J.H.Chen

Multifunctional Hybrid Nanocrystal-Carbon Nanotube Structures

Junhong Chen*

Department of Mechanical Engineering, University of Wisconsin-Milwaukee, Milwaukee, WI 53211
* jhchen@uwm.edu

Hybrid nanomaterials composed of nanocrystals distributing on the surfaces of carbon nanotubes (CNTs) represent a new class of materials. These materials could potentially display not only the unique properties of nanocrystals and those of CNTs, but also additional novel properties due to the interaction (e.g., electronic or optical) between the nanocrystal and the CNT. Such hybrid nanocrystal-CNT structures are promising for various innovative nanotechnological applications, including chemical sensors [1], biosensors [2], nanoelectronics [3], photovoltaic cells [4], fuel cells [5], and hydrogen storage [6]. In this talk, I will present a material-independent, dry route based on the electrostatic force directed assembly (ESFDA) to assemble aerosol nanocrystals onto CNTs [7-11]. The method takes advantage of the small diameter of CNTs for a significantly enhanced electric field near the CNT surface, which is then used to attract charged aerosol nanocrystals [12] onto oppositely-biased CNTs. The ESFDA technique works for both random CNTs and aligned CNTs without the need for chemical functionalization or other pretreatments of CNTs. There is an intrinsic nanocrystal size selection during the assembly process, which results in a narrower size distribution for nanocrystals on CNTs than that for as-produced nanocrystals. Moreover, the areal density and the actual size distribution of nanocrystals on the CNT can be controlled. The non-covalent attachment of nanocrystals also preserves the intrinsic properties of CNTs [13]. The new method enables in-situ coating of nanotubes with nanocrystals. Due to the inherent material-independence nature of the electrostatic force, various compositions of such nanocrystal-CNT hybrid structures can be produced using this new technique.

Video Content Length 36:54 Copyright: © 2008 Chen et al

References

1. Kong, J., M.G. Chapline, and H.J. Dai, Functionalized carbon nanotubes for molecular hydrogen sensors. Advanced Materials, 2001. 13(18): p. 1384-1386.

2. Chen, R.J., S. Bangsaruntip, K.A. Drouvalakis, N.W.S. Kam, M. Shim, Y.M. Li, W. Kim, P.J. Utz, and H.J. Dai, Noncovalent functionalization of carbon nanotubes for highly specific electronic biosensors. Proceedings of the National Academy of Sciences of the United States of America, 2003. 100(9): p. 4984-4989.

3. Hu, J.T., O.Y. Min, P.D. Yang, and C.M. Lieber, Controlled growth and electrical properties of heterojunctions of carbon nanotubes and silicon nanowires. Nature, 1999. 399(6731): p. 48-51.

4. Robel, I., B.A. Bunker, and P.V. Kamat, Single-walled carbon nanotube-CdS nanocomposites as light-harvesting assemblies: Photoinduced charge-transfer interactions. Advanced Materials, 2005. 17(20): p. 2458-63.

5. Robel, I., G. Girishkumar, B.A. Bunker, P.V. Kamat, and K. Vinodgopal, Structural changes and catalytic activity of platinum nanoparticles supported on C-60 and carbon nanotube films during the operation of direct methanol fuel cells. Applied Physics Letters, 2006. 88(7): p. 073113.

6. Yildirim, T. and S. Ciraci, Titanium-decorated carbon nanotubes as a potential high-capacity hydrogen storage medium. Physical Review Letters, 2005. 94(17): p. 175501.

7. Chen, J.H. and G.H. Lu, Controlled Decoration of Carbon Nanotubes with Nanoparticles. Nanotechnology, 2006. 17(12): p. 2891-2894.

8. Lu, G.H., L.Y. Zhu, P.X. Wang, J.H. Chen, D.A. Dikin, R.S. Ruoff, Y. Yu, and Z.F. Ren, Electrostatic-Force-Directed Assembly of Ag Nanocrystals onto Vertically Aligned Carbon Nanotubes. J. Phys. Chem. C, 2007. 111(48): p. 17919-17922.

9. Zhu, L.Y., G.H. Lu, and J.H. Chen, A Generic Approach to Coat Carbon Nanotubes with Nanoparticles for Potential Energy Applications. Journal of Heat Transfer, 2008. 130(4): p. 044502.

10. Liu, M., G.H. Lu, and J.H. Chen, Synthesis, Assembly, and Characterization of Si Nanoparticles and Si Nanoparticle-Carbon Nanotube Hybrid Structures. Nanotechnology, 2008. 19(26): p. 265705.

11. Lu, G.H., M. Liu, K.H. Yu, and J.H. Chen, Absorption Properties of Hybrid SnO2 Nanocrystal-Carbon Nanotube Structures. Journal of Electronic Materials, 37(11), 1686-1690, 2008.

12. Chen, J.H., G.H. Lu, L.Y. Zhu, and R.C. Flagan, A Simple and Versatile Mini-Arc Plasma Source for Nanocrystal Synthesis. Journal of Nanoparticle Research, 2007. 9(2): p. 203-213.

13. Zhu, L.Y., G.H. Lu, S. Mao, J.H. Chen, D.A. Dikin, X.Q. Chen, and R.S. Ruoff, Ripening of Silver Nanoparticles on Carbon Nanotubes. NANO, 2007. 2(3): p. 149-156.

Citation:

J.H.Chen, OAtube Nanotechnology 1, 1007 (2008). http://www.oatube.org/2008/10/jhchen.html

R.Vajtai

Carbon nanotubes: optimized growth for applications and practical use of large CNT structures

Robert Vajtai^1*, Géza Tóth^2, Krisztián Kordás^2, Xiaohong An^3, Pulickel M. Ajayan^1

^1 Department of Mechanical Engineering & Materials Science, Rice University, Houston, TX 77005 USA
^2 Microelectronics and Materials Physics Laboratories, Department of Electrical and Information Engineering, and EMPART research group of Infotech Oulu, P.O. Box 4500, FIN-90014 University of Oulu, Finland
^3 Department of Materials Science and Engineering, Rensselaer Polytechnic Institute, Troy, NY
*Robert.Vajtai@rice.edu

Carbon nanotubes attracted large-scale scientific interest and their properties are well-studied for the cases when theoretical model work, and at the same time growth routes and proof of the concept applications were demonstrated (see e.g. Ref. 1). In this talk I briefly summarize our latest result on the most important parameters of multiwalled carbon nanotube growth via the floating catalyst Ferrocene-Xylene route applied earlier with success to create large CNT structures [2]. We investigated the kinetics [3] of the process both experimentally and theoretically and optimized the parameters for carbon nanotube length and also for their quality. These studies were used to reach macroscopic carbon nanotube structures with unique properties optimized to use them as synergistic units. In the main part of the talk I focus on characterization of the structures and their recent applications. Aligned carbon nanotube forests grown with different methods showed wide range of density depending on growth parameters; the physical properties of these films, e.g. compressibility, optical absorbance, thermal and electrical conductivity are unparalleled. To demonstrate the usefulness of these properties I will cite laboratory level applications. First a chip cooler setup [4], made of aligned multiwalled carbon nanotube forest will be presented, where the cooling performance of the device is comparable to a copper cooler having similar geometry; however, the carbon nanotube cooler is much lighter, mechanically stronger and it has more potential for further optimization. Another family of application is printing carbon nanotubes from different kind of “inks” [5-6]. The most interesting feature of this use is the fact that different coverage of the carbon nanotube film results in either low resistance Ohmic (for high coverage) or a nonlinear (for low coverage) behavior which latter one can be driven by gate voltage [6]. Via controlled amount of materials printed on the multi-micrometer scale the method can prepare complete electronic circuits with active elements and wires made of the same carbon nanotube ink without requiring any expensive pre-selection of semi-conductive and metallic tubes. These applications, together with several other, shortly mentioned ones, outdraw the possibilities that large scale, organized carbon nanotube structures inherently infer.


Video Content Length 30:09 Copyright © 2008 Vajtai et al

References

[1] P.M. Ajayan, Chemical Reviews 99, 1787 (1999).
[2] B.Q. Wei, R. Vajtai, Y. Jung, J. Ward, R. Zhang, G. Ramanath and P.M. Ajayan, Nature 416, 495 (2002).
[3] N. Halonen, K. Kordás, G. Tóth, T. Mustonen, J. Mäklin, J. Vähäkangas, P. M. Ajayan and R. Vajtai, J. Phys. Chem. C 112, 6723 (2008).
[4] K. Kordás, G. Tóth, P. Moilanen, M. Kumpumäki, J. Vähäkangas, A. Uusimäki, R. Vajtai, and P. M. Ajayan, Appl. Phys. Lett. 90, 123105 (2007).
[5] K. Kordás, T. Mustonen, G. Tóth, H. Jantunen, M. Lajunen, C. Soldano, S. Talapatra, S. Kar, R. Vajtai and P. M. Ajayan, Small 2, 1021 (2006).
[6] T. Mustonen, J. Mäklin, K. Kordás, N. Halonen, G. Tóth, J. Vähäkangas, H. Jantunen, S. Kar, P. M. Ajayan, R. Vajtai, P. Helistö and H. Seppä, Phys. Rev. B 77, 125430 (2008).

Citation:
R. Vajtai, G. Toth, K. Kordas, X.H. An, and P. M. Ajayan,
OAtube Nanotechnology 1, 1006 (2008). http://www.oatube.org/2008/10/rvajtai.html