Nanostripe Arrays Research Articles

Assembly of Gold Nanowires on Gold Nanostripe Arrays: Simulation and Experiment

Nanowires (NWs) have a large aspect ratio and large available surface area, which have made them a potential platform for applications in biosensors as well as electronic/optic and power storage de...

Self-Organized Conductive Gratings of Au Nanostripe Dimers Enable Tunable Plasmonic Activity

Plasmonic metasurfaces based on quasi-one-dimensional (1D) nanostripe arrays are homogeneously prepared over large-area substrates (cm2), exploiting a novel self-organized nanofabrication method. Glass templates are nanopatterned by ion beam-induced anisotropic nanoscale wrinkling, enabling the maskless confinement of quasi-1D arrays of out-of-plane tilted gold nanostripes, behaving as transparent wire-grid polarizer nanoelectrodes. These templates enable the dichroic excitation of localized surface plasmon resonances, easily tunable over a broadband spectrum from the visible to the near- and mid-infrared, by tailoring the nanostripes’ shape and/or changing the illumination conditions. The controlled self-organized method allows the engineering of the nanoantennas’ morphology in the form of Au-SiO2-Au nanostripe dimers, which show hybridized plasmonic resonances with enhanced tunability. Under this condition, superior near-field amplification is achievable for the excitation of the hybridized magnetic dipole mode, as pointed out by numerical simulations. The high efficiency of these plasmonic nanoantennas, combined with the controlled tuning of the resonant response, opens a variety of applications for these cost-effective templates, ranging from biosensing and optical spectroscopies to high-resolution molecular imaging and nonlinear optics.

Ultra-broadband photon harvesting in large-area few-layer MoS2 nanostripe gratings.

Flat optics nanoarrays based on few-layer MoS2 are homogeneously fabricated over large-area (cm2) transparent templates, demonstrating effective tailoring of the photon absorption in two-dimensional (2D) transition-metal dichalcogenide (TMD) layers. The subwavelength subtractive re-shaping of the few-layer MoS2 film into a one-dimensional (1D) nanostripe array results in a pronounced photonic anomaly, tunable in a broadband spectral range by simply changing the illumination conditions (or the lattice periodicity). This scheme promotes efficient coupling of light to the 2D TMD layers via resonant interaction between the MoS2 excitons and the photonic lattice, with subsequent enhancement of absorption exceeding 400% relative to the flat layer. In parallel, an ultra-broadband absorption amplification in the whole visible spectrum is achieved, thanks to the non-resonant excitation of substrate guided modes promoted by MoS2 nanoarrays. These results highlight the potential of nanoscale re-shaped 2D TMD layers for large-area photon harvesting in layered nanophotonics, quantum technologies and new-generation photovoltaics.

Nanoantenna Structure with Mid-Infrared Plasmonic Niobium-Doped Titanium Oxide.

Among conductive oxide materials, niobium doped titanium dioxide has recently emerged as a stimulating and promising contestant for numerous applications. With carrier concentration tunability, high thermal stability, mechanical and environmental robustness, this is a material-of-choice for infrared plasmonics, which can substitute indium tin oxide (ITO). In this report, to illustrate great advantages of this material, we describe successful fabrication and characterization of niobium doped titanium oxide nanoantenna arrays aiming at surface-enhanced infrared absorption spectroscopy. The niobium doped titanium oxide film was deposited with co-sputtering method. Then the nanopatterned arrays were prepared by electron beam lithography combined with plasma etching and oxygen plasma ashing processes. The relative transmittance of the nanostrip and nanodisk antenna arrays was evaluated with Fourier transform infrared spectroscopy. Polarization dependence of surface plasmon resonances on incident light was examined confirming good agreements with calculations. Simulated spectra also present red-shift as length, width or diameter of the nanostructures increase, as predicted by classical antenna theory.

Crystal structure and magnetic properties of wafer-size Co nanostrip arrays self-organized on a step-bunched surface of Si(111)-5.55 × 5.55-Cu/(Cu, Cu2Si, W-O) buffers

Structure and magnetization reversal of Co nanostrips self-organized on a Si(111)-5.55 × 5.55-Cu step-bunched surface covered by Cu, Cu2Si and W-O buffer layers are systematically investigated and characterized in details. Optimal conditions for growth of well-ordered arrays of mm-long straight nanostrips with hexagonal close-packed and face-centered cubic crystal phases are defined. We find that the Co nanostrips with epitaxial and multiepitaxial structure grows on monocrystalline buffer layers of Cu and Cu2Si, respectively. The amorphous W-O buffer promotes the growth of polycrystalline Co nanostrips. We reveal the origin and compute the magnitude of magnetic anisotropy in Co nanostrips with different crystal phases. Structure-dependent magnetization reversal modes of nanostrip arrays are determined analytically using angular dependences of the coercive force. Our analysis of distributions of the switching and interaction fields by the first-order reversal curve diagram method specifies contributions of global and local interaction fields. Micromagnetic simulations considering the magnetostatic interaction between nanostrips demonstrate the crystal structure-dependent magnetization reversal mechanisms based on propagation of domain walls, whose type (symmetric or asymmetric transverse domain wall, vortex domain wall) and velocity are determined by the magnetic parameters, interaction fields and driving magnetic fields.

Active tuning of the hybridization effects of mid-infrared surface plasmon resonance in a black phosphorus sheet array and a metal grating slit

In this paper, the absorption characteristics of a hybrid structure composed of a black phosphorus (BP) nanostrip array based on localized surface plasmon resonance (LSPR) and a metal grating slit structure have been analyzed systematically. Firstly, we theoretically investigate light-matter interaction in different dimensions of BP nanostrip arrays along armchair and zigzag direction, revealing the absorption property and anisotropic plasmonic response. Besides, the transmission characteristics of the metal grating slit structure with different geometric dimensions are thoroughly analyzed by the transmission spectra and electric intensity distributions. At last, by combining the two structures, we increased the absorption of BP from 72% to 83.6% at 7.04 µm, and this hybrid BP structure demonstrates high absorption at mid-infrared wavelength regime, predicting a promising future for the directional dependent plasmonic devices based on two-dimensional (2D) materials.

Light-Induced Surface Potential Modification in MoS2 Monolayers on Au Nanostripe Arrays

In this work, the surface potential (VS) of exfoliated MoS2 monolayers on Au nanostripe arrays with period of 500 nm was investigated using Kelvin probe force microscopy. The surface morphology showed that the suspended MoS2 region between neighboring Au stripes underwent tensile-strain. In the dark, the VS of the MoS2 region on the Au stripe (VS-Au) was larger than that of the suspended MoS2 region (VS-S). However, under green light illumination, VS-Au became smaller than VS-S. To explain the VS modification, band diagrams have been constructed taking into consideration not only the local strain but also the electronic interaction at the MoS2/Au interface. The results of this work provide a basis for understanding the electrical properties of MoS2-metal contacts and improving the performance of MoS2-based optoelectronic devices.

Ultra-sensitive plasmonic sensing based on gold nanostrip arrays.

The extra-narrow reflection feature in angular dependence of reflectivity of periodic gold nanostrip arrays presents interest for sensing application. We explore its behavior in a modified dielectric environment and characterize the capability for sensing small changes in the dielectric permittivity of the environment.

Fast Dynamics of Guided Magnetic Flux Quanta

The dynamics of Abrikosov vortices in superconductors is usually limited to vortex velocities $v\simeq1$ km/s above which samples abruptly transit into the normal state. In the Larkin-Ovchinnikov framework, near the critical temperature this is because of a flux-flow instability triggered by the reduction of the viscous drag coefficient due to the quasiparticles leaving the vortex cores. While the existing instability theories rely upon a uniform spatial distribution of vortex velocities, the measured (mean) value of $v$ is always smaller than the maximal possible one, since the distribution of $v$ never reaches the $\delta$-functional shape. Here, by guiding magnetic flux quanta at a tilt angle of $15^\circ$ with respect to a Co nanostripe array, we speed up vortices to supersonic velocities. These exceed $v$ in the reference as-grown Nb films by almost an order of magnitude and are only a factor of two smaller than the maximal vortex velocities observed in superconductors so far. We argue that such high $v$ values appear in consequence of a collective dynamic ordering when all vortices move in the channels with the same pinning strength and exhibit a very narrow distribution of $v$. Our findings render the well-known vortex guiding effect to open prospects for investigations of ultrafast vortex dynamics.

Piezoelectric Nanotopography Induced Neuron‐Like Differentiation of Stem Cells

AbstractThe biophysical characteristics of the extracellular matrix, such as nanotopography and bioelectricity, have a profound influence on cell proliferation, adhesion, differentiation, etc. Recognition of the function of a certain biophysical cue and fabrication of biomaterial scaffolds with specific properties would have important implications and significant applications in tissue engineering. Herein, nanotopographic and piezoelectric biomaterials are fabricated and the combination effect of and individual contribution to proliferation, adhesion, and neuron‐like differentiation of rat bone marrow‐derived mesenchymal stem cells (rbMSCs) are clarified via nanotopography and piezoelectricity. Piezoelectric polyvinylidene fluoride with nanostripe array structures is fabricated, which can generate a surface piezoelectric potential up to millivolt by cell movement and traction. The results reveal a more favorable effect on neuron‐like differentiation of rbMSCs from the combination of piezoelectricity and nanotopography rather than nanotopography alone, whereas nanotopography can increase cellular adhesion. This research provides a new insight into designing biomaterials for the potential application in neural tissue engineering.

P3HT:PC61BM solar cell embedding silver nanostripes for light absorption enhancement

Periodic silver nanostripe arrays are introduced into poly (3-hexylthiophene) and [6, 6]-phenyl-C61-butyric acid methyl ester (P3HT:PC61BM) solar cells to enhance the light absorption in the active materials. The light absorption enhancements were experimentally and numerically investigated. The silver nanostripes with a width, height, and pitch of 82, 50, and 400 nm enhanced the light absorption of P3HT:PC61BM layer by 20%. Numerical calculations revealed not the magnetic resonance that is supported by a perfect absorber configuration but surface plasmon polaritons excited at the boundary between the P3HT:PC61BM layer and aluminum electrode is the dominant mechanism behind its light absorption enhancement.

Transverse Magneto-Optical Kerr Effect in Magnetite Covered by Array of Gold Nanostripes

We study theoretically and experimentally a magneto-optical Kerr effect (TMOKE) in magnetite film covered by sub-wavelength grating consisting of gold nanostripes. Our rigorous coupled wave analysis (RCWA) simulations of optical reflection and transmission coefficients of the structure under study predict a multiple enhancement of TMOKE response in transmission as compared with a plain magnetite film without gold nanostripes. We demonstrate that due to the high absorption losses in magnetite film, the quality factors of the optical resonances in our sample are low which results in wide areas on the dispersion diagram where the TMOKE can be observed.

Anisotropic Plasmonic Response of Black Phosphorus Nanostrips in Terahertz Metamaterials

Two-dimensional black phosphorus (BP) recently emerged as an outstanding material for optoelectronics and nanophotonics applications. In contrast to graphene, BP has a sufficiently large electronic bandgap and its high carrier mobility allows for efficient free-carrier absorption in the infrared and terahertz regimes. Here, we present a reflective structure to enhance the response of nanostructured monolayer BP at terahertz frequencies and investigate localized surface plasmon resonances in BP nanostrip arrays. Anisotropic absorption is observed in the proposed BP metamaterials due to the puckered crystal structure of the monolayer BP, and further investigations show that the plasmonic resonances are strongly depending on the geometric parameters of the nanostrips and the coupling between the adjacent nanostrips. We expect that the monolayer BP is an outstanding candidate of highly anisotropic plasmonic material for ultrascaled optoelectronic integration.

Symmetry and localization properties of defect modes in magnonic superlattices

Symmetry and localization properties of defect modes of a one-dimensional bi-component magnonic superlattice are theoretically studied. The magnonic superlattice can be seen as a periodic array of nanostripes, where stripes with different width, termed as defect stripes, are periodically introduced. By controlling the geometry of the defect stripes, a transition from dispersive to practically flat spin-wave defect modes can be observed inside the magnonic band gaps. It is shown that the spin-wave profile of the defect modes can be either symmetric or antisymmetric, depending on the geometry of the defect. Due to the localized character of the defect modes, a particular magnonic superlattice is proposed, wherein the excitation of either symmetric or antisymmetric flat magnonic modes is enabled at the same time. Also, it is demonstrated that the relative frequency position of the antisymmetric mode inside the band gap does not significantly change with the application of an external field, while the symmetric modes move to the edges of the frequency band gaps. The results are complemented by numerical simulations, where an excellent agreement is observed between both methods. The proposed theory allows exploring different ways to control the dynamic properties of the defect modes in metamaterial magnonic superlattices, which can be useful for applications on multifunctional microwave devices operating over a broad frequency range.

Controllable Hierarchical Surface Patterns of Supramolecular Hydrogels: Harnessing Buckling Instability by Confinement.

Patterned surfaces of responsive polymers find applications in diverse fields. However, it is still a great challenge to fabricate hierarchical patterns with long-range orders. Herein controllable hierarchical surface patterns that can be fabricated by combining nanoembossing techniques with the surface instability of supramolecular hydrogels are presented. Nanoembossed nanostripe arrays of polyethylene glycol (PEG)-based polyurethane-urea supramolecular hydrogels are fabricated and exposed to water, whereby the lateral expansion of nanostripes is confined and leads to the formation of folded in-plane or out-of-plane patterns depending on the aspect ratios. The direction of folds is perpendicular to the nanostripes. Both the amplitude and the wavelength of out-of-plane folds are proportional to the thickness of nanostripes. Therefore, hierarchical structures, in which one periodicity is defined by the nanoembossing processes and the other is determined by surface buckling, can be quickly fabricated in supramolecular hydrogel thin films.

Induced magnetic anisotropies dependent micromagnetic structure of epitaxial Co nanostrip arrays

Dipole-dipole interaction in the arrays of closely packed magnetic nanostrips plays an important role in the magnetization reversal processes and significantly affects the critical fields, spin dynamics, and magnetotransport properties. Shape anisotropy in such arrays leads to the closure of the magnetic flux at the poles of adjacent nanostrips. If to induce the magnetic anisotropy oriented across the nanostrip long axis, this will change the micromagnetic configuration of each nanostrip in the array due to the appearance of the domain structure formed by domains with an antiparallel orientation of the magnetization. In this paper, we study the field-dependent behavior of vortex and Neel domain walls of the laminar domain structure of the dipolarly coupled epitaxial Co/Pd nanostrips with mutually perpendicular anisotropies induced by the atomic steps on the surface and by the long shape of nanostrips. We investigate the effect of dipole–dipole interaction between nanostrips on the magnetization reversal modes and switching fields depending on direction of the applied magnetic field. Our investigation reveals rather complex mechanisms of magnetization reversal of the nanostrip arrays, which can be described using a combination of processes including magnetization curling, transverse domain wall nucleation and motion as well as coherent rotation of spins within domains.

Topology optimized gold nanostrips for enhanced near-infrared photon upconversion

This letter presents a topology optimization study of metal nanostructures optimized for electric-field enhancement in the infrared spectrum. Coupling of such nanostructures with suitable ions allows for an increased photon-upconversion yield, with one application being an increased solar-cell efficiency by exploiting the long-wavelength part of the solar spectrum. In this work, topology optimization is used to design a periodic array of two-dimensional gold nanostrips for electric-field enhancements in a thin film doped with upconverting erbium ions. The infrared absorption band of erbium is utilized by simultaneously optimizing for two polarizations, up to three wavelengths, and three incident angles. Geometric robustness towards manufacturing variations is implemented considering three different design realizations simultaneously in the optimization. The polarization-averaged field enhancement for each design is evaluated over an 80 nm wavelength range and a ±15-degree incident angle span. The highest polarization-averaged field enhancement is 42.2 varying by maximally 2% under ±5 nm near-uniform design perturbations at three different wavelengths (1480 nm, 1520 nm, and 1560 nm). The proposed method is generally applicable to many optical systems and is therefore not limited to enhancing photon upconversion.

Strong coupling of diffraction coupled plasmons and optical waveguide modes in gold stripe-dielectric nanostructures at telecom wavelengths

We propose a hybrid plasmonic device consisting of a planar dielectric waveguide covering a gold nanostripe array fabricated on a gold film and investigate its guiding properties at telecom wavelengths. The fundamental modes of a hybrid device and their dependence on the key geometric parameters are studied. A communication length of 250 μm was achieved for both the TM and TE guided modes at telecom wavelengths. Due to the difference between the TM and TE light propagation associated with the diffractive plasmon excitation, our waveguides provide polarization separation. Our results suggest a practical way of fabricating metal-nanostripes-dielectric waveguides that can be used as essential elements in optoelectronic circuits.

Nanoimprinted SERS Sensors for Chemical and Biological Detection

ABSTRACTHerein, we demonstrate a facile, rapid, and scalable method to fabricate polymer-based gratings for surface-enhanced Raman spectroscopy (SERS) sensors. To accomplish this, epoxy nanostripe arrays on silicon substrates were prepared using thermal annealing and UV-cross-linking. After preparation of the nanostripe arrays, the surface was briefly treated with oxygen plasma, which decreased the surface energy and enabled the growth of AgNPs on the polymer surface using a simple, low-cost, aqueous-based synthesis procedure. The SERS substrates exhibited a detection limit of ∼1 pM using rhodamine 6G (R6G). In addition, preliminary work with E. coli DH5 showed that the nanoimprinted substrates can be used to obtain Raman spectra of washed bacteria cells.

Nanomechanical electro-optical modulator based on atomic heterostructures.

Two-dimensional atomic heterostructures combined with metallic nanostructures allow one to realize strong light–matter interactions. Metallic nanostructures possess plasmonic resonances that can be modulated by graphene gating. In particular, spectrally narrow plasmon resonances potentially allow for very high graphene-enabled modulation depth. However, the modulation depths achieved with this approach have so far been low and the modulation wavelength range limited. Here we demonstrate a device in which a graphene/hexagonal boron nitride heterostructure is suspended over a gold nanostripe array. A gate voltage across these devices alters the location of the two-dimensional crystals, creating strong optical modulation of its reflection spectra at multiple wavelengths: in ultraviolet Fabry–Perot resonances, in visible and near-infrared diffraction-coupled plasmonic resonances and in the mid-infrared range of hexagonal boron nitride's upper Reststrahlen band. Devices can be extremely subwavelength in thickness and exhibit compact and truly broadband modulation of optical signals using heterostructures of two-dimensional materials.