When Marília Junqueira Caldas began working with IT in 1970, the use of computers was still in its early stages in Brazil, even at universities. However, from then on, computational tools constantly accompanied the scientist on her path of scientific discoveries.
At that time, Marília was a student in the undergraduate Physics course at the University of São Paulo (USP), where she had enrolled in 1968. She graduated in 1974 and, the following year, began her Master’s degree in Physics at the same institution. She obtained her Master’s degree in 1978 with a thesis on mathematical modeling applied to Oceanography. In the same year, she began her PhD in Physics, also at USP. In 1981, she defended her dissertation in Materials Physics, an area in which she works to this day, having made a series of impactful contributions in materials such as silicon, conductive polymers, graphene and hybrid structures.
Between 1983 and 1984, she did her postdoctoral studies at the Solar Energy Research Institute (SERI) in the United States. Back in Brazil, she became a professor at the Gleb Wataghin Institute of Physics (IFGW) at Unicamp. In 1986, she returned to her alma mater, USP, as a professor at the Physics Institute (IFUSP) in the Department of Mechanics and Materials Physics. Throughout the 1990s, the scientist worked as director and administrator of the IFUSP Electronic Computing Center. In 2000, she became a full professor at USP. From 2010 to 2014, she served as head of the department.
Now 74 years old, Marília continues to teach at USP. From her imminent retirement, she will dedicate herself entirely to continuing the research she has been conducting on organic and inorganic semiconductor materials with applications in devices that interact with light.
With over 100 scientific articles published in international journals and 23 supervisions of master’s and doctoral projects, Marília Caldas is a CNPq research productivity fellow at the Senior Researcher level.
At the opening of the XXII B-MRS Meeting, on September 29 of this year, she will deliver the Memorial Lecture Joaquim da Costa Ribeiro, an honor granted annually by B-MRS to senior researchers with outstanding careers within the Materials research community.
Learn more about this distinguished scientist in this interview she gave to the B-MRS Newsletter.
B-MRS Newsletter: Tell us how you became a scientist.
Marília Junqueira Caldas: Mathematics has always been a great attraction for me, starting as a game when I was a child and continuing throughout my adolescence – initially touching on geometry and the beauty of shapes, their appearances in nature, their movements, and so on. My father was an architect and at first I thought about becoming one too. During high school – which I chose, as it was called at the time, the “scientific” one – I had Physics classes with Professor “Dona” Célia, brilliant and motivating like few others! My classmates also remember Dona Célia, and it was she, in her classes, who encouraged me to take the Physics entrance exam (at the same time as the Architecture one!). Just to top it off, the textbook we used with Dona Célia was Halliday’s, which I later found in my first years at IFUSP!
During my undergraduate studies, right after those “lead years” of 1968-69, in 1970 I began my life in the computing environment. This was due to the existence of the Nuclear Physics particle accelerator (Pelletron) at IFUSP, which needed and implemented the Applied Mathematics Sector (SEMA), that is, a sector for analyzing data acquired by the accelerator and which needed to be “translated”. Under the guidance of Prof. Claudio Mammana, I began my career in IT, initially to assist users, which later led me to become a user. I was introduced to data analysis, the FORTRAN programming system, and so on, so that as my academic life progressed I continued to use computing resources to obtain results for problems that aroused my curiosity. Another very important factor was being able to visit the IFUSP library, since at the time it was the place where scientific news arrived from international journals.
As for the topics of interest, there were many, in different directions of Physics. I joined experimental laboratories and finally, at the beginning of my Master’s degree, I moved on to the sea, to ocean currents, how they develop and how they continue – an area of Fluid Dynamics that both fascinates and frightens us, especially if, like me, I have often been near the sea since childhood. Thus, during my Master’s degree I was able to go to the ocean (Oceanographic Ship Prof. Wladimir Besnard) to collect samples of “sea water”, an unparalleled experience. As for my dissertation specifically, under the guidance of Prof. Luiz Brunner de Miranda, I worked on analyzing current data collected to understand the flow of currents along our coast. This research already developed my interest in marine life and its dependence on the chemistry and photochemistry of the sea, the ocean, and led me to the study of molecules, etc. Thus, in another group now at IFUSP, I initially studied microsamples of various origins experimentally using gas chromatography. Later, I resumed my mathematical-computational characteristic and focused on the quantum mechanics of solids, which was of interest to me and to the general public at the time, specifically semiconductors such as silicon (Si) and the effect of the infinitesimal presence of other atoms and elements in their “body”, which are called defects in semiconductors. It is interesting to note that the term “defect” is strange, since they are what give the semiconductor the property we desire, such as photoactivity. In my case, I worked at the Group of Electronic Structure of Materials in the Department of Physics of Materials and Mechanics, where I did my doctorate under the supervision of Professor José Roberto Leite, who has unfortunately passed away.
I now turn to my doctoral work, which focused on “defect” states in Si, but which was carried out in a group that investigated several families of tetrahedral semiconductors, and which mainly introduced me to the use of electronic structure calculations, which are extremely important for the worldwide development of the entire science of electronic and optoelectronic devices.
B-MRS Newsletter: Think about the scientific discoveries you have made throughout your career and briefly describe those that you consider most relevant or interesting.
Marília Junqueira Caldas: Our first discovery, which was quite impressive for the entire semiconductor community, was an impurity in Si, the replacement of an atom in the crystal by an oxygen atom (O). Since the number of valence electrons in O is the same as in Si, plus 2 extra electrons, it was thought that it would act as a double donor, just like the isovalent impurities sulfur (S) and selenium (Se), with greater conductivity than the pure semiconductor. However, our study showed that in the case of O, a structural reorganization occurs at the location of the defect, electron-phonon coupling, which in fact introduces an acceptor state (captures electrons) in the Si band gap. Thus, the creation of a conductive state was ruled out, and the result was associated with a defect labeled at that time (late 1970s, early 1980s) as an A-center in Si, which extracts the conductive electrons from the system. This work was part of my PhD, and was carried out with what was available at the time for realistic first-principles calculations. As was common, my work became widely known by colleagues through its presentation at an international conference, and although it is rarely cited (based on today’s measurements), the result is now part of the knowledge base for Si devices [Caldas et al. 1980]. I continue to investigate defects in several different semiconductors to this day [Atambo et al. 2019]. On the other hand, after my PhD, I became interested in organic semiconductors, and I highlight here our work in the late 1980s on Polyaniline (PANI), a polymer that generated controversy in the community, as it was considered an insulator, or a high-gap semiconductor, even with doping, but experimentally it behaved like a p-type semiconductor with excellent conductivity. We showed that this very interesting property comes directly from the disorder inherent in polymeric systems, which caused quite an impact on the community. In this case, we used empirical and semi-empirical methods that allowed us to access very large systems [Galvão et al. 1989]. I continued working on polymeric systems, moving on to the conductors polyparaphenylene (PPP) and polyvinyl paraphenylene (PPV), now in collaboration with the University of Modena, focusing on electronic properties and moving on to optical properties, applying mostly first-principles functionals [Ferretti et al. 2003]. I believe that our contribution to understanding the behavior of these systems was impactful in the community. In another very common area now, I became interested in and we worked on two-dimensional systems such as graphene and variants, with defects or other atomic components, an area in which I also continue to work [Valência and Caldas 2017, Bonacci et al. 2022]. In another perspective, I focused on organic/inorganic interaction systems, such as polythiophene (PT) or oligothiophenes and oxide surfaces, and so on, where I continue to work given their importance for device assembly. In the last ten years (or more) I have focused mainly on devices for solar energy conversion, that is, photovoltaic devices, due to the global need for clean energy, which will continue to grow. As a final comment, I must say that the creation of the Brazilian National Institutes of Science and Technology (INCTs) was very important, of which I have been a member since the beginning through the IMMP (Multidisciplinary Institute of Polymeric Materials), which is now INEO (National Institute of Organic Electronics). Collaboration and interaction between researchers in Brazil was expanded and motivated by this great initiative of the INCTs, which in my case was very important due to the interaction with the experimental side.
B-MRS Newsletter: From the point of view of training researchers, creating laboratories, scientific dissemination and other aspects of a researcher’s career, what are your achievements that have had the greatest impact or given you the greatest satisfaction?
Marília Junqueira Caldas: It is difficult to choose, but probably what brought me the most satisfaction was, during my work as Coordinator of the USP Electronic Computing Center (CCE), the creation and implementation of a program which gave students at our university the opportunity to work directly with microcomputers, which at the time was very difficult and only possible for young people from high-income families. This achievement does not fall into the “categories” mentioned above, but the administration of a university is extremely important for the effectiveness and continuity of humanity’s progress. At the CCE, I dedicated myself to setting up the USPnet network, expanding and improving the quality of high-performance computers available for research activities, and, as I have already emphasized, making computing available to students. As for my research work, the interaction with Brazilian researchers outside my institute, whether in the state of São Paulo, in other states of Brazil, or abroad, has always been a very important stimulus for the continuity of my research activity. Finally, knowing that I helped to form, through mentoring activities, high-quality researchers, is my greatest return.
B-MRS Newsletter: In your profession as a teacher and researcher, have you encountered many difficulties related to the fact of being a woman?
Marília Junqueira Caldas: As in any profession, these difficulties exist, perhaps – I hope – less so now than in my time. I must say that due to my family, I have had fewer problems than usual, since my maternal grandmother was an anti-racism and anti-sexist activist, always applauded by my grandfather; my parents were extremely strong in these areas and always encouraged me. When working in the scientific community, I faced problems, as was common, but my advisor, Prof. José Roberto Leite, always had a positive and anti-sexist stance regarding the training of female students and supported our activities, including post-doctorate studies at other institutions, in an exemplary manner. As for the problem that I still remember as the most emblematic, it was when I asked for resources from a Brazilian funding agency to do my post-doctorate abroad, and it required a greater effort than usual – but I was granted the scholarship. I must also emphasize that, as advised by Prof. Leite, I did not put my full name when submitting a paper, only my initials and surname to avoid the sexist effect, and I remember to this day the first time I went to a conference abroad and presented a paper. At that time, we would put the complete article on paper, to be published in the proceedings or in a journal, and deliver it to the conference committee before the oral presentation. When I submitted my paper, I remember my colleague’s reaction: “Ah! So Caldas is a woman?”. I replied: “Yes, it is me!”.
B-MRS Newsletter: Leave a message for our younger readers who are starting a career as scientists in Brazil or are considering this possibility.
Marília Junqueira Caldas: Science is always a beautiful, intriguing road, and whenever you see something you don’t understand, it’s exciting. This beautiful road has a shortcut, a fork in the road every millimeter, where you can study, investigate, and learn. Apart from this almost poetic vision, the development of science in the current world brings many job opportunities to young people, in different directions, and along the way you can still learn and teach more.
References cited
Atambo, M.; Varsano, D.; Ferretti, A.; Ataei, S.S.; Caldas, M.J.; Molinari, E.; “Electronic and optical properties of doped TiO2 by many-body perturbation theory” – Physical Review Materials 3, p. 04501, 2019.
Bonacci, M.; Zanfrognini, M.; Molinari, E.; Ruini, A.; Caldas, M.J.; Ferretti, A.;” Excitonic effects in graphene-like C3N” – Physical Review Materials 6, p. 034009 2022.
Caldas, M.J.; Leite, J.R.;Fazzio, A.; “Theoretical-Study of the Si-A Center” – Physica Status Solidi B 98, p. K109, 1980.
Ferretti, A.; Ruini, A.; Molinari, E.; Caldas M.J.; “Electronic Properties of Polymer Crystals: The Effect of Interchain Interactions” – Physical Review Letters 90, p. 086401, 2003.
Galvão, D.S. ; Santos, D.A. ; Laks, B. ; Melo, C.P. ; Caldas, M.J.; “Role of Disorder in the Conduction Mechanism of Polyanilines” – Physical Review Letters 63, p. 786-789, 1989.
Valencia-García A.M.; Caldas, M.J.; “Single vacancy defect in graphene: Insights into its magnetic properties from theoretical modeling” – Physical Review B 96, p. 125431, 2017.
The call for thematic symposia is now open as part of the XXIII B-MRS Meeting program. The meeting will take place at the Salvador Convention Center, in Salvador, Bahia (Brazil), from September 28 to October 2, 2025. The chairs of the event are Luiza Amim Mercante (UFBA) and Daniel Souza Corrêa (Embrapa Instrumentação).
