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Magnesium silicate hydroxides (MSHs) with granular, schistose, and tubular morphologies were separately incorporated to enhance the tribological properties of phosphate/MoS2 composite coatings. The nano-schistose MSH demonstrated superior tribological performance due to its effective interactions with the worn surface and frictional synergies with solid lubricants. Incorporation of nano-schistose MSH decreased the friction coefficient of composite coatings by about 34.7% and increased the anti-wear performance of composite coatings by about thirteen times. Nano-schistose MSH facilitated the formation of a friction-induced multi-layer heterogenous slipping structure with layered solid lubricants at the friction interface. Moreover, tribo-chemical reactions between nano-schistose MSH and worn surface promoted the in-situ formation of a cermet supporting film, and this also induced the gradual in-situ formation of a lubrication film on the top of worn surface. Consequently, the contact state between tribo-pairs was timely regulated and the invalidation of the nanocomposite slipping structure was effectively restrained during the friction process. As a result, the service life of the phosphate composite coatings was significantly extended and further abrasion on the worn surface was notably reduced. [ABSTRACT FROM AUTHOR]

The layered structures of elastic solids have wide applications in various fields of engineering related to natural phenomena, foundations, composite structures, and ultrasonic devices, among others. To have a better understanding of the propagation characteristics of axisymmetric generalized Stoneley waves in a layered structure, the displacement is constructed using the Helmholtz decomposition method with the cylindrical formulation, and then the displacement and stress in the layered structure are presented with potential functions in the wave equations. The transfer matrix method is used to derive the equations of the axisymmetric Stoneley waves in layered elastic solids in the cylindrical coordinates for solutions of wave velocity and amplitudes. With a new formulation in cylindrical coordinates, numerical examples are presented for the dispersion and displacement characteristics of the generalized Stoneley wave of layered solids. The results show that if a low-speed interlayer is added between two semi-infinite media where Stoneley waves do not exist, a wave similar to the Stoneley wave, with displacement decaying exponentially in the semi-infinite direction, can exist. We refer to the Stoneley-like waves that exist in structures with several interlayers between two semi-infinite media as generalized Stoneley waves. [ABSTRACT FROM AUTHOR]

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Using two routes, this study designed and synthesized a novel azo-linked four-heterocyclic compound, 1,2-bis(5- (1H-tetrazol-5-yl)-4H-1,2,4-triazol-3-yl) diazene (3, H4BTTD), with high yields. It corroborated that large conjugated planar energetic molecules in energetic compounds, exemplified by H4BTTD, contribute to the formation of layered crystal stacking based on abundant hydrogen bonds and interlayer π-π interactions. This markedly diminishes the mechanical sensitivities of energetic compounds. Single-crystal X-ray diffraction (XRD) experiments revealed the presence of layered structures in H4BTTD hydrate, as well as its magnesium-based complex [Mg2(BTTD)(H2O)8] (4) and calcium salt [Ca(H2O)7] (H3BTTD)2 (5). Based on these structural data, this study analyzed the causes of these layered structures. Furthermore, this study systematically characterized the compounds’ physical and chemical properties, including mechanical sensitivities (IS ≥ 20 J, FS > 360 N), thermal stability (Td = 253.7–287.8 ◦C), and detonation performance (D = 6808–8253 m⋅s −1 ), confirming the influence of molecular structures on the macroscopic properties of energetic materials through crystal stacking. Additionally, pyrotechnic formulas based on compounds 3 and 5 exhibited the most intense light emission within a wavelength range of 658.6–689.8 nm, underscoring the potential application of both compounds as promising candidates in preparing high-purity red pyrotechnic formulation. [ABSTRACT FROM AUTHOR]

The synthesis of peptide nanocomposites from water-soluble components has many advantages. However, this raises the question of maintaining the functional properties and chemical structure of composites solid layers during long-term storage at ambient conditions. The processes of structural transformations during different stages of crystallization of hectapeptide composites with silver and gold nanoparticles in humid atmosphere were studied. The influence of temperature, humidity, nature of the substrate, its wetting, conformation of peptide molecules on the structure and electrophysical properties of the composites was considered also. Similarly to polymers two stages of crystallization were found: the initial fast and the subsequent slow. Unlike polymers, an increase in temperature does not affect this process, but even slows it down. Despite significant changes in the surface morphology of composites their electrophysical properties and conformation of molecules do not change. An increase in humidity accelerates the processes of the structural transitions. The results show that the changes in the surface morphology of PT composites under the influence of humidity relate only to the PT matrix itself and not to their locations or conformation of molecule. [ABSTRACT FROM AUTHOR]

Oscillations are one of the intrinsic features of many animate and inanimate systems. The oscillations manifest in the temporal periodic change of one or several physical quantities describing the systems. In chemistry and biology, this physical quantity is the concentration of the chemical species. In most chemical oscillatory systems operating in batch or open reactors, the oscillations persist because of the sophisticated chemical reaction networks incorporating autocatalysis and negative feedback. However, similar oscillations can be generated by periodically changing the environment providing non-autonomous oscillatory systems. Here we present a new strategy for designing a non-autonomous chemical oscillatory system for the zinc–methylimidazole. The oscillations manifested in the periodic change of the turbidity utilizing the precipitation reaction between the zinc ions and 2-methylimidazole (2-met) followed by a partial dissolution of the formed precipitate due to a synergetic effect governed by the ratio of the 2-met in the system. Extending our idea spatiotemporally, we also show that these precipitation and dissolution phenomena can be utilized to create layered precipitation structures in a solid agarose hydrogel. [ABSTRACT FROM AUTHOR]

Alkyl-methyl-imidazolium ionic liquidsCnmimX(n: alkyl-carbon number, X: anion) have short-range layer structures consisting of ionic and neutral (alkylchain) domains. To investigate the temperature dependences of the interlayer, interionic group, and inter-alkylchain correlations, we have measured the neutron diffraction (ND) of C16mimPF6, C9.5mimPF6, and C8mimPF6 in the temperature region from 4 K to 470 K. The quasielastic neutron scattering (QENS) of C16mimPF6 was also measured to study the dynamics of each correlation. C16mimPF6 shows a first-order transition between the liquid (L) and liquid crystalline (LC) phases at Tc = 394 K. C8mimPF6 exhibits a glass transition at Tg = 200 K. C9.5mimPF6, which is a 1:3 mixture between C8mimPF6 and C10mimPF6, has both transitions at Tc = 225 K and Tg = 203 K. In the ND experiments, all samples exhibit three peaks corresponding to the correlations mentioned above. The widths of the interlayer peak at ca. 0.2 Å-1 changed drastically at the L-LC transitions, while the interionic peaks at ca. 1 Å-1 exhibited a small jump at Tc. The peak position and area of the three peaks did not change much at the transition. The structural changes were minimal at Tg. The QENS experiments demonstrated that the relaxation time of the interlayer motion increased tenfold at Tc, while those of other motions were monotonous in the whole temperature region. The structural and dynamical changes mentioned above are characteristic of the L-LC transition in imidazolium-based ionic liquids. [ABSTRACT FROM AUTHOR]

The cellulose-based flower-like carbon-doped TiO2 particles were prepared by the one-step hydrothermal method, which was followed by high-temperature calcination. The morphology and composition of the samples were studied using Fourier-transform infrared spectroscopy, X-ray diffraction, scanning electron microscopy, and X-ray photoelectron spectroscopy. The flower-like carbon-doped TiO2 demonstrated a high absorption in the visible spectrum region, which originated from the combination of a layered solid structure and a narrow bandgap (Eg = 2.17 eV). The analysis of UV–Visible absorption spectra, photoluminescence spectra, and electron paramagnetic resonance spectroscopy revealed a high photocatalytic activity due to faster charge transfer in the visible region and a higher amount of ·O2−. The synergistic effect of the flower structure and carbon doping can significantly improve the photocatalytic activity. [ABSTRACT FROM AUTHOR]

Laser shock peening with ultrashort laser pulses has been studied by hydrodynamic and atomistic simulations, as well as experimentally. It has been shown that, in contrast to traditional nanosecond pulses, ultrashort laser pulses allow one to increase the produced pressures by two or three orders of magnitude from 1–10 GPa to 1000 GPa (1 TPa). The physics of phenomena changes fundamentally because shock waves generating pressures exceeding the bulk modulus of a metal melt it. It has been shown for the first time that the shock melting depth at pressures about 1 TPa is an order of magnitude larger than the thickness of the melt layer caused by heat conduction. The appearance, propagation, and damping of a melting shock wave in titanium have been studied. The damping of the shock wave makes it possible to modify the surface layer, where the melting regime changes from a fast one in the shock jump to a slow propagation of the melting front in the unloading tail behind the shock wave. It has been shown experimentally that the ultrafast crystallization of the melt forms a solid layer with a structure strongly different from that before the action. The measured depth of this layer is in good agreement with the calculation. [ABSTRACT FROM AUTHOR]

Background: Modern zirconia blanks for the fabrication of dental CAD/CAM restorations provide a layer structure with color and strength transitions. Variation in the yttria content has a particular effect on the characteristics of the materials. The properties of dental restorations may vary depending on the milling position within the blank. Especially for wide-span fixed partial dentures (FPDs), relevant effects on clinical performance might result. This study investigated if the application of high-translucent zirconia and positioning within multilayer zirconia blanks affect the in vitro performance of 4-unit FPDs. Methods: 4-unit FPDs were fabricated from monolayer 3Y-TZP-A, 3Y-TZP, 4Y-TZP, 5Y-TZP, 4Y/5Y-TZP, and different positions within multilayer zirconia blanks (3Y-TZP/5Y-TZP). The FPDs were adhesively luted to resin abutment teeth, divided into groups (n = 8 each): "baseline" (24 h water-storage)/"TCML" (chewing simulation by means of thermalcycling and mechanical loading), and loaded to fracture. The statistics included mean and standard deviation, one-way ANOVA, Bonferroni post hoc test, and Pearson correlation (α = 0.05). Results: The mean fracture force values varied between 803.8 ± 171.7 N (5Y) and 1474.1 ± 193.0 N (3Y) (baseline) and 713.5 ± 190.9 N (5Y) and 1337.4 ± 205.6 N (3Y) (TCML). Significantly different (p = 0.000) results between the groups and individual significant differences (p ≤ 0.039) were found. Conclusions: Positioning within multilayer blanks affected the fracture force only slightly. Multilayer, 3Y-TZP-A, 3Y-TZP, and 4Y-TZP seem appropriate for the clinical application with 4-unit molar FPDs. Application of 5Y-TZP is critical. [ABSTRACT FROM AUTHOR]

In this paper, we analyze the radiative heat transport in layered structures. The analysis is based on our prior description of the spectrum of thermally excited waves in systems with a heat flux. The developed method correctly predicts results for all known special cases for both large and closing gaps. Numerical examples demonstrate the applicability of our approach to the calculation of the radiative heat transport coefficient across various layered structures. [ABSTRACT FROM AUTHOR]

Screening is one of the most important concepts in the study of charged systems. Near a dielectric interface, the ion distribution in a salt solution can be highly nonuniform. Here, we develop a theory that self-consistently treats the inhomogeneous screening effects. At higher concentrations when the bulk Debye screening length is comparable to the Bjerrum length, the double layer structure and interfacial properties are significantly affected by the inhomogeneous screening. In particular, the depletion zone is considerably wider than that predicted by the bulk screening approximation or the WKB approximation. The characteristic length of the depletion layer in this regime scales with the Bjerrum length, resulting in a linear increase of the negative adsorption of ions with concentration, in agreement with experiments. For asymmetric salts, inhomogeneous screening leads to enhanced charge separation and surface potential. [ABSTRACT FROM AUTHOR]

For the first time, all stages of non-equilibrium crystallization of multicomponent peptide solutions have been studied in detail, starting with the formation of colloidal dispersions and ending with the growth of solid layers. The crystallization of a short dipeptide (DPT-0), its potassium salt (DPT-1) and K2CO3 in aqueous solutions was studied. DPT-0 and DPT-1 form colloidal solutions in which the particle size depends on the charge of the DPT molecule. In comparison with DPT-0, in the case of DPT-1 the particle size doubles and the coalescence of colloidal particles begins with the formation of micron-sized aggregates. When DPT solutions are applied to solid surfaces, colloidal particles disintegrate. With an excess of K2CO3, its stratification at the droplet border is observed. Depending on the charge of the DPT molecule (neutral or anion), not only the surface morphology of layers but also their electron energy and chemical structures change. In DPT-1 layers on gold and graphite, unlike DPT-0, in addition to bipolar resistive switching and residual polarization the sharp negative jumps of tunneling current appear. The reason for this are K+ ions, which create one-electron traps in the near-electrode region. Of particular interest is the opposite direction of the residual polarization vector of DPT-1 layers on graphite and gold. The molecular packaging, the structure and morphology of the growing layers are determined by the nature of the substrate–layer interfaces, which create a template for layer growth. The adsorption of DPT-1 leads to the destruction of salt bridges and a change in the ratio of α-helix to β-sheet structures. On gold all the layers of DPTs and K2CO3 are composed of globules, the sizes of which are 40–100 nm. On the graphite surface, islands are observed with a height of 1–2 monolayers and protofibrils with a width of 17–20 nm and a height of 1–2 nm. With increasing layer thickness, protofibrils form mature fibrils. An analysis of all the results obtained shows that they are determined by the nature of the conformational changes of peptide molecules in adsorption layers on different substrates, and the structure of the peptide solid layers laid already at the stage of its adsorption. The various models of the adsorption of DPT on different substrates and the possibility of practical use of the results are considered. [ABSTRACT FROM AUTHOR]

The Lennard-Jones potential is widely used to describe the interlayer interactions within layered materials like graphene. However, it is also widely known that this potential strongly underestimates the frictional properties for layered materials. Here, we propose to supplement the Lennard-Jones potential by a Gaussian-type potential, which enables more accurate calculations of the frictional properties of two-dimensional layered materials. Furthermore, the Gaussian potential is computationally simple as it introduces only one additional potential parameter that is determined by the interlayer shear mode in the layered structure. The resulting Lennard-Jones-Gaussian potential is applied to compute the interlayer cohesive energy and frictional energy for graphene, MoS2, black phosphorus, and their heterostructures. [ABSTRACT FROM AUTHOR]

The skyrmionic state is an exciting realm of study and the skyrmions are being explored as the promising candidates of information carriers. In most systems, the skyrmions originate from the Dzyaloshinsky-Moriya interaction (DMI). However, in this work, it is demonstrated that in the triple-layer CoPt/Co/CoPt structure, the skyrmion-like state can be formed not only in the CoPt layers but also in the middle Co layer, without DMI. In this new structure, the skyrmion-like state in Co layer can exist in a large CoPt thickness range with thick Co. It can be very stable even against the external field from –500 to 200mT along Z axis. The skyrmion number (S) in Co (SCo) can be as large as 0.9. These advanced properties make it high application potential for the future information-processing and storage devices. [ABSTRACT FROM AUTHOR]

A supersaturated solid solution nanostructure of an immiscible Co Cu system is among the promising nanocrystalline (NC) alloys offering enhanced thermal and mechanical stability. In this paper, experiments were conducted to study the phase transformation and tailoring microstructure from a homogeneous/single-phase to a heterogeneous/dual-phase solid solution layered Co Cu nanostructure via pulsed electrochemical deposition (PED). The increasing concentration of sodium dodecyl sulfate (SDS) in electrolyte played a crucial role in stabilizing a homogeneous solid solution Co Cu nanostructure. On the other hand, the opposite approach led to the formation of heterogeneous solid solution Co Cu alloys in the form of multilayered nanostructure consisting of the primary and secondary solid solution Co Cu differing in 10–15 at.% Cu. The separation of primary and secondary phase is more prominent with the extended pulsed periods. The mechanical properties of selected single- and dual-phase alloys were investigated through micro-pillar compression, revealing that a combination of a high yield strength and an elevated strain hardening can be achieved in NC materials through a combined solid solution strengthening and hardening through nano-twin (NT). [Display omitted] • Pulsed deposition of homogeneous and heterogeneous solid solution Co Cu nanostructure • SDS plays the vital roles to stabilize homogeneous nanostructure. • Heterogeneous nanostructure was more pronounced with extended pulse period. • The deposits show the highest yield strength among nanostructure Cu, Co, and Co Cu alloys. [ABSTRACT FROM AUTHOR]

Six recently developed exchange functionals for pairing with two different versions of van der Waals density functionals (vdW-DF) are tested for weakly bonded solids. The test, using 26 layered weakly bonded compounds, benchmarks the lattice constants against experimental data and the interlayer binding energies against reference data from the random-phase approximation (RPA). The investigated functionals tend to give interlayer binding energies higher than the RPA benchmark, and the overall performance for lattice constants is good. The exchange functionals optB86b and cx13 paired with the original vdW-DF and the B86R functional paired with vdW-DF2 are found to give particularly good results for equilibrium geometries. [ABSTRACT FROM AUTHOR]

The thin-film multilayer structure of the membrane-electrode assembly in a solid oxide fuel cell which involves a NiO/ZrO2:Y2O3 anode functional layer and a La0.6Sr0.4CoO3 cathode functional layer and also a bilayer ZrO2:Y2O3/Ce0.9Gd0.1O1.95 electrolyte is formed by magnetron sputtering onto a supporting NiO/ZrO2:Y2O3 anode. The effect of the functional electrode layers involved in the structure of a solid oxide fuel cell on its efficiency is studied. The volt–ampere characteristics of multilayer fuel cells are studied in the temperature range of 800–600°C. It is shown that the inclusion of a thin (600 nm thick) cathode functional layer into the structure of the membrane–electrode assembly enhances the fuel cell efficiency by reducing the polarization losses on electrodes. The maximum power density of the fuel cell with the cathode functional layer is 2290 and 500 mW/cm2 at 800 and 600°С, respectively. The simultaneous presence of anode and cathode functional layers is found to be unwelcome because gives rise to diffusion limitations on the anode. [ABSTRACT FROM AUTHOR]

In Present decade, polymer nanocomposites are extensively used for manufacturing of automotive, aircraft structural components. The polymer nanocomposites properties enhancement depends upon dispersion quality of nanofiller. Recently, hexagonal boron nitride (hBN) nanosheets is one of the most attractive nanofiller; a white solid with a layered structure, physically or structurally similar to graphite, also known as White graphene. In the present work, the hBN nanosheets are prepared by surfactant assisted liquid-phase exfoliation method using ethanol as solvent. The surfactant used is a block copolymer of polyethylene oxide-polypropylene oxide-polyethylene oxide (PEO-PPO-PEO). Although ethanol is a poor solvent, but it is a green solvent. A highly concentrated and stable dispersion of hBN nanosheets (~0.45 mg/ml) is obtained by probe sonication followed by centrifugation. The surfactant modified hBN nanosheets reinforced epoxy nanocomposites are prepared by an open casting method and characterized by various characterization techniques. At 0.08 wt% of surfactant modified hBN nanosheets incorporation in epoxy matrix show enhancement in flexural modulus and strength is by 3.6% and 5.7%. There is a multilayer dispersion of surfactant modified hBN nanosheets in epoxy matrix facilitating the dampening of cracks for flexural properties enhancement. [ABSTRACT FROM AUTHOR]

In this article, we describe one possible way to modify volume tasks in textbooks to promote conceptual understanding of the volume formula: length × width × height. From the results of previous studies regarding students' understanding of volume measurement, we identified three conceptual ideas key to understanding volume: filling three-dimensional space with equal-sized units, layer structure, and linking layer structure to the volume formula. Our examination of three popular US textbook series showed that these three conceptual ideas were not well-presented. We conclude with recommendations for one possible way to modify tasks to improve conceptually-based volume instruction. [ABSTRACT FROM AUTHOR]

Since the year 2000, Greenland ice sheet mass loss has been dominated by a decrease in surface mass balance rather than an increase in solid ice discharge. Southeast Greenland is an important region to understand how high accumulation rates can offset increasing Greenland ice sheet meltwater runoff. To that end, we derive a new 9-year long dataset (2009–17) of accumulation rates in Southeast Greenland using NASA Operation IceBridge snow radar. Our accumulation dataset derived from internal layers focuses on high elevations (1500–3000 m) because at lower elevations meltwater percolation obscured internal layer structure. The uncertainty of the radar-derived accumulation rates is 11% [using Firn Densification Model (FDM) density profiles] and the average accumulation rate ranges from 0.5 to 1.2 m w.e. With our observations spanning almost a decade, we find large inter-annual variability, but no significant trend. Accumulation rates are compared with output from two regional climate models (RCMs), MAR and RACMO2. This comparison shows that the models are underestimating accumulation in Southeast Greenland and the models misrepresent spatial heterogeneity due to an orographically forced bias in snowfall near the coast. Our dataset is useful to fill in temporal and spatial data gaps, and to evaluate RCMs where few in situ measurements are available. [ABSTRACT FROM AUTHOR]

Fast ice flow on the Antarctic continent constitutes much of the mass loss from the ice sheet. However, geophysical methods struggle to constrain ice flow history at depth, or separate the signatures of topography, ice dynamics and basal conditions on layer structure. We develop and demonstrate a methodology to compare layer signatures in multiple airborne radar transects in order to characterize ice flow at depth, or improve coverage of existing radar surveys. We apply this technique to generate synthetic, along-flow radargrams and compare different deformation regimes to observed radargram structure. Specifically, we investigate flow around the central sticky spot of Whillans Ice Stream, West Antarctica. Our study suggests that present-day velocity flowlines are insufficient to characterize flow at depth as expressed in layer geometry, and streaklines provide a better characterization of flow around a basal sticky spot. For Whillans Ice Stream, this suggests that ice flow wraps around the central sticky spot, supported by idealized flow simulations. While tracking isochrone translation and rotation across survey lines is complex, we demonstrate that our approach to combine radargram interpretation and modeling can reveal critical details of past ice flow. [ABSTRACT FROM AUTHOR]

2D van der Waals layered heterostructures allow for a variety of energy band offsets, which help in developing valuable multifunctional devices. However, p–n diodes, which are typical and versatile, are still limited by the material choice due to the fixed band structures. Here, the vanadium dopant concentration is modulated in monolayer WSe2 via chemical vapor deposition to demonstrate tunable multifunctional quantum tunneling diodes by vertically stacking SnSe2 layers at room temperature. This is implemented by substituting tungsten atoms with vanadium atoms in WSe2 to provoke the p‐type doping effect in order to efficiently modulate the Fermi level. The precise control of the vanadium doping concentration is the key to achieving the desired quantum tunneling diode behaviors by tuning the proper band alignment for charge transfer across the heterostructure. By constructing a p–n diode for p‐type V‐doped WSe2 and heavily degenerate n‐type SnSe2, the type‐II band alignment at low V‐doping concentration is clearly shown, which evolves into the type‐III broken‐gap alignment at heavy V‐doping concentration to reveal a variety of diode behaviors such as forward diode, backward diode, negative differential resistance, and ohmic resistance. [ABSTRACT FROM AUTHOR]

Jacutingaite (Pt2HgSe3) is a recently discovered layered platinum‐group mineral. Recent experimental studies have shown that it displays the properties of a quantum spin Hall insulator (QSHI), and theoretical studies indicate that its two‐dimensional monolayer is a QSHI with a robust topological gap of ∼0.5 eV. Jacutingaite is thus promising for potential applications to nanoelectronics and spintronics. The Raman spectrum of three‐dimensional bulk jacutingaite and the symmetries of its vibrational modes, fundamental for understanding structural modifications of this material, are still unexplored. Here, we address the zone‐center Raman optical phonons of bulk jacutingaite by experiments, symmetry, and first‐principles calculations. The improved synthesis used here provided crystals of higher purity and of micrometer size, allowing the study of single crystals. Polarized Raman spectroscopy was used to assign the symmetries of nine out of the 11 Raman‐active modes expected by group theory and their respective selection rules. The calculated wavenumbers of the Raman‐active modes, in addition to their atomic displacements, are in very good agreement with experiments. In addition, we discuss the use of different exchange correlation functionals within density functional theory, as local functionals and nonlocal functionals that best describe van der Waals interactions. The influence of the inclusion of spin–orbit coupling on calculated vibrational phonon wavenumbers and lattice parameters is commented, and it was found that the local density approximation provides a good description. Our results are of paramount importance to further exploitation of the effects of jacutingaite's structural modifications to tune its properties, as well as for its structural, optical, electronic, mechanical, and thermal applications. [ABSTRACT FROM AUTHOR]

Phase separation kinetics of a binary (A,B) mixture contained in a thin film of thickness D induced by a quench from the one-phase region into the miscibility gap is studied by simulations using a Cahn-Hilliard-Cook model. The initial randomly mixed state (50% A, 50% B) contains a concentration gradient perpendicular to the film, while the surfaces of the film are 'neutral' (no preference for either A or B). In thermal equilibrium, a pattern of large A-rich and B-rich domains must result, separated by domain walls oriented perpendicularly to the external surfaces of the thin film. However, it is shown that for many choices of D and the strength of the initial gradient Ψg, instead a very long-lived metastable layered structure forms, with two domains separated by a single interface parallel to the external walls. The transient time evolution that leads to this structure is interpreted in terms of a competition between domain growth in the bulk and surface-directed spinodal decomposition caused by the gradient during the initial stages. A surprising and potentially useful finding is that a moderate concentration gradient perpendicular to the film does not favor the layered structure but facilitates the approach toward the true equilibrium with just two domain walls perpendicular to the film. This mechanism may have useful applications in producing layered materials. [ABSTRACT FROM AUTHOR]

In situ x-ray diffraction experiments on rhenium hydride compressed up to 46 GPa reveal a hydrogen solubility (x) significantly larger than the previously assumed saturation limit of x ∼ 0.38(4). In the layered anti-CdI2-type structure of rhenium hydride, the hydrogen solubility was found to increase to x ∼ 0.5 at 15 GPa over time. When heated to temperatures above 420 K at pressures above 23 GPa, rhenium hydride undergoes an isomorphous phase transition into the NiAs-type structure accompanied by an increase in hydrogen solubility to x ∼ 0.85. The formation of fully stoichiometric rhenium hydride is discussed. [ABSTRACT FROM AUTHOR]

Early transition metal dichalcogenides (TMDC), characterized by their quasi-two-dimensional layered structure, have attracted intensive interest due to their versatile chemical and physical properties, but a comprehensive understanding of their structural and electronic properties from a first-principles point of view is still lacking. In this work, four simple TMDC materials, MX2 (M = Zr and Hf, X = S and Se), are investigated by the Kohn-Sham density functional theory (KS-DFT) with different local or semilocal exchange-correlation (xc) functionals and many-body perturbation theory in the GW approximation. Although the widely used Perdew-Burke-Ernzelhof (PBE) generalized gradient approximation (GGA) xc functional overestimates the interlayer distance dramatically, two newly developed GGA functionals, PBE-for-solids (PBEsol) and Wu-Cohen 2006 (WC06), can reproduce experimental crystal structures of these TMDC materials very well. The GW method, currently the most accurate first-principles approach for electronic band structures of extended systems, gives the fundamental band gaps of all these materials in good agreement with the experimental values obtained from optical absorption. The minimal direct gaps from GW are systematically larger than those measured from thermoreflectance by about 0.1-0.3 eV, implying that excitonic effects may be stronger than previously estimated. The calculated density of states from GW quasi-particle band energies agrees very well with photo-emission spectroscopy data. Ionization potentials of these materials are also computed by combining PBE calculations based on the slab model and GW quasi-particle corrections. The calculated absolute band energies with respect to the vacuum level indicate that that ZrS2 and HfS2, although having suitable band gaps for visible light absorption, cannot be used for overall water splitting as a result of mismatch of the conduction band minimum with the redox potential of H+/H2. [ABSTRACT FROM AUTHOR]

This study investigates the propagation of Lamb waves in a phononic crystal plate in the form of a staggered-layer structure. Using the analyses of the band structures and the transmission spectra, a significant modulation to the lower-order Lamb modes is demonstrated due to the staggered arrangement. The modulation leads to remarkable changes in the location and width of the phononic band gaps. We further identify the physical mechanism for the effects of the staggered-layer through the particle displacement fields of the eigenmodes. The symmetric mode converts to the antisymmetric mode and vice versa with the existence of the staggered arrangement. In addition, we find that the phononic band gaps are very sensitive to the degree of stagger, which could be indispensable to practical applications such as band gap tuning. [ABSTRACT FROM AUTHOR]

We conducted comparison of the original experimental data of the temperature dependences of thermal expansion in crystals with layered crystalline structure. It is shown that in most crystals with layered structure (graphite, boron nitride, GaSe, GaS, and InSe) the effect of negative thermal expansion can be explained by the specific character of the phonon spectra. It was shown, that in contrast to other crystals with layered structure, negative thermal expansion in the layers' plane of TlGaSe2 is the result of negative area compressibility. We demonstrate that the thermal expansion of TlGaSe2 crystals can be controlled by illumination, external electric field, and thermal annealing. The nature of observed effects and a special mechanism of the negative area compressibility in TlGaSe2 crystals are discussed. [ABSTRACT FROM AUTHOR]

Magnetic cobalt nanoparticles encapsulated in shells of layered structure have been produced by the technique of pulsed laser ablation in toluene. The morphology, microstructure, and magnetic properties of the prepared nanoparticles were characterized by electron microscopy, micro-Raman spectroscopy, and superconducting quantum interference device magnetometry, respectively. The results indicated that the cobalt nanoparticles fabricated are noncrystalline but coated with the graphitic carbon layers. It is believed that the formation of these carbon layers well-protect the cobalt nanoparticles to be oxidized thus maintaining the superparamagnetic property. This is an important feature that makes the cobalt nanoparticles a useful material for medical and many other magnetic based applications. [ABSTRACT FROM AUTHOR]

We propose to utilize multiple-graphene-layer structures with lateral p-i-n junctions for terahertz and infrared (IR) photodetection and substantiate the operation of photodetectors based on these structures. Using the developed device model, we calculate the detector dc responsivity and detectivity as functions of the number of graphene layers and geometrical parameters and show that the dc responsivity and detectivity can be fairly large, particularly, at the lower end of the terahertz range at room temperatures. Due to relatively high quantum efficiency and low thermogeneration rate, the photodetectors under consideration can substantially surpass other terahertz and IR detectors. Calculations of the detector responsivity as a function of modulation frequency of THz and IR radiation demonstrate that the proposed photodetectors are very fast and can operate at the modulation frequency of several tens of gigahertz. [ABSTRACT FROM AUTHOR]