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Coulomb Blockcade and Novel Conductance Quantization Related to 1D Electron-electron Interaction in Nano-porous Alumina Film

Junji Haruyama*

Department of Electrical Engineering and Electronics, Aoyama Gakuin University, Tokyo, JAPAN

This is an abstract for a presentation given at the
Sixth Foresight Conference on Molecular Nanotechnology.
There will be a link from here to the full article when it is available on the web.

 

Recent progress of nano-fabrication technologies has successfully brought observation of many attractive nano-phenomena. Coulomb blockade (CB) which is a typical phenomenon originated from single electron tunneling is one of such nano-phenomena. It has been well studied theoretically and experimentally in many nano-tunnel junction systems, e.g. semiconductor nano-tunnel junctions fabricated by nano-lithographies and crystal growth methods like an artificial atom, metal nano-particle array like a glanular film. The emergence of CB strongly depends on impedance of external environment around the junction, particularly in single junction system. Unless a high impedance block(>> resistance quantum) is much closely connected to the junction, the CB is easily smeared out by the electro-magnetic fluctuation from the external circuit. Hence it is the core importance to study the relation between CB and physics of electron transport in the external environment directly located to the junction. Also conductance quantization (CQ) is very interesting nano-phenomenon observable in some nano-structures, e.g. quantum hall effects, CQ in quantum point contact. Although CQ with universal value(i.e.2e2/h) has been well reported, its collapse has recently attracted much attention. Some one-dimensional(1D) semiconductor wires actually exhibited such collapse of universal CQ (so called non-universal CQ:NUCQ), e.g. with value of (2e2/h)(1/4). One of such structures is Tomonaga-Luttinger liquid (TLL) with electron-electron(e-e) interaction and impurity scattering (i.e. dirty TLL). The UCQ can be drastically collapsed in it depending on the wire length, mean free path, temperature, etc.

In contrast, we have recently reported novel nano-fabrication technique by utilizing nano-porous Alumina film template. Porous Alumina film is grown through self-organizing process by simply anodizing pure Aluminum film. It includes high packing density of pores like a honey-comb with high uniformity and repeatability. We have successfully developed how to control the structure parameters into nano-size order, e.g. pore diameter of 5 nm, inter-pore spacing of 30 nm[1]-[3]. One can easily build up varieties of unique nano-structure arrays by electrochemically depositing some materials in the nano-pores, e.g. metals, semiconductors, organic materials, superconductors. In this work, we, for the first time, report on novel CB and NUCQ observed in such nano-strutures.

The nano-structure reported here consists of array of a long Ni nano-wire/Al2O3 nano-tunnel junction/Al substrate. The most unique point is in the long nano-wire (2 µm length and nm order diameter) with tunnel junction only on the one end. In the sample with the wire diameter around 12 nm, only a CB was observed originating from the single tunnel junction, related to high impedance environment by e-e interaction in the Ni nano-wire. The detailed temperature measurements of the electrical characteristics revealed that the e-e interaction took transition from the 3D to 1D regimes with reducing applied voltage and the CB emerged in the 1D e-e interaction regime as the e-e scattering rate drastically decreased. This suggests that internal electrical fluctuation by strong e-e interaction smears the CB out even under high impedance environment. Hence this CB voltage is much different from that in orthodox theory (i.e. V=e/2C). On the other hand, in the sample with wire diameter around 7 nm, novel NUCQ was observed with value of (2e2/h)(1/200)2(-n) in addition to the CB. The conductance (G)-V curve was much asymmetric and the relation mentioned above is fit only in the +V region. In contrast, clearer G plateau can be observed with different relation in the -V region. This NUCQ emerged only in the 1D e-e interaction regime of the Ni-wire mentioned above. Besides it could be observed only in the 7 nm wire-diameter sample and the quantized value was extremely small as mentioned above. Based on those, the possibility of dirty TLL in the Ni nano-wire is discussed.

Both the CB and the NUCQ reported in this work are much novel. None has reported such effects because it can emerge only in much long nano-wire with single tunnel junction and only our method was much suitable for making such structure. This is one of the examples of unique nano-structures fabricatable by using our method. This nano-fabrication technique by using porous Alumina film will open up more chances to find out novel nano-phenomena.

References
  1. Tager, A.; Routkevitch, D.; Haruyama, J; et al. (1996) Future Trends in Microelectronics edited by S.Luryi, J.M.Xu, and A.Zalavsky, NATO ASI Series E-323, pages 171-183. Nonlithographic fabrication and physics of nanowire and nanodot array devices -present and future-
  2. Davydov, D.; Haruyama, J.; Routkevitch, D.; Ellis, D.; Statt, B.W.; Moskovits, M.; and Xu, J.M. (1998) Phys.Rev.B, Vol.57(21), pages 13550-13553. Nonlithographic nanowire-array tunnel devices: fabrication, zero-bias anomalies, and Coulomb blockade
  3. Haruyama, J.; Davydov, D.; Routkevitch, D.; Ellis, D.; Statt, B.W.; Moskovits, M.; and Xu, J.M. (1988) Solid-state Electronics as the proc. NPE'97, Vol.42(7-8), pages 1257-1266. Coulomb blockade in nanojunction array fabricated by nonlithographic method

*Corresponding Address:
Junji Haruyama
Department of Electrical Engineering and Electronics, Aoyama Gakuin University
6-16-1 Chitosedai, Setagaya, Tokyo, 157-8572 JAPAN,
phone: 81-35384-6411, fax 81-35384-6411 email: J-haru@joker.ee.aoyama.ac.jp



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