Ralph G. Nuzzo

Derivatized, high surface area, supported nickel catalysts

Abstract A new and general procedure for preparing high surface area, supported intermetallic compound and alloy catalysts is described. In this technique, the volatile Group IIIA and IVA organometallic compounds SiH 4 , Me 6 Si 2 , Me 6 Ge 2 , BH 3 · Et 3 N, and Et 3 Al are decomposed thermally on high surface area nickel, supported on either SiO 2 or Al 2 O 3 , to yield, directly, mixed metal catalysts of varied composition and structure. Using the competitive dehydrogenation and hydrogenolysis of cyclohexane as model reactions, the effects of intermetallic compound formation on catalytic activity are described.

The decomposition of silane and germane on Ni(111): Implications for heterogeneous catalysis

The chemisorption and subsequent decomposition of silane (SiH 4 ) and germane (GeH 4 ) on a Ni(111) single crystal surface is studied at temperatures ranging from −130°C to 1100°C using low-energy electron diffraction, Auger electron spectroscopy, thermal desorption mass spectrometry, and X-ray photoelectron spectroscopy. At low temperatures, stable silyl (SiH n , n n , n

Temperature induced reconstruction of model organic surfaces

Abstract The influences of temperature on the structure of hexadecanethiol (C 16 ) and heptadecanethiol (C 17 ) monolayers adsorbed on gold substrates are reported. Infrared Spectroscopy and molecular dynamics simulations show that defects in these layers (i.e. gauche conformations) are concentrated at the chain termini and decrease with decreasing surface temperature. Adsorption band intensity oscillations as a function of chain length show that the chain terminating group is highly oriented. Band splittings observed at low temperature establish that there must be at least two chains per unit cell. The temperature dependence of the spectral band intensities of the polymethylene chains is very similar to that found in bulk hydrocarbon crystals.

An XPS study of the reaction of silane with oxidized copper, silver, and gold surfaces

The reduction of copper, silver, and gold surface oxides by silane (SiH 4 ) is described. The silicon oxides generated by this process are characterized and the sensitivity of this class of reaction to such experimental parameters as substrate temperature, silane pressure, and metal oxide thickness are detailed. Oxidation of silver, as observed by X-ray photoelectron spectroscopy (XPS), is found to be complicated; the nature of the oxides generated by thermal and plasma assisted techniques is discussed.

The application of reflection infrared and surface enhanced Raman spectroscopy to the characterization of chemisorbed organic disulfides on Au

Abstract We have found that a variety of organic molecules containing the Sue5f8S linkage strongly adsorb on freshly evaporated or electrochemically cleaned gold surfaces. Adsorption stops at monolayer coverage and the packing density of the molecules can be close to the limit set by the size of the molecules. Reflection infrared spectra show that the films are strongly oriented and in the case of long alkyl-chain-substituted disulfides the films have structures similar to those of Langmuir-Blodgett type films. Most of the films were prepared by freshly evaporating gold onto polished single crystal silicon substrates. Immediately after the deposition the films were removed from the vacuum system (under N2) and placed in solutions of the disulfides. After rinsing the films were examined by ellipsometry at 6328A and 4420A and in general, the results are consistent with monolayer structures with close packing similar to bulk crystallites. Infrared spectra were obtained using a Digilab 15B Fourier transform infrared spectrometer with a high f/number optical system and small beam spot size for glancing reflection. Spectra were obtained between 800 and 3200cm−1 using a mercury cadmium telluride detector. The spectrum of a monolayer of the di-p-nitrobenzoate ester of trans-o-Dithiane-4,5-diol is shown in Figure 1. The structure of the diol is given below. The spectrum of the monolayer of the di-ester of the C16 acid (n-C15H31CO2H) is given in Figure 2. Notice the alkyl chain mode band series in the monolayer spectrum which indicates crystalline packing of the chains. The infrared spectra are consistent with oriented structures which maximize packing densities. No direct evidence is yet available for defining a Auue5f8S bond. However, a sample in which the monolayer of the p-nitrobenzoate derivative has been covered with 400A average thickness of CaF2 and 200A of smooth silver has yielded an enhanced Raman spectrum (λ(excite)=4880A ∼50mW power) in which the normally strong S-S stretching mode observed at 504cm−1 in bulk samples is absent in the monolayer. These studies demonstrate an application of surface vibrational spectroscopy to defining molecular structures at surfaces. Work is presently underway to quantitatively calculate molecular orientation from the infrared spectra and to more carefully determine the extent of any ordering in appropriate monolayers.

Model Organic Rearrangements on Aluminum Surfaces

To what extent are the reactivity patterns of discrete organometallic complexes predictive of reaction pathways on surfaces? This question is a central focus of much current research, and the general understanding which is beginning to emerge suggests that a close similarity may often exist. The best established correlations in these so-called cluster-surface analogies, are ones which are structural in nature [5.1]. Considerable advances have been made in recent years and it is now clear that the bonding patterns of hydrocarbon moieties on surfaces find many analogies in corresponding discrete transition and main group organometallic complexes. This progress notwithstanding, structural determinations of these often transient surface species remain far from routine, require the application of multiple techniques, and frequently are beset by controversy.

Polymeric and Polymerizable Surfactants

Temperature effect on the viscosity behaviour of dilute solutions of several styrene-butadiene two block copolymers in good and selective solvents was examined. Micelles formed by the block copolymers in solvents selectively good for polystyrene viz. dimethylformamide (DMF), dimethylacetamide (DMA), methyl ethyl ketone (MEK) and selectively good for polybutadiene viz. n-alkane (heptane, octane, decane, and dodecane) were characterized from viscosity, photon correlation spectroscopy, and electron microscopy. The micelle size is discussed in relation to the block copolymer characteristics, solvent selectivity, and temperature.