Building Petahertz Logic With Lasers And Graphene

There was a time when we thought a 50 MHz 486 was something to get excited about. In comparison, the computer this post was written on clocks in at about 3.8 GHz, which these days, isn’t an especially fast machine. But researchers at the University of Rochester and the  Friedrich-Alexander-Universität Erlangen-Nürnberg want to blow the doors off even the fastest modern CPUs. By using precise lasers and graphene, they are developing logic that can operate at nearly 1 petahertz (that’s 1,000,000 GHz).

These logic gates use a pair of very short-burst lasers to excite electrical current in graphene and gold junctions. Illuminating the junctions very briefly creates charge carriers formed by electrons excited by the laser. These carriers continue to move after the laser pulse is gone. However, there are also virtual charge carriers that appear during the pulse and then disappear after. Together, these carriers induce a current in the graphene. More importantly, altering the laser allows you to control the direction and relative composition of the carriers. That is, they can create a current of one type or the other or a combination of both.

This is the key to creating logic gates. By controlling the real and virtual currents they can be made to add together or cancel each other out. You can imagine that two inputs that cancel each other out would be a sort of NAND gate. Signals that add could be an OR or AND gate depending on the output threshold.

[Ignacio Franco], the lead researcher, started working on this problem in 2007 when he started thinking about generating electrical currents with lasers. It would be 2013 before experiments bore out his plan and now it appears that the technique can be used to make super fast logic gates.

We often pretend our logic circuits don’t have any propagation delays even though they do. If you could measure it in femtoseconds, maybe that’s finally practical. Then again, sometimes delays are useful. You have to wonder how much the scope will cost that can work on this stuff.

Graphene lattice

How Graphene May Enable The Next Generations Of High-Density Hard Drives

After decades of improvements to hard disk drive (HDD) technology, manufacturers are now close to taking the next big leap that will boost storage density to new levels. Using laser-assisted writes, manufacturers like Seagate are projecting 50+ TB HDDs by 2026 and 120+ TB HDDs after 2030. One part of the secret recipe is heat-assisted magnetic recording (HAMR).

One of the hurdles with implementing HAMR is finding a protective coating for the magnetic media that can handle this frequent heating while also being thinner than current coatings, so that the head can move even closer to the surface. According to a recent paper by N. Dwivedi et al. published in Nature Communications, this new protective coating may have been found in the form of sheets of graphene.

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3D Printed Transistor Goes Green

We’ll be honest, we were more excited by Duke University’s announcement that they’d used carbon-based inks to 3D print a transistor than we were by their assertion that it was recyclable. Not that recyclability is a bad thing, of course. But we would imagine that any carbon ink on a paper-like substrate will fit in the same category. In this case, the team developed an ink from wood called nanocelluose.

As a material, nanocellulose is nothing new. The breakthrough was preparing it in an ink formulation. The researchers developed a method for suspending crystals of nanocellulose that can work as an insulator in the printed transistors. Using the three inks at room temperature, an inkjet-like printer can produce transistors that were functioning six months after printing.

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Laser-Induced Graphene Supercapacitors From Kapton Tape

From the sound of reports in the press, graphene is the miracle material that will cure all the world’s ills. It’ll make batteries better, supercharge solar panels, and revolutionize medicine. While a lot of applications for the carbon monolayer are actually out in the market already, there’s still a long way to go before the stuff is in everything, partly because graphene can be very difficult to make.

It doesn’t necessarily have to be so hard, though, as [Zachary Tong] shows us with his laser-induced graphene supercapacitors. His production method couldn’t be simpler, and chances are good you’ve got everything you need to replicate the method in your shop right now. All it takes is a 405-nm laser, a 3D-printer or CNC router, and a roll of Kapton tape. As [Zach] explains, the laser energy converts the polyimide film used as the base material of Kapton into a sort of graphene foam. This foam doesn’t have all the usual properties of monolayer graphene, but it has interesting properties of its own, like extremely high surface area and moderate conductivity.

To make his supercaps, [Zach] stuck some Kapton tape to glass slides and etched a pattern into with the laser. His pattern has closely spaced interdigitated electrodes, which when covered with a weak sulfuric acid electrolyte shows remarkably high capacitance. He played with different patterns and configurations, including stacking tape up into layers, and came up with some pretty big capacitors. As a side project, he used the same method to produce a remarkable effective Kapton-tape heating element, which could have tons of applications.

Here’s hoping that [Zach]’s quick and easy graphene method inspires further experimentation. To get you started, check out our deep-dive into Kapton and how not every miracle material lives up to its promise.

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Graphene Generates A Little Power

We never know exactly what to make of university press releases, as we see plenty of them with breathless claims of new batteries or supermaterials, but then we don’t see much else. Sometimes, the claims in the press release don’t hold up in the paper, while other times the claims seem to be impractical for use in real life. We aren’t quite sure what to make of a press release from the University of Arkansas claiming they can draw current from a sheet of freestanding graphene purely from its temperature fluctuations.

The press release seems to claim that this is a breakthrough leading to “clean, limitless power.” But if you look at the actual paper, normal room temperature is causing tiny displacements in the graphene sheet as in Brownian motion. A scanning tunneling microscope with two diodes can detect current flowing even once the system reaches thermal equilibrium. Keep in mind, though, that this in the presence of a bias voltage and we are talking about nanometer-scale displacements and 20 pA of current. You can see a simple video from the university showing a block diagram of the setup.

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A Graphene Mouth Screen

We are all intimate with face coverings to slow the spread of the coronavirus. Some are reusable, and some become waste after one use. [Dr. Ye Ruquan] and a research team from City University of Hong Kong, CityU, are developing an inexpensive reusable mask with outstanding antibacterial properties, and, get this, the graphene it contains will generate a tiny current when moistened by human breath. There isn’t enough power to charge your phone or anything, but that voltage drops as the masks get dirty, so it can help determine when it needs cleaning. The video after the break shows the voltage test, and it reminds us of those batteries.

All the remarkable qualities of this mask come from laser-induced graphene. The lab is producing LIG by lasering polyimide film with a commercial CO2 infrared model. In a speed test, the process can convert 100cm² in ninety seconds, so the masks can be made more cheaply than an N95 version with that melt-blown layer that is none too good for the earth. Testing the antibacterial properties against activated carbon fiber and blown masks showed approximately 80% of the bacteria is inert after 8 hours compared to the others in the single digits. If you put them in the sun for 10 minutes, blown fabric goes to over 85%, but the graphene is 99.998%, which means that one bacteria in 50K survives. The exact mechanism isn’t known, but [Dr. Ye] thinks it may have something to do with graphene’s sharp edges and hydrophobic quality. A couple of coronavirus species were also affected, and the species that causes COVID-19 will be tested this year.

An overly damp mask is nothing to sneeze at, so keep yourself in check and keep yourself fabulous.

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Graphene Prints More Smoothly Under The Influence Of Alcohol

If you’ve ever sloshed coffee out of your mug and watched the tiny particles scurry to the edges of the puddle, then you’ve witnessed a genuine mystery of fluid mechanics called the coffee ring effect. The same phenomenon happens with spilled wine, and with functional inks like graphene.

Graphene and other 2D crystals print much better under the influence of alcohol.

The coffee ring effect makes it difficult to print graphene and similar materials onto silicon wafers, plastics, and other hard surfaces because of this drying problem. There are already a few commercial options that can be used to combat the coffee ring effect, but they’re all polymers and surfactants that negatively affect the electronic properties of graphene.

Recently, a group of researchers discovered that alcohol is the ideal solution. In the case of spilled graphene, the particles fleeing for the edges are naturally spherical. By adding a mixture of isopropyl and 2-butanol alcohol, they get flattened into a pancake shape, resulting in smoother deformation during the drying process and an easier printing process with better results.

Graphene is quite interesting by nature, and has many uses. It can shift from an insulator to a superconductor with the right temperature changes, and it can desalinate sea water for drinking.