Exploration on performance of two-dimensional GaN photocathodes with uniform-doping and variable-doping structure

In this paper, the properties of two-dimensional (2D) gallium nitride (GaN) photocathodes with a uniform doping and variable doping structure are studied by using Mg as a doping element based on first principles. The stability, bandstructure, work function, density of state and optical properties of the GaN bilayer and GaN trilayer in two-doped ways are investigated. The results show that formation energy of variable doping structure is less than that of the uniform doping structure, which means that the variable doping structure is more stable. At the same time, the formation energy increases with increase of layers. The pristine GaN bilayer has an indirect bandgap, while the doped GaN bilayer transforms into a direct bandgap. The impurity levels appear in a forbidden band of doped GaN trilayers, which is favorable for electron transition. The results of work function reveal that variable doping structure has lower vacuum barriers and more electron escape numbers, which proves that it can improve the quantum efficiency of photocathodes. Finally, the analysis of optical properties shows that the uniform doping structure has better optical properties than that of the variable doping structure.

RuO2 Nanorods as an Electrocatalyst for Proton Exchange Membrane Water Electrolysis

A custom-built PEM electrolyzer cell was assembled using 6” stainless-steel ConFlat flanges which were fitted with a RuO2 nanorod-decorated, mixed metal oxide (MMO) ribbon mesh anode catalyst. The current density–voltage characteristics were measured for the RuO2 nanorod electrocatalyst while under constant water feed operation. The electrocatalytic behavior was investigated by making a series of physical modifications to the anode catalyst material. These experiments showed an improved activity due to the RuO2 nanorod electrocatalyst, resulting in a corresponding decrease in the electrochemical overpotential. These overpotentials were identified by collecting experimental data from various electrolyzer cell configurations, resulting in an improved understanding of the enhanced catalytic behavior. The micro-to-nano surface structure of the anode electrocatalyst layer is a critical factor determining the overall operation of the PEM electrolyzer. The improvement was determined to be due to the lowering of the potential barrier to electron escape in an electric field generated in the vicinity of a nanorod.

A ação mediada e jogos educativos: um estudo junto a alunos do ensino médio em uma aula de Física

Esta pesquisa tem como objetivo analisar as interações verbais entre estudantes mediadas pelo jogo de tabuleiro Electron Escape e pela linguagem em uma aula de Física. Tal jogo envolve perguntas cujas respostas devem ser validadas pelos jogadores com base nos modelos científicos contidos nas cartas. Diante disso, interessa-nos saber: como os alunos conduzem a partida mediada pelo jogo e pela linguagem? Quais as potencialidades de Electron Escape, enquanto recurso, para o ensino da Física? Para tanto, realizamos uma pesquisa qualitativa e do tipo estudo de caso em uma turma da primeira série do ensino médio de uma escola da rede estadual de Vila Velha, Espírito Santo, no último trimestre de 2018. Os estudantes foram divididos em grupos e disputaram uma partida de Electron Escape. Coletamos as interações verbais por meio de registros de áudio. O processo analítico apoiou-se na perspectiva sociocultural. Os resultados mostram que o jogo estimulou o resgate de conteúdos e a utilização da linguagem científica escolar na construção das respostas, podendo contribuir para a revisão do conteúdo de Física. Os alunos modificaram o sistema de jogo de competitivo para cooperativo. Além disso, o rigor estabelecido para validação das respostas foi baixo, de modo que modelos incorretos foram aceitos. Consideramos que esses resultados trazem contribuições importantes para o repensar na forma de utilização do jogo Electron Escape e no papel do professor no uso de meios mediacionais.

Power-induced lasing state switching and bistability in a two-state quantum dot laser subject to optical injection

We theoretically investigate power-induced lasing state switching and bistability in a two-state quantum dot laser subject to optical injection. The simulated results show that, for a free-running two-state quantum dot laser operating at the ground state under low current, a power-induced lasing state switching between the ground state and the excited state can be achieved through introducing optical injection with a frequency (winj) close to the lasing frequency of excited state (wES). The injection power required for the state switching depends on the scanning route of injection power, i.e. there may exist state bistability for the injection power within a certain region. For forward scanning injection power, with the increase of frequency detuning (ΔΩ = winj – wES), the injection power required for the state switching shows a decreasing trend accompanied by slight fluctuations. However, for backward scanning injection power, the injection power required for the state switching exhibits obvious fluctuations with the increase of ΔΩ. The width of the hysteresis loop fluctuates with ΔΩ, and the fluctuation amplitude is increased with the increase of the injection current. Additionally, the influences of the inhomogeneous broadening factor and the electron escape rate on the bistability performances are analyzed.

Fingerprints of slingshot non-sequential double ionization on two-electron probability distributions

We study double ionization of He driven by near-single-cycle laser pulses at low intensities at 400 nm. Using a three-dimensional semiclassical model, we identify the pathways that prevail non-sequential double ionization (NSDI). We focus mostly on the delayed pathway, where one electron ionizes with a time-delay after recollision. We have recently shown that the mechanism that prevails the delayed pathway depends on intensity. For low intensities slingshot-NSDI is the dominant mechanism. Here, we identify the differences in two-electron probability distributions of the prevailing NSDI pathways. This allows us to identify properties of the two-electron escape and thus gain significant insight into slingshot-NSDI. Interestingly, we find that an observable fingerpint of slingshot-NSDI is the two electrons escaping with large and roughly equal energies.