Giant spin-orbit splitting of point defect states in monolayer WS2_2

The spin-orbit coupling (SOC) effect has been known to be profound in monolayer pristine transition metal dichalcogenides (TMDs). Here we show that point defects, which are omnipresent in the TMD membranes, exhibit even stronger SOC effects and change the physics of the host materials drastically. In this Article we chose the representative monolayer WS\sub{2} slabs from the TMD family together with seven typical types of point defects including monovacancies, interstitials, and antisites. We calculated the formation energies of these defects, and studied the effect of spin-orbit coupling (SOC) on the corresponding defect states. We found that the S monovacancy (V\sub{S} ) and S interstitial (adatom) have the lowest formation energies. In the case of V\sub{S} and both of the W\sub{S and W\sub{S2} antisites, the defect states exhibit giant splitting up to 296 meV when SOC is considered. Depending on the relative position of the defect state with respect to the conduction band minimum (CBM), the hybrid functional HSE will either increase the splitting by up to 60 meV (far from CBM), or decrease the splitting by up to 57 meV (close to CBM). Furthermore, we found that both the W\sub{S} and W\sub{S2} antisites possess a magnetic moment of 2 $\mu_{B}$ localized at the antisite W atom and the neighboring W atoms. All these findings provide new insights in the defect behavior under SOC point to new possibilities for spintronics applications for TMDs.Comment: 8 pages, 6 figure

Исследование устойчивости функционирования региональных природно-промышленных систем и принятие оптимальных управленческих решений

Предложена математическая модель, описывающая поведение горного массива при воздействии на него массовых сил. Найдены условия параметров задачи, при которых возможны геотектонические нарушения. Предложена методика исследований, заключающаяся в системном подходе решения вопроса, который состоит в выделении рассматриваемой системы, определении составляющих ее компонентов, определение связей между ними. Определяющим моментом методики исследования является наличие базы данных по факторам влияния. Рассматривается математическая модель, позволяющая описать слоистую структуру горного массива с учетом наличия геологических нарушений и техногенных воздействий. Исследование ее устойчивости базируется на анализе энергетического баланса внешнего и внутреннего потенциалов, комплексно воздействующих на горный массив, на котором расположен рассматриваемый регион. Выведены критерии (на основании дисбаланса потенциалов), позволяющие делать пространственно-временной прогноз возможных чрезвычайных горно-геологических процессов. Достоверность критериев устойчивости усиливается коэффициентом системности, который может рассчитываться как для всей природно-промышленной системы, так и для отдельных ее компонентов.Запропоновано математичну модель, яка описує поведінку гірничого масиву під час впливу на нього масових сил. Знайдено умови параметрів задачі, за яких можливі геотектонічні порушення. Пропонується методика досліджень, яка полягає у системному підході вирішення питання, яке складається у виділенні розглянутої системи, визначенні складових її компонентів, зв’язків між ними. Визначним моментом методики досліджень є наявність бази даних по факторам впливу. Розглядається математична модель, яка дозволяє описати шарову структуру гірничого масиву з обліком наявності геологічних порушень і ехногенних впливів. Дослідження її стійкості базується на аналізі енергетичного балансу зовнішнього і внутрішнього потенціалів, які комплексно впливають на гірничий масив, на якому розташовано регіон, що розглядається. Виведено критерії (на основі дисбалансу потенціалів), які дозволяють робити просторо-часовий прогноз можливих надзвичайних гірничо-геологічних процесів. Достовірність критеріїв стійкості посилюється коефіцієнтом системності, який може розраховуватись як для всієї природно-промислової системи, так і для окремих її компонентів.A mathematical model, which describes the behavior of the rock mass during it is affected by mass forces, is proposed. Conditions are found for the parameters of the problem, where geotectonic violation is possible. A method of study, which consists in systematic approach to problem solution (separate the system, determination of its components, the definition of relationships between components) is proposed. The key defining of research methods is the availability of a database on the factors of influence. A mathematical model that allows to describe the layered structure of the rock mass based on the availability of geological faults and technogenic impacts, is considered. Research of its stability is based on the analysis of the energy balance of internal and external potentials, the complex influence of the mountain range, which is located in this region. The criteria (based on the imbalance of potentials), which allow the space-time prediction of possible extreme geological processes, are derived. The reliability of stability criteria is enhanced by systemic factor that can be calculated for the entire faculty, and for the individual components

Formation Pathways of Lath-Shaped WO3 Nanosheets and Elemental W Nanoparticles from Heating of WO3 Nanocrystals Studied via In Situ TEM

WO3 is a versatile material occurring in many polymorphs, and is used in nanostructured form in many applications, including photocatalysis, gas sensing, and energy storage. We investigated the thermal evolution of cubic-phase nanocrystals with a size range of 5–25 nm by means of in situ heating in the transmission electron microscope (TEM), and found distinct pathways for the formation of either 2D WO3 nanosheets or elemental W nanoparticles, depending on the initial concentration of deposited WO3 nanoparticles. These pristine particles were stable up to 600 °C, after which coalescence and fusion of the nanocrystals were observed. Typically, the nanocrystals transformed into faceted nanocrystals of elemental body-centered-cubic W after annealing to 900 °C. However, in areas where the concentration of dropcast WO3 nanoparticles was high, at a temperature of 900 °C, considerably larger lath-shaped nanosheets (extending for hundreds of nanometers in length and up to 100 nm in width) were formed that are concluded to be in monoclinic WO3 or WO2.7 phases. These lath-shaped 2D particles, which often curled up from their sides into folded 2D nanosheets, are most likely formed from the smaller nanoparticles through a solid–vapor–solid growth mechanism. The findings of the in situ experiments were confirmed by ex situ experiments performed in a high-vacuum chamber

Epitaxial CdSe-Au Nanocrystal Heterostructures by Thermal Annealing

Abstract: The thermal evolution of a collection of heterogeneous CdSe−Au nanosystems (Au-decorated CdSe nanorods, networks, vertical assemblies) prepared by wet-chemical approaches was monitored in situ in the transmission electron microscope. In contrast to interfaces that are formed during kinetically controlled wet chemical synthesis, heating under vacuum conditions results in distinct and well-defined CdSe/Au interfaces, located at the CdSe polar surfaces. The high quality of these interfaces should make the heterostructures more suitable for use in nanoscale electronic devices

Thermal Stability and Sublimation of Two-Dimensional Co9Se8 Nanosheets for Ultrathin and Flexible Nanoelectronic Devices

An understanding of the structural and compositional stability of nanomaterials is significant from both fundamental and technological points of view. Here, we investigate the thermal stability of half-unit-cell thick two-dimensional (2D) Co9Se8 nanosheets that are exceptionally interesting because of their half-metallic ferromagnetic properties. By employing in situ heating in the transmission electron microscope (TEM), we find that the nanosheets show good structural and chemical stability without changes to the cubic crystal structure until sublimation of the nanosheets starts at temperatures between 460 and 520 °C. The real-time observations of the sublimation process show preferential removal at {110} type crystal facets. From an analysis of sublimation rates at various temperatures, we find that the sublimation occurs through noncontinuous and punctuated mass loss at lower temperatures while the sublimation is continuous and uniform at higher temperatures. Our findings provide an understanding of the nanoscale structural and compositional stability of 2D Co9Se8 nanosheets, which is of importance for their reliable application and sustained performance as ultrathin and flexible nanoelectronic devices

Morphology-Controlled Growth of Crystalline Ag-Pt-Alloyed Shells onto Au Nanotriangles and Their Plasmonic Properties

The surface plasmon resonance of noble-metal nanoparticles depends on nanoscale size, morphology, and composition, and provides great opportunities for applications in biomedicine, optoelectronics, (photo)catalysis, photovoltaics, and sensing. Here, we present the results of synthesizing ternary metallic or trimetallic nanoparticles, Au nanotriangles (Au NTs) with crystalline Ag-Pt alloyed shells, the morphology of which can be adjusted from a yolk-shell to a core-shell structure by changing the concentration of AgNO3 or the concentration of Au NT seeds, while the shell thickness can be precisely controlled by adjusting the concentration of K2PtCl4. By monitoring the growth process with UV-vis spectra and scanning transmission electron microscopy (STEM), the shells on the Au NT-Ag-Pt yolk-shell nanoparticles were found to grow via a galvanic replacement synergistic route. The plasmonic properties of the as-synthesized nanoparticles were investigated by optical absorbance measurements

Вимоги до матеріалів, що приймаються до друку в збірнику наукових праць «Сучасна українська політика. Політики і політологи про неї»

Whereas bulk zinc oxide (ZnO) exhibits the wurtzite crystal structure, nanoscale ZnO was recently synthesized in the rock salt structure by addition of Mg. Using first-principles methods, we investigated two stabilization routes for accessing rock salt ZnO. The first route is stabilization by Mg addition, which was investigated by considering ZnO-MgO mixed phases. The second route is through size effects, as surface energies become dominant for small nanocrystal sizes. We discovered that the surface energy of rock salt ZnO is surprisingly low at 0.63 J m-2, which is lower than those of wurtzite and zinc blende ZnO and lower than that of rock salt MgO. We predict that pure rock salt ZnO is stable for nanocrystals smaller than 1.6 nm, and that Mg additions can greatly extend the size range in which the rock salt phase is stable. Both mixed-phase and core-shell models were considered in the calculations. The present approach could be applied to predict the stabilization of many other nanocrystal phases in deviating crystal structures

Thermolysis-Driven Growth of Vanadium Oxide Nanostructures Revealed by In Situ Transmission Electron Microscopy: Implications for Battery Applications

Understanding the growth modes of 2D transition-metal oxides through direct observation is of vital importance to tailor these materials to desired structures. Here, we demonstrate thermolysis-driven growth of 2D V2O5 nanostructures via in situ transmission electron microscopy (TEM). Various growth stages in the formation of 2D V2O5 nanostructures through thermal decomposition of a single solid-state NH4VO3 precursor are unveiled during the in situ TEM heating. Growth of orthorhombic V2O5 2D nanosheets and 1D nanobelts is observed in real time. The associated temperature ranges in thermolysis-driven growth of V2O5 nanostructures are optimized through in situ and ex situ heating. Also, the phase transformation of V2O5 to VO2 was revealed in real time by in situ TEM heating. The in situ thermolysis results were reproduced using ex situ heating, which offers opportunities for upscaling the growth of vanadium oxide-based materials. Our findings offer effective, general, and simple pathways to produce versatile 2D V2O5 nanostructures for a range of battery applications

Описание и генерация перестановок, содержащих циклы

Запропоновано загальний підхід до генерації перестановок, що містять цикли, на основі введених конструктивних засобів опису комбінаторних множин. Формулюються та розв’язуються різні задачі генерації перестановок заданого класу. Для опису перестановок, представлених у вигляді добутку заданої кількості циклів, вводиться комбінаторна множина. Для введеної множини будуються комбінаторний вид та відповідний твірний ряд. Наводяться приклади.The paper proposes a general approach to generating permutations that contain cycles, based on constructive tools introduced to describe combinatorial sets. Different generation problems for permutations of definite class are formulated and solved. A combinatorial set is introduced to define permutations represented as the multiplication of a definite number of cycles. For this set, combinatorial species and associated generating series are constructed. Examples are given

Зміст і закономірності економічного зростання при інтенсифікації виробництва

Composite noble metal-based nanorods for which the surface plasmon resonances can be tuned by composition and geometry are highly interesting for applications in biotechnology, imaging, sensing, optoelectronics, photovoltaics, and catalysis. Here, we present an approach for the oxidative etching and subsequent metal overgrowth of gold nanorods, all taking place while the nanorods are embedded in mesoporous SiO2 shells (AuNRs@meso-SiO2). Heating of the AuNRs@meso-SiO2 in methanol with HCl resulted in reproducible oxidation of the AuNRs by dissolved O2, specifically at the rod ends, enabling precise control over the aspect ratio of the rods. The etched-AuNRs@meso-SiO2 were used as a template for the overgrowth of a second metal (Ag, Pd, and Pt), yielding bimetallic, core-shell structured nanorods. By varying the reaction rates of the metal deposition both smooth core-shell structures or gold nanorods covered with a dendritic overlayer could be made. This control over the morphology, including metal composition, and thus the plasmonic properties of the composite rods were measured experimentally and also confirmed by Finite-Difference Time-Domain (FDTD) calculations. The presented synthesis method gives great control over tuning over both plasmonic properties and the particle stability/affinity for specific applications