MINISTRY OF EDUCATION AND TRAINING HANOI UNIVERSITY OF SCIENCE AND TECHNOLOGY INTERNATIONAL TRAINING INSTITUTE FOR MATERIALS SCIENCE --------------------------------------- NGUYEN VAN CHINH STUDY AND FABRICATION OF SURFACE PLASMON POLARITON WAVEGUIDES MASTER THESIS OF MATERIALS SCIENCE ITIMS BATCHS 2014 Hanoi - 2016 17051113936011000000 MINISTRY OF EDUCATION AND TRAINING HANOI UNIVERSITY OF SCIENCE AND TECHNOLOGY INTERNATIONAL TRAINING INSTITUTE FOR MATERIALS SCIENCE --------------------------------------- NGUYEN VAN CHINH STUDY AND FABRICATION OF SURFACE PLASMON POLARITON WAVEGUIDES Specialized: Science and Engineering of Electronic Materials MASTER THESIS OF MATERIALS SCIENCE ITIMS BATCHS 2014 SUPERVISOR: Dr. CHU MANH HOANG Hanoi - 2016 ACKNOWLEDGEMENT Firstly, I would like to thank my supervisor, Dr Chu Manh Hoang who has supervised and encouraged me during my stay at ITIMS. Acknowledgement would be also sent to all the members of Micro-nano systems and sensors technology Laboratory International Training Institute for Materials Science (ITIMS). Finally, thanks should also be given to my family and friends, who always supported me in my study.
LIST OF PUBLICATIONS 1. Nguyen Van Chinh, Nguyen Thanh Huong, and Chu Manh Hoang (2015), 9th Vietnam National Conference of Solid Physics and Materials Science , pp. Nguyen Van Chinh, Nguyen Thanh Huong, Vu Ngoc Hung, Chu Manh Hoang (2015) -shaped plasmonic wave International Conference on Applied & E Physics, pp. Nguyen Van Chinh, Nguyen Thanh Huong, Vu Ngoc Hung, Chu Manh Hoang (2016)- 3rd International Conference on Advanced Materials and Nanotechnology, pp.
111- 114, 2016, ISBN: 978-604-95-0010-7 STATEMENT OF ORIGINAL AUTHORSHIP I hereby declare that the results presented in the thesis are performed by the author. The research contained in this thesis has not been previously submitted to meet requirements for an award at this or any higher education institution. Date: 30/09/2016 Signature: CONTENTS CHAPTER 1. FUNDAMENTALS OF PLASMONICS.
History of development. Fundamentals of Surface Plasmon Polaritons. Wedge surface plasmon polariton waveguides. Conventional wedge waveguides.
Hybrid wedge waveguides. Fabrication of wedge waveguides. Exciting surface plasmon polariton mode in the wedge waveguide. Applications of wedge waveguides.
15 Purpose of this thesis. DESIGN AND SIMULATION OF WAVEGUIDE. Basic theory for the simulation of waveguides. Structure of triangular waveguide.
The thickness of metal layer. The tip angle of triangular waveguide. Height of triangular waveguide. The refractive index of cladding medium.
Model of the waveguides. Results and discussion. FABRICATION OF WAVEGUIDE. Process of fabrication.
Oxidation of SOI wafer. Isotropic wet–etching in buffered Hydrofluoric acid solution. Anisotropic etching in Potassium Hydroxide. Sputtering metal layer.
Results of the fabrication of waveguide. 51 SUGGESTED FURTURE WORKS. 52 LIST OF FIGURES Figure 1.1: Lycurgus cup 1 Figure 1.2: Number of papers 2 Figure 1.3: SPPs at single interface 4 Figure 1.4: SPP on Three-layer system 6 Figure 1.5: Schematic of conventional wedge waveguide 8 Figure 1.6: Typical hybrid wedge waveguides 10 Figure 1.7: Fabrication steps of wedge waveguide 11 Figure 1.8: Schematic of 2PP technique 12 Figure 1.9: Prism coupling 13 Figure 1.10: Waveguide coupling 14 Figure 1.11: Grating coupling 15 Figure 1.12 Wedge ring - type hybrid microresonator 16 Figure 1.13 Plasmon nanolaser 18 Figure 2.1: Schematic of triangular waveguide 21 Figure 2.2: Distribution of mesh 22 Figure 2.3: Electric field depending on meshing 23 Figure 2.4: Electric field depending on the thickness of metal 25 Figure 2.5: The influence of metal on transmission characteristics 27 Figure 2.6: Electric field at the thickness of 20nm 28 Figure 2.7: Electric field at various wedge angles 29 Figure 2.8: Transmission properties at various wedge angles 30 Figure 2.9: Electric field at different heights 31 Figure 2.10: Propagation characteristic at different heights 32 Figure 2.11: WPP mode depend ing on surrounding medium 33 Figure 2.12: Sketch of trapezoidal waveguide 34 Figure 2.13: Distribution of hybrid WPP mode 35 Figure 2.14: Electric field at the top surface 36 Figure 2.15: y and z components of electric field 37 Figure 2.16: The confinement and attenuation of WPP mode 38 Figure 2.17: Characteristic of waveguide 39 Figure 3.1: Schematic of fabrication process 41 Figure 3.2: Array of mask 43 Figure 3.3: Coating photoresist 44 Figure 3.4: Double-Side Align System PEM-800 45 Figure 3.5: The sputtering system 47 Figure 3.6: Silicon dioxide mask line 48 Figure 3.7: Silicon dioxide mask line after under - etching 49 Figure 3.8: Silicon waveguide 50 GLOSSARY OF TERMS AND ABBREVIATIONS SPP Surface Plasmon Polariton WPP Wedge Plasmon Polariton CPP Chanel Plasmon Polariton 2PP Two Photon Polymerization TM Transverse Magnetic 2D Two Dimensional FIB Focus Ion Beam ATR Attenuated Total Reflectance SOI Silicon on - Insulator MEMS Microelectromechanical Systems BHF Buffered Hydrofluoric Acid RF Radio frequency DC Direction Current SEM Scanning Electron Microscope CHAPTER 1. FUNDAMENTALS OF PLASMONICS 1.
History of development So long before scientists study about Plasmonic, ancient artisans used their properties to generate vibrant colors in glass artifacts. One of the most famous examples is the Roman glass work dating from the Byzantine Empire in the 4th century AD - the Lycurgus Cup (Fig. Under normal lighting, the cup appears green, and when illuminated from within it becomes red color. Here, gold and silver nanoparticles of dierent sizes and shapes were embedded in glass to create beautiful color.1 Lycurgus cup illuminated under normal external lighting (left) and from within (right).
In the early 20th century, Robert Wood observed a pattern of extraordinary dark mirror with a di raction grating on its surface. This is considered as the first observation of plasmon. About fifty years later, in 1956, David Pines theorized to explain the characteristic energy losses experienced by fast electrons traveling through metals is due to the collective oscillations of free electrons in the metal. These oscillations are similar to the plasma oscillations 1 1957, Rufus Ritchie published a study on electron energy losses in thin film, in which it is shown that plasmon modes can exist near the surface of metals.
This study presented the first theoretical description of surface plasmons. One year later, bound electrons and light inside transparent media. In 1968, Andreas Otto and Erich Kretschmann presented two methods for exciting the surface plasmon on metal film, making experiments on surface plasmons easily accessible to many scientists. From here, the major advance in study of surface plasmon was made.2 Number of pape rs containing “surface plasmon” in the title [1] .2 shows the growth of the plasmonic field since 1960 to 2008.
In middle s on Plasmonic increased rapidly achievements of nanofabrication techniques, physical analysis techniques and simulation codes. 2 Although this is a promising field, it has not been extensively researched in Vietnam. Only a few scientists interested in this field as Prof. Van Hieu Nguyen, Bich Ha Nguyen, Van Hop Nguyen.
The study of th ese scientists mainly is on theoretical calculations of bulk plasmon and localized plasmon. Fundamentals of Surface Plasmon Polaritons Surface plasmon polaritons (SPPs) are resulting from strong coupling of the electromagnetic wave with the collective oscillations of electrons at metal dielectric interface. As a surface electromagnetic wave, we can use the Maxwell theory for describing this phenomenon. Firstly, we detail in SPPs that propagate on single interface of a metal and a dielectric medium.
For solving this problem, we consider the haft space z < 0 is 1 2 (Figure 1. By choosing the x axis in the direction of wave propagation, we get the dispersion of field at z = 0 plane [25] (1.1) with + for z > 0 and for z < 0. Here, kx and kz is the tangential and normal component of wave vector, respectively. Solving the Maxwell equations with the continuous conditions of field at the interface, we obtain the tangential component of wave vector of SPP (1.2) ko function has the form (1.3 Geometry for SPPs propagation at a single interface between a metal and a dielectric.
Typically, and , we get the complex (1.5) For real , we need and , this is the condition to occur SPP on the interface of two mediums. Cause of the continuity of through the interface, we have (i = 1,2) (1.6) Because of the confinement at surface, the SPP is p polarized and kz purely imaginary. That means SPP appears only as transverse magnetic (TM) wave and the number is larger than the wave number of light in vacuum k o. The imaginary part of tangential wave vector characterizes the attenuation of SPP.
The propagation length where the intensity reduce to 1/e is defined by (1.7) In the case of metal with low losses and , propagation length is given approximately by (1.8) 4 We see that if we want the propagation length to be as large as possible, we need a metal with a large negative real part and very low value of losses. In the case of sliver, the propagation length varies in the 50 - wavelength in the 0.5 We now turn to calculate the components of the wave number in the z-direction, in order to determine the penetration depths in the dielectric and metal, respectively.10) Because both wavenumbers are purely imaginary, the field perpendicular to the interface evanescent and have the property like the near-field. The penetration depth is determined from = 1/ (1.12) In the multilayer structures, SPP is occurred in each of single interface. If the separation between adjacent interfaces is comparable to or smaller than the penetration depth of the interface mode, interactions between SPP give rise to coupled modes (Figure 1.
Using Maxwell equations and the continuous conditions of field in each of medium interface, we have [20] (i = 1,2,3) (1.14) Here, d is the thickness of metal layer. These equations are so complex. In fact, we only study the simple cases such as the symmetric structure . In this condition, the coupling divides SPP into symmetric and anti-symmetric mode.4 Geometry of the three layers system.
symmetric mode reduces the wavenumber while anti-symmetric mode increases the wavenumber of SPP [15]. In the case SPP propagates in a metal wedge, we can approximate to the propagation of SPP in a thin metal film with the thickness d continuously changing to zero. Wedge surface plasmon polariton waveguides To achieve photonic circuits with high integration density, it is necessary to develop miniature optics components for high-speed signal generation, propagation, detection and processing. A recent research direction has been devoted for developing nano-scale optical waveguides which are capacity of wave propagation with strong field confinement permitting denser waveguide packaging without crosstalk and lower waveguide bending loss.
Three kinds of typical nanophotonic waveguides have been developed, which includes nanophotonic wires [13], [22], photonic-crystal waveguides [23] and nanoplasmonic waveguides [2]. The former two nanophotonic waveguides, which utilize nano-structures with ultra-high index contrast, are limited due to the classical optical diffraction phenomena. In contrast, a nanoplasmonic waveguide can break the diffraction limit and enable deep sub- wavelength confinement and wave-guiding of light, which makes it become a very 6 attractive candidate for ultra-high integration density.