Structure Of Metal Films Research Articles

Parametric Excitation and Instabilities of Spin Waves Driven by Surface Acoustic Waves

AbstractThe parametric excitation of spin waves by coherent surface acoustic waves in metallic magnetic thin film structures is demonstrated experimentally using Brillouin light scattering spectroscopy. Complementary micromagnetic simulations and analytical modeling reveal that, depending on the experimental conditions, the spin‐wave instabilities originate from different phonon‐magnon and magnon‐magnon scattering processes. This opens novel ways to create micro‐scaled nonlinear magnonic systems for logic and data processing that profit from the efficient excitation of phonons using piezoelectricity.

Transmission anomalies in 2D photonic crystals from the checkerboard family: from broken to hidden symmetries and plasmon “spoofing”

In a field representation, the main symmetry of the electromagnetic response of complementary metal film structures is described by the Babinet principle, which is expected to be strictly obeyed by structures in vanishingly thin films of a perfect electric conductor. On the other hand, a softer version of this based on transmittance, the transmittance Babinet principle (TBP), is not so restrictive. The goal of this work is to study how severely this broken symmetry affects the optical response of such structures. We consider two geometrically distinct series of planar complementary structures from the checkerboard family: regular and bowtie. The self-complementary structure of these series is known to be very singular and breaks even the rigorous Babinet principle. Here, we study complete simulated transmittance spectral maps (T-Maps), which accumulate the whole spectral response of an entire series of structures in a single plot. The ab initio simulated T-Maps of these 2D photonic crystals were simulated for linearly polarized waves propagating perpendicular to these planar structures, made in a vanishingly thin film of a perfect electric conductor. While we confirm the expected long wavelength validity of the TBP, we show that in the frequency range where diffraction effects dominate, the standard derivation of the TBP no longer applies, and with the help of our T-Maps, we demonstrate a total collapse of the TBP in the structures considered. We show that this broken symmetry practically eliminates all but one transmission band on the hole side of the T-Maps and that the remaining strong band is a “spoof” plasmon, free of multiple frequency replicas, an important feature for optical filter applications. In addition, by symmetry arguments and simulations, we discovered that the T-Maps for bowtie and doubled-period regular structures are identical. We discuss how this hidden symmetry can benefit various applications by providing a convenient scaling, whereby simplified structures can deliver a tailored response.

Surface reconstructions and electronic structure of metallic delafossite thin films

Surface reconstructions and electronic structure of metallic delafossite thin films

Modulation of photonic skyrmions in a thin metal film structure.

Photonic skyrmions have been a hot topic in recent years. However, modulating the spin distributions of the skyrmions is still a challenging topic. In this paper, we investigate the detailed spin distributions of photonic skyrmions in thin metal film sandwiched by different dielectrics. We find that the ratios of different spin components can be adjusted by the thickness of the metal film, while the absolute value of total spin can be controlled by the frequency of the light source. Therefore, by choosing proper metal thickness in the preparation process and certain beam frequency in actual experiment, we can get the exact type of spin distribution we prefer. In addition, when the dielectric layers are arranged asymmetrically, the spin distributions can also be modulated significantly by adjustig the ratio of the dielectric constants of the upper and lower dielectric layers. Our results provide a new pathway for the modulation of photonic skyrmions.

Microstructure and mechanical properties of nano dual-phase TiCuNi metallic glass films achieved by modulating magnetron sputtering temperature

Nano-dual phase TiCuNi metallic glass film having amorphous matrix with some ∼8.5 nm CuTi nanograins dispersed were achieved by magnetron sputtering at deposition temperature of 200 °C. The temperatures below or above that resulted in the totally amorphous or columnar crystalline structures of as-deposited TiCuNi films, respectively. The nano dual-phase TiCuNi metallic glass film exhibited the greatest hardness of 7.5 GPa, which was greatly higher than those of the uncoated Ti6Al4V substrate, amorphous and crystalline TiCuNi films by ∼114.3%, 11.9% and 23.0%, respectively. It also performed the highest wear resistance with the lowest wear rate of 1.32 × 10−5 mm3/Nm, slower than those of the uncoated substrate, amorphous and crystalline TiCuNi by 14.3%, 5.0%, and 7.0%, respectively. This work reveals an effective method to realize nano-dual phase structure of TiCuNi metallic glass films with mechanical properties improved, which is significant for the further development of titanium-based metallic glass films.

Perfect absorption of symmetric grating structure based on the continuous metal film

The perfect absorption is achieved by the structure of a continuous metal film with symmetrical grating structure on both sides. The maximum absorption coefficient can reach 99.47% for a optimal structural parameters with a silver film thickness of 20 nm, a lattice constant of 400 nm, and a medium refractive index of 1.46. The full width of half maximum of the absorption line is about 2.53 nm, and the quality factor <i>Q</i> is 296.06. When the absorption is perfect, the reflection and transmission of the incident light are effectively suppressed, and the phase gradient of the absorption coefficient reaches a maximum value. The perfect absorption is determined by the long-range surface plasma polariton (LRSPP) with a little transmission loss, long propagation distance and deep penetration depth. And the electric field is mainly distributed outside the silver film with a standing wave distribution. As the thickness of the silver film decreases, the line width of the absorption spectrum gradually decreases, while the <i>Q</i> value and electric field strength increase. When the thickness drops to about 12 nm, the minimum line width is 0.98 nm and the maximum <i>Q</i> value is 760.0. The sharp absorption curve and very high quality factor at the perfect absorption can be used in the design and application of the highly sensitive micro-nano sensor.

Study on the Crack Propagation of Stiff-Thin-Film-on-Soft-Substrate Structures under Biaxial Loading.

With the development of flexible electronic technology, lately, there has been an increase in demand for flexible electronic devices based on soft polymer-substrate metal film structures in challenging applications. These soft polymer-substrate metal film structures must tolerate bending, folding, stretching, and even deformation into any shape without failing to be used successfully. As a result, research into the fracture behavior of soft polymer-substrate metal film structures is essential. The purpose of this study was to investigate how fractures develop in Cr film attached to a polyimide (PI) substrate under biaxial stress. A fracture development model was built to determine the fracture propagation law of soft polymer-substrate metal film structures under biaxial stress. Experiments and finite element methods were applied to verify the correctness of the model. The theoretical analysis and finite element simulation results showed that fractures appeared initially at the perimeter of the film and then propagated to the center under biaxial stress. The theoretical and experimental results indicated that the crack propagation direction was related to the ratio of biaxial loading, which became progressively parallel to the direction of small loading as the biaxial loading ratio increased. The theoretical results were in line with the experiment results, which could be used as a preliminary step for further research on the fracture behavior of film-substrate structures.

Design, Analysis, and Optimization of a Plasmonic Slot Waveguide for Mid-Infrared Gas Sensing.

In this work, we investigated the optimization of a plasmonic slot waveguide (PSWG) in the mid-IR region particularly for a representative wavelength of 4.26 µm, which is the absorption line of CO2 and thus particularly relevant for applications. We analysed the mode features associated with metal-dielectric-metal (MDM), dielectric-metal-dielectric (DMD), and truncated metal film (TMF) structures with respect to the considered PSWG. Subsequently, the mode features of the PSWG were considered based on what we outlined for MDM, DMD, and TMF structures. Furthermore, as confinement factor and propagation length are two crucial parameters for absorption sensing applications, we optimized the PSWG based on a figure of merit (FOM) defined as the product of the aforementioned quantities. To characterize the propagation length, the imaginary part of the effective mode index of a guided mode was considered, leading to a dimensionless FOM. Finally, we investigated the PSWG also for other wavelengths and identified particularly attractive wavelengths and geometries maximizing the FOM.

Structure and Photocatalytic Activity of Copper and Carbon-Doped Metallic Zn Phase-Rich ZnO Oxide Films

ZnO is one of the most important industrial metal oxide semiconductors. However, in order to fully realise its potential, the electronic structure of ZnO has to be modified to better fit the needs of specific fields. Recent studies demonstrated that reactive magnetron sputtering under Zn-rich conditions promotes the formation of intrinsic ZnO defects and allows the deposition of metallic Zn phase-rich ZnO films. In photocatalytic efficiency tests these films were superior to traditional ZnO oxide, therefore, the purposeful formation of intrinsic ZnO defects, namely Zn interstitials and oxygen vacancies, can be considered as advantageous self-doping. Considering that such self-doped ZnO remains a semiconductor, the natural question is if it is possible to further improve its properties by adding extrinsic dopants. Accordingly, in the current study, the metallic Zn phase-rich ZnO oxide film formation process (reactive magnetron sputtering) was supplemented by simultaneous sputtering of copper or carbon. Effects of the selected dopants on the structure of self-doped ZnO were investigated by X-ray diffractometer, scanning electron microscope, X-ray photoelectron spectroscope and photoluminescence techniques. Meanwhile, its effect on photocatalytic activity was estimated by visible light activated bleaching of Methylene Blue. It was observed that both dopants modify the microstructure of the films, but only carbon has a positive effect on photocatalytic efficiency.

Optical Analysis of Hole Patterned Ag Nanoparticle Structure.

A structure with periodic sub-wavelength nanohole patterns interacts with incident light and causes extraordinary optical transmission (EOT), with metal nanoparticles leading to localized surface plasmon resonance (LSPR) phenomena. To explore the effects of metal nanoparticles (NPs), optical analysis is performed for metal NP layers with periodic hole patterns. Investigation of Ag NP arrangements and comparisons with metal film structures are presented. Ag NP structures with different hole configuration are explored. Also, the effects of increasing light incident angle are investigated for metal NP structures where EOT peak at 460 nm wavelength is observed. Moreover, electric field distributions at each transmittance peak wavelengths and optical noise are analyzed. As a result, optical characteristics of metal NP structures are obtained and differences in resonance at each wavelength are highlighted.

Enhanced Mechanical Properties of Metallic Glass Thin Films via Modification of Structural Heterogeneity.

The structure of Cu50Zr50 and Co56Ta35B9 metallic glass thin films (MGTF) was effectively tailored via various applied substrate temperatures by means of the magnetron sputtering technology. Obviously enhanced hardness and elastic modulus are achieved by different compositional MGTFs by increasing the substrate temperature. Compared with the CuZr MGTFs, the CoTaB MGTF deposited at 473 K displays the smaller strain-rate sensitivity exponent, m, and a weaker spectrum intensity based on the nanoindentation creep test, suggesting its better creep resistance. In addition, the STZ volume of the CoTaB MGTF significantly decreases after depositing at higher temperature. According to the nano-scratch analysis, the CoTaB MGTF at the substrate temperatures of 473 K performs the shallower scratch width and the larger H3/E2 value, indicating its better tribological property.

Microhotplates based on Pt and Pt-Rh films: The impact of composition, structure, and thermal treatment on functional properties

Recent progress in portable semiconductor and thermocatalytic gas sensors requires the development of the microhotplates with reduced power consumption, increased shock resistance, and low resistance drift. Rh is known as alloying component, which allows one to decrease the diffusion mobility of Pt in bulk resistive heating elements. Here, a comparison study on the stability of microhotplates based on Pt and Pt-Rh thin films is performed. The porous anodic alumina is used as a substrate, which provides high adhesion of the metal film and the thermal expansion coefficient compatible with Pt and Pt-Rh alloys. Morphology and crystal structure of metal films are studied after recrystallization annealing in air at the temperatures 600–810 °C. To simulate thermal effects of the microhotplates, a model based on the finite element method is developed. The perspectives of Pt-11 % Rh alloy as a material for microhotplates operating at the temperatures above 500 °C are discussed. The achieved characteristics of the fabricated Pt-Rh microhotplates on porous anodic alumina substrates allow one to use them as a universal platform for semiconductor and thermocatalytic gas sensors manufacturing.

Out-of-plane surface patterning by subsurface processing of polymer substrates with focused ion beams.

This work explores a new technique for the out-of-plane patterning of metal thin films prefabricated on the surface of a polymer substrate. This technique is based on an ion-beam-induced material modification in the bulk of the polymer. Effects of subsurface and surface processes on the surface morphology have been studied for three polymer materials: poly(methyl methacrylate), polycarbonate, and polydimethylsiloxane, by using focused ion beam irradiation with He+, Ne+, and Ga+. Thin films of a Pt60Pd40 alloy and of pristine Au were used to compare the patterning of thin films with different microstructures. We show that the height of Pt60Pd40 thin films deposited onto poly(methyl methacrylate) and polycarbonate substrates can be patterned by He+ ion beams with ultrahigh precision (nanometers) while preserving in-plane features, at the nanoscale, of the pre-deposited films. Ion irradiation of the Au-coated samples results in delamination, bulging, and perforation of the Au film, which is attributed to the accumulation of gases from radiolysis at the film–substrate interface. The irradiation with Ne+ and Ga+ ions destroys the films and roughens the surface due to dominating sputtering processes. A very different behavior, resulting in the formation of complex, multiscale 3D patterns, is observed for polydimethylsiloxane samples. The roles of the metal film structure, elastic properties of the polymer substrate, and irradiation-induced mechanical strain in the patterning process are elaborated and discussed.

M13 Bacteriophage-Assisted Morphological Engineering of Crack-Based Sensors for Highly Sensitive and Wide Linear Range Strain Sensing.

Despite their extraordinary mechanosensitivities, most channel-like crack-based strain sensors are limited by their poor levels of stretchability and linearity. This work presents a simple yet efficient way of modulating the cracking structure of thin metal films on elastomers to facilitate the development of high-performance wearable strain sensors. A net-shaped crack structure based on a thin platinum (Pt) film can be produced by coating an elastomer surface with M13 bacteriophages (phages) and consequently engineering the surface strain upon stretching. This process produces a Pt-on-phage (PoP) strain sensor that simultaneously exhibits high levels of stretchability (24%), sensitivity (maximum gauge factor ≈ 845.6 for 20-24%), and linearity (R2 ≈ 0.988 up to 20%). In addition, the sensor performance can be further modulated by either changing the phage coating volume or adding a silver nanowire coating to the PoP sensor film. The balanced strain-sensing performance, combined with fast response times and high levels of mechanical flexibility and operational stability, enables the devices to detect a wide range of human motions in real time after being attached to various body parts. Furthermore, PoP-based strain sensors can be usefully extended to detect more complex multidimensional strains through further strain engineering on a cross-patterned PoP film.

Optical biosensing with electromagnetic nanostructures

Abstract The recent development in the field of optical biosensors based on plasmonic metamaterials, all-dielectric metamaterials and two-dimensional (2D) materials inclusive of van der Waals heterostructure have been reviewed in this article. Plasmonic metamaterials are divided based on their geometrical design, such as thin metallic film structures, an array of periodic structures, and single nanoparticle that are governed by the physical phenomenon of plasmon resonance. On the contrary, all-dielectric metamaterials based sensors are governed by the Mie scattering. Two-dimensional material exhibits high surface area to volume ratios, which makes them a strong candidates for realizing high sensitivity. This review encompasses all the latest developments over the last decade and forecasts the roadmap.

Triple-band perfect metamaterial absorber with good operating angle polarization tolerance based on split ring arrays

In this paper, a triple-band perfect metamaterial absorber based on Cu-dielectric-Cu triple-layer nanostructure is reported. The top metal film structure consists of a ring and four pairs of capacitor plates, which has a frequency selection effect, allowing the absorber to resonate in the near infrared range. Theoretical study shows that the absorption of the three absorption peaks (872.54 nm, 1008.69 nm and 1138.62 nm) are 87.1%, 99.9% and 99.6%, respectively. The average absorption is 95.53%, including two perfect absorption peaks. Changing the structural parameters can affect its absorption peaks and resonant wavelengths. At the same time, due to the high symmetry of the absorber, it is not sensitive to the polarization angle and incident angle. Whether in the TE mode or the TM mode, the absorber at a wide incident angle (0-60°) also exhibits good operating angle polarization tolerance. Therefore, the perfect metamaterial absorber we designed can be widely used in sensing.

The Dependence and Evolution Mechanism of Surface Structure of Electrodeposited Ni Films on Wettability

Porous metal films directly electrodeposited by using hydrogen bubbles as template have attracted widely attentions. However, the formation and evolution mechanism of pores are unclear. Lots of hydrogen bubbles are produced during electrodeposition, which will affect the surface structure of porous metal films. Wettability is an intrinsic property to adjust bubble separation and expected to change surface structure of electrodeposited metal film. In the paper, electrodeposited Ni was used as a model, and the effects of wettability on bubble characteristics and surface structure of Ni films were studied. The formation mechanism of pores was analyzed based on COMSOL simulation. The results indicated that the break-off diameter of bubbles decreased with the addition of sodium dodecyl sulfate (SDS) due to the decrease of contact angle and surface tension. Therefore, the pore size can be reduced. On superhydrophilic copper foil, rough Ni films without uniform pores were electrodeposited. On compact copper foil with the contact angel of 76o, honeycomb Ni films were obtained. On superhydrophobic copper foil, irregular Ni films with weak adhesion were electrodeposited and surface peeling happened easily. It was confirmed that pore formation was related to the protrusion growth of electrodeposited Ni.

Atomic Structure Probing of Thin Metal Films via Vacuum Holographic Microscopy

A vacuum holographic microscope is designed to probe the atomic structure of thin metal films. The experimental setup is based on the use of a source of a monochromatic low-energy electron beam induced by a tip cathode spaced from the sample at a distance of several tens of nanometers. The visual resolution of atoms of the object requires a microscope magnification of at least 105, which necessitates high-accuracy movement of the electron source. The parameters of principal nodes of the microscope, which are responsible for the generation and recording of useful signals, are studied and optimized, as well.

Dual-Band Infrared Perfect Absorber Based on a Ag-Dielectric-Ag Multilayer Films with Nanoring Grooves Arrays

In this paper, we demonstrate a dual-band metamaterial perfect absorber based on a Ag-dielectric-Ag multilayer nanostructure. The structure of top metal film covers nanoring grooves array. A dielectric layer has a function of confining electromagnetic fields. Theoretical analysis shows that two absorption peaks (1059 nm and 1304 nm) with the absorption of 99.2% and 99.9% have been achieved, respectively. The physical origin of perfect absorption peaks are related to the Fabry-Perot resonance effect and localized surface plasmon resonance (LSPR) of the nanoring grooves. Its perfect absorption and resonance wavelength can be well regulated by adjusting the relevant structural parameters. Additionally, the absorber demonstrates good operation angle-polarization-tolerance at wide incident angles (0–60°). We believe that our design has a promising application in plasmon-enhanced photovoltaic, optical absorption switching, and modulator optical communications in the infrared regime.

Structural and electronic characterization of Cu/Au(111) near-surface alloys

Geometrical structure and electronic characteristics of ultrathin metallic films of one metal on another are strongly influenced by factors such as lattice mismatch and formation of near-surface alloys. Doped systems often show modified chemico-physical properties which may be amenable to different reactivity routes. Copper–gold surface alloys have received the attention of several studies, only a few of which have been undertaken in an ultra-high vacuum environment, using surface sensitive techniques. In this contribution, systems produced upon room temperature deposition of copper on the (22 × √3)-Au(111) surface, at various copper loadings and annealed to different temperatures, are investigated using scanning tunneling microscopy and synchrotron radiation based techniques (X-ray photoelectron diffraction, photoemission), with comparison with some theoretical modeling. Overall the fcc lattice is essentially maintained on preparation. Upon thermal treatments structural and compositional changes, in favor of alloyed structures with tetragonal packing, are seen.