Three types of amorphous-titania films prepared by ion- and electron-beam techniques have been annealed thermally. An amorphous-crystalline transformation is found in each of these film types at around 350 °C. Its resulting microcrystalline structure and the exact transition temperature appear to be dictated by the rutile microcrystalline seed present in the as-deposited films under different deposition conditions. An amorphous film with a weak rutile seed crystallizes at a lower temperature into the anatase structure, while a film with a relatively strong rutile base crystallizes into the rutile structure at a somewhat higher temperature. It is demonstrated that Raman spectroscopy is a simple and effective tool for characterization of these submicron-thick amorphous films and for the dynamical study of such a phase transformation. Accompanying this amorphous-crystalline transformation, a two-order increase in elastic light scattering is noted implying optical degradation associated with microcrystalline boundaries. In addition, results of the anatase–rutile transformation at a temperature near 900 °C are presented.
Nonequilibrium growth of thin-film ternary ZnS1−xSex semiconductor alloys was accomplished using physical vapor deposition with simultaneous electron cyclotron resonance H2S plasma activation. Substrate temperature, gas flow, and plasma power determine the ZnS1−xSex alloy composition and structure. Integrated optical transmission spectra for the ZnS1−xSex semiconductor alloys as a function of H2S plasma power are presented. Using the α2 vs hν plots for the various ZnS1−xSex films, the optical band gap Eg is extrapolated from each curve. This methodology yields the values of the band gap as a function of stoichiometry. We observe that the plasma induced isoelectronic substitution of S into the ZnSe lattice increases the band gap. This study shows that plasma-induced isoelectronic substitution is technologically feasible and useful for fabricating ternary II–VI alloys under nonequilibrium conditions.
Thin films of zirconium dioxide were produced by ion-beam sputter deposition onto fused silica substrates. The deposition process involved a Kaufman-type ion source with ion energy of 1100 eV, beam current density 1.5 mA/cm2, and argon to oxygen ratio of 40:60. Raman scattering was used to monitor crystallization. When the zirconia film was thermally annealed in air, it first crystallized into a mixed tetragonal and monoclinic phase at 450 °C. Further heating beyond 900 °C showed a transformation to a cubic phase. The crystalline transformations decreased the film refractive index from 2.2 to 2.0, significantly increased both the optical absorption and scattering, and lowered the optical band gap from 3.8 to 3.2 eV.
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