5 research outputs found
Holographic Plasmonic Nanotweezers for Dynamic Trapping and Manipulation
We
demonstrate dynamic trapping and manipulation of nanoparticles
with plasmonic holograms. By tailoring the illumination pattern of
an incident light beam with a computer-controlled spatial light modulator,
constructive and destructive interference of plasmon waves create
a focused hotspot that can be moved across a surface. Specifically,
a computer-generated hologram illuminating the perimeter of a silver
Bull’s Eye nanostructure generates surface plasmons that propagate
toward the center. Shifting the phase of the plasmon waves as a function
of space gives complete control over the location of the focus. We
show that 200 nm diameter nanoparticles trapped in this focus can
be moved in arbitrary patterns. This allows, for example, circular
motion with linearly polarized light. These results show the versatility
of holographically generated surface plasmon waves for advanced trapping
and manipulation of nanoparticles
Holographic Plasmonic Nanotweezers for Dynamic Trapping and Manipulation
We
demonstrate dynamic trapping and manipulation of nanoparticles
with plasmonic holograms. By tailoring the illumination pattern of
an incident light beam with a computer-controlled spatial light modulator,
constructive and destructive interference of plasmon waves create
a focused hotspot that can be moved across a surface. Specifically,
a computer-generated hologram illuminating the perimeter of a silver
Bull’s Eye nanostructure generates surface plasmons that propagate
toward the center. Shifting the phase of the plasmon waves as a function
of space gives complete control over the location of the focus. We
show that 200 nm diameter nanoparticles trapped in this focus can
be moved in arbitrary patterns. This allows, for example, circular
motion with linearly polarized light. These results show the versatility
of holographically generated surface plasmon waves for advanced trapping
and manipulation of nanoparticles
Super-Resolution Chemical Imaging with Plasmonic Substrates
We demonstrate super-resolution chemical
imaging with plasmonic
nanoholes via surface-enhanced Raman spectroscopy (SERS). Due to large
field enhancements, blinking behavior of SERS hot spots was observed
and processed using a stochastic optical reconstruction microscopy
(STORM) algorithm. This enabled localization to within 10 nm and high-resolution
imaging. However, illumination of the sample with a static laser beam
produced only SERS hot spots in fixed locations, leaving noticeable
gaps in the final images. By randomly altering the phase profile of
the incident beam with a simple optical diffuser, the hot spots were
shifted across the plasmonic surface to illuminate different areas
of the sample, thereby rendering a final image without the gaps. A
tunable band-pass filter was used to preserve spectral information,
allowing chemical contrast imaging. Images were then compared to those
obtained with a scanning electron microscope. Finally, we show that
super-resolution SERS images can also be obtained with our dynamic
illumination technique on even the most basic plasmonic substrate:
as-deposited rough silver films. These results show significant potential
for the use of simple plasmonic substrates with straightforward illumination
and collection schemes for super-resolution chemical imaging
Vertically Oriented Sub-10-nm Plasmonic Nanogap Arrays
Nanometric gaps in noble metals can harness surface plasmons, collective excitations of the conduction electrons, for extreme subwavelength localization of electromagnetic energy. Positioning molecules within such metallic nanogaps dramatically enhances light−matter interactions, increasing absorption, emission, and, most notably, surface-enhanced Raman scattering (SERS). However, the lack of reproducible high-throughput fabrication techniques with nanometric control over the gap size has limited practical applications. Here we show sub-10-nm metallic nanogap arrays with precise control of the gap’s size, position, shape, and orientation. The vertically oriented plasmonic nanogaps are formed between two metal structures by a sacrificial layer of ultrathin alumina grown using atomic layer deposition. We show increasing local SERS enhancements of up to 10<sup>9</sup> as the nanogap size decreases to 5 nm. Because these sub-10-nm gaps can be fabricated at high densities using conventional optical lithography over an entire wafer, these results will have significant implications for spectroscopy and nanophotonics
Fabrication of Smooth Patterned Structures of Refractory Metals, Semiconductors, and Oxides via Template Stripping
The template-stripping
method can yield smooth patterned films without surface contamination.
However, the process is typically limited to coinage metals such as
silver and gold because other materials cannot be readily stripped
from silicon templates due to strong adhesion. Herein, we report a
more general template-stripping method that is applicable to a larger
variety of materials, including refractory metals, semiconductors,
and oxides. To address the adhesion issue, we introduce a thin gold
layer between the template and the deposited materials. After peeling
off the combined film from the template, the gold layer can be selectively
removed via wet etching to reveal a smooth patterned structure of
the desired material. Further, we demonstrate template-stripped multilayer
structures that have potential applications for photovoltaics and
solar absorbers. An entire patterned device, which can include a transparent
conductor, semiconductor absorber, and back contact, can be fabricated.
Since our approach can also produce many copies of the patterned structure
with high fidelity by reusing the template, a low-cost and high-throughput
process in micro- and nanofabrication is provided that is useful for
electronics, plasmonics, and nanophotonics