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Scanning transmission electron microscopy-energy dispersive X-ray analysis line scans and mapping have been used to examine the large-angle grain-boundary chemistry of nickel-rich Ni3Al both with and without boron. The results suggest that the aluminium content is reduced while the nickel content is unchanged at the grain boundaries in all these alloys, with the percentage of reduction in aluminium at the grain boundaries decreasing as the boron concentration increases. There is a strong likelihood that radiation damage is influencing or controlling the measured profiles.

Transmission electron microscopy and localized electron energy loss (EEL) spectroscopy in the band gap energy regime were conducted in the GaN/3C–SiC system. Though grown on a cubic substrate, the GaN film exhibits hexagonal phases of two different orientation relationships with the substrate. One of these has transformed in parts into a cubic phase via sequential faulting. The band gap was determined in local regions of good crystallinity, in the proximity of stacking faults, dislocations, grain boundaries, and heterointerfaces. Extrapolation of the low EEL spectra gives a band gap value of 3.4 eV for the unfaulted hexagonal-close-packed (hcp) phase, which ties in with the predicted value. The band gap itself in the EEL spectra is heavily masked by near band edge states around 3.2 and 3.3 eV in particular in the faulted grains. Local variations in the midgap and near band edge density of states in the EEL spectra were found to relate to different amounts and kinds of microstructural defects in the GaN fi...

The structure and chemistry of planar defects in Nb2 O5- and Bi2O3-doped BaTiO3 ceramics that exhibit “core-shell” microstructures have been examined using a combination of conventional transmission (CTEM) and high-resolution (HREM) and scanning transmission (STEM) electron microscopy and microanalysis. In addition to ferroelectric domain boundaries within the core, twins and “stacking faults” were observed, both with interface planes lying along 1 1 1. Unlike the twins, stacking faults were observed only within the paraelectric shell region of the BaTiO3 grain; these planar defects are enriched in Nb and Bi relative to the surrounding matrix. The combined CTEM contrast analysis and HREM observations suggest a fault displacement vector normal to the fault plane of magnitude 1/2〈 1 1 1〉+x〈1 1 1〉(=0.1); a proposed fault structure is based on a double BiO33- layer with bismuth cations occupying barium sites and charge compensation by Nb5+ substitution in adjacent octahedral sites. In addition, the incorporation mechanism of Nb2O5 and Bi2O3 into BaTiO3is discussed with respect to microanalysis results.

Phase transformations in a continuously cooled Fe-9.14 mass%Ni alloy have been studied. Samples furnace cooled at 0.13 K.s -1 gave a thermal arrest of 555±5°C, while dilatometry indicated that this corresponded to 25±5% with initial transformation occurring at 575±5°C. Optical examination revealed a typical massive ferrite microstructure, while examination of pre-polished specimens showed this to consist of grain boundary ferrite and Widmanstatten ferrite within the grains. Transmission electron microscopy confirmed the presence of both approximately equi-axed grains and Widmanstatten ferrite within the prior austenite grains. Some areas of martensite/austenite (MA) constituent were observed indicating that partition of carbon had occurred during transformation. Quantitative analysis of the dilatation curve showed it to consist of two portions. One between 575±5°C and 558±3°C corresponding to the formation of grain boundary ferrite while the portion between 558 to 500°C was thought to correspond to Widmanstatten ferrite formation. In the latter temperature interval - In (1 - y) varied linearly with temperature, where y=fraction transformed. Microanalysis using a FEG-STEM system with a windowless LINK X-ray detector was carried out. This showed that the Ni content across a ferrite grain was constant at 8.8±0.2 mass%Ni with statistically significant values at grain boundaries e.g. 11.05±0.18 mass%Ni and 12.98±0.43 mass%Ni. The results are discussed in terms of paraequilibrium. A short description of microstuctures and transformation temperatures obtained on water quenching & oil quenching (bainitic ferrite) and ice brine quenching, (lath/massive martensite) is also given in the paper.

The possibilities of obtaining information about interband scattering processes in the bandgap regime of GaN from electron energy-loss spectra, taken in a dedicated scanning transmission electron microscope (STEM), are investigated. With the help of precise simulations of the zero-loss peak it is feasable to process, extract and analyse data in the extreme low-loss regime of a few electronvolts. The accuracy of the results is restricted predominantly by instrumental broadening functions. By modelling these accurately, it is possible to eliminate the effects of the tail of the zero-loss peak and to extract the low-loss spectrum together with the correct value for the bandgap of GaN. Furthermore, differences in the shapes of the low-loss spectra can be revealed, depending on the microstructural features, probed at different beam locations.

The possibilities of obtaining information about interband scattering processes from electron energy-loss spectra, taken in a VG601UX scanning transmission microscope, are investigated. With the help of precise simulations of the zero-loss peak it is feasible to process, extract and analyse data in the electron volt regime. The accuracy of the results is restricted predominantly by instrumental limitations. It is possible to extract band gaps of > 2 eV (e.g. for GaN) correctly. In the case of band gaps between 1 and 2eV (i.e. in GaAs), the uncertainty is larger, since the tail of the zero-loss peak interferes with the interband losses, and further refinements in the data analysis as well as the measurement techniques are discussed. ‘Band-gap mapping’ in the VG601UX can be carried out with a spatial resolution of a few nanometres.

X-ray analysis in a high-resolution scanning transmission electron microscope is carried out on III-V compound and SixGe1-x, quantum wells and quantum wires. Simulated X-ray profiles were obtained by convolving the electron beam profile with a composition function. From best fits with experimental data, quantitated composition profiles can be obtained with nanometre resolution. Compositions in wells and wires are inhomogeneous. Alloy clusters tend to form in III-V compound quaternary quantum well stacks. SixGe1-x quantum wells on patterned substrates show strong compositional asymmetries along the growth direction and so do quantum wires in both materials systems. In the case of the SixGe1-x, system, aspects of the growth dynamics which lead to the observed compositional behaviour are deduced.

In this study we have used high resolution parallel electron energy loss spectroscopy (PEELS) and X-ray excited optical luminescence (XEOL) to investigate the chemical nature of the luminescence centre in fresh and aged porous silicon. We find that regardless of the non-stoichiometric oxides which were observed by PEELS in our fresh porous silicon layers, SiSi bonded material is involved in the luminescence process. However, in the case of aged porous silicon both SiSi and SiO bonded material are involved.

This chapter discusses various principles used by aberration-corrected instruments and the performance they should be able to attain. This chapter also provides various application examples from areas chapter consider especially promising, and discuss what may be next for aberration-corrected scanning transmission electron microscopy (STEM). Aberration correction has greatly improved the performance and the range of useful applications of STEMs. It is now possible to form atomic resolution images and spectra at primary energies as low as 60 keV. Electron probes can be produced that are smaller than the typical atom and yet contain enough current for rapid EELS analysis with sensitivity down to the single atom level. This is leading to a new range of applications for the STEM- electron energy-loss spectroscopy (EELS) technique, which may well begin to rival the sensitivity of the atom probe.

Atomic-resolution conventional electron microscopy has become routinely possible at elevated voltages (200–400 keV). However, many specimens are sensitive to damage at these voltages (the silicon knock-on threshold energy is 120–190 keV), hence there is incentive to go to lower voltage. Silicon (111) lattice imaging at 1.92 A resolution with a 100 keV STEM in both axial bright-field (BF) and annular dark-field (ADF) mode using an ultra-high-resolution objective lens pole piece ( C s = 0.7 mm ) has been achieved, and the results are presented here. Although the dark-field resolution had been anticipated, the bright-field resolution was unexpected and is interpreted as arising from the third transfer band of the bright-field contrast transfer function.

Improved resolution made possible by aberration correction has greatly increased the demands on the performance of all parts of high-end electron microscopes. In order to meet these demands, we have designed and built an entirely new scanning transmission electron microscope (STEM). The microscope includes a flexible illumination system that allows the properties of its probe to be changed on-the-fly, a third-generation aberration corrector which corrects all geometric aberrations up to fifth order, an ultra-responsive yet stable five-axis sample stage, and a flexible configuration of optimized detectors. The microscope features many innovations, such as a modular column assembled from building blocks that can be stacked in almost any order, in situ storage and cleaning facilities for up to five samples, computer-controlled loading of samples into the column, and self-diagnosing electronics. The microscope construction is described, and examples of its capabilities are shown.

Through the correction of spherical aberration in the scanning transmission electron microscope (STEM), the resolving of a 78 pm atomic column spacing has been demonstrated along with information transfer to 61 pm. The achievement of this resolution required careful control of microscope instabilities, parasitic aberrations and the compensation of uncorrected, higher order aberrations. Many of these issues are improved in a next generation STEM fitted with a new design of aberration corrector, and an initial result demonstrating aberration correction to a convergence semi-angle of 40 mrad is shown. The improved spatial resolution and beam convergence allowed for by such correction has implications for the way in which experiments are performed and how STEM data should be interpreted.

For several decades the mercury cathode ignitron has been the most common switch choice for high voltage very high current applications. Such devices were capable of operation at voltages of typically up to 20kV and currents of 200kA providing they were carefully operated and maintained. However, in recent years the emergence of a number of specific applications with current and voltage requirements in excess of these levels, and increasing opposition to the use of mercury on environmental grounds, have defined a requirement for a switch of enhanced capability which does not use a mercury cathode. This paper outlines a program ofwork which has been undertaken at EEV to develop such a switch for operation at 24kV, 500kA, 130C/shot. The development progressed by the design, construction and testing of devices in a sequential manner, with design changes being made at each stage following post mortem analysis ofthe preceding iteration. This process has resulted in a device which has recently demonstrated operation at 24kV, 54OkA, 170C/shotover a test of several hundred shots duration.

Scanning Transmission Electron Microscope (STEM) Energy Dispersive X-Ray analysis (EDX) linescans and mapping have been used to examine the large angle grain boundary chemistry of Ni-rich Ni3AI both with and without boron. The results show that the Al content is reduced while the Ni content is unchanged at the grain boundaries in all these alloys, with the percentage of reduction of Al at the grain boundaries decreasing as boron concentration increases. This is ascribed to differential surface sputtering of the lighter Al atoms.

Extended abstract of a paper presented at Microscopy and Microanalysis 2006 in Chicago, Illinois, USA, July 30 – August 3, 2005

An ultra-high resolution pole piece with a coefficient of spherical aberration Cs=0.7mm. was previously designed for a Vacuum Generators HB-501A Scanning Transmission Electron Microscope (STEM). This lens was used to produce bright field (BF) and annular dark field (ADF) images of (111) silicon with a lattice spacing of 1.92 Å. In this microscope the specimen must be loaded into the lens through the top bore (or exit bore, electrons traveling from the bottom to the top). Thus the top bore must be rather large to accommodate the specimen holder. Unfortunately, a large bore is not ideal for producing low aberrations. The old lens was thus highly asymmetrical, with an upper bore of 8.0mm. Even with this large upper bore it has not been possible to produce a tilting stage, which hampers high resolution microscopy.

A new generation of UHV field-emission STEMs operating at up to 300 kV has been designed by VG Microscopes. The design philosophy of these instruments has been to improve further the analytical performance achieved by 100 kV cold field-emission STEMs, such as the VG HB501 series.There are three types of instrument with a common basic design:HB603: an analytical STEM with optimised X-ray microanalysis (0.3srad collection angle per detector) and parallel/serial electron energy-loss facilities;HB603U: a high-resolution STEM with optimised high-angle dark-field detection and < 0.13 nm resolution;HB603S: a full UHV STEM with Auger analyser and specimen preparation facilities at 3 × 10-10 mbar pressure throughout the instrument.

The 'crystal structure problem' in the heavier rare-gas solids is briefly reviewed. New calculations are presented which indicate that the relative free-energy difference between the FCC and HCP phases, Delta , is approximately=(2-5)*10-3 for Xe at low temperatures, falling with increasing temperature. New experimental measurements by transmission electron microscopy of the stacking fault energy gamma are reported. The parameters gamma and Delta are related by a simple model, and Delta is thereby found to be approximately=(6+or-2)*10-3 for Xe at T=25K, falling to (4+or-2)*10-3 at 55K. A measurement for Kr is reported as Delta =(4.6+or-1.2)*10-3 at 40K. The measurements for Xe constitute the first tentative evidence that gamma and Delta decrease with increasing T in the sense indicated by calculation.

The high-voltage electron microscope has been used to study the structure and morphology of electroless Ni–P deposits of varying phosphorus contents. Except for low (

A study is reported of the vapour growth of solid Kr and Xe, and the observation of the resulting crystals by transmission electron microscopy and diffraction. Growth has been conducted at higher temperatures, and pressures up to 100 Torr(1.33×104 Pa), in an effort to produce more perfect crystals than previous work. Large single crystals ( ≳100 μm grain size) which are suitably thin (

A liquid-helium stage with a window-type environmental stage has been developed for use in a 200 kV transmission electron microscope (JEOL 200A). The gas cell is a single tilt device which operates at relatively high pressure (