DEVELOPMENT OF A TWO DEGREES OF FREEDOM LENGTH MEASUREMENT SYSTEM USING A CRYSTAL AS THE SCALE REFERENCE

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We have investigated the possibility of using the lattice spacing of a crystal for metrology and accurate positioning. To carry out the research, we have built a scanning tunneling microscope (STM) with two tunneling-units (a dual tunneling-unit STM, DTU-STM), with an xy stage with two sample holders, The configuration enables simultaneous observation of a sample and the scale-reference crystal. As a result, it is possible to calibrate the lateral scales of the sample image by superposition of the crystalline lattice image. In order to access the accuracy of this measurement procedure, we have compared crystalline lattice images acquired simultaneously with the two tunneling-units. Matching of 99.98 +/- 0.03%. Although we have not measured the absolute accuracy of the system, the high repeatability of the experiment implies the procedure to give good results. We have succeeded in the software recognition of the atomic features, so it is safe to assume that an automated measurement machine, capable of measuring up to a few microns will be implemented in the near future.Study on the use of the STM and a crystal for sub-nanometer positioning control of the xy stage was also carried out. Lateral position modulation in the 10 pm order was used to measure the gradient of the surface with atomic resolution. By this technique, it becomes possible to recognize the local maximum and minimum of the topographic features, and thus implement active positioning of the xy stage using the lattice spacing as the reference. Positioning of the STM tip to a single atom was also confirmed for tens of minutes.