Ideal 3D Research Articles

Complete list of valley linear Weyl point phonons in two dimensions

The discovery of topological quantum states in two-dimensional (2D) systems is one of the most promising advancements in condensed matter physics. Linear Weyl point (LWP) phonons have been theoretically investigated in some 2D materials. Especially, Jin, Wang, and Xu [Nano Lett. 18, 7755 (2018)] proposed in 2018 that the candidates with threefold rotational symmetry at the corners of the hexagonal Brillouin zone can host LWP phonons with a quantized valley Berry phase. Note that all the candidates with hexagonal lattices may not host LWP phonons at $K$ (${K}^{\ensuremath{'}}$) high-symmetry points (HSPs). Hence a strategy for narrowing the search range for LWP phonons in 2D is highly required. This work provides an exhaustive list of valley LWP phonons at HSPs in 2D by searching the entire 80 layer groups (LGs). We found that the valley LWP phonons can be obtained at HSPs in 11 of the 80 LGs. Guided by the symmetry analysis, we also contributed to realizing the ideal 2D material with valley LWP phonons. We identified the existence of the valley LWP phonons in 11 2D material candidates with 11 LGs. This work offers a method to search for valley LWPs in 2D phononic systems and proposes 2D material candidates to obtain the valley LWP phonons.

Absence of edge reconstruction for quantum Hall edge channels in graphene devices.

Quantum Hall (QH) edge channels propagating along the periphery of two-dimensional (2D) electron gases under perpendicular magnetic field are a major paradigm in physics. However, groundbreaking experiments that could use them in graphene are hampered by the conjecture that QH edge channels undergo a reconstruction with additional nontopological upstream modes. By performing scanning tunneling spectroscopy up to the edge of a graphene flake on hexagonal boron nitride, we show that QH edge channels are confined to a few magnetic lengths at the crystal edges. This implies that they are ideal 1D chiral channels defined by boundary conditions of vanishing electronic wave functions at the crystal edges, hence free of electrostatic reconstruction. We further evidence a uniform charge carrier density at the edges, incompatible with the existence of upstream modes. This work has profound implications for electron and heat transport experiments in graphene-based systems and other 2D crystalline materials.

Time reversed states in barrier tunneling

Tunneling, though a physical reality, is shrouded in mystery. Wave packets cannot be constructed under the barrier and group velocity cannot be defined. The tunneling particle can be observed on either sides of the barrier but its properties under the barrier has never been probed due to several problems related to quantum measurement. We show that there are ways to bypass these problems in mesoscopic systems and one can even derive an expression for the quantum mechanical current under the barrier. A general scheme is developed to derive this expression for any arbitrary system. One can use mesoscopic phenomenon to subject the expression to several theoretical and experimental cross checks. For demonstration we consider an ideal 1D quantum ring with Aharonov-Bohm flux $\Phi$, connected to a reservoir. It gives clear evidence that propagation occur under the barrier resulting in a current that can be measured non-invasively and theoretically cross checked. Time reversed states play a role but there is no evidence of violation of causality. The evanescent states are known to be largely stable and robust against phase fluctuations making them a possible candidate for device applications and so formalizing current under barrier is important.

Analytical model for three-dimensional light-field displays based on voxel construction

Three-dimensional light-field displays (3D-LFDs) can provide viewers with glass-free 3D images. The display effect of reconstructed 3D images is closely related to the number of 3D object points that the 3D display system can construct, which can be regarded as the information quantity of the 3D-LFDs. However, the information quantity presented by a 3D-LFD is limited by fixed hardware parameters such as display panels and optical components. It is difficult to present an ideal 3D visual experience with the increase in display depth. In this paper, an analytical model based on voxel construction for 3D-LFDs is proposed, which can estimate the information quantity that a 3D-LFD can reproduce. The variation regularity of information quantity with display depth is analyzed and the influence of hardware parameters on display effect is discussed. With the proposed strategies, the display effect can be improved in a targeted manner without blurring and aliasing by adjusting the hardware parameters in display systems and matching the information quantity at different display depths.

Topology Hierarchy of Transition Metal Dichalcogenides Built from Quantum Spin Hall Layers.

The evolution of the physical properties of two-dimensional material from monolayer limit to the bulk reveals unique consequences from dimension confinement and provides a distinct tuning knob for applications. Monolayer 1T'-phase transition metal dichalcogenides (1T'-TMDs) with ubiquitous quantum spin Hall (QSH) states are ideal two-dimensional building blocks of various three-dimensional topological phases. However, the stacking geometry was previously limited to the bulk 1T'-WTe2 type. Here, we introduce the novel 2M-TMDs consisting of translationally stacked 1T'-monolayers as promising material platforms with tunable inverted bandgaps and interlayer coupling. By performing advanced polarization-dependent angle-resolved photoemission spectroscopy as well as first-principles calculations on the electronic structure of 2M-TMDs, we revealed a topology hierarchy: 2M-WSe2 , MoS2, and MoSe2 are weak topological insulators (WTIs), whereas 2M-WS2 is a strong topological insulator (STI). Further demonstration of topological phase transitions by tunning interlayer distance indicates that band inversion amplitude and interlayer coupling jointly determine different topological states in 2M-TMDs. We propose that 2M-TMDs are parent compounds of various exotic phases including topological superconductors and promise great application potentials in quantum electronics due to their flexibility in patterning with two-dimensional materials. This article is protected by copyright. All rights reserved.

Development of Three-Dimensional Breast Scan and Measurement Application Using Laser Imaging Detection and Ranging Sensor on iPhone.

Laser imaging detection and ranging (LiDAR) is a modern three-dimensional (3D) technology that uses a time-of-flight method based on the round-trip time of an infrared laser beam to detect the presence and features of objects. The iPhone 12 Pro is the first smart mobile device with built-in LiDAR sensors. The authors' team developed a software application based on iOS devices with built-in LiDAR sensors for 3D breast scanning and automatically analyzing the breast's geometric measurement. Breast geometry, including midclavicle-to-nipple distance, sternal notch-to-nipple distance, nipple-to-inframammary fold (IMF) distance, distance between nipples, and body circumference on nipple and IMF level were measured using the software application and tapeline. The relative technical error of measurement (rTEM) value was used to calculate the error ratios between the measurements acquired by the software application and those of the tapeline. Good rTEM values ranging from 2.99% to 5.19% were found in the midclavicle-to-nipple distance, sternal notch-to-nipple distance, distance between nipples, nipple-level circumference, and IMF-level circumference. However, there was a poor rTEM value greater than 10% in the nipple-to-IMF distance. The proposed software application using current iOS devices with built-in LiDAR sensors can provide an ideal 3D scanning system that has a low cost burden, good accuracy, portability, and ease of use.

Mesh generation for underwater acoustic modeling with KRAKEN

Underwater sound modeling is applied in several environmental studies, from assessing underwater noise induced by offshore wind farms to the influence of climate change on ocean temperature. One of the most well-known underwater acoustics models is KRAKEN, an open-source code requiring a mesh to simulate 3D environments. This paper presents OMesh2KRAKEN, a software toolkit that uses OceanMesh2D to generate unstructured meshes for KRAKEN based on realistic environmental data. Two practical study cases in the North Atlantic are presented and discussed. In addition, an idealized 3D shallow water wedge was simulated. Practically, OMesh2KRAKEN can assist in implementing underwater acoustic modeling studies from deep waters to nearshore regions where, for instance, sound propagation maps are required. Indeed, higher mesh resolutions may be required for areas with complex bathymetric features. In these cases, the new tool presents several advantages as it automatically implements different mesh resolutions in areas of interest and prepares the respective environmental files for acoustic computations.

Ullmann-Like Covalent Bond Coupling without Participation of Metal Atoms.

Ullmann-like on-surface synthesis is one of the most appropriate approaches for the bottom-up fabrication of covalent organic nanostructures and many successes have been achieved. The Ullmann reaction requires the oxidative addition of a catalyst (a metal atom in most cases): the metal atom will insert into a carbon-halogen bond, forming organometallic intermediates, which are then reductively eliminated and form C-C covalent bonds. As a result, traditional Ullmann coupling involves reactions of multiple steps, making it difficult to control the final product. Moreover, forming the organometallic intermediates will potentially poison the metal surface catalytic reactivity. In the study, we used the 2D hBN, an atomically thin sp2-hybridized sheet with a large band gap, to protect the Rh(111) metal surface. It is an ideal 2D platform to decouple the molecular precursor from the Rh(111) surface while maintaining the reactivity of Rh(111). We realize an Ullmann-like coupling of a planar biphenylene-based molecule, i.e., 1,8-dibromobiphenylene (BPBr2), on an hBN/Rh(111) surface with an ultrahigh selectivity of the biphenylene dimer product, containing 4-, 6-, and 8-membered rings. The reaction mechanism, including electron wave penetration and the template effect of the hBN, is elucidated by combining low-temperature scanning tunneling microscopy and density functional theory calculations. Our findings are expected to play an essential role regarding the high-yield fabrication of functional nanostructures for future information devices.

High‐Performance Transparent Silicon Nanowire Thin Film Transistors Integrated on Glass Substrates via a Room Temperature Solution Passivation

AbstractCatalytic synthesized ultrathin silicon nanowires (SiNWs) are ideal 1D channel materials to fabricate high‐performance transparent and low‐cost thin film transistors (TFTs) that are widely needed for flexible electronics and displays. In this work, a scalable integration of orderly array of SiNW array, with a uniform diameter of only 52 ± 4 nm, grown directly upon glass/wafer substrates, via a guided in‐plane solid–liquid–solid (IPSLS) process, and passivated by a new solution oxidizing/etching cycling technique is demonstrated. This has enabled an all‐low‐temperature (<350 °C) fabrication of high‐performance SiNW‐TFTs, achieving Ion/Ioff current ratio and subthreshold swing (SS) of >106 and 120 mV dec−1 respectively, with excellent negative and positive bias stabilities. Importantly, the SiNW‐TFTs fabricated on glasses with ITO/or metal electrodes demonstrate a high transparency of 90% or 73% respectively, making them ideal candidates for building the next generation of high aperture displays, transparent electronics, and augmented reality applications.

Application of in-cell fast photochemical oxidation of proteins (IC-FPOP) for the study of organoids.

Fast photochemical oxidation of proteins (FPOP) is a powerful, mass spectrometry (MS)-based, biophysical method used to probe protein structure, interactions, and conformations. FPOP was recently extended into cells (IC-FPOP) and can modify thousands of proteins in a single experiment, enabling proteome-wide structural biology. Although IC-FPOP can reveal critical structural information in 2D cell culture, the conditions do not emulate an in-vivo environment. Organoids are multicellular three-dimensional model systems that resemble the corresponding organ. They are the ideal 3D model system for evaluating drug penetration, drug efficacy, and chemoresistance since they mimic in vivo conditions. But the complexity of organoids makes them difficult for structural studies. Therefore, we have extended IC-FPOP into 3D bioprinted Huh-7 liver organoids. To obtain spatial resolution within the model, we integrated cryosectioning into the IC-FPOP workflow. This novel application of IC-FPOP revealed modifications in each section of the organoid, the top middle, and bottom. Pathway analysis revealed the interrogation of over 5 native pathways stemming from each region. Peptide level analysis revealed differences in the extent of modification for peptides identified in each region of the organoid, which confirms the acquisition of structural information. By coupling the organoid model with IC-FPOP we aim further validate its implementation for complex proteome-wide structural studies.

Efficient synergistic effect of trimetallic organic frameworks derived as bifunctional catalysis for the rechargeable zinc-air flow battery

Precise design of oxygen electrode catalysts can alleviate the problems of slow kinetic reaction and high overpotential in the rechargeable zinc-air flow batteries (ZAFBs). Herein, an ideal 3D carbon-based material for FeCo alloy inlaid to Fe/Co and N co-doped bamboo-like carbon nanotubes (CNTs) is prepared by means of a one-pot high-temperature pyrolysis strategy of three metal organic frameworks (MOFs) mixed-precursors. The concentration of active metal species, the amount of conductive CNTs and the hierarchical porous structure with high specific surface area in this material are regulated. The optimal catalyst, Fe/12Zn/Co-NCNTs, demonstrates excellent electrochemical activity with a high half-wave potential of 0.879 V for oxygen reduction reaction (ORR) and low overpotential of 340 mV at 10 mA cm−2 for oxygen evolution reaction (OER) in the half-cell. Moreover, the smaller bifunctional ΔE value of Fe/12Zn/Co-NCNTs and Fe/(12Zn/Co)-NCNTs catalyst are 0.693 V and 0.717 V, respectively, less than the commercial Pt/C+IrO2 (ΔE = 0.77 V). The ZAFB yields a high open circuit voltage of 1.518 V, peak power density of 166 mW cm−2, and specific capacity of 809.1 mAh g−1 when employing Fe/12Zn/Co-NCNTs as air cathode because of the synergistic effect that improves both OER and ORR. More importantly, both Fe/12Zn/Co-NCNTs and Fe/(12Zn/Co)-NCNTs as the bifunctional catalysts produce a low charge-discharge voltage gap and high cycle lifespan of more than 320 h at 10 mA cm−2. This work provides a facile strategy for fabricating high-efficiency and low-cost bifunctional electrocatalysts for ZAFBs and other clean energy applications.

Simulations of Wind Formation in Idealised Mountain–Valley Systems Using OpenFOAM

An OpenFOAM computational fluid dynamics model setup is proposed for simulating thermally driven winds in mountain–valley systems. As a first step, the choice of Reynolds Averaged Navier–Stokes k−ε turbulence model is validated on a 3D geometry by comparing its results vs. large-eddy simulations reported in the literature. Then, a numerical model of an idealised 2D mountain–valley system with mountain slope angle of 20° is developed to simulate thermally driven winds. A couple of top surface boundary conditions (BC) and various combinations of temperature initial conditions (IC) are tested. A transient solver for buoyant, turbulent flow of incompressible fluids is used. Contrary to classical approaches where buoyancy is set as a variable of the problem, here temperature linearly dependent with altitude is imposed as BC on the slope and successfully leads to thermally driven wind generation. The minimum fluid domain height needed to properly simulate the thermally driven winds and the effects of the different setups on the results are discussed. Slip wall BC on the top surface of the fluid domain and uniform temperature IC are found to be the most adequate choices. Finally, valleys with different widths are simulated to see how the mountain–valley geometry affects the flow behaviour, both for anabatic (daytime, up-slope) and katabatic (nighttime, down-slope) winds. The simulations correctly reproduce the acceleration and deceleration of the flow along the slope. Increasing the valley width does not significantly affect the magnitude of the thermally driven wind but does produce a displacement of the generated convective cell.

Constructing and regulating nanochannels in two-dimensional-material-based membranes for specified separation applications

The two-dimensional (2D) materials offer atomic-level thickness and unique physical and chemical properties for the preparation of a new class of membranes, i.e., nanochannel membranes. The nanochannel membranes have been utilized in a broad spectrum of new separation applications. However, the instability of the nanochannels, interfacial instability of 2D materials, and the swelling problem could damage the membrane performance, such as permeability, selectivity, and service lifetime. Innovative strategies for constructing and regulating the nanochannels are enthusiastically explored to address these challenges. Along this line, in this work, we first provide insight into the mechanisms of the nanochannel construction, the separation mechanism, and the effect of nanochannels on the separation performance. Then, the strategies developed in the literature, in particular, the strategies for the preparation of ideal 2D nanosheets, the strategies for constructing nanochannels, and the strategies for regulating the characteristics of nanochannels (channel size, channel length, channel morphology, and channel surface physicochemical properties) are systematically summarized. After that, we briefly introduce the application of 2D-material-based nanochannel membranes and outline the current challenges and provide an outlook in the further exploration of separation mechanism, large-scale manufacturing, and the eventual commercialization of the membranes.

Coupling between Abyssal Boundary Layers and the Interior Ocean in the Absence of Along-Slope Variations

Abstract To close the overturning circulation, dense bottom water must upwell via turbulent mixing. Recent studies have identified thin bottom boundary layers (BLs) as locations of intense upwelling, yet it remains unclear how they interact with and shape the large-scale circulation of the abyssal ocean. The current understanding of this BL–interior coupling is shaped by 1D theory, suggesting that variations in locally produced BL transport generate exchange with the interior and thus a global circulation. Until now, however, this picture has been based on a 1D theory that fails to capture the local evolution in even highly idealized 2D geometries. The present work applies BL theory to revised 1D dynamics, which more naturally generalizes to two and three dimensions. The BL is assumed to be in quasi-equilibrium between the upwelling of dense water and the convergence of downward buoyancy fluxes. The BL transport, for which explicit formulas are presented, exerts an influence on the interior by modifying the bottom boundary condition. In 1D, this BL transport is independent of the interior evolution, but in 2D the BL and interior are fully coupled. Once interior variables and the bottom slope are allowed to vary in the horizontal, the resulting convergences and divergences in the BL transport exchange mass with the interior. This framework allows for the analysis of previously inaccessible problems such as the BL–interior coupling in the presence of an exponential interior stratification, laying the foundation for developing a full theory for the abyssal circulation.

Large-Scale Dense Mapping System Based on Visual-Inertial Odometry and Densely Connected U-Net

SLAM-based 3D reconstruction system mainly relies on visual odometry, which uses detailed scanning to obtain better reconstruction results. Among the feature-based SLAM methods, it is difficult to have good reconstruction results where features are missing even when the camera moves slowly. For the direct methods, when exposure changes and blurring occurs, tracking loss will cause unsatisfactory reconstruction effects. This paper proposes a large-scale mapping system based on visual-inertial odometry to solve these problems. The combination of vision and IMU is used to constrain the trajectory estimation in areas where the corners are missing. The system supports depth both obtained by the depth camera and estimated by the neural network. According to the voxel hash mechanism, we only focus on the voxels within the cutoff distance and use the hash table to represent the voxels sparsely to reduce the memory usage. Experiments show that the proposed system can obtain an ideal 3D reconstruction model.

Atomic‐Scale Observation of the Local Structure and 1D Quantum Effects in vdW Stacking Mo6Te6 Nanowires

AbstractThe sub‐nanometer‐diameter transitional‐metal chalcogenides (M6X6) molecular wires are ideal 1D quantum systems. The electronic properties of such system are very sensitive to the interface interaction and local imperfection. Here, the atomic structure and local electronic structure of van der Waals (vdW) stacking Mo6Te6 nanowires fabricated by using molecular beam epitaxy are reported. Atomic‐resolution scanning tunneling microscopy measurement shows that the vdW interface distance varies from 0.71 to 1.05 nm when Mo6Te6 wires stacked on graphite, MoTe2, and Mo6Te6 surfaces. Scanning tunneling spectroscopy confirmed the 1D quantum effect of van Hove singularity and Tomonaga–Luttinger liquid behavior at 77.8 K. Single Te vacancies and their effect to the local structure distortion are observed as well. These observations shed light on the local structure and quantum effects of the M6X6 nanowire materials, which may find applications in future electronic devices.

Three-dimensional wet electrospun scaffold system for the differentiation of adipose-derived mesenchymal stem cells to islet-like clusters.

Stem cell-derived islet-like clusters (ILCs) are an alternative source of pancreatic beta cells for the treatment of diabetic mellitus. An ideal 3D culture platform for the generation of ILCs of desired cluster size is a challenge due to the clustering of islet cells in the 2D culture systems. The islet cells cultured in 2D conditions produce clusters of large size, which are less efficient in terms of insulin secretion and viability. In this study, we report that ILCs formed on a PCL-based wet electrospun fibrous scaffold with larger pore size produced clusters of the desired size, compared to that cultured on a conventional electrospun sheet. The collagen functionalization on this wet electrospun polycaprolactone (PCL) scaffold showed enhanced insulin secretion and cell viability compared to the non-functionalized or conventionally electrospun PCL scaffold. The collagen-coated wet electrospun 3D scaffold produced ILCs of cluster diameter 70±20μm and the conventionally electrospun PCL sheet produced larger ILC clusters of diameter 300±10μm. Hence the results indicate the collagen-functionalized wet electrospun scaffold system could be a potential scaffold for islet tissue engineering.

Exploring two-dimensional van der Waals heavy-fermion material: Data mining theoretical approach

The discovery of two-dimensional (2D) van der Waals (vdW) materials often provides interesting playgrounds to explore novel phenomena. One of the missing components in 2D vdW materials is the intrinsic heavy-fermion systems, which can provide an additional degree of freedom to study quantum critical point (QCP), unconventional superconductivity, and emergent phenomena in vdW heterostructures. Here, we investigate 2D vdW heavy-fermion candidates through the database of experimentally known compounds based on dynamical mean-field theory calculation combined with density functional theory (DFT+DMFT). We have found that the Kondo resonance state of CeSiI does not change upon exfoliation and can be easily controlled by strain and surface doping. Our result indicates that CeSiI is an ideal 2D vdW heavy-fermion material and the quantum critical point can be identified by external perturbations.

Nanoscale infrared imaging and spectroscopy of few-layer hexagonal boron nitride

Nanoscale evaluation of the number of layers and boundaries in two-dimensional (2D) materials is crucial for understanding relationships between structure and property. Here, using scattering-type scanning near-field optical microscopy, we systematically studied on a nanoscale the infrared spectra and imaging of hexagonal boron nitride (h-BN), an ideal 2D insulating material. We revealed that the main factor determining the infrared amplitude changes at an optical frequency of about 1370 cm−1, corresponding to the in-plane phonon mode of h-BN. At lower frequencies, the amplitude is mainly determined by the local dielectric function of a sample and depends on the number of h-BN layers. At higher frequencies, it is affected by the phonon polariton waves of h-BN, and thus edges and grain boundaries of h-BN can be visualized due to the reflection of the waves at the boundary. The infrared spectra show a shoulder peak at higher frequencies, derived from the resonance with the phonon polaritons, in addition to a peak due to the in-plane phonon mode.

Synthesis of Single-Atom and Dual-Atom Catalyst Using N-Defective C3N4

Single-atom catalysts, which have been studied tremendously in the past decade, are emerging as a new class of heterogeneous catalysts. It is now generally known that defect sites play an important role in forming single-atomic structures. In the case of SACs, defective sites provide not only space for fixation of metal precursor, but also electrons for stabilizing positive metal ions. Graphitic carbon nitride (g-C3N4) is one of the ideal 2D materials for the synthesis of SACs. C3N4 has enough anchoring sites which originate from the ordered structure of tri-s-triazines connected together. Furthermore, abundant nitrogen atoms in C3N4 can provide electrons to single metal atoms. however, C3N4 is unsuitable as support for electrochemical catalysts due to its low electrical conductivity. Therefore, we made a C3N4 shell on the outer surface of carbon black (Ketjen Black EC-600JD) to obtain conductive support (C@C3N4).[1] Pt was supported on C@C3N4 at 1, 2, 4, and 8 wt% by wetness impregnation method. Through XRD, HAADF-STEM, and XAFS analysis, it was confirmed that a single-atomic structure was formed only when the Pt content was 1 or 2 wt%. In addition, I confirmed that the H2O2 selectivity (%) in the electrochemical oxygen reduction reaction was different according to the Pt content of the catalysts.In terms of controlling reaction sites at the atomic level, the challenge above creating single-atomic structures is creating structures in which two or three atoms are formed as dimer or trimer. Unlike single-atom catalysts, in a dimer or trimer structure, two or more atoms are adjacent to each other, so they can exhibit completely different catalytic properties. Finely controlling the defect site of the support can be a good strategy. Therefore, I adopted the strategy of making a defect in C3N4 to synthesize a dimer structure. It has been reported that N-vacancy can be selectively formed on C3N4 by additional heat treatment with NaBH4.[2, 3] In addition, DFT calculation results have been reported that Pd-Cu dimer structure can be stably formed on nitrogen-defective C3N4.[4]In this work, I create N-vacancy on a Pt1/C@C3N4 by additional heat treatment with NaBH4, and Co atoms were deposited as a secondary transition metal. The research strategy was to anchor the Co atom to the N-vacancy formed around the Pt single-atom, resulting in the formation of a dimer structure. First of all, the formation of N-vacancy on C@C3N4 support was clearly confirmed by FT-IR and XPS analysis. To confirm the dimer structure of Pt and Co, XAFS analysis was conducted. As a result, although not all Pt and Co atoms formed a dimer structure due to the limitation of the synthesis method, the intended structure of Co atom connected to a Pt atom was confirmed. In the Pt L3 edge EXAFS, a peak arising from Pt-Co scattering was observed at 2.4 Å. Furthermore, to confirm that PtCo alloy particles were not formed, high-result HAADF-STEM images were taken. All metal atoms were atomically dispersed, and nanoparticles were not found. This research demonstrated that defect engineering on support material can successfully modify active site on the atomic scale.