Single electron capacitance spectroscopy of vertical quantum dots using   a single electron transistor
  We have incorporated an aluminum single electron transistor (SET) directly on top of a vertical quantum dot, enabling the use of the SET as an electrometer that is extremely responsive to the motion of charge into and out of the dot. Charge induced on the SET central island from single electron additions to the dot modulates the SET output, and we describe two methods for demodulation that permit quantitative extraction of the quantum dot capacitance signal. The two methods produce closely similar results for the determined single electron capacitance peaks. 
M. Koltonyuk, D. Berman, N. B. Zhitenev, R. C. Ashoori, N. Pfeiffer   and K. W. West