Featured paper: United atoms, adhered films.

[Paper: Identification of the Chemical Bonding Prompting Adhesion of a-C:H Thin Films on Ferrous Alloy Intermediated by a SiCx:H Buffer Layer. F. Cemin, L. T. Bim, L. M. Leidens, M. Morales, I. J. R. Baumvol, F. Alvarez, and C. A. Figueroa. ACS Appl. Mater. Interfaces, 2015, 7 (29), pp 15909–15917. DOI: 10.1021/acsami.5b03554]

United atoms, adhered films

With an innovative approach on an academic and industrial problem, a study wholly conducted in Brazil has brought significant advances in the understanding of the adhesion of DLC (diamond-like carbon) films on steels. The results of the work, which were recently published in the journal Applied Materials and Interfaces of the American Chemical Society (ACS), can help optimize such adhesion, thus prolonging the life of DLC films and expanding their use in the industry.

The team of scientists was particularly interested in the DLC potential to increase the energy efficiency of internal combustion engines. In fact, if all car engine components were coated with DLC films, the owner of that car would spend 5-10% less fuel and save the environment a good deal of greenhouse gas emissions and other pollutants, among other advantages. The reason for such saving lies in the ultra-low friction of DLC, since friction is the force responsible for wasting fuel while providing resistance to the motion that the parts of the engine make among themselves.

However, DLC has a drawback: it does not adhere to steel, causing quick delamination of the films from the substrate. To work around this problem, both in the laboratory and in industry, it is customary to deposit a layer containing silicon, known as interlayer, over the steel. The DLC film is then deposited on top of it. The result is a “sandwich”, which does not come undone easily.

In the paper published in the ACS journal, the authors experimentally analyzed a “sandwich” consisting of a steel substrate, an interlayer of silicon carbide (SiC) and a DLC film. Both the interlayer and the film were deposited by a quick process that generated thin layers of a few nanometers (up to 10). Mainly, two issues differentiated this study from other similar studies in the scientific literature. Firstly, the team focused in analyzing what happened in two regions corresponding to the interfaces of the interlayer with the film (upper) and with the steel (lower). Secondly, the scientists made a chemical approach on the matter of adhesion.

“This work has identified the chemical structure that generates adhesion in lower (SiCx: H/steel) and upper (a-C:H/SiCx:H) interfaces, which make up the a-C:H/SiCx:H/steel sandwich structure”, said Carlos A. Figueroa, professor at the University of Caxias do Sul (UCS) and corresponding author of the article. “The mechanisms found in the bibliography raised physical or mechanical aspects, but not chemical ones,” said Figueroa, who graduated in chemical sciences from the University of Buenos Aires (UBA) and has a doctorate degree in physics from the State University of Campinas (Unicamp). “However, adhesion is generated by the sum of all individual chemical bonds existing among DLC, the interlayer and steel,” he adds.

Scientists kept a constant film deposition temperature, but varied the interlayer deposition temperature, generating a group of samples deposited at 100° C and another one at over 300° C. After analyzing them by a variety of techniques, especially, X-ray photoelectron spectroscopy (XPS), researchers found that the lower interface of the interlayer, regardless of the deposition temperature, was largely composed of silicon atoms (from the interlayer) bonded to iron atoms (from the substrate). At the upper interface of the interlayer, the team found differences according to the deposition temperature of the interlayer. In the samples deposited at 100° C, oxygen atoms bonded many of the silicon and carbon atoms, preventing the carbon of the film to strongly bond to the silicon of the interlayer, and resulting in a film without good adhesion. In turn, scientists did not find oxygen in the interface of the samples deposited at over 300° C, but bonds between carbon and silicon atoms, which caused the film adhere well to the interlayer.

Schematic illustration of the chemical bonds present in the upper and lower interfaces of the interlayer deposited at 100° C (left) and over 300° C (right). In the center, a real engine cylinder displays, on the left side, a DLC film (in black) delaminated on the interlayer deposited at 100° C and, in the right side, the same film well adhered on the interlayer deposited over 300° C.

Besides Figueroa and students of the research group he leads in UCS, also authored the paper researchers from the Institute of Physics at Unicamp, where the XPS measures were made, as well as a scientist from the Federal University of Rio Grande do Sul (UFRGS) that, together with the other authors, participated in the discussion of results.

The work received the support from Brazilian Science funding bodies (Capes, CNPq through INCT National Institute of Surface Engineering, Fapergs), of Petrobras, UCS, the European Commission (Marie Skłodowska – Curie Actions) and Plasmar Tecnologia (a small company that is developing, through a TECNOVA RS project, an industrial equipment to deposit DLC on steel aiming to increase the energy efficiency of car engines).

SBPMat´s community people: an interview with Fernando Lázaro Freire Junior.

Professor Fernando Lázaro Freire Júnior.

On May 6th, at the Naval School of Rio de Janeiro, the Brazilian Academy of Sciences (ABC) held the tenure ceremony of its new members, elected in a process of nomination and evaluation by their peers, performed throughout 2013. In the event, 24 scientists were assigned as full members of ABC.  Among those, in the field of Physical Sciences, there was Professor Fernando Lázaro de Freire Junior, Materials researcher and former president of SBPMat.

Contemplating the ideia of being a researcher, Fernando Lázaro chose to graduate with a Bachelor’s degree in Physics by the Pontifical Catholic University of Rio de Janeiro (PUC-RIO), earning it in 1978. In 1979, he started teaching in the same university, while attending his Master’s (1979-1981) and Doctorate (1981-1985) courses in Physics there. During his graduate studies, Fernando Lázaro made his first scientific interventions in the field of Materials by means of an ion accelerator, initially used by him for works in Atomic Physics. In 1998, he went to Università degli Studi di Padova (in Italy) for his Postdoctoral studies, working with materials surfaces and interfaces.

From 2003 to 2008, he was the Director of PUC-Rio’s Physics Department. From 2008 to 2012, he coordinated the field of Physics and Astronomy in the Research Foundation of the State of Rio de Janeiro (FAPERJ). In Europhysics Letters (a journal from the European Physical Society), Professor Lázaro worked as coeditor between 2006 and 2010, and advisory editor from 2010 to 2013. In SBPMat, he served two consecutive terms as president, two as scientific director and one as financial director.

Currently, Fernando Lázaro is a Full Professor in PUC-Rio and director of Centro the Brazilian Center for Research in Physics (CBPF), in addition to being a member of the FAPERJ’s Higher Board and coordinator of the National Institute of Surface Engineering. Author of over 170 scientific articles, with more than 2500 citations, he is a level 1A researcher in the Brazilian National Research Foundation, CNPq. Among his most relevant papers, there are several studies on carbon-based materials: DLC (diamond-like carbon) films, nanotubes and, more recently, graphene.

Following there is a brief interview with the researcher.

SBPMat newsletter: – Tell us a little about your history: what led you to become a scientist and work in the field of Materials?

Fernando Lázaro: – I always enjoyed Physics and Mathematics during high school, but in 1974 I had no ideia, when I applied for college entrance exams, that it was possible to do research in Brazil. Because of this, I took the exam to major in Electrical Engineering in PUC-Rio, and only there I realized that it was possible to perform researches in the field of Physics, in Brazil. Then, I transferred myself to the Bachelor’s in Physics, which was easier, as in 1975 PUC-Rio already had a common Basic Cycle for the whole of its Scientific and Technical Center. So, I didn’t waste any time. I was in my second year in the undergraduate studies. My graduate studies, then, still in PUC-Rio, were in Atomic Physics, using an ion accelerator as a working tool. As such accelerator was also a great tool to analyze materials, it was through this path that I entered into the field of Materials.

SBPMat newsletter- What do you consider as your main contributions to the field of Materials?

Fernando Lázaro: – My research has always been conducted in collaboration with several colleagues and students, and I think we made an important contribution to the study of nanostructured carbon films (diamond-like carbon films, DLC), as attested by the papers with a high number of citations and all the invitations to be invited lecturer in many international congresses. It is evident that supervising students has been important too, as well the management positions in PUC-Rio, CBPF and SBPMat.

SBPMat newsletter: – Choose some of your more highlighted papers, and comment on them, if possible.

Fernando Lázaro: – My most cited paper is an article in Applied Physics Letters, published in 1992, coauthored by Carlos Achete, from COPPE/UFRJ, and Dante Franceschini, currently at UFF, on the nitrogen incorporation in DLC films  [Franceschini, D. F. ; Achete, C. A. ; Freire Junior, F. L. Internal Stress Reduction By Nitrogen Incorporation In Hard a-C:H Thin Films. Applied Physics Letters, New York, v. 60, p. 3229-3231, 1992]. It was released at the right time, and offered a relevant result for the issue of the applications of such materials, namely, the decrease of the internal tension of the film (an important factor in the debonding of films from the substrates), without a significant change in its hardness.

SBPMat newsletter: – In your opinion, what are the main challenges in your current research field for Materials Science and Engineering?

Fernando Lázaro: – I have been working with graphene and carbon nanotubes. For both, the production of good quality samples, in a controlled and profitable form, still represents a great obstacle for the use of those materials in a broader way than the one that has been verified up to this point.

SBPMat newsletter: – Send a message to our readers who are starting their careers as scientists.

Fernando Lázaro – An encouraging message. The material working conditions nowadays are much better than when I started, three decades ago; the same can be said about the wages in academia. So, things have improved and tend to keep getting better, and I think it is feasible to conduct good quality researches, with an international impact, in Brazil.