Tag Archives: Korea

Future cosmetics could contain fish guts

A September 6, 2024 news item on ScienceDaily features information that might be considered disconcerting,

There are some pretty strange ingredients in cosmetics and skin care products. One example is snail mucin — also known as snail slime — which is used for its moisturizing and antioxidant properties [emphasis mine]. But researchers reporting in ACS [American Chemical Society] Omega might have found something even weirder to put on your face: molecules made by fish gut bacteria. In cultured cells, the compounds had skin-brightening and anti-wrinkle properties, making them potential ingredients for your future skin care routine.

Snail slime? Well, if you’re going to use snail slime, then why not use fish guts? This September 5, 2024 ACS (American Chemical Society) news release (also on EurekAlert), which originated the news item, explains the reasoning behind using fish guts in cosmetics and provides a few technical details, Note: A link has been removed,

Though fish guts might seem like the absolute last place to look for cosmetic compounds, it’s not a completely far-fetched idea. Many important drugs have been found in bizarre places — famously, penicillin’s antibiotic properties were discovered after a failed experiment got moldy. More recently, the brain cancer drug candidate Marizomib was derived from microbes unearthed in marine sediments at the bottom of the ocean. Two potentially untapped sources of new compounds could be the gut microbes of the red seabream and the blackhead seabream, fish found in the western Pacific Ocean. Although these microbes were first identified in 1992 and 2016, respectively, no studies have been performed on the compounds they make. So, Hyo-Jong Lee and Chung Sub Kim wanted to see if these bacteria produce any metabolite compounds that could have cosmetic benefits.

The team identified 22 molecules made by the gut bacteria of the red seabream and blackhead seabream. They then evaluated each compound’s ability to inhibit tyrosinase and collagenase enzymes in lab-grown mouse cells. (Tyrosinase is involved in melanin production, which causes hyperpigmentation in aging skin. Collagenase breaks down the structural protein collagen, causing wrinkles.) Three molecules from the red seabream bacteria inhibited both enzymes the best without damaging the cells, making them promising anti-wrinkle and skin-brightening agents for future cosmetic products.

The authors acknowledge funding from the Marine Biotechnology Program of the Ministry of Oceans and Fisheries, the National Research Foundation of Korea, the Technology Development Program of the Ministry of Small and Medium Enterprises and Startups, Sungkyunkwan University and the BK21 FOUR program of the Ministry of Education of Korea.

Here’s a link to and a citation for the paper,

Collagenase and Tyrosinase Inhibitory Compounds from Fish Gut Bacteria Ruegeria atlantica and Pseudoalteromonas neustonica by Jonghwan Kim, Su Jung Hwang, Gyu Sung Lee, Ju Ryeong Lee, Hye In An, Hong Sik Im, Minji Kim, Sang-Seob Lee, Hyo Jong Lee and Chung Sub Kim. ACS Omega Vol 9/Issue 32 34259 DOI: 10.1021/acsomega.3c09585 Published: July 29, 2024 Copyright © 2024 The Authors. Published by American Chemical Society.

This paper is open access. This publication is licensed under CC-BY-NC-ND 4.0 .

Dual functions—neuromorphic (brainlike) and security—with papertronic devices

Michael Berger’s June 27, 2024 Nanowerk Spotlight article describes some of the latest work on developing electronic paper devices (yes, paper), Note 1: Links have been removed, Note 2: If you do check out Berger’s article, you will need to click a box confirming you are human,+

Paper-based electronic devices have long been an intriguing prospect for researchers, offering potential advantages in sustainability, cost-effectiveness, and flexibility. However, translating the unique properties of paper into functional electronic components has presented significant challenges. Traditional semiconductor manufacturing processes are incompatible with paper’s thermal sensitivity and porous structure. Previous attempts to create paper-based electronics often resulted in devices with limited functionality or poor durability.

Recent advances in materials science and nanofabrication techniques have opened new avenues for realizing sophisticated electronic devices on paper substrates. Researchers have made progress in developing conductive inks, flexible electrodes, and solution-processable semiconductors that can be applied to paper without compromising its inherent properties. These developments have paved the way for creating paper-based sensors, energy storage devices, and simple circuits.

Despite these advancements, achieving complex electronic functionalities on paper, particularly in areas like neuromorphic computing and security applications, has remained elusive. Neuromorphic devices, which mimic the behavior of biological synapses, typically require precise control of charge transport and storage mechanisms.

Similarly, physically unclonable functions (PUFs) used in security applications depend on the ability to generate random, unique patterns at the nanoscale level. Implementing these sophisticated functionalities on paper substrates has been a persistent challenge due to the material’s inherent variability and limited compatibility with advanced fabrication techniques.

A research team in Korea has now made significant strides in addressing these challenges, developing a versatile paper-based electronic device that demonstrates both neuromorphic and security capabilities. Their work, published in Advanced Materials (“Versatile Papertronics: Photo-Induced Synapse and Security Applications on Papers”), describes a novel approach to creating multifunctional “papertronics” using a combination of solution-processable materials and innovative device architectures.

The team showcased the potential of their device by simulating a facial recognition task. Using a simple neural network architecture and the light-responsive properties of their paper-based device, they achieved a recognition accuracy of 91.7% on a standard face database. This impressive performance was achieved with a remarkably low voltage bias of -0.01 V, demonstrating the energy efficiency of the approach. The ability to operate at such low voltages is particularly advantageous for portable and low-power applications.

In addition to its neuromorphic capabilities, the device also showed promise as a physically unclonable function (PUF) for security applications. The researchers leveraged the inherent randomness in the deposition of SnO2 nanoparticles [tin oxide nanoparticles] to create unique electrical characteristics in each device. By fabricating arrays of these devices on paper, they generated security keys that exhibited high levels of randomness and uniqueness.

One of the most intriguing aspects of this research is the dual functionality achieved with a single device structure. The ability to serve as both a neuromorphic component and a security element could lead to the development of highly integrated, secure edge computing devices on paper substrates. This convergence of functionalities addresses growing concerns about data privacy and security in Internet of Things (IoT) applications.

Berger’s June 27, 2024 Nanowerk Spotlight article offers more detail about the work and it’s written in an accessible fashion. Berger also notes at the end, that there are still a lot of challenges before this work leaves the laboratory.

Here’s a link to and a citation for the paper,

Versatile Papertronics: Photo-Induced Synapse and Security Applications on Papers by Wangmyung Choi, Jihyun Shin, Yeong Jae Kim, Jaehyun Hur, Byung Chul Jang, Hocheon Yoo. Advanced Materials DOI: https://doi.org/10.1002/adma.202312831 First published: 13 June 2024

This paper is behind a paywall.

Reversible assembly of platinum catalyst

A June 3, 2024 news item on phys.org announces research into making platinum catalysts reusable, Note: Links have been removed,

Chemists at the U.S. Department of Energy’s (DOE) Brookhaven National Laboratory, Stony Brook University (SBU), and their collaborators have uncovered new details of the reversible assembly and disassembly of a platinum catalyst. The new understanding may offer clues to the catalyst’s stability and recyclability.

The work, described in a paper just published in the journal Nanoscale, reveals how single platinum atoms on a cerium oxide support aggregate under reaction conditions to form active catalytic nanoparticles—and then, surprisingly, fragment once the reaction is stopped.

Fragmentation may sound shattering, but the scientists say it could be a plus.

A June 3, 2023 Brookhaven National Laboratory (BNL) news release (also on EurekAlert), which originated the news item, provides more detail, Note: Links have been removed,

“Such reversible fragmentation of a platinum nanocatalyst on cerium oxide could be potentially useful for controlling the catalyst’s long-term stability,” said Anatoly Frenkel, a chemist at Brookhaven Lab and professor at SBU who led the research.

When the platinum atoms return to their starting positions, they can be used again to remake active catalytic particles. Plus, the post-reaction fragmentation makes those active particles much less likely to fuse together irreversibly, which is a common mechanism that ultimately deactivates many nanoparticle catalysts.

“Part of the definition of a catalyst is that it helps disassemble and reassemble reacting molecules to form new products,” Frenkel noted. “But it was shocking to see a catalyst that also assembles and disassembles itself in the process.”

Assembly/disassembly

The paper describes how the scientists observed the nanoparticles forming as single platinum atoms aggregated on the cerium oxide surface at 572 degrees Fahrenheit (300 degrees Celsius) — the temperature of the reaction they were studying.

“After the reaction, we expected that these nanoparticles would stabilize once back at room temperature in whatever particle size they reached when they were activated,” Frenkel said. “But what we observed was a reverse process. The particles began fragmenting into single atoms again.”

The team had a hypothesis to explain what they were seeing, which was confirmed by thermodynamic calculations performed by theory colleagues at Chungnam National University in Korea. Carbon monoxide, one of the products of the reaction — often considered a “poison” for catalysts — was actively tearing the nanoparticles apart.

“Carbon monoxide molecules have a very strong repulsive interaction when they are next to each other,” Frenkel explained. During the “reverse water gas shift” reaction, which converts carbon dioxide (CO2) and hydrogen (H2) into carbon monoxide (CO) and water (H2O) at high temperatures, the CO typically leaves the catalyst surface as a gas. But once the heat is turned off, the CO molecules bind strongly to the platinum atoms of the catalyst. This brings the CO molecules closer to each other as the system cools down and their numbers rise.

That is a perfect storm,” said Frenkel.

“When the CO molecules find themselves very close together on the surface of the nanoparticles, they repel. And, when they repel, because they are strongly bound to the platinum atoms, they sort of pull the least-tightly bound platinum atoms from the perimeter of the nanoparticle and drag them onto cerium oxide support,” Frenkel said.

Multimodal imaging

The scientists used a combination of atomic-level spectroscopic and imaging techniques to make these observations.

One technique used bright X-rays at the Quick x-ray Absorption and Scattering beamline of the National Synchrotron Light Source-II (NSLS-II) to produce a spectrum of the energy absorbed by the atoms that make up the catalyst. The scientists used this technique to study the catalyst at different temperatures and stages of the reaction. These X-ray absorption spectra are strongly influenced by the electronic states of the atoms and can be used to decipher which atoms are nearby.

“This technique can tell us that the platinum atoms have oxygen neighbors from the cerium oxide particles of the catalyst support, carbon monoxide neighbors from the reaction products, or other metal neighbors — more platinum atoms,” Frenkel said. But it “lumps together information from many platinum atoms and only gives average information,” he noted.

“It can’t tell us whether all platinum atoms have the same environment or whether we have different groups of atoms — some dispersed on the support and some within the nanoparticles. We needed additional tools to unravel the possibilities,” he said.

Infrared spectroscopy, performed in Frenkel’s Structure and Dynamics of Applied Nanomaterials (SDAN) laboratory in the Brookhaven Lab Chemistry Division, revealed the presence of two distinct groups —single atoms with no metal neighbors and nanoparticles made only of platinum. The scientists used the technique to track the relative abundance of each group as the reaction progressed.  

“This technique tells us how molecules such as CO interact with our platinum atoms. Do they show features of single atoms only or nanoparticles only or both?” Frenkel said. “During the cooling down after the reaction, we observed that CO was interacting with single atoms again.”

Electron microscopy, performed by Lihua Zhang of Brookhaven’s Center for Functional Nanomaterials (CFN), produced nanoscale images of both species — single atoms and nanoparticles. These images show that, at room temperature before the catalyst is activated, there are no nanoparticles, and after the reaction, “we saw both nanoparticles and single atoms,” Frenkel said.

“These techniques together tell us that, once the reaction stops and the temperature drops, the nanoparticles have started to fragment into single atoms,” Frenkel said. “Each measurement independently would not have given us enough data to understand what we are dealing with. We couldn’t have done this work without our collaborators at NSLS-II and CFN and without the capabilities at these DOE Office of Science user facilities.”

Change and disorder

Understanding these differences at stages of the reaction is critical to understanding how the catalyst works, Frenkel said.

“In our experiment, we deliberately went from one extreme to the other. We went from only single atoms to only nanoparticles. In the process, we had them coexist at different fractions so we could systematically investigate how the catalytic activity changes, how the structure changes,” he said.

Frenkel noted that the nanoparticles don’t assemble perfectly. They have more defects — irregular atomic sites — compared to nanoparticles synthesized by commonly used methods. These defects could turn out to be another feature that improves catalytic performance. That’s because disorder, or strain, can contribute to the alignment of the electronic levels of chemical reactants and metal atoms in the catalyst so they can interact more easily, he explained.

“People try to design catalysts with these types of imperfections deliberately; our method incorporates strain naturally,” he said.

In addition, due to these relatively disordered structures, nanoparticles assembled from single atoms might not be as tightly bound as a perfect array of atoms would be. That could make it easier for them to disassemble for reuse when the reaction turns off.

This work was funded by the DOE Office of Science and by the National Research Foundation of Korea. In addition to making use of capabilities at NSLS-II and CFN, the scientists used computing resources at the Scientific Data and Computing Center, a component of the Computational Science Initiative at Brookhaven Lab.

Brookhaven National Laboratory is supported by the Office of Science of the U.S. Department of Energy. The Office of Science is the single largest supporter of basic research in the physical sciences in the United States and is working to address some of the most pressing challenges of our time. For more information, visit science.energy.gov.

.Here’s a link to and a citation for the paper,

Unravelling the origin of reaction-driven aggregation and fragmentation of atomically dispersed Pt catalyst on ceria support by Haodong Wang, Hyuk Choi, Ryuichi Shimogawa, Yuanyuan Li, Lihua Zhang, Hyun You Kim and Anatoly I. Frenkel. Nanoscale, 2024, DOI: https://doi.org/10.1039/D4NR01396D Advance Article First published: 15 May 2024

This paper is behind a paywall.

Desalination and toxic brine

Have you ever wondered about the possible effects and impact of desalinating large amounts of ocean water? It seems that some United Nations University (UNU) researchers have asked and are beginning to answer that question. The following table illustrates the rise in desalination plants and processes,


Today 15,906 operational desalination plants are found in 177 countries. Almost half of the global desalination capacity is located in the Middle East and North Africa region (48 percent), with Saudi Arabia (15.5 percent), the United Arab Emirates (10.1 percent) and Kuwait (3.7 percent) being both the major producers in the region and globally. Credit: UNU-INWEH [downloaded from http://inweh.unu.edu/un-warns-of-rising-levels-of-toxic-brine-as-desalination-plants-meet-growing-water-needs/]

A January 14, 2019 news item on phys.org highlights the study on desalination from the UNU,

The fast-rising number of desalination plants worldwide—now almost 16,000, with capacity concentrated in the Middle East and North Africa—quench a growing thirst for freshwater but create a salty dilemma as well: how to deal with all the chemical-laden leftover brine.

In a UN-backed paper, experts estimate the freshwater output capacity of desalination plants at 95 million cubic meters per day—equal to almost half the average flow over Niagara Falls.
For every litre of freshwater output, however, desalination plants produce on average 1.5 litres of brine (though values vary dramatically, depending on the feedwater salinity and desalination technology used, and local conditions). Globally, plants now discharge 142 million cubic meters of hypersaline brine every day (a 50% increase on previous assessments).

That’s enough in a year (51.8 billion cubic meters) to cover Florida under 30.5 cm (1 foot) of brine.

The authors, from UN University’s Canadian-based Institute for Water, Environment and Health [at McMaster University], Wageningen University, The Netherlands, and the Gwangju Institute of Science and Technology, Republic of Korea, analyzed a newly-updated dataset—the most complete ever compiled—to revise the world’s badly outdated statistics on desalination plants.

And they call for improved brine management strategies to meet a fast-growing challenge, noting predictions of a dramatic rise in the number of desalination plants, and hence the volume of brine produced, worldwide.

A January 14, 2017 UNU press release, which originated the news item, details the findings,

The paper found that 55% of global brine is produced in just four countries: Saudi Arabia (22%), UAE (20.2%), Kuwait (6.6%) and Qatar (5.8%). Middle Eastern plants, which largely operate using seawater and thermal desalination technologies, typically produce four times as much brine per cubic meter of clean water as plants where river water membrane processes dominate, such as in the US.

The paper says brine disposal methods are largely dictated by geography but traditionally include direct discharge into oceans, surface water or sewers, deep well injection and brine evaporation ponds.

Desalination plants near the ocean (almost 80% of brine is produced within 10km of a coastline) most often discharge untreated waste brine directly back into the marine environment.

The authors cite major risks to ocean life and marine ecosystems posed by brine greatly raising the salinity of the receiving seawater, and by polluting the oceans with toxic chemicals used as anti-scalants and anti-foulants in the desalination process (copper and chlorine are of major concern).

“Brine underflows deplete dissolved oxygen in the receiving waters,” says lead author Edward Jones, who worked at UNU-INWEH, and is now at Wageningen University, The Netherlands. “High salinity and reduced dissolved oxygen levels can have profound impacts on benthic organisms, which can translate into ecological effects observable throughout the food chain.”

Meanwhile, the paper highlights economic opportunities to use brine in aquaculture, to irrigate salt tolerant species, to generate electricity, and by recovering the salt and metals contained in brine — including magnesium, gypsum, sodium chloride, calcium, potassium, chlorine, bromine and lithium.

With better technology, a large number of metals and salts in desalination plant effluent could be mined. These include sodium, magnesium, calcium, potassium, bromine, boron, strontium, lithium, rubidium and uranium, all used by industry, in products, and in agriculture. The needed technologies are immature, however; recovery of these resources is economically uncompetitive today.

“There is a need to translate such research and convert an environmental problem into an economic opportunity,” says author Dr. Manzoor Qadir, Assistant Director of UNU-INWEH. “This is particularly important in countries producing large volumes of brine with relatively low efficiencies, such as Saudi Arabia, UAE, Kuwait and Qatar.”

“Using saline drainage water offers potential commercial, social and environmental gains. Reject brine has been used for aquaculture, with increases in fish biomass of 300% achieved. It has also been successfully used to cultivate the dietary supplement Spirulina, and to irrigate forage shrubs and crops (although this latter use can cause progressive land salinization).”

“Around 1.5 to 2 billion people currently live in areas of physical water scarcity, where water resources are insufficient to meet water demands, at least during part of the year. Around half a billion people experience water scarcity year round,” says Dr. Vladimir Smakhtin, a co-author of the paper and the Director of UNU-INWEH, whose institute is actively pursuing research related to a variety of unconventional water sources.

“There is an urgent need to make desalination technologies more affordable and extend them to low-income and lower-middle income countries. At the same time, though, we have to address potentially severe downsides of desalination — the harm of brine and chemical pollution to the marine environment and human health.”

“The good news is that efforts have been made in recent years and, with continuing technology refinement and improving economic affordability, we see a positive and promising outlook.”

¹The authors use the term “brine” to refer to all concentrate discharged from desalination plants, as the vast majority of concentrate (>95%) originates from seawater and highly brackish groundwater sources.

Here’s a link to and a citation for the paper,

The state of desalination and brine production: A global outlook by Edward Jones, Manzoor Qadir, Michelle T.H.van Vliet, Vladimir Smakhtin, Seong-mu Kang. Science of The Total Environment Volume 657, 20 March 2019, Pages 1343-1356 DOI: https://doi.org/10.1016/j.scitotenv.2018.12.076 Available online 7 December 2018

Surprisingly (to me anyway), this paper is behind a paywall.

World’s smallest magnetic resonance imaging (MRI) of a single atom

While not science’s sleekest machine, this microscope was able to capture M.R.I. scans of single atoms. Credit: IBM Research

Such a messy looking thing—it makes me feel better about my housekeeping. In any event, it’s fascinating to think this scanning tunneling microscope as seen in the above can actually act as an MRI device and create an image of a single atom.

There’s a wonderful article in the New York Times about the work but I’m starting first with a July 1, 2019 news item on Nanowerk,

Researchers at the Center for Quantum Nanoscience (QNS) within the Institute for Basic Science (IBS) at Ewha Womans University [Seoul, South Korea) have made a major scientific breakthrough by performing the world’s smallest magnetic resonance imaging (MRI). In an international collaboration with colleagues from the US, QNS scientists used their new technique to visualize the magnetic field of single atoms.

A July 2, 2019 IBS news release (also on EurekAlert but published July 1, 2019), which originated the news item, provides some insight into the research,

An MRI is routinely done in hospitals nowadays as a part of imaging for diagnostics. MRI’s detect the density of spins – the fundamental magnets in electrons and protons – in the human body. Traditionally, billions and billions of spins are required for an MRI scan. The new findings, published today [July 1, 2019] in the journal Nature Physics, show that this process is now also possible for an individual atom on a surface. To do this, the team used a Scanning Tunneling Microscope, which consists of an atomically sharp metal tip that allows researchers to image and probe single atoms by scanning the tip across the surface.

The two elements that were investigated in this work, iron and titanium, are both magnetic. Through precise preparation of the sample, the atoms were readily visible in the microscope. The researchers then used the microscope’s tip like an MRI machine to map the three-dimensional magnetic field created by the atoms with unprecedented resolution. In order to do so, they attached another spin cluster to the sharp metal tip of their microscope. Similar to everyday magnets, the two spins would attract or repel each other depending on their relative position. By sweeping the tip spin cluster over the atom on the surface, the researchers were able to map out the magnetic interaction. Lead author, Dr. Philip Willke of QNS says: “It turns out that the magnetic interaction we measured depends on the properties of both spins, the one on the tip and the one on the sample. For example, the signal that we see for iron atoms is vastly different from that for titanium atoms. This allows us to distinguish different kinds of atoms by their magnetic field signature and makes our technique very powerful.”

The researchers plan to use their single-atom MRI to map the spin distribution in more complex structures such as molecules and magnetic materials. “Many magnetic phenomena take place on the nanoscale, including the recent generation of magnetic storage devices.” says Dr. Yujeong Bae also of QNS, a co-author in this study. “We now plan to study a variety of systems using our microscopic MRI.” The ability to analyze the magnetic structure on the nanoscale can help to develop new materials and drugs. Moreover, the research team wants to use this kind of MRI to characterize and control quantum systems. These are of great interest for future computation schemes, also known as quantum computing

“I am very excited about these results. It is certainly a milestone in our field and has very promising implications for future research.” says Prof. Andreas Heinrich, Director of QNS. “The ability to map spins and their magnetic field with previously unimaginable precision, allows us to gain deeper knowledge about the structure of matter and opens new fields of basic research.”

The Center for Quantum Nanoscience, on the campus of Ewha Womans University in Seoul, South Korea, is a world-leading research center merging quantum and nanoscience to engineer the quantum future through basic research. Backed by Korea’s Institute for Basic Science, which was founded in 2011, the Center for Quantum Nanoscience draws on decades of QNS Director Andreas J. Heinrich’s (A Boy and His Atom, IBM, 2013) scientific leadership to lay the foundation for future technology by exploring the use of quantum behavior atom-by-atom on surfaces with highest precision.

You may have noticed that other than a brief mention in the first paragraph (in the Nanowerk news item excerpt), there’s no mention of the US researchers and their contribution to the work.

Interestingly, the July 1, 2019 New York Time article by Knvul Sheikh returns the favour by focusing almost entirely on US researchers while giving the Korean researchers a passing mention (Note: Links have been removed),

Different microscopy techniques allow scientists to see the nucleotide-by-nucleotide genetic sequences in cells down to the resolution of a couple atoms as seen in an atomic force microscopy image. But scientists at the IBM Almaden Research Center in San Jose, Calif., and the Institute for Basic Sciences in Seoul, have taken imaging a step further, developing a new magnetic resonance imaging technique that provides unprecedented detail, right down to the individual atoms of a sample.

When doctors want to detect tumors, measure brain function or visualize the structure of joints, they employ huge M.R.I. machines, which apply a magnetic field across the human body. This temporarily disrupts the protons spinning in the nucleus of every atom in every cell. A subsequent, brief pulse of radio-frequency energy causes the protons to spin perpendicular to the pulse. Afterward, the protons return to their normal state, releasing energy that can be measured by sensors and made into an image.

But to gather enough diagnostic data, traditional hospital M.R.I.s must scan billions and billions of protons in a person’s body, said Christopher Lutz, a physicist at IBM. So he and his colleagues decided to pack the power of an M.R.I. machine into the tip of another specialized instrument known as a scanning tunneling microscope to see if they could image individual atoms.

The tip of a scanning tunneling microscope is just a few atoms wide. And it moves along the surface of a sample, it picks up details about the size and conformation of molecules.

The researchers attached magnetized iron atoms to the tip, effectively combining scanning-tunneling microscope and M.R.I. technologies.

When the magnetized tip swept over a metal wafer of iron and titanium, it applied a magnetic field to the sample, disrupting the electrons (rather than the protons, as a typical M.R.I. would) within each atom. Then the researchers quickly turned a radio-frequency pulse on and off, so that the electrons would emit energy that could be visualized. …

Here’s a link to and a citation for the paper,

Magnetic resonance imaging of single atoms on a surface by Philip Willke, Kai Yang, Yujeong Bae, Andreas J. Heinrich & Christopher P. Lutz. Nature Physics (2019) DOI: https://doi.org/10.1038/s41567-019-0573-x Published 01 July 2019

This paper is behind a paywall.

An artificial synapse tuned by light, a ferromagnetic memristor, and a transparent, flexible artificial synapse

Down the memristor rabbit hole one more time.* I started out with news about two new papers and inadvertently found two more. In a bid to keep this posting to a manageable size, I’m stopping at four.

UK

In a June 19, 2019 Nanowerk Spotlight article, Dr. Neil Kemp discusses memristors and some of his latest work (Note: A link has been removed),

Memristor (or memory resistors) devices are non-volatile electronic memory devices that were first theorized by Leon Chua in the 1970’s. However, it was some thirty years later that the first practical device was fabricated. This was in 2008 when a group led by Stanley Williams at HP Research Labs realized that switching of the resistance between a conducting and less conducting state in metal-oxide thin-film devices was showing Leon Chua’s memristor behaviour.

The high interest in memristor devices also stems from the fact that these devices emulate the memory and learning properties of biological synapses. i.e. the electrical resistance value of the device is dependent on the history of the current flowing through it.

There is a huge effort underway to use memristor devices in neuromorphic computing applications and it is now reasonable to imagine the development of a new generation of artificial intelligent devices with very low power consumption (non-volatile), ultra-fast performance and high-density integration.

These discoveries come at an important juncture in microelectronics, since there is increasing disparity between computational needs of Big Data, Artificial Intelligence (A.I.) and the Internet of Things (IoT), and the capabilities of existing computers. The increases in speed, efficiency and performance of computer technology cannot continue in the same manner as it has done since the 1960s.

To date, most memristor research has focussed on the electronic switching properties of the device. However, for many applications it is useful to have an additional handle (or degree of freedom) on the device to control its resistive state. For example memory and processing in the brain also involves numerous chemical and bio-chemical reactions that control the brain structure and its evolution through development.

To emulate this in a simple solid-state system composed of just switches alone is not possible. In our research, we are interested in using light to mediate this essential control.

We have demonstrated that light can be used to make short and long-term memory and we have shown how light can modulate a special type of learning, called spike timing dependent plasticity (STDP). STDP involves two neuronal spikes incident across a synapse at the same time. Depending on the relative timing of the spikes and their overlap across the synaptic cleft, the connection strength is other strengthened or weakened.

In our earlier work, we were only able to achieve to small switching effects in memristors using light. In our latest work (Advanced Electronic Materials, “Percolation Threshold Enables Optical Resistive-Memory Switching and Light-Tuneable Synaptic Learning in Segregated Nanocomposites”), we take advantage of a percolating-like nanoparticle morphology to vastly increase the magnitude of the switching between electronic resistance states when light is incident on the device.

We have used an inhomogeneous percolating network consisting of metallic nanoparticles distributed in filamentary-like conduction paths. Electronic conduction and the resistance of the device is very sensitive to any disruption of the conduction path(s).

By embedding the nanoparticles in a polymer that can expand or contract with light the conduction pathways are broken or re-connected causing very large changes in the electrical resistance and memristance of the device.

Our devices could lead to the development of new memristor-based artificial intelligence systems that are adaptive and reconfigurable using a combination of optical and electronic signalling. Furthermore, they have the potential for the development of very fast optical cameras for artificial intelligence recognition systems.

Our work provides a nice proof-of-concept but the materials used means the optical switching is slow. The materials are also not well suited to industry fabrication. In our on-going work we are addressing these switching speed issues whilst also focussing on industry compatible materials.

Currently we are working on a new type of optical memristor device that should give us orders of magnitude improvement in the optical switching speeds whilst also retaining a large difference between the resistance on and off states. We hope to be able to achieve nanosecond switching speeds. The materials used are also compatible with industry standard methods of fabrication.

The new devices should also have applications in optical communications, interfacing and photonic computing. We are currently looking for commercial investors to help fund the research on these devices so that we can bring the device specifications to a level of commercial interest.

If you’re interested in memristors, Kemp’s article is well written and quite informative for nonexperts, assuming of course you can tolerate not understanding everything perfectly.

Here are links and citations for two papers. The first is the latest referred to in the article, a May 2019 paper and the second is a paper appearing in July 2019.

Percolation Threshold Enables Optical Resistive‐Memory Switching and Light‐Tuneable Synaptic Learning in Segregated Nanocomposites by Ayoub H. Jaafar, Mary O’Neill, Stephen M. Kelly, Emanuele Verrelli, Neil T. Kemp. Advanced Electronic Materials DOI: https://doi.org/10.1002/aelm.201900197 First published: 28 May 2019

Wavelength dependent light tunable resistive switching graphene oxide nonvolatile memory devices by Ayoub H.Jaafar, N.T.Kemp. DOI: https://doi.org/10.1016/j.carbon.2019.07.007 Carbon Available online 3 July 2019

The first paper (May 2019) is definitely behind a paywall and the second paper (July 2019) appears to be behind a paywall.

Dr. Kemp’s work has been featured here previously in a January 3, 2018 posting in the subsection titled, Shining a light on the memristor.

China

This work from China was announced in a June 20, 2019 news item on Nanowerk,

Memristors, demonstrated by solid-state devices with continuously tunable resistance, have emerged as a new paradigm for self-adaptive networks that require synapse-like functions. Spin-based memristors offer advantages over other types of memristors because of their significant endurance and high energy effciency.

However, it remains a challenge to build dense and functional spintronic memristors with structures and materials that are compatible with existing ferromagnetic devices. Ta/CoFeB/MgO heterostructures are commonly used in interfacial PMA-based [perpendicular magnetic anisotropy] magnetic tunnel junctions, which exhibit large tunnel magnetoresistance and are implemented in commercial MRAM [magnetic random access memory] products.

“To achieve the memristive function, DW is driven back and forth in a continuous manner in the CoFeB layer by applying in-plane positive or negative current pulses along the Ta layer, utilizing SOT that the current exerts on the CoFeB magnetization,” said Shuai Zhang, a coauthor in the paper. “Slowly propagating domain wall generates a creep in the detection area of the device, which yields a broad range of intermediate resistive states in the AHE [anomalous Hall effect] measurements. Consequently, AHE resistance is modulated in an analog manner, being controlled by the pulsed current characteristics including amplitude, duration, and repetition number.”

“For a follow-up study, we are working on more neuromorphic operations, such as spike-timing-dependent plasticity and paired pulsed facilitation,” concludes You. …

Here’s are links to and citations for the paper (Note: It’s a little confusing but I believe that one of the links will take you to the online version, as for the ‘open access’ link, keep reading),

A Spin–Orbit‐Torque Memristive Device by Shuai Zhang, Shijiang Luo, Nuo Xu, Qiming Zou, Min Song, Jijun Yun, Qiang Luo, Zhe Guo, Ruofan Li, Weicheng Tian, Xin Li, Hengan Zhou, Huiming Chen, Yue Zhang, Xiaofei Yang, Wanjun Jiang, Ka Shen, Jeongmin Hong, Zhe Yuan, Li Xi, Ke Xia, Sayeef Salahuddin, Bernard Dieny, Long You. Advanced Electronic Materials Volume 5, Issue 4 April 2019 (print version) 1800782 DOI: https://doi.org/10.1002/aelm.201800782 First published [online]: 30 January 2019 Note: there is another DOI, https://doi.org/10.1002/aelm.201970022 where you can have open access to Memristors: A Spin–Orbit‐Torque Memristive Device (Adv. Electron. Mater. 4/2019)

The paper published online in January 2019 is behind a paywall and the paper (almost the same title) published in April 2019 has a new DOI and is open access. Final note: I tried accessing the ‘free’ paper and opened up a free file for the artwork featuring the work from China on the back cover of the April 2019 of Advanced Electronic Materials.

Korea

Usually when I see the words transparency and flexibility, I expect to see graphene is one of the materials. That’s not the case for this paper (link to and citation for),

Transparent and flexible photonic artificial synapse with piezo-phototronic modulator: Versatile memory capability and higher order learning algorithm by Mohit Kumar, Joondong Kim, Ching-Ping Wong. Nano Energy Volume 63, September 2019, 103843 DOI: https://doi.org/10.1016/j.nanoen.2019.06.039 Available online 22 June 2019

Here’s the abstract for the paper where you’ll see that the material is made up of zinc oxide silver nanowires,

An artificial photonic synapse having tunable manifold synaptic response can be an essential step forward for the advancement of novel neuromorphic computing. In this work, we reported the development of highly transparent and flexible two-terminal ZnO/Ag-nanowires/PET photonic artificial synapse [emphasis mine]. The device shows purely photo-triggered all essential synaptic functions such as transition from short-to long-term plasticity, paired-pulse facilitation, and spike-timing-dependent plasticity, including in the versatile memory capability. Importantly, strain-induced piezo-phototronic effect within ZnO provides an additional degree of regulation to modulate all of the synaptic functions in multi-levels. The observed effect is quantitatively explained as a dynamic of photo-induced electron-hole trapping/detraining via the defect states such as oxygen vacancies. We revealed that the synaptic functions can be consolidated and converted by applied strain, which is not previously applied any of the reported synaptic devices. This study will open a new avenue to the scientific community to control and design highly transparent wearable neuromorphic computing.

This paper is behind a paywall.

I am a sound speaker/loudspeaker (well, maybe one day)

Caption: From left are Saewon Kang, Professor Hyunhyub Ko, and Seungse Cho in the School of Energy and Chemical Engineering at UNIST. Credit: UNIST

What are these scientists so happy about? A September 18, 2018 news item on ScienceDaily reveals all,

An international team of researchers, affiliated with UNIST [Ulsan National Institute of Science and Technology] has presented an innovative wearable technology that will turn your skin into a loudspeaker.

An August 6, 2018 UNIST press release (also on EurekAlert but published September 17,2018), which originated the news item, delves further into the research,

This breakthrough has been led by Professor Hyunhyub Ko in the School of Energy and Chemical Engineering at UNIST. Created in part to help the hearing and speech impaired, the new technology can be further explored for various potential applications, such as wearable IoT sensors and conformal health care devices.

In the study, the research team has developed ultrathin, transparent, and conductive hybrid nanomembranes with nanoscale thickness, consisting of an orthogonal silver nanowire array embedded in a polymer matrix. They, then, demonstrated their nanomembrane by making it into a loudspeaker that can be attached to almost anything to produce sounds. The researchers also introduced a similar device, acting as a microphone, which can be connected to smartphones and computers to unlock voice-activated security systems.

Nanomembranes (NMs) are molcularly thin seperation layers with nanoscale thickness. Polymer NMs have attracted considerable attention owing to their outstanding advantages, such as extreme flexibility, ultralight weight, and excellent adhesibility in that they can be attached directly to almost any surface. However, they tear easily and exhibit no electrical conductivity.

The research team has solved such issues by embedding a silver nanowire network within a polymer-based nanomembrane. This has enabled the demonstration of skin-attachable and imperceptible loudspeaker and microphone.

“Our ultrathin, transparent, and conductive hybrid NMs facilitate conformal contact with curvilinear and dynamic surfaces without any cracking or rupture,” says  Saewon Kang in the doctroral program of Energy and Chemical Engineering at UNIST, the first author of the study.

He adds, “These layers are capable of detecting sounds and vocal vibrations produced by the triboelectric voltage signals corresponding to sounds, which could be further explored for various potential applications, such as sound input/output devices.”

Using the hybrid NMs, the research team fabricated skin-attachable NM loudspeakers and microphones, which would be unobtrusive in appearance because of their excellent transparency and conformal contact capability. These wearable speakers and microphones are paper-thin, yet still capable of conducting sound signals.

“The biggest breakthrough of our research is the development of ultrathin, transparent, and conductive hybrid nanomembranes with nanoscale thickness, less than 100 nanometers,” says Professor Ko. “These outstanding optical, electrical, and mechanical properties of nanomembranes enable the demonstration of skin-attachable and imperceptible loudspeaker and microphone.”The skin-attachable NM loudspeakers work by emitting thermoacoustic sound by the temperature-induced oscillation of the surrounding air. The periodic Joule heating that occurs when an electric current passes through a conductor and produces heat leads to these temperature oscillations. It has attracted considerable attention for being a stretchable, transparent, and skin-attachable loudspeaker.

Wearable microphones are sensors, attached to a speaker’s neck to even sense the vibration of the vocal folds. This sensor operates by converting the frictional force generated by the oscillation of the transparent conductive nanofiber into electric energy. For the operation of the microphone, the hybrid nanomembrane is inserted between elastic films with tiny patterns to precisely detect the sound and the vibration of the vocal cords based on a triboelectric voltage that results from the contact with the elastic films.

“For the commercial applications, the mechanical durability of nanomebranes and the performance of loudspeaker and microphone should be improved further,” says Professor Ko.

Thankfully, the researchers have made video that lets us hear this sound speaker,


Paper-thin stick-on speakers, developed by Professor Hyunhyub Ko and his research team at UNIST.

Thank you to the folks at UNIST for including something with the sound. Strangely, it’s not common practice to include audio when publishing research on sound, not in my experience anyway..

Here’s a link to and a citation for the paper,

Transparent and conductive nanomembranes with orthogonal silver nanowire arrays for skin-attachable loudspeakers and microphones by Saewon Kang, Seungse Cho, Ravi Shanker, Hochan Lee, Jonghwa Park, Doo-Seung Um, Youngoh Lee, and Hyunhyub Ko. Science Advances 03 Aug 2018: Vol. 4, no. 8, eaas8772 DOI: 10.1126/sciadv.aas8772

This paper appears to be open access.

Cosmetics breakthrough for Ulsan National Institute of Science and Technology (UNIST)?

Cosmetics would not have been my first thought on reading the title for the paper (“Rates of cavity filling by liquids”) produced  by scientists from Ulsan National Institute of Science and Technology (UNIST).

A September 17, 2018 news item on Nanowerk announces the research,

A research team, affiliated with Ulsan National Institute of Science and Technology (UNIST) has examined the rates of liquid penetration on rough or patterned surfaces, especially those with pores or cavities. Their findings provide important insights into the development of everyday products, including cosmetics, paints, as well as industrial applications, like enhanced oil recovery.

This study has been jointly led by Professor Dong Woog Lee and his research team in the School of Energy and Chemical Engineering at UNIST and a research team in the University of California, Santa Barbara. Published online in the July 19th issue of the Proceedings of the National Academy of Sciences (“Rates of cavity filling by liquids”), the study identifies five variables that control the cavity-filling (wetting transition) rates, required for liquids to penetrate into the cavities.

A July 26, 2018 UNIST press release (also on EurekAlert but published on September 17, 2018), which originated the news item, delves further into the work,

In the study, Professor Lee fabricated silicon wafers with cylindrical cavities of different geometries. After immersing them in bulk water, they observed the details of, and the rates associated with, water penetration into the cavities from the bulk, using bright-field and confocal fluorescence microscopy. Cylindrical cavities are like skin pores with narrow entrance and specious interior. The cavity filling generally progresses when bulk water is spread above a hydrophilic, reentrant cavity. As described in “Wetting Transition from the Cassie–Baxter State to Wenzel State”, the liquid droplet that sits on top of the textured surface with trapped air underneath will be completely absorbed by the rough surface cavities.

Their findings revealed that the cavity-filling rates are affected by the following variables: (i) the intrinsic contact angle, (ii) the concentration of dissolved air in the bulk water phase, (iii) the liquid volatility that determines the rate of capillary condensation inside the cavities, (iv) the types of surfactants, and (v) the cavity geometry.

“Our results can used in the manufacture of special-purpose cosmetic products,” says Professor Lee. “For instance, pore minimizing face primers and facial cleansers that remove sebum need to reduce the amount of dissolved air, so that they can penetrate into the pores quickly.”

On the other hand, beauty products, like sunscreens should be designed to protect the skin from harmful sun, while preventing pores clogging. Because, clogged pores hinder the skin’s function of breathing or exchange of carbon dioxide and then cause further irritation, pimples, and blemished areas on your skin. In this case, it is better to reduce volatility and increase the amount of dissolved air in the cosmetic products, as opposed to facial cleansers.

“This knowledge of how cavities under bulk water are filled and what variables control the rate of filling can provide insights into the engineering of temporarily or permanently superhydrophobic surfaces, and the designing and manufacturing of various products that are applied to rough, textured, or patterned surfaces,” says Professor Lee. “Many of the fundamental insights gained can also be applied to other liquids (e.g., oils), contact angles, and cavities or pores of different dimensions or geometries.”

This study has been supported by the National Research Foundation of Korea (NRF) grant, funded by the Ministry of Science and ICT.

Here’s a link to and a citation for the paper,

Rates of cavity filling by liquids by Dongjin Seo, Alex M. Schrader, Szu-Ying Chen, Yair Kaufman, Thomas R. Cristiani, Steven H. Page, Peter H. Koenig, Yonas Gizaw, Dong Woog Lee, and Jacob N. Israelachvili. PNAS August 7, 2018 115 (32) 8070-8075 https://doi.org/10.1073/pnas.1804437115 Published ahead of print July 19, 2018

This paper is behind a paywall.