Single Crystal Grains Research Articles

Rapid preparation of Cu(111) foil with large single-crystal grains through a graphene induction and contactless annealing method

There is a growing interest in preparing large-size Cu(111) foil for achieving high performance in various applications. In this work, a simple two-step method using graphene induction and contactless annealing was designed to rapidly prepare Cu(111) foil with large single-crystal grains. The graphene film grown on the Cu surface in the first step by chemical vapor deposition serves as a template for the orientation transition of the Cu foil in a subsequent high-temperature annealing. The (111) orientation transformation of the entire Cu foil was achieved within 20 min with single-crystal grains in size of above 30 cm2, and the corresponding speed is ten times higher than that prepared in traditional annealing process. This work provides a facile and rapid fabrication approach for preparing Cu(111) foil with large grains.

Investigation on the microstructure, mechanical properties and chlorine resistance of fine aluminum alloy wires

Wire bonding is a fundamental and mature technology in semiconductor packaging process, primarily using materials such as gold, silver, aluminum, and copper for the wires. To address application limitations of aluminum wires, such as low electromigration resistance and limited ductility, techniques including to enhance alloying (with Zn and Si), heat treatment, and surface treatment are employed to enhance the performance of aluminum alloy wires and broaden their application value. This study selects Al-3Zn-0.3Si (AZS303) and Al-7Zn-0.3Si (AZS703), with AZS303 undergoing gold plating to produce AC-AZS303 wires. Various high-temperature heat treatments are applied, verifying that under 400 °C conditions, the AZS series aluminum alloy wires exhibit grain growth and form single-crystal equiaxed grain structures, resulting in stable mechanical properties and excellent electrical performance. Additionally, the AC-AZS303 wires optimize resistance values through gold layer diffusion induced by the electrothermal effect.Chlorine experiments indicates that the gold plating on AC-AZS303 can't enhance the aluminum wire's resistance to chlorine corrosion. However, the alloying effect of zine and silicon elements imparts excellent chlorine corrosion resistance to the Al-Zn-Si wires. This study of bonding properties examines the bond strength and observes the bonded area of Al-Zn-Si wires after bonding. It is noted that the H400-AZS303 wire exhibits the best bond strength and bonding area, demonstrating good bonding with the substrate.

Laser explosion-based fast lithography to modulate silicon crystals.

Laser direct lithography allows for the maskless production and alignment of nanocrystals. However, laser-induced crystal growth requires a complex process of nucleation followed by growth that takes a long time, resulting in low efficiency. Here, we used a laser explosion to pre-grow silicon seed crystals in a silicon precursor solution, simplified crystal growth and increased the lithography efficiency. By operating the laser exposure time, the crystal size can be controlled, and even inducing the fusion of nanocrystalline into single crystal grains. As a proof of concept, we fabricated silicon quantum dot architectures with a direct lithography rate of 350 µm/s by this strategy, achieving quantum dot growth within ∼0.54 milliseconds time in an ambient environment. The silicon quantum dots could be contact and fusion through a laser modulation, ultimately forming single silicon microcrystals within the architectures of lithography.

Cosserat-phase-field modeling of grain nucleation in plastically deformed single crystals

Thermomechanical processing of crystalline materials induces microstructural evolution such as grain nucleation and growth. In the numerical simulation of these processes, grain nucleation is generally treated as an additional ad hoc step in which circular or spherical grains are added in regions where a critical dislocation density, stress or strain are reached. In this paper, systematic finite element simulations are performed showing that the Kobayashi–Warren–Carter (KWC) phase field model and its coupling with Cosserat crystal plasticity predict spontaneous nucleation of new grains in single crystals in the presence of lattice orientation/rotation gradients. The numerical analysis of the stability of gradients of lattice rotation and dislocation-based stored energy indicates that a gradient of stored energy alone is not sufficient to trigger grain formation. As an application, the KWC–Cosserat model is used to simulate the torsion and annealing of a copper single crystal bar with a circular cross section. This mechanical loading produces a large, fairly uniform axial rotation gradient which induces nucleation in the form of a stack of cylindrical grains. Plastic strain gradients in cross-sections predicted by the 3D finite element simulation, are not strong enough to compete with the longitudinal nucleation process, as confirmed by experimental observations from the literature.

Effect of Single Crystal Growth and Solidification Grain Boundaries on Weld Solidification Cracking Behavior of CMSX-4 Superalloy

Single-crystal superalloys have been popularly employed in high-temperature parts of gas turbines, such as blades. However, the welds of such alloys are highly susceptible to solidification cracking, which limits their applicability to high-temperature turbine blades. In this study, the effects of characteristics of weld solidification on solidification cracking susceptibilities (solidification brittle temperature range, BTR) were fundamentally investigated for the CMSX-4 single-crystal superalloy. We applied a transverse-Varestraint test procedure for both the linear and oscillated arc welds by changing the weld solidification characteristics, such as the degree of single crystal growth and formation of solidification grain boundaries. The BTR for the CMSX-4 alloy is 336 K for linear welding condition, whereas the values are 434 K and 342 K for 0.6 and 1.5 Hz oscillated welds. Interestingly, the BTR continuously increases with the weld oscillation frequency. By contrast, almost no changes in the weld mushy-zone temperature range are theoretically calculated for each welding condition via the diffusion-controlled Scheil model. The mechanism underlying the increase in BTR under oscillation welding is clarified based on the relationship between the achievement ratio of the weld single crystal growth and fraction of high-angle (>15<sup>o</sup>) solidification boundaries, which affect severe dendrite coalescence undercooling. The lower fraction of the high-angle weld solidification grain boundaries attributed to the superior achievement ratio of weld single crystal growth, which reduces the dendrite coalescence undercooling and BTR. Consequently, it enhances the solidification crack propagation resistance.

Mitigating Lattice Distortion of High-Voltage LiCoO2 via Core-Shell Structure Induced by Cationic Heterogeneous Co-Doping for Lithium-Ion Batteries

HighlightsA simple two-step multi-element co-doping strategy is proposed to fabricate core-shell structured LiCoO2 based on the different diffusivities of dopant ions.The high diffusivity Al3+/Mg2+ ions occupy the core of single-crystal grain while the low diffusivity Ti4+ ions enrich the shell layer. In-situ XRD demonstrates the mitigated structural distortion under a high cut-off voltage of 4.6 V, resulting in a significantly improved cycling stability.

Does single-crystallization a feasible direction for designing Li-rich layered cathodes?

Although the synthesis technology of popular single-crystal electrode materials is mature, the large enough, greatly dispersed Li-rich single-crystal cathodes have been rarely reported. In this study, we overcome the challenge of elevated Mn-O breaking activation energy so that achieve micro-sized (∼3 μm) single-crystal Mn-Li-rich particles with extreme dispersity by regulating Li content and high temperature residence time step by step. However, the modified parameters during the sintering process severely intensify the Li/Ni mixing, leading to unavoidable dynamical hysteresis and structural damage. In addition, the long-range diffusion pathway in single-crystal Li-rich grains not only limits the effective Li⁺ transfer but also significantly weakens the kinetics of anionic redox. Hence, whether the single-crystal strategy is seriously applicable to Mn-based Li-rich cathodes remains a matter of debate, with promising outlets focusing on the enhancement of the dynamics in Li-rich cathodes.

Guest-Stimulated Nonplanar Porphyrins in Flexible Metal-Organic Frameworks.

Nonplanar porphyrins with out-of-plane distortions play crucial roles in many biological functions and chemical applications. The artificial construction of nonplanar porphyrins usually involves organic synthesis and modification, which is a highly comprehensive approach. However, incorporating porphyrins into guest-stimulated flexible systems allows to manipulate the porphyrin distortion through simple ad/desorption of guest molecules. Here, a series of porphyrinic zirconium metal-organic frameworks (MOFs) is reported that exhibit guest-stimulated breathing behavior. X-Ray diffraction analysis and skeleton deviation plots confirm that the material suffers from porphyrin distortion to form a ruffled geometry under the desorption of guest molecules. Further investigation reveals that not only the degree of nonplanarity can be precisely manipulated but also the partial distortion of porphyrin in a single crystal grain can be readily achieved. As Lewis acidic catalyst, the MOF with nonplanar Co-porphyrin exhibits active properties in catalyzing CO2 /propylene oxide coupling reactions. This porphyrin distortion system provides a powerful tool for manipulating nonplanar porphyrins in MOFs with individual distortion profiles for various advanced applications.

Role of Ag segregation on microscale strengthening and slip transmission in an asymmetric Σ5 copper grain boundary

Micropillar compression was used to investigate whether Ag segregation to an asymmetric Σ5[001] grain boundary will lead to measurable strength differences compared to the pure copper bicrystal. Ag segregation was accomplished by deposition and subsequent annealing of an Ag thin-film applied on the surface of the Cu bicrystal. Atom probe tomography analysis indicated Ag segregation at the grain boundary with a peak concentration of 2.3 at.%. While the pristine Σ5 grain boundary shows a yield strength of 288 ± 18 MPa when compressing 1 µm diameter pillars along 〈001〉, micropillars containing an Ag-segregated Σ5 grain boundary demonstrated an increased yield strength of 318 ± 17 MPa. In addition, post-deformation electron microscopy was carried out to examine the active slip systems and slip transmission across Ag-free and Ag-containing bicrystals. The results are compared to reference measurements of the adjacent single crystal grains. The 1 µm pillar diameter promoted deformation governed by dislocation-grain boundary interactions for the bicrystalline pillars. This is the first time that changes in flow stress associated with grain boundary segregation have been quantified locally without interference from other mechanisms such as solid solution strengthening, formation of precipitates or changes in stacking fault energy. The results clearly indicate that purely geometrical models for slip transmission are not sufficient as the local atomic structure and composition influence dislocation transmission through grain boundaries.

Large area MoS2 thin film growth by direct sulfurization

In this study, we present the growth of monolayer MoS2 (molybdenum disulfide) film. Mo (molybdenum) film was formed on a sapphire substrate through e-beam evaporation, and triangular MoS2 film was grown by direct sulfurization. First, the growth of MoS2 was observed under an optical microscope. The number of MoS2 layers was analyzed by Raman spectrum, atomic force microscope (AFM), and photoluminescence spectroscopy (PL) measurement. Different sapphire substrate regions have different growth conditions of MoS2. The growth of MoS2 is optimized by controlling the amount and location of precursors, adjusting the appropriate growing temperature and time, and establishing proper ventilation. Experimental results show the successful growth of a large-area single-layer MoS2 on a sapphire substrate through direct sulfurization under a suitable environment. The thickness of the MoS2 film determined by AFM measurement is about 0.73 nm. The peak difference between the Raman measurement shift of 386 and 405 cm−1 is 19.1 cm−1, and the peak of PL measurement is about 677 nm, which is converted into energy of 1.83 eV, which is the size of the direct energy gap of the MoS2 thin film. The results verify the distribution of the number of grown layers. Based on the observation of the optical microscope (OM) images, MoS2 continuously grows from a single layer of discretely distributed triangular single-crystal grains into a single-layer large-area MoS2 film. This work provides a reference for growing MoS2 in a large area. We expect to apply this structure to various heterojunctions, sensors, solar cells, and thin-film transistors.

Deconvoluting Cr states in Cr-doped UO2 nuclear fuels via bulk and single crystal spectroscopic studies

Cr-doped UO2 is a leading accident tolerant nuclear fuel where the complexity of Cr chemical states in the bulk material has prevented acquisition of an unequivocal understanding of the redox chemistry and mechanism for incorporation of Cr in the UO2 matrix. To resolve this, we have used electron paramagnetic resonance, high energy resolution fluorescence detection X-ray absorption near energy structure and extended X-ray absorption fine structure spectroscopic measurements to examine Cr-doped UO2 single crystal grains and bulk material. Ambient condition measurements of the single crystal grains, which have been mechanically extracted from bulk material, indicated Cr is incorporated substitutionally for U+4 in the fluorite lattice as Cr+3 with formation of additional oxygen vacancies. Bulk material measurements reveal the complexity of Cr states, where metallic Cr (Cr0) and oxide related Cr+2 and Cr+32O3 were identified and attributed to grain boundary species and precipitates, with concurrent (Cr+3xU+41-x)O2-0.5x lattice matrix incorporation. The deconvolution of chemical states via crystal vs. powder measurements enables the understanding of discrepancies in literature whilst providing valuable direction for safe continued use of Cr-doped UO2 fuels for nuclear energy generation.

Synthesizing pseudo-Kossel lines from neutron transmission data. I. An analytical approach for recovering single-crystal orientation

The energy-dispersive neutron spectra transmitted through single crystals are characterized by sharp Bragg dips at specific wavelengths, where Bragg's law is being fulfilled for certain crystallographic planes. This phenomenon allows for developing methods for crystal-orientation determination techniques similar to electron backscatter diffraction and X-ray diffraction microscopy. This work presents a new procedure to recover the orientation matrix for single crystals using transmission spectra recorded during rotation of a crystal about an axis perpendicular to a polychromatic neutron beam. The proposed method consists of an initial transformation of the as-collected wavelength–rotation maps to a wavevector K space, resulting in linear pseudo-Kossel lines that are suitable for analysis and indexing using image-processing procedures. Simulated neutron transmission spectra through a copper crystal with known orientations were used to set and prove the numerical approach. This technique may be expanded for cases where the neutron beam intersects multiple single-crystal grains with different orientations.

Organic heterostructured scintillators with a high pulse shape discrimination capability

Recently, we have developed a new type of the scintillation material, namely organic composite scintillators. It is a non-scintillating transparent gel composition (a polysiloxane elastomer) containing grains of organic single crystals. The grains are obtained after directional crystallization of the material by crushing a crystalline ingot under a layer of liquid nitrogen. This approach removes technological restrictions on the area of the entrance window of a scintillator, does not require the growth of structurally perfect single crystals and their subsequent mechanical treatment. In contrast to organic single crystals and liquids, these materials are not continuous media but heterostructured ones.The ability of single crystals and liquids to separate signals from radiations with different specific energy losses dE/dx is well known. Due to the peculiarities of the creation and recombination of triplet-excited (T) states in these objects is also well studied. Such information on heterostructured scintillation materials, for which the grain size can limit migration of T-states, is practically absent.We discuss the results of the investigation of the luminescence spectra upon excitation by light into the T-states absorption region and the relative light yield of composite scintillators containing p-terphenyl grains (both activated and non-activated) and trans-stilbene grains. We used the grain fractions from 0.04 to 1.0 mm. We obtained and studied both single-layer samples (the thickness of a sample practically corresponded to the grain size of the scintillation material) and samples of 5 mm thick. The research results showed that samples with grain fractions of less than 0.04, 0.06 and between 0.06 and 0.1 mm have low intensity of the delayed fluorescence and relative light output values. We obtained that to separate radiations with different dE/dx by the shape of the radioluminescence pulse it is advisable to use grain fractions larger than 0.1 mm. We also discuss the physical processes that can lead to such results.

A new lithium barium aluminum oxide fluoride, LiBa2AlO3F2

Single-crystal grains of a new quinary compound, LiBa2AlO3F2, were obtained from a polycrystalline sample prepared by heating a starting binary oxide and fluoride mixture with a composition richer in Li and Al than the stoichiometric composition at 1023 ​K. Single-crystal X-ray structure analysis revealed that LiBa2AlO3F2 crystallizes in an orthorhombic cell (a ​= ​7.9953 (3) Å, b ​= ​11.7763 (4) Å, c ​= ​5.6090 (2) Å, space group Pbcm). Al-centered O tetrahedra form zigzag chains in the c-axis direction by sharing vertex oxygen atoms. An OF4 four-sided pyramid is formed, and a Li atom is situated in the pyramid and near the F4 basement. A Li-OF4 pyramid layer is formed by sharing F atoms of the pyramid at x ∼0 around the (100) plane. Ba atoms are located between the slab of Al–O4 zigzag chains and the Li–OF4 pyramid layer. Rietveld analysis of the powder X-ray diffraction pattern indicated that a single-phase polycrystalline bulk sample of LiBa2AlO3F2 was synthesized from a starting-materials mixture with the stoichiometric composition. The conductivity measured for the sample prepared at 1173 ​K was 2.6 ​× ​10−9 ​S ​cm−1 ​at 301 ​K and 2.9 ​× ​10−6 ​S ​cm−1 ​at 443 ​K, and the Li+ transport number was 99%. LiBa1.94Eu0.06AlO3F2 was synthesized by partial substitution of Eu2+ for Ba2+. A broad emission spectrum with a peak at 610 ​nm and a full-width at half-maximum of 170 ​nm was recorded for this sample under ultraviolet-light excitation at a wavelength of 330 ​nm.

Analysis of a Single Crystal Solidification Process of an Ni-based Superalloy using a CAFE Model

The efficiency of gas turbines depends on the gas turbine working temperature. Single crystal blades are being applied more often than equiaxed blades in gas turbine engines, to increase the turbine inlet temperature, resulting in enhanced turbine engine efficiency. Single crystal blades endure creep conditions at high temperature better than polycrystal blades because the single crystals do not include grain boundaries. The single crystal process is a breakthrough technology, however, production yield is relatively low compared with polycrystal, and their mechanical properties depend on the crystallographic orientation of the single crystals. In this study, a thermal simulation model, the 3D cellular automation-finite element (CA-FE), was used on the single crystal process with the Bridgman method. The simulation model was well expected, by analysis of the microstructure and EBSD, on the grain selection in the single crystal process. The evolution of single crystal grains was analyzed on process of grain selection in start block and spiral selector. Single crystal orientation was also investigated to determine the effect of nucleation density, forming in the initial stage of solidification.

Nanowire single-crystal grain and single grain boundary silicon field effect transistors for direct electrical characterization of grain boundaries

Single crystal grain (s-G) and single grain boundary (s-GB) Si field effect transistors (FETs) were investigated for direct measurement of the electrical activity of GBs. Ultrahigh-performance nanowire s-G FET with 1360 cm2V−1s−1 electron field-effect mobility (μ ef) was achieved on a transparent substrate. The significant difference of μ ef values between nanowire and microwire FETs proved that uniaxial tensile strain typically contributed to μ ef enhancement in nanowire FETs. Longitudinal GBs typically increased the leakage current and S factor due to a large donor concentration. The donor concentration generated by Σ3 and other CSL-type s-GBs was estimated.

Effect of ZrO2 doping on the growth of lead-free piezoelectric 0.75(Bi1/2Na1/2)TiO3-0.25SrTiO3 single crystals by solid-state single crystal growth

Single crystals of 0.75(Bi1/2Na1/2)TiO3-0.25SrTiO3 have potential for use in piezoelectric actuators because of their large values of electric field-induced strain. Single crystals of 0.75(Bi1/2Na1/2)TiO3-0.25SrTiO3 have been prepared by solid-state single crystal growth, but growing large crystals is difficult due to matrix grain growth. Previous experiments with 0.95(Bi1/2Na1/2)TiO3-0.05BaTiO3 showed that doping with ZrO2 reduced matrix grain growth but also reduced single crystal growth. In this work, 0.75(Bi1/2Na1/2)TiO3-0.25SrTiO3 is doped with small amounts of ZrO2 and the effect on both single crystal and matrix grain growth is examined. ZrO2 addition has a minor effect on single crystal and matrix grain growth.

Strain-Induced Plasmon Confinement in Polycrystalline Graphene.

Terahertz spectroscopy is a perfect tool to investigate the electronic intraband conductivity of graphene, but a phenomenological model (Drude-Smith) is often needed to describe disorder. By studying the THz response of isotropically strained polycrystalline graphene and using a fully atomistic computational approach to fit the results, we demonstrate here the connection between the Drude-Smith parameters and the microscopic behavior. Importantly, we clearly show that the strain-induced changes in the conductivity originate mainly from the increased separation between the single-crystal grains, leading to enchanced localization of the plasmon excitations. Only at the lowest strain values explored, a behavior consistent with the deformation of the individual grains can instead be observed.

Analysis of the growth mechanism of hierarchical structure Ni0.8Co0.1Mn0.1(OH)2 agglomerates as precursors of LiNi0.8Co0.1Mn0.1O2 in the presence of aqueous ammonia

Hierarchical structure Ni0.8Co0.1Mn0.1(OH)2 agglomerates were formed by coprecipitation method in the presence of aqueous ammonia in a continuous stirred tank reactor (CSTR). The resultant spherical secondary particles are comprised of highly anisotropic primary grains as building blocks, which retain a distinct hexagonal flake morphology with six {010} equivalent crystal facets and two other {001} facets. The formation of hierarchical agglomerates typically undergoes three steps: (i) the formation of grain nuclei (homogeneous nucleation), (ii) anisotropic growth of grains and formation of hexagonal nanosheets, (iii) agglomeration of single crystal grains and formation and growth of spherical agglomerates. This unique hierarchical structures of Ni0.8Co0.1Mn0.1(OH)2 point to its promising applications in preparation of high-performance cathode materials for lithium-ion batteries.

Void space and secondary oriented attachment mechanisms in cerium oxide nanorods

Two new processes occurring during nanorod annealing of ceria are disclosed, both belonging to the wider “oriented attachment” (OA) scheme of crystal growth, which commonly drives nanoparticles growing into nanorods. The first new process is an inversion of the standard OA, where the usual solid particles are replaced by well-facetted shape-equilibrated voids inside larger single crystals. The internal facetted voids are then found to aggregate during dry heat treatment into rod-shaped elongated voids growing eventually towards nanotubes. For the case of CeO2, a perfect equivalence is found between positive OA, involving cuboctahedral {111}/{100} nanoparticles turning into {110}/{100} nanorods, and negative or void space OA, where cuboctahedral voids turn into negative tubular rods of same indexing. The second OA process (“secondary OA”) concerns aggregation of small nanorod segments into larger, double, or quadruple sized nanorods, with perfection of alignment and bonding exceeding simple van der Waals forces. Eventually, the new rods merge into single crystal grain boundary–free larger rods, but with an external shape, including double-ended rods, indicating their origin from several rods. Both processes are found on identical samples and occur in parallel.