Synthesis of single-crystalline silver sulfide nanowires by diffusion in porous anodic aluminium oxide template

Highly ordered single-crystalline silver sulfide (Ag₂S) nanowires have been successfully achieved directly using silver nitrate and thioacetamide (TAA) as the reactants, by diffusion in the channels of anodic aluminium oxide (AAO) membrane. The products have been characterized by scanning electron microscopy (SEM), transmission electron microscopy (TEM), energy-dispersive X-ray spectroscopy (EDX), selected area electron diffraction (SAED) and high-resolution transmission electron microscopy (HRTEM). The results of the research show that the as-prepared Ag₂S nanowires are monodisperse with sizes of about 50 nm in diameter, closely corresponding to the pore size of the AAO membrane. Furthermore, its photoluminescence properties and the growth mechanism are also discussed.     

Non-volatile flash memory with discrete bionanodot floating gate assembled by protein template

We demonstrated non-volatile flash memory fabrication by utilizing uniformly sized cobalt oxide (Co(3)O(4)) bionanodot (Co-BND) architecture assembled by a cage-shaped supramolecular protein template. A fabricated high-density Co-BND array was buried in a metal-oxide-semiconductor field-effect-transistor (MOSFET) structure to use as the charge storage node of a floating nanodot gate memory. We observed a clockwise hysteresis in the drain current-gate voltage characteristics of fabricated BND-embedded MOSFETs. Observed hysteresis obviously indicates a memory operation of Co-BND-embedded MOSFETs due to the charge confinement in the embedded BND and successful functioning of embedded BNDs as the charge storage nodes of the non-volatile flash memory. Fabricated Co-BND-embedded MOSFETs showed good memory properties such as wide memory windows, long charge retention and high tolerance to repeated write/erase operations. A new pathway for device fabrication by utilizing the versatile functionality of biomolecules is presented.     

On-demand production of hydrogen by reacting porous silicon nanowires with water

On-demand hydrogen generation is desired for fuel cells, energy storage, and clean energy applications. Silicon nanowires (SiNWs) and nanoparticles (SiNPs) have been reported to generate hydrogen by reacting with water, but these processes usually require external assistance, such as light, electricity or catalysts. Herein, we demonstrate that a porous SiNWs array, which is fabricated via the metal-assisted anodic etching (MAAE) method, reacts with water under ambient and dark conditions without any energy inputs. The reaction between the SiNWs and water generates hydrogen at a rate that is about ten times faster than the reported rates of other Si nanostructures. Two possible sources of enhancement are discussed: SiNWs maintain their high specific surface area as they don’t agglomerate, and the intrinsic strain of the nanowires promotes the reactivity. Moreover, the porous SiNWs array is portable, reusable, and environmentally friendly, yielding a promising route to produce hydrogen in a distributed manner.

     

Compound semiconductor interfaces obtained by direct wafer bonding in hydrogen or forming gas

A technique of direct bonding wafers up to 6-inch diameter without mechanical load after being heated to elevated temperatures in H₂ or in non-flammable forming gas (5% H₂/95% N₂) was applied to GaAs and GaAs/GaP. Electron microscopy revealed crystallographic bond interfaces containing the typical dislocation network. The density of dislocations can be easily chosen below a limit adverse to electrical properties. Current–voltage characteristics of doped GaAs wafer pairs showed ohmic behavior of p–p and n–n junctions, whereas p–n diodes showed 2 to 3 V breakdown voltage as well as an ideality factor between 1.0 and 1.8.     

Labeling ribonuclease S with a 3 nm Au nanoparticle by two-step assembly

We label ribonuclease S with a 3 nm Au nanoparticle (NP) by utilizing its two-piece structure. One portion, S-peptide, is mutated with a unique NP attachment site. NP-peptide self-assembles with the other portion, S-protein, to form an active enzyme. NP mobility decreases with peptide labeling and S-protein association. Surface plasmon shifts support conjugation. Higher S-peptide coverages on the NP surface reduce nonspecific adsorption, while sterically hindering assembly of RNaseS. Thiols displace nonspecific adsorption, maximizing site-specific labeling.     

Physicochemical properties of silver powders obtained by contact precipitation with magnesium

We study the influence of the concentrations of AgNO₃ (0.06–0.32 mole/liter) and NH₄NO₃ (0.1–0.5 mole/liter) in the initial solution and the hydrodynamic conditions for Rev varying within the range 12,950–46,700 on the physicochemical properties of silver powders obtained from secondary solutions of silver (I) nitrate by contact precipitation with magnesium chips within the range 293–323°K. At a temperature of 313°K, for the stoichiometric amount of magnesium chips, turbulization of the medium corresponding to Re _v = 24,200, and the contents of AgNO₃ and NH₄NO₃ in the initial solution equal to 0.06–0.1 mole/liter and 0.25 mole/liter, respectively, we obtain silver powders with a bulk density of 1.09 g/cm³, a specific surface area of 2520 cm²/g (determined according to the gas permeability), and mean particle sizes of 1.0–3.0 μm. Powder particles have perfect geometric shapes with tetragonal and hexagonal symmetry about the axis of growth. The content of Ag in the powder is equal to 99.9 wt.%. It is shown that, by choosing and combining the conditions of contact precipitation, we can get powders with prescribed physicochemical properties.     

Patterned silver nanoparticle films by an ion complexation process in thermally evaporated fatty acid films

The formation of silver nanoparticle films in a patterned manner on suitable substrates is described. The protocol for realising such structures comprises of the following steps. In the first step, patterned films of a fatty acid are thermally evaporated onto solid supports using suitable masks (e.g. a TEM grid). Thereafter, the fatty acid film is immersed in silver nitrate solution and Ag⁺ ions entrapped in the lipid matrix by electrostatic complexation with the carboxylate ions of the fatty acid molecules. The final step involves the reduction of the Ag⁺ ions in situ thus leading to the formation of silver nanoparticles within the patterned lipid matrix. The process of metal ion incorporation and reduction may be repeated a number of times to increase the nanoparticle density in the lipid matrix. The silver nanoparticle density may also be increased by dissolution of the fatty acid molecules in suitable solvents. The process of Ag⁺ ion entrapment and formation of silver nanoparticles within the patterned lipid matrix has been followed by quartz crystal microgravimetry, UV-VIS spectroscopy, FTIR, SEM and EDX. The process described shows immense potential for extension to assemblies of nanoparticles in more intricate patterns as well as to the growth of semiconductor quantum dots in such patterns.     

Investigation of the local electron emission from current-carrying silver nanoparticle films by an emission electron microscope

Emission electron microscopy was used to study the electron emission observed under the passage of a tunnel current through a silver nanoparticle film when a voltage is applied to it. The electron emission originates from separate emission centers emitting photons as well. The electron emission centers are visualized as separate spots in an emission electron microscope. A deformation of shape and size of these spots was studied at various applied voltages. It enables the energy spread of electrons emitted from an individual emission center or at least the width of its most intensive part ε as well as the magnitude of electric field E near this center to be estimated. It has been shown that ε comprises 0.5-0.6 eV, and E < < 10⁷ V/cm. The latter result means that the electron emission is not the field emission.     

Application of ZnO single-crystal wire grown by the thermal evaporation method as a chemical gas sensor for hydrogen sulfide

A zinc oxide single-crystal wire was synthesized for application as a gas-sensing material for hydrogen sulfide, and its gas-sensing properties were investigated in this study. The gas sensor consisted of a ZnO thin film as the buffer layer and a ZnO single-crystal wire. The ZnO thin film was deposited over a patterning silicon substrate with a gold electrode by the CFR method. The ZnO single-crystal wire was synthesized over the ZnO thin film using zinc and activated carbon as the precursor for the thermal evaporation method at 800 degrees C. The electrical properties of the gas sensors that were prepared for the growth of ZnO single-crystal wire varied with the amount of zinc contained in the precursor. The charged current on the gas sensors increased with the increasing amount of zinc in the precursor. It was concluded that the charged current on the gas sensors was related to ZnO single-crystal wire growth on the silicon substrate area between the two electrodes. The charged current on the gas sensor was enhanced when the ZnO single-crystal wire was exposed to a H2S stream. The experimental results obtained in this study confirmed that a ZnO single-crystal wire can be used as a gas sensor for H2S.     

Characterization of adsorption removal of hydrogen sulfide by waste biocover soil, an alternative landfill cover

Landfill is an important anthropogenic source of odorous gases. In this work, the adsorption characteristics of H(2)S on waste biocover soil, an alternative landfill cover, were investigated. The results showed that the adsorption capacity of H(2)S increased with the reduction of particle size, the increase of pH value and water content of waste biocover soil. The optimal composition of waste biocover soil, in regard to operation cost and H(2)S removal performance, was original pH value, water content of 40% (w/w) and particle size of ≤4 mm. A net increase was observed in the adsorption capacity of H(2)S with temperatures in the range of 4-35°C. The adsorption capacity of H(2)S on waste biocover soil with optimal composition reached the maximum value of 60±1 mg/kg at oxygen concentration of 10% (v/v). When H(2)S concentration was about 5% (v/v), the adsorption capacity was near saturation, maintaining at 383±40 mg/kg. Among the four experimental soils, the highest adsorption capacity of H(2)S was observed on waste biocover soil, followed by landfill cover soil, mulberry soil, and sand soil, which was only 9.8% of that of waste biocover soil.     

Non-destructive analysis of silver selenide films obtained by Pulsed Laser Deposition (PLD) with Micro-XRF

Thin films of silver selenide with varying composition have been deposited on magnesium oxide substrates with pulsed laser deposition and were investigated via micro-XRF. A calibration procedure was designed to determine the absolute thicknesses of the films. The lateral homogeneity was investigated by elemental mapping, thus delivering information about the deposition process. Wet chemical analysis was performed on the dissolved layers with ICP-OES and ICP-MS to determine the stoichiometry of the Ag _x Se _y . The results suggest a correlation between the composition of the layers and their thicknesses by showing a silver enrichment for thinner layers.     

Photocatalytic hydrogen evolution over surface-modified titanate nanotubes by 5-aminosalicylic acid decorated with silver nanoparticles

The efficiency of titanate-nanotubes-based photocatalysts towards hydrogen production was studied in the presence of the sacrificial agent, 2-propanol. The highest hydrogen production rate (~120 μmol h⁻¹ g⁻¹) was observed over surface-modified titanate nanotubes by 5-amino salicylic acid decorated with nanometer-sized silver nanoparticles. The X-ray diffraction analysis, transmission electron microscopy, nitrogen adsorption–desorption isotherms, and diffuse reflection spectroscopy were applied to characterize the prepared photocatalytic materials. The better photocatalytic performance of inorganic–organic hybrid materials in comparison to the pristine titanate nanotubes is a consequence of their improved light-harvesting ability due to the formation of interfacial charge transfer (ICT) complex, as well as the presence of metallic silver nanoparticles that suppress the recombination of photo-generated charge carriers. The spin trapping EPR experiments under irradiation of prepared photocatalysts with either UV or visible light were used to monitor the appearance of hydroxyl radicals and superoxide radical anions. The generation of superoxide radical anions under visible light irradiation was detected for hybrid materials, but not for the pristine titanate nanotubes. These results are a consequence of enhanced promotion of electrons to the conduction band due to extended absorption in visible spectral range in hybrids and support the higher efficiency of hydrogen generation observed for surface-modified titanate nanotubes by 5-amino salicylic acid decorated with silver nanoparticles.     

Electronic properties of ruthenium sulfide–carbon cluster composite material obtained by calcination of an alternating ruthenium–S–phenylene hybrid copolymer

Calcination of an alternating ruthenium–S–phenylene hybrid copolymer under an argon atmosphere was found to give nano-sized ruthenium sulfide/carbon cluster composite material. ESR spectral examinations of the material revealed that an electron transfer from ruthenium sulfide particles to carbon clusters took place to raise a visible-light responsive oxidation–reduction function with an oxidation site at ruthenium sulfide particles and a reduction site at carbon clusters. The surface of the calcined material was modified with Pt particles, and the reduction ability of the resulting modified material was examined.     

Coating carbon nanotubes with colloidal nanocrystals by combining an electrospray technique with directed assembly using an electrostatic field

A simple method that combines an electrospray technique with directed assembly using an electrostatic field was used for decorating carbon nanotubes (CNTs) with nanocrystals. Colloidal CdSe and Au nanocrystals were electrosprayed and assembled onto random CNTs and vertically aligned CNTs in a controlled manner. The high level of electrical charge on the electrosprayed aerosol nanocrystals was responsible for the assembly. The technique can be used to assemble various compositions of nanomaterials onto different substrates and provides a versatile route for producing novel hybrid nanostructures.     

Fabrication of ultrahigh hydrogen barrier polyethyleneimine/graphene oxide films by LBL assembly fine-tuned with electric field application

In this study, layer-by-layer self-assembly of polyethyleneimine (PEI)/graphene oxide (GO) was successfully controlled by an applied electric field. The influences of the applied electric field direction, voltage, and dipping time on the hydrogen barrier properties of PEI/GO self-assembled film were investigated. Ultraviolet–visible light absorption spectroscopy, ellipsometry, atomic force microscopy, and scanning electron microscopy were used to analyze the effects of the electric field on the growth, nanostructure, and micromorphology of the self-assembled film. Results indicated that an applied electric field accelerates the adsorption rate of assembly and increases the GO adsorption quantity. Additionally, such electric field modifies the composite structure of the self-assembled film and spreads out the GO sheets uniformly on the substrate, which results in the formation of a more compact and ordered gas barrier layer with significantly improved hydrogen barrier properties. Higher applied voltage results in a more noticeable field effect. Under 25 V, the hydrogen transmission rate of the PEI/GO self-assembled 10-layer film reached 81 cm³/m² 24 h 0.1 MPa, which was 65% lower than that of standard composite films prepared without using an electric field.     

Design of an arc heater with discharge stabilization by a gas eddy

General electrical and thermal characteristics are presented for an arc heater of this type.Translated from Inzhenerno-Fizicheskii Zhurnal, Vol. 25, No. 3, pp. 500–505, September, 1973.     

Microbial conversion of sulfur dioxide in flue gas to sulfide using bulk drug industry wastewater as an organic source by mixed cultures of sulfate reducing bacteria

Mixed cultures of sulfate reducing bacteria (SRB) were isolated from anaerobic cultures and enriched with SRB media. Studies on batch and continuous reactors for the removal of SO(2) with bulk drug industry wastewater as an organic source using isolated mixed cultures of SRB revealed that isolation and enrichment methodology adopted in the present study were apt to suppress the undesirable growth of anaerobic bacteria other than SRB. Studies on anaerobic reactors showed that process was sustainable at COD/S ratio of 2.2 and above with optimum sulfur loading rate (SLR) of 5.46kgS/(m(3)day), organic loading rate (OLR) of 12.63kg COD/(m(3)day) and at hydraulic residence time (HRT) of 8h. Free sulfide (FS) concentration in the range of 300-390mgFS/l was found to be inhibitory to mixed cultures of SRB used in the present studies.