Photoluminescence studies of spray pyrolytically grown nanostructured tin oxide semiconductor thin films on glass substrates

SnO2 nanocrystalline thin films were deposited on glass substrates by the spray pyrolysis technique in air atmosphere at 375, 400, 425, 450 and 500 ◦C substrate temperatures. The obtained films were characterized by using XRD. The room temperature photoluminescence (PL) spectra of these films have near band edge (NBE) and deep level emission under the excitation of 325 nm radiation. NBE PL peak intensity decreased consistently with temperatures for samples prepared at 400, 450 and 500 ◦C, while a sudden reduction in intensity is observed for the sample prepared at 425 ◦C. A similar effect was observed for the optical transmittance spectra. These effects can be explained on the basis of the change in population of oxygen vacancies as indicated by the change in a values

Reliable and Damage-Free Estimation of Resistivity of ZnO Thin Films for Photovoltaic Applications Using Photoluminescence Technique

This work projects photoluminescence (PL) as an alternative technique to estimate the order of resistivity of zinc oxide (ZnO) thin films. ZnO thin films, deposited using chemical spray pyrolysis (CSP) by varying the deposition parameters like solvent, spray rate, pH of precursor, and so forth, have been used for this study. Variation in the deposition conditions has tremendous impact on the luminescence properties as well as resistivity. Two emissions could be recorded for all samples—the near band edge emission (NBE) at 380 nm and the deep level emission (DLE) at ∼500 nm which are competing in nature. It is observed that the ratio of intensities of DLE to NBE ( DLE/ NBE) can be reduced by controlling oxygen incorporation in the sample. - measurements indicate that restricting oxygen incorporation reduces resistivity considerably. Variation of DLE/ NBE and resistivity for samples prepared under different deposition conditions is similar in nature. DLE/ NBE was always less than resistivity by an order for all samples.Thus from PL measurements alone, the order of resistivity of the samples can be estimated.

Nanocrystalline Ge Flash Memories: Electrical Characterization and Trap Engineering

Conventional floating gate non-volatile memories (NVMs) present critical issues for device scalability beyond the sub-90 nm node, such as gate length and tunnel oxide thickness reduction. Nanocrystalline germanium (nc-Ge) quantum dot flash memories are fully CMOS compatible technology based on discrete isolated charge storage nodules which have the potential of pushing further the scalability of conventional NVMs. Quantum dot memories offer lower operating voltages as compared to conventional floating-gate (FG) Flash memories due to thinner tunnel dielectrics which allow higher tunneling probabilities. The isolated charge nodules suppress charge loss through lateral paths, thereby achieving a superior charge retention time. Despite the considerable amount of efforts devoted to the study of nanocrystal Flash memories, the charge storage mechanism remains obscure. Interfacial defects of the nanocrystals seem to play a role in charge storage in recent studies, although storage in the nanocrystal conduction band by quantum confinement has been reported earlier. In this work, a single transistor memory structure with threshold voltage shift, Vth, exceeding ~1.5 V corresponding to interface charge trapping in nc-Ge, operating at 0.96 MV/cm, is presented. The trapping effect is eliminated when nc-Ge is synthesized in forming gas thus excluding the possibility of quantum confinement and Coulomb blockade effects. Through discharging kinetics, the model of deep level trap charge storage is confirmed. The trap energy level is dependent on the matrix which confines the nc-Ge.

El trabajo en equipo en el Proceso Administrativo y de Compras en OPL Carga de Bucaramanga

El proceso administrativo y de compras de OPL Carga tiene algunas falencias entre ellas: fallas en la Comunicación entre el personal operativo, no se realizan llamadas internas usando con frecuencia el email, produciendo la saturación de solicitudes las cuales terminan sin ser resueltas en cuanto a roles se refiere, no hay enfoque de procesos en vista que no se tiene claras las tareas de cada cargo, adicionalmente no hay claridad en los subprocesos, perjudicando el proceso con el aumento de costos, pérdida de tiempo, las responsabilidades de los funcionario no todas las veces se ejecutan en el tiempo asignado, el liderazgo compartido presenta ambigüedades. Objetivos: Definir el trabajo en equipo en el proceso administrativo y de compras en OPL carga de Bucaramanga. La investigación que a realizar es de tipo descriptivo, busca descubrir las falencias o características que permiten diseñar y desarrollar un modelo de solución para los problemas del equipo de OPL Carga S.A.S. Materiales y métodos: La investigación efectuada es de tipo descriptivo, el objetivo es definir el modelo del trabajo en equipo y describir las falencias en el proceso administrativo y de compras en OPL carga de Bucaramanga, que permitan obtener un diagnóstico integral que conlleve a la implementación de estrategias de solución. Resultados: Se identificaron las falencias en los siguientes aspectos: Variable comunicación, rendimiento, destrezas complementarias, propósito significativo y meta específicas de los funcionarios en OPL carga sección administrativa. Conclusiones: El modelo de trabajo en equipo que OPL aplica es jerárquico, en el que se ofrece estabilidad, seguridad, se toman decisiones en forma piramidal, mediante la planeación de tareas, la colaboración, igualdad y respeto por los miembros, trabajando en pro de la solución de problemas. Se construyó un plano conceptual que permitió exponer la interpretación que la estudiante tiene de las teorías, investigaciones y antecedentes válidos para la comprensión del problema investigado. Área comunicacional: Coordinar acciones tendientes para que los funcionarios respondan a tiempo los emails atenientes a su trabajo. Área condiciones de trabajo: Clarificar y diseñar las reglas de comportamiento al interior de los equipos de trabajo que redunden en el mejoramiento del mismo y la búsqueda de soluciones oportunas. Área metas específicas: Procurar mediante auditorías el cumplimiento de las metas y objetivos propuestos por cada equipo de trabajo.

Developing international business managers through international study visits to China

Globalization is a key factor in the success of business organizations today, impacting many aspects of management performance. Understanding the global business environment has therefore become a key objective in the teaching of international business on Executive MBA programs. Drawing on the theory of experiential learning, this study examines the relationship between program structure and learning activities of an international study visit (ISV) to China and the learning experience for Executive MBA students. The findings indicate that learning experience may be most effective where the structure of an ISV incorporates certain activities that promote experiential and deep-level learning. Educational implications are discussed.

Defeitos responsáveis pela isolação de GaAs irradiado com prótons

A Espectroscopia de Transientes de Níveis Profundos (DLTS – Deep Level Transient Spectroscopy) foi, detalhadamente, descrita e analisada. O processo de isolação por implantação em GaAs foi estudado. Sua dependência com a sub-rede, do As ou do Ga, em que o dopante é ativado foi investigada para material tipo-p. Semelhantes doses de implantação de prótons foram necessárias para se tornar semi-isolantes camadas de GaAs dopadas com C ou com Mg possuindo a mesma concentração de pico de lacunas livres. A estabilidade térmica da isolação nestas amostras foi medida. Diferenças no comportamento de recozimento destas apontaram a formação, provavelmente durante a referida etapa térmica, de uma estrutura diferente de defeitos em cada caso. Medidas de DLTS foram realizadas em amostras de GaAs tipo-n e tipo-p implantadas com prótons de 600 keV. A estrutura de picos observada apresentou, além de boa parte dos defeitos introduzidos para o caso de irradiação com elétrons, defeitos mais complexos. Um novo nível, com energia superior em ~0,64 eV ao valor correspondente ao topo da banda de valência, foi identificado nos espectros medidos em material tipo-p. A variação da concentração dos centros de captura introduzidos com diferentes etapas de recozimento foi estudada e comparada com o comportamento previamente observado para a resistência de folha em camadas de GaAs implantadas com prótons. Simulações foram feitas, indicando que a interpretação adotada anteriormente, associando o processo de isolação diretamente à formação de defeitos relacionados a anti-sítios, pode não estar completa.

Effect of pressure-assisted thermal annealing on the optical properties of ZnO thin films

ZnO thin films were prepared by the polymeric precursor method. The films were deposited on silicon substrates using the spin-coating technique, and were annealed at 330°C for 32h under pressure-assisted thermal annealing and under ambient pressure. Their structural and optical properties were characterized, and the phases formed were identified by X-ray diffraction. No secondary phase was detected. The ZnO thin films were also characterized by field-emission scanning electron microscopy, Fourier transform infrared spectroscopy, photoluminescence and ultraviolet emission intensity measurements. The effect of pressure on these thin films modifies the active defects that cause the recombination of deep level states located inside the band gap that emit yellow-green (575nm) and orange (645nm) photoluminescence. © 2012 John Wiley & Sons, Ltd.

Flicts, livro de artista

Coordenação de Aperfeiçoamento de Pessoal de Nível Superior (CAPES)

Naturalidade: o nível profundo da comunicaçao

Coordenação de Aperfeiçoamento de Pessoal de Nível Superior (CAPES)

Docweb: análise do documentário on-line HayMotivo.com

Fundação de Amparo à Pesquisa do Estado de São Paulo (FAPESP)

Bacterial cellulose as a template for preparation of hydrotalcite-like compounds

Fundação de Amparo à Pesquisa do Estado de São Paulo (FAPESP)

Investigation of photoinduced electrical properties in the heterojunction TiO2/SnO2

TiO2/SnO2 thin films heterostructures were grown by the sol-gel dip-coating technique. It was found that the crystalline structure of TiO2 depends on the annealing temperature and the substrate type. TiO2 films deposited on glass substrate, submitted to thermal annealing until 550 degrees C, present anatase structure, whereas films deposited on quartz substrate transform to rutile structure when thermally annealed at 1100 degrees C. When structured as rutile, this oxide semiconductor has very close lattice parameters to those of SnO2, making easier the heterostructure assembling. The electrical properties of TiO2/SnO2 heterostructure were evaluated as function of temperature and excitation with different light sources. The temperature dependence of conductivity is dominated by a deep level with energy coincident with the second ionization level of oxygen vacancies in SnO2, suggesting the dominant role of the most external layer material (SnO2) to the electrical transport properties. The fourth harmonic of a Nd:YAG laser line (4.65 eV) seems to excite the most external layer whereas a InGaN LED (2.75 eV) seems to excite electrons from the ground state of a quantized interfacial channel as well as intrabandgap states of the TiO2 layer.

Oceanic crust and island arc formation in Central Asia during late Neoproterozoic times - evidence from petrological and geochemical studies

Die vorliegende Arbeit behandelt die Entwicklung des 570 Ma alten, neoproterozoischen Agardagh - Tes-Chem Ophioliths (ATCO) in Zentralasien. Dieser Ophiolith liegt südwestlich des Baikalsees (50.5° N, 95° E) und wurde im frühen Stadium der Akkretion des Zentralasiatischen Mobilgürtels auf den nordwestlichen Rand des Tuvinisch-Mongolischen Mikrokontinentes aufgeschoben. Bei dem Zentralasiatische Mobilgürtel handelt es sich um einen riesigen Akkretions-Subduktionskomplex, der heute das größte zusammenhängende Orogen der Erde darstellt. Im Rahmen dieser Arbeit wurden eine Reihe plutonischer und vulkanischer Gesteine, sowie verschiedene Mantelgesteine des ATCO mittels mikroanalytischer und geochemischer Verfahren untersucht (Elektronenstrahlmikrosonde, Ionenstrahlmikrosonde, Spurenelement- und Isotopengeochemie). Die Auswertung dieser Daten ermöglichte die Entwicklung eines geodynamisch-petrologischen Modells zur Entstehung des ATCO. Die vulkanischen Gesteine lassen sich aufgrund ihrer Spurenelement- und Isotopenzusammensetzung in inselbogenbezogene und back-arc Becken bezogene Gesteine (IA-Gesteine und BAB-Gesteine) unterscheiden. Darüber hinaus gibt es eine weitere, nicht eindeutig zuzuordnende Gruppe, die hauptsächlich mafische Gänge umfasst. Der grösste Teil der untersuchen Vulkanite gehört zur Gruppe der IA-Gesteine. Es handelt sich um Al-reiche Basalte und basaltische Andesite, welche aus einem evolvierten Stammmagma mit Mg# 0.60, Cr ~ 180 µg/g und Ni ~ 95 µg/g hauptsächlich durch Klinopyroxenfraktionierung entstanden sind. Das Stammmagma selbst entstand durch Fraktionierung von ca. 12 % Olivin und geringen Anteilen von Cr-Spinell aus einer primären, aus dem Mantel abgeleiteten Schmelze. Die IA-Gesteine haben hohe Konzentrationen an inkompatiblen Spurenelementen (leichte-(L)- Seltenerdelement-(SEE)-Konzentrationen etwa 100-fach chondritisch, chondrit-normierte (La/Yb)c von 14.6 - 5.1), negative Nb-Anomalien (Nb/La = 0.37 - 0.62) und niedrige Zr/Nb Verhältnisse (7 - 14) relativ zu den BAB-Gesteinen. Initiale eNd Werte liegen bei etwa +5.5, initiale Bleiisotopenverhältnisse sind: 206Pb/204Pb = 17.39 - 18.45, 207Pb/204Pb = 15.49 - 15.61, 208Pb/204Pb = 37.06 - 38.05. Die Anreicherung lithophiler inkompatibler Spurenelemente (LILE) in dieser Gruppe ist signifikant (Ba/La = 11 - 130) und zeigt den Einfluss subduzierter Komponenten an. Die BAB-Gesteine repräsentieren Schmelzen, die sehr wahrscheinlich aus der gleichen Mantelquelle wie die IA-Gesteine stammen, aber durch höhere Aufschmelzgrade (8 - 15 %) und ohne den Einfluss subduzierter Komponenten entstanden sind. Sie haben niedrigere Konzentrationen an inkompatiblen Spurenelementen, flache SEE-Muster ((La/Yb)c = 0.6 - 2.4) und höhere initiale eNd Werte zwischen +7.8 und +8.5. Nb Anomalien existieren nicht und Zr/Nb Verhältnisse sind hoch (21 - 48). Um die geochemische Entwicklung der vulkanischen Gesteine des ATCO zu erklären, sind mindestens drei Komponenten erforderlich: (1) eine angereicherte, ozeaninselbasalt-ähnliche Komponente mit hoher Nb Konzentration über ~ 30 µg/g, einem niedrigen Zr/Nb Verhältnis (ca. 6.5), einem niedrigen initialen eNd Wert (um 0), aber mit radiogenen 206Pb/204Pb-, 207Pb/204Pb- und 208Pb/204Pb-Verhältnissen; (2) eine N-MORB ähnliche back-arc Becken Komponente mit flachem SEE-Muster und einem hohen initialen eNd Wert von mindestens +8.5, und (3) eine Inselbogen-Komponente aus einer verarmten Mantelquelle, welche durch die abtauchende Platte geochemisch modifiziert wurde. Die geochemische Entstehung der ATCO Vulkanite lässt sich dann am besten durch eine Kombination aus Quellenkontamination, fraktionierte Kristallisation und Magmenmischung erklären. Geodynamisch gesehen entstand der ATCO sehr wahrscheinlich in einem intraozeanischen Inselbogen - back-arc System. Bei den untersuchten Plutoniten handelt es sich um ultramafische Kumulate (Wehrlite und Pyroxenite) sowie um gabbroische Plutonite (Olivin-Gabbros bis Diorite). Die geochemischen Charakteristika der mafischen Plutonite sind deutlich unterschiedlich zu denen der vulkanischen Gesteine, weshalb sie sehr wahrscheinlich ein späteres Entwicklungsstadium des ATCO repräsentieren. Die Spurenelement-Konzentrationen in den Klinopyroxenen der ultramafischen Kumulate sind extrem niedrig, mit etwa 0.1- bis 1-fach chondritischen SEE-Konzentrationen und mit deutlich LSEE-verarmten Mustern ((La/Yb)c = 0.27 - 0.52). Berechnete Gleichgewichtsschmelzen der ultramafischen Kumulate zeigen grosse Ähnlichkeit zu primären boninitischen Schmelzen. Die primären Magmen waren daher boninitischer Zusammensetzung und entstanden in dem durch vorausgegangene Schmelzprozesse stark verarmten Mantelkeil über einer Subduktionszone. Niedrige Spurenelement-Konzentrationen zeigen einen geringen Einfluss der abtauchenden Platte an. Die Spurenelement-Konzentrationen der Gabbros sind ebenfalls niedrig, mit etwa 0.5 - 10-fach chondritischen SEE-Konzentrationen und mit variablen SEE-Mustern ((La/Yb)c = 0.25 - 2.6). Analog zu den Vulkaniten der IA-Gruppe haben alle Gabbros eine negative Nb-Anomalie mit Nb/La = 0.01 - 0.31. Die initialen eNd Werte der Gabbros variieren zwischen +4.8 und +7.1, mit einem Mittelwert von +5.9, und sind damit identisch mit denen der IA-Vulkanite. Bei den untersuchten Mantelgesteinen handelt es sich um teilweise serpentinisierte Dunite und Harzburgite, die alle durch hohe Mg/Si- und niedrige Al/Si-Verhältnisse gekennzeichnet sind. Dies zeigt einen refraktären Charakter an und steht in guter Übereinstimmung mit den hohen Cr-Zahlen (Cr#) der Spinelle (bis zu Cr# = 0.83), auf deren Basis der Aufschmelzgrad der residuellen Mantelgesteine berechnet wurde. Dieser beträgt etwa 25 %. Die geochemische Zusammensetzung und die petrologischen Daten der Ultramafite und Gabbros lassen sich am besten erklären, wenn man für die Entstehung dieser Gesteine einen zweistufigen Prozess annimmt. In einer ersten Stufe entstanden die ultramafischen Kumulate unter hohem Druck in einer Magmenkammer an der Krustenbasis, hauptsächlich durch Klinopyroxen-Fraktionierung. Bei dieser Magmenkammer handelte es sich um ein offenes System, dem von unten laufend neue Schmelze zugeführt wurde, und aus dem im oberen Bereich evolviertere Schmelzen geringerer Dichte entwichen. Diese evolvierten Schmelzen stiegen in flachere krustale Bereiche auf und bildeten dort meist isolierte Intrusionskörper. Diese Intrusionskörper erstarrten ohne Magmen-Nachschub, weshalb petrographisch sehr unterschiedliche Gesteine entstehen konnten. Eine geochemische Modifikation der abkühlenden Schmelzen erfolgte allerdings durch die Assimilation von Nebengestein. Da innerhalb der Gabbros keine signifikante Variation der initalen eNd Werte existiert, handelte es sich bei dem assimilierten Material hauptsächlich um vulkanische Gesteine des ATCO und nicht um ältere, möglicherweise kontinentale Kruste.

Surface-functionalized latex particles as additives in the mineralization of zinc oxide

Polystyrene latex particles modified at the surface with different hydrophilic functional groups were prepared by miniemulsion polymerization and applied to control the crystallization of zinc oxide in aqueous medium. The effects of both latex structure and concentration on the crystal growth, morphology, crystalline structure, and properties of the resulting zinc oxide were analyzed. Depending on the latex additive used, micro- and submicrosized crystals with a broad variety of morphologies were obtained. Among the studied latexes, the carboxyl-derived particles were shown to be a convenient system for further quantitative investigations. In this case, as the additive concentration increases, the aspect ratio of the crystals decreases systematically. Latex particles are assumed to adsorb preferentially onto the fast growing {001} faces of ZnO, interacting with the growth centers and reducing the growth rate in [001]. When zinc oxide is precipitated in the presence of latex, the polymer particles become incorporated into the growing crystals and polymer–inorganic hybrid materials are obtained. These materials are composed of an inorganic and largely undisturbed crystalline matrix in which organic latex particles are embedded. Increasing amounts of latex become incorporated into the growing crystals at increasing overall concentration in the crystallizing system. Photoluminescence (PL) spectra were measured to obtain information on defect centers. Emission spectra of all samples showed a narrow UV peak and a broad band in the green-yellow spectral region. The former emission is attributed to exciton recombination, whereas the latter seems to be related with deep-level donors. Latex appears to be a quencher of the visible emission of zinc oxide. Thus, compared to pure zincite, ZnO–latex hybrid materials show a significantly lower PL intensity in the visible range of the spectrum. Under continuous photoexcitation, a noticeable dynamic behavior of the PL is observed, which can be related to a photodesorption of adsorbed oxygen. These surface-adsorbed oxygen species seem to play a crucial role for the optical properties of the materials and may mediate the tunneling of electrons from the conduction band to preexisting deep-level traps, probably related to intrinsic defects (oxygen vacancies or interstitial zinc). The polymer particles can block the sites where oxygen adsorbs, and the disappearance of the “electron-shuttle” species leads to the observed quenching of the visible emission. Electron paramagnetic resonance (EPR) provided additional information about crystal defects with unpaired electrons. Spectra of all samples exhibit a single signal at g ≈ 1.96, typical for shallow donors. Contrary to the results of other authors, no correlation was possible between the EPR signal and the visible range of PL spectra, which suggests that centers responsible for the visible emission and the EPR signal are different.

Photoinduced electronic transitions and leakage correlation to defects/dislocations in GaN heterostructures

III-nitride materials are very promising for high speed electronics/optical applications but still suffer in performance due to problems during high quality epitaxial growth, evolution of dislocation and defects, less understanding of fundamental physics of materials/processing of devices etc. This thesis mainly focus on GaN based heterostructures to understand the metal-semiconductor interface properties, 2DE(H)G influence on electrical and optical properties, and deep level states in GaN and InAlN, InGaN materials. The detailed electrical characterizations have been employed on Schottky diodes at GaN and InAl(Ga)N/GaN heterostructures in order to understand the metal-semiconductor interface related properties in these materials. I have observed the occurrence of Schottky barrier inhomogenity, role of dislocations in terms of leakage and creating electrically active defect states within energy gap of materials. Deep level transient spectroscopy method is employed on GaN, InAlN and InGaN materials and several defect levels have been observed related to majority and minority carriers. In fact, some defects have been found common in characteristics in ternary layers and GaN layer which indicates that those defect levels are from similar origin, most probably due to Ga/N vacancy in GaN/heterostructures. The role of structural defects, roughness has been extensively understood in terms of enhancing the reverse leakage current, suppressing the mobility in InAlN/AlN/GaN based high electron mobility transistor (HEMT) structures which are identified as key issues for GaN technology. Optical spectroscopy methods have been employed to understand materials quality, sub band and defect related transitions and compared with electrical characterizations. The observation of 2DEG sub band related absorption/emission in optical spectra have been identified and proposed for first time in nitride based polar heterostructures, which is well supported with simulation results. In addition, metal-semiconductor-metal (MSM)-InAl(Ga)N/GaN based photodetector structures have been fabricated and proposed for achieving high efficient optoelectronics devices in future.