Stripe Structure Research Articles

Strain-modulated intercalated phases of Pb monolayer with dual periodicity in SiC(0001)-graphene interface

Intercalation of metal atoms at the SiC(0001)-graphene (Gr) interface can provide confined 2D metal layers with interesting electronic properties. The intercalated Pb monolayer (ML) has shown the coexistence of the Gr(10 × 10)-moiré and a stripe phase, which still lacks understanding. Using density functional theory calculation and thermal annealing with ab initio molecular dynamics as motivated by experiment, we have studied the formation energy of Gr/Pb/SiC(0001) for different Pb coverages. Near the coverage of a Pb(111)-like ML mimicking the (10 × 10)-moiré, we find a slightly more stable stripe structure, where one half of the structure has compressive strain with Pb occupying the Si-top sites and the other half has tensile strain with Pb off the Si-top sites. This stripe structure along the Gr zigzag direction has a periodicity of 2.3 nm across the [1 2¯ 10] direction agreeing with the previous observations using scanning tunneling microscopy. Analysis with electron density difference and density of states show the tensile region has a more metallic character than the compressive region, while both are dominated by charge transfer from Pb ML to SiC(0001). The small energy difference between the stripe and Pb(111)-like structures means the two phases are almost degenerate and can coexist, which explains the experimental observations.

Patterned Ultraslippery Surfaces of Stainless Steel Prepared by Femtosecond Laser Ablation for Directional Manipulation of Liquid Droplets.

Slippery liquid-infused porous surfaces (SLIPS) have promising applications in chip laboratories, nanofriction power generation, and microfluidics due to their excellent properties such as good hydrophobicity and low adhesion. However, the self-driven stability of conventionally lubricated surfaces is not high, and the velocity of liquid droplets is difficult to regulate. This greatly limits the potential applications of SLIPS. A strategy is offered to prepare microporous structures of SLIPS directly on a stainless-steel substrate using femtosecond laser processing technology as the main means to realize exhibiting smoothness to liquids. At the same time, the principle of bionics is utilized, the porous structure of SLIPS is combined with the groove structure of rice leaves, or porous structures are combined with the wedge structure of shorebird beak to prepare the three-dimensional structure of SLIPS. Droplets exhibit significant individual anisotropy on three-dimensional (3D) SLIPS of leaf-like groove stripe structure in rice, enabling the precise control of droplet motion direction. When droplets are transported in wedge-shaped SLIPS with an asymmetric structure, the wedge edge can limit the direction of droplet motion while squeezing the droplet to generate Laplace pressure gradient, which achieves continuous self-driven transport of droplets. In addition, based on the above two processing strategies, an information transfer device is designed: the splicing of the self-driven transport surface with anisotropic topological channels enables the differential drive for liquid transport, which provides the conditions for the information transfer of the droplets. This strategy not only is simple and efficient but also provides new ideas for the effective development of multifunctional SLIPS as well as lab-on-a-chip and microfluidic domains.

Formation of highly stable interfacial nitrogen gas hydrate overlayers under ambient conditions

Surfaces (interfaces) dictate many physical and chemical properties of solid materials and adsorbates considerably affect these properties. Nitrogen molecules, which are the most abundant constituent in ambient air, are considered to be inert. Our study combining atomic force microscopy (AFM), X-ray photoemission spectroscopy (XPS), and thermal desorption spectroscopy (TDS) revealed that nitrogen and water molecules can self-assemble into two-dimensional domains, forming ordered stripe structures on graphitic surfaces in both water and ambient air. The stripe structures of this study were composed of approximately 90 % and 10 % water and nitrogen molecules, respectively, and survived in ultra-high vacuum (UHV) conditions at temperatures up to approximately 350 K. Because pure water molecules completely desorb from graphitic surfaces in a UHV at temperatures lower than 200 K, our results indicate that the incorporation of nitrogen molecules substantially enhanced the stability of the crystalline water hydrogen bonding network on graphitic surfaces. Additional studies on interfacial gas hydrates can provide deeper insight into the mechanisms underlying formation of gas hydrates.

Environmental Influence on Stripe Formation at the Graphite-Water Interface.

Understanding the characteristics of graphite-water interfaces is of scientific significance and practical importance. Ordered stripe structures have been observed at this interface, with their origins debated between condensed gas molecules and airborne hydrocarbons. Atomic force microscopy (AFM) studies have revealed variations in the morphology, formation and growth of these ordered structures. Here, we investigate the graphite-water interface under different environmental conditions using PeakForce Quantitative Nanomechanical (PF-QNM) AFM. Our findings reveal that stripe structures with 4 nm width and 0.5 nm periodicity, form and grow under wet laboratory conditions but not in pure inert gas or cleanroom environments. These stripes appear more readily when the graphite surface is immersed in water, with growth associated with gas nanodomains on the surface. This suggests that atmospheric contaminants migrate to the water-graphite interface, potentially facilitated by gas states. These findings underscore the impact of environmental conditions on graphitic materials, providing new insights into the mechanisms underlying stripe formation and growth.

One-step laser interference lithography for large-scale preparation of a superhydrophobic Ti6Al4V surface with improved hardness, friction reduction and corrosion resistance

Metal workpieces are the bedrock of modern industries as aerospace, marine and car manufacturing. As the pursuit for machinery with excellent performance continues to increase, existing metals are unable to fulfill the requirements of machinery, so surface modification technology has emerged. In this paper, a highly efficient and cost-effective surface modification method using laser interference lithography (LIL) is proposed to prepare superhydrophobic surfaces with corrosion resistance over a large area on Ti6Al4V surfaces. Large-area uniform stripe structures were fabricated on the Ti6Al4V surface by controlling the interference process parameters and spot splicing paths, and then modifying FAS to obtain a superhydrophobic surface. The stripe structure provides more air pockets, which lays the foundation for improved superhydrophobicity and friction reduction. Furthermore, the dense recast layer formed by LIL cauterization completely isolates the Ti6Al4V materials from the corrosive medium, further improving corrosion resistance. The experimental results showed that the hardness reached 15.62 Gpa (313.65 % improvement), the coefficient of friction (COF) was reduced to 0.144 (66.5 % reduction), and the corrosion resistance was improved by two orders of magnitude. As a contactless fabrication technology for periodic structures, LIL has great potential in the field of surface modification.

Superlubric Sliding of Graphene Auto-Kirigami with Interfaces Containing Self-Assembled Stripe-Pattern Adsorbates.

Van der Waals heterostructures formed by stacked 2D materials show exceptional electronic, mechanical, and optical properties. Superlubricity, a condition where atomically flat, incommensurate planes of atoms result in ultra-low friction, is a prime example enabling, for example, self-assembly of optically visible graphene nanostructures in air via a sliding auto-kirigami process. Here, it is demonstrated that a subtle but ubiquitous adsorbate stripe structure found on graphene and graphitic surfaces in ambient conditions remains stable within the interface between twisted graphene layers as they slide over each other. Despite this contamination, the interface retains an exceptional superlubricious state with an estimated upper bound frictional shear strength of 10kPa, indicating that direct atomic incommensurate contact is not required to achieve ambient superlubricity for 2D materials. The results suggest that any phenomena depending on 2D heterostructure interfaces such as exotic electronic behavior may need to consider the presence of stripe adsorbate structures that remain intercalated.

Monte Carlo study of frustrated Ising model with nearest- and next-nearest-neighbor interactions in generalized triangular lattices

We investigate the frustrated J 1–J 2 Ising model with nearest-neighbor interaction J 1 and next-nearest-neighbor interaction J 2 in two kinds of generalized triangular lattices (GTLs) employing the Wang–Landau Monte Carlo method and finite-size scaling analysis. In the first GTL (GTL1), featuring anisotropic properties, we identify three kinds of super-antiferromagnetic ground states with stripe structures. Meanwhile, in the second GTL (GTL2), which is non-regular in next-nearest-neighbor interaction, the ferrimagnetic 3×3 and two kinds of partial spin liquid (PSL) ground states are observed. We confirm that residual entropy is proportional to the number of spins in the PSL ground states. Additionally, we construct finite-temperature phase diagrams for ferromagnetic nearest-neighbor and antiferromagnetic next-nearest-neighbor interactions. In GTL1, the transition into the ferromagnetic phase is continuous, contrasting with the first-order transition into the stripe phase. In GTL2, the critical temperature into the ferromagnetic ground state decreases as antiferromagnetic next-nearest-neighbor interaction intensifies until it meets the 3×3 phase boundary. For intermediate values of the next-nearest-neighbor interaction, two successive transitions emerge: one from the paramagnetic phase to the ferromagnetic phase, followed by the other transition from the ferromagnetic phase to the 3×3 phase.

Fabrication of Superhydrophobic–Hydrophilic Patterned Cu@Ag Composite SERS Substrate via Femtosecond Laser

Ultralow concentration molecular detection is critical in various fields, e.g., food safety, environmental monitoring, and disease diagnosis. Highly sensitive surface-enhanced Raman scattering (SERS) based on ultra-wettable surfaces has attracted attention due to its unique ability to detect trace molecules. However, the complexity and cost associated with the preparation of traditional SERS substrates restrict their practical application. Thus, an efficient SERS substrate preparation with high sensitivity, a simplified process, and controllable cost is required. In this study, a superhydrophobic–hydrophilic patterned Cu@Ag composite SERS substrate was fabricated using femtosecond laser processing technology combined with silver plating and surface modification treatment. By inducing periodic stripe structures through femtosecond laser processing, the developed substrate achieves uniform distribution hotspots. Using the surface wettability difference, the object to be measured can be confined in the hydrophilic region and the edge of the hydrophilic region, where the analyte is enriched by the coffee ring effect, can be quickly located by surface morphology difference of micro-nanostructures; thus, greatly improving detection efficiency. The fabricated SERS substrate can detect Rhodamine 6G (R6G) at an extraordinarily low concentration of 10−15 mol/L, corresponding to an enhancement factor of 1.53 × 108. This substrate has an ultralow detection limit, incurs low processing costs and is simple to prepare; thus, the substrate has significant application potential in the trace analysis field.

High-efficiency edge-emitting laser diodes with oxidation confinement stripe structure

High-efficiency, low-cost, high-power laser diodes (LDs) are in the spotlight due to the growing market demand. This study proposes a new edge-emitting LD structure that utilizes the facile oxidization properties of the high aluminum (Al) component AlGaAs material and simplifies LD fabrication to only one-step lithography. The key innovation is incorporating a ∼200 nm thick high-Al AlGaAs layer in the vertical epitaxial structure. This layer serves two purposes: 1) The low refractive index improves vertical mode confinement, enabling a thinner overall epitaxial structure. 2) Oxidation of this layer forms a dielectric isolator and a current aperture. Experimental LDs exhibited a peak efficiency of 77.8 %, peak power of 33.6 W, vertical divergence angle of 19.4°, and horizontal divergence angle of 8.8°. Compared to conventional edge-emitting LD, this LD demonstrates a 39 % lower thermal resistance, better optoelectronic performance, a simpler process, and a lower production cost.

S-Polarized Laser Oblique Incidence Induces “Leaf Vein-Like” Self-Organizing Stripe Structures (Invited)

s-Polarized Laser Oblique Incidence Induces “Leaf Vein-Like” Self-Organizing Stripe Structures (Invited)

Improved Far-Field Angle in Narrow-Ridge High-Power Laser Diodes Using a Double Stripe Structure

Improved Far-Field Angle in Narrow-Ridge High-Power Laser Diodes Using a Double Stripe Structure

Instability of cholesteric bridge in isotropic environment with break-up and satellite droplet formation

ABSTRACT We investigate quasi-two-dimensional coalescence of domains of isotropic liquid in chiral liquid crystal in flat optical cells. It is demonstrated that coalescence can be accompanied by instability of the liquid crystal bridge separating the domains. We analyse the transformation of the bridge for materials in a wide range of the pitch of the cholesteric helix and different spatially modulated structures: planar cholesteric, one-dimensional stripe structure, focal conic structure and Blue Phases. The instability is followed by cascade break-up and formation of satellite cholesteric droplets. This picture differs from the standard three-dimensional coalescence scenario, where only a bridge between the droplets forms and grows. Studies of thinning dynamics in the bridge region showed that at the final stage of instability the width of the cholesteric bridge decreased linearly with time. In cholesteric with high chirality and small helical pitch the bridge thinning occurs substantially slower than in cholesteric with large helical pitch.

Modeling and interpretation of bistatic bottom reverberation in deep water near seamounts.

The received reverberation signal can be beamformed by utilizing a vertical array, generating a vertical-angle time record (VATR) that enables analysis of spatiotemporal distribution characteristics. Due to the influence of multipath propagation effects, deep-sea reverberation exhibits highly complex characteristics, especially in a seabed with significant depth variation. In a recent bistatic reverberation experiment with a vertical array receiver, peculiar bright stripes were observed in the VATR. These stripes are the result of scattering caused by large-scale bottom structures and are closely associated with seamounts. To accurately model and interpret these stripes, a bistatic reverberation model is initially established to reproduce the VATR. This model enables us to numerically simulate the spatiotemporal distribution of reverberation in the VATR, offering a qualitative explanation for these stripes. However, the model alone is incapable of predicting the specific stripe structure associated with a particular seamount. To address this limitation, an equation system is introduced to calculate the stripe parameters based on the seamount parameters. By analyzing and deducing the dependency of the stripes on the seamount, conclusions were drawn using the equation system. Ultimately, the presented model and equation system successfully reproduce and comprehensively explain the observed abnormal stripes from the experiment.

Thermo–Solid Coupling Analysis of Bionic Piston for a Mud Pump in Tunnel Engineering

With the development of mud shield tunnel construction technology, the demands on the working performance of a mud pump are becoming higher and higher. As one of the critical components of a mud pump that is easy to wear, the performance of the piston directly affects the operational efficiency and lifespan of the mud pump. The bionic shape of the piston was designed under the guidance of non-smooth surface characteristics of natural organisms to enhance friction and wear performance as well as longevity. The stress field and temperature field characteristics of the pistons with three bionic structures (pit, stripe, and prismatic) were analyzed based on finite element simulation. The stress field analysis results indicated that, for the prismatic shape and pit shape pistons, the maximum stress was concentrated in the lip regions, and both of them bore large stress at the root. For the stripe-shaped piston, the stress was dispersed on both sides of the stripe structure, the stress at the root was small, and the stress gradient along the axial direction was relatively gentle. The stripe-shaped bionic structure can significantly improve the stress distribution state on the piston surface, and the optimal stripe width was recommended to be between 1 and 1.5 mm. The temperature field analysis results indicated that, for the stripe-shaped piston, the surface temperature and heat flux were the smallest, and the temperature gradient was relatively smaller than that of pit-shaped and prismatic-shaped pistons, so it was easier to dissipate heat. When the stripe width was 1.5 mm, the temperature distribution was the most uniform, and the heat flux in localized areas was the smallest, so the heat generated by friction was relatively easy to discharge in the unit area.

Dynamic tunable multiple plasmon induced transparency sensor and optical switch in dual-polarization excitation in a terahertz graphene metamaterial

This paper proposes the development of a simplified graphene-based terahertz device that exhibits multiple plasmon induced transparency (PIT) effects in x-polarized and y-polarized waves. The PIT device is composed of “Z-shaped” and “parallel strips” structures, which demonstrate multiple transparency windows under x-polarized and y-polarized incident light within the frequency range of 2-15 THz. Additionally, under x-polarized incident, the device demonstrates wideband transparency at 3.4 THz. By comparing the transmission spectra of individual and combined structures, we observe that the initial transmission valley of the single two horizontal stripes structure transforms into a PIT curve in the combined structure, while the transmission valley of the other individual structures remains transmission. The PIT device demonstrates a peak sensitivity of 3THz/RIU for x-polarized waves and 2.9THz/RIU for y-polarized waves when employed as a light sensor. PIT as a light switch can attain a maximum modulation depth of 81.4% for x-polarized waves and 71.2% for y-polarized waves at Fermi energy levels ranging from 0.5eV to 1.2eV. The presented PIT device shows promise for applications in high-sensitivity optical sensing and optical switching.

Mid-infrared thermal radiation resonating with longitudinal-optical like phonon from n++-doped GaN–semi-insulating GaN grating structure

The mid-infrared emission mechanism of line-and-space structures of metallic plates on dielectric materials is substantiated using high conductive n-doped (n++-) GaN–semi-insulating (SI-) GaN microstripe structures on an SI-GaN epitaxial layer, which was veiled when using line-and-space structures of Au plates. The present structure exhibits a few thermal emission lines originating from electric dipoles resonating with the coherent longitudinal optical (LO) phonon-like lattice vibration, which are formed by the local depolarization electric field in the surface n++-GaN/SI-GaN/n++-GaN regions. The energies of the LO-phonon-like modes shift from the original LO-phonon energy of GaN to the lower energy region, which contrasts with the LO-phonon resonant emission from the microstructures on GaAs. These emission lines have another notable feature, i.e. the observed peak energies are independent of the polar emission angle for both s- and p-polarizations, unlike the emissions by surface phonon polaritons showing a significant directive nature of peak energies. The results show that each peak energy of the present emission lines is positioned at the zero-point of the real part of the electric permittivity comprising the components of the transverse optical phonon and other electric dipoles induced by the LO-like modes, excluding the target mode. The significant peak-energy shift of the LO-like phonons is applicable to materials with wide Reststrahlen bands, which contrasts with that of the nearly LO-phonon resonating feature of materials with narrow Reststrahlen bands, such as GaAs. The peak energy shift depending on the emission direction is observed for Au–GaN stripe structures. This property is ascribed to the imperfect Au/GaN interface with surface states through the theoretical analysis of the modified electric permittivity in the surface region, numerical simulation of the local electric field via finite-difference time-domain calculation, and experimental studies on a Ti–GaN structure and emission peaks originating from an LO-like phonon of the α-Al2O3 substrate.

Aluminum-Based Heterogeneous Surface for Efficient Solar Desalination and Fog Harvesting Processed by a Picosecond Laser.

Solar desalination and fog harvesting are two common ways to obtain fresh water, and both are promising methods to solve the water shortage problem. However, through either the fabrication of interfacial evaporators for solar desalination or the preparation of superwetting surfaces for fog harvesting, current methods suffer from long preparation times, high costs, and low efficiency. Herein, we report an efficient and simple method to process heterogeneous surfaces (HSs) on aluminum (Al) by picosecond laser processing combined with chemical treatment used for fog harvesting and seawater desalination. The as-prepared HS simultaneously consists of regular periodic stripe structures with superhydrophilicity and superhydrophobicity. The spacing of the superhydrophilic and superhydrophobic regions can be adjusted through the processing path. This surface has a 44% improvement in fog harvesting efficiency compared to a pristine Al sheet, which is 0.53 kg·m-2·h-1. Furthermore, it shows a high evaporation rate of 2.35 kg·m-2·h-1 under one sun irradiation with an energy efficiency of 52.39%. Such functional surfaces can be applied to obtain fresh water resources in both coastal regions and arid areas, where water mist is relatively abundant, providing reference and guidance for fresh water collection, and being a promising way to solve the water shortage problem.

Spatially modulated control of pattern formation in a general nonlocal nonlinear system

Spontaneous symmetry breaking and pattern formation are notable and significant natural phenomena that occur in nonlinear systems. Further advancing such research to Bose–Einstein condensates (BECs) is of much interest for both fundamental physics and practical applications. We investigate the formation and selection of diverse self-organized ground-state patterns, as well as the control of their structural phase transition in a general nonlocal nonlinear system described by nonlocal Gross–Pitaevskii equation (GPE). We show a homogeneous matter wave can undergo roton instability (RI) and their control is addressed by spatially weak modulated nonlinearity, which may result in the formation of various ordered patterns (including square, stripe, annular, and different hexagonal structures, etc.) with and without the trapping potential. In particular, our findings reveal that when a spatially weak modulated nonlinearity is introduced, a hexagonal ground-state pattern (which is the only type of structure observed without such modulation) can transform into several distinct pattern types. In contrast to previous research, the patterns identified in our study can be easily controlled by modifying the nonlinear parameters. Our work opens a pathway for versatile manipulation of self-organized patterns as well as the associated structural phase transitions.

Structure and properties of the contact wire obtained by ECAP with forming

This paper presents the results of the development of a promising method for manufacturing contact wires for high-speed railways. The developed method is based on the principles of severe plastic deformation and the combination of metal-forming processes. The solution obtained is a combination of equal-channel angular pressing with the forming of a shaped contact wire with a cross-sectional area of 120 mm2 in one tooling. A feature of the work is that with the help of a comprehensive study by the methods of finite element computer modeling and a physical experiment, not only the stress-strain state of the deformation zone was investigated but also an analysis was made of the effect of deformation heating, which plays an important role when working with dispersion-hardened alloys, such as Cu-0.65Cr. It was established that the temperature in the equal-channel angular pressing zone reached 490℃ to 505℃, and during shaping, it rose to 510℃ to 530℃. In the course of a physical experiment, a laboratory sample of a contact wire with a tensile strength of 410 ± 8 MPa and an electrical conductivity of 35 ± 2% IACS was obtained. Post-deformation aging led to an increase in tensile strength up to 540 ± 20 MPa and restoration of electrical conductivity up to 76 ± 2% IACS. Due to the formation of a stripe structure of a grain-subgrain type with recrystallized grains along the boundaries, the plasticity of the contact wire sample reached 20%.

Two-dimensional Superconductivity in Misfit Layered Compound (BiSe)1.10NbSe2

Novel two-dimensional superconductivity in a misfit layered compound (BiSe)1.10NbSe2 with a critical temperature T c of 2.7 K is reported. The temperature dependence of H c2 is linear close to T c for both H ∥ c-axis and H ∥ ab-plane, suggesting that the superconductivity is three-dimensional with some anisotropy. However, the angular dependence of H c2 clearly reveals a cusp-like behavior, which can be explained by Tinkham model, indicating that the system is two-dimensional. In order to clarify the relationship between stripe structures on the surface and the two-dimensional superconductivity, we also performed the same measurement on a uniform microbridge sample. We found similar two-dimensional behavior even in a microbridge without linear defects, indicating that the origin of two-dimensional superconductivity in (BiSe)1.10NbSe2 is not related to the stripe structure.