Chemical and Biological Engineering ETDs

Publication Date

Spring 5-13-2025

Abstract

This thesis focuses on the guided self-assembly of metastable nanomembranes (NMs) that are either amorphous or polycrystalline. Guided self-assembly of NMs is a robust and scalable method to obtain a variety of three-dimensional structures such as helices, rolled-up tubes, and networks of interconnected channels. These 3D structures have important applications as on-chip actuators, sensors, inductors, transformers, waveguides, and antennas. Furthermore, a large amount of strain and strain gradient can be imparted in NMs by bending them to a nanoscale and microscale radius of curvature, making guided self-assembly on NMs a viable route to extreme strain engineering of amorphous and polycrystalline NMs.

Leveraging the tremendous potential of self-assembled NMs requires precise predictive control of their geometrical attributes, such as the diameter of rolled-up tubes, the diameter and pitch of helical structures, and the cross-sectional area of wrinkled channels. The last 20 years have shown much progress in controlling the self-assembly of single-crystalline and stable films, such as semiconductors. Nevertheless, there is a limited understanding of the relaxation of metastable amorphous and polycrystalline NMs. This work aims at filling this knowledge gap by a multidisciplinary approach that encompasses synthesis and processing of NMs, continuum mechanics modeling, and characterization of the structural and functional properties of the NMs.

Central to this effort is predictive modeling of the mechanical response of amorphous and polycrystalline NMs upon relaxation of residual stress in the deposited layers and any additional stress arising from the reconfiguration of atomic bonds under an externally applied stimulus, such as heat.

The thesis describes the application of the model to two selected case studies and systems, namely complex oxide and metal NMs. After heating, reconfiguration-driven assembly is observed in strontium titanate (STO) and Cr/Au/Cr heterostructures. Specifically, STO-based scrolls form into swiss roll structures due to the densification of the complex oxide layer, as measured by x-ray diffraction. End-tethered Cr/Au/Cr NM ribbons assemble into helices of uniform diameter and pitch as a result of plastic changes in the heterostructure during annealing.

Keywords

nanomembranes, self-assembly, reconfiguration, mechanical modeling, helices, metals

Sponsors

AFOSR, NSF, DOE

Document Type

Dissertation

Language

English

Degree Name

Chemical Engineering

Level of Degree

Doctoral

Department Name

Chemical and Biological Engineering

First Committee Member (Chair)

Dr. Francesca Cavallo

Second Committee Member

Dr. Tito Busani

Third Committee Member

Dr. Sang M Han

Fourth Committee Member

Dr. Nathan Jackson

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