Self-assembled monolayers of alcanethiols on nickel surfaces for low level electrical contact applications

Nickel can be used as final coating for separable electrical contacts in various types of applications: batteries, automotive connectors, etc. The possible growth of a poorly conducting layer on the metal due to environmental conditions has limited up to now the use of such coatings to common applications. However durable quality performances can be expected with a proper protective material avoiding corrosion. The new approach we have been working on, is to find compounds that bind to nickel and form well-defined layers. We report here the first results describing the behaviour of self-assembled monolayers of thiol molecules deposited on bare nickel substrates. We briefly describe the deposition method, the type of molecules and of substrates used and summarize the main physicochemical characterisations available. The electrical and tribological properties of the monolayers formed on nickel slabs are investigated in a ball/plane configuration simulating a real contact element. The influence of an electrochemical pretreatment of the nickel surface prior to the layer assembly is shown. Excellent tribological behaviours can already be obtained with corresponding values of the contact resistance varying between 1 /spl Omega/ and 10 m/spl Omega/. The results show that building organised monolayers acting as protective coatings is of high interest for electrical contacts.

[1]  M. Pecht,et al.  The effects of wipe on corroded nickel contacts , 1996, Electrical Contacts - 1996. Proceedings of the Forty-Second IEEE Holm Conference on Electrical Contacts. Joint with the 18th International Conference on Electrical Contacts.

[2]  D. Allara,et al.  Spontaneously organized molecular assemblies. 4. Structural characterization of n-alkyl thiol monolayers on gold by optical ellipsometry, infrared spectroscopy, and electrochemistry , 1987 .

[3]  George M. Whitesides,et al.  Formation of monolayers by the coadsorption of thiols on gold: variation in the head group, tail group, and solvent , 1989 .

[4]  G. R. Crane,et al.  Wear resistance of nickel and nickel phosphorus alloy electrodeposits , 1988, Electrical Contacts, 1988., Proceedings of the Thirty Fourth Meeting of the IEEE Holm Conference on Electrical Contacts.

[5]  G. Whitesides,et al.  Formation of Monolayers by the Coadsorption of Thiols on Gold: Variation in the Length of the Alkyl Chain , 1989 .

[6]  George M. Whitesides,et al.  Wet chemical approaches to the characterization of organic surfaces: self-assembled monolayers, wetting, and the physical-organic chemistry of the solid-liquid interface , 1990 .

[7]  G. Whitesides,et al.  Formation of Monolayer Films by the Spontaneous Assembly of Organic Thiols from Solution Onto Gold. , 1989 .

[8]  Effect of surface structure on the contact resistance measurements of electrodeposits , 1988, Electrical Contacts, 1988., Proceedings of the Thirty Fourth Meeting of the IEEE Holm Conference on Electrical Contacts.

[9]  Abraham Ulman,et al.  Packing and Molecular Orientation of Alkanethiol Monolayers on Gold Surfaces , 1989 .

[10]  J. Delhalle,et al.  Self-Assembled Monolayers of n-Dodecanethiol on Electrochemically Modified Polycrystalline Nickel Surfaces , 1997 .

[11]  Protective treatments for gold-flashed contact finishes with a nickel substrate , 1995 .

[12]  Ralph G. Nuzzo,et al.  Fundamental studies of microscopic wetting on organic surfaces. 1. Formation and structural characterization of a self-consistent series of polyfunctional organic monolayers , 1990 .