Fluorination, and tunneling across molecular junctions.
This paper describes the influence of the substitution of fluorine for hydrogen on the rate of charge transport by hole tunneling through junctions of the form Ag(TS)O2C(CH2)n(CF2)(m)T//Ga2O3/EGaIn, where T is methyl (CH3) or trifluoromethyl (CF3). Alkanoate-based self-assembled monolayers (SAMs) having perfluorinated groups (R(F)) show current densities that are lower (by factors of 20-30) than those of the homologous hydrocarbons (R(H)), while the attenuation factors of the simplified Simmons equation for methylene (β = (1.05 ± 0.02)n(CH2)(-1)) and difluoromethylene (β = (1.15 ± 0.02)n(CF2)(-1)) are similar (although the value for (CF2)n is statistically significantly larger). A comparative study focusing on the terminal fluorine substituents in SAMs of ω-tolyl- and -phenyl-alkanoates suggests that the C-F//Ga2O3 interface is responsible for the lower tunneling currents for CF3. The decrease in the rate of charge transport in SAMs with R(F) groups (relative to homologous R(H) groups) is plausibly due to an increase in the height of the tunneling barrier at the T//Ga2O3 interface, and/or to weak van der Waals interactions at that interface.
†Department of Chemistry and Chemical Biology, Harvard University, 12 Oxford Street, Cambridge, Massachusetts 02138, United States.
Kung-Ching
KC
Liao
†Department of Chemistry and Chemical Biology, Harvard University, 12 Oxford Street, Cambridge, Massachusetts 02138, United States.
Carleen M
CM
Bowers
†Department of Chemistry and Chemical Biology, Harvard University, 12 Oxford Street, Cambridge, Massachusetts 02138, United States.|‡Department of Chemistry, Korea University, Seoul 136-701, Korea.
Hyo Jae
HJ
Yoon
†Department of Chemistry and Chemical Biology, Harvard University, 12 Oxford Street, Cambridge, Massachusetts 02138, United States.|§Wyss Institute for Biologically Inspired Engineering, Harvard University, 60 Oxford Street, Cambridge, Massachusetts 02138, United States.
George M
GM
Whitesides
D004563:Electrochemistry; D005708:Gallium / Q000737:chemistry*; D054879:Halogenation; D006845:Hydrocarbons, Fluorinated / Q000737:chemistry; D006860:Hydrogen Bonding; D008958:Models, Molecular; D015394:Molecular Structure; D018030:Silver Compounds / Q000737:chemistry*; D013499:Surface Properties
D006845:Hydrocarbons, Fluorinated; D018030:Silver Compounds; C038863:gallium oxide; D005708:Gallium