In2O3, an n‐type semiconducting transparent transition metal oxide, possesses a surface electron accumulation layer (SEAL) resulting from downward surface band bending due to the presence of ubiquitous oxygen vacancies. Upon annealing In2O3in ultrahigh vacuum or in the presence of oxygen, the SEAL can be enhanced or depleted, as governed by the resulting density of oxygen vacancies at the surface. In this work, an alternative route to tune the SEAL by adsorption of strong molecular electron donors (specifically here ruthenium pentamethylcyclopentadienyl mesitylene dimer, [RuCp*mes]2) and acceptors (here 2,2′‐(1,3,4,5,7,8‐hexafluoro‐2,6‐naphthalene‐diylidene)bis‐propanedinitrile, F6TCNNQ) is demonstrated. Starting from an electron‐depleted In2O3surface after annealing in oxygen, the deposition of [RuCp*mes]2restores the accumulation layer as a result of electron transfer from the donor molecules to In2O3, as evidenced by the observation of (partially) filled conduction sub‐bands near the Fermi level via angle‐resolved photoemission spectroscopy, indicating the formation of a 2D electron gas due to the SEAL. In contrast, when F6TCNNQ is deposited on a surface annealed without oxygen, the electron accumulation layer vanishes and an upward band bending is generated at the In2O3surface due to electron depletion by the acceptor molecules. Hence, further opportunities to expand the application of In2O3in electronic devices are revealed.
The emergence of a 2D electron gas (2DEG) on the (001) surface of oxygen‐deficient strontium titanate (SrTiO3−δ) is investigated. Using in situ soft X‐ray spectroscopy and effective mass modeling, a series of quantitative band diagrams are developed to describe the evolution of near‐surface and bulk carrier concentrations, downward band bending, and Fermi level along a lateral gradient of oxygen vacancies formed on SrTiO3−δby direct‐current resistive heating under ultrahigh vacuum conditions. Electrons are accumulated over a 3 nm region near the surface, confined within a potential well with saturated 300 meV downward band bending. The relation between Fermi levels and carrier concentrations near the surface suggests the density of states near the surface is much lower than the bulk density of states, which is consistent with the quantum‐confined subbands of a 2DEG. The quantitative relationship between the surface and bulk electronic structures developed in this work provides a guide for precise engineering of the oxygen‐vacancy‐induced 2DEG in SrTiO3.
more » « less- NSF-PAR ID:
- 10079510
- Publisher / Repository:
- Wiley Blackwell (John Wiley & Sons)
- Date Published:
- Journal Name:
- Advanced Electronic Materials
- Volume:
- 5
- Issue:
- 1
- ISSN:
- 2199-160X
- Format(s):
- Medium: X
- Sponsoring Org:
- National Science Foundation
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