Position-controlled laser-induced creation of rutile TiO2 nanostructures.

For potential applications of nanostructures, control over their position is important. In this report, we introduce two continuous wave laser-based lithography techniques which allow texturing thin TiO2 films to create a fine rutile TiO2 structure on silicon via spatially confined oxidation or a solid-liquid-solid phase transition, for initial layers, we use titanium and anatase TiO2, respectively. A frequency-doubled Nd:YAG laser at a wavelength of 532 nm is employed for the lithography process and the samples are characterized with scanning electron microscopy. The local orientation of the created rutile crystals is determined by the spatial orientation of hydrothermally grown rutile TiO2 nanorods. Depending on the technique, we obtain either randomly aligned or highly ordered nanorod ensembles. An additional chemically inert SiO2 cover layer suppresses the chemical and electronic surface properties of TiO2 and is removed locally with the laser treatment. Hence, the resulting texture provides a specific topography and crystal structure as well as a high contrast of surface properties on a nanoscale, including the position-controlled growth of TiO2 nanorods.

Controlling the magnetic structure of Co/Pd thin films by direct laser interference patterning.

Nanosecond pulsed two-beam laser interference is used to generate two-dimensional temperature patterns on a magnetic thin film sample. We show that the original domain structure of a [Co/Pd] multilayer thin film changes drastically upon exceeding the Curie temperature by thermal demagnetization. At even higher temperatures the multilayer system is irreversibly changed. In this area no out-of-plane magnetization can be found before and after a subsequent ac-demagnetization. These findings are supported by numerical simulations using the Landau-Lifshitz-Bloch formalism which shows the importance of defect sites and anisotropy changes to model the experiments. Thus, a one-dimensional temperature pattern can be transferred into a magnetic stripe pattern. In this way one can produce magnetic nanowire arrays with lateral dimensions of the order of 100 nm. Typical patterned areas are in the range of several square millimeters. Hence, the parallel direct laser interference patterning method of magnetic thin films is an attractive alternative to the conventional serial electron beam writing of magnetic nanostructures.