2D Nanohole Arrays Research Articles

Characterization of an uncooled mid-infrared Schottky photodetector based on a 2D Au/PtSi/p-Si nanohole array at a higher light modulation frequency.

In this study, an uncooled 2D nanohole array PtSi/p-Si Schottky mid-infrared (MIR) photodetector, which is essential for on-chip Si-based low-barrier MIR detectors, is presented. Room temperature operation introduces susceptibility to thermal noise and can impact stability. Through modulation frequency and reverse bias optimization, the stability improved by 7 times at 170Hz and -3.5V, respectively. The effective light detection and stability were confirmed through ON/OFF response measurements over a longer time. The wavelength-dependent responsivity, measured with a tunable MIR laser, confirmed the responsiveness of the device in the MIR region of 2.5µm to 4.0µm, with a maximum specific detectivity (D*) of 2.0×103 c m H z 1/2 W -1 at 3.0µm; this result shows its potential applicability for noninvasive human lipid monitoring. Overall, this study focuses on the crucial role of signal analysis optimization in enhancing the performance of MIR photodetectors at room temperature.

Room-temperature plasmonic mid-infrared photodetector based on PtSi/p-Si low Schottky-barrier junction.

In this study, a low Schottky-barrier photodetector with a plasmonic assist using a two-dimensional (2D) nanohole array was demonstrated, which receives mid-infrared (MIR) light at room temperature. In the structural design, it was confirmed that the 2D nanohole-array photodetector has high absorbance in the MIR region using rigorous coupled-wave analysis. The result showed that the nanoholes formed in p-type silicon (p-Si), platinum silicide (PtSi), to form Schottky barriers, and gold (Au), for photocurrent extraction, had high absorbance in the MIR region along with the Fabry-Perot resonance mode toward the depth of the nanohole. The 2D nanohole array, with Au/PtSi/p-Si layers, has high absorbance for illuminating MIR light near 3.46 µm from the backside. The current-voltage characteristics indicated a low Schottky barrier of 0.32 eV, confirming the photoresponsive potential in the MIR photodetection. The photocurrent response to the modulation signal was obtained at room temperature. In addition, signal processing through transimpedance and lock-in amplifiers enabled us to obtain characteristics with high linearity for light intensities in milliwatts. Light acquisition for 2.5-3.8-µm-long MIR wavelength became possible, and applications in gas sensing, including vibrational absorption bands of alkane groups, are expected.

Simultaneously surface- and edge-emitting plasmonic laser operating in the near-infrared region

Near-infrared (IR) plasmonic lasers are a crucial stepping stone toward building sustainable nanoscale optoelectronic circuitry. Nevertheless, plasmonic lasers are at their infancy, and optimized designs for improved characteristics and novel applications are essential. We design an efficient plasmonic laser that simultaneously works in the near-IR region as a surface- and edge-emitting laser with collimated far-field beam pattern. While the surface emission is enhanced with a planar two-dimensional (2D) metal nanohole array (NHA) interfaced with the gain medium, the edge emission is enhanced with a 2D array of grooves. Additionally, 2D NHA or grooves on the metal layer collimate the far-field beam pattern of surface emission in the forward and backward direction, respectively. By contrast, the edge emission diverges at the far-field with an angle-resolved beam pattern from -90° to 90°. We propose and design a plasmonic collimator that uses groove-aperture nanostructures carved on gold slabs mounted on the laser facet to collimate the far-field beam patterns for edge emission. We determine the optimal dimensional parameters of the collimator. The optimized collimator produces a far-field beam that is focused to a narrow spot of 3° × 4° only.

Micro-Shaping of Nanopatterned Surfaces by Electron Beam Irradiation.

We show that planar nanopatterned thin films on standard polycarbonate (PC) compact discs (CD) can be micro-shaped in a non-contact manner via direct e-beam exposure. The shape of the film can be controlled by proper selection of the e-beam parameters. As an example of application, we demonstrate a two-dimensional (2D) array of micro-lenses/reservoirs conformally covered by an Al 2D nanohole array (NHA) film on a PC CD substrate. It is also shown that such a curvilinear Al NHA layer can be easily transferred onto a flexible polymeric support. The presented technique provides a new tool for creating lab-on-CD architectures and developing multifunctional (flexible) non-planar nanostructured films and surfaces.

Efficiency enhancement of top-illuminated ITO-free organic solar cells using plasmonic-assisted nanostructured reflective electrodes

A nanostructured back reflective electrode with nanobowl-shaped 2D nanohole arrays for enhancing the efficiency of top-illuminated organic solar cells.

Novel 3D Au nanohole arrays with outstanding optical properties

In this paper, a novel nanohole array with three-dimensional structure was generated by colloidal lithography existing of a free-standing nanohole array that experiences the same environment on both sides in 3D space. In a practicable way, the nanoholes were lifted up from the substrates, resulting in undulate morphology. Therefore we name this a 3D nanohole array (3D-NHA), and the performance in optical applications was much improved compared to conventional 2D nanohole arrays (2D-NHAs) due to a nearly perfect surface plasmon energy matching on both surfaces of the arrays. There was a 1.5-fold improvement in extraordinary optical transmission and 1.7-fold enhancement in response sensitivity towards a change of refractive index compared to 2D-NHAs. Furthermore, a (1, 1) Au/air transmission peak appeared in the transmission spectra and showed high relative sensitivity and an excellent linear response over a wide spectral range. Besides improved optical properties, good transferability of nanohole arrays without substrate dependence was designed and realized experimentally for the first time due to the unique protuberant holes of 3D-NHAs.

Colorizing silicon surface with regular nanohole arrays induced by femtosecond laser pulses

We report on the formation of one- and two-dimensional (1D and 2D) nanohole arrays on the surface of a silicon wafer by scanning with a femtosecond laser with appropriate power and speed. The underlying physical mechanism is revealed by numerical simulation based on the finite-difference time-domain technique. It is found that the length and depth of the initially formed gratings (or ripples) plays a crucial role in the generation of 1D or 2D nanohole arrays. The silicon surface decorated with such nanohole arrays can exhibit vivid structural colors through efficiently diffracting white light.

Transformation of metallic photonic structures from nano-hole to nano-island arrays through annealing process

Large-area metallic photonic crystals (MPCs) consist of two-dimensional (2D) periodical arrays of gold nano-holes are fabricated by solution-processible gold nanoparticles using interference lithography in combination with subsequent lift-off and annealing processes. By controlling the annealing temperature, the 2D nano-hole arrays are transformed into nano-island arrays, enabling easy achievements of two different photonic devices. The microscopic characterization shows convincingly the success of the fabrication techniques and verifies our proposed mechanisms for this kind of nanoscale morphology transformation. This kind of mechanisms can be applied extensively in the metallic nanofabrication and in the realization of plasmonic photonic devices. OCIS codes: 250.0250, 100.6640, 210.4770, 180.1790. doi: 10.3788/COL201210.S12502.

Surface-enhanced Raman scattering on gold quasi-3D nanostructure and 2D nanoholearrays

A new method was developed to fabricate unique gold quasi-3D plasmonic nanostructures onpoly(dimethylsiloxane) PDMS and 2D nanohole arrays on silicon as surface-enhanced Ramanscattering (SERS) substrates using electron beam lithography (EBL) with negative tone resistMa–N 2403 and soft lithography. The size and shape of nanopillars fabricated by EBL werewell controlled via different beam conditions. An enhancement factor (EF) as high as6.4 × 105 was obtained for 4-mercaptopyridine molecules adsorbed on the gold quasi-3Dnanostructure array on PDMS with 400 nm diameter, 100 nm spacing and 300 nm depth,while no enhancement was observed for the gold 2D nanohole array on siliconwith the same diameter and spacing. The experimental results were confirmed byfinite-difference time-domain (FDTD) calculations. Furthermore, the calculatedtotal electric fields showed that the strong SERS exhibited by the gold quasi-3Dnanostructure arrays on PDMS is due to the strong localized electric fields atthe gold–air interface of the bottom gold nanodisc. The strong and reproducibleSERS spectroscopy for molecules adsorbed on precisely controlled gold quasi-3Dnanostructure arrays on PDMS makes it possible for the integration of SERS-activenanopatterns into microfluidic devices as chemical and biological sensors with molecularspecificity.

Enhanced Fluorescence Microscopic Imaging by Plasmonic Nanostructures: From a 1D Grating to a 2D Nanohole Array

AbstractA two‐dimensional (2D) plasmonic coupling nanostructure for enhanced fluorescence observation using a microscope is presented. The substrate contained periodically assembled nanohole arrays with a pitch of 400 nm and a depth of 25 nm. In comparison with one‐dimensional (1D) gratings, this new substrate presented an excellent surface plasmon coupling ability to illuminate light from all directions. Under an optical microscope, an enhancement in the fluorescence intensity of up to 100 times compared with a plain glass slide was observed. The ability to markedly increase the fluorescence intensity means this technique has great potential for application in biodiagnostics, imaging, sensing, and photovoltaic cells.

Periodic Growth of ZnO Nanorod Arrays on Two-Dimensional SiNx Nanohole Templates by Electrochemical Deposition

Precisely positioned and spatially separated ZnO nanorod arrays were fabricated on holographically predefined two-dimensional (2D) SiNx nanohole-array-coated Pt/Si substrates using a simple electrochemical deposition process. The stems of the 2D nanohole-assisted ZnO nanorods had a single-crystal nature and a preferred (002) growth direction but polycrystalline contact with the Pt surface. This approach provides a facile large-scale method for fabricating periodic nanohole-supported ZnO nanorods at low growth temperatures (90 °C). The enhanced UV emission from these nanorods was associated with a lower defect density in the nanohole-templated ZnO nanorods, which was achieved by electrochemical deposition on a 2D nanohole array at a potential of −1.0 V for 30 min.

Positive and negative nanohole-fabrication on glass surface by femtosecond laser with template of polystyrene particle array

We demonstrate a new nano-processing technique using the near- electromagnetic field around a small transparent particle irradiated by an 820 nm femtosecond laser pulse. We fabricate a 2D nanohole array with negative and positive patterns on a soda lime glass surface by irradiating a monolayer of 790 nm diameter polystyrene (PS) particles, arranged in a close-packed hexagonal lattice, with a femtosecond laser pulse. At the lower laser fluence domain, PS particles act as focusing lenses and/or near-field enhancers due to Mie scattering; it enables nanohole processing just under the particle (positive patterning). Nanoholes with diameters ranging from 84 to 170 nm are fabricated in this regime. At the higher fluence domain, the PS particle acts as a mask; while the positive nanohole formation disappears, then it enables nano-patterning of the surface in gap areas corresponding to the region between particles (negative patterning). Nanoholes with diameters ranging from 65 to 110 nm are fabricated in this case. The switching of negative and positive nano-patterning by simply controlling the incident laser fluence is experimentally demonstrated for the first time to our knowledge. A simple theoretical explanation for the switching of the positive and negative patterning is presented by FDTD simulation of the near-field distribution.

Nanohole-templated organic light-emitting diodes fabricated using laser-interfering lithography: moth-eye lighting

We describe the architecture, fabrication, and electro-optical characteristics of a two-dimensional (2D), periodic, highly ordered array of subwavelength scale organic light-emitting diodes (OLEDs). A 2D nanohole array template was introduced onto a patterned ITO glass substrate by two-step irradiated hologram lithography and reactive ion etching, and then a 2D nanohole OLED array was prepared by following typical OLED fabrication procedures. Our analysis of the electro-optical characteristics of this device showed that shrinking the OLEDs to sub-wavelength scale has only a minimal effect on their optical properties. We also used the Bragg scattering effect to confirm the compounding of the millions of ~220 nm OLED light sources to form 2D periodic nanohole emission by comparing the angular dependence of the emission spectrum of the OLED array with that of a conventional OLED.