PhD Thesis Defense: Eldred Lee

For Info on how to attend this video conference, please email Eldred Lee at eldred.lee.TH@dartmouth.edu

"Towards the Photonic Efficiency Enhancement of Solar-Selective Absorbers and Si-Based High-Energy X-ray Detectors"

Abstract

Our everyday technologies are heavily influenced by light-matter interactions, or photonic interactions, that are engineered to our advantage. The two wavelength regimes that have been deeply scrutinized for several decades are solar (l=250-2500nm) and hard (or high-energy) X-ray regimes (l=0.062-0.124nm; 20-50keV). This thesis proposes and investigates novel methods to substantially alleviate the known issues of the state-of-the-art concentrated solar power (CSP) systems and high-energy X-ray detection technologies.

In the solar wavelength regime, this thesis focuses on development efforts of efficient and durable solar absorbers for CSP systems with Mn- and Fe-oxide nanoparticle-pigmented solar-selective absorber coatings and native oxide solar-selective absorbers of FeMnNiAlCr high entropy alloys (HEAs) that can complement and mitigate the current issues of PV technology that lacks the flexibility on long-term, low-cost energy storage by enhancing the output as CSP systems can enable high-efficiency solar energy harvesting and storage. The solar-selective absorbers developed during the thesis work demonstrated remarkably high solar absorbance while maintaining relatively low thermal emittance loss compared to the existing art; therefore, leading to high thermal efficiency.

This thesis also investigates the inception of a novel yet simple hard X-ray photon energy attenuation layer (PAL) to advance the high-energy X-ray detection (20-50keV range) and to mitigate major limitations of state-of-the-art high-energy X-ray detection technologies such as scintillation and Si direct detection. These prevalent methods have low photon-to-photoelectron conversion efficiencies and often inefficient for >10keV photons. In this thesis, a two-layer design with a top thin film high-Z PAL and a bottom Si detector has been conceptualized using Monte Carlo N-Particle software (MCNP6.2) to demonstrate that the principle of photon energy down conversion, where high-energy X-ray photon energies are attenuated down to ≤10keV via inelastic scattering suitable for efficient photoelectric absorption by Si. The computational results show that >10´ increase in quantum yield from Si direct detection can be achieved. Such enhancement has been experimentally confirmed via a preliminary demonstration using PAL-integrated CMOS image sensors, opening new doors for next-generation high-energy X-ray detection methods.

Thesis Committee

• Jifeng Liu, PhD (Chair)
• Eric R. Fossum, PhD
• Brian W. Pogue, PhD
• Weiyang Li, PhD
• Zhehui Wang, PhD (External, Los Alamos National Laboratory)

Contact

For more information, contact Theresa Fuller at theresa.d.fuller@dartmouth.edu.