Andrew W Wills

Publications (3)16.94 Total impact

• Article: Size control and quantum confinement in Cu2ZnSnS4 nanocrystals.

  Ankur Khare, Andrew W Wills, Lauren M Ammerman, David J Norris, Eray S Aydil
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  ABSTRACT: Starting with metal dithiocarbamate complexes, we synthesize colloidal Cu(2)ZnSnS(4) (CZTS) nanocrystals with diameters ranging from 2 to 7 nm. Structural and Raman scattering data confirm that CZTS is obtained rather than other possible material phases. The optical absorption spectra of nanocrystals with diameters less than 3 nm show a shift to higher energy due to quantum confinement.
  Chemical Communications 09/2011; 47(42):11721-3. · 6.17 Impact Factor
• Article: Effect of Different Manganese Precursors on the Doping Efficiency in ZnSe Nanocrystals

  Lijun Zu, Andrew W. Wills, Thomas A. Kennedy, Evan R. Glaser, David J. Norris
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  ABSTRACT: We prepare ZnSe nanocrystals in the presence of several different Mn precursors to investigate the incorporation of Mn as an intentional impurity. Four different Mn sources, including dimethylmanganese, tricarbonyl methylcyclopentadienylmanganese, Mn(II) cyclohexanebutyrate, and Mn2(μ-SeMe)2(CO)8 are tested in a standard hot-injection organometallic synthesis. The resulting ZnSe nanocrystals can exhibit two optical emission peaks: one related to the incorporation of Mn at around 585 nm and one due to electron−hole recombination in the nanocrystal at around 400 nm. We use the photoluminescence intensity ratio of these two peaks to extract information about the doping efficiency. These results are further verified with inductively coupled plasma atomic emission spectroscopy (ICP) and electron paramagnetic resonance (EPR) spectroscopy. Among the four Mn sources, dimethylmanganese leads to the highest doping efficiency, tricarbonyl methylcyclopentadienymanganese and Mn2(μ-SeMe)2(CO)8 lead to poor incorporation, and Mn(II) cyclohexanebutyrate leads to weak incorporation of Mn that appears to be mostly at or near the nanocrystal surface.
  11/2010;
• Article: Thermally degradable ligands for nanocrystals.

  Andrew W Wills, Moon Sung Kang, Ankur Khare, Wayne L Gladfelter, David J Norris
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  ABSTRACT: We exchanged the oleate ligands on as-prepared PbSe/CdSe core/shell nanocrystals with octyldithiocarbamate to enable the removal of insulating ligands by gentle heating. The octyldithiocarbamate ligand could readily be stripped from the surface by heating briefly to temperatures from 140 to 205 degrees C, which is substantially lower than the temperature (330 degrees C) required to remove oleate from the nanocrystal surface. X-ray diffraction and transmission electron microscopy reveal that the nanocrystals sinter around 250 degrees C, resulting in a loss of quantum confinement. Heating for 1 min to 205 degrees C removed 92% of the organics from the surface. We could therefore prepare densely packed films of quantum-confined nanocrystals via dithiocarbamate treatment. Conductivity increased by up to 4 orders of magnitude after annealing. In addition to PbSe/CdSe core/shell nanocrystals, we also examined the applicability of our ligand removal procedure to CdSe nanocrystals.
  ACS Nano 08/2010; 4(8):4523-30. · 10.77 Impact Factor