Laser-Induced Periodic Surface Structures (LIPSS) on Heavily Boron-Doped Diamond for Electrode Applications

Abstract

Diamond is known as a promising electrode material in the fields of cell stimulation, energy storage (e.g., supercapacitors), (bio)sensing, catalysis, etc. However, engineering its surface and electrochemical properties often requires costly and complex procedures with addition of foreign material (e.g., carbon nanotube or polymer) scaffolds or cleanroom processing. In this work, we demonstrate a novel approach using laser-induced periodic surface structuring (LIPSS) as a scalable, versatile, and cost-effective technique to nanostructure the surface and tune the electrochemical properties of boron-doped diamond (BDD). We study the effect of LIPSS on heavily doped BDD and investigate its application as electrodes for cell stimulation and energy storage. We show that quasi-periodic ripple structures formed on diamond electrodes laser-textured with a laser accumulated fluence of 0.325 kJ/cm² (800 nm wavelength) displayed a much higher double-layer capacitance of 660 μF/cm² than the as-grown BDD (20 μF/cm²) and that an increased charge-storage capacity of 1.6 mC/cm² (>6-fold increase after laser texturing) and a low impedance of 2.74 Ω cm² turn out to be appreciable properties for cell stimulation. Additional morphological and structural characterization revealed that ripple formation on heavily boron-doped diamond (2.8 atom % [B]) occurs at much lower accumulated fluences than the 2 kJ/cm² typically reported for lower doping levels and that the process involves stronger graphitization of the BDD surface. Finally, we show that the exposed interface between sp² and sp³ carbon layers (i.e. the laser-ablated diamond surface) revealed faster kinetics than the untreated BDD in both ferrocyanide and RuHex mediators, which can be used for electrochemical (bio)sensing. Overall, our work demonstrates that LIPSS is a powerful single-step tool for the fabrication of surface-engineered diamond electrodes with tunable material, electrochemical, and charge-storage properties.

Keywords: LIPSS; boron-doped diamond; charge-storage capacity; cyclic voltammetry; impedance spectroscopy; laser texturing; ripples; supercapacitor.

Figure 1

SEM images of (a, d) reference (untreated) BDD, (b, e) laser-textured sample BDD-42 (low accumulated fluence), and (c, f) laser-textured sample BDD-500 (high accumulated fluence). Top images (a–c): low magnification (×10⁴), same scale; bottom images (d–f): high magnification (×10⁵), same scale. The solid lines in (e, f) indicate approximate width values of the ripples; the dashed ellipses in (b, e) indicate faults in the periodicity of the ripples.

Figure 2

(a) Raman spectra of the laser-textured samples BDD-42 (low accumulated fluence) and BDD-500 (high accumulated fluence) before (1) and after (2) acid cleaning. The spectrum of the acid-cleaned reference BDD is also included for comparison. The as-measured curves were normalized relative to the background around 70 cm^–1. The dashed vertical line indicates the position of the (undoped) diamond one-phonon Raman line. (b–e) SEM images of laser-textured samples before (b, d) and after (c, e) acid cleaning, showing clear loss of material. (b,c) Low-fluence BDD-42, (d,e) high-fluence BDD-500. The arrows indicate clear signs of chemical etching.

Figure 3

Cyclic voltammograms of laser-textured samples BDD-42 (low accumulated fluence), BDD-500 (high accumulated fluence), and reference BDD, all (2) after acid cleaning, measured in 0.1 M KCl aqueous solution at 0.1 V/s scan rate. Measurement with a glassy carbon (GC) electrode was added for comparison. Each curve corresponds to the 10th cycle. The indicated background current values were measured at 0.1 V during the forward scan.

Figure 4

(a–c) Cyclic voltammograms of acid-cleaned samples in 0.1 M KCl aqueous solution containing 1 mM Fe(CN)₆^3–/4– at different scan rates. (a) Low accumulated fluence sample BDD-42, (b) high accumulated fluence sample BDD-500, and (c) reference BDD sample. Each CV curve corresponds to the 10th cycle. (d) Relationship between anodic peak current density and square root of the scan rate for each sample. The open symbols with dashed lines belong to measurements (1) before acid cleaning; the closed symbols with full lines correspond to measurements (2) after acid cleaning. The adjusted coefficients of determination, r², of the linear fits were all above 0.993.

Figure 5

(a–c) Cyclic voltammograms of acid-cleaned samples in 0.1 M KCl aqueous solution containing 1 mM Ru(NH₃)₆^3+/2+ at different scan rates. (a) Low accumulated fluence sample BDD-42, (b) high accumulated fluence sample BDD-500, and (c) reference BDD sample. Each CV curve corresponds to the 10th cycle. (d) Relationship between anodic peak current density and square root of the scan rate for each sample. The open symbols with dashed lines denote measurements (1) before acid cleaning; the closed symbols with full lines correspond to measurements (2) after acid cleaning. The adjusted r² values of the linear fits were all above 0.95.

Figure 6

Randles circuit modeling a single faradic reaction coupled with mass transfer. It contains the electric double layer in the constant-phase element (CPE), Q, the heterogeneous electron transfer in R_CT, and the diffusion of species near the electrode surface in the Warburg element, W. In the fitting, W was treated as a CPE with a phase of ∼45° (i.e., n_W ≈0.5). The series resistance, R_S, accounts for bulk electrode resistivity, electrolyte resistivity, and contact resistances.

Figure 7

XPS spectra of the laser-textured samples at different stages: (1) before acid cleaning, (2) after acid cleaning, and (3) after polarization in HNO₃. (a) Low accumulated fluence sample BDD-42; (b) high accumulated fluence sample BDD-500. Spectra of the reference BDD after acid cleaning were added for comparison. The spectra are shown as measured, i.e., without correction of conductivity-induced shift in energy.

Figure 8

Effect of strong polarization in HNO₃ on the subsequent electrochemical behavior of the laser-textured samples. (a, b) Cyclic voltammograms in 0.1 M KCl aqueous solution containing 1 mM Fe(CN)₆^3–/4– at different scan rates. (c, d) Cyclic voltammograms in 0.1 M KCl aqueous solution containing 1 mM Ru(NH₃)₆^3+/2+ at different scan rates. (e) Cyclic voltammograms in 0.1 M KCl aqueous solution without redox couple. Each curve corresponds to the 10th cycle. (f) Relationship between anodic peak current density and square root of the scan rate, for each sample, for both redox couples. The linearity was high in all cases, with all r² above 0.99.

Figure 9

(a) Raman spectra of the laser-textured BDD samples after strong polarization in 0.1 M HNO₃. The spectrum of the acid-cleaned reference BDD was added for comparison. The dashed vertical line indicates the position of the (undoped) diamond one-phonon Raman line. The inset shows a photograph of the BDD-500 sample after the treatment, highlighting the physical change of the surface inside the active area (yellow arrow). (b, c) SEM images of (b) BDD-42 and (c) BDD-500 after polarization in HNO₃.

Figure 10

Cross-sectional SEM images of (a) reference BDD (i.e., before texturing), (b) BDD-42 (low accumulated fluence) sample after texturing and acid cleaning, (c) BDD-42 after strong polarization in 0.1 M HNO₃, (d) BDD-500 (high accumulated fluence) sample after texturing and acid cleaning, (e) higher magnification of (d), and (f) BDD-500 after strong polarization in 0.1 M HNO₃. The images were acquired with 10° tilt toward the surface. Images are at the same scale, except for (e). (g) Schematic description of (a), (b), and (c), respectively, in (i), (ii), and (iii).

Figure 11

Time-dependent voltammograms (left axis) and total charge-storage capacity (right axis) of the laser-textured samples BDD-42 (low accumulated fluence), BDD-500 (high accumulated fluence), and reference BDD, all after acid cleaning, measured in 0.1 M KCl aqueous solution at 0.1 V/s scan rate. Each curve corresponds to the 10th cycle.