Measurement of the Indentation Modulus and the Local Internal Friction in Amorphous SiO2 Using Atomic Force Acoustic Microscopy

For the past two decades, atomic force acoustic microscopy (AFAM), an advanced scanning probe microscopy technique, has played a promising role in materials characterization with a good lateral resolution at micro/nano dimensions. AFAM is based on inducing out-of-plane vibrations in the specimen, which are generated by an ultrasonic transducer. The vibrations are sensed by the AFM cantilever when its tip is in contact with the material under test. From the cantilver’s contactresonance spectra, one determines the real and the imaginary part of the contact stiffness k*, and then from these two quantities the local indentation modulus M' and the local damping factor Q_loc^-1 can be obtained with a spatial resolution of less than 10 nm. Here, we present measured data of M' and of Q_loc^-1 for the insulating amorphous material, a-SiO₂. The amorphous SiO₂ layer was prepared on a crystalline Si wafer by means of thermal oxidation. There is a spatial distribution of the indentation modulus M' and of the internal friction Q_loc^-1. This is a consequence of the potential energy landscape for amorphous materials.