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Si-SiO2 multilayer nanocomposite (NCp) films, grown using pulsed laserdeposition with varying Si deposition time are investigated using Ramanspectroscopy/mapping for studying the variation of Si phonon frequency observedin these NCps. The lower frequency (LF) phonons (~ 495 - 510 cm-1) and higherfrequency (HF) phonons (~ 515 - 519 cm-1) observed in Raman mapping data (Fig.1A) in all samples studied are attributed to have originated from surface(Si-SiO2 interface) and core of Si nanocrystals, respectively. The consistentpicture of this understanding is developed using Raman spectroscopy monitoredlaser heating/annealing and cooling (LHC) experiment at the site of a desiredfrequency chosen with the help of Raman mapping, which brings out cleardifference between core and surface (interface) phonons of Si nanocrystals. Inorder to further support our attribution of LF being surface (interface)phonons, Raman spectra calculations for Si41 cluster with oxygen terminationare performed which shows strong Si phonon frequency at 512 cm-1 correspondingto the surface Si atoms. This can be considered analogous to the observedphonon frequencies in the range 495 - 510 cm-1 originating at the Si-SiO2interface (extended). These results along with XPS data show that nature ofinterface (oxygen bonding) in turn depends on the size of nanocrystals and thusLF phonons originate at the surface of smaller Si nanocrystals. Theunderstanding developed can be extended to explain large variation observed inSi phonon frequencies of Si-SiO2 nanocomposites reported in the literature,especially lower frequencies.

Correlation of size and oxygen bonding at the interface of Si nanocrystal in Si-SiO2 nanocomposite: A Raman mapping study