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We unified the number-of-layer dependence of the A1g and the E12g phonon frequencies of the layered MX2 (M = Mo and W; X = S and Se) semiconductors with derivative of quantitative information on the bond relaxation dynamics and clarification of their physical origins. Theoretical reproduction of observations confirms that atomic undercoordination stems the unusual behavior of phonons of the MX2. The difference in electronegativity and ionic radius between the constituent elements resolves the bond nature index m and the relaxation extents of phonon frequencies. It is also clarified that the dimer interaction dictates the blue shift of the E12g phonon but the collective interaction of an atom with its z-neighbors governs the red shift of the A1g phonon dynamics as the number-of-layer reduces. Copyright © 2017 John Wiley & Sons, Ltd. [ABSTRACT FROM AUTHOR]

The solute-solvent interaction of salts has a striking impact on various biological and industrial processes but its mechanism remains yet mysterious despite intensive studies since 1888 when Franz Hofmeister established the salt series. A combination of confocal Raman spectroscopy and contact angle measurements has enabled us to resolve the hydrogen bond relaxation (O:H-O, HB) and the associated charge polarization dynamics at different molecular site because of alkali halides hydration. Results show consistently that salt hydration softens the O:H phonon but stiffens H-O phonon cooperatively. The extent of HB relaxation and polarization is proportional to the electronegativity difference and ionic radius, following the order of Hofmeister series: X (R/η) = I (2.2/2.5) > Br (1.96/2.8) > Cl (1.81/3.0) > F (1.33/4.0) ≈ 0 for anions, and Y(R/η) = Na (0.98/0.9) > K (1.33/0.8) > Rb (1.49/0.8) > Cs (1.65/0.8) for cations. Observations suggest that ions create each an electric field that aligns, stretches, and polarizes water molecules, which relaxes the O:H-O bond cooperatively, depresses the molecular dynamics, and enhances the hydration shell viscosity and the skin stress. Exercises also demonstrate that Raman spectroscopy performs as a powerful tool for probing the molecular-site-resolved HB network relaxation dynamics in terms of phonon stiffness, molecular fluctuation dynamics, and phonon abundance transition under external stimulus. Copyright © 2016 John Wiley & Sons, Ltd. [ABSTRACT FROM AUTHOR]