The crystallisation behaviour of LPCVD silicon films has been investigatedby TEM from in situ isothermal annealing of undoped a-Sifilms deposited from disilane (Si2H6) at temperatures450,465 and 480 °C and at gas pressure of 200 MTorr. Nucleation kinetics,grain growth rates and crystallisation kinetics were determined fortemperatures ranging from 600 to 675 °C. Nucleation kinetics have beenexperimentally determined in the early first stages of annealing : they donot show any steady-state rate and are fitted according to a power law.Experimental data for crystallisation kinetics are fitted by an Avrami lawwithout introducing any incubation time.

Isothermal crystallization kinetics of Ni24Zr76amorphous alloy has been studied by differential scanning calorimetry (DSC).Theoretically estimated transient times are found to be consistent with theexperimentally observed incubation periods. The crystallization kinetics hasbeen analyzed in terms of Kolmogorov-Johnson-Mehl-Avrami (KJMA) Model andsignificant departure from the linear KJMA behavior was observed. Suchnon-linearity is due to the surface-induced crystallization, anisotropiegrowth of the crystals, impingement effects and variation of the nucleationrate during crystallization etc. By applying high-resolution electronMicroscopy (HREM), it has been shown that the nucleation and growth of thecrystals do not take place at a constant state of disorder.

Two-dimensional cellular automata simulations were carried out to study thecase of the crystallization (or recrystallization) of a matrix containing aninert, immobile second phase. A range of particle area fractions and aspectratios were investigated under continuous grain nucleation conditions,assuming that the effect of particles is limited to geometric impingementupon contact with the growing grains. Systematic deviations from theclassical Johnson, Mehl, Avrami, Kolmogo-rov equation for single-phasematerials are observed with increasing particle aspect ratio and particlefraction. Inert particles also influence both mean size and mean aspectratio of the final grains.

Thermal Mechanical analysis (TMA) has been used to study the crystallizationbehavior of poly (ether ether ketone) (PEEK) and its blends with poly (etherimide) (PEI). The two crystallization stages of PEEK are clearlydistinguished by measuring the variation of film thickness with time duringisothermal crystallization. Upon blending with PEI, the distinction of thetwo PEEK crystallization stages becomes obscure. This is attributed to thedepressions in both nucleation density and spherulite growth rate uponblending with PEI.

An Avrami analysis, Modified by considering both primary and secondarycrystallization, is used to extract the respective kinetic behavior of thesetwo crystallization stages. The results indicate that the secondarycrystallization proceeded slower than the primary crystallization in thediffusion-controlled crystallization region. On the other hand, these twocrystallization stages proceeded at comparable rate in thethermodynamically-controlled crystallization region. It is also found in thediffusion-controlled crystallization that blending with PEI induced a largerdepression in the secondary crystallization rate than in the primarycrystallization rate. Explanations for these observations are proposed anddiscussed.

Isothermal crystallization behavior of as-deposited thin amorphous Si50Ge50 films (∼1000Å-thick) at 580°C has beeninvestigated using transmission electron Microscopy (TEM). The crystalcounting method was employed in order to obtain directly the two-dimensionalsteady-state crystal nucleation rate of 3.9×103#/cm2sec (equivalent volumetric nucleation rate of 3.4×108 #/cm3sec). The Modified two-dimensionalJohnson-Mehl-Avrami analysis, in which the growth rate of the crystals wasthe only adjustable parameter, and in which the time-dependent nucleationrate and the size effect associated with the onset of the observation areconsidered, was developed in order to extract the crystal growth rate of16.5 Å/sec. When compared to the crystallization of a-Si films, thesenucleation and growth rates confirm the observation that it is possible toachieve significantly faster crystallization at lower temperatures whileproducing substantially better Microstructures (i.e., > 5 μ grain-sized poly-Si50Ge50obtained within two hours at 580°C vs. 1–2Μm grain-sized poly-Si obtained inabout > 10 hours at 600°C).

The semiconducting crystalline alloys, Ge1−xSnx, areof interest due to theoretical predictions about their electronic bandstructures which make them useful in infrared photodetectors. However thecomposition region where these alloys have the desired properties is greaterthan the equilibrium solid solubility limit of Sn in Ge (x<0.01). We havecircumvented the solubility limits and produced thin (2000Å) and thick(4–8Μm) films of Gei.xSnx (x<0.31) by rfsputtering. Differential scanning calorimetry (DSC) Measurements wereperformed to study grain growth and crystallization processes in thesehighly metastable semiconductors. X-ray and electron diffractionmeasurements indicated the materials were amorphous, but the fact that someof the films were fine grained polycrystalline samples only became apparentin their DSC spectra. We present models that describe quantitatively thetransformation behavior in both sets of films.

In order to understand thickness and interfacial effects on thecrystallization kinetics of amorphous solids, Ni(P) thin films electrolesslydeposited on Cu seed layers were annealed at constant heating rates or atconstant temperatures in a DSC to obtain activation energies andAvramiexponents. It was found that the activation energy of crystallization inNi(P) changes asa function of sample thickness when the sample thickness isless than 1.0 μm. Furthermore, the Avrami exponent was found to change notonly as a function of thickness but also as a function of annealingtemperature.

The effects of vanadium in the crystallization kinetics amorphous ribbons Fe80-yVyB12Si8 (0.5 < y < 15) has been investigated by DifferentialScanning Calorimetry, by using the Avrami, Kolmogorov-Johnson-Mehl-Avrami,and Calka and Radlinski equations. The addition of vanadium to Fe-B-Sialloys leads to an enhancement of stability against crystallization, asshown by an increase in the effective activation energy for crystallization (Eeff = 3.6eV) and an increase in the temperature for the firstcrystallization peak, as a function of vanadium content (from 780 to 855K).Results also show that the crystallization Mechanism, nucleation rate anddimensionality of growth are constant throughout the crystallization processin the composition range investigated.

Solid state reactions in mixtures of nanometer-sized Cu and Zr as well as Niand Zr crystallites -produced by inert-gas condensation followed by in situ compaction - have been investigated by x-raydiffraction and thermal analysis. The annealing behavior is compared to thatof corresponding multilayer samples. The results are discussed with emphasisplaced on the different parameters controlling solid state reactions.

Nucleation and growth studies were conducted on Al-Zn alloys at severaltemperatures using transmission electron Microscopy (TEM) with an in-situfurnace. The value of the critical undercooling was established by notingthe lowest temperature at which precipitates were no longer observed,following a quench into the two-phase metastable region. These results werecompared with the Langer-Schwartz Model of nucleation and growth in which itis predicted that the half-completion time (i.e, the time required for thesupersaturation to reach half its initial value) diverges for initialsupersaturations which are higher than those predicted by the classicalnucleation theory.

The kinetics of atomic ordering in a series of alloys in the Pt1Co1−xNix ternary system where0<x<0.5 were investigated by magnetic measurements. For all thealloys, the ordering kinetics as monitored by the saturation magnetizationas a function of isothermal ordering time at a series of specified orderingtemperatures, were found to be exponentially time dependent. The associatedtime constant was found to have an Arrhenius temperature dependencecharacterized by an activation energy that, with increasing nickelconcentration, initially increased to maximum value at a nickel compositionof x ∼.2 and then systematically decreased. This result for the activationenergy as a function of nickel content was found to correlate roughly withthe behavior of the saturation magnetization of the ordered alloys,suggesting that the kinetics of the transformation in this alloy system issensitive to the magnetic properties of the ordered state.

Glasses of stoichiometric cordierite composition Mg2(Al1−xFex)4Si5O18,containing very low iron contents (x=0.015 and 0.005) have been investigatedby 57Fe Mössbauer spectroscopy. At higher Fe concentrationsspinel exsolution has been observed in X-ray powder patterns. To allowMössbauer spectroscopy at very low Fe-concentrations (<0.8 weight* Fe2O), starting materials were doped with 100%57Fe. Glasses prepared in air at 1560°C were also oxidized Inwater saturated O2 stream. Glasses were crystallized tocordierite by heating In air at 1100 to 1400°C. 57Fe-Mössbauerspectra of all samples are governed by a doublet typical for Fe2+in octahedral coordination (IS: 1.09–1.15, QS: 2.00–2.31 in MM/s relative tometallic iron). X-ray powder patterns exhibit no additional phases. But, the295 K and 5 K Mössbauer spectra of treated and untreated glasses and ofcordierltes exhibit broad lines, which have been fitted by applying internalmagnetic hyperfine fields H of ca. 500 kG. These lines areattributed to heterogeneously nucleated, superparamagnetic (MgFe) (AlFe)2O4 spinels of complex compositions. From thecalculated subspec-tra one may conclude that 35 to 65% of the total iron,depending on preparation conditions, is incorporated in the spinels.

Differential Scanning Calorimetry has been used to investigate the mechanismof the isothermal crystallization kinetics in Fe80B20 Metallic glass. It is shown that the whole crystallizationanalysis must include, not only a crystal nucleation-and-growth process, butalso a grain-growth process and that these two processes are separated intime during isothermal annealing. These processes have been studied directlyfinding the parameters which characterize their Mechanism. From thetheoretical Johnson-Mehl-Avrami equation describing thenucleation-and-growth process, it was possible to calculate the evolution ofthe transformed fraction of the material as a function of the annealingtime. To infer the meaning of the transformed fraction, samples subjected todifferent thermal treatments have been studied by Mössbauer Spectroscopy.Our results reveal that the transformed fraction is the sum of thecrystalline component formed by all atoms located in the lattice of thegrains and the interfacial component composed of atoms in the interfacialregions between grains.

Ion beam synthesis of Si and Ge nanocrystals in an SiO2 Matrix isperformed by precipitation from supersaturated solid solutions created byion implantation. Films of SiO2 on (100) Si substrates areimplanted with Si and Ge at doses 1 × 1016/cm2 - 5 × 1016/cm2. IMplanted samples are subsequentlyannealed to induce precipitation of Si and Ge nanocrystals. Ramanspectroscopy and high-resolution transmission electron microscopy indicate acorrelation between visible room-temperature photoluminescence and theformation of diamond cubic nanocrystals approximately 2–5 nm in diameter inannealed samples. As-implanted but unannealed samples do not exhibitluminescence. Rutherford backscattering spectra indicate a steepening ofimplanted Ge profiles upon annealing. Photoluminescence spectra arecorrelated with annealing temperatures, and compared with theoreticalpredictions for various possible luminescence Mechanisms, such as radiativerecombination of quantum-confined excitons, as well as possible localizedstate luminescence related to structural defects in SiO2Potential optoelectronic device applications are also discussed.

Thermally-induced solid-phase epitaxial crystallisation (SPEC) andion-beam-induced epitaxial crystallisation (IBffiC) of amorphous GexSi1−x alloy layers is examined for threedifferent starting structures: a) strain-relaxed alloy layers of uniformcomposition, b) strained alloy layers of uniform composition, and c) Geimplanted Si layers. Thermal annealing experiments show that the activationenergy for strain-relaxed alloys is higher than that expected from a simpleextrapolation between the activation energies of Si and Ge, and exceeds thatof Si for x ≤ 0.3. Experiments on thin strained layers show that MBE grownstrained layers which are stable during annealing at 1100°C for 60 s arealso fully strained after SPEC, whereas layers which relax during annealingat 1100°C also relax during SPEC. Experiments on ion-implanted GexSi1−x structures show that fully strained Si/GexSi1−x/Si heterostructures can be fabricatedfor ion fluences below a critical fluence, and as for uniform alloy layersthat this critical fluence is accurately predicted by equilibrium theory.Strain relaxation during SPEC of uniform alloys and implanted structures isshown to be correlated with a sudden reduction in crystallisation velocitywhich is believed to be caused by stress-induced roughening or faceting ofthe crystalline/amorphous interface. SPEC of thick (800 nm) implanted layersis shown to be limited by competition from ion-beam induced randomcrystallisation, while thin (120 nm) uniform alloys and implanted structuresare shown to crystallise epitaxially and to exhibit similar behaviour tothermally annealed samples under certain conditions.

For the first time, ion beam induced epitaxial crystallization (IBIEC) hasbeen found in SiC. The effect of 300 keV Si+ irradiation throughan amorphous surface layer in single crystalline 6H-SiC at 477+5°C has beeninvestigated by RBS/C and XTEM. A shrinkage of the amorphous layer was foundafter ion irradiation at this temperature which is caused by both an iondose independent thermal regrowth of about 20 nm and an additional ion beaminduced epitaxial crystallization with a rate of about 1.5 nm/ 1016 cm−2.

Isothermal annealing of amorphous TiO2 films deposited fromacidic sol-gel precursor solutions results in film densification andconcomitant increase in refractive index. Subsequent heating above 300°Cleads to irreversible transformation to an anatase crystalline phase.Similar phenomena occur when such amorphous films are subjected to focusedcw laser irradiation. Controlled variations in laser fluence are used todensity or crystallize selected regions of the film. Low fluenceconditioning leads to the evolution of a subtle nanograin-size morphology,evident in AFM images, which appears to retard subsequent filmcrystallization when such regions are subjected to higher laser fluence.Time-resolved Raman spectroscopy has been used to characterize irradiatedregions in order to follow the crystallization kinetics, assess phasehomogeneity, and evaluate accompanying changes in residual film stress.

At cryogenic temperatures, the accumulation of vacancy-interstitial pairs in Al2O3 from atomic displacements associated with ionimplantation produces amorphization. At room temperature, these pairsrecombine, and amorphization occurs only at high doses. X-ray reflectivitymeasurements show that amorphization of the surface of Al2O3 implanted at room temperature with 160 keV Cr+ ions is preceded by a progressive reduction innear-surface density. Monte Carlo simulations show that this densityreduction can be accounted for by high-energy-transfer collisions whichknock atoms deep into the target, leaving widely separated vacancies andinterstitials, which do not recombine. Electron Microscopy shows that atleast some of these vacancies condense into voids. We propose that thisreduction in near-surface density can lead to amorphization at high doses.We present simple approximations for the density reduction expected fordifferent ions and targets.

The temperature dependence of the critical amorphization dose,Dc, of four A2BO4 compositions, forsterite (Mg2SiO4), fayalite(Fe2SiO4), synthetic Mg2GeO4,and phenakite (Be2SiO4) was investigated by in situ TEM during 1.5 MeV Kr+ion beam irradiation attemperatures between 15 to 700 K. For the Mg- and Fe-compositions, theA-site is in octahedral coordination, and the structure is a derivative hep (Pbnm); for the Be-composition, the A- and B-sitesare in tetrahedral coordination, forming corner-sharing hexagonal rings(R3). Although the Dc's were quite close at 15 K for all the fourcompositions (0.2–0.5 dpa), Dc increased with increasingirradiation temperature at different rates. The Dc-temperaturecurve is the result of competition between amorphization and dynamicrecovery processes. The Dc rate of increase (highest to lowest)is: Be2SiO4, Mg2SiO4, Mg2GeO4, Fe2SiO4. At roomtemperature, Be2SiO4 amorphized at 1.55 dpa; Fe2SiO4, at only 0.22 dpa. Based on the Dc-temperature curves, the activation energy, Ea,of the dynamic recovery process and the critical temperature, Tc,above which complete amorphization does not occur are: 0.029, 0.047, 0.055and 0.079 eV and 390, 550, 650 and 995 K for Be2SiO4, Mg2SiO4, Mg2GeO4 and Fe2SiO4, respectively. These results are explainedin terms of the materials properties (e.g., bonding and thermodynamicstability) and cascade size which is a function of the density of thephases. Finally, we note the importance of increased amorphizationcross-section, as a function of temperature (e.g., the low rate of increaseof Dc with temperature for Fe2SiO4).

The layer-by-layer amorphization process is explored in a temperature rangein which the kinetics of crystallization can be neglected. It has been foundthat the pure amorphization rate increases exponentially as the substratetemperature is decreased with an apparent activation energy of 0.48 eV.Moreover the rate increases with both the ion flux and the energy depositedinto elastic collisions. A phenomenological model is proposed to explain theexperimental results.