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CNAA / Theses / 2015 / June /

Phonon processes in graphene and silicon-based nanostructures


Author: Cocemasov Alexandr
Degree:doctor of Physics
Speciality: 01.04.02 - Theoretical and mathematical physics
Year:2015
Scientific adviser: Denis Nica
doctor habilitat, professor, Moldova State University
Institution: Moldova State University

Status

The thesis was presented on the 19 June, 2015
Approved by NCAA on the 7 October, 2015

Abstract

Adobe PDF document – 1.53 Mb / in romanian
Adobe PDF document – 1.48 Mb / in english

Thesis

CZU 539.21

Adobe PDF document 5.41 Mb / in english
140 pages

Keywords

phonons, electrons, nanolayer, superlattice, nanowire, graphene, lattice dynamics, modulation, thermal properties

Summary

Doctor thesis in physics, Chisinau, 2015. Introduction, 4 Chapters, General conclusions and recommendations, 200 References, 140 Pages, 66 Figures, 7 Tables. The results presented in the thesis are published in 33 scientific works.

Domain of study: physics of nanosystems.

Goal and objectives: investigation of phonon processes in graphene (single-, two-, three-layer graphene and twisted graphene) and silicon-based nanostructures (Si nanolayers, Si/Ge superlattices and Si-based modulated nanowires), and search of the methods for targeted control of their phonon properties.

Scientific novelty and originality: a Born – von Karman lattice dynamics model for nanolayers, planar superlattices, cross-section modulated nanowires and multilayer graphene with different atomic stacking was developed; the influence of shell material and cross-section modulation on phonon and electron processes in Si-based nanowires was studied; a theoretical approach for calculation of scattering time of phonons on interfaces of Si/Ge superlattices was developed and the influence of Si/Ge interface quality on phonon and thermal properties of these superlattices was investigated; the influence of different atomic stacking on phonon and thermal processes in multilayer graphene was studied.

Important scientific problem solved: it was demonstrated and investigated theoretically the possibility to control the phonon processes in two-layer graphene by rotation of graphene layers one against another around the axis perpendicular to the graphene plane. Theoretical model of lattice dynamics in rotated (“twisted”) two-layer graphene was developed.

Theoretical importance: were developed theoretical approaches for targeted control of phonon processes in graphene and silicon-based nanostructures. Practical significance: the practical implementation of the obtained theoretical results can lead to fabrication of new classes of nanostructures with specifically desired phonon properties.

Summary


1. PHONON AND ELECTRON PROCESSES IN GRAPHENE AND Si-BASED NANOSTRUCTURES
  • 1.1. Electron processes in Si-based nanostructures
  • 1.2. Theoretical models for phonons in nanostructures
  • 1.3. Phonon processes in Si-based nanostructures and graphene
  • 1.4. Conclusions to chapter 1 and objectives of the Thesis

2. PHONON PROCESSES IN Si NANOLAYERS AND PLANAR Si/Ge SUPERLATTICES
  • 2.1. Born – von Karman lattice dynamics model for nanolayers and planar superlattices
  • 2.2. Phonon processes in Si nanolayers
  • 2.2.1. Phonon energy spectra and scattering processes
  • 2.2.2. Phonon thermal conductivity
  • 2.3. Phonon processes in planar Si/Ge superlattices
  • 2.3.1. Phonon energy spectra
  • 2.3.2. Phonon scattering processes. Scattering on Si/Ge interface
  • 2.3.3. Phonon thermal conductivity
  • 2.4. Conclusions to chapter 2

3. PHONON AND ELECTRON PROCESSES IN Si-BASED MODULATED NANOWIRES
  • 3.1. Effective mass method and electron energy spectra in Si/SiO2 core/shell modulated nanowires
  • 3.2. Phonon processes in Si and Si/Ge core/shell modulated nanowires
  • 3.3. Electron-phonon interaction in Si-based modulated nanowires
  • 3.4. Conclusions to chapter 3
4. PHONON PROCESSES IN MULTILAYER GRAPHENE WITH DIFFERENT ATOMIC STACKING
  • 4.1. Theoretical model for phonons in multilayer graphene
  • 4.2. Phonon processes in single-layer, two-layer, three-layer graphene and graphite
  • 4.2.1. Energy spectra and vibrational properties
  • 4.2.2. Phonon scattering processes and thermal properties
  • 4.3. Twisted two-layer graphene. Engineering phonons with atomic plane rotations
  • 4.4. Conclusions to chapter 4

GENERAL CONCLUSIONS AND RECOMMENDATIONS