S. B. Newcomb

Specimen preparation methods for the examination of surfaces and interfaces in the transmission electron microscope

Various techniques for the preparation of cross‐sectional and plan view TEM specimens of surfaces and interfaces are described. Particular emphasis is given to preparative methods which are both generally applicable and which minimize differential thinning of the materials present on either side of the interface of interest, thereby improving the reliability of the approach.

Off-axis electron holography of pseudo-spin-valve thin-film magnetic elements

Magnetic remanent states in a rectangular array of 75×280-nm2NiFe∕Cu∕Co thin-film pseudo-spin-valve elements are studied using off-axis electron holography in the transmission electron microscope (TEM). An approach based on focused ion-beam milling is used to minimize damage to the magnetic properties of the elements during preparation for TEM examination in plan-view geometry. Experimental electron holographic phase images are used to measure the switching fields of the Co and NiFe layers in each of three adjacent elements separately, and comparisons with micromagnetic simulations are used to infer the true magnetic thicknesses and widths of the layers. Demagnetizing fields are included in the discussion of the results, and the possibility that the conclusions may be affected by the procedure used to analyze the holograms is discussed.

Remanent magnetization states and interactions in square arrays of 100-nm cobalt dots measured using transmission electron microscopy

Large area square arrays of circular cobalt dots, nominally 100nm in diameter and 20nm in thickness, were patterned using interference lithography. Magnetic remanent states were measured using off-axis electron holography in the transmission electron microscope (TEM). The results show that the dots are mostly single domain, although vortex states and multidomain configurations are occasionally observed. Significant magnetic interactions between adjacent dots result in variations in their magnetization direction away from the direction of the applied field. The suitability of such dots for data storage applications is discussed. Quantitative magnetic phase measurements were also obtained by applying the transport of intensity equation to images acquired using the Fresnel mode of Lorentz microscopy in the TEM. The consistency between the electron holography and transport of intensity equation (TIE) results is assessed.Large area square arrays of circular cobalt dots, nominally 100nm in diameter and 20nm in thickness, were patterned using interference lithography. Magnetic remanent states were measured using off-axis electron holography in the transmission electron microscope (TEM). The results show that the dots are mostly single domain, although vortex states and multidomain configurations are occasionally observed. Significant magnetic interactions between adjacent dots result in variations in their magnetization direction away from the direction of the applied field. The suitability of such dots for data storage applications is discussed. Quantitative magnetic phase measurements were also obtained by applying the transport of intensity equation to images acquired using the Fresnel mode of Lorentz microscopy in the TEM. The consistency between the electron holography and transport of intensity equation (TIE) results is assessed.

The application of high resolution electron microscopy to the study of oxidation

High resolution electron microscopy has been used to examine both the similarities and differences in the growth morphologies of Fe2O3, Cr2O3 as formed on iron alloys, and MgO as formed by burning Mg in moist air. A general discussion is also given of the relative advantages and disadvantages of a variety of TEM techniques as applicable to the study of oxidation phenomena.

The transmission electron microscopy of oxide scale formation on Fe‐Ni‐Cr alloys

The oxidation behaviour of 10Cr and 20Cr iron alloys, with nickel contents from 0 to 34 wt% both in air and in CO/CO2, is summarized with particular emphasis on the form and chemistry of the different scales as they were observed using transmission electron microscopy. The various modes of inward oxidation are for example characterized with ‘internal’ and ‘inner’ oxidation taking place under different circumstances. The role of carbon during oxidation in a CO/CO2 atmosphere is also discussed as is the way in which a given alloy can show either chemical or mechanical passivation failure in different environments.

Interpretation of electron beam induced charging of oxide layers in a transistor studied using electron holography

Off-axis electron holography has been used to characterize a linear array of transistors, which was prepared for examination in cross-sectional geometry in the transmission electron microscope using focused ion beam milling. In reconstructed phase images, regions of silicon oxide that are located between metal contacts show unexpected elliptical phase contours centered several hundreds of nm from the specimen edge. The experimental images are compared with simulations performed using three-dimensional calculations of the electrostatic potential inside and outside the specimen, which take into account the mean inner potential of the specimen and the perturbed vacuum reference wave. The simulations suggest that the oxide layers contain a uniform volume density of positive charge and that the elliptical contours result from the combined effect of the electrostatic potential in the specimen and the external electrostatic fringing field.

The characterization of interfacial structures in the oxidation of Fe and FeNiCr alloys by edge-on transmission electron microscopy

A wide range of scaling processes can occur during the high temperature oxidation of FeCr alloys. Here we discuss the relative merits of using alternative transmission electron microscopical (TEM) techniques, as applied to edge‐on foils, for characterizing some of the different diffusional and microstructurally limited processes which occur, in particular at oxide and metal‐oxide boundaries. We give results for interfaces in wüstite, which is formed very rapidly on pure iron, as well as for the more protective FeCr spinels and sesquioxides, as grown on FeNiCr alloys in both air and 1%C0–C02.

The form of the incommensurate shear distortions in the superconducting PbBiSrCaCuO compounds and their relation to Tc

The authors have examined the structure of the Pb-containing variants both of the Bi2Sr2CaCu2O8+ delta (2212) and of the Bi2Sr2Ca2Cu3O10+ delta (2223) high-Tc oxide superconductors, using TEM, and describe here the way in which there can be differences in the character of the various incommensurate distortions found in these materials. It is further demonstrated that, in at least one compound in this family, the form of the distortion structure can be changed by an anneal from being predominantly of shear wave character to being mainly compositional in nature, and that this is associated with a change in the superconducting characteristics.

Conventional and 360 degree electron tomography of a micro- crystalline silicon solar cell

Bright-field (BF) and annular dark-field (ADF) electron tomography in the transmission electron microscope (TEM) are used to characterize elongated porous regions or cracks (simply referred to as cracks thereafter) in micro-crystalline silicon (μc-Si:H) solar cell. The limitations of inferring the 3D geometry of a crack from a tilt series of images acquired from 100-nm-thick focused ion beam (FTB) milled TEM specimen are discussed. In an attempt to maximize the specimen tilt range and to reduce the effects of diffraction and phase contrast on the reconstruction, both BF and ADF electron tomography are used to acquire 360° tilt series of images from a FIB-prepared needle-shaped μc-Si:H specimen.

Three-dimensional analysis of the dopant potential of a silicon p-n junction by holographic tomography

Off-axis electron holography and tomography have been combined to examine the 3-D electrostatic potential associated with a Si p-n junction. The device was prepared in a novel specimen geometry using focused ion beam milling and a series of holograms was acquired over a tilt range of −70° to +70°. Simultaneous iterative reconstruction was used to reconstruct the 3-D electrostatic potential in the specimen. The experimental results were compared to simulations of the potential variation. Quantitative results from the central, ‘bulk’ semiconducting regions and from the surface layers were extracted from the 3-D reconstruction.