Introducing Ionic and/or Hydrogen Bonds into the SAM//Ga_2O_3 Top- Interface of Ag~(TS)/S(CH_(2)n)T//Ga_2O_3/EGaIn Junctions

摘要

Junctions with the structure Ag~(TS)/S(CH_(2)n)T// Ga_2O_3/EGaIn (where S(CH_(2)n)T is a self-assembled monolayer, SAM, of n-alkanethiolate bearing a terminal functional group T) make it possible to examine the response of rates of charge transport by tunneling to changes in the strength of the interaction between T and Ga_2O_3. Introducing a series of Lewis acidic/basic functional groups (T = ?OH, ?SH, ?CO_2H, ?CONH_2, and ?PO_3H) at the terminus of the SAM gave values for the tunneling current density, J(V) in A/cm~2, that were indistinguishable (i.e., differed by less than a factor of 3) from the values observed with n-alkanethiolates of equivalent length. The insensitivity of the rate of tunneling to changes in the terminal functional group implies that replacing weak van der Waals contact interactions with stronger hydrogen- or ionic bonds at the T//Ga_2O_3 interface does not change the shape (i.e., the height or width) of the tunneling barrier enough to affect rates of charge transport. A comparison of the injection current, J_0, for T = ?CO_2H, and T = ?CH_2CH_3?two groups having similar extended lengths (in ?, or in numbers of non-hydrogen atoms)?suggests that both groups make indistinguishable contributions to the height of the tunneling barrier.