Mechanically exfoliated 2D hexagonal boron nitride (h‐BN) is currently the preferred dielectric material to interact with graphene and 2D transition metal dichalcogenides in nanoelectronic devices, ...as they form a clean van der Waals interface. However, h‐BN has a low dielectric constant (≈3.9), which in ultrascaled devices results in high leakage current and premature dielectric breakdown. Furthermore, the synthesis of h‐BN using scalable methods, such as chemical vapor deposition, requires very high temperatures (>900 °C) , and the resulting h‐BN stacks contain abundant few‐atoms‐wide amorphous regions that decrease its homogeneity and dielectric strength. Here it is shown that ultrathin calcium fluoride (CaF2) ionic crystals could be an excellent solution to mitigate these problems. By applying >3000 ramped voltage stresses and several current maps at different locations of the samples via conductive atomic force microscopy, it is statistically demonstrated that ultrathin CaF2 shows much better dielectric performance (i.e., homogeneity, leakage current, and dielectric strength) than SiO2, TiO2, and h‐BN. The main reason behind this behavior is that the cubic crystalline structure of CaF2 is continuous and free of defects over large regions, which prevents the formation of electrically weak spots.
Calcium fluoride (CaF2) is an attractive high‐k dielectric for 2D electronics because its surface is terminated with fluorine atoms, which leads to a defect‐free van der Waals interface with 2D materials. Ultrathin CaF2 ionic crystals (grown by molecular beam epitaxy at 250 ºC) are shown to exhibit outstanding dielectric performance (i.e., homogeneity, leakage current, and dielectric strength), which is much better than that observed in SiO2, TiO2, and h‐BN.
. When building buildings and structures on unstable slopes, it becomes necessary to develop geotechnical technologies that ensure their stability. In addition, geotechnical techniques should be ...developed to ensure the safe operation of existing facilities built on them. Therefore, the main purpose of the work is to study one of the geotechnical technologies to ensure the stability of the fence fencing. As a rule, the opening of any foundation pit entails the emergence of additional efforts reducing the stability of the slopes. The task of ensuring the stability of the pit walls together with the loads on its bumps, as well as the general stability of the slope as a whole, is an urgent task of modern geotechnical construction. It is established that the structural solutions of the buried structures represent a special auxiliary containment structure, fence constructions, ground anchors that are arranged after the first stage of the excavation.
The construction of territories with problematic engineering and geological conditions in the presence of unstable, crossed relief is a complex geotechnical task. Therefore, the main purpose of the ...work is to study the features of the ground anchor, which is made by electric discharge technology, as a monolithic reinforced concrete structure. The questions related to the provision of safe methods of construction and erection works for the erection of any facility in such territories are related to a multifactor problem connected, primarily with the need to develop special geotechnical technologies tied to real engineering and geological conditions, loads from previously erected buildings and structures and, secondly, the actual implementation of them on a particular construction site. The case considered in the article from the geotechnical practice of construction of the facility is confirmed by the fact that due to the availability of modern design and construction and construction works, it is possible to solve any complex problems related to the issues of ensuring the stability of slopes.
Modern geotechnical construction has a wide range of technologies in its toolkit. Use of the Piles, manufactured with the help of different available technologies, represents one of the ways of the ...underground structures utilization at the objects zero level construction. The following basics shall be observed during zero cycle design and construction: 1) interactivity; 2) engineering viability; and cost efficiency. First principle suppose that interactivity utilization at the design is compulsory. This means: “initial design – test area – revised design”. It is necessary to adhere to the second principle for each of the elements of the formula given above. To ensure this, there are considered three and more Piles types (Bored Piles and Inclined Piles) in the initial design. It was determined that use of the Inclined Piles with multi point widening manufactured according to the Electric-Discharge Technology (EDT) is more preferable in comparison with the other Piles types. In effect, being Inclined Piles with the adjustable Holding Power, they have competitive advantages versus any other Pile. Therefore, use of the EDT Inclined Piles in the geotechnical construction after the interactive design has engineering viability and is a cost efficient way of underground structures construction.
•Annealing allows one to obtain nickel ferrite films with close to bulk parameters.•X-ray magnetic circular dichroism data simulation shows completely inverted spinel structure.•Spin waves with a ...small damping parameter were detected in the films.
An appropriate choice of growth conditions has made feasible fabrication of thin epitaxial NiFe2O4 / SrTiO3 films with parameters close to those of bulk nickel ferrite. Spin waves with a damping parameter as low as 10-2 and a very narrow ferromagnetic resonance line were observed in the samples subjected to post-growth high temperature annealing in oxygen. The analysis of electron and X-ray diffraction has shown substantial improvement of the crystalline quality of the annealed films. X-ray absorption spectroscopy and X-ray magnetic circular dichroism data simulation have revealed that the films exhibit a completely inverted spinel structure characterized by the maximal possible net magnetic moment.
In the present paper we discuss correlations between crystal structure and magnetic properties of epitaxial ε-Fe
2
O
3
films grown on GaN. The large magnetocrystalline anisotropy and room temperature ...multiferroic properties of this exotic iron oxide polymorph, make it a perspective material for the development of low power consumption magnetic media storage devices. Extending our recent progress in PLD growth of ε-Fe
2
O
3
on the surface of technologically important nitride semiconductors, we apply reciprocal space tomography by electron and x-ray diffraction to investigate the break of crystallographic symmetry occurring at the oxide-nitride interface resulting in the appearance of anisotropic crystallographic disorder in the sub-100 nm ε-Fe
2
O
3
films. The orthorhombic-on-hexagonal nucleation scenario is shown responsible for the development of a peculiar columnar structure observed in ε-Fe
2
O
3
by means of HRTEM and AFM. The complementary information on the direct and reciprocal space structure of the columnar ε-Fe
2
O
3
films is obtained by various techniques and correlated to their magnetic properties. The peculiar temperature dependence of magnetization studied by the small-field magnetization derivative method and by neutron diffraction reveals the existence of a magnetic softening below 150 K, similar to the one observed earlier solely in nanoparticles. The magnetization reversal in ε-Fe
2
O
3
films probed by X-ray magnetic circular dichroism is found different from the behavior of the bulk averaged magnetization measured by conventional magnetometry. The presented results fill the gap between the numerous studies performed on randomly oriented ε-Fe
2
O
3
nanoparticles and much less frequent investigations of epitaxial epsilon ferrite films with lattice orientation fixed by the substrate.
Thin (4-20 nm) yttrium iron garnet (Y
3
Fe
5
O
12
, YIG) layers have been grown on gadolinium gallium garnet (Gd
3
Ga
5
O
12
, GGG) 111-oriented substrates by laser molecular beam epitaxy in ...700-1000 °C growth temperature range. The layers were found to have atomically flat step-and-terrace surface morphology with step height of 1.8 Å characteristic for YIG(111) surface. As the growth temperature is increased from 700 to 1000 °C the terraces become wider and the growth gradually changes from layer by layer to step-flow regime. Crystal structure studied by electron and X-ray diffraction showed that YIG lattice is co-oriented and laterally pseudomorphic to GGG with small rhombohedral distortion present perpendicular to the surface. Measurements of magnetic moment, magneto-optical polar and longitudinal Kerr effect (MOKE), and X-ray magnetic circular dichroism (XMCD) were used for study of magnetization reversal for different orientations of magnetic field. These methods and ferromagnetic resonance studies have shown that in zero magnetic field magnetization lies in the film plane due to both shape and induced anisotropies. Vectorial MOKE studies have revealed the presence of an in-plane easy magnetization axis. In-plane magnetization reversal was shown to occur through combination of reversible rotation and abrupt irreversible magnetization jump, the latter caused by domain wall nucleation and propagation. The field at which the flip takes place depends on the angle between the applied magnetic field and the easy magnetization axis and can be described by the modified Stoner-Wohlfarth model taking into account magnetic field dependence of the domain wall energy. Magnetization curves of individual tetrahedral and octahedral magnetic Fe
3+
sublattices were studied by XMCD.
Mechanically exfoliated 2D hexagonal boron nitride (h-BN) is currently the preferred dielectric material to interact with graphene and 2D transition metal dichalcogenides in nanoelectronic devices, ...as they form a clean van der Waals interface. However, h-BN has a low dielectric constant (≈3.9), which in ultrascaled devices results in high leakage current and premature dielectric breakdown. Furthermore, the synthesis of h-BN using scalable methods, such as chemical vapor deposition, requires very high temperatures (>900 °C) , and the resulting h-BN stacks contain abundant few-atoms-wide amorphous regions that decrease its homogeneity and dielectric strength. Here it is shown that ultrathin calcium fluoride (CaF
) ionic crystals could be an excellent solution to mitigate these problems. By applying >3000 ramped voltage stresses and several current maps at different locations of the samples via conductive atomic force microscopy, it is statistically demonstrated that ultrathin CaF
shows much better dielectric performance (i.e., homogeneity, leakage current, and dielectric strength) than SiO
, TiO
, and h-BN. The main reason behind this behavior is that the cubic crystalline structure of CaF
is continuous and free of defects over large regions, which prevents the formation of electrically weak spots.
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