Thin films in the Cr-Ti-O system were atomic layer deposited from CrO2Cl2, TiCl4, and CH3OH on Si(1 0 0), fused SiO2, and a-Al2O3(0 1 2) substrates at 420 oC. The proportion between Ti and Cr resulted from the ratio of the
CrO2Cl2/CH3OH and TiCl4/CH3OH pulsing. The films were grown up to the thickness of about 70 nm. Annealing of the
films was performed in O2 at 1000 oC. A notable dependence of their microstructure, conductance, and conductometric
response to CO, H2, and CH4 in dry air on the substrates, Ti content, and annealing has been demonstrated. The films
were polycrystalline on Si and SiO2, and epitaxial on a-Al2O3. At temperatures above 400 oC, the films had a conductance, advantageous from the point of view of semiconductor gas sensors. In response to a 30-ppm CO exposure
at 450 oC, an annealed film on the a-Al2O3(0 1 2) substrate, distinguished by a relatively high Ti/Cr atomic ratio,
showed a 16-% conductance decrease in 20 s, with a 120-s recovery.
Atomic layer deposition (ALD) of SnO2 thin films from SnI4 and either H2O2 or O2 on the α-Al203(1 1- 2) substrates is
studied. Reactor temperature is varied from 100 to 750 °C. X-ray diffaction, x-ray reflection, x-ray fluorescence, x-ray
photoelectron spectroscopy, reflection high-energy electron diffraction, and UV-visible spectroscopy are used to obtain
the growth and structural data. The SnI4-H202 precursor pair brings forth the film growth even at temperatures as low as
100°C with a wholly amorphous outcome up to 150°C. For the pair SnI4-02, the films grown nearby the process
initiation temperature of 400°C are also amorphous. When the temperature is raised respectively above 250 and 500°C,
both pairs make epitaxial growth happen, generally in three-dimensional mode. Exceptionally, in a limited range of
grown thicknesses in the proximity of 50 nm, the growth from SnI4 and O2 at 750°C appears to be driven by the
predominantly two-dimensional nucleation, as the films grow extremely flat. The SnI4-02 precursor pair gives at 600-
750°C the highest growth per cycle of about 0.085 nm. The epitaxially grown tetragonal (cassiterite) films are (1 0 1)-
oriented. The iodine contamination in them is below 0.1%. All the film-substrate structures are highly transparent in the
visible region.
In order to characterize TiO2 films in terms of the overall optical response, spectroscopic ellipsometry studies of the system TiO2/Si were carried out. The films were grown by the atomic-layer chemical vapor deposition on Si(111) substrates. Optical measurements were performed by means of a photometric ellipsometer with rotating analyzer. Experimental results have been analyzed using multilayer and pseudodielectric function approximations.
The initial atomic-layer-chemical-vapor-deposition growth of titanium dioxide from TiCl4 and water on quartz glass substrates is monitored in real time by incremental dielectric reflection. An interesting means for bringing the growth from the very beginning into a time-homogeneous mode is proposed and preliminarily studied. It consists in an in situ TiCl4-treatment procedure. The crystal structure and surface morphology of the prepared ultrathin films are characterized.
The possibilities of the in situ real-time Brewster-angle interferometric reflectance probe to follow cycle-dependent film-quality changes during the atomic layer deposition (ALD) are investigated. Experiments are centered around the growth of amorphous TiO2 thin films on fused quartz substrates in a traveling-wave reactor using TiCl4 and H2O as reactants. It is concluded that ALD has prospects for the preparation of microstructurally homogeneous low- optical-loss TiO2 films in case the precise thickness control is needed. The main problem is the microporosity of the films and as a result their moderate refractive index.
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