Nanofabrication
It appears that when photons strike a metal surface, in the femtosecond regime, hot electrons are generated and diffuse into the metal before they can equilibrate with lattice vibrations. If the metal thickness is on the order of the electron mean free path, hot electrons can be collected during ballistic transport across the metal. We have demonstrated electronic excitations created during atomic or molecular processes at the surface.
This diode scheme has been utilized to show the analogous photocurrent process and its potential application in future solar energy conversion technologies. It was found that surface plasmon enhances the hot electron flow generated upon absorption of photons. We have looked into ways to improve conversion efficiency by tailoring the structures and materials of Schottky diodes. We plan to investigate the origin of hot electrons and their influence on various chemical and photocatalytic processes.
It is known that catalytic activity depends on the size, shape, and composition of nanoparticles. We have systematically expand this study by synthesizing multi-functional nanoparticles of different sizes, including core-shell, yolk-shell, and hybrid nanocatalysts. We collaborated other research group which has capability of synthesis and fabrication of novel nanocatalysts. Nanoparticles were characterized using various techniques, including TEM, SEM, XPS, and AFM.
We carried out catalytic reactions on nanoparticle arrays and study the change of turnover rate and activation energy as a function of the size and composition of nanoparticle arrays. We carried out in situ measurement of the oxidation state of the nanoparticles with ambient pressure XPS to elucidate a possible mechanism for changes in activity as the size and composition of the nanoparticles change. We combined the experimental results with atomic-scale simulation and DFT calculations for the smart design of catalytic materials in collaboration with other subgroup.
Surface science techniques allow us to determine reaction intermediates and surface mobility under catalytic reaction conditions. Atomic force microscopy (combined with friction and conductance measurements) were utilized in ambient and reaction conditions, which permits us to investigate nanomechanical (friction, adhesion, wear, indentation, modulus), charge transport (conductance, bandgap), and structural properties.
We have set up high-pressure scanning tunneling microscopy which allows us to study adsorption-induced surface restructuring as well as the adsorbate structure on surfaces. We used ambient pressure XPS allows us to monitor oxidation states, composition, and surface segregation under reaction conditions.