Perfect Crystal Lattice Research Articles

High temperature induced abundant closed nanopores for hard carbon as high-performance sodium-ion batteries anodes

Hard carbon (HC) stands out as the preeminent anode material for sodium-ion batteries (SIBs) which are deployed in expansive energy storage infrastructures. Herein, the large enough graphene nanosheets interlayer and abundant nanopores with a diameter of ∼2.1 nm induced by adjusting the pyrolysis temperature in the thermosetting phenolic resin-derived hard carbon matrix to augment the performance of the sodium ion storage. The presence of sufficiently large carbon interlayers has been proven to provide active sites for reversible adsorption, enabling effective storage of sodium ions in the high-voltage slope region, while also promoting rapid Na+ transport. Meanwhile, forming abundant closed nanopores with larger sizes helps sodium ion storage in the low-voltage plateau region. In the optimized samples, the formation of sufficient long graphene nanosheets with a perfect crystal lattice, which further shrinks to form enclosed nanopores, effectively reduces defective sites and specific surface area. Additionally, the appropriate content of C-O and C=O functional groups contributes to an exceptional initial Coulombic efficiency (ICE) of up to 93%. Simultaneously, the optimized sample HC-1500 contributes to a remarkable plateau capacity of 294 mAh g-1 during the charging process (high reversible capacity of 403 mAh g-1 at 0.1 C). Moreover, based on the microstructure evolution and Na storage behavior of hard carbon, an “adsorption (27%) – filling (73%)” sodium storage mechanism that the sodium storage as a quasi-metallic sodium state is demonstrated. Consequently, this study will offer valuable insights for the development of hard carbon anodes tailored for high-energy practical SIBs, while also advancing the understanding of sodium storage mechanisms.

Crystallographic anisotropy-dependent mechanochemical removal of GaAs: Nanoasperity experiments and atomistic simulations

In this paper, the nanoasperity wear tests on GaAs surfaces with different crystallographic orientations against SiO2 microsphere were performed using AFM. The removal behavior characterized by in-situ AFM imaging significantly relies on crystallographic anisotropy (111 > 110 > 100). The atomic structure of worn area characterized by HRTEM shows perfect crystal lattice, demonstrating the dominate role of the interfacial mechanochemical reactions during the material removal of GaAs. DFT calculations were conducted and the results reveal that the charge re-distribution behavior at the SiO2/GaAs interface governs the mechanochemical reactions, essentially leading to the crystallographic anisotropy dependence. This study not only enriches the mechanochemical reaction mechanism, but also benefits for the CMP optimization for GaAs.

Comparison between synthetic and natural clinoptilolites for adsorptive removal of metal ions

The present work evaluated the removal performances of Ni2+, Cd2+, Sr2+, Mn2+, and Fe3+ from an aqueous solution using a comparison between synthetic clinoptilolite (SCP) and natural CP (NCP). Unlike previous demonstrations that treated each metal ion individually, these five metal ions and the used adsorbents were combined in a single treatment and explored via various characterizations, such as XRD patterns, SEM images, N2 sorption isotherms, ICP, and AAS analysis. The results revealed that the capacities of SCP at pH 3.0–8.0 and 25–75 °C were nearly 20 times higher than those of NCP, showing 2000, 1720, 1875, 1510, and 22 mg g−1, for Ni2+, Fe3+, Cd2+, Mn2+, and Sr2, respectively. The reason is mostly attributed to its purity and perfect crystal lattice. The kinetic behaviors in both cases indicated that the pseudo-2nd-order model provided a better description. Their adsorption behaviors exhibited a better fit with the Freundlich models on the removal of Ni2+, Cd2+, and Mn2+, the Langmuir equation on the removal of Fe3+, and both Freundlich and Langmuir on the removal of Sr2+, respectively. The thermodynamic findings indicated that the SCP was used to be faster, more spontaneous, and had a better favorable adsorption performance than the NCP. Additionally, five times recyclability and different stability tests further supported the dominant adsorbent nature of using SCP as an adsorbent.

Score-based denoising for atomic structure identification

We propose an effective method for removing thermal vibrations that complicate the task of analyzing complex dynamics in atomistic simulation of condensed matter. Our method iteratively subtracts thermal noises or perturbations in atomic positions using a denoising score function trained on synthetically noised but otherwise perfect crystal lattices. The resulting denoised structures clearly reveal underlying crystal order while retaining disorder associated with crystal defects. Purely geometric, agnostic to interatomic potentials, and trained without inputs from explicit simulations, our denoiser can be applied to simulation data generated from vastly different interatomic interactions. The denoiser is shown to improve existing classification methods, such as common neighbor analysis and polyhedral template matching, reaching perfect classification accuracy on a recent benchmark dataset of thermally perturbed structures up to the melting point. Demonstrated here in a wide variety of atomistic simulation contexts, the denoiser is general, robust, and readily extendable to delineate order from disorder in structurally and chemically complex materials.

Acetic Acid‐Assisted Synergistic Modulation of Crystallization Kinetics and Inhibition of Sn2+ Oxidation in Tin‐Based Perovskite Solar Cells

AbstractTin‐based halide perovskites attract incremental attention due to the favorable optoelectronic properties and ideal bandgaps. However, the poor crystalline quality is still the biggest challenge for further progress in tin‐based perovskite solar cells (PVSCs) due to the unfavorable defects and uncontrollable crystallization kinetics. Here, acetic acid (HAc) is first introduced to reduce the supersaturated concentration of the precursor solution to preferentially form pre‐nucleation clusters, thus inducing rapid nucleation for effective regulation of crystallization kinetics. In particular, the hydrogen ion and acetate ion contained in HAc can effectively inhibit the oxidation of Sn2+, and the hydrogen bonding interaction between HAc and iodide ion (I‐) greatly reduces the loss of I‐, which guarantees the I‐/Sn2+ stoichiometric ratio of the corresponding perovskite film close to theoretical value, thus effectively reducing the defect density and maintaining the perfect crystal lattice. Consequently, the HAc‐assisted tin‐based PVSCs achieve a champion power conversion efficiency of 12.26% with superior open‐circuit voltage up to 0.75 V. Moreover, the unencapsulated device maintains nearly 90% of the initial PCE even after 3000 h storage in nitrogen atmosphere. This demonstrated strategy enables to prepare high‐quality tin‐based perovskite film with lower defect density and lattice distortion.

Puzzling Low-Temperature Behavior of the Van Der Waals Friction Force between Metallic Plates in Relative Motion

This paper presents the results of calculating the van der Waals friction force (dissipative fluctuation-electromagnetic force) between metallic (Au) plates in relative motion at temperatures close to 1 K. The stopping tangential force arises between moving plates along with the usual Casimir force of attraction, which has been routinely measured with high precision over the past two decades. At room temperatures, the former force is 10 orders of magnitude less than the latter, but at temperatures T<50 K, friction increases sharply. The calculations have been carried out in the framework of the Levin-Polevoi-Rytov fluctuation electromagnetic theory. For metallic plates with perfect crystal lattices and without defects, van der Waals friction force is shown to increase with decreasing temperature as T−4. In the presence of residual resistance ρ0 of the metal, a plateau is formed on the temperature dependence of the friction force at T→0 with a height proportional to ρ0−0.8. Another important finding is the weak force-distance dependence ~a−q (with q<1). The absolute values of the friction forces are achievable for measurements in AFM-based experiments.

Wave Packet Dynamical Simulation of Quasiparticle Interferences in 2D Materials

Materials consisting of single- or a few atomic layers have extraordinary physical properties, which are influenced by the structural defects. We present two calculation methods based on wave packet (WP) dynamics, where we compute the scattering of quasiparticle WPs on localized defects. The methods are tested on a graphene sheet: (1) We describe the perfect crystal lattice and the electronic structure by a local atomic pseudopotential, then calculate the Bloch eigenstates and build a localized WP from these states. The defect is represented by a local potential, then we compute the scattering by the time development of the WP. (2) We describe the perfect crystal entirely by the kinetic energy operator, then we calculate the scattering on the local defect described by the potential energy operator. The kinetic energy operator is derived from the dispersion relation, which can be obtained from any electronic structure calculation. We also verify the method by calculating Fourier transform images and comparing them with experimental FFT-LDOS images from STM measurements. These calculation methods make it possible to study the quasiparticle interferences, inter- and intra-valley scattering, anisotropic scattering, etc., caused by defect sites for any 2D material.

Casimir entropy and nonlocal response functions to the off-shell quantum fluctuations

The nonlocal response functions to quantum fluctuations are used to find asymptotic expressions for the Casimir free energy and entropy at an arbitrarily low temperature in the configuration of two parallel metallic plates. It is shown that by introducing an alternative nonlocal response to the off-the-mass-shell fluctuations the Lifshitz theory is brought into agreement with the requirements of thermodynamics. According to our results, the Casimir entropy calculated using the nonlocal response functions, which take into account dissipation of conduction electrons, remains positive and monotonously goes to zero with vanishing temperature, i.e., satisfies the Nernst heat theorem. This is true for both plates with perfect crystal lattices and for lattices with defects of structure. The obtained results are discussed in the context of the Casimir puzzle.

Casimir Puzzle and Casimir Conundrum: Discovery and Search for Resolution

This paper provides a review of the complicated problems in Lifshitz theory describing the Casimir force between real material plates composed of metals and dielectrics, including different approaches to their resolution. For both metallic plates with perfect crystal lattices and any dielectric plates, we show that the Casimir entropy calculated in the framework of Lifshitz theory violates the Nernst heat theorem when the well-approved dielectric functions are used in computations. The respective theoretical Casimir forces are excluded by the measurement data of numerous precision experiments. In the literature, this situation has been called the Casimir puzzle and the Casimir conundrum for the cases of metallic and dielectric plates, respectively. This review presents a summary of both the main theoretical and experimental findings on this subject. Next, a discussion is provided of the main approaches proposed in the literature to bring the Lifshitz theory into agreement with the measurement data and with the laws of thermodynamics. Special attention is paid to the recently suggested spatially nonlocal Drude-like response functions, which consider the relaxation properties of conduction electrons, as does the standard Drude model, but lead to the theoretical results being in agreement with both thermodynamics and the measurement data through the alternative response to quantum fluctuations of the mass shell. Further advances and trends in this field of research are discussed.

Constructing defect-related subband in silver indium sulfide QDs via pH-dependent oriented aggregation for boosting photocatalytic hydrogen evolution

Surface engineering of quantum dots (QDs) plays critical roles in tailoring carriers’ dynamics of I-III-VI QDs via the interplay of QDs in aggregates or assembly, thus influencing their photocatalytic activities. In this work, an aqueous synthesis and the followed pH tuned oriented assembly method are developed to prepare network-like aggregates, dispersion, or sheet-like assembly of GSH-capped Silver Indium Sulfide (AIS). FTIR, DLS, and HRTEM investigation revealed that surface protonation or deprotonation of QDs occurred at pH < 6 or pH > 12 favors the formation of network-like aggregates with various defects or sheet-like assembly with perfect crystal lattice, respectively, via the surface charge induced interaction among AIS QDs. Further UV–vis, steady and transient PL investigation confirm the narrowed band gaps and the prolonged PL lifetime of the acidic network-like aggregates. As a result, the optimized network-like aggregates (3.0-AIS) exhibits superior photocatalytic H2 evolution (PHE) rates (5.2 mmol·g−1·h−1), about 113 times that of alkaline sheet-like assembly (13.0-AIS) or 2.7 times higher than that of dispersed AIS QDs (AIS-8.0). The formation of defects and their roles in PHE mechanisms are discussed. This work is expected to give some new insight for designing efficient non-cadmium/non-novel metal I-III-VI photocatalysts for boosting PHE.

Study on the competitive growth mechanism of SiC polytypes using Kinetic Monte Carlo method

The competitive growth process of the 4H and 6H polytypes of SiC is studied by a competitive Kinetic Monte Carlo model(KMC), which takes the atoms of silicon and carbon as the elementary kinetic particle to fully account for the interaction energy between atoms. In the competitive KMC model, the crystal lattices of two polytypes are represented by a structured mesh which fixed the site positions at the perfect crystal lattice positions. Kinetic events with competitive growth, such as deposition, diffusion are considered in physical criterion in the model. Moreover, the model not only considers the interaction energy between the same kind of atoms (Si-Si), but also considers the interaction energy between different types of atoms (Si-C). Based on the KMC model, the effects of growth conditions on the competitive growth of 4H- and 6H- SiC were studied. The competitive KMC simulation results show that the higher temperature and the larger proportion of Si source in the mixture will promote the preferential growth of 6H polytype during competitive growth. Meanwhile, with the increase of temperature and Si/C ratio, the phenomenon of atom aggregation growth on crystal surface becomes more and more obvious.

Well-ordered spherical LiNi0.8Co0.1Mn0.1O2 cathode material for lithium-ion batteries

Abstract

Determination of the accuracy and reliability of molecular dynamics simulations in estimating the melting point of iron: Roles of interaction potentials and initial system configurations

Molecular dynamics (MD) simulations were carried out to investigate the melting transition of iron with an aim to determine the accuracy and reliability of simulated melting points (MP), computing efficiency, and the role played by initial configurations. Two simulation techniques with equilibrium and non-equilibrium heating, and two well-known potentials: Mendelev (EAM) and Etesami (MEAM) were used to investigate a variety of initial configurations containing perfect crystal solid lattice and solid-liquid (S-L) coexistence regions with a number of S-L interfaces and relative S-L proportions (PC, SLSS-2, SLSS-4, SLSS-2 (20%L) and SLSS-2(80%L)). The simulated magnitude of MPs using the non-equilibrium heating method was found to be ~2020 K, which is about 200 K higher than experimental MP of iron (1811 K). Similar values were obtained for both potentials, PC and SLSS-2 configurations; there was a strong evidence for hysteresis effects as well. Simulations with equilibrium heating technique showed that MPs were found to be identical for the wide range of S-L configurations investigated: Mendelev potential (1769 ± 1 K) and Etesami potential (1811 ± 1 K). Corresponding results from the purely solid PC configurations were found to be much higher (1981 ± 1 K and 1951 ± 1 K respectively). Results on other system properties including pair distribution functions, density, local melting and solidification are also reported. These studies have helped identify optimal simulation parameters, potentials and computational approaches to probe the melting region of iron towards applications to problems of industrial importance.

Green synthesis derived Pt-nanoparticles using Xanthium strumarium leaf extract and their biological studies

A bio-synthetic green route to the synthesis of Platinum nanoparticles (PtNPs) with extract of Xanthium strumarium Leaf is described. The synthetic procedure is very simple and one step without using of capping and reducing agent. The synthesized nanoparticles were extensively characterized by UV Visible spectroscopy, FT-IR, PXRD, SEM-EDAX and TEM analysis. The size, shape and purity were well analyzed. TEM analysis showed the formation of nanoparticles in the average size of 22 nm and parallal lines are present in the partilces which should be from perfect crystal lattice. SEM analysis clearly showed the formed nanoparticles are in the cubic to rectangular shape and smooth surface. The nanoparticles also showed potent cytotoxic effect against HeLa cancer cell lines with an IC50 value of 90 μg/ml/24 h by the MTT assay and other biological profile such as In vitro antibacterial activity and In vitro antifungal activity were also investigated and shows the significance activity.

Influence of residual plastic strain on the thermoelastic behavior of a titanium alloy

The thermoelastic effect that manifests as a change in temperature of a body undergoing adiabatic elastic deformation has been utilized for full-field stress analysis in solids using the infrared thermal imaging technique. This technique has been used for nondestructive evaluation of residual stresses in components. The present study endeavors to examine the effect of residual plastic strain, due to a previously imposed plastic deformation, on the thermoelastic behavior of solids. Near-α titanium alloy specimens have been plastically deformed, and after reaching a plastic strain level, the test has been interrupted. The thermoelastic response of the interrupted specimens has been examined. The infrared thermal imaging technique has been used to capture the spatiotemporal evolution of the surface temperature of the specimens. It has been observed that the thermoelastic coefficient of the alloy increases as a function of prior/residual plastic strain for small deformations. It has been shown that the theoretical framework used to explain the effect of residual stress on the thermoelastic coefficient assuming a perfect crystal lattice is not applicable to explain the effect of residual plastic strain on the thermoelastic coefficient. A modification of the existing theory has been proposed to explain the dependence of the thermoelastic coefficient on the residual plastic strain. A thermodynamic framework considering the local entropy and internal energy density has been developed to study the behavior. The microscopic aspects of the energetic of thermoelasticity have been discussed and based on this a continuum dislocation dynamic model has been proposed to explain the variation in the thermoelastic coefficient.

Lift-Off Mechanism of GaN Thin Films with Buried Nanocavities Investigated by SEM and TEM

A process to slice and separate GaN layers with buried nanocavities was presented via an annealing process of nanoporous GaN (0002) thin films at 1050°C in an NH3 ambient. We were able to separate and lift off GaN layers over a macroscopic area ( $$ \ge $$ cm2). The several growth stages of buried nanocavities were examined by scanning/transmission emission microscopy techniques. During the early stage of annealing, the annealing leads to variations in morphology from nanopores with rough sidewalls to columnar or hexagonal nanopores with smooth sidewalls. At the same time, amorphous gallium oxide and single crystal GaN with high dislocation density, which are formed by electrochemical etching, are converted into GaN with a perfect crystal lattice. Subsequently, the columnar or hexagonal nanopores are sealed, cut, and then spheroidized. Above a sufficiently high porosity (> 50%), the nanocavities will overlap one another and coalesce, allowing a stand-alone GaN thin film to be lifted off the original substrate.

Nondestructive nanofabrication on monocrystalline silicon via site-controlled formation and removal of oxide mask

A nondestructively patterned silicon substrate serves as an ideal support for forming high-quality optical structures or devices. A new approach was proposed for fabricating site-controlled structures without destruction on a monocrystalline silicon surface via local anodic oxidation (LAO) and two-step postetching. The nondestruction was demonstrated by conductivity detection with conductive atomic force microscopy (AFM), and an almost perfect crystal lattice was observed from the fabricated hillock by high-resolution transmission electron microscopy (HRTEM). By programming AFM tip traces for LAO processing, site-controlled nondestructive patterns with different layouts can be produced. This approach provides a new route for realizing nondestructive optical substrates.

Application of PDF analysis assisted by MD simulations for determination of the atomic structure and crystal habit of CdSe nanocrystals

A new methodology of performing structural analysis of nanocrystals based on wide angle powder diffraction is proposed. It combines molecular dynamics simulations with the analysis of pair distribution function. The actual analysis was performed on CdSe quantum dots. MD simulations of nanocrystals with shapes defined by low-index atomic planes, (1 0 0), (1 1 0), and (1 1 1) introduced bulk and surface relaxation in initially perfect crystal lattice. In search for the best atomistic model of the actual CdSe nanocrystals, experimental structure functions S(Q) and interatomic distance functions G(r) were matched to those calculated with MD models. Eventually it was concluded that CdSe nanocrystals with dimensions of 2.5–3.5 nm assume the shape of octahedrons terminated by (1 1 1) surfaces.

Influence of SiC surface defects on materials removal in atmospheric pressure plasma polishing

To study the influence of SiC surface defects on atmospheric pressure plasma polishing (APPP) process, quantum chemistry simulation and analysis is used to reveal the reaction features of typical defect topographies. Three groups of typical structures are modeled, including edge dislocation, screw dislocation and perfect crystal lattice. By using quantum chemistry calculation software, it is demonstrated that the existence of surface defects improves probability for chemical etching. The densities of states (DOS) and number of bonding electrons indicate that the defect structures have poor stability compared with perfect crystal lattice, which means defects are favorable for increasing the removal rate. The calculation results on activation energy also verify the conclusion further. Experimental machining and measurement have been performed to prove the theoretical analysis. Tests are made on selected single crystal SiC samples with different defect densities. Removal profiles measured by white light interferometer indicate that surface defects are helpful for raising the machining efficiency. But, measured surface topographies show that within certain range, surface defects deteriorate the surface roughness during the polishing process. Until most surface damage is removed, the surface roughness will be improved effectively which makes the interface smoother. Thus, the experimental investigation accords well with theoretical analysis.

The structure and composition of olivine grain boundaries: 40 years of studies, status and current developments

Interfaces in rocks, especially grain boundaries in olivine dominated rocks, have been subject to about 40 years of studies. The grain boundary structure to property relation is fundamental to understand the diverging properties of polycrystalline samples compared to those of single crystals. The number of direct structural observations is small, i.e. in range of 100 micrographs, and the number of measurements of properties directly linked to structural observations is even smaller. Bulk aggregate properties, such as seismic attenuation, rheology and electrical conductivity, are sensitive to grain size, and seem to show influences by grain boundary character distributions. In this context we review previous studies on grain boundary structure and composition and plausible relations to bulk properties. The grain boundary geometry is described using five independent parameters; generally, their structural width ranges between 0.4–1.2 nm and the commonly used 1 nm seems a good approximation. This region of enhanced disorder is often enriched in elements that are incompatible in the perfect crystal lattice. The chemical composition of grain boundaries depends on the bulk rock composition. We determined the 5 parameter grain boundary character distribution (GBCD) for polycrystaline Fo $$_{90}$$ and studied structure and chemistry at the nm-scale to extend previous measurements. We find that grain boundary planes close to perpendicular to the crystallographic c-direction dominate the grain boundary network. We conclude that linking grain boundary structure in its full geometric parameter space to variations of bulk rock properties is now possible by GBCD determination using EBSD mapping and statistical analyses.