NMR spectroscopy is beginning to provide quantitative information on short-and medium-range structure in silicate glasses and liquids, and onmolecular-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 veryuseful in models of nucleation and growth of immiscible liquid andcrystalline 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 characterizecompositional heterogeneity in glasses to distance scales of at leastseveral nanometers.

We report a new technique for probing polymer dynamics through therefocussing of multiple quantum (MQ) nuclear magnetic resonance (NMR)coherences. The MQ-NMR experiment follows the correlated behavior ofmultiple spin-1/2 nuclei interacting through dipolar couplings. Motion whichmodulates the dipolar coupling strengths on the same time scale as theexperiment (∼1 to 20 kHz) alters the intensity of the observed coherences.Temperature dependent 19F data are presented on polytetrafluoroethylenesamples of varying crystallinity. For the as-polymerized 98% crystallinePTFE sample, a sharp increase in MQ coherence refocussing occurs, centeredat -298 K. The 64% crystalline melt-quenched sample shows a increase at thesame temperature but which has a lower intensity. Thus, the ∼298 K peak ismost associated with motion in the crystalline phase. This temperature isintermediate between the two first order transition at 293 and 303 K.Oscillations in the refocussed fractions are observed from 208 to 230 K forthe 98% crystalline sample, while this ratio is constant over the sametemperature range for the 64% crystalline sample. These oscillations may beassociated with paracrystalline defects found only in the first sample.Thus, the MQ refocussing experiment is able to clearly differentiate betweenpolymer samples which have different thermal histories. The sharpness of theMQ refocussing features and their variations in magnitude, shape, and signwith temperature are signatures of the molecular level details of theunderlying dynamics which produce them.

A unified account of the structural relaxation and nonlinear deformation inglassy polymers is presented. The glassy state relaxation is derived fromthe local configurational rearrangements of molecular segments, and thedynamics of hole motion. We then apply this to predict the nonlinearstress-strain relationships.

A general approach to the dynamics of structural relaxation in amorphoussolids is developed. A form of the recombination kinetics of defects ischosen which removes the ad hoc assumption made in previoustheories that defects recombine only with others of identical activationenergy. The generalized theory is tested quantitatively by modelling thestructural relaxation of amorphous silicon, and comparing the results withthe experimental data on structural relaxation. It is found that thegeneralized theory is necessary in order to accurately describe thetime-resolved relaxation data. The generalized theory is also applied toestimate the effect of irradiation on the nucleation kinetics of crystalsilicon, and is found to agree well with experimental data.

Thermodynamic properties, structures, defects and their configurations of atwo-dimensional Lennard-Jones (LJ) system are investigated close to crystalto glass transition (CGT) via molecular dynamics simulations. The CGT isachieved by saturating the LJ binary arrays below glass transitiontemperature with one type of the atoms which has different atomic size fromthat of the host atoms. It was found that for a given atomic size differencelarger than a critical value, the CGT proceeds with increasing soluteconcentrations in three stages, each of which is characterized by distinctbehaviors of translational and bond-orientational order correlationfunctions. An intermediate phase which has a quasi-long range orientationalorder but short range translational order has been found to exist prior tothe formation of the amorphous phase. The destabilization of crystallinityis observed to be directly related to defects. We examine these results inthe context of two dimensional (2D) melting theory. Finite size effects onthese results, in particular on the intermediate phase formation, arediscussed.

Temperature dependences of magnetic susceptibility for Ti-Cu- andTi-Ni-based amorphous alloys have been obtained in the temperature range300–850 K. All investigated alloys are shown to be Pauli paramagnets. Fe andCo impurity atoms possess zero localized moment due to effect of spin momentquenching. Relaxation processes were studied using thermopower measurements.It was shown the thermal stability of investigated alloys is determinedpredominantly by Nagel-Tauc electronic criterion.

The amorphous-to-crystalline transition in sputter-deposited amorphous Tb33Fe66 films has been studied using aconversion-electron extended X-ray absorption (EXAFS) technique. Modeling ofthe EXAFS data using theoretical and empirical standards allowed thequantitative measurement of coordination, radial distance, and disorder oflocal atom shells around the Fe sites after varying degrees of heattreatments.

The dynamic structure of xLi2S-Ga2S3-6GeS2 (x=4 and 6)glasses has been investigated by 7Li nuclear magnetic resonance.In two samples similar values of spin-lattice relaxation time(T1) were obtained. The relaxation mechanism at 20MHz and 78MHzis therefore attributed to the local motion of lithium ions. In the glasscorresponding to x=6, which shows higher conductivity, the slow motion ofions showing an activation energy of 24.3kJ/Mol has been detected by thespin-lattice relaxation time in the rotating frame (T1p). Thisvalue is comparable to the activation energy determined by the conductivity.The existence of this mode is supported by the motional narrowing of theline width which is sensitive to the motion less than 10kHz.

Semicrystalline polyimide, Regulus™ NEW-TPI, is a thermoplastic polyimideproduced by mitsui Toatsu. This aromatic polyimide possesses outstandingheat resistance, high tensile strength, excellent electrical properties, andstrong solvent resistance. It has become the subject of recent study in ourgroup [1–6] and others [7–13]. The flexible ether and meta linkages in themonomer unit lower its glass transition temperature (Tg) to 250°C inquenched amorphous material.

The Brillouin light scattering technique was used to study short timerelaxations in glass forming oxide melts. The line shape analysis ofBrillouin spectra yields a complex mechanical Modulus. The temperaturedependence of this modulus provides insight into the structuraldisintegration above the glass transition, as well as the thermallyactivated mechanisms which facilitate the momentum transport in the processof viscous dissipation.

A series of binary and ternary alkali borates and alkali silicates have beeninvestigated. The results show fundamental differences in the way alkalications affect the network structure in borates as compared to silicates.While these cations move relatively freely within the rigid silicatenetwork, their motions are strongly coupled to the network relaxation inborates. The activation energies for cation motion are in good agreementwith those found by other methods.

A thermal study of the optical fiber manufacturing process involves some ofthe most challenging, and in some cases, unsolved fundamental problems inheat transfer and fluid Mechanics. The heating stage of the process, wherethe glass cylinder (preform) is heated radiantly by the cylindrical mufflefurnace, greatly influences the resultant quality of the fiber. During theprocess a neckdown region is formed that is characterized by the stretchingof the glass. The two-dimensional transient equations of motion and Massconservation, with viscosity dependent on temperature, were solved to obtainthe velocity profiles in the glass and the shape of the neckdown region.Axial velocity contours and the neckdown profiles were examined for variousdrawing conditions. Differences between the new method presented here andexisting one-dimensional method were examined. The analysis can be used fordrawing of other materials such as metals and polymers, and the modeling isapplicable to other viscous liquids.

Tungsten-carbon (W/C) Multilayer structures are used as X-ray mirrors andother optical elements. The optical properties of such elements are highlysensitive to changes in strain due to thermal processing. Sensitivecurvature measurements were performed on 40A period W/C Multilayerstructures on Si substrates using a two beam laser reflection technique. Acompressive stress of approximately 1530 MPa was measured in these sputteredmultilayer films. Thermal annealing to 500 C in air and under vacuumresulted in very little strain relaxation in the multilayers but X-raydiffraction data show a slight increase of the multilayer period.Significant strain relaxation, though, was observed when a 400Å W bufferlayer was included. Thermal annealing of these samples to 400–500°C resultedin large strain relaxation due to the formation of a-W crystals in thebuffer layer. Moderate oxide formation on air annealed samples as measuredby SIMS was shown not to be a dominant mechanism of strain relaxation.

A review is given of transient crystal nucleation in glassy or amorphoussolids. The types of behaviour are surveyed. It is shown that the kineticscan be quantitatively modelled and that the matching of experiment andtheory provides an important test of the classical theory. Examples areconsidered of homogeneous nucleation (affecting glass formation),heterogeneous nucleation, and nucleation at an interphase interface. Whilethe emphasis is on transient effects of the kind implicit in the classicaltheory, it is shown that transients can arise for other reasons as well,thus potentially complicating the interpretation of experiments.

Liquid-to-crystal nucleation has been studied extensively through dropletexperiments to locate examples of homogeneous nucleation. However, prior tothis work very few examples have been found, which implies that theexperiments have not been able to isolate heterogeneous nucleants in a smallpercentage of the droplets as is required. In this research,electrohydrodynamic atomization (EHD) is used to produce sub-Micron dropletsof pure elements that are largely free of heterogeneous nucleants.

Diffraction patterns of individual EHD-produced droplets are viewed todetermine the fraction of crystalline droplets produced as a function ofdroplet radius. These results are compared to theories for surface andvolume heterogeneous nucleation and for homophase nucleation. It is foundthat Si and Ge nucleate through either homogeneous nucleation or nucleationby homophase impurities. Nucleation results for vanadium and iron were notconclusive.

The principal problem in developing a theory of internal nucleation lies inthe constitution of the nascent nuclei. To get at this constitution in aninternally nucleating glass, oxygen and lithium core level x-rayphotoelectron spectra have been measured on glassy and nucleated lithiumdisilicate and on the three stable crystalline compounds in the Li2O-SiO2 system. Our results indicate thatnucleated lithium disilicate glass consists of completely polymerized silicain the formation of which non-bridging oxygens are consumed. During thissilica polymerization lithium atoms move away from presumably four-foldcoordinated sites towards higher coordinated ones.

The first stages of the nano-crystallization process of amorphous Fe75.5Cu1Nb3Si12.5B8into a nano-crystalline structure are investigated by the positronannihilation lifetime technique. Samples have been isothermally annealed at643 K for times varying between 600 and 105 seconds. The positronlifetime spectra have been analyzed allowing for three lifetimes. Theshortest and the longest lifetime, τ1 = 150 ± 2 ps and τ3 = 1500–2000 ps respectively, are attributed to annihilationof positrons in the amorphous phase and to the formation and annihilation ofortho-positronium at the surface of the stacked foils and did not changesignificantly upon the annealing. The intermediate positron lifetime τ2 increased from 324 ps to 387 ps. The intensity of thiscomponent increased from 5 to 15%. Comparison with resistivity measurementsindicates that the change of this lifetime component occurs at an earlystage in the crystallisation process, i.e. when the fraction of crystallinematerial is on the order of 10−3. The increase of τ2is attributed to positrons annihilating in a region with lower averagedensity surrounding the small crystallite.

We report the first direct observation of crystallization induced in theslipped planes of aluminum based amorphous alloys by bending the amorphousribbons. Nanometer-sized crystalline precipitates are found exclusivelywithin a thin layer (shear band) in the slipped planes extending across thedeformed amorphous alloy ribbons. It is also found that the nanocrystallinealuminum can be produced by ball-Milling. It is likely that local atomicrearrangements within the shear bands create the nanocrystals which appearafter plastic deformation.

The nucleation of intermediate phases at the interphase boundary indiffusion couples is examined theoretically. A variational procedure isdescribed which allows for a self consistent determination of the criticalnucleus size and shape, the work of formation of the critical nucleus andthe nucleation rate.

Eshelby's theory has been applied to the aragonite-calcite transformation inorder to calculate the elastic strain energy of coherent ellipsoidalprecipitates in anisotropie solids. Using a quasiNewton's Method and afinite-difference gradient, the elastic strain energy was incorporated inorder to calculate the activation energy ΔG* for homogeneous nucleationunder hydrostatic and non-hydrostatic conditions.

Extensive in situ investigations of the crystallization ofamorphous cobalt disilicide have been conducted using a transmissionelectron microscope with a hot stage. Thermodynamic and kinetic parametersdescribing the heterogeneous transformation have been evaluated. The angleof contact betwen crystalline and amorphous material was determined fromtilting experiments to be 76°. Nucleation rates in samples 40 nm thick wereevaluated at various temperatures and compared with thermodynamic models todeduce an interfacial energy between amorphous and crystalline COSi2 (σca) of 121 mJ/m2 and anactivation energy for crystallization of 1.27 eV. Johnson-Mehl-Avramianalysis of the observed continuous nucleation and steady state isotropiegrowth in 100 nm thick samples points to a gradual transition of thecrystallization mode from 3-dimensional (n=4) to 2-dimensional (n=3) growthas might be expected. Comparison of the nucleation and growth rates in 40 nmand 100 nm thick samples demonstrated the influence of surfaces oncrystallization phenomena in thin films.