Substitution Of Oxygen Atoms Research Articles

Olive pomace waste conversion to bio-fuel by application of integrated configuration of pyrolysis/hydrodeoxygenation process

Bio-oil obtained from non-catalytic pyrolysis of biomass, consists of a large number of oxygenated compounds. Hence, it is essential for the bio-oil to go through upgrading processes such as hydrodeoxygenation (HDO) to reform these compounds to aliphatic and aromatic hydrocarbons. This study works towards this purpose by initially deriving raw bio-oil from olive pomace waste biomass in a non-catalytic pyrolysis process at temperature of 400–700 ºC. Then for reducing the oxygen content of derived bio-oil, HDO of the raw bio-oil over NiMo/Al2O3 catalyst was performed in a batch reactor, in varying operational parameters: temperature of 200–250 °C, reaction time of 1–3 h, hydrogen pressure of 2–6 bar and catalyst: bio-oil ratio of 1:20, 1:10, 1:5. The results revealed that the catalytic HDO is an appropriate procedure, as fatty acids as the main oxygenated components in bio-oil were reduced from 81.8 % to 56.7 %, aldehydes and ketones were entirely removed, and there was a noticeable rise in aliphatic hydrocarbons from 2.8 % to 33.9 % at temperature of 250 ºC, hydrogen pressure of 6 bar and reaction duration of 3 h. In addition, by raising the catalyst to bio-oil ratio to 1:5, the content of fatty acids reached 47.6 %. Furthermore, a comparison was made between the O/C and H/C ratios of the obtained biofuels and the raw bio-oil, which results exhibited that this method worked successfully in substituting oxygen atoms of the raw bio-oil with hydrogen atoms.

Photocatalytic degradation of phenol and polycyclic aromatic hydrocarbons in water by novel acid soluble collagen-polyvinylpyrrolidone polymer embedded in Nitrogen-TiO2

The photocatalytic degradation of phenol, naphthalene, fluoranthene, phenanthrene, pyrene, benz[a]anthracene, and anthracene was investigated using a novel nitrogen-doped TiO2/acid-soluble collagen-polyvinyl pyrrolidone nanocomposite (N-TiO2/ASC-PVP). Characterization through X-ray diffraction (XRD), scanning electron microscopy (SEM), and transmission electron microscopy (TEM) revealed that the nanocomposite consists of spheroidal particles smaller than those of undoped TiO2. X-ray photoelectron spectroscopy (XPS) confirmed the incorporation of nitrogen within the TiO2 lattice, appearing as both substitutional nitrogen (OTiN) and interstitial nitrogen (TiON). The degradation process followed apparent first-order kinetics, with the N-TiO2/ASC-PVP calcined at 200°C and 400°C demonstrating high photocatalytic degradation efficiencies. The nanocomposite achieved a remarkable 98.6% degradation of the targeted compounds within 120 minutes at a concentration of 10 mg/L. The enhanced photocatalytic activity under visible light can be attributed to several factors: the smaller crystal size, increased surface hydroxyl groups, improved visible light absorption, and a reduced band gap energy. This N-TiO2/ASC-PVP photocatalyst shows significant potential for applications in materials science and nanotechnology, supporting advancements in environmental and energy-related fields.

Medium and high temperature H2S removal via phosphazene polyoxometalate ionic liquids: Performance evaluation and mechanism exploration

The development of non-aqueous solvent desulfurizer is crucial to addressing the challenges associated with traditional liquid-phase wet desulfurization technologies. Based on this, we prepared a series of phosphazene polyoxometalate ionic liquids (PPILs) based of 1-butyl-3-methylimidazolium chloride using different kinds of phosphazenes (PNs) combined with polyoxometalate (POM), and used for hydrogen sulfide (H2S) dynamic absorption experiments. The effects of PN type and ratio, temperature and desulfurizer concentration on the desulfurization performance of different PPILs were explored. Among them, PPILs@IBuPN-9 as the optimal desulfurizer could keep almost 100 % desulfurization efficiency in the medium and high temperature range (100–200 °C). The results showed that the combination of PNs with POM significantly improved and widened the H2S removal performance and the operational temperature window of the desulfurizer. Besides, PPILs@IBuPN-9 required only air regeneration to maintain relatively stable cycle performance for at least four times and the sulfur capacity could be efficiently increased during multiple regenerations. It was found that the hydrogen bonding sites on IBuPN network formed significantly enhanced the H2S capture ability of PPILs and the sulfur capacity was substantially improved by S2− substitution of oxygen atoms in the POM according to the characterization results and density functional theory calculations. This study promotes the deep integration of polyoxometalate chemistry with ionic liquids in the field of gas purification and promotes the development of non-aqueous phase desulfurization process.

Thionation of conjugated porphyrin with enhanced photodynamic and photothermal effects for cancer therapy

Phototherapy has emerged as a promising modality for cancer treatment in recent years, owing to its precise temporal control and minimally invasive nature. Here, two new organic porphyrin molecules, denoted as ONP and SNP, were designed and synthesized with an acceptor–donor–acceptor (A-D-A) architecture. The donor–acceptor (D-A) pairs in molecules facilitated the intermolecular charge transfer (ICT), thereby amplifying near-infrared (NIR) absorbance and promoting nonradiative heat generation. Notably, the substitution of oxygen atoms with sulfur in naphthalimides (NI) led to significant change of their photophysical and photochemical properties. Specifically, the sulfur atoms exhibited pronounced spin–orbit coupling (SOC) effect, leading to efficient photoinduced intersystem crossing (ISC) processes, thus facilitating the generation of reactive oxygen species (ROS). Upon self-assembly, the formed nanomaterials (ONP NPs and SNP NPs) exhibited spherical morphology with average size about 150 nm. The biocompatibility and photocytotoxicity of nanoparticles against Hepa1-6 cells were evaluated using the CCK-8 assay. Additionally, the synergistic effects (photodynamic therapy and photothermal therapy) of SNP NPs were confirmed through diverse in vitro experiment under 690 nm laser irradiation. The generation of intracellular ROS by SNP NPs was confirmed with DCFH-DA as probe. This study provides an ingenious strategy for developing organic nanomaterials with high treatment efficiency through synergistic photodynamic/photothermal effects.

Influence of non-metals doping on the structural, electronic, optical, and photocatalytic properties of rutile TiO2 based on density functional theory computations

This study investigates the influence of non-metal doping (C, F, N, and S) on the structural, electronic, and optical properties of rutile TiO2 using Hubbard-corrected density functional theory (DFT) within the Quantum ESPRESSO code. Rutile TiO2 is a promising material for environmental remediation and renewable energy applications. However, it has a large bandgap of 3.03 eV, which confines its use to UV light. By substituting oxygen atoms with a single dopant atom, we aim to shift the absorption edge toward the visible spectrum. Our findings reveal that doping with C, N, and S results in a redshift of the bandgap, while F doping does not exhibit this effect. The imaginary part of the dielectric function indicates shifted absorption edges for C, N, and S-doped TiO2, making them suitable for photocatalytic applications. Additionally, an increased refractive index after doping suggests the presence of excess charge carriers that affect light propagation. This work provides valuable insights for experimentalists exploring non-metal doping influences on rutile TiO2 for photocatalysis.

Tuning lanthanide luminescence from bipyridine-bis(oxazoline/thiazoline) tetradentate ligands

Organic ligands play a pivotal role in lanthanide luminescence by acting as sensitizers for energy absorption and transfer, a phenomenon known as the fluorescence antenna effect. Herein, we introduce two tetradentate nitrogen ligands renowned for their efficient sensitization of lanthanide luminescence, with their luminous efficacy finely adjustable through subtle modifications to their structure. Through the synthesis of four Eu(III)/Tb(III) mononuclear complexes via the complexation of ligands 6,6′-bis(4,5-dihydrooxazol-2-yl)-2,2′-bipyridine (bpybox, L1) and 6,6′-bis(4,5-dihydrothiazol-2-yl)-2,2′-bipyridine (thio-bpybox, L2) with europium/terbium trifluorosulfonate, structural analysis reveals that the lanthanide ion coordinates with eight nitrogen atoms from two ligands and one oxygen atom from trifluorosulfonate. Among them, two Eu(III) complexes ([Eu(L1)2(SO3CF3)](SO3CF3)2EuL1 and [Eu(L2)2(SO3CF3)](SO3CF3)2EuL2) and one Tb(III) complex ([Tb(L1)2(SO3CF3)](SO3CF3)2 TbL1) exhibit luminosity, displaying characteristic lanthanide metal ion luminescence characterized by high fluorescence quantum yields and prolonged excited state lifetimes. In contrast, TbL2 ([Tb(L2)2(SO3CF3)](SO3CF3)2) is non-luminous, with the sole structural distinction being the substitution of oxygen atoms with sulfur atoms within the ligand. This minor alteration significantly impacts the triplet (3T) state energy level of the ligands, thereby influencing their sensitizing effect on Tb(III) luminescence. These findings underscore the remarkable efficiency of bpybox-type ligands as sensitizers for Ln(III) luminescence, with their structural versatility enabling effective modulation of luminous capacities and efficiency.

Metal-organic framework derived S-doped anatase TiO2@C to store Na+ with high-rate and long-cycle life

The design of a reasonable structure and component regulation are valid methods for enhancing the electrochemical properties of TiO2, which serves as prominent anode in sodium-ion batteries with exceptional structural stability. Herein, the carbon-coated anatase TiO2 doped with S (S-TiO2 @C) was synthesized via a facile metal-organic framework-assisted approach. The S atoms partially substitute oxygen atoms in the lattice, thereby enhancing the capacitive behavior, facilitating charge transfer kinetics, and augmenting the diffusion coefficient of Na+. With exceptionally high porosity and substantial carbon content, the caky S-TiO2 @C electrode manifests superior rate capability of 167.7 mAh g−1 at 5.0 A g−1 and long-cycle life of 239.0 mAh g−1 at 2.0 A g−1 over 4000 cycles. It is foreseeable that the strategy of anionic doping and carbon coating on the metal oxide with porous structure to optimize the sodium storage capability of the electrode will be applied in the future.

Regulating fluorescent properties and ESIPT behavior of novel flavone-based fluorophore by replacing oxygen atom in proton donor/acceptor with sulfur atom: A TD-DFT study

Recently, the fluorescent phenomena of a new excited state intramolecular proton transfer (ESIPT) based fluorophore 3-hydroxy-2-(naphthalen-2-yl)-4H-chromen-4-one (HFN) has been reported experimentally. However, the first-hand dynamic information of its ESIPT process is still lacking theoretically. Based on density functional theory (DFT) and time-dependent DFT (TD-DFT) methods, the luminescent features and ESIPT processes of HFN and its two derivatives were studied in detail. Two HFN derivatives, 3-mercapto-2-(naphthalen-2-yl)-4H-chromen-4-one (TFN1) and 3-hydroxy-2-(naphthalen-2-yl)-4H-chromene-4-thione (TFN2) were obtained by replacing the oxygen atom of proton donor and proton acceptor in HFN with sulfur atom, respectively. The changes and effects of fluorescent properties and ESIPT process generated by different proton donors and proton acceptors are demonstrated. The simulated maximum absorption and emission peaks of HFN are well consistent with the experimental data. After replacing the oxygen atoms in proton donor and proton acceptor with sulfur atoms, the absorption wavelength of HFN slightly blue-shifts and red-shifts, respectively. And the fluorescence wavelengths of HFN obviously red-shift. The S0→S1 transitions of HFN and TFN1 are dominated by ππ* charge transfer transition, whereas the S0→S1/S0→S2 transition of TFN2 is a mixed charge transfer transition of nπ* and ππ*. The substitution of oxygen atom by sulfur atom in the proton donor or proton acceptor of HFN obviously decreases or increases the ESIPT barrier, due to its stronger proton-donating ability of S–H group or weaker proton-accepting ability of sulfur atom, respectively.

Effects of doping on electronic structure and ion diffusion of Li2FeSiO4

AbstractFirst‐principles calculations were performed to study the crystal structure, electronic structure, and ion diffusion of sulfur‐doped Li2FeSiO4. The sulfur atoms preferred to substitute oxygen atoms around different iron atoms and the most stable configurations were chosen for each Li16Fe8Si8O32‐xSx (x = 1, 2, 3, 4) system to study the influence of sulfur concentration. Moreover, the configuration of the Li16Fe8Si8O29S3 had the least band gap (2.456 eV), which indicated the best electronic conductivity. The results of mean square displacement confirmed that lithium ions could diffuse in a two‐dimensional path in Li2FeSiO4 and S‐doped Li2FeSiO4 along the a‐axis and c‐axis. Doping sulfur was able to reduce the energy barrier for diffusion to improve the diffusion of lithium ions. The diffusion coefficient of lithium‐ion was 8 orders of magnitude larger and the diffusion rate was 7 orders of magnitude larger than that of the intrinsic system at most.

Mechanical Properties, Biocompatibility and Antibacterial Behaviors of TaO0.2N0.8 and TaO0.2N0.8-Ag Nanocomposite Thin Coatings

TaOx = 0.2Ny = 0.8 was reported previously to have the highest modulus (E), hardness (H), and H to E ratio attributed to the embedment of substituting oxygen atoms in the TaN crystal structure, among some TaOxNy coatings studied. In the present study, TaO0.2N0.8-Ag nanocomposite coatings were fabricated by reactive multi-target sputtering with O/N ratio adjusted to the expected value. The various Ag contents were doped to induce antibacterial behaviors. After deposition and annealing with rapid thermal process (RTP) at 400 °C for 4 min, the coatings’ mechanical and structural properties were studied. After these examinations, the samples were then studied for their cell attachment, cell viability, and biocompatibility with 3-T-3 cells, as well as for their antibacterial behaviors against Escherichia coli. It appeared that hardness and crack resistance could be improved further with suitable amount of Ag doped to the coatings, followed by rapid thermal annealing treatment. The coating with 1.5 at. % Ag had the highest hardness and good H/E ratio. It was also found that the antibacterial efficiency of TaO0.2N0.8-Ag coatings could be much improved, comparing with that of TaO0.2N0.8 coatings. The antibacterial efficiency increased with the increased Ag contents. There was no negative effect of Ag on the biocompatibility of TaO0.2N0.8-Ag. Through the cell attachment and viability testing using MTT(3-(4,5-Dimethylthiazol-2-yl)-2,5-diphenyltetrazolium bromide) assay, it can be summarized that surface roughness could be the dominating factor for cell viability and attachment, which means the improvement of biocompatibility. Accordingly, the samples with 1.5 at. % and 11.0 at. % Ag show the best biocompatibility. The variation of surface roughness was affected by the incorporation of Ag and oxygen atoms after rapid thermal annealing.

Fluorine Substitution Promotes Air-Stability of P'2-Type Layered Cathodes for Sodium-Ion Batteries.

As one of the most promising cathode materials in sodium-ion batteries, manganese-based layered oxides have aroused wide attention due to their high specific capacity and plentiful reserves. However, they are plagued by poor air stability rooting in water/Na+ exchange and adverse structural reconstruction, hindering their practical applications. Herein, it is demonstrated that utilizing fluorine to substitute oxygen atoms can narrow the interlayer spacing of novel P'2-Na0.67 MnO1.97 F0.03 (NMOF) cathode material, which resists the attack of water molecules, significantly prolonging exposure time in air. Density functional theory (DFT) calculation results indicate that fluorine substitution alleviates the insertion of water molecules and spontaneous extraction of Na+ effectively. Benefiting from the structural modulation, NMOF can deliver a high specific capacity of 227.1mAhg-1 at 20mAg-1 and a promising capacity retention of 84.0% after 100 cycles at 200mAg-1 . This facile and available strategy provides a feasible way to strengthen the air-stability and expands the scope of practical applications of layered oxide cathodes.

Effects of oxygen group elements on thermodynamic stability, electronic structures and optical properties of the pure and pressed BaTiO3 perovskite

Thermodynamic stability, electronic structures, and optical properties of the pure and pressed BaTiO3 doped with different concentrations of oxygen group elements (Se, Te, and S) are investigated using the Density Functional Theory. It was found that when chalcogens elements in BaTiO3 compound substitute oxygen atoms, the forbidden gap is significantly decreased from 3.010 eV (for pressed BaTiO3) to 0.000 eV (for Te-doped BaTiO3 and pressed Se/Te-doped BaTiO3) indicating that chalcogens impurities have a crucial role in the reduction of the forbidden band of BaTiO3 compound. Moreover, 2.3% of compressive strain itself with and without the presence of chalcogens impurities transforms the pure BaTiO3 from indirect to direct semiconductor. Furthermore, the calculated formation energy confirms the thermodynamic stability of all studied compounds. Additionally, the doping changed the absorption behavior of BaTiO3 making the compound more useful for optoelectronic applications due to the introduction of addition carries into the system after the inclusion of chalcogens impurities.

Experimental and numerical investigation of specific behaviour of fluoride ions during filtration of pure salt water solutions with titania membrane

This work addresses the specific interactions between titania membrane and fluoride anions during ultrafiltration operation. In general, the salt transmission increases with salt concentration when pure salt-water solutions are ultrafiltrated, except for fluoride-based salts observed in our study, for which transmission decreased at low concentrations. This phenomenon was only observed with titanium dioxide membrane. A numerical tool based on a physical description of ionic mass transfer in porous material (generalized Nernst-Planck approach) was used to explore the modification-induced changes due to fluoride anions. Numerical investigations showed a modification of the electric charge of the membrane surface in the pore at low fluoride concentrations. This phenomenon screened the electric effect in a completely reversible way, and then enhanced the ion mass transfer through the porous membrane. These modifications can be explained by the substitution of oxygen atom (providing the surface electric charge) with a fluoride ion which was screening the electric charge and facilitated the ion transfer.

Sulfur-doped LaNiO3 perovskite oxides with enriched anionic vacancies and manipulated orbital occupancy facilitating oxygen electrode reactions in lithium-oxygen batteries

The rational design of effective bifunctional catalysts with enhanced activity toward oxygen reduction reaction and oxygen evolution reaction is of significance to develop high-performance lithium-oxygen (Li–O2) batteries. Herein, sulfur-doped LaNiO3 nanoparticles are elaborately synthesized, and their catalytic activity toward oxygen redox reactions in Li–O2 batteries is comprehensively studied. As confirmed by the density functional theory calculations and experimental results, the substitution of oxygen atoms by sulfur atoms with lower Pauling electronegativity can enhance the covalent feature of bonds, thus increasing electrical conductivity of catalyst. In addition, abundant oxygen vacancies created after sulfur doping are capable of providing concentrated active sites. Simultaneously, sulfur dopants boost the hybridization between Ni 3d orbital and O 2p orbital and increase the covalency of Ni–O bonds due to the increase of Ni3+ with the near-unity occupancy of the eg orbital, thereby increasing the adsorption strength of oxygen-containing intermediates on the surface. Eventually, lowered reaction energy barriers and accelerated reaction kinetics of oxygen electrode reactions are realized, contributing to the optimized electrochemical performance of Li–O2 battery. The Li–O2 battery based on sulfur-doped LaNiO3 with the optimized S-doping level of 2.89 wt% (marked as S2.89 wt%-LNO) delivers a high specific discharge capacity of 24067 mAh/g, an ultralow overpotential of 0.37 V and extended life of 347 cycles.

Theoretical calculations of the effect of nitrogen substitution on the structural, vibrational, and electronic properties of wolframite-type ScTaO4 at ambient conditions.

In this study, the effect of nitrogen substitution in wolframite-type ScTaO4 was investigated using density-functional theory calculations. First, structural and mechanical properties, as well as the dynamical stability of ScTaO4 were examined deeply for the ambient-pressure structure. Subsequently, we studied how lattice vibrations are affected by hydrostatic pressure and determined the elastic moduli of ScTaO4. The results of our study show that the monoclinic structure of ScTaO4 is rigid and non-compressible. In addition, band-structure calculations show that ScTaO4 has a wide direct band-gap of 4.04 eV, which in turn leads to a possible tuning of electronic properties. We have found that this task can be conducted by partially substituting oxygen atoms in the unit cell with nitrogen atoms. Both band-structure calculations and charge-density analyses revealed a narrowing in the band gap caused by the presence of nitrogen atoms, which act as a shallow acceptor state, resulting in weak repulsive interactions and structural distortions in both Sc and Ta coordination polyhedra; reducing the crystal symmetry from monoclinic to triclinic.

Electrical conductivity in oxygen-substituted SrTiO3-δ films

Enhancement of electrical conductivity in fundamentally insulating ABO3 perovskite oxide ferroelectrics is crucial for innovative applications in resistive switching, photovoltaics, and catalysis. One of the methods to raise conductivity in bulk crystals or ceramics relies on the possibility to remove and/or substitute oxygen atoms. Here, we explored this approach for thin films of the representative perovskite oxide SrTiO3. Small-signal AC conductivity was investigated in epitaxial and polycrystalline films, where oxygen vacancies (VO), nitrogen (N), or hydrogen (H) were introduced in situ during film growth. Hopping mechanism of conductivity was evidenced by the observed strong growth of AC conductivity with temperature, frequency, and AC voltage in all films. Small polarons were identified as charge carriers. Oxygen vacancies/substitutions were suggested to facilitate hopping probability by generating sites for carrier localization. Important ferroelectric devices were proposed to benefit from the revealed hopping conductivity owing to its unique increase with an electric field.

Chalcogens’ impurities and a single F-center in perovskite SrHfO3 compound: Ab initio calculations

The effects of Sulfur (S), Selenium (Se), or Tellurium (Te) doped SrHfO3 (SHO) on the electronic, optical and photocatalytic properties have been investigated using Density Functional Theory, taking into account the intrinsic F-center defect (Ov) in oxide materials. The findings showed that the substitution of oxygen atoms by chalcogens impurities decreased the forbidden band of SHO effectively. Furthermore, there is a huge improvement of the absorption coefficient in the visible spectrum when chalcogens’ impurities meet an Ov defect in SHO, especially when 8.333% of S or Se meet an Ov in SHO (S/Se@OII + Ov) due to the shifting of the Fermi level to the lowest unoccupied molecular orbital which caused the n-type semiconductor behavior giving rise to the enhancement of carrier concentrations. Otherwise, the positions of the highest occupied molecular orbital and the lowest unoccupied molecular orbital respect the limits necessary to split water except for 12.5% of Se or Te-doped SHO (Se/Te@OIII), 8.333% of Te doped SHO with the presence of an Ov (Te@OII + Ov), and 12.5% of Se or Te doped SHO with an Ov defect (Se/Te@OIII + Ov) structures. In addition, the formation energy confirms that all studied structures are thermodynamically stables. We believe that our research will serve as a base for future studies on SHO to be used as semiconductors for photovoltaic and photocatalytic hydrogen production from water splitting applications.1.

Chemical Dopant‐Free Doping by Annealing and Electron Beam Irradiation on 2D Materials

AbstractDoping is a key technique for forming complementary metal‐oxide‐semiconductor (CMOS) that is a basic building block for current state‐of‐the‐art semiconductor devices. However, conventional doping methods such as ion implantation are unsuitable for 2D materials due to their ultra‐thinness to accommodate substitutionally doped atomic structures and vulnerability to high energy ion bombardment. Chemical doping methods have been widely used for 2D materials to induce a charge exchange transfer; however, they are subjected to surface contamination which can be detrimental for high quality semiconductor device processing. In this work, the authors reveal the effects of chemicals‐free doping in which annealing induces a p‐doping effect by physisorption and substitution of oxygen atoms while electron beam irradiation selectively n‐dopes MoTe2, based on the results obtained by electrical characterization and Kelvin probe force microscopy. The annealing increases work‐function of MoTe2 which undergoes oxidation as observed in the reduction of surface potential and the transition of transfer curves toward the p‐type behavior. Electrical measurements and a significant reduction in surface potential after electron beam irradiation indicate the generation of trapped charges which is responsible for the n‐doping effect. Subsequently, the authors fabricate a CMOS inverter consisting of distinctively p‐ and n‐doped areas of MoTe2.

Plasmonic properties of nonstoichiometric zirconium nitride, oxynitride thin films, and their bilayer structures

Nonstoichiometric ${\mathrm{ZrN}}_{x}$ (ZrN) thin films, ${\mathrm{ZrO}}_{x}{\mathrm{N}}_{y}$ (ZrON) thin films, and bilayer ZrN/ZrON structures were prepared, and the effects of stoichiometry and interface on their plasmonic properties were investigated. We find that the samples are all B1 structured with similar lattice constants. Higher nitrogen and oxygen content can reduce the screened plasma frequency ${\ensuremath{\omega}}_{c}$. Interestingly, the bilayer ZrN/ZrON structures with some ZrON thickness are more metallic than ZrN films, which should be reasonable since the mutual diffusion through the ZrN/ZrON interface may cause a ZrON buffer zone with substitute oxygen atoms generating more free carriers. The postulation is further confirmed by the calculations about the band structure, which indicates that substitute oxygen atoms can depress the interband transition level and cause more carriers in conduction band. This work implies that oxygen substitution is an effective method to enhance the performances of nitride-based plasmonic materials and devices.

Influence of isotopic composition of silicon on local vibrational modes of vacancy-oxygen complex

Isotopic composition of natural silicon (28Si (92.23 %), 29Si (4.68 %) and 30Si (3.09 %)) affects noticeably the shape of infrared absorption bands related to the oxygen impurity atoms. The positions of local vibrational modes (LVMs), related to quasimolecules 28Si – 16OS – 29Si and 28Si – 16OS – 30Si (OS – substitutional oxygen atom) have been determined for the absorption spectra measured at Т ≅ 20 K and at room temperature (Т ≅ 300 K). An estimation of the isotopic shifts of corresponding modes in a semi empirical way has been done by the fitting the shape of the experimentally measured absorption band related to the vacancy-oxygen center in irradiated Si crystals. The LVM isotope shifts at Т ≅ 300 K are found to be (2.22 ± 0.25) сm–1 for 28Si – 16OS – 29Si and (4.19 ± 0.80) сm–1 for 28Si – 16OS – 30Si in relation to the most intense band with its maximum at (830.29 ± 0.09) cm–1 due to the vibrations of 28Si – 16OS – 28Si, and the full width at half maximum of the A-center absorption bands is (5.30 ± 0.26) cm–1. At Т ≅ 20 K the corresponding values have been determined as (1.51 ± 0.13); (2.92 ± 0.20); (835.78 ± 0.01) and (2.34 ± 0.03) сm–1. A model for the calculation of isotopic shifts in the considered case has been discussed. From an analysis of the observed isotopic shifts some information about the structure of the vacancy-oxygen complex in silicon at Т ≅ 20 K and at room temperature has been obtained.