Search

Polymer banknotes are being increasingly adopted to replace older banknotes. Since banknotes are forensically important substrates for fingermark detection and identification, we present a single-step process to enhance the visualization of fingermarks on banknotes using columnar thin films (CTFs) of nickel. This single-step vacuum technique enhances the quality grade of fingermarks maximally, whether the fingermarks are aged for one or seven days before CTF deposition. This work represents progress over currently available sequences of diverse techniques for enhancing fingermarks on polymer banknotes., 11 pages, 3 figures

CDs and DVDs are forensically important substrates for latent fingermarks. Upright columnar thin films (CTFs) grown conformally over these substrates were shown to significantly enhance the visual quality of fingermarks. Enhancement to maximum possible grade for visual quality occurred, even for the samples that were developed three days after the fingermarks were placed on them. The CTFs were deposited by directing a collimated vapor flux of an evaporant material towards the substrate placed at an angle and made to rotate rapidly., 12 pages, 4 figures

The propagation of surface-plasmon-polariton (SPP) waves at the planar interface of a metal and a dielectric material was investigated for a dielectric material with strongly temperature-dependent constitutive properties. The metal was silver and the dielectric material was vanadium multioxide impregnated with a combination of active dyes. Depending upon the volume fraction of vanadium multioxide, either attenuation or amplification of the SPP waves may be achieved; the degree of attenuation or amplification is strongly dependent on both the temperature and whether the temperature is increasing or decreasing. At intermediate volume fractions of vanadium multioxide, for a fixed temperature, a SPP wave may experience attenuation if the temperature is increasing but experience amplification if the temperature is decreasing.

The planewave response of a bicontrollable metasurface absorber with graphene-patched pixels was simulated in the X band using commercial software. Each square meta-atom is a 4x4 array of 16 pixels, some patched with graphene and the others unpatched. The pixels are arranged on a PVC skin which is placed on a copper-backed YIG substrate. Graphene provides electrostatic controllability and YIG provides magnetostatic controllability. Our design delivers absorptance equal to or in excess of 0.9 over a 100-MHz spectral regime in the X band, with 360 MHz/kA magnetostatic controllabity rate and 1 Hz m/V electrostatic controllability rate. Notably, electrostatic control via graphene in the GHz range is novel., 9 pages, 4 figures, 1 table

Vanadium dioxide (VO2) transforms from purely monoclinic to purely tetragonal on being heated from 58 deg C to 72 deg C, the transformation being reversible but hysteretic. Electromagnetically, VO2 transforms from a dissipative dielectric to another dissipative dielectric if the free-space wavelength is less than 1100 nm, but from a dissipative dielectric to a plasmonic metal (or vice versa) if the free-space wavelength exceeds 1100 nm. Calculating the extinction, total scattering, absorption, radiation-pressure, back-scattering, and forward-scattering efficiencies of a VO2 sphere, we found clear signatures of thermal hysteresis in (i) the forward-scattering, back-scattering, and absorption efficiencies for free-space wavelength less than 1100 nm, and (ii) the forward-scattering, back-scattering, total scattering, and absorption efficiencies for free-space wavelength more than 1100 nm. Vacuum and null-permittivity quasistates occur between 58 deg C and 72 deg C, when tetragonal VO2 is a plasmonic metal, once each on the heating branch and once each on the cooling branch of thermal hysteresis. But none of the six efficiencies show significant differences between the two quasistates., 11 pages, 4 figures

We conceptualized three-array scalable metasurfaces comprising only three thin strip grids and numerically demonstrated their characteristics in the mid-infrared spectral regime for switchable polarization manipulation and related asymmetric diodelike transmission (AT). A few or all of the grids were taken to be made of VO$_2$, a phase-change material. For each proposed metasurface, two effective structures and, therefore, two different functionalities exist, corresponding to the metallic and insulating phases of VO$_2$. The achieved scenarios of functionality switching that depend on the VO$_2$ phase are shown to significantly depend in the way in which VO$_2$ is incorporated to the metasurface. Switchable bands of polarization manipulation are up to 40 THz wide. The AT band can be modulated when Fabry--Perot (anti-)resonances come into play., 6 pages, 4 figures

The homogenization of vaterite impregnated with gold nanoparticles was accomplished using the extended Maxwell Garnett formalism. The extended formalism takes into account the intrinsic anisotropy of vaterite as well as the size, shape, and orientation of the nanoparticles. Size-dependent permittivity was used for the gold nanoparticles. Numerical studies revealed that the homogenized composite material's permittivity parameters are acutely sensitive to the size, shape, orientation, and volume fraction of the gold nanoparticles.

Guided by the planar interface of two dissimilar linear, homogeneous mediums, a Voigt surface wave arises due to an exceptional point of either of the two matrixes necessary to describe the spatial characteristics in the direction normal to the planar interface. There is no requirement for either or both partnering mediums to be dissipative, unlike a Voigt plane wave which can propagate only in a dissipative medium.

The propagation of Dyakonov-Tamm (DT) surface waves guided by the planar interface of two nondissipative materials $A$ and $B$ was investigated theoretically and numerically, via the corresponding canonical boundary-value problem. Material $A$ is a homogeneous uniaxial dielectric material whose optic axis lies at an angle $\chi$ relative to the interface plane. Material $B$ is an isotropic dielectric material that is periodically nonhomogeneous in the direction normal to the interface. The special case was considered in which the propagation matrix for material $A$ is non-diagonalizable because the corresponding surface wave-named the Dyakonov-Tamm-Voigt (DTV) surface wave-has unusual localization characteristics. The decay of the DTV surface wave is given by the product of a linear function and an exponential function of distance from the interface in material $A$; in contrast, the fields of conventional DT surface waves decay only exponentially with distance from the interface. Numerical studies revealed that multiple DT surface waves can exist for a fixed propagation direction in the interface plane, depending upon the constitutive parameters of materials $A$ and $B$. When regarded as functions of the angle of propagation in the interface plane, the multiple DT surface-wave solutions can be organized as continuous branches. A larger number of DT solution branches exist when the degree of anisotropy of material $A$ is greater. If $\chi = 0^\circ$ then a solitary DTV solution exists for a unique propagation direction on each DT branch solution. If $\chi > 0^\circ$, then no DTV solutions exist. As the degree of nonhomogeneity of material $B$ decreases, the number of DT solution branches decreases., Comment: arXiv admin note: text overlap with arXiv:1910.10972

Theoretical formalisms for the homogenization of particulate composites are identified as following either the direct scattering approach (DSA) or the indirect scattering approach (ISA). Both approaches can take inclusion size-dependence and distribution statistics into account. However, the DSA is generally limited to mediums with direction-independent constitutive properties and inclusions with simple shapes, but the ISA is not hobbled thus.

Degradation of metal-insulator-semiconductor (MIS) capacitors of gold/Parylene-C/Pentacene under constant voltage stress (CVS) was investigated to explore the electrical stability and reliability of Parylene C as a gate dielectric in flexible electronics. A stress voltage of fixed magnitude as high as 20 V, both negative and positive in polarity, was applied to each MIS capacitor at room temperature for a fixed duration as long as 10 s. The CVS effects on the capacitance-voltage curve-shift, the time-dependent leakage current, and the time-dependent dielectric breakdown were measured and analyzed. CVS is observed to induce charge in Parylene-C and its interfaces with gold and Pentacene. The net induced charge is positive and negative for, respectively, negative and positive gate bias polarity during CVS. The magnitude of the charge accumulated following positive gate CVS is significantly higher than that following negative gate bias CVS in the range of 4 to 25 nC cm$^{-2}$. In contrast, the leakage current during the negative gate stress is three orders of magnitude higher than that during the positive gate stress for the same bias stress magnitude. The charge buildup and leakage current are due to the trapping of electrons and holes near the Parylene-C/Pentacene interface as well as in the Parylene-C layer. Before the application of the CVS, a dielectric breakdown occurs at an electric field of 1.62 MV cm$^{-1}$. After the application of the CVS, the breakdown voltage decreases and the density of the trapped charges increases as the stress voltage increases in magnitude, with the polarity of the trapped charges opposite to that of the stress voltage. The magnitude and direction of the capacitance-voltage curve-shift depend on the trapping and recombination of electrons and holes in the Parylene-C layer and in the proximity of the Parylene-C/Pentacene interface during CVS., Comment: 11 pages, 4 figures

Anisotropic homogeneous metamaterials that are neither wholly dissipative nor wholly active at a specific frequency are permitted by classical electromagnetic theory. Well-established homogenization formalisms indicate that such a metamaterial may be realized quite simply as a random mixture of electrically small (possibly nanoscale) spheroidal particles of at least two different isotropic dielectric materials, one of which must be dissipative but the other active. The dielectric properties of this metamaterial are influenced by the volume fraction, spatial distribution, particle shape and size, and the relative permittivities of the component materials. Similar metamaterials with more complicated linear as well as nonlinear constitutive properties are possible. Dynamic control of the active component material, for example via stimulated Raman scattering, affords dynamic control of the metamaterial.

If a dissipative anisotropic dielectric material, characterized by the permittivity matrix $\underline{\underline{\epsilon}}$, supports Voigt-wave propagation, then so too does the analogous active material characterized by the permittivity matrix $\underline{\underline{{\tilde{\epsilon}}}}$, where $\underline{\underline{{\tilde{\epsilon}}}}$ is the hermitian conjugate of $\underline{\underline{\epsilon}}$. Consequently, a dissipative material that supports Voigt-wave propagation can give rise to a material that supports the propagation of Voigt waves with attendant linear gain in amplitude with propagation distance, by infiltration with an active dye.

The excitation of multiple SPP waves as Floquet harmonics was demonstrated in structures fabricated as one-dimensional photonic crystals (PCs) on top of two-dimensional gold gratings. Each period of the PC comprised nine layers of silicon oxynitrides of different compositions, and each PC had either two or three periods. Absorptances for obliquely incident $p$- and $s$-polarized light were measured in the 500--1000-nm wavelength regime and the sharp bands in the absorptance spectra were compared with the solutions of the underlying canonical boundary-value problem. The excitation of multiple surface-plasmon-polariton (SPP) waves as Floquet harmonics was confirmed. The structures demonstrated broadband absorption with overall weak dependences on the incidence angle and the polarization state of the incident light, and has potential application for harvesting solar energy.

An exact transition matrix was formulated for electromagnetic scattering by a vacuum-like sphere with magnetoelectric gyrotropy. Both the total scattering and forward scattering efficiencies are lower when the magnetoelectric gyrotropy vector of the sphere is co/anti-parallel to the electric field or magnetic field of an incident plane wave than when the magnetoelectric gyrotropy vector is coparallel to the propagation vector of the incident plane wave. Backscattering is absent when the propagation vector is co/anti-paralel to the magnetoelectric gyrotropy vector.

Developments that took place in the area of sculptured--thin--film technology after {\em Bianisotropics '98\/} are reviewed here. Devices addressed include: optical filters of various kinds, laser mirrors, gas--concentration sensors, optical interconnects, interlayer dielectrics, and biosensors. Pulse bleeding is related to the circular Bragg phenomenon in chiral sculptured thin films. Acoustic research is also identified., International Conference on Electromagnetics of Complex Media [8th], Held in Lisbon, Portugal on 27-29 September 2000. Bianisotropics 2000

The planar interface of a metal and a hyperbolic, dielectric, structurally chiral material can support the propagation of none, one, or multiple surface-plasmon-polariton (SPP) waves, at a specified frequency and along a specified direction in the interface plane. When multiple SPP waves can exist, they differ in phase speed, propagation length, degree of localization to the interface, and spatial profiles of the associated electromagnetic fields., 4 pages, 6 figures

Within the framework of quantum electrodynamics (QED), vacuum is a nonlinear medium which can be linearized for a rapidly time-varying electromagnetic field with a small amplitude subjected to a magnetostatic field. The linearized QED vacuum is a uniaxial dielectric-magnetic medium for which the degree of anisotropy is exceedingly small. By implementing an affine transformation of the spatial coordinates, the degree of anisotropy may become sufficiently large as to be readily perceivable. The inverse Bruggeman formalism can be implemented to specify a homogenized composite material (HCM) which is electromagnetically equivalent to the affinely transformed QED vacuum. This HCM can arise from remarkably simple component materials; for example, two isotropic dielectric materials and two isotropic magnetic materials, randomly distributed as oriented spheroidal particles.

An effective cylindrical cloak may be conceptualized as an assembly of adjacent local neighbourhoods, each of which is made from a homogenized composite material (HCM). The HCM is required to be a certain uniaxial dielectric-magnetic material, characterized by positive-definite constitutive dyadics. It can arise from the homogenization of remarkably simple component materials, such as two isotropic dielectric-magnetic materials, randomly distributed as oriented spheroidal particles. By carefully controlling the spheroidal shape of the component particles, a high degree of HCM anisotropy may be achieved, which is necessary for the cloaking effect to be realized. The inverse Bruggeman formalism can provide estimates of the shape and constitutive parameters for the component materials, as well as their volume fractions.

We explored the effects of relative motion on the excitation of surface-plasmon-polariton (SPP) waves guided by the planar interface of a metal film and a dielectric slab, both materials being isotropic and homogeneous. Electromagnetic phasors in moving and non-moving reference frames were related directly using the corresponding Lorentz transformations. Our numerical studies revealed that, in the case of a uniformly moving dielectric slab, the angle of incidence for SPP-wave excitation is highly sensitive to (i) the ratio $\beta$ of the speed of motion to speed of light in free space and (ii) the direction of motion. When the direction of motion is parallel to the plane of incidence, the SPP wave is excited by $p$-polarized (but not $s$-polarized) incident plane waves for low and moderate values of $\beta$, while at higher values of $\beta$ the total reflection regime breaks down. When the direction of motion is perpendicular to the plane of incidence, the SPP wave is excited by $p$-polarized incident plane waves for low values of $\beta$, but $s$-polarized incident plane waves at moderate values of $\beta$, while at higher values of $\beta$ the SPP wave is not excited. In the case of a uniformly moving metal film, the sensitivity to $\beta$ and the direction of motion is less obvious.

The planewave response of a linear passive material generally cannot be characterized by a single scalar refractive index, as directionality of energy flow and multiple wavevectors may need to be considered. This is especially significant for materials which support negative refraction, negative phase velocity, and counterposition. By means of a numerical example based on a commonly studied bianisotropic material, our theoretical investigation revealed that: (i) negative (positive) refraction can arise even though the phase velocity is positive (negative); (ii) counterposition can arise in instances of positive and negative refraction; (iii) the phase velocity and time-averaged Poynting vectors can be mutually orthogonal; and (iv) whether or not negative refraction occurs can depend upon the state of polarization and angle of incidence. A further numerical example revealed that negative phase velocity and positive refraction can co-exist even in a simple isotropic dielectric material.

The refraction of linearly polarized plane waves into a half-space occupied by a material moving at constant velocity was studied by directly implementing the Lorentz transformations of electric and magnetic fields. From the perspective of a co-moving observer, the moving material was a spatially local, pseudochiral omega material. Numerical studies revealed that whether or not negative refraction occurrs in the moving material depends upon the speed of movement as well as the angle of incidence and the polarization state of the incident plane wave. Furthermore, the phenomenons of negative phase velocity and counterposition in the moving material were similarly found not to be Lorentz covariant; both phenomenons were also found to be sensitive to the angle of incidence and the polarization state of the incident plane wave.

Surface plasmon polaritons (SPPs) at the interface of a columnar thin film (CTF) and metal exist over a range of propagation directions relative to the morphology of the CTF which depends on the tilt of the columns in the CTF. The phase speed of the SPP wave varies mainly as a function of the tilt of the CTF columns. Both the confinement of the SPP wave to the interface and the decay of the SPP wave along the direction of propagation depend strongly on the direction of propagation relative to the morphologically significant plane of the CTF. The greater the columnar tilt in relation to the interface, the shorter is the range of propagation. Because of its porosity and the ability to engineer this biaxial dielectric material, the CTF-metal interface may be more attractive than traditional methods of producing SPPs.

The selection of a higher vapor deposition angle when growing a columnar thin film (CTF) leads to surface-wave propagation at a planar metal-CTF interface with phase velocity of lower magnitude and shorter propagation range. Acordingly, a higher angle of plane-wave incidence is required to excite that surface wave in a modified Kretschmann configuration.

The phase velocity of light is co-parallel to the direction of energy flow in classical vacuum. However, in certain uncommon materials, these two vectors can be oppositely directed, in which case the phase velocity is termed `negative'. This negative phase velocity (NPV) gives rise to many exotic phenomenons, such as negative refraction, inverse Doppler shift and inverse Cerenkov radiation, and has technological allure. According to quantum electrodynamics, the presence of a magnetostatic field makes vacuum an anisotropic medium for the passage of light. Under the influence of a sufficiently strong magnetostatic field, vacuum supports NPV. Such ultrastrong magnetic fields are believed to arise due to dynamo action in newborn neutron stars and in binary neutron star mergers, for examples. In view of the possible occurrence of negative refraction, the influence of ultrastrong magnetostatic fields must be carefully taken into account in astronomical observations relating to neutron stars and associated gamma-ray bursts.

The presence of charge promotes the propensity of a rotating black hole to support the propagation of electromagnetic plane waves with negative phase velocity (NPV) in its ergosphere, whether the Kerr-Newman or the Kerr-Sen metric descriptions of spacetime are considered. Striking differences in the NPV characteristics for the Kerr-Newman and Kerr-Sen metrics emerge from numerical studies, particularly close to the outer event horizon when the magnitude of the charge is large.

When a circularly polarized plane wave is normally incident on a slab of a structurally chiral material with local $\bar{4}2m$ point group symmetry and a central twist defect, the slab can function as either a narrowband reflection hole filter for co-handed plane waves or an ultranarrowband transmission hole filter for cross-handed plane waves, depending on its thickness and the magnitude of the applied dc electric field. Exploitation of the Pockels effect significantly reduces the thickness of the slab., To be published in: Asian Journal of Physics

In an isotropic, homogeneous, nondissipative, dielectric-magnetic medium that is simply moving with respect to an inertial reference frame, planewave solutions of the Maxwell curl postulates can be such that the phase velocity and the time-averaged Poynting vector are mutually orthogonal. Orthogonal-phase-velocity propagation thus adds to the conventional positive-phase-velocity propagation and the recently discovered negative-phase-velocity propagation that is associated with the phenomenon of negative refraction.

Constitutive scalars that are absent in the fundamental differential equations of frequency-domain electromagnetism on the two sides of a boundary between two homogeneous mediums are shown to disappear from the boundary conditions as well., 4 pages

After a primer on nanotechnology and a review of current educational practices in secondary schools, the concept of just-in-time education is proposed to integrate technosciences and humanities so that both future technoscientists and non-technoscientists develop a common understanding, possibly even a common language, to deal with social, ethical, legal, and political issues that arise from the development of nanotechnology and its convergence with other technoscientific developments.

We report on the occurrence of negative-phase-velocity (NPV) planewave propagation in the ergosphere of a rotating black hole. By implementing the Kerr metric, it is demonstrated that regions of NPV propagation are concentrated at the equator of the ergosphere, while NPV propagation is less common towards the polar regions. Increasing the angular velocity of the black hole exaggerates the NPV concentration at the equator. NPV propagation is not observed outside the stationary limit surface., Typographical error in eq (51) of NJP version is corrected in arxiv version

The dispersion relations for conventional uniaxial dielectric mediums may be characterized as elliptical or elliptical-like, according to whether the medium is nondissipative or dissipative, respectively. However, under certain constitutive parameter regimes, the dispersion relations may be hyperbolic or hyperbolic-like. We investigate planewave propagation in a hyperbolic/hyperbolic-like uniaxial dielectric medium. For both evanescent and nonevanescent propagation, the phase velocity is found to be positive with respect to the time-averaged Poynting vector. A conceptualization of a hyperbolic--like uniaxial medium as a homogenized composite medium is presented.

We report on a strategy for achieving negative phase velocity (NPV) in a homogenized composite medium (HCM) conceptualized using the Bruggeman formalism. The constituent material phases of the HCM do not support NPV propagation. The HCM and its constituent phases are isotropic dielectric-magnetic mediums; the real parts of their permittivities/permeabilities are negative-valued whereas the real parts of their permeabilities/permittivities are positive-valued.

The reflection of a normally incident wideband pulse by a half-space whose permittivity and permeability obey the one-resonance Lorentz model is calculated. The results are compared with those from frequency-domain reflection analysis. In the spectral regime wherein the real parts of the permittivity and the permeability are negative, as well as in small adjacent neighborhoods of that regime, the time-domain analysis validates the conclusion that it is sufficient to ensure that the imaginary part of the refractive index is positive - regardless of the sign of the real part of the refractive index., Comment: 8 pages, 1 figure

Several issues relating to oppositely directed phase velocity and power flow are reviewed. A necessary condition for the occurrence of this phenomenon in isotropic dielectric-magnetic mediums is presented. Ramifications for aberration-free lenses, homogenization approaches, and complex mediums are discussed., Comment: 7 pages, will be presented at Complex Mediums III (Annual Meeting of SPIE, Seattle, WA, July 7-11, 2002)

The canonical problem of a perfect lens with linear bianisotropic materials is formulated. Its solution is shown to be directly connected with the concept of nihility, the electromagnetic nilpotent. Perfect lenses as well as nihility remain unrealizable., 5 pages, 1 figure

An electromagnetic trinity comprising vacuum, anti--vacuum, and nihility is postulated -- after making use of materials with "negative permittivity" and "negative permeability" -- to illuminate the structure of electromagnetic theory, at least insofar as the relationship of phase velocity with Poynting vector is concerned., 5 pages