Disentangling oxygen and water vapor effects on optoelectronic properties of monolayer tungsten disulfide
- 1 April 2020
- journal article
- research article
- Published by Royal Society of Chemistry (RSC) in Nanoscale
- Vol. 12 (15), 8344-8354
- https://doi.org/10.1039/c9nr09326e
Abstract
By understanding how the environmental composition impacts the optoelectronic properties of transition metal dichalcogenide monolayers, we demonstrate that simple photoluminescence (PL) measurements of tungsten disulfide (WS2) monolayers can differentiate relative humidity environments. In this paper, we examine the PL and photoconductivity of chemical vapor deposition grown WS2 monolayers under three carefully controlled environments: inert gas (N2), dry air (O2 in N2), and humid nitrogen (H2O vapor in N2). The WS2 PL is measured as a function of 532 nm laser power and exposure time and can be decomposed into the exciton, trion, and lower energy state(s) contributions. Under continuous illumination in either O2 or H2O vapor environment, we find dramatic (and reversible) increases in PL intensity relative to the PL in an inert environment. The PL bathochromically shifts in an O2 environment and is dominated by increased trion emission and diminished exciton emission. In contrast, the WS2 PL increase in a H2O environment results from an overall increase in emission from all spectral components where the exciton contribution dominates. The drastic increases in PL are anticorrelated with corresponding decreases in photoconductivity, as measured by time-resolved microwave conductivity. The results suggest that both O2 and H2O react photochemically with the WS2 monolayer surface, modifying the optoelectronic properties, but do so via distinct pathways. Thus, we use these optoelectronic differences to differentiate the amount of humidity in the air, which we show with 0%, 40%, and 80% relative humidity environments. This deeper understanding of how ambient conditions impact WS2 monolayers enables novel humidity sensors as well as a better understanding of the correlation between TMDC surface chemistry, light emission, and photoconductivity. Moreover, these WS2 measurements highlight the importance of considering the impact of the local environment on reported results.Keywords
Funding Information
- Institute for Basic Science (IBS-R011-D1)
- Basic Energy Sciences (DE-AC36-08GO28308)
This publication has 71 references indexed in Scilit:
- Modification of WS2 nanosheets with controllable layers via oxygen ion irradiationApplied Surface Science, 2018
- Water-Soluble 2D Transition Metal Dichalcogenides as the Hole-Transport Layer for Highly Efficient and Stable p–i–n Perovskite Solar CellsACS Applied Materials & Interfaces, 2017
- Modulating Electronic and Optical Properties of Monolayer MoS2 Using Nonbonded Phthalocyanine MoleculesThe Journal of Physical Chemistry C, 2017
- Improvement of Gas-Sensing Performance of Large-Area Tungsten Disulfide Nanosheets by Surface FunctionalizationACS Nano, 2016
- Atomically thin two-dimensional materials as hole extraction layers in organolead halide perovskite photovoltaic cellsJournal of Power Sources, 2016
- Modulating Optoelectronic Properties of Two-Dimensional Transition Metal Dichalcogenide Semiconductors by Photoinduced Charge TransferACS Nano, 2016
- High-mobility three-atom-thick semiconducting films with wafer-scale homogeneityNature, 2015
- Drastic Layer‐Number‐Dependent Activity Enhancement in Photocatalytic H2 Evolution over nMoS2/CdS (n ≥ 1) Under Visible LightAdvanced Energy Materials, 2015
- Deep-ultraviolet-light-driven reversible doping of WS2 field-effect transistorsNanoscale, 2014
- Chemically Driven Tunable Light Emission of Charged and Neutral Excitons in Monolayer WS2ACS Nano, 2014