Surface plasmon polaritons along metal surfaces with novel structures

156 Pages·2015·8.91 MB·English

Surface plasmon polaritons along metal
surfaces with novel structures
Author: Fan Ye
Persistent link: http://hdl.handle.net/2345/bc-ir:103747
This work is posted on eScholarship@BC,
Boston College University Libraries.
Boston College Electronic Thesis or Dissertation, 2014
Copyright is held by the author, with all rights reserved, unless otherwise noted.
Boston College
The Graduate School of Arts and Sciences
Department of Physics

SURFACE PLASMON POLARITONS ALONG
METAL SURFACES WITH NOVEL STRUCTURES

a dissertation by
FAN YE

submitted in partial fulfillment of the requirements
for the degree of
Doctor of Philosophy

April 2014
© Copyright by FAN YE
2014
Abstract
Surface plasmon polaritons (SPPs) are hybridized quasiparticles of photons and electron
density waves. They are confined to propagate along metal-dielectric interfaces, and
decay exponentially along the direction perpendicular to the interfaces. In the past two
decades, SPPs have drawn intensive attention and undergone rapid development due to
their potential for application in a vast range of fields, including but not limited to
subwavelength imaging, biochemical/biomedical sensing, enhanced light trapping for
solar cells, and plasmonic logic gates. These applications utilize the following intrinsic
properties of SPPs: (1) the wavelength of SPPs is shorter (and can be much shorter) than
that of free photons with the same frequency; (2) the local electric field intensity
associated with SPPs can be orders of magnitude larger than that of free photons; and (3)
SPPs are bound to metal surfaces, and are thus easily modulated by the geometry of those
surfaces. Here, we present studies on SPPs along metal surfaces with novel structures,
including the following: (1) SPP standing waves formed along circular metal surfaces
that lead to a “plasmonic halo” effect; (2) directional reflectionless conversion between
free photons and SPPs in asymmetric metal-insulator-metal arrays; and (3) broadband
absorbance enhancement of embedded metallic nanopatterns in a photovoltaic absorber
layer. These works may prove useful for new schemes for SPP generation, plasmon-
photon modulation, ultrasensitive dielectric/bio sensing, and high efficiency thin film
solar cells.
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Acknowledgement
The research that we present in this thesis would not have been possible without the
financial support from the W. M. Keck Foundation.
It has been the most fruitful and exciting 6 years in my life. I would like to thank
everyone who has companied and supported me along the way. There are so many names
on my “Thank You” list that there is no hope of finishing, but here we go.
First, my gratitude goes to my tutor, Prof. M. J. Naughton, without whose enthusiasm in
science, wealth of experience, unending stream of advices, and remarkable intuition,
none of these would have been possible. I am particularly grateful to Prof. Naughton for
his sincere devotion to supporting students, in lab, in publications, and in the world
beyond research. I still remember Prof. Naughton’s explanation of the word “research” to
me: “Research is a process of ‘re’ ‘searching’, you got to be patient enough.”
I would also like to thank my committee members, Prof. K. Kempa, Prof. W. J. Padilla,
and Dr. M. J. Burns for beneficial discussions, insightful suggestions, generous supports
in many aspects and friendly personal interactions during the past couple of years. I
would especially like to thank Dr. Burns for his numerous helps in simulation and
experimental techniques, as well as in my everyday life.
I would like to thank all of my course teachers here at Boston College, including Prof. P.
Bakshi, Prof. B. Di Bartolo, Prof. V. Madhavan, Prof. D. Broido, Prof. J. Engelbrecht,
Prof. Z. Wang, Prof. S. Wilson, Prof. K. Kempa and Prof. Y. Ran. I would especially like
to thank Prof. L. Dal Negro at Boston University for his guidance in the course “Guided-
wave Optoelectronics”, and Prof. K. Kempa for his course named “Foundations of
Plasmonics.” They guided me into the fields of photonics and plasmonics. I would also
like to thank Prof. Andrzej Herczynski for recommending me to the Donald J. White
Teaching Excellence Awards.
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I would like to thank all the group members in the Naughton Group that I have the
privilege to work with. I would like to do this in a chronological order. I started my
experimental training under the guidance of Dr. J. I. Oh, who was strict and patient
enough to explain everything to me. I have been working closely with Dr. P. Dhakal, Dr.
Tim Kirkpatrick, Binod Rizal, Jeff Naughton, and Dr. Juan M. Merlo. I would also like to
thank the helpful interactions with Aaron Rose, Chaobin Yang, Yitzi Calm, Nathan
Nesbitt and Luke D’Imperio. I owe my special thanks to Svet Simidjiysky, who has been
helping me constantly on machining.
I could have accomplished nothing without the effort of the technicians in the Integrated
Sciences Cleanroom and Nanofabrication Facility (ISCNF) in Boston College. I am
particularly grateful to Steve Shepard for his tremendous help with my device fabrication
and characterization, and his training on countless machines for me. I also owe my
gratitude to Dr. Gregory McMahon, who patiently trained me on the FIB system. I would
also like to thank Dr. Dezhi Wang for his training of the SEM and TEM systems for me.
I would like to go on thanking all the peoples who have particularly contributed my
happiness during my time here: Yi Zhang, Dr. Kevin Lukas (and his family), Dr.
Yuanming Lu, Dr. Yu Dai, Dr. Xianliang Liu (and his wife), Dr. Wen-Chen Chen (and
his wife), Dr. Steve Disseler (and his wife), Wenwen Zhou, Hang Chen, Chetan Dhital,
Muna Aryal, Zhensong Ren, Tianyi Sun (and his wife), Hua Li, James Stokes, Daniel
Walkup, Bing Ye (and his wife), Bolun Chen (and his wife), Claire Watts, Mengliang
Yao, Xinyu Liu, Kun Jiang, Shenghan Jiang, Dr. Yun Peng (and her husband), Michelle
M. Archibald and more, while I feel it would never come to an end.
Lastly I thank my parents and family for their encouragement, help and love during my
PhD and throughout my life. In particular, I’d like to thank my wife Xueyuan (Shirley)
Wu for believing in me and supporting me without fail, and for her beneficial and
insightful discussions with me in a broad range of topics in physics. She once told me
that: “Being your wife makes me a better woman.” I would like to say the same thing to
her: “Being your husband makes me a better man.”
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Table of Contents
Acknowledgement ...............................................................................................................i
Table of Contents ............................................................................................................. iii
List of Figures ..................................................................................................................... v
I. Introduction .................................................................................................................... 1
1.1 Brief introduction to surface plasmon polaritons (SPPs) ..................................... 1
1.2 Brief introduction to relevant fabrication techniques ........................................... 2
1.3 Relevant measurement techniques ....................................................................... 5
1.4 Organization of this thesis .................................................................................. 12
II. SPPs on confined 2D metal surfaces ......................................................................... 13
2.1 Excitation schemes of SPPs ............................................................................... 13
2.2 SPP cavity modes along confined circular metal surfaces: the SPP drumhead
modes ........................................................................................................................ 21
2.3 Modulation of transmission by SPP drumhead modes: the plasmonic halo
effect ......................................................................................................................... 25
2.4 SPP cavity modes along metal surfaces with other configurations: the reverse
halos .......................................................................................................................... 37
2.5 Conclusions and future directions ...................................................................... 41
2.6 Supplementary information ................................................................................ 44
III. Reflectionless directional visible SPP coupling along symmetry broken
metasurfaces ..................................................................................................................... 47
3.1 Gradient index metasurfaces for reflectionless directional SPP coupling.......... 47
3.2 Reflectance characterization of a micro-scaled sample under normal
incidence ................................................................................................................... 48
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3.3 Localized mode analysis ..................................................................................... 51
3.4 Broken inversion symmetry and propagating modes ......................................... 54
3.5 Interactions between propagating and localized modes ..................................... 56
3.6 Experimental verification of reflectionless directional SPP generation ............. 66
3.7 Discussions and conclusions .............................................................................. 67
3.8 Supplementary information ................................................................................ 70
IV. SPPs on metal nanopatterns embedded in photovoltaic (PV) absorbers ............. 83
4.1 Embedded metal nanopatterns (EMN) for enhancing optical absorption .......... 83
4.2 Absorption enhancement by EMN scheme in various PV absorbers ................. 96
4.3 An impedance matching model to understand the absorption enhancement of
EMN ....................................................................................................................... 101
4.4 Conclusions and future directions .................................................................... 105
V. Summary .................................................................................................................... 106
Appendix I. SPPs along aluminum (Al) nanowires..................................................... 107
AI.1 Fabrication of Al nanowires with various cross sections by stress induced
methods .................................................................................................................. 107
AI.2 SPPs along Al nanowires with crescent-shaped cross sections...................... 117
AI.3 Conclusions and future directions .................................................................. 122
Appendix II. Fabrication of nanocoax via focused ion beam..................................... 123
Bibliography ................................................................................................................... 132
List of Publications ........................................................................................................ 140

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List of Figures
1.1 Apparatus for measuring 0th order reflectance and transmittance ................................. 6
2.1 Schematic dispersion relations of surface plasmon polaritons (SPPs) ........................ 14
2.2 Schematic diagrams illustrating optical excitation schemes for SPPs ......................... 15
2.3 Schematics of the fabrication process of the step-gap structure for SPP coupling ...... 19
2.4 Structural properties of the step-gap plasmonic circular cavity ................................... 22
2.5 Calculated and measured SPP drumhead modes ......................................................... 24
2.6 Cross-section views of E field profiles under x-polarized bottom illumination .......... 26
2.7 The plasmonic halo effect ............................................................................................ 29
2.8 Modulation of transmission by surface plasmon drumhead modes ............................. 31
2.9 Transmission spectrum of a halogen lamb through a blank ITO-glass substrate ........ 32
2.10 Measured and simulated vertical transmission suppression bands ............................ 35
2.11 Transmission spectrum map of circular cavities fabricated on a PMMA film with
tuned thickness and radius ................................................................................................. 36
2.12 Comparison between the “plasmonic halo” effect and the “reverse halo” effect ...... 38
2.13 2D axial symmetric simulation for reverse halo effect .............................................. 40
2.14 Simulations revealing the physical origin of the “reverse halo” effect ..................... 42
2.15 AFM scan of an area between two circular holes ...................................................... 45
2.16 Electric field profiles under inclined incident ............................................................ 46
3.1 A modified reflectance measurement scheme for small samples at small-angle
incidence ............................................................................................................................ 50
3.2 Reflectance measurement of a symmetric single-element MIM array with tuning
maximum-incident-angle ................................................................................................... 53
v