Floating Catalyst CVD Method. Single- and Double-walled Carbon Nanotubes. Hui-Ming Cheng

Transcription

1 Floating Catalyst CVD Method for Controllable Synthesis of Single- and Double-walled Carbon Nanotubes Hui-Ming Cheng Shenyang National Laboratory for Materials Science Institute of Metal Research, Chinese Academy of Sciences 1

2 Where am I from? 2

3 Main Directions at my Division Synthesis, Properties and Applications of Carbon Nanotubes and Non-Carbon Nanostructures Carbon Nanotubes Non-Carbon Nanostructures New Materials for Clean Energy Applications Energy storage materials Solar energy materials Exploration of Hydrogen Storage Materials Fabrication and Applications of High-performance Carbon Materials 3

4 Main Directions at my Division Synthesis, Properties and Applications of Carbon Nanotubes and Non-Carbon Nanostructures Carbon Nanotubes Non-Carbon Nanostructures New Materials for Clean Energy Applications Energy storage materials Solar energy materials Exploration of Hydrogen Storage Materials Fabrication and Applications of High-performance Carbon Materials 4

5 Outline Synthesis of CNTs by Floating Catalyst CVD (SWNTs, DWNTs, MWNTs) Structural Control of SWNTs and DWNTs The effect of sulfur, carrier gas, and carbon feeding rate Synthesis of CNTs with narrow diameter distribution ib ti Growth mechanism of SWNTs/DWNTs by FCCVD Concluding remarks 5

6 Potential Applications of CNTs Large Scale Field emitters Energy storage Composites Individual Electronic devices STM/AFM tips Sensors Transistor D Tomànek, NT06 Presentation 6

7 Electronic Structure --- Structural Control n m 3p = 3 p ± 1 metal semiconductor E gap 1/ r R Saito et al., Appl. Phys. Lett. 60(1992) R Saito et al, Phys. Rev. B 61(2000)

8 Challenges for CNT Synthesis Development of low-cost, large-scale l processes for the synthesis of high-quality CNTs Control over the structure and electronic properties of CNTs Control over the location and orientation of CNTs on a flat substrate Development of a thorough understanding of the growth mechanism of CNTs J Liu, SS Fan and HJ Dai, MRS Bulletin,

9 Pioneered Methods for SWNT Synthesis Arc Discharge Method Laser Ablation Method Developed by S Iijima (Nature 1993) Developed by RE Smalley group (A Thess et al, Science 1996) 9

10 Growth of SWNTs by CVD method SWNTs H.J. Dai, et al., Chem. Phys. Lett Large scale: Carbon supply Catalyst supply Reaction time Ferrocene 10

11 Floating Catalyst CVD Method (FCCVD) 1998 Ferrocene SWNTs H 2 (Ar or their mixture) CH 4 (C 2 H 2, CO, C 6 H 6, Alcohol) Thiophene Potential for continuous preparation Possibility of structural control Low cost, high purity Simple post-treatment HM Cheng et al., Appl. Phys. Lett. 72 (1998) HM Cheng et al., Chem. Phys. Lett. 289 (1998)

12 SWNTs by FCCVD HM Cheng et al., Chem. Phys. Lett.289 (1998)

13 TEM Images of the SWNTs by FCCVD 13

14 Synthesis of DWNTs by FCCVD Numbe er of DWNTs Gaussian fit Mean diameter: 1.52 nm Inner diameter of DWNTs (nm) 35 Numbe er of DWNTs Gaussian fit Mean diameter: 2.26 nm Outer diameter of DWNTs (nm) > 70% WC Ren, HM Cheng et al., Chem. Phys. Lett. 359 (2002)

15 CNFs/MWNTs with Different Diameter and Wall Thickness < 10 nm nm 50-70nm nm 150 nm Carbon feeding rate Catalyst particle size Sulfur concentration YY Fan, HM Cheng et al., Carbon 38 (2000)789. YY Fan, HM Cheng et al., Carbon 38 (2000) 921. YY Fan, HM Cheng et al., J. Mater. Res. 13 (1998)

16 Outline Synthesis of CNTs by Floating Catalyst CVD (SWNTs, DWNTs, MWNTs) Structural Control of SWNTs and DWNTs The effect of sulfur, carrier gas, and carbon feeding rate Synthesis of SWNTs with narrow diameter distribution ib ti Growth mechanism of SWNTs/DWNTs by FCCVD Concluding remarks 16

17 The Effect of Sulfur-- Necessary? Ferrocene &Argon Without the addition of sulfur Without additional carbon Low productivity it 17

18 The effect of Sulfur on the Purity and Quality of SWNTs with sulfur without sulfur Higher purity Higher quality and narrower distribution 18

19 The Effect of Sulfur on the Diameter Distribution of SWNTs Without sulfur With sulfur Broad diameter distribution! 19

20 The Effect of Sulfur on Diameter and Shell Number WC Ren, HM Cheng et al., J. Nanosci. Nanotech. 6 (2006)

21 The Effect of Sulfur on the Diameter and Shell Number Sulfur is plays necessary an important for the role synthesis in structural of SWNTs and control DWNTs (diameter with a and high shell productivity number ) of CNTs ω = A 1/d t+a 2 WC Ren, HM Cheng et al., J. Nanosci. Nanotech. 6 (2006)

22 Hydrogen is beneficial to the synthesis of Diameter The Effect Narrowly-distributed of Carrier Gas SWNTs Ar Number of SWNTs Gaussian fit Mean diameter: d= 1.15 nm Raman Shift ( cm -1 ) Raman Diameters Shift of ( cmswnts -1 ) (nm) H 80 2 Number of SWNTs Gaussian fit Mean diameter: d= 1.72 nm 85% SWNTs with diameters of 1.7±0.2 nm Raman shift ( cm -1 ) Raman shift ( cm ) Diameters of SWNTs (nm)

23 Low carbon feeding rate is beneficial to the The synthesis Effect of of Carbon Narrowly-distributed Feeding Rate SWNTs Carbon source: Methane ml/min Intensity Intensity ml/min 1589 In ntensity 168 tensity Int Raman Shift ( cm -1 ) Raman Shift ( cm -1 ) 23

24 Aligned DWNT ropes by FCCVD > 10 cm WC Ren, HM Cheng et al., J. Phys. Chem. B 109 (2005)

25 Typical HRTEM Images of DWNTs Outer diameter: nm Inner diameter: nm > 90% 25

26 RBM Mapping of DWNT Ropes Raman shift cm -1 Narrow diameter distribution 26

27 Outline Synthesis of CNTs by Floating Catalyst CVD (SWNTs, DWNTs, MWNTs) Structural Control of SWNTs The effect of sulfur, carrier gas, and carbon feeding rate Synthesis of SWNTs with narrow diameter distribution ib ti Growth mechanism of SWNTs/DWNTs by FCCVD Concluding remarks 27

28 Structural Correlation between SWNTs and the Attached Catalyst Particles 70 (a) (b) 160 Number of SWNTs Number of Fe-NPs nm Diameters of SWNTs (nm) Diameter of Fe-NPs (nm) 2nm The size of catalyst particles : > 5nm The diameters of SWNTs or DWNTs: < 3 nm (in general) SWNTs growth on the localized region of the surface of catalyst Localized nucleation on big catalyst particles WC Ren, HM Cheng et al., J. Phys. Chem. B 110 (2006)

29 Structural Correlation between SWNTs Bundles and the Attached Catalyst Particles 2 nm Localized nucleation on big catalyst particles 29

30 Tip Structure of SWNTs at the Initial Nucleation Stage Caps Formation of the cap structure t Bending of graphite islands on the localized zone of the surface of catalyst particles 30

31 Role of Sulfur on the Formation of the Small Caps The role of sulfur VLS growth mechanism Precipitation of carbon from the localized liquid zone Decreasing melting point of localized zone Key point for the localized nucleation (the diameter of CNTs is closely correlated with the addition amount of sulfur) Enhancing the decomposition of carbon sources Inhibit the continuous extending of graphite islands Introduction of defects in the graphite islands Enhance the bending of graphite islands and consequently nucleation 31

32 Proposed Growth Model Sulfur-assisted localized nucleation at low temperature a b c I II III Fe atoms Temperature gradient Fe-C-S phase The liquid catalyst WC Ren, HM Cheng et al., J. Phys. Chem. B 110 (2006)

33 Concluding Remarks Developed a floating catalyst CVD method for the synthesis of SWNTs and DWNTs Attempted the diameter and shell number control of CNTs Obtained SWNTs and DWNTs with narrow diameter distribution Proposed a localized li nucleation model for the growth of SWNTs and DWNTs by FCCVD 33

34 Dr. Wencai Ren Dr. Feng Li Mr. Qingfeng Liu Mr. Bilu Liu Acknowledgment Prof. M Dresselhaus at MIT NSFC, MOST, and CAS for financial support JSPS for supporting this visit 34

35 Thank you very much for your attention! 35