Magnetic Alignment of Nanowires

Abstract

Spatial manipulation and ability to assemble and position nanostructures in a controlled manner so they are registered to lithographically defined contacts is a critical step toward scalable integration in high-density nanodevices. By integrating ferromagnetic ends on nanostructures and using the magnetic interaction between ferromagnetic ends and electrodes, we demonstrated assembling, positioning, and spatial manipulating of nanostructures on ferromagnetic contacts. Segmented nickel/gold/nickel (Ni/Au/Ni) and nickel/bismuth/nickel (Ni/Bi/Ni) nanowires with controlled dimensions were fabricated by template-directed electrodeposition. One hundred percent magnetic alignment of nanostructures to the imposed magnetic fields was achieved by applying a low external magnetic field of 200 Oe. In addition, directional controllability of the magnetic assembling technique was demonstrated by assembling nanostructures with angles from 45° to 135° with respect to the electrodes. This magnetic assembly technique was shown to have potential for high-density interconnects without registration and individually addressable nanostructures with the use of different substrate architectures for two-dimensional control of nanostructures placement.

Magnetic field alignment of template released ferromagnetic nanowires

“…This behaviour is demonstrated in the scanning electron micrographs shown in Figures 9(a) and 9(b), which show Ni nanowires lying perpendicular to each other produced by deposition in two sequential steps using high magnetic field strength orientated normal to each other. This result agrees well with the other results in literature 36,40,42 and demonstrates that the van der Waals and/or the electrostatic forces between the wires and the substrates are the dominant after deposition. This behaviour may be useful from a practical point of view in the fabrication of complex devices that needs sequential steps of nanowire alignment, for example to create memory or logic architectures.…”

“…Here, the efficacy of magnetic field alignment has been quantitatively assessed using magnetic nanowires; however, the results may be relevant to a wider range of functional materials where these nanostructures are capped, coated, or incorporate magnetic material as demonstrated elsewhere. 37,40,42,45 The applicability of such global magnetic alignment in technological applications depends upon the requirements of the particular application. The results show that at most $80% of nanowires were aligned within 20 of the field axis.…”

“…Therefore, a variety of techniques have been utilised to manipulate and control electrodeposited nanowires suspended in a solvent including thermocapillary motion of nanowire suspensions in microchannels, 25,26 electrostatics, [26][27][28] electric field, 26,29,30 and magnetic field [31][32][33][34][35][36][37][38][39][40][41][42][43][44][45] assisted alignment. Recently, magnetic field have been utilized by several researchers to control assembly and alignment of carbon nanotubes, 26,40 Ni, [31][32][33][34][35] semiconductor, 26 conductive polymer 26 nanowires, as well as metallic nanowires such as gold, 37,39 bismuth, 42 coppertin, 41 Pt, 43 and ZnO (Ref. 38) capped with Ni ends by manually drop casting a dilute suspension containing these nanowires between two electrodes predefined on a specimen by lithographic techniques and using two permanent magnets.…”

Progress Toward Nanowire Device Assembly Technology

“…Magnetic nanowires can be effectively trapped on templates with nanomagnet arrays under a low external magnetic field if magnetic charge and dimension are matched between the magnetic nanowires to be assembled and the gaps between the two nanomagnets . Nonmagnetic nanowires can be capped with magnetic ends and assembled using magnetic field (Hangarter & Myung, 2005). The field gradients can also control the alignment of nonmagnetic nanowires immersed inside magnetic fluids (Ooi & Yellen, 2008).…”

The bonding of nanowire assemblies using adhesive and solder

“…The complexity of the assembled structure can be increased by utilizing complex components whose surfaces have been engineered with different recognition sites that facilitate a variety of simultaneous orthogonal interactions of different magnitudes. Several interaction forces have been used to direct the assembly of nanocomponents including molecular recognition, [20][21][22][23] electrostatic forces, 24,25 dielectrophoresis, 26,27 magnetic forces, [28][29][30] or surface-tension-based forces. 31,32 Although the aforementioned strategies have succeeded in directing the assembly of nanocomponents into 2-D and 3-D integrated structures, in many cases, the structures formed are not well bonded to one another (i.e., the assemblies, although held together in the fl uidic medium in which they are assembled, fall apart when removed from the medium or during mild sonication).…”