ساخت لايه هاي نازك Pd/WO3 و بررسي تاثير آبدوستي بر رشد نانو ذرات پالاديم و پاسخ گاز و كروميك آن ها

چكيده انگليسي :

Preparation of Pd WO3 thin films and investigation the effect of hydrophilicity on Pd nanoparticle growth and their gasochromic response Marzieh Allaf Behbahani m allafbehbahani@ph iut ac ir Date of Submission 2013 01 08 Department of Physics Isfahan University of Technology Isfahan 84156 83111 Iran Degree M Sc Language Farsi Supervisor Dr Mehdi Ranjbar Ranjbar@cc iut ac ir Abstract Tungsten oxide thin films due to their gasochromic properties are widely considered to produce optical hydrogen gas sensors In the gasochromic process the color of tungsten oxide thin lms converts from a transparent to a dark blue state when atomic hydrogen incorporates into their lattice This process is often reversible i e whenever the colored lm is exposed to O2 gas the layer becomes bleached Previous studies shown that for a gasochromic coloration of WO3 thin lms it is necessary to deposit a very thin layer of metallic Pd or Pt as hydrogen catalyst over it Pd is a well known catalyst for hydrogen In gasochromic devise the characteristics of catalyst layer can determine the dissociation rate of absorbed gases and hence the gasochromic responses There are different ways to deposit a thin Pd lm such as sputtering e beam evaporation Electroless and hydrogen reduction Among them hydrogen reduction is known as a simple inexpensive and relatively successful method for Pd layer deposition In this method a drops of PdCl2 solution is put on the WO3 surface until dry to get a PdCl2 accumulated layer By exposing hydrogen gas to dried PdCl2 WO3 sample a layer involving distributed Pd nanoparticles grow on the tungsten oxide surfaces through a reduction reaction As a new approach the droplet of PdCl 2 without drying stage can also be used in gasochromic coloring of WO3 lms as an aqueous hydrogen catalyst In this study this idea was examined and an interesting gasochromic coloring effect was observed In the following a correlation between deposition method and preparation condition of tungsten oxide lms palladium top layer growth and gasochromic response of their using an aqueous hydrogen catalyst was investigated For this purpose tungsten oxide thin films were fabricated by sol gel and pulsed laser deposition methods In sol gel method the effect of annealing temperature and in pulsed laser deposition method the effect of substrate temperature on structural morphological chemical and optical properties of tungsten oxide thin films was studied by X ray Diffraction XRD Atomic Force Microscope AFM Field Emission Scanning Electron Microscope FE SEM Fourier Transform Infrared FTIR spectroscopy and UV VIS spectrophotometer Because of the aqueous nature of hydrogen catalyst hydrophilicity of samples was measured by means of contact angle These studies show the dependence of the properties of tungsten oxide thin films on deposition method and preparing condition of them Gasochromic investigation of the samples using an aqueous hydrogen catalyst and also morphological study of obtained palladium layer showed the hydrophilicity of tungsten oxide layers has the effective role in palladium top layer growth and consequently gasochromic response of them Using aqueous hydrogen catalyst it also was observed that the pulsed laser deposited tungsten oxide layers in comparison with sol gel derived films have a better gasochromic response This observation arises from the higher porosity and better hydrophilicity of the laser ablated tungsten oxide layer and more uniform distribution of palladium catalyst over the surface of them Keywords Tungsten oxide Sol gel Pulsed laser deposition PdCl2 Aqueous catalyst Hydrophilicity Gasochromic

علاف بهبهاني، مرضيه

ساخت لايه هاي نازك Pd/WO3 و بررسي تاثير آبدوستي بر رشد نانو ذرات پالاديم و پاسخ گاز و كروميك آن ها

اكسيد تنگستن , سل-ژل , لايه نشاني ليزر پالسي , كاتاليست مايع