Quantitative characterization of physical processes during nanometer surface modification

A scanning tunneling microscope developed for microscopy, spectroscopy, and lithography has been used for modification of metallic surfaces exposed to the atmosphere. We report here the first quantitative characterization of a submicrometer area of a metallic sample before and after pulsing the tip-sample voltage using both tunneling spectroscopy determination of the apparent mean barrier potential (φ) and imaging of the area in constant tunneling current mode. The before and after images show that the form of the created features ranges from craters to mounds. The current wave form recorded during a surface modification is indicative of the form of the feature. Diminution of the contamination layer often associated with surfaces exposed to the atmosphere is inferred from the values of φ before and after modification. Analysis of the results indicates that the observed features were caused by high electric fields and not by high temperatures.