Nanoscale characterization and modification of soft surface
thesisposted on 14.11.2017 by Yeonuk Kim
In order to distinguish essays and pre-prints from academic theses, we have a separate category. These are often much longer text based documents than a paper.
The aim of this research is to modify and characterize the surface of soft materials. Firstly, the surface morphology and physical attributes of biocompatible hydrogel are tailored at micro/nano scale for biomedical research. Utilizing gallium ion beam, thin film of hydrogel is irradiated with varied ion fluence, accelerating voltage and incident angle. The sputtering yield, surface morphology and mechanical properties of hydrogel film were investigated using Scanning Electron Microscopy (SEM) and Atomic Force Microscopy (AFM). The change in surface roughness, porosity and Young’s modulus (E) after the low kV ion beam irradiation was observed from nanoscale characterization of hydrogel with AFM. Furthermore, cell culture studies confirmed the biocompatibility of hydrogel after the irradiation. In the second phase of the research, AFM spectroscopy was utilized to investigate the physiochemical properties of tissues, aiming to identify and differentiate cell types. Young’s moduli were acquired with AFM force spectroscopy of each cell type and chemical characterization on the samples were also performed using the functionalized AFM tips. From the AFM spectroscopy, distinct distribution of stiffness and adhesion forces were observed among different cell types. Change in the surface stiffness and adhesion after ion beam ablation was also observed. The identification of unknown cell types was performed utilizing the Kolmogorov-Smirnov (K-S) test. Finally, novel approaches of rapid fabrication of metallic nanoparticles are proposed, for functionalizing soft surfaces, with both nanostencil method and FIB direct pattering method. FIB was utilized to fabricate predesigned nano holes on silicon nitride membrane and metallic nanoparticles were deposited on various surface using electron beam (E-beam) evaporator. Direct FIB etching on gold coated substrate was also performed. Both approaches were capable of fabricating sub-100 nm nanoparticles with predefined parameters such as diameter, height and spacing. The fidelity of the fabricated nanoparticles with the original design was confirmed from AFM and SEM images. The potential functionality of the nanoparticles was confirmed by investigating the nanoparticles with angle-resolved Cathodoluminescence (CL) nanoscopy. The proposed approach could offer advantages on various biomedical and bioengineering applications.