2-DIMENSIONAL POSITIONING OF THE SCANNING TUNNELING MICROSCOPE STAGE USING A CRYSTAL AS A SCALE REFERENCE

Two-dimensional positioning control of the sample stage of a scanning tunneling microscope (STM) was implemented by having an STM tip in reg ister with arrays of atoms of a crystal attached to the sample stage. The position of this reference crystal was modulated with an amplitude of 70 pm (p-p), at a frequency of 3.3 kHz, in the x and y directions consecutively, to obtain the differential of the tunneling current in the two directions. The differential signals were accumulated using tw o digital integrators and fed to the x and y piezo elements of the sam ple stage. With such a configuration, the lateral position of the samp le stage could be regulated using the crystalline lattice as the scale reference. For example, lateral drift between the sample stage and th e lip could be eliminated by aligning an atom of the crystal to the ti p. Also, incremental motions of the sample stage could be implemented by having an array of atoms move over the tip. Because the technique o ffers subnanometer level accuracy, it is a powerful tool for metrologi cal applications as well as for accumulation of weak signals that nece ssitate averaging without lateral drift of the scanned area.