Theoretical modeling within LDA, GGA, and PBE approximations was herein performed to determine the electronic band structures of MgGeN 2 , MgSiN 2 , ZnGeN 2 , and ZnSiN 2 nitride compounds and their optical properties. It is established that the compounds with germanium are direct-gap semiconductors with the band gap values of 3.0 eV (MgGeN 2 ) and 1.7 eV (ZnGeN 2 ), while the silicon-based compounds are indirect-gap semiconductors with the band gap values of 4.6 eV (MgSiN 2 ) and 3.7 eV (ZnSiN 2 ). Optical properties analysis showed the prospects of using MgGeN 2 and ZnGeN 2 in optoelectronics.

Theoretical modeling within LDA, GGA, and PBE approximations was herein performed to determine the electronic band structures of MgGeN2, MgSiN2, ZnGeN2, and ZnSiN2 nitride compounds and their optical properties. It is established that the compounds with germanium are direct-gap semiconductors with the band gap values of 3.0 eV (MgGeN2) and 1.7 eV (ZnGeN2), while the silicon-based compounds are indirect-gap semiconductors with the band gap values of 4.6 eV (MgSiN2) and 3.7 eV (ZnSiN2). Optical properties analysis showed the prospects of using MgGeN2 and ZnGeN2 in optoelectronics.

State-of-the-art technologies of fabrication of monolayers of transition metal dichalcogenides like MeX2, where Me = Mo, W; X = S, Se, Te, and their based heterostructures are considered. Results of theoretical modeling are analyzed and possibilities of band gap engineering by means of strains, impurities, vacancies, various layer stacking and combination of different materials are presented. Vacancies and impurities in the positions of metal atoms are shown to drastically change the band gap, even leading to an appearance of metallic properties, whereas a substitution of chalcogen atoms by isovalent atoms changes the properties not so dramatically. Possible applications of heterostuctures with tunable band gaps in transistors, light-emitting diodes, photoelectrochemical cells or photovoltaic devices are proposed and their advantages in comparison with commonly used analogues are discussed. (c) 2021 Elsevier Ltd. All rights reserved. Selection and peer-review under responsibility of the scientific committee of the International Conferences & Exhibition on Nanotechnologies, Organic Electronics & Nanomedicine - NANOTEXNOLOGY 2020.

The fertility and viability of pollen grains of two morphological forms of Taraxacum officinale Wigg. s.l. were estimated. These forms compose common coenopopulations growing in various coenotic and edaphic conditions. The forms studied possess developed gynoecia-a large number of fertile pollen grains capable of germinating under certain temperature conditions. This fact points to the amphimictic properties of the plants. Comparison of the data on the fraction of fertile pollen grains and seed productivity allows assuming that some seeds develop without fertilization. This can be considered as evidence of the apomictic properties of plants. Therefore, the presence of facultative apomixis in the species considered was confirmed indirectly in our work. The fertility of pollen grains was shown to be a characteristic of the male gametophyte that was more environmentally dependent than its viability. Under favorable conditions, the share of fertile pollen grains in f. dahlstedtii and f. pectinatiforme differ insignificantly. Under stress, the differences between the dandelion forms by this index increase. This can be considered as a mechanism of adaptation to adverse environmental factors. The revealed differentiation of the morphological forms of dandelions by the index of pollen grain fertility suggests that edaphic and coenotic stresses increase the differences between them in the degree of apomictic and amphimictic properties. The morphological forms of dandelions, by realizing two reproductive strategies under stress, ensure both the abundance and the genetic heterogeneity of the coenopopulations. The morphological forms studied do not differ in the proportion of viable pollen grains. This index increases in the gradient of coenotic competition only to a certain extent, which can be considered as a manifestation of the properties of the facultative apomict.

A new promising semiconductor material (phosphorene) is studied using theoretical simulation. The possibilities of changing the magnitude and nature of interband transitions under the action of compressive and tensile stresses on the phosphorene crystal lattice are determined. It is found that phosphorene can be both direct-gap and indirect-gap semiconductors, depending on the magnitude and direction of stress action. Phosphorene can be used in new generation nanoelectronic devices with controlled movement of charge carriers.

A new promising semiconductor material - phosphorene - was investigated and the possibilities of modifying of its interband transitions under compressive and tensile strains in the crystal lattice of the material were determined by means of theoretical modeling. It is shown that depending on the value and direction of the strains this material may be direct-gap or indirect-gap semiconductor. The potential for the use of phosphorene in nanoelectronic devices of new generation with controlled transport of charge carriers is shown.

The possibilities and conditions for modifying the band gap and the behavior of interband transitions under compressive and tensile strains in the crystal lattice of a molybdenum disulfide monolayer have been determined by theoretical modeling. It is shown that depending on the value and direction of the strains the compound may be a direct-gap or indirect-gap semiconductor, and the conditions for such transformations are determined. The results demonstrate a potential use of the molybdenum disulfide monolayer in nanoelectronic devices of new generation in which controlled transport of charge carriers is possible

Understanding the possibility of band-gap engineering in multilayers composed of two-dimensional materials is extremely important for modeling and creation of novel electronic and photonic devices. Stacking of WS 2 and WSe 2 monolayers looks particularly attractive for applications due to direct gap of resulting heterostructure, especially taking into account the indirect-gap nature of their bulk-state counterparts. We performed a theoretical investigation of chalcogen atoms replacement in WS 2 /WSe 2 heterostructure by isovalent Te atoms in order to reveal its effects on the band gap, electronic structure and density of states . The doped heterostructures were found to preserve semiconductor properties, whereas the gap changed its nature from direct to indirect in dependence on the position and the distance between substituting Te atoms. Te atoms in the S atom positions led preferably to an indirect gap and increased its value as compared to the pristine material; upon substitution of Se atoms, the direct gap of the heterostructure is preserved but with a small reduction, whereas the substitution of both S and Se atoms changed the gap in a different way depending on Te position. This information makes possible the creation of multilayered structures with tunable gap important for a novel generation of electronic and photonic devices.

An analysis of modern methods of modeling of the fundamental electronic properties of bulk semiconductors based on the electron density functional theory is performed and a technique taking into account the peculiarities of semiconductor compounds has been proposed. The procedure of creation of a model of the investigated object and an estimation of its adequacy is described. As an example the comparison of the results of calculations of electronic spectra and optical functions of MoS2 obtained in the framework of various functionals is given. The parameters which adequately describe the properties of investigated material in the framework of the presented technique are established.

An impact of positions of Te atoms substituting W atoms in two-dimensional WS2/WSe2 heterostructures on their electronic properties is investigated by theoretical simulation. The substitution of W by Te tends to reduce the energy band gap and can lead to metallic properties depending on the impurity position and concentration.

Electronic and dynamical properties of MoS2 are determined by means of theoretical calculations. Various numbers of layers with different thickness of the vacuum layer were considered. We have found that the band gap of bulk MoS2 is increasing upon decreasing of the number of layers from 0.76 eV up to 1.85 eV, and transforms from indirect to direct one in one-monolayer structure. The influence of vacancies on the electronic properties of MoS2 is analyzed and its dynamical properties are presented.

The electron energy band gap in one monomolecular layer of molybdenum dichalcogenide MoS2 is reduced upon substitution of S atoms by Te ones from 1,84 to 1,17 eV in the case of MoTe2. Both MoTe2 and MoS2 compounds in a bulk phase are indirect-gap semiconductors while one monomolecular layer of MoS2- x Tex compounds are transforming into direct-gap compounds for x < 0,5 or x > 1,5. The band gap dependence has a linear behavior in the case when the concentration of Te atoms is smaller than the concentration of S atoms.

Computer modeling of the electronic structure of heterostructures made of individual layers of two-dimensional crystals of MoS2, WS2, WSe2 and MoSe2 is performed by means of first-principles methods. Two variants of the mutual arrangement of the layers of two-dimensional crystals are suggested. Properties of such heterostructures in the presence of impurities and defects are investigated.

Electronic properties of heterostructures composed of two single molecular layers (monolayers) of MoS2, WS2, WSe2, and MoSe2 are ab initio simulated with an emphasis to the stacking peculiarities and an influence of point defects in their lattices. MoS2/MoSe2, MoS2/WS2, WS2/WSe2, and MoSe2/WSe2 heterostructures with the monolayers shifted like in the bulk material have been found to behave like semiconductors with the energy gaps of 0.88, 1.25, 1.06, and 1.07 eV, respectively. Such heterostructures possess indirect gaps in contrast to individual monolayers, while direct‐gap character is preserved in two layer stacking variants in WS2/WSe2 heterostructures and in MoS2/MoSe2 heterostructure with mirror stacking of the monolayers. Vacancies and Te atoms substituting other chalcogen atoms reduce the band gaps. The calculated orbital compositions of first direct band gap transitions in the defect‐free heterostructures and those with the point defects have demonstrated d‐electrons of Mo or W atoms to be mainly involved in the transitions.

The results of theoretical modeling from the first principles of atomic structure and properties of promising low-dimensional structures from semiconductors, performed for the past five years at the Center of Nanoelectronics and Novel Materials of Belarusian state university of informatics and radioelectronics, are summarized. The discovered principal new properties of two-dimensional structures from dichalcogenides of refractory metals and semiconductor silicides, one-dimensional structures of silicon, А3В5 semiconductors and semiconductor metal oxides, and zero-dimensional structures of carbon - nanodiamonds - are presented.

Two-dimensional (2D) semiconductor crystals can be applied to further increase the efficiency and speed of field-effect transistors. Such transistors are free from some of the adverse effects present in the traditional MOS transistors when their size is reduced. In this study, the model of the transistor MOS structure with the channel made of a 2D-crystal is proposed and its charge properties are investigated. The numerical simulation of such characteristics is carried out within the range of variations of the electrophysical properties of 2D-crystals representative of MoSe 2 , WS 2 , WSe 2 , ZrSe 2 , HfSe 2 , and PtTe 2 . The self-consistent correlation between electrophysical parameters of the structure via the chemical potential is found, and the effect of the potential of the field electrode and the gate insulator’s capacitance on them is demonstrated. The calculations of the steepness of the transfer characteristic and the voltage gain of such a transistor structure demonstrate that, for the channel made from transition metal dichalcogenides (TMD) with the forbidden gap band falling in the range 0.25–2.1 eV, the magnitudes of these parameters can attain 0.1 mA/V and 1000, respectively.

The results of theoretical modeling from the first principles of atomic structure and properties of promising low-dimensional structures from semiconductors, performed for the past five years at the Center of Nanoelectronics and Novel Materials of Belarusian state university of informatics and radioelectronics, are summarized. The discovered principal new properties of two-dimensional structures from dichalcogenides of refractory metals and semiconductor silicides, one-dimensional structures of silicon, А 3 В 5 semiconductors and semiconductor metal oxides, and zero-dimensional structures of carbon - nanodiamonds - are presented.

The results of calculations and system analysis of the properties of semiconducting compounds attractive for the fabrication of novel nanoelectronic devices are presented. The classes of semiconducting compounds of AIIBIVCV2, AI2BIVCVI3, AIVBVI and AVIBVI are considered, the most promising compounds are chosen on the base of the analysis of their properties and recommendations about possibility of their use in optoelectronics, photovoltaics and spintronics are made.

Ab initio simulation of phonon spectra and lattice thermal conductivity of monomolecular layers of transition metal dichalcogenides is performed. Size and temperature dependence of lattice thermal conductivity are analyzed and the difference between transition metal dichalcogenides is explained.

Physics, Chemistry and Application of Nanostructures, pp. 54-57 (2017) No AccessMAGNETIC ORDERING IN DOPED TWO-DIMENSIONAL DICHALCOGENIDESA. V. Krivosheeva, V. L. Shaposhnikov, and J.-L. LazzariA. V. KrivosheevaBelarusian State University of Informatics and Radioelectronics, P. Browka 6, 220013 Minsk, Belarus, V. L. ShaposhnikovBelarusian State University of Informatics and Radioelectronics, P. Browka 6, 220013 Minsk, Belarus, and J.-L. LazzariAix Marseille Université, CNRS, Centre Interdisciplinaire de Nanoscience de Marseille (CINaM) UMR 7325, Campus de Luminy, 13288 Marseille, Francehttps://doi.org/10.1142/9789813224537_0012Cited by:0 PreviousNext AboutSectionsPDF/EPUB ToolsAdd to favoritesDownload CitationsTrack CitationsRecommend to Library ShareShare onFacebookTwitterLinked InRedditEmail Abstract: Magnetic properties of the individual layers of MoS2, WS2, WSe2, MoSe2 upon substitution of metal atoms by manganese ones are studied. The magnetic moments on the impurity atoms and a possibility of a sustainable magnetic order are evaluated. FiguresReferencesRelatedDetails Physics, Chemistry and Application of NanostructuresMetrics History PDF download