Mike Post

Material chemistry of perovskite compounds as chemical sensors

The advantages of applying non-stoichiometric perovskite materials in chemical sensor applications are reviewed and highlighted with particular reference to the SrFeO2.5+x system. The phase relationships of SrFeO2.5+x for (0<x<0.5) are described and differences identified with the substituted material, SrFe0.9Cu0.1O2.5+x, such that the prospect of `tunable chemical and physical properties is identified. Thin-films of the parent perovskite have been prepared by the pulsed laser deposition technique and gas sensor functionality determined by exploiting the effects of gas exposure upon a number of physical properties. There is a large change in the electrical conductivity of SrFeO2.5+x thin-films when exposed to variations in oxygen partial pressure over a wide temperature range as shown in this and previous work. These changes are rapid and reversible at the temperature of the present work at 763 K. The chemical sensing properties of the subject perovskite are compared to two other perovskite materials. Many of the perovskite family of materials in the form of thin-films are well-suited to integration into microsensor devices on various substrate platforms.

SOL-GEL FILMS DOPED WITH SEMICONDUCTOR NANOCRYSTALS FOR OPTICAL APPLICATIONS

Sol-gel films doped with MeS (Me=Cd or Pb) nanocrystals or with MxOy (M=Ni or Co) nanocrystals have been fabricated. Two different strategies were used: for the sulfides a colloidal doping sol was prepared at room temperature and then mixed with the matrix sol. For the oxides a bifunctional ligand was used, bearing either an amine group capable of coordinating the M ions and hydrolysable siloxane groups for anchoring the metal complex moiety to the silicate matrix. In this case the oxide nanocrystals precipitate at 500°C. Films containing MeS nanocrystals showed both non-linear and active optical properties. Nanocomposite films doped with MxOy showed optical gas sensing properties.

Excimer laser annealing of perovskite thin films: morphology and gas-sensor properties

Pulsed laser annealing was used to modify surface morphology and to enhance crystallization of amorphous films of the p-type perovskite SrFeyCo1-yO2.5+x (y=0.5). The films were prepared by the pulsed laser deposition technique on sapphire substrates. Both film deposition and film annealing was done using a KrF excimer laser (wavelength = 248 nm). The effects of laser energy and pulse number on film morphology, structure and gas-sensing properties were investigated. An amorphous film did not show any sensor response to oxygen composition changes, while the same film after 80 pulses of annealing at 100mJ/cm2 showed a fast response at 300?C and 400?C. In comparison to a dense crystalline film deposited at 700?C, the annealed film showed a faster response to oxygen composition changes at 300?C.