Oxide thin films

Transition metal oxide thin films are widely used for basic materials science and in various device applications. We study the properties of oxides in confined geometries, typically in the form of thin films grown by Pulsed Laser Deposition (PLD). PLD gives us the flexibility to work with very many different oxide materials and to combine different oxides in heterostructures. With the help of in-situ electron diffraction (RHEED), oxide thin films can be grown with single atomic layer accuracy. The pulsed deposition regime can be used to control the kinetics of crystal growth. This is particularly useful in the growth of nanostructures. Since films are grown on single crystal substrates, it is often possible to choose the crystal orientation and the epitaxial strain state in a film. You can read more here about the design and construction of the PLD chambers that we use in our research.

Surfaces

Thin films are usually grown on single-crystal substrates and the crystallinity of the film is strongly affected by the morphology and stoichiometry of the substrate surface. It is therefore desirable to start film growth with an atomically flat surface that has a well-defined miscut angle and direction. Preparation of such 'step-and-terrace' surfaces requires a combination of polishing, annealing, and chemical etching treatments. The surface morphology can be characterized by atomic force microscopy and in-situ electron diffraction. The composition of the surface can be determined by ion scattering spectroscopy. Read more on surface dynamics and SrTiO3 surface preparation:

Interfaces

The properties of materials are different close to a surface or an interface. In the simplest cases, the properties change due to carrier density profiles caused by band bending, but more complex cases are possible as well. The most interesting cases are those where completely new phases appear at interfaces, such as metallic conductivity in an insulator or magnetic order in a nonmagnetic host material.
Due to the layer-by-layer growth of thin films, it is possible to fabricate atomically sharp interfaces and delta-doping layers. However, since oxide films are grown at high temperature, it is always questionable whether the interfaces are truly atomically sharp and no interdiffusion has occurred. Ion scattering spectroscopy is a useful tool for analyzing interdiffusion in ultrathin oxide films. Read more about film composition analysis and diffusion measurement:

Nanostructures

Combined thermodynamic and kinetic crystal growth control can be used to grow a variety of oxide nanostructures. Fast growth at low temperatures nucleates nanodots that can be grown into larger nanostructures, such as pyramids or pillars, or annealed to form percolative nanostructure arrays. Slow growth at high temperature can be used to fabricate nanowires on step-and-terrace crystal surfaces. As long as the nanostructure growth remains epitaxial, cation interdiffusion is minimal and even single unit cell nanostructures are stable. Read more about the materials and types of oxide nanostructures that can be grown by pulsed laser deposition: