DIFFUSION OF TUNGSTEN ON STEPPED TUNGSTEN SURFACES

被引:19
作者
CHOI, DS
KIM, SK
GOMER, R
机构
[1] UNIV CHICAGO,JAMES FRANCK INST,CHICAGO,IL 60637
[2] UNIV CHICAGO,DEPT CHEM,CHICAGO,IL 60637
基金
美国国家科学基金会;
关键词
D O I
10.1016/0039-6028(90)90559-Q
中图分类号
O64 [物理化学(理论化学)、化学物理学];
学科分类号
070304 ; 081704 ;
摘要
Self-diffusion of thermally generated tungsten atoms near (123) and (257), on the zone (011)-(112) and on (023), on the zone (011)-(001) of a tungsten field emitter has been investigated by the field-emission fluctuation method, using a rectangular probe in order to investigate diffusion anisotropy. In agreement with earlier findings of Gong and Gomer [J. Chem. Phys. 88 (1988) 1359, 1370] diffusion of single W atoms along and across (011) terraces separated by (011) steps, i.e. step edges running along [111] is essentially isotropic with Ed = 16 kcal, D0 ≈ 10-4 cm2 s-1, while atoms can cross (001) oriented steps only with much activation energy: Ed ≈ 35 kcal, D0 = 10-2 cm-2 s-1. Slow diffusion parallel to steps attributed previously by Gong Chem. Phys. 88 (1988) 1359, 1370] to kink motion was also seen along the zone (011)-(112) but seems more complicated than previously assumed, with several regimes, which may correspond to motions of different kink configurations. Distinct dips in the slow regime diffusion coefficients occurred at 910 K, somewhat higher than the previously seen onset of dips, 875 K, and may indicate roughening, as previously hypothesized. Slow diffusion perpendicular to steps was also seen in this zone and is not fully understood. It may arise from some step components always perpendicular to the short slit dimensions, or may correspond to more complicated surface configurations than the step and terrace pattern on an ideal emitter surface. © 1990.
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页码:262 / 272
页数:11
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