On one hand there are parallel-beam microgrippers, which have a rather compact and flexible design. However, they are not capable of supplying the gripping force necessary to detach structures that are firmly attached to the substrate surface, such as plasma enhanced chemical vapor deposition (PECVD)-grown carbon nanotubes (CNTs).
On the other hand there are rib-cage microgrippers, which are stronger. In our previous study published in Nanotechnology, we demonstrated the assembly of a CNT-enhanced AFM super-tip using rib-cage microgrippers inside a scanning electron microscope (SEM). However, this design is rather bulky and it is lacking flexibility as it is only able to close. Furthermore, both designs are not suitable for miniaturization.
We used topology optimization to combine strength, compactness and flexibility in a single microgripper design. Topology optimization is a finite element-based design approach, which relies on distribution of a certain amount of material within a well-defined design domain to perform a specific task. The resulting microgrippers are two orders of magnitude stronger than the parallel-beam microgrippers, and are still able to both open and close and have the same size.
The performance of the nanorobotic system is also of great importance for precise nanomanipulation and assembly. For this reason, we improved our manipulation system to offer a novel degree of freedom, i.e. rotatory axis for the microgripper and integrated sensors to all linear axes providing closed-loop actuation.
Taking advantage of the powerful topology-optimized microgrippers and our enhanced nanorobotic system, we demonstrated pick-and-place nanomanipulation of CNTs in a rapid and reproducible manner, in our recent work published in Nanotechnology. We successively assembled three CNT-enhanced AFM super-tips during the same experiment. Being more precisely assembled, the super-tips show an improved performance. We also placed CNTs on transmission electron microscope (TEM) grids and investigated their structural properties. TEM analyses reveal that the multi-walled tubes are coated with an amorphous carbon layer, which is locally removed at the contact points with the microgripper.
The results we achieved are preliminary steps towards the automation of the nanohandling procedure in the near future, which is the main target of the EU funded NANOHAND project.