Category Archives: electronics

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.

Second order memristor

I think this is my first encounter with a second-order memristor. An August 28, 2019 news item on Nanowerk announces the research (Note: A link has been removed),

Researchers from the Moscow Institute of Physics and Technology [MIPT} have created a device that acts like a synapse in the living brain, storing information and gradually forgetting it when not accessed for a long time. Known as a second-order memristor, the new device is based on hafnium oxide and offers prospects for designing analog neurocomputers imitating the way a biological brain learns.

An August 28, 2019 MIPT press release (also on EurekAlert), which originated the news item, provides an explanation for neuromorphic computing (analog neurocomputers; brainlike computing), the difference between a first-order and second-order memristor, and an in depth view of the research,

Neurocomputers, which enable artificial intelligence, emulate the way the brain works. It stores data in the form of synapses, a network of connections between the nerve cells, or neurons. Most neurocomputers have a conventional digital architecture and use mathematical models to invoke virtual neurons and synapses.

Alternatively, an actual on-chip electronic component could stand for each neuron and synapse in the network. This so-called analog approach has the potential to drastically speed up computations and reduce energy costs.

The core component of a hypothetical analog neurocomputer is the memristor. The word is a portmanteau of “memory” and “resistor,” which pretty much sums up what it is: a memory cell acting as a resistor. Loosely speaking, a high resistance encodes a zero, and a low resistance encodes a one. This is analogous to how a synapse conducts a signal between two neurons (one), while the absence of a synapse results in no signal, a zero.

But there is a catch: In an actual brain, the active synapses tend to strengthen over time, while the opposite is true for inactive ones. This phenomenon known as synaptic plasticity is one of the foundations of natural learning and memory. It explains the biology of cramming for an exam and why our seldom accessed memories fade.

Proposed in 2015, the second-order memristor is an attempt to reproduce natural memory, complete with synaptic plasticity. The first mechanism for implementing this involves forming nanosized conductive bridges across the memristor. While initially decreasing resistance, they naturally decay with time, emulating forgetfulness.

“The problem with this solution is that the device tends to change its behavior over time and breaks down after prolonged operation,” said the study’s lead author Anastasia Chouprik from MIPT’s Neurocomputing Systems Lab. “The mechanism we used to implement synaptic plasticity is more robust. In fact, after switching the state of the system 100 billion times, it was still operating normally, so my colleagues stopped the endurance test.”

Instead of nanobridges, the MIPT team relied on hafnium oxide to imitate natural memory. This material is ferroelectric: Its internal bound charge distribution — electric polarization — changes in response to an external electric field. If the field is then removed, the material retains its acquired polarization, the way a ferromagnet remains magnetized.

The physicists implemented their second-order memristor as a ferroelectric tunnel junction — two electrodes interlaid with a thin hafnium oxide film (fig. 1, right). The device can be switched between its low and high resistance states by means of electric pulses, which change the ferroelectric film’s polarization and thus its resistance.

“The main challenge that we faced was figuring out the right ferroelectric layer thickness,” Chouprik added. “Four nanometers proved to be ideal. Make it just one nanometer thinner, and the ferroelectric properties are gone, while a thicker film is too wide a barrier for the electrons to tunnel through. And it is only the tunneling current that we can modulate by switching polarization.”

What gives hafnium oxide an edge over other ferroelectric materials, such as barium titanate, is that it is already used by current silicon technology. For example, Intel has been manufacturing microchips based on a hafnium compound since 2007. This makes introducing hafnium-based devices like the memristor reported in this story far easier and cheaper than those using a brand-new material.

In a feat of ingenuity, the researchers implemented “forgetfulness” by leveraging the defects at the interface between silicon and hafnium oxide. Those very imperfections used to be seen as a detriment to hafnium-based microprocessors, and engineers had to find a way around them by incorporating other elements into the compound. Instead, the MIPT team exploited the defects, which make memristor conductivity die down with time, just like natural memories.

Vitalii Mikheev, the first author of the paper, shared the team’s future plans: “We are going to look into the interplay between the various mechanisms switching the resistance in our memristor. It turns out that the ferroelectric effect may not be the only one involved. To further improve the devices, we will need to distinguish between the mechanisms and learn to combine them.”

According to the physicists, they will move on with the fundamental research on the properties of hafnium oxide to make the nonvolatile random access memory cells more reliable. The team is also investigating the possibility of transferring their devices onto a flexible substrate, for use in flexible electronics.

Last year, the researchers offered a detailed description of how applying an electric field to hafnium oxide films affects their polarization. It is this very process that enables reducing ferroelectric memristor resistance, which emulates synapse strengthening in a biological brain. The team also works on neuromorphic computing systems with a digital architecture.

MIPT has provided this image illustrating the research,

Caption: The left image shows a synapse from a biological brain, the inspiration behind its artificial analogue (right). The latter is a memristor device implemented as a ferroelectric tunnel junction — that is, a thin hafnium oxide film (pink) interlaid between a titanium nitride electrode (blue cable) and a silicon substrate (marine blue), which doubles up as the second electrode. Electric pulses switch the memristor between its high and low resistance states by changing hafnium oxide polarization, and therefore its conductivity. Credit: Elena Khavina/MIPT Press Office

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

Ferroelectric Second-Order Memristor by Vitalii Mikheev, Anastasia Chouprik, Yury Lebedinskii, Sergei Zarubin, Yury Matveyev, Ekaterina Kondratyuk, Maxim G. Kozodaev, Andrey M. Markeev, Andrei Zenkevich, Dmitrii Negrov. ACS Appl. Mater. Interfaces 2019113532108-32114 DOI: https://doi.org/10.1021/acsami.9b08189 Publication Date:August 12, 2019 Copyright © 2019 American Chemical Society

This paper is behind a paywall.

Control your electronics devices with your clothing while protecting yourself from bacteria

Purdue University researchers have developed a new fabric innovation that allows the wearer to control electronic devices through the clothing. Courtesy: Purdue University

I like the image but do they really want someone pressing a cufflink? Anyway, being able to turn on your house lights and music system with your clothing would certainly be convenient. From an August 8, 2019 Purdue University (Indiana, US) news release (also on EurekAlert) by Chris Adam,

A new addition to your wardrobe may soon help you turn on the lights and music – while also keeping you fresh, dry, fashionable, clean and safe from the latest virus that’s going around.

Purdue University researchers have developed a new fabric innovation that allows wearers to control electronic devices through clothing.

“It is the first time there is a technique capable to transform any existing cloth item or textile into a self-powered e-textile containing sensors, music players or simple illumination displays using simple embroidery without the need for expensive fabrication processes requiring complex steps or expensive equipment,” said Ramses Martinez, an assistant professor in the School of Industrial Engineering and in the Weldon School of Biomedical Engineering in Purdue’s College of Engineering.

The technology is featured in the July 25 [2019] edition of Advanced Functional Materials.

“For the first time, it is possible to fabricate textiles that can protect you from rain, stains, and bacteria while they harvest the energy of the user to power textile-based electronics,” Martinez said. “These self-powered e-textiles also constitute an important advancement in the development of wearable machine-human interfaces, which now can be washed many times in a conventional washing machine without apparent degradation.

Martinez said the Purdue waterproof, breathable and antibacterial self-powered clothing is based on omniphobic triboelectric nanogeneragtors (RF-TENGs) – which use simple embroidery and fluorinated molecules to embed small electronic components and turn a piece of clothing into a mechanism for powering devices. The Purdue team says the RF-TENG technology is like having a wearable remote control that also keeps odors, rain, stains and bacteria away from the user.

“While fashion has evolved significantly during the last centuries and has easily adopted recently developed high-performance materials, there are very few examples of clothes on the market that interact with the user,” Martinez said. “Having an interface with a machine that we are constantly wearing sounds like the most convenient approach for a seamless communication with machines and the Internet of Things.”

The technology is being patented through the Purdue Research Foundation Office of Technology Commercialization. The researchers are looking for partners to test and commercialize their technology.

Their work aligns with Purdue’s Giant Leaps celebration of the university’s global advancements in artificial intelligence and health as part of Purdue’s 150th anniversary. It is one of the four themes of the yearlong celebration’s Ideas Festival, designed to showcase Purdue as an intellectual center solving real-world issues.

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

Waterproof, Breathable, and Antibacterial Self‐Powered e‐Textiles Based on Omniphobic Triboelectric Nanogenerators by Marina Sala de Medeiros, Daniela Chanci, Carolina Moreno, Debkalpa Goswami, Ramses V. Martinez. Advanced Functional Materials DOI: https://doi.org/10.1002/adfm.201904350 First published online: 25 July 2019

This paper is behind a paywall.

Gold sheets that are two atoms thick

The gold sheets in question are effectively 2D. I’m surprised they haven’t named them ‘goldene’ as everything else that’s 2D seems to have an ‘ene’ suffix (e.g. graphene, germanene, tellurene).

Of course, these gold sheets are not composed of single atoms but of two according to an August 6, 2019 news item on Nanowerk,

Scientists at the University of Leeds [UK] have created a new form of gold which is just two atoms thick – the thinnest unsupported gold ever created.

The researchers measured the thickness of the gold to be 0.47 nanometres – that is one million times thinner than a human finger nail. The material is regarded as 2D because it comprises just two layers of atoms sitting on top of one another. All atoms are surface atoms – there are no ‘bulk’ atoms hidden beneath the surface.

Caption: Image shows gold nanosheets that are just two atoms thick Credit: University of Leeds

I’m pretty sure they’ve added colour to those images and not just in the background; they’ve likely added a gold colour to the gold.

An August 6, 2019 University of Leeds press release (also on EurekAlert), which originated the news item, gives some insight into the scientists’ ambitions and some technical details about the work,

The material could have wide-scale applications in the medical device and electronics industries – and also as a catalyst to speed up chemical reactions in a range of industrial processes.

Laboratory tests show that the ultra-thin gold is 10 times more efficient as a catalytic substrate than the currently used gold nanoparticles, which are 3D materials with the majority of atoms residing in the bulk rather than at the surface.

Scientists believe the new material could also form the basis of artificial enzymes that could be applied in rapid, point-of-care medical diagnostic tests and in water purification systems.

The announcement that the ultra-thin metal had been successfully synthesised was made in the journal Advanced Science.

The lead author of the paper, Dr Sunjie Ye, from Leeds’ Molecular and Nanoscale Physics Group and the Leeds Institute of Medical Research, said: “This work amounts to a landmark achievement.

“Not only does it open up the possibility that gold can be used more efficiently in existing technologies, it is providing a route which would allow material scientists to develop other 2D metals.

“This method could innovate nanomaterial manufacturing.”

The research team are looking to work with industry on ways of scaling-up the process.

Synthesising the gold nanosheet takes place in an aqueous solution and starts with chloroauric acid, an inorganic substance that contains gold. It is reduced to its metallic form in the presence of a ‘confinement agent’ – a chemical that encourages the gold to form as a sheet, just two atoms thick.

Because of the gold’s nanoscale dimensions, it appears green in water – and given its shape, the researchers describe it as gold nanoseaweed.

Images taken from an electron microscope reveal the way the gold atoms have formed into a highly organised lattice. Other images show gold nanoseaweed that has been artificially coloured. The images are available for download: https://drive.google.com/drive/folders/
1-jxr7KW_RW4vF4-zReh9rnfOQMesb6MI?usp=sharing

Professor Stephen Evans, head of the Leeds’ Molecular and Nanoscale Research Group who supervised the research, said the considerable gains that could be achieved from using these ultra-thin gold sheets are down to their high surface-area to volume ratio.

He said: “Gold is a highly effective catalyst. Because the nanosheets are so thin, just about every gold atom plays a part in the catalysis. It means the process is highly efficient.”

Standard benchmark tests revealed that gold nanoscale sheets were ten times more efficient than the gold nanoparticles conventionally used in industry.

Professor Evans said: “Our data suggests that industry could get the same effect from using a smaller amount of gold, and this has economic advantages when you are talking about a precious metal.”

Similar benchmark tests revealed that the gold sheets could act as highly effective artificial enzymes.

The flakes are also flexible, meaning they could form the basis of electronic components for bendable screens, electronic inks and transparent conducting displays.

Professor Evans thinks there will inevitably be comparisons made between the 2D gold and the very first 2D material ever created – graphene, which was fabricated at the University of Manchester in 2004.

He said: “The translation of any new material into working products can take a long time and you can’t force it to do everything you might like to. With graphene, people have thought that it could be good for electronics or for transparent coatings – or as carbon nanotubes that could make an elevator to take us into space because of its super strength.

“I think with 2D gold we have got some very definite ideas about where it could be used, particularly in catalytic reactions and enzymatic reactions. We know it will be more effective than existing technologies – so we have something that we believe people will be interested in developing with us.”

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

Sub‐Nanometer Thick Gold Nanosheets as Highly Efficient Catalysts by Sunjie Ye, Andy P. Brown, Ashley C. Stammers, Neil H. Thomson, Jin Wen, Lucien Roach, Richard J. Bushby, Patricia Louise Coletta, Kevin Critchley, Simon D. Connell, Alexander F. Markham, Rik Brydson, Stephen D. Evans. Advnaced Science https://doi.org/10.1002/advs.201900911 First published: 06 August 2019

This paper is open access.

Make electricity by flowing water over nanolayers of metal

Scientists at Northwestern University (Chicago, Illinois) and the California Institute of Technology (CalTech) have developed what could be a more sustainable way to produce electricity. From a July 31, 2019 news item on Nanowerk,

Scientists from Northwestern University and Caltech have produced electricity by simply flowing water over extremely thin layers of inexpensive metals, including iron, that have oxidized. These films represent an entirely new way of generating electricity and could be used to develop new forms of sustainable power production.

A July 31, 2019 Northwester University news release (also on EurekAlert) by Megan Fellman, which originated the news item, provides details that suggest this discovery could prove beneficial in medical implants, as well as, in solar cells,

The films have a conducting metal nanolayer (10 to 20 nanometers thick) that is insulated with an oxide layer (2 nanometers thick). Current is generated when pulses of rainwater and ocean water alternate and move across the nanolayers. The difference in salinity drags the electrons along in the metal below.

“It’s the oxide layer over the nanometal that really makes this device go,” said Franz M. Geiger, the Dow Professor of Chemistry in Northwestern’s Weinberg College of Arts and Sciences. “Instead of corrosion, the presence of the oxides on the right metals leads to a mechanism that shuttles electrons.”

The films are transparent, a feature that could be taken advantage of in solar cells. The researchers intend to study the method using other ionic liquids, including blood. Developments in this area could lead to use in stents and other implantable devices.

“The ease of scaling up the metal nanolayer to large areas and the ease with which plastics can be coated gets us to three-dimensional structures where large volumes of liquids can be used,” Geiger said. “Foldable designs that fit, for instance, into a backpack are a possibility as well. Given how transparent the films are, it’s exciting to think about coupling the metal nanolayers to a solar cell or coating the outside of building windows with metal nanolayers to obtain energy when it rains.”

The study, titled “Energy Conversion via Metal Nanolayers,” was published this week [on July 29, 2019] in the journal Proceedings of the National Academy of Sciences (PNAS).

Geiger is the study’s corresponding author; his Northwestern team conducted the experiments. Co-author Thomas Miller, professor of chemistry at Caltech, led a team that conducted atomistic simulations to study the device’s behavior at the atomic level.

The new method produces voltages and currents comparable to graphene-based devices reported to have efficiencies of around 30% — similar to other approaches under investigation (carbon nanotubes and graphene) but with a single-step fabrication from earth-abundant elements instead of multistep fabrication. This simplicity allows for scalability, rapid implementation and low cost. Northwestern has filed for a provisional patent.

Of the metals studied, the researchers found that iron, nickel and vanadium worked best. They tested a pure rust sample as a control experiment; it did not produce a current.

The mechanism behind the electricity generation is complex, involving ion adsorption and desorption, but it essentially works like this: The ions present in the rainwater/saltwater attract electrons in the metal beneath the oxide layer; as the water flows, so do those ions, and through that attractive force, they drag the electrons in the metal along with them, generating an electrical current.

“There are interesting prospects for a variety of energy and sustainability applications, but the real value is the new mechanism of oxide-metal electron transfer,” Geiger said. “The underlying mechanism appears to involve various oxidation states.”

The team used a process called physical vapor deposition (PVD), which turns normally solid materials into a vapor that condenses on a desired surface. PVD allowed them to deposit onto glass metal layers only 10 to 20 nanometers thick. An oxide layer then forms spontaneously in air. It grows to a thickness of 2 nanometers and then stops growing.

“Thicker films of metal don’t succeed — it’s a nano-confinement effect,” Geiger said. “We have discovered the sweet spot.”

When tested, the devices generated several tens of millivolts and several microamps per centimeter squared.

“For perspective, plates having an area of 10 square meters each would generate a few kilowatts per hour — enough for a standard U.S. home,” Miller said. “Of course, less demanding applications, including low-power devices in remote locations, are more promising in the near term.”

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

Energy conversion via metal nanolayers by Mavis D. Boamah, Emilie H. Lozier, Jeongmin Kim, Paul E. Ohno, Catherine E. Walker, Thomas F. Miller III, and Franz M. Geiger. PNAS DOI: https://doi.org/10.1073/pnas.1906601116 First published July 29, 2019

This paper is behind a paywall.

Bringing a technique from astronomy down to the nanoscale

A January 2, 2020 Columbia University news release on EurekAlert (also on phys.org but published Jan. 3, 2020) describes research that takes the inter-galactic down to the quantum level,

Researchers at Columbia University and University of California, San Diego, have introduced a novel “multi-messenger” approach to quantum physics that signifies a technological leap in how scientists can explore quantum materials.

The findings appear in a recent article published in Nature Materials, led by A. S. McLeod, postdoctoral researcher, Columbia Nano Initiative, with co-authors Dmitri Basov and A. J. Millis at Columbia and R.A. Averitt at UC San Diego.

“We have brought a technique from the inter-galactic scale down to the realm of the ultra-small,” said Basov, Higgins Professor of Physics and Director of the Energy Frontier Research Center at Columbia. Equipped with multi-modal nanoscience tools we can now routinely go places no one thought would be possible as recently as five years ago.”

The work was inspired by “multi-messenger” astrophysics, which emerged during the last decade as a revolutionary technique for the study of distant phenomena like black hole mergers. Simultaneous measurements from instruments, including infrared, optical, X-ray and gravitational-wave telescopes can, taken together, deliver a physical picture greater than the sum of their individual parts.

The search is on for new materials that can supplement the current reliance on electronic semiconductors. Control over material properties using light can offer improved functionality, speed, flexibility and energy efficiency for next-generation computing platforms.

Experimental papers on quantum materials have typically reported results obtained by using only one type of spectroscopy. The researchers have shown the power of using a combination of measurement techniques to simultaneously examine electrical and optical properties.

The researchers performed their experiment by focusing laser light onto the sharp tip of a needle probe coated with magnetic material. When thin films of metal oxide are subject to a unique strain, ultra-fast light pulses can trigger the material to switch into an unexplored phase of nanometer-scale domains, and the change is reversible.

By scanning the probe over the surface of their thin film sample, the researchers were able to trigger the change locally and simultaneously manipulate and record the electrical, magnetic and optical properties of these light-triggered domains with nanometer-scale precision.

The study reveals how unanticipated properties can emerge in long-studied quantum materials at ultra-small scales when scientists tune them by strain.

“It is relatively common to study these nano-phase materials with scanning probes. But this is the first time an optical nano-probe has been combined with simultaneous magnetic nano-imaging, and all at the very low temperatures where quantum materials show their merits,” McLeod said. “Now, investigation of quantum materials by multi-modal nanoscience offers a means to close the loop on programs to engineer them.”

The excitement is palpable.

Caption: The discovery of multi-messenger nanoprobes allows scientists to simultaneously probe multiple properties of quantum materials at nanometer-scale spatial resolutions. Credit: Ella Maru Studio

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

Multi-messenger nanoprobes of hidden magnetism in a strained manganite by A. S. McLeod, Jingdi Zhang, M. Q. Gu, F. Jin, G. Zhang, K. W. Post, X. G. Zhao, A. J. Millis, W. B. Wu, J. M. Rondinelli, R. D. Averitt & D. N. Basov. Nature Materials (2019) doi:10.1038/s41563-019-0533-y Published: 16 December 2019

This paper is behind a paywall.