MESA+ University of Twente
Inorganic Materials Science Group

Research

Towards self-assembled inorganic measo-structures

The aim if this TOP-program project is to develop strategies, which combines synthesis and (self) assembly of nanosized particles to produce mesoscale materials. Nanosized particles will be embedded, as building blocks, in larger assemblies. The resulting property will not directly be related to the properties of the building blocks, but will be determined by the multiple length scales in the assembly. Nanoscale metal oxide building block objects of varying size (5-100 nm) and shape (e.g., spherical, cubic, triangular, rod- or wire-like) will be made by a variety of advanced synthesis and processing methodologies, involving both wet-chemical processing methods and physical deposition techniques.

More specifically the focus will be on self-assembly during Pulsed Laser Deposition (PLD), hereby benefiting from the advantages of epitaxial growth, while making nanostructures simultaneously. These PLD derived nanostructures could be combined with structures derived by other processes to create inorganic meso-structures. Part of the research will be focused on the mechanism behind the self-organization process, where a better understanding of the mechanism can allow for improved control of the nanostructures size and shape. Another part of the research will be devoted to the characterization of these nanostructures and the influence of the induced dimension reduction on the intrinsic material properties.

Such self organization takes place during the growth of mutually immiscible oxide composite mixtures, as for perovskite-type BaTiO3 and spinel-type CoFe2O4, which are technologically relevant high-k dielectric and paramagnetic phases, respectively. Thin films with nanopillar geometry of the spinel phase embedded in a ferroelectric matrix can be made, with lateral resolution of 20-30 nm. [1] Another example of such self-organization during PLD are the selective growth of SrRuO3 on B-site terminated surface areas of DyScO3 substrates (Figure 1), resulting in arrays of conducting nanowires or nano columns. This selective growth can be modeled by using kinetic Monte Carlo simulations. An example atomic force microscope image of the nanowire is depicted in figure 2 and a result of a simulation in figure 3.

SrRuO3 is a commonly used perovskite electrode material and an itinerant anti-ferromagnet in bulk form. On SrTiO3 substrates, SrRuO3 shows a critical thickness for ferromagnetism, above which the film becomes conducting. [2]. This indicates the SrRuO3 properties are strongly dependent on size and dimensions, which are being studied in the nanowire shapes as mentioned above. Within this project, also the properties of ultra-thin SrRuO3 film on DyScO3 will be studied, using X-Ray Photo emission Spectroscopy (XPS) and electrical/magnetic measurements.

picture

[1] Multiferroic BaTiO3-CoFe2O4 Nanostructures, H. Zheng et al, Science 30, 303 661-663 (2004)

[2] Critical thickness for itinerant ferromagnetism in ultrathin films of SrRuO3, Jing Xia et al, Phys. Rev. B 79, 140407 (2009)

PhD Student: Bouwe Kuiper

Supervisor: Gert Jan Koster