Ever since I was young it seemed like the pinnacle of common sense that if a very, very small component was required it would be foolish to try and break down bigger things to get it. Building what was required atom by atom was the way I thought it should be done. One of the ways scientists attempt to construct items from the ground up is by using optical tweezers. These tweezers are lasers that can exert a force based on the difference in refractive index between a particle and its surroundings in order to trap the molecule and so move it where required. Generally the ability to not just create but manipulate materials on this scale can do incredible things such as having a substance with a specifically changing conductivity across its surface or artificially create chemical functional groups.
Two photon polymerisation, where the laser is used to cause a tiny zone to undergo a chemical reaction, is one of the most common of the techniques for optical tweezers but there is still some trouble when it comes to fusing different materials together with multiple functions. This paper has aimed to try and abate this problem by applying a completely optical approach to fixing the materials together; sort of. The idea is to make a absolutely tiny screw and nut that are less than five μm in size and then position them using the optical tweezers method. The multi-stage process of attachment is shown below:
There are different approaches that have been tried for applying torque to a microstructure. The most basic way, which was used in this experiment, is to use four laser trapping spots (focused on the four protrusions) and then rotating them. A speed of twenty five revolutions per minute was found to be the maximum which is considered quite slow. Despite this there is always the possibility of upping the power of the laser and increasing the potency of the traps in order to achieve faster rotation.
It is quite amazing to consider that even on such tiny scales (which are still admittedly much larger than atoms) tangible feats of engineering can be achieved. The ability of the screw to convert forces into different directions and fasten materials can be used in microrobotics and other related fields with the easy ability to construct and disassemble mechanically stable devices.
Paper links: Optical screw-wrench for microassembly
Image also taken from paper