Nanolaminate Structure Research Articles

Structural features of bimetallic composites of the Me-Al type (Cu, Ni, Nb), obtained by ball milling of powder mixtures and consolidation by torsion under pressure

A comparative study of the features of the microstructure of bimetallic composites of the Me-Al (Cu, Ni, Nb) type, obtained by ball milling of powder mixtures and consolidation by torsion under pressure in Bridgman anvils, was carried out. In all systems studied in this work, the formation of a nanoband structural state is observed, the elements of which are elongated predominantly along the direction parallel to the anvil plane. It has been established that in local areas characterized by the absence of the aluminum component, an SMC state without a nanolaminate structure is formed. An analysis of the features of structure formation was carried out taking into account the comparison of the characteristics of powder systems components (melting point, shear modulus and stacking-fault energy). It was shown that low shear modulus of aluminum, compared to other components, in combination with a higher homologous temperature, provides it high accommodative ability. It has been suggested that under conditions of torsion under pressure, the aluminum component, being a kind of solid lubricant, ensures slipping and flattening of stronger layers of the second component, which contributes to the formation of a nanolaminate structure in the metal‑aluminum systems under consideration.

Demonstration of 1 V Reliable FeRAM Operation: Vc Engineering Using Quasi-Chirality of Hf1-xZrxO2 in a Nanolaminate Structure.

Hafnia thin films are known to demonstrate excellent performance with strong ferroelectricity and high scalability, making them promising candidates for CMOS-compatible materials. However, the reliability of ferroelectric devices must be further improved. This study developed a Hf1-xZrxO2 ferroelectric capacitor with a nanolaminate structure that operated at remarkably low voltages, demonstrating excellent retention (>10 years/85 °C) and endurance (>1010 cycles). The exceptional performance is attributed to the presence of thin tetragonal phase layers within the thick ferroelectric layers, which decreased the switching barrier in the nanolaminate films. Further, we verified phase crystallization via a detailed analysis of high-resolution transmission electron microscopy images. The improved switching propagation in the nanolaminate films was confirmed through switching speed measurements and theoretical models. Furthermore, we addressed pinching issues by precisely controlling the Hf/Zr ratio and O3 treatment. The initial imprint and retention characteristics were improved by interfacial engineering. Moreover, by reducing the thickness, we have achieved reliable operation at 1.0 V with a 5.5 nm-thick device while maintaining high retention and endurance. This study is a significant step toward the realization of the longstanding problem of ferroelectric random access memory operation voltage with respect to endurance and retention characteristics.

Entropy engineering promotes thermoelectric performance while realizing P–N switchable conduction in BiSbSe1.5Te1.5

BiSbSe1.5Te1.5, a typical multi-layered compound, can be utilized to fabricate p-n junctions with the identical chemical composition by regulating the antisite defects and anion vacancies via defect engineering. However, the thermoelectric performance of n-type BiSbSe1.5Te1.5 is limited due to poor electrical transport properties. Entropy engineering is a novel strategy for expanding the space of performance optimization in materials science, including the field of thermoelectric. Herein, we realize a largely enhanced thermoelectric performance for n-type BiSbSe1.5Te1.5 by employing entropy engineering. Both mass field fluctuations and stress variations field are introduced simultaneously in the lattice, leading to additional phonon scattering. Moreover, nano-laminate structure, nanoscale interstices and holes are formed in the samples. All of these defects and nanoscale structures are especially efficient on trapping phonons. As a result, the optimizing electrical transport properties while maintaining low thermal conductivity are achieved, showcasing a peak ZT of 0.54 at 475 K and a remarkable average ZT of 0.45 between 300 and 550 K for n-type BiSbSe1.25Te1.75.These findings not only provide a way to enhance the thermoelectric performance of n-type BiSbSe1.5Te1.5 but also push forward the promise of the applications in fabricating well-matched p-n junctions using thermoelectric materials with the identical chemical composition.

Magnetron Sputter Deposition of Amorphous Silicon–SiO2 Quantized Nanolaminates

Quantization effects in nanolaminate structures of oxide materials are proposed and experimentally demonstrated only recently. Herein, the material combination of amorphous silicon and SiO2 deposited by magnetron sputtering is investigated and it is shown that the quantization effect can be observed indeed. Transmission electron microscopy characterization gives evidence of continuous layers of amorphous silicon and SiO2 with well‐defined interfaces. The deposition process is described and the tunability of the refractive index and the bandgap energy is demonstrated. By doing so, the advantages of this novel material over classical optical materials are shown and feasibility is proved. As an example, a longpass optical interference filter with edge at 720 nm is deposited using quantized nanolaminates as the high and SiO2 as the low refractive index material. This filter can be deposited successfully with close match to the design. It shows a blocking range throughout the visible spectrum whereas a comparable filter based on SiO2–TiO2 only blocks 500–700 nm.

A Novel Nano-Laminated GdB2C2 with Excellent Electromagnetic Wave Absorption Performance and Ultra-High-Temperature Thermostability.

A novel nano-laminated GdB2C2 material was successfully synthesized using GdH2, B4C, and C via an in situ solid-state reaction approach for the first time. The formation process of GdB2C2 was revealed based on the microstructure and phase evolution investigation. Purity of 96.4 wt.% GdB2C2 was obtained at a low temperature of 1500 °C, while a nearly fully pure GdB2C2 could be obtained at a temperature over 1700 °C. The as-obtained GdB2C2 presented excellent thermal stability at a high temperature of 2100 °C in Ar atmosphere due to the stable framework formed by the high-covalence four-member and eight-member B-C rings in GdB2C2. The GdB2C2 material synthesized at 1500 °C demonstrated a remarkably low minimum reflection loss (RLmin) of -47.01 dB (3.44 mm) and a broad effective absorption bandwidth (EAB) of 1.76 GHz. The possible electromagnetic wave absorption (EMWA) mechanism could be ascribed to the nano-laminated structure and appropriate electrical conductivity, which facilitated good impedance matching, remarkable conduction loss, and interfacial polarization, along with the reflection and scattering of electromagnetic waves at multiple interfaces. The GdB2C2, with excellent EMWA performance as well as remarkable ultra-high-temperature thermal stability, could be a promising candidate for the application of EMWA materials in extreme ultra-high temperatures.

Formation of nanocrystalline and nanolaminate structures in a twinning induced plasticity Ti-12Mo alloy: The role played by {332} 〈113〉 twinning

Grain refinement is an effective strategy to strengthen metastable β titanium alloys. {332}<113> twinning, a typical deformation mode, its role on grain refinement still remains unelucidated. Here, we produced a gradient nanostructured layer with a depth of 800 μm in a metastable twinning induced plasticity β-Ti-12Mo (wt.%) alloy by means of surface mechanical rolling treatment. We found that {332}<113> deformation twinning, mainly dominated the deformation at moderate strain and strain rates, refining coarse grains into submicro-structures. With increasing strain and strain rates, dislocation slip instead of {332}<113> twinning prevailed. These dislocations were first arranged into extended boundaries and then into laminated structures to coordinate deformation. Eventually, shear banding and fragmentation of laminates result in the formation of nanocrystalline with size of 34 ± 8 nm. The nanostructured Ti-12Mo alloy exhibited the high hardness of 4.9 GPa at subsurface. The surface hardness decreased to 4.4 GPa which was mainly caused by the inhibition of stress-induced martensitic transformation α″ and the occurrence of its reversal transformation due to adiabatic heating induced by the high strain rate. This work expands our knowledge on strengthening β titanium alloys by {332}<113> twinning induced grain refinement at different deformation conditions.

Reducing Off-State and Leakage Currents by Dielectric Permittivity-Graded Stacked Gate Oxides on Trigate FinFETs: A TCAD Study.

Since its invention in the 1960s, one of the most significant evolutions of metal-oxide semiconductor field effect transistors (MOSFETs) would be the 3D version that makes the semiconducting channel vertically wrapped by conformal gate electrodes, also recognized as FinFET. During recent decades, the width of fin (Wfin) and the neighboring gate oxide width (tox) in FinFETs has shrunk from about 150 nm to a few nanometers. However, both widths seem to have been leveling off in recent years, owing to the limitation of lithography precision. Here, we show that by adapting the Penn model and Maxwell-Garnett mixing formula for a dielectric constant (κ) calculation for nanolaminate structures, FinFETs with two- and three-stage κ-graded stacked combinations of gate dielectrics with SiO2, Si3N4, Al2O3, HfO2, La2O3, and TiO2 perform better against the same structures with their single-layer dielectrics counterparts. Based on this, FinFETs simulated with κ-graded gate oxides achieved an off-state drain current (IOFF) reduced down to 6.45 × 10-15 A for the Al2O3: TiO2 combination and a gate leakage current (IG) reaching down to 2.04 × 10-11 A for the Al2O3: HfO2: La2O3 combination. While our findings push the individual dielectric laminates to the sub 1 nm limit, the effects of dielectric permittivity matching and κ-grading for gate oxides remain to have the potential to shed light on the next generation of nanoelectronics for higher integration and lower power consumption opportunities.

The thermal stability and degradation mechanism of Cu/Mo nanomultilayers

ABSTRACT The microstructural evolution of Cu/Mo nanomultilayers upon annealing was investigated by X-ray diffraction and transmission electron microscopy. The isothermal annealing process in the temperature ranges of 300–850°C was conducted to understand the thermal behavior of the sample and follow the transformation into a nanocomposite. Annealing at 600°C led to the initiation of grain grooving in the investigated nanomultilayer, and it degraded into a spheroidized nanocomposite structure at 800°C. The sample kept the as-deposited Cu {111}//Mo{110} fiber texture up to 850°C. The residual stress was investigated to explain microstructure changes. The activation energy of degradation kinetics of Cu/Mo nanomultilayers was determined to understand the rate-determining mechanism for the degradation of nanolaminate structures.

Exploring the oxidation behaviors of the Ti[sbnd]V[sbnd]Cr[sbnd]Mo high-entropy MAX at 800 °C for its self-lubricity

Given the unique nanolaminate structure, the MAX phase ceramics which are composed of alternatively stacked two-dimensional (2D) metal (M) carbides (X) and main group (A) atomic layers have shown promising properties at elevated temperatures. Recently, an excellent self-lubricating performance of a high-entropy (HE) (TiVCrMo)3AlC2 MAX is demonstrated at 800 °C in the air. However, the formation mechanism of a self-lubricative tribofilm is still waiting for clarified. In this work, the HE (TiVCrMo)3AlC2 MAX is synthesized and its oxidation behaviors are systematically evaluated at 800 °C in the air. A two-stage parabolic oxidation behavior is detected, which can be mainly ascribed to the volatilization of MoO3 species coupled with the thickening of the compound oxide scale. Meanwhile, the HE composition results in chemically complex phases including Rutile and vacancy-ordered TiO species in the oxide scale, which contribute to a higher ion diffusion rate for mass transportation. Consequently, the continued volatilization of MoO3 is beneficial for the enhanced lubricity and anti-wear performance of the (TiVCrMo)3AlC2 MAX at 800 °C.

Thermally driven evolution of deformation nanotwins into nanolaminated structures with low-angle boundaries in 316L stainless steel

Although twin boundary is a kind of low-energy boundary, the interactions between dislocations and twin boundaries promote the detwinning of twin layers. In this work, we investigated the thermally driven evolution of deformation nanotwins in 316L stainless steel. After high-temperature annealing, deformation nanotwins evolve into nanolaminated structures with low-angle boundaries, which are difficult to form in materials with low stacking fault energies. We explored the roles of dislocations and twin boundaries, as well as their interaction mechanism underlying microstructural evolution.

Chromium–Aluminum Coatings for Oxidation Protection of Titanium–Aluminum Intermetallic Alloys

This article explores the utilization of cathodic-arc deposition Cr-Al overlay coatings as oxidation protection for Ti-Al-Nb intermetallic alloys. The primary objective is to investigate PVD Al-Cr coatings deposited via cathodic-arc deposition without subsequent vacuum annealing. The microstructure, phase, and chemical composition of the coatings were characterized using scanning electron microscopy, energy-dispersive X-ray spectroscopy, and X-ray diffraction analysis. Isothermal exposure of samples in a laboratory air furnace was conducted, revealing the efficacy of Cr-Al coatings in protecting the Ti49-11Al-40Nb-1.5Zr-0.75V-0.75Mo-0.2Si (mass%) intermetallic alloy VTI-4 against oxidation. The findings highlight that the as-deposited coatings possess a layered structure and contain Al-Cr intermetallics. Post-exposure to the furnace without prior vacuum annealing results in coatings exhibiting a porous microstructure, raising concerns regarding oxidation protection. This investigation of Cr-Al coatings on a VTI-4 alloy substrate yields valuable insights into their nanolaminate structure and challenges associated with aluminum droplet fractions. The proposed additional vacuum heat treatment at 650 °C for 500 h effectively homogenizes the coating, leading to predominant Cr2Al and Ti-Al phases. Additionally, the formation of diffusion layers at the “coating–substrate” interface and the presence of oxide barriers contribute to the coatings’ heat resistance. Our research introduces possibilities for tailoring coating properties for specific high-temperature applications in aerospace, energy, or industrial contexts. Further refinement of the heat treatment process offers the potential for developing advanced coatings with enhanced performance characteristics.

Processing of V2AlC MAX phase: Optimization of sintering temperature and composition

The Vanadium MAX phase (V2AlC) was synthesized by the pressureless sintering method using elemental V, Al, and C powders as starting materials. The synthesis process involves varying the aluminum molar ratios and temperature to fully realize the optimal conditions for MAX phase synthesis. Systematic variation of the aluminum molar ratio in the range of 1.2 to 1.4 reveals that an aluminum ratio of 1.2 minimizes side reactions and compensates for aluminum loss due to the compound's volatility, optimizing Vanadium MAX phase synthesis. Furthermore, this research examines the profound impact of synthesis temperature on the composition and structure of the Vanadium MAX phases. The results indicate that the ideal temperature for achieving maximum yield, phase purity, crystallinity, and the desired microstructure is 1300 °C. Scanning electron microscopy (SEM) analysis reveals the intricate nanolaminate structure of MAX phases, characterized by fluctuations in layer thickness. Notably, we observe an average particle size of 8.27 μm, with sample 1 and sample 3 exhibiting the largest and smallest sizes at 9.51 μm and 7.28 μm, respectively. The highest conductivity, reaching 7.19E-5 S/m, and the purest samples are consistently obtained at 1300 °C with an aluminum ratio of 1.2, reaffirming the optimized conditions. In summary, this research unveils the intricate chemistry of factors influencing the synthesis of Vanadium MAX phases, shedding light on their immense potential and offering new perspectives and possibilities in MAX phase synthesis.

Crystal plasticity finite element modelling and mechanical deformation mechanism of nanolaminated graphene reinforced metal matrix composites

Metal matrix composites with certain hierarchical structures are potential to break out the conflicts between strength and toughness. Nano-carbon like graphene (Gn) reinforced metal matrix composites with nanolaminated structures have been largely developed to overcome this issue. However, the plastic deformation mechanism hiding behind the nanolaminated structures is still lacking. In this study, crystal plasticity finite element simulations and composite structure modeling are combined in order to uncover the mechanical deformation behavior of nanolaminated Gn/Al composites. Different lateral Gn sizes of 180, 360 and 720 nm are considered, while the hybrid lateral Gn sizes of 180 and 720 nm are applied as well. Good consistency between experimental and numerical results indicates the reliability of performed simulations. It is found that the strengthening and hardening behaviors of Gn/Al composites are dominated by Gn rather than Al matrix. The edges of Gn serving as a major dislocation nucleation source produce localization of plastic deformation, while the interiors of Gn activate more slip systems but reduce total shear strains. The edges and interiors of Gn determine the stability of plastic deformation of Gn/Al composites; large edge vs. interior area of Gn will lead to early necking. The rule of mixture fails in predicting the peak tensile strength and tensile strain of Gn/Al composites with hybrid lateral Gn sizes, because the microscopic plastic deformation can largely localize around 180 nm Gn in these hybrid Gn/Al composites. This work is enlightening to design and develop novel smart metal matrix composites.

Development of multilayer PVA-MMT and PVA-CS film structures by spin coating-assisted layer-by-layer technique: Effect of PVA, CS and MMT nanoclay orientation on oxygen barrier properties

The orientation of biopolymer macromolecules and nanoclay, specifically Montmorillonite (MMT) nanoplatelets, plays a crucial role in controlling the properties of multi-layer film structures. Understanding the impact of macromolecule and nanoclay platelets’ orientation on barrier properties of packaging films is essential. To investigate the influence of hydrogen bonding in multilayer films structures, two polymers, namely polyvinyl alcohol (PVA) and chitosan (CS), were selected and laminated nanocomposite films were fabricated using the spin coating-assisted layer-by-layer (Spin-LbL) assembly technique. This technique facilitates the production of highly oriented nanocomposite films, where polymer chains and nanoclay particles align parallel to the film surface. Multi-directional 2-D wide-angle X-ray diffraction (2D-WADX) was successfully used to accurately assess the orientation and distribution of MMT nanoplatelets. Additionally, the films underwent characterization using X-ray diffraction (XRD) and Fourier transform infrared spectroscopy (FTIR). The 2D-WADX analysis revealed a parallel alignment of both the PVA chains and MMT clay nanoplatelets parallel to film surface. The XRD results confirmed the formation of intercalated nanolaminate structures, hydrogen-bonding interactions, and adjustments in the crystalline structure of PVA matrix. Through contact angle and oxygen permeability measurements, we observed that all quadri-layer film structures exhibited hydrophobic properties and reduced oxygen permeability compared to neat PVA films. Furthermore, the integration of MMT nanoclay, even at low concentrations, contributed to the development of nanocomposite films with improved oxygen barrier properties. Consequently, the quadri-layer films demonstrate great potential for food packaging applications.

Strong Magneto-Optical Kerr Effects in Ni-Doped ZnO Nanolaminate Structures Obtained by Atomic Layer Deposition.

The magneto-optical (MO) Kerr effects for ZnO and ZnO:Ni-doped nanolaminate structures prepared using atomic layer deposition (ALD) have been investigated. The chemical composition and corresponding structural and morphological properties were studied using XRD and XPS and compared for both nanostructures. The 2D array gradient maps of microscale variations of the Kerr angle polarization rotation were acquired by means of MO Kerr microscopy. The obtained data revealed complex behavior and broad statistical dispersion and showed distinct qualitative and quantitative differences between the undoped ZnO and ZnO:Ni-doped nanolaminates. The detected magneto-optical response is extensively inhomogeneous in ZnO:Ni films, and a giant Kerr polarization rotation angle reaching up to ~2° was established. This marks the prospects for further development of magneto-optical effects in ALD ZnO modified by transition metal oxide nanostructures.

One-dimensional core-sheath Sn/SnOx derived from MAX phase for microwave absorption

One-dimensional (1D) metals are highly conductive and tend to form networks that facilitate electron hopping and migration. Hence, they have tremendous potential as microwave-absorbing (MA) materials. Traditionally, 1D metals are mainly precious metals such as gold, silver, nickel, and their preparation methods often have low yield and are not environmentally friendly, which has limited the exploration in this area. Herein, the unique nanolaminate structure and chemical bond characteristics of Ti2SnC MAX phase is successfully taken advantages for large-scale preparation of Sn whiskers, and then, core-sheath Sn/SnOx heterojunctions are obtained by simply annealing at different temperatures. The heterojunction annealed at 500 °C possesses favorable MA performance with an effective absorption bandwidth of 5.3 GHz (only 1.7 mm) and a minimum reflection loss value of −51.97 dB; its maximum radar cross section (RCS) reduction value is 29.59 dB·m2, confirming its excellent electromagnetic wave attenuation ability. Off-axis electron holography is used to visually characterize the distribution of charge density at the cylindrical heterogenous interface, confirming the enhanced interfacial polarization effect. Given the diversity of MAX phases and the advantages of the fabrication method (e.g., green, inexpensive, and easily scalable), this work provides significant guidance for the design of 1D metal-based absorbers.

Effects of uniaxial stress and temperature on the interfacial tensile strength and stability of Al/NiO nanolaminates: A first-principles study

Nanoenergetic multilayer films have been widely prepared due to their unique advantages in realizing “nanoenergetics-on-a-chip”. Recently, the potential for adjusting the performance of nanothermites without altering their film thickness has attracted much attention, prompting researchers to concentrate on film stress. Here, we employed first-principles tensile tests and ab initio molecular dynamics simulations to investigate the tensile properties, fracture mechanisms, and film stability of two Al/NiO interfaces under pre-stress. An analysis of electron localization function and bond overlap population shows that the weakest locations of the (100)-Top and (111)-Top interface systems are distinctly different, leading to two different fracture mechanisms. When the pre-stress and temperature are coupled, the reactivity of Al/NiO as an energetic material is enhanced. Particularly for (111)-Top, the amorphous, mixed region between the two phases replaces the original coherent interface. With the increase of the pre-stress, the crack evolves ahead of the critical strain, indicating that the coupling effects of the pre-stress and temperature have an important influence on the stability and fracture strength. This work not only reveals the mechanical properties of Al/NiO, but also provides a theoretical guidance for optimizing the structure of energetic nanolaminates.

Unique nanostructures and deformation mechanisms in a high-entropy alloy nanolaminates

Introducing nanolaminates structure is a promising strategy to obtain the controllable microstructure and mechanical properties of high entropy alloy (HEA). In this work, the Al0.5CoCrFeNi/CoCrCuFeNi nanolaminates with coherent interface and crystalline/amorphous hierarchical nanostructure was designed. On the one hand, the coherent interface with continuous slip direction and planes enables nanolaminates with great deformability. On the other hand, the hierarchical nanostructure in the nanolaminates contributes to high strength via the interaction between crystalline and amorphous structures. Microstructural observations indicated that abundant nanotwins and stack faults were filled in the columnar nanocrystalline cutting across the interface, leading to a high hardness due to the dislocation-interface interactions. The results of nanoindentation tests revealed that the hardness of the nanolaminates up to 8.02 GPa, which markedly exceeds many HEA films with face-centered cubic (FCC) phase. The findings provide a new avenue for improving the mechanical properties of HEA nanolaminates in a controllable manner.

From Nano-Alloy to Nano-Laminated Interfaces for Highly Stable Alkali Metal Anodes.

Metal anodes are considered as the holy grail for the next generation batteries because of their high gravimetric and volumetric specific capacity and low electrochemical potential. However, several unsolved challenges have impeded their practical applications, such as dendrite growth, interface side reaction, dead layer formation and volume change. An electrochemically, chemically, and mechanically stable artificial solid electrolyte interphase (SEI) is key to addressing the aforementioned issue with metal anodes. This study demonstrates a new concept of organic and inorganic hybrid interfaces for both Li and Na metal anodes. Through tailoring the compositions of the hybrid interfaces, we realize the nano-alloy structure to the nano-laminated structure. As a result, the nano-alloy interface (1Al2 O3 -1alucone or 2Al2 O3 -2alucone) presents the most stable electrochemical performances for both Li and Na metal anodes. The optimized thicknesses required for the nano-alloy interfaces for Li and Na metal anodes are different. A cohesive zone model was applied to interpret the underlying mechanism. Furthermore, the influence of the mechanical stabilities of the different interfaces on the electrochemical performances has been investigated experimentally and theoretically. Our approach provides a fundamental understanding and establishes the bridge between mechanical properties and electrochemical performance for alkali metal anodes. This article is protected by copyright. All rights reserved.

Investigating non-isothermal oxidation kinetics of a non-stoichiometrically synthesized Ti3AlC2 MAX phase

Synthesis protocol plays a crucial role in the large-scale production of Ti3AlC2 MAX phases and its derivative MXenes. A non-stoichiometric pressure-less sintering approach is proposed to obtain a highly pure Ti3AlC2 MAX phase at 1500 ºC. The variation in aluminum content plays a vital role during the synthesis of Ti3AlC2. The impurity phase (TiC) was minimal when the non-stoichiometric ratio was Ti:TiC:Al = 1:0.75:1.3. Microstructure analysis confirmed the typical nano-laminated structure of the MAX phase. Non-isothermal oxidation stability of Ti3AlC2 was also examined through TGA/DTA technique. Deconvolution kinetic analysis was performed to distinguish three peaks corresponding to the reactions responsible for the oxidation of the MAX phase. The kinetic triplets were estimated by following iso-conversional kinetic methods. Kissinger-Akahira-Sunose (KAS) and Freidman (FR) iso-conversional methods were used to calculate activation energy for oxidation peak I (KAS: 107.25 kJ/mol, FR: 104.80 kJ/mol), II (KAS: 140.61 kJ/mol, FR: 178.24 kJ/mol) and III (KAS: 173.72 kJ/mol, FR: 217.63 kJ/mol). The integral master plot method revealed that F1 reaction mechanism dominated oxidation peaks I and III; for oxidation peal II, A2 reaction mechanism was responsible.