Clean Interface Research Articles

Novel interface regulation of Sn1.0Ag0.5Cu composite solders reinforced with modified ZrO2: Microstructure and mechanical properties

• The concept of Sn/NiO/ZrO 2 interface system design is first proposed. • Surface modification of ZrO 2 is conducted with ball milling−pyrolysis methods. • The refinement mechanism of microstructure is systematically investigated. • A micro-mechanical lock and non-micropored clean interface is formed. • 5.The strength and ductility are simultaneously improved with NiO/ZrO 2 addition. With the trends of miniaturization and high density of electronic packaging, there has been an urgent demand to open up lead-free solders with high strength and ductility. In this study, a ZrO 2 -reinforced Sn1.0Ag0.5Cu composite solder was designed. First, surface modification on ZrO 2 was conducted with ball milling-pyrolysis method. Subsequently, NiO modified ZrO 2 (NiO/ZrO 2 ) was added to the solder matrix with ultrasonic stirring. The morphology and interface of NiO/ZrO 2 were discussed. Moreover, the microstructure, interface and mechanical properties of the composite solders were systematically studied. The results showed that NiO nanoparticles were evenly adhered to the ZrO 2 surface, and the interface relationship between them was semi-coherent and coherent. Further, an appropriate addition of NiO/ZrO 2 could refine the microstructure of composite solders. The refinement mechanism was systematically investigated. Besides, a micro-mechanical lock and non-micropored clean interface was formed between NiO/ZrO 2 and the solder matrix. The Sn/NiO/ZrO 2 interface system based on mutual solid solution was ingeniously designed. The ultimate tensile strength and elongation were increased synergistically, and the fracture mechanism transformed from a ductile−brittle mixed fracture mode to a ductile fracture mode. Therefore, a lead-free solder with high strength and ductility was obtained.

How the presence of particles at the interface influences the droplet deformation in a simple shear flow?

A lattice Boltzmann method is presented to simulate a particle-laden droplet subject to a simple shear flow, where the effect of particle concentration, viscosity ratio of droplet to ambient fluid and particle inertia on droplet deformation and particle movement is explored. With the increase of particle concentration, droplet deformation increases because of reduced interfacial free energy caused by reduced fluid-fluid interface length. When a sufficient number of particles are added to interface, droplet deformation monotonically decreases with viscosity ratio, but first rises and then declines for clean interface. This difference is attributed to an increased apparent viscosity of the ambient fluid by added particles. The particle inertia enhances droplet deformation remarkably only when the Reynolds number is relatively high. In addition, particles are found to revolve around the deformed droplet along the interface with a period, which is determined solely by deformation parameter at the viscosity ratio of unity. • A LBM is developed to simulate the fluid-fluid-solid three-phase flows. • The particle's revolution period can be determined by the droplet deformation. • The deposition of particles at the interface can enhance the droplet deformation.

Molecular beam homoepitaxy of N-polar AlN: Enabling role of aluminum-assisted surface cleaning

N-polar aluminum nitride (AlN) is an important building block for next-generation high-power radio frequency electronics. We report successful homoepitaxial growth of N-polar AlN by molecular beam epitaxy (MBE) on large-area, cost-effective N-polar AlN templates. Direct growth without any in situ surface cleaning leads to films with inverted Al polarity. It is found that Al-assisted cleaning before growth enables the epitaxial film to maintain N-polarity. The grown N-polar AlN epilayer with its smooth, pit-free surface duplicates the structural quality of the substrate, as evidenced by a clean and smooth growth interface with no noticeable extended defects generation. Near band-edge photoluminescence peaks are observed at room temperature on samples with MBE-grown layers but not on the bare AlN templates, implying the suppression of nonradiative recombination centers in the epitaxial N-polar AlN.

Tunable spin injection and detection across a van der Waals interface.

Van der Waals heterostructures with two-dimensional magnets offer a magnetic junction with an atomically sharp and clean interface. This attribute ensures that the magnetic layers maintain their intrinsic spin-polarized electronic states and spin-flipping scattering processes at a minimum level, a trait that can expand spintronic device functionalities. Here, using a van der Waals assembly of ferromagnetic Fe3GeTe2 with non-magnetic hexagonal boron nitride and WSe2 layers, we demonstrate electrically tunable, highly transparent spin injection and detection across the van der Waals interfaces. By varying an electrical bias, the net spin polarization of the injected carriers can be modulated and reversed in polarity, which leads to sign changes of the tunnelling magnetoresistance. We attribute the spin polarization reversals to sizable contributions from high-energy localized spin states in the metallic ferromagnet, so far inaccessible in conventional magnetic junctions. Such tunability of the spin-valve operations opens a promising route for the electronic control of next-generation low-dimensional spintronic device applications.

Space-Confined One-Step Growth of 2D MoO2 /MoS2 Vertical Heterostructures for Superior Hydrogen Evolution in Alkaline Electrolytes.

2D material-based heterostructures are constructed by stacking or spicing individual 2D layers to create an interface between them, which have exotic properties. Here, a new strategy for the in situ growth of large numbers of 2D heterostructures on the centimeter-scale substrate is developed. In the method, large numbers of 2D MoS2 , MoO2 , or their heterostructures of MoO2 /MoS2 are controllably grown in the same setup by simply tuning the gap distance between metal precursor and growth substrate, which changesthe concentration of metal precursors feed. A lateral force microscope is used first to identify the locations of each material in the heterostructures, which have MoO2 on the top of MoS2 . Noteworthy, the creation of a clean interface between atomic thin MoO2 (metallic) and MoS2 (semiconducting) results in a different electronic structure compared with pure MoO2 and MoS2 . Theoretical calculations show that the charge redistribution at such an interface results in an improved HER performance on the MoO2 /MoS2 heterostructures, showing an overpotential of 60mV at 10mA cm-2 and a Tafel slope of 47mV dec-1 . This work reports a new strategy for the in situ growth of heterostructures on large-scale substrates and provides platforms to exploit their applications.

In situ study on fracture behaviors of SiC/2A14Al composite joint： Co-construction of microstructure and mechanical properties via laser welding

SiC p /Al matrix composite (SiC p /AMCs) has been widely used in aerospace field of structural frames, but it is difficult to realize the lightweight connection of complex structural parts. Understanding the fracture mechanism from the source will provide a decisive insight into the preparation (e.g. additive manufacturing) and processing (e.g. welding) of new high strength lightweight aluminum matrix composite. In this work, the fracture characteristics and the correlative damage mechanisms near fracture crack tip in a notorious SiC/2A14Al joint was conducted by in-situ scanning electron microscopy tensile test and transmission electron microscopy . The sandwich eutectic microstructure Mg 2 Si–Al–AlCu of clean interface and micron scale heterogeneous heterostructure inhibited the crack propagation . The sandwich eutectic microstructure disperses the extra stress caused by deformation, and the dislocation multiplies and moves at the interface of Mg 2 Si–Al and Al–AlCu phase, which slows down the stress concentration at the interface and avoids catastrophic crack propagation. Based on the fracture crack initiation source characterization of the joint, a rapid solidification process strategy was designed to further improve the mechanical properties of the joint, and the joint with tensile strength of 255 MPa was successfully prepared. Under the premise of ensuring full penetration and the same heat input, it is easier to obtain satisfactory tensile strength with high laser power - high velocity welding parameters, which is due to the suppression of the Al 4 C 3 . This work can be regarded as a breakthrough in the research of high strength aluminum matrix composites guided by reverse failure analysis strategy.

Tensile hardness and wear properties of iron oxide (Fe3O4) reinforced aluminium 7075 metal matrix composites

ABSTRACT The Al-7075 aluminium alloy has been proposed for widespread use in automotive applications. This material has been researched in composite structures with various reinforcements in order to improve its usage. In this study, Fe3O4 (magnetite) is reinforced in an Al-7075 matrix to create a metal matrix composite by a stir casting process. Aside from the Neat Matrix samples, five samples were produced by adding Fe3O4 to Al 7075 matrix in various weight proportions such as 2, 4, 6, 8, and 10. The mechanical properties of the fabricated composite specimens were determined by different tests, including hardness, tensile, compression, and wear strength. The results were compared to a standard matrix alloy. In addition, SEM with EDAX studies was performed to examine the dispersion of the reinforced particles in the chosen matrix alloy. The homogeneous distribution of Fe3O4 particles in composites was observed to be intragranular in origin. Furthermore, Fe3O4 particles were found to be well attached to the matrix alloy, with a clean interface. The composite’s hardness and tensile strength along with wear resistance were also found to increase as the Fe3O4 concentration increased.

Bioinspired nacre-like 2024Al/B4C composites with high damage tolerance

The bio-inspired 2024Al/B4C composites with a laminate-reticular hierarchical architecture were constructed by squeeze casting of 2024Al into loose freeze-cast ceramic scaffolds. This pressurized infiltration process provided a clean and well-bonded interface without physical gaps. By regulating the initial suspension concentration (20, 25, 30 and 35 vol%), the effects of different ceramic content on the microstructure, damage-tolerance behavior and toughening mechanisms of the composites parallel and perpendicular to the ice-growth direction were investigated. The strength and toughness in the longitudinal direction were greater than that in the transverse direction. The 2024Al/20 vol% B4C composite in the longitudinal direction yielded the highest flexural strength of 658 MPa, crack-initiation toughness (KIc) of 18.4 MPa m1/2 and crack-growth toughness (KJc) of 27.5 MPa m1/2. The unique damage-tolerant properties were attributed to multiple toughening mechanisms, including crack deflection, branching and blunting, ductile-ligament bridging and multiple-crack propagation, as evidenced by the stable crack growth and rising R-curve behavior during fracture. The significantly decreased damage tolerance in the transverse direction was mainly due to inadequate toughening tools. On the other hand, both the flexural strength and fracture toughness reduced remarkably as the ceramic content increased. The 2024Al/35 vol% B4C composite fractured in a single-crack mode and the crack growth path was almost straight, showing a relatively low flexural strength (502 MPa) and crack-initiation toughness (9.1 MPa m1/2). The toughening mechanism was discussed in terms of the relationship between structural characteristics and cracking mode.

Resonant Scattering in Proximity-Coupled Graphene/Superconducting Mo2 C Heterostructures.

The realization of high‐quality heterostructures or hybrids of graphene and superconductor is crucial for exploring various novel quantum phenomena and devices engineering. Here, the electronic transport on directly grown high‐quality graphene/Mo2C vertical heterostructures with clean and sharp interface is comprehensively investigated. Owing to the strong interface coupling, the graphene layer feels an effective confinement potential well imposed by two‐dimensional (2D) Mo2C crystal. Employing cross junction device geometry, a series of resonance‐like magnetoresistance peaks are observed at low temperatures. The temperature and gate voltage dependences of the observed resonance peaks give evidence for geometric resonance of electron cyclotron orbits with the formed potential well. Moreover, it is found that both the amplitude of resonance peaks and conductance fluctuation exhibit different temperature‐dependent behaviors below the superconducting transition temperature of 2D Mo2C, indicating the correlation of quantum fluctuations and superconductivity. This study offers a promising route toward integrating graphene with 2D superconducting materials, and establishes a new way to investigate the interplay of massless Dirac fermion and superconductivity based on graphene/2D superconductor vertical heterostructures.

Low-Temperature Synthesis of Boron Nitride as a Large-Scale Passivation and Protection Layer for Two-Dimensional Materials and High-Performance Devices.

Two-dimensional materials (2DMs) with extraordinary electronic and optical properties have attracted great interest in optoelectronic applications. Due to their atomically thin feature, 2DM-based devices are generally sensitive to oxygen and moisture in ambient air, and thus, practical application of durable 2DM-based devices remains challenging. Here, we report a novel strategy to directly synthesize amorphous BN film on various 2DMs and field-effect transistor (FET) devices at low temperatures by conventional chemical vapor deposition. The wafer-scale BN film with controllable thickness serves as a passivation and heat dissipation layer, further improving the long-term stability, the resistance to laser irradiation, and the antioxidation performance of the underneath 2DMs. In particular, the BN capping layer could be deposited directly on a WSe2 FET at low temperature to achieve a clean and conformal interface. The high performance of the BN-capped WSe2 device is realized with suppressed current fluctuations and 10-fold enhanced carrier mobility. The transfer-free amorphous BN synthesis technique is simple and applicable to various 2DMs grown on arbitrary substrates, which shows great potential for applications in future two-dimensional electronics.

Ternary Logics Based on 2D Ferroelectric-Incorporated 2D Semiconductor Field Effect Transistors

Ternary logic has been proven to carry an information ratio 1.58 times that of binary logic and is capable to reduce circuit interconnections and complexity of operations. However, the excessive transistor count of ternary logic gates has impeded their industry applications for decades. With the modulation of the ferroelectric negative capacitance (NC) properties on the channel potential, MOSFETs show many novel features including steep subthreshold swing and non-saturation output characteristics, based on which an ultra-compact ternary inverter can be achieved. Compared with traditional bulk materials, layered 2D materials and 2D ferroelectrics provide a clean interface and better electrostatic control and reliability. Even though ultra-low SS (∼10 mV/dec) has been experimentally demonstrated in ferroelectric-negative capacitance-incorporated 2D semiconductor (NC2D) FETs, the available models are still rare for large-scale circuit simulations. In this study, the superb electrical properties of pure 2D material stack-based NC2D FETs (layered CuInP2S6 adopted as the 2D ferroelectric layer) are investigated through device modeling based on the Landau–Khalatnikov (LK) equations in HSPICE. We managed to realize an ultra-compact ternary inverter with one NC2D-PMOS (WSe2) and one NC2D-NMOS (MoS2) in HSPICE simulations, whose transistor count is significantly reduced compared with other counterparts. We also proposed a novel input waveform scheme to solve the hysteresis problem caused by ferroelectric modulation to avoid logic confusion. Additionally, the power consumption and propagation delay of the NC2D-based ternary inverter are also investigated. This work may provide some insights into the design and applications of ferroelectric-incorporated 2D semiconductor devices.

Imaging of Chemical Kinetics at the Water-Water Interface in a Free-Flowing Liquid Flat-Jet.

We present chemical kinetics measurements of the luminol oxidation chemiluminescence (CL) reaction at the interface between two aqueous solutions, using liquid jet technology. Free-flowing liquid microjets are a relatively recent development that have found their way into a growing number of applications in spectroscopy and dynamics. A variant thereof, called flat-jet, is obtained when two cylindrical jets of a liquid are crossed, leading to a chain of planar leaf-shaped structures of the flowing liquid. We here show that in the first leaf of this chain, the fluids do not exhibit turbulent mixing, providing a clean interface between the liquids from the impinging jets. We also show, using the example of the luminol CL reaction, how this setup can be used to obtain kinetics information from friction-less flow and by circumventing the requirement for rapid mixing by intentionally suppressing all turbulent mixing and instead relying on diffusion.

A study on the asymptotic approximation for surfactant adsorption onto a spherical air-water interface

The asymptotic approximation equation was derived as a simple means for determining the adsorption mechanism and estimating surfactant diffusivity for surfactant adsorption onto a clean, spherical air-water interface (Makievski et al., 1999). However, the applicability of this approximation is yet to be examined. In this study, a theoretical simulation was conducted to better understand its applicability and validity. The diffusion-controlled adsorption of a nonionic surfactant onto a clean spherical interface (with radius = 0.03, 0.1, 0.5, and ∞ cm) was considered, and theoretical dynamic surface tension (γ) profiles were generated using the Langmuir adsorption isotherm. The initial region of γ(t1/2) profiles was best-fitted with asymptotic approximation with only one unknown parameter, the surfactant diffusivity. The initial region of the γ(t1/2) profiles could be well-described by the asymptotic approximation (a parabolic equation), but a notable deviation was observed on the diffusivity obtained from the fitting. This deviation was dependent on the bulk concentration and the duration of the initial region fitted; whilst being only slightly dependent on bubble radius. Although the results demonstrated the viability of this approximation, there existed a possibility of obtaining multiple values of diffusivity by choosing different initial regions of a γ(t1/2) profile.

Effect of spark plasma sintering on microstructure and mechanical properties of AA7075/B4C/ZrC hybrid nanocomposite fabricated by powder metallurgy techniques

In the present work, AA7075/B4C/ZrC hybrid nanocomposite has been fabricated by spark plasma sintering (SPS) process at a temperature of 500 °C with a heating rate of 50 °C/min for a period of 5 min. Microstructures and crystal phase structures have been investigated by scanning electron microscopy and X-ray diffraction techniques, respectively. It is observed from the results that the strong and clean interfaces along with uniform distribution of reinforcement particles are present in the SPS-synthesized composites, while the conventionally sintered composites possessed microporous structures. Mechanical properties of the SPS composite are found to be superior as compared to the conventional-sintered composites, where the high tensile and compression strengths of 605 and 712 MPa, respectively, are noted for SPS composite, while it is 502 and 598 MPa, respectively for the conventional-sintered composites. These observed enhanced properties could be attributed to the unique features of the SPS process, such as limited grain growth, clean interface bond formed via the breakage of oxide layers on particle surfaces due to spark discharges, and enhanced diffusion phenomenon that made the interfaces of the composite to be stronger.

Scalable Moir\xe9 Lattice with Oriented TMD Monolayers

Moiré lattice in artificially stacked monolayers of two-dimensional (2D) materials effectively modulates the electronic structures of materials, which is widely highlighted. Formation of the electronic Moiré superlattice promises the prospect of uniformity among different moiré cells across the lattice, enabling a new platform for novel properties, such as unconventional superconductivity, and scalable quantum emitters. Recently, epitaxial growth of the monolayer transition metal dichalcogenide (TMD) is achieved on the sapphire substrate by chemical vapor deposition (CVD) to realize scalable growth of highly-oriented monolayers. However, fabrication of the scalable Moiré lattice remains challenging due to the lack of essential manipulation of the well-aligned monolayers for clean interface quality and precise twisting angle control. Here, scalable and highly-oriented monolayers of TMD are realized on the sapphire substrates by using the customized CVD process. Controlled growth of the epitaxial monolayers is achieved by promoting the rotation of the nuclei-like domains in the initial growth stage, enabling aligned domains for further grain growth in the steady-state stage. A full coverage and distribution of the highly-oriented domains are verified by second-harmonic generation (SHG) microscopy. By developing the method for clean monolayer manipulation, hetero-stacked bilayer (epi-WS2/epi-MoS2) is fabricated with the specific angular alignment of the two major oriented monolayers at the edge direction of 0°/ ± 60°. On account of the optimization for scalable Moiré lattice with a high-quality interface, the observation of interlayer exciton at low temperature illustrates the feasibility of scalable Moiré superlattice based on the oriented monolayers.

Lithography-free and high-efficiency preparation of black phosphorous devices by direct evaporation through shadow mask

Two-dimensional (2D) materials including black phosphorus (BP) have been extensively investigated because of their exotic physical properties and potential applications in nanoelectronics and optoelectronics. Fabricating BP based devices is challenging because BP is extremely sensitive to the external environment, especially to the chemical contamination during the lithography process. The direct evaporation through shadow mask technique is a clean method for lithography-free electrode patterning of 2D materials. Herein, we employ the lithography-free evaporation method for the construction of BP based field-effect transistors and photodetectors and systematically compare their performances with those of BP counterparts fabricated by conventional lithography and transfer electrode methods. The results show that BP devices fabricated by direct evaporation method possess higher mobility, faster response time, and smaller hysteresis than those prepared by the latter two methods. This can be attributed to the clean interface between BP and evaporated-electrodes as well as the lower Schottky barrier height of 20.2 meV, which is given by the temperature-dependent electrical results. Furthermore, the BP photodetectors exhibit a broad-spectrum response and polarization sensitivity. Our work elucidates a universal, low-cost and high-efficiency method to fabricate BP devices for optoelectronic applications.

Revealing effects of common nonmetallic impurities on the stability and strength of Cu–Sn solder joints: A first-principles investigation

Nonmetallic elements can affect the stability and usability of Cu–Sn solder joints intensively. The electronic structure, adhesion work, and tensile strength of Cu(111)/Cu3Sn(001) interface doping with H, C, O and S have been systematically investigated herein using the first-principles calculations. Cu(Cu)-terminated interface is the most stable among the clean Cu(111)/Cu3Sn(001) interfaces. In the non-metallic atoms doping Cu(111) surface system, H atom tends to occupy tetrahedral interstitial sites, while C, O and S atoms prefer to octahedral interstitial sites. The calculated segregation heat (ΔGseg) indicates that H and O atoms tend to stay in the interior, while C and S atoms tend to segregate to the Cu(111)/Cu3Sn(001) interface. From adhesion works, the order of binding strength is SOct > clean interface > OOct > COct > HTet. Finally, electronic structures of doping systems are analyzed to reveal the effects of nonmetallic impurities on the stability and strength of Cu–Sn solder joints. These results will provide guidance for the design of modified Cu–Sn solder joints.

Chemical vapor deposited WS2/MoS2 heterostructure photodetector with enhanced photoresponsivity

Two-dimensional transition metal dichalcogenides (TMDCs) have attracted great interest due to their unique semiconductor properties. Among all TMDC materials, MoS2 and WS2 are promising for composing heterostructures. However, traditional TMDC heterostructure fabrication depends on transfer process, with drawbacks of interface impurity and small size. In this work, a two-step chemical vapor deposition (CVD) process was applied to synthesize large-scale WS2/MoS2 heterostructure. Surface morphology and crystal structure characterizations demonstrate the high-quality WS2/MoS2 heterostructure. The WS2/MoS2 heterostructure photodetector fabricated by photolithography exhibits an enhanced photoresponsivity up to 370 A W−1 in comparison with single WS2 or MoS2 devices. This study suggests a direct CVD growth of large-scale TMDC heterostructure films with clean interface. The built-in electric field at interface contributes to the separation of photo-generated electron–hole pairs, leading to enhanced photocurrent and responsivity, and showing promising potentials in photo-electric applications.

Hf6Ta2O17/Ta2O5 composite ceramic: A new eutectic system

Eutectic oxides are considered as the most promising candidates applied in extreme environment for long periods, and the pace of exploring new eutectic systems has never stopped. In the present work, Hf6Ta2O17/Ta2O5 eutectic system is firstly prepared by the joint process of solvothermal method and spark plasma sintering (SPS). Eutectic liquid phase produced during the process of SPS fills the closed-pores and promotes the sintering process. Orthorhombic-Hf6Ta2O17 and tetragonal-Ta2O5 of both eutectic and hypereutectic systems show single crystal characteristics and are combined by coherent interface instead of grain boundaries. The clean and flat interface also shows the characteristics of single crystal diffraction without impurities and amorphous phase. Based on the analysis of microstructure, the sintering mechanism is proposed, and the potential application of Hf6Ta2O17/Ta2O5 eutectic system is analyzed.

Stability and tip streaming of a surfactant-loaded drop in an extensional flow. Influence of surface viscosity

We study numerically the nonlinear stationary states of a droplet covered with an insoluble surfactant in a uniaxial extensional flow. We calculate both the eigenfunctions to reveal the instability mechanism and the time-dependent states resulting from it, which provides a coherent picture of the phenomenon. The transition is of the saddle-node type, both with and without surfactant. The flow becomes unstable under stationary linear perturbations. Surfactant considerably reduces the interval of stable capillary numbers. Inertia increases the droplet deformation and decreases the critical capillary number. In the presence of the surfactant monolayer, neither the droplet deformation nor the stability is significantly affected by the droplet viscosity. The transient state resulting from instability is fundamentally different for drops with and without surfactant. Tip streaming occurs only in the presence of surfactants. The critical eigenmode leading to tip streaming is qualitatively the same as that yielding the central pinching mode for a clean interface, which indicates that the small local scale characterizing tip streaming is set during the nonlinear droplet deformation. The viscous surface stress does not significantly affect the droplet deformation and the critical capillary number. However, the damping rate of the dominant mode considerably decreases for viscous surfactants. Interestingly, shear viscous surface stress considerably alters the tip streaming arising in the supercritical regime, even for very small surface viscosities. The viscous surface stresses alter the balance of normal interfacial stresses and affect the surfactant transport over the stretched interface.