Raman study of E2 and surface phonon in zinc oxide nanoparticles surrounded by organic molecules

Abstract

Using Raman spectrometry, we obtained results showing the influence of organic ligands on the vibrational properties of small zinc oxide nanocrystals (2.1–6.8nm). It is shown that it is possible to distinguish both mechanical and dielectric effects from the E2 nonpolar phonon mode and from a surface mode, theoretically predicted but rarely observed. It has been found that E2 phonon is not dependent on the nanocrystal size, but its frequency decreases with increasing ligand length, characteristic of a tensile stress on the nanocrystal. We report also the observation of a surface optical mode, the experimental frequency of which is in reasonable agreement with available calculations.