Role of Defect Engineering at Nanoscale: Mechanistic Insights into Electronic Structure Modulation.

With the growing demand for high-performance, application-specific materials, defect engineering stands out as a transformative strategy to customize the fundamental properties of nanomaterials like conductivity, charge transfer, photoluminescence, sensing, etc. by achieving desired reactions and characteristics. Despite extensive progress, a fundamental understanding of how different defects evolve within the lattice and govern the property change are unexplored. This review provides a mechanistic and fundamental perspective on defect chemistry by redefining defect classification irrespective of material type or application, emphasizing how defects transform and interact within the lattice environment. We further propose that the change in electronic structure occurs via three fundamental pathways i.e., electronic route, phase transformation, and geometry change irrespective of the material class. These alterations eventually lead to band structure modifications which dictate the resulting functional properties. This review bridges the gap between defect formation, electronic structure evolution, and band structure modulation to guide the future research in designing of next-generation nanomaterials with deliberate and controlled introduction of defects.