Modeling and simulation of metal organic halide vapor phase epitaxy (MOHVPE) growth chamber

Over the last few decades, there was a substantial appeal on the growth of gallium-nitride (Ga-N) based alloy for high performance optoelectronic devices such as blue/violet laser diode, blue/white light emitting diode etc. In the recent years, there have been revolutionary changes in semiconductor field. Growth method for GaN-based film has been extensively explored, with success of thick film growth using halide vapor-phase epitaxy technique. The theoretical changes were attributed from the experimental results where modeling was vastly used for the purpose of design of equipment. This is because of the cost of the equipment and it is one of the major burdens in semiconductor processing. This process constitutes an important technology for manufacturing thin solid film in the semiconductor industry. To address these issues, a new development called metal organic halide vapor phase epitaxy (MOHVPE) reactor has been proposed in this study. Modeling with five inlet nozzles with 54 cm long is designed by design software. The numerical study of horizontal MOHVPE growth shows dependence on temperature and species flow rates. The inlet area is set to room temperature while the whole chamber is set in the temperature range from 1,273 to 1,473 K. Growth process reactor geometry that involved with temperature distribution stabilization and uniformity control flow pattern between the substrate holder are discussed. It is seen that the flow pattern is influenced more by the temperature distribution and geometry of the chamber. The numerical study of horizontal MOHVPE growth shows a function of temperature and species flow rates has been performed with specific condition to find the ideal position of the substrate for growth process in future

Preparation and characterization of ZnO/ZnAl₂O₄-mixed metal oxides for dye-sensitized photodetector using Zn/Al-layered double hydroxide as precursor

In this article, a simple new technique has been developed for the preparation of ZnO/ZnAl₂O₄-mixed metal oxide (MMO) as anode materials for visible light dye-sensitized (DS) photodetector using Zn/Al-layered double hydroxide (LDH) as precursor. Subsequently, a detailed correlation between the structural properties of the prepared samples and the photo-responsive behavior of the fabricated DS photodetectors was elucidated. Specifically, it is evidenced that a high surface area of the prepared mesoporous MMO anode materials exhibit excellent dye absorptivity and thus facilitate free electron transfer and increase the photocurrent in the fabricated DS photodetector. A significant bathochromic shift was observed in the optical energy of the prepared MMO samples under the increment of molar ratio, providing a short electron transfer pathway in the optimized Z7A DS photodetector, which in turn demonstrated photo-responsivity and photo-detectivity of 6 mA/W and 1.7 × 10⁺¹⁰ Jones, respectively. This work presents an alternative approach for the design of an eco-friendly MMO-based DS photodetector

Spotlight on available optical properties and models of nanofluids: A review

Optical characteristics besides unique thermo-physical properties of nanoparticles have encouraged researchers to use nanofluids in solar energy collectors or reservoirs as electromagnetic wave absorbing media. Recently, different analyses and approaches have been proposed by researchers. However, the appropriate electro-magnetic phenomenon of nanofluids is not established till date because of the complex dependence between nanoparticles and base fluids. In this work, optical properties of nanofluids are discussed on the basis of published data; mostly used models are presented along with their limitations and applications. (C) 2014 Elsevier Ltd. All rights reserved

Theoretical Power Output of Thermoelectric Power Generator based on Metal Oxide Semiconductor

Optimizing the structure and material combination of thermoelectric power generators (TEGs) is essential to their efficiency. In order to develop an efficient TEG based on an oxide semiconductor, we theoretically simulated the power output of a TEG based on potential oxide semiconductors (ZnO, TiO2, and CuO) combined with electrode materials (Au, Ag, Cu, graphene, graphite, ITO, IZO, and AZO), and determined the influence of this material combination on the TEG’s power output. In this study, the power output was evaluated from simulated heat distribution and output voltage of a single leg and thermopiles using a simulator. The combination of ZnO and graphene showed the highest power output. This is likely due to the high thermal conductivity of graphene which allowed a high temperature difference in the ZnO. Moreover, the power output increased with decreasing electrode thickness, which allowed high output voltage to be generated by the thermoelectric material. The power density of the TEG consisting of several thermopiles based on ZnO and graphene materials was 29 mW/cm2, which was comparable with that of the\ud reported TEG consisting of Te-based materials. Thus, a TEG based on oxide semiconductor materials could be developed to reduce the use of harmful thermoelectric materials

The role of electrolyte fluidity on the power generation characteristics of thermally driven electrochemical cells

Thermally driven electrochemical cells (thermocells) are able to convert thermal gradient applied across redox electrolyte into electricity. The performance of the thermocells heavily depends on the magnitude and integrity of the applied thermal gradient. Herein, we study the iodide/triiodide (I–/I3 –) based 1-Ethyl-3-methyl-imidazolium Ethylsulfate ([EMIM][EtSO4]) solutions in a thermocell. In order to comprehend the role of fluidity of the electrolyte, we prepared set of solutions by diluting [EMIM][EtSO4] with 0.002, 0.004, and 0.010 mol of Acetonitrile (ACN). We realized a significant improvement in ionic conductivity (σ) and electrochemical Seebeck (Se) of diluted electrolytes as compared to base [EMIM][EtSO4] owing to the solvent organization. However, the infra-red thermography indicated faster heat flow in ACN-diluted-[EMIM] [EtSO4] as compared to the base [EMIM][EtSO4]. Therefore, the maximum power density of base [EMIM][EtSO4] (i.e. 118.5 μW.m-2) is 3 times higher than the ACN-diluted-[EMIM][EtSO4] (i.e. 36.1 μW.m-2) because of the lower thermal conductivity. Hence this paper illustrates the compromise between the fast mass/flow transfer due to fluidity (of diluted samples) and the low thermal conductivity (of the pure [EMIM][EtSO4])

High Thermoelectric Performance of Multiwalled Carbon Nanotubes based Ionogels

Ionogels have emerged as promising thermoelectric materials with Seebeck coefficient 2–3 orders of magnitude higher than Seebeck coefficient of their inorganic counter parts. However, they suffer from the problem of low ionic conductivity, which can be improved with the addition of inorganic nanofillers to the ionogels. In the present work, thermoelectric performance of multiwall carbon nanotubes (MWCNTs) based ionogels (IGs) has been investigated. IGs were synthesized via in situ radical polymerization of polyethylene glycol 200 dimethacrylate (PEG200DMA) difunctional monomer in the presence of 1-butyl-3-methyl imidazolium tetrafluoroborate (an ionic liquid) and MWCNTs. Three composites namely MWCNTs-0.25, MWCNTs-0.5 and MWCNTs-1 were prepared having the concentration of MWCNTs by 0.25, 0.5 and 1 wt% respectively. A remarkable 75.3% enhancement in ionic conductivity was achieved for the MWCNTs-1 wt% ionogel compared to the base IG at 40 °C. This substantial improvement can be attributed to the "breathing polymer chain model," which describes the dissociation of ion aggregates due to the interaction between the ionic liquid and polymer chains. In terms of thermoelectric performance amongst the MWCNT ionogels, 0.25 wt% MWCNT-based ionogels was the optimized concentration with very high Seebeck coefficient of 1.70 mV/K and power factor of 4.1 µW/m. K along with excellent thermal stability up to 386 °C. These high-performing ionogels hold great promise for efficient utilization of low-grade thermal energy

Change in Spatial Distribution of Earthquakes against Hypocentral Depth

Personal data is constantly being compromised not just by the normal identity thefts but also abnormal attacks. The Islamic concept of Al-Mu’awwidhah inspired the discovery of non-parametric cryptographs for personal data protection against abnormal (paranormal and asymmetric) cyber-attacks. A continuous search on new paradigm of non- parametric cryptographs led to the discovery of ethno-mathematics for substitution block-cipher boxes. The objects based on extracted Al-Qur’an and Al-Hadith symbols by use of ethno-mathematical functions. The extracted objects were insufficient to build the 256 bit block-ciphers. The development of expanding objects from Aramaic, Hebrew, Chinese, Hindu and other symbols are found to fill the gap but only up to216bit out of the 256 bit block-cipher. Initial tests for algebraic attacks indicate Al-Mu’awwidhah Block Cipher resistance to be better than the random parameteic Khazad and Annubis Block Ciphers

Synergistic enhancement in the microelectronic properties of poly-(dioctylfluorene) based Schottky devices by CdSe quantum dots

This paper reports the potential application of cadmium selenide (CdSe) quantum dots (QDs) in improving the microelectronic characteristics of Schottky barrier diode (SBD) prepared from a semiconducting material poly-(9,9-dioctylfluorene) (F8). Two SBDs, Ag/F8/P3HT/ITO and Ag/F8-CdSe QDs/P3HT/ITO, are fabricated by spin coating a 10 wt% solution of F8 in chloroform and 10:1 wt% solution of F8:CdSe QDs, respectively, on a pre-deposited poly(3-hexylthiophene) (P3HT) on indium tin oxide (ITO) substrate. To study the electronic properties of the fabricated devices, current-voltage (I-V) measurements are carried out at 25 °C in dark conditions. The I-V curves of Ag/F8/P3HT/ITO and Ag/F8-CdSe QDs/P3HT/ITO SBDs demonstrate asymmetrical behavior with forward bias current rectification ratio (RR) of 7.42 ± 0.02 and 142 ± 0.02, respectively, at ± 3.5 V which confirm the formation of depletion region. Other key parameters which govern microelectronic properties of the fabricated devices such as charge carrier mobility (µ), barrier height (ϕ ), series resistance (R ) and quality factor (n) are extracted from their corresponding I-V characteristics. Norde's and Cheung functions are also applied to characterize the devices to study consistency in various parameters. Significant improvement is found in the values of R , n, and RR by 3, 1.7, and 19 times, respectively, for Ag/F8-CdSe QDs/P3HT/ITO SBD as compared to Ag/F8/P3HT/ITO. This enhancement is due to the incorporation of CdSe QDs having 3-dimensional quantum confinement and large surface-to-volume area. Poole-Frenkle and Richardson-Schottky conduction mechanisms are also discussed for both of the devices. Morphology, optical bandgap (1.88 ± 0.5 eV) and photoluminescence (PL) spectrum of CdSe QDs with a peak intensity at 556 nm are also reported and discussed