Control of localized nanorod formation and patterns of semiconducting CuTCNQ phase I crystals by scanning electrochemical microscopy

Use of the technique of scanning electrochemical microscopy (SECM) enables the surface of single crystals of 7,7',8,8'-tetracyanoquinodimethane (TCNQ) to be modified in a controlled manner to produce highly dense and micrometer sized regions of semiconducting phase 1 CuTCNQ nanorod crystals by a nucleation and growth mechanism. This method involves the localized reduction of solid TCNQ to TCNQ(-) by aqueous phase V-(aq)(2+) reductant generated at a SECM ultramicroelectrode tip by reduction of V-(aq)(2+), coupled with the incorporation and reduction of Cu-(aq)(2+) ions also present in the aqueous electrolyte. SECM parameters can be systematically varied to control the extent of surface modification and the packing density of the CuTCNQ crystals. Scanning electron microscopy (SEM) and atomic force microscopy (AFM) images provide evidence that the TCNQ to CuTCNQ solid-solid transformation is accompanied by a drastic localized crystal volume and morphology change achieved by fragmentation of the TCNQ crystal surface. Patterns of semiconducting CuTCNQ (phase 1) nanorod shaped crystals have been characterized by SEM, AFM, and infrared (IR) techniques. A reaction scheme has been proposed for the interaction between the electrogenerated mediator V-(aq)(2+), Cu-(aq)(2+), and the TCNQ crystal in the nucleation and growth stages of phase 1 CuTCNQ formation.