Visible light emission from single walled carbon nanotube-noble metal nanoparticle composites

Transcription

1 Visible light emission from single walled carbon nanotube-noble metal nanoparticle composites T. Pradeep Department of Chemistry and Sophisticated Analytical Instrument Facility Indian Institute of Technology Madras Chennai AsiaNANO 2008 November 3-7, 2008

2 Acknowledgements DST Nanomission Dr. C. Subramaniam Dr. Jaydeb Chakrabarti Prof. Takuji Ogawa Mr. Chockalingam Students 2

3 Chemical interactions with nanostructures leading to devices 3

4 A B Height (nm) C Distance (nm) Sajanlal and Pradeep, Adv. Mater., 20 (2008) 980 4

5 5

6 6

7 A B ~ 10.6 nm ~ 10.6 nm 100 nm 200 nm I A (111) (111) B B 0.5 µm ~ 10.6 nm (220) II II 100 nm 1 nm nm nm 10.6 nm 7

8

9 Sreeprasad et al. Langmuir

10 In this talk.. Visible emission from single walled carbon nanotubes Background Experiment Control experiments Uses 10

11 Flow induced potential in nanoparticle assemblies Counter ITO substrate Peristaltic pump 90 0 Spacer mV + - Au nanoparticle Keithley assembled ITO 2700 substrate 11

12 (a) Potential Difference, s (V) Potential Difference, s (V) Time (s) (b) With Jaydeb Chakrabarti Time (s) C. Subramaniam et al. Phys. Rev.Lett.2005 J. Phys. Chem. C Indian Patent application 2005

13 (n,m) indices Metallic Semiconducting 13

14 Electrical transport properties Semiconducting : (n-m) = 3l. Eg = ev Metallic : (n-m) = 3l. E g = ev Semiconducting Metallic A. Hartschuh et al., Chem. Phys. Chem. 6, 577 (2005) 14

15 Emission spectrum (red) of individual fullerene nanotubes suspended in SDS micelles in D 2 O excited by 8 ns, 532-nm laser pulses, overlaid with the absorption spectrum (blue) of the sample in this region of first van Hove band gap transitions. Sample is in liquid state. M. J. O Connell et al., Science 297, 593 (2002). 15

16 Raman spectroscopy of SWNTs (A) Radial Breathing Mode (RBM) Diameter dependent RBM ( cm 1 ) d ( nm) t 12.5 (B) Tangential G band In-plane vibrations (C) D-band Defect centered (D) G` band Occurs at 2ω D Intensity (arb. units) SWNTs powder Science, 1997, 275, 187. & Raman Shift (cm -1 ) 16

17 Purification of SWNT SWNT Sigma Aldrich (pre-purified) CNI (HiPCo) Sonication and centrifugation 1. Annealed 2. Acid treated 3. Neutralised 4. Washed and dried Centrifugate Purified SWNT 17

18 SWNT-nanoparticle composite Diethyl ether SWNT in DMF Diethyl ether Aqueous Nanoparticles M NPs/NRs M NPs Au/Ag nanoparticles, Citrate synthesized M NRs Au nanorods Au NPs Sample is in solid state. 18

19 SWNT mswnt Starting materials Au nanoparticles Ag nanoparticles Au nanorods NP-SWNT NR-mSWNT 100 nm 2 nm www1.eere.energy.gov 20 nm 5 nm 19

20 Nanoparticle composite 0.1 μm 0.1 μm TEM images of Au-SWNTs composite acquired at 100 kev. 20

21 Nanorod composite 10 nm TEM images of (A) AuNRs-SWNTs composite acquired at 300 kev. 21

22 Possible impurities 52k (A) 40k (B) 50k Intensity (arb. units) 48k 46k 44k Intensity (arb. units) 38k 36k 42k Binding energy (ev) 34k Binding Energy (ev) XPS spectra of Au-SWNT composite in the (A) Ni 2p and (B) Fe 2p regions. ICP - MS 22

23 (A) (B) Excitation wavelength (nm) Emission wavelength (nm) Emission wavelength (nm) Fluorescence contour plots of (A) supernatant solution and (B) blank water at ph

24 Instrumentation Confocal Raman Concept of confocality Raman Instrument 24

25 Scanning Near-field Optical Microscopy Resolution is limited by wavelength of light used. Near-filed microscopy was first proposed by Synge in Resolutions below the diffraction limit can be obtained when the tip-sample distance is smaller than the aperture diameter. In such a case, the aperture diameter controls the resolution and not the wavelength of light used E.H. Synge, Phil.Mag. 6, 356 (1928) 25

26 Raman spectra Intensity (arb. units) k 20k 15k 10k Wavelength (nm) k Wavelength (nm) (ii) (a) (b) (c) 669 2k 1k k G` band (d) Raman Shift (cm -1 ) (e) Raman Shift (cm -1 ) (i) Raman Spectra of (a) Ag-SWNTs composite, (b) Au-SWNTs composite, (c) AuNR-SWNTs composite, (d) pristine SWNTs, (e) Pristine SWNTs treated with trisodium citrate and (f) Au nanorods. 26

27 Raman spectral imaging Intensity (arb. units) 25k 20k 15k 10k 5k Raman Shift (cm -1 ) 7 μm 27

28 Varying excitation sources a b Wavelength (nm) Excitation : 532 nm a b Excitation : 633 nm c c Raman Shift (cm -1 ) Raman Shift (cm -1 ) Raman Spectra acquired with (A) 532 nm Nd-YAG and (B) 633 nm He-Ne as excitation sources. Traces (a), (b) and (c) correspond to Ag-SWNTs composite, Au-SWNTs composite and AuNR-SWNTs composite, respectively. 28

29 SNOM (A) SNOM images of Au-SWNT composite along with the (C) topography. (B) and (D) are their three dimensional representations. 29

30 (A) (B) Transmission SNOM images of pristine SWNT based on (A) topography and (B) light intensity. 30

31 Supporting experiments Intensity (arb.units) (A) C CTAB = 10-6 M C CTAB = 10-5 M C CTAB = 10-4 M C CTAB = 10-3 M C CTAB = 10-2 M C CTAB = 10-1 M (B) Raman Shift (cm -1 ) 100 nm (A) Raman spectra of Ag-SWNT composite measured as a function of CTAB concentration. (B) TEM image of Au-CTAB-SWNT at C CTAB = 10-4 M 31

32 Intensity (arb. units) 25k 20k 15k 10k 5k (A) Intensity (arb. units) 20k 10k (B) C SWNT = 1.7 mg/ml C SWNT /2 C SWNT /3 C SWNT /4 C SWNT /5 C SWNT / Raman Shift (cm -1 ) Raman Shift (cm -1 ) Raman spectra of Ag-SWNT composite, measured as a function of (A) concentration of Ag nanoparticles, (B) SWNT concentration. 32

33 XPS 90 (A) Au 4f 7/2 105 (B) Ag 3d 5/2 Intensity (arb. units) Au 4f 5/2 Intensity (arb. units) Ag 3d 3/ Binding energy (ev) Binding Energy (ev) XPS spectra of (A) Au-SWNT and (B) Ag-SWNT composites in the Au 4f and Ag 3d regions, respectively 33

34 (n,m) indexing d t RBM 3 C 1 C constants 2, where C1 and C2 are d a c c t n 2 nm m 2 (n,m) RBM d t (nm) (cm -1,Theoretical) (10,10) (18,0) (13,7) (17,0) (11,9) (12,8) m E 11 s s E / 23 E32 34

35 What we know so far Visible fluorescence from SWNTs is demonstrated. Raman spectral mapping is done to ascertain the origin of fluorescence. SNOM of SWNT structures is done using this fluorescence. 35

36 Origin of visible fluorescence Near-infrared fluorescence in isolated SWNT is known. This is not observed in bundles and metallic SWNTs. Metallic SWNTs offer non-radiative decay channels. As metallic SWNTs are present in the bundles, they are not expected to fluoresce. So what happens to the metallic SWNTs present in the composite? 36

37 Investigations on mswnts Separation protocol SWNT + isopropyl amine + THF Ultrasonicate, 1h SWNT dispersion 40,000 g, 16 0 C, 12h Centrifugate mswnt Maeda, S., et al J. Am. Chem. Soc., 2005, 127, Alkyl amines stabilize metallic SWNT Residue 37

38 (A) Measurement geometry (B) (C) Nanotube Mica/insulating substrate (A) Photograph of the scanning head, (B) schematic of the PCI-AFM measurement and (C) representative AFM image of pristine SWNTs 38

39 (A) Current (na) (B) (C) Bias Voltage (V) Electrode is 200 nm away from the image-edge 100 nm Conductivity (na/v) Bias Voltage (V) (A) PCI-AFM images of pure mswnt with (B) I-V curves and (C) plot of conductance versus bias voltage. 39

40 (A) 40 (B) Current (na) Bias Voltage (V) Current (na) nm 200 nm Bias Voltage (V) (C) 400 (D) Current (na) Current (na) nm Bias Voltage (V) nm Bias Voltage (V)

41 10 (B) 5 (A) Electrode is 420 nm away from the edge nm 2 Conductance (na/v) Current (na) Bias Voltage (V) (C) Bias Voltage (V) (A) PCI-AFM image of Au-mSWNT with (B) the corresponding I-V curves and (C) Plot of conductance versus bias voltage. 1 Au nanoparticle Carbon nanotubes 41

42 80 60 Bias Voltage (V) Pure mswnt Au-mSWNT Conductance (na/v) Conductance (na/v) Bias Voltage (V) Comparison of conductance versus bias voltage for pure mswnt and AumSWNT composite 42

43 G-band line shapes of metallic and semiconducting SWNT Changes observed in G-band for metallic (left) and pristine (right) SWNT R. Krupe et al., Science 301, 344 (2003). 43

44 Confocal Raman investigations 700 Intensity (arb. units) A s /A m = 65.0 A s /A m = 0.14 Extraction efficiency A s /(A s + A m )* 100 = 88% Raman Shift (cm -1 ) Raman spectra in RBM and G-band regions of pristine SWNT (black) and extracted mswnt (red). 44

45 Pure mswnt FWHM = 48 cm -1 Au- mswnt FWHM = 22 cm Raman Shift (cm -1 ) Raman Shift (cm -1 ) Comparison of G-band of pure mswnt and Au-mSWNT 45

46 What we know: Metallicity of SWNT is destroyed by interaction with nanoparticles. PCI-AFM and confocal Raman confirm this M-S transition. mswnt fluoresce when their metallicity is destroyed. M-S transition has far reaching implication in nanoelectronics and design of nanodevices. C. Subramaniam et al. Phys. Rev. Lett. (2007) C. Subramaniam and T. Pradeep Patent applications 2006,

47 Nanotube gas sensors using fluorescence 47

48 (A) Endohedral Groove sites Interstitial (B) Gold electrode B1 B2 B3 External B4 Au nanoparticles (C) 1 2 To gas source To Hg manometer To rotary pump 4 Open/close valve 3 To rotary pump (D) 50 Raman spectrometer Sample compartment Conductance (na/v) Au-mSWNT bundle B1 Au-mSWNT + Nitrogen Au-mSWNT + Hydrogen Bias voltage (V) (A) Schematic representation of a SWNT bundle with the adsorption sites indicated. (B)Topographic image of Au-mSWNT composite. Several points on various bundles marked B1 to B4 have been analyzed though PCI-AFM. The gold electrode and the bundles have been marked with guide lines. (C) Schematic representation of the microraman setup used for gas-exposure studies. (D) Plot of conductance versus bias voltage constructed from various points of the bundle labeled B1 in Figure 1B, under an atmosphere of nitrogen (red traces) and hydrogen (black traces). 48

49 Intensity (arb. units) 4.0k 3.2k 2.4k 1.6k 0 torr 10 torr 20 torr 30 torr 40 torr 60 torr 100 torr 145 torr 175 torr 200 torr 250 torr 300 torr 350 torr 450 torr 500 torr Raman Shift (cm -1 ) Au-SWNTs exposed to H 2 gas at various partial pressures. 49

50 Intenisty (arb. units) 5.0k 4.5k 4.0k 3.5k 3.0k 2.5k 2.0k 1.5k 100 torr 500 torr Raman Shift (cm -1 ) Au-SWNTs exposed to N 2 gas at various partial pressures. 50

51 Suggested mechanism Composite Metallic SWNT bundle H 2 /He Semiconducting SWNT bundle 51

52 N N H gas 10-2 Intensity (a.u.) (A) (d) (c) (b) (a) Raman Shift (cm -1 ) Fluorescence intensity (a.u.) (B) 10-2 H 2 /N 2 N 2 /H 2 AI BII III C IVD 100 H H gas +100 N (A) Raman spectra of (a) purified mswnts, (b) Au-mSWNT composite, (c) Au-mSWNT upon exposure to 500 torr H2 and (d) Au-mSWNT composite after pumping out H2 exposed in (c). Spectra (a) to (d) are recorded at the same point on the composite sample. (B) Variation of fluorescence intensity upon exposing mixture of gases. Regions A to D are explained in the text. Pressures are in torr. 52

53 Intensity (a.u.) (A) 1 Intensity 5k 4k 3k 2k 1k 2 0 torr 500 torr Raman shift (cm -1 ) -ln (k) (B) 2 E a (units of k B T) = 4.13 E a (units of k B T) = P* (x10-6 ) /T(K) (A)Plot of normalised fluorescence intensity versus P* for Au-mSWNT. The corresponding spectral variation with increasing pressure of H2 for some of the pressues is shown as inset. Grey trace shows the recovery spectrum upon immediatel pumping. Complete recovery is obtained upon pumping for 15 minutes. The two regions having different slopes are circled in green and marked as 1 (interstitial adsorption) and 2(external adsorption). (B) Arrhenius plot of lnk at different temperatures versus 1/T. Interstitial adsorption (1, black), groove and external adsorption (2, red) are indicated. 53

54 (A) Gas inlet Gas oulet Current ( A) A (B) ON OFF ON OFF H 2 N Time (s) (A) Photograph of the device setup with a cartoon representation of the microelectrode. The shaded circle in the cartoon is used to represent the sample with the yellow regions representing the gold electrode. (B) A plot of variation of current for a bias voltage of 5 V for Au-mSWNT composite in presence of H2 (500 torr, black line) and N2 (500 torr, red line).the ON and OFF states pertain to the presence and absence of gases, respectively. While the current for the ON state is constant, that due to the OFF state increases slowly with increase in cycles as hydrogen exposed during the previous cycle is not removed completely, consistent with the fluorescence data (Fig. 3A inset). Current measurements appear to be sensitive to tiny quantities of adsorbed gases. 54

55 Summary and conclusions Metal nanoparticles upon interaction, destroy the metallicity of carbon nanotubes. This makes SWNTs emit light in the visible region of the spectrum. Visible light emission is sensitive to gases which adsorb in the interstitial sites of SWNT bundles. A device based on this property has been demonstrated. C. Subramaniam and T. Pradeep Patent applications 2008 C. Subramaniam et al. Submitted 55

56 Nano Initiative of the DST 56

57 Swarnajayanti project, DST 57

58 IIT Madras Thank you all 58