Low-temperature scanning tunneling microscopes

Messerli, S., Schintke, S., Morgenstern, K., Sanchez, A., Heiz, U., and Schneider, W.-D., Imaging size-selected silicon clusters with a low-temperature scanning tunneling microscope. Surf. Sci. 465,331 (2000). 

Eigler, D.M. et al.. Imaging Xe with a low-temperature scanning tunneling microscope, Phys. Rev. Lett. 66, 1189-1192, 1991. 

Using a low-temperature scanning tunneling microscope, chemists at Tufts University successfully assembled and operated an electric motor consisting of a single molecule. 

Low-temperature scanning tunneling microscopes (LT-STMs) are designed in a way that the entire STM and the sample are kept at a low temperature inside a cryostat [8, 9]. Such instruments use liquid helium (f He) as the cooling medium, allowing for operation at temperatures down to 4 K. Even ultralow temperatures below 1 K can be achieved with a mixture of He and He and specially designed mixing cryostats [10, 11]. 

Meyer, G., Bartels, L., Zophel, S., and Rieder, K.H. (1999) Lateral manipulation of adatoms and native substrate atoms with the low-temperature scanning tunneling microscope. Appl. Phys. A, 68, 125-129. 

Our laboratories are currently equipped with three UHV Omicron microscopes, a variable-temperature scanning tunneling microscope (STM), a room-temperature atomic force microscope (AFM)/STM, and a low-temperature liquid helium bath cryostat STM, all of which are currently driven by Omicron Scala software and electronics. 

We want to point out that many analytical apparatus originally designed for room temperature have been modified to allow operation at low temperature with much better performances. An example is the STM (scanning tunnelling microscope) [1,2] which allows to image the morphology of a surface. Spectacular demonstrations have been provided of what could be done with a 4K STM [2,3], Today several low-temperature STM of different design are in operation [4-12],... 

See Surface Brillouin zone Scanning tunneling microscope 1 concentric-tube 111 low-temperature 275 pocket-size 270 schematic diagram 1 single-tube 273... 

The importance of low pressures has already been stressed as a criterion for surface science studies. However, it is also a limitation because real-world phenomena do not occur in a controlled vacuum. Instead, they occur at atmospheric pressures or higher, often at elevated temperatures, and in conditions of humidity or even contamination. Hence, a major thmst in surface science has been to modify existing techniques and equipment to permit detailed surface analysis under conditions that are less than ideal. The scanning tunnelling microscope (STM) is a recent addition to the surface science arsenal and has the capability of providing atomic-scale information at ambient pressures and elevated temperatures. Incredible insight into the nature of surface reactions has been achieved by means of the STM and other in situ techniques. 

The high resistivity allows very effective ohmic heating of Si and Ge by direct current Samples with a specific resistivity in the order of 20-500 mS2 cm, which corresponds to a doping level between Nd = 10 —10 cm are used either in scanning tunneling microscopic (STM) experiments at low temperatures down to 80 K or for experiments between room temperature and 800 °C when direct current heating of the sample is used. STM experiments at 5 K, however, require Si samples that are degenerately doped with Nq > 10 cm to ensure metaUic conductivity at these very low temperatures and thus avoid tip crashes. 

Meyer, G. (1996) A simple low-temperature ultrahigh-vacuum scanning tunneling microscope capable of atomic manipulation. Rev. Sci. Instrum., 67, 2960-2965. 

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