(Invited) Nanostructured Silicon with Incorporated Bi-Metallic Nanostructures

Silicon/bi-metal nanocomposites are fabricated in using porous silicon and silicon nanotubes as templates which are filled with magnetic bi-metal nanostructures (NiCo, FePt) and the magnetic response of the different systems is investigated. The morphology such as pore diameter and inner tube diameter of the two systems are comparable. The different metals (NiCo and FePt) offer drastic differences of the magnetic properties for both, porous silicon and silicon nanotubes. The porous silicon (PSi) is fabricated by anodizing a highly n-doped silicon wafer in aqueous hydrofluoric acid solution. By applying a current density of 90 mA/cm2 pore diameters of 60 nm in average are achieved. The silicon nanotube (SiNTs) formation is performed by silicon deposition on a ZO wire array and finally etching off the ZO [1]. The inner diameter and the wall thickness of the tubes are dependent on the chosen fabrication parameters. For comparison the inner diameters of the SiNTs are chosen comparable to the porous silicon structure. Co as well as FePt nanoparticles are chemically grown inside the pores and the tubes, respectively. In the case of FePt the molar ratio of Fe is varied (Pt:Fe 1:1, 1:3 and 1:6). The magnetic properties of the different composite systems are investigated. PSi and SiNTs with deposited NiCo, Co and FePt nanoparticles show significant differences whereat the FePt filled samples offer higher coercivities and higher remanence and thus a high resulting energy product. The variation of the molar ratio of the FePt deposits shows a small impact in the magnetic response for both template types. Furthermore the differences between the two template materials are figured out. Such systems consisting of hard magnetic materials within nanostructured silicon are promising for on-chip applications using three dimensional arrays of nanomagnets. [1] X. Huang, R. Gonzalez-Rodriguez, R. Rich, Z. Gryczynski, J.L. Coffer, Chem. Comm. 49, 5760 (2013).