Repeatability of Adhesion Force Measurement on Wood Longitunial Cut Cell Wall Using Atomic Force Microscopy

As a powerful tool to investigate the surface properties at a nano-scale resolution, the atomic force microscopy (AFM) encounters challenges in the measurement of plant materials such as wood surface. In particular, for rough and heterogeneous surfaces, a robust and easily performed positioning method is necessary for reproducible measurements. One of the critical issues is the ability to position the AFM tip after the specimens are removed for treatments from a device and repeatedly analyzed. If the tip is not repeatably positioned within the measured area, the natural variability of surface (such as surface roughness) can mask the effects of treatments of interest.  In this paper, a positioning method using the bordered pit of the wood radial surface as a natural marker is proposed and a systematic measurement procedure is presented. The idea results from the uniqueness of the anatomical features of a natural material (wood in this case) and low probability of having exactly the same geometry of pit clusters in the vicinity of the area of interest.  The results show that the anatomical features can be used as unique markers for precise positioning of the AFM tip.  The process is demonstrated using an example of the effect of temperature on adhesion forces on the wood surface. After the heat treatment, the wood surface layers were investigated with Fourier transform infrared spectroscopy and attenuated total reflection (FTIR-ATR).