Templates metal surfaces

Mesoporous carbon materials were prepared using ordered silica templates. The Pt catalysts supported on mesoporous carbons were prepared by an impregnation method for use in the methanol electro-oxidation. The Pt/MC catalysts retained highly dispersed Pt particles on the supports. In the methanol electro-oxidation, the Pt/MC catalysts exhibited better catalytic performance than the Pt/Vulcan catalyst. The enhanced catalytic performance of Pt/MC catalysts resulted from large active metal surface areas. The catalytic performance was in the following order Pt/CMK-1 > Pt/CMK-3 > Pt/Vulcan. It was also revealed that CMK-1 with 3-dimensional pore structure was more favorable for metal dispersion than CMK-3 with 2-dimensional pore arrangement. It is eoncluded that the metal dispersion was a critical factor determining the catalytic performance in the methanol electro-oxidation. 

One of the first attempts to explain e.s. was made by Wells and coworkers [234], who proposed that the L-shaped modifier could generate a chiral surface, by adsorption on Pt in ordered nonclose-packed arrays, allowing preferential adsorption on the metal surface of one of the faces of the prochiral substrate (template model). 

D. Brunei, N. Bellocq, P. Sutra, A. Cauvel, M. Lasperas, P. Moreau, F. Di Renzo, A. Galarneau, and F. Fajula, Transition-metal ligands bound onto the micelle-templated silica surface. Coord. Chem. Rev. 180, 1085-1108 (1998). 

Figure 15.1 Ordered nanoscale structures of mesoporous materials such as FSM-16 and HMM-1 (Et-HMM-1) as the silica and organosilica templates for surface-mediated synthesis of metal/alloy nanowires and nanoparticles.

Czuryszkiewicz T, Rosenholm J, Kleitz F, Linden M (2002) Synthesis and characterization of mesoscopically ordered surfactant/cosurfactant templated metal oxides. Impact of Zeolites and Other Porous Materials on the New Technologies at the Beginning of the New Millennium, Book Series Studies in Surface Science and Catalysis, Pts A and B 142 1117-1124... 

Abstract. Clean metal surfaces often display an atomic arrangement at the surface that differs from the one in the bulk. Some of these surface reconstructions show mesoscopic order and are very adequate to act as a template for the ordered growth of arrays of atoms, molecules or clusters. The electronic states at some surfaces can be prototypes of highly dense 2D electron gases where a number of fundamental properties can be addressed in detail. Localized surface states, on the other hand, are relevant in chemical processes at surfaces. The recent developments in experimental and theoretical techniques allow the exploration of these issues with unprecedented precision. 

F. Rosei, M. Schunack, P. Jiang, A. Gourdon, E. Laegsgaard, I. Stensgaard, C. Joachim and F. Besenbacher, Organic molecules acting as templates on metal surfaces, Science 296, 328 (2002). 

The last example we would like to discuss is a lattice of holes formed in stoichiometric hexagonal (h) BN double layers on Rh(lll), see Fig. 5(c) and [99]. The lattice is composed of holes in the BN-bilayer with a diameter of 24 2 A, and an average distance of 32 2 A. The holes in the upper layer are offset with respect to the smaller holes in the lower layer. We note that well-ordered superstructures with a large period have already been observed some time ago by means of LEED for borazine adsorption onto Re(0001) [102], while borazine adsorption onto other close-packed metal surfaces, such as Pt(lll), Pd(lll), and Ni(lll), leads to the self-limiting growth of commensurate ABN monolayers [103,104]. For BN/Rh(lll) it is not clear at present whether the Rh(lll) substrate is exposed at the bottom of the holes. If this was the case the surface would not only be periodic in morphology but also in chemistry, and therefore would constitute a very useful template for the growth of ordered superlattices of metals, semiconductors, and molecules. 

A template assisted synthesis of MWNTs in an anoidic almninum oxide (AAO) on metal surfaces has been shown to produce aligned MWNTs. Well-aligned MWNTs have been grown perpendicular to the substrate from a quartz plate and it has been noticed that the length of the tube increases... 

There has been considerable interest in recent years in the formation of condensed films of purine and pyrimidine bases at the solid-liquid interface. It is well recognised that non-covalent affinities between base pairs play a prevalent role in determining nucleic acid conformation and functionality. Likewise, there has been interest in the role of substrate and non-covalent intermolecular interactions in the configuration of ordered monolayers of purine and pyrimidine bases. There is also more general interest in the interaction of bases with metal surfaces and metal complexes. In the latter case it is noted that the biological role of nucleic acids and certain nucleotides are dependent on metal ions, particularly Mg, Ca, Zn, Mn, Cu and Ni. " Also certain metal complexes, notably of platinum, have the anti-tumour activity, which is linked to their ability to bind to bases on DNA. On a different note, the possibility that purine-pyrimidine arrays assembled on naturally occurring mineral surfaces might act as possible templates for biomolecular assembly has been discussed by Sowerby et al. 

A.N., Zancanela, D.C., Simao, A.M.S., Ciancaglini, P., and Ramos, A.P. (2014) Formation of carbonated hydroxyapatite films on metallic surfaces using dihex-adecyl phosphate-LB films as template. Colloids Surf, B Biointerfaces, 118, 31-40. 

Reconstructed clean metal surfaces may thus be interesting templates. However, their given structure does not provide the experimentalist with a control on the nature and physical dimensions of the nanostructure. This implies that these surfaces can be suitable candidates for the investigation of the basic properties of templates on an atomic scale but are less interesting in terms of appHcations. To overcome this limitation systems are needed for which the pattern formation by self-organization can to some extent be controlled by the experimentaUst. This leads us to two promising systems stepped metal surfaces and thin films on metal surfaces. 

Apart from the nanopattern, which can be derived by the deposition of atoms and the formation of inorganic films, a virtually unhmited number of structures can be generated by the adsorption and self-organization of large organic molecules on surfaces. It is far beyond the scope of this communication to explore the whole universe of these structures but a few cases, which have a direct application as templates, shall be covered below (see for example Fig. 24). In the Introduction the formation of ordered layers of PTCDA on metal surfaces was mentioned as an example of the template-assisted assembly of molecular layers, however, these layers have not been used as templates so far. 

From the above it is evident that metal surfaces may be utilized as templates if certain conditions are met. If we consider reconstructed surfaces the reconstruction has to be stable during further deposition of material. The same holds for nanopatterns formed by deposition of thin films. Likewise vicinal surfaces may facet during the deposition of further material. This section will therefore be dedicated to the use of metal surfaces as growth templates. We use the classification of the systems that was estabhshed in Sect. 2 and begin with reconstructed metal surfaces. 

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