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Mechanically polished copper surfaces modified with n-dodecanethiol and 3-perfluorooctyl-propanethiol
Colloids and Surfaces A: Physicochemical and Engineering Aspects 198– 200 (2002) 817– 827 www.elsevier.com/locate/colsurfa
Mechanically polished copper surfaces modified with n-dodecanethiol and 3-perfluorooctyl-propanethiol F. Laffineur a, J. Delhalle a, S. Guittard b, S. Ge´ribaldi b, Z. Mekhalif a,* a
Laboratoire Interdisciplinaire de Spectroscopie Electronique, Faculte´s Uni6ersitaires Notre-Dame de la Paix, Rue de Bruxelles, 61, B-5000 Namur, Belgium b Chimie des Mate´riaux Organiques et Me´talliques, Faculte´ des Sciences, Uni6ersite´ de Nice, Sophia-Antipolis, Parc Valrose 06108 Nice Cedex 2, France Received 30 August 2000; accepted 11 April 2001
Abstract Mechanically polished copper substrates modified with ethanolic solutions (10 − 3 and 10 − 2 M) of n-dodecanethiol and 3-perfluorooctyl-propanethiol have been evaluated by X-ray photoelectron spectroscopy, contact angles and cyclic voltammetry measurements. In spite of the fact that ethanol is not necessarily the best solvent, our results show that it is possible to graft highly perfluorinated alkanethiols as well as alkanethiols on copper substrates. © 2002 Published by Elsevier Science B.V. Keywords: Polished copper; n-dodecanethiol; 3-perfluorooctyl-propanethiol; X-ray photoelectron spectroscopy; Cyclic voltammetry
1. Introduction Copper, third after iron and aluminium in the world production, is a reddish coloured metal, malleable, ductile, having excellent thermal and electrical conductivities, and good corrosion resistance. This combination of properties make copper and its alloys materials of choice in many applications, some of which requiring the development of coatings and/or primers for efficient uses. Illustrations range from enhancing and con* Corresponding author. Tel.: + 32-81-72-5230; fax: + 3281-72-4530. E-mail address: [email protected] (Z. Mekhalif).
trolling the adhesion properties between rubber compounds and brass-plated steel cords reinforcing tire belts [1] to elaborating new thin films to protect against aqueous and atmospheric corrosion copper that is increasingly used as highly conductive interconnect in integrated circuits. In the latter case, for example, the initial work on self-assembly of organothiols on Cu by Whitesides et al. [2] has prompted a number of investigations on the use of organomercaptans as barriers towards corrosion ([3–15] and works cited therein). These investigations mainly encompass corrosion protection of Cu substrates (evaporated, electrodeposited, bulk) by n-alkanethiols (with CH3 or OH terminating groups) as such or further modified.
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In this work we report on our first attempts to modify surfaces of bulk copper with 3-perfluorooctyl-propanethiol, a highly fluorinated alkanethiol, with the future purpose of using such type of Self-assembled monolayers (SAMs) as adhesion primers between copper and fluorinated polymer matrices. In their recent study on ways to obtain reproducible oleophobic as well as hydrophobic surfaces by self-assembling of n-alkanethiols under ambient conditions on evaporated Cu surfaces [16], Rubinstein et al. have concluded that the effect of the solvent is more critical than surface oxidation. However, to achieve good quality self-assembled monolayers the concentration of the mercaptan was also found to play an important role. Ethanol, the most commonly used solvent for SAMs of organothiols, has been shown in their study to have a negative effect on the monolayer because of its chemical reactivity toward copper. It was also found that adsorption from concentrated alkanethiol solutions in toluene onto Cu surfaces with a thin layer of Cu2O leads to high-quality monolayers. In their recent woks on the protective properties of SAMs monolayers of alkanethiols on Cu, Jennings et al. [6,7] also resort to non-reactive solvents such as isooctane, anhydrous tetrahydrofurane and hexadecane. In our case, however, we are facing the conflicting situation where 3-perfluorooctylpropanethiol is not readily soluble in the purely hydrocarbon solvents, on the one hand, and working in ambient conditions probably makes ineffective the use of anhydrous tetrahydrofurane. Furthermore we aim at modifying bulk copper which, as received, is oxidised and contaminated. Hence these substrates require proper cleaning conditions prior to any attempt at their modification by organothiols. With all of the above in mind, we have chosen in this first attempt to follow a somewhat classical approach, which from a practical point of view is also simple. Bulk copper is first mechanically polished, then cleaned by exposure to UV/ozone, with or without immersion in ethanol, and finally modified with the organothiol in ethanol solution. XPS, contact angles and cyclic voltammetry measurements are used to assess the film quality.
2. Experimental
2.1. Substrates characterisations Photoelectron spectra of the substrates were recorded at a 35° take-off angle relative to the substrate with a SSX-100 (Surface Science Instrument) spectrometer using a monochromatised Xray AlKa radiation (1486.6 eV). Nominal resolution was measured as full width at half maximum of 1.0 (core-level spectrum) to 1.5 (survey spectrum) eV. The analysed core level lines were calibrated against the C1s binding energy set at 285 eV and characteristic of the alkyl moiety of the organothiols. In the case of the S2p core level the spectral decomposition takes into account the doublet structure of the level with a spacing of 1.1 eV and a theoretical intensity ratio (S2p3/2/S2p1/2) of 2. The signals were deconvoluted using mixed Gaussian– Lorentzian curves where the Gaussian character was set at 80%. Peak positions obtained after deconvolution are essentially constant (9 0.3 eV) and typical of those found in the literature for corresponding atomic environments [17–19]. Since the Cu2p line is rather insensitive to the oxidation state of copper (Cu2p3/2 component at: 932.6, 932.5, 933.7, 932.5, 932.2 eV for Cu, Cu2O, CuO, Cu2S and CuS, respectively), it is important to follow the energy position of the L3M45M45 Auger line of Cu (568, 570.4, 568.5, 569.2 and 568.7 eV for Cu, Cu2O, CuO, Cu2S and CuS, respectively) [15,16]. Contact angles (qw) were measured by using a VCA 2000 contact angle meter on 10 − 6 dm3 water drops that were allowed to equilibrate in air and at room temperature. Cyclic voltammetry curves were obtained with a PAR 273A potentiostat on the bare and modified substrates using a platinum counter as electrode and a saturated calomel electrode (SCE) as reference electrode. Cyclic voltammetry measurements, useful to assess the blocking of the chemisorbed layers, were carried out in aerated 0.1 M NaOH aqueous solutions at a sweep rate of 20 mV s − 1 for a potential ranging from −1.0 to + 0.4 V per SCE.
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2.2. Substrate preparation and modification The substrates are rectangular-shaped (20× 10 mm) 1 mm thick coupons of polycrystalline copper (Goodfellow, 99.99%, CU000748). Solvents and reagents are used without further purification: n-dodecanethiol (Acros, 99.2%, 11762.5000), ultra pure water (18 MV cm) and absolute ethanol p.a. (Merck, 99.8+%, 300403). 3-perfluorooctylpropanethiol has been prepared at Nice University using 3-perfluorooctyl-propanoic acid as starting material converted into 3-perfluorooctylpropanol and then into the thiol. All Cu coupons were mechanically polished on a Buehler–Phoenix 4000 instrument down to 1 mm using different grit diamond pastes and colloidal silica (0.5 mm). At the end of the polishing steps all substrates were treated with UV-ozone for 15 min (Jelight 42-220), these substrates will be denoted CuUVO. The CuUVO substrates that have been sonicated in absolute ethanol for 30 min will be referred to as CuEtOH. At the end of their preparation, the CuUVO and CuEtOH substrates are directly reacted for 2 h in n-dodecanethiol and 3-perfluorooctyl-propanethiol solutions (10 − 2 and 10 − 3 M) in ethanol. The time during which the substrates are exposed to ambient atmosphere before immersion in the mercaptan solution is approximately 10 s for all substrates, respectively. After reaction, all modified substrates were copiously rinsed with ethanol for 3 min to remove physisorbed molecules. Finally, the samples were dried under an argon flow and used immediately for characterisation.
3. Results and discussion This section is organised in three parts. In view of the negative conclusions by Rubinstein et al. [16] on using ethanolic solutions to modify copper evaporated surfaces with n-dodecanethiol, the chemical state of the interface copper/n-dodecanethiol obtained for both CuUVO and CuEtOH substrates is studied first. Second, results on the modification of CuEtOH substrates with 3-perfluorooctyl-propanethiol are reported. Finally,
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electrochemical measurements on CuEtOH modified with n-dodecanethiol and 3-perfluorooctyl-propanethiol (10 − 3 and 10 − 2 M) are compared.
3.1. Comparison of the modification of CuUVO and CuEtOH with n-dodecanethiol (10 − 2 M). We begin with an analysis of the surface chemical state of the CuUVO and CuEtOH substrates prior to their modification. For the sake of completeness, the results on the polished copper coupons (denoted Cupol), i.e. prior to the UV-ozone treatment, are also provided. Fig. 1 shows the XPS survey spectrum of a typical CuEtOH substrate as well as enlarged windows on the Cu2p3/2 and CuLMM lines. As expected, an intense Cu2p line is present (Cu2p3/2 and Cu2p1/2 at 933.5 and 952.5 eV, respectively), it corresponds to the underlying copper substrate. Also of significant intensity are the C1s (285 eV) and O1s (532 eV) levels corresponding to carbon contaminants and oxidised species (carbon, copper), respectively. Between 560 and 580 eV arise features characteristic of the CuL3M45M45 and CuL3M45M45 lines. Peaks at 123 and 75 eV correspond to Cu3s and Cu3p levels. No detectable traces of contaminants originating from the polishing materials such as silicon could be found in the three types of substrates (Cupol, CuUVO and CuEtOH) for which essentially the same spectral features are noted, but with slightly varying elemental relative abundance. Fig. 2(a–c) give a detailed view of the C1s line for the three types of substrate. The C1s line of Cupol and CuUVO (Fig. 2(a and b)) are qualitatively similar with a main peak at 285 eV, characteristic of aliphatic carbons due to adsorbed carbon contaminants, and another one at 289 eV typical of oxidised carbon species of the type C6 OOC and CC6 OC [18,19]. UV-ozone irradiation contributes to remove the original carbonaceous contaminants, but due to reexposure to ambient atmosphere the substrates have been contaminated again and it is observed that the activation has lead to increase the amount of oxidised carbon species. Sonication in ethanol of the CuUVO substrates does not lower the amount of C6 OOC and CC6 OC, but con-
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tributes to add a component at 286.2 eV (Fig. 2(c)) typical of alkoxy functions (C6 OC [18]), which could be due to the formation of stable ethoxy intermediates chemically bound to Cu [16,20–23]. The substrates Cupol, CuUVO and CuEtOH exhibit the characteristics of a thick CuO layer owing to the presence of the Cu2p3/2 and CuLMMM peaks at 933.5 and 568.5 eV in conjunction with intense shake-up features around 938–
945 eV. It is not obvious to infer from these data if some photoelectrons originate from metallic copper. The CuLMM lines of Cu (568 eV) and CuO (568.5 eV) are to close to be discriminated. Cu2O does not seem to be present since its characteristic features (Cu2p3/2 at 932.5 eV and CuLMM at 570.4 eV) are not detected. From this brief analysis, it is realistic to assume that the modification of the copper substrates by n-dodecanthiol will occur on
Fig. 1. XPS survey spectrum of a bare CuEtOH substrate and detailed views on the Cu2p and CuLMM lines.
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Fig. 2. XPS C1s level of bare (a) Cupol, (b) CuUVO and (c) CuEtOH substrates.
CuO layers mainly contaminated by atmospheric carbon pollutants in the case of CuUVO, but also modified by anchored ethoxy molecules in the case of CuEtOH. The XPS survey spectra of the CuUVO and CuEtOH substrates modified with the n-dodecanethiol (10 − 2 M in ethanol) are shown in Fig. 3(a and b), respectively. As expected, the intense Cu2p line is still present, but compared with Fig. 1, the O1s level (centred at 532 eV) has significantly decreased in intensity, while that of C1s (285 eV) has increased and a S2p line is now detected in the spectra. In the sequel we concentrate our attention on the informative spectral characteristics of the CuUVO and CuEtOH substrates modified with n-dodecanethiol, i.e. the C1s, S2p, Cu2p3/2 and CuLMM lines shown in Fig. 4(a– d), respectively. The C1s spectrum of CuUVO and CuEtOH modified substrates (Fig. 4(a)) exhibit a main peak at 285 eV characteristic of aliphatic carbons that certainly correspond to the chemisorbed
alkanethiol molecules. Compared with the bare substrates (Fig. 2(a– c)) the C1s lines of the modified surfaces (Fig. 4(a)) appear free of oxidised species suggesting that little contamination is left and that the ethoxy species bound to the surface have also been displaced by the reducing action of the thiols. Fig. 4(b) shows the S2p level for n-dodecanethiol chemisorbed on CuUVO and CuEtOH. According to literature data [24–26], binding energies 162, 164, 167 and 169 eV at the maximum of the S2p3/2 component are generally assigned to thiolates (CuS6 ), unbound thiols (S6 H), sulfi− nates (S6 O− 2 ) and sulfonates (S6 O3 ), respectively. For both types of substrates, the S2p signal is narrow with the S2p3/2 component centred at 162.4 eV and the intensity ratio between the S2p3/ 2 and S2p1/2 components being close to the theoretical value of 2. All of this supports the idea that essentially thiolates species are present at the copper/organothiol interface.
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Information on the copper chemical state is also useful to reach additional consistency to this picture. There is a striking difference between the bare CuUVO and CuEtOH substrates (Fig. 1) and the modified ones (Fig. 4(c and d)). The Cu2p3/2 component of the modified substrates arises at 932.5 eV and there is no sign of the shake-up features around 938– 945 eV, which within the detection limits of the XPS technique indicates the absence of CuII. This is corroborated with the shift of the CuLMM line towards 569.7 eV typical of Cu2S. Note, however, that part of the intensity under the Cu2p3/2 and CuLMM peaks in Fig. 4 could also be assigned to Cu2O. Indeed, oxygen is still present in Fig. 3(a) and (b) and it does not seem to be related to neither oxidised carbon nor sulphur species (Fig. 4(a and b)). It is thus conceivable that the ‘removal effect’ of the CuII species by the reducing thiols [27,28] was not
Fig. 3. XPS survey spectra of (a) CuUVO and (b) CuEtOH substrates modified with n-dodecanethiol (10 − 2 M in ethanol, 2 h).
complete and that islands of partially reduced copper (e.g. Cu2O) exist on the surface in analogy with the reported fact that CuII species react with Me2S to give CuI compounds [29]. Noting that the ratio between S2p3/2 and S2p1/2 components and the shape of the carbon C1s sign slightly better modification of CuETOH substrates than the CuUVO ones, accordingly CuETOH was selected for our attempts to chemisorb 3perfluorooctyl-propanethiol.
3.2. Modification CuEtOH with 3 -perfluorooctyl-propanethiol (10 − 2 and 10 − 3 M) The XPS survey spectra of CuEtOH substrates modified with 3-perfluorooctylpropanethiol 10 − 3 and 10 − 2 M in ethanol are shown in Fig. 5(a and b), respectively. In addition to the features previously observed in the case of the modifications by n-dodecanethiol, the F1s signal is clearly observed in these spectra. Fig. 6(a) show the C1s line of CuEtOH modified with 3-perfluorooctyl-propanethiol in ethanol, 10 − 3 and 10 − 2 M. The peak at 285 eV corresponds to carbons bearing hydrogen atoms. The shoulder on the high energy side of this peak, around 285.7 eV, corresponds to the C1s levels of the methylene group directly connected to the perfluorinated carbon sequence, CF3(CF2)7 C6 H2(CH2)2SH. The observed intensity ratio between these two types of methylene groups is close to 2, i.e. in good agreement with the theoretical value. At 290.5, 291.5 and 293.6 eV are found C1s levels typical of CF2C6 F2CH2, CF2C6 F2 CF2 and C6 F3CF2 groups, respectively. The intensity ratio of the C1s levels, C6 F2/C6 F3, is close to the theoretical ratio of 7 and supports the idea that the highly fluorinated organothiols present on the surface have kept their integrity. The shape of the S2p levels (Fig. 6(b)) is very close to ideal with the S2p3/2 component at 162 eV and a ratio between S2p3/2 and S2p1/2 components nearly equal to 2. Similarly the Cu2p and CuLMM lines (Fig. 6(c and d)) are of a quality comparable to that found previously in the case of n-dodecanethiol. The XPS spectroscopy measurements reveal almost no difference upon concentration increase in the 3-perfluorooctyl-propanethiol.
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Fig. 4. XPS C1s, S2p, Cu2p and CuLMM levels of a CuUVO and CuEtOH substrates modified with n-dodecanethiol (10 − 2 M in ethanol, 2 h).
It thus appears that grafting 3-perfluorooctylpropanethiol from ethanolic solutions (10 − 3 and 10 − 2 M) onto mechanically polished bulk copper pretreated with UV-ozone and sonicated in
ethanol leads to films of spectroscopically good quality. In the sequel we further assess the quality of the films by cyclic voltammetry measurements.
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3.3. Electrochemical assessment of CuEtOH modified with n-dodecanethiol and 3 -perfluorooctyl-propanethiol The measured contact angles, listed in Table 1, compare well with literature data on similar compounds self-assembled on gold. Fig. 7 shows the cyclic voltammograms obtained on a bare CuEtOH substrate chosen as reference, and the corresponding curves for CuEtOH substrates modified with n-dodecanethiol and 3perfluorooctyl-propanethiol, respectively. The mercaptan concentration of the reacting solution was 10 − 2 M in ethanol for both molecules. For the unmodified electrode two anodic peaks and two corresponding cathodic peaks (RedI, RedII) are observed. The oxidation peaks (OxI, OxII) are related to the electrochemical formation of Cu2O and CuO, respectively. Cathodic peaks represent
Fig. 5. XPS survey spectrum of CuEtOH substrates modified with 3-perfluorooctyl-propanethiol (a) 10 − 3 M and (b) 10 − 2 M in ethanol (2 h each).
the reduction of these two type of oxide, Cu2O for RedI and CuO for RedII which are formed on the surface electrode before and during the anodic cycling. The corresponding reactions are summarised below: 2 Cu + 2 OH− Cu2O + H2O + 2 e− OxI ( − 368.5 mV) Cu2O + 2 OH− 2 CuO + H2O + 2 e − Ox
II
( − 151.5 mV)
2 CuO + H2O + 2 e− Cu2O + 2 OH− Red
II
( − 523.2 mV)
Cu2O + H2O + 2 e− 2 Cu +2 OH− Red
I
( − 914 mV)
The modification of the surface with n-dodecanethiol decreases significantly the surface oxidation. The intensity of the anodic peaks are very close to zero while the cathodic peaks still exist but with very low intensity compared with the bare electrode. This could be the reduction of the oxide in monolayer defects. The 3-perfluorooctylpropanethiol monolayer induces less protection effect than n-dodecanethiol. It is therefore worth noticing that the electrochemical experiments reveal a much greater difference n-dodecanethiol and 3-perfluorooctyl-propanethiol films than XPS results do. The highly fluorinated mercaptan turns out to be much less blocking than the alkanethiol, while both have essentially similar backbone lengths. This is certainly related to the fact that in n-dodecanethiol the longer sequence of methylene moieties is more prone to form a dense and organised molecular films. This effect of the film organisation and crystallinity on the protective properties of self-assembled monolayers of alkanethiols on copper has been well illustrated in a recent paper [7]. Table 1 summarises the blocking factors of the CuEtOH surface modified with n-dodecanethiol and 3-perfluorooctyl-propanethiol in ethanolic solution with two different concentration (10 − 2 and 10 − 3 M). These data clearly evidence the fact, at least for the alkanethiol, that higher concentration allows the
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Fig. 6. XPS C1s, S2p, Cu2p and CuLMM levels of a CuEtOH substrate modified with 3-perfluorooctyl-propanethiol (10 − 3 and 10 − 2 M in ethanol, 2 h).
formation of better covering monolayer, which correlates with the XPS results and the literature data [16]. The measured contact angles, listed in Table 1, compare well with literature data on similar compounds self-assembled on gold.
4. Conclusion In this study, it has been shown that mechanically polished bulk copper substrates CuEtOH, i.e. pretreated with UV-ozone and sonicated in ethanol, can be successfully modified with ethanolic
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Table 1 Water contact angles and blocking factors measured for CuEtOH substrates modified with n-dodecanethiol and 3-perfluorooctylpropanethiol (10−3 and 10−2 M in ethanol) Molecule
n-dodecanethiol C12
Concentration Blocking factor Contact angle
10−3 M 66% 110°
3-perfluorooctyl-propanethiol F8C3 10−2 M 87% 111°
10−3 M 40% 117°
10−2 M 47% 116°
of using other solvents (diethylether, dichloromethane, etc.) on the relative efficiency in film forming and the quality of the final coating. Second, ageing studies in conjunction with electrochemical impedance spectroscopy will be necessary to assess the resistance of the films against the transport of aqueous ions to the copper surface. Finally, we plan to compare the merits of a series of mercaptans RF –RH –SH characterised by a fixed carbon backbone length but having variable RF and RH moieties. Acknowledgements The work is supported in part by the Belgian Interuniversity Research Program on Reduced Dimensionality Systems (PAI/IUAP 4/10). References
Fig. 7. Cyclovoltammograms for a bare CuEtOH substrate (dotted line) taken as reference, modified with n-dodecanethiol (10 − 2 M in ethanol, 2 h) (dashed line) and modified with 3-perfluorooctyyl-propanethiol (10 − 2 M in ethanol, 2 h) (solid line).
solutions of n-dodecanethiol and 3-perfluorooctylpropanethiol (10 − 3 and 10 − 2 M). We expect that the films prepared in this way will be of sufficient quality for the purpose of using them as specific adhesion primers between copper and fluorinated organic coatings. However, the present results call for the following improvements and additional investigations. First, in view of the work by Rubinstein et al. [16], it would certainly be interesting to study the effect
[1] G.S. Jeon, M.H. Han, G. Seon, J. Adhesion Sci. Technol. 13 (1999) 153. [2] P.E. Laibinis, G.M. Whitesides, D.L. Allara, Y.-T. tao, A.N. Parikh, R.G. Nuzzo, J. Am. Chem. Soc. 113 (1991) 7152. [3] T.P. Moffat, F.-R.F. Fang, A. Bard, J. Electrochem. Soc. 138 (1991) 3224. [4] P.E. Laibinis, G.M. Whitesides, J. Am. Chem. Soc. 114 (1992) 1990. [5] P.E. Laibinis, G.M. Whitesides, J. Am. Chem. Soc. 114 (1992) 9022. [6] G.K. Jennings, J.C. Munro, T.-H. Yong, P.E. Laibinis, Langmuir 14 (1998) 6130. [7] G.K. Jennings, J.C. Munro, P.E. Laibinis, Adv. Mat. 11 (1999) 1000. [8] Y. Feng, W.-K. Teo, K.-S. Siow, Z. Gao, K.-L. Tan, A.-K. Hseih, J. Electrochem. Soc. 144 (1997) 55. [9] F.P. Zamborini, J.K. Campbell, R.M. Crooks, Langmuir 14 (1998) 640. [10] K. Aramaki, M. Yamada, H. Nishihara, J. Electrochem. Soc. 138 (1991) 3389.
F. Laffineur et al. / Colloids and Surfaces A: Physicochem. Eng. Aspects 198–200 (2002) 817–827 [11] Y. Yamamoto, H. Nishihara, K. Aramaki, J. Electrochem. Soc. 140 (1993) 437. [12] M. Itoh, H. Nishihara, K. Aramaki, J. Electrochem. Soc. 141 (1994) 2018. [13] M. Itoh, H. Nishihara, K. Aramaki, J. Electrochem. Soc. 142 (1995) 1839. [14] R. Haneda, H. Nishihara, K. Aramaki, J. Electrochem. Soc. 144 (1997) 1215. [15] R. Haneda, K. Aramaki, J. Electrochem. Soc. 145 (1998) 1856. [16] H. Ron, H. Cohen, S. Matlis, M. Rappaport, I. Rubinstein, J. Phys. Chem. B 102 (1998) 9861. [17] J.F. Moulder, W.F. Stickle, P.E. Sobol, K.D. Bomben, Handbook of X-ray Photoelectron Spectroscopy, Perkin– Elmer Corp, Eden Prairie, 1992. [18] G. Beamson, D. Briggs, High Resolution XPS of Organic Polymers. The Scienta ESCA A300 Database, Wiley, Chichester, 1992.
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[19] D. Briggs, M.P. Seah (Eds.), Practical Surface Analysis, Wiley, Chichester, 1983. [20] M. Bowker, R. Madix, Surf. Sci. 95 (1980) 190. [21] M. Bowker, R. Madix, Surf. Sci. 116 (1982) 549. [22] B.A. Sexton, Surf. Sci. 88 (1979) 299. [23] B.A. Sexton, A.E. Hughes, Surf. Sci. 140 (1984) 227. [24] M. Stratmann, H. Viefhaus, Surf. Interf. Anal. 16 (1990) 278. [25] M. Volmer-Uebing, M. Stratmann, Appl. Surf. Sci. 55 (1992) 19. [26] D.G. Castner, K. Hinds, D.W. Grainger, Langmuir 12 (1996) 5083. [27] T.J. Wallace, J. Org. Chem. 31 (1996) 1217. [28] H. Keller, P. Simak, W. Schrepp, Thin Solid Films 244 (1994) 799. [29] F.A. Cotton, G. Wilkinson, Advanced Inorganic Chemistry, Wiley, New York, 1972.
Mechanically polished copper surfaces modified with n-dodecanethiol and 3-perfluorooctyl-propanethiol F. Laffineur a, J. Delhalle a, S. Guittard b, S. Ge´ribaldi b, Z. Mekhalif a,* a
Laboratoire Interdisciplinaire de Spectroscopie Electronique, Faculte´s Uni6ersitaires Notre-Dame de la Paix, Rue de Bruxelles, 61, B-5000 Namur, Belgium b Chimie des Mate´riaux Organiques et Me´talliques, Faculte´ des Sciences, Uni6ersite´ de Nice, Sophia-Antipolis, Parc Valrose 06108 Nice Cedex 2, France Received 30 August 2000; accepted 11 April 2001
Abstract Mechanically polished copper substrates modified with ethanolic solutions (10 − 3 and 10 − 2 M) of n-dodecanethiol and 3-perfluorooctyl-propanethiol have been evaluated by X-ray photoelectron spectroscopy, contact angles and cyclic voltammetry measurements. In spite of the fact that ethanol is not necessarily the best solvent, our results show that it is possible to graft highly perfluorinated alkanethiols as well as alkanethiols on copper substrates. © 2002 Published by Elsevier Science B.V. Keywords: Polished copper; n-dodecanethiol; 3-perfluorooctyl-propanethiol; X-ray photoelectron spectroscopy; Cyclic voltammetry
1. Introduction Copper, third after iron and aluminium in the world production, is a reddish coloured metal, malleable, ductile, having excellent thermal and electrical conductivities, and good corrosion resistance. This combination of properties make copper and its alloys materials of choice in many applications, some of which requiring the development of coatings and/or primers for efficient uses. Illustrations range from enhancing and con* Corresponding author. Tel.: + 32-81-72-5230; fax: + 3281-72-4530. E-mail address: [email protected] (Z. Mekhalif).
trolling the adhesion properties between rubber compounds and brass-plated steel cords reinforcing tire belts [1] to elaborating new thin films to protect against aqueous and atmospheric corrosion copper that is increasingly used as highly conductive interconnect in integrated circuits. In the latter case, for example, the initial work on self-assembly of organothiols on Cu by Whitesides et al. [2] has prompted a number of investigations on the use of organomercaptans as barriers towards corrosion ([3–15] and works cited therein). These investigations mainly encompass corrosion protection of Cu substrates (evaporated, electrodeposited, bulk) by n-alkanethiols (with CH3 or OH terminating groups) as such or further modified.
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In this work we report on our first attempts to modify surfaces of bulk copper with 3-perfluorooctyl-propanethiol, a highly fluorinated alkanethiol, with the future purpose of using such type of Self-assembled monolayers (SAMs) as adhesion primers between copper and fluorinated polymer matrices. In their recent study on ways to obtain reproducible oleophobic as well as hydrophobic surfaces by self-assembling of n-alkanethiols under ambient conditions on evaporated Cu surfaces [16], Rubinstein et al. have concluded that the effect of the solvent is more critical than surface oxidation. However, to achieve good quality self-assembled monolayers the concentration of the mercaptan was also found to play an important role. Ethanol, the most commonly used solvent for SAMs of organothiols, has been shown in their study to have a negative effect on the monolayer because of its chemical reactivity toward copper. It was also found that adsorption from concentrated alkanethiol solutions in toluene onto Cu surfaces with a thin layer of Cu2O leads to high-quality monolayers. In their recent woks on the protective properties of SAMs monolayers of alkanethiols on Cu, Jennings et al. [6,7] also resort to non-reactive solvents such as isooctane, anhydrous tetrahydrofurane and hexadecane. In our case, however, we are facing the conflicting situation where 3-perfluorooctylpropanethiol is not readily soluble in the purely hydrocarbon solvents, on the one hand, and working in ambient conditions probably makes ineffective the use of anhydrous tetrahydrofurane. Furthermore we aim at modifying bulk copper which, as received, is oxidised and contaminated. Hence these substrates require proper cleaning conditions prior to any attempt at their modification by organothiols. With all of the above in mind, we have chosen in this first attempt to follow a somewhat classical approach, which from a practical point of view is also simple. Bulk copper is first mechanically polished, then cleaned by exposure to UV/ozone, with or without immersion in ethanol, and finally modified with the organothiol in ethanol solution. XPS, contact angles and cyclic voltammetry measurements are used to assess the film quality.
2. Experimental
2.1. Substrates characterisations Photoelectron spectra of the substrates were recorded at a 35° take-off angle relative to the substrate with a SSX-100 (Surface Science Instrument) spectrometer using a monochromatised Xray AlKa radiation (1486.6 eV). Nominal resolution was measured as full width at half maximum of 1.0 (core-level spectrum) to 1.5 (survey spectrum) eV. The analysed core level lines were calibrated against the C1s binding energy set at 285 eV and characteristic of the alkyl moiety of the organothiols. In the case of the S2p core level the spectral decomposition takes into account the doublet structure of the level with a spacing of 1.1 eV and a theoretical intensity ratio (S2p3/2/S2p1/2) of 2. The signals were deconvoluted using mixed Gaussian– Lorentzian curves where the Gaussian character was set at 80%. Peak positions obtained after deconvolution are essentially constant (9 0.3 eV) and typical of those found in the literature for corresponding atomic environments [17–19]. Since the Cu2p line is rather insensitive to the oxidation state of copper (Cu2p3/2 component at: 932.6, 932.5, 933.7, 932.5, 932.2 eV for Cu, Cu2O, CuO, Cu2S and CuS, respectively), it is important to follow the energy position of the L3M45M45 Auger line of Cu (568, 570.4, 568.5, 569.2 and 568.7 eV for Cu, Cu2O, CuO, Cu2S and CuS, respectively) [15,16]. Contact angles (qw) were measured by using a VCA 2000 contact angle meter on 10 − 6 dm3 water drops that were allowed to equilibrate in air and at room temperature. Cyclic voltammetry curves were obtained with a PAR 273A potentiostat on the bare and modified substrates using a platinum counter as electrode and a saturated calomel electrode (SCE) as reference electrode. Cyclic voltammetry measurements, useful to assess the blocking of the chemisorbed layers, were carried out in aerated 0.1 M NaOH aqueous solutions at a sweep rate of 20 mV s − 1 for a potential ranging from −1.0 to + 0.4 V per SCE.
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2.2. Substrate preparation and modification The substrates are rectangular-shaped (20× 10 mm) 1 mm thick coupons of polycrystalline copper (Goodfellow, 99.99%, CU000748). Solvents and reagents are used without further purification: n-dodecanethiol (Acros, 99.2%, 11762.5000), ultra pure water (18 MV cm) and absolute ethanol p.a. (Merck, 99.8+%, 300403). 3-perfluorooctylpropanethiol has been prepared at Nice University using 3-perfluorooctyl-propanoic acid as starting material converted into 3-perfluorooctylpropanol and then into the thiol. All Cu coupons were mechanically polished on a Buehler–Phoenix 4000 instrument down to 1 mm using different grit diamond pastes and colloidal silica (0.5 mm). At the end of the polishing steps all substrates were treated with UV-ozone for 15 min (Jelight 42-220), these substrates will be denoted CuUVO. The CuUVO substrates that have been sonicated in absolute ethanol for 30 min will be referred to as CuEtOH. At the end of their preparation, the CuUVO and CuEtOH substrates are directly reacted for 2 h in n-dodecanethiol and 3-perfluorooctyl-propanethiol solutions (10 − 2 and 10 − 3 M) in ethanol. The time during which the substrates are exposed to ambient atmosphere before immersion in the mercaptan solution is approximately 10 s for all substrates, respectively. After reaction, all modified substrates were copiously rinsed with ethanol for 3 min to remove physisorbed molecules. Finally, the samples were dried under an argon flow and used immediately for characterisation.
3. Results and discussion This section is organised in three parts. In view of the negative conclusions by Rubinstein et al. [16] on using ethanolic solutions to modify copper evaporated surfaces with n-dodecanethiol, the chemical state of the interface copper/n-dodecanethiol obtained for both CuUVO and CuEtOH substrates is studied first. Second, results on the modification of CuEtOH substrates with 3-perfluorooctyl-propanethiol are reported. Finally,
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electrochemical measurements on CuEtOH modified with n-dodecanethiol and 3-perfluorooctyl-propanethiol (10 − 3 and 10 − 2 M) are compared.
3.1. Comparison of the modification of CuUVO and CuEtOH with n-dodecanethiol (10 − 2 M). We begin with an analysis of the surface chemical state of the CuUVO and CuEtOH substrates prior to their modification. For the sake of completeness, the results on the polished copper coupons (denoted Cupol), i.e. prior to the UV-ozone treatment, are also provided. Fig. 1 shows the XPS survey spectrum of a typical CuEtOH substrate as well as enlarged windows on the Cu2p3/2 and CuLMM lines. As expected, an intense Cu2p line is present (Cu2p3/2 and Cu2p1/2 at 933.5 and 952.5 eV, respectively), it corresponds to the underlying copper substrate. Also of significant intensity are the C1s (285 eV) and O1s (532 eV) levels corresponding to carbon contaminants and oxidised species (carbon, copper), respectively. Between 560 and 580 eV arise features characteristic of the CuL3M45M45 and CuL3M45M45 lines. Peaks at 123 and 75 eV correspond to Cu3s and Cu3p levels. No detectable traces of contaminants originating from the polishing materials such as silicon could be found in the three types of substrates (Cupol, CuUVO and CuEtOH) for which essentially the same spectral features are noted, but with slightly varying elemental relative abundance. Fig. 2(a–c) give a detailed view of the C1s line for the three types of substrate. The C1s line of Cupol and CuUVO (Fig. 2(a and b)) are qualitatively similar with a main peak at 285 eV, characteristic of aliphatic carbons due to adsorbed carbon contaminants, and another one at 289 eV typical of oxidised carbon species of the type C6 OOC and CC6 OC [18,19]. UV-ozone irradiation contributes to remove the original carbonaceous contaminants, but due to reexposure to ambient atmosphere the substrates have been contaminated again and it is observed that the activation has lead to increase the amount of oxidised carbon species. Sonication in ethanol of the CuUVO substrates does not lower the amount of C6 OOC and CC6 OC, but con-
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tributes to add a component at 286.2 eV (Fig. 2(c)) typical of alkoxy functions (C6 OC [18]), which could be due to the formation of stable ethoxy intermediates chemically bound to Cu [16,20–23]. The substrates Cupol, CuUVO and CuEtOH exhibit the characteristics of a thick CuO layer owing to the presence of the Cu2p3/2 and CuLMMM peaks at 933.5 and 568.5 eV in conjunction with intense shake-up features around 938–
945 eV. It is not obvious to infer from these data if some photoelectrons originate from metallic copper. The CuLMM lines of Cu (568 eV) and CuO (568.5 eV) are to close to be discriminated. Cu2O does not seem to be present since its characteristic features (Cu2p3/2 at 932.5 eV and CuLMM at 570.4 eV) are not detected. From this brief analysis, it is realistic to assume that the modification of the copper substrates by n-dodecanthiol will occur on
Fig. 1. XPS survey spectrum of a bare CuEtOH substrate and detailed views on the Cu2p and CuLMM lines.
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Fig. 2. XPS C1s level of bare (a) Cupol, (b) CuUVO and (c) CuEtOH substrates.
CuO layers mainly contaminated by atmospheric carbon pollutants in the case of CuUVO, but also modified by anchored ethoxy molecules in the case of CuEtOH. The XPS survey spectra of the CuUVO and CuEtOH substrates modified with the n-dodecanethiol (10 − 2 M in ethanol) are shown in Fig. 3(a and b), respectively. As expected, the intense Cu2p line is still present, but compared with Fig. 1, the O1s level (centred at 532 eV) has significantly decreased in intensity, while that of C1s (285 eV) has increased and a S2p line is now detected in the spectra. In the sequel we concentrate our attention on the informative spectral characteristics of the CuUVO and CuEtOH substrates modified with n-dodecanethiol, i.e. the C1s, S2p, Cu2p3/2 and CuLMM lines shown in Fig. 4(a– d), respectively. The C1s spectrum of CuUVO and CuEtOH modified substrates (Fig. 4(a)) exhibit a main peak at 285 eV characteristic of aliphatic carbons that certainly correspond to the chemisorbed
alkanethiol molecules. Compared with the bare substrates (Fig. 2(a– c)) the C1s lines of the modified surfaces (Fig. 4(a)) appear free of oxidised species suggesting that little contamination is left and that the ethoxy species bound to the surface have also been displaced by the reducing action of the thiols. Fig. 4(b) shows the S2p level for n-dodecanethiol chemisorbed on CuUVO and CuEtOH. According to literature data [24–26], binding energies 162, 164, 167 and 169 eV at the maximum of the S2p3/2 component are generally assigned to thiolates (CuS6 ), unbound thiols (S6 H), sulfi− nates (S6 O− 2 ) and sulfonates (S6 O3 ), respectively. For both types of substrates, the S2p signal is narrow with the S2p3/2 component centred at 162.4 eV and the intensity ratio between the S2p3/ 2 and S2p1/2 components being close to the theoretical value of 2. All of this supports the idea that essentially thiolates species are present at the copper/organothiol interface.
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Information on the copper chemical state is also useful to reach additional consistency to this picture. There is a striking difference between the bare CuUVO and CuEtOH substrates (Fig. 1) and the modified ones (Fig. 4(c and d)). The Cu2p3/2 component of the modified substrates arises at 932.5 eV and there is no sign of the shake-up features around 938– 945 eV, which within the detection limits of the XPS technique indicates the absence of CuII. This is corroborated with the shift of the CuLMM line towards 569.7 eV typical of Cu2S. Note, however, that part of the intensity under the Cu2p3/2 and CuLMM peaks in Fig. 4 could also be assigned to Cu2O. Indeed, oxygen is still present in Fig. 3(a) and (b) and it does not seem to be related to neither oxidised carbon nor sulphur species (Fig. 4(a and b)). It is thus conceivable that the ‘removal effect’ of the CuII species by the reducing thiols [27,28] was not
Fig. 3. XPS survey spectra of (a) CuUVO and (b) CuEtOH substrates modified with n-dodecanethiol (10 − 2 M in ethanol, 2 h).
complete and that islands of partially reduced copper (e.g. Cu2O) exist on the surface in analogy with the reported fact that CuII species react with Me2S to give CuI compounds [29]. Noting that the ratio between S2p3/2 and S2p1/2 components and the shape of the carbon C1s sign slightly better modification of CuETOH substrates than the CuUVO ones, accordingly CuETOH was selected for our attempts to chemisorb 3perfluorooctyl-propanethiol.
3.2. Modification CuEtOH with 3 -perfluorooctyl-propanethiol (10 − 2 and 10 − 3 M) The XPS survey spectra of CuEtOH substrates modified with 3-perfluorooctylpropanethiol 10 − 3 and 10 − 2 M in ethanol are shown in Fig. 5(a and b), respectively. In addition to the features previously observed in the case of the modifications by n-dodecanethiol, the F1s signal is clearly observed in these spectra. Fig. 6(a) show the C1s line of CuEtOH modified with 3-perfluorooctyl-propanethiol in ethanol, 10 − 3 and 10 − 2 M. The peak at 285 eV corresponds to carbons bearing hydrogen atoms. The shoulder on the high energy side of this peak, around 285.7 eV, corresponds to the C1s levels of the methylene group directly connected to the perfluorinated carbon sequence, CF3(CF2)7 C6 H2(CH2)2SH. The observed intensity ratio between these two types of methylene groups is close to 2, i.e. in good agreement with the theoretical value. At 290.5, 291.5 and 293.6 eV are found C1s levels typical of CF2C6 F2CH2, CF2C6 F2 CF2 and C6 F3CF2 groups, respectively. The intensity ratio of the C1s levels, C6 F2/C6 F3, is close to the theoretical ratio of 7 and supports the idea that the highly fluorinated organothiols present on the surface have kept their integrity. The shape of the S2p levels (Fig. 6(b)) is very close to ideal with the S2p3/2 component at 162 eV and a ratio between S2p3/2 and S2p1/2 components nearly equal to 2. Similarly the Cu2p and CuLMM lines (Fig. 6(c and d)) are of a quality comparable to that found previously in the case of n-dodecanethiol. The XPS spectroscopy measurements reveal almost no difference upon concentration increase in the 3-perfluorooctyl-propanethiol.
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Fig. 4. XPS C1s, S2p, Cu2p and CuLMM levels of a CuUVO and CuEtOH substrates modified with n-dodecanethiol (10 − 2 M in ethanol, 2 h).
It thus appears that grafting 3-perfluorooctylpropanethiol from ethanolic solutions (10 − 3 and 10 − 2 M) onto mechanically polished bulk copper pretreated with UV-ozone and sonicated in
ethanol leads to films of spectroscopically good quality. In the sequel we further assess the quality of the films by cyclic voltammetry measurements.
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3.3. Electrochemical assessment of CuEtOH modified with n-dodecanethiol and 3 -perfluorooctyl-propanethiol The measured contact angles, listed in Table 1, compare well with literature data on similar compounds self-assembled on gold. Fig. 7 shows the cyclic voltammograms obtained on a bare CuEtOH substrate chosen as reference, and the corresponding curves for CuEtOH substrates modified with n-dodecanethiol and 3perfluorooctyl-propanethiol, respectively. The mercaptan concentration of the reacting solution was 10 − 2 M in ethanol for both molecules. For the unmodified electrode two anodic peaks and two corresponding cathodic peaks (RedI, RedII) are observed. The oxidation peaks (OxI, OxII) are related to the electrochemical formation of Cu2O and CuO, respectively. Cathodic peaks represent
Fig. 5. XPS survey spectrum of CuEtOH substrates modified with 3-perfluorooctyl-propanethiol (a) 10 − 3 M and (b) 10 − 2 M in ethanol (2 h each).
the reduction of these two type of oxide, Cu2O for RedI and CuO for RedII which are formed on the surface electrode before and during the anodic cycling. The corresponding reactions are summarised below: 2 Cu + 2 OH− Cu2O + H2O + 2 e− OxI ( − 368.5 mV) Cu2O + 2 OH− 2 CuO + H2O + 2 e − Ox
II
( − 151.5 mV)
2 CuO + H2O + 2 e− Cu2O + 2 OH− Red
II
( − 523.2 mV)
Cu2O + H2O + 2 e− 2 Cu +2 OH− Red
I
( − 914 mV)
The modification of the surface with n-dodecanethiol decreases significantly the surface oxidation. The intensity of the anodic peaks are very close to zero while the cathodic peaks still exist but with very low intensity compared with the bare electrode. This could be the reduction of the oxide in monolayer defects. The 3-perfluorooctylpropanethiol monolayer induces less protection effect than n-dodecanethiol. It is therefore worth noticing that the electrochemical experiments reveal a much greater difference n-dodecanethiol and 3-perfluorooctyl-propanethiol films than XPS results do. The highly fluorinated mercaptan turns out to be much less blocking than the alkanethiol, while both have essentially similar backbone lengths. This is certainly related to the fact that in n-dodecanethiol the longer sequence of methylene moieties is more prone to form a dense and organised molecular films. This effect of the film organisation and crystallinity on the protective properties of self-assembled monolayers of alkanethiols on copper has been well illustrated in a recent paper [7]. Table 1 summarises the blocking factors of the CuEtOH surface modified with n-dodecanethiol and 3-perfluorooctyl-propanethiol in ethanolic solution with two different concentration (10 − 2 and 10 − 3 M). These data clearly evidence the fact, at least for the alkanethiol, that higher concentration allows the
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Fig. 6. XPS C1s, S2p, Cu2p and CuLMM levels of a CuEtOH substrate modified with 3-perfluorooctyl-propanethiol (10 − 3 and 10 − 2 M in ethanol, 2 h).
formation of better covering monolayer, which correlates with the XPS results and the literature data [16]. The measured contact angles, listed in Table 1, compare well with literature data on similar compounds self-assembled on gold.
4. Conclusion In this study, it has been shown that mechanically polished bulk copper substrates CuEtOH, i.e. pretreated with UV-ozone and sonicated in ethanol, can be successfully modified with ethanolic
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Table 1 Water contact angles and blocking factors measured for CuEtOH substrates modified with n-dodecanethiol and 3-perfluorooctylpropanethiol (10−3 and 10−2 M in ethanol) Molecule
n-dodecanethiol C12
Concentration Blocking factor Contact angle
10−3 M 66% 110°
3-perfluorooctyl-propanethiol F8C3 10−2 M 87% 111°
10−3 M 40% 117°
10−2 M 47% 116°
of using other solvents (diethylether, dichloromethane, etc.) on the relative efficiency in film forming and the quality of the final coating. Second, ageing studies in conjunction with electrochemical impedance spectroscopy will be necessary to assess the resistance of the films against the transport of aqueous ions to the copper surface. Finally, we plan to compare the merits of a series of mercaptans RF –RH –SH characterised by a fixed carbon backbone length but having variable RF and RH moieties. Acknowledgements The work is supported in part by the Belgian Interuniversity Research Program on Reduced Dimensionality Systems (PAI/IUAP 4/10). References
Fig. 7. Cyclovoltammograms for a bare CuEtOH substrate (dotted line) taken as reference, modified with n-dodecanethiol (10 − 2 M in ethanol, 2 h) (dashed line) and modified with 3-perfluorooctyyl-propanethiol (10 − 2 M in ethanol, 2 h) (solid line).
solutions of n-dodecanethiol and 3-perfluorooctylpropanethiol (10 − 3 and 10 − 2 M). We expect that the films prepared in this way will be of sufficient quality for the purpose of using them as specific adhesion primers between copper and fluorinated organic coatings. However, the present results call for the following improvements and additional investigations. First, in view of the work by Rubinstein et al. [16], it would certainly be interesting to study the effect
[1] G.S. Jeon, M.H. Han, G. Seon, J. Adhesion Sci. Technol. 13 (1999) 153. [2] P.E. Laibinis, G.M. Whitesides, D.L. Allara, Y.-T. tao, A.N. Parikh, R.G. Nuzzo, J. Am. Chem. Soc. 113 (1991) 7152. [3] T.P. Moffat, F.-R.F. Fang, A. Bard, J. Electrochem. Soc. 138 (1991) 3224. [4] P.E. Laibinis, G.M. Whitesides, J. Am. Chem. Soc. 114 (1992) 1990. [5] P.E. Laibinis, G.M. Whitesides, J. Am. Chem. Soc. 114 (1992) 9022. [6] G.K. Jennings, J.C. Munro, T.-H. Yong, P.E. Laibinis, Langmuir 14 (1998) 6130. [7] G.K. Jennings, J.C. Munro, P.E. Laibinis, Adv. Mat. 11 (1999) 1000. [8] Y. Feng, W.-K. Teo, K.-S. Siow, Z. Gao, K.-L. Tan, A.-K. Hseih, J. Electrochem. Soc. 144 (1997) 55. [9] F.P. Zamborini, J.K. Campbell, R.M. Crooks, Langmuir 14 (1998) 640. [10] K. Aramaki, M. Yamada, H. Nishihara, J. Electrochem. Soc. 138 (1991) 3389.
F. Laffineur et al. / Colloids and Surfaces A: Physicochem. Eng. Aspects 198–200 (2002) 817–827 [11] Y. Yamamoto, H. Nishihara, K. Aramaki, J. Electrochem. Soc. 140 (1993) 437. [12] M. Itoh, H. Nishihara, K. Aramaki, J. Electrochem. Soc. 141 (1994) 2018. [13] M. Itoh, H. Nishihara, K. Aramaki, J. Electrochem. Soc. 142 (1995) 1839. [14] R. Haneda, H. Nishihara, K. Aramaki, J. Electrochem. Soc. 144 (1997) 1215. [15] R. Haneda, K. Aramaki, J. Electrochem. Soc. 145 (1998) 1856. [16] H. Ron, H. Cohen, S. Matlis, M. Rappaport, I. Rubinstein, J. Phys. Chem. B 102 (1998) 9861. [17] J.F. Moulder, W.F. Stickle, P.E. Sobol, K.D. Bomben, Handbook of X-ray Photoelectron Spectroscopy, Perkin– Elmer Corp, Eden Prairie, 1992. [18] G. Beamson, D. Briggs, High Resolution XPS of Organic Polymers. The Scienta ESCA A300 Database, Wiley, Chichester, 1992.
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[19] D. Briggs, M.P. Seah (Eds.), Practical Surface Analysis, Wiley, Chichester, 1983. [20] M. Bowker, R. Madix, Surf. Sci. 95 (1980) 190. [21] M. Bowker, R. Madix, Surf. Sci. 116 (1982) 549. [22] B.A. Sexton, Surf. Sci. 88 (1979) 299. [23] B.A. Sexton, A.E. Hughes, Surf. Sci. 140 (1984) 227. [24] M. Stratmann, H. Viefhaus, Surf. Interf. Anal. 16 (1990) 278. [25] M. Volmer-Uebing, M. Stratmann, Appl. Surf. Sci. 55 (1992) 19. [26] D.G. Castner, K. Hinds, D.W. Grainger, Langmuir 12 (1996) 5083. [27] T.J. Wallace, J. Org. Chem. 31 (1996) 1217. [28] H. Keller, P. Simak, W. Schrepp, Thin Solid Films 244 (1994) 799. [29] F.A. Cotton, G. Wilkinson, Advanced Inorganic Chemistry, Wiley, New York, 1972.