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.