Adhesion of micrometer-sized polymer particles under a scanning electron microscope

Techniques for manipulating micrometer-sized objects and assembling them into a microstructure in a scanning electron microscope (SEM) are important for research related to microscale physics. It has been demonstrated that micro-objects ranging from sub-mu m to several 10 mu m can be freely manipulated by adhering them to the tip of a probe. However, the present micromanipulation technique in a SEM is still inefficient, because little is known about the adhesion mechanisms of micro-objects in a SEM environment. In this study, the adhesion forces of micrometer-sized polymer particles deposited on a substrate during SEM observation have been directly measured. The adhesion forces between a polyvinyltoluene sphere of 1 mu m radius deposited on a Au substrate, and a glass probe with a hemispherical tip with a typical radius of 0.75 mu m coated with Au, were found to show various complicated behaviors. An irreversible increase in the adhesion forces initiated by the electron-beam (EB) irradiation, and the dependence of the adhesion on the electron flux and the probe voltage were observed. On the other hand, the dependence on the pressing force and the probe diameter, predicted by a conventional theory, was not confirmed. This observed complicated phenomena were successfully explained using the model based on the formation of an electric double layer at the contact interface by the EB irradiation, and the successive progress of creep deformation. (C) 2000 American Institute of Physics. [S0021-8979(00)01618-2].