epitaxial nucleation and growth of organic crystals on inorganic substrates supervisors:willem van...
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![Page 1: Epitaxial nucleation and growth of organic crystals on inorganic substrates Supervisors:Willem van Enckevort Sander Graswinckel Mirjam Leunissen](https://reader034.vdocuments.mx/reader034/viewer/2022050723/56649d4d5503460f94a2c01f/html5/thumbnails/1.jpg)
Epitaxial nucleation and growth of organic crystals on inorganic substrates
Supervisors: Willem van Enckevort
Sander Graswinckel
Mirjam Leunissen
![Page 2: Epitaxial nucleation and growth of organic crystals on inorganic substrates Supervisors:Willem van Enckevort Sander Graswinckel Mirjam Leunissen](https://reader034.vdocuments.mx/reader034/viewer/2022050723/56649d4d5503460f94a2c01f/html5/thumbnails/2.jpg)
Outline
Introduction What is epitaxy? Why study it?
Systems & experimental methods
Alizarin GeneralOn NaCl {100}‘Hole experiment’On NaCl {111}
Anthraquinone GeneralOn NaCl {100}Molecular mechanics
Paraffins GeneralOn HOPG (0001)
Nucleation theory
Symmetry considerations
Discussion & conclusion What have we learned?Future
![Page 3: Epitaxial nucleation and growth of organic crystals on inorganic substrates Supervisors:Willem van Enckevort Sander Graswinckel Mirjam Leunissen](https://reader034.vdocuments.mx/reader034/viewer/2022050723/56649d4d5503460f94a2c01f/html5/thumbnails/3.jpg)
Introduction
Subject
Epitaxial three-dimensional nucleation and subsequent growth of organic substances on inorganic substrates from the solution and vapor phase
What is epitaxy?
Present use
Oriented growth of one crystal upon another
Etymology
• Greek derivation
• ‘under order’
• phalanx
Introduction
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Epitaxy is the oriented crystal growth of a substance on a crystal surface of the same (‘homo-epitaxy’) or another substance (‘hetero-epitaxy’) in which the structure of the substrate determines the orientation of the guest crystals
Definition
Introduction
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• homo -- hetero
• monolayer -- three-dimensional crystal
• inorganic -- organic
• polar -- apolar
• melt / solution / vapor / vacuum evaporation
Types of epitaxy
Introduction
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• flat substrate
• 2D unit cell of substrate matches 2D
cell of overlayer (not necessarily 1:1)
• substrate doesn’t dissolve
• similar type of force in substrate and
overlayer (polar/apolar)
Requirements
Substratea1'
a2'
Overlayer
a1
a2
Introduction
Overlayer
Substrate
a1
a2
a1'
a2'
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Examples of epitaxy
• ‘natural’: minerals growing together
• crystal growth/seeding
• GaN on sapphire (Al2O3): optical and electronic devices
GaN
Sapphire
[-1010]GaN
(a-axis)
[1-210]sapphire(b-axis)
[1-210]GaN
[10-10]sapphire
Introduction
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Goal of present study
To study aspects of epitaxial crystal growth from the solution and vapor phase (e.g. growth mechanism, symmetry aspects)
Why are we interested in epitaxy?
Applications
• grow thick monocrystalline layers of organic compounds on a substrate
• grow ‘on command’ new polymorphs and crystals of substances which
won’t crystallize under ‘normal’ conditions
Approach
Grow oriented three-dimensional nuclei on top of a substrate, which, on continued growth, coalesce and grow together.
Introduction
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Outline
Introduction What is epitaxy? Why study it?
Systems & experimental methods
Alizarin GeneralOn NaCl {100}‘Hole experiment’On NaCl {111}
Anthraquinone GeneralOn NaCl {100}Molecular mechanics
Paraffins GeneralOn HOPG (0001)
Nucleation theory
Symmetry considerations
Discussion & conclusion What have we learned?Future
![Page 10: Epitaxial nucleation and growth of organic crystals on inorganic substrates Supervisors:Willem van Enckevort Sander Graswinckel Mirjam Leunissen](https://reader034.vdocuments.mx/reader034/viewer/2022050723/56649d4d5503460f94a2c01f/html5/thumbnails/10.jpg)
Systems &
experimental methods
Substrate Guest Solutiondeposition
Vapordeposition
Systemtype
NaCl alizarin yes yes ‘polar’
NaCl anthraquinone yes yes ‘polar’
graphite(HOPG*)
paraffins yes no ‘apolar’
*HOPG: Highly Ordered Pyrolytic Graphite
Systems & experimental methods
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• substrate cooled to 0 ºC
• (saturated) solution of 45-55 ºC of the guest substance
• 2-10 minutes
• dry with a tissue
Substrate
Solution
Solution deposition
Systems & experimental methods
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• nitrogen atmosphere
• substrate same temperature as vapor: 165 ºC
• 15-20 hours
N2
Substrate
Guestcompound
Furnace
Vapor deposition
Systems & experimental methods
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Outline
Introduction What is epitaxy? Why study it?
Systems & experimental methods
Alizarin GeneralOn NaCl {100}‘Hole experiment’On NaCl {111}
Anthraquinone GeneralOn NaCl {100}Molecular mechanics
Paraffins GeneralOn HOPG (0001)
Nucleation theory
Symmetry considerations
Discussion & conclusion What have we learned?Future
![Page 14: Epitaxial nucleation and growth of organic crystals on inorganic substrates Supervisors:Willem van Enckevort Sander Graswinckel Mirjam Leunissen](https://reader034.vdocuments.mx/reader034/viewer/2022050723/56649d4d5503460f94a2c01f/html5/thumbnails/14.jpg)
OH
O
OOH
Alizarin
Alizarin: general
General
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Crystal structure according to Guilhem (1967): Pa
a = 21.04 Åb = 3.75 Åc = 20.12 Å
β = 104.5º
Alizarin: general
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• needle shaped crystals
• long, thin
• hexagonal or rectangular
• sometimes hollow
SEM
Crystallization without substrate
Alizarin: general
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Solution deposition: reproduction results of prof. Neuhaus
No great differences between solution and vapor deposition considering general aspects (morphology, orientation)
Alizarin on NaCl {100}
Solution: toluene + 2.5 mass% absolute ethanol
General
Vapor and solution deposition
Alizarin: NaCl {100}
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NaCl: cubic Fm-3m
{100} tetragonal symmetry
Orientation
{100}
a
b
c
Alizarin: NaCl {100}
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[010]
[001]
[011][0-11]Alizarin length axis // [011] and [0-11] of NaCl
20 m
20 m
Vapor
Solution
Polarization microscope
Alizarin: NaCl {100}
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Morphology
‘Roof’ like, pointed or topped of
SEM
AFM
Alizarin: NaCl {100}
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Contact face
104.5°
a
b
c
(001)
(-101)(201)
NaCl {100}
(010)
Based on morphology: (001)
Alizarin: NaCl {100}
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Verification with X-ray powder diffraction
Diffraction vector substrate surface for all diffraction anglesEnhanced reflection from (hkl) planes // contact face
Randomly oriented crystallites
(dashed)
Oriented crystallites on NaCl
(solid)(003)
Alizarin: NaCl {100}
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NaCl {100}
Contact face (001):
• alizarin molecules interface
• strong interaction protruding oxygen atoms with ionic substrate
Alizarin: NaCl {100}
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Epitaxial nucleation on faces other than {100}
What is the influence of the substrate orientation on the orientation of the guest crystals?
‘Hole experiment’
Alizarin: hole experiment
100
NaCl
R
ds
12
½ l
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110 111
113
112
102
+
100
[100] [110]
Asymmetric unit of point group m3m
Alizarin: hole experiment
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• oriented crystallites grow on all faces
• strong dependence substrate orientation and preferred directions
• transition from tetragonal to trigonal symmetry on going from {100} to {111}
• no relationship between size and amount of crystallites and specific substrate orientation
Alizarin: hole experiment
110 111
113
112
102
+
100
[100] [110]
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Alizarin on as-grown NaCl {111}
NaCl: {111} trigonal symmetry
Alizarin: NaCl {111}
{111}
a
b
c
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[-101]
[1-10]
[0-11]
10 m
Alizarin length axis // [-101], [1-10] and [0-11] of NaCl
Alizarin: NaCl {111}
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Outline
Introduction What is epitaxy? Why study it?
Systems & experimental methods
Alizarin GeneralOn NaCl {100}‘Hole experiment’On NaCl {111}
Anthraquinone GeneralOn NaCl {100}Molecular mechanics
Paraffins GeneralOn HOPG (0001)
Nucleation theory
Symmetry considerations
Discussion & conclusion What have we learned?Future
![Page 30: Epitaxial nucleation and growth of organic crystals on inorganic substrates Supervisors:Willem van Enckevort Sander Graswinckel Mirjam Leunissen](https://reader034.vdocuments.mx/reader034/viewer/2022050723/56649d4d5503460f94a2c01f/html5/thumbnails/30.jpg)
Anthraquinone
O
O
Alizarin structure analogue
Less complicated molecular structure
Monoclinic: P21/c
a = 7.87 Å
b = 3.96 Å
c = 15.78 Å
β = 102.7 º
Vapor and solution deposition
General
Anthraquinone: general
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[010]
[001]
[011][0-11]
Orientation
Anthraquinone on NaCl {100}
Anthraquinone length axis // [011] and [0-11] of NaCl
10 m
Optical microscope
Vapor
Solution
20 m
Anthraquinone: NaCl {100}
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Morphology
‘Roof’ like, pointed or topped of
AFMSEM
Anthraquinone: NaCl {100}
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(10-2)
(100)(002)
NaCl {100}
(010)
(002)
(10-2)
c
a(100)
Contact face
Contact face (10-2):
• anthraquinone molecules interface
• strong interaction protruding oxygen
atoms with ionic substrate
a
b
c
102.7°
Anthraquinone: NaCl {100}
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Dock ‘candidate’ faces onto the NaCl {100} lattice
Size a x b x c : a = # molecules in a row b = # rows per layer c = # layers
Rotate and translate plane until stage of minimal energy is reached
5x2x1
Molecular mechanics: prediction contact face and orientation
‘Candidate’ faces from morphology prediction (Eatt): (100), (002), (10-2)
Anthraquinone: molecular mechanics
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[010]
[001]
NaCl {100}
Plot energy as function of orientation angle φ
• 1 row of molecules
• orientation 45 °
Orientation of face (10-2)
• distance between protruding O-atoms within 0.2% identical to distance between Na-ions
Anthraquinone: molecular mechanics
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Outline
Introduction What is epitaxy? Why study it?
Systems & experimental methods
Alizarin GeneralOn NaCl {100}‘Hole experiment’On NaCl {111}
Anthraquinone GeneralOn NaCl {100}Molecular mechanics
Paraffins GeneralOn HOPG (0001)
Nucleation theory
Symmetry considerations
Discussion & conclusion What have we learned?Future
![Page 37: Epitaxial nucleation and growth of organic crystals on inorganic substrates Supervisors:Willem van Enckevort Sander Graswinckel Mirjam Leunissen](https://reader034.vdocuments.mx/reader034/viewer/2022050723/56649d4d5503460f94a2c01f/html5/thumbnails/37.jpg)
Paraffins
Dotriacontane: C32H66 (orthorhombic)
Tritriacontane: C33H68 (orthorhombic)
Tetracosane: C24H50 (triclinic)
General
Paraffin = n-alkane = CnH2n+2
Apolar
All-trans structure
Diluted n-heptane solutions
Paraffins: general
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n-Alkanes adsorb on graphite
Highly Ordered Pyrolytic Graphite (HOPG):
• apolar
• stacking of layers
• (0001) hexagonal
Paraffins: general
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Three preferred directions in trigonal pattern
Orientation
Paraffins on HOPG (0001)
Differently oriented domains
Cryo-SEM
Paraffins: HOPG (0001)
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Crystal length axis oriented // HOPG periodic bond chain directions
Determination precise orientation by atomic force microscopy
5 x 5 nm
Paraffins: HOPG (0001)
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• ‘plate’ like crystals
• steep and high
• flat top faces
• substrate surface
Morphology
Paraffins: HOPG (0001)
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Prediction based on morphology crystals without substrate: (100) or (110)
Contact face
a
b
(110)
a
b
(100)
Extinction
directions
Verification: reflection polarization microscopy - different extinction conditions
C32H66 and C33H68: (100)HOPG
(001)(110)
(100)
Molecules (0001)a
b
c
Paraffins: HOPG (0001)
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Growth mechanism
Onset of hetero-epitaxial growth: formation monolayer (2 types)
Paraffins: HOPG (0001)
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Assumption: same crystal structure with and without substrate
Dock (100) bulk face on HOPG: no existent monolayer structure is obtained
Chain directions in monolayer and bulk crystal
differ ~30º (or equivalent -30º and 90º )
Crystal
1 1 1 1
1' 1' 1' 1'
2 2 2 2
2' 2' 2' 2'
c
a
Paraffins: HOPG (0001)
b
c
Monolayer
30° 90°-30°
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Monolayer bulk crystal:
subsequent layers of n-alkane molecules have to be rotated
Gilbert et al. (1994): bilayer
• 1st and 2nd layer mutually rotated by 90 º
• 1st layer consists of rows of parallel n-alkane chains with molecule plane
perpendicular to HOPG surface
Stranski-Krastanov: monolayer followed by three-dimensional nucleation
Paraffins: HOPG (0001)
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Outline
Introduction What is epitaxy? Why study it?
Systems & experimental methods
Alizarin GeneralOn NaCl {100}‘Hole experiment’On NaCl {111}
Anthraquinone GeneralOn NaCl {100}Molecular mechanics
Paraffins GeneralOn HOPG (0001)
Nucleation theory
Symmetry considerations
Discussion & conclusion What have we learned?Future
![Page 47: Epitaxial nucleation and growth of organic crystals on inorganic substrates Supervisors:Willem van Enckevort Sander Graswinckel Mirjam Leunissen](https://reader034.vdocuments.mx/reader034/viewer/2022050723/56649d4d5503460f94a2c01f/html5/thumbnails/47.jpg)
Nucleation theory
Nucleation theory: general
General
Competition three-dimensional nucleation in bulk phase and on substrate surface
larger number of nucleation sites (bulk) lower activation barrier (substrate)
Assumption: spherical nuclei
Rate of nucleus formation (J)
• surface area critical nucleus
• rate of addition of monomers
• concentration critical nuclei
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Homogeneous:
Heterogeneous:
kT
Gf
kTfcfAJ
ochet
hom*
2/121
3/1 )(exp)()(''4
Surface area
substrate
f(α): correction factor for relative volume change critical nucleus
f’’(α): correction factor for reduced surface area critical nucleus
kT
Gc
kTVJ
oco
hom*
21
2/1
hom exp4
Kinetic factor
Activation barrier/ free enthalpy critical
nucleus
Volume fluid Volume
growth unit
Surface energy
Monomer concentration
Nucleation theory: general
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Contact angle α depends on the surface energy of:
• substrate
• crystal
• interface
γint
γcryst
γsub
Σ Fi,hor = 0
Nucleation theory: general
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Nucleation competition ratio (NCR)
)
)(ln)(
1
)(ln
)(
3
16exp(
)()(''
213
213
23
2/12/1
3/1
hom
beqb
seqs
c
s
b
o
het
Tcc
kTTcc
kT
f
T
Tff
V
A
J
JNCR
Temperature bulk
Temperature substrate
Nucleation theory: general
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Conditions for epitaxial nucleation to be favored over bulk nucleation:
1) rate of formation of nuclei on the substrate surface must be higher than in
the bulk: Jhet > Jhomo (NCR>1)
2) rate of formation of nuclei on substrate surface must be reasonable:
Jhet > 105 m-2sec-1 (= 102 nuclei per mm2 in 103 sec)
Nucleation theory: general
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Nucleation theory: vapor
Application to vapor deposition
Jhet increases dramatically for decreasing γ and α values
2 8 0 3 0 0 3 2 0 3 4 0 3 6 0 3 8 0 4 0 0T e m p e ra tu re (K )
1 E -4
1 E -3
1 E -2
1 E -1
1 E + 0
1 E + 1
1 E + 2
1 E + 3
1 E + 4
1 E + 5
1 E + 6
1 E + 7
1 E + 8
1 E + 9
1 E + 1 0
1 E + 1 1
Het
erog
eneo
us n
ucle
atio
n ra
te
2 8 0 3 0 0 3 2 0 3 4 0 3 6 0 3 8 0 4 0 0T emperature (K)
1 .0 E -4
1 .0 E -3
1 .0 E -2
1 .0 E -1
1 .0 E + 0
1 .0 E + 1
1 .0 E + 2
1 .0 E + 3
1 .0 E + 4
1 .0 E + 5
1 .0 E + 6
1 .0 E + 7
1 .0 E + 8
1 .0 E + 9
1 .0 E + 1 0
1 .0 E + 1 1
1 .0 E + 1 2
Het
erog
eneo
us n
ucle
atio
n ra
te (
1/m
2sec
)
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NCR decreases for decreasing surface energy and increasing contact angle
2 8 0 3 0 0 3 2 0 3 4 0 3 6 0 3 8 0 4 0 0 4 2 0 4 4 0T e m p era tu re (K )
1.0E-2
1.0E-1
1.0E+0
1.0E+1
1.0E+2
1.0E+3
1.0E+4
1.0E+5
1.0E+6
Log
(NC
R)
2 8 0 3 0 0 3 2 0 3 4 0 3 6 0 3 8 0 4 0 0 4 2 0 4 4 0T em p era tu re (K )
1 .0 E -2
1 .0 E -1
1 .0 E + 0
1 .0 E + 1
1 .0 E + 2
1 .0 E + 3
1 .0 E + 4
1 .0 E + 5
1 .0 E + 6
Log
(N
CR
)
Nucleation theory: vapor
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Outline
Introduction What is epitaxy? Why study it?
Systems & experimental methods
Alizarin GeneralOn NaCl {100}‘Hole experiment’On NaCl {111}
Anthraquinone GeneralOn NaCl {100}Molecular mechanics
Paraffins GeneralOn HOPG (0001)
Nucleation theory
Symmetry considerations
Discussion & conclusion What have we learned?Future
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Prediction number of overlayer domains with different orientation (n): two-dimensional point group symmetry of the two contacting faces
N(S) = number of symmetry operators applying to the two-dimensional point group of the surface
Ssubstrate = {Ss,1; Ss,2; Ss,3; ….; Ss,n}
Scrystal = {Sc,1; Sc,2; Sc,3;…..; Sc,n}
Ss/c,1 = E
)(
)(
crystalsubstrate
substrate
SSN
SNn
Symmetry operators = transformations
(x,y,z) (x,y,z) E
(x’,y’,z’) S2
(xn,yn,zn) Sn
Symmetry considerations
Symmetry considerations
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Example: alizarin on NaCl {100}
Alizarin: Pa
Contact face (001): m
N(Salizarin) = 2
NaCl: Fm-3m
Face {100}: 4mm
N(SNaCl) = 8
(x,y,z)
m
(x,y,z)
m
N(SNaCl Salizarin) = 2
42
8
)(
)(
alizarinNaCl
NaCl
SSN
SNn
Symmetry considerations
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Single domain monocrystalline layer:
substrate with lowest symmetry possible, i.e. Ssubstrate = {E}
[001]
[010]
NaCl {100}
Symmetry considerations
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Outline
Introduction What is epitaxy? Why study it?
Systems & experimental methods
Alizarin GeneralOn NaCl {100}‘Hole experiment’On NaCl {111}
Anthraquinone GeneralOn NaCl {100}Molecular mechanics
Paraffins GeneralOn HOPG (0001)
Nucleation theory
Symmetry considerations
Discussion & conclusion What have we learned?Future
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• expensive ultra high vacuum equipment not necessary
• close relationship between symmetry substrate surface and
preferred orientations
• understanding of processes underlying formation of oriented three-
dimensional nuclei and their subsequent growth
• general conditions for the formation of epitaxial three-dimensional
nuclei to be favored over bulk nucleation
What have we learned?
Discussion & conclusion
Discussion & conclusion
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• first onset epitaxial growth
• exact role of all factors by precise measurements
• nucleation theory for anisotropic nuclei
• let the separate nuclei grow together into a domain with a single orientation
• general rules to predict suitable combinations guest and substrate compounds
• induction of polymorphism
Future
Discussion & conclusion