A. Karthigeyan

Light enhanced NO2 gas sensing with tin oxide at room temperature: conductance and work function measurements

The NO2 gas sensing behaviour of nano-particular SnO2 is studied at room temperature under illumination. SnO2 samples were sputtered on interdigital contact (IDC) substrates for conductance measurements and Pt-coated Si-substrates for work function potential measurements by Kelvin probe. Moreover, we used spectral filters and attenuation filters to study light induced gas adsorption and desorption mechanisms. Two main effects have been observed: the conductance is increased and the time constant for NO2 desorption is drastically reduced. Furthermore, the gas induced baseline shift has been reduced. The results can be explained with a surface photovoltaic model.

Hydrogen detection at high concentrations with stabilised palladium

In order to improve the stability to high hydrogen concentrations, of hybrid suspended gate field effect transistors (HSGFETs) with thin palladium films as sensitive layer, Pd-Ni and Pd-Ag alloys h ...

Highly Sensitive, Room-Temperature Gas Sensors Prepared from Cellulose Derivative Assisted Dispersions of Single-Wall Carbon Nanotubes

We have developed highly sensitive gas sensors based on single-wall carbon nanotube (SWNT) networks prepared from aqueous hydroxypropylcellulose-assisted dispersions. Gas responses were monitored at room temperature for different concentrations of NO2. The stable baseline and its recovery (after NO2 exposure) were achieved by ultraviolet (UV)-induced photodesorption, for which a compact and low-power UV light emitting diode can be used as a light source. The sensors are capable of detecting 25 ppb or lower concentrations of NO2 and 5 ppm ammonia, and show almost no baseline drift after multiple NO2 exposures. The simple and low-cost fabrication process, reproducible performance and room-temperature operation bode well for industrial mass production and broad uses.

Influence of oxidation temperature, film thickness and substrate on NO2 sensing of SnO2 ultra thin films

Thin SnO2 films of different thickness were fabricated by sputtering of tin followed by thermal oxidation. The oxidation was performed at 600, 700 and 800 8C and silicon and silicon dioxide were chosen as substrates for their compatibility to silicon CMOS technology. Work function measurements were carried out on these films upon exposure to NO2 in the concentration range 5‐100 ppm at a particular temperature under dry and humid conditions using a commercial Kelvin probe measurement set-up. Kelvin probe measures contact potential difference (CPD) resulting from change in work function of a film material on exposure to a gas. The dependence of NO2 sensitivity of films on oxidation temperature, film thickness and substrate was investigated. The influence of temperature on NO2 response from 30 to 130 8C was investigated. It has been observed that humidity has negligible effect at 130 8C. It was further observed that response of SnO2 film on silicon to NO2 increases with oxidation temperature of the film whereas for the films grown on silicon dioxide the response was parabolic. In the later case, increase in signal was exhibited by the films oxidized up to 700 8C while it was found to decrease for films oxidized at 800 8C. The films of three different thickness (10, 35 and 55 nm) prepared at 800 8C on silicon showed negligible variation in sensitivity. However, sensitivity of the films grown on silicon dioxide is observed to be thickness dependent. The films were characterized using atomic force microscopy (AFM) and Auger electron spectroscopy (AES) to study the surface morphology and depth profile respectively. The observed results are discussed to understand the NO2 sensing behavior of ultra thin SnO2 films. # 2002 Elsevier Science B.V. All rights reserved.

Improvement in buried silicon nitride silicon-on-insulator structures by fluorine-ion implantation

As an effort to improve buried Si3N4–Si interfaces in silicon-on-insulator (SOI) structures, fluorine was implanted either before or after the synthesis of buried silicon nitride layers by high dose nitrogen ion implantation. In these synthesized SOI structures, the thickness of Si overlayer and the buried silicon nitride layer was found to be 2400±25 and 1725±25 A, respectively. Auger electron spectroscopy depth profile analysis illustrates that the fluorine ion implantation in the SOI structures modifies the distribution of nitrogen that results in better stoichiometry of the buried silicon nitride layers and abrupt Si3N4–Si interfaces. Current–voltage and high frequency capacitance–voltage characteristics were measured, and electrical breakdown measurements were performed on metal-nitride-silicon (MNS) structures, fabricated after removing the Si overlayer in the SOI structures. In the fluorine-implanted SOI specimens, the buried Si3N4 layers show a higher breakdown field strength of 4.4–5.2 MV/cm as c...

Optical gas sensing with dip-coated carbon nanotubes through the modulation of photoluminescence and optical absorption

Photoluminescence (PL) and optical absorption (OA) of single-wall carbon nanotube (CNT) thin films are shown to substantially change after exposure to NO2 or NH3 gas. These films prepared by dip-coating in surfactant-aided CNT dispersions consist of unbundled and well-exposed tubes; the former property enables the detection of PL, a task difficult for bundled CNTs, while the latter enlarges the effective surface area available for gas adsorption. The observed changes correspond well to those in electrical resistance, which are consistently explained by charge transfer between the CNTs and the gas molecules. Highly resolved spectral peaks in two-dimensional PL excitation contour maps and their changes induced by the gas exposure revealed that wider tubes are more sensitive to gas adsorption.