Lattice expansion/contraction triggered by etching-assisted strain engineering of cobalt sulfide heterostructures to boost electromagnetic wave absorption

Lattice-level design presents a promising avenue to overcome the bottleneck of achieving a broadband dielectric response in transition metal chalcogenides. However, the selective control of lattice characteristics (expansion or contraction) in multiphase systems remains challenging, and their specific effects on electromagnetic modulation are poorly understood. Herein, we propose an etching-assisted strain engineering strategy to deliberately trigger lattice distortions and regulate lattice expansion and contraction in cobalt sulfide heterostructures. We demonstrate that the sequence of processing steps is critical: an etching-first-sulfurization-later approach (Route 1) preferentially induces tensile strain and lattice expansion, whereas a sulfurization-first-etching-later (Route 2) pathway favors compressive strain and lattice contraction. Compared to the strain-free cobalt sulfide (C-0), the optimal sample (C-24) achieves a comparable coexistence of local lattice expansion and contraction via Route 1. This coexistence expedites localized lattice perturbations, enriches lattice distortion-related sulfur vacancies, and intensifies multiphase heterointerfaces, collectively boosting the dielectric polarization response. Consequently, this elaborate strategy enables an effective absorption bandwidth of 5.45 ​GHz with excellent polarization behavior, which are 1.83-fold and 1.93-fold improvement over C-0, respectively. This work provides a novel strategy for manipulating polarization response at the lattice level, offering valuable insights for the rational design of advanced heterogeneous absorbents based on lattice strain engineering.