Synergy of orientational relaxation between bound water and confined water in ice cold-crystallization.

Cold-crystallization of systems with high glass-forming ability, such as medium-concentrated aqueous solutions, metallic glass formers and polymers, is a phenomenon of fundamental interest. In medium-concentrated aqueous solutions, bulk-like free water disappears and water comprises bound water and confined water surrounded by closely compacted hydrated solutes. Here, we used dielectric spectroscopic measurements of aqueous glycerol solutions to show that bound water and confined water participate in the cold-crystallization of water in a dynamically synergetic manner. Cold-crystallization of water begins when orientational relaxations of these two kinds of water are in concert. Notably, complete dehydration of some glycerol molecules occurs upon cold-crystallization of water, and these molecules become fully rehydrated just after this event. Hence, bound water is also crystallizable in intermediate concentrated glycerol solutions; although the same amount of water molecules as that of bound water do not eventually participate in cold-crystallization. This observation is significantly different from the traditionally suggested non-crystallization of bound water in dilute solutions. This work suggests the need to reevaluate the role of bound water in water crystallization, and might also reveal the mechanism of cold-crystallization occurring in metallic glass formers and polymers.

Ultrasensitive Self-Powered Flexible Crystalline ß-Ga2O3-Based Photodetector Obtained through Lattice Symmetry and Band Alignment Engineering.

Due to its portable and self-powered characteristics, the construction of Ga2O3-based semiconductor flexible devices that can improve the adaptability in various complex environments have drawn great attention in recent decades. However, conventional Ga2O3-based flexible heterojunctions are based on either amorphous or poor crystalline Ga2O3 materials, which severely limit the performance of the corresponding devices. Here, through lattice-symmetry and energy-band alignment engineering, we construct a high-quality crystalline flexible NiO/ß-Ga2O3 p-n self-powered photodetector. Owing to its suitable energy-band alignment structure, the device shows a high photo-to-dark current ratio (1.71 × 105) and a large detection sensitivity (6.36 × 1014 Jones) under zero bias, which is superior than most Ga2O3 self-powered photodetectors even for those based on rigid substrates. Moreover, the fabricated photodetectors further show excellent mechanical stability and robustness in bending conditions, demonstrating their potential practical applications in flexible optoelectronic devices. These findings provide insights into the manipulation of crystal lattice and energy band engineering in flexible self-powered photodetectors and also offer guideline for designing other Ga2O3-based flexible electronic devices.

Freestanding Crystalline ß-Ga2O3 Flexible Membrane Obtained via Lattice Epitaxy Engineering for High-Performance Optoelectronic Device.

Wearable and flexible ß-Ga2O3-based semiconductor devices have attracted considerable attention, due to their outstanding performance and potential application in real-time optoelectronic monitoring and sensing. However, the unavailability of high-quality crystalline and flexible ß-Ga2O3 membranes limits the fabrication of relevant devices. Here, through lattice epitaxy engineering together with the freestanding method, we demonstrate the preparation of a robust bending-resistant and crystalline ß-Ga2O3 (-201) membrane. Based on this, we fabricate a flexible ß-Ga2O3 photodetector device that shows comparable performance in photocurrent responsivity and spectral selectivity to conventional rigid ß-Ga2O3 film-based devices. Moreover, based on the transferred ß-Ga2O3 membrane on a silicon wafer, the PEDOT:PSS/ß-Ga2O3 p-n heterojunction device with self-powered characteristic was constructed, further demonstrating its superior heterogeneous integration ability with other functional materials. Our results not only demonstrate the feasibility of obtaining a high-quality crystalline and flexible ß-Ga2O3 membrane for an integrated device but also provide a pathway to realize flexible optical and electronic applications for other semiconducting materials.

Unveiling Strong Ion-Electron-Lattice Coupling and Electronic Antidoping in Hydrogenated Perovskite Nickelate.

Despite being highly promising for applications in emergent electronic devices, decoding both the ion-electron-lattice coupling in correlated materials at the atomic scale and the electronic band structure remains a big challenge due to the strong and complex correlation among these degrees of freedom. Here, taking an epitaxial thin film of perovskite nickelate NdNiO3 as a model system, hydrogen-ion-induced giant lattice distortion and enhanced NiO6 octahedra tilting/rotation are demonstrated, which leads to a new robust hydrogenated HNdNiO3 phase with lattice expansion larger than 10% on a series of substrates. Moreover, under the effect of ion-electron synergistic doping, it is found that the proposed electronic antidoping, i.e., the doped electrons mainly fill the ground-state oxygen 2p holes instead of changing the Ni oxidation state from Ni3+ to Ni2+ , dominates the metal-insulator transition. Meanwhile, lattice modification with enhanced Ni-O-Ni bond tilting or rotation mainly modifies the orbital density of states near the Fermi level. Last, by electric-field-controlled hydrogen-ion intercalation and its strong coupling to the lattice and electron charge, selective micrometer-scale patterns with distinct structural and electronic states are fabricated. The results provide direct evidence for a strong ion-electron-lattice coupling in correlated physics and exhibit its potential applications in designing novel materials and devices.

Diffusions in Aqueous Solutions with Multivalent Cations and Especially in Cationic First Hydration Shell.

Compared with univalent cationic diffusion, little is known about the diffusion behavior of multivalent cations let alone the diffusion of water in their first hydration shell. Here, we show that all published translational diffusion coefficients of multivalent cations and water measured at room temperature exhibit the same concentration dependence when plotted as a function of the mass fraction of free water or of hydrated solute. This behavior is held until only hydration and confined water remain in solutions, wherein their concentration dependences become cationic charge number-dependent. We also found that the iceberg model can well describe the diffusions of multivalent cations with decreasing water content until only hydration water is present. However, 1H-pulsed-field-gradient nuclear magnetic resonance measurements confirmed that 1H in the first hydration shell diffuses faster than Al3+ at room temperature and they have the same diffusion coefficient only with decreasing the temperature down to about 243 K. Therefore, iceberg model only equivalently describes the effect of strong ion-water interaction on multivalent cationic diffusion. These results will also help us reconceive our current understanding of the pathway for hydration water affecting the diffusion behavior of solutes with relatively weak solute-water interactions.

Stress-driven buckling patterns in spheroidal core/shell structures.

Many natural fruits and vegetables adopt an approximately spheroidal shape and are characterized by their distinct undulating topologies. We demonstrate that various global pattern features can be reproduced by anisotropic stress-driven buckles on spheroidal core/shell systems, which implies that the relevant mechanical forces might provide a template underpinning the topological conformation in some fruits and plants. Three dimensionless parameters, the ratio of effective size/thickness, the ratio of equatorial/polar radii, and the ratio of core/shell moduli, primarily govern the initiation and formation of the patterns. A distinct morphological feature occurs only when these parameters fall within certain ranges: In a prolate spheroid, reticular buckles take over longitudinal ridged patterns when one or more parameters become large. Our results demonstrate that some universal features of fruit/vegetable patterns (e.g., those observed in Korean melons, silk gourds, ribbed pumpkins, striped cavern tomatoes, and cantaloupes, etc.) may be related to the spontaneous buckling from mechanical perspectives, although the more complex biological or biochemical processes are involved at deep levels.

New State-Diagram of Aqueous Solutions Unveiling Ionic Hydration, Antiplasticization, and Structural Heterogeneities in LiTFSI-H2O.

Here, we report a new state-diagram for aqueous solutions based on concentration-dependent glass-transition temperatures of concentrated and ice freeze-concentrated solutions. Different from the equilibrium phase diagram, this new state-diagram can provide comprehensive information about the hydration numbers of solutes, nonequilibrium vitrification/cold-crystallization, and vitrification/devitrification processes of aqueous solutions in three distinct concentration zones separated by two critical water-content points of only functions of the hydration number. Based on this new state-diagram, we observe the comparable hydration ability of LiTFSI to LiCl and an atypical concentration-dependent cold-crystallization behavior of the LiTFSI-H2O system. These results unveil the negligible hydration ability of TFSI- in a water-rich solution, characterize the antiplasticizing effect of water induced by the strengthened Li+-TFSI--H2O interaction when only hydration water and confined water are present, and confirm the increasing fraction of water-rich domains with the decrease in water content when the cation and anion become incompletely hydrated on average. These results highlight the novel water-content-mediated interactions among the anion, cation, and H2O for LiTFSI-H2O.

Tracing the ionic evolution during ILG induced phase transformation in strontium cobaltite thin films.

Ionic liquid gating (ILG) that drives the ions incorporate into or extract from the crystal lattice, has emerged as a new pathway to design materials. Although many intriguing emergent phenomena, novel physical properties and functionalities have been obtained, the gating mechanism governing the ion and charge transport remains unexplored. Here, by using the model system of brownmillerite SrCoO2.5 and the corresponding electric-field controlled tri-state phase transformation among the pristine SrCoO2.5, hydrogenated HSrCoO2.5 and oxidized perovskite SrCoO3-δ through the dual ion switch, the ionic diffusion and electronic transport processes were carefully investigated. Through controlling gating experiment by design, we find out that the collaborative interaction between charge transport and ion diffusion plays an essential role to prompt the hydrogen or oxygen ions incorporate into the crystal lattice of SrCoO2.5, and therefore leading to formation of new phases. At region closer to the electrode, the electron can shuttle more readily in (out) the material, correspondingly the incorporation of hydrogen (oxygen) ions and phase transformation is largely affiliated. With the compensated charge of electron as well as the reaction front gradually moving away from the electrode, the new phases would be developed successively across the entire thin film. This result unveils the underlying mechanism in the electric-field control of ionic incorporation and extraction, and therefore provides important strategy to achieve high efficient design of material functionalities in complex oxide materials.

Minimum Vertex-type Sequence Indexing for Clusters on Square Lattice.

An effective indexing scheme for clusters that enables fast structure comparison and congruence check is desperately desirable in the field of mathematics, artificial intelligence, materials science, etc. Here we introduce the concept of minimum vertex-type sequence for the indexing of clusters on square lattice, which contains a series of integers each labeling the vertex type of an atom. The minimum vertex-type sequence is orientation independent, and it builds a one-to-one correspondence with the cluster. By using minimum vertex-type sequence for structural comparison and congruence check, only one type of data is involved, and the largest amount of data to be compared is n pairs, n is the cluster size. In comparison with traditional coordinate-based methods and distance-matrix methods, the minimum vertex-type sequence indexing scheme has many other remarkable advantages. Furthermore, this indexing scheme can be easily generalized to clusters on other high-symmetry lattices. Our work can facilitate cluster indexing and searching in various situations, it may inspire the search of other practical indexing schemes for handling clusters of large sizes.

The decisive role of free water in determining homogenous ice nucleation behavior of aqueous solutions.

It is a challenging issue to quantitatively characterize how the solute and pressure affect the homogeneous ice nucleation in a supercooled solution. By measuring the glass transition behavior of solutions, a universal feature of water-content dependence of glass transition temperature is recognized, which can be used to quantify hydration water in solutions. The amount of free water can then be determined for water-rich solutions, whose mass fraction, Xf, is found to serve as a universal relevant parameter for characterizing the homogeneous ice nucleation temperature, the meting temperature of primary ice, and even the water activity of solutions of electrolytes and smaller organic molecules. Moreover, the effects of hydrated solute and pressure on ice nucleation is comparable, and the pressure, when properly scaled, can be incorporated into the universal parameter Xf. These results help establish the decisive role of free water in determining ice nucleation and other relevant properties of aqueous solutions.

Mutual Effects of Glycerol and Inorganic Salts on Their Hydration Abilities.

It is a tough challenge to understand the mutual interactions among various components in aqueous solutions of inorganic mixed with organic solutes. The hydration number, nh, and critical hydration number, ncr, determined by the measurements of glass transition of the solutions, in conjunction with tracing the change in local water structure, can provide some insights into the complicated interplays in such a mixture. Here, the nh and ncr for aqueous solutions of glycerol, various chlorides, and mixtures of glycerol with a chloride are determined. The ratio of ncr/nh measures 4 for glycerol and 1.7 for all the chlorides, and for mixtures of glycerol with all of the chlorides except ZnCl2, it falls within these two extremes. Glycerol content dependence of nh and ncr reveals a rich and interesting scenario of mutual effects therein, in particular, the glycerol's replacement and sharing of hydration water with salt. In the case of ZnCl2, at most, one hydration water molecule is replaced by glycerol, and the excess glycerol molecules continuously reduce the number of glycerol molecules that share hydration water with ZnCl2. Our results can help establish a pathway for the investigation of interactions among the organic and inorganic components in aqueous solutions, which is desirable for many applications.

Glass transition of aqueous solutions involving annealing-induced ice recrystallization resolves liquid-liquid transition puzzle of water.

Liquid-liquid transition of water is an important concept in condensed-matter physics. Recently, it was claimed to have been confirmed in aqueous solutions based on annealing-induced upshift of glass-liquid transition temperature, T(g) . Here we report a universal water-content, X(aqu) , dependence of T(g) for aqueous solutions. Solutions with X(aqu)>X(cr)(aqu)vitrify/devitrify at a constant temperature, ~T(g) , referring to freeze-concentrated phase with X(aqu)left behind ice crystallization. Those solutions with X(aqu)

A surface curvature oscillation model for vapour-liquid-solid growth of periodic one-dimensional nanostructures.

While the vapour-liquid-solid process has been widely used for growing one-dimensional nanostructures, quantitative understanding of the process is still far from adequate. For example, the origins for the growth of periodic one-dimensional nanostructures are not fully understood. Here we observe that morphologies in a wide range of periodic one-dimensional nanostructures can be described by two quantitative relationships: first, inverse of the periodic spacing along the length direction follows an arithmetic sequence; second, the periodic spacing in the growth direction varies linearly with the diameter of the nanostructure. We further find that these geometric relationships can be explained by considering the surface curvature oscillation of the liquid sphere at the tip of the growing nanostructure. The work reveals the requirements of vapour-liquid-solid growth. It can be applied for quantitative understanding of vapour-liquid-solid growth and to design experiments for controlled growth of nanostructures with custom-designed morphologies.

Directional scaling symmetry of high-symmetry two-dimensional lattices.

Two-dimensional lattices provide the arena for many physics problems of essential importance, a scale symmetry, which rarely exists as noticed by Galileo, in such lattices can help reveal the underlying physics. Here we report the discovery and proof of directional scaling symmetry for high symmetry 2D lattices, i.e., the square lattice, the equilateral triangular lattice and thus the honeycomb lattice, with aid of the function y = arcsin(sin(2πxn)), where the parameter x is either the platinum number µ = 2 - √3 or the silver number λ = √2 - 1, which are related to the 12-fold and 8-fold quasiperiodic structures, respectively. The directions and scale factors for the symmetric scaling transformation are determined. The revealed scale symmetry may have a bearing on various physical problems modeled on 2D lattices, and the function adopted here can be used to generate quasiperiodic lattices with enumeration of lattice points. Our result is expected to initiate the search of directional scaling symmetry in more complicated geometries.

Nearly constant electrical resistance over large temperature range in Cu3NMx (M = Cu, Ag, Au) compounds.

Electrical resistance is a material property that usually varies enormously with temperature. Constant electrical resistivity over large temperature range has been rarely measured in a single solid. Here we report the growth of Cu3NMx (M = Cu, Ag, Au) compound films by magnetron sputtering, aiming at obtaining single solids of nearly constant electrical resistance in some temperature ranges. The increasing interstitial doping of cubic Cu3N lattice by extra metal atoms induces the semiconductor-to-metal transition in all the three systems. Nearly constant electrical resistance over 200 K, from room temperature downward, was measured in some semimetallic Cu3NMx samples, resulting from opposite temperature dependence of carrier density and carrier mobility, as revealed by Hall measurement. Cu3NAgx samples have the best performance with regard to the range of both temperature and doping level wherein a nearly constant electrical resistance can be realized. This work can inspire the search of other materials of such a quality.

Self-assembled triangular and labyrinth buckling patterns of thin films on spherical substrates.

We investigated the possibility of controlling thin film buckling patterns by varying the substrate curvature and the stress induced therein upon cooling. The numerical and experimental studies are based on a spherical Ag core/SiO(2) shell system. For Ag substrates with a relatively larger curvature, the dentlike triangular buckling pattern comes out when the film nominal stress exceeds a critical value. With increasing film stress and/or substrate radius, the labyrinthlike buckling pattern takes over. Both the buckling wavelength and the critical stress increase with the substrate radius.

Effect of well confinement on photoluminescence features from silicon nanoparticles embedded in an SiC/SiN(x) multilayered structure.

Light emission from a quantum well-dot structure comprising amorphous Si nanoparticles (∼1.4 nm) embedded in SiC/SiN(x) multilayers (a few tens nm thick for individual sublayers) was investigated. Strong blue-green photoluminescence was measured at room temperature on the as-deposited samples and the spectral profile shows some markedly modulated features. It displays flattened profiles of roughly equal intensity when silicon particles in both nitride and carbide sublayers can be effectively excited, whereas when the nitride sublayer is less effectively activated at longer excitation wavelength the photoluminescence is pinned (here at 500 nm), showing a rather narrow, slowly decreasing profile. The phenomenon of narrowed emission is also observed in the Si-in-SiC multilayer consisting of particles of varying size distributions. Resonance energy transfer processes among particles modified by carrier confinement may provide a reasonable explanation.

Triangular and Fibonacci number patterns driven by stress on core/shell microstructures.

Fibonacci number patterns and triangular patterns with intrinsic defects occur frequently on nonplanar surfaces in nature, particularly in plants. By controlling the geometry and the stress upon cooling, these patterns can be reproduced on the surface of microstructures about 10 micrometers in diameter. Spherules of the Ag core/SiOx shell structure, possessing markedly uniform size and shape, self-assembled into the Fibonacci number patterns (5 by 8 and 13 by 21) or the triangular pattern, depending on the geometry of the primary supporting surface. Under proper geometrical constraints, the patterns developed through self-assembly in order to minimize the total strain energy. This demonstrates that highly ordered microstructures can be prepared simultaneously across large areas by stress engineering.

Formation of a rosette pattern in copper nitride thin films via nanocrystals gliding.

By sputtering synthesis of cubic Cu(3)N, which decomposes at moderate temperatures, film growth proceeds with simultaneous nitrogen reemission from inside, leading to the formation of some unusual structures or morphology. We report a relief morphology comprising densely packed rosette-like features. The rosettes, typically 20 microm in size, show a radial furcation followed by successive bifurcation at approximately 74 degrees , resulting in a fivefold symmetric structure sometimes. The area expansion of the features can be as large as ten per cent with regard to the underlying bottom. Scanning electron micrographs reveal that it is the gliding of Cu(3)N nanocrystals along the Cu-rich {111}-planes that is responsible for the unusually large area expansion. The gliding and packing along the {111}-planes also explain the bifurcation angle of the ramified rosettes. Such a relief morphology can serve as a template for large-area fabrication of concave structures by inverse duplication, adding to the already abundant innovative applications of this material.