Structural, morphological, and optical properties of AlGaN/GaN heterostructures with AlN buffer and interlayer

Cataloged from PDF version of article.AlxGa1-xN/GaN (x similar to 0.3) heterostructures with and without a high-temperature (HT) AlN interlayer (IL) have been grown on sapphire (Al2O3) substrates and AlN buffer/Al2O3 templates by metal organic chemical vapor deposition. The effects of an AlN buffer layer (BL) grown on an Al2O3 substrate and an AlN IL grown under the AlGaN ternary layer (TL) on structural, morphological, and optical properties of the heterostructures have been investigated by high-resolution x-ray diffraction, spectroscopic ellipsometry, atomic force microscopy, and photoluminescence measurements. The AlN BL improves the crystal quality of the AlGaN TL. Further improvement is achieved by inserting an AlN IL between GaN BL and AlGaN TL. However, experimental results also show that a HT AlN IL leads to relatively rough surfaces on AlGaN TLs, and an AlN IL changes the strain in the AlGaN TL from tensile to compressive type. In addition, an AlN BL improves the top surface quality of heterostructures. (c) 2007 American Institute of Physics

Current-voltage (I-V) characteristics of Au/InGaAs/n-GaAs Schottky barrier diodes

In this study, the forward and reverse bias current-voltage (I-V) characteristics of Au/InGaAs/n-GaAs Schottky barrier diodes (SBDs) have been investigated at room temperature. InGaAs epilayer was grown on (100) oriented n-GaAs substrate using V80-H solid source Molecular Beam Epitaxy (MBE) system. Atomic Force Microscope (AFM) was used in order to study the surface properties of InGaAs epilayer. The AFM measurement was performed by using an Omicron variable temperature STM/AFM instrument. The electrical parameters such as barrier height (Phi(b)), ideality factor (n), series resistance (R-s) and interface states (N-ss) of Au/InGaAs/n-GaAs SBDs have been calculated by using forward and reverse bias I-V measurements. The energy distribution of interface states of the structure was obtained from the forward bias I-V measurements by taking the bias dependence of the effective barrier height (Phi(e)) into account. In addition, the values of R-s and Phi(b), were determined by using Cheung's methods and results have been compared with each other

Effects of plasma-emulating light emitting diode (LED) versus conventional LED on cytotoxic effects of orthodontic cements as a function of polymerization capacity

Objectives: The study was aimed at evaluating, in vitro, cytotoxicity of four resin-based orthodontic cements (RBOC) as a function of degree of conversion (DC) and the light curing unit (LCU) employed on mouse fibroblast (L929). Materials and Methods: Nine samples were manufactured for each group of cements using plasma-emulating light-emitting diode (LED) and conventional LED. Toxicity was assessed by immersing four specimens to culture medium (24 h/37 degrees C) for extracting residual monomer or cytotoxic substance. Cell mitochondrial activity of L929 cell was evaluated using methyl tetrazolium (MTT) test. DC was evaluated by Fourier transform infrared spectroscopy for five samples. Results: Cements, LCUs, and interaction between cements and LCUs were found to play a statistically significant role in cytotoxicity (p 0.05). OPAL plasma LED displayed the highest levels of DC. The correlations between cell viability and DC were positive for three RBOCs. Conclusion: Therefore, high-intensity LCUs can be said to efficiently affect polymerization, so higher DC rates may achieve higher cell viability rates. Clinical Relevance: Cements and LCUs must be matched to each another to result in higher DC and maximal biocompatibility. Dual cure systems presented relatively high cell survival and higher DC, thus expressing superior to single-cure systems with plasma LED

Effects of plasma-emulating light-emitting diode (LED) versus conventional LED on cytotoxic effects and polymerization capacity of orthodontic composites

Objectives: The aim of this study was to evaluate, the cytotoxicity of orthodontic composites in vitro as a function of degree of conversion (DC) and the light curing units (LCU) employed on mouse fibroblast (L929). Materials and Methods: Cured samples of the composites Light bond (Reliance Orthodontic Products, Itasca, Illinois, USA), Ortho bracket paste (Bisco, Schaumburg, Illinois, USA), Opal bond MV (OPAL, South Jordan, Utah, USA), and Transbond XT (3M, Monrovia, California, USA) were prepared. Polymerization was performed with two LCUs: VALO Ortho (Ultradent, South Jordan, Utah, USA) is a third-generation LCU and Elipar S I 0 (3M, USA) is a second-generation LCU. Four samples were immersed in cell culture medium to obtain composite extracts. After incubation of L929 cell cultures with the extracts obtained, cytotoxicity was determined using the methyl tetrazolium test. Fourier transform infrared spectroscopy (FTIR) was used to evaluate DC for five samples. A multivariate analysis of variance (ANOVA), two-way ANOVA, and Tukey's honestly significant difference test were utilized for statistical analyses. Results: Cytotoxicity and DC of all tested composites (p 0.05). The correlations between cell viability and DC were positive for three composites but statistically insignificant. Conclusion: Composites and LCUs must be matched with one another to result in satisfactory maximal biocompatibility and DC. Opal Bond plasma light-emitting diode combination was a better choice for cell viability. Three composites showed a positive correlation between cytotoxicity and DC. Therefore high-intensity LCUs can be said to efficiently affect polymerization, and so, higher DC rates may achieve higher cell viability rates

Preparation of RF sputtered AZO/Au thin film hydrogen peroxide sensitive electrode for utilization as a biosensor

In this study, hydrogen peroxide (H2O2) sensitive Al doped ZO(AZO)/Au thin film electrode has been developed for the utilization as a biosensor. A preferred c-axis oriented AZO/Au thin film was deposited on quartz substrate by RF magnetron sputtering at room temperature. Structural, morphological and optical properties of the AZO film were analyzed by X-ray diffraction, atomic force microscopy and photoluminescence. The sensor performance was characterized by electrochemical analysis device. The sensibility of prepared thin film electrodes to H2O2 was studied. The dependence of amperometric response current on the glucose and cholesterol concentrations was also investigated