Nanoscience with molecular nanostructures

Seminar of a candidate for the J.E. Purkyně fellowship:

Hidetsugu Shiozawa: Nanoscience with molecular nanostructures

Abstract:

My research over the years has focused on nanoscience with molecular nanostructures, such as carbon nanotubes (CNTs) and metal-organic frameworks (MOFs).

Single-wall carbon nanotubes (SWCNTs) are one-dimensional (1D) conductors in which quantum confinements along the tube's circumference leads to the van Hove singularity and one-dimensional Tomonaga-Luttinger-liquid state to emerge. CNT's tubular voids are perfectly suited to admit foreign atoms and molecules. Encapsulated inside SWCNTs, molecules can be assembled in unique 1D arrays and react with one another to create new materials such as metal clusters whose properties outperforming their bulky counterparts. For instance, magnetic iron and nickel clusters formed inside SWCNTs behave as stable single-domain magnets exhibiting large coercive fields as the cluster size becomes as small as the exchange length.

Metal-organic frameworks (MOFs) are ordered 1D, 2D and 3D nanostructures composed of metal ions coordinated to organic ligands. A large variety of optical and magnetic properties can be exploited from uniquely designed and functionalized low-dimensional metal-organic hybrid structures. For example, magnetic metal arrays within MOFs are ideal systems in which one can study anisotropic magnetic coupling leading to magnetic order or spin crossover. Furthermore, metal ions exposed to the interior nano-voids react with foreign molecules, giving rise to MOF's excellent sensing ability. The magnetic ordering temperature and electrical conduction of the host can be tuned by molecular doping.

My experimental research, by means of photoemission, Raman, ultraviolet-visible absorption spectroscopy, X-ray diffraction, electron microscopy, magnetisation and magnetotransport measurements, aims at understanding low-dimensional properties of MOFs and SWCNTs functionalized by chemical and electrochemical doping, and elucidating electronic and magnetic interactions at guest-host molecular interfaces that are responsible for their unique physical properties.