What’s the Matter… with Spontelectrics?

An artist's impression of a blue electric field in gas. Source: Science AlertSpontelectrics

This blog is cool.  It’s spontaneous!  It’s electric!!  But not as cool as it has been at these cutting-edge laboratories on the outskirts of Europe.  Scientists there are dealing with an entirely new type of solid matter – ‘spontelectrics’.

Last year, scientists made a curious discovery.  Initially, it was just a routine experiment.  Something went amiss, and they thought they had made a mistake because it was not supposed to be possible for a current to pass through the film and be detected.

The Danish scientists had discovered a huge electric field in a thin layer of solid nitrous oxide, commonly known as ‘laughing gas’.  They had stumbled on a new and astounding electrical phenomenon.

A graph showing the Surface Potentials in Volts against the number of monolayers of N2O for pure nitrous oxide and mixtures of N2O and Xe from the Field et al. 2014 paper.
Surface potentials measured for mixtures of N2O and Xe deposited at 44 K for the dilutions shown. The thickness of the layer is expressed as the equivalent number of ML of N2O deposited, excluding Xe. Note the absence of a spontelectric effect at a dilution, ξ, of 67. Source: Field et al. 2014

The discovery occurred when physicists from Aarhus University in Denmark, were observing how electrons travel through nitrous oxide, or ‘laughing gas’, frozen to minus 233 degrees Celsius.  When brought down to this temperature, the gas formed a thin, solid film, about one tenth of a micron thick, hovering over a strip of gold.

As it transpired, cooled down, solid laughing gas holds an enormous electric field.  A potential of around 14.5 volts appeared spontaneously on the film, producing in turn an enormous electrical field of more than 100 million volts per metre.  Based on widely accepted notions in physics, there should have been no electric current whatsoever.

 

A photograph showing how to use an ammeter for measuring an external voltage.
No external voltage is involved.

‘Spontaneously Electric’

This has to be the most remarkable property of these spontelectric material is that they are spontaneously electric – hence the name ‘spontelectrics’.

No external voltage was applied.

 

When the spontelectric effect occurs, scientists observed something unusual happening with the dipolar molecules:

Keeping to experiments conducted with a thin layer of laughing gas, the laughing gas molecules in the upper layer will arrange themselves in such a way that the positive end of the molecule pokes up towards the surface, creating a voltage on the surface of the film.

 

The scientists looked for spontelectric events on other common substances, such as carbon monoxide CO, toluene CH3, propane C3H8, and methyl formate C2H4O2.  They cooled them all down to temperatures below minus 200 degrees Celsius and looked for an electric field. 

Sometimes they would need to apply many layers above their gold strip before they would see the electric field appear.  With toluene at 75 Kelvin, minus 198 degrees Celsius, more than a hundred layers are necessary for the effect to occur.

Incredibly, this kind of research has been done on thin layers of materials – including laughing gas films – for over half a century.  Yet no-one had ever discovered this powerful electrical phenomenon.

As in Quantum Mechanics, ‘Spontelectrics’ goes against our intuition.  It does not seem to make any sense when you consider what normally happens in Physics and Chemistry.

The molecules arrange themselves entirely spontaneously – in a way that you would think they would not like. Fundamentally, we don’t know what it is that makes them do it,”

The unexpected happens: the gas becomes a solid.

And it is NO ordinary solid.

 

A diagram showing common metallic crystal structures: body-centred cubic, face-centred cubic and hexagonal close-packed structures.No Ordinary Solid

First created by astrophysics professor David Field and his colleagues at Aarhus University in Denmark, spontelectrics are a new type of solid matter – the first one to be discovered for decades.

Until now, it has been possible to divide solid matter into two types:

  • If the molecules are regularly arranged, it’s a crystal.
  • Less regularly arranged, it’s an amorphous material, like glass.

 

Spontelectric materials break that binary.  In Edinburgh, McCoustra’s team is further exploring their properties.

Helium gas must be very cold before it turns to a liquid.  But liquid helium is only the beginning.  Creating spontelectrics requires not only low temperatures but what could be described as “very, very, very low pressures”.

But… How low can you go?

 

A diagram explaining atmospheric pressure - the pressure exerted by gravitational force on a surface by the weight of the atmosphere above it. A 1 square metre column of air, with mass equals about 10^4 kilograms, corresponds to one atmospheric pressure $ ($1 atm$ )$ at the surface of the Earth.
Atmospheric pressure is the pressure exerted on a surface by the weight of the atmosphere above it. The atmospheric pressure at the surface of the earth is approximately 100 kiloPascals.  Source: socratic.org

Absolute Zee

Take your average vacuum cleaner, the pressure is about one-hundredth of one atmospheric pressure.  In his lab at Heriot-Watt University, Prof Martin McCoustra and his team go to at least a hundred-billionth of atmospheric pressure.  That IS low!

They can also cool a little bit of the inside of that down to just a few degrees above absolute zeroAt these extremes, you can add a gas like nitrous oxide or carbon monoxide – any gas made up of fairly simple molecules.

 

Dipolar Molecules

The great majority of molecules are dipolar.  Dipolar molecules act sort of like magnets.  Each one tries to arrange itself so its south pole is facing the north pole of its neighbouring dipole molecule, which will do the same, and so on.

This means the molecular structure of laughing gas will end up with slightly more negative charge on one end than on the other. 

Nitrous oxide, also known as ‘laughing’ gas is a chemical compound with formula N2ONitrous oxide is an oxide of nitrogen.

At room temperature, nitrous oxide is a colourless, non-flammable gas, with a slightly sweet odour and taste.  It is used in surgery and dentistry for its anaesthetic and analgesic effects.  The euphoric effects that results from its inhalation has made nitrous oxide a modern staple of recreational use, as a dissociative anaesthetic, despite the clear associated dangers.

Nitrous oxide is also used as an oxidizer in rockets, and to increase the power output of engines in motor racing cars.  At elevated temperatures, it is a powerful oxidizer similar to molecular oxygen.

Nitrous_Oxide_Equation_Animation_NaturPhilosophieNitrous oxide consists of dipolar molecules, which means that one end of a laughing gas molecule has a slightly more negative electric charge than the other end.  In laughing gas (N2O), the oxygen end of the molecule is negative compared with the positive nitrogen end.

When the electric field spontaneously occurs, it does something weird to these individual molecules.  They behave the opposite way of what they would normally do.

The solid has a massive electric field of over 100 million volts per metre.

 

The laughing gas molecules in the upper layer will arrange themselves in such a way that the positive end of the molecule pokes up towards the surface, creating a voltage on the surface of the film.

There is one catch though… and you will not measure spontelectrics in metres – they’re a film just a few tens or hundreds of molecules thick.  So far, spontelectric solids are too small for us to see.  At least, directly…

 

A diagram comparing the size of different macro-particles and explaining how big a micron is. A human hair is 100 microns. A pet dander is 80 microns. Pollen is 30 microns. Dust mite is 10 microns. Smoke is 1 micron. And bacteria are about 0.3 microns.
How big is a Micron?

Too Small To See

The thickness of a human hair is around 100 microns (or micrometres) across.  Knowing this may help put things into perspective.

Here the scientists are dealing with films that are a hundred times smaller, typically between ten and 50 nanometres.

Spontelectrics can only be looked at indirectly for now.  To do so, you require an infra-red spectrometer.

An infographic showing one metre scale divided down to the Angstrom $ ($10^-10 metre$ )$. The caption reads: "The most common designation is micrometres or "microns". When very small, in colloid region, measured in nanometres, typically by ultra microscopes or by dynamic light scattering."
Understanding Particle Size

As well as laughing gas and carbon monoxide, the Heriot-Watt team is now working with a more complex molecule – ethyl formate.  The temperature required to transform that into a spontelectric solid is not quite so low.

In years to come, there could be spinoffs for our everyday world.  One possibility could be better and longer-lasting video displays if the spontelectric effect can be used to make new kinds of organic light emitting diodes.  So the size of your television needs never get any smaller.

 

A NASA picture of the NGC604 galaxy - a giant stellar nursery.
NGC604 – Giant Stellar Nursery  Source: NASA

And This Matters Because…?

Spontelectric materials carry a massive electric charge and could explain why life has been able to exist on Earth.  The stuff is like stardust.

The laboratory conditions in which spontelectrics are created – high vacuum, extreme cold, a silica substrate, along with simple gas molecules – mimic the clouds of dust and gas that dot the interstellar space environment.  Those clouds are the very nurseries in which stars are born.

We Are Made of Stars.

 

According to Prof McCoustra, if these observations of these electric fields are translated into that interstellar environment, then there is potential for impacting on the charge balance in these dense clouds from which we make stars and planets.  The presence in the dust clouds of molecules like carbon monoxide could have had huge implications for life on Earth.

It might sound strange that actually we need molecules to help us form small stars.

 

Why We are Here at all.

“If you take molecules out of the picture and you assume that all your gas is atomic hydrogen, the only things you can make are massive stars. If you want to make smaller stars like our Sun you need to have molecules.” says McCoustra.

And small stars matter, like our own Sun.  If you do not have small stars in the Universe, you will not necessarily get stars that live very long.  The large star will burn itself out rapidly.  This will not leave evolution long enough to get started on some planets.

So, until we get to the ever bigger TV screens…

Until then, we get to see a tantalising glimpse of an answer to one of the most fundamental questions of all:

How did Life come into Being…