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ISOLDE Workshop and Users Meeting 2009. Uncovering New Diffusion Phenomena in Compound Semiconductors. Th. Wichert 1 , J.Kronenberg 1 , K. Johnston 1 , J. Cieslak 1 , M. Deicher 1 , F. Wagner 1 , H. Wolf 1 , and The ISOLDE collaboration 2. - PowerPoint PPT Presentation
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11
Th. Wichert1, J.Kronenberg1, K. Johnston1, J. Cieslak1, M. Deicher1, F. Wagner1, H. Wolf1, and The ISOLDE collaboration2
1Technische Physik, Universität des Saarlandes, D-66123 Saarbrücken, Germany 2CERN, CH-1211 Geneva 23, Switzerland
Supported by the BMBF, contract 05 KK7TS1
Uncovering New Diffusion Phenomena in Uncovering New Diffusion Phenomena in Compound SemiconductorsCompound Semiconductors
ISOLDE Workshop and Users Meeting 2009ISOLDE Workshop and Users Meeting 2009
2
0 100 200 300 400 500108
109
1010
1011
1012
1013
1014
conc
entr
atio
n (c
m-3)
depth (µm)
concentrationof dopants
2
Diffusion in Solids
one-sidedsource
monotonously decreasing profile
"for his work on the use of isotopes as tracers in the study of chemical processes"
George de Hevesy
Nobel Prize in Chemistry 1943
3
Fick‘s First Law
Jx = - D dC/dx
dC
dx
4
828K (60 min)
Cd atmosphere
4
Diffusion of 111Ag in CdTe
• no loss of activity• diffusion towards increasing Ag concentration
0 100 200 300 400 500108
109
1010
1011
1012
1013
1014
conc
entr
atio
n (c
m-3)
depth (µm)
550K (30 min)
vacuum
implanted profile
5
Jx = - D dC/dx
dC
dx
Fick‘s First Law
violated by the present data ?
„uphill“
6
Table of Content
Radiotracer Diffusion in Binary Semiconductors
- Semiconductors and uphill diffusion
- Uphill diffusion and self-interstitials
- Self-interstitials and metal layers
On-line Diffusion Chamber
Following the set-up by the Stuttgart group (T1/2 > 10 min):
7
Radiotracer Technique
a
CdxZn1-xTeØ = 6 mmd = 800 µm
Implantation
CdTethermal
treatment
550 … 900 K60 keV
Used isotopes :111Ag, 67Cu, 24Na, 43K, 56Mn, 59Mn(59Fe), 65Ni, 61Mn(61Co), 101Cd(101Pd), 191Hg(191Pt), 193Hg(193Au)
2 gm
1...30 µm
0 100 200 300 400
1011
1012
1013
1014
depth (µm)co
nce
ntr
atio
n (
cm-3
)
CdTe:111Ag
Tdiff = 570 K tdiff = 30 min
DAg = 7.6·10-9 cm2/s
30nm
111Ag+
88 8
0 200 400 6001011
1012
1013
1014
0 200 400 600
1011
1012
1013
0 200 400 600108
109
1010
1011
0 200 400 600109
1010
1011
1012
828 K
con
cen
tra
tion
(cm
-3)
111Ag 67Cu 800 K
24Na 750 K
con
cen
tra
tion
(cm
-3)
depth (m)
193Au 800 K
depth (m)
t = 0:-layer at x = 0
profile symmetry:
dopant in equilibriumwith host crystal
profile shape:
result ofintrinsic defects
Uphill-diffusion
CdTeTe-saturated CdTe: tdiff = 60 min, external Cd pressure
Experimental Results
999
C: deviation from stoichiometry
T-C phase diagram (sketch)
C = CTeInitial CdTe:
Cd Cd
CTe CCdCCd
external Cd pressure
Control of Intrinsic Defects
CdTe
101010
Te sublattice: „perfect“
Cd sublattice
donors
acceptors
intrinsic extrinsic
i Cd CdC Cd V Ag
Defects Involved
… and all defects can be charged
=> Deviation from stoichiometry
111111
Fick‘s First Law revised
Particle Flux J
xJ D Cxusually C : concentration
(1 species)
in general µ : chemical potentials (several species)
xJ Lx
121212
AgAg
Ag
Ag
Cd
CdCd
Cd
F
FF
F
µ
µCq µ
C
µ
C C CC µ
µ
Ag Ag Ag
µµAg
q C
µ
µ
q
d d
q C
µµ
Fick‘s First Law revised
Changein the
concentrationsof
Ag atomsintrinsic defectscharge carriers
driven by thechemical potentials
1313
Modelling of Experimental Results
interaction of dopants with intrinsic defects
charge states of extrinsic and intrinsic defects
profile of C leads to formation of p/n junctions
drift in internal electric field
H. Wolf et al., Physica B 308-310 (2001) 963H. Wolf et al., Physica B, 340 - 342 (2003) 275 - 279H. Wolf et al., Phys. Rev. Lett. 94 (2005) 125901.H. Wolf et al., Defect and Diffusion Forum 237-240 (2005) 491.F. Wagner et al., Proc. of the 1st Int. Conf. on Diffusion in Solids and Liquids (DSL 2005)H. Wolf et al., J. Electr. Mater. 35 (2006) 1350.F. Wagner et al., Physica B: Condensed Matter 401-402 (2007) 286-290H. Wolf et al., Diffusion Fundamentals 8 (2008) 3.1-3.8F. Wagner, Dissertation, Universität des Saarlandes (2008)H. Wolf et al., Defect and Diffusion Forum Vols. 289-292 (2009) 587-592
14
0 200 400 600 800
1011
1012
1013
-4x1016
-3x1016
-2x1016
-1x1016
01x10
162x10
16
conc
entr
atio
n (
cm-3)
depth (µm)
[ ΔC
] (cm
-3)
-0,2
-0,1
0,0
0,1
µ F e
V
[ΔCini]
VCd
--Cd
i
++Cd
i
++n np
[ΔC] = [Cdi] - [VCd]
CdTe is Te-rich [ΔC] < 0
• [ΔC] determines µF
• Cd-atmosphere: Ag - diffusion
• [Ag] = [Agi+] highly mobile
• Agi+ behaves like h+
• Ag profile reflects µF and [ΔC]
Cdi Cdi
Profile Simulation
111Ag → CdTe
828 K(60 min)
1515
0 200 400 6001011
1012
1013
1014
0 200 400 600
1011
1012
1013
0 200 400 600108
109
1010
1011
0 200 400 600109
1010
1011
1012
828 K
conc
entr
atio
n (c
m-3)
111Ag 67Cu 800 K
24Na 750 K
conc
entr
atio
n (c
m-3)
depth (m)
193Au 800 K
depth (m)
C > 0n-type C < 0
p-type
C > 0n-type
D(Cdi) = 1.210-6 cm2/s
Experiment and Simulation
information about: diffusion coefficients formation energies ionizations energies
1616
0 200 400 6001011
1012
1013
1014
0 200 400 600
1011
1012
1013
0 200 400 600108
109
1010
1011
0 200 400 600109
1010
1011
1012
828 K
conc
entr
atio
n (c
m-3)
111Ag 67Cu 800 K
24Na 750 K
conc
entr
atio
n (c
m-3)
depth (m)
193Au 800 K
depth (m)
C > 0n-type C < 0
p-type
C > 0n-type
D(Cdi) = 1.210-6 cm2/s D(Cdi) = 7.010-7 cm2/s
D(Cdi) = 4.010-7 cm2/s D(Cdi) = 1.510-7 cm2/s
D(Cdi) should
not depend on
the dopant!
Experiment and Simulation
1717
0 200 400 600 800109
1010
1011
1012
1013
conc
entr
atio
n (c
m-3)
depth (µm)
0 200 400108
109
1010
1011
1012
1013
1014
conc
entr
atio
n (c
m-3)
depth (µm)
0 200 400 600 800
1011
1012
1013
conc
entr
atio
n (c
m-3)
depth (µm)
CdTe Cd0.96Zn0.04Te ZnTe828K, 60 min 828K, 60 min 928K, 24 h
comparable behavior in different II-VI semiconductors
Cd atmosphere Cd atmosphere Zn atmosphere
Ag in Different Semiconductors
104
18
Uphill Diffusion Profiles in Cd1-xZnxTe
18
Ag
Ia
IIa
IIIb IVb Vb VIb VIIb VIII Ib IIb
IIIa IVa Va VIa VIIa
VIII
Zn
Cd In
N
Sb
S
Se
Te
Cl
Br
I
As33
15
7
H
Be
Mg
Ca Sc Ti
Sr Y
V Cr Mn
Zr Nb Mo Tc
Fe Co Ni
Ru Rh Pd
B
Al
Ga
C
Si
Ge
Sn
P
O F
He
Ne
Ar
Kr
Xe
Cu
4
12
20 21 22 23 24 25 26 27 28 29 30 31
13
5
32
14
6
34
16
8
35
17
9
36
18
10
2
38 39 40 41 42 43 44 45 46 47 48 49 50 51 53 54
Li
Rb
Na
K
1
3
11
19
37
Ba La Hf Ta W Re Os Ir Pt Au Hg Tl Pb Bi56 57 72 73 74 75 76 77 78 79 80 81 82 83
Cs55
Matrix Isotope
0 200 400 600 800
1011
1012
1013
Kon
zent
ratio
n (c
m-3)
Tiefe (m)
peak
n p
19
Box shaped profiles in Cd0.97Zn0.03Te
19
Ag
Ia
IIa
IIIb IVb Vb VIb VIIb VIII Ib IIb
IIIa IVa Va VIa VIIa
VIII
Zn
Cd In
N
Sb
S
Se
Te
Cl
Br
I
As33
15
7
H
Be
Mg
Ca Sc Ti
Sr Y
V Cr Mn
Zr Nb Mo Tc
Fe Co Ni
Ru Rh Pd
B
Al
Ga
C
Si
Ge
Sn
P
O F
He
Ne
Ar
Kr
Xe
Cu
4
12
20 21 22 23 24 25 26 27 28 29 30 31
13
5
32
14
6
34
16
8
35
17
9
36
18
10
2
38 39 40 41 42 43 44 45 46 47 48 49 50 51 53 54
Li
Rb
Na
K
1
3
11
19
37
Ba La Hf Ta W Re Os Ir Pt Au Hg Tl Pb Bi56 57 72 73 74 75 76 77 78 79 80 81 82 83
Cs55
Matrix Isotope
0 100 200 300 400 5001010
1011
1012
1013
1014
30 min: vacuum 60 min: Cd atmosphere
conc
entr
atio
n (c
m-3)
depth (µm)
box
n p
2020
Influence of Metal Layers
111Ag in CdTe
Te-saturated (∆Cini = ∆C Te)
0 200 400 6001010
1011
1012
1013
1014
depth (µm)
D = 1.5·10-8 cm2/s
Tdiff = 500 K
co
nce
ntr
atio
n (
cm-3)
plus coppermetal layer
ΔCTeΔCCd
2121
Te-saturated (∆Cini = ∆C Te)
Influence of Metal Layers
111Ag in CdTe
0 200 400 6001010
1011
1012
1013
1014
depth (µm)
D = 1.5·10-8 cm2/s
Tdiff = 500 K
Tdiff = 580 K
Cu layer
co
nce
ntra
tion
(cm
-3)
plus coppermetal layer
ΔCTeΔCCd
2222
0 200 400 6001010
1011
1012
1013
1014
Tdiff
= 500 K
Tdiff
= 580 K
Cu layer
con
cent
ratio
n (
cm-3)
depth (µm)
Cd-saturated (∆Cini = ∆CCd )
Influence of Metal Layers
111Ag in CdTe
23
0 200 400 600 8001010
1011
1012
1013
1014
1015
1016
Cu Ni Au Al
conc
entr
atio
n (c
m-3)
depth (µm)
Influence of Metal Layers
111Ag in CdTe ( 580 K )
Te-saturated (∆Cini = ∆C Te)
24
0 200 400 600 8001010
1011
1012
1013
1014
1015
1016
Cu Ni Au Al
conc
entr
atio
n (c
m-3)
depth (µm)
Influence of Metal Layers
111Ag in CdTe ( 580 K )
Te-saturated (∆Cini = ∆C Te)
25
0 200 400 600 8001010
1011
1012
1013
1014
1015
1016
Cu Ni Au Al
conc
entr
atio
n (c
m-3)
depth (µm)
Influence of Metal Layers
111Ag in CdTe ( 580 K )
Te-saturated (∆Cini = ∆C Te)
26
0 200 400 600 8001010
1011
1012
1013
1014
1015
1016
Cu Ni Au Al
conc
entr
atio
n (c
m-3)
depth (µm)
Influence of Metal Layers
111Ag in CdTe ( 580 K )
Te-saturated (∆Cini = ∆C Te)
27
0 200 400 600 800
1011
1012
1013
conc
entr
atio
n (c
m-3)
depth (µm)
Uphill Diffusion
Cdi Cdi
ΔCTe ΔCCdΔCCd
evaporatedmetal
ΔCTeΔCCd
0 200 400 600 8001010
1011
1012
1013
1014
1015
1016
Cu Ni Au Al
conc
entr
atio
n (c
m-3)
depth (µm)
external Cd vapour pressure(symmetric Ag profile)
metal layer evaporated on surface (asymmetric Ag profile)
Injection of Cd Interstitials by
28
0 200 400 600 800109
1010
1011
1012
1013
1014
conc
entr
atio
n (c
m-3)
depth (µm)
0 200 400 600 800
1011
1012
1013
conc
entr
atio
n (c
m-3)
depth (µm)
evaporatedmetal
ΔCTe ΔCCdΔCCd
Cdi Cdi
ΔCTe ΔCCdΔCCd
at 800 K at 550 Kexternal Cd vapour pressure
(symmetric Ag profile)
Uphill Diffusion
29
• Catcher and tape-station• Germanium-detector + “PET”• Sample depot• Remote control (radioprotection)
Isotope T1/2 Detection
38Cl 37,3 min β-4800keV ; γ2168keV
11C 20,38 min β+ ; γ511keV
13N 9,96 min β+ ; γ511keV
29Al 6,6 min γ1273keV
(15O) 122 s β+ ; γ511keV
Sputter-sourceSputter-sourceCatcher, Tape station, DetectorCatcher, Tape station, Detector
BeamportBeamportDepotDepot
FurnaceFurnace ManipulatorManipulator
29
1) Open beamline2) Depot3) Implantation4) Annealing5) Sputtering
ManipulatorManipulator
On-line Diffusion Chamber
30
FurnaceFurnace
Sputter-sourceSputter-source
Tape stationTape station
BeamportBeamport
30
ManipulatorManipulatorD
etec
tor
Det
ecto
r
On-line Diffusion Chamber
31
Summary
1. Diffusion experiments in binary semiconductors
Importance of radioactive isotopes at ISOLDE :elements, implantation, purity.
2. Observation and understanding of unusual diffusion profiles
General formulation of Fick‘s law :uphill diffusion, quantitativ understanding, metal layers.
3. On-line diffusion chamber for short-lived isotopes
Access to well-needed light elements.
0 200 400 600 800
1011
1012
1013
Kon
zent
ratio
n (c
m-3)
Tiefe (m)
peak
n p
0 200 400 6001010
1011
1012
1013
1014
depth (µm)
D = 1.5·10-8 cm2/s
Tdiff = 500 K
Tdiff = 580 K
Cu layer
co
nce
ntr
atio
n (
cm-3)
Cu layer
w/o layer
Uni Münster:
H. MehrerN.A. StolwijkH. BrachtA. Rodriguez Schachtrup
Uni Bonn:
R. ViandenD. Eversheim
CERN:
ISOLDE Collaboration
BMBF for financial support
Uni Prague:
R. GrillE. Belas
Thanks to …
… you for your attention
33
Summary
1. Diffusion experiments in binary semiconductors
Importance of radioactive isotopes at ISOLDE :elements, implantation, purity.
2. Observation and understanding of unusual diffusion profiles
General formulation of Fick‘s law :uphill diffusion, quantitativ understanding, metal layers.
3. On-line diffusion chamber for short-lived isotopes
Access to well-needed light elements.
0 200 400 600 800
1011
1012
1013
Kon
zent
ratio
n (c
m-3)
Tiefe (m)
peak
n p
0 200 400 6001010
1011
1012
1013
1014
depth (µm)
D = 1.5·10-8 cm2/s
Tdiff = 500 K
Tdiff = 580 K
Cu layer
co
nce
ntr
atio
n (
cm-3)
Cu layer
w/o layer
34
36
Future : Short Lived Isotopes
36
Isotope T1/2
38Cl 37,3 min11C 20,38 min13N 9,96 min29Al 6,6 min
(15O) 122 s
Diffusion of C, N and O in semiconductors Self-diffusion in Al and in Al alloys Diffusion of C, N, and O in grain boundaries of nanomaterials
Following the set-up by the Stuttgart group (T1/2 > 10 min):
On-line diffusion chamber
3737
0 200 400 600
1x1011
1x1012
1x1013
1x1014
Tdiff = 729 K
60 min
con
cen
tra
tion
(cm
-3)
depth (µm)
CdTe:111Ag
x
1.0 1.5 2.0 2.5 3.01.5
2.0
2.5
1000100
tdiff (min)
log
(x/
µm
)log(tdiff/min)
10
1.0 1.5 2.0 2.5 3.01.5
2.0
2.5
1000100
tdiff (min)
log
(x/
µm
)
log(tdiff/min)
10
diffx t
dissolution ofprecipitates ...
... takeninto account
profile analysis
effective D(Cdi) depends on
● density and size● dissolution rate
of precipitates
taking into accountdissolution of precipitates:
quantitative descriptionof x(tdiff)
model predicts:
diffx t
used samples:
different with respectto precipitates
383838
Defect interactions
in local equilibrium:
charge states of defects:
Cdi0, Cdi
+, Cdi2+
VCd0, VCd
-, VCd2-
Agi0, Agi
+
AgCd0, AgCd
-
e-, h+
donor
acceptor
donor
acceptor
}}
intrinsic (6)
extrinsic (4)
free carriers (2)
defect concentration:
0B B
F(Y) (Y)Y C exp exp
k T k T
C0: number of available lattice sites
Three chemical
potentials
Three corresponding
concentration quantities
defects taken into account
393939
diffusion equations
unchanged upon
defect reactions
i CdAg Ag Ag
i Cd CdC Cd V Ag
2Cd Cd Cd
2i i i
Cq 2 V V Ag e
2 Cd Cd Ag h
i
i CdCd i
2 2
20
Ag i
q
V C
A
q
d
d d d
dt dx dxd d d
dt dx dx
e d
dx
DC
Ag D Ag
C
Cd D V
qAA
A qq
qA
µ
µCq µ
Cq Cq
µ
C
Ag Ag Ag
µAg µ
C CC µ
µ
µ
d d
Cq
µ
µ
µ
AgCd is regarded as not mobile
µA := µ(Agi0)
µ := µ(Cdi0)
µq := µ(e-)
4040
profile analysis
Ag dopant mostly incorporated as Agi
+
pn-transitions formedin front of penetrating
Cdi defects
Ag dopant inequilibrium with
host crystal
chemical potentialscharge density and
stoichiometry deviationincorporation sites
of Ag dopant
essentially the same results for Cu, Au, and Na dopant
0 200 400 600 800-1.0
-0.5
0.0
0.5
µ + 2 eV
µA + 1 eV
depth (µm)
ener
gy (
eV)
µq
0 200 400 600 800-1.0x1017
-5.0x1016
0.0
5.0x1016
1.0x1017
-1.0x1011
-5.0x1010
0.0
5.0x1010
1.0x1011
[C]
depth (µm)
con
cen
tra
tion
(cm
-3)
[Cq]
0 200 400 600 800109
1010
1011
1012
1013
[Ag0Cd]
[Ag-Cd]
[Ag0i ]
depth (µm)
co
nce
ntr
atio
n (
cm-3)
[Ag+i ]
414141
AgAg
Ag
Ag
Cd
CdCd
Cd
F
FF
F
µ
µCq µ
C
µ
C C CC µ
µ
Ag Ag Ag
µµAg
q C
µ
µ
q
d d
q C
µµ
424242
i CdCd i V Cd
Cd C
F
F dF
Cq
Cq CD D Cd
qD V
C C
2 2i i Cd Cd
2 2i i Cd Cd
Cd i Cd
CdF
F
2 Cd
C Cd V
Cd 2 V V
Cq 4 Cd Cd h 4 V V e
CqC
2 2Cd Cd i i2 V V e 2 CC d h 0q Cd
434343
Cu-layer CdTe
Cd-layer acting asstrong source for
intrinsic defects (Cdi)
CdTeCu-layer
Cu-Tealloy
550 K
2-3 ML Cd at the interface would be sufficient !
Cu and Au layer on surface
4444
t1/2 > 2 d 1 h < t1/2 < 2 dcurrent
t1/2 < 1 hfuture/current
Plasma ion sourceSurface ionization (+/-)Laser ionization
600 isotopes, 68 elements600 isotopes, 68 elements
Ag
Ia
IIa
IIIb IVb Vb VIb VIIb VIII Ib IIb
IIIa IVa Va VIa VIIa
VIII
Zn
Cd In
N
Sb
S
Se
Te
Cl
Br
I
As33
15
7
H
Be
Mg
Ca Sc Ti
Sr Y
V Cr Mn
Zr Nb Mo Tc
Fe Co Ni
Ru Rh Pd
B
Al
Ga
C
Si
Ge
Sn
P
O F
He
Ne
Ar
Kr
Xe
Cu
4
12
20 21 22 23 24 25 26 27 28 29 30 31
13
5
32
14
6
34
16
8
35
17
9
36
18
10
2
38 39 40 41 42 43 44 45 46 47 48 49 50 51 53 54
Li
Rb
Na
K
1
3
11
19
37
Ba La Hf Ta W Re Os Ir Pt Au Hg Tl Pb Bi56 57 72 73 74 75 76 77 78 79 80 81 82 83
Cs55
Ag
Ia
IIa
IIIb IVb Vb VIb VIIb VIII Ib IIb
IIIa IVa Va VIa VIIa
VIII
Zn
Cd In
N
Sb
S
Se
Te
Cl
Br
I
As33
15
7
H
Be
Mg
Ca Sc Ti
Sr Y
V Cr Mn
Zr Nb Mo Tc
Fe Co Ni
Ru Rh Pd
B
Al
Ga
C
Si
Ge
Sn
P
O F
He
Ne
Ar
Kr
Xe
Cu
4
12
20 21 22 23 24 25 26 27 28 29 30 31
13
5
32
14
6
34
16
8
35
17
9
36
18
10
2
38 39 40 41 42 43 44 45 46 47 48 49 50 51 53 54
Li
Rb
Na
K
1
3
11
19
37
Ba La Hf Ta W Re Os Ir Pt Au Hg Tl Pb Bi56 57 72 73 74 75 76 77 78 79 80 81 82 83
Cs55
Ag
Ia
IIa
IIIb IVb Vb VIb VIIb VIII Ib IIb
IIIa IVa Va VIa VIIa
VIII
Zn
Cd In
N
Sb
S
Se
Te
Cl
Br
I
As33
15
7
H
Be
Mg
Ca Sc Ti
Sr Y
V Cr Mn
Zr Nb Mo Tc
Fe Co Ni
Ru Rh Pd
B
Al
Ga
C
Si
Ge
Sn
P
O F
He
Ne
Ar
Kr
Xe
Cu
4
12
20 21 22 23 24 25 26 27 28 29 30 31
13
5
32
14
6
34
16
8
35
17
9
36
18
10
2
38 39 40 41 42 43 44 45 46 47 48 49 50 51 53 54
Li
Rb
Na
K
1
3
11
19
37
Ba La Hf Ta W Re Os Ir Pt Au Hg Tl Pb Bi56 57 72 73 74 75 76 77 78 79 80 81 82 83
Cs55
Ag
Ia
IIa
IIIb IVb Vb VIb VIIb VIII Ib IIb
IIIa IVa Va VIa VIIa
VIII
Zn
Cd In
N
Sb
S
Se
Te
Cl
Br
I
As33
15
7
H
Be
Mg
Ca Sc Ti
Sr Y
V Cr Mn
Zr Nb Mo Tc
Fe Co Ni
Ru Rh Pd
B
Al
Ga
C
Si
Ge
Sn
P
O F
He
Ne
Ar
Kr
Xe
Cu
4
12
20 21 22 23 24 25 26 27 28 29 30 31
13
5
32
14
6
34
16
8
35
17
9
36
18
10
2
38 39 40 41 42 43 44 45 46 47 48 49 50 51 53 54
Li
Rb
Na
K
1
3
11
19
37
Ba La Hf Ta W Re Os Ir Pt Au Hg Tl Pb Bi56 57 72 73 74 75 76 77 78 79 80 81 82 83
Cs55
Radioactive Tracers
600 isotopes, 68 elements