Physical surface modification method

The resultant tailored interface is often vastly superior for biomedical applications over the native silicone interface. Furthermore, surface modification maintains the low materials cost and favorable bulk properties of the original silicone elastomer. The modification methods can be divided into physical and chemical techniques. 

Micro- (and even nano-) electrode arrays are commonly produced with photolithography and electronic beam techniques by insulating of macro-electrode surface with subsequent drilling micro-holes in an insulating layer [136, 137], Physical methods are, however, expensive and, besides that, unsuitable for sensor development in certain cases (for instance, for modification of the lateral surface of needle electrodes). That s why an increasing interest is being applied to chemical approaches of material nanostructuring on solid supports [140, 141],... 

Application of the Mossbauer effect, which is essentially a bulk phenomenon, to the study of surfaces has received significant attention in recent years. The usefulness of this technique lies in its ability to determine the electronic environment and symmetry of the surface nucleus, and it offers a method of investigation that is clearly complementary to other physical methods for the characterization of solid surfaces. Mossbauer spectroscopy has the attractive advantage that it may be used at a variety of pressures and can be applied to the study of heterogeneous catalysis and adsorption processes to probe the nature of the solid surface and its electronic modification when holding adsorbed species. 

Physical methods include plasma treatments, UV irradiation, corona discharge, and flame treatment. Among these, plasma treatment is widely used for the surface modification of synthetic polymers. Plasma can be obtained by exciting gases into an energetic state by radio frequency, microwave, or electrons from a hot filament discharge. Generation of plasma requires a vacuum, which normally poses several... 

There are two types of surface modifications for CNTs noncovalent interactions (Figure 6.54) and covalent sidewall (Figure 6.55) or defect-sitet (Figure 6.56) functionalization.Both methods, as well as physical techniques such as sonica-tion, are successful in separating individual SWNTs from bundles - a process known as exfoliation. In general, it is most desirable to incorporate isolated SWNTs in a composite rather than bundles, since the latter features poor intertube interactions resulting in a lower overall strength - especially at low CNT concentrations. 

The four kinds of active carbons used in our laboratory were obtained from different commercial sources and in accordance with supplier information were produced from various precursors. Ash was removed from the raw carbon using concentrated hydrofluoric and hydrochloric acids by Korver s method [166]. Carbon samples were subjected to surface modification by oxidation in air or with concentrated HNO, annealing in a vacuum or an ammonia atmosphere. Afterwards, all carbon samples were desorbed under vacuum (10" Pa) at 150°C (423 K) for 3 h. The procedure used for carhon purification ensured the removal of nitric acid and nitrogen oxides (after nitric acid oxidative modification) or physically sorbed NHi (after heat treatment in ammonia). The samples thus prepared... 

Grinding, brushing or sanding (with the exception of the above-mentioned Saco method) do not cause chemical modifications of the material s surface. A clean surface results with a characteristic structure corresponding to the composition of the material, as shown in Figure 7.6. Therefore, physical and chemical pretreatment methods are aimed at the chemical modification of the surfaces. Thus, on the one hand it is possible to further enhance the adhesive forces for extremely high demands on bonded joints, and on the other hand, to make poorly bondable material (e.g., plastics) bondable at all. Since physical methods are mainly used in bonding of plastics, they are described in Section 9.2.4. 

The treatment with a fuel gas-oxygen flame (propane/butane or acetylene with excess oxygen, recognizable by the blue coloration of the flame) results in a chemical and physical surface modification, also with oxidative effects. This method is particularly suitable for handycraft applications, because of its low effort and expenditures. The flame treatment time is in the range of seconds, the distance of the flame to surface should be approximately 5-10 cm. In the case of thermoplastics like polyethylene and polypropylene, care should be taken that surface melting is avoided. 

In summary, this study shows the great possibility of generating Cu/n-Si junctions with a nearly perfect rectifying behavior from CuCN solutions. Diode characteristics are comparable to those reported for contacts prepared by physical methods and are not appreciably subject to modification with time. The second promising point is the high adherence of Cu films, which was exploited to electrodeposit adherent Ni films from a modified Watts bath. This two step procedure seems to solve the major difficulty encountered upon growing thick metal layers onto H-Si surfaces from acidic solutions and enables to prepare stable electrical junctions with defined electrical properties. 

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