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Center for Nonlinear Studies |
Colloidal quantum dots (QD) are chemically stable particles of the nanometer size, intermediate between crystal and free molecule. Their fundamental electronic and optical properties are critically size-dependent due to the quantum confinement effect. Quantization of charge and energy resulting from such confinement make NCs behave like artificial atoms. Many of the applications of colloidal NCs involve charge transport and recent technical progress allows create artificial solids from artificial atoms. Now it is possible to make large arrays of artificial atoms in which particle size, interparticle separation and chemical composition are controlled and creating artificial solids with tunable properties becomes possible. At present time, investigation of these arrays under different external conditions is attracting relentless interest. In present talk, the behavior of QDs after treating at high temperature in vacuum and air atmosphere will be discussed. Cadmium selenide QDs were investigated with density functional theory to explain the experimentally found near-infrared photo response in CdSe nanocrystal superlattice film. Calculations of several model nanoparticles in ligated, bare and oxidized states were performed. All the structures and linear absorption spectra were studied in details. It was shown that TOPO ligands preserve wurtzite structure of nanocrystals. Their evaporation results in modification of linear absorption spectra. In case of (CdSe)15 removal of TOPO ligands leads to considerable reduction of the band gap due to the appearance of significant number of dangling bonds on the surface of nanocrystal. Oxidation of (CdSe)15 leads to critical reordering of atoms in nanocrystal accompanied with its sizable stabilization due to reduction of the dangling bonds number. The unligated QDs with three-fold coordinated surface atoms represent structures with a wide band gap. Their oxidation destroys closed-shell structure and leads to the appearance of absorption band in NIR region.
If you are interested in meeting with the speaker, please contact Svetlana Kilina (skilina@lanl.gov) to make arrangements.