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On ranges in PPP and conductivity effects
Synthetic Metals, 24 (1988) 53 - 60
53
ION RANGES IN PPP AND CONDUCTIVITY EFFECTS J. L. DUROUX, A. HEJDUK and A. MOLITON LEPOFI, 123, rue A. Thomas, 87060 Limoges Cddex (France)
G. FROYER and M. GAUNEAU C N E T Laboratory, B.P. 40, 22301 Lannion (France)
Abstract In this paper, we present a theoretical and experimental study of ion ranges in a PPP (polyparaphenylene) target and the effect on the conductivity of the material, which is an intrinsic insulator.
1. Ion range
This essentially theoretical view has been studied with the classical semiconductors Si and Ge [1]. In our case, we have applied the methods used for amorphous materials to the PPP case.
1.1. Generalities We suppose that the ion-target interaction is limited to two independent phenomena: elastic nuclear collisions and successive inelastic ionelectron collisions. The energy loss AE for a displacement Ax between two collisions leads at the limit (homogeneous and continuous target) to the total stopping power: S t ( E ) = --dE/dx = Sn(E) + S e ( E )
where Sn(E ) is the nuclear stopping power, and Se(E) the electronic stopping power. The mean range for an incident ion of energy Ei is then determined by the relation R ( E i)
(R(Ei))= f 0
0
dE
dx = f S t ( E ) Ei
The mean projected range (on the incident direction) will be denoted Rp and the corresponding standard deviation, ARp. 0379-6779/88]$3.50
© Elsevier Sequoia/Printed in The Netherlands
54 1.2. Choice o f s t o p p i n g p o w e r (a) Nuclear s t o p p i n g p o w e r : in the program realized in our laboratory, the Moli~re potential det er m i ned by Biersack [2 ] has been utilized: 0.5 log(1 + e)
Sn(E) = A
C + A I 6A2
where e is the normalized energy: 103aM2E
C=
1 4 . 4 1 Z 1 Z 2 ( M 1 + M2)
a0 = B o h r radius, a = screening radius; A = 5 7 6 . 4 ~ a M 1 N Z a Z 2 / ( M 1 + M2); N = target atomic density; A 1 = 0.05983 and A 2 = 0.32011; M 1 and Z1 are t he mass and atomic n u m b e r of the ion and M2 and Zz are the mass and atomic n u m b e r o f the target. (b) Electronic s t o p p i n g p o w e r : we have utilized the Varelas and Biersack interpolation formula: 1
1
1
Se
SeL
SeB
where SeL is the Lindhard stopping pow er ( i m p o r t a n t at low energy: E ~< 100 keV/a.m.u.) and SeB is t he Bethe stopping pow er ( i m p o r t a n t at high energy). (c) C o m p o s i t e target: we take as the mean molecular mass (M2) -
~,M2in i
where n is th e n u m b e r o f identical atomic species of the molecule, and we suppose a linear law f or t he stopping power: S ( E ) = ~_,NiSi(E ) with N; = atomic density of the ith species and Si(E) = stopping pow er of t h e ith species. 1.3. I o n range in a material To consider the influence of the collisions on t he incident ion dispersion we can p e r f o r m : either a M o n t e ~ a r l o t r e a t m e n t or a calculation based on t h e inverted B ol t zm a nn linear relation [3, 4], which entails determining the solutions o f the differential equation g(E) = ~ , ( E )
d"X(E) dE n
A simplification o f this problem has been proposed b y Biersack [5] and already applied b y Xu [6] to certain i o n - p o l y m e r interactions. Those last two are t he m e t h o d s (general and simplified) that have been used in o u r study, and we have hereafter referenced t h e m with indexes H and X respectively.
55
2. Results
2.1. Stopping power On Fig. 1 we present the nuclear stopping power curves for halogens and alkali metals and o n Fig. 2 the electronic stopping power curves: at first sight the preponderance of nuclear stopping power at low energy can be noted.
} J
2
f
/
f
/
---+_
0
-.
L
,a
ENEAC~ LKE~} t A B C t l , PPp
LCbH4~
R~,
TaRCET, PPP
1.250 (C/Cm..~}
(C6.4>
I~,SODIUM
1
l ON ,EIAO~ INE
1
i~,Polasslu~
2
I{3N, LOOIM~
2
ION,CESIUM
4
~,
1,250
[51C~..3)
Fig. 1. Nuclear stopping p o w e r curves for halogens and alkali metals incident on a P P P target.
g
11,
a,I
J
,,.2 J J
J
J
f
f
j
I
J
~..--J
J
~S
//Y i
" TA~ET,
Ppp
ICGU41
iou,s~]luM
~0.
1.250
[g/CH..3]
~ E ~
TA~T, I~
I ~ N . P 0 1 ^ s S I ta~
a
10N,CESIUM
4
I
[~tvJ CCGHdl
~P
Rm,
I.Z~
[¢1C~..Xl
,OR~'IINE
ION,IOOI~
Z
Fig. 2. Electronic stopping p o w e r curves for halogens and alkali metals incident on a P P P target.
56 2.2. P r o j e c t e d ranges We indicate t h e p r o j e c t e d range Rp and t h e standard d e v i a t i o n A R p , c a l c u l a t e d w i t h t h e H and X p r o c e s s e s versus e n e r g y o f t h e i n c i d e n t i o n s in Tables 1 and 2 for R b and Cs (representative o f alkali m e t a l s ) and Br and I (representative o f h a l o g e n s ) . T h e d i f f e r e n c e b e t w e e n t h e results o b t a i n e d w i t h t h e t w o m e t h o d s is a b o u t 10%. TABLE 1 Projected ranges and their standard deviations as a function of incident ion energy (H process) ION E
[keY] 10 20 30 40 50 60 70 80 90 100 110 120 130 140 150 160 170 180 190 200
RUBIDIUM RANGEPR [MICRON]
RG.PR.DEV [MICRON]
0.149E-01 0.242E-01 0.32BE-Of 0.411E-OI 0.492E-01 0.573E-01 0.652E-01 0 731E-01 0811E-01 o.BgOE-01 0969E-01 O.I05E*O0 0.113E*00 0.121E+00 0129E+00 0 136E*00 0.144E+00 0152E+00 0.160E400 OI6BE+O0
0335E-02 0.533E-02 0.717E-02 0 894E-02 0 107E-01 0 123E-01 0 140E-OI 0.157E-01 0.173E-01 0189E-01 0.20SE-OI 0.221E-01 0237E-01 0252E-01 0.268E-01 0.284E-01 0.299E-01 0.314E-01 0330E-01 0345E-01
CESIUM RANGEPR IMICRON] 0.155E-01 0.237E-01 0 309E-01 0.377E-01 0441E-01 0504E-01 0 566E-01 0.626E-01 0.686E-01 0.745E-01 0.803E-01 O.B62E-01 0.920E-01 o.g77E-OI O.103E+O0 0.I09E+00 0.115E*00 0.121E+00 0.126E*00 0.132E+00
BROMINE
RGPRDEV [MICRON] 0.291E-02 0.436E-02 0.564E-02 0 684E-02 0 799E-02 0.9~2E-02 O.I02E-O! 0.113E-01 0.124E-01 0 134E-01 0.144E-01 0155E-01 0165E-01 0175E-01 O.18SE-O1 0.195E-01 0205E-01 0215E-01 0225E-01 0235E-01
IODINE
RANGEPR [MICRON]
ROPR.DEV [MICRON]
RANGEPR [MICRON]
RG.PRDEV [MICRON]
0.149E-01 0.245E-01 0.333E-01 0.419E-01 0,504E-01 O.SBBE-OI 0.671£-01 0.754E-01 0.837E-01 0.920E-01 0.100E÷O0 0.I09E*00 O.1ITE+O0 0125E+00 0.134E+00 0.142E*00 0150E*00 0.159E+00 0167E+00 0.176E+00
0 340E-02 0 552E-02 0 747E-02 0.935E-02 0.112E-01 0.130E-01 0 147E-01 0.165E-01 0 182E-01 0.200E-01 0 217E-01 0234E-01 02SGE-01 0267E-01 0284E-01 0.300E-01 0.317E-01 0333E-01 0349E-Or 0365E-01
0.153E-01 0.236E-01 0309E-01 0.377E-01 0.443E-01 0.507E-01 0.$70E-01 0.632E-01 0.693E-01 0.753E-01 OBI3E-OI 0.873E-01 0.932E-01 0992E-01 OlOSE+O0 0.111E*O0 0117E*00 0123E+00 0129E*00 0.134E+00
0.295E-02 0.442E-02 0.575E-02 0.699E-02 0.819E-02 0.936E-02 0. I05E-01 0.116E-01 0.127E-01 0.138E-01 0.149E-01 0.160E°OI O.170E-OI O.18IE-OI 0.191E-01 0.202E-01 0.212E-01 0.223E-01 0233E-01 0.243E-01
TABLE 2 Projected ranges and their standard deviations as a function of incident ion energy (X process) ION
RUBIDIUM
CESIUM
BROMINE
IODINE
E [keY]
RANGEPR [MICRON]
RO.PRDEV [MICRON]
RANGEPR [MICRON]
R(].PR.DEV [MICRON]
RANGEPR {MICRON]
RO.PRDEV [MICRON]
RANGEPR [MICRON]
I0 20 30 40 SO 60 70 80 90 I00 110 120 130 140 150 160 170 180 190 200
0105E-01 0,189E-01 0.266E-01 0.340E-01 0412E-01 0.484E-01 0 ~'5SE-OI 0.626E-01 0.697E-01 0.768E-01 0.838E-01 O.910E-OI 0981E-01 O. I05E+O0 O. II2E+O0 O.120E+O0 0.127E+00 0.134E+00 O.141E*O0 0.149E+00
0 267E-02 0.361E-02 0 439E-02 0.509E-02 0 574E-02 0 636E-02 0.695E-02 0.752E-02 0.807E-02 0.860E-02 0.912E-02 0 963E-02 O.IOIE-OI O. 106E-01 0.111E-01 0.115E-OI 0.120E-01 O.12SE-OI 0.129E-0I 0.134E-01
0.099E-01 0 174E-01 0.240E-01 0 302E-01 0,361E-01 0.418E-01 0.473E-01 0 528E-01 0 582E-01 0.636E-01 0689E-01 0.742E-0! 0794E-01 0847E-01 0.899E-01 0951E-01 0 IOOE+O0 O. I05E*O0 0.111E+O0 0.116E*O0
0.230E°02 0.291E-02 0.339E-02 0.382E-02 0.422E-02 0.460E-02 0.495E-02 0.529E-02 0.562E-02 0594E-02 0.625E-02 0.656E-02 O.605E-02 0.714E-02 0.743E-02 0.771E-02 0 798E-02 0.825E-02 0.852E-02 0.878E-02
O.IOBE-OI 0.192E°01 0.271E-01 0.348E-01 0.423E-01 0 497E-01 0.572E-01 0.646E-01 0.720E-01 0 794E-01 0.869E-01 0 944E-01 0 102E+00 0 I09E+O0 0. I 17E*00 0.125E*00 0 132E+00 0.140E*00 0.148E+00 O.155E+00
0.274E-02 0 375E-02 0.458E-02 0.534E-02 0 604E-02 0.671E-02 0.734E-02 0.795E-02 O.BS5E-02 0.912E-02 0.969E-02 O.I02E-OI O.I08E-OI 0.113E-01 0 118E-01 0.123E-01 0.128E-01 0 133E-01 0.138E-01 0.143E-01
0.099E-01 0.175E-Or 0.241E-01 0.304E-Or 0.364E-0l 0.422E-01 0.478E-01 0.534E-01 0589E-OI 0.644E-01 0.698E-01 0.753E-01 0.806E-01 0.860E-01 0.913E-01 0.967E-01 0. I02E+00 O. I07E+O0 0.113E+00 0.11BE+O0
RO.PR.DEV [MICRON] 0.232E-02 0296E-02 0.346E-02 0.392E-02 0.433E-02 0.472E-02 0.510E-02 0.546E-02 0.580E-02 0.614E-02 0.646E-02 0.678E-02 0.709E-02 0.740E-02 0.769E-02 0.799E-02 0.828E-02 0.857E-02 0.885E-02 0.912E-02
57
2.3. Spatial repartition of ions Taking into account the simplifications (for example, absence of sputtering) we assume [1] that a Gaussian distribution is a good approximation. The theoretical implantation profiles can be compared with those obtained experimentally by secondary ion mass spectrometry (SIMS). Figure 3 shows results for Rb ions; Fig. 4 for I ions and Fig. 5 for P ions (the ion initially studied in the classical case).
3. Discussion These profiles show quite a good agreement between theory and experiment, particularly for Rp. Moreover, we notice that the experimental RUBIDIUM
~. era-3 10E
1 ~h
-
50 key
-
101'
ions/ore'
22
-
10E 21
-
THEORY
-----
SIMS
-
N.
------
SIMS
-
hnn.atin
^ .... II~9 9
10E 20 i
10E I g
\ 10E 18
\
10E 17
micror~8 10E 1B 0. 50
1.00
1.50
Fig. 3. T h e o r e t i c a l a n d e x p e r i m e n t a l i m p l a n t a t i o n p r o f i l e s for r u b i d i u m i o n s i n c i d e n t o n a PPP t a r g e t .
58
> IM
E~ 1.13
E 0
'l
t.,.-(
I
E 0 ""~
ELI Z
aa to
//
•
=
H
r-t C)
I'I
H
i ,' E o
C 0
,-:
//
@ 0
. o_ :..'~-
4~ 0
o >
!
N W
W
tU
14/
o
Ill
..o
S o L~ v
> ..~ E 0
p3 Lfl I
?
(" 0 ""~
ELi Z
~.
®
~
•
z
r-1
<
P~ o
I!' I,
I !
/"
I E 0
az
E
C gl
C a~ m
I .
9
/
/
/
/
/
o £ 0 L 0
o
... "
I
I
|
i
!
• -, N
I~ N
Q ..~
m .=i
I,-
in
Ld m
b/ ~
I,, al
i,i m
ld m ,=~
Ld m
59 PHOSPHORUS
-
I ~h
I~ le i o n s / o m z ~-i. o r e - 3
10E 21 .........
THEORY
-
50
THEORY
-
150
50
kmV
- - - = S I M S
-
SIMS e
10E 2 0
\
!
// /l ' '
,
\,/
;
m
:
150 k ~ V
\
\ I
1 •
\
i
kaY
%
I /
IBE I g
%
kaY
\
,
\ Q
\ I
IBE 18
\ \
\.
m i ~ror~8 10E
17
I {~. 2 0
I 0. 40
I 0. 60
I 0. 00
Fig. 5. Experimental and theoretical implantation profiles for phosphorus ions incident on a PPP target.
profiles are larger than the theoretical ones: considering that the greater the irradiation current, the broader the experimental profiles, we can infer that during implantation, local heating takes place leading to thermal diffusion, which also appears during a severe annealing process carried out at 7OO K. Unlike classical semiconductors for which low energy implantation produces a surface amorphization with a resistivity increase, we directly obtain in the PPP case an important doping effect: the conductivity a is multiplied by about 10 ~2 and annealing does n o t produce any phase transition; the evolution of o v e r s u s temperature is shown in Fig. 6 in the case of doping with Cs ions (E = 50 keV, D = 1016 ions/cm 2, j = 0.5 pA/cm2). For
60 CESIUM
'\
8.5
ph
-
50 10"
keY ionl/cm
2
I. 5~
\ ii 50
\ I/T
-g. 50,
CK"~
,
-5. ~
w .4
,-:
.4
,=
-L 50.
-2. 58
-3.5~
•"-.,,.,...
".... "'".... '',. 1/T-W" (K-w,)
cq ¢q ~ Fig. 6. a vs. t e m p e r a t u r e for PPP d o p e d with Cs ions to m a k e the variable range h o p p i n g process apparent.
low temperatures, the conductivity process is explained by the variable range hopping theory [7] : a linear law for log ov/T = f(T -w4) is obtained but for higher temperatures, different thermally-activated phenomena can occur simultaneously. The surface damage in relation to nuclear stopping power is limited by the material structure: in linear polymers, Frenkel defects are not possible as in the classical semiconductor case. It is only for higher energies (E/> 100 keV) that, as the stopping power is enhanced, electronic bond breaking can be obtained: this idea is supported by i.r. spectra that are unaltered after low-energy implantation (E ~ 50 keV) and show important modifications after higher~nergy implantations (E ~ 150 keV). References 1 2 3 4 5 6 7
H. Ryssel and I. Ruge, Ion Implantation, Wiley, New York, 1986, Ch. 1, p. 14. K. L. Wilson, L. G. Haggmark and J. P. Biersack, Phys. Rev., 5 (1977) 2458. J. P. Biersack, Z. Phys., 305 A (1982) 95 - 101. J. B. Sanders, Can. J. Phys., 46 (1968) 455 - 465. J. P. Biersack, Nucl. Instrum. Meth., 182/183 (1981) 199 - 206. X. Xu, Thesis, L y o n , 1987. N. F. M o t t and E. A. Davis, Electronic Processes in Non-Crystalline Materials, Clarendon Press, Oxford, 2nd edn., 1979, Ch. 2, p. 32.
53
ION RANGES IN PPP AND CONDUCTIVITY EFFECTS J. L. DUROUX, A. HEJDUK and A. MOLITON LEPOFI, 123, rue A. Thomas, 87060 Limoges Cddex (France)
G. FROYER and M. GAUNEAU C N E T Laboratory, B.P. 40, 22301 Lannion (France)
Abstract In this paper, we present a theoretical and experimental study of ion ranges in a PPP (polyparaphenylene) target and the effect on the conductivity of the material, which is an intrinsic insulator.
1. Ion range
This essentially theoretical view has been studied with the classical semiconductors Si and Ge [1]. In our case, we have applied the methods used for amorphous materials to the PPP case.
1.1. Generalities We suppose that the ion-target interaction is limited to two independent phenomena: elastic nuclear collisions and successive inelastic ionelectron collisions. The energy loss AE for a displacement Ax between two collisions leads at the limit (homogeneous and continuous target) to the total stopping power: S t ( E ) = --dE/dx = Sn(E) + S e ( E )
where Sn(E ) is the nuclear stopping power, and Se(E) the electronic stopping power. The mean range for an incident ion of energy Ei is then determined by the relation R ( E i)
(R(Ei))= f 0
0
dE
dx = f S t ( E ) Ei
The mean projected range (on the incident direction) will be denoted Rp and the corresponding standard deviation, ARp. 0379-6779/88]$3.50
© Elsevier Sequoia/Printed in The Netherlands
54 1.2. Choice o f s t o p p i n g p o w e r (a) Nuclear s t o p p i n g p o w e r : in the program realized in our laboratory, the Moli~re potential det er m i ned by Biersack [2 ] has been utilized: 0.5 log(1 + e)
Sn(E) = A
C + A I 6A2
where e is the normalized energy: 103aM2E
C=
1 4 . 4 1 Z 1 Z 2 ( M 1 + M2)
a0 = B o h r radius, a = screening radius; A = 5 7 6 . 4 ~ a M 1 N Z a Z 2 / ( M 1 + M2); N = target atomic density; A 1 = 0.05983 and A 2 = 0.32011; M 1 and Z1 are t he mass and atomic n u m b e r of the ion and M2 and Zz are the mass and atomic n u m b e r o f the target. (b) Electronic s t o p p i n g p o w e r : we have utilized the Varelas and Biersack interpolation formula: 1
1
1
Se
SeL
SeB
where SeL is the Lindhard stopping pow er ( i m p o r t a n t at low energy: E ~< 100 keV/a.m.u.) and SeB is t he Bethe stopping pow er ( i m p o r t a n t at high energy). (c) C o m p o s i t e target: we take as the mean molecular mass (M2) -
~,M2in i
where n is th e n u m b e r o f identical atomic species of the molecule, and we suppose a linear law f or t he stopping power: S ( E ) = ~_,NiSi(E ) with N; = atomic density of the ith species and Si(E) = stopping pow er of t h e ith species. 1.3. I o n range in a material To consider the influence of the collisions on t he incident ion dispersion we can p e r f o r m : either a M o n t e ~ a r l o t r e a t m e n t or a calculation based on t h e inverted B ol t zm a nn linear relation [3, 4], which entails determining the solutions o f the differential equation g(E) = ~ , ( E )
d"X(E) dE n
A simplification o f this problem has been proposed b y Biersack [5] and already applied b y Xu [6] to certain i o n - p o l y m e r interactions. Those last two are t he m e t h o d s (general and simplified) that have been used in o u r study, and we have hereafter referenced t h e m with indexes H and X respectively.
55
2. Results
2.1. Stopping power On Fig. 1 we present the nuclear stopping power curves for halogens and alkali metals and o n Fig. 2 the electronic stopping power curves: at first sight the preponderance of nuclear stopping power at low energy can be noted.
} J
2
f
/
f
/
---+_
0
-.
L
,a
ENEAC~ LKE~} t A B C t l , PPp
LCbH4~
R~,
TaRCET, PPP
1.250 (C/Cm..~}
(C6.4>
I~,SODIUM
1
l ON ,EIAO~ INE
1
i~,Polasslu~
2
I{3N, LOOIM~
2
ION,CESIUM
4
~,
1,250
[51C~..3)
Fig. 1. Nuclear stopping p o w e r curves for halogens and alkali metals incident on a P P P target.
g
11,
a,I
J
,,.2 J J
J
J
f
f
j
I
J
~..--J
J
~S
//Y i
" TA~ET,
Ppp
ICGU41
iou,s~]luM
~0.
1.250
[g/CH..3]
~ E ~
TA~T, I~
I ~ N . P 0 1 ^ s S I ta~
a
10N,CESIUM
4
I
[~tvJ CCGHdl
~P
Rm,
I.Z~
[¢1C~..Xl
,OR~'IINE
ION,IOOI~
Z
Fig. 2. Electronic stopping p o w e r curves for halogens and alkali metals incident on a P P P target.
56 2.2. P r o j e c t e d ranges We indicate t h e p r o j e c t e d range Rp and t h e standard d e v i a t i o n A R p , c a l c u l a t e d w i t h t h e H and X p r o c e s s e s versus e n e r g y o f t h e i n c i d e n t i o n s in Tables 1 and 2 for R b and Cs (representative o f alkali m e t a l s ) and Br and I (representative o f h a l o g e n s ) . T h e d i f f e r e n c e b e t w e e n t h e results o b t a i n e d w i t h t h e t w o m e t h o d s is a b o u t 10%. TABLE 1 Projected ranges and their standard deviations as a function of incident ion energy (H process) ION E
[keY] 10 20 30 40 50 60 70 80 90 100 110 120 130 140 150 160 170 180 190 200
RUBIDIUM RANGEPR [MICRON]
RG.PR.DEV [MICRON]
0.149E-01 0.242E-01 0.32BE-Of 0.411E-OI 0.492E-01 0.573E-01 0.652E-01 0 731E-01 0811E-01 o.BgOE-01 0969E-01 O.I05E*O0 0.113E*00 0.121E+00 0129E+00 0 136E*00 0.144E+00 0152E+00 0.160E400 OI6BE+O0
0335E-02 0.533E-02 0.717E-02 0 894E-02 0 107E-01 0 123E-01 0 140E-OI 0.157E-01 0.173E-01 0189E-01 0.20SE-OI 0.221E-01 0237E-01 0252E-01 0.268E-01 0.284E-01 0.299E-01 0.314E-01 0330E-01 0345E-01
CESIUM RANGEPR IMICRON] 0.155E-01 0.237E-01 0 309E-01 0.377E-01 0441E-01 0504E-01 0 566E-01 0.626E-01 0.686E-01 0.745E-01 0.803E-01 O.B62E-01 0.920E-01 o.g77E-OI O.103E+O0 0.I09E+00 0.115E*00 0.121E+00 0.126E*00 0.132E+00
BROMINE
RGPRDEV [MICRON] 0.291E-02 0.436E-02 0.564E-02 0 684E-02 0 799E-02 0.9~2E-02 O.I02E-O! 0.113E-01 0.124E-01 0 134E-01 0.144E-01 0155E-01 0165E-01 0175E-01 O.18SE-O1 0.195E-01 0205E-01 0215E-01 0225E-01 0235E-01
IODINE
RANGEPR [MICRON]
ROPR.DEV [MICRON]
RANGEPR [MICRON]
RG.PRDEV [MICRON]
0.149E-01 0.245E-01 0.333E-01 0.419E-01 0,504E-01 O.SBBE-OI 0.671£-01 0.754E-01 0.837E-01 0.920E-01 0.100E÷O0 0.I09E*00 O.1ITE+O0 0125E+00 0.134E+00 0.142E*00 0150E*00 0.159E+00 0167E+00 0.176E+00
0 340E-02 0 552E-02 0 747E-02 0.935E-02 0.112E-01 0.130E-01 0 147E-01 0.165E-01 0 182E-01 0.200E-01 0 217E-01 0234E-01 02SGE-01 0267E-01 0284E-01 0.300E-01 0.317E-01 0333E-01 0349E-Or 0365E-01
0.153E-01 0.236E-01 0309E-01 0.377E-01 0.443E-01 0.507E-01 0.$70E-01 0.632E-01 0.693E-01 0.753E-01 OBI3E-OI 0.873E-01 0.932E-01 0992E-01 OlOSE+O0 0.111E*O0 0117E*00 0123E+00 0129E*00 0.134E+00
0.295E-02 0.442E-02 0.575E-02 0.699E-02 0.819E-02 0.936E-02 0. I05E-01 0.116E-01 0.127E-01 0.138E-01 0.149E-01 0.160E°OI O.170E-OI O.18IE-OI 0.191E-01 0.202E-01 0.212E-01 0.223E-01 0233E-01 0.243E-01
TABLE 2 Projected ranges and their standard deviations as a function of incident ion energy (X process) ION
RUBIDIUM
CESIUM
BROMINE
IODINE
E [keY]
RANGEPR [MICRON]
RO.PRDEV [MICRON]
RANGEPR [MICRON]
R(].PR.DEV [MICRON]
RANGEPR {MICRON]
RO.PRDEV [MICRON]
RANGEPR [MICRON]
I0 20 30 40 SO 60 70 80 90 I00 110 120 130 140 150 160 170 180 190 200
0105E-01 0,189E-01 0.266E-01 0.340E-01 0412E-01 0.484E-01 0 ~'5SE-OI 0.626E-01 0.697E-01 0.768E-01 0.838E-01 O.910E-OI 0981E-01 O. I05E+O0 O. II2E+O0 O.120E+O0 0.127E+00 0.134E+00 O.141E*O0 0.149E+00
0 267E-02 0.361E-02 0 439E-02 0.509E-02 0 574E-02 0 636E-02 0.695E-02 0.752E-02 0.807E-02 0.860E-02 0.912E-02 0 963E-02 O.IOIE-OI O. 106E-01 0.111E-01 0.115E-OI 0.120E-01 O.12SE-OI 0.129E-0I 0.134E-01
0.099E-01 0 174E-01 0.240E-01 0 302E-01 0,361E-01 0.418E-01 0.473E-01 0 528E-01 0 582E-01 0.636E-01 0689E-01 0.742E-0! 0794E-01 0847E-01 0.899E-01 0951E-01 0 IOOE+O0 O. I05E*O0 0.111E+O0 0.116E*O0
0.230E°02 0.291E-02 0.339E-02 0.382E-02 0.422E-02 0.460E-02 0.495E-02 0.529E-02 0.562E-02 0594E-02 0.625E-02 0.656E-02 O.605E-02 0.714E-02 0.743E-02 0.771E-02 0 798E-02 0.825E-02 0.852E-02 0.878E-02
O.IOBE-OI 0.192E°01 0.271E-01 0.348E-01 0.423E-01 0 497E-01 0.572E-01 0.646E-01 0.720E-01 0 794E-01 0.869E-01 0 944E-01 0 102E+00 0 I09E+O0 0. I 17E*00 0.125E*00 0 132E+00 0.140E*00 0.148E+00 O.155E+00
0.274E-02 0 375E-02 0.458E-02 0.534E-02 0 604E-02 0.671E-02 0.734E-02 0.795E-02 O.BS5E-02 0.912E-02 0.969E-02 O.I02E-OI O.I08E-OI 0.113E-01 0 118E-01 0.123E-01 0.128E-01 0 133E-01 0.138E-01 0.143E-01
0.099E-01 0.175E-Or 0.241E-01 0.304E-Or 0.364E-0l 0.422E-01 0.478E-01 0.534E-01 0589E-OI 0.644E-01 0.698E-01 0.753E-01 0.806E-01 0.860E-01 0.913E-01 0.967E-01 0. I02E+00 O. I07E+O0 0.113E+00 0.11BE+O0
RO.PR.DEV [MICRON] 0.232E-02 0296E-02 0.346E-02 0.392E-02 0.433E-02 0.472E-02 0.510E-02 0.546E-02 0.580E-02 0.614E-02 0.646E-02 0.678E-02 0.709E-02 0.740E-02 0.769E-02 0.799E-02 0.828E-02 0.857E-02 0.885E-02 0.912E-02
57
2.3. Spatial repartition of ions Taking into account the simplifications (for example, absence of sputtering) we assume [1] that a Gaussian distribution is a good approximation. The theoretical implantation profiles can be compared with those obtained experimentally by secondary ion mass spectrometry (SIMS). Figure 3 shows results for Rb ions; Fig. 4 for I ions and Fig. 5 for P ions (the ion initially studied in the classical case).
3. Discussion These profiles show quite a good agreement between theory and experiment, particularly for Rp. Moreover, we notice that the experimental RUBIDIUM
~. era-3 10E
1 ~h
-
50 key
-
101'
ions/ore'
22
-
10E 21
-
THEORY
-----
SIMS
-
N.
------
SIMS
-
hnn.atin
^ .... II~9 9
10E 20 i
10E I g
\ 10E 18
\
10E 17
micror~8 10E 1B 0. 50
1.00
1.50
Fig. 3. T h e o r e t i c a l a n d e x p e r i m e n t a l i m p l a n t a t i o n p r o f i l e s for r u b i d i u m i o n s i n c i d e n t o n a PPP t a r g e t .
58
> IM
E~ 1.13
E 0
'l
t.,.-(
I
E 0 ""~
ELI Z
aa to
//
•
=
H
r-t C)
I'I
H
i ,' E o
C 0
,-:
//
@ 0
. o_ :..'~-
4~ 0
o >
!
N W
W
tU
14/
o
Ill
..o
S o L~ v
> ..~ E 0
p3 Lfl I
?
(" 0 ""~
ELi Z
~.
®
~
•
z
r-1
<
P~ o
I!' I,
I !
/"
I E 0
az
E
C gl
C a~ m
I .
9
/
/
/
/
/
o £ 0 L 0
o
... "
I
I
|
i
!
• -, N
I~ N
Q ..~
m .=i
I,-
in
Ld m
b/ ~
I,, al
i,i m
ld m ,=~
Ld m
59 PHOSPHORUS
-
I ~h
I~ le i o n s / o m z ~-i. o r e - 3
10E 21 .........
THEORY
-
50
THEORY
-
150
50
kmV
- - - = S I M S
-
SIMS e
10E 2 0
\
!
// /l ' '
,
\,/
;
m
:
150 k ~ V
\
\ I
1 •
\
i
kaY
%
I /
IBE I g
%
kaY
\
,
\ Q
\ I
IBE 18
\ \
\.
m i ~ror~8 10E
17
I {~. 2 0
I 0. 40
I 0. 60
I 0. 00
Fig. 5. Experimental and theoretical implantation profiles for phosphorus ions incident on a PPP target.
profiles are larger than the theoretical ones: considering that the greater the irradiation current, the broader the experimental profiles, we can infer that during implantation, local heating takes place leading to thermal diffusion, which also appears during a severe annealing process carried out at 7OO K. Unlike classical semiconductors for which low energy implantation produces a surface amorphization with a resistivity increase, we directly obtain in the PPP case an important doping effect: the conductivity a is multiplied by about 10 ~2 and annealing does n o t produce any phase transition; the evolution of o v e r s u s temperature is shown in Fig. 6 in the case of doping with Cs ions (E = 50 keV, D = 1016 ions/cm 2, j = 0.5 pA/cm2). For
60 CESIUM
'\
8.5
ph
-
50 10"
keY ionl/cm
2
I. 5~
\ ii 50
\ I/T
-g. 50,
CK"~
,
-5. ~
w .4
,-:
.4
,=
-L 50.
-2. 58
-3.5~
•"-.,,.,...
".... "'".... '',. 1/T-W" (K-w,)
cq ¢q ~ Fig. 6. a vs. t e m p e r a t u r e for PPP d o p e d with Cs ions to m a k e the variable range h o p p i n g process apparent.
low temperatures, the conductivity process is explained by the variable range hopping theory [7] : a linear law for log ov/T = f(T -w4) is obtained but for higher temperatures, different thermally-activated phenomena can occur simultaneously. The surface damage in relation to nuclear stopping power is limited by the material structure: in linear polymers, Frenkel defects are not possible as in the classical semiconductor case. It is only for higher energies (E/> 100 keV) that, as the stopping power is enhanced, electronic bond breaking can be obtained: this idea is supported by i.r. spectra that are unaltered after low-energy implantation (E ~ 50 keV) and show important modifications after higher~nergy implantations (E ~ 150 keV). References 1 2 3 4 5 6 7
H. Ryssel and I. Ruge, Ion Implantation, Wiley, New York, 1986, Ch. 1, p. 14. K. L. Wilson, L. G. Haggmark and J. P. Biersack, Phys. Rev., 5 (1977) 2458. J. P. Biersack, Z. Phys., 305 A (1982) 95 - 101. J. B. Sanders, Can. J. Phys., 46 (1968) 455 - 465. J. P. Biersack, Nucl. Instrum. Meth., 182/183 (1981) 199 - 206. X. Xu, Thesis, L y o n , 1987. N. F. M o t t and E. A. Davis, Electronic Processes in Non-Crystalline Materials, Clarendon Press, Oxford, 2nd edn., 1979, Ch. 2, p. 32.