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

Techniques for manipulating micrometer-sized objects and assembling them in to a microstructure in a scanning electron microscope (SEM) are important f or research related to microscale physics. It has been demonstrated that mi cro-objects ranging from sub-mu m to several 10 mu m can be freely manipula ted by adhering them to the tip of a probe. However, the present micromanip ulation technique in a SEM is still inefficient, because little is known ab out 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 adhe sion 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 d ependence on the pressing force and the probe diameter, predicted by a conv entional theory, was not confirmed. This observed complicated phenomena wer e successfully explained using the model based on the formation of an elect ric double layer at the contact interface by the EB irradiation, and the su ccessive progress of creep deformation. (C) 2000 American Institute of Phys ics. [S0021-8979(00)01618-2].