Nanofabricated particles

In some cases, particularly at high monolayer surface pressures, formation of rod-like PbSe particles was observed (Fig. 117) [648]. The thickness of the rods was typically 10 nm or less and the length was of the order of 100 nm. In addition to the rods, there were also many dot-like particles in the 10-nm size range (Fig. 117). Generation of rod-like semiconductor particles under monolayers provides a potential approach to nanofabricated quantum wires. 

This leads us to the concept called nanocatalysis, and specifically to nanofabricated model catalysts, as an approach to bridge the structure gap. In Fig. 4.4, some examples of planar model structures of increasing complexity are depicted, which fulfill these criteria. At the top, there is a simple array of catalyst particles on an inactive support. The inactive support can be replaced by an active support (second picture from the top), meaning a support that significantly affects the properties of the nanoparticles via particle-support interactions (a clear distinction between inactive and active is not easy or not even possible—there is always some influence of the support on the supported particle). In some cases, the size of the support particle has an influence on the overall catalytic activity. This is, for example, the case when there is a spillover or capture zone for reactants or intermediates, which move by diffusion from the catalyst nanoparticle to the support or vice versa. In order to study such effects, one may want to systematically vary the radius of the... 

Step 3 The PS particles are removed by an O2 plasma treatment (2 min at 250 W, and SOOmTorr). In Chemical Properties we present XPS results, which describe the effect of O2 plasma treatment regarding removal of the PS particles by O2 plasma and oxidation of Pt. It should be noted that it is not possible to dissolve the PS particles in acetone after the Ar+ etching process, which is believed to be due to ion-induced crosslinking of the polymer chains during ion etching (111), making them resistant to normal solvents for PS. The radial distribution function, g r), from the initial colloidal adsorption step is preserved throughout the nanofabrication procedure. 

Heat treatments of nanofabricated catalyst particles in different reactant mixtures can result in restructuring and eventually crystallization. Figure4.36 shows two differently sized Pt/ceria samples made by EBL, before and after reaction in a lean H2 + O2 gas mixture for 10 h at 1,000 K. The smaller 130 nm particles reshaped and formed crystallites. In contrast, the larger 500-nm Pt particles (and 20 nm in height), were stable at 623 K, but were found to disintegrate and form clusters of smaller crystalline particles at 773 K [29]. The particle disintegration was also found to be dependent on the support material, occurring more readily on ceria than on silica [72,77]. 

Beyond single component metal catalysts, the nanofabricated model catalysts can be used to study alloy catalysts, with compositions controlled by co-evaporation from two or more PVD sources. Alternatively, arrays of alternating particles or areas of two different materials can be made to study lateral communication between two types of catalysts at the nanoscale. For example, sequential reactions consisting of a first step on one type of catalyst and a second step on another catalyst particle could be studied systematically. The role of reactants and reaction intermediates as surfactants, affecting particle shape and morphology [163], will be possible to study in detail by in situ TEM studies in reactive environments. 

Guimarsson L, Rindzevicius T, PrikuUs J, Kasemo B, KaeU M, Zou S, Schatz GC. 2005. Confined plasmons in nanofabricated single silver particle pairs Experimental observations of strong interparticle interactions. J. Phys. Chem. B 109 1079-1087. 

The first ordered structures for SERS were reported during the early 1980s by Liao et al. [95,96], who obtained regularly ordered SERS substrates by depositing Ag particles over periodic arrays of silica posts that were fabricated by photolithography. Since the 1990s, with the rapid development in the field of nanofabrication, many ordered periodic arrays of nanoparticles for SERS have been made. 

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