ICDIM 2012 presentation
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Transcript of ICDIM 2012 presentation
Implantation of sapphire by Zr and Zr plus O: threshold fluence for amorphization and optical properties
(a) Materials Science and Engineering Department, University of Tennessee, Knoxville, TN 37996 (b) University of Sussex, Brighton, BN1 9QH, United Kingdom (c) Center for Materials Processing, University of Tennessee, Knoxville, TN 37996-0750 (d) Instituto Tecnológico e Nuclear (ITN) Ion Beam Laboratory, Sacavém, Portugal
Younes Sina a, Peter D. Townsend b, Carl J. McHargue a,c, Edvardo Jorge da Costa Alves d
Important factors for amorphization during ion implantation: Sample temperature Ion mass Ion energy Fluence Ionicity degree Chemical effect Thermodynamic stability Topology of the atomic scale structure Physical properties Ease of glass formation
Background
During ion implantation: The ions displace atoms from lattice sites They create vacancy-interstitial pairs and other associated defects At higher fluences: Recombination of defects can occur at the same rate as their
production In other cases: • Amorphization is the result of damage accumulation during ion
bombardment, especially at low temperatures
Background
4
Zr amorphizes sapphire at relatively low damage.
Background
0
0.2
0.4
0.6
0.8
1
1.2
0 50 100 150 200 250 300 350 400
ΧA
l
dpa
Zr
Fe
Ti
Nb
Cr
5
-1
0
1
2
3
4
5
6
7
8
9
0
20
40
60
80
100
120
0 500 1000 1500 2000 2500 3000
E= 175 keV Φ= 4E16 Zr+/cm2
dpa Zr%
Depth [Å]
Buried amorphous layer suggest concentration of Zr may be controlling factor
Crystal Systems, Inc. (Salem, MA)
α-Al203
1) 120 h at 1450⁰C
Oxygen
To remove any residual polishing damage or surface contamination
α-Al203
I. Sample Preparation
2) slow cool
Zr (175 keV, 2x1015 -2x1016 /cm2) Room Temperature
α-Al203 Zr implanted α-Al203
RBS
OA, PL
O (55 keV, 1.1x1016 -2.3-x1016 /cm2) Room Temperature
Zr+ O implanted α-Al203
RBS
OA, PL Zr implanted α-Al203
7◦-off
7◦-off
I. Sample Irradiation
Zr
O
Rutherford backscattering/ Channeling (RBS-C) Disorder on the Al-sublattice Distribution of implanted species Verification of presence (or absence) of an amorphous phase Zr depth profiling Optical absorption (OA) Photoluminescence (PL) Verification of presence (or absence) of oxygen vacancies Check for F type color centers
III Characterization
8
IV Calculation of color centers concentration
Using Smakula’s equation for calculation of F+ F+ centers concentration
Results and discussion
1) Threshold fluence of amorphization 2) Effect of oxygen implantation on pre-Zr- implanted samples 3) Optical properties of the irradiated samples with Zr and Zr+ O 4) Calculating of true absorption coefficient of the induced bands 5) Concentration of F centres using Smakula’s equation
100 200 300 400 500 600 7000
400
800
1200
1600
2000
2400
2800
3200
Yie
ld
channel
<0001>
random =4º
ZrAl
Ox10
Sample 2x1015
Zr+.cm
-2
100 200 300 400 500 600 7000
400
800
1200
1600
2000
2400
Sample 7.5x1015
Zr+.cm
-2
Yie
ld
channel
<0001>
random =3º
ZrAl
O
x3
Fluence below the amorphization threshold
Fluence on the verge of amorphization
Rutherford backscattering spectrometry along a channeling direction (RBS-C) using 2.0 MeV He+
100 200 300 400 500 600 7000
400
800
1200
1600
2000Sample 1.5x10
16 Zr
+.cm
-2
<0001>
random
Y
ield
channel
ZrAl
O
Zr fluence just above amorphization threshold
175 keV
40 nm
0
0.5
1
1.5
2
2.5
3
3.5
0
5
10
15
20
25
30
35
40
45
0 50 100 150 200 250 300
Zr%
dp
a
Depth [nm]
dpa @ E=175keV, Φ=1.5E16
40 dpa
Φ=1.5×1016
Rutherford backscattering spectrometry along a channeling direction (RBS-C) using 2.0 MeV He+
100 200 300 400 500 600 7000
500
1000
1500
2000
2500
Yie
ld
channel
<0001>
random
Sample A
Zr (x3)Al
O
7.5 x1015
Zr+/cm
2 +1.1x10
16 O
+/cm
2
Oxygen implantation into a pre-Zr- implanted sample
100 200 300 400 500 600 7000
500
1000
1500
2000
25001.5 x10
16 Zr
+/cm
2 + 2.3x10
16 O
+/cm
2
Yie
ld
channel
<0001>
random
ZrAl
O
Sample IR
Effect of oxygen in pre-Zr implanted samples
Low fluence-damaged Not amorphous
Higher fluence-damaged amorphous
0
200
400
600
800
1000
1200
1400
1600
1800
300 800 1300 1800
Yie
ld
Energy [keV]
2E15 Aligned
7.5E15 Aligned
1.5E16 Zr+/cm2 Aligned
By increasing Zr fluence damage in Al and O- sublattices increase
By implantation of O in pre-implanted Zr samples, damage in Al sublattice increases and in O sublattice decreases
0
200
400
600
800
1000
1200
1400
1600
1800
300 800 1300 1800
Yie
ld
Energy [keV]
1.5E16 Zr+/cm2 & 2.3E16 O+/cm2 Aligned
7.5E15 Zr+/cm@ & 1.1E16 O+/cm2 Aligned
---- ----
0
50
100
150
200
250
300
350
400
1500 1550 1600 1650 1700 1750 1800
Yie
ld
Energy [keV]
7.5E15 Zr+/cm2 Random 1.5E16 Zr+/cm2 Random 7.5E15 Zr+/cm2 & 1.1E16 O+/cm2 Random 1.5E16 Zr+/cm2 & 2.3 E16 O+/cm2 Random
b
2) Effect of oxygen implantation on pre-Zr- implanted samples
Zirconium profiles in sapphire implanted with oxygen subsequent to implantation with Zr: (a) below and (b) at the threshold for amorphization.
The subsequent implantation of oxygen produces a slight broadening of the zirconium distribution, probably due to collisional mixing
a
Zr distribution
0
0.1
0.2
0.3
0.4
0.5
0.6
0.7
0.8
0.9
1
3 4 5 6 7
Inte
nsi
ty [
Arb
it.
Un
it]
Energy [eV]
1.5E16 Zr+/cm2 & 2.3E16 O+/cm2 , RT
2E16 Zr+/cm2 , RT
1.5E16 Zr+/cm2 ,RT
7.5E15 Zr+/cm2 & 1.1E16 O+/cm2 , RT
2E16 Zr+/cm2 & 4E16 O+/cm2 , RT
7.5E15 Zr+/cm2 , RT
Optical absorption spectra with the absorption from a virgin crystal subtracted
F+
F+F+
Optical properties of the irradiated samples with Zr and Zr+ O
F+
F
0
2
4
6
8
10
12
14
16
18
20
300 320 340 360 380 400 420 440 460 480
Inte
nsi
ty
nm
1.5E16 Zr+/cm2 & 2.3E16 O+/cm2
7.5E15 Zr+/cm2 & 1.1E16 O+/cm2
7.5E15 Zr+/cm2
1.5E16 Zr+/cm2
VIR
2E16 Zr+/cm2
Photoluminescence spectra obtained with 4.86 eV confirm that both types of oxygen vacancies are present in all implanted samples.
Concentration of retained simple oxygen defects (F-type centers) can be estimated by Smakula’s equation: NF= 0.87 x 1017 n µmax W1/2/f (n2 + 2)2
f is the oscillator strength and for the F band is ~1 n is the refractive index of implanted sapphire ~1.8 W1/2 is width (in eV) at half maximum of the optical absorption band characterized by a maximum optical density has a value of ~0.6 eV µm is maximum absorption coefficients of the induced bands
Important parameter in Smakula’s equation is absorption coefficient ( µm)
The absorption coefficient (µ) is given by log (I in/I out) = µt/2.3 where t is the path length
Calculated oxygen vacancy profiles produced by Zr and O irradiation in sapphire
The implant/damage depth, t, is only about 62 nm for the samples implanted with zirconium only and 68 nm for the dual implants
0
0.2
0.4
0.6
0.8
1
1.2
0 500 1000 1500 2000 2500
Nu
mb
er/
(An
gstr
om
-Io
n)
Depth [A]
7.5E15 Zr 1.1E16 O
O Vacancies after Zr
O Vacancies after O
Number of O vacancies/Cm3 = [Number/Å × Ions].[Ions]. [Å/Cm3]
-
=
The implant/damage depth, t, is only about 62 nm for the samples implanted with zirconium only and 68 nm for the dual implants
I in I out
log (I in/ I out) = µt/2.3
Sample N (F+F+
) (cm-3)
7.5E15 Zr+/cm2 & 1.1E16 O+/cm2 , RT 3.00E+21
7.5E15 Zr+/ cm2 , RT 3.646E+21
1.5E16 Zr+/ cm2 , RT 3.5E+21
1.5E16 Zr+/cm2 & 2.3E16 O+/cm2 , RT 3.27E+21
2E16 Zr+/ cm2 , RT
3.89E+21
Concentration of retained simple oxygen defects (F-type centers) estimated by Smakula’s equation:
Implanted species Oxygen vacancies retained as F &F+ defects
( from Smakula’s equation)
Oxygen vacancies predicted by SRIM
(99% dynamically annealed)
Zr 1 - 2.5 % 6 -8 %
Zr + O 0.7 - 1.1 % 4 -5 %
Some of the displaced oxygen may reside in interstitial positions as O2- leaving a
vacancy without a trapped electron(s). This defect has an optical absorption band near
7.0 eV, outside the range of the instrument used here.
At the relatively high fluences used in this study, there is considerable overlapping of the displacement cascades that may give rise to extended defects such as interstitial dislocations, nanometer-sized clusters, defects trapped at dislocations, etc.
Conclusion
1. Threshold fluence of 175 keV Zr is approximately 1.5×1016 Zr+/cm2.
2. Subsequent implantation of oxygen produces slight broadening of damage region of low fluence and no apparent effect at fluence above amorphization threshold.
3. Number of oxygen vacancies retained as F and F+ centers is very low.
4. Implantation of oxygen in pre implanted samples reduced the number of F and F+ centers.
Thank you
These slides were prepared for an oral presentation for ICDIM 2012 Santa Fe, NM ( June 24-29/2012)
http://icdim.newmexicoconsortium.org/conference-agenda-clickable