It has often been said, particularly by those responsible for cleaning, that a surface is only clean at the moment of its generation. The free surface energy created by the process of material polishing, it is thought, will maximize the rate at which dust will be attracted and firmly adhere to the surface. Thereafter we can only speak of degrees of cleanliness or amounts of contamination. Even after the most thorough cleaning process has been initiated we still have the problem of minimizing recontamination to consider. Due to its negative effect on system performance, contamination control from particles and films, and ways of cleaning surfaces have been subjects of continuous study. Components and systems known to be particularly affected by contamination include semiconducting wafers, micro-optics, high-power lasers, x-ray systems, low-light level imaging, and space optics.
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