We report on the rapid optical detection of gaseous hydrogen using hot electrons generated from resonantly excited substrate-based gold nanohemispheres (Au NHs). We consider hot electron induced H2 dissociation and the subsequent formation of a metastable gold hydride (AuHx) to account for changes in optical transmission. The excitation wavelength was varied to demonstrate a maximum response at the localized surface plasmon resonance (LSPR) wavelength of the AuNHs. Numerical simulations, using the discrete dipole approximation, were employed to corroborate the optical changes associated with the formation of metastable AuHx. Finite time difference domain (FDTD) calculations were also performed to account for the enhanced photocatalytic activity arising due to the confinement of electric fields by the Au NHs. FDTD simulations show that the excitation of the Au NHs plasmon modes generates stronger electric fields at the interface in comparison to a spherical geometry of similar dimensions.

Palladium (Pd) nanoparticles (5-20 nm) are used as the sensing layer on surface acoustic wave (SAW) devices for detecting H2. The interaction with hydrogen modifies the conductivity of the Pd nanoparticle film, producing measurable changes in acoustic wave propagation, which allows for the detection of this explosive gas. The nanoparticle-based SAW sensor responds rapidly and reversibly at room temperature.

Vibrational sum-frequency generation (SFG) spectroscopy of interfacial water at mineral/aqueous interfaces is extended to the near-IR range containing the low cross section stretch + bend combination bands (νcomb = νOH + δHOH) of liquid water at silica surfaces near 5000-5300 cm(-1), for the first time. The assignments of SFG spectra are supported by FTIR and Raman spectroscopic measurements of the bulk water νcomb modes. The SFG spectra contain significant contributions from two combinations, [νs + δ] ≈ 5060 cm(-1) and [νas + δ] ≈ 5300 cm(-1). These measurements provide the first, to our knowledge, reported probe of the bending mode of water at buried interfaces. The data suggest that the interfacial water bending mode is blue-shifted from that of bulk water.

Described is a straightforward procedure for forming organized substrate-immobilized nanoprisms which are single crystalline, surfactant-free and which form a heteroepitaxial relationship with the underlying substrate. The devised route utilizes truncated Au octahedrons formed through solid state dewetting techniques as high temperature heterogeneous nucleation sites for Ag adatoms which are arriving to the substrate surface in the vapour phase. Observed is a morphological and compositional transformation of the Au structures to triangular nanoprisms comprised of a homogeneous AuAg alloy. During this transformation, the localized surface plasmon resonance red-shifts, broadens and increases in strength. The shape transformation, which cannot be rationalized using thermodynamic arguments dependent on the surface energy minimization, is described in terms of a kinetically driven growth mode, previously predicted by molecular dynamic simulations. The so-formed structures, when coated with a thin layer of Pd, are demonstrated as plasmonic sensing elements for hydrogen detection.

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