III-V semiconductor nanowire for solid oxide fuel cells

Solid oxide fuel cells (SOFC) have much promise as efficient devices for the direct conversion of the energy stored in chemical fuels into electricity. The development of highly robust SOFC that can operate on a range of fuels, however, requires improvement in the electrodes, especially the anode, where nanoscale engineering of the structure is required in order to maximize the number of sites where the electrochemical reactions take place. In this article, we briefly explained the growth of III-V semiconductor nanowire layer on GaAs substrate as an anode electrodes using metal organic chemical organic vapor deposition (MOCVD). Field-emission scanning electron microscopy (FE-SEM), transmission electron microscopy (TEM) and conductivity atomic force microscopy (CAFM) analysis were carried out to investigate the structural properties and current-voltage changes in the wires. Results show that the III-V nanowires grow with less defect structure, uniform in composition and diameters with optimal growth parameters. The current-voltage measurement showed similar to that of a p-n junction characteristic which is suitable in the SOFC application

The study of optical gain for terahertz quantum cascade laser using density matrix method

Terahertz (THz) quantum cascade lasers (QCL) are currently increasing in popularity. It is expected to become the main source of emerging terahertz radiation technology and applications. However to produce the device within the application specification is costly and time consuming. This is because the manufacturing process of the superlattice growth and the device processing and testing are long and expensive processes. Thus a prediction tool is needed to overcome the problems in designing and producing THz QCL within the needed optical expectation. The density matrix method is used to calculate the performance of this device electronically and optically. The result obtained was compared to the experimental result conducted by previous researchers. The calculation result showed that the gain is 20 cm−1 when the population inversion occurs at threshold current density of 400 A cm-2. Meanwhile a negative gain or loss occurs below 350 A cm-2. As a conclusion, it is demonstrated that this method has a capability to explain the transport phenomena as well as to predict the performance of the THz QCL device design

Alsolation and characterization of a heavy metalreducing enterobacteriaceae bacterium strain DRY 7 with the ability to assimilate phenol and diesel

Background/Objectives: Molybdenum, phenol and diesel are toxic to organism, and are part of global pollution. Their removal using microorganisms with multiple detoxification ability is being intensely sought as a cleaner and economic approach. Methods/Statistical analysis: A soil suspension was spread plated on a minimal salts media supplemented with molybdenum. Blue colonies, indicating molybdenum reduction was then screened for phenol and diesel degradation capabilities. Findings: A molybdenum-reducing bacterium locally isolated showed the ability to grow on phenol and diesel. The bacterium required pHs of between 5.8 and 6.3 and temperatures of between 30 and 40oC for optimal reduction. Among the carbon sources tested for supporting reduction, glucose was the best. A critical concentration of phosphate at just 5 mM was required, while molybdenum (sodium molybdate) was required between 15 and 25 mM. The absorption spectrum of the Mo-blue produced showed a characteristic maximum peak at 865 nm. The reduction of molybdenum was inhibited by the ions mercury, copper, chromium, lead and silver by 78.9, 78.4, 77.4, 53.5 and 36.8%, respectively. Analysis using phylogenetic analysis identifies the bacterium as Enterobacteriaceae bacterium strain DRY7. Growth on phenol and diesel as carbon sources showed that the optimal concentrations supporting growth was between 300 and 400 mg/L and between 300 and 500 mg/L, respectively. Application/Improvements: The capacity of this bacterium to detoxify a number of toxicants is an important property or bioremediation of soils contaminated with multiple toxicants

The atomic force microscope study of self-assembled silicon nanodots growth using magnetron sputtering system

In this paper self-assembled silicon nanodots have been grown on silicon substrate using radio-frequency magnetron sputtering system. This system were settled at varying experimental conditions such as substrate temperature, time of deposition, RF power and fixed argon flow rate. Then the surface roughness was measured by AFM which resulted average dots size of 113 nm. However, the presence of a small amount of grain atoms formed on the surface was confirmed using SEM measurement. The crystalline Si-NDs with (100) plane contributed sharp diffraction peak located at 69.5° was confirmed using XRD measurement. These results of Si-NDs structural properties support the possible growth technique of radio-frequency magnetron sputtering

Synthesis and characterization of InGaAS nanowires grown by MOCVD

Semiconductor nanowires have been intensively investigated in order to study their unique fundamental and application properties that develop at the nano-scale. One of main problems in the growth of III-V semiconductor nanowire is uniformity both of in dimension and composition of chemical elements. We synthesized InGaAs nanowire on GaAs (111) substrate at 400 °C – 480 °C temperatures for 30 minutes using MOCVD. The nanowires grow perpendicular to the substrate via direct impinging mechanism and they have hexagonal shape with diameter of 80-150 nm. Dimension of nanowire, length and diameter, increase with increases of growth temperature. Formations of tapering could be controlled with growth at lower temperature

The effect of indium mole fraction on the growth behavior of inxga1-xas nanowires (NWS) grown using MOCVD

InxGa1-xAs NWs have been grown with various indium mole fractions (x) using MOCVD. The morphology of InxGa1-xAs NWs was observed using Field Emission-Scanning Electron Microscopy (FE-SEM) in order to study the growth behavior of the NWs. FE-SEM results show that the NWs growth mechanism has changed due to changing of indium mole fraction. At low indium mole fraction, the NWs grew via direct impinging mechanism which has produced NWs with relatively uniform diameter. By increasing the value of x the growth mechanism has transformed to the combination of direct impinging and diffusion of source atoms from the surface of substrate causing tapering of NWs. The degree of tapering increases with increasing value of indium mole fraction. InxGa1-xAs NW grown at x = 0.65 has the highest tapering factor, TF = 12.82, whereas NW grown at x = 0.41 has the lowest tapering factor, TF = 2.76

Growth of Ge/Si(100) nanostructures by radio-frequency magnetron sputtering: the role of annealing temperature

Surface morphologies of Ge islands deposited on Si(100) substrates are characterized and their optical properties determined. Samples are prepared by rf magnetron sputtering in a high-vacuum chamber and are annealed at 600°C, 700°C and 800°C for 2 min at nitrogen ambient pressure. Atomic force microscopy, field emission scanning electron microscopy, visible photoluminescence (PL) and energy dispersive x-ray spectroscopy are employed. The results for the annealing temperature-dependent sample morphology and the optical properties are presented. The density, size and roughness are found to be strongly influenced by the annealing temperature. A red shift of ∼0.29 eV in the PL peak is observed with increasing annealing temperature

Effect of GaAs multi-atomic steps thickness on the structural and optical properties of self-assembled In0.5Ga0.5As quantum dots

Self-assembled In0.5Ga0.5As quantum dots (QDs) were grown on various thickness of GaAs multi-atomic steps layer using Stranski-Kratanov (SK) growth mode. Atomic force microscopy (AFM) analysis indicates fluctuation of size and density of the dots. The varieties of dots formed on the surface are believed to be the affect of different structure of GaAs multi-atomic steps with different thicknesses. The high-density small dots are formed at 200 nm thick GaAs multi-atomic steps. The PL measurement shows evolution of peak shape as an effect of different surface morphology of the samples as a result of increasing thickness of GaAs multi-atomic steps layer. This study shows the formations of the dots grown by Stranski-Krastanov growth mode not only influenced by growth parameters but also strongly dependent on structures of GaAs multi-atomic steps layer. The modification of size, shape, uniformity, and density of QDs are essential for device applications especially for QD lasers

Effects of annealing temperature on shape transformation and optical properties of germanium quantum dots

The influences of thermal annealing on the structural and optical features of radio frequency (rf) magnetron sputtered self-assembled Ge quantum dots (QDs) on Si (100) are investigated. Preferentially oriented structures of Ge along the (220) and (111) directions together with peak shift and reduced strain (4.9% to 2.7%) due to post-annealing at 650 °C are discerned from x-ray differaction (XRD) measurement. Atomic force microscopy (AFM) images for both pre-annealed and post-annealed (650 °C) samples reveal pyramidal-shaped QDs (density ~ 0.26× 1011 cm−2) and dome-shape morphologies with relatively high density ~ 0.92 × 1011 cm−2, respectively. This shape transformation is attributed to the mechanism of inter-diffusion of Si in Ge interfacial intermixing and strain non-uniformity. The annealing temperature assisted QDs structural evolution is explained using the theory of nucleation and growth kinetics where free energy minimization plays a pivotal role. The observed red-shift ~ 0.05 eV in addition to the narrowing of the photoluminescence peaks results from thermal annealing, and is related to the effect of quantum confinement. Furthermore, the appearance of a blue-violet emission peak is ascribed to the recombination of the localized electrons in the Ge-QDs/SiO2 or GeOx and holes in the ground state of Ge dots. Raman spectra of both samples exhibit an intense Ge–Ge optical phonon mode which shifts towards higher frequency compared with those of the bulk counterpart. An experimental Raman profile is fitted to the models of phonon confinement and size distribution combined with phonon confinement to estimate the mean dot sizes. A correlation between thermal annealing and modifications of the structural and optical behavior of Ge QDs is established. Tunable growth of Ge QDs with superior properties suitable for optoelectronic applications is demonstrated

Structural, morphological and optical investigations of θ-Al2O3 ultrafine powder

Single-phase θ-Al2O3 nanopowder has been synthesized by co-precipitation technique. The synthesized powders were sintered at a temperature ranging from 900 to 1200 °C. A stable monoclinic phase is observed for the whole sintering temperature range. The purity, chemical bonds, morphology and optical properties of the powders were investigated by different characterization techniques. X-ray diffraction and Brunauer–Emmett–Teller analysis confirms the existence of ultrafine alumina powders with particle diameter of ∼5 nm and surface area of 100 m2/g. The novel optical results such as band gap of 5.8 eV would reveal the viability of observed phase of alumina in advanced semiconductor applications