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Updated on: March 16, 2014  
     
  FACULTY - Arun M. Umarji, Professor (Research Areas)  
 
 
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Last Updated: March 16, 2014
Default faculty mailing address: Materials Research Centre, Indian Institute of Science(IISc), Bangalore - 560012, INDIA.
Phone: Country code-91; Bangalore city code 80 from abroad and 080 from India.

 

Arun M. Umarji
Professor

Ph:
Off: +91-80-2293 2944
Res: +91-80-2337 5479
Fax: +91-80-2360 7316
E-mail: umarji@mrc.iisc.ernet.in

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Research:
  • Metal Oxide based Gas Sensors
  • Developing VO2 thin films for bolometric applications
  • Thermoelectric materials

Research in Brief:

Metal Oxide based Gas Sensors

Metal oxide semiconducting gas sensors are one of the most investigated groups of gas sensors till date. These have attracted the attention of many users and scientists interested in gas sensing under atmospheric conditions due to their low cost and flexibility associated to their production and operation.

The performance of these semiconducting metal oxide gas sensors depends on their structural and electronic properties such as microstructure, local doping, grain boundaries and surface states. These properties are influenced by the preparation techniques used for producing the gas sensor device. Hence it becomes interesting to study the effect of synthesis route employed, on the performance parameters of the gas senor.

Thin films of Chromium oxide (Cr2O3) and Tin oxide (SnO2) have been identified as a good candidate of metal oxide semiconductor for exploring their gas sensing properties. Chromium Oxide is a p-type semiconductor. It shows good response to various gases like H2, NH3, VOCs and NOx etc. So far, gas sensing properties of chromium Oxide has not been explored fully. On the other hand, Tin Oxide (SnO2) is a well established gas sensor material. It is being used in commercially available gas sensing devices.

Our aim is to study gas sensing properties of the films Produced by UNSPACM and compare it with well established methods like normal spray pyrolysis and MOCVD. The preparation of the above oxides in thin film form has been adopted by two following methods, i.e metal organic chemical vapor deposition (MOCVD) and the nebulized spray pyrolysis of a combustion mixture. The gas sensing properties of these films have been studied.

Developing VO2 thin films for bolometric applications

Developing Infrared thermal imaging devices like bolometers have become very popular of their applications in night surveillance, remote sensing, night vision cameras, biomedical equipment, fire and intruder alarms. IR detectors are classified into photon detectors and uncooled thermal detectors. Though photon detectors offer high sensitivity and quick operation, their cooling apparatus occupy large volume and is not cost effective as well. These uncooled thermal detectors are called bolometers and they employ a thermal sensing layer whose variation in electrical resistance as a function of temperature is measured. The heating of this layer due to absorption of infrared radiation, results in its variation of electrical resistance with respect to temperature. Some of the materials used commonly in IR bolometers are Si and Vanadium oxides.

Vanadium oxides are being used as the thermal sensing layer because of their large temperature coefficient of resistance, favorable electrical resistance, reduced noise (low 1/f) and compatibility with the machining process. Of all oxides of vanadium, only vanadium dioxide has been highly investigated as it shows first order transition near to room temperature. First order transition is understood as the sharp change in the electrical resistance at a particular temperature when resistance is measured as a function of temperature. The change in resistivity in this case is of the order of 105 over a temperature change of 0.1oC at 68oC in a single crystal. The main objective of this work is developing doped vanadium dioxide thin films prepared by Ultrasonic Nebulized Spray Pyrolysis of Aqueous Combustion Mixture in order to have reduced first order transition (close to room temperature) and understanding its transition characteristics.

Thermoelectrics

Silicides are a potential candidate for High temperature applications such as heating elements, protective coatings, ceramic engines etc. because of its non-toxicity, availability of raw materials, chemical and thermal stability. Despite its advantages, the thermoelectric performance (zT) of the material is low. So efforts are on in enhancing the thermoelectric performance of the material. Band structure engineering and phonon engineering are some of the methodologies in improving the material's properties. This can be done by chemical doping and nanostructurization. This in turn can be carried out by doping the material with Mn, Co, B, etc. Nanostructurization can enhance zT value by decreasing the thermal conductivity.


 
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