In this paper, Co-Al layered double hydroxide (LDH) and montmorillonite (MMT) have been exfoliated into charged single layers in the solvent of formamide and water, respectively. The structures of individual layers of LDH and MMT were characterized by X-ray diffraction (XRD) and atomic force microscopy (AFM). The delamination mechanisms of LDH and MMT were also discussed. Furthermore, heterogeneous ultrathin films of poly(vinyl alcohol) (PVA)/charged inorganic nanosheets, (PVA/MMT/PVA/LDH)(n), were fabricated by layer-by-layer (LBL) assembly via hydrogen bonding. The LBL assembly process was monitored by UV-vis spectroscopy, and the structures of the heterogeneous ultrathin films were analyzed by XRD.
Nanogermanium
is a material that has great potential for technological
applications, and doped and alloyed Ge nanocrystals (NCs) are actively
being considered. New alloys and compositions are possible in colloidal
synthesis because the reactions are kinetically rather than thermodynamically
controlled. Most of the Group V elements have been shown to be n-type
dopants in Ge to increase carrier concentration; however, thermodynamically,
Bi shows no solubility in crystalline Ge. Bi-doped Ge NCs were synthesized
for the first time in a microwave-assisted solution route. The oleylamine
capping ligand can be replaced by dodecanethiol without loss of Bi.
A positive correlation between the lattice parameter and the concentration
of Bi content (0.5–2.0 mol %) is shown via powder X-ray diffraction
and selected area electron diffraction. X-ray photoelectron spectroscopy,
transmission electron microscopy (TEM), scanning TEM, and inductively
coupled plasma–mass spectroscopy are consistent with the Bi
solubility up to 2 mol %. The NC size increases with increasing amount
of bismuth iodide employed in the reaction. Absorption data show that
the band gap of the Bi-doped Ge NCs is consistent with the NC size.
This work shows that a new element can be doped into Ge NCs via a
microwave-assisted route in amounts as high as 1–2 mol %, which
leads to increased carriers. Colloidal chemistry provides an inroad
to new materials not accessible via other means.
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