Crystallization Of Amorphous Films Research Articles

Crystallization dynamics of chalcogenide glass films under non-equilibrium conditions

Extremely fast glassification and recrystallization of chalcogenide films can be achieved by pulse (<1 μs) laser irradiation; the crystallization of amorphous films takes place under larger non-equilibrium conditions. Some structural change properties, such as metastable phase formation and inhomogeneous crystallization in the sub-micrometer domain, are reported in this paper. Computer modelling of the melting and recrystallization processes are presented, and experimentally verified by transient reflectivity change measurement. Transmission electron microscope (TEM) images and electron diffraction (ED) patterns of the micro-domains of chalcogenide films, irradiated by laser beams of different energies and pulse durations, are presented. Acceleration of the crystallization speed in micro-domains of chalcogenide films under laser irradiation is discussed.

Structure and Crystallization of Ag3SbS3 Layers Obtained by Pulse Laser Evaporation

The results of structural investigations by means of transmission electron microscopy, diffraction and scanning electron microscopy of films prepared by pulse laser evaporation Ag3SbS3 single crystals are presented. The chemical composition of the films was controlled by X-ray fluorescence spectroscopy and Auger-electron spectroscopy. The effect of laser-evaporator pulse frequency, average single-pulse energy and substrate temperature on elemental chemical and phase composition and structure of deposited films was studied. The results show that the crystallization of amorphous films occurs according to homogeneous and heterogeneous mechanisms.

Laser-induced crystallization in amorphous films of (C = S, Se, Te), potential optical storage media

The amorphous-to-crystalline phase change induced by a continuous-wave laser was investigated systematically in the case of as-grown amorphous films of , and and results were compared. The photo-thermal process is found to be responsible for the phase change in all three compounds. The minimum threshold laser power required to induce optical contrast at an irradiated site was found to depend on the film thickness; however, the required power density was found to be of the order of for all three films. All three films exhibited good potential for use as the WORM kind of storage devices, films having the minimum threshold power. and films in the non-stoichiometric phase exhibited potential for reversible storage.

Structure and magnetic properties of BaCoTiFe10O19 thin films with an easy-axis in-plane orientation

BaCoTiFe10O19 hexaferrite thin films with an easy-axis in-plane orientation were prepared by crystallization of amorphous films deposited by rf magnetron sputtering. The structure and magnetic properties were investigated. It is shown that CoTi-doping leads to a reduction of spontaneous magnetization and magnetic moment, which is caused by non-collinear magnetic structure and surface spin canting of small particles. The substitution of CoTi for Fe can adjust coercivity and Curie temperature over a very wide range, while still maintaining the room temperature magnetization. It is found that BaCoTiFe10O19 films exhibit a large squareness of hysteresis loop, Sq = 0.68. Thus, this film is desirable for high-density longitudinal recording systems.

Cold crystallization studies on PET/PEN blends as revealed by microhardness

The cold crystallization of amorphous films of poly(ethylene terephthalate) (PET) and poly(ethylene naphthalene-2,6-dicarboxylate) (PEN) blends, with different composition, prepared by co-precipitation from solution followed by melt-pressing for 2 min at 280°C and quenching in ice-water, was followed by measuring the microhardness, H, in real time as a function of crystallization temperature and time. An analytical model was derived, relating properties of the individual components to the blend microhardness based on an Avrami-type equation to account for the crystallization of the components upon heating. Fitting of the model to the experimental results revealed a two-step hardening process of the blends. The degree of transesterification of the blends, can be estimated with this model. Finally, a removal of the physical ageing, inducing a decrease in H of PET in the blend, was observed upon heating above its glass transition temperature.

Precisions on reaction monitoring from in-situ resistance measurements: relations between such measurements and actual reaction kinetics

Because of the current interest in using in-situ resistance measurements for the rapid investigation of thin film reactions and transformations, it is important to understand the various morphologies that the resistance versus temperature curves may assume. Several typical conditions for both planar reactions (as in silicide formation) and lateral transformations (as in the crystallization of amorphous films) have been explored. The characteristic features of the curves, e.g. inflection points, are analyzed for different conditions such as an increase or decreased in resistance. Emphasis is placed on understanding the appearance, or absence of such features, and on their relation to fundamental reaction characteristics such as heat generation.

Phase-field model for activated reaction fronts.

We propose a phase-field model to describe reaction front propagation in activated transitions obeying Arrhenius kinetics. The model is applicable, for example, to the explosive crystallization of amorphous films. Two coupled fields interact during the reaction, a temperature fieldT(x,t) and a field C(x,t) describing the amorphous/crystal transition, which are continuous functions of space x and time t. Unlike previous work, our model incorporates a nonzero front width e in a natural way, corresponding to that region in space where T and C undergo rapid variation. In the limit of e!0, our model reduces to the sharp interface approach of others. Treating the background temperature of the reacting sample as a control parameter, periodic solutions in C and T can be found which go through a series of period doubling bifurcations. We find that the substrate temperature marking the onset of period doubling bifurcations decreases with increasing concentration diffusion. Furthermore, it is shown that period doubling bifurcations of C-T solutions of period greater than 2 are generated by dynamics isomorphic to those of the one-dimensional logistic map, for all values of concentration diffusion studied.

Topics in solid phase epitaxy: Strain, structure and geometry

The effects of some experimental parameters on the solid-phase crystallization of amorphous films on single crystals, a process known as Solid Phase Epitaxy (SPE), are examined. Results from a large community of researchers concerning SPE of alloys and compounds, strained films, films in constrained geometries and films with unusual amorphous/crystal interfaces are reviewed. Our present understanding of mechanisms involved in SPE is given, and the implications of the wide range of experimental results are discussed.

Effects of Ge on Material and Electrical Properties of Polycrystalline Si1 − xGex for Thin‐Film Transistors

films deposited by very low pressure chemical vapor deposition (VLPCVD), with and without plasma enhancement, and by low‐pressure CVD (LPCVD) were studied to explore the effects of Ge on various properties of films. As the Ge content increases, growth rates increase for thermal and plasma‐deposited polycrystalline and amorphous films. The transition temperature for poly‐to‐amorphous deposition is lower, and the crystallization of amorphous films is faster. Enlarged grain sizes are achieved with Ge in films grown thermally, with plasma enhancement, and by solid‐phase crystallization, with grain sizes as large as 1.3 μm in films of 1000 Å thickness. Increased n‐type and p‐type Hall mobilities and decreased p‐type resistivities are achieved as functions of Ge content in films with . The Hall mobility in an n‐type film is 50 cm2/V‐s, the highest value reported to date for materials. thin‐film transistors (TFTs) have been fabricated and evaluated, leading to a proposal of a poly‐Si‐capped TFT structure.

Local anisotropic structure in amorphous Ba-Fe-O films and its role in determining magnetic anisotropy in crystallized Ba-hexaferrite films

Ba hexaferrite films with the easy direction of magnetization perpendicular or in-plane can be prepared by crystallization of amorphous films deposited under different sputtering conditions. Using polarization-dependent EXAFS (extended X-ray absorption fine structure), we have observed anisotropic local structure around the Fe atoms in as-sputtered amorphous Ba-Fe-O films. Such structure has not been detectable by conventional structural characterization techniques (X-ray diffraction, electron diffraction and transmission electron microscopy [TEM]). The results suggest that this local structural anisotropy determines the orientation of the fast-growing basal plane directions during post-deposition annealing and thus the directions of the c-axes and the magnetic anisotropy.

Elastic Properties of Thin Films

AbstractA technique has been developed for characterizing the disorder present in thin films through the measurement of their low temperature internal friction. The technique utilizes a substrate, in the form of a double paddle oscillator etched from a high purity silicon wafer, onto which the thin film of interest can be deposited. The oscillator possesses an internal friction of 3 × 10−8 at 4 K which is reproducible to within 1% upon thermally cycling to room temperature. This extremely small substrate internal friction coupled with the excellent reproducibility permits measurements of the internal friction of very thin amorphous films, with a 2 tun silica film producing a change in the internal friction of 4 × 10−9. By performing low temperature internal friction measurements on thin silica films with thicknesses ranging from 2 nm to 1000 nm, we have investigated the role of interacting defects in determining the universal nature of the anomalous low temperature thermal and elastic properties of amorphous solids. We have found no evidence for strong interactions between these tunneling defects. Other applications of the oscillator include monitoring of the crystallization of amorphous films through changes in the low temperature internal friction, internal friction measurements and vapor pressure measurements of quenched condensed rare gas solids and amorphous water ice, and internal friction studies of amorphous solids which can only be produced in thin film form.

Effects of crystallization on structural and dielectric properties of thin amorphous films of (1−x)BaTiO3-xSrTiO3 (x=0–0.5, 1.0)

The possibilities for fabricating solid solutions of (Ba1−x,Srx)TiO3 (x≤0.5,1.0) by crystallization of amorphous films and for improving their dielectric properties by adjusting the Sr content were investigated. Thin amorphous films were prepared from powder targets consisting of mixtures of BaTiO3 and SrTiO3 by sputtering with a neutralized Ar-ion beam. The amorphous films crystallized into (Ba1−x, Srx)TiO3 solid solutions with a cubic perovskite-type structure after annealing in air at 923 K for more than 1 h. The Debye-type dielectric relaxation was observed for the amorphous films, whereas the crystallized films showed paraelectric behavior. The relative dielectric constants were of the order of 20 for the amorphous samples, but increased greatly after crystallization to about 60–200, depending on the composition; a larger increase in the dielectric constant was observed in the higher Sr content films, in the range x≤0.5, which could be correlated with an increase in the grain size of the crystallites. The crystallization processes responsible for the difference in the grain size are discussed based on the microstructural observations.

Polarizing effects of magnetization on the crystallization of Co100−xPx amorphous alloys

Results are presented on the microstructure and magnetic properties of samples obtained by crystallization of amorphous films of composition Co100−xPx (10&amp;lt;x&amp;lt;25). Microstructural studies by means of scanning electron microscopy, x-ray diffractometry, as well as magnetic measurements showed the presence of a well-defined texture in the cobalt crystallites of samples of composition given by x&amp;lt;21, the easy axis direction of the amorphous samples being preserved during the crystallization. In these samples the thermal dependence of the coercive and anisotropy fields and of the remanence was studied. The crystallization product of samples of composition given by x≳21 is characterized by the presence of cobalt crystallites with random easy axes distribution. The polarizing effect of the magnetization was evidenced through the correlation between the two different types of microstructure and the presence or absence of magnetic order during the crystallization of the samples.

Solid Phase Heteroepitaxy of Barium Ferrite on Sapphire

ABSTRACTA new process for the crystallization of amorphous films on chemically dissimilar substrates, solid phase heteroepitaxy (SPHE), is described. Unlike SPE in Si, it is found that the kinetics can be modeled by nucleation and multi-dimensional growth with Johnson-Mehl kinetics modified for the effects of a finite film thickness and nucleation initiated at the interface with the substrate.

Effect of crystalline inclusions on the explosive crystallization of amorphous films of pure metals

The front velocity, U f, of the explosive crystallization (EC) of amorphous films of Yb and Bi was investigated as a function of relative volume, x, of crystalline inclusions. One-phase amorphous films with thicknesses between 40 and 70 nm were obtained by vapour deposition on liquid helium-cooled substrates. Partial crystallization of amorphous films was obtained by isothermal annealing. The EC of partially crystallized films was initiated by a local current pulse. The velocity of the EC front is found to diminish with growing x. At x ∼ 0.5, the EC ceases. Experimental results are quantitatively explained by a theory based on the approximation of the ‘renormalized’ temperature effect of crystalization T ̃ Q = (1 − x) T Q . Here T Q is the ‘initial’ (at x = 0) temperature effect of crystallization ( T Q = Q/ c, where Q is the crystallization heat and c is the specific heat). validity of the above approximation is discussed.

Island Growth during the Crystallization of Amorphous Ge48Te52 Films

Microstructural TEM studies have been combined with temperature-dependent measurements of laser reflection and transmission to study crystallization in amorphous films of near-stoichiometric germanium telluride. The transformation proceeds by rapid growth of crystalline islands through the film thickness followed by two-dimensional growth in the film plane. Isothermal studies find an Avrami exponent of 4.5 suggesting a non-linear crystal growth rate.75nm of Ge48Te52 was deposited by co-evaporation from separate Knudsen cells onto Si, carbon-coated mica, and glass substrates. Compositions were determined by x-ray fluorescence from films deposited on silicon.

Crystallization of Fe-Zr metallic glasses during ion irradiation

The crystallization of amorphous films of Fe-Zr, with and without heavy-ion irradiations, has been investigated. The results are compared with corresponding data of ion-beam mixing. Irradiation lowers the crystallization temperature, the effect being strongest where simple terminal phases form. We suggest that this is connected to differences in sensitivity to radiation of the various phases.

Possibilities of the Bend-Contour Method in the Analysis of the Lattice Disorientations in Crystals on Thin-Film Transformations

The paper summarized some of the authors data on the transmission electron microscope (TEM) investigations using bend-contours(BC)the transformations of crystal lattice orientations on crystallization of amorphous films and recrystallization. Most investigations were made in situ in JEOL and TESLA microscopes under the influence of the electron beam, Fig.3-5, 8,9. In some cases the video record was produced, some clippings supposed to be demonstrated.1. The possibilities of BC method were outlined earlier (e.g.1). In particular they are similar to Kikuchi lines method and sometimes are more powerful. However these and some other options are rarely used in practice though BC patterns often present on the TEM images and carry the unique diffraction information written in the image plane. The merits of BC method in the evaluation of the lattice orientation, if compared with traditional selected area diffraction(SAD)-high locality, the possibilities of simultaneous analysis of large areas(fields of orientations) and visual ability, the demerits - fitness only to crystals with large orientation gradients(more than 10−2rad/μm).

Magnetic properties and synthesis of high i H c Sm-Ti-Fe

The room-temperature intrinsic coercive force, iHc, of the hard Sm-Ti-Fe phase observed in film samples has been measured as a function of composition. The maximum iHc observed at room temperature was 38.5 kOe for a composition Sm19Fe73Ti8. Such samples were first made amorphous and then subsequently crystallized with an in-plane magnetic field, Hs, applied. Tentative tetragonal lattice parameters have been assigned to this phase based on a fitting of 30 x-ray lines between 30° and 80° 2θ for Cu radiation. The fitted tetragonal parameters are a=8.403 Å and c=12.401 Å. This high iHc Sm-Ti-Fe phase has not been observed in films that were directly crystallized onto heated substrates. The ferromagnetic Fe-rich phases in Sm-Ti-Fe samples have been synthesized by rf sputtering films onto heated as well as room-temperature substrates. The samples synthesized onto heated substrates were crystallized directly upon deposition, while the samples deposited onto room-temperature substrates were amorphous and were then subsequently crystallized. An in-the-film-plane magnetic field, Hs, was applied during the deposition as well as during the subsequent crystallization of amorphous film.

Role of boundaries in the crystallization of amorphous films

The nucleation and growth processes which lead to the formation of a thin film are particularly amenable to investigation by transmission electron microscopy either in situ or subsequent to deposition. In situ studies have enabled the observation of island nucleation and growth, together with addition of atoms to surface steps. This paper is concerned with post-deposition crystallization of amorphous alloys. It will be argued that the processes occurring during low temperature deposition of one component systems are related but the evidence is mainly indirect. Amorphous films result when the deposition conditions such as low temperature or the presence of impurities (intentional or unintentional) preclude the atomic mobility necessary for crystallization. Representative examples of this behavior are CVD silicon grown below about 670°C, metalloids, such as antimony deposited at room temperature, binary alloys or compounds such as Cu-Ag or Cr O2, respectively. Elemental metals are not stable in the amorphous state.