High Plasma Frequency Research Articles

Unraveling the relationships between heat-shielding properties and crystal structure using first-principles calculations

The relationship between plasma frequency and crystal structure was revealed in terms of the heat-shielding ability of materials wherein they transmit visible-light and absorb near-infrared light by localized surface plasmon resonance. It has been shown that the plasma frequency can be predicted from compositional information of a material, but its relationship with crystal structure remains unclear. It is important to clarify the relationship between them, because a change in crystal structure can lead to a change in electronic state. We calculated the plasma frequency of 1390 oxides and nitrides with high-throughput calculations under the first-principles framework. Subsequently, all the materials were classified into seven crystal systems. We found that the cubic system was the crystal system with the highest plasma frequency, whereas the monoclinic system had the lowest plasma frequency. We investigated crystal structures that exhibit high plasma frequencies. We evaluated structural similarity and found that the composition of cubic and monoclinic systems can be represented by the general chemical formula ABC3, that is, both have a perovskite crystal structure. The cubic and monoclinic perovskite structures can be distinguished based on the presence of the rotation of the BC6 octahedron. Therefore, changes in plasma frequency due to the rotation of the BC6 octahedron was calculated. We found that BC6 rotation reduced plasma frequency. Furthermore, we investigated the visible-light absorption characteristics of cubic structure to evaluate their suitability for heat-shielding materials. We found the cubic perovskite structure appropriate for heat-shielding materials.

Silver and Gold Containing Compounds of p-Block Elements As Perspective Materials for UV Plasmonics.

We present a review of phase formation tendencies, methods for preparation and optical properties of alloys and compounds from the binary systems of silver or gold with metals and metalloids from the p-block of the Periodic system of elements. Reference data about the homogeneity regions in the systems of interest, together with information about the crystalline structure of existing indexed compounds in them, is proposed and statistically analyzed. General background for the synthesis of intermetallic alloys and compounds, and the tendencies for their preparation for plasmonic purposes are presented. The high plasma frequency, ωp of p-block metals makes their alloys with silver and gold an interesting object of study, due to the possibility of ωp variation over a wide interval in the ultraviolet (UV) spectral region with a view to finding more efficient materials for excitation of a localized surface plasmon resonance (LSPR) necessary for various applications and techniques operating in this part of the electromagnetic spectrum. Unlike the alloys between the noble metals Cu, Ag, and Au, which form continuous series of solid solutions, different areas can be observed in the phase diagrams of the Ag(Au)-p-block systems, containing solid solutions, intermetallic compounds, and heterogeneous mixtures. The ability to vary the plasma frequency of solid solutions, like the alloys between the noble metals Cu, Ag, and Au, is the reason to pay attention to the compositions of the Ag(Au-p-block systems that fall in these regions of their phase diagrams. The analysis of the published results for complex permittivity shows that the addition of small amounts of conductive p-block elements to noble metals reduces the energy gap for interband transitions and increases their plasmonic activity in the UV spectral range. The article analyzes the relationship between electrical resistivity and LSPR excitation efficiency, which shows that the intermetallic compounds from Ag(Au)-p-block systems with a well-ordered crystalline structure and good conductivity level can be more effective materials for UV plasmonics than the boundary solid solutions. Intermetallic compounds can be easily obtained in the form of bulk samples, thin films, and nanoparticles with controlled size and geometric shape. The spectral dependences of the plasmon efficiency of the intermetallic compounds, determined from their complex permittivity functions, show that they are promising materials for excitation of LSPR in the UV spectral region.

Window layer based on ZnO and Ag thin films incorporated in solar cells as a part of hybrid energy-saving system

We have started a new research project on a hybrid power generation system consisting of piezoelectric, thermoelectric and solar cell modules. In the first step, we have focused on the antireflection coating based on zinc oxide (ZnO) and metal nanolayers incorporated in solar cells. In layered structure containing ZnO and metal nanoscale layers, we have presented the possibility of increasing wave transmission in the visible region by adding the top and bottom cap layers. The enhancement of optical transmission is very important in improving the performance of sensor protections, solar cells, UV protective films and transparent conductive display panels electrode. It is found that, the structure containing both the top and bottom cap layers (S3) yields larger transmittance than the structures S1 without any cap or S2 just with one cap layer. The maximum transmittance in the visible range can be increased from 33% to 67%. In addition, for the TE mode (TM mode), the maximum value of transmission in the S1 and S2 structures occurs at angles close to normal incidence while in the S3 multilayer it happens around 1 radian, that is, the behavior of the TE mode is the opposite of the TM mode. Also, when the incident angle varies, the band edges experience a blue shift. The amount of TE shift is more pronounced than TM one. Moreover, the metal with higher plasma frequency will move the band gap edges to the higher frequencies.

Radiation direction mutation in a spherical plasma filled multilayered core–shell particle

An actively tunable Fano resonance and the radiation direction mutation are supported in a multilayered core–shell particle composed of a spherical plasma-core and three-layered dielectric shells through varying plasma frequency. The simulated and theoretical results reveal that the Fano resonance relies on the interference between a narrow band electric dipole resonance and a broad band magnetic dipole resonance. The electric and magnetic dipole resonances can be controlled independently. The radiation direction mutates between forward and backward scatterings at Fano resonance frequency with lower plasma frequency, but there is a “delay” of the mutation in frequency with higher plasma frequency. The reasons for generating the mutation and delay are explained by using scattering amplitudes. The research results can be applied to antenna, directional emission control, and sensor areas.

The Application of Microplasma in the Terahertz Field: A Review

Terahertz functional devices are essential to the advanced applications of terahertz radiation in biology and medicine, nanomaterials, and wireless communications. Due to the small size and high plasma frequency of microplasma, the interaction between terahertz radiation and microplasma provides opportunities for developing functional terahertz devices based on microplasma. This paper reviews the applications of microplasma in terahertz sources, terahertz amplifiers, terahertz filters, and terahertz detectors. The prospects and challenges of the interdisciplinary research between microplasma and terahertz technology are discussed.

Plasmonic spin-Hall effect of propagating surface plasmon polaritons in Ni80Fe20 microstructures

Photoexcitation and shaping of a propagating surface plasmon polariton (SPP) on silver and gold microstructures are well established and lead to the discovery of the plasmonic spin-Hall effect recently. Whereas silver is often the material of choice due to its exceptional low plasma frequency and weak damping, similar observations have not been reported for ferromagnetic metals. In this work, we report on propagating SPPs on Ni80Fe20 microstructures imaged by photoemission electron microscopy (PEEM) in combination with a tunable femtosecond laser system at MHz repetition rate. Circular dichroic (CD) images in threshold PEEM show clear edge-induced SPPs with sub-micrometer wavelength and propagation length of about 3.5 μm. Analysis of the interference patterns as well as the coupling of the optical spin angular momentum to the observed fringe fields reveal propagation characteristics exclusive to evanescent waves and the presence of the plasmonic spin-Hall effect. Our work provides direct evidence that many materials with a high plasma frequency allow for excitation and observation of propagating SPPs at the dielectric/metal interface via CD PEEM imaging, enabling magnetoplasmonic investigation of common ferromagnets on nanometer length and femtosecond time scales.

Aluminum Plasmonics Enriched Ultraviolet GaN Photodetector with Ultrahigh Responsivity, Detectivity, and Broad Bandwidth.

Plasmonics have been well investigated on photodetectors, particularly in IR and visible regimes. However, for a wide range of ultraviolet (UV) applications, plasmonics remain unavailable mainly because of the constrained optical properties of applicable plasmonic materials in the UV regime. Therefore, an epitaxial single‐crystalline aluminum (Al) film, an abundant metal with high plasma frequency and low intrinsic loss is fabricated, on a wide bandgap semiconductive gallium nitride (GaN) to form a UV photodetector. By deliberately designing a periodic nanohole array in this Al film, localized surface plasmon resonance and extraordinary transmission are enabled; hence, the maximum responsivity (670 A W−1) and highest detectivity (1.48 × 1015 cm Hz1/2 W−1) is obtained at the resonance wavelength of 355 nm. In addition, owing to coupling among nanoholes, the bandwidth expands substantially, encompassing the entire UV range. Finally, a Schottky contact is formed between the single‐crystalline Al nanohole array and the GaN substrate, resulting in a fast temporal response with a rise time of 51 ms and a fall time of 197 ms. To the best knowledge, the presented detectivity is the highest compared with those of other reported GaN photodetectors.

A reconfigurable device based on the one-dimensional magnetized plasma photonic crystals nested with the Pell and Thue–Morse sequences

In this paper, the properties of a reconfigurable device which realizes the omnidirectional band gaps (OBGs), nonreciprocity (NR) and polarization beam splitting (PBS) based on the one-dimensional (1-D) magnetized plasma photonic crystals (MPPCs) nested with quasi-periodic Pell and Thue–Morse sequences are theoretically investigated by the transfer matrix method (TMM). The obtained results show that the OBGs, the NR region, and the scope of PBS can be notably manipulated by the plasma frequency, plasma cyclotron frequency, incident angle, and the plasma collision frequency. More specifically, the higher plasma frequency is needed for accomplishing the property of OBGs while the better performance of NR can be achieved with a larger incident angle and a higher plasma cyclotron frequency. Also, the lower plasma frequency and higher plasma cyclotron frequency are suitable for the splendid performance of PBS. The augment of the plasma collision frequency is adverse to the properties as mentioned above. Due to the Voigt magneto-optical effect generating from the magnetized plasma layers, the time-reversal symmetry is destroyed which is beneficial for obtaining the properties of NR and PBS. Besides, owing to the nested technology which breaks the spatial symmetry of the structure further, compared with the conventional 1-D single quasi-periodic structures, the proposed nested MPPCs have a preeminent strength in achieving the three functions through modulating the corresponding physical parameters. These findings provide theoretical guidance for the design and application of the multifunctional devices.

Synthesis and Multipole Plasmon Resonances of Spherical Aluminum Nanoparticles.

In comparison to Au and Ag, the high plasma frequency of Al allows multipole plasmon resonances from the ultraviolet to visible (UV-vis) range to be achieved by its nanoparticles with much smaller sizes and even a spherical shape. Herein, we report the high-supersaturation growth of monodisperse spherical Al nanoparticles (Al NPs) from 84 to 200 nm and their distinctive size-dependent multipole plasmon resonance properties in the UV-vis range. Linear relationships between the particle diameter and resonance peak positions of the dipole, quadrupole, and octupole were observed experimentally and confirmed by finite-difference time-domain (FDTD) calculations. FDTD calculations further reveal the high scattering-to-extinction ratio of multipole modes for the particle diameters >100 nm. The extinction coefficients of spherical Al NPs with different diameters were also determined. The excellent matching between the experimental and simulated results in the present work not only offers a standard for the synthesis and characterization of high-quality Al NPs but also provides new insight into the multipole plasmonic properties of Al NPs for advanced optical and sensing applications.

The RCS of the 3-D conductor sphere calculated in THz band and the homogeneous magnetized dense plasma sheath

The reentry vehicle of high speed has serious friction with the gas surrounding themselves which leads to a high temperature and high level of ionized of neutral particles thus forming a plasma sheath with a high plasma frequency and collision frequency. Microwave can’t penetrate it and arrive at the vehicle, correspondingly, the communication is cut off. Therefore, the radar cross section (RCS) of the conductor sphere in THz band is calculated to illustrate the strong penetration ability of the THz wave in a dense plasma sheath. The scattering characteristics in dense, magnetized plasma sheath is studied using the Finite-Difference Time-Domain method based on the Runge-Kutta Exponential Time Differencing formulation (RKETD-FDTD). 3-D conductor sphere model is established and the amount of the bistatic RCS is displayed in the polar coordinates. Influences on it caused by the direction of the magnetic field, the collision frequency, the frequency of plasma, the included angle between the incident wave and z coordinate axis and the polarized direction are discussed in detail. By comparing with the RCS in the no coating simulation conditions, it demonstrates that THz wave have a better penetration effect and may be chosen as an effective solution to the ‘black out’ problem.

Enhanced degradation of methylene blue by a solution plasma process catalyzed by incidentally co-generated copper nanoparticles.

This study presents a catalytic organic pollution treatment using the solution plasma process (SPP) with incidentally co-generated copper (Cu) nanoparticles via Cu electrode erosion. Methylene blue (MB) was used as a model organic contaminant. The treatment time was from 0 to 60 minutes at the plasma frequencies of 15 and 30 kHz. The treatment efficacy using the Cu electrode was compared with that of the tungsten (W) electrode. The high erosion-resistant W electrode provided no W nanoparticles, while the low erosion-resistant Cu electrode yielded incidental nanoparticles (10-20 nm), hypothesized to catalyze the MB degradation during the SPP. The percentage of MB degradation and the hydrogen peroxide (H2O2) generation were determined by an ultraviolet-visible spectrophotometer. The results showed that, after the SPP by the Cu electrode for 60 minutes, the MB was degraded up to 96%. Using the Cu electrode at a high plasma frequency strongly accelerated the Cu nanoparticle generation and MB treatment, although the amount of H2O2 generated during the SPP using the Cu electrode was less than that of the W electrode. The Cu nanoparticles were hypothesized to enhance MB degradation via both homogeneous (release of dissolved Cu ions) and heterogeneous (on the surface of the particles) catalytic processes.

Uniformly Accurate Oscillatory Integrators for the Klein--Gordon--Zakharov System from Low- to High-Plasma Frequency Regimes

We present a novel class of oscillatory integrators for the Klein--Gordon--Zakharov system which are uniformly accurate with respect to the plasma frequency $c$. Convergence holds from the slowly v...

Structural, optical and thermal characterization of PVC/SnO2 nanocomposites

The structural, optical, and thermal properties of PVC/SnO2 nanocomposites were investigated. XRD patterns were used to explore the structures of these prepared samples. Optical UV–Vis measurements were analyzed to calculate the spectroscopic optical constants of the prepared PVC/SnO2 nanocomposites. Both direct and indirect optical band gaps decreased with increasing SnO2 content. The refractive index, high frequency dielectric constant, plasma frequency, and optical conductivity values increased with SnO2. The single oscillator energy increased from 5.64 to 10.97 eV and the dispersion energy increased from 6.35 to 19.80 eV with the addition of SnO2. The other optical parameters such as optical moments, single oscillator strength, volume energy loss, and surface energy loss were calculated for different SnO2 concentrations. Raman spectra of the PVC/SnO2 nanocomposite films revealed the characteristic vibrational modes of PVC and surface phonon modes of SnO2. The thermal stability of PVC/SnO2 nanocomposite films was studied using DTA and thermogravimetric analysis. The glass transition (Tg) values abruptly changed from 46 °C for PVC to an average value of 59 °C for the polymer films doped with 2.0, 4.0, and 6.0 wt% SnO2. The weight loss decreased as the SnO2 concentration increased in the temperature range of 350–500 °C, corresponding to enhanced thermal stability.

Dielectric properties of vertically aligned multi-walled carbon nanotubes in the terahertz and mid-infrared range

We investigate the broadband dielectric properties of vertically aligned, multi-wall carbon nanotubes (VACNT), over both the terahertz (THz) and mid-infrared spectral ranges. The nominally undoped, metallic VACNT samples are probed at normal incidence, i.e. the response is predominantly due to polarisation perpendicular to the CNT axis. A detailed comparison of various conductivity models and previously reported results is presented for the non-Drude behaviour we observe in the conventional THz range (up to 2.5 THz). Extension to the mid-infrared range reveals an absorption peak at , reminiscent of that observed in single-wall CNT, only there it arises for polarisation parallel to the CNT axis. To account for the observed resonance here, we apply a Bergman-type effective-medium theory, based on first-principles’ electromagnetic simulations for the perpendicular polarisation including both the intra- and inter-tube response, which can reproduce the observed spectrum if one assumes a much higher plasma frequency and scattering rate than that reflected in the low-frequency spectra, and proposes an explanation for the non-Drude behaviour at low-frequencies.

Indium Tin Oxide Coated Two-Mode Fiber for Enhanced SPR Sensor in Near-Infrared Region

A surface plasmon resonance (SPR) sensor based on side-polished two-mode fiber (TMF) coated with indium tin oxide (ITO) film is proposed. ITO enables tuning of resonance wavelength of the sensor through changing its carrier concentration. The advantages of the TMF and ITO are combined in the sensor, which can achieve high sensitivity and plasma frequencies in the near-infrared region. The impact of ITO film thickness and residual fiber thickness on the sensing performance are numerically investigated with LP01 and LP11a modes coupled to specific surface plasmon modes. The results show that the resonance wavelength locates in 1500–2200 nm and an average sensitivity of ∼10149 and ∼10400 nm/RIU can be achieved for LP01 and LP11a modes, respectively, when the environmental refractive index varies between 1.33 and 1.39. The penetration depths of evanescent wave for the LP01 and LP11a modes are 460 and 502 nm, respectively. Both the sensitivity and penetration depth of the sensor are larger than those of single-mode fiber and multimode fiber based SPR sensors. The proposed sensor can play an important role in various applications, including environment, medicine, and security.

Radio‐frequency negative permittivity in the graphene/silicon nitride composites prepared by spark plasma sintering

AbstractGraphene/silicon nitride (GR/Si3N4) ceramic composites with uniformly dispersed GR sheets were prepared using spark plasma sintering. The effects of GR content on the microstructure and electrical properties of the composites were investigated in detail. With the GR content rising, the conductive GR network was formed in the composites, leading to the appearance of a percolation phenomenon, and the conductive mechanism also changed from hopping conductivity to metal‐like conductivity. When the GR content reached the percolation threshold, the composites showed a negative permittivity behavior, which resulted from the low frequency plasmonic state generated by the formative conducting GR networks. The increasing GR content resulted in a higher plasma frequency and larger magnitude of negative permittivity, which was consistent with the analysis of Drude model. A relatively high dielectric loss was observed in the composites and mainly induced by the high leakage current among GR sheets. Our work is beneficial to expound the regulation mechanism of negative permittivity, and the obtained ceramic composites present some potential applications in microwave absorption, shielding and capacitors.

Interacting fields and flows: Magnetic hot Jupiters

We present magnetohydrodynamic (MHD) simulations of the magnetic interactions between a solar‐type star and short‐period hot Jupiter exoplanets using the publicly available MHD code PLUTO. It has been predicted that emission due to magnetic interactions such as the electron cyclotron maser instability (ECMI) will be observable. In our simulations, a planetary outflow, due to UV evaporation of the exoplanets atmosphere, results in the build‐up of circumplanetary material. We predict the ECMI emission and determine that the emission is prevented from escaping the system. This is due to the evaporated material leading to a high plasma frequency in the vicinity of the planet, which inhibits the ECMI process.

Direct Electron Beam Writing of Silver-Based Nanostructures

Direct writing utilizing a focused electron beam constitutes an interesting alternative to resist-based techniques, as it allows for precise and flexible growth onto any conductive substrate in a single-step process. One important challenge, however, is the identification of appropriate precursors which allow for deposition of the material of choice, e.g., for envisaged applications in nano-optics. In this regard the coinage metal silver is of particular interest since it shows a relatively high plasma frequency and, thus, excellent plasmonic properties in the visible range. By utilizing the precursor compound AgO2Me2Bu, direct writing of silver-based nanostructures via local electron beam induced deposition could be realized for the first time. Interestingly, the silver deposition was strongly dependent on electron dose; at low doses of 30 nC/μm2 a dominant formation of pure silver crystals was observed, while at higher electron doses around 104 nC/μm2 large carbon contents were measured. A scheme for the enhanced silver deposition under low electron fluxes by an electronic activation of precursor dissociation below thermal CVD temperature is proposed and validated using material characterization techniques. Finally, the knowledge gained was employed to fabricate well-defined two-dimensional deposits with maximized silver content approaching 75 at. %, which was achieved by proper adjustment of the deposition parameters. The corresponding deposits consist of plasmonically active silver crystallites and demonstrate a pronounced Raman signal enhancement of the carbonaceous matrix.

A STUDY OF RADIO FREQUENCY BLACKOUT FOR SPACE PROBE DURING ATMOSPHERIC REENTRY PHASE

During the re-entry flight, the radio signal will be interrupted, which is commonly referred to as the communications blackout. Once the plasma sheath forms in the stagnation region of a small space probe, the probe losses more than 70 percent of its downlink data. This shows that the attenuation of the radio signal is very high during the re-entry. When the probe enters the Earth’s atmosphere, the high velocity, high surface temperature and high plasma frequency cause a shock wave layer, which is the main cause of radio blackout. For other reason, the completely reflection of the electromagnetic wave at all communication lines. This study describes the theoretical and numerical study of radio communication during reentry. The paper defines an approach to end radio signal blackout occurring in the wake region and how to exactly solve the radio blackout problem using new methods as injection of coolants, the aerodynamic shaping reducing the concentration of electrons, using transceiver with high operating frequency or interaction of Static Magnetic Field (SMF). Data from OREX probe are used to prove the solution to the Radio Frequency (RF) blackout problem. The significance of the used SMF method is established by computing the reduction in plasma attenuation.

Sn(II)-Containing Phosphates as Optoelectronic Materials

We theoretically investigate Sn(II) phosphates as optoelectronic materials using first principles calculations. We focus on known prototype materials Sn$_n$P$_2$O$_{5+n}$ (n=2, 3, 4, 5) and a previously unreported compound, SnP$_2$O$_6$ (n=1), which we find using global optimization structure prediction. The electronic structure calculations indicate that these compounds all have large band gaps above 3.2 eV, meaning their transparency to visible light. Several of these compounds show relatively low hole effective masses ($\sim$2-3 m$_0$), comparable the electron masses. This suggests potential bipolar conductivity depending on doping. The dispersive valence band-edges underlying the low hole masses, originate from the anti-bonding hybridization between the Sn 5s orbitals and the phosphate groups. Analysis of structure-property relationships for the metastable structures generated during structure search shows considerable variation in combinations of band gap and carrier effective masses, implying chemical tunability of these properties. The unusual combinations of relatively high band gap, low carrier masses and high chemical stability suggests possible optoelectronic applications of these Sn(II) phosphates, including p-type transparent conductors. Related to this, calculations for doped material indicate low visible light absorption, combined with high plasma frequencies.