Thermodynamic Transitions of Antiferromagnetic Ising Model on the Fractional Multi-branched Husimi Recursive Lattice

The multi-branched Husimi recursive lattice is extended to a virtual structure with fractional numbers of branches joined on one site. Although the lattice is undrawable in real space, the concept is consistent with regular Husimi lattice. The Ising spins of antiferromagnetic interaction on such a set of lattices are calculated to check the critical temperatures (T_c) and ideal glass transition temperatures (T_k) variation with fractional branch numbers. Besides the similar results of two solutions representing the stable state (crystal) and metastable state (supercooled liquid) and indicating the phase transition temperatures, the phase transitions show a well-defined shift with branch number variation. Therefore the fractional branch number as a parameter can be used as an adjusting tool in constructing a recursive lattice model to describe real systems.     

Thermodynamic Comparison and the Ideal Glass Transition of Antiferromagnetic Ising Model on Multi-branched Husimi and Cubic Recursive Lattice with the Identical Coordination Number

Two types of recursive lattices with the identical coordination number but different unit cells (2-D square and 3-D cube) are constructed and the antiferromagnetic Ising model is solved exactly on them to study the stable and metastable states. A multi-branched structure of the 2-D plaquette model, which we introduced in this work, makes it possible to be an analog to the cubic lattice. Two solutions of each model can be found to exhibit the crystallization of liquid, and the ideal glass transition of supercooled liquid respectively. Based on the solutions, the thermodynamics on both lattices, e.g. the free energy, energy density, and entropy of the supercooled liquid, crystal, and liquid state of the model are calculated and compared with each other. Interactions between particles farther away than the nearest neighbor distance and multi-spins interactions are taken into consideration, and their effects on the thermal behavior are examined. The two lattices show comparable properties on the thermodynamics, which proves that both of them are practical to describe the regular 3-D case, especially to locate the ideal glass transition, while the 2-D multi-branched plaquette model is less accurate with the advantage of simpler formulation and less computation time consumption.     

Thermodynamic Comparison and the Ideal Glass Transition of Antiferromagnetic Ising Model on Multi-branched Husimi and Cubic Recursive Lattice with the Identical Coordination Number

Two types of recursive lattices with the identical coordination number but different unit cells(2-D square and 3-D cube) are constructed and the antiferromagnetic Ising model is solved exactly on them to study the stable and metastable states. A multi-branched structure of the 2-D plaquette model, which we introduced in this work, makes it possible to be an analog to the cubic lattice. Two solutions of each model can be found to exhibit the crystallization of liquid, and the ideal glass transition of supercooled liquid respectively. Based on the solutions, the thermodynamics on both lattices, e.g. the free energy, energy density, and entropy of the supercooled liquid, crystal, and liquid state of the model are calculated and compared with each other. Interactions between particles farther away than the nearest neighbor distance and multi-spins interactions are taken into consideration, and their effects on the thermal behavior are examined. The two lattices show comparable properties on the thermodynamics, which proves that both of them are practical to describe the regular 3-D case, especially to locate the ideal glass transition, while the 2-D multi-branched plaquette model is less accurate with the advantage of simpler formulation and less computation time consumption.     

Surface-induced ordering in thin uniaxial liquid crystal films

The interface localization transition in thin uniaxial liquid crystal films with competing surface fields has been studied using Metropolis Monte Carlo simulations. The model is constructed from a lattice of continuously orientable interacting spins, and the Hamiltonian contains both bilinear and biquadratic contributions. The biquadratic contribution to the Hamiltonian is familiar from the Lebwohl-Lasher model, and accounts for the particle anisotropy in a liquid crystal. The head-tail asymmetry of the molecules in a uniaxial liquid crystal is taken into account through a bilinear contribution familiar from the classical ferromagnetic Heisenberg model with exchange anisotropy Lambda. The critical temperature T(c), characterizing the interface localization transition within the uniaxial liquid crystal film, depends strongly on the relative magnitudes of the bilinear and biquadratic interactions between the spins. For systems dominated by the biquadratic interaction, T(c) is found to be close to the bulk critical temperature of the system. But as the biquadratic interaction strength is reduced, T(c) departs markedly from the bulk critical temperature of the system.     

Influence of Surface Transition Layers on Phase Transformation and Pyroelectric Properties of Ferroelectric Thin Film

Taking into account surface transition layers （STLs）, we study the phase transformation and pyroelectric properties of ferroelectric thin films by employing the transverse Ising model （TIM） in the framework of the mean field approximation. The distribution functions representing the intra-layer and inter-layer couplings between the two nearest neighbour pseudo-spins are introduced to characterize STLs. Compared with the results obtained by the traditional treatments for the thin films using only the single surface transition layer （SSL）, it is shown that the STL model reflects a more realistic and comprehensive situation of films. The effects of various parameters on the phase transformation properties have shown that STL can make the Curie temperature of the film higher or lower than that of the corresponding Sulk material, and the thickness of STL is a key factor influencing the film properties. For a film with definite thickness, there exists a critical STL thickness at which ferroelectricity will disappear when the intra-layer and inter-layer interactions are weak.     

Pressure and Time Dependences of the Supercooled Liquid-to-Liquid Transition in Sulfur

Thermal behavior of bulk amorphous sulfur is investigated by in situ temperature measurements at high pressures of 0.9,1.4 and 2.1 GPa,and under different heating rates of 8,10 and 12K/min at 0.9 GPa.The results show that the onset temperature of the transition from the supercooled liquid to the liquid state for sulfur increases with the pressure and the heating rate.It is deduced that the transition does not follow the Clapeyron equation,indicating considerable coupling of the molecular structure change in the transition.Along with the data at ambient pressure and high pressure,we present a dynamic diagram to demonstrate the relationship between the amorphous solid,supercooled liquid,liquid,and crystal phases of sulfur,and suggest an experimental approach to establish pressure-temperature-time transition diagrams for supercooled liquid and liquid.     

Calorimetry at surfaces using high-resolution core-level photoemission

We have developed a method to measure simultaneously the internal energy of bulk and the first layer atoms of a crystal. The internal energy of bulk and the surface atoms of lithium (110) have been evaluated from 22 K up to above the melting transition, applying the Debye model to the thermal broadening of the respective 1s photoemission lines. Our measurements clearly reveal two phase changes: the known liquid to solid transition and the surface melting, occurring 50 K below the bulk melting point.     

Demixing transition in a quasi-two-dimensional surface-frozen layer

A thin/thick transition was observed by x-ray reflectivity in a surface-frozen crystalline bilayer on the surface of a molten binary mixture of long alcohols. This rare example of a solid-solid phase transition in a quasi-2D system is shown to result from an abrupt temperature-driven change in the layer's composition, kinetically enabled by the layer's ability to exchange molecules with the underlying 3D liquid bulk. Mean-field thermodynamics yields a Gibbs-adsorption-like expression which accounts very well for the transition.     

气液相变过程亚稳态体相内部界面分析

利用热力学理论对亚稳态体相内部活化分子的聚集状态进行讨论,发现在无外界扰动的平衡状态下,体相内部活化分子绝大多数以单体形式存在,并给出了单体与聚集体的浓度关系。在聚集体浓度与聚集体内部分子数之间关系分析的基础上,推导出临界聚集浓度的表达式,从而确定体相处于过热(过冷)极限点时的内部分子能量分布特性,借以从分子聚集的角度来描述气液相变的物理图景。同时,利用体相在过热(过冷)极限点处的宏观性质来逆推体相与微小新相之间的界面张力γ,从而对经典理论的形核率作出修正。     

Surface crystallography of rubidium on Ag(111), and the chemical reactivity of nitric oxide on rubidium-dosed silver

Rubidium chemisorbs amorphously on Ag(111) at coverages below one monolayer, but ordered structures are formed in the multilayer regime. For thin layers the Rb grows as an fcc crystal, but above a certain critical thickness a phase transition occurs to yield the ordinary bcc form. The reactivity of Rb-dosed Ag towards NO is examined and compared with earlier work on Ag/Na. Although there are broad similarities between the two systems, certain important differences in chemical behaviour are found. These are mainly the result of reduced penetration of the Ag lattice by Rb, and the very greatly reduced surface → bulk transport of chemisorbed oxygen as compared with the case of Na. Evidence is also found for the formation of surface compounds between Rb, O, and N on Ag(111), and auxilliary experiments with O₂ and N₂O are carried out in an attempt to shed further light on the nature of these compounds.     

Lattice dynamics and the ferroelectric and antiferrodistorsive instabilities in a bulk crystal and thin films of SrZrO3

The lattice dynamics and energies of phases related to antiferrodistorsive and ferroelectric distortions of bulk crystals and thin films of the SrZrO₃ crystal have been calculated within the framework of the ab initio model of an ionic crystal. In the case of a bulk crystal, it has been found that the most energetically favorable phases are related to antiferrodistorsive lattice distortions. Ferroelectricity in the SrZrO₃ crystal is suppressed by structural lattice distortions. In the case of thin films, it has been found that the ferroelectric instability is retained after the ??rotation?? of the oxygen octahedron and the film remains polar both in the case of a free surface and with the inclusion of the SrTiO₃ substrate in the calculation. The spontaneous polarization of thin films of different thicknesses in the ferroelectric phase has been calculated.     

Numerical Calculations for the Surface on a Semi-Infinite Ising Model with a Random Surface Field

We study the critical behavior of the surface on a semi-infinite simple cubic lattice Ising model with a bimodal random surface field by large cell mean-field renormaliza tion group method and Monte Carlo simulations. Our results show that the surface ferromagnetic phase exists in the weak random field range above the bulk critical temperature. The surface. specific heat is not divergence and the susceptibility show a cusp singularity at the surface ferromagnetic-paramagnetic transition for a relatively large and om field.     

On the role of surface energy in nanodimensional crystalline objects

The surface contribution to the thermodynamic potential for bulk and nanodimensional particles of ion crystals is estimated with the help of the electron statistical theory of ion crystal lattice. A number of size effects associated with the excess surface energy of ultradisperse particles are considered. In particular, the possibility of stability loss in the crystal lattice upon the transition of the surface energy to the range of negative values under a high pressure is predicted.     

Manifestation of the heterogeneous mechanism upon melting of low-dimensional systems

A melting process that is always heterogeneous in semi-infinite systems having a surface has been analyzed. It has been shown in terms of the classical thermodynamics that, in real one-component systems, a liquid layer on the solid-phase surface is formed at temperatures lower than the reference melting temperature of the bulk material at which the system is completely melted. Depending on the temperature, a liquid layer of particular thickness on the surface is in equilibrium with the other crystalline phase. The heterogeneous melting is shown to influence a number of processes and mechanisms, such as the dispersion of a thin film into droplets, the mechanism of vapor-liquid-solid epitaxy, the mechanism of layer-by-layer crystal growth, and the mechanism of growth of carbon nanotubes.     

Surface precrystallization of normal C24 alkane in porous glass

The behavior of the enthalpy and specific heat of normal C24 alkane in the bulk and in porous glasses is investigated using an adiabatic scanning microcalorimeter. Enthalpy jumps, which precede a phase transition in the entire volume of the pores, are found in porous glass with characteristic pore size 1000 Å at a transition from the isotropic liquid into the rotator phase RII. The enthalpy jumps are interpreted as a layerwise growth of a crystal phase on the surface of porous glass. It is also found that porous glass substantially changes the phase behavior of alkanes.     

Surface Segregation in Miscible Blends of Polystyrene and Poly(vinylmethyl ether): Comparison of Theory and Experiment

The effect of the interplay between bulk and surface free energy terms on surface segregation in miscible blends is probed by comparing angle-dependent x-ray photoelectron spectroscopy (ADXPS) measurements for polystyrene/polyvinylmethylether (PS/PVME) blends of with those for perdeuteropolystyrene/polyvinylmethylether (dPS/PVME) blends. The magnitudes of the bulk interaction parameters for the two systems differ markedly while the surface interactions are essentially identical. Experimental concentration depth profiles are almost identical for the two systems indicating that their surface properties are little affected by bulk interactions and dominated by surface energy effects.These data and previous data from our group are compared to the predictions of the square gradient theory developed by Schmidt and Binder in order to gain a more quantitative understanding of the factors that control surface segregation in miscible blends. While there is general qualitative agreement between theory and experiment, predicted surface compositions fall significantly below experimental values and predicted composition depth profiles decay more gradually than what is observed experimentally, especially for low PVME contents. The use of the more appropriate Sanchez-Lacombe-Balazs equation of state does not yield any significant improvement over the use of the Flory-Huggins lattice model for representing the bulk free energy terms. Careful analysis of the experimental behavior suggests that configurational effects associated with the flattening of surface adsorbed chains and differences in mer-mer interaction parameters in the bulk and near surface regions are possible origins for the discrepancies between theory and experiment.     

Surface triple points and multiple-layer transitions observed by tuning the surface field at smectic liquid-crystal-water interfaces

We present an ellipsometric study of the interface between a smectic liquid crystal and water in the presence of a nonionic surfactant. The surfactant concentration serves as a handle to tune the surface field. For sufficiently large surfactant concentrations, a smectic phase is present at the interface in the temperature range above the smectic-A-isotropic bulk transition; when the bulk transition is approached, the thickness of this surface phase grows via a series of layer-by-layer transitions at which single smectic layers are formed. At lower surfactant concentrations, transitions appear at which the thickness of the surface phase jumps by multiple smectic layers, thereby implying the existence of triple points at which surface phases with different smectic layer numbers coexist. This is the first experimental demonstration of such surface triple points which are predicted by theoretical models.     

Surface supercooling and stability of n-alkane films

The surface tension of n-octadecane was studied in the vicinity of the bulk melting point using both the maximum bubble pressure and Wilhelmy plate methods. The bubble surfaces were found to be supercooled below the surface freezing point. The onset of surface freezing is indicated by a sharp drop in surface tension at a constant temperature. This transition is accompanied by an increased film stability resulting in longer bubble lifetimes at the liquid surface. Variations in bubble lifetime reflect changes in the interfacial mechanical properties of the film from liquidlike to solidlike.     

Caloric curves and energy fluctuations in the microcanonical liquid-Gas phase transition

In this paper we study a microcanonical lattice gas model with a constrained average volume. We show that the caloric curve explicitly depends on the considered transformation of the volume with the excitation energy and so does not bear direct information on the characteristics of the phase transition. Conversely, partial energy fluctuations are demonstrated to be a direct measure of the equation of state. Since the heat capacity has a negative branch in the phase transition region, the presence of abnormally large kinetic energy fluctuations is a signal of the liquid-gas phase transition.     

Theory of chemisorption

The electronic structure of a semiinfinite crystal with a partial coverage by adatoms is studied within the tight-binding formalism. The effect of the surface is described via the surface Green function method, and the effect of disorder is treated within the coherent potential approximation. The local state densities at/near the surface and the interaction energy of adatoms are calculated as functions of the coverage. The examples representing the case of a gas adsorption on the transition metal surfaces, as well as the adsorption of the transition metal atoms on the transition metal surfaces are investigated numerically.