Crystalline lattice for metrological applications and positioning control by a dual tunneling-unit scanning tunneling microscope

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Abstract
A dual tunneling-unit (DTU) scanning tunneling microscope (STM) was built to verify the potential of crystalline lattices to metrological applications and positioning control. As an example of metrological application, imaging crystals for XY scale calibration of the other image was proposed. Two highly oriented pyrolitic graphite (HOPG) chips were imaged for comparison. Apparent lengths of lines defined within the images were measured by counting the number of lattices. The measurements matched to 99.7%. Different thermal drift rates of the two tips to the samples were confirmed to be the dominant factor of calibration accuracy, while effects of errors due to geometric asymmetry (e.g., Abbe's error) were evaluated to be less. Lateral dither vibrations [amplitude 14 to 70 pm (p-p), frequency 3.3 kHz] were applied to the XY scanners to implement feedback control of the XY scanners. The gradient signals obtained through application of dither vibrations were fed back to the XY scanners. Two active positioning functions implemented were: (i) tip to atom positioning for a duration of several minutes; and (ii) a well defined stepping action of the tip to the crystalline lattice. Both functions were confirmed to be robust and stable.

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