Interface Roughness Research Articles

Evolution of the liquid/solid interface roughness in Si1-xGex layers processed by nanosecond laser annealing

Pulsed laser annealing is a relevant alternative to conventional thermal processes for future technology nodes as it enables the application of a fast and local thermal budget. Such high-energy process can lead to the formation of a liquid phase that recrystallizes upon heat dissipation, through a high velocity liquid/solid interface moving towards the surface. Here, we report on the evolution of the liquid/solid interface roughness and its influence on the crystallinity of Si1-xGex layers depending on multiple parameters (strain state, doping level, Ge content, and pulse duration). This has been conducted with a roughness quantification method based on cross-section STEM-HAADF micrographs. It has been established that the liquid/solid roughness can be decreased by: (i) a compressive strain decrease, (ii) the use of short duration laser pulses or (iii) a reduction of the initial Ge content. The Ge content and strain must correspond to suitable values for optimized MOSFET performances. Consequently, strain and pulse duration were found to be pertinent levers for liquid/solid interface roughness reduction. Increasing the amount of boron atoms in s-Si1-xGex:B/Si systems is another relevant strategy, as compressive strain decrease would then be associated with a beneficial contact resistance lowering in the source-drain regions of p-type MOSFET devices.

Damage model of NC-UHPC interface zone in UHPC wet joint based on DIC

The bond interface of the ultra-high performance concrete (UHPC) wet joint composed of normal concrete (NC) and UHPC is a weak part, which can easily damage the interface zone and affects the structure's safety. However, the damage model of the NC-UHPC interface zone in UHPC wet joint has not been carried out yet. In this study, firstly, the effects of different interfacial moisture content and interfacial roughness on the interfacial bond strengths were investigated by splitting tensile tests, NC-UHPC specimens with different interfacial bond strength were obtained, and digital image correlation (DIC) technique was used to obtain the strain evolution regulation of the NC-UHPC interface zone; Secondly, the extended interface zone damage factor Df was used to investigate the damage differences of NC-UHPC interface zone with different bond strengths; Finally, the damage model of NC-UHPC interface zone with different interfacial bond strengths was established. This research will be of great significance in improving the theoretical system of UHPC wet joint structure design.

Microscopic insights into UiO-66@proton exchange composite membrane by molecular dynamics simulation

UiO-66 as one of the known metal-organic frameworks (MOFs) has been recognized as highly promising dopants for enhancing the proton conductivity of proton exchange membrane (PEM) owing to the large pore volume and structure tunability. Despite the numerous experimental reports on MOF-doped PEMs, their increased proton conductivity is commonly ascribed to enhanced water uptake. The underlying mechanisms from a microscopic perspective remain elusive. Therefore, this work explores the microstructure and water diffusion dynamics within composite membranes to decipher their mechanisms involved in proton conductivity using molecular dynamics (MD) simulations. Four types of composite membranes based on two representative MOFs i.e. UiO-66 and UiO-66-NH2 and two PEMs including Nafion and Dow, respectively, were taken into account. It is revealed that the UiO-66-NH2 doped Nafion composite membrane exhibits the highest water uptake among the four composite membranes resulting from the super hydrophilicity of UiO-66-NH2. Besides, the more concentrated distribution of sulfonic groups near the water-PEM interface and the higher interface roughness of UiO-66-NH2 doped Nafion lead to more water molecules surrounding its sulfonic groups that are favorable for the proton dissociation from sulfonic groups. Furthermore, the increased water channel connectivity of MOF-doped membranes that promotes proton transport through water via the Grotthuss mechanism demonstrates one of the mechanisms for increased proton conductivity. On the other hand, although the reduced lifetime of the hydrogen bond network and the enhanced water diffusion coefficient within MOF-doped membranes manifest the favorable proton transfer via the Vehicle mechanism. Overall, UiO-66-NH2 doped Nafion membranes exhibiting the highest water channel connectivity and water diffusion coefficients demonstrate the greatest potential of UiO-66-NH2 doping in advancing the proton conductivity. These findings provided microscopic insights into understanding the improved proton conductivity mechanism of MOF doped PEMs, and the approaches developed in this work may be extended to other composite membranes.

Reducing disorder in Ge quantum wells by using thick SiGe barriers

We investigate the disorder properties of two-dimensional hole gases in Ge/SiGe heterostructures grown on Ge wafers, using thick SiGe barriers to mitigate the influence of the semiconductor–dielectric interface. Across several heterostructure field effect transistors, we measure an average maximum mobility of (4.4±0.2)×106 cm2/Vs at a saturation density of (1.72±0.03)×1011 cm−2, corresponding to a long mean free path of (30±1)μm. The highest measured mobility is 4.68×106 cm2/Vs. We identify uniform background impurities and interface roughness as the dominant scattering mechanisms limiting mobility in a representative device, and we evaluate a percolation-induced critical density of (4.5±0.1)×109 cm−2. This low-disorder heterostructure, according to simulations, may support the electrostatic confinement of holes in gate-defined quantum dots.

Organic ferroelectric transistors with composite dielectric for efficient neural computing

Organic ferroelectric field-effect transistors (Fe-OFETs) exhibit exceptional capabilities in mimicking biological neural systems and represent one of the primary options for flexible artificial synaptic devices. Ferroelectric polymers, such as poly(vinylidene fluoride-trifluoroethylene) (P(VDF-TrFE)), given their strong ferroelectricity and facile solution processing, have emerged as the preferred choices for the ferroelectric dielectric layer of wearable devices. However, the solution processed P(VDF-TrFE) films can lead to high interface roughness, prone to cause excessive gate leakage. Meanwhile, the ferroelectric layer in neural computing and memory applications also faces a trade-off between storage time and energy for read/write operations. This study introduces a composite dielectric layer for Fe-OFETs, fabricated via a solution-based process. Different thicknesses of poly(N-vinylcarbazole) (PVK) are shown to significantly alter the ferroelectric hysteresis window and leakage current. The optimized devices exhibit synaptic plasticity with a transient current of 3.52 mA and a response time of approximately 50 ns. The Fe-OFETs with the composite dielectric were modeled and integrated into convolutional neural networks, achieving a 92.95% accuracy rate. This highlights the composite dielectric's advantage in neuromorphic computing. The introduction of PVK optimizes the interface and balances device performance of Fe-OFETs for neuromorphic computing.

Transport and material properties of doped BiSbX topological insulator films grown by physical vapor deposition

Abstract Topological Insulator (TI) BiSb is a promising material for spin-orbit torque (SOT) devices because of its high spin Hall angle, relatively higher electrical conductivity, and can be produced at room temperature by physical vapor deposition. In this work, we systematically investigate the effects of doping BiSb with several dopants. We found that doping with elemental dopants does not change the bulk conductivity, but doping with metal-nitride or metal-oxide molecular dopants can substantially increase or decrease BiSb’s bulk film conductivity with minor impacts on its TI properties. Furthermore, doping can significantly improve other TI film material properties such as increased melting point and film hardness, producing smaller grain sizes with improved interfacial roughness, and enhanced (012) film growth texture, all of which can contribute to enhanced atomic migration resistance in and out of the BiSb layer. Thus, our results open a path for using doped BiSb in integrated SOT devices

Interfacial shear behavior of salt freeze-thaw pre-damaged NC with ECC: Experimental and theoretical investigations

This study aims to clarify the interfacial shear behavior of salt freeze-thaw pre-damaged normal concrete (NC) with engineered cementitious composite (ECC). A comprehensive analysis was conducted to study the effects of the cycle number, interfacial roughness, and ECC curing age on the interfacial shear performance. The results showed that, as the cycle number increased, the interfacial shear strength decreased to varying degrees. The optimal interfacial roughness was 5.5 mm, and further increasing roughness would decrease the interfacial shear stiffness. When the ECC curing age was 7 days, it had already reached 85 % of the interfacial shear strength of specimens cured for 28 days. Additionally, considering the effects of cycle number and interfacial roughness, an interfacial shear strength calculation model and a shear-slip curve prediction model were established, providing a valuable reference for the engineering application of ECC repair for salt freeze-thaw damaged NC.

Modeling and calculation of ground penetrating radar detection on rough interface of soil media

Abstract Ground penetrating radar technology is an effective underground physical detection method. In order to better study the ground penetrating radar echo characteristics of complex soil media rough interfaces, a soil rough surface electromagnetic scattering model based on fractal rough surface geometry modeling and soil media dielectric properties modeling is established. The mixed soil characteristics including sand content, water content, clay content, and sand particle density are analyzed, and the radar echo image characteristic of soil rough media interfaces under different fractal dimensions is discussed.

Research on ultrasonic testing method for tangential contact stress based on equivalent medium theory

As a weak link, the joint surface of machine tools directly affects the stiffness and machining accuracy of the entire machine tool. However, obtaining the distribution of contact stress is a key problem that urgently needs to be solved in exploring the mechanical properties of joint surface connections. In this paper, a tangential contact stress ultrasonic testing method based on the equivalent medium theory is proposed, providing data support for accurately characterizing the contact state of the joint surface. A virtual material model of rough contact interface based on fractal theory is established to explore the coupling relationship between the propagation speed of ultrasonic critical refracted longitudinal waves, the tested object’s material parameters, and stress. Moreover, the expression of the equivalent material parameters of the ultrasonic critical refracted longitudinal wave propagation layer with stress variation is derived. An ultrasonic acoustic time difference model considering changes in contact surface material parameters is constructed based on the principle of acoustic elasticity of ultrasound. Furthermore, a critical refractive detection model for longitudinal wave’s tangential contact stress is established based on equivalent medium theory. Experimental specimens and stress detection plans are designed, and the tangential contact stress of the specimens is measured based on the division of surface grids. The equivalent stress value of each node is calculated based on the von Mises stress by measuring the stress in the X/Y direction. In addition, a shear stress distribution cloud map of the contact surface is drawn. Finally, the accuracy of the detection results is confirmed by combining theory, simulation, and experimental methods. The proposed tangential contact stress detection method based on critical refractive longitudinal waves is significant for low-stress assemblies.

Properties of Sn-3.0Ag-0.5Cu solder joints under various soldering conditions: Reflow vs. Laser vs. Intense Pulsed Light soldering

In this study, the properties of solder joints were compared after bonding process using different energy sources. Various soldering methods were employed, including reflow, laser, and Intense Pulsed Light (IPL) soldering. When reflow soldering was performed for a relatively long time, coarse solder microstructures and interfacial intermetallic compound (IMC) grains were formed. Laser and IPL soldering, which have rapid heating/cooling times, formed fine solder microstructure and thin interfacial IMCs. Then, it was confirmed that Cu6Sn5 and Cu3Sn IMCs were formed at the SAC305/OSP (organic solderability preservative) interface and (Cu,Ni)6Sn5, Ni–Sn–P, and Ni3P were formed at the SAC305/ENEPIG (electroless nickel electroless palladium immersion gold) interface. An observation of the IMC grain morphology under various soldering conditions revealed that (Cu,Ni)6Sn5 was formed on the ENEPIG substrate, which was polygonal and smaller than on the OSP substrate. The shear strength of the joint increased in the order of reflow, laser, and IPL soldering. Additionally, ductile fractures occurred under all conditions. The IPL soldering joint had a thinner IMC compared to reflow soldering, and moderate interface roughness and bonding area compared to laser soldering. Based on the obtained results, a next-generation IPL soldering method is proposed to improve the properties of Sn-3.0Ag-0.5Cu solder joints.

Aluminate-activated nano-SiO2 for enhancing water vapor barrier properties in polymers films: A safe and effective strategy

In this work, a series of nanocomposite films composed of polylactic acid (PLA), poly (butylene adipate-co-terephthalate) (PBAT), polybutylene succinate (PBS), nano-SiO2 activated by aluminate for different times were developed to enhance water vapor barrier properties. The physiochemical and thermal properties of the films were characterized. In addition, total and aluminum migration from the films was monitored, and non-targeted screening was performed to evaluate the potential safety of the composite films. Fourier Transform infrared spectroscopy analysis indicated that the nano-SiO2 was successfully activated by aluminate. Differential scanning calorimetry analysis indicated that incorporation of the activated nano-SiO2 slightly reduced the glass transition temperature (from 54 to 51 °C) and increased the crystallinity degree (from 6.9 % to 11.1 %) of PLA. Incorporation of 0.4 % nanofillers was found to give the highest crystallinity. Thermogravimetric analysis showed that the thermal stability of the PLA/PBAT/PBS films did not change significantly after adding the activated-nano-SiO2. However, the incorporation of these nanofillers did increase the interfacial roughness and crystallinity degree of the films, thereby reducing the water vapor permeability by around 30 %. Erucamide was detected in the composite films after exposure to food simulants, however, the films containing the nanofillers still met European Union safety standards. In summary, the nanofiller-loaded polymer films developed in this study were shown to be safe and have high water barrier properties, which means they may be suitable for application in the food, cosmetic, personal care, pharmaceutical, and agrochemical industries.

Evolution of interface and surface morphology of WC/SiC multilayers with increase in number of bilayers

WC/SiC multilayer mirrors are promising elements for operation in the short wavelength range of hard X-rays and even gamma-rays. A set of WC/SiC multilayers with nominal bilayer thickness of 3.0 nm with 30, 50, 100, and 200 bilayers have been deposited by magnetron sputtering method. The evolution of interface and surface morphology with addition of the number of bilayers has been investigated. The methods of grazing incidence X-ray reflectivity, X-ray diffuse scattering, optical profiler, atomic force microscope, transmission electron microscopy and energy-dispersive X-ray spectroscopy have been used. It is found that the interface roughness plays a dominant role in interface imperfections of WC/SiC and it exhibits slight accumulation across the multilayers with the number of bilayers increasing. The surface roughness also increases in relatively high spatial frequency range as the number of bilayers has been added, due to the cumulative increase in interface roughness. The interface roughness accumulation ultimately contributes to the diminishment of optical performance of WC/SiC multilayers with a large number of bilayers. At the wavelength of 0.154 nm, a peak reflectivity of 69.2 % is achieved for a 100 bi-layer multilayer under the grazing incidence of approximately 1.5°, while lower reflectivity of 67.2 % for a 200 bi-layer multilayer.

Centrifuge Modelling of the Load-Deflection Response of Single Piles in Sand Under One-Way Cyclic Lateral Loads

This article aims to present the experimental results of one-way cyclic lateral loading tests on centrifuged small-scale models of piles in sand, carried out in the IFSTTAR centrifuge, center of Nantes (France). After a literature review, the pile models, their instrumentation, the experimental devices, as well as the construction of the sand mass were described. Cyclic P-Y lateral reaction curves were derived and the effect of the number of cycles, the soil density, the pile/soil interface roughness, as well as the pile/soil stiffness ratio on their parameters were analyzed. The experimental evolution of the pile top deflection as well as the bending moment along the pile were compared to the usual formulations of the cyclic degradation law.

Constructing the Enamel-Like Dentin Adhesion Interface to Achieve Durable Resin-Dentin Adhesion.

Enamel adhesion is acknowledged as durable; however, achieving long-lasting dentin adhesion remains a formidable challenge due to degradation of exposed collagen matrix after acid-etching of dentin. The idea of developing an enamel-like adhesion interface holds great promise in achieving enduring dentin adhesion. In this study, we constructed an enamel-like adhesion interface using a rapid remineralization strategy comprising an acidic primer and a rapid remineralization medium. Specifically, the acidic primer of 10-methacryloyloxydecyl dihydrogen phosphate (MDP) and epigallocatechin-3-gallate (EGCG) nanocomplex (MDP@EGCG primer) was utilized to partially demineralize dentin within 30 s, and the MDP@EGCG nanocomplex showed a strong interaction with exposed collagen, enhancing collagen remineralization properties. Then, the rapid remineralization medium containing polyaspartate (Pasp) stabilized amorphous calcium and phosphorus nanoclusters (rapid Pasp-CaP) was applied to modified dentin collagen for 1 min, which caused rapid collagen remineralization within a clinically acceptable time frame. This strategy successfully generated an inorganic rough and porous adhesive interface resembling etched enamel, fundamentally addressed issues of collagen exposure, and achieved durable dentin adhesion in vitro and in vivo while also ensuring user-friendliness. It exhibited potential in prolonging the lifespan of adhesive restorations in clinical settings. In addition, it holds significant promise in the fields of caries and dentin sensitivity treatment and collagen-based tissue engineering scaffolds.

Influences of interface bonding behavior on the arresting performance of CFRP buckle arrestors - Part I: Experiments

CFRP can effectively serve as buckle arrestors for subsea pipelines in virtue of the advantages of lightweight, high strength, and corrosion resistance. In this paper, the interface bonding tests were firstly carried out to assess the bonding performance between the CFRP and pipelines. Three types of tests were designed to evaluate the circumferential, axial, and radial bonding properties, respectively, covering the double-strap joint shear test, axial tensile test, and normal tensile test. The stress-bonding slip responses were measured and various failure modes were identified. The effect of CFRP thickness, type of adhesive, adhesive thickness, and interface roughness on the interface bonding property was explored. Subsequently, SS304 pipe specimens wrapped with CFRP buckle arrestors were tested in a hyperbaric vessel. The pressure-variation in volume curves were obtained, and the flattening and U-shape modes were observed. The influences of adhesive type, adhesive thickness, interface roughness, number of CFRP layers, CFRP thickness, and CFRP length on the crossover pressure were examined. The results demonstrate that the number of CFRP layers and CFRP thickness remarkably affect the arresting performance of CFRP arrestors, and the influence of interface bonding properties on the arresting ability is not as significant as the adhesive strength.

Research on compression failure criteria and characteristics of rock-concrete assemblies with rough interfaces

The combination of rock and concrete lining structures is a typical composite structure in the field of engineering. This study is based on the concept of equivalent strain energy and establishes a mechanical equivalent model for rock-concrete assemblies (RCA). Assuming that both rock and concrete satisfy the Mohr-Coulomb criterion, we derive the shear failure criterion of the equivalent model considering the roughness of the rock-concrete interface. The applicability of the model was verified through uniaxial and triaxial tests on eight different types of RCA structures. The research results indicate that an increase in confining pressure enhances the strength of the RCA. When the confining pressure reaches a certain value, concrete only experiences shear failure, and no macroscopic cracks appear in the rock. The structure of the RCA tends towards isotropy. As the height ratio of the RCA increases, its strength decreases. At minimal concrete height ratios, the strength of the RCA gradually approaches that of concrete. This study can provide valuable insights for designing and evaluating stability in engineering rock bodies within diverse geological environments.

Peeling-induced interfacial roughness and charging for enhanced triboelectric power generation

To date, there have been a lot of efforts to enhance the conversion efficiency of triboelectric nanogenerators (TENGs) via physical and chemical modifications of the polymer surface. Herein, we report that a facile peeling of polymer from a substrate can enhance the triboelectric power output. The peeling of spin-coated polydimethylsiloxane (PDMS) from glass and polytetrafluoroethylene (PTFE) substrates has revealed a considerable increase in interfacial roughness and lateral friction. Surface-sensitive X-ray photoemission spectroscopy and non-contact current measurements have also revealed the transfer of counter-material and interfacial charging. The surface roughness of peeled PDMS is significant for the PTFE substrate, while the surface charge is significant for the glass substrate. The triboelectric output power density for peeled PDMS from the substrate is similar, 10.3 µW/cm2, but significantly larger than that for as-grown PDMS (2.2 µW/cm2). The peeling strength of PDMS significantly increases for glass compared to PTFE after the oxygen plasma treatment of substrates. The triboelectric charge of peeled PDMS from a plasma-treated glass substrate is almost 1.3 times larger than that from a PTFE substrate. This work implies that peeling polymer from a rough substrate with a large adhesion force would be a facile and effective way to increase the triboelectric power output, without any delicate surface treatments.

Enhancing interfacial heat conduction in diamond-reinforced copper composites with boron carbide interlayers for thermal management

In this work, we have synthesized a copper/boron carbide/diamond composite structure via magnetron sputtering. Surface roughness of the diamond layers was characterized using atomic force microscopy (AFM), and interfacial thermal conductance (ITC) between copper and diamond was experimentally measured by the Time-domain Thmoreflectance (TDTR) technique. Molecular dynamics (MD) simulations were conducted to investigate the influence of the <010> crystal plane thickness of boron carbide and interface roughness on the ITC. The results indicate a significant increase in ITC with the incorporation of a <010>-oriented boron carbide interlayer. The ITC initially rose and then fell as the boron carbide layer thickness increased, reaching a maximum of 286.52 MW m−2 K−1 for a three-layer (approximately 2 nm) interlayer, which is 14.1 times higher than that of the unmodified interface. Additionally, by creating a three-dimensional sinusoidal rough interface, we observed that increasing interface roughness can further enhance heat transfer efficiency up to a certain threshold, beyond which a saturation in phonon heat conduction is anticipated. The simulation outcomes are in good agreement with the experimental data, confirming the reliability of our findings.

Static and Dynamic Stress of the Combined Rotor with Curvic Couplings Considering the Rough Three-Dimensional Interface at Extreme Operating Conditions

The curvic coupling, as one of the common connecting structures for gas turbine combined rotors, is more susceptible to various dynamic and static loads at extreme operating conditions. But, traditional combined rotor models tend to neglect the influence of the connection structure, especially failing to consider the contribution of the curvic coupling interfaces. To address this problem, this paper establishes a solid geometric model of the combined rotor with curvic couplings considering the rough three-dimensional interfaces. The effectiveness of the proposed model method is indirectly verified through the compression tests and modal tests. Subsequently, combined with finite element calculations, the mechanical properties of the rotor with curvic couplings considering the rough interface are analyzed under static and dynamic load conditions. The results indicate that the roughness of the interface significantly affects the deformation of the contact surface under static load, but its impact on the overall deformation of the rotor is relatively insignificant. The dynamic stress at the interface exhibits periodic variations at the resonance speed. At the maximum operating speed, the dynamic stress is influenced by the magnitude of imbalance. The aforementioned methods and conclusions provide a reference for the design research and engineering application of combined rotors.

In situ observation and numerical analysis of temperature gradient effects on growth velocity during directional solidification of silicon

AbstractThe &lt; 110 &gt; directional solidification of silicon under varying overall temperature gradients was investigated using an in situ observation system. The growth velocity of an atomically rough interface was found to decrease with increasing temperature gradient. A theoretical model of the thermal field taking undercooling into account was developed to describe this phenomenon and was demonstrated to be valid. The results of this work indicate that the reported linear relationship between growth velocity (V) and undercooling (ΔT), given by V (mm s−1) = 120ΔT (K), is most accurate in the case of a rough interface. In the case that the overall temperature gradient is small, the melting point isotherm moves rapidly such that it becomes more difficult for the interface to keep pace with the isotherm compared with a large temperature gradient. This effect leads to increased undercooling at the interface and consequently a rapid growth velocity. Thermal field calculations confirm that a rapid increase in the ratio of the temperature gradient in the crystal to that in the melt should increase the latent heat release, again providing a more rapid growth velocity.