Conductive low impurity diamond for solar wind collection

The primary objective of NASA's Genesis Discovery Mission was to obtain acc urate data on the isotopic composition of the solar wind, particularly with respect to oxygen isotopes. CVD diamond provides an ideal collector materi al for a number of reasons: first, it can be made ultra-pure with respect t o nitrogen and oxygen; secondly, once ions are implanted in the diamond lat tice, little diffusion occurs within the bulk; thirdly, a large surface are a can be obtained; and finally, synthetic diamond can be enriched with carb on-13, which is critical for the analytical differentiation of the oxygen i sotopes. The major drawback associated with CVD diamond is its inherently h igh resistivity. Boron is typically added to the diamond growth environment in order to increase the conductivity; however, Genesis Mission specificat ions eliminated this option. Instead, reactor conditions were manipulated t o introduce small amounts of sp(2)-bonded carbon, which allowed the resisti vity specifications for the mission to be met. (C) 2000 Published by Elsevi er Science B.V.