kinetics of ordering and metastable phase of alloys
DESCRIPTION
Kinetics of ordering and metastable phase of alloys. Jun Ni Department of Physics Tsinghua University. Acknowledgement:. Dr.Z.H.Dai, Y.L.Xu , H.T.Shi L. Shi , X.B.Yang, Z.Q.Liu , Y.Sun, Y.L.Wang J.L.Pan, Y.Ding,Z.J.Xu. - PowerPoint PPT PresentationTRANSCRIPT
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Kinetics of ordering and metastable phase of alloys
Jun NiDepartment of Physics
Tsinghua University
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Dr.Z.H.Dai, Y.L.Xu, H.T.ShiL. Shi, X.B.Yang, Z.Q.Liu, Y.Sun, Y.L.WangJ.L.Pan, Y.Ding,Z.J.Xu
Supported by National Basic Research Program of China and the National Natural Science Foundation of China
Acknowledgement:
ReferencesL. Shi and J. Ni, Phys. Rev. Lett. 97, 126105 (2006).Z. Q. Liu and J. Ni, J.Phys.: Condens. Matter 17, 5355 (2005).L. Shi and J. Ni, Phys. Rev. B 69, 155428 (2004).L. Shi, H. T. Shi, and J. Ni, Comp. Materials Science 30, 326-330 (2004).
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Main Contents
Introduction Kinetics Phase Diagram in alloy growth Kinetics of ordering during alloy film growt
h Summary
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Introduction
Non-equilibrium growth: rapid quench, laser treatment, ion bombartment, and various epitaxial growth methods for the growth of materials in non-equilibrium state and metastable state.
It is important to understand the basic kinetic processes during the growth. The equilibrium phase diagrams can not deliver enough information on non-equilibrium growth.
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Methods
Kinetic processPPM methodMaster equation methodMonte-Carlo method
Energy parameters First principle methods
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Introduction
Epitaxial growth (MBE 、 MOCVD ): layer by layer growth.
Fcc ordering: Ordering structures in metal alloys: CuAu; CoPt; FePt;
Ⅲ-Ⅴ semiconductor alloys,
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Phase diagram with temperature and ratio as parameters
Disordered phase
Equililbrium ordered phase
Oscillated ordered phaseQuenched disordered phase
0 1.0, 0.25, 1.0, 1A B A AU P P J
Kinetical phase diagram
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Oscillated ordering
Kinetical induced oscillated ordering
30/ 0.06, 5 10 , 0.8, 0.25, 1.0B A B A Ak T J U P P
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-0.4 -0.2 0.0 0.2 0.4
0.0
0.1
0.2
0.3
0.4
k BT
/J
J(2)/J(1)
FD
O
D
OO
Nearest neighbor interaction
305 10 , / 1.0, 0.025A BU J eV
CuAuNiAl
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Kinetic phase diagrams ofepitaxial growth for SiC polytypes
The most common polytypes are zinc-blende SiC (3C-SiC), wurtzite SiC (2H-SiC), 4H-SiC,6H-SiC, and 15R-SiC.The origin of polytypism in SiC is still not completely understood. The polytypes should be viewed as the non-equilibrium structures arising from special growth mechanisms3C-SiC is a metastable phase. But it is easyly grown by epitaxial methods
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Phase diagram of ground states
-1.0 -0.8 -0.6 -0.4 -0.2 0.0 0.2 0.4 0.6 0.8 1.0-3.0
-2.5
-2.0
-1.5
-1.0
-0.5
0.0
0.5
1.0 PAW-LDA PAW-GGA
6H
3C
J2/J
1
J3/J1
4H
( 1 1 1)
the rearrangement of atoms in onesurface bilayer is allowed
-1.0 -0.8 -0.6 -0.4 -0.2 0.0 0.2 0.4 0.6 0.8 1.0-3.0
-2.5
-2.0
-1.5
-1.0
-0.5
0.0
0.5
1.0
PAW-LDA PAW-GGA
J2/J
1
J3/J1
3C
6H
4H
2H
( 1 1 1) ( 1 1 1) ( 1 1 1) , 或
-1.0 -0.8 -0.6 -0.4 -0.2 0.0 0.2 0.4 0.6 0.8 1.0-3.0
-2.5
-2.0
-1.5
-1.0
-0.5
0.0
0.5
1.0 PAW-LDA PAW-GGA
9R6H
4H
3C
J2/J
1
J3/J1
the rearrangement of atoms in two surface bilayer is allowed
Kinetic phase diagrams of SiC epitaxial growth
Z. Q. Liu and J. Ni, J.Phys.: Condens. Matter 17, 5355 (2005).
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-1.0 -0.8 -0.6 -0.4 -0.2 0.0 0.2 0.4 0.6 0.8 1.0-3.0
-2.5
-2.0
-1.5
-1.0
-0.5
0.0
0.5
1.0 PAW-LDA PAW-GGA
6H
4H
3C
J2
/J1
J3/J1
9R
the rearrangement of atoms in three surface bilayer is allowed
( 1 1 1) ( 1 1 1) ( 1 1 1) , 或
the rearrangement of atoms in four surface bilayer is allo
wed
( 1 1 1) ( 1 1 1) ( 1 1 1) , 或
-1.0 -0.8 -0.6 -0.4 -0.2 0.0 0.2 0.4 0.6 0.8 1.0-3.0
-2.5
-2.0
-1.5
-1.0
-0.5
0.0
0.5
1.0
PAW-LDA PAW-GGA
9R
6H
4H
3C
J2/J
1
J3/J1
-1.0 -0.8 -0.6 -0.4 -0.2 0.0 0.2 0.4 0.6 0.8 1.0-3.0
-2.5
-2.0
-1.5
-1.0
-0.5
0.0
0.5
1.0 PAW-LDA PAW-GGA
9R
4H
15R
6H
3C
J2/J
1
J3/J1
the rearrangement of atoms in five surface bilayer is allowed
( 1 1 1) ( 1 1 1) ( 1 1 1) , 或
the rearrangement of atoms in six
surface bilayer is allowed
-1.0 -0.8 -0.6 -0.4 -0.2 0.0 0.2 0.4 0.6 0.8 1.0-3.0
-2.5
-2.0
-1.5
-1.0
-0.5
0.0
0.5
1.0 PAW-LDA PAW-GGA
9R
6H
4H
3C
J2/J
1
J3/J1
( 1 1 1) ( 1 1 1) ( 1 1 1) , 或
Kinetic phase diagrams of SiC epitaxial growth
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The CoPt alloy films
The kinetic equations of growth consist of all the three contributions from the diffusion, evaporation, and adsorption processes
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Ordering of the CoPt alloy films
(O. Ersen, et al J. Appl. Phys. 93, 2987 (2003).)
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The average order parameters of 8 layer films as a function of with T=570 K
Variation of order parameters with the increase of growth rate
0.0 1.0x10-5 2.0x10-5
0.0
0.2
0.4
0.6
0.8
10-10 10-8 10-6
orde
r pa
ram
eter
s
[100]
[001]
[100]
[001]
(a) (b)
L. Shi and J. Ni, Phys. Rev. Lett. 97, 126105 (2006).
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Variation of order parameters with temperature
The average order parameters of 8 layer films as a function of temperature
0.0
0.2
0.4
0.6
0.8
1.0
300 400 500 600 700 800 900
0.0
0.2
0.4
0.6
0.8
1.0
300 400 500 600 700 800 900
=1.25x10-6
ord
er
pa
ram
ete
rs =5.0x10-6
=6.25x10-6
ord
er
pa
ram
ete
rs
T (K)
=20.0x10-6
T (K)
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Ordering orientation superlattice
(a) The superlattice with the ordering-orientation transition per 12 layers. (b) The order parameters of the ordering orientation superlattice.
12 layers 12 layers
CoPt L10[001] CoPt L1
0[100]Pt
Z
X
Y
0 10 20 30 40 50
0.0
0.2
0.4
0.6
0.8
1.0
ord
er
pa
ram
ete
r
layer number
[001]
[100]
(a)
(b)
L. Shi and J. Ni, Phys. Rev. Lett. 97, 126105 (2006).
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Summary
Kinetics of ordering in alloy films and Kinetic phase diagrams, there is an oscillated ordered phase with occurrence conditions of high deposition rate
The 3C-SiC phase would grow epitaxially in low temperature. The 4H-SiC phase would grow epitaxially in intermediate temperature. The 6H-SiC or 15R-SiC phases would grow epitaxially in higher temperature.This is in agreement with experiments
We have investigated the effect of the kinetic anisotropy on the formation of structures in the epitaxial growth of alloy films. the ordering orientation of the L10 ordered structure changes from the [001] direction to the [100] direction with the increase of the growth rate.
We propose a simple method to synthesize the ordering orientation surperlattice by periodically changing the growth rate.
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Master equation method
Master equation method
Pn (r1,…,rn;t): cluster probabilityRn (r1,…,rn;t): exchange rate. {x}: neighboring cluster of interacting neighborhood.
}){,,(}){,,(
}){,,(}){,,(),(
}{,,}{
}{,,
}{,,}{
}{,,
xrrPxrrR
xrrPxrrRtrPdt
d
jixjiij x
x
jixjiij x
xi
jiji
ijiji
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Oscillatory ordered phase
30/ 0.06, 5 10 , 0.8, 0.25, 0.5B A B A Ak T J U P P
Ordering in the odd layersEffects of underlayer on the broken factor
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Kinetic phase diagram
Phase diagram with temperature and energy barrieras parameters
35 10 , 0.25, 1.0A B A AP P
Critical point