Negative differential resistance at room temperature from resonant tunnelling in GaInAs/InP double-barrier heterostructures

We report the first observation of room-temperature negative differential resistance in the GaInAs/InP materials system. The double-barrier structure examined was grown by organometallic chemical vapour deposition.     

Observations on deformed electrolytically deposited Ni3P

Electrodeposited amorphous Ni₃P was deformed in situ on a brass substrate. The films, when observed in the electron microscope, showed both light and dark bands in bright field images which were not seen in undeformed material. It is proposed that the origin of this contrast is a change of both density and structure of the material within the deformation bands.     

A transformation anomaly in a Cu–Zn–Al alloy

A comparison is described of the structures of an M9R Cu–Zn–Al alloy as quenched directly into the martensitic state, and as stabilized, with the structure of the material after up-quenching into the β₁ state after which treatment the martensitic memory transformation occurs thermoelastically. Preliminary results on the increased tendency for the stabilized alloy to form f.c.c. stacking sequence regions are given and discussed.     

Observations on the ageing of the metallic glass Fe80B20

The commercial binary metallic glass, Fe₈₀B₂₀, was examined using transmission electron microscopy after a variety of ageing treatments. While the material was found to be susceptible to beam-induced oxidation, some tendency to crystallization at temperatures as low as 523 K was observed. Morphologically this was different from the essentially eutectic crystallization behaviour previously observed at 573 K and above.     

The use of moiré techniques to measure rigid body displacements

The relative advantages and disadvantages of a variety of experimental electron microscopical techniques for the measurement of rigid body displacements are considered. The principles of the application of a moiré method of great simplicity and high potential accuracy are then further discussed as are the experimental difficulties associated with the superposition of suitable reference latices on a substrate. The method is then applied to obtain an upper limit for the rigid body displacement at {111} Σ3 twin boundaries in stainless steel.     

Problem oriented transmission electron microscopy

The relative advantages and disadvantages of the variety of transmission electron microscopical techniques which can be applied to materials science problems are argued by the examination of problems from a range of different fields. The further developments which will be needed before the full potential of some of the more modern approaches can be achieved are also discussed, as are the increasing uses of ‘edge-on’ specimen preparation methods.     

Novel instabilities in the oxidation of a Nimonic alloy when YBaCuO is deposited upon it

When an YBaCuO film is deposited onto a Nimonic 80A alloy substrate using a plasma technique there is extensive inter-reaction. The microstructural and compositional relationships between the layered products in this interfacial scaling process are described using data obtained by conventional edge-on TEM techniques. Our results demonstrate the way in which the segregation of chromium to the YBaCuO overlayer dominates the scaling behaviour that is seen, despite the formation of intermediate layers which would normally have been expected to act as diffusion barriers, and highlight the potential difficulties in making well behaved electrical contacts for this superconductor.     

The analysis of a defect in ordered Ag3Mg

The high resolution image of an apparently displacive defect in the long period ordered structure of Ag₃Mg is analysed in terms of a simplified substitutional model. It is demonstrated by image simulation that the characteristics of the image could be described equally well on the basis of progressive relative substitution of Ag for Mg on two of the four sublattices in the structure.     

The stabilization of martensite in Cu-Zn-AI shape memory alloys

The martensitic transformation temperature in shape memory alloys can be affected differently by aging above and below the transformation temperature. Under such circumstances the normally reversible transformation can be prevented and the martensite structure “stabilized”. This effect has been studied using electron microscopy, differential scanning calorimetry, and mechanical testing. Evidence is given of an apparently martensitic high temperature transformation, and a careful comparison is made of the stabilized and unstabilized states of the alloy. Three possible models for stabilization are considered in the light of the results obtained, and it is concluded that no single mechanism can be responsible for all the phenomena observed. Formerly with the Department of Metallurgy and Materials Science, University of Cambridge, England     

The high resolution electron microscopy of stacking defects in Cu–Zn–Al shape memory alloy

The characteristic defects in the martensitic phase of the memory alloy Cu–Zn–Al have been investigated using the Cambridge University 600 kV High Resolution Electron Microscope. Conditions are found under which the images can be quantitatively simulated when this involves the transfer of structural information at resolutions beyond the first zero of the contrast transfer function. Defects of sequence-type were positively identified by the comparison of high-resolution micrographs with full dynamical image simulations.