World's smallest house unveiled


Rebecca Pool

Monday, May 21, 2018 - 14:15
Home sweet home: Microhouse comes with chimney and tiled roof [FEMTO-ST Institute]
Using dual-beam SEM with FIB and a microrobot, France-based researchers have fabricated the 'World's smallest house' - some twenty five microns in length - on an optical fibre.
Jean Yves-Rauch from Femto-ST Institute and colleagues used their experimental set-up, dubbed the μRobotex nanofactory, to assemble the tiny house at the centre of a cleaved facet of the fibre and weld its structure with ultra-high accuracy.
“For the first time we were able to realize patterning and assembly with less than two nanometres of accuracy, which is a very important result for the robotics and optical community,” highlights Yves-Rauch. “We built the microhouse on the fibre to show that we could realise these microsystem assemblies on top of an optical fibre with this high accuracy.”
Model of the final assembly. (a) Simulation view from the FIB when the top face of the fibre is located in the (x,y) plane of the SEM. (b) Cross section of the final assembly.
Researchers have long-used FIB to pattern and fold crystals, metals and polymers, assembling more and more sophisticated structures.
Yves-Rauch and colleagues harnessed this so-called origami process to build the microhouse, combining a Zeiss dual beam Auriga SEM/FIB with a six degree of freedom robot built with SmarAct components and gas injection system.
Using the robotic system with the FIB, the researchers etched silica membranes to trigger self-folding processes and form the microhouse doors.
With the walls folded into position, the FIB and gas injection system stuck the edges together, with windows, doors and a tiled roof then being patterned into the structure.
a) After the step of welding of the base of the microhouse on the facet of the optical fibre, researchers cut the thin last link between the base of the microhouse and the membrane. During the assembly time and the welding time, the stability of the system was important. In the case of drift of the robot, the microhouse could be broken. (b) The link was cut, and researchers extracted the microhouse by the background direction. [(c) and (d)] After patterning and self-folding the first roof at 35°, they installed the microhouse from the background like “mortise and tenon.” This step required a very high accuracy less than 10 nm. (e) After welding the first roof, the researchers installed the second roof under the same conditions and realised the welding step with naphthalene gas. (f) After welding the two roofs, they built the chimney. This image was realized with the ESB detector. The other pictures were always realized with the SE2 detector. 
During the process, the researchers worked across an area of only 300 micron2, with the FIB firing ions onto the cleaved fibre tip and silica membrane.
As Yves-Rauch points out: "It was very challenging to pilot the robot with high accuracy at the cross point between the two beams.”
As he explains, two researchers worked across several computers to control the process, and while many steps are already automated, he hopes to automate all the robotic stages of assembly in the future. 
Yves-Rauch also reckons that introducing a microrobot to an SEM vacuum chamber will enlarge the scope of clean room facilities to build more complex microsystems, including nanoantennas and 3D biosensors.
His team is already using the µRobotex system to attach microstructures onto optical fibers and create functionalised microstructures to detect specific molecules.
The researchers also hope to build smaller structures and fixing these onto carbon nanotubes. 
Research is published in Vacuum Science and Technology A.
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