Metal-dielectric Structures Research Articles

Numerical study on a random plasmonic laser in the metal-insulator-metal structure.

This Letter proposes a random plasmonic laser in the metal-insulator-metal (MIM) structure, in which the dielectric core with gain is dispersed with circular dielectric nanoscatterers. The numerical results from finite-difference time-domain simulation indicate that scattering by the randomly distributed dielectric nanoscatterers in the MIM waveguide provides feedback to the random laser with surface plasmon. The design bypasses the requirement of a distributed feedback structure for the plasmonic waveguide-based nanolasers, which is challenging and expensive in fabrication. Additionally, the MIM structure makes this type of random laser easily applicable to nanoscale integrated photonic devices and circuits.

Plasmon-induced coherence, exciton-induced transparency, and Fano interference for hybrid plasmonic systems in strong coupling regime.

We present an analytical model describing the transition to a strong coupling regime for an ensemble of emitters resonantly coupled to a localized surface plasmon in a metal-dielectric structure. The response of a hybrid system to an external field is determined by two distinct mechanisms involving collective states of emitters interacting with the plasmon mode. The first mechanism is the near-field coupling between the bright collective state and the plasmon mode, which underpins the energy exchange between the system components and gives rise to exciton-induced transparency minimum in scattering spectra in the weak coupling regime and to emergence of polaritonic bands as the system transitions to the strong coupling regime. The second mechanism is the Fano interference between the plasmon dipole moment and the plasmon-induced dipole moment of the bright collective state as the hybrid system interacts with the radiation field. The latter mechanism is greatly facilitated by plasmon-induced coherence in a system with the characteristic size below the diffraction limit as the individual emitters comprising the collective state are driven by the same alternating plasmon near field and, therefore, all oscillate in phase. This cooperative effect leads to scaling of the Fano asymmetry parameter and of the Fano function amplitude with the ensemble size, and therefore, it strongly affects the shape of scattering spectra for large ensembles. Specifically, with increasing emitter numbers, the Fano interference leads to a spectral weight shift toward the lower energy polaritonic band.

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.

Highly sensitive and reproducible SERS substrates with binary colloidal crystals (bCCs) based on MIM structures

Surface-enhanced Raman scattering (SERS) is a powerful molecular vibrational spectrum characterization method, and has shown promising applications in surface science, life science, environmental monitoring, etc. Developing new simple processes to fabricate low-cost substrates is an essential prerequisite to promote and strengthen the practical application of the SERS technique. For this purpose, the present work reports on the development of a metal/insulator/metal (MIM) structure combined with polystyrene (PS) binary colloidal crystals (bCCs) based on nanosphere self-assembly and electron-beam evaporation technologies. The PS bCCs are used to form a dielectric layer sandwiched between a bottom Ag reflection layer and an upper Ag shell layer. Compared with single-sized colloidal spheres, the PS bCCs exhibit considerably richer morphologies and structures. In addition, the closely packed Ag shell arrays enhance the density of electromagnetic field “hot spots” thus increasing the SERS activity. The PS bCCs-based MIM substrate could achieve an enhancement factor (EF) of 1.10 × 108 and an ultralow detection limit for the Rhodamine 6G (R6G) molecule of about 10−14 M. The results demonstrate that the proposed substrates with a facile fabrication strategy, low cost, large area and high sensitivity have high potential applications of SERS sensors for bio- and chemical molecular analysis.

Near-infrared narrow plasmonic resonances for high-performance optical sensing in a sodium-based nanograting

Plasmonic resonances are attractive and promising for biosensing applications benefiting from their strong nanoscale light confinement and sensitivity to the refractive index of surrounding medium. Here, we numerically and theoretically investigate a metal–insulator-metal (MIM) nanograting structure, where gold nanostrip arrays are placed on a thin dielectric layer with a sodium film underlay. The structure is obliquely excited by a transverse magnetic (TM) wave from a prism supporting the whole MIM structure. We found that the plasmonic surface lattice resonance (SLR) mode and gap plasmon resonance (GPR) mode can be efficiently excited in our structure at the near infrared wavelength. Remarkably, the SLR mode can achieve ultranarrow linewidth less than 3 nm (quality factor > 500), sensitivity over 1000 nm/RIU and the corresponding figure of merit (FOM) larger than 300 RIU−1. Our study may pay a way to achieve high-performance sensing in a simple plasmonic nanostructure that could be vastly used in biological and chemical circumstances.

Thickness-dependent dielectric breakdown in thick amorphous SiO2 capacitors

High-voltage dielectric breakdown of thick amorphous silicon dioxide capacitors for galvanic insulation is experimentally investigated and analyzed through numerical simulations carried out with a commercial TCAD tool. Silicon oxide metal-insulator–metal capacitors are used as back-end inter-level dielectric layers in integrated circuits. The large biases such devices must sustain and the material intrinsic defectivity give rise to a leakage current which is responsible of degradation and failure. Therefore, the understanding of the degradation mechanisms of the insulator is an essential prerequisite for its safe operation. For this reason, high-voltage dielectric breakdown measurements have been performed under DC-stress conditions on thick metal-insulator–metal structures with different oxide thickness and, in order to gain insight on the role of defects on breakdown, numerical simulations have been compared to experiments.

Hydrothermally formed copper oxide (CuO) thin films for resistive switching memory devices

This work presents the preliminary research on Metal-Insulator-Metal (MIM) structures containing copper oxide (CuO) layers for memory applications. Structural and optical investigations of fabricated materials have shown distinct differences in chemical compositions of ‘as grown’ and thermally annealed CuO, i.e., ‘HT + RTP’ film. Those differences strongly influence the electrical behavior of fabricated MIM structures. The examined electrical performance of fabricated devices revealed stability and repeatability of the HRS/LRS ratio over time. The presented results have demonstrated the possible application of CuO thin films in low-power and high-speed Resistive Random-Access Memory (RRAM) devices.

Broadband and Wide-Angle Performance of a Perfect Absorber Using a MIM Structure with 2D MXene

Due to the extraordinary optoelectronic properties and surface-rich functional groups, MXene has shown great promise in many applications, such as electromagnetic shielding, catalysis, sensors, ultrafast photons, etc. In this work, we propose a wide-angle absorber based on a metal-insulator-metal (MIM) metamaterial consisting of MXene. By optimizing the design, the absorption efficiency can be further improved throughout the entire wavelength range. More importantly, the absorber exhibits high-efficiency broadband and wide-angle (20–80°) absorption in the near-infrared range (NIR: 1.1–1.7 μm) by numerical calculation. It is foreseeable that the excellent absorption characteristics and easy-to-manufacture structure of the designed absorber will bring some inspiration to the absorption device in the NIR and its practical application.

3D visualization of microwave electric and magnetic fields by using a metasurface-based indicator

Visualizations of the microwave electric and magnetic near-field distributions of radio-frequency (RF) filters were performed using the technique of thermoelastic optical indicator microscopy (TEOIM). New optical indicators based on periodic dielectric-metal structures were designed for electric field visualization. Depending on the structure orientation, such metasurface-based indicators allow separately visualization of the Ex and Ey components of the in-plane electric field. Numerical simulations were conducted to examine the working principle of the designed indicator structures, and the results were compared to the experimental, showing good agreement. In addition, the 3D visualization of the microwave near-field distribution was built, to show the field intensity and distribution dependencies on the distance from the RF filter.

Metal-Dielectric Thin Film Structure Metamaterial for Obtaining High Equilibrium Temperature Under Direct Solar Optical Radiation

Metal-dielectric thin film structure metamaterials can be designed to absorb solar light radiation over a wide spectral band. By using Kirchhoff's law, metal-dielectric thin film metamaterials are investigated for obtaining high equilibrium temperatures under direct solar light radiation at normal incidence. It is found that among all metal-dielectric thin film structures, the dielectric layer on metal (DLM) surface structure is the optimal structure for producing the highest thermal equilibrium temperature under direct solar optical radiation.

Development of deposition technology and AC measurement of copper ultrathin layers

In this paper, the transport properties of discontinuous 4 nm copper layers obtained by dual-source non-reactive magnetron sputtering in the presence of argon are presented. The value of resistance and capacitance of the current parallel to the plane of these layers can be adjusted independently by changing the nominal thickness of the metallization. The influence of frequency on the conductivity of the obtained structures in the range from 4 Hz to 8 MHz was studied. Additionally, in order to compare the non-oxidized and oxidized layers, some of them were heated at 500 °C. Based on the results obtained, the mechanism of electric charge transfer was determined, the knowledge of which is essential for planning further experiments based on this sputtering method and potential selection of future application of the structures. Statistical measurements at room temperature will serve as a reference for the conductivity and resistivity values obtained by mathematical calculations from measurements of resistance, capacitance, phase shift angle, and dielectric loss tangent as a function of temperature from 20 K to 375 K, which are expected in further studies on the obtained structures. The work is an introduction to the technology of obtaining multi-layer metal-dielectric structures.

Novel glucose concentration sensor with unique resonance lineshapes in optical cavity

We report the acquired of Fano resonance based on metal–insulator-metal (MIM) waveguide structure, which first consists of a branched semi-closed T-shaped waveguide coupled to an open square ring resonator, demonstrate that the Fano resonance has an highly sensitive, observe rapid detection of glucose concentration and the Fano resonance spectrum redshift with increasing the glucose level. zong These features provide a solid foundation for the application of these novel MIM structures in the field of biochemical sensing.

Memristive synaptic device based on a natural organic material—honey for spiking neural network in biodegradable neuromorphic systems

Spiking neural network (SNN) in future neuromorphic architectures requires hardware devices to be not only capable of emulating fundamental functionalities of biological synapse such as spike-timing dependent plasticity (STDP) and spike-rate dependent plasticity (SRDP), but also biodegradable to address current ecological challenges of electronic waste. Among different device technologies and materials, memristive synaptic devices based on natural organic materials have emerged as the favourable candidate to meet these demands. The metal–insulator-metal structure is analogous to biological synapse with low power consumption, fast switching speed and simulation of synaptic plasticity, while natural organic materials are water soluble, renewable and environmental friendly. In this study, the potential of a natural organic material—honey-based memristor for SNNs was demonstrated. The device exhibited forming-free bipolar resistive switching, a high switching speed of 100 ns set time and 500 ns reset time, STDP and SRDP learning behaviours, and dissolving in water. The intuitive conduction models for STDP and SRDP were proposed. These results testified that honey-based memristive synaptic devices are promising for SNN implementation in green electronics and biodegradable neuromorphic systems.

Mechanism of emitters coupled with a polymer-based hyperbolic metamaterial.

We study a polymer-based hyperbolic metamaterial (HMM) structure composed of three Au-polymer bilayers with a hyperbolic dispersion relation. Using an effective refractive index retrieval algorithm, we obtain the effective permittivity of the experimentally fabricated polymer-based structure. In particular, the unique polymer-based HMM shows the existence of high-k modes that propagate in the metal-dielectric multilayered structure due to the excitation of bulk plasmon-polaritonic modes. Moreover, we compare the experimental luminescence and fluorescence lifetime results of the multilayered Au and a dye-doped polymer (PMMA) to investigate the dynamics of three different emitters, each incorporated within the unique polymer-based HMM structure. With emitters closer to the epsilon-near-zero region of the HMM, we observed a relatively high shortening of the average lifetime as compared to other emitters either close or far from the epsilon-near-zero region. This served as evidence of coupling between the emitters and the HMM as well as confirmed the increase in the non-radiative recombination rate of the different emitters. We also show that the metallic losses of a passive polymer-based HMM can be greatly compensated by a gain material with an emission wavelength close to the epsilon-near-zero region of the HMM. These results demonstrate the unique potential of an active polymer-based hyperbolic metamaterial in loss compensation, quantum applications, and sub-wavelength imaging techniques.

Characterization and numerical analysis of breakdown in thick amorphous SiO2 capacitors

Charge transport in thick amorphous silicon dioxide capacitors for integrated galvanic insulators is experimentally investigated and analyzed through numerical simulations carried out with a commercial TCAD tool. The material intrinsic defectivity and the large biases applied to such devices give rise to a leakage current which is responsible for degradation and failure. Hence it is crucial to have a complete understanding of the charge-transport main physical mechanisms in amorphous silicon oxide. In particular, charge injection at contacts and charge build-up due to trapping/de-trapping mechanisms in the bulk of the oxide are expected to play a crucial role and their complex coupled interaction needs to be investigated via a TCAD-based approach. For this reason, time-dependent dielectric breakdown measurements at constant-current stresses and voltage-ramp stresses up to breakdown have been performed on thick metal-insulator–metal structures, and numerical simulations have been carried out so to predict the failure mechanisms. To this purpose, special attention has been devoted to the physical modeling of defects and impact-ionization generation.

Broadband absorption enhancement of metal-dielectric structures in the optical range and their application in solar energy storage

In this work, scattering properties of a metal-dielectric structure are carried out in the optical range. In the proposed structure design, the absorption coefficient reaches more than 80% and has an almost constant character in the entire visible spectrum. Based on the obtained simulation results, such structures can be utilized in the field of solar energy storage applications. A review of works in the field of plasmonic solar cells is given, where the efficiency is usually increased due to the confinement of incident radiation in the active region of photoelectric conversion using localized modes, which are concentrated at the surface of conducting nanoparticles. That is, such batteries are operated in narrow wavelength intervals. However, in this article, the assumed solar cell efficiency enhancement can be achieved by incorporating the entire optical range due to the proposed metamaterial structure.

Surface Plasmon Resonance of Two-Dimensional Gold Colloidal Crystals Formed on Gold Plates.

The free electrons inside precious metals such as Au vibrate when the surface of the metal is irradiated with an electromagnetic wave of an appropriate frequency. This oscillation is referred to as surface plasmon resonance (SPR), and the resonance frequency varies with permittivity of the medium around the metal. SPR sensors are widely applied in the fields of bioscience and pharmaceutical sciences, including biosensing for drug discovery, biomarker screening, virus detection, and testing for food safety. Here, we fabricated a metal-insulator-metal (MIM) SPR sensor by constructing two-dimensional (2D) regular array of Au colloidal particles (2D colloidal crystals) on an insulator layer over a thin Au film coated on a glass substrate surface. The 2D crystals were fabricated by electrostatically adsorbing negatively charged three-dimensional crystals onto a positively charged thin insulator formed on Au film. The plasmon peaks/dips from the MIM structure were measured in aqueous solutions of ethylene glycol (EG) at various concentrations. Multiple plasmon peaks/dips were observed due to the localized SPR (LSPR) of the Au particles and the Fano resonance between the Au particles and thin film. The plasmon peaks/dips shifted to higher wavelengths on increasing EG concentrations due to an increase in the refractive index of the media. The observed peak/dip shift was approximately twice that of LSPR from an isolated Au particle. We expect the present MIM substrate will be useful as a highly sensitive sensor in the pharmaceutical field.

Design of metal-dielectric interference coatings

Subject of study. Multilayer structures comprising a thin metal layer facilitate the creation of new optical schemes for spectroscopy (selectors for laser cavities, multibeam reflection interferometers, and interference filters with thin absorbing layers). Method. Methods for the calculation of complex optical coatings are constantly improved. The novelty of this work is the design of a stacked structure with a thin metal layer when a conductive surface model is used to mathematically describe the properties of this layer. Results. This work presents numerical modeling of several multilayer metal-dielectric structures. A graphical method for designing an asymmetric front mirror of a reflection interferometer that uses circular charts of a complex reflection coefficient ensures visual clarity when searching for an optimal solution. The proposed multilayer structure with thin metal films placed at the layer boundaries ensures effective suppression of the reflected light with wavelengths different from the selected one. A narrow extrema (maxima and minima) transformation in the spectral or angular dependences of the reflection coefficient is shown to occur in the case of the oblique incidence of s-polarized light on the multibeam reflection interferometer and the variation of the “gap” thickness. It is established that, if a thin metal film is added to the front mirror, narrow bright fringes of reflected light can be obtained in a scheme with a Fabry-Perot interferometer in addition to the fringes in transmitted light. Practical significance. The obtained results can be applied to spectroscopy.

A comparative study of structural, mechanical & electrical properties of ZnO and AlN thin films for MEMS based piezoelectric sensors

In this work, a comparative study has been carried out to compare the relative performance of ZnO (Zinc Oxide) and AlN (Aluminum Nitride) thin films for their application in piezoelectric sensors. The thin films material properties are being characterized using various material characterization techniques such as SEM, XRD, and Nanoindentation. Further the MIM (Metal-Insulator-Metal) based devices have been fabricated with piezoelectric films sandwiched between Al electrodes. The devices have been evaluated for mechanical and electrical performances. The natural frequency of the devices recorded as 46.8 kHz (ZnO) and 40.8 kHz (AlN). The average nominal capacitance of the MIM structure is measured as ∼98 pF and ∼120 pF where as corresponding dissipation factor obtained as ∼0.03 and ∼0.0005 respectively for ZnO and AlN devices. The repeatability investigation carried out on the sample devices for up to 90 days and the output has been monitored. The result showed that the AlN devices exhibit better output stability compared to ZnO devices.

Analysis of luminescence decay dynamics in metal-dielectric photonic structures with organic layers

Metal-dielectric photonic structures with organic materials 4,4-bis(N-carbazolyl)-1,1-biphenyl and 4,4'-bis[4-(di-ptolylamino)styryl]biphenyl) as light emitting layers were investigated. The formation of the polaritonic modes in the investigated structures was experimentally demonstrated and a correlation between theoretical and experimental dispersion was shown. Was shown, that increase in interaction between organic exciton and optical mode leads to a significant decrease in the lower polariton emission bandwidth. Keywords: light-emitting layers, exciton, luminescence.