Night vision goggles normally look like this. They’re big, they’re clunky, and they require space for a battery. They’re not particularly graceful, and if you’ve got one on it’s pretty obvious that you’re someone who’s trying to skulk around at night. It’s just as well that other people won’t be able to see them in the dark, because if they could they’d know to sound an alarm somewhere.
A stealthier, more lightweight solution may come as a result of research by electrical engineer Zhaohui Zhong and his team from the University of Michigan. They’ve been looking at graphene, the single layer of carbon atoms arranged in a crystal structure that many have described as a wonder material for its startling range of qualities: it conducts electricity at room temperature like a superconductor at near-absolute zero; it’s incredibly strong, and could be used for building elevators to space; it’s as stiff as diamond, yet also extremely elastic; it’s the most impermeable substance ever discovered; and it’s almost completely transparent, but it can also absorb light across all wavelengths.
That last point makes it a potentially very useful tool for building sensors, yet it does have a weakness – as graphene is essentially two-dimensional, it only absorbs around 2.3 per cent of the light that hits it, even if it’s light of all types. The Michigan team were researching ways to overcome this shortcoming, because it would be awesome be to be able to build sensors as light, strong and flexible as graphene. And, according to the study, published in Nature Nanotechnology, they may have succeeded in a first step.
When light hits graphene it knocks some electrons out from the carbon atoms, causing a slight positive charge. Rigging up a meter to measure this charge isn’t going to work, because, per above, only 2.3 per cent of the light hitting it gets absorbed – too small an amount to be picked up on this scale as an electrical charge. So the Michigan team came up with a compromise: two layers of graphene, with a barrier in between. The bottom layer was kept charged with a current, and when light hit the top layer the electrons would jump across the barrier to the already-charged layer, affecting its current. That change in current could be measured, giving an indirect reading for the wavelengths of light hitting the top layer. Zhong said:
The challenge for the current generation of graphene-based detectors is that their sensitivity is typically very poor. It’s a hundred to a thousand times lower than what a commercial device would require. Our work pioneered a new way to detect light. We envision that people will be able to adopt this same mechanism in other material and device platforms.”
Right now, the device the Michigan team has rigged up is about the size of a fingernail, but with further refinement it’s not hard to see it being shrunk further. When that happens, Zhong said, “if we integrate it with a contact lens or other wearable electronics, it expands your vision”. It’s the kind of technology we might expect from one of the less-good Bond films, but contact lenses that allow the user to change the kind of light they see aren’t entirely an impossible idea.