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Most TCOs such as ITO, AZO(Al-doped ZnO), FTO(F-doped SnO 2 ) etc., which have been widely used in LCD, touch panel, solar cell, and organic LEDs etc. as transparent electrode material reveal n-type conductivity. But in order to realize transparent circuit, transparent p-n junction, and introduction of transparent p-type materials are prerequisite. Additional prerequisite condition is optical transparency in visible spectral region. Oxide based materials usually have a wide optical bandgap more than ~3.0 eV. In this study, single-phase transparent semiconductor of SrCu 2 O 2 , which shows p-type conductivity, have been synthesized by 2-step solid state reaction at 950 o C under N 2 atmosphere, and single-phase SrCu 2 O 2 thin films of p-type TCOs have been deposited by RF magnetron sputtering on alkali-free glass substrate from single-phase target at 500 o C, 1% H 2 /(Ar + H 2 ) atmosphere. 3% H 2 /(Ar + H 2 ) resulted in formation of second phases. Hall measurements confirmed the p-type nature of the fabricated SrCu 2 O 2 thin films. The electrical conductivity, mobility of carrier and carrier density 5.27 × 10 −2 S/cm, 2.2 cm 2 /Vs, 1.53 × 10 17 /cm 3 a room temperature, respectively. Transmittance and optical band-gap of the SrCu 2 O 2 thin films revealed 62% at 550 nm and 3.28 eV. The electrical and optical properties of the obtained SrCu 2 O 2 thin films deposited by RF magnetron sputtering were compared with those deposited by PLD and e-beam.

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Quartz crystal microbalance (QCM) gas sensor to detect methyl mercaptan (CH 3 SH) gas was fabricated by depositing TiO 2 nanoparticles and polyelectrolyte on the electrode of QCM. The TiO 2 /poly(sodium 4-styrenesulfonate) (PSS) thin film fabricated by a layer-by-layer self-assembly (LBL-SA) method showed a high surface area and increased the sensitivity of gas sensor. When the QCM sensors coated with triethanolamine (TEA) or (TiO 2 /PSS) were exposed to methyl mercaptan gas (1.0 ppm), the frequency shifts of QCM with TEA casting film and TiO 2 /PSS thin film were ca. 9 Hz and ca. 24 Hz, respectively. As the bilayer number of (TiO 2 /PSS) increased, the frequency shift of QCM sensor with (TiO 2 /PSS) thin film was gradually increased. In addition, the frequency shift of QCM sensor was gradually increased as the concentration of methyl mercaptan gas increased from 0.5 ppm to 2.0 ppm. In this study, the surface morphology and sensor property of QCM sensor coated with (TiO 2 /PSS) thin film were measured.