Backscattered current distribution

Electroplating processes, where a solid deposit is formed and its thickness can be directly measured, provide a relatively convenient means for determination of the current distribution. The deposit thickness can be measured by a number of commercially available devices, based on, e.g.. X-ray fluorescence, beta backscatter, magnetic properties, or controlled dissolution. A direct probe based on the induced field associated with the current flow has recently been introduced. Optical and electron microscopy of cross-sectioned deposits provide a common means for measuring the deposit thickness. Once the deposit thickness, d, has been measured, it can be related to the current density, i, through Faraday s law ... 

Bubble-size control was also critical. The intensity of scattering by nonresonant gas bubbles is proportional to the sixth power of the radius of the bubble. Hence, the larger the bubble, the better the scattering intensity. However, the acceptable upper size limit for in vivo administration is determined by the need for bubbles to cross capillary beds. Bubbles larger than 6-8 pm should be avoided as they are trapped in the lung capillaries. The current accepted sizes are in 1-7 pm, preferably around 3 pm, with as narrow a size distribution as possible. Bubble shell material needs to be biodegradable. Soft shells are generally preferable, as they minimally impede US backscatter. 

The basic experiment in HREELS in the backscattering geometry is straightforward [37], A monochromatized electron beam of 1-10 eV is directed toward the surface and the energy distribution of the reflected electrons is measured in an electron analyzer with a resolution of up to 7 meV. The spectrum consists of the elastic peak and peaks due to energy losses to the sample surface by the excitation of molecular vibrations. If plotted as wave numbers, these vibrations are very similar to those observed in IR techniques. The resolution achievable in this technique is, however, considerably less than in IR, which becomes clear if one considers that 1 meV = 8.066 cm , so the spectral resolution in HREELS is of the order of 100 cm (in IR the resolution is typically around 4 cm" or better). Detection of crystallinity or other high-resolution details as is possible in IR is therefore currently not achievable in HREELS. 

---