Reversible Diode Effect in Truncated-pyramid-shaped Bi₂O₂Se Modulated by Tip-Force-Induced Flexoelectric Field.

Abstract

Tunable diode devices with dynamically controllable conduction direction and rectification characteristics hold significant potential for applications such as artificial synapses and programmable logic circuits. Developing advanced systems to achieve high-performance tunable diodes has become a key research focus. In this work, truncated-pyramid-shaped Bi₂O₂Se (BOS) microstructures with varying inclination angles (θ) were fabricated on highly oriented pyrolytic graphite (HOPG) substrate. A W-metal-probe-BOS-HOPG system was constructed to systematically investigate reversible diode behavior jointly regulated by the Se-vacancy-induced built-in electric field (<i>E</i>_built-in) within the BOS and the tip-force-induced flexoelectric field (<i>E</i>_tip-flexo). Results indicate that as θ decreases, the upward <i>E</i>_built-in significantly strengthens, progressively enhancing the diode effect. At small θ, the rectification ratio can reach 10. Furthermore, the application of varying tip forces introduces a downward <i>E</i>_tip-flexo within the BOS, which competes with <i>E</i>_built-in to modulate the total electric field. This competition enables the reversal of the rectification direction and continuous tuning of the rectification ratio, with the reversed diode exhibiting a rectification ratio less than 0.1 under large tip forces. Finite element simulations systematically corroborate the electric field distribution and reversal behavior within the BOS under tip force. This work provides fundamental insights and a theoretical foundation for understanding microscale flexoelectric effects and their application in the design of tunable electronic devices.