The AC and DC conductivity in aggregates of ligand stabilized metal-cluster molecules

Brom, H.B.; Staveren, M. P. J. van; Jongh, L.J. de

doi:10.1007/bf01543992

Cited by 16 publications

(9 citation statements)

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“…The conductivity temperature dependence (i.e., its departure from Arrhenius behavior) is quite unique in that previous studies of other gold cluster systems − have not displayed the behavior illustrated in Figure . At present the mechanism of this behavior is unclear, but we have reproduced this behavior when octanethiol and hexanethiol are substituted for dodecanethiol in the cluster synthesis.…”

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confidence: 81%

Size-Induced Metal to Semiconductor Transition in a Stabilized Gold Cluster Ensemble

Snow

Wohltjen²

1998

Chem. Mater.

114

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Organic ligand stabilized metal clusters are a unique composite system possessing nanometer scale domains in which a metal core is encapsulated by an insulating organic monolayer. The confinement of a group of neutral metal atoms in such a small domain confers electronic properties that may be intermediate between continuous metals and quantized molecular species depending on the actual size of the domain. The insulating monolayer encapsulant is a conductivity barrier through which facile electron tunneling and/or hopping occurs. As a composite, both domains can exert strong influences on the macroscopic electrical conductivity. The strengths of these influences depend on their intrinsic nature and dimensions of each domain. Such materials are postulated to have exciting prospects for applications in microelectronics and possibly molecular electronics. 1 Our interest is in the development of these materials as the responsive component in a microelectronic chemical vapor sensor. In preparing and characterizing several series of these materials with variable core sizes and ligand shell thicknesses, we have ob-served a transition from a positive to a negative temperature coefficient of electrical conductivity for thin films of a homologous series of alkanethiol-stabilized gold clusters as described below and illustrated in Figures 1 and 2. As a model system, alkanethiol-stabilized gold clusters have a chemistry that is very amenable to systematic variation in both size of the gold core and thickness of the ligand shell. They are easily dispersed to concentrations as high as 10 wt % in nonpolar organic solvents and can be manipulated and characterized as soluble organic compounds. Recently, a synthesis of elegant simplicity was reported for this system where a nanometer scale gold cluster derivatized with a monolayer of dodecanethiol is described. 2 In this twophase system, gold chloride is dispersed by a phasetransfer agent in a toluene solution of the alkanethiol and is subsequently reduced by contact via rapid stirring with an aqueous sodium borohydride solution. As neutral gold particles nucleate and begin to grow, they are sequestered by a monolayer of the alkanethiol in a kinetically controlled fashion. Simple variation of the gold:alkanethiol stoichiometry generates a series of stabilized clusters with a large range in core size. 3 We have prepared such a series of dodecanethiol-stabilized gold clusters (see Table 1). As an abbreviated nomenclature for the normal alkanethiol-stabilized gold cluster we use the following general form: Au:C n (X:Y), where the subscript n denotes the number of carbon atoms in the alkane chain and (X:Y) denotes the gold:alkanethiol stoichiometric ratio used in the synthesis. As practical limits to desirable variations, a lower limit occurs where the electrical conductivity becomes very low and difficult to measure (e.g., X:Y ) 1:3 for the dodecanethiol system) (1) Schon, G.; Simon, U. Colloid Polym. Sci. 1995, 273, 101. (2) Brust, M.; Walker, M.; Bethell, D.; Schiffrin, D. J.; W...

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confidence: 81%

Size-Induced Metal to Semiconductor Transition in a Stabilized Gold Cluster Ensemble

Snow

Wohltjen²

1998

Chem. Mater.

114

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“…On the other hand, XPS results clearly revealed a steplike density of states at E F [11,12], indicating a metallic behavior of the cluster compound. Such behavior was also deduced from x-ray absorption spectroscopy studies [2] as well as from ac-and dc-conductivity measurements [8], the latter being discussed to reflect the absence of a gap in the density of states at E F . Optical experiments [4] suggested that the situation is even more complex.…”

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confidence: 94%

“…Among them, extended x-ray absorption fine-structure spectroscopy [2], x-ray absorption near edge spectroscopy [2], specific heat measurements [3], optical spectroscopy [4,5], scanning tunneling spectroscopy [6], atomic force microscopy [7], ac-and dcconductivity measurements [8], impedance spectroscopy [9], Mössbauer spectroscopy [10], as well as x-ray-induced photoelectron spectroscopy (XPS) [11,12] have been used to obtain access to the structural and electronic properties of Au 55 particles protected by a triphenylphosphine ligand shell. In addition, first principles calculations have been performed [13,14] for the naked clusters (i.e., Au 55 without any ligands) aiming to serve as a reference system for the cluster compound.…”

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confidence: 99%

Chemically Induced Metal-to-Insulator Transition inAu55Clusters: Effect of Stabilizing Ligands on the Electronic Properties of Nanoparticles

et al. 2001

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The cluster compound Au55(PPh3)12Cl6 has been reanalyzed by photoelectron spectroscopy giving direct evidence for a nonmetallic behavior of the individual Au clusters as long as their ligand shell remains intact. The exposure to x-rays during the measurements is found to partly decompose the shell by removal of the chlorine atoms, resulting in a metallic behavior of the clusters as demonstrated by a steplike intensity at the Fermi energy. These observations resolve a long-standing controversy about the metallic behavior of ligated Au clusters emphasizing, in addition, the influence of the local environment on the electronic properties of nanoscaled materials.

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“…One cluster that has attracted significant interest is the Au 55 (PPh 3 ) 12 Cl 6 “Schmid” cluster. , A number of experimental studies have been dedicated to the Schmid structure, including optical absorption, − XPS, − conductivity, and Mössbauer spectroscopy measurements …”

Section: Introductionmentioning

confidence: 99%

“…One cluster that has attracted significant interest is the Au 55 -(PPh 3 ) 12 Cl 6 "Schmid" cluster. 16,17 A number of experimental studies have been dedicated to the Schmid structure, including optical absorption, 18À21 XPS, 22À24 conductivity, 25 and M€ ossbauer spectroscopy measurements. 26 Measurements of the optical absorption of the Schmid cluster showed a featureless absorption spectra with decreasing absorption cross-section for increasing wavelength.…”

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confidence: 99%

TDDFT Study of the Optical Absorption Spectra of Bare and Coated Au₅₅ and Au₆₉ Clusters

Burgess

Keast

2011

J. Phys. Chem. C

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The optical absorption of bare and ligand-coated Au 55 and Au 69 "Schmid" clusters was calculated using time-dependent density functional theory (TDDFT). Calculations were performed using the explicit time propagation method with the local density approximation (LDA) for the exchange-correlation potential. Both icosahedral and cuboctahedral structures of the Au 55 gold core were simulated. The ligand coating was shown to have the effect reducing the features of the optical absorption spectrum of the clusters, giving a profile more similar to experimental results. The difference in the optical absorption between the different geometries and core sizes is also less marked when the clusters are coated. The results suggest that within the 1.4 nm size range, the absorption spectra are dominated by the coating and are not experimentally distinguishable. Binding energies were also calculated for the Au 55 cluster, showing that the cuboctahedral structure has lower energy although the energy difference is very small.The effect of the coating on the electron density of the gold cluster is also investigated by subtracting the electron densities of the bare clusters from those of the coated clusters.

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The AC and DC conductivity in aggregates of ligand stabilized metal-cluster molecules

Cited by 16 publications

References 19 publications

Size-Induced Metal to Semiconductor Transition in a Stabilized Gold Cluster Ensemble

Size-Induced Metal to Semiconductor Transition in a Stabilized Gold Cluster Ensemble

Chemically Induced Metal-to-Insulator Transition inAu55Clusters: Effect of Stabilizing Ligands on the Electronic Properties of Nanoparticles

TDDFT Study of the Optical Absorption Spectra of Bare and Coated Au₅₅ and Au₆₉ Clusters

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The AC and DC conductivity in aggregates of ligand stabilized metal-cluster molecules

Cited by 16 publications

References 19 publications

Size-Induced Metal to Semiconductor Transition in a Stabilized Gold Cluster Ensemble

Size-Induced Metal to Semiconductor Transition in a Stabilized Gold Cluster Ensemble

Chemically Induced Metal-to-Insulator Transition inAu55Clusters: Effect of Stabilizing Ligands on the Electronic Properties of Nanoparticles

TDDFT Study of the Optical Absorption Spectra of Bare and Coated Au55 and Au69 Clusters

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TDDFT Study of the Optical Absorption Spectra of Bare and Coated Au₅₅ and Au₆₉ Clusters