Surface layers preparation deposition

The other method of monolayer transfer from the air/water interface onto solid substrates is illustrated in Figure 2. This method is called the Langmuir-Schaefer technique, or horizontal lift. It was developed in 1938 by I. Langmuir and V. Schaefer for deposition of protein layers. Prepared substrate horizontally touches the monolayer, and the layer transfers itself onto the substrate surface. The method is often used for the deposition of rigid monolayers and for protein monolayers, hi both cases the apphcation of the Lang-muir-Blodgett method produces defective films. 

Electrochemically generated nickei(lll) oxide, deposited onto a nickel plate, is generally useful for the oxidation of alcohols in aqueous alkali [49]. The immersion of nickel in aqueous alkali results in the formation of a surface layer of nickel(ll) oxide which undergoes reversible electrochemical oxidation to form nickel(lll) oxide with a current maximum in cyclic voltammetry at 1.13 V vj. see, observed before the evolution of oxygen occurs [50]. This electrochemical step is fast and oxidation at a prepared oxide film, of an alcohol in solution, is governed by the rate of the chemical reaction between nickel oxide and the substrate [51]. When the film thickness is increased to about 0.1 pm, the oxidation rate of organic species increases to a rate that is fairly indifferent to further increases in the film thickness. This is probably due to an initial increase in the surface area of the electrode [52], In laboratory scale experiments, the nickel oxide electrode layer is prepared by prior electrolysis of nickel sulphate at a nickel anode [53]. It is used in an undivided cell with a stainless steel cathode and an alkaline electrolyte. 

When controlled nitridation of surface layers is required, as for example in the modification of the chemical properties of the surface of a support, the atomic layer deposition (ALD) technique can be applied." This technique is based upon repeated separate saturating reactions of at least two different reactants with the surface, which leads to the controlled build-up of thin films via reaction of the second component with the chemisorbed residues of the first reactant. Aluminium nitride surfaces have been prepared on both alumina and silica supports by this method wherein reaction cycles of trimethylaluminium and ammonia have been performed with the respective supports, retaining their high surface areas." This method has been applied to the modification of the support composition for chromium catalysts supported on alumina." ... 

The same dependence between concentration of M nanoparticles (Ns) on a surface of a dielectric substrate and their catalytic activity has been also found out in the investigation of an amorphous films of M nanoparticles [117], prepared by laser electrodispersion technique and deposited on Si02 dielectric surface layer of thermally oxidized Si (see Chapter 15). It has been shown that in various reactions of chlorinated hydrocarbons catalyzed by so prepared nanostructured Cu film with growth Ns the value of Y increases firstl, reaches a maximum at Ns 4 x 1012 particles/cm2, and then quickly falls. 

The Pt(l 11) surface alloyed by a small amount of Ge is a nice alloy substrate for studying the origin of the desorption activity in UV laser-induced desorption [87]. This surface alloy is prepared by repeated cycles of deposition of a few ML Ge and subsequent annealing to 1100°C until a constant Ge Auger electron signal was obtained. The total amount of Ge contained in several surface layers of this alloy is 0.1 ML and the Ge coverage in the top layer is 0.04 ML due to a 5 x 5 structure observed by STM [88]. Fukutani et al. call this surface the Pt(l 1 1)-Ge surface alloy. 

MALDI suffers from some disadvantages such as low shot-to-shot reproducibility and strong dependence on the sample preparation method. Each laser shot ablates a few layers of the deposit at the spot where the laser irradiates. This can produce variation in the shot-by-shot spectrum. Also, the impact position on the surface of the deposit can lead to spectral variations. Improvement of the deposit homogeneity gives a better reproducibility of the signal. This is very important if precise quantitative results must be obtained. A given... 

Nespurek (1984) and Nespurek et al. (1985) measured photogeneration efficiencies of vapor-deposited a-H c. Samples prepared with a surface layer of an acceptor compound, pyromellitic acid dianhydride or tetracyanoquinodimethane, were also studied. In the absence of an acceptor, the efficiencies were in the range of 0.01 to 0.02 at fields of KP V/cm. Nespurek and coworkers... 

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