Made available in DSpace on 2014-10-09T12:26:18Z (GMT). No. of bitstreams: 0 / Made available in DSpace on 2014-10-09T14:09:58Z (GMT). No. of bitstreams: 0 / Fundação de Amparo à Pesquisa do Estado de São Paulo (FAPESP) / A reconstrução do passado e o entendimento de vários aspectos históricos e culturais das sociedades que se desenvolveram em sítios arqueológicos, têm sido possibilitados por meio de trabalhos arqueométricos realizados sobre as cerâmicas resgatadas destas áreas. O presente estudo procurou contribuir para o esclarecimento acerca de tais aspectos, com a aplicação de três métodos físicos de análise: análise por ativação com nêutrons (AAN), datação por termoluminescência (TL) e ressonância paramagnética eletrônica (RPE) aos fragmentos cerâmicos do sítio arqueológico Hatahara, localizado na Amazônia central. As concentrações elementares obtidas por AAN de 120 fragmentos cerâmicos foram interpretadas por meio da análise de agrupamentos e a análise discriminante. Os resultados mostraram a existência de cinco grupos distintos de cerâmicas. Esta informação, associada à interpretação arqueológica, pôde confirmar a existência de quatro fases distintas de ocupação para o sítio Hatahara. Com o objetivo de estabelecer uma cronologia para as ocupações, foram determinadas as idades de três fragmentos cerâmicos, por meio da datação por termoluminescência (TL). A datação de dois fragmentos mostrou resultados que não confirmam interpretações arqueológicas quanto às suas Fases de ocupação. No entanto, a datação do terceiro fragmento permitiu confirmar que o mesmo pertence à Fase Manacapuru. A determinação da temperatura de queima de quatro fragmentos cerâmicos foi estudada por meio da técnica da ressonância paramagnética eletrônica (RPE) e os resultados mostraram que apesar das cerâmicas analisadas pertencerem a três grupos distintos, não houve variações significativas quanto às suas respectivas temperaturas de queima. / Dissertacao (Mestrado) / IPEN/D / Instituto de Pesquisas Energeticas e Nucleares - IPEN-CNEN/SP / FAPESP:06/59237-6

Submitted by Erika Demachki (erikademachki@gmail.com) on 2014-11-17T19:47:57Z No. of bitstreams: 2 Tese - Marcos Antonio de Sousa - 2013.pdf: 3239702 bytes, checksum: ac8fe1a06dac049cc609054fe4412a9d (MD5) license_rdf: 23148 bytes, checksum: 9da0b6dfac957114c6a7714714b86306 (MD5) / Approved for entry into archive by Erika Demachki (erikademachki@gmail.com) on 2014-11-17T19:48:11Z (GMT) No. of bitstreams: 2 Tese - Marcos Antonio de Sousa - 2013.pdf: 3239702 bytes, checksum: ac8fe1a06dac049cc609054fe4412a9d (MD5) license_rdf: 23148 bytes, checksum: 9da0b6dfac957114c6a7714714b86306 (MD5) / Made available in DSpace on 2014-11-17T19:48:11Z (GMT). No. of bitstreams: 2 Tese - Marcos Antonio de Sousa - 2013.pdf: 3239702 bytes, checksum: ac8fe1a06dac049cc609054fe4412a9d (MD5) license_rdf: 23148 bytes, checksum: 9da0b6dfac957114c6a7714714b86306 (MD5) Previous issue date: 2013-06-27 / Conselho Nacional de Pesquisa e Desenvolvimento Científico e Tecnológico - CNPq / This work reports the study of the phenomenon of exchange bias in NiFe/IrMn bilayers and NiFe/IrMn/Co trilayers. In the NiFe/IrMn bilayers, ferromagnetic resonance experiments at X and Q bands microwave frequencies reveal that spin wave and NiFe resonance modes are excited by the oscillating microwave field. Angular variations of the absorption fields in the plane of the films for both resonance modes shows the effect of the unidirectional anisotropy field, whose intensity is twice larger for the spin wave mode, due to an additional contribution of an unidirectional surface anisotropy. The experiments also indicate the presence of a uniaxial anisotropy of the NiFe layer, apparently dependent on the applied magnetic field. The magnetic parameters of both resonance modes were deduced considering a generalized phenomenological model which also includes the contribution of a rotatable anisotropy. In the NiFe/IrMn/Co trilayers, the angular variations of the resonance field in the plane of the films reveal the effect of the unidirectional anisotropy field for both independent resonance modes of NiFe and Co layers. The ferromagnetic resonance results combined with magnetometry data show that the exchange bias phenomenon at the NiFe/IrMn interface influences the same phenomenon at the IrMn/Co interface, and that this effect must be mediated by a spiral structure of spins across the IrMn antiferromagnetic layer. For both systems studied, the values of the exchange bias field deduced from the ferromagnetic resonance experiments are consistent with the values given by magnetization measurements. / Este trabalho relata o estudo do fenômeno de exchange bias em bicamadas NiFe/IrMn e tricamadas NiFe/IrMn/Co. Nas bicamadas NiFe/IrMn, experimentos de ressonância ferromagnética, em Bandas X e Q de frequência de micro-ondas, revelam que um modo de ressonância de ondas de spin e o modo de ressonância da camada de NiFe são excitados pelo campo oscilante de micro-ondas. Variações angulares dos campos de absorção no plano dos filmes mostram para os dois modos de ressonância o efeito do campo de anisotropia unidirecional, cuja intensidade é duas vezes maior para o modo de onda de spin, devido a uma contribuição adicional de uma anisotropia de superfície unidirecional. Os experimentos indicam também a presença de uma anisotropia uniaxial da camada de NiFe, aparentemente dependente do campo magnético aplicado. Os parâmetros magnéticos dos dois modos de ressonância foram deduzidos considerando um modelo fenomenológico generalizado que inclui também a contribuição de uma anisotropia rodável. Nas tricamadas NiFe/IrMn/Co, as variações angulares de campo de ressonância no plano dos filmes revelam o efeito do campo de anisotropia unidirecional sobre os modos de ressonância independentes das camadas de NiFe e Co. Os resultados de ressonância ferromagnética combinados com os dados de magnetometria, mostram que o fenômeno de exhange bias na interface NiFe/IrMn influencia o mesmo fenômeno na interface IrMn/Co, e que esta influência deve ser mediada por uma estrutura espiral de spins através da camada antiferromagnética de IrMn. Para os dois sistemas estudados, os valores do campo de exchange bias dados pelos experimentos de ressonância ferromagnética estão de acordo com os valores fornecidos por medidas de magnetização.

A interação da radiação ionizante com moléculas de alanina promove a quebra das ligações químicas entre o átomo de carbono central e os grupos que se ligam a ele, resultando na formação de radicais livres paramagnéticos. A técnica de dosimetria utilizando alanina e a ressonância de spin eletrônico (ESR) baseia-se na determinação da concentração dos radicais livres produzidos pela interação da radiação ionizante com as moléculas da alanina por meio do registro do espectro de ESR da alanina irradiada. Para propósitos de dosimetria, a amplitude da linha central do espectro pode ser correlacionada diretamente com a dose de radiação. Na atualidade, a alanina/ESR é uma técnica de dosimetria amplamente aceita para a dosimetria de altas doses como aquelas usadas nos processos de irradiação de alimentos, esterilização de produtos médicos e radioterapia. A expansão dos tratamentos de câncer por meio de procedimentos de radiocirurgia e radioterapia de intensidade modulada (IMRT) torna cada vez mais relevante a necessidade de realizar a dosimetria em pequenos campos de radiação. Para a dosimetria desses feixes estreitos de radiação, é necessário o uso detectores que também apresentem dimensões reduzidas de forma a proporcionar alta resolução espacial. Uma vez que a sensibilidade dos dosímetros de alanina depende do número de radicais formados pela radiação, a redução do tamanho do detector de alanina implica em redução de seu volume sensível e consequentemente de sua sensibilidade. Assim, pesquisas têm sido realizadas buscando uma melhora de sua sensibilidade. Neste trabalho foram investigados os mecanismos envolvidos na formação da nanoestrutura e a capacidade da alanina em estabilizar e acomodar nanopartículas metálicas de ouro e prata em sua matriz cristalina, para aplicação dos nanocompósitos como detectores de radiação utilizando a técnica de ressonância de spin eletrônico. Foi analisado o tamanho das partículas, sua interação com as moléculas do aminoácido, sua agregação e posicionamento dentro da matriz cristalina da alanina. Além disso, foi investigada a maneira como a morfologia e o estado de agregação e segregação das nanopartículas podem alterar a resposta dosimétrica dos detectores híbridos de alanina. O aumento de sensibilidade dos dosímetros de alanina mostrou estar diretamente associado ao aumento do número de elétrons ejetados por efeito fotoelétrico. No entanto, foi mostrado que aumento da sensibilidade dos dosímetros de alanina é governado por outros fatores além do número de eventos fotoelétricos. A auto-absorção dos elétrons oriundos de uma nanopartícula metálica, por outra nanopartícula vizinha, também influencia na resposta dosimétrica do detector. Assim, sistemas homogêneos onde não houve segregação, apresentaram menor auto-absorção e, consequentemente, os ganhos em sensibilidade foram maiores. Para sistemas onde houve aumento de tamanho e segregação das partículas metálicas, a auto-absorção se tornou mais relevante. Para fótons com energias próximas a energia da camada K do metal presente no nanocompósito, a absorção da radiação foi muito mais relevante do que a organização das nanopartículas na estrutura da alanina. Para energias maiores a probabilidade de eventos fotoelétricos somente diminui e, dessa forma, a agregação e segregação das partículas desempenharam papéis fundamentais na sensibilidade dos dosímetros. Assim, a sensibilidade dosimétrica dos detectores pode ser aumentada e otimizada por meio do uso da nanoestruturação, reduzindo a auto-absorção dos elétrons ejetados. / The interaction of ionizing radiation with alanine molecules produces free radicals. The room temperature stable alanine radical is molecule depleted of the amine group. The Alanine/ESR dosimetry technique is able to measure the amount of free radicals produced by the radiation. For dosimetric purposes, the amplitude of the central ESR spectral line is direct related to the absorbed dose by the alanine molecules. Nowadays, the alanine/ESR technique is largely used for dosimetry of high doses such as used in food irradiation, sterilization of medical products and radiotherapy. The growing need for cancer treatments using radiosurgery and intensity modulated radiation therapy (IMRT) makes important the dosimetry of small radiation fields. To this end, it is necessary to use small radiation detectors in order to obtain enough special resolution. Once the sensitivity of alanine dosimeters depends on the amount of free radical produced by the radiation, reducing the size of alanine detector also reduces its sensitivity. Thus there is an intense investigation to develop high sensitivity of Alanine/ESR dosimeters. In this work the mechanisms involved in the formation of nanostructures and the ability of alanine to stabilize and accommodate nanoparticles of silver and gold in its crystalline matrix, for applications of the nanocomposite as radiation detectors was investigated using the electron spin resonance technique. The effect of particle size, its interaction with alanine molecules, aggregation and segregation of particles inside the alanine matrix as well as the way the morphology and the state of agglomeration change the dosimetric sensitivity of the alanine detectors were investigated. The increase of sensitivity of the alanine detectors was direct related to the amount of photoelectric events in the nanocomposite. However, the self-absorption of the electrons ejected by one particle, by another nanoparticle in the vicinity, also dictates the sensitivity of the detectors. In this sense, homogeneous systems presented less self-absorption and, consequently, the increase in sensitivity was higher. For systems containing aggregated and segregated particles, self-absorption becomes more relevant. For incident photons with energies near de K-edge of the metal of the nanocomposite, the number of photoelectric events was more relevant than the organization of the particles inside the alanine crystals. For higher energies the probability of a photoelectric interaction decreases, therefore the aggregation and segregation of particles become essential in determining the sensitivity of the dosimeters.

Ribonucleotide Reductases (RNRs) are crucial enzymes that catalyze reduction of ribonucleotides to deoxyribonucleotides, required for the biosynthesis of DNA. Vital role played by RNR in the biosynthesis of DNA and its control on cell growth made it one of the main targets for anticancer therapy. Several laboratories clarified the aspects of reaction cascades at active site of RNR. Biochemical studies of RNR by Stubbe for the inactivation of RDPR by 2'-chloro-2'-deoxyuridine-5'-diphosphate emphasizes departure of chlorine as an anion, while biomimetic studies by Robins with 6'-O-nitro-2'-chloro-homonucleosides emphasizes the elimination of chlorine substituent from 2'-position as a radical. To clarify the ambiguity in the mechanism of inhibition of RNR by 2'-chloro-2'-deoxyuridine, biomimetic reactions with model 6-O-nitro-1,5-dideoxyhomosugar derivatives were investigated. The study includes several modes: (i) synthesis of 6-O-nitro-1,5-dideoxyhomosugar derivatives with chlorine, bromine or tosyl substituent at the C2 position with ribo and arabino configurations, (ii) biomimetic studies of 6-O-nitro-1,5-dideoxyhomosugar derivatives with Bu3SnH/AIBN to provide chemical evidences to distinguish the nature of elimination of chlorine from 2'-chloro-2'-deoxyuridine upon its incubation with enzyme, and (iii) kinetic studies to differentiate between heterolytic or homolytic C2'-chlorine bond cleavage. In the second half of this dissertation, azido and sulfenamide modified nucleosides and 2-azidolyxofuranoside derivatives have been synthesized with the azido or sulfenamide substitution at a specific site in the sugar or in the base moiety. The electron-induced site specific formation of neutral aminyl radicals (RNH●) and their subsequent reactions have been investigated using ESR spectroscopy. In 2'-AZdC the RNH● site is attached to a 2o C-atom, where as in 4'-AZdC, the RNH● site is attached to a 3o C-atom, respectively. These studies elucidated how stereo and electronic environment affect formation and subsequent reactivity of various types of RNH● generated from azidonucleosides. To avoid the interaction of transient radical with nucleoside heterocyclic bases, 2-azidolyxofuranoside derivatives as a simpler abasic model were synthesized and studied with ESR spectroscopy. Aminyl radical generated from 2-azidolyxofuranoside derivatives subsequently abstracted hydrogen from C5 intramolecularly. These studies were designed to understand the mechanism of damage in various DNA model structures.

Orientador: Pascoal José Giglio Pagliuso / Dissertação (mestrado) - Universidade Estadual de Campinas, Instituto de Fisica Gleb Wataghin / Made available in DSpace on 2018-08-14T11:11:25Z (GMT). No. of bitstreams: 1 HolandaJunior_LinoMartinsde_M.pdf: 2170608 bytes, checksum: 3abed7533be911b023d90094d4aa28f4 (MD5) Previous issue date: 2009 / Resumo: Nesta Dissertação desenvolvemos estudos de Ressonância de Spin Eletrônico (ESR) em monocristais dos compostos tipo férmions pesados YbR h2Si2 e YbAlB4. No caso do sistem YbRh2Si2, exploraramos os experimentos de ESR para três bandas de frequência existentes em nosso laboratório (n = 4,1 GHz (Banda-S), n = 9,4 GHz (Banda-X) e n = 34,0 GHz (Banda-Q)), o que situa o campo de ressonância da linha de ESR em diferentes regimes do diagrama de fase do YbRh2Si2, onde as fases antiferromagnética (AFM), líquido de Fermi (FL) e não-líquido de Fermi (NFL) podem ser encontradas. Foram investigados efeitos de campo cristalino e mudanças da dinâmica de spin dos elétrons 4¦ do Yb, para as diferentes bandas, e também para monocristais de YbR h2Si2 dopados com Lu e crescidos em uxo de Zn. Nossos resultados sugerem que o sinal de ESR observado em YbRh2Si2 consiste em um modo acoplado entre os 4f do Yb3+ e os elétrons de condução, em um regime tipo bottleneck com presença de interações antiferromagnéticas. Para o sistema YbAlB4, realizamos experimentos de ESR em banda-X nas duas fases iso-estequiométricas b -YbAl B4 e - a -YbAlB4. Para as amostras de b - YbAlB4 encontramos um comportamento interessante do sinal de ESR que apresenta características de uma ressonância de elétrons de condução (CESR) a altas temperaturas e adquire propriedades do íon de Yb3+ a baixas temperaturas. Tal dualidade não foi observada na fase a - YbAlB4. Nós discutiremos uma possível correlação entre o espectro de ESR observado nos dois sistemas férmions pesados que se situam em lados opostos de um ponto crítico quântico (Quantum Critical Point - QCP) em seus diagramas de fase. Essa correlação permitiu uma especulação sobre origem desse sinal de ESR em compostos férmions pesados, na qual a proximidade ao QCP desenvolve um papel crucial para o comportamento do espectro de ESR observado nessa classe de compostos. / Abstract: In this work we have performed Electron Spin Resonance (ESR) experiments on single crystals of YbR h2Si2 and YbAlB4 heavy fermion compounds. For YbRh2Si2, we explore the ESR measurements at three frequency bands (n = 4,1 GHz (S-Band), n = 9,4 GHz (X-Band) e n = 34,0 GHz (Q-Band)) which places the ESR resonance field within different regimes in the phase diagram of YbRh2Si2 where antiferromagnetic (AFM), Fermi liquid (FL) and non Fermi liquid (NFL) phases could be found. We have also explored the effects of crystal field and spin dynamics of Yb3+ for these different bands and also as a function of Lu-doping and single crystal growth methods. Our results indicate that the ESR signal found YbRh2Si2 behave such a Kondo coupled mode in a bottleneck-like regime with the presence of antiferromagnetic interactions. For YbAlB4, we have performed X-band experiments for single crystals the two different phases b -YbAl B4 and a -YbAlB4. For b -YbAlB4, we found a remarkable ESR signal that behaves as a conduction electron spin resonance (CESR) at high temperatures and acquires characteristics of the Yb3+ local moment ESR at low temperature. This behavior was not found in the a -YbAlB4. The striking and unique dual behavior observed in the same ESR spectra of b -YbAl B4 - a -YbAlB4 associated to the ESR results found for a -YbAlB4, YbRh2Si2 allow us to propose a qualitative scenario that may explain the origin of the ESR signal in HF systems. We speculate that for HF systems a strongly coupled 4¦ and ce give origin to Kondo coupled ESR modes with may behave as CESR or LM ESR, depending on the strength of Jfs. Moreover, HF systems near a QCP may have propitious conditions to present such a signal. / Mestrado / Física da Matéria Condensada / Mestre em Física

Investigation of spin dynamics in hybrid structures based on ferromagnetic semi- conductor (Ga,Mn)As Abstract: This dissertation deals with the study of hybrid ferromagnet/semiconductor structures, which are of particular for spintronics. We focused on heterostructures that contain ferromagnetic semiconductor (Ga,Mn)As, which is the most studied model ma- terial from the group of diluted magnetic semiconductors. The main goal of this work was a detailed study of the Optical Spin Transfer Torque (OSTT) phenomenon, which is an optical equivalent of the STT effect, which is used in ferromagnetic metal layers for non-thermal switching of the direction of magnetization. In the first part of the work, we describe experiments aimed at achieving non-thermal control of the direction of mag- netization in (Ga,Mn)As with the contribution of control of magnetic anisotropy using mechanical strain induced by a piezo-transducer (PZT) in hybrid structure (Ga,Mn)As/GaAs/PZT. For this purpose, the preparation of the structure was first opti- mized, which was tested in detail by means of X-ray diffraction and magneto-optical methods. However, we were unable to achieve magnetization switching due to the OSTT phenomenon. In addition, we found that the results measured at low temperature are very poorly reproducible, despite...

ESR, OSL and TT-OSL dating methods were applied to samples collected from six of the Ancient Coastal Deposits (ACDs) along the southern Georgia Coastline. Samples were collected from the Princess Anne (the youngest and most seaward ACD), Pamlico, Talbot, Penholoway, Wicomico, and Okefenokee ACDs with the goal of determining the age of formation of these features. Ground Penetrating Radar (GPR) was used to determine the subsurface morphology and target lithologies for age determination. OSL and TT-OSL dating was attempted on samples collected from the youngest two ACDs, the Pamlico and Princess Anne, at McMaster Universities AGE Lab. ESR samples collected from all of the ACDs studied were measured at Florida State University as well as Osaka University. ESR analysis measured the Al signal, the Ti-Li signal, measured using two different methods, as well as the Ti-H signal. A number of low additive dose points were added to the ESR dose plan to attempt to create a better dose response curve for the low saturating Ti-H signal in attempt to better utilize the signal. While the geochronological methodology did not prove useful for determining the age of all of the ACDs it did result in depositional age estimates for the Cypresshead Formation at 433-2978 ka and Satilla Formations at 243-417 ka using the Ti-Li ESR signal as a maximum age estimate. The GPR, ESR, and core data all point to the conclusion that the ACDs of the Georgia Coast are geomorphic modifications and not the result of a unique depositional process. Based on the discrepancy between the depositional age of the Cypresshead and Satilla Formations as determined by ESR in this study and the ages of the ACDs published by others from Georgia (Markewich et.al., 2013) or other areas of the Atlantic Coast (Wehmiller, 2004; Willis, 2006) it can be concluded that paleo sea-levels modified the Cypresshead and Satilla Formations in to the morphology seen today at some point after their initial deposition. / Dissertation / Doctor of Philosophy (PhD) / ESR, OSL and TT-OSL dating methods were applied to samples collected from six of the Ancient Coastal Deposits (ACDs) along the southern Georgia Coastline with the goal of determining the age of formation of these features. Ground Penetrating Radar (GPR) was used to determine the subsurface morphology and target lithologies for age determination. A number of low additive dose points were added to the ESR dose plan to attempt to create a better dose response curve for the low-dose saturation of the Ti-H signal in attempt to better utilize the signal. While the geochronological methodology did not prove useful for determining the age of all of the ACDs, it did result in depositional age estimates for the Cypresshead Formation at 433-2978 ka and Satilla Formations at 243-417 ka. The GPR, ESR, and core data all point to the conclusion that the ACDs of the Georgia Coast are geomorphic features without unique depositional events.

<p> The recent urban sprawl in the tectonically active region of California has prompted palaeoseismologists, to find ways of forecasting potentially hazardous earthquakes on existing faults. Electron spin resonance (ESR) can be used to date fault gouge from different regions in a fault zone thereby providing a history of fault movements in a particular region. Therefore, an earthquake frequency pattern can be established and the faults can be rated as to their potential danger. </p> <p> ESR dating of fault gouge is based on the premise that the ESR signals of quartz grains in the gouge have been completely reset by movements on the fault. The elapsed time since faulting is recorded by a gradual charge build up in the quartz corresponding to radioactive decay of radionuclides in the fault gouge matrix. The mechanism of zeroing of the ESR signals in quartz during fault activity is not well understood. In order to better comprehend the zeroing process, the variation of ESR signals, AD and age, with respect to quartz grains size were studied. These parameters are affected by induced stress to a greater extent in the smaller grain sizes. Therefore, with sufficient stress, the smallest grain sizes (smaller than a critical size) will be totally reset and define a "plateau" of equal age. This plateau criteria is used to define total resetting in a fault gouge sample and only these portions of the samples are used for dating. The establishment of an equal age plateau is confirmed for one of the fault samples collected from Southern California. </p> / Thesis / Master of Science (MS)

No description available.

A novel experimental setup has been realized to measure weak magnetic moments which can be modulated at radio frequencies (~1–5 MHz). Using an optimized radio-frequency (RF) pickup coil and lock-in amplifier, an experimental sensitivity of 10 -15 Am2 corresponding to 10 -18 emu has been demonstrated with a one second time constant. The detection limit at room temperature is 9.3 10 -16 Am2/√Hz limited by Johnson noise of the coil. In order to demonstrate the sensitivity of this technique it was used to electrically detect the polarized spins in semiconductors in zero applied magnetic fields. For example in GaAs, the magnetic moment due to a small number (~ 7 x 108) of spin polarized electrons generated by polarization modulated optical radiation was detected. Spin polarization was generated by optical injection using circularly polarized light which is modulated rapidly using an electro-optic cell. The modulated spin polarization generates a weak time-varying magnetic field which is detected by the sensitive radio-frequency coil. Using a radio-frequency lock-in amplifier, clear signals were obtained for bulk GaAs and Ge samples from which an optical spin orientation efficiency of ~ 10–20% could be determined for Ge at 1342 nm excitation wavelength at 127 K. In the presence of a small external magnetic field, the signal decayed according to the Hanle Effect, from which a spin lifetime of 4.6 ± 1.0 ns for electrons in bulk Ge at 127 K was extracted. The spin dynamics in n-Ge was further explored and the temperature dependence of the spin lifetime was plotted for a temperature range of about 90 K to 180 K. The temperature dependence of the optical pumping efficiency was also measured though no quantitative conclusions could be derived. The signals observed for semi-insulating GaAs, n-GaAs, GaSb and CdTe which are direct gap semiconductors are much larger than expected (almost two orders of magnitude). An attempt was made to explain this unexpected behavior of these direct gap semiconductors using the spin hall effect.