Twinning and Phase Control in Template-Directed ZnS and (Cd,Zn)­S Nanocrystals

We report on the nucleation and growth of ZnS and (Cd_<i>x</i>­Zn_1–<i>x</i>)­S nanocrystals on polydiacetylene Langmuir films. It was found that the 3–5 nm nanocrystals form ordered linear arrays aligned at a constant 27° angle with respect to the conjugated direction of the polydiacetylene film, as derived from the optimal alignment between the two phases. ZnS nanocrystals were found to nucleate specifically from the zinc blende (001) face. Because of closely matched interfacial relations, twinning defects were induced on the {111} planes. These nanometer-sized twin crystals exhibit extra {111} electron diffraction reflections due to elongation of reciprocal space spots, despite their off axis orientation. The composition of solid solution (Cd,Zn)­S nanocrystals depends on the Zn²⁺\Cd²⁺ ratio in the aqueous subphase. Their structure is affected by the template mismatch both by twinning, as is the case for ZnS, for which continuous compositional shift is observed, and by phase shift to hexagonal wurtzite, with a pure CdS composition. The nanocrystals exhibited a continuous energy-gap shift, reflecting the Zn/Cd ratio in the solid solution. We demonstrate control over the nanocrystals’ crystal structure, defect structure, orientation, and composition, providing a potentially effective tool for band-gap engineering in organic–inorganic hybrid assemblies

New Nanocrystalline Materials: A Previously Unknown Simple Cubic Phase in the SnS Binary System

We report a new phase in the binary SnS system, obtained as highly symmetric nanotetrahedra. Due to the nanoscale size and minute amounts of these particles in the synthesis yield, the structure was exclusively solved using electron diffraction methods. The atomic model of the new phase (<i>a</i> = 11.7 Å, <i>P</i>2₁3<i>)</i> was deduced and found to be associated with the rocksalt-type structure. Kramers–Kronig analysis predicted different optical and electronic properties for the new phase, as compared to α-SnS

Oriented Attachment: A Path to Columnar Morphology in Chemical Bath Deposited PbSe Thin Films

We have studied columnar PbSe thin films obtained using chemical bath deposition. The columnar microstructure resulted from an oriented attachment growth mechanism, in which nuclei precipitating from solution attached along preferred crystallographic facets to form highly oriented, size-quantized columnar grains. This is shown to be an intermediate growth mechanism between the ion-by-ion and cluster growth mechanisms. A structural zone model depicting the active growth mechanisms is presented for the first time for semiconductor thin films deposited from solution. The columnar films showed well-defined twinning relations between neighboring columns, which exhibited 2D quantum confinement, as established by photoluminescence spectroscopy. In addition, anisotropic nanoscale electrical properties were investigated using current sensing AFM, which indicated vertical conductivity, while maintaining quantum confinement