**5. Conclusions**

586 Recent Advances in Nanofabrication Techniques and Applications

calculation result. The calculation result has demonstrated that the resistance is 6.7 k, where the junction area is 1×1 nm2, which is expected as a size of one P3HT:PCBM organic molecule. The number of the conductance channel is four, taking into consideration the spin degeneracy. On the other hand, in experiments, the junction area of P3HT:PCBM organic molecules is 16×16 nm2, which corresponds to 1024 (=4×16×16) conductance channels.

Fig. 14. Experimental results of *I-V* characteristics for Ni/P3HT:PCBM/Ni QC devices with a junction area of 16×16 nm2 at room temperature. The inset represents the experimental

Therefore, the junction resistance in a size of 16×16 nm2 is calculated to be 26 (=6.7k/16/16), which is in good agreement with the experimental value of 32 This result indicates that electrons in nanoscale junctions can transport through the molecules in the ballistic regime without any scattering. This also demonstrates that our method to fabricate nanoscale junctions utilizing thin-film edges can be a useful tool for the creation of

Finally, we have discussed the possibility of Ni/P3HT:PCBM/Ni QC devices for switching devices with high on-off ratios. Fig. 15 shows the calculated *I-V* characteristics for Ni/P3HT:PCBM/Ni QC devices under the weak coupling condition. *V*T(B) is assumed to be

sharp steps at the positions of the energy level of the P3HT:PCBM organic molecule. The offstate current *I*0 is 3.8 pA at the voltage *V*0 of 0.03 V, and the on-state current *I*1 is 0.57A at the voltage *V*1 of 1.03 V. As we estimate the switching on-off ratio, the *I*1/*I*0 ratio is found to be in excess of 100000:1. Here, it should be noted that it is essentially important that the junction area is as small as nanometer scale in order to obtain such a high on-off ratio. When the junction area is as large as micrometer scale, the number of molecules sandwiched between the electrodes is large, so the energy level can be broadened. In contrast, when the

T(B) of 1.57 meV. From Fig. 15, the calculated result shows the

**4.3.3 Possibility of Ni/P3HT:PCBM/Ni QC devices for switching devices** 

setup.

nanoscale molecular devices.

0.2 meV, corresponding to

In this chapter, we have introduced structural and electrical properties of Ni/PEN films used as electrodes in QC devices and *I-V* characteristics for three types of QC devices. The three types of QC devices are as follows: (i) Ni/Ni QC devices (17 nm linewidth, 17×17 nm2 junction area), in which two Ni thin films are directly contacted with their edges crossed, (ii) Ni/NiO/Ni QC devices (24 nm linewidth, 24×24 nm2 junction area), in which NiO thin insulators are sandwiched between two Ni thin-film edges and (iii) Ni/P3HT:PCBM/Ni QC devices (16 nm linewidth, 16×16 nm2 junction area), in which P3HT:PCBM organic molecules are sandwiched between two Ni thin-film edges. In our study, we have successfully fabricated various types of QC devices with nano-linewidth and nanojunctions, which have been obtained without the use of electron-beam or optical lithography. Our method will open up new opportunities for the creation of nanoscale patterns and can also be expected as novel technique beyond conventional lithography. Furthermore, we have presented the calculation results of the electronic transport in Ni/organic-molecule/Ni QC devices and discussed their possibility for switching devices. According to our calculation, a high switching ratio in excess of 100000:1 can be obtained under weak coupling condition. These results indicate that QC devices fabricated using thin-film edges can be expected to have potential application in next-generation switching devices with ultrahigh on-off ratios.

Lithography-Free Nanostructure Fabrication Techniques Utilizing Thin-Film Edges 589

Huber, M. E., Koshnick, N. C., Bluhm, H., Archuleta, L. J., Azua, T., Bjornsson, P. G.,

Ishibashi, A. (2004). *Proceedings of International Symposium on Nano Science and Technology*, pp.

Ito, E., Oji, H., Furuta, M., Ishii, H., Oichi, K., Ouchi, Y. & Seki, K. (1999). *Synthetic Metals*

Kaiju, H., Ono, A., Kawaguchi, N., Kondo, K., Ishibashi, A., Won, J. H., Hirata, A., Ishimaru,

Kaiju, H., Kondo, K., Ono, A., Kawaguchi, N., Won, J. H., Hirata, A., Ishimaru, M., Hirotsu,

Kaiju, H., Kondo, K., Basheer, N., Kawaguchi, N., White, S., Hirata, A., Ishimaru, M., Hirotsu, Y. & Ishibashi, A. (2010). *Mater. Res. Soc. Symp. Proc.* 1252: J0208. Kaiju, H., Basheer, N., Kondo, K. & Ishibashi, A. (2010). *IEEE Trans. Magn.* 46: 1356.

Ishibashi, A., Kaiju, H., Yamagata, Y. & Kawaguchi, N. (2005). *Electron. Lett.* 41: 735.

Kaiju, H., Kawaguchi, N. & Ishibashi, A. (2005). *Rev. Sci. Instrum.* 76: 085111. Kaiju, H., Ono, A., Kawaguchi, N. & Ishibashi, A. (2008). *Jpn. J. Appl. Phys.* 47: 244. Kaiju, H., Ono, A., Kawaguchi, N. & Ishibashi, A. (2008). *J. Appl. Phys.* 103: 07B523.

*Instrum.* 79: 053704. Ishibashi, A. (2003). Jpn. Pat. 3974551.

Kale, B. M. (1985). *Opt. Eng.* 24: 267.

Kondo, K. (2010). *J. Appl. Phys.* 107: 09C709.

(2003). *Science* 300: 112.

*Microelectron. Eng.* 86: 448.

62: 221.

*Lett.* 5: 2557.

101: 654.

44-45, Tainan, Taiwan, November 20-21, 2004.

M. & Hirotsu, Y. (2009). *Appl. Surf. Sci.* 255: 3706.

Y. & Ishibashi, A. (2010). *Nanotechnology* 21: 015301.

Kaiju, H., Kondo, K. & Ishibashi, A. (2010). *Jpn. J. Appl. Phys.* 49: 105203.

Kondo, K., Kaiju, H. & Ishibashi, A. (2008). *Mater. Res. Soc. Symp. Proc.* 1067: B0301.

Kondo, K., Kaiju, H. & Ishibashi, A. (2010). *Mater. Res. Soc. Symp. Proc.* 1198: E0701.

Lau, C. N., Stewart, D. R., Williams, R. S. & Bockrath, M. (2004). *Nano Lett.* 4: 569.

Mendes, P. M., Flood, A. H. & Stoddart, J. F. (2005). *Appl. Phys. A* 80: 1197.

Miyazaki, T. & Tezuka, N. (1995). *J. Magn. Magn. Mater.* 139: L231.

Kuiper, P., Kruizinga, G., Ghijsen, J., Sawatzky, G. A. & Verweij, H. (1989). *Phys. Rev. Lett.*

Kwon, S., Yan, X., Contreras, A. M., Liddle, J. A., Somorjai, G. A. & Bokor, J. (2005). *Nano* 

Melosh, N. A., Boukai, A., Diana, F., Gerardot, B., Badolato, A., Petroff, P. M. & Heath, J. R.

Moodera, J. S., Kinder, L. R., Wong, T. M. & Meservey, R. (1995). *Phys. Rev. Lett.* 74: 3273. Nacereddine, C., Layadi, A., Guittoum, A., Cherif, S. –M., Chauveau, T., Billet, D., Youssef, J. B., Bourzami, A. & Bourahli, M. –H. (2007). *Mater. Sci. Eng. B* 136: 197. Naulleau, P. P., Anderson, C. N., Chiu, J., Denham, P., George, S., Goldberg, K. A.,

Goldstein, M., Hoef, B., Hudyma, R., Jones, G., Koh, C., Fontaine, B. L., Ma, A., Montgomery, W., Niakoula, D., Park, J.-o., Wallow, T. & Wurm, S. (2009).

Kardar, M., Parisi, G. & Zhang, Y. -C. (1986). *Phys. Rev. Lett.* 56: 889.

Kondo, K., Kaiju, H. & Ishibashi, A. (2009). *J. Appl. Phys.* 105: 07D522.

Kirtley, J. R. (2009). *Supercond. Sci. Technol.* 22: 064008. Kondo, K. & Ishibashi, A. (2006). *Jpn. J. Appl. Phys.* 45: 9137.

Mayadas, A. F. & Shatzkes, M. (1970). *Phys. Rev. B* 1: 1382.

Gardner, B. W., Halloran, S. T., Lucero, E. A. & Moler, K. A. (2008). *Rev. Sci.* 
