Computer simulations of laser ablation from simple metals to complex metallic alloys [Elektronische Ressource] = Computersimulationen der Laserablation von einfachen Metallen hin zu komplexen metallischen Phasen / vorgelegt von Steffen Sonntag

Steffen Sonntag

Sujets

• Physik

Informations

• Publié par: universitat_stuttgart
• Publié le: 01 janvier 2010
• Nombre de lectures: 48
• Langue: Deutsch
• Poids de l'ouvrage: 2 Mo

Extrait

Computer Simulations of
Laser Ablation from Simple Metals
to Complex Metallic Alloys
Computersimulationen der Laserablation von
einfachen Metallen hin zu Komplexen
Metallischen Phasen
Von der Fakultät für Mathematik und Physik der
Universität Stuttgart zur Erlangung der Würde eines Doktors der
Naturwissenschaften (Dr. rer. nat.) genehmigte Abhandlung
Vorgelegt von
Steffen Sonntag
aus Öhringen
Hauptberichter: Prof. Dr. H.-R. Trebin
Mitberichter: Prof. Dr. C. Holm
Tag der mündlichen Prüfung: 21. Februar 2011
Institut für Theoretische und Angewandte Physik
der Universität Stuttgart
2010Theresia und JosefContents
Abstract xiii
Zusammenfassung in deutscher Sprache xv
1 Introduction 23
2 Theoretical Background 27
2.1 Metal Physics . . . . . . . . . . . . . . . . . . . . . . . . . . 27
2.1.1 Metals and Alloys . . . . . . . . . . . . . . . . . . . 33
2.1.2 Electrons in Metals . . . . . . . . . . . . . . . . . . . 35
2.2 The Ablation Process . . . . . . . . . . . . . . . . . . . . . 38
2.2.1 Heat Conduction . . . . . . . . . . . . . . . . . . . . 41
2.3 The Two-Temperature Model (TTM) . . . . . . . . . . . . . 43
2.3.1 The Extended Two–Temperature Model (eTTM) . . 46
3 Numerical Methods and Implementation 49
3.1 Atomistic Computer Simulations . . . . . . . . . . . . . . . 49
3.2 The Direct Approach: Rescaling the Kinetic Energy . . . . 54
3.3 A Hybrid Approach with the Two–Temperature Model . . . 56
4 Calculations and Results 61
4.1 Pre–Survey: The Phase Diagram of Aluminum . . . . . . . 62
4.2 Laser Ablation in Isotropic Materials: Metals . . . . . . . . 68
4.2.1 Parameters for Aluminum . . . . . . . . . . . . . . . 70
4.2.2 Laser Induced Surface Melting . . . . . . . . . . . . 70
4.2.3 The Ablation Threshold . . . . . . . . . . . . . . . . 77
4.3 Non–reflecting Boundary Conditions . . . . . . . . . . . . . 80
4.4 Inhomogeneous Ablation Experiments on Metals . . . . . . 82
4.4.1 The Ablation Threshold . . . . . . . . . . . . . . . . 84
4.4.2 Cluster Detection in the Plume . . . . . . . . . . . . 85
4.4.3 Velocity and Angular Distribution . . . . . . . . . . 87
vvi Contents
4.5 Laser Ablation in Anisotropic Materials: A Case Study . . 92
4.5.1 Parameters for Al Co . . . . . . . . . . . . . . . . 9313 4
4.5.2 Laser Induced Surface Melting . . . . . . . . . . . . 95
5 Conclusion and Outlook 99
A Used Software 103
A.1 IMD . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 103
A.2 Rapidminer . . . . . . . . . . . . . . . . . . . . . . . . . . . 104
Bibliography 109
List of Publications 125List of Symbols
2hω i Averaged squared phonon frequency, page 44
α Inverse absorption length, page 55
γ Electron constant of specific heat, page 41
κ Electron–phonon coupling constant, page 41
λ(T) Electron–phonon enhancement parameter, page 44
D(E) Density of states, page 37
T Translation opererator, page 28Ri
τ Electron–electron scattering time, page 40ee
τ Electron–lattice relaxtion time, page 41el
C Specific heat of the electrons, page 38el
C Specific heat of the lattice, page 43l
d Ablation depth, page 77abl
d Melting depth, page 95melt
F Ablation threshold, page 77th
F Melting threshold, page 96melt
K Thermal conductivity of the electrons, page 38el
K Thermal conductivity of the lattice, page 43l
S(x,t) Laser power density, page 43
v Speed of sound, page 79s
viiviii List of Symbols
−δY(N) Yield distribution function, page 86
IMD ITAP Molecular Dynamics, page 51
CMA Complex Metallic Alloy, page 34
EAM Embedded atom method, page 53
FD Finete differences, page 58
MD Molecular dynamics, page 50
QC Quasicrystal, page 35
TTM Two–Temperature model, page 43List of Figures
2.1 Elementary cells and Wigner–Seitz cell. . . . . . . . . . . 29
2.2 Time scales of the ablation process. . . . . . . . . . . . . . . 39
2.3 Analytic solutions for the simplified TTM. . . . . . . . . . . 46
3.1 Molecular dynamics scheme. . . . . . . . . . . . . . . . . . . 52
3.2 Schematic representation of the hybrid simulation. . . . . . 58
4.1 Solid–liquid transition with MD simulations.. . . . . . . . . 63
4.2 Simulation scheme for the phase diagram. . . . . . . . . . . 64
4.3 Vapor–liquid transition with MD simulations. . . . . . . . . 65
4.4 Calculated phase diagram of aluminum. . . . . . . . . . . . 66
4.5 Phase diagrams for copper, iron and Ni Al. . . . . . . . . . 683
4.6 Partitioning scheme of the simulated volume. . . . . . . . . 69
4.7 Contour plot of the electronic temperature. . . . . . . . . . 71
4.8 Electron and lattice temperature at different times. . . . . . 72
4.9 Electron lattice relaxation.. . . . . . . . . . . . . . . . . . . 73
4.10 Contour plot of the lattice temperature. . . . . . . . . . . . 74
4.11 Contour plot of the mass density. . . . . . . . . . . . . . . . 76
4.12 Melting depth for homogeneous fluence. . . . . . . . . . . . 76
4.13 Contour plot of the density in case of ablation. . . . . . . . 77
4.14 Ablation depth for homogeneous pulses. . . . . . . . . . . . 79
4.15 Contour plot of the pressure. . . . . . . . . . . . . . . . . . 80
4.16 Non–reflecting boundary conditions. . . . . . . . . . . . . . 82
4.17 Melting and ablation depth for inhomogeneous pulses. . . . 84
4.18 Cluster size distribution in the ablated plume. . . . . . . . . 86
4.19 Velocity distribution in the plume. . . . . . . . . . . . . . . 88
4.20 Scheme of the angular distributions. . . . . . . . . . . . . . 89
4.21 Angular cluster distribution in the plume. . . . . . . . . . . 91
4.22 Real space snapshot of the ablated volume. . . . . . . . . . 91
4.23 Several unit cells of Al Co . . . . . . . . . . . . . . . . . . 9413 4
4.24 Melting depth for Al Co . . . . . . . . . . . . . . . . . . . 9513 4
ixx List of Figures
A.1 Screenshot of the Rapidminer work space. . . . . . . . . . . 106