STRUCTURAL AND GAS-SENSING PROPERTIES OF ULTRAFINE FE2O3 PREPARED BY PLASMA-ENHANCED CHEMICAL-VAPOR-DEPOSITION

Ultrafine Fe2O3 powders have been obtained using the plasma enhanced c hemical vapor deposition (PECVD) method for the gas sensor application . Ferrocene is used as the precursor source in the PECVD powder prepar ation procedure. The structural properties of these ultrafine Fe2O3 po wders have been systematically characterized using X-ray diffraction ( XRD), transmission electron microscopy (TEM), differential thermal ana lysis (DTA), and thermogravimetric analysis (TGA). DTA results show th at the oxygen-rich atmosphere is more favorable than nitrogen for the burn-off of residual organic compounds in the precursor powders. It is interesting to note from TEM and X-ray diffraction patterns that beta - and gamma-Fe2O3 phases can co-exist with the alpha-Fe2O3 phase due t o the size effect, depending upon processing conditions. The activatio n energy as a function of temperature and grain size is estimated. It is found that at lower temperatures, the activation energy for crystal lization predominates; while at higher temperatures, the larger activa tion energy is attributed to the grain growth process. The gas sensiti vities and dynamic conductance measurement for these ultrafine Fe2O3 g as sensors have also been investigated. (C) 1997 Elsevier Science S.A.