Self-Assembled Monolayers on Oxidized Metals. 4. Superior n-Alkanethiol Monolayers on Copper

Abstract

Self-assembly (SA) of long-chain alkanethiols on copper was studied. Two factors were found to have substantial influence on the SA process: (i) the chemical reactivity of Cu toward substances present in the adsorption solution, particularly the solvent, and (ii) surface pretreatment, which influences the amount of oxide and the surface morphology. Both factors are less important in the case of SA onto gold because of its chemical inertness. Monolayers of octadecanethiol (C18SH) were adsorbed from different solvents (ethanol, toluene, and bicyclohexyl) at various thiol concentrations onto Cu surfaces pretreated in several different ways. The monolayers were characterized by contact-angle measurements, grazing-incidence Fourier transform infrared spectroscopy, and scanning force microscopy. Ethanol, the most common solvent for alkanethiol SA, is found to have a negative effect on monolayer SA apparently because of its chemical reactivity toward copper. With toluene as a solvent, better oriented and more crystalline monolayers are obtained provided that a higher thiol concentration is used to compensate for the higher solubility of thiols in toluene. Treatment of the Cu surface prior to SA is shown to significantly improve the SA by reducing the amount of surface oxide and the surface corrugation. The effect of the solvent is more critical than surface oxidation; hence, high-quality monolayers are formed in the presence of thin oxide layers on Cu surfaces. Superior C18SH monolayers, in terms of organization and crystallinity, are obtained by SA from toluene onto Cu surfaces sputtered-annealed in high vacuum, even when the Cu surface is subjected to short exposure to air before SA.

Extraordinary IR Transmission with Metallic Arrays of Subwavelength Holes

“…Absorptions in the CH stretch region are >100-fold enhanced over those reported in RAIRS studies (28)(29)(30). The region of Snyder's CH 2 wagging progression (31) in the absorption spectrum can be seen in the expansion.…”

Electrochemical Deposition onto Self‐Assembled Monolayers: New Insights into Micro‐ and Nanofabrication

“…In fact, a redox reaction takes place during immersion between the copper oxides and the alkanethiolate molecules yielding metallic Cu and alkanesulfonates. [15] As the oxide is reduced the clean Cu atoms react with the alkanethiolate molecules yielding ordered monolayers. For self-assembly on Cu surfaces benzene, toluene or hexane are preferred.…”

Formation of Cu and Cu2O Nanoparticles by Variation of the Surface Ligand: Preparation, Structure, and Insulating-to-Metallic Transition

“…One reason is perhaps the defective quality of self-assembled monolayers on copper due to the hindrance of chemisorption of thiols, disulfides, and similar molecules by their facile oxidation (18). However, recently Rubinstein and co-workers have reported (19) superior SAM formation on oxidized metal surfaces and hence capped nanoparticles of copper may be synthesized if suitable capping molecules and appropriate preparation conditions are selected. This is further supported by the recent results on SAM formation of Jennings and Laibinis on underpotentially deposited copper substrates where highly organized monolayers, robust in liquid and vacuum environments, have been formed using different thiols (20).…”