Non-polar a-plane InGaN films were grown on a r-plane sapphire substrate by plasma assisted molecular beam epitaxy (PAMBE). The growth temperature and Indium flux were varied to optimize the desired composition of In0.23Ga0.77N on the (11-20) a-plane GaN epilayer grown on a (1-102) r-plane sapphire substrate. The structural, morphological and optical properties of the optimized composition have been studied. It was found that highly a-axis oriented InGaN epilayers with no phase separation can be grown at 540 °C with In/Ga flux ratio of 0.72. The composition of indium incorporation in single phase InGaN films was found to be 23% as estimated by high resolution X-ray diffraction. The room temperature band gap energy of single phase InGaN layers was determined by photoluminescence measurement and found to be around 2.56 eV.

We present a comparative density functional theory study of Li, Na, and Mg storage energetics and diffusion in α-Sn, including the effects of temperature (vibrations). We study several concentrations corresponding to initial stages of insertion (number densities x= 1/64, 1/32, 1/16, and 1/8) as well as the final state of charge (Li17Sn4, Na15Sn4, and Mg2Sn). While final states of charge correspond to positive anode voltages for all three types of metal, insertion energetics is favorable for insertion for Li at all concentrations studied, for Na up to the concentration of x = 3/64, and Mg insertion is thermodynamically disfavored at all x. Diffusion barriers at dilute concentrations are computed to be 0.23, 0.51, and 0.44 eV for Li, Na, and Mg, respectively. Vibrations have a noticeable and temperature-, concentration-, and dopant-type dependent effect on voltages, of the order of 0.1 eV at room temperature.

To modify the rigid structure of alginate, polyvinyl alcohol was mixed. Rheological properties and viscoelastic properties of the polymer blend solution were investigated. Complex and shear viscosity and tangent delta of the solution were obtained to find optimum condition of spinning dope. Effect of blend ratio on morphology and property change was investigated.

Electrochemical reduction of CO2 into useful organics combined with photovoltaics is thought to be one of the promising ways to effectively store and transport the solar energy. In most of the previous researches, CO2 bubbling in different solutions were used as the electrolyte. However, the effects of the electrolyte and the CO2 bubbling are not clear. Therefore, in this research, the effects of different electrolyte, CO2 bubbling, concentration of the electrolyte and temperature on the electrochemical reduction of CO2 on a Cu working electrode were studied. The results showed that the form of the carbon source in the electrolyte, such as HCO3 -, CO3 2- and H2CO3, had a strong effect on this reaction, which was controlled by the pH of the electrolyte. Furthermore, high concentration of the HCO3 - and elevated temperature can strongly improve the reaction current density.

Development of effective CO2 separation technologies is one of the most critical issues for implementation of CO2 Capture & Storage (CCS) because CO2 capturing covers about 60 % of the total CCS cost. CO2 capturing with solution absorption technology has gained current acceptance, and the actual operations have been demonstrated in many countries. However, This technology requires certain amount of energy in recovering CO2 from the CO2-capturing solution, which results in developing alternative CO2 capturing technologies. Because difference in partial pressure of the interest gas between feed and permeate side drives the separation, membrane separation does not need additional energy and can make CO2 separation much more effective. ☐In pre-combustion such as an integrated gasification combined cycle (IGCC) plant, CO2/H2 gas mixture after water-gas shift reaction has a pressure of 2.4 MPa, which would be preferable for membrane separation. Various membranes for CO2 separation over H2 have been investigated, however, the membrane separation has not been implemented due to lack in CO2 selectivity or permeability. In this paper, poly(amidoamine) (PAMAM) dendrimer is used to enhance affinity to CO2 and incorporated in a polymer matrix. The resulting polymeric membrane expressed excellent CO2 separation properties even under pressure. The CO2 permeance is relatively lower than the requirement value and 1.0 x 10-10 m3(STP)/(m2 s Pa). However, the permeance can be enhanced by reducing membrane thickness.

Simulation results of InGaN light-emitting diodes and efficiency droop are presented. A special method for investigating the changes in the semiconductor devices characteristics due to different influencing factors is developed.

The cause of efficiency droop was detected-large difference in carrier lifetimes. The simulation results are used to suggest several techniques for improving LED efficiency up to 10-15 %.

ZnO and ZnO/ZnFe2O4 nanocomposites were synthesized by mechanical-assisted thermal decomposition method. The results show that this method is a simple and low cost method to prepare ZnO and ZnO/ ZnFe2O4 nanocomposites. The nanorod's shape and size have been identified through SEM and TEM. The photocatalytic activity of ZnO and ZnO/ZnFe2O4 nanocomposites were tested by the degradation of methylene blue (MB) in aqueous medium under almost-visible light and the efficiency of the catalyst has been discussed in detail.

Organic semiconductor technology paves the way to low cost lightweight, flexible, printable electronics circuits and sensors. A novel lateral multilayer organic semiconductor photosensor is fabricated using small molecule organic semiconductor. A specialized interface layer is introduced between the metal electrodes and the organic semiconductor layer. The interface layer material is a large band gap and low electronic conductivity material. The use of interface layer limits the charge injection from the electrodes to the organic semiconductor and overall improves the photosensor dark current performance with an additional advantage to apply high voltage for improved collection. This design has low dark current with high photo-to-dark current ratio and can be set to high bias mode of operation.

Lateral interdigitated photodetector, with bottom contact Metal Semiconductor Metal (MSM) is fabricated consisting of interface layer and organic semiconductor bilayer. Small molecule organic semiconductor 3,4,9,10 perylenetetracarboxylic bisbenzimidazole (PTCBI) and Copper-Phthalocyanine (CuPc) are used as the active bilayer, where as polyamide forms the interface layer. Current through the sensor is measured in both dark and in light (wavelength 400nm). The dark current density in a 1mm2 photosensor area with 5μm lateral electrode spacing at 10V/μm measured equal to 10-5mA/cm2 and a photocurrent density of 10-3 mA/cm2 under 0.3mW/cm2 incident optical power. The photo to dark current ratio is measured to be equal to ∼103.

This photosensor has an application in large area imaging for example portable lightweight detectors. Other applications of this sensor include indirect medial imaging and as a biosensor in UV Spectroscopy study of bacteria cultures.

Hematite (α-Fe2O3) nanoparticles were diffused of two different shapes (spherical and cubical) in PEDOT:PSS matrices below the percolation threshold. Increases in conductivity within a distinct range in concentration were observed in the dark and under simulated solar illumination. The effect was ascribed to a generalized Poole-Frenkel effect in conjunction with basic properties of heterojunctions and electrostatic dipoles, and verified through data fitting. A difference in behaviour between sphere- and cube-based nanocomposites was also observed.

An introductory materials science course has been traditionally taught at Texas A&M University - like at many other universities - through lectures with minimal active student involvement. With this approach, most students just reproduce what they are given and accept it without any challenge or question. The authors have redesigned this course to include an active learning component. While the course consists of lecture-based classes during regular teaching hours to keep the essence of traditional teaching, the authors incorporated a research experience to their class in order to engage students and encourage them to apply the content seen in class to real-word problems with a higher level of expertise. The aim of the study was to discover the effectiveness of the authors’ redesign. We hypothesized that the research experience would facilitate the learning of knowledge content and the enthusiasm for the chosen field of study, i. e. engineering. The results reveal that students in the experimental condition consistently show a greater gain in knowledge, but there is no sufficient evidence suggesting that the research experience increase the student’s enthusiasm to be an engineer.

We investigate structural and magnetic properties of Co thin-film electrodes used in a new type of spin quantum cross (SQC) devices, in which a strong stray magnetic field could be generated between the both edges of magnetic thin-film electrodes. We also calculate the stray field between the two edges of Co thin-film electrodes in SQC devices and discuss the possibility to novel spintronics devices. As a result of magnetic force microscopy (MFM) observations, the stray fields are generated from the Co edges, and they are uniformly distributed. This result indicates that magnetic single-domain structures can be formed. This is consistent with the result obtained by magneto-optical Kerr effect (MOKE). The theoretical calculation reveals that the stray field exhibits as high as 7000 Oe under the condition that the distance between the two Co edges is 5 nm and the Co thickness is 19 nm. These results indicate that SQC devices utilizing stray fields can be expected as novel spintronics devices, such as spin filtering devices and beyond CMOS switching devices.

Silicon is emerging as a very attractive anode material for lithium ion batteries due to its low discharge potential, natural abundance, and high theoretical capacity of 4200 mAh/g, more than ten times that of graphite (372 mAh/g). This high charge capacity is the result of silicon’s ability to incorporate 4.4 lithium atoms per silicon atom; however, the incorporation of lithium also leads to a 300-400% volume expansion during charging, which can cause pulverization of the material and loss of access to the silicon. The architecture of the anode must therefore be able to adapt to this volume increase. Here we present a layered carbon nanotube and silicon nanoparticle electrode structure, fabricated using directed assembly techniques. The porous carbon nanotube layers maintain electrical connectivity through the active material and increase the surface area of the current collector. Using this architecture, we obtain an initial capacity in excess of 4000 mAh/g, as well as increased power and energy density as compared to anodes fabricated using the standard procedure of slurry casting.

Carbon nanotubes (CNTs) have been shown to be a viable conductive additive in Li-Ion batteries [1]. By using CNTs battery life, energy, and power capability can all be improved over carbon black, the traditional conductive additive. A significantly smaller weight percentage (5% CNTs) is needed to get the same conductivity as 20% carbon black. Many of the previous efforts found that a combination of conductive additives was most advantageous [2]. Unfortunately many of these efforts did not attend to the unique challenge that dispersing nanotubes presents and used non-optimal methods to disperse CNTs (e.g. ball milling) [3,4]. With poor dispersion a stable and resilient conductive network in the cathode is hard to form with CNTs alone. Here we investigate the formation of LiFePO₄ with CNTs using a polyol process synthesis.

Multi-walled nanofibers with their outstanding properties have found expanding applications on drug delivery systems, biosensors, self-healing materials and many other state-of-the-art technologies. This work investigates the fabrication and morphological control of multi-walled structured electrospun polymeric nanofibers by multi-axial electrospinning system. This process is based on a nozzle allowing multi-axial extrusion of different fluids with concentric orders. Two spinnable polymers of poly(methyl methacrylate) and polyacrylamide are chosen for the fabrication of middle and outer walls of co-axial hollow nanofibers, respectively. Hansen’s solubility parameters are used to systematically optimize the solvent selection for each layer and control the degree of miscibility of layers with the purpose of tailoring the final wall morphology of nanofibers. Characterization studies are performed by Scanning Electron Microscopy, Energy-Dispersive X-ray Spectroscopy, Fourier Transform Infrared Spectroscopy, and Thermal Gravimetric Analyzer.

We wish to propose an impedance spectroscopic method for the quality control of contact lenses by measuring the pore resistance. Silicone hydrogels are excellent materials for use as contact lenses and their on eye performance is dependent on salt intrusion characteristics which are related to the pore resistance and water uptake. When the contact lenses are placed on the eye, they are expected to permeate ions and molecules to maintain ocular health. The hydrogel pores control the permeability and can be viewed as a quality control parameter. Two models are considered here: in one, the contact lenses are considered as strong rigid films with no permeability. In another, the hydrogels are having ionic permeability. We designed a silicone hydrogel contact lens attachment holder that is amenable for electrochemical impedance measurements. The electrochemical impedance measurements were carried out in an inert medium of 0.1 M Na2SO4. The impedance measurement experimental parameters used were a) AC potential 10 mV rms b) frequency range 0.1-210 kHz and c) open circuit potential of 0.207 V. The impedance variation with frequency was constructed for a number of hydrogels. The ideally acceptable silicone hydrogel contact lenses showed an impedance change with frequency in a sigmoidal fashion with a characteristic phase angle (acceptable in the range of 70-75o). The hydrogel pore resistances for the acceptable contact lenses are in the range of 4.5-11 kΩ. When the impedance showed a linear decrease or no well defined phase angle, the contact lens is considered acting as an insulator-a test for rejection. A test of the model was done with several acceptable contact lenses in the market. This study revealed interesting aspects of the influence of pulsating electric field on the silicone hydrogels.

Recently there have been reports of hot carrier thermoelectric response in nanostructured materials like graphene and MoS. We report observing that thermoelectric nanowire junctions detect light. In these experiments we employed devices composed of bismuth nanowire arrays which are capped with a transparent indium tin oxide electrode. The incident surface features very low optical reflectivity and enhanced light trapping. The unique attributes of the thermoelectric arrays are the combination of strong temporal and optical wavelength dependences of the photocurrent. Under infrared illumination, the signal can be completely described by “quasi-equilibrium” thermoelectric effects considering cooling rates given by heat diffusion through the array. The thermal diffusivity is found to be less (by a factor of 3.5) than in the bulk, a result that we discuss in terms of phonon confinement effects. In addition to a thermoelectric response, under visible illumination, we observe a photovoltaic response.

Lead-free, piezoelectric (Na,K)NbO3-BaZrO3-(Bi,Li)TiO3 films were epitaxially grown onto (100) SrTiO3 substrate via pulsed laser deposition. The effects of post-annealing temperature on the crystal phases, mosaic spread, and chemical composition of the deposited (Na,K)NbO3 and (Na,K)NbO3-BaZrO3-(Bi,Li)TiO3 films were analyzed. Results indicate the epitaxial growth of (Na,K)NbO3-BaZrO3-(Bi,Li)TiO3 films deposited at an oxygen pressure (PO2) of ≥40 Pa and substrate temperature (Ts) of 800°C. The alkaline-deficiency could be suppressed in the (Na,K)NbO3-BaZrO3-(Bi,Li)TiO3 films deposited at PO2 ≥ 70 Pa. AFM profile of the (Na,K)NbO3 post-annealed at 1000°C indicates the epitaxial growth of film with atomically flat step-terrace structure, while that of the (Na,K)NbO3-BaZrO3-(Bi,Li)TiO3 film post-annealed at 1200°C shows relatively smooth surface with step-terrace structure and several cubic crystals. It was also found that the preferential evaporation of alkaline components could be suppressed by annealing under covered substrate condition.

The effect of compositional changes on the glass forming ability of Mg alloys containing Y was studied. Four rapidly-solidified Mg-alloys were investigated: Mg91Y7.5La1.5, Mg85Y12La3, Mg86Y9.5Cu2.5La2 and Mg82Y11La4Eu3. XRD and DSC spectra revealed that the Mg86Y9.5Cu2.5La2 was the most amorphous out of the investigated alloys. A model based on a spinodal-like decomposition of a supercooled liquid alloy was developed. The model provides qualitative and quantitative explanation for the variation in glass forming ability.

This article deals with the development of autoclaved composites (AC) with nanostructured additive (NSA) and reports on the beneficial effects of NSA in autoclaved lime-silica mixtures.

Based on the results of X-ray diffraction and electron microscopy investigation, the effects of hydrothermal conditions on the mechanisms of lime-silica interaction are revealed. It is demonstrated that the addition of NSA intensifies the formation of the C-S-H phase, reduces the quantities of amorphous phases and enables the formation of low-base calcium hydrosilicates (11Å-tobermorite and xonotlite).

The physical and mechanical properties of autoclaved composites with NSA are investigated and optimized. The reported research demonstrates the feasibility of NSA application to improve the performance of autoclaved materials.