A review: controlled synthesis of vertically aligned carbon nanotubes

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  • ABSTRACT

    Carbon nanotubes (CNTs) have developed into one of the most competitively researched nano-materials of this decade because of their structural uniqueness and excellent physical properties such as nanoscale one dimensionality, high aspect ratio, high mechanical strength, thermal conductivity and excellent electrical conductivity. Mass production and structure control of CNTs are key factors for a feasible CNT industry. Water and ethanol vapor en-hance the catalytic activity for massive growth of vertically aligned CNTs. A shower system for gas flow improves the growth of vertically aligned single walled CNTs (SWCNTs) by controlling the gas flow direction. Delivery of gases from the top of the nanotubes enables direct and precise supply of carbon source and water vapor to the catalysts. High quality vertically aligned SWCNTs synthesized using plasma enhance the chemical vapor deposi-tion technique on substrate with suitable metal catalyst particles. This review provides an in-troduction to the concept of the growth of vertically aligned SWCNTs and covers advanced topics on the controlled synthesis of vertically aligned SWCNTs.


  • KEYWORD

    vertically aligned carbon nanotubes , chemical vapor deposition , Ethanol based CVD , Water assisted CVD , Plasma enhanced CVD

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  • [Fig. 1.] Schematic drawing of ethanol based chemical vapor deposition system.
    Schematic drawing of ethanol based chemical vapor deposition system.
  • [Fig. 2.] Schematic drawing of chemical vapor deposition (CVD) proce-dure. (a) Si/SiO2 substrate. (b) Al2Ox film (20 nm thickness) was deposited by using a sputter coater or e-beam evaporator. (c) An ultra thin Co film(0.6-1 nm) was deposited as a catalyst on Al2Ox film for the growth of carbon nanotubes (CNTs) using e-beam evaporator. (d) Vertically aligned single walled CNT array grown by using ethanol based CVD process.
    Schematic drawing of chemical vapor deposition (CVD) proce-dure. (a) Si/SiO2 substrate. (b) Al2Ox film (20 nm thickness) was deposited by using a sputter coater or e-beam evaporator. (c) An ultra thin Co film(0.6-1 nm) was deposited as a catalyst on Al2Ox film for the growth of carbon nanotubes (CNTs) using e-beam evaporator. (d) Vertically aligned single walled CNT array grown by using ethanol based CVD process.
  • [Fig. 3.] (a) Optical microscope image of highly dense vertically aligned single walled carbon nanotubes (SWCNTs) grown with ethanol based chemical vapor deposition technique. (b) Low magnification scanning electron microscope (SEM) image of vertically aligned SWCNTs. (c) High magnification SEM image shows self-aligned SWCNTs. (d) Low magnifica-tion SEM image shows line pattern grown vertically aligned SWCNTs.
    (a) Optical microscope image of highly dense vertically aligned single walled carbon nanotubes (SWCNTs) grown with ethanol based chemical vapor deposition technique. (b) Low magnification scanning electron microscope (SEM) image of vertically aligned SWCNTs. (c) High magnification SEM image shows self-aligned SWCNTs. (d) Low magnifica-tion SEM image shows line pattern grown vertically aligned SWCNTs.
  • [Fig. 4.] single walled carbon nanotube (SWCNT) forest grown with water-assisted chemical vapor deposition. (a) Picture of a 2.5-mm-tall SWCNT forest on a 7-mm by 7-mm silicon wafer. The matchstick on the left and ruler with millimeter markings on the right are for size reference.(b) Scanning electron microscopy (SEM) image of the same SWCNT forest. Scale bar, 1 mm. (c) SEM image of the SWCNT forest ledge. Scale bar, 1㎛. (d) Low-resolution transmission electron microscopy (TEM) image of the nanotubes. Scale bar, 100 nm. (e) High-resolution TEM image of the SWCNTs. Scale bar, 5 nm. From Hata et al. [81]. Reprinted with permission from AAAS.
    single walled carbon nanotube (SWCNT) forest grown with water-assisted chemical vapor deposition. (a) Picture of a 2.5-mm-tall SWCNT forest on a 7-mm by 7-mm silicon wafer. The matchstick on the left and ruler with millimeter markings on the right are for size reference.(b) Scanning electron microscopy (SEM) image of the same SWCNT forest. Scale bar, 1 mm. (c) SEM image of the SWCNT forest ledge. Scale bar, 1㎛. (d) Low-resolution transmission electron microscopy (TEM) image of the nanotubes. Scale bar, 100 nm. (e) High-resolution TEM image of the SWCNTs. Scale bar, 5 nm. From Hata et al. [81]. Reprinted with permission from AAAS.
  • [Fig. 5.] (a) Optical images of carbon nanotube (CNT) forest with a height of 1 cm synthesized by top-flow growth. (b) Single walled CNTs grown on A4 substrate. Reprinted with permission from Yasuda et al. [85]. Copyright (2009) American Chemical Society.
    (a) Optical images of carbon nanotube (CNT) forest with a height of 1 cm synthesized by top-flow growth. (b) Single walled CNTs grown on A4 substrate. Reprinted with permission from Yasuda et al. [85]. Copyright (2009) American Chemical Society.
  • [Fig. 6.] Schematics of gas flow direction to catalysts at initial stage of the growth and with the presence of a forest for (a and b) conventional lateral-flow and (c and d) top-flow growth, respectively. Reprinted with permission from Yasuda et al. [85]. Copyright (2009) American Chemical Society.
    Schematics of gas flow direction to catalysts at initial stage of the growth and with the presence of a forest for (a and b) conventional lateral-flow and (c and d) top-flow growth, respectively. Reprinted with permission from Yasuda et al. [85]. Copyright (2009) American Chemical Society.
  • [Fig. 7.] Effect of support materials for Fe catalyst on carbon nanotube(CNT) growth. CNTs were grown for 10 min under standard conditions. (a) Cross-sectional optical images of CNTs grown by using combinatorial catalyst libraries, which had a nominal Fe thickness profile ranging from 0.2 nm (at left on each sample) to 3 nm (right) formed on either SiO2, Al2Ox, or Al2O3. (b) Relationship between the thickness of CNTs and the nominal Fe thickness of the catalyst. (c) Raman spectra of the same samples. Copy-right 2007 The Japan Society of Applied Physics.
    Effect of support materials for Fe catalyst on carbon nanotube(CNT) growth. CNTs were grown for 10 min under standard conditions. (a) Cross-sectional optical images of CNTs grown by using combinatorial catalyst libraries, which had a nominal Fe thickness profile ranging from 0.2 nm (at left on each sample) to 3 nm (right) formed on either SiO2,  Al2Ox, or Al2O3. (b) Relationship between the thickness of CNTs and the nominal Fe thickness of the catalyst. (c) Raman spectra of the same samples. Copy-right 2007 The Japan Society of Applied Physics.
  • [Fig. 8.] Molecular oxygen assisted plasma enhanced chemical vapor deposition (PECVD). (a) Atomic force microscopy image of Fe catalyst nanoparticles. (b) Optical image of vertically aligned single walled carbon nanotubes (SWCNTs) synthesized on 4 in wafer. (c) Low magnification scanning electron microscopy (SEM) image of vertically aligned SWCNTs. (d) Cross-sectional SEM images of vertically aligned SWCNTs. (e) Raman spectrum of vertically aligned SWCNTs grown with PECVD. (f ) High resolu-tion transmission electron microscopy image of SWCNTs. Reprinted with permission from Zhang et al. [96]. Copyright (2005) National Academy of Science, USA.
    Molecular oxygen assisted plasma enhanced chemical vapor deposition (PECVD). (a) Atomic force microscopy image of Fe catalyst nanoparticles. (b) Optical image of vertically aligned single walled carbon nanotubes (SWCNTs) synthesized on 4 in wafer. (c) Low magnification scanning electron microscopy (SEM) image of vertically aligned SWCNTs. (d) Cross-sectional SEM images of vertically aligned SWCNTs. (e) Raman spectrum of vertically aligned SWCNTs grown with PECVD. (f ) High resolu-tion transmission electron microscopy image of SWCNTs. Reprinted with permission from Zhang et al. [96]. Copyright (2005) National Academy of Science, USA.
  • [Fig. 9.] Optical images of 0.5 cm long vertically aligned single walledcarbon nanotubes (SWCNTs) grown on different substrates. (a) A honey-combmat (pitch size: 900 ㎛, hole diameter: 700 ㎛). (b) A cross-sec-tional-image. (c) Vertically aligned SWCNT rod array. (d) A crosssectionalimage. Reprinted with permission from Zhong et al. [97]. Copyright (2007) American Chemical Society.
    Optical images of 0.5 cm long vertically aligned single walledcarbon nanotubes (SWCNTs) grown on different substrates. (a) A honey-combmat (pitch size: 900 ㎛, hole diameter: 700 ㎛). (b) A cross-sec-tional-image. (c) Vertically aligned SWCNT rod array. (d) A crosssectionalimage. Reprinted with permission from Zhong et al.  [97]. Copyright (2007) American Chemical Society.
  • [Fig. 10.] Raman spectra of the as-synthesized and HIPco single walled carbon nanotubes (SWCNTs) using excitation laser with wavelengths of 488, 514, 633 and 785 nm. Reprinted with permission from Qu et al. [98]. Copyright (2008) American Chemical Society.
    Raman spectra of the as-synthesized and HIPco single walled carbon nanotubes (SWCNTs) using excitation laser with wavelengths of 488, 514, 633 and 785 nm. Reprinted with permission from Qu et al. [98]. Copyright (2008) American Chemical Society.