FULLERÉNEK ÉS SZÉN NANOCSÖVEK

Az előadások a következő témára: "FULLERÉNEK ÉS SZÉN NANOCSÖVEK"— Előadás másolata:

1 FULLERÉNEK ÉS SZÉN NANOCSÖVEK
előadás fizikus és vegyész hallgatóknak (2008 tavaszi félév – április 30.) Kürti Jenő ELTE Biológiai Fizika Tanszék www: virag.elte.hu/kurti

2 Kísérleti Kataura-plot

3 Spectrofluorimetric measurements, Science 298, 2361 (2002)
Cross-section model of a SWCNT in a cylindrical SDS micelle SDS: sodium dodecyl sulfate (SDS) surfactant.

4 Spectrofluorimetric measurements, Science 298, 2361 (2002)
(A) Contour plot of fluorescence intensity versus excitation and emission wavelengths for a sample of SWNTs suspended in SDS and deuterium oxide. (B) Circles show spectral peak positions from (A); lines show perceived patterns in the data.

5 Fluorescence: high selectivity

6 Szén nanocsövek válogatása lehetséges (Hersam, Kataura)
Fémes vagy félvezető, illetve átmérők szerint (Arnold et al, Nature Nanotech. 2006: density gradient ultracentrifugation, g)

7 trigonal warping K

8 triad structure of zigzag tubes
x triad structure of zigzag tubes 1/d (due to trigonal warping) n=3i+1 n=3i+2 n=3i M K G n mod3 = 0 n mod3 = 1 n mod3 = 2

9 Lines of allowed k vectors for the three nanotube families on a contour plot of the electronic band structure of graphene (K point at center). (a) metallic nanotube belonging to the ν = 0 family (b) semiconducting −1 family tube (c) semiconducting +1 family tube Below the allowed lines the optical transition energies Eii are indicated. Note how Eii alternates between the left and the right of the K point in the two semiconducting tubes. The assumed chiral angle is 15◦ for all three tubes; the diameter was taken to be the same, i.e., the allowed lines do not correspond to realistic nanotubes.

10 (a) Kataura plot: transition energies of semiconducting (filled symbols) and metallic (open) nanotubes as a function of tube diameter (Calculated from the Van-Hove singularities in the joint density of states within the third-order tight-binding approximation.) (b) Expanded view of the Kataura plot highlighting the systematics in (a) The optical transition energies follow roughly 1/d for semiconducting (black) and metallic nanotubes (grey). The V-shaped curves connect points from selected branches (2n+m = 22, 23 and 24). For each nanotube subband transition Eii it is indicated whether the ν = −1 or the +1 family is below or above the 1/d average trend. Squares (circles) are zigzag (armchair) nanotubes.

11 Nanocső lerakása szuszpenzióból forgótárcsás (spin-coating) technikával
Cees Dekker, Delft Univ of Tech 13 Cees Dekker, Delft Univ of Tech 13

12 Figure 16. Quantum-molecular wire—a 1-nanometer-diameter nanotube on a silicon/ silicon dioxide substrate with two metal electrodes—exhibits conductivity in a stepwise fashion. The device is similar to a transistor with the bias voltage applied between the platinum wires, and the gate varying the electrostatic potential of the nanotube. The tiny size of the nanotube permits just a few quantum energy levels for the electrons (above), so that only at a certain gate voltage does the state fit into the bias window, allowing electrons to smoothly tunnel through.

13 T=5mK

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17 Kis átmérőjű szén nanocsövek (görbületi effektusok)

18 NEM MOTIVÁCIÓ FELMERÜLŐ KÉRDÉS:
Lehetővé vált kis átmérőjű nanocsövek előállítása: HiPco ( 0.8 nm) - CoMocat ( 0.7 nm) - DWNTs, borsók (peapods) melegítésével ( 0.6 nm) - növesztés zeolit csatornákban ( 0.4 nm) FELMERÜLŐ KÉRDÉS: A KIS ÁTMÉRŐJŰ CSÖVEK TULAJDONSÁGAI (geometria, sávszerkezet, rezgési frekvenciák stb) KÖVETIK-E A NAGY ÁTMÉRŐJŰ CSÖVEKÉT? grafénból „zónahajtogatás”-sal NEM

19 High-Pressure CO method (HiPco)
diameter down to  0.7 nm M. J. Bronikowski et al., J. Vac. Sci. Technol. A 19, 1800 (2001)

20 double-walled carbon nanotubes
peapods heating double-walled carbon nanotubes inner tube diameter down to  0.5 nm S.Bandow et al., CPL 337, 48 (2001)

21 SWCNT in zeolite channel (AFI) (dSWCNT 0.4 nm)
Al or P O picture from Orest Dubay J.T.Ye, Z.M.Li, Z.K.Tang, R.Saito, PRB (2003)

22 CoMoCat HiPco AFI DWNTs 0.4 nm (zeolite) 0.7 nm (20,0)
picture from Orest Dubay 0.7 nm DWNTs  ZZ - zigzag (m=0)  AC - armchair (n=m)  CH - chiral achiral (11,11) S.Bandow et al., CPL 337, 48 (2001)