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Nuclear Instruments and Methods in Physics Research B 263 (2007) 458–462

NIMBBeam Interactions

with Materials & Atoms

Structural characterization of swift heavy ion irradiated polycarbonate

Lakhwant Singh, Kawaljeet Singh Samra *

Department of Physics, Guru Nanak Dev University, Amritsar-143005, Punjab, India

Received 10 April 2007; received in revised form 14 June 2007Available online 21 July 2007

Abstract

Makrofol-N polycarbonate thin films were irradiated with copper (50 MeV) and nickel (86 MeV) ions. The modified films wereanalyzed by UV–VIS, FTIR and XRD techniques. The experimental data was used to evaluate the formation of chromophore groups(conjugated system of bonds), degradation cross-section of the special functional groups, the alkyne formation and the amorphizationcross-section. The investigation of UV–VIS spectra shows that the formation of chromophore groups is reduced at larger wavelength,however its value increases with the increase of ion fluence. Degradation cross-section for the different chemical groups present in thepolycarbonate chains was evaluated from the FTIR data. It was found that there was an increase of degradation cross-section of chem-ical groups with the increase of electronic energy loss in polycarbonate. The alkyne and alkene groups were found to be induced due toswift heavy ion irradiation in polycarbonate. The radii of the alkyne production of about 2.74 and 2.90 nm were deduced for nickel(86 MeV) and copper (50 MeV) ions respectively. XRD analysis shows the decrease of the main XRD peak intensity. Progressive amor-phization process of Makrofol-N with increasing fluence was traced by XRD measurements.� 2007 Elsevier B.V. All rights reserved.

PACS: 61.10.Nz; 61.82.�d; 61.82.Pv; 78.30.�j; 78.30.Jw; 78.40.�q; 78.40.Pg

Keywords: Makrofol-N; Polycarbonate; Chromophore groups; Degradation cross-section; Amorphization

1. Introduction

In the last two decades, the drastic modifications in theproperties of polymeric materials such as: electrical, opti-cal, mechanical, thermal, etc. induced by ion beam irradia-tion have been noticed. Electronic excitation, ionization,chemical bonds disruption and rearrangements areaccepted as the fundamental events that give rise to theobserved macroscopical changes [1]. Generally physicaland chemical modifications induced in polymers underthe effect of ion irradiation are triggered by the energydeposited with in the target by the incident ion [2]. Com-plex diffusion and relaxation processes lead to the forma-tion of latent tracks. The most important modes of theenergy loss of ions in target atoms are associated to:

0168-583X/$ - see front matter � 2007 Elsevier B.V. All rights reserved.

doi:10.1016/j.nimb.2007.07.014

* Corresponding author.E-mail address: samraphy@gmail.com (K.S. Samra).

1. The effect of the electronic stopping power or energyloss corresponding to the interaction between the inci-dent ions and the electrons of the target atoms.

2. The contribution of the nuclear stopping power associ-ated to the Coulomb interaction among the target nucleiand the incident particles (elastic collisions).

For ion beam irradiated polymers, the weight of the sec-ond process is negligible. Due to the large energy depositedby the incident ions within a small volume and taking intoaccount the insulating features of the target, huge increasein the local temperature (thermal spike) was expected [3,4].The interaction between high-energy ions and the poly-meric chains lead to the scissoring of original bonds,production of radicals and excited atoms, bond rearrange-ments and cross-linking of oligomeric fragments. Theseprocesses are responsible for structural modification andfundamental property changes.

2

4

6

Aso

rban

ce f

e

dc

L. Singh, K.S. Samra / Nucl. Instr. and Meth. in Phys. Res. B 263 (2007) 458–462 459

The present paper reports the structural degradation ofpolycarbonate (PC, Makrofol-N) irradiated with swift heavyions at varying fluences. The purpose of the present investiga-tion is to shed light on the swift heavy ion induced effects inMakrofol-N for a better understanding of the track forma-tion using UV–VIS, Fourier-transform infrared (FTIR)spectroscopies and X-ray diffraction (XRD) analysis.

300 400 500 600 700 8000

Wavelength (nm)

b

a

Fig. 1. UV–VIS spectra of Makrofol-N irradiated with 50 MeV copperions with fluence (a) 0, (b) 1 · 1011, (c) 5 · 1011, (d) 1 · 1012, (e) 5 · 1012

and (f) 1 · 1013 ions cm�2.

0.0 2.0x1012

4.0x1012

6.0x1012

8.0x1012

1.0x1013

0

2

4

6 λ = 500 Copper (50 MeV) Nickel (86 MeV)

Fluence (ions cm-2)

A -

A0

Fig. 2. Change in the UV–VIS absorbance relative to the pristineMakrofol-N film plotted versus ion fluence, for the various irradiations.The solid lines are fits of the equation A(/) � ak nr/ + A0 to theexperimental points.

2. Experimental procedure

Makrofol-N polycarbonate (40 lm) in the form of flatpolished films was procured from Good Fellow Ltd. (Eng-land). Without any further treatment, the samples of thesize (1 · 1 cm2) were irradiated with copper (50 MeV) andnickel (86 MeV) ion beams available from the15 UD pelle-tron facility in the general purpose scattering chamber(GPSC) under ambient pressure of 10�6 Torr at Inter-Uni-versity Accelerator Center, New Delhi. The electronic stop-ping power of copper (50 MeV) and nickel (86 MeV) ionsin polycarbonate is 5.65 and 5.37 keV/nm, respectively[5]. A vacuum of the order of �4 · 10�6 Torr was main-tained during the irradiation. The beam current was keptlow to suppress thermal decomposition and was monitoredintermittently with a Faraday cup. Three techniques areemployed to study the structural characterization of swiftheavy ion irradiated polycarbonate. The samples were ana-lyzed with UV–VIS spectroscopy in transmission modeusing Hitachi Modal U-3000 spectrophotometer in therange 200–800 nm. The chemical-changes were studiedusing Nexus 870 FTIR Spectrometer in the range 4000–500 cm�1. The X-ray diffraction patterns were recordedusing the Cu-Ka (k = 1.54 A) radiation in h–h locked cou-ple mode from the Brukar AXS D8 diffractometer withscan speed of 1�/min. The diffraction angle (2h) has beenvaried from 5� to 45� with a step size of 0.02�. The mea-surements were done under ambient pressure conditionsat room temperature. Each experiment was repeated atleast twice and with both faces of the specimens alterna-tively exposed to the X-rays to check the reproducibility.

3. Results and discussion

3.1. UV–VIS analysis

UV–VIS measurements of the irradiated samplesshowed the similar trends for the different ion irradiations.As an example, the absorbance as a function of the wave-length for different copper (50 MeV) ion fluences is shownin Fig. 1. A shift in the absorption edge towards longerwavelength is observed with the increase of ion fluence.The increase in absorption may be attributed to the forma-tion of chromophore groups (conjugated system of bonds)as a consequence of the beam induced bond breaking andreconstruction [6,8]. The absorbance difference (A�A0)(where A and A0 are the absorbance of polycarbonate afterand before irradiation, respectively) versus ion fluence, /

was plotted in Fig. 2. The increase in absorbance is approx-imately linear within the fluence range employed in bothirradiations. The solid lines in Fig. 2 fit the experimentaldata using the relation [6]:

Akð/Þ � aknr/þ A0;

where Ak(/) is the absorbance at a wavelength k and at afluence /, ak is the chromophore absorption coefficient in(cm)2, n is the number of chromophores that absorb at acertain wavelength created per incident primary ion andper unit area and r is the cross-sectional area of a cylinderwithin which n chromophores are created (nr is the numberof chromophores created per incident ion). The efficiencyof the chromophore groups formation induced by the ionbeam can be represented by nr. The values of the productak nr, obtained by taking the plot of the difference (A�A0)against ion fluence at different wavelengths are summarizedin Table 1. It is observed that the obtained values of theproduct ak nr are smaller for larger wavelengths, and thesevalues increases with the increase of mean electronic energyloss. Our results are well supported by the earlier reportedresults on PPS [6] and on PP [7].

Table 1The formation of chromophore groups (ak nr) for the different ionirradiations

Ion andenergy

Electronicenergy loss(keV/nm)

ak nr (cm2)

k = 500 nm k = 600 nm k = 700 nm

Copper(50 MeV)

5.65 �5.7 · 10�13 �3.5 · 10�13 �1.6 · 10�13

Nickel(86 MeV)

5.37 �3.2 · 10�13 �9.8 · 10�14 �4.3 · 10�14

0.0 2.0x1011

4.0x1011

6.0x1011

8.0x1011

1.0x1012

-0.45

-0.30

-0.15

0.00 833, 889, 1467, 1507, 1770 and 2873

Fluence (ions cm-2)

A -

A0

Fig. 4. The absorbance change of the bands at 833, 889, 1467, 1507, 1770and 2873 cm�1 as a function of ion fluence for the copper ion irradiatedpolycarbonate at 5.65 keV/nm. Solid lines are fit results of experimentalpoints by using ðA� A0Þ ¼ A1ðe�rd/ � 1Þ.

460 L. Singh, K.S. Samra / Nucl. Instr. and Meth. in Phys. Res. B 263 (2007) 458–462

3.2. FTIR analysis

The FTIR spectra of polycarbonate samples irradiatedwith different ions exhibit similar features. For instance,the spectra corresponding to pristine and copper irradiatedMakrofol-N for varying fluence at the same electronicenergy loss of 5.65 keV/nm are shown in Fig. 3. The bandsbetween 1900 and 2800 cm�1 are not shown in Fig. 3 asthere are not obvious peaks in this region. The bands cor-responding to para-substituted phenyl groups appears at3040, 3060 cm�1 (m@CH), 1603, 1504 cm�1 (mC@C), 1084,1017 cm�1 (bC@CH) and 833 cm�1 (cC@CH), while the bandsfor methyl (–CH3) group appears at 2970 cm�1 (mas),2873 cm�1 (ms), 1467 cm�1 (das) and 1366, 1388 cm�1 (ds).The carbonyl (–C@O) stretching band absorbs at1770 cm�1. The quantitative analysis of the carbonyl deg-radation is difficult because of the effects of oxidation afterirradiation. The asymmetric stretching of the aromatic ether(C–O–C) absorbs at 1250 cm�1 while the symmetric stretch-ing absorbs at 889 cm�1. It is observed from the FTIR spec-tra that there is a reduction in the absorption intensity of allcharacteristic bands of the irradiated Makrofol-N. Fig. 4depicts the subtracted absorbance (A � A0) as a functionof copper (50 MeV) ion fluence at same energy loss for

3600 3300 3000

Ab

sorb

ance

Wavenumbe

pristine

1 x 1011 ions cm-2

5 x 1011 ions cm-2

1 x 1012 ions cm-2

5 x 1012 ions cm-2

1 x 1013 ions cm-2

Fig. 3. FTIR spectra of Makrofol-N irradiated with copper (50 MeV) io

the bands 833, 889, 1467, 1504, 1770 and 2873 cm�1. Thereduction reveals that the sample undergoes structural deg-radation under irradiation. Using the saturated track model(the damage of the functional group occurs in only cylinderof area r), the decay of a specific functional group can bedescribed as by an exponential law:

ðA� A0Þ ¼ A1ðe�rd/ � 1Þ;where rd = pr2 is the degradation cross-section associatedto a chemical group, / is the ion fluence and A1 is a fittingparameter [6,8,10]. From the experimental fitting as shownin Fig. 4, the degradation cross-section for the typicalbands were evaluated at different electronic energy lossesand plotted in Fig. 5. It is observed that the degradationcross-section of chemical groups (methyl, phenyl and ether)is increasing with the increase of electronic energy loss inpolycarbonate.

r (cm-1)

1800 1500 1200 900 600

ns to different fluences at the electronic energy loss of 5.65 keV/nm.

5.2 5.3 5.4 5.5 5.6 5.7

200

225

250 833 889146715072873

Electronic energy loss (keV/nm)

Cro

ss -

sec

tio

n (

nm

- 2 )

Fig. 5. Degradation cross-section as a function of the electronic energyloss.

L. Singh, K.S. Samra / Nucl. Instr. and Meth. in Phys. Res. B 263 (2007) 458–462 461

The appearance of new band after irradiation is impor-tant feature of swift heavy ion irradiated polymers. It canbe seen in Fig. 3 that a new peak appears at 3296 cm�1,which is assigned to alkyne end group (R–C§CH) asreported in case of polystyrene [9]. The little increasebetween 1550 and 1700 cm�1 indicates that double bondsare formed with different degrees of conjugation. Thebroad band around 3500 cm�1 is ascribed to the formationof hydroxyl group.

The absorbance change of the alkyne band (at3296 cm�1) as a function of ion fluence is plotted inFig. 6. The production of alkyne group can be describedby an exponential law:

ðA� A0Þ ¼ A2ð1� e�rp/Þ;where rp is the production cross-section of alkyne groupand A2 is a fitting parameter. The radii of the alkyne pro-duction of about 2.74 and 2.90 nm were evaluated for nickel(86 MeV) and copper (50 MeV) ions respectively. Ourresults are in well agreement with the previously reportedresults of Steckenreiter et al. [11,12]. They had deducedthe radius of alkyne production of about 3 nm on Mo ionirradiated PET at the elecronic energy loss of 5.7 keV/nm.

0.0 2.0x1012

4.0x1012

6.0x1012

8.0x1012

1.0x1013

0.0

0.1

0.2

0.3

Ni (86 MeV) Cu (50 MeV)

Fluence (ions cm-2)

A -

A0

Fig. 6. The absorbance change of the alkyne band at 3296 cm�1 as afunction of copper and nickel ion fluence. Solid lines are fit results ofexperimental points by using ðA� A0Þ ¼ A2A1ð1� e�rp/Þ.

All the degradation/production cross-sections discussedabove, were obtained by ex-situ measurements. This meansthat we had measured the overall result of the complex phe-nomena related to the ion irradiation and to the manychemical and physical relaxation phenomena that occurafter irradiation, when the sample was exposed to the oxy-gen and water present in the ambient air. So there is thepossibility that all the cross-sections deducted by thesemeasurements are not only related to the degradation/production, but also to the moieties that survive to the(drastic) chemical reactions induced by water and oxygenexposure. As reported by Steckenreiter et al. [11] that theyield of alkyne formation is enhanced under irradiationin oxygen environment as compared to the irradiation invacuum.

3.3. XRD analysis

Fig. 7 shows the XRD spectra of the samples irradiatedwith copper (50 MeV) ions at difference fluence. It can beseen that the main diffraction peak of pristine sampleappear at 2h = 16.54� d � 5.35 A, d = k/2sinh is the latticespacing or crystalline interplaner distance) and its intensitydecreases with the increase ion fluence. The contribution ofthe background (i.e. adhesive and substrate) is subtractedto analyze the actual spectrum. To estimate the degree ofamorphization, the integral intensity I (height) of the maindiffraction peak of polycarbonate irradiated under differentconditions were extracted. In Fig. 8 the normalized inten-sity is shown as a function of the ion fluence for copperand nickel irradiation. The data were well fitted by usingthe exponential equation:

ðI � I0Þ=I0 ¼ I1ðe�ra/ � 1Þ;

where ra is the amorphization cross-section, I0 is the inten-sity of the pristine sample and I1 is a fitting a parameter.From the above relation, the radius of amorphization ofabout 16.2 and 22 nm were evaluated for nickel and copperions respectively. These obtained values of the radius ofamorphization is larger as compared to that reported by

10 15 20 25 30 35 40 450

100

200

300

400

500

Pristine 1 x 1011 ions cm-2

1 x 1012 ions cm-2

1 x 1013 ions cm-2

Inte

nsi

ty (

Co

un

ts/ S

ec)

2θ (degree)

Fig. 7. XRD spectra of Makrofol-N irradiated with copper ions at5.65 keV/nm at different fluence.

0.0 2.0x1011

4.0x1011

6.0x1011 8.0x10

111.0x10

12-0.5

-0.4

-0.3

-0.2

-0.1

0.0

Ni (86 MeV) Cu (50 MeV)

Fluence (ions cm-2)

(I -

I 0)/ I

0

Fig. 8. The normalized X-ray diffraction peak intensity versus copper andnickel ion fluence. Solid lines are fit results of experimental points by usingðI � I0Þ=I0 ¼ I1ðe�ra/ � 1Þ.

462 L. Singh, K.S. Samra / Nucl. Instr. and Meth. in Phys. Res. B 263 (2007) 458–462

Sun et al. [8,13], which may be due to the presence of oxy-gen and water moieties during and after irradiation, as thevacuum of 10�6 Torr is not high enough to stop all suchkind of reactions.

4. Conclusion

UV–VIS, FTIR, XRD techniques were applied to inves-tigate the structural degradation of the Makrofol-N poly-carbonate irradiated with copper (50 MeV) and nickel(86 MeV) ions. The chromophore groups formation werededuced by a linear fit, degradation cross-section of thespecial functional groups, the alkyne formation and theamorphization cross-section were evaluated from anexponential fit as assumed in the saturated track model.UV–VIS analysis revealed that the obtained values forthe formation of chromophore groups is reduced at largerwavelength, however its value increases with the increase ofion fluence. Degradation cross-section for the variouschemical groups present in the polycarbonate chains wereextracted from the FTIR data. It was found that the degra-dation cross-section of chemical groups was increasing withthe increase of electronic energy loss in polycarbonate. Thealkyne and alkene groups were induced by the irradiation.The radii of the alkyne production of about 2.74 and

2.90 nm were deduced for nickel (86 MeV) and copper(50 MeV) ions respectively. XRD analysis shows thedecrease of the main XRD peak intensity. Progressiveamorphization process of Makrofol-N with increasing flu-ence was traced by XRD measurements. The comparisonof all degradation processes revealed that the radius ofamorphization was found to be the largest and the forma-tion radius of alkyne was larger than the formation of thechromophore groups.

Acknowledgement

The authors wish to thank Mr. Sandeep Chopra, Mr.Fouran Singh and to the other staff members of Inter Uni-versity Accelerator Centre, New Delhi for their help duringirradiation and also for providing XRD, UV–VIS andFTIR facilities.

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