Physics of Friction in Noncontact Atomic Force Microscopy

摘要

After the development of the scanning tunneling microscope [1], scanning probe methods allowing us to observe atomic scale images of the surface of test specimens by the probe scanning play an important role in the quick development of nanotribology. Among the methods, the atomic force microscope (AFM) [2] provides a scanning probe technique, which most closely relates to tribological studies. As AFM utilizes a force as a probe, mechanisms of its measurements are closely related to phenomena of friction and adhesion between solids. It is well known that using friction force microscopy (FFM) [3], which scans the surface of test specimens in the horizontal direction in the AFM contact mode, the establishment and breakage of links between the probe and the surface (called the stick-slip motion [4]) occurs repeatedly with the periodicity of the sample surface lattice. Understanding the mechanisms involved in stick-slip motion is related to the interpretation of images obtained by FFM [5,6]. On the other hand, when using a method based on noncontact atomic force microscopy (NC-AFM) [7], which uses movements of a cantilever vertical relative to the sample surface forced by mechanical resonance, the formation and the breakage of physical and chemical links between the probe and the surface and friction induced thermal fluctuations (i.e. the process of energy dissipation attracts the attention). However, the full particulars of the microscopic mechanisms involved in the process have not yet been clarified. In the present work, among friction phenomena appearing in NC-AFM, the basic concept of friction caused by adhesion and thermal fluctuations is considered.