Thin gold films grown in ultra high vacuum on mica substrates

In-situ evaporation was used to deposit thin gold films (640 A) on mica substrates held at room temperature. The samples were characterized by Auger Electron Spectroscopy (AES) and Scanning Tunneling Microscopy (STM) measurements. The deposition of gold on mica without pre-anneal of the mica substrate resulted in a grainy surface with an average grain size of -220 A. The evolution of the average grain size as a function of mica pre-deposition baking time and deposition rate was investigated. It was found that long bake-outs (48 hours or more), and low deposition rates (0.2 A/s) increased the average dimension of gold grains by a factor of 5 relative to the films evaporated onto unannealed mica. Post-annealing a film deposited at room temperature promoted grain enlargement and enhanced (111) termination. The thermal annealing treatments were done at temperatures between 80 and 340°C, and for periods of time ranging from 1 to 12 hours. In addition to prolonged annealing, /n-s/fu flash annealing produced surfaces with highly crystalline terraces extending for as much as 5000 A. Flashing experiments were carried out at temperatures between 300 and 650°C. Below 350°C, flash annealed and as grown films were visually similar

Some Spinel Oxide Compounds as Reducing Gas Sensors

Four spinel ferrites, MFe2O4 (M = Cu, Cd, Zn and Ni), having various grain sizes (100 – 700 nm) were prepared by sol-gel-selfcombustion and their sensing properties to reducing gases were investigated. The gas sensing characteristics were obtained by measuring the sensitivity as a function of various controlling factors, like operating temperature, composition and concentration of the gas, and finally the response time. The sensitivity of four ferrites to reducing gases like acetone, ethanol and LPG was been compared. It was revealed that CuFe2O4 is the most sensitive to LPG and ZnFe2O4 can be used as a sensor to selectively detect ethanol vapors in air. The strong interaction between ethanol and porous ZnFe2O4 can explain the selective sensitivity to ethanol and negligible sensitivity to the other reducing gases