Studies on Chemisorption of Nitrogen on Tantalum with the Field Emission Microscope

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Abstract
The chemisorption of nitrogen occurs on all crystal planes of tantalum and decrease the average work function as much as 0.00∼0.06 eV. Three multiplex states of chemisorption are found from the observation of the field emission pattern and the measurement of the work function change. The B 1-state exists on rough planes such as the (111) plane, vicinities of the (100) and (110) planes, and nitrogen chemisorbed at this state disappears below 620°K and increases the work function of these rough planes as much as 0.23 eV. The B 2-state exists on flat planes, that is, the (100) and (110) planes, and the B 2-nitrogen disappears below 970°K and lowers the work function as much as 0.42 eV. The B 3-state exists on rough planes such as the (111) plane and vicinities of the (211) and (111) planes, and the change of the work function caused by the B 3-adsorption is calculated as -0.05 eV. Nitrogen chemisorbed at this state begins to desorb at 970°K, and the desorption completes at 1370°K. The B 2-state is probably concerned with the direct absorption at its adsorption site.

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