3d Impurities Research Articles

Nature of the metallic and in-gap states in Ni-doped SrTiO3

Epitaxial thin films of SrTiO3(100) doped with 6% and 12% Ni are studied with resonant angle-resolved photoelectron spectroscopy at the Ti and Ni L2,3-edges. We find that the Ni doping shifts the valence band of n-doped pristine SrTiO3 toward the Fermi level (in the direction of p-doping) and reducing the bandgap. In the Ti t2g-derived mobile electron system (MES), the Ni doping depopulates the out-of-plane dxz/yz-derived bands, transforming the MES to two-dimensional and progressively reduces the electron density embedded in the in-plane dxy-derived bands as reflected in their Fermi momentum. Furthermore, the Ti and Ni L2,3-edge resonant photoemission is used to identify the Ni 3d impurity state in the vicinity of the valence-band maximum and decipher the full spectrum of the in-gap states originating from the Ni atoms, Ti atoms, and from their hybridized orbitals. Our experimental information about the dependence of the valence bands, MES, and in-gap states in Ni-doped SrTiO3 may help the development of this material toward its device applications associated with the reduced optical bandgap.

Effects of Cu, Zn Doping on the Structural, Electronic, and Optical Properties of α-Ga2O3: First-Principles Calculations.

The intrinsic n-type conduction in Gallium oxides (Ga2O3) seriously hinders its potential optoelectronic applications. Pursuing p-type conductivity is of longstanding research interest for Ga2O3, where the Cu- and Zn-dopants serve as promising candidates in monoclinic β-Ga2O3. However, the theoretical band structure calculations of Cu- and Zn-doped in the allotrope α-Ga2O3 phase are rare, which is of focus in the present study based on first-principles density functional theory calculations with the Perdew-Burke-Ernzerhof functional under the generalized gradient approximation. Our results unfold the predominant Cu1+ and Zn2+ oxidation states as well as the type and locations of impurity bands that promote the p-type conductivity therein. Furthermore, the optical calculations of absorption coefficients demonstrate that foreign Cu and Zn dopants induce the migration of ultraviolet light to the visible-infrared region, which can be associated with the induced impurity 3d orbitals of Cu- and Zn-doped α-Ga2O3 near the Fermi level observed from electronic structure. Our work may provide theoretical guidance for designing p-type conductivity and innovative α-Ga2O3-based optoelectronic devices.

Magnetic properties of oxides and silicon single crystals

The magnetic properties of single crystals Si, SrTiO3, LaAlO3, MgO, and (La,Sr)(Al,Ta)O3 were investigated systematically. Three origins of the magnetizations of these crystals, namely, an intrinsic diamagnetic, a paramagnetic, and a ferromagnetic contribution, have been found to influence the magnetic signals measured on the crystals, in some important application scenarios such crystals being served as substrates with the magnetic thin film epitaxially grown on. Quantitative analyses methodologies were developed and thorough investigations were performed on the crystals with the intrinsic materials parameters thus revealed, especially that the intrinsic diamagnetic susceptibility differential dχ dia/dT were identified quantitatively for the first time in SrTiO3, LaAlO3, MgO, and (La,Sr)(Al,Ta)O3. The paramagnetic contribution is found to be the key in terms of the magnetic properties of the crystals, which in turn is in fact a consequence of the 3d impurities doping inside the crystal. All the intrinsic materials parameters are given in this paper as datasets, the datasets are openly available at https://www.doi.org/10.57760/sciencedb.j00113.00028.

Coexisting ferromagnetic component and negative magnetoresistance at low temperature in single crystals of the VdW material GaGeTe

We report magnetoresistance and magnetization studies of single-crystal GaGeTe, which has been proposed as a Van der Waals material. Semi-metallic character is observed in the temperature (T) variation of resistivity (ρ), following ρ(T) ​∝ ​T2 ​at low temperature with a slope compatible with the usual spin-fluctuating system. Magnetoresistance (MR) at 2 ​K is negative and strongly dependent on the direction of the magnetic field (H) with respect to the crystallographic c-axis. MR changes sign with increasing temperature above ∼ 100 ​K, when H is applied along the c-axis. Hall measurements indicate the p-type conductivity with a considerable hole concentration of ∼ 8.7 ​× ​1019 ​cm−3. Angle-resolved photoemission spectroscopy reproduces the reported results and confirms a peculiar dispersion shape of the hole-like band at the bulk high-symmetry T point near the Fermi energy indicating band inversion. Magnetic hysteresis measurement at 2 ​K shows diamagnetic behaviour at high-H, whereas a ferromagnetic (FM)-like magnetic hysteresis loop is observed at low-H in between ​± ​4 ​kOe. The FM component disappears close to 3 ​K. Signature of spin-fluctuation in ρ(T), negative MR, and low-T FM component without 3d or 4f impurities in GaGeTe is attractive for the fundamental interest.

DFT Investigations of Aun Nano-Clusters Supported on TiO2 Nanotubes: Structures and Electronic Properties.

TiO2 nanotubes (TiO2NTs) are beneficial for photogenerated electron separation in photocatalysis. In order to improve the utilization rate of TiO2NTs in the visible light region, an effective method is to use Aun cluster deposition-modified TiO2NTs. It is of great significance to investigate the mechanism of Aun clusters supported on TiO2NTs to strengthen its visible-light response. In this work, the structures, electronic properties, Mulliken atomic charge, density of states, band structure, and deformation density of Aun (n = 1, 8, 13) clusters supported on TiO2NTs were investigated by DMOL3. Based on published research results, the most stable adsorption configurations of Aun (n = 1, 8, 13) clusters supported with TiO2NTs were obtained. The adsorption energy increased as the number of Au adatoms increased linearly. The Aun clusters supported on TiO2NTs carry a negative charge. The band gaps of the three most stable structures of each adsorption system decreased compared to TiO2NTs; the valence top and the conduction bottom of the Fermi level come mainly from the contribution of 5d and 6s-Au. The electronic properties of the 5d and 6s impurity orbitals cause valence widening and band gap narrowing.

U7Co 3d impurity energy level mediated photogenerated carriers transfer in Bi2S3/ZnS:Co/TiO2 photoanode

Photogenerated carriers' transfer efficiency as one of the most important criteria determines the efficiency of a photoanode for photoelectrochemical (PEC) water splitting. Energy barrier-free charge transfer of photogenerated carriers is achieved in a core–shell heterostructure of Bi2S3/ZnS:Co/TiO2, in which the arrayed TiO2 nanorods are covered with the Co doped ZnS inner layer and the Bi2S3 outer layer. The dual-shell structure ensures high photoconversion efficiency in PEC water splitting. The impurity energy state of Co in ZnS connects the conduction band edges of Bi2S3 and TiO2 to convey photogenerated electrons, without electrons hopping to Zn orbits at higher energy positions. The ABPE value of 1.07% at 1.23 V vs. RHE demonstrates the improved photoconversion efficiency of Bi2S3/ZnS:Co/TiO2 heterostructure. This work offers a photoanode construction strategy for the enhancement of the PEC water splitting via introducing impurity energy states at interlayer for barrier-free photogenerated charge migrating.

Technology for obtaining high-pure magnesium compounds using the hydrolytic processes of sedimentation

In nature, magnesium compounds are distributed in the form of such minerals as dolomite, magnesite, serpentinite, brucite, and in the form of such solutions as sea and ocean waters, salt lakes, bischofite. The main popular magnesium compounds are its chloride, hydroxide, and oxide. The most common technology for obtaining magnesium hydroxide is based on the action of alkaline reagents on solutions of magnesium. However, the technology has significant drawbacks. The main issue is that magnesium hydroxide cannot be obtained free of impurity metal ions, and the sediment itself has an extremely low filtration rate from the solution in which it is formed. Magnesium hydroxide is an excellent sorbent collector for the ions of most metals, so it is possible to utilize this property of absorption of magnesium hydroxide to produce other highly pure compounds, for medicine and pharmacopeia. This paper investigates the processes of alkaline hydrolysis of magnesium chloride and the formation of magnesium hydroxide sediment, the kinetics of processes, as well as the properties of sediments. Empirical formulas for sediment production parameters with a high filtration coefficient that exceeds the known values of 1·106have been derived. The study reported here hasrevealed the possibility of obtaining in a relatively simple way highly pure chloride, hydroxide, and magnesium oxide, sodium chlorides, potassium, calcium, in which the impurity 3d metals content does not exceed the value as a percentage of (1‒4)·10-7. Due to the properties of highly pure magnesium compounds to the sorption of metal ions, it is possible to create reference samples of chemical elements for the needs of metrology. For example, to create MR phantoms to verify measurements and check the operation of magnetic resonance imaging (MRI) in medical institutions. Especially pure magnesium hydroxide can be used for instrumental methods of analytical chemistry (X-ray fluorescent, neutron-activation methods) when fabricating chemical references for testing laboratories.

RF sheath induced sputtering on Proto-MPEX. I. Sheath equivalent dielectric layer for modeling the RF sheath

The pulsed linear plasma device Prototype Material Plasma Exposure eXperiment (Proto-MPEX) uses a radio frequency (RF) helicon antenna with an aluminum nitride ceramic window for plasma production. The RF sheath created under the helicon antenna is sufficient to cause ion impact energies to be greater than the sputtering threshold of the AlN helicon window material and for impurities to be created. Here, we investigate the RF sheath on the inner diameter of the helicon window and its impact on the impurity production rates in Proto-MPEX. Three models—a 3D COMSOL finite element RF model of the Proto-MPEX helicon region, a rectified DC sheath potential model, and the 3D Global Impurity TRansport code—are coupled together to study impurity production and transportation. This novel method of impurity generation and transport modeling spans length scales ranging from the sheath (millimeters or less) up to the full device (meters) and can be applied to other radio frequency sources and antennas in a wide range of plasma physics studies, including basic plasmas, low-temperature processing plasmas, plasma thrusters, and fusion plasmas.

Ab initio Simulation of Dissolution Energy and Bond Energy of Hydrogen with 3sp, 3d, and 4d Impurities in bcc Iron

Ab initio Simulation of Dissolution Energy and Bond Energy of Hydrogen with 3sp, 3d, and 4d Impurities in bcc Iron

3D impurity profiles of doped/intrinsic amorphous-silicon layers composing textured silicon heterojunction solar cells detected by atom probe tomography

Laser-assisted atom probe tomography was used to identify the impurity distribution in Si heterojunction (SHJ) solar cells composed of thin doped/intrinsic amorphous Si layers on the textured surface of a crystalline Si wafer. A site-specific lift-out technique involving a focused ion beam enabled the selection of a ∼2 × 2 μm2 area on an arbitrary pyramidal surface. The distributions of B, P and C in the amorphous Si layers introduced by p-type (trimethyl-borane or diborane) or n-type (phosphine) dopant gases were investigated. Standard guidelines for the assessment of the H content in amorphous Si of SHJ solar cells were provided.

Theoretical Study on Four-fold Symmetric Anisotropic Magnetoresistance Effect in Cubic Single-crystal Ferromagnetic Model

In this study, we present a theoretical interpretation of the experimental results that the anisotropic magnetoresistance (AMR) effect has a four-fold symmetric component, $c_4$, in cubic ferromagnetic metals. The theoretical model that we employ is based on the Anderson impurity model that includes a four-fold symmetric crystalline electric field, and we assume that the impurities have 3d electron orbitals and spin--orbit interaction (SOI). We describe the DC conductivity on the basis of the Kubo formula, and we investigate $c_4$ by analyzing the magnetization direction dependence of the resultant AMR ratio. Analytical and numerical calculations are performed; the analytical calculation reveals that $c_4$ arises from the fourth-order contribution of the SOI, and the numerical calculation provides the parameter dependencies of $c_{4}$ in our model. From the calculation results, we observe that the splitting of impurity 3d levels due to SOI is responsible for the existence of $c_{4}$ in cubic ferromagnetic metals.

DFTB Investigations on Transition Metals Doped TiO2 Quantum Dots

The structural, optical and electronic properties of different-sized pure as well as transition metals doped TiO2 quantum dots were investigated using density functional tight binding (DFTB) methods. The self-consistent charge density functional tight binding theory (SCC-DFTB) was used to model the TiO2 quantum dots (QDs) of increasing size up to 3.03 nm. The size dependence of density of states, position of molecular orbitals, and gap between highest orbital molecular orbitals (HOMO) and lowest unoccupied molecular orbitals (LUMO) of the QDs were studied. It appeared that, when the size of QDs approaches 3.03 nm, the energy gap narrowed down due to quantum confinement effects. The QD Ti27O54 was doped with 3d transition metals to further explore the possibility of tailoring the properties. The dopants introduced 3d impurity gap states which opens the opportunity to modify the band gap or positions of principal bands. The position of a shifted Fermi level was monitored to explore the changes in conductivity and n- or p-type behaviors of the doped QDs. It was observed that TiO2 QDs doped with V and Cr showed the n-type behavior while those doped with Sc, Mn and Fe showed p-type behavior. The findings are helpful to enhance the photocurrent efficiency of dye-sensitized solar cells and use the materials in electronic and optoelectronic properties.

Evolution of a Non-Uniform Deformed State in the Structure of Zinc-Chalcogenide Cubic Crystals Doped by 3d Ions

The real structure of bulk Zn1 – хМхSe (S) crystals of diluted magnetic semiconductors with М = V, Cr, Fe, Co, Ni 3d impurities is characterized by neutron diffraction. These impurities are known to greatly destabilize even the initial lattices of pure zinc chalcogenides. Data on the resulting non-uniform microstrain field induced by atomic displacements are obtained from the structural peaks along the tangential and radial directions on the above crystals within a dopant concentration range of 0.01 ≤ х ≤ 0.10. Additional nodes with q = (1/3 1/3 1/3) 2π/a (q is the wave vector and a is the cubic unit cell) emerging in the reciprocal lattice of the cubic structure are considered as evidence for a pre-transition to the fcc (face-centered cubic)–hcp (hexagonal close-packed) phase state, which implies transitions from the fcc lattice along an 8-ray non-Lifshitz star with the wave vector k5 = μ(b1 + b2 + b3), where b1, b2, b3 are the reciprocal lattice vectors and μ ≈ 1/3.

Parameters of ZnO Semiconductor Films Doped with Mn and Fe 3d Impurities

The effect of Fe and Mn impurities on the magnetic parameters of ZnO wide-gap semiconductor films produced by high-frequency sputtering with wide variations in the defect concentration is studied. The introduction of Mn and Fe magnetic impurities brings about the existence of a magnetically ordered state in the semiconductor matrix, with different positions of the axis of easy magnetization. In the case of doping with Mn, this axis lies perpendicularly to the film plane, and in the case of doping with Fe, this axis lies in the film plane.

The simultaneous effect of 3d impurities of transition metals and oxygen vacancy defect on TiO2 anatase and rutile

The simultaneous effect of 3d impurities of transition metals and oxygen vacancy defect on TiO2 anatase and rutile

Volume Rendering Method Applied to 3D Edge Impurity Emission in LHD to Produce Projection Image in Arbitrary Plane

Volume Rendering Method Applied to 3D Edge Impurity Emission in LHD to Produce Projection Image in Arbitrary Plane

Improved ERO modelling of beryllium erosion at ITER upper first wall panel using JET-ILW and PISCES-B experience

Abstract ERO is a 3D Monte-Carlo impurity transport and plasma-surface interaction code. In 2011 it was applied for the ITER first wall (FW) life time predictions [1] (critical blanket module BM11). After that the same code was significantly improved during its application to existing fusion-relevant plasma devices: the tokamak JET equipped with an ITER-like wall and linear plasma device PISCES-B. This has allowed testing the sputtering data for beryllium (Be) and showing that the “ERO-min” fit based on the large (50%) deuterium (D) surface content is well suitable for plasma-wetted areas (D plasma). The improved procedure for calculating of the effective sputtering yields for each location along the plasma-facing surface using the recently developed semi-analytical sheath approach was validated. The re-evaluation of the effective yields for BM11 following the similar revisit of the JET data has indicated significant increase of erosion and motivated the current re-visit of ERO simulations.

On the Effects of Doping on the Catalytic Performance of (La,Sr)CoO3. A DFT Study of CO Oxidation

The effects of modifying the composition of LaCoO3 on the catalytic activity are predicted by density functional calculations. Partially replacing La by Sr ions has benefical effects, causing a lowering of the formation energy of O vacancies. In contrast to that, doping at the Co site is less effective, as only 3d impurities heavier than Co are able to stabilize vacancies at high concentrations. The comparison of the energy profiles for CO oxidation of undoped and of Ni-, Cu-m and Zn-doped (La,Sr)CoO3(100) surface shows that Cu is most effective. However, the effects are less spectacular than in the SrTiO3 case, due to the different energetics for the formation of oxygen vacancies in the two hosts.

The manifestation of excitons in low-temperature luminescence spectra of solid solutions of zinc and nickel oxides

The X-ray luminescence spectra of Zn1–xNixO solid solutions of a number of compositions, including nickel oxide (x = 1), were studied in the vicinity of I1 and I2 lines with energies of 3.339 and 3.393 eV. A strong temperature dependence of these lines, similar to that which occurred during observation of donor and acceptor excitons of 3d impurities in compounds II–VI:3d, as well as a change in the intensity ratio with an increase in temperature and different decay kinetics, were found earlier, which made it possible to link the origin of I1 and I2 lines with radiative decay of excitons of various natures. Based on the results obtained in the work, it was confirmed that the band gap width of these compounds does not depend on the composition of the solutions (i.e., on the concentration x), and a set of nickel states, both d and s types, is found in NiO near the conduction band bottom. Based on the analysis of the electron energy spectrum calculated for the studied Zn1–xNixO solid solutions, it was established that one of the observed lines of the X-ray luminescence spectrum is associated with an exciton of s–p type, and the other one—with an exciton of p–d type.The X-ray luminescence spectra of Zn1–xNixO solid solutions of a number of compositions, including nickel oxide (x = 1), were studied in the vicinity of I1 and I2 lines with energies of 3.339 and 3.393 eV. A strong temperature dependence of these lines, similar to that which occurred during observation of donor and acceptor excitons of 3d impurities in compounds II–VI:3d, as well as a change in the intensity ratio with an increase in temperature and different decay kinetics, were found earlier, which made it possible to link the origin of I1 and I2 lines with radiative decay of excitons of various natures. Based on the results obtained in the work, it was confirmed that the band gap width of these compounds does not depend on the composition of the solutions (i.e., on the concentration x), and a set of nickel states, both d and s types, is found in NiO near the conduction band bottom. Based on the analysis of the electron energy spectrum calculated for the studied Zn1–xNixO solid solutions, it was establi...

Effect of Impurities on the Formation Energy of Point Defects in the γ-TiAl Alloy

The projector augmented-wave method within density functional theory is used to study the effect of 4d elements and Group IIIA and IVA elements on the energetics of point defect formation and elastic moduli of the γ-TiAl alloy. To calculate the point defect formation energy, the grand canonical formalism was used. It is shown that the formation energy of aluminum vacancies decreases by approximately 1.3 eV with increasing its content in the series of alloys Ti3Al–TiAl–TiAl3, whereas the formation energy of titanium vacancies changes insignificantly. In general, the formation of titanium vacancies in these alloys is preferred to the formation of aluminum vacancies. It has been found that Nb, Mo, Tc, Ru, Rh, and Pd impurities on the aluminum sublattice contribute to an increase in the formation energy of an aluminum vacancies, and Mo and Tc also lead to an increase in the formation energy of titanium vacancies. All 4d impurities, if they substitute for titanium, reduce the formation energy of aluminum vacancies, and Nb and Mo are favorable for increasing the formation energy of titanium vacancies. The influence of impurities on the chemical bond in the γ-TiAl alloy and its elastic moduli and characteristics based on them is discussed.