Nearly 90% Circularly Polarized Emission in Monolayer WS 2 Single Crystals by Chemical Vapor Deposition

Lim

et al. 2020

Small

Valley polarization is among the most critical attributes of atomically thin materials. However, increasing contrast from monolayer transition metal dichalcogenides (TMDs) has so far been challenging. In this work, a large degree of circular polarization up to 45% from a monolayer WS2 is achieved at room temperature by using a single chiral plasmonic nanoparticle. The increased contrast is attributed to the selective enhancement of both the excitation and the emission rate having one particular handedness of the circular polarization, together with accelerated radiative recombination of valley excitons due to the Purcell effect. The experimental results are corroborated by the optical simulation using the finite‐difference time‐domain (FDTD) method. Additionally, the single chiral nanoparticle enables the observation of valley‐polarized luminescence with a linear excitation. The results provide a promising pathway to enhance valley contrast from monolayer TMDs and utilize them for nanophotonic devices.

Section: Figurementioning

confidence: 99%

A Single Chiral Nanoparticle Induced Valley Polarization Enhancement

Lim

et al. 2020

Small

“…Such alternating defect domains in h-WS 2 monolayers have been widely studied in terms of their defect density, carrier transport, work function, and optical properties because of their unique properties inside a single crystal. [21][22][23][24] Notably, these distinctive defect domains can provide clues to understanding the macroscopic origin of material properties determined by the native defects in CVD-grown TMDs. Moreover, understanding the formation mechanism of these defect domains can pave the way to engineering native defects and intrinsic doping properties during growth.…”

Section: Introductionmentioning

confidence: 99%

Growth Mechanism of Alternating Defect Domains in Hexagonal WS₂ via Inhomogeneous W‐Precursor Accumulation

Yun

Lee

et al. 2020

Small

While a hexagonal WS2 monolayer, grown by chemical vapor deposition, exhibits distinctive patterns in photoluminescence mapping, segmented with alternating S‐vacancy (SV) and W‐vacancy (WV) domains in a single crystal, the formation mechanism for native alternating defect domains remains unresolved to date. Here, the formation mechanism of alternating defect domains in hexagonal WS2 via the precursor accumulation model is experimentally elucidated. A triangular WS2 seed is initially formed, followed by a hexagonal flake. Alternating W‐rich (SV) and W‐deficient (WV) domains are constructed in hexagonal WS2 flake, which is confirmed by confocal photoluminescence mapping and secondary ion mass spectroscopy. This is explained by the accumulation or scarcity of W‐precursors at the edge of the WS2 flake. The W‐precursors accumulate near the edges of the initial triangular WS2 seed over time, while they are deficient near the corners of the triangular WS2, eventually forming WV domains in the truncated hexagonal domains. The heterogeneous accumulation becomes more prominent in the presence of H2 gas through desorption of the W‐precursors.

“…So far, mechanical exfoliation, 18‐22 liquid exfoliation, 23‐26 and vapor phase growth 5,27‐34 are commonly utilized strategies for the preparation of the ultrathin 2D TMDCs materials. The obtained 2D TMDCs materials by different methods possess various structures, including size, number of layers, morphologies, phases, doping, defects, and grain boundaries, which have a crucial influence on their properties 35,36 .…”

Section: Introductionmentioning

confidence: 99%

Synthesis of two‐dimensional transition metal dichalcogenides for electronics and optoelectronics

Xiao

Zeng

et al. 2020

InfoMat

114

Tremendous efforts have been devoted to preparing the ultrathin two‐dimensional (2D) transition‐metal dichalcogenides (TMDCs) and TMDCs‐based heterojunctions owing to their unique properties and great potential applications in next generation electronics and optoelectronics over the past decade. However, to fulfill the demands for practical applications, the batch production of 2D TMDCs with high quality and large area at the mild conditions is still a challenge. This feature article reviews the state‐of‐the‐art research progresses that focus on the preparation and the applications in electronics and optoelectronics of 2D TMDCs and their van der Waals heterojunctions. First, the preparation methods including chemical and physical vapor deposition growth are comprehensively outlined. Then, recent progress on the application of fabricated 2D TMDCs‐based materials is revealed with particular attention to electronic (eg, field effect transistors and logic circuits) and optoelectronic (eg, photodetectors, photovoltaics, and light emitting diodes) devices. Finally, the challenges and future prospects are considered based on the current advance of 2D TMDCs and related heterojunctions.