You
are taking a test tomorrow. Your
teacher was generous enough to allow you to
bring a cheat-sheet, but only on one side of an A4
paper. How would you arrange the overwhelming
amount of information you need to know and
pack them in a space so limited? Naturally, you
would miniaturise your writings, compress your
equations and facts and cram in as much as you
can. Still, eventually you would reach the edges
of the paper, no longer able to smuggle those last
few equations into the exam hall.
And this, indeed, is the million-dollar question
of our information age.
The advent of the d ig i ta l age has seen
explosive growth in the complexity
and var iety of data. More
than a billion gigabytes of
new data are created
each day [1], a pace
u n m a t c h e d b y
t he advance s i n
information systems.
Data centres and
s e r ve r s t a ke u p
large spaces and
c o n s u m e e v e n
more energy each
year. Thus, ensu r i ng
each bit takes up the
minimal amount of space
i s paramount. The ultimate
so l ut i on? Cod i ng i nfo rmat i on at
the
atomic level, as Feynman envisioned nearly 60
years ago.
Scientists at Delft University have approached
the physical limit by reducing each bit to single
atoms. By arranging individual chlorine atoms in
an exactly ordered pattern, the research team
built a memory of 8000 bits (1 kilobyte) on an area
as small as 100 nm wide [2]. The hard drive was
assembled by coating a chlorine atom lattice
on a copper surface in ultrahigh vacuum, with
the precise locations of each individual atom
manipulated by injecting an electric current using
a Scanning Tunnelling Microscope. The presence
of a current allows the chlorine atoms to switch
places, res
sites and occupied sites. Each vacant site is
only 20 to 30 pm deep.
These combinations of vacant sites
(V) and occupied sites (Cl) come in
two distinct configurations, V-Cl and
Cl-V. Translated into binar y, they
can be represented as “0” and “1”,
for different numbers, letters and
symbols of data.
A d e n s i t y o f 5 0 2
t e r a b i t s p e r s q u a r e
inch was achieved, an
unprecedented density of
data that is 500 times higher
than the best commercial hard
d i sk ava i lab l e on the mar ket
[1]. To put that into perspective,
the entirety of the US librar y of
Congress can be stored within a
0.1 mm wide cube. Furthermore, the
atomic-scale device employs atoms
by removing them f rom a uniform
surface as opposed to employing atoms
in an additive manner, profoundly reducing
errors.
By David Iu
姚誠鵠
費曼的小抄－原子儲存
Feynman’s Cheat Sheet
–
Atomic Storage
Why can't we write the entire 24
volumes of the Encycolpaedia Brittanica
on the head of a pin?
— Richard Feynman,
“There’s Plenty of Space at the Bottom”, 1959
