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Or less in diameter, and fastened symmetrically on either side of the sample, for determining the temperature. A schematic is given in Fig. 10. The loop is Potential Leads Loop Tip (Sample) Fig. 10 Diagram of crystal support loop for FIM. 007 in tungsten wire, supports and allows heating sample. Probe wires (potential leads) attached to loop measure the temperature in terms of the resistivity. 2 μF 10Ω – + 1K 1N457 + – 1K LED Fig. 11 Electronic circuit for etching FIM crystal [17]. Etching current is interrupted automatically to ensure sharp tips.

In studying single atom diffusion directly by scanning tunneling microscopy, it is necessary to monitor the distance of other atoms to avoid long-range interactions of atoms with each other. For example, Morgenstern and Rieder [50] recently observed a metastable configuration of Cu dimers on the Ag(111) plane caused by the presence of atoms in the vicinity. The relative drift of sample and the tip, which may artificially change diffusion data, must also be carefully followed. The distance from imperfections such as steps or dislocations has to be controlled as well.

To calculate the rate of moving from the top of the barrier, we assume that all atoms in a small length δqc of the coordinate qc at the saddle are in the activated state. 3 Jump rates can be considered as a classical translation. Note, however, that δqc must be large in comparison with the de Broglie wavelength λdeB , where λdeB  1 2 h h2 $ ¼ : 2πmkT mv (1:112) This condition insures classical behavior for this degree of freedom. We now assume that the partition function for the activated state can be given by the product of the classical partition function for translation, ztrans , times a contribution from the remaining degrees of freedom, z# .