Growth of ZnO Polytypes: Multiple Facets of Diverse Applications

Zinc oxide has been considered as a specific and versatile bridging agent that bears an intrinsic relationship with the crystal structure-property application in physics, chemistry, materials, and biomedical sciences. Due to inherent polytypism through the abundance of crystal structures, the properties can interconnect from classical (bulk structures) to quantum (nanostructures) regimes that have been the subject of immense investigation using theoretical, experimental, and simulation perspectives. Prudent advances in the synthetic strategies have offered the opportunity to achieve diverse morphologies from ultrasmall to hierarchical superstructures employing chemical manipulation, and the possibility of maneuvering the crystal patterns has marked zinc oxide as an attractive recipe in the buffet of modern materials research. The interplay between the mere variation in the crystalline structures and spatial confinement of ZnO at the nanoscale dimension has become the epicenter of the emergence of unique physicochemical characteristics that can be exploited in a diverse range of niche multifarious applications. Moreover, the ease of syntheses which mostly follow green techniques, cost effectiveness, physical and chemical stability, and biocompatibility have made zinc oxide a semiconductor of great interest in the past three decades. An intrinsic n-type semiconductor with a wide band gap and large exciton binding energy have rendered ZnO as a fundamental material with a synergism of semiconducting, optoelectronic, piezoelectric, pyroelectric, photocatalytic, and biological properties with outstanding industrial and technological applications. The possibility to control the crystallinity through the manipulation of particle shape, size, exposed facets, composition, and doping imbues a diverse range of materials properties that can be tailored to pursue the preconceived applications. Althouth the onset of research with ZnO can be traced back to nearly a century ago, the renewed interest has been rekindled with the accessibility of high-quality single crystals, facile synthesis to various nanostructures, and the availability of p-type ZnO as the cornerstone. Based on these contexts at the backstage, it is now time to condense the large and voluminous work to assess the epicenter of the conceptive, to rationalize the perpectives between crystallographic and physical properties, and to design the objectives to explore the future technological applications in the realm of present major global challenges in the field of energy, environment, and biomedical applications.