Borophene has a nearly perfect partner in a form of silver that could help the trendy two-dimensional material grow to unheard-of lengths.
A well-ordered lattice of silver atoms makes it possible to speed the growth of pristine borophene, the atom-thick allotrope of boron that so far can only form via synthesis by molecular-beam epitaxy (MBE).
By using a silver substrate and through careful manipulation of temperature and deposition rate, scientists have discovered they can grow elongated hexagon-shaped flakes of borophene. They suggested the use of a proper metal substrate could facilitate the growth of ultrathin, narrow borophene ribbons.
New work published in Science Advances by researchers at Rice and Northwestern universities, Nanjing University of Aeronautics and Astronautics and Argonne National Laboratory will help streamline the manufacture of the conductive material, which shows potential for use in wearable and transparent electronics, plasmonic sensors and energy storage.
That potential has fueled efforts to make it easier to grow, led by Rice materials scientist Boris Yakobson, a theorist who predicted that borophene could be synthesized. He and collaborators Mark Hersam at Northwestern and lead author Zhuhua Zhang, a Rice alumnus and now a professor at Nanjing, have now demonstrated through theory and experimentation that large-scale, high-quality samples of borophene are not only possible but also allow qualitative understanding of their growth patterns.
In two breakthroughs in the realm of photonics, City College of New York graduate researchers are reporting the successful demonstration of an LED (light-emitting diode) based on half-light half-matter quasiparticles in atomically thin materials. This is also the first successful test of an electrically driven light emitter using atomically thin semiconductors embedded in a light trapping structure (optical cavity).
The research is led by graduate physics student Jie Gu and post-doctoral fellow Biswanath Chakraborty, in collaboration with another graduate student, Mandeep Khatoniyar.
According to Vinod Menon, chair of physics in City College’s Division of Science and the research team’s mentor, their double feat, reported in the journal “Nature Nanotechnology,” marks an important milestone in the field of 2D materials and, more broadly, LEDs.
2D Materials: Dicalcium nitride
An electride material, dicalcium nitride (Ca2N) is a compound in which an electron functions as the anion. Because dicalcium nitride is a layered material, it can be considered to be a 2D electride with the formula [Ca2N]+e–.
This material has a hexagonal crystal structure and forms a shiny green plate like crystal in the bulk. As with graphene, mechanical exfoliation can be used to separate the layers. Similar materials, such as those with strontium in the place of calcium, have also been shown to exist. However, these such materials are still relatively unknown and used for almost exclusively for research (electrides themselves are considered to be a fairly recent discovery, first synthesized in the early 1980s).
Scientists at the Center for Advancing Electronics Dresden (cfaed) at TU Dresden have succeeded in synthesizing sheet-like 2-D polymers by a bottom-up process for the first time. A novel synthetic reaction route was developed for this purpose. The 2-D polymers consist of only a few single atomic layers and, due to their very special properties, are a promising material for use in electronic components and systems of a new generation. The research result is a collaborative work of several groups at TU Dresden and the Ulm University and was published this week in two related articles in the scientific journals Nature Chemistry and Nature Communications.
Ever since Hermann Staudinger discovered the linear polymers in 1920, it has been a dream of synthetic scientists to extend the polymerization into the second dimension. A two-dimensional (2-D) polymer is a sheet-like monomolecular macromolecule consisting of laterally connected repeat units with end groups along all edges. Given the enormous chemical and structural diversity of the building blocks (i.e., monomers), 2-D polymers hold great promise in the rational material design tailored for next-generation applications, such as membrane separation, electronics, optical devices, energy storage and conversion, etc. However, despite the tremendous developments in synthetic chemistry over the last century, the bottom-up synthesis of 2-D polymers with defined structures remains a formidable task.
A hundred years ago, “2d” meant a two-penny, or 1-inch, nail. Today, “2-D” encompasses a broad range of atomically thin flat materials, many with exotic properties not found in the bulk equivalents of the same materials, with graphene—the single-atom-thick form of carbon—perhaps the most prominent. While many researchers at MIT and elsewhere are exploring two-dimensional materials and their special properties, Frances M. Ross, the Ellen Swallow Richards Professor in Materials Science and Engineering, is interested in what happens when these 2-D materials and ordinary 3-D materials come together.
“We’re interested in the interface between a 2-D material and a 3-D material because every 2-D material that you want to use in an application, such as an electronic device, still has to talk to the outside world, which is three-dimensional,” Ross says.
“We’re at an interesting time because there are immense developments in instrumentation for electron microscopy, and there is great interest in materials with very precisely controlled structures and properties, and these two things cross in a fascinating way,” says Ross.
Excess heat given off by smartphones, laptops and other electronic devices can be annoying, but beyond that it contributes to malfunctions and, in extreme cases, can even cause lithium batteries to explode.
To guard against such ills, engineers often insert glass, plastic or even layers of air as insulation to prevent heat-generating components like microprocessors from causing damage or discomforting users.
Now, Stanford researchers have shown that a few layers of atomically thin materials, stacked like sheets of paper atop hot spots, can provide the same insulation as a sheet of glass 100 times thicker. In the near term, thinner heat shields will enable engineers to make electronic devices even more compact than those we have today, said Eric Pop, professor of electrical engineering and senior author of a paper published Aug. 16 in Science Advances.
“We’re looking at the heat in electronic devices in an entirely new way,” Pop said.
You’re not so tough, h-BN: Rice University chemists find new path to make strong 2D material better for applications
Two-dimensional h-BN, an insulating material also known as “white graphene,” is four times stiffer than steel and an excellent conductor of heat, a benefit for composites that rely on it to enhance their properties.
Those qualities also make h-BN hard to modify. Its tight hexagonal lattice of alternating boron and nitrogen atoms is highly resistant to change, unlike graphene and other 2D materials that can be easily modified — aka functionalized — with other elements.
The Rice lab of chemist Angel Martí has published a protocol to enhance h-BN with carbon chains. These turn the 2D tough guy into a material that retains its strength but is more amenable to bonding with polymers or other materials in composites.
Sharp meets flat in tunable 2D material: Rice’s new atom-flat compounds show promise for optoelectronics, advanced computing
The Rice lab of materials scientist Pulickel Ajayan has created unique two-dimensional flakes with two distinct personalities: molybdenum diselenide on one side of a sharp divide with rhenium diselenide on the other.
From all appearances, the two-toned material likes it that way, growing naturally — though under tight conditions — in a chemical vapor deposition furnace.
The material is a 2D transition metal dichalcogenide heterostructure, a crystal with more than one chemical component. That’s not unusual in itself, but the sharp zigzag boundary between elements in the material reported in the American Chemical Society journal Nano Letters is unique.
Dichalcogenides are semiconductors that incorporate transition metals and chalcogens. They’re a promising component for optoelectronic applications like solar cells, photodetectors and sensing devices. Lead author Amey Apte, a Rice graduate student, said they may also be suitable materials for quantum computing or neuromorphic computing, which emulates the structure of the human brain.
A novel graphene-matrix-assisted stabilization method will help 2-D materials become a part of quantum computers
Scientists from Russia and Japan found a way of stabilizing two-dimensional copper oxide (CuO) materials by using graphene. Along with being the main candidates for spintronics applications, these materials may be used in forthcoming quantum computers. The results of the study were published in The Journal of Physical Chemistry C.
The family of 2-D materials has recently been joined by a new class, the monolayers of oxides and carbides of transition metals, which have been the subject of extensive theoretical and experimental research. These new materials are of great interest to scientists due to their unusual rectangular atomic structure and chemical and physical properties, and in particular, a unique 2-D rectangular copper oxide cell which does not exist in crystalline (3-D) form, as opposed to most of the 2-D materials, whether well-known or discovered lately, which have a lattice similar to that of their crystalline (3-D) counterparts. The main hindrance for practical use of monolayers is their low stability.
A group of scientists from MISiS, the Institute of Biochemical Physics of RAS (IBCP), Skoltech, and the National Institute for Materials Science in Japan (NIMS) discovered 2-D copper oxide materials with an unusual crystal structure inside the two-layer graphene matrix using experimental methods.
2D Materials: Germanene
As with the other elements sharing the same group on the periodic table (carbon, silicon, tin, and even lead), germanium is capable of forming a two dimensional material on its own known as germanene. And, just as with the other 2D materials of the same group, germanene’s most intriguing applications to many researchers are those that take advantage of the material’s novel electronic properties.
The synthesis of germanene was first reported in 2014, before tin and lead but after carbon and silicon. Unlike carbon, however, germanium does not have a layered structure that can be easily separated (relatively speaking) and, as such, germanene must be synthesized, often through molecular beam epitaxy – it cannot be exfoliated. Also, as shown in the upper left image above, germanene is not entirely flat due to the angle that forms between bonded germanium atoms.
Germanene is still in the early stages of research, like many other 2D materials, and easier forms of synthesis, as well as a deeper understanding of its properties, need to be developed before any commercial applications can be considered. That being said, key areas of interest for germanene include high-performance field-effect transistors, and for the usage in studying Dirac fermions. It is important to note that germanene does not have a band gap, though the addition of hydrogen can create one.