| Abstract
| - Single-molecule optical experiments carried out in conjunction with externally applied electricfields show deliberate spatial and intensity control over CdSe nanowire (NW) emission. In particular, byapplying external fields to electrically isolated (single) NWs, their emission can be localized in areas of thewire closest to the positive electrode. In a few cases, the resulting emission intensity increases over thecorresponding zero-field value by nearly an order of magnitude. More often than not, factors of 2−3 areseen. Reversing the field polarity causes the emission to localize in opposite regions of the wire. Emissionfrom individual NWs can therefore be modulated. Complementary ac electric field measurements showthat the effect persists up to 500 kHz. To explain the phenomenon, the effective passivation of surfacetrap states by mobile carriers is speculated. This, in turn, causes local changes in the NW emission quantumyield (QY). To verify the presence of such mobile charges, both ensemble and single NW bundleelectrophoresis experiments are conducted. By investigating subsequent NW rotational and translationaldynamics, an estimate for the number of mobile carriers is determined. A lower limit (best case) linearcharge density of ∼0.45−1.2 mobile electrons per micrometer of the wire is obtained. Apart from self-consistently explaining the field-induced NW emission modulation, the resulting data and subsequent analysisalso suggests that the same mobile carriers may be the root cause of NW emission intermittency.Furthermore, given the ubiquity of stray charges, the resulting hypothesis may have additional applicabilitytoward explaining blinking in other systems, a problem of current interest especially within the context ofcolloidal QDs.
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