A study on growth and crystallization behavior of nanostructured amorphous silicon nitride

For the first time, the growth and crystallization behavior in nanostructured amorphous silicon nitride (NASN) were systematically studied. NASN has excellent thermal stability below 1300°C, i.e. NASN does not grow below 1300°C. However, as soon as crystallization occurs the particles suddenly grow. This may be related to an interfacial effect in the NASN pellet. The relationship between growth and crystallization behavior is discussed.     

Finemet-Co非晶合金的结晶动力学研究

利用标准的单棍甩带技术在大气环境下制备了Fe73.5-xCOxSi13.5B9Cu1Nb3 (x=10、30,50)非晶条带.在550和600℃下分别对非晶条带进行真空等温退火1h,从而在非晶基体中形成纳米晶相.X射线衍射(XRD)分析结果表明,550和600℃真空等温退火1h后,Fe73.5-xCOxSi13.5B9...     

Small-angle X-ray scattering study on the structure and crystallization of amorphous Fe-P-C alloy

The change in structure of an amorphous Fe-P-C alloy during ageing was examined using small-angle X-ray scattering (SAXS) measurement and transmission electron microscopy. The SAXS intensity was related to two different types of scattering regions depending on ageing time and temperature. The major scattering was from the crystalline particles, which had two-phase lamella structures. The average thickness of the lamellae remained constant at about 5 nm during ageing. The interlamella distance was three to five times the lamellar thickness in the regular packing region. Another minor scattering was interpreted as being caused by the local ordering of atomic configuration in the amorphous state. The average size of the scattering region was 1.8 to 2.4 nm and quite similar to the critical range proposed by Giessen and Wagner, beyond which the shortrange order disappears.     

Ferromagnetic resonance study of structural relaxation and crystallization of the Metglas 2826A amorphous alloy

The ferromagnetic resonance technique was used to study the ageing behaviour of the metallic glass Fe₃₂Ni₃₆Cr₁₄P₁₂B₆ (Metglas 2826A). The peak-to-peak linewidth was measured for several isothermal annealing times in the temperature range 350 to 375° C. After an initial decrease, attributed to structural relaxation, the linewidth increases linearly with the transformed fraction of the first crystallization phase. For 0.05 <f< 0.50, the transformed fraction,f, as a function of time,t, satisfies the Avrami equation with the exponentn being between 1.58 and 1.71. The activation energy for the first crystallization phase is estimated from the times to reach 5 to 40% transformation to be 306 kJ mol^–1. The experimental results suggest that the second phase of crystallization begins when the transformed fraction of the first phase is of the order of 50%.     

Phase diagram study of the formation and crystallization of Ge-metal amorphous alloy films

The Ge-Au and Ge-Ag alloy films were deposited in vacuum at room temperature and then systematically observed in the TEM. The maximum metallic concentrations in the alloy films,C _max, which form the stable amorphous alloy phases of germanium with gold and silver, were obtained. The annealed crystallization temperatureT _c, which falls with increasing metallic content in these films was also found. The structures of these films and their annealed specimens were also studied. There are various factors which influence the formation of amorphous alloy films deposited in vacuum for Ge-metal systems. A new formula forC _max has been derived. The annealed crystallization character has been explained by means of the variation of the free energy and the activation energy of crystallization. The activation energy of crystallization,E _a, can be obtained from the data values ofT _c. For Ge-Au films,E _a (Au)=E _a ^o /(–18.66C _Au ² +16.83C _Au+1)±3.3 (kcal mol^–1); for Ge-Ag films,E _a (Ag)=E _a ^o /(–2.754C _Ag ² +3.815C _Ag+ 1)±2.6 (kcal mol^–1). In order to explain all these results, two kinds of phase diagram for the alloy films have been introduced. One is the three-dimensional relationship diagrams of phase formation in semiconductor-metallic alloy films; it was introduced to explain the influencing factors. The other is the three-dimensional phase diagrams of annealed semiconductor-metallic films systems. From this diagram all the phase transitions can be found.     

SAXS study on crystallization of an amorphous Pd76Au6Si18 alloy

The crystallization behaviour of an amorphous Pd₇₆Au₆Si₁₈ alloy has been investigated mainly by means of small angle X-ray scattering measurements. The amorphous alloy crystallized to form MS-I phase with composition Pd₇₈Au₂₂ in the amorphous matrix, which later crystallized as MS-II. The crystallization kinetics of MS-I phase were analysed in the framework of conventional nucleation theory. It was suggested that the considerable number of nuclei of MS-I phase had been already formed in the as-quenched specimen and the remaining nucleation attained within the short period of isothermal ageing. The remarkable increase of the scattering intensity corresponded to the growth of MS-I phase, the kinetics of which were found to be controlled by the diffusion mechanism. The interdiffusion constant was obtained fromD=6.0×10¹⁵ exp (–420 kJ mol^–1/RT) m² sec^–1, which agreed fairly with the reported values.     

CoNbZr非晶软磁薄膜晶化动力学研究

采用 DSC热分析技术,结合 XRD、TEM和AFM实验,对磁控溅射制备的 Co85.5Nb8.9Zr5.6非晶合金软磁薄膜进行了变温和等温晶化动力学的研究。研究结果表明:升温晶化时,薄膜的晶化的表观激活能为99.82kJ/mol;局域激活能随晶化度增加;在等温晶化过程中,平均激活能为 88. 51kJ/mol, Avrami 指数1.17~1.39, 晶化行为主要是一维表面晶化,晶核长大受扩散控制的过程。     

Substrate effects on the crystallization kinetics of amorphous selenium thin films

A thermoanalytical technique has been used to study crystallization in thin amorphous selenium (a-Se) films deposited on polyimide and on aluminum-coated polyimide substrates. Through analysis of thermograms obtained by differential scanning calorimetry, the activation enthalpy of crystallization for a-Se on these substrates has been measured. It has been found that the film deposited on Al-coated polyimide crystallizes with an activation enthalpy similar to that obtained for bulk-quenched a-Se, while the film deposited on bare polyimide crystallizes with a lower activation enthalpy than that for the bulk sample. This suggests that the structure of a-Se films can be influenced by the choice of substrate.     

Preparation and crystallization of chromium-based amorphous alloys

The glass formability of the Cr₇₂ (B, Si, C)₂₅Al₃ system has been investigated. Samples were prepared by rapid quenching from the melt by the melt spinning technique. Of the compositions investigated, only Cr₇₂B₁₀C₁₀Si₅Al₃ and Cr₇₁ C₁₇Si₈Al₃ formed fully amorphous alloys. These showed crystallization temperatures of 997 and 990 K, respectively, among the highest reported for transition metal-metalloid amorphous alloys. The crystallization products have been found to be Cr₇C₃ and Cr₃(Si, B) for Cr₇₂B₁₀C₁₀Si₅Al₃ and Cr₇C₃ and Cr₃Si for Cr₇₂C₁₇Si₈Al₃. The effects of substituting iron in place of chromium in Cr₇₂C₁₇Si₈AI₃ have been investigated. For up to 20 at% Fe the crystallization products are (Cr, Fe)₇C₃ and Cr₃Si. An alloy with 30 at% Fe crystallizes into (Cr, Fe)₇C₃ and hexagonal Cr-Si-C.     

Non-isothermal analysis of the crystallization of the amorphous germanium dioxide

The amorphous germanium dioxide devitrification has been investigated, with particular regard to the kinetic aspects and to the crystallization mechanism. The amorphous material transforms into the hexagonal dioxide modification, which is metastable at the considered temperatures. This fact is in accordance with the presence of tetrahedrally coordinated Ge in both the glass and the devitri fied material. The crystallization kinetics has been investigated by means of the DTA technique; a rigorous method of analysis has allowed the determination of the activation energy E_act, the Arrhenius preexponential factor A and the morphological index n characteristic of the devitrification reaction. We have so obtained the following values: E = 233 kJmol^?1, A = 6.57 · 10⁷s^?1 and n = 2.44. These results are not in total accordance with previous studies carried on with similar non-isothermal techniques. Our interpretation is supported also by the morphological study of the GeO₂ crystal growth carried out by scanning electron microscopy.     

Laser stimulated low-temperature crystallization of amorphous silicon

Laser annealing of amorphous silicon (a-Si) at different initial temperatures (77 and 300 K) has been studied. It is established that the laser-stimulated crystallization of silicon is possible at relatively low temperatures. A theoretical model is proposed, which explains this phenomenon by melting via the electron mechanism followed by recrystallization.     

Preparation and crystallization of Fe-Co-B amorphous powder

Ultrafine (Fe_0.7Co_0.3)_100–x B _x amorphous powders with boron contentx in the range 27–40 at % have been prepared by borohydride reduction. The preparation process shows that the powders have a catalysis property. The results of X-ray and electron diffractions show that all of the samples were spherical amorphous particles of dimension <0.2 m. The difference in the ease of composition between Fe-Co-B powder and ribbon indicates that the local environment of Fe-Co-B powder may be different from that of Fe-Co-B ribbon. The study of crystallization behaviour using Mössbauer, X-ray and differential scanning calorimetry measurements indicates that there are two steps in the crystallization process. These steps represent the formation of -Fe₇₀Co₃₀ phase and Fe₂B-like phase, respectively.     

Stress induced crystallization of hydrogenated amorphous silicon

Hydrogenated amorphous silicon films were grown on to thermally oxidized silicon wafers by Radio Frequency magnetron sputtering, and SiN_x and Al₂O₃ capping layers were used to control the residual thermal stress. After annealing, a comparison of the silicon films with and without capping layers indicates that tensile stress induced by the capping layer enhances the crystallinity of the annealed amorphous silicon film. The stress is due to the mismatch between the coefficients of thermal expansion for the capping layer and amorphous silicon film. These results highlight the potential of thermal stress as a means to alter the crystallization in thin film architectures and suggest that even larger effects can be obtained with suitable choices of capping layer chemistry.     

Formation and crystallization of Al-Fe-Si amorphous alloys

Rapid solidification experiments of Al-based Al-Fe-Si ternary alloys have been performed both by the gun and single roller methods. Glass forming tendency is found to be largest near theβ-phase (Al₉Fe₂Si₂) composition, where the amorphous state is obtained both by the gun and single roller methods. Crystallization behaviour of amorphous AlFe_13.0Si_17.4 alloy, nearβ-phase composition, followed the course of (i) the appearance of fineα-Al particles and (ii) the transformation of the matrix intoβ-phase. The ratio of crystallization temperature and the melting point,T _x/T _m, for AlFe_13.0Si₂17.4 amorphous alloy is smaller than 0.5 indicating the difficulty of glass formation of these alloys.     

Induced crystallization of an amorphous Cu-Zr alloy

The crystallization behaviour of the amorphous Cu₆₀Zr₄₀ has been examined by simultaneous deformation and annealing, just below the crystallization temperature T_c. This treatment causes a heterogeneous nucleation and growth of small crystals, belonging to the Cu₁₀Zr₇ phase near the Cu₆₀Zr₄₀ composition. It was also found that subsequent annealing at temperatures $\text{T}\text{≤}\text{T}{}_{\mathrm{<mtext>c</mtext><mtext>?</mtext>}}$ does not accelerate the crystal growth, but results in a copious nucleation surrounding the single crystals.