Szu Cheng Lai

Ultrasmooth silver thin film on PEDOT:PSS nucleation layer for extended surface plasmon propagation.

Poly(3,4-ethylene dioxythiophene):poly(styrene sulfonate) (PEDOT:PSS) layers are used as the nucleation (seed) layer to reduce surface roughness of the overlying silver (Ag). The technique leads to ultrasmooth Ag thin films with a minimum surface roughness of 0.8 nm. The mechanism contributing to the improvement is explained on the basis of better wetting of Ag on PEDOT:PSS, and properties of the nucleation layer on the aspects of surface energy, surface adhesive force, and surface morphology influencing Ag wetting and growth pattern are being discussed. The surface plasmon resonance (SPR) shows significant improvement, in terms of the Figure of Merits (FOM), as the surface roughness on Ag films is reduced. A lower light scattering and longer plasmon propagation of maximum 15.3 μm are also realized on a smoother Ag surface. The results indicate great potential on the application of combined PEDOT:PSS/Ag structure as an effective and economically feasible design solution for plasmonic and optical metamaterials devices.

Point defects analysis of zinc oxide thin films annealed at different temperatures with photoluminescence, Hall mobility, and low frequency noise

Zinc oxide (ZnO) thin films annealed at different temperatures were studied with photoluminescence (PL), electrical resistivity, Hall mobility, and 1/f noise spectroscopy. Relatively high electrical conductivity and carrier concentration in sample annealed at 400 °C suggested the presence of ZnO interstitials. Rapid reduction in electrical conductivity and carrier concentration upon increasing the annealing temperature suggested that ZnO interstitials could be eliminated by high temperature annealing. Presence of G-R noise in sample annealed at 400 °C indicated high level of electron trapping activities. Density of Zn vacancies acting as electron traps was estimated by Lorentzian fitting on the G-R noise. PL spectra exhibiting dominant green emission in all samples suggested the presence of Zn vacancies in high concentration. Yellow-orange emission in PL in samples annealed at 600 °C and below indicated the presence of O interstitials, while the same emission in samples annealed at higher temperatures wer...

An Ultraviolet (UV) Detector Using a Ferroelectric Thin Film With In-Plane Polarization

Different from the semiconductor photovoltaic device on the basis of an interfacial effect, UV detection was realized in this letter by using bulk photovoltaic mechanism involving the depolarization field in a W-doped Pb0.97La0.03(Zr0.52Ti0.48)O3 (PLWZT) ferroelectric thin film. A prototype of UV detector was demonstrated in the laboratory as well as under sunlight, in which the ferroelectric PLWZT thin film was polarized in the plane of the film surface. Characteristics of the photovoltaic response of the ferroelectric thin films and their application values for UV detection were analyzed.

A Photovoltaic UV Sensor With a Ferroelectric Thin Film on Transparent Substrate

A photovoltaic ultraviolet (UV) sensor is designed with a unique structure comprising of an in-plane polarized ferroelectric lead lanthanum zirconate titanate (PLZT) thin film on a transparent silica substrate and with an interdigital electrodes on the top surface. Both the experimental measurements and theoretical analyses showed that the UV sensor exhibited significantly enhanced responses with the incident UV irradiation input from the silica substrate in comparison with that from the top surface of the PLZT film. The proposed device configuration leads to a cost-effective scratch- and moisture-proof UV sensor with a flip-chip package, which promises great robustness for UV monitoring in harsh conditions.

A Ferroelectric Ultraviolet Detector With Constructive Photovoltaic Outputs

Photovoltaic outputs in semiconductor photodetectors are typically generated at an interfacial space charge region. Here, the output of our ultraviolet detector was enhanced by incorporating a photovoltaic output over the bulk of a ferroelectric thin film for providing a constructive photovoltaic effect in addition to the response from the interfacial mechanism. The working principle was demonstrated with a ferroelectric (Pb_0.97La_0.03)(Zr_0.52Ti_0.48)O₃ (PLZT) thin film sandwiched between a (La_0.7Sr_0.3)MnO₃ top electrode and a Pt bottom electrode, in which the depolarization electric field in the PLZT film was in the same direction with that at the Schottky barrier at the PLZT/Pt interface to realize the constructive photovoltaic effect.

Improved Photoelectrochemical Cell With Carbon Nanotubes

Single-walled carbon nanotubes (SWCNTs) were incorporated into a dye-sensitized titanium dioxide (TiO2)-based photoelectrode and characterized in a conventional three-arm system for water photolysis. Improvements in short-circuit current, efficiency, and lifetime were observed in the presence of an increase in SWCNT concentration at the TiO2-ITO (back-electrode) interface. The mechanism behind these improvements was explained on the basis of the SWCNTs acting as a conductive scaffolding network responsible for anchoring the TiO2 and transporting the photoelectrons to the back electrode.

A battery-less photo-detector enabled with simultaneous ferroelectric sensing and energy harnessing mechanism

A self-sustainable mechanism for simultaneously sensing and harnessing photon energy was proposed and implemented to create a battery-less and wire-less ultraviolet sensor made of ferroelectric lead lanthanum zirconate titanate thin film with in-plane polarization configuration. The mechanism involved accumulating and storing the photovoltaic charge, and transferring the stored charge via a piezoelectric switch to a radio frequency transmitter. The time-interval between the radio frequency pulses generated by the transmitter was inversely proportional to the photo-intensity. The sustainability of the operation was ascribed to the low leakage, high photovoltage, and linear current-voltage characteristics of ferroelectric sensing material instead of semiconductors.

Efficiency Optimization on Dye-Sensitized Solar Cells With Low-Frequency Noise Analysis

The effects of time durations for ZnO nanorod growth and dye loading on a ZnO-based dye-sensitized solar cells efficiency and 1/f low-frequency noise (LFN) spectral were analyzed. Sufficient time durations for ZnO growth and dye loading were required for achieving optimum photoconversion efficiency. Extending these two time parameters beyond the optimal, however, reduced the efficiency due to nanorod defects and dye agglomerations. The mechanisms inducing the change in the efficiency was reflected in the LFN spectral and explained on the basis of Kleinpennings noise equation and excessive noises in the presence of structural defects.