Self-similar evolution of the surface morphology of a stressed amorphous alloy foil

A time-ordered sequence of topographic images of a stressed amorphous Fe₇₀Cr₁₅B₁₅ ribbon is presented. It is shown that the surface of this material (unlike polycrystalline metal foil) has a fractal structure due to the nonequilibrium conditions of its formation. As a tensile stress of about 500 MPa is applied to the surface, the fractal dimension of the surface increases from 1.21±0.02 to 1.34±0.03, then drops to 1.12±0.03, and finally increases to 1.22±0.02. In about 1.5 hours, a complex surface morphology characterized by a roughness amplitude of several tens of nanometers evolves into a regular pattern of shear bands with amplitude of about 300 nm. Self-affine changes in surface morphology are explained by competition between several processes, including crack propagation, surface smoothing, and self-diffusion.     

Influence of annealing process on magnetic properties and Barkhausen noise of the Fe-W-B amorphous alloy

The study of structural changes followed by measuring of structure sensitive magnetic properties as the energy of total and stress induced anisotropy, the coercive field, the demagnetizing factor and the Barkhausen noise parameters of the as-cast and annealed Fe_81.4 W_2.6B₁₆ amorphous alloy was performed. The investigated structural changes were connected with the temperature range within which the Fe_81.4W_2.6B₁₆ amorphous alloy was characterized by the soft magnetic properties.     

Light scattering by the surface of amorphous alloy ribbons modified by annealing and cryogenic treatment

The modification of the microrelief and structure of the surface layers of ribbons of an amorphous metal alloy based on iron and cobalt after thermal treatment at elevated and cryogenic temperatures and under the action of an external magnetic field is studied by the method of light scattering. The parameters of the surface roughness were calculated from the experimentally found indicatrices of light scattering. It is shown that heating of the metal ribbons to T=650–750 K partially relieves stresses arising in the course of the ribbon preparation and reduces the surface roughness as compared to that of freshly prepared samples. Cryogenic treatment at T=78 K increases the surface roughness, and application of a magnetic field to a ribbon causes anisotropy in the surface layer due to the magnetostrictive effect.     

Domain structure fluctuations kinetics of amorphous alloys at low-temperature annealing

Previously reported spin orientation fluctuations of the amorphous Fe₈₁B₁₉ alloy at temperatures well below the onset of crystallization were directly shown by the time scanning experiment at 250 °C. The connection of this effect with the magnetostriction field and α-Fe nuclei at the contact surface was proved by the CEMS spectra and by vanishing the effect at both the etched-off Fe₈₁B₁₉ and a zero magnetostriction samples.     

Influence of low-temperature annealing on the microstructure of cryogenically deformed copper

The microstructure formation during annealing of cryogenically deformed copper was studied. It was shown that the primary recrystallization was completed already after a one-hour annealing at 150°C. It was found out that grains with the crystallographic orientation close to {112}〈111〉, {4; 4; 11}〈11; 11; 8〉, {110}〈122〉, and {130}〈132〉 had an advantage in the growth, which, apparently, was associated with a relatively low energy stored during the deformation.     

Fractalization of the surface relief of an amorphous alloy as an indication of rupture

Foils of an Fe₇₇Ni₁Si₉B₁₃ amorphous alloy were subjected to uniaxial tension up to their rupture. Techniques of scanning tunneling, atomic force, electron, and optical microscopy were applied to study the surface relief of loaded foils and their rupture faces. By means of wavelet transformation and by the box counting method, it was shown that, before rupture, the foil surfaces in the region of the future rupture tend to become monofractal and that the rupture face inherits this fractality.     

Influence of annealing on the magnetoimpedance effect in amorphous FeCoMoSiB ribbons

The effect of annealing by electric current passing through a sample prepared from the amorphous metallic alloy Vitrovac 6025 Z of the composition Fe₄Co₆₇Mo_1.5Si₁₆₅B₁₁ on the form of the dependence of the sample impedance on the external magnetic field is investigated. The results are explained on the basis of the concepts concerning the change in the preferred direction of the sample magnetization.     

A slow positron lifetime study of the annealing behaviour of an amorphous silicon layer grown by MBE

We have studied MBE grown amorphous silicon, which was recrystallized at different temperatures for one hour, with a pulsed positron beam. A positron lifetime of 538±10 ps in the as-grown state is attributed to microvoids containing at least 10 vacancies. An incompletely recrystallized sample annealed at 500°C shows an additional long lifetime from ortho-positronium (o-Ps) pick-off annihilation. The o-Ps component disappears for samples, recrystallized at 700°C and above, and the defect lifetime steadily decreases with higher annealing temperature until a value of 310 ps is reached for the layer annealed at 1200°C. This value is explained by positron trapping at dislocations or small vacancy defects stabilized by dislocations or impurities.Paper presented at the 132nd WE-Heraeus-Seminar on Positron Studies of Semiconductor Defects, Halle, Germany, 29 August to 2 September 1994     

Fast solid-phase crystallization of amorphous silicon films on glass using low-temperature multi-step rapid thermal annealing

Effects of multi-step rapid thermal annealing of plasma-deposited amorphous silicon films on Corning 7059 glass are investigated. A three-step rapid thermal annealing for 10 s/step at 730° C after film deposition reduces the activation energy of electrical conductivity for silicon films from 0.64 to 0.51 eV and causes (111) grain growth with a size of 1500 Å, which is determined using scanning electron microscopy, Raman spectroscopy and X-ray diffractometry.     

Dependence of alloy surface chemistry on sample morphology

We have examined the dependence of the chemical activity of a platinum/gold alloy on surface morphology and surface composition. Measurements of surface composition by Auger spectroscopy and surface chemical activity by CO flash desorption indicate that sample morphology strongly affects both the surface composition and surface chemical behavior. These results raise questions about the comparability of data obtained on differently prepared polycrystalline alloy samples.     

Effect of the amorphous thin layer on the surface growth of amorphous/crystalline binary multilayer films

The effect of the amorphous thin layer on the surface growth of amorphous/crystalline binary multilayer films has been studied by using a continuum model. It is shown that both the surface roughness and the growth exponent of amorphous/crystalline binary multilayer films decrease with increasing thickness ratio between amorphous and crystalline layers. Our simulations have also revealed, in contrast to the monotonous rise in surface roughness observed in single-layer films grown on flat substrates, the surface growth of a multilayer film consists of two processes: interface smoothing and roughening, namely the film roughness decreases during the growth of amorphous thin layers but increases monotonously during the growth of crystalline thin layers. The observed interface smoothing and roughening can be obviously influenced by the change in the thickness ratio between amorphous and crystalline layers. The rise in thickness ratio between amorphous and crystalline layers enhances the interface smoothing effect but lowers the interface roughening effect and consequently shows a marked smoothing effect on the surface roughness.     

Laser annealing study of PECVD deposited hydrogenated amorphous silicon carbon alloy films

The influence of carbon content on the crystallization process has been investigated for the excimer laser annealed hydrogenated amorphous silicon carbon alloy films deposited by Plasma Enhanced Chemical Vapour Deposition (PECVD) technique, using silane methane gas mixture diluted in helium, as well as for the hydrogenated microcrystalline silicon carbon alloy films prepared by PECVD from silane methane gas mixture highly diluted in hydrogen, for comparison. The study demonstrates clearly that the increase in the carbon content prevents the crystallization process in the hydrogen diluted samples while the crystallization process is enhanced in the laser annealing of amorphous samples because of the increase in the absorbed laser energy density that occurs for the amorphous films with the higher carbon content. This, in turn, facilitates the crystallization for the laser annealed samples with higher carbon content, resulting in the formation of SiC crystallites along with Si crystallites.     

Formation of near stoichiometric A15Nb3Si from annealing an amorphous alloy under high pressure

The A15Nb₃Si with a composition closed to stoichiometric compound has been synthesized under high pressure from a starting material of Nb₇₇Si₂₃ amorphous alloys. High pressure annealing was carried out in Bridgman anvils apparatus. The amorphous alloy would decompose into A15Nb₃Si, bcc Nb solid solution and hexagonal phase when it was annealed under a pressure lower or a temperature higher than that for forming single phase A15Nb₃Si. The yielded A15Nb₃Si exhibited a superconducting transition temperatureT _c of 19.1 K, and has been indexed unambiguously with a lattice parameter ofa=0.5093 nm. Moreover, a nonlinear relationship betweenT _c anda has been constructed from our experimental data, and aT _c of 27 K for stoichiometric A15Nb₃Si can be expected.     

Influence of the Si cap layer on the SiGe islands morphology

Transmission electron microscopy (TEM), atomic force microscopy (AFM), and EDX methods were used to study morphology and chemical composition of SiGe/Si(001) islands grown at 700 degrees C and covered at 550 degrees C and 700 degrees C by Si layers of different thickness. The samples were grown in ultra high vacuum chemical vapor deposition process (UHVCVD) controlled with in situ reflection of high-energy electron diffraction (RHEED). The islands transformed from initial pyramid and dome shapes to lens shape for 1.4 nm and 3.7 nm cap layer thickness at 550 degrees C and 700 degrees C, respectively. An increase of lateral to vertical ratio was observed during the transformation. For the higher depositing temperature the ratio was bigger and was increasing continuously with cap layer thickness. Also, with increasing Si cap layer thickness, the Ge concentration was decreasing, which was more observable for higher capping temperature.     

Ising-Nakano model for an amorphous alloy

A lattice model, taking into account the possibility of an atom being pinned at a site upon vitrification, has been developed for binary alloys. The Hamiltonian found for the problem is used in the average-field approximation to obtain equations for the parameters of atom pinning and long-range compositional order. The conditions under which mixing of the components promotes vitrification are analyzed.Translated from Izvestiya Vysshikh Uchebnykh Zavedenii, Fizika, No. 12, pp. 89–93, December, 1991.     

Electronic and topological parameters of the skin layer in amorphous metallic ribbons after thermal annealing

Data on spectral polarimetric measurements in the range of 0.05–0.60 eV are presented, along with calculations on the optical characteristics of the surface layers of ribbons of the amorphous alloy Co₅₉Fe₅Ni₁₀Si₁₁B₁₅ before and after thermal annealing in order to determine how the composition of the surface layer changes during this treatment. It is shown that after annealing at a temperature of 425°C or above, the optical conductivity and the real and imaginary parts of the dielectric constant revert to the values for typical metals in the IR. This treatment produces microregions with an ordered structure in the surface layer. The experimental data show that for ribbons annealed at T = 475°C the spectral optical characteristics do not obey the Drude relations and behave similarly to their amorphous analogs.     

钛合金表面激光熔覆TiC_p/Ni基合金复合耐磨涂层

采用激光熔覆技术在TC4合金表面制备TiC颗粒增强的Ni基合金复合材料涂层,测试了熔覆层的硬度和滑动摩擦磨损性能,分析了熔覆层的强化机制。结果表明,熔覆层中存在颗粒强化、固溶强化和细晶强化等多种强化作用,熔覆层的显微硬度达HV900～1100,耐磨性能比TC4合金显著提高。     

Crystallization behavior of iron-based amorphous nanoparticles prepared sonochemically

In general, a rapid quenching is required to obtain an amorphous metal. It is known that an intensive ultrasonication generates a very high temperature within cavitation bubbles in a very short moment, which enables a rapid quenching process in a liquid phase synthesis. In this study, the sonochemically-derived “amorphous iron” from Fe(CO)₅ was carefully examined by XRD, TEM, TG-DTA. The product was found to be an amorphous containing a certain amount (∼15%) of volatile component that can be removed by heating in a nitrogen flow. After annealed in the inert atmosphere at 600 °C, cooled down to room temperature, and then exposed in air (oxygen), the sample showed a strong exotherm accompanied by a weight gain. This is due to oxidation of fine metallic iron. Experimental operations of such a reactive material were examined.     

Influence of the short-range order parameter on the optical properties of amorphous nickel-phosphorus alloy

The influence of the short-range order of amorphous nickel-phosphorus alloy on the IR absorption is studied. The relation between the optical properties and the microstructure of amorphous nickel-phosphorus alloys obtained by various technological methods is considered. It is shown that a coating of amorphous Ni−P alloy obtained by electrolytic deposition has the most homogeneous structure; this permits the use of such coatings as protective layers for optical and magnetic memory disks. Optical methods permitting the estimation of the dimensions of the microcrystalline regions in an amorphous matrix are outlined. T. Shevchenko Kiev University. Translated from Izvestiya Vysshikh Uchebnykh Zavedenii, Fizika, No. 5, pp. 34–40. May, 1997.     

Silicon diffusion in an Fe-based amorphous alloy

The segregation rate of Si in amorphous as well as precrystallized Fe₈₁B_13.5Si_3.5C₂ was determined as a function of time at different temperatures below the crystallization temperature. Analysis of the segregation kinetics yielded diffusion parameters of E = 72±9 kJ/mol, D₀ = 1.7 × 10⁻¹⁵m²/s for the amorphous specimen and E = 154±5 kJ/mol, D₀ = 3.6 × 10⁻¹⁰m²/s for the crystalline specimen. The difference is explained by the initial presence of an oversaturated concentration of structural defects. The correct interpretation of segregation kinetics results for amorphous alloys is discussed.