Polymer Surface Topography and Nanomechanical Mapping

Hao Liu, So Fujinami, Dong Wang, Ken Nakajima , and Toshio Nishi  

The invention of scanning tunneling microscopy (STM) about three decades ago [1,2] opened a new age in which various related scanning probe microscopy (SPM) methods were developed and some of those were widely accepted as key tools for nanotechnology. Although the original STM limited its application to conductive materials, atomic force microscopy (AFM), which appeared soon after the invention of STM [3], proved applicable to various types of materials, including polymeric materials. 

AFM has a cantilever as its most basic component, with a very sharp probe at its free end in order to interact with sample surfaces. The interaction force induces the deflection of the cantilever, which is the most important signal of concern. The original AFM by the developers used STM to detect the cantilever deflection, while an optical beam method is mostly used nowadays due to easier handling. 

Applications of AFM to polymeric materials started mainly with the aim of studying the surface structures with superior lateral resolution [4-7]. For these purposes, AFM retains an advantage over other microscopic techniques because its environmental limitation is very little it can work in air, water, and some other solutions. What AFM users need to keep in mind is that the obtained image may be affected by interactions such as surface force and elastic repulsion that 

However, the fact that AFM is sensitive to these weak forces can be turned into an advantage. One of the most common ways to measure the interactions is a force-distance curve measurement, in which the scanner starts to move vertically to make contact with the probe and surface and then reverse to make them separated. During the process, the cantilever deflection is recorded as a function of vertical scanner movement. One can obtain the relation between normal load P and indentation depth 8 using simple relations (the detailed procedure is discussed later). Applying an appropriate contact mechanics theory, one can estimate the mechanical properties of the sample surfaces. 

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