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Intriguing spherical conformation of polyvinyl pyrrolidone (PVP) embedded with CdS nanocrystals in CdS-PVP nanocomposites grown via facile chemical bath deposition is probed using simultaneous Raman and AFM mapping. Observance of isolated or coagulated PVP spheres embedded with CdS nanocrystals at room temperature (RT) due to polymer collapse or clouding, respectively, is attributed to relative variation in Cd+/PVP concentration in the bath. With an additional external stimulus of temperature (70 °C) and subsequent growth at RT in the same chemical bath, observed only isolated and dimer PVP spheres are ascribed to opening (high temperature) and reformation (RT) of PVP spheres with dominating collapse mechanism of polymer. Formation of dimer PVP sphere due to lock and key binding mechanism is facilitated by the temperature. Transformation of RT grown mixed-phase structure to purely hexagonal phase further confirming the change in conformation of CdS-PVP nanocomposites on the application of an external stimulus. Stronger resonance Raman scattering for CdS nanocrystals embedded in the isolated PVP spheres is attributed to strain-related band gap tuning. The understanding developed of the application of the external stimulus leading to change in polymer conformation can be gainfully used in macromolecular actuators and biomedical field as delivery systems. Application of an external stimulus of temperature and subsequent growth at room temperature led to formation of only isolated and dimer PVP spheres embedded with CdS nanocrystals, wherein formation of dimer PVP spheres happen due to lock and key binding mechanism between two isolated PVP spheres. [ABSTRACT FROM AUTHOR]

Correlation between size, bonding of Si and O at the surface/interface of Si nanocrystals and frequency of Si phonons in Si-SiO 2 nanocomposites is established using Raman mapping and X-ray photoelectron spectroscopy. Corroboration of these results with absorption spectroscopy shows that lowering of direct transition of light electron conduction band to heavy hole valence band ∼2.8 and 2.95 eV is a result of the interplay between effect of electron confinement (increases band gap) and oxidation bonding environment at the surface/interface (decreases band gap) of a nanocrystal in Si-SiO 2 nanocomposites. These studies have generated deeper insight into the fundamental understanding of the nanocomposite, which can allow easy optical microscopy monitoring of Si-SiO 2 based device fabrication. [ABSTRACT FROM AUTHOR]

Nanocomposites of CdS nanocrystals (NCs) embedded in a polyvinyl pyrrolidone are grown using one-step chemical bath deposition technique. While this method eliminates an additional step for the growth of NCs, it also leads to the formation of nearly monodispersive CdS NCs as indicated by absorption, reflection, and photoluminescence spectroscopy. Further, scanning electron microscopy, energy-dispersive spectroscopy, and transmission electron microscopic investigations reveal the formation of nearly monodispersive CdS NCs (~6 to 10 nm) embedded in PVP spheres of sizes ~100 to 600 nm. Systematic study of variation in Cadmium acetate (Cd ion source), Thiourea (S ion source), PVP concentration, deposition time, and heating/cooling cycles elucidates the co-operative growth mechanism for CdS-PVP nanocomposite. The experimental observations of this study are corroborated with existing theoretical simulations for nanocomposite growth, which explicates that collapse of PVP into a sphere is crucial to inclusion of only nearly monodispersive CdS NCs. Important insights obtained from this work give control on the growth of nearly monodispersive CdS NCs embedded in PVP, using a simple and inexpensive growth technique. [ABSTRACT FROM AUTHOR]