Substrate Interface Research Articles

A novel fly ash bifunctional filler for epoxy coating with long-term anti-corrosion performance under harsh conditions

• Bifunctional platform with high corrosion resistance is prepared by Fe 3+ and PFOA. • Corrosion protection is provided by strong shielding and metal passivation function. • Bifunctional platform has strong resistance to extremely corrosive environments. A robust bifunctional platform (FA-PANI-Fe-F) with both shielding performance and corrosion inhibition activity was prepared and observed for its structure and morphology. During the corrosion test, Fe 2+ /Fe 3+ and perfluorinated groups effectively strengthened the shielding performance and corrosion inhibition activity of the coating. The results show that the perfluorinated group not only improved the hydrophobic performance of the functional filler but also provided effective inhibition against corrosion for the anode area. In addition, Fe 2+ /Fe 3+ resulted in the functional filler exhibiting anodic protection and cathodic inhibition properties, thereby forming a dense metal passivation film between the coating and the substrate interface. After the EIS test, the |Z| 0.01 Hz value of FPF-Fe 10% C still reached 7.91 × 10 8 Ω·cm 2 . Additionally, the FPF-Fe 10% C showed a lower cathodic corrosion trend in the SVET test, which indicated that Fe 2+ /Fe 3+ effectively inhibited the corrosion process in the cathode region. This study is expected to open new insights into the anti-corrosion inhibition process between the interior of the coating and the metal substrate, and prepare a robust bifunctional filler platform with long-term corrosion resistance.

Corrosion-controlled surface engineering improves the adhesion of materials for stable free-standing electrodes

Directly anchoring active materials on porous conductive substrates is considered an effective strategy to obtain a high-activity electrode since the direct contact between active materials and substrates benefits charge transfer, and the presence of porous structures provides more active sites. However, due to the presence of strong stress and weak adhesion, active materials loaded on the substrate are very easy to peel off during assembly and use, which can greatly shorten the lifetime of use. Herein, an ultrasonic corrosion strategy is proposed to regulate the surface of a metal substrate. We find that ultrasonic oxygen corrosion and interfacial water control play key roles in fabricating the complex electrode, which can help the surface of Cu foam to form special lamellar cross-linked CuO nanoarchitectures with strong adhesion and then overcome the defect of the deposited NiCo layered double hydroxides (NC LDH) on the stress and adhesion. The expected electrode shows more than 70% improvement in cycling stability at an ultra-high current density of 20 A g−1, relative to the active material layer of the electrode with strong stress and weak adhesion. Meanwhile, benefiting from its lamellar cross-linked nanoarchitectures having large specific surface area and many nano-pores, it presents a high specific capacitance of 3010.8F g−1 at 1 A g−1 and a good rate capability of 59.3% at 50 A g−1. It is foreseen that this finding provides a novel, universal strategy for managing the surface and interface of the metal substrate, thereby obtaining a reliable, stable electrode.

Simulation-based study of single-event burnout in 4H-SiC high-voltage vertical superjunction DMOSFET: Physical failure mechanism and robustness vs performance tradeoffs

We explore and elucidate physical failure mechanisms in a 4H-SiC, high voltage, superjunction (SJ) vertical DMOSFET from a single heavy ion strike using three-dimensional electro-thermal transient simulations. The single-event burnout (SEB) failure is thermal runaway from second breakdown, initiated by impact ionization and terminated with mesoplasma formation, at the center of the P-pillar/N+ substrate interface. We also demonstrate that the SEB performance of this SiC SJ DMOSFET is insensitive to the pillar width but sensitive to the strike location with ion strike at the P-pillar causing SEB at a lower blocking voltage than at the N-pillar. Compared to commercially available 1.2 kV blocking-rated non-SJ DMOSFETs, which have been demonstrated to survive SEB up to 525 V, the SJ DMOSFET increases SEB survival threshold voltage (VSEB) by a factor of 2.2, making it close to 1200 V, while the on-resistance is increased by only 11%. Using our recently developed figure of merit (FoM), which considers the trade-off between VSEB and on-state performance, we find that the SiC SJ DMOSFET achieves a FoM that is 14 times better, making it superior to conventional 1.2 kV SiC DMOSFETs for long-term radiation-tolerant operation in space applications.

EBSD and EDX analysis at the cladding–substrate interface of a laser clad railway wheel

Abstract Electron backscatter diffraction and energy-dispersive X-ray spectrometry were used to investigate the intermixed interface produced during laser cladding of a Co – Cr –Mo alloy on a steel substrate. A multi-component system and rapid solidification conditions together lead to a complex microstructure at the interface. The solidification of the cladding starts with the formation of an interface layer, which is about 75 μm in thickness and consists of randomly oriented equiaxed grains of Co–Cr –Fe solid solution and martensite. Orientation analysis of the grains in the interface layer revealed that some grains have a special orientation relationship with the former austenite grains in the heat affected zone but the cladding is not formed by epitaxial growth on the substrate. Intermixing of the materials at the interface is providing a strong bond between the substrate and the cladding. For a grain from the interface layer to emerge as columnar grain in the cladding, it was determined that its <001> crystallographic direction is not supposed to deviate more than 25° from the sample normal direction.

Instantaneous-Progressive nucleation and growth of palladium during electrodeposition

Potentiostatic electrodeposition of palladium (Pd) was performed at −0.380, −0.280, −0.230, −0.210 and −0.180 V overpotentials in 56 mM PdCl2+0.1 M HCl on Au substrate. The current density(j)–time(t) transients approach a maximum current density ( jmax) at a time tmax. The current density–time transients are also analyzed using the Scharifker–Hills model for instantaneous and progressive nucleation through (j/jmax)2-t/tmax plots. At times less than tmax, the experimental Scharifker–Hills plots are well within the Scharifker–Hills​ guidelines as prescribed by the model for both instantaneous and progressive nucleation. Prior to tmax Pd deposition is majorly due to instantaneous nucleation. The estimated charge density and the surface coverage by Pd nanostructures up to tmax, as validated by Scanning Electron Microscopy analysis, decrease with overpotential. All the deposits exhibit only partial coverage (20%–30% at −0.380 V; and 50%–60% at the other potentials) up to tmax. Beyond tmax, the deposition proceeds through progressive nucleation on the uncovered surface and through 3D and planar diffusional growth. The experimental Scharifker–Hills plots deviate from the corresponding guidelines beyond tmax. Moreover, the results from Electrochemical Impedance Spectroscopy performed at the deposition potentials exhibit mixed charge and mass transport contribution at the electrolyte–substrate interface. The overpotential leading to the mixed charge and mass transport is attributed as the reason for the deviation from the Scharifker–Hills model.

Large unidirectional spin Hall and Rashba−Edelstein magnetoresistance in topological insulator/magnetic insulator heterostructures

The unidirectional spin Hall and Rashba−Edelstein magnetoresistance is of great fundamental and practical interest, particularly in the context of reading magnetization states in two-terminal spin–orbit torque memory and logic devices due to its unique symmetry. Here, we report large unidirectional spin Hall and Rashba−Edelstein magnetoresistance in a new material family—magnetic insulator/topological insulator Y3Fe5O12/Bi2Se3 bilayers. Such heterostructures exhibit a unidirectional spin Hall and Rashba−Edelstein magnetoresistance that is about an order of magnitude larger than the highest values reported so far in all-metal Ta/Co bilayers. The polarized neutron reflectometry reveals a unique temperature-dependent magnetic intermediary layer at the magnetic insulator–substrate interface and a proximity layer at the magnetic insulator–topological insulator interface. These polarized neutron reflectometry findings echo the magnetoresistance results in a comprehensive physics picture. Finally, we demonstrate a prototype memory device based on a magnetic insulator/topological insulator bilayer, using unidirectional spin Hall and Rashba−Edelstein magnetoresistance for electrical readout of current-induced magnetization switching aided by a small Oersted field.

Shear testing and failure modelling of calcium phosphate coated AZ31 magnesium alloys for orthopaedic applications

Magnesium orthopaedic fracture fixation devices can potentially provide significant clinical benefits, such as the elimination of secondary surgeries for device removal due to in-vivo resorption and reduced stress shielding due to reduced device stiffness. However, development, approval, and clinical adoption of magnesium devices has been hindered by the excessively high rates of in-vivo corrosion such that the structural integrity of the device can be catastrophically reduced before fracture healing occurs. Coating of devices with calcium phosphate coatings has been shown to significantly reduce corrosion rates, while enhancing osseointegration. However, the adhesion strength between the CaP coatings and magnesium substrates has not been previously investigated. Clinical insertion of fracture fixation devices such as intramedullary nails and k-wires will impose significant shear loading on the coated surface of the implant. If the effective shear strength of the coating-device interface is not sufficiently high, the coating will be damaged and removed during device insertion. In the current study a bespoke experimental-computational approach is developed to provide a new understanding of the relationship between coating thickness, surface roughness, and effective shear strength of the CaP coating- Mg substrate interface. Nine test cases were created by adjusting either the deposition time (3 thickness values) or the surface treatment of the Mg alloy using SiC paper (3 roughness values) and double-lap shear testing was performed for these coating configurations. Strain development in the Mg substrates was monitored using strain gauges, and failure stress was determined for each configuration. Test results revealed that the effective shear strength of the coating-substrate interface is significantly higher for coatings on the rougher substrate surfaces when compared to those on smoother surfaces. Coating thickness was not found to significantly influence the effective shear strength over the range considered in this study (0.37–1.34 μm). Micro-scale finite element models of lap-shear tests were constructed using experimental profilometry data. Simulations of rough coating-substrate interfaces reveal that significant localised compression occurs at the coating-substrate interface in regions of large asperities. A novel cohesive zone formulation has been developed to simulate compression induced shear hardening, and the resultant simulations are found to accurately predict the significantly higher effective shear strength measured experimentally for rougher coatings compared to smoother Mg substrate surfaces.

Interfacial electronic properties of FeTPP-Cl on HOPG

Conjugated tetrapyrrole complexes have potential for novel spintronic and optoelectronic devices. Detailed understanding of electronic properties at molecule–substrate interface is essential for their potential applications. In this report, electronic properties of iron (III) chloride tetraphenylporphyrin (FeTPP-Cl, C44H28ClFeN4) thin films on highly oriented pyrolytic graphite (HOPG) have been investigated using photoemission and X-ray absorption spectroscopy. Photoemission analysis shows that no significant charge transfer takes between FeTPP-Cl and HOPG. Fe 2P3/2 core level analysis indicates towards dechlorination of FeTPP-Cl on HOPG in the monolayer regime. Fe L2,3 edge X-ray absorption spectroscopy reveal that iron oxidation state changes from +2 to +3 due to adsorption on to HOPG, suggesting a substrate driven dechlorination of FeTPP-Cl. Curve fitting analysis of XPS Fe 2p3/2 spectrum for the deposition of FeTPP-Cl on HOPG in the monolayer regime confirms +2 oxidation state of central metal atom. An interface dipole of 0.2 eV has been found at FeTPP-Cl/HOPG interface suggesting weaker molecule–substrate interactions.

In Situ Microfluidic SERS Chip for Ultrasensitive Hg2+ Sensing Based on I--Functionalized Silver Aggregates.

Mercury(II) ions are causing serious environmental pollution and health damage. Developing a simple, rapid, and sensitive sensor for Hg2+ detection is of great significance. Herein, we demonstrate an I--functionalized surface-enhanced Raman scattering (SERS) substrate for rapid and sensitive Hg2+ sensing on a highly integrated microfluidic platform. Based on the combination reaction between I- and Hg2+, the Hg2+ sensing is achieved via the SERS intensity "turn-off" strategy, where HgI2 precipitation is formed on an SERS substrate interface, dissociating the Raman reporters that coadsorbed with I-. Owing to the strong binding constant between I- and Hg2+, our I--functionalized substrate demonstrates a very fast sensing response (∼150 s). Through reliable in situ SERS detection, a robust calibration curve between the "turn-off" signal and "lgC" is obtained in a broad concentration range of 10-9 to 10-13 M. Additionally, the detectable Hg2+ concentration can be as low as 1 fM. The good selectivity toward Hg2+ is also verified by testing about a dozen common metal ions in water, such as K+, Na+, Ca2+, Mg2+, and so forth. Furthermore, we apply the SERS sensor for real tap and lake water sample detection, and good recoveries of 113, 97, and 107% are obtained. With its advantages of high integration, simple preparation, fast response, high sensitivity, and reliability, the proposed I--functionalized SERS sensor microfluidic chip can be a promising platform for real-time and on-site Hg2+ detection in natural water.

The influence of Ti plasma etching pre‐treatment on mechanical properties of DLC film on cemented carbide

The pre‐treatment of substrate surface had been a key part of DLC film preparation to improve mechanical and tribological properties. Ti plasma etching pre‐treatment was investigated in this paper as a new effective surface pre‐treatment method to substitute transition layer. This pre‐treatment used high‐energy Ti plasma to impact substrate surface. Ti plasma etched the substrate to a depth of 407 nm and increased the roughness from 1.36 to 40.39 nm. A trace layer of substrate, together with cobalt, oxides, and other impurities, was removed. Ti plasma broke some top WC crystals and combined with the free carbon ions separating from the substrate. A DLC film was deposited on the etched surface. Compared with DLC films deposited on the untreated substrate and Ti transition layer, the DLC film on the Ti plasma etched substrate had best adhesion strength of 34.14 N. The three DLC films had the same sp3 bonding carbon content, but Ti plasma etching treatment could promote the formation of sp3 bonds on the interface of substrate and DLC film. This DLC film had low friction coefficient of 0.12 and low wear rate of 5.11 × 10−7 mm3/m·N. In summary, Ti plasma etching pre‐treatment could significantly improve the adhesion of DLC film and keep its excellent tribological properties.

Effects of O2 flux on structure, optical properties and hydrophobicity of highly emissive antireflective HfO2 thin films by magnetron sputtering

We used magnetron sputtering to prepare high emissive HfO2 thin films with thickness 300–500 nm under different O2 flux. A dense uniform HfO2 thin film with a polycrystalline monoclinic structure had been achieved. The effects of O2 flux on structural, optical and mechanical properties of deposited thin films were investigated. With the increasing O2 flux, the thickness of both the thin film and HfSixOy interlayer found at the interface of HfO2 and Si substrate decreased while the grain size and surface roughness increased significantly. At an O2 flux of 30 sccm, the deposited HfO2 film achieved a high transmittance up to 93%, a high emissivity up to 90%, a low bandgap (5.65 eV), a high refractive index (2.03) and a good hydrophobicity with an optimum contact angle of 117.8°. The obtained results of high emissivity, optical transmission and hydrophobic behavior are best among the reported performance, with the implication for application in high-performance optical coatings of lenses, windshields and optoelectronic devices.

A mesoscopic analysis of a localized shear band propagation effect on the deformation and fracture of coated materials

The numerical simulations of the deformation and fracture in an iron boride coating – steel substrate composition are presented. The dynamic boundary-value problem is solved numerically by the finite-difference method. A complex geometry of the borided coating – steel substrate interface is taken into account explicitly. To simulate the mechanical behavior of the steel substrate, use is made of an isotropic strain hardening model including a relation for shear band propagation. Local regions of bulk tension are shown to arise near the interface even under simple uniaxial compression of the composition and in so doing they determine the mesoscale mechanisms of fracture. The interrelation between plastic deformation in the steel substrate and cracking of the borided coating is studied. Stages of shear band front propagation attributable to the interface complex geometry have been revealed. The coating cracking pattern, location of the fracture onset regions and the total crack length are found to depend on the front velocity in the steel substrate.

Effect of seeding density on the growth of diamond films by hot-filament chemical vapor deposition from sparse to dense range

A systematic study is reported on the effects of nano-diamond seeding density on the growth, quality, and morphology of diamond films. A process is described to examine nano-diamond seeding densities 4 × 108, 8 × 1010, and 2 × 1012 cm−2 on silicon wafers. The diamond film is grown using hot-filament chemical vapor deposition with CH4/H2/O2 feed gases and varying growth time to determine properties at coalescence and as thickness increases. Polycrystalline morphology is examined by scanning electron and atomic force microscopy. Both vertical and lateral growth rates are found to be higher for sparse seeding prior to coalescence. Following coalescence, the growth rate is similar for all densities. The development of polycrystals is found to be influenced by the initial growth with smaller mean lateral size at higher seeding density and reduced surface roughness that also improves with thickness to reach ≲90 nm at a thickness of 6.4 μm. The crystal quality is examined by micro-Raman spectroscopy from the sample surfaces and line images from cross sections. Narrowing of the diamond phonon peak shows material quality to improve with the thickness, at a given seed density, and as density increases. Concomitant improvements are seen from the relative intensity of the diamond phonon and Raman bands from non-diamond carbon. Cross-section micro-Raman results suggest improved diamond film quality and crystallinity near the substrate interface as well as at the growth surface for the film grown with 2 × 1012 cm−2 seed density compared to 4 × 108 and 8 × 1010 cm−2. X-ray photoelectron spectroscopy confirms these trends at the diamond surface.

Asymmetric carbon nanotube dimers embedded in a dielectric slab: new plasmonic resonance behavior

All prior work on modeling the full-wave electromagnetic response of carbon nanotubes (CNTs) have focused on CNTs in free-space, whereas in most practical applications, CNTs are embedded in a dielectric substrate. In this work, we use full-wave simulations to study the plasmonic resonances of CNT dimers embedded in a lossy dielectric slab with a finite thickness. The numerical results show that the finite thickness dielectric slab leads to the emergence of new CNT resonance behavior that is not present in a homogeneous environment. As a single CNT approaches the dielectric slab interfaces, the resonance frequency of the CNT increases due to reduced dielectric loading. The resonance behavior changes completely when two CNTs in proximity form a dimer near the slab interface. The bonding and antibonding resonances of CNT dimers and the absorbed power vary significantly with the distance between the slab interface and the CNT dimer. Using this phenomenon, we show that symmetric CNT dimers can behave like asymmetric CNT dimers. Also, the antibonding resonance of an asymmetric CNT dimer can be suppressed by adjusting the length and depth of the CNT dimer inside the slab. This work can guide future sensing modalities based on CNT dimer as well as can provide an accurate assessment of the proximity of a CNT network to the interface of the embedding substrate.

Preparation and characterization of calcium phosphate containing coating on plasma electrolytic oxidized magnesium and its corrosion behavior in simulated body fluids

A double layer coating (Ca-P/PEO) was designed to form on pure magnesium. The Ca-P coatings were prepared at three pH values of the solution. The morphology, phase composition, microstructure, corrosion resistance, and degradation properties of the samples were investigated by scanning electron microscopy (SEM), energy dispersive spectroscopy (EDS), X-ray diffraction (XRD), potentiodynamic polarization (PDP), electrochemical impedance spectroscopy (EIS), and in vitro assessments. The XRD results indicate that the 5.7Ca-P coating is mainly composed of octacalcium phosphate (OCP). The potentiodynamic polarization test indicates that the corrosion current density of the 5.7Ca-P/PEO coated Mg is 100 times and 3 times lower than that of uncoated Mg before and after immersion in SBF solution for 168 h, respectively. The 5.7Ca-P coating promotes the nucleation of osteoconductive minerals (i.e., bone-like apatite), and the hydroxyapatite (HA) layer formed on the surface of the 5.7Ca-P coating is dense, thick, and stable after immersion in SBF solution for 30 days. These experimental results have demonstrated that the 5.7Ca-P/PEO coating can introduce a high biocompatibility of the bone-Mg substrate interface and provide long-term stable protection in SBF solution in the initial degradation stage.

Resonant precession of magnetization and precession—induced DC voltages in FeGaB thin films

Measurements of frequency dependent ferromagnetic resonance and spin pumping driven dc voltage (V dc) are reported for amorphous films of Fe78Ga13B9 alloy to address the phenomenon of self-induced inverse spin Hall effect (ISHE) in plain films of metallic ferromagnets (FMs). The V dc signal, which is anti-symmetric on field reversal, comprises of symmetric and asymmetric Lorentzians centered around the resonance field. Dominant role of thin film size effects is seen in setting the magnitude of static magnetization, V dc and dynamics of magnetization precession in thinner films (⩽8 nm). The film thickness dependence of magnetization parameters indicates the presence of a magnetically disordered region at the film—substrate interface, which may promote preferential flow of spins generated by the precessing magnetization towards the substrate. However, the V dc signal also draws contributions from rectification effects of a ≈0.4% anisotropic magnetoresistance and a large (≈54 nΩ m) anomalous Hall resistivity (AHR) of these films which ride over the effect of spin–orbit coupling driven spin-to-charge conversion near the film—substrate interface. We have addressed these data in the framework of the existing theories of electrodynamics of a ferromagnetic film subjected to radio-frequency field in a coplanar waveguide geometry. Our estimation of the self-induced ISHE for the sample with 54 nΩ m AHR shows that it may contribute significantly (≈90%) to the measured symmetric voltage. This study is expected to be very useful for fully understanding the spin pumping induced dc voltages in metallic FMs with disordered interfaces and large anomalous Hall effect.

Getting a Grip on the Adhesion Mechanism of Epiphytic Orchids – Evidence From Histology and Cryo-Scanning Electron Microscopy

Plants and animals evolve different attachment structures and strategies for reversible or permanent adhesion to different substrate types. For vascular epiphytes, having the ability to permanently attach to their host plants is essential for establishment and survival. Unlike mistletoe roots, roots of vascular epiphytes do not penetrate the host tissues but instead achieve attachment by growing in close contact to the surface of the substrate. However, the fundamental understanding of the attachment functions of epiphytic roots remains scarce, where majority of studies focused on the general root morphology, their functional properties and the descriptions of associated microbial endophytes. To date, research on attachment strategies in plants is almost entirely limited to climbers. Therefore, this study aims to fill the knowledge gap and elucidate the attachment functions of roots of epiphytic orchids. With the use of histology and high-resolution cryo-scanning electron microscopy (cryo-SEM) technique with freeze fracturing, the intimate root-bark substrate interface of epiphytic orchid Epidendrum nocturnum Jacq was investigated. Results showed a flattened underside of the root upon contact with the substrate surface, and the velamen layer appeared to behave like a soft foam, closely following the contours of the substrate. Root hairs emerged from the outermost velamen layer and entered into the crevices in the substrate, whenever possible. A layer of amorphous substance (glue-like substance) was observed on the surface of the root hairs. Combining the observations from this study and knowledge from previous studies, we hypothesised that epiphytic orchid roots produced a layer of glue-like substance to adhere the root to the substrate. Then root hairs are produced and enter into the voids and crevices of the substrate. This further generates a mechanical interlocking mechanism between root and substrate, thus reinforcing the attachment of the root (and hence the whole plant) to its substrate.

Effect of the Graded Silicon Content in SRN/SRO Multilayer Structures on the Si Nanocrystals and Si Nanopyramids Formation and Their Photoluminescence Response.

Two multilayer (ML) structures, composed of five layers of silicon-rich oxide (SRO) with different Si contents and a sixth layer of silicon-rich nitride (SRN), were deposited by low pressure chemical vapor deposition. These SRN/SRO MLs were thermally annealed at 1100 °C for 180 min in ambient N2 to induce the formation of Si nanostructures. For the first ML structure (MLA), the excess Si in each SRO layer was about 10.7 ± 0.6, 9.1 ± 0.4, 8.0 ± 0.2, 9.1 ± 0.3 and 9.7 ± 0.4 at.%, respectively. For the second ML structure (MLB), the excess Si was about 8.3 ± 0.2, 10.8 ± 0.4, 13.6 ± 1.2, 9.8 ± 0.4 and 8.7 ± 0.1 at.%, respectively. Si nanopyramids (Si-NPs) were formed in the SRO/Si substrate interface when the SRO layer with the highest excess silicon (10.7 at.%) was deposited next to the MLA substrate. The height, base and density of the Si-NPs was about 2–8 nm, 8–26 nm and ~6 × 1011 cm−2, respectively. In addition, Si nanocrystals (Si-ncs) with a mean size of between 3.95 ± 0.20 nm and 2.86 ± 0.81 nm were observed for the subsequent SRO layers. Meanwhile, Si-NPs were not observed when the excess Si in the SRO film next to the Si-substrate decreased to 8.3 ± 0.2 at.% (MLB), indicating that there existed a specific amount of excess Si for their formation. Si-ncs with mean size of 2.87 ± 0.73 nm and 3.72 ± 1.03 nm were observed for MLB, depending on the amount of excess Si in the SRO film. An enhanced photoluminescence (PL) emission (eight-fold more) was observed in MLA as compared to MLB due to the presence of the Si-NPs. Therefore, the influence of graded silicon content in SRN/SRO multilayer structures on the formation of Si-NPs and Si-ncs, and their relation to the PL emission, was analyzed.

Role of transferred graphene on atomic interaction of GaAs for remote epitaxy

Remote epitaxy is a recently discovered type of epitaxy, wherein single-crystalline thin films can be grown on graphene-coated substrates following the crystallinity of the substrate via remote interaction through graphene. Although remote epitaxy provides a pathway to form freestanding membranes by controlled exfoliation of grown film at the graphene interface, implementing remote epitaxy is not straightforward because atomically precise control of interface is required. Here, we unveil the role of the graphene–substrate interface on the remote epitaxy of GaAs by investigating the interface at the atomic scale. By comparing remote epitaxy on wet-transferred and dry-transferred graphene, we show that interfacial oxide layer formed at the graphene–substrate interface hinders remote interaction through graphene when wet-transferred graphene is employed, which is confirmed by an increase of interatomic distance through graphene and also by the formation of polycrystalline films on graphene. On the other hand, when dry-transferred graphene is employed, the interface is free of native oxide, and single-crystalline remote epitaxial films are formed on graphene, with the interatomic distance between the epilayer and the substrate matching with the theoretically predicted value. The first atomic layer of the grown film on graphene is vertically aligned with the top layer of the substrate with these atoms having different polarities, substantiating the remote interaction of adatoms with the substrate through graphene. These results directly show the impact of interface properties formed by different graphene transfer methods on remote epitaxy.

The Composition and Magnetic Property of Co/Cu Alloy Microwires Prepared Using Meniscus-Confined Electrodeposition: Effect of [Co2+], [Cu2+] Concentration at the Tip of the Meniscus

Meniscus-confined electrodeposition (MCED) is an effective and versatile technique for fabrication of alloy structures with precise localization and high controllability. Here, the fabrication of cobalt-copper (Co/Cu) alloy microwires using MCED techniques is reported. Co/Cu microwires with a wide range of compositions (Co9Cu91 to Co100Cu0) and controllable morphology were printed using the co-electrodeposition mode from a single electrolyte. We utilized multiphysics finite element simulation to investigate the influence of electrolyte evaporation and electric field on the concentration distribution of metal ions in the meniscus. The concentration of ions at the substrate interface increases linearly with decreasing humidity and increasing current density, which can be used to fine turn the alloy composition. By further analyzing the alloy composition, we found that the electrodeposition of Cu is diffusion controlled, while Co is mainly electrochemical reaction controlled, as a results of combined action of surface evaporation and reaction dynamics in the meniscus. The prepared alloy wires are polycrystalline, dense and uniform composition distribution. The coercivity and magnetic anisotropy are enhanced by increasing of the copper content in the alloy wires. The high tunability of composition make this alloy a promising material for magnetic micro/nano-electromechanical devices.