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The vacuum chamber

The in situ analyses are performed in a stainless steel high vacuum chamber (see right panel in Figure 1.26). Inside the chamber, in which pressure is kept below 10$^{-7}$ mbar, a substrate (crystalline silicon) is placed in thermal contact with a cold finger whose temperature can be varied between 10 K and 300 K. A needle valve is used to admit pre-prepared gases (or mixtures) into the chamber, where they freeze on the substrate. A He-Ne laser can be used to monitor the thickness of the ice film during accretion; this is achieved by looking at the interference pattern (intensity versus time) given by the laser beam reflected at an angle of 45$^{o}$ both by the vacuum-film and film-substrate interfaces. Solid samples are simply mounted in thermal contact with the cold finger.

Innocenza Busa' 2005-11-14