Az előadások a következő témára: "FULLERÉNEK ÉS SZÉN NANOCSÖVEK előadás fizikus és vegyész hallgatóknak (2008 tavaszi félév – április 30.) Kürti Jenő ELTE Biológiai Fizika Tanszék e-mail:"— Előadás másolata:
FULLERÉNEK ÉS SZÉN NANOCSÖVEK előadás fizikus és vegyész hallgatóknak (2008 tavaszi félév – április 30.) Kürti Jenő ELTE Biológiai Fizika Tanszék e-mail: email@example.com: virag.elte.hu/kurti
Spectrofluorimetric measurements, Science 298, 2361 (2002) Cross-section model of a SWCNT in a cylindrical SDS micelle SDS: sodium dodecyl sulfate (SDS) surfactant.
(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. Spectrofluorimetric measurements, Science 298, 2361 (2002)
K M n=3i n=3i+1 x 1/d n mod 3 = 2n mod 3 = 0n mod 3 = 1 n=3i+2 triad structure of zigzag tubes (due to trigonal warping)
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 E ii are indicated. Note how E ii 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.
(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 E ii 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.
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.