HfO2 thin films are extensively applied in optical coatings and microelectronic devices. However, film defects, which are vital to the performance of the thin films, are still under intense investigation. In this work, the absorption, photoluminescence, and crystallization characteristics of HfO2 films prepared by electron-beam evaporation and ion-assisted deposition are investigated in detail. Experimental results showed that high-temperature thermal annealing in air resulted in a reduced absorption coefficient, an increased bandgap width, and an increased degree of crystallization. After thermal annealing, an absorption shoulder near 5.8 eV was caused by excitons in the films, which were independent of oxygen vacancy defects and crystallization. Under 6.4 eV (193 nm) laser excitation, the photoluminescence spectrum showed five emission peaks for HfO2 films both with and without thermal annealing. The emission peak near 4.4 eV was generated by the self-trapped exciton, and the peak near 4.0 eV was related to the OH group in the film. The oxygen vacancy defect-induced absorption of HfO2 films in a broad spectral range significantly increased when HfO2 film was re-annealed in Ar gas after first being annealed in air, while the photoluminescence spectrum showed no significant change, indicating that the emission peaks at 2.3, 2.8, and 3.4 eV were not related to oxygen vacancy defects.
A straightforward theoretical routine is proposed to design shadowing masks which are used for preparing uniform coatings on flat as well as strongly curved spherical substrates with large diameters in planetary rotation system. By approximating a spherical substrate in planetary rotation to a corresponding flat substrate in simple rotation around the revolution axis, the initial shape of a shadowing mask is determined. The desired uniformity for the spherical substrate is further realized through expanding appropriately the arc length of the initial shadowing mask. Utilizing the shadowing masks designed with the theoretical routine, film uniformities better than 97% are experimentally achieved for large-diameter spherical substrates with ratios of clear aperture to radius of curvature range from approximately -1.0 to 1.3.
A model taking into consideration the refractive index inhomogeneity and surface roughness of a film was proposed for the simultaneous determination of the optical constants, thickness, and surface roughness of a single-layer thin film from spectrophotometric measurements. In the model, the rough surface was treated as an effective absorbing layer. The model was applied to determine simultaneously the parameters of single-layer MgF(2) thin films deposited on fused silica substrates by the oblique-angle deposition technique. The film thicknesses and rms surface roughnesses extracted from spectrophotometric measurements with the proposed model were in good agreement with the values measured by a spectroscopic ellipsometer and an atomic force microscope, respectively.
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