Structured Metal Surface Research Articles

Experimental demonstration of Fabry-Perot open resonators in a surface-wave bandgap crystal

We report on the proposal and experimental realization of a type of retardation-based Fabry-Perot (FP) open resonator in a surface-wave bandgap crystal implemented on a single structured metal surface. This surface-wave FP open resonator is formed by introducing a finite line defect in the surface-wave bandgap crystal, whose resonance frequencies lie exactly within the forbidden bandgap of the surrounding crystal. Due to the complete surface-wave forbidden bandgap, a new FP plasmonic resonance mode exhibiting monopolar features which is missing in both traditional FP resonators and plasmonic resonators is emerged. Near-field response spectra and imaged mode profiles are presented to characterize the properties of these FP open resonators in the microwave regime.

Organic semiconductor film enhances Raman signals

Since its discovery in the 1970s, surface-enhanced Raman spectroscopy (SERS) has been used to boost the signal obtained from molecules sitting on rough or finely structured metal surfaces, typically made of either silver or gold. Now, Gokhan Demirel of Gazi University, Hakan Usta of Abdullah Gül University, Antonio Facchetti and George C. Schatz of Northwestern University, and coworkers have achieved signal enhancement using a nanostructured organic semiconductor as a SERS substrate (Nat. Mater. 2017, DOI: 10.1038/nmat4957). To make the substrate, the researchers start with an organic semiconductor called α,ω-diperfluorohexylquaterthiophene (DFH-4T). “This molecule is easy to synthesize, and the synthesis can be scaled up,” Usta says. “You can prepare micro- or nanostructured films of DFH-4T very easily” by depositing a vapor of the molecules onto a surface, Demirel adds. The researchers tweak the conditions conventionally used for physical vapor deposition to make their films. For instance, they move the source of

Nanosecond laser texturing of uniformly and non-uniformly wettable micro structured metal surfaces for enhanced boiling heat transfer

Microstructured uniformly and non-uniformly wettable surfaces were created on 25-μm-thin stainless steel foils by laser texturing using a marking nanosecond Nd:YAG laser (λ=1064nm) and utilizing various laser fluences and scan line separations. High-speed photography and high-speed IR thermography were used to investigate nucleate boiling heat transfer on the microstructured surfaces. The most pronounced results were obtained on a surface with non-uniform microstructure and non-uniform wettability. The obtained results show up to a 110% higher heat transfer coefficients and 20–40 times higher nucleation site densities compared to the untextured surface. We show that the number of active nucleation sites is significantly increased in the vicinity of microcavities that appeared in areas with the smallest (10μm) scan line separation. Furthermore, this confirms the predictions of nucleation criteria and proves that straightforward, cost-effective nanosecond laser texturing allows the production of cavities with diameters of up to a few micrometers and surfaces with non-uniform wettability. Additionally, this opens up important possibilities for a more deterministic control over the complex boiling process.

Enhanced near-field radiative heat transfer between corrugated metal plates: Role of spoof surface plasmon polaritons

We demonstrate with the finite-difference time-domain method that radiative heat transfer between two parallel gold plates can be significantly enhanced by engraving periodic grooves with a subwavelength width on the plate surfaces. The enhancement increases with a decrease in the separation distance at near-field regime and it can be further efficiently improved by having a supercell with multiple grooves with different depths. We attribute this near-field enhancement to coupling of thermally excited spoof surface plasmon polaritons, a type of artificial surface wave inherent to structured metal surfaces [J. B. Pendry, L. Mart\'{\i}n-Moreno, and F. J. Garcia-Vidal, Science 305, 847 (2004)]. The frequency-dependent contribution to the heat transfer, or transmission-factor spectrum, is confirmed by calculating the dispersion relation of guided modes by the two parallel corrugated plates through a finite-element method. Especially, the photonic density of states derived from the dispersion relation is found to have excellent agreement to the transmission-factor spectrum.

Ultrathin 90-degree sharp bends for spoof surface plasmon polaritons.

At low frequencies outside the plasmonic range, strongly confined surface waves can be achieved on periodically structured metal surfaces, thereby allowing for the design of compact electromagnetic guiding devices. Here, we propose an approach to realize highly efficient transmission of spoof surface plasmons around 90-degree sharp bends on ultrathin metallic films in the microwave regime. We demonstrate that by judiciously engineering the structure, the dispersion relation can be designed to reduce the scattering. Furthermore, the reflection can be suppressed by proper structural decoration at the bending corner. A one-dimensional scattering theory is employed to understand and verify the transmission properties of our waveguide bend structure. Our design scheme is not restricted to the specific structure we propose here but can be applied to other guiding components built up on two dimensional metal surfaces.

Odd-mode surface plasmon polaritons supported by complementary plasmonic metamaterial.

Surface plasmon polaritons (SPPs), either on metal-dielectric interfaces in optical frequencies or on structured metal surfaces in the lower frequencies, are dominantly even modes. Here we discover dominant odd-mode SPPs on a complementary plasmonic metamaterial, which is constructed by complementary symmetric grooves. We show that the fundamental SPP mode on such a plasmonic metamaterial is a tightly confined odd mode, whose dispersion curve can be tuned by the shape of groove. According to the electric field distributions of odd-mode SPPs, we propose a high-efficiency transducer using asymmetric coplanar waveguide and slot line to excite the odd-mode SPPs. Numerical simulations and experimental results validate the high-efficiency excitation and excellent propagation performance of odd-mode SPPs on the complementary plasmonic waveguides in the microwave frequencies.

One-step formation of multifunctional nano- and microscale structures on metal surface by femtosecond laser

Metals in nature exhibit a mediocre wettability and a high optical reflectance from the visible region to the infrared. This Letter reports that, by formation of nano- and microscale structures via a simple raster scanning of a focused femtosecond laser pulse without any further treatment, structured aluminum and nickel surfaces exhibit combined features of superhydrophobicity with a contact angle of 155.5°, and a high optical absorption with a reflectivity of several percent over a broad spectral range (0.2–2.5 μm). Thus, a multifunctional structured metal surface that integrates superhydrophobicity and a high broadband absorptivity has been easily realized by one-step femtosecond laser processing.

Study on Zeeman-split spoof surface plasmon polaritons by use of spin-sensitive enhanced electromagnetic transmission

Structured metal surfaces could support spoof surface plasmon polaritons (SPPs), the dispersion of which is determined by the cutoff condition of guided modes in the nanostructures. We show that we can achieve split spoof SPPs by breaking the degeneracy of guided helical modes in concentric nanostructures via the classic analogue of the Zeeman effect. This split effect is shown to be observable from the spectra of enhanced electromagnetic transmission. Spin-sensitive enhanced electromagnetic transmission and the associated characteristics of field are investigated. Transmission branches versus parallel wavevector can be satisfactorily fitted by using the dispersion of spoof SPPs.

Artificial TE-mode surface waves at metal surfaces mimicking surface plasmons

Manipulation of light in subwavelength scale can be realized with metallic nanostructures for TM-polarization components due to excitation of surface plasmons. TE-polarization components of light are usually excluded in subwavelength metal structures for mesoscopic optical interactions. Here we show that, by introducing very thin high index dielectric layers on structured metal surfaces, pseudo surface polarization currents can be induced near metal surfaces, which bring to excitation of artificial TE-mode surface waves at the composite meta-surfaces. This provides us a way to manipulate TE-polarized light in subwavelength scale. Typical properties of the artificial surface waves are further demonstrate for their excitation, propagation, optical transmission, and enhancement and resonances of the localized fields, mimicking those of surface plasmon waves.

Propagation speed calculation of a plasmonic THz wave trapping system

A graded metallic grating structure acts as a wave trapping system. Different frequencies of THz waves are trapped at different positions along this structured metal surface grating. The real wave propagation speed of such a system is reduced gradually from the light speed in vacuum to zero, which is demonstrated by calculation and simulation. Different frequencies of THz waves are propagated at a designed propagation speed by a partial graded grating according to the practical demand.

Dyakonons in hyperbolic metamaterials

We have analyzed surface-wave propagation that takes place at the boundary between an isotropic medium and a semi-infinite metal-dielectric periodic medium cut normally to the layers. In the range of frequencies where the periodic medium shows hyperbolic space dispersion, hybridization of surface waves (dyakonons) occurs. At low to moderate frequencies, dyakonons enable tighter confinement near the interface in comparison with pure SPPs. On the other hand, a distinct regime governs dispersion of dyakonons at higher frequencies. Full Text: PDF References Z. Ruan, M. Qiu, "Slow electromagnetic wave guided in subwavelength region along one-dimensional periodically structured metal surface", Appl. Phys. Lett. 90, 201906 (2007). CrossRef A. Yariv, P. Yeh,"Electromagnetic propagation in periodic stratified media. II. Birefringence, phase matching, and x-ray lasers", J. Opt. Soc. Am. 67, 438 (1977). CrossRef D.R. Smith, D. Schurig, "Electromagnetic Wave Propagation in Media with Indefinite Permittivity and Permeability Tensors", Phys. Rev. Lett. 90, 077405 (2003). CrossRef I.I. Smolyaninov, E. Hwang, E. Narimanov, "Hyperbolic metamaterial interfaces: Hawking radiation from Rindler horizons and spacetime signature transitions", Phys. Rev. B 85, 235122 (2012). CrossRef Z. Jacob, E.E. Narimanov, "Optical hyperspace for plasmons: Dyakonov states in metamaterials", Appl. Phys. Lett. 93, 221109 (2008). CrossRef M.I. D'yakonov, "New type of electromagnetic wave propagating at an interface", Sov. Phys. JETP 67, 714 (1988). DirectLink I.I. Smolyaninov, Y.J. Hung, C.C. Davis, "Magnifying Superlens in the Visible Frequency Range", Science 315, 1699 (2007). CrossRef J. Elser, V.A. Podolskiy, I. Salakhutdinov, I. Avrutsky, "Nonlocal effects in effective-medium response of nanolayered metamaterials", Appl. Phys. Lett. 90, 191109 (2007). CrossRef E. Popov, S. Enoch, "Mystery of the double limit in homogenization of finitely or perfectly conducting periodic structures", Opt. Lett. 32, 3441 (2007). CrossRef B. Wood, J.B. Pendry, D.P. Tsai, "Directed subwavelength imaging using a layered metal-dielectric system", Phys. Rev. B 74, 115116 (2006). CrossRef

Assembling polystyrenes spheres arrays in specified regions for required nanophotonic structures

We present an effective method to assemble the PSs in specified regions by hydrophiling the substrate in designed regions for the nanophotonics with nanostructures in well-definite regions. A hydrophilic positioning template which carries designed metal structures is prepared by lithography according to the specified requirement. Following that, the structured metal surface is treated to be hydrophobic by a 184 polydimethylsiloxane (PDMS) membrane. After self-assembly and metal lift-off process, the PSs can be assembled only in the well-defined pattern regions. The corresponding experiments were performed and PSs were assembled in the different shapes regions.

Broadband and broadangle SPP antennas based on plasmonic crystals with linear chirp

Plasmonic technology relies on the coupling of light to surface electromagnetic modes on smooth or structured metal surfaces. While some applications utilise the resonant nature of surface polaritons, others require broadband characteristics. We demonstrate unidirectional and broadband plasmonic antennas with large acceptance angles based on chirped plasmonic gratings. Near-field optical measurements have been used to visualise the excitation of surface plasmon polaritons by such aperiodic structures. These weakly aperiodic plasmonic crystals allow the formation of a trapped rainbow-type effect in a two-dimensional geometry as surface polaritons of different frequencies are coherently excited in different locations over the plasmonic structure. Both the crystal's finite size and the finite lifetime of plasmonic states are crucial for the generation of broadband surface plasmon polaritons. This approach presents new opportunities for building unidirectional, broadband and broad-angle plasmonic couplers for sensing purposes, information processing, photovoltaic applications and shaping and manipulating ultrashort optical pulses.

Interaction between viral particles and structured metal surface under surface plasmon propagation

Interaction between viral particles and structured metal surface under surface plasmon propagation

Controlling extraordinary transmission characteristics of metal hole arrays with spoof surface plasmons

We experimentally controlled the spectral characteristics of the extraordinary transmissions observed in metal hole arrays by analogy with spoof surface plasmon-polaritons (spoof SPPs). We constructed doubly periodic metal hole arrays. The larger and smaller periodic holes are for inducing extraordinary transmissions and modifying the spoof SPPs’ characteristics, respectively. Introducing the smaller holes that surround the larger hole arrays can modify the dispersion curve of the surface waves excited on a structured metal surface analogous to the spoof SPP model, and consequently, the extraordinary transmission peak will show a redshift.

Surface Plasmon Waves on Structured Metal Surface With Periodic Grooves Modified by Perpendicular Cuts

We study the mechanisms of the surface plasmon wave (SPW) resonance on a metallic periodic groove grating with perpendicular cuts using the finite-difference time-domain method. The dependence of cuts on the resonant frequency of the SPWs which is theoretically analyzed by a proposed inductance-capacitance transmission line model show a red or blue shift of the resonant frequency, which can be attributed to the change of the equivalent inductance and capacitance caused by the surface current flow and charge distribution.

Plasmonic metasurfaces for waveguiding and field enhancement

AbstractThe explosive progress in nanoscience has led to uncovering and exploring numerous physical phenomena occurring at nanoscale, especially when metal nanostructures are involved so that optical fields and electronic oscillations can be resonantly coupled. The latter is the subject of (nano) plasmonics with implications extending from subwavelength waveguiding to localized field enhancements. In this review paper, we consider making use of various phenomena related to multiple scattering of surface plasmons (SPs) at periodically and randomly (nano) structured metal surfaces. After reviewing the SP waveguiding along channels in nanostructured areas exhibiting band‐gap and localization effects, SP‐driven field enhancement in random structures and plasmonic fractal drums is discussed in detail. SP manipulation and waveguiding using periodic nanostructures on the long‐wavelength side of the band gap is also considered.

Brighter Light Sources from Black Metal: Significant Increase in Emission Efficiency of Incandescent Light Sources

By applying the femtosecond laser blackening technique directly to a tungsten incandescent lamp filament, we dramatically brighten the tungsten lamp and enhance its emission efficiency to approach 100%. A comparison study of emission and absorption for the structured metal surfaces shows that Kirchhoff's law is applicable for the black metal. Furthermore, we demonstrate that we can even obtain partially polarized light as well as control the spectral range of the optimal light emission from the laser-blackened tungsten lamp.

Cherenkov emission of terahertz surface plasmon polaritons from a superluminal optical spot on a structured metal surface

We propose to launch terahertz surface plasmon polaritons on a structured metal surface by using a femtosecond laser pulse obliquely incident on a strip of an electro-optic material deposited on the surface. The laser pulse creates a nonlinear polarization that moves along the strip with a superluminal velocity and emits surface terahertz waves via the Cherenkov radiation mechanism. We calculate the radiated fields and frequency distribution of the radiated energy for a grooved perfect-conductor surface with a GaAs strip illuminated by Ti:sapphire laser. This technique can be used to perform surface terahertz spectroscopy.

Ultra-broadband enhanced absorption of metal surfaces structured by femtosecond laser pulses

We investigate the enhanced absorption properties in a wavelength range of 0.2-25 microm for NiTi alloy targets structured by femtosecond laser pulses in air. Three different types of surface structures are produced with varying laser fluences. Measured reflectances through integrating sphere technique show that their couplings of incident electromagnetic irradiations are improved greatly over the broadband wavelength range. In particular, for coral-like micro-structures on the metal surfaces, approximate 90% absorption can be achieved from ultraviolet to mid-infrared region. Cut-off wavelengths of the enhanced absorption for the varied dimensional surface structures are determined experimentally. Chemical analysis by X-ray photoelectron spectroscopy indicates that blackness of metal surfaces is not attributed to the change in elemental composition. The physics of such remarkable absorption for the structured metal surfaces are discussed as well.