Drude Free-electron Model Research Articles

Method for measuring supercapacitor’s fundamental inherent parameters using its own self-discharge behavior: A new steps towards sustainable energy

In recent decades, research into energy storage systems has increased in order to make these technologies more competitive. The objective is to create an energy storage system that allows power to be stored and supplied more cheaply during off-peak hours. Supercapacitors, for example, are energy storage and delivery devices capable of storing and transferring large quantities of energy in a short amount of time. The Nippon supercapacitor's self-discharging behaviour, as well as that of many other supercapacitors, was investigated using data analytic techniques based on this supercapacitor property in order to make it more sustainable. The leaking parallel resistance of a Nippon Supercapacitor as a function of the voltage applied across the capacitor terminal was first calculated and tested. To explain such behaviour, the “Drude free-electron model” was utilised, which states that the electron density in any EDLC (electric double layer capacitance) is proportional to the value of the electric field across the capacitors. Based on this premise, we developed a technique for calculating the capacitance value of supercapacitors using self-discharge data as a function of the voltage applied. Only the self-discharge data of EDLC supercapacitors were used for such a high value of capacitance and voltage-dependent leakage resistance.

Ellipsometric study of the electronic behaviors of titanium-vanadium dioxide (TixV1−xO2) films for 0 ≤ x ≤ 1 during semiconductive-to-metallic phase transition

Titanium-vanadium dioxide or TixV1−xO2 films for 0 ≤ x ≤ 1 were examined using ellipsometry, and their optical constants (n and k) at visible and near-infrared wavelengths were determined at temperatures (T) below, at, and above the semiconductive-to-metallic phase transition (SMT) temperature (TSM). Ellipsometric analysis was performed for each x at each T using a wavelength dispersion model, i.e., a combination of Lorentz oscillators and a Drude free electron model. The ellipsometric analyses provided information on the electronic band transition caused by the SMT and the influence of cationic replacement (Ti↔V) on the SMT. The results revealed that when x ≤ 0.05, close to the SMT, the energy gap of the interband transition O2p→V3d varied from ≈3.5 eV to ≈3.1 eV, and the quantity of electrons in the interband transition decreased by half. In addition, the energy gap monotonically increased to 4.2 eV when x was increased to 1. Moreover, the energy gap of the split V3d intraband transition varied from ≈1.4 eV to zero, and the quantity of electrons in the intraband transition increased by a factor of four. Furthermore, when x ≥ 0.2, close to the SMT, the energy gap of the intraband transition varied from ≈1.4 eV to a constant positive value, with the generation of a small number of conductive electrons, depending on x.

Characterization of electric-field enhancement leading to circuit-layout dependent damage of low-k films when exposed to processing plasma

We investigated the effects of Cu-line layouts on plasma-induced radiation damage (PRD) to interline low-k dielectric films. We carried out a finite-element-method-based three-dimensional (3D) electromagnetic simulation (EMS), in which a Drude free-electron model was implemented for the dielectric function of Cu lines. The 3D EMS analysis revealed that the electric field in the low-k films was enhanced for specific Cu-line layouts exposed to N2 plasma irradiation, while no clear electric-field enhancement was observed for Ar plasma exposure. The specific optical emission lines produced in N2 plasmas are the root cause of damage creation in the low-k dielectric films with embedded Cu lines. The 3D EMS analysis predicted that the electric field was enhanced with decreasing the line and space (L/S) widths. The prediction implies that the Cu-line-layout dependent PRD should be more prominent as device dimensions shrink. We verified the predicted results experimentally using devices with low-k films between various L/S Cu lines, in addition to a blanket wafer—without Cu lines. We found that an increasing peak in the low-k dielectric constant appeared at a specific L/S width after N2 plasma exposure and no clear increase in the dielectric constant was observed after Ar plasma exposure. The obtained experimental results are consistent with the 3D EMS analysis. We propose a damage model, where the electric field enhancement plays an important role in the low-k dielectric films with embedded Cu lines. The proposed damage model is indispensable for minimizing PRD and designing Cu layouts in future devices.

Ultraviolet Analysis of Gold Nanorod and Nanosphere Solutions

The localized surface plasmon resonances of gold nanoparticles have been widely studied at visible and near-infrared frequencies but less so in the ultraviolet. The spectral extinction measurements of gold nanospheres at UV wavelengths reported here closely match calculated spectra down to 200 nm using the measured dielectric function of gold. The nanosphere volume attenuation coefficient, αv, is size-dependent in the 200–300 nm wavelength range where the dielectric function follows the Drude free electron model (as it does for wavelengths larger than 500 nm). In the interband transition region, the extinction is more closely proportional to mass and therefore has a value of αv that is largely independent of size. Gold nanorod solutions exhibit very strong UV extinction below 220 nm due to charge transfer to solvent (c.t.t.s.) excitations of the bromide counterion to the cationic surfactant. The gold nanorod UV properties depend on the alignment between the optical polarization and nanorod structure. For ...

Observation of the Wigner-Huntington transition to metallic hydrogen.

Producing metallic hydrogen has been a great challenge in condensed matter physics. Metallic hydrogen may be a room-temperature superconductor and metastable when the pressure is released and could have an important impact on energy and rocketry. We have studied solid molecular hydrogen under pressure at low temperatures. At a pressure of 495 gigapascals, hydrogen becomes metallic, with reflectivity as high as 0.91. We fit the reflectance using a Drude free-electron model to determine the plasma frequency of 32.5 ± 2.1 electron volts at a temperature of 5.5 kelvin, with a corresponding electron carrier density of 7.7 ± 1.1 × 1023 particles per cubic centimeter, which is consistent with theoretical estimates of the atomic density. The properties are those of an atomic metal. We have produced the Wigner-Huntington dissociative transition to atomic metallic hydrogen in the laboratory.

Normal Spectral Emissivity Measurement of Molten Cu–Co Alloy Using an Electromagnetic Levitator Superimposed with a Static Magnetic Field

The normal spectral emissivity of molten Cu–Co alloy with different compositions was measured in the wavelength range of 780 nm to 920 nm and in the temperature range of 1430 K to 1770 K including the undercooled condition by an electromagnetic levitator superimposed with a static magnetic field. The emissivity was determined as the ratio of the radiance from a levitated molten Cu–Co droplet measured by a spectrometer to the radiance from a blackbody calculated by Planck’s law at a given temperature, where a static magnetic field of 2.5 T to 4.5 T was applied to the levitated droplet to suppress the surface oscillation and translational motion of the sample. We found little temperature dependence of the normal spectral emissivity of molten Cu–Co alloy. Concerning the composition dependence, the emissivity decreased markedly above 80 at%Cu and reached that of pure Cu, although its dependence was low between 20 at%Cu and 80 at%Cu. In addition, this composition dependence of the emissivity of molten Cu–Co alloy can be explained well by the Drude free-electron model.

Doping Ga effect on ZnO radio frequency sputtered films from a powder target

Undoped ZnO and ZnO:Ga films have been radio frequency (RF) sputtered on glass substrates using powder targets. X-ray diffraction studies reveal that the films are polycrystalline with a hexagonal wurtzite structure and a preferential orientation along the c-axis. The (002) peak shift to lower 2θ values indicates that the films suffered compressive stress with Ga incorporation. The grain sizes are found in the range of 20–23nm showing a nanostructure. All the films are highly transparent (>85%) in the visible region and the optical band gap shows a blue shift with Ga incorporation up to 3wt.% then a red shift with further Ga content from 3.56 to 3.47eV due to band tail. Urbach energy increases from 0.06 to 0.15eV with Ga content revealing disorder increase in the lattice.Besides the near band emission peak, which shows the same trend for the optical band gap variation, Photoluminescence measurements show deep level emissions in the violet, blue and green regions.The electrical parameters were obtained with both optical reflectance based on the Drude free-electron model and the Hall method and similar tendencies were observed within the two methods. The highest figure of merit observed in this study was 3.57×10−3Ω−1 showing that the 3wt.% ZnO:Ga films are potentially attractive for application as transparent conductive oxide thin films in solar cells. RF sputtering from a powder target was found to be a simple and cost effective technique for the synthesis of ZnO thin films for potential applications in the renewable energy devices.

Imaging and Characterizing Long-Range Surface Plasmon Polaritons Propagating in a Submillimeter Scale by Two-Color Two-Photon Photoelectron Emission Microscopy

Long-range surface plasmon polaritons (SPPs), which propagate along metal/dielectric interfaces to submillimeter distances in the range of near-infrared (NIR) excitation wavelength, were examined by two-color two-photon photoelectron emission microscopy (2P-PEEM). Interferences between incident NIR photons and SPPs excited by the NIR photons at surface defects were imaged by detecting photoelectrons emitted from a gold surface, assisted by simultaneously irradiated ultraviolet photons which are to overcome the workfunction of the surface. The wavelength of the interference beat depends sensitively on the NIR wavelength. By analyzing the interference beat, the dispersion curve as well as phase and group velocities of SPP’s were experimentally obtained. The results closely match the theoretical one based on the Drude free electron model, indicating that two-color 2P-PEEM is applicable not only to the visualization of NIR-excited SPPs but also to the quantitative analysis of its physical properties. This method will be widely used to observe SPPs for various artificial plasmonic devices.

Terahertz conductivity of reduced graphene oxide films

We performed time-domain terahertz (THz) spectroscopy on reduced graphene oxide (rGO) network films coated on quartz substrates from dispersion solutions by spraying method. The rGO network films demonstrate high conductivity of about 900 S/cm in the THz frequency range after a high temperature reduction process. The frequency-dependent conductivities and the refractive indexes of the rGO films have been obtained and analyzed with respect to the Drude free-electron model, which is characterized by large scattering rate. Finally, we demonstrate that the THz conductivities can be manipulated by controlling the reduction process, which correlates well with the DC conductivity above the percolation limit.

Evaluation of Optical Properties of Ag, Cu, and Co Nanoparticles Synthesized in Organic Medium

The surface plasmon resonance evaluation of colloidal metal nanoparticles, synthesized in organic medium, is reported in this work. Metal salts were dissolved in dioxane/AOT solution and reduced by hydrazine hydrate under vigorous stirring. Optical properties of obtained colloidal nanoparticles were investigated by UV VIS spectroscopy. Theoretical predictions of optical properties of metal nanoparticles were made by means of the Mie theory and the Drude free-electron model. Geometrical parameters and distribution of metal nanoparticles in colloidal solutions were characterized by atomic force microscopy. The results show that Ag, Cu, and Co nanoparticles, synthesized in organic medium distinguish plasmonic properties. Surface plasmon resonance bands were obtained in all cases: Ag at 430 nm, Cu at 570 nm, Co at 350 nm (SPR1) and 430 nm (SPR2). Comparing theoretical evaluation of nanoparticles size with atomic force microscopy analysis, we can assume that our calculations are accurate. It was found that dominating nanoparticles diameter in Ag colloidal solution is ≈ 150 nm, in Cu colloidal solution is ≈ 70 80 nm and in Co colloidal solution is ≈ 150 nm. It can be concluded that nanoparticles with enhanced plasmonic properties synthesized in organic medium can be widely used in order to increase e ciency of various optical elements.

Optical dielectric function of gold

In metal optics gold assumes a special status because of its practical importance in optoelectronic and nano-optical devices, and its role as a model system for the study of the elementary electronic excitations that underlie the interaction of electromagnetic fields with metals. However, largely inconsistent values for the frequency dependence of the dielectric function describing the optical response of gold are found in the literature. We performed precise spectroscopic ellipsometry measurements on evaporated gold, template-stripped gold, and single-crystal gold to determine the optical dielectric function across a broad spectral range from 300 nm to 25 $\ensuremath{\mu}$m (0.05--4.14 eV) with high spectral resolution. We fit the data to the Drude free-electron model, with an electron relaxation time ${\ensuremath{\tau}}_{D}=14\ifmmode\pm\else\textpm\fi{}3$ fs and plasma energy $\ensuremath{\hbar}{\ensuremath{\omega}}_{p}=8.45$ eV. We find that the variation in dielectric functions for the different types of samples is small compared to the range of values reported in the literature. Our values, however, are comparable to the aggregate mean of the collection of previous measurements from over the past six decades. This suggests that although some variation can be attributed to surface morphology, the past measurements using different approaches seem to have been plagued more by systematic errors than previously assumed.

Normal spectral emissivity measurement of molten copper using an electromagnetic levitator superimposed with a static magnetic field

The normal spectral emissivity of molten copper was determined in the wavelength range of 780–920 nm and in the temperature range of 1288–1678 K, by directly measuring the radiance emitted by an electromagnetically levitated molten copper droplet under a static magnetic field of 1.5 T. The spectrometer for radiance measurement was calibrated using the relation between the theoretical blackbody radiance from Planck's law and the light intensity of a quasi-blackbody radiation source measured using a spectrometer at a given temperature. As a result, the normal spectral emissivity of molten copper was determined as 0.075 ± 0.011 at a wavelength of 807 nm, and it was found that its temperature dependence is negligible in the entire measurement temperature range tested. In addition, the results of the normal spectral emissivity and its wavelength dependence were discussed, in comparison with those obtained using the Drude free-electron model.

Electronic transport and carrier concentration in conductive ZnO:Ga thin films

Transparent and conductive Ga-doped ZnO (ZnO:Ga) films were post-annealed after sputter deposition, and their structural and electrical properties were investigated. Post-annealing led to an improvement of crystallinity along the [001] direction, but did not change lateral grain size. Therefore, carrier concentration and electron mobility of films were analyzed as a function of crystallinity. The electrical parameters were obtained with both optical reflectance based on the Drude free-electron model and the Hall method, and similar tendencies were observed within the two methods. Even though the lowest resistivity was demonstrated by the film annealed at 550 °C, the optimum values for carrier concentration and mobility were observed in films with different post-annealing temperatures.

In SituandEx SituStudies of Molybdenum Thin Films Deposited by rf and dc Magnetron Sputtering as a Back Contact for CIGS Solar Cells

Molybdenum thin films were deposited by rf and dc magnetron sputtering and their properties analyzed with regards to their potential application as a back contact for CIGS solar cells. It is shown that both types of films tend to transition from tensile to compressive strain when the deposition pressure increases, while the conductivity and the grain size decreas. The nucleation of the films characterized byin situand real time spectroscopic ellipsometry shows that both films follow a Volmer-Weber growth, with a higher surface roughness and lower deposition rate for the rf deposited films. The electronic relaxation time was then extracted as a function of bulk layer thickness for rf and dc films by fitting each dielectric function to a Drude free-electron model combined with a broad Lorentz oscillator. The values were fitted to a conical growth mode and demonstrated that the rf-deposited films have already smaller grains than the dc films when the bulk layer thickness is 30 nm.

Spectroscopic characterization of highly doped ZnO films grown by atomic-layer deposition for three-dimensional infrared metamaterials [Invited

We systematically study the optical spectra of ZnO grown by atomic-layer deposition as a function of Al (and Ti) doping concentration. The spectra measured on films are well described by fits using a Drude free-electron model. The derived plasma frequencies are consistent with the expected amount of doping and can be continuously and controllably tuned from small values to about 400 THz. The losses (damping) are also quantified. In addition, we achieve smooth conformal coatings of three-dimensional polymer templates made by direct laser writing. Altogether, Al:ZnO appears as an attractive “tunable metal” for three-dimensional infrared metamaterials or transformation-optics architectures.

Shock wave velocity measurement in the Al2O3 under ultrahigh pressure

In indirect-drive experiment, the blank effect caused by X-rays from Hohlraum will show the dark area in time scale of optical streak camera (OSC). This blank effect, which was a serious problem in indirect-drive shock wave experiments, has been explained by the semiconductor model. The X-rays cause the band to band transition and the probe laser is absorbed by the intraband transition, which leads to a dark region in time scale of the OSC image. In the experiment, the reflectivity of shock wave front was measured to be about 50% at shock wave velocity 32 km/s and was compared to the theoretical calculations with the Drude free electron model. From the experimental data, it is found that the blank effect can be avoided at radiation temperature of 170 eV if the Al layer is thicker than 60 μm.

Direct measurement technique for shock wave velocity under super high pressure

With the ionization mechanism for the transparent material under the super high pressure, the basic measurement method of shock wave has been analyzed. With the Drude-free electron model, the change in reflectivity of shock wave front under different pressures has been analyzed. The reflectivity of shock wave front for different probe lasers has been compared in theory. And it was found that the reflectivity of shock wave front for 660 nm of probe laser is higher than that for 532 nm. The effect of the detector was found to be caused by the X-ray ionization of the transparent material after analyzing the reflectivity data in space-time scale. From the experiment data, it is found that the beginning of "blank" effect coincides with the start point of laser pulse. The shock wave is later than the "blank" effect under the square laser pulse. In the experiment, the reflectivity of shock wave front is about 40% when the shock velocity is 35 km/s. The theoretical decreasing curve of shock velocity in the sapphire window is confirmed by the experiment data. The formula to calculate the shock wave velocity in the transparent material was deduced and verified.

Normal spectral emissivity of stable and undercooled liquid silicon using electromagnetic levitation in a dc magnetic field

Normal spectral emissivity of a stable and undercooled liquid (1660–1790 K) was determined for wavelengths of 780–920 nm using direct measurement of radiance of statically electromagnetically levitated liquid silicon: a dc magnetic field suppressed surface oscillation and the transitional motion of the silicon droplet. A spectrometer used for spectral radiance measurement was calibrated using a quasi-blackbody with a copper metal fixed point. The emissivity shows weak negative wavelength dependence, and negligible temperature dependence. The wavelength dependence of the normal spectral emissivity is expressible using the Drude free electron model.

Frequency-Dependent Complex Conductivities and Dielectric Responses of Indium Tin Oxide Thin Films From the Visible to the Far-Infrared

Transparent and conducting indium tin oxide (ITO) thin films form an integral part for various optoelectronic devices. In this paper, we report the frequency-dependent complex conductivities and dielectric responses of several sputtered ITO thin films with thicknesses in the range of 189–962 nm by using terahertz time domain spectroscopy (THz-TDS), optical reflectance spectroscopy, and electrical measurements. The plasma frequencies are verified to be from 1590 to 1930 <formula formulatype="inline" xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"><tex Notation="TeX">${\rm rad}\cdot{\rm THz}$</tex></formula> , while the scattering times are in the range 6–7 fs based on the Drude free-electron model. The mobilities of the above ITO thin films are calculated to be 32.7–34.2 <formula formulatype="inline" xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"><tex Notation="TeX">${\rm cm}^{2}{\rm V}^{-1}{\rm s}^{-1}$</tex></formula> , whereas the carrier concentrations lie in the range 2.79–4.10 <formula formulatype="inline" xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"><tex Notation="TeX">$\,\times 10^{20}~{\rm cm}^{-3}$</tex></formula> . The electrical properties derived from the THz-TDS technique agree well with those determined by Hall measurement. Parameters for the complex dielectric function suitable for ITO in the range 0.2–2 and 4–450 THz are also determined.

Effect of an interface charge density wave on surface plasmon resonance in ZnO/Ag/ZnO thin films

The optical transmission spectra of ZnO/Ag/ZnO films showed a broad range of transmission enhancement due to a harmonic generated by surface plasmon resonance. This resonance was correlated with interface electrons between metallic Ag and dielectric ZnO layer. The interface charge density wave was calculated and compared with experimental results using Maxwell’s equations with a modified boundary condition. Finally, an observed redshift in the transmission enhancement is discussed using both the Ohmic contact model and the Drude free electron model.