SCANNING TUNNELING MICROSCOPY - STM
fundamentals
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Since its invention (1983) and Nobel prize (1986), Scanning Tunneling Microscopy (STM) and related Scanning Probe Microscopy techniques have become some of the most important new laboratory techniques for studying sub-nanoscale surface phenomena. This technique allows scientists to visualize regions of high electron density and hence infer the position of individual atoms and molecules on the surface of a lattice.

STM works by scanning a sharp conductive tip over a surface. A bias voltage is applied between the tip and a conductive sample. When the sample is approached within a few Å from the tip, a tunneling current can be established indicating the proximity of the tip to the sample with very high accuracy. Most of the tunneling current can flow through a single protruding atom on the tip and sub-Å resolution in z can be achieved on a clean surface with a sharp tip.

There are two different modes in STM:

In constant height mode, the tip is moved only in plane. Thus, the current between the tip and the sample surface visualizes the sample relief. In this mode, adjustment of the surface height is not required and a higher scan speed can be obtained. However, constant height mode is only applicable if the sample surface is very flat, because surface corrugations higher than 5?-?10 Å will cause the tip to crash. In this case, maintaining a constant tunneling current by adjusting the height with a piezo element and monitoring the piezo voltage while scanning, allows to image the surface. This mode is called constant current mode.

STM gives true atomic resolution on selected samples even at ambient conditions. This technology can be applied to study conductive surfaces or thin nonconductive films and small objects deposited on conductive substrates.

aattocube systems STMs
All attocube microscope systems are compatible with cryogenic and vacuum environments as well as high magnetic fields. The STM is also suited to be used in combination with a He3 insert allowing measurement temperatures down to 300 mK.

attoSTM I:
The attoSTM I is designed particularly for the use at extreme environmental conditions such as ultra low temperature, high magnetic fields, and high vacuum. To perform low temperature microscopy, the attoSTM is cooled by a controlled exchange gas atmosphere in a liquid Helium bath cryostat. Alternatively, the STM can be operated under vacuum conditions.