This study investigates the influence of stacking architecture on the film growth and multiferroic properties of BiFeO3-based heterostructures grown on fluorine-doped tin oxide (FTO) substrates. Using radio-frequency magnetron sputtering, two heterostructures combining Bi0.85Pr0.15Fe0.97Mn0.03O3 (E) and Bi0.60Ba0.25Pr0.15Fe0.945Ni0.025Mn0.03O3 (M) were deposited: a continuous bilayer, S1 (E180/M30), and a multilayer architecture, S2 [3(E60/M10)], while maintaining the same total deposition time of 210 min. Cross-sectional electron microscopy revealed architecture-dependent differences in film growth, with average thicknesses of 184.9 ± 9.2 nm for S1 and 113.4 ± 3.8 nm for S2. X-ray diffraction analysis indicated contributions from rhombohedral (R3c) and orthorhombic (Pbam) structures in both heterostructures. PFM measurements showed butterfly-like loops and phase changes close to 180° in both architectures, supporting a predominantly ferroelectric/electromechanical local response. S1 exhibited the larger electromechanical response, with a displacement variation of approximately 1.12 nm and a broader butterfly loop, whereas S2 maintained a well-defined response despite its lower thickness and multilayer configuration. In contrast, S2 exhibited a volume-normalized magnetization amplitude of 18.30 emu/cm3, substantially higher than that of S1 (3.92 emu/cm3), although with lower coercivity (92.3 Oe compared with 295.8 Oe for S1). These findings highlight that, beyond chemical composition, layer engineering on low-cost polycrystalline substrates like FTO is a strategic route to tuning the functional balance between electromechanical and magnetic responses in thin-film heterostructures.
Polypyrrole (PPy) is a widely studied conducting polymer (CP) due to its low-cost synthesis, environmental stability, intrinsic electrical conductivity, bioactivity and inherent antibacterial activity. Strong antibacterial performance typically requires polymerisation under highly acidic conditions (pH ≤ 2) to obtain the doped conductive form. To enhance processability, support large-scale production, and tune the properties, the biopolymers such as chitosan (Ch) can be incorporated to form composites. In this study, PPy and PPy/Ch composites were synthesised using both the classical chemical synthesis (CS) and an eco-friendly enhanced microwave (MW) method. Two oxidising agents were evaluated: the standard ammonium persulfate ((NH4)2S2O8) and, for the first time in a scalable approach, potassium iodate (KIO3). Pristine PPy synthesised with (NH4)2S2O8 displayed a cauliflower-like granular morphology, while KIO3-based samples exhibited denser surfaces with well-defined spherical particles. MW-processed PPy/Ch composites showed more compact structures with uniformly dispersed globular PPy domains and demonstrated higher conductivity than CS-synthesised samples. FTIR spectra confirmed successful incorporation of PPy within the composite matrix. All PPy/Ch composites showed enhanced antibacterial activity against both bacteria and bacteriophage Phi X 174 compared with pure Ch. PPy/Ch composites were consistently more active against Gram-negative Escherichia coli than Gram-positive Staphylococcus aureus. The antiviral results indicate that PPy and PPy/Ch behave similarly at 0.5 wt%, independent of synthesis method, while the MW-derived PPy/Ch formulation is noticeably less potent, showing the weakest activity at 1 wt%. Overall, the results indicate that the rapid, scalable MW method enables controlled PPy formation and tuning of composite properties for targeted applications.
