We investigated the behavior of piezoelectric elements used in an STM for fine positioning of the tip. Special attention was paid to the influence of hysteresis. We found that the expansion coefficient of the elements depends on the magnitude of the displacements they produce. If the range is limited to several nanometers, the sensitivity can be taken constant and hysteresis can be neglected. However,if displacements of about a micron are involved, the sensitivity is about 40% higher and the hysteresis will significantly disturb the image. We also compared different calibration methods. An inductive displacement transducer yields results which correspond to those obtained with the known height of steps on a flat gold surface. A Michelson interferometer yields results which are valid for large displacements which cannot be used if small-scale structures are imaged.
We investigated ligand stabilized clusters Au55(PPh3)12Cl6 and Pd561(phen)38±2O≊200 on gold and graphite substrates with scanning tunneling microscopy (STM) under atmospheric conditions. We were able to image dense layers of clusters as well as free-lying clusters. Clusters are frequently picked up by the tip. This results in a tip with a well defined shape and electronic structure. Analysis of images of clusters scanned with another cluster attached to the tip can yield direct information on the tunnel distance. We found a tunnel distance of 24±5 Å.
scite is a Brooklyn-based organization that helps researchers better discover and understand research articles through Smart Citations–citations that display the context of the citation and describe whether the article provides supporting or contrasting evidence. scite is used by students and researchers from around the world and is funded in part by the National Science Foundation and the National Institute on Drug Abuse of the National Institutes of Health.