Effect of anode temperature on molybdenum field-emitter arrays

Thermal treatment of the molybdenum (Mo) tips of the ‘Spindt’ type field-emitter arrays (FEA) was investigated, which involved obtaining a certain level of cathode emission current at room temperature and then gradually increasing the anode temperature upto 670°C. The increase in temperature was achieved by increasing the anode voltage (VA) from an initial value of 700–1000 V and finally to 1500 V. Measurements were carried out in a stainless-steel pumped system with a base pressure <1.3×10−10 Pa (<10−10 Torr). The current–voltage (I–V) characteristics, during these various steps, were analyzed. Using Fowler–Nordheim (FN) plots, the work function changes (Δφ) were calculated. The work-function variation with anode temperature was linear. The emission current was determined as a function of the anode temperature. At constant applied voltage, the emission current increased by ∼23% on raising the anode temperature. This increase produced the same emission current for about a 30% smaller applied voltage than that required prior to increasing the temperature, and reasons for this increase are analyzed. The residual-gas analyzer (RGA) detected increasing concentrations of hydrogen and CO at elevated temperatures. Stability measurements at various levels of emission current demonstrated a high level of stability. Scanning electron microscopy (SEM) studies of the tip profile showed that the Mo tips were not affected by the thermal treatment at elevated temperatures.