Relations of Microstructure, Piezoelectricity, and Surface Forces at Nanoscale

Abstract

In small devices such as micro-electro-mechanical systems (MEMS) and nano-electro-mechanical systems (NEMS), adhesion and friction forces make them less reliable with unacceptable performance [1]. These forces need to be completely understood to make advances in the systems. In our previous research, it has been proven that using a functional material, polyvinylidene fluoride (PVDF), both stiction and friction could be modified or turned on-off. The phase of the polymer affects the adhesion and friction forces. β phase contents reduced the adhesion forces due to its less electrostatic forces. With higher phase difference, higher roughness of the polymer surface got higher friction forces. In this research, we continue our investigation in understanding microstructure aspects of the PVDF, its dipole structure, and piezoelectricity on surface adhesion and friction. Doing so, we used an atomic force microscope (AFM) with an external potential to study the piezeoelectrical behavior. The effects of the electrical potential on adhesion and friction force were tested. It was shown that when the electrical potential increases, the surface roughness increases under the AFM, however not with a profilometer. Changes were also found in adhesion. This paper discusses the mechanisms of nanoscale adhesion and friction of the PVDF with an AFM tip along with the microstructures and dipole structures. This article contributes to understanding in fundamental adhesion and friction forces at a nanometer length scale.