Patterned forest-assembly of single-wall carbon nanotubes and carbon nanotube atomic force microscopy nanoprobes

Date of Completion

January 2006


Engineering, Materials Science




Single-wall carbon nanotubes (SWNTs) are envisioned to greatly impact future science and technology particularly in the nanoscale range due to their unique one dimensional structure with tunable electrical conductivity. Thus they have received considerable attention in the development of nanodevices, field emitters and biosensors. The ability to place carbon nanotubes (CNTs) with controlled orientation at desired sites presents one major challenge in assembling these remarkable nanostructures into useful functional devices. In this dissertation a metal-assisted self-assembly technique was utilized in which dense rope-lattice-like SWNT forests with upright direction were obtained by immobilizing carboxylated nanotubes from dimethylformamide (DMF) nonaqueous media onto the underlying substrates with the linkage of FeO(OH)/FeOCl crystallites. In comparison with growing CNTs by chemical vapor deposition (CVD) on patterned catalyst pads, this self-assembly approach can take advantage of post-synthesis SWNT separation according to length and type (met allic versus semiconducting). ^ Since FeO(OH)/FeOCl crystallites acted as linkers to bridge CNTs onto the substrates, the appropriate placement of these iron deposits was pivotal to realize the desired SWNT patterns. To assist in localizing these FeO(OH)/FeOCl crystallites, three approaches on diverse substrates including Nafion, Si/SiO x and Au were investigated with the aid of low-energy electron-beam direct writing (on Nafion and Si/SiOx) and photolithography (on Au) by creating preferential precipitation sites for FeO(OH)/FeOCl crystallites. Such differential deposition of FeO(OH)/FeOCl crystallites provided the basis for the patterned site-specific self-assembly of SWNT forests as demonstrated by atomic force microscopy (AFM) and resonance Raman spectroscopy. ^ A second part of this dissertation resulted in CNT nanoprobes on conductive AFM probes fabricated with the help of a positive dielectrophoretic (DEP) process. Under the generated heterogeneous alternating current (AC) electric field, nanotubes aligned and migrated towards the high field region (AFM tip apex). Upon gradual pulling of the AFM probe away from SWNT suspension, capillary compression condensed nanotubes into a nanofibril protruding from the AFM probe. The precise length trimming of these nanoprobes was feasible by gradual re-immersion into sodium dodecyl sulfate (SDS) solution which micellarized SWNTs and re-dissolved them into solution. Finally, CNT nanoprobes with heterojunction structure were demonstrated by re-immersing the previously grown CNT nanofibril into the new functionalized-SWNT suspension at the desired depth and repeating the dielectrophoretic assembly to re-grow a new nanofibril on the top or/and at the end of the previous nanoprobe. These AFM probes with the CNT nanoprobes are qualified for deep structure imaging and cell piercing. ^