은과 금 나노 틈 및 나노 구조체에서의 4-아미노벤젠치올과 4-니트로벤젠치올의 표면 증강 라만 산란

학위논문 (박사)-- 서울대학교 대학원 : 화학부, 2015. 2. 김관.In Chapter 1, The General Introduction, we provide background information on surface-enhanced Raman scattering (SERS), along with the characteristics of finite-difference time-domain (FDTD) method adopted in this thesis. In Chapter 2, SERS spectra of 4-nitrobenzenethiol (4-NBT) and 4-aminobenzenethiol (4-ABT) on Ag obtained under ambient conditions and in icy environments at 77 K are presented. This study was conducted to resolve the debate on the origin of b2-type bands appearing in the SERS of 4-NBT and 4-ABT. The origin of b2-type bands in the SERS of 4-NBT and 4-ABT has recently been debated because these bands are very similar to those attributed to a photoreaction product such as 4,4′-dimercaptoazobenzene (4,4′-DMAB). We confirmed in this work that under ambient conditions, the b2-type bands distinctly appeared in the SERS spectra of both 4-NBT and 4-ABT. In contrast, no b2-type peaks appeared in the SERS of 4-NBT in icy environments, suggesting that 4-NBT did not undergo a photoreaction. However, the SERS spectral pattern of 4-ABT was the same both at room temperature and in icy conditions. Based on our separate observation that hot electrons are plasmonically generated from Ag even in icy environments, the lack of photoreaction of 4-NBT is likely a result of the small spaces between the ice crystals, rendering the N–O bond difficult to break. The situation of 4-ABT on Ag is identical to that of 4-NBT on Ag in the same conditionstherefore, the b2-type bands observed in icy conditions must be because of the 4-ABT, and not because of the production of 4,4′-DMAB or other photoreaction products. Regardless of temperature, hot electrons were more easily generated at lower excitation wavelengths, and the b2-type bands appeared more distinctly with a decrease in the excitation wavelength. From these observations, we conclude that the hot electrons, as well as the b2-type bands of 4-ABT, are associated with the charge-transfer chemical enhancement mechanism in SERS. In Chapter 3, SERS of 4-ABT at the nanogaps between metal nanoparticles and a flat Au substrate is described. This study was conducted to understand the characteristics of one kind of hot site for SERS. In fact, although no Raman signal is observable when 4-ABT, for instance, is self-assembled on a flat Au substrate, a distinct spectrum is obtained when Ag or Au nanoparticles are adsorbed on the pendent amine groups of 4-ABT. This is definitely due to the electromagnetic coupling between the localized surface plasmon of Ag or Au nanoparticle with the surface plasmon polariton of the planar Au substrate, allowing an intense electric field to be induced in the gap even by visible light. On this basis, firstly, we have thoroughly examined the size effect of Ag nanoparticles, along with the excitation wavelength dependence, by assembling 4-ABT between planar Au and a variable-size Ag nanoparticle (from 20- to 80-nm in diameter). Regarding the size dependence, a higher Raman signal was observed when larger Ag nanoparticles were attached onto 4-ABT, irrespective of the excitation wavelength. Regarding the excitation wavelength, the highest Raman signal was measured at 568 nm excitation, slightly larger than that at 632.8 nm excitation. The Raman signal measured at 514.5 and 488 nm excitation was an order of magnitude weaker than that at 568 nm excitation, in agreement with the three-dimensional finite-difference time domain (3-D FDTD) simulation. It is noteworthy that placing an Au nanoparticle on 4-ABT, instead of an Ag nanoparticle, the enhancement at the 568 nm excitation was several tens of times weaker than that at the 632.8 nm excitation, suggesting the importance of the localized surface plasmon resonance of the Ag nanoparticles for an effective coupling with the surface plasmon polariton of the planar Au substrate to induce an very intense electric field at the nanogap. In addition, secondly, the Raman spectral characteristics of 1,4-phenylenediisocyanide (1,4-PDI) and 4-ABT positioned at the nanogap formed by Au/Ag alloy nanoparticles and a flat Au substrate were examined, and 3-D FDTD calculations were carried out. More intense Raman signal was measured, regardless of the excitation wavelength, when Ag-rich Au/Ag alloy nanoparticles were used to form the nanogaps. Regarding the excitation wavelength, 568 nm light was the most effective in inducing a Raman signal, particularly when Ag nanoparticles were adsorbed on 1,4-PDI or 4-ABT, whereas 632.8 nm light was slightly more effective than 568 nm light when Au nanoparticles were adsorbed onto them. The Raman spectra of 1,4-PDI could be attributed to the electromagnetic enhancement mechanism. The dependencies of the Raman spectra of 1,4-PDI on the excitation wavelength and the type of Au/Ag alloy nanoparticle were comparable to those predicted by the 3-D FDTD calculations. From the measured NC stretching frequencies, the surface of 35-nm sized Au/Ag alloy nanoparticles containing more than 5 mole percent of Ag atoms was concluded to be covered fully with Ag atoms. The Raman spectra of 4-ABT were interpreted to be a product of electromagnetic and chemical enhancement mechanisms. Assuming that the Raman intensity ratios of the b2- and a1-type bands were indicative of the extent of chemical enhancement, the Ag-to-4-ABT electron transfer appeared more facile than the Au-to-4-ABT transfer did and more favorable by excitation with a 514.5 nm laser than 568 nm or 632.8 nm laser. In Chapter 4, SERS of 4-NBT at the nanogaps between a planar Au substrate and a Ag nanostructure is described. This study was conducted to appreciate the effectiveness of hot electrons plasmonically generated from Ag nanoparticles. As described in Chapter 2, 4-NBT adsorbed on a nanostructured Ag substrate can be reduced to 4-ABT by the irradiation of a visible laser. In order to evaluate the effectiveness of hot electrons generated from Ag, we have carried out a SERS study by forming a nanogap system composed of a planar Au substrate and an Ag-coated micrometer-sized silica bead, wherein 4-NBT was adsorbed firstly onto the Au substrate and then Ag-coated silica beads, derivatized with 1-alkanethiols, were spread over the 4-NBT layer: the distance between 4-NBT and a nanostructured Ag substrate was varied by the chain length of alkanethiol molecules. Although the planar Au substrate itself was ineffective in the reduction of 4-NBT, hot electrons usable in the reduction of 4-NBT were generated from the Ag-coated silica beads. The hot electrons generated by 514.5-nm radiation were more effective in the reduction of 4-NBT to 4-ABT than those generated by 632.8-nm radiation, although the nanogap was more SERS-active with the excitation at 632.8-nm than at 514.5-nm. The photoreduction efficiency of hot electrons nonetheless decreased linearly with the distance they travelled from the Ag surface: the reduction capability at a distance of 2 nm apart is about one fourth of that in contact situations.Contents Abstract i Contents vi List of Figures ix List of Tables xiv List of Schemes xv Chapter 1. Introduction 1 1.1. Raman Scattering 2 1.1.1. Basic Theory 2 1.1.2. Selection Rules 6 1.2. Surface-Enhanced Raman Scattering (SERS) 8 1.2.1. Mechanism of SERS 8 1.2.2. Electromagnetic (EM) Mechanism 8 1.2.3. Chemical (CHEM) Mechanism 13 1.2.4. Selection Rules 15 1.3. Finite-Difference Time-Domain (FDTD) Method 16 1.3.1. Short Description 16 1.3.2. Principles 17 Chapter 2. SERS of 4-Nitrobenzenethiol and 4-Aminobenzenthiol on Ag in Icy Environments at Liquid Nitrogen Temperature 19 2.1. Introduction 20 2.2. Experimental 24 2.3. Results and Discussion 26 2.4. Summary and Conclusion 36 Chapter 3. Enhanced Raman Scattering in Gaps Formed by Planar Au and Au/Ag Alloy Nanoparticles 38 3.1. Introduction 39 3.2. Experimental 44 3.3. Results and Discussion 47 3.3.1. SERS of 4-ABT sandwiched between flat Au and Ag nanoparticles 47 3.3.2. SERS of 4-ABT sandwiched between flat Au and Au/Ag alloy nanoparticles 63 3.4. Summary and Conclusion 76 Chapter 4. Photoreduction of 4-Nitrobenzenethiol on Au by Hot Electrons Plasmonically Generated from Ag Nanoparticles : Gap-Mode SERS Observation 78 4.1. Introduction 79 4.2. Experimental 81 4.3. Results and Discussion 83 4.4. Summary and Conclusion 96 Reference 98 Appendix 108 List of Publications 109 List of Presentations 113 Abstract (Korean) 116Docto

A Key Recovery Method by using Recovery DIDs in the DID-based Decentralized Key Management System

학위논문(석사)--아주대학교 일반대학원 :컴퓨터공학과,2021. 2블록체인을 기반으로 하는 자기 주권형 디지털 신원 증명 모델이 떠오르고 있다. 이 모델에서, 비밀키 관리와 같은 대부분의 행동에 대한 책임은 사용자에게 돌아오게 된다. 특히 키 관리에 대한 중요성이 높은데, 사용자가 비밀키를 잃어버린다면 키 복구를 위해 의지할 상위 기관이 없기 때문이다. 키 복구를 위해 하이퍼레저 인디의 탈중앙화 키 관리 시스템에서 복구 키를 여러 개의 share로 나누어 Recovery Trustee에게 저장하는 샤미르의 비밀 분산 방식을 이용한 연구가 있다. 이 방식은 몇 명의 배신자가 있더라도 특정 개수 이상의 share가 모이면 키 복구가 가능하다는 장점이 있다. 이 방식은 share를 맡게 되는 Recovery Trustee들이 share의 주인을 식별한 후 share를 돌려주는 방식이다. 이 방식에서 Recovery Trustee들은 키 복구를 할 수 있는 충분한 share를 모으기 위해 결탁할 수 있으므로 키가 유출될 가능성을 열어준다. 본 논문에서는 DID 기반 탈중앙화 키 관리 시스템에서 복구용 DID인 RDID를 사용하여 키를 복구하는 방법을 제안한다. 제안된 방법에서는 사용자의 키 복구를 도와주기 위해 Recovery Trustee Manager를 도입한다. Recovery Trustee Manager는 사용자를 식별하고 RDID를 이용해 키 복구에 도움을 준다. 여기서 Recovery Trustee들은 사용자 식별을 하지 않고 RDID 인증을 통해 share를 관리하는 역할을 한다. RDID를 사용해 Recovery Trustee의 사용자 식별 프로세스를 제거하여 Recovery Trustee들의 결탁을 방지할 수 있게 된다.제1장 서론 1 제2장 이론적 배경 3 제1절 공개키 기반 구조(PKI) 3 제2절 블록체인(Blockchain) 5 제3절 자기 주권형 디지털 신원 증명 모델 7 제1항 디지털 신원 증명 모델의 발전 과정 7 제2항 DID(Decentralized Identifier) 9 제3항 DID Architecture 10 제4항 Verifiable Credential 13 제3장 관련연구 15 제1절 탈중앙화 키 관리 시스템(DKMS) 15 제2절 탈중앙화 키 관리 시스템에서의 키 복구 18 제4장 제안 방식 23 제1절 RDID 발급 과정 27 제2절 복구 키 분배 29 제3절 키 복구 및 지갑 데이터 복구 32 제4절 평가 및 기존 방식과의 비교 35 제1항 가용성 35 제2항 기밀성 36 제3항 무결성 36 제4항 기존 방식과의 비교 37 제5항 한계 및 추후 연구 38 제5장 결론 39 참고문헌 40 Abstract 42MasterA self-sovereign digital identity verification model based on blockchain is emerging. In the model, the responsibility for most actions, such as managing secret keys falls to the owner. In particular, the importance of key management becomes higher because if a user loses the secret key, there is no upper-level organization to rely on for key recovery. In the Decentralized Key Management System of Hyperledger Indy, there is a study using Shamir's secret sharing method that divides the recovery key into several shares and stores them in the recovery trustees. This method has the advantage that even if there are several traitors, a key recovery is possible if more than a certain number of shares are collected. In this method, a recovery trustee returns a share only after it identifies the owner of the share. Recovery trustees could collude with one another to gather enough shares to recover the key, thereby opening the possibility of leaking the key. In this paper, we propose a key recovery method by employing Recovery DIDs (RDID) in the DID-based decentralized key management system. In the proposed method, we introduce a recovery trustee manager to help users recover their keys. The recovery trustee manager identifies the owner and uses the RDIDs to aid the key recovery. Recovery trustees manage shares through RDID authentication without user identification. By using RDIDs, it is possible to prevent the collusion of recovery trustees by removing the user identification process from the trustees