Surface electrical property

The transducing mechanism of semiconductor luminescence involves the modification of the semiconductors surface electrical properties through molecular adsorption. Changes in solid-state electro-optical properties result from adsorption of the molecule of interest onto the semiconductor surface. 

Also surface optical properties of a material sometimes need to be changed, for example in making anti-reflection coating for lenses or reflective surfaces for CDs, the magnetic properties may need to be influenced as in the case of giving a ferroelectric surface to a plastic for magnetic recording, and, perhaps most extensively of all, the surface electrical properties need to be controlled in microelectronic devices used in computers and all modern electronic equipment. 

Mott and Bott illustrated the effect of different materials on the accumulation of Pseudomonas fluor-escens biofilms on the inside of tubes under identical operating conditions (see Fig. 9). The differences between the effects of the materials occur for two reasons roughness and surface electrical properties. The quality of the surface, in terms of roughness, on which microorganisms attach, can affect the biofilm accumulation as discussed earlier. The effect of roughness is illustrated in Fig. 9 by the difference of biofilm accumulation between electropolished and as received 316 stainless steel. The rougher stainless steel is seen to be more hospitable to biofilm growth. 

Golikova, E.V. et al.. Surface electrical properties and aggregative stabihty of aqueous dispersions of a-AIjO, y-AIjO, and y-AlOfOH), Phys. Chem. Meeh. Surfaces, 11,994, 1995. 

Pownall, P.G., The surface electrical properties of calcium carbonate, Thesis, University of Bristol, 1987. cited after [291]. 

Information on surface electrical properties from charging studies... 

The co-deposition of transition metals can enhance chemical reactivity and further increase the sensitivity of the semiconductor detectors. Chemisorption-induced changes in surface electrical properties promise to be important in the chemical analysis of blood and in other biochemical applications. 

In addition to the internal reflection spectroscopic technique, there Is a host of supporting methods. They range from techniques that estimate precise film thickness and refractive Index to techniques that measure surface electrical property and wettability changes that are associated with protein film deposition (13). 

Electrostatic Force Microscopy (EFM) allows to obtain information on the surface electrical properties of materials by measuring electric forces between a charged tip and the surface. It is particularly suitable for the study and manipulation of ferroelectric thin films with large surface charge. Interestingly, an EFM can also be used to study the surface properties of dielectric materials, that are polarized by the electric field of the tip. In this mode of operation, the EFM is sometimes called Polarization Force Microscope and can be used to study and image even air-liquid interfaces [64]. 

Fig. 4 Chemical strategy to control the surface electrical properties using multifunctional molecules.

Fine-tuning of semiconductor surface electrical properties can be achieved by grafting multifunctional organic molecules onto the surface. In such molecules, one function takes care of the binding... 

It is reasonable to state that, where surface electrical properties are concerned, the vast bulk of the published hterature is consistent and indicates that the additirai of even a very small quantity ( 1 %) of a nanohller can significantly improve the performance of polymers. Although different authors have ascribed these effects to different mechanisms, examination of the broader literature provides credible mechanisms, which have a structural origin and are largely associated with a good dispersion of the nanofiller combined with the consequent close proximity of the nanoparticles and the polymer. 

The main thrust of this work has been to sufficiently characterize a latex to allow a check of the quantitative features of the present concepts of colloidal stability as applied to synthetic latices. Previous attempts (10,11,12) to accomplish this check have suffered from lack of an adequate description of the particle surface. In the past, the primary source of information on surface electrical properties has been electrophoretic mobilities, which, as was shown in Figure 3, are inadequate. In the study presented hei e, the actual concentration of potential determining ions at the particle surface has been measured and, in addition, the stability of the sol as a function of this concentration has been determined. This now allows a more thorough evaluation of the present stability theory without recourse to many of the questionable assumptions of the past. 

The technological importance of various suspensions of solid particles is enormous. The literature is therefore extensive and difficult to survey. It is, in principle, possible to make a suspension of practically all solid substances, provided that they are sufficiently insoluble in the liquid. The methods used to make them take advantage of a large number of different physical principles. However, in a brief overview such as this it is not possible to give a detailed account of all available preparation methods. In the following, we will present a short outline of the most frequently used preparation methods and references to more detailed accounts. The surface electrical properties are then described and this is subsequently used to give an account of how dispersions can be stabilized and how they aggregate. 

Polymer latexes have a great technological importance, particularly in paint formulations and coatings for paper. In the chapter by K. Tauer in this Vol. 1 (chapter 8), additional material about latexes can be found. As the latter can be prepared easily as nearly perfect spheres, they are also popular model systems for fundamental studies of colloids. However, a drawback is that their surface electrical properties are poorly understood, which means that the interaction potentials are also poorly known. 

Therefore the present review emphasizes the information provided and its biological relevance, but also its limitation regarding sample preparation and analytical performances. A particular attention is devoted to the relationships between the surface chemical composition as determined by XPS, and surface physico-chemical properties that are evaluated by other techniques (having also their own limitations) and that may play a major role in interfacial interactions the surface electrical properties and the surface hydrophobicity. A final section gives a survey of applications of XPS to better understand interfacial phenomena involving microorganisms. Previous reviews may be found in references 22 to 25. 

Relationship Between Chemical Composition and Surface Electrical Properties... 

The flotation performances of two strains of S. cerevisiae were examined in relation with cell separation in continuous fermentation. For batch cultures, the more hydrophobic strain (water contact angle 69°, compared to 27°), which showed a higher degree of flotation, showed a surface concentration higher in nitrogen and carbon of hydrocarbon type, and lower in oxygen. For continuous cultures, the relationship between surface chemical composition, surface electrical properties, surface hydrophobicity, and flotation was less clear. 

However, the separation characteristics of membrane interfaces do not depend solely on the physical form of surface features. In liquids, surface electrical properties and the adhesion of solutes to membrane surfaces may also have profound effects on separation performance. It is thus exceedingly fortunate that an atomic force microscope may also be used to determine both of these additional controlling factors. Finally, means may be devised to quantify all of these controlling factors in liquid environments that match those of process streams. 

Although most membrane technologists now recognize the important contribution of membrane surface electrical properties in defining the separation characteristics, there remains confusion as to how best to describe and quantify such interactions. There is an unfortunate tendency in the applied membrane... 

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