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Posted: Jun 07, 2006

Controlled decoration of carbon nanotubes with nanoparticles

(Nanowerk Spotlight) Researchers at the University of Wisconsin-Milwaukee developed an electrostatic force directed assembly (ESFDA) technique to efficiently coat carbon nanotubes (CNTs) with nanoparticles. This new method advances the current technology by enabling rapid and in-situ coating of CNTs, multicomponent hybrid nanostructures, more control over the assembly process, and the possibility of tuning properties of the resulted hybrid structures.
The assembly of nanoparticles along the external surface of CNTs is of both fundamental and technological interest. Combining unique properties of CNTs and nanoparticles, the nanoparticle– nanotube composite structure attracts a broad range of advanced applications, including nanoelectronics, chemical and biosensors, catalysis and fuel cells.
Existing methods for assembly of nanoparticles onto CNTs are primarily based on liquid-phase processing. These methods have created many interesting structures. However, they are generally slow and the associated interfacial chemistry is material dependent. Although the size of nanoparticles may be controlled in the solution before assembly, there is only limited control over the assembly process.
Professor Junhong Chen, first author of a new paper titled "Controlled decoration of carbon nanotubes with nanoparticles", published in the May 26, 2006 online edition of Nanotechnology, together with co-author Ganhua Lu, a graduate student in his group, explained their findings to Nanowerk:
"We have developed a generic, material-independent, dry route – electrostatic force directed assembly – to assemble nanoparticles onto both single-walled and multiwalled CNTs. An intrinsic nanoparticle size selection has been observed during the assembly process, which results in a narrower nano- particle size distribution on CNTs. The packing density and the final size distribution of nanoparticles docking on nanotubes can also be controlled during the assembly process."
 MWCNT and a small SWCNT bundle coated with Ag nanocrystals HRTEM images of a single MWCNT and a small SWCNT bundle coated with Ag nanocrystals, respectively. (Reprinted with permission from Institute of Physics Publishing)
Current predominant methods to produce CNTs are based on gas-phase processes. "Our method allows for the in-situ coating of CNTs or CNT arrays immediately after their growth" says Chen.
Due to the inherent material independence nature of the electrostatic force, nanoparticles of various materials can be assembled onto a single CNT using the new technique. Both of the above capabilities are quite difficult to achieve, if not impossible, with the liquid-phase processing.
"One can imagine that nanoparticles of multiple materials, particularly interweaving metal and semiconducting/magnetic nanocrystals, can be assembled onto CNTs" says Chen. "These interesting multicomponent structures will open up new opportunities in several interdisciplinary fields."
The nanoparticle-nanotube hybrid structures have potential for a wide range of advanced applications in nanoelectronics, gas sensors, biosensors, catalysis, fuel cells, hydrogen storage, solar cells, gas filtration, water purification, nanometrology, nanocomposites, waveguides, nanomanufacturing, spintronics, surface-enhanced Raman scattering, and growth of 3-D hybrid nanoarchitectures.
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