A comparative investigation of the crystal structure, morphology and electrochemistry of LiFe0.5Mn0.5PO4 (LFMP) prepared by the mechanochemically assisted solid-state synthesis (SS) and the ...solvothermal synthesis (ST) was performed. The as-prepared samples were studied by XRD, FTIR, Raman, Mӧssbauer, SEM, TEM, galvanostatic cycling, GITT, and EIS. The low-temperature carbon-free LFMP-ST displays nanoplatelets with 20–30 nm thickness in the b direction and is characterized by the low concentration of the MLi defects and more distorted MO6 octahedra compared to LFMP-SS. It shows poor conductivity and only one sloping voltage plateau at 3.4 V. Its post-coating with carbon at 750 °C leads to the appearance of two commonly observed plateaus, corresponding to the Fe2+/Fe3+ and Mn2+/Mn3+ redox couples, and improves cyclability and rate capability. Carbon-coated LFMP-SS consists of irregular-shaped submicron particles and demonstrates two two-phase plateaus and an additional one at 3.6–3.7 V upon discharge. According to the GITT study, this plateau increases with cycling rate and is most likely controlled by the slower kinetics of the Mn3+ ions reduction.
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•Nanoplate-like LiFe0.5Mn0.5PO4 (LFMP) was prepared by solvothermal synthesis (ST).•Submicron LFMP was prepared by mechanochemically assisted solid-state synthesis.•Comparative study of structure and electrochemical properties of LFMP was performed.•One sloping voltage plateau at 3.4 V is observed for LFMP-ST.•Additional plateau on discharge of LFMP-SS is caused by slower kinetics of Mn2+/Mn3+.
In the present study we investigated the nanostructuring processes in locally suspended few-layer graphene (FLG) films by irradiation with high energy ions (Xe, 26-167 MeV). For such an energy range, ...the main channel of energy transfer to FLG is local, short-term excitation of the electronic subsystem. The irradiation doses used in this study are 1 × 10
-5 × 10
ion/cm
. The structural transformations in the films were identified by Raman spectroscopy and transmission electron microscopy. Two types of nanostructures formed in the FLG films as a result of irradiation were revealed. At low irradiation doses the nanostructures were formed preferably at a certain distance from the ion track and had the form of 15-35 nm "bunches". We assumed that the internal mechanical stress that arises due to the excited atoms ejection from the central track part creates conditions for the nanodiamond formation near the track periphery. Depending on the energy of the irradiating ions, the local restructuring of films at the periphery of the ion tracks can lead either to the formation of nanodiamonds (ND) or to the formation of AA' (or ABC) stacking. The compressive strain value and pressure at the periphery of the ion track were estimated as ~0.15-0.22% and ~0.8-1.2 GPa, respectively. The main novel results are the first visualization of ion tracks in graphene in the form of diamond or diamond-like rings, the determination of the main condition for the diamond formation (the absence of a substrate in combination with high ion energy), and estimates of the local strain at the track periphery. Generally, we have developed a novel material and have found how to control the film properties by introducing regions similar to quantum dots with the diamond interface in FLG films.
•In the process of annealing InP(001) in an arsenic flux, an InP1-xAsx layer is formed on the surface•The activation energy Ea=1.17 eV of the formation of an arsenic-containing layer was ...determined•The amount of arsenic substitution for phosphorus at different annealing temperatures was determined, which is 7% at an annealing temperature of 480°C and increases to 41% with an increase in the annealing temperature to 540°C•The analysis of SEM images showed that InAs islands with sizes from 100 nm to 1 μm are formed on the surface•The area covered by such areas occupies about 1.5% of the sample surface area at an annealing temperature of 540°C
We report experimental study of the transformation of the oxide-coated InP(001) surface during annealing in an arsenic flux. Using the RHEED method, it was shown that an InP1-хAsх layer is formed on the surface. The transformation of an oxidized surface occurs at a temperature higher at about 60°C than the transformation of an atomically clean surface. The activation energy Ea = 1.17 eV of the formation of an arsenic-containing layer was determined. The amount of arsenic substitution for phosphorus at different annealing temperatures was determined, which is 7% at an annealing temperature of 480°C and increases to 41% with an increase in the annealing temperature to 540°C. SEM analysis of surface reveals areas with high arsenic content (InAs islands). The size and density of such regions increases with an increase in the annealing temperature and at 540°C reaches 5.5 × 103 nm2 and 6 × 109 cm−2, respectively. However, despite the local inhomogeneities, the main surface area is covered with a uniform InPAs layer. The area covered with InAs islands occupies about 1.5% of the surface area at an annealing temperature of 540°C.
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Three decades after the prediction of charge-vortex duality in the critical vicinity of the two-dimensional superconductor-insulator transition (SIT), one of the fundamental implications of this ...duality-the charge Berezinskii-Kosterlitz-Thouless (BKT) transition that should occur on the insulating side of the SIT-has remained unobserved. The dual picture of the process points to the existence of a superinsulating state endowed with zero conductance at finite temperature. Here, we report the observation of the charge BKT transition on the insulating side of the SIT in 10 nm thick NbTiN films, identified by the BKT critical behavior of the temperature and magnetic field dependent resistance, and map out the magnetic-field dependence of the critical temperature of the charge BKT transition. Finally, we ascertain the effects of the finite electrostatic screening length and its divergence at the magnetic field-tuned approach to the superconductor-insulator transition.
Mg2Si films have been grown on Si(111) and Si(001) surfaces at ~ 387–477 °C by ultra-fast deposition in vacuum. The original pulse-type evaporator used allows Mg deposition rates of ~103–104 nm/s ...which provide effective accumulation of Mg on hot Si surfaces despite its fast re-evaporation. The silicide films at different stages of formation and growth have been obtained by varying the pulse duration, Mg deposit amounts and substrate temperatures. The local structure and crystal quality of the obtained Mg2Si films have been studied. The mechanism of the Mg2Si film formation and growth process is considered. The role of high temperatures in the formation of film texture is demonstrated. The existing to date experimental data on Mg–Si intermixing and Mg2Si formation are explained. Technologies of Si/Mg2Si solar cells can be based on these results.
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•Different stages and mechanism of Mg2Si formation on Si above 300–400 °C are studied.•Textured Mg2Si films grow on Si(111) and (001) by fast deposition of Mg at 400 °C.•By XRD and HRTEM data, the films' crystal quality is the best to date.•11 nm-thick film is continuous, 45-90 nm-thick films have the columnar structure.•Texture forms during nucleation at high T; only the best-oriented nuclei are stable.
Fluorinated graphene (FG), the most stable derivative of graphene, is suggested for the role of functional material (weak fluorination degree) and the dielectric layers for graphene and other 2D ...materials, especially for flexible and printed electronics. The main findings discussed in the present study are (1) an excellent mechanical properties of FG in bending conditions for the first time measured for FG with different fluorination degree; (2) the 97–99% transparency of FG films with thickness up to 25 nm in wide range of wavelengths, (3) a ultralow leakage current and a high breakdown field in the printed cross-bar structures; (4) a smooth increase in interplanar spacing by 1–2% from the center of few-layered fluorinated graphene flakes to their edges; (5) observation of only CC related G line without defect related D line in Raman spectra in the case of giant amplification of Raman scattering for FG films printed at Ag layers. Unchanged characteristics of fluorinated graphene films up to stretching-strain values of 2.5–4% were demonstrated. Generally, it can be stated that fluorinated graphene films have great promise in flexible and printed electronics.
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•Excellent mechanical properties for the fluorinated graphene films with different fluorination degree are demonstrated.•FG films possess a unique combination of properties for 2D dielectric films including the transparency.•Fluorinated graphene suspension is suggested for the dielectric films, especially for flexible and printed electronics.
The use of low-temperature (LT) GaAs layers as dislocation filters in GaAs/Si heterostructures (HSs) was investigated in this study. The effects of intermediate LT-GaAs layers and of the post-growth ...and cyclic in situ annealing on the structural properties of GaAs/LT-GaAs/GaAs/Si(001) HSs were studied. It was found that the introduction of LT-GaAs layers, in combination with post-growth cyclic annealing, reduced the threading dislocation density down to 5 × 10
cm
, the root-mean-square roughness of the GaAs surface down to 1.1 nm, and the concentration of non-radiative recombination centers in the near-surface GaAs/Si regions down to the homoepitaxial GaAs level. Possible reasons for the improvement in the quality of near-surface GaAs layers are discussed. On the one hand, the presence of elastic deformations in the GaAs/LT-GaAs system led to dislocation line bending. On the other hand, gallium vacancies, formed in the LT-GaAs layers, diffused into the overlying GaAs layers and led to an increase in the dislocation glide rate. It was demonstrated that the GaAs/Si HSs obtained with these techniques are suitable for growing high-quality light-emitting HSs with self-assembled quantum dots.
Magnetic nanoparticles embedded into semiconductors have current perspectives for use in semiconducting spintronics. In this work, 40 keV Fe+ ions were implanted in high fluences of (0.5 ÷ 1.5) × ...1017 ion/cm2 into an oxide semiconductor and single-crystalline TiO2 plates of rutile structure with (100) or (001) face orientations. Microstructure, elemental-phase composition, and magnetic properties of the Fe-ion-implanted TiO2 were studied by scanning and transmission electron microscopies (SEM and TEM), X-ray photoelectron (XPS) and Rutherford backscattering (RBS) spectroscopies, as well as vibrating-sample magnetometry (VSM). The high-fluence ion implantation results in the formation of magnetic nanoparticles of metallic iron beneath the irradiated surface of rutile. The induced ferromagnetism and observed two- or four-fold magnetic anisotropy are associated with the endotaxial growth of Fe nanoparticles oriented along the crystallographic axes of TiO2.
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