The primary objective of NASA's Genesis Discovery Mission was to obtain accurate data on the isotopic composition of the solar wind, particularly with respect to oxygen isotopes. CVD diamond provides an ideal collector material for a number of reasons: first, it can be made ultra-pure with respect to nitrogen and oxygen; secondly, once ions are implanted in the diamond lattice, little diffusion occurs within the bulk; thirdly, a large surface area can be obtained; and finally, synthetic diamond can be enriched with carbon-13, which is critical for the analytical differentiation of the oxygen isotopes. The major drawback associated with CVD diamond is its inherently high resistivity. Boron is typically added to the diamond growth environment in order to increase the conductivity; however, Genesis Mission specifications eliminated this option. Instead, reactor conditions were manipulated to introduce small amounts of sp2-bonded carbon, which allowed the resistivity specifications for the mission to be met.
Baker, C., Laplante, J., & McNamara, K. M. (2000). Conductive low impurity diamond for solar wind collection. Diamond and Related Materials, 9(12), 1951–1956. https://doi.org/10.1016/S0925-9635(00)00333-2