Featured paper. Nanotubes that coil to the sound of music: tango or chorinho.

[Paper: Defect-Free Carbon Nanotube Coils. Nitzan Shadmi, Anna Kremen, Yiftach Frenkel, Zachary J. Lapin, Leonardo D. Machado, Sergio B. Legoas, Ora Bitton, Katya Rechav, Ronit Popovitz-Biro, Douglas S. Galvão, Ado Jorio, Lukas Novotny, Beena Kalisky, and Ernesto Joselevich. Nano Lett., 2016, 16 (4), pp 2152–2158. DOI: 10.1021/acs.nanolett.5b03417]

Nanotubes that coil to the sound of music: tango or chorinho

Among the many applications foreseen for carbon nanotubes, there are some nanoelectronic devices that make use of the excellent ability to conduct electricity, through the tiny graphene tubes. For the good performance of nanotubes in some of these applications, the most suitable are the coil configurations, formed by a single nanotube with its two ends free to make contact with other components within a device. Additionally, to not lose conductivity, the nanotube coil should have relatively low density of structural defects.

In practice however, it is not easy for a human being to achieve 1 nm diameter tubes to twist into spiral loops without generating imperfections and leaving their tips separate from the bundle.

Cover of Nano Letters. Representation of a coil formed by a single coiled carbon nanotube. Top right, the insert highlights, through a scanning electron microscopy image, the cross section of a real coil obtained by the team of scientists.

In an article published in the prestigious Nano Letters journal, highlighted in the cover of the April issue of this year, a team of 14 scientists reported the formation of defect-free nanotube coils with free ends, from a spontaneous coiling mechanism of single-wall carbon nanotubes. The study was led by researchers from the Weizmann Institute of Science (Israel) with the participation of four scientists from Brazilian universities (State University of Campinas, Unicamp; Federal University of Minas Gerais, UFMG, and Federal University of Roraima), from ETH Zürich (Switzerland) and from the Bar-Ilan University (Israel).

The team placed iron nanoparticles on silicon dioxide substrates and added a carbon-containing gas – a combination known to promote the growth of long single-wall nanotubes, which can reach more than 100 microns in height. The nanotubes grow perpendicular to the substrate like a forest of trees.

Under these conditions, the scientists created several carbon nanotubes samples, and some were spontaneously coil shaped. The authors analyzed the nanotube coils using SEM, TEM and AFM, obtaining information such as diameter, height and number of coil turns. Using the Raman spectroscopy technique, the authors continued investigating the nanotube coils and found a very low concentration of structural defects and also found that the diameter and chirality of the nanotubes were the same throughout the coil. The Raman spectroscopy analyses were partially carried out at the UFMG by Brazilian Professor Ado Jorio.

To understand the coil formation mechanism, the team used atomistic molecular dynamics simulations, used to depict the physical movements of atoms and molecules. These simulations were headed by Professor Douglas Soares Galvão (Institute of Physics Gleb Wataghin – Unicamp) and carried out by the postdoctoral researcher Leonardo Dantas Machado, former student of Galvão, and by Professor Sergio Benites Legoas (Federal University of Roraima), ex-postdoctoral grant holder in Galvão’s group. At IFGW – Unicamp, Prof. Galvão heads a research group specialized in simulation and computer modeling of nanostructured materials, particularly involving nanowires and nanotubes, and often collaborating with experimental groups from different countries. Through the simulations, the group is able to study, understand and predict phenomena that are sometimes not directly viewed or accessed experimentally in the time scale in which they occur.

Generally speaking, the simulations showed that after growing vertically, the nanotubes that had formed coils began to deposit on the substrate from the bottom up, forming the first turn as a result of their interaction with the carbon gas flow and with the substrate. After this first step, the nanotubes continued to spontaneously and steadily be deposited in a coil-like shape, completing up to 74 turns.

The team also investigated the performance of the coils as inductors (coiled devices that generate magnetic fields when an electrical current passes through, also known as electromagnetic coils) – a nanotube application that had not been studied until now. In the Nano Letters article the nanotube coils showed that despite being highly conductive, they are not yet ready to be used as efficient inductors. However, in the article the analysis of its electrical and magnetic behavior presented new and valuable information which can be used to develop inductive devices from nanotubes.

Cover of Physical Review Letters highlighted in 2013 another article of the international team of scientists, led by Galvão, on carbon nanotube coils.

According to Professor Galvão, the paper published in Nano Letters is a continuation of a previous project on carbon nanotube serpentines that involved his group, the group of Israel, led by Ernesto Joselevich, and Professor Ado Jorio (UFMG). This first study also produced an article featured on the cover of a prestigious journal, the Physical Review Letters (Dynamics of the Formation of Carbon Nanotube Serpentines, L. D. Machado, S. B. Legoas, J. S. Soares, N. Shadmi, A. Jorio, E. Joselevich, and D. S. Galvão, Phys. Rev. Lett. 110, 105502 – Published 8 March 2013).

Galvão recounts that the collaboration between the Brazilians and the Israel group began at a conference in Spain, where he attended a presentation by Joselevich on serpentine-shaped carbon nanotubes. “I believed it was a very interesting problem”, says Galvão. Coincidentally, the two scientists met again in a Brazilian event of condensed matter physics and had lunch together with Ado Jorio. That is when their collaboration began. “From the point of view of simulation, it was a very challenging and difficult project (in addition to specifically developing new protocols for the problem, the simulations involve millions of atoms), but Leonardo and Legoas were able to solve this”, says Galvão.

In addition to being consistent from the scientific point of view, the simulations were interesting from an aesthetic point of view. In this regard, Professor Galvão shares an anecdote. “Joselevich, who is Argentine by birth, knows Brazil and the Brazilian culture quite well. The first time he saw the serpentine simulations, he remembered the melody of “Brasileirinho” (a famous piece of chorinho music). We prepared some video versions incorporating the Brasileirinho as the soundtrack in his honor, jesting with the Brazil-Argentina rivalry, and others with tangos. The Brasileirinho wins, of course”, says the professor jokingly.

Two videos of nanotube dancing and forming coils can be accessed free of charge in the supporting info published with the paper in Nano Letters: http://pubs.acs.org/doi/abs/10.1021/acs.nanolett.5b03417

Interviews with plenary speakers of the XV B-MRS Meeting: Ado Jorio (UFMG, Brazil).

Sixteen years ago, working as a post-doctoral fellow at the Massachusetts Institute of Technology (MIT) in the group of professor Mildred Dresselhaus, the Brazilian physicist Ado Jorio de Vasconcelos headed a study that would produce the first successful result of the application of Optics, more precisely Raman spectroscopy, in the individual characterization of carbon nanotubes – keeping in mind that nanotube´s walls are just one atom thick, with diameters typically about one nanometer. In the MIT website, the page of Professor Mildred, who has been studying carbon nanostructures at MIT for more than 50 years, reinforces the importance of the work she has carried out with Jorio: 5 of the 6 publications selected by the emeritus professor are co-authored by Jorio.

When Ado Jorio began his postdoc he was 28 years old and had just finished his doctorate in Physics from the Federal University of Minas Gerais (UFMG). His thesis was on phase transitions in incommensurate systems, conducted under the guidance of Professor Marcos Assunção Pimenta. Prior to that, he earned his bachelor’s degree in Physics, also from UFMG, after studying Electrical Engineering for three years.

After the postdoc at MIT, Jorio returned to UFMG and was later accepted as associate professor of the university in 2002 via a public selection procedure. From 2007 to 2009 he held a position at the Brazilian National Institute of Metrology, Quality and Technology (Inmetro) to develop nanometrology-related activities. In 2010, he became full professor of UFMG and that same year took over the direction of the Coordination of Transfer and Innovation of the University until 2012. In 2013 he was at ETH Zurich (Switzerland) as a visiting professor, carrying out teaching and research activities. In August 2016 he became Dean for Research of UFMG.

Since 2002, Jorio has expanded the subject of his post-doctoral work. He has conducted research in optics and the development of scientific instrumentation, namely the study of carbon nanostructures with various applications. An example of this diversity is a study in which Jorio participates, in which nanotechnology field techniques are used to understand details of the composition of the “Indian black earth”, a highly fertile soil with carbon sequestration potential, which is found in places formerly inhabited by Indians in the Brazilian Amazon.

Jorio holds one of the highest H-index among scientists in Brazil: 74, according to Google Scholar. He is also one of the most cited researchers in the world, evidenced by the inclusion of his name in the latest Thomson Reuters international list, which tabulated 1% of the most frequently cited papers in each knowledge area among all the indexed scientific articles between 2003 and 2013. Jorio is the author of over 180 scientific articles and 20 books or book chapters, and 8 patent applications. According to Google Scholar, his publications combine more than 30,000 citations.

His contributions have received numerous acknowledgments from prestigious institutions, such as the Somiya Award from the International Union of Materials Research Societies in 2009; the ICTP Prize of the Abdus Salam International Centre for Theoretical Physics in 2011, and the Georg Forster Research Award by the Humboldt Foundation in 2015, among many other national and international awards.

In the XV Brazil-MRS (SBPMat) Meeting, Ado Jorio will deliver a plenary lecture on a topic in which he is one of the world’s leading experts, the use of Raman spectroscopy to study carbon nanostructures. The Brazilian scientist will talk about how the technique evolved until reaching the nanoscale. He also promises to reveal some tactics that allow using light, whose wavelength is at least hundreds of nanometers, as a probe to investigate structures of only few nanometers.

See our interview with this member of the Brazilian research community in Materials and plenary speaker at our annual event.

SBPMat Newsletter: – Tell us what led you to become a scientist and work in the Materials area.

Ado Jorio: – It was a winding path! I entered university to study electrical engineering. Back then I played in a progressive rock band, so I looked for scientific research in the area of music. I was told to talk to a teacher at the physics department who enjoyed music, studied acoustics and materials. That’s how my career began and which ended up in materials science.

SBPMat Newsletter: – In your own words, what are your main contributions to the Materials area.

Ado Jorio: – I would say there are two main contributions. The first is in the area of carbon nanotubes, I have shown that optics could be brought to the level of individual nanotubes. This gave way to a very broad research field because there are various types of nanotubes, depending on their diameter and chirality. Before this work, people were studying nanotubes. After this work, people began to study specific types of nanotubes. It would be equivalent to saying that researchers studying the atom then realized that there are different types of atoms. The article that was the linchpin of this discovery was the [PRL86, 1118 (2001)]. The second contribution was the advancement of optics to study carbon nanostructures more broadly. I worked on several fronts, from scientific instrumentation for optical measurements below the diffraction limit, to the study and characterization of defects, approaching materials of interest in soil science, biotechnology and biomedicine. Some key references are the books “Raman Spectroscopy in Graphene Related Systems” and “Bioengineering Applications of Carbon Nanostructures”.

SBPMat Newsletter: – We always invite the interviewee to leave a message for the readers who are beginning their scientific careers. Many of these readers would like to one day achieve an H index like yours. What do you say to them?

Ado Jorio: – Make a big effort to attend conferences and make great presentations, always! Science is a debate and you have to be heard. Never repeat the same presentation. Each public requires a specific focus. Of course this advice depends on funding, but since the beginning of my career I have always spent my own money to fund my travels, and I still do this.

SBPMat Newsletter: – Leave a message or invitation to your plenary lecture for the readers who will participate in the XV Brazil-MRS (SBPMat) Meeting.

Ado Jorio: – After all of the above, and since the title and abstract are available, I can only offer my thanks to those who will honor me with their presence. It will be an honor to have these colleagues in the auditorium.


Link to the summary of the plenary lecture of Ado Jorio: http://sbpmat.org.br/15encontro/speakers/abstracts/7.pdf

Featured paper: Vibrations of manipulated nanotubes.

[Paper: Strain Discontinuity, Avalanche, and Memory in Carbon Nanotube Serpentine Systems. Muessnich, Lucas C. P. A. M.; Chacham, Helio; Soares, Jaqueline S.; Neto, Newton M.; Shadmi, Nitzan; Joselevich, Ernesto; Cancado, Luiz Gustavo; Jorio, Ado. Nano Lett. 2015, 15 (9), pp 5899–5904. DOI: 10.1021/acs.nanolett.5b01982]

Vibrations of manipulated nanotubes.

Scientists from Brazilian institutions, in collaboration with researchers from Israel, “manipulated” carbon nanotubes of 1 nm diameter deposited on quartz surfaces and analyzed strain and displacements produced by this nanointervention. The team identified some behavior patterns in the nanotubes – quartz system and formulated a mathematical model applicable to systems formed by one- and two-dimensional materials over various substrates. The results of the study were recently published in Nano Letters.

To perform the experiments, the Brazilian investigators used samples idealized and produced in the Weizmann Institute of Science (Israel), in which the nanotubes are serpentine-shaped (composed of parallel segments connected together by U-shaped curves).These samples offered a desirable complexity, fostered by both the nanotubes format and the anisotropic character of quartz, which makes adhesion of nanotubes to the substrate not the same at all points.

In order to “manipulate” the system, the researchers used the tip of an atomic force microscope (AFM) built in the laboratory, which allows to change the position of nanometric particles and even of atoms, and to measure in situ the optical spectrum of nanostructures. In each sample, the tip touched a point of the quartz substrate and pushed toward the nanotube, and then proceeded to the optical analysis.

Before and after nanomanipulation, the scientists analyzed a number of points in the nanotube using the technique of Raman spectroscopy, which provides information about the frequency in which the atoms vibrate in the area being studied. More specifically, researchers focused on the frequency of the “G band”, which is used to infer the strain measurements of a considered point, since changes in the frequency of the “G band” are proportional to changes in strain.

Thus, scientists were able to identify and analyze different behavior of the nanotubes after nanomanipulation; for example, the detachment of the substrate and the intense displacement of a full stretch of the nanotube that had received two manipulations at the same point.

In addition to performing the experimental work, the authors of the article in Nano Letters managed to condense the complexity of behaviors they observed in a mathematical model (an equation) capable of explaining them theoretically and predicting these phenomena in similar systems. “The paper proposes a relatively simple model to describe complex effects of nanostructures adhesion in support media,” says Ado Jório, professor in the Department of Physics of the Federal University of Minas Gerais (UFMG) signing the letter as corresponding author.

The research that led to the Nano Letters article was developed within the master’s, doctoral and postdoctoral work of three authors of the letter, in the context of the Brazilian Network for Research and Instrumentation in Optical Nano-Spectroscopy, a project funded by the National Council for Scientific and Technological Development (CNPq) and coordinated by Ado Jório. “This is the result of a broad scientific instrumentation project, which aims at reaching the level of manipulating nanostructures and measuring, accurately, the effect of this process at the nanoscale,” says Jório.

The figure shows one of the 34 serpentine-shaped nanotubes on crystalline quartz substrate studied by the authors of the article. To the left of the reader is the nanotube before manipulation. To the right, following the sequence, the same nanotube after the intervention, with the consequent evident strain. The central segment of the nanotube, where the nanomanipulation occurred, was colorized, the gray scale indicating the frequency of the G band in that place. Finally, farther to the right, the chart displays the frequency of G band measured by Raman spectroscopy in successive points of this nanotube (graphical representation of gray hues): the black circles refer to non-manipulated nanotube and the gray colored circles, to the manipulated ones.