Nanoprotrusion (NP) on metal surface and its inevitable contamination layer under high electric field is often considered as the primary precursor that leads to vacuum breakdown, which plays an extremely detrimental effect for high energy physics equipment and many other devices. Yet, the NP growth has never been experimentally observed. Here, we conduct field emission (FE) measurements along with in situ transmission electron microscopy (TEM) imaging of an amorphous-carbon ($a\text{−}\mathrm{C}$) coated tungsten nanotip at various nanoscale vacuum gap distances. We find that under certain conditions, the FE current-voltage ($I\text{−}V$) curves switch abruptly into an enhanced-current state, implying the growth of an NP. We then run field emission simulations, demonstrating that the temporary enhanced-current $I\text{−}V$ is perfectly consistent with the hypothesis that a NP has grown at the apex of the tip. This hypothesis is also confirmed by the repeatable in situ observation of such a nanoprotrusion and its continued growth during successive FE measurements in TEM. We tentatively attribute this phenomenon to field-induced biased diffusion of surface $a\text{−}\mathrm{C}$ atoms, after performing a finite element analysis that excludes the alternative possibility of field-induced plastic deformation.

中文翻译：

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原位观察碳涂层钨纳米尖上的场诱导纳米突起生长

金属表面的纳米突起（NP）及其在高电场下不可避免的污染层通常被认为是导致真空击穿的主要前驱体，这对高能物理设备和许多其他装置产生极其不利的影响。然而，纳米粒子的生长从未在实验中被观察到。在这里，我们对非晶碳进行场发射（FE）测量以及原位透射电子显微镜（TEM）成像（$A\text{-}\mathrm{C}$）在各种纳米级真空间隙距离处涂覆钨纳米尖端。我们发现在一定条件下，FE 电流-电压 ($我\text{-}V$）曲线突然切换到增强电流状态，这意味着纳米粒子的生长。然后我们进行场发射模拟，证明临时增强电流$我\text{-}V$与 NP 在尖端顶点生长的假设完全一致。这种纳米突起的可重复原位观察及其在 TEM 连续 FE 测量过程中的持续生长也证实了这一假设。我们暂时将这种现象归因于场致表面的偏置扩散$A\text{-}\mathrm{C}$在进行有限元分析后，排除了场引起塑性变形的另一种可能性。