72 Science & technology The EconomistOctober 5th 2019
2 nology firms. Alibaba, an e-commerce
giantbasedinHangzhou,announcedits
firstrisc-vchipinJuly.Shanghai’smunici-
palgovernmenthasaprogrammewhich
supportsstartupsusingrisc-vintheirde-
signs.Huami,a bigwearable-devicefirmin
Hefei,ismassproducingsmartwatches
containing processors based on risc-v.
AndinShenzen,Huawei,oneoftheworld’s
largestelectronicscompanies,hasa team
ofdevelopersworkingonrisc-v. Inanin-
terviewinSeptemberWangChenglu,the
boss of Huawei’s consumer-electronics
business,pointedto therisc-vfounda-
tion’srecentmovetoSwitzerland,outof
America’sjurisdiction,assomethingthat
willencourageHuawei’suseoftheisa.
risc-vdoeshaveweaknesses.Armhas
spentdecadesbuildingsoftwaretoolstoworkwithitsdesigns,andspendsa lotof
its time helping customers implement
theseontheirchips.Thetoolsthatexistfor
risc-vdesignsarenotyetthatsophisticat-
ed.Intelmakesthingssimplerstill.Itcar-
riesoutallofthedevelopment,testingand
fabricationitself,deliveringonlyfinished
chipsto customers. Thisreliabilitywill
certainlykeepthesefirms’productscom-
petitivefora while.
Despiteallthat,though,risc-vseems
likelyto thrive,particularly inproducts
thatcontainchipsbutwhicharenotsmart-
phonesorcomputers.Open-sourcesoft-
warewasa prerequisiteforthesmartphone
boomthathastakenplaceoverthepastde-
cade. Open-source hardware, such as
risc-v, mayleadtoa similarexpansionof
otherdevicesinthedecadetocome. 7O
n september 13tha 16.78-carat yellow
diamond, worth $2m, which was on
display at the New York Stock Exchange,
disappeared from view. Police were not,
however, called to the scene. The disap-
pearance was intentional. The diamond,
part of an artwork called “The Redemption
of Vanity”, had been coated in a “super-
black” layer of carbon nanotubes which, by
absorbing 99.995% of the visible spectrum,
made the usually sparkling gemstone seem
practically invisible inside its dark case.
“The Redemption of Vanity” was a col-
laboration between Diemut Strebe, artist-
in-residence at the Massachusetts Insti-
tute of Technology, and Brian Wardle, the
institute’s professor of aeronautics and as-
tronautics. Whatever moral message this
artistic endeavour might or might not have
been intended to convey, it was a stark de-
monstration of allotropy—the fact that a
single element can come in many guises,
depending on the arrangement of its at-
oms. For, like Dr Wardle’s nanotubes, dia-
monds are made of carbon. And that allo-
tropic diversity is one of the reasons why
carbon is such a useful material.
The idea of creating super-black sur-
faces out of carbon nanotubes is not in it-
self new. Vantablack was developed by Sur-
rey NanoSystems, a British company, and
put on the market in 2014. Vantablack,
however, absorbs only 99.965% of the light
incident upon it. As Dr Wardle’s work
shows, things have moved on since then.
Nanotubes, which have an atomic
structure similar to graphite’s, are natural-lyblack.Tomakethemsuper-black means
growing them as forests that rise upward
from the surface to be blackened. That way,
once light enters the forest, it bounces
from tube to tube—with each encounter
bringing a high chance that the light will be
absorbed. Few photons survive this pro-
cess long enough to escape from the top of
the forest canopy and be reflected from the
surface. The effect is uncanny. A ball coated
in a super-black would appear more like a
hole in the air than a solid object.
The nanotubes involved in super-black
surfaces are created by encouraging carbon
atoms that start off in gas molecules such
as carbon dioxide to crystallise into small
cylinders which grow outward from thesurface to be coated. Conventionally, this is
done at a temperature of about 700°C. The
target surface is coated with tiny particles
of iron. These act both as catalysts for the
carbon-liberating reaction and as nuclei
for the growth of the cylinders.
Dr Wardle’s team has been experiment-
ing with aluminium surfaces instead of
iron nanoparticles, and employing sub-
stances like baking soda and salt to prepare
the aluminium. These materials remove
the thin oxide layer that forms naturally on
the metal when it is exposed to air. The so-
dium in them also seems to act as a catalyst
in the way that iron does. The result is a
process that operates at 400°C instead of
700°C, and which produces one of the su-
perest blacks around. The involvement of
aluminium means, of course, that to create
“The Redemption of Vanity” the team had
first to coat the diamond at the artwork’s
centre with aluminium—but aluminising
things in this way is a well-established pro-
cess. Indeed, that is part of the point. Sub-
stituting aluminium for iron should make
super-blacking things easier.
Since the introduction of Vantablack,
super-blacks have moved on commercially
as well as artistically. Vantablack was so
delicate that, once applied, it could not be
touched. It had to be secured behind a pro-
tective layer. Surrey NanoSystems’s more
recent products incorporate elements oth-
er than carbon. As with diamonds, these
dopants change a crystal’s properties.
(Pure-carbon diamonds are colourless; the
yellowness of the stone in “The Redemp-
tion of Vanity” is caused by traces of nitro-
gen.) Correct doping of nanotubes creates a
less fragile arrangement—more akin to a
coral reef than a forest. Some modern su-
per-blacks, indeed, are robust enough to
withstand being sprayed onto suitably pre-
pared surfaces at room temperature.
Moreover, besides their decorative ap-
plications super-blacks are used in manu-
factured products, particularly optical de-
vices. Since they absorb more stray light
than other coatings, using them to cover
the interior surfaces of lenses can result in
clearer images with better contrast and col-
our definition. According to Ben Jensen,
chief technical officer at Surrey Nano-
Systems, the firm is collaborating with an
as-yet-unnamed Japanese company to de-
velop cameras which work on this princi-
ple. Certain European carmakers are, he
says, also eyeing up super-blacks to im-
prove the accuracy of sensors such as those
employed to guide autonomous vehicles.
And there are, naturally, military applica-
tions—though these remain secret.
Altogether, then, this allotrope of car-
bon looks likely to have a profitable future.
Whether it will be as profitable as its cousin
diamond’s is remains to be seen. But in this
case, to say that things look black for it is
not a pessimistic assessment. 7The future of super-black coatings looks, as it were, brightOpticsDark business
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