Growth of thin films of single-chain magnets on functionalized silicon surfaces

Abstract

A one-pot strategy for the direct growth of continuous and regular thin films of a neutral oxamato-bridged heterobimetallic chain, synthesized from Co²⁺ nitrate and the tetramethylammonium salt of the anionic copper(II) complex (Me₄N)₂[Cu(2,6-Et₂pa)₂]·6H₂O (1) (2,6-Etpa = N-2,6-diethylphenyloxamate) over Si(111) surfaces functionalized with carboxylic acid terminating groups has been developed. Variation of the growth conditions can provide important differences in the morphology of the obtained films when working in H₂O at 20 °C. An anisotropic growth of 1-D fibers is observed under stoichiometric conditions (Co²⁺/1 = 1:1), while an isotropic growth of 3-D particles occurs for an excess of Co²⁺, as demonstrated by AFM. The dc magnetic measurements performed over the fiber- (3d) or particle-based films (3e) show a characteristic behavior of a 1-D ferrimagnetic chain compound. They are comparable to the ones of the bulk material of formula [CoCu(2,6-Et₂pa)₂(H₂O)₂] (2) prepared in H₂O at 20 °C which possesses slow magnetic relaxation effects typical of a SCM.

Keywords:

• Thin films
• surface chemistry
• single chain magnets
• atomic force microscopy
• molecular magnetism

Acknowledgements

All molecular films on silicon discussed in the manuscript have been prepared at Laboratoire de Physique de la Matière Condensée, Ecole Polytechnique (Palaiseau, France). One of us (M. C-S) thanks in particular Dr. C. Henry de Villeneuve for useful discussion and expertise about film preparation and characterizations. M. C-S. also wishes to thank H. Yuan for his help. The authors thank Drs Emilio Pardo and Rafael Ruiz-García (Universitat de València) for scientific discussions and for their help with the synthetic work. M. C. acknowledges financial support (postdoc grant) from the Val I+D program of the Generalitat Valenciana (Spain).