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Surfaces of α-Fe single crystal whiskers grown in various modes were investigated by means of scanning tunneling microscopy/spectroscopy (STM/STS) in ultra-high vacuum at room temperature. The whiskers were prepared in a single crystal phase by a hydrogen reduction from vapour of FeCl2. Whiskers in shapes of rectangular prism, tetragonal prism and hexagonal prism were obtained.
The growth directions of the obtained whisker single crystals were confirmed with Laue X-ray diffraction patterns on an imaging plate. All whiskers grew in α phase. The rectangular prism crystals grew in a <110> direction with two {100} and two {110} side surfaces. The tetragonal prism crystals grew in a <100> direction with four {100} side surfaces. The hexagonal prism crystals grew in a <111> direction with six {110} side surfaces.
After annealing at 983-993 K, on the (001) surface of the tetragonal prism crystal, atomic lines along the directions of <011> were observed at room temperature. The height of the lines was about 0.02 nm which is much less than atomic layer distance in a <001> direction (0.14 nm). This might be related to the crystal transformation between α and γ phase induced by impurities at a surface. Differential tunneling conductance showed no surface state peak on the lines.
The step height of the terraces on the (110) side surface of the hexagonal prism crystal was observed to be 1.0 nm which is five times higher than an atomic layer distance in a <110> direction (0.2 nm). On the terraces, ditches with a depth of 0.2 nm in six-fold symmetry were observed. The differential conductance curves obtained on the terraces showed a band gap of about 0.3 V.
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