Dielectric Hole Research Articles

Experimental verification of guided-wave lumped circuits using dielectric rod

Abstract This paper presents a method to realize equivalent lumped inductance/capacitance by adjusting the relative permittivity, diameter, and offset of the dielectric rod. The dielectric rod is used to replace the traditional reactance matching elements (metallic diaphragm, pin, and resonant window) in the substrate integrated waveguide, which avoids the problem of short circuit in the upper and lower metal plate of the substrate integrated waveguide, and has the advantage of high regulatory freedom, low radiation loss, and low crosstalk. Based on this method, three air rod filters are designed and verified by experiments. The three filters are designed based on the diameter and offset of a single dielectric hole and the offset of symmetrical dielectric rods. Compared with conventional filters, this method greatly adjusts the degree of freedom of media regulation in the substrate integrated waveguide. The experimental results are in good agreement with theoretical analysis and simulation results. It provides an effective platform for the design of substrate integrated waveguide functional lumped circuits.

Dielectric Screening and Charge-Transfer in 2D Lead-Halide Perovskites for Reduced Exciton Binding Energies.

Layered lead-halide perovskites have shown tremendous success as an active material for optoelectronics. This is attributed to the electronic structure of the inorganic sublattice and large exciton binding energies due to quantum and dielectric confinement. Expanding functionalities for applications that depend on free-carrier generation requires new material design routes to decrease the binding energy. Here we use electronic structure methods with model Bethe-Salpeter equation (BSE) to examine the contributions of the dielectric screening and charge-transfer excited-states to the exciton binding energy of phenylethylammonium (PEA2PbBr4) and naphthlethylammonium (NEA2PbBr4) lead-bromide perovskites. Our model BSE calculations show that NEA introduces hole acceptor states which impose charge-transfer character on the exciton along with larger dielectric screening. This substantially decreases the exciton binding compared to PEA. This result suggests the use of organic cations with high dielectric screening and hole acceptor states as a viable strategy for reducing exciton binding energies in two-dimensional halide perovskites.

Deep Trap Boosted Ultrahigh Triboelectric Charge Density in Nanofibrous Cellulose-Based Triboelectric Nanogenerators

For their use in self-powered implantable or wearable electronics, cellulose nanofiber (CNF)-based triboelectric nanogenerators (TENGs) have drawn a lot of attention. However, the low triboelectric charge density (TECD) hinders its further application as a tribolayer for TENGs. In this work, a sulfonated cellulose nanofiber was prepared as an electropositive tribolayer for TENGs to obtain ultrahigh electrical output performance. Since the introduction of sulfonic acid effectively increased the dielectric properties and hole deep trap density of the CNF film, the triboelectric charge storage capacity of the CNF-SO3Na film was improved. The results showed that the TECD of the CNF-SO3Na film increased by 460% compared with the pristine CNF film. Furthermore, the dielectric constant and deep trap density of the CNF-SO3Na film increased by 2.4 times and 8.1 times. This work encourages the use of TENGs in real-world wireless transmission applications by outlining an easy and effective method for building high-performance TENGs.

3D Dirac semimetals supported tunable terahertz BIC metamaterials.

Based on the 3D Dirac semimetals (DSM) supported tilted double elliptical resonators, the tunable propagation properties of quasi-bound in continuum (BIC) resonance have been investigated in the THz regime, including the effects of rotation angles, DSM Fermi level, and the configuration of resonators. The results manifest that by altering the rotation angle of elliptical resonator, an obvious sharp BIC transmission dip is observed with the Q-factor of more than 60. The DSM Fermi level affects the BIC resonance significantly, a sharp resonant dip is observed if Fermi level is larger than 0.05eV, resulting from the contributions of reflection and absorption. If Fermi level changes in the range of 0.01-0.15eV, the amplitude and frequency modulation depths are 92.75 and 44.99%, respectively. Additionally, with the modified configurations of elliptical resonators, e.g. inserting a dielectric hole into the elliptical resonator, another transmission dip resonance is excited and indicates a red shift with the increase of the permittivity of the dielectric filling material. The results are very helpful to understand the mechanisms of DSM plasmonic structures and develop novel tunable THz devices, such as modulators, filters, and sensors in the future.

High-quality-factor Fano resonance and tunable light absorption based on diagonal circles of the bound state in the continuum

This study proposes a novel metasurface structure made of dielectric diagonal round holes. It is possible to achieve the quasi-bound state in the continuum (quasi-BIC) resonance modes with high Q-factors by introducing symmetry breaking into the unit structure. The quality factor and line width can be controlled by asymmetric parameters, which are the offset and radius size of the nano round hole. Additionally, adjustable light absorption can be achieved at the quasi-BIC resonance by doping graphene, which corresponds to the preeminent characteristic of graphene of enhancing light absorption. We conclude that the theoretical fitting results for the dissipation rate of the diagonal round holes (DRH) structure with or without graphene are consistent with the simulated quasi-BIC data. The proposed metasurfaces are more feasible and potentially useful compared to other complex nanostructures, as they may contribute to applications such as high-performance graphene-based devices.

Reconfigurable switching between reflecting/absorbing modes in VO2 assisted graphene-coated hemispherical dielectric hole arrays

In this paper, a graphene-coated dielectric hole array is used to design a reconfigurable switchable optical reflector/absorber device. The design benefits from the collective excitation of localized surface plasmon resonances of graphene-coated hole array, providing simpler fabrication fellow and more compact structure with respect to graphene-coated spherical nanoparticle array with similar plasmonic behavior. Geometrical parametric study of the reflecting mode shows that the device has lots of degrees of freedom for spectrum tuning and can highly tolerate fabrication imperfections. Moreover, the reflection rate is slightly affected by the dielectric substrate height, which can be tuned to achieve strong absorption by backing it with a metallic mirror. The designed absorber efficiently captures a wide range of obliquely incident transverse electric (TE) and transverse magnetic (TM) waves. Also, the operating frequency of both reflecting and absorbing modes can be tuned after fabrication, thanks to the two-dimensional nature of graphene material. Finally, using vanadium dioxide (VO2) phase change material, the switchable reflector\\absorber mode of the device is also exhibited.

Constructing thermal phonon insulators by using photonic crystals

This paper designs a thermal waveguide using thermal phonon insulators, to manipulate the loss of thermal radiation. Two-dimensional (2D) photonic crystals with dielectric background and air holes have been used in the waveguide clad to suppress thermal radiation so that thermal radiation cannot escape out from the waveguide clad. The photonic crystals may reduce the loss of thermal radiation through waveguide clad which surges the thermal energy confinement in the waveguide core and propagation along the longitudinal axis. The photonic crystals have been designed with the bandgap covering the thermal phonon frequency range and thus can be used to construct thermal phonon insulators to suppress or trap thermal emission generated through phonon wave propagation. The finite-difference-time-domain simulation results demonstrate that electromagnetic bandgap in photonic crystals has enough width in the thermal phonon frequency range to confine the thermal energy within the core of the waveguide and effective transmission of thermal radiation can be conquered within the waveguide core.

Electrostatic field simulations and dynamic Monte Carlo simulations of a nanodosimetric detector

Nanodosimetry uses physical quantities based on ionization cluster size distributions to model the biological effectiveness of different radiation qualities. A nanodosimetric detector in operation is the FIRE (Frequency of Ion Registration) detector, but further design optimization of the detector is required. The simulations presented in this work will help guide future developments of the detector.Within the FIRE detector, the produced ions drift towards a dielectric plate hole, within which they are strongly accelerated towards the cathode and produce an electron avalanche through impact ionization. The electron avalanche is measured at the signal readout. COMSOL Multiphysics was used to calculate the electrostatic fields and Garfield＋＋ was used to simulate ion drift trajectories and electron avalanche formation employing Monte Carlo methods.The dependency of electron avalanche formation on experimental parameters, such as pressure or electric field configuration, was studied and compared to experimental results. Based on the funneling effect ions experience within the drift region, a calculation method for obtaining an optimized hole pitch for future multi-hole detector designs was presented. The results presented in this work offer valuable insights into the inner workings of the FIRE detector, as well as make clarify how different experimental parameters influence signal creation.

Induced circular dichroism of achiral dielectric elliptical hole arrays with a monolayer borophene film.

Induced circular dichroism (ICD) is widely used in miniature polarizers, molecular detection, and negative refractive index media. However, enhancing and the dynamic regulation of ICD signals of achiral nanostructures in the visible and near-infrared range remain the current challenges. Here, monolayer borophene (MB) with anisotropic conductance was incorporated into achiral nanostructures, which consisted of achiral dielectric elliptical hole arrays (DENAs) placed on a silver substrate. Two narrowband ICD signals for DENAs/MB were achieved in the near-infrared range under different circularly polarized lights. The distributions of the magnetic field of DENAs/MB could explain the two narrowband ICD signals originating from the coupling of surface plasmon polariton resonances along the x- and y directions. Not only could the ICD signals be tuned by the structural parameters of DENAs/MB, but they could also be actively tuned by the incident angles of the excitation light and the carrier concentration of MB. In addition, the sensitivity and the figure of merit of DENAs/MB could reach 302/RIU and 61.0. These results provide a concise method for the design of dynamically adjustable chiral devices based on borophene and promote its application in molecular recognition and chiral catalysis.

Theoretical study on structural, excitonic and electronic properties of Nb2O5 with five crystal structures

Using the first-principles density functional theory, we have studied the structural, excitonic and electronic properties of Nb2O5 with five different crystal structures. In this paper, the structural characteristics of monoclinic, orthorhombic and tetragonal systems have been studied. Different from the classical layered structure, Nb2O5 is a layered shear structure composed of a certain number of NbO6 octahedrons. Exciton effect plays an important role in the physical process of semiconductor. The absorption and recombination of excitons directly affect the light absorption and luminescence of semiconductors. In order to explore the strength of exciton effect, the binding energy of exciton is calculated. By calculating the exciton binding energies, we found that the exciton binding energy for monoclinic Nb2O5 (the space group is C2/c) and orthorhombic Nb2O5 were as high as 69.611 and 75.548 meV. The high exciton binding energy is mainly due to the weak dielectric shielding ability and effective electron hole coulomb interaction. The microcosmic reasons for the difference of exciton binding energies in different crystal structures were analyzed by electrical properties. By analyzing the energy band diagram, it is found that the band gap is closely related to the excitonic binding energy. In general, the position of the atom, the shape of the energy band and the strength of the bond are all factors that contribute to the differences in exciton binding energy.

Mechanical spectral hole burning in glassy polymers-Investigation of polycarbonate, a material with weak β-relaxation.

Mechanical spectral hole burning (MSHB) has been used to investigate the nonlinear dynamics in polymers, ranging from melts, solutions, block co-polymers, and glasses. MSHB was developed as an analog to the dielectric spectral hole burning method, which is not readily applicable in polymers due to weak dielectric response. While similar holes were observed in both mechanical and dielectric hole burning, the interpretations were different. In the latter case, it has been argued that the holes are related to dynamic heterogeneity as related to an increase in the local temperature of molecular sub-ensembles (spatial heterogeneity), while in the former case, the holes have been related to the type of dynamics (rubbery, Rouse, etc.). Recent work from our laboratories used MSHB to investigate glassy poly(methyl methacrylate) and showed evidence of hole burning and supported the hypothesis that the origin of holes was related to dynamic heterogeneity as evidenced by the holes being developed near the strong β-relaxation in PMMA. In this work, MSHB is used to study polycarbonate, which has a weak β-relaxation, and the results are compared with those observed in PMMA. We observe that the polycarbonate exhibits weak holes and the nature of the holes with a change in pump amplitude and frequency is different than observed in PMMA. These results support the hypothesis that the hole burning observed in amorphous polymers below the glass transition temperature is related to the strength of the β-transition, which, in turn, is related to molecular level heterogeneity in the material dynamics.

Anthracene-Pentacene Dyads: Synthesis and OFET Characterization.

The synthesis of a series of unsymmetrical derivatives of pentacene appended with functionalized anthracene moieties is reported. These anthracene-pentacene dyads have been characterized by UV-vis spectroscopy and cyclic voltammetry to examine their electronic properties. X-ray crystallographic analysis was used to examine the solid-state features of anthracene-pentacene dyads 1 a-d with H-, F-, Cl-, and Br- substituents on the 9-position of anthracene, and shows that the packing arrangement of anthracene-pentacene derivatives 1 b,d,e are remarkably similar irrespective of the presence of fluoride, bromide or methyl substituents. The pentacene-anthracene dyads have been incorporated into OTFTs to evaluate their semiconducting properties. The pentacene derivative 1 b shows ambipolar behavior using AlOx C14 PA as the gate dielectric (electron and hole mobilities of 7.6 ⋅ 10-3 and 1.6 ⋅ 10-1 cm2 V-1 s-1 ), while performance of all derivatives was poor using p-doped Silicon as the substrate. These studies highlight the importance of thin-film formation over molecular structure.

Contribution of remote interface polar phonons in the hole mobility of diamond

The role of remote interface polar phonon modes on the electronic transport properties of dimensionally confined diamond structures have been investigated in detail. By employing a dielectric continuum model, scattering rates, hole mobility and relaxation times in mesoscopic diamond-based devices are calculated. The performance has been analyzed by inserting polar over layers on diamond with wide-band gap materials such as AlN or w − BN. We have shown that a Fröhlich potential due to the interface optical phonon modes in the upper layer is created, that decays into diamond resulting in the existence of a remote polar phonon potential in the material. Hole scattering from remote polar phonons dominate on the order of two or more in magnitude resulting in substantial decrease in hole mobility in diamond. Thus, the present research will provide a milestone for understanding interface phonons that penetrate to the two-dimensional hole gas (2DHG) in confined diamond structures as compared to their bulk counterpart and can also be applied to other polar materials used for doping.

Nickel-nanoparticles-assisted direct copper-electroplating on polythiophene conductive polymers for PCB dielectric holes

The pursuit for high throwing power (TP) in copper-hole metallization has been regarded as a major issue in the field of printed circuit boards (PCB). In this work, a membrane composed by polythiophene (PT) conductive polymers to replace electroless-plating copper layer is developed and investigated. High value of TP for dielectric holes on PCB is achieved by distributing nickel nanoparticles (NiNPs) on the PT membrane. During the electroplating process, NiNPs acting as seed clusters adsorb onto the surface of PT, effectively improve the copper electrocrystallization and thus increase the deposition rate of copper in the holes, enhancing TP of dielectric through-holes (THs) and filling rate of blind via. The results from morphological, electrical and thermal shock characterization validate that the copper layer formed by electroplating in the presence of NiNPs on the PT membrane has outstanding practical qualities.

The Effect of Density and Concentration of Trapping Centers on Charge Carrier Mobility in Polymer Dielectrics

The spectra of the currents of thermostimulated depolarization and the time dependences of the electret potential difference were measured in polymers irradiated with soft X-rays of electric gas discharge. The results of measurements are used to determining the mobility of electrons and holes in polymer cable and capacitor dielectrics having different values of density and concentration of electrically active trapping centers.

Two-Dimensional Multimode Terahertz Random Lasing with Metal Pillars

Random lasers employing multiple scattering and interference processes in highly disordered media have been studied for several decades. However, it remains a challenge to achieve a broadband multimode random laser with high scattering efficiency, particularly at long wavelengths. Here, we develop a new class of strongly multimode random lasers in the terahertz (THz) frequency range in which optical feedback is provided by multiple scattering from metal pillars embedded in a quantum cascade (QC) gain medium. Compared with the dielectric pillars or air hole approaches used in previous random lasers, metal pillars provide high scattering efficiency over a broader range of frequencies and with low ohmic losses. Complex emission spectra are observed with over 25 emission peaks across a 0.4 THz frequency range, limited primarily by the gain bandwidth of the QC wafer employed. The experimental results are corroborated by numerical simulations that show the lasing modes are strongly localized.

Internal current amplification induced by dielectric hole trapping in monolayer MoS2 transistor

Carrier transport in layered transition-metal dichalcogenides is highly sensitive to surrounding charges because of the atomically thin thickness. By exploiting this property, we report a new internal current amplification mechanism through positive feedback induced by dielectric hole trapping in a MoS2 back-gate transistor on a tantalum oxide substrate. The device exhibits an extremely steep subthreshold slope of 17 mV/decade, which is strongly dependent on the substrate material and drain bias. The steep subthreshold slope is attributed to the internal current amplification arising from the positive feedback between hole generation in MoS2 triggered by large lateral electric field and Schottky barrier narrowing induced by localized hole trapping in tantalum oxide near the source contact.

Single-pulse perforation of thin transparent dielectrics by femtosecond lasers

The methods of elongation of the effective interaction area (>100 microns) of single femtosecond pulses with transparent dielectrics when focusing in the bulk of material are given. Principal diagrams of transparent materials perforation with single femtosecond laser pulses are proposed. Capability to form cylindrical holes in the transparent dielectrics as a result of material photodegradation subjected to single femtosecond laser pulses was successfully demonstrated. The diameter of through holes made in the polypropylene 50 microns thick film at the energy of femtosecond laser pulses of 5 µJ was 5 µm.

Influence of interface structure on performance of organic field effect transistors

In organic field effect transistors (OFETs), charge transport in the conducting channel and charge injection from metal electrodes into the conducting channel is highly dependent on the quality and reliability of the insulator-organic semiconductor (OSC) and electrodes-OSC interfaces respectively. In this regard, the choice of the dielectric and the metal is as important as that of OSC. In this paper, simulation is performed using organic transistor modelling software for Rubrene based OFETs with different dielectric materials and metal contacts. Further, influence of interface traps at the insulator-OSC interface and impact of charge injection barrier and density of states (DOS) at the source electrode-OSC interface on OFETs electrical characteristics is studied. In addition, surface Fermi level pinning effect and influence of the semiconductor layer thickness is also discussed. The obtained simulation data shows that the results can be further improved by introducing high dielectric material and high work function hole injecting source/drain contacts. It is found that there is a reduction in the charge carrier mobility in disordered OSC with interface traps as compared to crystalline OSC without interface traps. Variation of both threshold voltage and practical onset voltage is observed due to the Fermi level pinning. Also, increase of threshold voltage is observed when non-linear injection occurs due to injection barrier. It is observed that the reduction of OSC layer thickness results in an increase in the drain current and variation of sub threshold slope. Steeper sub-threshold slope correlates to the lower trap density that results in better switching behaviour of OFETs. This simulation clarifies a number of issues that can help in design, fabrication and characterisation of organic electronic devices.

A Novel Multilayer Electromagnetic Bandgap Structure Composed of Square Rings as Microwave Guiding Structures

This paper presents a novel electromagnetic bandgap (EBG) structure composed of stacked U-shaped 3-D lattice of metallic open square rings and its potential application to selected waveguide configurations. Five key geometrical parameters are shown to impact the bandgap and modal structure of the EBG. Using this insight, we demonstrate two different configurations for line defect that realize guiding through the structure at Ku-band. The proposed EBG structure overcomes the fabrication complexity of conventional 2-D EBGs that are composed of dielectric rods or holes in a dielectric material. Selected EBG waveguide configurations with transitions to conventional microwave guiding structures are fabricated and tested.