Thin films of GaNBi alloys with up to 12.5 at.% Bi were grown on sapphire using low-temperature molecular beam epitaxy. The low growth temperature and incorporation of Bi resulted in a morphology of nanocrystallites embedded in an amorphous matrix. The composition and optical absorption shift were found to depend strongly on the III:V ratio controlled by the Ga flux during growth. Increasing the incorporation of Bi resulted in an increase in conductivity of almost five orders of magnitude to 144 Ω-cm−1. Holes were determined to be the majority charge carriers indicating that the conductivity most likely results from a GaNBi-related phase. Soft x-ray emission and x-ray absorption spectroscopies were used to probe the modification of the nitrogen partial density of states due to Bi. The valence band edge was found to shift abruptly to the midgap position of GaN, whereas the conduction band edge shifted more gradually.

Schottky diodes have been fabricated on metalorganic chemical vapor deposition GaN epitaxial layers grown on sapphire substrates. Carbon impurities limit the ability of these films to be used in high-power devices. Although its effect can be mitigated by growing the films at higher pressure, higher flow rates, and larger V/III ratios, it still effectively limits the net carrier concentration to ∼1016 cm−3 and therefore the breakdown voltage to ∼1200 V by acting as a compensating deep acceptor for n-type material. The net carrier concentration is smaller than the carbon concentration indicating that not all of the carbon occupies a nitrogen site acting as a deep acceptor. It is not known whether some of the carbon occupies gallium sites acting as a donor, interstitial sites creating states in the midgap region, and/or is tied up in the large number of dislocations in the films where it is not electrically active.

We report controlled modifications in the semiconductor-to-metal transition characteristics of VO2 single-crystal thin films induced by swift heavy ion (SHI) irradiation with varying ion fluences. At very high energies of ions (200 MeV Au), the electronic stopping (∼2009 eV/Å) dominates over nuclear stopping (∼16 eV/Å). Under these extreme electronic excitation conditions caused by electronic stopping and the passage of SHIs through the entire thickness of the film, creation of certain unique type of defects and disordered regions occurs. X-ray diffraction, Raman spectroscopy, infrared transmission spectroscopy, x-ray photoelectron spectroscopy (XPS), and electrical measurements were performed to investigate the characteristics and role of these defects on structural, optical, and electrical properties of VO2 thin films. XPS and electrical resistivity measurements suggest that the ion irradiation induces localized defect states that appear to correlate well with the creation of disordered regions in the VO2 thin films. The high-energy heavy-ion irradiation changes the transition characteristics drastically from a first-order to a second-order transition (electronic—Mott type). The low-temperature conductance data for these ion-irradiated films fit well with the quasiamorphous model for resistivity of VO2, where ion irradiation is believed to create mid-bandgap defect states.

Nd3+/Yb3+ co-doped TiO2–La2O3 glasses modified by ZrO2 were fabricated by containerless method. Under the excitation of 980 nm lasers, three intense emissions centered at 521, 545, and 655 nm were observed, which are assigned to the Nd3+: 4G9/2→4I9/2, 4G7/2→4I9/2, and 4G7/2→4I13/2 transitions, respectively. Besides, two very weak emission bands at 496 and 603 nm were also found due to the Nd3+ transition of 2G9/2→4I9/2 and 4G5/2 (or 2G7/2)→4I9/2, respectively. Pumping powder dependence of emission intensity suggests a two-photon adsorption process responsible for the upconversion luminescence. A combined phonon-assisted and cooperative sensitization mechanism is presented to interpret the energy transfer from Yb3+ to Nd3+ ions. In addition, the highest intensity of luminescence was found for the glass with 1.2 mol% Nd3+, and the upconversion efficiency can be enhanced by increasing of ZrO2 content.

ZnO crystals have been investigated by scanning cathodoluminescence microscopy and spectroscopy at 80 K following hydrogen incorporation by plasma exposure. The intensity of the ZnO near-band-edge (NBE) emission is greatly enhanced while the defect-related green emission is quenched following plasma treatment. These effects are attributed to the passivation of zinc vacancies by hydrogen. The green and yellow intensities and their intensity ratios to the NBE vary with excitation depth for both undoped and H-doped ZnO crystals. The intensities of the green and yellow emissions exhibit sublinear dependencies on electron beam excitation density while the NBE intensity increases linearly with the excitation density. These saturation effects with increasing excitation density must be taken into account when assessing defects in ZnO by luminescence characterization.

Based on a citric acid-assisted hydrothermal method, series of Ce3+/Tb3+ activated fluorides have been synthesized. By controlling the amount of KNO3, the final products evolve from the Ce3+/Tb3+ codoped orthorhombic phase GdF3 to the Ce3+/Tb3+ codoped cubic phase KGdF4. The concentration of Ce3+ has great effects on the crystalline phases and the morphologies of final products. The Ce3+ concentration dependent samples illustrate the appearance of the hexagonal phase solid solution CeF3–GdF3–TbF3 in the final products. When the Ce3+ concentration is 20 mol%, the sample Ce20 presents the hexagonal phase CeF3 but the diffraction peaks move to higher degree. The x-ray diffraction patterns suggest the phase evolution of final products, the field emission scanning electron microscopy images present the variation in morphology of samples, and the photoluminescence excitation and emission spectra as well as the luminescent dynamic curves illustrate the optical properties of samples.

Locally Er3+-doped noncongruent, Li-deficient Ti:Er:LiNbO3 strip waveguide was fabricated with a technological process in sequence of preparation of Li-deficient LiNbO3 substrate using Li-poor vapor transport equilibration (VTE), Er3+, and Ti4+ diffusion in wet O2. The Li2O content change was evaluated from the measured birefringence. The Ti4+ and Er3+ profile characteristics in the waveguide were studied by secondary ion mass spectrometry. The results show that the VTE and subsequent Er3+ diffusion procedures resulted in totally ∼0.8 mol% Li2O content reduction. The Ti4+ profile follows a sum of two error functions in the width direction and a Gaussian function in the depth direction of waveguide. The Er3+ profile follows also a Gaussian function. At 1130 °C, the Ti4+ surface/depth diffusivity and surface concentration are 8.5 ± 1.3/1.98 ± 0.06 μm2/h and ∼7 mol%, respectively, and the Er3+ diffusivity and surface concentration are (12.8 ± 0.3) × 10−2 μm2/h and ∼0.6 mol%, respectively.

In this work, the silk fibroin/sericin (SF/SS) blend aqueous solutions with different SF/SS mass ratios (100/0, 90/10, 85/15, 75/25, and 65/35) were prepared and electrospun to get regenerated fibers. It was found that the addition of SS in the SF solution could increase the apparent viscosity of the solution and improve its electrospinnability so that the fine uniform electrospun SF/SS fibers could be obtained. The quantitative analysis result of Raman spectroscopy showed that the presence of SS facilitated the conformational transition of SF from random coil/α-helix structure to β-sheet structure. Combined with the differential scanning calorimetry result, it was further hypothesized that SS could affect the structural change of SF by dehydrating SF and inducing the formation of hydrogen bonds between SF molecules. Consequently, SS also played an important and positive role in the thermal and mechanical properties of the resultant SF/SS fibers.

Oxidized starch (OSt) films reinforced with natural halloysite were prepared by adding modified natural halloysite nanotubes into an OSt matrix. The halloysite/OSt films were characterized by x-ray diffraction, scanning electron microscopy, and ultraviolet spectrometry. The mechanical properties and moisture absorbability of the films were also studied. The modified halloysite nanotubes were well distributed in the starch matrix, and the tensile strength (TS) of the films was greatly enhanced, but the moisture adsorption ability of the films only changed slightly. The flexibility of the films was improved by adding glycerol but at a cost of reducing the TS. Incorporating a small amount of poly(vinyl alcohol) (PVA) improved both the TS and the percent elongation at break of the halloysite/OSt films.

Solid polymer electrolytes (SPEs) with poly(vinylidene fluoride-hexafluoropropylene) [P(VdF-HFP)] as polymer host, doped with lithium trifluoromethanesulfonate (LiTf) and 1-butyl-3-methylimidazolium trifluoromethanesulfonate (BMIMTf) have been synthesized via solution casting method. This P(VdF-HFP)/LiTf/BMIMTf-based SPE achieves ∼2.4 × 10−3 and ∼1.1 × 10−2 S·cm−1 at 30 and 80 °C, respectively, with 100 part by weight of BMIMTf incorporated into the system. A very interesting trend of temperature-dependence ionic conductivity has been obtained. A rationalization of the trend is given and the morphological changes observed in scanning electron micrographs seem to be commensurate with it. Thermogravimetric and differential thermogravimetric analyses reveal some changes in thermal properties of the SPEs, including the possibility of phase separation happening in the sample.

Organic plasma polymers are currently attracting significant interest for their potential in the areas of flexible optoelectronics and biotechnology. Thin films of plasma-polymerized polyterpenol fabricated under varied deposition conditions were studied using nanoindentation and nanoscratch analyses. Coatings fabricated at higher deposition power were characterized by improved hardness, from 0.33 GPa for 10 W to 0.51 GPa for 100 W at 500-μN load, and enhanced wear resistance. The elastic recovery was estimated to be between 0.1 and 0.14. Coatings deposited at higher RF powers also showed less mechanical deformation and improved quality of adhesion. The average (Ra) and root mean square (Rq) surface roughness parameters decreased, from 0.44 nm and 0.56 nm for 10 W to 0.33 nm and 0.42 nm for 100 W, respectively.

Peripherally and nonperipherally tetrakisoctylthio- and tetrakisoctyloxy-substituted lead(II) phthalocyanines (PbPcs) were synthesized and characterized using elemental analysis, nuclear magnetic resonance, ultra violet–visible (UV-Vis), infrared (IR), and mass spectroscopies. The mesogenic properties of PbPcs were studied by differential scanning calorimetry, polarized optical microscopy, and x-ray diffraction. The effects of the substitution position and nature of linkage heteroatom on the liquid-crystalline properties and the orientation of the molecules were also studied. Visible absorption spectroscopy yielded an evidence of a thermally induced molecular reorganization in the films. Reflection–absorption IR spectroscopy was used to study the preferential orientation of molecules relative to the substrate surface. The intense bands in the IR spectra of the PbPcs were assigned with the aid of quantum chemical (density functional theory) computations.

The bipolar plate is one of the most important components in proton exchange membrane fuel cell. In this article, the graphite/polymer composite bipolar plates have been developed by compression molding technique. The study on effects of different resin types on the electrical conductivity, mechanical property, and corrosion performance of the composite bipolar plates shows that the properties of graphite/novolac epoxy (NE) plate are all better than those of graphite/phenol formaldehyde resin plate. The triple continuous structure provides graphite polymer blends with high electrical conductivity, high flexural strength, less porosity, and high density. Most of the properties, such as electrical conductivity, flexural strength, water adsorption, porosity, and so on, are affected by the properties of the polymer. The graphite/NE composite bipolar plate when used in the unit fuel cell assembly showed single-cell performance comparable to that of the commercially available graphite bipolar plates.

Polyaniline nanofiber (PANF) was synthesized using interfacial polymerization and was mixed with aqueous solution of poly(vinyl alcohol) (PVA) to form PANF–PVA binaries. The PANF suspension in water could be stabilized by PVA for more than 3 months due to the hydrogen bonding interaction between PANF and PVA. The specific characteristics of PANF–PVA films was checked by scanning electron microscopy, conductivity measurement, thermogravimetric analysis, Fourier transform infrared spectroscopy, and cyclic voltammetry. The composite film contained 25 wt% PVA (PANF–PVA25) casting at 105 °C was found to have a porous structure and good conductivity. The presence of hydrogen bonding interaction between PANF and PVA improves the electroactivity and electroactive stability of PANF–PVA25 for electrochemical applications. However, an ether linkage between PANF and PVA polymer chain was also found as casting the PANF–PVA film at 200 °C, which is unfavorable for electrochemical applications.

Two high-temperature pore generators (porogens) have been used to study the effect of porogen structure on moisture uptake and k-value in methylsilsesquioxane/porogen hybrid films and their corresponding porous films in a postintegration porogen removal scheme. Poly(styrene-b-4-vinylpyridine) containing di-block structure and pyridine polar group leads to higher moisture uptake and k-value in the hybrid films as compared to poly(styrene-block-butadiene-block-styrene) with symmetrical structure and nonpolar groups. Moreover, the moisture uptake behavior in both as-prepared hybrid films is in physical sorption mode based on their reversible adsorption–desorption curve measured by quartz crystal microbalance. After porogen removal, the k-values of porous films are favorably not influenced by porogen structures, and their moisture uptake is as low as 1.78 wt% even at 40 vol.% porosity. However, based on the simulation of the modified-Rayleigh model, the porous films are found to possess 0.4 vol.% chemisorbed moisture on the pore surface, resulting in 17–23% deviation from the ideal k-values.