Electron irradiation effect on Al2O3

Kurt Sickafus Younes Sina

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

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.

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

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%

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

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

8

Dose = Absorbed Energy Density

1 Gy = 1 J

kgSI units

Absorbed energy normalized by weight, volume, atoms, etc.

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

Projectile-Target Interactions

# events

<volume> or <weight> t• • •

Projectile-Target Interactions

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cross- section

flux time • • •

Projectile-Target Interactions

projectiles

area

projectiles

areagtime

t time

fluence flux time = •

Projectile-Target Interactions

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Projectile-Target Interactions

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Projectile-Target Interactions Leading to Atomic Displacements

# atomic displacements

volume

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displacements

atom

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displacement cross- section

fluence • dpa =

Ballistic Dose

Electron irradiation-induced amorphization of sapphire (Al2O3)

1 MeV electrons room-temperature irradiation conditions

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)

1. Electronic Stopping

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.

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

E0 mec2 rest energy of the electron

me rest mass of the electron

c speed of light

e2 14.4 eV Å

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

e Z a

e electron density

Z atomic number

a atomic density

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.

W. H. Bragg, and M. A. Elder, Phil. Mag. 10, 318 (1905)

Bragg’s Rule for Additivity of Stopping Powers

Stopping Power

e Se E 1

a

dE

dx e

eV Å2

atom e

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.

Ionization stopping in Al2O3

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-

Electron fluence:

Φ=1×1028 e/m2=1×108 e/Ȧ2

Irradiation time= t= 2 hr = 7200 s

φ= 1.38×104 e-/Ȧ2s

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

Magnitude of dose: TeraGray !!

ρAl2O3= 3980 Kg/m3

Dose= 94.72×1012 J/Kg= 94.7 TGy

2. Nuclear Stopping

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.

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)

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

b2 4 Z 2 e2

E0

2

1

4 2

where

=1

1 2

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

E = 1000 keV

ZO = 8

ZAl = 13

ZAve =10

TmO =271

TmAl =161

TmAve =227

ZO = 8

ZAl = 13

Zave =10

EtO = 129,000

EtAl = 205,000

EtAve = 159,400

Ed = 20 eV

ZO= 8

ZAl= 13

ZAve=10

EO= 238,000

EAl= 365,000

Ed = 40 eV

ZO= 8

ZAl= 13

ZAve=10

EO = 290,000

EAl = 430,000

Ed = 50 eV

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

E=1 MeV

Ed=40 eV

σp @ 1 MeV =2.18 barns

α-Al2O3

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)

52

53

22

28

41

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):

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

RADIATION DAMAGE OF α-Al2O3 IN THE HVEM II. Radiation damage at high temperature and high dose G.P. PELLS and D.C. PHILLIPS

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)

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.

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.

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.

~1000 Å

Vacuum

High flux e-

Al ppt.

O2

>40 dpa Long time Surface at high stress

heat