Large Foil Research Articles

Reduction of spurious deformation in electron microscope thin foils

A technique is described for obtaining disc shaped specimens from large thin foils for the electron microscope with a minimum of spurious deformation due to foil handling. The technique is shown to be relatively simple and applicable to a variety of metals.

An electrostatic plunger device and the analysis of recoil-distance spectra

In the electrostatic plunger apparatus, a large stopper foil is drawn towards the target electrostatically. The attracting field is controlled in a feedback loop by the capacity, so that the distance is stabilized during the measurement. Formulae for line-shape analysis of γ-ray spectra from recoil-distance lifetime measurements (RDM) are given. A measurement of the lifetime of the 1759 keV level in 26Al is reported yielding (3.4 ± 0.6) ps, in agreement with results from Doppler-shift attenuation, but in disagreement with other RDM results. In addition, accurate stopping-power measurements are reported for 2–9 MeV alpha particles in Al, Ni, Cu, Au, and Mylar.

Jet-Polishing Iridium for TEM

Iridium is an extremely dense and chemically resistant element. These properties make it one of the most difficult metals to examine by TEM. Various electrochemical techniques for preparing Ir TEM samples which use the "window" method have been reported. Iridium has also been thinned by ion milling. However, the "window" method requires relatively large foil samples and the technique is likely to introduce dislocations into the microstructure. We also verified that techniques using KCN resulted in severe grain boundary attack. Ion milling is very slow and creates "black spot" ion damage which can mask small microstructural features such as precipitates or small dislocation loops. A relatively rapid jet-polishing technique which alleviates these problems is described below.

A theoretical model for the energy dependence of electron channelling patterns in scanning electron microscopy

Equations given by Hirsch and Humphreys (1970) and by Spencer et al (1972) for describing the contrast in electron-channelling patterns (ECP) are generalized by taking into account the energy losses which the fast electrons experience in the specimen. In this way a theory is established which considers diffraction, backscattering and energy losses. This theory is used and calculations are made of the dependence of the contrast in ECP on the energy of the backscattered electrons. Unlike earlier theories for ECP the present work gives the correct behaviour of the backscattering coefficient for large foil thicknesses. It is shown that the visibility can be strongly enhanced by using an energy-analysing detector, in agreement with experimental results. The signal-to-noise ratio is evaluated to find the energy window which gives optimum contrast. For Si, Cu and Au these windows are approximately E0 > E > E0 − 700eV, E0 > E > E0 − 250 eV and E0 > E > E0 − 400 eV respectively. Calculations of the mean escape depth as a function of energy show that the electrons are emitted from a thin surface layer for small energy losses. The resolution can therefore be significantly improved in the backscattered mode by using an energy-analysing detector.

In vivo tendon tension and bone strain measurement and correlation

Recent advances in strain gauges and bonding techniques permit the recording of bone strain in the living animal. Such strain is caused by tendon tension and by weight bearing. Both lateral and medial bone strain are recorded from the third metacarpal bone of the walking horse. These strains are typically 430 μ strain and 150 μ strain respectively, peak to peak. The tension in the common extensor tendon, recorded during walking, is found to be up to 170 N on occasions. The two sets of readings are cross-correlated and a theory is presented to account for the major features of the bone strain recordings in terms of tendon action, weight bearing, and locomotion. Comparison of results from large and small foil resistance strain gauges indicates that gauges covering 1 mm 2 of bone surface give valid results.