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This review focuses on the spectroscopy and chemical dynamics of bimolecular complexes of group II metal ions with formaldehyde using mass resolved photodissociation spectroscopy techniques. Photodissociation spectroscopy of isolated metal ion-molecule complexes gives quantitative information about the structure and bonding of the complex, and valuable insight into the electronic nonadiabatic interactions that determine the reaction pathways and energy partitioning. The experimental techniques of photodissociation spectroscopy are briefly reviewed. Results from several experiments are then discussed including the photodissociation of Mg + -, Ca + -, and Zn + -based complexes with formaldehyde. Despite the similarities in valence electronic structure for these metal ions, the spectroscopy and quenching dynamics show remarkable differences. We also compare results with the photodissociation spectroscopy of Mg + -acetaldehyde where additional chemical reaction channels are accessible.

We report on a study of the photodissociation spectroscopy of weakly bound Zn+(H2O) and Zn+(D2O) complexes. The work is supported by ab initio electronic structure calculations of the ground and low-lying excited energy surfaces. We assign two molecular absorption bands in the near UV correlating to Zn+ (4s-4p)-based transitions, and identify vibrational progressions associated with both intermolecular and intramolecular vibrational modes of the cluster. Partially resolved rotational structure is consistent with a C(2V) equilibrium complex geometry. Experimental spectroscopic constants are in very good agreement with ab initio theoretical predictions. Results are compared with previous work on main group and transition metal ion-H2O clusters.

Plasmonic hotspots located in the nanogaps of infrared optical antennas are mapped in the near-field. The enhanced evanescent field resonance is shown to depend strongly on excitation wavelength, the excitation and detection laser polarization, and gap size. In addition, we demonstrate that in nanogap hotspot imaging using scattering probes, the probe tip can be considered as a load in the gap of the antenna, and the impedance of the load can then be tuned from inductive to capacitive or vice versa by changing the dielectric value of the tip load. Experimental results are in agreement with finite-difference time-domain simulations.

We report on high resolution subsurface and material specific differentiation of silica, Au and silica-capped Au nanoparticles using scattering-type scanning near-field optical microscopy (s-SNOM) in the visible (λ=633 nm) and mid-infrared (λ=10.7 μm) frequencies. Strong optical contrast is observed in the visible wavelength, mainly because of the dipolar plasmon resonance of the embedded Au nanoparticles which is absent in the infrared. We show that the use of small tapping amplitude improves the apparent image contrast in nanoparticles by causing increased tip-particle and reduced tip-substrate interactions. Experimental results are in excellent agreement with extended dipole model calculations modified to include the capping layer characterized by its refractive index.

Tip-enhanced near-field scattering images of Ge quantum dots (QDs) with 20–40 nm height and 220–270 nm diameter grown on a Si substrate have been observed with a spatial resolution of 15 nm. Changing the wavelength of the incident light, the contrast of the images is reversed. It is found that the scattering intensity is caused by the dielectric constants of the materials under the probe. By changing the wavelength of the incident light, we have obtained information about the dielectric constant dispersion of single Ge QDs.

We have studied the structure and photodissociation of Mg(+)-acetic acid clusters. Ab initio calculations suggest four relatively strongly bound ground state isomers for the [MgC(2)H(4)O(2)](+) complex. These isomers include the cis and trans forms of the Mg(+)-acetic acid association complex with Mg(+) bonded to the carbonyl O atom of acetic acid, the Mg(+)-acetic acid association complex with Mg(+) bonded to the hydroxyl O atom of acetic acid, or to a Mg(+)-ethenediol association complex. Photodissociation through the Mg(+)-based 3p--3s absorption bands in the near UV leads to direct (nonreactive) and reactive dissociation products: Mg(+), MgOH(+), Mg(H(2)O)(+), CH(3)CO(+), and MgCH(3) (+). At low energies the dominant reactive quenching pathway is through dehydration to Mg(H(2)O)(+), but additional reaction channels involving C-H and C-C bond activation are also open at higher energies.

Several schemes to improve the efficiency of extraction of H− ions from a magnetized sheet plasma source are reported. Parameters that affect the optimization of the extraction process such as plasma electrode position relative to the core plasma, plasma electrode bias, extraction electrode bias, neutral gas pressure, and discharge current were investigated. The negative hydrogen ion current density extracted from pure hydrogen plasma under optimum conditions was 0.15 A/m2. Enhancement of the H− current density has been observed by as much as 73.3% when argon was mixed with hydrogen at a 10%/90% ratio. The addition of argon raised the electron density by ten times and increased the electron temperature by 40% at the center of the sheet plasma. These plasma parameters were of comparable value with and without argon at the periphery of the sheet. The existence of high-energy electrons at the core and the presence of cold electrons at the periphery of the sheet plasma conform to ideal conditions of H−product...

We describe a novel approach for the rational design and synthesis of self-assembled periodic nanostructures using martensitic phase transformations. We demonstrate this approach in a thin film of perovskite SrSnO3 with reconfigurable periodic nanostructures consisting of regularly spaced regions of sharply contrasted dielectric properties. The films can be designed to have different periodicities and relative phase fractions via chemical doping or strain engineering. The dielectric contrast within a single film can be tuned using temperature and laser wavelength, effectively creating a variable photonic crystal. Our results show the realistic possibility of designing large-area self-assembled periodic structures using martensitic phase transformations with the potential of implementing "built-to-order" nanostructures for tailored optoelectronic functionalities., Comment: 13 pages, 5 figures