bluuebunny/crossref_metadata_2025 huggingface dataset:
Determination Of Aluminum Coordination Environments In Amorphous AI2O3By Solid State Nmr Spectroscopy
Authors: Rees William S. , Chopin Lamy J.
Published: March 2011

It previously has been difficult to probe the localized coordination environment of aluminum atoms in amorphous alumina samples by solid state NMR spectroscopy. Such anin situtechnique has benefits in probing the structure of the material and monitoring the evolution of the microstructural development during thermal processing. The recent developments of more sophisticated NMR techniques by Pines,et al., specifically devised for treatment of problems unique to the solid state spectroscopy of quadrupolar nuclei, have permitted a glimpse into these Materials. As a result of applying these experimental techniques to new materials systems, a better understanding of the solid state structure of amorphous aluminas derived from polymer pyrolysis has emerged. Correlations between the onset and completion of crystallization and the localized structure may now be possible.
Dynamics of Crystalline and Amorphous Polytetrafluoroethylene Studied by Multiple Quantum NMR
Authors: Lathrop David A. , Gleason Karen K.
Published: March 2011

We report a new technique for probing polymer dynamics through the refocussing of multiple quantum (MQ) nuclear magnetic resonance (NMR) coherences. The MQ-NMR experiment follows the correlated behavior of multiple spin-1/2 nuclei interacting through dipolar couplings. Motion which modulates the dipolar coupling strengths on the same time scale as the experiment (∼1 to 20 kHz) alters the intensity of the observed coherences. Temperature dependent 19F data are presented on polytetrafluoroethylene samples of varying crystallinity. For the as-polymerized 98% crystalline PTFE sample, a sharp increase in MQ coherence refocussing occurs, centered at -298 K. The 64% crystalline melt-quenched sample shows a increase at the same temperature but which has a lower intensity. Thus, the ∼298 K peak is most associated with motion in the crystalline phase. This temperature is intermediate between the two first order transition at 293 and 303 K. Oscillations in the refocussed fractions are observed from 208 to 230 K for the 98% crystalline sample, while this ratio is constant over the same temperature range for the 64% crystalline sample. These oscillations may be associated with paracrystalline defects found only in the first sample. Thus, the MQ refocussing experiment is able to clearly differentiate between polymer samples which have different thermal histories. The sharpness of the MQ refocussing features and their variations in magnitude, shape, and sign with temperature are signatures of the molecular level details of the underlying dynamics which produce them.
Crystal to Glass Transition and Melting in Two Dimensions
Authors: Li M. , Johnson W. L. , Goddard W. A.
Published: March 2011

Thermodynamic properties, structures, defects and their configurations of a two-dimensional Lennard-Jones (LJ) system are investigated close to crystal to glass transition (CGT) via molecular dynamics simulations. The CGT is achieved by saturating the LJ binary arrays below glass transition temperature with one type of the atoms which has different atomic size from that of the host atoms. It was found that for a given atomic size difference larger than a critical value, the CGT proceeds with increasing solute concentrations in three stages, each of which is characterized by distinct behaviors of translational and bond-orientational order correlation functions. An intermediate phase which has a quasi-long range orientational order but short range translational order has been found to exist prior to the formation of the amorphous phase. The destabilization of crystallinity is observed to be directly related to defects. We examine these results in the context of two dimensional (2D) melting theory. Finite size effects on these results, in particular on the intermediate phase formation, are discussed.
Visco-Elastic Relaxations in Alkali Borates and Alkali Silicates
Authors: Kieffer J. , Masnik J. E. , Reardon B. J. , Bass J. D.
Published: March 2011

The Brillouin light scattering technique was used to study short time relaxations in glass forming oxide melts. The line shape analysis of Brillouin spectra yields a complex mechanical Modulus. The temperature dependence of this modulus provides insight into the structural disintegration above the glass transition, as well as the thermally activated mechanisms which facilitate the momentum transport in the process of viscous dissipation.

A series of binary and ternary alkali borates and alkali silicates have been investigated. The results show fundamental differences in the way alkali cations affect the network structure in borates as compared to silicates. While these cations move relatively freely within the rigid silicate network, their motions are strongly coupled to the network relaxation in borates. The activation energies for cation motion are in good agreement with those found by other methods.
An Investigation of the Viscous Flow Problem Associated with the Heating of the Glass Preform During Optical Fiber Processing
Authors: Rosenberg Sara E. , Papamichael Haris , Miaoulis Ioannis N.
Published: March 2011

A thermal study of the optical fiber manufacturing process involves some of the most challenging, and in some cases, unsolved fundamental problems in heat transfer and fluid Mechanics. The heating stage of the process, where the glass cylinder (preform) is heated radiantly by the cylindrical muffle furnace, greatly influences the resultant quality of the fiber. During the process a neckdown region is formed that is characterized by the stretching of the glass. The two-dimensional transient equations of motion and Mass conservation, with viscosity dependent on temperature, were solved to obtain the velocity profiles in the glass and the shape of the neckdown region. Axial velocity contours and the neckdown profiles were examined for various drawing conditions. Differences between the new method presented here and existing one-dimensional method were examined. The analysis can be used for drawing of other materials such as metals and polymers, and the modeling is applicable to other viscous liquids.
Crystal Nucleation in Submicron Droplets of Pure Elements
Authors: Holzman Louis M. , Kelly Thomas F. , Hitchon W. N. G.
Published: March 2011

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

Diffraction patterns of individual EHD-produced droplets are viewed to determine the fraction of crystalline droplets produced as a function of droplet radius. These results are compared to theories for surface and volume heterogeneous nucleation and for homophase nucleation. It is found that Si and Ge nucleate through either homogeneous nucleation or nucleation by homophase impurities. Nucleation results for vanadium and iron were not conclusive.
Plastic Deformation-Induced Nanocrystalline Aluminum in Al-Based Amorphous Alloys
Authors: Chen H. , He Y. , Shiflet G. J. , Poon S. J.
Published: March 2011

We report the first direct observation of crystallization induced in the slipped planes of aluminum based amorphous alloys by bending the amorphous ribbons. Nanometer-sized crystalline precipitates are found exclusively within a thin layer (shear band) in the slipped planes extending across the deformed amorphous alloy ribbons. It is also found that the nanocrystalline aluminum can be produced by ball-Milling. It is likely that local atomic rearrangements within the shear bands create the nanocrystals which appear after plastic deformation.
Solid State Reactions In Binary Mixtures Of Nanometer-Sized Particles
Authors: Dickenscheid W. , Birringer R.
Published: March 2011

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.
The Kinetics of the Order-Disorder Transformation in the Pt1Co1−xNix Alloy System
Authors: Tu Huan , Ruiz Eduardo O. , Orehotsky J.
Published: March 2011

The kinetics of atomic ordering in a series of alloys in the Pt1Co1−xNix ternary system where 0<x<0.5 were investigated by magnetic measurements. For all the alloys, the ordering kinetics as monitored by the saturation magnetization as a function of isothermal ordering time at a series of specified ordering temperatures, were found to be exponentially time dependent. The associated time constant was found to have an Arrhenius temperature dependence characterized by an activation energy that, with increasing nickel concentration, initially increased to maximum value at a nickel composition of x ∼.2 and then systematically decreased. This result for the activation energy as a function of nickel content was found to correlate roughly with the behavior of the saturation magnetization of the ordered alloys, suggesting that the kinetics of the transformation in this alloy system is sensitive to the magnetic properties of the ordered state.
Amortization And Dynamic Recovery Of A2BO4 Structure Types During 1.5 MeV Krypton Ion-Beam Irradiation
Authors: Wang L. M. , Gong W. L. , Ewing R. C.
Published: March 2011

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).
Defect Induced Amortization in Silicon: A Tight Binding Molecular Dynamics Simulation
Authors: Maric D. , Colombo L.
Published: March 2011

We present an investigation on the amorphization process of crystalline silicon induced by ion beam bombardment by simulating the insertion of self-interstitials at different temperatures. The simulation is carried out by tight-binding molecular dynamics which allows for a detailed characterization of the chemical bonding and electronic properties of the irradiated samples. The irradiation process consists of two steps: (i) insertion of defects at a constant rate; (ii) annealing of the sample and observation of its structural properties. Thanks to the large size of the simulation cell (up to 276 atoms) we can characterize the amorphous network both on the short-range and Medium-range length scale. Electronic properties are investigated as well and their evolution is monitored during the insertion process. Finally, we present a thorough comparison of the structural properties of the irradiated sample with amorphous silicon as obtained by rapid quench from the Melt.
Photoinduced Amorphous ↔ Crystalline Transitions In Sbx Sc1−x Films
Authors: Stradins Paul , Balors Ojars , Gerbreder Vyatcheslav
Published: March 2011

We present a study of laser pulse induced crystallization and amorphization in SbxSc1−x films. The time required to reach stable amorphous state after the pulse increases with exciting pulse length and becomes constant when stationary temperature field is approached by the end of the pulse. The time dependence of the excited spot's local temperature is deduced directly from amorphization threshold intensity dependence on the pulse length and is used to calculate the cooling times after the amorphizing pulse. Two photocrystallization regimes are distinguished depending on whether the melting starts before or after the end of crystallization, the condition depending on crystallization tendency for given composition x. The occurrence of melting limits the maximum optical contrast during photocrystallization. The results show that the crystallization tendency of SbxSei-x rises with x and has a local maximum between x = 0.5 and x = 0.7.
Questions And Answers On The Activation Strain
Authors: Aziz Michael J.
Published: March 2011

The activation strain tensor describes the effect of nonhydrostatic stresses on atomic or interfacial Mobilities. It has been measured for solid phase epitaxial growth of crystalline Si (001) into amorphous Si. The activation strain concept is explained and some subtle points are discussed. Implications for proposed mechanisms of solid phase epitaxy are reviewed, and new implications for combined bulk and interfacial control are presented. Questions raised during the oral presentation are answered.
Strain Relaxation During Solid-Phase Epitaxial Crystallisation Of GexSi1−x Alloy Layers with Depth Dependent Ge Compositions
Authors: Wong Wah-Chung , Elliman Robert G.
Published: March 2011

Solid-phase epitaxial growth (SPEG) of amorphous GeSi alloy layers has been examined. It is shown that fully strained depth dependent GeSi alloy layers can be produced by multiple ion-implantation and SPEG for implant doses below critical values. For doses above these critical values strain relaxation is shown to occur during SPEG at a well defined depth, and to be correlated with a reduction in the SPEG velocity caused by roughening or faceting of the crystalline/amorphous interface. The velocity reduction is shown to be a reliable indicator of strain relaxation. Both the critical dose and the depth at which strain relaxation occurs are shown to be in excellent agreement with equilibrium critical thickness theory.
Small-Angle Scattering Investigations of Crystalline Blend Morphologies of Poly (E-Caprolactone) (PCL)/Polycarbonate (PC) Blends
Authors: Wilson Cheung Y. , Stein R. S. , Wignall G. D. , Lin J. S.
Published: March 2011

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.
Interdiffusion of Amorphous Si/Ge Multilayers Under Hydrostatic Pressure
Authors: Theiss Steven D. , Mitha S. , Spaepen F. , Aziz M. J.
Published: March 2011

We report initial results of an x-ray diffraction study of the pressure-dependence of the interdiffusion rate in amorphous Si/Ge Multilayers. Anneals were performed in a diamond anvil cell at 700 K for various pressures and durations. Interdiffusion was measured by Monitoring the rate of decay of the artificial Bragg peaks associated with the multilayer periodicity. A consistent increase in diffusivity was seen with pressure, characterized by an activation volume of -25±11 percent of the atomic volume of Si. An atomistic mechanism that Might account for such behavior is discussed.
Crystallization Dynamics Of Ferroelectric Pzt (52/48) Thin Film Prepared By Reactive Cosputtering On Pt On Si(100)
Authors: Choo Woong Kil , Kim Hyo Jin , Kim Kwang Young , Kim Sung Tae
Published: March 2011

The crystallization process and microstructural evolution of PZT (52/48) thin films deposited on Pt thin film electrode on Si (100) by reactive multitarget cosputtering technique have been studied as a function of post-annealing temperature and holding time. As annealing temperature increases, the Amorphous PZT films as-deposited at low substrate temperature of 200 °C crystallize into pyrochlore at 450 °C and ferroelectric perovskite phase with pseudo-cubic structure at 550 °C in sequence. X-ray diffraction data show crystallization into perovskite phase to be complete in 30 Minutes at 550 °C. Furthermore, the change of PZT/Pt/Ti/SiO2/Si interfacial TEM Morphology during heat-treatment has been closely scrutinized.
Characterisation of Ferroelectric Lithium Tantalate Thin Films Prepared by a Sol-Gel Process
Authors: Ye Chianping , Baude Paul , Polla Dennis L.
Published: March 2011

Thin LiTaO3 films were prepared by spin coating of polymerized sol-gel precursor solution. Films have been deposited on single crystal silicon substrate, Ti/Pt or SiO2 coated silicon substrate. Films were characterized by x-ray diffraction, dielectric and pyroelectric Measurements. High Curie temperature (above 550 °C) was assumed for LiTaO3 thin films from the temperature dependence of dielectric constant. Replacing 35% of tantalum by titanium atoms in the LiTaO3 precursor solution has resulted the thin films with Curie temperature of 330 °C. The lower Curie temperature leads to the larger pyroelectric coefficient at room-temperature, which is more than double that of the undoped LiTaO3 thin films. The dielectric, pyroelectric, and ferroelectric properties have been compared to the single crystal LiTaO3 and ceramic Li0.91Ta0.73Ti0.36O3. LiTaO3 thin films are available by sol-gel process at low temperature, and their properties may possibly be controlled by varying the composition of the sol-gel precursor solution.
On Preparation of Crystalline MgO-Ceramics from Amorphous Precursors
Authors: Jost H. , Carius Ch. , Peplinski B.
Published: March 2011

Amorphous precursors are obtained as a result of the precipitation from magnesium acetate solutions with ammonia in the presence of citric acid. Compared with crystalline precursors they have a higher reactivity and a changed behaviour in calcination process as well as during sintering. Already at 1300 °C sintered pellets are achieved, whereas in technological process 1700 °C are needed.
A Comparative Study Between high and low Temperature Thermally Controlled Crystallization of thin films
Authors: Robinson Richard D. , Miaoulis Ioannis N.
Published: March 2011

Numerical simulation of zone-Melting recrystallization (ZMR) was conducted to determine the heat transfer dynamics over a wide range of temperatures. ZMR is a thermal processing technique used to recrystallize Materials. Therefore, the thermal effects induced by the ZMR process critically affect the crystallization dynamics. Parametric studies indicated that the conductive heat flux from the heat source through the gas accounted for at least 15% of the total energy heating the film for materials with melting points less than 800°C. The influence of this conductive heating has been neglected in past analyses. Also, Materials with higher melting points are less sensitive to changes in the heat flux from the heat source. Slight variations of thermal gradients in the film can lead to different qualities of crystal, so care must be taken when processing materials with lower melting points, since they are more sensitive to temperature variation. This paper analyzes the dominant modes of heat transfer in ZMR over a wide range of temperatures that influence the recrystallization dynamics.
Au0.80Cu0.10Y0.10, A Gold-Rich Ternary Alloy Glass with Tc > 400°C and its Crystallization Kinetics
Authors: Gokhale Sunil V. , Marchev Krassimir G. , Nowak Welville B. , Giessen Bill C.
Published: March 2011

There are no reported gold-rich alloys that are both readily glass forming (RGF) upon rapid solidification processing (RSP) and, in the glassy state, have crystallization temperatures Tc sufficiently high to insure long metastable life times at room temperature. A representative of a new family of ternary gold-based glasses is described that contain Cu and a rare earth (RE) Metal (or Y), with total addition element concentrations as low as 15 at. pet., and its crystallization characteristics are reported. Under RSP processing by arc furnace hammer-and-anvil quenching, the alloy Au0.80Cu0.10Y0.10 readily forms a ductile glass, with Tc = 685 K, ΔHc = 1.25 kJ/g-Mole and an activation energy of crystallization ΔE3 (cryst.) = 190 kJ/g-Mole.
Atomic Motion in Amorphous Ni81B19 Studied by Reverse Monte Carlo and Molecular Dynamics Simulation
Authors: Thijsse Barend J. , Van Ee Leon , Sietsma Jilt
Published: March 2011

Molecular dynamics simulations of glassy Ni81B19, starting with a configuration obtained by the Reverse Monte Carlo Method, indicate a calorimetrie glass transition at 960 K and point to a significant change in the atomic dynamics between 960 and 1200 K. Above this range, normal liquid-like behavior is found; at lower temperatures, we find a residual diffusivity and cooperative atomic Motion. Atomic jumps are processes smeared out in time and space over continuous rather than discrete scales.
Atomistic Details Of Disordering Processes in Superheated Polymethylene Crystals II. Effects of Surface Constraints
Authors: Wunderlich B. , Liang G. L. , Sumpter B. G. , Noid D. W.
Published: March 2011

Atomistic details of disordering in superheated polymethylene crystals have been studied using full molecular dynamics simulations of crystals containing 9600 CH2-groups. The crystal size was about 227 nm3 Simulations were carried out for up to 100 ps, starting at temperatures about 100 K above the melting temperature. Typically 1.5 h of CPU time on a Cray X-MP were necessary per ps simulation. Superheating causes a quick development of large-scale disorder throughout the crystal, including reorientation, translation, and the destruction of crystal symmetry. This is followed ultimately by surface Melting. Crystallization centers with hexagonal packing are found in superheated, unconstrained crystals. On cooling during the simulation, recrystallization processes compete with the disordering, resulting in a reorientation of the molecular chains and reorganization of the crystal. Neither the fully amorphous phase nor the ordered crystal are reached during these short-time simulations using an instantaneous temperature increase to above the melting temperature, followed by a slow cooling into the crystallization temperature region.
Film Softening Effects of ZrO2 on MoSi2
Authors: Czarnik C. M. , Gibala R. , Nastasi M. , Garrett J. D.
Published: March 2011

We have investigated the effect of thin films of ZrO2 on the mechanical behavior of [001] single-crystalline MoSi2. Previous work in our laboratories has shown there to be a 20-40% reduction in hardness in coated samples relative to the corresponding uncoated samples. We now compare fracture around the indentations as a function of thickness. Thicker ZrO2 coatings reduce radial crack length around the indentation through the intrinsic compressive stress at the film/substrate interface. In addition, ZrO2-coated materials tested in compression at 1250°C exhibit approximately twice the plastic strain of uncoated materials, indicating that reduction in hardness is associated with enhanced plasticity from dislocation activity associated with the film/substrate interface.
Strength and Toughness of Silicide Matrix Materials Consolidated by Hot Isostatic Pressing
Authors: Suryanarayanan R. , Sastry S. M. L. , Jerina K. L.
Published: March 2011

Substantial improvements have been reported in high temperature strength and creep resistance, and room temperature fracture toughness of molybdenum disilicide (MoSi2) reinforced with ductile or brittle reinforcements. The influence of Hot Isostatic Pressing (HIP) process parameters on the mechanical properties of MoSi2 based alloys was studied. Monolithic MoSi2 powder and MoSi2 powder blended with either niobium powder or silicon carbide whisker reinforcements were consolidated by HIP at 1200 − 1400°C, 207 MPa, and 1 - 4 hrs. The HIP'ed compacts were characterized for compression strength and creep resistance at 1100-1300°C. Fracture toughness was measured on single edge notched rectangular specimens at room temperature. Mechanical properties were correlated with post-HIP microstructural features.
Powder Processing of Refractory Metals and Alloys
Authors: German Randall M.
Published: March 2011

For the past century the processing of refractory metals and alloys has been linked to powder metallurgy (P/M). A firm understanding of processing has been critical to attaining the desired performance levels. Although the consolidation science is in good shape, the availability of tailored powders with appropriate attributes is a limitation. This presentation reviews the key issues related to refractory metal and alloy processing, with particular emphasis on tungsten and its alloys. An exciting growth area is in liquid phase sintering microelectronic systems where the concern is with thermal properties, specifically for W-Cu and Mo-Cu.
Microstructures, Defects and Deformation Mechanisms in Vanadium Modified Nb3Al
Authors: Smith L.S. , Aindow M. , Loretto M.H.
Published: March 2011

A transmission electron microscope study of the microstructure and defect structure in vanadium modified Nb3Al and its deformation mechanisms is presented. Two alloys are examined in which 20 and 40 atomic % V is substituted for Nb. The former alloy exhibits a microstructure containing a stable A15 phase and a metastable B2 phase which transforms to A15 upon heat treatment. The A15 grains contain defects similar to those observed previously in binary Nb3Al: i.e. large growth faults with R=1/4<012> and dissociated dislocations with a separation of =15nm and b=1/2<001> bounding a stacking fault with R=1/2<001>. The alloy containing 40 atomic % V consists only of an equilibrium B2 phase and exhibits greatly enhanced ductility. Slip occurs by the glide of dislocations with b=<111> on {011}.
Photodefinable Benzocyclobutene Formulations for Thin Film Microelectronic Applications. III. 1 to 20 Micron Patterned Films
Authors: Moyer E. S. , Becker G. S. , Rutter E. W. , Radler M. , Bremmer J. N. , Bernius M. T. , Castillo D. , Strandjord A. J. G. , Heistand R. , Foster P. , Harris R. F.
Published: March 2011

Negative working photodefinable benzocyclobutene formulations capable of obtaining patterned dielectric films from 1 to 20 microns thick are being developed using bisaryl azides as photocrosslinkers. Three different formulations are used to cover this range of film thicknesses. The formulations are very sensitive to the 365 nm and 405 nm wavelengths of light (i-line and h-line) of the high pressure mercury spectrum and require low exposure doses to produce resolved patterns. Twenty five micron round and square vias with sloping sidewalls (geometry good for metallization) have been successfully patterned in 10 micron thick films. The photodefined patterns can be obtained with good film retention using several developing solvents including: Stoddard solvent, ProglydeTM DMM, and n-butyl butyrate.
The Effect of Curing on the Thermomechanical Properties of BPDA-PDA Polyimide Thin Films
Authors: Leu J. , Kang Y. S. , Liou H. C. , Ho P. S.
Published: March 2011

The effect of the heating rate during curing on the thermal expansivity and mechanical properties of poly(p-phenylene biphenyltetracarboximide) (BPDA-PDA) polyimide thin films has been investigated in the range from 3 to 40 μm, which is commonly used for packaging application. Structural characterization was carried out using birefringence and wide-angle x-ray diffraction (WAXD) techniques. The morphology and packing order are found to be strongly influenced by the heating rate and, to a lesser extent, by the film thickness. The themomechanical properties of the polyimide films show an overall variation consistent with the changes in the molecular packing, thus demonstrating a close structure-property correlation. For slow-cure films, the variation of the molecular order is almost independent of film thickness. In contrast, the molecular order for the fast-cured films strongly depends on the thickness. The in-plane chain orientation decreases, but crystallinity increases with increasing film thickness. The heating rate gives rise to an opposite effect on the morphology for thin (∼ 5 μm) and thick films (∼ 38 μm). For thin films, high heating rate yields a high degree of crystallinity and in-plane chain orientation of the polymeric chains, leading to low thermal expansion coefficient (TEC) and high mechanical strength. In contrast, high heating rate for the thicker film gives a low in-plane chain orientation, leading to high TEC and low mechanical strength. The close correlation between morphology and the thermomechanical properties such as Young's modulus, stress-strain relationship, and lateral TEC is demonstrated.
Morphological Effects on the Materials Properties of Polyimides
Authors: Poon T. W. , Leu J. , Kang Y. S. , Liou H. C. , Ho P. S.
Published: March 2011

We have carried out a comparative study on the thermomechanical properties and interfacial fracture for two polyimides, a rigid-rod like BPDA-PDA and a flexible-chain PMDA-ODA. This study is focused on the correlation between material strength and polymeric chain morphology. A strong correlation was observed, with high chain packing order giving rise to strong material strength. Quantitatively, the mechanical strength of PMDA-ODA thin films along the direction tangential to the film plane is about 1/3 of that of BPDA-PDA, and its thermal expansivity 1.5 to 5 times larger. For fracture, the mechanical strength of the polyimide plays a different role. A softer polyimide such as PMDA-ODA will strengthen the confinement exerted by the metal lines with smaller interfacial strain, thereby decreasing the amount of deformation transmitted through the interface into the metal, and shifting the onset of delamination to a higher strain on the entire structure. However, the same softer polyimide layer also induces a larger amount of plastic deformation, leading to fracture of the film at a smaller strain. For a strong metal/polymer interface, the strength of the interfacial bonds is sufficient to hold the interface intact while the polymer near the interface deforms plastically because it is much softer mechanically than the metal. This continues until the deformation energy accumulated in the polymer is sufficient to delaminate the interface. Under this condition, the locus of failure will be determined by the relative fracture toughness of the polymer compared with the interface, which may very well occur in the polymer very close to the interface.
Adhesion of Cyclotene™ (BCB) Coatings on Silicon Substrates
Authors: Townsend P. H. , Schmidt D. , Stokich T. M. , Kisting S. , Burdeaux D. C. , Frye D. , Bernius M. , Lanka M. , Berry K.
Published: March 2011

This work examines the adhesion of coatings derived from divinylsiloxane bisbenzocyclobutene, mixed stereo and positional isomers of 1,3-bis(2-bicyclo[4.2.0]octa-1,3,5-trien-3-ylethenyl)-1,1,3,3-tetramethyl disiloxane (CAS 117732–87–3), on oxidized silicon substrates treated with silane coupling agents.This material, commercially available as Cyclotene™ 3022, can be used in the construction of high performance electronic circuits, such as multichip modules. Silane coupling agents examined in this study were 3-aminopropyltriethoxysilane (CAS 01760-24-3)(APTES)(, vinyltriethoxysilane (CAS 00078–08–0)(VTES), and 3-methacryloxypropyl trimethoxysilane (CAS 02530–85–0) (MOP-TMS).

Measurement of the interfacial adhesion was performed using microindentation. Bond strengths obtained by this method exceed 200 MPa for the most effective coupling agents. However, these high bond strengths were not found to correlate with acceptable adhesive performance in all cases. In addition to the choice and preparation of the coupling agent, process related chemical exposure has been found to be a key element in the observed adhesive performance. The effect of the cure schedule for the thermoset coating has also been found to be a controlling factor. A short cycle test vehicle was developed consisting of a single 20 gIm polymer layer etched with anisotropic sidewalls. This test vehicle was used to evaluate the efficacy of the coupling agents during process exposures and subsequent thermal shock testing. A solution of MOP-TMS pre-hydrolyzed in methanol was found to produce the most reliable interface with high bond strength.
New Techniques for Measuring Strain at Fracture of Thin Film Materials
Authors: Goforth R. C. , Chandran B. , Nasrazadani S. , Salamo G. J.
Published: March 2011

The High Density Electronics Center (HiDEC) at the University of Arkansas is developing advanced electronic packaging methods including multi-chip modules which utilize high temperature superconductor interconnects. A wide variety of materials have been proposed and investigated for these applications. Good knowledge of the mechanical properties of the candidate thin film materials is important for reliable device design.

Two new techniques have been developed to measure strain at fracture of thin film materials. The first is an acoustic technique in which an accelerometer is attached to the film. The film is then gradually strained. When the film fractures, an acoustic wave propagates through the film thereby creating a transient signal from the accelerometer. This signal is used to trigger an oscilloscope. The second technique is similar except that it utilizes a laser probe to detect the acoustic wave. In this photo-acoustic technique, the laser is reflected from the film onto a bi-sectional photodetector while the film is gradually strained. Upon film fracture, the acoustic wave modulates the laser beam and a transient voltage pulse is produced by the photodetector. Both techniques are capable of detecting extremely small cracks.
Effect of Microstructure on the Dissolution Kinetics of Copper Thin Films in Dilute Aqueous Solutions of Cupric Chloride
Authors: Walsh L. Harper , Feilchenfeld N. B. , Schwarz J. A.
Published: March 2011

Microstructural differences in copper deposited by four techniques commonly used in the microelectronics industry were previously reported. [1] The reaction rates were predicted using either grain size or grain orientation as the dominant microstructure characteristic. A practical method to monitor copper speciation was developed.[2] This technique was used to measure the reaction rates for the different copper films under two different etching conditions. The results are explained using grain size, grain orientation and near surface region composition.
High-Density, High-Speed Connectors Based on Flexible Etched Circuits
Authors: Wrisley David B.
Published: March 2011

With advances in semiconductor technology straining the ability of packaging to keep pace, conventional electrical connectors cannot always meet emerging requirements in interconnection density and signal transmission speeds.

Connectors using flexible etched circuits (FEC) can provide interconnection densities of up to 200 lines per inch and high transmission quality for signals with 250-picosecond risetimes. A practical connector design meeting these density and speed goals depends on careful consideration of connector and system tolerances, ease of application, manufacturability, and material properties.

This paper discusses a practical approach to an FEC-based connector and the influence of material properties on connector performance.
Real Time Process Monitoring with Multiwave-Length Pyrometric Interferometry (Pi)
Authors: BÖbel F.G. , Wowchak A. , Chow P.P. , Hove J. Van , Chow L.A.
Published: March 2011

Pyrometry Interferometry (PI) is a powerful technique for in-situ sensing of the wafer temperature and growth rate. Evaluation of the two parameters would allow exact process control required for sophisticated device fabrication and material processing. The PI technique analyzes the interference patterns of the thermal radiation from the growing layer with a changing thickness d at growth temperature T. Since it is non-contact, applicable to all semiconductor materials and insensitive to wafer motion, the method is an ideal candidate for real time process control. We use a reflection assisted method to aid real time computation of these parameters. One could select the wavlength of interest to optimize the temperature and layer thickness resolution. We present data on MBE grown quarter wavelength stacks of GaAs and AlAs, and silicon oxidation to show P1 is extremely useful for growth of surface emitting laser and for silicon processing.
Characterization of Quantum well Structures Using Microscope-Spectrophotometry
Authors: Geatches Rachel M , Reeson Karen J , Criddle Alan J , Webb Roger P
Published: March 2011

In this paper the application of microscope-spectrophotometry to the nondestructive characterization of a variety of multi-layer GaAs/A1GaAs structures, is described. Spectral reflectance results are used to indirectly determine variations in aluminium content, and the interdependency of aluminium content with layer thicknesses. The penetration depth of light from the visible spectrum is assessed from the correlation between spectral reflectance measurements and fitted optical models. Finally, a series of single quantum wells are investigated, and it is concluded that a significant improvement in the characterization of these materials will be achieved with an extension of the spectral measurement range into the ultra violet.
Photoluminescence Characterization of Inp-Based Hemt Structures
Authors: Hendriks Henry T. , Brierley Steven K. , Hoke William E. , Pan Noren
Published: March 2011

InP-based lattice matched high electron mobility transistor (HEMT) structures have been characterized by liquid nitrogen temperature photoluminescence. A phenomenological line shape model has been utilized to fit photoluminescence spectra in order to obtain key parameters, such as the subband energies and transition amplitudes. From transition amplitude ratios and subband energies, fundamental quantum well characteristics are inferred. Changes in these parameters are linked to variations in the growth conditions of the epitaxial layer structures.
Fiber Optics-Based Fourier Transform Infrared Spectroscopy for in-Situ Concentration Monitoring in OMCVD
Authors: Salim Sateria , Jensen K.F. , Driver R.D.
Published: March 2011

Fiber-based Fourier transform infrared spectroscopy for remote in-situ monitoring of organometallic delivery in organometallic chemical vapor deposition (OMCVD) is presented. The measurement is based on infrared absorbance of the organometallic reagent in a short single pass gas cell placed in the gas delivery line of an OMCVD system. The performance of the set-up is demonstrated for monitoring concentration transients during the delivery of two common OMCVD precursors, trimethylgallium (TMG) and trimethylindium (TMI). The time to reach saturation is shown to be faster for a TMG bubbler than for a TMI bubbler. This difference in delivery behavior is interpreted through a mathematical model of the gas handling lines and the monitoring gas cell. The utility of the system in monitoring temporal variations in TMI delivery is also demonstrated. Finally, the ability of the system to detect the chemical species unintentionally present in the feed lines is illustrated with the observation of methane gas from TMG and TMI bubblers that have been dormant for a period time. The methane gas is shown to quickly disappear with repeated used of the bubblers.
Photoluminescence Study of Hydrogen-Related Defects in Silicon
Authors: Henry A. , Monemar B. , LindstrÖm J.L. , Zhang Y. , Corbett J.W.
Published: March 2011

The effect of ion-implantation followed by a rapid thermal annealing was investigated in borondoped silicon using photoluminescence (PL) spectroscopy. The radiation induced defects giving rise to the G, W and C PL lines are completely passivated by a hydrogen plasma treatment. However this hydrogen exposure also introduces broad and deep luminescence structure as well as new sharp PL lines very near the silicon band gap. Up to twelve new lines are observed at low temperature (< 20K). One of them exhibits a very low exciton localisation energy (≈ 2 meV) compared to the value measured for classical shallow donors or acceptors, and is observed only at very low temperature (≈4K). A broad deep PL band with a halfwidth of 30 meV is observed at around 925 meV. The excitation power dependence and the temperature dependence of the PL intensity of these sharp lines and the broad band are presented. Tentative correlations with the data currently available in the literature are presented for the understanding of the formation of the defects associated to the broad band as well as the sharp near band gap PL lines.
Developing a Method for Wide-Control of the Self-Bias and its Adoption to Ion-Damage Control
Authors: Ohte Takeo , Goto Makoto , Sugawara Minoru
Published: March 2011

We have developed a technique which enables us to reduce the self-bias voltage without introducing any substantial disturbance to the main plasma. This approach is based on decreasing the floating potential of the powered electrode by means of injecting an electron current from the electrode. Instead of employing a hot cathode, we have used an auxiliary glow discharge to supply the electron emission. The controllable range of the self-bias has been extended to almost 0 V. A theoretical explanation of the variation of the floating potential with the emission current has been carried out. Measurements of the floating voltage(Vf) are plotted against ln(1/Iau), where Iau is the auxiliary discharge current. A good linear relationship of Vf vs. ln(1/Iau) is obtained as expected from the theory, and its slope gives the electron temperature.

In order to appraise the degree of damage induced by the bombardment of ions accelerated by the sheath voltage, we have estimated the damage by measuring the dark current of a sample diode fabricated from the film. It has been observed experimentally that when the sheath voltage was depressed from -73 V to -36 V at a pressure of 0.11 Torr, the dark current of the sample diode was suppressed drastically from 1.3 ×10−10 A to 5.3×10−11 A
Real-Time Surface and Near-Surface Optical Diagnostics for Epitaxial Growth
Authors: Aspnes D. E.
Published: March 2011

Various optical diagnostics are being developed to meet new challenges in semiconductor epitaxy. New data-analysis algorithms allow near-surface alloy compositions and interface properties to be obtained by kinetic ellipsometry (KE) without any knowledge of the underlying sample structure. New information about growth is being obtained by surface-oriented probes such as laser light scattering (LLS), surface photoabsorption (SPA), anrd reflectance-difference (-anisotropy) spectroscopy (RDS/RAS). Examples are provided and likely directions of further progress discussed.
Low Coherence Interferometry for Non-Invasive Semiconductor Monitoring
Authors: Lawson Chris M. , Michael Robert R.
Published: March 2011

We report on the first use of optical low coherence reflectometry (OLCR) for Edge Defined Film-Fed Growth (EFG) silicon characterization. This OLCR sensor system has been used to measure horizontal profiles of silicon thickness and flatness to an accuracy of 1.5 Rim with the sensor head positioned 1 cm away from the silicon. The use of this noninvasive sensor for EFG silicon growth monitoring may lead to more efficient solar cell manufacturing processes.
Study of Zener Diodes by Sem-DVC
Authors: Mil'shtein S. , Kharas D. , Iatrou S.
Published: March 2011

A Scanning Electron Microscopy method called Dark Voltage Contrast (DVC) was applied for the first time to investigate on a microscale, the narrow depletion region of a Zener diode. Zener diodes were fabricated by the Sprague Semiconductor Corp. using conventional boron diffusion into a n-type wafer with phosphorus.

Zener diodes were chosen because of the presence of a shallow p-n junction and for the ability of Zeners to work in the breakdown regime where the dynamics of the current might influence the field distribution in the p-n junction. The samples were examined in the SEM with a beam current below 50 pA to minimize injection of electrons into the depletion region.

Reverse and forward biased diodes were examined and potential distribution information was obtained, using Dark Voltage Contrast software. Doping information and C-V measurements were used to double check DVC depletion region measurements.

The main results of these studies include measurements of electrical field for three regimes of operation: forward, reverse, and breakdown, with almost ideal field distribution in some Zeners, and fluctuations in others. The field irregularities are related to the defects in the junction area. However the amount of charge build-up appears to depend on the current flow in the dynamic regime for the breakdown. The typical measurements of depletion region width were Wf=.14 μm when forward biased, Wr=0.35 μm at 3-4 volts when reverse biased and Wbr=0.44 gm for 6 v of breakdown. This data helps to reconstruct the diffusion profile.
Characterization of Polycrystalline Silicon Multilayers with thin Nitride/Oxide Films Using Spectroscopic Ellipsometry
Authors: Asinovsky L.M.
Published: March 2011

Spectroscopic ellipsometry has been used to characterize oxide/poly-Si/oxide with thin nitride/oxide layer. Films were deposited on Si substrate using low-pressure chemical vapor deposition (LPCVD) techniques. The measurements were taken at angles of incidence of 65 and 70 degrees in the wavelength range from 300 to 800 nm. The analysis of the data using effective medium and two-dimensional Lorentz oscillator approximations identified complete recrystallization of the poly-Si after annealing and and its transformation to µ c-Si. Three wafers taken at the sequential stages of the manufacturing process were studied. Although parameters of the thin nitride/oxide layers are strongly correlated, reasonable estimates of the thicknesses were found. The resuilts were consistent with the measured Auger electron spectroscopy (AES) profiles.
Simulation of Dry Etching Processes for III-V Compounds Technology Applications
Authors: Ketata K. , Koumetz S. , Ketata M. , Debrie R.
Published: March 2011

This work introduces a new dry etching simulation technique of the sputtering component of Reactive Ion Etching (R.I.E.) and presents experimental verifications for GaAs. The final objective is to correlate the etch rate to the plasma reactor parameters, which can be incorporated into a computer-simulation program.