Growth and characterization of CaFe$_{1-x}$Co$_x$AsF single crystals by   CaAs flux method
  Millimeter sized single crystals of CaFe$_{1-x}$Co$_x$AsF were grown using a self-flux method. It is found that high-quality single crystals can be grown from three approaches with different initial raw materials. The chemical compositions and crystal structure were characterized carefully. The c-axis lattice constant is suppressed by the Co substitution. Superconductivity with the critical transition $T_c$ as high as 21 K was confirmed by both the resistivity and magnetic susceptibility measurements in the sample with $x$ = 0.12. Moreover, it is found that $T_c$ can be enhanced for about 1 K under the very small hydrostatic pressure of 0.22 GPa, which is more quickly than that reported in the polycrystalline samples. Our results is a promotion for the physical investigations of 1111 phase iron-pnictide superconductors. 
Yonghui Ma, Kangkang Hu, Qiucheng Ji, Bo Gao, Hui Zhang, Gang Mu,   Fuqiang Huang, Xiaoming Xie
cond-mat.supr-con