Pulsed-laser deposition of MgB2 and B thin films

Thin films of the novel superconductor MgB2 were deposited from an Mg-enriched MgB2 target or by alternating ablation from Mg and B targets, depositing multilayers. The superconducting films were achieved in situ by a two-step process: deposition at low temperatures ranging from room temperature to 200 C and subsequently heating to 600 C. The color of the plasma originating from Mg or Mg-enriched MgB2 targets during the deposition is an indicator of the constituents of the plasma and can be used to adjust the plasma parameters like pressure and energy density. The films showed a reduced critical temperature (Tc) compared to the bulk value (39 K), which is attributed to the small grain sizes and the relatively high base pressure of the system (∝10-7 mbar) causing impurities (oxygen, carbon..). To investigate B oxidation and to determine the suitable deposition conditions for B, films made by pulsed-laser deposition (PLD) from B target were analyzed by XPS. The films are very sensitive to the ambient gas purity and the base pressure. We anticipate an improvement of Tc and the crystallinity of MgB2 thin films by using PLD in high vacuum and with a high purity Ar and H2 gas mixture. (orig.)