Chemical Fluctuations Research Articles

On the chemistry of grain boundaries in CuInS2 films

Abstract We conducted correlated transmission Kikuchi diffraction and atom probe tomography measurements to investigate the relationship between the structure and chemistry of grain boundaries in Cu-rich and Cu-poor sulfide chalcopyrite CuInS2 thin-films. We detect different elemental redistributions at random high‐angle grain boundaries, Σ9 twin boundaries and stacking faults in the Cu-rich and Cu-poor film but no chemical fluctuations at Σ3 twin boundaries. For the Cu-rich CuInS2 thin-film, our atom probe tomography analyses reveal Cu enrichment as well as In and S depletion at random grain boundaries, Σ9 twin boundaries and stacking faults. Hence, we may observe a ‘Cu on In’ scenario, which is accompanied by co-segregation of Na and C. In contrast, for the Cu-poor CuInS2 thin-film, our analyses show Cu depletion and In enrichment at random grain boundaries and at the vast majority of stacking faults. For S we do not observe a clear trend. Therefore, for the Cu-poor CuInS2 thin-film we may observe a ‘In on Cu’ scenario, which is accompanied by co-segregation of Na, K and O at the random grain boundaries but not at stacking faults. The amount of impurity segregation varies from one grain boundary to another in both thin-films.

Geochemical characterization of groundwater evolution south of Grand Canyon, Arizona (USA)

Better characterization of the geochemical evolution of groundwater south of Grand Canyon, Arizona (USA), is needed to understand natural conditions and assess potential effects from breccia-pipe uranium mining in the region. Geochemical signatures of groundwater at 28 sampling locations were evaluated; baseline concentrations for select trace elements (As, B, Ba, Cr, Li, Mo, Rb, Se, Sr, Th, Tl, U, V) were established, and anomalous chemistry characteristics were identified. Concentrations at some groundwater sites exceeded the USEPA drinking water standard for As of 10 μg/L (Red Canyon, Miners, JT, Havasu, and Warm Springs) and U of 30 μg/L (Salt Creek Spring). Four springs from the study area (Blue, Havasu, Fern, and Warm Springs) had unique chemistry, which may indicate a deep flow path or potential contribution of fluids from lower in the crust. Other springs in the study area were distinguished by major anion water type: sulfate, bicarbonate, and a mixture of the two. Water type distinctions were somewhat spatially segregated, with sulfate type present on the western side of the study area, bicarbonate type on the eastern side, and a mixture of the two interspersed between the endmember sites. Sulfate-type water from this study area had low strontium isotopic ratio (87Sr/86Sr) values. The location of spring discharge within single drainages of the Grand Canyon may influence chemistry, as groundwater discharging from bedrock was altered after flowing through alluvial material. Geochemical analysis of groundwater in Grand Canyon indicates the importance of continued monitoring and better understanding of short-term chemical fluctuations.

New Frontiers in Electrocatalyst Characterization – Three Dimensional Atomic-Scale Insights By Atom Probe Tomography

Developing electrocatalysts with enhanced properties requires a fundamental understanding of the processes that occur during operation as well as side reactions during the synthesis. Many of those processes, e.g. solute segregation to defects [1], the hydroxylation of near-surface regions [2], or the preferential oxidation/reduction of certain regions, are often governed by the local microstructure. Such phenomena commonly result in significant chemical heterogeneities within the material at the nanoscale, affecting the potential distribution across the surface during operation. This way, localized heterogeneities can control the local binding energetics for reactants, intermediates and products, and determine the overall reactivity and stability of the material.Atom probe tomography (APT) offers the opportunity to measure the composition of localized chemical fluctuations at the near-atomic scale and in three dimensions. Targeted APT specimen preparation of regions-of-interest, e.g. at specific grains or grain boundaries, enables the correlation of local structure and local composition. Recent method developments have enabled the measurement of free surfaces with APT [2,3], offering a new perspective into the first few atomic layers of electrocatalytic materials. APT thereby provides the chance to elucidate chemical processes within the near-surface region which underpin the electrochemical performance of the material.In this contribution, we showcase how APT can be instrumental to the precise characterization of various electrocatalytic materials. In a first example, we demonstrate how APT revealed the structural features in hydrous Ir oxides that are responsible for an accelerated degradation of the catalyst during the oxygen evolution reaction, due to release of molecular oxygen from the lattice [4]. Secondly, we present how APT can be combined with scanning photoemission electron microscopy to obtain spatially correlated chemical state information of the surface investigated with APT [1,3]. And finally, we show how APT enables the investigation of trace-element distribution in nanostructured materials, such as nanoparticles [5] or nanorods [6]. For example, APT can shed light on the incorporation of B, Na and N during the hydrothermal synthesis and partial reduction of hollow TiO2 nanorods, that are commonly used as a photocatalyst or catalyst support. Trace amounts of such light elements often remain undetected with other methods but may have a dramatic effect on the functionality of the material.

Incorporating Cellular Stochasticity in Solid-Fluid Mixture Biofilm Models.

The dynamics of cellular aggregates is driven by the interplay of mechanochemical processes and cellular activity. Although deterministic models may capture mechanical features, local chemical fluctuations trigger random cell responses, which determine the overall evolution. Incorporating stochastic cellular behavior in macroscopic models of biological media is a challenging task. Herein, we propose hybrid models for bacterial biofilm growth, which couple a two phase solid/fluid mixture description of mechanical and chemical fields with a dynamic energy budget-based cellular automata treatment of bacterial activity. Thin film and plate approximations for the relevant interfaces allow us to obtain numerical solutions exhibiting behaviors observed in experiments, such as accelerated spread due to water intake from the environment, wrinkle formation, undulated contour development, and the appearance of inhomogeneous distributions of differentiated bacteria performing varied tasks.

Frequency Spectrum of Chemical Fluctuation: A Probe of Reaction Mechanism and Dynamics

Even in the steady-state, the number of biomolecules in living cells fluctuates dynamically, and the frequency spectrum of this chemical fluctuation carries valuable information about the dynamics of the reactions creating these biomolecules. Recent advances in single-cell techniques enable direct monitoring of the time-traces of the protein number in each cell; however, it is not yet clear how the stochastic dynamics of these time-traces is related to the reaction mechanism and dynamics. Here, we derive a rigorous relation between the frequency-spectrum of the product number fluctuation and the reaction mechanism and dynamics, starting from a generalized master equation. This relation enables us to analyze the time-traces of the protein number and extract information about dynamics of mRNA number and transcriptional regulation, which cannot be directly observed by current experimental techniques. We demonstrate our frequency spectrum analysis of protein number fluctuation, using the gene network model of luciferase expression under the control of the Bmal 1a promoter in mouse fibroblast cells. We also discuss how the dynamic heterogeneity of transcription and translation rates affects the frequency-spectra of the mRNA and protein number.

Grain boundary structure and mobility in high-entropy alloys: A comparative molecular dynamics study on a Σ11 symmetrical tilt grain boundary in face-centered cubic CuNiCoFe

We employ atomistic computer simulations to study the structure and migration behavior of a Σ11 symmetrical tilt grain boundary in a 4-component model FCC high-entropy alloy (HEA) (CuNiCoFe). The results are compared to grain boundaries in elemental metals and a so-called ‘average-atom’ sample. We find that the repeating structural units characterizing the static grain boundary structure show the same repeating structural units for all samples, while the high temperature equilibrium grain boundary structure is most strongly influenced by presence of stacking faults. Under an applied synthetic driving force, this GB migrates by a mechanism assisted by partial dislocations in all materials. For this reason the grain boundary mobilities and stacking fault energies are directly related. Moreover, the HEA sample and the average-atom sample show almost identical mobilities suggesting that local chemical fluctuations play a minor role. Solute segregation to the GB in the HEA suppresses GB migration up to very high temperatures and might be the main cause for reduced grain growth in FCC HEAs.

Chemical freeze-out conditions and fluctuations of conserved charges in heavy-ion collisions within a quantum van der Waals model

The chemical freeze-out parameters in central nucleus-nucleus collisions are extracted consistently from hadron yield data within the quantum van der Waals (QvdW) hadron resonance gas model. The beam energy dependences for skewness and kurtosis of net baryon, net electric, and net strangeness charges are predicted. The QvdW interactions in asymmetric matter, $Q/B \neq 0.5$, between (anti)baryons yield a non-congruent liquid-gas phase transition, together with a nuclear critical point (CP) with critical temperature of $T_c=19.5$ MeV. The nuclear CP yields the collision energy dependence of the skewness and the kurtosis to both deviate significantly from the ideal hadron resonance gas baseline predictions even far away, in $(T,\mu_B)$-plane, from the CP. These predictions can readily be tested by STAR and NA61/SHINE Collaborations at the RHIC BNL and the SPS CERN, respectively, and by HADES at GSI. The results presented here offer a broad opportunity for the search for signals of phase transition in dense hadronic matter at the future NICA and FAIR high intensity facilities.

Frequency spectrum of chemical fluctuation: Aprobe of reaction mechanism and dynamics.

Even in the steady-state, the number of biomolecules in living cells fluctuates dynamically, and the frequency spectrum of this chemical fluctuation carries valuable information about the dynamics of the reactions creating these biomolecules. Recent advances in single-cell techniques enable direct monitoring of the time-traces of the protein number in each cell; however, it is not yet clear how the stochastic dynamics of these time-traces is related to the reaction mechanism and dynamics. Here, we derive a rigorous relation between the frequency-spectrum of the product number fluctuation and the reaction mechanism and dynamics, starting from a generalized master equation. This relation enables us to analyze the time-traces of the protein number and extract information about dynamics of mRNA number and transcriptional regulation, which cannot be directly observed by current experimental techniques. We demonstrate our frequency spectrum analysis of protein number fluctuation, using the gene network model of luciferase expression under the control of the Bmal 1a promoter in mouse fibroblast cells. We also discuss how the dynamic heterogeneity of transcription and translation rates affects the frequency-spectra of the mRNA and protein number.

Research progress on chemical constituents and quality control of Tripterygium wilfordii preparations

Tripterygium wilfordii preparations,with various biological activities such as immunosuppressive,anti-inflammatory and anti-cancer effects,are widely used in the treatment of autoimmune diseases such as rheumatoid arthritis,lupus erythematosus,and nephrotic syndrome. They have definite therapeutic effect,but often cause serious adverse reactions and result in damages to liver,kidney,blood,reproduction,and other systems due to their complex compositions,great toxicity,and narrow margin between the toxic and therapeutic dosages. At present,T. wilfordii preparations produced by different manufacturers exhibit large variations in clinical efficacy and side effects in account of their different chemical compositions and quality fluctuation due to differences in raw materials and production process. However,the existing quality standards are controversial in terms of index components and content limit,which cannot be effectively used for the overall quality control of the preparations. In this paper,the research progress on chemical constituents,quality standard and quality control methods of four T. wilfordii preparations including Tripterygium Tablets,Tripterygium Zongtie Tablets,Tripterygium Shuangceng Tablets and Tripterygium Glycosides Tablets was reviewed,in order to provide ideas and reference for the quality improvement of this type of preparations.

Aromaticity and Electron Density of Hypericin.

The influence of the substituents on the geometry of the central ring system of hypericin has been analyzed. Substitution that causes flattening of the hypericin central rings is connected with introducing the aromatic character of the empty rings. All the hypericin rings have an aromatic character illustrated by the Harmonic Oscillator Measure of Aromaticity (HOMA), Nucleus Independent Chemical Shift (NICS), Fluctuation Index (FLU), and Ellipticity Index (EL) indices. Quantum Theory of Atoms in Molecules (QTAIM) and Natural Bond Orbital (NBO) analyses performed on 7,14-dihydrophenanthro[1,10,9,8-opqra]perylene, its substituted analogues, and hypericin show an influence of this substitution on electron density of the central rings.

Structural Relaxation in Polyanionic Sodium Fluorophosphate Glasses

Structural heterogeneity is a common feature of all glasses, however, little is known about the underlying contributions of chemical fluctuations and modulations in free volume in concrete glass forming systems. In this investigation, we relate the dynamics of structural relaxation of (100-x)NaPO3–xAlF3 glasses to their heterogeneous structure as determined from multinuclear magnetic resonance spectroscopic analysis. For this, we evaluate differential scanning calorimetry (DSC) data using the integral isoconversional method to determine the variation in activation energy, Ea, of the glass transition as a function of temperature and conversion progress. Specific heat measurements from DSC allow for the determination of the effective size of the cooperatively rearranging region (CRR). From 31P, 19F and 27Al NMR, we observe that the introduction of AlF3 into the NaPO3 network increases the average connectivity (i.e., the number of heteronuclear Al—O—P bonds), rationalizing the higher Ea determined from the DSC measurements. We find highly constrained regions of Al(OP)4F2 with Al—F—Al cross-linking (high Ea) and, simultaneously, more flexible regions of phosphate chains containing P—F··(Na+)n bonds (low Ea); this results in a topologically and dynamically heterogeneous structure as evidenced by the increased variability in Ea with higher AlF3 content. The decreasing size of the CRR reflects the increased heterogeneity: at low AlF3 the CRR is large, while at high AlF3 (high heterogeneity), the CRR is significantly smaller (by a factor of 103). Finally, we relate the heterogeneity to other macroscopic properties, such as Tg and mechanical properties.

ʿAbd al-Karīm al-Jīlī, Waḥdat al-Wujūd, and Reconfiguring Epistemology

This study introduces some new ideas into the study of ideas in Sufism. Taking al-Jīlī and, esp., his al-Insān al-kāmil as a starting point this study argues a holistic worldview following the concepts of the oneness of being (waḥdat al-wujūd) will be able to integrate – and to be integrated – into contemporary scientific concepts like chemical fluctuation, the new synthesis, and holobionts. This will lead to creating a general philosophy of being beyond the Western biases.

Deformation behaviour of TiN and Ti–Al–N coatings at 295 to 573 K

Temperature-dependent nanoindentation testing was employed to investigate the deformation behaviour of magnetron sputtered (100) TiN and Ti1-xAlxN (x = 0.34, 0.52, 0.62) coatings in the temperature range from 295 to 573 K. The maximum temperature is sufficiently below the deposition temperature of 773 K to guarantee for stable microstructure and stress state during testing. The TiN coating displayed the same hardness as bulk single crystal (SC) TiNbulk. The addition of aluminium to TiN (to form single-phase face centred cubic structured Ti1-xAlxN coatings) increased the room temperature hardness due to increased bond strength, lattice strain and higher activation energy for the dislocation slip. For coatings with a low aluminium content, Ti0.66Al0.34N, the decrease in hardness with temperature was similar to the TiN coating and SC-TiNbulk. In contrast, the hardness of coatings with moderate, Ti0.48Al0.52N, and high, Ti0.38Al0.62N, aluminium contents varied little up to 573 K. Thus, the Ti1-xAlxN matrix is mechanically more stable at elevated temperatures than its TiN relative, by providing a lower decrease in lattice resistance to the dislocation flow with increasing temperature. The findings suggest that the addition of Al to TiN (to form Ti1-xAlxN solid solutions) not only improves the hardness but also leads to stable hardness with temperature, and emphasizes the importance of bonding states and chemical fluctuations, next to structure and morphology of the coatings that develop with changing the chemistry.

The critical role of N-vacancy on chemical composition fluctuations and degradation of InAlN layer

Due to its intrinsic properties and the possible lattice match to GaN, InAlN is expected to allow the fabrication of optimal high electron mobility transistors for high power and high frequency applications. However, the crystal quality of InAlN nearly lattice-matched to GaN degrades when the layer thickness is increased, and this is a strong limitation for the fabrication of devices in which thick barriers need to be used. In this work, we have carried out a detailed theoretical investigation of the behavior of indium atoms in the alloy. It is clearly shown that in the presence of nitrogen vacancies, which are common defects in these materials, indium nitride clusters will present excess formation energy up to diameters around 1.4 nm. In parallel, Z-contrast TEM observations close to the InAlN/GaN interface show that 2–5 nm size indium rich areas form and are systematically connected to the vertical degradation channels. This is at variance with published results, which concluded that the observed degradation was exclusively either due to the underlying threading dislocations or due to a characteristic three-dimensional growth mode.

Mesoscopic quantitative chemical analyses using STEM-EDX in current and next generation polycrystalline Ni-based superalloys

Quantitative chemical analyses of Ni3Al based hardening precipitates (γ′) in polycrystalline Ni based superalloys have been conducted using energy dispersive X-ray spectroscopy (EDX), coupled with a scanning transmission electron microscope (STEM). The aim of the current investigation is (1) to evaluate the accuracy of calibration (k factor determinations and absorption corrections using a combination of differential X-ray absorption (DXA) and convergent beam electron diffraction (CBED)) by comparing with thermodynamic calculations and (2) to demonstrate the importance of the EDX chemical analysis by taking advantage of its unique capabilities to analyse sub-micron scale chemistries within a mesoscopic field of view under STEM. Our experimental findings show good agreement with the mole fraction ratio of γ′ to the disordered γ matrix predicted using the Lever rule on a thermodynamically stabilised unimodal superalloy, RR1000. The significance of analysing a statistically viable number of samples in thermodynamically metastable superalloys and the chemical fluctuations found in coarse γ′, sized above 200 nm on a scale of a few hundred nanometres in the context of solving a complex morphological evolution of γ′ particles is demonstrated.

Increasing the Liquidus Temperature by Employing the Controlled Diffusion Solidification (CDS) Process: A Potential Route to Improved Castings

Recent theories suggest the existence of an incubation time, over which a liquid alloy prepares for nucleation by decomposing into compositional fluctuations. Accordingly, in a recent work by the present authors, the solidification path of a Controlled Diffusion Solidification (CDS) mixture was calculated. The calculated CDS path begins at a higher liquidus temperature comparing to conventional solidification and the fraction solid values are achieved at a relatively higher temperature. To provide information on the CDS mechanism and physical structure of the CDS mixture in the mushy zone, Al-7.8Zn-2.6Mg-2Cu alloy was solidified, in this study, via conventional and CDS process in the presence and absence of recalescence. Typical grain structures obtained via the two solidification conditions is characterized using Electron Back Scattered Diffraction. Results showed that the nucleation continues to occur in the presence of recalescence, while it is suppressed in its absence. According to the two step nucleation theory, the increase in the nucleation temperature causes sufficient recalescence in the mixture, allowing the unnucleated liquid phase to decompose into chemical fluctuations and prepares for further nucleation. As a result, in the presence of recalescence, nucleation in a CDS mixture is not as readily halted as during the conventional solidification, which is in contradiction with the recent theories developed based on the classical theory of nucleation.

Creep behavior in the new AD730TM nickel-based disk superalloy – Influence of aging heat treatment and local chemical fluctuations

Transmission electron microscopy (TEM) experiments combining conventional and weak beam observations, energy dispersive X-ray and electron energy loss spectroscopies have been used to identify and quantify, in the polycrystalline AD730TM Ni-Based superalloy, the effect of isothermal aging after solution treatment in the range 730–790 °C on the creep behavior at 700 °C – 500 MPa. The microstructure of different aged crept specimens has been first characterized as the creep behavior is directly influenced by the microstructural features (size of the γ′ precipitates and of the γ-channel). The analyzes show similar results whatever the heat treatment. Then, the investigation of the dislocation configurations indicate that the deformation occurs by the propagation of straight perfect dislocations, which shear the γ-matrix and the precipitates at 730 °C and 760 °C, whereas a combination of perfect and partial dislocations is observed after aging at 790 °C. The investigation of the local chemical composition has revealed some strong local variations in Cr content within the γ-phase and smaller ones in Ti content within the γ′-phase after aging at 790 °C. These elemental concentration quantifications have been used to evaluate the antiphase boundary and stacking fault energies. This allows to interpret the presence of partial dislocations after aging at 790 °C and thus the increase in the creep strain rate when the specimen is previously aged at 790 °C.

II-VI Based Inorganic-Organic Hybrid Quantum Structures with High Degree of Structural Ordering, Long-Term Stability, and Novel Properties

Translational symmetry ensures phase coherency of a physical process among different units of a crystal, and thus produces collective quantum effects beyond the sum of the units. Any significant physical and/or chemical fluctuation, which typically exists in a semiconductor alloy or self-assembled or artificially grown nanostructure array, would hinder our ability to study and use the collective behavior relying on this coherency. Man-made structures remain as one of the central interests since semiconductor superlattices were proposed by Esaki and Tsu in 1970. Unfortunately, man-made structures with both genuine long- and short-range order are rare. Here a new family of inorganic-organic hybrid quantum structures provides us a unique opportunity to explore coherency quantum phenomena in man-made structures. These self-assembled hybrid structures are ultra-thin slabs or atomic chains of II-VI semiconductors interconnected or coordinated by small organic molecules, exhibiting very high degree of structural perfectness comparable to a typical binary semiconductor, as manifested in a very small XRD and Raman linewidth. They exhibit several extraordinary properties, for instance, exceedingly strong excitonic absorption, large exciton binding energies, and zero thermal expansion. By varying either the inorganic or organic component, one can tune the coupling between the inorganic units to achieve quasi-1-D, quasi-2-D, and 3-D super-structures with tailored material properties for different basic research interests and potential applications (e.g., room temperature exciton-polariton condensation, high efficiency UV emission and detection, p-type transparent conducting material). Furthermore, some hybrid structures, such as β-ZnTe(en)0.5, have been found to retain the same structural perfectness after being stored under ambient condition over a decade, despite others show varying degrees of structural degradation. This finding indicates that the long-term stability of the material depends on both the intrinsic effect, the strength of chemical bonding, and the extrinsic effect, such as the presence of defects in the initial structure.

熱プラズマ流の可視化による物理・化学的変動現象の解明

熱プラズマ流の可視化による物理・化学的変動現象の解明

Наноразмерные флуктуации потенциала в SiO-=SUB=-x-=/SUB=-, синтезированном плазмохимическим осаждением

The atomic structure and electron spectrum of a-SiOx:H films deposited on silicon and glass substrates by the plasma enhanced chemical vapor deposition method are considered in this paper. The film stoichiometric parameter «x» varied in the range from 0.57 to 2 depending on the oxygen supply to the reactor conditions. The film structures and the electronic structure peculiarities characterization, depending on the parameter «x» value, were carried out using a set of structural and optical techniques, as well as the ab initio quantum-chemical simulation for the model SiOx structure. It was established that the studied SiOx:H films mainly consist of silicon suboxide SiOy with SiO2 and amorphous Si clusters. Based on the spatial chemical composition fluctuations, the electron and hole potential fluctuations model for SiOx is proposed. The obtained results will allow a more accurate charge transport modeling in a-SiOx:H films, which is important for creating nonvolatile memory and memristor elements on the base of SiOx.