Copper Single Crystals Research Articles

Local Heating Induced Single-Crystalline Phase Control in Electrochemical Synthesis of Nanomaterials.

Development of synthetic strategies selectively yielding single crystals is desired owing to the facet-dependent chemical reactivities. Recent advances in electrochemical materials synthesis yielded nanomaterials that are surfactant-free, however, typically in polycrystalline forms. In this work, an electrochemical synthetic strategy selectively yielding single-crystalline nanoparticles by implementation of surface-selective heating of the working electrode is developed. Single crystals of copper, silver, gold, and platinum are afforded, and the crystallinity verified by electron diffraction and chemical reactivity studies. Notably, Cu (100) surface prepared by electrochemical synthesis yielded high single product selectivity when applied to electrochemical CO2 reduction catalysis.

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.

Elastic size effect of single crystal copper beams under combined loading of torsion and bending

Among various strain gradient theories, the modified couple stress theory, which introduces a single length scale parameter as an additional material property, has garnered significant interest owing to its simplified portrayal of the material behavior. In this study, we investigated whether a single length scale parameter is sufficient to predict the mechanical behavior under two different type of strain gradients: torsion and bending. L-shaped beams made of single crystal copper with thicknesses ranging from 2.4μm to 9.1μm were fabricated, and loads were applied using an indenter. The contributions of bending and torsion were controlled by adjusting the loading position. Through these experiments, we demonstrated the existence of elastic size effect of single crystalline materials under strain gradients. Specifically, size effect was observed in both bending and torsion, with a larger effect observed in cases closer to pure bending. Moreover, we report that the modified couple stress theory and the modified strain gradient theory are not applicable for simulating size effect under combined loading. This discovery highlights the necessity for the development of a new theory capable of adequately simulating size effect under the intricate loading scenarios encountered in practical applications.

A microdamage model for FCC single crystals considering a mixed failure mechanism of slip and cleavage

In this study, a microdamage model is newly proposed to predict the failure process of FCC single crystals. Two micro damage mechanisms, slip and cleavage, are both involved in the model. A microscopic damage variable is first defined at the slip plane scale, and a damage coupled crystal plasticity constitutive equation in a co-rotational tensor framework is then established. A damage driving force consisting of generalized energies related to the resolved shear stress and the positive resolved normal stress is proposed to reflect the mixed failure mechanism of FCC single crystals induced by slip and cleavage. The damage evolution equation is then derived in the framework of thermodynamics. An explicit algorithm for the damage coupled crystal plasticity finite element method is given. The proposed microdamage model is utilized to predict the slip-dominant fracture behavior of a single crystal copper and the cleavage-dominant fracture behavior of a nickel-based single crystal alloy. The damage evolution process of slip planes is given and the influence mechanism is revealed. The calculated results agree well with the experimental data, which verifies the good capability of the proposed model in describing and predicting the multi failure processes of FCC metals. Finally, a 2D fracture simulation of a single crystal notched specimen under shear loading is conducted, and the effect of damage parameters on the fracture modes is also discussed.

The Relevance of the Interfacial Water Reactivity for Electrochemical CO Reduction on Copper Single Crystals.

The electrochemical reduction of CO2 is an important electrolysis reaction that enables the conversion of a waste gas to fuels or value-added chemicals. To make this reaction viable, a profound understanding of central intermediate steps, such as the CO electroreduction, is required. On Cu, the CO reduction reaction (CORR) is intimately linked to the hydrogen evolution reaction (HER) that proceeds via the reduction of water in alkaline or neutral electrolytes. Here, we demonstrate that the interaction of water or more specifically the water reduction kinetics on differently smooth Cu(100) and Cu(111) surfaces during the CORR in alkaline media significantly governs the CORR. On Cu(111), faster HER kinetics and the highest CORR activity are observed, even though HER and CORR onsets are more negative. While on Cu(100) small Cu ad-island clusters form in the cathodic potential range only when CO is present, structural changes appear on a larger length scale on Cu(111) both under CORR conditions and when no CO is present. These differences in the reconstruction characteristics may be attributed to the dominance of either the CORR and its intermediates or the HER on the different Cu surfaces. Therefore, the interfacial water reactivity is considered an essential activity descriptor for the CORR on Cu in alkaline media.

Nanoscratching of polycrystalline copper examined through strain gradient crystal plasticity

Nanoscratch testing is a method pivotal for evaluating the mechanical and tribological characteristics of materials which involves the controlled scratching of specimens with a nano-scale indenter. This research delves into the analysis of effect of grain size on the deformation mechanisms and material responses during nanoscratch tests on polycrystalline copper. By utilizing finite element method and adopting a lower-order strain gradient crystal plasticity framework, this study investigates results such as reaction forces on the indenter, apparent friction coefficients, and alterations in pile-up topography. These factors are examined with the aforementioned strain gradient theory, employing calculations of the density of geometrically necessary dislocations to obtain size-dependent material response. The crystal plasticity framework is implemented into ABAQUS as a user material subroutine (UMAT), and the model's accuracy is affirmed through comparisons with experimental data from single crystal copper studies available in the literature. 3D geometries are generated to model a single crystal and three polycrystal materials with average grain diameters of 5 µm, 15 µm, and 50 µm. These specimens are subjected to deformation by a rigid Berkovich indenter to simulate nanoscratching tests in the numerical examples, where the key point is to examine the grain size effects while keeping fixed any other variables that may influence the results.

Slip system level strengthening in nano-indentation of single crystalline copper: Numerical study via a non-local CPFEM model

A three-dimensional non-local crystal plasticity finite element model (CPFEM) integrating the evolution of geometrically necessary dislocations (GNDs) and statistically stored dislocations (SSDs) was developed to simulate the nano-indentation of single crystal copper. The simulation accurately reproduced published experimental results when considering force-depth curves, indentation size effect (ISE), anisotropic plastic deformation and sink-in phenomenon. The accumulated slip, i.e., shear strain in individual slip systems, was quantitively investigated. It is anticipated that the developed non-local CPFEM model can support future sub-micro and nanoscale manufacturing research as it enables the rapid exploration of slip system level mechanical response of a diverse range of crystalline alloys.

ATOMISTIC AND CONTINUAL DETERMINATION OF STRESS FIELDS AT A CRACK TIP IN ANISOTROPIC ENVIRONMENT WITH CUBIC SYSTEM

The article presents a comparative analysis of stresses associated with a crack tip in an anisotropic medium with cubic symmetry of elastic properties under mixed mode loading conditions, using two different approaches: atomistic and continuum approaches. The atomistic approach is based on the use of the molecular dynamics method implemented in the open source Large-scale Atomic/Molecular Massively Parallel Simulator (LAMMPS). The continuum approach is based on the classical theory of elasticity of anisotropic media, in which the mechanical fields associated with the crack tip are represented using series that generalize the well-known representation of M. Williams to the case of anisotropic media. Using the method of molecular dynamics, a large series of calculations of loading of single-crystal copper and aluminum plates with a face-centered crystal lattice, weakened by a central crack, was carried out using the embedded atom potential (EAM). Molecular dynamics modeling is aimed at determining atomistic stresses and strains near the crack tip. The calculated atomistic stresses were compared with the stress field determined by the continuum theory of elasticity of anisotropic media for crystal lattices with cubic symmetry of elastic properties. A comparative analysis was carried out for the angular dependences of the stress and strain tensor components at different distances from the crack tip for the entire range of mixed strain modes: from perfect normal tension to loadings close to perfect transverse shear. It is established that the fields found on the basis of two fundamentally different approaches (discrete and continuum) are fully consistent with each other. It is demonstrated that the mathematical methods of continuum fracture mechanics can be used to describe stress, strain, and displacement fields at the atomistic level.

Microstructure evolution of melt-extracted copper alloy wires

Copper alloy wires are regarded as essential for bonding in semiconductor packaging. However, the existing single-crystal copper wires are susceptible to oxidize, resulting in connection failure. And the current production process of multi-pass cold-drawing is complicated. In this study, nickel-aluminum-bronze (NAB) alloy wires by the melt-extracted method were investigated to avoid the problems mentioned above. The results showed that the microstructure of the copper alloy wire differs depending on the region. The nano-Ni3Al phase precipitates on the lath martensitic β' phase in the concave area, while the interior of the copper alloy wires contains a large number of reflection-twin of the β' phase. As the melt-extracted process continues, the cooling speed increases until the formation of the stable lamellar αw + β' structure. These results will shed new light on the formation mechanism of copper alloy bonding wires.

Magnetic-Field-Assisted Scratching Process of Single-Crystal Copper.

Energy-field-assisted cutting exhibits excellent ability to reduce cutting force and improve machining quality. In this study, a magnetic field was applied in an innovative way to aid in the cutting process, and magnetic-field-assisted scratching experiments of single-crystal copper were carried out. It was found that magnetic-field-assisted scratching increased the actual scratching force due to the additional Lorentz force in the cutting process. However, the friction coefficient of the magnetic-field-assisted scratching was reduced by 19.4% due to the tribological modification effect on tool/chip contact. Meanwhile, magnetic-field-assisted scratching was conducive to decreasing the degree of chip deformation, reducing microburrs on the machined surface, and obtaining a surface roughness reduction of an average of 26.8%. The possible reason for this effect was that the presence of a magnetic field in the cutting process promoted the dislocation slip of metal materials. The results indicated that magnetic-field-assisted cutting improves the machinability in the metal cutting process.

Interaction of Y and impurity P on the synergistic enhancement of elongation and electrical conductivity of single crystal copper rod

Single-crystal copper rods with high conductivity and mechanical properties are the decisive material for the production of microwires for chip bonding. To further improve the product of strength and elongation as well as electrical conductivity, rare earth Y is added to a single-crystal copper rod to adjust the microstructure and impurity state. The results show that Cu-0.03Y copper rods have excellent comprehensive properties. The electrical conductivity improves to 103.72 % IACS, and the product of strength and elongation improves to 8.772 GPa%. The precipitates in the Cu-0.03Y single crystal copper rod are nano-sized spherical particles composed of YP (NaCl type) and Cu5Y (Cu5Ca type) phases. The enthalpy of formation of Y and P is calculated using Miedema thermodynamics as ΔH = −173.45 kJ·mol−1. The precipitates formed by the preferential reaction of Y and P reduce the solid dissolved atoms in the copper, and the electrical conductivity increases accordingly. The 〈001〉 texture of a single-crystal copper rod decreases with the addition of Y, while the 〈101〉 texture increases with good plasticity, leading to an improvement in elongation.

Enhanced Characterisation Studies and Synthesis of Undoped and Copper Doped-Organic Nonlinear Optical Single Crystal: L-Alanine Aluminium Nitrate

Single crystals of untreated and copper (Cu2+) metal ion-doped L-alanine aluminium nitrate (LAAN), a room-temperature slow evaporation organic nonlinear optical material. Single crystals were studied for structural, spectral, optical, hardness, secondorder non-linear optical, electrical [(alternating current (AC) and direct current (DC)], and photoconductivity properties as they grew. Crystallinity, monoclinic structure with space collection P21, and lattice specifications were deliberate using single crystal X-ray diffraction investigation. The existence of functional clusters is revealed by the spectral properties, and the means of vibration of various molecular clusters existing in LAAN were evaluated using Fourier transform infrared (FTIR). The low cut-off wavelength and transmittance properties were determined using optical analysis. The band gap energy of LAAN and Cu-doped LAAN crystals was estimated to be 3.40 eV and 2.70 eV, respectively, using the Tauc plot. It was revealed that pure crystals had a lower dielectric constant than crystals that had been doped with copper. After doping with rising temperatures, AC conductivity started to rise. With the use of the Kurtz and Perry approach, the effectiveness of the grown crystal’s second harmonic generation was computed, Cu-doped LAAN was discovered to be 3.3 times more prominent than potassium dihydrogen phosphate (KDP) and 2.2 times more prominent than pure LAAN crystals. The nonlinear optical characteristics of LAAN crystals have therefore been improved by copper doping. It is most suited for use in electro-optic applications like laser technology, telecommunications and optical signal processing because of its negative photoconductivity.

Asperity contact analysis: coupling effects of normal interference and nanoscale offset by molecular dynamics simulations

This work investigates the offset contact behaviors of nanosized asperity with spherical and non-spherical shapes, aiming to provide a more realistic analysis of asperity contact for rough surfaces. Molecular dynamics models of nanosized asperity are established, using diamond and copper as exemplary materials. Differences between offset and non-offset contacts, as well as spherical and non-spherical asperities are compared through atomic variations including displacement, shear strain and structure. Coupling effects of normal interference and nanoscale offset on asperity contact behaviors are further analyzed. Comparisons between the established models and the microscopic asperity models in contact force-interference dependence are conducted for verification. Results indicate that atoms in central contact region move vertically with smaller shear strains, while those in peripheral region primarily move diagonally outward with larger shear strains due to directional atomic slip motion. Furthermore, the spherical asperity shows higher atomic deformation and contact force compared to the non-spherical asperity for identical interference and offset conditions. Additionally, the shear resistance of single-crystal copper with {100} crystal orientation can be enhanced along the [1 1 0] and [1 − 1 0] directions.

단결정 구리나노시트의 시간에 따른 성장 연구

In this study, we investigated the relationship between the synthesis time of single crystal copper nanosheets (Cu NSs) and their crystal growth, yield, size, and their electrical properties. The Cu NSs synthesized for 2 and 4 hours showed very low yields, while synthesis yields began to increase after 6 hours of synthesis time, reaching approximately 33% in a 12-hour reaction. The size of the Cu NSs was proportionally controlled by the synthesis time, and an average size of 16 μm could be recovered after a 12-hour reaction. In particular, when conductive films were prepared by Cu NSs of different sizes, the conductive films made with larger particle sizes exhibited lower sheet resistance characteristics. Due to the unique characteristics of Cu NSs in shape and structure, single crystal copper nanosheets are expected to be used as metal fillers for next-generation conductive inks for printed electronics in the future.

Micropillar compression using discrete dislocation dynamics and machine learning

Discrete dislocation dynamics (DDD) simulations reveal the evolution of dislocation structures and the interaction of dislocations. This study investigated the compression behavior of single-crystal copper micropillars using few-shot machine learning with data provided by DDD simulations. Two types of features are considered: external features comprising specimen size and loading orientation and internal features involving dislocation source length, Schmid factor, the orientation of the most easily activated dislocations and their distance from the free boundary. The yielding stress and stress-strain curves of single-crystal copper micropillar are predicted well by incorporating both external and internal features of the sample as separate or combined inputs. It is found that the machine learning accuracy predictions for single-crystal micropillar compression can be improved by incorporating easily activated dislocation features with external features. However, the effect of easily activated dislocation on yielding is less important compared to the effects of specimen size and Schmid factor which includes information of orientation but becomes more evident in small-sized micropillars. Overall, incorporating internal features, especially the information of most easily activated dislocations, improves predictive capabilities across diverse sample sizes and orientations.

Kinetic nature of electrochemical plasticization

The electrochemical plasticization (EP) of metallic materials has been known for decades, but the underlying mechanisms, especially the kinetic mechanisms, remain unclear. Herein, the kinetic nature of EP has been investigated by employing the electrochemical cold drawing of single-crystal copper (in a 0.35 mol L–1 dilute sulfuric acid aqueous electrolyte and with a current density of 0.67 × 10−2 A cm−2) through microstructural characterizations and reactive force field molecular dynamic simulations. The results intuitively reveal that the surface-loosened atoms, due to the selective corrosion dissolution, acts as the sources of dislocations to accelerate the formation of dislocations in a multi-slip manner, which then rapidly move toward the inside, and react with the internal early-formed dislocations to undergo abnormal slip of Lomer-Cottrell locks, cross-slip, and annihilation, leading the dislocation entanglements to reconfigure into the movable short-range wavy dislocations and their density to reduce, thus resulting in the softening and the weakening of work-hardening. These findings provide in-depth insights into the kinetic mechanism of EP, which will inevitably accelerate the development and engineering applications of new metal processing technologies based on EP as well as get a deeper understanding of stress corrosion cracking.

Processing and Properties of Single-Crystal Copper Wire.

The effects of drawing parameters and annealing process on the properties and microstructure of single crystal copper wire are studied using a wire-drawing machine, heat-treatment equipment, microcomputer-controlled electronic universal tester, resistance tester, and scanning electron microscope. The results show that, after drawing the single-crystal copper wire with a single-pass deformation of 14%, the grains elongate along the tensile direction, tensile strength increases from 500.83 MPa to 615.5 Mpa, and resistivity changes from 1.745 × 10-8 Ω·m to 1.732 × 10-8 Ω·m. After drawing at a drawing rate of 500 m/min, the degree of grain refinement increases and tensile strength increases from 615.5 Mpa to 660.26 Mpa. When a copper wire of Φ0.08 mm is annealed, its tensile strength decreases from 660.26 Mpa to 224.7 Mpa, and elongation increases from 1.494% to 19.87% when the annealing temperature increases to 400 °C. When the annealing temperature increases to 550 °C, the tensile strength and elongation decrease to 214.4 MPa and 12.18%, respectively.

Molecular dynamic simulation of the influence of vibration effects on scratching processes in Varied crystal orientations

The research delves into the uncharted terrain of crystal orientation’s effect on high-frequency vibration-assisted processing of single-crystal copper, employing molecular dynamics to devise non-vibration, one-dimensional (1D), and two-dimensional (2D) vibration-assisted scratching models. The innovative discovery is the ‘peak-shaving’ effect, invoked by high-frequency vibration, which significantly mitigates surface irregularities on single-crystal copper, enhancing surface quality and material plasticity, thereby facilitating machinability. A key revelation is the superior efficacy of 2D vibration in material fortification relative to 1D vibration. Another novel finding is the amplified plasticity of single-crystal copper with a (111) crystal orientation under vibration-assisted excitation, linked to the varying directions of dislocation slip contingent upon crystal orientations. The pioneering observation that the induction of vibration during scratching dynamically propels dislocation defect structures, leading to the generation of a significant volume of vacant and interstitial atomic sites, underscores the pronounced influence of 2D vibration. This research contributes invaluable microscopic perspectives into the operative mechanism of crystal orientation’s impact on high-frequency vibration-assisted processing.

Production of single-crystal copper by electrodeposition

Production of single-crystal copper by electrodeposition

Corrosion resistance and mechanism of (100), (110) and (111) preferred orientation of single crystal copper in NaCl solution

In present work, the immersion and electrochemical corrosion resistance of single-crystal copper with (100), (110), (111) preferred orientation were studied in 3.5 NaCl solution. The scanning electron microscopy and X-ray photoelectron spectroscopy, Laser Raman spectroscopy were used to observe corroded surface morphology and analyze the corroded products. The experimental results show that preferential orientation has a significant effect on the corrosion resistance of single crystal copper. The self-corrosion current densities of (100), (110), and (111) oriented single-crystal copper were 1.1455 μA/cm2,0.7312 μA/cm2 and 1.4117 μA/cm2 respectively. The corrosion resistance was in the order of (110) > (100) >(111). Optimally oriented surface can effectively improve the corrosion resistance of copper.