Sugimoto Yoshiaki, Pou Pablo, Abe Masayuki, Jelinek Pavel, Pérez Rubén, Morita Seizo, Custance Oscar
Graduate School of Engineering, Osaka University, 2-1 Yamada-Oka, 565-0871 Suita, Osaka, Japan.
Nature. 2007 Mar 1;446(7131):64-7. doi: 10.1038/nature05530.
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.
扫描探针显微镜是一种多功能且强大的方法，它使用尖锐的探针在表面以原子分辨率对物质进行成像、测量和操控。在低温下，扫描探针显微镜甚至能够提供电子隧穿光谱，这些光谱可作为吸附分子振动特性和磁性杂质原子电子特性的指纹，从而实现化学识别。但在许多情况下，尤其是对于绝缘体系，确定表面或纳米结构的确切化学成分仍然是一项颇具挑战的任务。原则上，动态力显微镜应该能够克服这个问题：它可以通过检测和精确测量随着探针与表面原子之间化学键形成而产生的短程力，以真正的原子分辨率对绝缘体、半导体和金属表面进行成像，而这些短程力敏感地依赖于所涉及原子的化学特性。在此，我们报告了对这类短程化学力的精确测量，并表明通过归一化程序可以克服它们对所用力显微镜探针的依赖性。这使我们即使在室温下也能将化学力测量用作原子识别的基础。我们通过对一个特别具有挑战性的合金体系表面进行成像，并成功识别出三种组成原子硅、锡和铅，展示了这种方法的性能，尽管这些原子表现出非常相似的化学性质以及相同的表面位置偏好，使得基于形貌测量的任何区分尝试都无法实现。
