Molecular Tunnel Junctions : Metal / OML – Si(111)

Understanding the electronic properties of tunnel junctions which incorporate a nanometer-thick organic insulator remains a fundamental issue for molecular electronics. Covalent grafting of a densely-packed monolayer of n-alkyl saturated chains to Si(111) surfaces provides MIS tunnel junctions (metal / OML / semiconductor) which can be easily tuned : n or p doping of Si, insulating chain length and coverage, chemical functionality of the chains at the top metal interface.
Electronic properties of MIS tunnel junctions Hg // OML - Si (111) were characterized in static (current-voltage) and dynamic (admittance) modes. The interpretation of transport mechanisms and dipolar relaxation relies on modeling the characteristics measured as a function of temperature and applied voltage. Dynamic studies of defects and disorder of molecular chains grafted to crystalline Si surfaces are analyzed with multiscale models.

Admittance of Hg // HOOC – (CH2)10 – Si molecular junctions:  - a) Experimental discrimination of the space charge response, observed at high temperature or direct polarization, and the dipolar response, observed at low temperature and inverse polarization. b) Temperature dependence of the peak intensity attributed to gauche chain conformations (inverse polarization) ; a more ordered phase (« all trans ») appears below 175 K.

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