Effect of catalyst pattern geometry on the growth of vertically aligned carbon nanotube arrays

Jeong, Goo‐Hwan; Olofsson, Niklas; Falk, L.K.L.; Campbell, Eleanor E. B.

doi:10.1016/j.carbon.2008.11.003

Cited by 54 publications

(43 citation statements)

References 19 publications

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“…We thus conclude that diffusion of the source gas through the forest is not the cause of the growth rate difference. This conclusion is consistent with previous reports [1,19,26,34].…”

Section: Discussionsupporting

confidence: 83%

“…The inner catalyst nanoparticles are surrounded by other nanoparticles consuming reactive carbon whereas the outer catalyst nanoparticles are only partially surrounded by other nanoparticles, and otherwise by non-carbon-consuming silicon dioxide. The source gas molecules impinging upon the silicon dioxide are not used for nanotube growth and thus create a larger local concentration of source gas near the edge of the forest [34]. Because the outer nanoparticles therefore receive more carbon than the inner nanoparticles, they grow faster (under the present conditions, the growth rate is limited by the carbon supply because increasing the flow rate increases the growth rate).…”

Section: Discussionmentioning

confidence: 97%

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Origin of periodic rippling during chemical vapor deposition growth of carbon nanotube forests

Vinten

Bond

Marshall

et al. 2011

Carbon

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Origin of periodic rippling during chemical vapor deposition growth of carbon nanotube forestsgrowth conditions, these forests can show a growth instability that gives rise to periodic ripples that are coherent over a forest-sized scale. Previously, we showed that the uniformity and synchronization of the ripples is sufficient for them to behave as diffraction gratings for visible light. Here, we identify the conditions that reproducibly promote the formation of these ripples. We investigate the formation mechanism via ex situ scanning electron microscopy and in situ optical imaging. While the rippling amplitude varies appreciably, the rippling wavelength varies very little and can be estimated from simple mechanical considerations. We provide evidence that the rippling is a consequence of cohesive interactions between nanotubes and the build up of strain, driven by a non-uniform growth rate. The origin of the non-uniform growth rate is explained.Crown

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“…We thus conclude that diffusion of the source gas through the forest is not the cause of the growth rate difference. This conclusion is consistent with previous reports [1,19,26,34].…”

Section: Discussionsupporting

confidence: 83%

Section: Discussionmentioning

confidence: 97%

Origin of periodic rippling during chemical vapor deposition growth of carbon nanotube forests

Vinten

Bond

Marshall

et al. 2011

Carbon

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“…We have also recently confirmed the high temperatures and temperature gradients by in situ measurement of black-body radiation from the heater during growth. The optimum initial catalyst growth temperature (defined here as the temperature for which the maximum length is found) for multiwalled nanotubes is found to be 700-750 o C, in very good agreement with studies of the optimum growth temperature for similar catalyst and precursor materials in normal thermal CVD experiments [9,10].…”

Section: Temperature Modellingsupporting

confidence: 75%

Local heating method for growth of aligned carbon nanotubes at low ambient temperature

Dittmer

Mudgal

Nerushev

et al. 2008

Low Temperature Physics

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We use a highly localised resistive heating technique to grow vertically aligned multiwalled nanotube films and aligned single-walled nanotubes on substrates with an average temperature of less than 100 o C. The temperature at the catalyst can easily be as high as 1000 o C but an extremely high temperature gradient ensures that the surrounding chip is held at much lower temperatures, even as close as 1µm away from the local heater. We demonstrate the influence of temperature on the height of multi-walled nanotube films, illustrate the feasibility of sequential growth of single-walled nanotubes by switching between local heaters and also show that nanotubes can be grown over temperature sensitive materials such as resist polymer.PACS: 61.46.Fg Nanotubes.

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“…Jeong et al, have studied the effect of growth geometry on the vertical alignment of VANTAs and showed that for a certain geometry a minimum thickness is required to achieve the necessary mechanical stability and therefore the vertical alignment. 119 Olofsson et al, reported a Young's modulus as low as 3.8 MPa for the VANTAs incorporated in their varactor. This extremely low Young's modulus (lower than that of a rubber) explains why the VANTAs were already bent before applying any bias voltage.…”

Section: Operating Voltagementioning

confidence: 98%

Vertically aligned carbon based varactors

Ghavanini

Enoksson

Bengtsson

et al. 2011

Journal of Applied Physics

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This paper gives an assessment of vertically aligned carbon based varactors and validates their potential for future applications. The varactors discussed here are nanoelectromechanical devices which are based on either vertically aligned carbon nanofibers or vertically aligned carbon nanotube arrays. A generic analytical model for parallel plate nanoelectromechanical varactors based on previous works is developed and is used to formulate a universal expression for their voltage-capacitance relation. Specific expressions for the nanofiber based and the nanotube based varactors are then derived separately from the generic model. This paper also provides a detailed review on the fabrication of carbon based varactors and pays special attention to the challenges in realizing such devices. Finally, the performance of the carbon based varactor is assessed in accordance with four criteria: the static capacitance, the tuning ratio, the quality factor, and the operating voltage. Although the reported performance is still far inferior to other varactor technologies, our prognosis which stems from the analytical model shows a promise of a high quality factor as well as a potential for high power handling for carbon based varactors.

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Effect of catalyst pattern geometry on the growth of vertically aligned carbon nanotube arrays

Cited by 54 publications

References 19 publications

Origin of periodic rippling during chemical vapor deposition growth of carbon nanotube forests

Origin of periodic rippling during chemical vapor deposition growth of carbon nanotube forests

Local heating method for growth of aligned carbon nanotubes at low ambient temperature

Vertically aligned carbon based varactors

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