Solution-liquid-solid (SLS) growth of diameter-controlled semiconductor quantum wires and their two-dimensional quantum confinement effects

The goal of this project is to grow monodisperse semiconductor quantum wires employing the solution-liquid-solid (SLS) mechanism first developed in our group. A key first step to achieve this goal is the preparation of monodisperse catalyst nanoparticles. Low-melting-point In, Sn and Bi nanoparticles with predictable sizes and narrow diameter distributions are obtained from the heterogeneous-seeded-growth mechanism. The mechanism we report has the potential to be a general synthesis of monodisperse nanoparticles of many compositions.; The size-controlled, monodisperse In nanoparticles were employed in the solution-liquid-solid (SLS) growth of InP and GaAs quantum wires; Bi nanoparticles were efficient in the SLS growth of high quality CdSe, CdS, and CdTe quantum wires. In all the SLS quantum-wire syntheses, the diameters of the wires are determined by the sizes of the catalyst nanoparticles used and are fairly monodisperse. These results justify the initial proposal for controlling SLS wire growth. Application of appropriate surfactants yields soluble quantum wires, which facilitates the study of the optical properties of these wires.; The above-mentioned syntheses afforded monodisperse InP and CdSe quantum wires having diameters within the strong confinement regime of ca. 3–11 nm is distinguishes the SLS mechanism from the vapor-liquid-solid (VLS) mechanism since the VLS mechanism only affords nanowires having much larger diameters. We propose a simple approximate model for analyzing the 2D quantum-confinement effects in these wires. We demonstrate experimentally that the quantum-confinement effect in the wires is weakened to the expected extent, relative to that in quantum dots, by the loss of one confinement dimension. We propose a rule-of-thumb: for quantum wires and quantum dots of the same composition, in the plot of Δ E_g vs. 1/d2, the slope of the quantum-wire line should be 0.585 times that of the quantum-dot line.; Quantum rods are anisotropically 3D confined, and so constitute an intermediate case to dots and wires. Here we show that the confinement behavior of CdSe quantum rods is indeed bounded by that of CdSe dots and wires at the two length extrema. We also determine experimentally how long a CdSe quantum rod must be to exhibit the 2D confinement of a true quantum wire. That length (∼30 nm) is surprisingly long in comparison to the bulk CdSe exciton Bohr radius (∼5 nm).