Interfacial Thermodynamics Research Articles

Thermodynamics of Nanosystems with a Special View to Charge Carriers.

Basic ingredients of interfacial thermodynamics are recapitulated with a special eye on the nanometer-size regime. Questions are then briefly tackled that arise if, in heterogeneous systems, the constituent phases shrink to atomistic dimensions. Particularly helpful in this context are thermodynamic approaches, in which the introduction of interfacial tension is avoided. While the first part addresses ground structure quantities, the second part deals with questions of size and confinement effects on entropy and energy of ionic and electronic defects. These defects represent the respective excitations within this ground structure. The article emphasizes the similarities between ions and electrons manifested in the statistics rather than elaborating on the discrepancies that are primarily reflected by different densities of states and mobilities. It is, therefore, not the intention of the article to address aspects of nanoelectronics that rely on quantum transport for which many reviews are available. Nonetheless all these discussed aspects are directly relevant for both nanoionics and nanoelectronics.

On the Line Tension of Curved Boundary Layers. I. Boundary Thermodynamics

We present a formally exact thermodynamic treatment of curved boundary layers. Specifically, we extend the boundary layer analysis of Mandell and Reiss [ J. Stat. Phys. 1975 , 13 , 107 ] for a spherical cavity located within a uniform bulk fluid to the case of a cavity intersecting a hard, structureless wall. We derive various expressions for the line tension of an intersecting cavity, all of which can be evaluated for a hard-sphere fluid using existing versions of scaled particle theory. Since the analysis is similar to the standard approach for describing curved interfacial layers, several boundary analogues to conventional interfacial relations appear. In some instances, we obtain results that apparently have not yet been derived either for boundary layers or for their parallel relations in interfacial thermodynamics. Several results offer interesting insights into the behavior of the line tension of a cavity when the cavity approaches macroscopic sizes or in the specific limit where the cavity no longer intersects the wall.

Fundamentals of Metal‐induced Crystallization of Amorphous Semiconductors

AbstractA general, quantitative model has been developed that provides fundamental understanding of the metal‐induced crystallization (MIC) of amorphous semiconductors. Interface thermodynamics has been shown to play a decisive role for the whether or not occurrence of MIC. The model has been employed to predict the MIC temperature for various metal/amorphous‐semiconductor systems. A consequence of the model is the prediction that the thickness of an ultrathin, pure Al film put on the top of an amorphous Si layer can be used as a very accurate tool to tune the crystallization temperature of amorphous Si. These theoretical predictions have been confirmed experimentally. The fundamental understanding reached may lead to pronounced technological progress in the low‐temperature manufacturing of crystalline‐Si‐based devices deposited on cheap and flexible substrates such as glasses, plastics, and possibly even papers.

Non-Equilibrium Thermodynamics of the Gas-Liquid Interface: Measurement of the Onsager Heat of Transport for Ammonia at the Surface of Water

Non-Equilibrium Thermodynamics of the Gas-Liquid Interface: Measurement of the Onsager Heat of Transport for Ammonia at the Surface of Water

Interdiffusion, phase formation, and stress development in Cu–Pd thin-film diffusion couples: Interface thermodynamics and mechanisms

Cu–Pd thin-film diffusion couples (individual layer thicknesses of 50nm) have been prepared by dc-magnetron sputtering on silicon substrates coated with a thin amorphous Si3N4 layer. Stress evolution, microstructural development, and phase formation during interdiffusion have been investigated employing Auger-electron spectroscopy (in combination with sputter-depth profiling), x-ray diffraction, wafer curvature measurements and transmission electron microscopy. Upon annealing at relatively low temperatures (175–250°C) for durations up to 10h, considerable diffusional intermixing occurs. Interdiffusion is accompanied by sequential formation of new phases. First, Cu3Pd forms; subsequently, CuPd forms and grows at the expense of Cu3Pd, which has been interpreted as a consequence of interface thermodynamics. Annealing leads to a slight sharpening of the pre-existing {111}-fiber textures and a little increase in the average grain size. A combination of ex situ (x-ray diffraction) and in situ (wafer curvature) stress measurements revealed that tensile stresses are generated during annealing. The obtained stress results have been discussed in the light of possible mechanisms of stress generation, and the dominant sources of stress buildup and relaxation have been identified.

Tailoring the Ultrathin Al-Induced Crystallization Temperature of Amorphous Si by Application of Interface Thermodynamics

It has been demonstrated theoretically and experimentally that the thickness of a very thin, pure Al film put on top of an amorphous Si (a-Si) layer can be used as a very accurate tool to control the crystallization temperature of a-Si. The effect has been explained quantitatively by application of surface-interface thermodynamics. The predictions have been confirmed experimentally by a real-time in situ spectroscopic ellipsometry investigation of the crystallization temperature of a-Si as a function of the thickness of ultrathin Al layers.

A model system for the optimization of lamination parameters of PTFE-based dielectrics and metal surfaces

In microelectronic packaging, organic dielectric materials continue to displace ceramic materials because of cost, reduced weight, and performance advantages. Because thermosetting dielectric composites have long found widespread use in printed wiring board (PWB) fabrication, they have been the components of choice for many organic chip carriers. Conversely, thermoplastic dielectrics, such as fluoropolymer (FP), and in particular poly(tetrafluoroethylene)-based dielectric composites (PTFE composites) have seldom found use in multilayer wiring packages in spite of their attractive electrical properties due to their processing challenges. In this paper, we report the use of a model system comprising pure PTFE film and Cr-coated copper surfaces to optimize the bonding process through lamination conditions for a fluoropolymer composite and chromium-coated copper surfaces and to study both the interface mechanics and its chemistry as a function of processing parameters. The significant finding of the investigation was the linkage between the macroscopic mechanical properties of the interface and the observable chemical alteration of the same under some lamination conditions. The relationship of the interface properties and the processing conditions extend a conceptual framework for the thermodynamics of the metal-polymer interface and the reliability of these electronic packages in their practical designs.

Interfacial thermodynamics of compressible polymer solutions

A variational model is developed to compute the coupled density and concentration fields that define the structure of planar interface between equilibrium phases of a compressible polymer solution. The solution of the model in conjunction with the modified Sanchez-Lacombe, with parametric data relevant to real polymer solutions, quantifies the role of compressibility on interfacial thermodynamics and interfacial tension. In particular, it is found that pressure pulses originating from density changes compensate chemical stresses. The interfacial tension, based on Bakker's equation, between equilibrium polymer solution phases and corresponding interfacial thickness exhibits pressure scaling behavior analogous to that predicted with temperature for incompressible polymer solutions.

Film characterization of poly(styrene-butylacrylate-acrylic acid)–silica nanocomposite

To improve the present unsatisfactory UV-shielding and water-resistance properties of many emulsion-type latexes, in this study, poly(styrene-butylacrylate-acrylic acid) (PSBA)-grafted–silica (PSBA-g-silica) hybrid nanoparticles were firstly prepared by suspension–dispersion–polymerization. The resulting hybrid nanoparticles were then used to add into PSBA latex to fabricate PSBA nanocomposites. The influence of PSBA-g-silica hybrid nanoparticles on the interfacial adhesion, film morphology, thermodynamics properties, UV-shielding, water-resistance and mechanical performance of PSBA films were investigated systematically. Our results revealed that filling 1.5 wt% PSBA-g-silica hybrid nanoparticles resulted in significant improvement in interfacial adhesion properties, UV-shielding, water-resistance and mechanical properties. Fabricating the silica-based latex nanocomposite is an effective approach to develop the new emulsion-type paints and adhesives.

Thermodynamics and mechanism of metal-induced crystallization in immiscible alloy systems: Experiments and calculations on Al/a-Ge and Al/a-Si bilayers

The mechanism of metal-induced crystallization (MIC) in immiscible alloy systems has been explained on a unified thermodynamic basis. Interface thermodynamics has been shown to play a decisive role for the occurrence of MIC. The thermodynamic predictions agree excellently with the corresponding experimental observations obtained in this project for the $\mathrm{Al}∕\mathrm{Ge}$ and $\mathrm{Al}∕\mathrm{Si}$ layer systems, which show two distinctly different types of MIC behaviors. As a result, a model has been developed that rationalizes and predicts MIC processes in immiscible alloy systems.

Interface thermodynamics of nano-sized crystalline, amorphous and liquid metallic systems

Abstract Expressions for the Gibbs energies of interfaces occurring in particular for solid and/or liquid/amorphous metals or alloys in contact with each other have been developed. To consider its energetics, an amorphous alloy has been modelled as a mixture of the undercooled liquid metal components near to the glass transition temperature making use of the enthalpy of melting, the entropy of melting and the temperature-dependent contribution of the heat capacity of the undercooled melt. Gibbs surface and interface energies have been obtained on the basis of the “macroscopic atom” Miedema model, where the entropy contributions of alloys have been derived applying a recently developed formalism. The Gibbs energy of a crystalline interface phase has been formulated. The molar fractions of the components of the alloy at the surfaces have been determined by minimising the surface energy. These results provide a thermodynamic basis for unusual phenomena observed in nano-sized systems. The formalism has been applied to calculate the thermodynamic stability of interface phases in a nano-sized, multi-layered system of iron and zirconium and to explain the aluminium-induced crystallisation of amorphous silicon and the layer exchange occurring in bi-layers of crystalline aluminium and amorphous silicon.

Thermodynamics of mechanical transduction of surface confined receptor/ligand reactions

Chemomechanics of surface stress is discussed in terms of interfacial thermodynamics. In the first section the paper shows how to quantitatively describe the chemical equilibrium of a receptor/ligand binding reaction confined at a solid–liquid interface and how the overall work of the reaction splits into chemical and surface work, that appears as a surface pressure. In the second section this thermodynamic model is applied to describe the experimental results of microcantilever bending induced by DNA hybridization occurring onto one of its faces.

First-Principles Thermodynamics of Coherent Interfaces in Samarium-Doped Ceria Nanoscale Superlattices

Nanoscale superlattices of samarium-doped ceria layers with varying doping levels have been recently proposed as a novel fuel cell electrolyte. We calculate the equilibrium composition profile across the coherent {100} interfaces present in this system using lattice-gas Monte Carlo simulations with long-range interactions determined from electrostatics and short-range interactions obtained from ab initio calculations. These simulations reveal the formation of a diffuse, nonmonotonic, and surprisingly wide (11 nm at 400 K) interface composition profile, despite the absence of space charge regions.

Anisotropy of Segregation at Grain Boundaries and Surfaces

The purpose of this article is to review analytical models of the anisotropy of segregation to grain boundaries (GBs) and surfaces, and to evaluate their predictions. A summary of Gibbsian interfacial thermodynamics is provided as an introduction to the topic. This is followed by a historical overview of previous analytical models. A recently developed model of the dependence of GB segregation on the five macroscopic parameters of GB orientation is outlined, and illustration of how this formulation reduces to the particular cases of segregation to simpler types of interfaces is provided. In addition, some specific aspects of interfacial segregation, which have either been problematic or have lacked satisfactory explanation, are addressed. These include (a) the relationship between the compositions on the two sides of a given GB; (b) the difficulty of meaningful definitions of segregation-free energy (and related thermodynamic quantities such as enthalpy and entropy); (c) the so-called compensation temperature, at which the anisotropy of interfacial segregation seems to vanish; (d) the relationship between surface and GB segregation; and finally (e) an attempt to determine whether segregation increases or decreases interfacial energy anisotropy, and the consequences thereof on the equilibrium crystal shape of alloys. Where possible, comparisons are made with the results of experiments or computer simulations.

Thermal stability of Fe, Co, Ni metal nanoparticles

AbstractThe thermal stability of metal nanoparticles is discussed in both melting thermodynamics and interface thermodynamics. Emphases are put on the size and shape dependence of melting temperature, critical size and vacancy‐formation energy of both freestanding and embedded metal nanoparticles. The melting temperature depression and superheating phenomena for reported nanoparticle systems are explained. Critical sizes of Fe, Co, Ni metal nanocrystals that the crystals keep their crystallinity are calculated and the corresponding minimum melting temperatures predicted. The vacancy‐formation energies of Fe, Co, Ni small particles are also calculated as a reference. Theoretical predictions are consistent with experimental results. (© 2006 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)

InN nanoflowers grown by metal organic chemical vapor deposition

Hexangular indium nitride nanoflower pattern is observed from scanning electron microscopy and atomic force microscopy. The sample is grown on c-plane (0001) sapphire by metal organic chemical vapor deposition with intentional introduction of hydrogen gas. With the aid of hydrogen, a stable existence of metallic indium is achieved. This will induce the growth of InN nanoflowers via self-catalysis vapor-liquid-solid (VLS) process. It is found that the VLS process is modulated by the interface kinetics and thermodynamics among the sapphire substrate, indium, and InN, which leads to the special morphology of the authors’ InN nanoflower pattern.

Polyethylene {201} crystal surface: interface stresses and thermodynamics

We describe a method to determine the mechanical and thermodynamic properties of the interface between a polyethylene crystal and melt by united-atom Monte Carlo simulations. In particular, the {201} fold surface is studied in the temperature range 380–450K. The interface properties are defined by using the concept of a sharp Gibbs dividing surface, which in turn is used to define the interface internal energy and the interface stresses. We find that the internal energy of the interface is of the order 0.3–0.35J/m2. The interface stresses are anisotropic for the {201} crystal surface with values of approximately −0.27 and −0.4J/m2 for the xx- and yy-components, respectively. By way of the Herring equation, the surface tension of the fold surface is independent of shear strains in the interface. The temperature and strain derivatives of the interface properties are also measured and discussed in detail. The influence of the interface internal energy and of phase change contributions on the macroscopic heat capacity of the semi-crystalline material is examined.

Experimental isotherms of HCl on H2O ice under stratospheric conditions: Connections between bulk and interfacial thermodynamics

The adsorption of HCl on the surface of H(2)O ice has been measured at temperatures and pressures relevant to the upper troposphere and lower stratosphere. The measured HCl surface coverage is found to be at least 100 times lower than currently assumed in models of chlorine catalyzed ozone destruction in cold regions of the upper atmosphere. Measurements were conducted in a closed system by simultaneous application of surface spectroscopy and gas phase mass spectrometry to fully characterize vapor/solid equilibrium. Surface adsorption is clearly distinguished from bulk liquid or solid phases. From 180 to 200 K, submonolayer adsorption of HCl is well described by a Bragg-Williams modified Langmuir model which includes the dissociation of HCl into H(+) and Cl(-) ions. Furthermore, adsorption is consistent with two distinct states on the ice substrate, one in which the ions only weakly adsorb on separate sites, and another where the ions adsorb as an H(+)-Cl(-) pair on a single site with adsorption energy comparable to the bulk trihydrate. The number of substrate H(2)O molecules per adsorption site is also consistent with the stoichiometry of bulk hydrates under these conditions. The ionic states exist in equilibrium, and the total adsorption energy is a function of the relative population of both states. These observations and model provide a quantitative connection between the thermodynamics of the bulk and interfacial phases of HCl/H(2)O, and represent a consistent physicochemical model of the equilibrium system.

Surface phase separation in complex mixed adsorbing systems: an interface-bulk coupling effect.

The interfacial thermodynamics and structure of ternary mixtures of the type A+B+solvent are investigated. According to the Gibbs phase rule, the coupling between the bulk phase and the interfacial region-which is related to the reversibility of the adsorption of the corresponding species-is a determinant as to whether phase separation can be observed at the interface. For an n-component adsorbing solution, at least one of the species has to adsorb irreversibly over the experimental time scales in order not to fix more intensive variables than those required to observe surface phase separation. We present results for a lattice model planar interface consisting of the ternary mixture A+B+solvent. The solvent molecules and the type A molecules have fixed chemical potentials at the interface since they are equilibrated with a bulk solution. In contrast, the type B molecules are irreversibly adsorbed at the interface and do not equilibrate with the bulk. Mean-field theory is compared with Monte Carlo simulation. Interestingly, the spinodal line in the interaction-composition plane shows a reentrant on the B-rich phase side. We discuss the implications of these results for surface phase separation of adsorbing mixtures of proteins and low-molecular-weight surfactants.

Effect of annealing on structure and biomedical properties of amorphous hydrogenated carbon films

The usual failure of blood-contacting biomedical materials and devices arises from thrombogenesis. When a biomaterial comes in contact with a biological body, interface interaction will be concomitant between the biomaterial surface and biological substance, such as blood protein denaturation resulting from electrical charge transfer of proteins and platelet activation induced by interface thermodynamics. Diamond-like carbon (DLC) has been proposed for use in blood contacting devices. Further understanding of the intrinsic relationship between biomedical properties and structure of amorphous carbon films will promote improvement of their biocompatibility. In this study, hydrogenated amorphous carbon (a-C:H) films were fabricated at room temperature using plasma immersion ion implantation-deposition (PIII-D). A series of a-C:H films with different structures and chemical bonds were obtained by adjusting the DC bias voltage from −75 to −900 V, then their structure and physical properties were further modified by thermal anneal in vacuum at 600 °C. Raman, elastic recoil detection (ERD) and atomic force microscope (AFM) were used to characterize their structures and chemical bonds. The physical properties and surface characteristics of the films were also examined, including the carrier concentration and mobility, resistivity, and surface wettability. The anticoagulation of the films was evaluated employing in vitro platelet adhesion test. The adhesion, activation, and morphology of the platelets were investigated using scanning electron microscopy (SEM). The relationship between their structure and blood compatibility was elucidated.