Effects of contemporary orthodontic composites on tooth color following short-term fixed orthodontic treatment: A controlled clinical study

Background/aim: To determine the color alterations of natural teeth associated with different orthodontic composites used in comprehensive short-term treatment. Materials and methods: Twenty-two patients were treated with fixed appliances and 22 untreated subjects were also evaluated. Lower incisors were bonded with different orthodontic composites: 42 with Grengloo, 41 with Light Bond, 31 with Kurasper F, and 32 with Transbond XT. The color parameters of the Commission Internationale de l’Eclairage (CIE) were measured for each tooth with a spectrophotometer. Color assessment in relation to time, adhesive material, and their interaction was made with 2-way mixed analysis of variance (ANOVA) and 1-way ANOVA for the color differences (ΔE*). Further analyses were done using Tukey’s honestly significant difference tests and paired-samples t-tests. Results: The color of teeth was affected by treatment. The mean L* and a* values increased, whereas the mean b* values decreased. Total color differences of teeth demonstrated visible color changes clinically after treatment, ranging from 1.12 to 3.34 ΔE units. However, there were no significant differences for color of enamel. Conclusion: Teeth may be discolored with fixed appliances during treatment. Moreover, contemporary orthodontic composites have similar effects of enamel discoloration. © TÜBİTAK

Characterization of an AlN buffer layer and a thick-GaN layer grown on sapphire substrate by MOCVD

An AlN buffer layer and a thick-GaN layer for high-electron-mobility transistors (HEMTs) were grown on sapphire substrate by metal-organic chemical vapor deposition (MOCVD). The structural and morphological properties of the layers were investigated by high resolution X-ray diffraction (HRXRD) and atomic force microscopy (AFM) techniques. The optical quality of the thick-GaN layer was also evaluated in detail by a photoluminescence (PL) measurement. It was found that the AlN buffer layer possesses high crystal quality and an atomically flat surface with a root-mean-square (rms) roughness of 0.16 nm. The screw-and edge-type dislocation densities of the thick-GaN layer were determined as 5.4 9 107 and 5.0 9 109 cm-2 by means of the mosaic crystal model, respectively. It was observed that the GaN layer has a smooth surface with an rms of 0.84 nm. Furthermore, the dark spot density of the GaN surface was estimated as 6.5 9 108 cm-2 over a scan area of 4 μm2. © Springer Science+Business Media, LLC 2010

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 (101 ¯ 2) 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 (101 ¯ 2) 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 × 108 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. © 2016, The Minerals, Metals & Materials Society

Effects of high-temperature AIN buffer on the microstructure of AlGaN/GaN HEMTs

Effects on AlGaN/GaN high-electron-mobility transistor structure of a high-temperature AlN buffer on sapphire substrate have been studied by high-resolution x-ray diffraction and atomic force microscopy techniques. The buffer improves the microstructural quality of GaN epilayer and reduces approximately one order of magnitude the edge-type threading dislocation density. As expected, the buffer also leads an atomically flat surface with a low root-mean-square of 0.25 nm and a step termination density in the range of 108 cm-2. Due to the high-temperature buffer layer, no change on the strain character of the GaN and AlGaN epitaxial layers has been observed. Both epilayers exhibit compressive strain in parallel to the growth direction and tensile strain in perpendicular to the growth direction. However, an high-temperature AlN buffer layer on sapphire substrate in the HEMT structure reduces the tensile stress in the AlGaN layer. © 2013 Pleiades Publishing, Ltd

Microstructural analysis with graded and non-graded indium in InGaN solar cell

In this study are graded and non graded InGaN/GaN samples grown on c-oriented sapphire substrate using the Metal Organic Chemical Vapour Deposition (MOCVD) technique. The structural and morphological properties of the grown InGaN/GaN solar cell structures are analyzed using High Resolution X-ray Diffraction (HRXRD), atomic force microscopy (AFM). Each structures c and a lattice parameters strain, biaxial strain, hydrostatic strain, stress, lattice relax, tilt angle, mosaic crystal size, dislocation densities of GaN and InGaN layers are determined by XRD measurements. In accordance with these calculations, the effect of graded structure on the defects, are discussed. As a dramatic result; although values of full width at half maximum (FWHM) are broad, a considerable decrease at dislocations is noticed. The AFM observations have revealed that the two dimensional growth of the graded sample is more significant and its roughness value is lower. JV measurements shown that the performance of the graded structure is higher. It is determined that all test results are consistent with each other. © Copyright 2017 by American Scientific Publishers. All rights reserved

Structural and optical properties of an InxGa1-xN/GaN nanostructure

The structural and optical properties of an InxGa1-xN/GaN multi-quantum well (MQW) were investigated by using X-ray diffraction (XRD), atomic force microscopy (AFM), spectroscopic ellipsometry (SE) and photoluminescence (PL). The MQW structure was grown on c-plane (0 0 0 1)-faced sapphire substrates in a low pressure metalorganic chemical vapor deposition (MOCVD) reactor. The room temperature photoluminescence spectrum exhibited a blue emission at 2.84 eV and a much weaker and broader yellow emission band with a maximum at about 2.30 eV. In addition, the optical gaps and the In concentration of the structure were estimated by direct interpretation of the pseudo-dielectric function spectrum. It was found that the crystal quality of the InGaN epilayer is strongly related with the Si doped GaN layer grown at a high temperature of 1090 °C. The experimental results show that the growth MQW on the high-temperature (HT) GaN buffer layer on the GaN nucleation layer (NL) can be designated as a method that provides a high performance InGaN blue light-emitting diode (LED) structure. © 2007 Elsevier B.V. All rights reserved

Examination of the temperature related structural defects of InGaN/GaN solar cells

In this study the effects of the annealing temperature on the InGaN/GaN solar cells with different In-contents grown on sapphire substrate by the Metal Organic Chemical Vapor Deposition (MOCVD) are analyzed by High Resolution X-ray Diffraction (HRXRD) and an Atomic Force Microscope (AFM). The plane angles, mosaic crystal sizes, mixed stress, dislocation intensities of the structure of the GaN and InGaN layers are determined. According to the test results, there are no general characteristic trends observed due to temperature at both structures. There are fluctuating failures determined at both structures as of 350 °C. The defect density increased on the GaN layer starting from 350 °C and reaching above 400 °C. A similar trend is observed on the InGaN layer, too. © 2015 Elsevier Ltd. All rights reserved

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.State of Planning Organization of TurkeyTurkiye Cumhuriyeti Kalkinma Bakanligi [2011K120290]This work is supported by the State of Planning Organization of Turkey under Grant no. 2011K120290WOS:0003025803000742-s2.0-8486014571

Structural investigation and electronic band transitions of nanostructured TiO2 thin films

Titanium dioxide (TiO2) thin film was deposited on n-Si (100) substrate by reactive DC magnetron sputtering system at 250 degrees C temperature. The deposited film was thermally treated for 3 h in the range of 400-1000 degrees C by conventional thermal annealing (CTA) in air atmosphere. The effects of the annealing temperature on the structural and morphological properties of the films were investigated by X-ray diffraction (XRD) and atomic force microscopy (AFM), respectively. XRD measurements show that the rutile phase is the dominant crystalline phase for the film annealed at 800 degrees C. According to AFM results, the increased grain sizes indicate that the annealing improves the crystalline quality of the TiO2 film. In addition, the formation of the interfacial SiO2 layer between TiO2 film and Si substrate was evaluated by the transmittance spectra obtained with FTIR spectrometer. The electronic band transitions of as-deposited and annealed films were also studied by using photoluminescence (PL) spectroscopy at room temperature. The results show that the dislocation density and microstrain in the film were decreased by increasing annealing temperature for both anatase and rutile phases. (C) 2011 WILEY-VCH Verlag GmbH & Co. KGaA, WeinheimDPTTurkiye Cumhuriyeti Kalkinma Bakanligi [2011K120290]; BAP (Gazi University)Gazi University [05/2010-65]This work was supported by DPT and BAP (Gazi University) under project No. 2011K120290 and 05/2010-65, respectively.WOS:0002969825000162-s2.0-8005494829

Electrical characteristics of Au/n-GaAs structures with thin and thick SiO2 dielectric layer

The aim of this study, to explain effects of the SiO2 insulator layer thickness on the electrical properties of Au/n-GaAs Shottky barrier diodes (SBDs). Thin (60 ) and thick (250 ) SiO2 insulator layers were deposited on n-type GaAs substrates using the plasma enganced chemical vapour deposition technique. The current-voltage (I-V) and capacitance-voltage (C-V) characteristics have been carried out at room temperature. The main electrical parameters, such as ideality factor (n), zero-bias barrier height (I center dot (Bo) ), series resistance (R (s) ), leakage current, and interface states (N (ss) ) for Au/SiO2/n-GaAs SBDs have been investigated. Surface morphologies of the SiO2 dielectric layer was analyzed using atomic force microscopy. The results show that SiO2 insulator layer thickness very affects the main electrical parameters. Au/n-GaAs SBDs with thick SiO2 insulator layer have low leakage current level, small ideality factor, and low interface states. Thus, Au/n-GaAs SBDs with thick SiO2 insulator layer shows better diode characteristics than other.Turkish Prime Ministry state Planning Agency [2001K120590]; European Transnational Access Program [RITA-CT-2003-506095 WISSMC]The authors would like to thank Michael Schneiderman at Submicron Research Center at Weizmann Institute of Science for SiO2 coating by PECVD. This study was supported by the Turkish Prime Ministry state Planning Agency under project no: 2001K120590 and The European Transnational Access Program no. RITA-CT-2003-506095 WISSMC.WOS:0002956968000072-s2.0-8005360719