Open Source Projects

The energy resolution of STM is largely influenced by the noise of the tunneling bias. In part, it comes from the thermal distribution of electrons, i.e. the electronic temperature. In many cases, however, the experimental resolution is significantly worse than the thermal smearing. In many cases, the actual potential is not free of noise caused by electronic noise of the voltage source, rf-signals picked up by the cables and voltage noise caused by induction due to time varying magnetic fields (typically from high power consumers running from the main power lines). Rf-noise can be easily filtered by dedicated low-pass filters but induction is harder to screen. Usually, all magnetic flux that crosses the loop between the grounded IV converter and the grounded voltage source of the tunneling voltage is relatively large limiting the energy resolution to an equivalent of several hundreds of mK. As the tunneling junction is the part with the highest resistance, the complete induction voltage drops here. To prevent this, we have developed an electronics with differential input, that resynthesizes the bias voltage locally next to the IV converter with the ground potential of the IV converter. This minimizes the induction loop to only the space between the voltage and current lines inside the STM chamber. Additionally, it provides low-pass filtering and the option to divide the voltage by a factor 10 or 100. This reduces the voltage noise to below 20μV rms over the full bandwidth of the measurement, or to an equivalent noise temperature of 69mK.