INVESTIGADORES
CALVO Ernesto Julio
artículos
Título:
SERS in PAH-Os and gold nanoparticle self-assembled multilayers
Autor/es:
NICOLAS TOGNALLI; ALEX FAINSTEIN; ERNESTO JULIO CALVO; CECILIA BONAZZOLA; LIA PIETRASANTA; MARIANO CAMPOY-QUILES; PABLO ETCHEGOIN
Revista:
JOURNAL OF CHEMICAL PHYSICS
Editorial:
American Physical Society
Referencias:
Año: 2005 vol. 123 p. 447071 - 447079
ISSN:
0021-9606
Resumen:
We present a surface enhanced Raman scattering (SERS) study of poly(allylamine) modified with
Os(byp)2ClPyCHO (PAH-Os) and gold nanoparticles self-assembled multilayers (PAH-Os+(Aunanoparticles/
PAH-Os)n, n = 1 and 5). AFM and variable angle spectroscopic ellipsometry measurements
indicate that the first nanoparticle layer grows homogenously by partially covering the
substrate without clustering. Analysing the samples thickness and roughness we infer that the
growth process advances thereafter by filling with nanoparticles the interstitial spaces between the
previously adsorbed nanoparticles. After five immersion steps the multilayers reach a more compact
structure. The more effective interaction between near gold nanoparticles plasmons provides a new
optical absorption around 650 nm which, in addition, allows a more effective SERS process in that
spectral region than at the single plasmon resonance (530 nm). We compare electronic resonance
Raman and SERS amplification mechanisms analyzing Raman resonance scans and Raman intensity
micromaps. As a function of nanoparticle coverage we observe dramatic changes in the Raman
intensity scans, with maxima that shift from the electronic transitions, to the plasmon resonance,
and finally to the coupled-plasmon absorption. The Raman micromaps, on the other hand, evidence
huge intensity inhomogeneities probably related to hot-spots. At the same time, the Raman spectra
evolve from a strong functional group enhancement selectively in the electronic resonance case,
to the observation of vibrations from the whole molecule at SERS resonance. Finally, we present
some qualitative numerical discrete dipole approximation (DDA) results that model the interaction
between gold nanoparticles and help to understand the origin of the coupled-plasmon absorption
and red-shifted Raman hot-spots.2ClPyCHO (PAH-Os) and gold nanoparticles self-assembled multilayers (PAH-Os+(Aunanoparticles/
PAH-Os)n, n = 1 and 5). AFM and variable angle spectroscopic ellipsometry measurements
indicate that the first nanoparticle layer grows homogenously by partially covering the
substrate without clustering. Analysing the samples thickness and roughness we infer that the
growth process advances thereafter by filling with nanoparticles the interstitial spaces between the
previously adsorbed nanoparticles. After five immersion steps the multilayers reach a more compact
structure. The more effective interaction between near gold nanoparticles plasmons provides a new
optical absorption around 650 nm which, in addition, allows a more effective SERS process in that
spectral region than at the single plasmon resonance (530 nm). We compare electronic resonance
Raman and SERS amplification mechanisms analyzing Raman resonance scans and Raman intensity
micromaps. As a function of nanoparticle coverage we observe dramatic changes in the Raman
intensity scans, with maxima that shift from the electronic transitions, to the plasmon resonance,
and finally to the coupled-plasmon absorption. The Raman micromaps, on the other hand, evidence
huge intensity inhomogeneities probably related to hot-spots. At the same time, the Raman spectra
evolve from a strong functional group enhancement selectively in the electronic resonance case,
to the observation of vibrations from the whole molecule at SERS resonance. Finally, we present
some qualitative numerical discrete dipole approximation (DDA) results that model the interaction
between gold nanoparticles and help to understand the origin of the coupled-plasmon absorption
and red-shifted Raman hot-spots.n, n = 1 and 5). AFM and variable angle spectroscopic ellipsometry measurements
indicate that the first nanoparticle layer grows homogenously by partially covering the
substrate without clustering. Analysing the samples thickness and roughness we infer that the
growth process advances thereafter by filling with nanoparticles the interstitial spaces between the
previously adsorbed nanoparticles. After five immersion steps the multilayers reach a more compact
structure. The more effective interaction between near gold nanoparticles plasmons provides a new
optical absorption around 650 nm which, in addition, allows a more effective SERS process in that
spectral region than at the single plasmon resonance (530 nm). We compare electronic resonance
Raman and SERS amplification mechanisms analyzing Raman resonance scans and Raman intensity
micromaps. As a function of nanoparticle coverage we observe dramatic changes in the Raman
intensity scans, with maxima that shift from the electronic transitions, to the plasmon resonance,
and finally to the coupled-plasmon absorption. The Raman micromaps, on the other hand, evidence
huge intensity inhomogeneities probably related to hot-spots. At the same time, the Raman spectra
evolve from a strong functional group enhancement selectively in the electronic resonance case,
to the observation of vibrations from the whole molecule at SERS resonance. Finally, we present
some qualitative numerical discrete dipole approximation (DDA) results that model the interaction
between gold nanoparticles and help to understand the origin of the coupled-plasmon absorption
and red-shifted Raman hot-spots.530 nm). We compare electronic resonance
Raman and SERS amplification mechanisms analyzing Raman resonance scans and Raman intensity
micromaps. As a function of nanoparticle coverage we observe dramatic changes in the Raman
intensity scans, with maxima that shift from the electronic transitions, to the plasmon resonance,
and finally to the coupled-plasmon absorption. The Raman micromaps, on the other hand, evidence
huge intensity inhomogeneities probably related to hot-spots. At the same time, the Raman spectra
evolve from a strong functional group enhancement selectively in the electronic resonance case,
to the observation of vibrations from the whole molecule at SERS resonance. Finally, we present
some qualitative numerical discrete dipole approximation (DDA) results that model the interaction
between gold nanoparticles and help to understand the origin of the coupled-plasmon absorption
and red-shifted Raman hot-spots.