Contents. Overview and Fundamentals

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1 Contents Part I Overview and Fundamentals 1 Introduction Conventional Laser Processing Laser Chemical Processing Thermal Activation Non-thermal Activation Local and Large-Area Processing Comparison of Techniques Planar and Non-planar Processing Thermal, Photophysical, and Photochemical Processes Excitation Mechanisms, Relaxation Times Thermal Processes Photochemical Processes Photophysical Processes A Simple Model Chemical Relaxation The Heat Equation The Source Term Dimensionality of Heat Flow Kirchhoff and Crank Transforms Phase Changes Limits of Validity Selective Excitations of Molecules Electronic Excitations Infrared Vibrational Excitations Surface Excitations External Photoeffect Internal Photoeffect Electromagnetic Field Enhancement, Catalytic Effects Adsorbed Molecules ix

2 x Contents 3 Reaction Kinetics and Transport of Species Photothermal Reactions Photochemical Reactions The Concentration of Species Basic Equations Dependence of Coefficients on Temperature and Concentration Heterogeneous Reactions Stationary Equations Transport Limitations Dynamic Solutions Heterogeneous Versus Homogeneous Activation Combined Heterogeneous and Homogeneous Reactions The Boundary-Value Problem Approximate Solutions Homogeneous Photochemical Activation Nucleation and Cluster Formation Homogeneous Processes Classical Kinetics Droplets Within a Laser Beam Transport of Clusters, Thermophoresis, Chemophoresis Fragmentation of Particles Nanoparticle Formation by Pulsed-Laser Ablation Gaseous Ambient Liquid Ambient Heterogeneous Processes Nucleation in LCVD Condensation of Clusters from Vapor/Plasma Plumes Nanotube Formation by Laser-CVD Shaping of Nanoparticles Cluster Formation Within Solid Surfaces Lasers, Experimental Aspects, Spatial Confinement Lasers CW Lasers, Gaussian Beams Pulsed and High-Power CW Lasers Semiconductor Lasers Experimental Aspects Micro-/Nanoprocessing The Reaction Chamber; Typical Setup Large-Area Processing Substrates Confinement of the Excitation The Thermal Field Non-thermal Substrate Excitations... 99

3 Contents xi Gas-, Liquid- and Adsorbed-Phase Excitations Plasma Formation Material Damages Non-linearities Optical Near-Field and Field-Enhancement Effects Part II Temperature Distributions and Surface Melting 6 General Solutions of the Heat Equation The Boundary-Value Problem The Attenuation Function, f (z) Boundary and Initial Conditions Analytical Solutions Pulse Shapes Single Rectangular Pulse Triangular Pulse Smooth Pulse Multiple-Pulse Irradiation Beam Shapes Circular Beam Rectangular Beam Uniform Illumination Characteristics of Temperature Distributions Center-Temperature Rise Width of Distribution Numerical Techniques Semi-infinite Substrates The Center-Temperature Rise Gaussian Beam Circular Laser Beam Rectangular Beam Stationary Solutions for Temperature-Independent Parameters Surface Absorption Finite Absorption Stationary Solutions for Temperature-Dependent Parameters Scanned CW-Laser Beam Pulsed-Laser Irradiation Gaussian Intensity Profile Uniform Irradiation Dynamic Solutions for Temperature-Dependent Parameters Infinite Slabs Strong Absorption Thermally Thin Film Scanned CW Laser

4 xii Contents 8.2 The Influence of Interferences Coupling of Optical and Thermal Properties Non-uniform Media Continuous Changes in Optical Properties Absorption of Light in Multilayer Structures Thin Films Two-Layer Structures Three-Layer Systems Temperature Distributions for Large-Area Irradiation Stationary Solutions for Thin Films Dynamic Solutions Temperature Distributions for Focused Irradiation Strong Film Absorption Finite Film Absorption The Ambient Medium Influence on Substrate Temperature Indirect Heating Free Convection Temperature Jump Surface Melting Temperature Distributions, Interface Velocities Boundary Conditions Temperature Dependence of Parameters Solidification Process Optimization Convection Surface Deformations Surface Patterning Welding Ultrashort-Pulse Laser Welding Liquid-Phase Expulsion Part III Material Removal 11 Vaporization, Plasma Formation Energy Balance One-Dimensional Model Stationary Evaporation Non-stationary Evaporation Optimal Conditions Knudsen Layer, the Recoil Pressure Influence of a Liquid Layer Limitations of Model Calculations Plasma Formation

5 Contents xiii Ionization Optical Properties of Plasmas Optical Breakdown Laser-Supported Absorption Waves (LSAW) Laser-Supported Combustion Waves (LSCW): I p I I d Laser-Supported Detonation Waves (LSDW): I I d Superdetonation Abrasive Laser Machining Cutting, Drilling, Shaping Non-metals Scribing, Marking, Engraving Comparison of Techniques Nanosecond-Laser Ablation Surface Patterning Ablation Mechanisms Models Photothermal Surface Ablation Influence of Screening Post-pulse Ablation Interactions Below Threshold The Threshold Fluence, φ th Thin Films Ablation Rates Dependence on Photon Energy and Fluence Dependence on Pulse Duration Influence of Spot Size, Screening Dependence on Pulse Number Influence of an Ambient Atmosphere Photothermal Volume Decomposition Photochemical Ablation Dissociation of Polymer Bonds Defect-Related Processes, Incubation Photophysical Ablation Long Pulses Short Pulses Thermal Versus Photochemical and Photophysical Ablation Thermo- and Photomechanical Ablation Basic Equations Material Damage, Debris Strong Absorption Finite Absorption Debris

6 xiv Contents 13 Ultrashort-Pulse Laser Ablation Material Patterning and Damage Wide-Bandgap Materials, Glasses, Polymers Nanostructures Overview on Interaction Mechanisms Low Fluence Photoexcitations Thermal Volume Decomposition Thermal Versus Photophysical Ablation Ablation Dynamics Molecular Dynamics (MD) Simulations The Two-Temperature Model Electron Transport, Damage Thresholds Melting, Surface Deformation and Ablation Processing of Metals and Semiconductors Multiphoton- and Avalanche Ionization Dielectrics Coulomb Explosion Processing of Dielectrics Comparison of Nanosecond and Ultrashort-Pulsed Laser Ablation Etching of Metals and Insulators Photochemistry of Precursor Molecules Halides Halogen Compounds Concentration of Reactive Species Ballistic Approximation Diffusion Influence of the Reaction Chamber Gas-Phase Recombination Gas-Phase Heating Dry-Etching of Metals Spontaneous Etching Systems Diffusive Etching Systems Passivating Reaction Systems Dry-Etching of Inorganic Insulators SiO 2 Glasses Oxides Wet-Etching Front-Side Etching Backside Etching Etching of Semiconductors Dark Etching Laser-Induced Etching of Si in Cl

7 Contents xv Surface Patterning Photochemical and Thermal Etching Chlorine Radicals Electron Hole Pairs Crystal Orientation and Doping Nanopatterning Si in Halogen Compounds Si in XeF Si in SF Microscopic Mechanisms Photochemical Etching Combined Photochemical and Thermal Etching Thermal Etching Dry-Etching of Compound Semiconductors III V Compounds Laser Etching of Atomic Layers Dopants, Impurities, and Defects Wet-Etching Silicon Compound Semiconductors Interpretation of Results Spatial Resolution, Waveguiding Part IV Material Deposition 16 Laser-CVD of Microstructures Precursor Molecules Pyrolytic LCVD of Spots Deposition from Halides Deposition from Carbonyls Modelling of Pyrolytic LCVD Gas-Phase Processes The Coupling Between T (x) and h(x) Temperature Distributions on Circular Deposits Simulation of Pyrolytic Growth Photolytic LCVD Metals Other Materials Process Limitations Growth of Fibers In Situ Temperature Measurements Microstructure and Physical Properties Kinetic Studies

8 xvi Contents Silicon Carbon Gas-Phase Transport The Coupling of Fluxes Thermal Diffusion (Soret Effect) Simulation of Growth Direct Writing Characteristics of Pyrolytic Direct Writing Dependence on Laser Parameters and Substrate Material Electrical Properties Temperature Distributions in Direct Writing Center-Temperature Rise D Approach, κ Numerical Solutions Simulation of Direct Writing D Model Comparison with Experimental Data D Model Photophysical LCVD Applications of LCVD in Microfabrication Planar Substrates Non-planar Substrates, 3D Objects Thin-Film Formation by Laser-CVD Direct Heating Stationary Solutions Non-stationary Solutions Pyrolytic Processing Rates Diffusion Recombination Photolytic Processing Rates Metals Deposition from Metal Halides Deposition from Alkyls and Carbonyls Semiconductors Photodecomposition of Silanes Crystalline Ge and Si Amorphous Hydrogenated Silicon (a-si:h) Compound Semiconductors Carbon Insulators Oxides Nitrides Heterostructures Comparison of LCVD and Standard Techniques

9 Contents xvii 20 Adsorbed Layers, Laser MBE Fundamental Aspects Influence of Laser Light Deposition from Adsorbed Layers Vacuum Gaseous Ambient Combined Laser and Molecular/Atomic Beams Laser-MBE Laser-ALE Laser-OMBD Laser-Focused Atomic Deposition Liquid-Phase Deposition, Electroplating Liquid-Phase Processing Without an External EMF Thermal Decomposition Electroless Plating Metal Liquid Interfaces Semiconductor Liquid Interfaces Further Experimental Examples Electrochemical Plating Jet-Plating Thin-Film Formation by Pulsed-Laser Deposition and Laser-Induced Evaporation Experimental Requirements Congruent and Incongruent Ablation Targets Uniform Ablation Cross-Beam PLD Volume and Surface Processes, Film Growth Plasma and Gas-Phase Reactions Substrate Temperature, Laser-Pulse-Repetition Rate Energy of Species Particulates Chemical Composition and Thickness of Films Overview of Materials and Film Properties High-Temperature Superconductors Non-reactive Deposition Reactive Deposition Heterostructures Metastable Compounds, Mixed Systems Films with Step-Like Morphology Buffer Layers, Applications Metals, Semiconductors, and Insulators Metals Semiconductors

10 xviii Contents Carbon Films Insulators Heterostructures Nanostructured Materials Nanoparticle films Nanocomposites Organic Materials MAPLE Laser-Induced Forward Transfer Transfer films Part V Material Transformations, Synthesis and Structure Formation 23 Material Transformations, Laser Cleaning Transformation Hardening Laser Annealing, Recrystallization Ion-Implanted Semiconductors Thin Films Glazing Shock Hardening Surface Polishing Transformations Within Bulk Materials Non-erasable Marking Gratings Waveguides D-Optical Storage Laser Cleaning Adhesion Forces Dry Cleaning Steam Cleaning Wet Cleaning Matrix Cleaning Doping Solid-Phase Diffusion Liquid-Phase Transport Sheet Doping Silicon Compound Semiconductors Local Doping Laser Implantation Cladding, Alloying, and Synthesis Laser-Assisted Cladding and Sintering D Rapid Prototyping Alloying

11 Contents xix Laser Surface Alloying Formation of Metastable Materials Silicides Synthesis Thin Films Fibers Oxidation, Nitridation, and Reduction Basic Mechanisms Very Thin Films Thin Films Thick Films Influence of Laser Light Metals Photothermal Oxidation Photochemical Contributions Oxidation by Pulsed-Laser Plasma Chemistry Nitridation Elemental Semiconductors Photothermal Oxidation of Si Photochemically Enhanced Oxidation of Si Nitridation of Silicon Compound Semiconductors Summary Oxide Transformation, Reoxidation Silicon Oxide Reduction and Metallization of Oxides Qualitative Description Oxidic Perovskites and Related Materials Superconductors Transformation and Functionalization of Organic Materials Surface Modification of Polymers Laser-Enhanced Adhesion Swelling, Amorphization, Crystallization Photochemical Exchange of Species Chemical Degradation Chemical Transformations Within Thin Films and Bulk Materials Laser Lithography Maskless Techniques Decomposition of Precursor Films D Photopolymerization Laser-LIGA, LAN

12 xx Contents 28 Instabilities and Structure Formation Coherent and Non-coherent Structures Equations Stability Coherent Structures Non-coherent Structures Ripple Formation Interference Pattern Distribution of Energy Feedback Comparison of Experimental and Theoretical Results Ripples Generated by Ultrashort-Laser Pulses Embedded Periodic Structures Spatio-Temporal Oscillations Zero Isoclines Instabilities in Laser-Induced Oxidation Explosive Crystallization Exothermal Reactions Instabilities in Direct Writing Discontinuous Deposition and Bistabilities Instabilities and Structure Formation in Laser Ablation Fundamental Aspects Conical and Columnar Structures Hydrodynamic Instabilities Kelvin Helmholtz Instabilities Rayleigh Taylor Instabilities Surface Corrugations, Droplets Stress-Related Instabilities Technological Aspects Part VI Diagnostic Techniques, Plasmas 29 Diagnostic Techniques Characterization of Laser-Beam Profiles Homogenization of Laser Beams Diffractive Methods Reflective Methods Refractive Methods Deposition, Etch, and Ablation Rates Optical Techniques Other Techiques Temperature Measurements Photoelectric Pyrometry Other Optical Techniques Other Techniques

13 Contents xxi 29.5 Analysis of Surfaces and Thin Films Surface Topologies, Microstructures Transport Measurements Analysis of Species and Plasmas Precursor and Product Species Optical Spectroscopy Mass Spectrometry MALDI, LAESI Species in Vapor and Plasma Plumes Species at Subthreshold Fluences Atomic and Molecular Neutrals Electrons and Ions Plasma Radiation, X-Rays Clusters and Fragments Plume Expansion in Vacuum Spherical Plume Elliptical Plume Mass- and Ion-Flux Measurements Plume Expansion in Gases, Shock Waves Point Blast Model Combined Propagation of Plume and SW Formation of Nanoparticles Comparison with Experimental Investigations Optical Breakdown in Liquids, Cavitation Absorbing Targets Transparent Media Part VII Lasers in Medicine, Biotechnology and Arts 31 Lasers in Medicine and Biotechnology Medical Applications Ophthalmology Dermatology and Surgery Photodynamical Therapy Prosthesis Biotechnology Laser Microdissection Micro-/Nanosurgery and Manipulation Biopolymers Interaction Mechanisms Chemical Effects Restoration and Conservation of Artworks Cultural Heritages Metal Artworks Oil-paintings, Frescos

14 xxii Contents 32.2 Analysis and Origin of Artworks Architecture, Modern Artwork Appendix A Definitions and Symbols A.1 Symbols and Conversion Factors A.2 Abbreviations, Acronyms Appendix B Mathematical Functions and Relations Appendix C Tables References Index

Laser Processing of Materials

Springer Series in Materials Science 139 Laser Processing of Materials Fundamentals, Applications and Developments Bearbeitet von Peter Schaaf 1st Edition. 2010. Buch. XIV, 234 S. Hardcover ISBN 978 3