Apr. 11, 2011 Effects of Water on Rapid Growth of Single-Walled Carbon Nanotubes

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1 Effects of Water on Rapid Growth of Single-Walled Carbon Nanotubes Millimeter-Scale Growth & Our Recipes Growth Curves & Changes Occurring in Catalyst & SWCNTs Key Growth Precursor, Simple Gas Condition, and Effects of H 2 O Countermeasures for Ostwald Ripening Toward Mass Production of Millimeter-Long SWCNTs Suguru NODA 1,2, * and Kei Hasegawa 1 1 Department of Chemical Systems Engineering, The University of Tokyo, Japan 2 PRESTO, Japan Science and Technology Agency, Japan * noda@chemsys.t.u-tokyo.ac.jp 1/34

2 Acknowledgements: Collaborations & Financial Supports Lee Yamaguchi-Noda Lab. ('10.04) Sekiguchi Mr. Osawa Sato Hashimoto Dr. Hasegawa Prof. Yamaguchi Kang Dr. Kim Park Na Suarpa Dr. Shiratori Mr. Ueda Dr. Tsuji Tashiro Hirota Lee Masuda Oshim あ Takano Kakehi(D'08) Itoh(M'08) Ishitsuka(M'10) Sugime(D'10) Shirai(M'09) Nomura(M'10) Morokuma(M'09) Mr. Furuichi('06-'07) Mr. Haba('07-'08) Dr. Fukai('08) Yamaguchi-Noda Laboratory Maruyama Laboratory (at Mechanical Engineering) DAINIPPON SCREEN MFG CO. Hitachi Chemical CO. NEDO Nanotech Challenge # JST PRESTO #3130 MEXT Grant-in-Aid for Young Scientists (A) # , # MEXT Grant-in-Aid for Scientific Research in Priority Areas # /34

3 Previous Studies on Vertically-Aligned CNTs Pioneering Work on MWCNTs Alcohol CVD of VA-SWCNTs MWCNT, φ~ 30 nm, 50 µm/ 2 h (Fe/porous SiO 2, C 2 H ºC) SuperGrowth of VA-SWCNTs Several years are MWCNT, φ~ 30 nm, 2 mm/ 48 h (Fe/porous-SiO 2, C 2 needed H 2 to establish ºC) keeping small catalyst particles active. 3/34

4 Early Reports on VA-SWCNTs Journal Catalyst Feedstock Height Y. Murakami, et al., CPL 385, 298 (2004). CoMo/SiO 2 C 2 H 5 OH 4 µm / 10 min K. Hata, et al., Science 306, 1362 (2004). Fe/Al 2 O 3 C 2 H 4 + H 2 O 2500 µm / 10 min G.F. Zhong, et al., JJAP 44, 1558 (2005). Al 2 O 3 /Fe/Al 2 O 3 CH 4 (PE) 200 µm / 40 min G. Eres, et al., JPCB 109, (2005). Fe/Al 2 O 3 C 2 H µm / 240 min G. Zhang, et al., PNAS 102, (2005). Fe/SiO 2 CH 4 (PE) ~ 50 µm / 50 min? L. Zhang, et al., CPL 422, 198 (2006). CoMo/SiO 2 CO 40 µm /?? min We focus on rapid growth of VA-SWCNTs to millimeters in tens minutes in this talk. 4/34

5 Our Method: Combinatorial Catalyst Screening Noda, et al., Appl. Surf. Sci. 225, 372 (2004), Appl. Phys. Lett. 86, (2005). Controlled thickness gradient by sputter-deposition through a mask Spontaneous formation of a series of particles at CVD temperatures Various CNTs in a single CVD run 5/34

6 Our Method: Real-time Monitoring Noda, Hasegawa, et al., 2008 MRS Spring Meeting, P1.4. Digital Camera Movie by Digital Camera 7.9vol% C 2 H 4 / 26 vol% H 2 / 100 ppmv H 2 O/ Ar at 1 atm, 820 C, τ~ a few s 2 mm 7 min 0.2 nm 3 nm nm Fe/ Al 2 O x Growth curves for a series of catalysts can be obtained in one experiment. 6/34

7 Reproduction of SuperGrowth: C 2 H 4 /H 2 + H 2 O C 2 H 4, Fe/Al 2 O Noda, et al., Jpn. J. Appl. Phys. 46, L399 (2007). Hasegawa, et al., J. Nanosci. Nanotechnol. 8, 6123 (2008). x 7.9vol% C 2 H 4 / 26 vol% H 2 / 100 ppmv H 2 O/ Ar at 1 atm, 820 C, τ~ a few s 3 mm/ 30 min Millimeter-tall, large diameter (3~4 nm) SWCNTs. 7/34

8 Rapid Growth with vs. without Water-Assist C 2 H 4, Fe/Al 2 O x With 100 ppmv H 2 O Noda, Hasegawa, et al., Jpn. J. Appl. Phys. 46, L399 (2007) MRS Spring Meeting, P1.4. Without H 2 O addition SWCNT grow similarly for a limited catalyst window. 8/34

9 Significant Effect of Aluminum Oxides Noda, et al., Jpn. J. Appl. Phys. 46, L399 (2007). Fe /nm Fe/ Al(O) /SiO 2 Al(O)/ Fe/ 15 nm Al(O) /SiO 2 Al(O)/ Fe/ SiO 2 Fe /nm 3 Coexistence of Al(O) is essential for rapid growth underlayer sandwich upperlayer Fe /nm Nomura, unpublished (2008) /34 Al /nm Al /nm Al /nm

10 Steady Growth Abrupt Termination [1] Alcohol CVD Maruyama, et al., Chem. Phys. Lett. 403, 320 (2005). C 2 H 4, Fe/Al-Si-O 1 mm Fe thickness [nm] Hasegawa & Noda, Jpn. J. Appl. Phys. 49, (2010). 1.5 h = h 0 τ [1-exp(-t/τ)] Fe 0.5 nm [2] SuperGrowth D.N. Futaba, et al., Phys. Rev. Lett. 95, (2005). height of forests, h [mm] Fe 1 nm Fe 3 nm Fe 0.4 nm H / t e t / τ time, t [s] 10/34 0 Abrupt self-termination, same as the finding by Meshot & Hart, Appl. Phys. Lett. 92, (2008).

11 Degrading CNT Quality with Length Hasegawa & Noda, Appl. Phys. Express 3, (2010). NT9, CT-23 (2008). Raman quality degrades from the top to the bottom of the forest, as Eres, et al. previously reported in JPCB 109, (2005). Changing from SWCNTs to MWCNTs? 11/34

12 Hasegawa & Noda Jpn. J. Appl. Phys, 49, (2010). Microstructures of VA-SWCNTs Hasegawa & Noda Appl. Phys. Express, 3, (2010). NT2008, CT-23. Abrupt loss of alignment. Gradual diameter increase while retaining single-walled. Catalyst coarsening, discussed later. Apr. cf. Wang, 11, 2011 et al., APL 88, Effects (2006). of Water on Rapid Growth of Single-Walled Carbon Nanotubes 12/34

13 What is the Growth Precursor in C 2 H 4 -CVD? C 2 H 4, Fe/Al-Si-O Hot-Wall Cold-Wall "Cold-Gas" gas gas gas Ito, et al., 2008 MRS Spring Meeting, P4.26. C 2 H 4 1 mm Why? 300 µm 10 1 µm Separate Control of Gas & Catalyst Temperature residence time ~ 10 s Gas-Heating T R.T.~ 950 C H 2 C 2 H 4 H 2 O CH 4 C 2 H 2 C 2 H 6 Cooling Down Joule heating Catalyst-Heating T cat = 650~850 C Fe: 1.0 nm Al 2 O 3 : 20 nm 1 mm Exhaust GC & CHEMKIN T gas = 850 C Pyrolysis of C 2 H 4 into C 2 H 2 is the key! 1 mm 2-4 Torr C 2 H 2 realizes such growth without gas heating. 13/34

14 VA-SWCNTs from C 2 H 5 OH by AP-CVD Sugime & Noda, Carbon 48, 2203 (2010). VA-CNTs on combinatorial library CHEMKIN simulation MW SW Pyrolyzed C 2 H 5 OH grows millimter-tall VA-CNTs. Al 2 O x underlayer is effective to activate small catalysts & grow VA-SWCNTs. 14/34

15 Millimeter-Tall SWCNTs from Pyrolyzed C 2 H 5 OH C 2 H 5 OH Sugime, et al., NT2008, B54. Separate Study of Gas-Phase & Catalytic Reactions by "Cold-Gas CVD" residence time ~ 10 s H 2 CH 4 C 2 H 5 OH H 2 O CO C 2 H 2 C 2 H 4 Joule heating Co: 0.25~2.8 nm Al 2 O 3 : 20 nm Exhaust Growth from 1.2 Torr C 2 H 5 OH at various T gas R.T Gas-phase reaction is essential for VA-SWCNTs! Gas-Heating T R.T.~ 1000 C 2.8 C 2 H 5 OH 1.2 Torr Co/nm 1.5 Total 760 Torr s H Again, pyrolysis of C 2 H 5 OH into C H488 2 nm 1 is the key for millimeter growth H 2 O C 2H 2 in 10 min. Partial Pressure [Torr ] Gas phase compositions simulated by CHEMKIN 0 Cooling Down C C 2 H 4 2 H 5 OH Gas Temperature [ o C ] C 2 H 5 OH pyrolyzes into C 2 H 2 at high T gas! Catalyst-Heating T cat = 800 C (fixed) Note: SWCNTs 0.5 grown directly CO from C 2 H 5 OH CH tend to be short but have higher 4 quality. Growth from 0.2 Torr C 2 H 2 at T gas = R.T. 2.8 Co/nm Raman shift [cm -1 ] 15/34 Intensity [a.u.] Co/nm Low pressure C 2 H 2 does yield VA-SWCNTs of high G/D!

16 Pioneering Work at Oak Ridge G. Eres, et al., J. Phys. Chem. B 109, (2005). "Molecular beam-controlled nucleation and growth of VA-SWCNT arrays." Identified C 2 H 2 as primary precursor. Grew 0.4-mm-tall SWCNTs in 240 min. 16/34

17 What Is Occurring in the Reactor? Series of Processes in Serial Nota, 4th Guadalupe Workshop (2009). (1) (2) (3) (4) (5) (6) C 2 H 4 C 2 H 2 (flow) C 2 H 2 (film) C 2 H 2 (cat) C (cat, in) C (cat, out) CNT Reactor CNT Films Catalyst C 2 H 4 reaction C 2 H 2 diffusion diffusion reaction growth diffusion Rate Determining Steps Serial: Slowest one governs the whole. Parallel: Fastest one governs the whole. (1) Gas-Phase (2) Gas-Phase (3) Diffusion in (4) Surface Reaction (5) Diffusion in/ Reaction Diffusion/ CNT Films cf. Slower reaction (6) Precipitation from Feedstock Supply of C 2 H 4 than C 2 H 2 Catalyst Catalyst deactivation Rapid & Thick by being covered with carbon byproducts?! 17/34

18 Millimeter-Tall SWCNTs from C 2 H 2 /Ar Hasegawa & Noda, ACS Nano 5, 975 (2011). 1.4 mm in 13 min Without adding H 2 O. 18/34

19 Effects of H 2 O Hasegawa & Noda, ACS Nano 5, 975 (2011). inhibited promoted Similar rate & prolonged lifetime at high P C2H2. G/D ratio was degraded by water. 19/34

20 Diameter Increase in SWCNTs Hasegawa & Noda, ACS Nano 5, 975 (2011). SWCNTs increase their diameter not with length but with time, due to coarsening of catalyst particles with time. 20/34

21 Detailed TEM Study by AFRL-Purdue-Rice Coarsening by "Ostwald ripening." Mass decrease by subsurface diffusion. Apr. P.B. 11, Amama, 2011 et al., Nano Effects Lett. of Water 9, 44 on (2009). Rapid Growth S. of M. Single-Walled Kim, et al., Carbon J. Phys. Nanotubes Chem. Lett. 1, 918 (2010). 21/34

22 Two Mechanisms for Coarsening of Particles Migration & Coalescence through particle motion Ostwald Ripening through adatom motion Particles simply increase in size Smaller particles evaporates and decrease in number. while larger particles grow. Both finally yields unimodal large particles due to slowing change in larger particles. Our finding: SWCNTs with bimodal diameter distribution. H. Sugime & S. Noda, Carbon 47, 234 (2009). Co/Mo: 0.11/ / / /0 [nm] "Mo suppressed surface diffusion of Co adatoms" "Ostwald ripening resulted in Co particles with a bimodal diameter distribution." Apr. 11, nm Effects of Water on Rapid Growth of Single-Walled Carbon Nanotubes 22/34

23 Two Mechanisms for Coarsening of Particles Migration & Coalescence through particle motion Ostwald Ripening through adatom motion Our finding: Catalyst particles with bimodal diameter distribution. "Half-Centimeter-Tall Single-Walled Carbon Nanotubes Growing Taller at Lower Temperatures More Slowly" by Poster. before CVD after CVD Evidence for Ostwald ripening. 23/34

24 Effect of H2O on Ostwald Ripening of Catalysts AFM after CVD at 800 ºC, C2H kpa, 30 min Fe 0.4 nm Fe 0.7 nm Fe 1.0 nm 1 µm nm 1.00 x 1.00 µm VD_H2O_0.4 / nm Height800C of_cparticle No H2O [nm] Number nm 1.00 x 1.00 µm VD_H2O_0.7 / nm Height800C of_cparticle [nm] nm 1.00 x 1.00 µm VD_H2O_1.0 / nm Height800C of_cparticle Number [nm] Number 50 ppmv H2O No obvious difference [nm] [nm] [nm] Number Number Number nm nm 1.00 x 1.00 µm 1.00 x 1.00 µm 1.00 x 1.00 µm nm C_C oh2oeffects _ C _C _N oh2o_ Cof _CVDparticle _NoH2O_1.0 Apr. 11, 2011 of Carbon Nanotubes 24/34 Height ofvd_nparticle / nmof Water on Rapid Growth Height ofvdsingle-walled particle / nm Height / nm

25 Key for Millimeter-Tall VA-SWCNTs Hasegawa & Noda, ACS Nano 5, 975 (2011). * *cf. T. Yamada, et al., Nano Lett., 2008, 8, The key for millimeter-tall SWCNTs is to keep C 2 H 2 at a moderate level so as not to kill the catalysts. 25/34

26 Lowering Temperature "Half-Centimeter-Tall Single-Walled Carbon Nanotubes Growing Taller at Lower Temperatures More Slowly" by Poster. With H 2 O (50 ppmv) Lower T Lower acceptable P C2H2 & slower Ostwald ripening Slower growth but even longer lifetime Larger final height 26/34

27 Lower Temperatures Taller but Slower "Half-Centimeter-Tall Single-Walled Carbon Nanotubes Growing Taller at Lower Temperatures More Slowly" by Poster. Other countermeasure like Mo co-catalyst for Co is WANTED! 27/34

28 Toward Mass Production of Long SWCNTs from Semiconductor Process VA-CNTs on 2D substrates to Chemical Process VA-CNTs on beads stuck in 3D surface area ~ 1,000x continuous process Tsinghua Bayer Showa -Denko A. Sputtering well-established but not practical Catalysts are deposited on beads by: B. Solution widely used and practical C. CVD maximum productivity 28/34

29 Submillimeter-Tall SWCNTs by Sputtered Catalysts "Fluidized-Bed Synthesis of Sub-Millimeter-Long Single-Walled and Multi-Walled Carbon Nanotubes" by D.Y. Poster. MWCNTs on Spheres by F. Wei & Coworkers 0.5-mm-tall SWCNTs, Carbon purity > 99 wt%, Carbon Yield: 65 at%, Residence time < 0.3 s Chem. Vap. Depos. 13, 533 (2007). 29/34

30 Fluidized Bed with CVD Catalysts D.Y. Kim, et al., Carbon 49, 1972 (2011). Movie Movie Apr. 11, 2011 Cycles are Effects repeated of Water at on a Rapid fixed Growth temperature of Single-Walled just Carbon by Nanotubes switching the gas. 30/34

31 Re-deposition of Catalyst/Support Layers Practical solution for catalyst coarsening. 31/34

32 TEM of CNTs Produced for Increasing Cycles D.Y. Kim, et al., Carbon 49, 1972 (2011). Steady production of few-walled CNTs (8 ± 2 nm). 32/34

33 Reforming of C 2 H 2 to CNTs + H 2! D.Y. Kim, et al., Carbon 49, 1972 (2011). Reactor ~ 50 ml 1 L-CNTs/ 20 cycle Purity: 99 wt% Diameter: 8±2 nm Length: ~400 µm SSA: 400 m 2 /g # of walls: ~3 Gas residence time < 0.3 s, Carbon yield > 70% Further development is ongoing to achieve automated semi-continuous production of submillimeter-long SWCNTs. 33/34

34 Summary C 2 H 2 is a key precursor rapidly growing millimeter-tall SWCNTs. Such growth is possible both by direct feeding of C 2 H 2 and by pyrolyzing various feedstocks (C 2 H 4, C 2 H 5 OH, and possibly others) into C 2 H 2. The key is to moderate C 2 H 2 supply. No additives are needed. Excess C 2 H 2 easily kills the catalysts possibly due to carbon byproducts. 5-Pa-H 2 O has significant effects. Suppressing catalyst deactivation under excess C 2 H 2 supply. Effective to enhance productivity by supplying C 2 H 2 at high concentration. Inhibiting SWCNT growth from small catalyst particles and introducing defects to SWCNTs. Having no effect on suppressing catalyst coarsening at least at 50 ppmv. Catalyst coarsening during SWCNT growth. Ostwald ripening is an important mechanism. Causes diameter increase in growing SWCNTs at millimeter-scale. Low P C2H2 at low T yield half-centimeter-long SWCNTs slowly. Countermeasure is wanted slowing coarsening while retaining rapid growth. Re-deposition of catalyst/support layers is a practical solution for it. 34/34