6. Pulse-reversed electrodeposition with QCM monitoring to make magnetic nanowires in a nanotemplate
Cobalt nanowires with high perpendicular magnetic anisotropy are formed in a diblock copolymer film template using a pulse-reversed voltage with QCM monitoring. This in situ monitoring system along with the pulse-reversed field enables new control over the magnetic crystal growth.
Contributors: Andrei Ursache, Mark Tuominen, T. P. Russell
Lab: NSF Center for Hierarchical Manufacturing
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Manufactured Nanomaterial: Cobalt nanowires (15 nm diameter, 500 nm long, in a hexagonally packed formation with 24 nm spacing.) Chemical composition: Cobalt, CoO impurities Physical Form: High aspect ratio nanowires Properties: High perpendicular magnetic anisotropy, coercivities as high as 2.7 kOe at 300K, CoO impurities |
Process:
| 1. | A gold-coated 5 MHz AT-cut crystal with a PS template acts as the electrodeposition template. |
| 2. | An electrolyte solution consisting of deionized water, methanol, cobalt sulfate, and boric acid is formed. To maintain a pH of 6.0, sodium tetraborate is added. |
| 3. | With the sample in solution, two pulses are applied (-1.0 and -0.35 V) for 10 ms each. The intention is to remove atoms with low binding energies from the surface to maintain better crystal formation. |
| 4. | By monitoring the resonant frequency of the (Maxtek RQCM) QCM and electrodeposition current simultaneously one can control the length of the nanowires accurately and have a full knowledge of current efficiency.  Dotted line: electrode potential, solid line: current, dashed line: EQCM frequency change  XRD data for pulse-reversed Co nanowire array |
Notes: A pH of 6.0 is important to maintain is needed to get the preferred crystalline orientation of the cobalt nanowires. This of course would differ for other materials.
Raw Materials
- P(S-b-MMA) block copolymer as described in this process (link to BCP process)
- Quartz crystal microbalance
- Saturated calomel electrode (SCE), reference electrode
- Platinum foil, counter electrode
- Electrolyte consisting of deionized water, methanol (surfactant, CH3OH, 20% by volume), cobalt sulfate (CoSO4·7H2O, 1 M), and boric acid (H3BO3, 0.6 M)
- Sodium tetraborate for pH adjustment (Na2B4O7·10H2O, 0.1 M)
Environmental Variables: Clean room environment
Related publications:
- A. Ursache, J.T. Goldbach, T.P. Russell, and M.T. Tuominen, J. Appl. Phys. 97, 10J322 (2005)10.1063/1.1861393
- A. Ursache, M. Bal, J.T. Goldbach, R.L. Sandstrom, C.T. Black, T.P. Russell, and M.T. Tuominen, Mater. Res. Soc. Symp. Proc. 721, E3.e (2002)
- T. Thurn-Albrecht, J. Schotter, G.A. Kästle, N. Emley, T. Shibauchi and L. Krusin-Elbaum et al., Science 290 p. 2126 (2000)10.1126/science.290.5499.2126
Tags: Block copolymers, Electrochemical quartz crystal microbalance (QCM), Electrodeposition, Electrodeposition, Magnetic
