Construction of Scanning Tunneling Microscope (STM)

Parties: Aarhus University, Newtec, others?

Contact person industry: Bjarke Jørgensen (Newtec)
Contact person AU: ​Mogens

Description:

Schematic drawing of the scanning tube of a STM, and an atoic level artist’s drawing of the tip-surface interface. [S. Woedtke, Ph.D. thesis, Inst. f. Exp. u. Ang. Phys. der CAU Kiel, 2002]


STM is a strong technique, able to give much information about a surface, and routinely producing atomic resolution in ultrahigh vacuum chambers. It is, however, possible to obtain atomic resolution under atmospheric conditions and even in liquids. However, here the high demands for variable control and noise removal is even more demanding, not to mention that material choices must consider the effect of any electrochemical processes.The STM relies on the quantum mechanical tunneling effect to detect a difference in electrical resistance from the outermost tip-atom in the probe to surface-atoms in a conducting sample, depending on the physical distance to the nearest surface-atom. As the tip is scanned across the surface, in sub nm distance, the distance to the nearest surface-atom changes according to their positions. When a constant bias voltage is applied, this causes a change in the tunneling-current from sample to tip

STM image of graphene [B. Jørgensen Ph.D. progress report, iNANO, Aarhus University, 2009]

and hence the positions of the surface-atoms can be mapped out. This implies precise current measurements in the pA-nA regime, and a fast feedback loop to control the tip position, a task performed by Piezo electrical elements.

The present state of the STM

A previous project running the past year, has initiated the construction of the STM. At present, the hardware for achieving a tunneling current exists, but now the project branches into at least two parts:Our research activities in surface science at Newtec Engineering implies a need for a good in air STM. Since there is no products on the market, that fulfill our demands, the solution is to build one. This construction is demanding in the areas of electronics, software and mechanics and it will be accomplished in collaboration with SDU and Aarhus University, centered at Newtec Engineering in Odense.

High voltage amplifier for a STM

To control the scanning tube in the three dimensions, a high voltage amplifier is needed. The requirements include fast response, voltage swing around 1kV and a peak current of some tens of mA. This project demands a skill set that includes analog electronics and high voltage design. We expect you to work with initiative and show involvement. In return, we can offer you experience with working in a small and dynamic private research group, while developing an important part of an advanced microscope setup.

Interface and instrumentation for a STM

The present state of the STM is an excellent opportunity to develop an interface to some control software. This implies controlling a large number of parameters, the tip position, tip voltage and other scanning parameters. Furthermore, a data acquisition and processing system is needed to map the data. An open source starting point could be “Gnome X Scanning Microscopy project” (GXSM), but you can move the project in the direction you want.

 

The STM project is open for work in many facets, so if you are interested in the STM but the above two projects do not spark an interest, feel free to contact us, so we can discuss a project suited for you.