Massood Z. Atashbar

Titanium dioxide thin films prepared for alcohol microsensor applications

Abstract Nanosized TiO2 thin films with different doping concentrations on alumina substrates were prepared using a sol–gel process for alcohol sensing. Experimental results indicated that the sensor is able to monitor alcohols selectively at ppm levels. The samples are insensitive (S

Room-temperature hydrogen sensor based on palladium nanowires

Palladium (Pd) nanowires, synthesized by template-nanomanufacturing techniques, has been studied for hydrogen gas-sensing applications at room temperature. In this study, parallel arrays of Pd nanowires were fabricated by electrodeposition from an aqueous plating solution onto the surface of highly oriented pyrolytic graphite (HOPG). The nanowires were then transferred onto a polystyrene film and silver electrical contact pads were fabricated by shadow masking. The morphology of the nanowires was analyzed using atomic force microscope (AFM) in noncontact mode and the diameter of the observed nanowires was measured to be approximately 250 nm. Scanning electron microscope (SEM) images revealed that the nanowires fabricated by this procedure were parallel and continuous. Electrodes were patterned by shadow masking and the I-V characteristics of the nanowires were studied. Experimental results indicated that the sensors are highly sensitive to hydrogen, showing a two-order change in conductance. The morphology of the nanowires was analyzed using SEM and AFM in order to understand the properties responsible for the high sensitivity of the nanowires. SEM images showed that the nanowires contain nanogaps in absence of H/sub 2/. Upon exposure to H/sub 2/, the Pd absorbed hydrogen, resulting in the expansion of Pd grains. This expansion results in the closing of the nanogaps. The expansion occurred due to the phase transition from /spl alpha/ to /spl beta/ and the Pd lattice expansion.

NO2 response of In2O3 thin film gas sensors prepared by sol-gel and vacuum thermal evaporation techniques

In2O3 thin films have been prepared by high vacuum thermal evaporation (HVTE) and by sol–gel (SG) techniques. The deposited HVTE and SG films have been annealed at 500°C for 24 and 1 h, respectively. After annealing at 500°C, the films are highly crystalline cubic In2O3. XPS characterization has revealed the formation of stoichiometric In2O3 (HVTE) and nearly stoichiometric In2O3−x (SG). SEM characterization has highlighted substantial morphological differences between the SG (highly porous microstructure) and HVTE (denser) films. All the films show the highest sensitivity to NO2 gas (0.7–7 ppm concentration range), at 250°C working temperature. Negligible H2O cross has resulted in the 40–80% relative humidity range. Only 1000 ppm C2H5OH has resulted in a significant cross to the NO2 response.

Improved detection limits of toxic biochemical species based on impedance measurements in electrochemical biosensors.

An impedance based electrochemical biosensor was designed and fabricated for the detection of various chemical and biological species, with glass as substrate material and gold interdigitated electrodes. A flow cell with inlet and outlet ports for the microfluidic chamber was designed and fabricated using acrylic material with a reservoir volume of 78 μl. The feasibility of the fabricated sensor for detecting very low concentration of chemical and biological species was demonstrated. Electrochemical impedance spectroscopy (EIS) was employed as the detection technique. The impedance based response of the two-terminal device revealed a very high sensitivity with low concentrations of mouse monoclonal IgG, sarcosine, cadmium sulphide (CdS) and potassium chloride (KCl) at pico mole levels.

Investigation on the cross sensitivity of NO2 sensors based on In2O3 thin films prepared by sol-gel and vacuum thermal evaporation

In2O3 thin films have been prepared from commercially available pure In2O3 powders by high vacuum thermal evaporation (HVTE) and from indium iso-propoxide solutions by sol-gel techniques (SG). The films have been deposited on sapphire substrates provided with platinum interdigital sputtered electrodes. The as-deposited HVTE and SG films have been annealed at 500°C for 24 and 1 h, respectively. The film morphology, crystalline phase and chemical composition have been characterised by SEM, glancing angle XRD and XPS techniques. After annealing at 500°C the films’ microstructure turns from amorphous to crystalline with the development of highly crystalline cubic In2O3−x (JCPDS card 6-0416). XPS characterisation has revealed the formation of stoichiometric In2O3 (HVTE) and nearly stoichiometric In2O3−x (SG) after annealing. SEM characterisation has highlighted substantial morphological differences between the SG (highly porous microstructure) and HVTE (denser) films. All the films show the highest sensitivity to NO2 gas (0.7–7 ppm concentration range), at 250°C working temperature. At this temperature and 0.7 ppm NO2 the calculated sensitivities (S=Rg/Ra) yield S=10 and S=7 for SG and HVTE, respectively. No cross sensitivity have been found by exposing the In2O3 films to CO and CH4. Negligible H2O cross has resulted in the 40–80% relative humidity range, as well as to 1 ppm Cl2 and 10 ppm NO. Only 1000 ppm C2H5OH has resulted to have a significant cross to the NO2 response.

Characterization of sol-gel prepared WO3 thin films as a gas sensor

Tungsten trioxide (WO3) thin films have been prepared by the sol-gel process and annealed at different temperatures of 400, 500, 600, and 700 °C for 1 h. The morphology, microstructure, crystalline structure, and composition of the films have been analyzed using scanning electron microscopy (SEM), x-ray diffraction, Rutherford backscattering spectroscopy (RBS), and x-ray photoelectron spectroscopy (XPS) techniques. The SEM analysis showed that the films annealed at 400 °C are smooth and uniform. However, these evolved as granular at an annealing temperature of 500 °C. The films annealed at still higher temperatures have two distinct grains of different shapes and sizes. The films annealed below 400 °C are amorphous. Annealing at 500 °C resulted in the films having polycrystalline structure. RBS and XPS characterization have revealed that the films annealed at 400 °C are stoichiometric. Annealing above this temperature resulted in the films becoming off-stoichiometric. The electrical resistance of the film...

Surface electrical conductivity in ultrathin single-wall carbon nanotube/polymer nanocomposite films

Ultrathin composite films of single-wall carbon nanotubes dispersed in polymer matrices of polystyrene and polyurethane elastomers with the thickness ranging from 100nmto3μm were formed by dip-coating procedure. Electrical conductivity in plane of the film was measured with application of silver electrodes deposited through shadow mask techniques at polymer-air and polymer-substrate interfaces. Peculiarities of the surface electrical conductivity in the nanocomposite films have been related to the surface free energy of the components and the strength of polymer-substrate interfacial interaction, which promotes a nonuniform distribution of the conductive filler within the film thickness (vertical phase separation).Ultrathin composite films of single-wall carbon nanotubes dispersed in polymer matrices of polystyrene and polyurethane elastomers with the thickness ranging from 100nmto3μm were formed by dip-coating procedure. Electrical conductivity in plane of the film was measured with application of silver electrodes deposited through shadow mask techniques at polymer-air and polymer-substrate interfaces. Peculiarities of the surface electrical conductivity in the nanocomposite films have been related to the surface free energy of the components and the strength of polymer-substrate interfacial interaction, which promotes a nonuniform distribution of the conductive filler within the film thickness (vertical phase separation).

Mechanical and electrical characterization of /spl beta/-Ga/sub 2/O/sub 3/ nanostructures for sensing applications

Single crystalline /spl beta/-Ga/sub 2/O/sub 3/ nanowire and nanoribbon materials were synthesized, and electrical and mechanical properties were studied for sensing applications. The structural analysis showed that the Ga/sub 2/O/sub 3/ nanomaterials were stoichiometric and had the same crystal lattice structure as the /spl beta/ phase Ga/sub 2/O/sub 3/ crystal. The mechanical study on individual Ga/sub 2/O/sub 3/ nanowires and nanoribbons showed that they had a bending modulus of around 300 GPa, are flexible (in bending and twisting), and are easy to be cleaved along their crystal lattice. The current-voltage electrical characterization through the thickness of nanoribbon and along the length of nanowire confirmed their semiconducting characteristic. A two-terminal device fabricated with an individual Ga/sub 2/O/sub 3/ nanowire showed good sensing response to ethanol gas at low-operating temperature, which revealed the potential of using such nanostructures for effective sensing applications.

Gravure Printing of ITO Transparent Electrodes for Applications in Flexible Electronics

The possibility to directly pattern indium-tin-oxide (ITO) layers at ambient conditions by printing has many benefits. Printing, being an additive process, would greatly reduce the amount of energy, labor and material used by the current manufacturing processes to deposit and pattern ITO. In this work, gravure printability of ITO nanoparticles on polyethylene terephthalate (PET) was studied. A wide range of sheet resistivites and film thicknesses was obtained by varying the specifications of the gravure cells. From the regression analysis of the results, a good estimation of sheet resistivity of the printed films at different gravure cell volumes and aspect ratios (AR) was achieved. The films also showed transparency above 95% in the visible light region. In addition, printed ITO films were assessed for mechanical flexibility and the results compared to commercially available sputtered ITO films on PET. The electrical performance of printed ITO layers was not deteriorated with bending in contrast to the sputtered films. Therefore, printed ITO films can be of great benefit for applications in flexible electronics such as organic photovoltaics (OPV), liquid crystal displays (LCD), organic light-emitting diodes (OLED), touch screens, biosensors and utilization in the field of energy efficiency, especially in buildings.

Screen Printing of Multilayered Hybrid Printed Circuit Boards on Different Substrates

This paper reports on the successful fabrication of a multilayered hybrid printed circuit board (PCB) for applications in the consumer electronics products, medical technologies, and military equipment. The PCB was fabricated by screen-printing silver (Ag) flake ink, as metallization layer, and UV acrylic-based ink, as dielectric layer, on different substrates such as paper, polyethylene terephthalate, and glass. Traditional electronic components were attached onto the printed pads to create the multilayered hybrid PCB. The feasibility of the hybrid PCB was demonstrated by integrating an embedded microcontroller to drive an liquid-crystal display (160 × 100 pixels). In addition, the amount of the ink spreading after printing, the effect of bending on the printed lines, and the effect of the roughness of the substrates on the resistance of the printed lines was investigated. It was observed that the resistance of the lines increased by ≈1.8%, after 10000 cycles of bending, and the lowest resistance of 1.06 Ω was measured for the 600 μm printed lines on paper, which had a roughness of 0.175 μm. The advantage of fabricating PCBs on flexible substrates is the ability to fold and place the boards on nearly any platform or to conform to any irregular surface, whereas the additive properties of printing processes allow for a faster fabrication process, while simultaneously producing less material waste in comparison with the traditional subtractive processes. The results obtained show the promising potential of employing screen printing process for the fabrication of flexible and light-weight hybrid PCBs.