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From nonmetal- and metal-chalcogen nanoclusters to chalcogenide nanotubes.

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Call No.	QD169.C5 B87 2005
Author	Burnin, Andrei.
Title	From nonmetal- and metal-chalcogen nanoclusters to chalcogenide nanotubes.
Date	2005
Abstract	A double-acceleration stage linear time of flight mass spectrometer (TOF MS) with Nd/YAG laser ablation cluster source was designed and constructed for cluster production, study and deposition. Cumulenic polycarbons SC n S ( n = 2-27) were generated by direct laser ablation of mixtures of elemental precursors. The resulting molecules were analyzed in the TOF MS. The spectra exhibited ideal odd/even intensity alternation attributed to their relative stability and the formation mechanism of the clusters. The structures and energies of the neutral and charged SC n S clusters were also studied by density functional theory at the B3LYP/6-311G* level. The computational results were consistent with the experimental observations. Evidence of sulfur poisoning of fullerene formation was observed and explained in terms of the existing model for fullerene formation and growth. Zinc sulfide clusters were produced by direct laser ablation and analyzed in the TOF MS, which indicated that clusters composed of 3, 6, 13 and 34 monomer units were ultrastable. The geometry and energies of Zn n S n and Zn n S n + ( n = 1-16) were obtained computationally at the B3LYP/6-311+G* level of theory. Small neutral and positive clusters have planar geometries; neutral three-dimensional clusters have the geometry of closed-cage polyhedra constructed from four- and six-membered rings of alternating metal and chalcogen atoms. Cationic three-dimensional clusters have structures with a pair of two-coordinated atoms. Physical properties of the clusters as a function of size are reported. The relative stability of the positive stoichiometric clusters provides a thermodynamic explanation for the relative intensities observed experimentally from the laser ablation of solid zinc sulfide and mixtures of elemental zinc and sulfur. Universal evidence of ultrastable clusters of the II-VI semiconductors has been obtained. The clusters include ZnS and analogous d 5 s 2 or d 10 s 2 metal sulfide and selenide clusters containing thirteen units of the monomer. Similar patterns of mass spectrometric cluster abundance were not observed in the metal-oxygen clusters or in clusters of metals from adjacent groups of the Periodic Table. Ab initio calculations indicate that the global minimum structure of the positive CdSe 13-mer is the same as for the ZnS 13-mer. The molecules include cavities of dimensions similar to fullerene. The concept of metal chalcogenide clusters was projected to the possibility of the synthesis of metal chalcogen nanotubes in a nontemplated fashion. Evidence of nascent zinc sulfide nanotube growth in an arc discharge process was obtained. A simple theoretical model of a single wall ZnS nanotube was optimized at a semiempirical level, demonstrating the stability.
Description	xii, 152 leaves : ill. (some col.) 28 cm.
Format	application/pdf
Advisor	Joseph J. BelBruno.
Subject	Chalcogenides. Nanotubes. ; Nanostructured materials.
College	Dartmouth College -- Department of Chemistry.
Issuing Body	Dartmouth Dissertations are made available through the Dartmouth Digital Library.
Degree	Thesis (Ph.D.)--Dartmouth College.
Copyright	All rights reserved. No part of this book may be reproduced in any form by any electronic or mechanical means without permission in writing from the author.
DOI	http://dx.doi.org/10.1349/ddlp.1645

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