  We present a comprehensive study on the effects of proton irradiation at
different energies (150 and 590 keV) with the fluence of 1x 1012 proton/cm2 on
monolayer MoS2. This study not only improves our understanding of the influence
of high-energy proton beams on MoS2 but also has implications for
radiation-induced changes in device processing and engineering of devices from
multilayer MoS2 starting material. Increasing defect density with decreasing
proton irradiation energy was observed from photoluminescence spectroscopy
study. These defects are attributed to sulfur vacancies observed through x-ray
photoelectron spectroscopy analysis and confirmed by transmission electron
microscope imaging. Scanning electron microscopy images showed the creation of
grain boundaries after proton irradiation. A higher degree of surface
deformation was detected with lower irradiation energies through atomic force
microscopy. Inter-defect distance is increased with the increase in proton
energy irradiation as estimated by transmission electron microscopy imaging.
Raman spectroscopy reveals negligible structural changes in the crystal quality
after the irradiation. These deformation damages due to proton irradiation are
insignificant at the MoS2 layer. Based on the overall influence of low energy
proton irradiation on the material characteristics, ML-MoS2 materials can be
considered robust and reliable building blocks for 2D material based devices
for space applications.
