Influence of irradiation damage on formation of iron nitrides in α-Fe

Pure iron foils were implanted with nitrogen ions at energy of 10 keV and with 1×10¹⁷N ions/cm². Doses of pre-self-implantation were 5×10¹⁶ and 3.7×10^{16 17}Fe ions/cm² respectively, and the iron ion energy was 27 keV. A comparison of iron nitrides formed on surfaces with and without pre-self-implantation has been obtained. The results show that radiation damage apparently influences the formation of iron nitrides. The formation and transformation of nitrides after N implantation or after annealing can be explained by a model of implantation-induced transformation.     

Fabrication of composite based on GeSi with Ag nanoparticles using ion implantation

Comparative analysis of the structural and optical properties of composite layers fabricated with the aid of implantation of single-crystalline silicon (c-Si) using Ge⁺ (40 keV/1 × 10¹⁷ ions/cm²) and Ag⁺ (30 keV/1.5 × 10¹⁷ ions/cm²) ions and sequential irradiation using Ge⁺ and Ag⁺ ions is presented. The implantation of the Ge⁺ ions leads to the formation of Ge: Si fine-grain amorphous surface layer with a thickness of 60 nm and a grain size of 20–40 nm. The implantation of c-Si using Ag⁺ ions results in the formation of submicron porous amorphous a-Si structure with a thickness of about 50 nm containing ion-synthesized Ag nanoparticles. The penetration of the Ag⁺ ions in the Ge: Si layer stimulates the formation of pores with Ag nanoparticles with more uniform size distribution. The reflection spectra of the implanted Ag: Si and Ag: GeSi layers exhibit a sharp decrease in the intensity in the UV (220–420 nm) spectral interval relative to the intensity of c-Si by more than 50% owing to the amorphization and structuring of surface. The formation of Ag nanoparticles in the implanted layers gives rise to a selective band of the plasmon resonance at a wavelength of about 820 nm in the optical spectra. Technological methods for fabrication of a composite based on GeSi with Ag nanoparticles are demonstrated in practice.     

Epitaxial growth of silicon on silicon implanted with iron ions and optical properties of resulting structures

The method of ultrahigh-vacuum low-temperature (T = 850°C) purification of silicon single crystals having the (100) and (111) orientation and implanted with low-energy (E = 40 keV) iron ions with various doses (Φ = 10¹⁵?1.8×10¹⁷ cm^?2) and subjected to pulsed ion treatment (PIT) in a silicon atom flow has been tested successfully. The formation of semiconducting iron disilicide (β-FeSi₂) near the surface after PIT is confirmed for a Si(100) sample implanted with the highest dose of iron ions. The possibility of obtaining atomically smooth and reconstructed silicon surfaces is demonstrated. Smooth epitaxial silicon films with a roughness on the order of 1 nm and a thickness of up to 1.7 μm are grown on samples with an implantation dose of up to 10¹⁶ cm^?2. Optical properties of the samples before and after the growth of silicon layers are studied; the results indicate high quality of the grown layers and the absence of iron disilicide on their surface.     

Nitrogen irradiation of Fe/Si bilayers: nitride versus silicide phase formation

In the course of a systematic investigation of heavy ion-irradiated Fe/Si layers, we have studied atomic transport and phase formation induced by 22-keV ¹⁴N²⁺ ion implantation in ⁵⁷Fe(30 nm)/Si bilayers at high fluences. We report here results obtained by Rutherford backscattering spectroscopy, X-ray diffraction, and conversion electron Mössbauer spectroscopy after implantation and post-implantation annealing treatments. The irradiations caused little sputtering, but significant interface mixing. During implantation, iron nitrides, but no silicides were formed, even at the highest nitrogen fluence of 2×10¹⁷ ions/cm². When heating these samples in vacuo up to 700 °C, the iron-rich phases -Fe₃N and -Fe₄N were produced. Starting at 600 °C the silicide phase -FeSi₂ was also identified. PACS 61.72.Ww; 61.80.-x; 68.35.Dv; 81.20.-n; 81.70.-q     

Sequence of structural-phase states during implantation of C+, N+, and Si+ ions into molybdenum

The sequence of structural-phase changes in the surface layer of molybdenum during pulsed implantation of N⁺, C⁺, and Si⁺ ions has been studied. At radiation doses 5·10¹⁶ cm^–2 we detected qualitatively similar structural-phase transformations with the formation of highly dispersed secondary-phase particles (nitrides, carbides, and silicides), dislocations, point defects, and clusters of defects. At radiation doses (1–2)·10¹⁷ cm^–2 implantation of C⁺ and Si⁺ ions causes amorphization of the surface layer; nitrogen implantation is accompanied by the formation of continuous layers of the nitride phase on the surface.Siberian Physicotechnical Institute at the V. D. Kuznetsov State University, Tomsk. Translated from Izvestiya Vysshikh Uchebnykh Zavedenii, Fizika, No. 2, pp. 3–9, February, 1994.     

Icems and dcems study of Fe layers evaporated onto Al and Si

Thin layers of⁵⁷Fe (2.5 nm, 10 nm and 70 nm thickness), vacuum evaporated onto Al and Si plates, have been investigated by conversion electron Mössbauer spectroscopy (CEMS). The measurements were performed employing both a proportional counter and a channeltron for conventional and ultrahigh-vacuum integral CEMS (UHV-ICEMS) studies, respectively, and a channeltron for depth-selective CEMS (DCEMS). The phase analysis of the layers on base of experimental results has indicated the presence of metallic iron and one or two iron compounds, ascribed to iron reaction products formed with the residual gas during evaporation. These products are most likely rather stable iron nitrides, are more or less clustered and are distributed throughout the whole layer.     

The role of a ZnO buffer layer in the growth of ZnO thin film on Al2O3 substrate

A ZnO buffer layer and ZnO thin film have been deposited by the pulsed laser deposition technique at the temperatures of 200 C and 400 C, respectively. Structural, electrical and optical properties of ZnO thin films grown on sapphire (Al₂O₃) substrate with 1, 5, and 9 nm thick ZnO buffer layers were investigated. A minute shift of the (101) peak was observed which indicates that the lattice parameter was changed by varying the thickness of the buffer layer. High resolution transmission electron microscopy (TEM) was used to investigate the thickness of the ZnO buffer layer and the interface involving a thin ZnO buffer between the film and substrate. Selected area electron diffraction (SAED) patterns show high quality hexagonal ZnO thin film with 30 in-plane rotation with respect to the sapphire substrate. The use of the buffer can reduce the lattice mismatch between the ZnO thin film and sapphire substrate; therefore, the lattice constant of ZnO thin film grown on sapphire substrate became similar to that of bulk ZnO with increasing thickness of the buffer layer.     

Solid-state Water-mediated Transport Reduction of Nanostructured Iron Oxides

The Fe²⁺/Fe³⁺ ratio in two-dimensional iron oxide nanosructures (nanolayers with a thickness of 0.3–1.5 nm on silica surface) may be precisely controlled using the transport reduction (TR) technique. The species –O–Fe(OH)₂ and (Si–O–)₂–FeOH forming the surface monolayer are not reduced at 400–600°C because of their covalent bonding to the silica surface, as demonstrated by Mössbauer spectroscopy. Iron oxide microparticles (microstructures) obtained by the impregnation technique, being chemically unbound to silica, are subjected to reduction at T 500°C with formation of metallic iron in the form of -Fe. Transport reduction of supported nanostructures (consisting of 1 or 4 monolayers) at T 600°C produces bulk iron(II) silicate and metallic iron phases. The structural-chemical transformations occurring in transport reduction of supported iron oxide nanolayers are proved to be governed by specific phase processes in the nanostructures themselves.     

Magnetic behaviour and DCEMS study of SnO2 films implanted with 57Fe

Fe implanted SnO₂ films (5 × 10¹⁶ and 1 × 10^{17 57}Fe ions/cm²) characterized by conversion electron Mossbauer spectroscopy (CEMS) are reviewed. The substrate temperatures affect the growth of precipitated iron oxides. The Fe ion implanted film at room temperature (RT) shows no Kerr effect and no magnetic sextet in CEM spectra. The SnO₂ film implanted with ⁵⁷Fe at the substrate temperature of 300 °C show a small Kerr effect although the magnetic sextet is not observed, but post-annealing results in the disappearance of the Kerr effect. This magnetism is considered to be due to defect induced magnetism. Some samples were measured by CEMS at 15 K. SnO₂ (0.1 at %Sb and 3 at %Sb) films, implanted at 500 °C and the post-annealed samples, show RT ferromagnetism due to formation of clusters of magnetite and maghemite, respectively. The layer by layer analysis of these films within 100 nm in thickness has been done by depth sensitive CEMS (DCEMS) using a He + 5 % CH₄ gas counter. The structures and compositions of Fe implanted SnO₂ films, and the effects due to post-annealing were investigated.     

Microstructure and thermal stability of Fe,Ti, and Ag implanted yttria-stabilized zirconia

Yttria-stabilized zirconia (YSZ) was implanted with 15 keV Fe or Ti ions up to a dose of 8×10¹⁶ at cm^–2. The resulting dopant concentrations exceeded the concentrations corresponding to the equilibrium solid solubility of Fe₂O₃ or TiO₂ in YSZ. During oxidation in air at 400° C, the Fe and Ti concentration in the outermost surface layer increased even further until a surface layer was formed of mainly Fe₂O₃ and TiO₂, as shown by XPS and ISS measurements. From the time dependence of the Fe and Ti depth profiles during anneal treatments, diffusion coefficients were calculated. From those values it was estimated that the maximum temperature at which the Fe- and Ti-implanted layers can be operated without changes in the dopant concentration profiles was 700 and 800° C, respectively. The high-dose implanted layer was completely amorphous even after annealing up to 1100° C, as shown by scanning transmission electron microscopy. Preliminary measurements on 50 keV Ag implanted YSZ indicate that in this case the amorphous layer recrystallizes into fine grained cubic YSZ at a temperature of about 1000° C. The average grain diameter was estimated at 20 nm, whereas the original grain size of YSZ before implantation was 400 nm. This result implies that the grain size in the surface of a ceramic material can be decreased by ion beam amorphisation and subsequent recrystallisation at elevated temperatures.     

Use of grazing incidence X-ray diffraction for the study of nitrogen implanted stainless steels

The identification of Fe, Ni and Cr nitrides formed by nitrogen-ion implantation (4×10¹⁷ N⁺ cm^-2, 50 keV) in austenitic steels is performed by X-ray diffraction under very low glancing angles (0.00 ⩽ i ⩽ 1.5°). Spectra obtained with increasing angles i permit the investigation of layers with depths varying from 20 to more than 1000 Å. This non-destructive technique allows the surface to be controlled at each step of the treatments. Spectra were recorded on polished steel prior to and after implantation, with or without electrochemical attack. A 100 Å martensitic layer formed during the mechanical polishing is observed on the austenitic substrate. This layer is destroyed by an anodic attack before implantation of the samples. After implantation a CrN or carbonitride overlayer of a few tens of Å in thickness, may be observed. In the subjacent layers several iron and nickel nitrides are present, mainly ϵ-Fe₂N-Fe₃N, ς-Fe₂N and Ni₃N.     

Combined analysis of static and dynamic magnetic characteristics of multilayer CoFeZr/α-Si nanostructures

The combined method of static and dynamic magnetic measurements is used to study nano-dimensional multilayer amorphous CoFeZr/α -Si films. It is established that at the thickness of magnetic layers x = 5–12 nm their magnetization does not differ from that of the bulk material. It is shown that as x is lowered to 2–3 nm, the magnetization of magnetic layers decreases, which may be due to the formation of mixed layers containing nonmagnetic silicides. At a thickness of nonmagnetic interlayers of less than 1 nm the features characteristic of a weak antiferromagnetic interaction of neighboring layers are observed.     

Study of Tb/Fe multilayers by temperature-dependent CEMS

A comparative study is accomplished in the domain where iron layers are amorphous. The dependence of the magnetic structure of Tb/Fe multilayered films on temperature have been investigated by Mössbauer spectrometry. When the iron layer is thinner than 2.3 nm, the average hyperfine field at the iron site remains nearly constant at 4.2 K, while it decreases strongly for iron thickness higher than 1.5 nm at room temperature. This decrease of H is due to the decrease of the Curie temperature, which can be explained from the structure of iron layers.     

Nanoparticles of Iron Nitride Encapsulated in Nitrogen-Doped Carbon Bulk Derived from Polyaniline/Fe2O3 Blends and Its Electrochemical Performance

Iron nitride nanoparticles encapsulated in nitrogen-doped carbon bulk is fabricated by a simple costep nitridation of Fe₂O₃ and carbonization of polyaniline. The microstructure and elemental composition of the materials are analyzed by transmission electron microscope, scanning electron microscope, X-ray diffraction, and X-ray photoelectron spectroscopy. The pore size distribution and specific surface area of the materials are identified using nitrogen adsorption and desorption method. The results illustrate that iron nitride nanoparticles with 5–20 nm in size are uniformly dispersed in the carbon bulk. The presence of carbon bulk effectively prevents the agglomeration of iron nitride nanoparticles, making the electrochemical performance of iron nitride nanoparticles/carbon nitride composite nanomaterials superior to that of pure iron nitride nanomaterials. At a current density of 0.5 A g⁻¹, the specific capacitance (257.5 F g⁻¹) of the iron nitride nanoparticles/nitrogen-doped carbon bulk is much higher than that (119.5 F g⁻¹) of pure iron nitride.     

CEMS study on aluminium implanted iron

Up to now a great deal of investigations in ion beam mixing of iron-aluminium layers are known. However, the easier way to produce such layers by direct implantation of aluminium ions in iron is less studied. In the present work aluminium implanted iron layers are studied. Iron samples were implanted with aluminium ions at 50, 100, and 200 keV, respectively, with doses between 5×10¹⁶ and 5×10¹⁷ cm⁻². Independent of energy, at doses up to 2×10¹⁷ cm⁻², besides alpha iron further magnetic fractions with a Fe₃Al-like structure are formed while at a dose of 5×10¹⁷ cm⁻² amorphous nonmagnetic components are formed.     

Growth stages of YSZ-buffer layers and YBa2Cu3O7−x thin films on silicon substrates studied by scanning probe microscopy

Scanning probe microscopy has been applied to study various growth stages of YSZ (yttria-stabilized zirconia) buffer layers on silicon and of YBa₂Cu₃O_7–x thin films on YSZ/Si. YSZ buffer layers of 75 nm thickness exhibit a remarkable smooth surface with a rms roughness of about 0.5 nm for a surface area of 5 m×5 m. The subsequent growth of YBa₂Cu₃O_7–x thin films was investigated from nucleation to the formation of growth hills. Screw dislocations were found only in very rare cases.     

Ultrasonic-assisted synthesis of porous S-doped carbon nitride ribbons for photocatalytic reduction of CO2

A series of porous S-doped carbon nitride ribbons (PSCN) were prepared by one-pot hydrothermal and sonochemical synthesis techniques. The morphologies and nanostructures of the catalysts were characterized by SEM, XRD and IR, which confirmed the pristine graphitic structures of carbon nitrides retained in the products. Due to sonication treatment, PSCN has porous structures in the thin ribbon and larger specific surface areas (PSCN 43.5 m²/g, SCN 26.6 m²/g and GCN 6.5 m²/g). XPS and elemental mappings verified that sulfur atoms were successfully introduced into the carbon nitride framework. Diffuse reflectance spectroscopy (DRS) results showed S-doping in the carbon nitride reduced the bandgap energy and enhanced their capability of the utilization of visible light, which contributed to higher photo-generated current. Photoluminescence (PL) analysis indicates the recombination of photogenerated carriers was suppressed in PSCN. Moreover, the photocatalytic performance showed that S-doping and porous and thin ribbon nanostructures may effectively boost the CO₂ reduction rate (to as much as 5.8 times of GCN) when illuminated by visible light (>420 nm) without the need of sacrificial materials. The preliminary mechanisms of the formation of PSCN and its applications in photocatalytic CO₂ reduction are proposed. It highlights the potential of the current technique to produce effective, nonmetal-doped carbon nitride photocatalysts.     

Effects of silicon negative ion implantation in semi-insulating gallium arsenide

ABSTRACT

In the present work, effects of silicon negative ion implantation into semi-insulating gallium arsenide (GaAs) samples with fluences varying between 1?×?10¹⁵ and 4?×?10¹⁷?ions?cm^?2 at 100?keV have been described. Atomic force microscopic images obtained from samples implanted with fluence up to 1?×?10¹⁷?ion?cm^?2 showed the formation of GaAs clusters on the surface of the sample. The shape, size and density of these clusters were found to depend on ion fluence. Whereas sample implanted at higher fluence of 4?×?10¹⁷?ions?cm^?2 showed bump of arbitrary shapes due to cumulative effect of multiple silicon ion impact with GaAs on the same place. GXRD study revealed formation of silicon crystallites in the gallium arsenide sample after implantation. The silicon crystallite size estimated from the full width at half maxima of silicon (111) XRD peak using Debye-Scherrer formula was found to vary between 1.72 and 1.87?nm with respect to ion fluence. Hall measurement revealed the formation of n-type layer in gallium arsenide samples. The current–voltage measurement of the sample implanted with different fluences exhibited the diode like behavior.     

Ferromagnetism and microstructure in Fe-implanted ZnO

Fe ions were implanted into ZnO single crystals with multiple energies between 50 and 380 keV up to a total fluence of 12.5×10¹⁷ cm⁻². The crystal quality of Fe⁺ implanted ZnO was investigated by X-ray diffraction 2θ scans and ω-rocking curve measurements. The appearance of Fe related diffraction peaks after C annealing of the implanted sample indicates possibly formation of Fe nanoparticles. Superconducting quantum interference device measurements revealed ferromagnetic behavior below 250 K for both the as-implanted and post-annealed ZnO. Photoluminescence and Raman scattering as well as X-ray rocking curve measurements all indicate introduction of structural defects after Fe implantation. Some of the defects act as nonradiative recombination centers, and suppress the visible and ultraviolet (UV) emission in ZnO. These defects also break the Raman selection rule, and lead to the activation of some silent phonon modes. Annealing of the implanted sample at C causes partial recovery of the defects, however, the X-ray diffraction results of the anneal ZnO show even an improvement of the crystal quality compared with the un-implanted one. This could be attributed to the recovery of the grown-in defects in ZnO.     

Silicon carbide synthesis with energy pulses

Polycrystalline SiC layers were synthesized through nanosecond pulse heating of thin carbon films deposited on single-crystalline silicon wafers. The samples were submitted to electron beam irradiation (25 keV, 50 ns) at various current densities in vacuum (10^–4mbar) and to XeCl excimer laser pulses (308 nm, 15ns) in air. Rutherford backscattering spectrometry (RBS) showed that in the e-beam annealed samples mixing of the elements at the interface starts at current densities of about 1200 A/cm². The mixed layer thickness increases almost linearly with current density. From the RBS spectra a composition of the intermixed layers close to the SiC compound was deduced. Transmission electron microscopy (TEM) and electron diffraction studies clearly evidenced the formation of SiC polycrystals. Using the XeCl excimer laser, intermixing of the deposited C film with the Si substrate was observed after a single 0.3 J/cm² pulse. Further analysis evidenced the formation of SiC nanocrystals, embedded in a diamond film.