Growth, modification and integration of carbon nanotubes into molecular electronics

Molecules are the smallest possible elements for electronic devices, with active elements for such devices typically a few Angstroms in footprint area. Owing to the possibility of producing ultrahigh density devices, tremendous effort has been invested in producing electronic junctions by using various types of molecules. The major issues for molecular electronics include (1) developing an effective scheme to connect molecules with the present micro- and nano-technology, (2) increasing the lifetime and stabilities of the devices, and (3) increasing their performance in comparison to the state-of-the-art devices. In this work, we attempt to use carbon nanotubes (CNTs) as the interconnecting nanoelectrodes between molecules and microelectrodes. The ultimate goal is to use two individual CNTs to sandwich molecules in a cross-bar configuration while having these CNTs connected with microelectrodes such that the junction displays the electronic character of the molecule chosen. We have successfully developed an effective scheme to connect molecules with CNTs, which is scalable to arrays of molecular electronic devices. To realize this far reaching goal, the following technical topics have been investigated. 1. Synthesis of multi-walled carbon nanotubes (MWCNTs) by thermal chemical vapor deposition (T-CVD) and plasma-enhanced chemical vapor deposition (PECVD) techniques (Chapter 3). We have evaluated the potential use of tubular and bamboo-like MWCNTs grown by T-CVD and PE-CVD in terms of their structural properties. 2. Horizontal dispersion of MWCNTs with and without surfactants, and the integration of MWCNTs to microelectrodes using deposition by dielectrophoresis (DEP) (Chapter 4). We have systematically studied the use of surfactant molecules to disperse and horizontally align MWCNTs on substrates. In addition, DEP is shown to produce impurityfree placement of MWCNTs, forming connections between microelectrodes. We demonstrate the deposition density is tunable by both AC field strength and AC field frequency. 3. Etching of MWCNTs for the impurity-free nanoelectrodes (Chapter 5). We show that the residual Ni catalyst on MWCNTs can be removed by acid etching; the tip removal and collapsing of tubes into pyramids enhances the stability of field emission from the tube arrays. The acid-etching process can be used to functionalize the MWCNTs, which was used to make our initial CNT-nanoelectrode glucose sensors. Finally, lessons learned trying to perform spectroscopic analysis of the functionalized MWCNTs were vital for designing our final devices. 4. Molecular junction design and electrochemical synthesis of biphenyl molecules on carbon microelectrodes for all-carbon molecular devices (Chapter 6). Utilizing the experience gained on the work done so far, our final device design is described. We demonstrate the capability of preparing patterned glassy carbon films to serve as the bottom electrode in the new geometry. However, the molecular switching behavior of biphenyl was not observed by scanning tunneling microscopy (STM), mercury drop or fabricated glassy carbon/biphenyl/MWCNT junctions. Either the density of these molecules is not optimum for effective integration of devices using MWCNTs as the nanoelectrodes, or an electroactive contaminant was reduced instead of the ionic biphenyl species. 5. Self-assembly of octadecanethiol (ODT) molecules on gold microelectrodes for functional molecular devices (Chapter 7). We have realized an effective scheme to produce Au/ODT/MWCNT junctions by spanning MWCNTs across ODT-functionalized microelectrodes. A percentage of the resulting junctions retain the expected character of an ODT monolayer. While the process is not yet optimized, our successful junctions show that molecular electronic devices can be fabricated using simple processes such as photolithography, self-assembled monolayers and dielectrophoresis.

THE PERFORMANCE AND MODIFICATION OF RECYCLED ELECTRONIC WASTE PLASTICS FOR THE IMPROVEMENT OF ASPHALT PAVEMENT MATERIALS

Bulk electric waste plastics were recycled and reduced in size into plastic chips before pulverization or cryogenic grinding into powders. Two major types of electronic waste plastics were used in this investigation: acrylonitrile butadiene styrene (ABS) and high impact polystyrene (HIPS). This research investigation utilized two approaches for incorporating electronic waste plastics into asphalt pavement materials. The first approach was blending and integrating recycled and processed electronic waste powders directly into asphalt mixtures and binders; and the second approach was to chemically treat recycled and processed electronic waste powders with hydro-peroxide before blending into asphalt mixtures and binders. The chemical treatment of electronic waste (e-waste) powders was intended to strengthen molecular bonding between e-waste plastics and asphalt binders for improved low and high temperature performance. Superpave asphalt binder and mixture testing techniques were conducted to determine the rheological and mechanical performance of the e-waste modified asphalt binders and mixtures. This investigation included a limited emissions-performance assessment to compare electronic waste modified asphalt pavement mixture emissions using SimaPro and performance using MEPDG software. Carbon dioxide emissions for e-waste modified pavement mixtures were compared with conventional asphalt pavement mixtures using SimaPro. MEPDG analysis was used to determine rutting potential between the various e-waste modified pavement mixtures and the control asphalt mixture. The results from this investigation showed the following: treating the electronic waste plastics delayed the onset of tertiary flow for electronic waste mixtures, electronic waste mixtures showed some improvement in dynamic modulus results at low temperatures versus the control mixture, and tensile strength ratio values for treated e-waste asphalt mixtures were improved versus the control mixture.