Traceable precision generation and measurement of pA direct currents
  We present the comparison of results from the generation and the measurement of direct currents in the pA range, performed with traceable state-of-the-art methods at highest accuracy. The currents were generated with the capacitor charging method, and measured with the first prototype of a novel picoammeter developed at PTB. The results confirm the agreement between both methods and the linearity of the new picoammeter at an uncertainty level of few microA/A. Also, they shed light on the ac-dc difference of capacitors, crucial for current generation with the capacitor charging method. 
Hansj\"org Scherer, Gerd-Dietmar Willenberg, Dietmar Drung, Martin   G\"otz, and Eckart Pesel
cond-mat.other physics.ins-det