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A size-dependent nanoscale metal–insulator transition in random materials

Nature Nanotechnology volume 6, pages 237–241 (2011)Cite this article

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Abstract

Insulators and conductors with periodic structures can be readily distinguished, because they have different band structures, but the differences between insulators and conductors with random structures are more subtle1,2. In 1958, Anderson provided a straightforward criterion for distinguishing between random insulators and conductors, based on the ‘diffusion’ distance ζ for electrons at 0 K (ref. 3). Insulators have a finite ζ, but conductors have an infinite ζ. Aided by a scaling argument, this concept can explain many phenomena in disordered electronic systems, such as the fact that the electrical resistivity of ‘dirty’ metals always increases as the temperature approaches 0 K (refs 4–6). Further verification for this model has come from experiments that measure how the properties of macroscopic samples vary with changes in temperature, pressure, impurity concentration and applied magnetic field4,5, but, surprisingly, there have been no attempts to engineer a metal–insulator transition by making the sample size less than or more than ζ. Here, we report such an engineered transition using six different thin-film systems: two are glasses that contain dispersed platinum atoms, and four are single crystals of perovskite that contain minor conducting components. With a sample size comparable to ζ, transitions can be triggered by using an electric field or ultraviolet radiation to tune ζ through the injection and extraction of electrons. It would seem possible to take advantage of this nanometallicity in applications.

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Figure 1: Optical evidence of metallic clusters and free carriers.
Figure 2: R–V dependence on thickness, composition and temperature.
Figure 3: UV-triggered HR-to-LR transitions.
Figure 4: Random perovskite solid solution.
Figure 5: R–δ and R–T dependencies.

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Acknowledgements

This work was supported by the National Science Foundation (grant nos DMR-05-20020, 07-05054 and 09-07523). For the TEM analysis, we are grateful to K.C. Hsieh and Y. Lu at the Frederick Seitz Materials Research Laboratory (University of Illinois), partially supported by the US Department of Energy (grants DE-FG02-07ER46453 and DE-FG02-07ER46471).

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Author notes

  1. Soo Gil Kim

    Present address: Present address: Hynix Semiconductor Inc., Icheon-Si, Korea,

  2. Albert B. K. Chen, Soo Gil Kim and Yudi Wang: These authors contributed equally to this work

Authors and Affiliations

  1. Department of Materials Science & Engineering, University of Pennsylvania, Philadelphia, 19104, Pennsylvania, USA

    Albert B. K. Chen, Soo Gil Kim, Yudi Wang, Wei-Shao Tung & I-Wei Chen

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Contributions

I-W.C. conceived and designed the experiments and wrote the paper. A.B.C. performed the SiO2:Pt and SiN:Pt experiments. S.G.K. and Y.D.W. performed the perovskite experiments. W.S.T. performed the optical experiments. All authors analysed the data, discussed the results and commented on the manuscript.

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Correspondence to I-Wei Chen.

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Chen, A., Kim, S., Wang, Y. et al. A size-dependent nanoscale metal–insulator transition in random materials. Nature Nanotech 6, 237–241 (2011). https://doi.org/10.1038/nnano.2011.21

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