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We present a simple, noncovalent method for anchoring CdSe quantum dots (QDs) onto individual single-walled carbon nanotubes (SWNTs) through a ligand-exchange approach. Trioctylphosphine oxide (TOPO)-capped CdSe quantum dots were prepared, and the cap was then exchanged for pyridine (Py). It was found that the pyridine-capped quantum dots assembled much more effectively onto the SWNTs compared to the original TOPO-capped quantum dots. The density of the coverage of the quantum dots on the nanotubes was controlled through varying the concentration of the quantum dot solution and the reaction time. Spectroscopic studies indicated that the favorable formation of (Py-QD)-SWNT conjugates resulted from the π-π stacking interaction between the electron-rich SWNTs and the aromatic pyridinecapped quantum dots. Furthermore, the photoluminescence quenching of the quantum dots due to their interaction with the nanotubes suggests that the electron transfer from the quantum dots to the nanotubes was enhanced by using the pyridine cap.

High-resolution x-ray diffraction and transmission electron microscopy (TEM) have been used to study BiFeO3 thin films grown on the bare and SrRuO3 buffered (001) SrTiO3 substrates. Reciprocal space mapping (RSM) around (002) and (103) reflections revealed that BFO films with a thickness of about 200 nm were almost fully relaxed and had a rhombohedral structure. Cross-sectional, high-resolution TEM showed that the films started to relax at a very early stage of growth, which was consistent with the RSM results. A thin intermediate layer of about 2 nm was observed at the interface, which had a smaller lattice than the overgrown film. Twist distortions about the c axis to release the shear strain introduced by the growth of rhombic (001) BiFeO3 on cubic (001) SrTiO3 were also observed. The results indicate that a strained, coherent BiFeO3 film on (001) SrTiO3 is very difficult to maintain and (111) STO substrates are preferable.