Abstract
We report on the synthesis and electrical properties of nine new alkylated silane self-assembled monolayers (SAMs) – (EtO)3Si(CH2)nN = CHPhX where n = 3 or 11 and X = 4-CF3, 3,5-CF3, 3-F-4-CF3, 4-F, or 2,3,4,5,6-F, and explore their rectification behavior in relation to their molecular structure. The electrical properties of the films were examined in a metal/insulator/metal configuration, with a highly-doped silicon bottom contact and a eutectic gallium-indium liquid metal (EGaIn) top contact. The junctions exhibit high yields (>90%), a remarkable resistance to bias stress, and current rectification ratios (R) between 20 and 200 depending on the structure, degree of order, and internal dipole of each molecule. We found that the rectification ratio correlates positively with the strength of the molecular dipole moment and it is reduced with increasing molecular length.
Highlights
MethodsThe molecules were synthesized from amino trialkoxysilanes by using standard procedures (see Fig. SI 1)
Internal dipole characteristic to each molecule, and may promote a rational design of compounds that can function as high-performance molecular rectifiers
The molecules were synthesized from amino trialkoxysilanes by using the condensation of commercially available amino alkyl triethoxysilanes with substituted benzaldehydes to prepare the precursors, following established procedures[25,26]
Summary
The molecules were synthesized from amino trialkoxysilanes by using standard procedures (see Fig. SI 1). The SAMs were deposited on highly-doped silicon wafers with native SiO2 formed at their surface by either solution or vapor-based techniques. The short SAMs (molecules 5 through 9) were amenable to deposition by vapor treatment, where the silicon wafer was placed into a sealed jar along with 11 μL of the pure SAM compound at 30 °C. Both methods typically took 18 to 24 hours. To remove the excess adsorbed molecules on the monolayer surface, the samples were thoroughly rinsed in chloroform followed by IPA and immediately dried in a stream of nitrogen
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