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The ACS Publishes a Chicken-Sh!T Article About Graphene

Posted By Graphene Council, Friday, February 14, 2020

A joke targeted at graphene research seems driven more by envy than providing a check on its excesses 

Last month, the venerable American Chemical Society (ACS) in its journal ACS Nano decided to take a step off the path of its mandate to promote scientific discovery and thought it might be fun to ridicule it. ("Will Any Crap We Put into Graphene Increase Its Electrocatalytic Effect?" by Lu Wang, Zdenek Sofer and  Martin Pumera*

Of course, the target of the ridicule was graphene, which over the last decade has been taking much of the research funding targeted for advanced materials. Let’s say it was an easy target to malign, especially for those who are not invested in graphene’s development.

The ridicule was formulated in this way: a lot of research papers are published on how to dope graphene (add impurities to it), so what if we published a paper on someone doping graphene with chicken guano. Hysterical, right?

There’s just one problem with this joke, one of the cornerstones of semiconducting engineering for at least the last half-century has been doping. Doping is used to enhance, or just tweak, the conductivity of semiconductors by intentionally introducing impurities into them. 

To forego a long explanation of solid-state physics and band gaps, suffice it to say that digital electronics (the kind of electronics that enables you to read this post) depends on doping of electronic materials to function.

In the decade-and-a-half since graphene was first isolated, researchers have been mesmerized by its extraordinary properties and by logical extension its enormous potential in electronics. However, graphene in its pure state is not a semiconductor, but rather a conductor. In order for it to be useful in electronic applications, especially digital electronics, it needs to behave as a semiconductor: possessing the capability of starting and stopping the flow of electrons through it thereby creating the on/off states for binary digital logic.

Of course, researchers have spent countless hours researching on how to best exploit graphene for electronics—attracted to its extraordinary electronic properties—and have often been funded handsomely to do so. This funding—which has come at the expense of other lines of research (making graphene research an easy target for envy)—has been so strong because of the hope that it would lead to some breakthrough that would stave off the end of Moore’s Law. 

Moore’s Law argued back in 1965 that the number of transistors placed in an integrated circuit (IC) or chip doubles approximately every two years.  It turns out graphene hasn’t saved Moore’s Law as of yet. And Moore’s Law may have seen its road come to a dead end two years ago when chip makers just threw up their hands at a 7-nm node and said, “No more.”

This means for the last decade there has been a pressing need and a fervent hope that graphene could come to the rescue of complimentary metal-oxide-semiconductor (CMOS) digital electronics. To meet this need and interest, graphene research had to devote much of its time to doping of the material.

It is a worthy argument to contest how effective this has all been in bringing graphene closer as a viable alternative in a post-CMOS world. However, it would be silly to argue that such research should never have been undertaken, or even taken on so aggressively and broadly. There was a need and the market pulled for such a use for the material. This was not an idle or wasted effort as the ACS Nano article insinuates.

The gist of the ACS Nano article in the form of a joke was to suggest that all doping of graphene research is nonsense because so much of it is performed and published. “Look how funny it would be to dope graphene with chicken droppings. That will really stick their noses in it.” While this may be funny to some, it’s highly detrimental to the spirit and inspiration for scientific inquiry.

And it certainly doesn’t do justice to the many innovative ways that graphene and a whole class of 2D materials are being applied to solve existing and new engineering challenges. 

Tags:  2D materials  American Chemical Society  Electronics  Graphene  Lu Wang  Martin Pumera  Semiconductors  Zdenek Sofer 

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Physicist obtain atomically thin molybdenum disulfide films on large-area substrates

Posted By Graphene Council, Thursday, January 23, 2020
Researchers from the Moscow Institute of Physics and Technology have managed to grow atomically thin films of molybdenum disulfide spanning up to several tens of square centimeters. It was demonstrated that the material's structure can be modified by varying the synthesis temperature. The films, which are of interest to electronics and optoelectronics, were obtained at 900-1,000 degrees Celsius. The findings were published in the journal ACS Applied Nano Materials.

Two-dimensional materials are attracting considerable interest due to their unique properties stemming from their structure and quantum mechanical restrictions. The family of 2D materials includes metals, semimetals, semiconductors, and insulators. Graphene, which is perhaps the most famous 2D material, is a monolayer of carbon atoms. It has the highest charge-carrier mobility recorded to date. However, graphene has no band gap under standard conditions, and that limits its applications.

Unlike graphene, the optimal width of the bandgap in molybdenum disulfide (MoS2) makes it suitable for use in electronic devices. Each MoS2 layer has a sandwich structure, with a layer of molybdenum squeezed between two layers of sulfur atoms. Two-dimensional van der Waals heterostructures, which combine different 2D materials, show great promise as well. In fact, they are already widely used in energy-related applications and catalysis. Wafer-scale (large-area) synthesis of 2D molybdenum disulfide shows the potential for breakthrough advances in the creation of transparent and flexible electronic devices, optical communication for next-generation computers, as well as in other fields of electronics and optoelectronics.

"The method we came up with to synthesize MoS2 involves two steps. First, a film of MoO3 is grown using the atomic layer deposition technique, which offers precise atomic layer thickness and allows conformal coating of all surfaces. And MoO3 can easily be obtained on wafers of up to 300 millimeters in diameter. Next, the film is heat-treated in sulfur vapor. As a result, the oxygen atoms in MoO3 are replaced by sulfur atoms, and MoS2 is formed. We have already learned to grow atomically thin MoS2 films on an area of up to several tens of square centimeters," explains Andrey Markeev, the head of MIPT's Atomic Layer Deposition Lab.

The researchers determined that the structure of the film depends on the sulfurization temperature. The films sulfurized at 500 ? contain crystalline grains, a few nanometers each, embedded in an amorphous matrix. At 700 ?, these crystallites are about 10-20 nm across and the S-Mo-S layers are oriented perpendicular to the surface. As a result, the surface has numerous dangling bonds. Such structure demonstrates high catalytic activity in many reactions, including the hydrogen evolution reaction. For MoS2 to be used in electronics, the S-Mo-S layers have to be parallel to the surface, which is achieved at sulfurization temperatures of 900-1,000 ?. The resulting films are as thin as 1.3 nm, or two molecular layers, and have a commercially significant (i.e., large enough) area.

The MoS2 films synthesized under optimal conditions were introduced into metal-dielectric-semiconductor prototype structures, which are based on ferroelectric hafnium oxide and model a field-effect transistor. The MoS2 film in these structures served as a semiconductor channel. Its conductivity was controlled by switching the polarization direction of the ferroelectric layer. When in contact with MoS2, the La:(HfO2-ZrO2) material, which was earlier developed in the MIPT lab, was found to have a residual polarization of approximately 18 microcoulombs per square centimeter. With a switching endurance of 5 million cycles, it topped the previous world record of 100,000 cycles for silicon channels.

Tags:  2D materials  ACS Applied Nano Materials  Andrey Markeev  Graphene  Moscow Institute of Physics and Technology  Optoelectronics  Semiconductors 

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Graphene nanoribbons lay the groundwork for ultrapowerful computers

Posted By Graphene Council, Friday, September 13, 2019
Smaller, better semiconductors have consistently allowed computers to become faster and more energy-efficient than ever before.

But the 18-month cycle of exponential increases in computing power that has held since the mid 1960s now has leveled off. That’s because there are fundamental limits to integrated circuits made strictly from silicon—the material that forms the backbone of our modern computer infrastructure.

As they look to the future, however, engineers at the University of Wisconsin-Madison are turning to new materials to lay down the foundations for more powerful computers.

They have devised a method to grow tiny ribbons of graphene—the single-atom-thick carbon compound—directly on top of silicon wafers.

Graphene ribbons have a special advantage over the material when it’s in its more common form of a broad, flat sheet; namely, thin strips of graphene become excellent semiconductors.

“Compared to current technology, this could enable faster, low power devices,” says Vivek Saraswat, a PhD student in materials science and engineering at UW-Madison. “It could help you pack in more transistors onto chips and continue Moore’s law into the future.”

Saraswat and his colleagues published details of their work July 9, 2019, in the Journal of Physical Chemistry.

The advance could enable graphene-based integrated circuits, with much improved performance over today’s silicon chips.

“The main advantage of graphene nanoribbons is that electrons can travel faster through them, compared to silicon so you can make faster chips that use less energy,” says Mike Arnold, a professor of materials science and engineering at UW-Madison and a world expert in graphene growth.

Arnold is pioneer of a strategy to lay down long, thin strips of graphene—structures known as nanoribbons—on top a material called germanium.

That’s useful in many ways. However, since germanium isn’t a widely used semiconductor, it can’t form the basis for computer chips.

Meanwhile, other researchers have not been able to overcome a major barrier in layering graphene nanoribbons onto silicon. Graphene reacts with silicon to form an inert and less useful compound called silicon carbide.

Arnold’s group has developed an ingenious method to avoid that obstacle.

By laying down a thin protective layer of germanium before applying graphene, the researchers could successfully grow graphene nanoribbons on top of silicon wafers. The thin germanium layers protected graphene from reacting with silicon, yet didn’t interfere with the nanoribbons’ semiconducting capabilities.

It’s an important first step toward creating graphene-based integrated circuits. And because the base layer is composed of silicon, the graphene nanoribbon technology can be easily integrated into existing electronic/computing components.

“Our vision is to integrate graphene with existing devices,” says Arnold.

The scientists have patented their technology through the Wisconsin Alumni Research Foundation. One advantage of their synthesis approach is that it takes advantage of a scalable, industry-compatible chemical vapor deposition technique. Now, they’re working to improve the precision with which they lay down their nanoribbons so that they can achieve the complex patterns found in modern computer chips.

“We are using a few strategies to control the thickness and the orientation for the nanoribbons,” says Arnold. “We have a few really cool ideas.”

Tags:  Graphene  Graphene Nanoribbons  Mike Arnold  Semiconductors  University of Wisconsin-Madison  Vivek Saraswat 

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How to enlarge 2D materials as single crystals?

Posted By Graphene Council, Friday, May 31, 2019

What makes something a crystal? When all of its atoms are arranged in accordance with specific mathematical rules, we call the material a single crystal. Like the natural world has its unique symmetry just as snowflakes or honeycombs, the atomic world of crystals is designed by its own structure and symmetry. This material structure has a profound effect on its physical properties as well. Specifically, single crystals play an important role in inducing material's intrinsic properties to its full extent. Faced with the coming end of the miniaturization process that the silicon-based integrated circuit has allowed up to this point, huge efforts have been dedicated to find a single crystalline replacement for silicon.


In search for the transistor of the future, two-dimensional (2D) materials, especially graphene have been the subject of intense research around the world. Being thin and flexible as a result of being only a single layer of atoms, this 2D version of carbon even features unprecedented electricity and heat conductivity. However, the last decade's efforts for graphene transistors have been held up by physical restraints graphene allows no control over electricity flow due to the lack of band gap. Then, what about other 2D materials? A number of interesting 2D materials have been reported to have similar or even superior properties. Still, the lack of understanding in creating ideal experimental conditions for large-area 2D materials has limited their maximum size to just a few mm 2.

Scientists at the Center for Multidimensional Carbon Material (CMCM) within the Institute for Basic Science (IBS) (located in the Ulsan National Institute of Science and Technology (UNIST)) have presented a novel approach to synthesize large-scale of silicon wafer size, single crystalline 2D materials. Prof. Feng Ding and Ms. Leining Zhang in collaboration with their colleagues in Peking University, China and other institutes have found a substrate with a lower order of symmetry than that of a 2D material that facilitates the synthesis of single crystalline 2D materials in a large area. "It was critical to find the right balance of rotational symmetries between a substrate and a 2D material," notes Prof. Feng Ding, one of corresponding authors of this study. The researchers successfully synthesized hBN single crystals of 10*10 cm2 by using a new substrate: a surface nearby Cu (110) that has a lower symmetry of (1) than hBN with (3).

Then, why does symmetry matters? Symmetry, in particular rotational symmetry, describes how many times a certain shape fits on to itself during a full rotation of 360 degrees. The most efficient method to synthesize large-area and single crystals of 2D materials is to arrange layers over layers of small single crystals and grow them upon a substrate. In this epitaxial growth, it is quite challenging to ensure all of the single crystals are aligned in a single direction. Orientation of the crystals is often affected by the underlying substrate. By theoretical analysis, the IBS scientists found that an hBN island (or a group of hBN atoms forming a single triangle shape) has two equivalent alignments on the Cu(111) surface that has a very high symmetry of (6). "It was a common view that a substrate with high symmetry may lead to the growth of materials with a high symmetry. It seemed to make sense intuitively, but this study found it is incorrect," says Ms. Leining Zhang, the first author of the study.

Previously, various substrates such as Cu(111) have been used to synthesize single crystalline hBN in a large area, but none of them were successful. Every effort ended with hBN islands aligning along in several different directions on the surfaces. Convinced by the fact that the key to achieve unidirectional alignment is to reduce the symmetry of the substrate, the researchers made tremendous efforts to obtain vicinal surfaces of a Cu(110) orientation; a surface obtained by cutting a Cu(110) with a small tilt angle. It is like forming physical steps on Cu. As a hBN island tends to place in parallel to the edge of each step, it gets only one preferred alignment. The small tilt angle lowers the symmetry of the surface as well.

They eventually found that a class of vicinal surfaces of Cu (110) can be used to support the growth of hBN with perfect alignment. On a carefully selected substrate with the lowest symmetry or the surface will repeat itself only after a 360degree rotation, hBN has only one preferred direction of alignment. The research team of Prof. Kaihui Liu in Peking University, has developed a unique method to anneal a large Cu foil, up to 10*10 cm2, into a single crystal with the vicinal Cu (110) surface and, with it, they have achieved the synthesis of hBN single crystals of same size.

Besides flexibility and ultrathin thickness, emerging 2D materials can present extraordinary properties when they get enlarged as single crystals. "This study provides a general guideline for the experimental synthesis of various 2D materials. Besides the hBN, many other 2D materials could be synthesized with the large area single crystalline substrates with low symmetry," says Prof. Feng Ding. Notably, hBN is the most representative 2D insulator, which is different from the conductive 2D materials, such as graphene, and 2D semiconductors, such as molybdenum disulfide (MoS2). The vertical stacking of various types of 2D materials, such as hBN, graphene and MoS2, would lead to a large number of new materials with exceptional properties and can be used for numerous applications, such as high-performance electronics, sensors, or wearable electronics."

Tags:  2D materials  Center for Multidimensional Carbon Material  Feng Ding  Graphene  Kaihui Liu  Peking University  Semiconductors 

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