XPS spectra were obtained for interface formation on the cleavage surfaces of In₄Se₃ layered semiconductor crystals that have been exposed in the air. Those exposed for 2-15 min are called fresh cleavages and those exposed for more than 24 hours are called the old cleavages.
The presence of the carbon on the fresh and old cleavage surfaces was shown using XPS analysis. The most intense XPS lines, viz. Se 3d, In 3d, C 1s, O 1s and the sharpest Auger lines were recorded in an expanded binding energy scale for the purpose of atomic concentration calculation and the charge transfer estimation. The exact peak position of these intense lines have been subsequently determined from the corresponding profiles, recorded on an expanded binding energy scale for Se 3d and In 3d. In each case Gausian line shape analysis has been done for the XPS expanded profiles after making the background correction using Shirley's method to determine the exact peak positions and peak areas. The chemical shifts have been calculated from the binding energy values of the XPS lines to Se, In, C and O, corrected with reference to vacuum level.
The strong decrease of the (O/C) and (N/C) ratios is observed in the case of the fresh, in comparison with the same ones for the old cleavages. This indicates, that in UHV chamber the adsorbed nitrogen is absent and carbon monoxide is the main adsorbate on the In₄Se₃ surface, and it forms In₄Se₃ -C interface.
The presence of non-simple interaction in the In₄Se₃ -C interfaces of old and fresh surfaces can be also confirmed by a closer inspection of the C 1s core level spectra. For the fresh cleavages of In₄Se₃ surface interface, the deconvoluted C 1s peak shows the presence of two types of carbon. They could be attributed to C-C (284.0 eV) and C-Se (284.39 eV). For the old In₄Se₃ surface interface, the presence of another carbon is detected at 284.39 eV attributed to C-C interaction in the "graphite phase".

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1. Cleavage surfaces atomic and electronic structure of the layered In₄Se₃ crystals as natural 2D-materials