研究目的
To develop and characterize liquid switchable radial polarization converters made of porous nanostructured sculptured thin films and multilayers using oblique angle physical vapor deposition, with a focus on their axisymmetric optical activity, wavelength-dependent response, and switchability through liquid infiltration.
研究成果
The study successfully developed porous nanostructured sculptured thin films and multilayers that function as radial polarization converters with axisymmetric optical activity. These devices exhibit wavelength-dependent responses tunable through multilayer design and are switchable via liquid infiltration, demonstrating reversibility. The one-step fabrication by physical vapor deposition offers advantages in simplicity and integration for applications in microfluidics and responsive optical devices, though the retardance is lower than conventional methods.
研究不足
The optical activity strength (retardance up to 0.35 rad) is lower than that of standard q-plates with half-wave retardation. The complex multilayer structure made spectroscopic ellipsometry fitting challenging due to the high number of variables. The method may have limitations in achieving higher retardance values or in applications requiring precise control over birefringence.
1：Experimental Design and Method Selection:
The study involved synthesizing porous nanostructured sculptured thin films and multilayers using electron beam evaporation at an oblique angle deposition (OAD) geometry. A specific geometrical setup with a slit mask was used to achieve axisymmetric microstructural arrangement. The methodology included physical vapor deposition with azimuthal sample rotation to create films with tailored birefringence.
2：Sample Selection and Data Sources:
Samples were deposited on fused silica plates or polished Si wafer substrates. Three types were prepared: single-layer TiO2 porous films (qTiO2), single-layer SiO2 porous films (qSiO2), and a Bragg microcavity multilayer (qBM) with a structure of HLHLHLH (H: TiO2, L: SiO2) and a central SiO2 defect layer. Data were sourced from SEM, UV-Vis transmission, spectroscopic ellipsometry (SE), and Mueller matrix (MM) polarimetry measurements.
3：List of Experimental Equipment and Materials:
Equipment included an electron beam evaporation system (brand not specified, model not specified), Hitachi S4800 field emission SEM, Varian Cary100 spectrophotometer, Woollam VASE spectroscopic ellipsometer, and a custom Mueller matrix polarimeter with photoelastic modulators. Materials included TiO2 and SiO2 pellets, fused silica substrates, Si wafers, and ethanol for infiltration.
4：Experimental Procedures and Operational Workflow:
Deposition was performed at a process pressure of 3x10-4 mbar with O2 inlet for oxidation, deposition rate of 0.1 nm/s, angle of incidence ~75°, and azimuthal rotation at ~30 rpm. Samples were characterized by SEM for microstructure, UV-Vis for transmission spectra, SE for thickness and birefringence mapping, and MM polarimetry for optical activity assessment. Liquid infiltration with ethanol was used to study switchability.
5：1 nm/s, angle of incidence ~75°, and azimuthal rotation at ~30 rpm. Samples were characterized by SEM for microstructure, UV-Vis for transmission spectra, SE for thickness and birefringence mapping, and MM polarimetry for optical activity assessment. Liquid infiltration with ethanol was used to study switchability.
Data Analysis Methods:
5. Data Analysis Methods: SE data were fitted using a biaxial model with effective medium approximation (Bruggeman model) to determine refractive indices and void percentages. MM data were analyzed to calculate linear birefringence (LB) magnitude and orientation using methods from references. Transmittance spectra were analyzed for wavelength dependence.
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