Film Thickness Regime Research Articles

Terahertz inverse spin Hall effect in spintronic nanostructures with various ferromagnetic materials

Bilayers of ferromagnetic and heavy metal nanolayers excited with femtosecond laser pulses emit subpicosecond bursts of electromagnetic radiation with spectral frequencies up to several THz. We fabricated such spintronic THz emitters containing various ferromagnetic materials with vastly different magnetic remanence, saturation magnetization, and coercive fields. In all cases, the THz amplitude versus magnetic-field dependence follows the independently measured magnetization hysteresis loops and the THz polarization direction is perpendicular to the sample’s magnetization M, both consistent with the inverse spin Hall effect (ISHE) as the physical origin. The mV-level signals of observed THz transients also favor the ISHE over the anomalous Nernst effect (ANE). The M(T) variation governs the temperature dependence of the THz generation. Emitters with weakly remanent ferromagnets are magnetic-field tunable, while moderately and strongly remanent ferromagnets, once magnetized, allow intense THz generation even without an external field, nevertheless exhibiting low susceptibility to magnetic perturbations if the hysteresis loop is square. Hence, exploiting the magnetic properties of the ferromagnetic layer enables tailoring of weakly temperature-dependent spintronic THz emitters. Finally, we explored the applicability of perovskite oxide materials such as La-Sr-Mn-O (LSMO) for THz transient generation. We detected weak (<40-µV amplitude) THz emissions from both LSMO/Au and pure LSMO nanostructures with no sign flip upon the sample reversal. Thus, we excluded the ISHE and believe it was likely governed by the ANE in the thick-film regime, although we cannot exclude the transient demagnetization mechanism.

Multiscale modelling of species transport in hydrophilic Nafion®-coated Cu catalysts for CO2 electro-reduction

Ionomers such as Nafion are being used for engineering the microenvironment of the CO2RR towards selectivity to higher hydrocarbons. Their cationic exchange qualities mitigate homogeneous bicarbonate reactions, providing favourable conditions for production of C2-C3 products. The proximity of Nafion® layers to the negatively charged electrode surface results in complex effects that have yet to be explored computationally. We combine mass transport equations and density functional theory (DFT) calculations to model the hydrophilic moieties in Nafion® layer on a 1D planar copper electrode. We vary the Nafion® layer thickness in the thick film regime (200–1100 nm), the ionic strength of supporting aqueous electrolyte and the applied voltage to investigate the concentration profile of participating species within the Nafion® layer. We find that the bicarbonate ion concentration and local pH decrease with decreasing thickness which makes thinner films better at mitigating bicarbonates at the cost of a relatively lower pH. We observe the breakdown of Donnan exclusion effects with higher ionic strength electrolytes which allows diffusion of both co-ions and counter-ions, promoting the bicarbonate reactions. Further, we find that the pKa of Nafion® generally increases as the local dielectric constant of the reaction medium decreases. This is primarily due to the accumulation of K+ and production of low dielectric constant products such as ethanol, albeit their concentrations are low on planar Cu electrodes. The lower permittivity of the reaction medium weakens the exclusion forces and changes the morphology of Nafion® which ultimately impacts its ability to mitigate homogeneous bicarbonate reactions.

Deposition and alignment of fiber suspensions by dip coating

Hypothesis: The dip coating of suspensions made of monodisperse non-Brownian spherical particles dispersed in a Newtonian fluid leads to different coating regimes depending on the ratio of the particle diameter to the thickness of the film entrained on the substrate. In particular, dilute particles dispersed in the liquid are entrained only above a threshold value of film thickness. In the case of anisotropic particles, in particular fibers, the smallest characteristic dimension will control the entrainment of the particle. Furthermore, it is possible to control the orientation of the anisotropic particles depending on the substrate geometry. In the thick film regime, the Landau-Levich-Derjaguin model remains valid if one account for the change in viscosity.Experiment: To test the hypotheses, we performed dip-coating experiments with dilute suspensions of non-Brownian fibers with different length-to-diameter aspect ratios. We characterize the number of fibers entrained on the surface of the substrate as a function of the withdrawal velocity, allowing us to estimate a threshold capillary number below which all the particles remain in the liquid bath. Besides, we measure the angular distribution of the entrained fibers for two different substrate geometries: flat plates and cylindrical rods. We then measure the film thickness for more concentrated fiber suspensions.Findings: The entrainment of the fibers on a flat plate and a cylindrical rod is primarily controlled by the smaller characteristic length of the fibers: their diameter. At first order, the entrainment threshold scales similarly to that of spherical particles. The length of the fibers only appears to have a minor influence on the entrainment threshold. No preferential alignment is observed for non-Brownian fibers on a flat plate, except for very thin films, whereas the fibers tend to align themselves along the axis of a cylindrical rod for a large enough ratio of the fiber length to the radius of the cylindrical rod. The Landau-Levich-Derjaguin law is recovered for more concentrated suspension by introducing an effective capillary number accounting for the change in viscosity.

Spin transport in thick insulating antiferromagnetic films

Spin transport of magnonic excitations in uniaxial insulating antiferromagnets (AFs) is investigated. In linear response to spin biasing and a temperature gradient, the spin transport properties of normal-metal--insulating antiferromagnet--normal-metal heterostructures are calculated. We focus on the thick-film regime, where the AF is thicker than the magnon equilibration length. This regime allows the use of a drift-diffusion approach, which is opposed to the thin-film limit considered by Bender {\it et al.} 2017, where a stochastic approach is justified. We obtain the temperature- and thickness-dependence of the structural spin Seebeck coefficient $\mathcal{S}$ and magnon conductance $\mathcal{G}$. In their evaluation we incorporate effects from field- and temperature-dependent spin conserving inter-magnon scattering processes. Furthermore, the interfacial spin transport is studied by evaluating the contact magnon conductances in a microscopic model that accounts for the sub-lattice symmetry breaking at the interface. We find that while inter-magnon scattering does slightly suppress the spin Seebeck effect, transport is generally unaffected, with the relevant spin decay length being determined by non-magnon-conserving processes such as Gilbert damping. In addition, we find that while the structural spin conductance may be enhanced near the spin flip transition, it does not diverge due to spin impedance at the normal metal|magnet interfaces.

Structure-property relationships at Nafion thin-film interfaces: Thickness effects on hydration and anisotropic ion transport

The effect of film thickness on water uptake and structure in ultra-thin Nafion is probed via in situ neutron reflectometry for a series of 10 films with thicknesses ranging from 5 to 153nm. Observed interfacial lamellae are used to understand anomalous transport limitations in such films. Results show three distinct thickness regimes: (i) in the truncated regime (< 12nm), the entire film consists of lamellae; (ii) in the thin-film regime (12–42nm), a non-lamellar bulk-like layer forms between the lamellae and vapor; (iii) in the thick-film regime (≥ 60nm), the bulk-like layer thickness exceeds the radius of gyration for thin-film Nafion. The water uptake in the sample varies non-monotonically with thickness, and can be ordered as: thin-film < truncated < thick-film. In the thin-film regime, the water uptake in the bulk-like layer and lamellae are equal, and both increase with thickness, except for a well-hydrated layer adjacent to the SiO2 substrate. In the thick-film regime, the bulk-like layer water uptake equals that in macroscopic Nafion membranes, and is invariant with film thickness, while the lamellar water uptake greatly exceeds this. Composition depth profiles are used to predict the anisotropic ionic conductivities. These are fitted to previously published experimental results to demonstrate that the lamellar structure is required for accurate conductivity predictions. These results provide key insights for minimizing transport losses in fuel cell catalyst layers.

Plasmonic Nanospectroscopy for Thermal Analysis of Organic Semiconductor Thin Films.

Organic semiconductors are key materials for the next generation thin film electronic devices like field-effect transistors, light-emitting diodes, and solar cells. Accurate thermal analysis is essential for the fundamental understanding of these materials, for device design, stability studies, and quality control because the desired nanostructures are often far from thermodynamic equilibrium and therefore tend to evolve with time and temperature. However, classical experimental techniques are insufficient because the active layer of most organoelectronic device architectures is typically only on the order of a hundred nanometers or less. Scrutinizing the thermal properties in this size range is, however, critical because strong deviations of the thermal properties from bulk values due to confinement effects and pronounced influence of the substrate become significant. Here, we introduce plasmonic nanospectroscopy as an experimental approach to scrutinize the thickness dependence of the thermal stability of semicrystalline, liquid-crystalline, and glassy organic semiconductor thin films down to the sub-100 nm film thickness regime. In summary, we find a pronounced thickness dependence of the glass transition temperature of ternary polymer/fullerene blend thin films and their constituents, which can be resolved with exceptional precision by the plasmonic nanospectroscopy method, which relies on remarkably simple instrumentation.

Gas Permeation Study in Thin and Ultra-Thin Ionomer Films

Significant advances in the performance of polymer-electrolyte fuel cells (PEFCs) can be attributed to perfluorinated sulfonic-acid (PFSA) ionomers, like Nafion and 3M-ionomer. They serve both as electrolyte membranes and as conductive binders in porous catalyst-layer structures. In PEFC catalyst structures, ionomers are thought to be major contributors to unexplained large mass-transfer overpotentials.[1-3] Thin (< 1 µm) and ultra-thin (< 0.025 µm) ionomer films in the catalyst layer serve as ionic charge carriers to catalytic sites, where low resistance to gas transport is required for optimal performance, yet it is believed that such resistance is increased compared to bulk ionomer. This resistance is further exasperated with decrease in platinum loading, which is an essential consideration for commercial viability and cost reduction of PEFCs.[4] Much has been done to shed light on the aberration of ionomer thin-film from bulk in other properties such as proton conductivity, morphology and water uptake. This has allowed many to attribute the rise in local mass-transfer resistance at the catalyst layer to the decrease in permeability of thin-film ionomers as compared to that of bulk membrane. However, direct measurement of permeability of thin-film ionomer has yet to be accomplished. A significant amount of work has been done to study gas transport and permeation in the bulk ionomer membrane.[5] However, much remains to be explored in thin and ultra-thin ionomer film thickness regime. Effects such as confinement, processing conditions, and surface and interfacial interactions have been pointed to as the prime cause of deviation of thin-film polymer behavior from that of the bulk. Linking the extent of impact of these effects to ionomer properties can elucidate source of transport resistance in the catalyst layer. In this work, we will present data for gas permeation in thin and ultra-thin PFSA films including free-standing thin ionomer films (> 400nm) as well as thin and ultra-thin ionomer films supported on well studied, highly permeable rubbery poly(dimethylsiloxane) (PDMS). O2, N2 and H2 permeability of the ionomer film is measured using a constant-volume, variable-pressure permeation system. Experimental results demonstrate dependence of gas permeation on thickness, and influence of physical aging on gas transport. AcknowledgementWe would like to thank Norman Su for providing assistance in permeation system assembly and operation. This work made use of facilities at the Biomolecular Nanotechnology Center at University of California, Berkeley and the Molecular Foundry at Lawrence Berkeley National Laboratory. This work was funded in part by the University of California Chancellor's Graduate Fellowship, National Science Foundation Graduate Fellowship and the Fuel Cell Technologies Office, Office of Energy Efficiency and Renewable Energy, U. S. Department of Energy under contract number DE-AC02-05CH11231.

Directed Assembly of Block Copolymers in Thin to Thick Films

The extent to which lamellae-forming polystyrene-block-poly(methyl methacrylate) (PS-b-PMMA, bulk period L0 = 48 nm) can be directed to assemble on chemically nanopatterned striped surfaces (period LS), with few defects and with domains registered to and extending vertically away from the underlying pattern, was studied as a function of film thickness, commensurability between L0 and LS, and annealing temperature. Two regimes of behavior are identified: thin film (<∼72 nm) and thick film. In the thin film regime, the range of LS/L0 over which the block copolymer could be directed to assemble into ordered linear arrays (with period L = LS) decreased with increasing film thickness. On identical chemical patterns, for example, a film thickness of 30 nm assembled at 0.89 < LS/L0 < 1.04, but a 72 nm film only assembled when LS ∼ L0. In the thin film regime, assembly is cooperative throughout the film thickness, and the behavior can be understood using thermodynamic arguments based on a phenomenological model that includes terms related to the configurational entropy of polymer chains, block–block interfacial energy, and film substrate interfacial energy. In the thick film regime, Directed Assembly occurs only for LS ∼ L0 but can occur in films as thick as 620 nm. In this regime, we present evidence that nucleation and growth of grains occurs independently at the free surface of the film and near the chemically patterned surface. Upon further annealing, the directed orientation and near perfect ordering nucleated on the chemical pattern eventually dominates the structure across the entire film. The thickness through which the directed structure may be realized increases with increasing annealing temperature and time such that under certain conditions (L0 = LS, annealing temperature = 230 °C) PS-b-PMMA films as thick as 620 nm (domain aspect ratio ≈25) exhibited very low levels of defectivity.

DIFFUSION AND EVAPORATION CONTROL THE SPREADING OF VOLATILE DROPLETS ONTO SOLUBLE FILMS

The spreading dynamics of a water droplet on a soluble polymer substrate is controlled by the rate of water transfers into the substrate. We provide a comprehensive description of the parameters controlling the wetting dynamics based on the analysis of the transfers between the spreading liquid and the solid substrate. Our model is supported by experimental results obtained on supported films of polymer with thickness e varied over two decades, on which droplets of water spread with a velocity U spanning two decades. Three different transfers are governing the hydration dynamics: (i) Water evaporates from the droplet, condenses on the substrate, and further diffuses through the polymer. (ii) Liquid water at the contact line diffuses in the polymer ahead of the contact line. (iii) Water in the droplet is convected at the droplet velocity U . The evaporative process is the most efficient at hydrating the substrate and controls the hydration of the polymer at distances ranging between a macroscopic cutoff length L and a microscopic length κ. L is set by the diffusion of vapor in air. κ results from a balance between the diffusion of water from the droplet at the contact line and the diffusion of water in the atmosphere. By analyzing the hydration profile at all distances to the contact line between L and κ, we define three different spreading regimes: a thick film regime where the film behaves as a semi-infinite medium, a thin film regime where hydration is homogeneous along the film thickness, and an intermediate regime where both situations coexist along the film away from the contact line.

Elastohydrodynamic Study of Blends of Bio‐Based Esters with Polyalphaolefin in the Low Film Thickness Regime

AbstractThe film thickness in elastohydrodynamic (EHD) conditions for soybean oil (SBO), oleic estolide ester (EST) and their binary blends with polyalphaolefins (PAO2 or PAO40) were studied at 30 and 100 °C. Changes with time, for up to 200 min, were monitored. SBO and its blends with the lower viscosity PAO2 showed initially good agreement with the Hamrock–Dowson (H–D) equation down to 1–3 nm film thickness. 60 min or more after the start of the measurements, boundary layers with thickness up to 4.7 nm were observed. The blend of SBO with the more viscous PAO40 showed initially a good agreement with H–D at 100 °C. Negative deviations in film thickness were observed 15 min after the start of the measurements. At extended periods of time, up to 200 min, they were less pronounced but still detectable. EST–PAO2 blend showed initially formation of boundary layers with thickness around 2 nm. The boundary layer at 30 °C did not change for 200 min, while at 100 °C showed a decrease in thickness and/or viscosity with time. The EST and the EST–PAO40 blends showed good agreement with the H–D equation and did not display a boundary or fractionation layer within 200 min.

Metal oxidation kinetics and the transition from thin to thick films

We report an investigation of growth kinetics and transition from thin to thick films during metal oxidation. In the thin film limit (<20 nm), Cabrera and Mott's theory is usually adopted by explicitly considering ionic drift through the oxide in response to electric fields, where the growth kinetics follow an inverse logarithmic law log(dl/dt) is proportional to 1/l. It is generally accepted that Wagner's theory, involving self-diffusion, is valid only in the limit of thick film regime (>1 μm) and leads to parabolic growth kinetics dl/dt is proportional to 1/l, where l is the oxide film thickness. Theory presented here unifies the two models and provides a complete description of oxidation including the transition from thin to thick film. The range of validity of Cabrera and Mott's theory and Wagner's theory can be well defined in terms of the Debye-Hückel screening length. The transition from drift-dominated ionic transport for thin film to diffusion-dominated transport for thick film is found to strictly follow the direct logarithmic law log(dl/dt) is proportional to -l that is frequently observed in many experiments.

Full Film, Boundary Lubrication and Tribochemistry in Steel Circular Contacts Lubricated with Glycerol

In this article, the lubricating properties of pure glycerol are investigated under both mild and severe EHL regimes. Amazingly low friction coefficients (about 0.01) are reported by experiments in thick film regimes compared to traditional base oils. EHL calculations of film thickness and friction (including thermal effects) predict friction coefficients that are twice those actually found for glycerol. Chemical analysis of glycerol before and after the friction tests were performed by NMR and Karl Fischer methods, and they reveal that water is produced by tribochemical reaction as well as other species like aldehydes. This finding is in agreement with a corrosion pattern observed inside the wear scars of the steel samples. This study provides an explanation to the anomalously low friction observed in the thick film regime. In fact, water produced in the lubricant decreases traction forces due to the drastic decrease of the viscosity of glycerol with water addition.

Thickness-dependent fcc–hcp phase transformation in polycrystalline titanium thin films

Polycrystalline Ti thin films are shown to gradually transform from face-centered cubic (fcc) to hexagonal close-packed structure (hcp) with increasing film thickness. Diffraction stress analysis revealed that the fcc phase is formed in a highly compressive hcp matrix (⩾2 GPa), the magnitude of which decreases with increasing film thickness. A correlation between stress and crystallographic texture vis-a-vis the fcc–hcp phase transformation has been established. The total free energy change of the system upon phase transformation calculated using the experimental results shows that the fcc–hcp transformation is theoretically possible in the investigated film thickness regime (144–720 nm) and the hcp structure is stable for films thicker than 720 nm, whereas the fcc structure can be stabilized in Ti films much thinner than 144 nm.

Morphology of Semicrystalline Diblock Copolymer Thin Films upon Directional Solvent Vapor Flow

AbstractThe possibility of achieving templates of highly ordered nanostructures with crystalline nano‐objects embedded inside an amorphous matrix is addressed. Atomic force microscopy and grazing incidence small‐angle X‐ray scattering (GISAXS) are used to probe the morphology at the surface and inside thin films of the diblock copolymer polystyrene‐block‐poly(ethylene oxide) P(S‐b‐EO). Directional benzene vapor flow introduces the orientation of poly(ethylene oxide) (PEO) cylinders inside the PS matrix. Within a limited film thickness regime, the cylinders are oriented parallel to the sample surface in domains of several micrometers due to shearing effects caused by the flow of benzene vapor parallel to the polymer surface. The crystallization of the PEO block by the benzene vapor treatment is also observed and crystals with sizes that approach that of the confined PEO domains are formed. Perpendicular orientation of the PEO crystalline stems with respect to the PEO cylindrical nanodomains is deduced from grazing incidence X‐ray diffraction. X‐ray reflectometry and scanning electron microscopy complement the investigation. magnified image

Combined Atomic Force Microscopy and Modeling Study of The Evolution of Octadecylamine Films on a Mica Surface

The time evolution of the film thickness and domain formation of octadecylamine molecules adsorbed oil a mica surface is investigated Using atomic force microscopy. The adsorbed Film thickness is determined by measuring the height profile across the mica-amine interface of a mica surface partially immersed in a 15 mM solution of octadecylamine in chloroform. Using this novel procedure, adsorption of amine on mica is found to occur in three distinct stages, with morphologically distinct domain Formation and growth occurring during each stage. In the first stage, where adsorption is primarily in the thin-film regime, all average Film thickness of 0.2 (+/- 0.3) nm is formed for exposure times below 30 s and 0.8 (+/- 0.2) nm for 60 s of immersion time. During this stage, large sample spanning domains are observed. The second stage, which occurs between 60-300 s, is associated with it regime of rapid film growth, and the film thickness increases from about 0.8 to 25 nm during this stage. Once the thick-film regime is established, further exposure to the amine solution results in all increase in the domain area, and it regime of lateral domain growth is observed. In this stage, the domain area coverage grows from 38 to 75%, and the FTIR spectra reveal an increased level of crystallinity in the film. Using it diffusion-controlled model and it two-step Langmuir isotherm, the time evolution of the film growth is quantitatively captured. The model predicts the time at which the thin to thick film transition occurs as well its the time required for complete film growth at longer times. The Ward-Tordai equation is also solved to determine the model parameters in the monolayer (thin-film) regime, which occurs during the initial stages of film growth.

Crystallization of D 2O thin films on Ru(0 0 1) surfaces

The phase conversion of amorphous solid water (ASW) to crystalline ice (CI) has been investigated in the very thin ( ∼ 10 monolayers) film regime on a Ru(0 0 1) surface. We analyze the converted CI fraction with the Avrami model, and recognize that one-dimensional CI growth occurs, which can be contrasted to the three-dimensional CI growth generally established in the thick ( ≥ 50 monolayers) film regime. We evaluate activation energy for the ASW crystallization to be about 1.0 eV. We suggest that the ASW crystallization is not influenced by the substrate even near the substrate–ice interface.

A Derivation of Continuum Nonlinear Plate Theory from Atomistic Models

We derive plate theory from atomistic models in the spirit of [G. Friesecke, R. D. James, and S. Muller, Comm. Pure Appl. Math., 55 (2002), pp. 1461–1506] as a Γ‐limit as the number of atoms tends to infinity. While in the “thick film regime,” i.e., when the film consists of many layers of atoms, we recover the well‐known plate theory derived from three‐dimensional elasticity in [G. Friesecke, R. D. James, and S. Muller, Comm. Pure Appl. Math., 55 (2002), pp. 1461–1506]; for “thin films” new terms in the limit functional are obtained. These terms are due to the discrete nature of atomic models and surface effects and cannot be detected from continuum elasticity.

Photo-Cross-Linkable PNIPAAm Copolymers. 4. Effects of Copolymerization and Cross-Linking on the Volume-Phase Transition in Constrained Hydrogel Layers

Photo-cross-linkable temperature and pH-responsive polymers based on N-isopropylacrylamide and 2-(dimethylmaleimido)-N-ethyl-acrylamide were synthesized and spin-coated to produce uniform thin films of cross-linked, responsive hydrogels. Surface plasmon resonance and optical waveguide spectroscopy were used to determine the effect on the volume-phase transition when these materials are confined to a thin film. The film thicknesses ranged from 10 nm to 2.5 μm, and the volume-phase transition temperature and swelling ratio of the films fell into two overlapping regimes separated by at least one critical thickness. In the thick-film regime, greater than 100−760 nm, depending on the cross-linking density, ionizable comonomer concentration, and reference state, the films exhibited two transition temperatures. This can be explained by the stress imposed on the hydrogel as it swells perpendicular to the substrate. In the thin-film regime, less than 270−440 nm, depending on cross-linking density, the presence of a fixed substrate also limited the collapse of the gel at temperatures above the volume-phase transition temperature. Nonequilibrium chain conformations resulting from the spin-coating process may explain this effect. Two different mechanisms for constraint are likely in the thin- and thick-film regimes, and existing models for the anisotropic swelling of hydrogel layers were used to explain these trends. The spin-coated hydrogel layers were also compared to dip-coated and free-radical polymerized hydrogel layers to provide additional insight to the constraint mechanism. The elastic modulus of the hydrogel layers was measured with atomic force microcopy. The modulus in the swollen state was a function of both the cross-linking density and the ionizable comonomer concentration and ranged from 4.48 to 26.6 kPa. The modulus in the collapsed state was primarily a function of the cross-linking density and ranged from 466 to 1540 kPa. The effect of the ionizable comonomer concentration on the modulus also suggests the presence of non-Gaussian chain conformations in the swollen network.

Solvent-mediated interactions and solvation close to fluid–fluid phase separation: A density functional treatment

We apply a general density functional approach for calculating the force between two big particles immersed in a solvent of smaller ones to calculate the solvent-mediated (SM) potential between two big Gaussian core particles in a binary mixture of smaller Gaussian particles, a simple model of polymers in solution. Within a mean-field free-energy functional, which generates the random phase approximation (RPA) for the bulk pair direct correlation functions, the binary solvent exhibits fluid–fluid phase separation and we show that the theory for calculating the SM potential captures effects of thick adsorbed films surrounding the big solute particles. For a single big particle there is a first-order thin–thick adsorbed film transition and in the thick-film regime—i.e., for solvent-state points lying close to the binodal, on the side where the solvent is poor in the species which is favored by the big particles—we find extremely attractive, long-ranged SM potentials between the big particles whose range is determined by the film thickness. For state points away from the binodal in the thin film regime, or above the “wetting point”, the SM potentials are short ranged and less attractive. We show that the effects of the thick adsorbed films around the big particles are not included when the SM potential is obtained from the big–big radial distribution function gbb(r), calculated using the RPA closure to the Ornstein–Zernike equations. In the region of the solvent critical point we also find extremely attractive SM potentials whose range is now set by the bulk correlation length in the binary solvent and which increases and eventually diverges for state points approaching the critical point. We calculate the excess chemical potential of the big solute particle in the binary solvent as a function of the concentration of one of the smaller species and show that this quantity also reflects the formation of thick adsorbed films. The form of the excess chemical potential and, hence, the solvation for the soft Gaussian core fluid is contrasted with that expected for a hard-core solute.

Breakdown of the approximations of small perturbations in continuum modeling of amorphous thin film growth

Morphology evolution of thin film growth can be quantitatively modeled by employing rate equations for two-dimensional, single-valued functions within a treatment of small perturbations. This description can be expected to be valid in an intermediate film thickness regime, where substrate influences and three-dimensional effects are minor. The breakdown of the mathematical description in its upper film thickness limit is systematically investigated by a detailed comparison of experiments and simulation. Possible reasons for the failure are discussed and improvements are suggested.