Research ArticleMATERIALS SCIENCE

Erasable and recreatable two-dimensional electron gas at the heterointerface of SrTiO3 and a water-dissolvable overlayer

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Science Advances  16 Aug 2019:
Vol. 5, no. 8, eaaw7286
DOI: 10.1126/sciadv.aaw7286
  • Fig. 1 Temperature-dependent transport property with different tair.

    A 2DEG is formed at (A) the a-LAO/STO (001), (B) a-SAO/STO (001) interfaces, and (C) a-STO–capped a-SAO/STO (001). The 2DEG at the a-LAO/STO interface is much more stable than that at the a-SAO/STO interface under ambient conditions of room temperature and 70% of relative humidity. RS as a function of tair at 300 and 2.5 K for (D) 4-nm a-LAO/STO, 4-nm a-SAO/STO, and (E)10-nm a-STO–capped 4-nm a-SAO/STO, respectively. Inset: The schematic view of oxygen-vacancy–induced 2DEG exists at the (A) a-LAO/STO, (B) a-SAO/STO, and (C) a-STO–capped a-SAO/STO interfaces.

  • Fig. 2 Water-dissolvable and recyclable electronic devices.

    A 20-nm a-SAO/STO (001) heterointerface with a Hall bar pattern (A) before and (B) after the a-SAO overlayer dissolving into the DI water. The a-AlN in (A) denotes amorphous aluminium nitride. (C) Time dependence of sheet conductance, σS, at 300 K in ambient conditions for 20-nm a-SAO/STO (001). The vertical dash lines indicate that a drop of water was added on the Hall bar device, and the horizontal dash line indicates the measurement limit. The right panels schematically illustrated the three states of the electronic device: (top) metallic just after growth (at each t = 0 min), (middle) a fast MIT with one drop of DI water added on the device (at each t = 30 min), and (bottom) becoming insulating after the a-SAO fully dissolved into the DI water (at each 30 min < t < 60 or 0 min).

  • Fig. 3 Room temperature PL and the schematic mechanism of oxygen vacancies formed and filled near STO surface.

    (A) PL intensity of an as-received STO substrate, 4-nm a-LAO/STO, 4-nm a-SAO/STO, and 10-nm a-STO–capped 4-nm a-SAO/STO just after deposition, after 1 hour of air exposure and after dissolving in water. The illustration of the oxygen vacancies formed and filled near the surface of STO equilibrium: (B) between a-SAO film and its surface and (C) between the ambient conditions and its surface. The VO″ represents oxygen vacancy occupying the in-gap state of STO, and the H2O in the black squre box represents a water molecule under ambient conditions absorbed at the STO surface.

  • Fig. 4 Two-band model fitting of Rxy(B) and tair-dependent carrier density and mobility.

    Hall resistance of a-SAO/STO as a function of magnetic field at T = 2.5 K for various tair (A) nonlinear and (B) almost linear Hall effect. The ring data points are the measured data, and the solid lines are fitted curves using the two-band model. The tair dependence of carrier (C) densities and (D) mobilities at T = 2.5 K. Two types of electrons are denoted by n1, n2, μ1, and μ2.

  • Fig. 5 First-principles calculations of electronic band structures of a 2 × 2 × 9 supercell of cubic STO with oxygen vacancies.

    Side view of the supercell structure with (A) zero, (B) one, (C) two, and (D) three vacancies, where, for clarity, only four layers along the vertical direction are shown. Corresponding band structures with (E) zero, (F) one, (G) two, and (H) three vacancies are also plotted, respectively.

Supplementary Materials

  • Supplementary material for this article is available at http://advances.sciencemag.org/cgi/content/full/5/8/eaaw7286/DC1

    Section S1. RHEED oscillations of 4 unit cells (uc) of SAO/STO (001)

    Section S2. Electrical transport properties of 4-nm a-SAO/STO and 4-nm a-LAO/STO

    Section S3. Microscopy images of 20-nm a-SAO/STO (001) before and after dissolving into the DI water

    Section S4. Microscopy images of 20-nm a-SAO/STO sample with different tair

    Section S5. Electrical transport properties of 4-nm a-SAO/STO with different tair

    Section S6. tair dependence of RS for 50-nm a-SAO/STO (001) and 10-nm a-STO–capped 4-nm a-SAO/STO

    Section S7. Nonlinear to linear Hall effect of 4-nm a-SAO/STO heterointerface with different tair

    Section S8. Magnetoresistance of 4-nm a-SAO/STO with different tair

    Section S9. Growth oxygen partial pressure dependence of RS

    Section S10. AFM images of reusable STO surface topography

    Section S11. Discussion of the possible chemical reactions to dissolve a-SAO and remove oxygen vacancies at STO surface by water

    Fig. S1. RHEED oscillations of 4 uc of single-crystalline SAO grown on STO (001).

    Fig. S2. Electrical transport properties of 4-nm a-SAO/STO and 4-nm a-LAO/STO.

    Fig. S3. Microscopy images of 20-nm a-SAO/STO (001) with Hall bar pattern.

    Fig. S4. Microscopy images of the surface of 20-nm a-SAO/STO sample with different tair.

    Fig. S5. Electrical transport properties of 4-nm a-SAO/STO with different tair.

    Fig. S6. tair dependence of RS.

    Fig. S7. Nonlinear to linear Hall effect of 4-nm a-SAO/STO heterointerface.

    Fig. S8. Magnetoresistance of 4-nm a-SAO/STO at 2.5 K with different tair.

    Fig. S9. Growth oxygen partial pressure dependence of RS at 300 K.

    Fig. S10. AFM images of reusable STO surface topography.

  • Supplementary Materials

    This PDF file includes:

    • Section S1. RHEED oscillations of 4 unit cells (uc) of SAO/STO (001)
    • Section S2. Electrical transport properties of 4-nm a-SAO/STO and 4-nm a-LAO/STO
    • Section S3. Microscopy images of 20-nm a-SAO/STO (001) before and after dissolving into the DI water
    • Section S4. Microscopy images of 20-nm a-SAO/STO sample with different tair
    • Section S5. Electrical transport properties of 4-nm a-SAO/STO with different tair
    • Section S6. tair dependence of RS for 50-nm a-SAO/STO (001) and 10-nm a-STO–capped 4-nm a-SAO/STO
    • Section S7. Nonlinear to linear Hall effect of 4-nm a-SAO/STO heterointerface with different tair
    • Section S8. Magnetoresistance of 4-nm a-SAO/STO with different tair
    • Section S9. Growth oxygen partial pressure dependence of RS
    • Section S10. AFM images of reusable STO surface topography
    • Section S11. Discussion of the possible chemical reactions to dissolve a-SAO and remove oxygen vacancies at STO surface by water
    • Fig. S1. RHEED oscillations of 4 uc of single-crystalline SAO grown on STO (001).
    • Fig. S2. Electrical transport properties of 4-nm a-SAO/STO and 4-nm a-LAO/STO.
    • Fig. S3. Microscopy images of 20-nm a-SAO/STO (001) with Hall bar pattern.
    • Fig. S4. Microscopy images of the surface of 20-nm a-SAO/STO sample with different tair.
    • Fig. S5. Electrical transport properties of 4-nm a-SAO/STO with different tair.
    • Fig. S6. tair dependence of RS.
    • Fig. S7. Nonlinear to linear Hall effect of 4-nm a-SAO/STO heterointerface.
    • Fig. S8. Magnetoresistance of 4-nm a-SAO/STO at 2.5 K with different tair.
    • Fig. S9. Growth oxygen partial pressure dependence of RS at 300 K.
    • Fig. S10. AFM images of reusable STO surface topography.

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