Electrical Conduction through Molecules

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Electrical Conduction through Molecules

• Geng-Chiau Liang
• School of Electrical and Computer Engineering
• Purdue University

Picture from Mark Reeds Group
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Outline

• I. Introduction
• Motivations
• Fundamental Concepts
• II. Modeling
• Calculation Approaches
• Results and Discussions
• III. Conclusions

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Switches (Molecular Junction)
PN Junction
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Resonant Tunneling Structure
10001 on-off peak-to-valley ration
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SAMFETs V.S. MOSFETs
SAMFETs
MOSFETs
Ref Schon, et al., nature Vol. 413, pp. 713 2001
Pierret, Semiconductor Device Fundamentals
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Fundamental Concepts
Lumo
Device (Molecule)
V0 Ef1Ef2Ef
qV
Homo
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Two-state Toy Model
Eta0.5
Eta1
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Two Experimental Results
Benzene 1,4-Dithiolate (PDT, BDT)
Schoen, 2002
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Modeling (Approaches)
E-field
F, S
P. Damle, et al, Phys. Rev. B (2001)
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Formulas
Ref Datta, S. Electronic Transport in Mesoscopic
System Cambridge University Press, 1997
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Results and Discussions (I)
Simulation
Experiment Schoen, 2002
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Results and Discussions (II)
Vg
Vd
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Results and Discussions (III)

• Reasons of Bad Results
• Not real voltage profile in the molecule (Image
  charge effect, Gaussians limitation, and so on)
• Unknown interactions

I
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Summary

• I. Successfully using method of DFT coupling
  with NEGF and Self-energy approach to model
  behavior of molecular devices
• II. Important topics in future
• Ef in Molecules?
• Interaction between Molecules and Surface
• Correct voltage profile through Molecule

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Acknowledgement

• Professor Jorge Rodriguez
• Group mates
• Professor Supriyo Datta, A. Ghosh, M. Paulsson,
  P. Damle, T. Rakshit, and F. Zahid.

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Energy states