the muppet’s guide to: the structure and dynamics of solids 5. crystal growth ii and defects
TRANSCRIPT
![Page 1: The Muppet’s Guide to: The Structure and Dynamics of Solids 5. Crystal Growth II and Defects](https://reader036.vdocuments.mx/reader036/viewer/2022062308/56649cc45503460f9498dcf7/html5/thumbnails/1.jpg)
The Muppet’s Guide to:The Structure and Dynamics of Solids
5. Crystal Growth II and Defects
![Page 2: The Muppet’s Guide to: The Structure and Dynamics of Solids 5. Crystal Growth II and Defects](https://reader036.vdocuments.mx/reader036/viewer/2022062308/56649cc45503460f9498dcf7/html5/thumbnails/2.jpg)
Crystal Growth
• All growth processes require conditions that promote formation of a crystal such as:
– Condensing from a supersaturated solution
– Freezing from a melt
– Evaporation
• Different methods needed for different materials
![Page 3: The Muppet’s Guide to: The Structure and Dynamics of Solids 5. Crystal Growth II and Defects](https://reader036.vdocuments.mx/reader036/viewer/2022062308/56649cc45503460f9498dcf7/html5/thumbnails/3.jpg)
Growth from SolutionEvaporation of the solvent causes super-saturation and hence the solute comes out of solution
![Page 4: The Muppet’s Guide to: The Structure and Dynamics of Solids 5. Crystal Growth II and Defects](https://reader036.vdocuments.mx/reader036/viewer/2022062308/56649cc45503460f9498dcf7/html5/thumbnails/4.jpg)
Growth from the melt
• Czochralski growth– Liquid encapsulated Czochralski growth
• Bridgman growth (directional freezing)– Interface shape– Thermal considerations
![Page 5: The Muppet’s Guide to: The Structure and Dynamics of Solids 5. Crystal Growth II and Defects](https://reader036.vdocuments.mx/reader036/viewer/2022062308/56649cc45503460f9498dcf7/html5/thumbnails/5.jpg)
Czochralski growth (crystal pulling)
![Page 6: The Muppet’s Guide to: The Structure and Dynamics of Solids 5. Crystal Growth II and Defects](https://reader036.vdocuments.mx/reader036/viewer/2022062308/56649cc45503460f9498dcf7/html5/thumbnails/6.jpg)
Czochralski growth (crystal pulling)
• A seed is lowered into the melt
• The seed is rotated and withdrawn
![Page 7: The Muppet’s Guide to: The Structure and Dynamics of Solids 5. Crystal Growth II and Defects](https://reader036.vdocuments.mx/reader036/viewer/2022062308/56649cc45503460f9498dcf7/html5/thumbnails/7.jpg)
Czochralski growth (crystal pulling)
• A seed is lowered into the melt
• The seed is rotated and withdrawn
• A rod or boule of crystal forms
• Industry standard for Si and Ge
Pure Material
Melt + Impurities
![Page 8: The Muppet’s Guide to: The Structure and Dynamics of Solids 5. Crystal Growth II and Defects](https://reader036.vdocuments.mx/reader036/viewer/2022062308/56649cc45503460f9498dcf7/html5/thumbnails/8.jpg)
Czochralski growth
• A seed is lowered into the melt
• The seed is rotated and withdrawn
• A rod or boule of crystal forms
• Industry standard for Si and Ge
"Smithsonian", Jan 2000, Vol 30, No. 10
![Page 9: The Muppet’s Guide to: The Structure and Dynamics of Solids 5. Crystal Growth II and Defects](https://reader036.vdocuments.mx/reader036/viewer/2022062308/56649cc45503460f9498dcf7/html5/thumbnails/9.jpg)
Liquid encapsulated Czochralski growth
• Growth takes place in a pressure vessel
• The melt is covered in boric oxide (B2O3) which is viscous and un-reactive
• This allows an over-pressure of inert gas to be applied so as to contain the melt – important for GaAs and CdTe (volatile components)
![Page 10: The Muppet’s Guide to: The Structure and Dynamics of Solids 5. Crystal Growth II and Defects](https://reader036.vdocuments.mx/reader036/viewer/2022062308/56649cc45503460f9498dcf7/html5/thumbnails/10.jpg)
Bridgman growth
• Boat is moved through the temperature gradient in a tube furnace
• Growth of the crystal is by directional freezing of the melt
T
x
solidliquid
![Page 11: The Muppet’s Guide to: The Structure and Dynamics of Solids 5. Crystal Growth II and Defects](https://reader036.vdocuments.mx/reader036/viewer/2022062308/56649cc45503460f9498dcf7/html5/thumbnails/11.jpg)
Directional freezing
• Material is contained in a capsule
• A concave growth surface allows secondary nuclei to form at the walls of the tube
• A convex growth surface causes secondary nuclei to be crowded out by the main crystal in the advancing solid
Freezing direction, x
solidliquid
solidliquid
![Page 12: The Muppet’s Guide to: The Structure and Dynamics of Solids 5. Crystal Growth II and Defects](https://reader036.vdocuments.mx/reader036/viewer/2022062308/56649cc45503460f9498dcf7/html5/thumbnails/12.jpg)
Hot Zone or Float ZoneCrucible free growth or anneal
Also used to remove impurities
![Page 13: The Muppet’s Guide to: The Structure and Dynamics of Solids 5. Crystal Growth II and Defects](https://reader036.vdocuments.mx/reader036/viewer/2022062308/56649cc45503460f9498dcf7/html5/thumbnails/13.jpg)
Impurities
Crystal
Melt
Ck
C
Segregation coefficient:
For k<1, impurities stay in melt
Diffusion mechanism
![Page 14: The Muppet’s Guide to: The Structure and Dynamics of Solids 5. Crystal Growth II and Defects](https://reader036.vdocuments.mx/reader036/viewer/2022062308/56649cc45503460f9498dcf7/html5/thumbnails/14.jpg)
Layer by Layer Growth
For epitaxial growth we want the layer to stick:
• Energy to remain on surface, Ea
• Energy to diffuse on surface, Ed
• Cohesive energy, Ec
• Strain Energy, (U)
![Page 15: The Muppet’s Guide to: The Structure and Dynamics of Solids 5. Crystal Growth II and Defects](https://reader036.vdocuments.mx/reader036/viewer/2022062308/56649cc45503460f9498dcf7/html5/thumbnails/15.jpg)
Thin film Growth Modes
Growth mode depends on energies when atoms arrive at substrateImage Courtesy, Nessa Fereshteh Saniee, PhD Thesis, UoW 2014
![Page 16: The Muppet’s Guide to: The Structure and Dynamics of Solids 5. Crystal Growth II and Defects](https://reader036.vdocuments.mx/reader036/viewer/2022062308/56649cc45503460f9498dcf7/html5/thumbnails/16.jpg)
Epitaxial growth
• Molecular beam epitaxy
Co-evaporation of the elements that make the compound at UHV
Base pressure of chamber <10-10Torr. Growth pressure <10-9Torr
![Page 17: The Muppet’s Guide to: The Structure and Dynamics of Solids 5. Crystal Growth II and Defects](https://reader036.vdocuments.mx/reader036/viewer/2022062308/56649cc45503460f9498dcf7/html5/thumbnails/17.jpg)
Sputtering
Base pressure of system <10-7 Torr. Growth in Ar <10-3 Torr
![Page 18: The Muppet’s Guide to: The Structure and Dynamics of Solids 5. Crystal Growth II and Defects](https://reader036.vdocuments.mx/reader036/viewer/2022062308/56649cc45503460f9498dcf7/html5/thumbnails/18.jpg)
Pulsed Laser Deposition (PLD)
Images Courtesy, Nessa Fereshteh Saniee, PhD Thesis, UoW 2014
Laser produces a plasma of material
which is then deposited on a
substrate. Good for oxides and high
melting point materials
![Page 19: The Muppet’s Guide to: The Structure and Dynamics of Solids 5. Crystal Growth II and Defects](https://reader036.vdocuments.mx/reader036/viewer/2022062308/56649cc45503460f9498dcf7/html5/thumbnails/19.jpg)
Heterostructures
Dislocation/Disorder
![Page 20: The Muppet’s Guide to: The Structure and Dynamics of Solids 5. Crystal Growth II and Defects](https://reader036.vdocuments.mx/reader036/viewer/2022062308/56649cc45503460f9498dcf7/html5/thumbnails/20.jpg)
Lattice Match through Rotations
Pt[100]//FeCo[110]
45° Rotation of unit cells
aPt=3.9242ÅaFe=2.8665Å
2 4.0538Fea A
4.0538 3.92423.3%
3.9242Miss match
![Page 21: The Muppet’s Guide to: The Structure and Dynamics of Solids 5. Crystal Growth II and Defects](https://reader036.vdocuments.mx/reader036/viewer/2022062308/56649cc45503460f9498dcf7/html5/thumbnails/21.jpg)
inac.cea.fr/Images/astImg/479_1.png
![Page 22: The Muppet’s Guide to: The Structure and Dynamics of Solids 5. Crystal Growth II and Defects](https://reader036.vdocuments.mx/reader036/viewer/2022062308/56649cc45503460f9498dcf7/html5/thumbnails/22.jpg)
Disorder in crystalline materials
• No such thing as a perfectly ordered material• Many materials are technologically of value because
they are disordered/imperfect in some way:
silicon devices – controlled levels of deliberate impurity additions (ppb) p-type : B Si B + h
n-type : P Si P + e
steels – additions of 0.1 to 1 at.% other metals to improve mechanical properties and corrosion resistance
![Page 23: The Muppet’s Guide to: The Structure and Dynamics of Solids 5. Crystal Growth II and Defects](https://reader036.vdocuments.mx/reader036/viewer/2022062308/56649cc45503460f9498dcf7/html5/thumbnails/23.jpg)
• Vacancy atoms• Interstitial atoms• Substitutional atoms
Point defects
Types of Imperfections
• Dislocations Line defects
• Grain Boundaries Area defects
![Page 24: The Muppet’s Guide to: The Structure and Dynamics of Solids 5. Crystal Growth II and Defects](https://reader036.vdocuments.mx/reader036/viewer/2022062308/56649cc45503460f9498dcf7/html5/thumbnails/24.jpg)
Imperfections in Solids
Linear Defects (Dislocations)– Are one-dimensional defects around which atoms are
misaligned• Edge dislocation:
– extra half-plane of atoms inserted in a crystal structure– b to dislocation line
• Screw dislocation:– spiral planar ramp resulting from shear deformation– b to dislocation line
Burger’s vector, b: measure of the magnitude and direction of lattice distortion.
![Page 25: The Muppet’s Guide to: The Structure and Dynamics of Solids 5. Crystal Growth II and Defects](https://reader036.vdocuments.mx/reader036/viewer/2022062308/56649cc45503460f9498dcf7/html5/thumbnails/25.jpg)
Dislocations – linear defectsSource:- growth- stress- temperature
Evidence:- metals more deformable than
predicted (but can be strengthened by impurities)
- spiral growths on surface of some crystals
- reactions occur at active surface sites
Types: edge, screw, intermediate
Transmission electron micrograph of Ti alloy – dark lines are dislocations(Callister: Materials Science and Engineering)
![Page 26: The Muppet’s Guide to: The Structure and Dynamics of Solids 5. Crystal Growth II and Defects](https://reader036.vdocuments.mx/reader036/viewer/2022062308/56649cc45503460f9498dcf7/html5/thumbnails/26.jpg)
Edge dislocation
– partial plane of atoms
– lattice distorted where plane ends
Dislocations characterised by the Burgers vector, b-for metals, b points in a close-packed direction and equals the interatomic spacing
(Callister: Materials Science and Engineering)
![Page 27: The Muppet’s Guide to: The Structure and Dynamics of Solids 5. Crystal Growth II and Defects](https://reader036.vdocuments.mx/reader036/viewer/2022062308/56649cc45503460f9498dcf7/html5/thumbnails/27.jpg)
Heterostructures
ct t┬
![Page 28: The Muppet’s Guide to: The Structure and Dynamics of Solids 5. Crystal Growth II and Defects](https://reader036.vdocuments.mx/reader036/viewer/2022062308/56649cc45503460f9498dcf7/html5/thumbnails/28.jpg)
Buffer Layers
┬ ┬
┬
![Page 29: The Muppet’s Guide to: The Structure and Dynamics of Solids 5. Crystal Growth II and Defects](https://reader036.vdocuments.mx/reader036/viewer/2022062308/56649cc45503460f9498dcf7/html5/thumbnails/29.jpg)
Screw dislocation• partial slip of a crystal
• on one side of dislocation line, crystal has undergone slip; on other side, crystal is normal
• continued application of shear stress causes dislocation to move through crystal
Shear stress
(Callister: Materials Science and Engineering)
![Page 30: The Muppet’s Guide to: The Structure and Dynamics of Solids 5. Crystal Growth II and Defects](https://reader036.vdocuments.mx/reader036/viewer/2022062308/56649cc45503460f9498dcf7/html5/thumbnails/30.jpg)
Edge, Screw, and Mixed Dislocations
Edge
Screw
Mixed
(Callister: Materials Science and Engineering)
![Page 31: The Muppet’s Guide to: The Structure and Dynamics of Solids 5. Crystal Growth II and Defects](https://reader036.vdocuments.mx/reader036/viewer/2022062308/56649cc45503460f9498dcf7/html5/thumbnails/31.jpg)
Interfacial (planar) defects
• boundaries separating regions of different crystal structure or crystallographic orientation– External surfaces (see final section of
module)– Internal boundaries
• Layer Interfaces (2D)• Region Interfaces (3D)
![Page 32: The Muppet’s Guide to: The Structure and Dynamics of Solids 5. Crystal Growth II and Defects](https://reader036.vdocuments.mx/reader036/viewer/2022062308/56649cc45503460f9498dcf7/html5/thumbnails/32.jpg)
• Freezing - result of casting of molten material– 2 steps
• Nuclei form • Nuclei grow to form crystals• Crystals grow until they meet each other
– grain structure
Planar Defects in Solids
nuclei crystals growing grain structureliquid
(Callister: Materials Science and Engineering)
![Page 33: The Muppet’s Guide to: The Structure and Dynamics of Solids 5. Crystal Growth II and Defects](https://reader036.vdocuments.mx/reader036/viewer/2022062308/56649cc45503460f9498dcf7/html5/thumbnails/33.jpg)
Polycrystalline Materials
Grain Boundaries• regions between crystals• transition from lattice of one
region to that of the other• slightly disordered• low density in grain
boundaries– high mobility– high diffusivity– high chemical reactivity
Adapted from Fig. 4.7, Callister 7e.
![Page 34: The Muppet’s Guide to: The Structure and Dynamics of Solids 5. Crystal Growth II and Defects](https://reader036.vdocuments.mx/reader036/viewer/2022062308/56649cc45503460f9498dcf7/html5/thumbnails/34.jpg)
Grain boundaries
D = b/
b
Internal surfaces of a single crystal where ideal domains (mosaic) meet with some misalignment: high-angle and small(low)-angle.
NB – in polycrystalline materials, grain boundaries are more extensive and may even separate different phases
Small-angle grain boundary equivalent to linear array of edge dislocations
bonding not fully satisfied region of higher energy, more reactive, impurities present.
(Callister: Materials Science and Engineering)
![Page 35: The Muppet’s Guide to: The Structure and Dynamics of Solids 5. Crystal Growth II and Defects](https://reader036.vdocuments.mx/reader036/viewer/2022062308/56649cc45503460f9498dcf7/html5/thumbnails/35.jpg)
Planar Defects in Solids 2
• Another case is a twin boundary (plane) – Essentially a reflection of atom positions across the twin
plane.
• Stacking faults– For FCC metals an error in ABCABC packing sequence– Ex: ABCABABC
(Callister: Materials Science and Engineering)