# AMaSiS 2021 - Abstract

**Fomin, Vladimir**

*Modeling of topological and geometrical effects in self-rolled micro- and nanoarchitectures*

Institut für Integrative Nanowissenschaft, Germany

The present study is motivated by the recent progress in fabrication of high-tech 3D nanoarchitectures (e.g., open nanotubes and multishells) by using the advanced strain-driven roll-up self-organization [1]. To simulate the superconducting properties of complex superconductor nanoarchitectures, a numerical platform has been developed based on a set consisting of the time-dependent Ginzburg--Landau equation coupled with the Poisson equation and the Maxwell equation. The topological transitions between vortex-chain and phase-slip transport regimes unveiled in curved superconductor nanostructures as a function of the applied magnetic field under a strong transport current [2] open up a possibility to efficiently tailor the superconducting properties of nanostructured materials by inducing a nontrivial topology of superconductor screening currents. In particular, the non-monotonous magnetic-field-voltage and current-voltage characteristics are found in open rolled-up Nb and Sn microtubes under a strong transport current due to the occurrence of a phase-slip area followed by reentrance of the superconducting state with a chain of moving vortices when the magnetic field further increases. The effect is promising for application design of novel superconductor switching-based detectors. The phonon energy spectra in the Si/SiO_{2} multishell nanotubes are obtained numerically within the atomistic lattice dynamics model [3]. Redistribution of the vibrational spectra in multishell nanotubes leads to a decrease of the phonon group velocity and the thermal conductivity as compared to homogeneous Si nanowires. Phonon scattering on the Si/SiO_{2} interfaces is another key factor of strong reduction of the thermal conductivity in these structures (down to 0.2 Wm^{-1}K^{-1} at room temperature). Phonon thermal transport in the multishell nanotubes can be efficiently suppressed by a proper choice of nanotube geometrical parameters: lateral cross section, thickness and number of shells. Such nanotubes have prospective applications in modern electronics, in cases when low heat conduction is required. A variety of chemical micromotors, which have attracted great attention in the last decades due to their high efficiency and thrust force, enabling several applications in the fields of environmental remediation and biomedicine. Using statistically relevant experimental data for Pt conical tubes, a holistic theoretical model is developed for bubble-propelled tubular catalytic micromotors that includes capillary forces, bubble growth, and bubble expulsion. and provides deeper insights into their propulsion physics toward optimized geometries and experimental conditions. Switching between propulsion mechanisms is unveiled at certain values of the fuel concentration, medium viscosity and surface tension [4]. This work has been partly supported by the German Research Foundation (DFG) project FO 956/6-1 and COST Action CA16218 of the European Cooperation in Science and Technology.

**References**

[1] V. M. Fomin, Self-rolled micro- and nanoarchitectures: Effects of topology and geometry, De Gruyter, Berlin/Boston, 2021, 148 p.

[2] R. O. Rezaev, E. I. Smirnova, O. G. Schmidt, V. M. Fomin, Communs Physics 3, 144, 1-8 (2020).

[3] C. Isacova, A. Cocemasov, D. L. Nika, V. M. Fomin, Appl. Sci. 11, 3419 (2021).

[4] P. Wrede, M. Medina‐Sánchez, V. M. Fomin, O. G. Schmidt, Small 17, 2006449 (2021).