Optical characteristics of CdSe quantum dots depending on growth conditions and surface passivation.

We investigated the effects of different growth conditions and surface passivation on the growth of CdSe quantum dots (QDs). The synthesis of CdSe QDs by pyrolysis of organometallic reagents was performed by using the hot-matrix method. In order to modify the size and quality of CdSe QDs, we controlled the growth temperature from 250 degrees C to 350 degrees C and the relative amount of trioctylphosphin (as the ligand of the Cd and Se precursors) to be injected into the coordinating solvent trioctylphosphineoxide. Moreover, an effective surface passivation of mono-disperse CdSe QDs was achieved by overcoating them with a larger band gap material, such as ZnS.

Spatial control of quantum sized nanocrystal arrays onto silicon wafers.

Monolayer arrays of monodispersed nanocrystals (<10 nm) onto three dimensional (3D) substrates have considerable potential for various engineering applications such as highly integrated memory devices, solar cells, biosensors and photo and electro luminescent displays because of their highly integrated features with nanocrystal homogeneity. However, most reports on nanocrystal arrays have focused on two dimensional (2D) flat substrates, and the production of wafer-scale monolayer arrays is still challenging. Here we address the feasibility of arraying nanocrystal monolayers in wafer-scale onto 3D substrates. We present both metal (Pd) and semiconductor (CdSe) nanocrystals arrayed in monolayer onto trenched silicon wafers (4 inch diameter) using a facile electrostatic adsorption scheme. In particular, CdSe nanocrystal arrays in the trench well showed superior luminescent efficiency compared to those onto the protruded trench flat, due to the densely arrayed CdSe nanocrystals in the vertical direction. Furthermore, the surface coverage controllability was investigated using a 2D silicon substrate. Our approach can be applied to generate highly efficient displays, memory chips and integrated sensing devices.

UV spectroscopic monitoring of vaporized monoaromatic hydrocarbons from petroleum-contaminated soils.

Fast and simple systems using ultraviolet (UV) absorbance were examined for on-line monitoring of monoaromatic hydrocarbons from petroleum-contaminated soils in this research. Since soil particles hinder the UV light transmittance, the absorbance measurement of vaporized monoaromatic hydrocarbons in soil gas extracted from petroleum-contaminated soils was proposed. In the fixed system that exhibited higher sensitivity than the portable one, the absorbance intensity of benzene, toluene, ethylbenzene, and xylene increased in proportion to the concentration of the contaminants. The portable system, however, was suitable for screening purpose, while it exhibited faster response. There was no interference from water, which helps the applicability of the proposed systems to the actual fields.