An ion processing apparatus for processing a target with ions includes a plasma ion source and a mass spectrometer for producing an ion beam for depositing ions onto the surface of the target to form a thin film or for implanting the ions into the target to modify the composition or properties of the target or for separation and collection of individual, separated isotopes. The plasma ion source is preferably an inductively coupled plasma ion source, and the mass spectrometer is preferably a quadrupole mass spectrometer. The stoichiometry of the deposited or implanted ions can be adjusted by controlling the mass spectrometer to produce an ion beam having a desired composition. Mixtures of different elements can be easily deposited or implanted in any desired stoichiometry by introducing a multielement sample into the plasma ion source and controlling the time the mass spectrometer transmits each element to be deposited or implanted.