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Synthesis, characterization and single particle spectroscopy of semiconductor quantum dots and quantum dot oligomers : 반도체 양자점과 양자점 올리고머의 합성을 통한 단일 입자 분광학 및 특성에 대한 연구

DC Field Value Language
dc.contributor.advisor정연준-
dc.contributor.advisorThomas Basché-
dc.contributor.author후 난-
dc.date.accessioned2017-07-14T05:56:41Z-
dc.date.available2017-07-14T05:56:41Z-
dc.date.issued2016-02-
dc.identifier.other000000132661-
dc.identifier.urihttps://hdl.handle.net/10371/125301-
dc.description학위논문 (박사)-- 서울대학교 대학원 : 화학부 물리화학 전공, 2016. 2. Thomas Basché.-
dc.description.abstract콜로이드 상태의 반도체 양자점은 크기에 따라 변화하는 광학적 특성으로 인하여 과학 및 기술분야에서 많은 관심을 받고 있다. 본 학위논문의 첫번째 파트에서는CdSe/CdS/ZnS 코어/쉘/쉘 양자점들을 합성하고, 이를 구조체로 하여 양자점 이합체들을 제조하였다. 이합체화 과정에서 양자점들의 침전/재분산 과정을 통해 양자점 올리고머를 형성시키고 밀도 구배 초원심분리를 통하여 농축시켰다. 얻어진 양자점 단량체와 호모-이합체에 대해서는 295K과 4.5K의 온도 하에서 단일 입자 분광법을 시행하였다. 비슷한 크기를 갖지만 서로 다른 조성을 가지는 양자점들로 구성된 양자점 헤테로-이합체에 대해서는 원자 힘 현미경과 공초점 형광 현미경을 결합한 장치 구성을 통해 식별 및 분석을 진행하였다. 두번째 파트에서는 InP/ZnSeS 양자점들을 원형 구배의 조성과 구조를 갖도록 제조 및 분석하여 Se의 양이 광물리적 특성에 중대한 영향을 끼침을 확인하였다. 최선의 시료인 0.2 mmol Se의 경우 높은 형광 양자 효율(85%)과 강한 형광 깜박임 억제를 보이며 단일 분자 실험에서 평균 on-time이 85%에 달하였다. 이러한 깜박임 억제는 계면 변형 및 결함의 감소, 구배를 갖는 내부 구조로 인한 quasi-type II 전자 구조 및 완만한 밴드 끝단 에너지 포텐셜에 의한 것으로 여겨진다.-
dc.description.abstractSemiconductor colloidal quantum dots (QDs) gain scientific and technological interest due to their size-dependent optical properties. In this thesis, (1) core/shell/shell CdSe/CdS/ZnS QDs have been synthesized and used as building blocks to construct QD dimers. The dimerization includes assembly of QDs into oligomers by a precipitation/re-dispersion process and subsequent enrichment of the dimers by density gradient ultracentrifugation. Single particle spectroscopy of the obtained monomers and homo-dimers has been performed at 295 K and 4.5 K. QD hetero-dimers, whose components have with similar sizes but different compositions, could be identified and characterized by a combined setup of atomic force and confocal fluorescence microscopy. (2) InP/ZnSeS QDs with radial gradient composition and structure have been prepared and characterized, whereas the amount of Se has a significant influence on the photo physical properties. The best sample with 0.2 mmol Se exhibits a high fluorescence quantum yield (85%) and a strong fluorescence blinking suppression, with an average on time fraction of 85%. This blinking suppression is tentatively attributed to the reduction of the interfacial strain and defects, the quasi-type-II electronic structure and the smooth band edge energy potential with a soft confinement derived from the gradient internal structure.-
dc.description.tableofcontents1 Introduction 1

2 Theoretical background 5
2.1 Semiconductor nanocrystal quantum dots (QDs) 5
2.1.1 Electronic states and optical properties 5
2.1.2 Synthesis, growth and crystal structures 13
2.1.3 Core/shell structure 19
2.1.4 InP based quantum dots 21
2.2 Preparation of quantumdot oligomers 23
2.2.1 Self-assembly and separation of nanoparticles 23
2.2.2 Density gradient ultracentrifugation (DGU) 28
2.3 Single particle spectroscopy of quantumdots 32
2.3.1 Confocal fluorescence microscopy 32
2.3.2 Detection of a single particle (QD) 35
2.3.3 Fluorescence blinking 36
2.3.4 Spectral diffusion 43
2.3.5 Single particle spectroscopy at cryogenic temperature 44

3 Experimentalmaterials and methods 51
3.1 Materials 51
3.2 Synthetic methods 53
3.2.1 Synthesis of CdSe/CdS/ZnS quantum dots 53
3.2.2 Assembly and enrichment of quantumdot oligomers 57
3.2.3 Synthesis of InP/ZnSeS quantumdots 57
3.3 Characterization techniques 58
3.3.1 Ensemble absorption and fluorescence spectroscopy 58
3.3.2 Transmission electron microscopy (TEM) 60
3.3.3 Energy dispersive X-ray spectroscopy (EDS) 60
3.3.4 X-ray diffraction (XRD) 60
3.3.5 Fluorescence lifetime measurements 61
3.4 Experimental setups for single particle investigations 61
3.4.1 Sample preparation 61
3.4.2 Excitation light sources 61
3.4.3 Confocal microscope for cryogenic temperature measurement 62
3.4.4 Confocal microscope for roomtemperature measurement 66
3.4.5 Experimental conditions for single particle measurements 67

4 Monomers, homo- and hetero- dimers of CdSe/CdS/ZnS QDs 69
4.1 Motivation and approaches 69
4.2 CdSe/CdS/ZnS QD monomers and homo-dimers 71
4.2.1 CdSe cores and CdSe/CdS/ZnS QDs 71
4.2.2 Assembly of CdSe/CdS/ZnS QDs 73
4.2.3 Enrichment and separation of QD oligomers 76
4.2.4 Fluorescence imaging of single QDs 83
4.2.5 Single particle spectroscopy of QD monomer and dimer samples at room temperature (T = 295 K) 85
4.2.6 Single particle spectroscopy of CdSe/CdS/ZnS QD monomers at cryogenic temperature (T = 4.5 K) 86
4.2.7 Single particle spectroscopy of QD dimer sample at cryogenic temperature (T = 4.5 K) 92
4.3 CdSe/CdS/ZnS QD hetero-dimers 96
4.3.1 Size dependent fluorescence of CdSe core particles 96
4.3.2 QD hetero-dimers whose QD components have different sizes 96
4.3.3 QD hetero-dimers whose QD components have similar sizes 103
4.3.4 Structure IIa: QD components with the same CdSe core 104
4.3.5 Structure IIb: QD components with different CdSe cores 105
4.4 Summary 111

5 Investigations of InP/ZnSeS QDs 113
5.1 Introduction and motivation 113
5.2 Sample description 115
5.3 Ensemble characterizations 115
5.3.1 HLim series 115
5.3.2 H series 116
5.3.3 L series 118
5.4 Single particlemeasurements at roomtemperature (T = 295 K) 127
5.4.1 HLim series 127
5.4.2 H and L series 134
5.5 Single particlemeasurements at cryogenic temperature (T = 4.5 K) 141
5.5.1 Typical emission spectrum of InP/ZnSeS QDs at 4.5 K 142
5.5.2 Phonons contributions 142
5.5.3 Categories of single particle spectra 146
5.5.4 Average optical phonon energies 148
5.5.5 Fluorescence blinking at 4.5 K 148
5.6 Comparison of the different samples 151
5.7 Possible mechanisms of the strong blinking suppression 153
5.8 Summary 156

Summary and outlook 159

References 163		-
dc.formatapplication/pdf-
dc.format.extent13741776 bytes-
dc.format.mediumapplication/pdf-
dc.language.isoko-
dc.publisher서울대학교 대학원-
dc.subjectquantum dots-
dc.subjectdimerization-
dc.subjectsingle particle spectroscopy-
dc.subjectquantum yield-
dc.subjectblinking suppression-
dc.subject.ddc540-
dc.titleSynthesis, characterization and single particle spectroscopy of semiconductor quantum dots and quantum dot oligomers-
dc.title.alternative반도체 양자점과 양자점 올리고머의 합성을 통한 단일 입자 분광학 및 특성에 대한 연구-
dc.typeThesis-
dc.contributor.AlternativeAuthorNan Hu-
dc.description.degreeDoctor-
dc.citation.pages188-
dc.contributor.affiliation자연과학대학 화학부-
dc.date.awarded2016-02-
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