Doping technique, liquid

Nearly all theories to date predict that IETS intensities should be proportional to n, the surface density of molecular scatterers. Langan and Hansma (21) used radioactively labeled chemicals to measure a surface concentration vs solution concentration curve ( Fig. 10 ) for benzoic acid on alumina using the liquid doping technique. The dashed line in Fig. 10 is a 2 parameter fit to the data using a simple statistical mechanical model by Cederberg and Kirtley (35). This model matched the free energy of the molecule on the surface with that in solution. The two parameters in this model were the surface density of binding sites ( 10" A )... 

Figure 10. Surface concentration (9) and peak intensities (O) vs. solution concentration using the liquid doping technique for benzoate ions on aluminum (---)...

McBride and Hall (37,38) reported the first observation of a controlled catalytic reaction on alumina using IETS. They studied the catalytically induced transfer hydrogenation from water vapor to unsaturated hydrocarbon chains chemisorbed on alumina at both ends of the chain. They absorbed muconic acid ( trans-trans-1,3 butadiene 1,4 dicarboxylic acid, HOOC-CH=CH-CH=CH-COOH ) onto oxidized aluminum strips using the liquid doping technique. The samples were returned to the vacuum system, and in the presence of 0.3 torr of D2O vapor, heated to up to 400° C by passing current through a heater strip evaporated on the back of the glass slide. The films were then allowed to cool and the junctions completed by evaporation of the Pb counter electrode. 

Before constructing an electrode for microwave electrochemical studies, the question of microwave penetration in relation to the geometry of the sample has to be evaluated carefully. Typically only moderately doped semiconductors can be well investigated by microwave electrochemical techniques. On the other hand, if the microwaves are interacting with thin layers of materials or liquids also highly doped or even metallic films can be used, provided an appropriate geometry is selected to allow interaction of the microwaves with a thin oxide-, Helmholtz-, or space-charge layer of the materials. 

The practical use of the desorption reaction requires a catalyst for the improvement of the kinetics. The first work on catalyzed alanates at MPI - Miilheim was derived from studies that used transition-metal catalysts for the preparation of MgH2- The NaAlH4 was doped with Ti by solution chemistry techniques whereby nonaqueous liquid solutions or suspensions of NaAlH4 and either TiCl3 or the alkoxide Ti(OBu )4 [titanium(IV) w-butoxide] catalyst precursors were decomposed to precipitate solid Ti-doped NaAlH4 [57, 58]. 

The technique of fluorescence spectral measurements has become very sensitive over the past decade. In order to obtain more information on the surface monolayers, a new method based on fluorescence was developed. It consisted of placing the monolayer trough on the stage of an epifluorescence microscope, with doped low concentration of fluorescent lipid probe. Later, ordered solid-liquid coexistence at the water-air interface and on solid substrates were reported. The theory of domain shapes has been extensively described by this method. 

These hydrogenations are rapid and quantitative. Conversely, the gas-solid hydrogenations of alkenes that were doped by platinum metal compounds on their recrystallization maybe incomplete as, for example, the hydrogenation of trans-cinnamic acid or N-vinylisatin [58,61], which should be milled for completion. Furthermore, the spillover technique by mixing powders of substrate and catalyst followed by application of hydrogen and several hours or days rest [69,70] appears inappropriate for quantitative conversions. Milling is, however, not applicable if volatile liquids have to be constantly pumped off [69] or if the products become liquid or sticky [70]. 

The experimental practice for the study of current/potential characteristics requires the formation of an ohmic contact on the back of the electrode. The simplest technique consists in the application of a very thin layer of Ga—In eutectic liquid alloy, which wets the surface easily. But in the most rigorous method used in production lines, a highly doped 750-nm... 

Conventional two-electrode dc measurements on ceramics only yield conductivities that are averaged over contributions of bulk, grain boundaries and electrodes. Experimental techniques are therefore required to split the total sample resistance Rtot into its individual contributions. Four-point dc measurements using different electrodes for current supply and voltage measurement can, for example, be applied to avoid the influence of electrode resistances. In 1969 Bauerle [197] showed that impedance spectroscopy (i.e. frequency-dependent ac resistance measurements) facilitates a differentiation between bulk, grain boundary and electrode resistances in doped ZrC>2 samples. Since that time, this technique has become common in the field of solid state ionics and today it is probably the most important tool for investigating electrical transport in and electrochemical properties of ionic solids. Impedance spectroscopy is also widely used in liquid electrochemistry and reviews on this technique be found in Refs. [198 201], In this section, just some basic aspects of impedance spectroscopic studies in solid state ionics are discussed. 

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