Clusters cluster deposition

Figure 2 illustrates a proposed growth process[3] of a polyhedral nanoparticle, along with a nanotube. First, carbon neutrals (C and C2) and ions (C )[16] deposit, and then coagulate with each other to form small clusters on the surface of the cathode. Through an accretion of carbon atoms and coalescence between clusters, clusters grow up to particles with the size fi-... 

Chemical alternation of the surface layer and deposition of a new layer on top of the silicone mbber can be achieved by physical techniques. For the inert surface of silicone rubber, the former requires the generation of high-energy species, such as radicals, ions, or molecules in excited electronic states. In the latter case, coatings of atoms or atomic clusters are deposited on polymer surfaces using technique such as plasma (sputtering and plasma polymerization) or energy-induced sublimation, like thermal or electron beam-induced evaporation. 

As pointed out above, an STM tip can be used to nucleate and grow single clusters. In this type of experiment, cluster deposition on a STM tip is achieved when it is retracted about 10 to 20 run from the substrate surface. Under these conditions, where the feedback loop is disabled, absence of mechanical contact between the tip and the substrate in ensured. Then a positive potential pulse is applied to the tip, the metal deposited on it is dissolved, and it diffuses toward the substrate surface, where a nucleus develops and grows to yield a cluster, typically 20 nm wide. 

Palladium clusters deposited on amorphous carbon have been studied by XPS and UPS [28] and both techniques show broadening of the d-band peak as cluster size increases. The d-threshold shifts towards Ep as cluster size increases. In UPS studies the d-emission of the single atom has its peak at 3.0 eV below Ep, whereas the d-threshold is 2eV below Ep. Palladium clusters evaporated onto Si02 have been studied by UPS [38]. At large coverages of the Pd metal evaporated (> 10 atoms/cm ), a high emission intensity at Ep excited with photons of 21.2 eV (He(I)) or 40.8 eV (He(II)) as excitation source, is observed. This feature is characteristic in the spectra from bulk Pd samples. At the lowest metal coverage (3 x 10 atoms/cm ),... 

Figure 35. Work function and energy gap as a function of the height of gold clusters deposited on single crystal of anatase Ti02 [103].

Figure 34. Scanning tunnel microscopy and local barrier height for gold clusters deposited on a single mtile Ti02 substrate [103].

Gold clusters deposited on the activated carbon had the smallest average diameter of 1.7nm, while gold on graphite and decolorizing carbon had average particle sizes of 2.8 and 6.8 nm respectively. 

Figure 3.9. Transient C02 formation rates on Pd30 (a) and Pd8 (b) mass-selected clusters deposited on a MgO(lOO) film at different reaction temperatures [74]. In these experiments CO was dosed from the gas background while NO was dosed via a pulsed nozzle molecular beam source. The turnover frequencies (TOFs) calculated from the experiments displayed in (a) and (b) are displayed in the last panel (c). C02 formation starts at lower temperatures but reaches lower maximum rates on the larger cluster. (Figure provided by Professor Heiz and reproduced with permission from Elsevier, Copyright 2005).

The talk will briefly review some of these developments ranging from high temperature equilibrium plasmas to cool plasmas, PECVD, ion implantation, ion beam mixing and ion assisted etching and deposition. Brief consideration will also be given to sputtering and ionised cluster beam deposition techniques in inorganic synthesis. 

Figure 21. Schematic representation of ionised cluster beam deposition and some of its features.

Table VI. Some uses of Ionised Cluster Beam Deposition...

Figure 10.31 STM images of Ag, Ag-Au, and Au clusters deposited on Ti02. (A) Imaged under UHV conditions.

In addition, the rate of Oz reduction, forming 02 by electron, is of importance in preventing carrier recombination during photocatalytic processes utilizing semiconductor particles. 02 formation may be the slowest step in the reaction sequence for the oxidation of organic molecules by OH radicals or directly by positive holes. Cluster deposition of noble metals such as Pt, Pd, and Ag on semiconductor surfaces has been demonstrated to accelerate their formation because the noble metal clusters of appropriate loading or size can effectively trap the photoinduced electrons [200]. Therefore, the addition of a noble metal to a semiconductor is considered as an effective method of semiconductor surface modification to improve the separation efficiency of photoinduced electron and hole pairs. 

A wide range of fhese materials has been investigated for fuel cell use, usually as supports for PfRu particles for DMFC testing (presumably due to the ease of experimenfafion). The fheoretically inerf surfaces of CNTs pose some difficulties for mefal cluster deposition because no sites exist for deposition or stabilization. Therefore, clusters fend to be deposited onto defecf and amorphous portions of samples (see Figure 1.18). 

We also compare our results to XPS data on bulk gold and on the smaller centered clustercompound Au 11L7X3 (with X = Cl or I) [74]. A comparison is also made to XPS results obtained on bare gold clusters deposited on poorly conducting substrates [75, 76]. This gives still more support to the idea of the metallic bonding of the Aujj clusters. 

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... 

Waddill GD, Vitomirov IM, Aldao CM, Weaver JH (1989) Cluster deposition on GaAs (110) formation of abrupt, defect-free interfaces. Phys Rev Lett 62(13) 1568... 

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