Interstitial Incorporation Research Articles

La Substitution into the Melilite Derivative Ca5Ga6O14: Prediction, Synthesis and Ionic Conductivity.

Melilite-type gallates of general formula RE1+xAE1-xGa3O7+x/2 are of interest for their ability to host mobile interstitial oxide ions in [Ga3O7+x] layers. The crystal structure of Ca5Ga6O14 is closely related to melilite, with [Ga3O7] layers stacked in a more complex way to accommodate an additional 0.5 interlayer cations per formula unit, suggesting the potential for similar oxide ion conduction behavior. We used a computational approach to identify the most promising routes to interstitial oxide incorporation into Ca5Ga6O14, leading to an experimental investigation of the system Ca5-xLaxGa6O14+x/2. Single-phase materials were obtained in the range 0 ≤ x ≤ 0.25 by solid state reactions, producing an ∼40× increase in ionic conductivity at 800 °C. This limited compositional range presents a challenge for characterization of the charge-compensating defects. The La substituents were observed directly by X-ray diffraction and STEM-EDX, and a combination of different structural characterization techniques and DFT calculations indicated the presence of interstitial oxide ions indirectly, explaining the conductivity response. As higher carrier concentrations (x > 0.25) are apparently inaccessible in this system, we conclude that its potential as a useful oxide ion conductor is more limited than that of established melilite materials such as La1+xCa1-xGa3O7+x/2.

Electronic and Surface Properties of Aluminum (111) Surface Modified by Interstitial and Substitutional Titanium Incorporation

This study investigates the influence of interstitial and substitutional titanium atoms on the electronic properties of aluminum surfaces using density functional theory (DFT). The study focuses on three variables: the presence and arrangement of Ti interstitials on the aluminum surface, the behavior of Ti substitutional and interstitial impurities, and the energetic stability and structural properties of these systems. Multiple DFT methods are employed to derive conclusions regarding the impact of these variables on the surface properties of aluminum. The study provides valuable insights into how different states of interstitial and substitutional Ti can alter the physical characteristics and performance behaviors of the aluminum surface. The understanding of these effects could enable engineers to design more efficient materials with enhanced properties suitable for various industries.

Influence of magnetic (Fe) and non-magnetic (In) doping on structural, magnetic, and weak anti-localization properties of Bi2Te3 topological insulator

In this article, we have studied the changes in structural, magnetic, and magneto-transport properties of Bi2Te3 topological insulator doped with magnetic (Fe) as well as non-magnetic (In) elements. The un-doped along with Fe, In-doped Bi2Te3 are grown using a melt growth technique. The Rietveld analysis of x-ray diffraction data expresses that both In and Fe-dopants substituted the Bi-position with a little bit of interstitial incorporation in host Bi2Te3. It is also noticed that In-doping is slightly more favorable for Bi-substitution than Fe. The magnetic characterization reveals a mixing of diamagnetic and Pauli paramagnetic behavior of un-doped and In-doped Bi2Te3, whereas, Fe-doping shows overall paramagnetism with local anti-ferromagnetic interactions among Fe-ions without long-range order. The electrical-transport study represents the metallic response of host Bi2Te3, which is well-maintained for In-doping; however, Fe-doping exhibits prominent anomalies in ρ xx –T profiles. Importantly, magneto-conductance research indicates a notable deviation of host quantum feature, weak anti-localization effect (WAL) upon magnetic (Fe) doping, whereas non-magnetic In-doping shows a comparatively weak deviation in WAL effect for high doping limit.

Redox-Guided Synthesis of Au–V2O5–MnO2 Nanoflower Composites with Enhanced Electrical Conductance for Supercapacitor Applications

This paper details an approach for the synthesis of stable electroactive Au–V2O5–MnO2 nanoflower composites using a simple redox-mediated methodology under modified hydrothermal (MHT) conditions. The nanocomposite was characterized by various techniques like X-ray diffraction, scanning electron microscopy, high-resolution transmisson electron microscopy, and X-ray photoelectron spectroscopy. MnO2 and Au formed a profitable hierarchical network morphology in the interstitial sites of V2O5, and this kind of synergetic architecture exhibits an elevated specific capacitance (388 F g–1 at 1 A g–1) compared to commercial V2O5 (85 F g–1 at 1 A g–1) in a neutral electrolyte. The as-synthesized nanocomposite contributed more to energy storage with superior energy density (49 Wh kg–1 at 1 A g–1 current density) and power density (4 kW kg–1 at 10 A g–1 current density) and demonstrated improved stability compared to commercial V2O5 of up to 2000 continuous charge/discharge cycles in a two-electrode system. Temperature- and field-dependent [both direct-current (dc) and alternating-current (ac)] studies exhibited enhanced conductance due to the incorporation of Au and MnO2 and non-Ohmic electrical conduction, characterized by the onset voltage V0 (dc) and onset frequency f0 (ac). These two onset parameters followed power-law behavior with Ohmic conductance with two onset exponents (xV and xf). Such electrical transport properties were explained using intrachain hopping conduction of charge carriers within the layers of pristine V2O5 and hopping of charge carriers between the layers of V2O5 in the Au–V2O5–MnO2 nanocomposite and supported the interstitial incorporation of the compounds.

Enhancing the thermoelectric performance of β-Zn4Sb3 via progressive incorporation of Zn interstitials

Owing to the intrinsically low lattice thermal conductivity, β-Zn4Sb3 is regarded as a promising candidate for thermoelectric applications. To further improve its thermoelectric performance, it is essential to increase the carrier mobility of β-Zn4Sb3 for enhanced electrical transport. While incorporating light ions is a useful approach for this purpose, the excess Zn ions tend to segregate in as-grown samples. Here, we present a design strategy to stabilize the excess Zn ions in the interstitial sites by applying electric current and uniaxial stress, which triggers a progressive directional migration of Zn ions towards one terminal of the sample. In this Zn-enriched end, a homogeneous distribution of excess Zn interstitials was achieved, as confirmed by atom probe tomography and transmission electron microscopy at the atomic scale. As revealed by ab initio simulations, the additional electrons brought by Zn interstitials connect the separated (Sb2)4- dimers, enhancing the carrier mobility and thus the electrical conductivity. In consequence, the detached Zn-enriched section shows a much improved thermoelectric figure of merit, a very high maximum ZT of ∼1.5 at 618 K, and an average ZT of ∼1.1 between 300 and 618 K, outperforming the majority of thermoelectric materials in this temperature range.

Novel Nb5+-doped hexagonal perovskite Ba5In2Al2ZrO13 (structure, hydration, electrical conductivity)

The new phase Ba5In2Al2Zr0.9Nb0.1O13.05 with hexagonal perovskite structure was obtained. The substitution of Zr4+ by smaller Nb5+ was accompanied by the incorporation of the oxygen interstitials and did not lead to a significant change in the lattice parameters. It was established that the investigated sample was capable for water incorporation from the gas phase, the hydration degree value was 0.24 mol H2O. IR-spectroscopy analysis defined the presence of OH−-groups with different thermal stability, which participate in different hydrogen bonds. The new phase Ba5In2Al2Zr0.9Nb0.1O13.05 demonstrates the predominant protonic conductivity at pH2O = 2·10−2 atm and Т600 °C.

Densities, sound velocities, refractive indices, and relevant excess properties for the binary solutions of 3-amino-1-propanol in aqueous and non-aqueous media at different temperatures between T = 298.15 K and 323.15 K

Density ρ, sound velocity, u, and refractive index, nD, were measured for the binary mixtures of Water (W) + 3-amino-1-propanol (AP) and Acetonitrile (ACN) + AP over the whole range of composition at different temperatures ranging between T = 298.15 and 323.15 K. From measured ρ, u and nD, some derived properties such as molar volume, Vm, partial molar volume, V¯i and its value at infinite dilution, V¯i∞, thermal expansivity, α, isentropic compressibility, κs, as well as molar refractions, Rm, followed by the relevant deviations/excess properties were computed. Data of ρ, α, u, κs, and nD were correlated to the concentration-dependent polynomials within satisfactory limits, whereas the calculated deviations/excess properties were fitted well to the Redlich-Kister equation. The temperature dependency of experimental ρ also finds satisfactory correlation to the Jouyban-Acree model.Data analysis reveals that, for both the systems cross H-bonding interaction occurs, and it is stronger between W and AP compared to that between ACN and AP. Effects due to the hydrophobicity of AP, as well as that due to interstitial incorporation of the W or ACN into the networks of AP also played significant roles. Moreover, in W + AP solutions the contribution in the overall volume reduction is remarkably greater due to W, while for the solutions of ACN + AP it is greater due to the component AP.

Surface-Enriched Boron-Doped TiO2 Nanoparticles as Photocatalysts for Propene Oxidation.

A series of nanostructured boron-TiO2 photocatalysts (B-X-TiO2-T) were prepared by sol–gel synthesis using titanium tetraisopropoxide and boric acid. The effects of the synthesis variables, boric acid amount (X) and crystallization temperature (T), on structural and electronic properties and on the photocatalytic performance for propene oxidation, are studied. This reaction accounts for the remediation of pollution caused by volatile organic compounds, and it is carried out at low concentrations, a case in which efficient removal techniques are difficult and costly to implement. The presence of boric acid during the TiO2 synthesis hinders the development of rutile without affecting the textural properties. X-ray photoelectron spectroscopy analysis reveals the interstitial incorporation of boron into the surface lattice of the TiO2 nanostructure, while segregation of B2O3 occurs in samples with high boron loading, also confirmed by X-ray diffraction. The best-performing photocatalysts are those with the lowest boron loading. Their high activity, outperforming the equivalent sample without boron, can be attributed to a high anatase and surface hydroxyl group content and efficient photo-charge separation (photoelectrochemical characterization, PEC), which can explain the suppression of visible photoluminescence (PL). Crystallization at 450 °C renders the most active sample, likely due to the development of a pure anatase structure with a large surface boron enrichment. A shift in the wavelength-dependent activity profile (PEC data) and the lowest electron–hole recombination rate (PL data) are also observed for this sample.

X-ray peaks profile analysis, optical and cathodoluminescence investigations of cobalt-doped ZnO nanoparticles

Effects of Co doping on the structural and optical properties of ZnO oxide nanoparticles (NPs) prepared by a solvothermal method are reported. X-ray diffraction examinations using Rietveld refinement confirms the hexagonal wurtzite symmetry ZnO phase nanostructure belonging to P63mc space group. No segregated secondary phases or Co rich clusters were detected. The X-ray diffraction peaks shifts towards higher angle gradually as the concentration of nominal Co content increases in ZnO. This shifting in peak position reflect that Co is well replaced Zn in ZnO matrix. With increasing the Co content to 3%, both lattice parameters a and c of the hexagonal ZnO tended to gradually decrease, suggesting substitutional doping of Co at the tetrahedral Zn2+sites. For Co loading of5%, these trends reversed and the lattice showed a gradual expansion, which is explained by additional interstitial incorporation of Co. The Williamson-Hall (W–H) method with various models i.e. uniform deformation model (UDM), uniform stress deformation model (USDM) and uniform deformation energy density model (UDEDM), as well as size-strain plot (SSP) method, and the morphological observations using transmission electron microscopy (TEM) image were used to evaluate the crystallite size as well as the lattice strain. Optical studies carried out by diffuse reflectance spectroscopy (DRS) indicated a decrease in the value of the band gap from 3.238 eV to 2.993 eV with increasing Co doping concentration. The obtained results are confirmed by cathodoluminescence technique.

Fabrication of 2D perovskite (PMA)2PbI4 crystal and Cu ion implantation improved x-ray detector

Two-dimensional (2D) perovskites have been demonstrated great promise in x-ray detection application because of their stability, tunability, and the unique electronic properties. The centimeter-sized 2D perovskite (PMA)2PbI4 single crystal and the corresponding x-ray detector were fabricated. The Cu ion implanted device exhibits an excellent sensitivity of 283 μC Gyair−1 cm−2, the significantly enhanced mobility-lifetime (μτ) product of 8.05 × 10−3 cm2 V−1, and the lowest detectable dose rate of 2.13 μGyair s−1. Experimental observation combined with the DFT calculations shows that the improvement in Cu ion implanted x-ray detection is ascribed to the enhanced photoinduced charge carrier density and μτ product, and the increased carrier dissociation capability associated deeply with the decreased binding energy of exciton in the inorganic layer quasi-quantum well. The incorporation of the Cu interstitials by high-energy Cu ion implantation is able to introduce the donor and acceptor states with additional charge transfer channeling, resulting in the decreased exciton binding energy and fast dissociation of the exciton and the quick carrier extraction. Cu ion implantation regulating the dissociation of charge carriers in low-dimensional perovskites will motivate the application for 2D perovskite in high-performance x-ray detectors.

Study of vibrational properties of Bi2 − xMnxTe3 nanocrystals in host glass: Effect of xMn‐concentration

AbstractThe Raman and infrared (IR) active lattice vibrations of xMn‐concentration Bi2 − xMnxTe3 nanocrystals (NCs) as a dopant in semiconductor Bi2Te3 nanocrystals grown in a host glass matrix, whose symmetries correspond to the space group, are investigated by Raman scattering. Transmission electron microscopy images confirm the formation of Bi2 − xMnxTe3 nanocrystals with an average size of around 5.4 nm. The observation of the six hyperfine structure lines in electron paramagnetic resonance spectra confirms the incorporation of Mn2+ ions in Bi2Te3 nanocrystals. The vibrational modes of quintuple layer (QL) of the diluted magnetic semiconductor Bi2 − xMnxTe3 nanocrystals are modified in relation to pure Bi2Te3 nanocrystals. The appearance of the (95.5 cm−1), (114 cm−1), and (103 cm−1) IR‐active modes is mainly due to quantum size effects. Indeed, the redshifts of the (95.5 cm−1), (103 cm−1), (110 cm−1), (114 cm−1), and (141 cm−1) vibrational modes give strong indications of the substitutional and interstitial incorporation of Mn2+ in the Bi2Te3 crystalline structure. In addition, the Raman spectra show the formation of Bi2OTe2 semiconductor due to the appearance of the (123 cm−1) mode. The investigation of the Bi2 − xMnxTe3 nanocrystal has promising potential to design new devices with magnetic and optical properties adjusted according to the xMn‐concentration.

Carrier Dynamics and Absorption Properties of Gold-Hyperdoped Germanium: Insight Into Tailoring Defect Energetics

Hyperdoping germanium with gold is a potential method to produce room-temperature short-wavelength-infrared radiation (SWIR; $1.4--3.0\phantom{\rule{0.2em}{0ex}}\ensuremath{\mu}\mathrm{m}$) photodetection. We investigate the charge carrier dynamics, light absorption, and structural properties of gold-hyperdoped germanium ($\mathrm{Ge}$:$\mathrm{Au}$) fabricated with varying ion implantation and nanosecond pulsed laser melting conditions. Time-resolved terahertz spectroscopy (TRTS) measurements show that $\mathrm{Ge}$:$\mathrm{Au}$ carrier lifetime is significantly higher than that in previously studied hyperdoped silicon systems. Furthermore, we find that lattice composition, sub-band-gap optical absorption, and carrier dynamics depend greatly on hyperdoping conditions. We use density functional theory (DFT) to model dopant distribution, electronic band structure, and optical absorption. These simulations help explain experimentally observed differences in optical and optoelectronic behavior across different samples. DFT modeling reveals that substitutional dopant incorporation has the lowest formation energy and leads to deep energy levels. In contrast, interstitial or dopant-vacancy complex incorporation yields shallower energy levels that do not contribute to sub-band-gap light absorption and have a small effect on charge carrier lifetimes. These results suggest that it is promising to tailor dopant incorporation sites of $\mathrm{Ge}$:$\mathrm{Au}$ for SWIR photodetection applications.

Improved UV photodetector performance of NiO films by substitutional incorporation of Li

In this study, NiO and Li0.2Ni0.8O (LNO) thin films are successfully deposited by sputtering technique. X-ray photoelectron spectroscopy (XPS) analysis revealed the existence of Ni vacancies. Here, we fabricated metal-semiconductor-metal (M-S-M) structure for exploring the ultra-violet (UV) photodetector (PD) performance. The impact of interstitial oxygen and substitutional incorporation of monovalent Li+ ion in Ni2+ sites of NiO on UV photodetector performance are explored. In a word, LNO exhibited superior responsivity (0.218 A/W) and detectivity (0.467 × 1012 Jones) even at lower power density of 0.31 mW/cm2.

The effect of interstitial-site nitrogen on structural, elastic, and magnetic properties of face-center cubic Co

Cobalt plays a crucial role in the systematic understanding of magnetic phenomena originating from 3d transition metals. Particularly, recent studies of Co systems doped with nitrogen (Co–N) have attracted a lot of attention for applications in spintronics and high-density magnetic data-storage devices. In this work, in order to understand the effect of interstitial incorporation of N atoms into a face-center cubic (fcc) Co lattice, we have studied the structure, elastic, and magnetic properties of spherical-like bulk CoNx (x = 0.06–0.07) samples. These samples were synthesized through a high-pressure solid-state metathesis reaction. We demonstrate that the use of a certain concentration of interstitial N atoms tends to stabilize the lattice of fcc Co at ambient conditions. Such a stabilizing effect is found to originate from the covalent bond between Co atoms and N atoms. High-pressure synchrotron x-ray diffraction indicates that the incorporation of N atoms into fcc Co has little effect on the elastic property up to 27.2 GPa with a bulk modulus (B0) of 200 GPa; the latter is found to be comparable to that of fcc and hcp Co. CoNx samples exhibited ferromagnetic behavior with saturation magnetization up to 153.55 emu/g and coercivity of 16.25 Oe. The introduction of small amounts of nitrogen in the cobalt matrix was found to induce a significant decrease in the coercive force parameter.

Synthesis of metallic mixed 3R and 2H Nb1+xS2 nanoflakes by chemical vapor deposition.

In this work, we report the synthesis and characterization of mixed phase Nb1+xS2 nanoflakes prepared by chemical vapor deposition. The as-grown samples show a high density of flakes (thickness ∼50 nm) that form a continuous film. Raman and X-ray diffraction data show that the samples consist of both 2H and 3R phases, with the 2H phase containing a high concentration of Nb interstitials. These Nb interstitials sit in between the NbS2 layers to form Nb1+xS2. Cross-sectional Energy Dispersive Spectroscopy analysis with transmission electron microscopy suggests that the 2H Nb1+xS2 region is found in thinner flakes, while 3R NbS2 is observed in thicker regions of the films. The evolution of the phase from 2H Nb1+xS2 to 3R NbS2 may be attributed to the change of the growth environment from Nb-rich at the start of the growth to sulfur-rich at the latter stage. It was also found that the incorporation of Nb interstitials is highly dependent on the temperature of the NbCl5 precursor and the position of the substrate in the furnace. Samples grown at high NbCl5 temperature and with substrate located closer to the NbCl5 source show higher incorporation of Nb interstitials. Electrical measurements show linear I-V characteristics, indicating the metallic nature of the Nb1+xS2 film with relatively low resistivity of 4.1 × 10-3Ω cm.

X-ray absorption spectroscopy study of Ga-doping in reactively sputtered ZnO films

Ga-doped ZnO (GZO) films were grown by reactive co-sputtering of a Zn-GaAs target (3% area coverage of Zn by GaAs) at 375 °C with different partial pressures of oxygen. The resistivity of GZO films increases drastically from ≲10−3 Ω-cm to ~ 0.2 Ω-cm as the O2 in the sputtering atmosphere is changed from 5 % to 6 %. The films grown at 5% or lower O2 have the Ga/Zn ratio of ~ 0.1 and display low resistivity with carrier concentration ~ 1021 cm−3, while the films grown at 6% or higher O2 have lower Ga/Zn ratio of ~ 0.01 and display high resistivity with carrier concentration ~ 1019 cm−3. Extended X-ray absorption fine structure (EXAFS) measurements at Zn and Ga K-edges reveal substitutional incorporation of Ga in low resistivity films. X ray photoelectron spectroscopy (XPS) studies reveal a substantial decrease in oxygen vacancies together with increase in oxygen interstitials, in high resistivity GZO films. EXAFS measurements of the high resistivity films show a substantial increase in Ga-O and Ga-Zn bond distances and Ga-O coordination, indicating incorporation of oxygen interstitials in the vicinity of Ga. The comparison of measured and simulated X–ray absorption near edge spectra at O K-edge, together with XPS and EXAFS results, provides adequate experimental evidence of the presence of acceptor type (GaZn+Oi) defect complex, which cause carrier compensation in high resistivity films.

Protonic transport in the new phases BaLaIn0.9M0.1O4.05 (M=Ti, Zr) with Ruddlesden-Popper structure

The new proton-conducting phases BaLaIn0.9M0.1O4.05 (M = Ti, Zr) with Ruddlesden-Popper structure were obtained. The substitution of In3+ ions by the Ti4+ and Zr4+ ions leads to the expansion of the ab plane due to the incorporation of the oxygen interstitials in the La–O rock-salt blocks. It was established that all investigated samples were capable for the water uptake from the gas phase due to the presence in the structure of La–O blocks. The degree of hydration increased with an increase in the size of the salt blocks. It was proved that doping led to the increase in the oxygen ionic conductivity due to the formation of interstitial oxygen. The conductivity values for doped sample BaLa0.9M0.1InO3.95 were higher than for undoped composition BaLaInO4 by ~1 order of magnitude. The new phases BaLaIn0.9M0.1O4.05 (M = Ti, Zr) demonstrate the predominant protonic conductivity at Т<450 °C and pH2O = 2·10−2 atm.

Improving ethanol sensing characteristics of indium oxide thin films by nitrogen incorporation

Incorporation of suitable dopants in semiconducting metal oxide (SMO) based gas sensors have been one proficient approach employed to improve their sensing characteristics. Indium oxide (In2O3), which is a n-type SMO, has been widely investigated for its ethanol sensing characteristics. For doping of In2O3, typically various metal based dopants have been considered, whereas non-metallic dopants have drawn only limited attention. In this work we have examined the impact of nitrogen incorporation on the ethanol sensing properties of In2O3 thin film. Using urea as a source, nitrogen has been doped at the interstitial site of In2O3 synthesised using sol-gel technique. Ethanol sensing properties of the nitrogen doped In2O3 thin film has been compared with pure In2O3 sensor over a wide range of temperature. Doping of nitrogen has been found to significantly enhance the ethanol sensing response of In2O3 (99.7 % at 250 °C), improves the stability of response under humid condition (change of response ∼ 4.5 % within relative humidity range 10–80 %) and offers very fast response time (1 s for 300 ppm ethanol). We discuss that modification of the electronic properties of In2O3 due to interstitial nitrogen incorporation leads to its superior sensing properties on exposure to ethanol vapour.

X-Ray Photoelectron Spectroscopy and Raman Studies of ZnO:Ce Nanocrystals*

Cerium-doped ZnO nanopowders were synthesized using the simple refluxing technique. The synthesized samples were characterized by X-ray diffraction, which confirmed their hexagonal structure. No additional peaks due to the interstitial incorporation or substitutions of Ce4+ ions into the ZnO lattice were observed. Ce 3d3/2 and 3d5/2 had well-separated orbits of Δ = 18.26 eV. The observed spin-orbit splitting as well as the separation between 3d5/2 peaks by 16.47 eV were in good agreement with those reported. The presence of 917.85 eV also confirmed the presence of Ce4+ ions. Raman studies showed that for Ce-doped ZnO the nonpolar interaction E2H grew strong and had a dominant intensity.

Doping of TiO2 nanotubes with nitrogen by annealing in ammonia for visible light activation: Influence of pre- and post-annealing in air

The ∼60 nm wide and ∼2 μm long TiO2 nanotubes were obtained by anodization of Ti films sputtered on F-doped tin oxide glass. For N-doping the samples were annealed in ammonia atmosphere. The effect of pre- and post-annealing in air on the nature and amount of incorporated N was studied by X-ray photoelectron spectroscopy. By measuring the absorption spectra of the obtained samples and interpreting the corresponding Tauc plots it was shown that the sample annealed just in ammonia showed the highest visible light absorption even after sputtering cleaning and a decrease of N amount from 3.8% to 1%. Pre and/or post annealing in air led to smaller amount of incorporated N, that caused less pronounced absorption enhancement and smaller band gap narrowing compared to the sample annealed only in ammonia. By fitting of N 1 s line, the contribution that was assigned to substitutional N was detected only in the samples that did not sustained post-annealing. The study showed that post-annealing in air might lead to partial conversion of N atoms in TiO2 to oxidized nitrogen species that are easily removed with sputtering. It is also possible that substitutional nitrogen was suppressed by oxygen from air to move to interstitial site. Weakly bonded NOx surface species, which are cleaned away by sputtering, can be removed by post-annealing in air. Those surface species could act as sensitizers and when their amounts are reduced, the core absorption properties, as a result of interstitial incorporation of N in TiO2 structure, were revealed. Much lower visible light sensitization was achieved in the case of pre-annealed sample in comparison to sample without pre-annealing, regardless the same quantity and type of incorporated nitrogen.