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In this paper we report the first observations by cathodoluminescence in TEM of radiative infrared emission from dislocations in silicon. These results were obtained at 23-25K in a Philips EM400 electron microscope. Our results are interpreted in the light of earlier photoluminescence work, and the prospects for obtaining spectra from a small number of well characterized dislocations with high spatial resolution are reviewed. Preliminary results are also reported showing the infrared band-gap emission spectrum of GaInAs at 90K recorded using a small Fourier Transform Spectrometer fitted to the same electron microscope. Finally, we describe timing coincidence experiments from samples in which only those visible CL photons are counted which arrive at the detector at the same time as the corresponding transmitted electron energy loss event. We describe the use of this technique for life-time mapping in semiconductors.
A scanning tunnelling microscope is described which operates inside a transmission electron microscope in the reflection mode. The device is used to study the mechanism of STM contrast in graphite and semiconductors. It allows for the observation of any strain during tunnelling, using the reflection electron diffraction contrast mechanism. The first results of our new transputer-based digital imaging system for STM are reported.
Using first-principles electronic structure calculations in the local density approximation combined with lattice dynamics, we investigate the effect of III/V impurities on the ideal strength of covalent solids (C, Si, and Ge). Our results show that undoped crystalline solids are stronger in tension along  than n-type crystalline solids. P doping has a negligible effect on ideal tensile strength, while n-type doping causes a small reduction in strength of about 6%. The n-type impurity effect is due to the negative (repulsive) contribution from the bottom state of the distorted conduction band to the ideal strength of the solid.
The design of a low voltage point-projection field-emission transmission electron microscope is described and images showing 0.7nm resolution at 100 volts are given. A scheme for low voltage reflection electron holography from bulk samples in UHV is outlined. A new STM is described which allows atomic clusters to be transferred onto the tip, then introduced into a time-of-flight analyser for species identification.
It is not presently possible to resolve the individual atoms in any semiconductor by high resolution electron microscopy (HREM). However symmetry arguments may be used to allow near-atomic resolution lattice images to be interpreted in rare favorable cases. This method is applied to the problem of distinguishing shuffle and glide set partial dislocations in silicon. It is also proposed that two dimensional characteristic loss energy selected diffraction patterns be used to reveal the local symmetry about selected substitutional species implanted in semiconductor lattices.
Measuring Na in silicate glasses can be difficult in transmission electron microscopy due to modifications induced by electron irradiation. The modifications involve not only the loss of Na from the illuminated region, but also the formation of Na and Na2O. This work compares the electron energy loss spectroscopy (EELS) of plasmon and Na L23 edge in Na2O–SiO2 glass with those in Na and Na2O. The interpretations of the fine structures in Na L23 edge were also given with the aid of full multiplescattering calculations. It demonstrates that the formation of metallic Na can be easily identified by its bulk plasmon at about 5.8 eV, and the formation of Na2O can be better seen by Na L23-edge fine structure.
We propose the formation of LEED patterns using a highly convergent
beam forming a probe of nanometer dimensions. A reflection rocking
curve may then be recorded in many diffraction orders simultaneously.
Multiple scattering calculations show that the intensity variations
within these rocking curves is as sensitive to the parameters
describing the surface dipole layer as conventional I/V scans.
However the data may be collected from areas sufficiently small to
avoid defects and surface steps, radiation damage controlled by use of
low voltages, and the information depth selected by choice of the
(constant) voltage. We briefly discuss also the application of this
method to oxides and the formation of atomic-resolution scanning images
in an idealized instrument in which coherent diffracted LEED orders
Alloy design has been a lifelong interest of Gareth Thomas,
and modern design algorithms include atomistic parameters which
are obtainable from new electron microscope techniques such
as ALCHEMI. In this paper, we discuss the relevance of ALCHEMI
site occupancy measurements to intermetallic alloys, and summarize
prior work. The results are found to lie in regions of a
site-occupancy diagram (SOC) relating ordering energies to
occupancy, as predicted by the Bragg–Williams theory of
short-range order. These predictions also explain previous
inconsistencies in the ALCHEMI measurements. A diffraction camera
and X-ray detector system of novel design is proposed for dedicated
ALCHEMI analysis for substitutional and interstitial dopant
site-occupancy measurement, and details of the design given.
Using this novel hardware design, the data-collection times
for two-dimensional ALCHEMI patterns should be reduced by an
order of magnitude or more, and the full data collection process
automated. The resulting occupancy information can provide
essential input parameters for atomistic alloy design algorithms,
and can provide entirely new information on interstitial
occupancies in minerals, ceramics, semiconductors, and alloys.