Modification of MoS2 structure by means of high energy ions in connection to electrical properties and light element surface adsorption

Abstract

MoS2 samples were intentionally modified using high energy ions (He, Si and Au) at the ion energy of 1.8 MeV and the ion fluence ranging between 1 × 1013 and 1 × 1015 cm−2 to tailor intentionally the surface electric and structural properties of MoS2. Light and medium energetic ions can be effectively used for ion beam microstructuring in various materials e.g. graphene and MoS2, thus the material modification study under high energy ions leading to electronic stopping of ions is mandatory for this application. Rutherford Back-Scattering spectrometry (RBS) and Elastic Recoil Detection Analysis (ERDA) were used for elemental analysis, including hydrogen surface depth profiling, of the modified MoS2 samples. Scanning Electron Microscopy (SEM) with Energy Dispersive X-ray (EDX) and X-ray Photoelectron Spectroscopy (XPS) analysis were used to investigate the surface morphology influenced by the irradiation as well as to follow the surface layer elemental composition. Raman spectroscopy was employed to study the structural modification and disorder accumulation caused by energetic ion irradiation. Simultaneously, two-point method was applied for electrical properties measurement. Surface morphology modification enhances with the increasing ion fluence for all ion species. Surface deterioration and sulphur depletion in MoS2 was observed not only for heaviest ion irradiation (Au) as was expected, but also for light ions (He). Interior structure damage was observed to be the most prominent in case of Au irradiation as it was concluded from the most significant A1g and E12g phonon shift and broadening with increasing Au ion fluence in Raman spectra. On the other hand, the interior structure deterioration was only negligible in case of He irradiated samples. Surface hydrogen content was observed to be a function of ion implantation fluence and ion mass. Electrical resistivity was increased as a consequence of ion irradiation for heaviest ions; after Si and Au irradiation; the resistivity increased for the lowest ion fluence and subsequently decreases with increasing ion fluence being higher for the irradiated samples compared to the pristine one.