The self-assembly of monodisperse gold and silver colloid particles into monolayers on polymer-coated substrates yields macroscopic surfaces that are highly active for surface-enhanced Raman scattering (SERS). Particles are bound to the substrate through multiple bonds between the colloidal metal and functional groups on the polymer such as cyanide (CN), amine (NH(2)), and thiol (SH). Surface evolution, which can be followed in real time by ultraviolet-visible spectroscopy and SERS, can be controlled to yield high reproducibility on both the nanometer and the centimeter scales. On conducting substrates, colloid monolayers are electrochemically addressable and behave like a collection of closely spaced microelectrodes. These favorable properties and the ease of monolayer construction suggest a widespread use for metal colloid-based substrates.

This paper details the kinetic aspects of covalent self-assembly of colloidal Au particles from solution onto immobilized organosilane polymers. On glass substrates, surface formation can be monitored using UV−vis spectroscopy and field emission scanning electron microscopy (FE-SEM). Correlation of these data allows the effect of nanostructure on bulk optical properties to be evaluated. At short derivatization times, particle coverage is proportional to (time)1/2. The particle sticking probability p, defined as the ratio of bound particles to the number of particles reaching the surface in a given time period, can be determined from a knowledge of the particle radius, solution concentration, temperature, and solution viscosity; for surfaces derivatized with (3-mercaptopropyl)trimethoxysilane (MPTMS), p ≈ 1. At longer derivatization times, interparticle repulsions result in a “saturation” coverage at ≈30% of a close-packed monolayer. Two approaches for modulating the rate of surface formation are described:  electrochemical potential control on organosilane-modified SnO2 electrodes and charge screening by organic adsorbates. Self-assembly of colloidal Au particles onto functionalized substrate surfaces is a reproducible phenomenon, as evidenced by UV−vis and surface enhanced Raman scattering (SERS) measurements on identically prepared substrates.

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The ammonioborane monoanion H(3)NB(12)H(11)(-) was per-B-fluorinated with elemental fluorine in liquid hydrogen fluoride to yield the first member of a new class of weakly coordinating anions, H(3)NB(12)F(11)(-) (isolated as [N(n-Bu)(4)](2)[H(2)NB(12)F(11)] in 41% yield). The pK(a) of the H(3)NB(12)F(11)(-) anion is 9.6. Several salts of the tri-N-alkylated anions Me(3)NB(12)F(11)(-) and Dd(3)NB(12)F(11)(-) (Dd = n-C(12)H(25)) were also prepared. The structure of [CPh(3)][Me(3)NB(12)F(11)] was determined by single-crystal X-ray diffraction: monoclinic, space group P2(1)/c, a = 18.053(3) A, b = 33.139(5) A, c = 9.600(2) A, beta = 91.459(4) degrees, V = 5742(2) A(3), Z = 8, T = 173(2) K, R(1) = 0.045. It revealed that the only direct interactions between the undecafluoroammonioborate monoanions and the trityl cations in the two independent ion pairs were long and weak BF...CPh(3) interactions of 2.992(6) and 2.942(6) A. Salts of the new anions were chemically, electrochemically, and thermally stable. The conductivity of Li(Me(3)NB(12)F(11)) in dimethoxyethane was comparable to that of LiPF(6) but less than half the value of Li(1-Me-CB(11)F(11)).

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