Luminous 2D semiconductors
A literally brighter future beckons with a recent pioneering method that raises the photoluminescence of a two-dimensional (2D) semiconductor by thousands of times. The seminal work led by NUS holds exciting promise of applying such semiconductors in advanced optoelectronic and photonic devices including thin-film solar cells, photodetectors, flexible logic circuits, optical fibre communications systems and sensors.
A group of multi-institutional scientists, headed by Physics Professor Andrew Wee of NUS Science, improved the photoluminescence of single-molecule-thick tungsten diselenide by up to 20,000-fold. Using an innovative approach of suspending monolayers of the ultrathin 2D compound onto gold substrates with nanosized trenches, they successfully achieved this amazing feat.
Tungsten diselenide belongs to an emerging class of materials called transition metal dichalcogenides (TMDCs), characterised by the ability to convert light to electricity and vice versa. This unique feature makes them strong candidates for optoelectronic devices that detect and control light. However, these TMDCs have limited practical applications owing to the atomically thin structure that restricts their absorption and photoluminescence properties.
Thus the latest breakthrough, published online in Nature Communications on 6 May, creates new opportunities of applying tungsten diselenide as a novel semiconductor material.
First author of the paper Ms Wang Zhuo, a PhD candidate from the NUS Graduate School for Integrative Sciences and Engineering, said, “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.”
Prof Wee explained, “The key to this work is the design of the gold plasmonic nanoarrays with sub-20nm trenches. Plasmons are collective excitations of electrons in solids that interact strongly with light, and the key to this work is the design of the gold plasmonic nanoarray templates. In our system, the plasmon 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 to facilitate light absorption and emission in tungsten diselenide.”
This original technique developed by the NUS team, together with researchers from the Singapore University of Technology and Design and Imperial College, opens up a fresh perspective for exploring novel electrical and optical properties in the hybrid system of gold with tungsten diselenide.
The investigators plan to examine the effectiveness of the lateral gold plasmon in intensifying the second harmonic generation and electroluminescence of TMDCs. They will also study these effects in other 2D TMDCs with different band gaps, as they are expected to show different interaction mechanisms.
See press release.
