Interfacial Misfit Research Articles

On the origin of superior stability of coherent nanoparticles under ion irradiation

Recently, a new anti-irradiation mechanism relying on reversible disorder-ordering transition of coherent nanoparticles was discovered, which significantly improves the microstructural stability and void swelling resistance of metallic materials. However, the factors that govern the outstanding stability and superb radiation tolerance are still not clear. Here, two kinds of FeCrAl alloys were designed, each strengthened by a different type of coherent phase: L21-ordered Fe2AlV and B2-ordered Ni (Al, Fe). It was observed that the two alloys exhibited disparate responses to high-dose ion irradiations at elevated temperatures. The L21-Fe2AlV precipitates were found to be completely dissolved after 50 dpa of ion irradiation at 500–600 °C, whereas the B2-NiAl precipitates remained stability even after 200 dpa irradiation. This research challenges the conventional wisdom that the stability of nanoparticles is governed by the balance between radiation-enhanced coarsening and radiation dissolution. Instead, it demonstrates the re-nucleation and subsequent interface-controlled solute reshuffling processes govern the stability of coherent chemically-ordered nanoparticles under radiation at high temperatures. We demonstrate that the low interfacial energy, which is related to both the simply chemically-ordered lattice structure and low lattice misfit interface, is crucial for enabling such short-range elemental reshuffling process to repeatedly form nanoprecipitates that cannot be suppressed by radiation.

Coherent to semi-coherent transition of precipitates in Van der Merwe epitaxial films

Abstract The interplay of stresses of two coherent systems, specifically a coherent precipitate within an epitaxial film (in Van der Merve growth mode), gives rise to an interesting scenario; wherein the configurational effects and the strain energy landscape are enriched. This leads to an interdependent evolutionary pathway for the coherent to semi-coherent transition. The transition of the film-substrate interface to the semi-coherent state occurs beyond a critical thickness ( t c ) which arises from energy minimization. Using the model example of the precipitation of NbH0.5 precipitate in a Nb/Sapphire epitaxial system, the critical radii ( r film ∗ ) for model geometries have been computed. 3D finite element models have been used to compute the stress state and energetics of precipitates growing in an epitaxial film. The following important observations can be made based on the simulations. (1) The epitaxial stresses can lead to the stabilization of the coherent precipitate. (2) The transition to a semi-coherent film interface, characterized by an array of interfacial misfit dislocations, can energetically favor the semi-coherent state of the precipitate over the coherent state. The magnitude of r film ∗ depends on the spatial coordinates within the film. (3) The presence of Nb–H coherent precipitates can stabilize the coherent state of the film interface.

Interface misfit of conventionally milled and novel hybrid full-arch implant-supported titanium frameworks

ObjectiveA hybrid manufacturing technique that combines selective laser melting (SLM) and computer numerical control (CNC) has been developed for the fabrication of implant-platform/framework interfaces (PFIs) for mandibular and maxillary full-arch implant-supported titanium frameworks. The aim of this study was to compare the discrepancies in specimens fabricated using the hybrid technique (termed SLM/m hereafter) with those in specimens fabricated by conventional CNC milling.Materials and methodsBased on a mandibular four-PFI CAD model and a maxillary six-PFI CAD model, four groups of titanium frameworks (eight per group, totaling 32) were fabricated according to the fabrication technique (SLM/m or milling) and number of PFIs (four or six). The frameworks were scanned by a structured light scanner and aligned with the CAD model in Geomagic Control X. Discrepancy was defined as the difference between the PFIs of the scanned framework and those of the CAD model. Discrepancies were measured and evaluated by multilevel analysis using a mixed-effects model (α = 0.05), followed by independent samples t-tests (α = 0.0125). Furthermore, the manufacturing times and raw-material costs were recorded and compared.ResultsThe maximum discrepancy values for the four-PFI and six-PFI hybrid frameworks were 52.2 and 64.3 μm, respectively. Multilevel analysis revealed that the fabrication technique and the number of PFIs had no significant effect on the discrepancy value. However, a significant interaction between the two factors was observed (P = 0.020). The discrepancies for the four-PFI hybrid frameworks were significantly lower than those for the four-PFI milled frameworks (P = 0.001). No significant difference in discrepancies between the six-PFI hybrid frameworks and six-PFI milled frameworks was observed (P = 0.697). Furthermore, the hybrid frameworks required only 11% of the raw materials and 25% of the milling time required for the conventionally milled frameworks.ConclusionSLM/m hybrid frameworks are viable, accurate alternatives to CNC-milled frameworks, with the added benefit of substantial cost reduction.

Growth Conditions and Interfacial Misfit Array in SnTe (111) Films Grown on InP (111)A Substrates by Molecular Beam Epitaxy.

Tin telluride (SnTe) is an IV-VI semiconductor with a topological crystalline insulator band structure, high thermoelectric performance, and in-plane ferroelectricity. Despite its many applications, there has been little work focused on understanding the growth mechanisms of SnTe thin films. In this manuscript, we investigate the molecular beam epitaxy synthesis of SnTe (111) thin films on InP (111)A substrates. We explore the effect of substrate temperature, Te/Sn flux ratio, and growth rate on the film quality. Using a substrate temperature of 340 °C, a Te/Sn flux ratio of 3, and a growth rate of 0.48 Å/s, fully coalesced and single crystalline SnTe (111) epitaxial layers with X-ray rocking curve full-width-at-half-maxima of 0.09° and root-mean-square surface roughness as low as 0.2 nm have been obtained. Despite the 7.5% lattice mismatch between the SnTe (111) film and the InP (111)A substrate, reciprocal space mapping indicates that the 15 nm SnTe layer is fully relaxed. We show that a periodic interfacial misfit (IMF) dislocation array forms at the SnTe/InP heterointerface, where each IMF dislocation is separated by 14 InP lattice sites/13 SnTe lattice sites, providing rapid strain relaxation and yielding the high quality SnTe layer. This is the first report of an IMF array forming in a rock-salt on zinc-blende material system and at an IV-VI on III-V heterointerface, and highlights the potential for SnTe as a buffer layer for epitaxial telluride film growth. This work represents an important milestone in enabling the heterointegration between IV-VI and III-V semiconductors to create multifunctional devices.

Deformation Mechanisms Dominated by Decomposition of an Interfacial Misfit Dislocation Network in Ni/Ni3Al Multilayer Structures.

Ni/Ni3Al heterogeneous multilayer structures are widely used in aerospace manufacturing because of their unique coherent interfaces and excellent mechanical properties. Revealing the deformation mechanisms of interfacial structures is of great significance for microstructural design and their engineering applications. Thus, this work aims to establish the connection between the evolution of an interfacial misfit dislocation (IMD) network and tensile deformation mechanisms of Ni/Ni3Al multilayer structures. It is shown that the decomposition of IMD networks dominates the deformation of Ni/Ni3Al multilayer structures, which exhibits distinct effects on crystallographic orientation and layer thickness. Specifically, the Ni/Ni3Al (100) multilayer structure achieves its maximum yield strength of 5.28 GPa at the layer thickness of 3.19 nm. As a comparison, the (110) case has a maximum yield strength of 4.35 GPa as the layer thickness is 3.01 nm. However, the yield strength of the (111) one seems irrelevant to layer thickness, which fluctuates between 10.89 and 11.81 GPa. These findings can provide new insights into a deep understanding of the evolution and deformation of the IMD network of Ni/Ni3Al multilayer structures.

Interband cascade light-emitting diodes grown on silicon substrates using GaSb buffer layer

Interband cascade light-emitting diodes (ICLEDs) offer attractive advantages for infrared applications, which would greatly expand if high-quality growth on silicon substrates could be achieved. This work describes the formation of threading dislocations in ICLEDs grown monolithically on GaSb-on-Silicon wafers. The epitaxial growth is done in two stages: the GaSb-on-Silicon buffer is grown first, followed by the ICLED growth. The buffer growth involves the nucleation of a 10-nm-thick AlSb buffer layer on the silicon surface, followed by the GaSb growth. The AlSb nucleation layer promotes the formation of 90° and 60° interfacial misfit dislocations, resulting in a highly planar morphology for subsequent GaSb growth that is almost 100% relaxed. The resulting GaSb buffer for growth of the ICLED has a threading dislocation density of ∼107/cm2 after ∼3 μm of growth. The fabricated LEDs showed variations in device performance, with some devices demonstrating comparable light–current–voltage curves to those for devices grown on GaSb substrates, while other devices showed somewhat reduced relative performance. Cross-sectional transmission electron microscopy observations of the inferior diodes indicated that the multiplication of threading dislocations in the active region had most likely caused the increased leakage current and lower output power. Enhanced defect filter layers on the GaSb/Si substrates should provide more consistent diode performance and a viable future growth approach for antimonide-based ICLEDs and other infrared devices.

Characterization of the interfacial structure and fracture behavior of in situ synthesized ceramics to reinforce Ni-based composite coatings

This work used the in-situ synthesis of molten-state nitride ceramic phase-reinforced Ni-based alloy coatings, aiming to improve the phase-interface bonding through the interdependent co-solidification between molten droplets. The XRD was used to analyze the physical phases of the composite coatings. The microstructure and phase-interface structure were characterized in detail by combining SEM, TEM, HRTEM, FFT, and SAED techniques. Microhardness tester and microforce microhardness tester were employed to measure the surface hardness and elastic modulus of the composite coatings. The fracture behavior of the composite coatings was characterized by observing the fracture morphology of the coatings using SEM combined with the EDS technique. It was found that the formation mechanisms of interfacial misfit dislocation assistance, lattice distortion, aggregation of stacking faults, and specific growth orientation between the γ-Ni matrix phase and each ceramic phase in NiCrBSi-TiCrN composite coatings improved the lattice matching between the two-phase interface, which resulted in the formation of atomically corresponding coherent lattice relations and stepped interfacial semi-coherent lattice relations, and enhanced the degree of phase-interface bonding. On this basis, the composite coatings with high Cr content further inhibited the expansion of interphase penetration cracks due to the existence of Cr-rich zones at the phase interface, thus exhibiting high fracture toughness. This work provides new opinions on the improvement of phase-interface bonding and composition design of Ni-based composite coatings.

Epitaxial growth of high-quality GaAs on Si(001) using ultrathin buffer layers

The direct growth of III–V semiconductors on silicon holds tremendous potential for photonics applications. However, the inherent differences in their properties lead to defects in the epitaxial layer, including threading dislocations (TDs), antiphase boundaries (APBs), and thermal cracks, significantly impacting device performance. Current processes struggle to suppress these defects simultaneously, necessitating the development of methods to inhibit TDs and APBs in a thin buffer on silicon. This study introduces a GaSb buffer layer during GaAs epitaxy on a silicon (001) substrate. This approach successfully suppresses defect formation by promoting the formation of interfacial misfit dislocation arrays at both the AlSb/Si and GaAs/GaSb interfaces. The resulting GaAs layer exhibits a step-flow surface with a rough mean square of ∼3.8 nm and a full width at half maximum of 158 arcsec. Remarkably, the growth is achieved without any observable interfacial intermixing. Building on this platform, InAs/GaAs quantum dots are grown with a density of 3.8 × 1010 cm−2, emitting at a wavelength of 1288 nm. This breakthrough holds immense promise for developing high-quality GaAs films with reduced defect densities on silicon for O band lasers, laying the foundation for the mass production of silicon-based integrated circuits.

Growth mechanisms of eta phase in 718Plus alloy

Growth mechanisms of eta phase in 718Plus alloy were investigated by high-resolution scanning transmission electron microscopy. The results demonstrated the nucleation and growth of the η platelets were arranged along the {111}γ habit planes. The fine lamellae γ phase, enveloped in the η platelets blocks, was determined. The possible occurrence of interfacial misfit dislocations could effectively release the mismatch strain, and enhance the ledges nucleation on the {0001}η plane. Analysis of the experimental observations, and possible mechanisms of growth were also addressed.

Free-surface proximity induced bistability and semi-semicoherency in precipitation systems

In systems without a ‘high misfit’ and in the early stage of growth, the precipitates tend to remain coherent with the parent matrix. On further growth beyond a critical size (r*), the precipitates undergo a coherent to semi-coherent transition by formation of interfacial misfit dislocation loops to minimize the total strain energy of the system. The variation of r* with domain size has been studied and the concept of re-entrant interface transition to the coherent state was demonstrated in finite crystals. Dislocations can exist in a state of mechanical equilibrium; but are thermodynamically metastable. In the proximity of ‘interfaces’ dislocations experience a configurational force. The current work pertains to study the stability of an interfacial misfit dislocation loop in the proximity of a free-surface; wherein we evaluate configurational effects in a semi-infinite body. The Cu-2 wt%γFe alloy is used as a model system in this study. In this work we: (i) demonstrate the stabilization of the coherent state (divergence of r*), induced by the proximity of the free-surface; (ii) discover the existence of bistability in materials at the microstructural scale, resulting from the destabilization of the equatorial position of the dislocation loop and arising from symmetry breaking in climb of the interfacial loop due to the vicinity of a free-surface. (iii) identify regimes of ‘equi-bistablity’ and regions with asymmetry in energy wells, (iv) establish the existence of a ‘semi’-semicoherent state. Here, one specific system has been chosen to illustrate the effects; however, we expect the conclusions to have a broader applicability.

Development of “GaSb-on-silicon” metamorphic substrates for optoelectronic device growth

The epitaxial development and characterization of metamorphic “GaSb-on-silicon” buffers as substrates for antimonide devices is presented. The approach involves the growth of a spontaneously and fully relaxed GaSb metamorphic buffer in a primary epitaxial reactor, and use of the resulting “GaSb-on-silicon” wafer to grow subsequent layers in a secondary epitaxial reactor. The buffer growth involves four steps—silicon substrate preparation for oxide removal, nucleation of AlSb on silicon, growth of the GaSb buffer, and finally capping of the buffer to prevent oxidation. This approach on miscut silicon substrates leads to a buffer with negligible antiphase domain density. The growth of this buffer is based on inducing interfacial misfit dislocations between an AlSb nucleation layer and the underlying silicon substrate, which results in a fully relaxed GaSb buffer. A 1 μm thick GaSb layer buffer grown on silicon has ∼9.2 × 107dislocations/cm2. The complete lack of strain in the epitaxial structure allows subsequent growths to be accurately lattice matched, thus making the approach ideal for use as a substrate. We characterize the GaSb-on-silicon wafer using high-resolution x-ray diffraction and transmission electron microscopy. The concept’s feasibility is demonstrated by growing interband cascade light emitting devices on the GaSb-on-silicon wafer. The performance of the resulting LEDs on silicon approaches that of counterparts grown lattice matched on GaSb.

Microstructure evolution and tensile strength of Al/Cu inertia friction welded joint

To save production costs and reduce the weight of structures, it is one of the common ways to replace copper (Cu) with aluminum (Al) in some industries such as the refrigeration industry. The high-quality welding of Al to Cu determines the application of the Al/Cu hybrid structure. The inertia friction welding process was used to weld Al pipe to Cu pipe and the Taguchi experiment method was used to study the effects of inertia friction welding parameters on the mechanical properties of the welded joints, and the results show that the initial speed has the greatest influence on the tensile strength of welded joints. Meanwhile, the analyses of the microstructures of the joint show that Al–Cu IMCs formed at the friction interface to realize the metallurgical bonding of the welded joints. The formation sequence of Al–Cu IMCs in the friction welding process is Al2Cu, Al4Cu9, and AlCu. Whereas the type and thickness of IMCs are closely related to the tensile strength of the joints. When the welded joint forms Al2Cu and Al4Cu9, the interfacial misfit between the IMCs layer and base materials is minimized and the tensile strength of the joint is optimized.

Direct Integration of GaSb with GaAs(111)A Using Interfacial Misfit Arrays

Direct Integration of GaSb with GaAs(111)A Using Interfacial Misfit Arrays

Influence of hydrogen on Kurdjumov-Sachs interfacial structure of M23C6/ferritic matrix at high temperatures

Secondary phase thermal stability and strengthening are strongly influenced by the interface structure between the secondary phase and the matrix. The influence of hydrogen on the interfacial structure of (Fe,Cr)23C6 carbides in ferritic matrix at high temperatures is systematically studied. The incoherent interface between (Fe,Cr)23C6 and ferrite matrix acts as a hydrogen trap region at high temperatures. Moreover, the hydrogen at high temperatures does not change the morphological features of (Fe,Cr)23C6 in the ferritic matrix. (Fe,Cr)23C6 obeys the Kurdjumov-Sachs orientation relationship with the ferritic matrix. Hydrogen at high temperatures decreases the mismatch between (Fe,Cr)23C6 and ferrite matrix interface from 7.65 % to 4.63 %. Furthermore, the (Fe,Cr)23C6 interface induced by hydrogen at high temperatures acts as a dislocation emission source. The decrease in interfacial misfit caused by hydrogen at high temperatures is the reason for (Fe,Cr)23C6 to maintain thermal stability and act as a dislocation emission source under a high-temperature hydrogen atmosphere.

Seed-crystal-induced directional solidification toward Al2O3/(Y0.2Er0.2Yb0.2Ho0.2Lu0.2)3Al5O12/ZrO2 ternary eutectic ceramics

The present work successfully prepared a novel Al2O3/(Y0.2Er0.2Yb0.2Ho0.2Lu0.2)3Al5O12/ZrO2 (or Al2O3/(5RE0.2)AG/ZrO2 in short) ternary eutectic ceramic with the seed-crystal-induced technique by directional solidification. ZrO2 was a cubic structure and was stabilized by all oxides of Y2O3, Er2O3, Yb2O3, Ho2O3, and Lu2O3. The three phases interpenetrated each other and ZrO2 was highly dispersed. Al2O3 inherited well the direction of the c-sapphire seed. The orientation relationship among the three was determined to be [0001]Al2O3 || [100](5RE0.2)AG || [110]ZrO2, (11–20)Al2O3 || (004)(5RE0.2)AG || (002)ZrO2. The three interfaces were all semi-coherent and showed higher interfacial misfit strain energy due to the solid solution effect of (5RE0.2)AG. The novel Al2O3/(5RE0.2)AG/ZrO2 ternary eutectic ceramic showed improved mechanical properties compared to other Al2O3-based eutectic ceramics. The solid solution effect was the main reason for its enhanced hardness and elastic modulus. Several toughening mechanisms including crack bridging, bifurcation, deflection, and screening can be found in the Al2O3/(5RE0.2)AG/ZrO2 ternary eutectic ceramic. The micro-scale suture-like deflection was newly found in the microstructure, which contributed to its fracture toughness.

Plastic deformation of Ag/MgO interface system during tensile fracture: A molecular dynamics study

Fracture experiments on layered metal-ceramic composites show that the plastic dissipation in the metal near the crack tip accounts for most of the macroscopic fracture toughness. In this work we studied the microscopic plastic deformation mechanisms of Ag/MgO interface systems using molecular dynamics (MD) method. As tensile strain increases, lattice dislocations nucleate at interface misfit dislocations and propagate in metal layer. The formation of immobile Hirth dislocations in Ag causes hardening. As the metal layer increases, the yield strength decreases and the hardening range is shortened. Large interface area increases the degree of inhomogeneity of dislocation motion and interface fracture behavior, leading to decreased interface yield strength.

High temperature interfacial dynamics in Nickel coated Aluminum nanoparticles

Molecular dynamics simulations are used to investigate the thermal stability of Al-Ni core–shell nanoparticles (NP) with different core sizes and shell thicknesses. Our study reveals that a distinct two-stage melting occurs during the continuous heating of bimetallic NPs. Unlike previous studies for single NP, where melting start from the outer surface and gradually encompass the core of the material, our result clearly indicates the interface dominated melting phenomena. It is evidenced in our analysis through microstructure, coordination number, and Lindemann index, that this interface dominated phenomena does not alter with decreased shell thickness. We estimate that the interfacial misfit, and bond energy orders (Ni-Al, Al-Al, and Al-Al) are the sources of such premelting phenomena to be nucleated at the interface. This study provides a fundamental perspective on the melting behavior of bimetallic nanoparticles and can be extended towards multimetallic NPs at the atomic level.

Atomistic Understanding of the Coherent Interface Between Lead Iodide Perovskite and Lead Iodide

AbstractMetal halide perovskite semiconductors have shown great performance in solar cells, and including an excess of lead iodide (PbI2) in the thin films, either as mesoscopic particles or embedded domains, often leads to improved solar cell performance. Atomic resolution scanning transmission electron microscope micrographs of formamidinium lead iodide (FAPbI3) perovskite films reveal the FAPbI3:PbI2 interface to be remarkably coherent. It is demonstrated that such interface coherence is achieved by the PbI2 deviating from its common 2H hexagonal phase to form a trigonal 3R polytype through minor shifts in the stacking of the weakly van‐der‐Waals‐bonded layers containing the near‐octahedral units. The exact crystallographic interfacial relationship and lattice misfit are revealed. It is further shown that this 3R polytype of PbI2 has similar X‐ray diffraction (XRD) peaks to that of the perovskite, making XRD‐based quantification of the presence of PbI2 unreliable. Density functional theory demonstrates that this interface does not introduce additional electronic states in the bandgap, making it electronically benign. These findings explain why a slight PbI2 excess during perovskite film growth can help template perovskite crystal growth and passivate interfacial defects, improving solar cell performance.

Development of MOVPE grown GaSb-on-GaAs interfacial misfit solar cells

GaSb grown on GaAs through interfacial misfit (IMF) arrays grown via molecular beam epitaxy has been heavily studied; there is limited research, however, on IMF growth through metal-organic vapor phase epitaxy. To demonstrate viability for integration in a multijunction solar cell for terrestrial use, it is imperative to demonstrate high quality GaSb grown on GaAs through metal-organic vapor phase epitaxy. The preferred gallium precursors for n-type and p-type GaSb for longest minority carrier diffusion length were determined to be trimethylgallium and triethylgallium, respectively. A heteroepitaxial GaSb-on-GaAs device attained an open-circuit voltage of 190 mV and an efficiency of 2.2%. Extracted threading dislocation density from the minority carrier lifetime for the heteroepitaxial GaSb-on-GaAs device was determined to be 7.5×106cm−2. In a modeled multijunction solar cell, this device attributes to an overall efficiency of 33.1% under AM1.5g illumination.

Surface Engineering of Metal and Semiconductor Nanocrystal Assemblies and Their Optical and Electronic Devices.

ConspectusColloidal nanocrystals (NCs) are composed of inorganic cores and organic or inorganic ligand shells and serve as building blocks of NC assemblies. Metal and semiconductor NCs are well known for the size-dependent physical properties of their cores. The large NC surface-to-volume ratio and the space between NCs in assemblies places significant importance on the composition of the NC surface and ligand shell. Nonaqueous colloidal NC syntheses use relatively long organic ligands to control NC size and uniformity during growth and to prepare stable NC dispersions. However, these ligands create large interparticle distances that dilute the metal and semiconductor NC properties of their assemblies. In this Account, we describe postsynthesis chemical treatments to engineer the NC surface and design the optical and electronic properties of NC assemblies. In metal NC assemblies, compact ligand exchange reduces the interparticle distance and drives an insulator-to-metal transition tuning the dc resistivity over a 1010 range and the real part of the optical dielectric function from positive to negative across the visible-to-IR region. Juxtaposing NC and bulk metal thin films in bilayers allows the differential chemical and thermal addressability of the NC surface to be exploited in device fabrication. Ligand exchange and thermal annealing densifies the NC layer, creating interfacial misfit strain that triggers folding of the bilayers and is used to fabricate, with only one lithography step, large-area 3D chiral metamaterials. In semiconductor NC assemblies, chemical treatments such as ligand exchange, doping, and cation exchange control the interparticle distance and composition to add impurities, tailor stoichiometry, or make entirely new compounds. These treatments are employed in longer studied II-VI and IV-VI materials and are being developed as interest in III-V and I-III-VI2 NC materials grows. NC surface engineering is used to design NC assemblies with tailored carrier energy, type, concentration, mobility, and lifetime. Compact ligand exchange increases the coupling between NCs but can introduce intragap states that scatter and reduce the lifetime of carriers. Hybrid ligand exchange with two different chemistries can enhance the mobility-lifetime product. Doping increases carrier concentration, shifts the Fermi energy, and increases carrier mobility, creating n- and p-type building blocks for optoelectronic and electronic devices and circuits. Surface engineering of semiconductor NC assemblies is also important to modify device interfaces to allow the stacking and patterning of NC layers and to realize excellent device performance. It is used to construct NC-integrated circuits, exploiting the library of metal, semiconductor, and insulator NCs, to achieve all-NC, solution-fabricated transistors.