Introducing Ionic and/or Hydrogen Bonds into the SAM//Ga2O3 Top-Interface of Ag/S(CH2)nT//Ga2O3/EGaIn Junctions

Junctions with the structure Ag/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, −CONH2, and −PO3H) at the terminus of the SAM gave values for the tunneling current density, J(V) in A/cm, 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 hydrogenor 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.