arXiv subjects

Wanfu Shen

Publications and source records attributed to Wanfu Shen.

3 recordsLinked to original sources

arXiv2026

Charge-conserving creation and annihilation of topological phase singularities in atomically thin semiconductors

Atomically thin transition metal dichalcogenides provide a promising material platform for optical phase manipulation, as rapid variations in their dielectric functions can give rise to topological phase singularities (PSs). However, PS evolution while preserving topological charge conservation has not yet been investigated in exciton enabled PS systems. Here, using atomically thin MoS2 films on sapphire as a model system, we theoretically and experimentally demonstrate that the evolution of dielectric dispersion determines the creation, trajectory, merging, and annihilation of optical PSs under topological charge conservation. By varying the MoS2 film thickness, we experimentally realize this evolution through the gradual shrinking of the high energy n-k dispersion loop, which modifies its intersection with the zero reflection condition. Our results provide a general strategy for exploring and manipulating topological optical states.

cond-mat.mtrl-sci↗

arXiv2020

Substrate Induced Optical Anisotropy in Monolayer MoS$_2$

In-plane optical anisotropy has been detected from monolayer MoS$_2$ grown on a-plane (11-20) sapphire substrate in the ultraviolet-visible wavelength range. Based on the measured optical anisotropy, the energy differences between the optical transitions polarized along the ordinary and extraordinary directions of the underlying sapphire substrate have been determined. The results corroborate comprehensively with the dielectric environment induced modification on the electronic band structure and exciton binding energy of monolayer MoS$_2$ predicted recently by first principle calculations. The output of this study proposes the symmetry as a new degree of freedom for dielectric engineering of the two-dimensional materials.

physics.app-ph↗

arXiv2018

Direct observation of the CVD growth of monolayer MoS$_2$ using $in-situ$ optical spectroscopy

Real-time monitoring is essential for understanding and eventually precise controlling of the growth of two dimensional transition-metal dichalcogenides (2D TMDCs). However, it is very challenging to carry out such kind of studies on chemical vapor deposition (CVD). Here, we report the first real time $in-situ$ study on the CVD growth of the 2D TMDCs. More specifically, CVD growth of molybdenum disulfide (MoS$_2$) monolayer on sapphire substrates has been monitored $in-situ$ using differential transmittance spectroscopy (DTS). The growth of the MoS$_2$ monolayer can be precisely followed by looking at the evolution of the characteristic optical features. Consequently, a strong correlation between the growth rate of MoS$_2$ monolayer and the temperature distribution in the CVD reactor has been revealed. Our result demonstrates the great potential of the real time $in-situ$ optical spectroscopy for the realization of the precisely controlled growth of 2D semiconductor materials.

cond-mat.mtrl-sci↗