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 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. iii Table of Contents Acknowledgments iii Table of Contents iv Abstract viii List of Tables x List of Figures xi Abbreviations xx Publications xxii Chapter 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 14 1.5 Scope of thesis 15 Reference 16 Chapter Development of nanosphere lithography 19 2.1 Introduction 19 2.2 Self-assembly of colloidal crystals 20 2.2.1 Introduction 20 2.2.2 Controls of self-assembled colloidal crystals 21 2.2.2.1 Self-assembly of a monolayer 24 2.2.2.2 Self-assembly of a bilayer 24 2.2.2.3 Selective self-assembly 26 iv 2.3 Applications of colloidal crystal as templates 32 2.3.1 Introduction 32 2.3.2 Ordered spherical nanocavities 33 2.3.3 Creating nanostructures with multi-features in one step 38 2.3.4 Shape engineering of nanostructures 43 2.3.4.1 Shape control through multi-cycle etching (MCE) 43 2.3.4.2 Shape control through 3D mask (3DM) 46 2.3.4.3 Shape control through dry etching mechanism 55 2.4 Summary 61 Reference 62 Chapter Nanosphere lithography applied to nanogrowth of III-V compounds 64 3.1 Introduction 64 3.2 Basics of MOCVD 65 3.3 GaN film grown on an array of Si (111) nanopillars 68 3.3.1 Introduction 68 3.3.2 Experiments 70 3.3.3 Results and discussion 72 3.4 Dual-sized (In)GaAs/GaAs nanobars grown by one step MOCVD 82 3.4.1 Introduction 82 3.4.2 Experiments 83 3.4.3 Results and discussion 83 3.4 Summary 87 Reference 88 Chapter Nanosphere lithography applied to formation of metal nanostructures 92 4.1 Introduction 92 4.2 Fabrication and characterization of metal 93 v nanostructures 4.2.1 Quasi-ordered 2D Au nanostructures with holes 93 4.2.1.1 Introduction 93 4.2.1.2 Experiments 94 4.2.1.3 Results and discussion 96 4.2.2 3D Au nanostructures formed by a 2D array of nanospheres 102 4.2.2.1 Introduction 102 4.2.2.2 Experiments 103 4.2.2.3 Results and discussion 104 4.2.3 Ag nanoparticle superlattices formed by template guided annealing 111 111 4.2.3.1 Introduction 111 4.2.3.2 Experiments 112 4.2.3.3 Results and discussion 113 4.3 Summary 126 Reference 126 Chapter Nanosphere lithography applied to LEDs for light extraction 129 5.1 Introduction 129 5.2 Effects of ordered surface nanostructures on LEDs 130 5.2.1 GaAs based red LEDs 130 5.2.1.1 Experiments 130 5.2.1.2 Results and discussion 133 5.2.2 GaN based blue LEDs 137 5.2.2.1 Experiments 137 5.2.2.2 Results and discussion 139 5.3 Effects of ordered surface Au nanostructures on LEDs 142 142 5.3.1 Experiments vi 5.3.2 Results and discussion 143 5.4 Summary 147 Reference 148 Chapter Summary and future plan 150 6.1 Summary 150 6.2 Future plan 154 vii 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 µm2 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 viii the vertical profiles of the created nanostructures. A 3D SiO2 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 SiO2 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 SiO2 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 SiO2 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. ix List of Tables Chapter Table 2.1 Etching duration for PS spheres vs. opening sizes of the nanostructures created onto the SiO2 film. 43 Table 2.2 Etching conditions for the wafers of wafer A, B and C. 45 Chapter Table 3.1 Growth parameters for the wafer of the Si nanopillar and flat Si substrate, which was started from AlN growth. x 71 List of Figures Chapter 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 nonexposed 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 10 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 dm = 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 dm = 30 nm thermally evaporated Ag metal after removing the nanospheres [39]. (e) and (f) show the definition of the parameters of D, a and dip for single and double layer arrangement, respectively. 12 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 dm = 50 nm e-beam deposited Ni metal after removing the nanospheres [39]. 13 Fig. 1.9 Schematic of the angle resolved deposition process. (a) Samples viewed at 0° (a), 30°, (b) and 45°, (c), respectively [46]. 14 Chapter Fig. 2.1 Schematic of the setup for the self-assembly of the nanospheres from colloidal solution. xi 22 Fig. 2.2 (a) Photograph and (b) SEM images of the monolayered PS spheres of 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. 25 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. 26 Fig. 2.4 Microscopic images (up panel) of different layered nanospheres assembled on glass substrates (as indicated in bottom panel). 26 Fig. 2.5 (a) Schematic of the self-assembly within the wells. (b) Microscopic image of the patterned Si substrate. 27 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. 28 Fig. 2.7 (a) Schematic illustration of the patterns created on a SiO2 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 SiO2 film with microwells. 30 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. 31 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. 32 Fig 2.10 A schematic diagram of the procedure to make the ordered array of nanocavities 33 Fig. 2.11 A cross-section view of a SEM image of the silica nanocavities. 34 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. 35 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. 37 Fig. 2.14 Schematic illustration of the principle to make nanoholes with twosize features 39 xii Fig. 2.15 The procedure for fabricating ordered SiO2 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 SiO2 of ~100 nm in thickness. Schematic top-views of the bilayered nanospheres (b) before and (c) after O2 RIE etching. (d) A top-view SEM image and (e) A schematic side-view of the as-formed SiO2 nanoholes after further O2/CHF3 RIE etching of the bilayered nanospheres and the SiO2 films underneath. 41 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 (~100) of SEM image of the nanoholes created on the thicker SiO2 region (after removing the PS spheres). 42 Fig. 2.17 SEM images of the nanoholes formed by a bilayer of PS spheres with 600 nm diameter. Before etching the SiO2 film and PS spheres, the PS spheres were etched by O2 RIE for (a) 75, (b) 115 and (c) 155s. 43 Fig. 2.18 Schematic illustration of the principle to make surface nanostructures with different cross-section shapes. 44 Fig. 2.19 SEM images showing the nanostructures of (a) pillars, (b) candlelike, and (c) and (d) bell-like, respectively, formed by the multi-cycle etching technique. 46 Fig. 2.20 SEM images of the lens-like microstructures formed by the multicycle etching technique. The number of repeat cycles was: (a) for sample A, (b) for sample B, and (c) 12 for sample C. 46 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. 47 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). 48 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). 49 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. 51 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 52 xiii 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). 54 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. 56 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. 57 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. Crosssection (c) and top (d) view SEM images showing the Si surface structures created under longer etching duration at the chamber pressure of 120 mTorr. 58 Fig. 2.30 (a) Cross-section of SEM images showing the Si surface structures created under different O2 flow while the SF6 is kept at 20 sccm. (b) The structural parameters of the Si surface structures created under different O2 flows. (c) The angle variation of the sidewall of the Si structures with the O flow. 59 Fig.2.31 (a) Outline of the procedure for fabricating an array of SiO2 nanodisks. (b) and (c) shows a tilted view and near cross-section view of the SEM images of the SiO2 nanodisks. 61 Chapter Fig. 3.1 The typical diagram of MOCVD system. 65 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. 66 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. 71 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. 72 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. 73 xiv 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. 74 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. 75 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. 76 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]. 76 Fig. 3.10 A schematic of evolution of the III-nitride nanostructures with growth stages. 78 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 InGaN/GaN quantum wells grown on the GaN film grown on the Si nanopillars (red), and a normal Si substrate (black). 80 Fig. 3.12 Epitaxial growth of ordered InGaAs/GaAs nanobars array in the openings of SiO2-coated GaAs substrate. A schematic side-view (a) and a top-view SEM image (b) of the ordered triangle openings on SiO2 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). 84 Fig. 3.13 High-magnification views at 45o of the InGaAs/GaAs nanobars in (a) perpendicular and (b) parallel directions. 84 Fig. 3.14 Site-selective growth of single-sized InGaAs/GaAs nanobars array on SiO2-patterned substrates. (a) Schematic micropatterning on SiO2-coated GaAs substrate. (b) Selective nanopatterning on the micropatterned SiO2 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 SiO2 nano-openings on GaAs substrate by MOCVD. 85 Fig. 3.15 Site-selective growth of dual-sized InGaAs/GaAs nanobars array on micropatterned GaAs substrate. (a) Selective nanopatterning of SiO2 nanocavities as templates for (b) selective growth of semiconductor nanobars with dual sizes. (c) A low magnification SEM image (top-view) of the dualsized InGaAs/GaAs nanobars grown selectively on the GaAs substrate by MOCVD. High magnification SEM images (45o view) of the dual-sized nanobars viewed from (d) parallel and (e) perpendicular directions of the bars. 87 xv Chapter Fig. 4.1Microscopic images of the arrangement of nanospheres at a diameter of 600 nm. (a) Ordered nanospheres and (b) quasi-ordered nanospheres. 94 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. 95 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). 97 Fig. 4.4 Transmission spectra of Au films at different thicknesses. (b), a plot of the transmittance against thickness of the Au film. 97 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). 98 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. 100 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). 102 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. 105 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. 106 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. 107 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. 108 Fig. 4.12 Transmission spectra of the wafer W1 (black) and W2 (red), W3 (blue) and W4 (green). 110 xvi Fig. 4.13 Outline of the process for fabricating periodic ordered Ag nanoparticles. 112 Fig. 4.14 (a) Schematic illustration of Ag growth with deposition. (b), (c) and (d) show the SEM images of Ag deposited onto the SiO2 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. 113 Fig. 4.15 A tilted-view of SEM image showing the Ag islands formed on the SiO2 patterned Si substrate by depositing 10 nm Ag. 114 Fig. 4.16 SEM images showing the thermal-annealing results for the samples with (a) and without (b) the SiO2 patterns. 116 Fig. 4.17 Statistical distribution of the island size for the samples with (blue) and without (black) the SiO2 pattern, after being annealed at 700 0C. 118 Fig. 4.18 Fast Fourier transform (FFT) image of 20 nm Ag deposited on the Si substrate with (left) and without (right) the SiO2 patterned after annealing at 700 0C for 30 min. 119 Fig. 4.19 A schematic model for the annealing mechanism. 120 Fig. 4.20 Microscopic images showing the effects of annealing at 500, 600 and 700 0C for Ag thicknesses of 10, 20, and 30 nm, respectively. 121 Fig. 4.21 Reflection spectra of the samples with 10 nm deposition on (a) a SiO2 templated Si substrate corresponding to Fig. 4.16 (a) and (b) on an 100 nm SiO2 film deposited on a Si substrate annealed at 500 (red) and 700 0C (blue). The black curve represents the spectra of the wafers before annealing. 122 Fig 4.22 (a) Reflection spectra of the samples with 10 nm deposition on a SiO2 templated Si substrate (black), an 100 nm SiO2 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 SiO2 templated Si substrate. 124 Fig. 4.23(a) Reflection spectra of the samples with 30 nm Ag deposition on a SiO2 templated Si substrate, before (black) and after (red) 700 0C annealing. (b) Reflection spectra of the samples with 30 nm Ag deposition on a 100 nm SiO2/Si substrate, before (black) and after (red) 700 0C annealing. Inserts show the SEM images of the relative wafers before (left) and after (right) annealing. 125 Chapter 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 O2 RIE and (d) semiconductor surface nanostructures after ICP dry etching. xvii 131 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 O2 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). 133 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). 134 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 mA dc forward current. (c) Angle resolved light output power of the LEDs with (red) and without (blue) the nanostructures. 137 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. 138 Fig. 5.6 A SEM image (inset, a cross-section view) showing the nanostructures created on the p-GaN surface. 140 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). 140 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. 141 Fig. 5.9 (a) Schematic showing the procedure to create Au nanostructures. (b) A micrograph and (c) a SEM image of the Au nanostructures. 143 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 45o, 60o, and 90o, respectively. 144 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. 146 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 147 xviii result of the wafer with surface nanostructures created on the GaP top layer [Fig. 5.4(b)] is also plotted (red) as comparison. xix 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 Dimension 3D 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 xx 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 xxi 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 coneshape 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 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 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 xxii [...]... to a thickness of 10 nm, 20 nm, and 30 nm, respectively 11 3 Fig 4 .15 A tilted-view of SEM image showing the Ag islands formed on the SiO2 patterned Si substrate by depositing 10 nm Ag 11 4 Fig 4 .16 SEM images showing the thermal-annealing results for the samples with (a) and without (b) the SiO2 patterns 11 6 Fig 4 .17 Statistical distribution of the island size for the samples with (blue) and without (black)... the radius of the cap was varied to be (a) W1:~5 61. 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 10 7 Fig 4 .11 Transmission spectra of the wafer S1 (black) and S2 (red) The blue line represents the wafer of 10 0 nm Au deposited on a flat substrate 10 8 Fig 4 .12 Transmission spectra of the wafer W1 (black) and W2 (red),... 700 0C 11 8 Fig 4 .18 Fast Fourier transform (FFT) image of 20 nm Ag deposited on the Si substrate with (left) and without (right) the SiO2 patterned after annealing at 700 0C for 30 min 11 9 Fig 4 .19 A schematic model for the annealing mechanism 12 0 Fig 4.20 Microscopic images showing the effects of annealing at 500, 600 and 700 0C for Ag thicknesses of 10 , 20, and 30 nm, respectively 12 1 Fig 4. 21 Reflection... and W2 (red), W3 (blue) and W4 (green) 11 0 xvi Fig 4 .13 Outline of the process for fabricating periodic ordered Ag nanoparticles 11 2 Fig 4 .14 (a) Schematic illustration of Ag growth with deposition (b), (c) and (d) show the SEM images of Ag deposited onto the SiO2 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... xxi 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 10 7 :13 9 14 3 (2 012 ) 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, 0 418 02 -1- 0 418 02-7 (2 012 ) 3 Enhanced light... coincidence of the AlN atoms with silicon (11 1) atoms [49] 76 Fig 3 .10 A schematic of evolution of the III-nitride nanostructures with growth stages 78 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... nm nanospheres and dm = 30 nm thermally evaporated Ag metal after removing the nanospheres [39] (e) and (f) show the definition of the parameters of D, a and dip for single and double layer arrangement, respectively 12 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. .. Schematic of the procedure for producing ordered Si nanopillars on a Si (11 1) substrate (b) A SEM image of the near side view of the Si nanopillars with the PS spheres above them 71 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 (11 1) substrate, and. .. resist, and the deflectors control the position of the beam on the resist 5 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] 7 Fig 1. 5 (a) side and (b) top-view of self-assembly of nanospheres 9 Fig 1. 6 Nanosphere. .. spectra of 11 0 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 10 0 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 . on LEDs 5.3 .1 Experiments 11 1 11 1 10 4 10 3 10 2 10 2 96 94 93 11 2 11 3 12 6 12 9 12 9 13 0 13 0 13 0 13 3 14 2 14 2 93 13 7 13 7 13 9 12 6 11 1 vii 5.3.2 Results and discussion. nanostructures after ICP dry etching. 11 2 11 3 11 4 11 6 11 8 11 9 12 0 12 1 12 2 13 1 12 4 12 5 xviii Fig. 5.2 SEM images showing the tilted view of surface nanostructures created on a. of 10 0 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). 94 95 97 98 10 0 10 2 10 5 10 6 10 7 10 8 11 0