ABSTRACT
In this work, we present the optical birefringence properties of the optical fiber cladding that exists as an evanescent field where the refractive index (RI) of the analysis solution is applied for optical sensor aspiration. To enhance the performance of the sensor, we have investigated the sensor with different thicknesses of TiO2 coating and bimetallic (Ag-Al) film alloy combinations by thermal evaporation coating. We described a special balanced homodyne detection method for the intensity difference change between the p- and s-polarization lights in the surface plasmon resonance sensing systems, which is strongly determined by the RI of the test medium. The plasmonic optical fiber can measure a very small change of the RI of a glycerol solution, which is a resolution of 4.37 × 10-8 RI unit (RIU). This method has great advantages of a small-sized optical setup, high stability, high selectivity, easy chemical modification, and low cost. Furthermore, because of the experiment results, we observe that our approach can also eliminate the surrounding noise in the Mach-Zehnder interferometer, which shows the feasibility of this proposed technique. We demonstrate the fluorescence enhancement in detecting the C-reactive protein antibody conjugated with fluorescein isothiocyanate by means of near-field coupling between surface plasmons and fluorophores at spectral channels of emission. This technique can also be extended for application in a biomedical assay and in biochemical science, including molecular diagnostics relying on multichannels that require a small volume of the analyte at each channel which would suffer from the weakness of fluorescence if it were not for the enhancement technology.
ABSTRACT
The transparent-conducting performance is estimated through figure-of-merit (FOM) value. To improve poor FOM value of pure ZnO thin films, boron (B) as a donor impurity was doped into the films. Direct-current magnetron sputtering was used to prepare B-doped ZnO (BZO) thin films from sintered ZnO targets with variable B2O3 content changing from 0 to 2 wt. %. The x ray diffraction analysis confirmed the preferably c-axis-oriented structure of hexagonal wurtzite ZnO host. The results also showed variation in the film structure versus the B2O3 content through calculations of crystal size and residual stress. Depending on the B2O3 content, a competition of interstitial and substitutional B3+ ions induced more stress or relaxation in lattice structure of the films. At 1% B2O3, the BZO thin film had the best crystalline characterization with the lowest stress and large crystal size. In consequence, the BZO 1% film obtained the lowest resistivity of 2.7×10-3Ωcm, average transmittance of 82.1%, and the best FOM value of 18.8×102Ω-1cm-1. The transparent-conducting performance of the ZnO thin films deposited by direct-current (DC) magnetron sputtering was significantly enhanced through B doping. The good-performance BZO film at 1% B2O3 is believed to be of use as electrodes in thin-film solar cells.