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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.

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.

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.

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.

Dual-energy computed tomography and the Alvarez and Macovski [Phys. Med. Biol. 21, 733 (1976)] transmitted intensity (AMTI) model were used in this study to estimate the maps of density (ρ) and atomic number (Z) of mineralogical samples. In this method, the attenuation coefficients are represented [Alvarez and Macovski, Phys. Med. Biol. 21, 733 (1976)] in the form of the two most important interactions of X-rays with atoms that is, photoelectric absorption (PE) and Compton scattering (CS). This enables material discrimination as PE and CS are, respectively, dependent on the atomic number (Z) and density (ρ) of materials [Alvarez and Macovski, Phys. Med. Biol. 21, 733 (1976)]. Dual-energy imaging is able to identify sample materials even if the materials have similar attenuation coefficients at single-energy spectrum. We use the full model rather than applying one of several applied simplified forms [Alvarez and Macovski, Phys. Med. Biol. 21, 733 (1976); Siddiqui et al., SPE Annual Technical Conference and Exhibition (Society of Petroleum Engineers, 2004); Derzhi, U.S. patent application 13/527,660 (2012); Heismann et al., J. Appl. Phys. 94, 2073–2079 (2003); Park and Kim, J. Korean Phys. Soc. 59, 2709 (2011); Abudurexiti et al., Radiol. Phys. Technol. 3, 127–135 (2010); and Kaewkhao et al., J. Quant. Spectrosc. Radiat. Transfer 109, 1260–1265 (2008)]. This paper describes the tomographic reconstruction of ρ and Z maps of mineralogical samples using the AMTI model. The full model requires precise knowledge of the X-ray energy spectra and calibration of PE and CS constants and exponents of atomic number and energy that were estimated based on fits to simulations and calibration measurements. The estimated ρ and Z images of the samples used in this paper yield average relative errors of 2.62% and 1.19% and maximum relative errors of 2.64% and 7.85%, respectively. Furthermore, we demonstrate that the method accounts for the beam hardening effect in density (ρ) and atomic number (Z) reconstructions to a significant extent.

This paper deals with the calculation of the thermal transport cross section and phase function of longitudinal phonons for scattering by nanoparticles and microparticles. Thermal transport cross section is different from the scattering cross section due to the anisotropic nature of scattering. Exact formulation of the phase function is given for the Rayleigh scattering. This paper also proposes an approximate method to calculate the thermal transport cross section for low contrast scatterers. The formulations developed in this paper will be useful for the predictive modeling of thermal conductivity of practical systems such as nanocomposites and nanomicro particle laden systems.

The paper compares the achievements of quantum well infrared photodetector (QWIP) technology with those of competitive technologies, with the emphasis on the material properties, device structure, and their impact on focal plane array (FPA) performance. Special attention is paid to two competitive technologies, QWIP and HgCdTe, in the long-wavelength IR (LWIR) and very-long-wavelength IR (VLWIR) spectral ranges. Because so far, the dialogue between the QWIP and HgCdTe communities is limited, the paper attempts to settle the main issues of both technologies. Such an approach, however, requires the presentation of fundamental limits to the different types of detectors, which is made at the beginning. To write the paper more clearly for readers, many details are included in the Appendix. In comparative studies both photon and thermal detectors are considered. Emphasis is placed on photon detectors. In this group one may distinguish HgCdTe photodiodes, InSb photodiodes, and doped silicon detectors. The potential performance of different materials as infrared detectors is examined utilizing the α/G ratio, where α is the absorption coefficient and G is the thermal generation rate. It is demonstrated that LWIR QWIP’s cannot compete with HgCdTe photodiodes as single devices, especially at higher operating temperatures (>70 K). This is due to the fundamental limitations associated with intersubband transitions. The advantage of HgCdTe is, however, less distinct at temperatures lower than 50 K due to problems inherent in the HgCdTe material (p-type doping, Shockley–Read recombination, trap-assisted tunneling, surface and interface instabilities). Even though QWIP is a photoconductor, several of its properties, such as high impedance, fast response time, long integration time, and low power consumption, comply well with the requirements imposed on the fabrication of large FPA’s. Due to a high material quality at low temperatures, QWIP has potential advantages over HgCdTe in the area of VLWIR FPA applications in terms of array size, uniformity, yield, and cost of the systems. The performance figures of merit of state-of-the-art QWIP and HgCdTe FPA’s are similar because the main limitations come from the readout circuits. Performance is, however, achieved with very different integration times. The choice of the best technology is therefore driven by the specific needs of a system. In the case of readout-limited detectors a low photoconductive gain increases the signal-to-noise ratio and a QWIP FPA can have a better noise equivalent difference temperature than an HgCdTe FPA with a charge well of similar size. Both HgCdTe photodiodes and QWIP’s offer multicolor capability in the MWIR and LWIR range. Powerful possibilities offered by QWIP technology are associated with VLWIR FPA applications and with multicolor detection. The intrinsic advantage of QWIP’s in this niche is due to the relative ease of growing multicolor structures with a very low defect density.

Molecular electronics studies how the molecular nature affects the probability of charge carriers to tunnel through the molecules. Nevertheless, transport is also critically affected by the contacts to the molecules, an aspect that is often overlooked. Specifically, the limited ability of non-metallic contacts to maintain the required charge balance across the fairly insulating molecule often have dramatic effects. This paper shows that in the case of lead/organic monolayer-silicon junctions, a charge balance is responsible for an unusual current scaling, with the junction diameter (perimeter), rather than its area. This is attributed to the balance between the 2D charging at the metal/insulator interface and the 3D charging of the semiconductor space-charge region. A derivative method is developed to quantify transport across tunneling metal-insulator-semiconductor junctions; this enables separating the tunneling barrier from the space-charge barrier for a given current-voltage curve, without complementary measurements. The paper provides practical tools to analyze specific molecular junctions compatible with existing silicon technology, and demonstrates the importance of contacts' physics in modeling charge transport across molecular junctions.

Cantilever beams under the influence of electrostatic force form an important subclass of microelectromechanical system(MEMS) and nanoelectromechanical system. Most of the studies concerning these micro-nano resonators are centered around uniform cantilever beams. In this paper, we have investigated another class of micro-resonators consisting of non-uniform cantilever beams. The study is focused around investigating pull-in voltage and resonance frequency of non-uniform cantilever beams when they operate in the linear regime about different static equilibriums. In this paper, we term this frequency as “linear frequency.” Calculation of the linear frequency is done at different static equilibriums corresponding to different DC voltages. We have studied two classes of beams, one with increasing cross sectional area from the clamped edge (diverging beam) and other with decreasing cross sectional area from the clamped edge (converging beam). Within each class, we have investigated beams with linear as well as quartic variation in width. We start by obtaining Euler beam equation for non-uniform cantilever beams considering large deflection and their corresponding exact mode shapes from the linear equation. Subsequently, using the Galerkin method based on single mode approximation, we obtain static and dynamic modal equations for finding pull-in voltage and resonance frequency as a function of DC voltage, respectively. We found that the linear frequency of converging beams increases with increase in non-uniform parameter (α) while those of diverging beams decreases with α. A similar trend is observed for pull-in voltage. Within the converging class, beams with quartic variation in width show significant increase in both frequency and pull-in voltage as compared to corresponding linearly tapered beams. In quantitative terms, converging beams with quartic variation in width and α=−0.6 showed an increase in linear frequency by a factor of 2.5 times and pull-in voltage by 2 times as compared to commonly used uniform beams. Our investigation can prove to be a step forward in designing highly sensitive MEMS sensors and actuators.

In this paper, we report on the wave transmission characteristics of a hybrid one dimensional (1D) medium. The hybrid characteristic is the result of the coupling between a 1D mechanical waveguide in the form of an elastic beam, supporting the propagation of transverse waves and a discrete electrical transmission line, consisting of a series of inductors connected to ground through capacitors. The capacitors correspond to a periodic array of piezoelectric patches that are bonded to the beam and that couple the two waveguides. The coupling leads to a hybrid medium that is characterized by a coincidence condition for the frequency/wavenumber value corresponding to the intersection of the branches of the two waveguides. In the frequency range centered at coincidence, the hybrid medium features strong attenuation of wave motion as a result of the energy transfer towards the electrical transmission line. This energy transfer, and the ensuing attenuation of wave motion, is alike the one obtained through internal resonating units of the kind commonly used in metamaterials. However, the distinct shape of the dispersion curves suggests how this energy transfer is not the result of a resonance and is therefore fundamentally different. This paper presents the numerical investigation of the wave propagation in the considered media, it illustrates experimental evidence of wave transmission characteristics and compares the performance of the considered configuration with that of internal resonating metamaterials. In addition, the ability to conveniently tune the dispersion properties of the electrical transmission line is exploited to adapt the periodicity of the domain and to investigate diatomic periodic configurations that are characterized by a richer dispersion spectrum and broader bandwidth of wave attenuation at coincidence. The medium consisting of mechanical, piezoelectric, and analog electronic elements can be easily interfaced to digital devices to offer a novel approach to smart materials.

Although Fowler and Nordheim developed the basics of field emission nearly one century ago with their introduction of the Fowler-Nordheim equation (FNE), the topic continues to attract research interest particularly with the development of new materials that have been proposed as field emitters. The first order analysis of experiments typically relies upon the FNE for at minimum a basic understand of the physical emission process and its parameters of emission. The three key parameters in the FNE are the work function, emission area, and field enhancement factor, all of which can be difficult to determine under experimental conditions. This paper focuses in particular, on the field enhancement factor β. It is generally understood that β provides an indication of the surface roughness or sharpness of a field emitter cathode. However, in this paper, we experimentally and computationally demonstrate that cathodes with highly similar surface morphologies can manifest quite different field enhancements solely through having different emission regions. This fact can cause one to re-interpret results in which a single sharp emitter is proposed to dominate the emission from a field emitting cathode.

This paper provides a detailed description explaining how to calculate the relation between the silicon Raman frequency and local stress or strain in the silicon, applied to stress measurements in microelectronics. This relation is well known for measurements from the (100) surface of silicon. However, it is often used in the wrong way, neglecting non-zero stress tensor elements. Especially, in current 3D microelectronics technology, where the stress caused by through Si vias or micro-bumps is of large importance, the vertical stress component, which highly affects the measured Raman frequency shift, is often erroneously neglected. In addition, the equations for the (100) surface are also often used incorrectly for cross-sectional measurements from a (110) surface. In this paper, different ways to calculate the relation between Raman frequency and triaxial stress, and the related Raman peak intensities, are discussed in detail.

In previous papers, a new model was proposed for the optical dielectric function of zinc blende semiconductors and was applied successfully to the alloy series AlxGa1−xAs. It was found to be more generally valid than any previous model. In this paper, it is used to obtain an analytic expression for the dielectric function of the II‐VI compound CdTe at room temperature. Unlike the previous application, additional polynomial terms in the real part of the optical dielectric function are not introduced, so that the Kramers‐Kronig relationship between the real and imaginary parts of the dielectric function is satisfied exactly. As demonstrated before, the model covers not only the entire photon energy range of the given spectral data, but also is valid below and somewhat above the given spectral range. This is advantageous especially when spectral data are not provided in the range of interest, or when joining two separate data causes an artificial discontinuity. The model determines the optical dielectric function in the limit as the line broadening approaches zero, which is useful in calculating the optical dielectric function at all temperatures. For demonstration, the optical dielectric function at 70 K and 600 K is calculated and presented.

One of the obstacles preventing wireless power transfer from becoming ubiquitous is their leakage of power: high-amplitude electromagnetic fields that can interfere with other electronic devices, increase health concerns, or hinder power metering. In this paper, we present near-field plates (NFPs) as a novel method to tailor the electromagnetic fields generated by a wireless power transfer system while maintaining high efficiency. NFPs are modulated arrays or surfaces designed to form prescribed near-field patterns. The NFP proposed in this paper consists of an array of loaded loops that are designed to confine the electromagnetic fields of a resonant transmitting loop to the desired direction (receiving loop) while suppressing fields in other directions. The step-by-step design procedure for this device is outlined. Two NFPs are designed and examined in full-wave simulation. Their performance is shown to be in close agreement with the design predictions, thereby verifying the proposed design and operation. A NFP is also fabricated and experimentally shown to form a unidirectional wireless power transfer link with high efficiency.

In this paper, we consider a plane electromagnetic wave incident onto a dielectric plate, which has one surface covered with a thin layer of metal. An oblique incident angle was considered for the TE (s polarization in optic) and TM (p polarization) plane waves. The thin metal layer is treated as an infinitesimal thickness. It was characterized by a surface conductivity and accounted for by a tangential magnetic field component step induced by the current flow in the metal layer. Compact expressions, which describe the reflection, transmission and absorption in a dielectric plate covered with a thin layer of metal, have been obtained. It was shown that by choosing the appropriate surface conductivity, the Fabry-Perot transmission resonances can be shifted to the position where the maximum reflection is observed in the case of an uncovered dielectric. On the other hand, the elimination of the Fabry-Perot resonances can be also achieved by choosing a proper metal surface conductivity. Measurements of the reflection from the glass covered with a thin layer of metal have been performed in a wide microwave frequency range (2–12 GHz) revealing a large difference in the measured reflection coefficient from the dielectric and metalized surfaces. The measured results fit well with those calculated by employing analytical expressions obtained in this paper.

International audience; In this paper, the influence of disorder on 1D periodic lattice of resonant scatterers is inspected. These latter have multiple resonance frequencies which produce band gaps in the transmission spectrum. One peculiarity of the presented system is that it is chosen with a nearly perfect overlap between the Bragg and the second hybridization band gaps. In the case of a perfectly ordered lattice, and around this overlap, this produces a narrow transparency band within a large second bandgap. As expected, the effect of the disorder is generally to increase the width of the band gaps. Nevertheless, the transparency band appears to be robust with respect to an increase in the disorder. In this paper, we study this effect by means of experimental investigations and numerical simulations.

Thin film transistors (TFTs) on elastomers promise flexible electronics with stretching and bending. Recently, there have been several experimental studies reporting the behavior of TFTs under bending and buckling. In the presence of stress, the insulator capacitance is influenced due to two reasons. The first is the variation in insulator thickness depending on the Poisson ratio and strain. The second is the geometric influence of the curvature of the insulator-semiconductor interface during bending or buckling. This paper models the role of curvature on TFT performance and brings to light an elegant result wherein the TFT characteristics is dependent on the area under the capacitance-distance curve. The paper compares models with simulations and explains several experimental findings reported in literature. (C) 2014 AIP Publishing LLC.

Optical transport behavior of organic photo-voltaic devices with nano-pillar transparent electrodes is investigated in this paper in order to understand possible enhancement of their charge-collection efficiency. Modeling and simulations of optical transport due to this architecture show an interesting regime of length-scale dependent optical characteristics. An electromagnetic wave propagation model is employed with simulation objectives toward understanding the mechanism of optical scattering and waveguide effects due to the nano-pillars and effective transmission through the active layer. Partial filling of gaps between the nano-pillars due to the nano-fabrication process is taken into consideration. Observations made in this paper will facilitate appropriate design rules for nano-pillar electrodes. (C) 2014 AIP Publishing LLC.

This paper presents a detailed theory which describes the response of a focused interferometer when a modulated laser source is incident upon a layered sample. In order to solve this problem it is necessary to solve the thermoelastic equations for a layered sample. The paper presents an analytical solution obtained using a symbolic manipulation program (reduce). In particular, we point out that the analytical form of the solution is necessary to achieve numerically stable results. In addition to calculating the actual displacement of the sample surface, the response of the instrument is considered in detail, in terms of the refractive index changes of the air above the sample and the optical transfer function of the probe optics.

The time centroid of the current pulse induced at the anode of a semiconductor drift detector is calculated as a function of the interaction coordinate for arbitrary drifting fields. The effects of its behavior on the determination of the absolute position of the interaction point are studied. For a typical bias condition of the detector, the paper shows that an error up to few hundred micrometers is made in the position reconstruction of the event if the described effects of the induction are not taken into account. The paper also shows that the time shift due to the perturbation of the drifting field caused by the discreteness of the field electrodes, is only of less than 1 ns, and therefore negligible in most applications.

Microwave interferometry appears to be a promising method for the study of wave and mass velocity in shocked dielectric materials. This paper discusses the mathematics concerning the frequencies and amplitudes in the microwave reflections from the shock wave and from an impacting piston which drives the shock into a nonreacting porous solid. Methods for the determination of the state variables in the compressed region between the shock wave and the piston are given. In this paper, these methods have been confirmed by experimental measurements in nonenergetic materials in which there is no ionization from chemical reaction. The microwave reflection from the shock wave traveling through an inert media is shown to result from a dielectric discontinuity at the wave front. Studies on energetic materials (explosives and propellants) are considered in a companion paper where ionization associated with the chemical reactions is required to explain the increased reflection from the shock front.

The electromagnetic field generated by a horizontal electric dipole in the air over a dielectric‐coated conducting or dielectric half‐space is evaluated in an earlier paper subject to the conditions k20≪k21≪‖k22‖ on the wave numbers of the three regions and the condition k1l≤ 0.6 on the thickness l of the dielectric layer. Unintentionally, the severe condition ‖k2 l‖2≪1 was also imposed in the determination of the field in the dielectric layer and the half‐space below it. That restriction is removed in this paper and new complete formulas are derived which have wide potential application.

In a recent paper Yokoyama [Mol. Cryst. Liq. Cryst. 165, 265 (1988)] showed that a correct thermodynamic definition of the anchoring energy at the interface between a nematic liquid crystal (NLC) and another medium requires the preliminary choice of a ‘‘Gibbs dividing surface.’’ As a consequence of this, the measured value of the anchoring energy coefficient can depend on which method is used to perform the experiment. This dependence probably explains the large discrepancies that are often reported in the literature between anchoring energy coefficients measured on the same substrate by different authors. To test this important point the anchoring energy coefficient at a SiOx nematic interface has been measured by using two different methods at the same time: a reflection light method and a transmitted light method. Both these methods have been already used in the literature. In this paper the latter method is analyzed in detail and it is shown that its accuracy is greatly reduced by the presence of spurious bulk contributions. To increase accuracy, a new experimental procedure is proposed that exploits the differing dependence of surface and bulk contributions on the intensity of the magnetic field. This new method allows one to separate bulk and surface contributions without using fitting procedures. Therefore both the anchoring energy and information on the bulk director distortion can be directly obtained from the experiment. The transmitted light and the reflected light methods are used simultaneously to measure the azimuthal anchoring energy coefficient at the SiOx nematic interface on the same NLC sample at the same temperatures. A satisfactory agreement between the anchoring energy coefficients measured by the two methods is found.

In this paper the authors applied an original transfer function method for calculations of radiation patterns in the case of Bessel circular transducers. It is known that the amplitudes of some natural vibration modes of circular plates are Bessel functions of zero order [R. R. Aggarval, JASA 24, 463 (1952)]. In the paper the natural vibrational modes of a circular disk‐shaped ultrasonic transducer were employed. As it follows from the numerical calculations, it is possible to obtain for Bessel‐like transducers the nondiffracting main lobe. The latter is in accordance with the suggestions of the paper [J. Durnin, J. Opt. Soc. Am. 4, 651 (1987)].

In this paper piezoelectric stress transducers are proposed on the base of GaAs and AlxGa(1−x)As. These materials exhibit reasonable piezoelectric properties and since GaAs based integrated circuits have reached a high maturity they are a promising choice for integrated stress transducers. An additional feature of the high band‐gap material GaAs is its superior high‐temperature performance in comparison with Si. In this paper the piezoelectric and related properties of GaAs and AlxGa(1−x) are discussed. Therefore the piezoelectric tensors for the commonly used (100) and (111) oriented substrates are derived. These calculations are verified by measurements of some realized sensors using different substrate orientations.

The recognition of subsurface defects is an important aspect of inverse heat transfer problems. The solution of direct problems is the basis of the inverse problems. In this paper, based on the non-Fourier heat conduction equation and using the image method and the wave function expansion method, an analytical method to study the multiple scattering of thermal waves and temperatures from the subsurface defect in semi-infinite functionally graded materials (FGMs) is presented. A general solution of the scattered fields of thermal waves is obtained. Without loss of generality, the incidence of thermal waves excited by the periodically modulated laser and the subsurface defect are treated as the line heat source and a cylindrical cavity with thermal insulation in the modelling, respectively. The amplitude of the changes in temperature at the frontal surface in the cylindrical defect due to different physical and geometrical parameters is analysed, discussed, and presented graphically using the analytical method. The significant changes in the temperature were found to occur at the frontal surface because of the existence of conducting defects. In addition, the influence of the defect state on the temperature was found to also be related to the nonhomogeneous parameters of FGMs, the wavenumber, the frequency of the thermal waves, and the depth of the buried defects. The numerical results and method proposed in this paper are expected to be applied for the analysis of infrared thermal waves in non-destructive evaluations of functionally graded materials and inverse problems of mathematical physics.

This paper presents a secure inductive wireless power transfer (WPT) system for electric vehicle (EV) applications, such as charging the electric devices inside EVs and performing energy exchange between EVs. The key is to employ chaos theory to encrypt the wirelessly transferred energy which can then be decrypted by specific receptors in the multi-objective system. In this paper, the principle of encrypted WPT is first revealed. Then, computer simulation is conducted to validate the feasibility of the proposed system. Moreover, by comparing the WPT systems with and without encryption, the proposed energy encryption scheme does not involve noticeable power consumption.

Ethernet transformers are mass produced broadband signal coupling transformers, used for interfacing copper twisted-pair networking cable to Ethernet devices. In this paper, we present a process for fabricating Ethernet transformers by embedding ferrite core materials within printed circuit board, and then fabricating the windings around the embedded core. Sample transformers were fabricated with different winding configurations and core materials. It is then possible to clad the board with copper and fabricate routes or mount components to the board faces, making the transformer a zero-footprint component. The sample transformer's performance is experimentally evaluated, and the results are presented in this paper. All transformers were found to successfully couple up to 1000Base-T Ethernet.

Current balance factor (CBF) value, the ratio of the recombination current density and the total current density of a device, has an important function in fluorescence-based organic light-emitting diodes (OLEDs), as well as in the performance of the organic electrophosphorescent devices. This paper investigates the influence of the applied voltage of a device on the CBF value of single layer OLED based on the numerical model of a bipolar single layer OLED with organic layer trap free and without doping. Results show that the largest CBF value can be achieved when the electron injection barrier ( ϕ n ) is equal to the hole injection barrier ( ϕ p ) in the lower voltage region at any instance. The largest CBF in the higher voltage region can be achieved in the case of ϕ n > ϕ p under the condition of electron mobility ( μ 0 n ) > hole mobility ( μ 0 p ), whereas the result for the case of μ 0 n μ 0 p , is opposite. The largest CBF when μ 0 n = μ 0 p can be achieved in the case of ϕ n = ϕ p in the entire region of the applied voltage. In addition, the CBF value of the device increases with increasing applied voltage. The results obtained in this paper can present an in-depth understanding of the OLED working mechanism and help in the future fabrication of high efficiency OLEDs.

The study presented in this paper relates mostly to impact testing of polymers and similar materials to measure their crack resistance and dynamic properties. For some impact testers, then, at low impact velocities the initial transient forces can be very small and short lived so as to be insignificant. This is so that the specimen mostly experiences a steadily increasing strain until it fails. At higher impact velocities both transient and generally increasing strain are both significant in taking the specimen to its failure point. With very high impact velocities, the specimen can fail mostly due to the initial impact forces. It is possible in some cases to cushion the specimen from the initial higher impact transients and related secondary effects such as bounce at the contact points. This is if a steadily increasing strain to fail the specimen is the main requirement. Of course, this is only feasible when the impact forces are not too dominant. However, as material technology has rapidly advanced so dynamic as well as toughness properties of materials have much improved. Also, the variety and mix of properties now available in different materials has greatly increased. With these trends, testing that can combine well impact, strong dynamic forces and steadily increasing strain loading of the specimen is of increasing interest. This can be so that the force‐time curve of such testing to failure of a specimen can also be regarded as its dynamic performance signature. A problem is in arranging and monitoring the dynamic forces of such tests so as to be able to analyze effectively test results. These are the factors examined in this paper.

Theoretical studies and numerical simulations on design, performance, and improvements of terahertz quantum-well photodetector (THz QWP) are presented. In the first part of this paper, we discuss the device band structure resulting from a self-consistent solution and simulation results. First, the temperature dependence of device characteristics is analyzed. Next, we deduce the condition of optimal doping concentration for maximizing dark current limited detectivity Ddet* when QWP is lightly doped. Accordingly, unlike in previously published reports, doping concentration is not fixed and is selected by the above condition. In the second part of this paper, we propose two schemes for improving operation temperature. The first is to incorporate an optical antenna which focuses incident THz wave. Numerical results show that the QWP with peak frequency higher than 5.5 THz is expected to achieve background-noise-limited performance at 77 K or above when employing a 106 times enhancement antenna. The second sch...