Colloidal GaAs Quantum Wires: Solution-Liquid-Solid Synthesis and Quantum-Confinement Studies Angang Dong, Heng Yu, Fudong Wang, and William E. Buhro* Department of Chemistry and Center for Materials InnoVation, Washington UniVersity, St. Louis, Missouri 63130-4899 Received December 26, 2007; E-mail: buhro@wustl.edu Abstract: Colloidal GaAs quantum wires with diameters of 5–11 nm and narrow diameter distributions (standard deviation ) 12–21% of the mean diameter) are grown by two methods based on the solution- liquid–solid (SLS) mechanism. Resolved excitonic absorption features arising from GaAs quantum wires are detected, allowing extraction of the size-dependent effective band gaps of the wires. The results allow the first systematic comparison of the size dependences of the effective band gaps in corresponding sets of semiconductor quantum wires and quantum wells. The GaAs quantum wire and well band gaps scale according to the prediction of a simple effective-mass-approximation, particle-in-a-box (EMA-PIB) model, which estimates the kinetic confinement energies of electron–hole pairs in quantum nanostructures of different shapes and confinement dimensionalities. Introduction Here we report quantum-confinement studies of colloidal GaAs quantum wires, synthesized by the solution-liquid–solid (SLS) method. 1 We compare the size dependence of the effective band gaps in GaAs quantum wires to the corresponding size dependence in GaAs quantum wells. The comparison agrees quantitatively with a simple theoretical model that accounts for the dependence of quantum confinement on the geometric dimensionality of confinement and confirms that GaAs quantum wires behave as two-dimensional (2D) confinement systems. The tuning of the optical and electrical properties of semiconductor nanostructures by varying their sizes has been extensively explored. 2 Recent advances in the synthesis of high- quality, 3D-confined, colloidal quantum dots have enabled a detailed understanding of the sensitive size dependence of their physical properties. 3 More recently, the realization that shape and dimensionality are other important factors for influencing quantum confinement and attendant physical properties 4–9 has spurred the development of various anisotropic colloidal nano- structures such as nanorods, 5–7 tetrapods, 8 and nanowires, 9 etc. Among the various quantum nanostructures currently avail- able, semiconductor nanowires are of interest for studies of 2D quantum confinement 9–11 and for their great potential for application in nanoscale devices. 12 Systematic investigation of quantum-confinement effects requires single-crystalline nanow- ires having diameters smaller than or close to the bulk semiconductor exciton Bohr radius, which typically ranges from 2 to 20 nm. 1b,9 Additionally, quantum-confined (effective) band gaps are routinely measured by UV–visible absorption and photoluminescence (PL) emission spectroscopies on ensembles of nanowires, 9 requiring nanowire ensembles with sufficiently narrow diameter distributions to exhibit resolved absorption or PL emission features. 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