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- ItemThree-Dimensional Superconducting Nanohelices Grown by He+-Focused-Ion-Beam Direct Writing(Washington, DC : ACS Publ., 2019) Córdoba, Rosa; Mailly, Dominique; Rezaev, Roman O.; Smirnova, Ekaterina I.; Schmidt, Oliver G.; Fomin, Vladimir M.; Zeitler, Uli; Guillamón, Isabel; Suderow, Hermann; De Teresa, José MaríaNovel schemes based on the design of complex three-dimensional (3D) nanoscale architectures are required for the development of the next generation of advanced electronic components. He+ focused-ion-beam (FIB) microscopy in combination with a precursor gas allows one to fabricate 3D nanostructures with an extreme resolution and a considerably higher aspect ratio than FIB-based methods, such as Ga+ FIB-induced deposition, or other additive manufacturing technologies. In this work, we report the fabrication of 3D tungsten carbide nanohelices with on-demand geometries via controlling key deposition parameters. Our results show the smallest and highest-densely packed nanohelix ever fabricated so far, with dimensions of 100 nm in diameter and aspect ratio up to 65. These nanohelices become superconducting at 7 K and show a large critical magnetic field and critical current density. In addition, given its helical 3D geometry, fingerprints of vortex and phase-slip patterns are experimentally identified and supported by numerical simulations based on the time-dependent Ginzburg-Landau equation. These results can be understood by the helical geometry that induces specific superconducting properties and paves the way for future electronic components, such as sensors, energy storage elements, and nanoantennas, based on 3D compact nanosuperconductors. © 2019 American Chemical Society.
- ItemSmall Scale Propulsion: How Systematic Studies of Low Reynolds Number Physics Can Bring Micro/Nanomachines to New Horizons(Wilmington DE: Scientific Archives LLC, 2022) Wrede, Paul; Medina-Sánchez, Mariana; Fomin, Vladimir M.Micromachines are small-scale human-made machines with remarkable potential for medical treatments, microrobotics and environmental remediation applications. However, meaningful real-world applications are missing. This is mainly caused by their small size leading to unintuitive physics of motion. Motivated by the aim of understanding the fundamental physics at the micrometer scale and thereby overcoming resulting challenges, we discuss the importance of robust models supported by experimental data. Our previously performed study on the switching in propulsion mechanisms for conical tubular catalytic micromotors will be summarized and serve as an example for discussion. We emphasize on the need for systematic experimental studies to enable the design of highly application-oriented micromachines, which can be translated into real-world scenarios.
- ItemSpin-Dependent Phenomena in Semiconductor Micro-and Nanoparticles - From Fundamentals to Applications(Basel : MDPI, 2020) Fomin, Vladimir M.; Timoshenko, Victor Y.The present overview of spin-dependent phenomena in nonmagnetic semiconductor microparticles (MPs) and nanoparticles (NPs) with interacting nuclear and electron spins is aimed at covering a gap between the basic properties of spin behavior in solid-state systems and a tremendous growth of the experimental results on biomedical applications of those particles. The first part of the review represents modern achievements of spin-dependent phenomena in the bulk semiconductors from the theory of optical spin orientation under indirect optical injection of carriers and spins in the bulk crystalline silicon (c-Si)—via numerous insightful findings in the realm of characterization and control through the spin polarization—to the design and verification of nuclear spin hyperpolarization in semiconductor MPs and NPs for magnetic resonance imaging (MRI) diagnostics. The second part of the review is focused on the electron spin-dependent phenomena in Si-based nanostructures, including the photosensitized generation of singlet oxygen in porous Si and design of Si NPs with unpaired electron spins as prospective contrast agents in MRI. The experimental results are analyzed by considering both the quantum mechanical approach and several phenomenological models for the spin behavior in semiconductor/molecular systems. Advancements and perspectives of the biomedical applications of spin-dependent properties of Si NPs for diagnostics and therapy of cancer are discussed.
- ItemPhonons and Thermal Transport in Si/SiO2 Multishell Nanotubes: Atomistic Study(Basel : MDPI, 2021) Isacova, Calina; Cocemasov, Alexandr; Nika, Denis L.; Fomin, Vladimir M.Thermal transport in the Si/SiO2 multishell nanotubes is investigated theoretically. The phonon energy spectra are obtained using the atomistic lattice dynamics approach. Thermal conductivity is calculated using the Boltzmann transport equation within the relaxation time approximation. 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/SiO2 interfaces is another key factor of strong reduction of the thermal conductivity in these structures (down to 0.2 Wm−1K−1 at room temperature). We demonstrate that phonon thermal transport in Si/SiO2 nanotubes can be efficiently suppressed by a proper choice of nanotube geometrical parameters: lateral cross section, thickness and number of shells. We argue that such nanotubes have prospective applications in modern electronics, in cases when low heat conduction is required.
- ItemPhonon spectrum engineering in rolled-up micro- and nano-architectures(Basel : MDPI, 2015) Fomin, Vladimir M.; Balandin, Alexander A.We report on a possibility of efficient engineering of the acoustic phonon energy spectrum in multishell tubular structures produced by a novel high-tech method of self-organization of micro- and nano-architectures. The strain-driven roll-up procedure paved the way for novel classes of metamaterials such as single semiconductor radial micro- and nano-crystals and multi-layer spiral micro- and nano-superlattices. The acoustic phonon dispersion is determined by solving the equations of elastodynamics for InAs and GaAs material systems. It is shown that the number of shells is an important control parameter of the phonon dispersion together with the structure dimensions and acoustic impedance mismatch between the superlattice layers. The obtained results suggest that rolled up nano-architectures are promising for thermoelectric applications owing to a possibility of significant reduction of the thermal conductivity without degradation of the electronic transport.
- ItemSupervised discriminant analysis for droplet micro-magnetofluidics(Heidelberg : Springer, 2015) Lin, Gungun; Fomin, Vladimir M.; Makarov, Denys; Schmidt, Oliver G.We apply the technique of supervised discriminant analysis (SDA) for in-flow detection in droplet-based magnetofluidics. Based on the SDA, we successfully discriminate bivariant droplets of different volumes containing different encapsulated magnetic content produced by a GMR-based lab-on-chip platform. We demonstrate that the accuracy of discrimination is superior when the correlation of variables for data training is included to the case when the spatial distribution of variables is considered. Droplets produced with differences in ferrofluid concentration of 2.5 mg/ml and volume of 200 pl have been identified with high accuracy (98 %), indicating the significance of SDA for e.g. the discrimination in magnetic immuno-agglutination assays. Furthermore, the results open the way for the development of a unique magnetofluidic platform for future applications in multiplexed droplet-based barcoding assays and screening.
- ItemNanomotoren aus Titandioxid - Nanoröhrchen für Bio-Anwendungen (TiNaTEng) : Laufzeit des Vorhabens: 01.10.2013-30.09.2015(Hannover : Technische Informationsbibliothek (TIB), 2016) Guix Noguera, Maria; Fomin, Vladimir M.; Schmidt, Oliver G.; Enachi, Mihail[no abstract available]
- ItemKontrolle supraleitender Wirbeldynamik in Nb rolled-up-Nanostrukturen : Laufzeit des Vorhabens: 01.04.2013-31.03.2016(Hannover : Technische Informationsbibliothek (TIB), 2016) Fomin, Vladimir M.; Schmidt, Oliver G.; Bürger, Danilo; Lösch, Sören; Rezaev, Roman; Levchenko, Evgenii; Dusaev, RenatDer Bericht enthält eine vollständige Beschreibung des wissenschaftlichen Forschungsprojekts, das durch die bilaterale BMBF-Russland-Forschungsförderung 01 DJ13009 finanziert wurde. Die Projektdauer wird in drei Perioden unterteilt, die jeweils dem Jahr der Umsetzung entsprechen. Die grundlegende Aufgabe des Projekts war es zu untersuchen, wie die Nanostrukturierung von Materialen die supraleitenden Eigenschaften ändert. Auf Basis der zeitabhängigen Ginzburg-Landau Theorie wurde das mathematische Modell der supraleitenden Phänomene in krummlinigen Nanostrukturen erstellt. Die Validierung des Modells wurde durch Vergleich mit verfügbaren experimentellen Daten für planare Strukturen durchgeführt. Weiterhin wurde das erarbeitete Modell zur Untersuchung der Wirbeldynamik in krummlinigen Nanostrukturen in einem Magnetfeld angewendet. Der Einfluss von Pinning-Zentren und die Dissipation der Energie in Abhängigkeit von den Randbedingungen wurden analysiert. Die im Rahmen des Projekts erhaltenen wissenschaftlichen Ergebnisse zeigen deutlich die Vorteile der gekrümmten supraleitenden Nanostrukturen in modernen Anwendungen der Supraleitung. Während des Projekts wurde eine innovative Software entwickelt, welche als Instrument für das virtuelle Design von Experimenten in supraleitenden gekrümmten Nano- und Mikrostrukturen genutzt werden kann.
- ItemSwitching Propulsion Mechanisms of Tubular Catalytic Micromotors(Weinheim : Wiley-VCH, 2021) Wrede, Paul; Medina-Sánchez, Mariana; Fomin, Vladimir M.; Schmidt, Oliver G.Different propulsion mechanisms have been suggested for describing the motion of 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. Bubble-recoil based motion, in particular, has been modeled by three different phenomena: capillary forces, bubble growth, and bubble expulsion. However, these models have been suggested independently based on a single influencing factor (i.e., viscosity), limiting the understanding of the overall micromotor performance. Therefore, the combined effect of medium viscosity, surface tension, and fuel concentration is analyzed on the micromotor swimming ability, and the dominant propulsion mechanisms that describe its motion more accurately are identified. Using statistically relevant experimental data, a holistic theoretical model is proposed for bubble-propelled tubular catalytic micromotors that includes all three above-mentioned phenomena and provides deeper insights into their propulsion physics toward optimized geometries and experimental conditions.
- ItemCritical current modulation induced by an electric field in superconducting tungsten-carbon nanowires([London] : Macmillan Publishers Limited, part of Springer Nature, 2021) Orús, Pablo; Fomin, Vladimir M.; De Teresa, José María; Córdoba, RosaThe critical current of a superconducting nanostructure can be suppressed by applying an electric field in its vicinity. This phenomenon is investigated throughout the fabrication and electrical characterization of superconducting tungsten-carbon (W-C) nanostructures grown by Ga+ focused ion beam induced deposition (FIBID). In a 45 nm-wide, 2.7 μm-long W-C nanowire, an increasing side-gate voltage is found to progressively reduce the critical current of the device, down to a full suppression of the superconducting state below its critical temperature. This modulation is accounted for by the squeezing of the superconducting current by the electric field within a theoretical model based on the Ginzburg–Landau theory, in agreement with experimental data. Compared to electron beam lithography or sputtering, the single-step FIBID approach provides with enhanced patterning flexibility and yields nanodevices with figures of merit comparable to those retrieved in other superconducting materials, including Ti, Nb, and Al. Exhibiting a higher critical temperature than most of other superconductors, in which this phenomenon has been observed, as well as a reduced critical value of the gate voltage required to fully suppress superconductivity, W-C deposits are strong candidates for the fabrication of nanodevices based on the electric field-induced superconductivity modulation.