Growth and control of nanoprotrusions on iridium field emitters

We report on the direct observation of the growth of nanoprotrusions on iridium held-emission tips. For clean, protrusion-free field emitters, the field emission originated from crystal planes with low-work-function values. However, with continuous operation, we observed the growth of nanoprotrusions on crystalline planes where there was initially no detectable emission. The protrusions were estimated to be approximately 2-3 nm in diameter and 5-15 nm in height. Protrusion growth led to an increase in held-emission current by several orders of magnitude. However, the tips were destroyed when operated with sustained emission current values greater than 10 muA. We found that stable operation and control of protrusion growth can be achieved by either progressively reducing the anode voltage or by adding a series resistor. (C) 2001 American Institute of Physics.