Using Gallium Oxide As A Resistive Memory Element

February 22, 2024 by Maya Posch 7 Comments

Resistive random-access memory (RRAM) is a highly attractive form of RAM, as it promises low-power usage with stable long-term storage, even in the absence of external power. Finding the right materials to create an RRAM cell which incorporates these features is however not easy, but recently researchers have focused their efforts on gallium(III) oxide (Ga₂O₃), with a research article by [Li-Wen Wang] and colleagues in Nanomaterials describing a two-bit cell (MLC) based around an aluminium-gallium oxide-graphene oxide stack which they tested for an endurance of more than a hundred cycles.

Filament models of the Al/GO/Ga2O3/ITO/glass device. (Credit: Li-Wen Wang et al., 2023)

The way gallium-oxide works in an RRAM cell is by forming a conductive filament formed by oxygen vacancies. These vacancies and the resulting conductive path are controlled by an externally applied current via the top (Al) and bottom (ITO) electrodes, with the graphene-oxide (GO) layer acting as a source of oxygen ions.

In related research, [Zhengchun Yang] and colleagues described in a 2020 article in Ceramics International how they constructed a device consisting out of gallium(III) oxide RRAM data storage with a piezoelectric ceramic element that served both as pressure sensor and power supply. The current generated by the piezo element is used to power the memory device and record measurements.

Then there is the somewhat more wild ‘FlexRAM’ idea pitched by [Ruizhi Yuan] and colleagues in Advanced Materials who describe how they created a device consisting out of flexible polymer called ‘EcoFlex’ with pockets in it for a ‘liquid gallium-based metal’ to create a flexible memory device. At millimeter-sized structures it’s hard to see practical applications for this technology, even if the associated PR article in IEEE Spectrum goes pretty hard on breathless speculation.

Measuring Trees Via Satellite Actually Takes A Great Deal Of Field Work

February 20, 2024 by Lewin Day 11 Comments

Figuring out what the Earth’s climate is going to do at any given point is a difficult task. To know how it will react to given events, you need to know what you’re working with. This requires an accurate model of everything from ocean currents to atmospheric heat absorption and the chemical and literal behavior of everything from cattle to humans to trees.

In the latter regard, scientists need to know how many trees we have to properly model the climate. This is key, as trees play a major role in the carbon cycle by turning carbon dioxide into oxygen plus wood. But how do you count trees at a continental scale? You’ll probably want to get yourself a nice satellite to do the job.

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Flux, From Scratch

January 29, 2024 by Jenny List 52 Comments

Soldering flux is (or at least, should be) one of the ubiquitous features of any electronics bench. It serves the purpose of excluding oxygen from a solder joint as it solidifies, and in most cases its base is derived from pine rosin. Most of us just buy flux, but [pileofstuff] is having a go at making his own.

He starts with a block of rosin and a couple of different solvents. Isopropanol we’re happy with, but perhaps using methanol for something to be vaporized within breathing distance isn’t something we’d do. At about 25% rosin to solvent ratio the result is a yellow liquid flux, which he tests against some commercial fluxes. The result is a reasonable liquid flux, something which perhaps shouldn’t be too much of a surprise, and is a handy piece of information to store away should we ever be MacGuyver-like stuck in a pine forest with a need to save the day with electronics.

It would be interesting to try the same technique but with a solvent selected to soften the rosin for a paste flux, and perhaps any chemists among our readership could enlighten us about just what rosin is beside the heavy fractions left after extracting the volatiles from pine resin.

In the past we’ve taken a close look at how solder really works.

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Could Moon Mining Spoil Its Untouched Grandeur And Science Value?

January 25, 2024 by Lewin Day 89 Comments

It’s 2024. NASA’s Artemis program is in full swing, and we’re hoping to get back to the surface of the Moon real soon. Astronauts haven’t walked on the beloved sky rock since 1972! A human landing was scheduled for 2025, which has now been pushed back to 2026, and we’re all getting a bit antsy about it. Last time we wanted to go, it only took 8 years!

Now, somehow, it’s harder, but NASA also has its sights set higher. It no longer wants to just toddle about the Moon for a bit to wave at the TV cameras. This time, there’s talk of establishing permanent bases on the Moon, and actually doing useful work, like mining. It’s a tantalizing thought, but what does this mean for the sanctity of one of the last pieces of real estate yet to be spoilt by humans? Researchers are already arguing that we need to move to protect this precious, unique environment.

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This Unique Flip-Flop Uses Chemistry And Lasers

January 24, 2024 by Dan Maloney 8 Comments

One of the first logic circuits most of us learn about is the humble flip-flop. They’re easy enough to build with just a couple of NOR or NAND gates, and even building one up from discrete components isn’t too much of a chore. But building a flip-flop from chemicals and lasers is another thing entirely.

That’s the path [Markus Bindhammer] took for his photochromic molecular switch. We suspect this is less of an attempt at a practical optical logic component and more of a demonstration project, but either way, it’s pretty cool. Photochromism is the property by which molecules reversibly rearrange themselves and change color upon exposure to light, the most common example being glass that darkens automatically in the sun. This principle can be used to create an optical flip-flop, which [Markus] refers to as an “RS” type but we’re pretty sure he means “SR.”

The electronics for this are pretty simple, with two laser modules and their drivers, a power supply, and an Arduino to run everything. The optics are straightforward as well — a beam splitter that directs the beams from each laser onto the target, which is a glass cuvette filled with a clear epoxy resin mixed with a photochromic chemical. [Markus] chose spiropyran as the pigment, which when bathed in UV light undergoes an intramolecular carbon-oxygen bond breakage that turns it into the dark blue pigment merocyanine. Hitting the spot with a red laser or heating the cuvette causes the C-O bond to reform, fading the blue spot.

The video below shows the intensely blue dot spot developing under UV light and rapidly fading thanks to just the ambient temperature. To make the effect last longer, [Markus] cools the target with a spritz from a CO₂ cartridge. We imagine other photochromic chemicals could also be employed here, as could some kind of photometric sensor to read the current state of the flip-flop. Even as it is, though, this is an interesting way to put chemistry and optics to work.

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Vulcan Nails First Flight, But Peregrine Falls Short

January 9, 2024 by Tom Nardi 24 Comments

For those with an interest in the history of spaceflight, January 8th promised to be a pretty exciting day. Those who tuned into the early morning live stream were looking forward to seeing the first flight of the Vulcan Centaur, a completely new heavy-lift booster developed by United Launch Alliance. But as noteworthy as the inaugural mission of a rocket might be under normal circumstances, this one was particularly special as it was carrying Peregrine — set to be the first American spacecraft to set down on the lunar surface since the end of the Apollo program in 1972.

Experience has taught us that spaceflight is hard, and first attempts at it doubly so. The likelihood of both vehicles performing as expected and accomplishing all of their mission goals was fairly remote to begin with, but you’ve got to start somewhere. Even in the event of a complete failure, valuable data is collected and real-world experience is gained.

Now, more than 24 hours later, we’re starting to get that data back and finding out what did and didn’t work. There’s been some disappointment for sure, but when everything is said and done, the needle definitely moved in the right direction.

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How To Refrigerate With Urine

January 9, 2024 by Maya Posch 13 Comments

It’s often said that the best science experiments are the ones which do not require any special devices or ingredients, which makes the use of what naturally comes out of one’s body clearly one of the winners. It’s also the beginning of yet another [Hyperspace Pirate] chemistry video that’s both fascinating and unforgettable — this time introducing a considerable collection of urine, and the many uses of the urea in it, including its use for refrigeration.

The respective cooling effect of a variety of compounds in solution. (Credit: Hyperspace Pirate)

As icky as this may sound, it doesn’t even rank in the top ten of quaint things people have historically done with urine, so extracting urea from it is rather benign. This is performed by adding sodium hydroxide to the starting component after heating, which creates gaseous ammonia (NH₃) which was then condensed into its liquid (dissolved) form. In order to create the target compound – being ammonium nitrate – nitric acid (HNO₃) had to be created first.

For this the older, but cheaper and easier Birkeland-Eyde process was used. This uses high-voltage electrical arcs to break down the nitrogen and oxygen in the air and cause the formation of nitric oxide (NO), that subsequently reacts with atmospheric oxygen to form nitrogen dioxide (NO₂). Running the NO₂ through water then creates the desired HNO₃, which can be combined with the ammonia solution to create ammonium nitrate. The resulting solution was then evaporated into solid ammonium nitrate, to use it in an aluminium cooling cylinder, with freshly added water.

This is the simplest way to use the cooling effect of such solutions (pictured), but the benefit of ammonium nitrate over the original urea seems minimal. The low efficiency of this cooling approach means that the next use of urine will involve a much more efficient vapor-absorption cycle, which we’re sure everyone is squeezing their legs together for in anticipation.

We’ve been covering the refrigeration experiments [Hyperspace Pirate] has been conducting for some time now. If you’re into the science of making things cold check out how seashells can be turned into dry ice, or what goes into building a home cryocooler.

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