The mobility of W atoms of the (320) and (221) regions of the W microcrystal surface with the tip curvature radius of about 300nm and the surface diffusion of Dy at an average coverage of about 0.1ML on these regions were investigated by spectral analysis of field emission current fluctuations at 500 to 800K. The diffusion appeared to be one-dimensional for the W(320) regions and two-dimensional for the W(221). The surface-diffusion coefficients were determined by comparison of the experimental results with the theoretical spectral density functions derived by Gesley and Swanson. The surface-diffusion parameters were calculated, and the results (figures 1 to 4) could be described by:

Dy on (320)W:     D (cm2/s) = 4.0 x 10-9 exp[-0.31(eV)/kT]

Dy on (221)W:     D (cm2/s) = 2.7 x 10-6 exp[-0.49(eV)/kT]

W on (320)W:     D (cm2/s) = 4.4 x 10-7 exp[-0.48(eV)/kT]

W on (221)W:     D (cm2/s) = 3.7 x 10-2 exp[-1.07(eV)/kT]

Surface Diffusion of Dysprosium on Stepped Surfaces of Tungsten Microcrystal. T.Biernat, R.Błaszczyszyn: Applied Surface Science, 2009, 255[13-14], 6593-7

Figure 2

Diffusivity of Dy on the (221) Surface of W