Effect of Oxygen Adsorption on Electrical and Thermoelectrical Properties of Monolayer <mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML" display="inline" overflow="scroll"><mml:msub><mml:mrow><mml:mi>Mo</mml:mi><mml:mi mathvariant="normal">S</mml:mi></mml:mrow><mml:mn>2</mml:mn></mml:msub></mml:math>
Swarup Deb, Pritam Bhattacharyya, Poulab Chakrabarti, Himadri Chakraborti, K. Das Gupta, Alok Shukla, Subhabrata Dhar
Abstract
The electrical and thermoelectrical properties of strictly monolayer ${\mathrm{Mo}\mathrm{S}}_{2}$ films, grown using a microcavity-based CVD growth technique, are studied under diverse environmental and annealing conditions. The resistance of a monolayer ${\mathrm{Mo}\mathrm{S}}_{2}$ device fabricated on an as-grown continuous single-layer film is found to be reduced by about six orders of magnitude upon annealing in vacuum at 525 K. The Seebeck coefficient of the layer is also reduced by almost an order of magnitude upon annealing. When the sample is exposed to an oxygen atmosphere, these parameters return to their previous values. It is found that the electron concentration, the mobility, and the thermoelectric power of the material can be varied significantly by annealing. Once a particular resistive state is established, it remains unchanged as long as the layer is not exposed to an oxygen environment. This may offer a unique way to control doping in the material provided an effective encapsulation method is devised. Such control is an important step forward for device applications. The effect is attributed to the passivation of disulfur-vacancy donors present in the ${\mathrm{Mo}\mathrm{S}}_{2}$ film by physisorbed oxygen molecules. Band-structure calculations using density-functional theory are carried out, the results of which validate this picture.