Metal-dielectric Systems Research Articles

Differentiating contribution of electron–phonon coupling to the thermal boundary conductance of metal–metal–dielectric systems

Electron–phonon coupling thermal resistance in metals is a key factor affecting the thermal boundary conductance (TBC) of metal–metal–dielectric systems. However, quantitatively differentiating the contribution of electron–phonon coupling to TBC is still a challenge, as various thermal resistances are coupled in a complicated manner at the metal–metal–dielectric interface. Herein, we propose a two-step strategy to study electron–phonon coupling. We first decouple the phonon–phonon thermal conductance (TBCp-p) between metallic interlayer and dielectric from the metal–metal–dielectric interface by experimentally characterizing the TBCp-p of a single metallic interlayer deposited dielectric with the transient thermoreflectance technique; Combining metal–metal–dielectric TBC measurement and a thermal circuit model with measured TBCp-p as input, the contribution of electron–phonon coupling to TBC of the metal–metal–dielectric system is differentiated quantitatively. For the Au–Ni–GaN system, the contribution of electron–phonon coupling thermal resistance in the Ni interlayer (Re−ph,Ni) is substantially higher at lower Ni interlayer thickness, reaching 35% at ∼1 nm Ni. The electron–phonon coupling constant of Ni (gNi) was fitted in the range of 6.4 × 1016–36 × 1016 W/m3K. The above results were also verified in the Au–Ni–SiC system. This study will promote a deeper understanding of the thermal transport in the metal–metal–dielectric system and provide an insightful indication for the manipulation of TBC in this system.

Physical Approaches to the Design of Functional Metal–Dielectric Systems Based on Opals in Photonics

Physical Approaches to the Design of Functional Metal–Dielectric Systems Based on Opals in Photonics

Role of vibrational properties and electron–phonon coupling on thermal transport across metal-dielectric interfaces with ultrathin metallic interlayers

We systematically analyze the influence of 5 nm thick metal interlayers inserted at the interface of several sets of different metal-dielectric systems to determine the parameters that most influence interface transport. Our results show that despite the similar Debye temperatures of Al2O3 and AlN substrates, the thermal boundary conductance measured for the Au/Al2O3 system with Ni and Cr interlayers is ∼2× and >3× higher than the corresponding Au/AlN system, respectively. We also show that for crystalline SiO2 (quartz) and Al2O3 substrates having highly dissimilar Debye temperature, the measured thermal boundary conductance between Al/Al2O3 and Al/SiO2 are similar in the presence of Ni and Cr interlayers. We suggest that comparing the maximum phonon frequency of the acoustic branches is a better parameter than the Debye temperature to predict the change in the thermal boundary conductance. We show that the electron–phonon coupling of the metallic interlayers also alters the heat transport pathways in a metal-dielectric system in a nontrivial way. Typically, interlayers with large electron–phonon coupling strength can increase the thermal boundary conductance by dragging electrons and phonons into equilibrium quickly. However, our results show that a Ta interlayer, having a high electron–phonon coupling, shows a low thermal boundary conductance due to the poor phonon frequency overlap with the top Al layer. Our experimental work can be interpreted in the context of diffuse mismatch theory and can guide the selection of materials for thermal interface engineering.

Numerical simulations of the surface plasmon-assisted photo-magnetic effect in metal-dielectric nanostructures [Invited

We study numerically plasmonic localization and enhancement of the photo-magnetic excitation in metal-garnet nanostructures with surface plasmons excited at the opposite interfaces of the metallic layer. Contrary to intuitive expectations, the resonance at the metal/air interface results in the highest photo-magnetic excitation efficiency. Our findings highlight the key role of the phase shift between the electric field components inside the garnet layer. A comprehensive analysis of the optical losses reveals the importance of absorption in the photo-magnetic dielectric. These results provide a fruitful perspective for future experiments on metal-dielectric photo-magnetic systems towards all-optical magnetization switching at the nanoscale.

Physical approaches to the design of functional metal-dielectric systems based on opals in photonics

The possibilities of practical implementation of physical approaches to the design of metal-dielectric photonic crystal systems based on opals, which allow controlling the propagation of electromagnetic waves, are shown. The implemented approaches are based on the effects of excitation of surface plasmon-polaritons capable of propagating along the metal-dielectric interface in plasmonic-photonic layered heterostructures, and modification of the photonic-energy structure of the nanocomposite as a result of dispersion of silver in the opal matrix. Experimental results are presented indicating the occurrence of extraordinary transmission and absorption of light in plasmonic-photonic heterostructures, as well as the asymmetric shape of curves in the reflection spectra of nanocomposites, which is associated with the Fano resonance. Keywords: photonic crystals, opals, surface plasmon-polaritons, metal-dielectric systems, Fano resonance.

PECULIAR PROPERTIES OF ELECTROMAGNETIC RADIATION 
 PROPAGATION IN PHOTONIC CRYSTALLINE 
 METAL-DIELECTRIC SYSTEMS BASED ON OPALS

The article studies the propagation of electromagnetic waves in metal-dielectric systems based on opals. We revealed anomalous transmission and absorption of light by hybrid plasmon- photonic layered heterostructures associated with the excitation of surface plasmon polaritons propagating along the metal-dielectric interface. The position of maxima in the reflection spectra of nanocomposites, obtained by filling the opal matrix with metal by the electrothermodiffusion method, is explained by the Bragg diffraction, and the asymmetric form of the spectral curves is attributed to the Fano resonance.

Tunable plasmonic resonator using conductivity modulated Bragg reflectors

We design a tunable plasmonic resonator that may have applications in sensing and plasmon generation—our design uses graphene-based Bragg reflectors of periodically modulated conductivity. Specifically, we explore and utilize the ability to use an array of Gaussian conductivity gratings as fully reflecting mirrors for surface plasmon polaritons (SPPs) propagating along a two-dimensional graphene sheet sandwiched between two dielectric materials. Graphene supports SPPs in the near-infrared to terahertz (THz) regime of the electromagnetic spectrum compared to those observed in metal-dielectric systems. Our resonator is fundamentally different from other similar published resonator designs because the distributed reflectors provide light confinement in both the horizontal and the vertical directions. As a result, the resonator is compact in the vertical-direction as we no longer use traditional mirrors or dielectric assisted gratings. Besides, conventional resonator designs only support a single, fixed resonant frequency, set by the mirror reflectivity and the cavity material’s properties. The versatility of graphene is that its Fermi energy can be electrically varied, thus allowing us to change the peak reflectivity of the graphene Bragg-grating without physically changing its physical dimensions. Therefore, by varying the Bragg wavelength, we can shift the resonance frequency of the cavity. One use of our resonator is in plasmonic lasers. We illustrate this use by analyzing the resonator parameters such as the linewidth and the quality factor of the plasmonic resonator.

Barrier heights of polymer-electrode interfaces measured via photo injection current method

The metal-polymer contact interface plays a major role in the conduction and breakdown process in flexible dielectrics. Enhancing barrier heights has been investigated for effectively blocking the charge injection and thus impeding the degradation of the dielectrics in the field. However, the electronic band structure at the metal-dielectric interface and its relationship with the electrical insulation properties are still not well understood due to the complex morphological details of the interfacial region. Here, we determine the barrier height profiles of various sets of metal electrodes and dielectric polymers systems by utilizing the photo injection current method. Our results reveal that all aromatic polymers tend to have lower barrier heights than aliphatic polymers, and thus we believe that the chemical structure plays a prominent role in determining the barrier heights. Additionally, an important trend for aromatic polymers/metal configurations has been found that those aromatic polymers with higher glass transition temperatures feature however lower injection barrier heights. The correlations uncovered in this work unveil an effective approach of rational modifying the chemical structure to build polymers that can efficiently block charge injection for reliable insulation performance at elevated temperatures.

Transmission and Conversion of Electromagnetic Radiation by Photonic Crystal Metal–Dielectric Systems Based on Opals

An experimental study of the optical properties of two types of metal–dielectric composites based on opal matrices has been carried out: (1) layered structures, obtained by successive deposition of metal and dielectric films on a monolayer of opal globules, where anomalous transmission and absorption of light was found due to the excitation of surface plasmon polaritons of various types; (2) “massive” opal samples, into which the metal was introduced by the method of electrothermal diffusion, where an asymmetric shape of Bragg resonance curves was observed, due to the Fano resonance.

Nonpolarizing Interference Systems Containing Metallic Layers

The structure of nonpolarizing interference systems incorporating the layers manufactured from metallic materials is considered. The method of searching for the structures of metal-dielectric interference systems providing a small deviation between the spectral characteristics of the energy reflection (transmission) coefficient for s- and р-polarizations is presented. The structures developed on the basis of the presented method have a rather simple structure, which makes them easy to implement. The analysis of the spectral characteristics of the obtained structures has demonstrated that the difference between the integral refl-ection coefficients for s- and p-polarizations within the considered spectral region (460–580 nm) is less than 1%.

Неполяризующие интерференционные системы, содержащие металлические слои

The structure of nonpolarizing interference systems containing metallic layers is considered. The technique of searching metal-dielectric interference systems, providing a small discrepancy between the spectral characteristics reflection (transmission) for s- and p- polarizations, is presented. The constructions developed on the basis of the presented method have a rather simple structure that ensures the ease of their implementation. Analysis of the spectral characteristics showed that in the spectral range (460–580) nm, the difference between the integral reflection coefficients for s- and p- polarizations does not exceed 1%.

Atomically modified thin interface in metal-dielectric hetero-integrated systems: control of electronic properties

We have performed first-principles studies of the electronic properties of Cu-diamond hetero-integrated systems, particularly placing emphasis on elucidating the effects of surface modification of diamond with H or O. It is found that the electronic properties crucially depend on the chemical compositions of the modified atomically thin interface region. The local density of states (LDOS) of the H-terminated diamond moiety near the Cu surface exhibits a clearly different distribution from that near the vacuum region, whereas the LDOS of the O-terminated diamond is almost independent of the Cu deposition. In other words, the effects of the electronic interactions between Cu and diamond on the electronic properties in the interface region are readily controlled by surface modification with only one atomic (i.e. H or O) layer. Electric field (EF) effects on the Cu-diamond systems also strongly depend on the electronic details, i.e. atomistic modification in the interface regions. In particular, at the interface between the H-terminated diamond moiety and the vacuum region, its conduction band energy is strongly affected by an applied EF much more than the valence band energy; that is, the band gap can be varied with an applied EF. The band gap variation is found to be attributed to an atomistic level difference in the spatial extension of the valence and conduction bands and thus is not explained with a macroscopic band diagram model. It has been demonstrated that the electronic properties of hetero-integrated systems are described and controlled well by carefully designing atomically thin interface regions.

Downscaling metal-dielectric interface fracture experiments to sub-micron dimensions: A feasibility study using TEM

In this study a bending beam approach is miniaturized to the sub-micrometer size regime for in-situ transmission electron microscopy (TEM) investigations. The purpose of this study was to evaluate the feasibility of this method for determining interface fracture energies for metal-dielectric systems, which are comparable to other methods. The interfaces under investigation are Cu/borophosphosilicate glass (BPSG) and W(20at.% Ti)/BPSG as examples for a weak and a strong interface, respectively. It was possible to fracture the Cu/BPSG interface during in-situ TEM experiments and to obtain estimates for the interface fracture energy comparable to literature values. However, the TEM approach imposes challenges which can complicate the determination of an interface energy release rate; these influences are discussed. The miniaturized TEM approach failed for W(20at.% Ti)/BPSG because no interface fracture occurred in this case. Thus it is concluded, that the experimental setup of the in-situ TEM bending beam method utilized in this study is useful for weak interfaces but for strongly adhering interfaces it is inappropriate.

Modified embedded-atom method interatomic potential and interfacial thermal conductance of Si-Cu systems: A molecular dynamics study

Thermal contact conductance of metal-dielectric systems is a key parameter that has to be taken into account for the design and reliability of nanostructured microelectronic systems. This paper aims to predict this value for Si-Cu interfaces using molecular dynamics simulations. To achieve this goal, a modified embedded atom method interatomic potential for Si-Cu system has been set based upon previous MEAM potentials for pure Cu and pure Si. The Si-Cu cross potential is determined by fitting key properties of the alloy to results obtained by ab initio calculations. It has been further evaluated by comparing the structure and energies of Cu dimmers in bulk Si and CumSin clusters to ab initio calculations. The comparison between MD and ab initio calculation also concerns the energy barrier of Cu migration along the (110) channel in bulk Si. Using this interatomic potential, non equilibrium molecular dynamics has been performed to calculate the thermal contact conductance of a Si-Cu interface at different temperature level. The results obtained are in line with previous experimental results for different kind of interfaces. This confirms that the temperature variation of the thermal conductance might not find its origin in the electron-phonon interactions at the interface nor in the quantification of the energy of the vibration modes. The diffuse mismatch model is also used in order to discuss these results.

Optical and tribomechanical stability of optically variable interference security devices prepared by dual ion beam sputtering

Optical security devices applied to banknotes and other documents are exposed to different types of harsh environments involving the cycling of temperature, humidity, chemical agents, and tribomechanical intrusion. In the present work, we study the stability of optically variable devices, namely metameric interference filters, prepared by dual ion beam sputtering onto polycarbonate and glass substrates. Specifically, we assess the color difference as well as the changes in the mechanical properties and integrity of all-dielectric and metal-dielectric systems due to exposure to bleach, detergent and acetone agents, and heat and humidity. The results underline a significant role of the substrate material, of the interfaces, and of the nature and microstructure of the deposited films in long term stability under everyday application conditions.

Negative Index Materials With Gain Media for Fast Optical Modulation

<para xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> We discuss the origin of negative index behavior that is observed in certain artificial structures known as metamaterials that are periodic structures supporting <emphasis emphasistype="italic">backward</emphasis> optical waves with generally antiparallel phase and group velocities. Slab-like metamaterials, metal-dielectric, and purely dielectric ones support surface-plasmon polaritons that may be coupled into by an incident field. When this is the case, these surface waves can be pumped by the source, lead to pumping of the evanescent waves, and, as a result, enable subwavelength resolution. The main limiting factors for subwavelength resolution are losses and surface imperfections. Metal-dielectric metamaterials and systems are of special interest to nanophotonics, the focus of this paper, since they obviously provide high dielectric contrast, much larger than all-dielectric/semiconductor systems. This makes them promising for applications in dense integrated optical systems, since the mode volume is small. We consider various ways of combining metallic materials for negative dielectric constant and a gain medium to compensate for optical losses. Ultimately, one would like to make Si-compatible subwavelength optical components using metamaterials. </para>

Strong influence of nonlinearity and surface plasmon excitations on the lateral shift

When surface plasmons are excited at a metal-dielectric interface, the electromagnetic field takes a very large value near the interface. If the dielectric is a nonlinear Kerr medium, then the effect of nonlinearity can be greatly amplified due to the field enhancement. In this paper, we calculate the lateral shift of p wave beams incident on metal-dielectric multilayer systems in the Otto configuration in a numerically exact manner, using the invariant imbedding method of wave propagation in nonlinear stratified media. In the linear case, we find that the lateral shift becomes very large at the incident angles where the surface plasmons are excited. As the nonlinearity is turned on, the value of the lateral shift changes rapidly. We find that even a small change of the intensity of the incident wave can cause a huge change of the lateral shift. We propose that this phenomenon can be applied to designing precise optical switches operating at small powers.

Charge transfer and dielectric properties of granular nanocomposites Cox(LiNbO3)100 − x

The electrical and dielectric properties of thin-film heterogeneous nanostructures of Cox(LiNbO3)100 − x were studied in a wide concentration range of the metallic phase at room temperature. The percolation threshold characteristic of granular metal-dielectric systems was found. At low concentrations of the metallic phase, the concentration dependence of the permittivity is described by the Bruggeman formula. The conduction mechanism was found to change at low temperatures.

Determining the colorimetric parameters and optimizing the design of colored mirrors based on metal-dielectric interference systems

Determining the colorimetric parameters and optimizing the design of colored mirrors based on metal-dielectric interference systems

Electric discharge in water as a source of UV radiation, ozone andhydrogen peroxide

Results are presented from investigations of multispark electricdischarge in water excited along multielectrode metal-dielectric systems withgas supply into the interelectrode gaps. The intensity distribution ofdischarge radiation in the region covering the biologically active soft UV(190⩽λ⩽430 nm) has been determined and the absolute number ofquanta in this wavelength interval has been measured. The potentiality of theslipping surface discharge in water for its disinfection is analysed. Theenergy expenditure for water cleansing is estimated to be as low as~10-4 kWh l-1.