The influence of thickness and ammonia flow rate on the properties of AIN layers

Cataloged from PDF version of article.Undoped AlN layers have been grown on c-plane sapphire substrates by metal-organic chemical vapor deposition in order to study the effects of ammonia (NH3) flow rate and layer thickness on the structural quality and surface morphology of AlN layers by high-resolution X-ray diffraction, scanning electron microscopy, and atomic force microscopy. Lower NH3 flow rate improves crystallinity of the symmetric (0 0 0 2) plane in AlN layers. Ammonia flow rate is also correlated with surface quality; pit-free and smooth AlN surfaces have been obtained at a flow rate of 70 standard cm(3) per minute. Thicker AlN films improve the crystallinity of the asymmetric (1 0 1 (1) over bar 2) plane. (c) 2011 Elsevier Ltd. All rights reserved

Effects of thermal annealing on the morphology of the AlxGa(1x)N films

Cataloged from PDF version of article.Effects of thermal annealing on the morphology of the AlxGa(1-x)N films with two different high Al-contents (x=0.43 and 0.52) have been investigated by atomic force microscopy (AFM). The annealing treatments were performed in a nitrogen (N-2) gas ambient as short-time (4 min) and long-time (30 min). Firstly, the films were annealed as short-time in the range of 800-950 degrees C in steps of 50-100 degrees C. The surface root-mean-square (rms) roughness of the films reduced with increasing temperature at short-time annealing (up to 900 degrees C), while their surface morphologies were not changed. At the same time, the degradation appeared on the surface of the film with lower Al-content after 950 degrees C. Secondly, the Al0.43Ga0.57N film was annealed as long-time in the range of 1000-1200 degrees C in steps of 50 degrees C. The surface morphology and rms roughness of the film with increasing temperature up to 1150 degrees C did not significantly change. Above those temperatures, the surface morphology changed from step-flow to grain-like and the rms roughness significantly increased. (C) 2009 Elsevier Ltd. All rights reserved

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

Fabrication of Densely Packed AlN Nanowires by a Chemical Conversion of Al2O3Nanowires Based on Porous Anodic Alumina Film

Porous alumina film on aluminum with gel-like pore wall was prepared by a two-step anodization of aluminum, and the corresponding gel-like porous film was etched in diluted NaOH solution to produce alumina nanowires in the form of densely packed alignment. The resultant alumina nanowires were reacted with NH3and evaporated aluminum at an elevated temperature to be converted into densely packed aluminum nitride (AlN) nanowires. The AlN nanowires have a diameter of 15–20 nm larger than that of the alumina nanowires due to the supplement of the additional evaporated aluminum. The results suggest that it might be possible to prepare other aluminum compound nanowires through similar process

A quantitative study of the aorta of the chicken (Gallus domesticus)

The different segments of the aorta were studied quantitatively in five age groups of chicken. It was observed that the widest diameter and the thickest media occur on the 56th day in each segment, except fur the thoracic aorta, which had the widest diameter on the 42nd day and the thickest media on the 70th day

A comparative study on the growth and survival characteristics of lambs produced by the transfer of in vitro produced (IVP) embryos

This study was carried out to determine the growth, survival rate and some body measurements until weaning of lambs produced by the in vitro production (IVP) method in comparison with those of lambs produced by artificial insemination. The lambs in the experimental group were produced by the transfer of IVP embryos developed to the blastocyst stage after the in vitro maturation and fertilisation of oocytes obtained from the ovaries of slaughtered ewes

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 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

Characterization of AlInN/AlN/GaN Heterostructures with Different AlN Buffer Thickness

Two AlInN/AlN/GaN heterostructures with 280-nm- and 400-nm-thick AlN buffer grown on sapphire substrates by metal-organic chemical vapor deposition (MOCVD) have been investigated by x-ray diffraction (XRD), atomic force microscopy (AFM), photoluminescence (PL) and Hall-effect measurements. The symmetric (0002) plane with respect to the asymmetric (102) plane in the 280-nm-thick AlN buffer has a higher crystal quality, as opposed to the 400-nm-thick buffer. The thinner buffer improves the crystallinity of both (0002) and (102) planes in the GaN layers, it also provides a sizeable reduction in dislocation density of GaN. Furthermore, the lower buffer thickness leads to a good quality surface with an rms roughness of 0.30 nm and a dark spot density of 4.0 x 10(8) cm(-2). The optical and transport properties of the AlInN/AlN/GaN structure with the relatively thin buffer are compatible with the enhancement in its structural quality, as verified by XRD and AFM results