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Charge Percolation Pathways Are Guided by Defects in Quantum Dot Solids

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Images of charge percolation pathways in QD solids. L) Electron percolation pathways (blue) are in the form of narrow stripes surrounded by electron-insulating areas (red/white). R) Hole percolation pathways (red/white) form larger domains surrounded by hole-insulating areas (blue)

Scientific Achievement
Presented the first imaging of charge transport pathways in 2D quantum dot (QD) arrays.

Significance and Impact
Understanding the microscopic nature of charge percolation in QD solids can allow for control over the degree to which charges move from one QD to the next, and thus control over material properties.

Research Details

  • Images using Kelvin probe force microscopy revealed that electrons and holes percolate through different spatial regions in QD arrays, via gap states (‘defects’ within the band gap) for electrons and valence band states for holes
  • Scanning tunneling spectroscopy confirmed the presence of in-gap states, and reveals heterogeneous electronic structure and energy level alignment in the QD array
  • This new understanding can guide the design of novel electronic devices, including photodiodes, by control of additives

Y Zhang, D Zherebetskyy, N Bronstein, S Barja, L Lichtenstein, D Schuppisser, L-W Wang, A Alivisatos, & M Salmeron, Nano Lett. 2015. DOI:10.1021/acs.nanolett.5b00454