Nanotube Y-junction

Lobovkina T, Dommersnes P, Joanny JF, Hurtig J, Orwar O (2006) Zipper dynamics of surfactant nanotube Y junctions. Phys. Rev. Lett. 97 188105. 

Bandaru PR, Daraio C, Jin S et al (2005) Novel electrical switching behaviour and logic in carbon nanotube Y-Junctions. Nat Mater 4 663-666... 

Abstract. Equilibrium geometry parameters, total energies, heats of formation, energies of HOMO and LUMO orbitals, and density of one-electron states for some nanotubes Y-junctions of twig types are computed in the frames of semi-empirical quantum chemistry PM3-method. 

Bandam PR (2007) Electrical characterization of carbon nanotube Y-junctions A foundation for new nanoelectronics. J. Mater. Sci. 42 1809-1818. 

Very recently, experimentalists have succeeded in developing template-based chemical vapor deposition CVD),[30] and pyrolysis of organometallic precursor with nickelocene and thiophene techniques[31] that allows for the reproducible and high-yield fabrication of carbon nanotube Y-junctions.[30, 31] The conductance measurements on these Y-j unctions have shown intrinsic rectifying I-V behavior at room temperature.[31, 32)... 

Xia H, Cheng D, Xiao C, Chan HS (2006). Controlled synthesis of Y-junction polyaniline nanorods and nanotubes using in situ self-assembly of magnetic nanoparticles. J. Nanosci. Nanotechnol. 6 3950-3954. 

Kim D, Huang J, Rao BK et al (2006) Pseudo Y-junction single-walled carbon nanotube based ambipolar transistor operating at room temperature. IEEE Trans Nanotechnol 5 731-736... 

Keywords Y-junctions of nanotubes, defects of bonds and geometrical distortions, molecular simulation, quantum-chemical calculations. 

Quantum chemistry computations based on employing of PC Gamess version of semi-empirical PM3-method [1-2] allows to define equilibrium configuration and calculate electronic structure of some of the simplest Y-junctions of carbon nanotubes, which have slang name twig . On the place of nanotubes conjunction defective cycles appear. Their type, number and mutual displacement can be enough various even in comparatively simple cases. Only the part of obtained results is presented here. 

The experimental setup employed by us for the synthesis of the Y-junction nanotubes employed a two-stage furnace system similar to that described earlier29 (Figure lc). A known quantity of metallocene was sublimed in the first furnace and carried along with a flow of argon (Ar)... 

Scanning tunneling spectroscopic studies of Y-junction carbon nanotubes show interesting diodelike device characteristics at the junctions. A typical /—V curve obtained from positioning the tip atop a Y-Junction (the point of contact between the three arms) as well as on the individual arms of the Y-junction is shown in Figure 10. The I—V plot at the junction is asymmetric (Figure 10b)... 

FIGURE 8. (a, b) TEM images of Y-junction carbon nanotubes obtained by the pyrolysis of nickel ocene and thiophene at 1000 °C.a... 

FIGURE 9. TEM images of Y-junction nanotubes (a, b) obtained by the pyrolysis of thiophene along with Ni phthalocyanine at1000 °C (c) obtained by the pyrolysis of thiophene along with Fe phthalocyanine at 1000 °C (d) obtained by the pyrolysis of an Fe(CO)5-thiopbene mixture... 

FIGURE 10. /— V curves collected from different points in a Y-junction carbon nanotube (a) from one of the arms away from the junction and (b) from the junction of the three arms. Inset show plots of d//dl/vs bias voltage. The observed gaps are indicated by... 

There have been a few reports on the electronic properties ofjunction nanotubes [1,6-10]. Rao and coworkers [1] carried out scanning tunneling spectroscopy (STS) measurements on Y-junction carbon nanotubes (CNTs)... 

Y-junction carbon nanotubes were prepared by the pyrolysis of nickelocene-thiophene employing the experimental set-up described earlier [1]. Pyrolysis of nickel phthalocyanine-thiophene mixtures was carried out to obtain N-doped carbon nanotubes with Y-junctions. 

TEM images of the products of pyrolysis of nickelocene-thiophene mixtures show the presence of highly crystalline Y-junction carbon nanotubes with well-formed arms (Fig. la). The images also reveal certain... 

Fig. 1. (a) TEM image of a Y-junction carbon nanotube obtained by the pyrolysis of nickelocene-thiophene mixture. The inset in (a) shows asparagus tips in the Y-Junction nanotube, (b) EELS mapping of carbon in the Y-junction carbon nanotube. The inset in (b) shows the TEM image of a Ni nanoparticle inside a carbon nanotube. 

Fig. 2. Selected area electron diffraction (SAED) patterns of the Y-junction carbon nanotubes (a) of the arms and (b) of the junction region, (c) and (d) Schematic drawings showing different ways of stacking of the graphene sheets in the Y-junction carbon nanotubes.

Fig. 4. (a) TEM image of N-doped Y-junction carbon nanotubes prepared by the pyrolysis of a Ni-phthalocyanine-thiophene mixture, (b) EEL spectrum showing the presence of doped nitrogen. 

We have carried out tunneling conductance measurements on a large number of N-doped Y-junction carbon nanotubes. The junction (JA) in Fig. 5a exhibits a rectification behavior with distinct change of slope in the I-V data at —1.5 and +1 V. A high value of rectification ratio of 4.75 is obtained for bias voltages of 1.5 V. Coulomb blockade is easily identifiable in the bias range, -0.4 to +0.6 V. The arms of the tube, however, are devoid of blockade but exhibit varied behavior. The arm-1 shows distinct features at 0.4 V. In the case of arm-2, similar... 

Fig. 5. I-V data of N-doped Y-junction carbon nanotubes shown along with the STM images. The regions where the I-V data were collected are marked with numbers.

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