Development of LEED apparatus using field-emission tips

Low-energy electron diffraction (LEED) apparatuses with field-emission (FE) tips were developed. The FE tips were fabricated by field-assisted gas etching to obtain an atomically sharp tip apex. These tips emit single-spot electron beams. Using the FE beams in conjunction with a lensless system, we observed backscattered electrons at the surface of few-layer graphene grown on SiC(0001). The obtained hexagonal patterns at sample biases of 93 V, 54 V, and 28 V were interpreted as diffraction spots derived from the graphene, the SiC(0001) substrate, and a buffer layer, respectively. On the basis of the opening angle of FE, the irradiated areas were estimated to be 350 nmφ when the sample bias was 100 V. Since the FE beams were easily focused by a magnetic lens, a LEED apparatus with the focused FE beams was also examined. This approach might be useful for improving the sharpness of LEED patterns. (author)