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Achieving high current emission from one-dimensional nanowire (NW) field emitters is essential for their application as X-ray sources. In this study, field emission (FE) from tungsten trioxide NWs ...

In pursuing high emission current density and high brightness, it is difficult to avoid vacuum breakdown in nanowire cold cathode systems, which will shorten the lifetime of the electron sources. Therefore, investigations on the vacuum breakdown process are important for semiconductor nanowire point electron sources. In this study, non-catastrophic breakdown phenomena that could extend the lifetime of the nanowire electron source were observed in the field emission processes of individual defective WO3−x nanowires. In this non-catastrophic breakdown process, only part of the nanowire emitter was destroyed. After the breakdown, the remaining part of the nanowire could still emit electrons, and due to the shortening of its length, the maximum field emission current density of the remaining nanowire was increased. These results are consistent with the prediction given by theoretical calculations. A defect-related electrical transport induced breakdown mechanism and Nottingham effect induced cooling effect were proposed to be the main causes of this phenomenon. Our work provides an approach for designing long lifetime semiconductor nanowire point electron sources.

Field emission current stability and brightness are important criteria for commercial field emission point electron sources. Here, field emission point electron sources were fabricated from individual WO3 nanowires (NWs) and stable emission was achieved under ∼10−5 Pa. The reduced brightness of one of the emitter was ∼6.08 × 109 A m−2·sr−1 V−1, which was comparable to commercial cold cathode sources. One of the individual WO3 field emitters could operate at an emission current of 0.68 μA for tens of hours without degradation using a ballast resistor regulator. A current fluctuation of the emitter, at a low emission current of 155 nA, was 0.045% for the short-term. Its long-term fluctuation, at 0.68 μA, was 3.89% for 38 h. Besides the ballast resistor, inert surface of the oxide NW and low tip temperature owing to the defect-related field emission mechanism were proposed as the reasons for such high emission stability under mild high vacuum. Our result was significant in the development of stable field emission point sources.

Field emission properties of $\mathbf{WO}_{\pmb{3-}\mathbf{x}}$ nanowires prepared on glass substrate were studied. Current up to 3 mA were achieved from an effective area of 0.25 cm2, corresponding to a current density of 12 mA/cm2. Field emission from individual $\mathbf{WO}_{\pmb{3}-\mathbf{x}}$ nanowires was also studied in order to understand the high current emission mechanism. Based on the experimental results on field emission behavior of individual $\mathbf{WO}_{\pmb{3-}\mathbf{x}}$ nanowires with different defect concentrations, it is proposed that the high current relates to the defect-induced transportation in the nanowire. The results were supported by theoretical calculation using a model considering the defect-related electric transport and Joule heating in the field emission process. Our results are important for exploring a large area high brightness X-ray flat panel source.

In pursuing high emission current density and high brightness, it is difficult to avoid vacuum breakdown in nanowire cold cathode systems, which will shorten the lifetime of the electron sources. Therefore, investigations on the vacuum breakdown process are important for semiconductor nanowire point electron sources. In this study, non-catastrophic breakdown phenomena that could extend the lifetime of the nanowire electron source were observed in the field emission processes of individual defective WO3-x nanowires. In this non-catastrophic breakdown process, only part of the nanowire emitter was destroyed. After the breakdown, the remaining part of the nanowire could still emit electrons, and due to the shortening of its length, the maximum field emission current density of the remaining nanowire was increased. These results are consistent with the prediction given by theoretical calculations. A defect-related electrical transport induced breakdown mechanism and Nottingham effect induced cooling effect were proposed to be the main causes of this phenomenon. Our work provides an approach for designing long lifetime semiconductor nanowire point electron sources.

In this study, we proposed a theoretical model for one-dimensional semiconductor nanowires (NWs), taking account of the defect-related electrical transport process. The maximum emission current density was calculated by considering the influence of Joule heating, using a one-dimensional heat equation. The field emission properties of individual CuO NWs with different electrical properties were studied using an in situ experimental technique. The experimental results for maximum emission current density agreed well with the theoretical predictions and suggested that multiple conduction mechanisms were active. These may be induced by the concentration of defects in the CuO NW. The concentration of defects and the transport mechanisms were found to be key factors influencing the maximum field emission current density of the semiconductor NW. As is limited by the change of resistivity with temperature, only thermal runaway can trigger breakdown in CuO NWs.

The temperature dependence of the field emission properties of CuO nanowires was studied from 163 to 453 K. Large current increases were observed with increasing temperature, which cannot be explained by band to band excitation or emission from the valence band. Two distinct sections were observed from the Arrhenius plot. Activation energies of 100 meV for the high-temperature range (273 to 453 K) and 26.4 meV for the low-temperature range (163 to 273 K) were obtained. Phonon-assisted and defect-assisted thermal field emission mechanisms from p-type CuO NWs were proposed to explain the observed phenomena in the two temperature ranges, which relate to the defect-induced localized states. Numerical simulation using the proposed mechanism was carried out and a good fit with the experimental results was achieved. The results suggest that defect-induced localized states play an important role in field emission from nanowires.

A theoretical model for one-dimensional CuO nanowire was established considering transport mechanisms induced by different defect concentration. By using a one-dimensional heat equation, the emission current was calculated by considering the temperature induced by the emission current. The maximum emission current density and maximum applied field was studied considering different electrical properties. From the obtained results, we elucidate the relationship between electrical properties and field emission properties. Finally, the theoretical results were compared with experimental field emission data measured from individual CuO nanowires of different electrical properties.