Scanning Microscopy


Conservation of current under steady-state conditions makes it possible to determine the sign of charges trapped in an insulator subjected to ionizing radiation. The maximum value of the surface potential can thus be estimated.

On the basis of a given trapped charge distribution, the pattern of the electrical field and of the potential can thus be established, and the influence of the shape of the sample and its environment can be clearly shown. Change of trapped charges with time (at the start and after irradiation) is then examined. Finally, the microscopic causes of trapping of charge is suggested by analogy with semiconductors . Each stage is illustrated with examples and a number of practical consequences are deduced.

To facilitate the understanding of the phenomena, this analysis begins with the better known macroscopic effects and works back to microscopic causes, which are often poorly controlled . Si nee the inverse process would be more logical, we have mentioned it in the conclusion, while pointing out some of the difficulties which arise.

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