Density and refractive index of TiO2 films prepared by reactive evaporation

Mergel, Dieter; Buschendorf, D; Eggert, Stefan; Grammes, R; Samset, B. H.

doi:10.1016/s0040-6090(00)01015-4

Cited by 213 publications

(130 citation statements)

References 10 publications

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“…Table II summarizes the pertinent values obtained. A key finding of the molecular dynamics modelling study was that, in the NPT ensemble, all of the preexisting potential models tested would drive the system towards a density much lower than expected from the experimental measurements [39] (Table I). As discussed above, the potentials of this work and the modified Teter potentials were adjusted in order to give the expected density at 2250 K. Figure 1 compares the densities obtained with these two sets of potentials over a wide temperature range, where they show excellent agreement with experimental data, including that for the densest (lowest porosity [17]) amorphous TiO 2 films at room temperature. Fig.…”

Section: Resultsmentioning

confidence: 78%

“…These were however conducted at fixed densities, independent of temperature, with the lowest liquid density used, 3.80 g cm -3 , corresponding to that of dense amorphous TiO 2 films [17], and much higher than the measured values [39] for the liquid. The structure and properties thus derived are therefore more pertinent to the high pressure liquid, where both density and coordination numbers would be higher.…”

Section: +mentioning

confidence: 93%

“…The apparent temperature was corrected using a Wien's displacement law approximation [34] with a spectral emissivity value of 0.87 for the molten TiO 2 at the pyrometer wavelength of 0.85 μm. The emissivity value was estimated from the Fresnel losses for a material with a refractive index of 2.1, which is the value appropriate to amorphous TiO 2 [17] at the density of the melt. The pyrometer temperature was also corrected for reflection losses from a window and lens that were in the optical path.…”

Section: A Diffraction Measurementsmentioning

confidence: 99%

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Structure of molten titanium dioxide

et al. 2014

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The x-ray structure factor of molten TiO 2 has been measured for the first time, enabled by the use of aerodynamic levitation and laser beam heating, to a temperature of T = 2250(30) K. Ti-O coordination number in the melt is close to n TiO = 5.0(2), with modal Ti-O bond length r TiO = 1.881(5) Å, both values being significantly smaller than for the high temperature stable Rutile crystal structure (n TiO = 6.0, r TiO = 1.959 Å). The structural differences between melt and crystal are qualitatively similar to those for alumina, which is rationalized in terms of the similar field strengths of Ti 4+ and Al 3+. The diffraction data are used to generate physically and chemically reasonable structural models, which are then compared to the predictions based on various classical molecular dynamics (MD) potentials. New interatomic potentials, suitable for modelling molten TiO 2 , are introduced, given the inability of existing MD models to reproduce the diffraction data. These new potentials have the additional great advantage of being able to predict the density and thermal expansion of the melt, as well as solid amorphous TiO 2 , in agreement with published results. This is of critical importance given the strong correlation between density and structural parameters such as n TiO . The large thermal expansion of the melt is associated with weakly temperature dependent structural changes, whereby simulations show that n TiO = 5.85(2) -(3.0(1) x 10 -4 )T (K, 2.75 Å cut-off). The TiO 2 liquid is structurally analogous to the geophysically relevant high pressure liquid silica system at around 27 GPa. We argue that the predominance of 5-fold polyhedra in the melt implies the existence of as yet undiscovered TiO 2 polymorphs, based on lowerthan-octahedral coordination numbers, which are likely to be metastable under ambient conditions. Given the industrial importance of titanium oxides, experimental and computational searches for such polymorphs are well warranted.

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Section: Resultsmentioning

confidence: 78%

Section: +mentioning

confidence: 93%

Section: A Diffraction Measurementsmentioning

confidence: 99%

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Structure of molten titanium dioxide

et al. 2014

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“…1,2 In particular, both the optical constants of films used in optics and their evolution in depth are very much dependent on the thin film microstructure. [3][4][5][6][7][8] Most works in literature addressing this question refer to thin films prepared by evaporation, while other procedures such as plasma enhanced chemical vapor deposition ͑PECVD͒ have not received similar attention.…”

Section: Introductionmentioning

confidence: 99%

Relationship between scaling behavior and porosity of plasma-depositedTiO2thin films

et al. 2007

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The growth of TiO 2 thin films prepared by plasma enhanced chemical vapor deposition has been studied by analyzing their roughness with the concepts of the dynamic scaling theory. Differences in the growth and roughness exponents have been found depending on the composition of the plasma by using either O 2 or mixtures Ar+ O 2 as plasma gas and titanium isopropoxide as the precursor. The slope of the representations of the film roughness against the deposition time yielded values of the exponent ␤ of 0.45 and 0.32 for, respectively, thin films prepared with plasmas of O 2 or mixtures Ar+ O 2 . Meanwhile, values of the exponent ␣ of 1.15 and 1.89/0.35 were deduced from the power spectral density representations for the films prepared under these two experimental conditions. These values are congruent with growth processes dominated, respectively, by shadowing or diffusion processes. A columnar microstructure was observed by scanning electron microscopy for the thin films prepared with pure oxygen. Meanwhile, homogeneous films were obtained with mixtures of Ar+ O 2 . The open porosity of the films was determined by measuring water adsorption-desorption isotherms with a quartz crystal monitor. This analysis showed that in the samples prepared with mixtures of Ar+ O 2 the porosity consisted exclusively of micropores ͑d Ͻ 2 nm͒, while in the films prepared with an oxygen plasma there were micro-and meso-pores ͑d Ͼ 2 nm͒. It is concluded that the different growth mechanisms found by just changing the chemistry of the plasma are responsible for the quite distinct microstructures, porosities, and optical properties obtained for the films.

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“…13 The high refractive index (n = 2.49) means that the TiO 2 film has a high packing density, since refractive indexes are proportionally related to densities of films. 13,22 Figure 3(a) and 3(b) show typical scanning electron microscope (SEM) images for a fabricated linear TiO 2 waveguide and its cross section, respectively. The top of the waveguide has a smooth surface.…”

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confidence: 99%

Development of microfabricated TiO2 channel waveguides

et al. 2011

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An optical channel waveguide is a key solution to overcome signal propagation delay. For the benefits of miniaturization, development of microfabrication process for waveguides is demanded. TiO2 is one of the suitable candidates for the microfabricated waveguide because of the high refractive index and the transparency. In the present study, conventional microfabrication processes manufactured TiO2 channel waveguides with 1-20 μm width on oxidized Si substrates and the propagation loss was measured. The prepared channels successfully guided light of 632.8 nm along linear and Y-branched patterns. The propagation loss for the linear waveguide was 9.7 dB/cm

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Density and refractive index of TiO2 films prepared by reactive evaporation

Cited by 213 publications

References 10 publications

Structure of molten titanium dioxide

Structure of molten titanium dioxide

Relationship between scaling behavior and porosity of plasma-depositedTiO2thin films

Development of microfabricated TiO2 channel waveguides

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