Nanostructured cobalt on porous silicon substrate: Structure and magnetic behaviour

During an anodization process, porous silicon (PS) consisting of pores with a diameter of about 40 nm and a depth from 5 µm to 40 µm has been produced. To achieve oriented channels in this mesoporous range, a p+-type Si wafer was electrochemically etched in an aqueous electrolyte of HF. We report the formation, after the anodization step, of a cobalt nanostructure in a porous silicon matrix. Co nanocrystals on and in a porous silicon layer have been prepared by the UHV evaporation technique and characterized by scanning electron microscopy (SEM), transmission electron microscopy (TEM) and electron energy loss spectroscopy (EELS). This technique was performed to show the chemical element distribution within the channels. It is found that the deposition condition is an important factor for obtaining nano-structures. Initial deposition leads to Co particle penetration in silicon pores whereas subsequent deposition results only in an increase of the thickness at the surface with no further penetration. Additional experiments were carried out by using the magneto-optical Kerr effect to obtain information about the magnetic properties. The first results show that the magnetic response for layers <5 nm presents an important perpendicular component of magnetization whereas for thicker deposited layers (8 nm < t < 20 nm) the magnetic response seems to act as that of a thin film in which the squareness of the hysteresis loop decreases with increasing film thickness. (© 2007 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim)