Just prior to the end of June, there were two articles on cement/concrete. “How to Make a ‘Smarter’ Cement” [Ref. 1] covers reports from Northwestern University’s team that introduced nanoparticles into ordinary cement. They investigated two types of nanoparticles and the impact on fracture toughness. The material employed was graphene in both the shape of rolled tubes (carbon nanotubes) and also as flakes. Incorporating small amounts of nanomaterial improved the bonding due to tightening the pore structure, which reduced the air voids. It was pointed out that this structure was replicating nature. They chose to replicate the multilevel structure with the nanoparticles and the cement.
The second article [Ref. 2] address the variety of application. This BBC report covers the vast array of cement that is being employed around the world. The article is interesting in the fact that it includes a vast array of structures both modern and ancient. The Pantheon in Rome was built in the second century AD and is still the world’s largest unreinforced concrete dome. This structure’s existence implies that Roman Cement was superior to what we are currently using in present day construction. (cf. last month’s blog)
There is more material in published reports on the need for 2D semiconductors. This is especially true as the dimensional for the 3nm and 2nm semiconductor nodes are investigated. Reference 3 is one of many such articles. As the dimensions of the transistor decrease, there needs to be a corresponding reduction in thickness. Control of the electron flow is critical. Nanosheets and nanowires are being considered along with the gate-all-around transistor. The issues arise at the 3nm scale with trapped imperfections in the materials. 2D material appears to provide a possible solution.
From my viewpoint, the issue with 2D material is the production of large quantities of defect free material. There are various materials being investigated with transition metal dichalcogenides (MoS2, WS2, and WSe2 are most commonly proposed). The materials of choice are flakes of material exfoliated from bulk material. (Might bring back some memories of the early carbon nanotube work.) Atomic Layer Deposition (ALD) can provide think layers but there are residues left behind by the process that can contaminate the desired material. There is a lot of research being conducted, but much more needs to be accomplished before the 2D process can be ready for producing semiconductors on the scale needed.
From the medical standpoint, graphene and CNTs are being employed in developing sensors. A team from Harvard [Ref. 4] has created a flexible electrode array that conforms to surfaces of the body. The example application was described as being applied in difficult to reach places in order to provide recording or stimulation of electrical pulses without the potential of damaging nearby organs. The team developed the gel and needed to create the required circuitry. They developed a combination of graphene flakes and CNTs that could provide a continuous conductor path. When created on the gel, the long CNTs provide a “long” continuous pathway by multiple point contact among numerous CNTs. They then insulate it on the gel so that only the desired points are exposed. They have successfully tested the gel in stimulation a mouse heart. A key point in their development is that they needed to find some means of reducing the metal content required for conductivity. And, they succeeded.
What we are witnessing is novel thinking in applying different type nanomaterials to solve problems that challenging to resolve with current technology applications.