Ultra-Low Vibration Scanning Tunneling Microscopy at mK temperature- Completed

We completed our ultra-low vibration laboratory for the UNISOKU USM1600 millikelvin Scanning Tunneling Microscope (mK-STM). Our USM1600 system has been customized, featuring atwo-axis vectorized superconducting magnet (providing 9T in the vertical direction and 4T in the horizontal direction, with a full vector rotation of 3.5T). It offers cooling capabilities down to a base temperature of 40 mK at the STM head.

Completed ULV laboratory (left) and CAD diagram (right)

In achieving optimal vibration isolation, we have taken meticulous measures to ensure that the area surrounding the STM is decoupled structurally from the surrounding buildings. Here, you will find a CAD schematic of our Ultra-Low Vibration (ULV) laboratory, situated on the ground floor of a five-story building within the Nanyang Technological University (NTU) campus in Singapore.

Critical Steps in the Ultra-Low Vibration Laboratory Setup:

Steps of lab construction. a) Excavation and structural decoupling b) Foundation and laboratory room construction c) T-shaped isolation block.

a)   Excavation and Structural Decoupling: In our endeavor to create a state-of-the-art laboratory environment, we initiated the process by excavating an area measuring (7.8 × 8.6) m² to a depth of 4.0meters, strategically positioned between four of the building's crucial structural support pillars. Structural decoupling is achieved via floated isolation block hosted in an isolated room.     

b)  Foundation and Laboratory Room Construction: To further enhance vibration isolation, a 1.5-meter-thick concrete foundation baseplate (1) was meticulously cast upon a layer of compacted rubble (250mm/50mm) positioned on the natural soil, thus forming a solid raft foundation on which the entire laboratory room would be constructed. A reinforced concrete cradle was then erected atop this foundation, which hosted a T-shaped mass block weighing approximately 55 tons.

c) Reinforced Structure with Mass Block T-shaped isolation block: A reinforced concrete cradle was then erected atop this foundation, which hosted a T-shaped mass block Central part of our vibration isolation is a T-shaped concrete mass block suspended by actively controlled pneumatic springs. To avoid forces on the superconducting magnet, we have decided for non-magnetic fiber glass reinforcement of the concrete block instead of conventional steel rebar.

These measures have allowed us to establish a laboratory environment meeting the VC-M vibration standard for frequencies higher than 3 Hz reached in only a limited number of labs worldwide as shown below.

In this tailored low-vibration environment, the STM achieves an energy resolution of 43 μeV (144 mK), among the state-of-the-art dilution-refrigerator mK-STMs [1], promising for the investigation and control of quantum matter at atomic length scales.