Metal filament growth in electrically conductive polymers for nonvolatile memory application.

Solution processable polymers that can reproducibly form metal filament by applying voltage are investigated for nonvolatile memory application. Up to present, the understanding of materials enabling to make the metal filament has not been well-documented and the vacuum deposition methods were dominantly used in device fabrication. After screening various polymers, we found that only the polymers having two functionalities, the presence of strongly coordinating heteroatom (S or N) with metal ions and the electrical conductivity, showed the reproducible filament formation behavior. Among the polymers screened, the regiorandom poly(3-hexylthiophene) showed the best switching endurance over 30,000 write-read-erase-read cycles without any switching failure.

Patterning of single-wall carbon nanotubes via a combined technique (chemical anchoring and photolithography) on patterned substrates.

Single-walled carbon nanotubes (SWNTs) have been chemically attached with high density onto a patterned substrate. To form the SWNT pattern, the substrate was treated with acid-labile group protected amine, and an amine prepattern was formed using a photolithographic process with a novel polymeric photoacid generator (PAG). The polymeric PAG contains a triphenylsulfonium salt on its backbone and was synthesized to obtain a PAG with enhanced efficiency and ease of spin-coating onto the amine-modified glass substrate. The SWNT monolayer pattern was then formed through the amidation reaction between the carboxylic acid groups of carboxylated SWNTs (ca-SWNTs) and the prepatterned amino groups. A high-density multilayer was fabricated via further repeated reaction between the carboxylic acid groups of the ca-SWNTs and the amino groups of the linker with the aid of a condensation agent. The formation of covalent amide bonding was confirmed by X-ray photoelectron spectroscopy (XPS) analysis. Scanning electron microscopy and UV-vis-near-IR results show that the patterned SWNT films have uniform coverage with high surface density. Unlike previously reported patterned SWNT arrays, this ca-SWNT patterned layer has high surface density and excellent surface adhesion due to its direct chemical bonding to the substrate.

Covalent attachment and hybridization of DNA oligonucleotides on patterned single-walled carbon nanotube films.

DNA oligonucleotides were covalently immobilized to prepatterned single-walled carbon nanotube (SWNT) multilayer films by amidation. SWNT multilayer films were constructed via consecutive condensation reactions creating stacks of functionalized SWNT layers linked together by 4,4'-oxydianiline. Aminated- or carboxylated-DNA oligonucleotides were covalently immobilized to the respective carboxylated or aminated SWNT multilayer films through amide bond formation using 1-ethyl-3-(3-dimethylaminopropyl)carbodiimide hydrochloride. UV-vis-NIR spectroscopic analysis indicated that the SWNT film surface density increased uniformly according to the number of reaction cycles. Scanning electron microscopy and contact angle measurements of the SWNT multilayer film revealed a uniform coverage over the substrate surface. The covalent attachment of DNA oligonucleotides to the SWNT multilayer films and their subsequent hybridization with complementary oligonucleotides were verified using X-ray photoelectron spectroscopy and fluorescence-based measurements. This is the first report demonstrating that DNA oligonucleotides can be covalently attached to immobilized SWNT multilayer films. The anchored DNA oligonucleotides were shown to exhibit excellent specificity, realizing their potential in future biosensor applications.

Carbon nanotube conducting arrays by consecutive amidation reactions.

Carbon nanotube conducting arrays were constructed via consecutive amidation reactions with the aid of a linker molecule and a condensation agent on a patterned amine-terminated glass substrate. The electrical resistivity of the nanotube films was sensitive to the degree of coverage for the substrate, making it possible to tailor nanotube multilayers suitable for use in micro- or nanoscale electronic devices and circuits.