Zhendong Zhu

Surface-plasmon-enhanced GaN-LED based on a multilayered M-shaped nano-grating.

A multilayered metallic M-shaped nano-grating is proposed to enhance the internal quantum efficiency, light extraction efficiency and surface-plasmon (SP) extraction efficiency of the gallium nitride-based light emitting diodes. This structure is fabricated by the low-cost nano-imprint lithography. The suitable grating based on quasi-symmetrical-waveguide structure has a high transmission in the visible region. The properties of SP mode and the Purcell effect in this type of LED is investigated. The experimental results demonstrate that its peak photoluminescence intensity of the proposed LED is over 10 times greater than that from a naked GaN-LED without any nanostructure.

Enhanced light extraction from a GaN-based green light-emitting diode with hemicylindrical linear grating structure

Significant enhancement in the light output from GaN-based green light-emitting diodes (LEDs) was achieved with a hemicylindrical grating structure on the top layer of the diodes. The grating structure was first optimized by the finite-difference time-domain (FDTD) method, which showed that the profile of the grating structure was critical for light extraction efficiency. It was found that the transmission efficiency of the 530 nm light emitted from the inside of the GaN LED increased for incidence angles between 23.58° and 60°. Such a structure was fabricated by electron-beam lithography and an etching method. The light output power from the LED was increased approximately 4.7 times compared with that from a conventional LED. The structure optimization is the key to the great increase in transmission efficiency. Furthermore, the light emitted from the edge of the LED units could be collected and extracted by the grating structures in adjacent LED units, thus enhancing the performance of the whole LED chip.

Experimental research on the spectral response of tips for tip-enhanced Raman spectroscopy

Based on unilateral total internal reflection illumination, a tip spectral response detection setup is built. This provides an experimental method for revealing the spectral response and resonance band, which are significant in investigating optical properties and the field enhancing mechanism. The spectral responses of silicon tips coated with gold and silver are detected. These tips are then used in tip-enhanced Raman spectroscopy (TERS) detection under 532 nm excitation to demonstrate the effect of resonant excitation on field enhancement. The corresponding relationship between the measured spectral response and the tip’s enhancement performance in TERS is discussed.

M‐shaped Grating by Nanoimprinting: A Replicable, Large‐Area, Highly Active Plasmonic Surface‐Enhanced Raman Scattering Substrate with Nanogaps

Plasmonic nanostructures separated by nanogaps enable strong electromagnetic-field confinement on the nanoscale for enhancing light-matter interactions, which are in great demand in many applications such as surface-enhanced Raman scattering (SERS). A simple M-shaped nanograting with narrow V-shaped grooves is proposed. Both theoretical and experimental studies reveal that the electromagnetic field on the surface of the M grating can be pronouncedly enhanced over that of a grating without such grooves, due to field localization in the nanogaps formed by the narrow V grooves. A technique based on room-temperature nanoimprinting lithography and anisotropic reactive-ion etching is developed to fabricate this device, which is cost-effective, reliable, and suitable for fabricating large-area nanostructures. As a demonstration of the potential application of this device, the M grating is used as a SERS substrate for probing Rhodamine 6G molecules. Experimentally, an average SERS enhancement factor as high as 5×10⁸ has been achieved, which verifies the greatly enhanced light-matter interaction on the surface of the M grating over that of traditional SERS surfaces.

Reusable three-dimensional nanostructured substrates for surface-enhanced Raman scattering

To date, fabricating three-dimensional (3D) nanostructured substrate with small nanogap was a laborious challenge by conventional fabrication techniques. In this article, we address a simple, low-cost, large-area, and spatially controllable method to fabricate 3D nanostructures, involving hemisphere, hemiellipsoid, and pyramidal pits based on nanosphere lithography (NSL). These 3D nanostructures were used as surface-enhanced Raman scattering (SERS) substrates of single Rhodamine 6G (R6G) molecule. The average SERS enhancement factor achieved up to 1011. The inevitably negative influence of the adhesion-promoting intermediate layer of Cr or Ti was resolved by using such kind of 3D nanostructures. The nanostructured quartz substrate is a free platform as a SERS substrate and is nondestructive when altering with different metal films and is recyclable, which avoids the laborious and complicated fabricating procedures.

A simple method for generating unidirectional surface plasmon polariton beams with arbitrary profiles.

The efficient steering of surface plasmon polariton (SPP) fields is a vital issue in various plasmonic applications, such as plasmonic circuitry. We present a straightforward and efficient method for generating unidirectionally propagating SPP beams with arbitrary amplitude and phase profiles by manipulating Δ-shaped nanoantennas. As an example, a second-order Hermite-Gauss SPP beam is generated with this method. The near-field distribution of the generated SPP beam is experimentally characterized to validate the effectiveness of the method.

UV-based nanoimprinting lithography with a fluorinated flexible stamp

A custom-made copolymer of a perfluoropolyether (PFPE) and a hyperbranched polymer (HP) was employed to prepare an UV-based nanoimprinting lithographic (NIL) flexible HPFPE stamp. The properties of the HP afforded the resultant HPFPE resist with low viscosity, suitable surface energy, high Young’s modulus, and enhanced stability. The HPFPE resist also presented excellent properties of antisticking, and durability, no deformation, or distortion after long time usage; therefore, demonstrating an improvement in the NIL pattern transfer fidelity and resolution. By optimizing the UV-based NIL process with this flexible HPFPE stamp, the imprinting results showed near zero residues at the bottom of the resist grooves, and no sticking over a large area. The structure of the HPFPE flexible stamp was transferred intact onto a soft substrate indium tin oxide/polyethylene terephthalate film with good resolution, achieving a 50 nm linewidth and a 200 nm period.

Versatile and tunable surface plasmon polariton excitation over a broad bandwidth with a simple metaline by external polarization modulation.

Surface plasmon polariton (SPP) sources and launchers are highly demanded in various applications of nanophotonics. Here, we propose a general approach that can realize complete control of the complex extinction ratio (including amplitude and phase) of any two linearly independent SPP modes excited by any elementary SPP excitation architecture just by manipulating the incident polarization state. In an optical system, it suffices to simply tune the orientation angles of a linear polarizer and a quarter wave plate, which may greatly simplify the design and application of SPP launchers and diversify their functionalities. As an example to show the broad application prospect of this method, we design and realize a metaline consisting of Δ-shaped plasmonic nanoantennas, which can effectively realize dual functionalities, i.e., the tunable directional SPP excitation at an arbitrarily chosen wavelength and the complete unidirectional SPP excitation over a broad bandwidth. This general approach can also be extended to the control of the complex extinction ratio of any two linearly independent excited modes in many other linear optical systems, such as two modes in a waveguide or two diffraction orders in a grating, over a broad bandwidth.

Fabrication of Dense Horizontally Aligned Arrays of Single-Wall Carbon Nanotubes from Vertically Aligned Arrays

The as-grown vertically aligned single-wall carbon nanotube (SWNT) arrays are transferred from the original silicon substrate to a poly(ethylene terephthalate) (PET) substrate, which acts as a stamp. Thin SWNT films can be applied from the stamp to the target substrate and subsequently treated by an ultrasonic process to reduce their thickness to 6.6 nm. The transferred SWNT thin film retains the advantageous super-alignment and high-density properties of the vertical SWNT arrays. The linear density, transmittance, and square resistance of the thin film are as high as 15 tubes per micrometer, 99% at 550 nm, and 16 kΩ, respectively.

Analysis method of microstructure surface topography based on wavelet filter

The surface topography of micro-structures would significantly affect the products quality and industrial performance of micro-nano devices [1]. In recent years, the application of micro-structures in Micro Electro Mechanical Systems (MEMS) and integrated circuit is more and more widely. How to reflect the 3D surface topography of these micro structures accurately and measure the surface’s parameters precisely as well as quickly are becoming a hot research area of precision measurement. White-light interference microcopy technology is one of the most widely used non-contacting measurement methods at present, which has the advantages of nondestructive, fast measurement and high accuracy, has been widely applied in surface topography measurement of micro structures. In this paper, an analysis method of microstructure surface topography algorithm based on wavelet filter to analyze white interference signals is proposed, this method utilizes R/G/B three channels color information which is significantly superior to traditional black and white imaging process method. The experimental results shows that this method has good accuracy and repeatability in 3D surface measurement.