We pressure tune the hydrogen bond in Fe-O-H⋅⋅⋅O-P structural segments of mixed-valence barbosalite (Fe 2+ Fe 3+ 2)(PO4)2(OH)2. Infrared spectroscopy evidences changes in softening of O-H stretch modes and excessive profile broadening onset below 10 GPa. Single-crystal X-ray diffraction shows pseudo-symmetrization of the original monoclinic unit cell concurs with these changes in the O-H vibrational mode. These are considered compelling indicators of proton delocalization onset below 10 GPa as hydrogen bonds are strengthened under pressure. Subsequently in the range 10−30 GPa, Fe Mössbauer spectroscopy discerns Fe 2+ ⇔ Fe 3+ valence fluctuations at proximate cations of the hydrogen bonds. When the original crystal potential at an Fe 2+ site is perturbed by proton delocalization at a ligand, electron exchange is induced along Fe 2+ →L→Fe 3+ pathways (ligand L = O or (OH)-of shared octahedral faces). Thus, (Fe 2+ Fe 3+ 2)(PO4)2(OH)2 under pressure exemplifies the interplay between proton (THz) and electron (MHz) dynamics on two disparate time scales in the same condensed phase.

The synthesis of multifunctional poly(amidoamine)(PAMAM)-based dendrimers containing a cleavable disulfide linkerwithin each armof the dendrimer, together with condensable triethoxysilyl groups on the periphery of the dendrimer, isdescribed. The dendrimers were mixed with bis(triethoxysilyl)benzene and subsequently transformed into silsesquioxanegels or periodic mesoporous organosilicas (PMOs) to generate materials with dendrimers covalently embedded within theinterior of the silsesquioxane networks. Subsequent treatment of the gels with dithiothreitol enabled the core of thedendrimers to be selectively cleaved at the disulfidesite, thus generating thiol functions localised within the pores.The effect of different dendrimer generations on the reactivity of the pendant thiol functions was probed by impregnationwith gold salts, which were reduced to obtain gold nanoparticleswithin the pore networks of the gels and PMOs. The gelsyielded polydisperse gold nanoparticles (2 to 70 nm) with dimensions modulated by the generation of thedendrimer,together with well-defined gold/thiolate clusters with Au...S distances of 2.3 Å. Suchclusters were also observed in the PMOsystem, together with monodispersed gold nanoparticles with diameters comparable to that of the organised pores in thePMO. The role of surface functionalisation in controlling the formation of gold clusters and/or nanoparticles is discusse

Low-dimensional boron nitride (BN) chains were prepared in the one-dimensional pores of the siliceous zeolites theta-one (TON) and Mobil-twelve (MTW) by the infiltration, followed by the dehydrocoupling and pyrolysis of ammonia borane under high-pressure, high-temperature conditions. High-pressure X-ray diffraction in a diamond anvil cell and in a large-volume device was used to follow in situ these different steps in order to determine the optimal conditions for this process. Based on these results, millimeter-sized samples of BN/TON and BN/MTW were synthesized. Characteristic B–N stretching vibrations of low-dimensional BN were observed by infrared and Raman spectroscopies. The crystal structures were determined using a combination of X-ray diffraction and density functional theory with one and two one-dimensional zig-zag (BN)x chains per pore in BN/TON and BN/MTW, respectively. These 1-D BN chains potentially have interesting photoluminescence properties in the far ultraviolet region of the electromagnetic spectrum.

We report a complete investigation of the structural, electronic, vibrational, elastic and piezoelectric properties of the P2 1 2 1 2 1 orthorhombic phase in cadmium diiodate (δ-Cd(IO 3) 2) by combining experiments and first-principles based calculations. We revisited the nature of the electronic band gap and suggest an indirect band gap with a value of 4.6 eV. The infrared and Raman responses were measured and the different phonon modes assigned. To date, the δ-Cd(IO 3) 2 piezoelectric response remains unknown. We reported the different mechanisms involved in its piezoelectric response from the density functional perturbation theory. The highest value of the piezoelectric-stress and piezoelectric-strain constants in the zero Kelvin limit is predicted for e 41 =-0.27 C/m 2 and d 41 =-10.32 pC/N. These sizable values associated with the thermal stability (no phase transition up to the thermal decomposition at 550°C) and a relative large electronic band gap make δ-Cd(IO 3) 2 a potential candidate for piezoelectric applications.

Photoluminescence of single-walled carbon nanotubes is monitored at the individual scale by molecule encapsulation into their hollow core. Depending on the electronic character (electron donor or acceptor) of the confined molecule, enhancement or quenching of the photoluminescence intensity is demonstrated. This behavior is assigned to a charge transfer, evidenced by the shift of the Raman G-band, and a correlated Fermi level shift shown by photoemission experiments. Our experimental results are supported by DFT calculations. A consistent picture of the physical interactions taking place in the hybrid systems and their effects on the optical and electronic properties is given. Our results indicate that the electron affinity or ionization potential of the encapsulated molecules and the diameter of the nanotube are relevant parameters to tune the light emission properties of the hybrid systems at the nanoscale.

Twisted bilayer graphene is a fascinating system due to the possibility of tuning the electronic and optical properties by controlling the twisting angle θ between the layers. The coupling between the Dirac cones of the two graphene layers gives rise to van Hove singularities (vHs) in the density of electronic states, whose energies vary with θ. Raman spectroscopy is a fundamental tool to study twisted bilayer graphene (TBG) systems since the Raman response is hugely enhanced when the photons are in resonance with transition between vHs and new peaks appear in the Raman spectra due to phonons within the interior of the Brillouin zone of graphene that are activated by the Moiré superlattice. It was recently shown that these new peaks can be activated by the intralayer and the interlayer electron–phonon processes. In this work we study how each one of these processes enhances the intensities of the peaks coming from the acoustic and optical phonon branches of graphene. Resonance Raman measurements, performed in many different TBG samples with θ between 4∘ and 16∘ and using several different laser excitation energies in the near-infrared (NIR) and visible ranges (1.39–2.71 eV), reveal the distinct enhancement of the different phonons of graphene by the intralayer and interlayer processes. Experimental results are nicely explained by theoretical calculations of the double-resonance Raman intensity in graphene by imposing the momentum conservation rules for the intralayer and the interlayer electron–phonon resonant conditions in TBGs. Our results show that the resonant enhancement of the Raman response in all cases is affected by the quantum interference effect and the symmetry requirements of the double resonance Raman process in graphene.

Metal oxide aluminosilicate and aluminogermanate nanotubes, called imogolite nanotubes, are custom made nanotubes with controlled diameter, morphology and organization. These nanotubes undergo major structural changes at high temperatures. Here, we report a complete analysis of the structural transformation of single and double-walled aluminogermanate nanotubes, organized or not in bundles, up to 800 • C. Complementary X-ray scattering and spectroscopy experiments were performed. The evolution of both Al and Ge atoms coordination during the transformation process was studied in-situ. Quantitative analysis of X-ray absorption spectra reveals that the dehydroxylation of nanotubes leads to intermediate stages of 'metaimogolite', which differ in the coordination of the aluminium atoms. A mechanism explaining the major structural reorganization is proposed based on atomic jump processes.