An extremely high vacuum cold-field electron emission (CFE) gun operating at pressures ranging from ∼10-8 Pa to ∼10-10 Pa was constructed. Only the CFE current emitting from W(310) surfaces revealed the existence of a "stable region" with high current angular density just after tip flash heating. In the "stable region," the CFE current was damped very slowly. The presence of non-hydrogen gas eliminated this region from the plot. Improvement of the vacuum prolonged the 90% damping time of the CFE current from ∼10 min to 800 min. The current angular density I′ of CFE current was 60 and 250 μA/sr in the "stable region" for total CFE currents of 10 and 50 μA, respectively. These results were about three times larger than I′ when measured after the complete damping of the CFE current. The CFE gun generated bright scanning transmission electron microscopy images of a carbon nanotube at 30 kV.
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