2 research outputs found
High Resolution Electron Microscopy Study of Nanocubes and Polyhedral Nanocrystals of Cerium(IV) Oxide
In this research, high resolution
transmission electron microscopy (HRTEM) and high angle annular dark
field–scanning transmission electron microscopy (HAADF-STEM)
studies of ceriaÂ(IV) oxide CeO<sub>2</sub> nanocrystals (NCs) synthesized
by a hydrothermal/two phase process were conducted. The synthesis
route affords the possibility of controlling the shape of the CeO<sub>2</sub> NCs by changing the oleic acid/cerium ([OLA]/[Ce<sup>3+</sup>]) ratio. At a relatively low [OLA]/[Ce<sup>3+</sup>] ratio of 4,
a polyhedral NC morphology was obtained with {111} and {200} termination
facets. Increasing the [OLA]/[Ce<sup>3+</sup>] ratio to 8, while maintaining
a constant reaction time and temperature during the synthesis, truncated
cube-like CeO<sub>2</sub> NCs with {200}, {220}, and {111} termination
facets was generated. These morphologies were identified by HRTEM
and HAADF-STEM characterization. Fourier transform infrared (FT-IR)
analysis and thermogravimetric analysis (TGA) confirm the presence
of chemically bonded oleic acid (OLA) on the CeO<sub>2</sub> NC surface.
It indicates that there is a relationship between the bonded OLA and
the shape of the NC. Additionally, the identification of concave surfaces
on {200} facets by HAADF-STEM characterization suggests that the formation
of the cube-like CeO<sub>2</sub> morphology is a multiple step mechanism.
On the basis of these observations new growth mechanisms for the CeO<sub>2</sub> morphology variants are proposed
The role of defects and growth directions in the formation of periodically twinned and kinked unseeded germanium nanowires
Here we show the impact of preferred growth directions and defects in the formation of complex Ge nanowire (NW) structures grown by a simple organic medium based synthesis. Various types of NWs 15 are examined including: straight defect free NWs; periodically bent NWs with precise angles between the NW segments; NWs with mutually exclusive lateral or longitudinal faults; and more complex ‘wormlike’ structures. We show that choice of solvent and reaction temperature can be used to tune the morphology of the NWs formed. The various types of NWs were probed in depth using transmission electron microscopy (TEM), scanning electron microscopy (SEM), selected area electron diffraction (SAED) and dark field TEM (DFTEM)