Electronic Properties of Modified Surfaces Using Contact and Non-Contact Scanning Probe Microscopy Techniques and SECM.
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Electronic Properties of Modified Surfaces Using Contact and Non-Contact Scanning Probe Microscopy Techniques and SECM. Aaron K Neufeld, Anthony O’Mullane1 and Alan M Bond1 CSIRO Manufacturing and Infrastructure Technology PO Box 56 Graham Rd Highett Victoria Australia 3190 1 School of Chemistry Monash University Clayton, Victoria 3800 Australia ABSTRACT Electrochemical experiments with tetracyanoquinodimethane (TCNQ) modified electrodes in contact with aqueous copper containing electrolytes leads to the incorporation and expulsion of copper ions. This process occurs concomitantly with nucleation and growth processes and significant crystal fragmentation to produce particles with dimensions of the order of 10's of nanometres. During reduction of TCNQ and intercalation of copper ions, different phases of the semiconducting compound CuTCNQ are formed.[1,2] The preparation of both conducting and insulating substrates coated with electroactive TCNQ and CuTCNQ particles of variable size have been made by dip and spin coating procedures. Results suggest that the phase and hence electronic properties of CuTCNQ is dependent on the size of particles that decorate the electrode surface. Combining atomic force microscope (AFM) based methods that interrogate the morphological and electronic properties of nanometre sized particles with use of a scanning electrochemical microscope (SECM) is a new advance in materials characterisation that has proved highly valuable in understanding the highly complex behaviour of these semi-conducting particles. INTRODUCTION The coordination polymer CuTCNQ (TCNQ = 7,7′,8,8′- tetracyanoquinodimethane) is a very interesting material: its electronic and optical properties have been of significant interest over the last few decades. With simple devices made from CuTCNQ, a switching effect from a high to a low impedance state results from the application of an electric field or optical excitation. [3-8] However, much controversy surrounds this switching effect and the mechanism. The identification of two distinct phases of CuTCNQ with differing conductivities may be part of this problem. Pelletised forms of the phase 1 material have a room temperature conductivity of 0.2 S cm-1 whereas phase II, shows more insulating behaviour with a conductivity of 10-5 S cm-1.[9] Scanning electrochemical microscopy (SECM) is a relatively new electrochemical technique, which is sensitive to the electrochemical activity of a solid surface or liquid-liquid interface. In feedback mode, the theory describing the measured responses at the Ultramicroelectrode (UME) as it comes into close proximity with a surface has been rigorously developed. The SECM has also been used to induce well-defined localized changes in the chemical or physical properties of a substrate.[10-12] The versatility of this technique makes it an extremely useful tool for monitoring and mapping changes in properties of many different materials in a quantitative manner.
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During the course of electrochemical experiments with tetracyanoq
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