Improvement of Morphology and Electrical Properties of Boron-doped Diamond Films via Seeding with HPHT Nanodiamonds Synthesized from 9-Borabicyclononane

TL;DR

This study demonstrates that boron-doped diamond films grown with boron-doped nanodiamond seeding layers exhibit improved morphology and electrical properties, with H-BND seeding producing the best results for electronic applications.

Contribution

It introduces a new boron-doped nanodiamond synthesis method and shows its effectiveness as a seeding layer for high-quality boron-doped diamond film growth.

Findings

H-BND seeding yields larger crystal sizes and lower sheet resistance.

All nanodiamond types enable dense, fully closed diamond films.

H-BND seeding results in films with superior electrical conductivity.

Abstract

Boron-doped diamond (BDD) films are becoming increasingly popular as electrode materials due to their broad potential window and stability in harsh conditions and environments. Therefore, optimizing the crystal quality and minimizing defect density to maximize electronic properties (e.g. conductivity) of BDD is of great importance. This study investigates the influence of different hydrogenated nanodiamond (H-ND) seeding layers on the growth and properties of BDD films. Three types of seeding H-NDs were examined: detonation (H-DND) and top-down high-pressure high-temperature NDs (TD_HPHT H-ND), and boron-doped NDs (H-BND) newly synthesized at high-pressure high-temperature from an organic precursor. Purified and oxidized BND (O-BND) samples yielded clear, blue, and stable colloidal dispersions. Subsequent thermal hydrogenation reversed their zeta potential from - 32 mV to + 44 mV and promoted the seeding of negatively charged surfaces. All three H-ND types formed dense seeding layers on SiO2 and Si/SiOx substrates, which enabled the growth of BDD films by chemical vapor deposition (CVD). Despite variations in initial surface coverage among the seeding layers (13-25%), all NDs facilitated the growth of fully closed BDD films approximately 1 {\mu}m thick. Significant differences in film morphology and electrical properties were observed. H-BND nucleation yielded the BDD films with the largest crystals (up to 1 000 nm) and lowest sheet resistance (400 ohm/sq). This superior performance is attributed to the uniform particle shape and monocrystalline character of H-BND, as corroborated by FTIR, TEM, and SAXS measurements. These findings highlight the critical role of seeding layer properties in determining consequent diamond film evolution and establish H-BNDs as promising seeding material for the growth of high-quality BDD films suitable for electronic and electrochemical applications.