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Growth of Prussian Blue Analogues Thin films

par Rosso Michel - publié le , mis à jour le

Participants : P. Allongue, C. Henry de Villeneuve, I. Maurin, T. Gacoin

PhD student : L. Lu

This project, aims at the realization of 2D photo responsive magnetic heterostructures coupling photo-strictive and piezomagnetic materials. We study the nucleation growth and the properties of thin / ultra-thin films of Prussian blue analogues Rb0.5Co[Fe(CN)6]0.8.zH2O (RbCoFe, photo-strictive) and Rb0.2Ni[Cr(CN)6]0.7.zH2O (RbNiCr, piezomagnetic) In collaboration with the Solid State Chemistry group.

The PBA films are grown on silicon surfaces functionalized by a dense monolayer of pyridine groups (2.6 1014/cm2), as stated by calibrated FTIR analysis. The pyridine groups substituted with an amino linker are covalently attached onto carboxylic acid monolayers grafted on oxide free silicon surfaces (Fig. 1), according to the protocols developed in the group. This surface chemistry favors the nucleation via surface a surface complexation of metal cations.

Figure1  : Scheme of the pyridine-functionalized surface.

The AFM images in Figure 2a-b evidence that the films are continuous and smooth (roughness about 1 nm). Layers exhibit a strong (00h) texture with an inter planar distance corresponding to that of the Rb0.2Ni[Cr(CN)6]0.7.zH2O compounds (Fig. 2c). Their chemical composition (Rutherford Back Scattering measurements at SAPHIR Van de Graaff Particles Accelerator, Université P. & M. Curie, Paris) gives the expected chemical composition. Films (thicker than 10 nm) exhibit a Curie Temperature of 60K and an in-plane magnetization. A magnetic moment of about 2µB/formula is found, which is in agreement with the chemical composition.

Figure 2 : Experimental characterizations of RbNiCr thin layers on Si(111). (a, b) AFM images showing the surface topography prior to (a) and after (b) the growth of a 2.7 nm thick RbNiCr layer. (c) XRD diagram for films of variable thickness. Note that only (00h) peaks are visible. (d) Magnetization curves obtained in parallel (black plot) and perpendicular (red plot) magnetic field. The inset gives the variation of the Curie temperature as a function of the RbNICr film thickness.