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The Zr/O/W Schottky-type thermal field emission cathode is a key component in advanced electron beam instrumentation, with its unique interfacial emission mechanism remaining a focus of research in cathode technology. Traditional understanding attributes the decrease of work function at the cathode tip to a monolayer adsorption of Zr-O dipoles on the W(100) facet, with the electropositive orientation directed outward, perpendicular to the surface. This study successfully fabricats a high-performance Zr/O/W Schottky-type thermal field emission cathode that exhibits exceptional emission characteristics, including a current density of 2.5×104 A/cm2 and operational stability exceeding 8000 h. Comprehensive microstructural characterization of the activated emission zone is performed utilizing energy-dispersive X-ray spectroscopy (EDS) and Auger electron spectroscopy (AES), thereby precisely determining elemental distribution profiles across both surface and subsurface regions. The results reveal that during cathode preparation, the zirconia coating diffuses in the form of Zr-O complexes within the tungsten matrix, forming nanoscale enrichment zones specifically on the W(100) facet. Under operational conditions combining elevated temperature (1700–1800 K) and high electric field (>107 V/m), the W(100) surface develops not an adsorbed Zr-O dipole monolayer, but a nanoscale Zr/O/W(100) composite oxide structure. This multilayer structure consists of three coherently integrated components: 1) an oxygen-enriched diffusion layer beneath the W(100) interface, 2) the crystalline W(100) substrate, and 3) an overlying Zr-O thin film with multiatomic-layer thickness. First-principles calculations simulating the dynamic evolution of the W(100) emission interface during thermal treatment corroborate the experimental findings. The computed work function of the cathode emission surface decreases significantly from 5.02 eV (characteristic of nano-WO3) to 2.85 eV, showing excellent agreement with experimental measurements. When the emission interface becomes unbalanced due to external perturbations, the continuous diffusion of the zirconia coating toward the tip region, combined with the diffusion of Zr-O complexes from the subsurface of the W(100) crystal plane to the interface, enables autonomous replenishment of surface-active sites. This dynamic process effectively maintains a stable low-work-function emission surface. Both theoretical and experimental evidence consistently demonstrate that the Zr/O/W(100) oxide film serves as the fundamental material basis for the exceptional emission current density, remarkable stability, and extended operational lifetime of Zr/O/W cathodes.
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Keywords:
- Zr/O/W /
- thermal field emission cathode /
- electron emission
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图 2 Zr/O/W肖特基式热场发射阴极(R = 600 nm)在不同温度下的肖特基曲线
Figure 2. Schottky plots of Zr/O/W Schottky thermal field emission cathode at three tip temperatures (R = 600 nm).
图 3 Zr/O/W肖特基式场发射阴极SEM图(20000 X) (a) 发射测试前; (b) 发射测试后
Figure 3. SEM images of Zr/O/W Schottky thermal field emission cathodes (20000 X): (a) Before emission testing; (b) after emission testing.
图 4 Zr/O/W肖特基式场发射阴极发射端SEM俯视图(50000 X)
Figure 4. Top-view SEM image of the emission tip on Zr/O/W Schottky thermal field emission cathodes (50000 X).
图 5 阴极涂层至发射区SEM图(300 X)
Figure 5. SEM image of coating-to-emitter transition region (300 X).
图 6 发射端表面SEM图(50000 X) (1) W(100)面取点1; (2) 侧发射区取点2和3; (3)非理想发射区取点4和5
Figure 6. Surface SEM morphology of emitter tip (50000 X) with selected analysis points: (1) Take point 1 from the W(100) surface; (2) take points 2 and 3 from the side emission area; (3) take points 4 and 5 from the non-ideal emission area.
图 7 图6中阴极表面点1的成分深度分布
Figure 7. Composition depth profile at Point 1 of Fig.6 on surface.
图 8 Zr/O/W肖特基式场发射阴极表面层晶胞模型 (a) W2Zr2O4; (b) W2Zr1O5; (c) W2O6
Figure 8. Unit cell models of surface layer in Zr/O/W Schottky thermal field emission cathodes: (a) W2Zr2O4; (b) W2Zr1O5; (c) W2O6.
图 9 Zr/O/W肖特基式场发射阴极表面层升温过程图
Figure 9. In-situ surface layer of Zr/O/W Schottky thermal field emission cathodes under thermal activation.
表 1 不同工作温度W(100)晶面的元素组成
Table 1. Elemental composition of the W(100) crystal plane at various working temperatures.
序号 温度/
KW atomic percent/% O atomic percent /% Zr atomic percent /% 110503 1700 96.91 2.59 0.51 120902 1750 95.22 3.78 1.01 122804 1800 91.54 6.49 1.98 
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表 2 阴极涂层至发射区AES分析结果
Table 2. AES analysis results of the cathode coating-to-emitter transition region.
序号 O atomic
percent/%Zr atomic
percent/%W atomic
percent/%a 34.66 7.11 58.22 b 29.86 6.78 63.35 c 29.92 5.17 64.9 d 32.46 4.6 62.94
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表 3 发射端表面AES分析结果
Table 3. AES analysis results of emitter tip surface.
序号 O atomic percent/% Zr atomic percent/% W atomic percent/% 1 70.27 10.39 19.34 2 65.04 4.54 30.42 3 33.13 2.2 64.67 4 43.31 2.15 54.54 5 47.92 2.51 49.58
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