bluuebunny/crossref_metadata_2025 huggingface dataset:
Radiative and Non-Radiative Recombinations at Er Centers in GaAlAs
Authors: Benyattou Taha , Seghier Djelloul , Guillot Gerard , Moncorge Richard , Galtier Pierre , Charasse Marie-Noelle
Published: March 2011

Photoluminescence (PL) of Molecular Beam Epitaxy grown Er doped Ga 0.55Al0.45As has been studied under continuous and pulsed laser excitation . The observed PL lines are attributed to transitions from the first excited stated 4I13/2 to the ground state 4I15/2 . The life time of the 4I13/2 level is found to be 1 ms at 10K, which is comparable to the decay time observed in insulators.

Using two-beam experiments we show that there are losses (Auger effect) that occur during the PL excitation.We propose the following model for the Er PL excitation process: excitons bound to Er are created and decay non radiatively by energy transfer to the rare earth (which is the cause of the Er related PL) or to free carriers by Auger effect (which is the cause of the observed losses).
Diffusion in Gallium Arsenide and GaAs-Based Layered Structures
Authors: Gösele U. , Tan T. Y. , Yu Shaofeng
Published: March 2011

The mechanisms of Ga self-diffusion can be derived from interdiffusion experiments in intrinsic and doped GaAs-based superlattices. These experiments allow to conclude that Ga self-diffusion in intrinsic and n-doped GaAs is carried by triply negatively charged gallium vacancies whereas in p-doped GaAs positively charged gallium self-interstitials dominate Ga self-diffusion. The diffusion mechanisms of Zn and Be are discussed with special emphasis on the difference between their in- and out-diffusion behavior which is due to diffusion-induced non-equilibrium point defects.
Effect of Local Atomic Configuration on DX Energy Level
Authors: Baba T. , Mizuta M. , Fujisawa T. , Yoshino J. , Kukimoto H.
Published: March 2011

The effects of specific local environments on DX centers were investigated for two different substitutional-site-donors of Si and Te in selectively-doped ordered-alloy samples. Capacitance transient technique under hydrostatic pressure was utilized for the determination of the DX energy-level structure. Downward movement of the energy levels for both Si- and Te-DX centers was observed when Al occupies the 2nd or 1st nearest neighbor site, respectively. A very large shift of the electron-emission activation-energy with pressure was found for the Te-DX centers surrounded by specific Al and Ga mixed-environments, whereas negligible shift for the Si-DX centers was observed regardless of the environment. These effects were discussed in relation to the lattice relaxation of the relevant DX centers.
DX-Center in Se-Doped AlxGa1-xAs
Authors: Hanak Thomas R. , Bakry Assem M. , Ahrenkiel Richard K. , Timmons Michael L.
Published: March 2011

We report the measurement of the thermal activation energy for the DX- center in Se-doped AlxGa1-xAs grown by metal-organic chemical vapor deposition (MOCVD) for different alloy compositions (x=0.19, 0.23, 0.27, 0.31). The peaks obtained from conventional DLTS are often broad or asymmetric with shoulders on one or both sides. These phenomena often arise from two or more traps which are active in the same temperature range.

The capacitive transients are recorded digitally and analyzed directly by applying a nonlinear double exponential fitting routine to the data. This fitting produces two Arrhenius plots and yields the densities of the defect states. From the Arrhenius plots, the capture cross sections at infinite temperature and the thermal activation energies are calculated. These results are then used to simulate the DLTS spectra. Excellent agreement between real and simulated spectra is shown.
Poole Frenkel Effect on the DX Centers in III-V Ternary Alloys
Authors: Altelarrea H. , Bosch J. , Perez A. , Samitier J. , Morante J.R.
Published: March 2011

The dependence of the DX centers thermal emission rates on the electric field has been measured by Isothermal Transient Spectroscopy (ITS) and differential ITS (DITS) techniques. These techniques allow us to achieve a more accurate analysis of these defects than the DLTS, which ability for the study of DX centers is discussed. This dependence has been found to be mainly due to a Poole-Frenkel effect and is the cause of the non-exponentiality of the thermal emission transients.
Transient Current and Transient Capacitance Measurements of Defects in AlGaAs Hemts
Authors: Magno R. , Shelby R.
Published: March 2011

The defects present in AlGaAs high electron mobility transistor (HEMT) devices subjected to accelerated lifetime tests have been studied by transient current, and when possible, by transient capacitance techniques. By measuring transient source-drain currents following the application of a voltage pulse to the gate it is possible to perform deep level transient spectros-copy (DLTS) experiments on HEMT devices which are too small for the conventional capacitance DLTS. The capacitance and current spectra for both stressed and unstressed HEMTs contain the AlGaAs DX defect. The current DLTS spectra for stressed devices contain an additional feature which is not found in capacitance DLTS measurements on the stressed HEMTs. This additional current DLTS feature is anomalous in that the transient has a sign which is opposite to that expected for a majority carrier trap. The absence of the new defect in the capacitance DLTS suggests that the defect is located in the channel between the gate and either the source or the drain. The current DLTS line shape of the stressed induced defect depends upon the polarity and size of the source-drain voltage.
Progress in Understanding the Optical Properties of EL2
Authors: Baraff G. A.
Published: March 2011

The material covered in the talk given under this title has already been published [1] or has been accepted for publication [2]. For this reason, the material to be presented below will consist only of a summary with references.
The Double Donor Issue of the EL2 Defect in GaAs.
Authors: Manasreh M. O. , Brown G. J.
Published: March 2011

Photo-induced changes in the infrared (IR) absorption spectrum of the EL2 defect in undoped and lightly alloyed unannealed GaAs materials grown by the liquid-encapsulated Czochralski technique were observed under a monochromatic light irradiation. These changes were attributed to the change of the charge states of EL2. The spectrum which is believed to be due to the charged EL2 exhibits a complex structure with two peaks at 1.07 and 1.32 eV and a shoulder at 0.94 eV. The EL2+/2+ → EL20/+ and EL20/+ → EL2+/2+ transitions were obtained by illuminating the sample with 0.7 ≤ hv ≤ 0.95 eV and 1.3 ≤ hv ≤1.5 eV, respectively. The transformation EL2+/2+ ↔ EL20/+ can be achieved in less than 10 sec and can be repeatedly switched back and forth between the two states. Fourier-transform photoconductivity (FTPC) measurements were performed on a large number of samples both semi-insulating and n-type. Two broad peaks were observed in the FTPC spectra with thresholds at 0.80 and 0.95 eV. The photoquenching and thermal recovery properties of these two peaks are identical to those of EL2. Both IR and FTPC results suggest strongly that EL2 is a double donor.
Absolute Pressure Dependence of the Second Ionization Level of EL2 in GaAs
Authors: Bliss D.E. , Walukiewicz W. , Nolte D.D. , Haller E.E.
Published: March 2011

We report the results of DLTS experiments under uniaxial stress on the second ionization level of EL2(++/+) in p-type GaAs. We measured the shift in the hole emission rate as a function of stress applied in the [100] and [110] directions. By modeling the valence band with two independently displacing bands and appropriately derived effective masses, we obtain a small absolute hydrostatic pressure derivative for the defect, 39 ±15 meV GPa-1. The shear contribution is negligible. This result is very different than for the first ionization level, EL2(+/o) with a emission energy pressure derivative of 90 ±15 meV GPa-1. The difference can be accounted for by the pressure dependence of the electron capture barrier of EL2(+/o), 49 ±15meV GPa-1. The absolute pressure derivatives of the two levels are then comparable and in good agreement with simple theory for Ga site point defects.
The Role of EL2 for the Mobility-Lifetime Product of Photoexcited Electrons in GaAs
Authors: Valley G. C. , von Bardeleben H.J. , Rajbenbach H.
Published: March 2011

abstract

The mobility lifetime products for photo-electrons in semi-insulating GaAs, which fit successfully the results of photorefractive studies undertaken in the presence of electric fields are three orders of magnitude smaller than those inferred from transport measurements or from the photorefractive effect with no applied electrical field. Consideration of enhanced recombination via EL2 effective-mass states linked to the L-conduction band minimum allows us to fit the dependence of the photorefractive beam coupling gain coefficient on the grating period for both AC fields and moving gratings. A cascade-capture process, which is three orders of magnitude faster than recombination by multiphonon emission from the Γ band to EL2, leads to greatly reduced mobility-lifetime products for field strengths greater than 1 kV/cm. Our results establish the dominant influence of the EL2 defect properties on the recombination processes essential for modelling and optimizing the photorefractive effect in semi-insulating GaAs.
Electron Scattering by Native Defects in Uniformly and Modulation Doped Semiconductor Structures
Authors: Walukiewicz W.
Published: March 2011

Formation of native defects in GaAs is described in terms of the amphoteric native defect model. It is shown that Fermi energy induced formation of gallium vacancies is responsible for the limitations of maximum free electron concentration in GaAs. The effect of the defects on electron mobility in heavily doped n-GaAs is quantitatively evaluated. Defect scattering explains the abrupt reduction of electron mobility at high doping levels. Also, it is demonstrated that native defects are responsible for the mobility reduction in inverted modulation doped GaAs/AlGaAs heterostructures. The amphoteric defect model also explains a distinct asymmetry in defect formation in n- and p-GaAs. In p-GaAs the Fermi level induced reduction of the defect formation energy is much smaller, and therefore the concentration of the native defects is negligible compared with the hole concentration.
Modified Optically Detected Magnetic Resonance Technique for Studies of Defects in Si and GaAs
Authors: Chen W.M. , Monemar B.
Published: March 2011

We discuss one of the major difficulties, namely the strong free carrier induced background signal, in studies of defects in Si and GaAs by optically detected magnetic resonance (ODMR) technique. A modified ODMR technique, namely delayed ODMR, is presented and is shown to be very successful in overcoming this difficulty.
Beryllium Doping in MBE-grown GaAs and AlGaAs
Authors: Pellegrino Joseph , Griffin James , Myers Leary , Spencer Michael
Published: March 2011

Beryllium is an effective p-dopant in GaAs and AlGaAs and plays an important role in device characterizations of hetero bipolar transistors. This work addresses the doping and mobility properties for two series of beryllium-doped samples: GaAs and AlGaAs. Within each series the doping ranged between 3×1015cm-3 to levels of 5×1019cm-3. Mobility and carrier concentrations were obtained through Hall and Polaron measurements. The doping concentration results suggest the onset of carrier compensation at higher doping levels. One possible explanation is that for high doping levels, Be is incorporated as interstitial donors. A thermodynamic model is used to explain the observations.
Nitrogen and Phosphorous Impurities in Diamond
Authors: Jackson Koblar , Pederson Mark R. , Harrison Joseph G.
Published: March 2011

In this paper we use a first-principles local density approximation-based approach to study the properties of the n-type impurities nitrogen and phosphorous in diamond. We determine impurity donor level positions of 0.90 eV and 1.09 eV, respectively for C:N and C:P, measured relative to the bottom of the conduction band. We also study the energetics of impurity atom relaxation along the <111> direction in the diamond lattice. While experimental observations indicate a trigonal distortion about the impurity site, we find the on-center position for both impurity atoms to be stable against the simple <111> relaxation.
Ordering in III/V Alloys
Authors: Stringfellow G.B.
Published: March 2011

Simple calculations using the delta-lattice-parameter (DLP) model indicate that the enthalpy of mixing is invariably larger than or equal to zero for III/V alloys, and increases with increasing difference in lattice constant for the constituent binary compounds. In terms of the regular solution model this suggests the occurrence of miscibility gaps. Solid phase immiscibility has indeed been observed in a number of systems. Nevertheless, such alloys can be grown by OMVPE, including the highly metastable alloys GaPSb and InPSb. Initially surprising was the occurrence of ordered structures in these same alloys. The regular solution model apparently specifically excludes immiscibility and ordering in the same system. However, when the positive enthalpy of mixing is due to strain energy effects, as in III/V alloys, Hume-Rothery recognized very early that such phenomena should be anticipated. This was later confirmed by detailed first principles calculations. In fact, the tendency for ordering is anticipated to increase as the difference in tetrahedral radii of the elements sharing a common sublattice increases. Thus, it is somewhat surprising that ordering was first observed in the AlGaAs system where Al and Ga have nearly equal sizes. Ordered structures have now been observed in several III/V alloy systems including the ternary systems GaAsSb and GalnP and the quaternaries GalnAsP, GalnAsSb, and AlGalnP. In this paper, ordering in other alloy systems such as GaPSb and InAsSb will be described. Surprisingly, no strong correlation between atomic size difference and the degree of ordering has been observed. Another unexpected observation is that the preferred ordered structure for most ternaries involves ordering along the {111}directions. Both first principles total energy and simple strain energy calculations indicate that such ordered structures are only slightly more stable than the disordered solid solution. Other ordered structures, including L10, where ordering occurs along the {100} directions, are considerably more stable. Both phenomena must be explained in terms of the surface kinetic processes occurring during epitaxial growth. Such an explanation is supported by the importance of kinetic parameters such as growth rate, temperature, and substrate orientation in determining both the degree of order and the specific ordered structures observed.
Ion Beam Etching of Silicon: Implantation and Diffusion of Noble Gas Atoms, and Gettering of Copper
Authors: Sawyer William D. , Schmälzlin Jörg , Weber Jörg
Published: March 2011

Defects introduced into silicon by ion beam etching are investigated by low-temperature photoluminescence (PL) and Rutherford backseattering (RBS) measurements. The RBS results show that during the ion beam etch a highly damaged surface layer is formed which contains a large concentration of Ar atoms. The Ar atoms then diffuse out of the surface and into the crystalline bulk by some form of radiation enhanced diffusion. Annealing of the etched samples at 350°C results in the formation of noble gas defects known from previous PL studies of ion implanted silicon. When the samples are annealed at 650βC PL lines due to new defects are formed. Although little is known about their structure, we show that the new Ar defects getter small copper contaminations very effectively.
Angle Resolved XPS Analysis of Surface Region Defects in Rapid Thermal Annealed Antimony Implanted Silicon
Authors: Kumar S.N. , Chaussemy G. , Laugier A. , Canut B. , Charbonnier M.
Published: March 2011

Angle-resolved X-ray photoelectron spectroscopy characterization of the surface region of high-dose Sb+ ion implanted silicon, after rapid thermal treatments over various temperatures, is reported. The results obtained are compared with the Rutherford backscattering data and the capacitance-voltage measurements on the metal-oxide-semiconductor mesa structures built on them. Rapid anneal at 1100 °C of the 1.4×1016 Sb+/cm2 samples showed an anomalous deep oxygen diffusion inside the implanted region.
Twinning Structure of {113} Defects in High-Dose Oxygen Implanted Silicon-on-Insulator Material.
Authors: Visitserngtrakul S. , Barry J. , Krause S.
Published: March 2011

Conventional and high resolution electron microscopy (HREM) were used to study the structure of the {113} defects in high-dose oxygen implanted silicon. The defects are created with a density of 1011cm-2below the buried oxide layer in the substrate region. The {113} defects are similar to the ribbon-like defects in bulk silicon. Our HREM observations show that two crystalline phases are present in the defect. Portions of the defects exhibit the original cubic diamond structure which is twinned across {115} planes. The atomic model shows that the {115} interface is a coherent interface with alternating five- and seven-membered rings and no dangling bonds.
Environmentally Stable, Low Dielectric Polymers from Soluble Intermediates
Authors: Mates T. , Ober C. K. , Angelopolous B. , Martin H.
Published: March 2011

We have investigated new polymers of poly(phenylene vinylene), PPV and poly(phenylene), PP. Like polyimides, these polymers can be spin-coated from soluble intermediates and converted to their thermally stable forms by elimination of small groups during a heating cycle. As such, these polymers are insulating. Both poly(phenylene vinylene) and poly(phenylene) also have the potential for metallic conductivity when properly doped. During curing, the complete removal of the leaving groups is important in determining the final behavior of the aromatized polymer film. Elimination of the leaving groups was followed by means of Rutherford Backscattering (RBS) and Forward Recoil Spectrometry (FRES) analysis for various curing conditions and environments. We will describe the curing and film-forming properties of these polymers, and discuss both their dielectric characteristics and thermal stability as a function of the curing conditions.
Ceramic/Polymer Nanocomposite Properties for Microelectronic Packages
Authors: Das Amitabh , Srinivasan Thallam T. , Newnham Robert E.
Published: March 2011

This paper reviews some of the research efforts in microelectronic packaging to develop composites with dimensions of the fillers ranging down to nanometer dimensions. Some initial experiments have been conducted with nanocomposites, where the thermal and dielectric properties of polymer/fumed silica composites have been studied. The bulk samples were prepared in different ratios of polymer to silica using polydimethyl siloxane and Cab-O-Sil. Differential thermal analyses carried out on these samples showed no changes in the samples till 330°C. The dielectric constant of the 70:30 (Cab-O-Sil- Polymer by Wt.%) composite is 3.8, similar to that of the pure silica. For the same composite the value of the thermal expansion coefficient is 350 ppm, closer to the value of pure polymer (439 ppm). It is suggested that the key to model these nanocomposites with ceramic and polymer phases is to understand the interfaces and their chemical bonding.
Structure and Properties of C-Axis Oriented AlN Films Reactively Deposited by DC Planar Magnetron Sputtering
Authors: Takahashi Takakazu , Takeda Fumio , Naoe Masahiko
Published: March 2011

Aluminum nitride (AlN) films have been deposited by reactive DC planar magnetron sputtering at a low substrate temperature of 80°C. An Al disk and either N2 or NH3 were used as a target and an ambient gas, respectively. In films deposited in N2, the c-axis of AlN crystallites was perpendicular to the film plane. On the other hand, in NH3, X-ray diffraction peaks from (100), (110) and (200) were observed. The surface and the cross-sectional microstructures of AlN films deposited in N2 were significantly different from that deposited in NH3. The surface of films deposited in NH3 was smoother than that deposited in N2. The transmittivity of films deposited in NH3 was superior to that deposited in N2 in wavelength of 275∼450 nm. Resistivities of films deposited in N2 and in NH3 were 1014sim;1015 Ω · cm. Dielectric constants of films deposited in N2, and of that deposited in NH3, were 9.7, and 9, respectively, in a frequency range of 20 kHz to 20 MHz. The structure and the properties of AlN films deposited by this method depended on kind of ambient gas.
A Technique for Brazing Aluminum Nitride Substrates
Authors: Norton M. Grant , Kajda Jacek M. , Steele Brian C. H.
Published: March 2011

A technique for brazing aluminum nitride (AIN) using conventional (non-active) brazing alloys has been investigated. The process involves the in-situ decomposition of a metal hydride. This process alters the surface chemistry of the substrate and improves the wettability of the molten braze. The development of high strength bonding between braze and ceramic results. The ceramic-braze interface was studied using scanning electron microscopy (SEM). The nature of the interfacial reactions and the reaction products have been identified using x-ray diffraction (XRD). The progress of the reaction has been followed using differential thermal analysis (DTA).

The experimental results have been correlated with thermodynamic predictions of the reaction process. In addition to joining ceramic to ceramic, braze joints of AIN to a low expansion iron-nickel lead frame alloy were made.
Microstructure and Microchemistry of Tungsten and Tungsten Compound Reactions with Aluminum Nitride Substrates
Authors: Westwood Alistair D. , Notis Michael R.
Published: March 2011

A clear understanding of the bonding process in the cofired tungsten-aluminum nitride (W-AIN) metallized system is not currently available. Therefore, in an attempt to obtain a fuller understanding of this process, reactions between metallic W, tungsten trioxide (WO3), and calcium tungstate (CaWO4) with aluminum nitride have been studied using a variety of electron microscopy techniques. The observed reaction was found to be similar in all cases, resulting in the formation of metallic tungsten particles within the AIN substrates. A reaction sequence is proposed to explain adhesion in the W-AIN metallized system; thermodynamic calculations support the proposed reaction sequence. The adhesion in this system is due to both a mechanical fastening by an interlocking and a chemical precipitation reaction. Finally thermal conductivity measurements across the interface have been made to assess the ability of the interface to transfer heat.
Contact Reactions at Thin Film Aluminium/Transition Metal Interfaces
Authors: Schuhmacher Bernd , Köster Uwe
Published: March 2011

Contact reactions at thin film Al/TM interfaces (TM = W, Cr, Co, Zr and Ta) have been studied by means of cross sectional transmission electron microscopy. In all cases the first phase formed at the interface was the most aluminium-rich compound as given in the correspondent phase diagram: In the case of Al/W, Al/Cr as well as Al/Co growth of Al12W, Al7Cr, and Al9Co2, respectively, with rather smooth, planar morphology has been observed. On the other hand, Al/Zr and Al/Ta contacts exhibit a irregular growth morphology of Al3Zr, and Al3Ta, respectively.

In addition, precipitation behaviour of rapidly solidified supersaturated Al(TM) solid solutions upon thermal annealing has been studied, in order to get a better insight on preferred orientation relationships between aluminium and the aluminides as well as on the influence of defects, e.g. grain boundaries.

Based on the observed morphologies and orientation relationships a model will be proposed for the different modes of interfacial reactions, i.e. with planar or irregular growth morphology.
Phase Stability and Mechanical Behavior of Ternary Bismuth-Lead-Tin Solders
Authors: Whealon W. J. , Stone D. S. , Chang Y. A.
Published: March 2011

Results from a phase stability study of the Bi-Pb-Sn ternary system and mechanical property data from the testing of the Bi-Pb-Sn ternary eutectic alloy are reported. It is found that the mechanical properties of the ternary eutectic alloy change considerably during cooling due to a solid state phase change at 79° C. After solidification, but prior to this phase transformation, the alloy exhibits brittle failure upon tensile loading. After the phase change high ductility is observed, bordering on superplasticity at low strain rates. Furthermore, having gone through the phase change once, the alloy remains ductile even after it is held at temperatures above 79° C. These results are interpreted in terms of the microstructures observed in the alloy.
Photosensitive Polyimides
Authors: Hiramoto Hiroo
Published: March 2011

Photosensitive polyimides are used as insulation and protection layers for microelectronics. They can easily give fine-patterned films with excellent characteristics of polyimides by photolithographic procedure.

Photosensitive groups such as double bonds, azides, o-nitrobenzyl and o-naphthoquinonediazides. These photosensitive groups are incorporated to polymer chains through covalent bonds or acid-base ion bonds. Some polyimides have photosensitivity even without intentionally introduced photosensitive groups. Most of photosensitive polyimides are negative working, and a few of them are positive working.

Characteristics of photosensitive polyimides are determined by two factors, the way of introducing photosensitive groups and the structures of polyimide backbone chains. Photosensitivity, resolution, purity and easiness of imidization mainly depends on the former factor. The film properties after curing are mainly determined by the latter. The film properties, however, are affected by the former when imide cyclization is imperfect.

Photosensitive polyimides are widely used as protection and insulation layers of VLSI, multi-chip modules for computers, telecommunication, linephotosensors, thermal-heads, etc.
Microprobe Study of Chemical Inter-Grain Variation In Class-F Fly Ash: Application of Fuzzy C-Means Cluster Analysis and Non-Linear Mapping
Authors: Pietersen Hans S. , Vriend Simon P. , Poorter Rene E. P. , Bijen Jan M.
Published: March 2011

The chemistry of individual grains of several Class F fly ashes has been investigated by electron microprobe analysis. To interpret the analytical data-set, a combination of two multivariate statistical procedures was applied. The method involves the use of both fuzzy c-means cluster analysis (FCM) and non-linear mapping (NLM). It allows for a quick visual interpretation of the fly ash analysis and provides information which is not obtained through the use of the commonly used classical two-or three dimensional data representation plots alone. The method provides information on the occurrence of “outlying” samples, such as quartz grains, lime, calcium-sulfate or iron-containing particles. When the data-set is truncated for these outlying particles, cluster analysis of all ash data indicates that a model of 4–5 clusters can best explain chemical differences between the bulk of the particles of several class-F fly ashes. These clusters are related to each other by an inverse relation between the SiO2 and the A12O3 content, and some clusters display marked differences of either the oxides of Ti, Fe, Ca, Mg, K and/or K and Na. Inter-grain variation of one separate fly ash indicates that similar variations occur within individual fly ashes, only the absolute differences being smaller. The results are interpreted to represent either the coalescence or fusion of chemically different particles or small chemical differences in precursor clay minerals. The method of data-reduction presented here provides quick information on chemical relationships and is particularly suited to evaluate small data-sets. The method has potential to be combined with other input parameters, such as pozzolanic activity, glass content, particle size distribution and others.
Evolution of Lime and Microstructural Development In Fly Ash-Portland Cement Systems
Authors: Larbi Joseph A. , Bijen Jan M.
Published: March 2011

The evolution and distribution of calcium hydroxide, CH, and the development of microstructure during the hydration of three low-calcium fly ash-Portland cement blends with water-solids ratio (w/s) of 0.40 have been investigated. During the first month of hydration, the CH content of the blends was found to be relatively higher than the plain mix, if a dilution effect due to replacement of cement by an inert material is taken into account. After 28 days of hydration the CH content in the blends began to decrease. SEM observations of specimens revealed the occurrence of large, well-crystallized CH plates in intimate contact with some of the fly ash particles at younger ages and even after six months of aging. The study also showed that the chemistry of the pore solution in contact with the hydrating cement system and the characteristics of the fly ashes, such as the glass content and the fineness of the ash particles seem to exert major influences on the rate of evolution of CH in the fly ash blends. Semi-quantitative X-ray diffraction analyses performed on specimens cast against polypropylene plastic plates used to “model coarse aggregates” showed reduction in the thickness of the interfacial zone for the fly ash-Portland cement pastes from about 60μm to less than 15μm within one month of hydration. In the case of the plain Portland cement paste no significant change was observed. The degree of orientation of CH crystals within the interfacial region also was significantly affected by the fly ashes, although by this age of hydration the CH data showed little or no evidence of pozzolanic reaction.
The Effect on Cement Mortar and Concrete by Admixture of Spray Drying Absorption Products
Authors: Jeppesen Kirsten G.
Published: March 2011

Spray dried absorption products (SDA) having special characteristics are used as substitutes for cement in the preparation of mortars; the qualities of the resulting mixed mortars are described. Conditions are described for mortar mixes, data for which were presented at the MRS Fall Meeting 1987.

The influence of the composition of the SDA on water requirement and setting time has been studied. A full scale project involving 3 precast, reinforced concrete front-elements containing 20 and 30 wt.% SDA is described. Strength development, mineralogical composition and corrosion were monitored for two years.

A non-standard freeze-thaw experiment was performed which compares mortars containing SDA and fly ash (FA) and also shows the effect of superplasticizer.

The possibility of improving the SDA by grinding has been tested and a limited improvement has been found. The strength of the mixed mortars seems slightly influenced by the grain size of SDA

Gypsum (CaSO4·2H2O), synthetic calcium-sulphite (CaSO3·½H2O) and 2 SDAs have been used as retarders for cement clinker. Mortar test prisms have been cast and comparative strengths after curing for 3 years are reported
Oxyanion Substituted Ettringites: Synthesis and Characterization; and their Potential Role In Immobilization of As, B, Cr, Se and V
Authors: Kumarathasan Premkumari , McCarthy Gregory J. , Hassett David J. , Pflughoeft-Hassett Debra F.
Published: March 2011

Long-term batch leaching studies of composites of lignite combustion and gasification ashes with a calcium-based scrubber waste have shown the prominent formation of an ettringite structure phase, accompanied by reductions in solution concentrations of potentially hazardous elements such as boron and selenium. The possibility that oxyanions such as arsenate, borate, chromate, molybdate, selenate and vanadate might substitute for sulfate in the ettringite structure has been explored. There are literature reports of fully substituted borate, chromate and selenate [ettringites]*, and of two minerals with partial borate for sulfate substitution. X-ray diffraction phase pure products with chromate and selenate, substituted completely for the sulfate in ettringite, and with arsenate, borate and vanadate partially substituted for sulfate, have been synthesized at room temperature by mixing soluble Ca, Al and sulfate sources and maintaining a pH> 12 with NaOH additions. Attempts to substitute substantial amount of molybdate for sulfate were unsuccessful. The resulting phases were characterized chemically by ICAP spectrometry, ion chromatography and thermal analysis, and for phase purity and unit cell size by XRD. The speciation of the oxyanions in the substituted [ettringite] were confirmed by FTIR spectrometry. In solid solutions, the sulfate/oxyanion ratio was greater in the precipitated solid than in the synthesis solution. Chemical analyses of the [ettringites] did not give simple stoichiometries analogous to Ca6Al2(SO4)(OH)12 ·26H2O. Because nonstoichiometry can be attributed to numerous possibilities for charge balance and defects, structural formulae of the oxyanion substituted [ettringites] could not be established.
Indentation Fracture of Macro-Defect-Free (MDF) Cements
Authors: Chou Yeong-Shyung , Mecholsky J. J. , Silsbee M. R. , Roy D. M , Adair J. H. , Heiland P.
Published: March 2011

The fracture toughness of MDF (macro-defect-free) cement with different polymer contents has been investigated by the indentation-strength method and fracture surface analysis. It was found that the fracture toughness obtained by these two different techniques showed good agreement for the low (3 wt.%) polymer cement. The ultimate (apparent) toughnesses are 1.3 Mpam1/2 for low polymer content and 2.2 Mpam1/2 for high (8 wt.%) polymer content cement. Different microcracking and sponge-like microstructures have been observed and discussed.
A View Of Macro-Defect-Free (MDF) Pastes
Authors: Silsbee M. R. , Roy D. M. , Perez-Pena M.
Published: March 2011

The automated analysis of backscattered SEM images from polished surfaces of macro-defect-free cements based on ordinary portland cements is examined. A comparison of several techniques for the determination of pore size distributions in these materials is made.
Characterization and Cementitious Behavior of a Rhone-Poulenc Reactive Alumina
Authors: Agrawal Dinesh K. , Silsbee M. R. , Roy D. M. , Roy R.
Published: March 2011

Highly reactive alumina (from Rhone-Poulenc), which is x-ray amorphous, offers a great potential as a new Al-source precursor for forming low-temperature chemically bonded ceramics. This alumina has been characterized for the first time. Its thermal behavior, structure, morphology, and hydration behavior have been determined using XRD, TGA, DTA, SEM, and TEM, and the data are compared with those of other conventional aluminas and precursors such as α-Al2O3, gibbsite, and boehmite.
The Hydration and Calcination Mechanism of Calcium Aluminate-Based Ultra-High Strength Cement with Calcium Sulphoaluminate Compound
Authors: Mino Iwao , Sakai Etsuo , Nishioka Asaaki , Daimon Masaki
Published: March 2011

The hardening shrinkage of calcium aluminate based ultra-high strength cement becomes nearly zero by using calcium sulphoaluminate compound, and very high bending strength can be obtained by calcinating at 300°-600°C. The starting materials are calcium aluminate, silica fume, calcium sulphoaluminate compound and superplasticizer, and the water-to-power ratio is 0.15–0.25. The main hydration products are C3AH6, AH3, C-S-H and ettringite, forming a densely packed structure, together with a large amount of unreacted cement particles. The hardening shrinkage is remarkably reduced, because of the ettringite formation in the early stage. The bending strength is about 55 MPa when calcined at 600°C. C12A7 is identified by XRD; needle-shaped skeletons of ettringite crystals are observed by SEM. It is suggested that chemically bonding substances are C12A7, amorphous A12O3, and C-S-H in calcined calcium aluminate based DSP with ettringite.
A Study of Low Porosity Polymerized β-C2S Paste
Authors: Ping Lu , Jing Zhao , Wei Shen
Published: March 2011

In this paper an active β-C2S was used to prepare compacted and polymerized pastes with low porosity. X-ray diffraction (XRD), mercury intrusion porosimetry (MIP), scanning electron microscopy (SEM), and tri-methy silanation-gel permeation chromatography (TMS-GPC) techniques were used to characterize the microstructure of the pastes both before and after additions of inorganic complexing ions, Fe2+and Ni2+, and organic silane VTES.

The results indicate that both inorganic complexing ions and organic silane can play a role in the polymerization of the native silicate anions in the cement pastes. These materials lead to a distinct increase of pentamer, octamer, and polymer components in the pastes, resulting in a decrease in the average C/S ratio in the C-S-H phase. The samples obtained from this processing have very high mechanical strengths, up to a compressive strength of 316 MPa, and fracture surface energy of 43 J/m2.
Mechanical Properties of Silica Coatings
Authors: Cornett Kenneth D. , Fabes B. D. , Oliver W. C.
Published: March 2011

Silica coatings with as-deposited densities ranging from approximately 50-100% were deposited on sapphire substrates by electron beam evaporation and sol-gel techniques. The shrinkage, hardness, and etch rates of the coatings were measured after various heat treatments. Differences in shrinkage indicated that hardness was not controlled by bulk porosity alone. Most films exhibited a surface “crust” that was significantly harder, and etched more slowly than the interior of the sample. We propose that the differences in mechanical and chemical behavior are caused by Si-O network reorganization starting at the film/air interface.
Mechanical Properties of Thin Film Aluminum Fibers: Grain Size Effects
Authors: Steinwall James E. , Johnson H. H.
Published: March 2011

Thin film aluminum fibers with grain sizes of 35 and 100 nm were pulled in a microtensile tester. The larger grains led to greater yield and tensile strengths but smaller strains to failure. Both samples had mechanical strengths 3–6 times greater than bulk aluminum. In addition, the small grained fibers had a strain rate sensitivity exponent of 0.26 suggesting diffusion controlled plastic deformation mechanisms.
Microscratci I Test on Carbon Films as Thin as 20 nm
Authors: Wu T. W. , shull A. L. , Lin J.
Published: March 2011

The capabilities to monitor tangential force and acoustic emission have been added to the microscratch mode of the IBM microindenter. These two new monitoring devices combined with the existing normal loadcell enhance the ability of the microscratch test to measure mechanical properties of thin film materials. As a demonstration of the upgraded microindenter, scratch tests were performed on 11 0nm and 20nm thick carbon films deposited on Si <100> substrates. The scratch morphology was examined by scanning electron microscopy to correlate the mechanical data to corresponding failure mechanisms.

In the case of the 110nm film, a brittle type fracture was taking place as the applied normal load exceeded a critical value. All three monitored outputs detected the first occurrence of the spallation ofthe film. In contrast to the thicker film, large scale spallation was not observed for thle 20nm film, and the acoustic emission detector did not show any significant output. An apparent friction coefficient(FR) is defined as the ratio ofthe tangential force to the normal load. FR is determined to be a useful parameter for monitoring the indenter's transition through the coating into the substrate, particularly in the case of small scale fracturing or simple ploughing through types of failure.
Ion Beam Annealing of Vapor-Deposited Carbon Film
Authors: Higuchi Kazuo , Noda Shoji , Iritani Sumiko , Ishiguro Tomoji , Kamigaito Osami
Published: March 2011

The effects of ion implantation on microtexture of vapordeposited carbon film were studied by Raman, XRD, TEM and sheet resistivity measurements. Growth of graphitemicrocrystals in the film was found when the film was implanted at the temperature above about 500 K. while graphite-sheet in the as-deposited film was distorted when it was implanted at the temperature below 300 K. The critical temperature for the ion beam annealing was estimated to be about 350 K. Ion implantation also caused the increase of the adhesion strength of the carbon film to a substrate.
Mechanical Properties of Compositionally Modulated Au-Ni thin films using Indentation and Microbeam Deflection Techniques
Authors: Baker Shefford P. , Jankowski Alan F. , Hong Soonil , Nix William D.
Published: March 2011

The “supermodulus effect” has been reported as an anomalous increase of as much as several hundred percent in the elastic moduli of compositionally-modulated thin metal films in a narrow range of modulation wavelength. The direct measurement of this effect has, however, been limited due to the very small dimensions of the test material. The mechanical properties of compositionally-modulated Au-Ni thin films (one of the first systems in which the supermodulus effect was reported) were studied on their substrates by indentation and microbeam-deflection techniques using a Nanoindenter. The films were fabricated by alternately sputtering Au and Ni onto [100] Si substrates for the indentation tests and onto prefabricated SiO2 cantilever beams with an initial Cr layer (for adhesion) for the beam deflection tests. All of the films have strong [111] textures and exhibit the structural characteristics of the films for which the modulus enhancement was reported. In particular, an increase in the average lattice parameter normal to the plane of the film over a narrow range of modulation wavelengths near 2 nm was noted. The modulation wavelengths range from 0.8 to 4.5 nm. The results from both indentation and microbeam deflection tests reveal no unusual plastic or elastic properties in these samples.
Measurement of Stresses in Thin Films Using Holographic Interferometry: Dependence on Atmospheric Conditions
Authors: Maden Michele A. , Tong Kun , Farris Richard J.
Published: March 2011

The direct measurement of stresses in spin-coated thin films is crucial for understanding their end use capabilities. A new technique for measuring the residual biaxial curing stresses in spin coated polymer films has been developed. This technique uses holographic interferometry to observe the modes of vibration of a membrane under biaxial tension. The stress in the film can then be determined by application of the vibrating membrane equation. A great advantage of this technique is that the material constants of the film do not enter into the analysis. The only material parameter needed is the density. In thispaper, we will examine membranes of polyimide and biaxially stretched rubber and latex. It is possible, using this technique to resolve the principal stresses and directions in films with complicated stress states.
Stresses in Passivated Films
Authors: Flinn Paul A.
Published: March 2011

Although wafer curvature measurement provides a rapid and accurate determination of stress in a uniform thin film, the technique is not applicable to patterned films. To study the stress in metal lines, and the effect of passivation on that stress, it is necessary to use X-ray diffraction. To obtain the sensitivity and precision required, a generalized focusing diffractometer (GFD), that had been developed especially for work on thin films, was used in this study.

The elastic strain tensors for aluminum and aluminum-silicon films and patterned lines were determined by X-ray diffraction. The corresponding stress tensors were calculated with the use of the known elastic constants of aluminum. The effect of various oxide and oxynitride passivations was investigated. Passivation over uniform metal films has very little effect, while passivation over patterned metal results in substantial triaxial tensile stress in the metal. Contrary to the conventional wisdom, high compressive stress in the passivation does not result in additional tensile stress in the metal. A possible explanation for the frequently observed deleterious effect (increased tendency for formation of cracks and voids) of highly compressive silicon nitride and silicon oxynitride passivations will be discussed.
Tribological and Mechanical Properties of Fe/Ti Multilayered films
Authors: Nastasi M. , Hirvonen J-P. , Jervis T. R. , Basu S. N.
Published: March 2011

A 900 Å as-deposited multilayered structure of alternating Fe and Ti on hardened tool steel has been examined for tribological and mechanical properties. The multilayer in contact with a 52100 steel ball counter surface possessed a 0.16 friction coefficient and showed good wear character after 1000 cycles in pin-on-disk experiments. Nanoindentation experiments show a 20 % increase in hardness for material in the wear track. Electron microscopy data suggests that the as-deposited bcc-Fe plus hcp-Ti multilayer composite transforms to a nanocrystalline alloy plus bcc-Fe by solid state reaction during pin-on-disk friction and wear test. The low friction observed in these surface films is attributed to the formation of a hard nanocrystalline alloy and improved interlayer and film/substrate adhesion which result during solid state reaction.
The Mechanical Properties of Cu/TiB2 Multilayer Structures
Authors: Hubbard Kevin M. , Basu S. N. , Hirvonen J-P. , Jervis T. R. , Nastasi M.
Published: March 2011

We have investigated the hardness and tribological properties of Cu/TiB2 multilayer structures deposited on substrates of tempered martensitic steel. Films of Cu and TiB2 were also deposited as hardness standards. The wear properties of the films were found to be poor, because of lack of adhesion. However, the films do appear to have good fracture toughness. The hardness of the multilayer was 18% greater than that predicted by the law of mixtures applied to the reference standards and, when corrected for variations in substrate hardness, very nearly equal to that of the TiB2 film. Irradiation by 400 keY Ne-ions to doses of 1.0, 6.0, and 12×1015 ion/cm2 results in a slight hardening of the multilayer. The structure was found to have excellent stability against radiation damage.
Mechanical Properties of Nanocomposite Coatings Fabricated by Sputttering
Authors: Chow G. M. , Holtz R. L. , Wu C. Cm. , Edelstein A. S. , Schlesinger T. E. , Cammarata R. C.
Published: March 2011

A brief study of the microhardness of nanocomposite coatings fabricated by a new technique is reported. The new fabrication technique utilizes sputtering at high pressures in a thermal gradient to produce nanometer-size particles, which are then embedded in a matrix produced by conventional sputtering. The microstructures and microhardness of nanocomposite coatings of Al matrix reinforced by Mo particles (grain diameter ranging from 7 to 20 nm) are reported.
In Situ Study of Stresses Generated During the Formation of Cobalt Disilicide and the Effect of Post Silicide Processing
Authors: Sitaram A. R. , Kalb J. C. , Murarka S. P.
Published: March 2011

Self aligned cobalt disilicide technology is emerging as an excellent choice for gate and interconnection and contact metallization in VLSI. The presence of an as deposited, intrinsic stress in the cobalt film and the generation of stresses during its subsequent reaction with the underlying silicon and during post silicide processing can affect the mechanical stability and the performance of the overall device structure. This study involved the in situ observation of the stresses generated in thin films of cobalt (or silicide formed on reaction) on silicon as they react during a continuously ramped and cooled temperature cycle. The results will be presented, and in the light of a well characterized reaction sequence, possible governing mechanisms will be presented and discussed.