Lasers help heal atomic defects

2 Jul 2015 NUS physicists have healed the atomic defects in tungsten diselenide (WSe₂) using a focused laser beam technique.

Semiconducting transition metal dichalcogenides (TMDs) are amongst the most promising two-dimensional materials. In monolayer form, Mo and W dichalcogenides become direct gap semiconductors and therefore attractive for optical and photoelectrical applications. However, due to their compound nature, TMDs are usually chalcogen-deficient. This means the defects of Se vacancies are a common issue that blocks the implementation of WSe₂ monolayers in practical applications. A team led by Prof Chorng Haur SOW, Prof A. H. Castro Neto and Dr Junpeng LU from the Department of Physics in NUS has devised a straightforward method to resolve this problem.

This method is based on a focused laser beam. Using the focused laser beam to treat the WSe₂ monolayer in air environment, the oxygen in atmosphere could be forced to fill the Se vacancies. After the oxygen substitution, the defects energy levels were removed.

The laser healed WSe₂ monolayer was fabricated into electronic and optoelectronic devices. As compared with the devices based on the pristine (non-healed) WSe₂ monolayer, both the conductivity and photoconductivity were found to increased more than two orders. The results were published in the journal Nano Letters.

The figure depicts that the Se vacancies can be substituted by oxygen atoms driven by focused laser beam. [Image credit: Junpeng Lu]

Reference

Lu JP, Carvalho A, Chan XK, Liu HW, Liu B, Tok ES, Loh KP, Neto AHC, Sow CH. “Atomic Healing of Defects in Transition Metal Dichalcogenides.” Nano Lett. 15 (2015) 3524.