Electron tunneling from a metallic TS2 layer underneath an ultra-thin MS layer with semiconducting properties for misfit-layer compounds

The effects of electron tunneling from the underlying TS2 (H) layer on the scanning tunneling microscopy (STM) images of the uppermost MS (Q) layer have been studied for the misfit-layer compounds which are represented by the chemical formula {(MS)1+x}m{TS2}n. Systematic STM observations have been carried out under ultra-high vacuum (UHV) conditions for the 1Q/1H, 1.5Q/1H and 2Q/1H types of misfit-layer compounds. As Q layer thickness increases from about 6 to 12 Å while going from the 1Q/1H type to the 2Q/1H type, pseudo-tetragonal arrays of bright spots as expected from the atomic arrangement of a Q layer are observed more easily and more distinctly. It is found that tunneling electrons from the underlying H layer play an important role on the STM observations of the 1Q/1H and 1.5Q/1H types of compounds. Fast Fourier transform (FFT) analyses give clear evidences for electron tunneling from the underlying H layer and scattering by surface atoms of the uppermost Q layer and a mutual modulation structure peculiar to the compounds.