BCMaterials Fortnightly Seminar #51: Maite Goiriena and Eugen Seif

MAITE GOIRIENA 

(BCMATERIALS)

NANODISCS MANUFACTURING BY SELF-ASSEMBLED TEMPLATES

The manufacturing based on self-assembled templates is presented as a simple, high-throughput and parallel processing route to obtain magnetic nanostructures. In this work, efforts are focused in the preparation of Permalloy (Py) nanodiscs down to 100 nm in diameter and 50 nm in thickness because, apart from their scientific interest, these structures can be used in promising biomedical applications [1]. Three different approaches are investigated: 1) In the Nanosphere Lithography (NSL) [2], the homemade spheres are deposited by spin-coating over a Py thin film sputtered onto silicon substrate. The spheres, assembled in ordered monolayers, are subsequently reduced in size by reactive ion etching in an oxygen atmosphere. The remaining pattern of spheres is used as a protective mask for creating nanodiscs by Py film ion-etching. 2) Alumina membranes [3] are prepared by a double-step oxidation process, and the obtained ordered hole-pattern is used as a template for Py deposition, which is performed by either physical vapor deposition or pulsed electrodeposition. Afterwards, the alumina membrane is removed obtaining the Py nanodiscs. 3) Hole-mask colloidal lithography (HCL) [4] utilizes a PMMA sacrificial layer coated with a positively charged PDDA polyelectrolyte to obtain a very homogeneous pattern of self-assembled functionalized PS beads. These beads are then covered by a titanium thin film which is tape-stripped to reveal a hole-pattern. Finally, Py is deposited within the holes and PMMA is removed as in the case of alumina membranes.   Left to right: silicon nanopillars made by NSL, alumina hole-pattern and Py nanodiscs prepared by HCL. References: [1]  D.-H. Kim, et. al. Nature Materials, 9 165 (2009). [2]  P. Tiberto, et. al, Journal of Nanoparticle Research, 13 4211 (2011). [3]  H. Masuda, et. al  App. Phys. Lett., 63 3155 (1993). [4]  H. Fredriksson, et. al  Advanced Materials, 19 4297 (2007).

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EUGEN SEIF

(BCMATERIALS)

MAGNETOTHERMOMECHANICAL PROPERTIES OF NI-MN-GA/POLYMER COMPOSITES: EXPERIMENT AND MODELLING

Previous research carried on the field of FSMA/polymer composites have proven that an increase of damping properties is possible due to the twinning of martensite variants. The goal of this work is to extend the fundamental research on energy harvesting considering the influence of volume fraction and morphology of FSMA by the means of Dynamical Mechanical Analyzer. The experiments for thermomechanical loading of the composites emphasize that an increase of both storage modulus and energy loss factor occurs because of a rising amount of FSMA-particles. Moreover, it is evident that a threshold of FSMA volume content has to be exceeded in order to detect a specific contribution of the inclusion phase. The same tests are performed under the exposition of the samples to a magnetic field of 340mT. In the case of the Ni-Mn-Ga(bar)/silicone composite additional energy dissipation is measured. It is suggested that the increment of energy dissipation originates from the favorable orientation of the martensite variants and the direction of loading. Finally, a finite element study sheds light on the stress-strain distribution for the spherical and bar inclusion under the influence of the matrix stiffness.