"Doping" is manipulation of the crystals of these, a class of solids found in transistors
He soon found that with higher quality crystals their finicky behaviour 
went... [DOC] [TLE] Advanced Materials - Early View - Wiley Online Library [PAR] A Solid Dual-Ions-Transformation Route to S,N Co-Doped Carbon ... is reported 
to achieve the goal of successfully doping S and N into hollow carbon nanotubes.