We show that post growth annealing of GaMnAs under As capping at temperatures in the range of 180-210ºC leads to significant surface modifications. Depending on GaMnAs layer thickness and composition, we obtain either a smooth continuous reacted (MnAs) surface layer or 3D islands (quantum dots). The surface modifications are due to a solid phase epitaxial process, in which Mn interstitials diffusing to the GaMnAs surface are bound with the As.
The evolution of iron silicide structure grown by solid state epitaxy on Si(111) vicinal surface was investigated by scanning tunnelling microscopy. The reactions, which occur on the surface, are compared for two various Fe coverages: 0.33 and 2 monolayers. The annealing at 250˚C does not enable substantial recovery of the surface ordering, deteriorated by Fe deposition at room temperature. The onset of 2×2 surface reconstruction is observed upon annealing at 400˚C. A three-dimensional growth tendency of iron silicide crystallites on a bare Si(111) 7×7 surface was found at 700˚C. In the case of 2 monolayer coverage crystallites nucleate along the edges of substrate terraces forming a regular array of nanometer size dots. Basing on atomically resolved spectroscopic effects and statistical considerations, structure of iron silicide nanocrystallites as well as Schottky-like character of the barrier at the interface between metallic crystallite and semiconducting substrate is deduced.
The subject of this study is the phase composition evolution of Ni₅₀Ti_{50-x}Moₓ (x=10, 25, 40 at.%) systems prepared by mechanical alloying in as-milled state and after subsequent heat treatment. During milling a mechanically induced solid state reaction between nickel, titanium and molybdenum was observed leading to the formation of nanocrystalline disordered solid solutions. As a result of heat treatment a creation of NiMo intermetallic phase was observed as well as structure relaxation of previously formed solid solutions.
CuCr_{1.65}Se_{4} nanoparticles crystallize in the monoclinic Cr_{2}Se_{3}-type structure of the space group I2/m. The average crystallite size basing on the line broadening is less than 10 nm. With decrease of the size of grains a change from ferromagnetic to ferrimagnetic order, a lack of the magnetization saturation and a strong spin-orbit coupling visible in the large value of the Landé factor g_{χ} = 2.72 are observed. The change in magnetic order is caused by the change of the crystalline symmetry from the cubic phase to monoclinic one.
CuCr₂Te₄ can be obtain by mechanical alloying followed by heat treatment. The obtained phase crystallizes in the spinel-type structure of the space group Fd3m. The calculated crystallite size equals to 100 nm. Magnetic susceptibility measurements showed ferrimagnetic order below 21 K.
In this paper, the effects of P_2O_5 and heat treatment on the crystalline phases and microstructure of lithium disilicate-barium disilicate glass were examined. A wider and broad peak in the differential thermal analysis curve indicates a presence of surface crystallization instead of volume crystallization despite the use of nucleating agent, P_2O_5. The heat treatment schedules were planned according to differential thermal analysis data. The controlled crystallization of the compositions studied was carried out using two-stage heat treatment procedure. The glass transition temperature, T_{g} of the as-cast sample were used to determine the optimum nucleation temperature. The optimum nucleation temperature was determined to be 520°C. The crystallization was carried out at 720C and 880C for 15 min. Lithium disilicate and sanbornite was the major phases and moganite or coesite were also present depending on the heat treatment duration. Due to coexistence of lithium disilicate and barium disilicate phases, the change in the melting entropy prevented the formation of spherulitic morphology and recrystallization after further heat treatments. The rise in the crystallization temperature enhanced grain coarsening and formed massive microstructures.
Promising potential of the Fe-40at.%Al type alloys is used only in a limited way as yet, mainly due to their high brittleness. With regard to attraction of the given type material, the plastometric research at temperatures 800C to 1200C was carried out as a basic one, namely using the uniaxial compression tests at strain rates 10^{-2} s^{-1} to 10^1 s^{-1}. Cylindrical samples were manufactured from laboratory castings, gained by means of the vacuum induction furnace. Two materials were tested - Fe-40Al and Fe-40Al+TiB_2. From the measured flow stress curves the values of maximum stress were obtained and used for determination of the activation energy in hot forming according to the classical equation of the hyperbolic sine type. Enumeration of its parameters led to a possibility to predict maximum deformation resistance values of the investigated alloys in dependence on temperature and strain rate. Pronounced effect of the added titanium diboride particles (< 10 μm) on the activation energy value and to a resistance to the formation of cracks was observed. Thanks to the obtained value of activation energy an equation sufficiently describing the initiation of dynamic recrystallization process in the Fe-40Al+TiB_2 material as a function of the Zener-Hollomon parameter could be derived.
In the present study, Fe_{41}Co_{41}B_{10}Zr_7Cu_1 alloy has been investigated in order to evaluate its thermal stability and structure after heat treatment, as well as the impact of heat treatment on magnetic properties. X-ray diffractometry, differential scanning calorimetry, chemical composition microanalysis, transmission electron microscopy, and magnetic hysteresis loop measurement techniques were employed. The crystallisation temperature of the as-quenched alloy is 490ºC (continuous heating at 5ºC/min). The melt-spun ribbon having 27μm in thickness was annealed for 1 hour at temperatures from 400 to 700ºC. The alloy after treatment at about 550ºC underwent primary crystallisation, with the average size of crystals under 20 nm. This specimen shows the coercive field of 38 A/m, as compared to about 160 A/m reported for a similar alloy (Fe_{44}Co_{44}B_4Zr_7Cu_1) with a similar structure, annealed at 600ºC.
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