Choolakadavil Khalid Najeeb

Patterning of hierarchically aligned single-walled carbon nanotube Langmuir-Blodgett films by microcontact printing.

We present a patterning method for hierarchically aligned assembly of single-walled carbon nanotubes (SWNTs) using a combination of the Langmuir-Blodgett (LB) technique and soft lithography. The LB technique allows one to control the alignment and the surface density of SWNTs by adjusting surface pressure of the film at the air-water interface. The aligned SWNT Langmuir films are successfully transferred onto the polydimethylsiloxane (PDMS) or silicon substrate with unidirectional alignment, and SWNT patterns with various shapes are fabricated on silicon and flexible poly(ethylene terephthalate) (PET) substrates by contacting and peeling off the PDMS stamp from the substrates via microcontact printing or lift-up methods. The SWNT patterning technique using the combination of soft lithography and the LB method can be applied in various fields, such as flexible high-speed transistors, high-efficiency solar cells, and transparent electrodes.

The effect of surface modifications of carbon nanotubes on the electrical properties of inkjet-printed SWNT/PEDOT–PSS composite line patterns

We prepared nanocomposite inks of poly(3,4-ethylenedioxythiophene)-poly(styrenesulfonate) (PEDOT-PSS) filled with single-walled carbon nanotubes (SWNTs) purified by acidic treatment, carboxylated by chemical oxidation and carboxyl-functionalized nanotubes physically modified with a natural gum, gum arabic. Inkjet printing of line patterns with a feature size of 100 microm width and lengths ranging from 1 to 5 cm was performed on glass substrates with a piezoelectric inkjet printer. The carboxyl-functionalized SWNT-based composite demonstrated a significant decrease (fourfold) of electrical resistance for the line patterns compared to that with a purified CNT-based composite due to improved dispersability of nanotubes in the polymer matrix. The use of gum arabic for the dispersion of carboxyl-functionalized nanotubes demonstrated a further drastic decrease (18-fold) of the resistance compared with a purified CNT-based composite owing to the formation of an extended continuous network within the line pattern. The inkjet-printed conductive patterns can be applied in various fields, such as flexible high speed transistors, high efficiency solar cells and transparent electrodes.

Preparation of semiconductor-enriched single-walled carbon nanotube dispersion using a neutral pH water soluble chitosan derivative.

Debundling and selective dispersion of semiconducting single-walled carbon nanotubes (SWNTs) has been demonstrated using a neutral pH water soluble chitosan derivative, N-acetylated chitosan (NACHI), which is synthesized by controlled N-acetylation of chitosan using acetic anhydride. The SWNT-NACHI supernatant solution demonstrated semiconductor-enriched property owing to the preferential adsorption of N-groups of the NACHI on semiconducting nanotubes with a fairly weak charge transfer. The dispersion of nearly individualized SWNTs achieved by surface modification of nanotubes with a biocompatible polymer can be utilized for electronic and biomedical applications such as field effect transistor, biosensor, cell culture medium and SWNT-biomacromolecule hybrid materials.

Highly efficient individual dispersion of single-walled carbon nanotubes using biocompatible dispersant.

Individual dispersion of single-walled carbon nanotubes (SWNTs) in biocompatible media is of particular interest for diverse biomedical and nanomedicine applications. Herein we present, for the first time, a neutral pH water-soluble chitosan derivative, chitosan-hydroxyphenyl acetamide (CHPA), prepared by functionalizing the amino groups of chitosan with 4-hydroxyphenyl acetic acid, as an efficient biocompatible dispersant to effectively debundle and individually disperse SWNTs in a neutral aqueous solution. For efficient individual dispersion of SWNTs, various process conditions such as centrifugation speed, sonication power, and CNT:dispersant ratio were optimized based on characterizations by atomic force microscopy, optical absorption spectroscopy, and Raman spectroscopy. Evaluation of the SWNT-CHPA solution showed superior individual dispersion to samples prepared using other biocompatible dispersants. The highly efficient individual dispersion of SWNTs with the biocompatible dispersant opens up possibilities for its applications in the bio- and nanomedical fields.

High-performance photoresponse from single-walled carbon nanotube–zinc oxide heterojunctions

Photoactive materials consisting of single-walled carbon nanotube (SWNT)–zinc oxide (ZnO) heterojunctions targeted for optoelectronic applications are investigated in terms of photoresponse and photovoltaic effects. The devices based on SWNT–ZnO heterojunction films are fabricated by two step processes: first, a well aligned SWNT monolayer is deposited on an oxide substrate by the Langmuir–Blodgett (LB) technique; then a ZnO film prepared by filtration of ZnO nanowire solution is transferred onto the SWNT film to form SWNT–ZnO junctions. The SWNT–ZnO heterojunction demonstrates faster photoresponse time (2.75 s) up to 18 times and photovoltaic efficiency (1.33 nA) up to 4 times higher than that of only a ZnO device. Furthermore, the mechanisms of UV sensitivity enhancement and photovoltaic effects are explained according to the high electron mobility in the SWNT–ZnO heterojunctions.

Single-Walled Carbon Nanotubes/Polymer Composite Electrodes Patterned Directly from Solution

This work describes a simple technique for direct patterning of single-walled carbon nanotube (SWNT)/poly(3,4-ethylenedioxythiophene)-poly(styrenesulfonate) (PEDOT-PSS) composite electrodes in a large area on a substrate based on the solution transfer process by microcontact printing using poly(dimethylsiloxane) (PDMS) stamps. Various shapes of SWNT/PEDOT-PSS composite patterns, such as line, circle, and square, can be easily fabricated with high pattern fidelity and structural integrity. The single parallel line pattern device exhibits high electrical conductivity (0.75 × 10(5) S/m) and electronic stability because of alignment of nanotubes and big-size SWNT bundles (∼5 nm). The electromechanical study reveals that the composite patterns show ∼1% resistance change along SWNT alignment direction and ∼5% resistance change along vertical alignment direction after 200 bend cycles. Our approach provides a facile, low-cost method to pattern transparent conductive SWNT/polymer composite electrodes and demonstrates a novel platform for future integration of conducting SWNT/polymer composite patterns for optoelectronic applications.