ABSTRACT
The nanosurface-confined nucleation and growth processes of Pt and TiO2 were investigated when Pt was sputter deposited and TiO2 was sol-gel coated on a unique surface-designed substrate. The substrate was an anodic aluminum oxide (AAO) film with self-assembled grouped nanopores (SGNPs). The SGNPs gave rise to unique nucleation sites comprising very small-sized boundaries and nanopores. Pt sputter deposition onto the SGNPs showed restricted growth of nanogranules. The TiO2 sol-gel coating onto the SGNPs resulted in unique formations of nanopore and network structures. The unique nucleation phenomena of Pt and TiO2 on the nanometer-sized surfaces are explained by a combination of two effects: confinement of the degree of freedom at the nucleation sites and growth direction. This is different from conventional surface nucleation that yields the growth of islands, layer-by-layer deposition, and epitaxy.
Subject(s)
Metal Nanoparticles/chemistry , Nanotechnology/methods , Photochemistry/methods , Platinum/chemistry , Titanium/chemistry , Aluminum Oxide/chemistry , Crystallization , Materials Testing , Microscopy, Electron, Scanning , Nanoparticles , Phase Transition , Silicon , Surface Properties , X-Ray DiffractionABSTRACT
In this communication, we experimentally report, for the first time, that the MnO nanoclusters with cluster diameters of 5-10 nm show a ferromagnetic behavior with a phase transition from ferromagnetic to paramagnetic phases at 27 K even though their bulk phase is antiferromagnetic. We observed large coercivities up to 9500 Oe and a large remanence of 1.72 emu/g at 2 K, which are typically observed values for ferromagnetic materials. Although it is not clear, this abnormal ferromagnetic behavior of MnO nanoclusters may arise from cluster size effects.
