National Institute for Materials Science, Tsukuba, Ibaraki 305-0047, Japan.
Graduate School of Pure and Applied Science, University of Tsukuba, Tsukuba, Ibaraki 305-8577, Japan.
Nat Nanotechnol. 2016 Mar;11(3):273-9. doi: 10.1038/nnano.2015.276. Epub 2015 Nov 30.
Electron sources in the form of one-dimensional nanotubes and nanowires are an essential tool for investigations in a variety of fields, such as X-ray computed tomography, flexible displays, chemical sensors and electron optics applications. However, field emission instability and the need to work under high-vacuum or high-temperature conditions have imposed stringent requirements that are currently limiting the range of application of electron sources. Here we report the fabrication of a LaB6 nanowire with only a few La atoms bonded on the tip that emits collimated electrons from a single point with high monochromaticity. The nanostructured tip has a low work function of 2.07 eV (lower than that of Cs) while remaining chemically inert, two properties usually regarded as mutually exclusive. Installed in a scanning electron microscope (SEM) field emission gun, our tip shows a current density gain that is about 1,000 times greater than that achievable with W(310) tips, and no emission decay for tens of hours of operation. Using this new SEM, we acquired very low-noise, high-resolution images together with rapid chemical compositional mapping using a tip operated at room temperature and at 10-times higher residual gas pressure than that required for W tips.
一维纳米管和纳米线形式的电子源是 X 射线计算机断层扫描、柔性显示器、化学传感器和电子光学应用等各种领域研究的重要工具。然而，场发射不稳定性以及需要在高真空或高温条件下工作的要求，对电子源的应用范围施加了严格的限制。在这里，我们报告了一种仅在尖端结合了少数几个 La 原子的 LaB6 纳米线的制造，该纳米线从单个点发射具有高单色性的准直电子。纳米结构尖端的功函数低至 2.07eV（低于 Cs 的功函数），同时保持化学惰性，这两个性质通常被认为是相互排斥的。在扫描电子显微镜（SEM）场发射枪中安装后，我们的尖端显示出的电流密度增益比 W(310)尖端高约 1000 倍，并且在数十小时的操作中没有发射衰减。使用这种新型 SEM，我们在室温下操作尖端，同时在比 W 尖端所需的残留气体压力高 10 倍的条件下，获得了非常低噪声、高分辨率的图像以及快速的化学成分映射。
