Biomaterial-Induced Stable Resistive Switching Mechanism in TiO2 Thin Films: The Role of Active Interstitial Sites/Ions in Minimum Current Leakage and Superior Bioactivity

Leakage of current in oxide layers is the main issue for higher speed and denser resistive random-access memory. Defect engineering played a substantial role in meeting this challenge by doping or producing controlled interstitial defects or active sites. These controlled active sites enabled memory cells to form a stable and reproducible conduction filament following an electrochemical metallization model. In this study, a defect-abundant lime peel extract (LPE)-mediated anatase TiO2 thin film was fabricated using a simple hydrothermal route. The detailed structural and morphological analysis of the bioactive anatase TiO2-LPE thin film reveals the homogeneous growth of TiO2 flowers and distinct features in terms of controlled defects as compared to simple anatase TiO2. These interstitial defects (Ti+3 and Ti+4) behave as active sites for cation migrations along highly conductive K1+ ions because of the mediation of LPE. The defect-free surface reveals slight surface roughness (4.8 nm) that successfully minimizes leakage of current. The strategy enabled a reliable conductive bridge filament, which can replicate with no more electric degradation. The Ag/TiO2-LPE/FTO-based memory cell demonstrates reproducible bipolar resistive switching along with a high ON/OFF ratio (>105), excellent endurance (1.5 × 103 cycles), and long-term retention (105 s) without any electrical degradation. Furthermore, green-synthesized TiO2-LPE nanoparticles have shown superior antibacterial activity as compared to other green syntheses of different plants or fruits against the toxic microorganisms present in inorganic media.

Crossover from compact to branched films in electrodeposition with surface diffusion

We study a model for thin film electrodeposition in which instability development by preferential adsorption and reduction of cations at surface peaks competes with surface relaxation by diffusion of the adsorbates. The model considers cations moving in a supported electrolyte, adsorption and reduction when they reach the film surface, and consequent production of mobile particles that execute activated surface diffusion, which is represented by a sequence of random hops to neighboring lattice sites with a maximum of G hop attempts (G≫1), a detachment probability ε<1 per neighboring particle, and a no-desorption condition. Computer simulations show the formation of a compact wetting layer followed by the growth of branched deposits. The maximal thickness z_{c} of that layer increases with G but is weakly affected by ε. A scaling approach describes the crossover from smooth film growth to unstable growth and predicts z_{c}∼G^{γ}, with γ=1/[2(1-ν)]≈0.43, where ν≈0.30 is the inverse of the dynamical exponent of the Villain-Lai-Das Sarma equation that describes the initial roughening. Using previous results for related deposition models, the thickness z_{c} can be predicted as a function of an activation energy for terrace surface diffusion and the temperature, and the small effects of the parameter ε are justified. These predictions are confirmed by the numerical results with good accuracy. We discuss possible applications, with a particular focus on the growth of multifuncional structures with stacking layers of different porosity.