Drude Model Research Articles

New Shear Horizontal (SH) Surface-Plasmon-Polariton-like Elastic Surface Waves for Sensing Applications.

The advent of elastic metamaterials at the beginning of the 21st century opened new venues and possibilities for the existence of new types of elastic (ultrasonic) surface waves, which were deemed previously impossible. In fact, it is not difficult to prove that shear horizontal (SH) elastic surface waves cannot exist on the elastic half-space or at the interface between two conventional elastic half-spaces. However, in this paper we will show that SH elastic surface waves can propagate at the interface between two elastic half-spaces, providing that one of them is a metamaterial with a negative elastic compliance s44(ω). If in addition, s44(ω) changes with frequency ω as the dielectric function ε(ω) in Drude's model of metals, then the proposed SH elastic surface waves can be considered as an elastic analogue of surface plasmon polariton (SPP) electromagnetic waves, propagating at a metal-dielectric interface. Due to inherent similarities between the proposed SH elastic surface waves and SPP electromagnetic waves, the new results developed in this paper can be readily transferred into the SPP domain and vice versa. The proposed new SH elastic surface waves are characterized by a strong subwavelength confinement of energy in the vicinity of the guiding interface; therefore, they can potentially be used in subwavelength ultrasonic imaging, superlensing, and/or acoustic (ultrasonic) sensors with extremely high mass sensitivity.

Design of high-entropy films as ultra-violet light reflector

This study proposes the design and implementation of high-entropy alloy (HEA) thin films as materials for the reflector of deep ultraviolet light-emitting devices and marks the first application of HEA in optical field. In the material design phase, an Al-Co-Zn-Ni alloy is designed by considering the reflectivity, phase stability and binary formation energy. Reverse Monte Carlo calculation is employed to establish stable atomic structure. Frequency-dependent dielectric equations are derived from first principles calculations, with dielectric constants incorporating contributions from ions and electrons and combining classical Drude and Lorentz models. The dielectric equations yield optical constants that are used to calculate the reflectance. In the experimental phase, we systematically vary the aluminum content and prepare Al-Co-Zn-Ni thin films ranging from pure aluminum to equimolar compositions. In the deep ultraviolet region, the reflectance of thermally treated Al65Zn12Co12Ni11 and Al50Zn16Co17Ni17 thin films is found superior to that of gold by three times. Structural and crystalline changes with varying aluminum content are found, as well as intriguing phase separation and superlattice formation that persist until equimolar compositions. This unique nanoscale structural variation causes the Young's modulus and hardness of Al-Co-Zn-Ni thin films to initially increase and then decrease with decreasing aluminum content. There is a significant increase in the corrosion potential difference when reducing Al contents in Al-Co-Zn-Ni, indicating improved passivation effects as the equimolar composition is approached. By modulating the aluminum content, the nanoscale structure of Al-Co-Zn-Ni can be adjusted, thereby improving its optical, mechanical, corrosion resistance, and thermal stability properties. This demonstrates the high versatility of this material for practical optical applications.

Tunable negative permittivity performance of carbon/silicon dioxide ceramic metacomposites under external DC bias voltage

Metacomposites with negative permittivity have gained increasing momentum in recent years due to their unique electromagnetic characteristics and considerable potential application. However, how to adjust negative permittivity is still a big technical challenge to overcome. In this paper, silicon dioxide (SiO2) ceramic metacomposites consisting of carbon fibers (CFs) were fabricated by vacuum hot press sintering, and their negative permittivity might be modified by adjusting the filler content and applying external direct current (DC) bias voltages. As the CF content increased, the electrical conductivity of composites increased markedly, and the conduction mechanism transformed to a metal-like conductivity from hopping conductivity. The permittivity values of composites with high CF contents were negative at the test frequency range owing to the appearance of a low plasmonic state of unbound electrons in the percolating carbon networks. The conductivity of the composites increased when DC bias voltage was applied, because some of the accumulated local electrons at the CF-SiO2 interface could absorb energy and become free electrons. Larger bias voltages led to increased concentration of free electrons, so the absolute values of the negative permittivity raised according to the Drude model and the frequency band of negative permittivity became wider. This work presents an effective approach for adjusting the negative permittivity value and frequency band, which is advantageous in clarifying the realization and regulation mechanisms of negative permittivity.

Spectroscopic Ellipsometry: Advancements, Applications and Future Prospects in Optical Characterization

Spectroscopic ellipsometry (SE), a non-invasive optical technique, is a powerful tool for characterizing surfaces, interfaces, and thin films. By analyzing the change in the polarization state of light upon reflection or transmission through a sample, ellipsometry provides essential parameters such as thin film thickness (t) and optical constants (n, k). This review article discusses the principles of ellipsometry, including the measurement of key values ∆ and Ψ, and the complex quantity ρ. The article also presents the Fresnel equations for s and p polarizations and the importance of oblique angles of incidence in ellipsometry. Data analysis in ellipsometry is explored, including the determination of bandgap and data referencing the electrical properties of materials. The article emphasizes the importance of choosing the appropriate models to fit ellipsometric data accurately, with examples of the Cauchy and Lorentz models. Additionally, the Kramers–Kronig relations are introduced, illustrating the connection between real and imaginary components of optical constants. The review underscores the significance of ellipsometry as a non-destructive and versatile technique for material characterization across a wide range of applications.

Tunable Negative Permittivity in Graphene/Poly(Vinylidene Fluoride) Composites with Low Percolation Threshold

Recently, metamaterials with fascinating dielectric behavior have drawn much attention for their potential applications. Herein, percolating graphene/poly(vinylidene fluoride) (GR/PVDF) composites consisting of GR sheets homogeneously dispersed in PVDF matrix are fabricated via hot‐pressing method in 20 Hz–1 MHz frequency regions, of which simultaneously realizing negative permittivity with low percolation threshold. It is demonstrated that the negative permittivity of GR/PVDF composites is resulted from the low‐frequency plasma oscillation of free electrons, and a universal regulatory mechanism of the Drude model is analyzed. At the same time, rapid formative 3D GR conductive networks contributed to the low percolation threshold (7.78 wt%) of composites. Moreover, it is shown that electrical percolation occurs in samples as GR content exceeds percolation threshold, indicating a typical metal‐like behavior. In addition, the reactance is discussed according to the equivalent circuit analysis. This work constructed the metacomposites with low filler content, which is a benefit for practical applications in electromagnetic devices.

Understanding the negative permittivity behavior of polyvinyl alcohol based metamaterials under radio frequency

Functional metamaterials that exhibit negative dielectric permittivity through percolative network formation have attracted immense attention due to their significant potential for a wide range of applications in electronic devices. Negative permittivity has taken off as a research topic recent years in percolative composites. The polymer nanocomposites (PVA/H-Pa-G) were prepared using the α-Fe2O3 modified GNP and HCl doped polyaniline (Pani) based nanofillers (H-Pa-G). The as prepared samples were characterized in order to analyze their dielectric response for understanding the negative permittivity behavior. Below the percolation threshold for the polymer nanocomposite with 0.10%, 0.25% H-Pa-G nanofiller weight fraction, an increase in σac conductivity is observed with increase in frequency. The dielectric study confirmed the negative permittivity behavior for the polymer nanocomposite (0.50%, 1.00% and 2.00%) above the percolation threshold. This can be mainly attributed to the presence of the conductive network of H-Pa-G nanofiller in the PVA matrix. On the contrary, the positive permittivity is due to the insulative nature of PVA matrix. The empirical data of real permittivity was fitted using the Drude model that corresponded well with the experimental data with the fp = 1.31 GHz which is further certified by the equivalent circuit model fitting. This proposed work strongly suggest the implication of the as prepared polymer nanocomposite for the negative permittivity materials based applications.

Negative Capacitance Effect Using a Pure Imaginary Electric Mobility Controlled By an Adiabatic Parameter in Thin Film Materials Based On Drude Model

Existence of a pure imaginary mobility of charge carriers in organic polymers materials, precisely the poly p-phenylene vinylene is explored in this work. Indeed, we propose a new model of dynamic equation of particles able to carry electric charges, we introduce a control parameter of the adiabatic evolution combined with a phase difference between the external perturbation of the material and the position of carrier, leading from then on to the non-use of the complex mobility. This model after transformation allowed us to demonstrate the existence of negative capacitance at low and high frequencies in the poly p-phenylene vinylene. Also thanks to this new model, we were able to obtain results in line with the experimental ones, thus confirming the validity of our model

Optical Parameters of Aluminum Alloy Samples Irradiated by High Current Relativistic Electron Beams

The aluminum alloys D16, D16AT are widely used as construction materials in the aircraft industry. Questions connected with the enhancement of the properties of the construction elements made of the alloys through surface modification are of great interest now. The objects of the study in our paper are the samples of the aluminum alloy D16AT subjected to irradiation by high-current relativistic electron beams. Leaving aside the material science aspects, in this work we focused on modeling the optical properties of the samples. The problem is relevant because optical methods for surface analysis have become widespread due to their versatility and efficiency. Through the treatment of the preliminary measured ellipsometry data, we obtain the optical constants of the samples and their dispersion in the visible region of wavelength. The method used consists of an approximation of the reflection coefficient calculated from the ellipsometry data by finding the values of the parameters in the model. The last is performed by the least squares method. The reflection coefficient is assumed to correspond to the semibounded uniaxial medium with the optical axis perpendicular to the interface between the medium and the homogeneous and dielectric ambient medium. The dielectric function of the semibounded medium is approximated by the Drude-Lorentz model. The possibility of birefringence of the samples caused by the irradiation with electron beams is discussed.

Insights into structural, electronic, optical properties, and impedance spectroscopy of semi-doped perovskite Nd0.5Ba0.5CoO3: A theoretical and experimental study

In this study, the electronic, structural, and optical properties of semi-doped perovskite Nd0.5Ba0.5CoO3 (NBCO) were investigate using the CASTEP software, which relies on density functional theory (DFT) along with the correlation function of generalized gradient approximation (GGA) and Perdew-Burke-Ernzerhof (PBE). The mesh parameters of the (super) cell indicate that NBCO adopts an orthorhombic structure in the Pmmm space group, featuring a Coulomb Energy (EC) of approximately −244 eV. DFT and total density of states (DOS) analyses reveal that the as-prepared perovskite manifests metallic characteristics, and a notable covalent interaction is observed between the O-p and Co-d spin states, indicating strong hybridization between these orbitals. Remarkably, NBCO demonstrates 100 % spin polarization (P) at the Fermi level, with a calculated total magnetic moment of approximately 3.44 μB. Moreover, low dielectric loss (tgδ) values suggest facile electron movement, and impedance spectroscopy illustrates a dielectric relaxation phenomenon. DFT calculations predict an orthorhombic crystal structure with higher electron density at cobalt atom positions. Band structure and DOS analyses affirm metallic behavior owing to the robust hybridization between oxygen-p and cobalt-d orbitals. Optical property assessments reveal potential applications in spintronics and optoelectronics, with notable absorption in the ultraviolet–visible range. The conductivity spectra from impedance spectroscopy contribute to understanding temperature-dependent charge transport mechanisms. Dielectric constants decrease with increasing frequency and temperature, while dielectric losses remain low, indicating efficient electron movement. The material adheres to a metallic conduction mechanism as described by Drude's law, and the material's 100 % spin polarization at the Fermi level and a total magnetic moment of 3.44 μB are significant findings. Negative dielectric constants observed at specific frequencies suggest potential applications in metamaterials. Overall, the determined properties position NBCO cobaltite as a promising candidate for high-frequency devices, spintronic components, and sensors.

A novel on-line microwave diagnostic for an atmospheric pressure air plasma based on an artificial neural network

Permittivity is an important aspect of the design of microwave devices. In order to design microwave devices that are more suitable for the excitation of air plasmas, this paper presents a method for the on-line measurement of the relative permittivity of an atmospheric pressure air plasma with 2.45 GHz microwaves. First, a ridged waveguide is designed and constructed to excite the air. Using the ridged waveguide, the plasma can be excited and measured simultaneously. An artificial neural network trained with simulated data is integrated into the system to invert the dielectric constant of the air plasma being measured. At a power of 786 W and an airflow rate of 1250 L/h, the real and imaginary parts of the permittivity are obtained to be −1244 and 60, respectively. The forecasted errors on the real part and the imaginary part of the relative permittivity are kept at around 5% and 3%. The Drude model is used to construct a relationship between the electronic and dielectric properties. This diagnostic method is simple to operate and has a high degree of generality. It should be useful in the design of microwave plasma devices and can greatly improve the efficiency of microwave plasma equipment.

The Effect of the Turbulence Coefficient on the Formation of a Turbulent Process: 2. Existing Scenarios for the Occurrence and Development of Turbulence

Some characteristic features of three scenarios for the occurrence and development of turbulenceare presented: the Landau-Hopf scenario, the scenario of transition to turbulence on a strange attractor, andthe scenario followed by the solutions of the multimoment hydrodynamics equations. The analysis of the presentedcharacteristic features allows us to conclude that these scenarios can be used to interpret turbulence.It is shown that only one of the scenarios satisfactorily interprets the experimental data: the scenario followedby the solutions of the multimoment hydrodynamics equations supplemented with stochastic components.The Landau-Hopf scenario leads to a system that has lost stability in the wrong direction. The scenario of thetransition to turbulence on a strange attractor correctly reproduces only the initial stage of the evolution ofthe liquid layer in the Bénard experiment, namely, heat transfer in the resting layer and convective shafts.Analysis of the behavior of solutions of the Lorentz model leaves no hope for the ability of this scenario tointerpret turbulence

Flexible Copper Nanowire/Polyvinylidene Fluoride Membranous Composites with a Frequency-Independent Negative Permittivity.

With the increasing popularity of wearable devices, flexible electronics with a negative permittivity property have been widely applied to wearable devices, sensors, and energy storage. In particular, a low-frequency dispersion negative permittivity in a wide frequency range can effectively contribute to the stable working performance of devices. In this work, polyvinylidene fluoride (PVDF) was selected as the flexible matrix, and copper nanowires (CuNWs) were used as the conductive functional filler to prepare a flexible CuNWs/PVDF composite film with a low-frequency dispersion negative permittivity. As the content of CuNWs increased, the conductivity of the resulting composites increased sharply and presented a metal-like behavior. Moreover, the negative permittivity consistent with the Drude model was observed when CuNWs formed a percolative network. Meanwhile, the negative permittivity exhibited a low-frequency dispersion in the whole test frequency range, and the fluctuation of the permittivity spectra was relatively small (-760 to -584) at 20 kHz-1 MHz. The results revealed that the high electron mobility of CuNWs is reasonable for the low-frequency dispersion of negative permittivity. CuNWs/PVDF composite films with a frequency-independent negative permittivity provide a new idea for the development of flexible wearable electronic devices.

Non-destructive mapping of electrical properties of semi-insulating compound semiconductor wafers using terahertz time-domain spectroscopy

With an increasing demand for THz electronics applications, it is essential to obtain the electrical properties of semiconductor materials used in their fabrication. This study presents an approach to estimate the electrical properties of semi-insulating compound semiconductors using terahertz time-domain spectroscopy (THz-TDS). By employing THz-TDS in transmission mode, the resistivity and carrier concentration of semi-insulating Silicon Carbide (SiC) and Indium Phosphide (InP) wafers are non-destructively measured. The study utilizes the simplified Drude model and the Nelder-Mead algorithm to estimate the electrical properties from the THz-TDS transmission (S21) measurement data. The resistivity values of the SiC and InP samples, (1.42 ± 0.15) × 105 Ω cm and (3.0 ± 0.1) × 107 Ω cm, respectively, are in accordance with the manufacturer specifications. Moreover, the feasibility of non-destructive mapping of the electrical properties of the wafers is demonstrated, offering a novel tomographic inspection approach for online monitoring. This technique holds significant promise for enhancing production yields in the semiconductor industry.

Terahertz optical Hall effect determination of carrier concentrations in component layers within low bandgap tin–lead halide perovskite photovoltaics and device simulation

Carrier concentration (N) of indium tin oxide (ITO), poly (3,4-ethylenedioxythiophene) polystyrene sulfonate (PEDOT:PSS), and low bandgap perovskite (FASnI3)0.6(MAPbI3)0.4 in the photovoltaic device configuration are determined using terahertz (THz) spectral range optical Hall effect measurements and analysis. Unlike direct electrical Hall effect, this technique is non-invasive as it does not need any direct electrical contacts and is able to probe free carrier transport properties of individual films inside the device stack. A modified Drude model is implemented to address the dominating free carrier absorption in the THz spectral range. N of the ITO, PEDOT:PSS, and (FASnI3)0.6(MAPbI3)0.4 are determined to be (2.8 ± 0.6) × 1020 cm-3, (2.6 ± 0.8) × 1022 cm-3, and (1.5 ± 0.1) × 1018 cm-3, respectively. PV device performance is simulated with SCAPS employing the findings from optical Hall measurements. Open circuit voltage (VOC), short circuit current (JSC), fill factor (FF), power conversion efficiency (PCE) are found to be 0.865 V, 29.2 mAcm-2, 66.7%, and 16.8% respectively which are within 3% of corresponding experimentally measured values. These optically measured N serve as essential parameters for device modeling to understand its physics in device performance and to optimize PCE; consistency between simulated and experimental device performance parameters using these values supports optical Hall effect as a reliable technique to extract electronic transport properties.

Optical Characteristics of Silver Thin Films from Island to Percolation in the Ultra-Wide Infrared Spectral Range

Silver (Ag) thin films have garnered significant attention due to their unique optical properties. This paper systematically investigates the optical characteristics of Ag films prepared using the electron beam evaporation method. The investigation was conducted using spectroscopic ellipsometry and covers a broad wavelength range of 1679 nm to 36 µm (0.738–0.034 eV), spanning from near-infrared to far-infrared regions. Optical and dispersion models were developed to analyze the impacts of Ag nanostructures on the complex refractive indices, dielectric functions, and reflectance. The results indicate that Ag particles and coalescence films exhibit non-metallic and low absorption properties, while Ag percolation and continuous films present a typical Drude model. The reflectance of Ag films increases as the film coverage ratio increases, and it can reach close to 100% in continuous film. Additionally, a non-destructive, non-contact, and vacuum-free means of confirming the percolation threshold of Ag films was proposed based on the slope of the imaginary part curve. This work is useful to guide simulations and provide a basis for the applications of Ag films in different fields.

Optical Absorption, Photocarrier Recombination Dynamics and Terahertz Dielectric Properties of Electron-Irradiated GaSe Crystals

Optical absorption spectra of 9 MeV electron-irradiated GaSe crystals were studied. Two absorption bands with the low-photon-energy threshold at 1.35 and 1.73 eV (T = 300 K) appeared in the transparency region of GaSe after the high-energy-electron irradiation. The observed absorption bands were attributed to the defect states induced by Ga vacancies in two charge states, having the energy positions at 0.23 and 0.61 eV above the valence band maximum at T = 300 K. The optical pump-terahertz probe technique (OPTP) was employed to study the dark and photoexcited terahertz conductivity and charge carrier recombination dynamics at two-photon excitation of as-grown and 9 MeV electron-irradiated GaSe crystals. The measured values of the differential terahertz transmission at a specified photoexcitation condition were used to extract the terahertz charge carrier mobilities. The determined terahertz charge carrier mobility values were ~46 cm2/V·s and ~14 cm2/V·s for as-grown and heavily electron-irradiated GaSe crystals, respectively. These are quite close to the values determined from the Lorentz–Drude–Smith fitting of the measured dielectric constant spectra. The photo-injection-level-dependent charge carrier lifetimes were determined from the measured OPTP data, bearing in mind the model injection-level dependencies of the recombination rates governed by interband and trap-assisted Auger recombination, bulk and surface Shockley–Read–Hall (SRH) recombination and interband radiative transitions in the limit of a high injection level. It was found that GaSe possesses a long charge carrier lifetime (a~1.9 × 10−6 ps−1, b~2.7 × 10−21 cm3ps−1 and c~1.3 × 10−37 cm6ps−1), i.e., τ~0.53 μs in the limit of a relatively low injection, when the contribution from SRH recombination is dominant. The electron irradiation of as-grown GaSe crystals reduced the charge carrier lifetime at a high injection level due to Auger recombination through radiation-induced defects. It was found that the terahertz spectra of the dielectric constants of as-grown and electron-irradiated GaSe crystals can be fitted with acceptable accuracy using the Lorentz model with the Drude–Smith term accounting for the free-carrier conductivity.

MSNNet: Multi-scale-abled networks with multi-groups channel attention for vibrational spectrum matching

In recent years, deep learning methods have exhibited superior performance in many applications in vibrational spectroscopy especially compared with conventional machine learning methods such as Support Vector Machine (SVM) and Partial Least Squares (PLS). On the other hand, almost all of these methods employ such as LeNet and ResNet as their backbones which are not designed for processing spectra originally. In this paper, we demonstrate that these widely-used neural network models are insufficient when dealing with vibrational spectra. Particularly they lack the ability to process multi-scale information hidden in vibrational spectra. To address this, we further propose a novel multi-scale-abled network named MSNNet which combines a modified Res2Net with the Multi-Groups Channel Attention (MGCA). Experiments on two publicly available spectrum datasets show that the proposed MSNNet significantly outperforms existing methods. Moreover, using the Lorentz model we also generat a number of synthetic datasets where the scale in spectra can be deliberately controlled. Results on these synthetic datasets not only validate the superiority of the proposed method, but also support our hypothesis that the scale information can play a vital role in recognition of vibrational spectra.

Single-Mode Dual-Band Patch Antenna Based on the Lorentz Model of Dispersive Metamaterials

Single-Mode Dual-Band Patch Antenna Based on the Lorentz Model of Dispersive Metamaterials

Extension of FLOD-FDTD Method for Multiterm Modified Lorentz Model

Extension of FLOD-FDTD Method for Multiterm Modified Lorentz Model

Thermally tunable electromagnetic surface waves supported by graphene loaded indium antimonide (InSb) interface

The thermal agitation plays a vital role in tunability of optoelectronic, structural and chemical characteristics of the temperature sensitive materials. Graphene enables the THz optics, due to its unprecedent controlling characteristics over the traditional materials. The influence of temperature on the monolayer graphene is very negligible due to its low free charge carrier density, to enhance the thermal sensitivity of graphene, the graphene loaded temperature sensitive material interface has been proposed. A theoretical analysis has been carried out on temperature dependent propagation characteristics of electromagnetic surface waves supported by the graphene loaded semi-infinite indium antimonide (InSb). The InSb has been taken as temperature sensitive material. The Drude model has been used for the modeling of InSb in the THz region while the modeling of the graphene has been done by random phase approximation-based Kubo’s formulism. To realize the graphene loaded indium antimonide interface, the impedance boundary conditions (IBCs) have been employed. The numerical analysis has been conducted to analyze the influence of temperature on the characteristics of electromagnetic surface waves i.e., dispersion curve, effective mode index (Neff), penetration depth (δ), propagation length (Lp), phase speed (Vp) and field profile, propagating along the graphene loaded InSb. In all the numerical results, the temperature variation has been considered from 200 to 350 K. It has been concluded that the graphene–InSb interface provides more temperature assisted tunability to the interfacial surface modes, commonly known as surface waves, as compared to monolayer graphene. Further, the graphene parameters can play a vital role in the dynamical tuning of electromagnetic surface waves in THz to IR frequency range. The numerically computed results have potential applications in designing of thermo-optical waveguides, temperature assisted communication devices, thermo-optical sensors and near field thermal imaging platforms.