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Identifier

uch.chemistry.msc//2004mpourmpakis

Title

Θεωρητική μελέτη ενθυλάκωσης μεταβατικών μετάλλων σε συσσωματώματα Si δημιουργία νανοσωλήνων

Alternative Title

Encapsulation of transition metal atoms by silicon clusters-Stabilization of silicon nanotubes

Creator

Mpourmpakis, Giannis

Abstract

The encapsulation of metal atoms within Si-based cage clusters leads to stable metal-encapsulated Si cage clusters (Si-cc). Using mainly DFT ab initio calculations at the level of the B3LYP approximation, we have studied the stability of Si-based cages and nanotubes stabilized by encapsulated transition metal atoms (TMAs). TBMD methods were also used for larger systems. It is demonstrated that the stabilization of these cages and tubes as well as their magnetic properties are strongly guided by a delicate interplay between the attainable symmetry of the system and the d-band filling of the encapsulated TMA. As a result, encapsulated TMAs of the early 3-d series lead to tubule structures of C6 symmetry and antiferromagnetic alignment between the magnetic moment of the TMA and that of the Si atoms. On the other hand, the encapsulated late 3-d elements lead to tubules of the C5 symmetry and to a ferromagnetic alignment of the metal and Si magnetic moments. Encapsulated Fe atoms (being close to the middle of the 3-d series) lead to tubule structures of either C6 or C5 symmetry. Especially for the systems with encapsulated Fe atoms a series of SinFe clusters were investigated to determine stable structures. Our results show that these clusters can form the building block for Fe-encapsulated Si-nanotubes. The Si10Fe and Si12Fe clusters are found to be very stable exhibiting large charge transfer and can lead to Si-based nanotubes of the type Si5nFen-1 and Si6nFen-1, respectively. The effect of Si-encapsulation on the magnetic properties of the Fe atom is also investigated. In the last section of the present work electronic and magnetic properties of small binary clusters containing one or two transition metal atoms are investigated using ab-initio calculations with a view to explain the experimentally observed magnetic enhancement/reduction in these systems. As the present investigations do not rely on spin-orbit effects, our results reveal the enhancement or reduction in the magnetic moment to depend on two main factors; namely geometry and, most importantly, the d-band filling. The results can be used as a guide in the experimental synthesis of high density magnetic grains.

Subject

silicon, Si nanotube, Si cluster, encapsulation, d band filling, magnetic enhancement, magnetic reduction, interplay, symmetry, ferromagnetic, antiferromagnetic, transition metal, πυρίτιο, νανοσωλήνας, κλουβί, ενθυλάκωση, κατάληψη d ζώνης, μαγνητική αύξηση, μαγνητική μείωση, σιδηρομαγνητισμός, αντισιδηρομαγνητισμός, μεταβατικά μέταλλα

Issue date

2004-04-01

Date available

2004-07-26

Collection

School/Department--School of Sciences and Engineering--Department of Chemistry--Post-graduate theses

Type of Work--Post-graduate theses

Permanent Link

https://elocus.lib.uoc.gr//dlib/f/d/3/metadata-dlib-2004mpourmpakis.tkl

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171

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