ne ions with different ion energies as well as incident angles. The results show that crystal structure alterations and, in some instances, phase transformation of Cu to Cu3Ga occurred when polishing with Ga ions. Polishing with high-energy Ne ions at a glancing angle maintains the crystal structure and significantly improves indexing in EBSD measurements. By milling down to a depth equaling the depth of the interaction volume, a steady-state condition of ion impurity concentration and number of induced defects is reached. The EBSD measurements and Monte Carlo simulations indicate that when this steady-state condition is reached more quickly, which can be achieved using high-energy Ne ions at a glancing incidence, then the overall damage to the specimen is reduced.

Experiments and simulation of the secondary effect during focused Ga ion beam induced deposition of adjacent nanostructures

Focused Ga ion beam can deposit various materials with high-resolution assisted by elaborately selected precursor gases. During the deposition process, the secondary effect arises due to the generation of secondary particles by primary ions. Prominent morphological changes are caused by the secondary effect between adjacent, densely arranged structures. This study analyzes the morphological changes and structural characterizations from the perspective of secondary particles, including scattered ions, sputtered atoms, and re-emitted precursor molecules, with the assistance of continuous cellular automata. C14H10 and W(CO)6 were utilized as the precursor gas in the experiments under the same parameters as the numerical model. The experimental and simulation results demonstrated that the deposit morphology on the adjacent structure, and the enhanced growth rate of the processing structure, could be precisely predicted, with a good estimation of secondary particles contribution. Furthermore, the deposition efficiency on the adjacent structure was improved, and the higher metal content in the deposits was validated by Energy Dispersive X-Ray Spectroscopy (EDS). This work, therefore, lays foundation for avoiding the secondary effect when fabricating nanostructure arrays, and utilizing it for coatings, chiral structure construction, and tuning material properties.

High transmission from 2D periodic plasmonic finite arrays with sub-20 nm gaps realized with Ga focused ion beam milling

Fabricating plasmonic nanostructures with good optical performances often requires lengthy and challenging patterning processes that can hardly be transferred to unconventional substrates, such as optical fiber tips or curved surfaces. Here we investigate the use of a single Ga focused ion beam process to fabricate 2D arrays of gold nanoplatelets for nanophotonic applications. While observing that focused ion beam milling of crossing tapered grooves inherently produces gaps below 20 nm, we provide experimental and theoretical evidence for the spectral features of grooves terminating with a sharp air gap. We show that transmission near 10% can be obtained via two-dimensional nano-focusing in a finite subset of 2D arrays of gold nanoplatelets. This enables the application of our nanostructure to detect variations in the refractive index of thin films using either reflected or transmitted light when a small number of elements are engaged.

A Study of the HTS Josephson Junction Formed by a Ga Focused Ion Beam

High Temperature Superconductor Josephson Junctions (HTS-JJs) are based on artificial grain boundaries. However, the layout of HTS Superconducting QUantum Interference Devices (SQUIDs) on a bi-crystal substrate was restricted. Therefore, we considered to form low noise nano-bridge JJs by Ga Focused Ion Beam (Ga-FIB) irradiation. An 100 nm thick and 4 μm wide YBa2Cu3O7-δ (YBCO) micro-channels protected by a 20 nm thick Au protection layer were irradiated by line scans of Ga-FIB (Acceleration voltage: 40 kV, Beam diameter: ∼30 nm) and they were became normal conductivity except for the restricted region. In those nano-bridges, W N = 500 nm and fluence Φ = 2.0×1015 ions/cm2 of the nano-bridge was I C = 170 μA and we confirmed Shapiro steps by microwave irradiation of f RF = 2 GHz.

Mechanical Properties of α-SiC and Correlation to SiC/Si Interface at Nanoscale from Reaction Bonded SiC/Si Composites (RBSC)

Reaction bonded SiC/Si (RBSC) composites composed of α-SiC, β-SiC and crystalline-Si phases manufactured at high temperature are widely used in different applications due to their outstanding performances in extreme service conditions. Although the macroscopic mechanical properties of these materials have been extensively explored, there are questions remaining unanswered such as the local material behavior compared to the SiC/Si interface, mechanistic responses in nanoscale and the micro- to nanoscale mechanical properties of major individual components after experiencing the reaction bonding process. In this study, nanoscale specimens were prepared by utilizing Ga focused ion beam (FIB) and an in-situ tensile testing platform was established with a testing stage accommodated inside a field emission scanning electron microscope (FE-SEM). Maximum tensile strength, elastic modulus and Weibull modulus of the nanoscale α-SiC specimens were measured to be 22.9 GPa, 321 GPa and 4.1, respectively. The maximum failure strength was found to be as high as 80% of the theoretical fracture strength. The fracture was found to originate at the side of the specimen surface and appeared to propagate in a brittle manner. The overlap of tensile strength ranges of α-SiC and SiC/Si interface suggests the consistency with an observation of mixed fracture modes in RBSC.

Structural characterization and continuous cellular automata simulation of micro structures by focused Ga ion beam induced deposition process

Focused ion beam induced deposition (FIBID) is a high-resolution micro/nano fabrication technique with the injection of precursor gas to produce complex three-dimensional structures, which can be used to construct nanodevices. Due to the complex interaction between precursor gas, incident ions, and the substrate, the morphology of deposition structure dramatically depends on the process parameters. In this paper, based on the Continuous Cellular Automata (CCA) and the extended precursor molecule diffusion model (EPMDM), the effects of different process parameters on the final deposition morphology, are systematically studied. The experimental and theoretical work explores the relationship between the characterization of the deposition structure and process parameters. Considering the variation of diffusion effect intensity, the diffusion coefficient matrix decaying with the structure height is established to calculate the contribution of diffusion effect more precisely, which can also explain the non-uniform growth of deposition structure in the FIBID process. The vacuum surface cells (VSCs) and solid surface cells (SSCs) are recognized for deposition and sputtering respectively in the CCA, so as to trace the dynamic deposition contour, and reproduce the coexistence of deposition and sputtering phenomena. In order to verify the proposed CCA simulation model, micro pillar array and other structures are fabricated by focused Ga ion beam induced C9H16Pt precursor gas. The experimental and simulation results show that the proposed model can well simulate the morphology of deposition structures under a wide range of process parameters of dwell time, refresh time, ion beam current and pixel overlap. Therefore, the model can provide a good prediction method for parameter optimization of focused Ga ion beam induced deposition process.

High yield of self-catalyzed GaAs nanowire growth on silicon (111) substrate templated by focused ion beam patterning

We report and detail a lithography-free method to pattern Si substrates. In particular, a focused Ga ion beam is used to create regular patterns of holes which serve as a template for the growth of vertically aligned GaAs nanowires (NW)s on Si(111) substrates using self-catalyzed molecular beam epitaxy. We show that the hole diameter plays a crucial role in the growth of the NWs at the drilled holes. The critical parameters defining the width of the holes are: ion dose quantities, wet etching procedures, and high-temperature steps at the process of growth. As a result, we obtained a yield of more than 80% for vertically aligned NW. Compared to other methods of patterning our approach provides the following advantages: (i) it is a lithography-free procedure, (ii) allows for quick patterning process and hole diameter optimization within a small window of trial and error, (iii) and provides potential applicability for different material systems.