Electro-assisted formation of organothiols self-assembled monolayers on polycrystalline copper surfaces

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Electro-assisted formation of organothiols self-assembled monolayers on polycrystalline copper surfaces

Maho, Anthony; Denayer, Jessica; Delhalle, Joseph; Mekhalif, Zineb

Publication date:

2011

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Peer reviewed version

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Citation for pulished version (HARVARD):

Maho, A, Denayer, J, Delhalle, J & Mekhalif, Z 2011, 'Electro-assisted formation of organothiols self-assembled monolayers on polycrystalline copper surfaces', ElecNano4- 7th ECHEMS, Paris, France, 23/05/11 - 26/05/11.

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Electro-assisted formation of organothiols

self-assembled monolayers on polycrystalline copper

surfaces

Anthony Maho, Jessica Denayer, Joseph Delhalle, Zineb Mekhalif

Laboratory of Chemistry and Electrochemistry of Surfaces (CES)

University of Namur (FUNDP), Belgium

Contact: zineb.mekhalif@fundp.ac.be

General context: organothiols films grafted on copper

• Organothiol Self-Assembled Monolayers (SAMs) can be successfully adsorbed on noble (Au) and oxidizable metals (Cu, Zn, Ni). They can be used as protective coatings against corrosion, lubricants, lithographic patterns, molecular (bio)sensors, … [1]

• Oxidation state of the substrate surface is a key factor for the SAMs formation => an electrochemical reduction pretreatment of the Cu oxides layer can be exploited to form reproducible high quality films [2].

• Molecular adsorption process has an important impact on the SAMs characteristics: passive self-assembly (open circuit potential) vs. active electro-assisted assembly (cathodic polarization of Cu) [3].

Results and discussion

Conclusions and perspectives

- Efficiency of active electro-assisted adsorption of organothiols on copper => formation of SAMs with excellent properties of organization, protective against corrosion, with high electrochemical

stability, and formed with a significant saving of time comparatively to the passive methodology (10min vs. 2h).

- Perspectives: variation and optimization of experimental conditions with other substrates and surfactants [3], use of ionic liquids (to reduce hydrocarbon contaminations), …

Two experimental approaches and methodologies

Electrochemical stability (CV, cath. desorption)

Protection against corrosion (pol. curves)

Local characterization: SECM

Chemical composition: XPS (active method)

Structure and organization: PM-IRRAS

Acknowledgments

: FNRS-FRIA for fellowship, Elecnano

4

– 7

th

ECHEMS

References

[1]_{P.E. Laibinis, G.M. Whitesides, D.L. Allara, Y.T. Tao, A.N. Parikh, R.G. Nuzzo, J. Am. Chem. Soc. 1991, 113, 7152-7167; G. Fonder, F. Laffineur, J. Delhalle, Z. Mekhalif, J. Colloid. Interf. Sci . 2008, 326, 333-338.}

[2]_{Z. Mekhalif, F. Sinapi, F. Laffineur, J. Delhalle, J. Electron. Spectrosc. 2001, 121, 149-161; J. Denayer, J. Delhalle, Z. Mekhalif, J. Electroanal. Chem. 2009, 637, 43-49; G. Fonder, C. Volcke, B. Csoka, J. Delhalle, Z. Mekhalif, Electrochim. Acta 2010, 55, 1557-1567.} [3]_{A. Maho, J. Denayer, J. Delhalle, Z. Mekhalif, Electrochim. Acta 2011, 56, 3954-3962.}

- Confirmed grafting: S2s & S2p, C1s increases

- Thiolate S-Cu bond at 162.3 eV => no unbound thiol (164 eV) or oxidized species (> 164 eV) - Reduction of the oxides layer (Auger Cu_LMM)

- Hydrocarbon contaminations: CH/S = 25.6 – th. = 13

-



_a

(CH

₂

) = 2920 cm

-1

_and



s

(CH

2

) = 2850

cm

-1

=> in both cases, densely packed

monolayers with alkyl chains in a trans

zig zag conformation

- Intensity of CH

₃

bands more important

with the active adsorption process =>

modification

of

the

alkyl

chain

inclination and orientation relative to

the substrate surface due to the

cathodic polarization of Cu

Blocking ratio (%) E_des (V/Ag-AgCl) Passive adsorption (2h, EtOH) 97 - 1.14 Active adsorption (10min, DMF) 97 - 1.23

I_cor (A/cm²) E_cor (mV/SCE) E_pit (mV/SCE)

Bare copper 6.4 10-6 _{- 374} _{- 45}

Passive adsorption (2h, EtOH) 4.4 10-7 _{- 308} _{- 95}

Active adsorption (10min, DMF) 4.1 10-7 _{- 312} _{- 165}

=> High anodic and cathodic stabilities

=> « Mixed-to-anodic » protection => Significant decrease of I_cor

I/I₀

Bare copper 1.73

Passive adsorption (2h, EtOH) 0.54

Active adsorption (10min, DMF) 0.19

NaOH 0.1 M, 20 mV/s LiClO₄ 0.5 M in CH₃CN, 50 mV/s

NaCl 0.5 M, 5 mV/s

10 µm/s, 1 mM FC-MeOH / 0.1 M KNO₃

=> Active adsorption reinforces the

insulating features of the grafted films (decreasing of I/I₀)