Structural change of radiation defects in graphite crystals induced by STM probing
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It was found that STM (scanning tunneling microscopy) images of defects in highly oriented pyrolytic graphite introduced by bombardment of 400 eV Ar+ ions in ultra-high vacuum exhibit substantial changes in the course of STM probing. Detailed examination of abrupt changes in the tunneling current measured at defect sites during voltage scans shows that the primary cause of the defect-image change was found to be neither the injected current nor the injected power but the absolute value of the voltage applied between the probe tip and the sample. We propose that an electric polarization induced force attracting the sample surface toward the probe tip widens the layer spacing of the graphite surface, leading to an acceleration of the lateral diffusion of interstitial atoms introduced by the ion irradiation, which results in a change in the defect structures and the accompanying electronic structures sensible in the STMimaging.
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