Ding-Wei Huang

Plasmonic ZnO/Ag Embedded Structures as Collecting Layers for Photogenerating Electrons in Solar Hydrogen Generation Photoelectrodes

A new fabrication strategy in which Ag plasmonics are embedded in the interface between ZnO nanorods and a conducting substrate is experimentally demonstrated using a femtosecond-laser (fs-laser)-induced plasmonic ZnO/Ag photoelectrodes. This fs-laser fabrication technique can be applied to generate patternable plasmonic nanostructures for improving their effectiveness in hydrogen generation. Plasmonic ZnO/Ag nanostructure photoelectrodes show an increase in the photocurrent of a ZnO nanorod photoelectrodes by higher than 85% at 0.5 V. Both localized surface plasmon resonance in metal nanoparticles and plasmon polaritons propagating at the metal/semiconductor interface are available for improving the capture of sunlight and collecting charge carriers. Furthermore, in-situ X-ray absorption spectroscopy is performed to monitor the plasmonic-generating electromagnetic field upon the interface between ZnO/Ag nanostructures. This can reveal induced vacancies on the conduction band of ZnO, which allow effective separation of charge carriers and improves the efficiency of hydrogen generation. Plasmon-induced effects enhance the photoresponse simultaneously, by improving optical absorbance and facilitating the separation of charge carriers.

Fast fabrication of a Ag nanostructure substrate using the femtosecond laser for broad-band and tunable plasmonic enhancement.

Using a femtosecond laser, we have transformed the laser-direct-writing technique into a highly efficient method that can process AgO(x) thin films into Ag nanostructures at a fast scanning rate of 2000 μm(2)/min. The processed AgO(x) thin films exhibit broad-band enhancement of optical absorption and effectively function as active SERS substrates. Probing of the plasmonic hotspots with dyed polymer beads indicates that these hotspots are uniformly distributed over the treated area.

Three‐Dimensional Plasmonic Micro Projector for Light Manipulation

photovoltaics, [ 5 ] super-resolution imaging, [ 6 ] and various twodimensional plasmonic lens. [ 7 ] Besides, using nanostructures to project SPP plane waves into the adjacent free space is also an important issue. The interactions of plasmonic nanostructure on SPP wave involve not only the in-plane behavior, but also out-of-plane scattering which is captured as the far-fi eld radiated light. [ 8 ] A few theoretical approaches to convert the confi ned surface plasmons into radiated waves have been proposed. [ 9 ] It is highly desirable to extend the application range of plasmonic devices into the domain of three-dimensional light manipulation. [ 10 ] Recently, three-dimensional focusing and diverging of SPP waves by a quarter circular structure composed of gold (Au) nanobumps were studied. [ 11 ] The forward and backward scattering from individual Au nanobump are observed above and below Au surface, respectively. Hence, the Au nanobumps confer additional three-dimensional propagating wave vectors ( k x , k y , k z ) on SPP wave for departing from surface. Therefore, it is possible to manipulate the three-dimensional plasmonic scattering into specifi c geometry by arranging the Au nanobumps, which is schematically depicted in Figure 1 a. In this paper, we manipulate the scattering of SPP waves by various plasmonic structures composed of arranged nanobumps on a gold thin fi lm. Upon controlling the geometry of the plasmonic structures, the height, position, and pattern of scattered light can be modifi ed as desired. It provides a simple and effi cient way to project a specifi c light pattern into free space, and demonstrate the capability of three-dimensional light manipulation.

Reconstruction of fiber grating refractive-index profiles from complex Bragg reflection spectra

Reconstruction of the refractive-index profiles of fiber gratings from their complex Bragg reflection spectra is experimentally demonstrated. The amplitude and phase of the complex reflection spectrum were measured with a balanced Michelson interferometer. By integrating the coupled-mode equations, we built the relationship between the complex coupling coefficient and the complex reflection spectrum as an iterative algorithm for reconstructing the index profile. This method is expected to be useful for reconstructing the index profiles of fiber gratings with any apodization, chirp, or dc structures. An apodized chirped grating and a uniform grating with a depression of index modulation were used to demonstrate the technique.

Fabrication of three-dimensional plasmonic cavity by femtosecond laser-induced forward transfer

We fabricated a three-dimensional five-layered plasmonic resonant cavity by low-cost, efficient and high-throughput femtosecond laser-induced forward transfer (fs-LIFT) technique. The fabricated cavity was characterized by optical measurements, showing two different cavity modes within the measured wavelength region which is in good agreement with numerical simulations. The mode volume corresponding to each resonance is found to be squeezed over 10(4) smaller than the cube of incident wavelength. This property may facilitate many applications in integrated optics, optical nonlinearities, and luminescence enhancement, etc.

Multi-level surface enhanced Raman scattering using AgOx thin film.

Ag nanostructures with surface-enhanced Raman scattering (SERS) activities have been fabricated by applying laser-direct writing (LDW) technique on silver oxide (AgOx) thin films. By controlling the laser powers, multi-level Raman imaging of organic molecules adsorbed on the nanostructures has been observed. This phenomenon is further investigated by atomic-force microscopy and electromagnetic calculation. The SERS-active nanostructure is also fabricated on transparent and flexible substrate to demonstrate our promising strategy for the development of novel and low-cost sensing chip.

Surface plasmon resonance in a hexagonal nanostructure formed by seven core shell nanocylinders

A hexagonal nanostructure formed by seven core shell nanocylinders filled with different dielectric cores is investigated. The surface plasmon resonance in such a hexagonal nanostructure under conditions of different illumination wavelengths, dielectric cores, angles of incidence, and thicknesses of silver shells is studied by use of the finite element method. Simulation results show that the resonant wavelength is redshifted as the dielectric constant and the size of the core increase. The peak resonant wavelength and the local field enhancement are approximately proportional to the radius of the dielectric core. Additionally, the surface plasmon field excited by TM-polarized light at the incident angle of theta=15 degrees is exactly a linear combination of those excited at incident angles of theta=0 degrees and 30 degrees, confirming the linear nature of the surface plasmon resonance in a nanostructure formed by linear media.

Cell death detection by quantitative three-dimensional single-cell tomography.

Ultrahigh-resolution optical coherence tomography (UR-OCT) has been used for the first time to our knowledge to study single-cell basal cell carcinoma (BCC) in vitro. This noninvasive, in situ, label-free technique with deep imaging depth enables three-dimensional analysis of scattering properties of single cells with cellular spatial resolution. From three-dimensional UR-OCT imaging, live and dead BCC cells can be easily identified based on morphological observation. We developed a novel method to automatically extract characteristic parameters of a single cell from data volume, and quantitative comparison and parametric analysis were performed. The results demonstrate the capability of UR-OCT to detect cell death at the cellular level.

Approach the angular sensitivity limit in surface plasmon resonance sensors with low index prism and large resonant angle

Surface plasmon resonance (SPR) sensors have been studied thoroughly for the past two decades. However, we found that the angular sensitivity in a prism-coupled SPR sensor can be as high as 500 deg/refractive index unit (RIU), which is two times higher than the sensitivity that has ever been achieved in previous studies. Such a high angular sensitivity can be fully achieved by simply choosing a proper low-index prism and a sufficiently large resonant angle for the light signal at an appropriate wavelength with an optimal metal film thickness. A feasible implementation of such an SPR sensor design concept was also proposed, and an even higher sensitivity of 600 deg/RIU can be achieved.

Numerical Study on Strain Measurements Using the Improved Bonding Fiber Bragg Grating

This study suggests an improved bonding method for a surface mounted fiber Grating strain sensor to significantly reduce the mechanical influences from the surrounding cement of a glued fiber grating in the conventional bonding method. The linear relationship between the voltage signals and the average strains within the glue-free fiber grating is the advantage of the improved bonding method over the conventional bonding method (distributing cement along the full fiber grating). The numerical computations based on the coupled-mode theory were conducted to obtain the reflection spectra of a fiber grating, that are induced from different strain fields. The one-dimensional strain fields, that vary linearly within a fiber grating, were considered in this research. In addition, the filtered spectral power interrogation system to obtain the voltage signals from an optical fiber framework was taken in consideration. The filtered spectral power interrogation system is economic, compact, and suitable for on site measurements compared with other systems such as the optical spectrum analyzer. For a glued fiber grating, results show that the distortions in shape and the dilations in area of its reflection spectrum are because of the varied strain gradients within the grating during a strain history. Also, the central wavelength shifts of a reflection spectrum are related to the average strains within a fiber grating. In applications using the improved bonding fiber grating strain sensor, its linear relationship between the voltage signals and the average strains shows the feasibility of obtaining calibrations by using a commonly used resistance strain gauge.