Project Report

Electronic Motions Inside Lead Selenide Quantum Dots Quantum dots have a wide range of applications from quantum computing to photovoltaic devices due to their energy quantization and band-gap tunability. The intra-dot dynamics of these semiconductor quantum dots are interesting because of interactions between the electronic and phonon modes. These collective vibrational motions can impact electronic excitation dynamics by providing an alternative relaxation pathway. Understanding the excitation dynamics and electronic-phonon interactions will aid in the design and synthesis of these quantum dots to better suit their desired function. This experiment aimed to elucidate the excited electronic motions in quantum dots, including any possible electronic coherence and interaction between electronic and phonon dynamics. We chose lead selenide (PbSe) quantum dots as the model system because of their potential application in solar cells. We expected to observe interaction between the manifolds of electronic states and phonon modes found inside the PbSe quantum dots. Femtosecond transient absorption spectroscopy is a simple yet powerful tool for probing the electronic structure and motions within the quantum dots. The excitation or decay will result in an increase or decrease in signal, respectively, while electronic or vibrational coherence will cause the signal to oscillate. The majority of my time at the East Asia and Pacific Summer Institute Fellowship in Singapore was dedicated to the building the femtosecond transient absorption spectroscopy instrument. The experimental apparatus was successfully assembled. Unfortunately, a necessarily laser service appointment prevented us from performing an experiment. The project will be continued by the Singaporean host and collaborator. We expect that the experimental result will provide an insight into the lifetime of different electronic states and relaxation pathways of quantum dots. We also mentored two Singaporean undergraduate students in the science of spectroscopy. The students assisted in the building of the optical apparatus and engaged in the discussion of excitation dynamics in quantum dot systems. This experience allowed the students to learn more about graduate research opportunities and encouraged them to consider applying to graduate schools in the United States.

National Science Foundation (NSF)
Office of International and Integrative Activities (IIA)
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Carter Kimsey
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Panitchayangkoon Gitt
United States
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