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Báo cáo hóa học: " Phonon Raman spectra of colloidal CdTe nanocrystals: effect of size, non-stoichiometry and ligand exchange"

Tuyển tập báo cáo các nghiên cứu khoa học quốc tế ngành hóa học dành cho các bạn yêu hóa học tham khảo đề tài: Phonon Raman spectra of colloidal CdTe nanocrystals: effect of size, non-stoichiometry and ligand exchange | Dzhagan et al. Nanoscale Research Letters 2011 6 79 http www.nanoscalereslett.eom content 6 1 79 o Nanoscale Research Letters a SpringerOpen Journal NANO EXPRESS Open Access Phonon Raman spectra of colloidal CdTe nanocrystals effect of size non-stoichiometry and ligand exchange 1 2 3 - I 2 2 4 Volodymyr Dzhagan Irina Lokteva Cameliu Himcinschi Xiaoping Jin Joanna Kolny-Olesiak Dietrich RT Zahn Abstract Resonant Raman study reveals the noticeable effect of the ligand exchange on the nanocrystal NC surface onto the phonon spectra of colloidal CdTe NC of different size and composition. The oleic acid ligand exchange for pyridine ones was found to change noticeably the position and width of the longitudinal optical LO phonon mode as well as its intensity ratio to overtones. The broad shoulder above the LO peak frequency was enhanced and sharpened after pyridine treatment as well as with decreasing NC size. The low-frequency mode around 100 cm-1 which is commonly related with the disorder-activated acoustical phonons appears in smaller NCs but is not enhanced after pyridine treatment. Surprisingly the feature at low-frequency shoulder of the LO peak commonly assigned to the surface optical phonon mode was not sensitive to ligand exchange and concomitant close packing of the NCs. An increased structural disorder on the NC surface strain and modified electron-phonon coupling is discussed as the possible reason of the observed changes in the phonon spectrum of ligand-exchanged CdTe NCs. PACS 63.20.-e 78.30.-j 78.67.-n 78.67.Bf Introduction Among semiconductor nanocrystals NCs colloidal CdTe NCs attract increasing interest due to their large exciton Bohr radius 7.3 nm pronounced quantum size effect optical activity both in the visible and near-infrared spectral ranges with a bulk band gap of 1.475 eV and chemical flexibility at the NC surface. These properties make the CdTe NCs promising for various optoelectronic and biological applications light-emitting diodes living .