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463 results on '"Wang, Gaoxue"'

1. A first-principles study of structural, elastic, electronic, and transport properties of Cs2Te

Author

Wang, Gaoxue, Zhang, Jinlin, Huang, Chengkun, Dimitrov, Dimitre A., Alexander, Anna M., and Simakov, Evgenya I

Subjects
Condensed Matter - Materials Science
Abstract

The pursuit to operate photocathodes at high accelerating gradients to increase brightness of electron beams is gaining interests within the accelerator community. Cesium telluride (Cs2Te) is a widely used photocathode material and it is presumed to offer resilience to higher gradients because of its wider band gap compared to other semiconductors. Despite its advantages, crucial material properties of Cs2Te remain largely unknown both in theory and experiments. In this study, we employ first-principles calculations to provide detailed structural, elastic, electronic and transport properties of Cs2Te. It is found that Cs2Te has an intrinsic mobility of 20 cm2/Vs for electrons and 2.0 cm2/Vs for holes at room temperature. The low mobility is primarily limited by the strong polar optical phonon scattering. Cs2Te also exhibits ultralow lattice thermal conductivity of 0.2 W/(m*K) at room temperature. Based on the energy gain/loss balance under external field and electron-phonon scattering, we predict that Cs2Te has a dielectric breakdown field in the range from ~60 MV/m to ~132 MV/m at room temperature dependent on the doping level of Cs2Te. Our results are crucial to advance the understanding of applicability of Cs2Te photocathodes for high-gradient operation.

Published
2024

35. Improved robustness of sequentially deposited potassium cesium antimonide photocathodes achieved by increasing the potassium content towards theoretical stoichiometry.

Author

Guo, Lei, Shiohara, Keisuke, Yamaguchi, Hisato, Wang, Gaoxue, Okabe, Yuki, Nakatake, Masashi, Takakura, Shoichi, Yamamoto, Masahiro, Ogawa, Shuichi, and Takashima, Yoshifumi

Subjects
PARTICLES (Nuclear physics), SYNCHROTRON radiation, X-ray photoelectron spectroscopy, PHYSICAL sciences, ELECTRON sources, PHOTOCATHODES
Abstract

Alkali antimonide semiconductor photocathodes are promising candidates for high-brightness electron sources for advanced accelerators, including free-electron lasers (FEL), due to their high quantum efficiency (QE), low emittance, and high temporal resolution. Two challenges with these photocathodes are (1) the lack of a universal deposition recipe to achieve crystal stoichiometries and (2) their high susceptibility to vacuum contamination, which restricts their operation pressure to ultrahigh vacuums and leads to a short lifetime and low extraction charge. To resolve these issues, it is essential to understand the elemental compositions of deposited photocathodes and correlate them to robustness. Here, we report depth profiles for potassium cesium antimonide photocathodes, which were investigated using synchrotron radiation x-ray photoelectron spectroscopy, and the robustness of those photocathodes. We prepared two types of photocathodes with different potassium contents via sequential thermal evaporation. Depth profiles revealed that the photocathodes with a potassium deficit had excess cesium at the surface, while the ratio of potassium and cesium to antimony decreased rapidly within the film. In contrast, the photocathodes with sufficient potassium had close to the theoretical stoichiometry of K2CsSb at the surface and maintained that stoichiometry for over half the entire film thickness. Both photocathode types had a similar maximum QE at 532 nm; however, exposure to oxygen revealed that the photocathode with a crystalline stoichiometry of K2CsSb maintained QE at one order of magnitude higher pressure compared to its potassium-deficit counterpart. These results highlight the importance of synthesizing potassium cesium antimonide photocathodes with sufficient potassium to achieve the theoretical crystalline stoichiometry for both high QE and improved robustness. [ABSTRACT FROM AUTHOR]

Published
2025
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49. Carbon Phosphide Monolayer with Superior Carrier Mobility

Author

Wang, Gaoxue, Pandey, Ravindra, and Karna, Shashi P.

Subjects
Condensed Matter - Materials Science
Abstract

Two dimensional (2D) materials with a finite band gap and high carrier mobility are sought after materials from both fundamental and technological perspectives. In this paper, we present the results based on the particle swarm optimization method and density functional theory which predict three geometrically different phases of carbon phosphide (CP) monolayer consisted of sp2 hybridized C atoms and sp3 hybridized P atoms in hexagonal networks. Two of the phases, referred to as {\alpha}-CP and \b{eta}-CP with puckered and buckled surfaces, respectively are semiconducting with highly anisotropic electronic and mechanical properties. More remarkably, they have lightest electrons and holes among the known 2D semiconductors, yielding superior carrier mobility. The {\gamma}-CP has a distorted hexagonal network and exhibits a semi-metallic behavior with Dirac cones. These theoretical findings suggest the binary CP monolayer to be yet unexplored 2D materials holding great promises for applications in high-performance electronics and optoelectronics.

Published
2016
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50. Degradation of Phosphorene in Air: Understanding at Atomic Level

Author

Wang, Gaoxue, Slough, William J., Pandey, Ravindra, and Karna, Shashi P.

Subjects
Condensed Matter - Materials Science
Abstract

Phosphorene is a promising two dimensional (2D) material with a direct band gap, high carrier mobility, and anisotropic electronic properties. Phosphorene-based electronic devices, however, are found to degrade upon exposure to air. In this paper, we provide an atomic level understanding of stability of phosphorene in terms of its interaction with O2 and H2O. The results based on density functional theory together with first principles molecular dynamics calculations show that O2 could spontaneously dissociate on phosphorene at room temperature. H2O will not strongly interact with pristine phosphorene, however, an exothermic reaction could occur if phosphorene is first oxidized. The pathway of oxidation first followed by exothermic reaction with water is the most likely route for the chemical degradation of the phosphorene-based devices in air.

Published
2015
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