imaging of plasmonic nanostructures
optical local field enhancement on nanometer length scales provides the
basis for plasmonic
metal nanostructures to serve
as molecular sensors
and as nanophotonic devices. Understanding the correlation
between particle size and shape, its spectral plasmon response, and the
related details of the local field distribution is the goal of this
project. Using interferometric
homodyne scattering Scanning
Near-field Optical Microscopy (s-SNOM),
spatially map the strong field variations around plasmonic
metal nanostructures and optical antenna geometries from the visible to
(a) and corresponding s-SNOM
image (b) for
a small rounded single-crystalline triangular Ag nanoprism. This
illustrates a single dipolar surface plasmon polariton excitation. The
in-plane electric field vector has been probed under in-plane optical
excitation conditions as indicated by the double-arrow.
Domain formation in
electron systems are often associated with electronic and structural
transitions with ordering and
formation on nanometer
length scale. Here we investigate the ferroelectric order parameter in
materials such as in rare-earth manganites (RMnO3),
and the metal-to-insulator transition in VO2.
The newly discovered multiferroic
present the possibility to control magnetization by means of an
electric field and vice versa which
has potential for
nonvolatile data storage and nanoelectronic devices. This
makes a detailed comprehension of the microscopic phase behavior and
in particular of the ferroelectric
domain structure very
undergoes a first-order phase transition
from a semiconducting
state which is
coupled to structural changes of the crystal
lattice as the temperature is raised through the transition temperature
at 341K. These changes of the structural and electrical
properties of VO2
are accompanied by significant
differences in the
domain topology of intrinsic
multiferroic single crystalline YMnO3.
SHG imaging of the 180◦
domains in YMnO3,
together with two color map
of the domain structure. Ferroelectric domains within the sample plane
along the z-direction are observed with length of 1- 2 μm and
typical width of 200 nm.
Here we use infrared scattering scanning near-field optical microscopy
to study the domain
behavior of the metal-insulator transition
(MIT) in VO2
with spatial resolution down the
nanometer length scale.
This research is in collaboration with the group of Prof. David Cobden
(Department of Physics at UW).
of the MIT in a VO2
single crystal wire as it is heated
temperature. a) Illustration of the experimental setup, b)
topography, c)-f) corresponding optical mappings of the
near-field distribution under illumination with 10.6μm light for
temperatures 332.5K, 340.8K, 345K, 349.1K, respectively showing the
emergence and growth of the metallic domains (bright stripes).
A nano-confined plasmonic light source
Plasmonic scanning probe
a central role in many
optical scanning probe experiments. Ongoing experiments are dedicated
to improve our
understanding and enhancing the optical response of metallic tips. This
includes the development of novel nanoscopic
light light sources
optical antenna design concepts in
combination with nanofabrication techniques. ...
||Surface plasmon polariton response of a Au
probe tip showing its capabilities for resonant light scattering and
local-field enhancement in the visible spectral region. Inset: electron
micrograph of tip (scale bar: 100 nm).
Nanofabrication by focused-ion-beam milling allows for the targeted
design of new nanoconfined, intense, and ultrashort light sources. For
surface plasmons onto the tip shaft allows for propagation and
subsequent conversion of the surface plasmon into a localized
excitation at the tip apex of only nanometer dimensions.
nanoconfined light source: By illuminating on the grating coupler
written on the
shaft of the tip (left), this will launch surface plasmon polaritoins
that propagate adiabatically towards the tip. The resulting optical
field concentration and enhancement is seen at the apex where the field
is reemitted due to the broken symmetry -
resulting in a nanoconfined light source.
dynamics on the nanoscale
of metallic nanostructures determines such interesting
properties as the photochemistry on metal surfaces or the
of plasmon polaritons for device applications.
The dephasing time is determined by both, the intrinsic electron
scattering time in the metal, and extrinsic effects due to the
nanoparticle shape, size, and
chemical environment. In order to distinguish different
relaxation channels contributing to this dephasing time probing on
level is desirable to avoid effects due to the inherent heterogeneity
of any ensemble. ...
integrated interferometric two-pulse second-harmonic correlation
response of a Au
nanotip. From the simulation using a three-level optical Bloch model
plasmon dephasing times of 3-5 fs are derived.
Raman spectroscopy on the nanoscale
Raman spectroscopy (TERS) has shown great potential
nano-analytical tool with diverse applications in material and surface
science as well as analytical chemistry. Drawing on the enhancement and
confinement of the electric field due to the plasmonic coupling between
a scanning probe tip and a metallic sample, this technique
Raman signal enhancement
up to 109
down to 10 nm. Having previously demonstrated the capability of TERS
sensitivity, we are currently exploring the
extension of this technique to the study of crystalline nanostructures.
spectral diffusion, blinking, and peak
fluctuations observed in time series of successive tip-scattered Raman
spectra are characteristic for single molecule Raman emission.
probing of organic nanocomposites
we have advanced infrared microscopy for chemical analysis achieving
unprecedented spatial resolution
than 10 nm
and a sensitivity
mole or just 103
This result demonstrates that infrared spectroscopy with access to
intramolecular dimensions is within reach. ...
nanodomains of a
block-copolymer surface. Contrast is obtained due to the spectral
differences between the C-H stretch vibrational resonances of the
respective polymer constituents.
Nonlinear optics on the
symmetry selectivity of the nonlinear
optical response compared to the linear one can be used for in new and
unique ways for optical probing on the nanoscale. We derived new
for asymmetric nanostructures that allow for the
distinction of different source polarizations and enable simultaneous
surface and bulk investigations.
generation (SHG) of
nanoscopic metal tips. As a partially asymmetric nanostructure the tips
allow for the distinction of otherwise inseparable local surface and
nonlocal bulk SH source polarizations via their different polarization
characteristics for emission.