Preparation of site-specific cross-sections of heterogeneous catalysts prepared by focused ion beam milling

Focused ion beam (FIB) milling offers a novel approach to preparation of site‐specific cross‐sections of heterogeneous catalysts for examination in the transmission electron microscope (TEM). Electron‐transparent sections can be obtained without the need to embed or grind the original sample. Because the specimen can be imaged in the FIB with submicrometre resolution before, during and after milling it is possible to select precisely the region from which the section is removed and to control the thickness of the section to within tens of nanometres. The ability to produce sections in this way opens the possibility of studying a range of catalyst systems that have previously been impossible to examine with the TEM.     

Transmission electron microscopy of fluorapatite–gelatine composite particles prepared using focused ion beam milling

In this paper, synthetic fluorapatite–gelatine composite particles are prepared for transmission electron microscopy (TEM) studies using two methods based on focused ion beam (FIB) milling. TEM studies on the FIB‐prepared specimens are compared with TEM observations on samples prepared using an ultramicrotome. The results show that ultramicrotome slicing causes significant cracking of the apatite, whereas the ion beam can be used to make high‐quality, crack‐free specimens with no apparent ion beam‐induced damage. The TEM observations on the FIB‐prepared samples confirm that the fluorapatite composite particles are composed of elongated, preferentially orientated grains and reveal that the grain boundaries contain many small interstices filled with an amorphous phase.     

Dopant profiling of focused ion beam milled semiconductors using off-axis electron holography; reducing artifacts,extending detection limits and reducing the effects of gallium implantation

Focused ion beam (FIB) milling is one of the few specimen preparation techniques that can be used to prepare parallel-sided specimens with nm-scale site specificity for examination using off-axis electron holography in the transmission electron microscope (TEM). However, FIB milling results in the implantation of Ga, the formation of amorphous surface layers and the introduction of defects deep into the specimens. Here we show that these effects can be reduced by lowering the operating voltage of the FIB and by annealing the specimens at low temperature. We also show that the electrically inactive thickness is dependent on both the operating voltage and type of ion used during FIB milling.     

Post‐thinning using Ar ion‐milling system for transmission electron microscopy specimens prepared by focused ion beam system

We investigate Ar ion‐milling rates and Ga‐ion induced damage on sample surfaces of Si and GaAs single crystals prepared by focused ion beam (FIB) method for transmission electron microscopy observation. The convergent beam electron diffraction technique with Bloch simulation is used to measure the thickness of the Ar‐ion milled samples to calculate the milling rates of Si and GaAs single crystals. The measurement shows that an amorphous layer is formed on the sample surface and can be removed by further Ar‐ion milling. In addition, the local symmetry breaking induced by FIB is investigated using quantitative symmetry measurement. The FIBed‐GaAs sample shows local symmetry breaking after FIB milling, although the FIBed‐Si sample has no considerable symmetry breaking.     

Focused ion beam milling of vitreous water: prospects for an alternative to cryo-ultramicrotomy of frozen-hydrated biological samples

The feasibility of using a focused ion beam (FIB) for the purpose of thinning vitreously frozen biological specimens for transmission electron microscopy (TEM) was explored. A concern was whether heat transfer beyond the direct ion interaction layer might devitrify the ice. To test this possibility, we milled vitreously frozen water on a standard TEM grid with a 30‐keV Ga⁺ beam, and cryo‐transferred the grid to a TEM for examination. Following FIB milling of the vitreous ice from a thickness of approximately 1200 nm to 200–150 nm, changes characteristic of heat‐induced devitrification were not observed by TEM, in either images or diffraction patterns. Although numerous technical challenges remain, it is anticipated that ‘cryo‐FIB thinning’ of bulk frozen‐hydratred material will be capable of producing specimens for TEM cryo‐tomography with much greater efficiency than cryo‐ultramicrotomy, and without the specimen distortions and handling difficulties of the latter.     

Off-axis electron holography of electrostatic potentials in unbiased and reverse biased focused ion beam milled semiconductor devices

Off‐axis electron holography in the transmission electron microscope (TEM) is used to measure two‐dimensional electrostatic potentials in both unbiased and reverse biased silicon specimens that each contain a single p–n junction. All the specimens are prepared for examination in the TEM using focused ion beam (FIB) milling. The in situ electrical biasing experiments make use of a novel specimen geometry, which is based on a combination of cleaving and FIB milling. The design and construction of an electrical biasing holder are described, and the effects of TEM specimen preparation on the electrostatic potential in the specimen, as well as on fringing fields beyond the specimen surface, are assessed.     

TEM sample preparation by FIB for carbon nanotube interconnects

A powerful method to study carbon nanotubes (CNTs) grown in patterned substrates for potential interconnects applications is transmission electron microscopy (TEM). However, high-quality TEM samples are necessary for such a study. Here, TEM specimen preparation by focused ion beam (FIB) has been used to obtain lamellae of patterned samples containing CNTs grown inside contact holes. A dual-cap Pt protection layer and an extensive 5 kV cleaning procedure are applied in order to preserve the CNTs and avoid deterioration during milling. TEM results show that the inner shell structure of the carbon nanotubes has been preserved, which proves that focused ion beam is a useful technique to prepare TEM samples of CNT interconnects.     

Embossed‐carving processing of cytoskeletons of cultured cells by using focused ion beam technology

The focused ion beam (FIB) technology has drawn considerable attention in diverse research fields. FIB can be used to mill samples at the nanometer scale by using an ion beam derived from electrically charged liquid gallium (Ga). This powerful technology with accuracy at the nanometer scale is now being applied to life science research. In this study, we show the potential of FIB as a new tool to investigate the internal structures of cells. We sputtered Ga⁺ onto the surface or the cross section of animal cells to emboss the internal structures of the cell. Ga⁺ sputtering can erode the cell surface or the cross section and thus emboss the cytoskeletons quasi‐3 dimensionally. We also identified the embossed structures by comparing them with fluorescent images obtained via confocal laser microscopy because the secondary ion micrographs did not directly provide qualitative information directly. Furthermore, we considered artifacts during the FIB cross sectioning of cells and propose a way to prevent undesirable artifacts. We demonstrate the usefulness of FIB to observe the internal structures of cells. Microsc. Res. Tech. 76:290–295, 2013. © 2013 Wiley Periodicals, Inc.     

Combining FIB milling and conventional Argon ion milling techniques to prepare high‐quality site‐specific TEM samples for quantitative EELS analysis of oxygen in molten iron

This paper reports a procedure to combine the focused ion beam micro‐sampling method with conventional Ar‐milling to prepare high‐quality site‐specific transmission electron microscopy cross‐section samples. The advantage is to enable chemical and structural evaluations of oxygen dissolved in a molten iron sample to be made after quenching and recovery from high‐pressure experiments in a laser‐heated diamond anvil cell. The evaluations were performed by using electron energy‐loss spectroscopy and high‐resolution transmission electron microscopy. The high signal to noise ratios of electron energy‐loss spectroscopy core‐loss spectra from the transmission electron microscopy thin foil, re‐thinned down to 40 nm in thickness by conventional Argon ion milling, provided us with oxygen quantitative analyses of the quenched molten iron phase. In addition, we could obtain lattice‐fringe images using high‐resolution transmission electron microscopy. The electron energy‐loss spectroscopy analysis of oxygen in Fe_0.94O has been carried out with a relative accuracy of 2%, using an analytical procedure proposed for foils thinner than 80 nm. Oxygen K‐edge energy‐loss near‐edge structure also allows us to identify the specific phase that results from quenching and its electronic structure by the technique of fingerprinting of the spectrum with reference spectra in the Fe‐O system.     

Analysis of FIB‐induced damage by electron channelling contrast imaging in the SEM

We have investigated the Ga⁺ ion‐damage effect induced by focused ion beam (FIB) milling in a [001] single crystal of a 316 L stainless steel by the electron channelling contrast imaging (ECCI) technique. The influence of FIB milling on the characteristic electron channelling contrast of surface dislocations was analysed. The ECCI approach provides sound estimation of the damage depth produced by FIB milling. For comparison purposes, we have also studied the same milled surface by a conventional electron backscatter diffraction (EBSD) approach. We observe that the ECCI approach provides further insight into the Ga⁺ ion‐damage phenomenon than the EBSD technique by direct imaging of FIB artefacts in the scanning electron microscope. We envisage that the ECCI technique may be a convenient tool to optimize the FIB milling settings in applications where the surface crystal defect content is relevant.     

A technique for the preparation of cross-sectional TEM samples of ZnSe/GaAs heterostructures which eliminates process-induced defects

Cross-sectional transmission electron microscopy (TEM) sample preparation of ZnSe/GaAs epitaxial films is investigated. Conventional argon ion milling is shown to produce a high density (～ 5–8 × 10¹¹/cm²) of small (diameter ～ 60–80 Å) extended defects (stacking faults, microtwins, double positioning twins, etc.). In addition, transmission electron diffraction results indicate a thin ZnO layer can also occasionally form upon ion milling or electron-beam irradiation although the exact conditions for ZnO formation are not well understood. Conventional TEM (amplitude contrast) and high-resolution TEM (phase contrast) imaging in combination with transmission electron diffraction studies were performed to determine the optimum method of removing the ion milling related damage and ZnO layers during sample preparation. HF/HCl, NaOH/H₂O, H₂SO₄/H₂O₂/H₂O and Br₂/CH₃OH etching mixtures as well as low voltage argon or iodine ion milling were studied. A low energy (2 ke V) iodine or argon ion milling step was shown to remove the ZnO layer and reduced the density of the extended defects associated with Ar⁺ ion milling, but was unsuccessful in removing all of the defects. Auger electron spectroscopy results indicate residual iodine was either left on the surface or implanted beneath the surface during iodine ion milling. Etching the XTEM samples in HF/HCl was shown to be effective in removing the ZnO layer but had little or no effect on the ion milling induced defects. Etching the samples in a 0.5% Br₂/CH₃OH solution resulted in complete elimination of the ion milling induced extended defects including the residual defects associated with iodine ion milling. In addition the Br₂/CH₃OH etch produced the best surface morphology. Thus a brief (1–2 seconds) Br₂/CH₃OH etch after conventional preparation (argon ion milling) of cross-sectional ZnSe/GaAs TEM samples appears to be an inexpensive and superior alternative to iodine ion milling.     

Simple method for the preparation of inp based samples for TEM investigation

A novel, rapid, and simple method is described for the preparation of InP based samples for investigation by transmission electron microscopy (TEM). The key feature of the technique is Ar⁺ ion bombardment in an iodine ambient. Cross sectional micrographs of Au/InP samples are shown as an example. The technique developed produces a large area of transparent region.     

Argon broad ion beam tomography in a cryogenic scanning electron microscope: a novel tool for the investigation of representative microstructures in sedimentary rocks containing pore fluid

The contribution describes the implementation of a broad ion beam (BIB) polisher into a scanning electron microscope (SEM) functioning at cryogenic temperature (cryo). The whole system (BIB‐cryo‐SEM) provides a first generation of a novel multibeam electron microscope that combines broad ion beam with cryogenic facilities in a conventional SEM to produce large, high‐quality cross‐sections (up to 2 mm²) at cryogenic temperature to be imaged at the state‐of‐the‐art SEM resolution. Cryogenic method allows detecting fluids in their natural environment and preserves samples against desiccation and dehydration, which may damage natural microstructures. The investigation of microstructures in the third dimension is enabled by serial cross‐sectioning, providing broad ion beam tomography with slices down to 350 nm thick. The functionalities of the BIB‐cryo‐SEM are demonstrated by the investigation of rock salts (synthetic coarse‐grained sodium chloride synthesized from halite‐brine mush cold pressed at 150 MPa and 4.5 GPa, and natural rock salt mylonite from a salt glacier at Qom Kuh, central Iran). In addition, results from BIB‐cryo‐SEM on a gas shale and Boom Clay are also presented to show that the instrument is suitable for a large range of sedimentary rocks. For the first time, pore and grain fabrics of preserved host and reservoir rocks can be investigated at nm‐scale range over a representative elementary area. In comparison with the complementary and overlapping performances of the BIB‐SEM method with focused ion beam‐SEM and X‐ray tomography methods, the BIB cross‐sectioning enables detailed insights about morphologies of pores at greater resolution than X‐ray tomography and allows the production of large representative surfaces suitable for FIB‐SEM investigations of a specific representative site within the BIB cross‐section.     

Novel techniques of preparing TEM samples for characterization of irradiation damage

Focus ion beam preparation of transmission electron microscopy (TEM) samples has become increasingly popular due to the relative ease of extraction of TEM foils from specific locations within a larger sample. However the sputtering damage induced by Ga ion bombardment in focus ion beam means that traditional electropolishing may be a preferable method. First, we describe a special electropolishing method for the preparation of irregular TEM samples from ex‐service nuclear reactor components, spring‐shaped spacers. This method has also been used to prepare samples from a nonirradiated component for a TEM in situ heavy ion irradiation study. Because the specimen size is small (0.7 × 0.7 × 3 mm), a sandwich installation is adopted to obtain high quality polishing. Second, we describe some modifications to a conventional TEM cross‐section sample preparation method that employs Ni electroplating. There are limitations to this method when preparing cross‐section samples from either (1) metals which are difficult to activate for electroplating, or (2) a heavy ion irradiated foil with a very shallow damage layer close to the surface, which may be affected by the electroplating process. As a consequence, a novel technique for preparing cross‐section samples was developed and is described.     

Minimization of amorphous layer in Ar+ ion milling for UHR-EM

We present a comprehensive study on the influence of Ar⁺ ion milling parameters in the range of low acceleration voltages (0.5-6 kV) and etching angles (3-10^°) on the quality of standard high resolution Si TEM samples. The quality was assessed by the evaluation of HR-TEM images acquired from real TEM samples considering the thickness of the amorphous layer and the interlocking between crystalline and amorphous parts of the sample created by ion-beam induced amorphization, as well as topographical BSE-SEM investigation of the surface of those TEM samples. Increasing voltage clearly results in increased amorphous layer thickness as well as interlocking. The impact of the etching angle is less significant but still influences the amorphous layer thickness. It has, however, a strong effect on the preparation time, which is inversely correlated to the etching angle. Finally the experimental data were compared to model estimations by TRIM and the Schuhrke-Winterbon approximation, which fitted well to the experimental data for low voltage and angle, but were less accurate for higher voltage and angle. Despite their limitations, the models could reproduce trend and order of magnitude of the data, thus making them a useful tool for estimating the amorphous layer thickness after TEM sample preparation.     

Tribological properties of nickel-base nanocrystalline coatings sputter-deposited on austenitic stainless steel

500 nm-thick films are deposited on austenitic stainless steel by neutral (Ar⁺) or reactive (N⁺) ion beam sputtering of Ni or NiTi targets, with (or without) high energy 160 keV-Ar⁺ ion beam assistance. Most of the time the coatings are nanocrystalline and induce a large (excellent in some conditions) increase of the wear resistance. Only Ar⁺ ion beam sputtering of a NiTi target gives an amorphous deposit which does not improve the substrate tribological properties. The hardness and wear resistance of ion beam assisted films are larger than those obtained with non-ion beam assisted coatings. The presence of a hard TiN phase inside a ductile Ni phase, of grains with preferential orientation beneficial to slip, as well as film densification are the main factors which increase the wear resistance. The best results are obtained when the structure is composed of two phases, Ni and TiN. The TiN phase strengthens the already good tribological Ni properties and the Ni ductility induces mechanical accommodation during the friction process.     

Localized grounding, excavation, and dissection using in-situ probe techniques for focused ion beam and scanning electron microscopy: experiments with rock varnish

While investigating rock varnish, we explored novel uses for an in‐situ micromanipulator, including charge collection, sample manipulation, as well as digging and dissection at the micron level. Dual‐beam focused ion beam microscopes (DB‐FIB or FIBSEM) equipped with micromanipulators have proven to be valuable tools for material science, semiconductor research, and product failure analysis. Researchers in many other disciplines utilize the DB‐FIB and micromanipulator for site‐specific transmission electron microscope (TEM) foil preparation. We have demonstrated additional applications for in‐situ micromanipulators. SCANNING 34: 279–283, 2012. © 2012 Wiley Periodicals, Inc.     

A convenient method for electron tomography sample preparation using a focused ion beam

Here we report a new sample preparation method for three‐dimensional electron tomography. The method uses the standard film deposition and focused ion beam (FIB) methods to significantly reduce the problems arising from the projected sample thickness at high tilt angles. The method can be used to prepare tomography samples that can be imaged up to a ±75° tilt range which is sufficient for many practical applications. The method can minimize the problem of Ga⁺ contamination, as compared to the case of FIB preparation of rod‐shaped samples, and provides extended thin regions for standard 2D projection analyses. Microsc. Res. Tech. 75:1165–1169, 2012. © 2012 Wiley Periodicals, Inc.     

Behaviour of TEM metal grids during in-situ heating experiments

The stability of Ni, Cu, Mo and Au transmission electron microscope (TEM) grids coated with ultra-thin amorphous carbon (α-C) or silicon monoxide film is examined by in-situ heating up to a temperature in the range 500–850 °C in a transmission electron microscope. It is demonstrated that some grids can generate nano-particles either due to the surface diffusion of metal atoms on amorphous film or due to the metal evaporation/redeposition. The emergence of nano-particles can complicate experimental observations, particularly in in-situ heating studies of dynamic behaviours of nano-materials in TEM. The most widely used Cu grid covered with amorphous carbon is unstable, and numerous Cu nano-particles start to form once the heating temperature reaches 600 °C. In the case of Ni grid covered with α-C film, a large number of Ni nano-crystals occur immediately when the temperature approaches 600 °C, accompanied by the graphitization of amorphous carbon. In contrast, both Mo and Au grids covered with α-C film exhibit good stability at elevated temperature, for instance, up to 680 and 850 °C for Mo and Au, respectively, and any other metal nano-particles are detected. Cu grid covered Si monoxide thin film is stable up to 550 °C, but Si nano-crystals appear under intensive electron beam. The generated nano-particles are well characterized by spectroscopic techniques (EDXS/EELS) and high-resolution TEM. The mechanism of nano-particle formation is addressed based on the interactions between the metal grid and the amorphous carbon film and on the sublimation of metal.