Regensburg 2010 – scientific programme

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O: Fachverband Oberflächenphysik

O 34: Methods: Scanning probe techniques IV

O 34.3: Talk

Tuesday, March 23, 2010, 15:30–15:45, H32

A sub-Kelvin scanning tunneling microscope with high energy resolution and high stability — •Lei Zhang and Wulf Wulfhekel — Physikalisches Institut, Karlsruhe Institut of Technology, Germany

We designed a new scanning tunneling microscope (STM) working at sub-Kelvin temperatures in ultra-high vacuum (UHV) in oder to study the magnetic properties on the nanoscale. Detecting excitations of single atoms and molecules, a high energy resolution instrument is needed. To achieve this, the set-up is operated at low temperatures and with high stability. A base temperature of 930 mK at the STM head is achieved using Joule-Thomson expansion of Helium-4, which can be reduced to approx. 400 mK when using Helium-3. Test experiments with a superconducting tip show a high energy resolution of 300 µeV when performing scanning tunneling spectroscopy (STS). The vertical stability of the tunnel junction is below 1pm (peak to peak) and the electric noise floor of tunneling current is about 6 fm/√Hz. The spatial drift is below 10 pm/h. Atomic resolution with a setpoint of 0.5 pA and 1 mV was achieved on Au (111). The set-up allow in-situ preparation of tip and samples under UHV condition. The fast cooling down of the samples (4h) guarantees high sample throughput.