DEFORMATIONS AND NONLINEARITY IN SCANNING TUNNELING MICROSCOPE IMAGES

We perform here a complete determination of the relation between applied voltage and displacement for a tripod piezoceramic scanning tunneling microscope (STM) scanner unit. The absolute calibration is obtained in two steps. First the gap between two capacitor plates is modified by the expansion of the piezoelectric tube driven at various voltages and frequencies. Second, we image by STM some well-known surfaces: an optical diffraction grating and highly oriented pyrolytic graphite for large and atomic scales, respectively. For the voltage versus expansion relation we consider both nonlinearity sources, which induced relevant image deformations: static hysteresis and time-retarded response or creep. This characterization of the scanning unit in the STM operating conditions (voltage and frequencies) allows a suitable image restoration.