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Inelastic Electron Tunneling Spectroscopy of Molecular Magnetic Tunnel Junctions

Due to the weak spin-orbital and hyperfine interactions in organic molecules, molecular magnetic tunnel junctions have been predicted as promising ultrasmall spintronic devices [1]. In this study, we fabricate molecular magnetic tunnel junctions (MTJs) approximately (40 nm)2 in area (Fig. la) and demonstrate that inelastic electron tunneling spectroscopy (IETS) can be utilized to characterize such junctions to confirm the existence of desired molecular species in the device area. In addition, this approach was used to study the impurity-assisted tunneling processes that can explain the reported strong bias-dependence of junction tunneling magnetoresistance (TMR). Recently, octanethiol (CH3(CH2)7SH) has been used to form a tunneling barrier between two ferromagnetic electrodes, and spin-dependent transport behavior reported [2]. In this previous work there is no unambiguous experimental evidence that the molecules are playing a role in the final device behavior. While it is widely accepted that alkanethiols can form robust self-assembled monolayers (SAMs) on gold surfaces, SAM formation on ferromagnetic metals or metal oxide surfaces is still under investigation. Furthermore, even for the case of SAMs on gold, reliable controls and methods are required to validate true molecular transport in nanometer scale device structures. A strong bias-dependence of the junction TMR has also been observed in the previous experiment [2], but the origin of this dependence remains unclear.