Somnath C. Roy

Toward Solar Fuels: Photocatalytic Conversion of Carbon Dioxide to Hydrocarbons

The past several decades have seen a significant rise in atmospheric carbon dioxide levels resulting from the combustion of hydrocarbon fuels. A solar energy based technology to recycle carbon dioxide into readily transportable hydrocarbon fuel (i.e., a solar fuel) would help reduce atmospheric CO2 levels and partly fulfill energy demands within the present hydrocarbon based fuel infrastructure. We review the present status of carbon dioxide conversion techniques, with particular attention to a recently developed photocatalytic process to convert carbon dioxide and water vapor into hydrocarbon fuels using sunlight.

Theory, Instrumentation and Applications of Magnetoelastic Resonance Sensors: A Review

Thick-film magnetoelastic sensors vibrate mechanically in response to a time varying magnetic excitation field. The mechanical vibrations of the magnetostrictive magnetoelastic material launch, in turn, a magnetic field by which the sensor can be monitored. Magnetic field telemetry enables contact-less, remote-query operation that has enabled many practical uses of the sensor platform. This paper builds upon a review paper we published in Sensors in 2002 (Grimes, C.A.; et al. Sensors 2002, 2, 294–313), presenting a comprehensive review on the theory, operating principles, instrumentation and key applications of magnetoelastic sensing technology.

Eliminating Unwanted Nanobubbles from Hydrophobic Solid/Liquid Interfaces : A Case Study Using Magnetoelastic Sensors

Air bubbles are known to form at the liquid/solid interface of hydrophobic materials upon immersion in a liquid (Holmberg, M.; Kdühle, A.; Garnaes, J.; Mørch, K. A.; Boisen, A. Langmuir 2003, 19, 10510-10513). In the case of gravimetric sensors, air bubbles that randomly form at the liquid-solid interface result in poor sensor-to-sensor reproducibility. Herein a superhydrophilic ZnO nanorod film is applied to the originally hydrophobic surface of a resonance-based magnetoelastic sensor. The superhydrophilic coating results in the liquid completely spreading across the surface, removing unwanted air bubbles from the liquid/sensor interface. The resonance amplitude of uncoated (bare) and ZnO-modified sensors are measured in air and then when immersed in saline solution, ethylene glycol, or bovine blood. In comparison to the bare, hydrophobic sensors, we find that the standard deviation of the resonance amplitudes of the liquid-immersed ZnO-nanorod-modified sensors decreases substantially, ranging from a 27% decrease for bovine blood to a 67% decrease for saline. The strategy of using a superhydrophilic coating can be applied to other systems having similar interfacial problems.

Study of Dielectric and Pyroelectric Properties of Sol-Gel Derived BST Thin Films

(Ba,Sr)TiO 3 (BST) thin films have received considerable interest in recent years due to their many attractive properties like high dielectric constant, high dielectric breakdown strength and high pyroelectric coefficent. These films have been identified as promising material for several applications such as ferroelectric non-volatile memories and uncooled infrared focal plane arrays [UFPAs]. Barium strontium titanate (Ba 0.75 Sr 0.25 TiO 3 ) thin films of thickness 0.5 μm have been deposited on Pt/TiO 2 /SiO 2 /Si substrate by sol-gel spin coating method. The glancing angle X-ray diffraction of these films sintered at 700°C in air shows polycrystalline nature. Dielectric constant (ϵ r ) and dielectric loss (tanδ) of the film measured at 1 KHz are found to be 400 and 0.02 respectively. The ferroelectric phase has been confirmed from the C-V and P-E studies. After poling the sample by corona charging technique, the pyroelectric coefficient at room temperature was found to be order of 10−8 C/cm 2 K.

Photoluminescence Study of the Sol–Gel Derived (Ba0.5Sr0.5) TiO3 Thin Films for the Characterization of Trap States

Room temperature photoluminescence (PL) spectroscopy was done to investigate luminescent trap states in sol–gel deposited (Ba,Sr)TiO3 thin films. The pre-sintered films showed three distinct PL peaks. Increase in the peak intensity was observed with increase in pre-sintering temperature. These PL peaks were assigned to (a) singly charged oxygen vacancies (b) TiO2 networks and (c) the contribution from the substrate. In contrast, the sintered samples showed only a band-edge luminescence with an intense peak near the band-gap energy. Identification of such observed trap states are important in understanding the results of dielectric measurements because they contribute to the leakage currents and loss mechanisms.

p-type gas sensing behaviour in high energy ion beam irradiated un-doped SnO 2 thin films

We report novel p-type behaviour in undoped SnO2 thin films irradiated with 75 MeV Ni+ ion beam. Gas response of the irradiated films with NH3 (reducing) and NO2 (oxidizing) gases shows an increase and decrease in resistance respectively indicating p-type conduction that also increases with increase in ion fluence. Photoluminescence spectroscopy of the irradiated films shows strong yellow peak corresponding to interstitial oxygen ions. The observed p-type conductivity is attributed to holes generated by these interstitial oxygen ions. Presence of interstitial oxygen ions is also supported by X-ray photoelectron spectroscopy.