Nanostructured thin films as surface‐enhanced Raman scattering substrates

Nanoporous thin films with silver nanoparticles were synthesized with a bottom–up approach, and its potential as effective surface‐enhanced Raman scattering (SERS) substrates was demonstrated. The use of mesoporous titania films as substrates allowed to control the growth of nanoparticles on the film surface. Atomic force microscopy measurements, Ultraviolet‐visible and X‐ray diffraction analysis confirmed the photoreduction of Ag⁺ to Ag⁰ with the formation of nanoparticles with crystallite dimensions of 32 to 36 nm. The new substrates allowed the detection of two analytes (rhodamine B isothiocyanate and cytochrome c), present in solutions at very low concentrations, highlighting their potential in SERS sensing. Reproducibility, homogeneity, enhancement factor of the substrate, consistency of results and detection limits were also assessed. Copyright © 2012 John Wiley & Sons, Ltd.     

Hybrid materials with an increased resistance to hard X‐rays using fullerenes as radical sponges

The protection of organic and hybrid organic–inorganic materials from X‐ray damage is a fundamental technological issue for broadening the range of applications of these materials. In the present article it is shown that doping hybrid films with fullerenes C₆₀ gives a significant reduction of damage upon exposure to hard X‐rays generated by a synchrotron source. At low X‐ray dose the fullerene molecules act as `radical scavengers', considerably reducing the degradation of organic species triggered by radical formation. At higher doses the gradual hydroxylation of the fullerenes converts C₆₀ into fullerol and a bleaching of the radical sinking properties is observed.     

Design of hybrid organic–inorganic materials through their structure control: The case of epoxy bearing alkoxides

Hybrid organic–inorganic materials from (3-glycidoxypropyl)methyldiethoxysilane (GPMD) and [3-(2-aminoethyl)aminopropyl]trimethoxysilane (AEAPTMS) have been synthesized. The structure of the hybrid material has been studied as a function of AEAPTMS content by a combination of vibrational and nuclear magnetic resonance spectroscopies. The amine groups in AEAPTMS have shown to be very effective epoxy curing agents and the degree of condensation inside the hybrid material can be finely tuned with the amount of AEAPTMS. Fourier transform near infrared spectroscopy coupled with 2D infrared analysis has been used to elucidate the role of amines in epoxy curing. Several reactions of the amines with the epoxies have been observed, via tertiary, secondary and primary amines. At low AEAPTMS contents the hybrid material exhibits a residual mobility of the organic species, as revealed by solid state NMR spectroscopy. This property has been evaluated comparing qualitatively the residual mobility in hybrid materials synthesized with different types of organically modified alkoxides containing epoxy functional groups.     

Spectrophotometric and Calorimetric Studies of Np(V) Complexation with Acetate at Various Temperatures from <Emphasis Type="Italic">T</Emphasis>=283 to 343 K

Spectrophotometric titrations were performed to identify the Np(V)/acetate complex and determine the equilibrium constants at various temperatures (T=283 to 343 K) and at the ionic strength 1.05 mol⋅kg⁻¹. The enthalpies of complexation at the corresponding temperatures were determined by microcalorimetric titrations. Results show that the complexation of Np(V) with acetate is weak but strengthens as the temperature increases. The complexation reaction is endothermic and entropy driven. The enhancement of complexation at higher temperatures is primarily due to the increasingly larger entropy gain when the solvent molecules are released from the highly-ordered solvation spheres of NpO₂⁺\mathrm{NpO}_{2}^{+} and acetate to the bulk solvent where the degree of disorder is higher at higher temperatures.     

Robust exponential attractors for the strongly damped wave equation with memory. I

We consider the singular limit of the semilinear strongly damped wave equation with memory

A sharp estimate for the Hilbert transform along finite order lacunary sets of directions

We prove, in ZFC, that there is an infinite strictly descending chain of classes of theories in Keisler’s order. Thus Keisler’s order is infinite and not a well order. Moreover, this chain occurs within the simple unstable theories, considered model-theoretically tame. Keisler’s order is a central notion of the model theory of the 60s and 70s which compares first-order theories, and implicitly ultrafilters, according to saturation of ultrapowers. Prior to this paper, it was long thought to have finitely many classes, linearly ordered. The model-theoretic complexity we find is witnessed by a very natural class of theories, the n-free k-hypergraphs studied by Hrushovski. This complexity reflects the difficulty of amalgamation and appears orthogonal to forking.     

A modulation invariant Carleson embedding theorem outside local <Emphasis Type="Italic">L</Emphasis><Subscript>2</Subscript>

Yen Do and Christoph Thiele developed a theory of Carleson embeddings in outer L_p spaces for the wave packet transform

$${F_\phi }(f)(u,t,\eta ) = \int {f(x){e^{i\eta (u - x)}}\phi \left( {\frac{{u - x}}{t}} \right)} \frac{{dx}}{t},(u,t,\eta ) \in R \times (0,\infty ) \times R$$

of functions f ∈ L_p(R) in the range 2 ≤ p ≤ ∞, referred to as local L². In this article, we formulate a suitable extension of this theory to exponents 1 < p < 2, answering a question posed by Do and Thiele. The proof of our main embedding theorem involves a refined multi-frequency Calderón-Zygmund decomposition in the vein of work by Di Plinio and Thiele and by Nazarov, Oberlin, and Thiele. We apply our embedding theorem to recover the full known range of L^p estimates for the bilinear Hilbert transforms without reducing to discrete model sums or appealing to generalized restricted weak-type interpolation.

     

Thin adsorbed films of a strong cationic polyelectrolyte on silica substrates

The adsorption of poly(diallyldimethyl ammonium chloride) (DADMAC) on planar silica substrates was examined as a function of ionic strength and pH. The study was carried out with reflectometry in an impinging-jet cell and complemented by atomic force microscopy (AFM) and ellipsometry investigations. The adsorption process is initially transport limited, whereby the adsorption rate increases somewhat with increasing ionic strength. This effect is caused by a simultaneous decrease of the hydrodynamic radius of the polymer. After a transient period, the adsorption process saturates and leads to an adsorption plateau. The plateau value increases strongly with increasing ionic strength. This increase can be explained by progressive screening of the electrostatic repulsion between the adsorbing polyelectrolyte chains, as can be rationalized by a random sequential adsorption (RSA) model. The adsorbed amount further increases with increasing pH, and this effect is probably caused by the corresponding increase of the surface charge of the silica substrate.     

Hard X-rays and soft-matter: processing of sol–gel films from a top down route

A current trend of applied research in the field of nanomaterials is the integration of bottom up and top down fabrication methods. Sol–gel chemistry is widely applied to obtain different functional materials from a bottom up route, especially in the case of thin films. To fabricate devices based on sol–gel films, which include nanocomposites and mesoporous ordered materials, application of lithography technologies is mandatory. Among the different lithographic approaches, photolithography is widely used by companies using micro-fabrication processes. In this context, photolithography is a typical top down method that requires to be integrated as much as possible with deposition of thin films from a liquid phase. Recently we have developed a new integrated fabrication method which uses high energy photons, such as hard X-rays, which typically have energies between 2.5 and 12 keV, for the manipulation and production of a large variety of functional materials and devices. In the present review a short overview of such achievements is presented.