C-axis transport of pnictide single crystals.

Mesa-type structures of $\sim $1 $\mu $m$^{2}$ area were fabricated on the (ab) plane of small LaO$_{0.9}$F$_{0.1}$FeAs single crystals. Resistance vs. temperature measurements showed a metallic behavior with a residual resistance ratio higher than 10. Both magnetic susceptibility and transport measurements showed the same value for the critical temperature, i.e. $\sim $20K. Current-voltage characteristics are typical for overdamped Josephson junctions with a critical current density of $\sim $10$^{5}$ A/cm$^{2}$. Moreover, the critical current vs. temperature dependence follows the Ambegaokar-Baratoff relation for the maximum dc Josephson current. One possible explanation could be that we have observed an intrinsic Josephson effect in $<$c$>$-direction. This is supported by recent measurements of radiation emission between 11 and 12 GHz. Finally, we discuss current injection effects on Josephson critical current and T$_{c}$.