This is a schematic of the light emission from a single crystal monolayer of a tungsten diselenide flake on a gold substrate. Part of the triangular flake rests on the patterned region of the substrate consisting of sub-20nm-wide trenches. Image: Andrew T. S. Wee.
This is a schematic of the light emission from a single crystal monolayer of a tungsten diselenide flake on a gold substrate. Part of the triangular flake rests on the patterned region of the substrate consisting of sub-20nm-wide trenches. Image: Andrew T. S. Wee.

A team led by researchers from the National University of Singapore (NUS) has developed a method to enhance the photoluminescence efficiency of tungsten diselenide, a two-dimensional (2D) semiconductor. This could pave the way for the application of such semiconductors in advanced optoelectronic and photonic devices.

Tungsten diselenide is a single-molecule-thick semiconductor that is part of an emerging class of materials called transition metal dichalcogenides (TMDCs), which have the ability to convert light into electricity and vice versa. This makes TMDCs strong potential candidates for use in optoelectronic devices such as thin film solar cells, photodetectors, flexible logic circuits and sensors. Unfortunately, however, the atomically-thin structure of tungsten diselenide reduces its absorption and photoluminescence properties, thereby limiting its practical applications.

Now, by incorporating monolayers of tungsten diselenide on gold substrates with nanosized trenches, the research team, led by Andrew Wee in the Department of Physics at the NUS Faculty of Science, successfully enhanced the nanomaterial’s photoluminescence by up to 20,000-fold. They did this by taking advantage of collective oscillations of electrons, known as plasmons, on the surface of the gold.

“This is the first work to demonstrate the use of gold plasmonic nanostructures to improve the photoluminescence of tungsten diselenide, and we have managed to achieve an unprecedented enhancement of the light absorption and emission efficiency of this nanomaterial,” said Wang Zhuo, a PhD candidate from the NUS Graduate School for Integrative Sciences and Engineering (NGS) and first author of a paper in Nature Communications describing the work.

Elaborating on the significance of the novel method, Wee said: “The key to this work is the design of the gold plasmonic nanoarray templates. In our system, the resonances can be tuned to be matched with the pump laser wavelength by varying the pitch of the structures. This is critical for plasmon coupling with light to achieve optimal field confinement.”

This novel method, developed in collaboration with researchers from the Singapore University of Technology and Design and Imperial College London in the UK, also opens up a new platform for investigating the electrical and optical properties of systems of gold with tungsten diselenide. Moving forward, the research team will further investigate the effectiveness of the lateral gold plasmon in enhancing the second harmonic generation and electroluminescence of TMDCs. They will also investigate these effects in other 2D TMDCs with different band gaps, which are expected to show different interaction mechanisms.

This story is adapted from material from the National University of Singapore, with editorial changes made by Materials Today. The views expressed in this article do not necessarily represent those of Elsevier. Link to original source.