Y-junction carbon nanotube

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 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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