  Transition metal oxide hetero-structure has great potential for
multifunctional devices. However, the degraded physical properties at
interface, known as dead-layer behavior, present a main obstacle for device
applications. Here we present the systematic study of the dead-layer behavior
in La0.67Sr0.33MnO3 thin film grown on SrTiO3 substrate with ozone assisted
molecular beam epitaxy. We found that the evolution of electric and magnetic
properties as a function of thickness shows a remarkable resemblance to the
phase diagram as a function of doping for bulk materials, providing compelling
evidences of the hole depletion in near interface layers that causes
dead-layer. Detailed electronic and surface structure studies indicate that the
hole depletion is due to the intrinsic oxygen vacancy formation. Furthermore,
we show that oxygen vacancies are partly caused by interfacial electric dipolar
field, and thus by doping-engineering at the single-atomic-layer level, we
demonstrate the dead-layer reduction in films with higher interfacial hole
concentration.
