27 February 2017

Tunable, 2D semiconductors could be tomorrow's nano-sensors

(a) 2D excitons in monolayer tungsten di-selenide, (WSe2) (b) The experiment: monolayer WSe2 is affixed to an optical fiber and encapsulated. (a) 2D excitons in monolayer tungsten di-selenide, (WSe2) (b) The experiment: monolayer WSe2 is affixed to an optical fiber and encapsulated.

Scientists discovered how to tune the optical properties of atomically-thin semiconductors, which will aid the design of future microscopic light sensors.

First, some background

The "wonder material" graphene, a version of carbon that is only one atom thick, boasts strength, flexibility and other promising properties. But in addition to graphene, there are hundreds of other atomically-thin, 2D materials. And best of all, some are bona fide semiconductors — the stuff that computer chips and LEDs are made from — that are incredibly efficient light absorbers.

What did scientists discover?

Scientists examined the optical and electronic properties of 2D semiconductors. They suspected that, because of the materials’ thinness, those properties would be strongly affected by nearby materials. They discovered that, in fact, the opto-electronic properties of these semiconductors do depend on the surrounding materials.

Why is this important?

Amazingly, these very thin semiconductors can absorb up to 20 percent of incident light. This property makes them promising materials for future nano-sensors, or extremely tiny light sensors, and knowing how to tune their absorption properties could be extremely useful.

When a particle of light (a photon) is absorbed by a semiconductor, it excites a single, negatively-charged electron to a higher energy level in the crystal. This leaves behind a positively charged "hole" in the original energy level. This electron-hole pair, called an exciton, is bound together because of their opposite charges. The binding in 2D materials is very strong because, being atomically thin, there is very little surrounding material to mitigate, or "screen," this attraction.

Scientists have shown that when materials with different screening properties are placed around a 2D semiconductor, the size and energy of these electron-hole pairs changes. They grow bigger and are less strongly bound together. This allows them to tune the absorption properties of 2D semiconductors by design.

Who did the research?

Andreas V. Stier1, Nathan P. Wilson2, Genevieve Clark2, Xiaodong Xu2, Scott A. Crooker1

1National High Magnetic Field Laboratory - Los Alamos National Laboratory; 2University of Washington

Why did they need the MagLab?

Scientists needed the very high magnetic fields of the MagLab because the electron-hole pairs are tiny (about 1 nanometer) and the effect they were looking for depends quadratically on the magnetic field strength.


This research was conducted in the 65 T pulsed magnet at the MagLab's Pulsed Field Facility.

Details for scientists


This research was funded by the following grants: G.S. Boebinger (NSF DMR-1157490); N.P. Wilson, G. Clark & X.Xu (DE-SC0008145&SC0012509)

For more information, contact Chuck Mielke.


  • Research Area: Condensed Matter Technique Development, Semiconductors
  • Research Initiatives: Materials
  • Facility / Program: Pulsed Field
  • Year: 2017
Last modified on 27 February 2017