Mitigating the Thermal Bottleneck in Polycrystalline Diamond Films by Gradient ICP Etching of the Nucleation Layer

A defect-rich nucleation layer near the substrate is widely regarded as a key thermal bottleneck in thick polycrystalline diamond films. Here, we quantitatively evaluate this effect by progressively removing the nucleation layer via depth-controlled inductively coupled plasma (ICP) etching and measuring the thermal conductivity. The thermal conductivity increases from 1549.9097 W·m^-1·K^-1 (as-grown) to 1656.1743 W·m^-1·K^-1 (1 h), 1783.3763 W·m^-1·K^-1 (3 h), and 1792.0250 W·m^-1·K^-1 after 5 h of etching, consistent with the reduction of defects and non-diamond carbon revealed by X-ray diffraction (XRD) and Raman analyses. These results provide a quantitative, depth-resolved validation of the nucleation-layer thermal resistance and establish an effective post-growth route to enhance thermal transport in thick polycrystalline diamond films.