Atomically Precise Manufacturing — Part 3
We’ve talked about where APM could take us, but what’s actually happening in this space today?
In Part 1 of this article we talked about what APM is, and explored the impact this technology could have in the future as it becomes more feasible. In Part 2 we discussed what is possible today with our current technologies, and the major hurdles that must be overcome for this to become a practical means of production. In this installment we will look at some of the research programs and commercialization pushes that are happening right now.
Examples of Commercialization
Graphene
Graphene is regarded as a wonder-material and for good reason. I’ve written about graphene in the past, and firmly believe that graphene and carbon nanotubes are going to change the world in countless ways; from completely reshaping our electronics to making impossibly strong structural materials, graphene has the potential to impact our material world with the same magnitude as the invention of plastics did. The challenge today is that graphene and other highly-ordered forms of carbon are hard to make. Although the material structures are relatively simple, consisting of repeating patterns of carbon atoms in 2D sheets, rolled tubes, or spherical balls, to achieve these amazing properties the atoms must be carefully arranged, with contaminants and impurities carefully avoided. Hence graphene and carbon nanotubes (CNTs) are a perfect application for atomically precise manufacturing.
Graphene and CNTs make excellent conductors of both heat and electricity, and can even act as superconductors under specific conditions. As such, these materials are being explored to replace metal traces and semiconductors in next generation miniaturized electronics. Graphene nanoribbons can be used in energy storage, data storage and as efficient semiconductors in quantum computers. Until recently, graphene nanoribbons had to be synthesized on a gold surface, which is itself highly conductive. The conductivity of the gold substrate nullifies the desirable aspects of the graphene nanoribbon for making circuitry. So to be useful as conductors the nanoribbons need to be transferred off of the growth substrate in an extraordinarily painstaking process. This slow process causes nanoribbon products to be very expensive to produce, and has dramatically limited their usability outside of labs. However, scientists have recently built graphene nanoribbons by joining individual atoms one by one on a titanium oxide surface, allowing the properties that would otherwise be nullified on a gold surface to remain intact. This is a compelling example of how bottom-up manufacturing processes can be used to open up new possibilities for powerful next-gen materials like graphene. Professor Konstantin Amsharov of Martin Luther University of Halle-Wittenberg in Germany worked on this project and notes that the new method “allows us to have complete control over how the graphene nanoribbons are assembled… The process is technologically relevant as it could also be used at an industrial level. It is also more cost-effective than previous processes” (Atom-by-atom assembly makes for cheap, tuneable graphene nanoribbons, New Atlas).
When we talk about APM we are most often referring to the bottom-up approach of adding individual atoms in a very controlled way, like atomic-scale additive manufacturing. But an interesting counterpoint can be seen in what is called kirigami graphene, in which very precise cuts are made in a sheet of graphene. The term kirigami is derived from two Japanese words: kiru (to cut) and kami (paper). The concept to yield microstructures with impressive mechanical properties. However, these features are on the order of microns, so don’t quite reach the nanometer-scale atomic precision we are discussing in this paper, but this approach does warrant honorable mention. (Kirigami graphene makes microscale devices)
Gas separation membranes are a technology that blends the two methods mentioned above (kirigami cutting, and atomic additive). Researchers at EPFL made a high-performance membrane for separating CO2 from air by making carbon dioxide sized holes in a flat sheet of graphene. The holes are sized to allow CO2 to pass through while blocking larger molecules like nitrogen and oxygen. These membranes are showing record-high performance in this gas separation application, and are likely to have many future uses tuning for other hole sizes. (Graphene filter makes carbon capture more efficient and cheaper)
Carbon Nanotube materials are where a lot of the early results of atomically precise manufacturing can be seen. For instance, thermal glue is used as an adhesive for electronic components. It is used in the satellite industry and is problematic because it takes a long time to dry and is hard to rework once applied. Carbice, a startup out of Atlanta, GA which raised a $15m Series A in November of last year, has created a carbon nanotube based material that replaces thermal glue and helps lower junction temperatures. Satellites are often equipped with solar panels, meaning they can get very hot and need to have ways of dissipating this heat. Carbice CEO Baratunde Cola notes that switching from thermal glue to Carbice’s materials help satellite makers save “hundreds of dollars per square inch of thermal interface” and that this cost saving allows for geostationary satellites to have “over 50,000 square inches of thermal interface” and for satellites operating in low Earth orbit to have 1000s of square inches of thermal interface (Carbice raises $15 million in Series A investment round, Spacenews.com).
Quantum Computers
In 2020, Scientists at Oak Ridge National Laboratory (ORNL) were able to use a focused beam of electrons to stitch platinum-silicon molecules into a sample of graphene. By doing this, the scientists were able to alter the graphene’s physical properties. This could be very useful for prototyping quantum computers from graphene. (Electron-beam introduction of heteroatomic Pt–Si structures in graphene, ScienceDirect).
In quantum computers, two-qubit gates use interactions between qubits to perform quantum operations. However, based on the positioning of qubits in silicon, oscillation can occur in their interactions, resulting in latency between the gate operations and making them hard to control. In late 2020, the team at Silicon Quantum Computing and researchers from the Centre of Excellence for Quantum Computation and Communication Technology at University of New South Wales recently discovered that the positioning of the qubits in silicon is vital to strong and reliable interactions between the qubits. Using a Scanning Tunneling Microscope, the teams were able to discover that “there is a special angle, or sweet spot, within a particular plane of the silicon crystal where the interaction between the qubits is most resilient” (Dr. Benoit Voisin, Hitting the Quantum Sweet Spot, Eureka Alert). This insight, derived from an atomically precise manufacturing technique, will have a direct impact on our ability to build scalable processors for quantum computers.
Coatings
Forge Nano is a Colorado-based startup that “is investigating processes for scaling atomic layer deposition (ALD) to create new core-shell materials, especially for battery applications. ALD is a chemical process for applying atomic scale coatings one atom at a time. With its specific ALD technology, Forge Nano aims to boost energy density of vehicle battery cells. For example, a higher energy density would have positive effects on the range of electric vehicles” (Volkswagen invests in US start-up Forge Nano). Forge Nano’s technology is used in products like lithium ion batteries, electronics and vaccines. In January 2021, the Department of Energy announced that Forge Nano had been awarded a $5MM grant to continue working on advancing understanding of ALD coating of catalysts in chemical manufacturing (Forge Nano Awarded 5-million-dollar Department of Energy Grant for Catalyst Optimization, The Daily Sentinel).
Scientists at Yale University’s Department of Mechanical Engineering recently implemented a new method for atomic scale imprinting. The scientists used magnetron sputtering, which is the collision process between gas ions and target atoms within a bulk metallic glass (BMG) (BMGs provide preferable electronic, thermal and mechanical properties for nanocomposites used in electronic applications). The collision between the ions and atoms “causes the target atoms to be ejected from the surface and travel across a vacuum until they reach the surface of interest, where they come together to form a thin film. This process essentially replicates the original surface down to the atomic level, creating an accurate imprint” (‘Revolutionizing’ nanomanufacturing: Yale researchers discover new method for atomic-scale imprinting, Yale Daily News). As the Yale Daily News notes, this technique “allows for not only a wide range of alloys to be used as targets, but also a large surface area to be replicated, which means that the process can be easily scaled up.” To give an idea of how this method can be applied in the real world, consider solar panels: one problem with putting solar panels in deserts, where there is an abundance of sunlight, is that there is also sand that can collect on the surface and block the incident sunlight, or can cause abrasion damage to the optical surfaces; a protective plastic coating applied to the cells via this type of method could negate this issue while maintaining the optical properties of the cell, while also being very cost effective to replicate.
Self-Assembly
An exciting bottom-up process for APM is self-assembly, which involves designing materials that will organize themselves in a defined way at the atomic level when certain reactions, such as chemical or physical exposure (such as heat, light, acids, etc), are initiated. Right now, materials that are used in self-assembly are usually protein, peptide and structural DNA. Self-assembly also encompasses foldamers, which are essentially simplified enzyme molecules that fold in a predefined way after a certain reaction occurs.
In 2020, Researchers at Johns Hopkins University made significant progress in their goal of manufacturing a functional, high-throughput and cost effective 3D nanodevice using a method called 3D NISE (3D Nanomanufacturing by Imprint and Strain Engineering), which combines the patterning of thin films and also manipulating their properties at the nanoscale. The nanodevices they created are called Theragrippers, which are made of metal and thin film and coated in heat-sensitive paraffin wax. These microstructures are deployed within the gastrointestinal tract to deliver medicine with an extended release time. As the NSF notes, “a challenge with extended-release drugs, however, is that they often make their way through the gastrointestinal tract before they’ve finished dispensing their medication.” The Theragrippers overcome this issue in the following manner: “When the paraffin wax coating on the grippers reaches the temperature inside the body, the devices close autonomously and clamp onto the intestinal wall. The closing action causes the tiny, six-pointed devices to remain attached, then they release their medicine payloads gradually into the body” (National Science Foundation).
Self assembly is very common in the natural world, serving to form organized structures in every living organism. DNA itself is one of the most ubiquitous examples of self assembly, forming the distinctive double helix shape without any external framework or guidance, but simply taking the shape that these particular molecules want to rest in. This is the hallmark of self assembly; creating molecules with certain tendencies to bend or flex due to their electron shells, such that they fold or arrange themselves against each other in certain stable orientations. Scientists and engineers have taken another page from nature’s playbook in trying to engineer their own versions of these useful molecular shapes to create geometries and structures that could not be produced by any other known method.
There have been a number of breakthrough developments in self-assembly in recent years. One example of which are molecular nanofibers that assemble themselves into strands to form a solid that is stronger than steel in the presence of water, and then fall apart into a powder when dried. Another such breakthrough involves tiny robots that assemble themselves through folding after a reaction. In 2019, researchers at NC State used kirigami (a variation of origami) techniques to create robotic devices from thin sheets of material that reconfigure themselves when heat is applied. The researchers were able to have these 2D materials reshape themselves into a 3D structure without any kind of mechanical inputs; using this approach, they were able to ”create a suite of thermoresponsive kirigami machines, including simple gripping devices and self-folding boxes. The researchers also created a soft robot with a kirigami body and pneumatic legs. By switching the orientation of the body, the researchers could rapidly reposition the legs, changing the robot’s direction of movement” (Robots Made From Self-Folding Kirigami Materials). While these devices are quite macro in size, they do demonstrate key principles of self-assembly that might also be used on the atomic scale. The image below from DesignNews shows what some of these the materials looked like pre and post-assembly:
Researchers at Harvard and Caltech accomplished something similar in 2019, when they created ‘Rollbots.’ Interestingly, the Rollbots incorporated hinges into their design; the hinges are programmed to respond differently under different temperatures, which allowed the researcher to program different functions for Rollbot with varied levels of heat. It should be noted that these are not nanoscale structures. They are macroscale objects with lengths on the order of centimeters; but the concepts are viable targets for future miniaturization. Here is a video from Caltech showing the Rollbots in action, and 3DPrintingIndustry provides a good summary of the self-assembly process:
“Integrating hinges into the design, the team has built several soft devices using an additive manufacturing approach. The Rollbot begins as an 8 cm x 4 cm flat sheet, and folds on a hot surface of about 200°C into a pentagonal wheel. Embedded on each of the five sides of the wheel is another set of hinges. When in contact with the hot surface, the hinge folds and propels the wheel to turn to the next side, where the next hinge folds. As they roll off the hot surface, the hinges unfold and are ready for the next cycle.”
Another device the team devised is a self-twisting origami polyhedron with three stable configurations. When placed in a hot environment, the robot can fold into a compact folded shape resembling a paper clip and unfold itself when cooled. These untethered structures can be passively controlled. In other words, by simply exposing the structures to specific temperature environments, the robots will respond according to how the hinges were programmed.”
Another development in the self-assembly space has seen scientists encase liquids in a 3D polymer membrane. A team of Italian scientists generated “a thin polymer film following the existing water profile and eventually sealing all the elements included in the water”(Quick liquid packaging: Encasing water silhouettes by three-dimensional polymer membranes). This type of development could allow us to package liquids without the use of rigid containers. The polymer membrane wrapping technique could also be applicable “as a natural layer for in vitro lab-in-a-drop experiments and in vivo indwelling devices that could find application in a clinic as an injectable system or for the creation of biomimetic materials that can be integrated into living organisms” Quick liquid packaging: Encasing water silhouettes by three-dimensional polymer membranes).
Scientists are also using self-assembly to 3D print biomaterial that can be used to replicate human tissue and organs in labs for use cases such as drug testing and discovery. Scientists at University of Nottingham and Queen Mary University in London 3D printed graphene oxide in combination with a protein such that it can assemble into a shape that replicates elements of vascular tissue. Until this experiment, the ability to build these types of materials through self-assembly of molecular components was minimal. As Dr. Yuanhao Wu, a researcher on the project noted to Scitech Daily, “This research introduces a new method to integrate proteins with graphene oxide by self-assembly in a way that can be easily integrated with additive manufacturing to easily fabricate biofluidic devices that allow us replicate key parts of human tissues and organs in the lab.” This type of development in self-assembly allows us to replicate elements of the human body, which will have promising implications for biomedical research.
There are a number of challenges to self-assembly, including programming the complex reactions that need to occur, a high error rate for self-assembly reactions, and difficulty in scaling them. In order to overcome these obstacles, we will need to be able to position the self-assembling materials with atomic precision and be able to do so with high frequency. This brings us to the concept of stereotactic control, which is simply the ability to move particles to desired locations.
Or as Eric Drexler put it in his 2013 book Radical Abundance: How a Revolution in Nanotechnology Will Change Civilization:
“stereotactic control — the ability to direct molecular assembly by guiding molecular motions” and “the most advanced forms of stereotactic control require moving small reactive molecules along complex, tightly constrained paths.”
“Stereotactic assembly is how you put a peg in a slot, or a shelf into a bookcase; it’s just the generic, common-sense way of building things: Move parts into place and put them together. The self-assembly method, by contrast, seems strange: Let parts move at random and require each part to encounter and bind to its own special place”
“Stereotactic control can repair a weakness of self-assembly, and self-assembly can reduce the challenges of stereotactic control. Loose stereotactic control can easily constrain general positions, and self-assembly then can provide fine-scale alignment”
We already use stereotactic control in the medical field for things such as radiosurgery, in which a radiation beam is focused at a tumor or cancerous cells, and the idea here is that we could use a similar technique to direct specific atoms where we want them to after self-assembly occurs. Or instead of directing radiation we can crudely position self-assembling molecules in specific locations and then trigger the self-assembly. Drexler was above speculating on how we might merge these concepts to one day achieve APM, through means that are known to be feasible today. But we still have many years of research ahead of us before machines at these nanoscales become achievable.
Stay Tuned
In Part 4 of this article we will explore in more detail some of the challenges holding this branch of research back, along with some promising solutions. And we will also take a closer look at how to image and inspect your work at these nanometer scales to determine if you have achieved the intended atomic precision.
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