Single Crystal Matrix Research Articles

Microscopic instabilities in single crystal matrix composites

A finite strain micromechanical analysis is presented for the prediction of the loss of microscopic stability of a class of metal matrix composites that are subjected to axial compressive loading and undergoing large deformations. The metallic constituent behavior is modeled by the single crystal anisotropic plasticity theory in which, due to the resolved shear stresses, plastic deformations occur along certain pre-defined slip planes. Thus, this incremental plasticity theory is capable of providing the effect of the applied axial loading on the induced shear stresses which dominate the microbuckling. The composites are assumed to possess slight imperfections at the interfaces, and in order to satisfy the interfacial conditions, a perturbation expansion is employed which yields zero and first order micromechanical analysis problems. The zero order problem corresponds to the micromechanical modeling of the composite with no imperfections, whereas the solution of the first order problem is utilized to obtain the critical stresses and deformations at which bifurcation buckling occurs. Both problems are solved by employing the finite strain high-fidelity generalized method of cells (HFGMC) micromechanics. Applications are given for various types of single crystal matrix composites including layered, particulate, continuous and short fiber composites. Finally, a comparison between the compressive strengths of a standard metal matrix boron/aluminum and SiC/single crystal composites is presented and discussed.

Probing the in-plane dipole moment vector between ground and excited state of single molecules by the Stark effect.

Single molecules, embedded inside a well-defined insertion site of a single-crystalline host matrix, are sensitive probes of electric field via the induced Stark shift on their lifetime-limited electronic transition. Though the response of molecules to electric field has been shown to be relatively homogeneous, crystal symmetry allows for several, spectroscopically-indistinguishable, orientations of the net permanent dipole moment between the ground and excited state - the dipole vector - and this is problematic for measuring field orientation and magnitude. In this work, we measure for each terrylene molecule, embedded inside a new host matrix, the dipole vector independently by an electric field that we can rotate in the plane of the crystal. This single crystal host matrix, called [1]BenzoThieno[3,2-b]BenzoThiophene, induces a moderate symmetry breaking of the embedded centrosymmetric terrylene molecule, and gives rise to a net dipole moment of 0.28±0.09 Debye. Based on quantum chemistry calculations we propose an insertion site that best matches the experimental findings.

Casting and recycling of insoluble, labile single-crystal coordination polymer through reversible solid-liquid-solid transition

•Reversible solid-liquid-solid transition of insoluble, labile Prussian blue •Casting single-crystal Prussian blue with diverse shapes or compositions •All the cast Prussian blue can be recycled in a loop •Casting process leads to a significant improvement in the properties/performance Reversible solid-liquid-solid transition controlled by temperature or solvent plays a vital role in manufacturing and recycling many important materials. However, this kind of transition is hard to be realized for insoluble and labile materials, for instance coordination polymers. In this work, we introduce a volatile dissociating agent to realize reversible liquification and solidification of a kind of coordination polymer, Prussian blue. The Prussian blue powders are disassociated into electrolytic solution by hydrochloride acid (the volatile dissociating agent) and transformed back to solids via volatilization of the hydrochloride vapor. Using this solid-liquid-solid transition, Prussian blue powders are cast into single crystals with various shapes (i.e., inverse opal, mesoporous) or single-crystal matrix composites with functional networks encapsulated (i.e., carbon, silicon, TiO2). Significant improvements of the performance of Prussian blue in secondary battery, seawater battery, water treatment, etc., are observed after casting. Moreover, all of the cast Prussian blue materials can be recycled. Reversible solid-liquid-solid transition controlled by temperature or solvent plays a vital role in manufacturing and recycling many important materials. However, this kind of transition is hard to be realized for insoluble and labile materials, for instance coordination polymers. In this work, we introduce a volatile dissociating agent to realize reversible liquification and solidification of a kind of coordination polymer, Prussian blue. The Prussian blue powders are disassociated into electrolytic solution by hydrochloride acid (the volatile dissociating agent) and transformed back to solids via volatilization of the hydrochloride vapor. Using this solid-liquid-solid transition, Prussian blue powders are cast into single crystals with various shapes (i.e., inverse opal, mesoporous) or single-crystal matrix composites with functional networks encapsulated (i.e., carbon, silicon, TiO2). Significant improvements of the performance of Prussian blue in secondary battery, seawater battery, water treatment, etc., are observed after casting. Moreover, all of the cast Prussian blue materials can be recycled.

Atomic insights into the size effect of glassy domain on the propagation of plastic deformation carriers in crystal-glass nanocomposite

Crystal-glass nanocomposites with the synergy of high strength and exceptional ductility are promising for future applications in micro-electromechanical systems. Deformation behaviors of crystal-glass nanocomposites are governed by the formation and propagation of their plastic deformation carriers, namely, dislocations in the crystalline phase and strain-activated atomic clusters (e.g., shear transformation zones and shear bands) in the glassy phase. Yet, it is challenging to unveil the size effect of a glassy domain on the propagation of plastic deformation carriers in crystal-glass nanocomposites. To clarify the above issue, in this work, we perform molecular dynamics simulation on simple configurations fabricated by embedding a series of cylinder glass domains with different radii into the single-crystal matrix. Their stress–strain response and microstructures, especially the deformation carriers in the two phases evolving with the applied compressive strain, are quantitively analyzed. The average shear strain of glassy atoms is found to significantly decrease with the increased glassy domain volume, accordingly alleviating the strain localization in the glassy phase. The formation and propagation of strain-activated atomic clusters are also suppressed by enlarging the glassy domain volume due to the lowered shear strains sustained by glassy atoms. Moreover, dislocation densities in the crystalline matrix also decrease in the configuration with a larger-volume glassy domain, which can be ascribed to the enhanced dislocation absorption effect from the amorphous-crystal interfaces. This work indicates that the mechanical properties of multi-phase nanocomposites can be improved by rationally optimizing the phase contents and provides new knowledge on designing high-performance nanocomposites.

Non-symmetric stiffness of origami-graphene metamaterial plates

Mechanical metamaterials exhibit exceptional mechanical properties that originate from their topological design. In the current study, we designed a novel metamaterial which incorporates origami-graphene with single crystal copper matrix. Unlike classical auxetic materials which have void phase, the proposed origami-graphene based metamaterials appear to be solid in the microscopic scale, and the origami-graphene metamaterial plates may have relative stronger stiffnesses. Based on the molecular dynamics (MD) simulations, we confirmed that the elastic properties of origami-graphene/Cu metamaterials are anisotropic, size-dependent, and temperature-dependent, and the in-plane Poisson’s ratios are negative. More important, we discovered that the stiffness of the origami-graphene/Cu metamaterial plates is non-symmetry in the phase of linear elasticity.

Designing highly luminescent nanocrystals embedded bulk single crystals for X-ray scintillators

Metal halide perovskite nanocrystals (PNCs) have demonstrated intense luminescence and short emission lifetime, which perfectly match the requirements of X-ray fast scintillators. However, the poor stability of PNCs restricts their applications. Herein, CsPbBr3 NCs in a wide band-gap Cs4PbBr6 perovskite single crystal (PSC) matrix for efficient light extraction is reported. Benefitting from the protection of the PSC matrix and the perfect lattice matching, the PNCs embedded PSC show highly minimized nonradiative recombination and greatly improved stability. Moreover, by controlling the chemical equilibrium, the self-absorption of PNCs is reduced and the quantum yield increased to 78.5%. Furthermore, the PNCs embedded PSC demonstrates an appreciable light yield of 15,290 photons MeV−1, much higher than the commercial scintillator BGO (8200 photons MeV−1), and a decay time of 12.8 ns, significantly shorter than almost all the representative scintillators. This work demonstrates unambiguously the potential of PNCs embedded PSC for next-generation fast scintillators.

Subsurface damage layer of bulk single-crystal potassium dihydrogen phosphate (KDP) after SPDT: studied by the grazing incidence X-ray diffraction technique

This work proposes a novel way of the subsurface damage layer characterization for bulk single-crystal optical material, based on the X-ray grazing incidence technique (GIXRD). The result shows that the subsurface damage layer of bulk single-crystal potassium dihydrogen phosphate (KDP) mainly consists of polycrystalline KDP and bulk single-crystal matrix after single-point diamond turning (SPDT). Meanwhile, it is found that the polycrystalline KDP presents some kinds of preferred orientations, which depend on the SPDT surfaces and SPDT track u . For example, the polycrystalline texture of (010) SPDT surface is p (103)// u and p (204)// u , while the polycrystalline texture of (111), I-type and II-type SPDT surfaces are p (312)// u , p (332)// u and p (202)// u , respectively. These findings allow us to further understand the subsurface damage layer of bulk single-crystal KDP after SPDT.

Plasma Deposition of Gallium Arsenide Nanoclusters on a Silicon Matrix

In the plasma state, a polar semiconductor gallium arsenide (GaAs) is deposited on a nonpolar silicon (Si) matrix in the <111> direction. Further qualitative and quantitative analyzes were carried out with the resulting GaAs/Si structure on a plasma‐beam device. We have chosen the optimal characteristics of this pulsed method for the deposition of GaAs from a plasma onto silicon (Si) created by a powerful ion beam. The optimal modes of the effect of temperature, electric field, and interval of pulse action on GaAs/Si quantum‐well heteronanostructures were considered. In the implementation of application of this structure in applied works related to opto‐ and nanoelectronics, active elements of solar cells require defect‐free compositions with ideal geometric parameters. Based on these experiments, the optimal mode of plasma influence on the formation of nanoclusters on the surface of the irradiated sample was chosen. SEM, EDS, and X‐ray diffraction analysis methods were used to determine such parameters as the structure, microhardness, phase and elemental composition of the irradiated Si silicon surface, as well as the penetration depth of GaAs deposited on a single‐crystal matrix. This work presents an experimental implementation of preparation of a gallium arsenide nanolayer and an applied theoretical analysis of the GaAs/Si heteronanostructure. We deposited gallium arsenide compounds from the plasma state on the surface of a silica crystal and studied the resulting structure by physicochemical methods.

Measurement of the single crystal elasticity matrix of polycrystalline materials

Many engineering metals are polycrystalline, as such the elasticity, crystalline orientation and grain distribution are cardinal factors in determining the physical properties of the material. The grain distribution can be measured using a number of different techniques and the orientation by a subset of these (electron back scatter diffraction, spatially resolved acoustic spectroscopy). These measurements are routinely deployed in materials development. However, the elasticity remains a more difficult parameter to measure and is rarely measured because the existing techniques are slow and cumbersome, with most current techniques requiring the laborious growth or destructive isolation of single crystals. In this work we present a technique that can determine the elasticity, crystalline orientation and grain distribution in a fast and easy measurement. The technique utilises SRAS imaging to provide the raw measurement of single grain velocity surfaces, this is input to a novel inverse solver that mitigates the problem of the inversion being very ill-conditioned, by simultaneously solving for multiple uniquely orientated grains at once in a brute-force approach. This allows simultaneous determination of the elastic constants and crystallographic orientation. Furthermore, this technique has the potential to work on polycrystalline materials with minimal preparation and is capable of high accuracy, with the potential to realise errors in the determination of elastic constants values of less than 1 GPa (∼1). In this work we demonstrate good agreement with EBSD (<6∘ disagreement on average for all Euler angles) and determine elastic constants in line with existing single-crystal values, with an expected accuracy of better than 4 GPa. Experimental results are presented for pure α-Ti (hexagonal), Ni and the more exotic Ni-base alloy CMSX-4 (both cubic). With the proposed method, once the initial measurement has been made, subsequent measurements of the elasticity on the same sample can be made rapidly so that the elasticity can be measured in real time, opening the possibility that on-line measurement of elasticity can be used to monitor processes and enable high-throughput materials screening. The current instrumentation approach is applicable to materials with grain sizes down to 50 µm, with the possibility of improving this to grain sizes of ∼5 µm. Further modifications to instrumentation and acoustic velocity calculation will facilitate greater accuracy in the determination of elastic constants.

Optical Properties of Monocrystalline Silicon Nanowires

The paper presents the results of a study of the optical reflection and transmission spectra of a silicon single crystal p-Si (100) with silicon nanowires grown on both sides and porous silicon p-Si (100) on a single crystal substrate in the spectral range 0.2 ÷ 1.7 μm. The layers of nanowires had a thickness of 5.5 µm, 20 µm, 50 µm and a porosity of 60 %. The porous silicon layers had a thickness of 5 μm, 50 μm and a porosity of 45 %, 55 % and 65 %. The change in the energy band structure in single-crystal silicon nanowires and in a single-crystal matrix of porous silicon is shown.

Microstructure transformation of Mo–3Nb single crystal used for space thermionic reactor during welding

Mo–3Nb single crystal is an important material used for processing the emitter of space thermionic reactor. The present research focuses on the microstructures of precipitated phases in the Mo–3Nb matrix and the joint welded by the vacuum electron beam, to reveal the microstructural transformation during the welding process. Characterization of the precipitates was conducted by transmission electron microscopy (TEM) with energy dispersive spectrum (EDS). The results show that the precipitated phases in the Mo single crystal matrix and the welds were all NbC of a crystalline cubic with space group: Fm-3m (225). After the welding, the morphology of NbC changed significantly, from a polygonal shape with a diameter of 100–200 nm to a thin rod with a length of 10–50 nm. High-temperature solution-quenching treatment on single crystal rods is suggested to further improve performance.

Surprising increase in yield stress of Mg single crystal using long-period stacking ordered nanoplates

Mg–Zn–Y ternary alloys containing the long-period stacking ordered (LPSO) phase exhibit superior mechanical properties. This is believed to be originating from the LPSO phase acting as the strengthening phase. However, we first clarify that the mechanical properties of the matrix Mg solid solution in the Mg/LPSO two-phase alloy are significantly different from those of pure Mg. The yield stress of a Mg99.2Zn0.2Y0.6 single crystal (matrix Mg solid solution) is almost the same as that of an LPSO single-phase alloy. This is ascribed to the formation of thin stacking-fault-like defects, named “LPSO nanoplate”. In Mg99.2Zn0.2Y0.6, kink-band formation is induced in the same manner as that in the LPSO phase in deformation, resulting in high strength accompanied with increased ductility. Our results suggest that the strengthening mechanism of the Mg/LPSO two-phase alloy must be reconsidered depending on the microstructure. Furthermore, the results suggest that new ultrahigh-strength Mg alloys, which have much lower Zn and Y contents but the mechanical properties are comparable or superior than the present Mg/LPSO two-phase alloys, are expected to be developed via the appropriate control of LPSO nanoplate microstructures.

Optical, Structural and Spectroscopic Characterization of ZnS Nanocrystals Embedded in KBr Single Crystal Matrix Grown by Czochralski Method

ZnS nanocrystals were embedded in a KBr single crystal matrix using the Czochralski growth technique. The X-ray diffraction, FT-IR and optical spectroscopy revealed the incorporation of ZnS nanocrystals. A blue shift of the absorption edge of the obtained samples has been observed, indicating the quantum confinement effect. The optical band-gap is estimated to be about 4.67 eV. Two excitonic peaks appeared at 300.4 nm and 271 nm. The average nanocrystal size was derived from the optical spectra. Annealing led to a shift in the absorption edge towards longer wavelengths and an increasing of the emissions intensity. Raman lines of the nanoparticles are broader and frequency-shifted compared to those of the bulk crystals. These results show that KBr is a good matrix-host of ZnS nanocrystals, and that the elaborated samples can be used for important technological applications.

Spacing-dependent nonlinear optical study of FePt nanoparticles composited films

Abstract The self-organized FePt nanoparticles were embedded in single crystal MgO matrix using pulse laser deposition method. The increasing FePt nanoparticles spacing (2–10 nm) were observed as the decrease of FePt deposition pulse number. The spacing between the FePt nanoparticles changing causes many subbands rooting in superlattice structure. With the decrease of the spacing, the mechanism of samples third-order nonlinear optical property revealed that the two-photonic absorption replaces saturated absorption. By adjusting the FePt deposition pulse number from 100 to 900 P, the third-order nonlinear polarizability χ(3) initially increased, and then decreased. The highest third-order nonlinear polarizability χ(3) of 4.1 × 10−10 esu was obtained with the deposition pulse number of 500 P. In combination with the small linear absorption α, the FePt NPs: MgO system is enough to become a prime candidate for nonlinear application near 580 nm.

Characterization of a Reactive Rh2 Nitrenoid by Crystalline Matrix Isolation.

The fleeting lifetimes of reactive intermediates in C-H functionalization chemistry often prevent their direct characterization. For example, the critical nitrenoid intermediates that mediate Rh2-catalyzed C-H amination have eluded characterization for more than 40 years. In the absence of structural characterization of these species, methodological development is often computationally guided. Here we report the first X-ray crystal structure of a reactive Rh2 nitrenoid, enabled by N2 elimination from an organic azide ligand within a single-crystal matrix. The resulting high-resolution structure displays metrical parameters consistent with a triplet nitrene complex of Rh2. The demonstration of facile access to reactive metal nitrenoids within a crystalline matrix provides a platform for structural characterization of the transient species at the heart of C-H functionalization.

Influence of Preheating on the Microstructure Evolution of Laser Re-Melting Thermal Barrier Coatings/Ni-Based Single Crystal Superalloy Multilayer System.

Laser surface re-melting (LSR) is a well-known method to improve the properties of atmospheric plasma-spraying thermal barrier coatings (APS TBCs) by eliminating the voids, incompletely melted particles and layered-structure. Laser energy density should be carefully selected to reduce the exposed thermal damage of the underlying single crystal (SX) matrix. Therefore, the purpose of this paper was to identify the effect of introducing induction heating to laser modifying of APS TBCs coated on Ni-based SX superalloy. The results indicated that the preheating of the substrate can lower the laser energy threshold that is required for continuously re-melting the coating. It proved that, in LSR processing of a APS TBCs/ SX matrix multilayer system, the combined method of adopting the low laser energy and preheating at elevated temperature is an effective means of minimizing the cracking susceptibility of top ceramic coating, resulting from decreasing the mismatch strain between the re-melted layer and residual APS TBCs, which can significantly improve the segmented crack condition in terms of crack dimension and crack density. Moreover, this combined method can remarkably lower heat input into an SX matrix and correspondingly the interface stored energy induced by pulsed laser thermal shock, which can effectively lower the tendency for surface recrystallization after the subsequent heat treatment.

Regulation and coupling effects on mechanical properties of copper-graphene/h-BN layered heterostructure via ion irradiation, interlayer sp3 bonds and temperature

In this paper, by using the molecular dynamics method, various defects have been created in graphene/h-BN with interlayer sp3 bonds (G/BN-sp3) by using ion irradiation. The copper-graphene/h-BN layered heterostructure (Cu-G/BN-sp3) were prepared by inserting G/BN-sp3 after irradiation damage into the single crystal copper matrix. The coupling effects of ion irradiation, interlayer sp3 bonds and temperature on defective copper-graphene/h-BN layered heterostructure were studied. The results show with the increase of ion irradiation doses, the mechanical properties of copper layered heterostructure decrease. When defects (caused by ion irradiation) and sp3 bonds coexist, if the defects are created around the sp3 bonds, the composite system is more vulnerable to damage. The location of the defects is an important factor to determine the crack position and fracture direction of copper layered heterostructure. Although ion irradiation and sp3 defects have adverse effects on mechanical properties, the mechanical properties of pure copper are still improved by introducing graphene/h-BN heterostructure. It provides a new way to enhance the radiation resistance and corrosion resistance of copper matrix composites. Meanwhile, controlling and strengthening the properties of copper matrix composites from a new perspective.

Non-equilibrium supersaturation behavior in a Cu/Sn/Cu interconnect induced by room temperature electromigration

The non-equilibrium supersaturation behavior in a Cu/Sn/Cu interconnect induced by electromigration was investigated, for the first time, under room temperature. The sub-micron dimension solder interconnect was fabricated using a magnetron sputtering technique. The athermal electromigration force, rather than the Joule heating, induced a net Cu diffusion flux across the cathode Cu/Sn interface toward the Sn matrix (along the electron flow direction). The accumulation of Cu atoms formed meta-stable supersaturation of Cu in Sn. A local distorted lattice structures was formed as evidenced by spherical aberration corrected scanning transmission electron microscope. The Cu supersaturation behavior was governed by grain boundary diffusion in the polycrystalline Cu electrode and interstitial diffusion in the single crystal Sn matrix. The extent of supersaturation in the metal matrix is affected by electromigration period and geometrical (cathode/anode electrode) parameter.

Model of Cooling of Compact Surfaces by Microchannel Recuperative Heat Exchangers with a Matrix of Filamentary Silicon Single Crystals

An analysis has been made of a novel class of recuperative heat exchangers for cooling of compact surfaces in electronic systems for various object-oriented purposes with a matrix of filamentary silicon single crystals grown directly on the heat-liberating boundary. A mathematical model has been proposed based on the assumption of the regime of ideal displacement of the heat-transfer agent in the form of a system of equations of two-temperature convective heat transfer with volume averaging over the element in a porous skeleton. The solution of the system has been obtained in analytical form. The experiment conducted on a pilot plant has confirmed the adequacy of the mathematical model.

Atomistic simulations of the strengthening effect of high-density bubble formation in helium irradiated single crystalline copper

We performed atomistic simulations to study the strengthening effect of He bubbles with different He atom concentrations within single crystal copper matrix. Uniaxial tensile deformation test demonstrated mechanical strengthening and enhanced ductility of single crystal copper hosting such He bubbles containing high-density He atoms. The yield strength and failure strain have been observed to increase up to vacancy/He ratio of 1:3, followed by a sharp decrease at the vacancy/He ratio of 1:4. Formation of 3D regions with distinct crystallographic orientation has been characterized during the evolution of high-density He bubbles. Considerable number of sessile dislocations have been observed to form in the boundary of those 3D regions for the sample with vacancy to He atom ratio of 1:2 and 1:3 during equilibration. These sessile dislocations contribute towards the observed mechanical strengthening along with Cu/He interfacial energetics. Higher He atom concentration also results into enhancement of total dislocation density with a substantial reduction in mobility of dislocations in copper which promotes homogeneous plastic deformation. During plastic flow, He bubbles undergo significant decrystallization, detwinning, and formation of Shockley partials, while copper exhibits ordinary dislocation-mediated plasticity. The rate of growth of the He bubbles shows significant influence on plastic deformation via coalescence of the He bubbles in the solid region and leads to ultimate failure of the sample.