Surface Observation of a Potassium-Doped C_<60> Thin Film by Scanning Tunneling Microscopy

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Using scanning tunneling microscopy (STM) and X-ray diffraction (XRD) studies, we find that a 500-nm-thick K_xC_<60> (x = 3) thin film deposited on a gold thin film grown on a mica substrate has the face-centered cubic (fcc)- (311) surface and that a K_xC_<60> (x = 4) film of the same thickness has the body-centered tetragonal (bct)-(112) surface. The potassium density x of a K_xC_<60> thin film is estimated by in situ measurement of the exposure time dependence of the sheet resistance of the film in potassium vapor, STM images of the K_3C<60> thin film, which are different from the reported images of C_<60> thin films, indicate that the observed surface is a fcc-K_3C_<60> (311) surface. The images also show that the lattice constant of the potassium-doped C_<60> thin film is about 0.5% larger than that of a nondoped one along <011>. From the I-V characteristics of the K_xC_<60> films as measured by STM, it is found that the band gap of films vary with the value of x in K_xC_<60> films.
社団法人応用物理学会の論文
1999-09-15