Tip expansion in a laser assisted scanning tunneling microscope.

The thermal expansion of a scanning tunneling microscope tip induced by femtosecond laser is investigated with various parameters including laser power, modulation frequency, illumination spot, and laser wavelength. The magnitude of tip expansion is measured to be proportional to the laser power. The response bandwidth is closely related to the length of the tip cone section, which is consistent with a two-rod model simulation. While visible lasers produce significant tip expansion, deep ultraviolet and near infrared lasers result in significantly reduced expansion magnitude, which can be explained with the tip induced surface plasmon in the tunneling junction. [ABSTRACT FROM AUTHOR]