Nanoneedle formation on silicon (111) surface using a scanning tunneling microscope tip

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Abstract
Nanoneedles are formed on the Si(111) surface when negative ramp voltages are applied to a scanning tunneling microscope (STM) tip. These nanoneedles allow the direct imaging of the STM tip, because of their extreme sharpness with an estimated diameter of ∼2 nm and a maximum height of 20 nm. In this article, voltage, time, and current dependences of nanoneedle growth are examined. Based on the experimental results, we propose that the nanoneedle formation mechanism is: Si atom extraction from the Si surface to the tip due to the applied high voltage, migration of the atoms to the tip apex, and redeposition from the tip apex to the sample surface. A nanoneedle can also be formed on the tip apex by applying a positive voltage and the growth process is observed by a nanoneedle on the sample surface.