Ellipsometry Techniques and Its Advanced Applications …
581
Figure 31a shows the measured Mueller matrix elements, m 22 , m 24 , m 31 , m 33 ,
m 42 , and m 44 (remaining elements are not shown) from Ag-nanoparticle arrays on
rippled-Si specimen for azimuthal rotation angles of 0°, 30°, 60°, and 90° at an angle
of light incidence of 75°. The presence of optical anisotropy is also evident from
the non-degeneracy of diagonal elements along with non-zero values of off-diagonal
elements [10, 17] shown at a scale multiplier of 20. The plasmonic response is
observed at 2.5 and 3.2 eV. The elements of Mueller matrix are fitted using a biaxial
optical model and the dielectric functions (obtained from the biaxial model fit) are
presented in Fig. 31b. The proposed model is able to reproduce diagonal elements,
albeit, the resonance feature at 2.5 eV is reproduced from the off-diagonal elements
along with a comparatively weaker signal at 3.2 eV.
4 Conclusions
In the present work, advanced applications of ellipsometry technique in plasmonics is
demonstrated along with basics of polarized light, brief introduction to spectroscopic
ellipsometry technique, and measuring methods. In particular, plasmonic response
of silver and gold nanoparticle-nanowire arrays and hexagonally arranged nanodots
are explored using different modes of ellipsometry techniques viz. spectroscopic,
generalized, and Mueller matrix ellipsometry. From the reflection measurements of
Ag and Au nanoparticle arrays, it is observed that the nanoparticle arrays show LSPR
peaks and it is strongly influenced by the size, shape, ordering, and interparticlegap of the nanoparticles. For instance, reflection measured along and across the
nanoparticle arrays exhibits in-plane plasmonic anisotropy which is a red shift in the
LSPR peak corresponding to reflection measured along the arrays compared to the
one measured across the arrays. Interestingly, the LSPR peak broadening is a measure
of the size-distribution of nanoparticles and generally, it reduces after annealing of
nanoparticles. However, the amplitude of LSPR peak indicates the strength of the
plasmonic field-coupling between nanoparticles. On the other hand, Jones matrix
elements are measured using GE and observed that nearly zero values of non-diagonal
elements show the isotropic nature of specimen, albeit, non-zero values confirm the
presence of optical anisotropy in the same. These Jones matrix elements are fitted
using a biaxial optical model which is constructed with the help of a combination
of well-defined models and oscillator viz. Drude model, Lorentz oscillators, TaucLorentz oscillators etc. The directional-dependent dielectric functions obtained from
the optical model, exhibit LSPR along and across the nanoparticle arrays, however,
field coupling remains weaker for across the nanoparticle arrays due to increased
interparticle-gap along this direction. Moreover, Ag-nanowire arrays exhibit LSPR
only across the nanowire arrays due to metallic nature along the nanowires. On
the other hand, bulk-like dielectric response is observed for perpendicular to the
specimen plane. Thus, the dielectric response of Ag- and Au-nanoparticle arrays on
rippled-Si is tuned by varying the wavelength of ripple patterns, growth angle etc.
Likewise, Ag-nanoparticle deposited on hexagonally self-aligned GaSb-nanodots are
581
Figure 31a shows the measured Mueller matrix elements, m 22 , m 24 , m 31 , m 33 ,
m 42 , and m 44 (remaining elements are not shown) from Ag-nanoparticle arrays on
rippled-Si specimen for azimuthal rotation angles of 0°, 30°, 60°, and 90° at an angle
of light incidence of 75°. The presence of optical anisotropy is also evident from
the non-degeneracy of diagonal elements along with non-zero values of off-diagonal
elements [10, 17] shown at a scale multiplier of 20. The plasmonic response is
observed at 2.5 and 3.2 eV. The elements of Mueller matrix are fitted using a biaxial
optical model and the dielectric functions (obtained from the biaxial model fit) are
presented in Fig. 31b. The proposed model is able to reproduce diagonal elements,
albeit, the resonance feature at 2.5 eV is reproduced from the off-diagonal elements
along with a comparatively weaker signal at 3.2 eV.
4 Conclusions
In the present work, advanced applications of ellipsometry technique in plasmonics is
demonstrated along with basics of polarized light, brief introduction to spectroscopic
ellipsometry technique, and measuring methods. In particular, plasmonic response
of silver and gold nanoparticle-nanowire arrays and hexagonally arranged nanodots
are explored using different modes of ellipsometry techniques viz. spectroscopic,
generalized, and Mueller matrix ellipsometry. From the reflection measurements of
Ag and Au nanoparticle arrays, it is observed that the nanoparticle arrays show LSPR
peaks and it is strongly influenced by the size, shape, ordering, and interparticlegap of the nanoparticles. For instance, reflection measured along and across the
nanoparticle arrays exhibits in-plane plasmonic anisotropy which is a red shift in the
LSPR peak corresponding to reflection measured along the arrays compared to the
one measured across the arrays. Interestingly, the LSPR peak broadening is a measure
of the size-distribution of nanoparticles and generally, it reduces after annealing of
nanoparticles. However, the amplitude of LSPR peak indicates the strength of the
plasmonic field-coupling between nanoparticles. On the other hand, Jones matrix
elements are measured using GE and observed that nearly zero values of non-diagonal
elements show the isotropic nature of specimen, albeit, non-zero values confirm the
presence of optical anisotropy in the same. These Jones matrix elements are fitted
using a biaxial optical model which is constructed with the help of a combination
of well-defined models and oscillator viz. Drude model, Lorentz oscillators, TaucLorentz oscillators etc. The directional-dependent dielectric functions obtained from
the optical model, exhibit LSPR along and across the nanoparticle arrays, however,
field coupling remains weaker for across the nanoparticle arrays due to increased
interparticle-gap along this direction. Moreover, Ag-nanowire arrays exhibit LSPR
only across the nanowire arrays due to metallic nature along the nanowires. On
the other hand, bulk-like dielectric response is observed for perpendicular to the
specimen plane. Thus, the dielectric response of Ag- and Au-nanoparticle arrays on
rippled-Si is tuned by varying the wavelength of ripple patterns, growth angle etc.
Likewise, Ag-nanoparticle deposited on hexagonally self-aligned GaSb-nanodots are