NCAFM2023 Programme Booklet

HIGH-TEMPERATURE FLAME ETCHING TO PREPARE TUNGSTEN TIPS FOR SCANNING PROBE MICROSCOPY

Toyoko Arai 1* , Nobuhiko Utsunomiya 1 , Masahiko Tomitori 2

1 Graduate School of Natural Science and Technology, Kanazawa University, 920-1192 Japan 2 Japan Advanced Institute of Science and Technology, 923-1292, Japan

Email: arai@staff.kanazawa-u.ac.jp

Control of the quality of a scanning tip is crucial to determine the performance of a scanning probe microscope (SPM). The tip should be atomically sharp with a stable atomic arrangement, and have reproducible physical and chemical properties. Recently, a quick and clean method of sharpening the tip of high-temperature-melting metal wires such as tungsten (W) by burning in flame was proposed, named flame etching method [1]. In comparison to electrochemical etching, chemical residues could be reduced. In the present study, we burned W wires in a high-temperature (~2500 °C) flame of a hydrogen-oxygen (H 2 :O 2 =2:1) gas burner which sublimated W oxides to be thin, and characterized the flame-etched W tips. The flame etching process was captured by a high-speed camera (Fig. 1). The W wire was sharpened in ~300 ms after insertion into the flame. The tip receded in the further flame etching. Figure 2 shows the SEM images of the flame-etched W tip. The tip apex was polyhedrally surrounded by facet-like surfaces. Electron backscattering diffraction (EBSD) analysis revealed that the crystal grain of the tip apex was extended over 100 µm oriented in the [110] direction of the tip axis. The facetted surfaces could correspond to its crystallinity. The surface was covered with oxygen, evidenced by scanning Auger electron analysis, which was reduced by heating in an ultra-high vacuum. This indicates that the heating of W is an essential procedure to control the tip quality. We will present the optimized procedure for the tip preparation.

Fig. 1 Fig. 1 High-speed optical-filtered camera images of the flame-etching process of a 0.1 W wire.

Fig. 2 SEM images of the flame-etched W tip.

References [1] T. Yamaguchi et al., Rev. Sci. Instrum., 2019, 90 , 063701.

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