Direct award of Low temperature scanning tunnelling microscope - 2025-0897314

Beskrivelse fra ordregiveren

Aarhus University wishes to buy a closed-cycle low temperature scanning tunnelling microscope (LT-STM) for a new experiment that will be established for structural and optical studies of molecular ices. The LT-STM is specially customized to adopt optical components that are cooled to 4K and also adopts a 1K cooler for cooling superconducting SNSPD detector - operating at 0.9K. The aim of the research is to investigate molecular ices formed at interstellar conditions, including measurements of their characteristic fingerprints by detection of infrared emission from vibrationally excited constituent molecules. The structure of polar molecular ices formed on e.g. graphitic surfaces are predominantly governed by the intermolecular interaction with a very weak interaction between the molecule and the substrate. Such weakly bound systems are known to be easily perturbed by the STM tip during the measurements. To avoid this, we demand a 4K STM setup with the capability to perform experiments with extremely small tunneling currents - down to 1pA. Another key requirement of the setup is the ability to provide a low temperature platform for detection of infrared (IR) light emission (down to 20um wavelength) from the tip-sample junction. The IR light is generated by deexcitation of vibrational modes in molecules primarily excited by the tunnelling current. Therefore, an extremely low count rate of photon emission is expected. It is thus of fundamental importance to have all optical components in the path from the tip to the detector cooled down to 4K. Consequently, the setup must accommodate and cool down to 4K a customized IR spectrometer as well as a separate 1K cooler for cooling superconducting SNSPD detector down to 0.9K. Considering high prices of liquid He a closed cycle system is needed to ensure continuous operation. The unique technical specifications of the systems are as follows: - closed cycle low temperature UHV STM system operating down to 4K - operation below 1pA tunnelling current - free volume space inside 4K shield for integration of customized spectrometer, SNSPD detector and a 1K cooling stage (minimum free space dimensions - 130 mm diameter, 195 mm height) - Adaptation of the 4K and 80K shields for the operation of a 1K coller down to 0.9K - two motorized parabolic mirrors maintaining focus to the tip-sample junction - o high frequency cabling (in GHz range) for the SNSPD detector - four separate ports for deposition of molecules into STM ScientaOmicron is the only commercial supplier on the market at the moment that can deliver a complete system with all parameters.

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