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Researchers Submit Patent Application, "Multi-Branched N-Doped Carbon Nanotubes and the Process for Making Same", for Approval

August 7, 2014



By a News Reporter-Staff News Editor at Politics & Government Week -- From Washington, D.C., VerticalNews journalists report that a patent application by the inventors SUN, Xueliang (London, CA); IONESCU, Minhea Ioan (London, CA); ABOU-RACHID, Hakima (Quebec, CA), filed on January 11, 2013, was made available online on July 24, 2014.

The patent's assignee is Her Majesty The Queen In Right Of Canada, As Represented By The Minister Of National Defence.

News editors obtained the following quote from the background information supplied by the inventors: "CNTs have drawn considerable attention from researchers due to their outstanding electrical and mechanical properties. Their complex spatial architecture has contributed to numerous applications of nanotubes in sensors, fuel cells, batteries, field emission devices, transistors, and logic circuits. Continuous requirements of miniaturization and complex nanoscale devices have generated an increasing interest in developing novel nanomaterials with complicated structures. In order to integrate nanomaterials with different properties into functional systems, attention is becoming focused on branched CNTs.

"Up to now, several techniques have been employed to produce branched carbon nanotubes. Initially, Y-shaped or branched CNTs have been synthesized by arc discharge and alumina template. Furthermore, a high-intensity electron beam has been used to join crossed CNTs. Another approach used a two-step process to attach catalyst particles to the grown CNTs during the chemical vapor deposition (CVD) growth process to initialize and sustain branches formation. Recently, more complicated branched CNTs have been reported by using a pyrolysis method, in which gas flow fluctuation has been considered the key factor that influences the branch occurrence. Inter-connected CNT networks have been prepared by Fu Y. et al. ('Templated Growth of Covalently Bonded Three-Dimensional Carbon Nanotube Networks Originated from Graphene' Advanced Materials Volume 24, Issue 12, pages 1576-1581, Mar. 22, 2012) by CVD on nickel template.

"However, previously reported deposition methods have disadvantages of inconsistent repeatability and introduction of external templates or additional steps that make the process complex and difficult to control. A single-step method to synthesize branched CNTs with a strong control of structure and composition is still desirable."

As a supplement to the background information on this patent application, VerticalNews correspondents also obtained the inventors' summary information for this patent application: "It is therefore an aim of the present invention to provide a multi-stage multi-branched N-doped carbon nanotube and a process for producing it in a single-step controlled operation.

"In accordance with one aspect of the present invention, there is provided a multibranched N-doped carbon nanotube comprising: a first-stage stalk having a direction and comprising a first-stage base, and a first-stage top opposite to and attached with the first-stage base, wherein the first-stage base includes a catalyst inclusion, at least two second-stage bundles, each of which comprises a second-stage base attached with the first-stage top, and a second-stage top opposite to and attached to the second-stage base, and wherein the second-stage bundles branch from the first-stage stalk in substantially the direction of the first stage stalk, and a plurality of third-stage nanotubes each of which comprises a third-stage base attached with the second-stage top, a third-stage top opposite to and attached to the third-stage base, and wherein the third-stage nanotubes branch from the second-stage bundles.

"In accordance with another aspect of the N-doped carbon nanotube herein described the third-stage nanotubes branch from the second-stage bundles in substantially the same direction as the first stage-stalk.

"In accordance with another aspect of the N-doped carbon nanotube herein described, the first-stage stalk has an average diameter of about 145 nm to about 450 nm.

"In accordance with yet another aspect of the N-doped carbon nanotube herein described, the first-stage stalk has an average diameter of about 200 nm to about 250 nm.

"In accordance with still another aspect of the N-doped carbon nanotube herein described, the first-stage stalk has an average diameter of about 210 nm.

"In accordance with yet still another aspect of the N-doped carbon nanotube herein described, the second-stage bundles has an average diameter of about 25 nm to about 60 nm.

"In accordance with a further aspect of the N-doped carbon nanotube herein described, the second-stage bundle has an average diameter of about 40 nm.

"In accordance with yet a further aspect of the N-doped carbon nanotube herein described, the plurality of third-stage nanotubes each has an average diameter of about 5 nm to about 25 nm.

"In accordance with still a further aspect of the N-doped carbon nanotube herein described, the plurality of third-stage nanotubes each has an average diameter of about 10 nm to about 20 nm.

"In accordance with yet still a further aspect of the N-doped carbon nanotube herein described, the plurality of third-stage nanotubes is from 10 to 30, branching from the second-stage bundles.

"In accordance with one embodiment of the N-doped carbon nanotube herein described, the plurality of third-stage nanotubes is from 20 to 25, branching from the second-stage bundles.

"In accordance with another embodiment of the N-doped carbon nanotube herein described, comprising a total length from the first-stage base to the third-stage top of about 4 .mu.m to about 6 .mu.m.

"In accordance with another aspect of the present invention, there is provided a process of producing vertically aligned multiple-branched nitrogen-doped carbon nanotubes, comprising the steps of: providing a temperature controlled deposition chamber adjusted to a temperature from 675.degree. C. and 850.degree. C.; providing a liquid having a carbon/nitrogen feedstock and an iron catalyst at a branching concentration, providing a carrier gas; providing a substrate in the chamber onto which the nanotubes are deposited; injecting a volume of the liquid into the gas to produce a fine mist in the chamber oriented towards the substrate for a period of time between 40 and 1 hour, wherein the liquid injected pyrolyzes the iron catalyst and the carbon/nitrogen feedstock into active species that adhere to the substrate and form the vertically aligned multiple-branched nitrogen-doped carbon nanotubes.

"In accordance with yet another embodiment of the process herein described, the carbon/nitrogen feedstock is acetonitrile.

"In accordance with still another embodiment of the process herein described, the iron catalyst is ferrocene.

"In accordance with yet still another embodiment of the process herein described, the branching concentration of the ferrocene is greater than 0.5 wt % in the liquid.

"In accordance with a further embodiment of the process herein described, the branching concentration of the ferrocene is from 2.5 wt % to 3.5 wt % of the liquid.

"In accordance with a further embodiment of the process herein described, injecting the volume of the liquid into the gas is at a rate of about 0.02 ml/min to about 0.06 ml/min.

"In accordance with yet a further embodiment of the process herein described, the substrate comprises a high purity silicon wafer comprising a native oxide layer.

"In accordance with still a further embodiment of the process herein described, the substrate includes an Al underlayer of an average thickness of about 30 nm.

"In accordance with yet still a further embodiment of the process herein described, the period of time is about 50 minutes.

"Further in accordance with another embodiment of the process herein described, the temperature of the deposition chamber is from about 700.degree. C. to about 800.degree. C.

BRIEF DESCRIPTION OF THE DRAWINGS

"Reference will now be made to the accompanying drawings, showing by way of illustration a particular embodiment of the present invention and in which:

"FIG. 1 is a schematic process flowsheet of a spray pyrolysis chemical vapour deposition system for producing N-doped carbon nanotubes according to one embodiment of the present invention;

"FIG. 2a is Scanning Electron Micrograph (SEM) image of a well-aligned branched CNTs array according to one embodiment of the present invention clearly indicating with different generations/stages visible;

"FIG. 2b is a further detailed smaller scale SEM image of a well-aligned branched CNTs of FIG. 2a indicating the positions of the end of the 1.sup.st generation/stage, the start of the second generation/stage; the end of the second generation/stage and the beginning of the third generation/stage of CNTs indicated;

"FIG. 3a Transmission Electron Micrograph (TEM) image a branched CNTs according to one embodiment of the present invention illustrating from left to right; Y-junctions on third-generation/stage of nanotubes; multiple branches formed between the third and second-generation/stage bundles of CNTs; multiple branches formed between second-generation/stage bundles of CNTs and a first generation/stage stalk nanotube; and the stalk nanotube with catalyst inclusion at the bottom right hand corner of the FIG. 3a;

"FIG. 3b is a further detailed smaller scale TEM image of a branched CNT according to another embodiment of the present invention a top of a CNT and Y-junctions of the third generation/stage of nanotubes, and a clear illustration of the multiple stalks of CNT;

"FIG. 4a is a Raman spectrograph of a multibranched CNTs according to one embodiment of the present invention;

"FIG. 4b is an X-ray photoelectron spectroscopic (XPS) survey scan of a multibranched CNTs according to one embodiment of the present invention;

"FIG. 4c is an (nitrogen) N 1s XPS spectrum of a multibranched CNTs according to one embodiment of the present invention;

"FIG. 5a is a SEM of a multibranched CNTs according to one embodiment of the present invention produced using 2.5 wt % ferrocene catalyst in solution;

"FIG. 5b is a SEM of a multibranched CNTs according to another embodiment of the present invention produced using 0.5 wt % ferrocene catalyst in solution; and

"FIG. 6 is a schematic diagram (not to scale) of a growth mechanism of the a branched CNT according to one embodiment of the present invention."

For additional information on this patent application, see: SUN, Xueliang; IONESCU, Minhea Ioan; ABOU-RACHID, Hakima. Multi-Branched N-Doped Carbon Nanotubes and the Process for Making Same. Filed January 11, 2013 and posted July 24, 2014. Patent URL: http://appft.uspto.gov/netacgi/nph-Parser?Sect1=PTO2&Sect2=HITOFF&u=%2Fnetahtml%2FPTO%2Fsearch-adv.html&r=2332&p=47&f=G&l=50&d=PG01&S1=20140717.PD.&OS=PD/20140717&RS=PD/20140717

Keywords for this news article include: Nitrogen, Fullerenes, Nanomaterial, Nanotechnology, Carbon Nanotubes, Emerging Technologies, Her Majesty The Queen In Right Of Canada As Represented By The Minister Of National Defence.

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