Single-Layer Tungsten Diene Used as SPEs in Quantum Optics

Scientists have discovered that the oxygen gaps in single-layer tungsten diene (WSe2) enables it to be used as single-photon emitters (SPEs) in quantum optics (QO).

In recent years, atomic thin honeycomb lattices of two-dimensional (2-D) materials have been found in experiments. SPEs emit light in the form of a single particle or photon, playing an important role in quantum optics and information processing, and they are developed using two-dimensional materials such as tungsten diene, providing flexibility for potential device and circuit integration in semiconductor manufacturing environments.

However, SPEs’ property in tungsten diene hasn’t been found yet, which hinders their potential applications in quantum applications. Professor Yingguo Su at the Department of Physics and the research groups of the National University of Singapore have determined that single-photon emission from localized exciton state of single-layer tungsten diene is due to the oxygen gap present in the single-layer two-dimensional material.

The research team combined theoretical calculations and experimental methods to attain results. With the further understanding of single-photon sources, this discovery will help to develop SPEs with two-dimensional materials and improve their emission performance. In the study, the team did not find a density functional theory to calculate the inherent point defects of the tungsten diene material and the correlation between spectra. They focused on the oxygen-related point defects associated with tungsten diene material. These defects could be easily embedded into the material during the synthesis process or by environmental passivation.

Through the elimination process, it is found that defects associated with the oxygen gap in the crystal lattice are most likely to produce localized exciton states at experimentally observed spectral positions. This study investigated point defects in monolayer tungsten diene and predicted property and energy of excitons at defect locations.

The study used first-principles calculations, scanning tunneling microscopy (STM) and scanning transmission electron microscopy experiments to show that there are no W vacancies in two-dimensional tungsten diene grown in CVD. The researchers predicted that there are O-passivated selenium vacancies (OSe) and interstitial (Oins) in two-dimensional tungsten diene, which may be due to O2 dissociation on the selenium vacancies or due to CVD growth. These defects made the STM image fit well with the experimental results. Due to the experimental observation of single-photon emission (SPE) of two-dimensional WSe2, the optical properties of two-dimensional midpoint defects are very important.

The point defect is a necessary condition for the exciton to be positioned on the length scale, enabling the photon to emit one at a time. Using the latest gwt-bethe-salpeter equation, it is predicted that in previous experiments, only Oins defects would generate localized excitons in the energy range of the SPE, making them likely to be the source of previously observed SPE. No other point defects (OSe, Se vacancies, W vacancies, and SeW inverted) produce local excitons in the same energy range.

The research proposes a method for realizing SPEs in related two-dimensional materials and points out to the experimenters the other energy ranges for achieving single-photon emission from single-layer tungsten diene in quantum optics.

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