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The physisorption of molecules in confined geometry, i.e., in pores of atomic size such as found in zeolites, has been investigated using a simple pairwise-additive Lennard-Jones potential and an effective-medium model. In a spherical geometry, it is found that the equilibrium distance D corresponding to the lowest equilibrium energy is reduced to about 90% of the pair equilibrium distance σe. This originates from the increased dominance of long-range forces in the condensed state. The enhancement of the physisorption energy due to surface curvature and confinement effects reaches its maximum value of 5.05, relative to the flat surface, when D=0.899σe. This value must be compared to the factor of 8 which was derived previously [D. H. Everett and P. C Powl, J. Chem. Soc. Faraday Trans. 1 72, 619 (1976); E. G. Derouane, J.-M. André, and A. A. Lucas, Chem. Phys. Lett. 137, 336 (1987)] using a simple van der Waals model neglecting repulsion forces. It is also concluded that molecules can be strongly trapped in pores which are substantially narrower than their free (gaseous phase) sizes, the situation of lowest energy corresponding to R=D=0.899σe and the sorption energy remaining negative down to R=D=0.749σe (R denotes the pore radius). [ABSTRACT FROM AUTHOR]

The problem of evaluating the van der Waals attraction energy of an atom or microparticle adsorbed near the edge of a straight material wedge of arbitrary opening angle is considered. In order to disentangle more clearly the effect of the wedge geometry from the material parameters, a simple model is used in which the particle is represented by a harmonic oscillator and the substrate by a perfect conductor. By a straightforward extension of the method of images of classical electrostatics, the dipolar coupling of the particle to the substrate is constructed from which new oscillator frequencies can be determined as a function of its position relative to the edge and of the wedge angle. The van der Waals energy is given by the shift in zero-point energy of the oscillator coupled to itself via its images. For a physisorbed atom crossing the edge of a wedge material, the detailed shape of the van der Waals energy barrier (respectively, well) offered by a convex (respectively, concave) wedge is displayed and compared with approximate results deduced from a pairwise summation of Lennard-Jones interactions. The interest of these results for the dynamics and kinetics of sorption by microporous solids is briefly discussed. [ABSTRACT FROM AUTHOR]

Mesoporous Bragg stacks are able to change color upon infiltration or displacement of liquid compounds inside their porous structure. Reversible switching from transparency to coloration offers additional functionality. Based on Bruggeman's effective medium theory, we derive a transparency master equation, which is valid for bilayers of arbitrary host materials and pore-filling compounds. The transparency condition fixes pore volume fractions such that the effective refractive index is homogenized through the bilayer, hence, through arbitrary layered optical media built from this bilayer. This general concept is applied to the case of switching of hygrochromic coatings made of mesoporous mixed oxide Bragg stacks. [ABSTRACT FROM AUTHOR]

The electrochemical deposition of indium sulfide layers is investigated with the aim of replacing cadmium sulfide layers in copper-indium-gallium diselenide thin film solar cells. In this paper the deposition conditions are first investigated from theoretical solution chemistry analysis. Experiments are then carried out using Mo-coated glass conducting substrates and gold-coated electrochemical quartz crystal microbalance. Indium chloride acidic aqueous solutions (pH ~ 3.5-4) containing thiosulfate ions as the sulfur source are used. Cyclic voltammetry studies are carried out. A potential domain is determined which allows to deposit compact layers. XPS analysis indicates the presence of both sulfur and oxygen in the films. The double structure of the O 1s spectra and the particular S 2p energy dispersion suggest two distinct chemical environments for indium whose respective prominence depends on the deposition potential. At low overpotential, an indium sulfide layer containing oxygen species (O, OH) is predominantly identified whereas at more negative potentials a second environment attributed to the presence of sulfate-type (SOx) groups emerge. These results are discussed in relation to solution chemistry analysis and possible reaction paths are proposed. [ABSTRACT FROM AUTHOR]

In this paper, we present two key process steps for potential applications in the fabrication of low-cost and high-efficiency ultrathin monocrystalline silicon (mono-Si) solar cells to effectively harvest solar energy. One is to grow an Al2O3 passivation layer on the rear side of an Si wafer by a successive atomic layer deposition (ALD) at room temperature (25 °C). The other is to produce a bio-inspired antireflection structure on the front side of the Si wafer by replicating butterfly wing patterns. The capacitance-voltage measurements reveal that the successive ALD procedure can yield a higher negative charge density at the Al2O3/Si interface relative to the conventional one. The measurement results of quasi-steady-state photoconductance indicate that after annealing, the 25 °C ALD Al2O3 layers reach a similar passivation level to the p-type Si wafers compared to that deposited at 250 °C. With the help of an ALD Al2O3 layer, butterfly wing patterns (Hypochrysops polycletus) are replicated on a PMMA layer which is on an SiO2/Si stack. This work demonstrates the ability for replicating the natural photonic features on Si wafers and other substrates by using nanoimprint. [ABSTRACT FROM AUTHOR]

Chalcogenide semiconductors, such as CuInSe2, are promising materials for optoelectronic applications such as solar cells. Conversion efficiencies up to 14% based on Cu-In-Se layers electrodeposited have been achieved. However, the electrocrystallization of this multinary system, whose components exhibit different electrochemical and chemical properties, is a complex process. In the present work, the electrocrystallization mechanism of CuInSe2 is investigated in dilute acidic solutions by in situ electrochemical investigation (polarization, electrochemical quartz crystal microbalance, and impedance spectroscopy) and ex situ chemical and structural analyses. A detailed X-ray photoelectron spectroscopy analysis is carried out to determine the surface composition and the chemical environment of the elements. Marked differences between surface and bulk concentrations are evidenced. At low polarizations, binary Cu-Se phases are obtained, which facilitate the reduction of Se(IV) species into elemental selenium. An intermediate CuSe2 phase is formed which, in turn, enables the incorporation of indium beyond a potential threshold close to -0.6 V/mercurous sulfate electrode. In this potential zone, major transitions are observed in composition, morphology, structure, and electrochemical behavior. A reaction path is proposed, which accounts for the main experimental observations. It emphasizes the role of surface reactions, occurring via passivating and nucleation sites, in the incorporation of indium. [ABSTRACT FROM AUTHOR]

A design is proposed for a stable infrared source suited to absorbance measurements. The source is a parallelepipedic cavity of tantalum, heated to 2600 K, with an apparent emissivity in excess of 0.7. It is observed to be three times brighter at 3000 cm[sup -1] than the 1440-K SiC bar. A model is constructed in order to estimate the temperature distribution. For this kind of source, the temperature and emissivity are found to be quite uniform. A comparison between estimated and experimental values of temperature and emissivity is discussed. [ABSTRACT FROM AUTHOR]

To achieve both high stability during scanning tunneling microscopy (STM) measurements at atomic resolution and long-range imaging of nonhomogeneous samples, we have developed a fully 2D vertical inertial nanopositioner which allows tunneling tip displacements in the 0.011000 µm range while keeping high-resolution STM conditions. The inertial sliding of the tip is obtained by overriding the static friction criterion between the tip and its support. By controlling the expansion of the piezotubes and the direction of the applied acceleration, one can obtain displacements as small as 100 Å in the vertical direction. The same piezotubes are also used to scan the sample during conventional STM measurements. Increasing the resonance frequency of the scanner above 10 kHz was essential to ensure good operation. The complete device has not altered the mechanical stability of the microscope; it works in air as well as in ultra-high vacuum conditions. Its reliability is demonstrated by the possibility of obtaining STM images of adjacent areas. [ABSTRACT FROM AUTHOR]

The aim of our study was to investigate the correlation between structural colour and scale morphology in butterflies. Detailed correlations between blue colour and structure were investigated in three lycaenid subfamilies, which represent a monophylum in the butterfly family Lycaenidae (Lepidoptera): the Coppers (Lycaeninae), the Hairstreaks (Theclinae) and the Blues (Polyommatinae). Complex investigations such as spectral measurements and characterization by means of light microscopy, scanning electron microscopy and transmission electron microscopy enabled us to demonstrate that: (i) a wide array of nanostructures generate blue colours; (ii) monophyletic groups use qualitatively similar structures; and (iii) the hue of the blue colour is characteristic for the microstructure and nanostructure of the body of the scales. [ABSTRACT FROM AUTHOR]

Using a finite difference time domain method, the authors study the electromagnetic transmission coefficient of a microwaveguide coupled to a lateral stub. It is shown that if the stub is covered with a thin metallic layer, the transmission spectrum contains several very narrow and deep depressions despite the small size of the resonator. The frequencies of the zeros of transmission are studied as a function of the geometrical parameters of the stub. The quality factor of the dips is increased when the waveguide is separated from the stub by a small air gap. [ABSTRACT FROM AUTHOR]