CrystEngComm PAPER Cite this: CrystEngComm, 2017, 19, 1535 Received 28th December 2016, Accepted 16th February 2017 DOI: 10.1039/c6ce02648f rsc.li/crystengcomm Structural study of TiO 2 hierarchical microflowers grown by aerosol-assisted MOCVD† Sayari Biswas,* ab Carmen Jiménez, b Afzal Khan, bc Sebastien Forissier, b Asit Kumar Kar, a David Muñoz-Rojas b and Jean-Luc Deschanvres * b TiO 2 is a promising n-type semiconductor for optoelectronic devices, in particular dye sensitized and hy- brid solar cells, and more recently for hybrid perovskite-based solar cells, as well as for lithium batteries. For these applications, TiO 2 structures offering a high mesoporosity and surface area are especially inter- esting as these increase the efficiency of phenomena taking place at the interfaces. We have used aerosol- assisted metal–organic chemical vapor deposition (AA-MOCVD) to deposit TiO 2 films containing hierarchi- cal TiO 2 microflowers. Both the film and the microflowers crystallize in the anatase structure. The micro- flowers have diameters of around 2–3 microns while the petals are only several nanometers thick. The den- sity of the microflowers and of the petals in each flower can be controlled by adjusting the deposition parameters. These microstructures are stable under high temperature annealing (950 °C). In this communi- cation, we describe the synthesis of the microflowers and present the detailed study of their structural and morphological properties. 1. Introduction Titanium is the most abundant transition metal on earth and its metal oxide TiO 2 is a wide band gap semiconductor with high chemical stability, low-cost, non-toxicity, strong photocatalytic activity and high photoelectric conversion effi- ciency. Being a wide band gap semiconductor, TiO 2 pos- sesses unique electronic properties combined with the pos- sibility of easy nanostructuring and chemical stability. Morphology, structure, phase and dimensionality will tune the physical and chemical properties of the TiO 2 nanostruc- tures. This remarkable versatility has sparked interest in many fields of applications such as electronic device fabri- cation, 1 photocatalysis, 2 energy storage, 3 gas sensing, 4 or dye sensitized solar cells (DSSC). 5–7 In all these examples, having nano and microstructures plays an important role in enhancing the performance of devices, mainly due to the increase of the specific surface area, 8 as for photocatalysed reactions (photoinduced molecular transformations take place at the surface of a catalyst), or for DSSCs (a large spe- cific surface area increases the sites for adsorption of dye molecules). Therefore, being able to design and synthesize TiO 2 with tuned morphologies, sizes and crystallographic phases is of key importance. Hierarchical structures are in this context very attractive since they combine morphological features at different scales while electronic percolation is ensured. 9 Tian 10 demonstrated that 3D flower-like TiO 2 showed the highest UV light absorp- tion when integrated in DSSCs compared to nanospheres and nanorod structures; even the photocatalytic activity (97% deg- radation efficiency) for flowers was higher than for spheres or rod-like structures (60% and 55%, respectively). These are mainly due the fact that 3D hierarchical flower-like structures are easily accessible to light and reactants. Thanks to an in- creased surface area (72 m 2 g -1 , compared to 48 m 2 g -1 for spheres and 40 m 2 g -1 for rods). The beneficial effect of the specific surface area, in particular that of flower-like struc- tures, has also been demonstrated in other materials. Flower- like α-NiIJOH) 2 microspheres composed of nanowires pre- pared through a solvothermal method showed a high specific capacitance of 1788.9 F g -1 at a current density of 0.5 A g -1 and excellent rate performance when used as an electrode material in supercapacitors. 11 Porous 3D Co/CoO flower structures benefit from electromagnetic wave scattering, which results in enhanced microwave absorption properties. Gas sensors based on flower-like SnO 2 nanostructures pre- pared by hydrothermal reactions exhibited good sensitivity towards ethanol vapour, with a short response/recovery time. They also exhibited high charge–discharge capacities as CrystEngComm, 2017, 19, 1535–1544 | 1535 This journal is © The Royal Society of Chemistry 2017 a Indian Institute of Technology (Indian School of Mines), Dhanbad-826004, Jharkhand, India. E-mail: jean-luc.deschanvres@grenoble-inp.fr b Univ. Grenoble Alpes, LMGP, CNRS, F-38000 Grenoble, France c Department of Physics, University of Peshawar, Pakistan † Electronic supplementary information (ESI) available. See DOI: 10.1039/ c6ce02648f