Our newspaper first wrote about Professor Viyacheslav Mykolayovych Horshkov from the Department of General and Solid State Physics in 2016. Then he became the leader of our university in international recognition of publications. Later, in 2017 and 2018, the results of his research were presented, they were included in the list of the best works of the year of the prestigious journal “Journal of Applied Physics”. Of course, every time it was about world-class publications. And this time the story will be about new extraordinary results obtained by prof. V.M. Horshkov, so extraordinary that it was not easy to publish them.
Anyway, at first,brief information about the field of research in which these results were obtained - computer modelling of physical processes in nanosystems. This field is currently experiencing a period of rapid development, the studiesare done and the scientists get results which thirty years ago no one dreamed of. All in all, we are talking about studying the behavior of systems consisting of millions of atoms, to simulate the motion of which the power of computers lacked for a long time. Calculations using simplified models did not make it possible to explain the most interesting physical phenomena studied by the experimenters.
Everything changed dramatically at the beginning of the XXI century. The development of technology in electronics caused the need of accurate knowledge of the evolution of nanoclusters, which consist of millions of atoms. Apart from that, the power of computer technology has increased significantly, and now the ability to solve relevant problems is largely determined by specialists who create mathematical models of certain processes and algorithms for their calculation.
Professor V. M. Horshkov works with specialists from the Center for Advanced Technologies in Materials Science at Clarkson University (Potsdam, New York) according to the agreement on collaboration between Igor Sikorsky Kyiv Polytechnic Institute and Clarkson University. It is important to note that these studies are of practical importance and immediately become used in the development of nanotechnology.
Prof. V.M. Horshkov reports:
For some time we have been doing mathematical modelling of nanoparticle growth. These results were used in the development of methods for the controlled synthesis of nanoparticles of various types, which could be changed in a wide range, and to obtain the desired physical properties of the particles.
In 2017, we began researching optimal methods for creating periodically modulated quasi-one-dimensional structures - unique in physical and optical properties of chip elements. In particular, the physics of the decay of nanowires into ordered chains of nanoclusters which can be used as waveguides. The researches were successful, as evidenced by three articles in prestigious scientific journals (Advanced Theory and Simulations, July 2019; Materials Today, November 2019; Crystal Engineering Communications, March 2020), co-authored with a post-graduate Volodymyr Tereshchuk.
Now I will briefly tell about the essence of the obtained results.
When nanowires are heated, their surface is disturbed (see figure). Moreover, this phenomenon is observed at temperatures signficantly below the melting point. The theory of this phenomenon (1965) has much in common with the classical Rayleigh theory of liquid streams instability. The main statements of this theory: a) significant periodic modulations of the surface can occur spontaneously only with a wavelength that exceeds 6.3 times the initial radius of the nanowire; b) at the final stage of decay the waves of 9 radii long dominate. Approximately such indicators were indeed obtained in majority of cases. Though, ultra-long perturbations with a period of 25-30 radii were as well observed very often and, surprisingly, sub-short ones with a length of 4.5 radii (i.e. well below the set threshold!) were also often observed. Nevertheless, experimenters ignored such inconsistencies with theory and wrote that their data were “in good agreement with theoretical predictions.” After extensive research, my young colleague and me have discovered the factors that cause these superdeviations from the provisions of a theory that has long been considered classical. The knowledge of these factors is extremely important for solving problems of preventing the decay of nanowires when they are heated by current in chips.
Now you can imagine what resistance of the reviewers could be expected when responding to our work. The first publication was sent back without the possibility of resubmission. Anyway, we were also feisty and found so many physical inconsistencies in the reviewers’ comments that, despite the editor's warning, we resubmitted the article to Advanced Theory and Simulations. A week later, the editorial board announced that the article had been accepted for publication without the need to make any adjustments. What is more, the results were later acceppted positively by our foreign colleagues (e.g., J. W. Evans, Iowa State University; Linwei Yu, Nanjing University; Harris Wong, Louisiana State University). As a result, new tasks have appeared, the solution of which we have found and now we are preparing another publication.
We will talk again about the decay of nanowires. In experiments performed at Hong Kong University, the gold nanowire was irradiated by an electron beam. 10 minutes later, significant modulations of the radius appeared, and then the wire did not disintegrate into nanodrops, in contrast, it retained it’s shape, despite further irradiation. Moreover, the wavelength of the perturbations was lower than the “classical threshold” (4.5 radius). Whereas during simple heating the same nanowire habitually disintegrated into fragments in length of 10 radii! We were able to find the reasons of these features (the figure shows the results of real and numerous experiments). I would note that previously we discovered similar short-wave stable modulations (in the absence of external influence) in the study of methods for suppressing the instabilities of tungsten nanowires.
In recent months, we have managed to perform process modelling on a completely different scale. Together with our colleagues from Los Alamos, New York and Canada, we conducted research on so-called “dark matter”, the presence of which now explains a number of features of the motion of galactic objects. There is a hypothesis that dark matter consists of particles - axions of different types. We considered the problem of fixing the two-component axion matter, developed methods for solving a system of specific nonlinear Schrödinger equations by numerical methods, and found conditions under which the hypothesis of multicomponent axion system can be tested experimentally.
Finally, topically relevant, I would note that both coronavirus and quarantine do not affect our research. After all, the computer, on which the simulation takes place, is installed at Clarkson University (Potsdam), it is controlled remotely. I think this once again demonstrates the great prospects for research in the field of computer modelling of physical processes.