Effects of substrate surface preparation on chemical vapor deposition growth of 4H-SiC epitaxial layers

The effects of chemical mechanical polish (CMP) and pre-growth oxidation and etching of vicinal 4H−SiC substrates on the quality of epitaxial films have been investigated. Samples with and without a collodial silica CMP and oxidation/etch treatment were studied with optical microscopy, cross section transmission electron microscopy (TEM) and atomic force microscopy (AFM) before and after chemical vapor deposition. Evidence of polishing damage was evident prior to growth in all samples without CMP treatment. Oxidation and etching appeared to generate defects by preferential etching of bulk defects such as dislocations and low angle grain boundaries. Evidence of the polishing damage remained after chemical vapor deposition (CVD) growth on the samples without CMP and the defect density was worse for the oxidized samples compared to the unoxidized ones. The unoxidized CMP wafer had the lowest defect density and rms roughness of the samples studied.     

Comparison of InGaSb/InAs superlattice structures grown by MBE on GaSb, GaAs, and compliant GaAs substrates

This paper contains the characterization results for indium arsenide/indium gallium antimonide (InAs/InGaSb) superlattices (SL) that were grown by molecular beam epitaxy (MBE) on standard gallium arsenide (GaAs), standard GaSb, and compliant GaAs substrates. The atomic force microscopy (AFM) images, peak to valley (P-V) measurement, and surface roughness (RMS) measurements are reported for each sample. For the 5 μm×5 μm images, the P-V heights and RMS measurements were 37 ? and 17 ?, 12 ? and 2 ?, and 10 ? and 1.8 ? for the standard GaAs, standard GaSb, and compliant GaAs respectively. The high resolution x-ray diffraction (HRXRD) analysis found different 0^th order SL peak to GaSb peak spacings for the structures grown on the different substrates. These peak separations are consistent with different residual strain states within the SL structures. Depending on the constants used to determine the relative shift of the valance and conduction bands as a function of strain for the individual layers, the change in the InAs conduction band to InGaSb valance band spacing could range from +7 meV to −47 meV for a lattice constant of 6.1532 ?. The cutoff wavelength for the SL structure on the compliant GaAs, control GaSb, and control GaAs was 13.9 μm, 11 μm, and no significant response, respectively. This difference in cutoff wavelength corresponds to approximately a −23 meV change in the optical gap of the SL on the compliant GaAs substrate compared to the same SL on the control GaSb substrate.     

Ionic liquid mediated green synthesis of Ag-Au/Y2O3 nanoparticles using leaves extracts of Justicia adhatoda: Structural characterization and its biological applications

In the present work, a facile synthesis was applied for the silver-gold decorated yttrium oxide nanoparticles with the use of Justicia adhatoda (leaves extract) and [BMIM] PF₆ (Ionic liquid) as a capping/stabilizing agent. The XRD analysis showed that Ag-Au/Y₂O₃ nanoparticles have a face-center cubic structure and crystallite size of 30 nm. The Y-O stretching bands were observed in the FT-IR spectrum at 464 to 495 cm^?1. The band gap of the silver-gold decorated Y₂O₃ nanoparticles was estimated as 5.75 eV from the UV-DRS spectrum. In the SEM and TEM images, the morphology of silver-gold/Y₂O₃ nanoparticles shows a nanoflake-like structure. The presence of silver, gold, yttrium and oxygen of elements has been confirmed by the EDX spectrum. The antibacterial activity of the nanoparticles was evaluated for the Staphylococcus aureus (Gram-positive) and Escherichia coli (Gram-negative) bacteria. The anticancer activity was also studied by the human cervical cancer cell line. The silver-gold decorated yttrium oxide nanoparticles revealed an exceptional microbicidal and antitumor activity when compared with yttrium oxide, silver decorated yttrium oxide and gold decorated yttrium oxide.     

Effect of nano-fuel additive on performance and emission characteristics of the diesel engine using biodiesel blends with diesel fuel

ABSTRACT

Biodiesel as an alternative source of petroleum fuel could reduce the dependence on petroleum products and control pollution problems. These biofuels are derived from various sources and if directly used in the engine it will not completely burn and will cause an increase in the emission level. In this experiment, 20% of rubber seed oil (B20) blended with pure diesel fuel along with aluminium oxide (Al₂O₃) was used in the proportions of 10?, 20 and 30?ppm. The obtained experimental results showed that the brake thermal efficiency was increased and the engine emission was reduced. And the brake-specific fuel consumption was reduced, but the NO_x level increased at the proportion level at 10?ppm of nano additives. This experiment has been carried out in a single cylinder water-cooled engine connected to an electrical dynamometer without engine modification and the injection pressure and timings were maintained at the standard level designed for the engine. The dynamic energy of aluminium oxide blend with the biodiesel improved the combustion characteristics in the engine, and caused a reduction in carbon deposits by 44.8% in the cylinder wall.     

Near-edge X-ray absorption fine structure spectroscopy as a tool for investigating nanomaterials

We have demonstrated near-edge X-ray absorption fine structure (NEXAFS) spectroscopy as a particularly useful and effective technique for simultaneously probing the surface chemistry, surface molecular orientation, degree of order, and electronic structure of carbon nanotubes and related nanomaterials. Specifically, we employ NEXAFS in the study of single-walled carbon nanotube and multi-walled carbon nanotube powders, films, and arrays, as well as of boron nitride nanotubes. We have focused on the advantages of NEXAFS as an exciting, complementary tool to conventional microscopy and spectroscopy for providing chemical and structural information about nanoscale samples.     

Hollow iron oxide nanoparticles for application in lithium ion batteries

Material design in terms of their morphologies other than solid nanoparticles can lead to more advanced properties. At the example of iron oxide, we explored the electrochemical properties of hollow nanoparticles with an application as a cathode and anode. Such nanoparticles contain very high concentration of cation vacancies that can be efficiently utilized for reversible Li ion intercalation without structural change. Cycling in high voltage range results in high capacity (～132 mAh/g at 2.5 V), 99.7% Coulombic efficiency, superior rate performance (133 mAh/g at 3000 mA/g) and excellent stability (no fading at fast rate during more than 500 cycles). Cation vacancies in hollow iron oxide nanoparticles are also found to be responsible for the enhanced capacity in the conversion reactions. We monitored in situ structural transformation of hollow iron oxide nanoparticles by synchrotron X-ray absorption and diffraction techniques that provided us clear understanding of the lithium intercalation processes during electrochemical cycling.     

Growth and characterization of lead selenide thin films

Growth of lead selenide thin films has been carried out electrochemically on indium doped tin oxide coated conducting glass substrates from an aqueous acidic bath consists of Pb(CH₃COO)₂ and SeO₂. X-ray diffraction analysis has been carried out to determine the crystal structure and phases of the deposited films. Microstructural parameters such as crystallite size, strain and dislocation density which have been evaluated from X-ray diffraction data. Surface morphology and film composition have been analyzed using scanning electron microscopy and energy dispersive analysis by X-rays. The effect of bath temperature on structural, microstructural, morphological and compositional properties of the films are studied and the results are discussed. Optical absorption measurements shows that the deposited films possess a direct band gap value of 0.38?eV.     

Application and Evaluation of Random Forest Classifier Technique for Fault Detection in Bioreactor Operation

Bioreactors and associated bioprocesses are quite complex and nonlinear in nature. A small change in initial condition can greatly alter the output product quality. It is pretty difficult at times to model the system mathematically. In this work, the fault detection problem is studied in the context of bioreactors, mainly, a reactor from the penicillin production process. It is very important to identify the faults in a live process to avoid product quality deterioration. We have focused on the process history-based methods to identify the faults in a bioreactor. We want to introduce random forest (RF), a powerful machine learning algorithm, to identify several types of faults in a bioreactor. The algorithm is simple, easy to use, shows very good generalization ability without compromising much on the classification accuracies, and also has an ability to give variable importance as a part of the algorithm output. We compared its performance with two popular methods, namely support vector machines (SVM) and artificial neural networks (ANN), and found that the overall performance is superior in terms of classification accuracies and generalization ability.     

Performance of novel hyperbranched poly(aryl‐ether‐urea)s doped with N3‐dye in nanocrystalline DSSC

An amine‐terminated hyperbranched poly(aryl‐ether‐urea) (HBPEU) was prepared from an AB₂‐type blocked isocyanate monomer and then its end groups were modified into urea (M‐HBPEU) by reaction with phenyl isocyanate. Both of the polymers were doped with N3‐dye along with KI/I₂ to work as efficient polymer electrolytes in nanocrystalline dye sensitized solar cell. The increment in the conductivity of doped HBPEU and doped M‐HBPEU was very significant and reached its value at 8.2 × 10⁻³ and 4.1 × 10⁻² S/cm, respectively. The current–voltage (I–V) characteristics of these two doped polymers measured under simulated sunlight with AM 1.5 at 60 mW/cm² generate photocurrent of 2.5 and 3.6 mA/cm², together with a photo voltage of 690 and 750 mV, and fill factor of 0.55 and 0.61 yielding a overall energy conversion efficiency of 2.4% and 4.1%, respectively. These results suggest that M‐HBPEU show better cell performance and conductance properties than the HBPEU. © 2014 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2014 , 131, 40408.     

Effect of heat treatment on microstructural and optical properties of CBD grown Al-doped ZnO thin films

Investigations on the effect of annealing temperature on the structural, optical properties and morphology of Al-doped ZnO thin films deposited on glass substrate by chemical bath deposition have been carried out. X-ray diffraction studies revealed that deposited films are in polycrystalline nature with hexagonal structure along the (0 0 2) crystallographic plane. Microstructural properties of films such as crystallite size, texture coefficient, stacking fault probability and microstrain were calculated from predominant (0 0 2) diffraction lines. The UV-Vis-NIR spectroscopy studies revealed that all the films have high optical transmittance (>60%) in the visible range. The optical band gap values are found to be in the range of 3.25-3.31 eV. Optical constants have been estimated and the values of n and k are found to increase with increase of heat treatment. The films have increased transmittance with increase of heat treatment. Al-doped ZnO thin films fabricated by this simple and economic chemical bath deposition technique without using any carrier gas are found to be good in structural and optical properties which are desirable for photovoltaic applications. Scanning electron microscopic images revealed that the hexagonal shaped grains that occupy the entire surface of the film with its near stoichiometric composition.