IBM scientists take you inside the workings of a scanning tunneling microscope and the discoveries they’ve made.
Want to see what an atom really looks like close up; or try to
actually move one? All you’ll need is a two-ton scanning tunneling microscope –
otherwise known as an STM. Not something you can easily buy or use as part of
a personal science lab.
But don’t worry. IBM Research has a couple at its lab in
Almaden, California. They work at negative 268 Celsius (the temperature needed to hold the atoms still) and operate in a completely clean and still environment. To demonstrate the precision of an STM – and
explain the properties and possibilities of nanotechnology and manipulating atoms
– my colleagues and I worked with animators and movie makers to produce several
videos, including the world’s smallest stop-motion film, "A Boy and His Atom."
Atomic
Memory
In
2012, IBM Research scientists create the world’s smallest
magnetic memory bit using only 12 atoms. The still-experimental
atomic-scale magnet memory is 100 times denser than today’s hard disk drives
and solid state memory chips.
The microscope works by moving a sharp metal needle. The tip
of the needle is both our eyes and our hands. It senses the atoms to make
images of where the atoms are located, and then we move it closer to the atoms
to tug them along the surface of a copper sheet to new positions.
The needle – a copper-tipped iridium wire – is moved around
by attaching it to three piezoelectric
crystals, which are little blocks of ceramic material that slightly change
their size when a voltage is applied to them. When we change the electrical
voltages, the piezos move, which then makes the needle move and pulls the atoms
into new places.
Making “A Boy and His Atom”
A tiny current flows between the needle tip and the
surface by a process called quantum mechanical tunneling – thus the reason
for the word “tunneling” in the name of the microscope.
A scanning tunneling microscope does not have an eyepiece
lens like typical light microscopes do. Each frame in the film is a computer-synthesized
image that measures where the needle feels a “bump” of carbon monoxide on top
of the tightly honeycombed copper surface – magnified about 100 million times.
Another way to understand this is to imagine you are in a
dark room, but want to draw a picture of the objects on a table in the room. To
do so, you would carefully sweep your hand over the objects to feel their
shape, and note down or remember the shape in order to draw a picture of the
shape you felt.
With atoms, the STM does this by sensing a small electrical
current that flows when the tip nearly touches the atoms.
Our team chose carbon monoxide – a molecule with only two atoms – because the oxygen atom
sticks out, or away from, the copper surface (the “bump”). It also holds its
position well, while also not being too sticky, so it’s easy to pull carbon
monoxide into new positions.
The team arranged and shot 242 different alignments of
carbon monoxide molecules to make the film.
Moving a single atom takes only a few seconds, but that's
after the days it takes to cool the microscope and prepare a clean surface, the
hours it takes to get the microscope poised over the surface, and the minutes
to zoom in on a suitably clean patch of the surface to find an atom.
Not just a fun way to make movies
IBM Fellow Don Eigler ushered in a new wave of
nanotechnology research by writing “IBM” with 35 xenon atoms in 1989. Since Don’s
experiment, we have learned how to move other kinds of atoms on a variety of
surfaces, and have invented new ways to move atoms.
Our biggest breakthroughs have come through building
structures that have never existed before, as we have tried to answer
scientific questions related to the magnetic effects of atomic structures, how
atoms move and interact and how they guide the flow of electrical current. We
demonstrated phenomena and technologies so unique that we needed to coin new
names for them: quantum corrals, molecule cascades, and atomic memory.
Last year, our team proved that a bit of data can be stored on a mere 12
iron atoms. Today’s storage devices use about one million atoms per bit. A
commercial device with this kind of density would be the size of a thumbnail and
could store every movie ever made. Right now that bit is being stored within 12
extremely cold atoms. But as we reach the limits of Moore’s
Law, nanotechnology experiments like this will be what keeps compute power –
and storage – on pace to double every two years, and perhaps well beyond that.
This article is by
Chris Lutz, physicist and research scientist at IBM Research – Almaden.
