9 Usage of Silicon for Label-Free Super-Resolved Imaging
223
An average of the electrical field was computed within a square with 1 nm vertex
centered at the indicated locations in order to perform the calculations of the field’s
enhancement factor (the intensity enhancement is the fourth power of the electric
field norm enhancement). The results were obtained for four pump intensities of:
6.2 × 10
−3
mW/μm
2
, 0.62
mW/μm
2
, 6.2
mW/μm
2
, 37.33
mW/μm
2
where the first two intensities are related to the nonconducting silicon nanoparticle
and the last two are related to a conducting silicon nanoparticle. In the case of highest
intensity, the concentration of free charge carriers in the silicon part is close to that
of silver nanoparticle.
b. Results
The structure examined in Fig. 9.7a consists of a single silver nanorod block on
top of a silicon nanorod. When the intensity of the illumination pump is high the
shape gradually changes from a silver nanorod on top of an insulator to two metal
nanorods attached to each other. This leads to a decrease in aspect ratio and causes a
blue shift to the extinction resonance (see in Fig. 9.7b). From Fig. 9.7c where typical
electric field distribution is shown, the change in the intensity of the pump results
in the change in the field’s magnitude. Since the sharper the feature, the higher is
the enhancement factor, the highest enhancement is obtained in the corners of the
nanorod. For conducting silicon nanorod the structure looks as one larger nanorod
and for non-conducting case, the structure is sharper with higher enhancement than
in the conducting case of Fig. 9.7d. For further understanding, the enhancement was
calculated along one of the vertical vertices of the nanorods and Fig. 9.7e shows
the tag. Indeed, for the low pump intensity (sharper structure) there is a comparable
enhancement between the two corners of the silver nanorods (z = 10 and z = 0)
while for high pump intensity there is a metal to metal transition at z = 0 and two
enhancement factors (there is only one corner enhancement at z = 0).
Another tested structure was a single-layer nanorod dimer composed of silicon
and silver nanorods being positioned along the long axis of the nanorods (Fig. 9.8a).
Here, if the pump intensity is increased, the silicon nanorod becomes metallic and
the extinction resonance (Fig. 9.8b) has a red shift due to the essentially higher aspect
ratio and longer nanorod.
In the case of weakly conduction (pump intensity of 0.62
mw/μm
2
) two close
resonance peaks are generated and are matched with the two different metal-like
nanoparticle. The resonator formed by the two nanoparticles in the conducting case
enlarges the middle point enhancement in comparison to the enhancement of the edge.
On the other hand, in the case of non-conducting, this situation is inverted. The electric
field distribution of the non-conducting case and the highly conducting cases are seen
in Fig. 9.8c and d, respectively. When the pump intensity is increased the electrical
field moves more and more from surrounding only the silver nanoparticle to be
surrounded also around the silicon nanoparticle while high electric field enhancement
is obtained between the two particles.
Figure 9.9a and b shows the spectral response of the two-layer nanorod dimer,
which is similar to the single two-layer nanorod structure and it is opposite to that
of the single-layer nanorod dimer.
223
An average of the electrical field was computed within a square with 1 nm vertex
centered at the indicated locations in order to perform the calculations of the field’s
enhancement factor (the intensity enhancement is the fourth power of the electric
field norm enhancement). The results were obtained for four pump intensities of:
6.2 × 10
−3
mW/μm
2
, 0.62
mW/μm
2
, 6.2
mW/μm
2
, 37.33
mW/μm
2
where the first two intensities are related to the nonconducting silicon nanoparticle
and the last two are related to a conducting silicon nanoparticle. In the case of highest
intensity, the concentration of free charge carriers in the silicon part is close to that
of silver nanoparticle.
b. Results
The structure examined in Fig. 9.7a consists of a single silver nanorod block on
top of a silicon nanorod. When the intensity of the illumination pump is high the
shape gradually changes from a silver nanorod on top of an insulator to two metal
nanorods attached to each other. This leads to a decrease in aspect ratio and causes a
blue shift to the extinction resonance (see in Fig. 9.7b). From Fig. 9.7c where typical
electric field distribution is shown, the change in the intensity of the pump results
in the change in the field’s magnitude. Since the sharper the feature, the higher is
the enhancement factor, the highest enhancement is obtained in the corners of the
nanorod. For conducting silicon nanorod the structure looks as one larger nanorod
and for non-conducting case, the structure is sharper with higher enhancement than
in the conducting case of Fig. 9.7d. For further understanding, the enhancement was
calculated along one of the vertical vertices of the nanorods and Fig. 9.7e shows
the tag. Indeed, for the low pump intensity (sharper structure) there is a comparable
enhancement between the two corners of the silver nanorods (z = 10 and z = 0)
while for high pump intensity there is a metal to metal transition at z = 0 and two
enhancement factors (there is only one corner enhancement at z = 0).
Another tested structure was a single-layer nanorod dimer composed of silicon
and silver nanorods being positioned along the long axis of the nanorods (Fig. 9.8a).
Here, if the pump intensity is increased, the silicon nanorod becomes metallic and
the extinction resonance (Fig. 9.8b) has a red shift due to the essentially higher aspect
ratio and longer nanorod.
In the case of weakly conduction (pump intensity of 0.62
mw/μm
2
) two close
resonance peaks are generated and are matched with the two different metal-like
nanoparticle. The resonator formed by the two nanoparticles in the conducting case
enlarges the middle point enhancement in comparison to the enhancement of the edge.
On the other hand, in the case of non-conducting, this situation is inverted. The electric
field distribution of the non-conducting case and the highly conducting cases are seen
in Fig. 9.8c and d, respectively. When the pump intensity is increased the electrical
field moves more and more from surrounding only the silver nanoparticle to be
surrounded also around the silicon nanoparticle while high electric field enhancement
is obtained between the two particles.
Figure 9.9a and b shows the spectral response of the two-layer nanorod dimer,
which is similar to the single two-layer nanorod structure and it is opposite to that
of the single-layer nanorod dimer.