Uniform Incorporation Research Articles

Adjustment of alkali element incorporations in Cu(In,Ga)Se2 thin films with wet chemistry Mo oxide as a hosting reservoir

Thin film Cu(In,Ga)Se2 solar cells remain one of the most promising devices for commercial photovoltaic panels. Aimed at high quality absorber film, alkali elements such as sodium and potassium incorporation can improve the crystal structure and electrical properties of the Cu(In,Ga)Se2 film. However, the precise control on sodium content as well as the incorporation mechanisms is yet comprehensively understood. We propose a facile wet chemistry oxidation approach for large area homogeneous Mo oxidation and allow for uniform sodium incorporation in a controllable manner. Eventually the oxidized Mo substrate in an optimal condition leads to a relative increase of 8% of conversion efficiency in the final solar device compared with the non-oxidized sample. We thoroughly examine the surface chemistry of the Mo substrate with X-ray photoelectron spectroscopy after a systematic H2O2 oxidation treatment. A qualitative analysis show that the predominant Mo trioxides as a reservoir can adjust alkali elements contents in Cu(in,Ga)Se2 films. Upon oxidation, the narrowing down of Mo grain boundaries has now suppressed the over sufficient sodium incorporation compared to uncontrolled diffusion from soda lime glass. Also, the emergence of potassium element in the thin film improves the electrical properties. Thermodynamic calculation indicate that the K2MoO4 as an intermediate from K2O and MoO3 reaction is a preferable reaction path compared the Na2O reaction and thus enhanced potassium ion diffusion. We have correlate the sodium contents by simply adjusting the H2O2 treatment time to improved Cu(InGa)Se2 film qualities, e.g., crystal structures, grain sizes, charge carrier concentrations and defect densities.

A novel hierarchical porous nitrogen-doped carbon derived from bamboo shoot for high performance supercapacitor

Porous N-doped carbons hold good prospects for application in supercapacitor due to their low-cost, large surface area, good surface wettability, high electrical conductivity as well as extra pseudocapacitance. However, most synthetic methods required the tedious and multiple-step process with the assistance of hard/soft templates or the massive use of chemical reagents, and exogenous nitrogen sources, which made them difficult to realize industrial production and application. Here, we described a novel hierarchical porous N-doped carbons fabricated by a facile and sustainable approach via hydrothermal treatment and subsequent carbonization process by using renewable bamboo shoots as the starting material without any templates, additional chemical activation and nitrogen source. The obtained bamboo shoot-derived carbons possessed a large BET surface area (up to 972 m2 g−1), hierarchically interconnected porous framework, rich and uniform nitrogen incorporation (3.0 at%). Benefiting from these unique features, the novel carbon-based electrode materials displayed a high capacitance of 412 F g−1 in KOH electrolyte and long cycling life stability. Thus, an advanced electrode material for high-performance supercapacitor was successfully assembled by a simple and scalable synthesis route with abundant renewable resources freely available in nature.

Antibacterial hydroxypropyl methyl cellulose edible films containing nanoemulsions of Thymus daenensis essential oil for food packaging

Edible films containing essential oils (EO) as natural antibacterial agents are promising systems for food preservation. In this work, nanoemulsions of Thymus daenensis EO (wild; F1 and cultivated; F2) were loaded in hydroxyl propyl methyl cellulose (HPMC) films and the effect of different parameters (polymer, plasticizer, and EO concentration) on the film properties were analyzed and optimized. Prepared HPMC films were characterized in terms of EO loading, morphology, mechanical properties, and the antibacterial activity. The results of SEM showed uniform incorporation of nanoemulsions into the edible film. Investigation of the mechanical properties of two edible films revealed a plasticizing effect of T. daenensis EO on the films. Also, edible films had noticeable antimicrobial activity against selected microorganisms, i.e. 47.0±2.5mm and 22.6±0.5mm zone of inhibition against S. aureus for films containing F1 and F2, respectively. Incorporation of nanoemulsions into the HPMC films can be used for active food preservation.

Photopatternable cadmium-free quantum dots with ene-functionalization

Photopatternable nanoparticles can be easily dispersed into polymeric matrices and used to fabricate optoelectronic devices for display, sensing and quantum information processing applications. Here we report the first instance of a cadmium-free photopatternable quantum dot. A ligand containing dithiolane group at one end and an ene-functionalization at the other end were synthesized for this purpose. The myristic acid ligands on as synthesized red indium zinc phosphide-zinc sulfide (In(Zn)P/ZnS) quantum dots were easily replaced by the newly developed ligand by a simple sonication procedure. The functionalized quantum dots could be easily incorporated into a commercially available photoresist. The quantum dot doped photoresist was used to fabricate three-dimensional quantum dot doped hierarchical microstructures by two-photon lithography. Confocal imaging microscopy was used to verify the uniform incorporation of the nanoparticles in the hybrid microstructure.

Improving Visible Light-Absorptivity and Photoelectric Conversion Efficiency of a TiO2 Nanotube Anode Film by Sensitization with Bi2O3 Nanoparticles

This study presents a novel visible light-active TiO2 nanotube anode film by sensitization with Bi2O3 nanoparticles. The uniform incorporation of Bi2O3 contributes to largely enhancing the solar light absorption and photoelectric conversion efficiency of TiO2 nanotubes. Due to the energy level difference between Bi2O3 and TiO2, the built-in electric field is suggested to be formed in the Bi2O3 sensitized TiO2 hybrid, which effectively separates the photo-generated electron-hole pairs and hence improves the photocatalytic activity. It is also found that the photoelectric conversion efficiency of Bi2O3 sensitized TiO2 nanotubes is not in direct proportion with the content of the sensitizer, Bi2O3, which should be carefully controlled to realize excellent photoelectrical properties. With a narrower energy band gap relative to TiO2, the sensitizer Bi2O3 can efficiently harvest the solar energy to generate electrons and holes, while TiO2 collects and transports the charge carriers. The new-type visible light-sensitive photocatalyst presented in this paper will shed light on sensitizing many other wide-band-gap semiconductors for improving solar photocatalysis, and on understanding the visible light-driven photocatalysis through narrow-band-gap semiconductor coupling.

In Situ Electron Microscopy of Plasmon-Mediated Nanocrystal Synthesis.

Chemical processes driven by nonthermal energy (e.g., visible light) are attractive for future approaches to energy conversion, synthesis, photocatalysis, and so forth. The growth of anisotropic metal nanostructures mediated by excitation of a localized surface plasmon resonance (LSPR) is a prototype example of such a reaction. Important aspects, notably the growth mechanism and a possible role of plasmonic "hot spots" within the metal nanostructures, remain poorly understood. Here, we use in situ electron microscopy to stimulate and image the plasmon-mediated growth of triangular Ag nanoprisms in solution. The quantification of the time-dependent evolution of the lateral size and thickness of the nanoprisms, enabled by nanometer-scale real-time microscopy in solution, shows a transition from an early stage of uniform Ag0 incorporation exclusively in the prism side facets to a size regime with accelerated growth in thickness. Differences in attachment rate at this advanced stage correlate with local plasmonic field enhancements, which allows determining the range over which charge carriers transferred from plasmonic hot spots can drive chemistry. Such data support the development of nonthermal chemical processes that depend on plasmonic light harvesting and the transfer of nonequilibrium charge carriers.

A Brief Research Review for Improvement Methods the Wettability between Ceramic Reinforcement Particulate and Aluminium Matrix Composites

The development of new methods for addition fine ceramic powders to Al aluminium alloy melts, which would lead to more uniform distribution and effective incorporation of the reinforcement particles into the aluminium matrix alloy. Recently the materials engineering research has moved to composite materials from monolithic, adapting to the global need for lightweight, low cost, quality, and high performance advanced materials. Among the different methods, stir casting is one of the simplest ways of making aluminium matrix composites. However, it suffers from poor distribution and combination of the reinforcement ceramic particles in the metal matrix. These problems become significantly effect to reduce reinforcement size, more agglomeration and tendency with less wettability for the ceramic particles in the melt process. Many researchers have carried out different studies on the wettability between the metal matrix and dispersion phase, which includes added wettability agents, fluxes, preheating the reinforcement particles, coating the reinforcement particles, and use composting techniques. The enhancement of wettability of ceramic particles by the molten matrix alloy and the reinforcement particles distribution improvement in the solidified matrix is the main objective for many studies that will be discussed in this paper.

Electrodeposition of Nickel/Titanium Carbide Nanocomposite Coatings

Due to their high hardness, anti-corrosion and anti-wear properties, Nickel/ceramic particle composites have gained significant attention as environmentally-friendly alternatives to chromium and cadmium based coatings typically used in the aerospace industry [1-3]. Electrodeposition of these Ni/ceramic particle composites has the advantage of lower operating cost and operating temperature than the conventional production methods [1-3]. Electrodeposition of Ni/TiC nanocomposites for these wear-resistant coatings is a commonly investigated example [2, 3]. Incorporation of nanoparticles into the deposit has a significant effect on the tribological and mechanical properties of the composites [1, 3]. Previous studies show that high and uniform particle incorporation into the deposit depends greatly on the dispersion of these ceramic particles in the electrolyte [1, 2]. Therefore to get superior properties, the agglomeration of the nanoparticles in the electrolyte should be decreased and the nanoparticle incorporation into the deposit should be increased [1]. However, a major challenge in this regard is that the dispersants that are used to stabilize the particles in the electrolyte can significantly affect the electrodeposition kinetics. The aim of this study is to investigate the effect of a cationic dispersant, polyethyleneimine (PEI), on the electrodeposition of Ni/TiC nanocomposites from a Watts bath. The effect of the dispersant on the particle stability in the electrolyte, on the nanoparticle incorporation rate into the deposit as well as on the electrodeposition kinetics are investigated simultaneously. Therefore, optimum dispersant bath concentration that increases particle dispersion in the electrolyte and TiC amount in the nanocomposite without affecting the electrodeposition kinetics is determined. In addition, electrodeposition of Ni/TiC nanocomposites in the presence of PEI is characterized as a function of ceramic particle bath concentration, current density and rotation speed. Firstly, in order to determine the effect of PEI on the stability of TiC nanoparticles in the electrolyte, zeta potentials of the particles are measured in 0.01 M NaCl solution at a pH of 4.4 for different PEI:TiC bath concentration ratios. It has seen that PEI is highly effective in enhancing the dispersion of TiC nanoparticles even at low concentrations; zeta potential of TiC particles increased from 19.6 to 40.6 mV with the addition of 50 ppm PEI. Secondly, the effect of PEI bath concentration on the Ni/TiC electrodeposition kinetics was investigated using linear sweep voltammetry as shown in Figure 1. It can be seen that the addition of PEI at concentrations of 125 ppm and lower does not create any significant inhibition except at low current densities. The shift in the potentials seen for a PEI concentration of 250 ppm may be interpreted as the adsorption of the polymer onto the electrode inhibiting the active sites for charge transfer. In order to further quantify the effect of PEI on electrodeposition kinetics, current efficiencies were measured for PEI concentrations of 0, 50, 125 and 250 ppm at a current density of 50 mA cm-2and determined as 97.0%, 97.5%, 96.2% and 58.5%, respectively. It can be concluded that PEI addition up to 125 ppm improves the particle dispersion significantly without inhibiting the electrodeposition. Finally, the effect of PEI on the amount and uniformity of TiC nanoparticles in the composite is analyzed by SEM/EDS. Backscattered SEM images show that the addition of PEI leads to more uniform particle incorporation into the deposit. In addition, volume fraction of TiC in the nanocomposite increased from 0.3% to 3.2% with the addition of 125 ppm PEI. Further enhancement on the incorporation rate will be done by the optimization of other critical parameters such as the particle bath concentration, current density and rotation speed. Figure 1. Polarization curves for Watts solution containing 5 g/L TiC and different PEI concentrations. In all cases the disk rotation speed was 2500 rpm. Acknowledgments This study is funded by The Scientific and Technological Research Council of Turkey (TUBITAK Project No: 116C005).

Tetracycline hydrochloride-loaded electrospun nanofibers mats based on PVA and chitosan for wound dressing

Fibrous mats built from biopolymer have been extensively explored for tissue engineering due mainly to their mimic structure to the extracellular matrix. The incorporation of drug in such scaffolds represents a growing interest for control drug delivery system in order to promote the tissue repair. In the present work, we present an experimental investigation of morphological, thermal, mechanical, drug release, antibacterial and cytotoxicity properties of electrospun PVA/Chitosan and PVA/Chitosan/Tetracycline hydrochloride (TCH) mats for wound dressing. Fibrous mats with cross-linked three-dimensional nanofibers were formed from the polymer blends. A uniform incorporation of drug was achieved along the nanofibers with not significant change on the morphological and thermal properties of the mats. Furthermore, the TCH release profile with a burst delivery during the first 2h allows an effective antibacterial activity on the Gram-negative Escherichia coli as well as on the Gram-positive Staphylococci epidermidis and Staphylococcus aureus. In vitro indirect MTT assay also showed that the developed drug-loaded nanofibrous scaffolds have good cytocompatibility, which was confirmed by scratch assay, indicating that the investigated scaffold may be used as antibacterial wound dressing for healing promotion.

Development of a novel alginate-polyvinyl alcohol-hydroxyapatite hydrogel for 3D bioprinting bone tissue engineered scaffolds.

Three-dimensional printed biomaterials used as personalized tissue substitutes have the ability to promote and enhance regeneration in areas of defected tissue. The challenge with 3D printing for bone tissue engineering remains the selection of a material with optimal rheological properties for printing in addition to biocompatibility and capacity for uniform cell incorporation. Hydrogel biomaterials may provide sufficient printability to allow cell encapsulation and bioprinting of scaffolds with uniform cell distribution. In this study, a novel alginate-polyvinyl alcohol (PVA)-hydroxyapatite (HA) hydrogel formulation with optimal rheological properties for 3D bioprinting of mouse calvaria 3T3-E1 (MC3T3) cells into scaffolds of high shape fidelity has been developed. A systematic investigation was conducted to determine the effect of varying concentrations of alginate, phosphate, calcium, and the PVA-HA suspension in the formulation on the resulting viscosity and thus printability of the hydrogel. HA, the main mineral component in natural bone, was incorporated into the hydrogel formulation to create a favorable bone-forming environment due to its excellent osteoconductivity. Degradation studies in α-MEM cell culture media showed that the 3D printed alginate-PVA-HA scaffolds remained in-tact for 14 days. MC3T3 cells were well distributed and encapsulated throughout the optimal hydrogel formulation and expressed high viability through the completion of the 3D printing process. Thus, the development of this novel, osteoconductive, biodegradable, alginate-PVA-HA formulation and its ability to 3D bioprint tissue engineered scaffolds make it a promising candidate for treating personalized bone defects. © 2017 Wiley Periodicals, Inc. J Biomed Mater Res Part A: 105A: 1457-1468, 2017.

Tunable Morphology and Doping of ZnO Nanowires by Chemical Bath Deposition Using Aluminum Nitrate

Mastering the properties of ZnO nanowires grown by the low temperature chemical bath deposition (CBD) is of crucial importance but is still challenging. We show that the shape, dimensions, and doping of ZnO nanowires can simultaneously be tuned by the addition of aluminum nitrate in the standard chemical system using zinc nitrate, hexamethylenetetramine, and ammonia in aqueous solution. The formation and doping mechanisms of ZnO nanowires are thoroughly investigated by combining chemical, structural, and optical analyses with in situ pH measurements correlated with thermodynamic simulations. We reveal that the electrostatic interactions of Al(OH)4– complexes with the positive m-plane sidewalls of ZnO nanowires at a given pH favor their adsorption as capping agents, reducing the radial growth and promoting the elongation, while favoring the aluminum uniform incorporation. Importantly, the aluminum doping is found to be thermally activated above the low temperature of 200 °C under oxygen atmosphere, as indicated by the occurrence of six related additional modes in the range of 200–900 cm–1 in temperature-dependent Raman spectroscopy. These findings show that CBD using aluminum nitrate is of high potential for tuning both the morphology of ZnO nanowires and their physical properties via the aluminum doping, which paves the way for their more efficient use into sensing, electronic, and optoelectronic devices on both flexible and rigid substrates.

Fabrication of membrane absorbers based on amphiphilic carbonaceous derivatives for selective endotoxin clearance.

In this study, several novel blend membranes based on ligand-immobilized amphiphilic carbonaceous particles (ACPs) and matrix polymer polyvinylidene fluoride (PVDF) were prepared by an immersion phase inversion method. The effects of the ACP content on filtration performance of the membrane were investigated. Endotoxin removal with blend membranes at different pH values and ionic strengths was analyzed and discussed. The results indicated that the use of ACPs not only achieved uniform and stable incorporation of water-soluble ligands into the hydrophobic polymer membrane but also improved its filtration properties, including permeability, strength, hydrophilicity and antifouling ability. The blend membranes with the optimum particle content showed good performances in filtration and were highly effective in removing endotoxins from both buffer and protein solutions under properly chosen conditions. More than 99.8% of endotoxin removal and more than 90% of BSA recovery were achieved when 1 mg L-1 of BSA solution with 116 EU mL-1 of the endotoxin content was treated at pH 4.7. All the above suggested that the carrier-dispersed method described herein was one of the effective methods in constructing functionalized blend membrane absorbers.

Improved Protein Conjugation with Uniform, Macroporous Poly(acrylamide-co-acrylic acid) Hydrogel Microspheres via EDC/NHS Chemistry.

We demonstrate a robust and tunable micromolding method to fabricate chemically functional poly(acrylamide-co-acrylic acid) (p(AAm-co-AA)) hydrogel microspheres with uniform dimensions and controlled porous network structures for rapid biomacromolecular conjugation. Specifically, p(AAm-co-AA) microspheres with abundant carboxylate functional groups are fabricated via surface-tension-induced droplet formation in patterned poly(dimethylsiloxane) molds and photoinduced radical polymerization. To demonstrate the chemical functionality, we enlisted rapid EDC/NHS (1-ethyl-3-(3-(dimethylamino)propyl)carbodiimide (EDC) and N-hydroxysuccinimide (NHS)) chemistry for fluorescent labeling of the microspheres with small-molecule dye fluorescein glycine amide. Epifluorescence imaging results illustrate the uniform incorporation of carboxylate groups within the microspheres and rapid conjugation kinetics. Furthermore, protein conjugation results using red fluorescent protein R-phycoerythrin demonstrate the highly porous nature of the microspheres as well as the utility of the microspheres and the EDC/NHS scheme for facile biomacromolecular conjugation. Combined, these results illustrate the significant potential for our fabrication-conjugation strategy in the development of biofunctionalized polymeric hydrogel microparticles toward rapid biosensing, bioprocess monitoring, and biodiagnostics.

Synthesis and characterization of Trichloroisocyanouric acid functionalized mesoporous silica nanocomposite (SBA/TCCA) for the Acylation of Indole

Trichloroisocyanouric acid (TCCA)-functionalized mesoporous silica nanocomposites (SBA/ TCCA) were synthesized and characterized for the acylation of indole. The uniform incorporation of TCCA inside the SBA-15 matrix was confirmed by standard characterization techniques (PXRD, Adsorption studies, FT-IR, etc.). The catalytic activity studies of SBA/TCCA nanocomposites for acylation of indole showed high selectivity (60–90%) of the 3-acetyl indole compared to homogeneous TCCA (50%). The advantage of solid support for higher selectivity is also explained. Synthesis of SBA-15/TCCA nanocomposites by in situ functionalization of ordered SBA-15 and acylation of indole in the liquid phase for higher selectivity of 3-acylated product are reported.

Soluble expression, purification and functional characterisation of carboxypeptidase G2 and its individual domains

Due to its applications in the treatment of cancer and autoimmune diseases, the 42 kDa zinc-dependent metalloenzyme carboxypeptidase G2 (CPG2) is of great therapeutic interest. An X-ray crystal structure of unliganded CPG2 reported in 1997 revealed the domain architecture and informed early rational drug design efforts, however further efforts at co-crystallization of CPG2 with ligands, substrates or inhibitors have not been reported. Thus key features of CPG2 such as the location of the active site, the presence of additional ligand-binding sites, stability, oligomeric state, and the molecular basis of activity remain largely unknown, with the current working understanding of CPG2 activity based primarily on computational modelling. To facilitate renewed efforts in CPG2 structural biology, we report the first high-yield (250 mg L−1) recombinant expression (and purification) of soluble and active CPG2 using the Escherichia coli expression system. We used this protocol to produce full-length enzyme, as well as protein fragments corresponding to the individual catalytic and dimerization domains, and the activity and stability of each construct was characterised. We adapted our protocol to allow for uniform incorporation of NMR labels (13C, 15N and 2H) and present preliminary solution-state NMR spectra of high quality. Taken together, our results offer a route for production and solution-state characterization that supports renewed effort in CPG2 structural biology as well as design of significantly truncated CPG2 proteins, which retain activity while yielding (potentially) improved immunogenicity.

Spontaneous incorporation of gold in palladium-based ternary nanoparticles makes durable electrocatalysts for oxygen reduction reaction.

Replacing platinum by a less precious metal such as palladium, is highly desirable for lowering the cost of fuel-cell electrocatalysts. However, the instability of palladium in the harsh environment of fuel-cell cathodes renders its commercial future bleak. Here we show that by incorporating trace amounts of gold in palladium-based ternary (Pd6CoCu) nanocatalysts, the durability of the catalysts improves markedly. Using aberration-corrected analytical transmission electron microscopy in conjunction with synchrotron X-ray absorption spectroscopy, we show that gold not only galvanically replaces cobalt and copper on the surface, but also penetrates through the Pd–Co–Cu lattice and distributes uniformly within the particles. The uniform incorporation of Au provides a stability boost to the entire host particle, from the surface to the interior. The spontaneous replacement method we have developed is scalable and commercially viable. This work may provide new insight for the large-scale production of non-platinum electrocatalysts for fuel-cell applications.

Ultrathin and Uniform Carbon Coating on Active Materials Using Liquid CO2 As a Coating Solvent

Some of cathode and anode active materials (e.g., LiFePO4, Li4Ti5O12, Li2FeSiO4, TiO2, MoO2) exhibit inherently low electronic conductivities and low ionic conductivities; thus, these materials typically suffer from poor electrochemical performance. The reduction of particle size to a nanoscale dimension to enhance lithium ion diffusivity and carbon coating to increase electronic conductivity are the most widely used strategies to improve the performance of the potential active materials. Incorporation of too much carbon content, thick carbon layer coating, and non-uniform carbon coating on individual particles can also deteriorate energy density and battery performance. The complete, uniform, and thin carbon layer coverage ensures that the particles receive electrons from all directions and the electrons penetrate easily through the carbon layer, resulting in low polarization and high-rate performance. Herein, the use of liquid carbon dioxide (l-CO2) for uniform and ultrathin carbon layer coverage on highly porous LiFePO4 and MoO2 particles is discussed. The extremely low surface tension and the low viscosity associated with l-CO2 make it an excellent coating solvent for uniform and ultrathin carbon layer formation on the highly porous active materials. In addition, the carbon content in the range of 1-10 wt% can be easily controlled by adjusting process parameters such as solution concentration or evaporation velocity. The hierarchically porous MoO2 microspheres are synthesized in supercritical methanol without using any surfactants or structure-directing chemicals. The highly porous LiFePO4 particles are synthesized using a co-precipitation method. The MoO2 and LiFePO4 particles exhibits hierarchically porous nano/micro structure, in which primary particles with 30-65 mn size are loosely aggregated and form secondary spheres with 0.5-10 mm size. Owing to the low viscosity and low surface tension of l-CO2, the coating solution is penetrated into the pores of the particles and uniform and ultrathin carbon layer is covered on the primary particles. The thickness of carbon layers were in range of 0.8-2.0 nm by adjusting the carbon precursor concentration in l-CO2. The TEM analysis on the cross-sectional area of the particles shows that the uniform incorporation of the carbon layer on the whole surface of the micron-sized secondary particles. The carbon-coated LiFePO4 exhibits ~108.6 mAh g-1 at a high charge-discharge rate of 30 C. In addition, after 1000 cycles of 10 C, ~ 85% of an initial capacity is maintained. The carbon-coated MoO2 exhibits enhanced high-rate performance and cell stability. Figure 1

Electrical Conductivity Studies of Conducting Polymer Nanocomposites in Ambient Conditions

Nanocomposites of conducting polymer (polyaniline, PANI) nanoparticles with zinc oxide (ZnO) nanoparticles as inorganic filler and cellulose acetate (CA) as supporting matrix were prepared by a solution-casting method using N-methyl-2-pyrrolidone (NMP) as solvent. The nanocomposites were studied for their DC electrical conductivity and stability in terms of electrical conductivity retention by isothermal accelerated ageing and cyclic accelerated ageing techniques using a four-in-line probe instrument. The nanocomposites were also characterized by FTIR, SEM, TEM, TGA and XRD. All the nanocomposite formulations followed an Arrhenius-type temperature dependence of electrical conductivity, which supported a semiconducting nature for their HCl doped state. The electrical conductivity of the as-prepared HCl doped nanocomposites was also found to be in the semiconducting region. The studied nanocomposite formulations showed good stability towards retention of their electrical conductivity up to 90°C. X-ray diffractometry (XRD) data suggested the uniform incorporation of zinc oxide nanoparticles in the polymer matrix.

Atom probe tomography evidence for uniform incorporation of Bi across the growth front in GaAs1−xBix/GaAs superlattice

The three-dimensional distribution of Bi atoms in a GaAs1−xBix/GaAs superlattice grown by metalorganic vapor phase epitaxy (MOVPE) was studied using atom probe tomography (APT). The Bi distribution in the growth direction deduced from APT agreed quantitatively with the complex Bi concentration profile that was discovered using high-angle annular dark-field scanning transmission electron microscopy in a previous study. More importantly, APT revealed the Bi atom distribution in the growth planes at near atomic resolution. Bi nearest neighbor distribution and concentration frequency distribution analysis of the APT data indicated a statistically random distribution of Bi atoms in 1–2nm thick layers oriented perpendicular to the growth direction. These results provide evidence that Bi is incorporated homogeneously across the growth front even when the concentration profile in the growth direction is complex. They also suggest that MOVPE growth conditions can promote uniform Bi distribution within GaAs1−xBix layers, opening a path for application of these materials in the optoelectronic devices for which they show much promise.

Buffer-Free GeSn and SiGeSn Growth on Si Substrate Using In Situ SnD4 Gas Mixing

Buffer-free GeSn and SiGeSn films have been deposited on Si via a cold-wall, ultra-high vacuum chemical vapor deposition reactor using in situ gas mixing of deuterated stannane, silane and germane. Material characterization of the films using x-ray diffraction and transmission electron microscopy shows crystalline growth with an array of misfit dislocation formed at the Si substrate interface. Energy dispersive x-ray maps attained from the samples show uniform incorporation of the elements. The Z-contrast map of the high-angle annular dark-field of the film cross section shows uniform incorporation along the growth as well. Optical characterization of the GeSn films through photoluminescence technique shows reduction in the bandgap edge of the materials.