Surface Science

Chemical effects of Ne+ bombardment on the MoS2(0001) surface studied by high-resolution photoelectron spectroscopy

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The effect of 1 keV Ne+ bombardment on the clean MoS2(0001)-1 × 1 surface with fluences between 4 × 1014 and 4 × 1016 Ne+/cm2 was studied using high-resolution photoelectron spectroscopy excited with synchrotron radiation. Spectra of the Mo 3d and S 2p core levels were measured with photon energies that ensured that the kinetic energy of the photoelectrons was the same, resulting in the same depth being probed for both core levels. For lower fluences (i.e., ≲2 × 1015 Ne+/cm2), S vacancy defect formation occurs in the MoS2 lattice, with the concurrent formation of a small amount (< 10%) of dispersed elemental molybdenum [Mo(0)]. For fluences greater than ∼l × 1016 Ne+/cm2, the Mo(0) is the predominant species in the surface region, while the remaining species consist of amorphous MoS2-x and polysulfide species. Valence band spectra taken with photon energies of 152 and 225 eV were consistent with the core level results. The movement of the valence band maximum toward the Fermi level indicated the formation of a metallic surface region. Annealing the sample to temperatures up to 1000 K resulted in the formation of metallic Mo coexisting, in approximately equal amounts, with reformed MoS2 in a surface with no long-range order as determined by LEED. Finally, a qualitative depth distribution of the chemical species present after Ne+ bombardment was determined by varying the photon energies used for the core level spectra. The results indicate that the preferential sputtering of sulfur over molybdenum occurs predominantly through a mechanism involving chemical bonding effects, specifically, through the preferential emission of polysulfide ions over other species in the bombarded region. © 1989.