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])

Fabrication of w-AlN Thin Films using Tilted Sputter Target and Unrotated Substrate Holder

Aluminium nitride (AlN) thin film is deposited by RF magnetron sputtering using Al sputtering target at room temperature. The sputter source was tilted 45° and the substrate holder was unrotated. The deposited AlN films were in the thickness range between 200 to 280 nm. The structural, elemental composition, morphological and topological properties of AlN with different thickness has been investigated. XRD analysis results revealed that all the AlN films deposited crystallize in hexagonal wurtzite phase (w-AlN). The crystal orientation of AlN (002) plane start to appear when the thickness of the AlN film increases and the thickest AlN film has a highest peak intensity of (002) plane with smallest FWHM indicated a good crystal quality of c-axis structure. The chemical composition of AlN analyze using EDS shows that all the films have AlN composition nearest to the stoichiometric and have a rice-like morphology regardless of the film thickness. The AFM analysis revealed that the surface roughness of the AlN films is increases along with the grain size as the thickness of the AlN films increased

Luminescence and Crystalline Properties of InGaN-based LED on Si Substrate with AlN/GaN Superlattice Structure

A crack-free indium gallium nitride (InGaN) based light emitting diode (LED) grown on silicon (Si) substrate was successfully demonstrated by introducing aluminium nitride/gallium nitride (AlN/GaN) superlattice structure (SLS) in the growth of the LED. The luminescence and the crystalline properties of the LED were discussed. From photoluminescence (PL) surface mapping measurement, the emission wavelength of the LED (453 nm) was almost uniform across the LED epi-wafer area. Temperature dependent PL revealed that the dominant emission peak of the LED was 2.77 eV at all temperatures. The emission peak was related to the quantum wells of the LED. Some additional peaks were also observed, in particular at lower temperatures. These peaks were associated to alloy fluctuations in the In0.11Ga0.89N/ In0.02Ga0.98N multiquantum wells (MQWs) of the LED. Furthermore, the dependence of PL intensity and PL decay time on temperature revealed the evidence related to indium and/or interface fluctuations of the quantum wells. From X-ray diffraction (XRD) ω-scan measurements, fringes of the AlN/GaN SLS were clear, indicating the SLS were grown with good interface abruptness. However, the fringes for the MQWs were less uniform, indicating another evidence of the alloy fluctuations in the MQWs. XRD-reciprocal surface mapping (RSM) measurement showed that all epitaxial layers of the LED were grown coherently, and the LED was fully under strain

Impedance spectroscopy analysis of Al/100-plane AlN/p-Si MIS prepared by HiPIMS method for tailoring dielectric properties

The effects of variation of sputtering pressure of AlN HiPIMS deposition on Si substrate to the structure and electrical properties were investigated through XRD, AFM and impedance spectroscopy method. The strong preferred 100-plane AlN was observed for all samples from XRD pattern. The AlN thin film thickness was observed decrease with the increase of sputtering pressure. AFM analysis shows the lowest surface roughness at 0.84 nm for 5 mTorr sputtering pressure. Impedance spectroscopy analysis of Al/100-plane AlN/Si MIS structure shows the electrical conductivity of AlN was directly proportional to the sputtering pressure and stable with temperature ranging from room temperature (299 K) to 353 K. Good dielectric stability was achieved at 3 mTorr sputtering pressure for all variation temperature and the dielectric constant calculated at average 3.5

Fabrication Of Deep Green Light Emitting Diode On Bulk Gallium Nitride Substrate

The indium composition in InxGa1-xN/GaN multi-quantum well structure e(MQW) is crucial because lower indium composition will shift the wavelength towards ultraviolet region. Nevertheless, at certain indium content in MQW, it will out diffuse from the MQW resulting in the wavelength shift from green to much shorter wavelength, after the annealing process for p-type activation. In this study, we had grown a full Light Emitting Diode device with the MQW layer at a relative high temperature for green LED with indium pre-flow at the top of n-type layer just beneath the MQW using Metal Organic Chemical Vapor Deposition (MOCVD). Transmission Electron Microscopy (TEM) image of the MQW prior and post the activation of p-type had been observed, which resulted in good contrast, showing the abruptness of the MQW layer of the device. Homogenous layers of InxGa1- xN/GaN has been observed. We also managed to reduce the wavelength shift of the device significantly. The optical, crystal properties of grown devices had been studied

Effects of radio-frequency power on structural properties and morphology of AlGaN thin film prepared by co-sputtering technique

To date, the deposition of AlGaN thin film using the co-sputtering technique at room temperature has not been reported yet. The use of AlGaN for electronic devices has been widely known because of its ultra-wide bandgap. However, to deposit the AlGaN thin film and achieved high quality of AlGaN films, higher temperature or extra time deposition are needed, which is not compatible with industrial fabrication process. Here, a co-sputtering technique between two power supplies of magnetron sputtering (which are RF and HiPIMS) is introduced to deposit the AlGaN thin films. The AlGaN thin films were deposited at various RF power to study their effect on structural properties and morphology of the thin films. AlGaN films were sputtered simultaneously on silicon (111) substrate for short time and at room temperature using GaN and Al target. Then, the films were characterized by X-ray diffraction (XRD), atomic force microscopy (AFM), and surface profiler to study their properties. XRD shows the GaN (101) and (013) plane for the AlGaN deposited at RF power of 30 W. Also there only GaN (101) for the AlGaN with 50 W RF power. Yet, the 70 W RF power shows the amorphous structure of AlGaN. The roughness and the grain size of AlGaN film from AFM analysis showed the trend of decreasing and increasing respectively. The roughness of the AlGaN films with 30 W power was 0.82 nm, 0.85 nm for 50 W, and 0.46 nm for 70 W RF power. The grain size of the AlGaN films was 30.06 nm, 32.10 nm, and 37.65 nm for RF power of 30 W, 50 W, and 70 W respectively. The profilometer found that the thickness of the AlGaN films was decreasing with increasing of RF power. This paper can demonstrate a successful co-sputtering technique of AlGaN. Despite AlGaN crystal structure was not able to found out in the XRD analysis, the effect of RF power has been studied to give significant effects on AlGaN thin film deposition

Effect of indium pre-flow on wavelength shift and crystal structure of deep green light emitting diodes

金沢大学先端科学・社会共創推進機構To produce a deep green (530 nm–570 nm) LED, the suitable indium (In) composition in the InxGa1-xN/GaN multi-quantum well (MQW) structure is crucial because a lower indium composition will shift the wavelength of emission towards the ultraviolet region. In this paper, we clarify the effects of an indium-rich layer to suppress such blue shifting, especially after the annealing process. According to characterizations by the uses of XRD and TEM, narrowing of the MQW layer was observed by the indium capping, while without the capping, the annealing results in a slight narrowing of MQW on the nearest layer to the p-type layer. By adding an indium capping layer, the blue shift of the photoluminescence was also suppressed and a slight red shift to keep green emission was observed. Such photoluminescence properties were consistent with the tiny change of the MQW as seen in the XRD and TEM characterizations

Pemodelan dinamik fitoplankton menggunakan model nutrien-fitoplankton-zooplankton (Dynamic modelling of Phytoplankton using nutrient-phytoplankton-zooplankton model)

Kadar pertumbuhan fitoplankton yang berlebihan boleh membawa impak yang negatif kepada ekosistem di Tasik Chini. Walau bagaimanapun, fitoplankton merupakan komponen penting dalam jaringan makanan akuatik. Oleh itu, kajian terhadap kepekatan fitoplankton dalam Tasik Chini adalah penting agar dapat memantau keadaan ekosistem tasik. Kajian ini bertujuan untuk membangunkan model matematik dinamik yang sesuai bagi fitoplankton di Tasik Chini dengan menggunakan model nutrien-fitoplankton-zooplankton, serta untuk mengenal pasti bahawa input nutrien adalah faktor kawalan bagi model ini. Persamaan pembezaan biasa (PPB) digunakan untuk simulasi model fitoplankton di Tasik Chini. Model fitoplankton ini terdiri daripada kepekatan nutrien (Nu), fitoplankton (F) dan zooplankton (Z). Sistem PPB ini diselesaikan dengan kaedah Runge-Kutta-Fehlberg, menggunakan perisian Maple 13. Model NuFZ yang dibangunkan ini memilih input nutrien sebagai parameter bifurkasi, iaitu model ini dikawal oleh input nutrien. Hasil kajian menunjukkan bahawa kesan daripada peningkatan input nutrien ke dalam sistem tasik telah menyebabkan sistem menjadi tidak stabil dan kepadatan fitoplankton berubah-ubah. Model ini berguna untuk membantu dalam pemahaman populasi fitoplankton di Tasik Chini