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Introduction

By combining uniquely structured plasmonic metals with stable metal oxides, hot electrons

can be harvested to drive difficult chemical reactions.1 Silver nanowires were used as light

absorbers because of their unique morphology, yielding broader light absorption. Nanowires

with unique structures were made that absorb light in the visible spectrum. With the ability to

create silver nanowires in different morphologies, we hope to find that the plasmonic effect is

amplified due to increased surface area of the nanowires. This could result in a plasmonic

device with increased efficiency for solar to fuel applications.

Motivation

Synthesis Part 1

Nanopores were formed on aluminum

stubstrate with the following process:

• Oxalic acid anodization

• Chromic acid etch

• Oxalic acid anodization

• Phosphoric acic anodization

• Widened in phosphoric acid

for 45 minutes.

Synthesis Part 2

The alumina template was then etched away

using 5 weight percent phosphoric acid

solution for 45 minutes to leave the nanowires

and silica template.

Nanowire Fabrication Results

Alumina Removal Results

Conclusions

Acknowledgements and References

• Refine nanostructure to achieve helices

• Remove silica template

• Increase inter-pore distances

• Create contacts and find a suitable catalyst for device

completion

• Experiment with other metals such as palladium,

copper, cobalt, or nickel

As we try to incorporate more renewable energy sources, the net load on non-renewable

sources will decrease. Renewable sources cannot supply enough energy to match the

flexibility demanded by the grid. A sustainable solution to this problem is to store solar energy

as chemical fuel. A realistic device must be efficient, scalable, and inexpensive, which is a

combination not yet achieved. Plasmonic devices could meet this criteria given their long

lifetime, scalable processing methods, and potential for efficiency improvements.

Plasmonically Active Silver Nanowire

Structures for Energy Storage ApplicationsCarina Hahn1, Dayton Horvath2, Kathleen Pacpaco2, Martin Moskovits2, Galen Stucky2

1Department of Materials Science and Engineering, University of Utah2Department of Chemistry and Biochemistry, University of California, Santa Barbara

1. S. Mubeen, et al., “An autonomous photosynthetic device in which all charge

carriers derive from surface plasmons,” Nature Nanotechnology, 8, 247-251 (2013).

To form the nanowires, silica–surfactant composite mesostructures were formed inside

cylindrical anodic alumina nanopores. The silica mesostructures were then used to synthesize

the unique silver nanowires using AC electrodeposition.

Spin coated silica-surfactant contained tetraethyl

orthosilicate, ethanol, P123 block copolymer and

water with a pH of 2.

The surfactant was left to age for 24 hours and

then heat treated at 500 oC for one hour.

Silver was AC electrodeposited at 28.28 V for

10 minutes using a nitrate based silver solution.

This schematic to the right shows a completed device

using a gold nanorod. In combination with platinum

nanoparticles, a TiO2 cap, and CO-OEC deposited on the

lower portion, this device is able to split water.1

SEM results before alumina removal revealed that a unique nanowire structure was formed.

The structure resembles stacked rings. The images also show that the pores were fully filled

from the electrodeposition of silver.

Absorbance results from UV/VIS spectroscopy revealed absorption in the visible region. The

absorbance starts dropping around 550 nm.

SEM results after the phosphoric acid etch revealed that the alumina was removed. The silica

template and silver nanowire structures were left undisturbed.

Through re-emitted photons,

localized surface plasmons

can decay radiatively.

Through the excitation of hot

electrons, localized surface

plasmons can decay non-

radiatively.

In the coming year, new energy storage technologies will be needed to meet the demand for

power at the peak ramp-up time between 4 pm and 8 pm.

This research was partially supported by the RISE internship

program through the UCSB Materials Research Laboratory Award

No. DMR -1121053.

Scanning electron microscopy (SEM) results of the porous anodic alumina showed highly

ordered pores. The pore diameters were around 65 nm, and varied depending on how long the

pores were widened in the phosphoric acid.

Top view of filled pores shows unique layered

ring structures. Side view of a unique structure.

Cross section of pores revealed

ordered structures of stacked rings.

Cross sections of a piece of a broken

alumina layer show a thickness of

approximately one micron and removal

of the barrier layer. The unfilled pores

extend all the way through the layer of

alumina.

• Pore diameters around 65 nm created a structure of

stacked rings.

• Absorption spectra shows absorbance in the visible

spectrum.

• Alumina removal left just the nanowires

• Results indicate increased surface area, which may

lead to an amplified plasmonic effect

Results agree with what is expected in previously

published work for 60 nm pore diameters.4 Around 60

nm, a stacked ring or helical structure may be observed.

The structures in this diagram to the right resemble

what was seen from SEM results.

Future Directions

4

1

2

3

In some samples, the barrier layer underneath

the pores was removed using a step-down

voltage method.

Radiative decay Non-radiative decay

0.4

0.8

1.2

1.6

300 500 700 900 1100

Ab

sorb

ance

(A

u)

Wavelength (nm)

65 nm

2. C. Clavero, “Plasmon-induced hot-electron generation at nanoparticle/metal-oxide

interfaces for photovoltaic and photocatalytic devices,” Nature Photonics, 8, 95-103 (2014).

3. J. Ferrari, M. Backman, “Managing future grid dynamics: an example from California,” Wartsila Tech 2013.

4. Y. Wu et al., “Composite mesostructures by nano-confinement,” Nature Materials, 3, 816-822, (2004).

65 nm

To prepare the nanowires for ultraviolet–visible spectroscopy (UV/VIS) the samples were

encased in polydimethylsiloxane. The alumina was then dissolved using a solution of copper

(II) chloride hydrate and hydochloric acid.