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We report optical near-field Raman imaging with subdiffraction resolution (~120 nm) without field enhancement effects. Chemical discrimination on tetracyanoquinodimethane organic thin films showing localized salt complexes is accomplished by detailed Raman maps. Acquisition times that are much shorter than previously reported are due to the high Raman efficiency of the materials and to a careful collection and detection of the optical signals in our near-field Raman spectrometer. OCIS codes: 180.0180, 180.5810, 300.0300, 300.6450.

We study the relaxation times ta in the water-methanol system. We examine new data and data from the literature in the large temperature range 163 < T < 335 K obtained using different experimental techniques and focus on how ta affects the hydrogen bond structure of the system and the hydrophobicity of the alcohol methyl group. We examine the relaxation times at a fixed temperature as a function of the water molar fraction XW and observe two opposite behaviors in their curvature when the system moves from high to low T regimes. This behavior differs from that of an ideal solution in that it has excess values located at different molar fractions (XW = 0.5 for high T and 0.75 in the deep supercooled regime). We analyze the data and find that above a crossover temperature T ~ 223 K, hydrophobicity plays a significant role and below it the water tetrahedral network dominates. This temperature is coincident with the fragile-to-strong dynamical crossover observed in confined water and supports the liquid-liquid phase transition hypothesis. At the same time, the reported data suggest that this crossover temperature (identified as theWidom line temperature) also depends on the alcohol concentration. [ABSTRACT FROM AUTHOR]

We study the self-diffusion coefficient and viscosity of a water-glycerol mixture for several glycerol molar fractions as a function of temperature well inside the metastable supercooled regime. We perform NMR experiments and verify that the system has at different concentration a fragileto- strong crossover accompanied by the violation of the Stokes-Einstein relation. We observe that the crossover temperature depends on the water amount. Studying the fractional representation of the Stokes-Einstein relation, we find that in these systems dynamical arrest does not exhibit criticality and the transport parameters have a universal behavior. [ABSTRACT FROM AUTHOR]

We study by means of nuclear magnetic resonance the self-diffusion of protein hydration water at different hydration levels across a large temperature range that includes the deeply supercooled regime. Starting with a single hydration shell (h = 0.3), we consider different hydrations up to h = 0.65. Our experimental evidence indicates that two phenomena play a significant role in the dynamics of protein hydration water: (i) the measured fragile-to-strong dynamic crossover temperature is unaffected by the hydration level and (ii) the first hydration shell remains liquid at all hydrations, even at the lowest temperature. [ABSTRACT FROM AUTHOR]

The thermodynamic response functions of water display anomalous behaviors. We study these anomalous behaviors in bulk and confined water. We use nuclear magnetic resonance (NMR) to examine the configurational specific heat and the transport parameters in both the thermal stable and the metastable supercooled phases. The data we obtain suggest that there is a behavior common to both phases: that the dynamics of water exhibit two singular temperatures belonging to the supercooled and the stable phase, respectively. One is the dynamic fragile-to-strong crossover temperature (TL ≃ 225 K). The second, T* ~ 315 ± 5 K, is a special locus of the isothermal compressibility KT(T, P) and the thermal expansion coefficient αP(T, P) in the P-Tplane. In the case of water confined inside a protein, we observe that these two temperatures mark, respectively, the onset of protein flexibility from its low temperature glass state (TL) and the onset of the unfolding process (T*). [ABSTRACT FROM AUTHOR]

The "dynamic" or "glass" transition in biomolecules is as important to their functioning as the folding process. This transition occurs in the low temperature regime and has been related to the onset of biochemical activity that is dependent on the hydration level. This protein transition is believed to be triggered by the strong hydrogen bond coupling in the hydration water. We study the vibrational bending mode and measure it using Fourier Transform Infrared spectroscopy. We demonstrate that at the molecular level the hydration water bending mode bonds the C=O and N-H peptide groups, and find that the temperature of the "dynamic" protein transition is the same as the fragile-to-strong dynamic transition in confined water. The fragile-to-strong dynamic transition in water governs the nature of the H bonds between water and peptides and appears to be universal in supercooled glassforming liquids. [ABSTRACT FROM AUTHOR]

The irreversible return of a supercooled liquid to stable thermodynamic equilibrium often begins as a fast process which adiabatically drives the system to solid-liquid coexistence. Only at a later stage will solidification proceed with the expected exchange of thermal energy with the external bath. In this paper we discuss some aspects of the adiabatic freezing of metastable water at constant pressure. In particular, we investigated the thermal behavior of the isobaric gap between the molar volume of supercooled water and that of the warmer ice-water mixture which eventually forms at equilibrium. The available experimental data at ambient pressure, extrapolated into the metastable region within the scheme provided by the reference IAPWS-95 formulation, show that water ordinarily expands upon (partially) freezing under isenthalpic conditions. However, the same scheme also suggests that, for increasing undercoolings, the volume gap is gradually reduced and eventually vanishes at a temperature close to the currently estimated homogeneous ice nucleation temperature. This behavior is contrasted with that of substances which do not display a volumetric anomaly. The effect of increasing pressures on the alleged volume crossover from an expanded to a contracted ice-water mixture is also discussed. [ABSTRACT FROM AUTHOR]

Group-IV semiconductor nanowires (NWs) are attracting the interest of a wide scientific community as building blocks for a wide range of future nanoscaled devices. We used metal-assisted chemical etching of Si substrates to synthesize Si NWs with different length and nanometer-size diameter. NWs obtained by this technique have exactly the same structure and doping of the substrate and present quantum confinement effects. Photoluminescence (PL) emission at room temperature from Si NWs is reported. We observed an increasing behaviour of the PL intensity as a function of the NWs length. The fabrication of light emitting devices based on Si NWs, showing electroluminescence emission at room temperature under low voltage excitation, is also reported. (© 2014 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim) [ABSTRACT FROM AUTHOR]