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

Crystalline Morphologies of poly (e-caprolactone) (PCL) and deuterated polycarbonate (PC) blends in both the semicrystalline/amorphous state and semicrystalline/semicrystalline state were probed by small-angle neutron and X-ray scattering (SANS and SAXS). Due to the different contrast between the phases for neutrons and X-rays, SANS exhibited a monotonie drop in intensity with increasing scattering angle while SAXS showed lamellar (peak) scattering.

Crystal- and amorphous-phase thickness were determined from the correlation function calculated from SAXS. This correlation function analysis suggested a transition from interlamellar exclusion to interlamellar incorporation of amorphous PCL in the PC lamellae. A two-correlation length model provided an excellent fit for the SANS data over the entire composition range. This Model not only reproduced the shape but also the absolute magnitude of the scattering profiles. The long range correlation length (∼102 Å) and the short range correlation length (∼ 10 Å) derived from this model were inferred to be associated with the crystalline PC domains and the local clusters found in the amorphous phase, respectively.

Microcrystalline silicon films were deposited by diluted-hydrogen method and hydrogen-atom-treatment method at 250°C in a plasma enhanced chemical vapor deposition system and they were characterized by nuclear magnetic resonance, Raman spectroscopy, and optical bandgap Measurements. One-Mask a-Si:H thin film transistors (TFT's) were fabricated with those microcrystalline materials as the channel layer. The highest electron mobilities of the TFT's fabricated by diluted-hydrogen method and hydrogen-atom-treatment method were 1.23 and 1.04 cm2/V•s, respectively without any thermal treatment steps.

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 at temperatures between 15 to 700 K. For the Mg- and Fe-compositions, the A-site is in octahedral coordination, and the structure is a derivative hep (Pbnm); for the Be-composition, the A- and B-sites are in tetrahedral coordination, forming corner-sharing hexagonal rings (R3). Although the Dc's were quite close at 15 K for all the four compositions (0.2–0.5 dpa), Dc increased with increasing irradiation temperature at different rates. The Dc-temperature curve is the result of competition between amorphization and dynamic recovery processes. The Dc rate of increase (highest to lowest) is: Be2SiO4, Mg2SiO4, Mg2GeO4, Fe2SiO4. At room temperature, 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, 0.055 and 0.079 eV and 390, 550, 650 and 995 K for Be2SiO4, Mg2SiO4, Mg2GeO4 and Fe2SiO4, respectively. These results are explained in terms of the materials properties (e.g., bonding and thermodynamic stability) and cascade size which is a function of the density of the phases. Finally, we note the importance of increased amorphization cross-section, as a function of temperature (e.g., the low rate of increase of Dc with temperature for Fe2SiO4).

The sorption of organic penetrants is found to be sensitive to thermal annealing conditions in a series of glassy, nematic, thermotropic, random copolyesters. Controlled thermal annealing of two polymers in this series permitted a systematic variation of chain packing and, presumably, higher order molecular suprastructure, ranging from a disordered amorphous morphology to More ordered nematic liquid crystalline and semi-crystalline morphologies. The development of liquid crystalline order appears to reduce or preclude small molecule solubility in nematically ordered forms of these polymers.

Ion beam synthesis of Si and Ge nanocrystals in an SiO2 Matrix is performed by precipitation from supersaturated solid solutions created by ion implantation. Films of SiO2 on (100) Si substrates are implanted with Si and Ge at doses 1 × 1016/cm2 - 5 × 1016/cm2. IMplanted samples are subsequently annealed to induce precipitation of Si and Ge nanocrystals. Raman spectroscopy and high-resolution transmission electron microscopy indicate a correlation between visible room-temperature photoluminescence and the formation of diamond cubic nanocrystals approximately 2–5 nm in diameter in annealed samples. As-implanted but unannealed samples do not exhibit luminescence. Rutherford backscattering spectra indicate a steepening of implanted Ge profiles upon annealing. Photoluminescence spectra are correlated with annealing temperatures, and compared with theoretical predictions for various possible luminescence Mechanisms, such as radiative recombination of quantum-confined excitons, as well as possible localized state luminescence related to structural defects in SiO2 Potential optoelectronic device applications are also discussed.

Thin film hydrogenated Amorphous silicon (a-Si:H) was deposited on Molybdenum (Mo) substrates by d.c. glow discharge. We investigated the a-Si:H crystallization using four anneal techniques; nitrogen atmosphere furnace, vacuum, rapid thermal anneal (RTA), and excimer laser anneal. Anneal temperature ranged from 100 to 1200 °C. Excimer laser energy per pulse ranged from 90 to 340 M.J. Transmission electron Microscopy (TEM) revealed microstructure of crystallized Si film with grain size over 0.5 μm. X-ray diffraction (XRD) and Raman spectroscopy were employed to determine the degree of crystallization. The a-Si:H started to crystallize at temperatures over 600 °C. An 850 °C anneal reduced film resistivity to 10s (ω-cm) for intrinsic and 1 (ω-cm) for n-type. Coplanar type thin film transistors (TFT) with gate channel length of 25 μm and width of 220 μm were fabricated with various insulating layers; if sputtered SiO2, Si3N4, BaTiO3, MgO, and evaporated SiO. The first two exhibited the least leakage current. The as-grown intrinsic a-Si:H field effect mobility was around 0.03 (cmVV.s) and delay time was 5×10−7 s. The solid phase crystallized silicon film exhibited high leakage current. The delay time of an excimer laser anneal treated TFT was reduced to 2.5×10−7 s. Crystallized Si film mobility was improved to 15 (cm2 /V.s).

X-ray diffraction analysis was used to study the pyrolytic conversion of a preceramic polysilazane into Si3N4. Quantitative data for crystallite size, phase composition, and degree of crystallinity versus pyrolysis temperature and atmosphere (N2 and NH3) are presented. Pyrolytic products produced under N2 and NH3 atmospheres consist of microcrystals of silicon and a- and β-Si3N4. Under both atmospheres, a majority of the char is crystalline at ∼ 1270°C, and the entire char is crystallized at 1400°C. Pyrolysis under an NH3 atmosphere produces near stoichiometric Si3N4, while pyrolysis under N2 produces a silicon-rich material.

This study investigates the stability of Metastable Si1-yCy/Si heterostructures during rapid thermal annealing (RTA) over a temperature range of 1000 – 1150° C Heterostructures of Si1-yCy/Si and Si1-x-yGexCy/Si (x=0.077, y ≤ .0014) were formed by solid phase epitaxy from C implanted, preamorphized substrates using a 30 Minute 700° C anneal in N2. The occupancy of C in substitution lattice sites was monitored by Fourier Transform Infrared Absorption spectroscopy. The layer strain was monitored by rocking curve x-ray diffraction and the structural changes in the layers were determined using plan-view and X-sectional transmission electron Microscopy (TEM). For anneals of 1150° C or above, all the substitutional C was lost from the Si lattice after 30 seconds. TEM verified that the strain relaxation was the result of C precipitating into highly aligned βSiC particles rather than by the formation of extended defects. No nucleation barrier was observed for the loss of substitutional C Preliminary results will also be discussed for Si1-x-yGexCy/Si heterostructures where there is the additional factor of the competition between strain energy and the chemical driving forces.

NMR spectroscopy is beginning to provide quantitative information on short- and medium-range structure in silicate glasses and liquids, and on molecular-scale dynamics in the liquids. Data on coordination numbers, second and higher neighbor connectivities, and larger scale heterogeneities, as determined by NMR at ambient and high temperatures, are potentially very useful in models of nucleation and growth of immiscible liquid and crystalline phases. New techniques such as dynamic angle spinning (DAS), high temperature magic angle spinning (MAS) are especially promising. Detailed studies of paramagnetic nuclear spin relaxation can characterize compositional heterogeneity in glasses to distance scales of at least several nanometers.

A critical regime has been identified for ion implanted silicon where only slight changes in temperature can dramatically affect the levels of residual damage. In this regime decreases of only 5° C aie sufficient to induce a crystalline-to-amorphous transformation in material which only exhibited the build-up of extended defects at higher temperatures. Traditional Models of damage accumulation and amorphization have proven inapplicable to this regime which exists whenever dynamic defect annealing and damage production are closely balanced. Irradiating ion flux, Mass and fluence have all been shown to influence the temperature—which varies over a range of 300° C for ion species ranging from C to Xe—at which the anomalous behaviour occurs. The influence of ion fluence suggests that complex defect accumulation plays an important role in amorphization. Results are presented which further suggest that the process is nucleation limited in this critical regime.

High-dose and multi-energy aluminum implantation of α-SiC (0001) was carried out to achieve a broad aluminum distribution extending from the sample surface to a depth of approximately 350 nm. Oxidation resistance of the implanted crystals was studied in 1 atm flowing oxygen at 1300°C. Aluminum implantation resulted in a 45% improvement in the oxidation resistance of α-SiC as compared with unimplanted crystals due to the formation of structurally dense mullite (3A12O3.2SiO2) in the oxidation scale.

Tungsten-carbon (W/C) Multilayer structures are used as X-ray mirrors and other optical elements. The optical properties of such elements are highly sensitive to changes in strain due to thermal processing. Sensitive curvature measurements were performed on 40A period W/C Multilayer structures on Si substrates using a two beam laser reflection technique. A compressive stress of approximately 1530 MPa was measured in these sputtered multilayer films. Thermal annealing to 500 C in air and under vacuum resulted in very little strain relaxation in the multilayers but X-ray diffraction data show a slight increase of the multilayer period. Significant strain relaxation, though, was observed when a 400Å W buffer layer was included. Thermal annealing of these samples to 400–500°C resulted in large strain relaxation due to the formation of a-W crystals in the buffer layer. Moderate oxide formation on air annealed samples as measured by SIMS was shown not to be a dominant mechanism of strain relaxation.

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

Results from As K-edge XAFS studies on polysulfone films implanted with 50 KeV As+ in the dose range of 1015 to 1016 ions/cm2 indicate that As reacts chemically with O atoms to form As- (3) 0 based molecular structures having As-0 bond lengths equal to 1.81±0.02 Å. In comparison to samples implanted in the dose range 101S to 1016 ions/cm2, the molecular environment surrounding As in polysulfone implanted at 1017 ions/cm2 has additional structure beyond the nearest-neighbor O atoms.

The technique of high-performance liquid chromatography (HPLC) provides unique detailed information regarding the structure of partially disordered or amorphous phosphate solids. Applications of the experimental technique of HPLC to phosphate solids are reviewed, and examples of the type of information that can be obtained with HPLC are presented.

Hydrogenated Amorphous silicon films deposited on molybdenum sheet metal substrates have been crystallized by thermal annealing at 850°C for 4 hours in a nitrogen atmosphere. X-ray diffraction and scanning electron microscopy results indicated that the average grain size in the crystallized films was approximately 200A. Palladium contacts were fabricated and the resulting Pd/Si/Mo structures were electrically characterized. Current-voltage-temperature measurements for phosphorus doped and undoped annealed samples resulted in a J “V characteristic consistent with space-charge-limited current. Using this data, Mobility as a function of temperature from 100K-300K was obtained. In phosphorus doped samples, the mobility appeared to be limited by energy barriers at the grain boundaries. In undoped samples, a σ “T’ exp (-b/T’) temperature dependence consistent with variable-range hopping conduction was observed.

Extensive in situ investigations of the crystallization of amorphous cobalt disilicide have been conducted using a transmission electron microscope with a hot stage. Thermodynamic and kinetic parameters describing the heterogeneous transformation have been evaluated. The angle of contact betwen crystalline and amorphous material was determined from tilting experiments to be 76°. Nucleation rates in samples 40 nm thick were evaluated at various temperatures and compared with thermodynamic models to deduce an interfacial energy between amorphous and crystalline COSi2 (σca) of 121 mJ/m2 and an activation energy for crystallization of 1.27 eV. Johnson-Mehl-Avrami analysis of the observed continuous nucleation and steady state isotropie growth in 100 nm thick samples points to a gradual transition of the crystallization mode from 3-dimensional (n=4) to 2-dimensional (n=3) growth as might be expected. Comparison of the nucleation and growth rates in 40 nm and 100 nm thick samples demonstrated the influence of surfaces on crystallization phenomena in thin films.

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

For fast-pulse laser-crystallized thin-film Si on non-crystalline substrates, the average grain size exhibits a peak as a function excimer laser energy density at a characteristic laserfluence FM. The average grain size increases with increasing laser fluence and can reach a maximum value on the order of 10 pm or about 100 times the film thickness. The grain size then decreases with further increases in fluence. This peak in grain size is accompanied by a similar peak in the Hall electron mobility and x-ray scattering intensity. Our experiments have investigated as-deposited and ion-implanted samples, using a double-scan laser crystallization process. Devices have also been fabricated and studied. The results are consistent with the increase in grain size occurring because of the destruction of nucleation sites with increasing laser fluence (i.e., increased heating and complete Melting). But substrate damage occurs in the vicinity of FM, creating nucleation sites which give rise to small grain sizes in the solidified film. The disruption of the interface causes substantial current leakage through the dielectric of bottom-gate transistors, implying that devices should be laser fabricated below Fm.