Recently discovered two-dimensional (or ‘2D’) single atom thick materials continue to be refined and further characterized, helping to find new ways to push nanoelectronics into ever more practical value-added fields. Specifically, single atom thick sheet graphene, with its conductivity, strength and surface to volume ratio advantages, lends itself well to what today seem like futuristic applications in the wearables, sensing and bio-detecting fields, just to name a few.
But when some of these atomic layer nano-materials are combined to perform together, the results can be even more stunning. Consider hexagonal Boron Nitride or ‘hBN’, sometimes referred to as ‘white graphene’ due to its highly transparent nature. As its name implies, at the atomic level this material resides in a hexagonal pattern with alternating atoms of Boron and Nitride creating the hexagon. This pattern is ‘Isoelectronic’ to graphene and very closely aligns with the near identical hexagonal lattice of carbon that makes up the graphene ‘crystal’ structure. This means that these two materials are very compatible when layered together, providing advantages in bonding strength and making them relatively easy to work with when combined.
On its own, hBN has some very interesting characteristics; as mentioned, it is almost completely transparent, absorbing very little visible light. The material is also quite strong, is an excellent thermal conductor but an electric insulator and has also been shown to provide many advantages to materials it is applied to. For example, hBN when applied to acrylic sheets can help make them fire retardant and anti-microbial. This means that someday we may see airplane interiors and surgery room walls coated with hBN layers to provide desirable characteristics for the occupants.
The field of biosensing is one of the first areas where single layer graphene is being leveraged for its advanced performance capabilities. Graphene based hand held blood analyzers about the size of a smart phone that a doctor could use in the field to real time detect diseases are already available. Companies like Nanomedical Diagnostics have been characterizing diseases such as Lyme disease and Zika virus with such a tool. The sensitivity, stability and small scale of graphene makes this kind of mobility and instantaneous feedback possible. Doctors can now take blood analysis out to remote destinations and get immediate feedback for treating patients in desolate areas, thousands of miles from conventional medical care.
But the performance of graphene in this biosensing use case can be enhanced even more when combined with our new friend hBN. The silicon-based chip described above in the Nanomedical Diagnostics’ device has a layer of graphene doing the blood sensing and disease detection. The performance of this graphene sensor on silicon is very high but can be made even higher when the graphene is set on top of a layer of hBN, and THEN on top of the silicon. In this case, the hBN performs several important functions; it planarizes the underlying silicon layer, it blocks much of the oxide interference that comes out of the silicon and finally it provides much better adhesion to the graphene than the silicon alone could allow.
Layering graphene on top of hBN when building silicon-based biosensors could enable such breakthroughs as using the perspiration from one’s skin in a resting state to real time monitor glucose levels and many other aspects of one’s health – all simply by wearing a patch, a bracelet or a properly outfitted garment. When picked up by such a sensor, this information could be stored or sent real time through the wearer’s smartphone to a medical professional or other data gathering facility for later analysis.
The sensing capability of graphene is quite stunning and is only now beginning to be leveraged in advanced micro-device designs for the future, particularly in life science applications. But this atomic level sensing performance can be enhanced even further when the graphene layer is combined with ‘white graphene’ or hBN. The potential of this combination is only just starting to be appreciated. The graphene producers and users that have the ability to characterize and implement these materials together can provide real unique value to sensing device makers and will establish performance capabilities to enable new fields that haven’t even been thought of yet.