Radiation damage and defect dynamics in 2D WS2: a low-voltage scanning transmission electron microscopy study

Electron irradiation effects in transmission electron microscopy: Random displacements and collective migrations.

Bond-free integration of two-dimensional (2D) materials yields van der Waals (vdW) heterostructures with exotic optical and electronic properties. Manipulating the splitting and recombination of photogenerated electron–hole pairs across the vdW interface is essential for optoelectronic applications. Previous studies have unveiled the critical role of defects in trapping photogenerated charge carriers to modulate the photoconductive gain for photodetection. However, the nature and role of defects in tuning interfacial charge carrier dynamics have remained elusive. Here, we investigate the nonequilibrium charge dynamics at the graphene–WS2 vdW interface under electrochemical gating by operando optical-pump terahertz-probe spectroscopy. We report full control over charge separation states and thus photogating field direction by electrically tuning the defect occupancy. Our results show that electron occupancy of the two in-gap states, presumably originating from sulfur vacancies, can account for the observed rich interfacial charge transfer dynamics and electrically tunable photogating fields, providing microscopic insights for optimizing optoelectronic devices.

https://pubs.acs.org/doi/pdf/10.1021/acs.nanolett.2c04795

Reversible Electrical Control of Interfacial Charge Flow across van der Waals Interfaces

Abstract Localization due to disorder has been one of the most intriguing theoretical concepts that evolved in condensed matter physics. Here, we expand the theory of localization by considering two types of disorders at the same time, namely, the original Anderson’s disorder and the structural defect disorder, which has been suggested to be a key component in recently discovered two-dimensional amorphous materials. While increasing the degree of both disorders could induce localization of wavefunction in real space, we find that a small degree of structural defect disorder can significantly enhance the localization. As the degree of structural defect disorder increases, localized states quickly appear within the extended phase to enter a broad crossover region with mixed phases. We establish two-dimensional diagrams for the wavefunction localization and conductivity to highlight the interplay between the two types of disorders. Our theoretical model provides a comprehensive understanding of localization in two-dimensional amorphous materials and highlights the promising tunability of their transport properties. 

Regulating Anderson Localization with Structural Defect Disorder

Hydrovoltaic, which converts the energy of water into electrical energy, is a regenerative energy harvesting method that utilizes the earth's sufficient water resources. Electricity production relies on water molecules interaction with functional materials. Strategies like surface modification, structure engineering, and ion doping can be used to increase output performance. We present an electric field-assisted laser-induced plasma deposition method to prepare WO3-x/WSe2 sponges for water-induced electricity generation. By adjusting the electric field strength, we are able to control the porosity, Se vacancies, and O doping of the sponges. These modifications directly impact the performance of water-induced electricity generation by altering the streaming potential and ion diffusion gradient of sponge structures. The prepared WO3-x/WSe2 sponges can participate in the complete water cycle to achieve the energy harvesting of different forms of water, obtaining droplet-induced voltages of 65.4 mV and moisture-induced voltages of 207.1 mV. This overcomes the limitation of single-stimulation water-induced electricity systems that require specific conditions. When exposed to Sunlight, the photosensitive properties of WO3-x and WSe2 can lead to a current up to 7 times higher than that produced in darkness. Furthermore, this research can be expanded to develop other two-dimensional materials and be utilized in various applications, such as the self-powering of flexible and wearable electronic devices. 

Well-controlled preparation of WO3-x/WSe2 sponges by electric field-assisted laser-induced plasma deposition for hydrovoltaic

A unique dense network of multi-member-ring round hole defects is formed in monolayer WSe${}_{2}$ from the evolution of multivacancies by suitable control of a scanning focused electron beam, whereas the same process leads predominantly to chalcogen-vacancy line defect array in other trigonal-prismatic transition metal dichalcogenide (TMDC) monolayers. Density functional theory (DFT) calculations track the formation of the observed complex multivacancy structures and find that the underlying atomic-scale processes are quasi-thermodynamic, which elaborates the formation mechanism of dense round hole defects in WSe${}_{2}$ monolayers. The high-density round holes in WSe${}_{2}$ hold promise for novel applications such as atomic and molecular sieving.

Preferential hole defect formation in monolayer W Se 2 by electron-beam irradiation

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Preferential hole defect formation in monolayer W Se 2 by electron-beam irradiation