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Posted: May 11, 2009
New morphologies of graphitic carbon in nanotechnology applications
(Nanowerk Spotlight) Many nanotechnology research efforts have explored the use of hollow nanochannels formed by carbon nanotubes (CNTs). However, the usually large length/diameter aspect ratio of CNTs has made it challenging to insert other materials into them in a controlled manner. A team of scientists has now developed the idea of using a nanocup morphology to solve this problem. The length/diameter ratio of these new graphitic architectures is 1,000 to 100,000 times smaller compared to conventional carbon nanotubes.
"Using these diverse nanoscale structures as templates, we can successfully insert various metals inside their pores to create multicomponent nanostructures and nanoscale container systems, " Yung Joon Jung tells Nanowerk. "Our results will allow us to build highly engineered and multicomponent functional nano building blocks for various applications including nanomedicine – containers for nanogram quantities of materials, in drug delivery – and nanometrology."
SEM image showing architecture of individual carbon nanocups. (Image: Dr. Jung, Northeastern University)
Jung, an assistant professor in the Department of Mechanical and Industrial Engineering at Northeastern University, together with collaborators from Tokyo University of Science, and Rice University, reported their findings in the May 1, 2009 online edition of ACS Nano ("Engineering Low-Aspect Ratio Carbon Nanostructures: Nanocups, Nanorings, and Nanocontainers"), where the team, for the first time, demonstrates novel morphologies which were challenging to make before, such as nanocups, nanorings, and continuous films of connected nanocups.
"For the synthesis of such engineered nanostructures, we developed a precisely controlled rational approach for creating extremely short nanochannels inside an anodized aluminum oxide (AAO) template, and then we deposited the graphitic cup morphologies by the pyrolysis of acetylene at a temperature of 660°C, without the use of any catalyst material," explains Jung.
To make the graphitic nanoring morphology and to produce fully separated and length controlled individual nanocups, the scientists used argon ion milling on the connected arrays of nanocup film deposited in the AAO templates.
"We observed a striking change in the structure and morphology of the nanocup films during argon ion irradiation" says Jung. "After approximately 70 seconds of argon ion irradiation on the two-dimensional nanocup films, etching of a graphitic layer connecting the arrays of individual nanocups occurred and resulted in individually separated nanocup structures. We were able to obtain different lengths of nanocups could by controlling the ion milling time used for etching of the preformed nanocup films".
Jung notes that the cup morphology enable them to insert most of materials such as metal, organic and inorganic as well as liquid very easily inside of nanocups with a very uniform nanogram quantity and dimension.
"We effectively have used nanocups and nanocup films to hold and contain other nanomaterials, for example, metal, silica, and polymer nanoparticles, leading to the formation of multi-component hybrid nano building blocks," he says.
The graphitic nature of nanocup structures can be an excellent template to fabricate multi-component and multi-functional nano building block systems. One can modify and fabricate these not only by inserting other materials easily inside a cup but also chemically functionalize the outside of cups.
Jung says that these published result is only the first step of the team's idea and plans. "We are currently developing a room temperature process that assembles other various nanoelements inside of cups. Therefore the next step will be fabricating well designed multi-component and highly functional nanocup systems for nanomedicine application".