The wonderful world of wonder materials

[rhoenix]

Fun with materials science!

In July, scientists at the University of Darmstadt in Germany succeeded in stopping light completely inside a crystal. Some rays of light (in this case from a laser) were barreling along at the universal speed limit of 300 million meters per second — and then, when they entered the crystal, the waves simply stopped dead. These photons can remain stored inside and retrieved from the crystal for up to a minute, effectively creating the first feasible light memory, for use in long-range quantum networks. This breakthrough was only possible because of the crystal that they used — and the crystal could be created due to recent advances in materials science.

Materials science, sometimes known as materials engineering, is the study of the properties of matter. More succinctly, it is the study of how the structure of a material at an atomic scale affects its properties. Because materials science relies on being able to inspect and manipulate matter at a nanoscale, and our machines and tools are only just starting to reach the necessary levels of finesse and fidelity, this is a relatively new field. Thus, the last few years have been disproportionately exciting as scientists and engineers finally discover why and how materials behave the way they do — and perhaps more importantly, use their newfound knowledge to create new materials that behave in weird and wonderful ways.

In the case of the light memory crystal, the new material being used is yttrium silicate, doped with praseodymium (a rare earth element). We’ll discuss doping in more detail later. This crystal has been specifically engineered so that it is transparent, but only when it’s struck by a laser (electromagnetically induced transparency, or EIT, if you want to know the technical term). When it isn’t illuminated, it becomes opaque. Thus, light from a second source (such as digital data being fed into the crystal from a fiber-optic cable) can be trapped inside the crystal.

Fairly wondrous, you might think, but materials science has furnished us with so many semi-magical materials in the last few years that stopping light almost seems mundane. Graphene, carbon nanotubes, molybdenite, metamaterials, self-healing oleophobic coatings — these materials, which are generally referred to as wonder materials, could revolutionize everything from computer chips to space exploration, and even allow the creation of invisibility cloaks.

Wonder materials

Because there’s almost an infinite number of ways of arranging atoms and other nanoscale features (such as tiny, nanometer-scale grooves and whirls), wonder materials can assume any number of weird and wonderful properties. Graphene, which has hardly skipped a news cycle since its discovery in 2004, is the strongest and most electrically conductive material known to man — and yet all it is is a single layer of carbon atoms, mechanically exfoliated (a scientific euphemism for “removed with a piece of sticky tape”) from a piece of graphite (as found in your pencil lead).

Despite its fantastical characteristics, though, graphene’s properties are entirely down to mother nature, and the ubiquitous carbon-carbon bond (without which, life wouldn’t exist). Metamaterials, on the other hand, are materials that have been engineered to have properties that absolutely don’t exist in nature — such as negative refraction. By creating patterns and pathways that are exactly the right shape and size to bend and contort a specific frequency of light waves, you can make light behave in exceedingly peculiar ways. Generally, when light transitions from one medium to another (say, from air into water), it always refracts in a very specific way (skewing how things appear under water, for example). Negative refraction allows light to be bent in the opposite way, seemingly breaking Snell’s law, which has existed in some form or another for over 1000 years.

The discovery of negative refraction has led to the creation of the first handful of invisibility cloaks, which seamlessly bend light and other electromagnetic radiation around an object. These cloaks aren’t yet practical — they’re large and unable to leave the laboratory — but it probably won’t be too long until metamaterials provide you with a Harry Potteresque invisibility cloak.

Construction and observation

For the most part, we have the semiconductor industry to thank for the construction of these wonder materials. In general, creating and manipulating wonder materials involves equipment that operates on an atomic level — and the machines that make computer chips are, by some stretch, the most intricate tools created by man. With modern chips like Intel’s 22nm Ivy Bridge and Haswell, there are layers of silicon and metal oxides that can be measured in numbers of atoms, rather than nanometers. Likewise, these wonder materials often owe their whacky properties to features and patterns that are just a few atoms or nanometers across.

Many wonder materials, such as graphene, are mass-produced using chemical vapor deposition (CVD), which is also a key process in the CMOS (silicon chip) industry. Likewise, the nanostructures that give metamaterials their ability to create invisibility cloaks, can be created using lithography — the same process that is used by the CMOS industry to trace out the locations of billions of transistors on a chip.

Creating something is one thing, but actually observing how and why it works is something else entirely. With a bridge, you can build it, and then use cameras, gyroscopes, and other sensors to measure how it reacts as cars drive across it. Observing individual carbon-carbon bonds in graphene, though, and measuring the voltage potential of a single electron passing over that bond, is considerably more tricky. It is only because of the scanning tunneling microscope (STM), which was developed by IBM in the ’80s, and other similar devices such as the atomic force microscope (AFM), that researchers can now build up an atom-by-atom image of a material. The STM, which has only reached maturity in the last few years, also has the ability to pick up and move single atoms, which makes it the choice instrument for materials scientists looking to create new wonder materials, too.
What a wonderful world it would be

From space elevators to computers the size of a grain of sand, there are scant few areas of life that would be untouched by the maturity, mass production, and proliferation of wonder materials.

The good news is that, at this point, it’s now more of a matter of when, rather than if, graphene and co. will come to market. The bad news is that, as of today, there probably isn’t more than a few grams of graphene in existence, and the road to mass production will be long and expensive. Likewise, commercial metamaterials that can create superlenses and invisibility cloaks, are still years away.

Still, we are producing these wonder materials today, using tools that we’ve only really had at our disposal for a few years. Over the next decade, these materials will slowly work their way into military and space applications (as always), and then eventually the consumer market. More excitingly, though, just take a moment and think about all of the possible ways of arranging the hundred-odd elements that populate our universe, and the billions of structure and pattern permutations that are possible with our modern machines. In all likelihood, there are quite literally millions of other wonder materials that are still left to be discovered or synthesized, each with magical and never-before-seen properties that have the potential to change life as we know it.

This is a pretty good "look at the shiny" kind of overview of the advances made in materials science in recent years.