Spontaneous thinning of necks between STM tip and the Pb(110) surface

Recent studies show that the so-called "jump to contact" phenomenon, which often happens between a sharp tip and a flat surface in close proximity and results in formation of a neck between the two, is probably the origin of friction. By studying the phenomenon with a scanning tunneling microscope (STM) and monitoring the conductance evolution, we have found that such necks between the STM tip and the Pb(110) sample surface, after being stretched to a certain degree, may shrink spontaneously till its break. The fact that surface cleanness and temperature have significant influence on the shrinking process suggests that the process is a result of surface diffusion of Pb atoms.