Reversible crystalline-to-amorphous phase transformation in monolayer MoS₂ under grazing ion irradiation

Abstract

By combining scanning tunneling microscopy, low-energy electron diffraction, photoluminescence and Raman spectroscopy experiments with molecular dynamics simulations, a comprehensive picture of the structural and electronic response of a monolayer of MoS2 to 500 eV Xe+ irradiation is obtained. The MoS2 layer is epitaxially grown on graphene/Ir(1 1 1) and analyzed before and after irradiation in situ under ultra-high vacuum conditions. Through optimized irradiation conditions using low-energy ions with grazing trajectories, amorphization of the monolayer is induced already at low ion fluences of ions cm−2 and without inducing damage underneath the MoS2 layer. The crystalline-to-amorphous transformation is accompanied by changes in the electronic properties from semiconductor-to-metal and an extinction of photoluminescence. Upon thermal annealing, the re-crystallization occurs with restoration of the semiconducting properties, but residual defects prevent the recovery of photoluminescence.

Impact of S-Vacancies on the Charge Injection Barrier at the Electrical Contact with the MoS2 Monolayer

“…The above findings demonstrate that our sputtering method is selective toward S-vacancy creation within the MoS 2 ML structure without the concurrent removal of Mo atoms, in contrast with previous sputtering-based defect engineering methods. , In particular, as the S atoms are removed by controlled ion bombardment, the MoS 2 phase and corresponding XPS signal are gradually converted into MoS 2– x substoichiometric ones, thus leaving the total Mo 3d XPS area almost unaffected. Selective S atom removal by ion sputtering was also reported in a recent scanning probe measurement on MoS 2 ML, as conducted in a similar grazing angle condition by using lower energy (500 eV) but higher atomic mass xenon atoms . While entirely deduced from XPS peak fitting results, the S-vacancy selectivity of the present defect engineering method is also supported by the difference analysis of Mo 3d XPS raw data (Figure S1 in Supporting Information), showing gradual “spectral weight transfer” toward the low binding energy peaks’ region as the sputtering time increases.…”

“…Finally, we note that the sample amorphization upon sputtering is supported by a recent scanning probe investigation on a MoS 2 ML where S-vacancies were created by sputtering in similar grazing incident configuration by using lower energy (0.5 keV) but higher mass xenon ions. According to the above results and considerations, we then exclude the interpretation of the tailing as the valence band of MoS 2– x material.…”

“…Ar sputtering were conducted at 297 K with an ion energy of 3 keV and an incident angle with respect to the normal to the MoS 2 plane of 75°. With this experimental setup, theoretical simulations predict Mo sputtering yield to be negligible, while S-sputtering continues to occur albeit at a reduced yield (∼3 times less than the maximum value). , This enhances the selectivity toward S-vacancy creation, which is critical for the present study. Furthermore, the reduced sputtering rate allows for better control of the irradiation process by controlling the exposure time.…”

Vertically Coupling ZnO Nanorods onto MoS2 Flakes for Optical Gas Sensing

“…Plasma sputtering may induce the amorphization of MoS 2, resulting in the disappearance of the two E 2g and A 1g Raman modes [41,42]. The Raman spectra of an MoS 2 flake which underwent the ZnO deposition steps of sample G did not show appreciable differences, as reported in Figure 4b, demonstrating that the structure of the 2D MoS 2 is preserved.…”

Ultra-broadband photon harvesting in large-area few-layer MoS2 nanostripe gratings

“…In order to address this question, different approaches have been recently developed for the growth of large-area 2D layers 26,41,42 that readily enable conformal nanopatterning. [43][44][45] So far, large-area flat-optics configurations based on 2D semiconductor layers have not been reported, although this represents a crucial step for the implementation of real-world photon harvesting applications in 2D TMDs for broadband photo-conversion and/or -detection.…”