Watching electrochemistry with BALM optical microscopy
Résumé
Backside Absorbing Layer Microscopy (BALM) is a new optical microscopy technique developed by D. Ausserré at IMMM, which uses absorbing anti-reflection layers to achieve extreme contrast at an interface. It combines a sub-nm vertical sensitivity comparable to the one of AFM with the versatility and real-time imaging capabilities of an optical microscope. Recently, we showed how this technique allows observing 2D materials and their chemical modification with unprecedented Z-resolution (1). The BALM geometry (Fig. 1a) and its capability to image surfaces and nanomaterials in liquid are ideally suited to its coupling with electrochemistry. This optical technique is extremely sensitive to minute changes of refractive index therefore it allows following in real-time the deposition or the electro-grafting of molecules with a precision significantly below the monolayer thickness. This is exemplified in Fig. 1b for the electro-grafting of nitrobenzene diazonium salt on gold by cyclic voltammetry. The optical signal being directly proportional to the layer thickness in a large thickness range, the technique proves capable of monitoring layer growth with angstrom precision in the vertical direction. More importantly, as a microscopy technique, it is also spatially resolved. As a simple example, Fig. 2 presents the in situ monitoring of the electrodeposition of copper by chronoamperometry respectively on gold (a) and on Graphene Oxide flakes (b). In this communication, we will show how the coupling of BALM and electrochemistry allows addressing different classes of problems in electrochemistry by taking advantage of real-time imaging and high sensitivity.
Domaines
Matériaux
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