Surface nanostructuring

Tsuji I, Kato H, Kobayashi H, Kudo A (2004) Photocatalytic H2 evolution reaction from aqueous solutions over band structure-controlled (AgIn)xZn2(i-x)S2 solid solution photocatalysts with visible-light response and their surface nanostructures. J Am Chem Soc 126 13406-13413... 

FIGURE 36.1 Schematic illustration of some electrochemical techniques employed for surface nanostructuring (a) tip-induced local metal deposition (b) defect nanostructuring (c) localized electrochemical nucleation and growth d) electronic contact nanostructuring. 

Characterization of the surface impurities on the catalyst is also essential, and photoreactivity data should be analyzed in terms of active and accessible surface area. The defect state of the surface and nanostructure are also important aspects to understand. Current advances in the synthesis allow preparing Titania or titanate nanorods with different diameter and aspect ratio, and different surface nanostructure as well. Limiting the discussion here to only preparations by hydrothermal treatment (for reasons of conciseness), various mechanisms of growing of the nanorods has been reported. The differences in the mechanism of formation would imply differences in the surface characteristics of the nanorods, but there is no literature available on this topic. 

H. Kato, K. Asakura, A. Kudo, Highly efficient water splitting into H2 and O2 lanthanum-doped NaTa03 photocatalysts with high crystallinity and surface nanostructure,/. Am. Chem. Soc. 125 (2003) 3082-3089. 

Electronic and optical properties of complex systems are now accessible thanks to the impressive development of theoretical approaches and of computer power. Surfaces, nanostructures, and even biological systems can now be studied within ab-initio methods [53,54]. In principle within the Born-Oppenheimer approximation to decouple the ionic and electronic dynamics, the equation that governs the physics of all those systems is the many-body equation ... 

Firstly it can be used for obtaining layers with a thickness of several mono-layers to introduce and to distribute uniformly very low amounts of admixtures. This may be important for the surface of sorption and catalytic, polymeric, metal, composition and other materials. Secondly, the production of relatively thick layers, on the order of tens of nm. In this case a thickness of nanolayers is controlled with an accuracy of one monolayer. This can be important in the optimization of layer composition and thickness (for example when kernel pigments and fillers are produced). Thirdly the ML method can be used to influence the matrix surface and nanolayer phase transformation in core-shell systems. It can be used for example for intensification of chemical solid reactions, and in sintering of ceramic powders. Fourthly, the ML method can be used for the formation of multicomponent mono- and nanolayers to create surface nanostructures with uniformly varied thicknesses (for example optical applications), or with synergistic properties (for example flame retardants), or with a combination of various functions (polyfunctional coatings). Nanoelectronics can also utilize multicomponent mono- and nanolayers. 

Jing, D.W. and L.J. Guo (2006). A novel method for the preparation of a highly stable and active CdS photocatalyst with a special surface nanostructure. Journal of Physical Chemistry B, 110(23), 11139-11145. 

The Raman techniques combined with AEM microscopic imaging, as for instance TERS (tip-enhanced Raman scattering) spectroscopy [27], allow to analyze surface nanostructures beyond the diffraction limit, but the cost of the instrumental apparatus is not affordable for any research laboratory. Therefore, in this chapter, the results obtained with those techniques will not be presented, though they increased Raman enhancement factors by up to lO, with the possibility of single-molecule detection. Conversely, confocal micro-Raman apparatus is affordable to every research group allowing SERS investigations with more comparable results. 

Havel, M., and Colomban, P., Rayleigh and Raman image of the bnlk/snrface surface nanostructure of SiC based fibres. Composite B Eng., 35B, 353, 2004. 

The most widely used technique to get information on the electronic structure of clean surfaces, nanostructures on surfaces, or even molecules adsorbed on surfaces is ultraviolet photoelectron spectroscopy (UPS). The difficulty of this method, when applying it to clusters on surfaces, is to obtain sufficient spectral contrast between the low number of adsorbed clusters and the substrate [45]. Thus, electron energy loss spectroscopy (EELS) is more successfully used as a tool for the investigation of the electronic structure of supported clusters. An interesting test case for its suitability is the characterization of supported monomers, i.e., single Cu atoms on an MgO support material [200], as this system has been studied in detail before with various surface science techniques [201-204]. The adsorption site of Cu on MgO(lOO) is predicted... 

Dick, L.A., McEarland, A.D., Haynes, G.L., and Van Duyne, R.P. (2002) Metal film over nanosphere (MEON) electrodes for surface-enhanced Raman spectroscopy (SERS) improvements in surface nanostructure stability and suppression of irreversible loss. Journal of Physical Chemistry B, 106, 853-860. 

Kato, H., Asakura, K., Kudo, A., Highly Efficient Water Splitting into H2 and 02 Over Lanthanum doped NaTa03 Photocatalysts with High Crystallinity and Surface Nanostructure, J. Am. Chem. Soc. 2003, 125, 3082 3089. 

The increase in the intrinsic oxidation state of EM base after one cycle of acid-base treatment is observed only in film samples. Similar treatment does not result in a significant increase in the intrinsic oxidation. state of EM powders [86]. Thus, sample morphologies play an important role during protonation-deprotonation in aqueous media. Each particle of EM powder is an aggregate of many small granules [87], while atomic force microscopic (AFM) study of EM films cast from NMP reveals featureless and dense surface nanostructures before and after protonation [88]. The difference in behaviour between EM film and powder towards protonation—de-protonation and the changes in the intrinsic oxidation states of EM films as a funetion of aeid exposure time during aeid-base treatment are thus attributable to the hindranee to water diffusion and the assoeiated hydrolysis reaetion [89] in the dense EM films. An earlier study [84] has also shown that... 

Abstract Some aspects of self-assembly of quantum dots in thin solid films are considered. Nonlinear evolution equations describing the dynamics of the fihn instability that results in various surface nanostructures are analyzed. Two instability mechanisms are considered the one associated with the epitaxial stress and the other caused by the surface-energy anisotropy. It is shown that wetting interactions between the film and the substrate transform the instability spectrum from the long- to the short-wave type, thus yielding the possibility of the formation of spatiaUy-regular, stable arrays of quantum dots that do not coarsen in time. Pattern formation is analyzed by means of ampbtude equations near the insta-bibty threshold and by numerical solution of the strongly nonlinear evolution equations in the small-slope approximation. 

Figure 2.6a shows that this can be achieved by rapid quenching as, for example, with binary alloys [12]. However, this possibility fails with the formation of surface nanostructures, and hence practically (with the exception of pol5uners where diffusion is slow enough) no reports for spinodal structures exist. This problem could be overcome in a study in which about 50% of the atoms of the topmost layer of a Au(l 11) surface were removed within 20 ps by an electrochemical pulse techniques [13]. The result is shown in Fig. 2.10. In the STM image of Fig. 2.10a, the dark arrow...

Surface Nanostructures in Photocatalysts for Visible-Light-Driven Water Splitting... 

Hasegawa M, Keum C D, Watanabe O. 2002. Enhanced photofabrication of a surface nanostructure on azobenzene functionalized pol5mer films with evaporated gold Nanoislands. Adv Mater 14(23) 1738 1741. 

Electronic communication between electrode surfaces and biocatalysts can be achieved by direct electron transfer if the active site of the biocatalyst is not located too remote from the protein surface, as discussed elsewhere in this book (Chapter 17). Direct electron transfer is an attractive process for fuel cells as no other molecules except the substrate and the enzyme are involved in the electrocatalytic reaction, as depicted in the schematic in Fig. 12.2. The enzyme is the relay for the electron transfer between the substrate and the electrode surface. Recent advances in tailoring surface nanostructural features to match the size of co-substrate channels in biocatalysts, and in reconstituting active prosthetic groups tethered to, and communicating electronically with, surfaces, with apo-enzymes, are elegant demonstrations of direct electron transfer to biocatalyst active sites that were previously considered inaccessible to electrode surfaces [8-17]. 

Manzke A, Pfahler C, Dubbers O et al (2007) Etching masks based on miniemulsions a novel route towards ordered arrays of surface nanostructures. Adv Mater 19 1337-1341 Schreiber E, Ziener U, Manzke A et al (2009) Preparation of narrowly size distributed metal-containing polymer latexes by miniemulsion and other emulsion techniques applications for nanoUthography. Chem Mater 21 1750-1760... 

Electrochemical techniques employed for surface nanostructuring utilizing SPM. 

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