The First Fifty Years of Atom Probe
The First Fifty Years of Atom Probe
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原子探测器的前五十年
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发表时间：
2017
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通讯作者：
J. Panitz
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作者：
T. Kelly;J. Panitz
在简要回顾历史先例的基础上，讲述了原子探针的诞生及其关键演变步骤：从最早的场发射实验到最新的先进发光二极管的三维竞争分析。我们注意到，电子显微镜和原子探针几乎是20世纪提供原子级成像的兄弟技术。考虑到发展的速度，下一个五十年应该更令人惊讶。1967年之前的事件原子探针的历史是与电子显微镜和原子成像探索的共同历史。它从一个经典的实验开始，为物质的量子理论提供了初步的验证。1928年，Eyring，Mackeown和Millikan（后来的油滴名声）发表了“Field Currents from Points”，其中他们测量了真空玻璃灯泡中尖锐金属阴极的电流（图1），这是当时已知的经典物理学无法预测的[1]。Eyring，Mackeown和Millikan进一步表明，“......当该点成为阳极时，尝试引出电流。当从本实验室建造的直流发电机施加100，000伏电压时，没有获得电流。这相当于每厘米35 × 108伏的电场。”他们几乎不知道，他们所处的电场比从尖端场蒸发铁原子所需的电场大一个数量级。1928年，福勒和诺德海姆通过调用被称为“隧道”的纯量子力学过程，从理论上解释了他们测量的电流对电压的指数依赖性[2]。1937年，约翰逊和肖克利发表了圆柱形几何结构的电子发射图像[3]的一年后，埃尔温·威廉·穆勒将一种细粉矿物（在电子轰击下会发出荧光的硅锌矿）放在一台设备的阴极上，场发射显微镜，或我们所知道的FEM，诞生了[4]。FEM中的电子图像反映了在106的放大率和约10 nm的分辨率下阴极点的顶点上的功函数的变化。通过改变阴极和阳极之间的距离可以改变放大率，并且图像对外部振动不敏感。有限元分析表明，金属表面的功函数取决于其晶体结构。因此，它解释了自密立根1914年的实验证实了爱因斯坦在1905年对光电效应的解释以来，从平坦阴极表面测量到的光电子发射的令人困惑的变化。有限元法对新兴的真空管工业也是一个布恩，因为穆勒表明，添加低功函数的材料，如钡，可以蒸发到阴极尖端，以降低其功函数，从而大大增加其电子的电子发射。可以在发射模式中看到与样本中存在的晶体对称性一致的结构[5]。在接下来的十年里，随着图案的质量和分辨率的稳步提高，人们对这项技术是否能一直改进到分辨原子产生了极大的兴趣。穆勒在1940年代一直追求这一理想。他的工作被第二次世界大战严重中断。事实上，他几乎死于饥饿在德国在这段时间以来，科学家谁不合作，第三赖希被排斥。战争结束后，穆勒被邀请移民到美国，他选择了宾夕法尼亚州立大学（现在的大学），因为现场提醒他的家乡地区。在这里，他的工作发生了转变。用于提高FEM图像分辨率的技术之一是通过反转极性来清洁尖端。这似乎去除了吸附的气体，并给出了更清晰的FEM图像。在某个时候，穆勒和他的团队考虑了解吸气体的投影中是否有任何结构，就像FEM图像一样。他们将气体引入真空中，以确保针上的气体原子供应（图2a），并确实在图1中找到了详细的结构：Eyring等人在1928年的场发射实验中使用的设备。使用钢针和阳极。
With a brief look to historical precedence, the birth of atom probe and its key evolutionary steps are recounted: from the earliest field emission experiments to the latest three-dimensional competitive analysis of advanced light emitting diodes. We note that electron microscopy and atom probe have been almost sibling twentiethcentury technologies that provide atomic-level imaging. Given the rate of development, the next fifty years should be even more amazing. Events Prior to 1967 The history of the atom probe is a shared history with electron microscopy and the quest to image atoms. It begins with a classic experiment that provided an initial verification for the quantum theory of matter. In 1928 Eyring, Mackeown, and Millikan (later of oil drop fame) published “Field Currents from Points” in which they measured a current from a sharply pointed metal cathode in an evacuated glass bulb (Figure 1), which was not predicted by the classical physics known at the time [1]. Eyring, Mackeown, and Millikan further showed that “... an attempt was made to draw a current when the point was made the anode. No current was obtained when 100,000 volts was applied from a direct current generator built in this laboratory. This corresponds to a field at the point of 35 × 108 volts per centimeter.” Little did they know that they were at an order of magnitude greater electric field than needed to field evaporate iron atoms from the tip. The exponential dependence of the current on the voltage that they measured was explained theoretically in 1928 by Fowler and Nordheim by evoking the purely quantum mechanical process known as “tunneling” [2]. In 1937, a year after Johnson and Shockley published electron emission images from a cylindrical geometry [3], Erwin Wilhelm Müller placed a finely powdered mineral (Willemite, that fluoresces under electron bombardment) on the cathode of an apparatus and the field emission microscope, or FEM as we know it, was born [4]. The electron image in the FEM reflects the variation in work function on the apex of the cathode point at a magnification of 106 and a resolution of about 10 nm. The magnification can be varied by changing the distance between the cathode and the anode, and the image is insensitive to external vibrations. The FEM demonstrated that the work function of a metal surface depends on its crystallography. It therefore explained the puzzling variation in photoelectron emission measured from flat cathode surfaces since Millikan’s 1914 experiment that confirmed Einstein’s explanation of the photoelectric effect in 1905. The FEM was also a boon to the emerging vacuum tube industry because Müller showed that the addition of a low-work-function material like barium could be evaporated onto a cathode tip to decrease its work function, thereby greatly increasing its thermionic emission of electrons. It was possible to see structure in the emission pattern that was consistent with the crystallographic symmetry present in the specimen [5]. Over the next decade, with steady improvement in quality and resolution of the patterns, there was great interest to see if the technique could be improved all the way to resolving atoms. Müller pursued this ideal into the 1940s. His work was interrupted severely by World War II. Indeed, he almost died of starvation in Germany during that time since scientists who did not cooperate with the Third Reich were ostracized. After the war, Müller was invited to emigrate to the USA, and he chose Pennsylvania State College (now University) because the locale reminded him of his home region. Here, his work took a turn. One of the techniques used to improve the resolution of FEM images was to clean the tip by reversing the polarity. This seemed to remove adsorbed gases and gave sharper FEM images. At some point, Müller and his group considered whether there was any structure in the projection of the desorbed gasses, much like FEM images. They introduced a gas into the vacuum to ensure a supply of gas atoms on the needle (Figure 2a) and indeed found detailed structure in the Figure 1: Apparatus used in the 1928 field emission experiments by Eyring et al. [1]. A steel needle and anode were used.