Laser-patterned boron-doped diamond electrodes with precise control of sp2/sp3 carbon lateral distribution

A thorough study on sp³ to sp² carbon conversion in undoped and boron-doped diamond (BDD) thin (approx 500 nm) layers leading to the desired sp²/sp³ carbon ratio and lateral distribution, which utilises boron atom incorporation and infrared (IR) material laser processing has been performed. Polycrystalline as-grown (AG) or chem-mechanically polished (CMP) undoped diamond/BDD layers were investigated with respect to boron content and laser wavelength (800, 1030 nm). Boron incorporation leads to an increase in IR optical absorption and reduction of required energy fluence (F_th ~ 1 Jcm^-2) needed for sp³ to sp² carbon conversion. Raman spectroscopy was performed to identify carbon conversion stages and to tailor the ideal parameters for other IR laser sources and required sp²/sp³ carbon ratio. Electrochemical parameters (Delta E_p and Delta I_Ap/I_Cp ratio) were obtained from cyclic voltammetry measurements of outer-([Ru(NH₃)₆]^3-/4-) and inner-([Fe(CN)₆]^3+/2+) sphere redox markers. Values of Delta E_p and I_Ap/I_Cp are mainly influenced after conversion of 10% of sp³ to sp² carbon. This trend is most pronounced for the [Fe(CN)₆]^3-/4- redox marker, by decrease or increase of these parameters on AG or CMP BDD electrodes respectively. Electrochemical findings were supported by electrochemical impedance spectroscopy where R_ct keeps the same trend as Delta E_p values and double layer capacitance profoundly increases between 10 and 25% of surface conversion.

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