“Physics of Glasses, Amorphous Solids and Disordered Crystals” Prof. Miguel Angel Ramos PROGRAMME 1. INTRODUCTION TO NON-CRYSTALLINE SOLIDS Introduction. Definitions. Types of disorder. Amorphous solids and glasses. 2. PREPARATION METHODS AND APPLICATIONS OF AMORPHOUS MATERIALS Melt quenching. Melt spinning. Splat cooling. Thermal evaporation. Chemical vapour deposition. Sol- gel processes. Irradiation. Pressure-induced amorphization. Applications of amorphous materials. 3. THE GLASS STATE AND THE GLASS TRANSITION a) The glass transition phenomenon: Thermodynamic and kinetic aspects. Is the glass transition a true thermodynamic phase transition? The Kauzmann paradox. The Angell’s classification: Strong and fragile glass-forming liquids. Relaxation processes in glasses and supercooled liquids. b) Old and current theories for the glass transition. The energy landscape. 4. STRUCTURE OF AMORPHOUS SOLIDS The Zachariasen model of Continuous Random Network. Experimental techniques: X-ray and neutron diffraction. The radial distribution function. Short-range and intermediate-range order. The First Sharp Diffraction Peak.

“Physics of Glasses, Amorphous Solids and Disordered Crystals” Prof. Miguel Angel Ramos PROGRAMME 5. ATOMIC DYNAMICS IN AMORPHOUS SOLIDS Consequences of the lack of long-range order. Experimental techniques: Raman, Infrared and Brillouin spectroscopies. Inelastic neutron and X-ray scattering. The “boson peak”. Computational methods and molecular dynamics simulations. 6. LOW-TEMPERATURE PROPERTIES OF NON-CRYSTALLINE SOLIDS Universal “glassy anomalies” at low temperatures. Specific heat. Thermal conductivity. Acoustic and dielectric properties. The Tunnelling Model. The Soft Potential Model. 7. OTHER FAMILIES OF GLASSES AND DISORDERED CRYSTALS Quasicrystals. Plastic crystals and orientational glasses. Biomolecules and “Soft Matter”.

BIBLIOGRAPHY Fundamental textbooks:  S. R. Elliott, Physics of Amorphous Materials, 2nd ed. (Longman, 1990).  R. Zallen, The Physics of Amorphous Solids, (Wiley, 1983).  I. Gutzow, J. Schmelzer, The Vitreous State (Springer, 1995).  S. A. Brawer, Relaxation in viscous liquids and glasses (Am. Ceram. Soc., 1983).  W. A. Phillips (ed.), Amorphous Solids: Low Temperature Properties (Topics in Current Physics, Vol. 24, Springer, 1981). Specialized review articles and books:  Science 267 (1995), pp  P. G. Debenedetti and F. H. Stillinger, Nature 410, 259 (2001).  P. Esquinazi (ed.), Tunneling Systems in Amorphous and Crystalline Solids (Springer, 1998).  A. Cavagna, Physics Reports 476, (2009).

1. INTRODUCTION TO NON-CRYSTALLINE SOLIDS * What is a solid ?  A substance that does not flow, that is, its viscosity is:   poise Maxwell equation for shear relaxation time:  = G  

Types of disorder: Topological disorder Spin disorder Vibrational disorder Substitutional disorder

CRYSTALAMORPHOUS solidity  crystallinity !

 = G  

Differential Scanning Calorimetry Differential Thermal Analysis

nucleation rate rate of crystal growth

v = L (T m -T) / 3  a 2  T m velocity of crystallization:

DEFINITIONS: AMORPHOUS SOLIDS  NON-CRYSTALLINE SOLIDS are solid materials that do NOT possess the long-range order (periodicity) characteristic of crystals. GLASSES are amorphous solids obtained by cooling a melt. Or, more generally, amorphous solids that exhibit a glass transition when heated.

DEFINITIONS and CLASSIFICATIONS Perfect crystal: solid for which the atoms (or groups of atoms) exhibit a perfect periodicity towards the infinity. –i.e. long-range translational order  Disordered solids NON-CRYSTALLINE SOLIDS = AMORPHOUS SOLIDS Solids which do not possess long-range translational order GLASSES: amorphous solids exhibiting a “glass transition” Cuasicrystals = aperiodic crystals (“ordered in 6-D”)

Preparation methods of amorphous materials  Melt quenching  Splat cooling  Melt spinning  Thermal evaporation  Sputtering  Glow-discharge decomposition  Chemical vapor deposition  Sol-gel processes  Electrolytic deposition  Reaction amorphization  Irradiation  Pressure-induced amorphization  Solid-state diffusional amorphization 2. PREPARATION METHODS AND APPLICATIONS OF AMORPHOUS MATERIALS

melt quenchingsplat coolingthermal evaporation melt spinning ~ K/s~ 10 2 K/s~ 10 5 K/s~ K/s ~ 10 7 K/s

thermal evaporation sputtering glow-discharge decomposition

sol-gel processes

Preparation methods of amorphous materials  Melt quenching  Splat cooling  Melt spinning  Thermal evaporation  Sputtering  Glow-discharge decomposition  Chemical vapor deposition  Sol-gel processes  Electrolytic deposition  Reaction amorphization  Irradiation  Pressure-induced amorphization  Solid-state diffusional amorphization 2. PREPARATION METHODS AND APPLICATIONS OF AMORPHOUS MATERIALS

APPLICATIONS OF AMORPHOUS SOLIDS Type of amorphous solid Representative material ApplicationSpecial properties used Oxide glass(SiO 2 ) 1-x (Na 2 O) x + Other oxides Window glass Artistic, commercial, chemical glassware… Transparency, solidity, formability as large sheets Oxide glass(SiO 2 ) 1-x (Ge 2 O) x Fiber optic waveguides for communication networks Ultratransparency, purity, formation as uniform fibers Organic polymerPolystyrene, PVC, PMMA.. Structural materials, plastics Strength, light weight, ease of processing Amorphous semiconductor Te 0.8 Ge 0.2 Computer-memory elements Electric-field induced am  cryst transformations Amorphous semiconductor Si 0.9 H 0.1 Solar cellsPhotovoltaic optical propt. Large-area thin films Metallic glassFe 0.8 B 0.2 Transformer coresFerromagnetism, low losses formation as long ribbons Chalcogenide (S, Se, Te) glasses Se, As 2 Se 3 XerographyPhotoconductivity, formability as large-area films

APPLICATIONS OF AMORPHOUS SOLIDS Type of amorphous solid Representative material ApplicationSpecial properties used Oxide glass(SiO 2 ) 1-x (Na 2 O) x + Other oxides Window glass Artistic, commercial, chemical glassware… Transparency, solidity, formability as large sheets (the most familiar format of glasses) It exemplifies 2 general aspects common to many applications of a-solids: 1) These materials harden continuously with decreasing T approaching T g  ability to control the viscosity and thereby the flow properties 2) Glasses much better than crystals when an application demands large- area sheets or films In addition, for window-glass like applications: 1)The glass is optically ISOTROPIC while the crystal is anisotropic 2) The glass is a far better thermal insulator, and a window should keep heat and cold out as well as let light in!

APPLICATIONS OF AMORPHOUS SOLIDS Type of amorphous solid Representative material ApplicationSpecial properties used Oxide glass(SiO 2 ) 1-x (Ge 2 O) x Fiber optic waveguides for communication networks Ultratransparency, purity, formation as uniform fibers They are glass-wires transmitting an optical signal (EM wave, 2  Hz) with extremely low losses CLAD CORE n CLAD < n CORE

APPLICATIONS OF AMORPHOUS SOLIDS Type of amorphous solid Representative material ApplicationSpecial properties used Organic polymerPolystyrene, PVC, PMMA.. Structural materials, plastics Strength, light weight, ease of processing The most ubiquitous amorphous solids in present-day society are organic glasses: polymeric (amorphous) solids composed of entangled long-chain organic molecules

APPLICATIONS OF AMORPHOUS SOLIDS Type of amorphous solid Representative material ApplicationSpecial properties used Amorphous semiconductor Te 0.8 Ge 0.2 Computer-memory elements Electric-field induced am  cryst transformations It exploits the phenomenon of electric-field induced crystallization of the glass. Both crystalline and amorphous forms of Te-Ge are semiconductors, but with different energy gaps. A current pulse converts the low- conductivity glass to a high-conductivity crystal (  it pulses the material from OFF to ON state!). The crystal-glass transition is reversible.

APPLICATIONS OF AMORPHOUS SOLIDS Type of amorphous solid Representative material ApplicationSpecial properties used Amorphous semiconductor Si 0.9 H 0.1 Solar cellsPhotovoltaic optical propt. Large-area thin films a-Si can be prepared in large-area films much cheaper than c-Si. Because of disorder, a-Si has a much higher optical absorption than c-Si. In fact, it is not pure a-Si the material of interest for solar-cell technology applications but rather the hydogenated [a-Si:H]. The role of H is to eliminate electronic defects.

APPLICATIONS OF AMORPHOUS SOLIDS Type of amorphous solid Representative material ApplicationSpecial properties used Metallic glassFe 0.8 B 0.2 Transformer coresFerromagnetism, low losses formation as long ribbons They combine high saturation magnetization with the useful property of being “magnetically soft” (i.e. low coercivity, easily magnetized by small magnetic fields), at the same time they remain mechanically quite hard! Magnetic glasses are isotropic, without a crystalline axis of easy magnetization  allows to rotate the magnetization direction at a much smaller energy cost than in crystals. Other potential applications: magnetic disks memories, read/write recorder heads…

APPLICATIONS OF AMORPHOUS SOLIDS Type of amorphous solid Representative material ApplicationSpecial properties used Chalcogenide (S, Se, Te) glasses Se, As 2 Se 3 XerographyPhotoconductivity, formability as large-area films

xerography