Z. A. Ansari

A novel method for preparing stoichiometric SnO2 thin films at low temperature

Tin oxide is a well known nonstoichiometric material with dual valency. The invariance of stoichiometry is very intriguing. As of today no report is available for preparing perfect stoichiometric tin oxide. Here we report a novel method to prepare stoichiometric tin oxide by modifying the known plasma enhanced chemical vapor deposition technique using SnCl(4)-xH(2)O as precursor and O(2) as reactant gas at various temperatures from 300 to 800 degrees C. Tetragonal rutile structure of SnO(2) was found, grown along the [110] direction. X-ray photoelectron spectroscopic measurement showed constant Sn/O ratio. Sn 3d and O 1s were found composed of only Sn(4+) (487.2 eV) and O-Sn(4+) (531.2 eV) with equal peak widths. Raman band intensity ( approximately 633 cm(-1)) was found increasing with temperature, indicating the morphological changes. Sheet resistance of approximately 0.5 kOmega/at 300 degrees C was measured that reduces to approximately 0.1 kOmega/at 600 degrees C. It is found that film stoichiometry remains unaltered, while the structural morphology changes significantly.

A simple method to deposit palladium doped SnO2 thin films using plasma enhanced chemical vapor deposition technique

This work presents a simple method to deposit palladium doped tin oxide (SnO(2)) thin films using modified plasma enhanced chemical vapor deposition as a function of deposition temperature at a radio frequency plasma power of 150 W. Stannic chloride (SnCl(4)) was used as precursor and oxygen (O(2), 100 SCCM) (SCCM denotes cubic centimeter per minute at STP) as reactant gas. Palladium hexafluroacetyleacetonate (Pd(C(5)HF(6)O(2))(2)) was used as a precursor for palladium. Fine granular morphology was observed with tetragonal rutile structure. A peak related to Pd(2)Sn is observed, whose intensity increases slightly with deposition temperature. Electrical resistivity value decreased from 8.6 to 0.9 mΩ cm as a function of deposition temperature from 400 to 600 °C. Photoelectron peaks related to Sn 3d, Sn 3p3, Sn 4d, O 1s, and C 1s were detected with varying intensities as a function of deposition temperature.

Thick film urea sensor based on nanostructured zinc oxide

Flower-like structures of ZnO was synthesised by solution method using zinc acetate dihydrate and sodium hydroxide. Hydroxylamine hydrochloride (0.4M and 0.8M) was used as a structure directing agent. Structural morphology significantly changed with precursor concentration from a flower-like structure to sea-urchin like structure. Thick films of this powder were prepared on Al-sheet, by conventional doctor blade method using organic additives and used for urea sensing. Urease was attached with zinc oxide (by soaking in urease solution containing 100 units for three hours). In general, film conductivity increases after urease immobilisation. Urease immobilised films were found sensitive to urea concentration from 1 mM to 100 mM. Flowery structure resulted in higher urea sensitivity. The sensor responses are reproducible, reliable, reversible and selective, with a response time of 6S.