Remarkable Anisotropy Research Articles

2D quasi-layered material with domino structure

Interlayer coupling strength dichotomizes two-dimensional (2D) materials into layered and non-layered types. Traditionally, they can be regarded as atomic layers intrinsically linked via van der Waals (vdW) forces or covalent bonds, oriented orthogonally to their growth plane. In our work, we report a material system that differentiates from layered and non-layered materials, termed quasi-layered domino-structured (QLDS) materials, effectively bridging the gap between these two typical categories. Considering the skewed structure, the force orthogonal to the 2D QLDS-GaTe growth plane constitutes a synergistic blend of vdW forces and covalent bonds, with neither of them being perpendicular to the 2D growth plane. This unique amalgamation results in a force that surpasses that in layered materials, yet is weaker than that in non-layered materials. Therefore, the lattice constant contraction along this unique orientation can be as much as 7.7%, tantalizingly close to the theoretical prediction of 10.8%. Meanwhile, this feature endows remarkable anisotropy, second harmonic generation enhancement with a staggering susceptibility of 394.3 pm V−1. These findings endow further applications arranged in nonlinear optics, sensors, and catalysis.

Controlled Growth of Vertically Aligned Nanocomposites through a Au Seeding-Assisted Method.

Heteroepitaxial metal-oxide vertically aligned nanocomposites (VAN) have piqued significant interest due to their remarkable vertical interfacial coupling effects, strong structural and property anisotropy, and potential applications in magnetoelectrics, photocatalysts, and optical metamaterials. VANs present a unique pillar-in-matrix structure with uniform but rather random pillar distributions. Achieving a well-controlled pillar growth remains a major challenge in this field. Here, we use BaTiO3 (BTO)-Au as a model VAN system to demonstrate the effects of Au seedings on achieving such pillar-growth control with enhanced ordering and morphology tuning. The Au seedings are introduced using an anodic aluminum oxide (AAO) template through pulsed laser deposition (PLD). TEM characterization reveals that the Au seedings result in straighter and more evenly distributed Au pillars in the BTO matrix compared to those without seeding, with the diameter of the Au seedings increasing with the number of pulses. Additionally, spectroscopic ellipsometry demonstrates distinct permittivity dispersion for all samples. This demonstration lays a foundation for future controlled and selective growth of VAN systems for on-chip integration.

In situ synchrotron x-ray imaging and diffraction study of additively manufactured AlSi10Mg alloy under uniaxial tension

In situ synchrotron x-ray imaging and diffraction are used to investigate deformation dynamics in two kinds of additively manufactured AlSi10Mg with different pore configurations. The pre-existing pore configurations are characterized with synchrotron x-ray computed tomography. The specimens are subjected to tensile loading along the build direction and the longitudinal direction. Bulk stress–strain curves (macroscale), strain fields (mesoscale) and x-ray diffraction patterns (microscale) are obtained simultaneously. Scanning electron microscopy characterization is performed as a complement. For the small-pored AlSi10Mg, preferred orientations of pores lead to anisotropic ductility, and only ductile dimples are observed. For the large-pored AlSi10Mg, ductility loss is significant due to its higher porosity, and no remarkable anisotropy is found; both ductile and brittle fracture features are identified. For both types of AlSi10Mg, strain localization occurs around the pores. At the lattice scale, the Al matrix deforms plastically but the Si phase is still strained elastically, and thus, significant stress concentration occurs in the Si phase for the small-pored AlSi10Mg, while stress is more evenly partitioned between the Al matrix and the Si phase for the large-pored AlSi10Mg.

Directed exciton transport highways in organic semiconductors

Exciton bandwidths and exciton transport are difficult to control by material design. We showcase the intriguing excitonic properties in an organic semiconductor material with specifically tailored functional groups, in which extremely broad exciton bands in the near-infrared-visible part of the electromagnetic spectrum are observed by electron energy loss spectroscopy and theoretically explained by a close contact between tightly packing molecules and by their strong interactions. This is induced by the donor–acceptor type molecular structure and its resulting crystal packing, which induces a remarkable anisotropy that should lead to a strongly directed transport of excitons. The observations and detailed understanding of the results yield blueprints for the design of molecular structures in which similar molecular features might be used to further explore the tunability of excitonic bands and pave a way for organic materials with strongly enhanced transport and built-in control of the propagation direction.

Anisotropic reversing motion in laser-induced periodic surface structures

Observation of the evolution process of laser-induced periodic surface structure (LIPSS) will provide clues to its formation mechanism. We constructed a pulse-by-pulse image capture setup using oil-immersion optical microscopy with which we observed the evolution process on a coverslip of borosilicate glass, finding three LIPSS patterns: stripe patterns parallel and perpendicular to the electric field of the laser pulse, and a dot pattern. Furthermore, “reversing” motion was observed, that is, bright and dark interchange from pulse to pulse. The reversing motion had remarkable anisotropy, moving only perpendicular to the electric field of the laser pulse.

Anisotropic Electronic Structure of the 2D Electron Gas at the AlOx/KTaO3(110) Interface

AbstractOxide‐based 2D electron gases (2DEGs) have generated significant interest due to their potential for discovering novel physical properties. Among these, 2DEGs formed in KTaO3 stand out due to the recently discovered crystal face‐dependent superconductivity and large Rashba splitting, both of which hold potential for future oxide electronics devices. In this work, angle‐resolved photoemission spectroscopy is used to study the electronic structure of the 2DEG formed at the (110) surface of KTaO3 after deposition of a thin Al layer. The experiments reveal a remarkable anisotropy in the orbital character of the electron‐like dispersive bands, which form a Fermi surface consisting of two elliptical contours with their major axes perpendicular to each other. The measured electronic structure is used to constrain the modeling parameters of self‐consistent tight‐binding slab calculations of the band structure. In these calculations, an anisotropic Rashba splitting is found with a value as large as 4 meV at the Fermi level along the [−110] crystallographic direction. This large unconventional and anisotropic Rashba splitting is rationalized based on the orbital angular momentum formulation. These findings provide insights into the interpretation of spin‐orbitronics experiments and help to constrain models for superconductivity in the KTO(110)‐2DEG system.

First principles study on magnetic anisotropy of 5d transition metal doped graphdiyne

The exceptional porous architecture of graphdiyne (GDY) renders it a potential candidate for magnetic storage media. This paper delves into the magnetic properties of GDY doped with 5d transition metal (TM) atoms via first-principles calculations. Our results divulge the stable embedding of these TM atoms within the triangular cavities of GDY, yielding a significant magneto-crystal anisotropy energy. In particular, Ta@GDY exhibits a remarkable magneto-crystal anisotropy energy value of 11.72 meV. By introducing TM atoms at the top, one could significantly change the magneto-crystal anisotropy energy value of the system, subsequently flipping the easy magnetization axis. The MAE values of Os-@GDY and Re-@GDY are −21.60 meV and −41.68 meV, which are expanded by a factor of 4 and 6 compared to those before the introduction of the top atom. Furthermore, we observed that the magneto-crystal anisotropy energy value of Ta@GDY is modulated by strain. Our research uncovers GDY as a promising substrate for two-dimensional magnetic materials that could be exploited in forthcoming magnetic memory devices.

Effects of microstructure and texture on the deep drawability of C10200 copper sheets

Formability of copper sheet is generally affected by microstructure and crystallographic texture. In this study, the effects of two different microstructure and textures on the deep drawability of C10200 copper sheets were analyzed by the optical microscopy (OM), the scanning electron microscopy (SEM) and the electron back-scattered diffraction (EBSD) technique. The results show that the first rolling reduction rate before intermediate annealing decreased, and the strong {001}<100> (Cube) texture was formed after final annealing. When the second rolling reduction decreased, Cube texture was weak and final annealing textures dominated by {123}<634> (S), {112}<111> (Copper) and {110}<112> (Brass) components were obtained. The texture difference had a great influence on the deep drawing quality. Strong Cube texture was unfavorable for deep drawing because of the more heterogeneous strain distribution resulted from the remarkable planar anisotropy, while the coexistence of S, Copper, Brass, and {110}<001> (Goss) texture components was conducive to improving the average r-values, which was beneficial to the deep drawability.

Opening a Band Gap in Biphenylene Monolayer via Strain: A First-Principles Study.

A biphenylene network is a novel 2D allotropy of carbon with periodic 4-6-8 rings, which was synthesized successfully in 2021. In recent years, although the mechanical properties and thermal transport received a lot of research attention, how to open the Dirac cone in the band structure of a biphenylene network is still a confused question. In this work, we utilized uniaxial and biaxial lattice strains to manipulate the electronic properties and phonon frequencies of biphenylene, and we found an indirect band gap under 10% biaxial strain through the first-principles calculations. This indirect band gap is caused by the competition between the band-edge state A and the Dirac cone for the conduction band minimum (CBM). Additionally, the lightest carrier's effective mass in biphenylene is 0.184 m0 for electrons along x (Γ→X) direction, while the effective mass for holes shows a remarkable anisotropy, suggesting the holes in the tensile biphenylene monolayer are confined within a one-dimensional chain along x direction. For phonon dispersion, we discovered that the Raman-active Ag3 phonon mode shows a robust single phonon mode character under both compressive and tensile strain, but its frequency is sensitive to lattice strain, suggesting the lattice strain in biphenylene can be identified by Raman spectroscopy.

Thermal switch based on ferroelasticity VA-N binary compounds

Ferroelastic materials possess two or more equally stable orientation variants and can be effectively modulated via external fields, including stress and electronic field. In this paper, taking the VA-N ferroelastic materials as examples, we propose a thermal switch device based on their ferroelastic characteristics. The results show that the VA-N binary compound exhibits excellent ferroelasticity, high reversible elastic strain (5.5%–54.1%), and suitable switching energy barriers (0.012–0.386 eV/atom) in both δ and α phases. Utilizing the advanced on-the-fly machine learning potential, we obtain physically well-defined quadratic dispersion curves in the long-wavelength limit and further evaluate their lattice thermal conductivity of δ and α phase VA-N binary compounds. Due to the difference in phonon group velocities, the lattice thermal conductivity of VA-N binary compounds along the armchair direction is obviously smaller than that along the zigzag direction. Such remarkable anisotropy and easily switchable features based on ferroelasticity endow reversible and real-time regulation of thermal conductivity of VA-N binary compounds. The ferroelastic-based thermal switch hosts high switch ratios range from 2.08 to 5.99 and does not require additional energy to maintain the modulation state. The results presented herein provide a pavement for designing next-generation thermal switches and propose a reliable solution for eliminating the nonphysical pseudo-phenomenon of phonon dispersion curve violation of quadratic dispersion in the long-wavelength limit.

Remarkable Conductive Anisotropy of Ag-Coated Glass Microbeads/UV Adhesive Composites Made by Electric Field Induced Alignment

We successfully prepared highly anisotropic conductive composites (ACCs) made of Ag-coated glass microbeads/UV adhesive via electric field-induced alignment, which was achieved using custom patterned microelectrode arrays. An optimized AC electric field (2 kV/cm, 1 kHz) with pole-plate spacing (50 μm) was utilized to effectively assemble the microbeads into chain arrays, which were precisely positioned on the microelectrode arrays to construct ordered conductive channels. In this case, tangling and cross-connection of the assembled microchains could be reduced, resulting in enhanced performance of the ACCs with high conductivity as well as excellent anisotropy. With a minor loading (3 wt %), the conductivity in the alignment direction could reach ∼24.9 S/m, which was the highest among the reported ACCs to the best of our knowledge, and it could also be 6 orders of magnitude higher than that within the plane. Besides, the samples exhibited high reliability in wire connections with low resistances. Due to these fascinating properties, the ACCs demonstrate promising applications for reliable electrical interconnects and integrated circuits.

Laser CVD Growth of Uniquely -oriented β-Ga2 O3 Films on Quartz Substrate with Ultrafast Photoelectric Response.

The oriented growth of β-Ga2 O3 films has triggered extensive interest due to the remarkable and complex anisotropy found in the β-Ga2 O3 bulks. Remarkable properties, including stronger solar-blind ultraviolet (SBUV) absorption, better mobility, and higher thermal conductivity, are usually observed along <010> direction as compared to other low-index axes. So far, <010>-oriented β-Ga2 O3 film growth has been hindered by the lack of suitable substrates and higher surface energy of the (010) crystal plane. Herein, the first growth of uniquely <010>-oriented β-Ga2 O3 films on quartz substrates by laser chemical vapor deposition (LCVD) are reported. By investigating the effects of deposition temperature (Tdep ) and O2 flow rate (RO2 ) on the growth of β-Ga2 O3 films, it is found that the formation of <010> orientation is closely related to the higher stability of oxygen close-packed planes under O-rich condition. As a result, a grain size of up to ≈2µm and a deposition rate of up to ≈ 40µm h-1 are obtained. Metal-semiconductor-metal (MSM) type detector based on <010>-oriented β-Ga2 O3 film exhibits ultra-fast response speed, 1-2 orders of magnitude higher than those of most detectors based on β-Ga2 O3 films with other orientations.

Influence of domain walls thickness, density and alignment on Barkhausen noise emission in low alloyed steels

This study deals with the characterization of low alloyed steels of different yield strengths (varying in the range of 235–1100 MPa) via Barkhausen noise emission. The study investigates the potential of this technique to distinguish among the low alloyed steels and all significant aspects contributing to Barkhausen noise, such as the residual stress state, microstructure expressed in terms of dislocation density, grain size, prevailing phase, as well as associated aspects of the domain wall substructure (domain wall thickness, energy, their spacing and density in the matrix). Barkhausen noise in the rolling as well as transversal direction grows along with the yield strength (up to 500 MPa) and the corresponding grain refinement of ferrite. As soon as the martensite transformation occurs in a high strength matrix, this evolution saturates, and remarkable magnetic anisotropy is developed when Barkhausen noise in the transversal direction grows at the expense of the rolling direction. The contribution of residual stresses as well as the domain wall thickness is only minor, and the evolution of Barkhausen noise is driven by the density of the domain walls and their realignment.

A first-principles study of hydrostatic strain engineering on the electronic properties of β-Ga2O3

β-Ga2O3 has some prominent advantages over other wide band gap semiconductors for application in electronics and optoelectronics. Through density functional theory, the effects of hydrostatic strain on the electronic properties of β-Ga2O3 are investigated. It is found that the band gap of β-Ga2O3 increases and subsequently decreases almost linearly with the hydrostatic strain from −8% to 7%, thus, resulting in the band gap within 3.45–6.28eV. As the strain exceeds −8% or 7%, the phase transition emerges, and its electronic properties exhibit abnormal variation trends as compared to primitive β-Ga2O3. In addition, properties, such as electron effective mass, elastic constants, relaxation time and mobility, show remarkable anisotropy. For the β-Ga2O3 phase with strains, electron mobility along a, b and c directions can be modulated about 2–3 times. The significant range of electronic parameters indicates that strain engineering may be an important approach to meet the different requirements of future electronics.

Strain-induced giant enhancement of anisotropic dielectric constant in layered nitrides SrHfN2 and SrZrN2.

The development of information technology puts forward huge demand for electronic materials with high dielectric constants; first-principles calculations and simulations have been demonstrated as an efficient technique for screening and exploring novel dielectric materials. In the present study, first-principles calculations combined with density functional perturbation theory are employed to study the dielectric properties of two newly discovered layered nitrides SrHfN2 and SrZrN2 under strain. By analyzing the evolution of lattice distortion, dielectric constant, Born effective charge, and phonon modes along with the applied strain, we find that the biaxial strain and isotropic strain can effectively modulate the dielectric constant. The two nitrides SrHfN2 and SrZrN2 are dynamically stable up to biaxial tensile strains of 2.1% and 1.8%, and the dielectric constants have been enlarged to about 500 and 2000. Furthermore, the dielectric constant is dramatically enhanced by 15 (9) times to a maximum value of ∼2600 (2700) under an isotropic tensile strain of 1.2% (0.7%) for SrHfN2 (SrZrN2), which is mainly due to the softening of the lowest-frequency infrared-active phonon mode and the increasing octahedral distortion degree. Particularly, the ionic contribution of the dielectric constant shows very remarkable anisotropy and plays a dominant role in the change of the dielectric constant, whose in-plane components exhibit giant enhancement by 18 (10) times for SrHfN2 (SrZrN2). This work not only sheds light on the experimentally observed high dielectric constants of SrHfN2 and SrZrN2, but also provides an effective route to regulate the anisotropic dielectric constants by applied strain, which indicates promising applications in optical and electronic devices.

Auxetic and multiferroic MP5 (M = Al, Ga): a novel 2D material with negative Possion's ratio and high anisotropic carrier mobility.

In the field of materials science, the development of multifunctional 2D materials has been a long-standing research objective. In this study, we employ first-principles calculations to predict a novel 2D material named MP5 (M = Al, Ga), which exhibits ferroelasticity, ferroelectricity, negative Poisson's ratio, and high anisotropic carrier mobility. Our investigation reveals that a single layer of MP5 displays multiferroic behavior, wherein ferroelasticity and ferroelectricity are coupled. The remarkable structural anisotropy of MP5 enables easy switching between ferroelastic and ferroelectric states, rendering it suitable for nonvolatile memory applications. Simultaneously, monolayer AlP5 (GaP5) demonstrates a negative Poisson's ratio of -0.074 (-0.058) and a carrier mobility of up to 91 720 cm2 V-1 S-1 (99 690 cm2 V-1 S-1). These exceptional properties position monolayer MP5 as a highly versatile and promising 2D material for implementation in nanomechanical and microelectromechanical devices.

Giant magnetic anisotropy of adatoms on the graphane surface.

Remarkable magnetic anisotropy provides more possibilities in electronic devices such as quantum information storage and processing. Here, based on first-principles calculations, we identified a series of magnetic adatoms including 12 d-type and 8 p-type members with estimated high structural stability and large magnetic anisotropy energy (MAE). Among the p-type systems, a giant MAE up to 157 meV was predicted for the Pb adatom with out-of-plane magnetization and up to 313 meV for Bi with in-plane magnetization. By analyzing the density of states and the p-orbital-resolved MAE, the large MAEs are found to mainly derive from the orbital hybridization of degenerated px/y near the Fermi levels, which is induced by the synergistic effect of the ligand field and significant spin-orbit coupling interaction. In addition, by comparing various magnetic configurations of Pb/Bi atomic kagome/hexagonal/triangular magnetic lattices, we found that their magnetization keeps the same direction as that of the single Pb/Bi adatom, which further confirms the robust magnetic anisotropy of the individual Pb/Bi adatom on the graphane surface. Our findings provide a promising platform for the realization of atomic scale memory.

Comparative analysis of morphology 1D and 2D particles effect in starting powders on microstructure and thermoelectric properties of grained Bi2Te2.7Se0.3 compound

Features in microstructure and thermoelectric properties of grained Bi2Te2.7Se0.3 compound, prepared by spark plasma sintering of starting powders with various morphologies, are comparatively examined. The 1D samples, prepared from the starting powder consisting of 1D bar-shaped particles, were weakly-textured (orientation factor is equal to ∼0.07) and preferentially consisted of bar-shaped grains. The 2D samples, prepared from the starting powder consisting of 2D plate-shaped particles, were highly-textured (orientation factor is equal to ∼0.28) and consisted of plate-shaped grains. Both weakly-textured 1D sample and highly-textured 2D sample demonstrated remarkable anisotropy in the behavior of their transport properties (specific electrical resistivity and total thermal conductivity). For highly-textured sample, this anisotropy is a typical phenomenon, resulting from recovering in crystal anisotropy, which is inherent for single-crystalline Bi2Te3-based material. For the weakly-textured 1D sample, the anisotropy in the transport properties is unexpected enough. In this case, anisotropy can be attributed to the anisotropic grain size effect on the transport properties. This effect is due to a different number of grain boundaries, overcome by the electrons or phonons under different measuring orientations. The highest value of the thermoelectric figure-of-merit (∼0.68) was found for the 1D and 2D samples and at perpendicular measuring orientation.

A Post-Processing Method for Improving the Mechanical Properties of Fused-Filament-Fabricated 3D-Printed Parts

Fused-filament fabrication is one of the most popular 3D printing techniques for thermoplastic materials because it is easy to use and is low-cost. On the other hand, it has the great limit of being suitable only for developing prototypes, because the printed object generally has low mechanical properties, and this prevents its use in structural applications. To solve this issue, the scientific literature has mainly focused on the optimization of the printing parameters and on performing some post-printing treatments, e.g., annealing, but despite some results being very promising, the topic has not yet been exhaustively investigated. In this paper, a post-printing treatment was studied that was based on two subsequent stages of remelting and compaction within a mold made of a granular material. The material chosen for this study was a green composite made of poly-(lactic acid) and poly-(hydroxyalkanoate) filled with wood fibers. The density, mechanical properties in terms of tension and microscopic observations were used to evaluate the treatment effectiveness. The main results were that voids were reduced, and the quality of the interlayer welding was increased, and this improved the mechanical properties, both in terms of stiffness and strength. In particular, the initial specimens displayed remarkable anisotropy, being stronger and stiffer in the longitudinal direction. After the post-processing treatment, despite the longitudinal properties having a very limited increase, the transversal properties increased significantly until they reached the longitudinal properties, thus leading to a more isotropic material.

β -Ga2O3 Schottky barrier diodes with 4.1 MV/cm field strength by deep plasma etching field-termination

In this work, we demonstrate a deep mesa etch design for efficient edge field termination in β-Ga2O3 Schottky barrier diodes (SBDs). The proposed design enabled parallel plate fields higher than 4.1 MV/cm with negligible change to the device ON characteristics. The effect of BCl3/Cl2-based dry etch on (100) and (010) etched vertical sidewalls is also analyzed. A remarkable anisotropy in depletion was observed for etch along (100) and (010) sidewalls. This work provides insight into the impact of etching on n-type Ga2O3 and shows a promising method to realize efficient field termination for high breakdown field strength SBDs.