Isolation of Smaller Nanocrystal Au Molecules:  Robust Quantum Effects in Optical Spectra

Abstract

Five massive gold-cluster molecules have been isolated in high yield and have undergone separate structural characterization, and their electronic structure has been deduced by optical absorption spectroscopy. These new molecules are distinguished by a crystalline (or quasicrystalline) core of densely packed Au atoms, ranging in size from ∼1.1 nm (∼40 atoms) to ∼1.9 nm (∼200 atoms), surrounded by a compact monolayer of various thio (RS) adsorbates. They are obtained as the thermally and environmentally stable products of the reductive decomposition of nonmetallic (−AuS(R)−) polymer in solution, are separated according to size by fractional crystallization or column chromatography, as monitored by high-mass spectrometry, and are characterized structurally by methods including X-ray diffraction (small and large angle), high-resolution electron microscopy, and scanning tunneling microscopy. The optical absorption spectra of dilute solutions of these molecules show size-dependent steplike structure with an onset near the fcc Au interband edge (Δ = 1.7), indicative of transitions to the discrete lowest unoccupied levels of the conduction band. This structure is evident in the smallest clusters even at room temperature, is enhanced at low temperature, and emerges generally as predicted by Kubo's criterion for quantum size effects. It thus requires no assumption of a transition from the bulk metallic bonding character to a nonmetallic (rehybridized or oxidized) state.

Fabrication of capped gold nanoparticles by using various amino acids

“…When the electron transfer is carried out with less energy, the UV-Vis spectrum shifted to the longer wavelengths [32][33][34][35][36]. Hence, if the number of gold atoms increases in the cluster, the corresponding UV-Vis spectrum will have longer wavelength rather than the spectrum of gold clusters with fewer numbers of atoms.…”

Quantized Capacitance Charging of Monolayer-Protected Au Clusters

“…11 We believe that voltammetric quantized capacitance charging is likely to be very sensitive to dispersity, so it is worthwhile to model its effects. A simple case is a mixture of two monodisperse clusters of different core size.…”

Investigating the structural evolution of thiolate protected gold clusters from first-principles

“…The composition of Au 38 (SR) 24 was first reported by Whetten and co-workers in 1997 from their mass spectrometric experiments. 14,20 However, the internal atomic structure has puzzled both experimentalists and theorists for more than ten years. Since 1999, more theoretical efforts have been made to explain the unique stability and structure of Au 38 (SR) 24 from ab initio calculations.…”

“…96 It was found from previous experimental studies that the Au 38 (SG) 24 exhibits strong circular dichroism (CD) signals which are five times stronger than those from Au 25 (SG) 18 . 14,19,97 The strong CD signals were assigned to metal-based transitions, which possibly included contributions from both the Au core and ligandlayer Au atoms. In our originally proposed Au 38 model, the longer staple motif units are arranged in an idealized C 3h symmetry and the whole cluster exhibits a C 3h point-group symmetry.…”

“…[13][14][15][16][17] The first experimental method for synthesizing RSAuNPs was demonstrated by Brust et al in 1994. 18 Although many variants of the original method were subsequently developed, 19 the key route is essentially the same, i.e., to involve the reduction of high valence Au salts.…”