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Magnetic Nanostructures by self-organized electrochemical growth

by Rosso Michel - published on

Participants : P. Allongue, R. Cortès and F. Maroun

We have investigated the magnetic properties of a self-organized array of Co/Au islands on a vicinal Si(111) surface. The sample is realized as follows:
 (i) Au is first deposited from an alkaline solution of pH 14 to favor selective nucleation at the Si step edges. Figure 1 is a SEM image of the deposit showing nm Au islands are replicating the substrate stepped structure.
 (ii) Selective electrochemical Co deposition is then performed by proper choice of applied potential so as to avoid Co deposition on silicon.
The Co/Au nanostructures are assembled within dense rows which are paralle to each other. The spacing distance between two rows is equal to the width of one terrace Si(111). When 20 MLs of cobalt are deposited on the Au dots, the system presents a strong magnetic anisotropy since magnetization curve M - H presents a smaller coercive field when the magnetic field is transverse (red curve). This effect is related to stronger dipolar interactions between islands within a given row.

Figure 1 : SEM view of a self-organized array of Au islands on Si(111). (a) Scheme showing the rectangular unit cell of the array obtained by selective decoration of the Si step; (b) Schematic cross section of Au/Co/Au islands obtained by selective Co deposition on the Au island and then Au capping. (c) Magnetization curves M – H of the sample with a transverse and a longitudinal magnetic field. The cobalt thickness is 20 ML.

Publications :

 P. Allongue et F. Maroun, “Self-ordered electrochemical growth on single crystal electrode surfaces”, J. Phys.: Condens. Matter 18 (2006) S97-S114
 M. L. Munford, R. Cortès et P. Allongue, “Electrochemical growth of gold on well defined vicinal H-Si(111) surfaces studied by AFM and XRD”, Surf. Sci., 537 (2003) 95 – 112