Mössbauer study of gamma‴-iron nitride film

A single-phase γ?-FeN film with the rock-salt structure was produced by pulsed laser deposition of Fe onto an Al substrate in a N₂ atmosphere. Its Mössbauer spectra and powder X-ray diffraction patterns were measured. γ?-FeN was found to be antiferromagnetic exhibiting a hyperfine magnetic field of 30 T at a temperature of 5 K. It was found to have a Néel temperature of 220 K. A minor component with a higher hyperfine magnetic field of 49 T at 5 K was also observed. It is thought to originate from defects in γ?-FeN.     

CEMS study on diluted magneto titanium oxide films prepared by pulsed laser deposition

6% ⁵⁷Fe doped titanium oxide films, prepared by pulsed laser deposition (PLD) on sapphire substrate at 650°C under various vacuum conditions, were characterized mainly by conversion electron Mössbauer spectrometry (CEMS). Two magnetic sextets with hyperfine fields 33 and 29 T, and one doublet were observed in the CEMS spectra of TiO₂ films prepared under PO₂ = 10^?6 and 10^?8 torr, which showed ferromagnetism at room temperature, whereas only the doublet of paramagnetic Fe³⁺ species was observed for the film prepared under PO₂ = 10^?1 torr.     

Identification of optimal ALD process conditions of Nd2O3 on Si by spectroscopic ellipsometry

Variable angle spectroscopic ellipsometry (VASE) is used to investigate the thickness and optical properties of Nd₂O₃ films deposited by atomic layer deposition (ALD) at various process conditions. It is found that the films exhibit good thickness uniformity and an almost constant growth rate of 0.42 ?/cycle in the temperature region of 290–330 °C. Further examination of the imaginary part of the dielectric functions of the selected samples demonstrates that all optically observable dielectric-related defects are located in the interface layer between the silicon substrate and the native oxide rather than in the bulk Nd₂O₃ layer. And, the defects within the band gap of the interface are found to be strongly affected by the deposition temperature. In the deposition temperature range of 300–320 °C, only one absorption peak of 3.53 eV besides the silicon substrate’s critical features is observed, indicating that the Si/SiO₂/Nd₂O₃ stacks contain the fewest interfacial defects. Then the optimal ALD process condition for Nd₂O₃ is determined as Nd(thd)₃ (thd = 2,2,6,6,-tetramethyl-3,5-heptanedionato) evaporation temperature: 185 °C, deposition temperature: 300–320 °C, saturation condition: Nd(thd)₃ and pulse time longer than 0.5 s.     

57Fe conversion electron Mössbauer spectrometric study of boron and carbon ion implanted irons

Amorphous layers produced at the surface of iron by B⁺ and C⁺ implantation (50 kV, 1×10¹⁸ ions cm⁻²) were analyzed by CEMS. The CEM spectrum of B⁺ implanted layer was composed of broad doublet and sextet. Spread hyperfine field distribution, P(H), indicates the formation of extremely disordered FeB layer. Annealing at 400°C brought about precipitation of FeB, which was converted to Fe₂B by annealing at 500°C. The P(H) for C⁺ implanted iron was resolved to 3 subpeaks with H values of 11.0, 18.0 and 22.5 T. The amorphous FeC phase was strongly correlated to crystalline Fe₅C₂ and Fe₂C, which precipitated at 300°C and were transformed into Fe₃C at 500°C. The amorphous layer disappeared by annealing at 600°C.     

New mineralogical phases identified by Mössbauer measurements in Morasko meteorite

The 0.9FeTiO₃–0.1Fe₂O₃ solid solution was prepared by solid state reaction with FeTiO₃ and α-Fe₂O₃ powders, and studied by x-ray diffraction, Mössbauer spectroscopy, and vibrating sample magnetometer (VSM). The crystalline structure was found to be single phase rhombohedral structure with lattice constant a?=?5.089 Å and c?=?14.051 Å. Mössbauer spectra of 0.9FeTiO₃–0.1Fe₂O₃ solid solution were taken at various temperatures ranging from 4.5 to 300 K. The anomalous absorption curves at low temperature are observed. Mössbauer spectra at 4.5 K was fitted to four six-line hyperfine pattern with magnetic hyperfine fields H _hf?=?504, 424, 115, and 58 kOe, respectively. At 40 K the spectrum shows the mixture of ferromagnetic six-line pattern and paramagnetic two-line and above 50 K it show asymmetry two-line patterns. The fitted curves at room temperature are obtained by superimposing two doublets corresponding to Fe^2?+ and Fe^3?+. The isomer shift δ and quadrupole splitting ΔE _Q of sample are 0.92 and 0.69 mm/s for Fe^2?+ and 0.14 and ??0.29 mm/s for Fe^3?+, respectively. Corresponding relative absorption subspectral areas are 89.2% for Fe^2?+ and 10.8% for Fe^3?+. Magnetization measurements indicate ferromagnetic behaviour with 92 Oe coercivity value at 50 K but at 300 K it show no hysteresis loop.     

Magnetization and Mössbauer studies of 57Fe doped SrCoO3

⁵⁷Fe (1%) doped SrCoO₃ obtained by high-pressure method, has been investigated by magnetization and Mössbauer spectroscopy studies (MS) in the temperature range 4.2 K to 300 K. The ferromagnetic ordering temperature T _C obtained is 272(2) K. Isothermal magnetization curves have been measured at various temperatures, from which the saturation moments (M _sat) have been deduced. The ⁵⁷Fe MS spectra display standard six-line patterns with an isomer shift typical of Fe^3?+? and a very small quadrupole splitting (QS = 0.14(1) mm/s above T _C). The magnetic hyperfine field at 4.2 K is 276(1) kOe. The temperature dependencies of the iron hyperfine field and M _sat (1.83 µ _B at 5 K) are almost identical. This shows that the Fe^3?+? is replacing Co^4?+?, both of the same electronic configuration. They also interact similarly, namely the Fe–Co exchange is almost identical to the Co–Co exchange.     

Reaction and deposition of laser-evaporated iron

Reaction of laser-evaporated iron atom was investigated by Mössbauer spectroscopy and was applied for the production of films. Iron oxide films were produced by laser-deposition of Fe metal and hematite solid onto Al substrates, and the compositions of the films changed depending on the pressure of the O₂ atmosphere and the temperature of the substrates. The spin orientations of α-Fe films deposited by three types of deposition methods were compared. The nuclear spin of iron films produced by deposition of Fe atoms vaporized by resistive heating was perpendicular to the substrate surface, while that of films produced by laser-deposition of Fe was parallel to the substrate surface. The nuclear spins of iron films produced using an arc-plasma-gun were linear orientations along nanometer-sized grooves on the Al substrate surface.     

Interrelatedness of Fe composition on structural and magnetic properties in Fe-doped SrRuO3 thin films

Fe-doping (up to 11 mole%) into SrRuO₃ (SRO) thin films on SrTiO₃ substrates decreased correlation lengths of both surface and interface. It turned out that Fe was doped in the valence state of 3+ without formation of the Fe₂O₃ phase, which caused orthorhombic distortion. T _C values decreased from 145 K to 97 K with increasing Fe concentration (C _Fe). High magnetic switching fields were observed for all Fe-doped SRO thin films and their strengths showed a linear relationship with C _Fe. Detail structural characterization using synchrotron X-ray diffraction and X-ray photoemission spectroscopy were used to understand its unique magnetic switching field properties.     

High-rate reactive magnetron sputtering of zirconia films for laser optics applications

ZrO₂ exhibits low optical absorption in the near-UV range and is one of the highest laser-induced damage threshold (LIDT) materials; it is, therefore, very attractive for laser optics applications. This paper reports explorations of reactive sputtering technology for deposition of ZrO₂ films with low extinction coefficient k values in the UV spectrum region at low substrate temperature. A high deposition rate (64 % of the pure metal rate) process is obtained by employing active feedback reactive gas control which creates a stable and repeatable deposition processes in the transition region. Substrate heating at 200 °C was found to have no significant effect on the optical ZrO₂ film properties. The addition of nitrogen to a closed-loop controlled process was found to have mostly negative effects in terms of deposition rate and optical properties. Open-loop O₂ gas-regulated ZrO₂ film deposition is slow and requires elevated (200 °C) substrate temperature or post-deposition annealing to reduce absorption losses. Refractive indices of the films were distributed in the range n = 2.05–2.20 at 1,000 nm and extinction coefficients were in the range k = 0.6 × 10^?4 and 4.8 × 10^?3 at 350 nm. X-ray diffraction analysis showed crystalline ZrO₂ films consisted of monoclinic + tetragonal phases when produced in Ar/O₂ atmosphere and monoclinic + rhombohedral or a single rhombohedral phase when produced in Ar/O₂ + N₂. Optical and physical properties of the ZrO₂ layers produced in this study are suitable for high-power laser applications in the near-UV range.     

Structural, magnetic and electrical transport properties of the La0.70Sr0.30Mn0.96 57Fe0.04O3 + δ perovskite

The perovskite La_0.70Sr_0.30Mn_0.96 ⁵⁷Fe_0.04O_3?+?δ compound has been investigated. The sample showed orthorhombic structure of Pbmn symmetry. Room temperature (RM) as well as low temperature (77 K) Mössbauer measurements indicate superparamagnetic character. Electrical investigations showed that the sample exhibits semiconductor-metal transition at 180 K. The behavior of the electrical and magnetic properties could be interpreted on the basis of the obtained hyperfine structure of the doped iron rich at 300 and at 77 K.     

Enhancement of in-plane magnetic anisotropy in (111)-oriented Co0.8Fe2.2O4 thin film by deposition of PZT top layer

The CoFe₂O₄ and Co_0.8Fe_2.2O₄ single layer (CFO) as well as PZT/CoFe₂O₄ and PZT/Co_0.8Fe_2.2O₄ bilayer thin films were grown using the pulsed laser deposition technique on Pt(111)/Si substrates at 600 °C. All films had a perfect (111)-orientation and the degree of orientation of CFO films was improved by the deposition of a PZT top layer. Precision X-ray diffraction analysis (avoiding the shift of peaks due to sample misalignment) revealed that the CFO films on Pt(111)/Si substrate were under an out-of-plane contraction and the deposition of a PZT top layer led to the increase in the out-of-plane contraction. The (111)-oriented CFO single layer films had a strong in-plane magnetic anisotropy as a result of orientation as well as the stress-induced magnetic anisotropy. The magnetic properties of CFO film were altered by the deposition of a PZT top layer leading to the enhancement of in-plane magnetic anisotropy. The enhanced in-plane magnetic anisotropy was more detectable in PZT/Co_0.8Fe_2.2O₄ rather than PZT/CoFe₂O₄ bilayer film, which could be expected from its higher magnetocrystalline as well as magnetostriction constants.     

Hematite thin films: growth and characterization

We have grown hematite (α–Fe ₂ O ₃) thin films on stainless steel and (001)-silicon single-crystal substrates by RF magnetron sputtering process in argon atmosphere at substrate temperatures from 400 to 800°C. Conversion Electron Mössbauer (CEM) spectra of the sample grown on stainless steel at 400°C exhibit values for hyperfine parameter characteristic of bulk hematite phase in the weak ferromagnetic state. Also, the relative line intensity ratio suggests that the magnetization vector of the polycrystalline film is aligned preferentially parallel to the surface. The X-ray diffraction (XRD) pattern of the polycrystalline thin film grown on steel substrates also corresponds to α–Fe ₂ O ₃. The samples were also analyzed by Atomic Force Microscopy (AFM), those grown on stainless steel reveal a morphology consisting of columnar grains with random orientation, given the inhomogeneity of the substrate surface.     

Structural studies of iron in vitrified toxic wastes

The formation of iron carbides by reactive milling of α-Fe and C powders is reported. The products formed were analyzed by Mössbauer spectroscopy and X-ray diffraction. It was found that iron carbide phases start forming after an incubation period of about 3 h depending on the ball-to-powder weight ratio (BPR). Carbide amounts increased with increasing milling time while α-Fe content decreased. Energy transfer increased with increasing BPR and high BPR resulted in an increase in the reaction rate. Although it was not possible to selectively synthesise a specific Fe _x C phase, samples containing predominantly one type of carbide phase, either Hägg carbide or cementite, were successfully prepared. The formation of the different iron carbide phases is discussed within the context of the Fe–C phase diagram for non-equilibrium processes.     

Rare earth doped cobalt ferrite thin films deposited by PLD

CoFe₂O₄ thin films with preferential texture structure, small grain size, and perpendicular magnetic anisotropy can be obtained by the pulsed laser deposition (PLD) technique. In this work, we studied the influence of the Fe³⁺ ions substitution by three elements from lanthanide group (Dy, La, and Gd) on the structural properties of the thin films. The samples were deposited by Nd:YAG laser (λ=532 nm, 10 ns) ablation of CoFe_1.8RE_0.2O₄, (RE=Dy, La, Gd) targets at various substrate temperatures ranging from room temperature to 600 °C. The microstructure and chemical composition of the thin films were investigated by Raman spectroscopy, XRD, SEM-EDS, and ToF-SIMS. The XRD patterns and Raman spectra of the thin films indicated the formation of a single spinel structure. Thus, the desired substitution of the iron ions in the spinel lattice with the RE elements was achieved in the thin films, although in the bulk material, their presence determined the formation of a residual phase with a perovskite-type structure.     

Physical investigations on pulsed laser deposited nanocrystalline ZnO thin films

The nanocrystalline ZnO thin films were deposited by pulsed laser deposition on quartz and i-Si (100) substrates at different substrate temperatures (473 K–873 K) and at different mixed partial pressures (0.05, 0.01, and 0.5 mbar) of Ar+O₂. The structural studies from XRD spectra reveals that the films deposited at 0.05 mbar and at lower substrate temperatures were c-axis oriented with predominant (002) crystallographic orientation. At 873 K along with (002) orientation, additional crystallographic orientations were also observed in case of films deposited at 0.01 and 0.5 mbar pressures. The composition of Zinc and Oxygen in ZnO films from EDAX reveals that the films deposited at lower partial pressures were have high at.% of O₂ whereas higher partial pressures and substrate temperatures had high at.% Zn. The surface microstructure of the films show that the films deposited at lower partial pressures (0.05 mbar ) and at lower substrate temperatures (473 K) were found to have nanoparticles of size 15 nm where as films deposited at 873 K have nanorods. The length of these nanorods increases with increasing Ar+O₂ partial pressure to 0.5 mbar. The optical energy gap of the film deposited at lower partial pressure and substrate temperature was 3.3 eV and decrease with the increase of substrate temperatures. The films deposited at 0.5 mbar and at 873 K emitted an intense luminescence at a wavelength of 390 nm. The measured thickness of deposited films by spectroscopic ellipsometry is around 456 nm.     

Growth of Fe<Subscript>3</Subscript>O<Subscript>4</Subscript> films on the Si(111) surface covered by a thin SiO<Subscript>2</Subscript> layer

Magnetite polycrystalline films are grown by variously oxidizing a Fe film on the Si(111) surface covered by a thin (1.5 nm) SiO₂ layer. It is found that defects in the SiO₂ layer influence silicidation under heating of the Fe film. The high-temperature oxidation of the Fe film results in the formation of both Fe₃O₄ and iron monosilicide. However, the high-temperature deposition of Fe in an oxygen atmosphere leads to the growth of a compositionally uniform Fe₃O₄ film on the SiO₂ surface. It is found that such a synthesis method causes [311] texture to arise in the magnetite film, with the texture axis normal to the surface. The influence of the synthesis method on the magnetic properties of grown Fe₃O₄ films is studied. A high coercive force of Fe₃O₃ films grown by Fe film oxidation is related to their specific morphology and compositional nonuniformity.     

157 T internal magnetic field in Fe[C(SiMe3)3]2 compound at 20 K

Fe[C(SiMe₃)₃]₂ compound, in which iron is coordinated by two carbons, was prepared using the reaction of FeCl₂ with (Me₃Si)₃CLi, and investigated by XRD, ⁵⁷Fe Mössbauer spectroscopy and DFT calculations. 157.5 T hyperfine magnetic field was found at the site of the iron nucleus of this compound at 20 K. DFT calculations predict the quintet states to be clearly favored energetically over the lower spin states. The population analysis reveals considerable 4s as well as large unpaired 3d electron contributions, which can be responsible for the extremely high hyperfine field.     

Effects of deposition temperature and hydrogen flow rate on the properties of the Al-doped ZnO thin films and amorphous silicon thin-film solar cells

A compound of 98 mol% ZnO and 1 mol% Al₂O₃ (AZO, Al:Zn = 98:2) was sintered at 1350 °C as a target and the AZO thin films were deposited on glass using a radio frequency magnetron sputtering system. The effects of deposition temperature (from room temperature to ～300 °C) on the optical transmission spectrum of the AZO thin films were studied. The Burstein–Moss shift was observed and used to prove that defects in the AZO thin films decreased with increasing deposition temperature. The variations in the optical band gap (E _g) values of the AZO thin films were evaluated from plots of (αhv)²=c(hν?E _g), revealing that the measured E _g values increased with increasing deposition temperature. The effects of the H₂ flow rate during deposition (0 %～11.76 %, deposition temperature of 200 °C) on the crystallization, morphology, resistivity, carrier concentration, carrier mobility, and optical transmission spectrum of the AZO thin films were measured. The chemical structures of the Ar-deposited and 2 % H₂-flow rate-deposited AZO thin films (both were deposited at 200 °C) were investigated by XPS to clarify the mechanism of improvement in resistivity. The prepared AZO thin films were also used as transparent electrodes to fabricate amorphous silicon thin-film solar cells, and their properties were also measured.     

Structural and electrical properties of lithium manganese oxide thin films grown by pulsed laser deposition

LiMn₂O₄ thin films were deposited by reactive pulsed laser deposition technique and studied the microstructural and electrical properties of the films. The LiMn₂O₄ thin films deposited in an oxygen partial pressure of 100 mTorr and at a substrate temperature of 573 K from a lithium rich target were found to be nearly stoichiometric. The films exhibited predominantly (111) orientation representing the cubic spinel structure with Fd3m symmetry. The intensity of (111) peak increased and a slight shift in the peak position was observed with the increase of substrate temperature. The lattice parameter increased from 8.117 to 8.2417 Å with the increase of substrate temperature from 573 to 873 K. The electrical conductivity of the films is observed to be a strong function of temperature. The evaluated activation energy for the films deposited at 873 K is 0.64 eV.     

Giant temperature coefficient of resistance in Co-doped ZnO thin films

A novel high-performance thermistor material based on Co-doped ZnO thin films is presented. The films were deposited by the pulsed laser deposition technique on Si (111) single-crystal substrates. The structural and electronic transport properties were correlated as a function of parameters such as substrate temperature and Co-doped content for Zn_1?x Co _x O (x=0.005,0.05,0.10 and 0.15) to prepare these films. The Zn_1?x Co _x O films were deposited at various substrate temperatures between 20 and 280 °C. A value of 20 %/K for the negative temperature coefficient of resistance (TCR) with a wide range near room temperature was obtained. It was found that both TCR vs. temperature behavior and TCR value were strongly affected by cobalt doping level and substrate temperature. In addition, a maximal TCR value of over 20 %?K^?1 having a resistivity value of 3.6 Ω?cm was observed in a Zn_0.9Co_0.1O film near 260 °C, which was deposited at 120 °C and shown to be amorphous by X-ray diffraction. The result proved that the optimal Co concentration could help us to achieve giant TCR in Co-doped ZnO films. Meanwhile, the resistivities of the films ranged from 0.4 to 270 Ω?cm. A Co-doped ZnO/Si film is a strong candidate of thermometric materials for non-cooling and high-performance bolometric applications.