Interband polarized absorption in InP polytypic superlattices

Recent advances in growth techniques have allowed the fabrication of semiconductor nanostructures with mixed wurtzite/zinc-blende crystal phases. Although the optical characterization of these polytypic structures is well eported in the literature, a deeper theoretical understanding of how crystal phase mixing and quantum confinement change the output linear light polarization is still needed. In this paper, we theoretically investigate the mixing effects of wurtzite and zinc-blende phases on the interband absorption and in the degree of light polarization of an InP polytypic superlattice. We use a single 8$\times$8 k$\cdot$p Hamiltonian that describes both crystal phases. Quantum confinement is investigated by changing the size of the polytypic unit cell. We also include the optical confinement effect due to the dielectric mismatch between the superlattice and the vaccum and we show it to be necessary to match experimental results. Our calculations for large wurtzite concentrations and small quantum confinement explain the optical trends of recent photoluminescence excitation measurements. Furthermore, we find a high sensitivity to zinc-blende concentrations in the degree of linear polarization. This sensitivity can be reduced by increasing quantum confinement. In conclusion, our theoretical analysis provides an explanation for optical trends in InP polytypic superlattices, and shows that the interplay of crystal phase mixing and quantum confinement is an area worth exploring for light polarization engineering.Comment: 9 pages, 6 figures and 1 tabl

Representação computacional de construções e relevos tridimensionais usando fractais

Neste Projeto de Iniciação Cientifica será desenvolvido um software que permite visualização tridimensional de mapas cartográficos bidimensionais utilizando fractais par a representação geométrica de relevos e edificações. Metodologia: Inicialmente, será realizada a etapa de Analise em que se define a melhor maneira d executar a tarefa e que recursos serão necessários como por exemplo: números d programadores, linguagem de programação, hardware, etc. Na próxima fase, chamada d Projeto, determinam-se os ¿Lay-outs¿ das telas e características do softwar Posteriormente insere-se o Código do software na linguagem de programaçã determinada na fase de analise. Em seguida, realiza-se os testes no produto para verifica se os requisitos concordados na especificação (Fase de projeto) estão sendo atendido Quando o procedimento automatizado estiver pronto inicia-se a fase de Manutençã Resultados: No atual estágio de desenvolvimento um protótipo está em operação. Conclusão: Neste artigo de Iniciação Cientifica, será desenvolvido um software que permite visualização tridimensional de mapas cartográficos

Exploring the adoption of precision agriculture for irrigation in the context of agriculture 4.0: The key role of internet of things

In recent years, the concept of Agriculture 4.0 has emerged as an evolution of precision agriculture (PA) through the diffusion of the Internet of things (IoT). There is a perception that the PA adoption is occurring at a slower pace than expected. Little research has been carried out about Agriculture 4.0, as well as to farmer behavior and operations management. This work explores what drives the adoption of PA in the Agriculture 4.0 context, focusing on farmer behavior and operations management. As a result of a multimethod approach, the factors explaining the PA adoption in the Agriculture 4.0 context and a model of irrigation operations management are proposed. Six simulation scenarios are performed to study the relationships among the factors involved in irrigation planning. Empirical findings contribute to a better understanding of what Agriculture 4.0 is and to expand the possibilities of IoT in the PA domain. This work also contributes to the discussion on Agriculture 4.0, thanks to multidisciplinary research bringing together the different perspectives of PA, IoT and operations management. Moreover, this research highlights the key role of IoT, considering the farmer’s possible choice to adopt several IoT sensing technologies for data collection

Unusual spin properties of InP wurtzite nanowires revealed by Zeeman splitting spectroscopy

In this study, we present a complete experimental and theoretical investigation of the fundamental exciton Zeeman splitting in wurtzite InP nanowires. We determined the exciton gyromagnetic factor, $g_{exc}$, by magneto-photoluminescence spectroscopy using magnetic fields up to 29 T. We found that $g_{exc}$ is strongly anisotropic with values differing in excess of 50\% between the magnetic field oriented parallel and perpendicular to the nanowire long axis. Furthermore, for magnetic fields oriented along the nanowire axis, $g_{exc}$ is nearly three times larger than in bulk zincblende InP and it shows a marked sublinear dependence on the magnetic field, a common feature to other non-nitride III-V wurtzite nanowires but not properly understood. Remarkably, this nonlinearity originates from only one Zeeman branch characterized by a specific type of light polarization. All the experimental findings are modeled theoretically by a robust approach combining the $k \cdot p$ method with the envelope function approximation and including the electron-hole interaction. We revealed that the nonlinear features arise due to the coupling between Landau levels pertaining to the A (heavy-hole like) and B (light-hole like) valence bands of the wurtzite crystal structure. This general behavior is particularly relevant for the understanding of the spin properties of several wurtzite nanowires that host the set for the observation of topological phases potentially at the base of quantum computing platforms

Realistic multiband k.p approach from ab initio and spin-orbit coupling effects of InAs and InP in wurtzite phase

Semiconductor nanowires based on non-nitride III-V compounds can be synthesized under certain growth conditions to favor the appearance of the wurtzite crystal phase. Despite reports in the literature of ab initio band structures for these wurtzite compounds, we still lack effective multiband models and parameter sets that can be simply used to investigate physical properties of such systems, for instance, under quantum confinement effects. In order to address this deficiency, in this study we calculate the ab initio band structure of bulk InAs and InP in the wurtzite phase and develop an 8 x 8 k . p Hamiltonian to describe the energy bands around the Gamma point. We show that our k . p model is robust and can be fitted to describe the important features of the ab initio band structure. The correct description of the spin-splitting effects that arise due to the lack of inversion symmetry in wurtzite crystals is obtained with the k-dependent spin-orbit term in the Hamiltonian, often neglected in the literature. All the energy bands display a Rashba-like spin texture for the in-plane spin expectation value. We also provide the density of states and the carrier density as functions of the Fermi energy. Alternatively, we show an analytical description of the conduction band, valid close to the Gamma point. The same fitting procedure is applied to the 6 x 6 valence band Hamiltonian. However, we find that the most reliable approach is the 8 x 8 k . p Hamiltonian for both compounds. The k . p Hamiltonians and parameter sets that we develop in this paper provide a reliable theoretical framework that can be easily applied to investigate electronic, transport, optical, and spin properties of InAs- and InP-based nanostructures

Experimental study of He6+Be9 elastic scattering at low energies

New data for the He6+Be9 reaction at Elab=16.2 and 21.3 MeV have been taken and analyzed. The effect of the collective couplings to the excited states of the target has been studied by means of coupled-channels calculations, using a double-folding potential for the bare interaction between the colliding nuclei, supplemented with a phenomenological imaginary part of Woods-Saxon type. In addition, three- and four-body continuum-discretized coupled-channels calculations have been performed to investigate the effect of the projectile breakup on the elastic scattering. Both effects, the coupling to target and projectile excited states, are found to affect significantly the elastic scattering. The trivial local polarization potential extracted from the continuum-discretized coupled-channels calculations indicates that continuum couplings produce a repulsive real part and a long-range imaginary part in the projectile-target interaction. © 2011 American Physical Society.This work has been partially supported by the Spanish Ministerio de Ciencia e Innovacion´ under Projects FPA2009-07653 and PCI2006-A7-0654 and by the Spanish Consolider-Ingenio 2010 Programme CPAN (CSD2007-00042).Peer Reviewe

Projeto em rede de biossegurança de organismos geneticamente modificados da Embrapa BioSeg.

A BioSeg teve por objetivo dotar a Embrapa da capacitação e infra-estrutura necessárias à geração de dados científicos para que seus OGM, seguros do ponto de vista alimentar e ambiental, e em consonância com a legislação vigente, possam ser disponibilizados à população