In situ control and analysis of the scanning tunneling microscope tip by formation of sharp needles on the Si sample and W tip

Abstract
Sharp needles on the Si(111)7×7 and Si(100)2×1 surfaces are formed in a controlled manner by applying a sample bias Vs ranging from +5.0 to +10.0 V while keeping the scanning tunneling microscope (STM) tunneling current constant. The size of the needle-shaped structure is 1–20 nm in height and 1–5 nm in diameter depending on the bias voltage and duration (1–30 s). The needle structures are utilized to counter image the scanning tip with an atomic resolution (needle formation and tip imaging=NFTI). The STM resolution for the Si(111)7×7 structure is evaluated in relation to the atomic structure of the scanning tip imaged by the NFTI method. When a bias voltage of Vs=−10.0 V is used, needle formation on the scanning tip is observed. The NFTI method gives us a conventional technique to modify and monitor in situ the scanning tip of STM.

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