Impurity Clusters Research Articles

Comprehensive theoretical study of the effects of facet, oxygen vacancies, and surface strain on iron and cobalt impurities in different surfaces of anatase TiO2.

We report the results of systematic ab initio modelling of various configurations of iron and cobalt impurities embedded in the (110), (101), and (100) surfaces of anatase TiO2, with and without oxygen vacancies. The simulation results demonstrate that incorporation into interstitial voids at the surface level is significantly more favourable than other configurations for both iron and cobalt. The calculations also demonstrate the crucial effect of the facet as well as the lesser effects of other factors, such as vacancies and strain on the energetics of defect incorporation, magnetic moment, bandgap, and catalytic performance. It is further shown that there is no tendency towards the segregation or clustering of impurities on the surface. The calculated free energies of the hydrogen evolution reaction in acidic media predict that iron impurities embedded in the (101) surface of anatase TiO2 can be a competitive catalyst for this reaction.

First-principles investigation on the structural, optical, and laser-induced damage characteristics of boron impurity and boron-oxygen defect cluster in potassium dihydrogen phosphate crystals

The DFT+U method combined with HSE06 hybrid functional and finite-size correction has been employed to investigate the defect formation energies, lattice modifications and optical spectra of Potassium Dihydrogen Phosphate (KDP) crystals with Boron. The B defects contain the B interstitials (Bi), the B substituted P sites (BP), and the boron-oxygen defect clusters ([BP+VO]). The results demonstrate that these B defects can trigger lattice distortions. The BP and [BP+VO] have a minor lattice change rate and greater stability, while Bi has a relatively large local distortion inducing crystal damage. We have also utilized conformational coordinate diagrams to explore the optical absorption/emission processes arising from B defects. The BP and [BP+VO] were found to generate absorption peaks at 330 nm and 255 nm, while the Bi leads to absorption peaks near the absorption edge. The absorption peaks within the near-ultraviolet range might have an energy buildup at the defects, which would decrease laser utilization and harm the crystal.

Electronic and magnetic properties of Janus ZrSSe monolayer doped with V impurity and VX3(X = C, N, O, and F) clusters

In this work, doping with V impurity and VX3 (X = C, N, O, and F) clusters is proposed to modify the electronic and magnetic properties of Janus ZrSSe monolayer. Pristine ZrSSe monolayer is an indirect-gap semiconductor two-dimensional (2D) material with energy gap of 0.73 eV. This value is reduced to 0.13 eV under effects of single Zr vacancy, which corresponds to the reduction of the order of 82.19%. V impurity magnetizes significantly ZrSSe monolayer, inducing feature-rich magnetic semiconductor nature. Herein, the magnetism with a total magnetic moment of 1.00 μ B is produced mainly by V-3d orbital. Investigations indicate that the antiferromagnetic state with zero total magnetic moment is stable when V impurities are located close to each other. Further separating impurities causes the antiferromagnetic-to-ferromagnetic state transition, such that a total magnetic moment of 2.00 μ B is obtained. ZrSSe monolayer is metallized by doping with VC3, VN3 and VF3 clusters. In the first two cases, the non-magnetic nature is preserved. Meanwhile, significant magnetization with a total magnetic moment of 3.00 μ B is achieved by VF3 cluster substitution. Similarly, VO3 cluster induces significant magnetic properties in ZrSSe monolayer with a total magnetic moment of 1.00 μ B , which are originated mainly from the antiparallel spin orientation between V atom and Se atoms closest to the doping sites. Herein, VO3 cluster substitution in ZrSSe monolayer makes new magnetic semiconductor 2D material. The Bader charge analysis indicates that all four clusters attract charge from the host monolayer. Our work may introduce efficient approaches to modify the ZrSSe monolayer electronic and magnetic properties towards spintronic and optoelectronics applications.

Element partitioning and stabilization for impurities removal between liquid silicon and silicate melts: Ab initio insights into electronic structure

The partitioning and stabilization of common impurity elements challenge the impurity removal process during slag refining for developing high-purity metals. The role of electronic properties remains indistinct in the stability of non-metallic, alkaline earth metal, and transition metal impurity clusters in silicon and silicate melts, impeding the advancement of separation medium and purification process. Herein, local structures of impurity atoms are explored through ab initio molecular dynamics, and notable configurations are [PSi4], [TiSi10], [MgSi12] in silicon melts and [PO4], [TiO5], [MgO5] in silicate melts. A novel partition model based on impurity coordination predicted the impurity atoms’ distribution behavior consistent with industrial experiments. Furthermore, this model proposes a critical parameter k that evaluates impurity oxidation levels in coexisting systems and establishes a quantitative link between melt structures and distribution ratio, enabling precise predictions from two-phase ab initio calculations. Innovatively, the electronic structure analysis assessed element partitioning through bonding characteristics and interactions within impurity clusters via parameters: electron density distribution, partial density of states, electron localization function, and Mayer bond order. This yields a distinctive mapping relationship between impurity distribution ratio and stability, evidenced by quantitative associations with 12 key ab initio-derived descriptors through Pearson correlation analysis. This work unveils the electronic properties governing partitioning and endows modeling approach for distribution, driven by cluster structure analysis and ab initio calculations.

Synthesizing impurity clustering in the edge plasma of tokamaks using neural networks

This work investigates the behavior of impurities in edge plasma of tokamaks using high-resolution numerical simulations based on Hasegawa–Wakatani equations. Specifically, it focuses on the behavior of inertial particles, which has not been extensively studied in the field of plasma physics. Our simulations utilize one-way coupling of a large number of inertial point particles, which model plasma impurities. We observe that with Stokes number (St), which characterizes the inertia of particles being much less than one, such light impurities closely track the fluid flow without pronounced clustering. For intermediate St values, distinct clustering appears, with larger Stokes values, i.e., heavy impurities even generating more substantial clusters. When St is significantly large, very heavy impurities tend to detach from the flow and maintain their trajectory, resulting in fewer observable clusters and corresponding to random motion. A core component of this work involves machine learning techniques. Applying three different neural networks—Autoencoder, U-Net, and Generative Adversarial Network (GAN)—to synthesize preferential concentration fields of impurities, we use vorticity as input and predict impurity number density fields. GAN outperforms the two others by aligning closely with direct numerical simulation data in terms of probability density functions of the particle distribution and energy spectra. This machine learning technique holds the potential to reduce computational costs by eliminating the need to track millions of particles modeling impurities in simulations.

Space charge and screening of a supercritical impurity cluster in monolayer graphene

Space charge and screening of a supercritical impurity cluster in monolayer graphene

Effect of nanoclusters formed by metal impurity on magnesium vapor condensation in silicothermic process: a molecular dynamics study

In the silicothermic process, some metal oxide impurities that coexist with dolomite are inevitably reduced to metal vapors, which condense to metal impurities in the magnesium crystallizer. In this paper, the molecular dynamics simulation method was adopted to investigate the effect of impurity clusters on the crystallization transition of undercooled magnesium vapor. The results showed that saturated vapor atoms tend to nucleate on the pre-existing impurity cluster, promoting the crystallization rate of magnesium vapor. The promoting effects of impurity clusters on the crystallization of magnesium vapor depend on their sizes and species. The cluster with a larger size demonstrated a more substantial promoting impact. Moreover, in the three impurities studied in this paper, magnesium vapor condenses on the Fe cluster at the fastest rate due to the bcc structure of the Fe cluster and the strong interaction between Fe and Mg atoms. For Ni and Cu clusters with the same fcc structure, the promoting effect of the Ni cluster on the crystallization of Mg vapor is more evident because the interaction between Ni-Mg atoms is stronger than between Cu-Mg atoms.

Impact of clustering of substitutional impurities on quasiparticle lifetimes and localization

Impact of clustering of substitutional impurities on quasiparticle lifetimes and localization

The Effect of Thermal Annealing on the Electrophysical Properties of Samples n-Si<Ni,Сu>

This paper presents the results of studies of the effect of isothermal annealing at temperatures T = 673¸1473 K in the time interval 5¸60 minutes on the electrical properties of silicon, simultaneously alloyed with nickel and copper. Samples of n-Si<Ni,Cu> were obtained on the basis of the starting material - single-crystal silicon, grown by the Czochralski method with the initial resistivity r = 0.3 Ohm×cm. Diffusion was carried out at a temperature of 1523 K for 2 hours. After that, the samples were cooled at a rate of 0.1 K/s. The morphological parameters of impurity nickel and copper atom clusters formed in the bulk of silicon were measured by electron probe microanalysis on a modern Superprobe JXA-8800R setup. As it turned out, in the volume of n-Si<Ni,Cu> samples, clusters of impurity atoms with different geometric shapes are formed, the sizes of which reach up to 500 nm. The electrical properties of the samples were studied by the Hall effect method using an Ecopia HMS-7000 instrument. It was revealed that under the influence of thermal annealing (TA) at T≥1273 K, impurity clusters decompose, which leads to an increase in the resistivity of n‑Si<Ni,Cu> samples. After exposure to TA at Т=1273 K for 15 minutes, the density of impurity nanoaccumulations of acicular and lenticular shapes sharply decreases in the sample volume. Under the influence of TA at T = 1473 K for 10 minutes in the volume of the sample, the decay of impurity nanoclusters with a spherical shape is observed. Also presented are the results of changes in the density of impurity clusters, as well as structural analyzes of the samples before and after exposure to thermal annealing.

Suppression of 1/f noise in graphene due to anisotropic mobility fluctuations induced by impurity motion

Low frequency resistance variations due to mobility fluctuations is one of the key factors of 1/f noise in metallic conductors. According to theory, such noise in a two-dimensional (2D) device can be suppressed to zero at small magnetic fields, implying important technological benefits for low noise 2D devices. In this work, we provide evidence of anisotropic mobility fluctuations by demonstrating a strong field-induced suppression of noise in a high-mobility graphene Corbino disk, even though the device displays only a tiny amount of 1/f noise inherently. The suppression of the 1/f noise depends on charge density, showing less non-uniform mobility fluctuations away from the Dirac point with charge puddles. We model our results using an approach based on impurity clustering dynamics and find our results consistent with the 1/f noise induced by scattering of carriers on mobile impurities forming clusters.

Chemical and visual characterisation of EGRIP glacial ice and cloudy bands within

Abstract. Impurities in polar ice play a critical role in ice flow, deformation, and the integrity of the ice core record. Especially cloudy bands, visible layers with high impurity concentrations, are prominent features in ice from glacial periods. Their physical and chemical properties are poorly understood, highlighting the need to analyse them in more detail. We bridge the gap between decimetre and micrometre scales by combining the visual stratigraphy line scanner, fabric analyser, microstructure mapping, Raman spectroscopy, and laser ablation inductively coupled plasma mass spectrometry 2D impurity imaging. We classified approximately 1300 cloudy bands from glacial ice from the East Greenland Ice-core Project (EGRIP) ice core into seven different types. We determine the localisation and mineralogy of more than 1000 micro-inclusions at 13 depths. The majority of the minerals found are related to terrestrial dust, such as quartz, feldspar, mica, and hematite. We further found carbonaceous particles, dolomite, and gypsum in high abundance. Rutile, anatase, epidote, titanite, and grossular are infrequently observed. The 2D impurity imaging at 20 µm resolution revealed that cloudy bands are clearly distinguishable in the chemical data. Na, Mg, and Sr are mainly present at grain boundaries, whereas dust-related analytes, such as Al, Fe, and Ti, are located in the grain interior, forming clusters of insoluble impurities. We present novel vast micrometre-resolution insights into cloudy bands and describe the differences within and outside these bands. Combining the visual and chemical data results in new insights into the formation of different cloudy band types and could be the starting point for future in-depth studies on impurity signal integrity and internal deformation in deep polar ice cores.

Investigations of the Spin-Hamiltonian Parameters and Defect Structure for the (TiO4)5− Tetrahedral Clusters in ZrSiO4: Ti3+ Crystal

The spin-Hamiltonian parameters (g factors g//, g⊥ and hyperfine structure constants 47Ai, 49Ai, where i = // or ⊥, 47Ai and 49Ai denote the values of isotopes 47Ti3+ and 49Ti3+) of Ti3+ ions at the tetragonal tetrahedral Si4+ sites in ZrSiO4 crystal are computed from the high-order perturbation formulas based on the cluster approach where the contributions due to both the d orbitals of central dn ion and p orbitals of ligand ion are considered. The calculated results are reasonably coincident with the experimental values. The defect structure of tetragonal (TiO4)5− impurity cluster which differs from the replaced host (SiO4)4− cluster in ZrSiO4 is evaluated from the calculation. The results are discussed.

Dissolution Energies of Impurities and Their Clusters in Powellite CaMoO4

The impurity defects in CaMoO4 are simulated by the method of interatomic potentials. The dissolution energies of monovalent, divalent, and trivalent impurities are calculated, their comparative analysis is performed, and the main patterns of change are presented. The most probable localization of defects is determined. In the case of heterovalent impurities, the most energetically favorable mechanism for their charge compensation has been found, both due to intrinsic crystal defects and under conjugate isomorphism. It is shown that the formation of impurity clusters with intrinsic crystal defects and (to a greater extent) the formation of clusters of different-valence impurities may significantly reduce the dissolution energy of impurities. The formation of neutral clusters of univalent impurities with oxygen vacancies not only makes it possible to increase the solubility of impurities but also reduces the probability of the formation of color centers.

CRYSTAL CHEMICAL FEATURES OF GREEN AND LIGHT-BLUE AMAZONITE AND GEOCHEMICAL ASPECTS OF THEIR FORMATION PROCESSES

A study was carried out in order to identify the aspects of geochemical processes occurring during the formation of green and light-blue amazonite crystals. Green, light-blue and greenish-blue amazonites from rare-metals deposits of Ukraine (Perzhanske, Ukrainian Shield), rf (Gora Parusna, Ploskogirske, Kola Peninsula; Orlovske, Western Transbaikalia), and USA (Rutherford, Virginia) were investigated using X-ray luminescence (XRL), infrared (IR) spectroscopy and X-ray diffraction. The rock-forming microcline from the Perzhanske, Orlovske and Katuginske (rf) deposits was also studied. It was found that the multi-colored crystals of amazonite have similar degrees of Si/Al ordering. They are represented by the maximum microcline with 2t1 = 0.959-1.0. The various samples only differ significantly in their lead contents that range between 2000 and 10000 ppm in green amazonite and 200 ppm in light-blue colored crystals. Differences between untreated crystals and those annealed in air (1173 K) or under a stream of He (923 K) samples were observed in terms of the composition, ratio of optically active centers and oxygen-hydrogen defects. Their composition and concentration in the untreated natural crystals reflect the genesis conditions of parent rocks, and, first of all, the redox and fO2 conditions of water-containing fluids, which affect the isomorphism of plumbum in the structures of the green and light-blue crystals, mechanisms of crystal chemical compensation of Pb2+ ions and correlates with different degree of ferum oxidation (Fe3+ → Fe2+). Changes in redox and fO2 parameters of the mineral-forming fluid are the most important factors affecting the activity and acid-base properties in the residual water fluids, the process of reduction following 2H2O + 2e– → H2 + 2OH– or oxidation via 2H2O – 4e– → O2 + 4H+. A complex combination of these factors allows the formation of certain nanosized defects in the structures of the amazonite crystals. These include impurity ([Pb2+ – Pb+]3+) and impurity-vacancy (Pb2+ – VK) clusters that serve as chromophore centers for green and light-blue color, respectively.

Study on the local compressibility of (MnF6)2− centres in KNaSiF6: Mn4+ red phosphor material by analysing its pressure-induced spectral line shifts

The local linear compressibility of (MnF6)2− centres in KNaSiF6: Mn4+ red phosphor material is estimated by analysing its pressure-induced R-line red-shift. The result is confirmed by calculating the pressure-induced E(4T2)-line blue-shift. The evaluated local linear compressibility of (MnF6)2− impurity centres is much smaller than the linear compressibility of host KNaSiF6 crystal as a whole obtained from the theoretical calculation. The causes (i.e., the local compressibility of impurity cluster being smaller than the corresponding host one, and the local compressibility of the corresponding host cluster being also smaller than the compressibility of whole crystal) about the difference between the local compressibility of (MnF6)2− impurity centre and the compressibility of whole host KNaSiF6 crystal are discussed.

Morphology controlled synthesis of Fe and Mn co-doped In2O3 nanocubes and their Dopant-Atom effects on electronic structure and magnetic properties

Fe and Mn co-doped In2O3 single-phase cubic crystal structure nanocubes of uniform size and control over dopant concentration (In1.96Fe0.02Mn0.02O3, In1.94Fe0.02Mn0.04O3, In1.92Fe0.02Mn0.06O3 and In1.90Fe0.02Mn0.08O3) and microstructure were prepared using the hydrothermal-annealing technique. On a wider vision, we systematically investigated the influence of Fe and Mn co-doping in In2O3 through complementary experimental techniques and density functional theoretical (DFT) calculations to reveal the physical mechanisms involved in the origin of observed ferromagnetism. DFT calculations demonstrated that the substitution of surface indium atom by iron (FeIn) leads to impurity states on the top of In2O3 valence band maximum (VBM). Conversely, incorporation of interstitial (Mni) impurities in the host matrix without oxygen vacancies (VO) slightly shifts the top of the valence band and incorporation of interstitial Mn-impurity in the In2O3 (111) surface with oxygen vacancy does not provide noticeable changes in the electronic structure of the defective surface. High-resolution transmission electron microscopy measurements showed the formation of regular nanocubes in shape with 36.9–37.6 nm in average edge length. X-ray photoelectron spectroscopy investigations revealed that valence state of Fe mostly as Fe2+ and Fe3+ and Mn2+ for Mn atom in the In1.96Fe0.02Mn0.02O3, In1.94Fe0.02Mn0.04O3, In1.92Fe0.02Mn0.06O3 and In1.90Fe0.02Mn0.08O3. Magnetic studies exhibited room temperature ferromagnetism (RTFM) in the investigated samples with the high coercivity and saturation magnetization of 145.48 Oe and 0.023 emu/g, respectively for the In1.94Fe0.02Mn0.04O3. The origin of observed RTFM was described based on the bound magnetic polaron (BMP) model mechanism. DFT investigations demonstrated the clusters of impurities (FeIn-nMni) robust magnetic interactions within the cluster and between the clusters. Interestingly, only FeIn-nMni clusters contribute ferromagnetism observed in the investigated co-doped systems. Therefore, increasing the concentration of defects leads to the improvement of ferromagnetism. The comprehensive experimental and DFT investigations present new evidence to the observed ferromagnetism and electronic structure of Fe,Mn co-doped In2O3 nanocubes.

A new form of impurity cluster in casting quasi-single crystalline silicon

The casting quasi-single crystalline silicon technology is very promising in the development of high quality and low cost crystals for manufacturing photovoltaic devices. In this study, we find a new type of impurity cluster named as “black spot” in the casting quasi-single crystalline, which is different from the “shadows” caused by SiC/Si3N4 particles discovered in previous research. The “black spot” is systematically studied and characterized using inductively coupled plasma mass spectrometry (ICP-MS), photoluminescence (PL), and infrared (IR) detectors. The test results show that the “black spot” is composed of metal impurities. According to our analysis, the formation mechanism of the “black spot” may be caused by the accumulation of the metal impurities in certain region of the solid/liquid interface. These clustering impurities are not absorbed by enough grain boundaries in the casting quasi-single crystalline after being solidified into the crystal and thus exhibit as “black spot”. An optimization method is proposed in the direction of numerical simulation and verified by experiments to avoid the formation of the “black spot”.

Yu-Shiba-Rusinov multiplets and clusters of multiorbital adatoms in superconducting substrates: Subgap Green's function approach

We discuss all the characteristics of Yu-Shiba-Rusinov states for clusters of impurities with classical magnetic moments in a superconducting substrate with s-wave symmetry. We consider the effect of the multiorbital structure of the impurities and the effect of the crystal field splitting. We solve the problem exactly and calculate the subgap Green's function, which has poles at the energies of the Shiba states and defines the local density of states associated to their wave functions. For the case of impurities sufficiently separated, we derive an effective Hamiltonian to describe the hybridization mediated by the substrate. We analyze the main features of the spectrum and the spectral density of the subgap excitations for impurities in dimer configurations with different relative orientations of the magnetic moments. We also illustrate how the same formalism applies for the solution of a trimer with frustration in the orientation of the magnetic moments.

Improving the efficiency of an industrial silicon solar cell by doping with nickel

The possibility of adjusting the operational parameters of industrial solar cells produced by the company Suniva based on monocrystalline silicon by means of additional diffusion doping with nickel in the temperature range 700–1200 °C has been investigated. It is shown that the optimal temperature of nickel diffusion is Tdiff = 800–850 °C. In this case the value of the maximum power Pmax increases by 20–28 % in relation to the parameters of the original industrial photocell. At diffusion temperatures Tdiff > 1000 °C, a sharp decrease in Pmax occurs, which is associated with an increase in the depth of the p–n-junction due to the distillation of phosphorus atoms during high-temperature diffusion of nickel. The positive effect of diffusion alloying with nickel on the electrophysical parameters of photocells is greatest in the case when the nickel impurity clusters are in the region of the p–n-junction, i. e. with diffusion alloying to the front side of the plate. The action of electrically neutral nickel clusters is less pronounced when they are located in the region of the isotypic p–p+ transition; in case of diffusion alloying with nickel in the opposite side of the plate.

Role of impurity clusters for the current-driven motion of magnetic skyrmions

We study how impurities influence the current-induced dynamics of magnetic Skyrmions moving in a racetrack geometry. For this, we solve numerically the generalized Landau-Lifshitz-Gilbert equation extended by the current-induced spin transfer torque. In particular, we investigate two classes of impurities, non-conducting and magnetic impurities. The former are magnetically rigid objects and yield to an inhomogeneous current density over the racetrack which we determine separately by solving the fundamental electrostatic equations. In contrast, magnetic impurities leave the applied current density homogeneous throughout the stripe. Depending on parameters, we observe four different scenarios of Skyrmion motions in the presence of disorder, the Skyrmion decay, the pinning, the creation of additional Skyrmions, and ordinary Skyrmion passage. We calculate and discuss phase diagrams in dependence of the impurity concentration and radii of the impurities.