High-frequency four-tip scanning tunneling microscope in ultrahigh vacuum

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We aim to develop a high frequency (HF) four-tip scanning tunneling microscope (4-tip STM) capable of lateral electric nanoprobing. It will be employed to samples that are relevant for future information technology. All four tips can operate either in all-electric pump-probe mode with time resolution ~100 ps or in continuous wave mode up to ~30 GHz and with amplitude at the tip-sample junction up to 50 mV. Versatile contact geometries including tunnel contacts can be realized on the same device while having access to images of the sample geometry and the local density of states down to the atomic scale. The instrument additionally operates as nm-scale tunneling potentiometer, probing, e.g., the build-up and relaxation of electrochemical potentials at sub-ns time scales. Ultrahigh vacuum (UHV) conditions in combination with a contact-free shadow mask evaporation enable the investigation of ultraclean device structures, never exposed to non-UHV conditions or any type of chemical resist.Anticipated applications of the novel instrument include magnetoelectronics for mapping the current-induced dynamics of magnetic textures, spin pumping of topological materials to detect the resulting lateral spin and charge distributions, mapping the dynamics of electrically induced phase transitions such as the phase front propagation of metal-insulator transitions, controlled electron dynamics at individual dopants or adsorbates, and the dynamics of the gate-induced build-up and relaxation of electrochemical potentials within field effect transistors. The unprecedented control on contact geometries combined with the high spatial resolution of the STM will foster a comprehensive understanding of GHz dynamics on the atomic scale including the role of defects. The instrument developed within this project will be the first instrument combining lateral nanoscale transport measurements with high frequency capabilities, with the additional benefit to correlate the electric results with structural information on the atomic scale. This ultimately will lead to optimized design criteria in nano-electronic devices.