Cross-sectional transmission electron microscope observation of small structures made by field-induced scanning tunneling microscope fabrication

We observed cross-sectional transmission electron microscope images of small structures on a GaAs substrate made by the scanning tunneling microscope (STM) field-induced fabrication method. A cross-sectional image of a GaAs dot, fabricated by applying a voltage pulse to a W tip, was 400 nm wide and had a highly symmetric double ditch structure. The inside of the dot consisted of GaAs polycrystal and the boundary was clearly limited by specific crystal planes. If the fabrication mechanism is considered to be field-induced evaporation in the STM regime; the anisotropy would have arisen due to a difference in work function between each plane. We also observed a Ni dot fabricated using a Ni-coated tip. The dot was a spherical with about a 110 nm diameter and it consisted of Ni polycrystal. Using the tip, we could obtain only one or two Ni dots: suggesting it behaves like a solid source rather than a liquid ion source.