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Fluorescence Quenching in single CdSe/CdS Dot-In-Rod Nanostructures using Modified Atomic Force Microscopy tips

Karumbamkandathil, Arshad (2016)
Master's Thesis (54 pages)
Committee Chair / Thesis Adviser: Lian, Tim
Committee Members: Widicus Weaver, Susanna ; Evangelista, Francesco
Research Fields: Physical chemistry
Keywords: Fluorescence Quenching; AFM; Single particle fluorescence
Program: Laney Graduate School, Chemistry
Permanent url: http://pid.emory.edu/ark:/25593/rq061

Abstract

The main objective of this thesis is to study the quenching of fluorescence in

single CdSe/CdS dot-in-rod (DIR) nanostructures via electron transfer (ET) using

modified AFM tips. AFM tips where either modified with TiO2 nanoparticles (NP), or

commercially available Pt AFM tips were used for this study. Electron Transfer from

DIR to TiO2 or Pt was shown, by measuring the quenching in photoluminescence (PL)

intensities and lifetimes of single CdSe/CdS DIRs.

It was seen that the fluorescence quenching is uniform along the length of the

DIR, suggesting the ET process from DIR to TiO2 NP or Pt is the rate-determining step

and dominates over ionization, diffusion, and recombination rates. Cross-section

dependent study showed that quenching occurs only within the tip radius in contact with

the DIR and is dependent on the tip material and geometry. Vertical tip-DIR separation

study showed that the quenching can occur only when the tip is in close contact with the

DIR. Control experiments with regular Si AFM tips showed that quenching can occur

only when an electron acceptor like TiO2 or Pt is attached to the AFM tip, suggesting

charge transfer to be occurring.

Table of Contents

Chapter 1 Introduction ................................................................................................... 1

1.1 Theory of Fluorescence.............................................................................1

1.2 Fluorescence Lifetime and Quantum Yield.............................................3

1.3 Semiconductor Nanoparticles ...................................................................4

1.4 From bulk CdSe to quantum confined nanocrystals..................................5

1.5 Relaxation process in Semiconductor Nanocrystals: Non-radiative and

radiative transitions .........................................................................................7

1.5.1 Non-radiative relaxations........................................................7

1.5.2 Radiative relaxation or Fluorescence................................................9

1.6 Core/Shell Nanocrystals...........................................................................11

1.7 CdSe/CdS dot-in-rods...........................................................................13

1.8 CdSe/CdS DIRs coupled with metal nanocrystals........................................15

1.9 Fluorescence Quenching...........................................................................16

Chapter 2 Experimental Setup and Sample Preparation .............................................. 20

2.1 Synthesis of CdSe/CdS DIRs: ...........................................................20

2.2 Synthesis of TiO2 Nanoparticles:............................................................20

2.3 Atomic Force Microscopy (AFM) and Tip Functionalization (single TiO2 NP

attachment to an AFM Tip):.........................................................................21

2.4 Single Molecule Fluorescence Spectroscopy......................................22

2.5 Time-Correlated Single Photon Counting (TCSPC) Technique....................................24

2.6 Fluorescence Intensity and Lifetime Measurements.......................................25

2.7 Fluorescence Intermittency or Blinking......................................26

2.8 Using Single Molecule Fluorescence to study interfacial ET....................................29

Chapter 3 Results and Discussion......................................................................................32

Summary and Future Outlook........................................................................................41

References .........................................................................................................................42

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