Test ion transport in a collisional, field-reversed configuration

Diffusion of test-ions in a flux-coil generated, collisional, field-reversed configuration is measured via time-resolved tomographic reconstruction of Ar+ optical emission in the predominantly nitrogen plasma. Azimuthal test ion diffusion across magnetic field lines is found to be classical during the stable period of the discharge. Test ion radial confinement is enhanced by a radial electric field, reducing the observed outward radial transport rate below predictions based solely on classical cross-field diffusion rates. Test ion diffusion is ∼500m2s-1 during the stable period of the discharge. The electric field inferred from plasma potential measurements and from equilibrium calculations is consistent with the observed reduction in argon transport. © 2014 IOP Publishing Ltd

Quantum Study of the Optical Conductivity of Composite Films Formed by Bilayer Graphene and Single-Walled Carbon Nanotubes under Axial Stretching

In this article, quantum methods are used to study the optical properties of composite films formed by AB-stacked bilayer graphene and chiral single-walled carbon nanotubes (SWCNT) (12, 6) with a diameter of 1.2 nm. The analysis of optical properties is carried out on the basis of the results of calculating the diagonal elements of complex optical conductivity tensor in the wavelength range of 0.2–2 μm. Two cases of electromagnetic radiation polarization are considered: along the X axis (along the graphene bilayer) and along the Y axis (along the nanotube axis). The calculations are performed for three topological models (V1, V2, V3) of composite films, which differ in the width of the graphene bilayer and in the value of the shift between graphene layers. It is found that in the case of polarization along the X axis, the profile of the real part of optical conductivity in the region of extremal and middle UV radiation is determined by SWCNT (12, 6), and in the region of near UV and visible radiations, it is determined by bilayer graphene. In the case of polarization along the Y axis, the profile of the real part of optical conductivity in the region of extremal, near UV, and visible radiation is determined by SWCNT (12, 6), and in the region of the mid-UV range, it is determined by bilayer graphene. Regularities in the change in the profile of the surface optical conductivity of bilayer graphene-SWCNT (12,6) composite films under the action of stretching deformation along the Y axis are revealed. For models V1 (width of the graphene nanoribbon is 0.5 nm, the shift between layers is 0.48 nm) and V2 (width of the graphene nanoribbon is 0.71 nm, the shift between layers is 0.27 nm), the shift of the conductivity peaks in the region of extreme UV radiation along the wavelength to the right is shown. For the model V3 (width of the graphene nanoribbon is 0.92 nm, the shift between layers is 0.06 nm), the shift of the conductivity peaks to the right along the wavelength is observed not only in the region of extreme UV radiation, but also in the region of visible radiation. It is assumed that graphene-SWCNT (12,6) composite films with island topology are promising materials for photodetectors in the UV-visible and near-IR ranges

Mechanical and Electroconductive Properties of Mono- and Bilayer Graphene–Carbon Nanotube Films

This article presents the results of a computer study of electrical conductivity and deformation behavior of new graphene⁻carbon nanotube (CNT) composite films under bending and stretching. Mono- and bilayer hybrid structures with CNTs (10,0) and (12,0) and an inter-tube distance of 10 and 12 hexagons were considered. It is revealed that elastic deformation is characteristic for mono- and bilayer composite films both in bending and stretching. It is found that, in the case of bending in a direction perpendicular to CNTs, the composite film takes the form of an arc, and, in the case of bending in a direction along CNTs, the composite film exhibits behavior that is characteristic of a beam subjected to bending deformation as a result of exposure to vertical force at its free end. It is shown that mono- and bilayer composite films are more resistant to axial stretching in the direction perpendicular to CNTs. The bilayer composite films with an inter-tube distance of 12 hexagons demonstrate the greatest resistance to stretching in a direction perpendicular to CNTs. It is established that the CNT diameter and the inter-tube distance significantly affect the strength limits of composite films under axial stretching in a direction along CNTs. The composite films with CNT (10,0) and an inter-tube distance of 12 hexagons exhibit the highest resistance to stretching in a direction along CNTs. The calculated distribution of local stresses of the atomic network of deformed mono- and bilayer composite films showed that the maximum stresses fall on atoms forming covalent bonds between graphene and CNT, regardless of the CNT diameter and inter-tube distance. The destruction of covalent bonds occurs at the stress of ~1.8 GPa. It is revealed that the electrical resistance of mono- and bilayer composite films decreases with increasing bending. At the same time, the electrical resistance of a bilayer film is 1.5⁻2 times less than that of a monolayer film. The lowest electrical resistance is observed for composite films with a CNT (12,0) of metallic conductivity

Improving the Sensory Properties of Layered Phospholipid-Graphene Films Due to the Curvature of Graphene Layers

This article is devoted to the in silico study of the sensory properties of mono- and bilayer phospholipid-graphene films with planar and curved graphene sheets. The DPPC (dipalmitoylphosphatidylcholine) molecules are considered as phospholipid structures. These molecules are part of lipid bilayers, liposomes and cell membranes. To find a way to improve the sensory properties of phospholipid-graphene films, we studied the effect of the curvature of the graphene sheet on the charge transfer and electrical conductivity of the films. The distribution of the electron charge density over the film atoms was calculated using the self-consistent-charge density-functional tight-binding method (SCC-DFTB). The calculation of the current through phospholipid-graphene films was carried out within the framework of the Landauer–Buttiker formalism using the Keldysh nonequilibrium Green function technique. As a result of the calculations, the optimal configuration of the arrangement of DPPC molecules between two graphene layers was established. This configuration provides the maximum possible increase in current to 1 μA at low voltages of ~0.2 V and is achieved for curved graphene with a radius of curvature of ~2.7 nm at individual points of graphene atomic network

Novel Van Der Waals Heterostructures Based on Borophene, Graphene-like GaN and ZnO for Nanoelectronics: A First Principles Study

At present, the combination of 2D materials of different types of conductivity in the form of van der Waals heterostructures is an effective approach to designing electronic devices with desired characteristics. In this paper, we design novel van der Waals heterostructures by combing buckled triangular borophene (tr-B) and graphene-like gallium nitride (GaN) monolayers, and tr-B and zinc oxide (ZnO) monolayers together. Using ab initio methods, we theoretically predict the structural, electronic, and electrically conductive properties of tr-B/GaN and tr-B/ZnO van der Waals heterostructures. It is shown that the proposed atomic configurations of tr-B/GaN and tr-B/ZnO heterostructures are energetically stable and are characterized by a gapless band structure in contrast to the semiconductor character of GaN and ZnO monolayers. We find the phenomenon of charge transfer from tr-B to GaN and ZnO monolayers, which predetermines the key role of borophene in the formation of the features of the electronic structure of tr-B/GaN and tr-B/ZnO van der Waals heterostructures. The results of the calculation of the current–voltage (I–V) curves reveal that tr-B/GaN and tr-B/ZnO van der Waals heterostructures are characterized by the phenomenon of current anisotropy: the current along the zigzag edge of the ZnO/GaN monolayers is five times greater than along the armchair edge of these monolayers. Moreover, the heterostructures show good stability of current to temperature change at small voltage. These findings demonstrate that r-B/GaN and tr-B/ZnO vdW heterostructures are promising candidates for creating the element base of nanoelectronic devices, in particular, a conducting channel in field-effect transistors

Regenerative AC Electronic Load with One-Cycle Control

Variable linear or nonlinear loads are critical for testing AC power supplies and power equipment in various operating conditions. At present, most testing loads are based on bulky resistors, capacitors, and inductors on which the testing energy is consumed to generate excessive heat, and moreover, the impedance value is limited by finite combination of these bulky loads. Some commercial electronic loads are available, which provide flexible impedance control but the energy absorbed by the load is still dissipated as heat. The work presented in this paper is a continuous effort of UCI Power Electronics AC load project. A Regenerative AC Electronic Load (RACEL) is developed with One-Cycle Controller (OCC), which doesn't require any Digital Signal Processor (DSP) and software in the control loop. Using a reconfigurable Field Programmable Analog Array (FPAA), the OCC can be integrated into a single FPAA with easy reconfiguration and simple interface structure. The proposed RACEL can emulate any impedance load, linear or nonlinear as well steady or dynamic with the regeneration of the testing energy. Simulation and experimental results are presented to verify the proposed RACEL performanc

First-Principles Study of Electronic and Optical Properties of Tri-Layered van der Waals Heterostructures Based on Blue Phosphorus and Zinc Oxide

The creation of van der Waals heterostructures with tunable properties from various combinations of modern 2D materials is one of the promising tasks of nanoelectronics, focused on improving the parameters of electronic nanodevices. In this paper, using ab initio methods, we theoretically predict the existence of new three-layer van der Waals zinc oxide/blue phosphorus/zinc oxide (ZnO/BlueP/ZnO) heterostructure with AAA, ABA, ABC layer packing types. It is found that AAA-, ABA-, and ABC-stacked ZnO/BlueP/ZnO heterostructures are semiconductors with a gap of about 0.7 eV. The dynamic conductivity and absorption spectra are calculated in the wavelength range of 200–2000 nm. It is revealed that the BlueP monolayer makes the greatest contribution to the formation of the profiles the dynamic conductivity and absorption coefficient spectrums of the ZnO/BlueP/ZnO heterostructure. This is indicated by the fact that, for the ZnO/BlueP/ZnO heterostructure, conductivity anisotropy is observed at different directions of wave polarization, as for blue phosphorus. It has been established that the absorption maximum of the heterostructure falls in the middle ultraviolet range, and, starting from a wavelength of 700 nm, there is a complete absence of absorption. The type of layer packing has practically no effect on the regularities in the formation of the spectra of dynamic conductivity and the absorption coefficient, which is important from the point of view of their application in optoelectronics

New van der Waals Heterostructures Based on Borophene and Rhenium Sulfide/Selenide for Photovoltaics: An Ab Initio Study

One of the urgent tasks of modern materials science is the search for new materials with improved optoelectronic properties for various applications of optoelectronics and photovoltaics. In this paper, using ab initio methods, we investigate the possibility of forming new types of van der Waals heterostructures based on monolayers of triangulated borophene, and monolayers of rhenium sulfide (ReS), and rhenium selenide (ReSe2), and predict their optoelectronic properties. Energy stable atomic configurations of borophene/ReS2 and borophene/ReSe2 van der Waals heterostructures were obtained using density functional theory (DFT) calculations in the Siesta software package. The results of calculating the density of electronic states of the obtained supercells showed that the proposed types of heterostructures are characterized by a metallic type of conductivity. Based on the calculated optical absorption and photocurrent spectra in the wavelength range of 200 to 2000 nm, it is found that borophene/ReS2 and borophene/ReSe2 heterostructures demonstrate a high absorption coefficient in the near- and far-UV(ultraviolet) ranges, as well as the presence of high-intensity photocurrent peaks in the visible range of electromagnetic radiation. Based on the obtained data of ab initio calculations, it is predicted that the proposed borophene/ReS2 and borophene/ReSe2 heterostructures can be promising materials for UV detectors and photosensitive materials for generating charge carriers upon absorption of light

Effect of Functionalization with Potassium Atoms on the Electronic Properties of a 3D Glass-like Nanomaterial Reinforced with Carbon Nanotubes: In Silico Study

In this paper, using the self-consistent charge density-functional tight-binding (SCC DFTB) method, we perform an in silico study of the effect of functionalization by potassium atoms on the electronic properties of a new configuration of the glass-like carbon (GLC) reinforced with (4,4) and (6,5) single-walled carbon nanotubes (SWCNTs). The method of classical molecular dynamics was used to obtain energetically stable GLC configurations with different mass fractions of potassium. It is found that with an increase in the mass fraction of SWCNTs, the elasticity of GLC increases. It is shown that when the GLC structure reinforced with SWCNTs is filled with potassium, the number of available electronic states at the Fermi level increases compared to GLC without nanotubes, which significantly improves the emission and electrophysical characteristics of the carbon nanomaterial. For most structures, at a potassium/carbon mass ratio of 1:100 (0.01), an increase in the Fermi energy is observed, and, hence, a decrease in the work function. The maximum decrease in the work function by ~0.3 eV was achieved at a mass ratio of potassium/carbon of 1:4.5 (0.23) for GLC reinforced with (6,5) SWCNTs. It is revealed that, at a mass ratio of potassium/carbon of 1:28.5 (0.035), the quantum capacitance of GLC reinforced with (4,4) and (6,5) SWCNTs increases by ~9.4% (1752.63 F/g) and 24.1% (2092.04 F/g), respectively, as compared to GLC without nanotubes (1587.93 F/g). Based on the results obtained, the prospects for the application of the proposed GLC configuration in emission electronics devices are predicted