THE USE OF ARRAYED NANO-DIMENSIONAL TEMPLATE STRUCTURES FOR CONTROLLED GROWTH

Open Access
- Author:
- Peng, Chih-Yi
- Graduate Program:
- Engineering Science and Mechanics
- Degree:
- Doctor of Philosophy
- Document Type:
- Dissertation
- Date of Defense:
- March 03, 2005
- Committee Members:
- Stephen Joseph Fonash, Committee Chair/Co-Chair
S Ashok, Committee Member
Osama O Awadelkarim, Committee Member
Jian Xu, Committee Member
Sanjay B Joshi, Committee Member - Keywords:
- nanochannel
nanowire
nanoribbon
template
polymer - Abstract:
- The objective of this research is to develop a fabrication procedure for producing nanowires and nanoribbons in arrays and circuits without the need for any post-synthesis pick-and-place processing. A general procedure for the fabrication of nano-dimensional channels and their use as templates for the formation of nanomaterial arrays is presented in this thesis. The approach developed uses nanodimensional channels as permanent templates for the formation of nanomaterial arrays with precise dimensional, positional, and orientational control as well as with built-in electrical access, when appropriate. The procedure is general, allowing the synthesis of different materials inside the nanochannels, and opens the door to “grow-in-place” manufacturing. Two versions of nanochannels for the nanomaterial growth were fabricated, and different nanomaterials grown in the nanochannels were demonstrated. The first version of the template is a nanochannel without the built-in electrodes. The nanochannel template can be completely open and allows nanowire growth, alignment, precise positioning, and geometrical confinement. In the case of polymers this template approach allows different kinds of chain-growth polymerization, such as poly(methyl methacrylate) (PMMA) by radical polymerization, polythiophene (PT) by photopolymerization. It was also shown that polymer nanofilaments can even be released without breaking. The oxygen plasma etching and atomic force microscope tip cutting were used to verify the presence of polymer material. We also demonstrated the carbon nanofiber growth in this first version of the nanochannels using a catalyst metal in the middle in a chemical vapor deposition (CVD) system. Carbon nanofibers can grow inside and even grow out of the nanochannels, and the dimension, location and orientation of carbon nanofibers followed the pre-designed nanochannels which establish that the nanochannel is also an effective growth template for carbon nanofibers. Fully enclosed horizontal nanochannels, in a pre-arranged array with built-in electrical contacts and chemical access regions, were used as the second version of templates for electrochemical synthesis of conducting polymer nanoribbons. In this “grow-in-place” approach, the nanochannel templates are part of the final array structure and remain after fabrication of the nanoribbons. The built-in electrical contacts, which provide the electrical potential for electrochemical polymerization, also remain and become contacts/interconnects to the array components. The “grow-in-place” architecture and methodology removes the need for template dissolution, any post-synthesis nanoribbon “grow-and-then-place” manipulation, and any post-synthesis electrical contacting. The fact that the templates are fully enclosed prohibits dendrite formation during growth, ensures precise dimensionality, and provides the encapsulation needed in any real device application. Polyaniline nanostructures electrochemically polymerized in the nanochannels were found to be fibrils that grow from the central region of the growth-template cross-section. Two-point and four-point electrical characterization of these polyaniline nanoribbons, obtained using the built-in electrodes, was employed to yield the true polyaniline conductivity and to assess the ohmicity of the contacting approach. Conductivity studies show conductivity increases as the width decreases. We also show that electrochemical polymerization is superior to the chemical polymerization using nanochannel growth template.