High Plasma Frequency Research Articles

Optical Properties of Multilayers TiO2/SnO2:F Thin films

AbstractThin films of TiO2/SnO2:F multilayers were prepared by spray pyrolysis technique on glass substrate. The samples were prepared using titanium (IV) isopropoxide 98%, ammonium fluoride and tin(II) chloride dehydrate extra pure as precursor materials. Thus, a TiO2 thickness dependence optical study of TiO2/SnO2:F/glass system is presented. The optical property was characterized by UV-Visible transmittance spectroscopy. For all the samples, the average transmissions in the visible wavelength region (400-800 nm) were between 69 and 84%. The optical parameters, such as the real part dielectric function ε1 and the imaginary part dielectric function ε2, of TiO2 and SnO2:F in the TiO2/SnO2:F thin films structure, determined by fitting the measured optical transmittance spectra, are presented and analyzed. Among the various classical dispersion relations for the dielectric function, the Drude model combined with the Lorentzian oscillators was used to get a good fit of transmittance in the measured spectral range. Results on related parameters such as high frequency dielectric constant, plasma frequency, film thickness and band gap are presented.

Superconducting circuit boundary conditions beyond the dynamical Casimir effect

We study analytically the time-dependent boundary conditions of superconducting microwave circuit experiments in the high plasma frequency limit, in which the conditions are Robin-type and relate the value of the field to the spatial derivative of the field. We give an explicit solution to the field evolution for boundary condition modulations that are small in magnitude but may have arbitrary time dependence, in a formalism that applies both to a semiopen waveguide and to a closed waveguide with two independently adjustable boundaries. The correspondence between the microwave Robin boundary conditions and the mechanically moving Dirichlet boundary conditions of the dynamical Casimir effect is shown to break down at high field frequencies, approximately 1 order of magnitude above the frequencies probed in the 2011 experiment of Wilson et al. Our results bound the parameter regime in which a microwave circuit can be used to model relativistic effects in a mechanically moving cavity, and they show that beyond this parameter regime moving mirrors produce more particles and generate more entanglement than their nonmoving microwave waveguide simulations.

Material effects on V-nanoantenna performance

There is great interest in aluminum based plasmonic devices due to the relatively high plasma frequency of this material as well as its low cost and self-passivating oxide layer. The passivation layer provides aluminum plasmonics with the long-term stability required for practical applications. While several studies have investigated the impact of this oxide layer on the plasmon resonances of aluminum nanostructures on glass substrates, little is known about the effect of high-refractive index substrates on these resonances. Here we present an investigation of aluminum V-shaped antennas resonant in the visible on a silicon substrate. Through comparison between numerical and experimental results, we show that the aluminium passivation layer has little effect on the antenna resonances by comparing numerical simulations both with and without. We show, however, that inclusion of the native oxide layer of the silicon substrate in numerical models is critical for achieving good agreement with experimental data. Furthermore, we computationally explore the influence of the 1.5 eV interband transition of aluminum on plasmon resonances, and find that its effect on the material properties of the resonant structures results in narrower resonances in the blue part of the spectrum than if it was not present.

Polarization Filters for Visible Light Consisting of Subwavelength Slits in an Aluminum Film

We fabricated arrays of subwavelength slits in an Al film and measured their optical properties in the visible light region. Al crossbeams were installed as supports between the Al lines to enable us to precisely fabricate the nanoslits. Visible light polarized parallel to the slits transmits at shorter wavelengths, similar to that of a wire grid array at infrared wavelengths. On the other hand, for light polarized perpendicular to the slits, the transmission is at longer wavelengths and significant absorption takes place at shorter wavelengths due to Fano-type interference. This absorption in the visible wavelength region is due to the precise nanofabrication process and the high plasma frequency of Al. These results show that Al nanoslits can be used as polarization filters in the visible wavelength region.

Single-crystal growth and optical conductivity of SrPt2As2superconductors

SrPt${}_{2}$As${}_{2}$ single crystals with CaBe${}_{2}$Ge${}_{2}$-type structure were synthesized by self-melting technique. X-ray diffraction, transmission electron microscopy, electrical resistivity, magnetic susceptibility, specific heat, and optical spectroscopy measurements were conducted to elucidate the properties of SrPt${}_{2}$As${}_{2}$. SrPt${}_{2}$As${}_{2}$ single crystals undergo a structural phase transition well above room temperature (about 450 K) and become superconducting at 5.18 K. The superconducting and structural phase transition temperatures are reduced by 6$%$ iridium doping. Both the pure SrPt${}_{2}$As${}_{2}$ and the Ir-doped single crystals are demonstrated to be highly metallic with rather high plasma frequencies. In particular, the optical spectroscopy measurement revealed two gaplike suppression structures: a stronger one at high energy near 12 000 cm${}^{\ensuremath{-}1}$ ($\ensuremath{\sim}$1.5 eV), and a less prominent one at lower energy near 3200 cm${}^{\ensuremath{-}1}$ ($\ensuremath{\sim}$0.4 eV) for the pure compound. We elaborate that the former is related to the correlation effect, while the latter could be attributed to the partial energy gap formation associated with structural phase transition.

Investigation of image magnification properties of hyperlenses formed by a tapered array of metallic wires using a spatially dispersive finite-difference time-domain method in cylindrical coordinates

In this paper, the spatially dispersive finite-difference time-domain (FDTD) method in cylindrical coordinates is applied to model the hyperlenses formed by a tapered array of metallic wires. The hyperlens device is modeled using the effective medium theory as a frequency and spatially dispersive dielectric. The gradual increase in spacing between wires along the radial direction of the physical structure is represented by the reduction of plasma frequency of the effective medium. Simulation results show that the image transfer and magnification capability of the hyperlens is insensitive to its transverse dimension. A seven-fold magnification of a subwavelength source distribution transferred to a distance of three wavelengths is demonstrated using a hyperlens with high plasma frequency at its front interface.

ENHANCEMENT OF NEAR-INFRARED PHOTONIC BAND GAP IN A DOPED SEMICONDUCTOR PHOTONIC CRYSTAL

In this work, the enhancement in photonic band gap (PBG) in a dielectric-semiconductor photonic crystal (DS PC) is investigated. We consider two possible schemes that can be used to enhance the PBG in the near-infrared region. The flrst scheme is to add an ultrathin metal layer into the DS PC such that a structure of ternary metal-dielectric-semiconductor (MDS) PC is formed. The second scheme is to make use of the heterostructured PC. In scheme 1, it is found that the addition of metal layer will signiflcantly move the left band edge to the shorter wavelength position, leading to an enlargement in the PBG. This enlargement can be extended as the thickness of metal fllm is increased. In addition, a pronounced enhancement in PBG is achieved when the metal with a higher plasma frequency is used. In scheme 2, we flnd that the PBG can be signiflcantly enlarged compared to scheme 1. In addition, the increase in the band extension is shown to be four times larger than that in scheme 1. The results illustrate that, in order to enhance the PBG, the use of scheme 2 is superior to scheme 1. The enhancement of near- infrared (NIR) PBG is of technical use in the optical communications.

Color Filter Based on Surface Plasmon Resonance Utilizing Sub-Micron Periodic Hole Array in Aluminum Thin Film

We investigated optical transmission characteristics of aluminum thin films with periodic hole arrays in sub-wavelength. We divided white light into several color spectra using a color filter based on the surface plasmon resonance (SPR) utilizing aluminum showing high plasma frequency. By optimizing a hole-array period, hole shape, polarization and index difference of two surface, transmittance of 30% and full-width at half-maximum of around 100nm were achieved.

Analysis of optical and related properties of tin oxide thin films determined by Drude-Lorentz model

In this paper, optical parameters, such as refractive index n and extinction coefficient κ, of tin oxide thin films determined by fitting the measured and simulated optical reflectance spectra, are presented and analysed. Among the various classical dispersion relations for the dielectric function, we use the Drude model combined with the Lorentzian oscillators to get a good fit of R in the measured spectral range. Results on related parameters such as high frequency dielectric constant, plasma frequency, relaxation lifetime, electron density, film thickness and band gap are discussed. Pure tin oxide films deposited at different temperature exhibit the same reflectance behaviour in the entire range while antimony doped films exhibit a deep minimum of reflectance in the visible domain and a maximum in the infrared domain. The results show also that the refractive index and extinction coefficient of antimony-doped SnO2 films increase with the increase of the Sb/Sn ratios. The dispersion of κ of doped films is higher than that the undoped ones in a wide photon energy spectral range while the dispersion of n exhibit an opposite behaviour. The high frequency dielectric constant ε∞ decreased with increasing percentages of Sb in SnO2 and the optical band gap Eg depend on the doping amount. The deposited films present a great reflection in the NIR wavelength region which may originate from the fact that these layers contain many carriers resulting in a large nonstochiometry in the chemical composition. The optically determined film thickness agrees with that obtained by ellipsometry.

Polarization independent visible color filter comprising an aluminum film with surface-plasmon enhanced transmission through a subwavelength array of holes

The enhanced transmission through periodic arrays of sub-wavelength holes in optically-thick metallic films has many potential applications, such as in wavelength filters, light extraction from light emission diodes, and subwavelength photolithography. A color filter comprising arrays of subwavelength holes in an aluminum film has been fabricated. In addition to the simplicity of the process, the aluminum film enables the excitation of visible-range surface plasmons due to its high plasma frequency. Periodic nanostructures in the aluminum film open the way for new visible color filters.

Solid-state traveling-wave amplifiers and oscillators in the THz range: effect of electron collisions

Due to their high plasma frequencies, drifting semiconductor plasmas interacting with slow electromagnetic waves hold promise for terahertz amplifiers and oscillators. In these devices, the gain and the type of instabilities are influenced by electron collisions. To study the effect of collisions, we developed a two-wave model describing the interaction between drifting solid-state plasmas and electromagnetic waves. This paper analyzes the two-wave dispersion relation for representative examples. As the examples show, convective and absolute instabilities can occur at high and low collision frequencies depending on the relationship between the collision frequency and the coupling coefficient. Surprisingly, an absolute instability occurs when collision-dominated plasmas interact with backward waves. The model can be used to determine the potential of a particular configuration in a solid-state amplifier or oscillator.

시분해 테라파 분광학을 이용한 고전도성 탄소나노튜브 박막의 광학계수 측정

본 연구에서는 전도성이 매우 높은 탄소나노튜브 박막을 제작하고 테라파 영역에서의 광학상수를 측정하였다. 탄소나노튜브박막은 스핀코팅법 또는 진공여과법을 이용하여 연성플라스틱 기판 위에 증착되었다. 테라파 영역의 전자파 투과율은 박막의 두께조절을 통해 가능하며, 산처리 등의 후속공정을 통해서도 조절이 가능하다. 시분해 테라파 투과파의 진폭과 위상 측정을 통해유전상수를 포함한 광학상수의 스펙트럼을 측정하였다. 이를 통해 탄소나노튜브 박막이 Drude 자유전자 모델에 잘 부합하며, 높은 플라즈마 진동수를 가지는 등, 우수한 금속의 특성을 가지고 있음이 밝혀졌다. 또한 산처리 전후 유전상수가 변화하는 것을 직접확인할 수 있었다. 마지막으로 셀룰로즈 멤브레인에 증착된 CNT 필름의 경우엔 기판의 효과가 제거된 광학계수 측정이 가능함을 보여준다. We performed time-domain terahertz (THz) spectroscopy to determine optical constants of highly conductive carbon nanotube (CNT) films. The CNT films have been fabricated on a flexible plastic substrate by using spin-coating or vacuum filtration. We found that the transmission of THz waves can be controlled by manipulating the thickness of the films and by post-treatments. From amplitude and phase information of the transmitted THz waves, we obtain optical constants such as refractive indices and dielectric constants of the CNT films. The frequency dependent dielectric constants show good metallic behaviors, relevant to the Drude free electron models with high plasma frequencies. It is also found that the dielectric constants are higher for the acid-treated films. Finally, the frequency dependent dielectric constants which are free from substrate effects have been demonstrated by using CNT films deposited on cellulose membranes.

Plasmonic mode-gap waveguides using hetero-metal films

We propose a novel waveguide structure using a hetero-metal film which is composed of two metals of different plasma frequencies. In the proposed waveguide, a long-range surface plasmon-polariton (LR-SPP) mode in the central metal film of a higher plasma frequency are horizontally confined since no propagation mode is allowed in the outer films of a lower plasma frequency for a certain frequency range which is dubbed a plasmonic mode-gap (PMG). The propagation characteristics of the proposed PMG waveguide are numerically analyzed. The proposed waveguide shows tight horizontal confinement close to the diffraction limit and notable suppression of radiation loss in bendings due to the PMG effect. It seems that the PMG guiding can improve integration densities of optical devices based on the LR-SPPs without exacerbating their propagation losses.

Optical Properties of the High-Pressure Phases of SnO2: First-Principles Calculation

We present a detailed investigation on the optical properties, including dielectric function, reflectivity, absorption, refractive index, and electron energy-loss spectrum, of the high-pressure phase SnO(2) in the rutile, pyrite, fluorite, and cotunnite structures by using the density functional theory (DFT) plane-wave pseudopotential method. The results indicate that with the increasing of pressure the band gaps become larger, the density of states are broader, so the curves of optical properties have a little blue shift. Except that the fluorite phase has some metallic properties, the other three phases exhibit excellent dielectric behavior. Interestingly, the fluorite and cotunnite SnO(2) phases always have some special characteristics, such as higher plasma frequency, which need further fundamental and application research.

Origin of the structural phase transition inBaNi2As2at 130 K: A combined study of optical spectroscopy and band structure calculations

${\text{BaNi}}_{2}{\text{As}}_{2}$ exhibits a first-order structural transition at 130 K. Understanding this structural transition is a crucial step toward understanding the electronic properties of the material. We present a combined optical spectroscopy and band structure calculation study on the compound across the transition. The study reveals that ${\text{BaNi}}_{2}{\text{As}}_{2}$ is a good metal with a rather high plasma frequency. The phase transition leads to a small reduction of conducting carriers. We identify that this reduction is caused by the removal of several small Fermi-surface sheets contributed dominantly from the As-As bonding and Ni-As antibonding.

Search for the Ideal Plasmonic Nanoshell: The Effects of Surface Scattering and Alternatives to Gold and Silver

The optical absorption efficiency of nanospheres and nanoshells of the elements Na, K, Al, Ag, and Au are compared, and the effects of surface scattering, as introduced by the billiard model [Moroz, A. J. Phys. Chem. C 2008, 112 (29), 10641−10652] are discussed. We find that the introduction of surface scattering has comparatively little effect on the optimized absorption efficiency of nanospheres, with the maximum absorption efficiency of K nanospheres falling from 14.7 to 13.3. Conversely, the reduction in absorption efficiency in nanoshells is substantial. This effect is compounded in metals with higher plasma frequency. We show that the high comparative plasma frequencies in silver and gold result in a greatly reduced optimized absorption efficiency when compared to nanoshells in the absence of surface scattering. Whereas sodium and potassium, with low plasma frequencies, are not affected as much.

Effective medium approach for subwavelength resolution

In a wire medium there can propagate ordinary and extraordinary waves. In a single-wire medium the line source excites two extraordinary modes: TM and TEM fields. In the far-field region one of them is the transmission-line mode, which can be used for transfer of an image to a long distance with a resolution that is determined by the ratio of the operating and the plasma frequency in wire medium. Subwavelength resolution is achieved with sufficiently high plasma frequencies.

Silicon nanowire grid polarizer for very deep ultraviolet fabricated from a shear-aligned diblock copolymer template

A silicon (Si) nanowire grid ultraviolet (UV) transmission polarizer has been fabricated, and its performance was measured over the visible to deep UV range. A cylinder-forming polystyrene-b-poly(hexylmethacrylate) diblock copolymer was coated onto an amorphous Si layer supported on a fused silica substrate, then shear aligned and employed as a mask for reactive-ion etching, resulting in a Si grid of 33 nm period and multi-centimeter-squared area. Due to the high plasma frequency and UV reflectance of the deposited Si, this nanowire grid was able to polarize light down into the deep UV, including 193 nm.

Study of macroscopic quantum tunnelling inBi2Sr2CaCu2O8+δ intrinsic Josephson junctions

We report an experimental observation of the macroscopic quantum tunnelling (MQT) in ad-wave high-temperature superconductor (HTSC)Bi2Sr2CaCu2O8+δ intrinsic Josephson junction (IJJs). It is well known that the current-biased Josephsontunnel junction provides an ideal stage for studying a variety of macroscopicquantum phenomena such as MQT. They have been studied and observed inlow-temperature superconductor (LTSC) Josephson junctions since the early 1980s andhave been established well by now. On the other hand, in the case of HTSC thed-wave pairing symmetry allows for dissipative quasiparticle excitations within thesuperconducting energy gap, which is expected to severely interfere with an observation ofMQT. Contrary to this naive conception, our experimental results have explained that theeffects of the nodal quasiparticles are not strong enough to obscure the observation of theMQT. Furthermore, we found that the MQT in IJJs was observed at approximately 1 K,which was ten times higher than that of LTSC Josephson junctions. This higherclassical-to-quantum crossover temperature is due to their high plasma frequency. We alsodiscuss the resonant activation of IJJs in the presence of microwave radiation.

Evolution of hydrogen induced defects during annealing of plasma treated Czochralski silicon

Transmission electron microscopy (TEM) and atomic force microscopy (AFM) are used to study the temperature evolution of hydrogen plasma induced defects in silicon. Hydrogen plasma treated n- and p-doped Czochralski silicon samples were annealed at temperatures between 200 and 1000°C for up to 10h in air. Platelets are formed on {111} and {100} crystallographic planes. The structural defects are similar in n-type and p-type material. Small defects at the surface anneal out at temperatures above 400°C and {111} platelets start to dissolve above 500°C, except in highly p-doped samples where the platelets are stable up to 600°C. The hydrogen penetrates deeper into a low doped than a high doped sample, resulting in platelet formation deeper into the sample. At annealing temperatures above 800°C, an amorphous oxide layer forms at the surface of the sample. New platelets form after 1h annealing at 1000°C. The roughest surface is found in highly n-doped samples, hydrogenated at high plasma frequency for long exposure times. For high annealing temperatures the roughness decreases.