Article,
Surface Sol−Gel Synthesis of Ultrathin Semiconductor Films
Chemistry of Materials, 12 (2): 383--389 (February 2000)
Abstract
Ultrathin films of ZnS, Mn-doped ZnS, ZnO, and SiO2 were grown on
silicon substrates using surface solgel reactions, and the film growth
process was characterized by ellipsometry, atomic force microscopy,
X-ray photoelectron spectroscopy, UVvisible absorbance, and photoluminescence
(PL) spectroscopy. The Si substrates were pretreated by chemical
oxidation, or by derivatization with 4-((dimethylmethoxy)silyl)butylamine.
On the oxidized Si/SiOx surface, nanoparticulate films of ZnS and
Mn-doped ZnS were grown by sequential immersion in aqueous metal
acetate and sodium sulfide solutions. During the first four adsorption
cycles, there was little film growth, but thereafter the amount of
material deposited was linear with the number of adsorption cycles.
This behavior is consistent with the formation of ZnS nuclei at low
coverage, followed by particle growth in subsequent cycles. PL spectra
are consistent with incorporation of Mn2+ into the ZnS nanoparticles.
In contrast, the growth of SiO2 films from nonaqueous SiCl4 on the
same Si/SiOx substrates was regular from the first adsorption cycle,
indicating a high density of nucleation sites. On amine-derivatized
substrates, ZnO thin films grew as relatively smooth islands, suggesting
that the interaction of Zn2+ ions or primary ZnO clusters with the
amine surface priming layer was sufficiently strong to prevent the
formation of isotropic nanoparticles upon exposure to aqueous base.
