Imaging nanoclusters in the constant height mode of the dynamic SFM

Abstract

For the first time, high quality images of metal nanoclusters which were recordedin the constant height mode of a dynamic scanning force microscope (dynamicSFM) are shown. Surfaces of highly ordered pyrolytic graphite (HOPG) were usedas a test substrate since metal nanoclusters with well defined and symmetricshapes can be created by epitaxial growth. We performed imaging of goldclusters with sizes between 5 and 15 nm in both scanning modes, constantΔf mode and constant height mode, and compared the image contrast. We noticethat clusters in constant height images appear much sharper, and exhibit morereasonable lateral shapes and sizes in comparison to images recorded in the constantΔf mode. With the help of numerical simulations we show that only a microscopically smallpart of the tip apex (nanotip) is probably the main contributor for the imagecontrast formation. In principle, the constant height mode can be used for imagingsurfaces of any material, e.g. ionic crystals, as shown for the system Au/NaCl(001).