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The performance of a quartz crystal microbalance (QCM) used as a sensor/detector relies on the performance and quality of the film coated onto the quartz crystal sensor. This study focuses on the sensor coating preparation for the detection of glycine. Cellulose nanofibrils (CNFs), natural polymers, were coated on a quartz crystal (QC) surface by a spin-coating method. The prepared CNF-coated QC was characterized by scanning electron microscopy (SEM), atomic force microscopy (AFM), cyclic voltammetry (CV), Fourier transform infrared spectrophotometry-attenuated total reflectance (FTIR-ATR), Raman spectroscopy, and water contact angle (WCA). The stable and fully covered QCs without further modification were then employed for aqueous glycine detection. Detection with a wide concentration range (3–1000 μg/mL) of glycine was studied. The resonance frequency shifts obtained from the samples during each step of the measurement are presented and discussed. The data show a linear range of detection (R2 = 0.9945) for 6–500 μg/mL of glycine and a limit of detection (LOD) of 8 μg/mL. This study indicates that the CNF-coated QCM has a potential application as a biodetector for glycine detection.

Design and fabrication of highly efficient and low-cost oxygen reduction reaction (ORR) electrocatalysts is of paramount importance for practical applications. Herein, we proposed a cost-effective, metal-free catalyst based on ZIF-8 metal-organic framework nanoparticles/electro-polymerized poly(3,4-ethylenedioxythiophene) (PEDOT) film on the surface of flexible carbon cloth (CC) electrode (ZIF-8/PEDOT/CC) via a two-step procedure. For this purpose, worm-like PEDOT nanostructures were deposited on the surface of carbon fibers using a pulse electro-polymerization technique followed by facile growth of ZIF-8 polyhedra nanoparticles via a chemical bath deposition method. The ORR measurements in O2-saturated KOH electrolyte solution using the modified CC electrode demonstrated that the prepared electrode exhibits remarkable electrocatalytic activity towards ORR with 8 times increase in the cathodic current density compared to bare CC (J = 0.13–1.1 mA/cm2) along with lower overpotential due to the synergetic effects between ZIF-8 nanoparticles as particularly porous nanostructure act as electrolyte reservoirs and highly conductive PEDOT film. The Kouteckey-Levich analysis for the ZIF-8/PEDOT-modified CC electrode revealed that the oxygen reduction reaction proceeds via a nearly four-electron pathway along with superior tolerance to methanol crossover as well as enhanced stability in alkaline solution compared to the gold standard commercial Pt catalyst.

Despite their potential applications, a limited number of studies for synthesizing vertical MoS2 nanoflakes especially via CVD have been reported so far, which generally involve tedious complex- and/or multi-step growth processes. In this study, direct synthesis of vertical MoS2 nanoflakes grown on the SiO2/Si substrate during a rapid sulfidation process by CVD method has been reported. Material characterization was performed using Raman spectroscopy, XRD and FE-SEM. The XRD results indicated the dominant phase of 2H–MoS2 within the synthesized layers. The characteristic distance between the two dominant peaks of E12g and A1g in the Raman spectra confirms the multi-layered structure for grown nanoflakes. Based on the experimental results, the growth mechanism has been explained considering nucleation and growth of two-dimensional islands, followed by coalescence of these islands. Subsequently, in the final stage, standing nanoflakes grow vertically. The vertical MoS2 nanoflakes film forms n-channel for back-gated FET gas sensor, of which gas sensing performance towards ethanol and methanol vapors have been studied. These structures with an increased number of edge sites presented high and fast responses to ethanol and methanol at 1 and 10 ppm concentrations and showed significant potential and promising application as a gas sensor transistor.

Polyaniline/graphene oxide (PANI/GO) co-doped with Zn2+ and Fe3+ was synthesized via a simple and low cost one-step chronoamperometry method on stainless steel (SS) as the substrate. The Fe3+-Zn2+-PANI/GO nanocomposite is characterized using X-ray diffraction as well as Fourier transform infrared spectroscopy, energy-dispersive X-ray spectroscopy, transmission electron microscopy, and field emission scanning electron microscopy. Also, cyclic voltammetry, galvanostatic charge-discharge, and electrochemical impedance spectroscopy are used to study the electrochemical performance of the as-prepared electrode materials. Significantly, the Fe3+-Zn2+-PANI/GO nanocomposite exhibits a specific capacitance of 1140 F g−1 at a current density of 10 A g−1, which is far better than PANI (250 F g−1), PANI/GO (610 F g−1), Fe3+-PANI/GO (744 F g−1), and Zn2+-PANI/GO (964 F g−1). After 4000 cycles, the fabricated Fe3+-Zn2+-PANI/GO/SS electrode shows 85% capacitance retention at a current density of 5 A g−1. The resulting good electrochemical performance is owing to the combination of electrical double layer capacitance of GO and pseudocapacitive characteristic of PANI and transition metal ions, which can effectively increase the specific capacitance value and cycling performance of the prepared nanocomposite.

A new ternary nanocomposite based on graphene oxide (GO), polypyrrole (PPy) and vanadium pentoxide (V2O5) is obtained via one-step electrochemical deposition process. Electrochemical deposition of V2O5, PPy and GO on a stainless steel (SS) substrate is conducted from an aqueous solution containing vanadyl acetate, pyrrole and GO to get V2O5/PPy/GO nanocomposite. Characterization of the electrode material is carried out by X-ray diffraction (XRD), Fourier transform infrared spectroscopy (FT-IR), scanning electron microscopy (SEM), energy dispersive X-ray spectroscopy (EDX) and atomic force microscopy (AFM). The electrochemical performance of the as-prepared nanocomposite is evaluated by different electrochemical methods including cyclic voltammetry, galvanostatic charge-discharge and electrochemical impedance spectroscopy (EIS) in 0.5 M Na2SO4 solution. Remarkably, V2O5/PPy/GO nanocomposite shows a specific capacitance of 750 F g−1 at a current density of 5 A g−1, which is far better than PPy (59.5 F g−1), V2O5/PPy (81.5 F g−1) and PPy/GO (344.5 F g−1). Furthermore, V2O5/PPy/GO maintains 83% of its initial value after 3000 cycles, which demonstrates good electrochemical stability of the electrode during repeated cycling. These results demonstrate that the combination of electrical double layer capacitance of GO and pseudocapacitive behavior of the PPy and V2O5 can effectively increase the specific capacitance and cycling stability of the prepared electrode. Also, a symmetric supercapacitor device assembled by V2O5/PPy/GO nanocomposite yielded a maximum energy density of 27.6 W h kg−1 at a power density of 3600 W kg−1, and a maximum power density of 13680 W kg−1 at an energy density of 22.8 W h kg−1.

In the present study, a 3D porous graphene-carbon nanotube (G-CNT) network is successfully constructed on the surface of glassy carbon electrode (GCE) by electrochemical co-deposition from a concentrated graphene dispersion. The large accessible surface area provided by the interpenetrated graphene backbone in one hand and the enhanced electrical conductivity of the 3D network by incorporating CNTs on the other hand, dramatically improved the electrochemical performance of GCE in determination of Methotrexate (MTX) as an important electroactive drug compound. Under the optimum conditions, the electrode modification led to a significant increase in the anodic peak current (∼25 times) along with a considerable shift in the peak potential (∼111 mV). Voltammetric investigations revealed that the proposed method can determine MTX in a wide dynamic linear range with a low detection limit of 70 nM. Moreover, good sensitivity and high accuracy of the prepared modified electrode in voltammetric detections of MTX, which was further confirmed by UV–vis spectroccopy and HPLC methods, make it very suitable for accurate determinations of MTX in pharmaceutical formulations (commercial tablets) and clinical preparations (blood serum) with excellent recoveries.

In the present paper, new H2S gasochromic nanomaterial of mixed silver nickel ammonium phosphomolybdate synthesized by microwave assisted technique is reported. The microwave treatment was performed in the solid phase using urea and ammonium nitrate as the promoter and oxidizer agents. The designed process allows rapid synthesis of large amounts of this product in nanosized particulate morphology. Morphological and structural features of the prepared products were studied in detail. Chemical analyses indicated a stoichiometry of (NH4)0.5Ni0.75AgPMo12O40·4H2O revealing a Keggin-type framework with substitution of silver and nickel cations in its secondary structure. A home-made set-up was used to test gasochromic effect via monitoring light intensity variations passing through the samples based on their color change during exposure to different H2S gas concentrations. Response in coloration was obtained about 12% to 61.8% for concentrations from 8.5 to 100 mg L−1. It is suggested that the presence of Ag and Ni ions (especially silver as counter cations) in the secondary structure of a Keggin ion plays an important role in the coloration effect of the substituted phosphomolybdate compared with the un-substituted one. In fact, color centers can be originated from the interaction of these cations of the phophomolybdate network with thiol functional group of H2S molecules.

The electrical bending instability in charged liquid jets is the phenomenon determining the process of electrospinning. A model of this phenomenon is lacking however, mostly due to the complicated interplay between the viscosity and elasticity of the solution. To investigate the bending instability, we performed electrospinning experiments with a solution of polyethylene oxide in water/ethanol. Using a fast camera and sensitive multimeter, we deduced an experimental dispersion relation describing the helix pitch length as a function of surface charge. To understand this relation, we developed a theoretical model for the instability for a wide range of visco-elastic materials, from conducting to nonconducting. The theoretical dispersion relation shows good agreement with the experimental results. Using the new model, we find that the elastic tension in the visco-elastic threads plays an important role in triggering the instability. © 2016 Wiley Periodicals, Inc. J. Polym. Sci., Part B: Polym. Phys. 2016, 54, 1036–1042

Here in this research, we report on surface engineering of bulk Cu2O photocathode thorough employing nanostructured materials. Nanorods (NRs) of copper oxide with average lengths of 150 nm have been synthesized by anodization of Cu foil in aqueous KOH electrolyte, followed by annealing treatment. Several heating processes were examined to reach pure Cu2O nanostructures and lastly the moderate annealing procedure at 700 °C under Ar gas flow resulted in pure Cu2O nanostructures, confirmed by XRD analysis. Surface modified nanorod/bulk Cu2O electrode was prepared by spin coating of sediments suspension of anodized drop on bulk Cu2O film fabricated through thermal oxidation method, followed by final heating process. Photoelectrochemical analysis indicates that nanorod/bulk Cu2O electrodes have noticeable enhancement in photocurrent, around 76% at −0.6 V and the favorable decrease in interface resistance about 103 Ω in comparison to the bulk Cu2O thermal oxidized electrode. This novel bulk Cu2O electrode with modified nanostructured surface can be a good candidate as the electrode of either photoelectrochemical systems for hydrogen generation or the photocathode of bulk heterojunction photovoltaic cells.

A novel AC impedance study on three-dimensional hybrid structures of graphene sheets/MoS2 nanorose (GMS) toward ethanol vapor detection is presented in this work. These defective 3D hybrid porous structures are sensitive to the presence of different gases as a result of charge transfer with gas species, as well as a change in the effective capacitance of the system. The sensing behavior of the samples is investigated throughout time-dependent impedance measurement and electrochemical impedance spectroscopy (EIS). The sensor response is estimated at about 20% to 10 ppm ethanol vapor, with the response and recovery times about 3.2 s and 0.8 s, respectively. Sensing mechanism proposed to describe the EIS impedance spectra involves three different procedures: charge transfer, double layer formation and diffusion process. Moreover, these processes are probed using equivalent circuits modeled by the impedance spectra curves.

Aggregated sub-micron size nitrogen doped TiO 2 (N-TiO 2 ) particles with superior optical and electrical features were successfully synthesized for embedding into commercial mesoporous TiO 2 photoelectrode of dye sensitized solar cells (DSSCs) as the light scattering particles compared to undoped one. X-ray photoelectron spectroscopy and absorption spectra confirmed that the titanium dioxide is sufficiently doped by nitrogen in N-TiO 2 sample. Employing these high-surface N-TiO 2 in mesoporous photoelectrode of solar cells, the power conversion efficiency of 8% has been achieved which shows 17% improvement for the optimum embedded level of doping (30 wt%) compared to commercial photoelectrode without additive; while enhanced efficiency is only 3% embedding undoped sub-micron size TiO 2 particles. These results can introduce the novel multifunctional photoelectrode for nanostructured solar cells with enhanced values of scattering efficiency and improved electrical features including trap states density reduction in comparison to commercial mesoporous photoelectrodes.

A green mechanochemical technique has been developed for the synthesis of mixed ammonium silver phosphomolybdate salt, (NH 4 ) 1.6 Ag 1.4 PMo 12 O 40 .4H 2 O with sheet-like nanostructure. The reaction was prompted using acetamide/NH 4 NO 3 at room temperature. The change of driving agent to urea at the same conditions led to an epitaxial growth of hierarchical microstructure of this polyoxoanion. The morphological and structural features of the prepared specimens were discussed in detail. The photocatalytic performance of the resulting nanosheets for removing 4-nitrophenol (4-NP) in water under visible light irradiation was also studied. It was found that the substitution of positively charged units by Ag + ions and production of reduced ion improves the photocatalytic activity of prepared product compared with entire one. The obtained results allow introducing this product as a usable choice with a high degree of removal efficiency in catalytic and photocatalytic treatments.

CuInS2 nanoparticles as the visible (wurtzite, 1.67 eV) or near infrared (chalcopyrite, 1.50 eV) light absorbing material in thin film solar cells, were synthesized using facile, one step heating up method by dissolving of CuCl, InCl3 and SC(NH2)2 as precursors in oleylamine (OLA) alone or in combination with oleic acid (OA) and 1-octadecene (ODE) as solvent. The phase, size, morphology, and size distribution were controlled by the coordination ability between solvent molecules and metal precursors, reaction temperature and time. The presence of higher amounts of thiourea or OA to OLA led to the formation of chalcopyrite phase in comparison to wurtzite structure. Also, higher reaction temperatures (>240 °C) resulted in favour of more chalcopyrite phase and higher crystallinity but the nanoparticles got agglomerated. As synthesized nanoparticles was characterized by transmission electron microscopy, X-ray diffraction, X-ray photoelectron spectroscopy, high resolution-transmission electronic microscopy, ultraviolet–visible-near infrared, photoluminescence. The high resolution TEM confirmed the existence of chalcopyrite structure along with wurtzite structure in the nanocrystal (polytypism). Well controlled chalcopyrite CuInS2 triangular pyramidal shape with an average size ranging from ~10–20 nm size was obtained by using 20 ml OLA or 20 ml OLA along with 4 ml OA and ODE, respectively, with 210 °C heating up and 4 h annealing time.

Rather vertically aligned ZnO rods with flower-like structures were grown on quartz substrates through vapor phase transport method. X-ray diffraction (XRD) analysis and photoluminescence (PL) measurement were performed to determine crystalline structure and defects, respectively. H 2 S gas sensing properties of the grown structure were investigated at both room temperature and 250 °C for comparison. A remarkable increase in response and selectivity at room temperature compared to 250 °C was observed. High response and selectivity to low concentrations of H 2 S at room temperature as well as good stability make the sensor a promising candidate for practical applications.

This paper describes the photoluminescence study of titanium dioxide (TiO2) nanorods grown by a hydrothermal synthesis method on the surface of fluorine doped tin oxide (FTO) coated glass. The effects of growth conditions including: reaction time, precursor concentration and adding NaCl to hydrothermal solution on the structural and optical properties of productions are examined by using SEM, XRD, TEM and room temperature photoluminescence measurements. Also, the performance of the TiO2 nanorods as a photoanode of dye sensitized solar cells is investigated. The different excitation energies and intensities are chosen to verify the discrete electronic state of radiative recombination centers in nanorods. The photoluminescence studies show the profound effect of the excitation light energy and intensity on the emission spectra. The nanorods have extended emission spectra from UV to visible region. The near band edge emission is observed at 3.04±0.01 eV. Also, the spectra consist of high emission peaks around at 3.44 and 3.14 eV and other emissions at 2.90±0.01, 2.83±0.02, 2.70±0.01, 2.56, 2.36±0.03, 2.30±0.02, 2.03, and 1.66 eV. The photoluminescence study of TiO2 nanorods and photoconversion efficiency of dye sensitized solar cells indicate a correlation among some PL emission peaks, the aspect ratio and efficiency of photoanode based solar cells.

Understanding the dynamics of direct electrospinning is the key to control fiber morphologies that are critical for the development of new electrospinning methods and novel materials. Here, we propose the theory for direct electrospinning based on theories for (liquid) "rope coiling" and experimentally test it. For the experiments, the buckling of microscale liquid ropes formed from polymer solutions is studied systematically using three different electrospinning setups and for different polymer concentrations. We show that different buckling regimes exist, whose dynamics are governed by an interplay of electrical, inertial, and viscous forces, and that three different buckling regimes emerge depending on the dominant forces. For low polymer concentrations, we observe an inertial regime similar to that observed for viscous liquid ropes at high velocities. By increasing the polymer concentration and consequently decreasing the rope velocity, we enter an inertial-electrical regime for which discontinuities occur in the buckling frequency as a function of applied voltage. These observations can be accounted for quantitatively by replacing the gravitational forces in viscous rope coiling theory with the electrical forces of our electrospinning experiment. Finally, for the highest polymer concentration, we observe a purely electrical regime for a solidified rope; this regime is well described by "elastic" rope coiling theory.

The high capacitance and cyclic stability of graphene nanosheets decorated with Co3O4 nanoparticles as a material for supercapacitor electrodes are reported here. Hydrothermal method is adopted to deposit cobalt oxides on the reduced graphene oxide (RGO) sheets in a mixture of water and dimethylformamide (DMF) as the solvent with different volume ratios. The water volume ratio presents a crucial factor in the nucleation and growth process. In addition, it affects dispersion, particle size and the amount of nucleated cobalt oxide particle on the graphene sheets. By decreasing the water volume, the nucleation and growth occur mainly on graphene rather than in solution. According to the obtained results from transmission electron microscopy, scanning electron microscopy and thermogravimetric analysis, a model for growth of nanoparticles on graphene sheets is proposed. Based on the obtained results, the presented model can also be used for the synthesis of other graphene-metal (oxide) composites. Electrochemical measurements indicate that water volume ratio in the mixture solvent influences on capacitance of the RGO/Co3O4 composite electrodes. The highest obtained specific capacitance is 440.4 F g−1 with 50% volume ratio of water at current density of 5 A g−1.

In this study, we present fabrication and characterization of a gas ionization sensor based on high aspect ratio one-dimensional CuO nanowires as the field enhancing medium. Self-organized arrays of CuO nanowires have been synthesized based on a low-cost thermal oxidation method and integrated into a gas ionization sensor (GIS). The self-organized arrays of CuO nanowires have been employed to detect the identity of several gas species such as He, Ar and CO at ambient temperature and pressure. The sharp nanoscale size of CuO tips provide very high electric fields at moderate voltages (less than 100 V) and provoke the breakdown of different gases. The reduced breakdown current of the metal oxide CuO nanowire electrodes result in reduced structural deformation. The proposed GIS based on CuO nano-tips exhibits good repeatability and selectivity for various types of gases and their mixtures.

Here, a solvothermal method for synthesis of porous Ni–Co binary oxide (NiCo2O4) nanorods followed by thermal decomposition is described. The prepared nanorods were characterized by X-ray diffraction (XRD), scanning electron microscopy (SEM), and Brunauer Emmett Teller (BET) methods. These porous NiCo2O4 nanostructures were promising candidates in the development of high capacity supercapacitors and having excellent cycling performance due to high specific surface area. In addition, the influence of annealing rate on the structure and electrochemical behavior of the synthesized nanorods was investigated. The results showed that the annealing rate had a direct effect on the crystalline properties and porosity of the nanorods and influenced on their electrochemical behaviors. The nanorods prepared by the annealing rate of about 1 °C min−1 indicated a rather high capacitance of 600 F g−1; moreover, a high retention capacitance of 80 % was achieved even after 1,500 cycles at 5 A g−1.

Uniform layers of ZnO nanostructures were formed on quartz and alumina substrates through a simple vapor phase transport (VPT) method without any catalyst or buffer layer by making proper growth conditions. The effect of substrate on morphology, crystalline structure and photoluminescence spectra has been investigated. Scanning electron microscopy images revealed that morphlogical grwoth depends on used substrate, aligned rods with flower-like bundels and entangled rods are vertically aligned rods on the quartz and alumina substrates, respectively. X-ray diffraction studies showed that grown films on the quartz substrates possess stronger c -axis orientation compared to those on the alumina ones. Consequently, growth mechanism is discussed and illustrated schematically. Acetone sensing measurements indicated that the oriented rods on the quartz substrates have better sensing properties than entangled ones on the alumina substrates.

The present paper demonstrates the capability of narrow graphene nanoribbons (GNRs) in constructing new sensing platforms. Graphene nanoribbons have been synthesized via a simple solvothermal route through unzipping of carbon nanotubes, which was confirmed by scanning electron microscopy (SEM), transmission electron microscopy (TEM), X-ray diffraction (XRD) and Raman spectroscopy analysis. These narrow carbon sheets were used to form a composite film by in-situ electro-polymerization with aniline. The produced graphene nanoribbon/polyaniline (GNR/PANI) composite film showed impressive performance in electrochemical determination of dobutamine (DBT). Under optimal conditions, in comparison to bare glassy carbon electrode a significant increase in peak current was observed on the surface of GNR/PANI modified glassy carbon electrode (up to 10 times), which is ascribed to the higher specific surface area induced by GNRs in combination with the electrocatalytic effect of polyaniline layer. We believe that such a composite film has a great potential in different applications including sensors, supercapacitors and etc.

Well-crystallized TiO 2 and neodymium (Nd)-doped TiO 2 nanoparticles with various doping levels were synthesized by hydrothermal method and utilized as the photoanode of nanostructured solar cells. The results indicated that Nd-doping was caused the absorption spectra shift to higher wavelength while the morphology and surface area were unchanged. As a result, by employing 0.4 mol% Nd in the TiO 2 photoelectrode, the overall conversion efficiency of the cell reached 9.08% which is 26% higher than pure one. Based on the photo-electrochemical characterizations, the improvement is a consequence of electrons injection increment from dye to TiO 2 conduction band, charge collection efficiency enhancement, and trap states density reduction in the Nd-doped photoanode.

In this study, tungsten oxide films were deposited by pulsed-laser deposition (PLD) technique. The as-deposited films were annealed at 250 °C in air for 1 h. The surface morphology, microstructure, crystalline phase, and chemical composition of the films were characterized by SEM, XRD and XPS techniques. Pt nanoparticles were deposited onto the tungsten oxide films through a two-step process. First of all, a layer of PtCl 2 was coated on the WO 3 surface by drop-drying the PtCl 2 solution onto the WO 3 surface at 60 °C. Consequently, the reduction of the PtCl 2 into the metallic Pt nanoparticles was performed at 200 °C. In this study, the effect of the temperature during hydrogen reduction of PtCl 2 as well as the influence of operating temperature on the gasochromic performance of Pt–WO 3 samples were investigated. Results revealed that the gasochromic responses of the Pt–WO 3 samples have attained approximately a constant value at temperatures above 90 °C. On the other hand, their responses are insignificant at temperatures below 90 °C. Additionally, for the sake of comparison, some results of the gasochromic performance of Pd-WO 3 films were presented.

The cauliflower like ZnO nanostructures are grown on ZnO nanorods using spray pyrolysis method. First, ZnO nanorod arrays are grown on p-type silicon substrate without catalyst by chemical vapor transport and condensation method in a horizontal tube furnace. Afterwards, the cauliflower like ZnO nanostructures is deposited on top of the ZnO nanorod array. The PL spectra of cauliflower like ZnO nanostructures consist of UV emission bands around 387 nm and a visible emission at ∼440 nm. The current–voltage ( I – V ) measurement under dark and UV illumination condition are performed to study photodetection of the cauliflower like ZnO–ZnO nanorod/p-Si heterostructure. The experimental data of dark I – V curve show that the tunneling-recombination model is the dominant current transport mechanism in our device heterostructure below 2 V. It is observed that UV photons are absorbed in ZnO and device exhibit 0.07 A/W responsivity at 5 V reverse bias which correspond to quantum efficiency of 26%.

A uniformly distributed ZnO nanowire array has been grown on silicon (100) substrates by catalyst-free chemical vapor transport and condensation. The effect of growth conditions including source heating temperature, substrate temperature, and gas flow rate on growth properties of ZnO nanowire arrays are studied. Scanning electron microscopy, X-ray diffraction, and room temperature photoluminescence are employed to study the structural features and optical properties of the samples. The results show a correlation among experimental growth parameters. There is a zone for substrate temperature, by controlling gas flow rate, that uniformly distributed and well aligned ZnO nanowire arrays can be grown. Also, experiments indicate that ZnO nanowire arrays with different diameter along their length have been formed under various growth conditions in the same distance from source material. It is found that supersaturation is a crucial parameter determining the growth behavior of ZnO nanowire arrays. The growth mechanism of ZnO nanowires is discussed. The room temperature photoluminescence spectrums of ZnO nanowire array show two emission bands. One is the exciton emission band (centered at 380 nm) and the other is a broad visible emission band centered at around 490 nm. As the substrate temperature decreases, the intensity of UV emission increases while the intensity of visible emission peak decreases.

In this study, tungsten oxide films were synthesized by pulsed laser deposition (PLD) method. The as-deposited films were annealed at a temperature of 250 and 350 °C in air for 1 h. The surface morphology, microstructure, crystalline phase and chemical composition of the as-prepared and annealed films were characterized by SEM, XRD and XPS techniques, respectively. Deposition of Pd nanoparticles onto the tungsten oxide surface was performed by hydrogen reduction of a drop-drying PdCl 2 solution onto a WO 3 surface at 60 °C. The influence of the annealing temperature on microstructure and gasochromic performance as well as the effect of operating temperature is presented in this work. Results show that the gasochromic responses of the amorphous samples at temperatures below 100 °C has attained approximately a constant value but these values for polycrystalline samples shows a significant increase with increasing temperature and the maximum gasochromic response was achieved at operating temperatures between 90 and 100 °C. Because of the low surface to volume ratio and negligible diffusion length, the polycrystalline film shows intense decrease in ΔOD m values compared to the amorphous film at operating temperatures above 100 °C. Also the effect of water desorption at T ∼ 100 °C on gasochromic response was investigated.

Here, the UV photodetection of ZnO rods grown on porous silicon substrates are reported. Laterally interconnected ZnO rods have been synthesized by chemical vapor transport and condensation method on porous silicon substrates. As characterized by current–voltage measurements the I–V characteristics have linear behavior, indicating space charge effect. The device exhibits photocurrent response of 0.027 A/W for 325 nm UV light under −5 V bias. The rise and decay time constants under these conditions are 19 and 62 s, respectively.

A density functional theory (DFT) study of graphene synthesis from graphite oxidation and exfoliation is presented. The calculated DFT results for O adsorption predict C O as a most stable bond on the graphene oxide (GO) sheet. The obtained exfoliation energy for the graphene and the GO are 143 and ∼70 mJ/m 2 that verify easier exfoliation of the graphite oxide compared with the graphite. Furthermore, the DFT results show that for decreasing the exfoliation energy of the GO at least two layers of the graphite should be oxidized during the oxidation process.

We fabricated gas sensors based on field ionization from multiwalled carbon nanotube (MWCNT) arrays grown on porous silicon templates. MWCNTs were grown through thermal chemical vapor deposition. We measured breakdown voltages, discharge and pre-discharge currents of the device for various gases in different concentrations. Our gas ionization sensors (GIS) presented good sensitivity, selectivity and short response time. The GISs based on porous substrates showed higher discharge current and good mechanical stability in comparison to those which were fabricated on polished silicon substrates. Additionally, we applied a high electric field to align CNTs. This increased the pre-breakdown current. Also, introducing humidity in dry air caused enhancement in pre-breakdown current and lowered breakdown voltage. We also used our GIS in monitoring gas mixtures.

We report a simple and inexpensive synthesis route of TiO2 nanoparticles using electrical arc discharge between titanium electrodes in oxygen bubbled deionized (DI) water followed by heat treatment. The resulting nanoparticles were characterized using X-ray diffraction (XRD), X-ray photoelectron spectroscopy (XPS), dynamic light scattering (DLS), scanning electron microscopy (SEM) and transmission electron microscopy (TEM). XRD patterns demonstrate formation of TiO2 phase in oxygen bubbled water after heat treatment and dominance of rutile to anatase phase. The size and morphology of TiO2 nanoparticles were studied using different arc currents as a crucial parameter in properties of final product. Microscopic studies reveal nanosize spherical particles. DLS results indicate that at 20 A arc current, the size of the particles is about 37 nm and increases to 59 nm by increasing the arc current up to 40 A. Photodegradation of Rhodamine B (Rh. B) as a standard pollution shows that heat treated samples in oxygen bubbled water for 2 h at 500 °C, have more photocatalytic activity due to enhancement in crystallinity.

Multi-Walled Carbon nanotube (MWCNTs) films were obtained by Thermal Chemical Vapor Deposition method and coated by palladium sputtering process. Raman spectroscopy was used to study alteration in quality of the carbon nanotubes after the sputtering process. Fourier Transform Infra Red (FTIR) spectroscopy showed that hydrogenation process can reduce the C O to C–O and also produce O–H bond. Furthermore, the electrical resistance measurement for Pd/MWNTs films was performed in a chamber with 1% hydrogen gas in a constant dry air flow. Hydrogen sensing behavior of the films was investigated at 50 °C. Pd/MWCNTs films presented an irreversible gas response to hydrogen in the first cycle of gas exposure due to chemically adsorption of the gas. Finally, the effect of hydrogen-sample reaction on electrical conduction was presented.

We prepared porous silicon samples coated by continuous palladium layer in electroless process. Scanning electron microscopy (SEM) showed cauliflower-shape Pd clusters on the surface. I–V curves of Schottky like Pd/porous Si samples were measured in air and in hydrogen. These measurements showed a metal–interface–semiconductor configuration rather than an ideal Schottky diode. Variations of the electrical current in the presence of diluted hydrogen at room temperature revealed that the samples can sense hydrogen in a wide range of concentration (100–40,000 ppm) without any saturation behavior. Hydrogen sensing properties of these samples were investigated at room temperature for a duration of nine months. Sample sensitivity (response time) decreased (increased) to a saturated value after 45 days. We discussed sensing and Schottky contact properties of the fresh and aged Pd/porous Si samples by variation of structure and chemical composition using SEM, X-ray diffraction (XRD) and X-ray photoelectron spectroscopy (XPS) data.

The sol gel method was employed to prepare peroxopolytungstic acid (P-PTA). Palladium chloride salt was dissolved in the sol with different Pd:W molar ratios and coated on Al2O3 substrates by spin coating method. XRD and XPS techniques were used to analyze the crystal structure and chemical composition of the films before and after heat treatment at 500 °C. We observed that Pd can modify the growth kinetic of tungsten trioxide nanoparticles by reducing the crystallite size and as a result can improve hydrogen sensitivity. Resistance-sensing measurements indicated sensitivity of about 2.5 × 104 at room temperature in hydrogen concentration of 0.1% in air. Considering all sensing parameters, an optimum working temperature of 100 °C was obtained.

We report experimental evidence of Cu surface segregation in Ni/Cu system, during deposition of Ni film onto Cu substrate at room temperature and during heat treatment in vacuum. Auger electron spectroscopy (AES) and X-ray photoelectron spectroscopy (XPS) by Tougaard's analysis results show that surface segregation defeats in competition with increase in Ni thickness and terminates when thickness of Ni increase to more than 4 nm. Surface energy and concentration were calculated using contact angle measurements and the results confirm that segregation reduces the surface energy. Surface segregation during heat treatment at 150–220 °C range as a function of time initially shows linear mass transfer. By solving Fick's equation and taking empirical diffusion coefficient, 125 ± 20 kJ/mol is obtained for activation enthalpy of effective diffusion.

We report a novel method of growing red luminescent (635 nm) Mn-doped CdS (CdS:Mn) nanoparticles capped by an inorganic shell of Mn(OH) 2 . CdSO 4 , Na 2 S 2 O 3 and Mn(NO 3 ) 2 were used as the precursors, and thioglycerol (C 3 H 8 O 2 S) was employed as the capping agent and also the catalyst of the reaction. Using these materials resulted in very slow rate of the reaction and particles growth. The self-assembled one-pot process was performed at pH of 8 and Mn:Cd ratio of 10, and took about 10 days for completion. CdS:Mn nanoparticles are slowly formed in the first day of the process; however, the luminescence is weak. After 7 days, the solution turns white turbid through the formation of additional particles, which precipitate on the walls on the next day. At this stage, a relatively strong red luminescence at 635 nm appears from transparent solution of the CdS:Mn nanoparticles. The white deposit on the walls turns to dark-brown color and luminescence increases on the 9th day. Finally, the CdS:Mn nanoparticles agglomerate and precipitate out of the solution on 10th day. X-ray diffraction and optical spectroscopy showed crystalline phase CdS nanoparticles with an average size of 3.6 nm. We explain the luminescence enhancement based on the formation of a Mn(OH) 2 shell on the surface of the CdS:Mn nanoparticles during the precipitation stage. This can passivate the S dangling bonds located on the particles surface. As the surface Cd sites are previously capped with thioglycerol molecules, a complete surface passivation is achieved and results in emergence of high-intensity luminescence.

The effects of Pd addition to Fe (Pd/Fe = 0, 2.5/7.5, 5/5, 7.5/2.5 and 1) and growth temperatures (920 and 970 °C) on density, diameter and growth mode of carbon nanotubes (CNTs) have been studied. SEM observations and TG analyses confirmed that the CNT yields depend on Pd/Fe ratios as (7.5/2.5) > (5/5) > Pd > (2.5/7.5) > Fe at both growth temperatures. TEM data showed that addition of Pd results in tip growth mode. From Raman spectroscopy data, the order of samples’ structural quality ( I G / I D ratio) are Fe > Pd/Fe (2.5/7.5) > (5/5) > (7.5/2.5) > Pd and the I G / I D ratios increase by decreasing the growth temperature. Films with higher concentration of Fe (Pd/Fe = 0, 2.5/7.5) contain some single-walled carbon nanotubes.

Porous silicon samples were obtained from p+- and n-type silicon wafers. Gas sensing measurements showed that the electrical conductivity of porous Si on p+- and n-type wafers increases strongly and decreases weakly in the presence of methanol gas, respectively. Scanning tunneling spectroscopy (STS) indicates that the adsorption of methanol on the surface of n-porous silicon decreases the average density of states especially in the band gap. Fourier transform infrared (FTIR) spectroscopy reveals that after methanol exposure partial surface oxidation occurs which produces electron traps as well as methanol adsorption on the porous surfaces. These observations imply that the number of free-carriers in p+-type (n-type) porous silicon increases (decreases) in methanol environment. These results explain the change in electrical conductivity of porous Si in the presence of methanol.

Porous silicon samples were obtained by the electrochemical method and were impregnated with Pd by the electroless process. X-ray photoelectron spectroscopy illustrated that the surface of the samples is oxidized during the palladium deposition. Scanning electron microscopy showed how factors such as morphology and pre-oxidations of porous samples and the plating parameters including Pd-salt concentration, HCl concentration, temperature of the electroless solution and the time of process affect the growth and nucleation of Pd particles. Observations demonstrated that the illumination-assisted process on p-type samples has a drastic effect on the growth of palladium. Hydrogen sensing of these samples, which works on the basis of change in the Schottky barrier between the silicon and the palladium interface, was tested. Variations of the electrical resistance in the presence of diluted hydrogen at room temperature revealed that the best samples can sense hydrogen at levels down to several thousand ppm. This value is far below the flammability limit of hydrogen gas. In addition, the best samples have a very good selectivity to hydrogen.

The effect of etching time scale of glass surface on its statistical properties has been studied using atomic force microscopy technique. We have characterized the complexity of the height fluctuation of a etched surface by the stochastic parameters such as intermittency exponents, roughness, roughness exponents, drift and diffusion coefficients and find their variations in terms of the etching time., Comment: 5 pages, 6 figures

Commercially available track-etched polyester membranes were used as templates to electrodeposit Co–Ni–Cu/Cu multilayered nanowires, giving room-temperature current perpendicular to plane (CPP) giant magnetoresistance (GMR) values of up to ∼12%. In contrast to similar nanowires electrodeposited in track-etched polycarbonate membranes, the GMR obtained in multilayered nanowires electrodeposited in the polyester membranes increased with decreasing Cu-layer thickness t Cu , for t Cu in the 2–7 nm range, indicating a lack of ferromagnetic coupling through pinholes, etc. Transmission electron micrographs showed clear evidence for smooth, parallel layer interfaces in the nanowires.

We have investigated segregation of copper at the surface of V 2 O 5 films deposited onto Cu substrate by employing surface analysis techniques. X-ray photoelectron spectroscopy (XPS) and Auger electron spectroscopy (AES) confirmed that the Cu is segregated at the surface and its chemical state is Cu 2 O. According to secondary ion mass spectroscopy (SIMS) and glow discharge spectroscopy (GDS), the Cu concentration inside the deposited V 2 O 5 layer is low. Ultraviolet photoelectron spectroscopy (UPS) and scanning tunneling spectroscopy (STS) revealed the segregation alters the surface local density of states. Surface analysis of deposited samples in ultra high vacuum (UHV) condition verified that the segregation occurs during the deposition. We have extended kinetic tight binding Ising model (KTBIM) to explain the surface segregation during the deposition. Simulation data approve the possibility of surface segregation during room temperature deposition. These results point out that on pure Cu substrate, oxidation occurs during the segregation and low surface energy of Cu 2 O is the original cause of the segregation.

In this research, we used the scanning tunneling spectroscopy (STS) technique to probe the local electrical properties of the surface of meso-porous silicon and its substrate, including local density of states (DOS) in air and in methanol environment to increase our knowledge of sensing phenomena. Meso-porous silicon was prepared on p + -type Si which has high sensitivity toward methanol. Observations revealed that while the surface electrical properties of p + -type Si have not sensible change toward methanol, average local density of state of the porous layer increases after the exposure to methanol especially in the E E F region. Moreover, large number of surface states is produced in band gap which implies that the number of free-carriers in porous silicon increases in methanol environment. This phenomenon explains the change in electrical resistivity of meso-porous Si in the presence of methanol which is the base of organic gas sensitivity of this structure.

The effects of liquid environment on nucleation, growth and aggregation of gold nanoparticles were studied. Gold nanoparticles were prepared by pulsed laser ablation in deionised water with various concentrations of ethanol and also in pure ethanol. UV/visible extinction and TEM observations were employed for characterization of optical properties and particle sizes respectively. Preparation in water results in smaller size, shorter wavelength of maximum extinction and stable solution with an average size of 6 nm. Nanoparticles in solution with low concentration ethanol up to 20 vol% are very similar to those prepared in water. In the mixture of deionised water and 40 up to 80 vol% ethanol, wavelength of maximum extinction shows a red shift and mean size of nanoparticles was increased to 8.2 nm. Meanwhile, in this case, nanoparticles cross-linked each other and formed string type structures. In ethanol, TEM experiments show a mean size of 18 nm and strong aggregation of nanoparticles. The data were discussed qualitatively by considering effects of polarity of surrounding molecules on growth mechanism and aggregation. This study provided a technique to control size, cross-linking and aggregation of gold nanoparticles via changing the nature of liquid carrier medium.

Porous silicon samples obtained from p+-type silicon wafers were impregnated with Pd by electroless process in different conditions. Scanning electron microscopy was used to study the change in the features of the surface after palladium plating. Results showed how the factors like Pd-salt concentration, HCl concentration, temperature of the electroless solution and the time of process affect on the growth and nucleation of Pd particles. Observations demonstrated that illumination-assisted process and pre-oxidation of the surface before process have drastic effect on the growth of palladium. Variation of the electrical resistance in the presence of diluted hydrogen at room temperature revealed that response of samples depends rather strongly on the palladium configuration on the surface.

We report on magnetoresistance measurements in thin nickel films modulated by a periodic magnetic field emanating from micromagnetic arrays fabricated at the film surface. By increasing the strength of the magnetic potential using nickel and dysprosium micromagnets, we are able to quench the anisotropic magnetoresistance (AMR) in the film.

In the present study, the surface chemical and depth profile composition of the electrodeposited Ni–Fe base alloy layers on the Cu substrates were investigated with compositions of the Ni 80 –Fe 20 (binary) and Ni 77 –Fe 20.7 –Cr 1.7 –Mo 0.6 (quaternary) deposits. Auger electron spectroscopy (AES) and X-ray photoelectron spectroscopy (XPS) results showed the surface accumulation of copper on the surface layers of binary alloy films in the form of Cu 2 O. In the quaternary films, addition of Cr and Mo reduced the amount of the Cu accumulation at the surface, while Cu accumulation was enhanced under air-exposed condition for both alloy films. Depth profiles using the secondary ion mass spectroscopy (SIMS) revealed that in the binary layers, the amount of oxide phases of the Ni–Fe was greater than that quaternary deposit. It is concluded that addition of the Cr and Mo impurities reduced the amount of the copper at the surface layers and oxygen inside the quaternary films.

The roughness of glass surfaces after different stages of etching is investigated by reflection measurements with a spectrophotometer, light scattering, and atomic-force microscopy (in small scale), and Talysurf (in large scale). The results suggest, there are three regimes during etching, according to their optical reflectivity and roughness. The first and second regimes are studied by the Kirchhoff theory and the third one is studied by the geometric theory. Also, we compare the roughness obtained by the optical scattering to the AFM results.

Porous poly-silicon (PPS) samples, obtained by electrochemical anodization of p-type poly-silicon wafers, were doped with Pd by the electroless process. Rutherford backscattering spectroscopy shows that Pd has diffused a few micrometres into the PPS layer. Scanning electron microscopy and energy dispersive x-ray analysis results demonstrate the presence of Pd as dispersed clusters on the surface. The variation of the electrical resistance in the presence of dry air diluted with hydrogen at room temperature shows that Pd/PPS samples have the ability to sense hydrogen at levels down to several thousands of ppm. This value is far below the flammability limit of hydrogen gas. It was found that the increase in the time of anodization causes an increase in the penetration depth of Pd and, consequently, an increase in the sensitivity to hydrogen. By raising the device temperature to 60°C, the sensor response falls.