A low temperature scanning tunneling microscope designed for imaging molecular adsorbates

We report on the development of a low temperature scanning tunneling microscope (STM) used for imaging molecular adsorbates. The microscope operates near 85 K and features in situ tip and sample exchange. Cooling is accomplished via a clamping mechanism that provides a direct mechanical link between a liquid nitrogen dewar and the STM stage. During imaging, the clamping mechanism is released, and the STM stage is isolated from vibrations using a dual spring suspension system that incorporates magnetic eddy current damping. Additional isolation is provided by uncoupling the liquid nitrogen dewar from the vacuum chamber. We have used this STM to image benzene and carbon monoxide coadsorbed on the Pd (1 1 1) surface. The resulting acquired images show both the ordered arrangement and internal structure of the benzene molecules. Depending on the dosing conditions, three different ordered overlayer structures were formed, only one of which has been previously reported. Future plans include using the low temperature imaging capability of the STM to observe molecular binding sites, orientation, and tilt, as well as dynamical processes on the surface, such as chemical reactions. © 2002 Elsevier Science B.V. All rights reserved.