graphene

43 Articles

The Challenges Of Producing Graphene In Quantity

April 12, 2023 by 26 Comments

We’ve all heard the incredible claims made about graphene and its many promising applications, but so far the wonder-material has been held back by the difficulty of producing it in large quantities. Although small-scale production was demonstrated many years ago using basic Scotch tape, producing grams or even kilograms of it in a scalable industrial process seemed like a pipedream — until recently. As [Tech Ingredients] demonstrates in a new video, the technique of flash Joule heating of carbon may enable industrial graphene production.

The production of this flash graphene (FG) was first demonstrated by Duy X. Luong and colleagues in a 2020 paper in Nature, which describes a fairly straightforward process. In the [Tech Ingredients] demonstration it becomes obvious how easy graphene manufacturing is using this method, requiring nothing more than carbon black as ingredient, along with a capacitor bank, vacuum chamber and a number of reasonably affordable items.

Perhaps best of all is that no refinement or other complicated processes are required to separate the produced graphene from the left-over carbon black and other non-graphene products. Using multiple of these carbon black-filled tubes in parallel, producing graphene could conceivably be scaled up to industrial levels. This would make producing a few kilograms of graphene significantly easier than coating hard drive platters with the substance.

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A Transistor? Memory? Wait, It’s Both!

December 18, 2022 by 13 Comments

What do you get if you cross graphene, hexagonal boron nitride, and tungsten diselenide? Well, according to researchers at Hunan University, you get a field effect transistor that can act as both a switching element or a memory cell. The partial floating-gate field-effect transistor or PFGFET uses 2D van der Waals heterostructures to deal with isolated atomic layers. The paper in Nature is unfortunately behind a pay wall, but you can read a summary over on [TechExplore].

The graphene acts as the gate, and the transistor can be switched between n-type behavior and p-type behavior. It can also be configured as a switching element or as a memory element similar to an EEPROM cell.

One advantage of having configurable transistor types is that a single transistor structure can produce CMOS or complementary circuits. Traditionally, a CMOS IC has two different transistor structures and often producing one of them requires extra effort.

The configuration takes place by applying a control voltage pulse. A negative control voltage produces a p-type FET and a positive voltage configures the same transistor as an n-type. If you don’t have access to the paper, the figures available online offer a good bit of insight into the device’s design.

If you want to learn more about ordinary MOSFETs, we talk about them often. You can also get the skinny on CMOS from [Bil Herd].

There’s Gold In That There Graphene

August 23, 2022 by 14 Comments

There’s gold all around us, embedded in our electronics. There are people who collect e-waste and use various methods to extract gold from them. However, it is hard to qualify it as a “get rich quick” scheme because the amount of gold recovered is usually minute. Still, if you can do volume, you can make some money and recycling is always a good idea. At the University of Manchester, they have a better way to extract gold from e-waste using graphene. You can see a brief video about the process below, or read the full paper.

The process is relatively simple. You dissolve the e-waste in a solvent, add some graphene oxide, and the gold appears bound to the graphene. You pull out the graphene and burn it off to result in the gold you want. A gram of graphene can grab 2 grams of gold and graphene is relatively cheap per gram compared to gold.

Graphene oxide nanosheets are processed using ascorbic acid into a colloid suspension. The chemical process converts gold bound with chlorine into elemental gold. After diving into why the process works, they were able to increase the selectivity of the process by manipulating the pH so that the majority of the residue is actually gold.

The team believes they can build a continuous process that takes liquefied e-waste and extracts gold as it flows through the system. If you’d rather go with the traditional method, here’s a start for you. Then again, there are other metals to recover besides gold.

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Next Floor: Geosynchronous Satellites, Orbiting Laboratories

August 3, 2022 by 40 Comments

On Star Trek, if you want to go from one deck to another, you enter a “turbolift” and tell it where you want to go. However, many people have speculated that one day you’ll ride an elevator to orbit instead of using a relatively crude rocket. The idea is simple. If you had a tether anchored on the Earth with the other end connected to a satellite, you could simply move up and down the tether. Sound simple, so what’s the problem? The tether has to withstand enormous forces, and we don’t know how to make anything practical that could survive it. However, a team at the International Space Elevator Consortium could have the answer: graphene ribbons.

The concept is not new, but the hope of any practical material able to hold up to the strain has been scant. [Arthur C. Clarke] summed it up in 1979:

How close are we to achieving this with known materials? Not very. The best steel wire could manage only a miserable 31 mi (50 km) or so of vertical suspension before it snapped under its own weight. The trouble with metals is that, though they are strong, they are also heavy; we want something that is both strong and light. This suggests that we should look at modern synthetic and composite materials. Kevlar… for example, could sustain a vertical length of 124 mi (200 km) before snapping – impressive, but still totally inadequate compared with the 3,100 (5,000 km) needed.

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Graphyne Finally Created

May 24, 2022 by 22 Comments

Before you jump down to the comments to chastise us for misspelling graphene, note that graphyne is similar to graphene but not the same. Like graphene, it is a two-dimensional structure of carbon. Unlike graphene, it contains double and triple bonds and does not always form hexagons. Scientists have postulated its existence for decades, but researchers at the University of Colorado Boulder have finally managed to pull it off. You can also download the paper if you want to wade through the details.

Carbon forms like fullerene and graphene are well-known and have many novel uses. Other allotropes of carbon include graphite and diamonds — certainly two things with wildly varying properties. Graphyne has conductivity similar to graphene but may also have other benefits.

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Building Petahertz Logic With Lasers And Graphene

May 17, 2022 by 19 Comments

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

June 23, 2021 by 30 Comments

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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