nanotechnology (15)

Xenobots...

 

Topics: Applied Physics, Biology, Nanotechnology, Robotics


A team of researchers have built what they claim to be the first living robots. The “xenobots,” they say, can move, pick up objects, and even heal themselves after being cut.

The team is hoping the biological machines could one day be used to clean up microplastics in the ocean or even deliver drugs inside the human body, The Guardian reports.

To build the robots, the team used living cells from frog embryos and assembled them into primitive beings.

“These are novel living machines,” research co-lead Joshua Bongard, robotics expert at the University of Vermont, said in a statement. “They’re neither a traditional robot nor a known species of animal. It’s a new class of artifact: a living, programmable organism.”

The millimeter-length robots were designed by a supercomputer running an “evolutionary algorithm” that tested thousands of 3D designs for rudimentary life forms inside a simulation. The scientists then built a handful of the designs, which were able to propel themselves forward or fulfill a basic task inside the simulation using tweezers and cauterizing tools.

The tiny robots had about a week to ten days of “power” courtesy of living heart muscle cells that were able to expand and contract on their own.

 

Scientists Build “First Living Robots” From Frog Stem Cells
Victor Tangermann, Futurism

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Nonvolatile Charge Memory...

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Light irradiation-controlled nonvolatile charge memory. Left: schematic of the memory device. Right: the optical-controlled writing and erasing process of source-drain current. (Courtesy: Q Li et al J. Phys. D: Appl. Phys. 10.1088/1361-6463/ab5737)

 

Topics: Applied Physics, Device Physics, Electrical Engineering, Materials Science, Nanotechnology


Qinliang Li, Cailei Yuan and Ting Yu from Jiangxi Normal University, along with Qisheng Wang and Jingbo Li from South China Normal University, are developing nonvolatile charge memory devices with simple structures. Wang explains how the optically controllable devices combine the functions of light sensing and electrical storage.

The research is reported in full in Journal of Physics D: Applied Physics, published by IOP Publishing – which also publishes Physics World.

What was the motivation for the research and what problem were you trying to solve?

 


Nonvolatile memory devices are central to modern communication and information technology. Among various material systems, emerging two dimensional (2D) materials offer a promising platform for next-generation data-storage devices due to their unique planar structure and brilliant electronic properties. However, 2D materials-based nonvolatile memory devices have complicated architectures with multilayer stacking of 2D materials, metals, organics or oxides. This limits the capacity for device miniaturization, scalability and integration functionality.

 


In this work, we are trying to design a nonvolatile charge memory with simple device architecture. We also expect to explore a new type of optical control on the charge storage devices, which may bring us smart operation on data deposition and communication.

 

Nonvolatile charge memory device shows excellent room-temperature performance, Physics World
Qisheng Wang is professor at the Institute of Semiconductor Science and Technology, South China Normal University

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Electron River...

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A river made of graphene with the electrons flowing like water.
Courtesy: Ryan Allen and Peter Allen, Second Bay Studios

 

Topics: Electron Configuration, Graphene, Nanotechnology


Electrons can behave like a viscous liquid as they travel through a conducting material, producing a spatial pattern that resembles water flowing through a pipe. So say researchers in Israel and the UK who have succeeded in imaging this hydrodynamic flow pattern for the first time using a novel scanning probe technique. The result will aid developers of future electronic devices, especially those based on 2D materials like graphene in which electron hydrodynamics is important.

We are all familiar with the distinctive patterns formed by water flowing in a river or stream. When the water encounters an obstacle – such as the river bank or a boat – the patterns change. The same should hold true for electron flow in a solid if the interactions between electrons are strong. This rarely occurs under normal conditions, however, since electrons tend to collide with defects and impurities in the material they travel through, rather than with each other.

Making electrons hydrodynamic

Conversely, if a material is made very clean and cooled to low temperatures, it follows that electrons should travel across it unperturbed until they collide with its edges and walls. The resulting ballistic transport allows electrons to flow with a uniform current distribution because they move at the same rate near the walls as at the center of the material.

If the temperature of this material is then increased, the electrons can begin to interact. In principle, they will then scatter off each other more frequently than they collide with the walls. In this highly interacting, hydrodynamic regime, the electrons should flow faster near the center of a channel and slower near its walls – the same way that water behaves when it flows through a pipe.

 

Electrons flow like water in ultra-pure graphene, Belle Dumé, Physics World

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The Next FET...

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Source: Modeling Carbon Nanotube FET Physics in COMSOL Multiphysics®
 

Topics: Applied Physics, Carbon Nanotubes, Field Effect Transistors, Nanotechnology


Silicon field-effect transistors (FETs) were developed in the late 1950s as a scaled-down, energy-efficient substitute for bipolar junction transistors. They paved the way for the high-density integrated circuits that today underlie most electronics (see the article by Alan Fowler, Physics Today, October 1993, page 59). With their lower gate voltages, carbon nanotube FETs could surpass silicon FET energy efficiency by nearly a factor of 10. In 2013 Subhasish Mitra, Max Shulaker (then at Stanford University), and coworkers made the first CNFET microprocessor; it comprised 178 transistors and could run a single operation.

Variability caused by the production process has made moving beyond that proof-of-concept computer challenging. Gage Hills, Christian Lau, and coworkers in Shulaker’s group at MIT have now overcome that hurdle with a protocol for wafer-scale CNFET microprocessor production. Their technique is also compatible with existing CMOS infrastructure, which lowers the bar for future commercial implementation.

To remove carbon nanotube aggregates—a common contaminant from CNT deposition on silicon wafers—the researchers spin-coated a layer of adhesive polymer over the device and then removed the aggregates using ultrasonic vibrations. In previous attempts, sonication damaged the nonaggregated CNTs. Using the photoresist binds them to the wafer, which preserves their function while removing more than 99% of the aggregates.

 

Production of carbon nanotube microprocessors gets scaled up
Christine Middleton, Physics Today

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2D MXenes...

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Helper two-dimensional metal-carbide layers could improve perovskite solar cell stability and help make these complex solar cells a viable green energy option. Credit: iStock Milos-Muller

 

Topics: Condensed Matter Physics, Green Tech, Materials Science, Metamaterials, Nanotechnology, Solar Power


With the reality of climate change looming, the importance of realistic green energy sources is higher than ever. Solar cells are one promising avenue, as they can convert readily available visible and ultraviolet energy into usable electricity. In particular, perovskite materials sandwiched between other support layers have demonstrated impressive power conversion efficiencies. Current challenges reside in optimizing perovskite/support layer interfaces, which can directly impact power conversion and cell degradation. Researchers Antonio Agresti et al. under the direction of Aldo Di Carlo at the University of Rome Tor Vergata in Italy have investigated how cells containing two-dimensional titanium-carbide MXene support layers could improve perovskite solar cell performance.

To obtain good power conversion within a perovskite solar cell, all layers and layer interfaces within the cell must have good compatibility. Typical cells contain the active perovskite material sandwiched between two charge transport layers, which are then adjacent to their corresponding electrodes. Support layers may also be added. Charge mobility, energy barriers, interface energy alignment, and interfacial vacancies all impact compatibility and subsequent cell performance and stability. Thus, engineering well-suited interfaces with the cell is paramount to cell success and long-term stability, an important criterion for potential commercialization.

Two-dimensional buffer materials could help to modify and promote useful interface interactions. MXenes, a growing class of two-dimensional transitional metal carbides, nitrides, and carbonitrides, have shown impressive electronic properties that are easily tuned via surface modification. For example, the band gap of an MXene can be modified by changing the surface termination group from an oxygen atom to a hydroxide molecule. Additionally, MXene composition impacts the overall material performance. This type of fine-tuning allows impressive control over MXene properties and makes them ideal for interface adjustments.

 

Two-dimensional MXenes improve perovskite solar cell efficiency
Amanda Carr, Physics World

#P4TC: MXenes...August 24, 2015

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Boiling Superconductivity...

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Under pressure: calculated structure of lithium magnesium hydride. Lithium atoms appear in green, magnesium in blue and hydrogen in red. (Courtesy: Ying Sun et al/Phys. Rev. Lett.)

 

Topics: Chemistry, Materials Science, Nanotechnology, Superconductors


A material that remains a superconductor when heated to the boiling point of water has been predicted by physicists in China. Hanyu Liu, Yanming Ma and colleagues at Jilin University have calculated that lithium magnesium hydride will superconduct at temperatures as high as 473 K (200 °C).

The catch is that the hydrogen-rich material must be crushed at 250 GPa, which is on par with pressures at the center of the Earth. While such a pressure could be achieved in the lab, it would be very difficult to perform an experiment to verify the prediction. The team’s research could, however, lead to the discovery of more practical high-temperature superconductors.

Superconductors are materials that, when cooled below a critical temperature, will conduct electricity with zero resistance. Most superconductors need to be chilled to very low temperatures, so the holy grail of superconductivity research is to find a substance that will superconduct at room temperature. This would result in lossless electricity transmission and boost technologies that rely on the generation or detection of magnetic fields.

 

Superconductivity at the boiling temperature of water is possible, say physicists
Hamish Johnston, Physics World

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Nanocones...

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A carbon nanocone includes nitrogen atoms around the periphery to improve the material’s solubility. Carbon atoms are shown in gray; hydrogen in white; nitrogen in blue; and oxygen in red.

 

Topics: Applied Physics, Chemistry, Graphene, Nanotechnology


Graphene, buckyballs, and carbon nanotubes now have a new family member, the nanocone, adding to the types of all-carbon nanostructures with remarkable electronic and optical characteristics and bringing its own promising properties. (J. Am. Chem. Soc., 2019, DOI: 10.1021/jacs.9b06617) Such molecules could be useful for developing efficient organic solar cells or as sensor molecules.

Organic chemist Frank Würthner and postdoctoral researcher Kazutaka Shoyama of the University of Würzburg came up with the method for synthesizing the nanocones, which are 1.68 nm in diameter and 0.432 nm tall. A five-atom ring of carbons forms the cone’s tip. The team used a cross-coupling annulation cascade to add hexagons around the edges of the ring until the molecule grew to 80 carbons. The team added five nitrogen atoms around the periphery of the cone, increasing the crystal’s solubility.

 

Nanocones extend the graphene toolbox, Neil Savage, Chemical & Engineering News

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Decoding Sweat...

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New wearable sensors developed by scientists at UC Berkeley can provide real-time measurements of sweat rate and electrolytes and metabolites in sweat. (Credit: Bizen Maskey, Sunchon National University)

 

Topics: Biophysics, Biotechnology, Microfluidics, Nanotechnology, Research


A new scalable, high-throughput fabrication process that makes use of roll-to-roll printing and laser cutting can produce wearable sweat sensors rapidly and reliably and on a large scale. The devices, which can almost instantly detect and analyse electrolytes, metabolites and other biomolecules contained in sweat, could be employed in real-world applications and not just as laboratory prototypes.

Analyzing sweat is a non-invasive way to monitor a range of biomolecules, from small electrolytes to metabolites and hormones and larger proteins that come from deeper in the body. Indeed, sweat sensing has already been used to medically diagnose diseases like cystic fibrosis and autonomic neuropathy and to assess fluid and electrolyte balance in endurance athletes.

Traditional sweat sensors collect sweat from the body at different times and then analyse it. This means that the devices can’t be used to detect real-time changes in sweat composition – during physical activity, for example, or to monitor glucose levels in diabetic patients. Wearable sensors, which make use of flexible and hybrid electronics, overcome this problem by allowing for in-situ sweat measurements with real-time feedback. However, it is still difficult to reliably make sweat sensor components (including microfluidic chip and sensing electrodes) in large quantities and with good reproducibility.

 

Wearable patches could ‘decode’ sweat, Belle Dumé, Physics World

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Lamina Tenuissima...

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Illustration of a tungsten disulfide monolayer suspended in air and patterned with a square array of nanoholes. Upon laser excitation, the monolayer emits photoluminescence. A portion of this light couples into the monolayer and is guided along the material. At the nanohole array, periodic modulation in the refractive index causes a small portion of the light to decay out of the plane of the material, allowing the light to be observed as guided mode resonance. Courtesy: E Cubukcu, UCSD

 

Note: lamina tenuissima = thinnest (Latin)

Topics: Applied Physics, Nanotechnology, Optical Physics, Photonics


Researchers have succeeded in making the thinnest ever optical device in the form of a waveguide just three atomic layers thick. The device could lead to the development of higher density optoelectronic chips.

Optical waveguides are crucial components in data communication technologies but scaling them down to the nanoscale has proved to be no easy task, despite important advances in nano-optics and nanomaterials. Indeed, the thinnest waveguide used in commercial applications today is hundreds of nanometres thick and researchers are studying nanowire waveguides down to 50 nm in the laboratory.

“We have now pushed this limit down to just three atoms thick,” says Ertugrul Cubukcu of the University of California at San Diego, who led this new research effort. “Such a thin waveguide, which is at the ultimate limit for how thin an optical waveguide can be built, might potentially lead to a higher density of waveguides or optical elements on an optoelectronic chip – in the same way that ever smaller transistors have led to a higher density of these devices on an electronic chip.”

Cubukcu and colleagues’ waveguide is just six angstroms thick. This makes it 104 times thinner than a typical optical fiber and about 500 times thinner than on-chip optical waveguides in integrated photonic circuits.

 

Three-atom-thick optical waveguide is the thinnest ever, Belle Dumé, Physics World

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Cyclocarbon...

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From left to right, precursor molecule C24O6, intermediates C22O4 and C20O2 and the final product cyclo [18]carbon C18 created on surface by dissociating CO masking groups using atom manipulation. The bottom row shows atomic force microscopy (AFM) data using a CO functionalized tip. Credit: IBM Research

 

Topics: Applied Physics, Atomic Force Microscopy, Chemistry, Nanotechnology, Research


A team of researchers from Oxford University and IBM Research has for the first time successfully synthesized the ring-shaped multi-carbon compound cyclocarbon. In their paper published in the journal Science, the group describes the process they used and what they learned about the bonds that hold a cyclocarbon together.

Carbon is one of the most abundant elements, and has been found to exist in many forms, including diamonds and graphene. The researchers with this new effort note that much research has been conducted into the more familiar forms (allotropes) how they are bonded. They further note that less well-known types of carbon have not received nearly as much attention. One of these, called cyclocarbon, has even been the topic of debate. Are the two-neighbor forms bonded by the same length bonds, or are there alternating bonds of shorter and longer lengths? The answer to this question has been difficult to find due to the high reactivity of such forms. The researchers with this new effort set themselves the task of finding the answer once and for all.

The team's approach involved creating a precursor molecule and then whittling it down to the desired form. To that end, they used atomic force microscopy to create linear lines of carbon atoms atop a copper substrate that was covered with salt to prevent the carbon atoms from bonding with the subsurface. They then joined the lines of atoms to form the carbon oxide precursor C24O6, a triangle-shaped form. Next, the team applied high voltage through the AFM to shear off one of the corners of the triangle, resulting in a C22O4 form. They then did the same with the other two corners. The result was a C18 ring—an 18-atom cyclocarbon. After creating the ring, the researchers found that the bonds holding it together were the alternating long- and short-type bonds that had been previously suggested.

 

Ring-shaped multi-carbon compound cyclocarbon synthesized, Bob Yirka , Phys.org

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Smart Packaging...

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Cheaper flexible integrated circuits open up new markets. (Courtesy: PragmatIC)

 

Topics: Applied Physics, Moore's Law, Semiconductor Technology, Nanotechnology


For more than 50 years, progress in the electronics industry has been guided by Moore’s law: the idea that the number of transistors in a silicon-based integrated circuit (IC) will double approximately every 18 months. The consequences of this doubling include a continual reduction in the size of silicon ICs, as it becomes possible to provide increasingly complex and high-performance functionality in smaller and smaller areas of silicon, and at progressively lower cost relative to the circuits’ processing power.

Moore’s law is an empirical rule of thumb rather than a robust physical principle, and much has been written about how, why and when it will eventually fail. But even before we reach that point, manufacturers are already finding that, in practice, the cost savings associated with reducing the size, or “footprint”, of ICs will only carry them so far. The reason is that below a certain minimum size, ICs become difficult to handle easily or effectively. For highly complex circuitry, such as that found in computers with many millions of transistors in a single IC, this limit on handling size may not be a consideration. However, for applications that require less complex circuits, the size constraint imposed by the physical aspect of handling ICs becomes a limiting factor in their cost.

The approach we have taken at PragmatIC is to use thin, flexible substrates, rather than rigid silicon, as the base for building our circuits. The low cost of the materials involved and the relatively low complexity of our target applications alters the economics around circuit footprint and overall IC cost. Accepting a larger footprint can lower capital expenditure because it means that ultrahigh-end precision tooling is not required to fabricate our circuits during the manufacturing process. In turn, for low-complexity applications, this can lead to a lower final IC cost.

The resulting flexible integrated circuits, or FlexICs, are thinner than a human hair, so they can easily be embedded in everyday objects. They also cost around 10 times less than silicon ICs, making it economically viable for them to appear in trillions of smart objects that engage with consumers and their environments. Since the technology was developed, PragmatIC FlexICs have been trialed in a wide variety of markets, including consumer goods, games, retail, and the pharmaceutical and security sectors.

 

A smart approach to smart packaging
Catherine Ramsdale is vice-president of device development at PragmatIC

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TBG and Ferromagnets...

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Magic angle graphene superlattice. Scale=10 nm. Courtesy: P Jarillo-Herrero

 

Topics: Ferromagnetism, Graphene, Hall Effect, Magnetic Resonance Imaging, Nanotechnology


Researchers have found that electrons organize themselves into a new kind of ferromagnet in twisted bilayer graphene (TBG). In this system, which forms when two sheets of graphene are stacked on top of one another with a small twist angle between them, it is the orbital motion of electrons, rather than their spins, that aligns. Such behavior could produce emergent topological states that might be exploited in applications such as low-power magnetic memory in the future.

Graphene is a flat crystal of carbon just one atom thick. When two sheets of the material are placed on top of each other and misaligned by rotating them relative to each other, they form a moiré pattern. Last year, researchers at the Massachusetts Institute of Technology (MIT) found that at a “magic” twist angle of 1.1°, the material becomes a superconductor (that is, it can carry currents with no losses) at 1.7 K. This effect, which occurs thanks to miniband flattening at this angle that strongly enhances interactions between electrons in the material, disappears at slightly larger or smaller angle twists.

A team of researchers led by David Goldhaber-Gordon of Stanford University has now found unambiguous evidence of ferromagnetism – as the giant anomalous Hall (AH) effect – in TBG when its flat conduction miniband is three-quarters filled.

 

Ferromagnetism appears in twisted bilayer graphene, Belle Dumé, Physics World

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How We See the Small...

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View of cantilever on an atomic force microscope (magnification 1000x).
Credit: SecretDisc GFDL, CC-BY-SA-3.0

 

Topics: Atomic Force Microscopy, Nanotechnology, Optics, Scanning Electron Microscope


Cell reproduction, disease detection and semiconductor optimization are just some of the areas of research that have exploited the atomic force microscope. First invented by Calvin Quate, Gerd Binnig and Christoph Gerber in the mid 1980s, atomic force microscopy (AFM) brought the atomic resolution recently achieved by the scanning tunnelling microscope to non-conducting samples, and helped to catalyse the avalanche of science and technology based on nanostructures that now permeates all aspects of modern life from smartphones to tennis rackets. On 6 July 2019 Calvin Quate died aged 95 at his home in Menlo Park, California.

Long before the development of AFM, Quate’s research had made waves in microscopy. 1978 had seen the announcement of the scanning acoustic microscope, which achieved the sensitivity of optical microscopy but probed samples so softly that it could image the interiors of living cells without damaging them. The technique uses high frequency sound waves in place of light, which penetrate deep into structures to image internal structures non-destructively. It is widely used in quality control of electronic component assembly among other applications such as printed circuit boards and medical products.
 

Advanced microscopy pioneer leaves broad ranging legacy
Anna Demming, Physics World

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Your iPhone as Tricorder...

Silicon chips similar to those that would be used in the detection process. Credit: Vanderbilt University/Heidi Hall

 

Topics: Applied Physics, Medical Physics, Nanotechnology, Star Trek


The simplest home medical tests might look like a deck of various silicon chips coated in special film, one that could detect drugs in the blood, another for proteins in the urine indicating infection, another for bacteria in water and the like. Add the bodily fluid you want to test, take a picture with your smart phone, and a special app lets you know if there's a problem or not.

That's what electrical engineer Sharon Weiss, Cornelius Vanderbilt Professor of Engineering at Vanderbilt University, and her students developed in her lab, combining their research on low-cost, nanostructured thin films with a device most American adults already own. "The novelty lies in the simplicity of the basic idea, and the only costly component is the smart phone," Weiss said.

"Most people are familiar with silicon as being the material inside your computer, but it has endless uses," she said. "With our nanoscale porous silicon, we've created these nanoscale holes that are a thousand times smaller than your hair. Those selectively capture molecules when pre-treated with the appropriate surface coating, darkening the silicon, which the app detects."
 

 

iPhone plus nanoscale porous silicon equals cheap, simple home diagnostics
Heidi Hall, Vanderbilt University, Phys.org

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SLIPS...

A novel, highly sensitive molecular sensor together with a first-of-its-kind histamine detector comprise abbieSense, a device that can diagnose and assess the severity of an allergic reaction within five minutes. Credit: Wyss Institute at Harvard University

 

Topics: Applied Physics, Fluid Mechanics, Microfluidics, Nanofluidics, Nanotechnology

 


The need for an inexpensive, super-repellent surface cuts across a vast swath of societal sectors—from refrigeration and architecture, to medical devices and consumer products. Most state-of-the-art liquid repellent surfaces designed in the last decade are modeled after lotus leaves, which are extremely hydrophobic due to their rough, waxy surface and the physics of their natural design. However, none of the lotus-inspired materials designed so far has met the mark: they may repel water but they fail to repel oils, fail under physical stress, cannot self-heal – and are expensive to boot.

‘SLIPS’ technology, inspired by the slippery pitcher plant that repels almost every type of liquid and solid, is a unique approach to coating industrial and medical surfaces that is based on nano/microstructured porous material infused with a lubricating fluid. By locking in water and other fluids, SLIPS technology creates slick, exceptionally repellent and robust self-cleaning surfaces on metals, plastics, optics, textiles and ceramics. These slippery surfaces repel almost any fouling challenge a surface may face—whether from bacteria, ice, water, oil, dust, barnacles, or other contaminants.

 

Wyss Institute, Harvard: Slippery Liquid Infused Porous Surfaces

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