Lattice Mismatch Research Articles

Mechanism of SiC formation by Si surface carbonization using CO gas

SiC thin films formed by Si surface carbonization can be used as buffer layers for the heteroepitaxial growth of nitride semiconductors. We propose a Si surface carbonization method using CO gas. In this study, we investigate the dependence on CO activity (aCO) of the carbonization of Si(100), Si(110), and Si(111). The Si surface reacts with the CO molecules to form SiC nuclei during the initial carbonization stage. Following nucleation, carbonization proceeded based on the thermodynamic carbonization driving force. At a lower aCO with a larger driving force but smaller nucleation density, a thicker SiC film comprising larger grains with higher crystal coherency was formed, whereas the roughness of the SiC surface and SiC/Si interface is larger. Furthermore, voids with larger sizes and densities were formed at the SiC/Si interface. The thickness, grain size, and crystal coherency of the SiC film were on Si(110)≳Si(111)≫Si(100). All the SiC films were singly oriented. The SiC films were oriented to Si(100) and Si(111), regardless of carbonization conditions. In contrast, SiC(111) or SiC(110) was formed on Si(110) carbonized at lower and higher aCO, respectively, as determined by the SiC formation rate, structural stability of the plane, and lattice mismatch.

Hierarchically three-dimensional ZrO2/Fe3O4/C nanocomposites with Janus structure for high-efficiency electromagnetic wave absorption

Hierarchically three-dimensional (3D) materials present a pivotal challenge and opportunity in achieving effective microwave absorption with synergistic effects. In this work, α-Fe2O3@ZrO2 with core-shell structure were fabricated in-situ on aramid nanofibers by a solvothermal method. Following calcination, 3D ZrO2/Fe3O4/C nanocomposites with Janus structure have been successfully synthesized. By controlling the lattice match and mismatch in both processes, a core-shell structure of α-Fe2O3@ZrO2 and Janus structure of ZrO2/Fe3O4 have been well-define performed. The composite material ZrO2/Fe3O4/C-700 has a minimum reflection loss (RLmin) of −67.4 dB at a thickness of 2.0 mm. The effective absorption bandwidth (EAB) at a thickness of 2.4 mm is 6.0 GHz (11.0–17.0 GHz). This study provides a novel strategy for fabricating high-efficiency electromagnetic wave absorption materials with dual synergistic effects in nanosized scale.

Mechanical properties of VC/ZrC and VC/HfC superlattices

Face-centered cubic transition metal carbides exhibit high melting points and hardness, making them prominent candidates for protective coating applications. Vanadium carbide (VC) has typical characteristics of transition metal carbides. It serves as model material in this study, in which we showcase the effect of superlattice architecture on mechanical properties and fracture toughness. While beneficial effects of superlattice arrangement have been demonstrated for a series of nitride-based coatings, transition metal carbides remain largely unexplored territory. Following density functional theory based ab initio predictions on lattice and shear modulus mismatch, we develop VC/ZrC and VC/HfC superlattice coatings synthesized via pulsed DC sputter deposition. The bilayer periods (Λ) of our fully fcc-structured polycrystalline coatings range between 2–50 nm (indicated by X-ray diffraction, transmission and scanning electron microscopy). The chemical composition is close to 1:1 stoichiometry (from X-ray fluorescence, elastic back-scattering spectrometry and elastic recoil detection analysis). Both superlattice series exhibit a strong dependence of hardness, elastic modulus, and fracture toughness on their bilayer periods, which can only be correlated with the in-plane stress variations for VC/ZrC. The VC/HfC superlattices provide their peak-hardness of 36.0 ± 1.6 GPa for Λ = 6 nm and their peak in fracture toughness of 3.5 ± 0.5 MPa√m for Λ = 10 nm.

Screening ideal MXene electrodes for monolayer MoSe2: A first-principles study

Exploring proper electrodes with low-resistance contacts is vital for promoting the performance of nanoelectronics. We have screened 35 kinds of metallic monolayer (ML) MXenes for possible low-resistance contact electrodes with ML MoSe2 through first-principles calculations. The lattice mismatch and work function (WF) are used as two indicators to screen for possible electrodes. Then, we validate the interface contact characteristics of ten selected van der Waals (vdW) heterostructures. Notably, n-type Ohmic contacts are observed for the MoSe2/Mo2C(OH)2, MoSe2/Zr2C(OH)2, MoSe2/Sc2N(OH)2, MoSe2/Nb2C(OH)2, MoSe2/Zr2N(OH)2, and MoSe2/Zr2NF2 interfaces, while p-type (quasi) Ohmic contacts are observed at the MoSe2/Mo2NO2 and MoSe2/Sc2CO2 interfaces. All the above interfaces are stable, and the bands from each component layer are well preserved. The screening strategy is also suitable for identifying other low-resistance vdW contacts.

Activating multiple slip systems in the laves phase improves the high-temperature strength and elastic coordination of (TiZr)65-XNb15Mo20CrX alloy

Introducing Laves phase into refractory multi-principal elements alloys (RMPEAs) is a new exploration direction to improve the alloy strength. In this work, we have prepared a series of (TiZr)65-XNb15Mo20CrX (x = 5,10,15,20) multi-principal elements alloys, by the addition of Cr to introduce the Laves phase for excellent high-temperature performance. The microstructure, phase constituents, and mechanical properties of the refractory high-entropy alloy were studied in the present work. Most of these alloys exhibited typical dendrite morphology, except for the alloy Cr5. Excessive Cr results in the formation of TiZr-enriched zones. In addition, twins can appear in as-cast alloys as a result of a significant lattice mismatch between the matrix and the Laves phase, which is caused by the rapid cooling process during melting. All alloys demonstrate remarkable strength when exposed to high temperatures, with compressive yields surpassing 552 MPa, peaking at 712 MPa at 800 °C, and compressive strains exceeding 30%. Benefiting from the Laves phase, the alloys do not show significant softening, making it possible for this alloy to work stably at 800 °C. Analyses of high-temperature specimens under different degrees of deformation reveal that small-sized Laves phases containing nano-twins precipitate in the matrix. The small-sized Laves phases and nano-twins restrict the movement of dislocations, leading to a large amount of dislocation accumulation, which improves the strength and plasticity of the alloy. Therefore, the current work on designing novel alloys provides new ideas for developing RMPEAs with synergistic strength and plasticity.

Strain Solitons in an Epitaxially Strained van der Waals-like Material.

Strain solitons are quasi-dislocations that form in van der Waals materials to relieve the energy associated with lattice or rotational mismatch. Novel electronic properties of strain solitons were predicted and observed. To date, strain solitons have been observed only in exfoliated crystals or mechanically strained crystals. The lack of a scalable approach toward the generation of strain solitons poses a significant challenge in the study of and use of their properties. Here, we report the formation of strain solitons with epitaxial growth of bismuth on InSb(111)B by molecular beam epitaxy. The morphology of the strain solitons for films of varying thickness is characterized with scanning tunneling microscopy, and the local strain state is determined from atomic resolution images. Bending in the solitons is attributed to interactions with the interface, and large angle bending is associated with edge dislocations. Our results enable the scalable generation of strain solitons.

InGaAs/Si PIN photodetector with low interfacial recombination rates realized by wafer bonding with a polycrystalline Si interlayer

In this Letter, we proposed a robust InGaAs/Si bonded heterojunction by polycrystalline Si (poly-Si) and amorphous interlayers. The ultra-thin amorphous layer is induced through Ar plasma treatment. The synergism of poly-Si and amorphous interlayers effectively blocks the lattice mismatch and releases the interfacial thermal stress. A bubble- and defect-free bonding interface is achieved even if after annealing at 500 °C, demonstrating compatibility with high-temperature processes. The heavily doped poly-Si interlayer sweeps the electric field from the poly-Si layer and concentrates in the amorphous layer, rendering electron tunneling through the bonding interface and reducing the interfacial recombination rates. As a result, the bonded InGaAs/Si PIN photodetector harvests a saturated and low dark density of 0.26 mA/cm2 at −1 V and a high rectification ratio of 3.5 × 105 at ±1 V. Additionally, the non-optimized device achieves a high responsivity of 0.82 A/W at 1550 nm. These results indicate that the proposed bonding strategy provides a viable route to tackle the electronic, optical, and thermal barriers of integrating single-crystal InGaAs into Si platforms. This enables the photodetection of InGaAs/Si devices with a high signal-to-noise ratio.

Reduced Lattice Mismatch at the Interface of Perovskite and LaNiO3 Hole Transport Layers for Highly Efficient p–i–n Perovskite Solar Cells

Reduced Lattice Mismatch at the Interface of Perovskite and LaNiO₃ Hole Transport Layers for Highly Efficient p–i–n Perovskite Solar Cells

Thermodynamic Origin-Based In Situ Electrochemical Construction of Reversible p-n Heterojunctions for Optimal Stability in Potassium Ion Storage.

Heterojunctions in electrode materials offer diverse improvements during the cycling process of energy storage devices, such as volume change buffering, accelerated ion/electron transfer, and better electrode structure integrity, however, obtaining optimal heterostructures with nanoscale domains remains challenging within constrained materials. A novel in situ electrochemical method is introduced to develop a reversible CuSe/PSe p-n heterojunction (CPS-h) from Cu3 PSe4 as starting material, targeting maximum stability in potassium ion storage. The CPS-h formation is thermodynamically favorable, characterized by its superior reversibility, minimized diffusion barriers, and enhanced conversion post K+ interaction. Within CPS-h, the synergy of the intrinsic electric field and P-Se bonds enhance electrode stability, effectively countering the Se shuttling phenomenon. The specific orientation between CuSe and PSe leads to a 35° lattice mismatch generates large space at the interface, promoting efficient K ion migration. The Mott-Schottky analysis validates the consistent reversibility of CPS-h, underlining its electrochemical reliability. Notably, CPS-h demonstrates a negligible 0.005% capacity reduction over 10,000 half-cell cycles and remains stable through 2,000 and 4,000 cycles in full cells and hybrid capacitors, respectively. This study emphasizes the pivotal role of electrochemical dynamics in formulating highly stable p-n heterojunctions, representing a significant advancement in potassium-ion battery (PIB) electrode engineering.

Boosting hydrogen production from alkaline water splitting by regulating interlayer stress via lattice mismatch in NiS/MoS2

Alkaline water splitting currently represents one of the most promising routes for sustainable hydrogen production. However, the key challenge with this method lies in the development of low-cost catalysts showing high-performance for hydrogen evolution reaction (HER). Given the rapid advances in the structural design of HER catalysts, a potential procedure to boost their performance is introduced herein. A controllable interlayer stress is generated at the homojunction NiS/NiS interface of electrodeposited hybrid transition metal sulphide NiS/MoS2, by precisely regulating lattice mismatches of NiS nanostructures, achieve a precise control over its charge transfer resistance and the effective balance of electrochemical area. Accordingly, an optimal design, NM5030 (NiS(50 mA/cm2)-NiS(20 mA/cm2)/MoS2/CC), showing an excellent HER performance in alkaline electrolyte is produced. It can drive a high current density of 10 mA/cm2, 100 mA/cm2 and 400 mA/cm2 at a low overpotential of 18 mV, 93 mV and 161 mV, respectively. Under chronoamperometric test, no obvious reduction in current density is observed after 48 h, indicating its high stability. Overall, this work demonstrates the feasibility and effectiveness of the strategy of fabricating lattice mismatch to find an optimal layered structure based catalyst for efficient HER.

Microstructure refinement and mechanical properties enhancement of Mg[sbnd]Al alloys via a novel of MgO nanoparticles modified graphene nanoplates refiner by in-situ synthesis

Grain refinement by inoculation treatment is one of the simplest and most efficient ways to improve the mechanical properties of MgAl alloys. In this study, a novel GNP@MgO grain refiner was designed by an in-situ reaction of CO2 gas and Mg melt. It can significantly reduce the average grain sizes of Mg9Al alloys from 126.9 μm to 12.7 μm. The mechanical properties of Mg9Al alloys were significantly enhanced, and its ultimate compressive strength was increased from 370 MPa to 436 MPa. HRTEM characterization and atomic interface analyses have shown that the Al4C3 phase has an orientation relationship with α-Mg as (009)Al4C3//(002)Mg, and [11−20]Al4C3//[11–20]Mg, which has a low degree of lattice mismatch of 5.79%. Besides, these MgO nanoparticles can adsorb on the surface of α-Mg grains and play a role in hindering growth and solute diffusion. The ultra-high grain refinement efficiency of 90% is achieved through the synergistic effects of GNP promoting heterogeneous nucleation and MgO nanoparticles inhibiting grain growth. This work sheds new light on designing innovative and effective grain refiners for Mg alloys.

Study on Epitaxial Growth of High‐Quality InSb Materials

AbstractThis paper discusses the optimization of the growth temperature and Sb/In ratio of 1 µm InSb thin films grown on GaAs substrates by molecular beam epitaxy due to the InSb materials with larger lattice constants have smaller growth windows. The results show that atomic steps can be clearly seen in InSb thin films grown at 420 °C with a Sb/In ratio of 6. The InSb material grown under this condition has the smallest FWHM, indicating the best crystal quality. At the same time, the highest electron mobility measured at room temperature is 38860 cm2 V−1 s−1. The transport properties and crystal quality of InSb/AlxIn1‐xSb heterostructures corresponding to different Al compositions are also studied. The results show that as the Al component increases, dislocation scattering caused by lattice mismatch affects the electron mobility of the channel layer. The highest electron mobility of InSb/AlxIn1‐xSb heterostructures obtained is 18900 cm2 V−1 s−1 at room temperature.

Recoverable tuning of lattice mismatch and strength in ultrastable-nanostructured Cu/Ag spinodoid alloys

The strengthening effect of interface in materials is usually studied by monitoring the change of strength in response to varying structure sizes, such as the varying grain or phase sizes. In this study, we demonstrate that the strength of a nanostructured material can be recoverably tuned by modifying interfacial structure without changing structure size. Specifically, we studied the Cu/Ag spinodoid alloys fabricated by dealloying and electrochemical deposition, which exhibit a cube-on-cube orientation relationship between two interpenetrating nanophases. This material remains stable against coarsening even at temperatures near the eutectic melting point, due to the presence of low-energy semi-coherent interfaces and the lack of defects such as grain boundaries. Using cyclic thermal annealing, we are able to alter the solid solubility of both nanophases and, consequently, the lattice mismatch between them, resulting in a recoverable tuning of hardness and strength. The amplitude of hardness modulation decreases with increasing feature size (λ), and changes sign when λ exceeds ∼500 nm. This is attributed to a competition between two strengthening mechanisms: the interface-induced strengthening that is more prominent at a lower λ, and the solid solution hardening that is largely λ-insensitive. The finding indicates that interface hardening prevails over solution hardening when λ is below ∼500 nm. Current study paves the way for the development of strong and stable nanostructured materials whose properties can be optimized by independently tailoring feature sizes and interfacial structures.

Improved Alcohol Oxidation through Combined Effects of Tensile Lattice Strain and Twin Defects in Core-Shell Electrocatalysts.

The direct alcohol fuel cells (DAFCs) rely on alcohol oxidation reactions (AORs) to produce electricity, which require catalysts with optimized electronic structure to accelerate the sluggish AORs. Herein, an epitaxial growth of Pd layer onto the pentatwinned Au@Ag core-shell nanorods (NRs) is reported to synthesize highly strained Au@AgPd core-shell NRs. The tensile strain in the AgPd shell of the Au@AgPd nanorods (NRs) arises not only from the core-shell lattice mismatch but also from twinning and lattice distortion occurring at the five twinned boundaries present in the structure. Theoretical simulations prove that the presence of tensile strains in the AgPd layer leads to a significant upward shift of the d-band center of the Pd site toward the Fermi level which remarkably changes the adsorption energy of alcohols on the surface. Highly strained Au@AgPd NRs show exceptional mass activities in electrochemical oxidation of biomass-derived alcohols (ethylene glycol, ethanol, and glycerol) reaching up to 18.66, 15.6, and 7.90 A mgpd -1, respectively. These values are 23.3, 23.6, and 23.2 times higher than commercial Pd/C catalysts. This strain engineering strategy set the platform for the design and synthesis of highly efficient and versatile catalysts for the construction of high-performance DAFCs.

Unlocking Invisible Defects of ZnSe Alloy Shells in Giant Quantum Dots with Near Unity Quantum Yield

AbstractPhotoluminescence quantum yield (PL QY) of colloidal quantum dots (QDs) can be improved by growing a shell, but it is rather limited if the shell thickness exceeds a threshold. Lattice mismatch between the core and shell is known to determine this critical shell thickness, securing QDs from defect formation through strain release. However, it cannot explain the recently reported high efficiency QDs with giant shells. Based on CdSe/ZnSe thick shell QDs, this study aims to identify the culprit limiting PL QY. In the shell growth process, the gradual reduction in PL QY is accompanied by a low‐energy tail emission, but the additional compressive strain by the outmost shell eliminates such abnormalities. It is revealed that the zinc vacancy in the shell provides shallow hole trap states. The computational study successfully explains the hole‐accepting zinc vacancy states above the CdSe 1Shh state, raised by compressive strain along radial direction. Additional hydrostatic compressive strain lifts the 1Shh state for this strained heterostructure to minimize the energetic gap with the zinc vacancy states. The finding suggests that critical shell thickness can be limited by atomic vacancy incorporated during shell growth, not by formation of misfit dislocation caused by strain release.

Surface Li+/Ni2+ Antisite Defects Construction for Achieving High‐Voltage Stable Single‐Crystal Ni‐Rich Cathode by Anion/Cation Co‐Doping

AbstractNi‐rich cathode material possesses a considerable theoretical capacity, yet achieving their full capacity potential remains challenging. Elevating its operation voltage is an effective approach, while the stability of Ni‐rich cathode material is relatively poor, which is limited by Li+/Ni2+ mixing. Herein, a strategy of cation/anion co‐doping is proposed for single‐crystal ultrahigh‐nickel cathode LiNi0.92Co0.04Mn0.04O2 operated at 4.5 V. The enhancement mechanism is explicitly revealed by in situ/ex situ tests and theory calculations. Specifically, Mo6+ and F− are introduced to construct an appropriate Li+/Ni2+ antisite defects structure at the particle surface, which can maintain the low‐defect Li+ layered channel inside the bulk simultaneously, inducing a stable access portal for Li+ transport from the cathode/electrolyte interface. More importantly, the Li+/Ni2+ antisite passivation layer on the surface can uphold the stability of Li‐layer and optimize the reactive behavior of Ni2+, thus boosting the interfacial stability and reducing the lattice mismatch. As a result, it can achieve high capacity (204 mAh g−1 at 1 C) and stable retention during long‐term high‐voltage measurements both in half‐cell (87.1% after 200 cycles) and full‐cell (91.9% after 400 cycles). This facile strategy provides a feasible technical reference for further exploiting the ultrahigh‐capacity of Ni‐rich cathode for commercial application.

Inhibiting sensitivity of microstructure and properties to heat input in DED-arc of 7075 aluminum alloys: The role of TiC-nanoparticles

Achieving high-quality 7075 high-strength aluminum alloy manufactured via directed energy deposition-arc (DED-Arc) remains challenging due to its sensitivity of microstructures and properties to heat inputs. This study examines how TiC nanoparticles can effectively reduce the adverse effects of high heat input from the arc on the surface morphology, microstructure, and properties of 7075 aluminum alloy deposits. The surface morphology, defects, microstructures, and mechanical properties of the deposited alloy parts were characterized. The analysis revealed that reducing the heat input results in smoother surface morphology but has little effect on the number of defects, grain morphology, grain size, and tensile strength. Even under various heat inputs, all deposited samples containing TiC nanoparticles exhibit equiaxed grain structures with an average grain size of approximately 8.98 ± 0.27 μm and possess a tensile strength exceeding 500 MPa with minimal variance. Further studies involving microstructures and computational fluid dynamics suggest that the incorporation of TiC nanoparticles mitigates the impact of thermal dynamic conditions within the molten pool. It was discovered for the first time that there is a significant lattice mismatch of about 18% between the crystal planes of TiC and the Al-matrix in the deposited samples. This mismatch increases the free energy of the growth phase, effectively creating a pinning effect for the growing grains. Consequently, this nanoparticle-induced physical barrier disrupts the conventional control of grain growth dictated by thermodynamic conditions, effectively limiting grain size under various heat inputs by arc. This work demonstrates a promising strategy to reduce the sensitivity of microstructure and properties to heat input during DED processes.

Microstructure, mechanical performance and nucleation mechanism of laser powder bed fused novel Sc/Zr/Ti-modified Al-Mg alloys

In this study, the modification of 0.70 wt% ScH3alone did not substantially fine the grain and eliminate the hot-cracking of Al-Mg-Sc alloy, resulting in low strength of as-built material. In contrast, the 0.70 wt% ScH3 and 0.34 wt% ZrH2 modified Al-Mg alloy (hereafter denoted as Al-Mg-Sc-Zr1) was demonstrated to be an exceptionally effective inoculation for Al-Mg-Sc-Zr1 alloy, owing to the low lattice mismatch (0.4 %) between Al3(Sc,Zr) and α-Al. The considerable grain refinement was ascribed to the L12-Al3(Sc,Zr) nucleis, which efficiently promoted heterogeneous nucleants of α-Al grains, contributing to significant refined grain size. Consequently, the as-built Al-Mg-Sc-Zr1 alloy demonstrated outstanding tensile strength with sound elongation to fracture due to crack-free and fine grain strengthening. Additionally, compared with Al-Mg-Sc-Zr1 alloy, the further modification with more ScH3 and ZrH2 promoted substantial grain refinement via inoculation treatment of 1.15 wt% ScH3 + 0.55 wt% ZrH2. Moreover, the grain refinement effect of ScH3 and TiH2 modification was also studied and correlated to the resulted ultrafine equiaxed grains and performance. These results indicate that grain microstructure and mechanical properties of as-built Al alloys can be tailored by suitable inoculants which can be further employed to other engineering alloys.

Chemically Tailored Semiconductor Moiré Superlattices of Janus Heterobilayers

Janus monolayers of transition metal dichalcogenides (TMDCs) are promising building blocks for moiré superlattices because of their built‐in electric field and clean fabrication process. In particular, Janus TMDC monolayers can be chemically converted from conventional TMDC monolayers by atomic substitution, enabling the direct formation of lattice‐mismatched heterobilayers from TMDC bilayers. However, the moiré superlattices of Janus heterobilayers have not been studied experimentally. Herein, this work reports the fabrication and characterization of semiconductor moiré superlattices in chemically tailored Janus heterobilayers. The MoSSe/MoSe2 (or WSSe/WSe2) Janus heterobilayers are prepared by replacing the top layer Se atoms with S atoms in MoSe2 (or WSe2) bilayer using H2 plasma treatment. Scanning transmission electron microscopy reveals that an average moiré period of about 14 nm formed due to lattice mismatch resulting from the chalcogen substitutions. The cryogenic photoluminescence spectra show sharp, near‐infrared emissions, which are attributed to excitons trapped by moiré potentials based on comparison with theoretical calculations. The Janus‐based heterostructures provide a long‐period moiré system with built‐in potential even for nontwisted heterobilayers, allowing the functionalization of confined and correlated electron systems.

Tunable wrinkle patterns in Moiré pattern of interlayer-bonding strained bilayer graphene

Moiré patterns are important structures in two-dimensional (2D) materials, showcasing unique electronic correlated states, which have garnered considerable research interests in recent years. However, current researches on moiré patterns primarily focus on honeycomb patterns induced by lattice mismatches at 2D material hetero-interfaces. In this work, we have demonstrated the ability to generate diverse and tunable wrinkle patterns in interlayer bonding strained bilayer graphene (IB-SBG) through a “stretch-crosslink-release” strategy, facilitated by the interlayer bonding that provides effective in-plane load transfer and interlayer constraint. Three energetically favorable wrinkle patterns are identified, including herringbone, irregular hexagon and honeycomb patterns. In general, wrinkle patterns are determined by two parameters, i.e., pre-strain and the portion of interface with interlayer bonding, and the phase diagram of wrinkle patterns corresponding to the two parameters is provided. Furthermore, strain engineering can be employed in IB-SBG to generate a series of new patterns by precisely adjusting the biaxial strain applied to IB-SBG. The present strategy to achieve tunable wrinkle patterns holds the potential to open new avenues for novel electronic applications based on bilayer graphene systems.