Study of Ion Velocity Effect on the Band Gap of CVD-Grown Few-Layer MoS2

Abstract

The present work reports on a simple chemical vapor deposition (CVD) technique that employs alkali halide (NaCl) to synthesize high-quality few-layer MoS2 by reducing growth temperature from 850 to 650 °C, and its ion irradiation study for band gap modification. The Raman peak position difference of A1g to E12g of ≈24.5 cm-1 for the synthesized MoS2 corresponds to a few layers (<5 monolayers) of MoS2 on the substrate, as also confirmed by atomic force microscopy (AFM). The optical image shows the continuous distribution of flakes throughout the substrate and the average area of flakes ≈0.2 μm2 as confirmed by scanning electron microscopy (SEM) and transmission electron microscopy (TEM) analysis. Swift heavy-ion (SHI) irradiation at 60, 100, and 150 MeV ion energies of 1 × 1012 ions/cm2 ion fluence have been used to modify the band gap in few-layer MoS2. The ions with two different energies are chosen at two sides of the Bragg peak of energy loss curve in such a way as to have the same value of electronic energy loss (Se) but different ion energies to examine the velocity effect for the ion-induced modification. The absorbance peaks for 60 and 150 MeV irradiated samples show the same effect in the band gap modification.