Charge Transfer to LaAlO3/SrTiO3 Interfaces Controlled by Surface Water Adsorption and Proton Hopping

• Published in: Advanced functional materials 2016-08, Vol.26 (30), p.5453-5459
• Main Authors: Adhikari, Sanjay, Garcia-Castro, Andrés C., Romero, Aldo H., Lee, Hyungwoo, Lee, Jung-Woo, Ryu, Sangwoo, Eom, Chang-Beom, Cen, Cheng
• Format: Article
• Language: English
• Subjects: 2DEG; c-AFM; DFT calculations; oxide interfaces; surface states
• ISSN: 1616-301X; 1616-3028
• DOI: 10.1002/adfm.201600820

Electronic properties of low dimensional systems are particularly sensitive to surface adsorbates. Clear understanding of such phenomena can lead to highly effective and nondestructive material engineering techniques. In this work, water adsorption at the surface of LaAlO3/SrTiO3 heterostructures is systematically studied. The saturation of surface dangling bonds by spontaneous water chemisorptions is found to be a main enabler of the formation of the interface 2D electron gas. In particular, when imbalanced distributions of water based ions, namely protons and hydroxyls, are generated, interface electron doping or depletion becomes surface adsorbates dominant and independent of the LaAlO3 layer thickness. The investigations also reveal the importance of hydrogen bonding through molecular water layers, which provides an energetically feasible pathway for manipulating the surface‐bond protons and thus the interface electrical characteristics. Surface water layers strongly affect the 2D electron gas (2DEG) formed at LaAlO3/SrTiO3 interfaces. While surface hydrogens and hydroxyls contribute distinct electron donating and charge trapping surface states, the hydrogen bond network generated from molecular water provides an energetically feasible pathway for the proton exchange with the environments and therefore makes the interface 2DEG highly sensitive to thermodynamic processes.