You can measure the change in resistance with respect to Time in semiconducting material with dynamic flow of different gases (CO2 or NH3 etc.).

There are several methods to measure the resistance that Ravi mentioned. We used wash-coting technique for powders (you may find the details in the following paper:

CO sensitive nanocrystalline LaCoO< sub> 3 perovskite sensor prepared by high energy ball milling

M Ghasdi, H Alamdari - Sensors and Actuators B: Chemical, 2010

Regards;

Hi Bramhaiah,

Have a peek at the following sites:

http://onlinelibrary.wiley.com/doi/10.1002/9781118354162.ch11/summary

and

http://www.crcpress.com/product/isbn/9781439813874

Cheers,

Frank

thank you very much sir (Frank  and Houshang)

for your help

Chemiresistors consisting of Ti/Au interdigitated electrodes is a relatively simple start.  They are the easier of devices to fabricate and measure.  You will need a method sample chemical analytes of a known concentration and a measurement system to accurately measure and collect the data.  You will want to do concentration dependent studies and use the Stern-Volmer relationship to do so once you have data.   Are you referring to organic semiconductors or inorganic?

Fairly simple. For a simple chemi-resistive sensor setup you will need

1. Any volume in which gas can be contained (chamber, quartz tube, flat/round bottom flask, glove box etc) with provision for electrical wires for measurement and gas flow (in and out)

2. Substrate on which your semiconducting material is deposited

3. Electrodes on substrate for resistance/current/voltage measurement and the leads from it from inside the gas volume to outer air through leak free feedthrough

4. Gas flow at known concentration/flow rate

5. leak tight arrangement and proper vent of gases