Study on the AFM Force Curve Common Errors and Their Effects on the Calculated Nanomechanical Properties of Materials

D Almasi,M R Abdul Kadir,T Kamarul,R Sharifi,G Krishnamurithy

doi:10.1155/2016/2456378

Abstract

The atomic force microscope (AFM) force curve has been widely used for determining the mechanical properties of materials due to its high resolution, whereby very low (piconewton) forces and distances as small as nanometers can be measured. However, sometimes the resultant force curve obtained from AFM is slightly different from those obtained from a more typical nanoindentation force curve due to the AFM piezo’s hysteresis. In this study the nanomechanical properties of either a sulfonated polyether ether ketone (SPEEK) treated layer or bare polyether ether ketone (PEEK) were evaluated via AFM nanoindentation and a nanomechanical test system to probe the possible error of the calculated nanomechanical properties due to the AFM piezo’s hysteresis. The results showed that AFM piezo’s hysteresis caused the error in the calculated nanomechanical properties of the materials.

Highlights

Due to the increased applications of thin film polymeric materials and polymeric coating layers in different fields of research, probing the nanomechanical properties of polymeric materials has become essential to scientists
The Oliver-Pharr model can be used for calculating the elastic modulus with an assumption of zero residual indentation depth. In this particular comparative study, we found that the prediction of elastic modulus from the Atomic force microscopy (AFM) was less accurate than the nanomechanical test system (NTS) due to the cantilever effect and piezo hysteresis from the AFM
A study was done to compare the predicted elastic modulus from two types of equipment—AFM and NTS. Force curves from both types of equipment were used with the mathematical models of Oliver-Pharr and Hertz to calculate Young’s modulus of polyether ether ketone (PEEK) and sulfonated polyether ether ketone (SPEEK)

Summary

Introduction

Due to the increased applications of thin film polymeric materials and polymeric coating layers in different fields of research, probing the nanomechanical properties of polymeric materials has become essential to scientists. Based on Buckle’s one-tenth rule for probing the mechanical properties of a coating or thin layer of a particular material, the maximum indentation depth must be less than one-tenth of the thickness of that layer to prevent an effect of the substrate in the resultant force curve [1]. Atomic force microscopy (AFM) and nanomechanical test system have been used widely to probe the nanomechanical properties of the surface of materials. Burnham and Colton [3] used AFM in a nanoindentation study for the first time and measured nanomechanical properties of material surfaces at piconewton resolution. The nanomechanical test system (NTS) is another example of typical equipment that has been used to draw force-indentation depth graphs [19,20,21] and has been used to measure Young’s modulus for various materials such as hydroxyapatite [22] and titanium [23]. Several formulations to calculate the elastic modulus from the force curve are

Methods

Results

Discussion

Conclusion