4.6 Article

Nature of the surface space charge layer on undoped SrTiO3 (001)

期刊

JOURNAL OF MATERIALS CHEMISTRY C
卷 9, 期 38, 页码 -

出版社

ROYAL SOC CHEMISTRY
DOI: 10.1039/d1tc03436g

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资金

  1. National Research Foundation of Korea [NRF-2019R1A2C2008052, NRF-2015R1A5A1009962]
  2. GIST Research Institute Grant - Gwangju Institute of Science and Technology (GIST) [GRI-2021]
  3. MSICT
  4. POSTECH [NRF-2018R1D1A1B07048177, NRF-2019M3D1A1079309]
  5. National Research Foundation of Korea [PAL-2021] Funding Source: Korea Institute of Science & Technology Information (KISTI), National Science & Technology Information Service (NTIS)

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Precise characterization of surface/interfacial properties of SrTiO3, a popular substrate for heterostructures, is crucial for understanding exotic physical phenomena related to electron/ion exchanges. Under different pressure conditions, the undoped SrTiO3 (001) surface forms different oxide structures, affecting its electronic properties and band bending.
SrTiO3, an ABO(3)-type perovskite structure, has been a popular choice of substrate for many important heterostructures, e.g., ferroelectric thin films and superlattices. As numerous exotic physical phenomena are closely related to delicate electron/ion exchanges at the interfacial layer between the substrate and overlayer, precise characterization of surface/interfacial properties has become the center of many research studies. In most cases of SrTiO3 research, Nb-doping is applied on the SrTiO3 surface in order to characterize electrical properties with a negligible effect of contact potential between SrTiO3 and overlayer. On the other hand, the presence of doping can possibly interfere with a correct interpretation of the surface defect states, which become critical to apprehend the electrical properties of heterostructures. In this report, the undoped SrTiO3 (001) surface is investigated utilizing ambient-pressure XPS (AP-XPS) and low energy electron diffraction (LEED). We identified the complete chemical/structural/electronic states of O and Sr vacancies on the undoped SrTiO3 surface from ultra-high vacuum (UHV, <10(-9) mbar) to O-2 gas pressure of 0.1 mbar conditions. Under oxygen pressure conditions, chemically stable SrO1+x surface oxide with a c(6 x 2) superstructure is formed, generating electron depletion and band bending, i.e., the formation of a space charge layer underneath the surface. On the other hand, under UHV, the surface oxide comes from the O vacancy, which has different electronic properties from those of Sr vacancy-related oxides.

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