Ekasiddh Wongrat

Metal-Oxide Nanowires for Gas Sensors

In past decades, gas sensors based on the metal oxide semiconductors (MOSs) have been studied in diverse field for wide applications. A gas sensor is a device that can be used to detect various gas such as ethanol, LPG, CO2 and CO gases etc. The gas sensors based on MOSs such as SnO2, TiO2, WO3, ZnO, Fe2O3, and In2O3 have an important role in environmental monitor‐ ing, chemical process controlling, personal safety (Q. Wan et al., 2004), industrial process controls, for the detection of toxic environmental pollutants in human health, and for the prevention of hazardous gas leaks, which comes from the manufacturing processes (K. Arshak&I. Gaidan, 2005), wine quality monitoring, and traffic safety (X.F. Song et al., 2009).

Metal-Oxide Nanowires by Thermal Oxidation Reaction Technique

The metal-oxides are very interesting materials because they possess wide and universal properties including physical and chemical properties. For example, metal-oxides exhibit wide range of electrical property from superconducting, metallic, semiconducting, to insulating properties (Henrich & Cox, 1994). The wide ranges of properties makes metaloxide suitable for many applications including corrosion protection, catalysis, fuel cells, gas sensor, solar cells, field effect transistor, magnetic storage (Henrich, 2001), UV light emitters, detectors, piezoelectric transducers, and transparent electronics (Hsueh & Hsu, 2008) etc. Recently, nanostructures of metal-oxide such as nanowire, nanorod, nanobelt, nanosheet, nanoribbon, and nanotube have gained a great attention due to their distinctive and novel properties from conventional bulk and thin film materials for new potential applications. These unique properties cause by quantum confinement effect (Manmeet et al., 2006), lower dimensionality (Wang et al., 2008), change of density of state (Lyu et al., 2002), and high surface-to-volume ratio (Wangrat et al., 2009). Nanowires can be regarded as one-dimensional (1D) nanostructures which have gained interest for nanodevice design and fabrication (Wang et al., 2008). As an example of metaloxide nanowires, the materials are focused on zinc oxide (ZnO) and copper oxide (CuO). ZnO which is n-type semiconductor has been widely studied since 1935 with a direct band gap of 3.4 eV and large exciton binding energy of 60 meV at the room temperature (Coleman & Jagadish, 2006). ZnO has a wurtzite structure, while CuO, which is p-type semiconductor with narrow band gap of 1.2 eV , has a monoclinic crystal structure (Raksa et al., 2009). ZnO and CuO can be synthesized by various techniques such as pulse laser deposition (PLD) (Choopun et al., 2005), chemical vapor deposition (VD) (Hirate et al., 2005), thermal evaporation (Jie et al., 2004; Ronning et al., 2004), metal-catalyzed molecular beam epitaxy (MBE) (Wu et al., 2002; Chan et al., 2003; Schubert et al., 2004), chemical beam epitaxy (CBE) (Bjork et al., 2002) and thermal oxidation technique (Wongrat et al., 2009). Thermal oxidation technique is interesting because it is a simple, and cheap technique. Many researchers have reported about the growth of ZnO and CuO by thermal oxidation technique with difference conditions such as temperature, time, catalyst, and gas flow. The list of metal-oxide nanowires synthesized by thermal oxidation is shown in Table 1.

Ethanol Sensing Characteristics of ZnO Nanostructures Impregnated by Gold Colloid

ZnO nanostructures were synthesized by thermal oxidation reaction from zinc powder and then impregnated by gold colloid. The gold colloid was prepared by chemical reduction technique and had red color. The heating temperature and sintering time of thermal oxidation were 700 °C and 24 hours, respectively under oxygen atmosphere. The morphology of ZnO nanostructures and ZnO impregnated gold colloid were studied by field emission scanning electron microscope (FE-SEM). The diameter and length of pure ZnO and ZnO impregnated gold colloid were about the same value and were in the range of 100-500 nm and 2.0-7.0 µm, respectively. The ethanol sensing properties of ZnO impregnated by gold colloid were tested in ethanol atmosphere at ethanol concentrations of 1000 ppm and at an operating temperature of 260-360 °C. It was found that the sensitivity and response time were improved for gold impregnated sensor with an optimum operating temperature of 300°C due to the enhanced reaction between the ethanol and the adsorbed oxygen at an optimum temperature.

Rapid synthesis of Au, Ag and Cu nanoparticles by DC arc-discharge for efficiency enhancement in polymer solar cells

Abstract In this work, Au, Ag and Cu nanoparticles (AuNPs, AgNPs and CuNPs) were rapidly synthesized by the DC arc-discharge technique. The applied electrical DC voltages of 225, 125 and 275 V were utilized to synthesize the AuNPs, AgNPs and CuNPs, respectively. The plasma arc-discharge was created from two identical metallic electrodes separated by a distance of 1 mm in liquid with a volume of 100 ml. The surface plasmon resonance peaks were analysed via UV–Visible spectroscopy and appeared at wavelengths of 578, 441 and 526 nm for CuNPs, AgNPs and AuNPs, respectively. The size distributions calculated from TEM images indicate mean particle sizes of 31, 73 and 99 nm for AuNPs, AgNPs and CuNPs, respectively. For solar cell application, the nanoparticles (NPs) introduced in the ZnO electron-transport layer and P3HT:PCBM active layer can improve the PCE of the devices with a significant increase in the short-circuit current density (J sc ). The PCE enhancement of polymer solar cells with NP incorporation may originate from the localized surface plasmon effect, which leads to light-harvesting enhancement due to the light-absorption and light-scattering mechanisms.