Introducing ionic and/or hydrogen bonds into the SAM//Ga₂O ₃ top-interface of Ag^TS/S(CH₂) _nT//Ga₂O₃/EGaIn junctions

Junctions with the structure Ag^TS/S(CH₂) _nT//Ga₂O₃/EGaIn (where S(CH₂) _nT 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 Ga₂O₃. Introducing a series of Lewis acidic/basic functional groups (T = -OH, -SH, -CO₂H, -CONH ₂, and -PO₃H) at the terminus of the SAM gave values for the tunneling current density, J(V) in A/cm², 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//Ga₂O₃ 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, J₀, for T = -CO₂H, and T = -CH₂CH₃-two groups having similar extended lengths (in Å, or in numbers of non-hydrogen atoms)-suggests that both groups make indistinguishable contributions to the height of the tunneling barrier.