From Stems (and Stars) to Roses: Shape-Controlled Synthesis of Zinc Oxide Crystals

• Published in: Crystal growth & design Vol. 9; no. 8; pp. 3432 - 3437
• Main Authors: Palumbo, Marco, Lutz, Thierry, Giusca, Cristina E, Shiozawa, Hidetsugu, Stolojan, Vlad, Cox, David C, Wilson, Rory M, Henley, Simon J, Silva, S. Ravi P
• Format: Journal Article
• Language: English
• Published: Washington,DC American Chemical Society 05.08.2009
• Subjects: Condensed matter: electronic structure, electrical, magnetic, and optical properties; Condensed matter: structure, mechanical and thermal properties; Cross-disciplinary physics: materials science; rheology; Exact sciences and technology; Materials science; Nanoscale materials and structures: fabrication and characterization; Optical properties and condensed-matter spectroscopy and other interactions of matter with particles and radiation; Other topics in nanoscale materials and structures; Photoluminescence; Physics; Structure of solids and liquids; crystallography; Structure of specific crystalline solids; Defect density; Work functions; Nanosheet; Photoluminescence; XRD; Citric acid; Ammonia; Light emission; Zinc oxide; Scanning transmission electron microscopy; Crystal morphology; Hydrates; X-ray photoelectron spectra; Crystal structure
• ISSN: 1528-7483; 1528-7505
• DOI: 10.1021/cg8013333

A novel, scalable, solution-based method suitable for the control of ZnO crystal morphology at moderate temperature from rods/stars to rose-shaped, flowerlike structures is presented here. The synthesized ZnO roselike crystals are composed by wide nanosheets folded several times on themselves. This study represents the first step toward the full understanding of the growth mechanism that led to the formation of such a structure. It is now widely acknowledged that both size and shape of the metal oxide crystals have a profound effect on their properties. The influence that two morphology directing agents, ammonia and citric acid trisodium salt dihydrate, have on the shape-controlled synthesis is illustrated. The analysis of various possible mechanisms and forces that might contribute to the roselike crystals formation, such as the influence of polar surfaces, is discussed. The chemical composition and work function of the ZnO roses is investigated via XPS and UPS. XRD analysis suggests wurtzite as the most likely crystal structure for both the ZnO stars and roses, albeit these latter have a more elusive diffractogram because of their folded configuration. PL data suggest a lower level of interstitial oxygen for both crystals synthesized, starlike and flowerlike. Analysis of the ratio of the emission in the Blue range upon the ultraviolet emission indicates that the ZnO stars are slightly more conductive than the ZnO roses, a factor associated with the lower native defect concentration in these latter structures.