Copper Single Crystal Surfaces Research Articles

Interfacial reaction of Sn-1.5Ag-2.0Zn low-silver lead-free solder with oriented copper

High density packaging technology reduces the pad size and the number of grains contained in the pad. When the polycrystalline pad turns into a single crystal pad, the grain orientation has an important impact on the formation of the intermetallic compound (IMC) at the interface. The growth of IMC at the interface between the solder and the single-crystal copper substrate is investigated by selecting the prospective Sn-1.5Ag–2Zn as the solder alloy. Sn-1.5Ag-2.0Zn lead-free solder joints soldered with single crystal (111) copper substrate and polycrystalline red copper substrate are reflowed at 250 °C for 5 min. Samples are subsequently aged at 160 °C. The uneven scallop like Cu6Sn5 IMC layer grows rapidly when the alloy solder contacts with the copper substrate. The Cu6Sn5 grain size formed on the surface of single crystal copper is larger than that of polycrystalline copper. Single crystal copper has no grain boundary to block atomic diffusion, which affects grain nucleation and growth. The growth rate of Cu6Sn5 formed by alloy solder and the single crystal (111) copper solder joint after aging treatment at 160 °C for 20 h is about twice that of the polycrystalline copper solder joint. Then it grows slowly with the increase of aging treatment time. The thick layer Cu6Sn5 breaks due to crack diffusion after 600 h of aging treatment, and the thickness of IMC remains at 3.5 μm. Cu5Zn8 generated at the solder and polycrystalline copper solder joint during aging treatment acts as a barrier layer, preventing the solder from contacting the copper substrate and inhibiting the formation of Cu6Sn5. Cu5Zn8 is broken and decomposed after 300 h of aging treatment, and Cu6Sn5 grows rapidly after the barrier layer disappeared. The thickness of Cu6Sn5 is about 2.8 μm. The thickness of IMC of solder joint on single crystal copper is 0.7 μm more than that on polycrystalline copper. After aging treatment, the IMC formed at the interface between alloy solder and single crystal copper has better compactness and basically no pores, while there are obvious pores between IMC grains at the interface between alloy solder and polycrystalline copper, which can predict that the soldering quality of the interface between alloy solder and single crystal copper is better. This will provide application prospects for solder joint interface reliability research.

Prediction of yield surface of single crystal copper from discrete dislocation dynamics and geometric learning

The yield surface of a material is a criterion at which macroscopic plastic deformation begins. For crystalline solids, plastic deformation occurs through the motion of dislocations, which can be captured by discrete dislocation dynamics (DDD) simulations. In this paper, we predict the yield surfaces and strain-hardening behaviors using DDD simulations and a geometric manifold learning approach. The yield surfaces in the three-dimensional space of plane stress are constructed for single-crystal copper subjected to uniaxial loading along the [100] and [110] directions, respectively. With increasing plastic deformation under [100] loading, the yield surface expands nearly uniformly in all directions, corresponding to isotropic hardening. In contrast, under [110] loading, latent hardening is observed, where the yield surface remains nearly unchanged in the orientations in the vicinity of the loading direction itself but expands in other directions, resulting in an asymmetric shape. This difference in hardening behaviors is attributed to the different dislocation multiplication behaviors on various slip systems under the two loading conditions.

Considerably Increased Dynamics of CO-Water Complexes over CO and Water Alone.

Solvents are increasingly known to influence chemical reactivity. However, the microscopic origin of solvent effects is scarcely understood, particularly at the individual molecule level. To shed light on this, we explored a well-defined model system of water (D2O) and carbon monoxide on a single-crystal copper surface with time-lapsed low-temperature scanning tunneling microscopy (STM) and ab initio calculations. Through detailed measurements on a time scale of minutes to hours at the limit of single-molecule solvation, we find that at cryogenic temperatures CO-D2O complexes are more mobile than individual CO or water molecules. We also obtain detailed mechanistic insights into the motion of the complex. In diffusion-limited surface reactions, such a solvent-triggered increase in mobility would substantially increase the reaction yield.

Atomic simulations of tip-based nanomilling on single-crystal copper

An atomic force microscopy (AFM) tip-based scratching method was used to machine 2D/3D micro-nanostructures. However, the machining efficiency is too low for these structures to find wide used in applications. An AFM tip-based nanomilling approach is more efficient due to the associated higher material removal rate. This paper compares the material removal mechanisms of single-scratch and nanomilling processes close to the atomic scale on a single-crystal copper surface using molecular dynamics simulations. By analyzing the groove morphology, atomic flow behavior, and the variation in scratching force, the material removal mechanism is revealed. Moreover, the effects of tip trajectory and crystallographic orientation on atomic removal are studied by analyzing the relationship between the evolution of subsurface defects and material removal. This work reveals the mechanism underlying material removal in nanomilling in detail, which will greatly improve the ability of the tip-based nanomachining method.

Molecular Dynamics Simulations of Ripple Nanostructure Formation During Nanomachining via Atomic Force Microscopy

Molecular dynamics (MD) constant force simulation mode is first used to study the formation of the ripple nanostructures on the single-crystal copper surface by combining the topography generated by machined grooves with the accumulated pile-up material on the side of these grooves via a triangular pyramid atomic force microscopy (AFM) tip. Groove morphologies, lateral forces, the evolution of subsurface defects, and atomic flow laws generated by different machining parameters are discussed. Specifically, the normal load, the feed value between grooves, and the scratching direction significantly affect groove formation. The simulated morphologies of the ripple nanostructures indicate that groove consistency and symmetry increase with increasing feed, and an optimized feed for various normal loads can be determined. The interaction between adjacent grooves produces a variation in the lateral forces with the groove number and feed. This is mainly related to the evolution of subsurface defects, the atomic flow law, and the volume of material pile-ups. The distributions of subsurface defects affect the atomic flow directions, and the atomic flow laws determine groove formation. The simulations provide important guidance for ripple nanostructure fabrication on single-crystal copper surface via AFM tips.

Numerical Analysis of Multi-Angle Precision Microcutting of a Single-Crystal Copper Surface Based on Molecular Dynamics.

The molecular dynamics method was used to study the removal mechanism of boron nitride particles by multi-angle microcutting of single-crystal copper from the microscopic point of view. The mechanical properties and energy conversion characteristics of single-crystal copper during microcutting were analyzed and the atomic displacement and dislocation formation in the microcutting process are discussed. The research results showed that during the energy transfer between atoms during the microcutting process of boron nitride particles, the crystal lattice of the single-crystal copper atom in the cutting extrusion region was deformed and displaced, the atomic temperature and thermal motion in the contact area between boron nitride particles and Newtonian layer of workpiece increased, the single-crystal copper atom lattice was defective, and the atomic arrangement structure was destroyed and recombined. The interface of different crystal structures formed a dislocation structure and produced plastic deformation. With the increase of the impact cutting angle, the dislocation density inside the crystal increased, the defect structure increased and the surface quality of the workpiece decreased. To protect the internal structure of the workpiece and improve the material removal rate, a smaller cutting angle should be selected for the abrasive flow microcutting function, which can reduce the formation of an internal defect structure and effectively improve the quality of abrasive flow precision machining. The research conclusions can provide a theoretical basis and technical support for the development of precision abrasive flow processing technology.

Theoretical understanding of the electrochemical reaction barrier: a kinetic study of CO2 reduction reaction on copper electrodes.

The electrochemical reduction of CO2 is a promising route for converting intermittent renewable energy into storable fuels and useful chemical products. A theoretical investigation of the reaction mechanism and kinetics is beneficial for understanding the electrocatalytic activity and selectivity. In this report, a kinetic model based on Marcus theory is developed to compute the potential-dependent reaction barrier of the elementary concerted proton-electron transfer steps of electrochemical CO2 reduction reactions, different from the previous hydrogen atom transfer model. It is found that the onset potentials and rate-determining steps for CO and CH4 formation are determined by the first and third concerted proton-electron transfer steps C1 and C3. The influence of binding energy, electrode potential, and reorganization energy on the computed reaction barriers of the C1 and C3 reactions is discussed. In general, the calculated reaction barrier shows a quadratic relationship with the applied electrode potential. Specifically, the reaction barrier is merely determined by the reorganization energy at equilibrium potential. The present kinetic model is applied to compare the electrocatalytic activities in the electrochemical reduction of CO2 on various copper crystal surfaces. Among the four studied copper single-crystal surfaces, Cu(211) exhibits the best electrocatalytic activity for CO formation and CH4 formation due to its low onset potential and overpotential.

Photochemical Synthesis of Azoarenes from Aryl Azides on Cu(100): A Mechanism Unraveled

Thermal, photochemical, and metal-facilitated routes to aryl nitrenes via the extrusion of dinitrogen from aryl azides adsorbed on a single-crystal copper surface have been investigated. Only by ir...

Effects of diamond tip orientation on the dynamic ploughing lithography of single crystal copper

In the present study, molecular dynamics (MD) simulation and experimental tests are employed to investigate the influence of the probe orientation on the machined depth, generation of the material pile-up, and average cutting force when implementing dynamic ploughing process on a single crystal copper surface. A typical triangular pyramid diamond AFM tip is selected, and three probe orientations are studied. The energy dissipation per oscillation of the AFM cantilever is utilized to describe the interaction between the probe and sample surface experimentally. Results show that the probe orientation has a significant effect on the machined depth and material pile-up on the sides of the groove. The MD simulations mainly agree well with the experimental results. Based on the MD simulations, the difference of the machined depth results from the various material flow directions during the ploughing process. The average cutting force is also studied by the MD simulations, which shows good consistency with the variation of probe-sample contact area during the dynamic ploughing along each machined groove. These results indicate the tip orientation is also an important factor in the dynamic ploughing process, which can be used as a reference to improve the machining accuracy and optimize machining parameters in the dynamic ploughing lithography to broaden its practical application.

Quasicontinuum multiscale modeling of the effect of rough surface on nanoindentation behavior

Roughness of surface has as an important influence on identifying the mechanical behavior and performance of crystalline metals. In this study, nanoindentation simulations are conducted by the two dimensional quasicontinuum method to determine the load–penetration response and the critical load associated with the onset of plasticity in rough surfaces of a face-centered cubic single crystal copper. The arithmetic roughness index, ranging between 2 and 13 A, is used to specify the roughness of surface. Results of indentation with different roughnesses are in good agreement with previous studies for the indenter size of 10–140 A. The resultant load–penetration scattering, which stems from the roughness, indicates different dislocation nucleation steps, different subsequent dislocations intervals and varying stiffness values of samples. It can be concluded that the surface roughness has a significant effect on the first dislocation emission because of the indenter position and surface interactions beneath it. Moreover, the critical penetration depth for the first dislocation emission increases by the increase of the contact area between the indenter and surface.

Nonadiabatic Hydrogen Dissociation on Copper Nanoclusters.

Copper surfaces exhibit high catalytic selectivity but have poor hydrogen dissociation kinetics; therefore, we consider icosahedral Cu13 nanoclusters to understand how nanoscale structure might improve catalytic prospects. We find that the spin state is a surprisingly important design consideration. Cu13 clusters have large magnetic moments due to finite size and symmetry effects and exhibit magnetization-dependent catalytic behavior. The most favorable transition state for hydrogen dissociation has a lower activation energy than that on single-crystal copper surfaces but requires a magnetization switch from 5 to 3 μB. Without this switch, the activation energy is higher than that on single-crystal surfaces. Weak spin-orbit coupling hinders this switch, decreasing the kinetic rate of hydrogen dissociation by a factor of 16. We consider strategies to facilitate magnetization switches through optical excitations, substitution, charge states, and co-catalysts; these considerations demonstrate how control of magnetic properties could improve catalytic performance.

EBSD Analysis of Lattice Rotation near Fracture Surfaces of Fatigued Copper Single Crystals

EBSD Analysis of Lattice Rotation near Fracture Surfaces of Fatigued Copper Single Crystals

Electrochemical Reduction of CO2 Using Copper Single-Crystal Surfaces: Effects of CO* Coverage on the Selective Formation of Ethylene

Copper oxide-derived Cu catalysts are known to exhibit enhanced energetic efficiencies and selectivities towards the reduction of carbon dioxide to commercially vital C2 products such as ethylene (C2H4). However, the cause of this selectivity is not fully understood. In this work, we elucidated a fundamental reason underlying the selectivity of CO2 reduction toward C2 products by studying its reactivity on Cu(100), Cu(111), and Cu(110) single-crystal surfaces. A combination of cyclic and linear sweep voltammetries, chronoamperometry, online gas chromatography, 1H nuclear magnetic resonance spectroscopy, and density functional theory (DFT) calculations was employed for this end. A wide range of electrochemical potentials from −0.28 to −1.25 V versus the reversible hydrogen electrode was investigated. Aqueous 0.1 M KHCO3 was used as the electrolyte. We report here two general trends on Cu2O-derived Cu and Cu single-crystal surfaces: (i) the onset potential for the formation of C2H4 always starts 300–400 mV ...

Disappearing Enantiomorphs: Single Handedness in Racemate Crystals

Although crystallization is the most important method for the separation of enantiomers of chiral molecules in the chemical industry, the chiral recognition involved in this process is poorly understood at the molecular level. We report on the initial steps in the formation of layered racemate crystals from a racemic mixture, as observed by STM at submolecular resolution. Grown on a copper single-crystal surface, the chiral hydrocarbon heptahelicene formed chiral racemic lattice structures within the first layer. In the second layer, enantiomerically pure domains were observed, underneath which the first layer contained exclusively the other enantiomer. Hence, the system changed from a 2D racemate into a 3D racemate with enantiomerically pure layers after exceeding monolayer-saturation coverage. A chiral bias in form of a small enantiomeric excess suppressed the crystallization of one double-layer enantiomorph so that the pure minor enantiomer crystallized only in the second layer.

Laws of Development of Deformation Folds in [1<sup>-</sup> 11] Copper Single Crystal at Axis Compression

.Deformation folds on the surface of copper single crystal with compression axis orientation [] are analysed. Folds are an element of the deformation relief on meso-and macro-level secondary to macrobands. Folds are generated in several major crystal areas due to sample bending or striation in its end area.

Interference effect on friction behavior of asperities on single crystal copper

By using Green function molecular dynamics method, we systematically study the friction behavior of a single asperity and asperity array over the (111) surface of single crystal copper. We find that internal plastic behavior (burst of stacking faults, dislocation emission and propagation) is a promising reason for the higher value of static friction coefficient than that of dynamics friction in non-adhesive scratch. For the rough surface, however, the difference between static and dynamic friction coefficients disappear due to the interference between asperities. The interference dramatically increases the friction coefficient by introducing atomic scale plastic features (pile-up atoms, stacking faults, and U-shape dislocation loop).

Molecular dynamics simulation of nanoscale contact and sliding processes for probes with different tip radius of curvature

Three-dimensional molecular dynamics (MD) simulations were carried out to study the contact and sliding processes between diamond points with different tip radius of curvature and surfaces of single crystal copper. The material deformation, abrasion mechanism, lattice defects, the force of contact process, and the sliding friction process were investigated. The simulation results show that the contact force, dislocations, and stacking fault defects, increase during the contact process with increasing contact depth or tip radius of curvature. The dislocations emit along the $$ \left[ {10\bar{1}} \right] $$ and $$ \left[ {\bar{1}0\bar{1}} \right] $$ direction and then a glide band is formed. It was also found that a greater tip radius of curvature results in a larger groove and more material deformation. The normal force and friction increase with increasing tip radius of curvature, but the coefficient of friction decreases. The stacking faults spread along the sliding direction and increase with increasing tip radius of curvature. In addition, the number of upheaval atoms increases as the radius of tip curvature or sliding distance increases.

An Investigation of Pool Boiling Heat Transfer on Single Crystal Surfaces and a Dense Array of Cylindrical Cavities

The pool boiling heat transfer characteristics of smooth single crystal and densely packed cylindrical cavity surfaces were investigated using two highly wetting fluids, perfluoro-n-hexane (FC-72) and n-hexane. Three single crystal copper surfaces and five undoped single crystal silicon surfaces with different plane orientations were considered. In addition, silicon surfaces with densely packed cylindrical cavities with diameters ranging from 9 to 75 μm, depth ranging from 9 to 20 μm, and spacing ranging from 75 to 600 μm were tested for comparison. It is observed that the copper single crystal surfaces show increasing heat transfer coefficient with decreasing atomic planar density. The single crystal silicon surfaces show increasing heat transfer coefficient with increasing atomic planar density. Plausible molecular scale mechanisms are discussed. In contrast, the silicon surfaces seeded with cylindrical cavities having diameters of 27 μm or less generally yield higher heat transfer coefficients than the single crystal silicon surfaces. A decrease in the cavity spacing results in a larger number of cavities on the surface, and the heat transfer coefficient increases as a result. Cavity depths of 6 and 20 μm result in the same heat transfer coefficient irrespective of cavity diameter. The nucleation site density for the cylindrical cavity surfaces is measured and reported at low superheat using a novel imaging technique.

Molecular Dynamics Simulations of Sliding Friction of Rigid Sphere with Single Crystal Copper Surface

Using LAMMPS to establish the three-dimensional sliding friction model of the nanoscale diamond hemisphere with the single-crystal copper surface. Simulation and solving the process of sliding friction, research the micro-contact area atomic states change in sliding friction process, and study the friction characteristics change when the rigid sphere sliding on rough surface of the single crystal copper with minute projections. The results indicate that, in the sliding friction process, the lattice of substrate atoms are damaged under the forces of the extrusion which also cause corresponding dislocation and deformation. In the direction of the hemisphere movement, generate the pileup and side stream phenomena, and produce furrows. Friction and normal force rapidly increase with the depth of contact, and then enter into a stable sliding phase. For the thermal motion of atoms, formation of dislocations and the stick-slip effect, the curves of friction and normal force present waves of sawtooth. Small defect on surface of the substrate almost have no effect on the process of sliding friction.

The evolution of machining-induced surface of single-crystal FCC copper via nanoindentation

The physical properties of the machining-induced new surface depend on the performance of the initial defect surface and deformed layer in the subsurface of the bulk material. In this paper, three-dimensional molecular dynamics simulations of nanoindentation are preformed on the single-point diamond turning surface of single-crystal copper comparing with that of pristine single-crystal face-centered cubic copper. The simulation results indicate that the nucleation of dislocations in the nanoindentation test on the machining-induced surface and pristine single-crystal copper is different. The dislocation embryos are gradually developed from the sites of homogeneous random nucleation around the indenter in the pristine single-crystal specimen, while the dislocation embryos derived from the vacancy-related defects are distributed in the damage layer of the subsurface beneath the machining-induced surface. The results show that the hardness of the machining-induced surface is softer than that of pristine single-crystal copper. Then, the nanocutting simulations are performed along different crystal orientations on the same crystal surface. It is shown that the crystal orientation directly influences the dislocation formation and distribution of the machining-induced surface. The crystal orientation of nanocutting is further verified to affect both residual defect generations and their propagation directions which are important in assessing the change of mechanical properties, such as hardness and Young's modulus, after nanocutting process.