In-plane Modulation Research Articles

π Phase Interlayer Shift and Stacking Fault in the Kagome Superconductor CsV_{3}Sb_{5}.

The stacking degree of freedom is a crucial factor in tuning material properties and has been extensively investigated in layered materials. The kagome superconductor CsV_{3}Sb_{5} was recently discovered to exhibit a three-dimensional CDW phase below T_{CDW}∼94 K. Despite the thorough investigation of in-plane modulation, the out-of-plane modulation has remained ambiguous. Here, our polarization- and temperature-dependent Raman measurements reveal the breaking of C_{6} rotational symmetry and the presence of three distinct domains oriented at approximately 120° to each other. The observations demonstrate that the CDW phase can be naturally explained as a 2c staggered order phase with adjacent layers exhibiting a relative π phase shift. Further, we discover a first-order structural phase transition at approximately 65K and suggest that it is a stacking order-disorder phase transition due to stacking fault, supported by the thermal hysteresis behavior of a Cs-related phonon mode. Our findings highlight the significance of the stacking degree of freedom in CsV_{3}Sb_{5} and offer structural insights to comprehend the entanglement between superconductivity and CDW.

Task-based detectability in anatomical background in digital mammography, digital breast tomosynthesis and synthetic mammography

Objective. Determining the detectability of targets for the different imaging modalities in mammography in the presence of anatomical background noise is challenging. This work proposes a method to compare the image quality and detectability of targets in digital mammography (DM), digital breast tomosynthesis (DBT) and synthetic mammography. Approach. The low-frequency structured noise produced by a water phantom with acrylic spheres was used to simulate anatomical background noise for the different types of images. A method was developed to apply the non-prewhitening observer model with eye filter (NPWE) in these conditions. A homogeneous poly(methyl) methacrylate phantom with a 0.2 mm thick aluminium disc was used to calculate 2D in-plane modulation transfer function (MTF), noise power spectrum (NPS), noise equivalent quanta, and system detective quantum efficiency for 30, 50 and 70 mm thicknesses. The in-depth MTFs of DBT volumes were determined using a thin tungsten wire. The MTF, system NPS and anatomical NPS were used in the NPWE model to calculate the threshold gold thickness of the gold discs contained in the CDMAM phantom, which was taken as reference. Main results. The correspondence between the NPWE model and the CDMAM phantom (linear Pearson correlation 0.980) yielded a threshold detectability index that was used to determine the threshold diameter of spherical microcalcifications and masses. DBT imaging improved the detection of masses, which depended mostly on the reduction of anatomical background noise. Conversely, DM images yielded the best detection of microcalcification s. Significance. The method presented in this study was able to quantify image quality and object detectability for the different imaging modalities and levels of anatomical background noise.

The future of photonic crystal surface-emitting lasers

Semiconductor lasers are the heart for the development of technologies in many fields. In recent decades, a new type of large-area surface-emitting lasers based on the in-plane photonic crystal modulation and feedback have emerged to show superior advantages of high output power, low-divergence, high beam quality and brightness, and compact and monolithic structure. In this paper, we review the design and development of photonic crystal surface-emitting laser and discuss the future investigation and improvements.

Self-powered MSM solar-blind AlGaN photodetector realized by in-plane polarization modulation.

Solid-state self-powered UV detection is strongly required in various application fields to enable long-term operation. However, this requirement is incompatible with conventionally used metal-semiconductor-metal (MSM) UV photodetectors (PDs) due to the symmetric design of Schottky contacts. In this work, a self-powered MSM solar-blind UV-PD was realized using a lateral pn junction architecture. A large built-in electric field was obtained in the MSM-type UV-PD without impurity doping, leading to efficiency carrier separation and enhanced photoresponsivity at zero external bias. The solar-blind UV-PD exhibits a cutoff wavelength of 280 nm, a photo/dark current ratio of over 105, and a responsivity of 425.13 mA/W at -10 V. The mechanism of self-powered UV photodetection was further investigated by TCAD simulation of the internal electric field and carrier distributions.

Synergistic creation of highly stable strain-insensitive pressure sensors by in-plane strain modulation and quasi-homogenous interfacial design

The urgent requirement of electronic skin conformably attached to nonplanar surfaces to provide stable monitoring in areas of healthcare, prosthetics, and robotics promotes the development of strain-insensitive/unperturbed pressure sensors. The main challenges lie in: (1) stretchability and conductive stability of flexible electrodes and (2) mechanical stability of heterogeneous interfaces. This study presents a highly stable strain-insensitive pressure sensor achieved by in-plane strain modulation and quasi-homogenous interfacial design. Strain modulation of stretchable electrodes by both periodic microstructured engineering and pre-stretching strategies (called “island-ripple”) was employed to suppress microcracks propagation. The improvement in stretchability and cyclic conductive stability of electrodes was identified by finite element analysis and experimental verification. The pre-stretched microconed stretchable electrode with a low sheet resistance of 0.546 Ω sq−1 shows a maximum deformation of up to 80% and excellent cyclic conductive stability over 10000 times under 30% strain. Quasi-homogenous interface strategy by the CNTs/PDMS system was employed to enhance the mechanical and electrical stability of the electrode-active materials interface, demonstrating a strong peel strength and shear strength of >40.9 N/m and >124.8 kPa, respectively. The as-prepared strain-insensitive pressure sensor provides constant sensing performance over 5000 stretching-releasing cycles within 20% stretching. In addition, a 4 × 4 pixel strain-insensitive pressure sensor array with reduced cross-talk circuit design was further integrated to identify the shape and weight of different objects under strains. The stretchability and stability of our sensor enable it to be applied in stretchable electronics with great potential.

Organic electrochemical transistors as on-site signal amplifiers for electrochemical aptamer-based sensing

Electrochemical aptamer-based sensors are typically deployed as individual, passive, surface-functionalized electrodes, but they exhibit limited sensitivity especially when the area of the electrode is reduced for miniaturization purposes. We demonstrate that organic electrochemical transistors (electrolyte gated transistors with volumetric gating) can serve as on-site amplifiers to improve the sensitivity of electrochemical aptamer-based sensors. By monolithically integrating an Au working/sensing electrode, on-chip Ag/AgCl reference electrode, and Poly(3,4-ethylenedioxythiophene)-poly(styrenesulfonate) counter electrode — also serving as the channel of an organic electrochemical transistor— we can simultaneously perform testing of organic electrochemical transistors and traditional electroanalytical measurement on electrochemical aptamer-based sensors including cyclic voltammetry and square-wave voltammetry. This device can directly amplify the current from the electrochemical aptamer-based sensor via the in-plane current modulation in the counter electrode/transistor channel. The integrated sensor can sense transforming growth factor beta 1 with 3 to 4 orders of magnitude enhancement in sensitivity compared to that in an electrochemical aptamer-based sensor (292 μA/dec vs. 85 nA/dec). This approach is believed to be universal, and can be applied to a wide range of tethered electrochemical reporter-based sensors to enhance sensitivity, aiding in sensor miniaturization and easing the burden on backend signal processing.

Ordered-Range Tuning of Flash Graphene for Fast-Charging Lithium-Ion Batteries

Graphene has yet to be mass produced, so practical fast-charging lithium-ion battery (LIB) prototypes based on graphene are scarce. Graphene suffers from long in-plane and reluctant in-depth lithium diffusion due to its defect-free atomic arrangement, resulting in unsatisfactory rate performance as LIB anodes. In this work, combinatorial flash joule heating and ball milling treatment are implemented to enable gram-scale production of graphene in seconds (known as flash graphene, FG) and in-plane ordered-range modulation of graphene architectures. Following the ball milling, the defect-deficient turbostratic FG is transformed to defect-rich cracked FG (CFG), which has shortened ordered ranges and larger interlayer spacings. The CFG anode outperforms FG, commercial carbon black, and graphite electrodes in terms of specific capacity and rate performance due to open channels and shortened pathways for Li+ transport. Moreover, it shows outstanding cycling stability with a high capacity retention of 99% at the 500th cycle. Furthermore, it works well with the LiFePO4 cathode, enabling fast-charging LIB full battery with a state of charge of 77 and 62% at 2C and 4C, respectively. This research on graphene production and structural engineering provides a practical application for the commercial potential of fast-charging LIBs.

Enhanced light output from deep ultraviolet light-emitting diodes enabled by high-order modes on a photonic crystal surface.

The authors demonstrate the enhanced light output from 275-nm AlGaN-based deep ultraviolet (DUV) light-emitting diode (LED) structures via the in-plane modulation of shallow photonic crystal (PC) patterns that were fabricated on the p-AlGaN contact layer surface. The employed PC lattice constants are in the range of 270-780 nm, much larger than the fundamental Bragg order lattice constant (∼95 nm). As compared to the unpatterned sample, the intensity of the top (or bottom) emission can be enhanced by up to 331% (or 246%), attributed to the high-order coherent diffraction of the internal trapped light and also the Purcell enhancement of spontaneous emission. The findings in this Letter suggest an easier way for the realization of more energy-efficient DUV LEDs which offer the advantage of high emission for various applications in disinfection and sterilization.

Kerker Effects and Bound States in the Continuum in PT-Symmetric Dielectric Metasurfaces

We investigate the light transmission and reflection spectra of parity-time (PT) symmetric dielectric metasurfaces composed of high refractive index nanostructures with in-plane gain-loss modulation through the scattering matrix and semianalytical Cartesian multipoles methods. We find that the Kerker effects, i.e., the strong forward-to-backward asymmetric scattering originating from overlapping the electric and magnetic multipolar resonances, can be tailored by the gain and loss. In addition, we observe another kind of high-Q resonances, i.e., quasi-bound states in the continuum which couple to the electric and magnetic multipolar radiations, in the transmission and reflection spectra with different incident polarizations lights by manipulating the gain and loss in the metasurfaces. Our results suggest the ways to achieve Kerker effects and engineer the resonances in non-Hermitian metasurfaces for many practical applications in nanophotonics.

Effect of optical blurring of X-ray source on breast tomosynthesis image quality: Modulation transfer function, anatomical noise power spectrum, and signal detectability perspectives

We investigated the effect of the optical blurring of X-ray source on digital breast tomosynthesis (DBT) image quality using well-designed DBT simulator and table-top experimental systems. To measure the in-plane modulation transfer function (MTF), we used simulated sphere phantom and Teflon sphere phantom and generated their projection data using two acquisition modes (i.e., step-and-shoot mode and continuous mode). After reconstruction, we measured the in-plane MTF using reconstructed sphere phantom images. In addition, we measured the anatomical noise power spectrum (aNPS) and signal detectability. We constructed simulated breast phantoms with a 50% volume glandular fraction (VGF) of breast anatomy using the power law spectrum and inserted spherical objects with 1 mm, 2 mm, and 5 mm diameters as breast masses. Projection data were acquired using two acquisition modes, and in-plane breast images were reconstructed using the Feldkamp-Davis-Kress (FDK) algorithm. For the experimental study, we used BR3D breast phantom with 50% VGF and obtained projection data using a table-top experimental system. To compare the detection performance of the two acquisition modes, we calculated the signal detectability using the channelized Hotelling observer (CHO) with Laguerre-Gauss (LG) channels. Our results show that spatial resolution of in-plane image in continuous mode was degraded due to the optical blurring of X-ray source. This blurring effect was reflected in aNPS, resulting in large β values. From a signal detectability perspective, the signal detectability in step-and-shoot mode is higher than that in continuous mode for small spherical signals but not large spherical signals. Although the step-and-shoot mode has disadvantage in terms of scan time compared to the continuous mode, scanning in step-and-shoot mode is better for detecting small signals, indicating that there is a tradeoff between scan time and image quality.

Magnetically driven in-plane modulation of the 3D orientation of vertical ferromagnetic flakes.

External magnetic fields are known to attract and orient magnetically responsive colloidal particles. In the case of 2D microplatelets, rotating magnetic fields are typically used to orient them parallel to each other in a brick-and-mortar fashion. Thanks to this microstructure, the resulting composites achieve enhanced mechanical and functional properties. However, parts with complex geometries require their microstructure to be specifically tuned and controlled locally in 3D. Although the tunability of the microstructure along the vertical direction has already been demonstrated using magnetic orientation combined with sequential or continuous casting, controlling the particle orientation in the horizontal plane in a fast and effective fashion remains challenging. Here, we propose to use rotating magnetic arrays to control the in-plane orientation of ferromagnetic nickel flakes distributed in curable polymeric matrices. We experimentally studied the orientation of the flakes in response to magnets rotating at various frequencies and precessing angles. Then, we used COMSOL to model the magnetic field from rotating magnetic arrays and predicted the resulting in-plane orientations. To validate the approach, we created composites with locally oriented flakes. This work could initiate reverse-engineering methods to design the microstructure in composite materials with intricate geometrical shapes for structural or functional applications.

Coiling-Up Space Metasurface for High-Efficient and Wide-angle Acoustic Wavefront Steering

The recent advent of acoustic metasurface displays tremendous potential with their unique and flexible capabilities of wavefront manipulations. In this paper, we propose an acoustic metagrating made of binary coiling-up space structures to coherently control the acoustic wavefront steering. The acoustic wave steering is based on the in-plane coherent modulation of waves in different diffraction channels. The acoustic metagrating structure with a subwavelength thickness is realized with 3D printed two coiling-up space metaunits. By adjusting structural parameters of the metaunits, the −1st-order diffraction mode can be retained, and the rest of the diffraction orders are eliminated as much as possible through destructive interference, forming a high-efficiency anomalous reflection in the scattering field. The anomalous reflection performance of the designed metagrating is achieved over a wide range of incident angles with high efficiency.

Freestanding multi-gate IZO-based neuromorphic transistors on composite electrolyte membranes

Brain-inspired neuromorphic computing would bring a breakthrough to the classical computing paradigm through its massive parallelism and potential low power consumption advantages. Introduction of flexibility may bring vitality to this area by expanding its application areas to such as wearable and implantable electronics. At present, the development of flexible neuromorphic devices makes it a choice with wide prospect for next-generation wearable artificial neuromorphic computing. In this study, a freestanding graphene oxide/polyvinyl alcohol composite solid electrolyte membrane is utilized as the gate dielectric and support material, and indium-zinc-oxide (IZO) neuromorphic transistors are fabricated on such membrane. Based on the in-plane gate modulation, many key synaptic plasticity behaviors have been successfully emulated, including excitatory postsynaptic current, paired-pulse facilitation, high-pass filtering, and spatiotemporal signal processing. Moreover, transition of the spiking logic and the superlinear and sublinear dendritic integration function are realized. Our results indicate that these freestanding IZO-based neuromorphic transistors may of great significance for future flexible anthropomorphic robots, wearable bionic perception.

Crystal Field Effect and Electric Field Screening in Multilayer Graphene with and without Twist.

We address the intrinsic polarization and screening of an external electric field in a broad range of ordered and twisted configurations of multilayer graphene, using an ab initio approach combining density functional theory and the Wannier function formalism. We show that multilayer graphene is intrinsically polarized due to the crystal field effect, an effect that is often neglected in tight-binding models of twisted bilayer graphene and similar systems. This intrinsic polarization of the order of up to a few tens of millielectronvolts has different out-of-plane alignments in ordered and twisted graphene multilayers, while the in-plane potential modulation is found to be much stronger in twisted systems. We further investigate the dielectric permittivity ε in same multilayer graphene configurations at different electric field strengths. Our findings establish a deep insight into intrinsic and extrinsic polarization in graphene multilayers and provide parameters necessary for building accurate models of these systems.

Polarization-differentiated band dynamics of resonant leaky modes at the lattice Γ point.

In the physical description of photonic lattices, leaky-mode resonance and bound states in the continuum are central concepts. Understanding of their existence conditions and dependence on lattice parameters is of fundamental interest. Primary leaky-wave effects are associated with the second stop band at the photonic lattice Γ point. The pertinent band gap is defined by the frequency difference between the leaky-mode band edge and the bound-state edge. This paper address the polarization properties of the band gaps resident in laterally periodic one-dimensional photonic lattices. We show that the band gaps pertinent to TM and TE leaky modes exhibit significantly differentiated evolution as the lattice parameters vary. This is because the TM band gap is governed by a surface effect due to the discontinuity of the dielectric constant at the interfaces of the photonic lattice as well as by a Bragg effect due to the periodic in-plane dielectric constant modulation. We find that when the lattice is thin (thick), the surface (Bragg) effect dominates the Bragg (surface) effect in the formation of the TM band. This leads to complex TM band dynamics with multiple band closures possible under parametric variation. In complete contrast, the TE band gap is governed only by the Bragg effect thus exhibiting simpler band dynamics. This research elucidates the important effect of polarization on resonant leaky-mode band dynamics whose explanation has heretofore not been available.

Gigapixel and 1440-perspective extended-angle display by megapixel MEMS-SLM.

Orders-of-magnitude increases are desired in the pixel count and density of spatial light modulators (SLMs) for next-gen displays. We present in-plane and simultaneous angular-spatial light modulation by a micro electro mechanical system (MEMS)-based SLM, a digital micromirror device (DMD), to generate gigapixel output by time and angular multiplexing. Pulsed illumination synchronized to the micromirror actuation achieves pixel-implemented and diffraction-based angular modulation, and source multiplexing increases angular selectivity. We demonstrate 1440-perspective image output across a 43.9∘×1.8∘ FOV, 8-bit multi-perspective videos at 30 FPS, and multi-focal-plane image generation. We discuss scalability to terapixels and implications for near-to-eye displays.

In-plane image quality and NPWE detectability index in digital breast tomosynthesis

A rigorous 2D analysis of signal and noise transfer applied to reconstructed planes in digital breast tomosynthesis (DBT) is necessary for system characterization and optimization. This work proposes a method for assessing technical image quality and system detective quantum efficiency (DQEsys) for reconstructed planes in DBT. Measurements of 2D in-plane modulation transfer function (MTF) and noise power spectrum (NPS) were made on five DBT systems using different acquisition parameters, reconstruction algorithms and plane spacing. This work develops the noise equivalent quanta (NEQ), DQEsys and detectability index (d’) calculated using a non-prewhitening model observer with eye filter (NPWE) for reconstructed DBT planes. The images required for this implementation were acquired using a homogeneous test object of thickness 40 mm poly(methyl) methacrylate plus 0.5 mm Al; 2D MTF was calculated from an Al disc of thickness 0.2 mm and diameter 50 mm positioned within the phantom. The radiant contrast of the MTF disc and the air kerma at the system input were used as normalization factors. The NPWE detectability index was then compared to the in-plane contrast-detail (c-d) threshold measured using the CDMAM phantom.The MTF and NPS measured on the different systems showed a strong anisotropy, consistent with the cascaded models developed in the literature for DBT. Detectability indices calculated from the measured MTF and NPS successfully predicted changes in c-d detectability for details between 0.1 mm and 2.0 mm, for DBT plane spacings between 0.5 mm and 10 mm, and for air kerma values at the system input between 157 µGy and 1170 μGy. The linear Pearson correlation between the detectability index and threshold gold thickness of the CDMAM phantom was −0.996. The method implements a parametric means of assessing the technical image quality of reconstructed DBT planes, providing valuable information for optimization of DBT systems.

The lipid composition affects Trastuzumab adsorption at monolayers at the air-water interface

Trastuzumab (Tmab), an antibody for breast cancer, was incorporated in Langmuir monolayers with different lipidic compositions to investigate the drug action in lipidic interfaces of pharmaceutical interest. Tmab caused all lipid films to expand as confirmed with by surface pressure-area isotherm, proving its incorporation. It also affected the compressional and structural properties as observed by in-plane elasticity curves and polarization modulation reflection-absorption infrared spectroscopy (PM-IRRAS), respectively. Although Tmab did not change significantly the compressional modulus for dipalmitoylphosphatidylcholine (DPPC) monolayers, it decreased it for the mixtures of DPPC with cholesterol. In contrast, for dipalmitoylphosphoethanolamine (DPPE), Tmab increased the compressional modulus for both monolayers, pure DPPE or mixed with cholesterol. While Brewster Angle Microscopy showed discrete distinctive morphological patterns for the monolayers investigated, PM-IRRAS showed that Tmab caused an increased number of gauche conformers related to the CH2 stretching mode for the lipid acyl chains, suggesting molecular disorder. Furthermore, the antibody kept the β-sheet structure of the polypeptide backbone adsorbed at the lipid monolayers although the secondary conformation altered according to the film composition at the air-water interface. As a result, the results suggest that the membrane lipid profile affects the adsorption of Tmab at lipid monolayers, which can be important for the incorporation of this drug in lipidic supramolecular systems like in liposomes for drug delivery and in biomembranes.

Measurement of the third order nonlinear susceptibility of paratellurite single crystal using multiplex CARS

We report the extraction of the real part of the third order nonlinear susceptibility for a c-cut paratellurite (TeO2 − α) single crystal using the nonresonant contribution of the multiplex coherent anti-Stokes Raman scattering (M-CARS) signal. Using fused silica and SF57 as nonlinear reference materials, we derive the absolute value of the real part of the electronic third order susceptibility and we evidence the in-plane modulation of the nonlinear refractive index. These results are in total agreement with those recently obtained by the z-scan method.

Skyrmion lattice with a giant topological Hall effect in a frustrated triangular-lattice magnet.

Geometrically frustrated magnets can host complex spin textures, leading to unconventional electromagnetic responses. Magnetic frustration may also promote topologically nontrivial spin states such as magnetic skyrmions. Experimentally, however, skyrmions have largely been observed in noncentrosymmetric lattice structures or interfacial symmetry-breaking heterostructures. Here, we report the emergence of a Bloch-type skyrmion state in the frustrated centrosymmetric triangular-lattice magnet Gd2PdSi3 We observed a giant topological Hall response, indicating a field-induced skyrmion phase, which is further corroborated by the observation of in-plane spin modulation probed by resonant x-ray scattering. Our results may lead to further discoveries of emergent electrodynamics in magnetically frustrated centrosymmetric materials.