Biomedical Engineering Reference
In-Depth Information
nanowires. To this aim we positioned “dot-in-a-rod” colloidal core-
shell nanorods in the vicinity of one tip of Au nanowires with 150
nmwidthandseveralmicronsinlengthfabricatedbyelectronbeam
lithography. The exciting laser beam was coupled off-axis into the
confocal imaging optics, which allowed us to illuminate the rod-
functionalized tip of the nanowire while recording the emission
from the opposite end. Spatially resolved conventional confocal
luminescence mapping was used to verify the presence of nanorods
solely at one tip of the nanowires. The architecture of the nanorods
was chosen such that their absorption was in the UV-blue spectral
range and the band edge emission of the core material in the range
between 600-650 nm. The nanorods were excited locally by laser
light in resonance with the band gap of the shell, and the far field
light emission at the opposite end of the nanowire was detected.
By this approach we were able to spectrally decouple the laser
excitation from the band in which the plasmon coupling occurred.
The experimental data will be compared with the results obtained
from finite elements (FEM) calculations on the propagation of SPPs
in the metallic nanowires.
15.3.1
Optical Properties of Rod-Shaped Colloidal
Core-Shell Nanocrystals
Colloidal CdSe/CdS core-shell nanorods with a dot-in-a-rod ar-
chitecture [52] were used as light emitters, since this material
shows very bright and stable emission and because the emission
wavelength can be tuned via the size of the CdSe core [53].
The optical absorption and emission spectra of such nanorods is
displayed in Fig. 15.6, where the onset in absorption at 500 nm is
dominated by the CdS shell material, while the weaker absorption
of the CdSe cores can be noted in the regime from 650-500 nm.
The strong photoluminescence centered at 650 nm is slightly red-
shiftedwithrespecttothegroundstateabsorptionduetotheStokes
shift.Foradetailedreviewontheopticalpropertiesofnanorodssee
Chapter2inRef.[54].Thecore-shellarchitectureandtheassociated
energylevelsinthevalenceandconductionbandaresketchedinthe
inset of Fig. 15.6.
