- Email: [email protected]
Morphological changes induced in PPS by ion bombardment: amorphisation and recrystallization ability
Nuclear Instruments and Methods in Physics Research B 91(1994) 442-446 North-Holland
Morphological amorphisation
NOWB
Beam Interactions with Materials 81Atoms
changes induced in PPS by ion bombardment: and recrystallization ability
M.R. Rizzatti *, R.M. Papal&
and R.P. Livi
Institute de Fisica, Uniuersidade Federal do Rio Grande do Sul, Campus do Vale, 91501-970 Port0 Alegre, RS, Brazil
M.A. de AraCjo Institute de Q&mica, Universidade Federal do Rio Grande do Sul, Campus do Vale, 91501-970 Port0 Alegre, RS, Brazil
Thin poly(paraphenylene sulfide) (PPS) films (Torelina, from Toray Co., Japan, 2 pm thick) were bombarded with energetic lHf (300 keV), 4He+ (380 keV), l”Bc (350 keV) and 4oAr‘+ (700 keV) ions at fluences ranging from 1O1’ to 8 X 1014 ions/cm’. The beam current density was kept at 20 nA/cm’ in order to avoid excessive heating and outgassing damage. The modified samples were analysed by differential scanning calorimetry (DSC). Both the melting onset temperature and the enthalpy of fusion, that are related to the crystalline structure, decrease with increasing ion fluence. This systematic study, made with successive heating and cooling cycles in the DSC measurements, shows that the ion bombarded polymer gradually lost its crystallinity and its ability for recrystallization, as the ion fluence increases. Over a critical fluence, which depends on the bombarding ion and energy, the amorphisation process accelerates and above a certain fluence the polymer becomes completely amorphous. The above discussed modification in_the PPS morphology occurs in a fluence range where the chemical degradation was not significantly noticed by Fourier transform infrared spectroscopy (FTIR) measurements. The modification radii for the amorphisation process were extracted and the results discussed considering the energy deposition density.
1. Introduction The ion beam bombardment changes the physical and chemical properties of polymeric films drastically. The elastic and inelastic collisions between the ener-
getic incident ion and the target atoms result in a large energy deposition in the polymeric film. The ion beam induced modification of the physical properties and chemical structure of polymeric films can be analysed through different techniques, depending on the relevant parameters to be evaluated [l-7]. The above mentioned effects are being studied in our laboratory for different thermoplastics, and recently in particular for poly(phenylene sulfide), PPS. PPS offers a wide range of technological applications due to its high dimensional stability and relatively low susceptibility to ionizing radiation. Previous work in ion beam modification of PPS was focused mainly on the electrical properties [8,9]. The present investigation reports on preliminary results of the ion beam amorphisation process on biaxially oriented PPS thin films. A systematic approach is taken for the morphological changes in PPS caused by the nature, energy and fluence of the bombarding ion. Modified samples are
* Corresponding author.
characterized by differential scanning calorimetry (DSC), X-ray diffractometry (XRD) and Fourier transform infrared spectroscopy (FTIR).
2. Experimental
Commercial grade 2 p,rn thick PPS films produced by Toray Company, Japan, were mounted in annular aluminium supports. The pristine film degree of crystallinity is of the order of 40% [lo], its glass transition temperature, T’,, is around 92°C and its melting temperature is approximately 285°C. The samples were bombarded by ‘H+ (300 keV), 4He+ (380 keV), 1°B+ (350 keV) and 40Ar2t (700 keV) ions using the HVEE 400 kV ion implanter at the IFUFRGS, Porto Alegre, in, vacuum of the order of 10W6 Torr. The ion beam current density was maintained constant and equal to 20 nA/cm’ to avoid sample heating. The ‘H+ and 4He+ ions went through the whole sample thickness and the “B+ and @Ar2+ bombardments were made on both sample sides in order to modify all its thickness [ll]. The ion fluences ranged from 1012 to 8 X 1014 cmp2. The differential scanning calorimetry measurements were made in a Perkin-Elmer DSC-4 System. The two complete cycles were performed between 50°C
0168-583X/94/$07.00 0 1994 - Elsevier Science B.V. All rights reserved SSDZ 0168-583X(93)E1058-T
443
M.R. Rizzatti et al. /Nucl. Ins@. and Meth. in Phys. Rex B 91 (1994) 442-446
and 33o”C, using heating and cooling rates of 20”C/min. At the beginning of each cycle the temperature was kept constant for 5 min. The X-ray diffraction measurements were performed in a Siemens D-500 apparatus using CU K radiation and a graphite monochromator. The Fourier transform infrared absorption spectroscopy measurements were made in a Perkin-Elmer FTIR 1750 spectrometer.
fluences are shown in Fig. 4. As can be seen the main diffraction peak area decreases continuously with increasing ion fluence, confirming the gradual reduction in the samples crystallinity. Fig. 5 shows the FTIR spectra for the pristine and for He+ bombarded samples. For ion fluences below 8 x 1013 cmp2 the spectra reveal very little change (< 15%) in the bond structure of the bombarded PPS.
4. Discussion 3. Results Typical DSC heating and cooling thermograms corresponding to pristine PPS and samples bombarded with 4He+ ions and with different ion fluences are shown in Fig. 1. It is observed that with increasing ion fluence the melting and the recrystallization peaks are shifted to lower temperatures; also a peak area reduction is quite evident. In order to study the crystallinity changes through these thermal cycles, three quantities are defined as follows. For the heating cycle, a crystallinity index, X,, is determined by the ratio between the enthalpy of fusion corresponding to the sample bombarded with a certain ion fluence, AH,, and the enthalpy of fusion corresponding to the pristine PPS, AH:,
For all irradiated samples, independently of the nature of the bombarding ion, a decrease of the melting onset temperature with increasing ion fluence is observed. Such a behavior reveals a reduction of the crystallinity of the biaxially oriented PPS samples, which can be related to the increasing number of defects in the polymeric crystallites induced by the ion energy deposition. Further analysis of the thermograms indicates a relative broadening, followed by a small decrease of the area of the melting endotherm peak, thus revealing a reduction of the number of crystalline aggregates; it also becomes less morphologically homogeneous. Additional support for this behavior is given
I
X, = AH,/AHf.
PRISTINE
For the cooling cycle a similar parameter, X,,, is termed recrystallization index. In order to allow a quantitative treatment of the recrystallizability of the modified polymeric material, a recrystallization factor is defined by the following equation [12]:
The indexes of crystallinity and recrystallization obtained from the DSC heating and cooling cycles, X, and X, respectively, are plotted as a function of ion fluence in Fig. 2. The crystallinity index X, drops slowly for samples bombarded with lH+, but such changes become more abrupt as the atomic number of the irradiating ion is increased. However, analysis of the X,, values reveals a steeper drop for all ion bombardments, indicating a decrease in the ability for recrystallization. The numerical values for X,, X,, and F,, are shown in Table 1. Fig. 3 shows the crystallinity and recrystallization indexes as function of energy fluence. Energy fluence is a measure of the average energy deposited per repeating unit of the polymeric chain, regardless how this energy is deposited [13]. The PPS X-ray diffractograms corresponding to nonbombarded and bombarded samples at several ion
4He’380 KeV
10” He’/cm*
2: \
\
w
TEMPERATURE
(“Cl
120
180
I
240
TEMPERATURE
300
(“Cl
Fig. 1. DSC thermograms for He+ bombarded PPS: (left) heating cycle, 20”C/min, (right) cooling cycle, 20”C/min. VI. POLYMERS
MR. Rizzatti et al. /Nucl. I&r.
444
and Meth. in Phys. Res. B 91 (1994) 442-446
+++SH Dfl HB+ WAr”
0.8
0.8
1
MB+ +--+Ar-
300 He+ 380 350 700
keV keV keV keV
350 keV 700 keV
0.2
0.0
,
i
40.0 60.0 20.0 Ion Fluence (1 013ions/cm”)
20.0 40.0 Ion Fluence (1013 ions/cm’)
Fig. 2. Crystallinity (left) and recrystallization (right) indexes, X, and X,,, as a function of ion fluence for the different ions.
A--+6’
0.8
MB’
>A,
350keV
m
40.0
350 keV
120.0 80.0 Energy Fluence (eV/mer)
0.0 160.0
C 1*
40.0 Energy Fluence (eV/mer)
Fig. 3. Crystallinity (left) and recrystallization (right) indexes, X, and X,,, as a function of energy fluence for the different ions.
I
M.R. Rizatti et al. /Nucl.
Instr. and Meth. in Phys. Res. B 91 (1994) 442-446
Table 1 Crystallinity and recrystallization indexes X, and X,, as well as recrystallization factor F, extracted from DSC results for HC, He+, B+ and Ar 2+ bombarded samples Fluence
Xf
X,
4,
Pristine 1013 4~10~~ 8~10~~ 1014 4~10~~ 6~10~~ 8~10’~ 1012 1013 4~10~~ 8~10~~ 1014 2x 1014 1012 1013 2x 1013 4 x 10’3 1012 2x1012 4x1012 6 x 1012 8x10r2 10’3
1.00 0.89 0.89 0.85 0.76 0.69 0.68 0.66 1.00 0.89 0.70 0.56 0.53 0.00 0.83 0.70 0.24 0.00 1.00 0.89 0.70 0.39 0.18 0.00
1.00 0.95 0.95 0.87 0.84 0.57 0.09 0.00 0.97 0.96 0.68 0.00 0.00 0.00 0.94 0.55 0.00 0.00 1.00 0.89 0.57 0.00 0.00 0.00
1.0 1.0 1.0 1.0 1.0 0.8 --* QG 0.1 0.0 1.0 1.0 0.9 + Qc 0.0 0.0 0.0 + @a 1.0 0.8 --) GG 0.0 0.0 --) @= 1.0 1.0 0.8 -+ Qc 0.0 0.0 0.0 + @=
II+ H+ ;: H+ H+ H+ He+ He+ He+ He+ He+ He+ BC ;: 22+
Ara+ A?+ Ara+ A++ A?+
44.5
He+380 Ke\
by the analysis of the recrystallization thermograms, since lower temperatures are required to form crystalline aggregates as ion fhrence is increased. Also, these aggregates are formed in smaller amounts and I
3000
2Moo
1
1
I
2000
I
1000
T(cm-‘)
h
-----
pristine
Fig. 4. Main X-ray diffraction peak corresponding different He+ bombardment fluences.
to several
Fig. 5. Fourier transform infrared spectroscopy (FTIR) spectra for pristine and He+ bombarded samples.
are less homogeneous in their morphological characteristics, leading to broader and less intense recrystallization exotherm peaks. In Table 1, a comparison of the melting enthalpies of PPS samples irradiated with 4-8 X 1014 H+/cm’ reveals no sharp difference in their values. However, the recrystallization process indicates for these same samples a strong broadening of the exotherm peak, with an abrupt change of this thermal event at 4 X 1014 H+/cm2 fluence, indicating that at this Ruence the polymeric material lost its ability for recrystallization. This fluence is called the critical ion fluence, Qc. For fluence higher than Gc, the polymeric material shows a morphology strongly dominated by an amorphous fase. For every bombarding ion a similar behavior is obVI. POLYMERS
446
M.R Rizzatti et al. /Nucl. Instr. and Meth. in Phys. Res. B 91 (1994) 442-446
served. A new quantity is defined for the heating process when no endotherm peak is observed for an irradiated sample; the quantity is termed amorphisation fluence, Qa. These quantities, Qc and Gap,,depend on the energy deposition process and fluence of the bombarding ion in the polymeric material and on the nature of the ion. To make this point more clear it is useful to discuss our results in terms of the energy fluence. For instance, if the average deposited energy per repeating unit is the only relevant parameter to the amorphisation process it would be expected that the individual curves for the various ions, as depicted in Fig. 3, would collapse into one curve. Since the four curves do not collapse into one, the energy fluence is not the only important parameter in the amorphisation process. However, above a certain ion mass apparently the energy fluence dependence is the same as it can be seen for B+ and A?+ ions. The PPS crystallinity reduction with increasing ion bombardment fluence is confirmed by the decrease in the main X-ray diffraction peak area as a function of the ion fluence. Above 4 X 1014 He+/cm’ the X-ray results indicate the complete sample amorphisation. The amorphisation process occurs in a fluence range where the FTIR measurements indicate less than 15% change in the bond structure of the bombarded PPS. The mean radius R, of the amorphised zone, around the ion track, can be-estimated from the critical fluence Qc. For H+, 4He+, “B+ and 40Ar2f bombarded PPS samples, the R, values are: 0.3, 0.9, 1.8 and 2.8 nm respectively.
5. Conclusions Bombardment of energetic ions like ‘H’, 4He+, l”B+ and 40Ar2f, on PPS thin films alters the polymer mo&hology (crystalline regions) by the generation and accumulation of structural defects. This process, as
monitored by DSC and X-ray diffractometry, develops smoothly up to a certain critical ion fluence. Beyond that, abrupt changes are observed leading to a completely amorphous material. This critical ion fluence depends on the nature of the incident ion. The deposited energy per polymer chain repeating unit by the ion is not the only important parameter in the amorphisation process. Apparently the energy deposition density and the kind of energy deposition process are also important parameters.
References Dl J. Davenas, P. Thevenard, G. Boiteux, M. Fallavier and X.L. Xu, Nucl. Instr. and Meth. B 46 (1990) 317. t21 A.M. Foti, L. Calcagno, G.A. Baratta, F. Spinella and G. Strazzula, Radiat. Eff. 112 (1990) 61. [31 G. Marletta, Nucl. Instr. and Meth. B 46 (1990) 295. [41 M.L. Kaplan, S.R. Forrest, P.H. Schmidt and T. Venkatesan, J. Appl. Phys. 55 (1984) 732. [51 M.C. Wintersgill, Nucl. Instr. and Meth. B 1 (1984) 595. 161H. Mazurek, D.R. Day, E.W. Maby, J.S. Abel, S.D. Senturia, M.S. Dresselhaus and G. Dresselhaus, J. Polymer Sci.: Pol. Phys. Ed. 21 (1983) 537. VI R.M. Papaleo, M.A. Araujo and R.P. Livi, Mater. Res. Sot. Symp. Proc. 157 (1990) 617. Bl J. Bartko, B.Q. Hall and K. Schoch Jr., J. Appl. Phys. 59 (1986) 1111. [91 J.H. Lob, R.W. Olivier and P. Sioshani, Nucl. Instr. and Meth. B 34 (1988) 337. m Product information bulletin, “Torelina”, Toray Co., Japan. WI J.F. Ziegler, J.P. Biersack and U. Littmark, The Stopping and Range of Ions in Solids (Pergamon, Great Britain, 1985). WI R.M. Papaelo, M.R. Rizzatti, R.P. Livi and M.A. Araujo, Proc. Congress0 Brasileiro de Polimeros 1, edited by AssociaEb Brasileira de Polimeros, SCo Paulo, Brasil, 1991, vol. 1, p. 375. 1131K. RGssler, Radiat. Eff. 99 (1986) 505.
Morphological amorphisation
NOWB
Beam Interactions with Materials 81Atoms
changes induced in PPS by ion bombardment: and recrystallization ability
M.R. Rizzatti *, R.M. Papal&
and R.P. Livi
Institute de Fisica, Uniuersidade Federal do Rio Grande do Sul, Campus do Vale, 91501-970 Port0 Alegre, RS, Brazil
M.A. de AraCjo Institute de Q&mica, Universidade Federal do Rio Grande do Sul, Campus do Vale, 91501-970 Port0 Alegre, RS, Brazil
Thin poly(paraphenylene sulfide) (PPS) films (Torelina, from Toray Co., Japan, 2 pm thick) were bombarded with energetic lHf (300 keV), 4He+ (380 keV), l”Bc (350 keV) and 4oAr‘+ (700 keV) ions at fluences ranging from 1O1’ to 8 X 1014 ions/cm’. The beam current density was kept at 20 nA/cm’ in order to avoid excessive heating and outgassing damage. The modified samples were analysed by differential scanning calorimetry (DSC). Both the melting onset temperature and the enthalpy of fusion, that are related to the crystalline structure, decrease with increasing ion fluence. This systematic study, made with successive heating and cooling cycles in the DSC measurements, shows that the ion bombarded polymer gradually lost its crystallinity and its ability for recrystallization, as the ion fluence increases. Over a critical fluence, which depends on the bombarding ion and energy, the amorphisation process accelerates and above a certain fluence the polymer becomes completely amorphous. The above discussed modification in_the PPS morphology occurs in a fluence range where the chemical degradation was not significantly noticed by Fourier transform infrared spectroscopy (FTIR) measurements. The modification radii for the amorphisation process were extracted and the results discussed considering the energy deposition density.
1. Introduction The ion beam bombardment changes the physical and chemical properties of polymeric films drastically. The elastic and inelastic collisions between the ener-
getic incident ion and the target atoms result in a large energy deposition in the polymeric film. The ion beam induced modification of the physical properties and chemical structure of polymeric films can be analysed through different techniques, depending on the relevant parameters to be evaluated [l-7]. The above mentioned effects are being studied in our laboratory for different thermoplastics, and recently in particular for poly(phenylene sulfide), PPS. PPS offers a wide range of technological applications due to its high dimensional stability and relatively low susceptibility to ionizing radiation. Previous work in ion beam modification of PPS was focused mainly on the electrical properties [8,9]. The present investigation reports on preliminary results of the ion beam amorphisation process on biaxially oriented PPS thin films. A systematic approach is taken for the morphological changes in PPS caused by the nature, energy and fluence of the bombarding ion. Modified samples are
* Corresponding author.
characterized by differential scanning calorimetry (DSC), X-ray diffractometry (XRD) and Fourier transform infrared spectroscopy (FTIR).
2. Experimental
Commercial grade 2 p,rn thick PPS films produced by Toray Company, Japan, were mounted in annular aluminium supports. The pristine film degree of crystallinity is of the order of 40% [lo], its glass transition temperature, T’,, is around 92°C and its melting temperature is approximately 285°C. The samples were bombarded by ‘H+ (300 keV), 4He+ (380 keV), 1°B+ (350 keV) and 40Ar2t (700 keV) ions using the HVEE 400 kV ion implanter at the IFUFRGS, Porto Alegre, in, vacuum of the order of 10W6 Torr. The ion beam current density was maintained constant and equal to 20 nA/cm’ to avoid sample heating. The ‘H+ and 4He+ ions went through the whole sample thickness and the “B+ and @Ar2+ bombardments were made on both sample sides in order to modify all its thickness [ll]. The ion fluences ranged from 1012 to 8 X 1014 cmp2. The differential scanning calorimetry measurements were made in a Perkin-Elmer DSC-4 System. The two complete cycles were performed between 50°C
0168-583X/94/$07.00 0 1994 - Elsevier Science B.V. All rights reserved SSDZ 0168-583X(93)E1058-T
443
M.R. Rizzatti et al. /Nucl. Ins@. and Meth. in Phys. Rex B 91 (1994) 442-446
and 33o”C, using heating and cooling rates of 20”C/min. At the beginning of each cycle the temperature was kept constant for 5 min. The X-ray diffraction measurements were performed in a Siemens D-500 apparatus using CU K radiation and a graphite monochromator. The Fourier transform infrared absorption spectroscopy measurements were made in a Perkin-Elmer FTIR 1750 spectrometer.
fluences are shown in Fig. 4. As can be seen the main diffraction peak area decreases continuously with increasing ion fluence, confirming the gradual reduction in the samples crystallinity. Fig. 5 shows the FTIR spectra for the pristine and for He+ bombarded samples. For ion fluences below 8 x 1013 cmp2 the spectra reveal very little change (< 15%) in the bond structure of the bombarded PPS.
4. Discussion 3. Results Typical DSC heating and cooling thermograms corresponding to pristine PPS and samples bombarded with 4He+ ions and with different ion fluences are shown in Fig. 1. It is observed that with increasing ion fluence the melting and the recrystallization peaks are shifted to lower temperatures; also a peak area reduction is quite evident. In order to study the crystallinity changes through these thermal cycles, three quantities are defined as follows. For the heating cycle, a crystallinity index, X,, is determined by the ratio between the enthalpy of fusion corresponding to the sample bombarded with a certain ion fluence, AH,, and the enthalpy of fusion corresponding to the pristine PPS, AH:,
For all irradiated samples, independently of the nature of the bombarding ion, a decrease of the melting onset temperature with increasing ion fluence is observed. Such a behavior reveals a reduction of the crystallinity of the biaxially oriented PPS samples, which can be related to the increasing number of defects in the polymeric crystallites induced by the ion energy deposition. Further analysis of the thermograms indicates a relative broadening, followed by a small decrease of the area of the melting endotherm peak, thus revealing a reduction of the number of crystalline aggregates; it also becomes less morphologically homogeneous. Additional support for this behavior is given
I
X, = AH,/AHf.
PRISTINE
For the cooling cycle a similar parameter, X,,, is termed recrystallization index. In order to allow a quantitative treatment of the recrystallizability of the modified polymeric material, a recrystallization factor is defined by the following equation [12]:
The indexes of crystallinity and recrystallization obtained from the DSC heating and cooling cycles, X, and X, respectively, are plotted as a function of ion fluence in Fig. 2. The crystallinity index X, drops slowly for samples bombarded with lH+, but such changes become more abrupt as the atomic number of the irradiating ion is increased. However, analysis of the X,, values reveals a steeper drop for all ion bombardments, indicating a decrease in the ability for recrystallization. The numerical values for X,, X,, and F,, are shown in Table 1. Fig. 3 shows the crystallinity and recrystallization indexes as function of energy fluence. Energy fluence is a measure of the average energy deposited per repeating unit of the polymeric chain, regardless how this energy is deposited [13]. The PPS X-ray diffractograms corresponding to nonbombarded and bombarded samples at several ion
4He’380 KeV
10” He’/cm*
2: \
\
w
TEMPERATURE
(“Cl
120
180
I
240
TEMPERATURE
300
(“Cl
Fig. 1. DSC thermograms for He+ bombarded PPS: (left) heating cycle, 20”C/min, (right) cooling cycle, 20”C/min. VI. POLYMERS
MR. Rizzatti et al. /Nucl. I&r.
444
and Meth. in Phys. Res. B 91 (1994) 442-446
+++SH Dfl HB+ WAr”
0.8
0.8
1
MB+ +--+Ar-
300 He+ 380 350 700
keV keV keV keV
350 keV 700 keV
0.2
0.0
,
i
40.0 60.0 20.0 Ion Fluence (1 013ions/cm”)
20.0 40.0 Ion Fluence (1013 ions/cm’)
Fig. 2. Crystallinity (left) and recrystallization (right) indexes, X, and X,,, as a function of ion fluence for the different ions.
A--+6’
0.8
MB’
>A,
350keV
m
40.0
350 keV
120.0 80.0 Energy Fluence (eV/mer)
0.0 160.0
C 1*
40.0 Energy Fluence (eV/mer)
Fig. 3. Crystallinity (left) and recrystallization (right) indexes, X, and X,,, as a function of energy fluence for the different ions.
I
M.R. Rizatti et al. /Nucl.
Instr. and Meth. in Phys. Res. B 91 (1994) 442-446
Table 1 Crystallinity and recrystallization indexes X, and X,, as well as recrystallization factor F, extracted from DSC results for HC, He+, B+ and Ar 2+ bombarded samples Fluence
Xf
X,
4,
Pristine 1013 4~10~~ 8~10~~ 1014 4~10~~ 6~10~~ 8~10’~ 1012 1013 4~10~~ 8~10~~ 1014 2x 1014 1012 1013 2x 1013 4 x 10’3 1012 2x1012 4x1012 6 x 1012 8x10r2 10’3
1.00 0.89 0.89 0.85 0.76 0.69 0.68 0.66 1.00 0.89 0.70 0.56 0.53 0.00 0.83 0.70 0.24 0.00 1.00 0.89 0.70 0.39 0.18 0.00
1.00 0.95 0.95 0.87 0.84 0.57 0.09 0.00 0.97 0.96 0.68 0.00 0.00 0.00 0.94 0.55 0.00 0.00 1.00 0.89 0.57 0.00 0.00 0.00
1.0 1.0 1.0 1.0 1.0 0.8 --* QG 0.1 0.0 1.0 1.0 0.9 + Qc 0.0 0.0 0.0 + @a 1.0 0.8 --) GG 0.0 0.0 --) @= 1.0 1.0 0.8 -+ Qc 0.0 0.0 0.0 + @=
II+ H+ ;: H+ H+ H+ He+ He+ He+ He+ He+ He+ BC ;: 22+
Ara+ A?+ Ara+ A++ A?+
44.5
He+380 Ke\
by the analysis of the recrystallization thermograms, since lower temperatures are required to form crystalline aggregates as ion fhrence is increased. Also, these aggregates are formed in smaller amounts and I
3000
2Moo
1
1
I
2000
I
1000
T(cm-‘)
h
-----
pristine
Fig. 4. Main X-ray diffraction peak corresponding different He+ bombardment fluences.
to several
Fig. 5. Fourier transform infrared spectroscopy (FTIR) spectra for pristine and He+ bombarded samples.
are less homogeneous in their morphological characteristics, leading to broader and less intense recrystallization exotherm peaks. In Table 1, a comparison of the melting enthalpies of PPS samples irradiated with 4-8 X 1014 H+/cm’ reveals no sharp difference in their values. However, the recrystallization process indicates for these same samples a strong broadening of the exotherm peak, with an abrupt change of this thermal event at 4 X 1014 H+/cm2 fluence, indicating that at this Ruence the polymeric material lost its ability for recrystallization. This fluence is called the critical ion fluence, Qc. For fluence higher than Gc, the polymeric material shows a morphology strongly dominated by an amorphous fase. For every bombarding ion a similar behavior is obVI. POLYMERS
446
M.R Rizzatti et al. /Nucl. Instr. and Meth. in Phys. Res. B 91 (1994) 442-446
served. A new quantity is defined for the heating process when no endotherm peak is observed for an irradiated sample; the quantity is termed amorphisation fluence, Qa. These quantities, Qc and Gap,,depend on the energy deposition process and fluence of the bombarding ion in the polymeric material and on the nature of the ion. To make this point more clear it is useful to discuss our results in terms of the energy fluence. For instance, if the average deposited energy per repeating unit is the only relevant parameter to the amorphisation process it would be expected that the individual curves for the various ions, as depicted in Fig. 3, would collapse into one curve. Since the four curves do not collapse into one, the energy fluence is not the only important parameter in the amorphisation process. However, above a certain ion mass apparently the energy fluence dependence is the same as it can be seen for B+ and A?+ ions. The PPS crystallinity reduction with increasing ion bombardment fluence is confirmed by the decrease in the main X-ray diffraction peak area as a function of the ion fluence. Above 4 X 1014 He+/cm’ the X-ray results indicate the complete sample amorphisation. The amorphisation process occurs in a fluence range where the FTIR measurements indicate less than 15% change in the bond structure of the bombarded PPS. The mean radius R, of the amorphised zone, around the ion track, can be-estimated from the critical fluence Qc. For H+, 4He+, “B+ and 40Ar2f bombarded PPS samples, the R, values are: 0.3, 0.9, 1.8 and 2.8 nm respectively.
5. Conclusions Bombardment of energetic ions like ‘H’, 4He+, l”B+ and 40Ar2f, on PPS thin films alters the polymer mo&hology (crystalline regions) by the generation and accumulation of structural defects. This process, as
monitored by DSC and X-ray diffractometry, develops smoothly up to a certain critical ion fluence. Beyond that, abrupt changes are observed leading to a completely amorphous material. This critical ion fluence depends on the nature of the incident ion. The deposited energy per polymer chain repeating unit by the ion is not the only important parameter in the amorphisation process. Apparently the energy deposition density and the kind of energy deposition process are also important parameters.
References Dl J. Davenas, P. Thevenard, G. Boiteux, M. Fallavier and X.L. Xu, Nucl. Instr. and Meth. B 46 (1990) 317. t21 A.M. Foti, L. Calcagno, G.A. Baratta, F. Spinella and G. Strazzula, Radiat. Eff. 112 (1990) 61. [31 G. Marletta, Nucl. Instr. and Meth. B 46 (1990) 295. [41 M.L. Kaplan, S.R. Forrest, P.H. Schmidt and T. Venkatesan, J. Appl. Phys. 55 (1984) 732. [51 M.C. Wintersgill, Nucl. Instr. and Meth. B 1 (1984) 595. 161H. Mazurek, D.R. Day, E.W. Maby, J.S. Abel, S.D. Senturia, M.S. Dresselhaus and G. Dresselhaus, J. Polymer Sci.: Pol. Phys. Ed. 21 (1983) 537. VI R.M. Papaleo, M.A. Araujo and R.P. Livi, Mater. Res. Sot. Symp. Proc. 157 (1990) 617. Bl J. Bartko, B.Q. Hall and K. Schoch Jr., J. Appl. Phys. 59 (1986) 1111. [91 J.H. Lob, R.W. Olivier and P. Sioshani, Nucl. Instr. and Meth. B 34 (1988) 337. m Product information bulletin, “Torelina”, Toray Co., Japan. WI J.F. Ziegler, J.P. Biersack and U. Littmark, The Stopping and Range of Ions in Solids (Pergamon, Great Britain, 1985). WI R.M. Papaelo, M.R. Rizzatti, R.P. Livi and M.A. Araujo, Proc. Congress0 Brasileiro de Polimeros 1, edited by AssociaEb Brasileira de Polimeros, SCo Paulo, Brasil, 1991, vol. 1, p. 375. 1131K. RGssler, Radiat. Eff. 99 (1986) 505.