Vacancy and Doping States in Monolayer and bulk Black Phosphorus.

The atomic geometries and transition levels of point defects and substitutional dopants in few-layer and bulk black phosphorus are calculated. The vacancy is found to reconstruct in monolayer P to leave a single dangling bond, giving a negative U defect with a +/- transition level at 0.24 eV above the valence band edge. The V(-) state forms an unusual 4-fold coordinated site. In few-layer and bulk black P, the defect becomes a positive U site. The divacancy is much more stable than the monovacancy, and it reconstructs to give no deep gap states. Substitutional dopants such as C, Si, O or S do not give rise to shallow donor or acceptor states but instead reconstruct to form non-doping sites analogous to DX or AX centers in GaAs. Impurities on black P adopt the 8-N rule of bonding, as in amorphous semiconductors, rather than simple substitutional geometries seen in tetrahedral semiconductors

Gradient Optics of subwavelength nanofilms

Propagation and tunneling of light through subwavelength photonic barriers, formed by dielectric layers with continuous spatial variations of dielectric susceptibility across the film are considered. Effects of giant heterogeneity-induced non-local dispersion, both normal and anomalous, are examined by means of a series of exact analytical solutions of Maxwell equations for gradient media. Generalized Fresnel formulae, visualizing a profound influence of gradient and curvature of dielectric susceptibility profiles on reflectance/transmittance of periodical photonic heterostructures are presented. Depending on the cutoff frequency of the barrier, governed by technologically managed spatial profile of its refractive index, propagation or tunneling of light through these barriers are examined. Nonattenuative transfer of EM energy by evanescent waves, tunneling through dielectric gradient barriers, characterized by real values of refractive index, decreasing in the depth of medium, is shown. Scaling of the obtained results for different spectral ranges of visible, IR and THz waves is illustrated. Potential of gradient optical structures for design of miniaturized filters, polarizers and frequency-selective interfaces of subwavelength thickness is considered

RuCl3 supported on N-doped graphene as reusable catalyst for one-step glucose oxidation to succinic acid

[EN] Impregnation of RuCl3 on N-doped graphenes results in the formation of well-dispersed, small ruthenium oxyhydroxide nanoparticles supported on N-doped graphene that may exhibit high selectivity (87%) for the conversion of glucose into succinic acid under wet oxidation conditions (160 degrees C, 18atm O-2 pressure). Ruthenium loading and N-atom distribution on graphene influence the catalytic activity, the best performing catalyst having 1wt.% Ru loading on a graphene having a large population of graphenic N atoms. The high catalytic selectivity to succinic acid was correlated with the presence of small ruthenium nanoparticles. The present catalyst improves the best one previously reported because it does not require the continuous addition of an excess of amine to reach high succinic acid selectivity and reusability.Financial support by the Spanish Ministry of Economy and Competitiveness (Severo Ochoa, Grapas and TQ2015-69563-CO2-R1) and by the Generalitat Valenciana (Prometeo 2013-014) is gratefully acknowledged. J.A. also thanks the Universitat Politecnica de Valencia for a postdoctoral scholarship. Prof. Simona M. Coman kindly acknowledges UEFISCDI for financial support (project PN-II-PT-PCCA-2013-4-1090, Nr. 44/2014).Rizescu, C.; Podolean, I.; Cojocaru, B.; Parvulescu, VI.; Coman, SM.; Albero-Sancho, J.; García Gómez, H. (2017). RuCl3 supported on N-doped graphene as reusable catalyst for one-step glucose oxidation to succinic acid. ChemCatChem. 9(17):3314-3321. https://doi.org/10.1002/cctc.201700383S3314332191

A review of non-destructive testing techniques for the in-situ investigation of fretting fatigue cracks

© 2020 The Authors Fretting fatigue can significantly reduce the life of components, leading to unexpected in-service failures. This phenomenon has been studied for over a century, with significant progress being made during the past decade. There are various methods that have been used to study fretting fatigue cracks in order to gain a greater understanding of the effects of fretting fatigue. Destructive methods are traditionally used to observe fretting fatigue cracks. Although useful in determining crack location, crack length, crack propagation modes, crack path and shape, it is not efficient or reliable for time based measurements. Non-destructive testing has developed in recent years and now in-situ monitoring can be used during testing in order to increase the understanding of fretting fatigue. This paper presents a review of non-destructive testing techniques used in-situ during fretting fatigue testing, which are compared in order to conclude the suitability of each technique. Recent developments in non-destructive techniques that could be also applied for fretting fatigue tests are also discussed, as well as recommendations for future research made

Writ to Sheriff to take John Snowden, Negro, before court to answer to trespassing, October 1, 1864-November 30, 1864

Writ to Sheriff to take John Snowden, Negro, before court to answer to trespassing, [Frederick County], October 1, 1864-November 30, 1864