Showing papers by "Christopher B. Murray published in 1993"

Synthesis and characterization of nearly monodisperse CdE (E = sulfur, selenium, tellurium) semiconductor nanocrystallites

Abstract: A simple route to the production of high-quality CdE (E=S, Se, Te) semiconductor nanocrystallites is presented. Crystallites from ∼12 A to ∼115 A in diameter with consistent crystal structure, surface derivatization, and a high degree of monodispersity are prepared in a single reaction. The synthesis is based on the pyrolysis of organometallic reagents by injection into a hot coordinating solvent. This provides temporally discrete nucleation and permits controlled growth of macroscopic quantities of nanocrystallites. Size selective precipitation of crystallites from Portions of the growth solution isolates samples with narrow size distributions (<5% rms in diameter). High sample quality results in sharp absorption features and strong «band-edge» emission which is tunable with particle size and choice of material

Size-dependent optical spectroscopy of II-VI semiconductor nanocrystallites (quantum dots)

Abstract: We use low temperature (10K) optical hole-burning and fluorescence line narrowing spectroscopy to investigate the electronic properties of CdSe nanocrystallites (quantum dots) as a function of crystallite diameter (20–80A). We discuss how the homogeneous linewidth of the HOMO-LUMO transition, the energy shift between the absorbing and emitting state, and the LO phonon frequency vary with nanocrystallite size.

Surface electronic properties of CdSe nanocrystallites

Abstract: The surface electronic properties of CdSe nanocrystallites have been probed using low temperature and Zeeman spectroscopies. Fluorescence line narrowed spectra show dramatic changes between 1.75 and 10 K and also as a function of applied magnetic field. These effects are attributed to the localization of the photogenerated charge carriers on the surface. A simple model has been constructed to calculate the charge distribution within the nanocrystallite.

Synthesis and structural characterization of II–VI semiconductor nanocrystallites (quantum dots)

Abstract: A methodology for the production of II–VI semiconductor nanocrystallites employing organometallic precursors has been developed. The rapid pyrolysis of reagents in a coordinating solvent provides temporally discrete nucleation. Subsequent controlled growth allows the production of macroscopic quantities of nanocrystallites with consistent structure, surface derivatization and a high degree of monodispersity. The samples produced are structurally characterized with a combination of X-ray and Electron Beam based techniques.

Size-dependent spectroscopy and photodynamics of some II-VI semiconductor nanocrystallites (quantum dots)

Abstract: The relaxation dynamics of photoexcited CdSe nanocrystallites (quantum dots) are dominated by the surface. Surface electronic properties of CdSe nanocrystallites have been probed using low temperature fluorescence line narrowing and time resolved luminescence. We find that the surface structure creates a random potential for the hole with a size dependent barrier for site to site hopping.

Preparation of II-VI Quantum Dot Composites by Electrospray Omcvd

Abstract: A novel technique combining electrospray and organometallic chemical vapor deposition (OMCVD) has been developed for synthesis of VI-II quantum dot composites. CdSe nanocrystallites dispersed in a mixture of pyridine and acetonitrile were electrosprayed into the gas-phase in the growth zone of an OMCVD reactor and then incorporated into a ZnSe matrix grown by OMCVD. Hydrogen selenide and diethylzinc were used to deposit the ZnSe matrix at temperatures of 150 - 240°C. The ZnSe/CdSe quantum dot composites were characterized by visible absorption spectroscopy, room temperature photoluminescence and Auger electron spectroscopy. The optical properties of the composites are determined by the size of the original CdSe nanocrystallites.