Template Synthesis of Magnetic Nanowire Arrays

Abstract

IntroductionDuring the late 20th century, the growing interest in creating advanced materials using nanoscaled building blocks was employed to develop synthetic techniques for re-engineering existing materials to novel functional materials such as quantum dots, nanodots, nanorods, nanotubes, nanofibrils and quantum wires. These nanowires can act as one-dimensional conductors with interesting electronic and optical properties. Moreover, nanowires may find applications in ultrasensitive chemical and biological sensors.To date, a physical vapor deposition (PVD) technique followed by lithography is usually considered to represent the ultimate method for producing nanoscaled materials. Although a number of successful efforts have been reported on the fabrication of freestanding nanopillars or nanowells using lithographic techniques, there is a whole range of potential obstacles for these approaches. These arise mainly from the fact that, when the technologies are pushed to smaller sizes, the cost rapidly escalate and the tolerances are more difficult to maintain. The lithographic processes used to pattern nanoelectronic structures also currently limit the dimensions of the electronic components such as nanowires. Optical lithography is limited by the wavelength of the light used to produce the wires. Consequently, the wavelength of light used is moving into the deeper regions of the ultraviolet (UV) spectrum, and the cost of fabricating optical components to achieve this is expected to rise at an astronomic rate. These challenges have forced many to seek new nanofabrication techniques, especially those which grow nanostructures directly in the openings of a template. One of the most successful approaches to these nanofabrication methods is known as the membrane-based synthesis of nanomaterials [1][2][3][4], where the membrane acts as a template for the electrodeposition of multilayered nanowires, as well as for single metallic nanowires [5,6]. The advantage of using template synthesis of nanowires is that it can be considered as an alternative solution to overcome the difficulty in fabricating fibrils with very small diameters by lithographic methods [7].

Modeling the Growth of Nanowire Arrays in Porous Membrane Templates

“…The "S" shape response has been reported in several publications. 4,6,7,9,10,12,20,21 Toimil et al 20 identified the relationship between the advances of the growing stages with the chronoamperometric response for the deposition of copper nanowires, and confirmed the results with micrographs obtained by scanning electron and transmission electron microscopies. Additionally, Dobrev, 6 Konishi 7 and Motoyama 21 also confirmed the growth of the nanowires by SEM.…”

“…Valizadeh et al 9,10 studied the electrochemical deposition of cobalt nanowires into ion track etched polycarbonate membranes. They developed an expression to describe the current density i tot to the randomly distributed array at time t during the growth of nanowires under diffusion control,…”

“…where nF is the molar charge transferred, D is the diffusion coefficient of the electrodepositing species, c b its concentration in the bulk of the solution, c m its concentration at the mouth of the pores, and N is the number density of pores with radius r p and length L. Equation 1 is based upon the expression obtained by Bond et al 11 for recessed disks, with planar fluxes under steady state, and without deposition inside pores, i.e., with constant diffusion length inside pores along the process. Valizadeh et al 9,10 hence did not consider flux variations inside the pores as the nanowires grew, nor the possibility of changes of the concentration of electrodepositing species at the mouth of the pores during electrodeposition.…”