A transition of porous structures in monolithic poly(methylsilsesquioxane) (PMSQ, CH3SiO1.5) gels from uniform mesopores to hierarchical pore structures consisting of macro- and mesopores, has been investigated using a sol-gel system containing surfactant Pluronic F127. A broad variation of porous morphology is controlled by changing the concentration of F127. Sufficient concentrations of F127 inhibit the occurrence of macroscopic phase separation of hydrophobic PMSQ condensates and lead to well-defined mesoporous transparent aerogels with high specific pore volume. Mesopores are developed through microscopic phase separation of PMSQ colloid-surfactant complexes in the solvent. Macroscopic phase separation regulates well-defined macropores in the micrometer range on decreasing concentrations of F127, in which microscopic phase separation concurrently takes place in the PMSQ-rich gelling phase after the onset of macroscopic phase separation. Monolithic PMSQ gels with hierarchical macro- and mesopore structures are consequently obtained.

Transparent conducting oxides have been previously investigated for both bulk and thin film thermoelectric applications, and have shown promising results due to their thermal stability and electrical conductivity. Alloys of two or more transparent conducting oxides have been deposited using pulsed laser deposition (PLD) and combinatorial sputtering, and the resulting films were optimized for optical applications. In this study, thermoelectric materials were prepared by co-sputtering techniques, whereby a chemical gradient was formed across an alumina substrate that was patterned using photolithography to form hundreds of micro-thermocouples. The systems indium tin oxide (ITO), indium zinc oxide (IZO), and zinc tin oxide (ZTO) were investigated for this purpose and the resulting combinatorial libraries were rapidly screened to establish room temperature resistivity, Seebeck coefficient, and power factor as functions of both composition and heat treatment, in nitrogen and air ambients. Due to their chemical stability, oxidation resistance, and large Seebeck coefficients relative to metal thermocouples, these materials are ideal for temperature measurement or energy harvesting in harsh environments such as gas turbine engines.

Surface modification of jute fibers was accomplished by performing chemical treatments including detergent washing, dewaxing, alkali, and acetic acid treatment. Morphology of modified surfaces examined using scanning electron microscopy (SEM) revealed improved surfaces for better adhesion with matrix. Better thermal performance of treated fibers was found from thermogravimetric analysis (TGA). Enhanced tensile properties of treated fibers were obtained from tensile tests. Using solution intercalation technique and magnetic stirring, 2%, 3%, and 4% by weight Montmorillonite K10 nanoclay were dispersed into a biodegradable polymer, Biopol. Thermal performance of nanoclay infused Biopol characterized using dynamic scanning calorimetry (DSC) showed improved degree of crystallinity by 7%. Jute fiber reinforced Biopol biocomposites with and without nanoclay were manufactured using treated and untreated jute fibers by compression molding process. Thermal and mechanical responses of treated fiber reinforced Biopol composites (TJBC) without nanoclay evaluated using dynamic mechanical analysis (DMA) and flexure tests showed 9% and 12% increase in storage modulus and flexure strength, respectively, compared to untreated jute fiber reinforced composites (UTJBC). The respective values were 100% and 35% for 4% nanoclay infused TJBC compared to UTJBC without nanoclay.

Green laser crystallization of a-Ge0.85Si0.15 films deposited using Low Pressure Chemical Vapour Deposition is studied. Large grains of 8x2 μm2 size were formed using a location-controlled approach. Characterization is done using Scanning Electron Microscopy, Atomic Force Microscopy, X-Ray Photoelectron Spectroscopy and X-Ray Diffraction.

Magnet-attractive carbon nanopowder can be produced by a pulsed Nd:YAG laser (10 Hz) vaporization of pure carbon in a few % of H2 containing Ar gas at 1000°C. On the other hand, magnet-attractive nanopowder cannot be formed when vaporizing in pure Ar. As-grown carbon nanopowder includes a few to ten % of micron sized graphite flakes as the impurity. Removal of such flakes can be achieved by a centrifugal separation and the supernatant is checked by X-ray diffractometry (XRD) and transmission electron microscopy (TEM). Magnetization curve at 400 K is easy to saturate at low magnetic field of 10 kG, and no hysteresis is observed. This feature is explained by a superparamagnetism of finely dispersed ferro- or ferri-magnetic nanoparticles. Elementary analyses using electron energy loss spectroscopy (EELS) and atomic absorption spectroscopy (AAS) suggest that the observed strong magnetism should be an intrinsic carbon magnetism.

Electronic structure calculations are reported for Gd in GaN on Ga as well as on N site and for pairs of Gd on neighboring Ga and N sites, using the full-potential linearized muffin-tin orbital method in the local spin density approximation with Hubbard U corrections (LSDA+U). The energy of formation for the N site is found to be much higher than for the Ga site even after relaxations are included. The GdN configuration is found to be at best metastable (in ZB). In WZ and in the pair configurations, the Gd is found to move toward an interstitial site leaving a nitrogen vacancy behind. The electronic structure of these structures and their magnetic moments are discussed.

ZnO nanobridge sensors were selectively grown and electrically connected using lithographically patterned carbonized photoresist (C-PR). As ZnO is known to dissolve in deionized (DI) water, parylene-A was investigated as a moisture barrier and potential functionalization platform. A chemical vapor deposition (CVD) process for parylene-A was developed and it was demonstrated that parylene-A coated ZnO NWs do not show any signs of dissolution after 24 hours in an aqueous solution. The impact of the parylene-A coating on the electrical performance and sensitivity of ZnO nanobridge devices was investigated. A comparison of UV, O2, and H2O sensitivity between uncoated and coated devices revealed that a thin coating of parylene-A attenuated all of these responses, suggesting the ability to modulate environmental sensitivity using this non-covalently bound polymer passivation layer.

One of the challenges on the way to optimized solar cells is to make the thickness of the individual layers smaller than the diffusion length of the charge carriers. In this work, we propose 3C-SiC microcrystals grown by a sol-gel based process as a promising acceptor material for photovoltaic applications. The μc-SiC samples were characterized by optical spectroscopy and electron paramagnetic resonance (EPR). The experimental data is analyzed with the help of ab-inito calculations in the framework of density functional theory (DFT) resulting in electronic band structures and g-tensors. Based on this, a possible scenario for the observed acceptor process is discussed.

Single orientation ZnO (00.2) films were deposited by means of high temperature high vacuum reactive magnetron sputtering onto Al2O3 (0001) and GaN (0001) substrates. In order to obtain films of high crystalline quality a novel approach to ZnO sputter deposition was employed, adapting the practice used in MBE technology, of using a MgO buffer layer deposited on sapphire at a high-temperature followed by a ZnO nucleation layer deposited at low temperature. ZnO films were also grown on epitaxial GaN/Al2O3 substrates where the GaN layer was treated as the buffer layer. Following the deposition, all samples were annealed ex-situ in an O2 flow at 800°C. The obtained ZnO films have a lattice constant c equal to 5.2036 Å and 5.214 Å for the films deposited on Al2O3 and GaN substrates, respectively. Secondary ion mass spectroscopy depth profiles, scanning and transmission electron microscopy cross sectional images and atomic force microscope were used to characterize the structural properties of the films. Electrical properties were assessed using Hall effect measurement. Photoluminescence spectra were also taken.

ZnO nanostructures have proven to be versatile functional materials with promising electronic, piezoelectric and optical properties. Here, we report on the application of (CdSe) ZnS Core Shell quantum dots decorated ZnO Nanowires (ZnONWs) and Nanobelts (NBs) in solar energy harvesting. Results indicate that both as grown and decorated ZnO Nanostructures are photoactive, have a fast response time and generate photocurrent under excitation in a photoelectrochemical cell setup. An order of magnitude enhancement in the photocurrent response of (CdSe) ZnS Core Shell quantum dots decorated ZnONBs is seen as compared to response from as grown ZnONBs. Generated photocurrent decreases with time but stabilizes at higher value for (CdSe) ZnS Core Shell quantum dots coated ZnONBs. Detailed performances of these devices are discussed.

Recent advances in fabricating controlled-morphology vertically aligned carbon nanotube (VA-CNTs) with ultrahigh volume fraction create unique opportunities for markedly improving the electromechanical performance of ionic polymer conductor network composite actuators (IPCNCs). Actuator experiments show that the continuous paths through inter-VA-CNT channels and low electrical conduction resistance due to the continuous CNTs in the composite electrodes of the IPCNC lead to fast ion transport and actuation speed (>10% strain/second). One critical issue in developing advanced actuator materials is how to suppress or eliminate unwanted strains generated under electric stimulation, which reduce the actuation efficiency and also the actuation strains. We observe that the VA-CNTs in the composite electrodes yields non-isotropic elastic modulus that suppresses the unwanted strain and markedly enhances the actuation strain (>8% strain under 4 volts). A transmission line model has been developed to understand the electrical properties of the actuator device.

Staggered bottom-gate hydrogenated nanocrystalline silicon (nc-Si:H) thin-film transistors (TFTs) were demonstrated on flexible colorless polyimide substrates. The dc and ac bias-stress stability of these TFTs were investigated with and without mechanical tensile stress applied in parallel to the current flow direction. The findings indicate that the threshold voltage shift caused by an ac gate-bias stress was smaller compared to that caused by a dc gate-bias stress. Frequency dependence of threshold voltage shift was pronounced in the negative gate-bias stress experiments. Compared to TFTs under pure electrical gate-bias stressing, the stability of the nc-Si:H TFTs degrades further when the mechanical tensile strain is applied together with an electrical gate-bias stress.

Double-shelled nanotubes composed of inner shell Pb(Zr0.52Ti0.48)O3 (PZT) and outer shell TiO2 are successfully fabricated by a spin coating of each sol-gel solution on porous anodic alumina template. Field emission transmission electron microscopy images show that they have a ~ 10 nm wall thickness. The selected area electron diffraction patterns show that they have two mixed crystalline phases of tetragonal PZT and anatase TiO2. The analyses of scanning transmission electron microscopy equipped with energy dispersive X-ray spectroscopy confirm their uniform distribution of each element.

We have demonstrated and studied polymeric solid-state dye lasers (SSDLs) fabricated by three-dimensional (3D) polystyrene colloidal crystals and tert-butyl roadamine B (t-Bu RhB) doped Poly (methyl methacrylate) (PMMA) films with different film thickness. The sandwich-typed resonator cavities with different active layer thickness display single-mode lasing oscillations in the reflection bandgap of the colloidal crystals. The lasing thresholds could be optimized by changing the thickness of t-Bu RhB doped PMMA films, which is as low as 7.43 W/cm2. Adjusting active layer thickness would provide an opportunity to accelerate the development of fabricating polymeric SSDLs with low threshold.

Electrochromics is a key “green” technology for massive energy savings in the built environment jointly with indoor comfort. This paper surveys basic electrochromic (EC) device designs, useful oxide materials and their nanostructures, and elements of a theoretical description of the EC phenomenon. It also outlines critical manufacturing technologies and their pros and cons. Focus is on EC foil technology, which is shown capable of mass fabrication via roll-to-roll web coating and continuous lamination.

Electrophoretic displays, the rewritable non-light-emitting display technology based on the movement of colored pigments inside a low dielectric liquid as a voltage is applied, have attracted a great deal of academic and commercial interests due to the combination of the advantages of both electronic displays and conventional paper, including paper-like high contrast appearance, ultra-low power consumption, thinness, flexibility etc. Fabrication of electrophoretic ink by microencapsulating the electrophoretic suspension into individual microcapsules is one way to realize such application. However, there are still some limitations for its commercial application, such as the dispersion and the electrophoretic mobility of charged particles due to the nano-particles aggregation, the barrier property and stability of microcapsule wall due to the suspension releasing, etc. In this presentation, systematic studies on the preparation of electrophoretic particles and microencapsulation by complex coacervation method were carried out to solve the mentioned problems. The obtained microcapsules can be quasi-monolayer coated on ITO/PET substrate and driven by static mode to obtain a matrix character display prototype.

Mineralized biological materials such as nacre and bone achieve remarkablecombinations of stiffness and toughness through staggered arrangements ofstiff components bonded by softer materials. These natural composites aretherefore substantial source of inspiration for emerging syntheticmaterials. In order to gain new insights into structureperformancerelationships of these staggered structures, nacres from four species werecompared in terms of fracture toughness and damage propagation pattern.Fracture tests revealed that all nacres display rising crack resistancecurves, but to different extents. Using in-situ optical and atomic forcemicroscopy, two distinct patterns of damage propagation were identified incolumnar and sheet nacre respectively. These two different patterns werefurther confirmed by means of large scale numerical models of staggeredstructures. Similar mechanisms possibly operate at the smallest scales ofthe microstructure of bone.

High-quality InGaN/GaN multiple quantum wells (MQWs) were fabricated on nano-scale epitaxial lateral overgrown (NELO) GaN layers which was prepared using nanometer-scale SiO2 islands, with an average diameter and interdistance of 300nm and 200nm respectively, as the growth mask. The active region of the device consists of five periods of GaN/InGaN MQWs were grown on top of the NELO layer using MOCVD technique. It is observed that some of the dislocations from the undoped GaN were blocked by the SiO2 growth mask and typical threading dislocation (TD) density found in the NELO samples is ~7.5×107cm-2. Significant improvement in the electroluminescence (EL) is observed which is believed to partly arise from the improvement in the internal quantum efficiency (ηi ). The experimental data on the temperature dependence of the photoluminescence (PL) were fitted to a proposed model using Levenberg-Marquardt approximation. Based on our analyses it is found that the relative improvement in ηi at 300K over a control device grown in the same growth condition but without the NELO layer to a NELO device is only 0.59. It is generally accepted that TD is the non-radiative recombination center which affects the IQE. Therefore, room-temperature IQE values also support that NELO device exhibits lower TD density.

Studies of the electronic transport properties of n-type doped hydrogenated amorphous/nanocrystalline silicon (a/nc-Si:H) films deposited in a dual-plasma co-deposition reactor are described. For these doped a/nc-Si:H, the conductivity increases monotonically for increasing crystal fractions up to 60% and displays marked deviations from a simple thermally activated temperature dependence. Analysis of the temperature dependence of the activation energy for these films finds that the dark conductivity is best described by a power-law temperature dependence, σ = σo (T/To)n where n = 1 – 4, suggesting multiphonon hopping as the main transport mechanism. These results suggest that electronic transport in mixed-phase films occurs through the a-Si:H matrix at lower nanocrystal concentrations and shifts to hopping conduction between clusters of nanocrystals at higher nanocrystal densities.