The ability to control the bandgap in two-dimensional graphene-like semiconductors is an essential task for the development of optoelectronic and nanoelectronic devices. Complex compositions alloys ...of transition metal dichalcogenides, such as Mo x W 1-x Se 2y S 2(1-y) , are the most optimal candidates for this purpose. Here we present spectrally selective photodetectors based on such quaternary transition metal dichalcogenides monolayers. It is shown that the spectral selectivity of optical detectors can be changed in a wide range if the composition of these quaternary monolayer transition metal dichalcogenides varies. This effect is directly related to the significant influence of the composition of such two-dimensional semiconductors on their bandgap. A theoretical model for estimation of quaternary transition metal dichalcogenides optical coefficients and optical detectors on their basis is proposed. The optical absorption simulation in created detectors was made, the results of which qualitatively coincided with the detectors performance. Thus, the obtained results can contribute to the development of valleytronics for two-dimensional semiconductor structures.
In this work, we present a result of PFM measurements on perforated and nonperforated Ba
0,8
Sr
0,2
TiO
3
thin epitaxial films. A huge enhancement of effective values for both lateral and vertical ...piezoelectric tensors during polarization reversal was experimentally detected. An assumption of short-range quadrant domain pattern in perforated ferroelectric structure was discussed. The obtained results are crucial for calculations of ferroelectric polarization in ferroelectric photonic crystals and metamaterials.
In this review, our recent results on the electron-beam domain writing (EBDW) on the nonpolar surfaces of LiNbO3 crystals of different compositions are presented. Under EB irradiation of the nonpolar ...surfaces, domains nucleated in irradiation points grow frontally along the polar
Z
-direction in a thin (of microns in thickness) surface layer; the driving force is the tangential component of space-charge fields induced by EB in irradiation points. This geometry of the experiment provides a possibility of three-dimensional (3D) characterization of domain patterns using the combination of atomic force microscopy (AFM) and second harmonic generation (SHG) confocal microscopy methods. The obtained results permitted us to relate the main characteristics of domain formation (the domain sizes and velocity
V
f
of the frontal motion) to the irradiation conditions (the accelerating voltage
U
of scanning electron microscopy (SEM), EB current
I
, the inserted charge
Q
). The domain depth
T
d
is controlled by
U
via the electron penetration depth; the domain length
L
d
increases linearly with
Q
owing to the domain frontal growth by the viscous friction law. The electron emission coefficient
σ
affects the domain formation due to the fundamental dependence of
σ
on
U
. In the framework of current approach to EB charging of insulators, the effect of an enhanced conductance on EBDW characteristics is analyzed. The difference between EBDW characteristics observed in varied LiNbO3 compositions is discussed in the framework of the intrinsic defect structure of LiNbO3. The obtained results extend the possibility of EBDW application to a wider range of crystals.
We sequenced the nearly complete mtDNA of 3 species of parasitic wasps, Nasonia vitripennis (2 strains), Nasonia giraulti, and Nasonia longicornis, including all 13 protein-coding genes and the 2 ...rRNAs, and found unusual patterns of mitochondrial evolution. The Nasonia mtDNA has a unique gene order compared with other insect mtDNAs due to multiple rearrangements. The mtDNAs of these wasps also show nucleotide substitution rates over 30 times faster than nuclear protein-coding genes, indicating among the highest substitution rates found in animal mitochondria (normally <10 times faster). A McDonald and Kreitman test shows that the between-species frequency of fixed replacement sites relative to silent sites is significantly higher compared with within-species polymorphisms in 2 mitochondrial genes of Nasonia, atp6 and atp8, indicating directional selection. Consistent with this interpretation, the Ka/Ks (nonsynonymous/synonymous substitution rates) ratios are higher between species than within species. In contrast, cox1 shows a signature of purifying selection for amino acid sequence conservation, although rates of amino acid substitutions are still higher than for comparable insects. The mitochondrial-encoded polypeptides atp6 and atp8 both occur in F0F1ATP synthase of the electron transport chain. Because malfunction in this fundamental protein severely affects fitness, we suggest that the accelerated accumulation of replacements is due to beneficial mutations necessary to compensate mild-deleterious mutations fixed by random genetic drift or Wolbachia sweeps in the fast evolving mitochondria of Nasonia. We further propose that relatively high rates of amino acid substitution in some mitochondrial genes can be driven by a "Compensation-Draft Feedback"; increased fixation of mildly deleterious mutations results in selection for compensatory mutations, which lead to fixation of additional deleterious mutations in nonrecombining mitochondrial genomes, thus accelerating the process of amino acid substitutions.
Objectives
. Two-dimensional transition metal dichalcogenides (TMDs) are utilized for various optical applications due to the presence in these materials of a direct band gap corresponding to the ...visible and near-infrared spectral regions. However, a limited set of existing TMDs makes the region of the used spectral range discrete. The most effective way to solve this problem is to use two-dimensional TMD films based on multicomponent alloys, including three or more different chemical elements (while TMDs consist of two). By varying their morphological composition, one can control the value of the band gap and thus their optical absorption spectrum. However, since the band gap in such structures is highly nonlinear as far as their chemical composition is concerned, it can be challenging to select the required concentration in order to achieve uniform absorption. In this regard, the purpose of this work is to theoretically determine the dependence of the band gap of four-component two-dimensional Mo
x
W
1–x
S
2y
Se
2(1–y)
alloys on their morphological composition.
Methods.
The calculations were performed within the framework of the density functional theory using the Quantum Espresso software package. Flakes of two-dimensional TMDs alloys were prepared from bulk TMDs crystals by mechanical exfoliation on a Si/SiO
2
substrate. An experimental study of the photoluminescence characteristics was carried out using photoluminescence microscopy-spectroscopy. Results. In this work, the dependence of the band gap on the morphological composition of two-dimensional Mo
x
W
1–x
S
2y
Se
2(1–y)
alloys was determined. Upon varying the composition of TMDs alloys, it was found that the band gap changes from 1.43 to 1.83 eV. The obtained theoretical results are in qualitative agreement with the experimental data.
Conclusions
. The minimum band gap is observed in alloys close to MoSe
2
, while alloys close to WS
2
have the maximum band gap value.
The transfer matrix method has been widely used to calculate wave propagation through the layered structures consisting entirely of either linear or nonlinear optical materials. In the present work, ...we develop the transfer matrix method for structures consisting of alternating layers of linear and nonlinear optical materials. The result is presented in a form that allows one to directly substitute the values of material constants, refractive index and absorption coefficient, into the expressions describing the second harmonic generation (SHG) field. The model is applied to the calculation of second harmonic (SH) field generated in nano-thin layers of transition metal dichalcogenides exfoliated on top of silicon oxide/silicon Fabry-Perot cavity. These structures are intensively studied both in view of their unique properties and perspective applications. A good agreement between experimental and numerical results can be achieved by small modification of optical constants, which may arise in an experiment due to a strong electric field of an incident focused pump laser beam. By considering the SHG effect, this paper completes the series of works describing the role of Fabry-Perot cavity in different optical effects (optical reflection, photoluminescence and Raman scattering) in 2D semiconductors that is extremely important for characterization of these unique materials.
Electro-optic properties of Ba0.8Sr0.2TiO3 (BST) film with a thickness of 1 μm deposited on the MgO (001) substrate by the rf sputtering have been studied. Structural features of the film were ...identified by X-ray diffraction method. It was shown, that the BST film exhibited a predominantly linear EO behavior under the applied static electric field, that have been explained according to the strong compressive stresses in the film. The polarization distribution across the gap between the electrodes when electric field is applied was also investigated experimentally and calculated. The linear EO coefficient of Ba0.8Sr0.2TiO3 film with a thickness of 1 μm film was found to be rc = 99.4 p.m./V, that is promising for various EO applications, for example, high performance EO modulator.
Two-dimensional molybdenum disulfide crystallites grown by mechanical exfoliation and chemical vapor deposition have been studied. It is shown that both methods can be used to obtain individual ...crystallites with a monoatomic thickness and similar optical properties. It is found that crystallites grown by chemical vapor deposition have a higher defect concentration than those grown by mechanical exfoliation.
Accelerators are used in many areas of modern science and technology (FCC-ee, CEPC, ILC, ESS, MYRRHA, etc.). One of the main elements of accelerators is the superconducting cavity based on ...high-purity niobium sheets. In addition to RRR requirements (over 300) niobium sheets for the SRF cavities should meet rather tough requirements for the grain size, recrystallization degree and mechanical properties. Development of the manufacture regimes of the niobium sheets with the required characteristics for the SRF cavities is a promising and relevant task. The paper presents the study results of the deformation route, true strain value, recrystallization heat treatment regimes influence on the structural and mechanical characteristics of the high-purity niobium sheets.
Complex flue gas cleaning of thermal power plants Protsko, D S; Panov, S Yu; Lobachova, N N ...
IOP Conference Series: Earth and Environmental Science,
07/2021, Letnik:
808, Številka:
1
Journal Article
Recenzirano
Odprti dostop
Abstract
Currently, there are significant emissions of pollutants from electric power facilities in our country. At the TPP, sulfur and nitrogen purification technologies are practically not used, ...most of the installed ash collectors operate with low efficiency and using outdated technology, and environmental indicators are significantly inferior to foreign analogues. At the same time, there is experience in the development and development on an industrial scale of various methods and tools that provide a significant reduction in emissions of particulate matter, sulfur oxides and nitrogen. The article considers an example of such a technology. For particle cleaning, a ceramic high-temperature filter with a catalytic coating is used to selectively remove nitric oxide when interacting with carbomide. The sulfur is removed by chemical neutralization with a lime sorbent.
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