Forces and Currents in Carbon Nanostructures: Are We Imaging Atoms?

Thanks to its special material properties and expected applications in nanotechnology the carbon materials has been recently a subject of an intensive research. Although the atomic resolution of an image from scanning electron microscope (SEM) can be achieved rather routinely, accurate measurement of positions of single atoms creating various carbon structures is very difficult. In collaboration with colleagues from Spain we have proved by detailed theoretical calculations that maximum contrast in images with atomic resolution may not correspond with individual atoms. On the contrary, areas with increased signal correspond with hollow inter-atomic positions. Theoretic simulations furthermore confirmed the origin of atomic contrast in SEM is not caused by van der Waals force as it has been assumed so far but by a short-range force induced by creation of chemical bonding between individual atoms of an examined material and a tip of the microscope. Precise localization of single atoms is of essential importance for further research of properties of these materials as well as physical and chemical processes within them.

a)–c) schematically show possible types of atomically differentiated graphen images obtained with SEM; d) are results of computer simulations of contrast of microscopic graphene image for various models of atomic force microscope tip and different tip-surface distance.

¹Institute of Physics, Academy of Sciences of the Czech Republic, Cukrovarnická 10, 162 00, Prague, Czech Republic
²Departamento de Física Teórica de la Materia Condensada, Universidad Autónoma de Madrid, E-28049 Madrid, Spain
³Instituto de Ciencia de Materiales de Madrid (ICMM-CSIC), E-28049 Madrid, Spain