M.C. Bhatnagar

IMPROVEMENT OF THE OXYGEN GAS SENSITIVITY IN DOPED TIO2 THICK FILMS

Abstract The titania (TiO2) thick films were prepared by using screen-printing technology of 0.00, 0.20 and 0.40 wt.% Nb and 0.40 wt.% Cr concentration on alumina substrate. These thick films were sintered at 1300°C for 5 h in the atmosphere to obtain rutile phase of TiO2. The material characterization was done by using X-ray diffraction (XRD) and scanning electron microscope (SEM). The sensitivity measurements were carried out as a function of operating temperature (400–600°C) in Nb doped TiO2 sensor and (600–800°C) in Cr doped sensor as a function of oxygen partial pressure. The response time measurements in Nb doped sensors were carried out at operating temperatures (400–600°C) at 1200 ppm oxygen partial pressure and operating temperatures (600–800°C) at 1000 ppm oxygen partial pressure in Cr doped TiO2 sensor. The results show that Nb doped sensor exhibits higher sensitivity at 550°C as compared to pure TiO2 sensor, while in the other case, Cr doped sensor shows high sensitivity towards oxygen at 700°C. The result indicates that grain growth cab can be modified by using suitable doping which is responsible for improving stability and sensitivity of the sensor.

Graphene as a transparent conducting and surface field layer in planar Si solar cells

This work presents an experimental and finite difference time domain (FDTD) simulation-based study on the application of graphene as a transparent conducting layer on a planar and untextured crystalline p-n silicon solar cell. A high-quality monolayer graphene with 97% transparency and 350 Ω/□ sheet resistance grown by atmospheric pressure chemical vapor deposition method was transferred onto planar Si cells. An increase in efficiency from 5.38% to 7.85% was observed upon deposition of graphene onto Si cells, which further increases to 8.94% upon SiO2 deposition onto the graphene/Si structure. A large increase in photon conversion efficiency as a result of graphene deposition shows that the electronic interaction and the presence of an electric field at the graphene/Si interface together play an important role in this improvement and additionally lead to a reduction in series resistance due to the conducting nature of graphene.

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.

Structural and photoluminescence properties of tin oxide and tin oxide: C core–shell and alloy nanoparticles synthesised using gas phase technique

In the present study, we report a controlled growth of tin oxide and tin oxide: carbon nanoparticles by an integrated method comprising of the gas phase agglomeration, electrical mobility based size selection, and in–flight sintering steps. The effect of in-flight sintering temperature and variation in growth environment (N2, H2 and O2) during nanoparticle formation, morphology and composition has been investigated by carrying out High Resolution Transmission Electron microscopy and X-Ray diffraction studies. The results highlight the novelty of the present technique to grow alloy and core-shell nanoparticles in which the stoichiometery (x) of SnOx and the mode of incorporation of carbon into the tin oxide lattice (alloy or core-shell structure), along with well-defined size can be controlled independently. Detailed Photoluminescence (PL) studies of well sintered monocrystalline SnO, SnOx and SnO2 nanoparticles along with SnOx:C and SnO2:C alloy and C@SnO core-shell nanoparticle has been carried out. The ...

Preparation, structure and conductivity of Sn modified NASICON material

The samples of tin (Sn) modified NASICON (Na3Zr2Si2PO12) type solid electrolyte are prepared and their electrical properties are investigated. The two modified compositions of NASICON in which zirconium (Zr) atoms are replaced by Sn atoms i.e., Na3ZrSnSi2PO12 (NASN) and Na3Sn2Si2PO12 (NASN2), are prepared by solid state reaction technique. The structural studies show variation in the lattice parameters a and c which enhance the bottle neck size. The FT-IR results also confirm structural modification (stretching of bond lengths) on addition of Sn. The electrical studies show when one atom of Zr is replaced by one atom of Sn (NASN), both DC and AC electrical conductivities increase as compared to unmodified NASICON material while for replacement of both the Zr atoms by Sn atoms (NASN2), the electrical conductivity decreases.

Detection of very low concentration of water in ethanol by using NASICON probe

NASICON based low cost, highly sensitive sensor probe for detection of very small content of the water nearly ppm level in ethanol has been fabricated and characterized. The sensor utilizes the electrochemical cell method for detection of water content in ethanol. The results indicate nearly linear variation of emf with increase in water content upto 10 % with a sensitivity of 0.001mV per ppm. Such a high value of sensitivity is extremely useful in detection of water in medical science and chemical industries where ethanol is used as an organic solvent.

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.