Edge phonons in black phosphorus

Exfoliated black phosphorus has recently emerged as a new two-dimensional crystal that, due to its peculiar and anisotropic crystalline and electronic band structures, may have potentially important applications in electronics, optoelectronics and photonics. Despite the fact that the edges of layered crystals host a range of singular properties whose characterization and exploitation are of utmost importance for device development, the edges of black phosphorus remain poorly characterized. In this work, the atomic structure and the behavior of phonons near different black phosphorus edges are experimentally and theoretically studied using Raman spectroscopy and density functional theory calculations. Polarized Raman results show the appearance of new modes at the edges of the sample, and their spectra depend on the atomic structure of the edges (zigzag or armchair). Theoretical simulations confirm that the new modes are due to edge phonon states that are forbidden in the bulk, and originated from the lattice termination rearrangements.Comment: 15 pages, 4 figure

Bis[glycinium(0.5+)] perrhenate

All the residues of the title compound, (C2H5.5NO2)2[ReO4], are located in general crystallographic positions. The glycine mol­ecules have usual conformations [Rodrigues Matos Beja et al. (2006 ▶). Acta Cryst. C62, o71–o72] with the H atom of the carboxylate group half-occupied, thus bearing a formal half-positive charge per molecule. The perrhenate anion has nearly ideal tetra­hedral geometry. A large number of strong hydrogen bonds give rise to the overall three-dimensional network. A two-dimensional network, parallel to (100), is made up of strong O—H⋯O hydrogen bonds with a donor acceptor distance of 2.445 (2) Å. A large number of weaker O—H⋯O and N—H⋯O hydrogen bonds consolidates the structure into an overall three-dimensional network

Characterization of the second- and third-order nonlinear optical susceptibilities of monolayer MoS2_2 using multiphoton microscopy

We report second- and third-harmonic generation in monolayer MoS$_\mathrm{2}$ as a tool for imaging and accurately characterizing the material's nonlinear optical properties under 1560 nm excitation. Using a surface nonlinear optics treatment, we derive expressions relating experimental measurements to second- and third-order nonlinear sheet susceptibility magnitudes, obtaining values of $|\chi_s^{(2)}|=2.0\times10^{-20}$ m$^2$ V$^{-1}$ and for the first time for monolayer MoS$_\mathrm{2}$, $|\chi_s^{(3)}|=1.7\times10^{-28}$ m$^3$ V$^{-2}$. These sheet susceptibilities correspond to effective bulk nonlinear susceptibility values of $|\chi_{b}^{(2)}|=2.9\times10^{-11}$ m V$^{-1}$ and $|\chi_{b}^{(3)}|=2.4\times10^{-19}$ m$^2$ V$^{-2}$, accounting for the sheet thickness. Experimental comparisons between MoS$_\mathrm{2}$ and graphene are also performed, demonstrating $\sim$3.4 times stronger third-order sheet nonlinearity in monolayer MoS$_\mathrm{2}$, highlighting the material's potential for nonlinear photonics in the telecommunications C band.Comment: Accepted by 2D Materials, 28th Oct 201

A utilização de SAFs na recuperação de APPS em mesobacias hidrográficas no Nordeste paraense: a experiência do Projeto Gestabacias.

Este trabalho traduz um esforço de pesquisa empreendido no sentido de promover a recuperação de áreas de proteção permanente ? APP privilegiando a reintrodução de espécies da flora nativa e a adoção de SAFs que simulem a sucessão florística dessas áreas em mesobacias hidrográficas no nordeste paraense e como também incentivam e viabilizam a sua recuperação, como uma das estratégias encontradas para o envolvimento de diferentes atores em torno da construção de um modelo de gestão participativa para o uso dos recursos naturais. Em razão dos passivos ambientais atualmente existentes nas áreas dessas mesobacias, foram instaladas 04 Unidades de Observação, nas quais os tratamentos previstos têm a finalidade de oferecer diferentes alternativas aos atores locais, que poderão dispor de sistemas que sejam dotados de uma complexidade que se aproxime dos ecossistemas originalmente existentes nas APPs, e ao mesmo tempo sejam viáveis do ponto de vista socioeconômico e ambiental.Editores técnicos: Roberto Porro, Milton Kanashiro, Maria do Socorro Gonçalves Ferreira, Leila Sobral Sampaio e Gladys Ferreira de Sousa

On the Hydrogen Atom via Wigner-Heisenberg Algebra

We extend the usual Kustaanheimo-Stiefel $4D\to 3D$ mapping to study and discuss a constrained super-Wigner oscillator in four dimensions. We show that the physical hydrogen atom is the system that emerges in the bosonic sector of the mapped super 3D system.Comment: 14 pages, no figure. This work was initiated in collaboration with Jambunatha Jayaraman (In memory), whose advises and encouragement were fundamental. http://www.cbpf.b

High-redshift objects and the generalized Chaplygin gas

Motivated by recent developments in particle physics and cosmology, there has been growing interest in an unified description of dark matter and dark energy scenarios. In this paper we explore observational constraints from age estimates of high-$z$ objects on cosmological models dominated by an exotic fluid with equation of state $p = -A/\rho^{\alpha}$ (the so-called generalized Chaplygin gas) which has the interesting feature of interpolating between non-relativistic matter and negative-pressure dark energy regimes. As a general result we find that, if the age estimates of these objects are correct, they impose very restrictive limits on some of these scenarios.Comment: 5 pages, 3 figures, to appear in Phys. Rev.

2-Amino-5-nitro­pyridinium tetraoxido­rhenate(VII) monohydrate

All the residues of the title compound, (C5H6N3O2)[ReO4]·H2O, are located on general crystallographic positions. The 2-amino-5-nitro­pyridinium cation has a typical planar conformation with one of the nitro O atoms −0.058 (5) Å out of plane; the amine H atoms are also a little out of the main ring plane towards the opposite side of the aforementioned O atom [by 0.02 (4) and 0.04 (4) Å]. The perrhenate anion is nearly ideally tetra­hedral. Three distinct N—H⋯O hydrogen bonds give rise to C(8) zigzag chains running along [100]. R 4 4(12) rings involving the two hydrogen bonds in which the water mol­ecules inter­act with the perrhenate anions are also present

Conditional large Fock state preparation and field state reconstruction in Cavity QED

We propose a scheme for producing large Fock states in Cavity QED via the implementation of a highly selective atom-field interaction. It is based on Raman excitation of a three-level atom by a classical field and a quantized field mode. Selectivity appears when one tunes to resonance a specific transition inside a chosen atom-field subspace, while other transitions remain dispersive, as a consequence of the field dependent electronic energy shifts. We show that this scheme can be also employed for reconstructing, in a new and efficient way, the Wigner function of the cavity field state.Comment: 4 Revtex pages with 3 postscript figures. Submitted for publicatio