Hf Atoms Research Articles

First principles study of structural, electronic and optical properties of perovskites CaZrO3 and CaHfO3 in cubic phase

In this work, we present the first principles calculations for structural, electronic and optical properties of perovskites CaZrO3 and CaHfO3 using the full-potential linearized augmented plane wave method (FP-LAPW) within the framework of density functional theory (DFT) as implemented in WIEN2k package. The exchange-correlation potential is treated with local density approximation (LDA) and generalized gradient approximation (GGA-PBE and PBESol). Additionally, the Tran Blaha modified Becke-Johnson exchange potential (mBJ) also is employed for electronic and optical calculations due to that it gives very accurate band gap of solids. Our obtained structural parameters are in good agreement with experimental datas and other theoretical results. The energy band gap obtained with mBJ is 4.56 eV for CaZrO3 and 5.27 eV for CaHfO3. The hybridization of states of O atom with those of Zr and Hf atoms in CaZrO3 and CaHfO3, respectively, is observed. The spin-orbit coupling effect on electronic properties of considered compounds also is investigated. Finally, the linear optical properties of CaZrO3 and CaHfO3 are derived from their complex dielectric function calculated with mBJ potential for wide energy range up to 45 eV, and all of them analyzed in details.

Effect of laser conditioning on nanoprecursor for improving laser damage resistance of HfO2 coatings

An experimental and analytical approach is described to investigate the effect of laser conditioning on the nanoprecursor of the Hf cluster for improving the damage resistance of HfO2 coatings. Two test methods of 1-on-1 and R-on-1 (usually, R-on-1 is referred to as laser conditioning) were employed to measure the damage probabilities of samples of HfO2 coating. In addition, the measured damage probabilities of 1-on-1 and R-on-1 were compared with the simulations based on Mie scatter theory, heat transfer and damage probability calculation to determine the size distribution of the nanoprecursor of the Hf cluster, which indicates the decrease in their sizes. X-ray photoelectron spectroscopy analysis reveals that laser conditioning has increased the relative oxygen content, which implies that a portion of Hf atoms in the nanoprecursors are oxidized to HfO2 due to O atoms from the decomposed water and air, with a resulting decrease in their size and absorption and an increase in their laser damage threshold. The experimental and simulative results indicate that the size decrease and distribution variation of the Hf clusters may be another one of the mechanisms for laser conditioning to increase the damage resistance of HfO2 coatings.

Role of the Counteranion in the Reaction Mechanism of Propylene Polymerization Catalyzed by a (Pyridylamido)hafnium(IV) Complex

We studied the stereoselective propylene polymerization catalyzed by the ion pair (IP) active species of (pyridylamido)hafnium(IV) complex, the catalyst. In particular, we focused on the role of the counteranion (CA) for the reaction mechanism of propylene insertion because it had never been investigated from the molecular point of view. First, we searched for a variety of IP configurations by the molecular dynamics (MD) method and quantum chemical calculation, and located the transition states (TSs) of propylene insertion. By comparing the CA-bound catalysts with the isolated ones, it was revealed that the manner of energetically favorable insertion is interestingly altered due to the location of the CA. Next, we showed that the CA is essential to determine the coordination structures of the Hf atom at transition state. Therefore, it was concluded that the role of the CA is critical to accurately control the polymerization mechanism. Finally, we proposed a synthesis experiment which would be advantageous...

Electronic structures and optical properties of HfO2–TiO2 alloys studied by first-principles GGA + U approach**Project supported by the National Natural Science Foundation of China (Grant Nos. 11672087, 11502058, and 11402252).

The phase diagram of HfO2–TiO2 system shows that when Ti content is less than 33.0 mol%, HfO2–TiO2 system is monoclinic; when Ti content increases from 33.0 mol% to 52.0 mol%, it is orthorhombic; when Ti content reaches more than 52.0 mol%, it presents rutile phase. So, we choose the three phases of HfO2–TiO2 alloys with different Ti content values. The electronic structures and optical properties of monoclinic, orthorhombic and rutile phases of HfO2–TiO2 alloys are obtained by the first-principles generalized gradient approximation (GGA)+U approach, and the effects of Ti content and crystal structure on the electronic structures and optical properties of HfO2–TiO2 alloys are investigated. By introducing the Coulomb interactions of 5d orbitals on Hf atom (), those of 3d orbitals on Ti atom (), and those of 2p orbitals on O atom (Up) simultaneously, we can improve the calculation values of the band gaps, where , , and Up values are 8.0 eV, 7.0 eV, and 6.0 eV for both the monoclinic phase and orthorhombic phase, and 8.0 eV, 7.0 eV, and 3.5 eV for the rutile phase. The electronic structures and optical properties of the HfO2–TiO2 alloys calculated by (Up = 6.0 eV or 3.5 eV) are compared with available experimental results.

Hafnium Impurity Defects in Silicon: A Characterization

The aim of this work is to characterize the electrical properties of the defects induced by hafnium (Hf) contamination in silicon by means of different experimental techniques. Hf is introduced in silicon by shallow ion implantation at low doses in order to match experimental conditions close to an accidental contamination; moreover annealing is performed in RTP, that allows to maintain the metallic contaminant in solution. During the annealing the most part of Hf atoms segregate at the SiO2/Si interface, increasing the density of interface states. A detectable part of Hf atoms diffuse through the silicon bulk producing generation and recombination centers and traps for holes and electrons. Eight levels are detected, six in the upper and two in the lower half of the silicon bandgap, respectively. Hf acts differently in p- or n-type substrates: it is more effective as hole trap and as a recombination center in p-type and it de-activates above an implanted dose of 3 × 1011 cm−2 only in p-type silicon. The accurate determination of Hf-induced defects even at low concentration allows to find and pinpoint possible hafnium contamination affecting electronic devices.

Effect of structural defects on electronic and magnetic properties in pristine and Cr-doped HfS2 monolayer

Based on density functional theory, we investigate electronic and magnetic properties of pristine and Cr-doped monolayer HfS2 with vacancy defects. Nine possible vacancy defects types are considered. The results show that one hafnium (Hf) atom vacancy defect at monolayer HfS2 (V1Hf) will induces to 1.824μB magnetic moment and shows magnetic metallic property and the magnetic moments mainly comes from the nearest six S atom p orbitals. For two Hf atoms vacancy defects (V2Hf), the magnetic moment vanishes and the system shows semiconductor property. For the case of sulfur vacancy defects (VnS, n = 2, 3), all of these systems show magnetic metallic properties, and the total magnetic moment increases with increasing S vacancy defected atoms. When Hf+6S atoms are removed, the system is a magnetic metal with 0.501μB magnetic moment. In addition, we find 2V2S and 1V3S have the most stable structures when two and three S atoms are removed, respectively. When one Cr atom substitutes Hf atom in V1Hf, 2V2S and 1V3S systems (2Cr + V2S, 1Cr + V3S), 2.332μB, 2.806μB and 3.501μB magnetic moments are introduced, respectively. Cr atom is antiferromagnetic coupling to the nearest S atoms. These results show that S vacancy defects induce the charge redistribution of the nearest Hf atoms and appear the large charge polarization, thereby forming the larger local magnetic moment.

Nanoscale Metal–Organic Layers for Deeply Penetrating X‐ray‐Induced Photodynamic Therapy

AbstractWe report the rational design of metal–organic layers (MOLs) that are built from [Hf6O4(OH)4(HCO2)6] secondary building units (SBUs) and Ir[bpy(ppy)2]+‐ or [Ru(bpy)3]2+‐derived tricarboxylate ligands (Hf‐BPY‐Ir or Hf‐BPY‐Ru; bpy=2,2′‐bipyridine, ppy=2‐phenylpyridine) and their applications in X‐ray‐induced photodynamic therapy (X‐PDT) of colon cancer. Heavy Hf atoms in the SBUs efficiently absorb X‐rays and transfer energy to Ir[bpy(ppy)2]+ or [Ru(bpy)3]2+ moieties to induce PDT by generating reactive oxygen species (ROS). The ability of X‐rays to penetrate deeply into tissue and efficient ROS diffusion through ultrathin 2D MOLs (ca. 1.2 nm) enable highly effective X‐PDT to afford superb anticancer efficacy.

Nanoscale Metal–Organic Layers for Deeply Penetrating X‐ray‐Induced Photodynamic Therapy

We report the rational design of metal-organic layers (MOLs) that are built from [Hf6 O4 (OH)4 (HCO2 )6 ] secondary building units (SBUs) and Ir[bpy(ppy)2 ]+ - or [Ru(bpy)3 ]2+ -derived tricarboxylate ligands (Hf-BPY-Ir or Hf-BPY-Ru; bpy=2,2'-bipyridine, ppy=2-phenylpyridine) and their applications in X-ray-induced photodynamic therapy (X-PDT) of colon cancer. Heavy Hf atoms in the SBUs efficiently absorb X-rays and transfer energy to Ir[bpy(ppy)2 ]+ or [Ru(bpy)3 ]2+ moieties to induce PDT by generating reactive oxygen species (ROS). The ability of X-rays to penetrate deeply into tissue and efficient ROS diffusion through ultrathin 2D MOLs (ca. 1.2 nm) enable highly effective X-PDT to afford superb anticancer efficacy.

Effect of component substitution on the atomic dynamics in glass-forming binary metallic melts

We investigate the substitution of early transition metals (Zr, Hf, and Nb) in Ni-based binary glass-forming metallic melts and the impact on structural and dynamical properties by using a combination of neutron scattering, electrostatic levitation (ESL), and isotopic substitution. The self-diffusion coefficients measured by quasielastic neutron scattering (QENS) identify a sluggish diffusion as well as an increased activation energy by almost a factor of 2 for Hf35Ni65 compared to Zr36Ni64. This finding can be explained by the locally higher packing density of Hf atoms in Hf35Ni65 compared to Zr atoms in Zr36Ni64, which has been derived from interatomic distances by analyzing the measured partial structure factors. Furthermore, QENS measurements of liquid Hf35Ni65 prepared with 60Ni, which has a vanishing incoherent scattering cross section, have demonstrated that self-diffusion of Hf is slowed down compared to the concentration weighted self-diffusion of Hf and Ni. This implies a dynamical decoupling between larger Hf and smaller Ni atoms, which can be related to a saturation effect of unequal atomic nearest-neighbor pairs, that was observed recently for Ni-rich compositions in Zr-Ni metallic melts. In order to establish a structure-dynamics relation, measured partial structure factors have been used as an input for mode-coupling theory (MCT) of the glass transition to calculate self-diffusion coefficients for the different atomic components. Remarkably,MCT can reproduce the increased activation energy for Hf35Ni65 as well as the dynamical decoupling between Hf and Ni atoms.

Photophysical Features of Phthalocyanines Metallocomplexes with Out-of-Plane Ligands

The objective of this work was synthesizing of Ti-, Zr-, Hf-phthalocyanines, containing chloride ions or dibenzoylmethanate fragments coordinated in out-of-plane positions to macrocycle. Spectroscopic and photophysical parameters of phthalocyanines metallocomplexes with metal atoms Ti(IV), Zr(IV) and Hf(IV) and spectroscopic features of Mg- and Zn-phthalocyanines have been detected and characterized at ambient and liquid nitrogen temperatures. The efficient intersystem crossing observed for Hf-phthalocyanine leads to very weak fluorescence and suppresses the fluorescence lifetimes to less than 1 ns. Changing of nature of central metals from heavy Hf(IV) atom to lighter atoms: Zr(IV), Zn(II), Ti(IV), Mg(II) lead to noticeable increasing of fluorescence lifetimes up to maximum value of 6,6 ns for Mg-phthalocyanine. At the same time the values of fluorescence quantum yield rises from 1 % for Hf-phthalocyanine to 56 % for Mg-phthalocyanine. The heavy atom effect has a substantially greater impact on photophysical parameters metallocomplexes of phthalocyanines than influence of attachment out-of-plane ligands.

Hyperfine interaction study of pressure induced phase transformations in Hafnia

Time Differential Perturbed Angular correlation (TDPAC) study of pressure dependent phase transition in HfO2 has been performed for the first time to reveal the change in local structure around Hf atom. The results show that the nuclear hyperfine interaction parameters namely, quadrupole interaction frequency and asymmetry parameter at atmospheric pressure are in agreement with literature while that at 45 GPa are significantly different from that at atmospheric pressure.

Ferroelectric of HfO2 dielectric layer sputtered with TiN or ZrN for sandwich-like metal-insulator-metal capacitors

In this study, metal-insulator-metal (MIM) capacitors, which use HfO2 as the intermediate insulating layer, and TiN or ZrN as the upper/lower capping layers were fabricated to form the sandwich-like structures, i.e. Al/TiN/HfO2/TiN/Mo/p-Si and Al/ZrN/HfO2/ZrN/Mo/p-Si. The crystallization of high-k HfO2 thin-film is induced by high power impulse magnetron sputtering (HIPIMS) during the deposition of TiN and/or ZrN capping layers. The ferroelectric performance became better in both two structures as the thickness of metal nitride layer decreased. As the rapid thermal annealing (RTA) temperature after TiN layer deposition increased, the ferroelectric performance of the structure with TiN layer became better. On the other hand, the structure with ZrN layer exhibited opposite trends. According to X-ray diffraction (XRD) measurement, both TiN and ZrN layers offered stress and produced orthorhombic phase on HfO2 layer. Both two layers at any thicknesses also protected Mo layer from the invasion of Hf atoms. The structure with TiN layer exhibited a higher remanent polarization (Pr) value as the roughness of TiN layer increased. However, the higher the roughness that the structure with ZrN layer had, the worse the ferroelectric performance obtained.

Effect of Trace Element Hf on the Precipitation Process and Recrystallization Resistance of Al-Er-Zr Alloys

Vickers hardness and electric conductivity measurements as well as micro-structure analysis were used to investigate the effects of trace element Hf atoms on the precipitation and recrystallization resistance in Al-Er-Zr alloys. The results of the present study indicated that the behaviors of precipitation process in Al-0.04Er-0.08Zr and Al-0.04Er-0.08Zr-0.05Hf (at. %) alloys are similar. When alloys were annealed at 350 °C for 96h, the nanoscale and coherent Al3(Er, Zr) and Al3(Er, Zr, Hf) precipitates form, corresponding to the peak hardness values of 56.2 ± 0.9 (ternary alloy), 58.9 ± 1.5 HV (quaternary alloy), respectively. The higher peak hardness in Al-0.04Er-0.08Zr-0.05Hf alloys mainly benefit from the decomposition of Hf. It was shown that the existence of precipitates could improve the recrystallization resistance obviously. Due to the similar retarding force, recrystallization temperatures of both alloys are almost the same, approximate 450 °C.

Double and Triple Si-H-M Bridge Bonds: Matrix Infrared Spectra and Theoretical Calculations for Reaction Products of Silane with Ti, Zr, and Hf Atoms.

Infrared spectra of matrix isolated dibridged Si(μ-H)2MH2 and tribridged Si(μ-H)3MH molecules (M = Zr and Hf) were observed following the laser-ablated metal atom reactions with SiH4 during condensation in excess argon and neon, but only the latter species was observed with titanium. Assignments of the major vibrational modes, which included terminal MH, MH2 and hydrogen bridge Si-H-M stretching modes, were confirmed by the appropriate SiD4 isotopic shifts and density functional vibrational frequency calculations (B3LYP and BPW91). The Si-H-M hydrogen bridge bond is calculated as weak covalent interaction and compared with the C-H···M agostic interaction in terms of electron localization function (ELF) analysis and noncovalent interaction index (NCI) calculations. Furthermore, the different products of Ti, Zr, and Hf reactions with SiH4 are discussed in detail.

Synthesis, X-ray structure and reactivity of the vinyl-terminated iron(II) clathrochelate precursors and their cage derivatives with non-equivalent capping groups

A novel vinyl-terminated boron, antimony-capped iron(II) tris-dimethylglyoximate with labile triethylantimony cross-linking group was prepared using two-step synthetic procedure including template condensation of dimethylglyoxime and triethylantimony(V) dibromide on an iron(II) ion as a matrix followed by transmetallation with 4-vinylphenyl boronic acid. This labile clathrochelate precursor and its bis-methoxyboron-capped analog underwent the same capping group exchange (transmetallation) reactions with more strong Lewis acids, such as trigonal boron compounds or hafnium(IV) phthalocyaninate (HfPc), giving the macrobicyclic iron(II) tris-dimethylglyoximates with non-equivalent capping groups and a binuclear HfPc-capped phthalocyaninoclathrochelate, respectively. The complexes obtained were characterized using elemental analysis, 1H and 13C{1H} NMR, MALDI-TOF MS, IR and UV–vis data as well as by single crystal X-ray diffraction. The number, positions and multiplicity of the signals in the solution 1H and 13C{1H} NMR spectra of these clathrochelates as well as the ratios of their integral intensities in 1H NMR spectra confirmed the composition and symmetry of the macrobicyclic molecules, suggesting the presence of their molecular C3 symmetry pseudoaxis. In the 1H NMR spectrum of a hybrid phthalocyanine-capped cage complex, the π-electron current in its apical macroheterocyclic fragment caused the substantial high-field shifts of the signals of protons of the ribbed methyl substituents because their nuclei are located in its shielding region. Single crystal X-ray diffraction data for the monovinyl-terminated mixed Sb, B- and Hf, B-capped iron(II) cage complexes suggest that their FeN6-coordination polyhedra possess the geometry of a rotationally distorted truncated trigonal pyramid that is close to intermediate between a trigonal prism and a trigonal antiprism with slightly expanded trigonal bases, which are connected with a heavy (Sb or Hf) atom. The encapsulated iron(II) ion is slightly shifted from the center of these polyhedra in the direction of such capping atom.

Molecular structure, vibrational, HOMO-LUMO, MEP and NBO analysis of hafnium selenite

In hydrothermal condition hafnium selenite with estimated chemical composition Hf(SeO3)2·n(H2O) was obtained and characterized by powder X-Ray diffraction, IR spectroscopy and thermogravimetrical analysis. The composition of the obtained crystalline phase was established as dihydrate of tetraaqua complex of the hafnium selenite [Hf(SeO3)2(H2O)4]·2H2O. The results of the thermogravimetrical analysis are shown that the two hydrated water molecules are released in the temperature interval 80–110°С, while the four coordinated water molecules – at 210–300°С. By DFT method, with Becke's three parameter exchange-functional combined with gradient-corrected correlation functional of Lee, Yang and Parr and 6-31G(d), 6-311 + G(d,p) basis sets and LANL2DZ for Hf atom were calculated the molecular structure, vibrational frequencies and thermodynamic properties of the structure. The UV–Vis spectra and electronic properties are presented. The energy and oscillator strength calculated by time-dependent density functional theory corresponds well with the experimental ones. Molecular electrostatic potential (MEP) was performed. Mulliken population analysis on atomic charges was also calculated. The stability and intramolecular interactions are interpreted by NBO analysis.

Unusual magnetotransport from Si-square nets in topological semimetal HfSiS

The class of topological semimetals comprises a large pool of compounds. Together they provide a wide platform to realize exotic quasiparticles for example Dirac, nodal line Dirac and Weyl fermions. In this letter, we report the Berry phase, Fermi surface topology and anisotropic magnetoresistance of HfSiS which has recently been predicted to be a nodal line semimetal. This compound contains large carrier density, higher than most of the known semimetals. Massive amplitudes of de Haas-van Alphen and Shubnikov-de Haas oscillations up to 20 K in 7 T assist us in witnessing nontrivial pi-Berry phase which is a consequence of topological Dirac-type dispersion of bands originating from the hybridization of px + py and dx2-y2 orbitals of square-net plane of Si and Hf atoms, respectively. Furthermore, we establish the 3D Fermi-surface which consists of very asymmetric water caltrop-like electron and barley seed-like hole pockets which account for the anisotropic magnetoresistance in HfSiS.

First-principles study of new quaternary Heusler compounds without 3d transition metal elements: ZrRhHfZ (Z = Al, Ga, In)

Plane-wave pseudo-potential methods based on density functional theory are employed to investigate the electronic structures, and the magnetic and half-metallic properties of the newly designed quaternary Heusler compounds ZrRhHfZ (Z = Al, Ga, In) without 3d transition metal elements. The calculated results show that ZrRhHfZ (Z = Al, Ga, In) compounds are half-metallic, with 100% spin polarization around the Fermi level. The structural stability of these compounds has been tested from the aspects of their cohesion energy and formation. The spin-flip/half-metallic gaps of ZrRhHfZ (Z = Al, Ga, In) compounds are quite large, with values of 0.2548 eV, 0.3483 eV, and 0.2866 eV, respectively. These compounds show Slater-Pauling behavior, and the total spin magnetic moment per unit cell (Mt) scales with the total number of valence electrons (Zt) following the rule: Mt = Zt − 18. The magnetization of ZrRhHfZ (Z = Al, Ga, In) compounds mainly comes from the 4d electrons of the Zr atoms and the 5d electrons of the Hf atoms. Furthermore, the effects of uniform strain and tetragonal deformation on the half metallicity has been investigated in detail, which is important for practical application. Finally, we reveal that the half-metallicity can be maintained when the Coulomb interactions are considered.

Features of the band structure and conduction mechanisms of n-HfNiSn heavily doped with Y

The crystalline and electronic structures, energy, kinetic, and magnetic characteristics of n-HfNiSn semiconductor heavily doped with Y acceptor impurity are studied in the ranges: T = 80–400 K, N A Y ≈ 1.9 × 1020–5.7 × 1021 cm–3 (x = 0.01–0.30), and H ≤ 10 kG. The nature of the mechanism of structural defect generation is determined, which leads to a change in the band gap and the degree of semiconductor compensation, the essence of which is the simultaneous reduction and elimination of structural donor-type defects as a result of the displacement of ~1% of Ni atoms from the Hf (4a) site, and the generation of structural acceptor-type defects by substituting Hf atoms with Y atoms at the 4a site. The results of calculations of the electronic structure of Hf1–x Y x NiSn are in agreement with the experimental data. The discussion is performed within the Shklovskii–Efros model of a heavily doped and compensated semiconductor.

First-principles studies of the influences mechanism of Y, Hf elements on the high temperature oxidation of γ-TiAl alloys

The influences mechanisms of Y, Hf elements on the high temperature oxidation of γ-TiAl alloys were studied by using a first-principle plane wave pseudopotential method within the density functional theory. It is shown that Y, Hf atoms segregate to the γ-TiAl surface by substituting Ti atoms, and Y atom is easier to segregate than Hf. Y, Hf atoms segregated at γ-TiAl surface decrease the adhesion of O and γ-TiAl surface, which decreases the oxidation rate of γ-TiAl alloys and thereby hinders the growth of oxide films. The electron structure calculations suggest that the interaction between O and Ti, Al, Y, Hf atom exists both ionic and covalent binding characteristics, the decrease of the adhesion of O and γ-TiAl surface with the doped Y, Hf is mainly attributed to the weaken covalent interactions. As a result, the results obtained by first principles can make us get a deeper understanding of the mechanism of the segregation of Y, Hf to the γ-TiAl surface and the influence mechanism of surface active elements Y, Hf on the initial oxidation of γ-TiAl alloys.