A new, very fast synthesis technique for the creation of high-quality, large-area Bernal (or AB) stacked bilayer graphene films has been developed by researchers at the University of California–Santa Barbara.
The new technique will open up new possibilities in the fields of digital electronics and transparent conductors, according to the researchers.
The new research also constitutes the “first demonstration of a bilayer graphene double-gate field-effect transistor (FET), showing record ON/OFF transistor switching ratio and carrier mobility that could drive future ultra-low power and low-cost electronics.”
By now nearly everyone who is at all familiar with what graphene is knows about the material’s potentially very useful electrical and thermal properties — less well known, though, is the fact that many potential applications are “significantly restricted by the zero band gap of graphene that results in leaky transistors not suitable for digital electronics.”
“In addition to its atomically smooth surfaces, a considerable band gap of up to ~0.25 eV can be opened up in bilayer graphene by creating a potential difference between the two layers, and thereby breaking the inherent symmetry, if the two layers can be aligned along a certain (Bernal or AB) orientation,” explained Kaustav Banerjee, professor of electrical and computer engineering and Director of the Nanoelectronics Research Lab at UCSB. “The dual-gated transistors were specifically designed to allow such potential difference to be established between the layers through one of the gates, while the second gate modulated the carriers in the channel.”
The press release from UCSB provides specifics on the new work:
The graphene films were grown in a deterministic manner using an engineered bifunctional (Cu:Ni) alloy surface at a relatively low temperature of 920 °C. Large-area (> 3 inch × 3 inch) Bernal (or AB) stacked bilayer graphene growth was demonstrated within few minutes and with nearly 100% area coverage. The bilayer graphene films exhibited electron mobility as high as 3450 cm2/(V•s), which is comparable to that of exfoliated bilayer graphene, thereby confirming very high-quality. The quality of grown graphene was further corroborated by demonstration of high-performance FETs with record ON/OFF ratio that is a key requirement in low-power digital electronics.
“Achieving surface catalytic graphene growth mode and precise control of the surface carbon concentration were key factors for the favorable growth kinetics for AB stacked bilayer graphene,” stated Wei Liu, a post-doctoral researcher in Banerjee’s group and a co-author of the article.
If you’re wondering why this work is important, it’s worth being aware that bilayer graphene has a number of other advantages over monolayer graphene as well, not just the band-gap tunability.
“It has higher density of states and suffers much less from interface effects, which are beneficial for improving the current carrying capability,” Liu explained.
It seems like every other day there’s a new story about graphene. Sometimes hyping it, sometimes talking about potential applications, sometimes talking about possible effects on human health. As far as recent news goes, I’d recommend checking out our coverage of the beginning of commercial graphene production in Poland and our coverage of a new means of making graphene with “nothing” but a blender and some graphite.
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