Ultrathin oxide films interface

On the other hand, the progress of wet-processes as preparative techniques of metal oxide films has been remarkable. The so-called soft solution process that provides oxide layers by means of electrochemical oxidation of a metal surface is expanding as a synthetic method of various mixed metal oxides with controlled thickness [2], The two-dimensional (2D) sol-gel process based on the hydrolysis of metal alkoxides at the air/water interface has been reported as a preparative technique of ultrathin oxide films (Fig. 6.1a) [3]. It is also known that LB films of metal complexes of long-chain alkyl carboxylic acid can be converted to metal oxide films after removal of organic component by oxygen plasma [4] and UV-ozone treatments (Fig. 6.1b) [5]. Preparation of metal oxide... 

An interesting example of the application of the slab model approach to the study of interfaces is the modeling of ultrathin oxide films on metallic substrate, which has been the subject of recently published papers by Pisani et It deals with a model of the epitaxially grown MgO (100) thin... 

All Fe oxide films on Pt have strongly relaxed, unreconstructed bulk-terminated surfaces, but while the Fe304 and Fe203 oxide layers are similar to their respective bulk compounds, the ultrathin FeO layers are true 2D oxide phases that are different from the FeO bulk and stabilized by the metal-oxide interface. 

Ultrathin Nanocrystalline Films of Metals, Chalcogenides, and Oxides. J. Colloid Interface Sci. 2005, 289, 305-31B. 

Hardacre el al. (7 75, 174) investigated the properties, structure, and composition of cerium oxide films prepared by cerium deposition on Pt(lll), finding that the activity for CO oxidation is enhanced on Pt(lll) that is partially covered by ceria. It was suggested that new sites at the Pt-oxide interface become available for reaction. A remarkable observation is the high activity for CO oxidation when the Pt(lll) sample is fully encapsulated by ceria (Pt was undetectable by XPS and AES). It was proposed that an ultrathin, disordered ceria film becomes the active catalyst. It was also demonstrated by XPS and AES that Pt dramatically increases the reducibility of cerium oxide that is in intimate contact with Pt. This result suggests that intimate contact between the noble metal and oxide phases is indeed crucial to facile oxygen release from ceria. High-resolution electron microscopy demonstrated the presence of direct contact between ceria and noble metal for supported Pt-Rh catalysts (775). Hardacre et al. (173,174) related the catalytic activity of the ceria phase to partially reduced cerium oxide. 

RAIRS is used for characterization of adsorbates on metal surfaces, their transformations and kinetics (for example CO on metallic surfaces), catalytic reactions, characterisation of semiconductor structures, high-temperature oxidation of metals (use of so-called Berreman effect), electrode/electrolyte interface, Langmuir-Blodgett and other ultrathin organic films. 

Sanabria-Chinchilla J, Baricuatro JH, Soriaga MP, Hernandez F, Baltruschat H (2007) Electrocatalytic hydrogenation and oxidation of aromatic compounds studied by DBMS benzene and p-dihydroxybenzene at ultrathin Pd films electrodeposited (m Au(hkl) surfaces. J Colloid Interface Sci 314 152-159... 

The key effect of oxide supports on the catalytic activities of metal particles is exerted through the interface between oxides and metal particles. The key objective of this study is to develop synthesis methodologies for tailoring this interface. Here, an SSG approach was introduced to modify the surface of mesoporous silica materials with ultrathin films of titanium oxide so that the uniform deposition of gold precursors on ordered mesoporous silica materials by DP could be achieved without the constraint of the low lEP of silica. The surface sol-gel process was originally developed by Kunitake and coworkers.This novel technology enables molecular-scale control of film thickness over a large 2-D substrate area and can be viewed as a solution-based... 

Figure 6.1. Wet processes for the preparation of ultrathin metal oxide thin films, (a) 2D sol-gel process at the air/water interface [3], (b) repeated adsorption and UV-ozone oxidation of alkylsiloxane monolayer (R = C18H37) [5], and (c) two-step adsorption cycle of alternate electrostatic adsorption of linear polymers and inorganic sheets [7] ((b) is with permission of American Chemical Society and (c) is with permission of...

The electrochemical oxidation of silicon is of interest for the formation of ultrathin dielectric layers due to its low temperatures and easy controllability of the process [3]. In this case, the efficiency of the electrochemical treatment of the materials when oxide layers of low thicknesses are synthesized on their surfaces depends on the uniformity of the charge distribution at the solid phase/electrolyte interface. A great impact on this factor is made by adsorption processes, particularly, chemisorption ones, but their role in the formation of nano-sized films is, not yet understood. 

Fig. 12 Schematic of base-catalyzed hydrolysis reaction in a SAMs of NHS-CIO and b ultrathin films of PNHSMA on oxidized silicon together with the definitions of surface and surface-near regions of the polymer film. The approximate depths in this tentative model were assigned based on the information depths of the techniques (CA 1 nm [148], IR the entire film, in other words 40 nm), the fact that only 25% of the NHS ester groups can be hydrolyzed, and that the reaction can be expected to start at the film-solution interface and to proceed homogeneously into the amorphous film. (Reprinted with permission from [128], copyright (2003), American Chemical Society)...

The concept of ATR at the interface of two media is described in 1.4.10° and Section 1.8.3. In situ ATR measurements of ultrathin films started in the mid-1960s with studies of the adsorption of a stearic acid monolayer from D2O onto Ge [448], and chemical [449] and electrochemical [450] oxidation of Ge, where a Ge multiple internal reflection element (MIRE) acts as both the substrate and the electrode. Later, coated ATR [60, 451-454] and MO ATR with the SEIRA effect [455] were introduced in in situ experiments. The principal advantage of the ATR geometry is that the corresponding in situ cells are free from diffusion effects (the volume of solution phase in contact with the IRE is arbitrary), which is useful when studying time-dependent phenomena (Section 4.9.1). 

The delamination rate was determined with a scanning Kelvin probe. A small amount of fine sodium chloride was introduced into a circular deepening in the middle of the polished and ethanol-cleaned iron sample. After the sample was introduced into the plasma reactor, it was cleaned and activated in one step by an oxygen plasma, leading to a carbon-free and highly oxidized iron surface. In the next step an ultrathin plasma polymer of hexamethyldisilane was deposited on the cleaned substrate, leading to a well-defined metal-polymer interface. The thickness of the deposited polymer was controlled by the in situ measurement of the resonance frequency of the quartz crystal and was about 5 nm, so that the film thickness is in the range of the escape depth of the photoelectrons. 

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