Controlling the morphology of polycrystalline diamond films via seed density: Influence on grain size and film texture

Controlling polycrystalline diamond (PCD) film morphology is crucial for various applications, including thermal management and quantum sensors. PCD films are commonly produced through plasma-enhanced chemical vapor deposition (CVD) on substrates seeded with nanodiamonds, and various film morphologies are achieved by adjusting the deposition parameters. Still, the impact of seed density on film morphology remains vastly unexplored. In this study, we observe that decreasing the seed density leads to an increase in grain size accompanied by the gradual emergence of (1 0 0) facets. This trend persists until reaching a critical seed density, below which films exhibit facets-on-ballas texture. Such films consist of large grains with (1 0 0) facets surrounded by clusters of small grains. The morphology of the films is investigated in-depth with scanning electron microscopy, Raman spectroscopy, and X-ray diffraction. Our observations imply that the concentration of diamond growth precursors increases as seed density decreases. This assertion is supported by a detailed deposition rate study, incorporating reflectance data acquired through the deposition process and film thickness measurements. Moreover, our measurements point to a decrease in deposition rate as the fraction of diamond covering the substrate increases. Finally, we provide a tentative explanation for our observations. In summary, our research underscores the crucial influence of seed density on the morphology of PCD films synthesized by CVD. It also highlights that maintaining a relatively low seed density can be essential for producing facets-on-ballas films. These films typically contain pyramid-shaped grains, which offer numerous applications due to their unique shape.