The mean size of the gold (Au) core in the synthesis of dodecanethiolate-stabilized Au cluster compounds can be finely adjusted by choice of the Au:dodecanethiolate ratio and the temperature and rate at which the reduction is conducted. The Au clusters have been examined with a large number of independent analytical tools, producing a remarkably consistent picture of these materials. Average cluster and core dimensions, as ascertained by 1H NMR line broadening, high-resolution transmission electron microscopy, small-angle X-ray scattering, and thermogravimetric analysis, vary between diameters of 1.5 and 5.2 nm (∼110−4800 Au atoms/core). The electronic properties of the Au core were examined by UV/vis and X-ray photoelectron spectroscopy; the core appears to remain largely metallic in nature even at the smallest core sizes examined. The alkanethiolate monolayer stabilizing the Au core ranges with core size from ∼53 to nearly 520 ligands/core, and was probed by Fourier transform infrared spectroscopy, differential scanning calorimetry, contact-angle measurements, and thermal desorption mass spectrometry. The dodecanethiolate monolayer on small and large core clusters exhibits discernable differences; the line dividing “3-dimensional” monolayers and those resembling self-assembled monolayers on flat Au (2-dimensional monolayers) occurs at clusters with ∼4.4 nm core diameters.

Alloy particles 1 can exhibit electronic, 2-4 optical, 5-10 and catalytic properties 11,12 that are distinct from those of the corresponding mono-metal particles, 13-17 prompting numerous preparations of multi-metal nanoparticles, including those that can be considered core/shell bimetallic, partially segregated alloy, and pure alloy. 1-12 These earlier alloy particles typically required specialized equipment or handling procedures, posed difficulties in isolation and analysis, and could not be redissolved in airstable forms.This paper describes a simple synthesis of nanometer-sized monolayer-protected alloy clusters (MPACs) that are the first examples of stable, large, alloy molecules that can be isolated in solvent-free forms and redissolved without change. The stable alkanethiolate monolayer is the key to preventing metal core aggregation. The MPAC core compositions can be systematically varied in regards to ratios and numbers of groups 10 (Pt, Pd) and 11 (Cu, Ag, Au) metals, creating a pathway to studying the S0002-7863(98)01454-1 CCC: $15.00

Self-assembling of nanocrystals involves organization of nanocrystals encapsulated by protective compact organic molecules into a crystalline material. The adsorbed molecules not only serve as the protection layer for the nanocrystals but also provide the dominant cohesive interactions (or “bonding”) sustaining the nanocrystal superlattices. The length of the adsorbed molecules is a controllable parameter, making the ratio of particle size to interparticle distance an adjustable parameter that sensitively tunes the interparticle interaction/coupling and resulting collective properties. In this paper, bundling and interdigitation of thiolate molecules adsorbed on Ag nanocrystals are observed using the chemical imaging technique in energy-filtered transmission electron microscopy (EF-TEM) at a resolution of ∼2 nm. In these orientationally ordered, self-assembled Ag−nanocrystal superlattices, the bundling of the adsorbed molecules on the nanocrystal surfaces is the fundamental structural principle. A model consistent with the nanocrystal's morphology and the interdigitation of the adsorbed thiolates is proposed.

This paper is a description of the stopping power routine utilized in the CASINO program that is based on the experimental measurement of the energy loss function (ELF). In addition, we present an ANSI C standard program that can be used to generate the data needed for the stopping power routine. Both optical and energy loss spectrum (ELS) measurements of the ELF can be used as input to compute the stopping power. For ELS, only the single scattering spectrum is needed. Hence, measurement of the stopping power for a given element or compound of interest can easily be performed and used in the CASINO program. The resulting effect of using these stopping powers in Monte Carlo simulations is generally to increase the backscattering coefficient. Except for carbon, the change of stopping power for pure elements so far compiled is relatively small. In some compounds (i.e., Al 2 O 3 and ZnSe), the discrepancy with the Joy and Luo (1989) expression is significant.