Assessment of the Thermal Conductivity of BN-C Nanostructures

Chemical and structural diversity present in hexagonal boron nitride ((h-BN) and graphene hybrid nanostructures provide new avenues for tuning various properties for their technological applications. In this paper we investigate the variation of thermal conductivity ($\kappa$) of hybrid graphene/h-BN nanostructures: stripe superlattices and BN (graphene) dots embedded in graphene (BN) are investigated using equilibrium molecular dynamics. To simulate these systems, we have parameterized a Tersoff type interaction potential to reproduce the ab initio energetics of the B-C and N-C bonds for studying the various interfaces that emerge in these hybrid nanostructures. We demonstrate that both the details of the interface, including energetic stability and shape, as well as the spacing of the interfaces in the material exert strong control on the thermal conductivity of these systems. For stripe superlattices, we find that zigzag configured interfaces produce a higher $\kappa$ in the direction parallel to the interface than the armchair configuration, while the perpendicular conductivity is less prone to the details of the interface and is limited by the $\kappa$ of h-BN. Additionally, the embedded dot structures, having mixed zigzag and armchair interfaces, affects the thermal transport properties more strongly than superlattices. Though dot radius appears to have little effect on the magnitude of reduction, we find that dot concentration (50% yielding the greatest reduction) and composition (embedded graphene dots showing larger reduction that h-BN dot) have a significant effect

On Calculation of Thermal Conductivity from Einstein Relation in Equilibrium MD

In equilibrium molecular dynamics, Einstein relation can be used to calculate the thermal conductivity. This method is equivalent to Green-Kubo relation and it does not require a derivation of an analytical form for the heat current. However, it is not commonly used as Green-Kubo relationship. Its wide use is hindered by the lack of a proper definition for integrated heat current (energy moment) under periodic boundary conditions. In this paper, we developed an appropriate definition for integrated heat current to calculate thermal conductivity of solids under periodic conditions. We applied this method to solid argon and silicon based systems; compared and contrasted with the Green-Kubo approach.Comment: We updated this manuscript from second version by changing the title and abstract. This paper is submitted to J. Chem. Phy

Microstructural defect properties of InGaN/GaN blue light emitting diode structures

Cataloged from PDF version of article.In this paper, we study structural and morphological properties of metal-organic chemical vapour deposition-grown InGaN/GaN light emitting diode (LED) structures with different indium (In) content by means of high-resolution X-ray diffraction, atomic force microscopy (AFM), Fourier transform infrared spectroscopy (FTIR), photoluminescence (PL) and current-voltage characteristic (I-V). We have found out that the tilt and twist angles, lateral and vertical coherence lengths of mosaic blocks, grain size, screw and edge dislocation densities of GaN and InGaN layers, and surface roughness monotonically vary with In content. Mosaic defects obtained due to temperature using reciprocal lattice space map has revealed optimized growth temperature for active InGaN layer of MQW LED. It has been observed in this growth temperature that according to AFM result, LED structure has high crystal dimension, and is rough whereas according to PL and FTIR results, bandgap energy shifted to blue, and energy peak half-width decreased at high values. According to I-V measurements, it was observed that LED reacted against light at optimized temperature. In conclusion, we have seen that InGaN MQW structure's structural, optical and electrical results supported one another

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

Influence of RF power on the opto-electrical and structural properties of gallium-doped zinc oxide thin films

GZO thin films were succesfully deposited onto n-Si and glass substrates by RF magnetron sputtering at room temperature. The structural, morphological and opto-electrical properties of the films were investigated in terms of RF power, using various methods such as XRD, AFM, SEM, EDX, XPS, SIMS, UV-Vis-NIR spectroscopy and Hall effect measurements. The achieved results revealed that the all films have highly c-axis (002) oriented polycrystalline structure with high transmittance in Vis and high reflectance in NIR region as well as good conductivity. Meanwhile, surface of the films was uniform, compact and crack-free. With incerasing of RF power, it was seen that crystallinity of the films improved and the grain size became larger. It was also observed that optical band gap of the films was increased to the order of 0.15 eV as well as decreasing the resistivity to the order of 6.38 Omega cm with increasing RF power from 100 to 200 W. Deposited film at 200 W, which can be optimum sputtering power for coating GZO films, having high concentration of free electrons and lowest resistivity exhibited the highest IR reflectivity (55%) in NIR region. In addition, deposited GZO films at this power have larger particle size and highly optical transmittance (87%) in visible region. Obtained both of optical and electrical results suggested that the deposited GZO films can be used in low thermal emissivity coating for energy efficient glass and the UV-blocking layer as well as transparent conductive oxide electrode for flexible opto-electronic devices

The effects of annealing temperature on RF-coated GZO thin films on n-Si and PET substrates

In this study, the effects of thermal annealing on RF-coated GZO thin films on n-Si and PET substrates at room temperature at 200 W RF power were investigated systematically. Deposited film on the n-Si substrate was annealed at range of 100 - 600 degrees C for 1 hour in air at atmospheric pressure with CTA. UV-Vis measurements of flexible films prepared at 100 and 200 degrees C were evaluated due to the deterioration of the PET substrate form at 300 degrees C temperature. The energy band gaps of the films were found as 3.10 and 3.30 eV, respectively. It was revealed from the XRD results that GZO films grown on Si have c-oriented hexagonal wurtzite structure. UV sensor fabrication was performed from the flexible GZO film annealed at 200 degrees C with the highest band gap energy. The UV-light sensitivity of the produced sensor was determined by I-V measurements in light (lambda = 365 nm) and dark conditions. Photo-sensitivity of the flexible sensor was found to be 8.07 at 2V

The study on characterizations of SrTiO3 thin films with different growth temperatures

Strontium titanate (SrTiO3) thin films were deposited on cleaned p-type (100) oriented silicon substrates using radio frequency (RF) magnetron sputtering method at a substrate temperatures of 200 degrees C, 300 degrees C, 400 degrees C and 500 degrees C. During deposition, sputtering pressure (P-S) was maintained at 3.9 x 10(-3) Torr using argon (A(r)) gas, and RF power (P-RF) was set to a constant value of 100W for all experiments. Crystalline quality, surface morphology and band gap of the films were investigated by X-ray diffraction (XRD) analysis, atomic force microscopy (AFM) and photoluminescence (PL) measurements. Experimental results showed crystalline quality, and surface morphology of the films were remarkably improved by high substrate temperature. In addition to above analyzes, SrTiO3/p-Si structure deposited at 500 degrees C substrate temperature have been investigated using temperature dependent currentvoltage (I-V-T) characteristics in the temperature range of 110-350 K by steps of 30 K due to its better characteristics. The ideality factor (n), barrier height (Phi(b)) and series resistance (R-s) values were extracted. Moreover, Phi(b) and R-s values were recalculated using Norde's method. (C) 2014 Elsevier Ltd. All rights reserved