Bandgap narrowing in Mn doped GaAs probed by room-temperature photoluminescence

The electronic band structure of the (Ga,Mn)As system has been one of the most intriguing problems in solid state physics over the past two decades. Determination of the band structure evolution with increasing Mn concentration is a key issue to understand the origin of ferromagnetism. Here we present room temperature photoluminescence and ellipsometry measurements of Ga_{100%-x}Mn_{x}As alloy. The up-shift of the valence-band is proven by the red shift of the room temperature near band gap emission from the Ga_{100%-x}Mn_{x}As alloy with increasing Mn content. It is shown that even a doping by 0.02 at.% of Mn affects the valence-band edge and it merges with the impurity band for a Mn concentration as low as 0.6 at.%. Both X-ray diffraction pattern and high resolution cross-sectional TEM images confirmed full recrystallization of the implanted layer and GaMnAs alloy formation.Comment: 24 pages, 7 figures, accepted at Phys. Rev. B 201

High Curie temperature and perpendicular magnetic anisotropy in homoepitaxial InMnAs films

We have prepared the dilute magnetic semiconductor (DMS) InMnAs with different Mn concentrations by ion implantation and pulsed laser melting. The Curie temperature of the In1-xMnxAs epilayer depends on the Mn concentration x, reaching 82 K for x=0.105. The substitution of Mn ions at the Indium sites induces a compressive strain perpendicular to the InMnAs layer and a tensile strain along the in-plane direction. This gives rise to a large perpendicular magnetic anisotropy, which is often needed for the demonstration of electrical control of magnetization and for spin-transfer-torque induced magnetization reversal.Comment: 16 pages, 5 figure

Extended Infrared Photoresponse in Te-Hyperdoped Si at Room Temperature

Presently, silicon photonics requires photodetectors that are sensitive in a broad infrared range, can operate at room temperature, and are suitable for integration with the existing Si-technology process. Here, we demonstrate strong room-temperature sub-band-gap photoresponse of photodiodes based on Si hyperdoped with tellurium. The epitaxially recrystallized Te-hyperdoped Si layers are developed by ion implantation combined with pulsed-laser melting and incorporate Te-dopant concentrations several orders of magnitude above the solid solubility limit. With increasing Te concentration, the Te-hyperdoped layer changes from insulating to quasi-metallic behavior with a finite conductivity as the temperature tends to zero. The optical absorptance is found to increase monotonically with increasing Te concentration and extends well into the mid-infrared range. Temperature-dependent optoelectronic photoresponse unambiguously demonstrates that the extended infrared photoresponsivity from Te-hyperdoped Si p-n photodiodes is mediated by a Te intermediate band within the upper half of the Si band gap. This work contributes to pave the way toward establishing a Si-based broadband infrared photonic system operating at room temperature.Comment: 18 pages, 7 figure

A seleção de critérios no zoneamento agroecológico: proposta metodológica.

A seleção de critérios espaciais para um trabalho de zoneamento agroecológico envolve critérios de aptidão, biodiversidade, socioeconomia, recursos hídricos, legais, ambientais, políticas etc. É necessário identificar a questão-chave e traçar diretrizes do zoneamento que representem as orientações do setor. Essas diretrizes são econômicas, estratégicas, empresariais, sociais, técnicas e políticas, obtidas em negociação com representantes de diferentes setores da sociedade e, ao fim, ponderar os diversos critérios segundo a importância de cada um, no contexto em análise. Este trabalho tem por objetivo apresentar uma metodologia de identificação coletiva desses critérios com o aporte de recursos de sistemas de suporte à decisão espacial e de planejamento estratégico territorial. A metodologia apresenta as seguintes etapas: diagnóstico estratégico, identificação de critérios determinantes (não ponderáveis), identificação dos critérios a serem ponderados e uma proposta de fluxo de procedimentos para a seleção de critérios espaciais. Visa subsidiar a formulação de políticas públicas de ordenamento territorial do setor rural. O resultado é composto de um conjunto de procedimentos e de uma lista de perguntas-chave para compor os diagnósticos e selecionar os critérios espaciais que podem ser aplicados em trabalhos de planejamento territorial adicionado a visão estratégica

Deactivation of Li by vacancy clusters in ion-implanted and flash-annealed ZnO

Li is present in hydrothermally grown ZnO at high concentrations and is known to compensate both n- and p-type doping due to its amphoteric nature. However, Li can be manipulated by annealing and ion implantation in ZnO. Fast, 20 ms flash anneals in the 900–1400°C range result in vacancy cluster formation and, simultaneously, a low-resistive layer in the implanted part of the He- and Li-implanted ZnO. The vacancy clusters, involving 3-4 Zn vacancies, trap and deactivate Li, leaving other in-grown donors to determine the electrical properties. Such clusters are not present in sufficient concentrations after longer (1h) anneals because of a relatively low dissociation barrier ∼2.6 ± 0.3 eV, so ZnO remains compensated until Li diffuses out after 1250°C anneals.Peer reviewe

Retroviral transfer of the p16INK4a cDNA inhibits C6 glioma formation in Wistar rats

BACKGROUND: The p16(INK4A) gene product halts cell proliferation by preventing phosphorylation of the Rb protein. The p16INK4a gene is often deleted in human glioblastoma multiforme, contributing to unchecked Rb phosphorylation and rapid cell division. We show here that transduction of the human p16INK4a cDNA using the pCL retroviral system is an efficient means of stopping the proliferation of the rat-derrived glioma cell line, C6, both in tissue culture and in an animal model. C6 cells were transduced with pCL retrovirus encoding the p16INK4a, p53, or Rb genes. These cells were analyzed by a colony formation assay. Expression of p16INK4a was confirmed by immunohistochemistry and Western blot analysis. The altered morphology of the p16-expressing cells was further characterized by the senescence-associated β-galactosidase assay. C6 cells infected ex vivo were implanted by stereotaxic injection in order to assess tumor formation. RESULTS: The p16INK4a gene arrested C6 cells more efficiently than either p53 or Rb. Continued studies with the p16INK4a gene revealed that a large portion of infected cells expressed the p16INK4a protein and the morphology of these cells was altered. The enlarged, flat, and bi-polar shape indicated a senescence-like state, confirmed by the senescence-associated β-galactosidase assay. The animal model revealed that cells infected with the pCLp16 virus did not form tumors. CONCLUSION: Our results show that retrovirus mediated transfer of p16INK4a halts glioma formation in a rat model. These results corroborate the idea that retrovirus-mediated transfer of the p16INK4a gene may be an effective means to arrest human glioma and glioblastoma

Áreas prioritárias para ações de transferência de tecnologia em integração lavoura, pecuária e floresta no estado de São Paulo.

Resumo: Este trabalho irá explorar a generalização espacial em sistemas de informações geográficas (SIG) da escala local à municipal. O trabalho original é o mapeamento de áreas prioritárias para ações de transferência de tecnologia (TT) em Integração Lavoura-Pecuária-Floresta (ILPF), no estado de São Paulo. Essa utilizou o Método de Análise Hieráquica (AHP) e a modelagem em SIG nas avaliações. Assim, calculou-se a proporção entre a área de classe de prioridade e a área agrícola do município para esta generalização. Foi concluído que é possível explicar a classe de prioridade a partir dos critérios originais. Além disso, este tipo de trabalho poderia contribuir na consolidação de uma economia agrícola de baixo carbono. Como resultado, foi identificado que as classes de prioridade maiores estão em regiões com alto potencial agrícola. Finalmente, São Paulo apresenta: 21,8% dos municípios com alta prioridade; 25,2% com média; 23,7% com baixa e 27,4% com muito baixa. ? Abstract: This paper will explore the upscale of results of thematic integration in Geographic Information System (GIS) from local scale to municipal scale. The original work is the priority areas mapping for technology transfer actions (TT) of Crop-Livestock-Forest Integration (CLFI) in São Paulo State. It was a Multicriteria Analysis using together Analytic Hierarchy Process and GIS modeling. Thus, we calculate the ratio of each amount of priority class area and the agricultural area of each municipality for this upscale. We conclude that was preserved the possibility of explain the priority class from combined evaluation of the original criteria. Furthermore, this kind of work could contributes to consolidate a Low Carbon Agricultural Economy. As a result, we identified that the higher priority classes to CLFI-TT are in regions with high agricultural potential. Finally, São Paulo has: 21,8% municipality with high class; 25,2% with average; 23,7% with low and 27,4% with very low

Disturbing-free determination of yeast concentration in DI water and in glucose using impedance biochips

Deionized water and glucose without yeast and with yeast (Saccharomyces cerevisiae) of optical density OD600 that ranges from 4 to 16 has been put in the ring electrode region of six different types of impedance biochips and impedance has been measured in dependence on the added volume (20, 21, 22, 23, 24, 25 µL). The measured impedance of two out of the six types of biochips is strongly sensitive to the addition of both liquid without yeast and liquid with yeast and modelled impedance reveals a linear relationship between the impedance model parameters and yeast concentration. The presented biochips allow for continuous impedance measurements without interrupting the cultivation of the yeast. A multiparameter fit of the impedance model parameters allows for determining the concentration of yeast (cy) in the range from cy = 3.3 × 107 to cy = 17 × 107 cells/mL. This work shows that independent on the liquid, i.e., DI water or glucose, the impedance model parameters of the two most sensitive types of biochips with liquid without yeast and with liquid with yeast are clearly distinguishable for the two most sensitive types of biochips