Composition, structure and morphology of oxide layers formed on austenitic stainless steel by oxygen plasma immersion ion implantation

Oxygen ions were implanted in to austenitic stainless steel by plasma immersion ion implantation at 400 °C. The implanted samples were characterized by XPS, GIXRD, micro-Raman, AFM, optical and scanning electron microscopies. XPS studies showed the presence of Fe in elemental, as Fe²⁺ in oxide form and as Fe³⁺ in the form of oxyhydroxides in the substrate. Iron was present in the oxidation states of Fe²⁺ and Fe³⁺ in the implanted samples. Cr and Mn were present as Cr³⁺ and Mn²⁺, respectively, in both the substrate and implanted samples. Nickel remained unaffected by implantation. GIXRD and micro-Raman studies showed the oxide to be a mixture of spinel and corundum structures. Optical and AFM images showed an island structure on underlying oxide. This island structure was preserved at different thicknesses. Further, near the grain boundaries more oxide growth was found. This is explained on the basis of faster diffusion of oxygen in the grain boundary regions. Measurement of total hemispherical optical aborptance, α and emittance, ? of the implanted sample show that it has good solar selective properties.     

Marker experiments to determine diffusing species and diffusion path in medical Nitinol alloys

The out-diffusion of toxic Ni ions from NiTi (Nitinol), often used for biomedical applications, can be strongly reduced using oxygen plasma immersion ion implantation (PIII). Non-radioactive isotope markers, ⁶⁰Ni and ⁴⁶Ti, were implanted at 180 keV into NiTi prior to the oxygen implantation with fluences between 0.4 × 10¹⁶ and 4 × 10¹⁶ at./cm². Implanting oxygen ions by PIII in the temperature range of 400-550 °C leads to a surface oxide layer consisting of pure TiO₂. The results prove that Ni cations are the mobile species, while Ti is immobile during the oxygen insertion.     

Effect of heat treatment on morphology, crystalline structure and photocatalysis properties of TiO2 nanotubes on Ti substrate and freestanding membrane

Highly ordered titanium oxide (TiO₂) nanotubes were prepared by electrolytic anodization of titanium electrodes. Morphological evolution and phase transformations of TiO₂ nanotubes on a Ti substrate and that of freestanding TiO₂ membranes during the calcinations process were studied by scanning electron microscopy, transmission electron microscopy, and X-ray diffraction microscopy. The detailed results and mechanisms on the morphology and crystalline structure were presented. Our results show that a compact layer exists between the tubular layer and Ti substrate at 600 °C, and the length of the nanotubes shortens dramatically at 750 °C. The freestanding membranes have many particles on their tubes during calcinations from 450 to 900 °C. The TiO₂ nanotubes on the Ti substrate transform to rutile crystals at 600 °C, while the freestanding TiO₂ membranes retain an anatase crystal with increasing temperature to 800 °C. The photocatalytic activity of TiO₂ nanotubes on a Ti substrate annealed at different temperatures was investigated by the degradation of methyl orange in aqueous solution under UV light irradiation. Due to the anatase crystals in the tubular layer and rutile crystals in the compact layer, TiO₂ nanotubes annealed at 450 °C with pure anatase crystals have a better photocatalytic activity than those annealed at 600 °C or 750 °C.     

Ion mixing in Al,Si, and their oxides

The redistribution of thin metallic markers due to ion irradiation was studied by backscattering spectrometry in Al, Al₂O₃, Si, and SiO₂. Marker species were selected for their similar masses and different chemical reactivities with the host media and included Ti, Fe, W, Pt, and Au. It was found that the marker signals are Gaussian and that the variance ² of the marker atom distributions increases linearly with the dose of the irradiation, is insensitive to the temperature of irradiation in the range of 80–300 K, and depends linearly on the nuclear stopping power of the incident ions. The absolute values of ² for Ti, Fe, W, Pt, and Au markers in Al and Al₂O₃, W, and Pt in SiO₂ and W in Si is, within±50 %, of 6.5×10³Å² for 300 keV, 8×10¹⁵ Xe ions/cm². These observations suggest that collisional cascade mixing is a dominant mechanism in this type of impurity-matrix combinations. Only Au and Pt in Si mix at a larger rate: ² for Pt is about 3 and for Au about 5 times larger than ² for all other markers. Lower threshold displacement energies and/or the contribution of processes other than cascade mixing are possible considered reasons. In polycrystalline Al, a rapid migration of Au and Pt atoms throughout the Al layer, similar to grain boundary diffusion, is observed.     

Chemical bonding and interface analysis of ultrathin silicon-nitride layers produced by ion implantation and Electron Beam Rapid Thermal Annealing (EB-RTA)

¹⁵N ₂ ⁺ ions were implanted into c-Si with an energy of 5 keV/atom and fluences ranging from 5×10¹⁶ to 2×10¹⁷ atoms/cm² at RT to form ultrathin silicon-nitride layers (SiN _x ) with different N/Si ratios depending on the fluences (up to an overstoichiometric N/Si ratio of 1.65). The ¹⁵N depth distributions were analysed by the resonant nuclear reaction ¹⁵N(p, )¹²C(E _res=429 keV). The implanted samples were processed by Electron Beam Rapid Thermal Annealing (EB-RTA) at 1150° C for 15 s (ramping up and down 5° C/s). The chemical structure of the ¹⁵N implantation into Si was investigated by EXAFS and NEXAFS. Channeling-RBS (⁴He⁺, E ₀=1.5 MeV) measurements were performed to observe the transition region (disordered-Si layer, d-Si) being underneath of the SiN _x layer (typical values of layer thicknesses:SiN _x 24 nm, d-Si 6 nm).     

Nano-crystallite Fe3C with giant magnetic coercivity in SiO2

⁵⁷Fe and ¹²C ions were implanted at room temperature into single crystal SiO₂ with energies yielding approximately the same calculated ranges. The energies were 60 and 20 keV, respectively for ⁵⁷Fe and ¹²C and their corresponding doses were 5 × 10¹⁶ and 2 × 10¹⁷ at/cm². The cementite Fe₃C was formed after annealing at 650°C with a size of about 7 nm. Magnetic coercive forces of 900 and 800 Oe were obtained at RT and 80 K, respectively. An explanation for such a strong coercivity is suggested.     

Oxidation state of Fe and Ti ions implanted in yttria-stabilized zirconia studied by XPS

The oxidation state of Fe and Ti ions implanted in yttria stabilized zirconia (YSZ) was studied by XPS (X-ray photoelectron spectroscopy) in combination with depth profiling using Ar⁺ sputtering. In the as-implanted state of the sample Fe was found to be present as Fe³⁺, Fe²⁺ and as metallic Fe⁰. This is in agreement with earlier conversion electron Mössbauer Spectroscopy measurements. For Ti-implanted YSZ in the as-implanted state the majority of the Ti is present as Ti⁴⁺, Ti³⁺, and Ti²⁺ ions, while a part of the Zr cations is present in the divalent oxidation state (Zr²⁺). After oxidation in air, the Fe and Ti ions are present only in the valence three and four oxidation states, respectively.     

Reaction products and oxide thickness formed by Ti out-diffusion and oxidization in poly-Pt/Ti/SiO2/Si with oxide films deposited

In the paper, we present experimental results to enhance the understanding of Ti out-diffusion and oxidization in commercial poly-Pt/Ti/SiO₂/Si wafers with perovskite oxide films deposited when heat-treated in flowing oxygen ambient. It indicates that when heat-treated at 550 and 600 °C, PtTi₃+PtTi and PtTi are the reaction products from interfacial interaction, respectively; while heat-treated at 650 °C and above, the products become three layers of titanium oxides instead of the alloys. Confirmed to be rutile TiO₂, the first two layers spaced by 65 nm encapsulate the Pt surface by the first layer with 60 nm thick forming at its surface and by the next layer with 35 nm thick inserting its original layer. In addition, the next layer is formed as a barrier to block up continuous diffusion paths of Ti, and thus results in the last layer of TiO_2−x formed by the residual Ti oxidizing.     

Ordered nickel-iron-nitrogen phase produced by elevated temperature nitrogen ion implantation

Implantation of 1×10¹⁸N ₂ ⁺ /cm² at 60 keV ion energy into pure bcc-Fe held at 400°C during implantation yields the well-known ferromagnetic '-Fe₄N ordered fcc compound with two inequivalent crystallographic sites, one of which consists of two different magnetic sites. These sites are readily identified via their hyperfine interaction parameters as detected by conversion electron Mössbauer spectroscopy of the near-surface layer. X-ray diffraction confirms the N sublattice ordering. Here, nitrogen implantation under identical conditions into a disordered fcc Ni_0.8Fe_0.2 alloy (permalloy) yields a paramagnetic phase with only one site defined by a rather large quadrupole interaction (1.15 mm/s). The X-ray pattern is clearly that of the ordered '-(Ni_0.8Fe_0.2)₄N structure so we conclude that the Fe atoms occupy only the face-centered lattice sites where each can bond with two nearest-neighbour N atoms on opposite sides. Thus, additional ordering within the Ni-Fe sublattice has been induced by the elevated temperature implantation process. Post-implantation annealing at 400°C decomposes the ' phase.     

Amorphization of armco iron by boron implantation and subsequent crystallization by heat treatment: A CEMS,X-ray and ultramicrohardness study

The phase compositon of the near-surface zone of armco iron implanted with B⁺ ions (100 keV) at 200 °C was analyzed by CEMS and X-ray diffraction. The existing phases (bcc iron, Fe₂B and an amorphous Fe-B phase) were subsequently modified by heat treatment at various temperatures. The influence of the phase modifications upon the mechanical properties was studied by ultramicohardness measurements.     

Studies of structure and composition of a Pt-based basic electrode for deposition of PZT ferroelectric films on silicon substrates

In this study it has been found that a TiO₂/Ti double adhesion layer is used for SiO₂/Si substrate and a YSZ layer is used for SiO₂/Si and Si substrates to achieve high residual polarization of PZT layers on platinum. Epitaxial deposition of YSZ on Si(100) provides an atomically smooth platinum layer textured in the [100] direction. The produced PZT films are mostly textured in the [111] direction; their residual polarization is 5–15 μC/cm².     

Role of interstitial “caged” Fe in the superconductivity of FeTe1/2Se1/2

All samples are synthesized through a standard solid state reaction route and are quenched to room temperature systematically at 700 °C, 500 °C, 300 °C, and room temperature (RT); the samples are denoted 700Q, 500Q, 300Q, and RTQ, respectively. The structural, and magnetic properties are studied. Careful Rietveld analysis of the X-ray diffraction patterns revealed that all samples except 700Q crystallized in a single phase with space group P4/nmm; the amount of interstitial Fe (Fe_int) at the 2c site increased from 5% for RTQ to 8% for 500Q. Sample 700Q crystallized in the Fe₇Se₈ phase. The magnetization result revealed that RTQ and 300Q are superconducting at 10 K and 13 K, respectively, while 500Q and 700Q are not superconducting. Magnetic ordering was observed at around 125 K for all the samples. The prominence of in terms of effective moment is sufficiently higher for 500Q and 700Q than for RTQ and 300Q. Summarily, it is found that quenching-induced disorder affects the occupancy of interstitial Fe in FeTe_1/2Se_1/2 and thus both its superconducting and magnetic properties. Further, it clear that limited presence of interstitial Fe at 2c site is not completely contrary to the observation of superconductivity, because the 300Q sample possesses higher T_c (13 K) for higher Fe_int (6%) than the RTQ sample with relatively lower T_c (10 K) having lower Fe_int (5%). Further, the 500Q sample, with much higher Fe_int (8%), is non-superconducting.     

Improved optical response and photocatalysis for N-doped titanium oxide (TiO2) films prepared by oxidation of TiN

In order to improve the photocatalytic activity, N-doped titanium oxide (TiO₂) films were obtained by thermal oxidation of TiN films, which were prepared on Ti substrates by ion beam assisted deposition (IBAD). The dominating rutile TiO₂ phase was found in films after thermal oxidation. According to the results of X-ray photoelectron spectroscopy (XPS), the residual N atoms occupied O-atom sites in TiO₂ lattice to form TiON bonds. UV-vis spectra revealed the N-doped TiO₂ film had a red shift of absorption edge. The maximum red shift was assigned to the sample annealed at 750 °C, with an onset wavelength at 600 nm. The onset wavelength corresponded to the photon energy of 2.05 eV, which was nearly 1.0 eV below the band gap of pure rutile TiO₂. The effect of nitrogen was responsible for the enhancement of photoactivity of N-doped TiO₂ films in the range of visible light.     

Thickness-Dependent Phase Transformations in Implanted Iron

The dependence of iron nitride formation and phase transformations on the thickness of the nitrogen implanted Fe layers is investigated. The iron nitrides formation in N-implanted Fe-layers of various thickness (60–860 nm) implanted with 100 keV N₂ ⁺ ions with doses ranging from 1×10¹⁷ to 4.5×10¹⁷ at. N/cm² is studied by CEMS and supplemented by GXRD. It was found that nitride formation is strongly enhanced in thin Fe films as compared to thicker layers or the bulk samples. A given nitride phase is formed in thin (60, 130 nm) Fe layers at significantly lower N-doses and the transformation of the original Fe layer into iron nitrides is more complete than in the bulk -Fe. It is suggested that high stresses in thin Fe layers, revealed by the GXRD measurements, may enhance nitrides formation.     

Hydrodynamic cavitation degradation of Rhodamine B assisted by Fe3+-doped TiO2: Mechanisms,geometric and operation parameters

In this paper, a novel method, hydrodynamic cavitation (HC) combined with Fe³⁺-doped TiO₂, for the degradation of organic pollutants in aqueous solution is reported. The venturi tubes with different geometric parameters (size, shape and half divergent angle) are designed to obtain a strong HC effect. The structure, morphology and chemical composition of prepared Fe³⁺-doped TiO₂ as catalyst are characterized via using XRD, SEM, TEM, XPS, UV-vis DRS and PL methods. The effects of added TiO₂ (heat-treated at different temperatures for different times) and Fe³⁺-doped TiO₂ (with different mole ratios of Fe and Ti) on the HC catalytic degradation of RhB are discussed. The influences of operation parameters including inlet pressure, initial RhB concentration and operating temperature on the HC catalytic degradation of RhB are studied by Box-Behnken design (BBD) and response surface methodology (RSM). Under 3.0 bar inlet pressure for 10 mg/L initial concentration of RhB solution at 40 °C operating temperature in the presence of Fe³⁺-doped TiO₂ with 0.05:1.00 M ratio of Fe and Ti, the best HC degradation ratio can be obtained (91.11%). Furthermore, a possible mechanism of HC degradation of organic pollutants in the presence of Fe³⁺-doped TiO₂ is proposed. Perhaps, this study may provide a feasible method for a large-scale treatment of dye wastewater.     

Mössbauer Optimization of the Direct Synthesis of β-FeSi2 by Ion Beam Mixing of Fe/Si Bilayers

At present, there is an increasing interest in the iron di-silicide phase -FeSi₂, which is supposed to be a direct band gap semiconductor and one of the most promising materials for silicon-based optoelectronics, e.g., light-emitting devices, solar cells, and photo detectors. But this phase is very difficult to be produced. Here, the successful direct synthesis of this phase by ion beam mixing of Fe/Si bilayers at temperatures in the range of 400 to 600°C is reported. The aim of the experiments was to achieve a complete reaction of the deposited Fe layer with the Si substrate that results in the formation of a pure, single-phased -FeSi₂ surface layer. The obtained silicide layers, their structure and composition are investigated by conversion electron Mössbauer spectroscopy (CEMS), Rutherford backscattering spectrometry (RBS), and X-ray diffraction (XRD). The fraction of the -FeSi₂ formed is determined by CEMS as function of ion species, energy, fluence and temperature. Complete growth and formation of a single-phased -FeSi₂ layer was achieved by 205 keV Xe ion irradiation at a fluence of 2×10¹⁶ ions/cm² at 600°C.     

Diffusion behaviour of Nb in yttria-stabilized zirconia single crystals: A SIMS, AFM and X-ray reflectometry investigations

Using secondary ion mass spectrometry (SIMS) we have investigated the concentration vs. depth profile of Nb, thermally diffused into (1 0 0)-oriented yttria-stabilized zirconia (YSZ) single crystal substrates. The surface morphology of Nb films and YSZ substrates was analyzed using atomic force microscopy (AFM). The structural disorder and the interface configuration of the samples were investigated by X-ray reflectometry (XRR). Two kinds of substrates were used: as-received (AR) and reduced (R) ones. The R-substrates were obtained by thermal annealing of AR-substrates in air for 2 h at 1250 °C. The bulk diffusion coefficients D_T in the temperature range of 780-1000 °C, activation energy Q, and the pre-exponential factor, D₀, have been obtained for Nb in YSZ. For the AR single crystals, the results can be well represented by the expression:

     

Crystal orientation dependence of ferromagnetism in Fe-implanted MgO single crystals

Single crystals of MgO with (100), (110) and (111) orientations were implanted with 64 keV Fe ions at a dose of 1.9×10¹⁷ ions/cm² by using metal-vapor vacuum arc ion source (MEVVA). The magnetic properties were investigated by a superconducting quantum interference device magnetometer and Rutherford backscattering spectrometry (RBS) was used to analyze the Fe concentration and distribution. The presence of Fe nanoparticles in MgO matrix was verified by magnetization measurements. Results show that all the samples behave with ferromagnetism at 5 K and 300 K, and the coercive field, H_C, follow well the relation: at measured temperatures. The orientation dependence of the coercive field may result from the different distribution of Fe nanoparticle size.     

CEMS Investigations of Fe-Silicide Phases Formed by the Method of Concentration Controlled Phase Selection

Conversion electron Mössbauer spectroscopy (CEMS) measurements have been made on Fe-silcide samples formed using the method of concentration controlled phase selection. To prepare the samples a 10 nm layer of Fe₃₀M₇₀ (M=Cr, Ni) was evaporated onto Si(100) surfaces, followed by evaporation of a 60 nm Fe layer. Diffusion of the Fe into the Si substrate and the formation of different Fe–Si phases was achieved by subjecting the evaporated samples to a series of heating stages, which consisted of (a) a 10 min anneal at 800°C plus etch of the residual surface layer, (b) a further 3 hr anneal at 800°C, (c) a 60 mJ excimer laser anneal to an energy density of 0.8 J/cm², and (d) a final 3 hr anneal at 800°C. CEMS measurements were used to track the Fe-silicide phases formed. The CEMS spectra consisted of doublets which, based on established hyperfine parameters, could be assigned to - or -FeSi₂ or cubic FeSi. The spectra showed that -FeSi₂ had formed already at the first annealing stage. Excimer laser annealing resulted in the formation of a phase with hyperfine parameters consistent with those of -FeSi₂. A further 3 hr anneal at 800°C resulted in complete reversal to the semiconducting -FeSi₂ phase.