Carbon surfaces roughness

These problems have been improved in recent years by the microfabrication of sharp tips with radii less than 10 nm, the observation in an SEM or STEM of the exact radius before and after the experiment, the use of robust carbon-nanotube probes, and general improvements in control electronics. However, another method used initially was the attachment of a small colloid particle in place of the AFM tip. These particles were considered a reasonably good approximation to a single-asperity contact their radii were accurately known and remained the same for the duration of the experiment. Such probes have also been used to investigate colloids where surface roughness is an important aspect of the colloid interaction. 

Ismail, l.M.K. Pfeifer, P. (1994) Fractal analysis and surface roughness of nonporous carbon fibers and carbon blacks. Langmuir 10 1532-1538... 

The primary objective of the discussion that follows is to establish a basis for choosing and applying carbon electrodes for analytical applications. As with any electrode material or electroanalytical technique, the choice depends on the application there is no ideal electrode for all situations. We first discuss the criteria that drive the chemist s choice of electrode or procedure. These criteria include background current, potential limits, and electrode kinetics, and may be considered dependent variables that are ultimately controlled by the properties of the carbon surface. Then we consider the independent variables that determine electroanalytical behavior. These include the choice of carbon material, surface roughness, cleanliness, etc. By considering the dependence of electroanalytical behavior on surface variables that the user can control, it should be possible to make rational choices of electrodes and procedures to lead to the desired analytical objective. 

An infrared C02 laser (1060 nm) was used to cut through a polycarbonate PC (black) (carbon-coated) wafer of 250-pm thickness to create microfluidic channels. The laser-machined black PC wafer was then thermally bonded between two transparent PC wafers at 139°C under two tons of pressure for 45 min [937], A C02 laser was also used to ablate Mylar sheets (with adhesive). Then the machined Mylar sheets were laminated together [1051]. Moreover, a PMMA substrate was machined by a C02 laser [201,202]. However, the microchannel ( 200 pm deep) has a Gaussian-like cross section and a certain degree of surface roughness [201], The C02 laser has also been used to machine PET substrates [203],... 

Table 2.7. Surface roughness factor for biogenic carbonates and ratios of surface roughness factors versus specific surface area ratios (Walter and Morse, 1984b).

For the characterization of surface roughness of carbon blacks, different experimental techniques have been applied in the past. Beside microscopic investigations, e.g., AFM that give an impressive but more qualitative picture [90-92], scattering techniques such as SANS [93] and SAXS [94-96] as well as gas adsorption techniques [79-84, 97-99] have been used for a fractal analysis of surface roughness. The results discussed in the literature appear somewhat controversy, since almost flat surfaces with ds 2 [98, 99] and also rough surfaces with 2.2[Pg.12]

In the present chapter we will summarize results of two different evaluation procedures for the surface roughness of carbon blacks. In the mono-layer regime we refer to the scaling behavior of the estimated BET-surface area with the size of adsorbed probe molecules (yardstick method). On smooth flat surfaces the BET-area is independent of the adsorbed probe or applied yardstick, while on rough surfaces it decreases with increasing probe (yardstick) size due to the inability of the large molecules to explore smaller cavities. This is shown schematically in Fig. 5. 

An alternative approach to the characterization of surface morphology of carbon blacks is the consideration of film formation of adsorbed molecules in the multi-layer regime. In this case, the surface roughness is evaluated with respect to a fractal extension of the classical Frenkel-Halsey-Hill (FHH)-theory, where, beside the van der Waals surface potential, the vapor-liquid surface tension has to be taken into account [100, 101]. Then the... 

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