Structural and magnetic characterization of Ni-filled porous silicon

During an anodization process, porous silicon (PS) consisting of pores with a diameter of about 60 nm and a depth from 10 μm to 30 μm has been produced. To achieve oriented channels in this mesoporous range, an n-type Si wafer with a doping density of 1019 cm− 3 was electrochemically etched in an aqueous electrolyte of 10% HF. The essential parameters like the current density and bath temperature are variable only in a narrow range to influence the result with respect to sample characteristics like pore diameter, interpore spacing and degree of orientation. In a further electrochemical step, this array of quasi-regular self-assembled channels grown along the (100)-axis is filled with Ni. Pulsed electrodeposition of metallic Ni from a NiCl2 solution offers a quite good possibility to fill the channels with Ni. The characterization of the structure was performed by various methods like AES [data presented in P. Granitzer, K. Rumpf, S. Surnev, H. Krenn. JMMM 290–291 (2005) 735], EDXS, and SEM to demonstrate the filling of the pores, to show the chemical element distribution within the channels, and to figure out the nature and regularity of the self-assembly of the pores. Additional experiments were carried out by SQUID-magnetometry to receive information about the magnetic properties. In summary, all investigations refer to a nanoscopic ferromagnetic system consisting of particles as well as wires which results in a peculiar magnetization behaviour with a second high field switching prior to saturation.