Hydrogen in amorphous and crystalline ytterbium films

Ytterbium vapor condensation on a liquid-helium cooled substrate in a hydrogen atmosphere is used to obtain Yb-H films containing up to 55 at.% hydrogen. Various thermodynamic and kinetic parameters of the transition of these films from the amorphous to the crystalline state (a→c transition) are investigated along with the electrical conductivity of these states. It is shown that the investigated properties of Yb-H films containing up to 40 at.% hydrogen are essentially indistinguishable from those of pure Yb films in the temperature interval 4.2–293 K. Increasing the hydrogen concentration to 55 at.% leads to an insignificant increase in the electrical resistivity, the kinetic temperature, and the activation energy of the a→c transition, and also to a decrease of the propagation speed of self-maintaining avalanche (explosive) crystallization. Reasons for the observed influence of hydrogen on the properties of Yb-H films are analyzed. The examined low-temperature Yb-H condensates can be characterized as a “frozen” solid solution of hydrogen in ytterbium in the temperature interval 4.2–293 K. Storing such films at room temperature leads to the formation of ionic ytterbium dihydride YbH₂. Fiz. Tverd. Tela (St. Petersburg) 41, 177–182 (February 1999)     

Interfacial reactions of ultrahigh vacuum deposited ytterbium thin films on silicon

Epitaxial ytterbium silicide thin films were grown on (111)Si by ultrahigh vacuum deposition and subsequent thermal annealing. The epitaxial YbSi(2-x) thin films consist of various kinds of defects such as vacancies, stacking faults, and pinholes. The vacancies were ordered so as to relax the compressive stress in Si sublattice of YbSi(2-x) thin films. The vacancy ordering structure is of an out-of-step structure with higher vacancy concentration after higher temperature annealing so that the compressive stress was further relaxed. A high density of stacking faults was present in the epitaxial YbSi(2-x) thin films. The stacking faults were annihilated by high temperature annealing. Pinholes also formed in the epitaxial YbSi(2-x) thin films and could be avoided by appropriate fabrication process. The epitaxial YbSi(2-x) thin films were thermally stable up to 1000 degrees C.     

Characterization of laser-nitrided iron and sputtered iron nitride films

Laser-nitriding may be a promising technique for substituting conventional nitriding processes. We have irradiated pure iron with pulses of an excimer laser and achieved high nitrogen contents in a thin surface layer. We found that the nitrogen is dissolved into -Fe, leading to a large amount of retained austenite. This was also verified by X-ray diffraction (XRD) measurements. Three subspectra can be resolved in the Mössbauer spectra (CEMS) for this nitrogen austenite. The nitrogen concentration can be calculated in terms of site occupation, indicating a content as high as 16(1) at%, which is consistent with the results of Rutherford backscattering spectroscopy (RBS), resonant nuclear reaction analysis (RNRA) and Auger electron spectroscopy (AES) measurements. This is more than the solubility limit for -Fe(N). By reactive magnetron-sputtering it is possible to produce thin iron nitride films of various stoichiometries. We report on the production of-Fe _x N and FeN _y films. These films were again characterized by CEMS, RBS, RNRA (¹⁵N(p, )) and XRD. For-Fe _x N, produced in the range 2x3 with medium nitrogen flows during reactive sputtering, the Mössbauer spectra can be well resolved in terms of different iron sites, enabling an accurate calculation of the nitrogen content. For high nitrogen flows during sputtering a phase FeN _y withy>0.5 is produced. This phase is not reported in the Fe-N phase diagram.     

Spinwave resonance in MBE grown iron films

Spinwave resonance (SWR) has been observed at 9.5 and 35 GHz on a number of single crystal iron films prepared by the molecular beam epitaxy technique. The external magnetic field is applied both normal to and in the plane of the films. The deduced exchange stiffness constant A is (1.91±0.10)×10^-6 erg/cm. The SWR data is interpreted in terms of a non-uniform distribution of the magnetization near the film surface.     

Susceptibility of iron films near remanence

Susceptibility in the direction perpendicular to the average magnetization of a not completely saturated polycrystalline film is influenced by the magnetic anisotropy of the crystallites (or defects) and by the energy connected with the non-uniformity of magnetization.The results of measurements on iron films are compared with the simple theory of susceptibility [1] and with a further analysis of the role of anisotropy.The authors thank Dr. J. Kaczér and Dr. E. Feldtkeller for valuable discussions.     

Nucleation of bcc iron in ultrathin fcc films

Needle-shaped bcc nucleation centers in fcc films of Fe on Cu(100) are observed by scanning tunneling microscopy. They form virtually without mass transfer and nearly under conservation of volume, which causes a large strain within the nascent bcc grain. The corresponding strain energy almost equals the gain in structural energy, rendering the bcc nucleation very sensitive to any effect influencing this subtle balance. We suggest that modifying the film by straining, alloying, or surface adsorption may inhibit the bcc nucleation and lead to thick metastable fcc films.     

Magnetooptical studies on thin iron films

Magnetooptical measurements on Fe-films in the layer system ZnS-Fe-MgF₂-Ag showed a decrease of the Kerr-intensity values with Fe-film thicknesses below 15nm, not predicted by theoretical calculations. Magnetization curves obtained magnetooptically indicate a significant influence of the layer system on the magnetic properties of Fe-films.     

Magnetic transport properties in iron/iron-oxide films

Iron/iron-oxide granular films were fabricated using reactive dc magnetron sputtering. Their structural, magnetic and transport properties were systematically studied. XPS and TEM confirmed the coexistence of Fe, FeO and Fe₂O₃. A metal–insulator transition was observed with the increasing of the oxygen component in the film. The temperature dependencies of longitudinal resistivity ρ_xx and anomalous Hall resistivity ρ_xy were discussed. We found the enhancement of ρ_xy and investigated the scaling law between anomalous Hall coefficient R_s and ρ_xx. In all the samples, R_s was found to be proportional to ρ_xx when ρ_xx is small, which indicated the skew scattering is dominant.     

Friedel oscillations in ytterbium films deposited on the Si(111) 7 × 7 surface

The nonmonotonic dependence of the work function of ytterbium nanofilms deposited on singlecrystal Si(111) on their thickness is experimentally revealed and studied. This dependence is shown to be caused by electron density oscillations in the films (Friedel oscillations), which are generated by the ytterbium-silicon interface. These oscillations originate, in turn, from appreciable charge transfer from the ytterbium film having a low work function to silicon.     

Proton beam enhanced adhesion of iron films

Depth-selective surface Mössbauer and adhesion measurements were pertormed on as evaporated and proton bombarded⁵⁷Fe and⁵⁶Fe/⁵⁷Fe films supported by glass and fused silica. The results contribute to the understanding of the mechanism responsible for adhesion enhancement of metallic films induced by ion bombardment in the electronic stopping region.     

The magnetization curves of thin iron films

The magnetization curves of evaporated iron films 125–7870 Åthick were measured. A torsion magnetometer was used for the magnetic measurements. In the neighbourhood of 1100 Åan anomaly was found in the dependence of the work of magnetization and a quantity which replaces remanence on the thickness of the film. Decreased density of the film in comparison with the density of the compact metal was found by weighing.     

Evolution of magnetoresistance effect in iron–bismuth films

A unique time-dependent magnetotransport behavior has been observed in Fe–Bi films. Approximately one month was required to stabilize resistance after samples were fabricated. Initially, the as-prepared Fe–Bi films exhibit both ordinary magnetoresistance (MR) and anisotropic magnetoresistance. Fe precipitation changes the microstructure. Eventually, an isotropic and negative MR, like a giant MR effect was observed; it arises from electronic transport between Fe granules separated by Bi.     

Deposition and properties of high-carbon iron films

Thin high-carbon iron films were deposited by pulsed laser deposition onto grids for transmission electron microscopy using pre-combined carbon/iron targets with equal area ratio. The deposited films of about 20 nm in thickness were directly characterized by transmission electron microscopy. The films showed a variety of phases, surprisingly also including the NaCl-type FeC phase, which was theoretically predicted in the literature. For comparison, thin high-carbon stainless-steel films were deposited onto oxidized Si wafers with different carbon ratios in the targets (10, 20, 40 and 50 at.%). These films were characterized by means of Mössbauer Spectroscopy, the magneto-optical Kerr-effect, grazing incidence X-ray diffraction and Rutherford backscattering spectrometry. With these methods clearly defined multilayer-structures were observed which could lead to interesting magneto-resistance phenomena if the thickness of the multilayers can be controlled by the processing parameters.     

The Hall effect of thin iron films

A curvature invariant of spacetimes that are solutions to the Einstein-Cartan-Weyl equations is studied. It is found that in the static plane symmetric case this invariant is singular.     

Reversible-adsorption-induced variation of domain width in iron garnet films

It has been found using the Faraday-effect magneto-optic method that the width of magnetic domains of the labyrinth domain structure in bismuth-containing iron garnet films with perpendicular anisotropy changes considerably after the adsorption of methanol molecules. A maximum change in domain width of 50% has been observed in methanol saturated vapor. This effect is reversible. A decrease in domain width under adsorption has been attributed to a decrease in the effective constant of the perpendicular magnetic anisotropy of the film caused by the adsorption of methanol molecules.     

Dispersion of the Voigt effect in thin iron films

The dispersion characteristics of the Voigt effect in thin (<70 nm) films of Fe have been measured and interpreted in the spectral region from 0.6 to 2.8 eV.