1. Implantation of sapphire by Zr and Zr plus O:
threshold fluence for amorphization and optical properties
Younes Sina a, Peter D. Townsend b, Carl J. McHargue a,c, Edvardo Jorge da Costa Alves d
(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
2. Background
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
3. 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
4. Background
Zr amorphizes sapphire at relatively low damage.
1.2
Zr
1
0.8 Fe
0.6
Ti
0.4
ΧAl
Nb
0.2
0 Cr
0 50 100 150 200 250 300 350 400
dpa
4
6. I. Sample Preparation
To remove any residual polishing damage or surface contamination
Crystal Systems, Inc. (Salem, MA)
Oxygen
1) 120 h at 1450⁰C
α-Al203
2) slow cool
α-Al203
7. I. Sample Irradiation
7◦-off
RBS
Zr
OA, PL
α-Al203
Zr implanted α-Al203
2x1015 -2x1016
Zr (175 keV, /cm2)
Room Temperature
RBS
O
7◦-off
OA, PL
Zr implanted α-Al203
Zr+ O implanted α-Al203
O (55 keV,1.1x1016 -2.3-x1016 /cm2)
Room Temperature
8. III Characterization
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
IV Calculation of color centers concentration
Using Smakula’s equation for calculation of F+ F+ centers concentration
8
9. 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
10. 15 + -2
Sample 2x10 Zr .cm Rutherford backscattering spectrometry along a
3200
2800
<0001> channeling direction (RBS-C) using 2.0 MeV He+
random =4º
2400
O
2000 x10
Yield
1600 Al Fluence below the amorphization threshold
Zr
1200
800
400
0
100 200 300 400 500 600 700
channel
15 + -2
Sample 7.5x10 Zr .cm
2400
<0001>
2000 random =3º
O
1600 x3
Fluence on the verge of amorphization
Yield
1200 Al
Zr
800
400
0
100 200 300 400 500 600 700
channel
12. 15 + 2
7.5 x10 Zr /cm +1.1x10 O /cm
16 + 2
Effect of oxygen in pre-Zr implanted samples
2500
Sample A <0001>
2000 O random
1500
Al Zr (x3)
Low fluence-damaged
Yield
1000
Not amorphous
500
0
100 200 300 400 500 600 700
channel
Oxygen implantation into a pre-Zr- implanted sample
16 + 2 16 + 2
1.5 x10 Zr /cm + 2.3x10 O /cm
2500
Sample IR <0001>
2000 O random
Higher fluence-damaged
1500
Al amorphous
Yield
1000 Zr
500
0
100 200 300 400 500 600 700
channel
13. 1800
1600 2E15 Aligned
1400 7.5E15 Aligned
1200
1.5E16 Zr+/cm2 Aligned
1000
Yield
800
600
400
200
By increasing Zr fluence damage in Al and
0 O- sublattices increase
300 800 Energy [keV] 1300 1800
1800
1600 ---- 1.5E16 Zr+/cm2 & 2.3E16 O+/cm2 Aligned
1400
1200
---- 7.5E15 Zr+/cm@ & 1.1E16 O+/cm2 Aligned
1000
Yield
800
By implantation of O in pre-implanted Zr
600
samples, damage in Al sublattice
400
increases and in O sublattice decreases
200
0
300 800 1300 1800
Energy [keV]
14. Zr distribution 2) Effect of oxygen implantation on pre-Zr- implanted samples
400
7.5E15 Zr+/cm2 Random
b
350 1.5E16 Zr+/cm2 Random
7.5E15 Zr+/cm2 & 1.1E16 O+/cm2 Random
300
1.5E16 Zr+/cm2 & 2.3 E16 O+/cm2 Random
250
Yield
200
a
150
100
50
0
1500 1550 1600 1650 1700 1750 1800
Energy [keV]
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
15. Optical properties of the irradiated samples with Zr and Zr+ O
F+F+
1
1.5E16 Zr+/cm2 & 2.3E16 O+/cm2 , RT
0.9
2E16 Zr+/cm2 , RT
0.8
Intensity [Arbit. Unit]
0.7 1.5E16 Zr+/cm2 ,RT
0.6
F+ 7.5E15 Zr+/cm2 & 1.1E16 O+/cm2 , RT
0.5 2E16 Zr+/cm2 & 4E16 O+/cm2 , RT
0.4
7.5E15 Zr+/cm2 , RT
0.3
0.2
0.1
0
3 4 5 6 7
Energy [eV]
Optical absorption spectra with the absorption from a virgin crystal subtracted
16. Photoluminescence spectra obtained with 4.86 eV confirm that both types of oxygen
vacancies are present in all implanted samples.
20
F+ 1.5E16 Zr+/cm2 & 2.3E16 O+/cm2
18
7.5E15 Zr+/cm2 & 1.1E16 O+/cm2
16 7.5E15 Zr+/cm2
1.5E16 Zr+/cm2
14
VIR
Intensity
12
2E16 Zr+/cm2
10
F
8
6
4
2
0
300 320 340 360 380 nm 400 420 440 460 480
17. 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
18. Calculated oxygen vacancy profiles produced by Zr and O irradiation in sapphire
1.2
7.5E15 Zr
1 1.1E16 O
Number/(Angstrom-Ion)
0.8
O Vacancies after Zr
0.6
O Vacancies after O
0.4
0.2
0
0 500 1000 1500 2000 2500
Depth [A]
The implant/damage depth, t, is only about 62 nm for the samples implanted with
zirconium only and 68 nm for the dual implants
Number of O vacancies/Cm3 = [Number/Å × Ions].[Ions]. [Å/Cm3]
19. I in I out
-
=
log (I in/ I out) = µt/2.3
The implant/damage depth, t, is only about 62 nm for the samples implanted with
zirconium only and 68 nm for the dual implants
21. Implanted species Oxygen vacancies Oxygen vacancies predicted by
retained as F &F+ defects SRIM
( from Smakula’s equation) (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.
22. 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.
23. Thank you
These slides were prepared for an oral presentation for ICDIM 2012 Santa Fe, NM ( June 24-29/2012)
