Cadmium Selenide Quantum Wires and the Transition from 3D to 2D Confinement

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Abstract
Soluble CdSe quantum wires are prepared by the solution−liquid−solid mechanism, using monodisperse bismith nanoparticles to catalyze wire growth. The quantum wires have micrometer lengths, diameters in the range of 5−20 nm, and diameter distributions of ±10−20%. Spectroscopically determined wire band gaps compare closely to those calculated by the semiemipirical pseudopotential method, confirming 2D quantum confinement. The diameter dependence of the quantum wire band gaps is compared to that of CdSe quantum dots and rods. Quantum rod band gaps are shown to be delimited by the band gaps of dots and wires of like diameter, for short and long rods, respectively. The experimental data suggest that a length of ca. 30 nm is required for the third dimension of quantum confinement to fully vanish in CdSe rods. That length is about six times the bulk CdSe exciton Bohr radius.