Synthesis and Characterization of TiO 2 Nanocrystals Prepared from n-Octadecylamine-Titanyl Oxalate Langmuir-Blodgett Films A. Serra, A. Genga, D. Manno, G. Micocci, T. Siciliano, and A. Tepore Dipartimento di Scienza dei Materiali, Universita ` di Lecce ed Unita ` INFM, I-73100 Lecce, Italy R. Tafuro and L. Valli* Dipartimento di Ingegneria dell’Innovazione, Universita ` di Lecce ed Unita ` INSTM, I-73100 Lecce, Italy Received October 19, 2002. In Final Form: January 22, 2003 TiO2 nanosized clusters have been prepared by the Langmuir-Blodgett technique starting from the n-octadecylamine-titanyl oxalate complex. The floating film morphology has also been investigated by Brewster angle microscopy (BAM). The presence of TiO2 in the subphase promotes the formation of aggregates of n-octadecylamine on the subphase surface. LB films initially contain TiO2 nanosized clusters embedded in the organic amorphous matrix; their structural evolution induced by thermal annealing has been investigated. UV-vis spectroscopy, high-resolution transmission electron microscopy (HRTEM), and small area electron diffraction (SAD) characterization methods are used as synergic techniques giving complementary information regarding both structural features and photophysical properties. Introduction Semiconducting nanosized clusters reveal dimension- dependent properties totally different from those of the corresponding polycrystalline materials. 1 Organized as- semblies of crystallites show intriguing physical properties and form the subject of intense research in recent years. 2 The reduction of the particle size to nanoscale alters electrical, magnetic, electro-optical, and chemical proper- ties. Therefore, the control of particle size represents an interesting opportunity to afford great flexibility to band- gap engineering in materials. This leads to applications such as nonlinear optical devices, fast switches, photo- voltaic converters, and so on. 3-5 Nanometer-sized semiconductor particles have been prepared by a wide range of synthetic methods, which involve homogeneous aqueous solutions, 6 glasses, 7 and surfactant systems such as vesicles, air-water mono- layers, reversed micelles, and Langmuir-Blodgett films. 8-10 According to the novel trend of assembling both nan- ometer scale structure and bulk materials using nanosized particles as building blocks, our approach uses the Langmuir-Blodgett technique for the deposition of lay- ered organic-inorganic composite systems. Not only do Langmuir-Blodgett films offer the chance of built-in architectural control at the monolayer level, but they also provide useful media for the controlled construction of nanosized particles under very mild conditions. 11 The aim of this paper is to analyze photophysical, structural, and morphological properties of TiO 2 nanosized clusters embedded in Langmuir-Blodgett films deposited from an n-octadecylamine-titanyl oxalate complex and also the film properties evolution after thermal annealing. UV-vis spectroscopy, high-resolution transmission elec- tron microscopy (HRTEM), and small area electron diffraction (SAD) characterization methods are used as synergic techniques giving complementary information regarding both structural features and photophysical properties. Experimental Section Potassium titanyl oxalate, K2TiO(C2O4)2 (CARLOERBA ana- lytical grade), and n-octadecylamine (Fluka, >99%) were used as received without further purification. The Langmuir-Blodgett films were deposited by a KSV5000 system 3 Langmuir-Blodgett apparatus (850 cm 2 ). n-Octadecylamine was dissolved in chlo- roform with a concentration of 4.9 × 10 -4 M; the spreading solution was always used as soon as possible after preparation and stored in the dark in a refrigerator. In our depositions, 200 µL of the spreading solution was spread onto the subphase, whose temperature was regulated at 20 °C by a Haake GH D8 apparatus. The subphase was prepared by dissolving potassium titanyl oxalate (10 -4 M solution) in ultrapure water (Millipore Milli-Q, resistivity 18.2 MΩ cm); the pH value was automatically buffered at 3.9. After the solvent evaporated off, the floating film was compressed at a speed of 10 mm/min. The transfer on the substrates was performed at the surface pressure 30 mN/m and at the speeds 1 mm/min during the upstroke and 10 mm/min during the downstroke. The substrates were strongly hydrophilic quartz slides. 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Sci. 1998, 5, 599. 3486 Langmuir 2003, 19, 3486-3492 10.1021/la026720w CCC: $25.00 © 2003 American Chemical Society Published on Web 03/04/2003