Low temperature annealing effects on the structure and optical properties of ZnO films grown by pulsed laser deposition

ZnO thin films were deposited on glass substrates at room temperature (RT) similar to 500 degrees C by pulsed laser deposition (PLD) technique and then were annealed at 150-450 degrees C in air. The effects of annealing temperature on the microstructure and optical properties of the thin films deposited at each substrate temperature were investigated by XRD, SEM, transmittance spectra, and photoluminescence (PL). The results showed that the c-axis orientation of ZnO thin films was not destroyed by annealing treatments: the grain size increased and stress relaxed for the films deposited at 200-500 degrees C, and thin films densified for the films deposited at RT with increasing annealing temperature. The transmittance spectra indicated that E-g of thin films showed a decreased trend with annealing temperature. From the PL measurements, there was a general trend, that is UV emission enhanced with lower annealing temperature and disappeared at higher annealing temperature for the films deposited at 200-500 degrees C; no UV emission was observed for the films deposited at RT regardless of annealing treatment. Improvement of grain size and stoichiometric ratio with annealing temperature can be attributed to the enhancement of UV emission, but the adsorbed oxygen species on the surface and grain boundary of films are thought to contribute the annihilation of UV emission. It seems that annealing at lower temperature in air is an effective method to improve the UV emission for thin films deposited on glass substrate at substrate temperature above RT.

Effect of rapid thermal annealing on electron emission and DX centers in strained InGaAs/GaAs single quantum well laser diodes

Thermal processing of strained In0.2Ga0.8As/GaAs graded-index separate confinement heterostructure single quantum well laser diodes grown by molecular beam epitaxy is investigated. It is found that rapid thermal annealing can improve the 77K photoluminescence efficiency and electron emission from the active layer, due to the removal of nonradiative centers from the InGaAs/GaAs interface. Because of the interdiffusion of Al and Ga atoms, rapid thermal annealing increases simultaneously the density of DX centers in the AlGaAs graded layer. The current stressing experiments of postgrowth and annealed laser diodes are indicative of a corresponding increase in the concentration of DX centers, suggesting that DX centers may be responsible for the degradation of laser diode performance.

Effects of annealing treatment on the formation of CO2 in ZnO thin films grown by metal-organic chemical vapor deposition

Post-growth annealing was carried out on ZnO thin films grown by metal-organic chemical vapor deposition (MOCVD). The grain size of ZnO thin film increases monotonically with annealing temperature. The ZnO thin films were preferential to c-axis oriented after annealing as confirmed by Xray diffraction (XRD) measurements. Fourier transformation infrared transmission measurements showed that ZnO films grown at low temperature contains CO2 molecules after post-growth annealing. A two-step reaction process has been proposed to explain the formation mechanism of CO2, which indicates the possible chemical reaction processes during the metal-organic chemical vapor deposition of ZnO films.

Effect of rapid thermal annealing on electron emission and DX centers in strained InGaAs/GaAs single quantum well laser diodes

nThermal processing of strained ln(0.2)Ga(0.8)As/GaAs graded-index separate confinement heterostructure single quantum well laser diodes grown by molecular beam epitaxy is investigated. It was found that rapid thermal annealing can improve the 77 K photoluminescence efficiency and electron emission from the active layer, due to removal of nonradiative centers from the InGaAs/GaAs interface. Because of the interdiffusion of Al and Ga atoms, rapid thermal annealing increases simultaneously the density of DX centers in the AlGaAs graded layer. The current stressing experiments of post-growth and annealed laser diodes are indicative of a corresponding increase in the concentration of DX centers, suggesting that DX centers may be responsible for the degradation of laser diode performance.

Effect of post-weld-annealing on the tensile deformation characteristics of laser-welded NiTi thin foil

Laser welding is an important process for fabricating complex components involving NiTi shape memory
alloy. As welding is a thermal process, the amount of heat input and the rate of cooling have significant
impact on the microstructure and hence the resultant characteristics of NiTi. In this study, the effect of
laser welding and post-weld-annealing from 573 K to 1173 K on the thermal phase transformation behaviors,
tensile deformation and micro-hardness characteristics of the laser-welded NiTi thin foils were investigated.
It was found that the as-welded sample exhibited inferior super-elasticity compared to the base
material, and the super-elasticity could be partially restored by annealing at 573 K. On the other hand,
annealing of the weldment above the recrystallization temperature would lower the super-elasticity.

Application of a cw quantum cascade laser CO2 analyser to catalytic oxidation reaction monitoring

Catalytic oxidation reaction monitoring has been performed for the first time with a trace gas carbon dioxide analyser based on a continuous wave (cw), thermoelectrically cooled (TEC), distributed feedback (DFB) quantum cascade laser (QCL) operating at around 2307 cm^-1. The reaction kinetics for carbon monoxide oxidation over a platinum catalyst supported on yttria-stabilised zirconia were followed by the QCL CO₂ analyser and showed that it is a powerful new tool for measuring low reaction rates associated with low surface area model catalysts operating at atmospheric pressures. A detection limit was determined of 40 ppb (1 standard deviation) for a 0.1 s average and a residual absorption standard deviation of 1.9×10^-4. © 2012 Springer-Verlag.

DCOOD optically pumped by a (CO2)-C-13 laser: new terahertz laser lines

In this work we report on new optically pumped THz laser lines from deuterated formic acid (DCOOD). An isotopic (CO2)-C-13 laser was used for the first time as a pump source for this molecule, and a Fabry-Perot cavity was used as a THz laser resonator. Optoacoustic absorption spectra were used as a guide to search for new THz laser lines. We could observe six new laser lines in the range from 303.8 mu m (0.987 THz) to 725.1 mu m (0.413 THz). The lines were characterized according to wavelength, relative polarization, relative intensity, and optimum working pressure. The transferred lamb-dip technique was used to measure the frequency absorption transition for both of these laser lines. Furthermore, we also present a catalogue of all THz laser lines generated from DCOOD.

Aplicação do processo laser CO2 de soldagem em aço ARBL na fabricação de rotores para máquinas elétricas

Pós-graduação em Engenharia Mecânica - FEG

Tratamento de sequelas de queimadura de face com laser de CO2 fracionado em pacientes com fototipos III a VI

INTRODUÇÃO: Relatos sobre melhora em cicatrizes pós-traumáticas ou patológicas com o uso do laser de CO2 fracionado (CO2F) concluem tratar-se de tecnologia segura e efetiva, apesar de utilizado apenas em pacientes com fototipos II a III. O objetivo deste estudo foi avaliar a eficácia do CO2F em pacientes com sequela de queimadura facial com fototipos III a VI. MÉTODO: No total, 14 pacientes, com média de idade de 29 anos, portadores de sequela de queimadura facial e fototipos III a VI, foram submetidos a uma aplicação do laser de CO2F. Após dois meses, a queimadura foi avaliada por meio de escala com 6 parâmetros: cor, textura, hidratação, irregularidades de superfície, volume e distensibilidade. RESULTADOS: A duração média da dor foi de 19 horas; do edema, 1,3 dia; e da hiperemia, 6,5 dias. A queda das crostas finalizou entre 5 dias e 36 dias, com média de 13,4 dias. Dois meses após a sessão, 5 pacientes evoluíram com hipocromia puntiforme no padrão quadriculado correspondente aos pontos de ablação do laser. A satisfação subjetiva dos avaliadores (pacientes e médicos) com o tratamento foi de 84,6%. Para os pacientes, houve melhora das irregularidades de superfície, da distensibilidade e da textura da pele (57% dos casos), da hidratação (43%), do volume (28%) e da cor (14%). Para os médicos, houve melhora das irregularidades de superfície e da distensibilidade (43%). CONCLUSÕES: O tratamento com laser de CO2F com parâmetros suaves foi bem tolerado e apresentou alto índice de satisfação em pacientes com sequela de queimadura facial, com melhora de textura, distensibilidade e irregularidades de superfície. A alta incidência de hipopigmentação é um fator a ser considerado na indicação do laser de CO2F em pacientes com fototipos IV a VI.

Organic distributed feedback laser to monitor solvent extraction upon thermal annealing in solution-processed polymer films

Solution-processed polymer films are used in multiple technological applications. The presence of residual solvent in the film, as a consequence of the preparation method, affects the material properties, so films are typically subjected to post-deposition thermal annealing treatments aiming at its elimination. Monitoring the amount of solvent eliminated as a function of the annealing parameters is important to design a proper treatment to ensure complete solvent elimination, crucial to obtain reproducible and stable material properties and therefore, device performance. Here we demonstrate, for the first time to our knowledge, the use of an organic distributed feedback (DFB) laser to monitor with high precision the amount of solvent extracted from a spin-coated polymer film as a function of the thermal annealing time. The polymer film of interest, polystyrene in the present work, is doped with a small amount of a laser dye as to constitute the active layer of the laser device and deposited over a reusable DFB resonator. It is shown that solvent elimination translates into shifts in the DFB laser wavelength, as a consequence of changes in film thickness and refractive index. The proposed method is expected to be applicable to other types of annealing treatments, polymer-solvent combinations or film deposition methods, thus constituting a valuable tool to accurately control the quality and reproducibility of solution-processed polymer thin films.

Annealing and spectral characteristics of femtosecond laser inscribed long period gratings written into a photonic crystal fibre

A series of LPGs with the same period was inscribed by femtosecond laser into photonic crystal fibre with various powers. All suffered post-fabrication spectral evolution at low temperatures, apparently related to inscription power.

Annealing and spectral characteristics of femtosecond laser inscribed long period gratings written into a photonic crystal fibre

A series of LPGs with the same period was inscribed by femtosecond laser into photonic crystal fibre with various powers. All suffered post-fabrication spectral evolution at low temperatures, apparently related to inscription power.