Egger, W.

Kanda, G. S.

Keeble, D. J.

Lowe, B.

Ravelli, L.

Journal of Physics D Applied Physics

English

G S Kanda

L Ravelli

B Löwe

W Egger

D J Keeble

Crossref

Positron annihilation lifetime spectroscopy study of Kapton thin foils

Variable Energy Positron Annihilation Lifetime Spectroscopy (VE-PALS) experiments on polyimide material Kapton are reported. Thin Kapton foils are widely used in a variety of mechanical, electronic applications. PALS provides a sensitive probe of vacancy-related defects in a wide range of materials, including open volume in polymers. Varying the positron implantation energy enables direct measurement of thin foils. Thin Kapton foils are also commonly used to enclose the positron source material in conventional PALS measurements performed with unmoderated radionuclide sources. The results of depth-profiled positron lifetime measurements on 7.6 µ m and 25 µ m Kapton foils are reported and determine a dominant 385(1) ps lifetime component. The absence of significant nanosecond lifetime component due to positronium formation is confirmed

University of Dundee Online Publications

                                                                    University of DundeePositron annihilation lifetime spectroscopy study of Kapton thin foilsKanda, G. S.; Ravelli, L.; Lowe, B.; Egger, W.; Keeble, D. J.Published in:Journal of Physics D: Applied PhysicsDOI:10.1088/0022-3727/49/2/025305Publication date:2016Licence:CC BYDocument VersionPublisher's PDF, also known as Version of recordLink to publication in Discovery Research PortalCitation for published version (APA):Kanda, G. S., Ravelli, L., Lowe, B., Egger, W., & Keeble, D. J. (2016). Positron annihilation lifetime spectroscopystudy of Kapton thin foils. Journal of Physics D: Applied Physics, 49(2), [025305]. https://doi.org/10.1088/0022-3727/49/2/025305General rightsCopyright and moral rights for the publications made accessible in Discovery Research Portal are retained by the authors and/or othercopyright owners and it is a condition of accessing publications that users recognise and abide by the legal requirements associated withthese rights. • Users may download and print one copy of any publication from Discovery Research Portal for the purpose of private study or research. • You may not further distribute the material or use it for any profit-making activity or commercial gain. • You may freely distribute the URL identifying the publication in the public portal.Take down policyIf you believe that this document breaches copyright please contact us providing details, and we will remove access to the work immediatelyand investigate your claim.Download date: 16. Aug. 2023This content has been downloaded from IOPscience. Please scroll down to see the full text.Download details:IP Address: 134.36.212.127This content was downloaded on 11/12/2015 at 09:52Please note that terms and conditions apply.Positron annihilation lifetime spectroscopy study of Kapton thin foilsView the table of contents for this issue, or go to the journal homepage for more2016 J. Phys. D: Appl. Phys. 49 025305(http://iopscience.iop.org/0022-3727/49/2/025305)Home Search Collections Journals About Contact us My IOPscience1 © 2016 IOP Publishing Ltd Printed in the UK1. IntroductionThe polyimide material Kapton belongs to a group of poly-mers that exhibit excellent chemical resistance, mechanical, thermal and dielectric properties, and are used in a diverse range of applications including dielectrics, nonlinear optical materials, and membranes [1]. The low dielectric constant, high dielectric strength, and high resistivity make polyimide materials suitable for a range of insulation applications [2, 3]. Positron annihilation lifetime spectroscopy (PALS) is capable of providing information on the size distribution of open volume in polymeric systems, and on vacancy-related point defects in inorganic materials and metals. Free volume in polymers is normally characterised by detecting the lifetimes and intensities of ‘pick-off’ annihilation events caused by the interaction of positronium (Ps), formed by positron implan-tation within open volume sites, with the cavity walls. This process can be analysed using a simple quantum mechanical model and information of cavity sizes determined [4, 5]. However, in contrast to the majority of polymers the Ps pick-off lifetime component, typically in the range ~1–30 ns, is absent in Kapton. This absence, combined with its excellent chemical and mechanical properties, contribute to make thin Kapton foils ideal supporting substrates for the deposition of radionuclide sources for various positron annihilation experi-ments on materials, in particular PALS measurements on bulk samples.The most commonly used radionuclide is 22Na which emits positrons with a β-spectrum of energies, up to a maximum of 0.546 MeV. In consequence these are implanted to range of depths within the material under study. PALS measurements performed using a Kapton foil enclosed 22Na source require detailed knowledge of the positron lifetime spectrum resulting from the small fraction of positrons implanted into the foil [6, 7]. The PALS spectrum is dominated by the contributions from positrons annihilating within the material under study. However, the inverse problem decomposition of these lifetime components due to the material is sensitive to the subtrac-tion of the extrinsic annihilation events, the source correction terms. Here we report the direct measurement of the positron Journal of Physics D: Applied PhysicsPositron annihilation lifetime spectroscopy study of Kapton thin foilsG S Kanda1, L Ravelli2, B Löwe2, W Egger2 and D J Keeble11 Division of Physics, SUPA, School of Engineering, Physics, and Mathematics, University of Dundee, Dundee DD1 4HN, UK2 Universität Bundeswehr München, D-85577 Neubiberg, GermanyE-mail: d.j.keeble@dundee.ac.ukReceived 6 July 2015, revised 2 September 2015Accepted for publication 11 September 2015Published 1 December 2015AbstractVariable energy positron annihilation lifetime spectroscopy (VE-PALS) experiments on polyimide material Kapton are reported. Thin Kapton foils are widely used in a variety of mechanical, electronic applications. PALS provides a sensitive probe of vacancy-related defects in a wide range of materials, including open volume in polymers. Varying the positron implantation energy enables direct measurement of thin foils. Thin Kapton foils are also commonly used to enclose the positron source material in conventional PALS measurements performed with unmoderated radionuclide sources. The results of depth-profiled positron lifetime measurements on 7.6 μm and 25 μm Kapton foils are reported and determine a dominant 385(1) ps lifetime component. The absence of significant nanosecond lifetime component due to positronium formation is confirmed.Keywords: positron annihilation, polymers, positron annihilation lifetime spectroscopy(Some figures may appear in colour only in the online journal)G S Kanda et alPrinted in the UK025305JPAPBE© 2016 IOP Publishing Ltd201649J. Phys. D: Appl. Phys.JPD0022-372710.1088/0022-3727/49/2/025305Papers2Journal of Physics D: Applied PhysicsIOPContent from this work may be used under the terms of the Creative Commons Attribution 3.0 licence. Any further distribution of this work must maintain attribution to the author(s) and the title of the work, journal citation and DOI.0022-3727/16/025305+3$33.00doi:10.1088/0022-3727/49/2/025305J. Phys. D: Appl. Phys. 49 (2016) 025305 (3pp)G S Kanda et al2annihilation lifetime spectra obtained using monochromatic positrons implanted exclusively within thin Kapton foils.Previous measurements of the positron lifetime spectrum of Kapton have been performed using thick Kapton [8], or on stacks of Kapton foils [9–13]. Recently measurements have been reported on stacks approximately 40 pieces of 125 μm Kapton using an 8 μm Kapton supported 22Na positron source [13]. The aim of the study was to investigate the effect tem-perature and of high dose electron beam irradiation. The single lifetime decompostion were reported to give the best fits. The as-received lifetime was 385(3) ps, this reduced to ~378 ps after a ~66 MGy absorbed electron beam dose, and remained approx-imately constant up to 200 MGy. The lifetime also increased with increasing temperature reaching ~397 ps at ~360 °C.An age momentum correlation (AMOC) study of Kapton, performed using a high energy positron beam, fitted the resulting spectra using two positron lifetime components and two associated Doppler broadening spectroscopy (DBS) S-parameter values [14]. The lifetime components were reported to be 229 ps and 378 ps, the latter with an intensity of 87 %; the nature of the Kapton studied was not described. Bulk lifetime measurements on stacked 125 μm Kapton HN foils using an 8 μm Kapton HN foil supported source reported two lifetime components, at ~277 ps and at ~410 ps, the latter with an intensity of ~70%, giving an average lifetime of 369(3) ps [12]. Measurements on bulk 1 mm plates of Kapton polyimide (PI2540), pyromellitic dianhdride-oxydianiline (PMDA-ODA), report a single lifetime value of 354 ps [8], earlier measurements by the same author were performed on a large number of stacked 3μm Kapton (PMDA-ODO) foils and reported two components, one at 220 ps and a second at 376 ps with intensity of 86 % giving an average lifetime of 354 ps [11]. The deconvolution into two components is attributed to an artefact of the spectrum analysis that arises when the positron lifetime distributions are particularly broad [14, 15].The adoption of Kapton foils for use in PALS followed a study by MacKenzie and Fabian [16], that reported a single lifetime component of 382 ps and a weak temperature depend-ence. Subsequently studies on stacked Kapton foils reported lifetime values of 386(7) ps [9], and of 382(3) ps [10]. The latter measurement used a stack of fifty 25 μm Kapton foils, measurements were also performed with some of the foils replaced by 8 μm Kapton with no change in the results.The depth distribution of implanted positrons can be described by a Makhovian profile, with the median depth obtained using a power law expression, ( )ρ=z A E/ n1/2 , were A is normally given in units of μg.cm−2 and E is in keV. Measurements using three different polymers obtained values A  =  2.81(20) μg.cm-2 keV−n and n  =  1.71(5) [17]. The den-sity of Kapton is 1.42 g.cm−3, and the resulting implantation profiles are shown in figure 1. The mean implantation depth increases with increasing implantation energy, for 10 keV monoenergetic positrons it is approximately 1 μm.2. ExperimentVariable energy (VE) PALS measurements were performed on a 7.6 μm and 25 μm Kapton® HN foils using the PLEPS instru-ment on the neutron induced positron source (NEPOMUC) at the Heinz Maier–Leibnitz Zentrum (MLZ) Munich research reactor (FRMII) [18–20]. The foils were carefully mounted with double-sided conducting tape on to the sample holders. Measurements on the 25 μm foils were performed using posi-tron beam energies between 1 to 18 keV, and each lifetime spectra contained greater 3  ×  106 counts. Measurements on the 7.6 μm foil were made at 16 keV and 18 keV, the spectra contained 4.0  ×  106 counts. The instrument timing resolution function is described by a sum of Gaussian functions and the mean width is energy dependent. The value, averaged over all implantation energies, was 254(26) ps.3. Results and discussionThe measurements on the 25 μm and 7.6 μm Kapton exhibit a single dominant positron lifetime component with an intensity of greater than 99.3%, and a second negligible intensity nano-second component. The lifetimes obtained for the dominant first component are shown in figure  2, the average value is Figure 1. Makhovian positron implantation profiles for Kapton determined using the empirical parameters A  =  2.81 μg·cm−2 keV−n, m  =  2, and n  =  1.71, and the density of 1.42 g·cm-3.Figure 2. The positron lifetime value for the dominant component of VE-PALS measurements on 7.6 μm (open squares) and 25 μm (triangles) Kapton HN foils. Individual sets of measurement on  25 μm Kapton HN foils are denoted by different triangle symbols.J. Phys. D: Appl. Phys. 49 (2016) 025305G S Kanda et al3385(1) ps. Figure 1 shows representative Markovian implan-tation profiles demonstrating that the positrons were con-fined to the Kapton foils for all implantation energies used. Implantation energies of 16 keV and 18 keV where selected for the 7.6 μm Kapton as the resulting depth distributions optimally sample the foil and provide lifetime values of direct relevance to conventional PALS experiments using Kapton supported positron sources.These results provide clear evidence for a dominant single positron lifetime component with a value of 385(1) ps in Kapton HN for both foil thickness studied. This is in agree-ment with the early bulk PALS reports of a single lifetime value of 382 ps [16], and 382(3) ps [10], and with the most recent study giving 385(3) ps [13]. The measurements provide further evidence that previously reported two component fits result from an artefact of the fitting process [11, 12, 14]. The AMOC results require the existence of at least two positron states [14], but are complicated by in-flight annihilation and by the high (3.5 MeV) positron energy and hence the require-ment for thick samples. The low values reported for Kapton PI2540 of ~354 ps suggest that this is different to Kapton HN [8]. The low average lifetime for Kapton HN of ~370 ps reported by McGuire and Keeble [12], resulted from incor-rect 22NaCl source correction, the value obtained by applying a systematic source correction procedure was reported to be 385(4) ps [6].These measurements demonstrate that conventional, bulk, positron lifetime measurements using radionuclide positron sources supported thin Kapton HN foils can be analysed by fixing the lifetime of the foil source correction component to a value of 385(1) ps. The results of Hirade et al [13], suggest that this value may decrease with time for high activity sources.4. ConclusionsPositron lifetime spectra were directly measured from 7.6 μm and 25 μm Kapton HN foils with VE-PALS using implantation energies for which all the positrons annihilate from within the foil. A single dominant lifetime component with an intensity greater than 99% was obtained from all measurements with a lifetime value of 385(1) ps.AcknowledgmentsD J K acknowledges European Commission Programme (RII3-CT-2003–505925), G S K was supported by an EPSRC DTA studentship (EP/J500392/1).References [1] Liaw D J, Wang K L, Huang Y C, Lee K R, Lai J Y and Ha C S 2012 Prog. Polym. Sci. 37 907 [2] Diaham S and Locatelli M L 2013 J. Phys. D: Appl. Phys. 46 185302 [3] Raju G G, Shaikh R and Haq S U 2008 IEEE Trans. Dielectr. Electr. Insul. 15 663 [4] Jean Y C 1990 Microchem. J. 42 72 [5] Eldrup M, Lightbody D and Sherwood J N 1981 Chem. Phys. 63 51 [6] McGuire S and Keeble D J 2006 J. Appl. Phys. 100 103504 [7] Staab T E M, Somieski B and Krause-Rehberg R 1996  Nucl. Instrum. Methods A 381 141 [8] Dlubek G, Borner F, Buchhold R, Sahre K, Krause-Rehberg R and Eichhorn K J 2000 J. Polym. Sci. Pol. Phys. 38 3062 [9] Plotkowski K, Panek T J and Kansy J 1988 Nuovo Cimento D 10 933 [10] Djourelov N and Misheva M 1996 J. Phys.: Condens. Matter 8 2081 [11] Dlubek G, Buchhold R, Hubner C, Nakladal A and Sahre K 1999 J. Polym. Sci. Pol. Phys. 37 2539 [12] McGuire S and Keeble D J 2006 J. Phys. D: Appl. Phys. 39 3388 [13] Hirade T, Oka T, Morishita N, Idesaki A and Shimada A 2012 Mater. Sci. Forum 733 151 [14] Dauwe C, De Baerdemaeker J, Djourelov N, Laforest N and Van Waeyenberge B 2008 Acta Phys. Pol. A 113 1315 [15] Dlubek G, Eichler S, Hubner C and Nagel C 1999  Nucl. Instrum. Methods B 149 501 [16] Mackenzie I K and Fabian J 1980 Nuovo Cimento B  58 162 [17] Algers J, Sperr P, Egger W, Kogel G and Maurer F H J 2003 Phys. Rev. B 67 125404 [18] Hugenschmidt C, Lowe B, Mayer J, Piochacz C, Pikart P, Repper R, Stadlbauer M and Schreckenbach K 2008.  Nucl. Instrum. Methods A 593 616 [19] Hugenschmidt C, Piochacz C, Reiner M and Schreckenbach K 2012 New J. Phys. 14 055027 [20] Sperr P, Egger W, Kogel G, Dollinger G, Hugenschmidt C, Repper R and Piochacz C 2008 Appl. Surf. Sci. 255 35J. Phys. D: Appl. Phys. 49 (2016) 025305

                                                              University of DundeePositron annihilation lifetime spectroscopy study of Kapton thin foilsKanda, G. S.; Ravelli, L.; Lowe, B.; Egger, W.; Keeble, DavidPublished in:Journal of Physics D: Applied PhysicsDOI:10.1088/0022-3727/49/2/025305Publication date:2016Document VersionPublisher's PDF, also known as Version of recordLink to publication in Discovery Research PortalCitation for published version (APA):Kanda, G. S., Ravelli, L., Lowe, B., Egger, W., & Keeble, D. J. (2016). Positron annihilation lifetime spectroscopystudy of Kapton thin foils. Journal of Physics D: Applied Physics, 49(2), [025305]. 10.1088/0022-3727/49/2/025305General rightsCopyright and moral rights for the publications made accessible in Discovery Research Portal are retained by the authors and/or othercopyright owners and it is a condition of accessing publications that users recognise and abide by the legal requirements associated withthese rights. • Users may download and print one copy of any publication from Discovery Research Portal for the purpose of private study or research. • You may not further distribute the material or use it for any profit-making activity or commercial gain. • You may freely distribute the URL identifying the publication in the public portal.Take down policyIf you believe that this document breaches copyright please contact us providing details, and we will remove access to the work immediatelyand investigate your claim.Download date: 19. Mar. 2016This content has been downloaded from IOPscience. Please scroll down to see the full text.Download details:IP Address: 134.36.212.127This content was downloaded on 11/12/2015 at 09:52Please note that terms and conditions apply.Positron annihilation lifetime spectroscopy study of Kapton thin foilsView the table of contents for this issue, or go to the journal homepage for more2016 J. Phys. D: Appl. Phys. 49 025305(http://iopscience.iop.org/0022-3727/49/2/025305)Home Search Collections Journals About Contact us My IOPscience1 © 2016 IOP Publishing Ltd Printed in the UK1. IntroductionThe polyimide material Kapton belongs to a group of poly-mers that exhibit excellent chemical resistance, mechanical, thermal and dielectric properties, and are used in a diverse range of applications including dielectrics, nonlinear optical materials, and membranes [1]. The low dielectric constant, high dielectric strength, and high resistivity make polyimide materials suitable for a range of insulation applications [2, 3]. Positron annihilation lifetime spectroscopy (PALS) is capable of providing information on the size distribution of open volume in polymeric systems, and on vacancy-related point defects in inorganic materials and metals. Free volume in polymers is normally characterised by detecting the lifetimes and intensities of ‘pick-off’ annihilation events caused by the interaction of positronium (Ps), formed by positron implan-tation within open volume sites, with the cavity walls. This process can be analysed using a simple quantum mechanical model and information of cavity sizes determined [4, 5]. However, in contrast to the majority of polymers the Ps pick-off lifetime component, typically in the range ~1–30 ns, is absent in Kapton. This absence, combined with its excellent chemical and mechanical properties, contribute to make thin Kapton foils ideal supporting substrates for the deposition of radionuclide sources for various positron annihilation experi-ments on materials, in particular PALS measurements on bulk samples.The most commonly used radionuclide is 22Na which emits positrons with a β-spectrum of energies, up to a maximum of 0.546 MeV. In consequence these are implanted to range of depths within the material under study. PALS measurements performed using a Kapton foil enclosed 22Na source require detailed knowledge of the positron lifetime spectrum resulting from the small fraction of positrons implanted into the foil [6, 7]. The PALS spectrum is dominated by the contributions from positrons annihilating within the material under study. However, the inverse problem decomposition of these lifetime components due to the material is sensitive to the subtrac-tion of the extrinsic annihilation events, the source correction terms. Here we report the direct measurement of the positron Journal of Physics D: Applied PhysicsPositron annihilation lifetime spectroscopy study of Kapton thin foilsG S Kanda1, L Ravelli2, B Löwe2, W Egger2 and D J Keeble11 Division of Physics, SUPA, School of Engineering, Physics, and Mathematics, University of Dundee, Dundee DD1 4HN, UK2 Universität Bundeswehr München, D-85577 Neubiberg, GermanyE-mail: d.j.keeble@dundee.ac.ukReceived 6 July 2015, revised 2 September 2015Accepted for publication 11 September 2015Published 1 December 2015AbstractVariable energy positron annihilation lifetime spectroscopy (VE-PALS) experiments on polyimide material Kapton are reported. Thin Kapton foils are widely used in a variety of mechanical, electronic applications. PALS provides a sensitive probe of vacancy-related defects in a wide range of materials, including open volume in polymers. Varying the positron implantation energy enables direct measurement of thin foils. Thin Kapton foils are also commonly used to enclose the positron source material in conventional PALS measurements performed with unmoderated radionuclide sources. The results of depth-profiled positron lifetime measurements on 7.6 μm and 25 μm Kapton foils are reported and determine a dominant 385(1) ps lifetime component. The absence of significant nanosecond lifetime component due to positronium formation is confirmed.Keywords: positron annihilation, polymers, positron annihilation lifetime spectroscopy(Some figures may appear in colour only in the online journal)G S Kanda et alPrinted in the UK025305JPAPBE© 2016 IOP Publishing Ltd201649J. Phys. D: Appl. Phys.JPD0022-372710.1088/0022-3727/49/2/025305Papers2Journal of Physics D: Applied PhysicsIOPContent from this work may be used under the terms of the Creative Commons Attribution 3.0 licence. Any further distribution of this work must maintain attribution to the author(s) and the title of the work, journal citation and DOI.0022-3727/16/025305+3$33.00doi:10.1088/0022-3727/49/2/025305J. Phys. D: Appl. Phys. 49 (2016) 025305 (3pp)G S Kanda et al2annihilation lifetime spectra obtained using monochromatic positrons implanted exclusively within thin Kapton foils.Previous measurements of the positron lifetime spectrum of Kapton have been performed using thick Kapton [8], or on stacks of Kapton foils [9–13]. Recently measurements have been reported on stacks approximately 40 pieces of 125 μm Kapton using an 8 μm Kapton supported 22Na positron source [13]. The aim of the study was to investigate the effect tem-perature and of high dose electron beam irradiation. The single lifetime decompostion were reported to give the best fits. The as-received lifetime was 385(3) ps, this reduced to ~378 ps after a ~66 MGy absorbed electron beam dose, and remained approx-imately constant up to 200 MGy. The lifetime also increased with increasing temperature reaching ~397 ps at ~360 °C.An age momentum correlation (AMOC) study of Kapton, performed using a high energy positron beam, fitted the resulting spectra using two positron lifetime components and two associated Doppler broadening spectroscopy (DBS) S-parameter values [14]. The lifetime components were reported to be 229 ps and 378 ps, the latter with an intensity of 87 %; the nature of the Kapton studied was not described. Bulk lifetime measurements on stacked 125 μm Kapton HN foils using an 8 μm Kapton HN foil supported source reported two lifetime components, at ~277 ps and at ~410 ps, the latter with an intensity of ~70%, giving an average lifetime of 369(3) ps [12]. Measurements on bulk 1 mm plates of Kapton polyimide (PI2540), pyromellitic dianhdride-oxydianiline (PMDA-ODA), report a single lifetime value of 354 ps [8], earlier measurements by the same author were performed on a large number of stacked 3μm Kapton (PMDA-ODO) foils and reported two components, one at 220 ps and a second at 376 ps with intensity of 86 % giving an average lifetime of 354 ps [11]. The deconvolution into two components is attributed to an artefact of the spectrum analysis that arises when the positron lifetime distributions are particularly broad [14, 15].The adoption of Kapton foils for use in PALS followed a study by MacKenzie and Fabian [16], that reported a single lifetime component of 382 ps and a weak temperature depend-ence. Subsequently studies on stacked Kapton foils reported lifetime values of 386(7) ps [9], and of 382(3) ps [10]. The latter measurement used a stack of fifty 25 μm Kapton foils, measurements were also performed with some of the foils replaced by 8 μm Kapton with no change in the results.The depth distribution of implanted positrons can be described by a Makhovian profile, with the median depth obtained using a power law expression, ( )ρ=z A E/ n1/2 , were A is normally given in units of μg.cm−2 and E is in keV. Measurements using three different polymers obtained values A  =  2.81(20) μg.cm-2 keV−n and n  =  1.71(5) [17]. The den-sity of Kapton is 1.42 g.cm−3, and the resulting implantation profiles are shown in figure 1. The mean implantation depth increases with increasing implantation energy, for 10 keV monoenergetic positrons it is approximately 1 μm.2. ExperimentVariable energy (VE) PALS measurements were performed on a 7.6 μm and 25 μm Kapton® HN foils using the PLEPS instru-ment on the neutron induced positron source (NEPOMUC) at the Heinz Maier–Leibnitz Zentrum (MLZ) Munich research reactor (FRMII) [18–20]. The foils were carefully mounted with double-sided conducting tape on to the sample holders. Measurements on the 25 μm foils were performed using posi-tron beam energies between 1 to 18 keV, and each lifetime spectra contained greater 3  ×  106 counts. Measurements on the 7.6 μm foil were made at 16 keV and 18 keV, the spectra contained 4.0  ×  106 counts. The instrument timing resolution function is described by a sum of Gaussian functions and the mean width is energy dependent. The value, averaged over all implantation energies, was 254(26) ps.3. Results and discussionThe measurements on the 25 μm and 7.6 μm Kapton exhibit a single dominant positron lifetime component with an intensity of greater than 99.3%, and a second negligible intensity nano-second component. The lifetimes obtained for the dominant first component are shown in figure  2, the average value is Figure 1. Makhovian positron implantation profiles for Kapton determined using the empirical parameters A  =  2.81 μg·cm−2 keV−n, m  =  2, and n  =  1.71, and the density of 1.42 g·cm-3.Figure 2. The positron lifetime value for the dominant component of VE-PALS measurements on 7.6 μm (open squares) and 25 μm (triangles) Kapton HN foils. Individual sets of measurement on  25 μm Kapton HN foils are denoted by different triangle symbols.J. Phys. D: Appl. Phys. 49 (2016) 025305G S Kanda et al3385(1) ps. Figure 1 shows representative Markovian implan-tation profiles demonstrating that the positrons were con-fined to the Kapton foils for all implantation energies used. Implantation energies of 16 keV and 18 keV where selected for the 7.6 μm Kapton as the resulting depth distributions optimally sample the foil and provide lifetime values of direct relevance to conventional PALS experiments using Kapton supported positron sources.These results provide clear evidence for a dominant single positron lifetime component with a value of 385(1) ps in Kapton HN for both foil thickness studied. This is in agree-ment with the early bulk PALS reports of a single lifetime value of 382 ps [16], and 382(3) ps [10], and with the most recent study giving 385(3) ps [13]. The measurements provide further evidence that previously reported two component fits result from an artefact of the fitting process [11, 12, 14]. The AMOC results require the existence of at least two positron states [14], but are complicated by in-flight annihilation and by the high (3.5 MeV) positron energy and hence the require-ment for thick samples. The low values reported for Kapton PI2540 of ~354 ps suggest that this is different to Kapton HN [8]. The low average lifetime for Kapton HN of ~370 ps reported by McGuire and Keeble [12], resulted from incor-rect 22NaCl source correction, the value obtained by applying a systematic source correction procedure was reported to be 385(4) ps [6].These measurements demonstrate that conventional, bulk, positron lifetime measurements using radionuclide positron sources supported thin Kapton HN foils can be analysed by fixing the lifetime of the foil source correction component to a value of 385(1) ps. The results of Hirade et al [13], suggest that this value may decrease with time for high activity sources.4. ConclusionsPositron lifetime spectra were directly measured from 7.6 μm and 25 μm Kapton HN foils with VE-PALS using implantation energies for which all the positrons annihilate from within the foil. A single dominant lifetime component with an intensity greater than 99% was obtained from all measurements with a lifetime value of 385(1) ps.AcknowledgmentsD J K acknowledges European Commission Programme (RII3-CT-2003–505925), G S K was supported by an EPSRC DTA studentship (EP/J500392/1).References [1] Liaw D J, Wang K L, Huang Y C, Lee K R, Lai J Y and Ha C S 2012 Prog. Polym. Sci. 37 907 [2] Diaham S and Locatelli M L 2013 J. Phys. D: Appl. Phys. 46 185302 [3] Raju G G, Shaikh R and Haq S U 2008 IEEE Trans. Dielectr. Electr. Insul. 15 663 [4] Jean Y C 1990 Microchem. J. 42 72 [5] Eldrup M, Lightbody D and Sherwood J N 1981 Chem. Phys. 63 51 [6] McGuire S and Keeble D J 2006 J. Appl. Phys. 100 103504 [7] Staab T E M, Somieski B and Krause-Rehberg R 1996  Nucl. Instrum. Methods A 381 141 [8] Dlubek G, Borner F, Buchhold R, Sahre K, Krause-Rehberg R and Eichhorn K J 2000 J. Polym. Sci. Pol. Phys. 38 3062 [9] Plotkowski K, Panek T J and Kansy J 1988 Nuovo Cimento D 10 933 [10] Djourelov N and Misheva M 1996 J. Phys.: Condens. Matter 8 2081 [11] Dlubek G, Buchhold R, Hubner C, Nakladal A and Sahre K 1999 J. Polym. Sci. Pol. Phys. 37 2539 [12] McGuire S and Keeble D J 2006 J. Phys. D: Appl. Phys. 39 3388 [13] Hirade T, Oka T, Morishita N, Idesaki A and Shimada A 2012 Mater. Sci. Forum 733 151 [14] Dauwe C, De Baerdemaeker J, Djourelov N, Laforest N and Van Waeyenberge B 2008 Acta Phys. Pol. A 113 1315 [15] Dlubek G, Eichler S, Hubner C and Nagel C 1999  Nucl. Instrum. Methods B 149 501 [16] Mackenzie I K and Fabian J 1980 Nuovo Cimento B  58 162 [17] Algers J, Sperr P, Egger W, Kogel G and Maurer F H J 2003 Phys. Rev. B 67 125404 [18] Hugenschmidt C, Lowe B, Mayer J, Piochacz C, Pikart P, Repper R, Stadlbauer M and Schreckenbach K 2008.  Nucl. Instrum. Methods A 593 616 [19] Hugenschmidt C, Piochacz C, Reiner M and Schreckenbach K 2012 New J. 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Idesaki A and Shimada A

Nakladal A and Sahre K

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Positron annihilation lifetime spectroscopy study of Kapton thin foils

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