The effect of Cu coating on the sensing properties of nano SnO2:Cu based sensors for the CH4, CH3CH2CH3 gas was studied. This work was focussed on investigating the change of sensitivity of nano SnO2:Cu based sensors for CH4, CH3CH2CH3 gas by Cu coating. Nano sized SnO2 powders were prepared by solution reduction method using stannous chloride(SnCl2·2H2O), hydrazine(N2H2) and NaOH and subsequent heat treatment. XRD patterns showed that nano SnO2 powders with rutile structure were grown with (110), (101), (211) dominant peak. The particle size of nano SnO2:Cu powders at 8 wt% Cu was about 50 nm. SnO2 particles were found to contain many pores, according to SEM analysis. The sensitivity of nano SnO2:Cu based sensors was measured for 5 ppm CH4 gas and CH3CH2CH3 gas at room temperature by comparing the resistance in air with that in target gases. The sensitivity for both CH4 and CH3CH2CH3 gases was improved by Cu coating on the nano SnO2 surface. The response time and recovery time of the SnO2:Cu gas sensors for the CH4 and CH3CH2CH3 gases were 18∼20 seconds, and 13∼15 seconds, respectively.

SnO2 nano powders were prepared by solution reduction method using tin chloride(SnCl2·2H2O), hydrazine(N2H4) and NaOH. The SnO2 thick films for gas sensors were fabricated by screen printing method on alumina substrates and annealed at 300℃ in air, respectively. XRD patterns of the SnO2 nano powders showed the tetragonal structure with (110) dominant orientation. The particle size of SnO2 nano powders at the ratio of SnCl2:N2H4+NaOH= 1:6 was about 60 nm. The sensing characteristics were investigated by measuring the electrical resistance of each sensor in a test box. Sensitivity of SnO2 gas sensor to 5 ppm CH4 gas and 5 ppm CH3CH2CH3 gas was investigated for various SnCl2:N2H4+NaOH proportion. The highest sensitivity to CH4 gas and CH3CH2CH3 gas of SnO2 sensors was observed at the SnCl2:N2H4+NaOH= 1:8 and SnCl2:N2H4+NaOH= 1:6, respectively. Response and recovery times of SnO2 gas sensors prepared by SnCl2:N2H4+NaOH= 1:6 was about 40 s and 30 s, respectively.

Diamond thin films were deposited on pretreated Co cemented tungsten carbide (WC-6%Co) inserts as substrate by microwave plasma chemical vapor deposition (MPCVD) system, equipped with a 915MHz, 30kW generator for generating a large-size plasma. The substrates were pretreated with two solutions Murakami solution [KOH:K3Fe(CN)6:H2O] and nitric solution [HNO3:H2O] to etch, WC and Co at cemented carbide substrates, respectively. The deposition experiments were performed at an input power of 10 kW and in a total pressure of 100 torr. The influence of various CH4 contents on the crystallinity and morphology of the diamond films deposited in MPCVD was investigated using scanning electron microscopy (SEM) and Raman spectroscopy. The diamond film synthesized by the CH4 plasma shows a triangle-faceted (111) diamond. As CH4 contents was increased, the thickness of diamond films increased and the faceted planes disappeared. Finally, Faceted diamond changed into nano-crystalline diamond with random crystallinity.