an improved apparatus is provided for in - situ cleaning of electron microscopes and other vacuum chambers . a special rf plasma electrode is housed in a compact cylinder constructed of standard vacuum components and a electrical feedthrough . the device allows oxygen radicals to be generated from air by a low powered rf plasma . the oxygen radical flow by convection into the electron microscope or vacuum chamber to be cleaned and react with hydrocarbons to form co and h2o vapor which is pumped away .