Vapor-deposited gold surfaces

Referring to the right-hand side of an equation or portion of an equation Radius of vapor deposited gold layer on quartz disk Fraction of light reflected from electrode surface... 

Gas-phase grafting (GG) is characteristic in that gold can be deposited even on the acidic surfaces, such as activated carbon and on Si02 [27]. The vapor of gold acac complex is adsorbed on the support powder probably through the interaction of electron-rich oxygen atoms in acetylacetonate and then calcined in air to decompose it into metallic gold particles. 

The adsorption of alkyl and aryl isocyanides on Au film [26, 32, 33], powder [36, 37] and nanoparticles [39, 41, 42] has been studied using several different techniques IR methods (RAIR, ATR-IR, DRIFT), Raman methods (SERS), X-ray methods (NEXAFS), ellipsometry (OE, SWE) and contact angle measurements (ACA). The gold surface is not oxidized under normal conditions consequently, the experiments were performed in air at room temperature. The gold film was obtained by physical vapor deposition of 100-200 nm of gold on different substrates glass [28, 33], mica [33], silicon [25, 27, 31, 32], ZnSe crystal [26]. A... 

Fisher GL, Hooper AE, Opila RL, Allara DL, Winograd N (2000) The interaction of vapor-deposited A1 Atoms with CO2H groups at the surface of a self-assembled alkanethiolate monolayer on gold. J Phys Chem B 104(14) 3267-3273... 

This device comprises a hydrophobic surface using the wettability pattern of hydrophilic stripes for a surface-guided flow, micro channels [102], As substrates, hydrophobic materials were employed. The hydrophilic stripes were generated by mask-through thermal vapor deposition of MgF2 on a silicone mbber or thiolated gold substrate. 

Polymer films were prepared by spin-coating, under controlled inert atmosphere, from typically a 1 mg/ml solution of the polymer in appropriate solvents. Films were generally made on aluminum (with a natural oxide of about 20 A), or on gold. The metals were in the form of vapor-deposited films, of about 2000-3000 A in thickness, deposited in UHV on the surfaces of optically flat Si( 110) substrates. Occasionally, the bare (natural oxide) surface of the Si substrate was used directly, depending upon the preferences for film formation displayed by the particular polymer/solvent combination, or to... 

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. 

Consider the polymer-on-metal interface, which might be prepared by coating a thin metal film with polymer in a polymer-based LED. The case of the counter electrode, formed by vapor-deposition, is discussed subsequently. First, assume that the substrates have clean surfaces hydrocarbon and oxide free, or naturally oxidized but still hydrocarbon free (pointed out as necessary). Typically, in connection with polymer-based LEDs, the metallic substrate could be gold, ITO (indium tin oxide) coated glass, the clean natural oxide of aluminum ( 20 A in thickness), the natural oxide which forms upon freshly etched Si( 110) wafers ( 10 A), or possibly even a polyaniline film. Dirt , which may be either a problem or an advantage, will not be taken up here. Discussions will alternate between coated polymer films and condensed model molecular solid films, as necessary to illustrate points. 

Thin-film electrode — An electrode covered with a thin film of a given substance. The purpose of placing a thin film on the electrode surface is to obtain desired electrode properties. Many different substances have been used to prepare film electrodes they include among others mercury (see - thin mercury film electrodes) gold, boron-doped diamond (see - boron-doped diamond electrode), conductive polymers (see - polymer-modified electrode), and alkanethiols. The film thickness can vary from several micrometers (mercury) to monomolecular layers (thiols). In some cases (e.g., for - spectroelectrochemistry purposes) very thin layers of either gold or tin oxide are vapor-deposited onto glass plates. Thin film electrodes are often called - surface-modified electrodes. 

Alternatively PAA can be obtained without solvent by vapor deposition polymerization as described first by Salem et al. [2], In this technique the dianhydride py-romellitic and the dianhydride diamine (4,4 -oxidianiline) are codeposited onto a substrate, where they react to form PAA. Again the transformation to Polyimide is obtained by subsequent heating to temperatures up to 350°C. By comparison to spun dn films, initial interaction of the polymer with the substrate occurs in the uncomplexed PAA state. The chemical interaction between PAA and the metal establishes the adhesion of the final polyimide film. This is discussed in this communication for evaporated gold cluster and bulk silver surfaces. 

A quantitative measurement of the depth of penetration of the diffracted electrons has been made previously by the author (1) by depositing silver vapor onto a gold crystal surface, using a calibrated silver source. Since the lattice structures are the same and the lattice constants differ by less than 0.4%, the silver was found to deposit as a thin crystal on the gold surface. Because of the different indices of refraction and certain fine-structure characteristics for the two metals, the diffraction beams from silver and gold were readily distinguished. 

Peptide microarrays are prepared by immobilizing many peptide molecules on the surface of a solid support in a small area in an addressable fashion. The immobilization can be achieved via in situ synthesis or chemical ligation through a covalent bond. A hydrophihc linker between the sohd surface and the peptide usually is added to minimize steric hinderance caused by the sohd support. The most commonly used solid support for microarray printing is a standard microscope glass slide. Other solid supports also have been used such as polystyrene, nitrocellulose membranes, PVDF membranes, Hybond ECL membranes, gold surfaces, and chemical vapor deposited diamond films. 

Fig. 3.3 Surface modification with Pd thin films by UHV vapor deposition (Left) Gold surface modified with Pd thin film (a) Rotating disc electrode (RDE) polarization curves for electrochemical hydrogen oxidation reaction on pure Au(lll), Au(lll)-Pd (for different rpm ) and Pt(lll) surfaces [51] (b) and (c) LEIS spectra of Au(lll)-Pd surfaces after vapor deposition of Pd in the amount that corresponds to four atomic monolayers. (Right) Platinum surface modified with Pd thin film (d) LEIS spectra of the Pt(l 11)-Pd surface with 65% of Pd and (e) LEIS spectra of Pd monolayer on Pt(lll) (red line) and pure Pt(lll) (dashed line), (a) Reprinted with permission from [51], copyright 2002 Elsevier...

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