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![HYDROTHERMAL SYNTHESIS AND GROWTH OF
SINGLE CRYSTALS
• Ability of certain non-centrosymmetric crystals like quartz
to generate a voltage in response to applied mechanical
stress - Greek piezein - squeeze or press
• Effect reversible - piezoelectric crystals, subject to an
externally applied voltage, change shape by a small amount
• Compressive stress along [100] disturbs crystal symmetry
distorting SiO4 tetrahedra along 3-fold axis (not for [001] 2-
fold axis) creating charge asymmetry and electrical charges
across opposite crystal faces that generates a V
• Berlinite alpha-AlPO4 more polar Al-O larger than alpha-
quartz Si-O with which it is isoelectronic and isostructural -
use as a high frequency oscillator and mass monitor](https://image.slidesharecdn.com/crystalgrowth-220816085915-0a96b3f9/85/Crystal_growth-pptx-21-320.jpg)
Uploaded bySc Pattar
Crystal_growth.pptx
The document discusses several methods for growing single crystal materials, including Czochralski, Bridgman, Stockbarger, zone melting, and Verneuil techniques. The Czochralski method involves pulling a crystal seed from a melt of the material using precise temperature control. The Bridgman and Stockbarger methods use controlled solidification of a melt in a temperature gradient. Zone melting and hydrothermal crystal growth allow for purification or synthesis of crystals. These growth methods are important for producing large, high-quality single crystals for applications in electronics, optics, and other devices.
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Crystal_growth.pptx
- 1. GROWTH OF SINGLECRYSTALS MICRONS TO METERS • Vapor, liquid, solid phase crystallization techniques • Single crystals - meaningful materials property measurements • Single crystals allow measurement of anisotropic phenomena in crystals with symmetry lower than cubic (isotropic) • Single crystals important for fabrication of devices, like silicon chips, yttrium aluminum garnet solid state lasers, beta-beryllium borate for doubling and tripling the frequency of CW or pulsed laser light, lithium niobate optoelectronic switch for guiding light in miniature optical circuits, quartz crystal oscillators for ultra-sensitive nanogram mass monitors
- 2. LET'S GROW CRYSTALS •Key point to remember when learning how to be a crystal grower (incidentally, an exceptionally rare profession and extraordinarily well paid) • Many different techniques exist, hence one must think very carefully as to which method is the most appropriate for the material under consideration • Think also about size of crystal desired, stability in air, morphology or crystal habit required, orientation, doping, defects, impurities • So let's proceed to look at some case histories.
- 3. Pulling direction of seedon rod Heater CZOCHRALSKI Crucible Inert atmosphere under pressure prevents material loss and unwanted reactions Layer of molten oxide like B2O3 prevents preferential volatilization of one component - precise stoichiometry control Melt just above mp High viscosity low vapor pressure Growing crystal Crystal seed Counterclockwise rotation of melt and crystal being pulled from melt, helps maintain uniform T, composition and homogeneity of crystal growth
- 4. CZOCHRALSKI METHOD • Interestingcrystal pulling technique (but can you pronounce and spell the name!) • Single crystal growth from the melt precursor(s) • Crystal seed of material to be grown placed in contact with surface of melt • Temperature of melt held just above melting point, highest viscosity, lowest vapor pressure favors crystal growth • Seed gradually pulled out of the melt (not with your hands of course, special crystal pulling equipment is used)
- 5. CZOCHRALSKI METHOD • Seedgradually pulled out of the melt (not with your hands of course, special crystal pulling equipment is used) • Melt solidifies on surface of seed • Melt and seed usually rotated counterclockwise with respect to each other to maintain constant temperature and to facilitate uniformity of the melt during crystal growth, produces higher quality crystals, less defects • Inert atmosphere, often under pressure around growing crystal and melt to prevent any materials loss and undesirable reactions like oxidation, nitridation etc
- 6. GROWING BIMETALLIC SINGLECRYSTALS LIKE GaAs REQUIRES A MODIFICATION OF THE CZOCHRALSKI METHOD • Layer of molten inert oxide like B2O3 spread on top of the molten feed material to prevent preferential volatilization of the more volatile component of the bimetal melt • Critical for maintaining precise stoichiometry, e.g., Ga1+xAs and GaAs1+x when made rich in Ga and As, become p- and n-doped!!! • The Czochralski crystal pulling technique is invaluable for growing many large single crystals as a rod, to be cut into wafers and polished for various applications like silicon, germanium, lithium niobate • Utility of some single crystals made by Czochralski listed below
- 7. EXAMPLES OF CZOCHRALSKIGROWN SCs SOLIDIFICATION OF STOICHIOMETRIC MELT • LiNbO3 - NLO material - Perovskite - temperature dependent tetragonal-cubic-ferroelectric-paraelectric phase transition at Curie T – electrical control of refractive index – use electrooptical switch • SrTiO3 - Perovskite substrate – used for epitaxial growth of high Tc defect Perovskite - YBa2Cu3O7 superconducting films - SQUIDS • GaAlInP - quaternary alloy semiconductor - near IR diode lasers • GaAs wafers – red laser diodes - photonic crystal devices • NdxY3-xAl5O12 – neodynium YAG - NIR solid state lasers - 1.06 microns • Si - microelectronic chips, Ge - semiconductor higher electron mobility faster electronics than Si
- 8. BRIDGMAN AND STOCKBARGERMETHODS Controlled Crystallization of a Stoichiometric Melt STOCKBARGER fixed temperature gradient - moving crystal BRIDGEMAN changing temperature gradient - static crystal T T Distance Distance Crystallization of melt on seed as crucible gradually displaced through temperature gradient from hotter to cooler end melt crystal Furnace gradually cooled and crystallization begins on seed at cooler end of crucible Tm Tm T1 T2 T3 Temperature gradient
- 9. BRIDGMAN AND STOCKBARGERMETHODS • Stockbarger method is based on a crystal growing from the melt, involves the relative displacement of melt and a temperature gradient furnace, fixed gradient and a moving melt/crystal • Bridgman method is again based on crystal growth from a melt, but now a temperature gradient furnace is gradually lowered and crystallization begins at the cooler end, fixed crystal and changing temperature gradient • Both methods are founded on the controlled solidification of a stoichiometric melt of the material to be crystallized in a temperature gradient
- 10. BRIDGMAN AND STOCKBARGERMETHODS • Stockbarger and Bridgman methods both involve controlled solidification of a stoichiometric melt of the material to be crystallized in a temperature gradient • Enables oriented solidification • Melt passes through a temperature gradient • Crystallization occurs at the cooler end • Both methods benefit from seed crystals, predetermined orientation and controlled atmospheres
- 11. T Distance Crystal or powder Localizedmelt region - impurities concentrated in melt – energetic benefit Crystal growing from seed Temperature profile furnce Pulling direction Tm ZONE MELTING CRYSTAL GROWTH AND PURIFICATION OF SOLIDS
- 12. ZONE MELTING CRYSTALGROWTH AND PURIFICATION OF SOLIDS • Method related to the Stockbarger technique - thermal profile furnace employed - material contained in a boat • Only a small region of the charge is melted at any one time - initially part of the melt is in contact with the seed • Boat containing sample pulled at a controlled velocity through the thermal profile furnace • Zone of material melted, hence the name of the method - oriented solidification of crystal occurs on the seed - simultaneously more of the charge melts
- 13. ZONE MELTING CRYSTALGROWTH AND PURIFICATION OF SOLIDS • Partitioning of impurities occurs between melt and crystal • Basis of the zone refining methods for purifying solids • Impurities concentrate in melt more than the solid phase where structure-energy constraints of crystal sites more severe than melt - impurities swept out of crystal by moving the liquid zone • Used for purifying materials like W, Si, Ge, Au, Pt to ppb level of impurities, often required for device applications
- 14. O2 + powderedprecursor(s) O2 + H2 Fusion flame Liquid drops of molten precursor(s) Growing crystal Support for growing crystal VERNEUIL FUSION FLAME METHOD
- 15. VERNEUIL FUSION FLAMEMETHOD • 1904 first recorded use of the method, useful for growing crystals of extremely high melting and refractory metal oxides, examples include: • Ruby red from Cr3+/Al2O3 powder, sapphire blue from Cr2 6+/Al2O3 powder, luminescent host CaO powder • Starting material fine powder form, passed through O2/H2 flame or plasma torch • Melting of the powder occurs in the flame, molten microdroplets fall onto the surface of a seed or growing crystal, leads to controlled crystal growth
- 16. CRYSTAL GROWING METHODS CZOCHRALSKI,BRIDGMAN, STOCKBARGER, ZONE MELTING, VERNEUIL • All methods have the advantage of rapid growth rates of large crystals required for many advanced device applications • BUT the CRYSTAL QUALITY obtained by all of these techniques must be checked for inhomogeneities in surface and bulk composition and structure, gradients, domains, impurities, point-line-planar defects, twins, grain boundaries • THINK how you might go about checking this if you were confronted with a 12"x12"x12" crystal - useful methods for small crystals include: confocal optical microscope, polarization optical microscope birefringence, Raman microscope, spatially resolved OM, XRD, TEM, ED, EDX, AFM – what does one use for large ones?
- 17.
- 18. HYDROTHERMAL SYNTHESIS AND GROWTHOF SINGLE CRYSTALS • Basic methodology, water medium and high temperature growth, above normal boiling point • Water functions as solublizing phase, pressure transmitting agent, often mineralizing agent added to enhance dissolution, transport of reactants and crystal growth, speeds up chemical reactions between solids • Useful technique for the synthesis and crystal growth of phases that are unstable in a high temperature preparation in the absence of water
- 19. HYDROTHERMAL AUTOCLAVE Growth region Dissolvingregion Crystal seeds Separating baffle Source nutrient
- 20. HYDROTHERMAL SYNTHESIS ANDGROWTH OF SINGLE CRYSTALS • Temperature gradient reactor - dissolution of reactants at one end - with help of mineralizer transport to seed at the other end - crystallization at seeded end • Because some materials have negative solubility coefficients, nutrients dissolve at cooler end and crystals grow at the hotter end in a temperature gradient hydrothermal reactor, counterintuitive!!! • Good example is a-AlPO4 known as Berlinite, isoelectronic and isostructural with Quartz, important for its high piezoelectric coefficient - application of pressure to a crystal of Quartz or Berlinite creates a distortion of structure, electrical polarization of the lattice and associated voltage
- 21. HYDROTHERMAL SYNTHESIS ANDGROWTH OF SINGLE CRYSTALS • Ability of certain non-centrosymmetric crystals like quartz to generate a voltage in response to applied mechanical stress - Greek piezein - squeeze or press • Effect reversible - piezoelectric crystals, subject to an externally applied voltage, change shape by a small amount • Compressive stress along [100] disturbs crystal symmetry distorting SiO4 tetrahedra along 3-fold axis (not for [001] 2- fold axis) creating charge asymmetry and electrical charges across opposite crystal faces that generates a V • Berlinite alpha-AlPO4 more polar Al-O larger than alpha- quartz Si-O with which it is isoelectronic and isostructural - use as a high frequency oscillator and mass monitor
- 22. HYDROTHERMAL GROWTH OF QUARTZSINGLE CRYSTALS • Water medium - Nutrients 400oC - Seed 360oC • Pressure 1.7 Kbar - Mineralizer 1M NaOH dissolves silica • Uses of single crystal quartz: radar, sonar, piezoelectric transducers, mass monitors • Annual global production hundreds of tons of quartz crystals, amazing
- 23. HYDROTHERMAL METHODS SUITABLEFOR GROWING MANY TYPES OF SINGLE CRYSTALS • Ruby: Cr2O3/Al2O3 Cr3+/Al2O3 and sapphire: Cr2 6+/Al2O3 • Chromium dioxide: Cr2O3 + CrO3 3CrO2 • Yttrium aluminum garnet: 3Y2O3 + 5Al2O3 Y3Al5O12 • Corundum: alpha-Al2O3 • Zeolites: Al2O3.3H2O + Na2SiO3.9H2O + NaOH/H2O Na12(AlO2)12(SiO2)12.27H2O • Emerald: 6SiO2 + (Al/Cr)2O3 + 3BeO Be3Al(Cr)2Si6O18 • Berlinite: alpha-AlPO4 • Metals: Au, Ag, Pt, Co, Ni, Tl, As
- 24. QUARTZ CRYSTALS GROWIN HYDROTHERMALAUTOCLAVE 400°C T2 360°C T1 SiO2 powder nutrient dissolving region Baffle allows passage of minerlized species to quartz seed crystal NaOH/H2O mineralizer SiO2 seed
- 25. ROLE OF THEMINERALIZER IN HYDROTHERMAL SYNTHESIS AND CRYSTAL GROWTH • Consider growth of quartz crystals - control of crystal growth rate, through mineralizer, temperature pressure • Solubility of quartz in water is important • SiO2 + 2H2O Si(OH)4 • Solubility about 0.3 wt% even at supercritical temperatures >374oC • A mineralizer is a complexing agent (not too stable) for the reactants/precursors, which have to be solublized (dissolved not too quickly) and transported to the growing crystal
- 26. ROLE OF THEMINERALIZER IN HYDROTHERMAL SYNTHESIS AND CRYSTAL GROWTH • NaOH mineralizer, dissolving reaction, 1.3-2.0 KBar • 3SiO2 + 6OH- Si3O9 6- + 3H2O • Na2CO3 mineralizer, dissolving reaction, 0.7-1.3 KBar • CO3 2- + H2O HCO3 - + OH- • SiO2 + 2OH- SiO3 2- + H2O • NaOH creates growth rates about 2x greater than with Na2CO3 because of different concentrations of hydroxide mineralizer
- 27. EXAMPLES OF HYDROTHERMALCRYSTAL GROWTH AND MINERALIZERS • Berlinite alpha-AlPO4 - larger piezoelectric coefficient than quartz – polarity effect Al-O > Si-O • Powdered AlPO4 cool end of reactor, negative solubility coefficient T2 > T1 - try to explain this effect • H3PO4/H2O mineralizer • AlPO4 seed crystal at hot end T1 T2 a-AllPO4 powder Baffle H3PO4/H2O mineralizer a-AlPO4 seed
- 28. EMERALD CRYSTALS GROWIN HYDROTHERMALAUTOCLAVE T2 T1 T2 SiO2 powder nutrient at hot end Al2O3/Cr2O3/BeO powder nutrients at hot end Emerald - Cr(3+) doped beryl seed crystal at cool center of hydrothermal synthesis - crystal growth autoclave NH4Cl or HCl mineralizer
- 29. EXAMPLES OF HYDROTHERMALCRYSTAL GROWTH AND MINERALIZERS • Emeralds Be3Al(Cr)2Si6O18 Beryl contains Si6O18 12- six rings • SiO2 powder at hot end 600oC • NH4Cl or HCl/H2O mineralizer, 0.7-1.4 Kbar • Cool central region for seed, 500oC • Al2O3/BeO/Cr3+ dopant powder mix at other hot end 600oC • 6SiO2 + Al(Cr)2O3 + 3BeO Be3Al(Cr)2Si6O18
- 30. EXAMPLES OF HYDROTHERMALCRYSTAL GROWTH AND MINERALIZERS • Metal crystals - metal powder at hot end 500oC • Mineralizer 10M HI/I2 - metal seed at cool end 480oC • Dissolving reaction transports Au to the seed crystal: • Au + 3/2I2 + I- AuI4 - • Metal crystals grown include • Au, Ag, Pt, Co, Ni, Tl, As at 480-500oC T2 T1 Metal Powder Baffle 10MHI/I2 mineralizer Metal seed