Fabrication and Magnetic Properties of N-type Porous Silicon/Nickel Microtubes Composite

The highly ordered n-type porous Si template was prepared via electrochemical etching and back side illumination method. Pores of the Si template had squarish shape with side length of about 2 m and depth of about 50 m, respectively. Three growth stages, nucleation, self-assembly, and stable growth were observed by scanning electron microscope (SEM) during the formation process of the porous n-silicon template. Subsequently, nickel microtubes arrays were synthesized by electro-deposition. And the formation mechanism of the microtubes was also investigated. The content and particle size of Ni particles embedded in n-type porous Si templates increase with the increase of deposition time. Ni microtubes are formed by gathering the Ni particles over pore sidewall, which is different from that of insulative AAO template. In addition, the crystal structure of Ni microtubes keeps fcc-Ni in the whole growth process. In particular, due to the fewer defects and grain boundaries of Ni microtubes than that of Ni particles, the coercivity value of Ni microtubes is smaller. Moreover, the magnetic anisotropy of Ni microtubes is mainly contributed to the strong demagnetization energy.