Category Archives: electronics

Purifying carbon nanotubes with dietary fiber

This work comes out of Japan according to a November 2, 2019 news item on Nanowerk,

A new, cheaper method easily and effectively separates two types of carbon nanotubes. The process, developed by Nagoya University researchers in Japan, could be up-scaled for manufacturing purified batches of single-wall carbon nanotubes that can be used in high-performance electronic devices.

Single-wall carbon nanotubes (SWCNTs) have excellent electronic and mechanical properties, making them ideal candidates for use in a wide range of electronic devices, including the thin-film transistors found in LCD displays. A problem is that only two-thirds of manufactured SWCNTs are suitable for use in electronic devices. The useful semiconducting SWCNTs must be separated from the unwanted metallic ones. But the most powerful purification process, known as aqueous two-phase extraction, currently involves the use of a costly polysaccharide, called dextran.

Caption: The unwanted metallic SWCNTs deposited at the bottom of the solution, while the wanted semiconducting ones floated to the top. Credit: Haruka Omachi

An October 29, 2019 Nagoya University press release (also on EurekAlert but dated Nov. 2, 2019), which originated the news item, describes how dextran could be replaced with something much cheaper in the SWCNT purification process,

Organic chemist Haruka Omachi and colleagues at Nagoya University hypothesized that dextran’s effectiveness in separating semiconducting from metallic SWCNTs lies in the linkages connecting its glucose units. Instead of using dextran to separate the two types of SWCNTs, the team tried the significantly cheaper isomaltodextran, which has many more of these linkages.

A batch of SWCNTs was left for 15 minutes in a solution containing polyethylene glycol and isomaltodextrin and then centrifuged for five minutes. Three different types of isomaltodextrin were tried, each with a different number of linkages and a different molecular weight. The team found that metallic SWCNTs separated to the bottom isomaltodextrin part of the solution, while the semiconducting SWCNTs floated to the top polyethylene glycol part.

The type of isomaltodextrin with high molecular weight and the most linkages was the most (99%) effective in separating the two types of SWCNTs. The team also found that another polysaccharide, called pullulan, whose glucose units are connected with different kinds of linkages, was ineffective in separating the two types of SWCNTs. The researchers suggest that the number and type of linkages present in isomaltodextrin play an important role in their ability to effectively separate the carbon nanotubes.

The team also found that a thin-film transistor made with their purified semiconducting SWCNTs performed very well.

Isomaltodextrin is a cheap and widely available polysaccharide produced from starch that is used as a dietary fibre. This makes it a cost-effective alternative for the SWCNT extraction process. Omachi and his colleagues are currently in discussions with companies to commercialize their approach. They are also working on improving the performance of thin-film transistors using semiconducting SWCNTs in flexible displays and sensor devices.

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

Aqueous two-phase extraction of semiconducting single-wall carbon nanotubes with isomaltodextrin and thin-film transistor applications by Haruka Omachi, Tomohiko Komuro, Kaisei Matsumoto, Minako Nakajima, Hikaru Watanabe, Jun Hirotani, Yutaka Ohno, and Hisanori Shinohara. Applied Physics Express, Volume 12, Number 9 DOI: https://doi.org/10.7567/1882-0786/ab369 Published 14 August 2019 • © 2019 The Japan Society of Applied Physics

This paper is open access.

Double-walled carbon nanotubes have superior electrical properties?

A March 27, 2020 news item on Nanowerk suggests that double-walled carbon nanotubes (DWCNTs) may offer some advantages over single-walled carbon nanotubes (SWCNTs), NOTE: A link has been removed,

One nanotube could be great for electronics applications, but there’s new evidence that two could be tops.

Rice University engineers already knew that size matters when using single-walled carbon nanotubes for their electrical properties. But until now, nobody had studied how electrons act when confronted with the Russian doll-like structure of multiwalled tubes.

There’s a diagram representing the work,

Caption: Rice University theorists have calculated flexoelectric effects in double-walled carbon nanotubes. The electrical potential (P) of atoms on either side of a graphene sheet (top) are identical, but not when the sheet is curved into a nanotube. Double-walled nanotubes (bottom) show unique effects as band gaps in inner and outer tubes are staggered. Credit: Yakobson Research Group/Rice University

A March 27, 2020 Rice University news release (also on EurekAlert), which originated the news item, delves further (NOTE: Links have been removed),

The Rice lab of materials theorist Boris Yakobson has now calculated the impact of curvature of semiconducting double-wall carbon nanotubes on their flexoelectric voltage, a measure of electrical imbalance between the nanotube’s inner and outer walls.

This affects how suitable nested nanotube pairs may be for nanoelectronics applications, especially photovoltaics.

The theoretical research by Yakobson’s Brown School of Engineering group appears in the American Chemical Society journal Nano Letters.

In an 2002 study, Yakobson and his Rice colleagues had revealed how charge transfer, the difference between positive and negative poles that allows voltage to exist between one and the other, scales linearly to the curvature of the nanotube wall. The width of the tube dictates curvature, and the lab found that the thinner the nanotube (and thus larger the curvature), the greater the potential voltage.

When carbon atoms form flat graphene, the charge density of the atoms on either side of the plane are identical, Yakobson said. Curving the graphene sheet into a tube breaks that symmetry, changing the balance.

That creates a flexoelectric local dipole in the direction of, and proportional to, the curvature, according to the researchers, who noted that the flexoelectricity of 2D carbon “is a remarkable but also fairly subtle effect.”

But more than one wall greatly complicates the balance, altering the distribution of electrons. In double-walled nanotubes, the curvature of the inner and outer tubes differ, giving each a distinct band gap. Additionally, the models showed the flexoelectric voltage of the outer wall shifts the band gap of the inner wall, creating a staggered band alignment in the nested system.

“The novelty is that the inserted tube, the ‘baby’ (inside) matryoshka has all of its quantum energy levels shifted because of the voltage created by exterior nanotube,” Yakobson said. The interplay of different curvatures, he said, causes a straddling-to-staggered band gap transition that takes place at an estimated critical diameter of about 2.4 nanometers.

“This is a huge advantage for solar cells, essentially a prerequisite for separating positive and negative charges to create a current,” Yakobson said. “When light is absorbed, an electron always jumps from the top of an occupied valence band (leaving a ‘plus’ hole behind) to the lowest state of empty conductance band.

“But in a staggered configuration they happen to be in different tubes, or layers,” he said. “The ‘plus’ and ‘minus’ get separated between the tubes and can flow away by generating current in a circuit.”

The team’s calculations also showed that modifying the nanotubes’ surfaces with either positive or negative atoms could create “substantial voltages of either sign” up to three volts. “Although functionalization could strongly perturb the electronic properties of nanotubes, it may be a very powerful way of inducing voltage for certain applications,” the researchers wrote.

The team suggested its findings may apply to other types of nanotubes, including boron nitride and molybdenum disulfide, on their own or as hybrids with carbon nanotubes.

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

Flexoelectricity and charge separation in carbon nanotubes by Vasilii I. Artyukhov, Sunny Gupta, Alex Kutana, Boris I. Yakobson. Nano Lett. 2020, XXXX, XXX, XXX-XXX DOI: https://doi.org/10.1021/acs.nanolett.9b05345 [Online] Publication Date:March 10, 2020 Copyright © 2020 American Chemical Society

This paper is behind a paywall.

Are nano electronics as good as gold?

“As good as gold” was a behavioural goal when I was a child. It turns out, the same can be said of gold in electronic devices according to the headline for a March 26, 2020 news item on Nanowerk (Note: Links have been removed),

As electronics shrink to nanoscale, will they still be good as gold?

Deep inside computer chips, tiny wires made of gold and other conductive metals carry the electricity used to process data.

But as these interconnected circuits shrink to nanoscale, engineers worry that pressure, such as that caused by thermal expansion when current flows through these wires, might cause gold to behave more like a liquid than a solid, making nanoelectronics unreliable. That, in turn, could force chip designers to hunt for new materials to make these critical wires.

But according to a new paper in Physical Review Letters (“Nucleation of Dislocations in 3.9 nm Nanocrystals at High Pressure”), chip designers can rest easy. “Gold still behaves like a solid at these small scales,” says Stanford mechanical engineer Wendy Gu, who led a team that figured out how to pressurize gold particles just 4 nanometers in length — the smallest particles ever measured — to assess whether current flows might cause the metal’s atomic structure to collapse.

I have seen the issue about gold as a metal or liquid before but I can’t find it here (search engines, sigh). However, I found this somewhat related story from almost five years ago. In my April 14, 2015 posting (Gold atoms: sometimes they’re a metal and sometimes they’re a molecule), there was news that the number of gold atoms present means the difference between being a metal and being a molecule .This could have implications as circuit elements (which include some gold in their fabrication) shrink down past a certain point.

A March 24, 2020 Stanford University news release (also on Eurekalert but published on March 25, 2020) by Andrew Myers, which originated the news item, provides details about research designed to investigate a similar question, i.e, can we used gold as we shrink the scale?*,

To conduct the experiment, Gu’s team first had to devise a way put tiny gold particles under extreme pressure, while simultaneously measuring how much that pressure damaged gold’s atomic structure.

To solve the first problem, they turned to the field of high-pressure physics to borrow a device known as a diamond anvil cell. As the name implies, both hammer and anvil are diamonds that are used to compress the gold. As Gu explained, a nanoparticle of gold is built like a skyscraper with atoms forming a crystalline lattice of neat rows and columns. She knew that pressure from the anvil would dislodge some atoms from the crystal and create tiny defects in the gold.

The next challenge was to detect these defects in nanoscale gold. The scientists shined X-rays through the diamond onto the gold. Defects in the crystal caused the X-rays to reflect at different angles than they would on uncompressed gold. By measuring variations in the angles at which the X-rays bounced off the particles before and after pressure was applied, the team was able to tell whether the particles retained the deformations or reverted to their original state when pressure was lifted.

In practical terms, her findings mean that chipmakers can know with certainty that they’ll be able to design stable nanodevices using gold — a material they have known and trusted for decades — for years to come.

“For the foreseeable future, gold’s luster will not fade,” Gu says.

*The 2015 research measured the gold nanoclusters by the number of atoms within the cluster with the changes occurring at some where between 102 atoms and 144 atoms. This 2020 work measures the amount of gold by nanometers as in 3.9 nm gold nanocrystals . So, how many gold atoms in a nanometer? Cathy Murphy provides the answer and the way to calculate it for yourself in a July 26, 2016 posting on the Sustainable Nano blog ( a blog by the Center for Sustainable Nanotechnology),

Two years ago, I wrote a blog post called Two Ways to Make Nanoparticles, describing the difference between top-down and bottom-up methods for making nanoparticles. In the post I commented, “we can estimate, knowing how gold atoms pack into crystals, that there are about 2000 gold atoms in one 4 nm diameter gold nanoparticle.” Recently, a Sustainable Nano reader wrote in to ask about how this calculation is done. It’s a great question!

So, a 3.9 nm gold nanocrystal contains approximately 2000 gold atoms. (If you have time, do read Murphy’s description of how to determine the number of gold atoms in a gold nanoparticle.) So, this research does not answer the question posed by the 2015 research.

It may take years before researchers can devise tests for gold nanoclusters consisting of 102 atoms as opposed to nanoparticles consisting of 2000 atoms. In the meantime, here’s a link to and a citation for the latest on how gold reacts as we shrink the size of our electronics,

Nucleation of Dislocations in 3.9 nm Nanocrystals at High Pressure by Abhinav Parakh, Sangryun Lee, K. Anika Harkins, Mehrdad T. Kiani, David Doan, Martin Kunz, Andrew Doran, Lindsey A. Hanson, Seunghwa Ryu, and X. Wendy Gu. Phys. Rev. Lett. 124, 106104 DOI:https://doi.org/10.1103/PhysRevLett.124.106104 Published 13 March 2020 © 2020 American Physical Society

This paper is behind a paywall.

In the future your clothing may be a health monitor

It’s not ready for the COVID-19 pandemic but if I understand it properly, wearing this clothing will be a little like wearing a thermometer and that could be very useful. A March 4, 2020 news item on Nanowerk announces the research (Note: A link has been removed),

Researchers have reported a new material, pliable enough to be woven into fabric but imbued with sensing capabilities that can serve as an early warning system for injury or illness.

The material, described in a paper published by ACS Applied Nano Materials (“Poly(octadecyl acrylate)-Grafted Multiwalled Carbon Nanotube Composites for Wearable Temperature Sensors”), involves the use of carbon nanotubes and is capable of sensing slight changes in body temperature while maintaining a pliable disordered structure – as opposed to a rigid crystalline structure – making it a good candidate for reusable or disposable wearable human body temperature sensors. Changes in body heat change the electrical resistance, alerting someone monitoring that change to the potential need for intervention.

I think this is an artistic rendering of the research,

Caption: Researchers have reported a new material, pliable enough to be woven into fabric but imbued with sensing capabilities that could serve as an early warning system for injury or illness. Credit: University of Houston

A March 4, 2020 University of Houston (Texas, US) news release (also on EurekAlert) by Jeannie Kever, which originated the news item, describes the work in more detail,

“Your body can tell you something is wrong before it becomes obvious,” said Seamus Curran, a physics professor at the University of Houston and co-author on the paper. Possible applications range from detecting dehydration in an ultra-marathoner to the beginnings of a pressure sore in a nursing home patient.

The researchers said it is also cost-effective because the raw materials required are used in relatively low concentrations.

The discovery builds on work Curran and fellow researchers Kang-Shyang Liao and Alexander J. Wang began nearly a decade ago, when they developed a hydrophobic nanocoating for cloth, which they envisioned as a protective coating for clothing, carpeting and other fiber-based materials.

Wang is now a Ph.D. student at Technological University Dublin, currently working with Curran at UH, and is corresponding author for the paper. In addition to Curran and Liao, other researchers involved include Surendra Maharjan, Brian P. McElhenny, Ram Neupane, Zhuan Zhu, Shuo Chen, Oomman K. Varghese and Jiming Bao, all of UH; Kourtney D. Wright and Andrew R. Barron of Rice University, and Eoghan P. Dillon of Analysis Instruments in Santa Barbara.

The material, created using poly(octadecyl acrylate)-grafted multiwalled carbon nanotubes, is technically known as a nanocarbon-based disordered, conductive, polymeric nanocomposite, or DCPN, a class of materials increasingly used in materials science. But most DCPN materials are poor electroconductors, making them unsuitable for use in wearable technologies that require the material to detect slight changes in temperature.

The new material was produced using a technique called RAFT-polymerization, Wang said, a critical step that allows the attached polymer to be electronically and phononically coupled with the multiwalled carbon nanotube through covalent bonding. As such, subtle structural arrangements associated with the glass transition temperature of the system are electronically amplified to produce the exceptionally large electronic responses reported in the paper, without the negatives associated with solid-liquid phase transitions. The subtle structural changes associated with glass transition processes are ordinarily too small to produce large enough electronic responses.

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

Poly(octadecyl acrylate)-Grafted Multiwalled Carbon Nanotube Composites for Wearable Temperature Sensors by Alexander J. Wang, Surendra Maharjan, Kang-Shyang Liao, Brian P. McElhenny, Kourtney D. Wright, Eoghan P. Dillon, Ram Neupane, Zhuan Zhu, Shuo Chen, Andrew R. Barron, Oomman K. Varghese, Jiming Bao, Seamus A. Curran. ACS Appl. Nano Mater. 2020, XXXX, XXX, XXX-XXX DOI: https://doi.org/10.1021/acsanm.9b02396 (Online) Publication Date:January 28, 2020 Copyright © 2020 American Chemical Society

This paper is behind a paywall.

Connecting biological and artificial neurons (in UK, Switzerland, & Italy) over the web

Caption: The virtual lab connecting Southampton, Zurich and Padova. Credit: University of Southampton

A February 26, 2020 University of Southampton press release (also on EurekAlert) describes this work,

Research on novel nanoelectronics devices led by the University of Southampton enabled brain neurons and artificial neurons to communicate with each other. This study has for the first time shown how three key emerging technologies can work together: brain-computer interfaces, artificial neural networks and advanced memory technologies (also known as memristors). The discovery opens the door to further significant developments in neural and artificial intelligence research.

Brain functions are made possible by circuits of spiking neurons, connected together by microscopic, but highly complex links called ‘synapses’. In this new study, published in the scientific journal Nature Scientific Reports, the scientists created a hybrid neural network where biological and artificial neurons in different parts of the world were able to communicate with each other over the internet through a hub of artificial synapses made using cutting-edge nanotechnology. This is the first time the three components have come together in a unified network.

During the study, researchers based at the University of Padova in Italy cultivated rat neurons in their laboratory, whilst partners from the University of Zurich and ETH Zurich created artificial neurons on Silicon microchips. The virtual laboratory was brought together via an elaborate setup controlling nanoelectronic synapses developed at the University of Southampton. These synaptic devices are known as memristors.

The Southampton based researchers captured spiking events being sent over the internet from the biological neurons in Italy and then distributed them to the memristive synapses. Responses were then sent onward to the artificial neurons in Zurich also in the form of spiking activity. The process simultaneously works in reverse too; from Zurich to Padova. Thus, artificial and biological neurons were able to communicate bidirectionally and in real time.

Themis Prodromakis, Professor of Nanotechnology and Director of the Centre for Electronics Frontiers at the University of Southampton said “One of the biggest challenges in conducting research of this kind and at this level has been integrating such distinct cutting edge technologies and specialist expertise that are not typically found under one roof. By creating a virtual lab we have been able to achieve this.”

The researchers now anticipate that their approach will ignite interest from a range of scientific disciplines and accelerate the pace of innovation and scientific advancement in the field of neural interfaces research. In particular, the ability to seamlessly connect disparate technologies across the globe is a step towards the democratisation of these technologies, removing a significant barrier to collaboration.

Professor Prodromakis added “We are very excited with this new development. On one side it sets the basis for a novel scenario that was never encountered during natural evolution, where biological and artificial neurons are linked together and communicate across global networks; laying the foundations for the Internet of Neuro-electronics. On the other hand, it brings new prospects to neuroprosthetic technologies, paving the way towards research into replacing dysfunctional parts of the brain with AI [artificial intelligence] chips.”

I’m fascinated by this work and after taking a look at the paper, I have to say, the paper is surprisingly accessible. In other words, I think I get the general picture. For example (from the Introduction to the paper; citation and link follow further down),

… To emulate plasticity, the memristor MR1 is operated as a two-terminal device through a control system that receives pre- and post-synaptic depolarisations from one silicon neuron (ANpre) and one biological neuron (BN), respectively. …

If I understand this properly, they’ve integrated a biological neuron and an artificial neuron in a single system across three countries.

For those who care to venture forth, here’s a link and a citation for the paper,

Memristive synapses connect brain and silicon spiking neurons by Alexantrou Serb, Andrea Corna, Richard George, Ali Khiat, Federico Rocchi, Marco Reato, Marta Maschietto, Christian Mayr, Giacomo Indiveri, Stefano Vassanelli & Themistoklis Prodromakis. Scientific Reports volume 10, Article number: 2590 (2020) DOI: https://doi.org/10.1038/s41598-020-58831-9 Published 25 February 2020

The paper is open access.

Improving batteries with cellulosic nanomaterials

This is a cellulose nanocrystal (CNC) story and in this story it’s derived from trees as opposed to banana skins or carrots or … A February 19, 2020 news item on Nanowerk announces CNC research from Northeastern University (Massachusetts, US),

Nature isn’t always generous with its secrets. That’s why some researchers look into unusual places for solutions to our toughest challenges, from powerful antibiotics hiding in the guts of tiny worms, to swift robots inspired by bats.

Now, Northeastern researchers have taken to the trees to look for ways to make new sustainable materials from abundant natural resources—specifically, within the chemical structure of microfibers that make up wood.

A team led by Hongli (Julie) Zhu, an assistant professor of mechanical and industrial engineering at Northeastern, is using unique nanomaterials derived from cellulose to improve the large and expensive kind of batteries needed to store renewable energy harnessed from sources such as sunlight and the wind.

A February 18, 2020 Northeastern University news release by Roberto Molar Candanosa, which originated the news item, provides more detail (Note: Links have been removed),

Cellulose, the most abundant natural polymer on Earth, is also the most important structural component of plants. It contains important molecular structures to improve batteries, reduce plastic pollution, and power the sort of electrical grids that could support entire communities with renewable energy, Zhu says.  

“We try to use polymers from wood, from bark, from seeds, from flowers, bacteria, green tea—from these kinds of plants to replace plastic,”  Zhu says.

One of the main challenges in storing energy from the sun, wind, and other types of renewables is that variation in factors such as the weather lead to inconsistent sources of power. 

That’s where batteries with large capacity come in. But storing the large amounts of energy that sunlight and the wind are able to provide requires a special kind of device.

The most advanced batteries to do that are called flow batteries, and are made with vanadium ions dissolved in acid in two separate tanks—one with a substance of negatively charged ions, and one with positive ones. The two solutions are continuously pumped from the tank into a cell, which functions like an engine for the battery. 

These substances are always separated by a special membrane that ensures that they exchange positive hydrogen ions without flowing into each other. That selective exchange of ions is the basis for the ability of the battery to charge and discharge energy. 

Flow batteries are ideal devices in which to store solar and wind energy because they can be tweaked to increase the amount of energy stored without compromising the amount of energy that can be generated. The bigger the tanks, the more energy the battery can store from non-polluting and practically inexhaustible resources.

But manufacturing them requires several moving pieces of hardware. As the membrane separating the two flowing substances decays, it can cause the vanadium ions from the solution to mix. That crossover reduces the stability of a battery, along with its capacity to store energy.

Zhu says the limited efficiency of that membrane, combined with  its high cost, are the main factors keeping flow batteries from being widely used in large-scale grids.

In a recent paper, Zhu reported that a new membrane made with cellulose nanocrystals demonstrates superior efficiency compared to other membranes used commonly in the market. The team tested different membranes made from cellulose nanocrystals to make flow batteries cheaper.

“The cost of our membrane per square meter is 147.68 US dollars, ” Zhu says, adding that her calculations do not include costs associated with marketing. “The price quote for the commercialized Nafion membrane is $1,321 per square meter.”

Their tests also showed that the membranes, made with support from the Rogers Corporation and its Innovation Center at Northeastern’s Kostas Research Institute, can offer substantially longer battery lifetimes than other membranes. 

Zhu’s naturally derived membrane is especially efficient because its cellular structure contains thousands of hydroxyl groups, which involve bonds of hydrogen and oxygen that make it easy for water to be transported in plants and trees. 

In flow batteries, that molecular makeup speeds the transport of protons as they flow through the membrane.

The membrane also consists of another polymer known as poly(vinylidene fluoride-hexafluoropropylene), which prevents the negatively and positively charged acids from mixing with each other. 

“For these materials, one of the challenges is that it is difficult to find a polymer that is proton conductive and that is also a material that is very stable in the flowing acid,” Zhu says. 

Because these materials are practically everywhere, membranes made with it can be easily put together at large scales needed for complex power grids. 

Unlike other expensive artificial materials that need to be concocted in a lab, cellulose can be extracted from natural sources including algae, solid waste, and bacteria. 

“A lot of material in nature is a composite, and if we disintegrate its components, we can use it to extract cellulose,” Zhu says. “Like waste from our yard, and a lot of solid waste that we don’t always know what to do with.” 

Here’s a link to and a citation for the paper mentioned in the news release,

Stable and Highly Ion-Selective Membrane Made from Cellulose Nanocrystals for Aqueous Redox Flow Batteries by Alolika Mukhopadhyay, Zheng Cheng, Avi Natan, Yi Ma, Yang Yang, Daxian Cao, Wei Wan, Hongli Zhu. Nano Lett. 2019, 19, 12, 8979-8989 DOI: https://doi.org/10.1021/acs.nanolett.9b03964Publication Date:November 8, 2019 Copyright © 2019 American Chemical Society

This paper is behind a paywall.

A lipid-based memcapacitor,for neuromorphic computing

Caption: Researchers at ORNL’s Center for Nanophase Materials Sciences demonstrated the first example of capacitance in a lipid-based biomimetic membrane, opening nondigital routes to advanced, brain-like computation. Credit: Michelle Lehman/Oak Ridge National Laboratory, U.S. Dept. of Energy

The last time I wrote about memcapacitors (June 30, 2014 posting: Memristors, memcapacitors, and meminductors for faster computers), the ideas were largely theoretical; I believe this work is the first research I’ve seen on the topic. From an October 17, 2019 news item on ScienceDaily,

Researchers at the Department of Energy’s Oak Ridge National Laboratory ]ORNL], the University of Tennessee and Texas A&M University demonstrated bio-inspired devices that accelerate routes to neuromorphic, or brain-like, computing.

Results published in Nature Communications report the first example of a lipid-based “memcapacitor,” a charge storage component with memory that processes information much like synapses do in the brain. Their discovery could support the emergence of computing networks modeled on biology for a sensory approach to machine learning.

An October 16, 2019 ORNL news release (also on EurekAlert but published Oct. 17, 2019), which originated the news item, provides more detail about the work,

“Our goal is to develop materials and computing elements that work like biological synapses and neurons—with vast interconnectivity and flexibility—to enable autonomous systems that operate differently than current computing devices and offer new functionality and learning capabilities,” said Joseph Najem, a recent postdoctoral researcher at ORNL’s Center for Nanophase Materials Sciences, a DOE Office of Science User Facility, and current assistant professor of mechanical engineering at Penn State.

The novel approach uses soft materials to mimic biomembranes and simulate the way nerve cells communicate with one another.

The team designed an artificial cell membrane, formed at the interface of two lipid-coated water droplets in oil, to explore the material’s dynamic, electrophysiological properties. At applied voltages, charges build up on both sides of the membrane as stored energy, analogous to the way capacitors work in traditional electric circuits.

But unlike regular capacitors, the memcapacitor can “remember” a previously applied voltage and—literally—shape how information is processed. The synthetic membranes change surface area and thickness depending on electrical activity. These shapeshifting membranes could be tuned as adaptive filters for specific biophysical and biochemical signals.

“The novel functionality opens avenues for nondigital signal processing and machine learning modeled on nature,” said ORNL’s Pat Collier, a CNMS staff research scientist.

A distinct feature of all digital computers is the separation of processing and memory. Information is transferred back and forth from the hard drive and the central processor, creating an inherent bottleneck in the architecture no matter how small or fast the hardware can be.

Neuromorphic computing, modeled on the nervous system, employs architectures that are fundamentally different in that memory and signal processing are co-located in memory elements—memristors, memcapacitors and meminductors.

These “memelements” make up the synaptic hardware of systems that mimic natural information processing, learning and memory.

Systems designed with memelements offer advantages in scalability and low power consumption, but the real goal is to carve out an alternative path to artificial intelligence, said Collier.

Tapping into biology could enable new computing possibilities, especially in the area of “edge computing,” such as wearable and embedded technologies that are not connected to a cloud but instead make on-the-fly decisions based on sensory input and past experience.

Biological sensing has evolved over billions of years into a highly sensitive system with receptors in cell membranes that are able to pick out a single molecule of a specific odor or taste. “This is not something we can match digitally,” Collier said.

Digital computation is built around digital information, the binary language of ones and zeros coursing through electronic circuits. It can emulate the human brain, but its solid-state components do not compute sensory data the way a brain does.

“The brain computes sensory information pushed through synapses in a neural network that is reconfigurable and shaped by learning,” said Collier. “Incorporating biology—using biomembranes that sense bioelectrochemical information—is key to developing the functionality of neuromorphic computing.”

While numerous solid-state versions of memelements have been demonstrated, the team’s biomimetic elements represent new opportunities for potential “spiking” neural networks that can compute natural data in natural ways.

Spiking neural networks are intended to simulate the way neurons spike with electrical potential and, if the signal is strong enough, pass it on to their neighbors through synapses, carving out learning pathways that are pruned over time for efficiency.

A bio-inspired version with analog data processing is a distant aim. Current early-stage research focuses on developing the components of bio-circuitry.

“We started with the basics, a memristor that can weigh information via conductance to determine if a spike is strong enough to be broadcast through a network of synapses connecting neurons,” said Collier. “Our memcapacitor goes further in that it can actually store energy as an electric charge in the membrane, enabling the complex ‘integrate and fire’ activity of neurons needed to achieve dense networks capable of brain-like computation.”

The team’s next steps are to explore new biomaterials and study simple networks to achieve more complex brain-like functionalities with memelements.

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

Dynamical nonlinear memory capacitance in biomimetic membranes by Joseph S. Najem, Md Sakib Hasan, R. Stanley Williams, Ryan J. Weiss, Garrett S. Rose, Graham J. Taylor, Stephen A. Sarles & C. Patrick Collier. Nature Communications volume 10, Article number: 3239 (2019) DOI: DOIhttps://doi.org/10.1038/s41467-019-11223-8 Published July 19, 2019

This paper is open access.

One final comment, you might recognize one of the authors (R. Stanley Williams) who in 2008 helped launch ‘memristor’ research.

Colloidal quantum dots as ultra-sensitive hyper-spectral photodetectors

An October 16, 2019 news item on Nanowerk announces some of the latest work with colloidal quantum dots,

Researchers of the Optoelectronics and Measurement Techniques Unit (OPEM) at the University of Oulu [Finland] have invented a new method of producing ultra-sensitive hyper-spectral photodetectors. At the heart of the discovery are colloidal quantum dots, developed together with the researchers at the University of Toronto, Canada.

Quantum dots are tiny particles of 15-150 atoms of semiconducting material that have extraordinary optical and electrical properties due to quantum mechanics phenomena.

By controlling the size of the dots, the researchers are able to finetune how they react to different light colors (light wavelengths), especially those invisible for the human eye, namely the infrared spectrum.

The figure briefly introduces the concept of the study conducted by the researchers of the University of Oulu and the University of Toronto. The solution consisting of colloidal quantum dots is inkjet-printed, creating active photosensitive layer of the photodetector. Courtesy: Oulu University

An October 16, 2019 Oulu University press release, which originated the news item, provides more detail,

-Naturally, it is very rewarding that our hard work has been recognized by the international scientific community but at the same time, this report helps us to realize that there is a long journey ahead in incoming years. This publication is especially satisfying because it is the result of collaboration with world-class experts at the University of Toronto, Canada. This international collaboration where we combined the expertise of Toronto’s researchers in synthesizing quantum dots and our expertise in printed intelligence resulted in truly unique devices with astonishing performance, says docent Rafal Sliz, a leading researcher in this project.
 
Mastered in the OPEM unit, inkjet printing technology makes possible the creation of optoelectronic devices by designing functional inks that are printed on various surfaces, for instance, flexible substrates, clothing or human skin. Inkjet printing combined with colloidal quantum dots allowed the creation of photodetectors of impresive detectivity characteristics. The developed technology is a milestone in the creation of a new type of sub-micron-thick, flexible, and inexpensive IR sensing devices, the next generation of solar cells and other novel photonic systems.

-Oulus’ engineers and scientists’ strong expertise in optoelectronics resulted in many successful Oulu-based companies like Oura, Specim, Focalspec, Spectral Engines, and many more. New optoelectronic technologies, materials, and methods developed by our researchers will help Oulu and Finland to stay at the cutting edge of innovation, says professor Tapio Fabritius, a leader of the OPEM.

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

Stable Colloidal Quantum Dot Inks Enable Inkjet-Printed High-Sensitivity Infrared Photodetectors by Rafal Sliz, Marc Lejay, James Z. Fan, Min-Jae Choi, Sachin Kinge, Sjoerd Hoogland, Tapio Fabritius, F. Pelayo García de Arquer, Edward H. Sargent. ACS Nano 2019 DOI: https://doi.org/10.1021/acsnano.9b06125 Publication Date:September 23, 2019 Copyright © 2019 American Chemical Society

This paper is behind a paywall.

MXene-coated yarn for wearable electronics

There’s been a lot of talk about wearable electronics, specifically e-textiles, but nothing seems to have entered the marketplace. Scaling up your lab discoveries for industrial production can be quite problematic. From an October 10, 2019 news item on ScienceDaily,

Producing functional fabrics that perform all the functions we want, while retaining the characteristics of fabric we’re accustomed to is no easy task.

Two groups of researchers at Drexel University — one, who is leading the development of industrial functional fabric production techniques, and the other, a pioneer in the study and application of one of the strongest, most electrically conductive super materials in use today — believe they have a solution.

They’ve improved a basic element of textiles: yarn. By adding technical capabilities to the fibers that give textiles their character, fit and feel, the team has shown that it can knit new functionality into fabrics without limiting their wearability.

An October 10, 2019 Drexel University news release (also on EurekAlert), which originated the news item, details the proposed solution (pun! as you’ll see in the video following this excerpt),

In a paper recently published in the journal Advanced Functional Materials, the researchers, led by Yury Gogotsi, PhD, Distinguished University and Bach professor in Drexel’s College of Engineering, and Genevieve Dion, an associate professor in Westphal College of Media Arts & Design and director of Drexel’s Center for Functional Fabrics, showed that they can create a highly conductive, durable yarn by coating standard cellulose-based yarns with a type of conductive two-dimensional material called MXene.

Hitting snags

“Current wearables utilize conventional batteries, which are bulky and uncomfortable, and can impose design limitations to the final product,” they write. “Therefore, the development of flexible, electrochemically and electromechanically active yarns, which can be engineered and knitted into full fabrics provide new and practical insights for the scalable production of textile-based devices.”

The team reported that its conductive yarn packs more conductive material into the fibers and can be knitted by a standard industrial knitting machine to produce a textile with top-notch electrical performance capabilities. This combination of ability and durability stands apart from the rest of the functional fabric field today.

Most attempts to turn textiles into wearable technology use stiff metallic fibers that alter the texture and physical behavior of the fabric. Other attempts to make conductive textiles using silver nanoparticles and graphene and other carbon materials raise environmental concerns and come up short on performance requirements. And the coating methods that are successfully able to apply enough material to a textile substrate to make it highly conductive also tend to make the yarns and fabrics too brittle to withstand normal wear and tear.

“Some of the biggest challenges in our field are developing innovative functional yarns at scale that are robust enough to be integrated into the textile manufacturing process and withstand washing,” Dion said. “We believe that demonstrating the manufacturability of any new conductive yarn during experimental stages is crucial. High electrical conductivity and electrochemical performance are important, but so are conductive yarns that can be produced by a simple and scalable process with suitable mechanical properties for textile integration. All must be taken into consideration for the successful development of the next-generation devices that can be worn like everyday garments.”

The winning combination

Dion has been a pioneer in the field of wearable technology, by drawing on her background on fashion and industrial design to produce new processes for creating fabrics with new technological capabilities. Her work has been recognized by the Department of Defense, which included Drexel, and Dion, in its Advanced Functional Fabrics of America effort to make the country a leader in the field.

She teamed with Gogotsi, who is a leading researcher in the area of two-dimensional conductive materials, to approach the challenge of making a conductive yarn that would hold up to knitting, wearing and washing.

Gogotsi’s group was part of the Drexel team that discovered highly conductive two-dimensional materials, called MXenes, in 2011 and have been exploring their exceptional properties and applications for them ever since. His group has shown that it can synthesize MXenes that mix with water to create inks and spray coatings without any additives or surfactants – a revelation that made them a natural candidate for making conductive yarn that could be used in functional fabrics. [Gogotsi’s work was featured here in a May 6, 2019 posting]

“Researchers have explored adding graphene and carbon nanotube coatings to yarn, our group has also looked at a number of carbon coatings in the past,” Gogotsi said. “But achieving the level of conductivity that we demonstrate with MXenes has not been possible until now. It is approaching the conductivity of silver nanowire-coated yarns, but the use of silver in the textile industry is severely limited due to its dissolution and harmful effect on the environment. Moreover, MXenes could be used to add electrical energy storage capability, sensing, electromagnetic interference shielding and many other useful properties to textiles.”

In its basic form, titanium carbide MXene looks like a black powder. But it is actually composed of flakes that are just a few atoms thick, which can be produced at various sizes. Larger flakes mean more surface area and greater conductivity, so the team found that it was possible to boost the performance of the yarn by infiltrating the individual fibers with smaller flakes and then coating the yarn itself with a layer of larger-flake MXene.

Putting it to the test

The team created the conductive yarns from three common, cellulose-based yarns: cotton, bamboo and linen. They applied the MXene material via dip-coating, which is a standard dyeing method, before testing them by knitting full fabrics on an industrial knitting machine – the kind used to make most of the sweaters and scarves you’ll see this fall.

Each type of yarn was knit into three different fabric swatches using three different stitch patterns – single jersey, half gauge and interlock – to ensure that they are durable enough to hold up in any textile from a tightly knit sweater to a loose-knit scarf.

“The ability to knit MXene-coated cellulose-based yarns with different stitch patterns allowed us to control the fabric properties, such as porosity and thickness for various applications,” the researchers write.

To put the new threads to the test in a technological application, the team knitted some touch-sensitive textiles – the sort that are being explored by Levi’s and Yves Saint Laurent as part of Google’s Project Jacquard.

Not only did the MXene-based conductive yarns hold up against the wear and tear of the industrial knitting machines, but the fabrics produced survived a battery of tests to prove its durability. Tugging, twisting, bending and – most importantly – washing, did not diminish the touch-sensing abilities of the yarn, the team reported – even after dozens of trips through the spin cycle.

Pushing forward

But the researchers suggest that the ultimate advantage of using MXene-coated conductive yarns to produce these special textiles is that all of the functionality can be seamlessly integrated into the textiles. So instead of having to add an external battery to power the wearable device, or wirelessly connect it to your smartphone, these energy storage devices and antennas would be made of fabric as well – an integration that, though literally seamed, is a much smoother way to incorporate the technology.

“Electrically conducting yarns are quintessential for wearable applications because they can be engineered to perform specific functions in a wide array of technologies,” they write.

Using conductive yarns also means that a wider variety of technological customization and innovations are possible via the knitting process. For example, “the performance of the knitted pressure sensor can be further improved in the future by changing the yarn type, stitch pattern, active material loading and the dielectric layer to result in higher capacitance changes,” according to the authors.

Dion’s team at the Center for Functional Fabrics is already putting this development to the test in a number of projects, including a collaboration with textile manufacturer Apex Mills – one of the leading producers of material for car seats and interiors. And Gogotsi suggests the next step for this work will be tuning the coating process to add just the right amount of conductive MXene material to the yarn for specific uses.

“With this MXene yarn, so many applications are possible,” Gogotsi said. “You can think about making car seats with it so the car knows the size and weight of the passenger to optimize safety settings; textile pressure sensors could be in sports apparel to monitor performance, or woven into carpets to help connected houses discern how many people are home – your imagination is the limit.”

Researchers have produced a video about their work,

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

Knittable and Washable Multifunctional MXene‐Coated Cellulose Yarns by Simge Uzun, Shayan Seyedin, Amy L. Stoltzfus, Ariana S. Levitt, Mohamed Alhabeb, Mark Anayee, Christina J. Strobel, Joselito M. Razal, Genevieve Dion, Yury Gogotsi. Advanced Functional Materials DOI: https://doi.org/10.1002/adfm.201905015 First published: 05 September 2019

This paper is behind a paywall.

Harvard professor and leader in nanoscale electronics charged with making false statements about Chinese funding

I may be mistaken but the implication seems to be that Charles M. Lieber’s lies (he was charged today, January 28, 2020 ) are the ‘tip of the iceberg’ of a very large problem. Ellen Barry’s January 28, 2020 article for the New York Times outlines at least part of what the US government is doing to discover and ultimately discourage the theft of biomedical research from US laboratories.

Dr. Lieber, a leader in the field of nanoscale electronics, was one of three Boston-area scientists accused on Tuesday [January 28, 2020] of working on behalf of China. His case involves work with the Thousand Talents Program, a state-run program that seeks to draw talent educated in other countries.

American officials are investigating hundreds of cases of suspected theft of intellectual property by visiting scientists, nearly all of them Chinese nationals or of Chinese descent. Some are accused of obtaining patents in China based on work that is funded by the United States government, and others of setting up laboratories in China that secretly duplicated American research.

Dr. Lieber, who was arrested on Tuesday [January 28, 2020], stands out among the accused scientists, because he is neither Chinese nor of Chinese descent. …

Lieber is the Chair of Harvard’s Department of Chemistry and Chemical Biology and much more, according to his Wikipedia entry (Note: Links have been removed),

Charles M. Lieber (born 1959) is an American chemist and pioneer in the field of nanoscience and nanotechnology. In 2011, Lieber was recognized by Thomson Reuters as the leading chemist in the world for the decade 2000-2010 based on the impact of his scientific publications.[1] Lieber has published over 400 papers in peer-reviewed scientific journals and has edited and contributed to many books on nanoscience.[2] He is the principal inventor on over fifty issued US patents and applications, and founded the nanotechnology company Nanosys in 2001 and Vista Therapeutics in 2007.[3] He is known for his contributions to the synthesis, assembly and characterization of nanoscale materials and nanodevices, the application of nanoelectronic devices in biology, and as a mentor to numerous leaders in nanoscience.[4] Thompson Reuters predicted Lieber to be a recipient of the 2008 Nobel Prize in Chemistry [to date, January 28, 2020, Lieber has not received a Nobel prize].

Should you search Charles Lieber or Charles M. Lieber on this blog’s search engine, you will find a number of postings about his and his students’ work dating from 2012 to as recently as November 15, 2019.

Here’s another example from Barry’s January 28, 2020 article for the New York Times which illustrates just how shocking this is (Note: Links have been removed),

In 2017 he was named a University Professor, Harvard’s highest faculty rank, one of only 26 professors to hold that status. The same year, he earned the National Institutes of Health Director’s Pioneer Award for inventing syringe-injectable mesh electronics that can integrate with the brain.

Harvard’s president at the time, Drew G. Faust, called him “an extraordinary scientist whose work has transformed nanoscience and nanotechnology and has led to a remarkable range of valuable applications that improve the quality of people’s lives.”

Here’s a bit more about the Chinese program that Lieber is affiliated with,

Launched in 2008, its [China] Thousand Talents Program is an effort to recruit Chinese and foreign academics and entrepreneurs. According to a report in the China Daily, new recruits receive 1 million yuan, or about $146,000, from the central government, and a pledge of 10 million yuan for their ongoing research from the Chinese Academy of Sciences.

The recruitment flows both ways. Researchers of Chinese descent make up nearly half of the work force in American research laboratories, in part because American-born scientists are drawn to the private sector and less interested in academic careers.

I encourage you to read Barry’s entire article. It is jaw-dropping and, where Lieber is concerned, sad. It’s beginning to look like US universities are corrupt. The Jeffrey Epstein (a wealthy and convicted sexual predator and more) connection to the Massachusetts Institute of Technology, which led to the resignation of a prominent faculty member (Sept. 19, 2019 article by Anna North for Vox.com), and the Fall 2019 cheating scandal (gaining admission to big name educational institutions by paying someone other than the student to take exams, among many other schemes) suggest a reckoning might be in order.

ETA January 28, 2020 at 1645 hours: I found a January 28, 2020 article by Antonio Regalado for the MIT Technology Review which provides a few more details about Lieber’s situation,

Big money: According to the charging document, Lieber, starting in 2011,  agreed to help set up a research lab at the Wuhan University of Technology and “make strategic visionary and creative research proposals” so that China could do cutting-edge science.

He was well paid for it. Lieber earned a salary when he visited China worth up to $50,000 per month, as well as $150,000 a year in expenses in addition to research funds. According to the complaint, he got paid by way of a Chinese bank account but also was known to send emails asking for cash instead.

Harvard eventually wised up to the existence of a Wuhan lab using its name and logo, but when administrators confronted Lieber, he lied and said he didn’t know about a formal joint program, according to the government complaint.

I imagine the money paid by the Chinese government is in addition to Lieber’s Harvard salary (no doubt a substantial one especially since he’s chair of his department and one of a select number of Harvard’s University Professors) and in addition to any other deals he might have on the side.