Scanning Tunneling Luminescence of Individual CdSe Nanowires

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.

Spectroscopic Properties of Phase-Pure and Polytypic Colloidal Semiconductor Quantum Wires

“…Despite this, experimental comparisons with theoretical results of either pure WZ or ZB QW structures are often made using polytypic structures without considering the effects of planar defects, and discrepancies are thus expected (see above and Figure ). − ,, …”

“…Despite this, experimental comparisons with theoretical results of either pure WZ or ZB QW structures are often made using polytypic structures without considering the effects of planar defects, and discrepancies are thus expected (see above and Figure 4). [19][20][21][22][23][24][25]27,29 Role of Crystal-Phase Purity on Line Width. An ensemble spectrum is the sum of single-nanocrystal spectra having properties that depend on the size, shape, and crystalphase purity of the nanocrystals.…”

“…Semiconductor nanowires and QWs, as one-dimensional nanostructures, possess intriguing optical and electronic properties that are fundamentally different from their quantum-dot (QD) and quantum-rod (QR) counterparts, and have been of considerable interest over about two decades. ,− Both experimental and theoretical studies of the optical and electronic structures of semiconductor QWs have appeared, − but direct comparisons between the studies are hindered by dissimilar QW properties. The experimental results are primarily based on studies of colloidal polytypic II–VI and III–V QWs that contain high densities of planar defects, such as twinning boundaries, stacking faults, and WZ–ZB phase alternations. − ,, This is due to the experimental unavailability, until recently, of phase-pure, defect-free, colloidal II–VI and III–V QWs and a lack of spectroscopic data on the few phase-pure systems that had been obtained by VLS growth. − In contrast, the theoretical results are typically based on phase-pure cubic (e.g., diamond or ZB) or hexagonal (e.g., WZ) crystal structures. − , The WZ–ZB alternations in polytypic QW specimens make theoretical calculations in these random polytypes economically impractical. Consequently, direct comparisons of experimental and theoretical results based on QWs having the same crystal structures, the same stacking sequences, or the same distributions of planar defects are still lacking.…”

“…The experimental results are primarily based on studies of colloidal polytypic II−VI and III−V QWs that contain high densities of planar defects, such as twinning boundaries, stacking faults, and WZ−ZB phase alternations. [20][21][22][23][24][25]27,29 This is due to the experimental unavailability, until recently, 4 of phase-pure, defect-free, colloidal II−VI and III−V QWs and a lack of spectroscopic data on the few phase-pure systems that had been obtained by VLS growth. 30−32 In contrast, the theoretical results are typically based on phase-pure cubic (e.g., diamond or ZB) or hexagonal (e.g., WZ) crystal structures.…”

Electroluminescence properties of organic nanostructures studied by scanning tunnelling microscopy

“…We analyzed the effect of the reduced crystal size on the emission spectrum. Exciton confinement in a nanostructure can provide a shift of the emission energy, which could be clearly resolved by STL on individual CdSe quantum wires 64. The evaluation of Pc spectra from a large number of studied nanocrystals, however, provides no correlation between peak energy and nanocrystal dimension within experimental precision.…”