Three-dimensional displacement measurement of a tube scanner for a scanning tunneling microscope by optical interferometer

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Abstract
The scanning tunneling microscope (STM) is known for its high lateral resolution. The unreliability of the scanning and positioning motion of the STM were monitored by interferometer and capacitance recently. The widely used conventional lead zirconium titanate (PZT) tube scanner has good mechanical properties; however, the motion of the tube includes angular motion which generates large error. Even with an optical interferometer to calibrate STM tip motion, the angular motion reduces or eliminates the visibility of interference. We have developed an eight-segmented tube scanner which reduces angular motion for maintaining the visibility of interference and reduces Abbe error. The residual error of the value measured by a high-accuracy interferometer which measured the motion of the newly developed eight-segmented tube scanner was estimated by measuring a standard pattern. The accuracy of the interferometer, which used a balanced detection technique, the principle of which is also reported in this paper, was measured by a capacitance gauge.