Focused Ion Beam Processing Research Articles

Chemical segregation in metallic glass nanowires.

Nanowires made of metallic glass have been actively pursued recently due to the superb and unique properties over those of the crystalline materials. The amorphous nanowires are synthesized either at high temperature or via mechanical disruption using focused ion beam. These processes have potential to cause significant changes in structure and chemical concentration, as well as formation of defect or imperfection, but little is known to date about the possibilities and mechanisms. Here, we report chemical segregation to surfaces and its mechanisms in metallic glass nanowires made of binary Cu and Zr elements from molecular dynamics simulation. Strong concentration deviation are found in the nanowires under the conditions similar to these in experiment via focused ion beam processing, hot imprinting, and casting by rapid cooling from liquid state. Our analysis indicates that non-uniform internal stress distribution is a major cause for the chemical segregation, especially at low temperatures. Extension is discussed for this observation to multicomponent metallic glass nanowires as well as the potential applications and side effects of the composition modulation. The finding also points to the possibility of the mechanical-chemical process that may occur in different settings such as fracture, cavitation, and foams where strong internal stress is present in small length scales.

X-선 회절 패턴 측정과 투과 전자 현미경을 이용한 구리 나노분말의 수소 환원 처리 시 발생하는 미세조직 변화 및 치밀화 시편의 물성 분석

In this study, nano-scale copper powders were reduction treated in a hydrogen atmosphere at the relatively high temperature of <TEX>$350^{\circ}C$</TEX> in order to eliminate surface oxide layers, which are the main obstacles for fabricating a nano/ultrafine grained bulk parts from the nano-scale powders. The changes in composition and microstructure before and after the hydrogen reduction treatment were evaluated by analyzing X-ray diffraction (XRD) line profile patterns using the convolutional multiple whole profile (CMWP) procedure. In order to confirm the result from the XRD line profile analysis, transmitted electron microscope observations were performed on the specimen of the hydrogen reduction treated powders fabricated using a focused ion beam process. A quasi-statically compacted specimen from the nano-scale powders was produced and Vickers micro-hardness was measured to verify the potential of the powders as the basis for a bulk nano/ultrafine grained material. Although the bonding between particles and the growth in size of the particles occurred, crystallites retained their nano-scale size evaluated using the XRD results. The hardness results demonstrate the usefulness of the powders for a nano/ultrafine grained material, once a good consolidation of powders is achieved.

A haptic digital tool to assist the design, planning and manufacture of micro- and nanostructures

This work addresses the engineering demands for precise interactive process planning for the manufacture of high precision in the manufacturing of 3D micro- and nanoproducts. It outlines the development of a digital tool based on a haptics-based human–machine interface. This interface is underpinned using an empirical model derived from a series of experimental results obtained from a focused ion beam machine through a series of experiments, which produced the surface topographies of a number of micro- and nanograting arrays; these were systemically analysed to provide an underpinning empirical database, which could be accessed via the haptic process planning system. On accessing these data, highly accurate geometrical models are then input into a haptics human machine interface to emulate the focused ion beam machining process as defined by the customised fabrication parameters. The haptic planning system predicts and simulates the shape and form of the finished product profiles as the haptic device is passed across a virtual substrate. Once the simulation is complete and the outputs verified by the user, the system then automatically outputs a stream file to drive the focused ion beam process to produce the surface topographies required. The simulation results reveal that compared with trial and error method, the haptics-based simulation method is a reliable way to plan and optimise the fabrication parameters in design and manufacture of micro- and nanogratings by focused ion beam machining cost-effectively. This could potentially provide substantial lead time and cost reductions associated with these currently inherently expensive unit cost products as well as demonstrate a novel tool not only for the planning of nanomachining cutting sequences but also for the interactive design of such products. This work also highlights the benefits of an empirical model as a means of underpinning and supporting real-time haptics interaction, something not possible using more numerical-based techniques.

Direct observation of dopant distribution in GaAs compound semiconductors using phase-shifting electron holography and Lorentz microscopy

Phase-shifting electron holography and Lorentz microscopy were used to map dopant distributions in GaAs compound semiconductors with step-like dopant concentration. Transmission electron microscope specimens were prepared using a triple beam focused ion beam (FIB) system, which combines a Ga ion beam, a scanning electron microscope, and an Ar ion beam to remove the FIB damaged layers. The p-n junctions were clearly observed in both under-focused and over-focused Lorentz microscopy images. A phase image was obtained by using a phase-shifting reconstruction method to simultaneously achieve high sensitivity and high spatial resolution. Differences in dopant concentrations between 1 × 10(19) cm(-3) and 1 × 10(18) cm(-3) regions were clearly observed by using phase-shifting electron holography. We also interpreted phase profiles quantitatively by considering inactive layers induced by ion implantation during the FIB process. The thickness of an inactive layer at different dopant concentration area can be measured from the phase image.

Piezoresistive cantilever working in a shear force mode for in situ characterization of exposed micro- and nanostructures

This paper presents a method of characterization micro- and nanostructures defined in a photolithography process. To implement this method a measurement system composed of an atomic force microscope (AFM) integrated with a system for maskless lithography was developed. This integration enables exposed patterns to be examined in situ, without any necessity for a developing process. The microscope works in a shear force mode, uses a cantilever with a piezoresistive method of detecting deflection and can be used for measuring surfaces with high aspect ratio by applying an appropriate technology of sharpening in a focused ion beam process. The cantilever fabrication process, its calibration and examination procedures are presented. Finally, the AFM images of structures scanned directly after exposure are shown.

Semipolar (202¯1) GaN laser diodes operating at 388 nm grown by plasma-assisted molecular beam epitaxy

Laser diodes (LDs) were grown by plasma-assisted molecular beam epitaxy on semipolar (202¯1) GaN substrates. Metal-rich conditions provided smooth surface morphology and good structural quality as confirmed by atomic force microscopy and transmission electron microscopy studies. No stacking faults or any linear defects were formed during the growth in the InGaN/InGaN multiquantum well active region. Devices were processed with ridge-waveguide along the [1¯21¯0] direction. Mirrors were cleaved or fabricated by focused ion beam (FIB) processing. LDs operated at 388.2 nm with the threshold current density 13.2 kA/cm2 and the threshold voltage 10.8 V. The device with mirrors fabricated by FIB processing reached practically the same threshold current and slope efficiency as the one with cleaved mirrors. The authors present the beneficial role of the InGaN optical confinement layers in semipolar LDs, which can be optimized to improve the threshold current of these devices.

Focused Ion Beam Processing of Superconducting Junctions and SQUID Based Devices

AbstractFocused ion beam (FIB) has found a steady and growing use as a tool for fabrication, particularly in the length-scale of micrometres down to nanometres. Traditionally more commonly used for materials characterisation, FIB is continually finding new research areas in a growing number of laboratories. For example, over the last ten years the number of FIB instruments in the U.K. alone has gone from single figures, largely supplied by a single manufacturer, to many tens of instruments supplied by several competing manufacturers. Although the smaller of the two research areas, FIB fabrication has found itself to be incredibly powerful in the modification and fabrication of devices for all kinds of experimentation. Here we report our use of FIB in the production of Superconducting QUantum Interference Devices (SQUIDs) and other closely related devices for metrological applications. This is an area ideally suited to FIB fabrication as the required precision is very high, the number of required devices is relatively low, but the flexibility of using FIB means that a large range of smallbatch, and often unique, devices can be constructed quickly and with very short lead times.

&lt;i&gt;In Situ &lt;/i&gt;Microfabrication and Measurements of Bi&lt;sub&gt;2&lt;/sub&gt;Se&lt;sub&gt;3 &lt;/sub&gt;Ultrathin Films in a Multichamber System with a Focused Ion Beam, Molecular Beam Epitaxy, and Four-Tip Scanning Tunneling Microscope

Ultrathin films of Bi2Se3 grown on Si(111) substrate were etched into submicron-width wires by using a focused ion beam (FIB), and their electrical resistance was measured using the four-probe method with a four-tip scanning tunneling microscope. All of the procedures were performed in situ in ultrahigh vacuum without exposing the sample to air. One-dimensional conduction of the films was confirmed from the dependence of the resistance on the length of wire under measurement, meaning that successful lossless current path control laterally as well as vertically can be obtained with FIB etching. Protecting the sample surface from unintentional gallium ion beam irradiation in the FIB process was also found to be important for maintaining the intrinsic electrical properties of the Bi2Se3 films. [DOI: 10.1380/ejssnt.2014.423]

A combined approach to predict spatial temperature evolution and its consequences during FIB processing of soft matter

Accessing local temperatures and their evolution during focused ion beam (FIB) processing is of particular importance in the context of polymers or biomaterials as they tend to undergo severe chemical and morphological damage due to the high temperatures arising. In this study we present a combination of ion trajectory simulations and thermal spike model based calculations, which allows predicting local temperatures, lateral distributions and evolution during FIB patterning. Simulations and calculations have been done without any approximation or correction factors and lead to results in very good agreement with experiments on polymers taking into account their thermal behaviour. Finally, the model is applied to different scanning strategies which demonstrate how classically applied patterning strategies lead to massive temperature increases which can be the knock out criteria for low melting materials.

Chemical degradation and morphological instabilities during focused ion beam prototyping of polymers

Focused ion beam processing of low melting materials, such as polymers or biological samples, often leads to chemical and morphological instabilities which prevent the straight-forward application of this versatile direct-write structuring method. In this study the behaviour of different polymer classes under ion beam exposure is investigated using different patterning parameters and strategies with the aim of (i) correlating local temperatures with the polymers' chemistry and its morphological consequences; and (ii) finding a way of processing sensitive polymers with lowest chemical degradation while maintaining structuring times. It is found that during processing of polymers three temperature regimes can be observed: (1) at low temperatures all polymers investigated show stable chemical and morphological behaviour; (2) very high temperatures lead to strong chemical degradation which entails unpredictable morphologies; and (3) in the intermediate temperature regime the behaviour is found to be strongly material dependent. A detailed look reveals that polymers which rather cross-link in the proximity of the beam show stable morphologies in this intermediate regime, while polymers that rather undergo chain scission show tendencies to develop a creeping phase, where material follows the ion beam movement leading to instable and unpredictable morphologies. Finally a simple, alternative patterning strategy is suggested, which allows stable processing conditions with lowest chemical damage even for challenging polymers undergoing chain scission.

Growth and FIB-SEM analyses of C60 microtubes vertically synthesized on porous alumina membranes

The vertical growth of C60 microtubes (C60MTs) on anodic aluminum oxide (AAO) membranes was investigated. The C60MT size dependence on isopropyl alcohol (IPA) injection rate, into C60-saturated toluene solutions through AAO membranes, was measured. A longitudinal section of the interface between a vertically grown C60MT (V-C60MT) and a membrane was prepared by focused ion beam processing, and observed with scanning electron microscopy. No cracking was observed along the interface, suggesting good bonding. V-C60MTs exhibited spiral growth. V-C60MT planar density, wall thickness and aspect ratio all decreased with increasing IPA injection rate. The relationships among length, inner and outer diameters of V-C60MTs were also investigated by varying IPA injection rate.

Focused ion beam processing to fabricate ohmic contact electrodes on a bismuth nanowire for Hall measurements

Ohmic contact electrodes for four-wire resistance and Hall measurements were fabricated on an individual single-crystal bismuth nanowire encapsulated in a cylindrical quartz template. Focused ion beam processing was utilized to expose the side surfaces of the bismuth nanowire in the template, and carbon and tungsten electrodes were deposited on the bismuth nanowire in situ to achieve electrical contacts. The temperature dependence of the four-wire resistance was successfully measured for the bismuth nanowire, and a difference between the resistivities of the two-wire and four-wire methods was observed. It was concluded that the two-wire method was unsuitable for estimation of the resistivity due to the influence of contact resistance, even if the magnitude of the bismuth nanowire resistance was greater than the kilo-ohm order. Furthermore, Hall measurement of a 4-μm-diameter bismuth microwire was also performed as a trial, and the evaluated temperature dependence of the carrier mobility was in agreement with that for bulk bismuth, which indicates that the carrier mobility was successfully measured using this technique.PACS81.07.Gf

Fabrication Using Focused Ion Beam Processing of Devices Employing Silicon-Based Nanowires Synthesized by Vapor-Liquid-Solid Growth

Undoped and B-doped silicon-based nanowires (SiNWs) were synthesized by vapor-liquid-solid growth, and SiNW devices using Au electrodes were prototyped using focused ion beam (FIB) processing. Needle-shaped thin SiNWs were formed at a substrate temperature between 1170 and 1313 °C. The average and minimum diameters of the B-doped SiNWs were 72 nm and 52 nm, respectively. According to the current-voltage characteristics, SiNW devices have ohmic properties, and the estimated resistivity of the undoped and B-doped SiNWs are about 3.8 × 103Ωcm and 1.7 × 103Ωcm, respectively.

Fabrication and Evaluation of Flowmeter with Focused-Ion-Beam System

In this paper, we fabricated and evaluated the piezoresistive type flowmeter with focused-ion-beam (FIB) system. The flowmeter body is made up of the low stress silicon nitride, and the nanometer sized piezoresistive layer is deposited with FIB system for the smaller measuring area. The flowmeter is evaluated in the wind tunnel, and the 0~4m/s air flows are applied. Although the sensitivity, ΔR/R shows the negative behavior unlike the conventional piezoresistive layer due to the added materials during the FIB process, the measurement results show the ΔR/R has a suitable sensitivity (-1.04E-2/ms-1) and a rapid response time (0.8sec). Those results represent the fabricated piezoresistive type air flowmeter has the possibility for the small area detection.

Focused ion beam induced Ga-contamination—An obstacle for UV-nanoimprint stamp repair?

Ultravoilet (UV)-nanoimprint lithography (NIL) master stamps are subject to wear due to the mechanical nature of the imprint process. To extend the useful lifespan of expensive NIL master stamps, a focused ion beam repair process is highly desirable. Due to the inevitable Ga-staining induced by the focused ion beam processing the transmissivity of repaired NIL stamps is locally degraded. In this work, the authors investigate the impact of Ga-induced transmission losses on the imprint process. Experimental results indicate that the reduced transparency mainly impacts the amplitude of bow deformations in the imprint. These deformations are strongly enhanced by Ga-staining of the master stamp. The authors present a method for quantification of such bow-deformations. The introduced bowing-factor allows to make a qualified decision on whether the occurring deformation is acceptable for the target application. The authors have achieved control over the extent of the Ga-induced bow-deformation by tuning the UV-dose applied during NIL resist exposure. The bowing-factor provides excellent guidance for adapting the required exposure-dose of the NIL resist to reduce the bow-deformation to an acceptable level. With the presented approach, the mitigation of Ga-staining induced defects in the imprint is successfully achieved.

TEM observations of radiation damage in tungsten irradiated by 20 MeV W ions

Polycrystalline, recrystallized W targets were subjected to implantation with 20MeVW6+ ions in order to simulate radiation damage caused by fusion neutrons. Three samples with cumulative damage of 0.01, 0.1 and 0.89dpa were produced. The near-surface zone of each sample has been analyzed by transmission electron microscopy (TEM). To this end, lamellae oriented perpendicularly to the targets implanted surface were milled out using focused ion beam (FIB). A reference lamella from non-irradiated, recrystallized W target was also prepared to estimate the damage introduced during FIB processing. TEM studies revealed a complex microstructure of the damaged zones as well as its evolution with cumulative damage level. The experimentally observed damage depth agrees very well with the one calculated using the Stopping and Range of Ions in Matter (SRIM) software.

ナノロッドの引張試験手法の開発

We develop a new test method for evaluating tensile properties of nano-mateirals and apply it to a single crystalline gold nanorod with a square section of 189nm. The nanorod, which is carved out of a bulk material by focused ion beam processing, is mounted on a lozenge-shaped silicon frame and is pulled by a compressive load on the top face of the frame. Although the applied load increases monotonically in the early stages of deformation, it drops rapidly at a certain displacement. In-situ TEM observation indicates that the rapid decrease of applied load is due to crystallographic slip generation in the nanorod. The critical resolved shear stress on the primary slip system at yielding is evaluated to be 325.8MPa, which is about 600times larger than that of bulk. When the tensile elongation becomes large, the nanorod shows necking and isotropic plastic behavior independent on crystalline structure.

Editorial—advances in nanomanufacturing: process repeatability, scalability and affordability for nanomaterials and manufacturing

Nanomanufacturing comprises the technologies for designing, producing, manipulating, and assembling devices and systems that have features in the nanometer scale. The past few decades have seen substantial progress in the research of nanomaterials and processes development. However, many challenges still remain in the areas of repeatability and scalability of nanomanufacturing processes. Without process repeatability, production scale-up, and a strong market pull, nanomaterials will remain a benchtop exercise without real commercial impact or societal benefits. There is a profound need for innovation-driven and cost-effective translational technologies that will address these challenges. This special issue was an attempt to gather recent developments that address the issues of repeatability and scalability in nanomanufacturing. This special issue contains six papers addressing the areas of process modeling, monitoring, control, and scale-up of nanomanufacturing processes. The first paper, Chen et al., proposes a new method for making backlighting devices from carbon nanotube buckypaper using laser irradiation. The authors apply a fractional factorial experimental design and a response surface model to rapidly search the feasible laser parameter settings for processing buckypaper field emitters and improving field emission properties within few experimental runs. The second paper, Desai et al., proposes a new direct inkjet writing method to deposit enriched single-wall nanotubes for fabricating flexible thin film transistors. The authors show that the direct writing technique has the benefit of accurately controlling the deposition and high reproducibility in printing nanotubes over large areas. In the third paper, Abuhimd et al. investigate a new approach to control the output repeatability of the chemical vapor deposition process when growing single-wall carbon nanotubes. The method relies on applying statistically designed experiments to determine an effective combination of the process variables, such as hydrocarbon gas flow rate, chamber temperature, and chamber pressure, for the precise control of nanotube lengths. In the fourth paper of the special issue, Tolle and Martin study an optimization-based methodology in order to identify network process–structure–property relationships in multiphase polymeric materials. A computationally efficient decomposition approach is developed in order to extract important patterns of the material structure from X-ray and neutron scattering imaging data with minimal a priori information. In the fifth paper, Tseng et al. presents a continuous precipitation method for the fabrication of ceria nanoparticles using a new micromixer process. It is shown that the approach has a higher throughput, which is important for scaling up, and that it is capable of producing more uniform porous film structures than standard batch mixing process. In the sixth and final paper, Qin et al. discuss a large-scale process optimization method to be used for planning a focused ion beam process when performing threedimensional patterning. It is shown, using the proposed process planning method, that significant improvement in computational time and economical cost can be achieved in the beam scanning process. O. A. Vanli (*) Florida State University, Tallahassee, FL, USA e-mail: avanli@fsu.edu

Analysis of optical filtering in waveguides with a high index modulation using the extended coupled mode theory by hybridization of a matrix method

In this paper the authors present an hybrid approach for the analysis of the optical filtering function in corrugated waveguide filters with a high index modulation. This approach is based on the hybridization of the extended couple mode theory (CMT) with the transfer matrix approach. The authors chose to treat the case of high index corrugation because in this case the theory elaborated before is not rigorously applicable. The proposed approach allows the calculation of the reflection coefficient and the full width at half maximum (FWHM) for any index modulation scheme. The hybridization of both methods mentioned above explains the impact and effects of opto-geometric parameters on the reflection coefficient and the bandwidth at mid-height. The theoretical results are verified by experimental measurements realized on Ti:LiNbO3 waveguides with a high index modulation experimentally implemented by engraving using Focused Ion Beam (FIB) process.

Nanorobotic Assembly and Focused Ion Beam Processing of Nanotube-Enhanced AFM Probes

In this paper, a focused ion beam processing technique is presented that facilitates the modification of carbon nanotubes (CNTs) in terms of length, diameter, and orientation. The CNTs are mounted onto an atomic force microscope (AFM) probe by using a nanorobotic microgripper-based pick-and-place handling strategy. Such CNT-enhanced AFM probes are needed for metrology measurements of nanostructures with critical dimensions and high aspect ratios. The complete process of assembly and processing is realized inside a nanorobotic dual beam scanning electron microscope (SEM) and focused ion beam (FIB) machine.