Mössbauer and x-ray absorption studies in Fe and V co-doped SnO2

Ferromagnetic nanoparticles of iron and vanadium co-doped SnO₂ were synthesized by a sol-gel method. Fe and V co-doped SnO₂ enhanced the magnetization, which showed the maximum saturation magnetization (M_s) at 1 % of Fe and 1 % of V co-doping. With further increasing the amounts of Fe and V co-doping into SnO₂ host, the M_s decreased. Chemical states of vanadium ions were deduced as V⁵⁺ states by x-ray absorption spectroscopy. Mössbauer spectrometry revealed that the intensities of sextet components are related to the M_s, which indicates that small amounts of Fe and V co-doping is effective to enhance M_s.     

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.     

Characterization of iron(III) oxide films used for photoelectrode by means of cems

Thin iron oxides deposited on semi-conductive glass by a spray pyrolysis technique were analysed by Conversion Electron Mössbauer Spectrometry (CEMS). Iron oxide deposited on SnO₂ coated glass was composed of a large grained particles of crystalline α?Fe₂O₃, which showed sextet. The doublet and sextet appeared in CEM spectra of iron oxides deposited on In₂O₃ and WO₃ coated glasses. The sextet was due to α?Fe₂O₃ and the doublet was attributted to the superparamagnetic microcrystalline α?Fe₂O₃ (≈15nm) rather than to spinel compounds of iron. The iron oxide deposited on ZnO coated glass gave a doublet in CEM spectra. It was supporsed to be due to very fine particle of α?Fe₂O₃ (<100nm). It was found that iron oxide films obtained by spray pyrolysis were dependent on the kinds and the temperature of the semi-conductive materials coated on glass.     

57Fe Mössbauer study of sol–gel synthesized Sn1 − x − y Fe x Sb y O2 − δ powders

Samples of SnO₂ doped with different amount of Fe (10–20%) and Sb (5–25%) were prepared by sol–gel method. Room temperature ferromagnetism was found to increase as a result of co-doping with Sb, as compared to SnO₂ doped only with Fe. ⁵⁷Fe Mössbauer spectra of almost all samples exhibited two paramagnetic doublets and a small subspectrum referring to magnetic relaxation at room temperature. Only the samples Sn_0.65Fe_0.2Sb_0.15O_2???δ and Sn_0.85Fe_0.1Sb_0.05O_2???δ with 4 h long annealing time showed well developed sextets and larger magnetic coercivity compared to that of the other samples. The sextet observed was considered to be due to precipitates like Sn doped α-Fe₂O₃. The results suggest that the origin of the magnetic interactions is enhanced by the presence of magnetic defects, which can interact with the iron ions by free carrier electrons. For the sample with precipitates, the grain boundary defects may play an important role of enhanced ferromagnetism.     

Electric field gradient in nanostructured SnO2 studied by means of PAC spectroscopy using 111Cd or 181Ta as probe nuclei

Electric quadrupole interactions were studied in pure and Mn-doped powder samples and thin films of SnO₂ using perturbed γγ angular correlation spectroscopy (PAC). The powder samples were prepared by Sol gel method and the thin film were prepared on the Si (100) substrate by sputtering technique using Sn in the oxygen atmosphere. The samples were characterized by x-ray diffraction, energy dispersive spectroscopy and scanning electron microscopy. The thickness of the film was 100 nm. The average particle size of the SnO₂ powder samples was determined to be smaller than 60 nm. The radioactive ¹¹¹In and ¹⁸¹Hf tracers were introduced in the powder samples during the sol gel chemical process. Radioactive ¹¹¹In was implanted on the SnO₂ thin films using the University of Bonn ion implanter (BONIS). PAC measurements were carried out in a four BaF₂ detector spectrometer in the temperature range of 77–973 K for samples annealed at different temperatures. The PAC results for both nuclear probes show the presence of two electric quadrupole interactions. The major fractions in both cases correspond to the substitutional sites in the rutile phase of SnO₂. The results are compared with previous PAC measurements.     

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.     

Volume of precursor solution effect on the properties of SnO<Subscript>2</Subscript> thin films prepared by nebulized spray pyrolysis technique

Undoped SnO₂ thin films have been deposited on amorphous glass substrates with different precursor solution volume (10, 15, 20 and 25 ml) using simple and cost-effective nebulized spray pyrolysis technique. The influence of precursor solution on structural, optical, photoluminescence and electrical properties had been studied. The X-ray diffraction spectra prove the polycrystalline nature of SnO₂ with tetragonal structure. All the films show a preferred growth orientation along (110) diffraction plane. The average transmittance of SnO₂ thin films varied between 82 and 75% in the visible as well as IR region. The band gap energy decreases from 3.74 to 3.64 eV corresponding to direct transitions with the precursor solution volume had increased from 10 to 20 ml and then increased as 3.72 eV for 25 ml. SEM pictures demonstrated polyhedrons like grains. EDX confirmed the existence of Sn and O elements in all the prepared SnO₂ thin films. Photoluminescence spectra at room temperature revealed that the four emission bands in all the samples such as sharp dominant peak at 361 nm with shoulder peak at 377 nm (UV region), a broad and low intensity peak at 492 nm (blue region) and 519 nm (green region). The electrical parameters were examined by Hall effect measurements, which demonstrated that the film prepared at 20 ml precursor solution volume possess minimum resistivity 2.76?×?10^?3 Ω-cm with activation energy 0.10 eV and maximum figure of merit 1.54?×?10^?2 (Ω/sq)^?1.     

Investigation of characteristic properties of Pr-doped SnO2 thin films

In the present work, an investigation study on the crystal structure, surface morphology, electrical conductivity and optical transparency of spray-deposited Pr-doped SnO₂ was made as a function of Pr doping content. The X-ray diffraction studies indicated that the films were grown at the (2 1 1) preferential orientation. The values of crystallite size and strain were determined using Williamson–Hall method and they varied between 71.47 and 208.76 nm, and 1.98 × 10^?3 – 2.78 × 10^?3. As seen from Scanning Electron Microscope micrographs, the films were composed of homogenous dispersed pyramidal-shaped grains. The n-type conductivity of films was confirmed with Hall Effect measurements, and the best electrical parameters were found for 3 at.% Pr doping level. The highest optical band gap and transmittance values were observed for undoped SnO₂ sample. The highest figure of merit (Φ), which is a significant parameter to interpret the usage efficiency of conductive and transparent materials in the optoelectronic and solar cell applications, was calculated to be 2.85 × 10^?5 Ω^?1 for 1 at.% Pr doping content. As a result of this study, it may be concluded that Pr-doped SnO₂ films with above properties can be used as a transparent conductor in various optoelectronic applications.     

Electric field gradients at 151Eu sites in GaN

The electric field gradients at Eu sites in GaN have been investigated in conversion electron Mössbauer spectroscopy (CEMS) in which ¹⁵¹Eu probe ions were implanted into an undoped GaN layer grown on a sapphire substrate. The sample was implanted with 120 keV ¹⁵¹Eu ions to a fluence of 1 × 10¹⁵, and annealed at 1,200 K. CEMS spectra of the ¹⁵¹Eu 21.6 keV transition were collected, of the GaN sample as well as of a Si sample implanted with overlapping profiles of ¹⁵¹Eu and O. The GaN spectra were fitted with two symmetric doublets, D1 and D2, with isomer shifts and quadrupole splittings of δ?=??0.27 mm/s (relative to Eu₂O₃), ΔE _Q?= 0.85 (3) mm/s; and δ?=?? 0.22 mm/s, ΔE _Q?= 2.90 (5) mm/s, respectively. D1 is attributed to Eu at substitutional Ga lattice sites; D2 to Eu at or near substitutional sites but with extensive lattice damage. The splittings of D1 and D2 correspond to quadrupole coupling frequency of 15 (2) and 50 (4) MHz, consistent with measurements of ⁶⁹Ga, ⁷¹Ga and ¹¹¹In in GaN.     

Electrical properties of Sb-doped epitaxial SnO2 thin films prepared using excimer-laser-assisted metal–organic deposition

Excimer-laser-assisted metal–organic deposition (ELAMOD) was used to prepare Sb-doped epitaxial (001) SnO₂ thin films on (001) TiO₂ substrates at room temperature. The effects of laser fluence, the number of shots with the laser, and Sb content on the electrical properties such as resistivity, carrier concentration, and carrier mobility of the films were investigated. The resistivity of the Sb-doped epitaxial (001) SnO₂ thin film prepared using an ArF laser was lower than that of the film prepared using a KrF laser. The van der Pauw method was used to measure the resistivity, carrier concentration, and carrier mobility of the Sb-doped epitaxial (001) SnO₂ thin films in order to determine the effect of Sb content on the electrical resistivity of the films. The lowest resistivity obtained for the Sb-doped epitaxial (001) SnO₂ thin films prepared using ELAMOD with the ArF laser and 2 % Sb content was 2.5 × 10^?3 Ω cm. The difference between the optimal Sb concentrations and resistivities of the films produced using either ELAMOD or conventional thermal MOD was discussed.     

Cems characterization of SnO2 films obtained by sputtering and sol-gel route

Conversion electron Mössbauer spectroscopy (CEMS) has been used to study tin oxide films prepared by sol-gel dipping and sputtering. The spectra of films prepared by sol-gel route result close to that of crystalline SnO₂ after heat treatment at a temperature as low as 150°C. The Mössbauer parameters of as sputter deposited films indicate that the structure of the deposited stannic oxide has an amorphous character more pronounced for thinner samples. The structure becomes predominantly that of crystalline SnO₂ by heating at 550°C for 30 min provided the film thickness is higher than 10 nm.     

Mössbauer spectroscopical investigation of the exchange biased Fe/MnF2 interface

Two different Fe/MnF₂ samples have been prepared by e-beam evaporation on MgO(001) substrates. The Fe layer in the samples includes a 10 Å thick ⁵⁷Fe probe layer either at the Fe/MnF₂ interface (interface sample) or 35 Å away from the interface (center sample). The samples are characterized by X-ray diffraction, conversion electron Mössbauer spectroscopy (CEMS) and SQUID magnetometry. ⁵⁷Fe CEMS has been employed to study the depth dependent hyperfine interactions in Fe/MnF₂ as a function of temperature between 18 K to 300 K. The hyperfine field B _hf has been obtained for the interfacial and off-interfacial ⁵⁷Fe layers. At the interface, besides B _hf of bcc-Fe, the presence of a component with a distribution P(B _hf ) is observed. The latter is assigned to interfacial ⁵⁷Fe atoms, indicating some (～15%, equivalent to ～1 Fe atomic layer) intermixing at the Fe/MnF₂ interface and a decrease of the average hf > by 21%. The influence of the interface disappears as the ⁵⁷Fe probe layer is placed away from the interface. The temperature dependence of the average hf > of the interface has been measured. The Fe spins, at remanence, are found to lie in the film plane.     

Cu-supported carbon networks containing SnO<Subscript>2</Subscript> as three-dimensional anodes for lithium-ion batteries

Cu-supported SnO₂@C composite coatings constructed by interconnected carbon-based porous branches were fabricated by annealing Cu foils with films formed by knife coating DMF solution containing SnCl₂, polyacrylonitrile (PAN), and poly(methyl methacrylate) (PMMA) on their surface in vacuum. The carbon-based porous branches consist of amorphous carbon matrices, SnO₂ nanoparticles with a size of 30–100 nm mainly encapsulated inside, and many micropores with a size of 1–5 nm. The three-dimensional (3D) porous network structures of the SnO₂@C composite were achieved by volatilization of PMMA and pyrolysis of SnCl₂. The SnO₂@C composite coatings demonstrate good cyclic performance with a high reversible capacity of 642 mA h g^?1 after 100 cycles at a current density of 50 mA g^?1 without apparent capacity fading during cycling and excellent rate performance with a capacity of 276 mA h g^?1 at a high current density up to 10 A g^?1.     

Effect of N 2 + ion implantation on the oxidation behaviour of Fe50Ni50 alloy

The high temperature oxidation behavior of Fe₅₀Ni₅₀ alloy foils implanted with 100 KeV N₂ ⁺ ions at a different dose values is studied by using the technique of conversion electron Mössbauer spectroscopy (CEMS). It has been shown that the implanted foils exhibit considerable adherence of scales and higher oxidation resistance as compared to the virgin foils. This excessive adherence of scales to the surface and higher resistance to oxidation of implanted samples is attributed to nickel enrichment in the surface layers. Various oxides of Fe, Ni and Fe?Ni are identified from the hyperfine interaction parameters of the corresponding CEMS spectra and also from x-ray diffraction measurements.     

<Superscript>119</Superscript>Sn CEMS study of Sb doped SnO<Subscript>2</Subscript> film

Sb doped SnO₂ films prepared by DC sputtering and heating were characterized by ¹¹⁹Sn conversion electron Mössbauer spectrometry (CEMS). An asymmetric doublet was observed in the Mössbauer spectra of 1 %, 3 %, and 10 % Sb doped SnO₂ films. The peak ratios of doublets are considered to be due to the columnar crystal growth on the substrate. With the doping level of Sb, both the isomer shift (δ) and the quadrupole splitting (Δ) increased. After annealing, δ increased and Δ decreased for each sample. These results suggest the followings. The electron doping of the SnO₂ lattice by pentavalent Sb induces the increase of the electron density at the Sn^IV nucleus. The annealing process leads to more complete accommodation of the Sb dopant that results in more effective electron doping and therefore increasing isomer shift for tin. Simultaneously, the distortion of the lattice caused by Sb is relaxed and the quadrupole splitting decreases.     

Mössbauer spectroscopy of the new iron oxide Fe3B7O13(OH)

In order to investigate the electronic state, the local structure, and the magnetic structure of a new ion oxide Fe₃B₇O₁₃(OH), we have applied ⁵⁷Fe Mössbauer spectroscopy. The room-temperature values of isomer shift and quadrupole splitting are 1.16 mm/s and 3.21 mm/s, respectively, which indicate that the Fe ions are in high spin Fe^2?+? state. The spectrum at 4.2 K is composed of a well-resolved hyperfine sextet with the hyperfine field of 3.6 T. In a trimer, each Fe^2?+? magnetic moment is supposed to be directed from Fe^2?+? to OH^???.     

A Mössbauer investigation of SnO2 films with preferred orientation of crystallites

The textured SnO₂ films with different thickness in the range of 600–11200Å prepared by chemical vapour deposition (CVD) have been characterized by using conversion electron Mössbauer spectroscopy (CEMS) couping with X-ray diffraction (XRD) and Auger electron spectroscopy (AES). The evidence for the existence of an interaction between SnO₂ and glass substrate with the formation of a interface layer about 200Å thick has been discussed. SnO₂ existing in polycrystalline state with preferred crystal face orientation is found as long as the SnO₂ films are thick than 1800Å.     

Low temperature CEMS of Sn-implanted SiO2

Conversion electron Mössbauer spectroscopy (CEMS) at room and low temperature has been used to study thin SiO₂ films implanted with Sn atoms and annealed at 900°C. This work focuses on the determination of the Debye temperature (θ _D) and Debye–Waller factors (f) of the Sn oxidized phases formed in this system. The Sn²⁺ oxidation state is the predominant one, even if a small percentage of the Sn atoms is in the Sn⁴⁺ oxidation state. The real Sn-oxides fractions are calculated by normalizing the resonant areas to the f values, as calculated from the temperature dependence of the related resonant areas within a Debye model. The Sn⁴⁺ oxidation state, possibly related to Sn atoms close to the SiO₂ surface, represents less than 20% of the Sn atoms. For the Sn²⁺ oxidation state, two different electronics configurations a and b, having different Debye temperature and hyperfine parameters are identified. The component a, with a lower θ _D (137 K), is the predominant one and might be related to small (2–3 nm) amorphous SnO _x clusters in the SiO₂ matrix. The component b could be related to substitutional Sn atoms in the SiO₂ network forming a local Sn environment similar to the SnO amorphous compound.     

Characterization of Fe states in dilute 57 Mn implanted SnO 2 film

States of dilute Fe in SnO₂ have been monitored using ⁵⁷Fe emission Mössbauer spectroscopy following implantation of ⁵⁷Mn (T _1/2 = 85.4 s) in the temperature range from 143 K to 711 K. A sharp annealing stage is observed at ~330 K where the Fe^3?+?/Fe^2?+? ratio shows a marked increase. It is suggested that this annealing stage is due to the dissociation of Mn-V_O pairs during the lifetime of ⁵⁷Mn; the activation energy for this dissociation is estimated to be 0.9(1) eV. Fe^3?+? is found in a paramagnetic state showing spin-lattice relaxation rates consistent with an expected T ² dependence derived for a Raman process. In addition, a sharp lined doublet in the Mössbauer spectra is interpreted as due to recoil produced interstitial Fe.     

Mössbauer and XRD study of pulse plated Fe–P and Fe–Ni thin layers

⁵⁷Fe conversion electron Mössbauer spectroscopy, X-ray diffraction, electrochemical and magnetic measurements were used to study pulse electroplated Fe–P and Ni–Fe coatings. XRD and ⁵⁷Fe CEMS measurements revealed the amorphous character of the novel pulse plated Fe–P alloys. CEM spectra indicated significant differences in the short range order and in the magnetic anisotropy between the Fe–P deposits pulse plated at medium long deposition time (t _on?=?2 ms), with short relaxation time (t _off?=?9 ms) and low current density (I _p?=?0.05 Acm^?2) or at short deposition time (t _on?=?1 ms) with long relaxation time (t _off?=?250 ms) and high current density (I _p?=?1.0 Acm^?2). The broad peaks centred around the fcc reflections in XRD of the pulse plated Ni-22 wt.% Fe deposit reflected a microcrystalline Ni–Fe alloy with a very fine, 5–8 nm, grain size. The CEM spectrum of the pulse plated Ni-22 wt.% Fe coating corresponded to a highly disordered solid solution alloy containing a minute amount of ferrihydrite. Extreme favourable soft magnetic properties were observed with these Ni–Fe and Fe–P pulse plated thin layers.