Crystal Orientation Research Articles

Stable and unstable fall motions of plate-like ice crystal analogues

Abstract. The orientation of ice crystals affects their microphysical behaviour, growth, and precipitation. Orientation also affects interaction with electromagnetic radiation, and through this it influences remote sensing signals, in situ observations, and optical effects. Fall behaviours of a variety of 3D-printed plate-like ice crystal analogues in a tank of water–glycerine mixture are observed with multi-view cameras and digitally reconstructed to simulate the falling of ice crystals in the atmosphere. Four main falling regimes were observed: stable, zigzag, transitional, and spiralling. Stable motion is characterised by no resolvable fluctuations in velocity or orientation, with the maximum dimension oriented horizontally. The zigzagging regime is characterised by a back-and-forth swing in a constant vertical plane, corresponding to a time series of inclination angle approximated by a rectified sine wave. In the spiralling regime, analogues consistently incline at an angle between 7 and 28°, depending on particle shape. Transitional behaviour exhibits motion in between spiral and zigzag, similar to that of a falling spherical pendulum. The inclination angles that unstable planar ice crystals make with the horizontal plane are found to have a non-zero mode. This observed behaviour does not fit the commonly used Gaussian model of inclination angle. The typical Reynolds number when oscillations start is strongly dependent on shape: solid hexagonal plates begin to oscillate at Re =237, whereas several dendritic shapes remain stable throughout all experiments, even at Re > 1000. These results should be considered within remote sensing applications wherein the orientation characteristics of ice crystals are used to retrieve their properties.

Inhibiting the current spikes within the channel layer of LiCoO2-based three-terminal synaptic transistors

Synaptic transistors, which emulate the behavior of biological synapses, play a vital role in information processing and storage in neuromorphic systems. However, the occurrence of excessive current spikes during the updating of synaptic weight poses challenges to the stability, accuracy, and power consumption of synaptic transistors. In this work, we experimentally investigate the main factors for the generation of current spikes in the three-terminal synaptic transistors that use LiCoO2 (LCO), a mixed ionic-electronic conductor, as the channel layer. Kelvin probe force microscopy and impedance testing results reveal that ion migration and adsorption at the drain–source-channel interface cause the current spikes that compromise the device's performance. By controlling the crystal orientation of the LCO channel layer to impede the in-plane migration of lithium ions, we show that the LCO channel layer with the (104) preferred orientation can effectively suppress both the peak current and power consumption in the synaptic transistors. Our study provides a unique insight into controlling the crystallographic orientation for the design of high-speed, high-robustness, and low-power consumption nano-memristor devices.

Effect of pure (ligand-free) nanoparticles of magnetite in sodium chloride matrix on hematological indicators, blood gases, electrolytes and serum iron

AbstractOne of the physical methods for obtaining magnetite nanoparticles (NPs) is electron beam physical vapor deposition (EB PVD), which requires complex equipment, but allows obtaining a significant amount of pure (ligand-free) NPs. The biomedical application of such NPs is less studied than materials from other synthesis methods. The objective is to study the effect of pure magnetite NPs in the NaCl matrix obtained by EB PVD on hematological indicators, gases, electrolytes and parameters of iron metabolism in the blood of intact animals. The physical characteristics of NPs were studied using high-resolution transmission electron microscopy, scanning transmission electron microscopy, energy-dispersive X-ray spectroscopy mapping, electron energy-loss spectroscopy, selected area electron diffraction and fast Fourier transform. In vivo experiments were conducted on albino male rats, which were injected with solution of magnetite-sodium chloride NPs (1.35 mg Fe/kg). After 3 and 72 h, hematological parameters, blood gases, electrolytes, and serum iron were determined. The synthesized NPs had an average size of 11 nm. They were identified as magnetite, where polycrystals and single crystals were present. The absence of contamination in crystal boundaries, clear orientation and orderliness of atoms in crystals were established. The administration of NPs in the sodium chloride matrix to animals was characterized by a transient increase in the main indicators of red blood accompanied by an increase in the saturation of erythrocytes with hemoglobin and their mean volume after 3 h. It did not worsen blood gases and pH, but decreased blood Na+ content after 72 h. The investigated NPs caused changes in the parameters of serum iron characteristic to iron preparations, which after 3 h were smaller compared to the reference iron drug, and after 72 h—similar to it. More intense rapid effects on hematological parameters at lower serum iron indicate greater activity of the studied pure magnetite NPs obtained by EB PVD syntesis compared to the reference iron preparation.

Self-Sacrificed Additive in Preparing PbI2 Film Enables the Oriented Growth of Perovskite Crystals for Improved Solar Cell Performance.

Due to the limitation of the diffusion kinetics of organic amine salts on the PbI2 layer in the two-step method, prepared perovskite particles are small in size, have many defects, and are randomly oriented, and the cell efficiency and stability are difficult to guarantee due to PbI2 residues. Here, we added a volatile additive, N,N,N',N'-tetramethylethylenediamine (TMEDA), to the PbI2 precursor solution and formed preaggregated atomic clusters with PbI2 through TMEDA, which reduced the Gibbs free energy of nucleation to obtain a porous PbI2 layer, and finally obtained a perovskite film with large particles, few defects, ideal crystal plane orientation, and no additive residues. The results show that the photoelectric conversion efficiency of the optimized device is increased by 1.68% (from 21.68% to 23.36%), and the unpackaged optimized device still maintains the maximum efficiency of 77% after being placed in the air for 1200 h. This study provides an effective way to fabricate efficient and stable perovskite solar cells by promoting the nucleation-induced crystallization orientation by volatile additives.

Enhancing magnetostriction in FeAl alloys via crystal growth orientation tuning by a trace amount of Pt doping

Iron-based cubic alloy systems opened the door to the development of magnetostrictive materials with moderate magnetostriction, low cost, and good mechanical properties. At the as-cast state, the grain growth orientation of these alloy systems is close to random, which deteriorates magnetostriction. Doping with certain elements can tune the growth orientation to enhance magnetostriction. However, the driving force for the crystal growth along preferential orientation is still not clear. Here in this work, revealed by density functional theory (DFT) calculation, Pt doping can tune the crystal growth direction of FeAl along <100> crystal direction (same as easy magnetization direction), which can be utilized to realize 90° domain-switching and thus magnetostriction is enhanced greatly. These are confirmed by experimental results. The magnetostriction increases from 29 ppm to 80 ppm, representing a 176% enhancement through doping with 0.4 at.% Pt. The maze magnetic domain structures, observed by magnetic force microscope, are also preferentially <100> oriented and feature stripes. In consideration of the similarity between this study and our previous study on FeGa alloy (C. Zhou et al., 2020), it can be expected that our methods can be extended to other magnetostrictive materials and help develop polycrystals with desired orientations.

Electrochemical grafting of diazonium salts on silica-terminated versus H-terminated silicon

Diazonium salts are one of the most widely used molecules for functionalising electrode surfaces, due to their high reactivity toward a range of different electrodes but have mostly been studied on carbon and gold. Recent work has demonstrated that diazonium salts can be reduced on silica-terminated silicon (Si/SiOx) despite silica (SiOx) being an electrically insulating material, but this interesting phenomenon was only demonstrated on one specific crystal orientation, Si(111) using specific diazonium salts molecules – a more complete understanding of the electrochemical properties of these silica-terminated silicon electrodes remains unclear. In this work, we develop a thorough understanding of the reduction of diazonium compounds on silica-terminated silicon using silicon with different crystal orientation and using nano-structured silicon surfaces that are chemically etched to simultaneously expose different crystal orientations. A comparison between the reduction process on oxide free silicon (Si–H) and silica-terminated Si is then made to reveal the effect of the crystal orientation (amorphous vs crystalline) and the insulating nature of the distal surface (Si‒H vs SiOx) on the reduction process. Results show that diazonium salts form, well-packed thin films on silica-terminated silicon regardless of the crystal orientation of the silicon. The rate of diazonium reduction was found to be sensitive to the crystal orientation of Si only when the diazonium salts are in direct contact with the crystal plane (i.e. in contact with Si–H) as opposed to when there is a thin layer of native amorphous oxide material in between. The reduction rate is sufficiently slow on silica-terminated silicon that at slow scan rates, the system reaches a steady state current and become diffusion controlled. This is not observed on oxide-free silicon electrodes which are observed to be governed by a kinetically driven mechanism. These findings deepen our understanding of the electrochemical activity of silica-terminated silicon surfaces which are widely used in solar cells, electronics, chemical and biosensors.

Insights into the Effect of Crystal Facets and Sulfur Defects on the Product Selectivity of Various CdS Configurations for CO2 Photoreduction: A DFT Study

CO2 photoreduction into valuable hydrocarbons, such as CO, CH4, and C2H4, delivers a promising approach to address both environmental and energy challenges. Transition metal chalcogenides, particularly cadmium sulfide (CdS), have emerged as prominent candidates due to their tunable electronic properties and availability. This study delves into a comprehensive investigation of how CdS crystalline facets and sulfur-deficient surfaces modulate the product selectivity. Through employing density functional theory (DFT), we unravel the catalytic performance of various CdS crystal orientations and sulfur vacancy configurations. The results have shown that different CdS facets exhibit unique electronic characteristics and surface energetics, which influence the adsorption dynamics and reaction pathways. The introduction of sulfur vacancies further modulates the nature of active sites, leading to substantial shifts in product selectivity. A detailed investigation on the reaction mechanisms unveils that specific facets preferentially facilitate the formation of CO, while others are more conducive to the generation of hydrocarbons such as CH4 and C2H4, due to the variations in activation barriers and intermediate stabilities. These findings underscore the importance of crystal facet engineering and defect manipulation in tailoring catalyst performance thus providing valuable insights for the rational design of efficient and selective CO2 reduction metal catalysts.

Customizing H2O‐Poor Electric Double Layer and Boosting Texture Exposure of Zn (101) Plane towards Super‐High Areal Capacity Zinc Metal Batteries

The catastrophic dendrite hyperplasia and parasitic reactions severely impede the future deployment of aqueous Zn‐ion batteries. Controlling zinc orientation growth is considered to be an effective method to overcome the aforementioned concerns, especially for regulating the (002) plane of deposited Zn. Unfortunately, Zn (002) texture is difficult to obtain stable cycling under high deposition capacity resulting from its large lattice distortion and nonuniform distribution in electric field. Herein, different from traditional cognition, a crystallization orientation regulation tactic is proposed to boost Zn (101) texture exposure and inhibit zinc dendrite proliferation during plating/stripping. Experimental results and theoretical calculations demonstrate the malate molecules preferentially adsorb on the Zn (002) facet, leading to the texture exposure of distinctive Zn (101) plane. Meanwhile, the –COOH and –OH groups of malate molecules exhibit strong adsorption on the Zn anode surface and chelate with Zn2+, achieving H2O‐poor electrical double layer. Very impressively, the multifunctional malate additive enlists zinc anode to survive for 600 h under a harsh condition of 15 mAh cm−2/15 mAh cm−2. Moreover, the symmetric cell harvests highly‐reversible cycling life of 6600 h at 5 mA cm−2/1.25 mAh cm−2, remarkably outperforming the ZnSO4 electrolyte. The assembled Zn//MnO2 full cells also demonstrate prominent electrochemical reversibility.

Customizing H2O-Poor Electric Double Layer and Boosting Texture Exposure of Zn (101) Plane towards Super-High Areal Capacity Zinc Metal Batteries.

The catastrophic dendrite hyperplasia and parasitic reactions severely impede the future deployment of aqueous Zn-ion batteries. Controlling zinc orientation growth is considered to be an effective method to overcome the aforementioned concerns, especially for regulating the (002) plane of deposited Zn. Unfortunately, Zn (002) texture is difficult to obtain stable cycling under high deposition capacity resulting from its large lattice distortion and nonuniform distribution in electric field. Herein, different from traditional cognition, a crystallization orientation regulation tactic is proposed to boost Zn (101) texture exposure and inhibit zinc dendrite proliferation during plating/stripping. Experimental results and theoretical calculations demonstrate the malate molecules preferentially adsorb on the Zn (002) facet, leading to the texture exposure of distinctive Zn (101) plane. Meanwhile, the -COOH and -OH groups of malate molecules exhibit strong adsorption on the Zn anode surface and chelate with Zn2+, achievingH2O-poorelectrical double layer. Very impressively, the multifunctional malate additive enlists zinc anode to survive for 600 h under a harsh condition of 15 mAh cm-2/15 mAh cm-2. Moreover, the symmetric cell harvests highly-reversible cycling life of 6600 h at 5 mA cm-2/1.25 mAh cm-2, remarkably outperforming the ZnSO4 electrolyte. The assembled Zn//MnO2 full cells also demonstrate prominent electrochemical reversibility.

Precise Size Determination of Supported Catalyst Nanoparticles via Generative AI and Scanning Transmission Electron Microscopy.

Transmission electron microscopy (TEM) plays a crucial role in heterogeneous catalysis for assessing the size distribution of supported metal nanoparticles. Typically, nanoparticle size is quantified by measuring the diameter under the assumption of spherical geometry, a simplification that limits the precision needed for advancing synthesis-structure-performance relationships. Currently, there is a lack of techniques that can reliably extract more meaningful information from atomically resolved TEM images, like nuclearity or geometry. Here, cycle-consistent generative adversarial networks (CycleGANs) are explored to bridge experimental and simulated images, directly linking experimental observations with information from their underlying atomic structure. Using the versatile Pt/CeO2 (Pt particles centered ≈2nm) catalyst synthesized by impregnation, large datasets of experimental scanning transmission electron micrographs and physical image simulations are created to train a CycleGAN. A subsequent size-estimation network is developed to determine the nuclearity of imaged nanoparticles, providing plausible estimates for ≈70% of experimentally observed particles. This automatic approach enables precise size determination of supported nanoparticle-based catalysts overcoming crystal orientation limitations of conventional techniques, promising high accuracy with sufficient training data. Tools like this are envisioned to be of great use in designing and characterizing catalytic materials with improved atomic precision.

Molecular dynamics study on the effect of crystal orientation on the plasticity and fracture behavior of α-Fe crack tip

Abstract In this paper, the molecular dynamics technique is utilized to simulate crack propagation within the localized vicinity of the crack tip, aiming to investigate the plastic deformation behavior of the α-Fe crack tip under different crystal orientations. The influences of crystal orientation on the mechanical properties of the models were obtained, and the weakest crystal orientation associated with fracture was determined. Meanwhile, the plastic deformation mechanism of the α-Fe model under different crystal orientations was obtained by analyzing the microscopic atomic evolution process of the four models.

In situ seed layer bandgap engineering leading to the conduction band offset reversion and efficient Sb2Se3 solar cells with high open-circuit voltage

Sb2Se3 solar cells have achieved a power conversion efficiency (PCE) of over 10%. However, the serious open-circuit voltage deficit (VOC-deficit), induced by the hard-to-control crystal orientation and heterojunction interface reaction, limits the PCE of vapor transport deposition (VTD) processed Sb2Se3 solar cells. To overcome the VOC-deficit problem of VTD processed Sb2Se3 solar cells, herein, an in-situ bandgap regulation strategy is innovatively proposed to prepare a wide band gap Sb2(S,Se)3 seed layer (WBSL) at CdS/Sb2Se3 heterojunction interface to improve the PCE of Sb2Se3 solar cells. The analysis results show that the introduced Sb2(S,Se)3 seed layer can enhance the [001] orientation of Sb2Se3 thin films, broaden the band gap of heterojunction interface, and realize a “Spike-like” conduction band alignment with ΔEc = 0.11 eV. In addition, thanks to the suppressed CdS/Sb2Se3 interface reaction after WBSL application, the depletion region width of Sb2Se3 solar cells is widened, and the quality of CdS/Sb2Se3 interface and the carrier transporting performance of Sb2Se3 solar cells are significantly improved as well. Moreover, the harmful Se vacancy defects near the front interface of Sb2Se3 solar cells can be greatly diminished by WBSL. Finally, the PCE of Sb2Se3 solar cells is improved from 7.0% to 7.6%; meanwhile the VOC is increased to 466 mV which is the highest value for the VTD derived Sb2Se3 solar cells. This work will provide a valuable reference for the interface and orientation regulation of antimony-based chalcogenide solar cells.

A novel concurrent multiscale method based on the coupling of Direct FE2 and CPFEM

Performing concurrent simulations of macroscopic behaviors and microscopic structures using the crystal plasticity finite element method (CPFEM) presents a substantial difficulty with existing numerical techniques. To address this issue, a novel multi-scale method is proposed that couples CPFEM with a multiscale FEM, specifically Direct FE2. This facilitates the implementation of Direct CP-FE2 in this work. The micro representative volume elements (RVEs) equipped with a crystal plasticity constitutive model and the macro mesh are integrated into a monolithic solution scheme within the Direct FE2 framework. The proposed method integrates the multiscale simulation capability of Direct FE2 with the crystal plasticity model of CPFEM. Alpha titanium (α-Ti), which exhibits two distinct plastic mechanisms of slip and twinning, is chosen as the subject of investigation for conducting numerical experiments. The accuracy and efficiency of the Direct CP-FE2 model are evaluated through multiple plate tension and beam bending tests. The effective validation against the FEM model demonstrated the capability of Direct CP-FE2 to forecast macroscopic deformation behaviors. Meanwhile, the Direct CP-FE2 model can reveal the activation of slip/twinning systems and the evolution of crystal texture at a microscopic level. The influence of the grain orientation-dependent effect can be well considered into the macroscopic analysis with the help of Direct CP-FE2. Based on the testing examples, we demonstrate that the yield state of the macrostructure is enhanced when the crystal orientation is closer to the (0001) direction. Consequently, there exist very little crystal rotation behavior, hindering the evolution of the crystal texture.

Influence of cold plasma on material removal behavior during diamond grit scratching single crystal silicon

As a typical brittle crystal material, single crystal silicon has high hardness and brittleness, which makes the machined surface prone to microscopic cracks and other subsurface damage. In addition, the anisotropic crystal structure may cause large differences in the material removal behavior along different crystal orientations. To solve these problems, researchers have proposed the methods of machining along the easy-to-cut direction and inducing external energy fields assisted machining, but there remain problems like cracks and surface thermal damage. In this study, we propose to modulate the deformation process of single crystal silicon by atmospheric pressure cold plasma and elucidate the influence of plasma on the material removal behavior based on diamond grit scratching experiments along different directions. The results show that before plasma treatment, the toughness along <110> direction is higher than that along <100> direction, and plasma has significant improvement effects on the plastic deformability in both directions. The critical load for plastic-brittle transition along <110> direction can be increased from 76.2 mN to 107.1 mN, and from 69.6 mN to 109.8 mN along <100> direction. The plasticity regulation mechanism is that the interaction of multiple shear bands dissipates the energy of crack propagation and inhibits the premature generation of cracks. Compared with the conventional scratching along <110> direction, the material removal rate of plasma-assisted scratching under normal loads of 20 mN, 40 mN and 80 mN can be increased by 30.2%, 24.2% and 21.9%, respectively; while that along <100> direction can also be increased by 33.7% and 19.5% under 20 mN and 40 mN, respectively. This study may provide a novel approach for realizing high-quality and efficient processing of hard and brittle materials.

Link between b.c.c.-f.c.c. orientation relationship and austenite morphology in CF8M stainless steel.

Slow-cooled CF8M duplex stainless steel is used for critical parts of the primary coolant pipes of nuclear reactors. This steel can endure severe service conditions, but it tends to become more brittle upon very long-term aging (tens of years). Therefore, it is essential to understand its specific microstructure and temporal evolution. As revealed by electron backscatter diffraction (EBSD) analyses, the microstructure consists of millimetre-scale ferritic grains within which austenite lath packets have grown with preferred crystallographic orientations concerning the parent ferritic phase far from the ferrite grain boundaries. In these lath packets where the austenite phase is nucleated, the lath morphology and crystal orientation accommodate the two ferrite orientations. Globally, the Pitsch orientation relationship appears to display the best agreement with the experimental data compared with other classical relationships. The austenite lath packets are parallel plate-shaped laths, characterized by their normal n. A novel methodology is introduced to elucidate the expected relationship between n and the crystallographic orientation given the coarse interfaces, even though n is only partly known from the observation surface, in contrast to the 3D crystal orientations measured by EBSD. The distribution of retrieved normals n is shown to be concentrated over a set of discrete orientations. Assuming that the ferrite and austenite obey the Pitsch orientation relationship, the determined lath normals are close to an invariant direction of the parent phase given by the same orientation relationship.

Saturation absorbed sodium benzenesulfonate as crystallization modulating additive for dendrite-free Zn anode

Aqueous Zn metal batteries face significant obstacles such as rampant Zn dendrite growth and side reactions besides their benefits. Adding trace amounts of organic additives in electrolyte is considered as an application strategy to achieve long cycling performance. In this study, sodium benzenesulfonate (SBS) composed of an electron-withdrawing sulfonate group and a benzene ring is introduced as a crystallization modulating additive into ZnSO4 solution. We find that the saturation absorption concentration of SBS plays a key role in realizing the uniform deposition of Zn metal anode. SBS is vertically adsorbed onto Zn surface, building a top-down internal electric field that promotes the three-dimensional diffusion of Zn2+. SBS shows a crystallization modulating behavior in terms of grain nucleation, grain morphology and crystal orientation. The well-tailored crystallization structure contributes to a uniform Zn metal deposition for long cycling, which improved from 300 to 4000 cycles with the addition of SBS. At the saturation concentration of SBS, the Zn||Zn symmetric cell shows a lifespan of over 2200 h at 1 mA cm−2. This work not only provides a new option for Zn metal batteries additives but also offers new insights into the function of electrolyte additives.

Establishing the temperature and orientation dependence of the threshold displacement energy in ThO2 via molecular dynamics simulations

ThO2 is a promising fuel for next-generation nuclear reactors. As a critical quantity measuring its radiation tolerance, the dependence of the threshold displacement energy on temperature and crystal orientation in ThO2 is unclear and established using comprehensive molecular dynamics simulations in this work. For both Th and O primary knock-on atoms (PKAs), the thresholds, denoted as EdTh and EdO, respectively, are calculated using two different interatomic potentials. Similar temperature and orientation dependence are observed, albeit with some quantitative differences. While on average over all orientations, higher energy is required for Th PKAs than O PKAs to displace atoms, the polar-averaged EdTh is significantly lower than that for EdO. Further, EdTh and EdO show different crystal orientation dependence and temperature dependence. Notably, the cubic symmetry in the fluorite structure is followed by EdTh, but does not hold for EdO because of the existence of two sublattices. The much higher average EdO than EdTh and their different temperature dependence are interpreted by the distinct recombination rates of Th and O Frenkel pairs in thermal spikes, resulting from the substantially lower migration barriers of O vacancies and interstitials. The recombination of O vacancies and interstitials, both of which are charged, is further enhanced by the Coulomb interaction at small Frenkel pair separations. The new findings are discussed for their generality in fluorite-structured oxides by comparing the results in ThO2 and UO2.

Fast tailoring the ZIF-8 surface microenvironment at ambient temperature to boost glucose oxidase-like activity of AuNPs for biosensing

Rational design and tailoring of the surface microenvironment surrounding the catalytic sites, such as noble metal nanoparticles, is an effective way to enhance the catalytic activity of mimicking enzymes. However, it remains on-going challenges to regulate the microenvironment of the catalytic sites due to the lack of tunable variability in structural precision of conventional solid catalysts. Herein, three types of zeolitic imidazolate framework-8 (ZIF-8) with different major crystal facet orientations, i.e., cubic with (100) facets (denoted ZIF-8c), truncated dodecahedral with (100), (110) facets (denoted ZIF-8tr), and dodecahedral with (110) facets (denoted ZIF-8r), were developed facilely using an electrochemical method by switching the potential at ambient temperature. Because the Zn2+ nodes were predominantly exposed on the (100) facets of ZIF-8, while the ligands were mainly exposed on the (110) facets. Hence, gold nanoparticles (AuNPs) showed differential glucose oxidase (GOx)-like activities when anchored in situ on different crystal facets of ZIF-8 and obeyed the following order ZIF-8c/Au>ZIF-8tr/Au>ZIF-8r/Au. Notably, both the metal nodes and aromatic linkers of ZIF-8 interacted with AuNPs through coordination and π-π interactions. The Zn2+ nodes facilitated the formation of the electron-deficient Au species. The electron transfer from AuNPs to Zn2+ sites effectively boosted the catalytic activity. It was known that directly tailoring the microenvironment at the supporting sites of noble metal catalysts to boost catalysis through a facile electrochemical method was not reported. Based on the favorable GOx-like activity and long-term stability of ZIF-8tr/Au, a highly sensitive electrochemical biosensing platform for assaying squamous cell carcinoma antigen (SCCA) was developed. It enabled fg-level detection of cancer marker.

Understanding the deformation creep and role of intermetallic compound-microstructure in Sn-Ag-Cu solders

Tin-based alloys are commonly used in lead-free solder joints in electronic interconnection applications, where creep can limit joint reliability. In this work, directionally solidified bulk solder alloys of different compositions (pure tin, SAC105 and SAC305) are mechanically tested under a constant load for each composition at room temperature to understand mechanical creep performance and quantify the role of different content of Ag3Sn and Cu6Sn5 intermetallic compounds (IMCs) in terms of secondary creep strain rate, microstructural evolution, and total amount of accumulated strain. In this work, microstructures are fabricated using directional solidification to promote a systematic variation in IMC sizes, shapes, and distributions within similar crystal orientations of the primary β-Sn matrix. Analysis of creep data indicates that secondary creep is dominated by obstacle-controlled dislocation motion. This is further confirmed by electron backscatter diffraction (EBSD) analysis, which reveals that the formation of subgrains and internal structure, correlating to the initial microstructure of the sample, i.e. changes in secondary dendrite arm spacing (λ2) and eutectic intermetallic spacing (λe). The experimental observations are supported further by crystal plasticity simulations that explicitly model the presence of IMCs within the Sn-based samples and show the dependence of the secondary creep rate upon the IMC content, and therefore be beneficial for the possible future composition design in solders.

The effects of crystal orientation and common coal impurities on electronic conductivity in copper–carbon composites

The electronic conduction properties of copper–graphene composite materials including common coal impurities are studied. Exploring the transport properties for three crystallographic orientations [(111), (110), and (100)] of copper in copper–graphene composites, a strong orientational dependence on electronic conductivity is shown. Graphene exhibits near-ideal registries for (111) and (110) orientations, forming a connected network between grains that enables efficient carrier transport. The influence of non-carbon elements: nitrogen (N), oxygen (O), and sulfur (S) in graphene, representing possible structures in coal-based graphene are investigated. N, O, and S in graphene negatively impact the composite’s electronic conductivity relative to pristine graphene. A new method is introduced for visualizing the spatial distribution of electrical conduction activity in materials using the square of the electronic charge density near the Fermi level, based on the work of Mott. We call this technique the N2 method.