S. Henrichs et al., The dielectric function of silver nanoparticle Langmuir monolayers compressed through the metal insulator transition, J AM CHEM S, 122(17), 2000, pp. 4077-4083
Algorithms and experimental techniques for extracting the complex dielectri
c function of thin films (monolayers and bilayers) of quantum dots are deve
loped. The algorithms are based on a combination of the so-called Newton-Ra
phson method, used in conjunction with a Kramers-Kronig analysis, and are u
sed to analyze normal-incidence reflectance and transmission measurements o
f organically passivated silver quantum dot Langmuir monolayers. single, un
ambiguous solutions to the dielectric function were determined for several
particle monolayers and at various stages of compression. A transition of t
he quantum dot superlattice from the insulating to a metallic state was obs
erved. When a monolayer of 6-nm-diameter Ag nanocrystals is compressed to a
n interparticle separation distance of similar to 8-9 Angstrom, a negative-
valued featureless component of the real part of the dielectric function is
detected. This indicates the onset of Drude-like behavior that is characte
ristic of a metallic film. The impact of superlattice disorder on this Drud
e response is also investigated.