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- All Subjects: Quantum Dots
- Creators: Bennet, Peter
- Creators: Buttry, Daniel
Description
Colloidal quantum dots (QDs) or semiconductor nanocrystals are often used to describe 2 to 20 nm solution processed nanoparticles of various semiconductor materials that display quantum confinement effects. Compared to traditional fluorescent organic dyes, QDs provide many advantages. For biological applications it is necessary to develop reliable methods to functionalize QDs with hydrophilic biomolecules so that they may maintain their stability and functionality in physiological conditions. DNA, a molecule that encodes genetic information, is arguably the smartest molecule that nature has ever produced and one of the most explored bio-macromolecules. DNA directed self-assembly can potentially organize QDs that are functionalized with DNA with nanometer precision, and the resulting arrangements may facilitate the display of novel optical properties. The goal of this dissertation was to achieve a robust reliable yet simple strategy to link DNA to QDs so that they can be used for DNA directed self assembly by which we can engineer their optical properties. Presented here is a series of studies to achieve this goal. First we demonstrate the aqueous synthesis of colloidal nanocrystal heterostructures consisting of the CdTe core encapsulated by CdS/ZnS or CdSe/ZnS shells using glutathione (GSH), a tripeptide, as the capping ligand. We next employed this shell synthesis strategy to conjugate PS-PO chimeric DNA to QDs at the time of shell synthesis. We synthesized a library of DNA linked QDs emitting from UV to near IR that are very stable in high salt concentrations. These DNA functionalized QDs were further site-specifically organized on DNA origami in desired patterns directed by DNA self-assembly. We further extended our capability to functionalize DNA to real IR emitting CdxPb1-xTe alloyed QDs, and demonstrated their stability by self-assembling them on DNA origami. The photo-physical properties of the QDs were further engineered by attaching a QD and a gold nanoparticle in controlled distances on the same DNA origami, which revealed a much longer range quenching effect than usual Forster Resonance Energy Transfer. We are currently engaged in enhancing photoluminescence intensity of the QDs by bringing them in the plasmonic hot spots generated by cluster of larger plasmonic nanoparticles.
ContributorsSamanta, Anirban (Author) / Yan, Hao (Thesis advisor) / Liu, Yan (Thesis advisor) / Buttry, Daniel (Committee member) / Gould, Ian (Committee member) / Arizona State University (Publisher)
Created2014
Description
he accurate simulation of many-body quantum systems is a challenge for computational physics. Quantum Monte Carlo methods are a class of algorithms that can be used to solve the many-body problem. I study many-body quantum systems with Path Integral Monte Carlo techniques in three related areas of semiconductor physics: (1) the role of correlation in exchange coupling of spins in double quantum dots, (2) the degree of correlation and hyperpolarizability in Stark shifts in InGaAs/GaAs dots, and (3) van der Waals interactions between 1-D metallic quantum wires at finite temperature. The two-site model is one of the simplest quantum problems, yet the quantitative mapping from a three-dimensional model of a quantum double dot to an effective two-site model has many subtleties requiring careful treatment of exchange and correlation. I calculate exchange coupling of a pair of spins in a double dot from the permutations in a bosonic path integral, using Monte Carlo method. I also map this problem to a Hubbard model and find that exchange and correlation renormalizes the model parameters, dramatically decreasing the effective on-site repulsion at larger separations. Next, I investigated the energy, dipole moment, polarizability and hyperpolarizability of excitonic system in InGaAs/GaAs quantum dots of different shapes and successfully give the photoluminescence spectra for different dots with electric fields in both the growth and transverse direction. I also showed that my method can deal with the higher-order hyperpolarizability, which is most relevant for fields directed in the lateral direction of large dots. Finally, I show how van der Waals interactions between two metallic quantum wires change with respect to the distance between them. Comparing the results from quantum Monte Carlo and the random phase approximation, I find similar power law dependance. My results for the calculation in quasi-1D and exact 1D wires include the effect of temperature, which has not previously been studied.
ContributorsZhang, Lei (Author) / Shumway, John (Thesis advisor) / Schmidt, Kevin (Committee member) / Bennet, Peter (Committee member) / Menéndez, Jose (Committee member) / Drucker, Jeff (Committee member) / Arizona State University (Publisher)
Created2011