Nanograting Structure Research Articles

Nanoscale viscosity of confined polyethylene oxide.

Complex fluids near interfaces or confined within nanoscale volumes can exhibit substantial shifts in physical properties compared to bulk, including glass transition temperature, phase separation, and crystallization. Because studies of these effects typically use thin film samples with one dimension of confinement, it is generally unclear how more extreme spatial confinement may influence these properties. In this work, we used x-ray photon correlation spectroscopy and gold nanoprobes to characterize polyethylene oxide confined by nanostructured gratings (<100nm width) and measured the viscosity in this nanoconfinement regime to be ∼500 times the bulk viscosity. This enhanced viscosity occurs even when the scale of confinement is several times the polymer's radius of gyration, consistent with previous reports of polymer viscosity near flat interfaces.

Improving the luminous efficiency of gallium nitride-based light-emitting diodes using Ag nanograting structure

In order to improve the traditional gallium nitride (GaN)-light-emitting diode (LED) luminous efficiency, a structure of the GaN-LED is designed based on the local field enhancement of surface plasmon (SP). The principle of improving LED luminous properties using the SP features is described in detail. The factors that affect the light extraction efficiency of this LED structure are simulated with the COMSOL software. The thickness of p-GaN layer, the thickness of indium tin oxide (ITO) layer, the grating period T , the duty ratio r , as well as the shape of the interface between p-GaN and ITO are studied. The normalized radiated powers, the normalized absorbed powers, and the electric field distribution of this structure under different structure parameters have been achieved. The results show that when the thickness of p-GaN layer is 110 nm, the thickness of ITO buffer layer is 120 nm, the period T is 370 nm, the duty ratio is 0.5, and the value of D 1 / T is 0.6. The luminous intensity of LED is higher than that of the traditional LED nearly 43 times and is nearly 36 times higher than that of the Ag nanosphere structure, and SPs can be coupled with the active layer effectively to improve the luminous efficiency of LED, providing a theoretical guide for the preparation of high-performance GaN-LED chips.

WITHDRAWN: Light absorption enhancement of plasmonic based photo-detector with double nanograting structure

Abstract This era of high speed photonic systems demands photo detectors to have large bandwidth, gain and improved light enhancement competence. Amongst the different light absorption enhancement methods being researched by the investigators, plasmonic has acquired increased attention in the last decades. Although single layer plasmonic supported metal semiconductor metal photo detector has been explored for higher light absorption efficiency, but exploration for double layer structure is lacking in literature. This paper presents performance of plasmonic based photodetector with double layer of nanogratings optimized at wavelength of 1.4 µm for night vision applications. Proposed design of plasmonic supported photodetector with double nanograting reports quenching factor of 92.14% and provides highest light enhancement with subwavelength aperture height of 60 nm. This can be credited to fact that both top and bottom layer of grating contributes to light trapping.

Nanopillar Diffraction Gratings by Two-Photon Lithography.

Two-dimensional photonic structures such as nanostructured pillar gratings are useful for various applications including wave coupling, diffractive optics, and security features. Two-photon lithography facilitates the generation of such nanostructured surfaces with high precision and reproducibility. In this work, we report on nanopillar diffraction gratings fabricated by two-photon lithography with various laser powers close to the polymerization threshold of the photoresist. As a result, defect-free arrays of pillars with diameters down to 184 nm were fabricated. The structure sizes were analyzed by scanning electron microscopy and compared to theoretical predictions obtained from Monte Carlo simulations. The optical reflectivities of the nanopillar gratings were analyzed by optical microscopy and verified by rigorous coupled-wave simulations.

Nanograting layers of Si

The paper presents research regarding the complex behavior of materials based on Si and SiO2, geometrically processed at nano-scale. The geometry, which induces the doping effect (G-doping), occurred when it was possible to fabricate nanograting structures. Studies on the influence of nanograting structures on the properties of materials have shown that this process may lead to effects similar to those created by doping with donors. The resistivity values measured in Si-based nanograting layers, for example, were approximately 10−2 Ω cm, similar to those of Si semiconductors doped with phosphorus ‘impurities’ having a volume concentration of 1018 cm−3. This increase in electronic properties, as a result of the nanograting structure, seems to appear due to the fact that the electrons rejected in the process are placed in the structure vacancies. It has been experimentally proven that, in the case of semiconductors, the nanograting structuring makes the rejected electrons from the valence band to be placed in the conduction band. In the paper, after samples fabrication with nanograting structures on Si films placed on SiO2 support, the I–V curves of the obtained layers were drawn, both by measuring in four points and also in two points. The resistivity measurements were made in two directions: along and perpendicular to the strips of the structure and showed the existence of an anisotropy.

Indium‐rich InGaN/GaN solar cells with improved performance due to plasmonic and dielectric nanogratings

AbstractIn this study, we propose an indium‐rich InGaN/GaN p‐i‐n thin‐film solar cell which incorporates a dual nanograting (NG) structure: Ag nanogratings (Ag‐NGs) on the backside of the solar cell and gallium nitride nanogratings (GaN‐NGs) on the frontside. Finite‐difference time‐domain (FDTD) simulation results show that the dual NG structure couples the incident sunlight to the plasmonic and photonic modes, thereby increasing the absorption of the solar cell in a broad spectral range. It is observed that the solar cells having the dual nanograting structures have a significant enhancement in light absorption as compared to cells having either no nanogratings or having only the frontside nanogratings or only the backside nanogratings. Analysis of light absorption in solar cells containing the dual NG structures showed that the absorption enhancement of longer wavelengths is mostly due to the Ag‐NGs on the backside and of shorter wavelengths is mostly due to the GaN‐NGs on frontside of the solar cell. The Jsc and power conversion efficiency (PCE) are calculated under AM1.5G solar illumination and are observed to be significantly enhanced due to the presence of optimized dual NG structures. While there is an increase in Jsc from 17.88 to 23.19 mA/cm2 (~30% enhancement), there is an increase in PCE from 15.49% to 20.24% (~31% enhancement) under unpolarized light (average of TM and TE). Moreover, the study of oblique light incidence shows significantly larger Jsc of the dual nanograting solar cells compared to the cells with no nanogratings.

Surface-plasmon-enhanced LED based on multilayer gratings and core-shell Ag/SiO2 nanoparticles

This paper proposes a novel GaN-based LED with nano-grating structure based on surface plasmons. This structure mainly contains n-GaN, multiple quantum wells and p-GaN, Ag–SiO2 grating, core–shell Ag/SiO2 nanoparticle and ITO triangular grating. The basic principle of the light emitting characteristics of LED is described in detail. The COMSOL software is used to analyse properties and optimise parameters based on the finite element method. The radiated intensity, absorbed intensity and electric field distribution are obtained. The results indicate that this structure has a higher luminous efficiency with the luminous intensity increased to about 58.59 times compared with the ordinary structure and about 3.94 times compared with the reference structure, and can enhance the internal quantum efficiency and the external quantum efficiency of the LED simultaneously.

Fabrication of flexible and economical plasmonic biosensor using gold nanograting imprinted on hot-melt adhesive film for label-free sensing of immunoglobulin proteins

We report here, the fabrication of plasmonic nanograting patterned on hot-melt adhesive (HMA) film via thermal nanoimprint lithography. A soft polymer stamp textured with nanograting pattern was used as a mold to imprint nanograting structure on HMA film overlaid on a flexible polyethylene terephthalate substrate. Thereafter, a 50 nm thickness of gold film was evaporated over surface of the nanograting to prepare a plasmonic sensing layer. The surface plasmon resonance excitation on gold coated nanograting was characterized with the reflectance measurement under the normal incidence of light, which was further verified with theoretical calculations. The bulk refractive index sensitivity of our prepared sensor was obtained 886 ± 55 nm/refractive index unit (RIU). Additionally, a label-free detection of specific target analytes was shown by recording the specific interactions between rabbit immunoglobulin (R-IgG) and anti R-IgG proteins. A surface mass detection limit of 162 pg mm−2 was found in the detection of 100 nM anti R-IgG proteins. Thus, our proposed plasmonic sensor based on low-cost HMA represents another promising thermoplastic material for nanostructure fabrications that have potential applications in the development of affordable, flexible, label-free, and highly sensitive optical/biological sensor.

Improving the Water Oxidation Efficiency with a Light-Induced Electric Field in Nanograting Photoanodes.

Severe charge recombination in solar water-splitting devices significantly limits their performance. To address this issue, we design a frustum of a cone nanograting configuration by taking the hematite and Au-based thin-film photoanode as a model system, which greatly improves the photoelectrochemical water oxidation activity, affording an approximately 10-fold increase in the photocurrent density at 1.23 V versus the reversible hydrogen electrode compared to the planar counterpart. The surface plasmon polariton-induced electric field in hematite plays a dominant role in efficiency enhancement by facilitating charge separation, thus dramatically increasing the incident photon-to-current efficiency (IPCE) by more than 2 orders of magnitude in the near band gap of hematite. And the relatively weak electric field caused by light scattering in the nanograting structure is responsible for the approximate maximum 20-fold increase in IPCE within a broadband wavelength range. Our scalable strategy can be generalized to other solar energy conversion systems.

Effect of incidence and sidewall taper angles on plasmonic metal–semiconductor–metal photodetector enhancements

We investigate an interdigitated nanograting structure on a GaAs substrate for plasmonic metal–semiconductor–metal photodetector applications. This computational work has studied the effects that the taper angle of the nanograting sidewall and the light wave angle of incidence have on the optical and current enhancements in the device. The study, involving two types of taper angle structures—positive and negative—showed that both taper angle directions can generate more optical and electrical enhancements than perfectly vertical wall structures for light incident at both the Brewster angle and the normal incident angle. The enhanced electric field value at the optimum positive taper angle is ∼22% and ∼120% greater than the negative taper angle and vertical wall structure, respectively. In addition, the total weighted optical enhancement value for the optimal positive taper angle structure is ∼65% and ∼120% greater than the optimal negative taper angle and vertical wall structure, respectively. This work demonstrates that the increased enhancements are due to the nanoscale focusing of light and impedance matching. The incident wave angle along with the taper angle can significantly promote these enhancements, especially at the Brewster angle.

A Comprehensive Study on the Impact of Various Nano-gratings on MSM-PDs for Enhancement in the Light Absorption

In this paper, we have analyzed metal-semiconductor-metal photodetectors (MSM-PDs) with different nano-grating structures or shapes to improve the light absorption capacity into the device in details for high-speed communication systems and networks. The plasmonic-based MSM-PD structure demonstrates a significant improvement in light absorption capacity for the developed device compared to conventional MSM-PDs i.e., devices that have not employed the nano-gratings. The light absorption capacity of the device is varied with the variation of geometrical shapes and parameters of the nano-gratings, such as the nano-grating height, slit width and so on. These nano-grating structures are assisting in light transmission through the central slit (i.e., subwavelength apertures) efficiently, resulting in the excitation of surface plasmon polaritons (SPPs) as the incident photons interact with the nano-gratings/ nano-corrugations. This improved light transmission in the central slit along with excited SPPs results in resonant light absorption in the device. This means the light trapped inside the central slit is triggered by the SPPs to a higher order magnitude. This causes the light absorption enhancement for the device, i.e., more light is transmitted through the device instead of reflecting back to the surface. The simulation results demonstrated that the light absorption enhancement factor (LAEF) for these devices have improved dramatically due to the nano-gratings. For modeling and simulation of these devices, Opti-FDTD tool is used which is based on finite difference time domain (FDTD) method. The application of these simulated devices is in the range of 800-850-nm. The simulation results are suitable for the design of nano-structured MSM-PDs that can be used in high-speed communication systems and sensor network systems.

Embedded nanograting-based waveplates for polarization control in integrated photonic circuits

Femtosecond laser direct writing (FLDW) enables precise three-dimensional structuring of transparent host materials such as fused silica. With this technique, reliable integrated optical circuits can be written, which are also a possible candidate for future quantum technologies. We demonstrate the manufacturing of integrated waveplates with arbitrary orientations and various phase delays by combining embedded birefringent nanograting structures and FLDW waveguides in fused silica glass. These waveplates can be used both for classical applications and for quantum gates.

Fabrication of highly homogeneous and controllable nanogratings on silicon via chemical etching-assisted femtosecond laser modification

Abstract Femtosecond laser direct writing is widely exploited in surface periodic structures processing. However, this technique still faces challenges in obtaining high surface homogeneity and flexible morphology controllability. In this study, a flexible and efficient approach has been proposed to fabricate highly homogeneous and controllable nanogratings on silicon via chemical etching-assisted femtosecond laser modification. By precisely manipulating the laser-material interaction process, alternating amorphous-crystalline nanofringes are generated when employing femtosecond laser scanning over a Si sample, with almost no material removal. Following auxiliary chemical etching, highly homogeneous nanograting structures are obtained, and the morphology of the nanogratings can be flexibly managed through precisely controlling the duration of the etching process. Complex cross-scale patterns with remarkable structural colors that are visible under indoor light illumination are readily achieved on the sample surfaces exploiting our method. In addition, compared with traditional methods for laser-induced periodic surface structures, the fabrication efficiency is considerably improved. Our processing procedure offers potential applications in the fields of optics, nanoelectronics, and mechatronics.

Design and fabrication of a linear polarizer in the 8–12μm infrared region with multilayer nanogratings

The design and fabrication of a ZnSe-based linear polarizer operating in the 8–12 μm infrared region with multilayer nanogratings is demonstrated. The multilayer structure is formed by a low- and a high-refractive index thin layer that are evaporated successively on a ZnSe substrate, followed by a dielectric nanograting that is etched into the high-refractive index thin layer, and then a double-layer metallic nanograting that sits on the dielectric nanograting. Polarization characteristics of the proposed polarizer on structural parameters are investigated and an optimized multilayer structure is obtained. Experimental fabrication of the multilayer nanograting structure using UV lithography and thin-film deposition is conducted in a way in which no ion etching process is needed for the formation of metallic nanogratings. An extinction ratio (ER) of 35 dB and TM-transmission (TMT) of averagely higher than 80% are obtained experimentally in the whole 8–12 μm waveband with 250-nm-period multilayer nanogratings. The ZnSe-based multilayer structure shows the possibility of achieving large-area and high-performance polarization in the 8–12 μm infrared region with relatively easy fabrication.

Surface plasmon resonance behaviors of a highly Ga-doped ZnO nano-grating structure

Surface nano-gratings of different periods are fabricated on a Ga-doped ZnO (GaZnO) thin film with a high electron concentration for the study of their surface plasmon (SP) resonance behaviors in the near-infrared range. The dispersion curve of the surface plasmon polariton (SPP) based on the ellipsometry measurement of the GaZnO dielectric constant helps in designing the grating period for effective SPP excitation. Spectral depressions of grating reflection under certain incident polarization conditions, corresponding to SP resonance features, are observed in the wavelength range between 1400 and 2200 nm. From the numerical simulation of light scattering from a GaZnO grating structure based on the measured dielectric constant and the fitted Drude model, we can identify either SPP or localized SP modes among the observed SP resonance features. Essentially, it is difficult to excite below 1600 nm SPP at an air/GaZnO interface due to its lossy nature. The potential application of SP resonance on GaZnO is evaluated.

Molecular orientation and stability of poly(3-hexylthiophene) nanogratings affected by the fabricated solvent vapor.

During the nanoimprinting lithography (NIL) process, the role of solvent vapor in fabricating the pattern structure and inducing the molecular alignment of nanoimprinted polymer film has been attracting significant attention. We demonstrate here that the molecular orientation and thermal stability of poly(3-hexylthiophene) (P3HT) nanograting film can be affected obviously by the fabricated solvent vapor. A solvent-vapor nanoimprinting lithography (SV-NIL) technique based on a polydimethylsiloxane (PDMS) template is employed to fabricate a P3HT nanograting structure film successfully and solvent vapor is offered by chlorobenzene, chloroform and carbon disulphide, respectively. The molecular orientation of the polymer film is carefully characterized by grazing incidence wide angle X-ray diffraction (GIWAXD) measurements to investigate the effect of various solvent vapors on the molecular orientation of the P3HT nanograting film. For the P3HT nanograting film fabricated by chloroform and chlorobenzene solvent, the edge-on molecular orientation of the typical form II crystallographic structure is induced. However, this indicates that there are both the face-on molecular orientations of the form II and form I crystallographic conformation present for the P3HT nanograting film fabricated by carbon disulphide solvent. Therefore, the fabricated solvent vapor plays a significant role in determining the formation of the molecular orientation of the polymer nanostructure. Then, the role of thermal annealing in the stability of the molecular orientation was investigated for the P3HT nanograting film after a fixed temperature. As for the annealed nanograting film fabricated by chlorobenzene and chloroform solvent vapor, a single edge-on molecular orientation mode of the form I crystallographic structure has been obtained. However, for the annealed nanograting film fabricated by the carbon disulphide solvent, the edge-on and face-on molecular orientations of the form I crystallographic structure are still retained. This indicates that the stability of the form II crystallographic conformation is mainly dependent on the thermal annealing process. Therefore, after the annealing process, the final determining of the molecular alignment and crystallographic conformation depends significantly on the orientation type of the nanograting film before the annealing history, and it can be further inferred that the molecular orientation of the annealed polymer film is still affected by the fabricated solvent vapor significantly. Thus this will provide new understanding and guidance for the research of the topographical structure and molecular alignment of conjugated polymers.

Optimization of 1D Plasmonic Grating of Nanostructured Devices for the Investigation of Plasmonic Bandgap

The present work investigates the effect of geometrical parameters of 1D nanograting on surface plasmon resonance (SPR) and plasmonic bandgap (PBG). The use of plasmonic grating device in various electronic devices is based on correct value of bandgap energy. For this purpose, various nanograting structures having regular periodic ridges in 1D has been modeled in the form of a gold film on glass substrate using finite element analysis in RFRF Module of COMSOL (Multiphysics) 5.3a licensed version. In the designed structures, firstly, the periodicity of the grating varied while keeping the slit width and film thickness constant. Furthermore, the thickness of the grating also varied while the periodicity and slit width is kept constant and transmitted mode for each structure is studied to find the suitable value of film thickness for optimizing the device. At the end, the slit width varied while keeping the periodicity and film thickness constant. Due to increase in slit width, the bandgap energy increases until slit width equals to nearly half of periodicity after this bandgap energy decreases and associated with the sinusoidal behavior of the device which support fundamental plasmonic mode. The increase in film thickness results a linear increase in bandgap energy as long as the film thickness is comparable to the skin depth of gold and plasmonic bandgap energy is high for smaller values of periodicity and decreases with increasing periodicity. Due to the ability to control the optical properties, the PBG is expected to have a major impact on technology.

Subwavelength nanostructured grating for generating visible radially and azimuthally polarized light

A polarizer element with subwavelength nanostructured indium-tin-oxide grating for visible light (λ = 532 nm) is designed and fabricated to convert circularly polarized light into radially and azimuthally polarized light. To analyze the optical performance, a mathematical model is developed for the subwavelength nanostructured grating. Parameters associated with the polarized beam generated by the element are measured in the experiment, and optical characteristics of the element are discussed.

Dispersion engineering with plasmonic nano structures for enhanced surface plasmon resonance sensing

We demonstrate numerically and experimentally the enhancement of Surface Plasmon Resonance (SPR) sensing via dispersion engineering of the plasmonic response using plasmonic nanograting. Following their design and optimization, the plasmonic nanograting structures are fabricated using e-beam lithography and lift-off process and integrated into conventional prism based Kretschmann configuration. The presence of absorptive nanograting near the metal film, provides strong field enhancement with localization and allows to control the dispersion relation which was originally dictated by a conventional SPR structure. This contributes to the enhancement in Q factor which is found to be 3–4 times higher as compared to the conventional Kretschmann configuration. The influence of the incident angle on resonance wavelength is also demonstrated both numerically and experimentally, where, only a negligible wavelength shift is observed with increasing the incident angles for plasmonic nanograting configuration. This surprising feature may be helpful for studying and utilizing light-matter interaction between plasmons and narrow linewidth media (e.g. Rb atom or molecule) having nonlocalities in their susceptibility-momentum relation. Finally, we analyze the role of plasmonic nanograting in enhancing the performance of an SPR sensor. Our results indicate that the integrated SPR-nanograting device shows a great promise as a sensor for various types of analytes.

Near-Perfect Spectral Transmission Properties for Two Cascaded Plasmonic Ultrathin Nanograting Structures

A high-performance plasmonic transmission structure consisting of two longitudinally cascaded ultrathin metallic nanogratings with a half period lateral dislocated and separated by two heterogeneous dielectric layers is proposed and theoretically studied. Three near-unity spectral transmission peaks are observed for the cascaded plasmonic nanograting structure due to the evanescent field coupling of surface plasmon polariton waves supported by the two neighboring plasmonic nanogratings. The physical mechanism responsible for the near-perfect peak transmissions is discussed based on the corresponding spatial distributions of electromagnetic fields and is found to be two possible ways: by the excitation of hybrid anti-symmetric surface plasmon polariton leaky mode on the incident and transmission surfaces of the cascaded plasmonic nanograting structure or by the formation of localized surface plasmon polariton resonance modes within horizontally butt-jointed metal/insulator/metal coupled waveguides between the two cascaded plasmonic nanogratings. It is the two heterogeneous dielectric layers inserted between the two cascaded plasmonic nanogratings that is indispensable for the formation of the hybrid anti-symmetric surface plasmon polariton leaky mode, resulting in the near-unity transmission peak with an ultra-narrow bandwidth of 20 nm. The high-tunability of spectral transmission behaviors with varying structural parameters and dielectric layer are explored, which promise numerous potential applications in nano-optics devices, such as plasmonic filters, sensors, and nanoscale distance ruler.