Designing Huge Colloidal Quantum Dots for Scalable & Deterministic Placement of Single-Photon Emitters

Abstract

Colloidal quantum dots (QDs) have been widely explored as light-emitting materials due to their tunable optical properties, high quantum yield, and solution-processability. In quantum photonics, individual QDs can serve as single-photon emitters that are critical for quantum technologies, including communication, computing, cryptography, and metrology, where discrete photons function as qubits. However, conventional emissive QDs, including Cd-, In-, Pb-, and Hgbased materials, typically have diameters below 10 nm due to the Bohr radius limitation and synthetic feasibility. Even with core/shell architectures, where materials like CdS or ZnS encapsulate the core QDs to enhance stability and emission, they rarely exceed 20 nm. This size constraint creates a fundamental challenge in integrating QDs into photonic devices, as optical cavities and resonant structures often have mode volumes on the micrometer scale, leading to poor spatial overlap and limiting efficient light-matter interaction. To address this size mismatch while maintaining desirable optical properties, this dissertation explores three complementary approaches. First, a machine learning framework is developed to refine CdSe and InP QD syntheses by extracting synthetic parameters from literature, addressing data inconsistencies, and predicting optimized reaction conditions. Using data augmentation and predictive modeling, this method enables precise control over emission wavelengths and sizes, complementing experimental efforts to design QDs with targeted properties (Chapter 3). Next, Chapter 4 explores silica encapsulation as a method to enlarge QDs and enhance their stability in air. By coating QDs with a protective silica shell, the particle size increases to around 90 nm. This enlargement enables deterministic patterning of emissive particles onto planar substrates while preserving single-photon emission. Finally, a stepwise CdS shelling strategy is introduced in Chapter 5 to synthesize colossal CdSe/CdS QDs with diameters exceeding 100 nm, significantly expanding the range of QD-based light emitters. Using electrohydrodynamic inkjet printing, these QDs are patterned into large arrays and deterministically positioned into nanobeam cavities for scalable quantum light sources. Beyond their advantages for particle placement, colossal QDs exhibit exceptional stability under ambient excitation, making them well-suited for studies requiring sustained high excitation conditions. Their large size also provides a platform for investigating nanocrystal growth mechanisms, as structural evolution can be directly visualized using electron microscopy with greater clarity than smaller QDs allow. Together, the approaches presented herein advance the synthesis and integration of QDs for scalable quantum photonics by combining data-driven synthesis optimization, silica shelling for size enlargement, and the development of colossal core/shell QDs. These approaches address key challenges in QD-based single-photon emitters and provide strategies for improving stability, deterministic placement, and scalability. Beyond photonics, the findings contribute to a deeper understanding of QD growth and stability, supporting their broader application in quantum information science and next-generation optoelectronics.