Unless you’re really into graphene (or other two-dimensional advanced materials) you’ve probably never heard of these guys. Takashi Tanaguchi and Kenji Watanabe at Tsukuba’s National Institute of Materials Science are basically the only source in the world for high-quality crystals of hexagonal boron nitride (hBN), and that is apparently the idea substrate for studying all sorts of other two-dimensional sheets that can lie on top of it. hBN itself is not a rare substance – it’s found in all sorts of high-end lubricants, and it shows up in cosmetics (eyeliners especially), printers, electronics, dental cements, pencils and who knows what else. But growing large defect-free single crystals of it is another matter entirely. That takes a gigantic high-pressure setup like the one in Tsukuba, and that device is apparently given over now almost entirely to turning these out. It’s not even what they had ever planned to do:
Neither Taniguchi nor Watanabe is a graphene researcher, and they had no idea that their gems would become so desirable. The researchers now have several patents related to their hBN-making process, but say they don’t expect to be able to commercialize it — at the moment, only research groups need the highest-purity crystals. There is a sizeable perk, however. Because the pair are credited with authorship on studies using their crys- tals, they have become among the world’s most-published researchers. Together, Taniguchi and Watanabe appeared as authors on 180 papers last year — and, since 2011, they have co-authored 52 papers in Science and Nature, making them the most prolific researchers in these journals over the past 8 years. . .
There are other groups and facilities working on increasing the supply, but as that article points out, researchers are going to have to run head-to-head tests before they’ll trust any other suppliers. Single-sheet graphene will conform to the shape of whatever it’s sitting on, and if it’s not absolutely flat many of its unusual properties disappear. (Note that getting really good graphene to start with is not always so easy unless you’re isolating it yourself). The substrate also has to be extremely nonreactive and pure, so as to reduce the possibility of interaction with the electrons in the delocalized graphene orbitals. And hBN checks all these boxes, as became apparent around 2009. The first work using Tanaguchi and Watanbe’s crystals as a key component showed up in 2010 and seems to have caused a frenzy in the graphene field when people realized just how good they were. Like all crystal-growing, it’s full of witchcraft:
Taniguchi is cagey about the exact recipe: this is his secret sauce, and he likes to change the composition of the barium layer from batch to batch. “Using the same recipe every time is not that fun,” he says. For first-time users, he’ll send some baseline crystals, but with long-time users, he wants feedback on each slight change to the process. By measuring electron mobility in graphene, they can detect impurities in the underlying hBN with more sensitivity than Taniguchi and Watanabe can measure. At first, no one had any complaints about their crystals. Only in the past two years, Taniguchi says, have researchers begun reporting impurities that affect their results — a result of them pushing the limits of the material. And that motivates Taniguchi to improve. “I’m a crystal grower,” he says proudly.
The whole field has been advanced tremendously by these crystals, but at the same time, you have to worry a bit when it all depends on these two dudes in Japan, only one of whom knows all the subtle details and is approaching retirement age, to boot. There are those other suppliers tooling up (and other methods as well, from similar high pressure work to chemical vapor deposition), but for now, it’s the Tsukuba lab or bust. I’ve heard of situations like this in molecular and cell biology, where one particular antibody or cell line is available from this one particular lab (or maybe not!), but this is the first time I’ve come across quite this situation in chemistry/materials science. Anyone have any comparable examples? I’ll bet they don’t involve 180 publications a year!