Electroreduction of Si(NCO)₄ for Electrodeposition of Si

The electrochemical reduction and concomitant suitability of tetraisocyanatosilane, Si(NCO)(4), as a precursor for Si electrodeposition has been examined. At T = 25 degrees C, voltammetric data indicated that the electroreductive pathway of Si(NCO)(4) paralleled the electroreduction of SiCl4, albeit with attenuated current densities. At T = 150 degrees C, the measured current density increased significantly due to coupled reaction likely involving an electropolymerization of the tetraisocyanato ligand. At either temperature, the electrochemical response of Si(NCO)(4) did not strongly depend upon the identity of the anion in the supporting electrolyte. A combination of chronoamperometric, electron microscopy, and X-ray photoelectron spectroscopy data were used to study the morphology and composition of the electrodeposited Si films at room temperature. The composition and morphology of the as-electrodeposited films were consistent with the formation of amorphous Si when using solid n (+)-Si electrodes, similar to what is observed during the electroreduction of SiCl4. Attempts to use Si(NCO)(4) for Si crystal growth by the electrochemical liquid-liquid-solid (ec-LLS) process with a liquid e-GaIn electrode resulted in no appreciable crystalline Si product. Although Si(NCO)(4) can be used for electrodeposition of amorphous Si onto solid electrodes at room temperature, more work is needed to identify conditions that would facilitate its use for ec-LLS.