Exciton emission in tetrahedral carbon self‐organized and ring‐shaped quantum dots

Abstract

AFM topography, TEM data, spectra of radiative annihilation of excitons in tetrahedral nano carbon quantum dots (QDs) and quantum rings (QRs) were studied in detail. Anti‐Stokes exciton emission (ASEE) spectra in 6.3–4.7 eV energy interval at 4.2–200 K were induced via cascade Urbach tail states transitions under femtosecond laser radiation (λ=266 nm) pumping. Near diamond in composition nano carbon layers (nt‐C) on cleaved KCl and polished Si substrates with high density of self‐organized surface QDs, isolated, aggregated QRs and fractal bulk networks were grown using carbon ion beam of low energy and fluence. Regular networks of QDs 3–20 nm in diameter less than 1 nm in height and up to 3×1011 cm‐2density were obtained. In ASEE spectra fine–structured via 5–6 meV narrow and week 6.0596 eV, 6.0557 eV and 6.0032 eV lines have been resolved at low level of excitation. The strong, fine‐structured via 3.0–4.5 meV lines and bands above and below the energy of indirect exciton transition in diamond have been found in two types of nt‐C layers as well. The parameter dependences of lines and bands upon the level of laser pumping were studied. We suppose that above mentioned components of ASEE spectra are originated from radiative annihilation of excitons in surface and bulk QDs and ring‐like quantum networks. At strong excitation level fine‐structured with 3.5–4.0 meV energy period new 4.8394 eV and 4.7925 eV exciton lines were induced and dominated in emission spectra. These lines are result of exciton annihilation in bulk quantum confined fractal features. (© 2011 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)