Paul E. Laibinis

Orthogonal Self-Assembled Monolayers: Alkanethiols on Gold and Alkane Carboxylic Acids on Alumina

This work demonstrates the practicality of forming two self-assembled monolayers (SAMs), independently but simultaneously, by adsorption of two different adsorbates from a common solution onto a substrate exposing two different materials at its surface. The experimental procedure and the degree of independence achieved in the resulting SAMs are illustrated by examination of monolayers obtained by adsorption of alkanethiols on gold and alkane carboxylic acids on alumina. This procedure provides a method for modifying the surface characteristics of microlithographically generated patterns and offers a versatile technique for controlling solid-vapor and solid-liquid interfacial properties in systems having patterns with dimensions of the order of 1 micrometer.

Molecular self-assembly of two-terminal, voltammetric microsensors with internal references.

Self-assembly of a ferrocenyl thiol and a quinone thiol onto Au microelectrodes forms the basis for a new microsensor concept: a two-terminal, voltammetric microsensor with reference and sensor functions on the same electrode. The detection is based on measurement of the potential difference of current peaks for oxidation and reduction of the reference (ferrocene) and indicator (quinone) in aqueous electrolyte in a two-terminal, linear sweep voltammogram in which a counterelectrode of relatively large surface area is used. The quinone has a half-wave potential, E�, that is pH-sensitive and can be used as a pH indicator; the ferrocene center has an E1/2 that is a pH-insensitive reference. The key advantages are that such sensors require no separate reference electrode and function as long as current peaks can be located for reference and indicator molecules.

X-ray Damage to CF3CO2-Terminated Organic Monolayers on Si/Au: Principal Effect of Electrons

The relative importance of x-rays alone and of x-ray-generated primary and secondary electrons in damaging organic materials was explored by use of self-assembled monolayers (SAMs) on multilayer thin-film supports. The substrates were prepared by the deposit of thin films of silicon (0, 50, 100, and 200 angstroms) on thick layers of gold (2000 angstroms). These systems were supported on chromium-primed silicon wafers. Trifluoroacetoxy-terminated SAMs were assembled on these substrates, and the samples were irradiated with common fluxes of monochromatic aluminum Kα x-rays. The fluxes and energy distributions of the electrons generated by interactions of the x-rays with the various substrates, however, differed. The substrates that emitted a lower flux of electrons exhibited a slower loss of fluorine from the SAMs. This observation indicated that the electrons—and not the x-rays themselves—were largely responsible for the damage to the organic monolayer.

Heterogeneous catalysis on platinum and self-assembled monolayers on metal and metal oxide surfaces

This paper describes research in two areas: heterogeneous catalysis and molecular self-assembly. The work in heterogeneous catalysis used the platinum-catalyzed hydrogenation of diolefin(dialkyl)platinum(II) complexes to generate platinum surface alkyls of known structure. The structure and reactivity of these suiface alkyls were inferred from characteristic processes occurring on the surface. The incorporation of deuterium from isotopically labelled protic solvents (e.g. EtOD) was particularly useful mechanistically. The technique of self-assembly was used to form organic monolayers by coordination of a ligand to a metal or metal oxide surface. In addition to the chemisorption of alkyl thiols on gold (as alkyl thiolates, RS-Au+), a number of other systems were demonstrated to givs ordered organic surface species.

Self-assembled monolayers of alkanethiols on gold: the adsorption and wetting properties of monolayers derived from two components with alkane chains of different lengths

This paper describes the preparation and wetting properties of two-component self-assembled monolayers (SAMs) obtained by the competitive adsorption of one short-chain (HS(CH2)10Sh) and one long-chain (HS(CH2)21Lg) alkanethiol onto gold from dilute ethanolic solutions. The four possible combinations of the tail groups CH3 and CH2OH were investigated: Sh = CH3/Lg = CH2OH, Sh = CH2OH/Lg = CH3, Sh = CH2OH/Lg = CH2OH, and Sh = CH3/Lg = CH,. The compositions of these SAMs are not the same as the compositions of the solutions from which they were formed. Although the relationship between the composition of the SAM and the composition of the solution suggests that some phase separation may be occurring within the SAM, contact angles with water and hexadecane show that significant disorder still remains in the interfacial region.

The reaction of indium(III) chloride with tris(trimethylsilyl)phosphine: a novel route to indium phosphide

InP has been prepared by the reaction of InCl3 with P(SiMe3)3; the intermediates and product have been characterised by X-ray photoelectron spectroscopy, elemental analysis, and X-ray powder diffraction.