Nanomaterials that mimic nerve impulses (spikes) discovered

Nanomaterials that mimic nerve impulses (credit: Osaka University)

A combination of nanomaterials that can mimic nerve impulses (“spikes”) in the brain have been discovered by researchers at Kyushu Institute of Technology and Osaka University in Japan.

Current “neuromorphic” (brain-like) chips (such as IBM’s neurosynaptic TrueNorth) and circuits (such as those based on the NVIDIA GPGPU, or general purpose graphical processing unit) are devices based on complex circuits that emulate only one part of the brain’s mechanisms: the learning ability of synapses (which connect neurons together).

(Left) Schematic of the SWNT/POM complex network, showing single-wall nanotubes and polyoxometalate (POM) molecules, with gold contacts. (Right) Conductive atomic force microscope image of a molecular neuromorphic network device. (Inset) Molecular structure of polyoxometalate (POM) molecules. (credit: Hirofumi Tanaka et al./Nature Communications)

The researchers have now developed a way to simulate a large-scale spiking neural network. They created a complex SWNT/POM molecular neuromorphic device consisting of a dense and complex network of spiking molecules. The new nanomaterial comprises polyoxometalate (POM) molecules that are absorbed by single-wall carbon nanotubes (SWNTs).

Unlike ordinary organic molecules, POM consists of metal atoms and oxygen atoms that form a three-dimensional framework that can store charges in a single molecule. The new nanomaterial emits spikes and can transmit them via synapses to and from other neurons.

The researchers also demonstrated that this molecular model could be used as a component of reservoir computing devices, which are anticipated as next-generation neural network devices.

Ref: Nature Communications (open access). Source: Osaka University

Overcoming transistor miniaturization limits due to ‘quantum tunneling’

An illustration of a single-molecule device that blocks leakage current in a transistor (yellow: gold transistor electrodes) (credit: Haixing Li/Columbia Engineering)

A team of researchers at Columbia Engineering and associates* have synthesized a molecule that could overcome a major physical limit to miniaturizing computer transistors at the nanometer scale (under about 3 nanometers) — caused by “leakage current.”

Leakage current between two metal transistor electrodes results when the gap between the electrodes narrows to the point that electrons are no longer contained by their barriers — a phenomenon known as quantum tunneling.

The researchers synthesized the first molecule** capable of insulating (preventing electron flow) at the nanometer scale more effectively than a vacuum barrier (the traditional approach). The molecule bridges the nanometer gap between two metal electrodes.

Constructive interference (left) between two waves increases the resulting wave; destructive interference (right) decreases the resulting wave. (credit: Wikipedia)

The silicon-based molecule design uses “destructive quantum interference,” which occurs when the peaks and valleys of two waves are placed exactly out of phase, annulling oscillation.

“We’ve reached the point where it’s critical for researchers to develop creative solutions for redesigning insulators. Our molecular strategy represents a new design principle for classic devices, with the potential to support continued miniaturization in the near term,” said Columbia Engineering physicist Latha Venkataraman, Ph.D.

The research bucks the trend of most research in transistor miniaturization, which aims to create highly conducting contact electrodes, typically using carbon nanotubes (see “Method to replace silicon with carbon nanotubes developed by IBM Research”).

* Other researchers on the team were from Columbia University Department of Chemistry, Shanghai Normal University, and the University of Copenhagen.

** The molecule is bicyclo[2.2.2]octasilane.

Self-healing material mimics the resilience of soft biological tissue

A self-healing material that spontaneously repairs itself in real time from extreme mechanical damage, such as holes cut in it multiple times. New pathways are formed instantly and autonomously to keep this circuit functioning and the device moving. (credit: Carnegie Mellon University College of Engineering)

Carnegie Mellon University (CMU) researchers have created a self-healing material that spontaneously repairs itself under extreme mechanical damage, similar to many natural organisms. Applications include bio-inspired first-responder robots that instantly heal themselves when damaged and wearable computing devices that recover from being dropped.

The new material is composed of liquid metal droplets suspended in a soft elastomer (a material with elastic properties, such as rubber). When damaged, the droplets rupture to form new connections with neighboring droplets, instantly rerouting electrical signals. Circuits produced with conductive traces of this material remain fully and continuously operational when severed, punctured, or have material removed.

“Other research in soft electronics has resulted in materials that are elastic, but are still vulnerable to mechanical damage that causes immediate electrical failure,” said Carmel Majidi, PhD, a CMU associate professor of mechanical engineering, who also directs the Integrated Soft Materials Laboratory. “The unprecedented level of functionality of our self-healing material can enable soft-matter electronics and machines to exhibit the extraordinary resilience of soft biological tissue and organisms.”

The self-healing material also exhibits high ability to conduct electricity, which is not affected when stretched. That makes it ideal for uses in power and data transmission, as a health-monitoring device on an athlete during rigorous training, or an inflatable structure that can withstand environmental extremes on Mars, for example.

Reference: Nature Materials. Source: Carnegie Mellon University.

Magnetically storing a bit on a single atom — the ultimate future data storage

Dysprosium atoms (green) on the surface of nanoparticles can be magnetized in one of two possible directions: “spin up” or “spin down.” (credit: ETH Zurich / Université de Rennes)

Imagine you could store a bit on a single atom or small molecule — the ultimate magnetic data-storage system. An international team of researchers led by chemists from ETH Zurich has taken a step toward that idea by depositing single magnetizable atoms onto a silica surface, with the atoms retaining their magnetism.

In theory, certain atoms can be magnetized in one of two possible directions: “spin up” or “spin down” (representing zero or one); information could then be stored and read based on the sequence of the molecules’ magnetic spin directions. But finding molecules that can store the magnetic information permanently is a challenge, and it’s even more difficult to arrange these molecules on a solid surface to build actual data storage devices.

Magnetizing atoms on nanoparticles

Strategy for immobilization of dysprosium atoms (blue, surrounded by molecular scaffold) on a silica nanoparticle surface, based on a grafting step (a) and a thermolytic (chemical decomposition caused by heat) step (b) (credit: Florian Allouche et al./ ACS Central Science)

Nonetheless, Christophe Copéret, a professor at the Laboratory of Inorganic Chemistry at ETH Zurich, and his team have developed a method using a dysprosium atom (dysprosium is a metal belonging to the rare-earth elements). The atom is surrounded by a molecular scaffold that serves as a vehicle. The scientists also developed a method for depositing such molecules on the surface of silica nanoparticles and fusing them by annealing (heating) at 400 degrees Celsius.

The scaffold molecular structure disintegrates in the process, yielding nanoparticles with dysprosium atoms well-dispersed at the surface. The scientists showed that these atoms can then be magnetized and that they maintain their magnetic information.

One advantage of their new method is its simplicity. Nanoparticles bonded with dysprosium can be made in any chemical laboratory. No cleanroom and complex equipment required. And the magnetizable nanoparticles can be stored at room temperature and re-utilized.

Their magnetization process currently only works at around minus 270 degrees Celsius (near absolute zero), and the magnetization can only be maintained for up to one and a half minutes. So the scientists are now looking for methods that will allow the magnetization to be stabilized at higher temperatures and for longer periods of time. They are also looking for ways to fuse atoms to a flat surface instead of to spherical nanoparticles.

Other preparation methods also involve direct deposition of individual atoms onto a surface, but the materials are only stable at very low temperatures, mainly due to the agglomeration of these individual atoms. Alternatively, molecules with ideal magnetic properties can be deposited onto a surface, but this immobilization often negatively affects the structure and the magnetic properties of the final object.

Scientists from the Universities of Lyon and Rennes, Collège de France in Paris, Paul Scherrer Institute in Switzerland, and Berkeley National Laboratory were involved in the research.

Abstract of Magnetic Memory from Site Isolated Dy(III) on Silica Materials

Achieving magnetic remanence at single isolated metal sites dispersed at the surface of a solid matrix has been envisioned as a key step toward information storage and processing in the smallest unit of matter. Here, we show that isolated Dy(III) sites distributed at the surface of silica nanoparticles, prepared with a simple and scalable two-step process, show magnetic remanence and display a hysteresis loop open at liquid 4He temperature, in contrast to the molecular precursor which does not display any magnetic memory. This singular behavior is achieved through the controlled grafting of a tailored Dy(III) siloxide complex on partially dehydroxylated silica nanoparticles followed by thermal annealing. This approach allows control of the density and the structure of isolated, “bare” Dy(III) sites bound to the silica surface. During the process, all organic fragments are removed, leaving the surface as the sole ligand, promoting magnetic remanence.