Anal. Chem. 2006, 78, 5436-5442
Characterization of Microfabricated Probes for Combined Atomic Force and High-Resolution Scanning Electrochemical Microscopy Maurizio R. Gullo, Patrick L. T. M. Frederix,† Terunobu Akiyama, Andreas Engel,† Nico F. deRooij, and Urs Staufer*
Institute of Microtechnology, University of Neuchaˆ tel, rue Jaquet-Droz 1, 2001 Neuchaˆ tel, Switzerland
A combined atomic force and scanning electrochemical microscope probe is presented. The probe is electrically insulated except at the very apex of the tip, which has a radius of curvature in the range of 10-15 nm. Steadystate cyclic voltammetry measurements for the reduction of Ru(NH3)6Cl3 and feedback experiments showed a distinct and reproducible response of the electrode. These experimental results agreed with finite element simulations for the corresponding diffusion process. Sequentially topographical and electrochemical studies of Pt lines deposited onto Si3N4 and spaced 100 nm apart (edge to edge) showed a lateral electrochemical resolution of 10 nm. Scanning electrochemical microscopy (SECM) is a member of the scanning probe microscopy (SPM) family. In SECM, ultramicroelectrodes (UMEs) having a diameter less than 10 µm are used to perform local electrochemical experiments. The implementation of this method has been demonstrated for a wide range of applications.1-26 The achievable spatial resolution for * Corresponding author. E-mail:
[email protected]. † M. E. Mu ¨ller-Institute for Structural Biology, Biozentrum, University of Basel, Switzerland. (1) Bard, A. J.; Fan, F.-R. F.; Kwak, J.; Lov, O. Anal. Chem. 1989, 61, 132138. (2) Bard, A. J.; Fan, F.-R. F.; Pierce, D. T.; Unwin, P. R.; Wipf, D. O.; Zhou, F. Science 1991, 254, 68-74. (3) Mirkin, M. V.; Fan, F.-R. F.; Bard, A. J. Electroanal. Chem. 1992, 328, 4762. (4) Bard, A. J.; Fan, F.-R.; Mirkin, M. V. In Electroanalytical Chemistry: A Series of Advances; Bard, A. J., Ed.; Marcel Dekker: New York, 1994; Vol. 18, pp 243-273. (5) Mirkin, M. V. Mikrochim. Acta 1999, 130, 127-153. (6) Macpherson, J. V.; Unwin, P. R. Anal. Chem. 2000, 72, 276-285. (7) Bard, A. J., Mirkin, M. V., Eds. Scanning Electrochemical Microscopy; Marcel Dekker: New York, 2001. (8) Bard, A. J.; Faulkner, L. R. Electrochemical Methods, Fundamentals and Applications; Wiley: New York, 2001. (9) Zoski, C. G. Electroanalysis 2002, 14, 1041-1051. (10) Zoski, C. G.; Mirkin, M. V. Anal. Chem. 2002, 74, 1986-1992. (11) Zoski, C. G.; Liu, B.; Bard, A. J. Anal. Chem. 2004, 76, 3646-3654. (12) Wipf, D. O.; Bard, A. J. J. Electrochem. Soc. 1991, 138, 469-474. (13) Ervin, E. N.; White, H. S.; Baker, L. A. Anal. Chem. 2005, 77, 5564-5569. (14) Frederix, P. L. T. M.; Gullo, M. R.; Akiyama, T.; Tonin, A.; de Rooij, N. F.; Staufer, U.; Engel, A. Nanotechnology 2005, 16, 997-1005. (15) Abe, T.; Itaya, K.; Uchida, I. Chem. Lett. 1988, 399-402. (16) Gewirth, A. A.; Craston, D. H.; Bard, A. J. J. Electroanal. Chem. 1989, 261, 477-482. (17) Nagahara, L. A.; Thundat, T.; Lindsay, S. M. Rev. Sci. Instrum. 1989, 60, 3128-3130.
5436 Analytical Chemistry, Vol. 78, No. 15, August 1, 2006
analytical purposes strongly depends on the shape and size of the electrode10 as well as on the distance between UME and sample.2 A way to scale down the electrodes and thus improve the resolution is to microfabricate the UMEs. In addition, by using microfabrication, it is possible to combine SECM with other SPM techniques, such as aomic force microscopy27 (AFM) or scanning near-field optical microscopy, which helps to simultaneously obtain complementary information.28 In particular, a combination of SECM and AFM offers the possibility of correlating chemical surface activity with topography. The AFM allows probing the surface with relative low forces (
