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Seven rules for nanotech innovation

Back in 2000, the field of nanotechnology was just starting to shift from something that involved tiny robots and molecular gearwheels to real, tangible science with potential applications. In October that year, I organized the first Trends in Nanotechnology (TNT) conference in Toledo, Spain, and as with all conferences, the real work happened in the hotel bar.

The atmosphere inside the Hotel Maria Cristina was febrile. The US National Science Foundation was predicting a trillion-dollar nanotechnology market by 2015. Huge national and European nanotechnology projects were taking shape, and there we were, the cream of the nanoscience community, poised and ready to change the world. New sensors, new ways of delivering drugs, molecular memories – even carbon nanotube-based space elevators to the stars – all seemed within reach. Surely, within a decade, we’d have changed all manufacturing from “top down” to “bottom up”, solving the interlinked problems of clean energy, climate change and human happiness at a stroke.

Ten years later, when I found myself having a similar discussion about graphene, I realized that the nanoscience and materials community could do with a few basic rules to avoid getting overexcited and wasting both time and money.

Rule 1: forget about the science

When you’re deeply involved in a particular field or technology, it is hard to imagine that there could be alternative views about its usefulness. However, before you can commercialize anything, you have to find someone who wants it. Your investors or funders (if any) need to know who will buy products based on your technology, what they will buy and why they will buy it. And the biggest problem you face when you step outside the laboratory door into the real world is…indifference.

Let’s face it. Most things, from medical imaging systems to communications devices, work pretty well these days. I gave up the annual iPhone upgrades years ago because the improvements in technology weren’t compelling enough to justify the hassle. New technologies have to be 10 times faster, 10 times cheaper and come with a highly scalable business model before they get much attention.

To avoid having doors repeatedly slammed in your face, start with the market, not the science. Find an unmet need, then quantify it by talking to people who have that need

A similar situation exists in the composites industry. While there are advantages to be gained from adding carbon nanotubes or graphene to a product, carbon fibre also works in many applications, is well understood and has a robust supply chain. Why would, say, Airbus base major business decisions on an immature technology from a company that might cease to exist long before its material makes it through the lengthy aerospace qualification process?

To avoid having doors repeatedly slammed in your face, start with the market, not the science. Find an unmet need, then quantify it by talking to people who have that need. If the answer to their problem is your technology, then go ahead. If it isn’t, then you’ll spend a lot of time battling indifference.

Rule 2: don’t assume anything

When I worked with the Massachusetts Institute of Technology (MIT) on the M+Vision IDEA³ programme, we offered a structured scheme to help our students find unmet needs. Often, the students would start with a woolly concept such as “better detection of cancer”, to which we’d ask questions like “What sort of cancer? At what stage? Using imaging or biopsies or genetics or something else?” Once we had a focus, we would then start talking to clinicians and radiographers to find out what issues they had. In many cases, the response was that current technology was okay, with room for incremental improvements but no urgent demand for change.

The lesson here is that if you don’t properly research your end users or customers, you may end up producing a solution to a problem that doesn’t exist. But you probably won’t even get that far. Any business plan needs to show investors how they will get their money back. It doesn’t matter whether you are selling widgets or a service or licensing the technology: before you can make any predictions, you need to understand the market.

Learning from experience: Tim Harper. (Courtesy: Tim Harper)

Here’s an example. When I was putting together my company G₂O Water Technologies, which makes graphene-based water filtration membranes, I spent a lot of time talking to people in the water industry. I needed to understand how membranes are used, what their limitations are, and how often they are replaced. I spoke with water research institutes and membrane experts, and I attended multiple talks and conferences until I was sure that our product fulfilled an unmet need in the water industry. Only when I fully understood the market did it become possible to make sense of the myriad (and often contradictory) market research reports that purported to give me definitive numbers about an industry.

This information-gathering stage is also when you will often find out about some hitherto unknown regulatory issue surrounding the use of new materials in certain environments – with the result that all your revenue forecasts move a couple of years to the right on your spreadsheet. Once you’ve completed this exercise, though, you should have a good idea of how to answer questions about who will buy your widget, how much will they pay, and when.

Rule 3: build a team

I spent six years at the European Space Agency, mostly working on electron microscopy, surface analysis and atomic force microscopy for failure analysis, and I’ll never forget the feeling I had when I left to set up my first business, Cientifica. After spending months designing a set of wings that would, I hoped, enable me to soar like an eagle, I was about to test them by jumping off a clifftop. I didn’t hit the ground with a big splat, but I came pretty close, and on the way down I had to learn all sorts of things: cash flow, margins, sales channels and (not least) the Kafkaesque bureaucracy that was, at the time, involved in filing social security and tax returns in Spain.

But perhaps the most valuable lesson I learned is the importance of working out what you are good at, where you need help, and then building a team to fill the gaps. For my second start-up, NanoSight, I brought in a chair who knew his way around the financial world and a managing director who could keep on top of the day-to-day issues – leaving me free to develop our technology to match our vision.

It is also important to build a good external team. I often recruit a scientific advisory board – half a dozen well-connected, respected and highly knowledgeable experts – and meet with them several times a year to check whether we are still on the right track. When you are 100% focused on building and promoting a business it is all too easy to start believing your own marketing story. Having to justify your strategy to independent people helps keep your feet on the ground. It also keeps you abreast of technology or competitive developments that you may have missed.

A note of caution, though: executive teams, like rock bands, do break up. Senior-level disagreements within a team are very common, and once money (or lack of money) is involved, best friends and colleagues can become bitter enemies. There’s always someone on the team who thinks they could do a better job of running the show.

Rule 4: don’t suffer fools

If you’ve followed rules one to three you will be confident that you have something that someone wants, as well as the team to take it to market. That’s when the hard work begins. There will always be people who will tell you it can’t be done. Sometimes the reason is a simple fear of change or corporate inertia; maybe you came up with a better idea than the people paid to come up with ideas. Other times it’s a lack of understanding of the technology. Occasionally, it might just be pure, bloody-minded stupidity.

The worst mistake I have made by far was to continue trying to salvage a failing business when everything pointed to closing it down. It was my business, my life, and what everyone knew me for

When I started testing the first nanoparticle imaging systems for NanoSight, several learned professors told me that what we were doing was impossible. Even after I ran a demo for them and explained the distinction between imaging and detecting the light scattered from a particle, some people were adamant that it was impossible to use optical methods to detect anything smaller than the wavelength of the laser we used.

The world is full of people who are so certain of their own beliefs that they will never change their minds, however wrong they may be. Don’t take it personally. Move on.

Rule 5: choose the right funder

How much is a start-up worth? I take the Adam Smith view that it is worth whatever someone is willing to pay for it, but no-one parts with money willingly – especially for a risky early-stage business. There are, however, some warning signs. Once, a potential investor offered me €100,000 for 90% of the business and received a lecture on idiotic time-wasting in return. Many other “investors” don’t actually have any money. Instead, they are looking for interesting deals that they can hawk around to people who do in the hope of taking a cut of the transaction. (California and China seem to be particularly good locations for people trying to squeeze themselves between you and a funder.)

In most cases, no deal is better than a bad deal. If your investors don’t believe in your team and your company’s vision, then it is going to be a long hard slog. Instead of building value into the business, you will end up having board meetings that focus on whether the CEO really needed an extra shot of espresso in their latte before the 6 a.m. Ryanair flight. However, there are times when you just can’t wait. In that case, make sure you go in with your eyes open, get your own legal advice and try to avoid joining the unfortunate group of founders whose stake gets diluted to almost zero by subsequent investors.

The best funding sources bring more than just money to the table. Expertise, contacts and access to markets can all add value. Good investors may help you flesh out your board of directors or introduce you to other companies in their portfolios. That may present opportunities. Investors like the idea of their portfolio companies working together to add even more value (and create a potential exit through acquisitions).

Rule 6: mind your ego

The life of an entrepreneur is a tough one. For every Mark Zuckerberg who hits the bullseye at the first attempt there are millions who fail, and that’s perfectly okay. I’ve had great businesses and terrible businesses. Sometimes it has been my fault that they failed, sometimes it was because of circumstances no-one could predict, but I’ve learned from them all. Most importantly, I’ve learned not to worry too much about what anyone else thinks. For every person who takes the plunge and tries to create a business, there will be hundreds waiting to tell you how you ought to have done it. Ignore the armchair entrepreneurs.

A year down the road, it may become apparent that the opportunity you are pursuing is not the right one, or that there is a more easily accessible prize. Sometimes a rethink is necessary. One medical diagnostics technology I helped develop ended up being used for water-quality testing. Of course, I had to go back to our investors and tell them that our game-changing diagnostics technology was actually being used in sewage treatment, but in a world where nine out of 10 start-ups fail completely, any return is better than nothing.

It’s embarrassing, at first, to have to admit that you didn’t get it right, but the biggest mistake is to be afraid to fail. The worst mistake I have made by far was to continue trying to salvage a failing business when everything pointed to closing it down. It was my business, my life and what everyone knew me for. Leaving it was tough. But in the end, a clean bail-out is always preferable to a messy failure; it’s quicker and you don’t get sued. When the time comes, bite the bullet and jump.

Rule 7: have fun

The past 25 years of entrepreneurship have produced some incredible highs and some terrible lows, but if I had the chance to do it all again, I’d jump at it. Success isn’t all about money and there’s nothing quite like the feeling of seeing an opportunity you identified, nurtured and grew become a success. And while there have been times when I worked 18-hour days and still struggled to pay the bills, the pain was more than balanced by having no office, no commute, no boss and complete responsibility for my own destiny.

Enjoy the rest of the 2019 Physics World Focus on Nanotechnology & Nanomaterials in our digital magazine or via the Physics World app for any iOS or Android smartphone or tablet.

Mechanically guided needle eases difficult injections

Researchers at Harvard Medical School have developed a mechanical syringe that can automatically guide a needle into specific, hard-to-access regions of tissue.

Drugs often have to be injected into highly precise locations in order to have the greatest effect. To deliver drugs into the back of the eye, for instance, one new method involves injecting directly into the suprachoroidal space, a very thin region between the white outer surface of the eye (sclera) and the layer below that includes the retina. The needle must be positioned with extreme precision to ensure that the drug reaches the right place, and to avoid causing damage to the eye. This is made even harder because the sclera is around 10 times stiffer than the tissue behind it, requiring great skill to place the needle in the correct location without overshooting.

The new device — the intelligent injector for tissue targeting (I2T2) — is similar to a normal syringe but has a needle that can move independently of the barrel when pressure is applied to the plunger. The tip of the needle is inserted into the tissue and is advanced by the clinician pushing the syringe’s plunger. The force created when moving through the stiffer outer tissue pushes the needle in. However, when it reaches the soft target tissue, the needle stops advancing and the plunger instead forces the drug out of the tip.

“The device was designed with simplicity in mind,” says Girish Chitnis, lead author of the paper describing the new injection system (Nature Biomed. Eng. 10.1038/s41551-019-0350-2).

An alternative approach

The gold standard for performing injections in difficult-to-access locations is to use real-time imaging such as ultrasound, which can track the tip of the needle as it passes through different regions of tissue.

“I don’t think the i2T2 will replace the image-guided technique altogether,” says Chitnis. “However, based on feedback from clinicians, we have learnt that image-guided techniques are not very convenient and are time consuming.” As a result, the majority of injections performed today are “blind” and rely on the physician’s skill and experience.

“The device is best suited to fill the gap where such image-guided techniques are not suitable, due to low resolution, availability, imaging time, probe size or emergent situations,” Chitnis adds. “Additionally, the imaging systems can only provide feedback about the location of the needle tip, while the i2T2 has an active mechanism that stops needle motion after reaching the target site, and effectively reduces the reliance on the physician to perform the injection.”

One downside in the current design is that it makes it less obvious to the clinician exactly how much drug has been injected, as only some of the distance moved by the plunger actually results in fluid being expelled. However, there are ways to mitigate this.

The device has not yet been trialled on patients, but preliminary tests on animal tissues showed that it is effective in controlled settings. The team successfully delivered a dye to the suprachoroidal space in cow, pig and rabbit eyes, showing good distribution within the space, with limited spread into other regions, and without adverse effects such as bleeding or movement of the retina.

The researchers are confident that the device could easily be used in other difficult injection sites. They have tested it at several other sites in animal tissues, including the spinal canal, the middle layers of the skin and the space between internal organs in the abdomen, achieving good results with each.

“If all goes well, this could be ready for human testing in one to two years”, says team leader Jeffrey Karp.

Six things we learned at the EGU meeting

Tourists smoking on the terrace of the Sphinx Observatory at the Jungfraujoch may have altered measurements of atmospheric gases.

Delegates entering the Austria Center Vienna stride over anthropogenic sediments more than 8 m thick, whereas the press centre inside lies above a layer less than 1 m thick.

Geoscientists are better at spotting fake landscapes than gamers.

An unexpected radioactive threat lurks on top of glaciers worldwide.

This year women received more than 30% of nominations for EGU awards compared to 21% in 2018.

Europeans built less in times of plague, according to tree ring records.

SpaceIL loses contact with craft moments before Moon landing

The first attempt by a private organization to land a spacecraft on the Moon has ended in failure after contact with the Beresheet lander was lost at around 19.30 GMT today just minutes before it was due to touch down. Had SpaceIL’s craft landed successfully, it would have made Israel the fourth nation to reach the Moon, after the US, the Soviet Union and China.

“If at first you don’t succeed, you try again,” said Israeli prime minister Benjamin Netanyahu from the control room, moments after the presumed crash was announced.

Beresheet was aiming to touch down within the Mare Serenitatis (The Sea of Serenity), which lies in the northern hemisphere of the Moon. Designed to inspire an Israeli “Apollo Effect”, the mission has been closely followed across the world and despite falling at the final hurdle its endeavours will surely have inspired many.

“Beresheet offers inspiration to all those who are fascinated by Space exploration but feel it is too hard or too expensive,” said mission scientist Oded Aharonson from the Weizmann Institute, Israel, ahead of the attempted landing. “In addition to learning something new about the Moon, it also offers a unique opportunity for educating young people in subjects of science and technology.”

Founded in 2011, SpaceIL is an Israeli not-for-profit organization that originally sought to win the Google Lunar XPRIZE – to build, launch and land an unmanned spacecraft on the Moon. Although Google’s competition ended on 31 March 2018 with no winners, the team pushed on, making up the required $100m budget with support from philanthropists and the Israel Space Agency.

A rocky start to a new era for space travel

Beresheet, meaning “Genesis” in Hebrew, launched on 22 February this year, hitching a ride on one of Elon Musk’s SpaceX Falcon 9 rockets. About the size of a standard washing machine, the Beresheet craft weighed 585 kg at launch. Initially, it was put into a high-Earth orbit where its furthest point from Earth (its apogee) was approximately six Earth radii. Once the team had a clear idea of the craft’s performance, they fired its rockets to send it into progressively larger orbits, swirling its way ever closer to the Moon.

Having spent some time sharing the same path the Moon takes around the Earth, Beresheet rockets were fired once more to enable it to be captured into the Moon’s orbit on 4 April. On 11 April, the craft entered the point of no return in its landing process at around 19.10 GMT. Shortly afterwards it temporarily lost contact with its telemetry system before experiencing an issue with its engine.

Beresheet's mission timeline — Timeline for Beresheet’s journey to the Moon. (Courtesy: SpaceIL)

Not everything had been plain sailing for the SpaceIL team even before its fateful final minutes. During its journey to the Moon, the craft’s onboard computer system crashed several times and its navigation system was blinded by the intensity of light from the Sun. “You run into the unexpected so you always have to have a plan B or to have some reserves because you will use that eventually,” admitted Chris Russell, member of the SpaceIL Science team, ahead of the landing.

On a magnetic mission

Russell led the team at the University of California Los Angeles that designed the mission’s most significant scientific instrument: its magnetometer. Recent analysis of data collected during the Apollo era – mainly seismic and gravitational – suggest that the Moon is geologically stratified, with a heavy iron-rich core. Geophysicists believe that the Moon could have once generated its own magnetic field through the swirling movement of molten iron in the core. This geodynamo effect is the same mechanism behind the Earth’s magnetic field, which acts as a vital shield protecting life from lethal solar radiation.

Chris Russell on SpaceIL

Undoubtedly, however, Beresheet’s biggest legacy would always have been its status as the first private mission to land on our closest neighbour. Had it successfully landed on the Moon, the SpaceIL team would have been awarded a $1m Moonshot Award by the XPRIZE Foundation in recognition of its achievements.

“Don’t stop believing! We came close but unfortunately didn’t succeed with the landing process,” said the SpaceIL team on its Twitter account.

NASA has also issued a statement offering its congratulations for sending the first privately funded mission into lunar orbit. “Every attempt to reach new milestones holds opportunities for us to learn, adjust and progress. I have no doubt that Israel and SpaceIL will continue to explore and I look forward to celebrating their future achievements.”

Missing methane magnifies Mars mystery

A mysterious mechanism acting on, or near, the surface of Mars is removing methane from the planet’s atmosphere, according to new results from the ExoMars Trace Gas Orbiter (TGO). The joint European–Russian mission has released interim results covering the period of April to August 2018, revealing that it did not detect methane in the red planet’s atmosphere during that time.

This seems surprising, since NASA’s Curiosity rover, situated in Gale Crater, has detected a constant average background level of 0.4 ppbv (parts per billion by volume) of methane in the atmosphere for the last three Martian years, punctuated by occasional spikes in intensity of up to 7 ppbv. Furthermore, scientists had recently confirmed that the European Space Agency’s Mars Express spacecraft had observed one of the same spikes in methane levels that Curiosity measured in 2013, verifying the rover’s detection.

TGO detects atmospheric gases by watching how they absorb sunlight. “We should see a little dip [in the spectrum] where the methane absorption line is, but we see no dip whatsoever,” says Manish Patel of the Open University, UK, who is a co-principal investigator on TGO’s NOMAD spectrometer, and a co-author of the new findings. “It’s pretty obvious that there is no methane there.”

The new results set an upper limit of 0.05 ppbv of methane, which is the limit of TGO’s sensitivity. But, says Marco Giuranna of the National Institute of Astrophysics in Rome, they are not necessarily contradictory to previous findings from Curiosity and Mars Express, and nor are they unexpected. Instead, he says, they are “two parts of the same story”.

Giuranna led the Mars Express observations that confirmed the Curiosity detection of a spike in methane on 16 June 2013. However, he points out, in that study “we did not detect any other methane aside from that one single definite detection”. Indeed, on many previous occasions neither the rover nor Mars Express have detected methane; it took two years after Curiosity landed in 2012 for it to detect methane for the first time.

“The presence of methane on Mars is likely characterized by small, short emissions and transient events, rather than by large emissions and a global presence,” Giuranna told Physics World.

Methane removal

The origin of methane on Mars has remained uncertain ever since it was first observed in 2003, with both geological and biological mechanisms being considered. The new TGO results now make the fate of that methane a mystery too. After all, methane should survive in the Martian atmosphere for three centuries before solar ultraviolet light destroys it.

Methane sources and sinks on Mars — Possible sources and sinks of methane on Mars. (Courtesy: NASA/JPL/SAM-GSFC/University of Michigan)

The observation that any methane seems to vanish almost instantly means some unknown mechanism must be at work that “destroys or sequesters methane in the lowest part of the atmosphere,” says Giuranna. Theories have already been put forward to explain this process, including the possibility that methane could be attaching itself to eroded grains of quartz that blow in Mars’ winds, and absorption by regolith [dust] on the surface.

There is also the possibility of a biological solution, although Patel – who is Chair of the Astrobiology Society of Britain – is sceptical. He points out that there are organisms on Earth, called methanotrophs, that use methane to metabolize, but to account for the removal of all the methane on Mars, methanotrophic microbes would “have to be everywhere in order to get rid of it that fast”.

Atmospheric mixing

On the ground, Curiosity has been able to confirm that methane levels rise and fall with the Martian seasons, ranging from 0.24 ppbv in winter and 0.65 ppbv in Martian summer. The problem with this explanation, though, is atmospheric circulation. Even if the release of methane into the atmosphere is localized and seasonal, mixing in the atmospheric should cause the methane to be distributed globally at an abundance detectable by TGO. While a huge dust storm that engulfed Mars between June and August 2018 reduced TGO’s sensitivity to atmospheric gases, Patel points out that the observations made before the storm – in April and May 2018 – also detected no methane. This contrasts with measurements made in June 2018 by Curiosity, which according to Chris Webster of NASA’s Jet Propulsion Laboratory (JPL) detected 0.5 ppbv of methane. This is “in agreement with expectations from our seasonal cycle to date,” comments Webster.

Whatever the mechanism for removing methane might be, Patel is confident that it won’t remain a mystery for much longer. He is awaiting observations from TGO that cover an entire Martian year – 687 Earth days – and is also planning to work in concert with the Curiosity project to create a more complete picture. Patel has already been in touch with Webster’s team at JPL to discuss coordinating observations on occasions when TGO flies over Gale Crater, with the aim of replicating what Mars Express achieved with the June 2013 spike.

“We will be able to properly answer this question after a few more [Earth] years of observations,” says Patel.

The research is published in Nature.

Across the snowfields to NIST

I have to say I was a bit disappointed in Denver yesterday. I was doing a bit of sightseeing before the APS April Meeting and the museums were shutting early because there was some sort of snow cyclone on the way. Never mind that it wasn’t really snowing yet, I thought that Denver was a city that didn’t balk in the face of a blizzard.

Well it did snow as you can see from the photo of nearby Boulder this morning, but I’d call that a dusting. The good news is that it looks like my visit to NIST is going ahead this morning and I’m looking forward to recording lots of audio about everything from quantum metrology to neural networks of light.

Ionic scissors cut out phosphorene nanoribbons

Researchers have succeeded in making the first nanoribbons from phosphorene – graphene’s 2D phosphorus cousin. The materials, which can be just one atom thick and under a 100 atoms wide, and made from pure crystalline phosphorus, are theoretically predicted to have a wide range of technologically useful and even exotic properties. The high-quality ribbons produced means that these properties can now be measured and the materials tested in various real-world applications.

Phosphorene, which is also known as few-layer black phosphorus, can be obtained by mechanically cleaving black phosphorus crystals (in the same way that graphene layers are mechanically exfoliated from bulk graphite). Although bulk black phosphorus has been known about for over a century, it is only in the last decade that researchers have tried to isolate single layers of the material.

The material’s electronic, thermal and ionic transport properties come from its atomic structure, in which the phosphorus atoms are arranged in corrugated sheets with two different P-P bond lengths.

The researchers, led by Chris Howard of University College London, employed an ion scissoring technique to produce their phosphorene nanoribbons (PNRs). They say they weren’t originally trying to make ribbons but were instead trying out their own method to synthesise various 2D materials in liquids. “In this method, we first take a layered material and insert arrays of alkali metal ions between each layer, which leaves the layers negatively charged,” explains Howard. “The resulting intercalated layered material is then placed in an appropriate solvent and the negatively charged sheets dissolve to form solutions of monolayers.”

Mitch Watts, the study lead author adds: “We were applying this method to black phosphorus crystals and not having much luck. However, after trying several different modifications, we started noticing some ribbon-like fragments in our samples. It took us another three years of hard work and several more adaptations to understand what was happening and to finally be able to produce samples that contained mainly PNRs.”

“Stripes” of ions along phosphorus corrugated channels

Put simply, Howard and colleagues make their PNRs by mixing black phosphorus with lithium ions dissolved in liquid ammonia at -50°C. After 24 hours, they slowly remove the ammonia and replace it with an organic solvent to make a solution of nanoribbons with different sizes. The lithium ions diffuse incredibly fast along the corrugated channels in the black phosphorus crystals, leading to “stripes” of these ions along these channels, explains Howard. The associated high local electron doping causes bond breaking (or cutting) along the stripes and ribbon formation.

“The lithium ions also transfer charge to the ribbons so that when placed in certain solvents, the ribbons can dissolve in a way that is similar to the negatively-charged 2D materials in our previous work.”

The electronic properties of phosphorene lie in between those of the two main classes of 2D materials – that is, graphene and the transition metal dichalcogenides (TMDCs), he adds. Theory calculations predict that the properties of PNRs could surpass those of phosphorene and that their electronic structure, carrier mobilities, optical and mechanical properties can be further tuned by varying the number of layers, the width of the ribbons, edge atom arrangement, roughness of the edges and edge terminating atoms (for example, hydrogen atoms).

Real-world applications

The materials could also possess other interesting properties. These include: an extremely low diffusion barrier for Li, Na and Mg ions along their length, which means they could be useful in high-capacity fast-charging batteries; a high figure of merit for thermoelectrics; and large exciton splitting and favourable bandgap and band positions for photocatalytic water splitting.

Transistors could also benefit thanks to predictions of high charge carrier mobilities in PNRs and fast switching speeds, says Howard. Optoelectronics too, because the materials emit near-infrared light in the 0.2 to 2 eV range.

For applications, the fact that the ribbons can be processed in solution will make a big difference, he adds, since this means that they can be more easily manipulated on the large scale. And because they are flexible, they might be used to make wearable thermoelectric devices.

Exotic states

That is not all: “The materials are also predicted to host a number of exotic states that would be exciting to study as they are at the forefront of several fundamental areas of condensed matter physics,” Howard tells Physics World. “These include: a large singlet-triplet spitting, which could potentially be exploited in quantum information; the spin-dependent Seebeck effect, which could come in useful for low-power consumption technology; topologically-protected edge states; spin-density waves and strain-dependent antiferromagnetism; and half-metallicity for spintronics applications.

“Our technique is the first to produce individual, high-quality PNRs that we can now investigate collectively (for example, using magnetisation measurements) or individually (with a scanning tunnelling microscope or by making them into nanoelectronic devices) to search for these exotic states,” he says.

Phosphorene sees the light

Photo of the experimental set-up to measure phosphorene's photoresponse

The team, which includes scientists from the University of Bristol, Virginia Commonwealth University and the École Polytechnique Fédérale de Lausanne, is now busy studying the fundamental properties of the PNRs. “We are in particular following up some interesting preliminary work on their optical and electronic properties,” adds Watts. “With our internal collaborators at UCL, we are also working on applications, especially for energy conversion and storage and plan to immediately test the ribbons in some suggested devices – including batteries.”

The researchers, reporting their work in Nature, say they will also be continuing to develop their scanning probe techniques to study the surface of their ribbons.

Whole-body PET for your pet

The multi-institutional EXPLORER Consortium is building the world's first total-body PET scanner. The device, which has a sensitivity around 40 times higher than current clinical scanners, can capture a 3D image of the entire human body. And late last year, the EXPLORER PET/CT successfully produced its first human images.

Alongside, the consortium has developed two smaller-scale PET/CT scanners: the Mini-EXPLORERs. Mini-EXPLORER I is a long axial field-of-view (FOV) scanner containing detectors that are appropriate for clinical scanners. It is currently being employed to prototype total-body scanning in non-human primates.

"We wanted to build it for two main reasons -- firstly, to learn more about issues that may arise with clinical-type PET scanners built with these longer geometries, and secondly, to develop new imaging methods with animals that could be translated for use in humans," explains lead author Ramsey Badawi from UC Davis.

Mini-EXPLORER II, meanwhile, is designed to be a fully functional scanner for testing all the major components that are used in the human-scale total-body scanner. It also provides a high-resolution, high-sensitivity platform for clinical veterinary applications and human brain imaging. The team has now built a fully-functioning prototype Mini-EXPLORER II and performed the first in vivo imaging of a canine patient (Phys. Med. Biol. 10.1088/1361-6560/aafc6c).

Testing the design

Mini-EXPLORER II comprises a time-of-flight PET scanner with a ring diameter of 52 cm and an axial FOV of 48.3 cm, plus a 16-slice CT system. The PET scanner has two axial sections, each having 16 detector modules containing LYSO scintillator crystal arrays coupled to silicon photomultipliers.

Each section has a coincidence processor that receives single events from its own detector modules and can also share events with other coincidence processors -- generating both "local" and "inter-section" coincidences. This design facilitates the integration of multiple PET sections to extend the scanner's axial FOV.

"Mini-EXPLORER II uses the same PET detectors and electronics that are in the full-sized device," Badawi notes. "The full-sized device has eight rings of detector modules and we needed to test that we could get the rings to talk to each other. The Mini-II has two rings of detector modules and uses the same communications board to get the rings to talk to each other."

Badawi and colleagues performed a series of tests to assess the performance of the Mini-EXPLORER II. The prototype device exhibited an average system energy resolution of 11.7±1.5% and a timing resolution of 409±39 ps. Tests using the NEMA NU 2-2012 standard revealed a sensitivity of 52--54 kcps/MBq. The average spatial resolution at 10 mm from the centre of the FOV was 2.61 mm.

They also measured the peak noise-equivalent count rate, which was 314 kcps at 9.2 kBq/cc and 1712 kcps at 56 kBq/cc, using the NEMA NU 2-2012 and NU 4-2008 standards, respectively. The CT component of the system met all performance requirements for a diagnostic head CT imaging system.

Next, the researchers used various phantoms to evaluate image uniformity, spatial resolution and quality. Images of a long cylinder phantom that encompassed the entire axial FOV contained no significant artefacts. Scans of a mini-Derenzo hot-rod phantom clearly resolved the 2.4 mm rods, with 2.0 mm rods partially resolved. Reconstructed PET images of a Hoffman brain phantom showed the fine structures of the cerebral grooves and distinguished the white matter and ventricles.

Brain phantom images — PET and CT images of a Hoffman brain phantom. The pixel size of the PET image is 1.2 x 1.2 mm.

In vivo study

Mini-EXPLORER II is an ideal size for veterinary applications, where the animals -- typically dogs and cats -- are too large for small-animal scanners and mostly too small for optimal imaging in clinical systems. The team scanned their first patient at the UC Davis School of Veterinary Medicine: a six year-old Corgi dog that had a small peripheral nerve sheath tumour surgically excised two years previously, followed by radiation therapy. The scan was performed to help characterize mild non-painful swelling.

The first canine patient — CT (upper row) and PET (lower row) images of the first canine patient. (a) head (arrow indicates normal grey matter uptake); (b) thorax (arrow indicates normal myocardial uptake); (c) proximal pelvic limbs (arrows indicate unexpected bilateral uptake in the gracilis muscles); (d) PET/CT overlay image.

PET images of the dog, recorded in three bed positions for 12 min each, exhibited excellent overall quality. Scans at the site of previous treatment revealed contrast uptake in the antebrachial musculature. Biopsy of this site confirmed a Grade I perivascular wall tumour, thought to have been radiation induced.

Badawi says that the Mini-EXPLORER II is now in routine clinical use for veterinary medicine. It is also being employed in clinical trials to develop new approaches for treating cancer in companion animals. "Some of these trials have direct relevance for future treatments for humans, so we are excited about that prospect," he adds.

"One of the research projects that we are working on with the Mini-EXPLORER II, along with our colleagues in the School of Veterinary Medicine, is to develop methods for ultralow-activity imaging, specifically in the context of being able to track relatively small numbers of radiolabelled cells (for example stem cells) in the body," co-author Simon Cherry told Physics World.

Mapping Vienna’s hidden depths

In places beneath Vienna, the depth of sediment containing man-made material is as much as 42 m. And although Kira Lappé of the University of Vienna expected the largest amounts of man-made debris to lie underneath the middle of the city, the highest figures were at the edge, beneath landfill sites.

People in Vienna have deposited more anthropogenic material in the last century than in the whole history of Vienna, Lappé told a press conference at the European Geosciences Union (EGU) meeting in Vienna.

Lappé and colleagues examined roughly 63,000 well cores extracted to check Vienna’s geology before construction work between 1844 and today, as well as data from more than a thousand archaeological digs. Two-thirds of the well cores contained anthropogenic deposits; the depth of anthropogenic sediment ranged from 2 cm to 42 m – at the Rautenweg, a waste disposal site created in the 1960s where this figure is projected to reach 75 m.

In the centre of Vienna the anthropogenic sediment was up to 12 m thick, where the city’s fortification walls, built in the 16th century, were knocked down in the mid-19th century. Shortly after this, in 1862, geologist Eduard Sueβ was first to map anthropogenic debris beneath Vienna – he included the material from the fortifications in the second version of his map.

Outside the main entrance to the Austria Center Vienna, where the EGU meeting is taking place, the anthropogenic sediment is more than 8 m thick, whereas beneath the press centre inside the building it’s less than 1 m thick, Lappé revealed.

The scientists will also create a digital elevation model to examine changes in the surface level of the city, while artist Katrin Hornek will animate the well-core data to produce a piece that helps people imagine, feel and examine the meaning of these hidden manmade deposits.

Organic transistors reach new heights

While the looming end of Moore’s law may pose a threat to increasing computation demands, the chances of achieving transistors with high integration and performance may be looking up. A research team led by Thomas Weitz at Ludwig-Maximilians University in Munich has recently developed a vertical organic field effect transistor (VOFET) with both high current and low power applications. The device, first reported in Nature Nanotechnology, is the first organic transistor capable of driving current densities in the MA cm^-2 regime, which is critical for high performance electronics.

Towards high performance

Although organic transistors are gaining appeal due to their inherent flexibility and ease of large-scale processing, they suffer from low current densities in the range of only kA cm^-2. To overcome this limitation, the researchers implemented a technique called electrolyte gating, where a droplet of electrolyte controls the charge carrier density in the semiconducting channel by supplying ions. Electrolyte gating is particularly useful as the scale of transistors shrink, since the electrolyte enhances the capacitance, which combats certain technological limitations such as short-channel effects.

The team also demonstrated that electrolyte gating allows their device to outperform other VOFETs by reducing susceptibility to heat-induced damage. While previous VOFETs have only sustained current densities above 1 kA cm^-2 for a few milliseconds before deteriorating, the electrolyte gated device supports current densities on the order of MA cm^-2 for nearly an hour without any decline in performance.

The design Weitz’s team use offers several other key advantages over existing organic transistors. In comparison to a lateral device made from identical materials, the vertical design showed significantly better performance and attained a channel length of just 40 nm without needing to rely on high resolution fabrication techniques.

“We were very much surprised that organic materials can perform so extremely well at such nanoscopic channel lengths and withstand these enormous current densities,” says Weitz, “Up to now [this type of] continuous operation could only be realized in inorganic materials.”

Neural networks and beyond

Whereas high performance electronics demand large currents, other applications like neural networks, or computing architectures inspired by the brain, are more invested in low-power. Neural networks often rely on tunable memory elements in order to mimic the adaptable connections between neurons that enable learning. To show that their device could also be used in this application, the team reduced their operation voltage to only 10 µV, and demonstrated that the transistor acted as a type of memory component called a memristor, with a switching energy only one order of magnitude larger than that of a biological neuron. Such versatile behaviour suggests that the team’s device offers a promising platform for dense, low-power artificial synapses, potentially extending the use of organic transistors into future neural networks.

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