In situ studies on dynamic properties of carbon nanotubes with metal clusters

Transcription

1 In situ studies on dynamic properties of carbon nanotubes with metal clusters Jason Chang, Yuan-Chih Chang, Der-Hsien Lien, Shaw-Chieh Wang*, Tung Hsu*, and Tien T. Tsong Institute of Physics, Academia Sinica, Taiwan *Department of Materials Sciences and Engineering, National Tsing Hua University, Hsinchu, Taiwan Supported by the National Program for Nanoscience and Nanotechnology, National Science Council

2 Outline! Capillarity of molten silver droplets

3 Ultrahigh vacuum HR-TEM UHV-TEM e - gun C1 Evaporators C2 C2 Ap OBJ lens specimen OBJ Ap SAD Ap Intermediate lenses Base pressure 2 x torr optical axis Projector lens screen

4 In situ deposition PHYSICAL REVIEW B 74, (2006)

5 Structure of carbon nanotube 5

6 Structure of carbon nanotube 5

7 From nucleation to coalescence T ~ 300 K N Flux! 125 atoms/s min min

8 Growth of Ag clusters on CNTs 3.46 nm 4.28 nm 5.45 nm 10.4 nm nm nm

9 Boundary effect 9 8 particle size (nm) Diameter of CNT (nm)

10 Cluster density vs deposition time

11 Multi-twinned phases in clusters Icosahedra Marks decahedra Size-dependent structures calculated for Ni clusters: Icosahedra for atoms; Marks decahedra for atoms; Single crystal for > atoms. C.L. Cleveland and Uzi Landman, J. Chem. Phys. 94, 7376 (1991).

12 Varying structures of Ag clusters stable Unstable

13 Stability of crystalline phases T ~ 300K N ~ atoms 4500 atoms

14 Summary The growth of Ag clusters on carbon nanotubes has revealed that the ultimate size, the nucleation density, and the stable crystalline structure of a grown cluster are closely related to the size of the tube. The effect can be attributed to the curvature change of the tube surface that is determined by its size and chirality.

15 UHV-TEM Base pressure 2 x torr

16 UHV-TEM Base pressure 2 x torr

17 UHV-TEM Gold knife AFM tip Base pressure 2 x torr

18 Making CNT tips by blade tip

19 Nano electromechanical oscillator

20 Quartz crystal microbalance front back

21 Electromechanical Resonances of Carbon Nanotubes Philippe Poncharal, Z. L. Wang, Daniel Ugarte, and Walt A. de Heer, Science 283, 1513 (1999).

22 Zeptogram Nanomechanical Sensing " M D /" t = ma D (" N C /" t)/# L 2 $M ~ (M eff /Q)10 -DR/20 Y. T. Yang, C. Callegari, X. L. Feng, K. L. Ekinci, and M. L. Roukes, Nano Lett. 6, 583 (2006).

23 Criteria for an atom balance $m ~ 2m 0 (kt/e c ) 1/2 ($f/qf 0 ) 1/2! Small balance mass! Sensitive detection mechanism! Minimal thermal effects! Well-controlled environment

24 Shaping a nanotube into telescope

25 Peeling the nanotube from inside

26 Peeling the nanotube from inside

27 Atom balance 3 nm Ag cluster 80 nm 6 nm Y.C. Chang et al., Small 4, 2195 (2008). 40 CNT only (m 0 = 3.1 ag) Lorentz fit of Data (CNT only) m ~ -m 0 35 (%f/2f 0 ) ~ 1.8x10 CNT with -19 Ag g particle (mass of 1000 Ag atoms) 30 Lorentz fit of Data (CNT with Ag particle) nm Q ~ MHz

28 Mass resolution $m ~ 2m 0 (kt/e c ) 1/2 ($f/qf 0 ) 1/2 Parameters of the tailored CNT resonator: Mass of balance : m 0 = 3.1 ag Thermal energy: kt = 26 mev Drive energy: E c! 200 mev Measurement bandwidth: $f! 100Hz Quality factor: Q!1000 Resonance freq: f 0!130 MHz!m ~ 0.1 zg < 0.18 zg (mass of Ag atom)

29 Shift of resonance frequency

30 Analytical and Experimental Results L Z m/m 0 = 1.3%

31 Nanotube resonator as mass sensor

32 In situ measurement of freq. shift

33 Gradient Coating Effect of Vibrating CNTs

34 Self-weighting ability Euler-Bernoulli Beam theory Rayleigh-Ritz Theory Experiment Data

35 Weighting resolution Flux (E-Beam Evaporator): 10 na! 250 atoms/s

36 Summary Several in situ techniques under the UHV environment have been developed in the STM-TEM system to design a suitable CNT resonator for measuring neutral atoms/ molecules. A mass resolution of a single Ag atom has been indirectly demonstrated with the tailored CNT resonator. The shift of resonance frequency subject to the cluster s position on the CNT has been measured and analyzed with the classical analytical formula. In real time detection, the distribution of adsorbed mass on the vibrating CNT cannot be assumed uniform but close to linear.

37 Paper : Nature Vol. 361, , 1993 Pb Pb seems to wet CNT Cu grid

38 Macroscopic capillarity Sign and magnitude of the pressure %P across the liquid meniscus depend on contact angle! c "P = 2# cos$ c / a! c < 90! c > 90 resulting in spontaneous absorption of the liquid into the capillary tube not be drawn inside the hollow unless external forces are applied With this model, Dujardin et al. (Science 265 (1994) 1850) predicted the capillary action can happen only for the materials with surface tension & < 200 mn/m. Surface tension (&) for Ag ~ 900 mn/m

39 Applied Physics A: Materials Science &Processing 86 (2007) 265 contact angle between Cu and inner carbon wall is 120 o ~135 o Cu Relatively poor wetting characteristics of Cu on the carbon surface Capillary forces may be efficient to drive filling of CNTs by metallic nanoparticles of various transition metals such as Pd, Ni, and Cu.

40 Capillarity for small droplet According to Young- Laplace equation: R t ex: droplet (spherical)! c! R d The droplet is unsupported " For the contact angle! c ~125 o of molten Ag nanodroplet inside the MWNT in our results When the droplet is supported, the effect of Laplace pressure will be reduced.

41 Paper : Nano Letter Vol. 8, , 2008 Part A : Present a simple model to demonstrate the capillary absorption for nonwetting liquid nanoparticles by CNT Initial state Parameter: No absorption Full absorption or or

42 Molecular dynamics simulation CNT 220 Å long and 30 Å in diameter Molten Pd cluster with a radius of ~23 Å Droplet potential Distance of insertion of Pd cluster Contact angle! c between Pd cluster and inner shell of SWNT! c ( 130! c ' 132! c > 133 Molten nanoparticle were drawn almost immediately. The presence of a small energy barrier. The absorption is activated. did not yield capillary absorption of the droplets.

43 Approaching Ag nanoparticle with open-ended MWCNT Ag R i R t MWNT 10nm STM probe

44 Capillary absorption of Ag droplet carbon onion #=1.664 MWNT 20nm (a) I STM probe (b) (c) (d) (e) (f) Retract the tube slightly to eliminate the effect due to compression

45 Capillary absorption at TV rate Current-induced joule heat caused the state change of Ag nanodroplet to melt and then triggered the capillary absorption #=1.55 CCD record: two frames per second TV record: ~30 frames per second

46 Ag nanoparticle between a thin and thick open-ended MWCNT (a) #=2.617 #=1.156 thick MWNT thin MWNT I 20nm (b) (c)

47 No absorption for large ) (a) (b) (c) #= nm I The Ag nanodroplet drained out gradually from the hollow core of MWNT as the passing current increased

48 Capillary absorption as function of ) The critical #~1.7 for capillary absorption in our experiment agrees well with the calculated result for tube s diameter > 5nm. Contact angle ~ 125 o

49 Exclusion of electromigration effect Capillary absorption occurs independent of the current direction I 20nm

50 (a) (b) (c) Fabrication of Ag nanowire in a CNT 20nm I Ag@CNT structure (d) (e) (f) I

51 Summary 1. The dynamic process of capillary absorption of nonwetting Ag nanodroplets by the MWCNT was in-situ observed. 2. The electromigration effect is not the main attribute for absorption of Ag nanodroplet. 3. For a large ratio of! = R i /R t, the Ag nanodroplet tends to cohere to itself and drains out from the hollow core of MWCNT. Therefore, the! value for the occurrence of capillary absorption must be below a critical value ~ The one-dimensional Ag nanowire with a specific length can be fabricated inside a MWCNT by capillary absorption for NEMS electronics or other applications.