Scanning probe lithography on Ge(111)-c(2×8) surface

The paper describes nanometer scale lithography on atomically clean Ge(111)-c(2×8) surface performed in the ultra-high vacuum scanning tunneling microscope operating at 300 K. Using a standard Pt80Ir20 probe tip and applying bias voltages between 0.5 and 3 V, the Ge surface could be reliably imaged with atomic resolution without any modification of the sample. However, surface modification in highly localized area under the probe tip was observed at the bias voltages from 4 to 5 V. Such modification could occur in the form of the deposition of the tip material onto the scanned area of the sample, extraction of the sample material or generation of defects in the sample crystalline structure. Possible physical mechanisms of the processes outlined above as well as the strategies to achieve reliable scanning probe nanolithography are discussed.