M. Pichaud’s research while affiliated with Aix-Marseille University and other places

A field emission technique is described to measure the influence of a definite adsorption layer on surface self-diffusion. The rate determining activation energy for this diffusion is determined in a field electron microscope by measuring time and temperature of the transformation of a build-up form into an annealed form of an emitter crystal.If a clean tungsten surface is covered with one tenth or less of a monolayer of carbon, the surface self-diffusion remains unchanged. However, coverage of one half to one monolayer of carbon leads to an increase of the surface self-diffusion energy from 3.1 to 8.7 eV. If oxygen is adsorbed on clean tungsten an increase of the surface self-diffusion energy from 3.1 to 4.2 eV is found. These results imply some earlier self-diffusion data on other metals may be influenced by undetected adsorption layers.

To determine the temperature of a heated crystal in a field electron or ion microscope, not only the temperature of the heated loop, but also the temperature gradient along the emitter tip due to heat conduction and radiation must be considered. A method is described to calculate the temperature distribution along the tip. Typical numerical results are given for tips of tungsten and some other metals at temperatures between 1000 and 2900 °K. Considered are conical tips of different length (half cone angle between 0.5° and 6°) and some non-conical tips. The temperature gradient near the apex (which influences the shape change by surface diffusion) has a maximum for a particular angle of the conical tip. Very high gradients occur at tip constrictions.

To determine the temperature of a heated crystal in a field electron or ion microscope, not only the temperature of the heated loop, but also the temperature gradient along the emitter tip due to heat conduction and radiation must be considered. A method is described to calculate the temperature distribution along the tip. Typical numerical results are given for tips of tungsten and some other metals at temperatures between 1000 and 2900 °K. Considered are conical tips of different length (half cone angle between 0.5° and 6°) and some non-conical tips. The temperature gradient near the apex (which influences the shape change by surface diffusion) has a maximum for a particular angle of the conical tip. Very high gradients occur at tip constrictions.