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We propose a new generation of unbiased (biasfree) antenna-less CW THz photomixer emitters array made of asymmetric MSM gratings with subwavelength pitch, operating in optical nearfield regime. We take advantage of the size effects in near-field optics and electrostatics to demonstrate the possibility of enhancing the THz power by four orders of magnitude, as compared with a similar array of the same size that operates in the far-field regime. We show that with an appropriate choice of grating parameters in such THz sources the first plasmonic resonant cavity mode in nano-slit between two adjacent MSM can enhance the optical near-field absorption and hence the photo carriers' generation under the slit in the active medium. These photo carriers, on the other hand, are accelerated by the large built-in electric field sustained under the nano-slits by two dissimilar Schottky barriers to create the desired large THz power that is mainly radiated downward. A hybrid numerical simulation method is used to model and analyze these phenomena. [ABSTRACT FROM AUTHOR]

Based on existing model for dielectric function of an effective medium in response to H-polarized (TE) mode, we have developed a new comprehensive analytic model for dielectric function (\varepsilonTE) of an individual multi-wall carbon nanotube (MWCNT) that satisfies the Kramers-Kronig relation. Taking advantage of this model and utilizing the 2D Finite difference time domain (FDTD) method we have calculated the photonic response of \beta-aligned ordered arrays of MWCNTs to TE mode, over the frequency range of 0.5–10 PHz. Dependence of the photonic response on the lattice periodicity, CNTs' inner and outer radii, and the lattice orientation with respect to the propagation direction have been studied, systematically. Furthermore, using an existing model for \varepsilonTM, similar dependencies for the photonic response to E-polarized (TM) mode, have also been obtained. The numerical results can be used in designing photonic devices applicable in the range of near to deep UV, such as filtering, switching, superlensing, plasmonic antennas, and optical sensors. [ABSTRACT FROM PUBLISHER]

All-optical communication systems are under continuous development to address different core elements of inconvenience. Here, we numerically investigate an all-optical modulator, realizing a highly efficient modulation depth of 22 dB and a low insertion loss of 0.32 dB. The tunable optical element of the proposed modulator is a layer of Al-doped Zinc Oxide (AZO), also known as an epsilon-near-zero transparent conductive oxide. Sandwiching the AZO layer between a carefully designed distributed Bragg reflector and a dielectric metasurface—i.e., composed of a two-dimensional periodic array of cubic Si—provides a guided-mode resonance at the OFF state of the modulator, preventing the incident signal reflection at λ = 1310 nm. We demonstrate the required pump fluence for switching between the ON/OFF states of the designed modulator is about a few milli-Joules per cm2. The unique properties of the AZO layer, along with the engineered dielectric metasurface above it, change the reflection from 1 to 93%, helping design better experimental configurations for the next-generation all-optical communication systems. [ABSTRACT FROM AUTHOR]

We propose a metasurface THz modulator based on split-ring resonators (SRRs) formed by four interconnected horizontal Si–Au Schottky diodes. The equivalent junction capacitance of each SRR in the proposed modulator is much smaller than that of the previously reported metasurface counterparts with vertical Schottky junctions, leading to a higher modulation speed. To modulate a THz incident signal by the proposed metasurface, we vary the bias voltage externally applied to the Schottky junctions. Applying a reverse bias of VA = − 5 V to the Au gate, two LC resonances at 0.48 THz, and 0.95 THz are excited in the metasurface. Switching the applied voltage to VA = + 0.49 V, we diminish the oscillator strengths of the LC resonances, creating one dipole resonance at 0.73 THz in the transmission spectrum of the metasurface modulator. The modulation depths at these resonances are more than 45%, reaching 87% at 0.95 THz. The phase modulation for this THz modulator is about 1.12 rad at 0.86 THz. Furthermore, due to the particular design of the meta-atoms, the modulation speed of this device is estimated up to approximately several hundred GHz, which makes this device an appropriate candidate for high-speed applications in wireless communications systems based on external modulators. [ABSTRACT FROM AUTHOR]

We present a Nyquist stability criterion based on transmission line modeling for graphene nanoribbon (GNR) interconnects. This is the first instance that such an analysis has been presented for GNR, so far. In this analysis, the dependence of the degree of relative stability for multilayer GNR (MLGNR) interconnects on the geometry of each ribbon has been acquired. It is shown that, increasing the length and width, MLGNR interconnects become more stable. [ABSTRACT FROM AUTHOR]

Surface plasmons in graphene have mainly been affected by intrinsic optical phonons due to the vibrations of the carbon atoms and surface polar optical phonons (S-POPs) of the underlying dielectric surface. This plasmon hybridization dramatically changes the features of the plasmonic devices. However, a complete theoretical model for the graphene impedance to consider the optical phonons effects is yet remained to be developed. Here, we show how to derive a model for graphene impedance to include such impacts on graphene surface plasmons. Earlier models suffer from two limitations—i.e., the inability to show (i) the transformation of a single pure plasmonic mode into multiple hybrid plasmon–phonon excitations and (ii) the damping effect for energies beyond that of the intrinsic optical phonons due to the phonon emission. Our new model overcomes these two limitations. Then, we calculate the extinction spectra for a one-dimensional periodic array of graphene ribbons obtained through the impedance boundary condition method, addressing these obstacles. These spectra are directly related to graphene impedance, modeled using the dielectric function we developed in our earlier work. The extinction spectra show the presented model overcoming the limitations, firmly fitting the experimental data reported by others. Furthermore, we introduce our developed model for graphene to the CST Studio software to verify the accuracy of our extinction relation and impedance model. This study can be a step forward correctly predicting the behavior of graphene-based plasmonic devices. [ABSTRACT FROM AUTHOR]

We investigate the propagation of a normally incident squeezed coherent state of light through dispersive non-Hermitian optical bilayers, particularly at a frequency that the bilayers hold parity-time (đť'«đť'Ż) symmetry. To check the realization of đť'«đť'Ż-symmetry in quantum optics, we reveal how dispersion and loss/gain-induced noises and thermal effects in such bilayers can affect quantum features of the incident light, such as squeezing and sub-Poissonian statistics. The numerical results show thermally induced noise at room temperature has an insignificant effect on the propagation properties in these non-Hermitian bilayers. Moreover, tuning the bilayers’ loss/gain strength, we show that the transmitted squeezed coherent states through the structure can retain to some extent their nonclassical characteristics, specifically for the frequencies far from the emission frequency of the gain layer. Furthermore, we demonstrate, only below a critical value of gain, quantum optical effective medium theory can correctly predict the propagation of quantized waves in non-Hermitian and đť'«đť'Ż-symmetric bilayers. [ABSTRACT FROM AUTHOR]

In this paper, by integrating InP/InGaAsP/InP Photonic crystal semiconductor optical amplifier (PhC-SOA) with photonic crystal channel drop filters (PhC-CDF), we present a novel fully integrated ultra-small low-power all-optical analog to digital converter (AO-ADC). The self-phase modulation in the PhC-SOA can shift the frequency of the Gaussian input pulse. The two output PhC-CDFs are designed in a way that appropriately codes the frequency-shifted pulse by the PhC-SOA, which consequently converts them to four desired digital output levels. The numerical results indicated that the center wavelength of an amplitude modulated Gaussian pulse with a center wavelength of 1551.228 nm, temporal pulse-width of 10.6 ps, and energy of 74.4 fJ can be shifted by 1.652 nm. This shift is accommodated by utilizing a PhC-SOA with a length of 9 µm and an injection current of 6.5 mA. The shifted pulse is then quantized and coded to the four digital levels of (00, 01, 10, 11) by two point-defect PhC-CDFs. The PhC-CDFs minimize the AO-ADC integral and differential nonlinearity (INL/DNL) errors by compensating for the effect of the nonlinear frequency shift induced by PhC-SOA. The proposed design offers a footprint of 142 µm2 AO-ADC working at 10 Gs/s. [ABSTRACT FROM AUTHOR]

We present a computational study on the electrical behavior of the field-effect transistor based on vertical graphene-hBN- χ 3 borophene heterostructure and vertical graphene nanoribbon-hBN- χ 3 borophene nanoribbon heterostructure. We use nonequilibrium the Green function formalism along with an atomistic tight-binding (TB) model. The TB parameters are calculated by fitting tight-binding band structure and first-principle results. Also, electrical characteristics of the device, such as ION/IOFF ratio, subthreshold swing, and intrinsic gate-delay time, are investigated. We show that the increase of the hBN layer number decreases subthreshold swing and degrades the intrinsic gate-delay time. The device allows current modulation 177 at room temperature for a 1.2 V gate-source bias voltage. [ABSTRACT FROM AUTHOR]

The effect of Stone-Wales (SW) defect on the performance of an armchair graphene nanoribbon (AGNR)-based photodetector is studied. To model the SW defect two new tight-binding (TB) parameters are proposed that provide results that are in good agreement with density functional theory calculations. SW defect is introduced in different locations in the channel of the AGNR detector and the photocurrent, quantum efficiency and responsivity of defected structures are calculated using TB approximation and non-equilibrium Green's function formalism. By inspecting the photo-generated hole density in different points of the channel, the way that photocurrent is affected by SW defect in different defected structures is investigated. Our results show that the photocurrent of AGNR photodetector varies with the number and position of SW defect in the channel. Among the defected structures highest quantum efficiency is observed in the structure in which the SW defect is located near the contact with a higher bias voltage. However, the quantum efficiency in all defected structures is lower than their perfect counterpart. Since the low ratio of the photocurrent to the dark current limits the performance of photodetectors, improving this ratio is of great importance. We show that the presence of SW defect in the channel of AGNR photodetector increases this ratio. It is observed that the ratio of photocurrent to the dark current in the double-defect structure in which two SW defects are located at two ends of the channel is 4.7 times larger than the perfect photodetector. Our results also show that by inserting SW defect in the channel of AGNR photodetector its photo-detection range can be tuned to higher energies. • Effect of SW defect on the performance of an AGNR-based photodetector is investigated. • Photocurrent is calculated using tight-binding approximation and non-equilibrium Green's function formalism. • Presence of SW defect in the channel of AGNR photodetector increases the ratio of the photocurrent to the dark current. • Photo-detection energy can be tuned by adding defects in the channel. [ABSTRACT FROM AUTHOR]

We report a first principles study on the electronic and transport properties of bilayer armchair graphene nanoribbons (BLAGNRs) containing Stone-Wales (SW) defect. It is shown that in the presence of SW defect in BLAGNRs, some electron localization occurs in defect atoms and degradation of transmission is observed in specific energy regions. The strength of electron localization is dependent on the symmetry of SW defect. In case of symmetric SW defect, stronger electron localization leads to sharper dip in its transmission spectrum in comparison with the broad dip in the transmission spectrum of the BLAGNR containing asymmetric SW defect. The effect of electron localization is also evident from the calculated I-V characteristics of pristine and defected structures which shows the reduced current in defected structures with respect to pristine structure. Most current reduction is observed in symmetric SW defected BLAGNR due to the stronger electron localization in symmetric SW defect. [ABSTRACT FROM AUTHOR]

In artificial reproductive technologies mirroring in vivo fertilization, there is a correlation between sperm motility and fertilization outcomes. Here, we present a technology for separating sperm based on motility, which uses a biocompatible, pump-less, and simple acoustofluidic approach. Our developed and fabricated sperm separation configuration is an acoustofluidic platform consisting of a circular glass capillary tube mounted on top of a ZnO-based surface acoustic wave (SAW) device. It can separate highly motile sperm from small volumes of normal raw human semen samples. This configuration allows the generated traveling SAW to couple into the capillary, causing highly motile sperm cells to swim against the propagation direction of the traveling SAW along the capillary tube. We term this fascinating acoustic-induced sperm swimming behavior acoustotaxis in analogy with the well-known rheotaxis, in which sperm orientate to swim against a continuous fluid flow frequently generated by using an external pump in the microfluidic systems. Here, we benefit from the acoustotaxis for a pump-less separation of an effective highly motile sperm concentration from raw human semen samples at low volumes of up to 20–30 µL within a short period of about 4 minutes free from any centrifugation step. This sperm separation device exhibits a successful selection capability that leads to sperm progressive motility increase by 45 %, sperm curvilinear velocity by 23 %, sperm average path velocity by 69 %, and sperm linearity by 78 % in the selected cells in comparison with the raw sample. This acoustotaxic sperm selection separation approach provides an easy-to-use and effective method for the selection of highly motile sperm cells without adversely affecting sperm viability, paving the way for efficient and rapid sperm separation platforms, applicable for patients with low semen volumes, and up-scalable for a large volume of raw semen processing in a short time. [Display omitted] • An acoustofluidic platform is investigated for highly motile sperm separation. • An acoustic-induced sperm swimming behavior is observed, termed acoustotaxis. • This device benefits from a successful selection capability from a raw semen sample. • Unaffected sperm viability, and rapidly efficient sperm separation is provided. • The device is applicable for low semen volume and up-scalable for large volumes. [ABSTRACT FROM AUTHOR]

The crystallization processes that occur in amorphous melt-spun ribbons of nominal composition Fe 80 B 10 Si 8 Nb 1 Cu 1 during preparation and heat treatment affect the soft magnetic properties of this alloy. Fe 80 B 10 Si 8 Nb 1 Cu 1 alloys are prepared by different quenching rates (wheel speeds of 10, 20 and 40 m/s) and their soft magnetic properties are studied. The XRD data reveal that as the wheel speed increases, the fraction of crystallinity and the Fe–Si grain size both decrease. These data also show that the sample prepared by the wheel speed of 10 m/s exhibits α-Fe particles on its free surface. The data for the samples prepared by the wheel speed of 20 and 40 m/s are in good agreement with the HRTEM images. VSM measurements show that these nanostructured samples exhibit coercivity in the range of 3–21 A/m and magnetic saturation in the range of 1.55–1.78 T. [ABSTRACT FROM AUTHOR]

Abstract: Based on the transmission line model (TLM), we present an exact and general transfer function formula, useful for both single multiwall carbon nanotube (MWCNT) and MWCNT bundle interconnects. Using the standard parameters for 22-nm technology node we perform the Nyquist stability analysis, to investigate the dependence of the degree of relative stability for both single and bundle interconnects on the number of walls in each MWCNT its geometry and also on the bundle geometry. The numerical results, for 1- to 30-μm long interconnects composed of 3- to 7-wall-CNTs, show that by increasing the length or the outer shell diameter, both single and bundle interconnects become more stable. On the other hand, an increase in the number of walls, keeping the outer shell diameter constant, increases the relative stability of the single MWCNT and decreases that of the bundle interconnects. [Copyright &y& Elsevier]

The finite difference method is exploited for a full-vectorial analysis of mushroom-type waveguides for traveling wave electroabsorption modulators (TWEAM) based on asymmetric intra-step-barrier coupled double strained quantum wells (AICD-SQW). In this analysis, the discontinuities of the normal components of the electric field across abrupt dielectric interfaces which are known as the limitations of scalar and semivectorial approximation methods are considered. The optical field distributions in mushroom-type TWEAM based on AICD-SQW and conventional ridge-type TWEAM of the same active region for 1.55 μm operation are presented. The important parameters in the high-frequency TWEAM design such as optical effective index which defines optical velocity and transverse mode confinement factor are calculated. Then, the transmission line microwave properties (microwave index, microwave loss, and characteristic impedance) of TWEAMs are obtained. The modulation response of mushroom-type TWEAM is calculated using circuit model by considering interaction between microwave and optical fields in waveguide and compared with conventional ridge-type TWEAM. It is found that increasing the width of p-cladding layer with the same i-layer to reduce the resistance in p-i-n mushroom-type waveguide of TWEAM based on AICD-SQW can improve the microwave propagation loss and thus the high-speed electro-optical response. [ABSTRACT FROM AUTHOR]

Abstract Growth of the gold plasmonic shells on the iron based nanoparticles could enhance the linear and nonlinear optical properties of the iron based nanostructures, due to the coupling of the localized surface plasmon (LSP) modes on the inner and outer surface of each Au-shell. We have fabricated the iron based nanoparticles via arc discharge technique in water that is a cost effective and simple single-step synthesis route. Then, the gold shells have been grown chemically on the iron-based cores. The structural properties of core-shell nanoparticles have been investigated using X-ray diffraction (XRD) and transmission electron microscopy (TEM). XRD measurements have exposed the existence of three phases of iron (oxides) including pure iron, magnetite, and wustite within the cores. TEM images have shown that the average core-shell size with the size distribution in the range of 10 to 80 is 25 ± 10 nm. The UV–visible optical and closed-aperture Z -scan measurements have verified the coupling LSP modes coupling between the inner and outer surfaces of the Au-shells covering the iron based cores. The experimentally obtained UV–visible spectra have qualitatively verified the numerical results obtained using the finite element simulation method. Graphical abstract Unlabelled Image Highlights • Nonlinear optical properties of Fe–Au core-shells and Au and Fe NPs are compared. • XRD verifies the presence of Fe, Ai, Fe 3 O 4 , and FeO in the Fe–Au core-shells. • Absorption of Fe NPs at 360 nm is weak, due to the transition of Fe3+ d5 electrons. • The Au seeds due to LSPR show a strong absorption peak at 520 nm. • Absorption in Fe–Au NPs, due to LSPR effect is stronger than those in Au seeds. [ABSTRACT FROM AUTHOR]

Optofluidic biolasers indicate promising potential and properties that make them highly competitive in the development of state-of-the-art biophotonics technologies. One of the bright outlooks and perspectives that could have a profound impact on the current developing situation and trend of such a new found technology is the photonic crystal based optofluidic biolaser. In this article, we theoretically propose a new lab-on-a-chip design of slotted photonic crystal optofluidic biolaser. Within this scheme, the air slot and medial air holes of the miniaturized photonic crystal slab are infiltrated with organic dye solution, acting as the laser gain region. This structure provides a facility for incorporation of the biological molecules in those fluidic gain mediums. Simulations show that, in addition to the proper lasing characteristics, like the spectral linewidth of 0.27 nm and power conversion efficiency of 26%, the proposed device is highly sensitive to the subtle biological changes that may occur in its cavity and shows the sensitivity of 277 nm/RIU. [ABSTRACT FROM AUTHOR]

In this work, we present Dual Material Gate Tunneling Graphene Nano-Ribbon Field Effect Transistors (DMG-T-GNRFET) mainly to suppress the am-bipolar current with assumption that sub-threshold swing which is one of the important characteristics of tunneling transistors must not be degraded. In the proposed structure, dual material gates with different work functions are used. Our investigations are based on numerical simulations which self-consistently solves the 2D Poisson based on an atomistic mode-space approach and Schrodinger equations, within the Non-Equilibrium Green’s (NEGF). The proposed device shows lower off-current and on-off ratio becomes 5order of magnitude greater than the conventional device. Also two different short channel effects: Drain Induced Barrier Shortening (DIBS) and hot-electron effect are improved in the proposed device compare to the main structure. [ABSTRACT FROM AUTHOR]

An attempt is made to study the effect of substituting Si and Cu atoms for B in Fe 84 B 16 alloys on the microstructure and magnetic properties of the resulting melt spun compositions (i.e., Fe 84 B 14 Si 2 and Fe 84 B 12 Si 3.3 Cu 0.7 ). As-spun and annealed samples were characterized by various techniques to investigate their crystallization kinetics and the magnetic properties of the resulting microstructures. Experiments have revealed that Fe 84 B 12 Si 3.3 Cu 0.7 composition exhibits the optimum magnetic properties of M S =1.92 T and H C =11 A/m among the three samples under study. [ABSTRACT FROM AUTHOR]

By inserting a lightly doped region between the highly doped drain and the intrinsic channel of a graphene nanoribbon tunnel field effect transistor (GNR-TFET), we propose a new lightly doped drain (LDD)-GNR-TFET. Transport characteristics of the proposed transistor is numerically simulated, employing the third-nearest-neighbor tight-binding approximation in mode space non-equilibrium Green’s function formulism (NEGF), in ballistic regime. Simulations show, in comparison with a conventional GNR-TFET of the same dimensions, the proposed LDD-GNR-TFET exhibits a 10 2 –10 3 times smaller OFF-current, an up to 10 5 times larger ON/OFF ratio, a shorter time delay, a smaller power-delay product (PDP) and a less drain induced barrier thinning (DIBT), besides preserving the subthreshold swing. [ABSTRACT FROM AUTHOR]

• Non-invasive and contactless manipulation techniques enable us to measure the physical properties of living cells and organisms. • Optical tweezers are indispensable tools for contactless and non-invasive manipulation of micro-scale objects. • Trapping nanoscale objects becomes feasible by exploiting surface plasmons to confine the light beyond the diffraction limit. • Plasmonic tweezers are suitable for particle trapping and positioning with an extremely high spatial accuracy. • Plasmonic tweezers based on their geometries can be classified into tweezers based on either the propagating or localized surface plasmons. Reconfigurable plasmonic tweezers realize dynamic control over the position of the plasmonic hotspots and the shape of the trapping potential landscape. Amongst the most promising structures are plasmonic tweezers with built-in light sources, tunable, and mobile plasmonic tweezers. Since their invention in 1986, optical tweezers have become indispensable tools for contactless and non-invasive manipulation of micro and nano-objects. However, the diffraction limit hinders the trapping of nanoscale particles, as the optical gradient force scales with the third power of the particle radius. Trapping of nanometer and sub-nanometer-sized particles becomes feasible by exploiting surface plasmons to confine the light beyond the diffraction limit. Due to the sub-wavelength confinement of light, plasmonic tweezers are fit for particle positioning with an extremely high spatial accuracy. Moreover, by engineering the geometry of the plasmonic nanostructures, one can reconfigure the trapping-potential landscape. Herein, we review the recent developments in the area of plasmonic tweezers. In doing so, we discuss various types of plasmonic tweezers introduced so far and highlight their differences concerning their structures, materials, and functionalities. We finally review some of the most promising advances that would determine the future direction in this field of research, such as tunable and mobile plasmonic tweezers and tweezers with built-in light sources. [ABSTRACT FROM AUTHOR]

Abstract: We report the results of simulating a dual-gated grapheme nanoribbon field-effect transistor (GNR-FET) working in the ballistic regime, when its channel is under various tensile uniaxial strain. Simulations are performed based on self consistent solutions of the Poisson equation coupled with the Non-Equilibrium Green’s Function (NEGF) formalism in mode space representation, assuming a tight-binding Hamiltonian. The results show that the transistor I–V characteristics exhibit a zigzag behavior as the strain increases from ε =0% to ε =10.17%, at which the GNR bandgap equals that of the unstrained one. The simulations also reveal that initially the current decreases while the strain increases to ε =5%. However, as the strain increases further, the current also increases, albeit at a rate that is less than that of the initial decrease. This behavior is consistent with the variations of GNR band gap under strain. Furthermore, other switching characteristics such as transconductance, DIBL and I on/I off are also studied, for which similar zigzag behaviors are observed. [Copyright &y& Elsevier]

We are proposing a next-generation graphene nanoribbon field-effect transistor (GNRFET) with superlattice source, channel, and drain (SLSCD-GNRFET), with significantly improved switching performance. The presence of superlattice in each region is for energy filtering. The simulation results indicate that the addition of an appropriate superlattice in the channel region, it reduces the subthreshold swing. Also, using proper superlattice in the drain region leads to an increase of more than a decade in the I ON / I OFF ratio by intensely reducing the OFF-current. These improvements make the proposed transistor potentially suitable for the next-generation logical digital applications. Comparison of the simulation results for the proposed SLSCD-GNRFET with those of the conventional GNRFET, its tunneling counterpart (GNRTFET), and the one with superlattice source (SLS-GNRFET) show that the device OFF-current and subthreshold swing have improved significantly. • Superlattice structure in the source, channel and drain of graphene nanoribbon field-effect transistor for improving switching performance. • The superlattice structure as an energy filter in different regions of the transistor. • The appropriate superlattice in the channel region reduces the subthreshold swing. • The proper superlattice in the drain region leads to an increase of the I ON / I OFF ratio by intensely reducing the OFF-current. [ABSTRACT FROM AUTHOR]

• M-phenylenediamine (MPD) molecules can crosslink the adjacent Fe@Au nanoparticles. • There is a tradeoff between the Fe@Au/MPD mass ratio and the arrays formation. • Fe@Au/MPD ≈ 0.4% is the optimum mass ratio for forming a long-chain array of Fe@Au. • The optical absorbance of an Fe@Au array depends on the incoming light polarization. We are proposing a novel method to form thin films that are composed of ordered arrays of iron-gold core-shell (Fe@Au) nanoparticles with tunable optical responses. The method is based on the crosslinking of the adjacent Fe@Au nanoparticles using bifunctional group organic molecules. Molecules of m-phenylenediamine (MPD) as conjugated diamines can crosslink the adjacent Fe@Au nanoparticles. Experimental results show that the larger the Fe@Au/MPD mass ratio, the more intense the corresponding plasmon resonance. Images of the optical microscopy and FE-SEM show that there is a tradeoff between the Fe@Au/MPD mass ratio and the formation of ordered arrays of Fe@Au nanoparticles. In particular, Fe@Au/MPD ≈ 0.4% is the optimum mass ratio for forming long-chain arrays of Fe-Au core-shell nanoparticles. Moreover, the results of optical spectroscopy show that the absorbance spectrum of the optimum sample strongly depends on the incoming light polarization, making it a good nominee for optical grating. Finally, a comparison of the Kerr rotations for the optimum sample and the one with an excessive number of cross-linking molecules confirms that the nanoparticles in the latter sample, unlike in the optimum sample, are more densely packed and could not form the ordered arrays. [ABSTRACT FROM AUTHOR]

To examine the second-order coherence of light propagation of quantum states in arbitrary directions through dispersive non-Hermitian optical media, we considered two sets of non-Hermitian periodic structures that consist of gain/loss unit cells. We show that each batch can satisfy the parity-time symmetry conditions at a distinct frequency. We then varied the gain/loss strength in the stable electromagnetic regime to evaluate the transmittance of N-photon number states through each structure. The results show both sets preserve their antibunching characteristics under specific incident light conditions. Furthermore, s(p)-polarized light exhibits higher (lower) second-order coherence at larger incident angles. In addition, the antibunching features of the transmitted states degrade with an increase in the number of unit cells in multilayered structures for both polarizations., (© 2024. The Author(s).)

The presence of species other than the target biomolecules in the fluidic analyte used in the refractive index biosensor based on the surface plasmon resonances (SPRs) can lead to measurement ambiguity. Using graphene-based acousto-plasmonic biosensors, we propose two methods to eliminate any possible ambiguity in interpreting the measured results. First, we take advantage of the dynamic tunability of graphene SPRs in the acousto-plasmonic biosensor with a surface acoustic wave (SAW) induced uniform grating, performing measurements at different applied voltages. Second, a single measurement employing a similar biosensor but with SAW-induced dual-segment gratings. The numerical results show the capability of both methods in decoupling the effect of the target analyte from the other species in the fluid, enabling interpreting the measurement results with no ambiguity. We also report the results of our numerical investigation on the effect of measuring parameters like the target layer effective refractive index and thickness, and the fluid effective refractive index, in addition to the controlling parameters of the proposed acousto-plasmonic biosensor, including graphene Fermi energy and electrical signaling on the sensing characteristics. Both types of proposed biosensors show promising features for developing the next generation lab-on-a-chip biosensors with minimal cross-sensitivities to non-target biomolecules.

Employing a second-quantization of the electromagnetic field in the presence of media with both gain and loss, we investigate the propagation of the squeezed coherent state of light through a dispersive non-Hermitian multilayered structure, in particular at a discrete set of frequencies for which this structure is P T -symmetric. We detail and generalize this study to cover various angles of incidence and s- and p-polarizations to reveal how dispersion, gain/loss-induced noises in such multilayered structures affect nonclassical properties of the incident light, such as squeezing and sub-Poissonian statistics. Varying the loss layers' coefficient, we demonstrate a squeezed coherent state, when transmits through the structure whose gain and loss layers have unidentical bulk permittivities, retains its nonclassical features to some extent. Our results show by increasing the number of unit cells and incident angle, the quantum features of the transmitted state for both polarizations degrade.

We propose investigating the electro-optical properties of photodetectors based on mono- and bilayer graphene quantum dots or nanodots (GNDs). These photodetectors consist of dissimilar metals (gold, silver and titanium) that are in contact with the GNDs. To obtain photoelectrical characteristics, we employed density functional theory to solve the non-equilibrium Green's function. Photo-responsivities and quantum efficiencies obtained for these nanostructures were far better than those for structures based on graphene nanoribbons. Among the proposed photodetectors, the best performance belonged to the bilayer structures illuminated by in-plane polarized incident light. The proposed photodetectors operate without a need for externally applied voltage and are suitable for parallel light propagation using directional couplers based on the evanescent field of incident light; hence, they have applications in optical integrated circuits.

Taking advantage of highly confined evanescent fields to overcome the free-space diffraction limit, we show plasmonic tweezers enable efficient trapping and manipulation of nanometric particles by low optical powers. In typical plasmonic tweezers, trapping/releasing particles is carried out by turning the laser power on and off, which cannot be achieved quickly and repeatedly during the experiment. We introduce hybrid gold-graphene plasmonic tweezers in which the trap stiffness is varied electrostatically by applying suitable voltages to a graphene layer. We show how the graphene layer absorbs the plasmonic field around the gold nanostructures in particular chemical potentials, allowing us to modulate the plasmonic force components and the trapping potential. We show graphene monolayer (bilayer) with excellent thermal properties enables more efficient heat transfer throughout the plasmonic tweezers, reducing the magnitude of thermophoretic force by about 23 (36) times. This thermophoresis suppression eliminates the risk of photothermal damage to the target sample. Our proposed plasmonic tweezers open up possibilities to develop tunable plasmonic tweezers with high-speed and versatile force-switching functionality and more efficient thermal performance.

Intrinsic optical phonons and extrinsic polar optical phonons (POPs) strongly affect the graphene surface plasmons. Specifically, extraneous POPs present on the surface of an underlying substrate change the behavior of the graphene's surface plasmons sharply due to the plasmon-phonon hybridization. Here, we report modeling of exact dispersion relations for graphene's surface plasmons affected by intrinsic optical phonons and extrinsic POPs of the surface of polar dielectric substrates with one or more vibrational frequencies. In doing so, we have employed random phase approximation with modified two-dimensional polarizability (2D-Π 0 ). The adapted Π 0 addresses limitations of the previously derived plasmons dispersion, obtained using classical two-dimensional polarizability. We show the new model overcomes the unsatisfying behavior of the plasmonic dispersion relation obtained by the classical 2D-Π 0 at high-wavenumbers and its inability to indicate the starting point of the mode damping. Our new simple model eliminates the complexity of the other presented models in describing the surface plasmons' behavior, specifically at high wavenumbers. Besides, we use our dispersion model to learn about the plasmon content of the hybrid modes, which is a vital value to compute output current in plasmonic graphene-based devices. The coupled-mode lifetime due to the hybrid nature depends on both plasmon and phonon lifetimes. We capture this value here. There is an excellent agreement between our theoretical results and the experimental data reported earlier. They pave the way for the exact modeling of graphene plasmons on common polar substrates and bring in the closeness of the theoretical approaches and experimental results.