Computational simulations carried out by researchers from IFGW and IQ explain the formation of nanowires and silver nanoparticles
Research conducted collaboratively by professors Edison Zacarias da Silva and Miguel San-Miguel, both from Unicamp, with the support of researchers from the Center for Functional Materials (CDMF) at the Federal University of São Carlos (UFSCar), deciphered the mechanism responsible for the formation of silver nanoparticles from silver tungstate (α-Ag2WO4), after this material is irradiated by an electron beam. “We carried out computer simulations that provided results very close to those obtained by bench experiments”, explains da Silva, who is a professor at the Gleb Wataghin Institute of Physics (IFGW). The study data were described in an article published on May 2nd by a high-impact scientific journal, the Journal of Physical Chemistry C.
According to Silva, the silver nanoparticles were obtained by CDMF researchers, during a study coordinated by professor Elson Longo. Scientists were investigating the properties of silver tungstate when they decided to analyze the material under an electron microscope. “After the tungstate was irradiated with the electron beam emitted by the electron microscope, something unexpected happened. The procedure caused a reaction that caused new structures to emerge within the material. When analyzing these new structures, Professor Longo's team verified that they were silver nanowires and nanoparticles, with some nanoparticles remaining free in a vacuum”, reports the IFGW professor.
The UFSCar group also found that these nanoparticles moved and met at a given moment, generating larger particles. This process, called coalescence, is similar to what occurs when two drops of water meet and merge, forming a larger drop. Given these findings, the challenge for researchers became understanding the mechanisms involved in both phenomena. The explanation fell to Silva and San-Miguel, the latter a professor at the Institute of Chemistry (IQ).
Simply put, the two professors from Unicamp, who had the collaboration of professor Giovani M. Faccin, from the Federal University of Grande Dourados (UFGD), produced computer simulations based on experimental data obtained by the UFSCar group. “We were very careful. We built several scenarios to try to understand the processes of nanoparticle formation and their joining. What we found is that the electric field of the electron beam causes a very interesting effect in these particles called surface plasma resonance. The particle is electrically neutral, but the electric field causes its electrical charges to oscillate, producing electric nanodipoles. When two nanodipoles align, they experience mutual attraction. This is when the nanoparticles meet and form a third, larger structure”, details Silva.
The scientists also found that at the moment coalescence occurs, a “defect” is formed in the area where the nanoparticles join. “The region is in disarray. The curious thing is that, suddenly, it becomes orderly again and the 'defect' disappears”, adds Silva. But how important is this type of discovery? According to the IFGW professor, the answer is related to the application of silver tungstate. The material has been used, for example, in photoluminescent devices or in bactericidal products. “By understanding these mechanisms, we pave the way for manipulating them in the future. The objective is obviously to improve the properties of interest”, explains the physicist.
One aspect he emphasizes is the complementary nature of experimental studies and computational simulations. “By producing virtual models, we can not only help explain a given phenomenon, we can also make some predictions. This is important because we can anticipate certain situations, which can be avoided or taken advantage of by our colleagues working in the experimental field.” Another point highlighted by Silva is that the study in question involved support from different areas of knowledge and the participation of postgraduate students and post-doctors in Physics and Chemistry. “This environment guided by interdisciplinary work is very valuable, mainly because it helps to train highly qualified professionals who will later work in academia or industry”, ponders da Silva.
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Watch video with testimony from professor Edison Zacarias da Silva
