Rutiles films

Titanium dioxide, Ti02, has three stable allotropic forms the low temperature phases of anatase and brookite and the stable high temperature phase of rutile. Initial reports of CVD Ti02 films using Ti(0-i-Pr)4 in the presence of O2 described the deposition of anatase films over the temperature range of 320-750°C [122], Whereas, studies using Ti(OEt)4 (b.p. = 102°C, 0.05 Torr) as the precursor showed that rutile films are formed at substrate temperatures below 500°C or if high mass flows [123]. 

In addition to electron diffraction, the measurement of the film refractive index also enables distinction between anatase and rutile. According to Hass [27], polycrystalline rutile films have a refractive index value of 54 = 2.70 and that of the anatase films is 546 = 2.39. 

The optical properti es of thin polycrystalline films are influenced by the extent of grain orientation, which is also manifested in the Raman band intensities for vibrational modes of different symmetry. Figure 9a illustrates the two strongest Raman active modes for the rutile phase of Ti02. The Eg assigned mode exhibits a vibrational frequency of 444 cm"l, while the frequency for the Aig mode is 608 cm l. A series of 0.6 micrometer thick rutile films with variable ordering in the grain structure was prepared by sputter deposition techniques. Refracti ve indices... 

Intensity Analysis of Raman Scattering Characterizes Columnar Grain Orientation in Polycrystalline Rutile Films... 

One of the attributes of Raman spectroscopy is the ability to discern different crystalline (or amorphous) phases having the same stoichiometry. Figure 10 depicts several Raman spectra of mixed anatase/ruti1e phase films of Ti02 sputter deposited on silica. The phase composition can easily be discerned from measured band intensities. In fact, trace amounts of anatase in rutile films (.1 wt%) can be determined from the magnitude of the 143 cm"l anatase feature, which is a factor of ten more intense than vibrational bands intrinsic to other phases of Ti02. 

Murata and coworkers have thermally prepared rutile films on alloys of Ti with various 4d and 5d transition metals [133]. 

The actual surface and in-depth composition of the mixed oxide films (Ti02)o 6(Ta205)o 2 treated at 200°C and 800°C was studied by XPS. Figure 3.13 shows the survey spectra of the rutile film (Ti02)o6(Ta205)o.2 treated at 200°C (a) and at 800°C (b) after 30 min of sputtering, which demonstrates the presence of Ti and Ta for both films. 

Dip coating. A solution or a sol dispersion of the precursor is first prepared. Then the substrate is vertically introduced in the solution or dispersion and slowly pulled out the covered substrate is then dried and the film formed upon calcination. The method has been used to prepare anatase, brookite, or rutile films [61]. The width of the film depends on the pulling rate, viscosity, and density of the liquid medium, its concentration, the liquid-vapor surface tension, and the temperature. 

Figure 3.25 shows an example where 30% higher current was achieved when anatase was used compared with rutile. The SEM studies of the particle shape and size showed that the surface area of the rutile film was about 25% less than that of anatase film. The absorption spectra showed... 

Langmuir-Blodgett films (LB) and self assembled monolayers (SAM) deposited on metal surfaces have been studied by SERS spectroscopy in several investigations. For example, mono- and bilayers of phospholipids and cholesterol deposited on a rutile prism with a silver coating have been analyzed in contact with water. The study showed that in these models of biological membranes the second layer modified the fluidity of the first monolayer, and revealed the conformation of the polar head close to the silver [4.300]. 

General Titanium is intrinsically very reactive, so that whenever the metal surface is exposed to air, or to any environment containing available oxygen, a thin tenacious surface film of oxide is formed. This oxide, which is present on fabricated titanium surfaces at normal or slightly elevated temperatures, has been identified as rutile, a tetragonal form of titanium dioxide, and it is the presence of this surface film which confers upon titanium excellent corrosion resistance in a wide range of corrosive media. 

It is a valve metal and when made anodic in a chloride-containing solution it forms an anodic oxide film of TiOj (rutile form), that thickens with an increase in voltage up to 8-12 V, when localised film breakdown occurs with subsequent pitting. The TiOj film has a high electrical resistivity, and this coupled with the fact that breakdown can occur at the e.m.f. s produced by the transformer rectifiers used in cathodic protection makes it unsuitable for use as an anode material. Nevertheless, it forms a most valuable substrate for platinum, which may be applied to titanium in the form of a thin coating. The composite anode is characterised by the fact that the titanium exposed at discontinuities is protected by the anodically formed dielectric Ti02 film. Platinised titanium therefore provides an economical method of utilising the inertness and electronic conductivity of platinum on a relatively inexpensive, yet inert substrate. 

Polycrystalline oxide materials, both undoped and doped, have been extensively examined for use as photoanodes. Ti02 electrodes have been prepared by thermal oxidation of a Ti plate in an electric furnace in air at 300-800°C (15-60 min) and in a flame at 1300°C (20 min) [27-30]. XRD analysis of thermally oxidized samples indicates the formation of metallic sub-oxide interstitial compounds, i.e. TiOo+x (x < 0.33) or Ti20i y (0 < y < 0.33) and Ti30 together with rutile Ti02 [27]. The characteristic reflection of metallic titanium decreases in intensity after prolonged oxidation (60 min) at 800° C indicating the presence of a fairly thick oxide layer (10-15 pm). Oxidation at 900°C leads to poor adhesion of the oxide film... 

Pilling-Bedworth ratio of 1 96, anatase phase films can show cracks and fissures with, consequendy, a loss of mechanical stability, however a hydrogen reduction treatment above 600°C leads to phase transition from anatase (101) to rutile (110) [43] with XRD detecting TiH2 upon prolonged hydrogen treatment of titania. As shown in Fig. 4.4, introduction of vanadium increases the intensity of the anatase Ti02 peak above 700°C disappearance of the vanadium (001) peak and the simultaneous appearance of the rutile (110) peak are observed, but anatase continues to dominate even after heat treatment at 800° C. A sharp vanadium (001) peak is observed for heat treatments carried out in air, while no vanadium peak has been seen in the case of heat treatment at 600°C in presence of Ar/H2. 

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