Chế tạo các cấu trúc nano vàng, bạc dạng hoa, lá trên silic để sử dụng trong nhận biết một số phân tử hữu cơ bằng tán xạ raman tăng cường bề mặt tt tiếng anh

1 MINISTRY OF EDUCATION AND TRAINING VIETNAM ACADEMY OF SCIENCE AND TECHNOLOGY GRADUATE UNIVERSITY OF SCIENCE AND TECHNOLOGY - Kieu Ngoc Minh FABRICATION OF FLOWER-LIKE, DENDRITE-LIKE NANOSTRUCTURES OF GOLD AND SILVER ON SILICON FOR USE IN THE IDENTIFICATION OF SOME ORGANIC MOLECULES BY SURFACE ENHANCED RAMAN SCATTERING Major: Electronic material Code: 44 01 23 SUMMARY OF MATERIAL SCIENCE DOCTORAL THESIS Ha Noi – 2020 This thesis was accomplished in: Graduated University of Science and Technology – Vietnam Academy of Science and Technology Supervisor: Prof Dr Dao Tran Cao Dr Cao Tuan Anh Peer reviewer 1: Peer reviewer 2: Peer reviewer 3: This thesis will be defended in: The dissertation will be defended in front of the Institute of Doctoral Dissertation Assessment Council, taking place at the Academy of Science and Technology - Vietnam Academy of Science and Technology at hour ', day month year 2020 This thesis will be stored in: - Library of Graduated University of Science and Technology - Vietnam National Library Prologue SERS (surface-enhanced Raman scattering) is a modern analytical technique that is being strongly researched in the world and Vietnam to detection trace (ppm-ppb range) of many different molecules, especially organic and biological molecules In SERS technique, the most important is the SERS substrate The SERS substrate is a rugged continuous or discontinuous precious metal (silver or gold) at the nano-scale When analyte molecules are added to this surface, the signal of Raman scattering of the analyte molecule is greatly enhanced Thus, it can be said that SERS substrate is the device that amplifies Raman scattering signal of the analyte molecule In Vietnam, there are some researches on the fabrication of Ag, Au precious metal nanostructures and using as SERS substrates However, the researches mainly focus fabricate nanoparticle structures and so far, fabrication of silver nano-dendrites (AgNDs), silver nano-flowers (AgNFs) and gold nanoflowers (AuNFs ) very few, especially the statements on fabrication of these structures on silicon For the purpose of studying and researching AgNDs, AgNFs and AuNFs materials on silicon as well as the properties and applications of this material, I chose the title of the thesis is “Fabrication of flowers-like, dendrites-like nanostructure of silver and gold on silicon for using in detection some organic molecules by surface enhanced Raman scattering” In this thesis, we research and fabricate AgNDs, AgNFs, AuNFs structures on silicon by chemical deposition and electrochemical deposition method for the main purpose of using as SERS substrate To this target, we have studied the morphology, structure and some properties of the nanostructures produced Then, we use the nanostructures mentioned above as SERS substrates to detect traces of some toxic organic molecules, to test their effectiveness as a SERS substrate The scientific significance of the thesis The AgNDs, AgNFs, AuNFs structures on silicon have been successfully fabricated by two methods of chemical deposition and electrochemical deposition with the main purpose for using as SERS substrate The influence of fabrication parameters on morphology and structure of AgNDs, AgNFs, AuNFs was studied in orderly The mechanism of formation of the above structures has been studied Đã nghiên cứu sử dụng cấu trúc nano nói đế SERS để phát số phân tử hữu độc hại nồng độ thấp These nanostructures have been used as SERS substrates to detect some toxic organic molecules in low concentrations The thesis includes chapters as follows: This thesis includes of 125 pages (excluding references) with the following layout: Introduction: Presenting the reasons for choosing topic, methods, purposes of researching Chapter 1: Overview of surface enhanced Raman scattering Chapter 2: Methods to fabricate and investigate SERS substrates Chapter 3: Fabrication and investigation of silver and gold nanostructures on silicon Chapter 4: Using gold, silver nanostructures like flowers and dendrites as SERS substrates to detect traces of some organic molecules Conclusion: Presenting the conclusions drawn from the research results Chapter Overview of surface enhanced Raman scattering 1.1 Raman scattering Raman scattering is inelastic scattering of a photon with material, discovered by Raman and Krishnan in 1928 The frequency of scattering light changes compared to incident light frequency This amount of change is exactly equal to the oscillation frequency of the matter molecule and does not depend on the frequency of the incident light So, Raman scattering is specific to each molecule Raman scattering include of two types: Stockes Raman and antiStockes Raman It should be noted that the intensity of the Raman effect is usually very low (about 10-8 - one hundred million incident photons then one photon is Raman scattering) 1.2 Surface enhanced Raman scattering Surface enhancement Raman scattering is a phenomenon that when light fly to the analyte molecule adsorbed on the surface of a rugged metal nanostructure, the intensity of the Raman scattering is greatly increased The metal nanosurface is called SERS substrate There are two enhancement mechanisms for SERS, which are electromagnetic enhancement mechanism and chemical enhancement mechanism In which, electromagnetic enhancement mechanism is main contributor 1.2.1 Electromagnetic enhancement mechanism Surface localized plasmon resonance (LSPR) occurs when the surface plasmon is confined to a nanostruc-ture that Size is smaller than the wavelength of light From the Fig 1.5, it can see that the electric field of the incident light is an oscillating electric field In the first half of the cycle, the incident electric field is directed upwards, which has the effect of causing the conduction electrons to move downwards in metal nanoparticles Thus, the top part of the metal nanoparticles will be positively charge, resulting the metal nanoparticles becoming an dipole In the second half of the cycle, the electric field of the incident light changes direction, the dipole also changes direction As a result, the Fig 1.5 Schematic illustration of surface dipole also oscillates with the localized plasmon resonance (LSPR) frequency of the incident light The with free conducting electrons in metal vibrating dipole produces an nanoparticles that are oriented by electromagnetic field (new light oscillation due to strong connection with incident light source) If the new electromagnetic field vibrates with the oscillation frequency of the incident light, then we have a resonance The result, the incident light field is enhanced by E2 times while the scattering field is also enhanced by E2 times, the total field is enhanced by E4 times 1.2.2 Chemical enhancement mechanism The presence of chemical mechanism with Raman scattering was observed when plasmonic metals are not used Studies of non-electromagnetic enhancement mechanisms have shown that resonancing between incident light and metal nanostructures can induce charge transfer between analyte Fig 1.6 Three different types of chemical molecules and metal enhancement mechanisms in SERS Charge transmission occurs, the metals and molecules of the analyte must be in direct contact with each other In other words, charge transmission occurs only when the metals and molecules are close enough that the wave functions overlap The exact mechanism of charge transfer has not been fully understood until now 1.3 SERS enhancement factor The SERS enhancement factor used in the thesis is the SERS substrate enhancement factor (SSEF) and is calculated by the following formula: I N SSEF  SERS Normal I Normal N SERS Where, ISERS and INomarl are intensity of Raman spectrum of organic molecule adsorbed on SERS and non-SERS substrate NNormal, NSERS are the medium number of molecules in the volume scattering (V) of non-SERS measurement, and SERS measurement 1.4 Dependence of SERS on surface morphology of metal nanostructures Fig.1.7 Simulation dependence of the SERS enhancement factor on the distance between two spherical nanoparticles lying close together It can be seen that when the distance between the two nanoparticles is nm, the SERS enhancement factor is 108 and the enhancement factor decreased rapidly to only 105 when the distance between the two particles increased to nm The formation of nanoparticle structures with a narrow between them leading to problems First, it was difficult to bring the nanoparticles closer together with a distance of nm Second, analyte molecules into nm gap between particles is also extremely difficult Therefore, the researchers proceeded to change the shape of the metal nanoparticles in the direction enhancing tips of particles to obtain a Fig 1.7 The dependence of SERS strong SERS enhancement In 2009, P R enhancement factor on distance Sajanlal et al demonstrated that SERS of the spherical nanoparticles enhancement factor of the triangular gold nanoparticle system was 108 (Fig 1.8 a) L Feng et al fabricated the bow-like silver nanoparticles and the SERS enhancement factor was 109 (Fig 1.8 b) Comparison of SERS enhancement factor obtained from spherical and prism silver nanostructures was also published by S H Ciou et al in 2009 (Fig 1.8 (c)) In this comparison, SERS measurements was in solution The results showed that enhancement factor of the spherical silver nanoparticle was 103, while enhancement factor of the prismlike silver nanoparticle was 105 Fig 1.8 SEM images of nanoparticles with different shapes: a) gold triangularlike; b) silver bow-like; c) silver prism-like Fig 1.9 SEM image of metal structures: a) Ag-Cu dendrites; b) silver dendrites on an aluminum substrate; c) silver dendrites on a copper substrate and coated with graphene Dendritic metal structures have tips more than spherical structures Dendritic structure of precious metals with different shapes was fabricated as shown in Fig 1.9 X Chen et al fabricated silver - dendrites on a copper substrate and analyzed R6G to a concentration of 10-6 M (Fig 1.9 (a)) Deposition silver on aluminum substrate, then separate the silver dendritic and cover with a layer of gold and identify 1,2-benzenedithiol at a concentration of 10-4 M (Fig 1.9 (b)) L Hu et al fabricated silver dendrites on a copper substrate, then coated with graphene oxide on top They demonstrated that for the same analytes, when coated with graphene oxide on top, enhancement factor is 1.2x107 (Fig 1.9 (c)) One of the metal structures for good SERS enhancement that we cannot fail to mention are metal structures in shape of flowers (Fig 1.10) H Fig 1.10 SEM images of metal flowers-like: a) Liang et al in 2009 silver nano flower-like; b) gold nano flower-like; successfully fabricated c) Gold nano flower-like with holes silver flower structures in suspension and used them to detect malachite green with concentrations as low as 10-10 M Z Wang et al used electrochemical deposition method to fabricate the gold nanotubes and using this SERS substrate they detected R6G with concentrations as low as 10-10 M S Ye et al published results for the fabrication of gold nano-structure with holes in the middle and showed that SERS enhancement factor for the biphenyl-4-thiol analyte of this structure was 105 1.5 Application of SERS During the time since its discovery, SERS has been using as an extremely useful tool for environmental, food, and biomedical analysis The target molecules analyzed by SERS are also very abundant including pesticides, herbicides, pharmaceutical, chemicals in water, dyes, aromatic chemicals in normal aqueous solutions and in seawater, chlorophenol derivatives and amino acids, war chemicals, soil organic pollutants, and biological molecules such as DNA, RNA 1.6 Researching of SERS in Vietnam In Vietnam, researching and fabrication on SERS substrates and using of SERS to detect molecules at low concentrations have been starting since 2010 Up to now, in Vietnam, there are several groups has been researching on SERS Such as, group of GS.VS Nguyen Van Hieu, Professor's group Nguyen Quang Liem and Assoc Ung Thi Dieu Thuy (Institute of Materials Science), Associate's Group Tran Hong Nhung (Institute of Physics), group of Assoc Nguyen The Binh (Hanoi University of Science), Assoc Pham Van Hoi (Institute of Materials Science), group of Professors Dao Tran Cao (Institute of Materials Science) - this is also the research group that helps me make this thesis In addition, there are some of other research groups that are also researching on SERS and obtained some good results, we would like to not list here Chapter Fabrication and investigation methods of SERS substrate 2.1 Introduction to SERS substrates Currently, there are two types of SERS substrates used SERS substrate is suspension of precious metal nanoparticles (Ag, Ag) inside a certain liquid SERS substrate is a heterogeneous metal surface Requirements of a good SERS substrate Strong SERS enhancement factor (> 105) Uniformity on the surface and uniformity between samples (