Microstructure and electrical properties of palladium oxide thin films for oxidizing gases detection

Palladium oxide thin and ultrathin films have been presented as promising materials for detection of oxidizing gases. PdO films were prepared by thermal oxidation of previously formed Pd layers on different substrates: SiO2/Si (100), Si (100), optical quality quartz, and KCl (100) with a buffer layer of amorphous carbon. By X-ray analysis, reflection high-energy electron diffraction, and high resolution transmission electron microscopy investigations it has been established that homogenous polycrystalline PdO films (thickness was about 5-40nm) were formed by oxidation at dry oxygen at temperatures T = 770-870 K. The experimental results of X-ray analysis and transmission electron microscopy have shown that the increase in oxidation temperature led to uniformity and enlargement of crystalline grains in homogeneous PdO films. It has been found that the energy band gap values increased monotonically from Delta E-g = 2.15 eV to 2.3 eV for PdO films with p-type conductivity oxidized at T-an = 670 K and 1070 K, respectively. At ozone detection PdO films fabricated on polished poly-Al2O3 have shown high values of sensitivity, signal stability, and reproducibility of sensor response. For fabrication of gas sensors the application of PdO thin and ultrathin films has some advantages in comparison with other materials because PdO films have shown good values of sensor functional parameters, and their synthesis procedure is rather simple and is compatible with planar processes of the microelectronic industry also. (C) 2017 Elsevier B.V. All rights reserved.