Development of nanosphere lithography and its applications 1

DEVELOPMENT OF NANOSPHERE LITHOGRAPHY AND ITS
APPLICATIONS





WANG BENZHONG
(B.Sc, M. Eng., Jinlin Univ)



A THESIS SUBMITTED
FOR THE DEGREE OF DOCTOR OF PHILOSOPHY


DEPARTMENT OF ELECTRICAL AND COMPUTER ENGINEERING
NATIONAL UNIVERSITY OF SINGAPORE
2014




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Acknowledgments

I would like to express my gratitude to all of those who have
helped and inspired me during my doctoral study. My utmost thanks
go to my advisor, Prof. Chua Soo Jin for his patient guidance and
constant encouragement in my research and study. His exceptional
intuition in physics and material science and persistent desire for high
quality research has motivated all his advisees, including me.
I would like to thank Dr. Soh Chew Beng, Dr. Zang Keran, Mr.
Rayson Tan Jen Ngee, Dr. Dong Jianrong, and Mr. Eng Cher Sing, for
their helpful discussions and assistance in MOCVD growth.
I would like to thank Dr Teng Jinghua, Dr. Han Mingyong, Lau
Jun Yong, Teo Siew Lang, Yong Anna Marie, Chew Ah Bian, Dr. Liu
Hong, Dr. Liu Yanjun. Dr. Ke Lin, and Ang Soo Seng, for their
assistance in fabrication processes and materials characterizations.
They are my colleagues in the Institute of Materials Research and
Engineering.
I would like to thank Mr. Tan Beng Hwee and Ms. Musni bte
Hussain for their assistance in the use of facilities in the Centre for
Optoelectronics, Department of Electrical and Computer Engineering,
NUS.
Special thanks go to Gao Hongwei for the help in many aspects.

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Table of Contents
Acknowledgments
Table of Contents
Abstract
List of Tables
List of Figures
Abbreviations

Publications
Chapter 1 Introduction
1.1 Introduction
1.2 Review of nanofabrication technologies
1.2.1 Lithography with Photons
1.2.2 Lithography with Particles
1.2.3 Nanoimprinting
1.3 Nanosphere lithography
1.4 Motivation and objectives
1.5 Scope of thesis
Reference
Chapter 2 Development of nanosphere lithography
2.1 Introduction
2.2 Self-assembly of colloidal crystals
2.2.1 Introduction
2.2.2 Controls of self-assembled colloidal crystals
2.2.2.1 Self-assembly of a monolayer
2.2.2.2 Self-assembly of a bilayer
2.2.2.3 Selective self-assembly
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2.3 Applications of colloidal crystal as templates
2.3.1 Introduction
2.3.2 Ordered spherical nanocavities
2.3.3 Creating nanostructures with multi-features in one step
2.3.4 Shape engineering of nanostructures
2.3.4.1 Shape control through multi-cycle etching (MCE)
2.3.4.2 Shape control through 3D mask (3DM)
2.3.4.3 Shape control through dry etching mechanism
2.4 Summary
Reference
Chapter 3 Nanosphere lithography applied to nano-
growth of III-V compounds
3.1 Introduction
3.2 Basics of MOCVD

3.3 GaN film grown on an array of Si (111) nanopillars
3.3.1 Introduction
3.3.2 Experiments
3.3.3 Results and discussion
3.4 Dual-sized (In)GaAs/GaAs nanobars grown by one
step MOCVD
3.4.1 Introduction
3.4.2 Experiments
3.4.3 Results and discussion
3.4 Summary
Reference
Chapter 4 Nanosphere lithography applied to
formation of metal nanostructures
4.1 Introduction
4.2 Fabrication and characterization of metal
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nanostructures
4.2.1 Quasi-ordered 2D Au nanostructures with holes
4.2.1.1 Introduction
4.2.1.2 Experiments
4.2.1.3 Results and discussion
4.2.2 3D Au nanostructures formed by a 2D array of
nanospheres
4.2.2.1 Introduction
4.2.2.2 Experiments
4.2.2.3 Results and discussion
4.2.3 Ag nanoparticle superlattices formed by template
guided annealing
4.2.3.1 Introduction
4.2.3.2 Experiments
4.2.3.3 Results and discussion
4.3 Summary
Reference

Chapter 5 Nanosphere lithography applied to
LEDs for light extraction
5.1 Introduction
5.2 Effects of ordered surface nanostructures on LEDs
5.2.1 GaAs based red LEDs
5.2.1.1 Experiments
5.2.1.2 Results and discussion
5.2.2 GaN based blue LEDs
5.2.2.1 Experiments
5.2.2.2 Results and discussion
5.3 Effects of ordered surface Au nanostructures on
LEDs
5.3.1 Experiments
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5.3.2 Results and discussion
5.4 Summary
Reference
Chapter 6 Summary and future plan
6.1 Summary
6.2 Future plan

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Abstract
Nanosphere lithography (NSL) has been recognized as an inexpensive,
high throughput and flexible technology to fabricate nanostructures used in
many fields. However, the weaknesses of this technology limit its widespread
applications. For example, a single layer of nanospheres is difficult to obtain
in a large area due to the nature of self-assembly; only limited shapes and
arrangements of nanostructures are obtained due to the nature of spherical
particles and its 2D hexagonal arrangement. Here, I provide my solutions to
overcome these weaknesses and widen its applications into the nano-growth of
semiconductor, nano-formation of metals and in light extraction of light
emitting diodes.
This thesis addresses two aspects of work viz. forming the nanostructures
which could also be used as template and applying them to enhance the

intensity and tailor the luminescence spectrum of semiconductors. In forming
the nanostructures, the main considerations are:
i) Position control of the nanosphere arrays. A simple and efficient
method, combining photolithography and the self-assembly
characteristics, has been devised to control an entire area filled with
either single or double layer on an area as large as 400 µm
2
to match
the standard size of a LED. In addition, the nanosphere arrays can be
formed at specified areas of the substrates by modifying the surface
properties.
ii) Shape engineering of the nanostructures created through the
nanospheres. A multi-step-etch technique has been invented to control
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the vertical profiles of the created nanostructures. A 3D SiO
2
network
formed through a bilayer of polymer nanospheres acting as a mask is
demonstrated to fabricate various 2D and 3D surface nanostructures.
Three applications of the nanostructures created through NSL are
described. They are: i) Fabrication of an ordered array of InGaAs/GaAs
nanobars using the SiO
2
template created by the one-step-NSL technique.
They are grown on the selected regions of a GaAs substrate by MOCVD.
Ordered arrays of InGaAs/GaAs nanobars with two-sized features are obtained
by a one-step MOCVD growth. In addition, GaN films have been successfully
grown on a nanopillar array created by NSL on a Si (111) substrate. Strong
enhancement (7 times) of PL intensity has been observed from the GaN film. I

have also demonstrated that surface energies play a main role in the initial
growth stages on top of the nanopillars. ii) Formation of 3D Au
nanostructures on the template created through the multi-cycle-etching
technique. A honeycomb of holes in SiO
2
template created through NSL and
combined with thermal annealing, enables Ag nanoparticles to be formed on a
Si substrate. Surface energy and the boundary formed by the SiO
2
template
play a main role in forming the well arranged Ag nanoparticles as deduced
from temperature annealing studies. These metal nanostructures show unique
surface plasmon properties. iii) Enhancement of light extraction in LEDs
through NSL. An increase in the output power by 2.4 times and 1.9 times is
obtained for the red and blue LEDs, respectively. Strong enhancement of
output power is also observed for the red LEDs with a thin Au honeycomb
nanostructure created through NSL.

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List of Tables

Chapter 2
Table 2.1 Etching duration for PS spheres vs. opening sizes of the
nanostructures created onto the SiO
2
film.

Table 2.2 Etching conditions for the wafers of wafer A, B and C.

Chapter 3
Table 3.1 Growth parameters for the wafer of the Si nanopillar and flat Si
substrate, which was started from AlN growth.



















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List of Figures

Chapter 1

Fig. 1.1 Quantum effects of matter.

Fig. 1.2 Basic outline of optical lithography processes. The diagram shows
the optical radiation entering the system, which is then filtered by the
chromium mask. The image is then projected on to the resist, and any non-
exposed material is removed during developing.

Fig. 1.3 Basic electron optical column in which the beam is formed. The
image is formed on the resist, and the deflectors control the position of the
beam on the resist.

Fig.1.4 (a) Schematic of the originally proposed NIL process. (b) Scanning
electron microscopy (SEM) image of a fabricated mold with a 10 nm
diameter array. (c) SEM image of hole arrays imprinted in poly(methyl
methacrylate) by using such a mold [34].

Fig. 1.5 (a) side and (b) top-view of self-assembly of nanospheres
Fig. 1.6 Nanosphere lithography used to create various nanostructures

Fig. 1.7 Schematic illustration (a) and representative AFM image (b) of SL
PPA. The AFM image was captured from a SL PPA fabricated with D = 542
nm nanospheres and d
m
= 48 nm thermally evaporated Ag metal after
removing the nanospheres; Schematic illustration (c) and representative AFM
image (d) of DL PPA. The AFM image was captured from a SL PPA
fabricated with D = 400 nm nanospheres and d
m
= 30 nm thermally
evaporated Ag metal after removing the nanospheres [39]. (e) and (f) show

the definition of the parameters of D, a and d
ip
for single and double layer
arrangement, respectively.

Fig. 1.8 Schematic illustration (a) and representative AFM image (b) of
nanoring and SL PPA fabrication. The AFM image was captured from a
sample fabricated with D = 979 nm nanospheres and d
m
= 50 nm e-beam
deposited Ni metal after removing the nanospheres [39].

Fig. 1.9 Schematic of the angle resolved deposition process. (a) Samples
viewed at 0° (a), 30°, (b) and 45°, (c), respectively [46].

Chapter 2
Fig. 2.1 Schematic of the setup for the self-assembly of the nanospheres from
colloidal solution.

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Fig. 2.2 (a) Photograph and (b) SEM images of the monolayered PS spheres
of 2 μm diameter self-assembled on a Si substrate. (c) A SEM image of the
monolayered PS spheres of 400 nm diameter self-assembled on a Si substrate.

Fig. 2.3 (a) A cross-section viewed SEM image showing the bilayer arranged
PS spheres with 400 nm diameter. (b) A top viewed microscopy image
showing the distribution of the bilayer array (green color) and the single layer
(purple color) formed by the 400 nm spheres.

Fig. 2.4 Microscopic images (up panel) of different layered nanospheres
assembled on glass substrates (as indicated in bottom panel).

Fig. 2.5 (a) Schematic of the self-assembly within the wells. (b) Microscopic
image of the patterned Si substrate.

Fig. 2.6 Microscopic images of 300 nm diameter nanospheres self-assembled
in device-sized wells. (a) Monolayer formation at the conditions of
concentration, ~7 wt%, spin speed, 1900 rpm, (b) Monolayer formation at the
conditions of concentration, ~7 wt%, spin speed, 1800 rpm, (c) Bilayer
formation at the conditions of concentration, ~15 wt%, spin speed, 900 rpm.

Fig. 2.7 (a) Schematic illustration of the patterns created on a SiO
2
surface by
photolithography from top (up) and side views (bottom). (b) A SEM image of
the monolayer arrays of 300 nm PS spheres formed at a SiO
2
film with micro-
wells.

Fig. 2.8 (a) A SEM image of the 300 nm PS spheres selectively formed inside
a circular well created on a GaAs substrate. (b) A microscopic image of the
arrangement of the wells created by photolithography.

Fig. 2.9 (a) A microscopic images of the 400 nm spheres selectively formed
inside micro-wells created on hydrophobic polymer substrate by imprinting.
(b) The front form of the colloidal solution indicating the selection of the
self-assembly inside the micro-wells.

Fig 2.10 A schematic diagram of the procedure to make the ordered array of
nanocavities

Fig. 2.11 A cross-section view of a SEM image of the silica nanocavities.

Fig. 2.12 Top-view SEM images of the periodic ordered nanocavities. To
form the nanocavities the top of the silica film was etched down (a) 150 nm
and (b) 170 nm to expose the PS spheres.

Fig. 2.13 (a) Perspective view of the sample, where the silica was etched
below the horizontal diameter plane of the sphere at step g shown in Fig. 10.
(b) and (c) show line scan taken along the directions of mm’ and nn’ as
illustrated in (d). (d) Top view of AFM image for the same sample. (e)
Schematic illustrations of the evolution [cross-section views along mm’ and
nn’ direction, respectively, as shown in (d)] of the hexagonal close-packed
silica nanostructure arrays at different stages of etching.

Fig. 2.14 Schematic illustration of the principle to make nanoholes with two-
size features

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Fig. 2.15 The procedure for fabricating ordered SiO
2
nanostructures via dry
etching using two layers of PS nanospheres of ~300 nm in diameter. (a) A
side-view SEM image of the bilayered nanospheres on substrate coated with
SiO
2
of ~100 nm in thickness. Schematic top-views of the bilayered
nanospheres (b) before and (c) after O
2
RIE etching. (d) A top-view SEM
image and (e) A schematic side-view of the as-formed SiO
2
nanoholes after
further O

2
/CHF
3
RIE etching of the bilayered nanospheres and the SiO
2
films
underneath.

Fig. 2.16 (a) SEM image of the ordered arrays of nanoholes with two-size
features (before removing the PS spheres). (b) A tilted-view (~10
0
) of SEM
image of the nanoholes created on the thicker SiO
2
region (after removing the
PS spheres).

Fig. 2.17 SEM images of the nanoholes formed by a bilayer of PS spheres
with 600 nm diameter. Before etching the SiO
2
film and PS spheres, the PS
spheres were etched by O
2
RIE for (a) 75, (b) 115 and (c) 155s.

Fig. 2.18 Schematic illustration of the principle to make surface
nanostructures with different cross-section shapes.

Fig. 2.19 SEM images showing the nanostructures of (a) pillars, (b) candle-
like, and (c) and (d) bell-like, respectively, formed by the multi-cycle etching

technique.

Fig. 2.20 SEM images of the lens-like microstructures formed by the multi-
cycle etching technique. The number of repeat cycles was: (a) 6 for sample A,
(b) 9 for sample B, and (c) 12 for sample C.

Fig. 2.21 (a) Schematic illustration of the formation of 3D silica
nanostructures. (b) A simulation result of the 3D network formed by
bilayered PS spheres. (c) A SEM image of the 3D silica network formed by
bilayered PS spheres of 300 nm diameter obtained from experiments.

Fig. 2.22 Simulation results of the 3D networks formed by (a) two and (b)
three layers of PS spheres. The silica network is colored in red, green and
white, the black color represents the watched substrate. SEM images of the
3D silica networks formed by (c) two and (d) three layer of PS spheres with
300 nm diameter. (e) A top-view of SEM image showing the 2D nanoholes
created by the mask shown in (c). (f) A tilted-view of SEM image showing
the 2D nanoholes created by the mask shown in (d).

Fig. 2.23 Schematic illustration showing the formation of 3D silica
nanostructures at different dry etching stages (a)-(d). SEM images showing
the relative 3D nanostructures (e)-(h).

Fig. 2.24 SEM images showing the effects of O2 RIE for bilayered PS
spheres on the template. The bright spots show the top layer of PS spheres.
The etching duration is (a) 90s and (d) 140s. (b) and (e) show the templates
formed from (a) and (d). (c) and (f) show the surface structures created
through (b) and (e), respectively.

Fig. 2.25 A cross-section (a) and top (b) views of schematic illustration of the

template formed by bilayered nanospheres. (c) A top-view of schematic
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illustration of the simplified hexagonal structures to represent the circles
shown in (b). (d) A SEM image of the etched nanostructures by using a 3D
mask like that shown in (b). The dark areas are etched away.

Fig. 2.26 SEM images of the complex surface nanostructures. (a) and (b) are
obtained through different templates but the same dry etching duration. (a)
and (c) are obtained through the same templates but with different dry etching
duration. (d) is obtained through the same template of which the top layer
etched much more deeply than in (c).

Fig. 2.27 (a) Schematic showing the RIE process. (b) Schematic showing the
procedure for creating Si surface structures. (c) Schematic showing the define
of the structural parameters of the Si surface structures.

Fig. 2.28 (a) Cross-section of SEM images of the effects of diameter of
residual PS spheres on the Si nanostructures; (b) the structural parameters of

the Si surface structures created under different diameter of the spheres.

Fig. 2.29 (a) Cross-section of SEM images of the Si surface structures created
by etching under different chamber pressures. (b) The structural parameters
of the Si surface structures created under different chamber pressures. Cross-
section (c) and top (d) view SEM images showing the Si surface structures
created under longer etching duration at the chamber pressure of 120 mTorr.

Fig. 2.30 (a) Cross-section of SEM images showing the Si surface structures
created under different O
2
flow while the SF
6
is kept at 20 sccm. (b) The
structural parameters of the Si surface structures created under different O
2

flows. (c) The angle variation of the sidewall of the Si structures with the O
2

flow.

Fig.2.31 (a) Outline of the procedure for fabricating an array of SiO
2

nanodisks. (b) and (c) shows a tilted view and near cross-section view of the
SEM images of the SiO
2
nanodisks.

Chapter 3
Fig. 3.1 The typical diagram of MOCVD system.

Fig. 3.2 (a) GaN chemical reaction pathway consisting of upper (adduct) and
lower (decomposition) routes. (b) An diagram showing the kinematics
reaction process in MOCVD.
Fig. 3.3 (a) Schematic of the procedure for producing ordered Si nanopillars
on a Si (111) substrate. (b) A SEM image of the near side view of the Si
nanopillars with the PS spheres above them.

Fig. 3.4 Schematic diagram of the layers grown on (a) a Si nanopillared and
(b) a flat Si substrate. SEM images showing the cross-section view of the
GaN film grown on the (c) Si nanopillars formed on a Si (111) substrate, and
(d) a flat Si (111) substrate.

Fig. 3.5 High amplification of SEM image of the cross-section view of GaN
films grown (a) on a Si nanopillared substrate and (b) on a normal Si
substrate.
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Fig. 3.6 A top-view of SEM images of the GaN film grown (a) on the Si
nanopillars and (b) on the flat Si substrate.

Fig. 3.7 SEMs showing evolution of the III-N nanostructures grown at
different stages. (a) after AlGaN(80 nm)/AlN(40 nm)/Si layer growth, (b)
after GaN(100 nm)/AlGaN(80 nm)/AlN(40 nm)/Si layer growth, (c) after
GaN(200 nm)/AlGaN(80 nm)/AlN(40 nm)/Si layer growth, and (d) after
GaN(300 nm)/AlGaN(80 nm)/AlN(40 nm)/Si layer growth.

Fig. 3.8 (a) A SEM image of the cross-section of the 40 nm thick AlN growth
on the Si pillars and (b) A 80 nm AlGaN was grown on the AlN layer.

Fig. 3.9 Projection of the bulk basal plane of (111) silicon and the AlN cation
positions for the observed epitaxial growth orientation. Arrows indicate the
coincidence of the AlN atoms with silicon (111) atoms [49].

Fig. 3.10 A schematic of evolution of the III-nitride nanostructures with
growth stages.

Fig. 3.11 (a) Rocking curve of XRD of the GaN layer grown on the
nanopillar Si substrate (red), and normal flat Si substrate (black). (b) PL
spectra of the GaN film grown on the Si nanopillars (red), and a normal Si
substrate (black). (c) PL spectra of 3 InGaN/GaN quantum wells grown on
the GaN film grown on the Si nanopillars (red), and a normal Si substrate
(black).

Fig. 3.12 Epitaxial growth of ordered InGaAs/GaAs nanobars array in the
openings of SiO

2
-coated GaAs substrate. A schematic side-view (a) and a
top-view SEM image (b) of the ordered triangle openings on SiO
2
thin film as
template for selectively growing InGaAs/GaAs nanobars on substrate, which
are clearly revealed in a schematic side-view (c) and a top-view SEM image
(d).

Fig. 3.13 High-magnification views at 45
o
of the InGaAs/GaAs nanobars in
(a) perpendicular and (b) parallel directions.

Fig. 3.14 Site-selective growth of single-sized InGaAs/GaAs nanobars array
on SiO
2
-patterned substrates. (a) Schematic micropatterning on SiO
2
-coated
GaAs substrate. (b) Selective nanopatterning on the micropatterned SiO
2
thin
films using hcp nanospheres to form nanoopenings on the GaAs substrate. (c)
Selective growth of InGaAs/GaAs nanobars in the ordered microsized-wells.
(d) Low magnification and (e) high magnification SEM image of
GaAs/InGaAs nanobars arrays grown selectively in the SiO
2
nano-openings
on GaAs substrate by MOCVD.

Fig. 3.15 Site-selective growth of dual-sized InGaAs/GaAs nanobars array on
micropatterned GaAs substrate. (a) Selective nanopatterning of SiO
2

nanocavities as templates for (b) selective growth of semiconductor nanobars
with dual sizes. (c) A low magnification SEM image (top-view) of the dual-
sized InGaAs/GaAs nanobars grown selectively on the GaAs substrate by
MOCVD. High magnification SEM images (45
o
view) of the dual-sized
nanobars viewed from (d) parallel and (e) perpendicular directions of the bars.

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Chapter 4
Fig. 4.1Microscopic images of the arrangement of nanospheres at a diameter
of 600 nm. (a) Ordered nanospheres and (b) quasi-ordered nanospheres.

Fig. 4.2 Outline of the process for fabricating Au nanostructures. (a)-(d),

side-views of the steps for fabricating Au nanostructures. (e), a top-view of
the final Au nanostructures.

Fig. 4.3 SEM images of typical Au nanostructures created though a
monolayer of PS nanospheres with diameter of 500 nm which was reduced to
450 nm (a) and 400 nm (b).

Fig. 4.4 Transmission spectra of Au films at different thicknesses. (b), a plot
of the transmittance against thickness of the Au film.

Fig. 4.5 Transmittance spectrum of the 110 nm-thick Au film with nanohole
arrays created through 500 nm nanospheres. The r/a value of the Au
nanostructures varied from 0.35 (blue), 0.4 (red) to 0.45 nm (black). The
spectrum of the 110 nm-thick Au film without nanoholes is also presented
(dark yellow).

Fig. 4.6 Transmittance spectra of 110 nm-thick Au film with nanohole arrays
created through 400 nm (top), 500 nm (middle) and 600 nm (bottom)
nanospheres. For the etched wafer, r/a of the Au nanostructures was kept as
0.35 (blue), 0.4 (red) and 0.45 nm (black), respectively.

Fig.4.7 The calculated results of the periodicity of the nanostructures plotted
against the wavelength for the mode (1,0) (red), mode (1,1) (black) and
experimental results (blue).

Fig. 4.8 (a) Outline of the procedure of fabricating 3D nanostructures in a
two-step process by using a 2D nanosphere array. (b) A top-view of SEM
image showing the 3D Au nanostructures fabricated by the method. Diagram
shows the dimension of the Au nanostructures deposited on the template
formed (c) by one-cycle etching for sample S1 and (d) two-cycle-etching for

sample S2. The green dashed line represents original PS sphere with 600 nm
diameter, the blue dashed line represents the sphere on the first etching cycle
and the yellow dashed line represents the sphere on the second etching cycle.

Fig. 4.9 Schematic illustration of the 3D Au nanostructure viewed from side
for the wafers, (a) S2 formed by two-step etching and (c) S1, one-step etching.
(b) and (d) show tilted-view SEM images for the wafer of S2 and S1,
respectively.

Fig. 4.10 SEM images showing top-view of wafers formed by one-cycle
etching, where the radius of the cap was varied to be (a) W1:~561.6 nm, (b)
W2: ~495.8 nm, (c) W3: ~292.4 nm, and (d) W4:~205.4 nm. (e) Diagram
shows the Au nanostructures change from wafer W1 to W4.

Fig. 4.11 Transmission spectra of the wafer S1 (black) and S2 (red). The blue
line represents the wafer of 100 nm Au deposited on a flat substrate.

Fig. 4.12 Transmission spectra of the wafer W1 (black) and W2 (red), W3
(blue) and W4 (green).
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Fig. 4.13 Outline of the process for fabricating periodic ordered Ag
nanoparticles.

Fig. 4.14 (a) Schematic illustration of Ag growth with deposition. (b), (c) and
(d) show the SEM images of Ag deposited onto the SiO
2
patterned Si
substrate to a thickness of 10 nm, 20 nm, and 30 nm, respectively. (e), (f) and
(g) show the SEM images of Ag deposited on the bare Si substrate to a
thickness of 10 nm, 20 nm, and 30 nm, respectively.

Fig. 4.15 A tilted-view of SEM image showing the Ag islands formed on the
SiO
2
patterned Si substrate by depositing 10 nm Ag.

Fig. 4.16 SEM images showing the thermal-annealing results for the samples
with (a) and without (b) the SiO
2
patterns.

Fig. 4.17 Statistical distribution of the island size for the samples with (blue)
and without (black) the SiO
2
pattern, after being annealed at 700
0

C.

Fig. 4.18 Fast Fourier transform (FFT) image of 20 nm Ag deposited on the
Si substrate with (left) and without (right) the SiO
2
patterned after annealing
at 700
0
C for 30 min.

Fig. 4.19 A schematic model for the annealing mechanism.

Fig. 4.20 Microscopic images showing the effects of annealing at 500, 600
and 700
0
C for Ag thicknesses of 10, 20, and 30 nm, respectively.

Fig. 4.21 Reflection spectra of the samples with 10 nm deposition on (a) a
SiO
2
templated Si substrate corresponding to Fig. 4.16 (a) and (b) on an 100
nm SiO
2
film deposited on a Si substrate annealed at 500 (red) and 700
0
C
(blue). The black curve represents the spectra of the wafers before annealing.

Fig 4.22 (a) Reflection spectra of the samples with 10 nm deposition on a
SiO

2
templated Si substrate (black), an 100 nm SiO
2
film deposited on a bare
Si substrate (red). (b) Reflection spectra of the samples with 10 (black), 20
(red) and 30 nm (blue) Ag deposition on the SiO
2
templated Si substrate.

Fig. 4.23(a) Reflection spectra of the samples with 30 nm Ag deposition on a
SiO
2
templated Si substrate, before (black) and after (red) 700
0
C annealing.
(b) Reflection spectra of the samples with 30 nm Ag deposition on a 100 nm
SiO
2
/Si substrate, before (black) and after (red) 700
0
C annealing. Inserts
show the SEM images of the relative wafers before (left) and after (right)
annealing.

Chapter 5
Fig. 5.1 (a) Schematic showing the procedure for producing ordered surface
nanostructures on a LED wafer. SEM images showing (b) the top view of
self-assembled hcp monolayer of PS spheres, (c) the monolayered spheres
after reducing their diameters on site by O
2

RIE and (d) semiconductor
surface nanostructures after ICP dry etching.

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113
114
116
118
119
120
121
122
131
124
125
xviii

Fig. 5.2 SEM images showing the tilted view of surface nanostructures
created on a LED wafer by using ICP etching for duration of 90s for
semiconductor and PS spheres. The PS sphere diameter was reduced by O
2

RIE before ICP etching to (a) 450 nm (sample B), (b) 300 nm (sample C). (c)
PL spectra taken from the sample B (green), the sample C (red), and an area
without the surface structures (black).

Fig. 5.3. Microscopic images showing the arrangement of PS spheres on the
LED wafers with (a) random and (b) ordered styles. (c) PL spectra taken from
the two kind wafers after forming the surface nanostructures under the
conditions are the same as that shown in Fig. 5.2(a).

Fig. 5.4. (a) A tilted view of a SEM image showing the part of a p-type
electrode formed on the LED wafer with ordered surface nanostructures. (b)
Light output power of the LEDs with periodically ordered (red), random
(green) and without (black) the nanostructures as function of the forward dc
current, inset showing photographs of light emitting taken for the LEDs with
(left) and without the nanostructures under 5 mA dc forward current. (c)
Angle resolved light output power of the LEDs with (red) and without (blue)
the nanostructures.

Fig. 5.5 (a) Schematic showing the photoresist patterns (dark region) formed
by photolithography. (b) A micrograph of the arrays of the nanostructures
created on the p-GaN surface inside the patterns. (c) An optical micrograph
of an LED die.

Fig. 5.6 A SEM image (inset, a cross-section view) showing the
nanostructures created on the p-GaN surface.

Fig. 5.7 (a) The photoluminescence (PL) mapping across the region with and
without (blue area) the nanostructures, and (b) line scan of the PL along the
line showing in (a).

Fig.5.8 (a) Electroluminescence spectra from the LEDs with nanostructures
created on the p-GaN surface. (b) Plots of the light output power as a function
of injection currents for both LEDs with and without the surface
nanostructures.

Fig. 5.9 (a) Schematic showing the procedure to create Au nanostructures. (b)
A micrograph and (c) a SEM image of the Au nanostructures.

Fig. 5.10 (a)-(d) Top-view of the SEM images showing the Au nanostructures
formed through 500, 460, 420 and 370 nm residual spheres etched from 520
nm PS spheres. (e)-(g), Au nanostructures formed from the 370 nm residual
spheres viewed at near 45
o
, 60
o
, and 90
o
, respectively.

Fig. 5.11 PL spectra of the wafers: original surface (black), covered with 100
nm Au film (red), nanostructured Au film with 420 nm holes (green) and
nanostructured Au film with 500 nm holes (blue), respectively.

Fig. 5.12 (a) Photographic images showing the light emitting from the wafer
with (lift) and without (right) the Au nanohoneycomb structures. (b) Plots of
the light output power as a function of injection currents for both LEDs with
(blue) and without (black) the surface Au nanostructures. In addition, the
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137
138
140
140
141
143
144
146
147

xix

result of the wafer with surface nanostructures created on the GaP top layer
[Fig. 5.4(b)] is also plotted (red) as comparison.

xx

Abbreviations

NSL Nanosphere lithography
NIL Nanoimprint lithography
UV Ultraviolet
EUV Extreme ultraviolet lithography
SEM Scanning electron microscopy
AFM Atomic force microscopy
hcp Hexagonally close-packed
SL Single layer
DL Double layer
PPA Periodic particle array
2D 2 Dimension
3D 3 Dimension
EBD Electron beam deposition
LED Light emitting diode

PS Polystyrene
PECVD Plasma-enhanced chemical vapor deposition
MOCVD Metal-organic chemical vapor deposition
RIE Reactive-ion etching
ICP Inductive coupled plasma
MCE Multi-cycle etching
3DM 3D mask
PC photonic crystal
XRD X-ray diffraction
PL Photoluminescence
EL Electroluminescence
SAG Selective-area growth
xxi

SP Surface plasmon

EOT Extraordinary optical transmission
SPP Surface plasmon polariton
LSPR Local surface plasmon resonance
FWHM Full width at half maximum
NP Nanoparticle
FFT Fast Fourier transform
MQW multi-quantum well

xxii

Publications


1. Investigation of transmission of Au films with nanohole arrays created by
nanosphere lithography
Benzhong Wang, Hongwei Gao, Jun Yong Lau and Soo Jin Chua
Appl Phys A 107:139–143 (2012).

2. 2D ordered arrays of nanopatterns fabricated by using colloidal crystals as
templates
Benzhong Wang, Mingyong Han, and Soo Jin Chua
J. Vac. Sci. Technol. B 30, 041802-1- 041802-7 (2012).

3. Enhanced light output from light emitting diodes with two-dimensional cone-
shape nanostructured surface
Benzhong Wang and Soo-Jin Chua
J. Vac. Sci. Technol. B 31 032205-1- 032205-5(2013).

4. Analysis of shapes of surface nanostructures on the light extraction in LED
Benzhong Wang, Jun Yong Lau and Soo Jin Chua
Oral presentation, International conference on materials for advanced
technologies, Singapore, 26 June to 1 July, 2011.

5. Investigation of transmission of Au film with nano-hole arrays created by

nanosphere lithography
Benzhong Wang, Jun Yong Lau and Soo Jin Chua
Oral presentation, International conference on materials for advanced
technologies, Singapore, 26 June to 1 July 2011

6. Fabrication and optical properties of arrays of caped Au multi-step-nano-holes
Benzhong Wang, Hongwei Gao, Ning Xiang and Soo Jin Chua
Oral presentation, The 4th International Conference on Metamaterials, Photonic
Crystals and Plasmonics University of Sharjah, Sharjah – UAE March 18, 2013 –
March 22, 2013

7. A facile approach to form Ag particles in an ordered fashion
Benzhong Wang, Hongwei Gao, Ning Xiang and Soo Jin Chua
Invited talk, The 4th International Conference on Metamaterials, Photonic
Crystals and Plasmonics University of Sharjah, Sharjah – UAE March 18, 2013 –
March 22, 2013