Surface area roughness

Although the rate of dissolving measurements do thus give a quantity identified as the total surface area, this area must include that of a film whose thickness is on the order of a few micrometers but basically is rather indeterminate. Areas determined by this procedure thus will not include microscopic roughness (or fractal nature). 

The currently useful model for dealing with rough surfaces is that of the selfsimilar or fractal surface (see Sections VII-4C and XVI-2B). This approach has been very useful in dealing with the variation of apparent surface area with the size of adsorbate molecules used and with adsorbent particle size. All adsorbate molecules have access to a plane surface, that is, one of fractal dimension 2. For surfaces of Z> > 2, however, there will be regions accessible to small molecules... 

Wynne-Jones and Marshfound somewhat similar results with a number of carbons made by pyrolysis of eight organic polymers at a series of temperatures. The isotherms of Nj at 77 K and of COj at 195 K were measured, and the apparent surface area calculated by the usual BET procedure. (Owing to the microporous nature of the solids, these figures for area will be roughly proportional to the uptake at saturation and therefore... 

The abihty of fillers to improve paper brightness increases with their intrinsic brightness, surface area, and refractive index. According to the Mie theory, this abiUty is maximum at an optimum filler particle size, about 0.25 pm in most cases, where the filler particle size is roughly one-half the wavelength of light used for the observation. 

Tubes were removed for routine inspection. Internal surfaces had rough contours due to mutually intersecting areas of metal loss (Fig. 4.26). Wall thickness varied from 0.080 in. (0.20 cm) to as little as 0.032 in. (0.081 cm). 

If a sample of polycrystalline material is rotated during the sputtering process, the individual grains will be sputtered from multiple directions and nonuniform removal of material can be prevented. This technique has been successfully used in AES analysis to characterize several materials, including metal films. Figure 9 indicates the improvement in depth resolution obtained in an AES profile of five cycles of nickel and chromium layers on silicon. Each layer is about 50 nm thick, except for a thinner nickel layer at the surface, and the total structure thickness is about 0.5 pm. There can be a problem if the surface is rough and the analysis area is small (less than 0.1-pm diameter), as is typical for AES. In this case the area of interest can rotate on and off of a specific feature and the profile will be jagged. 

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