▎ 摘　　要

We performed spin transport measurements on boron nitride based single layer graphene devices with mobilities up to 40 000 cm(2) V-1 s(-1). We could observe spin transport over lengths up to 20 mu m at room temperature, the largest distance measured so far for graphene. Due to enhanced charge-carrier diffusion, spin relaxation lengths are measured up to 4.5 mu m. The relaxation times are similar to values for lower quality SiO2-based devices, around 200 ps. We find that the relaxation rate is determined in almost equal measures by the Elliott-Yafet and D'Yakonov-Perel mechanisms.