| Single crystals of MoS(,2) and WS(,2) were grown by chemical vapor transport both in the presence and absence of cobalt. Hall measurements indicate that cobalt cannot diffuse appreciably into the bulk of MoS(,2) or WS(,2) and, therefore, can be present only on the surface. Similar results were obtained for as-grown crystals annealed or sulfided in contact with Co(,9)S(,8) or sulfided after being dipped in a 0.1M CoSO(,4)/methanol solution.; The photoelectrochemical behavior of MoS(,2) single crystals grown in the presence of cobalt was investigated. Photocurrents measured in acetonitrile containing the redox couple ferrocene ('+/0) were appreciably lower than that found for pure, synthetic MoS(,2) crystals, indicating that cobalt is present on the surface. Surface peeling restores the photoresponse by removing most of the cobalt.; Single crystals of WS(,2) were oxidized in a carbon dioxide atmosphere. The oxidation was found to occur preferentially along the surface edge planes. X-ray diffraction indicated that the oxide phase was WO(,3). Scanning electron microscopy indicated that the crystal morphology changed as a function of oxidation time. |
