†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.
J Am Chem Soc. 2015 Mar 25;137(11):3852-8. doi: 10.1021/jacs.5b00137. Epub 2015 Mar 16.
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.
本文描述了氢原子被氟原子取代对通过 Ag(TS)O2C(CH2)n(CF2)(m)T//Ga2O3/EGaIn 结的空穴隧穿电荷传输速率的影响，其中 T 是甲基（CH3）或三氟甲基（CF3）。具有全氟化基团（R(F)）的烷酸酯基自组装单分子层（SAM）的电流密度较低（低 20-30 倍），而亚甲基（β=（1.05±0.02）n(CH2)(-1)）和二氟亚甲基（β=（1.15±0.02）n(CF2)(-1)）的简化 Simmons 方程衰减因子相似（尽管 n(CF2)的值在统计学上显著更大）。一项针对 ω-甲苯基和 -苯基烷酸酯 SAM 中末端氟取代基的对比研究表明，CF3 较低的隧穿电流归因于 T//Ga2O3 界面处隧穿势垒高度的增加，和/或该界面处较弱的范德华相互作用。与具有 R(H)基团的 SAM 相比，具有 R(F)基团的 SAM 中电荷传输速率的降低可能是由于 T//Ga2O3 界面处隧穿势垒高度的增加，和/或该界面处较弱的范德华相互作用。
