Tag Archives: Queen Mary University of London (QMUL)

A step forward for graphene-based memristors

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This research comes from the UK according to an October 26, 2024 news item on phys.org, Note: A link has been removed,

Researchers from Queen Mary University of London and Paragraf Limited have demonstrated a significant step forward in the development of graphene-based memristors and unlocking their potential for use in future computing systems and artificial intelligence (AI).

This innovation, published in ACS Advanced Electronic Materials [this should be ACS Applied Electronic Materials] and featured on the cover of this month’s issue, has been achieved at wafer scale. It begins to pave the way toward scalable production of graphene-based memristors, which are devices crucial for non-volatile memory and artificial neural networks (ANNs).

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An October 23, 2024 Queen Mary University of London press release, which originated the news item, explains why memristors are important and gives a little information about the researchers’ solution to a problem with incorporating them into electronics,

Memristors are recognised as potential game-changers in computing, offering the ability to perform analogue computations, store data without power, and mimic the synaptic functions of the human brain. The integration of graphene, a material just one atom thick with the highest electron mobility of any known substance, can enhance these devices dramatically, but has been notoriously difficult to incorporate into electronics in a scalable way until recently. “Graphene electrodes bring clear benefits to memristor technology,” says Dr Zhichao Weng, Research Scientist at School of Physical and Chemical Sciences at Queen Mary. “They offer not only improved endurance but also exciting new applications, such as light-sensitive synapses and optically tuneable memories.”

One of the key challenges in memristor development is device degradation, which graphene can help prevent. By blocking chemical pathways that degrade traditional electrodes, graphene could significantly extend the lifetime and reliability of these devices. Its remarkable transparency, transmitting 98% of light, also opens doors to advanced computing applications, particularly in AI and optoelectronics.

This research is a key step on the way to graphene electronics scalability. Historically, producing high-quality graphene compatible with semiconductor processes has been a significant hurdle. Paragraf’s proprietary Metal-Organic Chemical Vapour Deposition (MOCVD) process, however, has now made it possible to grow monolayer graphene directly on target substrates. This scalable approach is already being used in commercial devices like graphene-based Hall effect sensors and field-effect transistors (GFETs).

“The opportunity for graphene to help in creating next generation computing devices that can combine logic and storage in new ways gives opportunities in solving the energy costs of training large language models in AI,” says John Tingay, CTO at Paragraf. “This latest development with Queen Mary University of London to deliver a memristor proof of concept is an important step in extending graphene’s use in electronics from magnetic and molecular sensors to proving how it could be used in future logic and memory devices.”

The team used a multi-step photolithography process to pattern and integrate the graphene electrodes into memristors, producing reproducible results that point the way to large-scale production. “Our research not only establishes proof of concept but also confirms graphene’s suitability for enhancing memristor performance over other materials,” adds Professor Oliver Fenwick, Professor of Electronic Materials at Queen Mary’s School of Engineering and Materials Science.

This work, part of an Innovate UK Knowledge Transfer Partnership between Queen Mary and Paragraf, is a new milestone in expanding graphene’s role in the semiconductor industry.

Cover of ACS Applied Electronic Materials October issue
Cover of ACS Applied Electronic Materials October issue

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

Memristors with Monolayer Graphene Electrodes Grown Directly on Sapphire Wafers by Zhichao Weng, Robert Wallis, Bryan Wingfield, Paul Evans, Piotr Baginski, Jaspreet Kainth, Andrey E. Nikolaenko, Lok Yi Lee, Joanna Baginska, William P. Gillin, Ivor Guiney, Colin J. Humphreys, Oliver Fenwick. ACS Appl. Electron. Mater. 2024, 6, 10, 7276–7285 DOI: https://doi.org/10.1021/acsaelm.4c01208 Published September 16, 2024

This article appears to be open access.

You can find Paragraf here.

A candy cane supercapacitor?

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Courtesy: Queen Mary University of London

It takes a lot more imagination than I have to describe the object on the right as resembling the  candy cane on the left, assuming that’s what was intended when it was used to illustrate the university’s press release. I like being pushed to see resemblances to things that are not immediately apparent to me. This may never look like a candy cane to me but I appreciate that someone finds it to be so. An August 16, 2017 news item on ScienceDaily announces the ‘candy cane’ supercapacitor,

Supercapacitors promise recharging of phones and other devices in seconds and minutes as opposed to hours for batteries. But current technologies are not usually flexible, have insufficient capacities, and for many their performance quickly degrades with charging cycles.

Researchers at Queen Mary University of London (QMUL) and the University of Cambridge have found a way to improve all three problems in one stroke.

Their prototyped polymer electrode, which resembles a candy cane usually hung on a Christmas tree, achieves energy storage close to the theoretical limit, but also demonstrates flexibility and resilience to charge/discharge cycling.

The technique could be applied to many types of materials for supercapacitors and enable fast charging of mobile phones, smart clothes and implantable devices.

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The Aug. 16, 2017 Queen Mary University of London (QMUL) press release (also on EurekAlert), which originated the news item, provides more detail about the technology,

Pseudocapacitance is a property of polymer and composite supercapacitors that allows ions to enter inside the material and thus pack much more charge than carbon ones that mostly store the charge as concentrated ions (in the so-called double layer) near the surface.

The problem with polymer supercapacitors, however, is that the ions necessary for these chemical reactions can only access the top few nanometers below the material surface, leaving the rest of the electrode as dead weight. Growing polymers as nano-structures is one way to increase the amount of accessible material near the surface, but this can be expensive, hard to scale up, and often results in poor mechanical stability.

The researchers, however, have developed a way to interweave nanostructures within a bulk material, thereby achieving the benefits of conventional nanostructuring without using complex synthesis methods or sacrificing material toughness.

Project leader, Stoyan Smoukov, explained: “Our supercapacitors can store a lot of charge very quickly, because the thin active material (the conductive polymer) is always in contact with a second polymer which contains ions, just like the red thin regions of a candy cane are always in close proximity to the white parts. But this is on a much smaller scale.

“This interpenetrating structure enables the material to bend more easily, as well as swell and shrink without cracking, leading to greater longevity. This one method is like killing not just two, but three birds with one stone.”

The outcomes

The Smoukov group had previously pioneered a combinatorial route to multifunctionality using interpenetrating polymer networks (IPN) in which each component would have its own function, rather than using trial-and-error chemistry to fit all functions in one molecule.

This time they applied the method to energy storage, specifically supercapacitors, because of the known problem of poor material utilization deep beneath the electrode surface.

This interpenetration technique drastically increases the material’s surface area, or more accurately the interfacial area between the different polymer components.

Interpenetration also happens to solve two other major problems in supercapacitors. It brings flexibility and toughness because the interfaces stop growth of any cracks that may form in the material. It also allows the thin regions to swell and shrink repeatedly without developing large stresses, so they are electrochemically resistant and maintain their performance over many charging cycles.

The researchers are currently rationally designing and evaluating a range of materials that can be adapted into the interpenetrating polymer system for even better supercapacitors.

In an upcoming review, accepted for publication in the journal Sustainable Energy and Fuels, they overview the different techniques people have used to improve the multiple parameters required for novel supercapacitors.

Such devices could be made in soft and flexible freestanding films, which could power electronics embedded in smart clothing, wearable and implantable devices, and soft robotics. The developers hope to make their contribution to provide ubiquitous power for the emerging Internet of Things (IoT) devices, which is still a significant challenge ahead.

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

Semi-Interpenetrating Polymer Networks for Enhanced Supercapacitor Electrodes by Kara D. Fong, Tiesheng Wang, Hyun-Kyung Kim, R. Vasant Kumar, and Stoyan K. Smoukov. ACS Energy Lett., 2017, 2, pp 2014–2020 DOI: 10.1021/acsenergylett.7b00466 Publication Date (Web): August 14, 2017

Copyright © 2017 American Chemical Society

This paper is behind a paywall.

Reindeer antlers and resistance to breakage

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The press office at Queen Mary University of London (UK) must have had fun with the press release (titled, Rudolph’s antlers inspire next generation of unbreakable materials) for this timely piece of research. From a Dec. 19, 2016 news item on ScienceDaily,

Scientists from Queen Mary University of London (QMUL) have discovered the secret behind the toughness of deer antlers and how they can resist breaking during fights.

The team looked at the antler structure at the ‘nano-level’, which is incredibly small, almost one thousandth of the thickness of a hair strand, and were able to identify the mechanisms at work, using state-of-the-art computer modelling and x-ray techniques.

A Dec. 19, 2016 QMUL press release on EurekAllert, which originated the news item, provides a bit more detail,

First author Paolino De Falco from QMUL’s School of Engineering and Materials Science said: “The fibrils that make up the antler are staggered rather than in line with each other. This allows them to absorb the energy from the impact of a clash during a fight.”

The research, published today [Dec. 19, 2016] in the journal ACS Biomaterials Science & Engineering, provides new insights and fills a previous gap in the area of structural modelling of bone. It also opens up possibilities for the creation of a new generation of materials that can resist damage.

Co-author Dr Ettore Barbieri, also from QMUL’s School of Engineering and Materials Science, said: “Our next step is to create a 3D printed model with fibres arranged in staggered configuration and linked by an elastic interface.

The aim is to prove that additive manufacturing – where a prototype can be created a layer at a time – can be used to create damage resistant composite material.”

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

Staggered fibrils and damageable interfaces lead concurrently and independently to hysteretic energy absorption and inhomogeneous strain fields in cyclically loaded antler bone by Paolino De Falco, Ettore Barbieri, Nicola M. Pugno, and Himadri S. Gupta. ACS Biomater. Sci. Eng., Just Accepted Manuscript DOI: 10.1021/acsbiomaterials.6b00637 Publication Date (Web): December 19, 2016

Copyright © 2016 American Chemical Society

This paper is behind a paywall.