Self-erasing "invisible ink" chip alerts users to unauthorized access

Researchers at the University of Michigan have developed a kind of electronic “invisible ink” that can help alert users to any unauthorized tampering with a device. When the chip is exposed to light it will erase information printed on it, making it clear that someone’s opened the box.

The device is made up of a semiconductor layer of tungsten diselenide just three atoms thick, above a layer of azobenzene molecules. When the azobenzene is exposed to UV light, it shrinks, stretching out the tungsten diselenide atoms above it. That in turn changes the wavelength of the light they emit.

In practice, that means a user can write a message or draw a symbol into the azobenzene using UV, and when a certain wavelength of light is shone over the tungsten diselenide, that same shape will appear to glow on the surface. If the azobenzene is exposed to visible light, it will relax again, wiping the message completely.

The idea, the team says, is that if a chip was tampered with, the crooks would inadvertently wipe this logo when they open the box. A user could easily spot any shenanigans by checking for that symbol.

“It’s very hard to detect whether a device has been tampered with,” says Parag Deotare, corresponding author of the study. “It may operate normally, but it may be doing more than it should, sending information to a third party.”

Currently the azobenzene only retains its memory for about a week, before it will relax and wipe itself, but this can be extended by storing it in a cold, dark place. On the other hand, a flash of blue light will wipe the slate clean on demand, ready to be written anew.

The team says that the next steps for the work are to figure out ways to extend the time that the material will retain messages, which could see it put it to work in anti-counterfeiting.

The research was published in the journal Advanced Optical Materials. The team demonstrate the device in the video below.

Source: University of Michigan