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High-speed roll-to-roll manufacturing of graphene using a concentric tube CVD reactor.

Polsen ES, McNerny DQ, Viswanath B, Pattinson SW, John Hart A - Sci Rep (2015)

Bottom Line: We show that a smooth isothermal transition between the reducing and carbon-containing atmospheres, enabled by injection of the carbon feedstock via radial holes in the inner tube, is essential to high-quality roll-to-roll graphene CVD.We discuss how the foil quality and microstructure limit the uniformity of graphene over macroscopic dimensions.We conclude by discussing means of scaling and reconfiguring the CTCVD design based on general requirements for 2-D materials manufacturing.

View Article: PubMed Central - PubMed

Affiliation: Department of Mechanical Engineering, University of Michigan, 2350 Hayward St., Ann Arbor, MI 48109, USA.

ABSTRACT
We present the design of a concentric tube (CT) reactor for roll-to-roll chemical vapor deposition (CVD) on flexible substrates, and its application to continuous production of graphene on copper foil. In the CTCVD reactor, the thin foil substrate is helically wrapped around the inner tube, and translates through the gap between the concentric tubes. We use a bench-scale prototype machine to synthesize graphene on copper substrates at translation speeds varying from 25 mm/min to 500 mm/min, and investigate the influence of process parameters on the uniformity and coverage of graphene on a continuously moving foil. At lower speeds, high-quality monolayer graphene is formed; at higher speeds, rapid nucleation of small graphene domains is observed, yet coalescence is prevented by the limited residence time in the CTCVD system. We show that a smooth isothermal transition between the reducing and carbon-containing atmospheres, enabled by injection of the carbon feedstock via radial holes in the inner tube, is essential to high-quality roll-to-roll graphene CVD. We discuss how the foil quality and microstructure limit the uniformity of graphene over macroscopic dimensions. We conclude by discussing means of scaling and reconfiguring the CTCVD design based on general requirements for 2-D materials manufacturing.

No MeSH data available.


Improvement of graphene coverage and quality by exploring a matrix of process parameters using the CTCVD system, focusing on the influence of a static annealing step, process temperature, and cooling atmosphere. a) Measured I2D/IG ratio values. In-process annealing time is determined by the substrate velocity. b) SEM images indicating graphene coverage and Cu grain size at various reactor temperatures, where the same temperature is maintained in both zones, and all substrates are processed at 25 mm/min.
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f7: Improvement of graphene coverage and quality by exploring a matrix of process parameters using the CTCVD system, focusing on the influence of a static annealing step, process temperature, and cooling atmosphere. a) Measured I2D/IG ratio values. In-process annealing time is determined by the substrate velocity. b) SEM images indicating graphene coverage and Cu grain size at various reactor temperatures, where the same temperature is maintained in both zones, and all substrates are processed at 25 mm/min.

Mentions: Last, we sought to identify principles for improved R2R production of graphene using the CTCVD system. It is understood that annealing prior to carbon exposure improves the viability of the Cu substrate for high-quality graphene growth by reducing surface oxides, healing surface defects on Cu, and by promoting Cu grain growth293035. While it appears (based on the rate and degree of surface charging during SEM imaging) that the oxide layer on the as received Cu substrate is removed during annealing, qualitatively this does not change comparing annealing speeds of 500 mm/min to 25 mm/min (see Supporting Information, Fig. S9). To explore the utility of a more thorough foil pre-treatment step, Cu substrates were annealed in place for three hours at 1010 oC and then the carbon source was turned on in the growth zone, and translation motion was started for graphene growth. We compared speeds of 25 and 125 mm/min, at which we had previously observed full graphene coverage on most Cu grains, and disconnected nanoscale graphene domains, respectively in the baseline study. With the extended pre-annealing step, a significant increase in the graphene I2D/IG ratio to 1.39 was realized at 125 mm/min (Fig. 7a), as compared to the baseline process I2D/IG ratio of 0.74 (Fig. 3). However, the I2D/IG ratio for the 25 mm/min sample remained roughly the same at 1.48 as compared to the baseline value of 1.57. Representative Raman spectra are shown in Fig. S10 (see Supporting Information). Finally, previous studies have attributed the increase in the I2D/IG ratio after similar annealing treatment to Cu grain growth40; however, on our samples we did not notice significant grain growth after annealing. Therefore, we attribute the higher quality to improvement of the foil surface chemistry and removal of surface defects.


High-speed roll-to-roll manufacturing of graphene using a concentric tube CVD reactor.

Polsen ES, McNerny DQ, Viswanath B, Pattinson SW, John Hart A - Sci Rep (2015)

Improvement of graphene coverage and quality by exploring a matrix of process parameters using the CTCVD system, focusing on the influence of a static annealing step, process temperature, and cooling atmosphere. a) Measured I2D/IG ratio values. In-process annealing time is determined by the substrate velocity. b) SEM images indicating graphene coverage and Cu grain size at various reactor temperatures, where the same temperature is maintained in both zones, and all substrates are processed at 25 mm/min.
© Copyright Policy - open-access
Related In: Results  -  Collection

License
Show All Figures
getmorefigures.php?uid=PMC4440526&req=5

f7: Improvement of graphene coverage and quality by exploring a matrix of process parameters using the CTCVD system, focusing on the influence of a static annealing step, process temperature, and cooling atmosphere. a) Measured I2D/IG ratio values. In-process annealing time is determined by the substrate velocity. b) SEM images indicating graphene coverage and Cu grain size at various reactor temperatures, where the same temperature is maintained in both zones, and all substrates are processed at 25 mm/min.
Mentions: Last, we sought to identify principles for improved R2R production of graphene using the CTCVD system. It is understood that annealing prior to carbon exposure improves the viability of the Cu substrate for high-quality graphene growth by reducing surface oxides, healing surface defects on Cu, and by promoting Cu grain growth293035. While it appears (based on the rate and degree of surface charging during SEM imaging) that the oxide layer on the as received Cu substrate is removed during annealing, qualitatively this does not change comparing annealing speeds of 500 mm/min to 25 mm/min (see Supporting Information, Fig. S9). To explore the utility of a more thorough foil pre-treatment step, Cu substrates were annealed in place for three hours at 1010 oC and then the carbon source was turned on in the growth zone, and translation motion was started for graphene growth. We compared speeds of 25 and 125 mm/min, at which we had previously observed full graphene coverage on most Cu grains, and disconnected nanoscale graphene domains, respectively in the baseline study. With the extended pre-annealing step, a significant increase in the graphene I2D/IG ratio to 1.39 was realized at 125 mm/min (Fig. 7a), as compared to the baseline process I2D/IG ratio of 0.74 (Fig. 3). However, the I2D/IG ratio for the 25 mm/min sample remained roughly the same at 1.48 as compared to the baseline value of 1.57. Representative Raman spectra are shown in Fig. S10 (see Supporting Information). Finally, previous studies have attributed the increase in the I2D/IG ratio after similar annealing treatment to Cu grain growth40; however, on our samples we did not notice significant grain growth after annealing. Therefore, we attribute the higher quality to improvement of the foil surface chemistry and removal of surface defects.

Bottom Line: We show that a smooth isothermal transition between the reducing and carbon-containing atmospheres, enabled by injection of the carbon feedstock via radial holes in the inner tube, is essential to high-quality roll-to-roll graphene CVD.We discuss how the foil quality and microstructure limit the uniformity of graphene over macroscopic dimensions.We conclude by discussing means of scaling and reconfiguring the CTCVD design based on general requirements for 2-D materials manufacturing.

View Article: PubMed Central - PubMed

Affiliation: Department of Mechanical Engineering, University of Michigan, 2350 Hayward St., Ann Arbor, MI 48109, USA.

ABSTRACT
We present the design of a concentric tube (CT) reactor for roll-to-roll chemical vapor deposition (CVD) on flexible substrates, and its application to continuous production of graphene on copper foil. In the CTCVD reactor, the thin foil substrate is helically wrapped around the inner tube, and translates through the gap between the concentric tubes. We use a bench-scale prototype machine to synthesize graphene on copper substrates at translation speeds varying from 25 mm/min to 500 mm/min, and investigate the influence of process parameters on the uniformity and coverage of graphene on a continuously moving foil. At lower speeds, high-quality monolayer graphene is formed; at higher speeds, rapid nucleation of small graphene domains is observed, yet coalescence is prevented by the limited residence time in the CTCVD system. We show that a smooth isothermal transition between the reducing and carbon-containing atmospheres, enabled by injection of the carbon feedstock via radial holes in the inner tube, is essential to high-quality roll-to-roll graphene CVD. We discuss how the foil quality and microstructure limit the uniformity of graphene over macroscopic dimensions. We conclude by discussing means of scaling and reconfiguring the CTCVD design based on general requirements for 2-D materials manufacturing.

No MeSH data available.