New method for the mass production of boron/nitrogen co-doped graphene nanoplatelets

This is a schematic representation for the formation of BCN-graphene via solvothermal reaction between carbon tetrachloride (CCl4) boron tribromide (BBr3) and nitrogen (N2) in the presence of potassium (K). Photograph is of the autoclave after the reaction, showing the formation of BCN-graphene (black) and potassium halide (KCl and KBr, white).

Image: UNIST

Ulsan National Institute of Science and Technology (UNIST) announced a method for the mass production of boron/nitrogen co-doped graphene nanoplatelets, which led to the fabrication of a graphene-based field-effect transistor (FET) with semiconducting nature. This opens up opportunities for practical use in electronic devices.

The Ulsan National Institute of Science and Technology (UNIST) research team led by Prof. Jong-Beom Baek have discovered an efficient method for the mass production of boron/nitrogen co-doped graphene nanoplatelets (BCN-graphene) via a simple solvothermal reaction of BBr3/CCl4/N2 in the presence of potassium. This work was published in "Angewandte Chemie International Edition" as a VIP ("Very Important Paper".

Since graphene was experimentally discovered in 2004, it has been the focus of vigorous applied research due to its outstanding properties such as high specific surface area, good thermal and electrical conductivities, and many more properties.

However, its Achilles heel is a vanishing band-gap for semiconductor application. As a result, it is not suitable for logic applications, because devices cannot be switched off. Therefore, graphene must be modified to produce a band-gap, if it is to be used in electronic devices.

Various methods of making graphene-based field effect transistors (FETs) have been exploited, including doping graphene, tailoring graphene-like a nanoribbon, and using boron nitride as a support. Among the methods of controlling the band-gap of graphene, doping methods show the most promisinge in terms of industrial scale feasibility.

Although world leading researchers have tried to add boron into graphitic framework to open its band-gap for semiconductor applications, there has not been any notable success yet. Since the atomic size of boron (85 pm) is larger than that of carbon (77 pm), it is difficult to accommodate boron into the graphitic network structure.

A new synthetic protocol developed by a research team from UNIST, a leading Korean university, has revealed that boron/nitrogen co-doping is only feasible when carbon tetrachloride (CCl4 ) is treated with boron tribromide (BBr3 ) and nitrogen (N2) gas.

In order to help boron-doping into graphene structure, the research team used nitrogen (70 pm), which is a bit smaller than carbon and boron. The idea was very simple, but the result was surprising. Pairing two nitrogen atoms and two boron atoms can compensate for the atomic size mismatch. Thus, boron and nitrogen pairs can be easily introduced into the graphitic network. The resultant BCN-graphene generates a band-gap for FETs.

"Although the performance of the FET is not in the ranges of commercial silicon-based semiconductors, this initiative work should be the proof of a new concept and a great leap forward for studying graphene with band-gap opening," said Prof. Jong-Beom Baek.

"I believe this work is one of the biggest advancements in considering the viability of a simple synthetic approach," said Ph.D. candidate Sun-Min Jung, the first author of this article.

Prof. Baek explains the next step: "Now, the remaining challenge is fine-tuning a band-gap to improve the on/off current ratio for real device applications."

 

Information about the research

Other researchers in the team include Profs. Joon Hak Oh, Noejung Park, HuYoung Jeong and 6 graduate students.

The research work was funded by the National Research Foundation (NRF) of Korea, and the US Air Force Office of Scientific Research through the Asian Office of Aerospace R&D (AFOSR-AOARD).

Homepage of Jong-Beom Baek : http://jbbaek.unist.ac.kr

Source: http://www.unist.ac.kr

Graphene nanoribbons for “reading” DNA

One of the methods used for examining the molecules in a liquid consists in passing the fluid through a nano-sized hole so as to detect their passage. EPFL researchers have found a way to improve this technique by using a material with unique properties: graphene.

If we wanted to count the number of people in a crowd, we could make on the fly estimates, very likely to be imprecise, or we could ask each person to pass through a turnstile. The latter resembles the model that EPFL researchers have used for creating a “DNA reader” that is able to detect the passage of individual DNA molecules through a tiny hole: a nanopore with integrated graphene transistor.

The DNA molecules are diluted in a solution containing ions and are driven by an electric field through a membrane with a nanopore. When the molecule goes through the orifice, it provokes a slight perturbation to the field, detectable not only by the modulations in ionic current but also by concomitant modulation in the graphene transistor current. Based on this information, it is possible to determine whether a DNA molecule has passed through the membrane or not.

A thickness of one third of a nanometer
This system is based on a method that has been known for over a dozen years. The original technique was not as reliable since it presented a number of shortcomings such as clogging pores and lack of precision, among others. “We thought that we would be able to solve these problems by creating a membrane as thin as possible while maintaining the orifice’s strength”, said Aleksandra Radenovic from the Laboratory of Nanoscale Biology at EPFL. Together with Floriano Traversi, postdoctoral student, and colleagues from the Laboratory of Nanoscale Electronics and Structures, she came across the material that turned out to be both the strongest and most resilient: graphene, which consists of a single layer of carbon molecules. The strips of graphene or nanoribbons used in the experiment were produced at EPFL, thanks to the work carried out at the Center for Micro Nanotechnology (CMI) and the Center for Electron Microscopy (CIME).

“Through an amazing coincidence, continued the researcher, the graphene layer’s thickness measures 0.335 nm, which exactly fits the gap existing between two DNA bases, whereas in the materials used so far there was a 15 nm thickness.” As a result, while previously it was not possible to individually analyze the passage of DNA bases through these “long” tunnels – at a molecular scale –, the new method is likely to provide a much higher precision. Eventually, it could be used for DNA sequencing.

However they are not there yet. In only 5 milliseconds, up to 50’000 DNA bases can pass through the pores. The electric output signal is not clear enough for “reading” the live sequence of the DNA strand passage. “However, the possibility of detecting the passage of DNA with graphene nanoribbons is a breakthrough as well as a significant opportunity”, said Aleksandra Radenovic. She noted that, for example, the device is also able to detect the passage of other kinds of proteins and provide information on their size and/or shape.

This crucial step towards new methods of molecular analysis has received an ERC grant and is featured in an article published today in Nature Nanotechnology.

Source: http://actu.epfl.ch/news/graphene-nanoribbons-for-reading-dna/