Drude Model Research Articles

A promising high-sensitive 1D photonic crystal magnetic field sensor based on the coupling of Fano\\Tamm resonance in far IR region

This paper presents a novel investigation of a magnetic sensor that employs Fano/Tamm resonance within the photonic band gap of a one-dimensional crystal structure. The design incorporates a thin layer of gold (Au) alongside a periodic arrangement of Tantalum pentoxide () and Cesium iodide () in the configuration . We utilized the transfer matrix method in conjunction with the Drude model to analyze the formation of Fano/Tamm states and the permittivity of the metallic layer, respectively. These states can be manipulated based on the left-handed and right-handed circular polarization of electromagnetic waves, along with an applied magnetic field. Several key parameters were optimized, including material selection, layer thickness, unit cell periodicity, and the angle of incidence, to enhance the sensor performance. Additionally, we investigated how variations in magnetic field strength influence the position of Fano/Tamm resonance in the reflectivity spectrum of the interacting electromagnetic waves within a specific wavelength range of 60 μm to 140 μm. The proposed sensor displays good performance investigated by calculating several parameters like, sensitivity, figure of merit, quality factor and resolution. One of them, it shows a maximum sensitivity of 57 nm/Tesla within a magnetic field strength of 20 to 140 Tesla, positioning it as a promising candidate for various applications in magnetic field measurement and telecommunications, particularly in the unique far-infrared region.

Radiative Warming Glass for High-Latitude Cold Regions.

Traditional window glazing, with inherently adverse energy-efficient optical properties, leads to colossal energy losses. Energy-saving glass requires a customized optical design for different climate zones. Compared with the widely researched radiative cooling technology which is preferable to be used in low-altitude hot regions; conversely in high-latitude cold regions, high solar transmittance (Tsol) and low mid-infrared thermal emissivity (εMIR) are the key characteristics of high-performance radiative warming window glass, while the current low-emissivity (low-e) glass is far from ideal. To address this issue, Drude's theory is used to numerically design a near-ideal film with specified electron density (ne) and electron mobility (µe). The fabricated hydrogen-doped indium oxide (IHO) could achieve high Tsol (0.836) and low εMIR (0.117). Energy-saving simulations further reveal a substantial decrease in annual heating energy consumption up to 6.6% across high-latitude regions (climate zones 6 to 8), translating to a corresponding reduction in CO2 emissions (20.0kg m-2), outperforming 1165 high performance commercial low-e glass. This radiative warming glass holds the promise of making a significant contribution to sustainable building energy savings specifically for high-latitude cold regions, advancing the goal of carbon neutrality.

Modeling Europium (II/III) ion solvation in the LiCl-KCl eutectic mixture with polarizable force fields

The solvation processes of Europium (II/III) ions within the molten salt eutectic mixture, 3LiCl-2KCl, are investigated over temperatures ranging from 673 K to 1173 K. New polarizable ion force fields are proposed to model Europium ions in a molten salt eutectic mixture with a goal of accurately capturing the underlying physics in the solutions. In contrast to rigid-ion models, the polarizable Drude model with an adjusted WBK (Wang-Buckingham) force field significantly improves predictions for diffusion coefficients, the average diffusion activation energy, and changes in excess ion chemical potential and partial molar entropy, producing good agreement with experimental measurements.

New Torsional Surface Elastic Waves in Cylindrical Metamaterial Waveguides for Sensing Applications.

In this paper, we demonstrate that torsional surface elastic waves can propagate along the curved surface of a metamaterial elastic rod (cylinder) embedded in a conventional elastic medium. The crucial parameter of the metamaterial rod is its elastic compliance s44(1)ω, which varies as a function of frequency ω analogously to the dielectric function εω in Drude's model of metals. As a consequence, the elastic compliance s44(1)ω can take negative values s44(1)ω<0 as a function of frequency ω. Negative elastic compliance (s44(1)ω<0) enables the emergence of new surface states, i.e., new types of surface elastic waves. In fact, the proposed torsional elastic surface waves can be considered as an elastic analog of Surface Plasmon Polariton (SPP) electromagnetic (optical) waves propagating along a metallic rod (cylinder) embedded in a dielectric medium. Consequently, we developed the corresponding analytical equations, for the dispersion relation and group velocity of the new torsional elastic surface wave. The newly discovered torsional elastic surface waves exhibit virtually all extraordinary properties of their electromagnetic SPP counterparts, such as strong subwavelength concentration of the wave energy in the vicinity of the cylindrical surface (r=a) of the guiding rod, very low phase and group velocities, etc. Therefore, the new torsional elastic surface waves can be used in: (a) near-field subwavelength acoustic imaging (super-resolution), (b) acoustic wave trapping (zero group and phase velocity), etc. Importantly, the newly discovered torsional elastic surface waves can form a basis for the development of a new generation of ultrasonic sensors (e.g., viscosity sensors), biosensors, and chemosensors with a very high mass sensitivity.

Ti3C2T x MXene Thin Films and Intercalated Species Characterized by IR-to-UV Broadband Ellipsometry.

MXenes are two-dimensional (2D) materials with versatile applications in optoelectronics, batteries, and catalysis. To unlock their full potential, it is crucial to characterize MXene interfaces and intercalated species in more detail than is currently possible with conventional optical spectroscopies. Here, we combine ultra-broadband ellipsometry and transmission spectroscopy from the mid-infrared (IR) to the deep-ultraviolet (UV) to probe quantitatively the composition, structure, transport, and optical properties of spray-coated Ti3C2T x MXene thin films with varying material properties. We find film thickness heterogeneity and surface roughness in the low-nanometer range as well as depth-dependent conductivity properties, which we quantify with a graded Drude model. The optically determined sheet resistance is confirmed by four-point probe measurements. Furthermore, we employ density-functional-theory calculations to assign the observed absorption bands in the MXene dielectric function to various interband transitions from mixed MXene surface terminations. The prominent 1.48 eV (833 nm) spectral feature is found to be related to oxygen termination. Additional plasmonic effects are also suggested. Finally, we leverage the chemical sensitivity of state-of-the-art IR ellipsometry to separate the fingerprints of intercalated species within the MXene from the dominant Drude contributions, presenting for the first time a set of infrared optical constants of intercalated water. This work lays the foundation for optical metrology for interface engineering of MXene and other 2D materials.

On chip glucose sensing using guided waves at terahertz frequencies

This paper demonstrates an on-chip anhydrous D-glucose sensor using a coplanar stripline (CPS) on a thin (1 m) silicon nitride membrane at terahertz (THz) frequencies. A thin layer ( 10 m) of D-glucose was placed in close proximity to the CPS and the transmission response was measured using a modified THz-TDS setup. The D-glucose introduces frequency-dependent changes to the effective permittivity of the CPS resulting in a modified spectral response at the receiver. Measurement results show absorption signatures at 1.42 THz and 2.07 THz corresponding to the first two significant resonances beyond 1 THz for D-glucose allowing for label-free detection. The frequency-dependent attenuation coefficient was estimated by simulation for several D-glucose layer thicknesses using a modified Lorentz model. Measurement results align with simulations and other literature that use free-space THz radiation. This work verifies on-chip THz sensing of D-glucose and presents a pathway toward on-chip sensing of other materials at THz frequencies.

Leaf-Shaped Nanostrip Fed Graphene Plasmonic Nano-Antenna for Optical Near-Field Applications

The manuscript investigates the leaf-shaped nanostrip-fed graphene plasmonic nanopatch on a silicon dioxide surface for optical near-field applications. The dispersion properties of graphene and silicon dioxide are demonstrated through Drude and Lorentz modeling to examine the suitability of the materials for the plasmonic nano-antenna design. The nano-antenna parameters TSUB (substrate thickness), W (width of the nanostrip feed line) and RL(nano-antenna size) are adjusted to modify the plasmonic resonance frequency from 7.9 THz to 40.9 THz. The proposed leaf-shaped nanostrip-fed graphene plasmonic nanopatch exhibits a reflection of -43.27 dB at 36 THz with a gain of 8.19 dB at TSUB =125 nm, W = 40 nm and RL = 50 nm.

Advanced spectroscopic approach for exploring the structural, optical, and electronic properties in dye-functionalized chitosan biopolymers

This study employed advanced spectroscopic techniques to investigate the structural and optical properties of chitosan (CS) biopolymer films modified with natural dyes from Cosmos Sulphureus Cav. (CSC) flowers. FTIR results indicated that the inclusion of CSC dyes led to broader absorbance and decreased transmittance. Distinct absorption regions were identified, and the optical energy band gap (OEBG), transport gap, and exciton binding energy were calculated using Tauc’s method. The OEBG was found to be 5.44 eV for CS while for CS-CSC dye samples, it dropped to 2.24 eV and The Urbach energy increased from 0.44 eV to 0.60 eV, indicating the presence of high tail states in the band gap region. The electron–phonon interaction was found to increase from 11.35 to 15.58. The oscillator energy values (4.13 eV-2.33 eV) at low energies obtained using Wemple-DiDomenico model are found to be close to OEBGs using Tauc’s model. Additionally, from the Drude-Lorentz model the N/m* was found to increase from 1.69 × 1052 to 1.27 × 1054. The third order non-linear polarizability parameter, the linear optical susceptibility and the non-linear index of refractions were all found to increase upon increasing the CSC dye concentrations.

Optical and Plasmonic Properties of Epitaxial and Oxidative Controlled Titanium Nitride Thin Films

The present study is an effort to develop negative-permittivity, high melting point, mechanically hard, and chemically stable materials beyond commonly employed plasmonic metals such as gold and silver, which are often device incompatible in terms of real operating environments. The material studied here is titanium nitride (TiN), which possess free electron gas density similar to of gold and silver, and embodies refractory metals’ characteristics. The aforementioned advantages of TiN are taken to the next level by transforming them to oxynitrides (TiON) with a precise control in oxygen composition that can, in turn, be used to tune the electronic band structure of transition metal nitrides, opening another new dimension to transition metals nitride based plasmonics and metamaterials research. This presentation will report a pulsed laser-assisted synthesis, detailed structural characterization using x-ray diffraction (XRD), x-ray photoelectron spectroscopy (XPS), soft x-ray absorption spectroscopy (XAS), non-Rutherford Backscattering spectrometry (RBS), and plasmonic properties of three sets of TiN/TiON thin films. The first two sets of TiN films were grown 600 and 700 °C under a high vacuum condition. The third set of TiN film was grown in the presence of 5 mTorr of molecular oxygen at 700 °C. The purpose of making these three sets of TiN/TiON films was to understand the role of film crystallinity and role of oxygen content of TiN films on their optical and plasmonic properties. The results have shown that TiN films deposited in a high vacuum are metallic, have large reflectance, and high optical conductivity. The TiN films, grown in 5 mTorr, were found to be partially oxidized with room temperature resistivity nearly three times larger than those of the TiN films grown under high vacuum conditions. The optical conductivity these films were analyzed using a Kramers-Kronig transformation of reflectance and a Lorentz-Drude model; the optical conductivity determined by two different methods agrees very well, indicative of reliable estimate of the absolute value of reflectance in the first place. Then, it allows us to determine and analyze the complex dielectric function over a broad spectral range. We notice the existence of significant spectral weight below the interband absorptions, described by two Lorentzians, one around 250 cm-1 and one around 2,500 cm-1. We discuss here the dependence of the two bands on the deposition conditions and their effect on the plasmonic performances of TiN/TiON thin films, in particular on the surface plasmon polariton (SPP) and localized surface plasmon resonance (LSPR) quality factors.

Electron confinement-induced plasmonic breakdown in metals.

Plasmon resonance represents the collective oscillation of free electron gas density and enables enhanced light-matter interactions in nanoscale dimensions. Traditionally, the classical Drude model describes plasmonic excitation, wherein plasma frequency exhibits no spatial dispersion. Here, we show conclusive experimental evidence of the breakdown of plasmon resonance and a consequent metal-insulator transition in an ultrathin refractory plasmonic material, hafnium nitride (HfN). Epitaxial HfN thick films exhibit a low-loss and high-quality Drude-like plasmon resonance in the visible spectral range. However, as the film thickness is reduced to nanoscale dimensions, Coulomb interaction among electrons increases because of electron confinement, leading to the spatial dispersion of plasma frequency. With a further decrease in thickness, electrons lose their ability to shield the incident electric field, turning the medium into a dielectric. The observed metal-insulator transition might carry some signatures of Wigner crystallization and indicates that such transdimensional, between 2D and 3D, films can serve as a promising playground to study strongly correlated electron systems.

Modified negative permittivity and X-band microwave absorption in polyvinyl Alcohol–MWCNT metacomposites

Metacomposite films with modifiable negative permittivity are promising for wearable cloaking, sensing, electromagnetic interference shielding, and microwave absorption. The purpose of this study is to fabricate metacomposite films composed of polyvinyl alcohol (PVA) and multi-walled carbon nanotubes (MWCNTs) and demonstrate control of permittivity by varying MWCNT concentration. Drude-Lorentz and Drude models show negative permittivity behaviour as the MWCNT content increases. The Drude-Lorentz and Drude models confirm that at 1 wt% MWCNT loading, percolation occurs, leading to increased conductivity and a transition from positive to negative permittivity (−9 at 10 kHz and −200 at 34 kHz). Drude's model predicts negative permittivity across the entire frequency range of PVA with 3 wt% MWCNT. Metacomposite films exhibit electrical percolation, conductivity switching, permittivity shift, and capacitive-to-inductive transitions. These composites also demonstrate excellent X-band microwave absorption properties (up to −50 dB reflection loss) and a shielding efficiency of 22 dB, suggesting an absorption-dominated shielding mechanism.

Innovative active terahertz modulator based on dynamic graphene-silicon arrays

This paper presents an innovative active terahertz (THz) modulator that utilizes dynamic graphene-silicon arrays (DGSAs) to overcome the challenges of dynamically manipulating THz waves. The DGSA combines the exceptional electrical properties of graphene with the enhanced optical absorption capabilities of silicon arrays, enabling dual-mode active control through optical pumping and electrical biasing. An 808 nm laser is used to photoexcite carriers in the silicon arrays for optical pumping while a bias voltage modulates the Fermi level of graphene, subsequently varying Si conductivity and influencing the transmission properties of THz waves. Simulations have demonstrated modulation depths of up to 94% at 2.5 THz in the transmission mode and 89% at 1 THz in the reflection mode. Furthermore, this study delves into a theoretical analysis and numerical simulations, exploring the modulation mechanisms, including the role of graphene’s Drude model and PN junction effects. These insights provide a robust theoretical framework for understanding the DGSA’s operation and lay a solid foundation for the design and optimization of high-performance THz modulation devices.

Dissipative split-charge formalism: Ohm's law, Nyquist noise, and non-contact friction.

The split-charge equilibration method is extended to describe dissipative charge transfer similarly as the Drude model, whereby the complex-valued frequency-dependent dielectric permittivities or conductivities of dielectrics and metals can be mimicked at non-zero frequencies. To demonstrate its feasibility, a resistor-capacitor circuit is simulated using an all-atom representation for the resistor and capacitor. The dynamics reproduce the expected charging process and Nyquist noise, the latter resulting from the thermal voltages acting on individual split charges. The method bears promise to model friction caused by the motion of charged particles past metallic or highly polarizable media.

Diffusion, long-time tails, and localization in classical and quantum Lorentz models: A unifying hydrodynamic approach

Diffusion, long-time tails, and localization in classical and quantum Lorentz models: A unifying hydrodynamic approach

Unraveling the origin of conductivity change in Co-doped FeRh phase transition

Phase-changing materials have been a cornerstone of condensed matter physics for decades. A quintessential example is iron-rhodium (FeRh), which undergoes a first-order phase transition from antiferromagnetic to ferromagnetic states near room temperature. The pivotal aspect of this transition is a marked alteration in electrical conductivity. However, its underlying origin still remains elusive, largely due to the difficulties of directly probing fundamental transport during this phase transition. In this study, we investigate the fundamentals of FeRh’s electrical transport employing terahertz time-domain spectroscopy (THz-TDS). Leveraging the Drude model, we discerned the distinct contributions of extrinsic (momentum scattering time, τ) and intrinsic (charge density, n, and effective mass, m*) factors to electrical conductivity independently. Notably, our investigation unveiled a sharp alteration in n and m* during the phase transition, contrasting with the gradual monotonic decrease of τ with rising temperature. Consequently, our findings provide compelling evidence that the conductivity change in FeRh during the phase transition originates from a restructuring of its band structure. This work provides a crucial step towards a comprehensive understanding of the electrical transport changes occurring during the phase transition, offering valuable insights into the behaviour of phase changing materials.

Enhanced plasmonic performance of TiO2 derived TiN films via gas nitridation

This study demonstrates a cost-effective method for planar titanium nitride plasmonic film by nitriding spin-coated TiO2 in ammonia atmosphere. The effect of nitridation temperature on the structural, morphological, electrical and optical characteristics of the coated films were investigated. The films exhibited high carrier concentration of 1022/cc with significant reduction in resistivity of more than three order of magnitude, indicating the conversion to the nitride phase. Negative permittivity, crucial for plasmonic applications in the visible wavelength region, was verified for wavelengths > 463 nm using Drude-Lorentz model. A three-layer model was employed to verify the material’s plasmonic behaviour. The straightforward fabrication route, which combines spin-coating and ammonia nitridation at 950 °C, offers a new approach for titanium nitride films for plasmonic based gas and biosensing device applications in the visible region. In addition, for fabricating titanium nitride coatings for applications that require abrasion resistance, electrical conductivity, chemical stability, and biocompatibility.

Exciton dynamics in CsPbBr3 single crystal: LT splitting energy, exciton-polariton dispersion, and biexciton binding energy.

Metal halide perovskite materials (MHPs) are promising for several applications due to their exceptional properties. Understanding excitonic properties is essential for exploiting these materials. For this purpose, we focus on CsPbBr3 single crystals, which have higher crystal quality, are more stable, and have no Rashba effect at low temperatures compared to other 3D MHPs. We have estimated exciton energy positions, longitudinal-transverse splitting energy, and damping energy using low-temperature reflection spectra. Under high excitation intensity, two biexciton emissions (M-emission) and exciton-exciton scattering emission (P-emission) were observed. We assign the two M-emissions to the emission to the states of longitudinal and transverse excitons, i.e., ML and MT emissions. From the energy position of the MT emission, the biexciton binding energy has been estimated to be ∼2meV. By analyzing P-emission obtained from the back side of the sample, we have estimated the exciton binding energy to be 17.8-23.7meV. This estimation minimizes the influence of the wavenumber distribution in the scattering process. In addition, time-resolved transmittance measurements using pulsed white light have revealed the group velocity dispersion. Comparing experimental results with theoretical calculations using the Lorentz model clarifies that exciton dynamics in CsPbBr3 can be described with a simple Lorentz model. These insights enhance the understanding of exciton behavior and support the development of exciton-based devices using MHPs.

Tunable negative permittivity behavior and excellent electromagnetic shielding performance of pyrolytic carbon‐glass fiber felt/epoxy resin metacomposites

AbstractEffective and accurate adjustment of negative permittivity behavior is worthy of further investigation. Herein, pyrolytic carbon‐glass fiber felt/epoxy resin (PyC‐GFF/ER) metacomposites with tunable negative permittivity were prepared using an impregnation‐calcination method. The permittivity, electrical conductivity, and electromagnetic shielding performance of the polymer metacomposites were investigated. Due to the inherent three‐dimensional structural network of GFF, the PyC adhering to the surface of glass fiber easily formed a conductive network in the composites. As the PyC content increased in the ER composites, the conductivity mechanism changed from hopping conduction to metal‐like conduction. The ER composites with high PyC contents showed negative permittivity behavior and the epsilon‐near‐zero response owing to the low frequency plasma state of free electrons in the PyC‐conduction network. By controlling the PyC content, the negative permittivity behavior of ER composites could be effectively tuned. With the increase in PyC content, the values of negative permittivity increased, and the epsilon‐near‐zero frequency shifted to a higher frequency. Moreover, the ER composites with high PyC contents showed excellent electromagnetic shielding properties (29.4 dB) at X‐band. This work not only provided a feasible method to realize the tunable negative permittivity of polymer metacomposites, but also promoted its application in the microwave field.Highlights The pyrolytic carbon‐glass fiber felt/epoxy resin composites were fabricated. The negative permittivity was first reported in the PyC‐GFF/ER composites. Tunable negative permittivity could be well explained by Drude model. The polymer composites had excellent electromagnetic shielding property.

Theoretical Evaluation of Complex Dielectric Constant for Gamma Relaxation of Poly(methyl methacrylate), A Study of Quantum Chemistry and Linear Response Theory.

It is widely accepted that the γ relaxation of poly(methyl methacrylate) (PMMA) arises from the hindered rotational motion of the side chain around the C-C bond, which links to the main chain. However, the physical model to explain this process has been unknown. The hybrid density functional theory calculation showed that the PMMA intramolecular hindered rotation has an activation energy of 6.53 kcal/mol. This activation energy causes the friction coefficient to the intramolecule to hinder rotation. The qualitative value of the friction coefficient was evaluated on the basis of linear response theory by using the calculated value of the activation energy. The Lorentz model is adopted to calculate the complex dielectric constant of the γ relaxation using the calculated value of the friction coefficient. The calculated value of the complex dielectric constant agreed reasonably well with experimental results.

Tunable negative permittivity behavior in alumina ceramic composites with different carbon fillers

Carbon/ceramic composites with negative permittivity have motivated a considerable concern due to their special properties and various applications. Herein, series of alumina ceramic composites consisting of different carbon fillers were prepared by the hot-pressed sintering, and the carbon fillers included carbon sphere (CS), carbon black (CB), carbon fibre (CF), carbon nanofibre (CNF) and graphene nanosheet (GN). The impact of various carbon fillers on the electrical performance of composites were investigated comparatively. It was found that CF ceramic had hopping conduction, capacitive character and positive permittivity, and micron-sized CFs were embedded in isolation within the ceramic composite. The other ceramics with carbon nanofillers demonstrated metallic-type conductance, inductive character and negative permittivity. The carbon nanofillers evenly dispersed and easily formed carbon network that improve the flow of free electrons in the composites, and the negative permittivity behavior imputed to the low frequency plasmonic state of abundant free electrons in the carbon networks. Furthermore, the magnitude of negative permittivity was in connection with the type of carbon nanofiller. The one- or two-dimensional carbon nanofillers were more easily connected to each other to form a denser carbon network, and thus the CNF and GN ceramics had the larger absolute values of negative permittivity, which was in accord with Drude model.