We report the fabrication and operation of an ion source that can be incorporated into a micro-time-of-flight mass spectrometer. The ion source consists of an array of triode emitters with carbon-nanoparticle cathodes. We were able to extract an anode current as large as 94.3 mu A at a gate-bias voltage of 85 V with a concomitant gate current of 38 nA by using the triode structure having a recessed cathode with no gate overhang. Ion-generation tests with acetone molecules were carried out successfully, and we measured monotonic increases in the ion current and ratio between ion and electron currents with respect to acetone pressure. We also present simulation results that show equipotential and electric-field lines under different electrode-bias configurations. (C) 2008 American Vacuum Society.