A new cell design for potentiostatically controlled in situ atomic force microscopy

Abstract

We describe the design and construction of a new type of AFM cell for in situ imaging under potentiostatic control. The cell is specifically designed for a Rasterscope 4000 TM AFM instrument with no need for instrumental modification, but can easily be adapted to other commercial instruments. The cell is a closed system with insignificant sample evaporation. It is a chemically and mechanically robust two-component system which enables fast assembly and testing prior to insertion and minimizes leakage problems. The cell is also laterally flexible, facilitating scanning of large areas, holds inlets for rapid flushing and change of solution, and contains an optical device for adjusting the laser beam deflection in aqueous and gas ambient environments.Cyclic voltammetry of a simple redox couple and combined cyclic voltammetry and in situ AFM of copper deposition/dissolution cycles testify to perfect cell performance.Atomic force microscopy (AFM) of nanoscale structure and dynamics at the interface between a solid and an aqueous solution has received broad recent attention in a range of contexts. In some cases the single most central issue is the natural aqueous medium for the systems addressed. This applies, for example to ionic crystal dissolution [1-3], surface chemical processes [4,5] and, conspicuously, to the imaging of proteins and of protein and protein-membrane complexes [6][7][8][9][10][11] in solution. Water is here both an integrated structural element of the molecules imaged and an absolute prerequisite for observation of the conformational changes and other dynamic features associated directly with protein function.AFM imaging of molecular structure and dynamics in aqueous solution could be assigned the appellation in situ AFM. This notion is, however, reserved for configurations where, in addition to the aqueous environment, potentiostatic substrate (and tip) control is required, i.e. for imaging of electrochemical interfaces. In situ images of physically rather different electrochemical interfacial systems specifically in this AFM mode have been reported recently. These include:a) Metal deposition and nanostructure formation and dissolution [12-16]; (b) electrochemical oxide and hydride growth at metal and semiconductor surfaces [17-20]; (c) anion adsorption [21, 22]; (d) supramolecular organization of large nanometer-size adsorbate molecules [23, 24]; and (e) synthesis and characterization of nanoscale metallic and semiconductor particles with microelectrode or other device-like properties [25, 26]. Such investigations hold highly important perspectives for direct imaging of the surface morphology and its time evolution. They are also complementary to in situ scanning tunneling microscopy (STM), where conductivity and electronic properties are primary observables rather than the outer system morphology, such as in AFM.In the present work we describe the design and function of a new type of AFM cell for in situ imaging under potentiostatic control. The cell is specifically designed to fit a commercial ...