Scanning Tunneling Luminescence of Individual CdSe Nanowires

Max-Planck-Institute for Solid State Research, Heisenbergstr. 1, 70569 Stuttgart, Germany. .
Small (Impact Factor: 7.51). 08/2011; 7(16). DOI: 10.1002/smll.201100434
Source: PubMed

ABSTRACT The local luminescence properties of individual CdSe nanowires composed of segments of zinc blende and wurtzite crystal structures are investigated by low-temperature scanning tunneling luminescence spectroscopy. Light emission from the wires is achieved by the direct injection of holes and electrons, without the need for coupling to tip-induced plasmons in the underlying metal substrate. The photon energy is found to increase with decreasing wire diameter due to exciton confinement. The bulk bandgap extrapolated from the energy versus diameter dependence is consistent with photon emission from the zinc blende-type CdSe sections.

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    ABSTRACT: Electroluminescent (EL) metal-semiconductor-metal nanojunctions are prepared by electrodepositing nanocrystalline cadmium selenide (nc-CdSe) within ∼250 nm gold (Au) nanogaps prepared by focused ion beam milling. The electrodeposition of nc-CdSe is carried out at two temperatures: 20 °C (“cold”) and 75 °C (“hot”), producing mean grain diameters of 6 ± 1 nm and 11 ± 2 nm, respectively, for the nc-CdSe. Light-emitting nanojunctions (LEnJs) prepared at both temperatures show a low threshold voltage for light emission of <2 V; just above the 1.74 eV bandgap of CdSe. The EL intensity increases with the injection current and hot-deposited LEnJs produced a maximum EL intensity that is an order of magnitude higher than the cold-deposited LEnJs. Emitted photons are bimodal in energy with emission near the band gap of CdSe, and also at energies 200 meV below it; consistent with a mechanism of light emission involving the radiative recombination of injected holes with electrons at both band-edge and defect states. The quantum yield for “hot” electrodeposited nc-CdSe LEnJs is comparable to devices constructed from single crystalline nanowires of CdSe, and the threshold voltage of 1.9 (±0.1) V (cold) and 1.5 (±0.2) V (hot) is at the low end of the range reported for CdSe nanowire based devices.
    Chemistry of Materials 02/2013; 25(4-4):623-631. DOI:10.1021/cm304001f · 8.54 Impact Factor


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