Electron irradiation effect on Al2O3
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Electron irradiation effect on Al2O3
Kurt Sickafus Younes Sina
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Ionization vs. Excitation
Excitation transfers enough energy to an orbital electron to displace it further away from the nucleus.
High energy incident electron
In ionization the electron is removed, resulting in an ion pair.
IONISATION
Ejected electron
Incident electron with a specific energy
Atomic electron absorbs energy and moves into a higher orbit
EXCITATION
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Bremsstralung (or Braking) Radiation
•High speed electrons may lose energy in the form of X-rays when they quickly decelerate upon striking a heavy material.
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Bremsstrahlung
Probability of bremsstrahlung production per atom is proportional to the square of Z of the absorber
Energy emission via bremsstrahlung varies inversely with the square of the mass of the incident particle
Protons and alpha particles produce less than one-millionth the amount of bremsstrahlung radiation as electrons of the same energy
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Bremsstrahlung Ratio of electron energy loss by bremsstrahlung production to
that lost by excitation and ionization = EZ/820
E = kinetic energy of incident electron in MeV
Z = atomic number of the absorber
Energy loss for Al: Brem./ (Exc. & Ion.) = 1×13/820 = 1.58%
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Charged Particle Tracks Electrons follow tortuous paths in matter as the result of multiple
scattering events
• Ionization track is sparse and nonuniform
Larger mass of heavy charged particle results in dense and usually linear ionization track
Path length is actual distance particle travels; range is actual depth of penetration in matter
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Particle interactions
Energetic charged particles interact with matter by electrical forces and lose kinetic energy via:
Excitation
Ionization
Radiative losses
~ 70% of charged particle energy deposition leads to nonionizing excitation
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8
Dose = Absorbed Energy Density
1 Gy = 1 J
kgSI units
Absorbed energy normalized by weight, volume, atoms, etc.
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9
Water: heat to boiling point
cpH2O = 4.1813
J
g K (@ 25°C)
specific heat of water
T 80 K
cpH2O T = 334.5
J
g
103 g
kg
3.345 105 J
kg
0.3345 MGyAbsorbed Energy
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Projectile-Target Interactions
# events
<volume> or <weight> t• • •
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Projectile-Target Interactions
# events
volume a
atoms
volume
area
atom
projectiles
areagtime
t time
# events
weight w
atoms
weight
area
atom
projectiles
areagtime
t time
atomic density
cross- section
flux time • • •
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Projectile-Target Interactions
projectiles
area
projectiles
areagtime
t time
fluence flux time = •
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Projectile-Target Interactions
# events
volume a
atoms
volume
area
atom
projectiles
area
# events
weight w
atoms
weight
area
atom
projectiles
area
atomic density
cross- section
fluence • •
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Projectile-Target Interactions
# events
volume
aatoms
volume
area
atom
projectiles
area
cross- section
fluence •
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Projectile-Target Interactions Leading to Atomic Displacements
# atomic displacements
volume
aatoms
volume
area
atom
projectiles
area
displacements
atom
area
atom
projectiles
area
displacement cross- section
fluence • dpa =
Ballistic Dose
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Electron irradiation-induced amorphization of sapphire (Al2O3)
1 MeV electrons room-temperature irradiation conditions
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Two components of damage: 1. electronic component (electron excitation/ionization; radiolysis) 2. nuclear component (ballistic or displacement damage)
Electron irradiation-induced amorphization of sapphire (Al2O3)
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1. Electronic Stopping
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Electron Excitation/Ionization Bethe-Ashkin expression for ionization energy loss per unit length
H. A. Bethe, and J. Ashkin, in Experimental Nuclear Physics. Volume I, edited by E. Segrè (John Wiley &
Sons, Inc., New York, 1953), pp. 166-357.
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Electron Excitation/Ionization Bethe-Ashkin expression for ionization energy loss per unit length
dE
dx
2e4
E0
e 2
LnE0
2E
2J 2 (1 2 )
2 1 2 1 2 Ln2
1 2
1
81 1 2
2
relativistic expression
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E0 mec2 rest energy of the electron
me rest mass of the electron
c speed of light
e2 14.4 eV Å
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v
c
v velocity of electron
c speed of light
1E0
E0 E
2
E0 rest energy of the electron
E kinetic energy of the electron
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e Z a
e electron density
Z atomic number
a atomic density
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J 9.76 Z 58.5 Z 0.19 (eV)
mean electron excitation potential
M. J. Berger, and S. M. Seltzer, Nat. Acad. Sci. / Nat. Res. Council Publ. 1133 (Washington, 1964), p. 205.
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W. H. Bragg, and M. A. Elder, Phil. Mag. 10, 318 (1905)
Bragg’s Rule for Additivity of Stopping Powers
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Stopping Power
e Se E 1
a
dE
dx e
eV Å2
atom e
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Bragg’s Rule for Additivity of Stopping Powers
e
AmBn m e
A n e
B
where m is the number of A atoms in molecule AmBn
and n is the number of B atoms in molecule AmBn
For binary compound with molecular unit, AmBn
:
One can show that:
dE
dx e
AmBn
mAmBn
e
AmBn dE
dx e
A
dE
dx e
B
where mAmBn is the molecular density of A
mBn
molecules in the compound.
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Ionization stopping in Al2O3
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dE/dx (E = 1 MeV) = -0.0377 eV/Å . e-
E = 1000 keV= 1 MeV
thickness = 1000 Å TEM sample thickness
Total ionization energy loss over sample thickness
= 37.7 eV/e- = 6.032x10-18 J/e-
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Electron fluence:
Φ=1×1028 e/m2=1×108 e/Ȧ2
Irradiation time= t= 2 hr = 7200 s
φ= 1.38×104 e-/Ȧ2s
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Areal Energy Density = dE
dx electronic
3.504 1011 J
Å2
Total Energy Density = Areal Energy Density
thickness
3.504 1014 J
Å3
=37.7×108 eV/Ȧ2= 3.77×10-10 J/Ȧ2
=3.77×10-13 J/Ȧ3
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Magnitude of dose: TeraGray !!
ρAl2O3= 3980 Kg/m3
Dose= 94.72×1012 J/Kg= 94.7 TGy
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2. Nuclear Stopping
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Electron displacement damage calculation
Primary damage cross-section after Seitz & Koehler (1956): F. Seitz, and J. S. Koehler, in Solid State Physics: Advances in Research & Applications, edited by F. Seitz, and D. Turnbull (Academic Press, 1956), pp. 305-448.
Based on the relativistic electron cross-section expression derived by McKinley & Feshbach (1948): W. A. McKinley, Jr., and H. Feshbach, Physical Review 74, 1759 (1948).
Total cross-section (primary plus secondaries) after Oen (1973): O. S. Oen, (Oak Ridge National Laboratory, Oak Ridge, TN, 1973), pp. 204.
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Differential displacement cross-section, dσ
d (T ) b
2
4Tm
12 T
Tm
T
TmT
Tm
dT
T 2
where T is the kinetic energy of the electron
v / c 1E0
E0E
2
Z
where is the fine structure constant (~1/137)
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Tm maximum energy transfer from e to target atom
Tm 4 me M
me M 2E 1
E
2 E0
where E is the incident electron energy
Ca O
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b2 4 Z 2 e2
E0
2
1
4 2
where
=1
1 2
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p (E) dEd
Tm
(T ) area
atom
where Ed is the displacement threshold energy
Primary displacement cross-section:
Cascade cross-section:
tot (E) (T ) dEd
Tm
(T ) area
atom
where (T ) is the number of secondary displacements,
given most simply by the Kinchin-Pease expression:
(T ) 0; T < Ed
(T ) 1; Ed T < 2Ed
(T ) T
2Ed; T 2Ed
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E = 1000 keV
ZO = 8
ZAl = 13
ZAve =10
TmO =271
TmAl =161
TmAve =227
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ZO = 8
ZAl = 13
Zave =10
EtO = 129,000
EtAl = 205,000
EtAve = 159,400
Ed = 20 eV
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ZO= 8
ZAl= 13
ZAve=10
EO= 238,000
EAl= 365,000
Ed = 40 eV
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ZO= 8
ZAl= 13
ZAve=10
EO = 290,000
EAl = 430,000
Ed = 50 eV
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ZO= 8
ZAl= 13
ZAve=10
EtO= 290,000 eV
EtAl= 430,000 eV
E=1 MeV
Ed=40 eV
TmAve=227 eV
2Ed=80 eV
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E=1 MeV
Ed=40 eV
σp @ 1 MeV =2.18 barns
α-Al2O3
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Ethresholdave 295 keVZ ave 15.67
Ed 25 eV
Tmave 25.54 eV
2Ed 50 eV
E 300 keV
tot (E) p (E) 0.588 barns = 5.88 109 Å2
atom
powellite (CaMoO4)
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52
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53
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22
28
41
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1 barn = 10-24 cm2 108 Å2
tot (E) (T ) dEd
Tm
(T ) area
atom
where (T ) is the number of secondary displacements,
given most simply by the Kinchin-Pease expression:
(T ) 0; T < Ed
(T ) 1; Ed T < 2Ed
(T ) T
2Ed; T 2Ed
tot (E) (T ) dEd
Tm
(T ) area
atom
where (T ) is the number of secondary displacements,
given most simply by the Kinchin-Pease expression:
(T ) 0; T < Ed
(T ) 1; Ed T < 2Ed
(T ) T
2Ed; T 2Ed
σtot=42 barns/atom= 4.2×10-7 Å2/atom
Cross section calculation for Al (Ed=20 eV):
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Electron fluence:
Φ=1×1028 e/m2=1×108 e/Å2
Irradiation time, t = 2 hr = 7200 s
φ= 1.38×104 e-/Å2s
σtot=42 barns/atom= 4.2×10-7 Å2/atom
displacements per atom = tot
5.88 106 Å2
atom 3 106 e
Å2
= 0.018 dpa
dpa=(4.2×10-7 Å2/e).(1×108 e/Å2) = 42
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RADIATION DAMAGE OF α-Al2O3 IN THE HVEM II. Radiation damage at high temperature and high dose G.P. PELLS and D.C. PHILLIPS
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C. L. Chen, H. Furusho and H. Mori
• The decomposition of α- Al2O3 under 200 keV
(Ultra High Vacuum) electron irradiation
• Aluminum precipitated from α- Al2O3 under 200
keV electron irradiation for less than 1 min over
the temperature range 700 to 1273 K.
• φ (electron dose rate)= 1023 e m-2s-1
• Vacuum level < 3×10-8 Pa
Model: Thermally activated atom movement Forced atom displacement ( knock-on collision)
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RADIATION DAMAGE OF α-Al2O3 IN THE HVEM
II. Radiation damage at high temperature and high dose G.P. PELLS and D.C. PHILLIPS
Single-crystal α-Al2O3 irradiated with 1 MeV electrons in a high-voltage electron microscope at several fixed temperatures in the range 320-1070 K.
• At 770 K and below the nature of the observed damage could not be resolved.
• At 870 K and above island-like surface features rapidly formed followed by dislocations which grew to form a dense network.
• After high doses (>l0 dpa) precipitates were observed. • The associated diffraction patterns and their temperature dependence
suggested that the precipitates were of aluminum metal.
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Cryogenic radiation response of sapphire R. Devanathan, W.J. Weber, K.E. Sickafus, M. Nastasi, L.M. Wang, S.X. Wang
Sapphire (a-Al2O3) irradiated by heavy-ion and electron at cryogenic temperatures using a high-voltage electron microscope. 1.5 MeV Xe 1 MeV Kr Dual beam of 1 MeV Kr and 900 keV electrons T=20 to 100 K At 20 K, α-alumina is amorphized by 1.5 MeV Xe about 3.8 (dpa) Critical temperature for amorphization is about 170 K The material remains crystalline when irradiated at 26 K with a dual beam of heavy ions and electrons.
Electron irradiation can promote damage annealing, even at cryogenic temperatures, by causing the migration of point-defects produced in ceramics by ion irradiation.
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Effects of ionizing radiation in ceramics R. Devanathan ,K.E. Sickafus, W.J. Weber, M. Nastasi
α-Al2O3 was irradiated with 1 MeV Kr+ or 1.5 MeV Xe+ and 1 MeV electrons in a high-voltage electron microscope interfaced to an ion accelerator that enabled the in situ observation of the structural changes. The results indicate that simultaneous electron irradiation can retard or prevent amorphization by heavy ions. Comparison with similar experiments in metals suggests that highly ionizing radiation can anneal damage to the crystal lattice in ceramics by enhancing the mobility of point defects.
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~1000 Å
Vacuum
High flux e-
Al ppt.
O2
>40 dpa Long time Surface at high stress
heat