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A novel method was developed for studying the ink-paper interface and the structural variations of a deposited layer of ink. Combining high-resolution x-ray tomography with laser ablation, the depth profile of ink (toner), i.e., its varying thickness, could be determined in a paper substrate. X-ray tomography was used to produce the 3D structure of paper with about 1 μm spatial resolution. Laser ablation combined with optical imaging was used to produce the 3D structure of the printed layer of ink on top of that paper with about 70 nm depth resolution. Ablation depth was calibrated with an optical profilometer. It can be concluded that a toner layer on a light-weight-coated paper substrate was strongly perturbed by protruding fibers of the base paper. Such fibers together with the surface topography of the base paper seem to be the major factors that control the leveling of toner and its penetration into a thinly coated paper substrate.

A model for the electrostatic detection apparatus is presented. An electrostatic potential models the effects of indented writing, erasures, and fingerprints. Poole–Frenkel emission from Mylar surface states is employed to model the discharge process. Experimental evidence is provided which supports the model. The role of the Mylar sheet is identified. The electric effect of indented writing is identified as a surface charge created by paper-to-paper friction.

The temperature-dependence of the electrical and dielectric properties of paper substrates was studied using experimental papers with different NaCl contents, different thicknesses, and different grammages. Physical processes related to the charging potential, charge decay rate, conductivity, dielectric constant, and dielectric loss of papers are dependent on thermal energy, and this dependence on temperature can be described by exponential expressions. The ion content of paper not only determines the level of these properties at a given temperature, as expected but also influences their temperature-dependence. Frequency analysis of the dielectric loss confirms that new structures are formed in paper by the addition of NaCl. The results may be applicable to the design of materials and equipment, e.g., for the electrophotographic printing processes.

A new equivalent circuit model for electrographic recording on dielectric paper with a backing electrode is presented. It is shown that the conductivity of a thin layer between the dielectric layer and basepaper is more important than bulk conductivity in the basepaper.

We demonstrate a simple interferometric probe to detect nanoscale dynamics of sessile fluid drops on arbitrary rough or flexible substrates. The technique relies on producing high-contrast Newton-ring like dynamical fringes by interference between a weak Fresnel reflection from the air-fluid interface of the drop and an air-glass interface of a convex lens placed above the drop in quasi-normal geometry. By analyzing the dynamical fringes, we observed 100–700 nm/s fluctuations in water drops evaporating on metal, leaves, insect wing, and sand paper due to their surface roughness. Similar fluctuations were also observed during spreading of non-volatile glycerin drops on various rough surfaces. Another application of the technique is demonstrated in precision measurement of change in evaporation rate of a water drop due to cooling of a metal substrate. This technique can be further miniaturized with a microscope objective with potential for wide applications.

Graphene oxide and reduced graphene oxide thin films are very promising materials because they can be used in optoelectronic devices and in a growing range of applications such as touch screens and flexible displays. In this work, graphene oxide (GO) and thermally reduced graphene oxide (rGO) thin films, deposited on Ti/glass substrates, have been obtained by electrophoretic deposition. The morphological and the structural properties of the samples have been investigated by micro-Raman technique, X-ray reflectometry, and SEM analysis. In order to study the optical and electrical properties, variable angle spectroscopic ellipsometry and impedance analysis have been performed. The thermal annealing changes strongly the structural, electrical, and optical properties, because during the thermal processes some amount of sp3 bonds originally present in GO were removed. In particular, the annealing enhances the Ohmic behavior of the rGO film increasing its conductivity and the estimated optical density. Moreover...

In this work, charge transport through interpoly thin nitride/oxide stacked films, including nitride/oxide dual- and oxide/nitride/oxide tri-layer films, was studied. Extensive experimental results, concerning current conduction in single oxide layer, single nitride layer, nitride/oxide dual-layer, and oxide/nitride/oxide tri-layer films are presented. An effective investigation of the various mechanisms that can explain current conduction and charge trapping in these dielectrics was performed. To this aim, different approaches to transport modeling, namely, a classical current continuity model, a transmission model, and a two-step trap assisted model are proposed. The gains and trade offs offered by each model are pointed out. A comprehensive model for the conduction mechanisms in thin nitride/oxide stacked films is proposed.

To develop excellent silicon oxide film using low temperature method, ion plating (IP) oxide is investigated. Physicochemical characterizations of the IP oxide are studied using ellipsometry, Fourier transform infrared spectrometry, and P-etch rate measurement. The IP oxide is a high-density dielectric with strained bonds. Electrical characterizations are also analyzed using capacitance–voltage and current–voltage techniques through metal-oxide-semiconductor capacitors. The IP oxide has a low leakage current, a high breakdown field, and low interface state density. In addition, IP oxide annealed in N2 ambient is also studied. After high-temperature annealing, the characteristics of IP oxide become comparable to those of thermal oxide. The novel oxide film is successfully applied as a gate insulator to low-temperature processed (⩽620 °C) polysilicon thin-film transistors.

Efficient control of intercalation of epitaxial graphene by specific elements is a way to change properties of the graphene. Results of several experimental techniques, such as X-ray photoelectron spectroscopy, micro-Raman mapping, reflectivity, attenuated total reflection, X-ray diffraction, and X-ray reflectometry, gave a new insight into the intercalation of oxygen in the epitaxial graphene grown on 4H-SiC(0001). These results confirmed that oxygen intercalation decouples the graphene buffer layer from the 4H-SiC surface and converts it into the graphene layer. However, in contrast to the hydrogen intercalation, oxygen does not intercalate between carbon planes (in the case of few layer graphene) and the interlayer spacing stays constant at the level of 3.35–3.32 A. Moreover, X-ray reflectometry showed the presence of an oxide layer having the thickness of about 0.8 A underneath the graphene layers. Apart from the formation of the nonuniform thin oxide layer, generation of defects in graphene caused by...

Suspended graphene has the highest measured thermal conductivity of any material at room temperature. However, when graphene is supported by a substrate or encased between two materials, basal-plane heat transfer is suppressed by phonon interactions at the interfaces. We have used frequency domain thermoreflectance to create thermal conductance maps of graphene contacts, obtaining simultaneous measurements of the basal-plane thermal conductivity and cross-plane thermal boundary conductance for 1–7 graphitic layers encased between titanium and silicon dioxide. We find that the basal-plane thermal conductivity is similar to that of graphene supported on silicon dioxide. Our results have implications for heat transfer in two-dimensional material systems, and are relevant for applications such as graphene transistors and other nanoelectronic devices.

Resist residue from the device fabrication process is a significant source of contamination at the metal/graphene contact interface. Ultraviolet Ozone (UVO) treatment is proven here, by X-ray photoelectron spectroscopy and Raman measurement, to be an effective way of cleaning the metal/graphene interface. Electrical measurements of devices that were fabricated by using UVO treatment of the metal/graphene contact region show that stable and reproducible low resistance metal/graphene contacts are obtained and the electrical properties of the graphene channel remain unaffected.

This study elucidates the correlation among conductivity of graphene and interface aspects in GaN light-emitting diodes (LEDs). Using a multilayer graphene of low sheet resistance, it is demonstrated that graphene alone can make ohmic contact with p-GaN without necessitating additional interlayer. Large-area blue LED with relatively low contact resistance in the order of 10−2 ohm-cm2 and improved forward voltage of 3.2 ± 0.1 V was realized irrespective of the use of the interlayer. The results from parallel evaluation experiments performed by varying the layer numbers of graphene with ultrathin NiOx interlayer revealed that the poor lateral conductivity of monolayer or few layer graphene can be well compensated by the interlayer. A combination of three layer graphene and NiOx offered device with enhanced electro-optical performance. But the Schottky barrier associated with the inadequate adhesion of transferred graphene dominates all the benefits and becomes a major bottleneck preventing the formation of low resistance stable ohmic contact.

The electronic properties of epitaxial graphene (EG) on SiC (0001) depend sensitively on the surface morphology of SiC substrate. Here, 2–3 layers of graphene were grown on on-axis 6H-SiC with different step densities realized through controlling growth temperature and ambient pressure. We show that epitaxial graphene on SiC (0001) with low step density and straight step edge possesses fewer point defects laying mostly on step edges and higher carrier mobility. A relationship between step density and EG mobility is established. The linear scan of Raman spectra combined with the atomic force microscopy morphology images revealed that the Raman fingerprint peaks are nearly the same on terraces, but shift significantly while cross step edges, suggesting the graphene is not homogeneous in strain and carrier concentration over terraces and step edges of substrates. Thus, control morphology of epitaxial graphene on SiC (0001) is a simple and effective method to pursue optimal route for high quality graphene and will be helpful to prepare wafer sized graphene for device applications.

GaN-based nanorod light-emitting diodes (LEDs) with multilayer graphene (MLG) transparent electrodes have been fabricated. Two types of nano-LEDs with graphene on and under the metal pads are fabricated and their performances are investigated. And LEDs with graphene on the metal-pads exhibiting lower forward voltage and higher electroluminescence intensity are obtained. Using scanning electron microscope and Raman spectroscopy, we have demonstrated that graphene transferred after the metal deposition remains intact and has much less damages than graphene under the metal during the fabrication of LEDs with nanorods.

Integration of graphene with other materials by direct growth, i.e., not using mechanical transfer procedures, is investigated on the example of metal/graphene/dielectric heterostructures. Such structures may become useful in spintronics applications using graphene as a spin-filter. Here, we systematically discuss the optimization of synthesis procedures for every layer of the heterostructure and characterize the material by imaging and diffraction methods. 300 nm thick contiguous (111) Ni-films are grown by physical vapor deposition on YSZ(111) or Al2O3(0001) substrates. Subsequently, chemical vapor deposition growth of graphene in ultra-high vacuum (UHV) is compared to tube-furnace synthesis. Only under UHV conditions, monolayer graphene in registry with Ni(111) has been obtained. In the tube furnace, mono- and bilayer graphene is obtained at growth temperatures of ∼800 °C, while at 900 °C, non-uniform thick graphene multilayers are formed. Y2O3 films grown by reactive molecular beam epitaxy in UHV covers the graphene/Ni(111) surface uniformly. Annealing to 500 °C results in crystallization of the yttria with a (111) surface orientation.

Graphene grown by chemical vapor deposition can be used as the conductive channel in metal oxide semiconductor field effect transistors, metallic electrodes in capacitors, etc. However, substrate-induced corrugations and strain-related wrinkles formed on the graphene layer impoverish the properties of these devices by lowering the conductance and increasing their variability. Using the scanning electron microscopy, Auger electron spectroscopy, scanning tunneling microscopy, and atomic force microscopy, we investigated the morphology of as-grown and transferred graphene sheets on different substrates. We show that while the compressive strain (from the growth process) in the graphene sheet on flat substrates is minimized by generating wrinkles, and on rough substrates, it can be minimized by improving the graphene-substrate adhesion, leading to lower densities of wrinkles. This method paves the way to the design of wrinkle-free graphene based devices.

The study of epitaxial graphene layers grown on SiC by two techniques, namely, the traditional Si sublimation method and the recent chemical vapor deposition (CVD) using temperature induced shift of the Raman 2D line, is presented. The measurements of thermal shift rate of 2D line on 4 H-SiC(0001) allowed us to determine notable differences in interaction of graphene with SiC substrate. The obtained results show that graphene layers grown by Si sublimation of 4 H-SiC(0001) are pinned strongly to the substrate. In contrast, the layers of graphene grown on 4 H-SiC(0001) substrates by CVD showed much weaker pinning. It was found that the film consisting of two or three graphene layers grown by CVD was already unpinned and thus showing Raman shift expected for freestanding graphene. The obtained differences in pinning of epitaxial graphene layers are explained in terms of basic growth mechanism differences between these two methods: graphene growth by Si sublimation is a “bottom-up” process and by CVD—a “top-...

In situ analysis was performed on the graphene growth in ultrahigh vacuum chemical vapor deposition by exposing the epitaxial Ni(111) thin film to benzene vapor at 873 K. It is shown that the highly uniform single- and bi-layer graphenes can be synthesized by the control of benzene exposure in the range of 10–105 langmuirs, reflecting a change in the graphene growth-rate by three orders of magnitude in between the first and second layer. Electron energy loss spectroscopy measurements of single- and bi-layer graphenes indicates that the interface interaction between bi-layer graphene and Ni(111) is weakened in comparison with that between single-layer graphene and Ni(111). It is also clarified from the micro-Raman analysis that the structural and electrical uniformities of the graphene film transformed on a SiO2 substrate are improved remarkably under the specific exposure conditions at which the growths of single- and bi-layer graphenes are completed.

We mechanically clean graphene devices using an atomic force microscope (AFM). By scanning an AFM tip in contact mode in a broom-like way over the sample, resist residues are pushed away from the desired area. We obtain atomically flat graphene with a root mean square (rms) roughness as low as 0.12 nm after this procedure. The cleaning also results in a shift of the charge-neutrality point toward zero gate voltage, as well as an increase in charge carrier mobility.

Metal-catalyst-free chemical vapor deposition (CVD) of large area uniform nanocrystalline graphene on oxidized silicon substrates is demonstrated. The material grows slowly, allowing for thickness control down to monolayer graphene. The as-grown thin films are continuous with no observable pinholes, and are smooth and uniform across whole wafers, as inspected by optical-, scanning electron-, and atomic force microscopy. The sp 2 hybridized carbon structure is confirmed by Raman spectroscopy. Room temperature electrical measurements show ohmic behavior (sheet resistance similar to exfoliated graphene) and up to 13 of electric-field effect. The Hall mobility is ∼40 cm 2/Vs, which is an order of magnitude higher than previously reported values for nanocrystalline graphene. Transmission electron microscopy, Raman spectroscopy, and transport measurements indicate a graphene crystalline domain size ∼10 nm. The absence of transfer to another substrate allows avoidance of wrinkles, holes, and etching residues which are usually detrimental to device performance. This work provides a broader perspective of graphene CVD and shows a viable route toward applications involving transparent electrodes.

A rotating ball display was tested with a thin monolayer sheet. An oil cavity was formed in the shape of a spheroid in a thin elastomer sheet. The rotation of a bichromal ball was investigated from the point of rotation time from one color to the other color. Bichromal balls were under friction during rotation. The friction caused an abnormal change in the rotation time. The rotation time of the elastomer sheet was compared with that of a microcup rotating ball display. The friction explained the difference of rotation time variation between the elastomer sheet display and the microcup display.

This paper describes a pulse technique for measuring the properties and charge‐transfer characteristics of electrographic receptors. This method has the unique capability, as compared with electrometer methods or ac bridge methods, of separately measuring the charge deposited on the surface of the dielectric layer, the displacement charge, and the charge passing through the dielectric. The technique is used to obtain a detailed analysis of the electrographic properties of a dielectric coated paper, including the relaxation of the paper substrate, the capacitances of the virtual air gap and the dielectric layer, and the threshold voltage for charge transfer.

A computer program has been written to produce pole figures using the data from an x‐ray texture goniometer. The data are corrected for background and absorption. The pole figure is also stored on magnetic or paper tape in a form suitable for quantitative calculations. As an example, the Hall coefficient of a poly‐crystalline sample of a close‐packed hexagonal material is computed from the pole figure of the sample in terms of the single‐crystal components of the Hall tensor.

Two scanning techniques are now being used to determine the vibrational patterns and far‐field sound radiation of complex vibratory systems. One technique is a near‐field scanning apparatus which scans the vibrator and gives a three‐dimensional display on graph paper of the nodal patterns. The other scanning technique uses the principles of holography to locate far‐field sound sources on the vibrator. These two methods, coupled together, have demonstrated a unique capability to locate acoustic sources and hot spots on vibratory systems.

Using the transfer matrix method, the absorption, reflection, and nonreciprocity of the cylindrical photonic crystals (CPCs) consisting of graphene and two layers of ordinary medium cascaded by a periodic sequence and a Rudin–Shapiro quasiperiodic sequence are investigated under a large incidence angle of electromagnetic wave. By comparing the cascade of two periodic structures and the case of a single periodic structure, it is concluded that the structure proposed in this paper has better nonreciprocal phenomena and wider relative absorption bandwidth at a large incidence angle, reaching 162.2%, which is also much higher than the general planar photonic crystals. The absorption performance of this structure in TE and TM modes is compared at different angles and it is found that TM mode has a wider absorption bandwidth and has an ideal bandwidth in a large range of incident angle from 20° to 80°. Meanwhile, the optimum parameters of chemical potential and medium thickness are discussed, which can meet the requirements of large absorption bandwidth and significant nonreciprocity at a large incident angle. The CPCs embedded in graphene adopted in this paper are structures that have never been studied before. The electrical conductivity of graphene can be adjusted by the chemical potential, which can more conveniently realize many optical phenomena and provide reference and application values for optical sensing, optical filtering, and optical detection.

In this paper, circularly polarized metasurface radiators (meta-radiator) are elaborately designed with low-profile, small footprint, and highly efficient specifications. The proposed array consists of single-feed dense radiating meta-atoms that overall occupies a small area of 1.57 λ 0 × 1.57 λ 0 at f = 5.8 GHz. The inter-element coupling is involved by analyzing the contributing meta-atoms with Floquet boundary conditions. For demonstration purposes, an 8 × 8 sample of meta-radiators excited by an isolated network beneath the ground plane is fabricated. Both numerical and experimental results demonstrate that the meta-radiator exposes a pure left-hand circularly polarized radiation with a peak broadside directivity, a realized gain, and an axial ratio of 14.9 dBi, 14.2 dB, and 1.28 dB, respectively. Numerical simulations indicate that the aperture, radiation, and total efficiencies are as high as 99%, 97.5%, and 84.3%, respectively. In comparison with the conventional array antennas with similar performances, the proposed meta-radiator provides a higher aperture efficiency, in a simpler manner to achieve circular polarization, and more compact size as discussed throughout the paper. This new class of radiating architectures may find great potential applications in target detection systems and wireless communications.

Due to the exciting physical mechano-bactericidal approach developed in recent years using nanopatterned surfaces with its potential applications in biomedical engineering, now it becomes crucially important to fabricate optimal surface structures so as to achieve the best bactericidal ability. In this paper, the bactericidal efficacy of the cylindrical nanopillar-patterned surface and the sinusoidal nanopillar-patterned surface is presented via minimizing total free energy for a bacterial cell adhered on these two kinds of surfaces. Our theoretical analyses show that the adhesion depth at equilibrium along the nanopillar shafts and the corresponding stretching degree is related to the the nanopillar density and nanopillar radius. The bactericidal efficacy on the nanopillar-patterned surface is determined by the combination of nanopillar density and naopillar radius, which is also supported by the phase diagrams obtained, showing that at large internanopillar spacing and nanopillar radius, the sinusoidal nanopillar-patterned surface is more advantageous in bactericidal efficacy, while in small interspacing and nanopillar radius, the cylindrical nanopillar-patterned surface structure is more powerful. The conclusions obtained in this paper unveil how the mechano-bactericidal effect is achieved by tuning the topography of the nanopatterned surface, a technique helpful to the optimal design and fabrication of bio-mimicking nanotextured surfaces.

We have been observing the kinetic buildup of electrical conduction current upon x-ray irradiation in ZnSe single crystals. The objective is to understand the behavior of ZnSe crystals under x-ray irradiation, toward their potential use in x-ray detectors that do not require cooling and can operate above room temperature. The paper focuses on the factors that affect the behavior of traps at room temperature. A model is developed to understand the origin of the behavior of the conduction current under x-ray irradiation, taking into account the contributions from three types of traps for electrons (shallow, phosphorescent, and deep) and two luminescence centers (luminescence bands of 630 and 970 nm). Principally, the model is applied to the fitting of the experimental curves. Consequently, the work puts in evidence the role of electron accumulation on traps on the x-ray conduction current buildup on ZnSe crystals. We have obtained experimental dependencies of x-ray conduction current buildup current at 85 K, which indicates the presence of delay in comparison with x-ray luminescence buildup. This paper will demonstrate the effectiveness of our theoretical method in the framework of the multi-center model for wide-gap semiconductors.

Defects influence the electronic and optical properties of crystals, so their identification is crucial to develop device technology for materials of micro-/optoelectronics and photovoltaics. The identification requires the accurate calculation of the electronic transitions and the paramagnetic properties of defects. The achievable accuracy is strongly limited in the case of the (semi)local approximations to density functional theory, because of the underestimation of the gap and of the degree of localization. In the past two decades, hybrid functionals, mixing semilocal and nonlocal exchange semiempirically, have emerged as an alternative. Very often, however, the parameters of such hybrids have to be tuned from material to material. In this paper, we describe the theoretical foundations for the proper tuning and show that if the relative positions of the band edge states are well reproduced, and the generalized Koopmans's theorem is fulfilled by the given parameterization, the calculated defect levels and localizations can be very accurate. As demonstrated here, this can be achieved with the two-parameter Heydt-Scuseria-Ernzerhof hybrid, HSE(α,μ) for diamond, Si, Ge, TiO2, GaAs, CuGaS(Se)2, GaSe, GaN, and Ga2O3. The paper describes details of the parameterization process and discusses the limitations of optimizing HSE functionals. Based on the gained experience, future directions for improving exchange functionals are also provided.

InGaN-based light-emitting diodes (LEDs) have higher luminescence efficiency than other materials used for the blue and green LEDs in spite of their relatively high dislocation density. Localization theory has been used to explain this phenomenon, but the direct observation of localization states in the InGaN active region has been rarely reported. In this paper, we propose an LED structure to obtain higher luminescence efficiency in the yellow-green LEDs and directly observe the transition of carriers between different localization states. The localization states were investigated and confirmed by temperature-dependent photoluminescence and excitation power-dependent photoluminescence. The value of the external quantum efficiency also exhibited a higher radiative efficiency of the quantum well with a higher degree of localization states. These results offer a promising means of realizing high-luminescence LEDs.InGaN-based light-emitting diodes (LEDs) have higher luminescence efficiency than other materials used for the blue and green LEDs in spite of their relatively high dislocation density. Localization theory has been used to explain this phenomenon, but the direct observation of localization states in the InGaN active region has been rarely reported. In this paper, we propose an LED structure to obtain higher luminescence efficiency in the yellow-green LEDs and directly observe the transition of carriers between different localization states. The localization states were investigated and confirmed by temperature-dependent photoluminescence and excitation power-dependent photoluminescence. The value of the external quantum efficiency also exhibited a higher radiative efficiency of the quantum well with a higher degree of localization states. These results offer a promising means of realizing high-luminescence LEDs.

This paper presents a novel thermochromic induced transmittance filter (ITF) based on VO2 films. The ITF structure enables high transmittance in the short wavelength range with wide rejection at longer wavelengths, which meets the requirements of thermochromic VO2 for the metal-insulator transition. Thus, the VO2-based ITFs are designed and fabricated based on the induced transmittance effect, and a graded-index material TiO2 is initially adopted for the simplified structure of VO2-based ITF comparing standard ITFs. The VO2-based ITF's properties are characterized systematically and compared with those of VO2 films. Favorable results of crystallinity, surface roughness, hydrophobicity, the thermal hysteresis width, and pleasant appearance color are achieved in these VO2-based ITFs. Moreover, luminous transmittance Tlum (380–780 nm) of 48.8% and a solar modulation ability ΔTsol of 6.2% are achieved with an ideal spectrum shape in the VO2-based ITF, which provides a highly efficient solution to improve thermochromic VO2 films and related field.This paper presents a novel thermochromic induced transmittance filter (ITF) based on VO2 films. The ITF structure enables high transmittance in the short wavelength range with wide rejection at longer wavelengths, which meets the requirements of thermochromic VO2 for the metal-insulator transition. Thus, the VO2-based ITFs are designed and fabricated based on the induced transmittance effect, and a graded-index material TiO2 is initially adopted for the simplified structure of VO2-based ITF comparing standard ITFs. The VO2-based ITF's properties are characterized systematically and compared with those of VO2 films. Favorable results of crystallinity, surface roughness, hydrophobicity, the thermal hysteresis width, and pleasant appearance color are achieved in these VO2-based ITFs. Moreover, luminous transmittance Tlum (380–780 nm) of 48.8% and a solar modulation ability ΔTsol of 6.2% are achieved with an ideal spectrum shape in the VO2-based ITF, which provides a highly efficient solution to improve ther...

In this paper, a gradient-index lens is designed to implement an acoustic Bessel beam. Here, the wave from the point source is reshaped to the Bessel beam with the energy concentrated near the axial direction and almost no divergence. The two-dimensional distribution of the gradient refractive index is obtained based on the analysis of the impedance matching theory. The interface reflection is reduced significantly due to the impedance matching with air. The effect of the acoustic Bessel lens is found to work in a broadband with the use of the subwavelength unit cell and the finite-element simulations. Our results may provide the potential applications for medical ultrasound imaging and signal detection.In this paper, a gradient-index lens is designed to implement an acoustic Bessel beam. Here, the wave from the point source is reshaped to the Bessel beam with the energy concentrated near the axial direction and almost no divergence. The two-dimensional distribution of the gradient refractive index is obtained based on the analysis of the impedance matching theory. The interface reflection is reduced significantly due to the impedance matching with air. The effect of the acoustic Bessel lens is found to work in a broadband with the use of the subwavelength unit cell and the finite-element simulations. Our results may provide the potential applications for medical ultrasound imaging and signal detection.

This paper reports the fabrication of InN layers on the epitaxial graphene (EG) using radio-frequency plasma-assisted molecular beam epitaxy (RF-MBE). Prior to the fabrication of InN, single crystalline EG with step and terrace structure was formed on 6H-SiC (0001) substrate in an Ar ambient by the Si sublimation method. Single crystalline epitaxial layers of InN with smooth surfaces are successfully fabricated on the EG using RF-MBE. InN layers with terrace and step structure are grown on the graphene surface up to 2MLs, and InN are grown in a layer by layer 2D growth mode. If the number of layers is increased above 3 MLs, the terrace and steps disappear, and the growth mode changes to 3D mode. The Raman spectroscopy analysis shows that the interfacial stress is reduced for the InN layer grown on the EG surface. The quality of the grown InN layer on the EG surface achieved at present is comparable to the InN film grown on sapphire. This work opens the possibility of growing high-quality InN layers on the EG surface in the near future.This paper reports the fabrication of InN layers on the epitaxial graphene (EG) using radio-frequency plasma-assisted molecular beam epitaxy (RF-MBE). Prior to the fabrication of InN, single crystalline EG with step and terrace structure was formed on 6H-SiC (0001) substrate in an Ar ambient by the Si sublimation method. Single crystalline epitaxial layers of InN with smooth surfaces are successfully fabricated on the EG using RF-MBE. InN layers with terrace and step structure are grown on the graphene surface up to 2MLs, and InN are grown in a layer by layer 2D growth mode. If the number of layers is increased above 3 MLs, the terrace and steps disappear, and the growth mode changes to 3D mode. The Raman spectroscopy analysis shows that the interfacial stress is reduced for the InN layer grown on the EG surface. The quality of the grown InN layer on the EG surface achieved at present is comparable to the InN film grown on sapphire. This work opens the possibility of growing high-quality InN layers on the...

In this paper, we demonstrate a new method to control the enhanced transmission due to Fabry–Perot resonances through an array of dielectric-loaded slots in a thick metallic screen. We obtain approximate analytical formulas for each polarization (TM and TE) using a mode-matching technique based on the assumption that the slots are small compared to a free-space wavelength and that the metallic screen is a perfect electric conductor as is appropriate for microwave frequency applications. We show that the bandwidth and locations of enhanced transmission can be controlled by the angle of incidence or by making the material filling the slots inhomogeneous. Computational results are given that demonstrate the influence of the angle of incidence on the enhanced transmission bandwidth. We show that the separation between enhanced transmission frequencies can be controlled by introducing a gap within the slot with a different dielectric constant. Also, we illustrate how the total transmission bandwidth can be increased by adjusting the angle of incidence and the gap size.In this paper, we demonstrate a new method to control the enhanced transmission due to Fabry–Perot resonances through an array of dielectric-loaded slots in a thick metallic screen. We obtain approximate analytical formulas for each polarization (TM and TE) using a mode-matching technique based on the assumption that the slots are small compared to a free-space wavelength and that the metallic screen is a perfect electric conductor as is appropriate for microwave frequency applications. We show that the bandwidth and locations of enhanced transmission can be controlled by the angle of incidence or by making the material filling the slots inhomogeneous. Computational results are given that demonstrate the influence of the angle of incidence on the enhanced transmission bandwidth. We show that the separation between enhanced transmission frequencies can be controlled by introducing a gap within the slot with a different dielectric constant. Also, we illustrate how the total transmission bandwidth can be inc...

III-V optoelectronics grown epitaxially on Si substrates have large networks of dislocations due to a lattice constant mismatch between the device layers and the substrate. Recombination-enhanced dislocation glide (REDG) allows these dislocations to move and increase in length during device operation, which degrades performance. In this paper, we study REDG dynamics of threading dislocations in situ in (In)AlGaAs double heterostructures grown on Si substrates using scanning electron microscopy cathodoluminescence. The driving force for REDG arises due to the coefficient of thermal expansion differences between Si and the III-V layers leading to large residual strains in the films. Tracking of threading dislocations as moving dark spot defects reveals glide characteristics that vary based on the nature of the dislocation. Remarkably, the alloying of a few atom percent of indium using metamorphic structures arrests threading dislocation glide by more than two orders of magnitude. Finally, we present REDG-based filtering as a pathway to reducing the threading dislocation density in select areas, removing a large fraction of the mobile dislocations. Together, these techniques will enable the understanding of dislocation–dislocation and carrier–dislocation interactions that have so far remained elusive during device operation, leading to reliable III-V integrated optoelectronics on silicon.III-V optoelectronics grown epitaxially on Si substrates have large networks of dislocations due to a lattice constant mismatch between the device layers and the substrate. Recombination-enhanced dislocation glide (REDG) allows these dislocations to move and increase in length during device operation, which degrades performance. In this paper, we study REDG dynamics of threading dislocations in situ in (In)AlGaAs double heterostructures grown on Si substrates using scanning electron microscopy cathodoluminescence. The driving force for REDG arises due to the coefficient of thermal expansion differences between Si and the III-V layers leading to large residual strains in the films. Tracking of threading dislocations as moving dark spot defects reveals glide characteristics that vary based on the nature of the dislocation. Remarkably, the alloying of a few atom percent of indium using metamorphic structures arrests threading dislocation glide by more than two orders of magnitude. Finally, we present REDG-ba...

Mechanical resonators are excellent transducers for ultrasensitive detection applications. Recent advances such as vectorial force sensing and ultrahigh-resolution mass spectra rely on the identification of two flexural vibrational modes of a resonator. The orientations of the flexural modes with respect to the incident optical axis are crucial parameters for a cantilevered resonator. Previous methods have adopted complex experimental setups using quadrant photodetectors or have required simultaneous detection of two flexural modes of the cantilever. In this paper, we propose a method for determination of the orientations of the flexural vibrations of a cantilever using a microlens optical fiber interferometer that takes both the light interference and the lateral light scattering of the cantilever into account. We demonstrated the method by experimentally determining the orientation of the first three flexural vibrational modes of a thermally driven microwire. Our method can be used to characterize individual flexural modes with arbitrary orientations and thus provides a new tool for detecting vectorial forces.Mechanical resonators are excellent transducers for ultrasensitive detection applications. Recent advances such as vectorial force sensing and ultrahigh-resolution mass spectra rely on the identification of two flexural vibrational modes of a resonator. The orientations of the flexural modes with respect to the incident optical axis are crucial parameters for a cantilevered resonator. Previous methods have adopted complex experimental setups using quadrant photodetectors or have required simultaneous detection of two flexural modes of the cantilever. In this paper, we propose a method for determination of the orientations of the flexural vibrations of a cantilever using a microlens optical fiber interferometer that takes both the light interference and the lateral light scattering of the cantilever into account. We demonstrated the method by experimentally determining the orientation of the first three flexural vibrational modes of a thermally driven microwire. Our method can be used to characterize indiv...

In this paper, we propose a simple and effective method to manipulate photonic spin accumulation with an applied magnetic field. When a linearly polarized Gaussian light beam is reflected from the prism-air interface at the Brewster angle, the magnitude and direction of the photonic spin accumulation can be flexibly modulated by adjusting the applied magnetic field. Importantly, the maximum displacement of photonic spin accumulation can reach about 39.14 μ m, which provides the opportunity to directly observe photonic spin accumulation without weak measurements. These findings may hold potential applications for manipulating and detecting the electron spin current, leading to the development of a new spintronic device.In this paper, we propose a simple and effective method to manipulate photonic spin accumulation with an applied magnetic field. When a linearly polarized Gaussian light beam is reflected from the prism-air interface at the Brewster angle, the magnitude and direction of the photonic spin accumulation can be flexibly modulated by adjusting the applied magnetic field. Importantly, the maximum displacement of photonic spin accumulation can reach about 39.14 μ m, which provides the opportunity to directly observe photonic spin accumulation without weak measurements. These findings may hold potential applications for manipulating and detecting the electron spin current, leading to the development of a new spintronic device.

Plasmonic structure (PS) has recently been demonstrated to provide full control of dispersion characteristics by virtue of spoof surface plasmonic polariton (SSPP). In this paper, a comprehensive scheme is proposed, which develops the non-planar PS as a covering on the absorber to enhance the k-vector matching absorption in a wider frequency band. Owing to the dispersion engineering of SSPP, our theoretical investigation shows that the PS covering based on a straight wire array can not only enhance the k-vector matching absorption of the ground absorber at low frequency, but also achieve the broadband absorption at high frequency. As a proof, two hybrid plasmonic metamaterial absorbers (PMAs) based on the combinations of PS covering and various absorbers are proposed here. Simulations and experimental measurements demonstrate that two kinds of hybrid PMAs can simultaneously achieve broadband absorption enhancement, especially for the lower-frequency absorption. Our proposed strategy succeeds in the comprehensive utilization of dispersion engineering for broadband absorption enhancement, and a wide range of applications is expected to emerge from our design concept ranging from microwave to optical frequencies.Plasmonic structure (PS) has recently been demonstrated to provide full control of dispersion characteristics by virtue of spoof surface plasmonic polariton (SSPP). In this paper, a comprehensive scheme is proposed, which develops the non-planar PS as a covering on the absorber to enhance the k-vector matching absorption in a wider frequency band. Owing to the dispersion engineering of SSPP, our theoretical investigation shows that the PS covering based on a straight wire array can not only enhance the k-vector matching absorption of the ground absorber at low frequency, but also achieve the broadband absorption at high frequency. As a proof, two hybrid plasmonic metamaterial absorbers (PMAs) based on the combinations of PS covering and various absorbers are proposed here. Simulations and experimental measurements demonstrate that two kinds of hybrid PMAs can simultaneously achieve broadband absorption enhancement, especially for the lower-frequency absorption. Our proposed strategy succeeds in the compre...

In this paper, we investigate the strong modification and reshaping of the Laguerre-Gaussian (LG) beam using a tailored magnetized plasma photonic crystal (PPC), based on the angular spectrum expansion and 4 × 4 matrix method. It is numerically shown that by manipulating both external magnetic field and plasma number density, the reflected and transmitted beam shape is perfectly controlled. In addition, to show the domain role of magnetized PPC birefringence in the shaping of the twisted beam (TB), vertical incidence and oblique incidence of the LG beam are analyzed. We believe that these results open the door to use PPC structures in modulating the shape of a reference TB for new optical traps. Meanwhile, this study gives a new insight into the diagnostic of plasma systems using analyses of TB shapes.In this paper, we investigate the strong modification and reshaping of the Laguerre-Gaussian (LG) beam using a tailored magnetized plasma photonic crystal (PPC), based on the angular spectrum expansion and 4 × 4 matrix method. It is numerically shown that by manipulating both external magnetic field and plasma number density, the reflected and transmitted beam shape is perfectly controlled. In addition, to show the domain role of magnetized PPC birefringence in the shaping of the twisted beam (TB), vertical incidence and oblique incidence of the LG beam are analyzed. We believe that these results open the door to use PPC structures in modulating the shape of a reference TB for new optical traps. Meanwhile, this study gives a new insight into the diagnostic of plasma systems using analyses of TB shapes.

In this paper, the design, fabrication, and measurement of a high-performance metamaterial absorber (MMA) have been presented. The three major concerns of MMA's are narrow bandwidth, angle sensitivity, and uncontrollable polarization. By smartly controlling the proposed design, the solutions to these three concerns of MMA are given in this paper. By integrating the design with varactor diodes, we make the MMA tunable to wide frequency ranges. Frequency tunability ranges from 4.2 to 7 GHz. By using circular sectors in the resonator, wide incident angle insensitivity has been achieved. The presented MMA exhibits more than 80% absorptivity up to 70° incident angles. With the proposed design, it is possible to control either TM or TE polarization resonant frequency by fixing the resonant frequency of other polarization. Also, a biasing technique which is simple and effective to control both TM and TE resonant frequencies simultaneously is given in this paper. Moreover, all these advantages have been achieved by using a single layer low cost FR4 material having thickness 0.6 mm as a substrate. By using a standard parameter retrieval technique, the real and imaginary parts of both permittivity and permeability of the presented MMA are calculated. It is expected that the presented work improves the state-of-the-art in the smart metamaterial absorber domain.

Quantum annealing machines based on superconducting qubits, which have the potential to solve optimization problems faster than digital computers, are of great interest not only to researchers but also to the general public. In this paper, we propose a quantum annealing machine based on a semiconductor floating gate (FG) array. The purpose of using the architecture of nand flash memories is to reuse a mature technology to create large arrays of silicon qubits. Current high-density nand flash memories use sufficiently small FG cells to make the number of electrons stored in each cell small and countable. The high packing density of these cells creates mutual capacitive couplings that can be used to generate cell-to-cell interactions. We explore these characteristics to derive an Ising Hamiltonian for the FG system in the single-electron regime. Considering the size of a cell (10 nm), the ideal operation temperature of a quantum annealer based on FG cells is estimated to be approximately that of liquid nitrogen. Assuming the parameters of a commercial 64 Gbit nand, we estimate that it is possible to create 2-megabyte (MB) qubit systems solely using conventional fabrication processes. Our proposal demonstrates that a large qubit system can be obtained as a natural extension of the miniaturization of commercial-grade electronics, although more effort will likely be required to achieve high-quality qubits.Quantum annealing machines based on superconducting qubits, which have the potential to solve optimization problems faster than digital computers, are of great interest not only to researchers but also to the general public. In this paper, we propose a quantum annealing machine based on a semiconductor floating gate (FG) array. The purpose of using the architecture of nand flash memories is to reuse a mature technology to create large arrays of silicon qubits. Current high-density nand flash memories use sufficiently small FG cells to make the number of electrons stored in each cell small and countable. The high packing density of these cells creates mutual capacitive couplings that can be used to generate cell-to-cell interactions. We explore these characteristics to derive an Ising Hamiltonian for the FG system in the single-electron regime. Considering the size of a cell (10 nm), the ideal operation temperature of a quantum annealer based on FG cells is estimated to be approximately that of liquid nitr...

This paper investigates energy filtering in silicon nanowires and nanosheets by resonant electron tunneling through a geometric superlattice. A geometric superlattice is any kind of periodic geometric feature along the transport direction of the nanowire or nanosheet. Multivalley quantum-transport simulations are used to demonstrate the manifestation of minibands and minibandgaps in the transmission spectra of such a superlattice. We find that the presence of different valleys in the conduction band of silicon favors a nanowire with a rectangular cross section for effective energy filtering. The obtained energy filter can consequently be used in the source extension of a field-effect transistor to prevent high-energy electrons from contributing to the leakage current. Self-consistent Schrodinger-Poisson simulations in the ballistic limit show minimum subthreshold swings of 6 mV/decade for geometric superlattices with indentations. The obtained theoretical performance metrics for the simulated devices are compared with conventional III-V superlatticeFETs and TunnelFETs. The adaptation of the quantum transmitting boundary method to the finite-element simulation of 3-D structures with anisotropic effective mass is presented in Appendixes A and B. Our results bare relevance in the search for steep-slope transistor alternatives which are compatible with the silicon industry and can overcome the power-consumption bottleneck inherent to standard CMOS technologies.This paper investigates energy filtering in silicon nanowires and nanosheets by resonant electron tunneling through a geometric superlattice. A geometric superlattice is any kind of periodic geometric feature along the transport direction of the nanowire or nanosheet. Multivalley quantum-transport simulations are used to demonstrate the manifestation of minibands and minibandgaps in the transmission spectra of such a superlattice. We find that the presence of different valleys in the conduction band of silicon favors a nanowire with a rectangular cross section for effective energy filtering. The obtained energy filter can consequently be used in the source extension of a field-effect transistor to prevent high-energy electrons from contributing to the leakage current. Self-consistent Schrodinger-Poisson simulations in the ballistic limit show minimum subthreshold swings of 6 mV/decade for geometric superlattices with indentations. The obtained theoretical performance metrics for the simulated devices are ...

Fiber Bragg Gratings (FBGs) are gaining acceptance as velocity/pressure gauges in the fields of detonation and shock physics on account of their sensitivity, small size, flexibility, electromagnetic immunity, and wavelength-encoded feature. Chirped FBGs (CFBGs) are investigated as wavelength-to-position discriminators with the purpose of monitoring pressure/velocity profiles over a distance range of typically 100 mm. The use of CFBGs simplifies both sensor deployment and data retrieval and finally improves the accuracy due to the increased number of measurement data. In this paper, the metrological performance of CFBGs used as in situ distributed shock pressure/velocity gauges is investigated both theoretically and experimentally in a planar shock loading configuration with an aluminum-based flyer and target. In the intermediate range for shock stress, i.e., less than the Hugoniot Elastic Limit (HEL) of silica, CFBGs provide simultaneous measurements of both shockwave velocity and stress within the target material. A Bragg wavelength-to-stress model is proposed that takes into account (i) the state-of-stress within the target material, (ii) the stress coupling coefficient due to imperfect impedance matching between the target material and the silica fiber, (iii) the conversion of the state-of-stress into a state-of-strain within the silica fiber, and (iv) the conversion of strain data into observable Bragg wavelength shifts. Finally, the model also takes into account the pressure dependence of constitutive parameters for silica and aluminum. Experiments were performed in planar shock loading using CFBGs as stress gauges, bonded along the target axis with Araldite glue. 6061-T6 aluminum flyers were launched at several velocities by a gas gun onto targets of the same material. A free-space Czerny-Turner (CT) spectrometer and an integrated-optics Arrayed-Waveguide Grating (AWG) were both used as dynamic spectrum analyzers. Experimental Bragg wavelength shifts agree well with theoretical predictions for both elastic and hydrodynamic planar shock loading of 6061-T6 aluminum, opening up large perspectives for shock physics experiments.Fiber Bragg Gratings (FBGs) are gaining acceptance as velocity/pressure gauges in the fields of detonation and shock physics on account of their sensitivity, small size, flexibility, electromagnetic immunity, and wavelength-encoded feature. Chirped FBGs (CFBGs) are investigated as wavelength-to-position discriminators with the purpose of monitoring pressure/velocity profiles over a distance range of typically 100 mm. The use of CFBGs simplifies both sensor deployment and data retrieval and finally improves the accuracy due to the increased number of measurement data. In this paper, the metrological performance of CFBGs used as in situ distributed shock pressure/velocity gauges is investigated both theoretically and experimentally in a planar shock loading configuration with an aluminum-based flyer and target. In the intermediate range for shock stress, i.e., less than the Hugoniot Elastic Limit (HEL) of silica, CFBGs provide simultaneous measurements of both shockwave velocity and stress within the target...

In this work, we report on the emergence of a photonic Hall effect (PHE) system within a narrow filtered background of a one-dimensional defective optical dielectric structure with graphene under the influence of a constant magnetic field regime. It is observed that at low temperature and relatively strong applied magnetic fields, electromagnetic defective transmission spectra corresponding to the two decoupled right- and left-handed polarized modes possess a step-like transmission feature which is referred to as “quantum Hall defect modes” (QHD modes or QHDs) in this paper. Tunable growing transitional transmission steps for QHDs with increasing magnetic field intensity were shown to be possible. Observation of sensitive magneto-transmission oscillations to the thermal excitations in the last plateaus slowly ascending toward unity is another special feature noted in this work. The results of this study, which is carried out based on rapid standard calculations for the transfer matrix approach is supplied with commercial simulations marking the first PHE system, promise an proper candidate for new photonic applications, especially new tunable magneto-based lenses and photonic magneto-thermal sensors.In this work, we report on the emergence of a photonic Hall effect (PHE) system within a narrow filtered background of a one-dimensional defective optical dielectric structure with graphene under the influence of a constant magnetic field regime. It is observed that at low temperature and relatively strong applied magnetic fields, electromagnetic defective transmission spectra corresponding to the two decoupled right- and left-handed polarized modes possess a step-like transmission feature which is referred to as “quantum Hall defect modes” (QHD modes or QHDs) in this paper. Tunable growing transitional transmission steps for QHDs with increasing magnetic field intensity were shown to be possible. Observation of sensitive magneto-transmission oscillations to the thermal excitations in the last plateaus slowly ascending toward unity is another special feature noted in this work. The results of this study, which is carried out based on rapid standard calculations for the transfer matrix approach is supplied...

An all-solid-state AlGaN/GaN based ion-sensitive heterostructure field effect transistor (ISHFET) pH sensor was fabricated by integrating a noble metal (Au) quasi-reference electrode to improve the device stability when measuring the pH value of a small aqueous volume. In this paper, the influence of the size of the quasi-reference electrode against the stability of the pH readings was investigated. Through optimizing the size of the integrated quasi-reference electrode, the all-solid-state ISHFET pH sensor can sustain stable pH measurements for aqueous solutions of micro-litre size. A sensitivity of 55 mV/pH was achieved by the pH sensor at room temperature. Thus, the device may have potential uses in biomedical applications which require small volume pH measurements.An all-solid-state AlGaN/GaN based ion-sensitive heterostructure field effect transistor (ISHFET) pH sensor was fabricated by integrating a noble metal (Au) quasi-reference electrode to improve the device stability when measuring the pH value of a small aqueous volume. In this paper, the influence of the size of the quasi-reference electrode against the stability of the pH readings was investigated. Through optimizing the size of the integrated quasi-reference electrode, the all-solid-state ISHFET pH sensor can sustain stable pH measurements for aqueous solutions of micro-litre size. A sensitivity of 55 mV/pH was achieved by the pH sensor at room temperature. Thus, the device may have potential uses in biomedical applications which require small volume pH measurements.

In this paper, we propose a demodulation method for refractive index (RI) sensing with tilted fiber Bragg gratings (TFBGs). It operates by monitoring the TFBG cladding mode resonance “cut-off wavelengths.” The idea of a “cut-off wavelength” and its determination method are introduced. The RI sensitivities of TFBGs are significantly enhanced in certain RI ranges by using our demodulation method. The temperature-induced cross sensitivity is eliminated. We also demonstrate a parallel-double-angle TFBG (PDTFBG), in which two individual TFBGs are inscribed in the fiber core in parallel using a femtosecond laser and a phase mask. The RI sensing range of the PDTFBG is significantly broader than that of a conventional single-angle TFBG. In addition, its RI sensitivity can reach 1023.1 nm/refractive index unit in the 1.4401–1.4570 RI range when our proposed demodulation method is used.In this paper, we propose a demodulation method for refractive index (RI) sensing with tilted fiber Bragg gratings (TFBGs). It operates by monitoring the TFBG cladding mode resonance “cut-off wavelengths.” The idea of a “cut-off wavelength” and its determination method are introduced. The RI sensitivities of TFBGs are significantly enhanced in certain RI ranges by using our demodulation method. The temperature-induced cross sensitivity is eliminated. We also demonstrate a parallel-double-angle TFBG (PDTFBG), in which two individual TFBGs are inscribed in the fiber core in parallel using a femtosecond laser and a phase mask. The RI sensing range of the PDTFBG is significantly broader than that of a conventional single-angle TFBG. In addition, its RI sensitivity can reach 1023.1 nm/refractive index unit in the 1.4401–1.4570 RI range when our proposed demodulation method is used.