MEASURING THE ELASTIC MODULUS OF POLYMERS BY NANOINDENTATION WITH AN ATOMIC FORCE MICROSCOPE Daniel Hoffman 1 , Ibrahim Miskioglu 2 , Jaroslaw Drelich 1 , Katerina Aifantis 3 1 Department of Materials Science and Engineering 2 Department of Mechanical Engineering Engineering Mechanics Michigan Technological University Houghton, MI 49931, USA 3 Lab of Mechanics and Materials College of Engineering Aristotle University of Thessaloniki Thessaloniki, Greece Keywords: Atomic force microscopy, elastic modulus, nanoindentation, polymers. Abstract A new method to determine the elastic modulus of a material using the atomic force microscope (AFM) has been proposed by Tang et al. (Nanotechnology 2008, 19, 495713). This method models the cantilever and the sample as two springs in a series. The ratio of the cantilever spring constant (k) to diameter of the tip (2a) is treated in the model as one parameter ( =k/2a). The value of a, along with the cantilever sensitivity, are determined on two reference samples with known mechanical properties and then used to find the elastic modulus of an unknown sample. To determine the reliability and accuracy of this technique it was tested on several polymers. Traditional depth-sensing nanoindentation was preformed for comparison. Using both methods, the elastic modulus of the polymers tested was calculated. The elastic modulus values from the AFM were within ±(5-20)% of the nanoindenter results. Introduction The atomic force microscope (AFM) has proven to be a useful tool for characterizing materials on the micro- to nano-scale. The most common use of AFM is to image and measure the topography of the sample surface, but AFM has also been used to characterize the mechanical properties of materials [1-3]. With AFM’s ability to scan the sample surface, features of interest can be found and indented. It provides an advantage over traditional nanoindenters that use optical microscopes and thus cannot resolve nano-scale features. This makes AFM a useful tool for characterizing materials on the nano-scale. Traditional depth-sensing indentation measures the penetration of the indenter against the force applied. Using relationships proposed by Oliver and Pharr, the depth versus load data can be used to determine hardness and elastic modulus [1, 4]. While purpose built nanoindentation devices can be used for these tests, it has been shown that the AFM is also capable of performing nanoindentations [5-8]. 243 EPD Congress 2011 TMS (The Minerals, Metals & Materials Society), 2011