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Growth and characterization of tungsten and tungsten oxide nano particles

Growth and characterization of tungsten and tungsten oxide nano particles. By Phanindra Kondagari Department of Chemical Engineering University of Tulsa. Introduction.

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Growth and characterization of tungsten and tungsten oxide nano particles

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  1. Growth and characterization of tungsten and tungsten oxide nano particles By Phanindra Kondagari Department of Chemical Engineering University of Tulsa

  2. Introduction • Nano particles or nanocrystals made of metals, semiconductors, or oxides are of interest for their electrical, optical and chemical properties. • These particles are characterized by different techniques like SEM, TEM, AFM, XRD and FITR. • Transition metal and metal oxides have good electrochromic, gaschromic and photochromic properties which spurred interest in tungsten and tungsten oxide. • Recent findings have proved that nanosize crystalline tungsten oxide has better electrochromic properties than its amorphous form. • Tungsten oxide can me produced by several methods like sputtering method, chemical vapor deposition, spray pyrolysis, pulse vapor deposition and colloidal solution. • Chemical vapor deposition is an easy method to produce and control the size of tungsten oxide.

  3. Properties and applications of tungsten and tungsten oxide • Electrochromic, gaschromic and photochromic properties are most important properties exhibited by metal and metal oxides. • These properties have several applications like gas sensing, smart windows and displays. • Tungsten oxide has good catalytic and semi conducting properties which help in designing gas sensors. • The band gap of monoclinic tungsten oxide lies between 1.1-2.5 eV. This property is useful in designing photo catalysts and photo conductors. Basic block diagram of smart windows.

  4. Chemical vapor deposition • Chemical vapor deposition (CVD) is a material synthesis process whereby constituents of the vapor phase react chemically near or on the substrate surface to form a solid product. • Depending upon energy sources there are different types of CVD like Hotwire CVD, Thermal CVD, PECVD, MPECVD etc. • Hotwire CVD (HWCVD) and thermal CVD are simplest and cheapest chemical vapor deposition techniques used to grow novel materials. • Tungsten oxide was produced by oxidizing tungsten coil (99.9% pure) directly at different conditions.

  5. Hot Wire Chemical Vapor Deposition (HWCVD) Reactor Gas inlet Metalcoil Bell jar Pressuregauge To vacuum pump

  6. Production of tungsten and tungsten oxide • Tungsten oxide is produced by oxidation of tungsten coil. The deposit is formed in the ceramic boat at the bottom of the tungsten coil and on the walls of the bell jar. • Of several forms of tungsten oxide interest are monoclinic tungsten oxide (m-WO3), and W18O49. • Pure oxygen was passed through the reactor to produce monoclinic tungsten oxide. • Other gases like methane, argon and oxygen passed through the water bubbler to produce nanorods of W18O49. • Nanostructures of tungsten is prepared by reduction of tungsten oxide in hydrogen atmosphere.

  7. Run conditions and summary • Monoclinic tungsten is pale yellow in color and was produced by passing oxygen directly at base pressure of 400 torr and they were rhombic spheroids. • W18O49 was produced by passing any gas through water bubbler. The deposit was dark blue and has nanorod structure. • Irrespective of temperature all tungsten oxides have nanostructures. • Tungsten was produced by 60 min reduction of both the oxides in hydrogen atmosphere at 9300C and 800 torr pressure. Deposit was of same shape and size as of the respective oxides. • All the samples were characterized by SEM,TEM and XRD.

  8. XRD pattern for tungsten oxide prepared by passing oxygen TEM image of the monoclinic tungsten oxide

  9. XRD pattern for W18O49 formed by passing methane through water bubbler TEM images of the same sample

  10. XRD pattern of tungsten reduced from tungsten oxide SEM image of tungsten TEM image of tungsten

  11. References • M.L.Hitchman, and K.F.Jensen; Chemical Vapor Deposition Principles and Application, Academic, London (1993). • B.J.Chen, X.W.Sun, and C.X.Xu; Ceramics International30, 1725 (2004) • J.Liu, Z.Zhang, X.Su, and Y.Zhao; J. Phys. D: Appl. Phys.38, 1068 (2005). • C.Kee, D.Ko, and J.Lee; J. Phys. D: Appl. Phys.38, 3850 (2005). • R.Deshpande, A.C.Dillon, A.H.Mahan, J.Alleman, S.Mitra; Thin Solid Films501, 224 (2006). • H.J.Jeong, Y.M.Shin, S.Y.Jeong, Y.C.Choi, Y.S.Park, S.C.Lim, G.Park, I.Han, J.M.Kim, and Y.H.Lee; Chemical Vapor Deposition8, 1, 11 (2002). • C.Bower, W.Zhu, S.Jin, and O.Zhou; Applied Physics Letters77, 830 (2000). • K.B.K.Teo, M.Chhowalla, G.A.J.Amaratunga, W.I.Milne, D.G.Hasko, G.Pirio, P.Legagneux, F.Wyczisk, and D.Pribat; Applied Physics Letters79, 10, 1534 (2001). • E.Cazzanelli, C.Vinegoni, G.Mariotto, A.Kuzmin, and J.Purans; Solid State Ionics123, 67 (1999). • G.Gu, B.Zheng, W.Q.Han, S.Roth, and J.Liu; Nanoletters2, 8, 849 (2002). • J.Liu, Z.Zhang, Y.Zhao, X.Su, S. Liu, and E.Wang; Small1, 3, 310 (2005). • M.Boulova, and G.Lucazeau; Journal of Solid State Chemistry167, 425 (2002). • A.H.Jayatissa, S.Cheng, and T.Gupta; Materials Science and Engineering B109, 269 (2004).

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