A FIELD-EMISSION MICROSCOPIC STUDY OF HYDROGEN ADSORPTION ON A STEPPED TUNGSTEN PLANE - W(310)

Using a newly developed Derivative Field Emission Current (DFEC) metho ds, the heat of desorption and the work-function-change of W(310) plan e induced by hydrogen adsorption are measured. The average work functi on of the W(310) plane increases initially as the hydrogen dose increa ses for the low coverage region, decreases for the dose higher than ab out 0.7 Languimir, and saturates at about 4 Languimir. We find the eig ht hydrogen adsorption sites on the W(310) plane. Three of these sites are on the terrace (100) plane and the hydrogen adsorption on these s ites lower the work function. The other three sites are on the step-wa ll (110) plane raising the work function. Last two sites are probably on the step-edge. The heats of desorption for these sites ranges from 16.6 +/- 2.0 kcal/mol for the gamma(2) state to 32.0 +/- 1.0 kcal/mol for the beta(6) state. An indirect comparison and analysis show that o ur findings are quite reasonable.