In situ grazing-incidence small-angle X-ray scattering observation of block-copolymer templated formation of magnetic nanodot arrays and their magnetic properties
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The fabrication of bit-patterned media (BPM) is crucial for new types of hard disk drives. The development of methods for the production of BPM is progressing rapidly. Conventional lithography reaches the limit regarding lateral resolution, and new routes are needed. In this study, we mainly focus on the dependence of the size and shape of magnetic nanodots on the Ar+-ion etching duration, using silica dots as masks. Two-dimensional (2D) arrays of magnetic nanostructures are created using silica-filled diblock-copolymer micelles as templates. After the self-assembly of the micelles into 2D hexagonal arrays, the polymer shell is removed, and the SiO2 cores are utilized to transform the morphology into a (Co/Pt)2-multilayer via ion etching under normal incidence. The number of preparation steps is kept as low as possible to simplify the formation of the nanostructure arrays. High-resolution in situ grazing-incidence small-angle X-ray scattering (GISAXS) investigations are performed during the Ar+-ion etching to monitor and control the fabrication process. The in situ investigation provides information on how the etching conditions can be improved for further ex situ experiments. The GISAXS patterns are compared with simulations. We observe that the dots change in shape from cylindrical to conical during the etching process. The magnetic behavior is studied by utilizing the magneto-optic Kerr effect. The Co/Pt dots exhibit different magnetic behaviors depending on their size, interparticle distance, and etching time. They show ferromagnetism with an easy axis of magnetization perpendicular to the film. A systematic dependence of the coercivity on the dot size is observed.
Keywordspoly(styrene)-b-poly(vinyl pyridine) argon ion etching self-assembly grazing-incidence small-angle X-ray scattering (GISAXS) simulation magnetic nanodot coercivity
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This research was supported by the SFB 668 of the Deutsche Forschungsgemeinschaft and by the University of Hamburg. The authors thank S.V. Roth and the HASYLAB staff for the support at the beamline BW4 and the ESRF staff for their support during beamtime at ID01. We thank A. Kornowski for the helpful advices about the SEM analysis.
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