Search

Lead based bulk piezoelectric materials, e.g., PbZrxTi1‐xO3 (PZT), are widely used in electromechanical applications, sensors, and transducers, for which optimally performing thin films are needed. The results of a multi‐domain Landau–Ginzberg‐Devonshire model applicable to clamped ferroelectric thin films are used to predict the lattice symmetry and properties of clamped PZT thin films on different substrates. Guided by the thermal strain phase diagrams that are produced by this model, experimentally structural transitions are observed. These can be related to changes of the piezoelectric properties in PZT(x = 0.6) thin films that are grown on CaF2, SrTiO3 (STO) and 70% PbMg1/3Nb2/3O3‐30% PbTiO3 (PMN‐PT) substrates by pulsed laser deposition. Through temperature en field dependent in situ X‐ray reciprocal space mapping (RSMs) and piezoelectric force microscopy (PFM), the low symmetry monoclinic phase and polarization rotation are observed in the film on STO and can be linked to the measured enhanced properties. The study identifies a monoclinic ‐rhombohedral MC‐MA‐R crystal symmetry path as the polarization rotation mechanism. The films on CaF2 and PMN‐PT remain in the same symmetry phase up to the ferroelectric‐paraelectric phase transition, as predicted. These results support the validity of the multi‐domain model which provides the possibility to predict the behavior of clamped, piezoelectric PZT thin films, and design films with enhanced properties. [ABSTRACT FROM AUTHOR]

Microplasmas can be used for a wide range of technological applications and to improve the understanding of fundamental physics. Scanning electron microscopy, on the other hand, provides insights into the sample morphology and chemistry of materials from the mm‐ down to the nm‐scale. Combining both would provide direct insight into plasma‐sample interactions in real‐time and at high spatial resolution. Up till now, very few attempts in this direction have been made, and significant challenges remain. This work presents a stable direct current glow discharge microplasma setup built inside a scanning electron microscope. The experimental setup is capable of real‐time in situ imaging of the sample evolution during plasma operation and it demonstrates localized sputtering and sample oxidation. Further, the experimental parameters such as varying gas mixtures, electrode polarity, and field strength are explored and experimental V–I curves under various conditions are provided. These results demonstrate the capabilities of this setup in potential investigations of plasma physics, plasma‐surface interactions, and materials science and its practical applications. The presented setup shows the potential to have several technological applications, for example, to locally modify the sample surface (e.g., local oxidation and ion implantation for nanotechnology applications) on the µm‐scale. [ABSTRACT FROM AUTHOR]

Objective of this study is to examine the impact of medication adherence on the timing of non-cardiovascular serious events (NCDS) onset in patients with acute coronary syndrome (ACS) after percutaneous coronary intervention (PCI). Methods: This prospective study was conducted at a single center and involved 220 ACS patients who underwent sequential PCI with stenting. The Morisky Green Levine Medication Adherence Scale was employed to assess adherence to dual antiplatelet therapy (DAPT) and its impact on NCDS occurrence. Early in their hospitalization, all patients received education at the Coronary Heart Disease School. The survival rates of patients in both the main group and a control group (n=355) were subsequently evaluated. Results: The study findings indicated an inverse relationship between stent thrombosis development (Rho=− 0.334; p=0.001) and the timing of recurrent myocardial ischemia. There was also an inverse correlation between patient adherence and stent thrombosis development (Rho=− 0.275; p=0.009). Non-adherent individuals had a 16.8 times higher likelihood of experiencing stent thrombosis compared to compliant patients (p< 0.001). Following participation in the CHD School program, treatment adherence increased from 56.5% to 88.2%. Education for ACS patients post-stenting was significantly associated with all-cause mortality within the first 6 months (p=0.040). Conclusion: Secondary preventive measures, including education, impact the success of endovascular interventions in both the early hospital phase and the long term. Patient education can serve as a supplementary intervention to enhance DAPT adherence, thus diminishing the risk of recurrent cardiovascular events and mortality post endovascular intervention. [ABSTRACT FROM AUTHOR]

The development of coatings with tunable performances is critical to meet a wide range of technological applications each one with different requirements. Using the plasma-enhanced chemical vapor deposition (PECVD) process, scientists can create hydrogenated amorphous carbon coatings doped with metal (a-C:H:Me) with a broad range of mechanical properties, varying from those resembling polymers to ones resembling diamond. These diverse properties, without clear relations between the different families, make the material selection and optimization difficult but also very rich. An innovative approach is proposed here based on projected performance indices related to fracture energy, strength, and stiffness in order to classify and optimize a-C:H:Me coatings. Four different a-C:H:Cr coatings deposited by PECVD with Ar/C2H2 discharge under different bias voltage and pressures are investigated. A path is found to produce coatings with a selective critical energy release rate between 5–125 J/m2 without compromising yield strength (1.6–2.7 GPa) and elastic limit (≈0.05). Finally, fine-tuned coatings are categorized to meet desired applications under different testing conditions. [ABSTRACT FROM AUTHOR]

Graphitic carbon nitride (gCN) is a promising n-type semiconductor widely investigated for photo-assisted water splitting, but less studied for the (photo)electrochemical degradation of aqueous organic pollutants. In these fields, attractive perspectives for advancements are offered by a proper engineering of the material properties, e.g., by depositing gCN onto conductive and porous scaffolds, tailoring its nanoscale morphology, and functionalizing it with suitable cocatalysts. The present study reports on a simple and easily controllable synthesis of gCN flakes on Ni foam substrates by electrophoretic deposition (EPD), and on their eventual decoration with Co-based cocatalysts [CoO, CoFe2O4, cobalt phosphate (CoPi)] via radio frequency (RF)-sputtering or electrodeposition. After examining the influence of processing conditions on the material characteristics, the developed systems are comparatively investigated as (photo)anodes for water splitting and photoelectrocatalysts for the degradation of a recalcitrant water pollutant [potassium hydrogen phthalate (KHP)]. The obtained results highlight that while gCN decoration with Co-based cocatalysts boosts water splitting performances, bare gCN as such is more efficient in KHP abatement, due to the occurrence of a different reaction mechanism. The related insights, provided by a multi-technique characterization, may provide valuable guidelines for the implementation of active nanomaterials in environmental remediation and sustainable solar-to-chemical energy conversion. [ABSTRACT FROM AUTHOR]

BACKGROUND AND OBJECTIVES: Purpose of the study is the assessment of the effectiveness of renal denervation with different types of catheters, as well as its long-term effects, in the patients with resistant hypertension. MATERIALS AND METHODS: This single-center prospective study included 81 patients who underwent a renal denervation procedure using 2 types of catheters: monopolar and helical (Medtronic Inc., Minneapolis, Minnesota, the USA) between 2015 and 2018. Baseline demographics, clinical, functional and laboratory characteristics of the patients were assessed. A comparative analysis of the dynamics of office systolic and diastolic blood pressure during 5 years of follow-up was carried out. The Kaplan-Meier method was used to study the survival of the patients with resistant hypertension after renal denervation. RESULTS: A total of 81 patients with a mean age of 57.79±9.87 years, of whom 37.04 % were men, were included in the 2-stage study (first stage using monopolar catheters and second stage using spiral catheters). At the time of inclusion, study participants were receiving an average of 4.5±1.4 antihypertensive medications. In 36 (or 44.4 %), the procedure was performed using a monopolar catheter; in 45 (or 55.6 %), a spiral catheter was used. There were no statistically significant differences between the two groups of the patients. The analysis established statistically significant changes in the dynamics of office SBP and DBP (p < 0.001) assessed 1, 2, 3, 4, and 5 years after the renal denervation procedure. The analysis demonstrated a stability in the reduction of office SBP and DBP during the 5-year follow-up. The results of the study showed that the median survival time was 1061 days from the beginning of follow-up (95% CI: 728.03 to 1 393.97 days); the median survival time in the monopolar catheter group was 777 days (95% CI: 692.314 to 861.686) and in the spiral catheter group 1 294 days (95% CI: 713.079 to 1 874.921). FINDINGS: Our results demonstrated the efficiency and safety of renal denervation in both short-term and long-term follow-up using monopolar and spiral catheters in the treatment of uncontrolled hypertension with combined antihypertensive therapy. The most significant is the demonstrated stability of the effect after the procedure. In addition, the survival rate of the patients with resistant hypertension after the intervention has been carried out (Tab. 2, Fig. 3, Ref. 22). Text in PDF www.elis.sk [ABSTRACT FROM AUTHOR]

We consider an approach to mathematical modeling of photodegradation of polymer nanocomposites with photoactive additives using the Monte Carlo methods. We principally pay attention to the strength decrease of these materials under solar light action. We propose a new term, "photocatalytic fatigue", which we apply to the particular case when the mechanical strength decreases only owing to the presence of photocatalytically active components in polymeric nanocomposite material. The propriety of the term is based on a relative similarity of photostimulated mechanical destructive processes in nanocomposites with photoactive additives and mechanical destructive processes typical for metal high-cycle fatigue. Formation of the stress concentrations is one of the major causes of fatigue cracks generation in metals. Photocatalytic active nanoparticles of semiconductors initiate a generation of the stress concentrations under sunlight irradiation. The proposed mathematical model is a Wöhler curve analog for the metal high-cycle fatigue. We assume that equations for high-cycle fatigue curves of samples with stress concentrations could be used in mathematical modeling of polymer nanocomposites photodegradation. In this way, we replace the number of loading cycles with the exposition time in the equations. In the case of polypropylene and polyester samples with photoactive titanium dioxide, the experimental parameters of phenomenological equations for "photocatalytic fatigue" are calculated using one of the Monte Carlo methods based on the random search algorithm. The calculating scheme includes a solution of the extreme task of finding of the minimum of nonnegative transcendent multivariable function, which is a relative average quadratic deviation of calculated values of polymeric nanocomposite stress in comparison with corresponding experimental values. The applicability of the "photocatalytic fatigue" model for polymer nanocomposites with photoactive nanoparticles is confirmed by the example of polypropylene and polyester samples. The approximation error of the experimental strength values for them did not exceed 2%. [ABSTRACT FROM AUTHOR]

A method to prepare TEM specimens from metallic microwires and based on conventional twin‐jet electropolishing is introduced. The wire is embedded in an opaque epoxy resin medium and the hardened resin is mechanically polished to reveal the wire on both sides. The resin containing wire is then cut into discs of the appropriate size. The obtained embedded wire is electropolished in a conventional twin‐jet electropolishing machine until electron transparency in large areas without radiation damage is achieved. [ABSTRACT FROM AUTHOR]

Following an extensive investigation of various monolayer transition metal dichalcogenides (MX2), research interest has expanded to include multilayer systems. In bilayer MX2, the stacking order strongly impacts the local band structure as it dictates the local confinement and symmetry. Determination of stacking order in multilayer MX2 domains usually relies on prior knowledge of in-plane orientations of constituent layers. This is only feasible in case of growth resulting in well-defined triangular domains and not useful in-case of closed layers with hexagonal or irregularly shaped islands. Stacking order can be discerned in the reciprocal space by measuring changes in diffraction peak intensities. Advances in detector technology allow fast acquisition of high-quality four-dimensional datasets which can later be processed to extract useful information such as thickness, orientation, twist and strain. Here, we use 4D scanning transmission electron microscopy combined with multislice diffraction simulations to unravel stacking order in epitaxially grown bilayer MoS2. Machine learning based data segmentation is employed to obtain useful statistics on grain orientation of monolayer and stacking in bilayer MoS2. [ABSTRACT FROM AUTHOR]

To transform a monocrystalline diamond into monocrystalline graphite, the exposure of an ultrafast laser to a (111) diamond face was investigated for the first time. The single pulse of the third harmonic of a Ti:sapphire laser (100 fs, 266 nm) was used to produce graphitized inclusions embedded in a (111) diamond substrate. Three different regimes of (111) diamond graphitization are discussed in this paper. Raman spectroscopy, scanning electron microscopy, and transmission electron microscopy were used to investigate the graphitized material, which was found to resemble highly oriented graphite at certain laser fluencies. The proposed approach to the problem of perfect local diamond graphitization is an important step toward creating all-carbon composite systems consisting of conductive and dielectric phases. [ABSTRACT FROM AUTHOR]

A new method for synthesis of 2D nanocrystals in water was proposed. The use of perfluorothiophenolate ions as surfactant allowed us to produce 2D single-crystal nanosheets of CaS at pH=9 and flat nanocrystals of PbS at pH=9 at room temperature. Mesocrystalline nanobelts of CdS and mesocrystals of PbS were obtained at pH=3–5 and pH=10–12, respectively. Morphology, structure and chemical composition of nanoparticles were characterized by high-resolution transmission electron microscopy, electron diffraction and energy dispersive X-ray spectroscopy. A mechanism of nanoparticles formation was discussed. [ABSTRACT FROM AUTHOR]

Substrates pretreatment in suspensions of a detonation nanodiamond is widely used for nucleation of diamond growth by chemical vapor deposition (CVD). We found that iron inclusions in the nanodiamond provide catalytical growth of carbon nanotubes during CVD in a hot filament reactor (HF CVD). Carbon nanotubes grow in the area between two adjacent Si wafers. The diameters of such obtained nanotubes were in the range of 10–100 nm and the length of the tubes reaches about 10 µm. The proposed HF CVD method has convincing potential for the fabrication of carbon nanotube coatings on a large surface area. [ABSTRACT FROM AUTHOR]

The formation of active component of Fe–Mo and Co–Mo catalysts for carbon nanotube growth with variable Mo content is studied with in situ XRD, XPS, and STEM&EDX. The activation of bimetallic Fe–Mo catalysts under the growth conditions leads to the formation of Fe–Mo alloy particles in contrast to Co‐containing catalysts in which active alloy incorporates only a small portion of Mo (<2–3 at.%). The stable carbide formation for these systems is not detected. The effect of Mo content in Fe–Mo and Co–Mo catalysts on the properties of MWCNTs is additionally investigated using the Raman spectroscopy in combination with measurements of the temperature dependence of conductivity. It is shown that MWCNT defectiveness depends on the active component composition for both Fe–Mo and Co–Mo catalysts. The current carrier concentration for the MWCNTs grown on Fe–Mo catalysts slightly increases with the Mo content. The opposite effect is observed for the tubes grown on Co–Mo catalysts, showing a decrease in the current carrier concentration with the increase of Mo concentration. [ABSTRACT FROM AUTHOR]

In this article, we present a comparative study of field emission (FE) properties of the films of pristine, annealed and CuCl-filled single-walled carbon nanotubes (SWCNTs). The current-voltage dependencies and emission site distributions were measured in the diode configuration with a flat phosphor-coated anode. A significant increase of the threshold field was observed after annealing and doping of the films. It was explained by the selective oxidation of the small-diameter nanotubes confirmed by the Raman spectroscopy. The FE properties of annealed and filled SWCNTs were found to coincide with each other. At the same time, their Raman spectra differ significantly indicating the strong p-type doping induced by encapsulated CuCl. The obtained result reveals that the CuCl filling leads to significant changes in macroscopically averaged electronic properties but do not change the local work function at the apexes of emitting nanotubes, which is important for the further development of SWCNTs-based FE cathodes. [ABSTRACT FROM AUTHOR]

Abstract: One of the most effective ways to increase the current-carrying ability of Nb3Sn superconductor is doping of the superconducting phase by Ti, since it leads to Hc2 increase due to the rise of Nb3Sn phase electrical conductivity in normal state, and also to acceleration of the Nb3Sn layer growing during reaction and to critical current density increasing. The investigations of structure and composition of Nb3+xSn superconducting strands by SEM, TEM and EDXS microanalysis have been carried out. The structure and composition of Nb3Sn superconducting phase of the strands after reaction at 575°C 150 h+650°C 200h have been studied. The dependence of Ti content in Nb3Sn phase from the amount of Ti introduced in Nb filaments or in bronze matrix has been also studied. It was found, that the lowest Ti content corresponds to introduction of it through the matrix doping. It has been established that Nb content in Nb3Sn essentially exceeds the stoichiometric one (3:1). The Nb3Sn lattice parameters have been defined by XRD. It was found, that the lattice parameters in the samples with Ti doped matrix were the closest to the stoichiometric Nb3Sn. The correspondence between grain morphology and composition of superconducting phase and critical current density of studied strands has been established. [Copyright &y& Elsevier]

This paper aims to consider approximation-estimation tests for decision-making by machine-learning methods, and integral-estimation tests are defined, which is a generalization for the continuous case. Approximation-estimation tests are measurable sampling functions (statistics) that estimate the approximation error of monotonically increasing number sequences in different classes of functions. These tests make it possible to determine the Markov moments of a qualitative change in the increase in such sequences, from linear to nonlinear type. If these sequences are trajectories of discrete quasi-deterministic random processes, then moments of change in the nature of their growth and qualitative change in the process match up. For example, in cluster analysis, approximation-estimation tests are a formal generalization of the "elbow method" heuristic. In solid mechanics, they can be used to determine the proportionality limit for the stress strain curve (boundaries of application of Hooke's law). In molecular biology methods, approximation-estimation tests make it possible to determine the beginning of the exponential phase and the transition to the plateau phase for the curves of fluorescence accumulation of the real-time polymerase chain reaction, etc. [ABSTRACT FROM AUTHOR]

The paper is dedicated to solving the problem of optimal text classification in the area of automated detection of typology of texts. In conventional approaches to topicality-based text classification (including topic modeling), the number of clusters is to be set up by the scholar, and the optimal number of clusters, as well as the quality of the model that designates proximity of texts to each other, remain unresolved questions. We propose a novel approach to the automated definition of the optimal number of clusters that also incorporates an assessment of word proximity of texts, combined with text encoding model that is based on the system of sentence embeddings. Our approach combines Universal Sentence Encoder (USE) data pre-processing, agglomerative hierarchical clustering by Ward's method, and the Markov stopping moment for optimal clustering. The preferred number of clusters is determined based on the "e-2" hypothesis. We set up an experiment on two datasets of real-world labeled data: News20 and BBC. The proposed model is tested against more traditional text representation methods, like bag-of-words and word2vec, to show that it provides a much better-resulting quality than the baseline DBSCAN and OPTICS models with different encoding methods. We use three quality metrics to demonstrate that clustering quality does not drop when the number of clusters grows. Thus, we get close to the convergence of text clustering and text classification. [ABSTRACT FROM AUTHOR]

This paper reports the analysis of the intensity of diamond line in the Raman spectra of laser modified layers with different thickness on a diamond surface. Since the diamond line passing from substrate through the absorbing layer of moderate thickness can be registered, the thickness of local area is estimated from its micro‐Raman spectra. The comparison between Raman scattering and direct observation of the graphitized layer by transmission electron microscopy shows that Raman spectroscopy can be used as an alternative non‐destructive method for measuring a moderate thickness of graphitized layers. [ABSTRACT FROM AUTHOR]

The synthesis of graphene on thin copper film deposited on quartz substrate is reported. The copper films are fabricated with different thickness of 300 and 1150 nm and then crystallized during thermal annealing that occurs at temperature of 950 and 1000 °C for 30 or 90 min. The size of copper grains increases with increasing of the temperature and the time of annealing that results in increasing of graphene film size. The deposited copper films are studied by electron backscatter diffraction and synthesized graphene films are analyzed by Raman spectroscopy and scanning probe microscopy. Proposed phase contrast mode of the scanning probe microscopy demonstrates high lateral resolution and sensitivity to the presence of graphene with different number of layers. It is found that graphene monolayer is preferably formed on the surface of copper grains with orientation {111} and proposed techniques can be used for the analysis of the evolution of graphene growth. [ABSTRACT FROM AUTHOR]

Phase formation and transitions in platinum silicide films on polycrystalline Si in the process of Pt magnetron sputtering and heat treatments at different temperatures are studied using X-ray photoelectron spectroscopy, high-resolution transmission electron microscopy and X-ray diffractometry. Phases of amorphous and polycrystalline Pt 3 Si and Pt 2 Si are shown to form during the room-temperature Pt deposition on poly-Si beneath the Pt layer. The relaxation of the interfacial film and partial transformation of Pt 3 Si into Pt 2 Si occurs as a result of the thermal treatment for 30 min in the temperature range from 125°C to 300°С. The Pt 3 Si and Pt 2 Si phases crystallize to PtSi due to annealing at the temperatures from 320°C to 480°С for the same time period. Image 1 • Interface domain in magnetron sputtered and annealed Pt/poly-Si film is studied. • Pt 3 Si and Pt 2 Si phases form at room temperature during Pt deposition on poly-Si. • Interfacial film relaxation turns Pt 3 Si to Pt 2 Si due to annealing at 100 < T < 200 °C. • Pt 3 Si and Pt 2 Si transit to PtSi due to annealing at temperatures from 320 to 480 °C. • Pt 3 Si phase is detected up to the annealing temperature of 350 °C. [ABSTRACT FROM AUTHOR]