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Chemical identification of individual surface atoms by atomic force microscopy

机译：通过原子力显微镜对单个表面原子进行化学鉴定

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摘要

Scanning probe microscopy is a versatile and powerful method that uses sharp tips to image, measure and manipulate matter at surfaces with atomic resolution. At cryogenic temperatures, scanning probe microscopy can even provide electron tunnelling spectra that serve as fingerprints of the vibrational properties of adsorbed molecules and of the electronic properties of magnetic impurity atoms thereby allowing chemical identification. But in many instances, and particularly for insulating systems, determining the exact chemical composition of surfaces or nanostructures remains a considerable challenge. In principle, dynamic force microscopy should make it possible to overcome this problem: it can image insulator, semiconductor and metal surfaces with true atomic resolution, by detecting and precisely measuring the short-range forces that arise with the onset of chemical bonding between the tip and surface atoms and that depend sensitively on the chemical identity of the atoms involved. Here we report precise measurements of such short-range chemical forces, and show that their dependence on the force microscope tip used can be overcome through a normalization procedure. This allows us to use the chemical force measurements as the basis for atomic recognition, even at room temperature. We illustrate the performance of this approach by imaging the surface of a particularly challenging alloy system and successfully identifying the three constituent atomic species silicon, tin and lead, even though these exhibit very similar chemical properties and identical surface position preferences that render any discrimination attempt based on topographic measurements impossible.
机译：扫描探针显微镜是一种多功能且功能强大的方法，它使用锋利的尖端以原子分辨率成像，测量和处理表面上的物质。在低温下，扫描探针显微镜甚至可以提供电子隧道光谱，这些光谱可以用作被吸附分子的振动特性和磁性杂质原子的电子特性的指纹，从而可以进行化学识别。但是在许多情况下，尤其是对于绝缘系统，确定表面或纳米结构的确切化学组成仍然是一个巨大的挑战。原则上，动态力显微镜应该可以克服这个问题：它可以检测并精确测量由尖端之间的化学键合产生的短程力，从而以真实的原子分辨率对绝缘体，半导体和金属表面进行成像和表面原子，并且敏感地取决于所涉及原子的化学特性。在这里，我们报告了这种短程化学力的精确测量结果，并表明可以通过归一化程序克服它们对所用力显微镜尖端的依赖性。这样，即使在室温下，我们也可以将化学力测量值用作原子识别的基础。我们通过对特别具有挑战性的合金系统的表面进行成像并成功地识别出三个组成原子种类的硅，锡和铅来说明这种方法的性能，即使它们表现出非常相似的化学性质和相同的表面位置偏好，从而导致任何基于鉴别的尝试在地形测量上是不可能的。

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