Ultra-thin semiconductors such as monolayer transition metal dichalcogenides (TMDC) and Lead iodide (PbI2) nanosheets exhibits remarkable optical properties due to their reduced dimensionality and crystal symmetry. The visible direct bandgap, robust valley polarisation and strong tunability make them ideal for optoelectronic devices. The unique valley polarisation can also be considered as a new degree of freedom, which enables new opportunities in the field of valleytronics. Manipulating the valley polarisation by the optical method is the key to realise valleytronic devices. However, the atomic thickness limits the light-matter interaction length and efficiency. An important solution to enhance the light-matter interactions, including photoluminescence (PL) and nonlinear emissions from such ultra-thin semiconductors is to couple them to photonic nanostructures.
In this seminar, I will first present the enhanced and polarisation-selective directional PL emission from a monolayer WSe2 coupled to a silicon grating waveguide nanostructure. Next, I will present how to spatially separate the PL originating from the different valleys of the monolayer WSe2 by photonic nanoantennas. Besides PL, I will demonstrate the nonlinear microscopy of several novel ultra-thin semiconductors such as PbI2 nanosheets and InP quantum wells. By using the nonlinear harmonic emission, we can precisely determine their thickness, strain and crystalline orientation with a non-invasive optical method. At last, I will show the tunable nonlinear emissions from TMDC metasurfaces by using nonlinear microscopy techniques.
Meeting ID: 619 402 6562