Annealing Effects on the Metal and Semiconductor Nanowires Loaded Inside the Alumina Pores

Abstract

Alumina template synthesis is a simple and cheap method for preparing arrays of nanostructural materials, such as wires, fibrils, tubes, which entails the synthesis of desired material within the cylindrically shaped pores by the respective method. To date various materials possessing anisotropic, tunneling, and giant magnetoresistance, superconductivity, semiconductivity, unusual non-linear optics, surface enhanced Raman scattering, and enhanced catalytic properties have been loaded inside the alumina pores and applied in practice. Currently the advancement of nm-scaled materials technology has prompted investigations devoted to their stability during storage in air, exploitation, irradiation, and heat-treatments under various environments. Furthermore, the heat treatment of some materials such as iron oxyhydroxides deposited inside the alumina pores seems still probably the most appropriate route to fabricate prospective magnetic nanowire arrays. The knowledge of semiconducting nanospecies thermal behavior is also crucial in their successful use to destroy selectively the tumor cells. This paper presents our recent progress in transformation, design, characterization and potential applications of nanowired materials encased within the alumina pores upon heat treatment in air. Unexpected behavior of some metal nanowires loaded inside the alumina pores, such as iron and tin, upon heat treatment in air is presented here for the first time. As will be shown below, the heating of such arrays at proper conditions results in the formation of spinel-type FeAl2O4 films and SnO/SnO2 barbed-shaped nanowire arrays. Also, the transformations of some semiconducting nanowires, particular FeO(OH), Cu3Se2 and Cu2xSe, upon heating are also presented herein. Finally, new fields of prospective applications of annealed nanowire arrays owing to gained magnetic and non-linear optical properties are discussed. The paper is organized as follows: In the next subsection, the formation, structure and composition of most popular porous alumina templates are briefly presented. In subsection 2.2, a short overview of annealing effects, which have been reported to date for nanowire arrays loaded inside the alumina pores, is given. Our results obtained by heat treatment of nanowires of metallic iron, tin and semiconducting iron oxyhydroxide, FeO(OH), encapsulated within the alumina pores, are presented in section 3, while section 4 is devoted