Gold atoms deposition

Fig. 1.47. Absorption spectrum of gold atoms deposited on an amorphous silica surface investigated by cavity ring-down spectroscopy...

To illustrate the power of this method, the absorption spectrum (between 1.85 and 2.82 eV) of gold atoms deposited on a-Si02 is depicted in Fig. 1.47. The spectrum clearly shows a first band of two well-resolved transitions at 1.90 and 1.95 eV. A second band is observed with three transitions at 2.46, 2.48, and 2.49 eV while a third band reveals transitions at 2.73, 2.75, and 2.79 eV. 

Iodine and bromine adsorb onto Au(l 11) from sodium iodide or sodium bromide solutions under an applied surface potential with the surface structure formed being dependent on the applied potential [166]. The iodine adsorbate can also affect gold step edge mobility and diffusion of the Au surface. Upon deposition of a layer of disordered surface iodine atoms, the movement of gold atoms (assisted by the 2-dimensional iodine gas on the terrace) from step edges out onto terraces occurs. However, this diffusion occurs only at the step edge when an ordered adlayer is formed [167]. 

The presence of both single gold atoms and gold clusters, evident in Figure 3(b), indicates that the deposition flux is largely atomic or very small clusters as expected from the process gas pressure. 

Studies of Ag on Au(lll)87 yield very similar results in terms of the structure of the deposited monolayer (i.e., the silver atoms are bonded to three surface gold atoms and are located at three-fold hollow sites forming a commensurate layer) with again strong interaction by oxygen from water or electrolyte (perchlorate). 

The fabrication and characterization of atomic metal contacts have been based mainly on electro-deposition/dissolution [182] and break junction techniques (see review [134] and literatures cited therein). In particular, gold nanocontacts have been studied in great detail, due to the chemical inertness of the material, the malleability and ductility of gold. The processes of formation, evolution, and breaking of gold atomic contacts leads to step-like features in the current-distance curves [188, 189]. The abrupt changes in the current (conductance) response were... 

Maitani MM, Daniel TA, Cabarcos OM, Allara DL (2009) Nascent metal atom condensation in self-assembled monolayer matrices coverage-driven morphology transitions from buried adlayers to electrically active metal atom nanofilaments to overlayer clusters during aluminum atom deposition on alkanethiolate/gold monolayers. J Am Chem Soc 131 (23) 8016-8029... 

Vandamme N, Snauwaert J, Janssens E, Vandeweert E, Lievens P, Van Haesendonck C (2004) Visualization of gold clusters deposited on a dithiol self-assembled monolayer by tapping mode atomic force microscopy. Surf Sci 558 57-64... 

It is perhaps obvious that the nature of the interface between a molecular solid (polymer) and a (clean) metal surface is not necessarily equivalent to the interface formed when a metal is vapor-deposited (essentially atom-by-atom ) on to the (clean) surface of the polymer or molecular solid. Atoms of all metals are active in the form of individual atoms , even gold atoms. In the context of the new polymer LEDs, some of the works discussed in chapter 7 involve the study of the early stages of formation of the interface in the latter configuration (metal-on-polymer interfaces). Very little has been reported on conjugated polymer-on-metal interfaces, however, primarily because of the difficulties in preparing monolayers of polymer materials on well defined metal substrates appropriate for study (via PES or any other surface sensitive spectroscopy). The issues discussed below are based upon information accumulated over two decades of involvement with the surfaces of condensed molecular solids and conjugated polymers in ultra-thin form, represented by the examples in the previous chapter. 

Very small gold particles can also be formed on magnesia and brucite (Mg(OH)2).55,83 Au/MgO made by deposition-precipitation contained particles smaller than 1 nm that were claimed to show icosahedral and fee cubo-octahedral structures,170 but this is hard to believe as the diameter of a single gold atom is already 0.29 nm, and lnm particles afflxed at the steps... 

The other method consists of the sputtering of a high-purity gold target with argon ions, followed by the subsequent deposition of the sputtered gold atoms on the surface of the moving powder support.127 The... 

Chemical analysis of solids and solutions indicate that in all cases metallic ruthenium, platinum, and gold are deposited on copper. Ruthenium, deposit is restricted to approximately 0.33 of the copper surface atoms, demonstrating that the redox reaction between Cu and Ru3+ can occur only on some special copper sites [11]. With platinum or gold, for the highest amount of modifier introduced (M"+/Cu(s) > 100), a deposit larger than a monolayer is obtained, indicating that all accessible copper atoms and subsurface copper atoms are involved in the redox reaction [13]. 

Particles of Raney copper, modified by redox deposition of ruthenium, platinum, or gold were characterized by energy dispersive spectroscopy. Ruthenium is deposited preferentially on the rims of the copper particles while low Miller-index planes are totally free of deposited ruthenium atoms. For platinum or gold the deposition can occur over the whole copper surface [11]. 

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