Sample preparation by focused ion beam micromachining for transmission electron microscopy imaging in front-view

This article deals with the development of an original sample preparation method for transmission electron microscopy (TEM) using focused ion beam (FIB) micromachining. The described method rests on the use of a removable protective shield to prevent the damaging of the sample surface during the FIB lamellae micromachining. It enables the production of thin TEM specimens that are suitable for plan view TEM imaging and analysis of the sample surface, without the deposition of a capping layer. This method is applied to an indented silicon carbide sample for which TEM analyses are presented to illustrate the potentiality of this sample preparation method.     

On the formation of temperature-induced defects at the surface of TEM specimens prepared from TiAl using high-energy Gallium and low-energy Argon ions

ABSTRACT

Specimens for transmission electron microscopic (TEM) investigations were prepared from γ titanium aluminide alloys with Gallium and Argon ions using a focused ion beam (FIB) and a precision ion polishing system (PIPS). Preparation to electron transparency by Gallium ions alone leads to the formation of crystalline platelets of the α titanium phase at the specimen surfaces, revealed through conventional and high resolution (HR) TEM analysis. The platelets are assumed to precipitate from priorly formed amorphous layers. The required crystallisation temperature of about 480°C is generated through the ion bombardment implying that the γ titanium aluminides can be heated substantively during sputtering. The primary reason for this is the restricted transfer of heat away from the beam impact point when the specimen thickness comes close to the beam diameter. The formation of the platelets can be avoided by terminating the Gallium ion treatment prior to that, while providing for a sufficient thermal bonding of the specimen to the grid as well and polishing off the remaining material by Argon ions, which are much less focused and less energetic, so that the local heat peaks are reduced.     

Self-organized amorphous material in silicon (0 0 1) by focused ion beam (FIB) system

A method using a focused ion beam (FIB) to prepare a silicon amorphous material is presented. The method involves the redeposition of sputtered material generated during the interaction of the Ga⁺ ion beam with a silicon substrate material. The shape and dimensions of this amorphous material are self-organized and reproducible. The stability of this amorphous material under electron irradiation was investigated in the transmission electron microscopy (TEM). Electron irradiation can induce recrystallization of the amorphous material, resulting in the lateral and vertical growth, starting at an amorphous-crystalline interface, of polysilicon containing defects.     

单级衍射量子点阵光栅的聚焦离子束直写法制备及光学性能检测

采用聚焦离子束直写技术,成功制作了面积为200μm×200μm,线密度500 mm 1,圆孔直径800 nm,金吸收体厚度为500 nm的单级衍射量子点阵光栅.研究了该光栅在波长442 nm激光下不同传输距离的衍射特性以及相对衍射效率.实验结果表明,量子点阵光栅不存在高级衍射,只保留了±1级和0级衍射,具有良好的单级衍射特性.1级衍射与0级衍射间距随传输距离的增大而增大,实测值与理论计算值相符.     

Large-deformation analysis in microscopic area using micro-moiré methods with a focused ion beam milling grating

In this study, the focused ion beam (FIB) milling method is applied to fabricate sub-micron grating on TiNi shape memory alloy materials. With self-made FIB milling gratings, scanning electron microscope (SEM) micro-moiré and digital moiré methods are successfully used to measure large deformation of porous TiNi shape memory alloys (SMA) in uni-axial compressive tests. The principles of the SEM micro-moiré method and digital moiré method are introduced, and applied to calculate large strain. The full field deformation around shear bands can be measured precisely. During the investigation, the phenomenon of furcated moiré fringes was found, and a corresponding explanation is given in this paper. The furcated fringes are generated in the locations of combined shear bands where sudden changes of strain occur. Successful results also verify that the FIB milling gratings are suitable for micro-moiré measurement and can generate high quality moiré fringes.     

Ultrastructural examination of dentin using focused ion-beam cross-sectioning and transmission electron microscopy

Focused ion-beam (FIB) milling is a commonly used technique for transmission electron microscopy (TEM) sample preparation of inorganic materials. In this study, we seek to evaluate the FIB as a TEM preparation tool for human dentin. Two particular problems involving dentin, a structural analog of bone that makes up the bulk of the human tooth, are examined. Firstly, the process of aging is studied through an investigation of the mineralization in ‘transparent’ dentin, which is formed naturally due to the filling up of dentinal tubules with large mineral crystals. Next, the process of fracture is examined to evaluate incipient events that occur at the collagen fiber level. For both these cases, FIB-milling was able to generate high-quality specimens that could be used for subsequent TEM examination. The changes in the mineralization suggested a simple mechanism of mineral ‘dissolution and reprecipitation’, while examination of the collagen revealed incipient damage in the form of voids within the collagen fibers. These studies help shed light on the process of aging and fracture of mineralized tissues and are useful steps in developing a framework for understanding such processes.     

Occurrence of particle debris field during focused Ga ion beam milling of glassy carbon

To explore the machining characteristics of glassy carbon by focused ion beam (FIB), particles induced by FIB milling on glassy carbon have been studied in the current work. Nano-sized particles in the range of tens of nanometers up to 400 nm can often be found around the area subject to FIB milling. Two ion beam scanning modes - slow single scan and fast repetitive scan - have been tested. Fewer particles are found in single patterns milled in fast repetitive scan mode. For a group of test patterns milled in a sequence, it was found that a greater number of particles were deposited around sites machined early in the sequence. In situ EDX analysis of the particles showed that they were composed of C and Ga. The formation of particles is related to the debris generated at the surrounding areas, the low melting point of gallium used as FIB ion source and the high contact angle of gallium on glassy carbon induces de-wetting of Ga and the subsequent formation of Ga particles. Ultrasonic cleaning can remove over 98% of visible particles. The surface roughness (R_a) of FIB milled areas after cleaning is less than 2 nm.     

Redeposition effects in transmission electron microscope specimens of FeAl-WC composites prepared using a focused ion beam

Artifacts associated with transmission electron microscope (TEM) specimens prepared using a focused ion beam (FIB) are not well understood, especially those in non-semiconductor materials. In this paper the extent and origins of artifacts associated with redeposition of milled material in TEM specimens of a FeAl--WC metal matrix composite prepared by FIB were investigated. Cross-sections were prepared normal to an initial FIB cut that allowed direct observation of any damage layers, which are believed to be associated with both redeposition of sputtered material and amorphisation of the surface of the specimen by the ion beam. Techniques for the minimisation of redeposition using either final cleaning mills at low accelerating voltages or plasma cleaning were also investigated and found to be ineffective in removing or reducing these damaged layers. TEM cross-sections of specimens treated using low energy mills and plasma cleaning, further confirmed that these techniques did little to reduce any redeposited or amorphous material.     

Crystallographically-dependent ripple formation on Sn surface irradiated with focused ion beam

The metallographically polished polycrystalline Sn surface was sputtered by 30 kV focused Ga⁺ ions at room temperature. The experiment was carried out using various FIB incidence angles (0°, 15°, 30°, and 45°) over a wide range of doses (10¹⁶–10¹⁸ ions/cm²). The surface morphology was carefully characterized under the optical microscope, scanning electron microscope (SEM) and atomic force microscope (AFM). Ripples were observed on the irradiated areas even at the normal FIB incidence angle, which is not consistent with the Bradley–Harper (BH) rippling model. The orientation of ripples relies on crystallographic orientation rather than projected ion beam direction as predicted by BH model. The ripple wavelength is independent of ion dose, while ripple amplitude increases with ion dose. It is found that the ripples are formed by self-organization due to anisotropic surface diffusion in the low melting point metal.     

Implementation of focused ion beam (FIB) system in characterization of nuclear fuels and materials

Beginning in 2007, a program was established at the Idaho National Laboratory to update key capabilities enabling microstructural and micro-chemical characterization of highly irradiated and/or radiologically contaminated nuclear fuels and materials at scales that previously had not been achieved for these types of materials. Such materials typically cannot be contact handled and pose unique hazards to instrument operators, facilities, and associated personnel. Over the ensuing years, techniques have been developed and operational experience gained that has enabled significant advancement in the ability to characterize a variety of fuel types including metallic, ceramic, and coated particle fuels, obtaining insights into in-reactor degradation phenomena not achievable by any other means. The following article describes insights gained, challenges encountered, and provides examples of unique results obtained in adapting dual beam FIB technology to nuclear fuels characterization.     

Controlling the nanodot formation on GaAs surface during focused ion beam processing

GaAs processed using gallium-focused ion beams for the fabrication of photonic devices mostly results in gallium nanodots on the surface. These gallium nanodots may produce unwanted effects and deteriorate the optical and electrical properties of the devices. We have investigated the FIB processing of GaAs with and without exposure to an insulator-enhanced etching precursor gas (XeF₂) to explore the use of XeF₂ during GaAs processing. It is reported that without the gas, FIB processing results in nanodots on the surface that vary in size and density depending on processing parameters such as incident energy, beam current, angle and dwell time. Processing with insulator (XeF₂)-enhanced etching gas irrespective of the process parameters eliminates the nanodots and results in a smooth surface, as characterized by scanning electron microscopy and atomic force microscopy. This method will be useful for surfaces which require dry processing without exposure to any wet chemical etching.     

Analysis of polished polycrystalline diamond using dual beam focused ion beam microscopy

This paper presents a study on polycrystalline diamond (PCD) polished by dynamic friction polishing (DFP) with the aid of advanced dual beam FIB (focused ion beam) microscopy. After disclosing a variety of wear tracks by DFP using electron imaging in combination with the ion channelling effect, a dual beam FIB was successfully employed at wear track sites to specifically create both the large cross-sectional specimen for microanalysis and thin foil for nanoanalysis. The study concluded that the polished PCD subsurface was free from microscale cracking. However, the attached debris layer on the top surface contained metal oxides and non-diamond carbon phase with inhomogeneous distributions of C, Fe, Cr, Ni, Si and O across the layer. An attached layer directly above a diamond grain was composed of essentially amorphous carbon, suggesting that a direct phase transformation from diamond crystalline to amorphous occurred during DFP.     

射频聚焦离子源熔石英高确定去除特性研究

在离子束抛光工艺过程中,材料确定性去除特性对预测光学元件的各工位材料去除量和驻留时间具有极其重要的作用。采用射频离子源对熔石英光学元件的离子束刻蚀特性进行了研究,利用ZYGO激光干涉仪获得准确的去除函数,系统分析了气体流量、屏栅电压、离子束入射角和工作距离等因素对熔石英去除函数的影响,并分析了各单一工艺因素微小扰动时,材料峰值去除率、半高宽和体积去除率的相对变化率。实验结果表明,相同工作真空条件下,工作气体质量流量的微小变化对去除函数影响极小,在典型的工艺条件下,屏栅电压在±5 V、离子束入射角±1°、工作距离在±0.5 mm范围内变化时,熔石英峰值去除率、体积去除率和峰值半高宽的相对变化均小于5%,去除函数具有较好的确定性和稳定性。     

Three-dimensional vertical ZnO transistors with suspended top electrodes fabricated by focused ion beam technology

Three-dimensional(3D)vertical architecture transistors represent an important technological pursuit,which have distinct advantages in device integration density,operation speed,and power consumption.However,the fabrication processes of such 3D devices are complex,especially in the interconnection of electrodes.In this paper,we present a novel method which combines suspended electrodes and focused ion beam(FIB)technology to greatly simplify the electrodes interconnection in 3D devices.Based on this method,we fabricate 3D vertical core-double shell structure transistors with ZnO channel and Al₂O₃ gate-oxide both grown by atomic layer deposition.Suspended top electrodes of vertical architecture could be directly connected to planar electrodes by FIB deposited Pt nanowires,which avoid cumbersome steps in the traditional 3D structure fabrication technology.Both single pillar and arrays devices show well behaved transfer characteristics with an Ion/Ioff current ratio greater than 106 and a low threshold voltage around 0 V.The ON-current of the 2×2 pillars vertical channel transistor was 1.2μA at the gate voltage of 3 V and drain voltage of 2 V,which can be also improved by increasing the number of pillars.Our method for fabricating vertical architecture transistors can be promising for device applications with high integration density and low power consumption.     

A knife-edge measurement of the beam profile of STXM 5.3.2.2 using a focussed ion beam milled metallic glass

We present a simple knife-edge measurement of the STXM 5.3.2.2 synchrotron X-ray beam width. The knife edge was constructed by ion beam milling a metallic glass alloy consisting of 60% gold, 20% nickel and 20% hafnium and was determined to be well-defined to within 2 nm by TEM. An asymmetric beam profile of 120 nm FWHM in the vertical direction and 150 nm FWHM in the horizontal direction was determined and was observed to depart from the expected Airy function profile.     

Orientation sensitivity of focused ion beam damage in pure zirconium: direct experimental observations and molecular dynamics simulations

A high-purity predominantly single crystalline zirconium was subjected to controlled focused ion beam (FIB) damage. Damage estimates were obtained from electron backscattered diffraction (EBSD) and nano-indentation measurements on exactly the same area/orientation. The damage kinetics, between different crystallographic orientations, differed by one order of magnitude and a clear hierarchy of orientation sensitive ion damage emerged. Use of a simple geometric approach, linear density of atoms and corresponding scattering cross-sections to impinging gallium ions, could differentiate between extreme damage kinetics; but failed when such differences were relatively minor. Numerically intensive molecular dynamics (MD) simulations, on the other hand, were more effective. However, MD simulations or direct EBSD observations failed to justify anisotropic irradiation hardening (AIH): 3–8 times more hardening for near basal. Though explanation for AIH is indirect, evidence and rationalization for orientation-sensitive radiation damage appears clear and statistically reproducible.     

Study of temperature rise during focused Ga ion beam irradiation using nanothermo-probe

Estimation of temperature rise during focused ion beam irradiation is of immense importance, since it affects various processes related to micro-machining and deposition. When ion beam impinges on a surface, it transfers its kinetic energy by way of electronic excitations and collisions, which eventually gets converted in the form of heat leading to rise in local temperature. This temperature rise affects and governs the properties of the machined region. The temperature rise can be calculated on the basis of energy deposition and heat transfer. However, there are very few reports on the measurement of such local temperature rise which lasts for very short time. We have designed and fabricated nanothermocouples of Pt-W to monitor local temperature rise (i) near a microheater and (ii) in the close proximity of an intense focused ion beam spot on a substrate. The junctions having size of 100 nm × 100 nm have been fabricated using focused ion beam chemical vapor deposition (FIB-CVD). The nanothermocouples have shown a fast response to the changes in temperature. These nanothermocouples can find useful applications in thermal characterization of nanomaterials and for understanding of temperature mediated phenomena in the samples treated under directed energy deposition processes, e.g. ion, laser and electron beam treatment.     

Imaging characterization of carbon nanotube tips modified using a focused ion beam

A carbon nanotube (CNT) tip, which assembled on the sharp end of a Si tip by dielectrophoresis, was structurally modified using focused ion beam (FIB). We described the imaging characterization of the FIB-modified CNT tip in noncontact AFM mode in terms of wear, deep trench accessibility, and imaging resolution. Compared to a conventional Si tip, the FIB-modified CNT tip was superior, especially for prolonged scanning over 10 h. We conclude that modified CNT tips have the potential to obtain high-quality images of nanoscale structures.     

A guide on FIB preparation of samples containing stress corrosion crack tips for TEM and atom-probe analysis

The preparation of samples containing stress corrosion crack tips for 3D atom-probe tomography and transmission electron microscopy is of ultimate importance for understanding the mechanisms controlling crack propagation. In this paper, it will be shown that a focused ion beam machine equipped with an in situ micromanipulator is an ideal tool to systematically prepare such demanding samples. The methodology is described and discussed in detail, and several results are presented to demonstrate the potential of the technique.