Self-Assembled Monolayer Formation on Copper: A Real Time

ARTICLE pubs.acs.org/JPCC

Self-Assembled Monolayer Formation on Copper: A Real Time Electrochemical Impedance Study V. S. Dilimon, G. Fonder, J. Delhalle, and Z. Mekhalif * Laboratory of Chemistry and Electrochemistry of Surfaces, FUNDP-University of Namur, Rue de Bruxelles, 61, B-5000, Namur, Belgium

bS Supporting Information ABSTRACT: Even though electrochemical impedance spectroscopy (EIS) has already been used for the in situ electrochemical study of organothiol self-assembled monolayer (SAM) formation on gold, such studies are not available on oxidizable metals. A scrupulous study of SAM formation on oxidizable metals is a challenge, even by ex situ techniques, because of their highly oxidizable nature and their high interaction with the solvent which are irrelevant with the noble metals. In this report, the self-assembling of n-dodecanethiol, n-dodecaneselenol, didodecyl disulfide, and didodecyl diselenide on copper substrate is studied in real time by in situ electrochemical impedance spectroscopy. The interfacial capacitance variation with time was used to study the adsorption process as a function of time. The selfassembling of n-dodecanethiol and n-dodecaneselenol results in the formation of a layer with coverage of around 90% within 10 s. This fast step happens with an effective removal of the surface copper oxide layer. The second stage involves a long-term additional adsorption and consolidation of the SAM. Didodecyl disulfide is incapable for the effective removal of copper oxide layer, and its adsorption is slow and ineffective. Monolayer formation with didodecyl diselenide takes longer time due to slow copper oxide removal. The in situ EIS results were supported by the polarization modulation infrared reflection absorption spectroscopic (PMIRRAS) studies.

1. INTRODUCTION Gold and silver are undoubtedly the best choice as substrates for self-assembled monolayers (SAMs).1,2 However, copper having high electromigration resistance and high thermal as well as electrical conductivity may replace aluminum and expensive gold in various applications such as in small integration circuit assemblies.2 Therefore, the modification of Cu with SAMs is attracting much attention. Even though the modification of Cu with organothiols and organoselenols has been studied extensively,3
9 Cu presents an enigmatic case in the chemistry of SAMs.1 The process of organized molecular assembly on Cu, which is highly susceptible to oxidation in air, remains incompletely understood.2 The reduction of the copper oxide during organothiol adsorption has been claimed by various researchers by spectroscopic analyses of SAMs.4,7,10 Ex situ spectroscopic and electrochemical studies from our laboratory have shown that not only organothiol adsorption but also organoselenol adsorption result in the reduction of copper oxide.5,6 All of these ex situ studies are on already formed SAMs, and no real time for the in situ study, which is more reliable, is available on SAM formation on Cu so far. Electrochemical impedance spectroscopy (EIS) has been used as a powerful technique for the in situ study of SAM formation on gold.11,12 In the case of SAM formation on Cu, unlike with Au substrate, the interaction of solvent ethanol with Cu is significant.4,13 Considerable care is also needed to prepare good quality SAMs on Cu due to its highly oxidizable nature. Hence, no reports on the in situ electrochemical study of SAM formation on oxidizable metals are available so far. However, once a dense r 2011 American Chemical Society

and highly organized SAM is formed, it can protect Cu from further oxidation.2,3 In this paper, we show that EIS can be used as a powerful and reliable technique for the real time in situ study of SAM formation on Cu. In spite of the highly oxidizable nature of copper and its interaction with solvent, the reliability of the EIS technique is high to make reasonable conclusions since the variation in capacitance caused by SAM formation is too significant.

2. EXPERIMENTAL METHODS Synthesis. n-Dodecanethiol (R
SH) (98%) was purchased from Sigma Aldrich. Didodecyl disulfide (R
S
S
R), n-dodecaneselenol (R
SeH), and didodecyl diselenide (R
Se
Se
R) were synthesized in the laboratory. Syntheses of these chemicals were carried out under argon atmosphere in a 25 mL two-necked flask fitted with a reflux condenser. The flask was fitted with a rubber septum and with an argon inflated balloon. The liquid regents were introduced through the rubber cap using syringes. A magnetic stirrer was used throughout the reaction for stirring. Unless otherwise specified, all solvents and reagents were purchased from Sigma Aldrich or Chem. Lab and were used without further purification. Ultrapure water (18.2 MΩ cm) was used. Received: April 19, 2011 Revised: August 3, 2011 Published: August 11, 2011 18202

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The Journal of Physical Chemistry C Didodecyl Disulfide.14 Sulfuryl chloride (SO2Cl2) (2.97 g, 22 mM) was added dropwise to R
SH (8.10 g, 40 mM) for 5
10 min at 0 °C. The mixture was stirred for 30 min at 0 °C. A portion of 20 mL of water was added, and R
S
S
R was extracted with ether. The organic layer was separated and then dried over magnesium sulfate. After filtration, the solvent was removed under vacuum. The yield of R
S
S
R was 8.10 g. n-Dodecaneselenol.15 Anhydrous ethanol (1.66 g, 36 mM) was added dropwise to a mixture of sodium borohydride (NaBH4) (0.45 g, 12 mM) and elemental selenium (Se) (0.47 g, 6 mM) at ambient temperature. A white
gray solid was formed. Anhydrous DMF (10 ML) was added, and the solution was stirred for 30 min. Formic acid (HCO2H) (0.56 g, 12.50 mM) was then added dropwise, and the mixture was stirred for 20 min. n-Dodecyl bromide (R
Br) (1.25 g, 5 mM) was then added dropwise to the solution. The mixture was stirred for 2 h and was then hydrolyzed with 10 mL of 10% hydrochloric acid (HCl). Water (50 mL) was then added to the mixture, and R
SeH was then extracted with ether. The organic layer was separated, washed with 10% HCl, and then dried over magnesium sulfate. Crude R
SeH (0.98 g) was obtained by the removal of solvent by evaporation. Distillation (boiling point 120 °C/0.05 mmHg) of the crude sample gave pure R
SeH (0.63 g). Didodecyl Diselenide.15 Anhydrous ethanol (1.38 g, 30 mM) was added dropwise to a mixture of NaBH4 (0.38 g, 10 mM) and Se (0.40 g, 5 mM) at ambient temperature. A white
gray solid was formed. Anhydrous DMF (10 ML) was added, and the solution was stirred for 30 min. Anhydrous ethanol (0.94 g, 20 mM) and water (0.36 g, 20 mM) were then added dropwise, and a white precipitate was formed. After 20 min of reaction, Se (0.40 g) was again added, and the reaction was allowed to continue for 30 min. R
Br (1.99 g, 8 mM) was then slowly injected to the reaction medium. After 48 h of reaction, the solution was hydrolyzed with 10 mL of 10% HCl. A portiong of 50 mL of water was added, and R
Se
Se
R was then extracted with ether. The organic layer was separated, washed with 10% HCl, and then dried over magnesium sulfate. The removal of solvent by evaporation gave pure R
Se
Se
R (1.61 g). Substrate Preparation. Rectangular polycrystalline copper electrodes (Goodfellow, 99.99+%) were mechanically polished to mirror finish (1200 grit silicon carbide paper and 9, 3, and 1 μm diamond paste suspensions). The polished electrodes were washed with ultrapure water and then sonicated in absolute ethanol (VWR) for 15 min. The electrodes were immediately dried with a high-purity N2 stream. The electrode was then subjected to UV O3 activation for 15 min and then electrochemically reduced (
800 mV/SCE (saturated calomel electrode)) for 10 min in a deaerated 0.5 M aqueous solution of HClO4 (Acros Organics, 70%). The electrode was removed from the HClO4 electrolyte, rinsed with absolute ethanol, and blown dry with a stream of high-purity N2. Even though care was taken to immediately start the electrochemical impedance studies with an electrochemically reduced electrode, the electrode removed from the HClO4 electrolyte was in contact with the atmospheric air for around 1 min before the commencement of the study. Hence the presence of copper oxide on the electrode surface could not be avoided. In Situ Electrochemical Impedance Analysis. Electrochemical studies were carried out using a potentiostat/galvanostat (EG&G model 273) and a Solartron impedance gain
phase analyzer (model SI 1260). A platinum foil auxiliary electrode and

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an SCE reference were used. EIS studies were carried out with control E versus time setup in which the alternating current (ac) frequency, ac amplitude, and direct current (dc) potential are constant, and the impedance behavior of the system is monitored for changes over time. The experiments were carried out at the open circuit potential with an applied ac amplitude of 5 mV peakto-peak in deaerated ethanol solution of the respective molecules with a 0.1 M LiClO4 (Aldrich, 95%) supporting electrolyte. The frequency (f) was 1000 Hz, and the duration of the experiments was 7 h. The electrolyte was blanketed with N2 throughout the experiment. Even though the experiment was started immediately after the Cu electrode was immersed into the electrolyte, an instrumental delay of maximum 10 s was there for receiving the initial impedance values. The real (Z0 ) and the imaginary (Z00 ) components of the impedance are monitored for changes over time. It is possible to write Z0 and Z00 components for an ideal Randles type circuit as,11 Z0 ¼ Ru þ Z00 ¼

Rct 1 þ ω2 Rct 2 Cdl 2

Cdl Rct 2 ω 1 þ ω2 Rct 2 Cdl 2

ð1Þ ð2Þ

where Rct and Ru are the charge transfer resistance and uncompensated solution resistance, respectively, Cdl is the interfacial double layer capacitance, and ω = 2πf (f is the frequency of the applied ac potential). In a system where ω2Rct2Cdl2 . 1, (e.g., a thiol film), it can be assumed that Z00 = (1/Cdlω).11 The calculation of Cdl is thus possible from Z00 at a high enough frequency. Surface coverage (θ) of SAM can be calculated from the capacitance at any time t (Ct) using eq 3,11,16   C 0
Ct θ¼ ð3Þ C0
Cf where C0 and Cf are the capacitance of bare electrode and fully covered monolayer, respectively. Ex Situ PM-IRRAS Analysis. Polarization modulation infrared reflection absorption spectroscopic (PM-IRRAS) analyses of the monolayers were carried out by a Bruker Equinox55 PMA37 spectrometer equipped with a liquid nitrogen cooled mercury
cadmium
telluride (MCT) detector and a zinc
selenide photoelastic modulator. The measurements were carried out with the photoelastic modulator set at half-wave retardation of 2600 cm
1. The infrared light, reaching the sample surface at an angle of 80°, was modulated between s- and p-polarization at a frequency of 50 kHz. Signals generated from each polarization (Rs and Rp) were detected simultaneously by a lock-in amplifier and used to calculate the differential surface reflectivity (4R/R) = (Rp
Rs)/(Rp + Rs). The number of scans was 512, and the resolution was 2 cm
1.

3. RESULTS AND DISCUSSION Adsorption of n-Dodecanethiol. Figure 1 shows the capacitance versus time curves recorded during the adsorption of R
SH. The capacitance at any time decreases with an increase in R
SH concentration. This result proves that the extent of surface coverage increases with an increase in R
SH concentration. Ex situ cyclic voltammetric studies of the SAMs prepared on copper with different concentrations of R
SH have shown an 18203

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Figure 1. Capacitance vs time curves for copper in different concentrations of R
SH: 1 mM (a), 2 mM (b), 5 mM (c), 10 mM (d), 20 mM (e). Inset a shows the lowering of capacitance vs time curves due to SAM formation on copper. Inset b shows the capacitance vs time curves recorded for a short time with electrochemically reduced copper in different concentrations of R
SH: 5 mM (a), 10 mM (b), 20 mM (c), and oxidized copper (by UV
O3 activation for 1 min) in 20 mM (d) R
SH. Solvent: ethanol, supporting electrolyte: 0.1 M LiClO4.

increase in the insulating behavior with an increase in the R
SH concentration.8 This observation can be explained based on the results of the present in situ study showing an increase in the extent of surface coverage with an increase in R
SH concentration. Interestingly, the concentration of thiol is of less importance in the SAM formation on noble metals such as Au.17 Even though Cu in blank electrolyte also shows a decrease in capacitance for the initial 1 h, probably due to its interaction with ethanol, the variation in capacitance caused by SAM formation is too significant to make reasonable conclusions from our study (Figure 1 a (inset)). The initial capacitance value measured in the solutions with R
SH is considerably lower than that measured in the blank electrolyte (Figure 1a (inset)) indicating a sudden adsorption of thiol (as per eq 4) within 10 s, (i.e., within the experimental delay). Cuð0Þ þ RSH f CuSR þ 1=2H2

ð4Þ

This sudden adsorption step is followed by a long-term additional adsorption and consolidation of the SAM. A similar twostep adsorption of thiol with a fast first step followed by a slow second step has been reported on gold.11,18 Most of the studies in 5 mM R
SH and a few studies in 10 mM R
SH showed an initial rise in capacitance for around 3 min and 1.5 min, respectively (Figure 1b (inset)). It definitely happens after the initial sudden adsorption step (which happens within an experimental delay) since the measured initial capacitance values were considerably lower than that of the Cu in blank solution. This observed capacitance rise with 5 mM and 10 mM R
SH is attributed to the reduction of copper oxide. A similar initial capacitance rise is not observed with lower concentrations of R
SH since they were less effective for the metal oxide reduction. With higher concentrations of R
SH also, due to a very fast copper oxide removal with concurrent SAM formation, a similar capacitance rise was not observed. To clarify our statements, electrochemically reduced Cu substrate (Section 2) was subjected to oxidation by UV O3 activation for 1 min and was then studied in 20 mM R
SH solution. In this way we could see the characteristic initial capacitance rise with 20 mM R
SH solution also confirming our assumptions (Figure 1b (Inset)).

Figure 2. Capacitance vs time curves for copper in different concentrations of R
S
S
R: 0 mM (a), 2 mM, 5 mM, and 10 mM (b) (no considerable difference in capacitance vs time curves by changing the R
S
S
R concentration). Inset shows the surface coverage vs time curves for copper in 10 mM R
SH (a) and 10 mM R
S
S
R (b). Solvent: ethanol, supporting electrolyte: 0.1 M LiClO4.

Thus we could give the first in situ analytical support to the ability of R
SH for copper oxide reduction (eqs 5 and 6),4
8,10 which is more effective at higher concentrations.8 CuO þ 2RSH f Cuð0Þ þ RSSR þ H2 O

ð5Þ

Cu2 O þ 2RSH f 2Cuð0Þ þ RSSR þ H2 O

ð6Þ

We propose that the initial step of sudden capacitance decrease is due to the SAM formation on bare Cu (eq 4) which obviously happens with an effective reduction of the metal oxide (eqs 5 and 6). Our attempts to fit the plots of θ versus t with the adsorption kinetic models were not successful probably due to this complex adsorption kinetics. Adsorption of Didodecyl Disulfide. Figure 2 shows that the concentration of R
S
S
R has little effect on the surface coverage of SAM. The SAM formation rate is also significantly slower than that with R
SH. Figure 2 (inset) shows that the surface coverage of SAM is considerably lower, and it is not much stable on the electrode surface (see the gradual rise in capacitance after around 2 h). The slow adsorption rate can be attributed to the essential cleavage of S
S bond before SAM formation. As per eqs 5 and 6, we cannot expect an effective copper oxide removal by R
S
S
R. Corroborating with our previous spectroscopic evidence,6 the observed low surface coverage can be attributed to the inability of R
S
S
R for the copper oxide reduction. Adsorption of n-Dodecaneselenol. The concentration of R
SeH is not as important as that of R
SH in determining the surface coverage of SAM (Figure 3) due to its higher power for the copper oxide reduction.9 Similar to R
SH, adsorption of R
SeH follows a two-step process with a fast first step followed by a slow second step (Figure 3a (inset)) but with a comparatively slower initial R
SeH adsorption. However, the monolayer is more compact than that of R
SH (Figure 3b (inset)). Capacitance is related, based on the Helmholz model, to the dielectric constant (ε), the length of the molecule (or thickness of SAM) (d), and the permittivity of free space (εo) by the relationship Cdl = εε0/d.11,19 Reports showing almost similar dielectric constants for R
SH and R
SeH SAMs19 help us to compare the thickness of R
SH and R
SeH SAMs. Lower capacitance values of R
SeH adsorption (Figure 3) than that of 18204

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Figure 3. Capacitance vs time curves for copper in different concentrations of R
SeH: 5 mM (a), 10 mM (b), 15 mM (c). Inset a shows the lowering of capacitance vs time curves due to SAM formation on copper. Inset b shows the surface coverage vs time curves for copper in 10 mM R
SH (a) and 10 mM R
SeH (b). Solvent: ethanol, supporting electrolyte: 0.1 M LiClO4.

Figure 4. Capacitance vs time curves for copper in different concentrations of R
Se
Se
R: 0 mM (a), 5 mM (b), 10 mM (c), 15 mM (d). Inset shows the capacitance vs time curves for copper in 10 mM R
Se
Se
R (a), 10 mM R
SeH (b), 10 mM R
S
S
R (c). Solvent: ethanol, supporting electrolyte: 0.1 M LiClO4.

R
SH adsorption (Figure 1) indicate a thicker layer due to its probable better orientation. Adsorption of Didodecyl Diselenide. The adsorption of R
Se
Se
R follows a three-step mechanism (Figure 4). The rate of SAM formation is significantly slower than that with R
SeH due to the required cleavage of Se
Se bond. Ex situ studies from our laboratory have shown that R
Se
Se
R is more effective than R
S
S
R for the copper oxide reduction;6 however, the SAM formed for 2 h with R
Se
Se
R is more or less of the same quality as that with R
S
S
R.5 These observations are very relevant at this point because, from Figure 4, the quality of SAM depends much on its formation time. Figure 4 (inset) shows that the SAM formed with R
Se
Se
R for around three hours is of the same quality as that formed with R
S
S
R. This similarity is because initially both R
S
S
R and R
Se
Se
R form SAM on the oxide-free Cu surface. While R
S
S
R was unable to continue SAM formation due to its inability for copper oxide reduction, R
Se
Se
R could slowly reduce the metal oxide, and SAM formation was continued on the exposed surface to get the same coverage as that attained with R
SeH (Figure 4 (inset)).

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Figure 5. Capacitance vs time curves recorded for part a: electrochemically reduced copper in 20 mM R
SH (a), electrochemically reduced copper in 10 mM R
S
S
R (b), oxidized copper in 20 mM R
SH (c), oxidized copper in 10 mM R
S
S
R (d), oxidized copper in blank electrolyte (e); and part b: electrochemically reduced copper in 10 mM R
SeH (a), electrochemically reduced copper in 10 mM R
Se
Se
R (b), oxidized copper in 10 mM R
SeH (c), oxidized copper in 10 mM R
Se
Se
R (d), oxidized copper in blank electrolyte (e). Inset shows the capacitance versus time curves for the electrochemically reduced copper (a) and oxidized copper (b) in blank electrolyte. The oxidation of copper was carried out by UV O3 activation for 10 min. Solvent: ethanol, supporting electrolyte: 0.1 M LiClO4.

Evaluation of Copper Oxide Reduction Efficiency. The copper oxide reduction efficiency of R
SH, R
SeH, R
S
S
R, and R
Se
Se
R was studied to justify their observed difference in the self-assembling process. Electrochemically reduced Cu substrates (Section 2) were subjected to oxidation by UV
O3 activation for 10 min so as to form a stable oxide layer. We have already observed that, while at least 20 mM of R
SH is required to get a good monolayer, an optimum concentration of 10 mM is sufficient for R
S
S
R, R
SeH, and R
Se
Se
R. Therefore, the capacitance versus time curves of the oxidized copper was studied in the solution of R
SH having 20 mM concentrations and in the solutions of R
S
S
R, R
SeH, and R
Se
Se
R having a 10 mM concentration. Figure 5a compares the capacitance versus time curves recorded for the electrochemically reduced copper and oxidized copper in R
SH and R
SeH solutions. The identical capacitance versus time curves for the electrochemically reduced and oxidized copper in both R
SH and R
SeH solutions confirm the high copper oxide reduction efficiency of both R
SH and R
SeH. Figure 5b compares the capacitance versus time curves recorded for the electrochemically reduced copper and oxidized copper in R
S
S
R and R
Se
Se
R solutions. The higher capacitance values shown by the oxidized copper in both R
S
S
R and R
Se
Se
R solutions than that of the electrochemically reduced copper prove the lower copper oxide reduction efficiency of both R
S
S
R and R
Se
Se
R (Figure 5b). The oxide reduction efficiency of R
Se
Se
R is higher than that of R
S
S
R. The capacitance versus time curves recorded for the electrochemically reduced copper and oxidized copper in the blank electrolyte solution is also shown as Figure 5b (inset). The oxidized copper shows significantly lower capacitance values than that of the electrochemically reduced copper in blank electrolyte showing the existence of a stable oxide layer after UV O3 activation for 10 min. Ex Situ PM-IRRAS Studies. Figure 6 shows the PM-IRRAS spectra recorded for the SAMs formed for 10 s and 7 h with R
SH and R
S
S
R (Figure 6a) as well as with R
SeH and R
Se
Se
R (Figure 6b). All of the monolayers exhibit four 18205

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with R
SH depends much on R
SH concentration. Selfassembling of R
S
S
R was slow due to its inability for oxide reduction. The SAM formed with R
S
S
R was of low quality. Good monolayer formation with R
Se
Se
R takes a long time due to slow oxide reduction.

’ ASSOCIATED CONTENT

bS

Supporting Information. Illustration of the capacitance calculation from the impedance spectra (Figure S1); fixing of the frequency for the impedance study from the capacitance versus frequency curve (Figure S2). This material is available free of charge via the Internet at http://pubs.acs.org.

Figure 6. PM
IRRAS spectra recorded for the SAMs prepared for 10 s and 7 h with R
SH and R
S
S
R ( part a) and R
SeH and R
Se
Se
R (part b). Part a: R
SH for 7 h (a), R
SH for 10 s (b), R
S
S
R for 7 h (c), R
S
S
R for 10 s. Part b: R
SeH for 7 h (a), R
SeH for 10 s (b), R
Se
Se
R for 7 h (c), R
Se
Se
R for 10 s.

bands in the
C
H stretching mode region between 3000 cm
1 and 2800 cm
1 due to asymmetric
CH3 stretching (υa (
CH3)) at ∼2965 cm
1, asymmetric
CH2 stretching (υa (
CH2)) at ∼2918 cm
1, symmetric
CH3 stretching (υs (
CH3)) at ∼2877 cm
1, and symmetric
CH2 stretching (υs (
CH2)) at ∼2850 cm
1. Symmetric
CH3 stretching band splits due to Fermi resonance interactions with the lower frequency asymmetric
CH3 deformation bands. Due to these interactions, a shoulder at ∼2934 appears in the υa (
CH2) band. The wavenumbers corresponding to the asymmetric
CH2 stretching (υa (
CH2) at ∼2918 cm
1) and symmetric
CH2 stretching (υs (
CH2) at ∼2850 cm1) vibrations are particularly interesting for the determination of the monolayer organization. The shift of these bands to higher frequencies indicates a molecular organization of lesser quality with randomly oriented methylene groups with dominant gauche defects, rather than a trans zigzag extended conformation.4,20
22 The positions of υa (
CH2) at 2919 cm
1 and υs (
CH2) at 2850 cm
1 for the monolayers formed with R
SH for both 10 s and 7 h indicate their high degree of organization. The positions of υa (
CH2) at 2925 cm
1 and υs (
CH2) at 2854 cm
1 for the monolayer formed with R
S
S
R for both 10 s and 7 h indicate their poor organization. The PM-IRRAS spectra recorded for the SAM formed for 10 s and 7 h with R
SeH as well as R
Se
Se
R shows asymmetric
CH2 stretching (υa (
CH2)) at ∼2924 cm
1 and symmetric
CH2 stretching (υs (
CH2 )) at ∼2853 cm
1. The higher frequencies of these bands show the existence of a monolayer with lesser organization.

4. CONCLUSIONS While a scrupulous study of SAM formation on oxidizable metals is a challenge even by highly developed techniques, we show that simple electrochemical impedance can be used as a reliable technique for its in situ study. Molecules with different copper oxide reduction capacities (R
SH, R
S
S
R, R
SeH, and R
Se
Se
R) were self-assembled on Cu at different concentrations to study the influence of these parameters, which are irrelevant with noble metals, on the self-assembling mechanism. Self-assembling of R
SH and R
SeH are fast with effective reduction of metal oxide layer and the quality of the SAM formed

’ AUTHOR INFORMATION Corresponding Author

*Tel.: +32 (0) 81 72 52 30; fax: +32 (0) 81 72 46 00. E-mail address: [email protected] (Z. Mekhalif).

’ ACKNOWLEDGMENT V.S.D. acknowledges FUNDP-CERUNA for the postdoctoral fellowship. ’ REFERENCES (1) Love, J. C.; Estroff, L. A.; Kriebel, J. K.; Nuzzo, R. G.; Whitesides, G. M. Chem. Rev. 2005, 105, 1103–1169. (2) Ulman, A. Chem. Rev. 1996, 96, 1533–1554. (3) Laibinis, P. E.; Whitesides, G. M. J. Am. Chem. Soc. 1992, 114, 9022–9028. (4) Ron, H.; Cohen, H.; Matlis, S.; Rappaport, M.; Rubinstein, I. J. Phys. Chem. B 1998, 102, 9861–9869. (5) Fonder, G.; Volcke, C.; Csoka, B.; Delhalle, J.; Mekhalif, Z. Electrochim. Acta 2010, 55, 1557–1567. (6) Mekhalif, Z.; Fonder, G.; Auguste, D.; Laffineur, F.; Delhalle, J. J. Electroanal. Chem. 2008, 618, 24–32. (7) Sung, M. M.; Sung, K.; Kim, C. G.; Lee, S. S.; Kim, Y. J. Phys. Chem. B 2000, 104, 2273–2277. (8) Fonder, G.; Laffineur, F.; Delhalle, J.; Mekhalif, Z. J. Colloid Interface Sci. 2008, 326, 333–338. (9) Mekhalif, Z.; Fonder, G.; Laffineur, F.; Delhalle, J. J. Electroanal. Chem. 2008, 621, 245–253. (10) Keller, H.; Simak, P.; Schrepp, W.; Dembowski, J. Thin Solid Films 1994, 244, 799–805. (11) Subramanian, R.; Lakshminarayanan, V. Electrochim. Acta 2000, 45, 4501–4509.  .; Metikos-Hukovi
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