In the last few years, the study of the adsorption of cyclodextrins (CDs), mainly chemically modified derivates and inclusion complexes, on crystalline surfaces at a molecular level has drawn much attention. It has been found that CDs form Self-Assembled Monolayers (SAMs) on surfaces such as HOPG and Au(111),1 and the potential applications of that systems are enormous.2 However, there are not many studies using scanning tunneling microscopy (STM) and only a few of them deal with native CDs.3

In this work, we present results for the adsorption of a- and b-CDs on HOPG. The molecules were adsorbed by evaporating small drops of millimolar solutions of CDs. STM images in air show well ordered domains (Figure 1) with an hexagonal pattern. The periodicity is dependent on the preparation conditions and is compatible with agregates of CDs molecules. However, step heights correspond to single-molecule dimensions. Structural models are proposed to explain the periodicity of the STM images.