Generation and Characterization of Multilayer Systems Consisting of Au₅₅(PPh₃)₁₂Cl₆ Double Layers and SiO₂ Barrier Films

Abstract

Multilayer systems, consisting of Au55(PPh3)12Cl6 double layers and SiO2 barrier films of different thickness, have been generated and characterised. The formation of the double layer between the barrier films was carried out by using spin‐coating techniques. For the generation of the SiO2 films, a plasma‐assisted physical vapour deposition (PAPVD) procedure has been applied, based on an anodic plasma arc process. Samples of up to nine cluster/SiO2 combinations have been produced and have been characterised by AFM and SEM. Impedance measurements showed that there is a characteristic thermally activated frequency dependence of the capacitance of the different systems. The cluster layers interact by dipoles formed in the double layers at low frequencies. It has also been shown that multilayer systems with SiO2 films thicker than 15 nm tend to spontaneously crystallise. Furthermore, wetting problems during the spin‐coating processes have been investigated. (© Wiley‐VCH Verlag GmbH & Co. KGaA, 69451 Weinheim, Germany, 2005)

The Electronic Interaction Between Au55(PPh3)12Cl6 Monolayers Through SiO2 Films

“…The quality of the monolayers depends exclusively on the spin-coating conditions and the use of dichloromethane as solvent that has a distinct yield of moisture for improving the wetting conditions. [4] As an example of the successful generation of cluster/ SiO 2 multilayers, a transmission electron microscopic (TEM) image of a four-layered system is shown in Figure 3. As can be seen, the cluster monolayers are properly separated by the SiO 2 barrier films.…”

“…[4] For the current (I)-voltage (U) investigations we used a novel kind of contacting technique that is shown in Figure 1. A 1 × 1-cm 2 mica platelet was provided with a 0.5-mm borehole at the periphery (a).…”

“…[4] Depending on the intended number of layers, the processes were repeated correspondingly. Figure 1d shows a system with four cluster/SiO 2 double layers.…”

“…[6][7][8][9][10] The corresponding behaviour of cluster double layers or thin films is the subject of another contribution in this issue. [4] There is a principal difference to be expected between thin films and monolayers. Dipolar interactions between cluster layers dominate the behaviour in thin films, whereas electronic tunnelling is observed in the case of monolayers.…”

“…Au 55 (PPh 3 ) 12 Cl 6 and its derivatives are ideal quantum dots, since this compound is the only metal nanoparticle that shows well-expressed quantum behaviour already at room temperature. [1] Current investigations of the electric conductivity of 2D arrangements of Au 55 (PPh 3 ) 12 Cl 6 clusters over about 80 nm indicate that it is below the detection limit, [4] whereas the conductivity of only 20-nm areas shows a typical Coulomb blockade. [5] In this connection, there arose another interesting question, namely the ability of communication of extended monolayers in the vertical direction, separated from each other by insulating barriers.…”