Columnar-to-Disk Structural Transition in Nanoscale(SiO2)NClusters

Abstract

Extensive large-scale global optimizations refined by ab initio calculations are used to propose SiO 2 N N 14-27 ground states. For N < 23 clusters are columnar and show N-odd-N-even stability, energetically and electronically. At N 23 a columnar-to-disk structural transition occurs reminiscent of that observed for Si N . These transitions differ in nature but have the same basis, linking the nanostructural behavior of an element (Si) and its oxide (SiO 2 ). Considering the impact of devices based on the nanoscale manipulation of Si=SiO 2 the result is of potential technological importance. DOI: 10.1103/PhysRevLett.95.185505 PACS numbers: 61.46.+w, 36.40.Ei, 36.40.Mr, 68.65.2k The technological importance of nanoscale silica (SiO 2 ) can hardly be overstated considering its established utilization in microelectronics, catalysis, and composite materials and its promise in the emerging field of photonics. Although much experimental and theoretical work has focused upon the stabilities and structures of the many silica bulk polymorphs and their surfaces, the low energy structures and potential energy surface (PES) of nanoscale SiO 2 clusters is relatively unknown. In this Letter we provide the beginnings of an energetic baseline of the complex PES of nanoscale SiO 2 by finding the lowest energy forms of silica for SiO 2 N N 14-27 providing new limits on the stability of this centrally important material in the physical, chemical, and geophysical sciences. The clusters we study all have at least one dimension between 1 and 2.5 nm and are all substantially lower in energy than any previously reported. Our results strongly indicate that one-dimensional columnar structures are energetically favored up to a length scale of at least 2 nm where upon a transition to two-dimensional trigonal disklike structures occurs at N 23. The transition is characterized by sharp changes in measures of the structural form, electronic structure, and bonding topology of the cluster series, but appears smooth with respect to cluster energies. The structural transition in SiO 2 N clusters is compared to that known for clusters of its parent element Si N [1]. In both cases for N 23-25 a structural transition from elongated to more compact forms appears to occur in the thermodynamically preferred clusters [2]. Usually oxides and their parent elements display different but complementary physical and chemical properties and typically bear little structural relation to one another. Our finding that, at the nanoscale, the size-dependent structural behavior of SiO 2 and its parent element follow a similar general pattern is at once relatively unexpected and fundamentally suggests an inherent link between the two materials. Because of the immense dependence on the combined structural and physical properties of both nanoscale Si and SiO 2 in electronic and optical devices, our demonstration of such a connection is of potential significant technological importance.Although relatively small, M 20 homogeneous clusters of low atomic weight atoms are...

First-principles identification of two- and four-membered-ring hybrid structures of silica nanorings

“…For 11 < n < 22, the 2-4MR-NCs are the most stable structures, whereas the NRs made up of 2-4MR hybrid units become the most favorable configurations when n > 24. It should be mentioned that these NRs and NCs are less stable than the ground state structures of silica clusters reported in prior literatures [13,14]. We calculated the relative energies of (SiO 2 ) 18 clusters with the models of Ref.…”

“…Although, these silica NRs and NRs are metalstable compared to the clusters reported in Ref. [14], they still have high plausibility in view of their energetic advantageous over the 2MR-based fibrous silica-w and NRs. The electronic structures and IR spectra predicted in this work are also available for identifying these NRs and NCs in experiments.…”

“…Theoretical studies of smallsize silica clusters have revealed diverse metastable building blocks with chain [5,6], ring [7][8][9], cage [10], and tubular [11,12] configurations formed by assembling two-, three-and four-membered rings (2MRs, 3MRs, and 4MRs). Using a global optimization algorithm, Bromley et al, predicted the ground state candidates for the (SiO 2 ) N cluster with N = 6-27 [13][14][15], which are more stable than the other available clusters of similar size. The structures of these clusters differ significantly from the network of silicon-centered corner-sharing SiO 4 tetrahedral of bulk silica where six-membered rings (6MRs) were found to be the most frequent.…”

First Principles Study on Sino (N=14-18) and Si10-Mom(M=1-8) Clusters

“…In recent years, the oxide silicon was investigated in both experiment [1,4,5,[10][11][12][13] and theory [10][11][12][13][14][15][16][17][18][19][20][21] for its broad prospect in the application. Desjardin and co-workers [1] studied oxidation of Si (111)-(7×7) surface by STM.…”

“…Lu and coworkers [17] obtained the results that the binding energies of Si m O n (m=1-5, n=1, 2m+1) clusters increase with the number of oxygen atoms, and the dissociation energies of these clusters are strong relative to the O and Si atoms ratio in one cluster. In addition, some researches focused on the (SiO 2 ) n nanoclusters [15,16,18]. A number of ringed, tube-like, cage shape, columnar and disk-like nanostructures based on SiO 2 unit were illustrated in detail.…”