A 32-face 3-D truncated icosahedron mesh was created to test the simulation’s ability to precisely construct complex geometries. The SEM image of the final experimental product (left) was highly consistent with the structure predicted by the virtual SEM image (center) and the simulated design model (right). Credit:ORNL
It is difficult to 3D print a structure that is just inches or feet in size. Imagine reducing this product to smaller than a water droplet, even smaller than a human hair, until it is smaller than a standard bacterium.
Now, with the use of focused electron beam induced deposition (FEBID), this extremely tiny structure can be 3D-printed at the nanoscale.
In the FEBID technique, a beam of electrons from a scanning electron microscope is used to convert gaseous precursor molecules into a rock-hard deposit on a surface. Earlier, this method was prone to errors, was labor-intensive, and not viable for producing intricate structures measuring more than several nanometers.
Researchers at the Department of Energy’s Oak Ridge National Laboratory, in association with the Graz University of Technology and the University of Tennessee, have created a robust simulation-guided drafting process to enhance the FEBID method, providing novel possibilities in nanomanufacturing.
According to Jason Fowlkes, team leader and a research staff member at ORNL’s Center for Nanophase Materials Sciences, a DOE Office of Science User Facility, the innovative system combines design and construction into a single efficient process, which yields intricate 3D nanostructures.
According to Harald Plank, study co-author in Graz, Austria, the capacity to accurately design customized nanostructures
“opens up a host of novel applications in 3-D plasmonics, free-standing nano-sensors and nano-mechanical elements on the lower nanoscale which are almost impossible to fabricate by other techniques.”
A 3D simulation is used in the process to guide the beam of electrons and simulate intricate meshes and lattices between 10 nm and 1 µm in size. Electron scattering paths are then tracked by the model, followed by the emission of secondary electrons to predict the deposition pattern on the material’s surface and eventually view the end structure of an experiment.
According to Fowlkes, the novel aspect of this study lies in the convergence of simulation and experiments. The experimental construction is guided by simulation, whereas the concluded experiments give feedback regarding the simulation’s strength and accuracy.
The simulation and drafting program is then fed with designs, and any variations between the two, induced by the activity of secondary electrons, can be easily captured prior to the experiment.
In its simplest form, once we know the emission profile of those secondary electrons we don’t want, we can design around them.
Jason Fowlkes, Research Staff Member, ORNL
Fowlkes explained that while the FEBID process is slower compared to other nanofabrication techniques available at CNMS’ clean room, it is the only method that is capable of creating high-fidelity 3D nanostructures.
As there were no options to view the nanostructures during construction, scientists used to depend on trial and error method and physically modify the build parameters to create the preferred shapes.
Fowlkes further added that the group will be mainly focusing on purifying carbon contamination structures. In the purification process, referred to as in situ purification, the impurities are removed during construction with a laser and oxygen or water to release the remaining carbon from the precursor, ultimately flushing it out from the structure. In addition, 3D simulation can integrate the stresses of the carbon removal procedure and predict the change in the end product.
We can design structures in a way where the actual writing pattern might look distorted, but that’s taking into account the fact that it’s going to retract and contract during purification and then it will look like the proper structure.
Jason Fowlkes, Research Staff Member, ORNL
Additional data about the simulation and nanostructures are described in the team’s paper, “Simulation-guided 3-D nanomanufacturing via focused electron beam induced deposition” published in the ACS Nano journal.
The Center for Nanophase Material Sciences, a DOE Office of Science User Facility, supported the ORNL part of this work.
Video Credit: Oak Ridge National Laboratory/Youtube.com