INVESTIGADORES
SCAFFARDI Lucia Beatriz
artículos
Título:
SIZE DEPENDENCE OF REFRACTIVE INDEX OF GOLD NANOPARTICLES
Autor/es:
LUCIA B. SCAFFARDI; JORGE O. TOCHO
Revista:
NANOTECHNOLOGY
Editorial:
Institute of Physics Publishing (IOP)
Referencias:
Lugar: Londres; Año: 2006 vol. 17 p. 1309 - 1315
ISSN:
0957-4484
Resumen:
The extinction spectra of spherical gold nanoparticles suspended in a
homogeneous media were measured and the results were adjusted with Mie¡¦s
theory together with an appropriate modification of the optical properties of
bulk material considering the limitation that introduces the size of
nanoparticles on the dielectric function. Usually, the contribution of free
electrons to the dielectric function is modified for particle size, while the
contribution of bound electrons is assumed to be independent of size. This
work discusses the separated contribution of free and bound electrons on the
optical properties of particles and their variation with size for gold
nanoparticles. The effects of dielectric function and its changes with size on
extinction spectra near plasmon resonance are considered. The damping
constant for free electrons was changed with size as usual and a scattering
constant of C = 0.8 was used. For the bound electron contribution, two
different models were analysed to fit the extinction spectra: on the one hand,
the damping constant for interband transitions and the gap energy were used
as fitting parameters and on the other, the electronic density of states in the
conduction band was made size-dependent. For the first model, extinction
spectra corresponding to particles with radius R = 0.7 nmwere fitted using
two sets of values of the energy gap and damping constant: Eg = 2.3 eV andC = 0.8 was used. For the bound electron contribution, two
different models were analysed to fit the extinction spectra: on the one hand,
the damping constant for interband transitions and the gap energy were used
as fitting parameters and on the other, the electronic density of states in the
conduction band was made size-dependent. For the first model, extinction
spectra corresponding to particles with radius R = 0.7 nmwere fitted using
two sets of values of the energy gap and damping constant: Eg = 2.3 eV andR = 0.7 nmwere fitted using
two sets of values of the energy gap and damping constant: Eg = 2.3 eV andEg = 2.3 eV and
£^b = 158 meV/¡Âh or Eg = 2.1 eV and £^b = 200 meV/¡Âh. For the second
model, a simple assumption for the electronic density of states and its
contribution to the dielectric function in terms of size allowed to adjust
extinction spectra for all samples explored (from 0.3 to 1.6 nm radius). This
last model uses only one parameter, a scale factor R0 = 0.35 nm, that
controls the contribution of the bound electrons in nanoparticles. Contrast
between the maximum and the minimum in the extinction spectra near the
resonance at 520 nm or alternatively the broadening of the plasmon band can
be used to determine the size of gold nanoparticles with radius smaller
than 2 nm.b = 158 meV/¡Âh or Eg = 2.1 eV and £^b = 200 meV/¡Âh. For the second
model, a simple assumption for the electronic density of states and its
contribution to the dielectric function in terms of size allowed to adjust
extinction spectra for all samples explored (from 0.3 to 1.6 nm radius). This
last model uses only one parameter, a scale factor R0 = 0.35 nm, that
controls the contribution of the bound electrons in nanoparticles. Contrast
between the maximum and the minimum in the extinction spectra near the
resonance at 520 nm or alternatively the broadening of the plasmon band can
be used to determine the size of gold nanoparticles with radius smaller
than 2 nm.R0 = 0.35 nm, that
controls the contribution of the bound electrons in nanoparticles. Contrast
between the maximum and the minimum in the extinction spectra near the
resonance at 520 nm or alternatively the broadening of the plasmon band can
be used to determine the size of gold nanoparticles with radius smaller
than 2 nm.