Visualization of Polymer Structures with Atomic Force Microscopy

Abstract

In last two decades, microscopic characterization of materials has significantly advanced with the inventions of scanning tunneling microscopy (STM) and atomic force microscopy (AFM) [1, 2]. In STM, tunneling current between a sharp metallic probe placed in close proximity to a conducting surface is used as a probing interaction. Tunneling current in the range of nanoamperes originates when a bias voltage is applied between this probe and the conducting sample. Rastering of the probe is performed over the surface at separations small enough for stable detection of tunneling current between these two electrodes. This is realized with high accuracy using a three-dimensional piezoceramic actuator. In scanning tunneling microscopes, a feedback mechanism keeps the tip-sample current constant in every surface location by adjusting the vertical tip-sample separation. Changes in the applied voltage to the piezoactuator, which are needed to adjust the tip-sample separation, are presented in the height image. This image, to a first approximation, reproduces surface topography of the sample. Atomic-scale resolution, routinely achieved in STM, has made it an invaluable addition to the family of microscopic techniques. Another remarkable feature of such microscopes is their ability to examine samples not only in an ultrahigh (DRV) vacuum but also at ambient conditions and even under liquids. At present, STM has become a mature technique that is widely applied to the visualization of atomic structures and atomic-scale processes on different substrates, especially in DRV conditions.