COMPOSITION AND THICKNESS OF SURFACE-LAYER ON MOLYBDENUM TIPS FOR SCANNING TUNNELING MICROSCOPY (STM) STUDIED BY SEM/AES/(AR)XPS

A combination of SEM, AES and angle-resolved XPS (ARXPS) has been applied to analyse the distribution of chemical compounds in the surface region of electrochemically etched molybdenum tips and to determine the contamination layer thickness. Carbon monoxide, graphite, molybdenum carbide and molybdenum oxide were found to be the main surface contaminants on molybdenum tips. Auger line profiling revealed a significant enrichment of carbon and oxygen upon the tip. The thickness of the oxygen-carbon contamination layer on the tip was estimated to be 13.5 +/- 1.0 nm as measured by AES. The thickness of the contamination layer on a molybdenum sheet was found to be 8.0 +/- 1.5 and 6.8 nm using AES and ARXPS respectively. Quantitative analysis of the surface concentrations of carbon, oxygen and molybdenum has been performed.