Massachusetts Institute of Technology (MIT) researchers have developed a technique for building molybdenum disulfide (MoS2) light emitters tuned to different frequencies, an essential requirement for optoelectronic chips. The researchers also have described a theoretical characterization of the physical phenomena that explain the emitters’ tunability, which could aid in the search for even better candidate materials. The researchers tuned their emitters by depositing two layers of MoS2 on a silicon substrate, in which top layers rotate relative to the lower layers based on the wavelength of the emitted light. The researchers say the rotation of the layers relative to each other sufficiently changes the crystal geometry to preserve the band gap, and they were able to accurately characterize the relationship between the geometries of the rotated layers and the wavelength and the intensity of the light emitted. “For different twisted angles, the actual separation between the two layers is different, so the coupling between the two layers is different,” notes MIT’s Shengxi Huang. “This interferes with the electron densities in the bilayer system, which gives you a different photoluminescence.” He notes this hypothetical characterization should simplify prediction of whether other transition-metal compounds will display similar light emission.
More info here: MIT News (09/17/14) Larry Hardesty