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Mitigating graphene etching on SiO2 during fluorination by XeF2
Materials Letters 252 (2019) 11–14
Contents lists available at ScienceDirect
Materials Letters journal homepage: www.elsevier.com/locate/mlblue
Mitigating graphene etching on SiO2 during fluorination by XeF2 G. Copetti a, E.H. Nunes b, G.V. Soares a, C. Radtke b,⇑ a b
Instituto de Física, UFRGS, 91509-900 Porto Alegre, Brazil Instituto de Química, UFRGS, 91509-900 Porto Alegre, Brazil
a r t i c l e
i n f o
Article history: Received 3 April 2019 Received in revised form 11 May 2019 Accepted 20 May 2019 Available online 21 May 2019 Keywords: Carbon materials XPS Surfaces Graphene Fluorination
a b s t r a c t Fluorination is a promising functionalization method for bandgap opening in graphene on SiO2 substrates. Exposure to XeF2 is a simple approach among several techniques. However etching of the graphene layer occurs. We observed that the mechanism behind etching is the interaction of fluorine containing species with the underlying SiO2. Pulsed XeF2 exposure is shown to suppress etching, resulting in high-quality and homogeneous fluorographene in large areas. Ó 2019 Published by Elsevier B.V.
1. Introduction High transparency, flexibility, electron mobility, and thermal conductivity combined with its extremely reduced thickness makes graphene a candidate to numerous applications in microelectronics [1]. However, bandgap opening is required for its insertion in CMOS technology. Moreover, the ability to pattern regions of variable conductivity is also necessary. Bandgap opening can be induced by graphene functionalization with oxygen, hydrogen, and Halogens [2–5]. Fluorination stands out among these methods, since fluorographene (C1F1) has a bandgap around 3–4 eV [2,6]. One of the most promising aspects of fluorinated graphene is its reversibility [7]. Nevertheless, the production of fluorographene with the desired characteristics is still a challenge. On one hand, exfoliation of fluorinated graphite lack quality, scale-up potential, and/or reproducibility. On the other hand, plasma fluorination of CVD graphene can lead to defects [2]. By exposing graphene on SiO2 substrates continuously to XeF2 only 25% fluorination was obtained [8]. Moreover, Nair and coworkers [9] reported graphene etching due to XeF2. Highly fluorinated graphene (C1F0.6) on SiO2 substrates was finally achieved using XeF2 exposure by Stine and coworkers [10] using the XactixÓ setup, which is an equipment originally used for Si etching using pulses of XeF2. This last work suggested that the way by which graphene is exposed to XeF2 has an important role in the result of the fluorination process. This is quite intriguing since the underlying substrate of graphene is ⇑ Corresponding author. E-mail address: [email protected] (C. Radtke). https://doi.org/10.1016/j.matlet.2019.05.086 0167-577X/Ó 2019 Published by Elsevier B.V.
SiO2, which was thought to be resistant to XeF2 [11], suggesting no influence in the fluorination process. In this work, continuous and pulsed exposures of graphene to XeF2 are compared for the production of fluorographene on SiO2, aiming at unraveling the mechanisms underlying this process. 2. Experimental details Fluorination was performed by exposing commercial monolayer graphene on SiO2(300 nm)/Si substrates (Graphene SupermarketÓ) to XeF2 gas. Solid XeF2 (Sigma-Aldrich 99.99% purity) is placed on a metallic bottle connected to a chamber where the samples are positioned. This chamber is pumped down to 10-3 Torr. After the valve separating the bottle from the chamber is opened, pressure inside stabilizes within 10 s at 4 Torr. Pulsed fluorination was performed in cycles, corresponding to 30 s exposure to XeF2 and subsequent pumping of the chamber. Samples were analyzed by X-ray photoelectron spectroscopy (XPS) using Al-Ka radiation. Raman spectroscopy was performed using a laser excitation wavelength of 473 nm and spatial resolution of approximately 1 lm. Atomic force microscopy (AFM) was used to investigate the surface morphology of samples. 3. Results Fig. 1 shows the F/C ratio (obtained by XPS) as a function of time for continuous and pulsed exposure. Samples exposed continuously to XeF2 evidence F/C ratio decrease with time, while a sharp increase is observed for samples submitted to pulses, reaching a
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Fig. 1. F/C ratio as function of exposure time for continuous and pulsed fluorination.
plateau of 0.9. Since the C signal is not exclusively originated from the graphene layer (including contaminants deposited on the sample), the attained F/C ratio can be regarded as quasi-stoichiometric fluorographene. XPS spectra of graphene samples prepared in these conditions are shown in Fig. 2. The O 1 s signal at 533 eV was mainly attributed to oxygen in the SiO2 substrate, while the F 1 s signal at 688 eV is consistent with fluorinated carbon compounds [12,13]. F bonding to C is evident by the deconvolution of the C 1 s region, in which components of high energy chemical displacement appear after fluorination. This last observation is particularly evident in the sample submitted to the pulsed process (Fig. 2c). Moreover, the component attributed to C with sp3 hybridization is intensified after fluorination, which indicates the modification
Fig. 2. Survey and C 1 s region of XPS spectra obtained from (a) pristine monolayer graphene on SiO2(300 nm)/Si substrate, the same sample following (b) continuous (5 min) and (c) pulsed (10 pulses of 30 s) exposure to XeF2. (d) Spectra of SiO2/Si submitted to pulsed fluorination is also shown. a. u. stands for arbitrary units.
Fig. 3. (a) AFM measurements of graphene on SiO2/Si submitted to fluorination in continuous (5 min) and pulsed exposure (10 pulses of 30 s). (b) Optical microscopy image with 10x magnification of the edge of the sample exposed continuously to XeF2.
Fig. 4. (a) Raman spectra and 7 7 lm2 maps of 2D/G (b) and D/G (c) Raman peaks ratio of graphene sample before and after undergoing pulsed fluorination (10 pulses of 30 s).
G. Copetti et al. / Materials Letters 252 (2019) 11–14
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Fig. 5. (a) XPS survey spectra before and after continuous fluorination for 5 and 60 min. (b) O/Si ratio as a function of the fluorination time, and (c) Si 2p region of samples exposed continuously to XeF2 for different time periods. a. u. stands for arbitrary units.
of graphene structure. Minimal F incorporation (likely on C contaminants) occurs when 300 nm SiO2/Si is fluorinated (Fig. 2d), evidencing the inertness of SiO2 to this atmosphere. The survey spectrum shown (Fig. 2d) is almost identical to that before fluorination. Morphology differences were also observed by AFM (Fig. 3a). While the continuous fluorinated sample has RMS roughness of 1.3 nm, pulsed exposure reduces this value to 0.3 nm. Inspection by optical microscopy following continuous XeF2 exposure evidences the deterioration of the sample surface, while pulsed exposure did not induce such effect (see Supplementary data). In Fig. 3b one can clearly see some modification taking place from the sample’s border towards its center. Raman measurements from a sample before and after being submitted to pulsed fluorination are shown in Fig. 4a. The spectrum of the pristine sample is characteristic of monolayer graphene [1], with the 2D almost two times the height of the G peak. After pulsed fluorination, the spectrum of typical highly fluorinated graphene is observed [2]: the 2D peak is diminished and the D band increases. This is due to the change in C hybridization from sp2 to sp3 resulting from F bonding. Fig. 4(b,c) shows how the graphene changes homogeneously over large areas by mapping 2D/G and D/G intensity ratios. Further insight into the effects of XeF2 was obtained by exposing samples continuously to XeF2 for longer times. XPS analyses show that the relative intensity of the Si signals raises for higher fluorination times (Fig. 5a). The relative intensities of Si 2p, C 1 s, O 1 s, and F 1 s XPS signals are shown in Supplementary data. The inspection of the O/Si ratio (Fig. 5b) and the evolution of the Si 2p signal (Fig. 5c) show that besides graphene removal, fluorination also induces etching of the underlying SiO2. This is quite astonishing since SiO2 is resistant to XeF2 etching [14]. O and C losses suggest that not only graphene is being removed but also the SiO2 underneath. Veyan et al. [14] have shown that by-products of the reaction between XeF2 and Si from the substrate (XeF and atomic F) can etch SiO2 thicker than 100 nm. Such mechanism should take place mainly at the exposed edges of the substrate. In fact, such etching was observed in our samples by optical microscopy (Fig. 3b), where the process begins at the edges and spreads towards the center of the sample. The pulsed exposure by pumping the reaction chamber after 30 s prevents the buildup of such by-products. 4. Conclusions The reaction of XeF2 with the Si substrate plays an important role on the quality of fluorographene layers on SiO2/Si substrates.
Pulsed exposure allows the by-products of this reaction to be removed, preventing SiO2 etching and, consequently, graphene deterioration. Samples produced by this method possess low roughness and high homogeneity. Further improvement of these processes can be achieved by optimizing the pulse time, paving the way for a simple and quick method of graphene functionalization. Author contributions The manuscript was written through contributions of all authors. All authors have given approval to the final version of the manuscript. Declaration of Competing Interest None. Acknowledgment We would like to thank the financial support of INCT Namitec, INCT INES, MCT/CNPq, CAPES, and FAPERGS. Appendix A. Supplementary data Supplementary data to this article can be found online at https://doi.org/10.1016/j.matlet.2019.05.086. References [1] A.C. Ferrari et al., Science and technology roadmap for graphene, related twodimensional crystals, and hybrid systems, Nanoscale 7 (2015) 4598–4810, https://doi.org/10.1039/C4NR01600A. [2] F. Karlicky´, K.R. Datta, M. Otyepka, R. Zborˇil, Halogenated graphenes: rapidly growing family of graphene derivatives, ACS Nano 7 (2013) 6434–6464, https://doi.org/10.1021/nn4024027. [3] M. Acik, Y. Chabal, A review on reducing graphene oxide for band gap engineering, J. Mater. Sci. Res. 2 (2013). [4] Z. Liu, Z. Chenb, F. Yu, Microencapsulated phase change material modified by graphene oxide with different degrees of oxidation for solar energy storage, Sol. Energy Mater Sol. Cells 174 (2018) 453–459. [5] B. Martín-García, Y. Bi, M. Prato, D. Spirito, R. Krahne, G. Konstantatos, I. Moreels, Sol. Energy Mater Sol. Cells 183 (2018) 1–7. [6] W. Feng, P. Long, Y. Feng, Y. Li, Two-dimensional fluorinated graphene: synthesis, structures, properties and applications, Adv. Sci. 3 (2016) 1500413, https://doi.org/10.1002/advs.201500413. [7] F. Withers, T.H. Bointon, M. Dubois, S. Russo, M.F. Craciun, Nanopatterning of fluorinated graphene by electron beam irradiation, Nano Lett. 11 (2011) 3912– 3916, https://doi.org/10.1021/nl2020697. [8] J.T. Robinson, J.S. Burgess, C.E. Junkermeier, S.C. Badescu, T.L. Reinecke, F.K. Perkins, M.K. Zalalutdniov, J.W. Baldwin, J.C. Culbertson, P.E. Sheehan, E.S.
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Snow, Properties of fluorinated graphene films, Nano Lett. 10 (2010) 3001– 3005, https://doi.org/10.1021/nl101437p. [9] R.R. Nair, W. Ren, R. Jalil, I. Riaz, V.G. Kravets, L. Britnell, P. Blake, F. Schedin, A.S. Mayorov, S. Yuan, M.I. Katsnelson, H.-M. Cheng, W. Strupinski, L.G. Bulusheva, A.V. Okotrub, I.V. Grigorieva, A.N. Grigorenko, K.S. Novoselov, A.K. Geim, Fluorographene: a two-dimensional counterpart of Teflon, Small 6 (2010) 2877–2884, https://doi.org/10.1002/smll.201001555. [10] R. Stine, W.-K. Lee, K.E. Whitener, J.T. Robinson, P.E. Sheehan, Chemical stability of graphene fluoride produced by exposure to XeF2, Nano Lett. 13 (2013) 4311–4316, https://doi.org/10.1021/nl4021039. [11] S. Joyce, J.G. Langan, J.I. Steinfeld, Reactions of XeF2 with thermally grown SiO2, Surf. Sci. 195 (1988) 270, https://doi.org/10.1016/0039-6028(88)90796-0.
[12] M.L. Miller, R.W. Linton, X-ray photoelectron spectroscopy of thermally treated silica (SiO2) surfaces, Anal. Chem. 57 (12) (1985) 2314–2319, https://doi.org/10.1021/ac00289a033. [13] D.T. Clark, D. Kilcast, D.B. Adams, W.K.R. Musgrave, An, ESCA study of the molecular core binding energies of the fluorobenzenes, J. Electron Spectrosc. Relat. Phenom 1 (1972) 232, https://doi.org/10.1016/0368-2048(72)85013-8. [14] J.F. Veyan, M. Halls, S. Rangan, D. Aureau, X.M. Yan, Y.J. Chabal, XeF2-induced removal of SiO2 near Si surfaces at 300 K: an unexpected proximity effect 114914 Appl. Phys. 108 (2010), https://doi.org/10.1063/1.3517148.
Contents lists available at ScienceDirect
Materials Letters journal homepage: www.elsevier.com/locate/mlblue
Mitigating graphene etching on SiO2 during fluorination by XeF2 G. Copetti a, E.H. Nunes b, G.V. Soares a, C. Radtke b,⇑ a b
Instituto de Física, UFRGS, 91509-900 Porto Alegre, Brazil Instituto de Química, UFRGS, 91509-900 Porto Alegre, Brazil
a r t i c l e
i n f o
Article history: Received 3 April 2019 Received in revised form 11 May 2019 Accepted 20 May 2019 Available online 21 May 2019 Keywords: Carbon materials XPS Surfaces Graphene Fluorination
a b s t r a c t Fluorination is a promising functionalization method for bandgap opening in graphene on SiO2 substrates. Exposure to XeF2 is a simple approach among several techniques. However etching of the graphene layer occurs. We observed that the mechanism behind etching is the interaction of fluorine containing species with the underlying SiO2. Pulsed XeF2 exposure is shown to suppress etching, resulting in high-quality and homogeneous fluorographene in large areas. Ó 2019 Published by Elsevier B.V.
1. Introduction High transparency, flexibility, electron mobility, and thermal conductivity combined with its extremely reduced thickness makes graphene a candidate to numerous applications in microelectronics [1]. However, bandgap opening is required for its insertion in CMOS technology. Moreover, the ability to pattern regions of variable conductivity is also necessary. Bandgap opening can be induced by graphene functionalization with oxygen, hydrogen, and Halogens [2–5]. Fluorination stands out among these methods, since fluorographene (C1F1) has a bandgap around 3–4 eV [2,6]. One of the most promising aspects of fluorinated graphene is its reversibility [7]. Nevertheless, the production of fluorographene with the desired characteristics is still a challenge. On one hand, exfoliation of fluorinated graphite lack quality, scale-up potential, and/or reproducibility. On the other hand, plasma fluorination of CVD graphene can lead to defects [2]. By exposing graphene on SiO2 substrates continuously to XeF2 only 25% fluorination was obtained [8]. Moreover, Nair and coworkers [9] reported graphene etching due to XeF2. Highly fluorinated graphene (C1F0.6) on SiO2 substrates was finally achieved using XeF2 exposure by Stine and coworkers [10] using the XactixÓ setup, which is an equipment originally used for Si etching using pulses of XeF2. This last work suggested that the way by which graphene is exposed to XeF2 has an important role in the result of the fluorination process. This is quite intriguing since the underlying substrate of graphene is ⇑ Corresponding author. E-mail address: [email protected] (C. Radtke). https://doi.org/10.1016/j.matlet.2019.05.086 0167-577X/Ó 2019 Published by Elsevier B.V.
SiO2, which was thought to be resistant to XeF2 [11], suggesting no influence in the fluorination process. In this work, continuous and pulsed exposures of graphene to XeF2 are compared for the production of fluorographene on SiO2, aiming at unraveling the mechanisms underlying this process. 2. Experimental details Fluorination was performed by exposing commercial monolayer graphene on SiO2(300 nm)/Si substrates (Graphene SupermarketÓ) to XeF2 gas. Solid XeF2 (Sigma-Aldrich 99.99% purity) is placed on a metallic bottle connected to a chamber where the samples are positioned. This chamber is pumped down to 10-3 Torr. After the valve separating the bottle from the chamber is opened, pressure inside stabilizes within 10 s at 4 Torr. Pulsed fluorination was performed in cycles, corresponding to 30 s exposure to XeF2 and subsequent pumping of the chamber. Samples were analyzed by X-ray photoelectron spectroscopy (XPS) using Al-Ka radiation. Raman spectroscopy was performed using a laser excitation wavelength of 473 nm and spatial resolution of approximately 1 lm. Atomic force microscopy (AFM) was used to investigate the surface morphology of samples. 3. Results Fig. 1 shows the F/C ratio (obtained by XPS) as a function of time for continuous and pulsed exposure. Samples exposed continuously to XeF2 evidence F/C ratio decrease with time, while a sharp increase is observed for samples submitted to pulses, reaching a
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G. Copetti et al. / Materials Letters 252 (2019) 11–14
Fig. 1. F/C ratio as function of exposure time for continuous and pulsed fluorination.
plateau of 0.9. Since the C signal is not exclusively originated from the graphene layer (including contaminants deposited on the sample), the attained F/C ratio can be regarded as quasi-stoichiometric fluorographene. XPS spectra of graphene samples prepared in these conditions are shown in Fig. 2. The O 1 s signal at 533 eV was mainly attributed to oxygen in the SiO2 substrate, while the F 1 s signal at 688 eV is consistent with fluorinated carbon compounds [12,13]. F bonding to C is evident by the deconvolution of the C 1 s region, in which components of high energy chemical displacement appear after fluorination. This last observation is particularly evident in the sample submitted to the pulsed process (Fig. 2c). Moreover, the component attributed to C with sp3 hybridization is intensified after fluorination, which indicates the modification
Fig. 2. Survey and C 1 s region of XPS spectra obtained from (a) pristine monolayer graphene on SiO2(300 nm)/Si substrate, the same sample following (b) continuous (5 min) and (c) pulsed (10 pulses of 30 s) exposure to XeF2. (d) Spectra of SiO2/Si submitted to pulsed fluorination is also shown. a. u. stands for arbitrary units.
Fig. 3. (a) AFM measurements of graphene on SiO2/Si submitted to fluorination in continuous (5 min) and pulsed exposure (10 pulses of 30 s). (b) Optical microscopy image with 10x magnification of the edge of the sample exposed continuously to XeF2.
Fig. 4. (a) Raman spectra and 7 7 lm2 maps of 2D/G (b) and D/G (c) Raman peaks ratio of graphene sample before and after undergoing pulsed fluorination (10 pulses of 30 s).
G. Copetti et al. / Materials Letters 252 (2019) 11–14
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Fig. 5. (a) XPS survey spectra before and after continuous fluorination for 5 and 60 min. (b) O/Si ratio as a function of the fluorination time, and (c) Si 2p region of samples exposed continuously to XeF2 for different time periods. a. u. stands for arbitrary units.
of graphene structure. Minimal F incorporation (likely on C contaminants) occurs when 300 nm SiO2/Si is fluorinated (Fig. 2d), evidencing the inertness of SiO2 to this atmosphere. The survey spectrum shown (Fig. 2d) is almost identical to that before fluorination. Morphology differences were also observed by AFM (Fig. 3a). While the continuous fluorinated sample has RMS roughness of 1.3 nm, pulsed exposure reduces this value to 0.3 nm. Inspection by optical microscopy following continuous XeF2 exposure evidences the deterioration of the sample surface, while pulsed exposure did not induce such effect (see Supplementary data). In Fig. 3b one can clearly see some modification taking place from the sample’s border towards its center. Raman measurements from a sample before and after being submitted to pulsed fluorination are shown in Fig. 4a. The spectrum of the pristine sample is characteristic of monolayer graphene [1], with the 2D almost two times the height of the G peak. After pulsed fluorination, the spectrum of typical highly fluorinated graphene is observed [2]: the 2D peak is diminished and the D band increases. This is due to the change in C hybridization from sp2 to sp3 resulting from F bonding. Fig. 4(b,c) shows how the graphene changes homogeneously over large areas by mapping 2D/G and D/G intensity ratios. Further insight into the effects of XeF2 was obtained by exposing samples continuously to XeF2 for longer times. XPS analyses show that the relative intensity of the Si signals raises for higher fluorination times (Fig. 5a). The relative intensities of Si 2p, C 1 s, O 1 s, and F 1 s XPS signals are shown in Supplementary data. The inspection of the O/Si ratio (Fig. 5b) and the evolution of the Si 2p signal (Fig. 5c) show that besides graphene removal, fluorination also induces etching of the underlying SiO2. This is quite astonishing since SiO2 is resistant to XeF2 etching [14]. O and C losses suggest that not only graphene is being removed but also the SiO2 underneath. Veyan et al. [14] have shown that by-products of the reaction between XeF2 and Si from the substrate (XeF and atomic F) can etch SiO2 thicker than 100 nm. Such mechanism should take place mainly at the exposed edges of the substrate. In fact, such etching was observed in our samples by optical microscopy (Fig. 3b), where the process begins at the edges and spreads towards the center of the sample. The pulsed exposure by pumping the reaction chamber after 30 s prevents the buildup of such by-products. 4. Conclusions The reaction of XeF2 with the Si substrate plays an important role on the quality of fluorographene layers on SiO2/Si substrates.
Pulsed exposure allows the by-products of this reaction to be removed, preventing SiO2 etching and, consequently, graphene deterioration. Samples produced by this method possess low roughness and high homogeneity. Further improvement of these processes can be achieved by optimizing the pulse time, paving the way for a simple and quick method of graphene functionalization. Author contributions The manuscript was written through contributions of all authors. All authors have given approval to the final version of the manuscript. Declaration of Competing Interest None. Acknowledgment We would like to thank the financial support of INCT Namitec, INCT INES, MCT/CNPq, CAPES, and FAPERGS. Appendix A. Supplementary data Supplementary data to this article can be found online at https://doi.org/10.1016/j.matlet.2019.05.086. References [1] A.C. Ferrari et al., Science and technology roadmap for graphene, related twodimensional crystals, and hybrid systems, Nanoscale 7 (2015) 4598–4810, https://doi.org/10.1039/C4NR01600A. [2] F. Karlicky´, K.R. Datta, M. Otyepka, R. Zborˇil, Halogenated graphenes: rapidly growing family of graphene derivatives, ACS Nano 7 (2013) 6434–6464, https://doi.org/10.1021/nn4024027. [3] M. Acik, Y. Chabal, A review on reducing graphene oxide for band gap engineering, J. Mater. Sci. Res. 2 (2013). [4] Z. Liu, Z. Chenb, F. Yu, Microencapsulated phase change material modified by graphene oxide with different degrees of oxidation for solar energy storage, Sol. Energy Mater Sol. Cells 174 (2018) 453–459. [5] B. Martín-García, Y. Bi, M. Prato, D. Spirito, R. Krahne, G. Konstantatos, I. Moreels, Sol. Energy Mater Sol. Cells 183 (2018) 1–7. [6] W. Feng, P. Long, Y. Feng, Y. Li, Two-dimensional fluorinated graphene: synthesis, structures, properties and applications, Adv. Sci. 3 (2016) 1500413, https://doi.org/10.1002/advs.201500413. [7] F. Withers, T.H. Bointon, M. Dubois, S. Russo, M.F. Craciun, Nanopatterning of fluorinated graphene by electron beam irradiation, Nano Lett. 11 (2011) 3912– 3916, https://doi.org/10.1021/nl2020697. [8] J.T. Robinson, J.S. Burgess, C.E. Junkermeier, S.C. Badescu, T.L. Reinecke, F.K. Perkins, M.K. Zalalutdniov, J.W. Baldwin, J.C. Culbertson, P.E. Sheehan, E.S.
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Snow, Properties of fluorinated graphene films, Nano Lett. 10 (2010) 3001– 3005, https://doi.org/10.1021/nl101437p. [9] R.R. Nair, W. Ren, R. Jalil, I. Riaz, V.G. Kravets, L. Britnell, P. Blake, F. Schedin, A.S. Mayorov, S. Yuan, M.I. Katsnelson, H.-M. Cheng, W. Strupinski, L.G. Bulusheva, A.V. Okotrub, I.V. Grigorieva, A.N. Grigorenko, K.S. Novoselov, A.K. Geim, Fluorographene: a two-dimensional counterpart of Teflon, Small 6 (2010) 2877–2884, https://doi.org/10.1002/smll.201001555. [10] R. Stine, W.-K. Lee, K.E. Whitener, J.T. Robinson, P.E. Sheehan, Chemical stability of graphene fluoride produced by exposure to XeF2, Nano Lett. 13 (2013) 4311–4316, https://doi.org/10.1021/nl4021039. [11] S. Joyce, J.G. Langan, J.I. Steinfeld, Reactions of XeF2 with thermally grown SiO2, Surf. Sci. 195 (1988) 270, https://doi.org/10.1016/0039-6028(88)90796-0.
[12] M.L. Miller, R.W. Linton, X-ray photoelectron spectroscopy of thermally treated silica (SiO2) surfaces, Anal. Chem. 57 (12) (1985) 2314–2319, https://doi.org/10.1021/ac00289a033. [13] D.T. Clark, D. Kilcast, D.B. Adams, W.K.R. Musgrave, An, ESCA study of the molecular core binding energies of the fluorobenzenes, J. Electron Spectrosc. Relat. Phenom 1 (1972) 232, https://doi.org/10.1016/0368-2048(72)85013-8. [14] J.F. Veyan, M. Halls, S. Rangan, D. Aureau, X.M. Yan, Y.J. Chabal, XeF2-induced removal of SiO2 near Si surfaces at 300 K: an unexpected proximity effect 114914 Appl. Phys. 108 (2010), https://doi.org/10.1063/1.3517148.