High In-plane Research Articles

Collective Mie Resonances for Directional On-Chip Nanolasers.

A highly efficient nanocavity formed by optically coupled nanostructures is achieved by optimization of the collective Mie resonances in a one-dimensional array of semiconductor nanoparticles. Analysis of quasi-normal multipole modes enables us to reveal the close relation between the collective Mie resonances and Van Hove singularities. On the basis of these concepts, we experimentally demonstrate a directional GaAs nanolaser at cryogenic temperatures with well-defined, in-plane emission, which, moreover, can be controlled by selective excitation. The lasing threshold is shown to be significantly reduced by optimizing the interparticle gap such that the optimal near-field confinement is achieved at a resonant wavelength corresponding to the highest gain of GaAs. We show that the lasing performance of this nanolaser is orders of magnitude better than a nanowire-based laser of the same dimensions. The present work provides design guidelines for high performance in-plane emission nanolasers, which may find applications in future photonic integrated circuits.

Quantifying the spreading resistance of an anisotropic thin film conductor

Recently, highly anisotropic conductors, such as multilayer graphene, have been attracting much attention. The local resistivity can be determined by measuring the contact resistance; however, the theoretical expressions of contact resistance have been developed for isotropic slabs but have not been well developed for highly anisotropic film conductors. We obtain theoretical expressions of the spreading resistance below the circular contact for a highly anisotropic film on a bulk slab. The film spreading resistance of isotropic conductors deviates from the bulk spreading resistance when the film thickness is smaller than the contact radius. Nevertheless, the spreading resistance of anisotropic conducting films can be approximated by that of the bulk slabs even when the film thickness is smaller than the contact radius if the in-plane electrical conductivity is larger than the out-of-plane electrical conductivity. Owing to the high in-plane conductivity, the spreading resistance of anisotropic bulk conductors can be lowered from that predicted by the Holm’s equation obtained using the out-of-plane conductivity and the contact radius. We show that these characteristics are beneficial to use the highly anisotropic film as a cover layer when the in-plane conductivity of the film is high and the conductivity of the base slab is low.

Pressure tuning of structural and magnetic transitions in EuAg4As2

We report temperature dependent measurements of ambient pressure specific heat, magnetic susceptibility, anisotropic resistivity and thermal expansion as well as in-plane resistivity under pressure up to 20.8 kbar on single crystals of EuAg$_4$As$_2$. Based on thermal expansion and in-plane electrical transport measurements at ambient pressure this compound has two, first order, structural transitions in 80 - 120 K temperature range. Ambient pressure specific heat, magnetization and thermal expansion measurements show a cascade of up to seven transitions between 8 and 16 K associated with the ordering of the Eu$^{2+}$ moments. In-plane electrical transport is able to detect more prominent of these transitions: at 15.5, 9.9, and 8.7 K as well as a weak feature at 11.8 K at ambient pressure. Pressure dependent electrical transport data show that the magnetic transitions shift to higher temperatures under pressure, as does the upper structural transition, whereas the lower structural transition is suppressed and ultimately vanishes. A jump in resistivity, associated with the upper structural transition, decreases under pressure with an extrapolated disappearance (or a change of sign) by 30-35 kbar. In the 10 - 15 kbar range a kink in the pressure dependence of the upper structural transition temperature as well as the high and low temperature in-plane resistivities suggest that a change in the electronic structure may occur in this pressure range. The results are compared with the literature data for SrAg$_4$As$_2$.

A high transmittance and fast response in-plane switching liquid crystal display with the zero-azimuth anchoring layers on the electrodes

An in-plane switching (IPS) liquid crystal display (LCD) containing the zero-azimuth anchoring layers formed only on the electrodes and rubbed polyimide (PI) covered on the other areas was successfully developed. This configuration was realized using photoreactive PI with photo-radical generation units and the mask exposure technique. The maximum transmittance (Tmax) of this LCD was 1.12 times higher than that of a conventional IPS LCD. This was attributed to a large aperture in the voltage-on state because the nematic liquid crystals (NLCs) on the electrodes were barely anchored to the surface, such that the NLCs could be rotated by applying a small in-plane electric field above the electrodes, and by an elastic torque caused by the twisted NLCs between the electrodes. Furthermore, the response times of this LCD were equivalent to those of a conventional IPS LCD because the NLCs between the electrodes quickly recovered to their initial orientation after removing the electric field, and the NLCs on the electrodes followed this movement. This novel LCD is termed a ‘partially zero-azimuth anchoring IPS (PZ-IPS) LCD’, which is the first practical LCD utilizing these weak anchoring characteristics in the history of LCDs.

The High Anisotropy of the Epitaxial Growth of the Well-Aligned Sb2Se3 Nanoribbons on Mica.

One-dimensional semiconductor nanostructures, which are different from those of bulk materials, have attracted considerable interest in either scientific research or practical application. Herein, the Sb2Se3 nanoribbons have been successfully synthesized by the epitaxial growth process on mica using the rapid physical vapor deposition method. The density of the Sb2Se3 nanoribbons increased quickly when the temperature decreased, and finally, the nanoribbons connected to each other and formed a network structure even in film. These nanoribbons were all well aligned along the preferred direction that either is parallel to each other or forms 60° angles. Further structural investigation demonstrated that the Sb2Se3 nanoribbons grew along the [001] directions, which are aligned along the directions [11̅0] and [100] or [100] and [110] on the mica surface. Then, an asymmetric lattice mismatch growth mechanism causing incommensurate heteroepitaxial lattice match between the Sb2Se3 and mica crystal structure was suggested. Furthermore, a polarized photodetector based on the film with the well-aligned Sb2Se3 nanoribbons was constructed, which illustrated strong photosensitivity and high anisotropic in-plane transport either in the dark or under light. The incommensurate heteroepitaxial growth method shown here may provide access to realize well-ordered nanostructures of other inorganic materials and promote the anisotropic photodetector industrialization.

Earthquake-proof system for masonry infills in RC frame structures

The use of masonry infill walls in RC frame structures is common in many countries, even in seismically active areas, where the observations made after strong earthquakes have shown that masonry infills significantly modify the dynamic behaviour of the structure, thus causing total collapses of buildings and loss of human lives. The innovative system called Innovative Decoupled Infill System (INODIS) was developed with the aim to improve the behaviour of infilled RC frames by decoupling the frame and the masonry infill. Description of the system with the installation steps is given with the experimental tests showing that INODIS system highly reduces the activation of infills, thus enables reaching high in-plane drifts without having any damage and at the same time provides stable and reliable connection in out-of-plane direction. Also, the micro model showed that INODIS system improves the behaviour of AAC masonry infills by reducing the level of damage in the walls and postponing infill activation to higher drift levels.

A Study on Steel Plate Shear Wall

The main objective of this research study was to evaluate the parameters of stiffened and unstiffened steel plate shear wall under seismic loads. The scope of effort included simulating five unstiffened steel plate shear wall with varying thickness, three singly stiffened steel plate shear wall, and three doubly stiffened steel plate shear wall. The validation and simulation was done using software package ANSYS v16 using loads derived from ETABS. Overall, Unstiffened steel plate shear walls produced high in-plane and out of plane displacements which decreased with increase in thickness of plate; than singly stiffened followed by doubly stiffened steel plate shear walls. With introduction of stiffener in steel plate shear wall, the in-plane displacement values reduced by about 1%, and about 3% when doubly stiffened on the other hand the out of plane came down by 50% when stiffened singly and also when doubly stiffened. It was noteworthy that stiffener does not play any significant effect on any parameter except for out of plane displacement.

Numerical-Experimental Correlation of Interlaminar Damage Growth in Composite Structures: Setting Cohesive Zone Model Parameters

Composite laminates are characterized by high mechanical in-plane properties while experiencing, on the contrary, a poor out-of-plane response. The composite laminates, indeed, are often highly vulnerable to interlaminar damages, also called “delaminations.” One of the main techniques used for the numerical prediction of interlaminar damage onset and growth is the cohesive zone model (CZM). However, this approach is characterised by uncertainties in the definition of the parameters needed for the implementation of the cohesive behaviour in the numerical software. To overcome this issue, in the present paper, a numerical-experimental procedure for the calibration of material parameters governing the mechanical behaviour of CZM based on cohesive surface and cohesive element approaches is presented. Indeed, by comparing the results obtained from the double cantilever beam (DCB) and end-notched flexure (ENF) experimental tests with the corresponding numerical results, it has been possible to accurately calibrate the parameters of the numerical models needed to simulate the delamination growth phenomenon at coupon level.

Facile Liquid-Exfoliation Process of Boron Nitride Nanosheets for Thermal Conductive Polyphthalamide Composite.

In this study, we describe the fabrication of thermally conductive composites based on a polyphthalamide (PPA) matrix by the exfoliation of hexagonal BN nanosheets (BNNs) via the melt-mixing method. Boron nitride (BN) particles were hydroxyl groups surface-treated with sodium hydroxide (NaOH). Compared with existing BN peeling experiments, we successfully produced BNNs that are simpler, more economical, and have an excellent aspect ratio. For the same weight content of BN and BNNs, PPA/BN composites surface-treated with high aspect ratio BNNs have a high in-plane and through-plane thermal conductivity because of the intercalation of the hydroxyl group surface treatments between BN and PPA, which not only increases the wettability but also provides a good heat transfer path. Moreover, wide and thin BNNs are evenly dispersed inside the PPA/BN composite to provide excellent heat transfer paths in both in-plane and through-plane directions.

Flame-retardant poly(vinyl alcohol)/MXene multilayered films with outstanding electromagnetic interference shielding and thermal conductive performances

With the miniaturized and high-frequency development in electronic products, polymeric films synchronously with high electromagnetic interference (EMI) shielding effectiveness (SE) and thermal conductivity (TC) are urgently needed. In this work, poly (vinyl alcohol)/transition metal carbide (PVA/MXene) films featured with alternating multilayered structure were fabricated through multilayered casting. The continuous MXene layer provided a compact network for conducting heat and electron, endowing the multilayered film with excellent EMI SE and TC synchronously. In particular, the 27-μm-thick PVA/MXene multilayered film (containing 19.5 wt% MXene in total) exhibited an electrical conductivity of 716 S/m, a maximum EMI SE of 44.4 dB and a specific EMI SE (SSEt) of 9343 dB cm2 g−1. Meanwhile, the multilayered film showed a high in-plane TC of 4.57 W/mK, enhanced by almost 23-fold compared with that of neat PVA. Moreover, the multilayered architecture endowed the film with remarkable anti-dripping performance. This work provides a novel and feasible strategy for fabricating flame-retardant polymeric thermal conductive and EMI shielding films, which will have enormous prospect in advanced electrical devices.

Optical Contrast and Raman Spectroscopy Techniques Applied to Few-Layer 2D Hexagonal Boron Nitride.

The successful integration of few-layer thick hexagonal boron nitride (hBN) into devices based on two-dimensional materials requires fast and non-destructive techniques to quantify their thickness. Optical contrast methods and Raman spectroscopy have been widely used to estimate the thickness of two-dimensional semiconductors and semi-metals. However, they have so far not been applied to two-dimensional insulators. In this work, we demonstrate the ability of optical contrast techniques to estimate the thickness of few-layer hBN on SiO2/Si substrates, which was also measured by atomic force microscopy. Optical contrast of hBN on SiO2/Si substrates exhibits a linear trend with the number of hBN monolayers in the few-layer thickness range. We also used bandpass filters (500–650 nm) to improve the effectiveness of the optical contrast methods for thickness estimations. We also investigated the thickness dependence of the high frequency in-plane E2g phonon mode of atomically thin hBN on SiO2/Si substrates by micro-Raman spectroscopy, which exhibits a weak thickness-dependence attributable to the in-plane vibration character of this mode. Ab initio calculations of the Raman active phonon modes of atomically thin free-standing crystals support these results, even if the substrate can reduce the frequency shift of the E2g phonon mode by reducing the hBN thickness. Therefore, the optical contrast method arises as the most suitable and fast technique to estimate the thickness of hBN nanosheets.

Numerical–Experimental Correlation of Impact-Induced Damages in CFRP Laminates

Composite laminates are characterized by high mechanical in-plane properties and poor out-of-plane characteristics. This issue becomes even more relevant when dealing with impact phenomena occurring in the transverse direction. In aeronautics, Low Velocity Impacts (LVIs) may occur during the service life of the aircraft. LVI may produce damage inside the laminate, which are not easily detectable and can seriously degrade the mechanical properties of the structure. In this paper, a numerical-experimental investigation is carried out, in order to study the mechanical behavior of rectangular laminated specimens subjected to low velocity impacts. The numerical model that best represents the impact phenomenon has been chosen by numerical–analytical investigations. A user defined material model (VUMAT) has been developed in Abaqus/Explicit environment to simulate the composite intra-laminar damage behavior in solid elements. The analyses results were compared to experimental test data on a laminated specimen, performed according to ASTM D7136 standard, in order to verify the robustness of the adopted numerical model and the influence of modeling parameters on the accuracy of numerical results.

Flash foam stamp-inspired fabrication of flexible in-plane graphene integrated micro-supercapacitors on paper

Developing patterning techniques with practicability, cost-effectiveness and safety are essential for shape-confirmable integrated energy storage devices. Herein we design a novel flash foam stamp-inspired technique for simple fabrication of flexible high energy in-plane micro-supercapacitors based on interdigital electrodes of self-depositing electrochemically exfoliated graphene on paper substrates. This technique is an attractive and novel bottom-up microfabrication technology due to its advantages of simplicity and low-cost. These novelly developed all-solid-state, paper-based in-plane graphene micro-supercapacitors exhibit excellent electrochemical performances, such as high area specific capacitance of ∼4.02 mF cm−2 and excellent cycling stability (95.6% retention at 0.08 mA cm−2 for 5000 cycles). And these solid-state flexible micro-supercapacitors are observed non-obvious structural change and loss of performance under bending state, suggesting remarkable flexibility and mechanical stability. Therefore, such all-solid-state, flexible paper-based graphene micro-supercapacitors can potentially be used for wearable and portable electronics.

Distortion-free imaging: A double encoding method (DIADEM) combined with multiband imaging for rapid distortion-free high-resolution diffusion imaging on a compact 3T with high-performance gradients.

Distortion-free, high-resolution diffusion imaging using DIADEM (Distortion-free Imaging: A Double Encoding Method), proposed recently, has great potential for clinical applications. However, it can suffer from prolonged scan times and its reliability for quantitative diffusion imaging has not been evaluated. To investigate the clinical feasibility of DIADEM-based high-resolution diffusion imaging on a novel compact 3T (C3T) by evaluating the reliability of quantitative diffusion measurements and utilizing both the high-performance gradients (80 mT/m, 700 T/m/s) and the sequence optimization with the navigator acquisition window reduction and simultaneous multislice (multiband) imaging. Prospective feasibility study. Diffusion quality control phantom scans to evaluate the reliability of quantitative diffusion measurements; 36 normal control scans for B0 -field mapping; six healthy and two patient subject scans with a brain tumor for comparisons of diffusion and anatomical imaging. 3T; the standard single-shot echo-planar-imaging (EPI), multishot DIADEM diffusion, and anatomical (2D-FSE [fast-spin-echo], 2D-FLAIR [fluid-attenuated-inversion-recovery], and 3D-MPRAGE [magnetization prepared rapid acquisition gradient echo]) imaging. The scan time reduction, the reliability of quantitative diffusion measurements, and the clinical efficacy for high-resolution diffusion imaging in healthy control and brain tumor volunteers. Bland-Altman analysis. The scan time for high in-plane (0.86 mm2 ) resolution, distortion-free, and whole brain diffusion imaging were reduced from 10 to 5 minutes with the sequence optimizations. All of the mean apparent diffusion coefficient (ADC) values in phantom were within the 95% confidence interval in the Bland-Altman plot. The proposed acquisition with a total off-resonance coverage of 597.2 Hz wider than the expected bandwidth of 500 Hz in human brain could yield a distortion-free image without foldover artifacts. Compared with EPI, therefore, this approach allowed direct image matching with the anatomical images and enabled improved delineation of the tumor boundaries. The proposed high-resolution diffusion imaging approach is clinically feasible on C3T due to a combination of hardware and sequence improvements. 3 TECHNICAL EFFICACY: Stage 1 J. Magn. Reson. Imaging 2020;51:296-310.

Unprecedented Capacitance-Based Nondestructive Evaluation of Steels

This work reports for the first time capacitance-based nondestructive evaluation (NDE) of a monolithic metal, namely steel. This means that the structural material is self-sensing, without the need for embedded or attached sensors. The capacitance (2 kHz) can be through-thickness (involving sandwiching electrodes) or in-plane (involving coplanar electrodes), with the latter being superior for NDE, partly due to the relative permittivity being higher in-plane (2 × 106) than through-thickness (28), and partly due to the more effective spreading of the in-plane electric field lines between the coplanar electrodes than the spreading of the through-thickness field lines between the sandwiching electrodes. The fringing field serves as the probe for the flaws at various distances from the electrodes, which are much smaller in area than the specimen. Due to the electrical conductivity of the specimen and the fact that an LCR meter is not designed for measuring the capacitance of a conductive material, each electrode is separated from the specimen by a dielectric film. The conductivity of the specimen accentuates the fringing field. The flaws cause the apparent capacitance to increase, due to the increase in the effective area reached by the fringing field. The capacitance increases monotonically with increasing damage, except that it decreases when the damage in the form of through holes is severe enough to cause the permittivity to decrease. The defect sensing effectiveness is superior for low carbon steel than stainless steel, due to the higher electrical conductivity of low carbon steel and the consequent greater fringing field (current spreading).

A high speed X-Y nanopositioner with integrated optical motion sensing.

High speed in-plane (X-Y) nanopositioners are of central importance in scanning probe microscopy for performing fast imaging and manipulation. Reducing the size of the nanopositioning stage improves the response speed of the positioner but also introduces challenges in integration of conventional motion sensors. This paper presents the design and development of a novel high speed flexure-guided, piezo-electrically actuated nanopositioner with integrated optical beam deflection-based motion sensing. The sensing strategy eliminates spatial constraints even for small stages. A simple lumped-parameter model is proposed for the nanopositioner. Subsequently, the model is used to design and fabricate the nanopositioner. The measurement system is integrated with the nanopositioning stage and is employed to characterize the quasi-static and dynamic response of the stage. Finally, the in-plane motion measurements are employed to control the stage when it is commanded to track both slow- and fast-varying position signals. In both cases, the use of control is shown to significantly improve the tracking accuracy.

Realtime in-plane displacements tracking of the precision positioning stage based on computer micro-vision

Abstract This study presents a micro-vision-based measurement method for realtime and high accuracy in-plane displacements tracking of the precision positioning stage. In this method, to realize high magnification ratio and high video rate imaging of the measured stage’s surface, a micro-vision imaging system is established. In addition, an accelerated inverse optimized searching (AIOS) algorithm is developed in which an optimal template chosen (OTC) strategy and a piecewise update (PU) scheme are proposed and integrated with the IOS method to achieve template matching with high accuracy and high frame rate. Simulation studies are presented to demonstrate the validity of the OTC strategy, PU scheme, and AIOS algorithm, respectively. Experimental results demonstrate that the proposed method can effectively realize displacement measurement of the precision positioning stage at a frequency of hundreds Hertz with accuracy of nanometer degree.

Vibrational spectra of hydrogenated and halogenated graphene CX; X = H, F, Cl

In this paper, we investigate the Raman and infra-red (IR) spectra of fully hydrogenated and halogenated graphene in a chair, boat and washboard conformations. The IR spectra of chair conformations have two peaks due to Eu and phonons, while their Raman spectra have four peaks due to Eg and phonons. There are low and high frequency in-plane Eg phonons and out-of-plane phonons which give rise to four peaks in the Raman spectra. The optimized structures of the boat and washboard conformations of CH have different point group symmetries. The optical phonons of these conformations of CH are either IR active or Raman active. However, the optimized structures of the boat and washboard conformations of CF and CCl are a bit twisted and have the same (mm2) point group symmetries. In these conformations, there are four Raman active A2 phonons and several other A1, B1 and B2 phonons which are both Raman and IR active.

Binder-free heat dissipation films assembled with reduced graphene oxide and alumina nanoparticles for simultaneous high in-plane and cross-plane thermal conductivities

Binder-free layer-by-layer assembled multilayers consisting of reduced graphene oxide and alumina nanoparticles are prepared for implementing heat dissipation films with outstandingly high in-plane and cross-plane thermal conductivities.

Photovoltaic light valving induced in a vertically aligned nematic liquid crystal on a x-cut Fe:LiNbO3substrate

Abstract Photovoltaic fields induced in x-cut Fe-doped lithium niobate (Fe:LiNbO3)were used to achieve optically induced defect formation and light valving in a vertically aligned nematic liquid crystal. Initially, the optical axis of the LC was vertically aligned (along the surface-normal of the planar, photovoltaic substrates) throughout the whole sample. Samples were exposed with a focused continuous wave laser beam and investigated via microscopic imaging in-between crossed polarizers. The optical axis of the planar, x-cut Fe:LiNbO3 substrates was in the substrate plane and oriented parallel to one of the polarizers, which resulted in an initially dark state. Optically induced surface fields (with high in-plane components) generated within the substrates led to director reorientations and defect formation. Accordingly, the samples were locally switched into a transmissive state. The area affected by exposure was larger (300 μm) than the FWHM of the Gaussian exposure beam (14 μm). Switching from dark to bright states (light valving) could be achieved in the investigated samples much more eficiently than in previously investigated samples with z-cut Fe:LiNbO3-substrates. Realignments of the LC director were induced at lower optical power density (140 mW/cm2) than would be required to excite the intrinsically present nonlinear optical responses in a nematic LC such as the light induced Fredericks transition.