The modification of Si nanocrystallites embedded in a dielectric matrix by high energy ion irradiation
We have followed the effects of heavy ion irradiation on the structural, electrical, and photoluminescence properties of ensembles of silicon nanocrystallites embedded in a dielectric (SiO2) matrix. This was done as a function of the irradiation dose and the content of the Si phase. The results obtained can be accounted for self-consistently assuming that a relatively small dose of the irradiation enhances the crystallization while for higher doses the irradiation enhances the amorphization. The corresponding processes suggest that tuning of the above properties can be achieved by swift heavy ion irradiation.
Charge spectroscopy of SiO2 layers with embedded silicon nanocrystals modified by irradiation with high-energy ions
The method of charge deep-level transient spectroscopy (Q-DLTS) is used to study and compare the ejection of charge carriers from silicon nanocrystals (NCs) located in an ordered or random way in the SiO2 matrix. It is shown that, in all cases, this ejection is a thermally activated process. The parameters of energy barriers characterizing the processes of ejection of charge carriers from the levels of nanocrystals in the layers NCs:SiO2 before (random distribution) and after their modification by irradiation with high-energy ions (ordered distribution of nanocrystals) are determined. It is found that the activation energies for ejection of charge carriers from nanocrystals and the size of nanocrystals estimated from the difference between energies of two levels observed by the Q-DLTS method decrease as the ion fluence is increased. The density of nanocrystals observed by the Q-DLTS method decreases by approximately an order of magnitude as a result of irradiation with fluence of 1012–1013 cm−2 in comparison with an initial unirradiated structure; this decrease is due to formation of conducting chains of nanocrystals in tracks.
Resonant Auger decay study of C1s -> pi* core-excited OCS
The present work aims at characterizing short-lived C1s((-1)) pi*((1)) core-excited states of the OCS molecule based on the analysis of the vibrational fine structure and lineshape profiles of the high-resolution resonant Auger decay spectra recorded at the excitation energies along the C1s -> pi* resonance in the binding energy region 15-19eV. Very different behavior in terms of lineshape and resonant enhancement is observed for the (A) over tilde, (B) over tilde and (C) over tilde final states. This is explained by (1) the variation in the C-O bond lengths for the states involved in the electronic relaxation and (2) different contributions in terms of Mulliken population to the molecular orbitals determining the electronic character of the corresponding states. Since the final-state geometries are known from a number of previous experiments and ab initio calculations, the geometry of the C1s((-1)) pi*((1)) intermediate states can be predicted in analogy with e.g. the N-2, CO2 and N2O molecules. (C) 2009 Elsevier B.V. All rights reserved. (Less)