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To understand the practical effects of pressure-transmitting media (PTM) on neutron diffraction using Paris–Edinburgh presses, diffraction patterns of MgO were collected to approximately 20 GPa using PTMs of Pb, AgCl, 4:1 methanol–ethanol (ME) mixture with and without heating, N2, and Ar. Hydrostaticity in the sample chamber estimated from the MgO 220 peak width improves in the order of Pb, AgCl, Ar, ME mixture, N2, and the heated ME mixture. Unlike previous results using diamond anvil cells, the unheated ME mixture is superior to Ar even after freezing, probably due to the cup on the anvil face. Considering these results and the sizable coherent scattering of Ne, which would show good hydrostaticity, we conclude that the ME mixture (preferably the heated one) is the best PTM in neutron experiments up to 20 GPa, while Ar can be substituted when a sample is reactive to alcohols.

International audience; Carbon disulphide (CS2) is, together with its closest analogue CO2, one of the simplest molecular systems made of double covalent bonds. Under high pressure, the molecular structure is expected to break up to form extended crystalline or polymeric solids. Here we show that by compression at 300 K to ∼10 GPa (100 kbar) using large-volume high pressure techniques, a sudden reaction leads to a mixture of pure sulphur and a well-defined compound with stoichiometry close to C2S which can be recovered to ambient pressure. We present neutron and x-ray diffraction as well as Raman data which show that this material consists of sulphur bonded to sp2 graphite layers of nanometric dimensions. The compound is a semiconductor with a gap of 45 meV, as revealed by temperature dependent resistivity measurements, and annealing at temperatures above 200 °C allows to reduce its sulphur content up to C10S. Its structural and electronic properties are fundamentally different to “Bridgman black” reported from previous high pressure experiments on CS2.

Nano-antennas are replicas of antennas that operate at radio-frequencies, but with considerably smaller dimensions when compared with their radio frequency counterparts. Noble metals based nano-antennas have the ability to enhance photoinduced phenomena such as localized electric fields, therefore-they have been used in various applications ranging from optical sensing and imaging to performance improvement of solar cells. However, such nano-structures can be damaged in high power applications such as heat resisted magnetic recording, solar thermo-photovoltaics and nano-scale heat transfer systems. Having a small footprint, nano-antennas cannot handle high fluences (energy density per unit area) and are subject to being damaged at adequately high power (some antennas can handle just a few milliwatts). In addition, given that nano-antennas are passive devices driven by external light sources, the potential damage of the antennas limits their use with high power lasers: this liability can be overcome by employing materials with high melting points such as chromium (Cr) and tungsten (W). In this article, we fabricate chromium and tungsten nano-antennas and demonstrate that they can handle 110 and 300 times higher fluence than that of gold (Au) counterpart, while the electric field enhancement is not significantly reduced.

A dissociative force field for all-atomistic molecular dynamics calculations has been developed to investigate impact fracture of polymers accompanying dissociation of chemical bonds of polymer main chain. Energy of dimer molecules was evaluated as a function of both bond-length b and bond-angle θ by CASPT2 calculations, whose quality is enough to describe dissociation of chemical bonds. Because we found that the bond dissociation energy D decreases with increasing bond-angle, we employed the Morse-type function VBond (b, θ) = {D - VAngle (θ)}[1 - exp{-α(b - b0 ) - β(b - b0 )2 }] where a quartic function VAngle (θ) = k1 (θ - θ0 ) + k2 (θ - θ0 )2 + k3 (θ - θ0 )3 + k4 (θ - θ0 )4 . This function reproduced well the CASPT2 potential energy surface in a wide range of b and θ. The parameters have been obtained for four popular glassy polymers, polyethylene, poly(methyl methacrylate), poly(styrene), and polycarbonate. © 2019 Wiley Periodicals, Inc.

In this paper, we analyze the performance of two tantalum-based boride (TaB and TaB2) microparticles as potential saturable absorbers for high-power fiber lasers. Both materials are ultrahigh temperature ceramics with melting points above 3000 °C, but with different crystalline structures: TaB has an orthorhombic structure (nearly isotropic), whereas TaB2 has a hexagonal structure (uniaxial, anisotropic). Despite their different crystalline structures, the microparticles have a similar low fluence attenuation (between 2.3 and 2.60 dB/μm) and modulation depths (around 2.0 dB/μm), but remarkable different saturation fluences: TaB has a saturation fluence of 160 μJ/cm2, whereas TaB2 has a saturation fluence of 110 μJ/cm2. The measured damage thresholds are 112 and 106 mJ/cm2/pulse for TaB and TaB2, respectively. When incorporated to a fiber laser, the materials produce pulses with durations of 345 ns, lower than those reported by our group in previous papers. The results show that the materials can find potential applications in high-power Q-switched lasers.

Hafnium diboride (HfB2) is used in hypervelocity re-entry vehicles (such as intercontinental ballistic missile (ICBM) or ICBM heat shields), nuclear reactors and aerodynamic leading edges because o...

Fast detection of near-infrared (NIR) photons with high responsivity remains a challenge for photodetectors. Germanium (Ge) photodetectors are widely used for near-infrared wavelengths but suffer from a trade-off between the speed of photodetection and quantum efficiency (or responsivity). To realize a high-speed detector with high quantum efficiency, a small-sized photodetector efficiently absorbing light is required. In this paper, we suggest a realization of a dielectric metasurface made of an array of subwavelength germanium PIN photodetectors. Due to the subwavelength size of each pixel, a high-speed photodetector with a bandwidth of 65 GHz has been achieved. At the same time, high quantum efficiency for near-infrared illumination can be obtained by the engineering of optical resonant modes to localize optical energy inside the intrinsic Ge disks. Furthermore, small junction capacitance and the possibility of zero/low bias operation have been shown. Our results show that all-dielectric metasurfaces can improve the performance of photodetectors.

A spectrally selective radiative cooling structure is proposed with improved emissivity. The structure is optimized by using alternating high- and low refractive index layers. Almost 99% emissivity is achieved in the atmospheric transparency window.

We will discuss new metamaterials with tunable photon and phonon transport properties achieved by either sculpting the meso-scale structure of polymers or using polymers to sculpt the internal structure of nanoparticle arrays.

We show that the addition of an array of silicon nitride nanowire resonator can boost the absorbance of a monolayer of WS2 from around 5-10% to 62% at the exciton wavelength of 620 nm.

Ultra-high temperature ceramics are widely used in hypersonic vehicles, nuclear reactors, and in other equipment that operates under extreme conditions. In particular, Zirconium Boride (ZrB12) is an ultra-high temperature refractory ceramic material with a melting point above 3000 °C. The measured laser damage threshold of ZrB12 is 132 mJ/cm2, higher than in many materials commonly used as saturable absorbers, making it suitable for work in high-power laser systems. Zirconium Boride is also used as a saturable absorber in an ytterbium-doped Q-switched fiber laser, producing pulses between 239 and 2600 ns.

In this article, we study a linear array of bowtie nanoantennas placed between two metallic strips that can work from 800 to 1420 nm (600 nm linewidth), with an electric field enhancement factor cl...

Silicon photonics has begun to use index tunable plasmonic materials, such as graphene and indium tin oxide (ITO), because these materials can have their properties tailored by an external voltage. In this article, a compact plasmonic device, which can work as an optical mode controller and electro-absorption (EA) modulator at 1550 nm, is proposed. The performance of the device is theoretically investigated for ITO. Numerical simulations show that, with a suitable applied voltage to thin ITO layers, the proposed structure can select either only one mode (TE/TM) or both modes initially and then modulate the selected mode: a modulation depth of about 30–50 dB/μm is achieved with a proper choice of the dielectric spacer material. In addition, the proposed structure performance is analysed by replacing the waveguide materials with germanium. The proposed nanoscale device, with high modulation bandwidth (f3 dB = 700–250 GHz) and low-energy consumption (~4.0 fJ/bit), may find applications in the future ...

Plasmonic metamaterial absorbers are particularly important in different applications such as photodetectors, microbolometers and solar cells. In this paper, we propose a tungsten boride (WB, a refractory ceramic) based broadband metamaterial absorber whose optical properties is numerically analyzed and experimentally characterized. We have also analyzed the damage characteristics of this absorber using a femtosecond laser and compared with an ordinary Au metamaterial absorber. We observe that WB has almost the double absorption bandwidth with absorption more than 90% over the spectral range of 950 to 1400 nm when compared with the Au counterpart. Furthermore, we show that Au metamaterial is damaged at the power of around 36.4 mW whereas WB metamaterial is not damaged at that power (WB has high Tammann temperature than Au)-however the atom of WB material was knocked off by the bombardment of a femtosecond laser.

We present the results for two tantalum borides (TaB and TaB 2 ) as potential saturable absorbers for Q-switched lasers. When incorporated to a ring ytterbium laser operating at 1080 nm, they produced pulse widths as short as 345 ns.

Nano-antennas on silica or semiconductor substrate cannot handle high power due to their low thermal conductivity. This paper shows that high thermal conductivity substrates such as diamond can handle 20 times higher fluence than silica substrate based nano-antenna without affecting their electrical field enhancement capacities.

In this paper, we experimentally study broadband perfect absorber based upon tungsten boride. We show that the absorptance of the WB perfect absorber has much better temperature stability when compared with an Al based absorber: its absorptance changes little from 25° C to 270° C.

In this research, we have developed a new chloride ion image sensor that displayed dynamic 2D images of the local concentration. The chloride sensitive membrane was prepared by casting a tetrahydrofuran solution containing a PVC membrane with manganese (III) porphyrin onto a CCD-type pH image sensor. The fabricated chloride ion sensor showed a near Nernst response at the concentration of 10−1-10−2 M and a super-Nernst response at the concentration of 10−2-10−3 M. In addition, the selectivity for anion ions did not follow the classical Hofmeister series. The selectivity for chloride ion was higher than those of perchlorate ion, bromide ion and iodide ion. These results were due to the complexation with the chloride ion peculiar to the metalloporphyrin.

Graphene is a two-dimensional material with outstanding properties such as high electronic and thermal conductivities that may bring a revolution in the miniaturization of electronic and optical circuits. In this letter, we analyze a tunable grating structure that combines a graphene grating and a vertical silica grating based upon a pseudonoise function. We show that the properties of the compound grating can be tailored by applying an external voltage to the graphene grating.

Gold nano-antennas with silica substrate may not be suitable for high power applications such as heat resisted magnetic recording, solar thermophotovoltaics, and nano-scale heat transfer systems. When a laser beam reaches to these nano-antennas, part of the light is absorbed by the metallic regions, leading to a temperature rise of the device. If these devices reach a temperature beyond its Tamman temperature (the temperature at which sintering of atoms or molecules start to occur), the antenna can be damaged. One strategy to allow the antenna to work at higher fluences (energy density) is to employ substrates that can quickly carry the heat away from the antennas. In this paper, we show that high thermal conductivity substrates, such as diamond, can allow the antenna to withstand 20 times higher fluence than a low thermal conductivity silica substrate.

Nano-antennas cannot handle high energy density (fluences) due to their small footprint. In this paper, we propose chromium based nano-antenna and experimentally show that it can handle 110 times higher fluence than gold (Au) counterpart without a significant reduction in their electrical field enhancement capacities.

In general, noble metals based nano-antennas cannot work at high power applications such as heat resisted magnetic recording, solar thermo-photovoltaics, and nano-scale heat transfer systems. These antennas are prone to being damaged at sufficiently high energy density due to their small footprint and low Tamman temperature. This paper proposes tungsten refractory plasmonic material based nano-antennas as an alternative gold nano-antennas: we show that the antennas can handle 300 times higher fluence than gold (Au) counterpart. In addition, it can achieve 7.22 higher magnitude of electric field intensity than gold antennas.

We report the electrical control of the optical attenuation by a manganese dioxide (MnO 2 ) metasurface. The attenuation is varied by 25% with the change of current of 5.33 μA. The device shows the potential of this material in tunable devices.

This paper proposes a new and flexible approach to control the electric field enhancement of bow-tie nano-antennas by integrating them on the lateral of a ∼ 9 μm tapered optical fiber. The device may find applications in bio-sensing and imaging.

This paper analyzes a multilayered bowtie nano-antenna, consisting of alternate layers of silica (SiO 2 ) and gold (Au). We show that the multi-layered structure can produce six times higher relative electric field enhancements than a purely gold bowtie antenna.

Nano-antennas are used in optical data storage, near-field imaging, photovoltaics, sensing, and spectroscopy applications. In many cases, the antennas work with linear polarization, but some applications require circularly polarized (CP) light such as field-enhanced circular dichroism spectroscopy. Circular dichroism spectroscopy is a technique used to study organic molecules and is widely used in biology and medicine. In this article, we analyze a star-gap nano-antenna array. The antenna combines concentric circular gratings and a symmetric gap to provide a maximum electric field enhancement factor of around 48 at 780 nm with the average electric field enhancement factor of about 34.75. Due to its geometry, the antenna can work for both linearly polarized and CP light, having similar electric field enhancement factors. Due to its symmetry and capacity to work with different polarizations, the antenna can find applications in sensing and spectroscopy. As an example of application, we have characterized the antenna for surface enhanced Raman scattering (SERS) and obtained a SERS factor of 4.18×106 for the 880cm−1 Raman line of ethanol.

Metal-based perfect absorbers that use metals such as aluminum (Al) can have their optical properties changed with temperature, subsequently affecting the device’s performance. The changes with temperature can critically limit the applications of absorbers at high powers or high temperatures. In this paper, we show a thermally stable broadband absorber based on an ultrathin layer of refractory ceramic, tungsten boride (WB). We experimentally analyze and compare the performance of the absorber with an aluminum (Al) based absorber. The multilayer perfect absorber has absorption higher than 85% in the wavelength range between 500 and 1600 nm over a large range of incident angles (up to 60°). We show that a WB absorber has significantly better temperature stability when compared with its Al counterpart, achieving stable operation up to temperatures as high as 270°C. These absorbers may find applications in solar thermo-photovoltaic energy conversion.

This work was supported by the Asian Office of Aerospace Research and Development (AOARD) (FA2386-15-1-4064) and the Linkage grant LP160100253.

In recent years, many researchers have studied photonic nanojets. These nanojets are created when an incident plane wave is focused into a narrow and high intensity emerging optical beam leaving a micro-object (e.g. microcylinder). These narrow beams may find applications in particle imaging and detection, optical sensors, enhanced Raman scattering, and particle manipulation. They also allow the projection of a particle to the far-field where it can be easily visualized. In this paper, it is shown that the electric field enhancement factor can be dynamically controlled by the application of an external intense magnetic flux density.

We design and experimentally characterize terahertz (THz) electric split-ring-resonator metamaterials infiltrated with nematic liquid crystals (LCs). We demonstrate that the resonant response of such metamaterials can be tuned by temperature due to the change of the LC arrangement from nematic to isotropic phase. In particular, we show that the frequency tuning is strongly dependent on the initial LC orientation, with resonant frequency shifting towards lower frequencies for LC director perpendicular to the gap and towards higher frequencies for LC director parallel to the gap of the electric split ring resonators. Our results open new opportunities for the design of tunable THz filters based on LCs.

While plasmonic nano-antennas can produce intense electric fields in a very small area, in general, these devices cannot handle high power, because of their small footprints. In order to increase the maximum peak power that these devices can withstand, they can be driven by nano-second pulses from a larger diameter Q-switched laser, which reduces the fluence reaching the devices, thus avoiding their destruction. Furthermore, we show that an increase in the power density capacity of the nano-antennas can be achieved by replacing gold with titanium: more than 18 dB greater power density can be handled by titanium based nano-antennas without significant reduction in their electric field enhancement capabilities.

Charnia was a pre-Cambrian life-form that exhibited a fractal structure to improve the extraction of nutrients from the pre-historic seas. Inspired by its fractal structure, this paper studies the potential application of these self-similarity fractal structures to create a plasmonic nano-antenna that can operate over a large linewidth. These devices are studied both theoretically and experimentally. It is shown that these nano-antennas can produce electric field enhancements above 8 over 200 nm range and surface enhanced Raman scattering (SERS) enhancements higher than 105.

A hybrid Q-switched ring laser combining tungsten disulfide (WS 2 ) nano-particles and an in-fiber acousto-optical modulator is constructed. Pulses ranging from 35 ns to 8 μs are obtained with this laser.

We analyze a multi-layered nano-antenna made of alternating layers of silica and gold. We show that a multi-layered structure can produce higher (two times) electric field enhancement than a pure gold antenna.

Graphene, a single layer of carbon atoms arranged in a honeycomb lattice, is attracting significant interest because of its potential applications in electronic and optoelectronic devices. Although graphene exhibits almost uniform absorption within a large wavelength range, its interaction with light is weak. In this paper, the enhancement of the optical absorption in graphene photonic crystal structures is studied: the structure is modified by introducing scatterers and mirrors. It is shown that the absorption of the graphene photonic crystal structure can be enhanced about four times (nearly 40%) with respect to initial reference absorption of 9.8%. The study can be a useful tool for investigating graphene physics in different optical settings.

Nano-antennas are the optical equivalent of antennas that are used to transmit and receive information at radio frequencies. These antennas have been used in different applications in photonics such as optical imaging, particle manipulation, bio-sensing, and improvement of the performance of solar cells. In this article we study composite nano-antennas made of alternating layers of silica and gold. We show that a 50% filling factor leads to a 2.0 times increase in the electric-field enhancement factor when compared with a pure-gold antenna.

The enhancement in absorption of photonic graphene structure is reported in this article: it can be enhanced about four times (40%) compared to a reference absorption (9.8%) at certain wavelengths by adding defects and mirrors.

A polarization splitter based on a gold filled photonic crystal fiber (PCF) is reported in this article: it can work from 1420 nm to 1980 nm with 254.6 μm length, covering communications and sensing applications.

Interface reactions of a Ce-oxide layer with Si(100) wafers have been characterized by X-ray photoelectron spectroscopy. The ratio of Ce atoms in Ce3+ states within the Ce-oxide layer has been found to decrease from 47% at as-deposited sample to 26% after annealing. From detailed reaction analysis of valence number transitions of Ce atoms and the creation of SiO2 layer at the interface, the reacted Ce3+ atoms are converted into silicates and Ce4+ with a ratio of 2:1. The energy bandgap of Ce-silicate layer has been determined as 7.67 eV and the valence band offset with respect to Si(100) wafer has been extracted as 4.35 eV.

This paper reports on the control of the direct-contact La-silicate/Si interface structure with the aim of achieving scaled equivalent oxide thickness (EOT) and small interface state density. The interface state density at the direct-contact La-silicate/Si interface is found to be reduced to 1.6 × 1011 cm-2eV-1 by annealing at 800 °C for 30 min in forming gas ambient, whereas excess silicate reaction concurrently induced a significant increase in EOT. By utilizing metal-inserted poly-Si (MIPS) stacks and their annealing at high temperature, the increase in EOT is drastically suppressed. At the same time, a superior interfacial property is obtained because the Si layer in the MIPS stacks prevents the excess oxygen diffusion from the atmosphere during the annealing process. As a result, the effective electron mobility of 155 cm2/V·s at 1 MV/cm and an EOT of 0.62 nm are successfully achieved by utilizing direct-contact La-silicate/Si structure. This result is comparable with the recorded effective electron mobility achieved by utilizing Hf-based oxides/Si structure. This demonstrates the advantage of our proposed method to realize the scaled EOT with a superior interfacial property for state-of-the-art metal-oxide-semiconductor field-effect transistors.

Wavelength division multiplexing (WDM) is a common technique used to increase the capacity of optical communication networks. In this technique, data coming from different sources are transmitted through the same optical fiber using different optical carriers. We study a thermally controlled tunable photonic-crystal optical coupler. The device is designed using a triangular lattice of air holes in an epitaxially layered structure (InGaAsP/InP). In this configuration, the input and output waveguides are separated from each other, in contrast to other devices that require a reflective grating and circulators or beam splitters. We use the two-dimensional finite-difference time-domain method (2D-FDTD) to analyze the performance of this device. After optimization the parameters of this device, we study the effects of changing the temperature. Not only has the position of the resonant peak changed linearly with the temperature, but the efficiency is also doubled. A linear regression of the spectral response gives a slope of dλ/dT = +0.1 nm/°C in a temperature range of ΔT = 50°C for wavelengths close to 1550 nm. These results show the possibility of tuning this contra-directional coupler using the thermo-optical effect.

SB-MOSFETs were fabricated on SOI substrates by applying novel Schottky barrier height modulation technique of Er interlayer insertion at the interface of Ni/Si prior to Ni silicidation process. It was found that Er interlayer insertion lowered Schottky barrier height for electrons while no significant increase of the resistivity in the Er interlayer inserted films compare to pure Ni silicide films in the annealing temperature range of 500-750 oC. Effects of Er insertion to the transistor characteristics of SOI SB-MOSFETs are also discussed.

Recently, many have studied various configurations of metal nanoparticle-quantum dot (MNP-QD) hybrid molecules based on different metals and tunable parameters. In this paper, we aim to incite the interest in using MNP-QD nanohybrids, which possess sensing capabilities superior to those of the individual constituents, for sensing applications that rely on scattered light. When assessing whether a given MNP-QD configuration is suited for an application, sometimes it is hard to assess the pros and cons of a given configuration against other candidates. Here we propose a simple, elegant relative figure of merit (RFoM), which focuses on maximizing the scattered intensity and the refractive index sensitivity of the nanohybrid, to rank the suitability of viable MNP-QD configurations for a particular sensing application. We use the proposed RFoM to analyse the optical spectra of noble, transition, post transition and alkali metal based MNP-QD nanohybrids using the representative metals Au, Ag, Cu, Al and Na, adopting a generalized nonlocal optical response (GNOR) method based cavity QED approach. Based on our observations, we suggest how the usage of MNP-QD nanohybrids could improve the conventionally studied tumour targeting applications. Moreover, we propose potential substitutes for noble metals conventionally considered for MNP-QD nanohybrids.

In this paper, we analyze the coupling of light from a GaAs microdisk laser into a waveguide. Starting from an air cladding, we examine several configurations to couple light into the waveguide with different cladding structures aimed to foster light coupling into the waveguide: photonic crystal and metallic (plasmonic cladding). In these coupling schemes, we tried to optimize the coupling of the emitted light into the waveguide, while maintaining a reasonable quality factor to allow the lasing operation of the device. We show that a plasmonic layer, introduced beside the waveguide can lead to a significant improvement in the coupling efficiency, reaching an efficiency close to 80%.