one-dimensional ostwald ripening on island growth an-li chin ( 秦安立 ) department of physics...
Post on 21-Dec-2015
220 views
TRANSCRIPT
![Page 1: One-dimensional Ostwald Ripening on Island Growth An-Li Chin ( 秦安立 ) Department of Physics National Chung Cheng University Chia-Yi 621 Taiwan, ROC Prof](https://reader034.vdocuments.net/reader034/viewer/2022042702/56649d5d5503460f94a3b840/html5/thumbnails/1.jpg)
One-dimensional Ostwald Ripeningon
Island Growth An-Li Chin (秦安立 )
Department of PhysicsNational Chung Cheng University
Chia-Yi 621Taiwan, ROC
Prof. Fu-Kwo Men (門福國 ) Prof. Chin-Rong Lee( 李進榮 )
![Page 2: One-dimensional Ostwald Ripening on Island Growth An-Li Chin ( 秦安立 ) Department of Physics National Chung Cheng University Chia-Yi 621 Taiwan, ROC Prof](https://reader034.vdocuments.net/reader034/viewer/2022042702/56649d5d5503460f94a3b840/html5/thumbnails/2.jpg)
OutlineIntroduction Growth modes Experimental setupOur works Nucleation and growth of islands Selective growth Coalescence of islands ‘1-D’ island ripeningConclusion
![Page 3: One-dimensional Ostwald Ripening on Island Growth An-Li Chin ( 秦安立 ) Department of Physics National Chung Cheng University Chia-Yi 621 Taiwan, ROC Prof](https://reader034.vdocuments.net/reader034/viewer/2022042702/56649d5d5503460f94a3b840/html5/thumbnails/3.jpg)
RT-Scanning Tunneling Microscopy
![Page 4: One-dimensional Ostwald Ripening on Island Growth An-Li Chin ( 秦安立 ) Department of Physics National Chung Cheng University Chia-Yi 621 Taiwan, ROC Prof](https://reader034.vdocuments.net/reader034/viewer/2022042702/56649d5d5503460f94a3b840/html5/thumbnails/4.jpg)
Substrate structure
(7×7)
24×24nm2
(5×2)
10×10nm2
![Page 5: One-dimensional Ostwald Ripening on Island Growth An-Li Chin ( 秦安立 ) Department of Physics National Chung Cheng University Chia-Yi 621 Taiwan, ROC Prof](https://reader034.vdocuments.net/reader034/viewer/2022042702/56649d5d5503460f94a3b840/html5/thumbnails/5.jpg)
The force equilibrium can be written as γS= γF/S + γF cosφ
φ : the island wetting layerγS : the surface tension of the substrateγF/S : the inter-surface tension of the film/substrateγF : the surface tension of the film substrate
γS ≧ γF/S + γF (layer-by-layer)
γS < γF/S + γF (island growth))
Growth modes
γS γF/S
γF φ
![Page 6: One-dimensional Ostwald Ripening on Island Growth An-Li Chin ( 秦安立 ) Department of Physics National Chung Cheng University Chia-Yi 621 Taiwan, ROC Prof](https://reader034.vdocuments.net/reader034/viewer/2022042702/56649d5d5503460f94a3b840/html5/thumbnails/6.jpg)
-200
0
200
400
600
Growth of Cobalt on clean Si(111)
0.1ML 0.3ML
• (√7 × √7) structure.
• Steps of double bi- layer height transformed to single bi-layer height.
• CoSi2 islands emerging at Co coverages above 0.3 ML.
500 Å × 500 Å1000 Å × 1000 Å
0
(Å)
620℃
![Page 7: One-dimensional Ostwald Ripening on Island Growth An-Li Chin ( 秦安立 ) Department of Physics National Chung Cheng University Chia-Yi 621 Taiwan, ROC Prof](https://reader034.vdocuments.net/reader034/viewer/2022042702/56649d5d5503460f94a3b840/html5/thumbnails/7.jpg)
Cobalt on Si(111)-5 × 2/Au0.1ML 0.3ML
0.5ML 0.5ML
• Islands are formed on surface with only 0.1ML Co deposition.
6000 Å × 6000 Å
500℃ 700℃
600℃600℃
2000 Å × 2000 Å
0.0 0.2 0.4 0.6 0.8 1.0
Isla
nd d
ensi
ty
Coverage(ML)
![Page 8: One-dimensional Ostwald Ripening on Island Growth An-Li Chin ( 秦安立 ) Department of Physics National Chung Cheng University Chia-Yi 621 Taiwan, ROC Prof](https://reader034.vdocuments.net/reader034/viewer/2022042702/56649d5d5503460f94a3b840/html5/thumbnails/8.jpg)
0.0 0.2 0.4 0.6 0.8 1.0
6X6
5X2
7x7
Rec
onst
ruct
ion
Au coverage (ML)
(7×7)
24×24nm2
(5×2)
36×36nm2
Surface structure vs. Au coverage
√3× √3
( 4° )
![Page 9: One-dimensional Ostwald Ripening on Island Growth An-Li Chin ( 秦安立 ) Department of Physics National Chung Cheng University Chia-Yi 621 Taiwan, ROC Prof](https://reader034.vdocuments.net/reader034/viewer/2022042702/56649d5d5503460f94a3b840/html5/thumbnails/9.jpg)
Controlled structural change via Au deposition
2000 Å × 2000 Å(5 × 2) (7 × 7)
240 Å × 240 Å 240 Å × 240 Å
500 Å × 4000 Å(7 × 7)
(5 × 2)
700℃ 630℃
![Page 10: One-dimensional Ostwald Ripening on Island Growth An-Li Chin ( 秦安立 ) Department of Physics National Chung Cheng University Chia-Yi 621 Taiwan, ROC Prof](https://reader034.vdocuments.net/reader034/viewer/2022042702/56649d5d5503460f94a3b840/html5/thumbnails/10.jpg)
12000 Å × 4000 Å
• Islands grow only on (5 × 2) terraces.
• No islands grows on (√7 × √7) terraces up to 0.3 ML of Co.
• The island is consisted of Si and Co atoms.
The selective island growth
4000 Å × 4000 Å
500 Å × 500 Å
√7 × √7
5 × 2
![Page 11: One-dimensional Ostwald Ripening on Island Growth An-Li Chin ( 秦安立 ) Department of Physics National Chung Cheng University Chia-Yi 621 Taiwan, ROC Prof](https://reader034.vdocuments.net/reader034/viewer/2022042702/56649d5d5503460f94a3b840/html5/thumbnails/11.jpg)
Growth Scheme
I. Depositing Au onto a nominally flat Si(111)-(77) surface to induce a (52) reconstruction. (Au coverage 0.443 ML);
II. Depositing Co onto the Si(111)-(52)/Au surface at
room temperature; (A disordered surface results.)
III. Observing surface morphological change as a function
of sample heating time.
![Page 12: One-dimensional Ostwald Ripening on Island Growth An-Li Chin ( 秦安立 ) Department of Physics National Chung Cheng University Chia-Yi 621 Taiwan, ROC Prof](https://reader034.vdocuments.net/reader034/viewer/2022042702/56649d5d5503460f94a3b840/html5/thumbnails/12.jpg)
Coalescence of islands
0.5 ML Co on Si(111)-(52)/Au at RT followed by 620C heating
30 sec 210 sec90 sec
900 sec510 sec
200200nm2
330 sec
With islands on terrace decreasing gradually in size, atoms diffuse away from edges of terrace islands and feed the growth of islands at step edges.
![Page 13: One-dimensional Ostwald Ripening on Island Growth An-Li Chin ( 秦安立 ) Department of Physics National Chung Cheng University Chia-Yi 621 Taiwan, ROC Prof](https://reader034.vdocuments.net/reader034/viewer/2022042702/56649d5d5503460f94a3b840/html5/thumbnails/13.jpg)
Islands on step edge and terrace
0 1 2 3 4 5 6 70
5
10
15
20
25
0 1 2 3 4 5 6 70
10
20
Percen
tage (
%)
0 1 2 3 4 5 6 70
10
20
Height (nm)
Heating for 30sec
Heating for 90sec
Heating for 210sec
terracestep edge
![Page 14: One-dimensional Ostwald Ripening on Island Growth An-Li Chin ( 秦安立 ) Department of Physics National Chung Cheng University Chia-Yi 621 Taiwan, ROC Prof](https://reader034.vdocuments.net/reader034/viewer/2022042702/56649d5d5503460f94a3b840/html5/thumbnails/14.jpg)
Relative populations of two types of islands
Most islands appear at step edges at late stage of ripening process. (note that the number density of the islands at step edges decreases as well.)
0 200 400 600 800 10000
20
40
60
80
100
Per
cen
tag
e (
% )
Time ( sec )
Cluster at step edgeCluster on terrace
![Page 15: One-dimensional Ostwald Ripening on Island Growth An-Li Chin ( 秦安立 ) Department of Physics National Chung Cheng University Chia-Yi 621 Taiwan, ROC Prof](https://reader034.vdocuments.net/reader034/viewer/2022042702/56649d5d5503460f94a3b840/html5/thumbnails/15.jpg)
0 200 400 600 800 10001x104
2x104
3x104
4x104
5x104
6x104
Sum
of
volu
me
/ 200
x 2
00 n
m2
Heating time(sec)
Conservation of sum of island volume
Total island volume is conserved during the ripening process.
![Page 16: One-dimensional Ostwald Ripening on Island Growth An-Li Chin ( 秦安立 ) Department of Physics National Chung Cheng University Chia-Yi 621 Taiwan, ROC Prof](https://reader034.vdocuments.net/reader034/viewer/2022042702/56649d5d5503460f94a3b840/html5/thumbnails/16.jpg)
Average island size vs. growth time
2.0
2.5
3.0
3.5
4.0
4.5
5.0
Hig
ht(n
m)
0 200 400 600 800 1000
12
14
16
18
20
22
cros
s-se
ctio
nal
len
gth
( n
m )
Heating time(sec)
![Page 17: One-dimensional Ostwald Ripening on Island Growth An-Li Chin ( 秦安立 ) Department of Physics National Chung Cheng University Chia-Yi 621 Taiwan, ROC Prof](https://reader034.vdocuments.net/reader034/viewer/2022042702/56649d5d5503460f94a3b840/html5/thumbnails/17.jpg)
2D-adatom gasdiffusion length
low
high
/rkT)νexp(2γcc(r) CMCV
Ripening growthGibbs-Thomson effect:
![Page 18: One-dimensional Ostwald Ripening on Island Growth An-Li Chin ( 秦安立 ) Department of Physics National Chung Cheng University Chia-Yi 621 Taiwan, ROC Prof](https://reader034.vdocuments.net/reader034/viewer/2022042702/56649d5d5503460f94a3b840/html5/thumbnails/18.jpg)
isla
nd d
ensi
ty
energy (heating time)
Overview of clustering
nucleation
aggregation
late stage growth
![Page 19: One-dimensional Ostwald Ripening on Island Growth An-Li Chin ( 秦安立 ) Department of Physics National Chung Cheng University Chia-Yi 621 Taiwan, ROC Prof](https://reader034.vdocuments.net/reader034/viewer/2022042702/56649d5d5503460f94a3b840/html5/thumbnails/19.jpg)
Model for island ripening 1/2
Consider the adatom diffusion among neighboring islands resulting from the chemical potential differences in islands of different sizes, the change in island radius, r, can be expressed as
I.M. Lifshitz and V.V. Slyozov (1958)
where rcr is some critical grain radius. A grain in the solution grows (shrinks) if its radius is larger (smaller) than rcr. D is the diffusion coefficient and the S size of the region involved in the adatom exchange process, the concentration of the solution, the grain surface energy per unit area, and the molar volume of the dissolved material.
(1)
where W has the width of a step if the diffusing atoms are confined to move along step edges.
r > rcr, island growsr < rcr, island shrinks
)11
(SD 3
rrr
r
dt
dN
cr
cr
)
11(
D2
)11
(D2
)3
4(
3
3
3
rrr
rW
rrrπ
rπ
dt
d
cr
crline
crcrsurf (i)
(ii)
![Page 20: One-dimensional Ostwald Ripening on Island Growth An-Li Chin ( 秦安立 ) Department of Physics National Chung Cheng University Chia-Yi 621 Taiwan, ROC Prof](https://reader034.vdocuments.net/reader034/viewer/2022042702/56649d5d5503460f94a3b840/html5/thumbnails/20.jpg)
Model for island ripening 2/2
With the constraint that the number of adatoms on the surface is conserved, we solve equations (1) and (2). The results are
rcr(t) t 1/5
N(t) t -3/5
(Experimental results: )
Let f(r, t) be the number distribution function of island with radius r at time t, from the equation of continuity we have
(2)
rcr(t) t 0.201
N(t) t -0.55
0)(
dt
drf
rt
f
rcr(t) t 01/4
N(t) t -3/4(i) (ii)
![Page 21: One-dimensional Ostwald Ripening on Island Growth An-Li Chin ( 秦安立 ) Department of Physics National Chung Cheng University Chia-Yi 621 Taiwan, ROC Prof](https://reader034.vdocuments.net/reader034/viewer/2022042702/56649d5d5503460f94a3b840/html5/thumbnails/21.jpg)
3 4 5 6 7
3
4
5
ln(I
slan
d nu
mbe
r)(2
00n
m)2
ln(Time)(sec)
3 4 5 6 7
0.8
1.0
1.2
1.4
1.6
ln(i
slan
d h
eigh
t)(n
m)
ln(Time)(sec)
Island distributions vs. time
Island density decreases as time to the -0.55 power.
Island height increases as time to the 0.2 power.
(Island shape independent of island size.)
Slope = -0.55 Slope = 0.2
Average island density Average island height
![Page 22: One-dimensional Ostwald Ripening on Island Growth An-Li Chin ( 秦安立 ) Department of Physics National Chung Cheng University Chia-Yi 621 Taiwan, ROC Prof](https://reader034.vdocuments.net/reader034/viewer/2022042702/56649d5d5503460f94a3b840/html5/thumbnails/22.jpg)
Diffusing species diffusion pathway
Single bi-layer-heightstep (3.1 Å)
1. escape from islands on terraces;
2. diffuse toward step edges, which act as sinks;
3. diffuse along step edges(rate-limiting)
4. attach to islands at step edges followed by edge diffusion.
Diffusing species must
![Page 23: One-dimensional Ostwald Ripening on Island Growth An-Li Chin ( 秦安立 ) Department of Physics National Chung Cheng University Chia-Yi 621 Taiwan, ROC Prof](https://reader034.vdocuments.net/reader034/viewer/2022042702/56649d5d5503460f94a3b840/html5/thumbnails/23.jpg)
Conclusion
We have demonstrated the self-selective growth of CoSi2 islands with narrow size distribution on only one of the two domains by depositing up to 0.3 ML of Co.
We have observed a unique 1D diffusion process leading to the growth of step-edge islands at the expense of terrace islands.
![Page 24: One-dimensional Ostwald Ripening on Island Growth An-Li Chin ( 秦安立 ) Department of Physics National Chung Cheng University Chia-Yi 621 Taiwan, ROC Prof](https://reader034.vdocuments.net/reader034/viewer/2022042702/56649d5d5503460f94a3b840/html5/thumbnails/24.jpg)
Island distribution
0 1 20.0
0.1
0.2
P
erce
nta
ge
Island height/<island height>
30sec1 90sec11 120sec121 60sec1 150sec1 210sec1 330sec1