One Carbon Matters: The Origin and Reversal of Odd鈥揈ven Effects in Molecular Diodes with Self-Assembled Monolayers of Ferrocenyl-Alkanethiolates

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• 作者：Li Yuan ; Damien Thompson ; Liang Cao ; Nisachol Nerngchangnong ; Christian A. Nijhuis
• 刊名：Journal of Physical Chemistry C
• 出版年：2015
• 出版时间：August 6, 2015
• 年：2015
• 卷：119
• 期：31
• 页码：17910-17919
• 全文大小：624K
• ISSN：1932-7455

文摘

We investigated the origin of odd鈥揺ven effects in molecular diodes based on self-assembled monolayers (SAMs) of ferrocenyl-terminated n-alkanethiolates S(CH₂)_nFc with n = 6鈥?5 on Ag or Au surfaces contacted with EGaIn top electrodes. These SAMs have different M鈥揝鈥揅 bond angles of 180掳 when M = Ag and 104掳 when M = Au causing a multitude of odd鈥揺ven effects in the performance of the diodes. By changing the M鈥揝鈥揅 bond angles and using several characterization techniques, we were able to systematically identify and rationalize odd鈥揺ven effects in the electronic structure of the device. Changing n from 6 to 15 resulted in an odd鈥揺ven effect in the tilt angle of the Fc units (伪), which, in turn, caused odd鈥揺ven effects in the surface dipole, work function, and HOMO onset (HOMO = highest occupied molecular orbital). These odd鈥揺ven effects caused an odd鈥揺ven modulation of the tunneling current across the diode in the on state (the current that flows across the junctions when the diode allows the current to pass through). The current that flows across the diodes in their off state (the leakage current) also followed an odd鈥揺ven effect that was related to an odd鈥揺ven effect in the packing energy: SAMs with small tilt angles of the ferrocenyl units 伪 (with the Fc units standing up) pack better than SAMs with large 伪 values (with the Fc units in a parallel orientation with the plane of the electrode). All these odd鈥揺ven effects were completely and consistently reversed when the Ag electrodes were replaced with Au electrodes proving they are induced by the M鈥揝鈥揅 bond angle.