Nanobelts see light

24 July 2014. NUS professors demonstrate visible-light photodetectors usingmolybdenum oxide nanobelts.

A team led by Professor CHEN Wei from the Departments of Chemistry and Physics in NUS has succeeded to fabricate a high-performance photodetectorbased on molybdenum oxide (MoO3) nanobelts that responds to visible light (see Figure). Nanobelts are a member of the zoo of nanomaterials where the length of the material is much longer than its width, which in turn is much wider than its thickness. The strong enhancement in response to visible light was achieved by baking the material in hydrogen gas. This causes gap states to form in the MoO3 nanobelts. Normally the material only absorbs ultraviolet light, because of its large bandgap. However when gap states within material, electronic transitions can occur from these states to the bandedges to give rise to absorption of visible light. This also improves the electrical conductance of the nanobelt.


“This research opens a way to extend the photoresponsivity range of wide bandgap transition metal oxide nanomaterials into the visible light region,” says Wei, “which can open new applications in optoelectronic devices and photocatalysis.” 




Figure 1. (a) Schematic illustration of the MoO3 nanobelt device. (b) Time dependent photocurrent of the MoO3 device before and after annealing, when illuminated periodically with 660-nm laser light. (c) Plot of the responsivity and external quantum efficiency versus light wavelength. (d) Schematic diagram of the energy level alignment for MoO3 film before and after annealing. (Image credit: CHEN Wei)


Xiang D, Han C, Zhang JL, Chen W. “Gap States Assisted High Performance MoO3 Nanobelt Photodetector with Wide Spectrum Response.” Scientific Reports 4 (2014) 4891.