Why some interfaces cannot be sharp


A central goal of modern materials physics and nanoscience is the control of materials and their interfaces to atomic dimensions. For interfaces between polar and nonpolar layers, this goal is thwarted by a polar catastrophe that forces an interfacial reconstruction. In traditional semiconductors, this reconstruction is achieved by an atomic disordering and stoichiometry change at the interface, but a new option is available in multivalent oxides: if the electrons can move, the atoms do not have to. Using atomic-scale electron energy loss spectroscopy, we have examined the microscopic distribution of charge and ions across the (001) LaAlO3/SrTiO3 interface. We find that there is a fundamental asymmetry between the ionically compensated AlO2/SrO/TiO2 interface, and the electronically compensated AlO2/LaO/TiO2 interface, both in interfacial sharpness and charge density. This suggests a general strategy to design sharp interfaces, remove interfacial screening charges, control the band offset and, hence, markedly improve the performance of oxide devices.

Access options

Rent or Buy article

Get time limited or full article access on ReadCube.


All prices are NET prices.

Figure 1: The polar catastrophe illustrated for atomically abrupt (001) interfaces between LaAlO3 and SrTiO3.
Figure 2: ADF-STEM images of the interface structures.
Figure 3: SrTiO3/LaAlO3/SrTiO3 multilayer.
Figure 4: Repeated growth of LaAlO3/SrTiO3 multilayers.
Figure 5: O-K edge EELS profile across a AlO2/SrO/TiO2 p-type interface.
Figure 6: Chemical profiles of LaAlO3 on (001) SrTiO3 for both interface terminations.
Figure 7: Tuning the band offset.


  1. 1

    Fong, D. D. et al. Ferroelectricity in ultrathin perovskite films. Science 304, 1650–1653 (2004).

    Article  Google Scholar 

  2. 2

    Junquera, J. & Ghosez, P. Critical thickness for ferroelectricity in perovskite ultrathin films. Nature 422, 506–509 (2003).

    Article  Google Scholar 

  3. 3

    Ahn, C. H., Triscone, J.-M. & Mannhart, J. Electric field effect in correlated oxide systems. Nature 424, 1015–1018 (2004).

    Article  Google Scholar 

  4. 4

    Ohtomo, A., Muller, D. A., Grazul, J. L. & Hwang, H. Y. Artificial charge-modulation in atomic-scale perovskite titanate superlattices. Nature 419, 378–380 (2002).

    Article  Google Scholar 

  5. 5

    Okamoto, S. & Millis, A. J. Electronic reconstruction at an interface between a Mott insulator and a band insulator. Nature 428, 630–633 (2004).

    Article  Google Scholar 

  6. 6

    Tung, R. Formation of an electric dipole at metal-semiconductor interfaces. Phys. Rev. B 64, 205310 (2001).

    Article  Google Scholar 

  7. 7

    McKee, R. A., Walker, F. J., Nardelli, M. B., Shelton, W. A. & Stocks, G. M. The interface phase and the Schottky barrier for a crystalline dielectric on silicon. Science 300, 1726–1730 (2003).

    Article  Google Scholar 

  8. 8

    Harrison, W. A., Kraut, E. A., Waldrop, J. R. & Grant, R. W. Polar heterojunction interfaces. Phys. Rev. B 18, 4402–4410 (1978).

    Article  Google Scholar 

  9. 9

    Baraff, G. A., Appelbaum, J. A. & Hamann, D. R. Self-consistent calculation of the electronic structure at an abrupt GaAs-Ge interface. Phys. Rev. Lett. 38, 237–240 (1977).

    Article  Google Scholar 

  10. 10

    Ohtomo, A. & Hwang, H. Y. A high-mobility electron gas at the LaAlO3/SrTiO3 heterointerface. Nature 427, 423–426 (2004).

    Article  Google Scholar 

  11. 11

    Klenov, D. O., Schlom, D. G., Li, H. & Stemmer, S. The interface between single crystalline (001) LaAlO3 and (001) silicon. Jpn J. Appl. Phys. 44, L617–L619 (2005).

    Article  Google Scholar 

  12. 12

    Voyles, P. M., Muller, D. A., Grazul, J. L., Citrin, P. H. & Gossmann, H.-J. L. Atomic-scale imaging of individual dopant atoms and clusters in highly n-type bulk Si. Nature 416, 826–829 (2002).

    Article  Google Scholar 

  13. 13

    Muller, D. A., Nakagawa, N., Ohtomo, A., Grazul, J. L. & Hwang, H. Y. Atomic-scale imaging of nanoengineered oxygen vacancy profiles in SrTiO3 . Nature 430, 657–661 (2004).

    Article  Google Scholar 

  14. 14

    Batson, P. E. Simultaneous STEM imaging and electron energy-loss spectroscopy with atomic column sensitivity. Nature 366, 727–728 (1993).

    Article  Google Scholar 

  15. 15

    Varela, M. et al. Spectroscopic imaging of single atoms within a bulk solid. Phys. Rev. Lett. 92, 095502 (2004).

    Article  Google Scholar 

  16. 16

    Müller, J. E. & Wilkins, J. W. Band-structure approach to the x-ray spectra of metals. Phys. Rev. B 29, 4331–4348 (1984).

    Article  Google Scholar 

  17. 17

    Kirkland, E. J., Loane, R. F. & Silcox, J. Simulation of annular dark field STEM images using a modifed multislice method. Ultramicroscopy 23, 77–96 (1987).

    Article  Google Scholar 

  18. 18

    Abbate, M. et al. Soft-x-ray-absorption studies of the location of extra charges induced by substitution in controlled-valence materials. Phys. Rev. B 44, 5419–5422 (1991).

    Article  Google Scholar 

  19. 19

    Ohtomo, A., Muller, D. A., Grazul, J. L. & Hwang, H. Y. Epitaxial growth and electronic structure of LaTiOx films. Appl. Phys. Lett. 80, 3922–3925 (2002).

    Article  Google Scholar 

  20. 20

    Browning, N. D., Moltaji, H. O. & Buban, J. P. Investigation of three-dimensional grain-boundary structures in oxides through multiple-scattering analysis of spatially resolved electron-energy-loss spectra. Phys. Rev. B 58, 8289–8300 (1998).

    Article  Google Scholar 

  21. 21

    Francis, R. J., Moss, S. C. & Jacobson, A. J. X-ray truncation rod analysis of the reversible temperature-dependent [001] surface structure of LaAlO3 . Phys. Rev. B 64, 235425 (2001).

    Article  Google Scholar 

Download references


We thank A. Ohtomo and M. Kawasaki for helpful discussions. This work was supported by the Mitsubishi Foundation, a Grant-in-Aid for Scientific Research on Priority Areas, and the US Office of Naval Research through the ONR EMMA MURI monitored by Colin Wood. N.N. acknowledges partial support from QPEC, Graduate School of Engineering, University of Tokyo. The Cornell Electron Microscope facilities have been supported by the NSF through the MRSEC and IMR programs.

Author information



Corresponding author

Correspondence to David A. Muller.

Ethics declarations

Competing interests

The authors declare no competing financial interests.

Rights and permissions

Reprints and Permissions

About this article

Cite this article

Nakagawa, N., Hwang, H. & Muller, D. Why some interfaces cannot be sharp. Nature Mater 5, 204–209 (2006). https://doi.org/10.1038/nmat1569

Download citation

Further reading


Quick links

Sign up for the Nature Briefing newsletter for a daily update on COVID-19 science.
Get the most important science stories of the day, free in your inbox. Sign up for Nature Briefing