LATERALLY INHOMOGENEOUS SURFACE-POTENTIAL DISTRIBUTION AND PHOTOVOLTAGE AT CLUSTERED IN/WSE2(0001) INTERFACES

Small increments of indium were evaporated at 300 and 100 K onto the van der Waals (0001) surface of p-type WSe2 crystals. The interface formation was investigated in vacuo with x-ray photoemission spectroscopy, ultraviolet photoemisson spectroscopy, soft-x-ray photoemission spectroscopy, and low-energy electron diffraction. Additional scanning tunneling microscopy (STM), scanning electron microscopy (SEM), and microprobe measurements were performed ex situ. For deposition at 300 K a nonreactive interface is formed and the indium layer grows in the Volmer-Weber growth mode. The size and distribution of the In clusters for specific coverages were determined ex situ by STM and SEM. The band bending of 0.55 eV, as determined from binding-energy shifts of the substrate emissions, is far below the expected Schottky-limit value of 1.1 eV. The observed surface-photovoltage (SPV) shifts of the substrate emission lines are smaller (up to 0.2 eV) than those from the adsorbate lines. The maximum adsorbate SPV shift of 0.6 eV at 150 K exceeds the measured band bending, indicating that the band bending beneath the In clusters must be larger than between them. At a sample temperature of 100 K, In forms atomically flat layers (Frank-van der Merwe growth) allowing the determination of the actual band bending of 0.9-1.0 eV below the In-covered surface. For these conditions, the SPV is only 0.1 eV due to an electrical leakage current. During warmup to 300 K, a transition to the clustered interface occurs. For this interface, the band bending below the indium clusters could also be determined from temperature-dependent SPV measurements. The determined barrier height of 1.04 eV is in good agreement with the value measured at the unclustered interface.