Electronic Thesis and Dissertation Repository

Degree

Doctor of Philosophy

Program

Physics

Supervisor

Dr. Leo W. M. Lau

Abstract

The development of simple and effective methods of incorporating molecular moieties with desirable properties into new functional materials is one of the ultimate goals of material scientists. The work presented in this thesis demonstrates an easy way to accomplish this using a beam of gaseous H2, which we call hyperthermal hydrogen induced cross-linking (HHIC). We prove theoretically and experimentally that when the kinetic energy of H2 is raised to ~20 eV, it becomes a light-mass projectile which is energetic enough to knock hydrogen atoms off of organic molecules, but not other heavier atoms. By developing a reactor to inexpensively generate a high flux of H2 with the appropriate kinetic energy, we exploit this selective C–H cleavage method to create carbon radicals, which then recombine to yield covalent cross-links. Using this method to cross-link organic moieties of our choice with no change in their desirable properties, we have a) fabricated functional materials with tailor-made mechanical, chemical, and biomedical properties, and b) modified electrical properties of conducting and semiconducting polymers.

Chapter 2 provides an insight into the inception of the HHIC reactor, its operation, and necessary theoretical background of electron cyclotron resonance plasma, gas phase collisions involved in HHIC, and hydrogen abstraction. We also discuss energy distribution of cross-linking projectiles as measured by quadrupole mass spectrometer and Faraday cup detector. We have found that under standard HHIC conditions, the number of hyperthermal projectiles doubles with respect to the number of collision initiating particles, yielding a high-throughput of the HHIC method.

Chapter 3 focuses on the evaluation of the HHIC method in terms of degree of cross-linking, topographical, chemical, and electrical changes, and selectivity towards chemical functional groups. We show that the HHIC method is very gentle in treating chemical functionalities. However, we also show that the HHIC reactor in its current configuration is responsible for exposing sensitive organic semiconducting materials to deep vacuum UV irradiation, damaging their pi–pi* conjugated system and negatively effecting their electrical properties.

Chapter 4 extends the study of HHIC by exploring its capability of grafting organic moieties onto polymer surfaces disallowed under normal conditions.


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