Ag1-xCuxI (x= 0.10, 0.20, and 0.50) thin films with thicknesses upto15 nm produced by thermal co-evaporation onto
glass substrates were systematically iodized and carefully characterized. Optical absorption spectra of uniodized Ag-Cu
films show intense surface plasmon resonance (SPR) features with maxima at 430, 445 and 445 nm for the films of
thickness 5, 10 and 15 nm respectively and a gradual transition to zincblende AgI exciton with optical signatures at 425
nm. Delayed evolution and inhomogeneous broadening of the exciton absorption at 425 nm of the spatially confined γ-
AgI nanoparticles were clearly seen by the development of Z1,2 and Z3 exciton peaks iodization kinetics being controlled
by the as-quenched Ag-Cu clusters. Cu addition not only restricts the particle size, but also favors the island type growth
mode. PL observed at 428 nm shows a thickness and Cu-composition dependent intensity suggesting the involvement of
Frenkel defects in non-radiative recombination.
Ultrathin Ag films (2-10 nm thick) were fabricated on clean glass microslides by thermal
evaporation. XRD shows them to be X-ray amorphous implying absence of long range order. AFM
pictures show the presence of 2D triangular nanoplatelets arranged in a random manner, the sizes of
the platelets grow with increasing film thickness Optical absorption spectra in the UV-visible give
evidence for the presence of Mie particles through surface plasmon resonance whose peak positions
and intensities depend sensitively upon thickness of Ag films. Surface plasmon resonance(SPR)
features occur with maxima at 440, 457 and 484nm for the films of thickness 2, 5 and 10nm
respectively with 5nm films showing properties characteristic of a optimally matched dielectric and
electronic properties of the substrate and sample respectively.
AgI nanoparticles with zincblende structure are promising materials for laser based optical communication systems and therefore deserve to be optimally synthesized. We have explored ambient iodization as a strategy for controlled AgI nanoparticle growth on (a) mesoporous Ag foils, (b) Ag-Cu quasi-amorphous thin films and (c) Ag-Sb crystalline alloy films. The modified Ag surfaces obtained by chemical etching, Cu and Sb substitution seem to display an amazingly varied degree of interfacial control over the growth of AgI nanoparticles as investigated by XRD, SEM, optical transmission and photoluminescence. The nature of interfacial control and the associated modification of thin film growth mode are discussed on the basis of the present experimental results and currently available theoretical models.
Our efforts to nucleate and grow AgI nanoparticles in Sb-doped Ag thin films by a closed chamber ambient iodization process has been delineated. The Ag-Sb thin films are characterized by XRD to be nanocrystalline; Sb prolongs the iodization process by delaying the nucleation of AgI nanoparticles, so that optimization of concentration, thickness and iodization duration yields films with self-assembled nanoparticle structure. The retarded growth of AgI particles is reflected in the slow but controlled evolution of the exciton band and variation in the Sb concentration dependent cluster density directly seen in the SEM micrographs.
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