New developments in fast image processing and data acquisition for STM

We have developed new easy-to-use but powerful software in order to obtain the best scan rates in data acquisition and image processing for a PC-AT microcomputer. The programs have been completely written in the C-language, which made it possible to combine low-level characteristics (quick access to memory, interrupt control, etc.) without losing the advantages of a high-level language. The data acquisition software was intended to be sufficiently flexible to acquire either topographical or spectroscopic data with no configuration changes. In topographical (z=f(x,y)) and spectroscopic (I=f(V, z)) measurements, we can obtain up to 15,000 samples/s rates, with 12-bit resolution in a ±10V range. Spectroscopic measurements are done by acquiring I(V) with the feedback off at several z values (up to 256) until I reaches a preset value; afterwards, z is reset automatically to the initial voltage to avoid tip-sample contact. The image processing was designed to get the best performances in time and quality with a simple system such as a PC-AT equipped with an IBM Professional Graphics Display (640times480 pixels and 256 simultaneous colours). It was structured in three parts: plane subtraction, image display (3-D shaded surfaces, 3-D surfaces with colour scales or 2-D contour maps), and filtering (smoothing filters or FFT convolution-deconvolution techniques).