DOI: 10.1002/cphc.201000136 Structure of Glancing Incidence Deposited TiO 2 Thin Films as Revealed by Grazing Incidence Small-Angle X-ray Scattering Lola Gonzµlez-García, [b] Angel Barranco, [b] Adela MuÇoz Pµez, [b] Agustín R. Gonzµlez-Elipe, [b] Mari-Cruz García-GutiØrrez,* [a] Jaime J. Hernµndez, [a] Daniel R. Rueda, [a] Tiberio A. Ezquerra, [a] and David Babonneau [c] 1. Introduction Titanium dioxide thin films possess outstanding properties, such as high optical transmittance and refractive index, photo- activity, chemical stability, and so forth, that make them suita- ble for many technological applications. [1] Regarding film mor- phologies, the formation of ordered nanorods is important for improving the photocatalytic, photovoltaic or sensor proper- ties of nanostructured TiO 2 thin films. [2, 3] Among the various methods available to produce nanostructured thin films a very versatile procedure is the use of glancing angle physical vapor deposition (GLAD). [4, 5] This method produces porous thin films formed by columns tilted by a certain angle with respect to the substrate. Although different methods of characterization have been used to ascertain the morphology of this type of thin films, to our knowledge grazing incidence small-angle X- ray scattering (GISAXS) [6, 7] has not yet been applied. Herein we report on the GISAXS analysis of TiO 2 thin films prepared by GLAD. One of the advantages of GISAXS is the ability to pro- vide averaged statistical information over the entire illuminat- ed sample area, as well as the ability to access buried struc- tures located well below the surface [8] that are not accessible to local probe techniques like scanning electron microscopy (SEM) or atomic force microscopy (AFM). We found that the GLAD thin films give rise to a new kind of asymmetric GISAXS patterns that may result from a morphological evolution of the columns across the thickness of the films. The data analysis also shows that the GISAXS technique is a powerful tool to de- scribe the nanostructure of this kind of thin films. Experimental Section TiO 2 thin films were prepared by GLAD at room temperature on sil- icon substrates. Evaporation was carried out in an electron bom- bardment evaporator, using TiO pellets as a target. Stoichiometric and columnar thin films of TiO 2 were obtained by evaporation at 10 4 torr O 2 , placing the substrates at a glancing angle of 808 with respect to the evaporation source. Si-substrates (rectangular pieces of about 1  4 cm 2 ) were positioned with the shortest edge parallel to the vapor flow direction. Films with thicknesses between 45 nm and 600 nm were prepared. The microstructure of the TiO 2 thin films deposited on a silicon wafer was examined by field emission scanning electron microsco- py (FESEM) in a Hitachi S5200 microscope. GISAXS experiments were performed at the BW4 beamline (HASY- LAB, Hamburg) using a wavelength of l = 0.138 nm and a sample- to-detector distance of 2.175 m. A moderate microbeam focusing was achieved using beryllium compound refractive lenses (beam size 42  22 mm 2 ). The scattering signal was recorded with a 2D de- tector (MAR CCD camera with 79 mm 2 pixel size). For the first time, grazing incidence small-angle X-ray scatter- ing (GISAXS) analysis is used to characterize the morphology of TiO 2 thin films grown by glancing angle physical vapor de- position (GLAD). According to cross-section scanning electron microscopy (SEM) images, the films consist of near isotilted TiO 2 columns of different length and width depending on film thickness. The obtained GISAXS patterns show a characteristic asymmetry with respect to the incidence plane, which is asso- ciated with the tilted geometry of the TiO 2 columns. The pat- terns also show the existence of two populations of columns in these GLAD-TiO 2 films. The population of the thinnest col- umns appears related to the first grown layer and is common for all the films investigated, while the second population of columns grows with the thickness of the films and has been related to wider columns formed by shadowing at the expense of the initially formed columns. [a] Dr. M.-C. García-GutiØrrez, J. J. Hernµndez, Dr. D. R. Rueda, Prof. T. A. Ezquerra Instituto de Estructura de la Materia, CSIC Serrano 121, 28006 Madrid (Spain) Fax: (+ 34) 915645557 E-mail : maricruz@iem.cfmac.csic.es [b] L. Gonzµlez-García, Dr. A. Barranco, Dr. A. M. Pµez, Prof. A. R. Gonzµlez-Elipe Instituto de Ciencia de Materiales de Sevilla CSIC—Universidad de Sevilla Avda. AmØrico Vespucio 49, 41092 Sevilla (Spain) [c] Dr. D. Babonneau Institut P’, UPR 3346 CNRS UniversitØ de Poitiers, SP2 MI Bvd M. et P. Curie, BP 30179 86962 Futuroscope Chasseneuil Cedex (France) ChemPhysChem 2010, 11, 2205 – 2208  2010 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim 2205