The effects of ion beam induced atomic mixing at the Fe-Polyethylene interface have been investigated by means of conversion electron Mossbauer spectroscopy [CEMS]. It is shown that the as deposited and ion beam mixed composites exhibit distinctly different features. In particular, the ion beam mixed composite shows that presence of Fe2+ state in polyethylene matrix along with the Fe-C austenite like phase

Bhide, V.G.

Date, S. K.

Ghaisas, S. V.

Kulkarni, Neelima

Ogale, S. B.

Patil, P. P.

English

Publications of the IAS Fellows

Hyperfine Interactions 35 (1987) 919-922 919 
A CONVERSION ELECTRON MOSSBAUER 
SPECTROSCOPY STUDY OF ION BEAM MIXING AT 
Fe: POLYETHYLENE INTERFACE 
P.P. PATIL, Neelima KULKARNI, S.V. GHAISAS and S.B. OGALE 
Department of Physics, University of Poona, Pune 411007, India 
V.G. BHIDE 
School of Energy Studies, University of Poona, Pune 411007, India 
S.K. DATE 
National Chemical Laboratory, Pune 411008, India 
The effects of ion beam induced atomic mixing at the Fe-Polyethylene 
interface have been investigated by means of conversion electron MSssbauer 
spectroscopy [CEMS]. It is shown that the as deposited and ion beam mixed 
compos i tes  exh ib i t  d i s t inc t ly  d i f fe rent  features. ln particular,the ion 
beam mixed compos i te  shows the presence  of Fe 2+ state in po lyethy lene  
matrix along with the Fe-C austenite like phase. 
1.INTRODUCTION : 
In recent years there is a rapid growth of polymer science from the point of 
view of applications. Polymeric materials are used in number of applications such 
as adhesive coatings, electrical and thermal insulations, moisture barriers etc. 
/1-5/. In addition to these conventional applications,the polymers are found to be 
potentially useful in the solar technology. Surface processing and modification of 
polymers is a new emerging trend and very interesting results have been reported 
by irradiating the high energy ion beam on polymers /1-3/. The fact that polymers 
undergo dissociation and those atoms which form volatile species are selectively 
depleted from the polymer surface can be utilised in producing useful inorganic 
composites by ion bombardment of polymers. Recently, synthesis of novel inorganic 
films was attempted by using ion-polymer film interaction and the formation of Si- 
C bond was reported /i/. Ion beam mixing /6/ is yet another method to obtain novel 
metastab le  phases. In this paper, we demonst ra te  the potent ia l  use of ion beam 
induced react ions  to synthes ize  usefu l  mater ia ls .  This,to our knowledge , i s  the 
first study of its nature in the context of ion beam modification of materials. We 
have chosen Fe :po lyethy lene  sys tem and the ion beam induced micros t ruc tura l  
changes are characterised by using conversion electron M~ssbauer probe /7/. 
2. EXPERIMENTAL : 
Polyethylene [PE] substrates were coated with --,230 ~ thick iron overlayer 
containing 30% of Fe 57 isotope by vacuum evaporation at a background pressure of 
10 -6 tort. Care was taken to avoid the heat ing of the subst ra tes  dur ing the 
depos i t ion.  The evaporat ion  unit was equ ipped with fore l ine traps [molecu lar  
sieves] and liquid nitrogen traps to avoid contamination. A number of such freshly 
prepared  compos i tes  were sub jec ted  to 80 keY Ar + ion bombardment  to induce ion 
beam mixing. The ion doses in the range between ixl015 and ixl016 ions/cm 2 were 
employed.  The process  of ion imp lantat ion  was carr ied out using a mach ine  
fabricated in our laboratory /8/. During the ion bombardment the pyrolysis of the 
po lyethy lene  subst ra te  was avo ided by mainta in ing  the ion current  in the range 
0.1-0.2 ~A/cm 2. Room temperature  convers ion  e lec t ron  M~ssbauer  spectra  were 
recorded for as-deposited Fe:Polyethylene composite as well as the ion beam mixed 
compos i te  using the s tandard  MSssbauer  spect rometer  with gas f low propor t ina l  
detector. The source used was Co57:Rh with 50 mCi strength. Experimental M~ssbauer 
curves were least square fitted using MOSFIT programme /9/. Wherever necessary, 
the composite MSssbauer spectra were deconvoluted following the procedure by G. Le 
Caer et al./10/ to obtain information regarding the distribution of quadrupole 
interaction. 
9 J.C. Baltzer A.G., Scientific Publishing Company 
920 P.P. Patil et aL, CEMS study of ion beam mixing 
3. RESULTS AND DISCUSSION : 
Fig.l(a) shows the convers ion e lectron M~ssbauer {CEMS] spect rum of the as- 
deposi ted Fe:Polyethylene composite.  The spec imen was subsequent ly  bombarded with 
d i f fe rent  ion doses.  The cor respond ing  CEMS spect ra  are presented  in F igs. l (b) -  
l(e). The d istr ibut ion of quadrupole  interact ion [P(QS)] associated wi th  each of 
these  spect ra  is p resented  in F igs. l ( f ) - l ( j ) .  The best  f it  CEMS spect rum of the 
as -depos i ted  sample  compr ises  of  a broad  doub le t  w i th  an i somer  sh i f t  of  0.39 
mm/sec  [w i th  respect  to ~-Fe]  and quadrupo le  in teract ion  of  0.78 mm/sec .  The 
typical nature of the hyperf ine interact ion indicates the presence of Fe 3+ state 
z 
< 
u~ 
z 
_z 
(bl 
~FIN 
n n 
. {c )  
4,~ / "~,.,:~;. 
in n (d) 
:9;#?.. ;;~v;, 
VELOClTY'( m.,/~,e~ I 
II) 
91 
0 }0 15 
O..S.( m m/s~c 
z 
c~ 
o4 
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Fig.l : Room temperature  CEMS spectra and the corresponding P(QS) d is t r ibut ions  of 
Fe:Polyethylene composi te  at var ious ion doses. 
P.P. Patil et al., CEMS study of ion beam mixing 921 
in the as-deposited sample. Similar result was observed in the case of iron doped 
polymers presumably due to the superparamagnetic behavior of Fe incorporated in 
the polymer chain /11,12/. The notable feature of this doublet is the broadening 
of the resonance  l ines and it can be a t t r ibuted  to the d is t r ibut ion  of non- 
equ iva lent  Fe s i tes  in the po lyethy lene  matrix. The quadrupo le  in teract ion  
d i s t r ibut ion  curve [Fig.l(f)] a lso shows  c lear ly  the var ia t ion  in the e lec t r i c  
f ie ld grad ient  [efg] due to s l ight ly  d i f fe rent  bond lengths and ang les  of Fe 3+ 
ions. 
Upon ion bombardment  w i th  80 keV Ar + ions at a dose of ixlO 15 ions /cm 2, 
the nature of CEMS spectrum [Fig.l(b)] shows a drastic change. It is clearly seen 
that the ion beam mixing leads to the growth of entirely different non-magnetic 
components. The CEMS spectra contain a singlet with small isomer shift and two 
doublets. The singlet along with the doublet having isomer shift 0.36 mm/sec and 
quadrupole interaction 0.36 mm/sec can be the result of Fe-C austenite like order 
/13/. The Fe-C austen i te  is an in ters t i t ia l  so l id  so lu t ion  in which the carbon 
atoms are randomly distributed on octahedral voids in the fcc structure of ~-iron. 
Such a phase conf igurat ion  is metastab le  in nature  but can be re ta ined  at room 
temperature  through the quench ing  e f fec ts  /14/. It is we l l  known that the 
quench ing  rates of i0 I0 k'/s can be ach ieved  dur ing the ion beam mix ing  process  
leading to novel metastable phase formation /6/. It is interesting to observe that 
the Ar + ion bombardment also produces carbon free radicals which eventually take 
part  in ion beam mix ing  process  to prec ip i ta te  new local a r rangements  or 
compositions. It is already reported that the dominant effect of energy deposition 
in the polymer is the creation of free carbon radicals which are chemical ly highly 
reactive and our results are consistant with this observation /2/. The hyperfine 
interaction values corresponding to the Fe-C austenite like order are different 
than the repor ted  va lues and such d i f fe rences  are expected  in the rad ia t ion  
processed  mater ia l s  wh ich  have high concent ra t ion  of de fects  [vacanc ies]  and 
assoc ia ted  compress ive  stresses.  The other  doub let  with a large isomer shift  
[1.27 mm/sec] can be attributed to the presence of Fe2+state in the polyethylene 
network. This conversion of Fe 3+ to Fe 2+ may be due to the association of carbon 
wh ich  essent ia l l y  acts as a donor of e lectron.  Such a t rans format ion  of a ionic 
state due to the radiation has been reported in the case of Sn atoms in organo-tin 
compound used for the po lyethy lene  s tab i l i za t ion  /15/. The cor respond ing  
quadrupole interaction distribution [Fig.l(g)] also clearly reveals the ion beam 
induced mix ing  in Fe :Po lyethy lene  compos i te  and shows the vary ing  env i ronment  
experienced by Fe 57 atoms in polyethylene matrix. 
The CEMS spect ra  of the samples  bombarded w i th  h igher  doses of Ar + ions 
[ Figs.l(c)-l(e)] bas ica l ly  reta in  all the non-magnet ic  component  but the 
sys temat ic  changes  in the va lues  of hyper f ine  in teract ions  ind icate  the dose 
dependent  mic ros t ructura l  changes  due to the ion beam induced react ions.  The 
intensity of the doublet associated with Fe-C austenite-l ike order is increased at 
a dose of 3x1015 ions /cm 2 and is observed  to be s tab i l i zed  at h igher  ion dose. 
This may be due to the availabil ity of large number of carbon free radicals due to 
the fur ther  degradat ion  of po lymer  network  at high ion dose bombardment ,  The 
substant ia l  inc rease  in i somer  shi f t  of Fe 2+ doub le t  due to the h igher  ion dose 
t reatment  can be ,attributed to the increase in the number  of carbon ne@r 
neighbours of Fe atoms in certain regions of polyethylene matrix. The distribution 
of quadrupo le  in teract ion  [Figs.l(h)-l( j)] p r imar i ly  reveal  the same features  
exhibited by the corresponding CEMS spectra. Finally, it is interesting to observe 
the s ign i f i cant  improvement  in the overa l l  sharpness  of the quadrupo le  
distr ibution curves as well as CEMS resonance lines with the increase of the ion 
dose. This dose dependent  feature  of Fe :Po lyethy lene  in teract ion  exh ib i t s  the 
microstructural  changes via the local atomic order. 
4. CONCLUSION : 
The  ion beam induced react ions  in Fe :Po lyethy lene  compos i te  produce 
s ign i f i cant  changes  in the po lymer  matr ix  wi th  the growth  of a metastab le  Fe-C 
austen i te - l i ke  s t ructure .  Further  exper iments  such as resistivity measurements, 
922 P.P. Patil et al., CEMS study of ion beam mixing 
ox idat ion  are being carr ied  out to obta in  ins ight  in the role p layed by Fe 
a toms for the s tab i l i za t ion  of po lyethy lene  network.  These resu l ts  wi l l  be 
published elsewhere. 
ACKOWLEDGEMENTS : 
This work is supported by the Department of Science and Technology, Government 
of India. One of us [P.P.P.] gratefully acknowledges the financial assistance by 
the Council of Scientific and Industrial Research, India. 
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A conversion electron Mossbauer spectroscopy study of ion beam mixing at Fe: polyethylene interface

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A conversion electron Mossbauer spectroscopy study of ion beam mixing at Fe: polyethylene interface

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