Sharif Digital Repository

Tungsten trioxide has been prepared by using P-PTA as a precursor on alumina substrates by spin coating method. Palladium introduced on WO 3 film via electrolysis deposition by using palladium chloride as catalytic precursor. The catalytic precursor was introduced on the series of films with different morphologies. X-ray diffractometry (XRD), Scanning electron microscopy (SEM) and XPS were applied to analyze structure and morphology of the fabricated thin films. Then we measured variation of samples' electrical conductivity of pure and Pd added films in air and diluted hydrogen. Addition of Pd resulted in a remarkable improvement of the hydrogen sensing properties of WO 3 by detection of... 

A novel approach for particles size separation based on dielectrophoresis (DEP) method is introduced and analyzed both computationally and experimentally. The proposed technique has been utilized for the separation of polystyrene (PS) particles with 8, 6 and 2 μm diameters passing through microchannels with planar electrodes. The performance of the technique has been computationally analyzed using the finite element method (FEM). Considering the structure of the planar electrodes, we propose an approach based on applying an electric potential between one of the global electrodes, and a needle touched the top of the cell suspension. Results of both simulation and experiment show that by... 

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,... 

In the present work we report an approach to resistive hydrogen sensing based on graphene quantum dots(GQDs)/WO3 thin films that work reproducibly at low temperatures. GQDs were chemically synthesized and evenly dispersed in WO3 solution with 1:1 molar ratio. The structural evaluation and crystallization of the prepared films was studied by X-ray diffraction, Raman and scanning electron microscopy (SEM) techniques. The SEM images showed uniform distribution of the GQDs in WO3 films with sizes around 50 nm. Raman experiment showed the GQDs are partially reduced with high edge defects as hydroxyl and carboxyl groups which involve both in bridging between WO3 grains via bindings as well as... 

Pursuing a sensing structure with a large effective surface area, partial ordered arrays of ZnO nanorods with flower-like structures are introduced for gas sensing applications. Room temperature H2S response of the grown structure shows significant enhancement after modification with Au nanoparticles. High response (about 1270 at 6 ppm H2S gas) and selectivity were achieved by depositing an Au layer with nominal thickness ∼6 nm. X-ray photoelectron spectroscopy (XPS) was utilized to describe the H2S sensing mechanism  

This paper reports on hydrogen sensing based graphene oxide hybrid with Co-based metal organic frameworks (Co-MOFs@GO) prepared by the hydrothermal process. The texture and morphology of the hybrid were characterized by powder x-ray diffraction, scanning electron microscopy and Brunauer-Emmett-Teller analysis. Porous flower like structures assembled from Co-MOFs and GO flakes with sufficient specific surface area are obtained, which are ideal for gas molecules diffusion and interactions. Sensing performance of Co-MOFs@GO were tested and also improved by sputtering platinum (Pt) as a catalyst. The Pt-sputtered Co-MOFs@GO show outstanding hydrogen resistive-sensing with response and recovery... 

A triboelectric nanogenerator (TENG) electrode sensitive to the adsorption of water molecules has been introduced to create a self-powered humidity sensor. Graphene oxide (GO) nanosheets and graphene oxide nanoribbon (GONR) possessing oxygenated functional groups, as well as high dielectric constants, have been proposed as appropriate candidates for this purpose. GO papers have been fabricated in three forms, i.e. pure GO paper, uniform composites of GONR and GO, and double-layer structures of GONR on top of GO. Results showed that all of the prepared paper-based TENGs revealed excellent performances by maximum output voltage above 300 V. As active humidity sensors, the maximum voltage... 

A new triple-component sensor for detection of H2 was developed based on porous silicon and CNTs. An increase in deposition of CVD catalysis was shown to promote a high and fast response. Also, it was shown that the composite system exhibited good selectivity  

We present fabrication, characterization, and experimental results describing electrical actuation and readout of the mechanical vibratory response of electrospun ZnO nanofibers. For a fiber with an approximate radius of 200 nm and a length of 70 ìm, a resonance frequency around 3.62 MHz with a quality factor (Q) of about 235 in air at ambient conditions is observed. It is shown that the measured frequency of the resonance is consistent with results from finite element simulations. Also, the measurements were performed in an enclosed chamber with controlled levels of ethanol vapor. The adsorption of ethanol causes a shift in the resonance frequency of the fibers, which can be related to the... 

Titanium trisulfide (TiS3), a transition metal chalcogenide, bears the potential to replace silicon, when taking the form of nanoflakes, due to its favorable band gap and optical response. In this paper, we investigate the response of TiS3 nanoflakes to gas detection through a careful quantum computational approach and a few succinct measurements. The computations are benchmarked and compared with a relevant experiment at each step, where their results/conclusions are discussed. The most stable surface of TiS3 particles is determined as (001), in agreement with the literature. The adsorption of 5 gas molecules is characterized through formulating and estimating their adsorption intensity... 

Triboelectric nanogenerators (TENGs) offer an emerging market of self-sufficient power sources, converting the mechanical energy of the environment to electricity. Recently reported high power densities for the TENGs provide new applications opportunities, such as self-powered sensors. Here in this research, a flexible graphene oxide (GO) paper was fabricated through a straightforward method and utilized as the electrode of TENGs. Outstanding power density as high as 1.3 W.m−2, an open-circuit voltage up to 870 V, and a current density of 1.4 µA.cm−2 has been extracted in vertical contact-separation mode. The all-flexible TENG has been employed as a self-powered humidity sensor to...