Madhav Gautam

Adsorption kinetics of ammonia sensing by graphene films decorated with platinum nanoparticles

Ammonia sensing behavior of graphene synthesized by a chemical vapor deposition on a copper substrate using a methane and hydrogen gas mixture has been investigated. The Raman spectroscopy is used to monitor the quality of graphene films transferred onto SiO2/Si substrates. The sensitivity and the recovery time of the device are enhanced by the decoration of platinum nanoparticles on the surface of graphene. The effects of the operating temperature on the sensing response have been studied. The adsorption and desorption curves have been analyzed using Langmuir kinetic theory for the adsorption of ammonia, and the influence of surface inhomogeneity was analyzed by Freundlich isotherm. The activation energy of adsorption and the heat of adsorption estimated from the above theories indicate that the platinum decorated surface has two different adsorption sites whereas bare graphene has only one adsorption site. This effect caused 80%–85% enhancement of sensor response for platinum decorated surface compared ...

Graphene based field effect transistor for the detection of ammonia

Graphene synthesized by chemical vapor deposition has been used to fabricate the back-gated field effect transistor to study the sensing of ammonia (NH3) in ppm levels. Graphene has been synthesized directly on a target substrate using a thin Cu film as a catalyst, which has several advantages over deposition of graphene on Cu foil followed by a transferring process to another substrate. Raman spectroscopy was used to monitor the quality of the deposited graphene films on SiO2/Si substrates. The adsorption/desorption behavior of NH3 on graphene in dry air was analyzed from the progressive shift of the Dirac peak at smaller/larger gate voltages based on different time exposures to different concentrations of NH3. The relative change in the shift of the Dirac peak was consistent with a small charge transfer (0.039 ± 0.001 electrons per molecule at room temperature). The response of the device was found to increase with increasing NH3 concentrations and operating temperatures. The dependence of device respon...

Detection of organic vapors by graphene films functionalized with metallic nanoparticles

Graphene synthesized by chemical vapor deposition has been used to study the sensing behavior of graphene for different organic vapors in ppm level. All the measurements were carried out at a room temperature with dry air as the background gas. Synthesis of graphene was carried out on a copper foil using methane gas as a precursor. The Raman spectroscopy was used to monitor the quality of graphene films transferred to SiO2/Si substrates, revealing the sensing channel to be mostly monolayer, bilayer, or tri-layer graphene. Graphene surface was functionalized with gold and platinum nanoparticles to enhance the gas sensing behavior. The adsorption/desorption behavior of organic vapors in dry air was analyzed based on the change in the conductivity with the different exposure times in different concentrations. Among the vapors tested, the sensitivity was in the order: acetic acid > ethanol > acetone from all surfaces (bare graphene, graphene decorated with gold and platinum nanoparticles). The devices were su...

Optical properties of zinc nitride films deposited by the rf magnetron sputtering method

Photoconductivity of zinc nitride films prepared by the reactive radio frequency (rf) magnetron sputtering method is reported. It was observed that the as-deposited zinc nitride films did not exhibit photoconductivity whereas the annealed films under ambient conditions above 275 °C indicated some photoconductivity. The photoconductivity of annealed zinc nitrides exhibited at a measurement temperature as high as 100 °C suggesting that the carrier generation was governed by band gap transition. Photoconductivity was observed for the films annealed in air while the films annealed in nitrogen and ammonia ambient did not exhibit any photoconductive phenomenon. The results indicate that the content of nitrogen in the zinc nitride films plays an important role in electronic properties. The effect of annealing on photoconductivity was interpreted as due to the removal of extra nitrogen, which was included in the films during the sputter deposition process.

Ammonia sensor device using graphene modified with platinum

Gas sensing behavior of graphene with platinum nano-particles on graphene films was investigated. Synthesis of graphene was carried out on a copper substrate under the flow of methane and hydrogen gas mixture by a CVD process at the atmospheric pressure. The graphene films were transferred to different substrates after wet etching of the copper substrates. Graphene based device for gas sensing was fabricated using photolithography technique and lift off process. The device showed a better sensitivity when the platinum nano-particles are deposited on graphene surface as compared to graphene without platinum particles.

Sputter coated nanocrystalline ZnO for fabrication of thin film transistors

Fabrication of zinc oxide based thin-film transistors (ZnO-TFT), by RF magnetron sputtering at room temperature has been realized on thermally oxidized silicon wafer followed by the metal evaporation and lift-off process. The configuration of the TFT was bottom gate with the gold contacts on P-doped silicon. The device was observed to be a “normally on” device. Electrical characteristics, mainly, channel mobility, on/off ratio, and threshold voltage were extracted from the electrical characterization of TFT. The ZnO-TFT was found to operate with a threshold voltage of 12.075 V, channel mobility of 110.44 cm2/Vs, and an on/off ratio of approximately 105. Thickness of the ZnO film was confirmed by the UV spectrometer. No photo effect was observed, making it an ideal material for flat-panel displays. X-ray diffraction was performed to find out the orientation of the ZnO layer on the substrates. Preferred orientation was in the 002 plane. The high mobilities, ease of fabrication and cost-effectiveness make the ZnO-TFT a very desirable electronic device for futuristic flexible electronics.