7th International Conference on Nanomaterials - Research & Application
October 14th - 16th 2015 / Hotel Voronez I, Brno, Czech Republic, EU
The quantum size effect and very strong electron correlation are two hallmarks of nano electronic structure. While the quantum size effect is a one electron property, electron correlation involves interactions among the electrons. In electronic structure theory, electron-electron repulsion causing correlation is normally considered only in an average (or mean field) sense, as for example in a single Hartree-Fock determinant. This is the simple molecular orbital model which is often a good approximation for molecules. In infinite systems this averaging treatment leads to delocalized electronic bands -- an excellent description of bulk 3D sp3 semiconductors. However in reality electrons try to instantaneously avoid each other; their relative motion is correlated. In nanoscience strong electron-electron repulsion and correlation create new collective states and cause new femtosecond kinetic processes. This is especially true in 1D and 2D systems. I discuss strong correlation in carbon nanotubes, graphene, zero dimensional quantum dots, , trans-polyacetylene chains, transition metal dichalcogenides, organic/inorganic Pb iodide perovskites, and pentacene van der Waals crystals. The independent contributions of screening and dimensionality are analyzed.
TiO2 nanomaterials have over the last 30 years attracted tremendous scientific and technological interest. Main research direction using TiO2 in functional applications are still the use in photocatalysis e.g. for the direct splitting of water into H2 and O2 to generate the potential fuel of the future, hydrogen, or the use in Grätzel type solar cells. In order to achieve a maximum turn-over rate (by creating a high surface area), usually nanoparticles are used either suspended or compacted to a photoelectrode. Over the past decades various 1D and highly defined TiO2 morphologies were explored for the replacement of nanoparticle networks and were found in many cases far superior to nanoparticles. Nanotubes or wires can be grown by hydrothermal or template methods, or even more elegantly, by self-organizing anodic oxidation. The latter is not limited to TiO2 but to a full range of other functional oxide structures on various metals and alloys can be formed. These advanced and doped morphologies can be grown on conductive substrates as ordered layers and therefore can be directly used as functional electrodes (e.g. photo-anodes). The presentation will focus on these highly ordered nanotube arrays of TiO2 and discuss most recent progress in synthesis, modification and applications.
REFERENCES:
P. Roy, S. Berger, P. Schmuki, Angew. Chem. Int. Ed. (2011), 2904
K. Lee, A. Mazare, P. Schmuki, CHEMICAL REVIEWS, 114 (2014) 9385