Effect of TiO2 Crystal Orientation on the Adsorption of CdSe Quantum Dots for Photosensitization Studied by the Photoacoustic and Photoelectron Yield Methods

We describe the adsorption and growth of CdSe quantum dots (QDs) on single crystals of rutile TiO2 with different crystal orientations. We used atomic force microscopy (AFM) to characterize the morphology of the QDs and photoacoustic (PA) spectroscopy to measure the optical absorption. Photoelectron yield (PY) spectroscopy was applied to characterize the valence band maximum (VBM) of the single crystal TiO2. The AFM images and the absorbance measurements showed that the number of CdSe QDs grown on the (111) surface was larger than those grown on the (110) and (001) surfaces. The absorbance measurements showed that the adsorption becomes linearly proportional to the adsorption time. However, the rate of adsorption is different for each crystal orientation. The crystals grow higher on (111) surfaces than on (110) and (001) surfaces. The position of the VBM for the (111) surface is higher than those for the (110) and (001) surfaces. Hence, the formation and growth of CdSe QDs on (111) surfaces is more active than on the other orientations. The increase in the average diameter of CdSe QDs with adsorption time is independent of the crystal orientation. Although the growth rate of CdSe QDs on (001) surfaces is lower than on (110) and (111) surfaces, the crystal quality is better on the former.