Nanoscale water condensation on click-functionalized self-assembled monolayers

We have examined the nanoscale adsorption of molecular water under ambient conditions onto a series of well-characterized functionalized surfaces produced by Cu(I)-catalyzed alkyne-azide cycloaddition (CuAAC or "click") reactions on alkyne-terminated self-assembled monolayers on silicon. Water contact angle (CA) measurements reveal a range of macroscopic hydrophilicity that does not correlate with the tendency of these surfaces to adsorb water at the molecular level. X-ray reflectometry has been used to follow the kinetics of water adsorption on these "click"-functionalized surfaces, and also shows that dense continuous molecular water layers are formed over 30 h. For example, a highly hydrophilic surface, functionalized by an oligo(ethylene glycol) moiety (with a CA = 34°) showed 2.9 ? of adsorbed water after 30 h, while the almost hydrophobic underlying alkyne-terminated monolayer (CA = 84°) showed 5.6 ? of adsorbed water over the same period. While this study highlights the capacity of X-ray reflectometry to study the structure of adsorbed water on these surfaces, it should also serve as a warning for those intending to characterize self-assembled monolayers and functionalized surfaces to avoid contamination by even trace amounts of water vapor. Moreover, contact angle measurements alone cannot be relied upon to predict the likely degree of moisture uptake on such surfaces.     

Translocation of biomolecules through solid‐state nanopores: Theory meets experiments

The interest in polynucleotide translocation through nanopores has moved from purely biological to the need of realizing nanobiotechnological applications related to personalized genome sequencing. Polynucleotide translocation is a process in which biomolecules, like DNA or RNA, are electrophoretically driven through a narrow pore and their passage can be monitored by the change in the ionic current through the pore. Such a translocation process, which will be described here offers a very promising technology aiming at ultra‐fast low‐cost sequencing of DNA, though its realization is still confronted with challenges and drawbacks. In this review, we present the main aspects involved in the polynucleotide translocation through solid‐state nanopores by discussing the most relevant experimental, theoretical, and computational approaches and the way these can supplement each other. The discussion will expose the goals that have been reached so far, the open questions, and contains an outlook to the future of nanopore sequencing. © 2011 Wiley Periodicals, Inc. J Polym Sci Part B: Polym Phys 49: 985–1011, 2011     

On the spectral theory of trees with finite cone type

We study basic spectral features of graph Laplacians associated with a class of rooted trees which contains all regular trees. Trees in this class can be generated by substitution processes. Their spectra are shown to be purely absolutely continuous and to consist of finitely many bands. The main result gives stability of the absolutely continuous spectrum under sufficiently small radially label symmetric perturbations for non-regular trees in this class. In sharp contrast, the absolutely continuous spectrum can be completely destroyed by arbitrary small radially label symmetric perturbations for regular trees in this class.     

Soliton dynamics for fractional Schrödinger equations

We investigate the soliton dynamics for the fractional nonlinear Schrödinger equation by a suitable modulational inequality. In the semiclassical limit, the solution concentrates along a trajectory determined by a Newtonian equation depending of the fractional diffusion parameter.     

Jet substructure with analytical methods

We consider the mass distribution of QCD jets after the application of jet-substructure methods, specifically the mass-drop tagger, pruning, trimming and their variants. In contrast to most current studies employing Monte Carlo methods, we carry out analytical calculations at the next-to-leading order level, which are sufficient to extract the dominant logarithmic behaviour for each technique, and compare our findings to exact fixed-order results. Our results should ultimately lead to a better understanding of these jet-substructure methods which in turn will influence the development of future substructure tools for LHC phenomenology.     

Shape‐Tailored Polymer Colloids on the Road to Become Structural Motifs for Hierarchically Organized Materials

Anisometric polymer colloids are likely to behave differently when compared with centrosymmetric particles. Their study may not only shine new light on the organization of matter; they may also serve as building units with specific symmetries and complexity to build new materials from them. Polymer colloids of well‐defined complex geometries can be obtained by packing a limited number of spherical polymer particles into clusters with defined configurations. Such supracolloidal architectures can be fabricated at larger scales using narrowly dispersed emulsion droplets as templates. Assemblies built from at least two different types of particles as elementary building units open perspectives in selective targeting of colloids with specific properties, aiming for mesoscale building blocks with tailor‐made morphologies and multifunctionality. Polymer colloids with defined geometries are also ideal to study shape‐dependent properties such as the diffusion of complex particles.

     

A frequency-modulated quantum-cascade laser for spectroscopy of CH4 and N2O isotopomers

We report the development of a novel laser spectrometer for high-sensitivity detection of methane and nitrous oxide. The system relies on a quantum-cascade laser source emitting wavelength of around 8.06 μm, where strong fundamental absorption bands occur for the considered species and their isotopomers. The detection technique is based on audio-frequency and radio-frequency modulation of laser radiation. First experimental tests have been performed to estimate the achievable detection limits and the signal reproducibility levels in view of possible measurements of ¹³C/¹²C, ¹⁸O/¹⁶O, ¹⁷O/¹⁶O and ¹⁵N/¹⁴N isotope ratios.     

Elastic scattering cross section of photons by water: limits for the free atom approximation

Several papers can be found in the literature in which elastic and inelastic experimental scattering cross sections of photons by water with energies in the keV range are measured. Usually, the authors use some kind of normalization with theoretical values, because of the difficulties in obtaining some parameters necessary to obtain absolute cross sections from the measurements. A reasonable range of momentum transfer has been covered, but nevertheless, inconsistencies and gaps still remain. In this work, we address the problem performing absolute cross section measurements in the high momentum transfer region (0.33 Å^?1 ≤ x ≤ 4.5 Å^?1), where no structure effects can be observed. We compare the results with theory to validate it in an intermediary region (0.33 Å^?1 ≤ x ≤ 1.72 Å^?1) and then use the experimental values to normalize data in the low‐energy region (0.078 Å^?1 ≤ x ≤ 1.72 Å^?1) to obtain the experimental cross section in that region. From the comparison, we concluded that for momentum transfers, x between 0.7 and 4.5 Å^?1 the scattering can be considered as being due to free atoms in free molecules. Therefore, the scattering cross sections may be considered as a sum of those from free atoms. Theoretically, the scattering cross sections can be obtained from the form factors as well as from the second‐order perturbation theory (S‐matrix) because there is no significant difference between both. On the other hand, for x ≤ 0.7 Å^?1, interference between the photon‐scattered amplitudes due to liquid structure generates oscillations in the cross section values. Copyright © 2014 John Wiley & Sons, Ltd.     

Light absorption in Ge nanoclusters embedded in SiO2: comparison between magnetron sputtering and sol–gel synthesis

SiGeO films have been produced by a sol–gel derived approach and by magnetron sputtering deposition. Post-thermal annealing of SiGeO films in forming gas or nitrogen atmosphere between 600 and 900 °C ensured the phase separation of the SiGeO films and synthesis and growth of Ge nanoclusters (NCs) embedded in SiO₂. Rutherford backscattering spectrometry analysis evidenced a similar Ge concentration (~12 %), but a different Ge out-diffusion after annealing between the two types of techniques with the formation of a pure SiO₂ surface layer (~30 nm thick) in sol–gel samples. The thermal evolution of Ge NCs has been followed by transmission electron microscopy and Raman analysis. In both samples, Ge NCs form with similar size increase (from ~3 up to ~7 nm) and with a concomitant amorphous to crystalline transition in the 600–800 °C temperature range. Despite a similar Ge concentration, a significant lower NCs density is observed in sol–gel samples attributed to an incomplete precipitation of Ge, which probably remains still dispersed in the matrix. The optical absorption of Ge NCs has been measured by spectrophotometry analyses. Ge NCs produced by the sol–gel method evidence an optical band gap of around 2 eV, larger than that of NCs produced by sputtering (~1.5 eV). These data are presented and discussed also considering the promising implications of a low-cost sol–gel based technique towards the fabrication of light harvesting devices based on Ge nanostructures.