Fluorescent concentric triangles

19 Dec 2016. NUS physicists have discovered fluorescent concentric triangles in an atomically thin layer of semiconductor for potential optoelectronic applications.

Tungsten disulfide (WS₂) is a new class of two-dimensional (2D) material with potential applications for novel photonic and optoelectronic devices. Recently, different 2D semiconductors were combined together to form heterojunctions to develop new optical properties which can enhance the performance of optoelectronic devices. However, there are many challenges in fabricating heterojunctions, which involve putting two different materials together. Making such functional junctions in a homogeneous material (known as homojunctions) is a more desired approach.

A team led by Prof Chorng Haur SOW from the Department of Physics, NUS devised a method to fabricate in-plane periodical and lateral homojunctions in a WS₂ monolayer.

Such lateral homojunctions produce an alternate dark and bright band in fluorescence emission. This gives rise to a beautiful triangular WS₂ monolayer with concentric fluorescent triangles. The fluorescent patterning is a result of the lateral homojunctions formed directly in the monolayer by a one-step growth process.Such lateral homojunctions are formed by alternating monolayers of WS₂ which are either sulphur atom-rich or sulphur atom-poor.This is the first report of such fluorescent concentric triangles in as grown 2D semiconductors.

The discovery of these concentric fluorescent patterns is exciting as it could open up new forms of optoelectronic/ photonic functionality and applications in devices.

Figure shows the schematic diagram of the atomic structure of WS₂ monolayer with sulphur vacancies (left), optical image (centre) and fluorescence microscopy image of a typical WS₂ monolayer (right).

Reference

Liu HW; Lu JP*; Ho K; Hu ZL; Dang ZY; Carvalho A*; Tan HR; Tok ES; Sow CH*, “Fluorescence Concentric Triangles: A Case of Chemical Heterogeneity in WS2 Atomic Monolayer” NANO LETTERS Volume: 16 Issue: 9 Pages: 5559-5567 DOI: 10.1021/acs.nanolett.6b02111 Published: 2016