Thickness Fluctuations Produce Apparent Long-Range Tunneling in Large-Area Junctions: The Case of Polyelectrolyte Multilayers

MALDONADO, LILIANA; HERRERA, SANTIAGO E.; WILLIAMS, FEDERCIO J.; TAGLIAZUCCHI, MARIO

Journal of Physical Chemistry C

American Chemical Society

Año: 2022 vol. 126 p. 9956 - 9964

The electron-tunneling (ET) current through a barrier of thickness h is generallyanalyzed with the Simmons model, j ∼ exp(−βh), where β is the tunneling decay coefficient. Weshow that fluctuations in barrier thickness produce apparent β values systematically smaller thanthe real ones, which may lead to incorrectly postulating long-range electron tunneling. We reachedthis conclusion by performing the first tunneling studies through polyelectrolyte-multilayer films ofdifferent average thicknesses using impedance spectroscopy and EGaIn/Ga2O3 top contacts. Weexplained these measurements with a model that considers ET through a film with a Gaussiandistribution of thicknesses, as observed by atomic force microscopy. It is shown that even relativelysmall thickness fluctuations can introduce a systematic error in the determination of β and thatwhen the average film thickness and its standard deviation become commensurable, it is impossibleto determine β.