Atomic Scale Research Articles

Molecular dynamics simulation study of nitrogen vacancy color centers prepared by carbon ion implantation into diamond

Nitrogen vacancy (NV) color centers in diamond have useful applications in quantum sensing and fluorescent marking. They can be generated experimentally by ion implantation, femtosecond lasers, and chemical vapor deposition. However, there is a lack of studies of the yield of NV color centers at the atomic scale. In the molecular dynamics simulations described in this paper, NV color centers are prepared by ion implantation in diamond with pre-doped nitrogen and subsequent annealing. The differences between the yields of NV color centers produced by implantation of carbon (C) and nitrogen (N) ions, respectively, are investigated. It is found that C-ion implantation gives a greater yield of NV color centers and superior location accuracy. The effects of different pre-doping concentrations (400–1500 ppm) and implantation energies (1.0–3.0 keV) on the NV color center yield are analyzed, and it is shown that a pre-doping concentration of 1000 ppm with 2 keV C-ion implantation can produce a 13% yield of NV color centers after 1600 K annealing for 7.4 ns. Finally, a brief comparison of the NV color center identification methods is presented, and it is found that the error rate of an analysis utilizing the identify diamond structure + coordination analysis method is reduced by about 7% compared with conventional identification methods.

Cross-scale deciphering thermal failure process of Ni-rich layered cathode

Ni-rich LiNixCoyMn1-x-yO2 (NCM) layered oxides are low-cost high-energy density cathode materials, but plagued by its poor thermal stability incurred safety concerns. The thermal failure process of the layered cathode is accompanied by heat generation and oxygen release, which drives the battery into thermal runaway (TR). Aiming to fully understand the TR process and the structure evolution, this work applies diverse characterization techniques onto a polycrystalline Ni-rich layered cathode (LiNi0.83Mn0.05Co0.12O2 (PCN83)) to comprehensively investigate its thermal failure process at multiple scales. From macro level, we validate that it is the cathode thermal failure that drives the battery from the heat accumulation stage into TR in adiabatic conditions. From micro level, transmission electron microscopy (TEM) verifies that the thermal failure of PCN83 starts from 150 °C, which is much lower than the TR temperature measured from macro level tests. We reveal that the PCN83 cathode experiences sequential phase transitions before the TR, where the phase transition mechanism is illustrated from the atomic scale and the pore evolution process is unraveled. In situ heating TEM further reveals that thermal failure is preferentially initiated from grain boundaries and defect regions. These findings provide an in-depth understanding of the whole thermal failure process of NMC-based layered cathode materials and sheds new lights on the rational design of Ni-rich cathode materials with improved thermal safety.

The Formation and Transformation of Low-Dimensional Carbon Nanomaterials by Electron Irradiation.

Low-dimensional materials based on graphene or graphite show a large variety of phenomena when they are subjected to irradiation with energetic electrons. Since the 1990s, electron microscopy studies, where a certain irradiation dose is unavoidable, have witnessed unexpected structural transformations of graphitic nanoparticles. It is recognized that electron irradiation is not only detrimental but also bears considerable potential in the formation of new graphitic structures. With the availability of aberration-corrected electron microscopes and the discovery of techniques to produce monolayers of graphene, detailed insight into the atomic processes occurring during electron irradiation became possible. Threshold energies for atom displacements are determined and models of different types of lattice vacancies are confirmed experimentally. However, experimental evidence for the configuration of interstitial atoms in graphite or adatoms on graphene remained indirect, and the understanding of defect dynamics still depends on theoretical concepts. This article reviews irradiation phenomena in graphene- or graphite-based nanomaterials from the scale of single atoms to tens of nanometers. Observations from the 1990s can now be explained on the basis of new results. The evolution of the understanding during three decades of research is presented, and the remaining problems are pointed out.

Atomic scale mechanism of reorientation induced plasticity in titanium alloys - experimental and first principles investigation of the mobile [formula omitted] interfaces

Recent experiments identified a new type of stress induced structural transformation allowing to combine high strength, great work hardening and good ductility in multiphase Ti alloys. These properties are achieved through reorientation of the α′ martensite plates being in specific self accommodating 〈54‾1‾3〉 type II twin relation, i.e. under applied load one martensite variant reconfigure to its twinned configuration with visible motion of the {134‾1} twin boundary. This mechanism of plastic deformation was never observed before thus, its current understanding is fragmentary. In this article we present the results of experimental observations and ab initio calculations of 〈54‾1‾3〉 type II twins determining the crystallography of twin formation, structure and energy of the {134‾1} interface as well as mobility of the corresponding twinning disconnections. It was found that the investigated boundary has one of the lowest energies among known twinning modes in hexagonal Ti. Moreover, the 〈54‾1‾3〉{134‾1} disconnections have the smallest Burgers vector and step height in comparison to other active twinning systems. As a result, these disconnections are highly mobile which rationalize migration of the {134‾1} twin boundaries at straining. Furthermore, energy of the twin boundary and mobility of disconnections can be adjusted by particular alloying elements enabling the conscious development of new alloys exhibiting reorientation induced plasticity.

DFT study on Mo-stabilized passive films: Hydroxylation effects on chromium and iron oxide surfaces

Hydrous Cr2O3 and Fe2O3 surfaces without and with substitutional molybdenum were simulated by DFT modelling to investigate at the atomic scale the role of Mo in improving the corrosion resistance of passive films on stainless steels. The surface structures most energetically favoured were determined in the conditions of interest. For surfaces with a high degree of hydroxylation, the preferential location of substitutional Mo is just under the hydroxyl groups, in agreement with the experimental observations. The substitution by Mo is exothermic and Mo preferentially substitutes in Fe- than in Cr-rich zone of the inner barrier layer of passive films.

I2 and aqueous TBHP induced aerial oxidative coupling of 2-aminobenzyl alcohols and nitriles: A novel metal-free route towards quinazolines synthesis

A series of 2-phenylquinazolines were synthesized by using I2/tert-butyl hydroperoxide via oxidative coupling of 2-aminobenzyl alcohols and nitriles. Metal free approach, shorter reaction time, high atom efficiency and scale up synthesis are the salient features of the protocol. Experimental evidence followed by DFT calculations indicate that the reaction pathway of quinazoline formation proceed through radical intermediate.

All-Electrical Driving and Probing of Dressed States in a Single Spin.

The subnanometer distance between tip and sample in a scanning tunneling microscope (STM) enables the application of very large electric fields with a strength as high as ∼1 GV/m. This has allowed for efficient electrical driving of Rabi oscillations of a single spin on a surface at a moderate radiofrequency (RF) voltage on the order of tens of millivolts. Here, we demonstrate the creation of dressed states of a single electron spin localized in the STM tunnel junction by using resonant RF driving voltages. The read-out of these dressed states was achieved all electrically by a weakly coupled probe spin. Our work highlights the strength of the atomic-scale geometry inherent to the STM that facilitates the creation and control of dressed states, which are promising for the design of atomic scale quantum devices using individual spins on surfaces.

Growth of {10 [formula omitted] 1}-{10 [formula omitted] 2} double twinning in Mg-Sm-Zn alloy

This study obtains different growth states of the {101¯ 1}-{10 1¯ 2} double twin in the magnesium alloy under relatively high speed tensile strain. The double twin boundary is found to be a terrace-step structure consisting of (10 1¯ 1) and (10 1¯ 2) planes on the atomic scale. We propose a specific model of the growth of double twin nuclei mainly by analyzing the initial growth stage of double twin. This work is expected to enrich the double twinning mechanism of magnesium alloys.

Nanotechnology in Medicine: A Paradigm Shift

Nanotechnology, operating at the molecular and atomic scale, has revolutionized the field of medicine. In this paper, we delve into the multifaceted role of nanotechnology, spanning diagnostics, drug delivery, and tissue regeneration. Our discussion encompasses current applications, existing challenges, and promising prospects, all underscored by the profound potential impact on healthcare.

AI for Materials Design and Discovery Using Atomistic Scale Information [Industrial and Governmental Activities

AI for Materials Design and Discovery Using Atomistic Scale Information [Industrial and Governmental Activities

Multiscale modeling for enhanced battery health analysis: Pathways to longevity

AbstractThe issues of health assessment and lifespan prediction have always been prominent challenges in the large‐scale application of lithium‐ion batteries (LIBs). This paper reviews the multiscale modeling techniques and their applications in battery health analysis, including atomic scale computational chemistry, particle scale reaction simulations, electrode scale structural models, macroscale electrochemical models, and data‐driven models at the system level. Multiscale modeling offers a profound insight into material behavior and the aging process of batteries, thereby providing a valuable reference for both estimation and management strategies of battery state of health. To extend the battery lifespan, the utilization of artificial intelligence for material discovery and manufacturing process optimization, the implementation of end‐cloud collaborative battery management systems, and the design of a multiscale simulation integration platform are considered. A management framework aimed at extending battery life is further proposed. This framework offers a promising roadmap for addressing health analysis challenges in LIBs, ultimately leading to more reliable, efficient, and durable solutions for next‐generation batteries.

Atomic scale quantum anomalous hall effect in monolayer graphene/MnBi2Te4 heterostructure.

The two-dimensional quantum anomalous Hall (QAH) effect is direct evidence of non-trivial Berry curvature topology in condensed matter physics. Searching for QAH in 2D materials, particularly with simplified fabrication methods, poses a significant challenge in future applications. Despite numerous theoretical works proposed for the QAH effect with C = 2 in graphene, neglecting magnetism sources such as proper substrate effects lacks experimental evidence. In this work, we propose the QAH effect in graphene/MnBi2Te4 (MBT) heterostructure based on density-functional theory (DFT) calculations. The monolayer MBT introduces spin-orbital coupling, Zeeman exchange field, and Kekulé distortion as a substrate effect into graphene, resulting in QAH with C = 1 in the heterostructure. Our effective Hamiltonian further presents a rich phase diagram that has not been studied previously. Our work provides a new and practical way to explore the QAH effect in monolayer graphene and the magnetic topological phases by the flexibility of MBT family materials.

First-principles evaluation of Pd–Pt–Ag and Pd–Pt–Au ternary alloys as high performance membranes for hydrogen separation

Membrane technologies are considered as a promising candidate for high purity hydrogen separation. Ternary alloys membranes show high permeance, high purity quality and good stability for separation of hydrogen, while the relational separation mechanism at atomic scale is still unclear for the most of ternary alloys. In current work, molecular dynamics (MD) and first-principles simulation are applied to predict H2 separations performances of Pd–Pt–Au and Pd–Pt–Ag membranes from CH4, CO, N2, CO2, H2S and H2O mixed gases. The separation properties of the alloys are evaluated by permeability and selectivity of various gases, and the performance of Pd–Pt–Ag and Pd–Pt–Au three-phase membranes are compared to those of Pd–Pt alloy. Our calculations indicate that Pd–Pt–Au alloy present superior selectivities of 3.6 × 1047, 1.1 × 1028, 3.7 × 1011, 4.9 × 1018, 2.2 × 1010, 1.1 × 106 for H2/CO, H2/CO2, H2/CH4, H2/N2, H2/H2S, H2/H2O, respectively, and a permeability of 1.24 × 10−1mols−1m−2pa−1 toward separation of hydrogen from the gases mixture, which is accorded to experimental conclusions. H2 permeance of the alloys exceeds industrial production limit from 100 to 600 K, while other impurity gases do not reach the permeability limits of industrial production even at high temperatures of 600 K.

Miniaturized gas exposure devices for atom probe experiments.

To detect hydrogen in materials at the atomic scale, atom probe tomography is now regularly used. In order to avoid cumbersome cryo-preparation to suppress diffusion, often hydrogen is charged only into the finished specimen. Here, the use of hydrogen gas over electrochemical hydrogen has the advantage that the specimen is not contaminated with an electrolyte. So far, this "charging" has been done in large, expensive systems. Here, we introduce small devices that enable the exposure of atom probe specimens to hydrogen and potentially other gases, using only very small gas volumes. This enables the operation in regular laboratory environments without additional safety measures. These devices can be used to expose the specimen to hydrogen up to 10 bar/90°C. Higher temperatures may be attained with small changes. Validation of the success of charging with these setups is demonstrated through experiments employing deuterium charging of palladium atom probe tips. RESEARCH HIGHLIGHTS: Enabling the exposure of atom probe specimens to hydrogen and potentially other gases, using only very small gas volumes. Built setups can be assembled with little money and from freely available parts, making specimen charging much easier. Validation of the success of charging with these setups is demonstrated through experiments employing deuterium charging of palladium atom probe tips.

In Vitro Release from Polymeric Core/Shell Nanoparticles through the Lens of Multiscale Modeling.

The large number of studies involving nanoparticles for cancer therapy is due to their peculiar features: they protect loaded active molecules while extending circulation time and can extravasate from the blood flow to the tumor to deliver drugs directly in the target area. Mathematical modeling can provide a preliminary in silico exploration of design space to optimize an experimental activity that often relies on a trial-and-error approach. However, because of the characteristic size of these vectors (10-1000 nm), numerous phenomena of interest occur at different time and length scales, making a single modeling technique insufficient to fully characterize the system of interest. In this work we employed a multiscale modeling approach, which bridges the phenomena of interest across different scales, to study the in vitro release from polymeric core/shell nanoparticles for cancer therapy loaded with an active compound assembled as a hydrophobic ion pair. The "computational microscope" provided by molecular dynamics simulations was used to track drug molecules through the release process at an atomic scale. The outcomes suggested that the drug is mainly partitioned in the polymer and released as hydrophobic ion pair rather than a free molecule, and that the hydrophobic ion pair is preferentially partitioned in Tween 20 micelles in the release media. A model at macroscale, aimed at describing the release rate and elucidating the release mechanism, was developed according to the results from molecular simulations and validated against experimental data. The outcomes provided insights that are challenging to be obtained experimentally and which supported the development and validation of a release model at macroscale. Overall, the adopted multiscale approach corroborated the experimental findings and provided significant insights into the mechanisms of release.

Conductance Quantization in 2D Semi-Metallic Transition Metal Dichalcogenides.

Conductance quantization of 2D materials is significant for understanding the charge transport at the atomic scale, which provides a platform to manipulate the quantum states, showing promising applications for nanoelectronics and memristors. However, the conventional methods for investigating conductance quantization are only applicable to materials consisting of one element, such as metal and graphene. The experimental observation of conductance quantization in transition metal dichalcogenides (TMDCs) with complex compositions and structures remains a challenge. To address this issue, an approach is proposed to characterize the charge transport across a single atom in TMDCs by integrating in situ synthesized 1T'-WTe2 electrodes with scanning tunneling microscope break junction (STM-BJ) technique. The quantized conductance of 1T'-WTe2 is measured for the first time, and the quantum states can be modulated by stretching speed and solvent. Combined with theoretical calculations, the evolution of quantized and corresponding configurations during the break junction process is demonstrated. This work provides a facile and reliable avenue to characterize and modulate conductance quantization of 2D materials, intensively expanding the research scope of quantum effects in diverse materials.

Atomic-scale investigation of interactions between Cu solute and defects in Zr alloys

The effects of dilute Cu solute on dislocations and grain boundaries in Zr alloys have been investigated at the atomic scale by atom probe tomography measurements, molecular dynamics, and molecular statics simulations. We demonstrate that Cu can segregate at dislocations and form nanoclusters in Zr alloys to retard the dislocation motion at high-stress creep. The solid solution strengthening of Cu is stronger than Sn and Nb at the same concentration and 673 K. Moreover, Cu is inclined to segregate at grain boundaries in Zr alloys, which is expected to reduce the Coble creep rate. As such, minor Cu alloying is an effective strategy to tailor the properties of dislocations and grain boundaries for enhancing the creep performance of Zr alloys.

Determinative scrolling and folding of membranes through shrinking channels.

Flat membranes ubiquitously transform into mysterious complex shapes in nature and artificial worlds. Behind the complexity, clear determinative deformation modes have been continuously found to serve as basic application rules but remain unfulfilled. Here, we decipher two elemental deformation modes of thin membranes, spontaneous scrolling and folding as passing through shrinking channels. We validate that these two modes rule the deformation of membranes of a wide thickness range from micrometer to atomic scale. Their occurrence and the determinative fold number quantitatively correlate with the Föppl-von Kármán number and shrinkage ratio. The unveiled determinative deformation modes can guide fabricating foldable designer microrobots and delicate structures of two-dimensional sheets and provide another mechanical principle beyond genetic determinism in biological morphogens.

In Situ TEM Tracking of Disconnection Motion and Atomic Cooperative Reorientation in the Oriented Attachment of Pt Nanoparticles.

The oriented attachment (OA) of nanoparticles (NPs) is an important crystal growth mechanism in many materials. However, a comprehensive understanding of the atomic-scale alignment and attachment processes is still lacking. We conducted in situ atomic resolution studies using high-resolution transmission electron microscopy to reveal how two Pt NPs coalesce into a single particle via OA, which involves the formation of atomic-scale links and a grain boundary (GB) between the NPs, as well as GB migration. Density functional theory calculations showed that the system energy changes as a function of the number of disconnections during the coalescence process. Additionally, the formation and annihilation processes of disconnection are always accompanied by the cooperative reorientation motion of atoms. These results further elucidate the growth mechanism of OA at the atomic scale, providing microscopic insights into OA dynamics and a framework for the development of processing strategies for nanocrystalline materials.

Towards optimal control: the probabilistic route in quantum systems

There is a fundamental limit to what is knowable about atomic and molecular scale systems. This fuzziness is not always due to the act of measurement. Other contributing factors include system parameter uncertainty, functional uncertainty that originates from input functions, and sensors noises to mention a few. This indeterminism has led to major challenges in the development of accurate control methods for atomic scale systems. To address the probabilistic and uncertain nature of these systems, this work proposes a novel control framework that considers the representation of the quantum system states and the quantification of its physical properties following a probabilistic approach. Our framework is fully probabilistic. It uses the Shannon relative entropy from information theory to design optimal randomised controllers that can achieve a desired outcome of an atomic scale system. Two experiments are carried out to illustrate the applicability and effectiveness of the proposed approach.