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Researchers discover new boron-lanthanide nanostructure

Posted By Graphene Council, Friday, June 26, 2020
The discovery of carbon nanostructures like two-dimensional graphene and soccer ball-shaped buckyballs helped to launch a nanotechnology revolution. In recent years, researchers from Brown University and elsewhere have shown that boron, carbon’s neighbor on the periodic table, can make interesting nanostructures too, including two-dimensional borophene and a buckyball-like hollow cage structure called borospherene.

Now, researchers from Brown and Tsinghua University have added another boron nanostructure to the list. In a paper published in Nature Communications, they show that clusters of 18 boron atoms and three atoms of lanthanide elements form a bizarre cage-like structure unlike anything they’ve ever seen. 

“This is just not a type of structure you expect to see in chemistry,” said Lai-Sheng Wang, a professor of chemistry at Brown and the study’s senior author. “When we wrote the paper we really struggled to describe it. It’s basically a spherical trihedron. Normally you can’t have a closed three-dimensional structure with only three sides, but since it’s spherical, it works.”

The researchers are hopeful that the nanostructure may shed light on the bulk structure and chemical bonding behavior of boron lanthanides, an important class of materials widely used in electronics and other applications. The nanostructure by itself may have interesting properties as well, the researchers say. 

“Lanthanide elements are important magnetic materials, each with very different magnetic moments,” Wang said. “We think any of the lanthanides will make this structure, so they could have very interesting magnetic properties.”

Wang and his students created the lanthanide-boron clusters by focusing a powerful laser onto a solid target made of a mixture of boron and a lanthanide element. The clusters are formed upon cooling of the vaporized atoms. Then they used a technique called photoelectron spectroscopy to study the electronic properties of the clusters. The technique involves zapping clusters of atoms with another high-powered laser. Each zap knocks an electron out of the cluster. By measuring the kinetic energies of those freed electrons, researchers can create a spectrum of binding energies for the electrons that bond the cluster together.

“When we see a simple, beautiful spectrum, we know there’s a beautiful structure behind it,” Wang said. 

To figure out what that structure looks like, Wang compared the photoelectron spectra with theoretical calculations done by Professor Jun Li and his students from Tsinghua. Once they find a theoretical structure with a binding spectrum that matches the experiment, they know they’ve found the right structure. 

“This structure was something we never would have predicted,” Wang said. “That’s the value of combining theoretical calculation with experimental data.”

Wang and his colleagues have dubbed the new structures metallo-borospherenes, and they’re hopeful that further research will reveal their properties.

Tags:  2D materials  boron nanostructure  Brown University  Graphene  Lai-Sheng Wang  nanostructures  Tsinghua University 

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Industrial scale production of layer 2D materials via intermediate-assisted grinding

Posted By Graphene Council, Tuesday, November 26, 2019
The large number of 2D materials, including graphene, hexagonal boron nitride (h-BN), transition metal dichalcogenides (TMDCs) like MoS2 and WSe2, metal oxides (MxOy), black phosphorene (b-P), etc, provide a wide range of properties and numerous potential applications.

In order to realize their commercial use, the prerequisite is large-scale production. Bottom-up strategies like chemical vapor deposition (CVD) and chemical synthesis have been extensively explored but only small quantities of 2D materials have been produced so far.

Another important strategy to obtain 2D materials is from a top-down path by exfoliating bulk layer materials to monolayer or few layer 2D materials, such as ball milling, liquid phase exfoliation, etc. It seems that top-down strategies are most likely to be scaled-up, however, they are only suitable for specific materials.

So far, only graphene and graphene oxide can be prepared at the tons level, while for other 2D materials, they still remain in the laboratory state because of the low yield.

Therefore, it is necessary to develop a high-efficiency and low-cost preparation method of 2D materials to progress from the laboratory to our daily life.

The failure of solid lubricants is caused by the slip between layers of bulk materials, and the result of the slip is that the bulk materials will be peeled off into fewer layers. Based on this understanding, in a new research article published in the Beijing-based National Science Review ("Mass Production of Two-Dimensional Materials by Intermediate-Assisted Grinding Exfoliation"), the Low-Dimensional Materials and Devices lab led by Professor Hui-Ming Cheng and Professor Bilu Liu from Tsinghua University proposed an exfoliation technology which is named as interMediate-Assisted Grinding Exfoliation (iMAGE).

The key to this exfoliation technology is to use intermediate materials that increase the coefficient of friction of the mixture and effectively apply sliding frictional forces to the layer material, resulting in a dramatically increased exfoliation efficiency.

Considering the case of 2D h-BN, the production rate and energy consumption can reach 0.3 g h-1 and 3.01×106 J g-1, respectively, both of which are one to two orders of magnitude better than previous results.

The resulting exfoliated 2D h-BN flakes have an average thickness of 4 nm and an average lateral size of 1.2 µm. Besides, this iMAGE method has been extended to exfoliate a series of layer materials with different properties, including graphite, Bi2Te3, b-P, MoS2, TiOx, h-BN, and mica, covering 2D metals, semiconductors with different bandgaps, and insulators.

It is worth mentioning that, with the cooperation with the Luoyang Shenyu Molybdenum Co. Ltd., molybdenite concentrate, a naturally existing cheap and earth abundant mineral, was used as a demo for the industrial scale exfoliation production of 2D MoS2 flakes.

"This is the very first time that 2D materials other than graphene have been produced with a yield of more than 50% and a production rate of over 0.1g h-1. And an annual production capability of 2D h-BN is expected to be exceeding 10 tons by our iMAGE technology." Prof. Bilu Liu, one of the leading authors of this study, said, "Our iMAGE technology overcomes a main challenge in 2D materials, i.e., their mass production, and is expected to accelerate their commercialization in a wide range of applications in electronics, energy, and others."

Tags:  2D materials  Bilu Liu  CVD  Graphene  Hui-Ming Cheng  Tsinghua University 

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Graphene and silk make self-healable electronic tattoos

Posted By Graphene Council, Tuesday, March 26, 2019
Updated: Tuesday, March 26, 2019
Researchers have designed graphene-based e-tattoos designed to act as biosensors. The sensors can collect data relate to human health, such as skin reactions to medication or to assess the degree of exposure to ultraviolet light.

Considerable research has gone into electronic tattoos (or e-tattoos), as part of the emerging field of or epidermal electronics. These are a thin form of wearable electronics, designed to be fitted to the skin. The aim of these lightweight sensors is to collect physiological data through sensors.

The types of applications of the sensors, from Tsinghua University, include assessing exposure to ultraviolet light to the skin (where the e-tattoos function as dosimeters) and for the collection of ‘vital signs’ to assess overall health or reaction to a particular medication (biosensors).

The use of graphene aids the collection of electric signals and it also imparts material properties to the sensors, allowing them to be bent, pressed, and twisted without any loss to sensors functionality.

The new sensors, developed in China, have shown – via as series of tests – good sensitivity to external stimuli like strain, humidity, and temperature. The basis of the sensor is a material matrix composed of a graphene and silk fibroin combination.

The highly flexible e‐tattoos are manufactured by printing a suspension of graphene, calcium ions and silk fibroin. Through this process the graphene flakes distributed in the matrix form an electrically conductive path. The path is highly responsive to environmental changes and it can detect multi-stimuli.

The e‐tattoo is also capable of self-healing. The tests showed how the tattoo heals after damage by water. This occurs due to the reformation of hydrogen and coordination bonds at the point of any fracture. The healing efficiency was demonstrated to be 100 percent and it take place in less than one second.

The researchers are of the view that the e-tattoos can be used as electrocardiograms, for assessing breathing, and for monitoring temperature changes. This means that the e‐tattoo model could be the basis for a new generation of epidermal electronics.

Commenting on the research, chief scientist Yingying Zhang said: “Based on the superior capabilities of our e-tattoos, we believe that such skin-like devices hold great promise for manufacturing cost-effective artificial skins and wearable electronics.”

Tags:  biosensors  Electronics  Graphene  Healthcare  Tsinghua University  Yingying Zhang 

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