Influence of Tip Wear on Atomic Force Acoustic Microscopy Experiments Malgorzata Kopycinska-Müller, Roy H. Geiss, Paul Rice, and Donna C. Hurley Materials Reliability Division, National Institute of Standards and Technology Boulder, CO 80303-3328 U.S.A. ABSTRACT Tip wear and its corresponding change in geometry is a major impediment for quantifying atomic force acoustic microscopy (AFAM). To better understand the process of tip wear and its influence on AFAM measurements of material elastic properties, we have performed a series of experiments and compared tip geometries calculated from experimental data with direct tip visualization in the scanning electron microscope (SEM). Using a sample with known elastic properties, the tip-sample contact stiffnesses for several different cantilevers were determined. Hertz and Derjaguin-Müller-Toporov (DMT) contact-mechanics models were applied to calculate values of the tip radius R from the experimental data. At the same time, values for R before and after each sequence of AFAM measurements were obtained from SEM images. Both methods showed that the tip radius increased with use. However, values of R calculated with the theoretical models varied indeterminately from those obtained from the SEM images. In addition, in some cases analysis of the AFAM measurements suggested a hemispherical tip, while the corresponding SEM images showed that the end of the tip was flat. We also observed other changes in tip shape, such as an increase in the tip width. By combining theoretical models for contact mechanics with visual information on the tip geometry we hope to better understand contact characteristic in AFM-based systems. Contribution of NIST, an agency of the US government; not subject to copyright. INTRODUCTION The efforts of several groups have focused on the evaluation of elastic properties with dynamic enhancements of AFM [1-4]. Despite individual differences in the techniques, such as excitation amplitudes and the range of frequencies involved, all of these methods rely on Hertz or DMT contact-mechanics models to describe the contact between the tip and the sample [5, 6]. Quantitative measurements depend strongly on the characterization of the tip-sample contact. Quantitative elastic-property values have been obtained with the AFAM technique [3, 4]. Values of the indentation modulus obtained with AFAM methods agree very well with results either obtained by nanoindentation or calculated from elastic constants available in the literature. It was noticed, however, that the best agreement is obtained by use of a reference or calibration sample with elastic properties similar to those of the unknown material (or by use of two reference materials, respectively stiffer and more compliant than the unknown sample). In addition, in order to minimize the influence of tip wear and uncertainties connected with the cantilever spring constant and the AFM force calibration, it is important to perform measurements on the reference sample before and after every measurement of the unknown material [3]. In this paper, we describe our work to better understand the process of tip wear that occurs in AFAM experiments. From these experiments, we hope to simplify the calibration procedure described above and improve the accuracy of quantitative elastic-property measurements with AFAM. Mater. Res. Soc. Symp. Proc. Vol. 838E © 2005 Materials Research Society O10.16.1