Tag Archives: R. Martel

Replace silicon with black phosphorus instead of graphene?

I have two black phosphorus pieces. This first piece of research comes out of ‘La belle province’ or, as it’s more usually called, Québec (Canada).

Foundational research on phosphorene

There’s a lot of interest in replacing silicon for a number of reasons and, increasingly, there’s interest in finding an alternative to graphene.

A July 7, 2015 news item on Nanotechnology Now describes a new material for use as transistors,

As scientists continue to hunt for a material that will make it possible to pack more transistors on a chip, new research from McGill University and Université de Montréal adds to evidence that black phosphorus could emerge as a strong candidate.

In a study published today in Nature Communications, the researchers report that when electrons move in a phosphorus transistor, they do so only in two dimensions. The finding suggests that black phosphorus could help engineers surmount one of the big challenges for future electronics: designing energy-efficient transistors.

A July 7, 2015 McGill University news release on EurekAlert, which originated the news item, describes the field of 2D materials and the research into black phosphorus and its 2D version, phosperene (analogous to graphite and graphene),

“Transistors work more efficiently when they are thin, with electrons moving in only two dimensions,” says Thomas Szkopek, an associate professor in McGill’s Department of Electrical and Computer Engineering and senior author of the new study. “Nothing gets thinner than a single layer of atoms.”

In 2004, physicists at the University of Manchester in the U.K. first isolated and explored the remarkable properties of graphene — a one-atom-thick layer of carbon. Since then scientists have rushed to to investigate a range of other two-dimensional materials. One of those is black phosphorus, a form of phosphorus that is similar to graphite and can be separated easily into single atomic layers, known as phosphorene.

Phosphorene has sparked growing interest because it overcomes many of the challenges of using graphene in electronics. Unlike graphene, which acts like a metal, black phosphorus is a natural semiconductor: it can be readily switched on and off.

“To lower the operating voltage of transistors, and thereby reduce the heat they generate, we have to get closer and closer to designing the transistor at the atomic level,” Szkopek says. “The toolbox of the future for transistor designers will require a variety of atomic-layered materials: an ideal semiconductor, an ideal metal, and an ideal dielectric. All three components must be optimized for a well designed transistor. Black phosphorus fills the semiconducting-material role.”

The work resulted from a multidisciplinary collaboration among Szkopek’s nanoelectronics research group, the nanoscience lab of McGill Physics Prof. Guillaume Gervais, and the nanostructures research group of Prof. Richard Martel in Université de Montréal’s Department of Chemistry.

To examine how the electrons move in a phosphorus transistor, the researchers observed them under the influence of a magnetic field in experiments performed at the National High Magnetic Field Laboratory in Tallahassee, FL, the largest and highest-powered magnet laboratory in the world. This research “provides important insights into the fundamental physics that dictate the behavior of black phosphorus,” says Tim Murphy, DC Field Facility Director at the Florida facility.

“What’s surprising in these results is that the electrons are able to be pulled into a sheet of charge which is two-dimensional, even though they occupy a volume that is several atomic layers in thickness,” Szkopek says. That finding is significant because it could potentially facilitate manufacturing the material — though at this point “no one knows how to manufacture this material on a large scale.”

“There is a great emerging interest around the world in black phosphorus,” Szkopek says. “We are still a long way from seeing atomic layer transistors in a commercial product, but we have now moved one step closer.”

Here’s a link to and a citation for the paper,

Two-dimensional magnetotransport in a black phosphorus naked quantum well by V. Tayari, N. Hemsworth, I. Fakih, A. Favron, E. Gaufrès, G. Gervais, R. Martel & T. Szkopek. Nature Communications 6, Article number: 7702 doi:10.1038/ncomms8702 Published 07 July 2015

This is an open access paper.

The second piece of research into black phosphorus is courtesy of an international collaboration.

A phosporene transistor

A July 9, 2015 Technical University of Munich (TUM) press release (also on EurekAlert) describes the formation of a phosphorene transistor made possible by the introduction of arsenic,

Chemists at the Technische Universität München (TUM) have now developed a semiconducting material in which individual phosphorus atoms are replaced by arsenic. In a collaborative international effort, American colleagues have built the first field-effect transistors from the new material.

For many decades silicon has formed the basis of modern electronics. To date silicon technology could provide ever tinier transistors for smaller and smaller devices. But the size of silicon transistors is reaching its physical limit. Also, consumers would like to have flexible devices, devices that can be incorporated into clothing and the likes. However, silicon is hard and brittle. All this has triggered a race for new materials that might one day replace silicon.

Black arsenic phosphorus might be such a material. Like graphene, which consists of a single layer of carbon atoms, it forms extremely thin layers. The array of possible applications ranges from transistors and sensors to mechanically flexible semiconductor devices. Unlike graphene, whose electronic properties are similar to those of metals, black arsenic phosphorus behaves like a semiconductor.

The press release goes on to provide more detail about the collaboration and the research,

A cooperation between the Technical University of Munich and the University of Regensburg on the German side and the University of Southern California (USC) and Yale University in the United States has now, for the first time, produced a field effect transistor made of black arsenic phosphorus. The compounds were synthesized by Marianne Koepf at the laboratory of the research group for Synthesis and Characterization of Innovative Materials at the TUM. The field effect transistors were built and characterized by a group headed by Professor Zhou and Dr. Liu at the Department of Electrical Engineering at USC.

The new technology developed at TUM allows the synthesis of black arsenic phosphorus without high pressure. This requires less energy and is cheaper. The gap between valence and conduction bands can be precisely controlled by adjusting the arsenic concentration. “This allows us to produce materials with previously unattainable electronic and optical properties in an energy window that was hitherto inaccessible,” says Professor Tom Nilges, head of the research group for Synthesis and Characterization of Innovative Materials.

Detectors for infrared

With an arsenic concentration of 83 percent the material exhibits an extremely small band gap of only 0.15 electron volts, making it predestined for sensors which can detect long wavelength infrared radiation. LiDAR (Light Detection and Ranging) sensors operate in this wavelength range, for example. They are used, among other things, as distance sensors in automobiles. Another application is the measurement of dust particles and trace gases in environmental monitoring.

A further interesting aspect of these new, two-dimensional semiconductors is their anisotropic electronic and optical behavior. The material exhibits different characteristics along the x- and y-axes in the same plane. To produce graphene like films the material can be peeled off in ultra thin layers. The thinnest films obtained so far are only two atomic layers thick.

Here’s a link to and a citation for the paper,

Black Arsenic–Phosphorus: Layered Anisotropic Infrared Semiconductors with Highly Tunable Compositions and Properties by Bilu Liu, Marianne Köpf, Ahmad N. Abbas, Xiaomu Wang, Qiushi Guo, Yichen Jia, Fengnian Xia, Richard Weihrich, Frederik Bachhuber, Florian Pielnhofer, Han Wang, Rohan Dhall, Stephen B. Cronin, Mingyuan Ge1 Xin Fang, Tom Nilges, and Chongwu Zhou. DOI: 10.1002/adma.201501758 Article first published online: 25 JUN 2015

© 2015 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim

This paper is behind a paywall.

Dexter Johnson, on his Nanoclast blog (on the Institute for Electrical and Electronics Engineers website), adds more information about black phosphorus and its electrical properties in his July 9, 2015 posting about the Germany/US collaboration (Note: Links have been removed),

Black phosphorus has been around for about 100 years, but recently it has been synthesized as a two-dimensional material—dubbed phosphorene in reference to its two-dimensional cousin, graphene. Black phosphorus is quite attractive for electronic applications like field-effect transistors because of its inherent band gap and it is one of the few 2-D materials to be a natively p-type semiconductor.

One final comment, I notice the Germany-US work was published weeks prior to the Canadian research suggesting that the TUM July 9, 2015 press release is an attempt to capitalize on the interest generated by the Canadian research. That’s a smart move.

Dye your carbon nantubes for better resolution

A team at the Université de Montréal has developed a technique for making nanoscale objects more easily seen. From a Dec. 2, 2013 news item on Nanowerk (Note: A link has been removed),

Richard Martel and his research team at the Department of Chemistry of the Université de Montréal have discovered a method to improve detection of the infinitely small. Their discovery is presented in the November 24 online edition of the journal Nature Photonics (“Giant Raman scattering from J-aggregated dyes inside carbon nanotubes for multispectral imaging”).

“Raman scattering provides information on the ways molecules vibrate, which is equivalent to taking their fingerprint. It’s a bit like a bar code,” said the internationally renowned professor. “Raman signals are specific for each molecule and thus useful in identifying these molecules.”

The discovery by Martel’s team is that Raman scattering of dye-nanotube particles is so large that a single particle of this type can be located and identified. All one needs is an optical scanner capable of detecting this particle, much like a fingerprint.

I haven’t been able to track down the English language version of the Dec. 2, 2013 Université de Montréal news release but here are some excerpts from the French language version by Dominique Nancy,

Grâce à l’alignement de molécules de colorants encapsulées dans un nanotube de carbone, les chercheurs ont réussi à amplifier le signal Raman jusqu’ici pas assez puissant de ces colorants pour permettre leur détection. L’article présente les données expérimentales d’une diffusion extraordinaire de lumière visible sur une particule de taille nanométrique.

«La diffusion Raman contient de l’information sur les modes de vibration des molécules, ce qui équivaut à relever leurs empreintes digitales. C’est un peu comme un code à barres, explique le professeur de renommée internationale. Le signal Raman est propre à chaque molécule et donc très utile pour la repérer.»

Le mode de diffusion Raman est un phénomène optique mis au jour en 1928 par le physicien Chandrashekhara Venkata Râman. L’effet consiste en la diffusion inélastique d’un photon, c’est-à-dire le phénomène physique par lequel un milieu peut modifier la fréquence de la lumière qui y circule. ….


Mais jusqu’à ce jour, le signal Raman des molécules était trop faible pour répondre efficacement aux besoins en imagerie optique. Les chercheurs avaient donc recours à d’autres techniques optiques plus sensibles mais moins précises, car elles ne possèdent pas de «code à barres». «Il est toutefois possible techniquement de voir les signaux Raman avec un spectromètre lorsque la concentration des molécules est assez élevée, indique M. Martel. Mais cela limite les applications du Raman.»


Composé d’une centaine de molécules colorées et alignées dans le cylindre, le nanotraceur est 50 000 fois plus petit qu’un cheveu. Il mesure environ un nanomètre de diamètre et 500 de long. Et pourtant les particules colorées encapsulées dans le nanotube de carbone donnent un signal Raman un million de fois plus intense que celui des autres molécules autour de l’objet.

On peut aussi imaginer un douanier qui scannerait notre passeport avec un mode Raman multispectral (aux signaux multiples). Ces nanotraceurs pourraient également être utilisés dans les encres des billets de banque, rendant la contrefaçon presque impossible.

La beauté de la chose, affirme Richard Martel, c’est que le phénomène est général et plusieurs types de colorants peuvent servir à la fabrication des nanotraceurs, dont les «codes à barres» sont tous différents. «On a fabriqué jusqu’ici plus de 10 traceurs et il semble qu’il n’y a pas de limite, dit-il. On pourrait donc en principe créer autant de nanotraceurs qu’il y a de bactéries et utiliser ce principe pour les déceler avec un microscope fonctionnant en mode Raman.»

As I have noted many times here, my linguistic skills are shaky but here’s my overview:

Due to the colouring agent researchers have added to the carbon nanotubes in the experiement, it is possible to amplify the Ramen signal allowing for an extraordinary resolution making nanoscale objects optically visible.

With the dyed carbon nanotubes, the new technique offers the equivalent of a unique digital fingerprint or, Martel also describes it, as a unique bar code for nanoscale objects. Standard Raman technique can be used to detect nanoscale objects when there’s a high concentration but is not not powerful enough to optically detect nanoscale objects in lower concentrations or with any precision, i.e., the ability to detect a unique ‘fingerprint’ or ‘bar code’.

The nanotracer, the dyed carbon nanotube, is 1/50,000 the diameter of a human hair and can measure object of approximately 500 nm in diameter.

Martel sees a number of applications for this new technique include biomedical applications.

You may want to take a look at the news item on Nanowerk for a better and more complete translation.

Here’s a link to and a citation for the English language paper,

Giant Raman scattering from J-aggregated dyes inside carbon nanotubes for multispectral imaging by E. Gaufrès, N. Y.-Wa Tang, F. Lapointe, J. Cabana, M.-A. Nadon, N. Cottenye, F. Raymond, T. Szkopek, & R. Martel. Nature Photonics (2013) doi:10.1038/nphoton.2013.309 Published online 24 November 2013

This article is behind a paywall.