Oxidation of Monolayer WS in Ambient is a Photoinduced Process
arXiv:1906.00375 · doi:10.1021/acs.nanolett.9b01599
Abstract
We have studied the ambient air oxidation of chemical vapor deposition (CVD) grown monolayers of the semiconducting transition metal dichalcogenide (S-TMD) WS using optical microscopy, laser scanning confocal microscopy (LSCM), photoluminescence (PL) spectroscopy, and atomic force microscopy (AFM). Monolayer WS exposed to ambient conditions in the presence of light (typical laboratory ambient light for weeks, or typical PL spectroscopy map), exhibits damage due to oxidation which can be detected with the LSCM and AFM; though may not be evident in conventional optical microscopy due to poorer contrast and resolution. Additionally, this oxidation was not random, and correlated with 'high-symmetry' and red-shifted areas in the PL spectroscopy map - areas thought to contain a higher concentration of sulfur vacancies. In contrast, samples kept in ambient and darkness showed no signs of oxidation for up to 10 months. Low-irradiance/fluence experiments showed that samples subjected to excitation energies at or above the trion excitation energy (532 nm/2.33 eV and 660 nm/1.88 eV) oxidized in as little as 7 days, even for irradiances and fluences eight and four orders of magnitude lower (respectively) than previously reported. No significant oxidation was observed for 760 nm/1.63 eV light exposure, which lies below the trion excitation energy in WS. The strong wavelength dependence and apparent lack of irradiance dependence suggests that ambient oxidation of WS is initiated by photon-mediated electronic band transitions, that is, photo-oxidation. These findings have important implications for prior, present and future studies concerning S-TMDs measured, stored or manipulated in ambient conditions.
35 pages, 3 figures, 1 table, submitted to ACS Nano Letters
References in corpus (8)
- Electric Field Effect in Atomically Thin Carbon Films
- Two Dimensional Atomic Crystals
- Valley polarization in MoS2 monolayers by optical pumping
- Exciton Binding Energy of Monolayer WS2
- Measurement of high exciton binding energy in the monolayer transition-metal dichalcogenides WS2 and WSe2
- Strain-tunable magnetic and electronic properties of monolayer CrI3
- The Effect of Preparation Conditions on Raman and Photoluminescence of Monolayer WS2
- Reliable Synthesis of Large-Area Monolayer WS2 Single Crystals, Films, and Heterostructures with Extraordinary Photoluminescence Induced by Water Intercalation