4-probe STM UHV System microscope

4-probe STM UHV System is a low-temperature four-probe scanning tunneling microscope (STM) with windows for optical access with laser. It is a unique specialized instrument that merges several advanced features to allow for unique experiments at the nanoscale. The STM is equipped with low-noise amplifiers for measuring tunnelling currents as low as 10-11 A (with bandwidth above 800 Hz) or 10-9 A (above 20 kHz).

Unlike standard STM with a single probe tip, a four-probe STM has multiple probe tips, which allows for local voltage measurements. This feature can be crucial for studying inhomogeneities in samples or extracting resistivity information without the influence of contact resistances. In addition, different biases can be applied to separate probes, allowing for advanced experiments.

A bath cryostat of the STM allows working at the base temperature of 4.2 K for an uninterrupted period of up to 36 hours or at 77 K for up to 120 hours. Precise control of the sample temperature is possible using special sample plates with in-built heater and sensor. –Working at low-temperature has the benefit to reduce thermal noise and enhance the resolution and stability of measurements. Low-temperature phenomena that can be investigated with this instrument include superconductivity, quantum effects, and other temperature-sensitive phenomena. The improved stability of the 4-probe STM reduces thermal drift and enhances the positional stability of the microscope tip.

A scanning electron microscope mounted on top of the STM allows for the precise tip positioning at distances down to 2 um between the tunnelling tips. The optical setup allows for positioning of a laser beam (as small as 50 x 50 um) with a precision down to 20 um for optical excitation of the samples. The samples can be mechanically exfoliated directly in UHV conditions (below 10-10 mB) or thermally treated (annealed) in a separate preparation chamber.

Among the most common applications of this instrument: characterization of surfaces with atomic resolution, measurement of electric characteristic of nanostructures, manipulation of nanostructures and individual atoms, measurement of circuits, study of local density of states.

Responsible for the instrument: Dr. Dragan Mihailović.