This document describes an experiment involving ion implantation and thermal annealing of chromium ions in alpha aluminum oxide single crystals. Chromium ions were implanted at energies of 280-300 keV and doses of 1016-1017 ions/cm2. Backscattering spectroscopy measurements showed the implantation caused damage in the aluminum and oxygen sublattices but did not amorphize the surface region. Thermal annealing from 800-1600°C led to damage recovery and incorporation of chromium into substitutional lattice sites. Angular scans and calculations determined the chromium was substituting into sites in the aluminum sublattice rather than the oxygen sublattice.

1. H. Naramoto, C.W. White, J.M. Williams, C.J. McHargue,
O.W. Holland., M.M. Abraham, and B.R. Appleton
Solid State Division, Oak Ridge National Laboratory, Oak Ridge, Tennessee
Presentation by: Younes Sina
Ion implantation and thermal
annealing of α-Al2O3 single
crystals

2. Experimental
Single crystal of Al2O3 of high purity
(100 ppm total) with low dislocation
density (103-104 cm-2) from Union
Carbide Corp., and Crystal System,
Inc.
Sample preparation
Disc specimens were cut
perpendicular (to within ± 2°) to the
<0001> (c axis) and <1-210> (a axis)
from single crystalline rods using a
diamond saw.

3. Experimental
Sample preparation
These specimens were polished to a mirrorlike
surface finish with a fine diamond paste(< 1 m
mesh) and annealed at 1200 °C in air for 120 h to
remove the surface damage induced by mechanical
polishing.

4. 280 or 300 keV
52 Cr+
1016-1017 ions/cm2
7° off
Current density : < 2×10-6 amp/cm2
Estimated temperature during implantation due
to beam heating : 150°C
Implanted
region
Unimplanted
region
(virgin)
musk
Experimental

5. Thermal annealing in
air
1 hr
800°C to 1600 °C
RBS
Ion scattering /channeling
Using 2 MeV 4He+
Experimental

6. Determine the depth profile of the implanted
species
Depth distribution of damage in the lattice
Lattice location of the impurity
Using RBS to
Experimental

7. Experimental
Some details about RBS
There are no strong nuclear reaction to complicate the
backscattering analysis using 2 MeV 4He+.
Random spectra were obtained while continuously
rotating the crystal to average over all crystallographic
directions.
The specimens were covered with a stainless- steel plate
with a small open aperture for analysis to minimize the
charge buildup.
The probing beam current was held to 10 nA ( 1 mm
diameter).
The scattered ion detector was cooled with Freon to
22°C, which improved the energy resolution to 14 keV.
A scattering angle of 160˚was used for analysis.

8. Lattice location measurements were carried out using
both aligned axial channeling spectra as well as
detailed angular scans across the following major axes
and planes:
<0001> , <1-210> , <10-10> , {0001} , {1-210} , and {10-10}

9. Experimental
Angular scan measurements were taken only after
annealing to T=1300° and 1500°.
After these temperatures, substantial recovery of
displacement damage in both the Al and O
sublattices occurs.

10. Experimental
The valence state of the implanted impurity after
thermal annealing was determined using standard
Electron Paramagnetic Resonance (EPR)
absorption measurements.

11. Experimental
EPR absorption measurement were made using a
Kα- band microwave spectrometer (35 GHz, 1.2
cm-1) with the magnetic field applied perpendicular
to the <0001> axis of the crystal.

12. Experimental
Changes in the hardness were measured by the
use of the Knoop microhardness technique.
A force of 0.147 N was used in
order to confine the
impression depth to the near-
surface region (0.3 which is
corresponds roughly to the
full width of a typical Gaussian
distribution of the implanted
impurity ).

13. Results and Discussion
Implantation damage
2- MeV He+ backscattering spectra from 52Cr(280
keV, 3×1016/cm2) implanted α-Al2O3.
Random
<0001> aligned
virgin

14. Results and Discussion
Implantation damage
2- MeV He+ backscattering spectra from 52Cr(280
keV, 3×1016/cm2) implanted α-Al2O3.
Random
<0001> aligned
virgin
Al surface peak
O surface peak
(Random)Yield
(Aligned)Yield
χmin 
%1.2(Al)χmin 
%6.0(O)χmin 

15. Results and Discussion
The near-surface region was not turned
amorphous by implantation (the aligned
yield after implantation dose not reach
the random value).
We have not observed a completely disordered surface
region up to dose of 1×1017/cm2. This is in contrast to
the case of semiconductors such as Si, where dose of
1014-1015/cm2 would be sufficient to turn the near-
surface region completely amorphous.
Random<0001> aligned
virgin
The implanted Cr shows a small
channeling effect (the aligned yield
is 85% of the random yield)

16. Results and Discussion
The fact that Al2O3 is not turned amorphous at these
implantation energies and doses is inconsistent with the
existence of a reordering process during implantation.
The implanted Cr shows a small channeling effect (the
aligned yield is 85% of the random yield), again
suggesting a reordering process during implantation.
Sample temperatures during implantation are
estimated to less than 150°C, and if the ion beam
current is reduced by an order of magnitude, there is
no significant change in the damage distribution.

17. Results and Discussion
Effect of integrated dose
Effect of integrated dose on the damage distribution produced
as a result of 300- keV implantation.
Random
<0001>Align virgin
<0001>Align (1×1016/cm2)
<0001>Align (1×1017/cm2)
The near-surface region
is relatively damage free.

18. Results and Discussion
The main effect of increasing dose is to broaden the
damage profile to greater depth with little or no increase
in the magnitude of the damage level.
Higher surface peak
1×1017/cm2)
1×1016

19. Results and Discussion
Plot of the dose dependence of χmin
measured in the Al substrate at a depth
corresponding to the peak in the implanted
Cr distribution.
These result shows that χmin
(Al) is essentially
independent of implantation
dose, indicating a saturation
of damage along all three
crystallographic direction.

20. Results and Discussion
Thermal annealing behavior of 52Cr(300 keV, 1×1017/cm2) implanted α-
Thermal annealing behavior No change in the damage distribution in the O or
Cr
Damage recovery for Cr &O

21. Results and Discussion
Thermal annealing behavior
Thermal annealing behavior of 52Cr(280 keV, 3×1016/cm2) implanted α-
Al O
Change in the damage distribution in the Al & O & Cr
Damage recovery for Cr &O

22. Results and Discussion
Thermal annealing behavior
From the results presented so far, it is impossible to
determine whether Cr becomes substituonal in the Al
or O sublattice, but the angular scan results clearly
show that Cr is substitutional in the Al sublattice.

23. Results and Discussion
Thermal annealing behavior
52Cr(300 keV, 1×1017/cm2)
52Cr(280 keV, 3×1016/cm2)
Random
<0001> aligned
virgin
Random<0001> aligned
virgin
Aligned yield for Al and O is very close to the virgin yield.
Aligned yield for Al is very close to the virgin yield.
The dechanneling rate in the near-surface region is greater for the high-
dose crystal compared to the lower dose case.

24. Results and Discussion
Thermal annealing behavior
This increased dechanneling in the near-surface
region, which is a function of the dose (or
concentration) of the impurity, may be due to either
residual defects or to lattice strain resulting from the
incorporation of large concentrations of Cr into the Al
sublattice.

25. Results and Discussion
Thermal annealing
behavior
Comparison of total and substitutional concentration for 52Cr(300 keV,1×1017/cm2)
in α-Al2O3 after annealing at 1500°C
%98
(Al)]χ[1
(Cr)]χ[1
(%)Fractiononalsubstituti
min
min





26. Results and Discussion
Thermal annealing behavior
Thermal annealing behavior for 52Cr (300 keV, 1×1016/cm2) in α-Al2O3
Random
<0001> aligned
virgin
Random
<0001> aligned
virgin
Random
<0001> aligned
virgin
Substantial redistribution of the dopant occurs
in the range of 1500-1600 °C.

27. Results and Discussion
Thermal annealing behavior
Concentration profile for 52Cr(300 keV, 1×1017/cm2) in α-Al2O3 after annealing at
1500°C and 1600°C compared to as-implanted profile.
Substantial redistribution of the dopant occurs
in the range of 1500-1600 °C.
After annealing at 1600°C, Cr is
observed to be redistribution both
toward the surface and into the
crystal.
Cr diffuses by a substitutional
diffusion mechanism

28. Results and Discussion
Thermal annealing behavior
Results:
Damage recovery begins selectively in the Al
sublattice at a temperature of 800°C.
Damage recovery begins in the O sublattice at
1000°C.
Incorporation of Cr into substitutional lattice sites
occurs predominantly in the temperature range 1200-
1500°C. After 1500°C annealing, Cr is 95%
substitutional in the lattice.
The onset of substitutional Cr diffusion occurs in the
temperature range 1500-1600°C.

29. Results and Discussion
Thermal annealing behavior
The features of Cr incorporation can be better
distinguished by separating the Cr profile into
three different segments:
(1)0.05 m
(2)0.05-0.15 m
(3)0.15-0.3 m
Results:

30. Results and Discussion
Thermal annealing behavior
Results:
(1) 0.05 m
(2) 0.05-0.15 m
(3) 0.15-0.3 m
Where damage is the least in the as-implanted condition
The χmin(Cr) value increases slightly with annealing temperature
up to 1200°C even though χmin(Al) decreases, indicating no
further incorporation of Cr at this depth into substitutional lattice
sites in this temperature range.
In region (1):

31. Results and Discussion
Thermal annealing behavior
Results: (1) 0.05 m
(2) 0.05-0.15 m
(3) 0.15-0.3 m
Surface side of the damage distribution, χmin(Cr) change very
little with annealing to 1200°C
In region (2):

32. Results and Discussion
Thermal annealing behavior
Results: (1) 0.05 m
(2) 0.05-0.15 m
(3) 0.15-0.3 m
Saturation of damage occurred in the as-implanted state,
χmin(Cr) decreased with annealing up to 1200°C.
In region (3):

33. Results and Discussion
Thermal annealing behavior
Results:
(1) 0.05 m
(2) 0.05-0.15 m
(3) 0.15-0.3 m
These results suggest that up to 1200°C, damage
recovery in Al sublattice competes with Cr
incorporation. With annealing to 1500°C, χmin(Cr)
decreases substantially in region (2) and (3), while
the aligned yield in the oxygen sublattice increases
slightly. These results suggest that Cr incorporation
in region (2) and (3) may be accompanied by oxygen
indiffusion from the surface during annealing at the
higher temperatures.

34. Results and Discussion
Results:
Thermal annealing behavior
Summary of thermal annealing result for 52Cr(300 keV, 1×1017/cm2) in α-Al2O3

35. Results and Discussion
Lattice location of implanted 52Cr in α–Al2O3 after thermal annealing
4a
4c
4b
4d 7b
7c7a
5a5b
5c
Results presented in previous Figs. suggest that
implanted Cr is substitutional in α-Al2O3 after thermal
annealing to temperatures in the range of 1300-1500 °C,
because the implanted Cr exhibits a pronounced
channeling effect. However these measurements alone are
not sufficient to determine weather Cr is substitutional in
the Al or O sublattice.

36. Results and Discussion
Lattice location of implanted 52Cr in α–Al2O3 after thermal annealing
To determine whether Cr is substitutional in the Al
or O sublattice, angular scans across the major
axis and planes are necessary.

37. Results and Discussion
Lattice location of implanted 52Cr in α–Al2O3 after thermal annealing
Axial angular scans for 2-MeV He+ incident on virgin α-Al2O3(depth range=0.05-0.35)
Yield of particles scattered from Al and O atoms in depth interval 0.05-0.35 m
normalized to the random value plotted as a function of tilt angle away from the
major axis or plane
2 ψ1/2: full width at half maximum of the channeling dip

38. Results and Discussion
Lattice location of implanted 52Cr in α–Al2O3 after thermal annealing
Planar angular scans for 2-MeV He+ incident on virgin α-Al2O3(depth range=0.05-0.35)
2 ψ1/2: full width at half maximum of the channeling dip

39. Results and Discussion
Lattice location of implanted 52Cr in α–Al2O3 after thermal annealing
 1021cutx0001cutz

40. Results and Discussion
Lattice location of implanted 52Cr in α–Al2O3 after thermal annealing
Calculated and measured planar channeling critical half
angles (ψ1/2) for 2-MeV He+ scattering from Al, O, and Cr
atoms in virgin and Cr-implanted α-Al2O3.
Uncertainties in the experimental critical half angles are estimated to be 10% of the measured
value.

41. Results and Discussion
Lattice location of implanted 52Cr in α–Al2O3 after thermal annealing
Calculated and measured axial channeling critical half angles
(ψ1/2) for 2-MeV He+ scattering from Al, O, and Cr atoms in
virgin and Cr-implanted α-Al2O3.
Uncertainties in the experimental critical half angles are estimated to be 10% of the measured
value.

42. Results and Discussion
Lattice location of implanted 52Cr in α–Al2O3 after thermal annealing
Critical angles for both axis and planar were
calculated using Barrett method:
2/1
12/1 )]/)([ EmVk  
Adjustable parameters
k=0.76, m=1.6 (for planar critical angles)
k=0.83, m=1.2 (for axial critical angles)
Mean one- dimensional vibrational amplitude( for planes)
Mean two- dimensional vibrational amplitude( for axis)

43. Results and Discussion
Lattice location of implanted 52Cr in α–Al2O3 after thermal annealing
The potential was calculated using a model given by :
0VVV il ji  
Contribution to the continuum potential due
to the jth atomic species in the ith plane
A constant to make the minimum potential energy equal to zero
Such a model assumes that mixed atomic sheets
such as the Al2 + O sheet in the {10-10} planar
channel can be treated as a superposition of atomic
sheets each with a unique atomic species.

44. Results and Discussion
Lattice location of implanted 52Cr in α–Al2O3 after thermal annealing
Thermal vibrational amplitudes were determined
using a Debye model of the solid with a Debye
temperature of 1034°K.

45. Results and Discussion
Lattice location of implanted 52Cr in α–Al2O3 after thermal annealing
Static continuum potential for the various major planes in Al2O3. The atomic
constituent is indicated for each plane in a given configuration by the
atomic symbol, and a superscript which indicates relative atomic
abundance.

46. Results and Discussion
Lattice location of implanted 52Cr in α–Al2O3 after thermal annealing
O3
Al

47. Results and Discussion
Lattice location of implanted 52Cr in α–Al2O3 after thermal annealing
(Al green, O red)

48. Results and Discussion
Lattice location of implanted 52Cr in α–Al2O3 after thermal annealing
There is a good agreement between experiment
and theory data of channeling critical half angles.
Therefore all assumptions during calculated angles
can be justified.

49. Results and Discussion
Lattice location of implanted 52Cr in α–Al2O3 after thermal annealing
Angular scans on implanted crystals were obtained using
crystals implanted to dose of 1 and 3×1016/cm2 after
thermal annealing at temperatures of 1300 and 1500 °C.
Angular scan across the <0001> axis for 52Cr (300 keV, 1×1016/cm2) in α–Al2O3
after 1300°C annealing.
Critical angles for scattering from Al and Cr have approximately the same width.

50. Results and Discussion
Lattice location of implanted 52Cr in α–Al2O3 after thermal annealing
Critical angles for scattering from Al and Cr have
approximately the same width but different from O.
Most of Cr atoms are substitutional in the Al sublattice
There are some Cr and O atoms in interstitial
lattice sites after annealing at 1300°C. Interstitial Cr
can trap O atoms and diffuses in from surface
during annealing.

51. Results and Discussion
Lattice location of implanted 52Cr in α–Al2O3 after thermal annealing
Al & O critical angle after Cr implantation and annealing
Al O
1300°C
Al & O critical angle for the virgin sample
Al critical angle is considerably wider on the
implanted crystal compared to the virgin,
indicating that damage recovery is not
complete after annealing at this temperature.

52. Results and Discussion
Lattice location of implanted 52Cr in α–Al2O3 after thermal annealing
Axial angular scan for 52Cr(280keV, 3×1016/cm2) in α-Al2O3
1500 °C thermal annealing

53. Results and Discussion
Lattice location of implanted 52Cr in –Al2O3 after thermal annealing
Planar angular scan for 52Cr(280keV, 3×1016/cm2) in α-Al2O3
1500 °C thermal annealing

54. Results and Discussion
Lattice location of implanted 52Cr in –Al2O3 after thermal annealing
Axial angular scan for
52Cr(280keV, 3×1016/cm2) in
α-Al2O3
1500 °C thermal annealing
Al & O critical angle for the
virgin sample
Axial angular scan for
52Cr(300keV,
3×1016/cm2) in α-Al2O3
1300 °C thermal annealing
Comparison of axial/planar angular scans for different cases shows that critical
angle in higher annealing temperature is closer to the virgin case.

55. Results and Discussion
Lattice location of implanted 52Cr in –Al2O3 after thermal annealing
Conclusion:
 Near-surface region is not turn completely
amorphous with Cr implantation on sapphire at
doses less than 1017/cm2.
 Upon annealing, damage recovery begins
selectively in the Al sublattice at T~800 °C.
 Recovery in the oxygen sublattice begins at
T~1000 °C for Cr.
 After Cr implantation followed by thermal
annealing at ~1500 °C, the implanted impurity is
observed to be >95% substitutional in the Al
sublattice.

56. Valence state of implanted 52Cr
The valence state of the implanted impurity can be
determined using Electron Paramagnetic
Resonance absorption (EPR) techniques.
The EPR spectrum of substitutional trivalent
chromium ions (Cr3+) in Al2O3 may be described by
the following spin Hamiltonian:
]3/)1([)(
2
  SSSDSHSHgSHgH zyyxxBzzB 
1
cm0.382D1.987,g1.984,g3/2,S 
 

57. EPR spectroscopy is the measurement and interpretation
of the energy differences between the atomic or molecular
states.
These measurements are obtained because the
relationship between the energy differences and the
absorption of electro-magnetic radiation.
To acquire a spectrum, the frequency of the
electromagnetic radiation is changed and the amount of
radiation which passes through the sample with a detector
is measured to observe the spectroscopic absorptions.
EPR Spectroscopy

59. EPR
•Like a proton, an electron has a spin, which gives it a
magnetic property known as a magnetic moment.
•When an external magnetic field is supplied, the
paramagnetic electrons can either orient in a direction
parallel or antiparallel to the direction of the magnetic field .
•This creates two distinct energy levels for the unpaired
electrons and measurements are taken as they are driven
between the two levels.

60. α-Al2O3 with trace Cr3+ impurity
Valence state of implanted 52Cr
52Cr(300keV, 1×1016/cm2) in α-Al2O3
EPR line shape of high
field Cr3+ absorption line
(Ms=-1/2↔Ms=-3/2)

61. Microhardness change of Al2O3 with 52Cr implantation followed by thermal
annealing
HARDNESS CHANGES DUE TO ANNEALING
For implanted Cr(1017/cm2) and Zr (4×1019/cm2) in α- Al2O3
Annealing temperature(˚C)

62. Kurdish rug with hexagonal grid
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63. EPR spectroscopy is the measurement and interpretation
of the energy differences between the atomic or molecular
states.
These measurements are obtained because the
relationship between the energy differences and the
absorption of electro-magnetic radiation.
To acquire a spectrum, the frequency of the
electromagnetic radiation is changed and the amount of
radiation which passes through the sample with a detector
is measured to observe the spectroscopic absorptions.
EPR Spectroscopy

65. EPR
•Like a proton, an electron has a spin, which gives it a
magnetic property known as a magnetic moment.
•When an external magnetic field is supplied, the
paramagnetic electrons can either orient in a direction
parallel or antiparallel to the direction of the magnetic field .
•This creates two distinct energy levels for the unpaired
electrons and measurements are taken as they are driven
between the two levels.