Size-dependent characterization of embedded Ge nanocrystals: structural and thermal properties

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dc.contributor.authorAraujo, LLen_AU
dc.contributor.authorGiulian, Ren_AU
dc.contributor.authorSprouster, DJen_AU
dc.contributor.authorSchnohr, CSen_AU
dc.contributor.authorLlewellyn, DJen_AU
dc.contributor.authorKluth, Pen_AU
dc.contributor.authorCookson, DJen_AU
dc.contributor.authorForan, GJen_AU
dc.contributor.authorRidgway, MCen_AU
dc.date.accessioned2009-10-01T23:56:46Zen_AU
dc.date.accessioned2010-04-30T05:07:34Zen_AU
dc.date.available2009-10-01T23:56:46Zen_AU
dc.date.available2010-04-30T05:07:34Zen_AU
dc.date.issued2008-09en_AU
dc.date.statistics2008-09en_AU
dc.description.abstractA combination of conventional and synchrotron-based techniques has been used to characterize the size-dependent structural and thermal properties of Ge nanocrystals (NCs) embedded in a silica (a-SiO2) matrix. Ge NC size distributions with four different diameters ranging from 4.0 to 9.0 nm were produced by ion implantation and thermal annealing as characterized with small-angle x-ray scattering and transmission electron microscopy. The NCs were well represented by the superposition of bulklike crystalline and amorphous environments, suggesting the formation of an amorphous layer separating the crystalline NC core and the a-SiO2 matrix. The amorphous fraction was quantified with x-ray-absorption near-edge spectroscopy and increased as the NC diameter decreased, consistent with the increase in surface-to-volume ratio. The structural parameters of the first three nearest-neighbor shells were determined with extended x-ray-absorption fine-structure (EXAFS) spectroscopy and evolved linearly with inverse NC diameter. Specifically, increases in total disorder, interatomic distance, and the asymmetry in the distribution of distances were observed as the NC size decreased, demonstrating that finite-size effects govern the structural properties of embedded Ge NCs. Temperature-dependent EXAFS measurements in the range of 15-300 K were employed to probe the mean vibrational frequency and the variation of the interatomic distance distribution (mean value, variance, and asymmetry) with temperature for all NC distributions. A clear trend of increased stiffness (higher vibrational frequency) and decreased thermal expansion with decreasing NC size was evident, confirming the close relationship between the variation of structural and thermal/vibrational properties with size for embedded Ge NCs. The increase in surface-to-volume ratio and the presence of an amorphous Ge layer separating the matrix and crystalline NC core are identified as the main factors responsible for the observed behavior, with the surrounding a-SiO2 matrix also contributing to a lesser extent. Such results are compared to previous reports and discussed in terms of the influence of the surface-to-volume ratio in objects of nanometer dimensions. © 2008, American Physical Societyen_AU
dc.identifier.articlenumber094112en_AU
dc.identifier.citationAraujo, L. L., Giulian, R., Sprouster, D. J., Schnohr, C. S., Llewellyn, D. J., Kluth, P., Cookson, D. J., Foran, G. J. & Ridgway, M. C. (2008). Size-dependent characterization of embedded Ge nanocrystals: structural and thermal properties. Physical Review B, 78(9), 094112. doi:10.1103/PhysRevB.78.094112en_AU
dc.identifier.govdoc1485en_AU
dc.identifier.issn1098-0121en_AU
dc.identifier.issue9en_AU
dc.identifier.journaltitlePhysical Review Ben_AU
dc.identifier.urihttp://dx.doi.org/10.1103/PhysRevB.78.094112en_AU
dc.identifier.urihttp://apo.ansto.gov.au/dspace/handle/10238/1909en_AU
dc.identifier.volume78en_AU
dc.language.isoenen_AU
dc.publisherAmerican Physical Societyen_AU
dc.subjectThermodynamic propertiesen_AU
dc.subjectGermaniumen_AU
dc.subjectSilicaen_AU
dc.subjectMolecular dynamics methoden_AU
dc.subjectCrystalsen_AU
dc.subjectSizeen_AU
dc.titleSize-dependent characterization of embedded Ge nanocrystals: structural and thermal propertiesen_AU
dc.typeJournal Articleen_AU
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