Hybrid Dual Porosity CNTs Function as Sliding Electrical Contacts
- PDF / 663,811 Bytes
- 1 Pages / 576 x 783 pts Page_size
- 40 Downloads / 170 Views
Hybrid Dual Porosity CNTs Function as Sliding Electrical Contacts D.N. Futaba and co-workers from the National Institute of Advanced Industrial Science and Technology of Japan, together with S. Sasaki from the Tokyo University of Science have demonstrated the first known hybrid dual-porosity carbon nanotube (CNT) material composed of a section of highly porous and a section of much less porous assemblies of aligned nanotubes seamlessly connected by locally collapsing the initially sparse CNT material using the capillary forces of liquids. The researchers demonstrated the potential of this hybrid material as a low wear tribological material, useful as a sliding electrical contact, in the September 9 issue of Nano Letters (DOI: 10.1021/nl901581t; p. 3302). The researchers grew millimeter-tall single-walled nanotubes (SWNTs) with a porosity of ~97% by chemical vapor deposition on Si substrates with an oxidized layer 600-nm thick and covered with a thin catalytic Al2O3(40 nm)/Fe(1 nm) metal layer. They used ethylene (99.999%) as the carbon source flowing at 50–100 cm3 STP per minute. Water vapor (100–200 ppm) was used as a catalyst preserver and enhancer. The water vapor was supplied by flowing the helium (99.9999%) and hydrogen (99.99999%) carrier gas through
a water bubbler. In a first demonstration of the concept, the researchers delivered a controlled amount of liquid (a mixture of water and alcohol) to a precise location on the CNT structure using drop delivery from toothpicks. In the location where the liquid was applied, the CNT volume collapsed, greatly reducing the porosity of the section. The researchers were thus able to transform the uniformly porous CNT forest into a hybrid dual porosity material where a forest (high porosity, ~97%) and a solid (low porosity, ~50%) were seamlessly and smoothly connected similar to a whisk broom. The researchers said that the forest section possessed interesting mechanical properties, such as elastic recovery, dry adhesion, and field emission, while the solid section showed excellent mechanical robustness and strength. By controlling the contact point of liquids, the researchers created different structures such as “mushroom” type structures, “tepee” structures with an abrupt change in porosity along the cylinder length, and high density “shell” structures with a metallic luster surrounding the sparse interior. The researchers were able to demonstrate other structures using application of liquid thin films, bubbles, vapors, and superink-jet printing, such as beds of needles and porcupine-like structures.
MOCVD Standard and Custom Tools: Vertical - Horizontal - Rotating Custom Deposition Services GaN ZnO GeS:Ag InSb SiGe II-VI’s Graphene GeSbTe Oxides Nitrides Carbides Diamond Nanowires x x x x
Structured Materials Industries, Inc. Voice: 732-302-9274; Fax 732-302-9275 E-mail: [email protected] Web: www.structuredmaterials.com
MRS BULLETIN • VOLUME 34 • NOVEMBER 2009 • www.mrs.org/bulletin
The researchers demonstrated the functionality of this hybrid materia
