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223 Pages·2015·6.41 MB·English

by  Ali Altun

ETH Library
Multiscale Plasmonics for Energy
and Environment
Doctoral Thesis
Author(s):
Altun, Ali Ö.
Publication date:
2015
Permanent link:
https://doi.org/10.3929/ethz-a-010553970
Rights / license:
In Copyright - Non-Commercial Use Permitted
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Multiscale Plasmonics for Energy
and Environment

A dissertation submitted to attain the degree of
DOCTOR OF SCIENCES of ETH ZURICH
Dissertation number: 23026

presented by
ALI ÖZHAN ALTUN
M. Sc. Mechanical Engineering,
Korea Advanced Institute of Science and Technology
(KAIST), Daejeon
Born on May 5th 1981, citizen of Turkey

accepted on the recommendation of
Prof. Dr. Hyung Gyu Park, examiner
Prof. Dr. David J. Norris, co-examiner
Dr. Tiziana C. Bond, co-examiner

Zurich, 2015
Copyright © Ali Özhan Altun, Zurich 2015
i

Acknowledgements
First of all, I would like to thank Prof. Dr. Hyung Gyu Park for
giving me the opportunity to work under his supervision, I really
appreciate the free research environment he provided in his
group. I am also grateful to him for his constant support,
encouragement and many life lessons he taught to me.
I would like to express my sincere gratitude to Dr. Tiziana Bond
for her warm hosting, enlightening suggestions and guidance
during my two-years-long stay in Lawrence Livermore National
Laboratory (LLNL).
I would like to extend my gratitude to:
Dr. Emanuela Felley-Bosco, for her collaboration in preparation
of microRNA solutions as well as the qPCR detection.
Dr. Wouter Pronk for his comments and discussions on
micropollutant detection.
Dr. Seul Ki Youn and Ning Yang for their support in CNT growth.
And the experienced personnel of the cleanroom in BRNC as well
as LLNL for their valuable support in realizing the experiments.
Furthermore, my sincere thanks to the past and present
members of NETS group, Jakob Buchheim, Amir Droudian,
Mengmeng Deng, Roman Wyss, Meng Li, Lokesh Mahesh, Karl-
Philipp Schlichting, Dr. Kemal Celebi, Dr. Jeongwon Choi,
Eunjeong Gross, Ji Hyun Lee for their helpful comments, helps
as well as the positive working environment that they provided.
Without the patience and the support of my wife and our families,
probably I would not have been able to complete this thesis.
Thank you very much. I love you all.

iii

Abstract
Plasmonics is one of the cutting-edge fields of science to which
nanotechnology has been making an evident contribution.
Discovery of an interaction of collective oscillations of electrons
on a metal surface with electromagnetic radiation has opened up
new perspectives in a variety of areas where the outcome of the
interaction, such as electromagnetic field enhancement, acts
importantly. Two representative fields which benefit from strong
field enhancement are surface enhanced Raman spectroscopy
(SERS) and broadband light absorption. The light absorption
and the SERS enhancement are correlated in theory with the
second and fourth powers of the electric-field enhancement,
respectively. Therefore, a plasmonic platform that could embody
strong field enhancements has been of great demand in both
areas.
The field of plasmonics has seen a fascinating progress in the last
two decades. The advent of nanomanufacturing technologies as
well as the development of strong computational techniques has
enabled the engineering of complex plasmonic architectures.
Numerous studies have unveiled the mechanism of surface-
plasmon mediated field enhancement and the effects of geometry,
material and dielectric environment. In spite of the level of
physical understanding, active commercialization of the
plasmonic substrates has not been realized. The challenges lie in
the fabrication of low-cost and high-performance substrates. The
main goal of this Ph.D. thesis is to design and manufacture such
plasmonic substrates to bring the field closer to real-world
applications.
Our main strategy to accomplish this task is to avoid expensive
nanolithographic techniques. Therefore, we would not design a
structure composed of a periodic array of a well-defined
nanometer-scale geometry. Conversely, we make use of the
random geometries. Randomness in plasmonic structure does
not only reduce the cost, but also broadens the resonance
bandwidth effectively. Obviously, the broadband resonance is
necessary for the light absorption purposes. SERS also benefits
from the broad resonance bandwidth because it can effectively
enhance both incident and scattered fields.
It should be noted that the broadband absorption phenomenon
can stem from several factors. Overlapping multiple resonances
can lead to a broad, single resonance peak. Similarly, non-
resonant coupling of light to geometric singularities does not
depend significantly on the excitation frequency. Regardless of
the mechanism, we name such substrates showing the
broadband light interaction as non-resonant. For either of the
applications, we design and fabricate non-resonant substrates.
In this thesis, femtomolar sensitivity is demonstrated using a
non-resonant SERS substrate. The SERS substrate is a composite
structure built at the top of a forest of vertically aligned carbon
nanotubes (VA-CNT) by coating individual CNTs with a few-nm-
thick dielectric material conformally and then depositing a few
nanometers of metal at the canopy of the forest. The resultant
useful structure is a canopy of densely intertwined nanowires
(NW). The intermediate dielectric layer has a critical role in
accomplishing great chemical-detection sensitivity because it
helps eliminate possible surface plasmon quenching by CNTs. It
is this sensitive SERS substrate that allows potential sensor
applications of SERS in two areas: environmental monitoring
and biodetection.
Using the substrate out of concentric metal-dielectric-CNT
nanowires, we detect characteristic micropollutants found in
freshwater resources: e.g., Ibuprofen (Ibu) and Benzotriazole
(BTAH). The femtomolar detection sensitivity is once again
demonstrated for BTAH having a strong affinity to the NW metal
surface. We can also achieve picomolar detection of the weakly
binding Ibu if adopting a proper surface-functionalization
v

technique. We draw a relation of the binding-energy-dependent
surface adsorption of molecules with concentration-dependent
SERS signal. In addition, the multiplex detection capability of
SERS is discussed.
The second application of our SERS substrate is the biological
detection. We can detect microRNAs as low as subfemtomolar in
concentration. This biodetection part of the SERS performance
investigation begins with comparing synthetic microRNA with
ones extracted from a human blood sample. The selectivity of
SERS on three different solutions comprising distinct blends of
microRNAs is then determined. We show that both SERS and the
state-of-the-art RT-qPCR methods achieve similar sensitivities.
Immediacy in biodetection is a key feature of SERS, which bears
great potential in clinic applications.
Following, we provide a mechanistic understanding of field
enhancement of our SERS substrate based on a simplified model:
a NW dimer. By use of the finite element method, we find out
multiple resonant and non-resonant enhancement modes that
our SERS substrate poses. Enormous field enhancement can take
place for “kissing nanowire” configurations in which one of the
NWs is obliquely oriented against a horizontal one.
For the broadband light absorption, we design a novel
architecture that places a nanoporous-spacer in between random
islands of plasmonic absorber atop a perfect reflector. The
nanoporous spacer is formed by using a block copolymer (BCP)
self-assembly technique. Here again, based on the mechanistic
understanding and prediction, the tunability and angular
dependence of an absorption spectrum is verified experimentally.
Finally, we demonstrate the nanoporous polymer film coated on
a flat metal surface. This porosity design is achieved by use of
energetic ion beams through pores of a BCP etch mask. By
producing an ultradense array (50 nm in pitch) of metallic
nanopores over a 10-cm-diameter wafer via simple minimization
of the roughness of the underlying metal thin film, this technique
embodies the concept of manufacturing over many length scales.
Zusammenfassung
Plasmonik ist eines der cutting-edge Forschungsgebiete zu dem
Nanotechnologie spürbare Beiträge geleistet hat. Die
Entdeckung der Interaktion zwischen kollektiver Oszillation von
Elektronen auf einer Metalloberfläche und elektromagnetischer
Strahlung hat neue Möglichkeiten in einer Vielzahl von Gebieten,
in denen der Einfluss dieser Interaktion, wie zum Beispiel
elektromagnetische Feldverstärkung, von Bedeutung ist, eröffnet.
Zwei repräsentative Gebiete, die von dieser starken
Feldverstärkung profitieren, sind oberflächenverstärkte
Ramanspektroskopie (SERS) und Breitbandlichtabsorption. Die
Lichtabsorption und die SERS-Verbesserung sind theoretisch
jeweils durch die zweite und vierte Potenz der elektrischen
Feldverstärkung miteinander korreliert. Daher war eine
plasmonische Basis, welche starke Feldverstärkung bereitstellen
kann, in beiden Gebieten besonders nachgefragt.
Das Gebiet der Plasmonik durchlief faszinierenden Fortschritt in
den letzten zwei Jahrzehnten. Der Beginn von sowohl
Nanofabrikationstechnologien als auch die Entwicklung von
starken rechnergestützen Techniken ermöglichten die
Entwicklung von komplexen plasmonischen Strukturen.
Verschiedene Studien haben den Mechanismus der
Feldverstärkung durch Oberflächenplasmonen und die Einflüsse
von Geometrie, Material, und dielektrischer Umgebung enthüllt.
Trotz dem Niveau des physikalischen Verständnisses ist es noch
nicht gelungen plasmonische Substrate zu kommerzialisieren.
Die Herausforderungen liegen bei der Herstellung preisgünstiger
und leistungsfähiger Substrate. Das Ziel dieser Dissertation ist es
solche plasmonischen Substrate zu entwickeln und zu fertigen,
vii

um dieses Forschungsgebiet näher in Richtung kommerzieller
Anwendungen zu führen.
Die Hauptstrategie um diese Aufgabe zu erfüllen ist es teure
Nanolithographietechnik zu vermeiden. Daher wird keine
periodische Struktur mit genau definierter, nanometergrosser
Geometrie entwickelt. Stattdessen werden zufällig entstehende
Geometrien strategisch genutzt. Zufälligkeit in plasmonischen
Strukturen verringert nicht nur die Kosten, es verbreitet die
Resonanzbandbreite auch effektiv. Dieses verbreiterte
Resonanzband ist offensichtlich notwendig für
Breitbandlichtabsorption. SERS profitiert ebenfalls von einem
verbreiterten Resonanzband, weil es sowohl das eintreffende als
auch das gestreute Feld effektiv verstärken kann.
Das Phänomen der Breitbandabsorption kann von
verschiedenen Faktoren herrühren. Überlappen von
verschiedenen Resonanzfrequenzen kann zu einem breiten,
einzelnen Resonanzmaximum führen. Ebenso hängt
nichtresonante Lichtkopplung an geometrischen Singularitäten
nur schwach von der Anregungsfrequenz ab. Wir entwickeln und
fertigen nichtresonante Substrate für beide Anwendungen.
In dieser Dissertation wird femtomolare Sensitivität durch ein
nichtresonantes SERS-Substrat demonstriert. Das SERS-
Substrat ist eine Verbundstruktur, welche auf der Oberfläche
eines Waldes aus vertikal ausgerichteten
Kohlenstoffnanoröhrchen (VA-CNT) hergestellt wird indem das
Baumkronendach der individuellen Kohlenstffnanoröhrchen
konform mit einer weniger Nanometer dicken Schicht
dielektrischen Materials und anschliessend einer wenigen
Nanometer dicken Schicht Metall beschichtet wird. Die daraus
entstehende nützliche Struktur ist ein Baumkronendach aus eng
verwobenen Nanodrähten (NW). Die zwischengelagerte
dielektrische Schicht ist besonders wichtig um hohe chemische
Detektionssensitivität zu erreichen, da sie hilft mögliche
Oberflachenplasmonenlöschung durch die CNTs zu