Optimized hand fabricated AFM probes for simultaneous topographical and electrochemical tapping mode imaging Raul D. Rodriguez a , Agn  es Anne a , Edmond Cambril b , Christophe Demaille a,n a Laboratoire d’Electrochimie Mole ´culaire, Unite´ Mixte de Recherche Universite´—CNRS No. 7591, Universite´ Paris Diderot (Paris 7), 15 rue Jean-Antoine de Baı ¨f, 75205 Paris Cedex 13, France b Laboratoire de Photonique et de Nanostructures, CNRS-UPR20, Route de Nozay, 91460 Marcoussis, France article info Article history: Received 17 August 2010 Received in revised form 16 December 2010 Accepted 5 February 2011 Available online 16 February 2011 Keywords: Hand fabricated AFM probes Hybrid AFM probes AFM–SECM Scanning electrochemical microscopy Tapping mode imaging abstract In this work hybrid AFM–electrochemical (SECM) probes to be used in dynamic atomic force microscopy are presented. These nanosensors are hand fabricated from gold microwires using a simple benchtop method. They display proportions close to commercially available silicon and silicon nitride cantilevers giving comparable performance in terms of resolution and imaging stability. The remark- able characteristic of these hybrid nanosensors is that they allow the coupling of 3D imaging ability and versatility of atomic force microscopy with the power of electrochemical methods. Local measurement of electrochemical-activity of a test sample consisting of gold bands functionalized by redox-labeled nanometer-sized polyethylene glycol chains has been achieved with simultaneous imaging of the 3D surface topography at high resolution. These hybrid AFM–SECM tips are capable of sensing local electrochemical currents down to 10 fA emphasizing the sensitivity and resolution of this technique. & 2011 Elsevier B.V. All rights reserved. 1. Introduction Scanning electrochemical microscopy (SECM) is an in-situ scanning probe technique allowing the electrochemical reactivity of surfaces to be probed at the micron or even nanometer scale [1–3]. The local probe plays the role of a microelectrode, which, for example, oxidizes a redox species (the mediator) introduced into the electrolyte liquid environment. In the con- ventional SECM feedback mode, the microelectrode-probe (tip) approaches within a few tip radii distance from an electrochemi- cally active sample surface (substrate). The tip-generated form of the mediator reaches the substrate by diffusion where it is reduced and fed back to the tip. This so called positive feedback redox cycling results in an increase of the tip current. The magnitude of the faradaic current recorded at the tip is therefore modulated by the local electrochemical reactivity of the substrate. Scanning the tip over the substrate allows current, i.e. ‘‘reactiv- ity’’, images of the sample surface to be acquired. Yet, for a given local reactivity, the tip current is also a function of the tip–substrate distance which has to be held constant while scanning the surface for reliable electrochemical reactivity images to be acquired. This problem is particularly acute if sub-micron resolution is sought. Hence SECM is often coupled with other local probe techniques allowing a perfect control of the tip–substrate distance. In particular SECM has been coupled with AFM [4–19]. Obviously, this requires that combined AFM–SECM probes are fabricated. Ideally these probes should behave as standard AFM tips, i.e. allow to acquire the surface topography with nanometric resolution, but their very apex should also behave as a micro- electrode. This later condition implies that the probes are elec- trically insulated over all of their surface but their tip-apex. Combined AFM–SECM probes were fabricated using sophisticated microfabrication techniques [4–12], by modifying commercially available cantilevers [13], or using much simpler benchtop methods [15–20]. Microfabricated AFM–SECM probes display superior imaging performances but are, to date, largely inacces- sible to most experimentalists since they are not commercially available. In comparison, hand fabricated AFM–SECM probes may display lower performances but have the great merit of being readily available. Hand fabricated probes for electrochemical measurements and AFM were introduced by the pioneering work of Macpherson et al. [15]. The initial versions corresponded to a platinum wire, which was flattened, bent and electrochemically etched. Flattening of the wire formed the flexible and reflecting cantilever arm of the probe, while etching formed a sharp tip apex. These probes were used in contact mode or in two-pass lift- mode when tip–substrate contact had to be avoided, but never in tapping mode. Following Macpherson et al. [14–16], our group has since fabricated probes from gold microwires for dual AFM and electrochemical measurements. These probes were initially Contents lists available at ScienceDirect journal homepage: www.elsevier.com/locate/ultramic Ultramicroscopy 0304-3991/$ - see front matter & 2011 Elsevier B.V. All rights reserved. doi:10.1016/j.ultramic.2011.02.001 n Corresponding author. E-mail address: demaille@univ-paris-diderot.fr (C. Demaille). Ultramicroscopy 111 (2011) 973–981