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In the present article, the position-controlled and catalytic-free synthesis of vanadium dioxide (VO2) nanowires (NWs) grown by the chemical vapor deposition (CVD) on nanoimprinted silicon substrates in the form of nanopillar arrays was analyzed. The NW growth on silicon nanopillars with different cross-sectional areas was studied, and it has been shown that the NWs’ height decreases with an increase in their cross-sectional area. The X-ray diffraction technique, scanning electron microscopy, and X-ray photoelectron spectroscopy showed the high quality of the grown VO2 NWs. A qualitative description of the growth rate of vertical NWs based on the material balance equation is given. The dependence of the growth rate of vertical and horizontal NWs on the precursor concentration in the gas phase and on the growth time was investigated. It was found that the height of vertical VO2 NWs along the [100] direction exhibited a linear dependence on time and increased with an increase in the precursor concentration. For horizontal VO2 NWs, the height along the direction [011] varied little with the growth time and precursor concentration. These results suggest that the high-aspect ratio vertical VO2 NWs formed due to different growth modes of their crystal faces forming the top of the growing VO2 crystals and their lateral crystal faces related to the difference between the free energies of these crystal faces and implemented experimental conditions. The results obtained permit a better insight into the growth of high-aspect ratio VO2 NWs and into the formation of large VO2 NW arrays with a controlled composition and properties.

In the present article, the position-controlled and catalytic-free synthesis of vanadium dioxide (VO

Memristors currently attract much attention as basic building blocks for future neuromorphic electronics. Due to their unusual electronic, optical, magnetic, electrochemical, and structural properties, transition metal oxides offer much potential in the development of memristors. Recent trends in the design and fabrication of electronic devices have led to miniaturization of their working elements, with nanometer-sized structures enjoying increasing demand. In the present study, we investigated resistive switching on individual vanadium oxide (V2O5) crystal-hydrate nanoparticles, 2 to 10 nm in size, encapsulated in fluorinated graphene (FG). Measurements using a conductive atomic force microscope (c-AFM) probe showed that the core–shell V2O5/FG nanoparticles make it possible to achieve bipolar resistive switching, reproducible during 104 switching cycles, with the ON/OFF current ratio reaching 103–105. The switching voltage of the structures depends on the thickness of the FG shells of the composite particles and equals ∼2–4 V. It is shown that the encapsulation of V2O5 particles in fluorinated graphene ensures a high stability of the resistive switching effect and, simultaneously, prevents the escape of water from the crystalline vanadium oxide hydrates. A qualitative model is proposed to describe the bipolar resistive switching effect in examined structures. Results reported in the present article will prove useful in creating bipolar nanoswitches.

In the present study, a strategy for the formation of hybrid Si/VO2 nanostructures that is fully compatible with well-established standard silicon technology has been developed. The strategy is based on the selective synthesis of VO2 NCs and their arrays on three-dimensional (3D) silicon structures with nanosharp tips, edges, and scallops. The possibility of highly selective synthesis of precise arrays of VO2 nanorings on the surface of silicon cylinders, at the locations of Bosch scallops has been discovered and demonstrated. The optimum conditions for the MOCVD synthesis of high-quality single VO2 (M-phase) NCs on nanosharp Si tips and edges were determined. The obtained results provide important information regarding the synthesis of VO2 crystals on 3D Si nanostructures, and open up the possibility of the formation of a wide range of 3D hybrid nanostructures and their arrays for post-silicon optoelectronics and neuromorphic circuits and for active metamaterials and devices. The developed strategy can be easily integrated into standard silicon technology.

A new approach for the formation of free-standing vertical resistive nanoswitches based on VO2 nanocrystals (NCs) with embedded conductive nanosharp Si tips is demonstrated in the present article. This approach consists in the chemical vapor deposition synthesis of VO2 NCs on the apices of sharp conductive nanotips formed on a Si substrate by the standard methods of planar silicon technology. The amplification of the electric field and current density at the tip apex inside a high-quality VO2 NC leads to a record-breaking reduction of switching voltage (by a factor of 20–70) in comparison with conventional geometry devices with planar contacts. Our pulse measurements showed that the extremely low energy equal to 4.2 fJ was consumed for the switching in such NCs, and the total number of switching cycles in one NC without degradation exceeded 1011. The proposed approach can be extended to the formation of large arrays of such nanoswitches. We showed that periodic arrays of individual VO2 NCs were selectively synthesized on sharp Si tips. The nanosizes of the switches, ultra-low power consumption for switching and the possibility of forming dense arrays of such objects make the fabricated nanoswitches promising devices for future neuromorphic systems.

In recent years, there has been explosive growth in the number of investigations devoted to the development and study of biomimetic micro- and nanorobots. The present review is dedicated to novel bioinspired magnetic micro- and nanodevices that can be remotely controlled by an external magnetic field. This approach to actuate micro- and nanorobots is non-invasive and absolutely harmless for living organisms in vivo and cell microsurgery, and is very promising for medicine in the near future. Particular attention has been paid to the latest advances in the rapidly developing field of designing polymer-based flexible and rigid magnetic composites and fabricating structures inspired by living micro-objects and organisms. The physical principles underlying the functioning of hybrid bio-inspired magnetic miniature robots, sensors, and actuators are considered in this review, and key practical applications and challenges are analyzed as well.

Memristors currently attract much attention as basic building blocks for future neuromorphic electronics. Due to their unusual electronic, optical, magnetic, electrochemical, and structural properties, transition metal oxides offer much potential in the development of memristors. Recent trends in the design and fabrication of electronic devices have led to miniaturization of their working elements, with nanometer-sized structures enjoying increasing demand. In the present study, we investigated resistive switching on individual vanadium oxide (V

In the present study, the possibility of a selective MOCVD growth of vanadium dioxide on silicon substrates locally coated with aluminum is demonstrated. By diluting the precursor flow with an inert gas, it was possible to achieve a situation in which the growth of vanadium dioxide proceeded only on the surface of aluminum, with its complete absence from the rest of the surface. It is shown that the M -phase of vanadium dioxide grows on aluminum films.

Vanadium dioxide (VO 2 ) is one of the most promising materials for new electronic devices and neuromorphic systems. Great interest in this material has arisen due to the unique reversible semiconductor-metal phase transition observed at 68°C. Recently, selective synthesis of nanosized VO 2 single crystals on silicon nanostructures has been demonstrated and opens up the possibility of forming resistive switches with ultra-low energy consumption. This work is devoted to the design optimization of such switches. A new design of two-contact resistive switches based on VO 2 nanocrystals with embedded cone-shaped needles was proposed and investigated. We simulated and analyzed the distributions of electric field strength, temperature, and current density inside a VO 2 single crystal. It was shown that that the most energy-efficient geometry of the switches includes two cone-shaped nanocontacts embedded into the nanocrystal. The established optimum switch design is important for the formation of high sensitive switching elements for sensors and neuromorphic systems.

Vanadium dioxide (VO 2 ) has a wide range of physical properties due to the existence of polymorphs. The most interesting ones for practical applications are the M- and B- phases of VO 2 . The M-phase exhibits a reversible structural and ultrafast (26 fs) electronic semiconductor-metal phase transition, and the B-phase offers a promising semimetal for electronics. For controlling the properties of VO 2 , it is important to be able to selectively synthesize structures containing a given phase of the deposited material. In the present study, the possibility of area-selective synthesis of VO 2 films with M- and B-phases on silicon substrates was discovered for the first time. It was found that only the B-phase grew on the substrate area treated with polyvinyl alcohol (PVA), and only the M-phase of VO 2 was synthesized on the initial (virgin) surface of the substrate. The dependence of the morphology of the VO 2 films on the thickness of the PVA layer was revealed. The ability to control the growth of various phases of polymorphic materials under identical synthesis conditions opens up prospects for the formation of laterally arranged heterostructures with new functional properties.

Vanadium dioxide VO 2 is a promising functional material for many practical applications, due to its large jump in conductivity observed during the phase transition. One of the main tasks for VO 2 material is to improve its phase transition characteristics. In this paper, we study the effect of post growth annealing on the phase transition properties in two types of VO 2 films synthesized by LP CVD on $\mathrm {S}\mathrm {i}O_{2}/\mathrm {S}\mathrm {i}$ substrates: with a low $( 10^{3})$ resistance ratio during the phase transition. Using layer-by-layer etching, we showed that both types of VO 2 films are not uniform in thickness due to the presence of a non-stoichiometric $VO_{2-\mathrm {x}}$ layer. The location of this layer determines the experimentally measured value of the jump in the conductivity of VO 2 films, as well as the possibility of improving the phase transition characteristics in the films by annealing. As a result, we found annealing conditions that increase the value of the jump in resistance during a phase transition up to 700 times. The results of this work are promising both for using VO 2 as the basis for novel electrical and optical micro- and nanodevices, and for studying the physicochemical properties of VO 2 films synthesized by CVD.

Spectral characteristics of chiral metamaterials based on an array of propeller-like double helices are studied. A possibility of large optical activity in resonators with C4 symmetry is shown. A new type of dynamically controllable chiral structure based on vanadium dioxide is proposed. The investigated devices are promising for polarization converters, filters and modulators.

A new approach for the formation of free-standing vertical resistive nanoswitches based on VO2 nanocrystals (NCs) with embedded conductive nanosharp Si tips is demonstrated in the present article. This approach consists in the chemical vapor deposition synthesis of VO2 NCs on the apices of sharp conductive nanotips formed on a Si substrate by the standard methods of planar silicon technology. The amplification of the electric field and current density at the tip apex inside a high-quality VO2 NC leads to a record-breaking reduction of switching voltage (by a factor of 20-70) in comparison with conventional geometry devices with planar contacts. Our pulse measurements showed that the extremely low energy equal to 4.2 fJ was consumed for the switching in such NCs, and the total number of switching cycles in one NC without degradation exceeded 1011. The proposed approach can be extended to the formation of large arrays of such nanoswitches. We showed that periodic arrays of individual VO2 NCs were selectively synthesized on sharp Si tips. The nanosizes of the switches, ultra-low power consumption for switching and the possibility of forming dense arrays of such objects make the fabricated nanoswitches promising devices for future neuromorphic systems.

Enhancement of magneto-optical response by coupling of propagating with localized plasmons in a structure based on silver and bismuth-substituted ferrite garnet has been numerically studied. It is shown that the absolute value of the magneto-optical response in the examined structure reaches a high value of 0.04, and the structure has a reflection coefficient sufficiently high for a number of practical applications. The strong coupling between localized and propagating plasmons, which caused the significant enhancement of the magneto-optical response, was manifested in the reflection spectrum of the structure in the form of an asymmetric Fano-like resonance. The proposed structure, intended for operation in the near infrared range, is a promising one for solving various problems in magnonics and bionanophotonics.

Electromagnetic properties of high contrast gratings covered by a thin layer of vanadium dioxide have been studied. It is shown that phase transition of the vanadium dioxide from semiconductor to metallic state allows to effectively controlling the polarization of the transmitted electromagnetic radiation in the subterahertz range. Effects of Mie and guided-mode resonances on polarization characteristics of metasurfaces are investigated. Results can be useful for development of ultrafast polarization modulators of microwave and terahertz range.

Electron transport in a semiconductor cylindrical nanomembrane placed in a magnetic field normal to the cylinder axis was numerically studied. The adopted experimental geometry ensured a transport of the two-dimensional electron gas (2DEG) in the magnetic field gradient, since the electron motion was governed by the magnetic field vector component normal to the nanomembrane surface. Both the filamentation of electron current along one of the edges of the sample and the formation of a current filament connecting the edges of the sample in the region where the field gradient changes its sign are demonstrated. The calculation results clearly illustrate the cause of the giant magnetoresistance asymmetry of the 2DEG in the cylindrical nanomembrane. Establishment of characteristic features of the distribution of electric current in a nanomembrane and calculation of the quantitative characteristics of this distribution enables the development of new non-planar systems based on various 2D materials for applications and research.

We have developed a technology for fabricating infrared polarizers based on double- and four-layer metal-dielectric nanogratings. Due to the use of nanoimprint lithography, the size of fabricated samples with 190-nm grating period could be made exceeding 170 cm2. The fabricated polarizers are flexible, and they have high quality over the entire area of the sample. Spectrophotometric measurements and numerical simulations have showed that the polarizers exhibited a large transmission coefficient and a high extinction ratio (over 3 ⋅ 104). In order to expand applications of polarizers to the bio-inspired wide field-of-view systems, technology for fabricating polarizers on curved surfaces prepared by 3D printing has been developed. The obtained results offer much promise for polarimetry purposes.

A detailed study of the effect due to Lorentz-force gradient on the Hall voltage of a two-dimensional electron gas (2DEG) was carried out on specially prepared cylindrical nanomembranes with 2DEG. In the fabricated nanomembranes, weak and strong magnetic-field gradients and, also, sign-alternating magnetic fields acting on the electrons in the nanomembranes were obtained. It was found that an increase in the magnetic-field gradient led to an increase of the Hall constant of 2DEG in weak fields, whereas a change in the field sign caused an inversion of this constant in weak fields. An explanation based on the analysis of the dependence of electron drift velocities on the magnetic field gradient is proposed. The investigated system is of interest both for applications and fundamental research.

A metamaterial absorber is realized for microwave and terahertz ranges using two-dimensional bianisotropic omega-elements by thorough analysis of their distribution on substrate as well as properly choosing omega's geometrical and material parameters. Simulations and experimental studies of the metamaterial confirm its low reflectance in a wide microwave range and high absorbance at the resonance.

Electromagnetic metamaterials opened the way to extraordinary manipulation of radiation. Terahertz (THz) and optical metamaterials are usually fabricated by traditional planar-patterning approaches, while the majority of practical applications require metamaterials with 3D resonators. Making arrays of precise 3D micro- and nanoresonators is still a challenging problem. Here we present a versatile set of approaches to fabrication of metamaterials with 3D resonators rolled-up from strained films, demonstrate novel THz metamaterials/systems, and show giant polarization rotation by several chiral metamaterials/systems. The polarization spectra of chiral metamaterials on semiconductor substrates exhibit ultrasharp quasiperiodic peaks. Application of 3D printing allowed assembling more complex systems, including the bianisotropic system with optimal microhelices, which showed an extreme polarization azimuth rotation of 85° with drop by 150° at a frequency shift of 0.4%. We refer the quasiperiodic peaks in the polarization spectra of metamaterial systems to the interplay of different resonances, including peculiar chiral waveguide resonance. Formed metamaterials cannot be made by any other presently available technology. All steps of presented fabrication approaches are parallel, IC-compatible and allow mass fabrication with scaling of rolled-up resonators up to visible frequencies. We anticipate that the rolled-up meta-atoms will be ideal building blocks for future generations of commercial metamaterials, devices and systems on their basis.

Optical filter based on multilayer structure was designed and fabricated by means of nanoimprint lithography. Spectral properties were simulated numerically. Working principle was shown to found on combination of Fabry-Perot and plasmon resonances.

A micro-Raman study of optical phonons in GaAs/InGaAs and InGaAs/InAs bilayer microtubes is presented. From the analysis of optical phonon frequencies the built-in mechanical strain in the microtubes was estimated and compared with theoretical predictions. (© 2009 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim)

In present study infuence of different substrates and protective coatings on graphene electrical properties has been investigated. Hexagonal boron nitride (h-BN) was shown to ensure the highest conductivity and carrier mobility if graphene. MoS 2 provided increase of carrier mobility compared to conventional SiO 2 substrate. Utilization of GO and FG as a substrates and protective layers has been found very promising way for fexible electronics. Encapsulation by organic layers such as Novec 1700 and poly(4-venylphenol) allowed graphene to be protected and did not lead to degradation of graphene properties.

We have applied supercritical CO2 drying technique to fabricate free-standing semiconductor nanotubes, in order to solve the problem of tube collapsing caused by the capillary forces in the final drying process. We have successfully fabricated damage-free single-turn nanotubes with ultra-thin walls (lesser than 3 nm) and very high tube-length/wall-thickness ratios (higher than 103), which so far could not been realized. These extremely small and light structures with unique geometry are promising for future nanoelectromechanical systems.

We developed a new technology for fabricating InGaAs/GaAs and GeSi/Si semiconductor micro- and nanoneedles, syringe for intracellular injections. Within this technology, a novel method for directional roll-up of strained heterostructures is proposed, which fits nicely into the well-established integrated-circuit technology. The tubes obtained by this method are mechanically strong enough to many times puncture thick-walled plant cells, and they can be easily integrated into other semiconductor devices to form a “lab-on-a-chip”.

A new material system for creating InAs-based free-standing micro- and nanoobjects is proposed. For the first time, InAs/InGaAs microtubes and microspirals were obtained, including tubes containing two-dimensional electron gas, ordered arrays of tubes, and tubes protruding over the substrate edge. First measurements of the electrical conductivity of InAs/InGaAs microtubes were performed.

In the present work, we report on fluorination of multilayer graphene by means of HF treatment, which results in dramatic changes in its structural and electrical properties. This statement is based on transport measurements, Raman spectroscopy and atomic force electron microscopy. It is found that the local regions of fluorographene appear on the graphene films surface after hydrofluoric acid treatment of few layer graphene. Fluorine ions are found to require for the fluorination reactions. Periodic nanoswell relief with 100 nm and 10 nm in diameter and height respectively had formed on the surface of graphene films after the HF treatment.

Possibility to create the hybrid structures based on graphene and N-methylpyrrolidone (NMP) is demonstrated in the report. Properties of these structures such as conductivity, carrier mobility, band gap value are found to strongly depend on fabrication temperature.

The possibility to create the nanocomposite layers based on graphene and organic monolayers is demonstrated in the report. Conductivity of the nanocomposite layers is found to strongly vary depending upon the temperature used during fabrication process. The opening of band gap for these layers under some fabrication regimes is also found.

New data on the fabrication and study of semiconductor micro- and nanotubes, and also on the application of such micro- and nanotubes as basic elements in sensors and actuators are reported. Fabrication methods for tubular micro- and nanosensors and actuators are described, and examples of fabricated devices are presented. The potential offered by the fabricated pilot devices in aerodynamic applications is demonstrated.

New type of sensor for thermal anemometry – hot-tube sensor is presented. Some details on manufacture procedure and mechanical properties of sensors are given. Hot-tube response on pulse heating is checked. It is found that time constant of hot-tube is 80 times less that hot-wire one. Pulsations measurements in subsonic flow show that hot-tube does not require thermal inertia compensation for frequencies up to 20-40 kHz and that hot-tube has much better signal/noise ratio than hot-wire. I. Introduction HE fast-responsible flow microsensors with high spatial and temporal resolution are necessary for the solution of key challenges in aero-gas-dynamics. One of such unresolved problems is the problem of the laminarturbulent transition and description of turbulent flows. The measurement of the high-frequency oscillations of low amplitude at the early stage of the laminar-turbulent transition is an important task 1 . The only sensor fit to measure the disturbances in the high-speed flows is a hot-wire probe, its sensitive element being a thin metal wire or film. The time constant of these sensors normally lies within the range of 0.2 – 1 ms, and is limited, in the case of wire sensors, by the wire thermal capacity; and in the case of film sensors – by the heat exchange with the substrate 2,3,4,5,6 . As a result, the sensitivity of the hot-wire anemometers rapidly decreases at the frequencies above 1 kHz, and becomes insufficient to measure the high-frequency (higher than 100 kHz) pulsations, which are typical for the high-speed flows. A search for new methods of batch production of the anemometers sensors involving integral circuit technology is active in the world. Attempts are made to increase the sensitivity with the aid of suspended bridges or membranes 3-6, 7 . Recently 8 an original method of production of monocrystal semiconductor micro- and nano-tubes has been proposed and realized. The method is based on self-rolling of a thin heterofilms detached from the substrate under the action of inner mechanics stresses (Fig. 1). The diameter of the tubes formed in this way can be precisely controlled in the range of 100 µm -2 nm by a proper choice of thicknesses and compositions of the layers in the starting heterostructure. The proposed method has been successfully applied to a number of dielectrics, metals, and semiconductors 8,9, . The purpose of the present paper is to fabricate pilot models of the hot-tube sensors for thermal anemometers from hybrid Metal/GaAs/InGaAs heterofilms using self-scrolling heterostructure technology.

Arrays of graphene or few-layer graphene quantum dots (QDs) embedded in a partially fluorinated graphene matrix were created by chemical functionalization of layers. Charge transient spectroscopy employed for investigation of obtained QD systems (size 20–70 nm) has allowed us to examine the QD energy spectra and the time of carrier emission (or charge relaxation) from QDs as a function of film thickness. It was found that the characteristic time of carrier emission from QDs decreased markedly (by about four orders of magnitude) on increasing the QD thickness from one graphene monolayer to 3 nm. Daylight-assisted measurements also demonstrate a strong decrease of the carrier emission time.

A few-layer graphene-based hybrid material with high thermal and chemical stability and reproducible and tunable electronic properties was fabricated by intercalation of N-methylpyrrolidone into a few-layer graphene combined with heat treatment. Depending on the process temperature, the obtained material could be produced with the following properties: a broad range of resistivity values (six to seven orders of magnitude) in combination with a high carrier mobility, a tunable band-gap (from 0 up to 3-4 eV) and sp² or sp³ hybridization of carbon atoms. The extremely strong step-like temperature dependence (within 10 °C) of its properties observed in the vicinity of two temperatures, 90 and 200 °C, seems to be important for various applications. The hybrid material opens viable routes to progress in the design of three-dimensional nanostructures.

The passivating effects of organic monolayers of 1-octadecene deposited onto the silicon surfaces of both n and p conductivities were studied for Si∕SiGe∕Si structures grown by molecular beam epitaxy and chemical vapor deposition. Measurements of the capacitance versus voltage and current versus voltage were made on structures covered with the organic monolayer and compared with unpassivated structures covered with native silicon dioxide. The results demonstrate that the organic passivation provides a decrease of surface charge and an increase of carrier concentration in the near-surface layers and/or the SiGe quantum wells.

The electrical properties of 1-octadecene (CnH2n, n=18) monolayers deposed onto the oxide-free silicon surface were analyzed as a function of surface pretreatment (hydrogen- or iodine-terminated silicon surface) and layer deposition regime (a thermally or photo-activated process). Two types of traps (for electrons and holes) were found to exist in the monolayers. The density of these traps is shown to depend on the orientation of the Si substrate, on H- or I-termination of the surface, on the illumination intensity during photo- activated deposition, and on the duration of thermally activated deposition. The possibility to introduce, in a controllable manner, either hole or electron traps into the 1- octadecene monolayers provides a potential in managing the conductivity of thin silicon layers by producing at the surface either a near-flat band situation or the accumulation regime.