Search

The optical response of semiconducting monolayer transition-metal dichalcogenides (TMDCs) is dominated by strongly bound excitons that are stable even at room temperature. However, substrate-related effects such as screening and disorder in currently available specimens mask many anticipated physical phenomena and limit device applications of TMDCs. Here, we demonstrate that that these undesirable effects are strongly suppressed in suspended devices. Extremely robust (photogain > 1,000) and fast (response time < 1 ms) photoresponse allow us to study, for the first time, the formation, binding energies, and dissociation mechanisms of excitons in TMDCs through photocurrent spectroscopy. By analyzing the spectral positions of peaks in the photocurrent and by comparing them with first-principles calculations, we obtain binding energies, band gaps and spin-orbit splitting in monolayer TMDCs. For monolayer MoS2, in particular, we obtain an extremely large binding energy for band-edge excitons, Ebind ⩾ 570 meV. Along with band-edge excitons, we observe excitons associated with a van Hove singularity of rather unique nature. The analysis of the source-drain voltage dependence of photocurrent spectra reveals exciton dissociation and photoconversion mechanisms in TMDCs. [ABSTRACT FROM AUTHOR]

A spectrometer for optical detection of the electron spin resonance (ESR) spectra of short-lived radical-ion pairs produced by ionizing radiation is described. The setup is based on a standard ESR spectrometer equipped with an adapter for optical detection of spectra and a microwave amplifier. In a solution of n-terphenyl in alkanes, the spin-locking effect has been observed. At a microwave power of 10 W, the microwave magnetic induction is 0.5 mT. [ABSTRACT FROM AUTHOR]