Preparation of Superconducting Niobium Tips for Atomic-Resolution Scanning Tunneling Microscopy/Spectroscopy

We present a new reliable method to prepare superconducting niobium (Nb) tips for scanning tunneling microscopy/spectroscopy (STM/STS). Sharp Nb tips were fabricated by chemical etching using an electrolyte based on a hydrofluoric acid and hydrogen peroxide solution, followed by field evaporation ut...

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Bibliographic Details
Published inJapanese Journal of Applied Physics Vol. 49; no. 2; pp. 028004 - 028004-2
Main Authors Shimizu, Ryota, Hitosugi, Taro, Hashizume, Tomihiro, Fukuo, Noritaka, Hasegawa, Tetsuya
Format Journal Article
LanguageEnglish
Published The Japan Society of Applied Physics 01.02.2010
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Summary:We present a new reliable method to prepare superconducting niobium (Nb) tips for scanning tunneling microscopy/spectroscopy (STM/STS). Sharp Nb tips were fabricated by chemical etching using an electrolyte based on a hydrofluoric acid and hydrogen peroxide solution, followed by field evaporation utilizing field ion microscopy to remove Nb oxide layers from the tip apex. STM/STS measurements of Si(111) and Au(111) surfaces confirmed that the tips had atomic resolution capability together with bulk-like superconducting properties, indicating that the prepared Nb tips can be used as a unique probe for investigating local superconducting and magnetic properties on an atomic scale.
Bibliography:(a) Typical SEM image of an electrochemically etched Nb tip, and (b) a close-up near the tip apex. (a) Typical FIM image of an electrochemically-etched Nb tip on a (011) plane with a satellite of a {112} face. The number of rings between the (011) and {112} faces was evaluated to be 12 or 13, indicating a tip curvature radius of ${\sim}22$ nm. The tip bias voltage was 5.2 kV. (b) Constant current STM image of the Si(111)-$7{\times}7$ reconstruction surface at room temperature obtained using an FIM-treated Nb tip ($12\times 12$ nm 2 , $V_{\text{s}}=+1.5$ V, $I_{\text{t}}=10$ pA). Differential tunneling conductance spectra obtained on an Au(111) thin film sample using a Nb tip at 4.3 K. The circles denote experimental data, and the solid line is the Dynes function assuming $\Delta = 1.4$ meV and $\Gamma = 0.50$ meV. The inset shows an STM image ($60 \times 40$ nm 2 ) taken on the surface of an Au(111) thin film sample at 4.3 K.
ISSN:0021-4922
1347-4065
DOI:10.1143/JJAP.49.028004