A glow discharge treatment of Polytetrafluoroethylene avoids charging effects and permits observation of the sample in Scanning Electron Spectroscopy; x-ray Photoelectron Spectroscopy has been used to study changes in the surface chemical composition and electronic structure of the polymer produced by this treatment

Duraud, J. P.

Le Gressus, C.

Le Moël, A.

Okuzumi, H.

English

DigitalCommons@USU

Scanning Electron Microscopy Volume 1986 Number 4 Article 8 10-3-1986 Glow Discharge Effects on Polytetrafluoroethylene Polymers Investigated by Secondary Electron Microscopy and X-Ray Photoelectron Spectroscopy A. Le Moël Centre d'Etudes Nucléaires de Saclay J. P. Duraud Centre d'Etudes Nucléaires de Saclay C. Le Gressus Centre d'Etudes Nucléaires de Saclay H. Okuzumi JEOL Follow this and additional works at: https://digitalcommons.usu.edu/electron  Part of the Life Sciences Commons Recommended Citation Le Moël, A.; Duraud, J. P.; Le Gressus, C.; and Okuzumi, H. (1986) "Glow Discharge Effects on Polytetrafluoroethylene Polymers Investigated by Secondary Electron Microscopy and X-Ray Photoelectron Spectroscopy," Scanning Electron Microscopy: Vol. 1986 : No. 4 , Article 8. Available at: https://digitalcommons.usu.edu/electron/vol1986/iss4/8 This Article is brought to you for free and open access by the Western Dairy Center at DigitalCommons@USU. It has been accepted for inclusion in Scanning Electron Microscopy by an authorized administrator of DigitalCommons@USU. For more information, please contact digitalcommons@usu.edu. SCANNING ELECTRON MICROSCOPY /1986/IV (Pages 1319-1322) SEM Inc., AMF O'Hare (Chicago), IL 60666-0507 USA 0586-5581/86$1.00+05 GLOW DISCHARGE EFFECTS ON POLYTETRAFLUOROETHYLENE POLYMERS INVESTIGATED BY SECONDARY ELECTRON MICROSCOPY AND X-RAY PHOTOELECTRON SPECTROSCOPY A. Le Moel, J.P. Duraud, C. Le Gressus, H.Okuzumi 1 IRDI-DESICP-DPC-SPCM-SES Centre d'Etudes Nucleaires de Saclay 91191 Gif sur Yvette cedex, FRANCE 1JEOL, 92503 Rueil-Malmaison, FRANCE (Received for publication December 23, 1985, and in revised form October 03, 1986) Hbstract R glow discharge treatment or Polytetrafluoroethylene avoids charging effects and permits observation of the sample in Scanning Electron Spectroscopy; X-ray Photoelectron Spectroscopy has been used to study changes in the surface chemical composition and electronic structure of the polymer produced by this treatment. ~ey words: SEM and X-ray Photoelectron Spectroscopy analysis, polymer surface radiation effects, glow discharge. * Address for correspondence: R.Le Moel IRDI- □ ESICP-DPC-SPCM-SES CEN Saclay 91191 Gif sur Yvette cedex FRANCE Phone n": (1) 69.08.54.85 1319 Introduction Studying organic or mineral insulators by means of an electronic probe is very difficult owing to charge build up which occurs under the beam (3, 6, 12). In Scanning Electron Microscopy CSEMJ, this effect hampers any high magnification observation. On Polytetrafluoroethylene (Teflon, PfFE), this problem can be rartly overcome by putting the sample in a glow discharge. This paper deals with this phenomenon. In order to understand the physical and chemical process induced on the samples by the discharge which Leads to better observation conditions, PTFE surface sample were studied in X-ray Photoelectron Spectroscopy (XPS). Impurity metal atoms are deposited on the treated surface and other structural modifications occur which change the surface conductivity. Experimental Sarl!fJ.l_es Technological PTFE CTF 7 synthetized by Dupont de NemoursJ was used in the form of J 15 mm x 2 mm cylindrical disk samples. ~irstly, the samples were cleaned in acetone in an ultrasonic bath. Glow discharges in Hrgon were generated by a JEOL 111 Fine Coat. The experimental conditions were: vacuum 10·1 torr, current: 4 mR, voltage: 800 V, time 5 to 8 min. To check the spatial resolution some metal coated samples (Ru Pd) were also prepared. Methods Secondary obtained with Microscope JSM Electron images were a JEOL Scanning Electron 840. The accelerating the observations was 1, voltage used for 2 or 3 keV. X-ray Photoelectron performed in a V.G. MK II. This instrument non-monochromatized Spectroscopy was Instruments ESCRLRB is equipped with a X-ray source A. Le Moel, J.P. Duraud et al. Fig. 1. S.E. images of P1'FE sanples. la) Pl'FE-nt - magnificaticn 103• lb) Pl'FE-t - magnificaticn 103• le) Pl'FE-rn - magnificaticn 104 • ld) PTFE-rn - magnificaticn 103. le) Pl'FE-rn - magnificaticn 104 • I 1· u. : fiw= 1486,6 eV I [~ - a PTFE. nt 1r~t LJ 100eV •,s b PTFE.t I I I C J\~KLL jl KLL j Co,Fe,Mn.c, 1~ ~,s o,s-i-/ Fe,~i,C< L.1~~ ---.J 1000 500 FiJ. 2. X-ray :p,otoelectrcn lines. 2a Pl'FE-nt aarrple. 2b) Pl'FE-t sanple. 500 250 1000 1 320 -fiw= 1486,6 eV 675 680 885 890 PTFE.nt PTFE.t 695 BE(ov) Fig, 3. Fis lines for the Pl'FE-nt and Pl'FE-t sanples. a.u. "'c.>= 1486,6 eV 270 280 290 ._ _ _..TFE.nt PTFE.t 300 Fig, 4. c18 lines for the Pl'FE-nt and Pl'FE-t sanples, 310 BE (ov) Glow discharge effects on PTFE polymers (Rl um1num I<. a. = 1486. 6 eV). The base pressure 1s normally around 5_·10-ll forr. Because of out-gasing effects due to the PTFE samples, the pressure rose to about 10-9 Torr· at the end of the experiment. The analysis chamber is fitted with a 150 mm spherical sector analyzer operating 1n constant pass energy mode and equal t □ 50 eV. In tnis experiment, tne energy calibration was made Du using the 4f7;2 =84.0 ev X-ray photoelectron Line of clean bulk polycrystalline gold. Results 5.E.images: Three PTFE samples were investigated by means of a scanning electron microscope at a magnification of 1~ . The first sample was cleaned in a ultrasonic bath (PTFE-nt), the second one was submitted to a glow discnarge CPTFE-tl, the Last one was coated with metal (PTFE-mJ. It 1s interesting to note that the "non-treated" polymer CF 1g. 1a) charged up under the electronic probe even at a low accelerating voltage. However, the PTFE-t CFig. 1b) and the PTFE-m CFig. 1cl samples present a good imaging contrast and a clear4topography. Rt a higner magnification (10 ) , it was quite impossible to get an useful image on the non--treated polymer CPTFE-nt). On the two otner samples CFig. 1d and 1el, we obtain good details of the surface. The PTFE-t sample shows some morphological surface modifications: etch pits and crosslinking like features. X-ray_ photoelectron Lines: Owing to the positive charge created by X-ray irradiation (10) a correction of the energy position of the photoelectron and Ruger Lines is necessary. Comparison with previous work (1, 7) on PTFE Led us to choose the value of 690.2 eV for the Fis Line. This value enabled us to evaluate the Fis shift due to the charging of the sample as 7 .0 eV for the PHE-nt and .'.L.__§ ev for the PTFE-t. In the fol Lowing we will only consider the corrected values of the binding energies. E!_) __ EL eme_ntal_ E!_nE!_Lysi_s __ of_ _th~ !:'_TE_E.:_n_t ~ur:_fE!_c~ __(_Fi_g_,__ ££) - We note the presence of oxygen C01s l due to atmospheric contamination and a very small photo-electron Line Located at 625 eV and probably due to the presence of iodine CI 3d5;2 l used to fluorinate the compound before polymerization CIF4 l. c 1s Line appears as a convolution of two peaks. It we compare the complete spectrum CFig. 2al to that obtained for the PTFE-t sample CFig. 2b) we observe some modifications: splitting of the els Line shape, and a higher concentration of oxygen. Other photoelectron and Ruger Lines are found which are due to the 1321 presence of metallic atoms CCo, Fe, Mn, Cr) on the PTFE-t. Q J __ F 1 s l_ 1 !:!_ e ?.. i Fi g .:.. ;n - F or the PT FE - n t sample we only get d simple Fls line at 690.2 ev. On the other hand, the Fls Line of the PfFE-t reveals a main structure at 590.2 ev which corresponds to the fluorine photoelectron Line in PTFE and a second one at Lower binding energy (689.2 eV) which can be attributed to metallic fluoride compounds due to depositied metal atoms C2, 9). f_l _c 15 _l_!_n~s ___ CE_ig_. '<) - The c 1s Line corresponding to the PTFE-nt sample reveals two distinct structures at 292.4 eV and 288.2 eV which are respectively attributed to the -cF 2 - and ~CF groups in the polymer C2, 8, 11J; photoelectron lls line of the PTFE-t exhibits a less prominent structure at 293.6 ev C-CF2-l and a new structure at 287.8 eV which can be explained by the presence of a double bond C~C=C(l 1n tne modified polymer. Discussion rwo effects can explain the good contrast of the S.E.image made on PTFE-t: Low concentration deposit of metallic atoms and partial graphitizat1on of the polymer surface. The metal atoms were deposited during the short glow discharge and were extracted from the stainless steel surface of the sample holder of the JFC-111. Their concentration is very Low (t1%l as the Line intensity is very weak and as they could not be detected with an Ruger microprobe. Rt this Low concentrations, metal atoms cannot produce a conductive surface Layer but they can make trapped electron surface sites disappear, leading to a better conductivity. On the other hand, the energy mosition, the chemical shifts and the shapes of the photoelectron Lines of PTFE (Cls F1s l reveal structural modifi-cations after the glow discharge treatment. Rppearance of-[=[- groups is correlated to the decrease of -CF2- and "F" Lines. This shows that the glow discharge induced carbon-fluorine bonds to break with the formation of [=[. bonds and this partial graphitization Leads to reticulation on the PTFE surface C4, 5). This phenomenon has also been observed after much more energetic ion bombardment C> 1 keV) C2, 11). The effect is apparent on 4the 5.E.image at high magnification C10 ). Ref r.>rence . .2_ 1. Briggs 05, Practical surface Seah MP. (Eds) C1983l analysis by ~uger and H.Le Moel, J.P.Ouraud et al. X-ray photoelectron spectroscopy. J.Wiley, '1-396. 2. Cardona M, Ley L. CEdsl C1978J Photoemission in sol ids, I, 26, Topics in Hpplied Physics, Springer Verlag, 1-93. 3. Clark 07. (19781 The investigation of polymer surface by means of ESCH. Polym. Surf. O.T.Clark and W.J.Feast, CEdsl, J.Wiley, 309-350. 4. Clark OT, Dilks H. C1977l ESCH applied to polymers. XV -Glow discharge modifications of polymers, studied by means of ESCH in term5 of direct a•nd radiative energy tran5fer model, J. Polym. Sci. - Polym. Ed . .J.2, 2321-2345. 5. Clark OT, Dilks H. (1978) ESCH applied to polymer5. XVIII RF Glow di5charge modifications of polymers in Helium, Neon, Hrgon and Krypton. J. Polym. Sci. - Polytn. Chern. Ed. IQ, 9·1·1-936. 6. Clarke OR, Stuart PR. C1970l Hn anomalou5 contra5t effect in the scanning electron microscopy, J. Phy5. E: Scientific ln5truments, J, 705-707. 7. Dilks H. (1980) X-ray photoelectron spectro5copy for the investigation ot polymer surfaces. Dwight OW, Fabi5h TJ, lhomas HR. CEd5l Photon, electron and ion proDe5 of polymer 5tructure and properties, HCS Symposium, Wasnington O.C. 293-3'16. 8. Grobman WO, Koch EE. C1979l Photoemi5sion from organic molecular cry5tals. Ley L, Cardona M. CEdsl Photoemission in in Hpplied Physics, 294. solids, II, 27. Topics Springer Verlag, 261-9. Holm R, Storp S. (1980) Surface and interface analysis in polymer technology, H review. Surface and Interface Hnalysis, :i;_ (3) 96-106. 10. Petite G, Hgostini P, Boiziau C, Vigouroux JP, Le Gressus C, Ouraud JP. (1985) Temperature dependence of the electron emission of amorphous silica under intense Laser irradiation. Optics Communications, 53 __ (3), 169-'193. 11. Pivin JC. (1984) Sp~cificite et Limites de quelques techniques d'analyse des couches minces, J. Microsc. Spectrosc. ~Lectron., ~, 75-94. 12. Shaffner TJ, Hearle JWS. (1976) Recent advances in understanding specimen charging. Scanning Electron Microsc. 1976; I: 6·1-70. Discussion with reviewers T.J.Shaiiner: Have you been able to repeat tne expPriments on otner □ rganic and plastic materials? Rutnors: We dio not repeat these experiments on otner organic materials, but we started a progra1n on polymers modification Dy electronic excitation. 7322 T.J.Shaffner: Could not one deposit gold, silver or other metal of choice instead of the stainless steel? What properties of such a metal would be the most desirable? Huthors: The stainless steel was accidently deposited during the RF glow discharge. It is known tnat non oxid1zable metals Like gold, platinum or non-metallic compounds Like graphite sputtered onto metal insulator materials Led to good 5EM observations because of the disappearance of the superficiel charging effects. T.J.Shaffner: How does the time of exposure to glow discharge affect the apparent conductivity of the PTFE and your ability to form images free from ch a r g 1 n g '! Ruthors: H glow discharge in an inert gas 1s generally used to clean a sample surface, but this method applied to polymer compounds alters the polymer itself because of the temperature increase of the sample during the treatment. This temperature increase generally Leads to partial carbonization or grapnitization of the polymer and in this case improves the conductivity. L._J.,__'.?.Di!. f f n e r : r h e i ma g e s o f F i g . ·1 d a n d 1e show that glow discharge has altered the surface morphology. Hlthough this reduces charging for high magnification work, tne image one obtains does not correctly portray the original surface. Does tnis not invalidate practical application of the method for reducing c h a r g i n g ':' Rut hors: HS original carefully surfacE'. the glow discharge alters the surface, it must be used to get correst images of the fS'_.,__!j_Ql_m: What is the reason for the etch pits and other inhomogeneities after the rather short Low voltage glow discharge treatment'? Author~~ We suggest that during the glow discharge, inert gas ions interact with the atoms of tne polymer surface to initiate raoicals and ions. These species rapidly evolve and give backbone fragmentations, cross-linking and volatile species. These modifications can explain the new topography of the surface. fL.t:I.Q_lfll_:_ What happens to the sample after extended treatment or in tne case 01 other oiscnarge parameters~ 8uthors: We did not modify the parameters of the surface treatment of the sample, as our aim was only to understand the modifications of the SEM imaging. 

Glow Discharge Effects on Polytetrafluoroethylene Polymers Investigated by Secondary Electron Microscopy and X-Ray Photoelectron Spectroscopy

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Glow Discharge Effects on Polytetrafluoroethylene Polymers Investigated by Secondary Electron Microscopy and X-Ray Photoelectron Spectroscopy

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