研究目的
To determine the optical properties (refractive indices, absorption coefficients, and optical band gaps) of as-deposited and annealed BST thin films deposited by RF magnetron sputtering under varying conditions, and relate these properties to deposition and post-deposition treatments for light-based applications.
研究成果
Annealing BST thin films leads to densification, increased refractive indices, thickness shrinkage, and deteriorated transparency, especially for films deposited at higher temperatures and with oxygen. As-deposited films are recommended for light-based applications due to better-defined optical properties. Optical band gaps range from 3.6 to 4.5 eV, dependent on deposition conditions, enabling band gap and refractive index engineering for optoelectronic applications.
研究不足
The study is limited to specific deposition conditions (substrate temperatures and gas mixtures) and annealing at 900°C; no exact knowledge of Ba to Sr content in films is available. Transmittance of some annealed samples could not be satisfactorily fitted, indicating potential issues in measurement or analysis. The findings may not generalize to other deposition techniques or compositions.
1：Experimental Design and Method Selection:
BST thin films were deposited on Si wafer and SiO2 substrates using RF magnetron sputtering with variations in substrate temperature and gas atmosphere (Ar or Ar+O2). Post-deposition annealing at 900 °C was performed. Optical transmittance spectroscopy and XRD measurements were used to analyze structure and optical properties. A global optimization procedure based on genetic algorithm and Tauc-Lorentz dispersion model was employed for data analysis.
2：2). Post-deposition annealing at 900 °C was performed. Optical transmittance spectroscopy and XRD measurements were used to analyze structure and optical properties. A global optimization procedure based on genetic algorithm and Tauc-Lorentz dispersion model was employed for data analysis.
Sample Selection and Data Sources:
2. Sample Selection and Data Sources: Samples No. 21-25 were prepared with different deposition temperatures (RT, 100°C, 400°C) and gas mixtures. Data were collected from transmittance spectra (190-1100 nm) and XRD patterns.
3：List of Experimental Equipment and Materials:
BOC Edwards TF 600 coating system for sputtering, Ba0.1Sr0.9TiO3 target (3 inch, 99.9 at.% purity), Kla Tencor Profilometer for thickness measurement, Anton Paar 1200 high-temperature chamber for annealing, XPert Pro automatic powder diffractometer for XRD, Specord 210 spectrophotometer for transmittance measurements.
4：1Sr9TiO3 target (3 inch, 9 at.% purity), Kla Tencor Profilometer for thickness measurement, Anton Paar 1200 high-temperature chamber for annealing, XPert Pro automatic powder diffractometer for XRD, Specord 210 spectrophotometer for transmittance measurements.
Experimental Procedures and Operational Workflow:
4. Experimental Procedures and Operational Workflow: The deposition chamber was evacuated to 2×10-4 Pa base pressure. Target surface was cleaned by sputtering. Films were deposited at 400 W RF power, 0.6 Pa pressure, with Ar flow at 5 sccm and O2 at 0.25 sccm for some samples. Thickness was measured. Annealing was done at 900°C. XRD was performed using Bragg-Brentano and Seemann-Bohlin geometries. Transmittance was measured at normal incidence.
5：6 Pa pressure, with Ar flow at 5 sccm and O2 at 25 sccm for some samples. Thickness was measured. Annealing was done at 900°C. XRD was performed using Bragg-Brentano and Seemann-Bohlin geometries. Transmittance was measured at normal incidence.
Data Analysis Methods:
5. Data Analysis Methods: Refractive indices and absorption coefficients were extracted from transmittance spectra using genetic algorithm optimization and Tauc-Lorentz model. Optical band gaps were determined via Tauc plots and iso-absorption levels (E04). Crystallite sizes were analyzed using Voigt function line profile analysis.
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