Yuri Nakayama

Tunable nanowire nonlinear optical probe

One crucial challenge for subwavelength optics has been the development of a tunable source of coherent laser radiation for use in the physical, information and biological sciences that is stable at room temperature and physiological conditions. Current advanced near-field imaging techniques using fibre-optic scattering probes have already achieved spatial resolution down to the 20-nm range. Recently reported far-field approaches for optical microscopy, including stimulated emission depletion, structured illumination, and photoactivated localization microscopy, have enabled impressive, theoretically unlimited spatial resolution of fluorescent biomolecular complexes. Previous work with laser tweezers has suggested that optical traps could be used to create novel spatial probes and sensors. Inorganic nanowires have diameters substantially below the wavelength of visible light and have electronic and optical properties that make them ideal for subwavelength laser and imaging technology. Here we report the development of an electrode-free, continuously tunable coherent visible light source compatible with physiological environments, from individual potassium niobate (KNbO3) nanowires. These wires exhibit efficient second harmonic generation, and act as frequency converters, allowing the local synthesis of a wide range of colours via sum and difference frequency generation. We use this tunable nanometric light source to implement a novel form of subwavelength microscopy, in which an infrared laser is used to optically trap and scan a nanowire over a sample, suggesting a wide range of potential applications in physics, chemistry, materials science and biology.

Complex Structures and Electrochemical Properties of Magnesium Electrolytes

Magnesium organohaloaluminate in tetrahydrofuran [0.25 mol/L Mg(AlCl 2 EtBu) 2 /THF, Et:C 2 H 5 ,Bu:C 4 H 9 ] is an electrolyte solution that is able to deposit and dissolve magnesium electrochemically and reversibly at room temperature. It has been reported that the electrochemical window is ruled by Lewis acidity of the aluminum compounds involved, and some complex species formed in the electrolyte have been suggested based on the analysis of nuclear magnetic resonances and Raman spectroscopy. Because in these analytical methods there are not enough controls to identify all the included compounds, neither the complete complex structures nor the mechanism of the reversible reaction has been revealed yet. Here, we show the complete complex structures in this electrolyte directly observed by the X-ray absorption fine structure measurements, which reveal the reversible equilibrium reaction as well as the other electrochemical properties of this electrolyte.