Mass Spectrometric Studies of Pulsed Laser Ablation: Existence of Rydberg State Atoms

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Abstract
An unusual aspect of the pulsed laser deposition (PLD) process is that highly oriented (sometimes epitaxial) films of complex, multicomponent materials can often be prepared at low substrate temperatures. It is argued, using a simple model, that the arrival of even minor quantities of electronically excited species (Rydberg atoms and ions) can significantly affect the local surface temperature of the growing film. The present study experimentally confirms the existence of these energetic components in an ablation plume using a specially-modified time-of-flight quadrupole mass spectrometer. Ions as well as long-lived, excited state (Rydberg state) atoms were detected from laser ablation from a YBa2Cu307-5 (YBCO) target. Multiple peaks in the TOF profiles appear to derive from electron/ion recombination from higher charged species; the high kinetic energies observed are explainable from simple electrostatics involving localized holes trapped on the target surface.