"Spicy world of NanoScience"
The use of external electric and magnetic fields as a control factor allows to manage the structure of the synthesised nanoparticles. The detailed research will be published in the May issue of the Russian Nanotechnologies. The study was conducted as part of the Federal Task Program “The Research and Development of the Prior...
Multiple methods exist allowing to generate nanoparticles. Those methods all have an important flaw, however, as the synthesis often results in particles heterogeneous in structure and composition. At the same time, such science-intensive industries as electronics require more of completely identical and standard nanoparticles. Therefore, the researchers have to learn to effectively select the right nanoparticles out of the lump and invent new methods of synthesis allowing to increase the percentage of such particles.
In order to ensure a high percentage of the required particles, the synthesis process must be controlled. Researchers at Vladimir State University and NT-MDT, CJSV, have discovered a way to control the structure of nanoparticles generated using the laser-induced target evaporation method. To do that, they put a pure graphite sample to be evaporated into continuous electric field and heterogeneous magnetic field.
In the former example (Figure 1) the synthesis was performed as follows: The laser resulted in the evaporation and ionisation of the graphite target atoms. Due to external electric field, the ionised atoms deviated from the main flow in the direction of a negatively charged plate.
After studying the layer precipitated on the plate using an electric microscope the researchers managed to confirm that carbon nanofibres were formed. It was possible to control the precipitation process by reducing the voltage on the plate. It resulted in changes in the structure of the precipitated particles: there formed nanoclusters with fractal structures that were characterised using fractal geometry methods.
In the latter case, during the synthesis in a heterogeneous magnetic field (Figure 2), the same pure graphite sample is placed into the heterogeneous field in between the two magnets. In this case, the laser-evaporated atoms of the target were precipitated on the substrate situated above it. In order to create a gap for the distribution of plasma generated as a result of the laser beam action on the target, a ceramic ring plate was placed between the substrate and the target.
After studying the precipitated layer, is was proved that the process of nanostructured carbon generation was similar to dendrite growth. At the first stage, “germs” were formed on the substrate — small atom aggregates from which dendrite structures were branching out and growing like trees.
The researchers believe that by changing the magnetic field it is possible to change the precipitation mode which offers an opportunity to form the required “germs.” In turn, the “germ” structure determines further dendrite growth.
Analysis of the research results made it possible to conclude that an electric field provides the necessary focus of the spreading particles along its lines of force. Such orientation allows the formation of chemical bonds between the atoms, and directed nanofibres generation. Similar observations are true for the process of nanoparticle spreading in the magnetic field — however, dendrite structures are formed due to significant heterogeneity of the field.
The researchers believe that the methods of nanoparticle generation described above are rather promising. It is possible to manage the nanoparticle formation process by changing the level of electric or magnetic fields.
Source of information:
А. А. Antipov, S. М. Arakelyan, S. V. kutrovskaya, А. О. Kucherik, А. V. Osipov, V. G. Prokoshev, А. А. Shchekin: “The Laser Synthesis of Carbon Nanofibres and Nanoclusters.” The Russian Nanotechnologies, vol. 6, #5–6.
Azat Hadiev, published by STRF.ru