Distinct plasmon resonance enhanced microwave absorption of strawberry-like Co/C/Fe/C core–shell hierarchical flowers via engineering the diameter and interparticle spacing of Fe/C nanoparticles

Abstract

Strawberry-like Co/C/Fe/C core–shell hierarchical flowers (CSHFs) consisting of separated Fe/C nanoparticles (NPs) anchoring on a Co HF surface were prepared by decomposing Fe(CO)₅ in the presence of Co HFs. Changing the decomposition temperature (T_d) and Fe(CO)₅ volume (δ) could also facilely modulate the phase structure, surface morphology and composition of the products. The low T_d and small δ helped form Co/C/Fe/C CSHFs with a strawberry-like plasmon surface. The diameter and interparticle spacing-dependent electromagnetic properties were investigated at 2–18 GHz. The interparticle-spacing-to-diameter ratio determines the plasmon resonance and coupling. The permittivity and permeability enhanced by strong plasmon resonance were exhibited by Co/C/Fe/C CSHFs formed at δ = 3–4 mL with the interparticle-spacing-to-diameter ratio of 1.36–0.76. The collective oscillation of the conduction band electrons and near field on the Co/C and Fe/C surfaces generated a surface plasmon resonance and coupling, which were responsible for significantly enhanced permittivity and permeability with negative values. In view of the synergistic effect of the enhanced permittivity and permeability, dual dielectric relaxations, dual magnetic resonances, high attenuation and good impedance matching, Co/C/Fe/C CSHFs with particle size of 110 ± 20–380 ± 100 nm and interparticle spacing of 150 ± 50 nm were excellent absorbers that feature strong absorption, broad bandwidth and light weight. An optimal reflection loss (R_L) of −45.06 was found at 17.92 GHz for an absorber thickness of 1.6 mm, and the frequency range (R_L ≤ −20 dB, 99% absorption) was over 2–18 GHz. Our findings demonstrated that optimally designed plasmonic heterostructures must be fabricated to improve microwave absorption performances for future applications.