Super-powers of ultra-thin materials: in materials science, 2D is the new 3D

A vacuum chamber, where X-ray spectroscopy measures the properties of materials - tiny squares of different colors mounted on a copper holder.

In recent years, devices connected to the Internet have reached many new frontiers - on wrists, refrigerators, doorbells and cars. However, some researchers believe that the “Internet of things” is not yet very developed.

“What if we could embed electronics anywhere,” said Thomas Palacios, an electrical engineer at the Massachusetts Institute of Technology, recently. - What if we could receive energy from solar panels built into the highway, and load cells could be built into tunnels and bridges to monitor the condition of concrete? What if we could look outside and see the weather forecast on the glass? Or embed electronics that track human health in a jacket? ”

In January 2019 Palacios and colleagues published in the journal Nature jobsdescribing the invention, able to bring this future a little closer: an antenna that can absorb Wi-Fi, Bluetooth and cell phones from it more and more, and effectively turn them into usable electricity.

The key to this technology is a promising material: molybdenum sulfide , MoS ₂ , laid in a flat layer with a thickness of only three atoms. In the engineering world, it’s almost impossible to do anything thinner.

And such a small thickness is a useful thing. For example, with MoS _2, you can cover the surface of the table, turning it into a laptop charger that does not require wires.

From the point of view of researchers, two-dimensional materials will become the pillar of the “Internet of everything”. They will "paint" the bridges and make them sensors that monitor the load and cracks. They will be imposed on the windows with a transparent layer, which will become visible only when the information is displayed. And if the team succeeds in creating a device for absorbing radio waves, it will be able to power this ubiquitous electronics. The future is looking more and more flat.

“Interest in this topic is growing exponentially,” said Jeff Urban, a two-dimensional materials researcher at the Molecular Factory at the Lawrence Berkeley National Laboratory in California. “You cannot say otherwise.”


Thomas Palacios believes that the future of electronics lies in flat surfaces


MIT engineers created tiny electronic circuits from graphene, a two-dimensional type of carbon


Palacios with a bubble containing several thousand microelectronic graphene circuits


Yuxuan Lin, a researcher from the Palacios laboratory, is preparing equipment for working with two-dimensional circuits

Flat designs open all doors

The fashion for two-dimensional chemistry began in 2004, when two researchers from the Manchester Institute used adhesive tape to peel a carbon atom from a graphite into a single atom thick film to produce graphene. Graphene is identical in composition to graphite and diamond, but its small thickness gives it very special properties: it is flexible, transparent, extremely strong and conducts electricity and electricity exceptionally well.

Researchers immediately began to make all sorts of new and improved gadgets with it. Several companies have already released headphones, in which the diaphragm - a vibrating membrane that reproduces sound in audio devices - consists of graphene. Some paint manufacturers add graphene to their formulas to keep the coating longer. In October, Huawei introduced the large and powerful Mate 20 X phone, which uses graphene to cool the processor. Samsung used graphene to develop a battery with accelerated charging, and it may appear on phones in the near future.

Urban works with two-dimensional materials to improve the properties of fuel cells, one of the options for "clean" fuel for "environmentally friendly" transport. Most of the fuel cells generate electricity from hydrogen, but even at high pressure, hydrogen takes up several times more space than gasoline comparable in energy content, as a result of which it becomes impractical to use hydrogen in cars.

Instead, Urban introduces hydrogen atoms into solid materials whose density is many times greater than the density of gases. In March, he and his colleagues announced the creation of a new type of storage: tiny magnesium crystals wrapped in narrow strips of so-called graphene nanoribbons. They found that the hydrogen stored in this way produces almost as much energy as gasoline of a similar volume, and weighs much less.

Urban compared this process to baking cookies with chocolate chips, the role of which is magnesium that holds hydrogen. “We need cookies containing as many chocolate chips as possible,” he said, and graphene nanoribbons make an excellent cookie dough. Nanoribbons also help hydrogen quickly enter and exit magnesium crystals, holding oxygen outside, fighting hydrogen for a place inside the crystals.

Urban looks into the world of ultra-thin materials in the Advanced Light Source laboratory, located under a dome, which offers panoramic views of the city of San Francisco and the bay. Here the electrons, dispersed almost to the speed of light, generate powerful x-rays that can be used for fine sensing of the atomic structure of materials.

At ALS, Urban and his colleagues figured out exactly how graphene wraps around magnesium and attaches to it. This connection of the two materials guarantees the stability of the composite material over long periods of time - this is an important property for using the compound in real conditions.


Advanced Light Source Lab


Jeff Urban, two-dimensional materials researcher, at the Molecular Factory at the Lawrence Berkeley National Laboratory in California


Experimental fuel cells help measure the properties of ultrafine materials under various conditions (when exposed to gas, liquids, sunlight, or chemicals) using X-ray spectroscopy using soft X-ray radiation.


A radiation specialist, Y-Sheng Liu, one of the members of the Urban team, uses a controller to setting material sample location that X-rays will be irradiated

Other researchers ultrathin layers of folded material in the stack to obtain three-dimensional blocks, the properties of which ichayutsya from both two-dimensional and three-dimensional from conventional materials.

Kwabena Bedyako, a chemist at the University of California at Berkeley, published a study last year in the journal Nature, describing how she and her colleagues placed lithium ions between multiple layers of two-dimensional materials, including graphene.

“We started with a piece of bread, spread it with mayonnaise, put it on cheese, and then on ham,” she said. “You can repeat as many times as you like, and you get a sandwich.”

By changing the layers of the stack, the researchers were able to fine-tune the storage process of lithium, and this can lead to the creation of new high-capacity batteries for electronic devices.

Xining Zang, Ph.D. in Materials Science from MIT, recently discovered a surprisingly simple way to lay two-dimensional materials on top of each other using gelatin, a product that gives marmalade and marshmallows their structure. He and his colleagues combined gelatin, metal ions, and water. Gelatin formed a multilayer structure (as usually happens with the formation of jelly), which gave a layered structure to metal ions. Part of the carbon in the gelatin reacted with the metal, producing two-dimensional metal carbide leaves; they acted as catalysts, helping to separate water into oxygen and hydrogen - and this process can be used in fuel cells to generate electricity.

“I can’t say that the technology was crude, because if you think about it, it turned out to be pretty elegant,” said Nate Hochman, who previously worked at the Molecular Factory, and one of the authors of the work. “Everything came out at the junction of high and low technologies.”

Making materials thinner

If two-dimensional materials are flourishing, it’s in Singapore, in the laboratory of Liu Zheng, at Nanyang University of Technology. Singapore is trying to become a "garden city", and this tiny country is actively filling its territory with greenery - including the university, where gardens are planted in all corners of its modern buildings.

Zheng considers his research a variation on the method of growing plants. “I'm a gardener,” he said. - I have a two-dimensional garden with a variety of colors. And they are all beautiful. ”

Last year, Zheng and colleagues significantly expanded their garden, creating dozens of new two-dimensional materials from a class of composite materials called transition metal chalcogenides(transition metal chalcogenides, TMC). A key discovery was the use of table salt to lower the melting point of metals; as a result, it became possible to vaporize the metal so that it deposited in the form of thin films.


In the laboratory of Liu Zheng at Nanyang Technological University, layers of two-dimensional materials are placed on silicon substrates and stored in containers.


Nanyang Technological University in Singapore.


In the laboratory of Zheng, chemical vapor is deposited by two-dimensional layers on silicon substrates in quartz tubes.


Instruments for the careful control and monitoring of the flow of gases into the quartz tubes tubes

“Once my student told me: I can do TMC with salt,” said Zheng. - I was surprised. It has been my dream for many years. ”

One of the shelves in Zheng's stuffed lab is crammed with transparent airtight containers; silicon substrates with deposits of two-dimensional materials are stored there. Often the films form a visible triangle or hexagon, in accordance with the geometric structure of the material crystals.

After placing the films, Zheng's team moves to a nearby laboratory to carefully study the resulting structures. Most of the room is occupied by a four-meter transmission electron microscope and a weight of one and a half tons - a huge device for viewing individual atoms.

Many TMCs, including MoS ₂Palacios, absorbing radio waves, are potentially applicable in various industrial applications. The two-dimensional platinum selenide from the Singapore laboratory can serve to produce cheaper fuel cells, which usually use platinum, which separates the proton of the hydrogen atom from the electron. Switching to two-dimensional platinum selenide could reduce the amount of platinum used by 99%, Zheng said. Nanyang University of Technology is already discussing technology commercialization with manufacturers. So far, the future is not yet completely two-dimensional, but it is already close to this.

“I see the huge commercial potential of this material,” said Zheng. “We can seriously affect the market.”


Flexible thermoelectric device of Urban from two-dimensional carbon nanosheets. Thermoelectric devices take energy from the environment and turn it into usable electrical energy.

Source: https://habr.com/ru/post/undefined/