Asymmetric I-V characteristics of  1,4-dithiolbenzene Molecular wire

¹⁾Aissa Boudjella  ²⁾N. M. Ahmed, Kifah Q. Salih and  ²⁾ Yarub Al-Douri

¹⁾Faculty of Science, Engineering and Technology, University Tunku Abdul Rahman,

                    Jalan University, Bandar Barat, 31900 Kampar, Perak, Malaysia 

     ²⁾School of Microelectronic Engineering, University Malaysia Perlis,Jejawi. Block A,

     Arau,  02600, Kangar, perils, Malaysia

aissab@mail.utar.edu.my     naser@unimap.edu.my   yarub@unimap.edu.my

        The purpose of this paper is to study the electronic transport through molecular assembly system (MAS) by presenting the I-V and G-V characteristics analysis for different geometry structure at constant temperature T=300 K.  The model involves 1,4-dithiolbenzene (DTB) (HSC₆H₄SH)  molecules stacked in  (1D) ordered structure. The MAS can contain up to six  DTB molecules packed in the parallel geometrical arrangement. The calculations were performed into two steps. First, the energy levels HOMO (the highest occupied molecular orbital) and LUMO (the lowest unoccupied molecular orbital) were obtained with an approach based on Landauer formalism¹⁾ combined with the density functional theory Kohn-Sham.²⁾ Then, the current-voltage (I-V) as well as the conductance-voltage (G-V) characteristics of the MAS connected between two metal electrodes were calculated using the molecular conduction toy (MolCtoy).^{3, 4)} With the Fermi level E_f  located in the middle of the HOMO-LUMO gap Energy (HLG) ^{3, 5)} , the calculations were carried out for various number of DTB molecular units in the range of N=1~6. The molecule-metal coupling strength s_i (s₁ for the electrode 1 and s₂ for electrode 2) ranges from 0.1 to 0.6 eV. Similar simulation methodology was reported by the author in the recent work.^6-9) In such molecular assembly system junctions, the connection between the molecule and the electrodes greatly affects the current voltage characteristics particularly in the saturation region. More interestingly effect is the asymmetry of the I-V and G-V characteristics that can be observed if s₁¹s₂.The relationship between the threshold voltage V_th, the metal-molecule interaction strength s_i and  N the number of DTB  molecular units which involves the p-orbital interactions is also investigated. The simulation results show  that V_th changes significantly and depends on N. The system in the regime of stronger p-interactions obtained with larger N reduces the threshold voltage. On the contrary, the metal-molecule coupling strength s_i shows no effect on the threshold voltage which remains approximately constant when s_i varies from 0.1 to 0.6 eV.

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3) 1 F. Zahid, M. Paulsson, and S. Datta.  Electrical conduction through molecules.     In semiconductors and Organic Nano-tecniques.  edited by H. Morkoc (Academic  Press,  New York, 2003)

4)  www.nanohub.org

5) S. N. Yaliraki, M. Kemp, and M. A. Ratner. J.  Am.  Chem. Soc. 121(1999) 3428.

/6/ Aissa Boudjella andKuek Chian Shiun.  International Conference on nanoscience and nanotechnology (NANO-SciTech 2008).18-21    November 2008 Shah Alam, Selangor, Malaysia.  

/7/ Aissa Boudjella and  Kuek Chian Shiun. 21^th International conference on Microprocessor and

    Nanotechnology      (MNC2008), Japan, 2008.

/8/ Kuek Chian Shiun,  Aissa Boudjella. International conference: Trends in nanotechnology 2008, Oviedo,

     Spain,september,01-05, 2008.

/9/ Aissa Boudjella, Adel B. Gougam, Hossein Alizadeh. Japanese Journal of Applied Physics, Vol. 47, No. 6, 2008,

    pp. 4969-49-74.