Characteristics of titanium oxide films deposited by an activated reactive evaporation method
- PDF / 878,219 Bytes
- 6 Pages / 576 x 792 pts Page_size
- 60 Downloads / 187 Views
Yoshihiro Daitoh and Mikio Takano Institute for Chemical Research, Kyoto University, Uji, Kyoto-fu 611, Japan (Received 6 December 1993; accepted 3 February 1994)
Titanium di- and sesquioxide films were epitaxially grown on the (001) surface of sapphire single-crystalline substrates by an activated reactive evaporation method. Formation range for each titanium oxide was determined as a function of oxygen pressure (Po2) by means of x-ray diffraction, transmission electron microscopy, and Raman spectroscopy. Films prepared at P 02 & 2.0 X 10 ~4 Torr were stoichiometric (lOO)-oriented rutile of TiO2, and with decreasing P 02 they would accommodate more and more Ti3+ ions in the rutile structure. At P 02 = 0.6 X 10~4 Torr, on the other hand, (OOl)-oriented Ti 2 O 3 was formed and an electrical transition was clearly detected at about 400 K. However, the large lattice mismatch between the substrate and these films leads to a periodic introduction of misfit dislocations in the case of the TiC>2 films and a mixing of stacking sequences for the Ti 2 O 3 films.
I. INTRODUCTION Preparation and characterization of thin films of a variety of transition metal oxides are current subjects of materials science because of their interesting optical, electrical, or magnetic properties and also because of their potential applications as film devices.1'2 It is well known that certain oxides including titanium oxides change their properties sensitively with their metal to oxygen ratios. Rutile, TiC>2, has unique properties such as a high dielectric constant, a high refractive index, and a high resistivity, while its resistivity is decreased if it is reduced so that Ti3+ ions form in the structure.3"6 The titanium sesquioxide, Ti 2 O 3 , crystallizes in the corundum structure and shows a semiconductor-tometal transition.7'8 A bulk single-crystal of Ti 2 O 3 grown by a Czochralski-Kyropoulos method7 exhibited a drop of 102 Clem in a temperature range between 400 and 500 K on heating. There are many nonstoichiometric phases between TiO2 and Ti2O3 generating a homologous series formulated as Tin02«_i.9 Activated reactive evaporation is a powerful technique to prepare well-crystallized ceramic films with controlled stoichiometry. Metal atoms thermally evaporated in vacuum are condensed onto a substrate and react with an excited reactive gas. By modifying the evaporation conditions such as the substrate temperature, gas pressure, and evaporation rate, stoichiometry of deposited films can be controlled precisely. One of the most remarkable successes of this method is the growth of high-temperature superconducting films of YBa 2 Cu 3 O 7 _ 5 on SrTiO3 substrate crystals10 and of ferroelectric BaTiO3 films on a - A l 2 O 3 . n 1468 http://journals.cambridge.org
J. Mater. Res., Vol. 9, No. 6, Jun 1994 Downloaded: 08 Sep 2014
In the present work we have made an effort to determine the formation ranges of various titanium oxide films on a - A l 2 O 3 (001) substrates as a function of oxygen pressure. Well-crystallized titanium oxide films were
Data Loading...
