Atomic Substitution Method Research Articles

Synthesis, crystals structures, DFT, and anticancer activities of polycyclic heterocyclic quinones

In this work, we synthesized six polycyclic heterocyclic quinones (PHQs) and one unexpected product (compound 6). We verified all of their structures by 1HNMR, 13CNMR, and HRMS and obtained four crystal structures of the seven products. At first, we compared the crystal structures with crystal structures similar to those reported in the literature and explained their differences by conjugative effect, hyperconjugative effect, and electrostatic effect. Then, we compared the crystal structure of compound 6 with the calculated structure of compound 6. The natural bond orbital analysis showed that the calculated structure formed intramolecular hydrogen bonds, whereas the crystal structure formed intermolecular hydrogen bonds but not intramolecular hydrogen bonds. The main reason for this difference was not due to the atomic charge or the interatomic distance, but rather the energy levels of the orbitals of the lone-pair electrons. In crystal structures, the intermolecular interactions contained many weak interactions, and we used the hydrogen atom substitution (HAS) method to divide the total intermolecular interactions as several independent weak interactions and to calculate their energies. The HAS method was often successful if the substituted group did not have a strong effect on the electronic structure of the entire molecule, and we found examples in the calculations of energies of weak interactions of crystal structure of compound 6 and compound 3a. An unsuccessful example of the HAS method was the substitution of C = O group with CH2 group to eliminate the O…H-N hydrogen bond interaction from the total interaction. According to the HAS method, our calculations showed that the strength order of the weak interactions was as follows: π-π stacking > hydrogen bond > n-π stacking > σ-π stacking. For the hydrogen bond, the strength order was as follows: C = O…H-N > CCl…H-N > C-F…H-N. For n-π stacking interaction, the strength order was as follows: Cl-π > N-π > F-π. Finally, we selected five synthesized PHQs to test anticancer activities and some of them showed better anticancer activities than the positive control drugs.

Рост пленок SiC, AlN и GaN на кремниевых изделиях произвольной геометрии для микроэлектромеханических применений

A technique is proposed for the formation of epitaxial films of silicon carbide, gallium and aluminum nitrides on the surface of non-planar silicon parts. Using the technique, a GaN/AlN/SiC/Si heterostructure was grown on the surface of a silicon ring. The samples were studied by scanning electron microscopy, as well as raman and energy dispersive spectroscopy. It is shown that the preliminary deposition of a SiC layer on silicon by the atomic substitution method, in which (111) facets are inevitably being formed regardless of the local crystallographic orientation of the substrate surface, makes it possible to efficiently grow subsequent layers of III-nitrides of both wurtzite and sphalerite types on silicon parts.

Change of the elastic strain in SiC films growing on Si substrates by the method of consistent atomic substitution

Sequential stages of synthesis of SiC epitaxial films on n- and p-type Si(111) substrates in a mixture of carbon monoxide and silane are studied by X-ray diffraction (XRD) and Raman scattering methods. It was found that the elastic strain in SiC films grown on n-type Si(111) is absent in contrast to SiC films grown on p-type Si(111), where the deformations are formed and completely relaxed by the 40 min of synthesis. A dramatic change in the SiC film structure is observed on the third minute of the growth, which is associated with the formation and growth of pores in the SiC layer. Differences in the lattice constants of SiC films grown on p- and n-type Si substrates are determined and verified via analysis of the change in the curvature of SiC/Si wafers. Keywords: Silicon carbide on silicon, elastic strain, nanostructures, microstructure evolution.

Change in Elastic Deformations in SiC Films during Their Growth by the Coordinated Atomic Substitution Method on Si Substrates

Change in Elastic Deformations in SiC Films during Their Growth by the Coordinated Atomic Substitution Method on Si Substrates

The Mechanical Properties of a SiC Composite Coating on Graphite Produced by the Atom-Substitution Method

The Mechanical Properties of a SiC Composite Coating on Graphite Produced by the Atom-Substitution Method

Study of silicon-to-silicon carbide transformation stages in the process of atomic substitution by the methods of total external X-ray reflection and X-ray diffractometry

X-ray diffraction and total external reflection of X-rays (X-ray reflectometry) methods were used to study the successive stages of synthesis of epitaxial SiC films on Si (100) X-ray diffraction and total external X-ray reflection (XRD) methods were used to study successive stages of synthesis of epitaxial SiC films on Si (100) surfaces, (110) and (111) surfaces by the atom substitution method. The data on the transformation evolution of (100) surfaces were studied, (110) and (111) Si, into SiC surfaces. A comparative analysis of the X-ray structural quality of the SiC layers grown on Si by the atom substitution method with the quality of SiC layers grown by Advanced Epi by the standard CVD method. A modified technique for the total outer X-ray reflection method, based on measurements of the intensity of the reflected X-rays using a special parabolic mirror. It is shown that the method of total external reflection method makes it possible to obtain important information about the degree of surface roughness of SiC layers, the evolution of their crystal structure and plasmon energy in the process of Si to SiC conversion. Keywords: total external reflection, X-ray reflectometry, silicon carbide, plasmons.

Исследование этапов превращения кремния в карбид кремния в процессе атомного замещения методами полного внешнего отражения рентгеновских лучей и рентгеновской дифрактомерии

X-ray diffraction and total external reflection of X-rays (X-ray reflectometry) methods were used to study the successive stages of synthesis of epitaxial SiC films on Si (100) X-ray diffraction and total external X-ray reflection (XRD) methods were used to study successive stages of synthesis of epitaxial SiC films on Si (100) surfaces, (110) and (111) surfaces by the atom substitution method. The data on the transformation evolution of (100) surfaces were studied, (110) and (111) Si, into SiC surfaces. A comparative analysis of the X-ray structural quality of the SiC layers grown on Si by the atom substitution method with the quality of SiC layers grown by Advanced Epi by the standard CVD method. A modified technique for the total outer X-ray reflection method, based on measurements of the intensity of the reflected X-rays using a special parabolic mirror. It is shown that the method of total external reflection method makes it possible to obtain important information about the degree of surface roughness of SiC layers, the evolution of their crystal structure and plasmon energy in the process of Si to SiC conversion.

Study of silicon-to-silicon carbide transformation stages in the process of atomic substitution by the methods of total external X-ray reflection and X-ray diffractometry

X-ray diffraction and total external reflection of X-rays (X-ray reflectometry) methods were used to study the successive stages of synthesis of epitaxial SiC films on Si (100) X-ray diffraction and total external X-ray reflection (XRD) methods were used to study successive stages of synthesis of epitaxial SiC films on Si (100) surfaces, (110) and (111) surfaces by the atom substitution method. The data on the transformation evolution of (100) surfaces were studied, (110) and (111) Si, into SiC surfaces. A comparative analysis of the X-ray structural quality of the SiC layers grown on Si by the atom substitution method with the quality of SiC layers grown by Advanced Epi by the standard CVD method. A modified technique for the total outer X-ray reflection method, based on measurements of the intensity of the reflected X-rays using a special parabolic mirror. It is shown that the method of total external reflection method makes it possible to obtain important information about the degree of surface roughness of SiC layers, the evolution of their crystal structure and plasmon energy in the process of Si to SiC conversion. Keywords: total external reflection, X-ray reflectometry, silicon carbide, plasmons.

Peculiarities of nucleation and growth of InGaN nanowires on SiC/Si substrates by HVPE

The growth of InGaN layers on hybrid SiC/Si substrates with orientations (100), (110), and (111) by the HVPE method was studied at temperatures that wittingly exceed the temperature of InN decomposition onto nitrogen atoms and metallic In (1000oC). On substrates with orientations (110) and (111), the formation of InGaN whisker nanocrystals was observed. The shape and growth mechanisms of nanocrystals were investigated. It is shown that nanocrystals nucleate on the (111) surface only inside V-defects formed at the points where screw dislocations exit onto the surface. On the (110) surface, nanocrystals are formed only on pedestals that arise during the film growth. An explanation is given for the difference in the growth mechanisms of nanocrystals on substrates of different orientations. Keywords: InGaN, heterostructures, SiC on Si, silicon, whisker nanocrystals, nanostructures, atomic substitution method

Elastic properties of porous silicon layer of hybrid SiC/Si substrates

Elastic properties of porous silicon layer of hybrid SiC/Si substrates grown by the atomic substitution method are investigated. The feature of the growth method is the formation of the macroporous silicon layer at the SiC/Si interface during growth. The elastic properties of the layer are studied using the finite element method. The biaxial modulus of the porous silicon is obtained as a function of porosity considering the different shape of the pores and presence of thin SiC boundary layer. The presence of the pores in the silicon layer adjacent to SiC results in the decrease of the elastic moduli by about 35%. However, this leads to a negligibly small change of the substrate curvature.

Atom substitution method to construct full-solar-spectrum absorption MoSeS/TiO2 nanotube arrays for highly efficient hydrogen evolution

Two-dimensional semiconductor shows highly efficient photocatalytic H2 generation due to plasma enhancement effect. Herein, a large area layered MoSeS in conjunction with TiO2 nanotube arrays is achieved by Ti foil anodization and chemical vapor deposition processes. MoSeS/TiO2 heterojunction has been prepared by one-step and two-step atom substitution methods, we found that the one-step atomic substitution method had higher photocatalytic performance than that. The composites can greatly reduce the charge transfer resistance and accelerate the carrier transport, leading to a high photocurrent response. UV–vis absorption spectra indicated an obvious redshift, which greatly improved the utilization efficiency of visible light. Photoelectrochemical properties of the composites showed that one-step atom substituted MoSeS has the highest performance. For the MoSeS/TiO2 by one-step (ES-TNTs), the hydrogen production efficiency reaches 92.74μmolh−1cm−2, which is 11 times higher than that of pure TiO2 nanotube arrays (TNTs). Also, the photocurrent density is 1.2 mAcm−2 at a bias of 0V, which is about 6 times higher than that of pure TNTs. In comparison to the two-step atom substitution method (S-E-TNTs, E-S-TNTs), the result is that MoSeS is easy to agglomerate on the surface of TNTs, which greatly reduces the contacted area and photocurrent density.

The Influence of the Porosity of Silicon Layer on the Elastic Properties of Hybrid SiC/Si Substrates

The effect of the porosity of a silicon layer containing macropores on the elastic and thermomechanical properties of SiC/Si substrates obtained by the atomic substitution method has been studied. The calculation of the elastic constants of porous silicon is performed by the finite element method. The results of calculating of Young’s modulus in the [111] direction agree with the estimates obtained by the method of nanoindentation of SiC/Si (111) substrates. The derived theoretical model can be used to determine the elastic properties of SiC/Si substrates of various orientations.

Влияние пористости слоя кремния на упругие свойства гибридных подложек SiC/Si

In this work, the influence of porosity of silicon layer with macropores on elastic and thermomechanical properties of SiC/Si substrates synthesized by the atom substitution method has been studied. Calculation of elastic constants of porous silicon has been performed by the finite element method. The results of calculation of the Young’s modulus in [111] direction are in agreement with the estimates obtained by the nanoindentation method of SiC/Si(111) substrates. The proposed theoretical model can be used for determination of elastic properties of SiC/Si substrates of different orientation.

The Optical Properties, Energy Band Structure, and Interfacial Conductance of a 3C-SiC(111)/Si(111) Heterostructure Grown by the Method of Atomic Substitution

Epitaxial films of single-crystalline silicon carbide (3C-SiC cubic polytype) with 20- to 120-nm thickness grown on a silicon substrate by the method of atomic substitution have been studied by the spectroscopic ellipsometry technique at 0.5−9.3 eV photon energies. It is established that the dielectric permittivity of a thin intermediate layer formed at the 3C-SiC(111)/Si(111) interface is characteristic of a semimetal. This result was confirmed by quantum-chemical simulation of the properties of 3C-SiC(111)/Si(111) heterointerface, showing that the conductance of this intermediate layer is related to p-electrons of interfacial Si atoms that are most remote from Si atoms of the substrate.

Photoluminescence properties of Sr2MgSi2O7:Pb2+ and tunable emission from UVB to UVC based on ion substitution

Ultraviolet light is a necessary light source for humans. As typical ultraviolet emission materials, Pb2+ doped phosphors have been widely investigated. Here, we report a Pb2+ activated silicate material. Under the excitation of 258 nm ultraviolet light, Sr2MgSi2O7:Pb2+ can emit broadband ultraviolet light with a peak at 333 nm. The luminescence intensity can be adjusted by changing the Pb2+ doping concentration, and the experiments show that the optimum concentration is 0.02. The critical distance for the corresponding concentration quenching was calculated to be 19.92 Å. By gradually decreasing the Sr/Ba ratio, the luminescence wavelength is gradually shifted from 333 to 383 nm due to the increase of Pb2+-O2−covalency. The continuous replacement of Sr by Ba atoms does not change the crystal structure, and the emission wavelength adjustable range is 50 nm. Our research adds new members to the Pb2+-activated phosphor family. At the same time, the successful use of atomic substitution method provides a reference for the adjustment of the emission wavelength of Pb2+ doped materials.

Coating with boron nitride on SiC fiber using atomic substitution

To increase the mechanical properties of ceramic matrix composite, it is important that formation of lubricant layer for crack deflection between matrix and fiber. Therefore, we fabricated uniform boron nitride (BN) lubricant layer using atomic substitution method. Silicon carbide (SiC) fiber surface was modified with amine groups using (3-amonipropyl)triethoxysilane to coat SiC fiber with BN as a solid lubricant. Then, surface was coated with graphene oxide (GO). Boric acid powder was supplied to the GO-coated fibers and the samples were heat-treated at 1200–1400 ℃ under N2 and NH3 atmospheres. An uniform BN layer could be coated on SiC fiber with 10 nm-1.11 μm. Crystallinity and thickness of BN layer could be controlled by reaction temperature. It was also confirmed that crystalline BN formed under process conditions of higher than 1400 ℃.

Оптические свойства, зонная структура и проводимость межфазной границы раздела гетероструктуры 3C-SiC(111)/Si(111), выращенной методом замещения атомов

Spectral ellipsometry in the photon energy range 0.5–9.3 eV was used to study epitaxial films of single-crystal silicon carbide of a cubic polytype 3C-SiC of 20–120 nm grown from silicon Si by atom substitution method. It was found that at the 3C-SiC (111) / Si (111) interface a thin intermediate layer is formed with a dielectric function corresponding to semimetal. This result is confirmed by quantum chemical modeling of the properties of the 3C-SiC (111) / Si (111) interface. It was shown that the conductivity of the layer is associated with p-electrons of Si atoms of SiC at the interface of the phases which are as far as possible from the Si atoms of the substrate.

Study of Elastic Properties of SiC Films Synthesized on Si Substrates by the Method of Atomic Substitution

The elastic properties of nanoscale silicon carbide film grown on a silicon substrate by the method of atomic substitution were studied. The Young modulus of nanoscale silicon carbide was for the first time measured by nanoindentation method. The structural characteristics of silicon carbide film on silicon were studied by the optical profilometry and spectral ellipsometry; the roughness and thickness of film were m-easured.

A New Method of Growing AlN, GaN, and AlGaN Bulk Crystals Using Hybrid SiC/Si Substrates

The main principles of a new method of growing bulk single-crystal AlN, AlGaN, and GaN films with thickness from 100 μm and more on silicon substrates with a buffer silicon carbide layer with its subsequent detachment from Si substrates are presented. The main substance of this method is a combination of the method of chloride-hydride epitaxy that determines high growth rates of III nitride layers and the use a Si substrate with a buffer layer of nanoscale SiC film grown by the atomic substitution method as the growth substrate. The Si substrate with a SiC layer grown by the atomic substitution method has a number of structural, physical, and chemical features as compared to SiC layers grown on Si by the standard methods. It is shown that it is precisely this feature that enables the growth on their surfaces of thick crack-free AlN, AlGaN, and GaN layers with subsequent and quite simple their detachment from the substrate. The single-crystal crack-free AlN layers with thickness to 300 μm, AlGaN layers with thickness to 400 μm, GaN layers with thickness to 200 μm, and GaN films of the semipolar ($$11\bar {2}4$$) orientations with thickness to 30 μm have been grown.

Рост полупроводниковых III-V гетероструктур на подложках SiC/Si

A heterostructure consisting of three thick layers: AlN (thickness 0.72 μm), AlGaN (thickness 1.82 μm) and GaN (thickness 2.2 μm) was grown by the method of chloride hydride epitaxy on Si with a buffer layer of nano-SiC. The nano-SiC layer was obtained by the method of atomic substitution. The grown heterostructure was studied by scanning electron microscopy, back-reflected electron diffraction, energy dispersive analysis, and Raman scattering. Studies have shown that the use of nano-SiC/Si substrates makes it possible to grow III-V layers with a high growth rate (~ 66 μm/h) without cracks and with small residual elastic stresses (~ 160 MPa).