2024 MSE Senior Design Project

Materials Science seniors presented research projects at the annual Columbia Senior Design Expo on May 2, 2024. Participants from the APAM Department included:
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Kaylynn Chen
Advisor: James Hone

Title of Project: Benchmarking Dielectrics for Quantum Computing: Second Harmonic Generation in Merged Element Transmon Qubits

Abstract: Van der Waals (vdW) heterostructures represent a promising platform for quantum devices, leveraging their low-loss characteristics due to the single-crystal nature of the constituent two-dimensional (2D) materials and the absence of dangling bonds at their atomically sharp interfaces. We have demonstrated the integration of NbSe2 and WSe2 into standard transmon circuits to fabricate superconducting microwave resonators. Here, we introduce second harmonic generation (SHG), a novel characterization technique, to probe the WSe2 dielectric within the vdW heterostructure. SHG, which is sensitive to the absence of inversion symmetry in materials and arises in the electric-dipole limit, serves as a non-invasive tool for assessing the crystal symmetry of WSe2. This study underscores the utility of nonlinear optical methods for elucidating structure-property relationships at the nanoscale, which are crucial for the development of quantum functionalities in superconducting quantum devices. This work marks the addition of a characterization step which could be useful towards harnessing vdW heterostructures for advanced quantum applications.

Keywords: Van der Waals materials, superconducting qubits, nonlinear optics
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Mier Liu
Advisor: James S. Im

Title: Computational Investigation into Nucleation in Thin Films under Temperature Gradient 

Abstract: Classical nucleation theory (CNT) models geometric evolution (grain growth) as a sequence of sharp interface geometries. A central feature of classical nucleation theory is the assumption that energy is minimized at any given volume. The present work utilizes Surface Evolver to model nucleation in systems with discontinuous changes in boundary conditions and in the presence of temperature gradients.

Keywords: Classical Nucleation Theory, Grain Growth, Nucleation Modeling, Material Temperature Gradients

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Kunlun Wu, Cheng-Chia Tsai, Shiqi Yang
Advisor: Professor Siu-Wai Chan, Professor Nanfang Yu

Title: Refractive Index Enhancement of Nano-Ceria infused SU8 Nanocomposite Thin Films

Abstract: Polymer nanocomposites are increasingly relevant for their potential to be used in nano-photonic devices, offering an attractive alternative to current materials due to their cost-effectiveness and manufacturability. These composites provide tunable refractive indices, a desirable characteristic for managing light propagation in devices operating within the visible light spectrum.In this context, our study examines the potential of cerium oxide nanoparticle-infused SU8 photoresist films to enhance refractive indices. CeO2 is selected for its high refractive index and optical transparency, aiming to enhance the refractive index of the polymer film by various amounts. We synthesized nanoparticles over two timeframes, 6-hour and 72-hour periods, to generate different particle sizes and dispersed them within the SU8 polymer at weight ratios including 0.1%, 0.5%, and 1%; additionally, we also made control samples with pure polymer films. Ellipsometry measurements were made to ascertain various optical properties. The refractive index of the films measured at 632.8 nm demonstrated a somewhat linear increase in refractive index with nanoparticle concentration, with larger nanoparticles contributing more effectively to this enhancement. Cerium oxide nanoparticle incorporation into SU8 polymer films increases the refractive index, affirming the potential for its use in nano-photonic applications. Further exploration into the incorporation of metal-doped CeO2 nanoparticles, variation of polymer materials, and the interplay between absorption and refractive index, both varied by film thickness, affecting reflection intensities, is suggested to enhance the functional scope of the study. Keywords: Polymer Nanocomposites, Refractive Index, Cerium Oxide, Nanoparticles, Visible Light Spectrum 

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Kunlun Wu, Xinyi Zhang, Zhaowen Lin, Jianing Zhou
Advisor: Professor Siu-Wai Chan

TItle: Conductivity Enhancement of Cerium Oxide Nanoparticles through Copper Doping 

Abstract: Cerium oxide has been an option for low temperature catalysts used in the Water-Gas-Shift Reaction (WGS) for its ability to shuttle oxygen atoms due to its facile redox cycle between Ce(IV) and Ce(III) oxidation states at relatively low temperatures, which is a key redox mechanism. This study focuses on the optimization of catalytic properties of cerium oxide nanoparticles through copper doping to augment their electrical conductivity, thereby aiming to reduce the activation energy necessary for electron and surface ion transfer processes. Enhanced charge carrier mobility, a direct result of this increased conductivity, is essential for boosting catalytic efficiency by facilitating more effective charge transfer and lowering the reaction's energy barriers. We prepared copper-doped cerium oxide nanoparticles with atomic doping concentrations of 1%, 2%, 4%, 8%, and 16%, and compared them with undoped control groups. The nanoparticles were pressed into pellets and sintered at 350 degrees Celsius for 4 hours. The resulting pellets were evaluated across a temperature range of 50°C to 200°C at 25°C intervals using impedance spectroscopy. Our findings indicate a peak in conductivity at a doping level of 8%, beyond which conductivity decreases, suggesting the passing of optimal doping concentration for enhanced electrical properties. A decrease in impedance with increased temperature was also observed. The behavior generally aligns with expectation in that doping at low concentration creates electron carriers and oxygen vacancies enhances conductivity as well as catalytic activity, while excessive doping does not lead to better performance. Keywords: Cerium Oxide, Nanoparticles, Copper Doping, Impedance Spectroscopy, Conductivity, WGS Reaction