bluuebunny/crossref_metadata_2025 huggingface dataset:
Stimulated Opticaltransitions in Er-Doped Silicon Nanostructures
Authors: Kamenev B. V. , Emel'yanov V. I. , Timoshenko V. Yu. , Kashkarov P. K. , Lomonosov M.V. , Terukov E. I. , Kudoyarova V. Kh.
Published: April 2011

Photoluminescence (PL) of Er3+ ions in nanocrystalline (amorphous) silicon matrix has been investigated under a high level of optical excitation. A superlinear increase of the PL intensity, a shortening of the PL decay time, and strong angular dependence were found at the excitation intensity above 200 kW/cm2. These effects are observed only in samples with presence of silicon nanocrystalls and explained by stimulated optical transitions.
Controlled Deposition and Applied Field Alignment of Single Walled Carbon Nanotubes for CNT Device Fabrication.
Authors: Smits Jan , Wincheski Buzz , Ingram JoAnne , Watkins Neal , Jordan Jeff
Published: April 2011

Carbon nanotubes (CNTs) offer great potential for advanced sensing devices due to their unique electronic transport properties. However, a significant obstacle to the realization of practical CNT devices is the formation of controlled, reliable and reproducible CNT to metallic contacts. In this work, a procedure for the deposition and alignment of CNTs onto metallic electrodes using chemically functionalized lithographic patterns is reported. This method uses photo and electron beam lithography to pattern simple Cr/Au thin film circuits on oxidized Si substrates. The circuits are then re-patterned with a self-assembled monolayer (SAM) of 3-aminopropyltriethoxysilane (APTES) to specify desired CNT locations between electrodes. The application of an electric field to the metallic contacts during the deposition of solution suspended single walled CNTs causes alignment of the CNTs in the field direction. This method consistently produces aligned CNTs in the defined locations.
Bio-inspired Self-Assembly of Micro and Nano-Structures for Sensing and Electronic Applications
Authors: McNally H. , Lee S. W. , Guo D. , Pingle M. , Bergstrom D. , Bashir R.
Published: April 2011

Bio-inspired assembly, through the use of bio-molecules such as DNA and proteins, will play a critical role in the advancement of novel sensing techniques and for the realization of heterogeneous integration of materials. For many of these applications, such as antibody-based biosensor and the study of controlled cell growth, DNA and protein patterning techniques are crucial. We will present an update of our work on protein patterning techniques using microelectronic fabrication, DNA hybridization and biotin-streptavidin pairing. To show its application in biological inspired self-assembly, this technique was used successfully in the self-assembly of 20 nm streptavidin conjugated gold particles. In addition, the integration of nano-and micro-scale heterogeneous materials is very important for novel material synthesis and electro-optic applications. We will present an update on our work to assemble silicon electronic devices using DNA/charged molecules and electric fields. Devices are fabricated, released, charged with molecules, and subsequently manipulated in electric fields. The techniques described can be used to integrate the hybrid devices such as nano- or micro-scale resistors, PN diodes, and MOSFETs on silicon or other substrates such as glass, plastic, etc.
Phonon Frequencies and Thermal Expansion of III-V Compounds
Authors: Reeber Robert R.
Published: April 2011

Thermal expansion is an important parameter for the design and manufacturing of dimensionally thermally stable opto-electronic integrated circuits and superlattices. In earlier work1, 2 we established the quantitative relationships between phonon frequencies and thermal expansion for Group IV semiconductors. In this paper we extend this approach to the III-V compounds GaAs, GaP, InP, GaSb, InAs, AlSb and InSb.
The compositional and optical characterizations of InGaAsN alloy semiconductor grown by MOVPE
Authors: Sanorpim Sakuntam , Nakajima Fumihiro , Katayama Ryuji , Onabe Kentaro , Shiraki Yashihiro
Published: April 2011

We report on the compositional and optical investigation of InGaAs(N) alloy films grown on GaAs (001) substrates by low-pressure (60 Torr) metalorganic vapor phase epitaxy (MOVPE). The alloy films with the room-temperature photoreflactance (PR) signal (Eo transition) wavelength range of 0.98–1.36 m have been grown. The variation in PL characteristics of the InGaAs(N) alloy films has been investigated as a function of alloy composition, excitation power and temperature. At low temperatures (T<100K), the PL spectra with several sub-peaks include localization emission as well as near-band-edge emission. On the other hand, the room-temperature PL properties for InxGa1-xAs1-yNy (x = 10.5% and 17.0% and y < 2%) are excellent with a single near-band-edge emission peak corresponding to their own Eo transition. The evolution of PL spectra with excitation power and temperature led to an insight into the nature of the near-band-edge states. The temperature dependence of integrated PL intensity indicates the presence of a large density of non-radiative recombination centers, showing a behavior characterized by two activation energies. Our results suggest that the origin of localization in InGaAsN alloy films is the alloy inhomogeneities of both In and N, which may results in the characteristic carrier dynamics.
Process Control of Epi-Layers for SiGe:C Hetero-Structure Bipolar Transistors
Authors: Xie Qianghua , Duda Erika , Kottke Mike , Qin Wentao , Wang Xiang-Dong , Lu Shifeng , Erickson Martha , Kretzschmar Heather B.
Published: April 2011

The SiGe:C hetero-structure bipolar transistor (HBT) has turned into a key technology for wireless communication. This paper describes the metrology tools for SiGe epitaxy process control. Two types of analysis are critical, (1) routine control of SiGe base and Si cap thicknesses, location and thickness of the doping layer, doping dose, Ge composition profile, and their uniformity across the wafer; and (2) root-cause analysis on non-routine problems. This is achieved by developing a transmission electron microscopy (TEM) technique allowing a thickness measurement with a reproducibility better than 3 Å. Charge-compensated low-energy secondary ion mass spectrometry (SIMS) using an optical conductivity enhancement (OCE) allows a Ge composition measurement to a required precision of 0.5 at. %.
High Efficiency Bulk Crystalline Silicon Light Emitting Diodes
Authors: Zhao Jianhua , Wang Aihua , Trupke Thorsten , Green Martin A.
Published: April 2011

A high power conversion efficiency above 1% from a bulk crystalline silicon (c-Si) light-emitting diode (LED) has been demonstrated at near room temperature. These devices are based on normally weak one- and two-phonon assisted sub-bandgap light emission processes. Their improved performance results from device designs that take advantage of enhanced light absorption by a light trapping scheme which was developed for high efficiency silicon solar cells, and from reducing scope for parasitic non-radiative recombination within the diode. Each feature individually is shown to improve efficiency by a factor of ten, accounting for an improvement by factor of one hundred compared to baseline devices.

Also demonstrated is a greatly improved band-edge light emission and detection using bulk c-Si diodes. A bulk c-Si LED is combined with a similar diode used as a detector that collects the light emitted with a high quantum collection efficiency of 33%, to produce a silicon to silicon optically coupled system that demonstrates 0.18% coupling quantum efficiency. The crystalline silicon LED demonstrates similarly high performance at very low power levels, where it has even higher power efficiency than a high efficiency GaAlAs LED.
Effect of Growth Temperature and Annealing on ZnO
Authors: Cai A. L. , Muth J. F. , Reed M. J. , Porter H. L. , Jin C. , Narayan J.
Published: April 2011

A series of epitaxial single crystal ZnO samples were grown by Pulsed Laser Deposition (PLD) on c-axis, double-side polished sapphire at temperatures ranging from 600°C to 800°C. A comprehensive optical study, consisting of cathodoluminescence (CL) and transmission spectroscopy measurements, was performed before and after annealing the samples in air and oxygen environments. The structural characteristics of the films were observed by x-ray diffraction and transmission electron microscopy (TEM). Using these measurements, the data revealed that annealing significantly improved the luminescence and exciton line-width of the better material grown at the higher end of the temperature range. In lower quality samples grown at the lower end of the temperature range, the optical quality of the material was degraded. In the samples grown at higher temperatures, annealing improved the optical qualities. An increase in the below band-gap, green band emission was also observed under some annealing conditions.
Novel resistance reduction and phase changes of contacts to n-type InP by rapid thermal annealing
Authors: Huang J.S. , Nguyen T. , Bar-Chaim N. , Vartuli C.B. , Anderson S. , Shearer J. , Fisher C.
Published: April 2011

We studied the influence of n-metal alloy on the long wavelength InP device performance. Various alloy schemes of rapid thermal annealing (RTA) were experimented to obtain the optimized contact resistance for the n-InP/AuGe/Ni/Au/Cr/Au metallization systems. Significant resistance reduction was achieved at 390°C for 45sec with wafer flattening step at 310°C. Using scanning transmission electron microscopy (STEM) and Auger electron spectroscopy (AES) analyses, we showed that resistance was correlated with interfacial reaction at the n-InP/metal. For the high resistance devices, little interfacial reaction between n-InP and Au occurred. For the low resistance devices, significant out-diffusion of P in the bottom Au and Ni layers occurred, forming Au-P and Ni-P metallic compounds. In addition, accumulation of Ge in the Ni layer was also detected. We suggest that Ni-P is very critical in obtaining low contact resistance for n-InP.
A Differential Scanning Calorimetry (DSC) Study on The Pyrolysis Mechanism of Zinc Oxide CVD Precursor, Zinc Acetylacetonate
Authors: Chang Yuneng , Hsieh Junhsuan , Wang Chonan , Hong Liting
Published: April 2011

In this study, we used differential scanning calorimetry (DSC) to study pyrolysis kinetics of zinc acetylacetonate (Zn(acac)2) in chamber ambient simulating real CVD condition, with heating rate from 10 to 20 °C/min. For Zn(acac)2 heated in pure N2, inert environment, DSC showed three endothermic peaks locating at 91–106 °C, 121–128 °C, and 135–142 °C, with peak area being 88 KJ/mol, 14 KJ/mol, and 18 KJ/mol, respectively. The DSC residuals analyzed by IR indicated all peaks might be originated from physical phenomena, since no compositional change observed. Further study by temperature programmed polarized optical microscope (POM) showed these peaks might be related to dehydration, phase transition, and melting of Zn(acac)2 and its hydrates. DSC in oxygen-containing ambient with O2 concentration from to 13 to 40 % showed three endothermic peaks and two additional exothermic broad peaks at higher temperature, 209–236 °C, and 330–400 °C. These exothermic peaks are assigned to oxidative decomposition of Zn(acac)2 and releasing of ligands. When oxygen concentration increased, peak area grew. Positions of these peaks depend on heating rate. Increasing the heating rate caused every peak to shift toward higher temperatures, with the first two endothermic peaks merged into one broad one.
Formation of Defects in MBE Re-Grown GaAs Films on GaAs/AlGaAs Heterostructures
Authors: Lamberti M. , Tokranov V. , Moore R. , Yakimov M. , Katsnelson A. , Oktyabrsky S.
Published: April 2011

In the present work, we examine the formation of defects on the sidewall slope in 1 μm - thick GaAs layers regrown on GaAs/AlGaAs heterostructures. Site-specific TEM specimens of sidewall slopes are obtained using focused ion beam combined with lift-out method. TEM analysis shows planar defects, such as stacking faults and microtwins, dislocations and large twinned areas, nucleating on the AlGaAs surfaces. SIMS and EDX reveal an increase in carbon and oxygen at the interface. The defect density increased with Al content exceeding 1010 cm-2 on Al0.4Ga0.6As. The defect formation is related to the oxidation of Al-containing surfaces.
Electronic Properties of n-type AlXGa1-XAs Alloys
Authors: Ferreira da Silva A. , Pepe I. , Haratizadeh H. , Holtz P.O. , Persson C. , Ahuja R. , Souza de Almeida J. , de Oliveria A.G.
Published: April 2011

We have investigated, theoretically and experimentally, the reduced and optical bandgap shift of Si-doped AlXGa1-XAs alloys as a function of both the Al composition and the Si concentration. The calculations were carried out within a framework of the many particle random phase approximation with the Hubbard local-field correction, considering electron populations in the conduction minima located at the Γ, X and L-points of the Brillouin zone. The experimental data have been obtained by means of photoluminescence spectroscopy. The theoretical predictions are found to be in good agreement with the experimental results.
Optical and EPR Study of Defects in Cadmium Germanium Arsenide
Authors: Bai Lihua , Garces N. Y. , Yang Nanying , Schunemann P. G. , Setzler S. D. , Pollak T. M. , Halliburton L. E. , Giles N. C.
Published: April 2011

Bulk crystals of CdGeAs2 have been characterized using photoluminescence (PL), optical absorption, Hall effect, and electron paramagnetic resonance (EPR) techniques. An absorption band near 5.5 microns at room temperature is observed in all of the p-type samples we have studied. A correlation between the magnitude of this optical absorption and the excess hole concentration at room temperature is established. Also, an EPR signal is found to correlate with the strength of this absorption band. PL data are consistent with an increased concentration of shallow acceptors being present in high-absorption samples. From the EPR data, we suggest that a model for the paramagnetic defect associated with the absorption at 5.5 microns may be an acceptor on an anion site.
Spectral Response Modification Of Quantum Well Infrared Photodetector By Quantum Well Intermixing
Authors: Shin J. C. , Choi W. J. , Han I. K. , Park Y. J. , Lee J. I. , Kim E. K. , Kim H. J. , Choi J. W.
Published: April 2011

We have studied the change of the spectral response in a quantum well infrared photodetector (QWIP) by using the impurity-free vacancy disordering (IFVD) to change the bandgap of the GaAs/AlGaAs multiple quantum well absorption layer. IFVD process has been carried out with PECVD-grown SiO2 capping on the MOCVD-grown QWIP structure, whose absorption region consists of 25 periods of 3.6nm thick Si-doped GaAs well and 50nm thick Al0.24Ga0.76As barrier. The PL peak of MQW decreased with the increase of annealing temperature and time from 802 nm to 700 nm at 15 K. The fabricated QWIP whose absorption region was intermixed at 850 °C by IFVD technique showed the maximum change in spectral response from 8 to 10 um when compared to a QWIP without intermixing. This result implies that the intermixing technology can be used to make multicolor QWIP without growing multiple IR absorption regions.
Micromagnetic Simulation of Thermal Effects in Magnetic Nanostructures
Authors: Dittrich Rok , Schrefl Thomas , Tsiantos Vassilios , Forster Hermann , Suess Dieter , Scholz Werner , Fidler Josef
Published: April 2011

A path finding method and a stochastic time integration scheme for the simulation of thermally activated magnetization processes are introduced. The minimum energy path and the saddle points for the thermally induced transitions between the ground states of NiFe magnetic nano-elements are calculated.
Simulations of the Domain State Model
Authors: Nowak U. , Misra A. , Usadel K. D.
Published: April 2011

The domain state model for exchange bias consists of a ferromagnetic layer exchange coupled to an antiferromagnetic layer. In order to model a certain degree of disorder within the bulk of the antiferromagnet, the latter is diluted throughout its volume. Extensive Monte Carlo simulations of the model were performed in the past. Exchange bias is observed as a result of a domain state in the antiferromagnetic layer which develops during the initial field cooling, carrying a remanent domains state magnetization which is partly irreversible during hysteresis. A variety of typical effects associated with exchange bias like, e. g., its dependence on dilution, positive bias, temperature and time dependences as well as the dependence on the thickness of the antiferromagnetic layer can be explained within this model.
A Small Angle Polarized Neutron Scattering Investigation of Magnetic Correlations in Nanocrystalline Fe89Zr7B3Cu1
Authors: Agosti Enrico , Moze Oscar , Cadogan John , Suzuki Kiyonori , Heinemann Andre , Hoell Armen
Published: April 2011

The technique of small angle neutron scattering (SANS) is ideally suited for determining the length scale of magnetic correlations in nanocrystalline materials. The additional use of polarized neutrons also allows for a clear separation between magnetic and non-magnetic scattering. The temperature dependence of the SANS cross-section from a two-phase alloy, consisting of both amorphous and nano-crystalline parts, Fe89Zr7B3Cu1, has been measured in the temperature range from 293 to 500 K. The SANS measurements are accompanied by bulk magnetization and Mössbauer transmission data. In this range of temperatures, the magnetic contrast between the nanocrystalline and amorphous phases, which are both magnetic, changes dramatically. This phase contrast increases up to 380 K, which is the proposed decoupling temperature for the inter-granular exchange stiffness. Above this temperature, the contrast levels off slowly, being totally dominated by the decreasing magnetization of the nanocrystalline phase.
Real-time x-ray scattering study of homoepitaxial growth of SrTiO3 by sputtering
Authors: Lee Hsin-Yi , Hsu C.-H. , Hsieh Y.-W. , Liang K. S.
Published: April 2011

The real-time x-ray scattering measurements under in-situ sputtering conditions were employed to study the growth behavior of sputter-deposited SrTiO3 films on SrTiO3 (001) substrate. A condition for conformal growth between deposited layers and substrate was found by observing the oscillation fringe in the diffuse scattering of measured reflectivity. The azimuthal scan around surface Bragg peak of the film peak shows that the epitaxial relationship between film and substrate can be achieved by sputtering.
Study of Surface Morphological Evolution by Cluster Ion Irradiation on Solid Targets
Authors: Aoki Takaaki , Nakai Atsuko , Matsuo Jiro , Takaoka Gikan
Published: April 2011

Smoothing effect by large gas cluster ion irradiation was studied. Ar cluster ion beams were irradiated on rough Si surface with various ion dosage. 100×100μm2 AFM image was measured for each surface. These AFM images were treated with fast Fourier transform in order to examine the change of surface morphologies with cluster ion irradiation. Power spectra analysis showed that the intensity at each wave number (the inverse number of wavelength) exponentially decreases with ion dose. The relationship between smoothing rate and wave number was derived. The surface smoothing process was modeled with the use of this wave number dependence on decreasing rate. The calculated and the experimental surface profiles are in good agreements. With this model, roughness of cluster-irradiated surface can be calculated from initial surface images.
Low Temperature Growth of Silicon Dioxide Thin Films by UV Photo-oxidation
Authors: Fukano Atsuyuki , Oyanagi Hiroyuki
Published: April 2011

The low-temperature growth of thin SiO2 layers for gate insulators in very large-scale integrated (VLSI) circuits is becoming an urgent topic of silicon technology. In contrast, to conventional thermal oxidization processes (T>900°C), ultraviolet (UV) photo-oxidation of silicon technology is a promising approach for low-temperature growth of silicon dioxide thin films. We have grown silicon dioxide thin films at low temperature (T<500 °C) using an excimer lamp with various wavelengths and evaluated the quality of thin SiO2 layers as well as the SiO2–Si interface. We found that the SiO2 layers (t<5 nm) grown by UV photo-oxidation show significant differences in physical properties, such as density profile, from those of thermal oxidization, i.e., the higher average density 2.23 g/cm3 and more constant distribution, making the SiO2–Si interface region, so-called “transition layer” less eminent. Superior characteristics of ultra-thin SiO2 layer grown by UV photo-oxidation are demonstrated.
Analysis of Primary Crystallization in Amorphous Aluminum Alloys
Authors: Perepezko John H. , Tong William S. , Hamann Joe , Hebert Rainer J. , Rösner Harald R. , Wilde Gerhard
Published: April 2011

The annealing response of amorphous Al based alloy samples were investigated to assess the role of the as-quenched state on primary crystallization of Al nanocrystals(nc). Continuous heating differential scanning calorimetry (DSC) traces of amorphous Al87Ni10Ce3powders were compared to those from melt spun ribbon (MSR) to examine the effect of sample subdivision on primary crystallization. While the powders exhibited the same onset temperature as MSR, thermal cycling experiments show fine powder sizes reacting at the onset temperature and coarse powder sizes with the lowest melt quench rate transforming at the highest primary reaction temperature. In Al92Sm8MSR, a kinetics analysis of Al nc distributions indicates a notable effect of the as-quenched state on primary crystallization during isothermal annealing. With Al88Y7Fe5MSR intense deformation can induce thedevelopment of an Al nc distribution without thermal annealing. In each case examined, the results support the inclusion of quenched in clusters in the analysis of primary crystallization reactions.
Structure, Annealing Characteristics and Mechanical Properties of Mg60Cu30-yY10Siy Bulk Amorphous Alloys
Authors: Wolff U. , Yang B. , Pryds N. , Wert J.A.
Published: April 2011

The effect of different Si contents on the glass forming ability (GFA) and the amorphous-to-crystalline transformation has been investigated for the Mg-Cu-Y-Si system. Four Mg60Cu30-yY10Siy (y = 1–5 at.%) alloys were prepared using a relatively simple technique of rapid cooling of the melt in a copper mould. Crystallization was induced by heat treatment of the alloys and the samples were then characterized concerning their microstructure and thermal stability by X-ray diffraction (XRD), optical (OM) and scanning electron microscopy (SEM) and differential scanning calorimetry (DSC) at a constant heating rate. Partial substitution of Cu by Si leads to a transition of the as-cast structure at a constant cooling rate from amorphous to crystalline with increasing Si content. Furthermore, the glass transition temperature (Tg) of the Mg-Cu-Y-Si alloy is lower compared to the Mg-Cu-Y system. The mechanical properties of the bulk Mg-Cu-Y-Si alloys have been investigated and found to vary with the Si content.
Free Volume Evolution in Bulk Metallic Glass during High Temperature Creep
Authors: Sundar Daniel B. S. , Heilmaier Martin , Bartusch Birgit , Kanzow Jörn , Günther-Schade Katja , Rätzke Klaus , Eckert Jürgen , Faupel Franz
Published: April 2011

Metallic glasses lack long-range translational symmetry and have excess volume trapped within their amorphous structure, which has a direct bearing on their physical properties including deformation characteristics. Moreover, the trapped excess free volume is directly correlated to the defect concentration facilitating the possibility to model the temperature and time dependence of the free volume changes during creep as a trade off between defect generation and annihilation. Using differential scanning calorimetry (DSC) analysis the residual free volume of a metallic glass can be characterised based on the glass transition peak height (Δcp). In the present work constant strain rate tests were carried out at the ‘onset’ (Tgon = 685 K) and ‘point of inflection’ (Tgp = 705 K) of the calorimetric glass transition to study the time dependent flow behaviour in Zr55Cu30Al10Ni5 bulk metallic glass. Modelling based on DSC analysis and positron lifetime spectroscopy on samples creep deformed to different plastic strain values corroborate the stress decrease after the peak stress (‘stress overshoot’) occurring in bulk metallic glasses with increasing plastic strain to be associated with a small increase in free volume.
Elastic Properties and Microstructure of Metallic Glasses Pd39Ni10Cu30P21 Studied by Microacoustical Technique
Authors: Levin Vadim M. , Petronyuk Julia S. , Wang Limin , Hu Jiankai , Zhang Qianlin
Published: April 2011

The elastic properties of Pd39Ni10Cu10P21 bulk metallic glass (BMG) have been analysed using measurements of sound velocities. Different states of the Pd39Ni10Cu10P21 system (glassy state, supercooled liquid (SCL) and polycrystalline state) were obtained by annealing the samples near the glass transition and crystallization onset temperature. The microacoustical technique has been applied to measure local values of longitudinal and transverse elastic wave velocities and their distribution over a specimen. Finally sound velocities VL and VT, density ρ, bulk K and shear G elastic moduli were measured for different states. The values of ρ, VL and K decrease as temperature increases and the transition from glass to SCL takes place. In the crystalline state ultrasonic measurements were performed by the standard pulse ultrasonic technique with low-frequency flat transducer because of high ultrasonic attenuation in this state. Acoustic images (C-scans) demonstrate coarse-grained microstructure in this state. This is assumed to be characteristic of the microstructure obtained by crystallizing BMG.
Mechanical Properties of La-based Bulk Amorphous Alloys and Composites
Authors: Lee M.L. , Li Y. , Carter W.C.
Published: April 2011

The influence of different microstructures of La-based fully amorphous samples and its composites on the impact fracture energy were investigated and discussed. Results showed improvement in fracture energy of glassy metals with intermetallic phases, but deteriorated in the presence of dendrite phases and high volume % of crystalline phases.
On The Glass Forming Ability Criteria Of Bulk Metallic Glasses
Authors: Lu Z. P. , Liu C. T.
Published: April 2011

A new criterion γ, defined as Tx/(Tg+Tl) (where Tx is the onset crystallization temperature, Tg the glass transition temperature and Tl the liquidus temperature), has been proposed for glass formation in bulk metallic glasses (BMGs). The interrelationship between this new parameter and glass-forming ability (GFA) was elaborated and discussed in comparison with other established criteria. It was found that the new criterion γ had a much better correlation with GFA than other established parameters. An approximation of the critical cooling rate for glass formation was also formulated and evaluated in the light of this new parameter.
Measured and Calculated Electronic Structure of Ni0.40Pd0.400P0.20 and Cu0.400Pd0.400P0.20
Authors: Nicholson D. M. C. , Alamgir Faisal M. , Jain Himanshu , Williams David B. , Schwarz Ricardo B.
Published: April 2011

X-ray Photoemission spectra of Ni0.40Pd0.40P0.20 and Cu0.40Pd0.40P0.20 in the amorphous states are compared to each other and to first principles calculations of the electronic density of states. The electronic structure is calculated for a previously validated amorphous model of Ni0.40Pd0.40P0.20 and for the same amorphous structure but with Cu replacing Ni. The measured and calculated electronic structures of Ni0.40Pd0.40P0.20 agree and exhibit very little charge transfer to Pd. However, the measured and calculated electronic structures of Cu0.40Pd0.40P0.20 differ considerably. In Cu0.40Pd0.40P0.20 there is a large electron transfer to Pd. The local densities of states on Pd atoms in different CuPdP local environments that arise in the amorphous model shed light on this dramatic charge redistribution.
Effect of Compositional Short Range Order on Glass Formation in Binary Metallic System
Authors: Chen Hao , Khantha Mahadevan , Egami Takeshi
Published: April 2011

Molecular Dynamics simulation was carried out to study the glass transition and crystallization in the metal-metalloid binary system with pair-wise potentials. The results show that a repulsive potential between metalloid (small) atoms increases the glass forming ability. The observation is consistent with the recent theory of bulk metallic glass formation through local glass transition and nano-glass formation. The theory predicted that the compositional short-range order (CSRO) prevents the small atom pairing so as to increase the glass forming ability (GFA). The present results demonstrate the important role of CSRO in bulk metallic glass formation.
Theoretical scheme for the study of thermodynamic and transport properties of simple fluids at the liquid-glass transition line.
Authors: Robles M. , Uruchurtu L. I. , López de Haro M.
Published: April 2011

In this work we present a theoretical scheme to study the thermodynamic and transport properties of simple fluids at the liquid-glass transition line. This scheme makes use of a recent reformulation of the classical perturbation theory of liquids [M. Robles and M. López de Haro, Phys. Chem. Chem. Phys. 3, 5528 (2001)]. Using the hard-sphere fluid as a reference system our approach requires the choice of an equation of state for the hard-sphere system and a criterion to determine an effective (density and temperature dependent) diameter. Selecting the diameter in the same way as in the Mansoori-Canfield /Rasaiah-Stell variational perturbation theory and two different equations of state for the hard-sphere system, the liquid-glass transition line in the density vs. temperature plane for a Lennard-Jones fluid derived with our approach is shown to be in very good agreement with recent numerical simulations. The transition line in the pressure vs density plane and the value of the transport coefficients in the vicinity of the liquid-glass transition for the Lennard-Jones fluid are also examined.
Neutron Scattering Experiments on the Short-Range Order in Undercooled Metallic Melts
Authors: Holland-Moritz Dirk , Schenk Thomas , Simonet Virginie , Bellissent Robert , Convert Pierre , Hansen Thomas , Herlach Dieter M.
Published: April 2011

This work presents investigations on the short-range order of stable and deeply undercooled melts of the pure elements Fe, Zr and Ni. The liquids were undercooled by use of the electromagnetic levitation technique, which was combined with elastic neutron scattering in order to determine the structure factors of the liquids as a function of the temperature. The diffraction experiments provide evidence that a short-range order based on aggregates of icosahedral symmetry prevails in the melt. This short-range order is observed even at temperatures above the melting temperature and gets more pronounced if the liquids are undercooled.
Nonlinear Density Fluctuations and Spatial Heterogeneities near the Colloidal Glass Transition
Authors: Tokuyama Michio , Terada Yayoi , Oppenheima I.
Published: April 2011

How the spatial heterogeneities play an important role in the dynamics of density fluctuations near the colloidal glass transition is discussed from a new viewpoint. A nonlinear stochastic diffusion equation for the density fluctuations recently proposed by one of the present authors (MT) is numerically solved in two different initial states, an equilibrium state and a nonequilibrium state. Depending on initial states, the dynamics of the spatial heterogeneities are shown to be quite different from each other. Such differences are thus shown to influence the slow relaxations of density fluctuations, leading to different types of two-step relaxations.
Accounting For Corrosion Of Hlw Glasses By Humid Air In TSPA
Authors: Ebert W. L. , Cunnane J. C. , Dietz N. L.
Published: April 2011

This paper describes how the results of vapor hydration tests (VHTs) are used to model the corrosion of waste glasses exposed to humid air in the glass degradation model for total system performance assessment (TSPA) calculations for the proposed Yucca Mountain disposal system. Corrosion rates measured in VHTs conducted at 125, 150, 175, and 200°C are compared with the rate equation for aqueous dissolution to determine parameter values that are applicable to glass degradation in humid air. These will be used to determine the minimum for the range and distribution of parameter values in calculations for the Yucca Mountain disposal system license application (TSPA-LA). The rate equation for glass dissolution is rate = kE • 10 η • pH • exp(–Ea/RT). Uncertainties in the calculated rate due to the range of waste glass compositions and water exposure conditions are taken into account by using a range of values for the rate coefficient kE. The parameter values for the pH dependence (η) and temperature dependence (Ea) and the upper limit for kE are being determined with other tests. Using the values of η and Ea from the site recommendation model, the VHT results described in this paper provide a value of log kE = 5.1 as the minimum value for the rate expression. This value will change slightly if different pH-and temperature-dependencies are used for the TSPA-LA model.
Formation factor measurements in granite in the laboratory – Comparison of through diffusion and electromigration techniques.
Authors: Löfgren Martin , Neretnieks Ivars
Published: April 2011

Traditionally the effective diffusivity in and the formation factor of intrusive igneous rock have been measured in the laboratory by through diffusion (TD) experiments, which are very time consuming in larger samples with low porosity. In previous work alternating current (AC) has been used to measure the formation factor directly in large samples. In this paper direct current is used to actually transport the tracers through the rock sample in so called through electromigration (TEM) experiments. In these experiments electoosmosis has to be corrected for. The experimental time is reduced substantially when adding an electromigratory flux to the diffusive flux. TD, TEM and AC experiments were performed on a 15 mm thick unweathered granite sample from Laxemar, Sweden. The tracers uranin and iodide were used. The formation factor measured with the three methods varied between 1.2·10-4 - 2.87·10-4.
Fitting Element Profiles for Predicting Glass Dissolution Rates in Synthetic Interstitial Clay Water
Authors: Aertsens Marc , Lemmens Karel , Van Iseghem Pierre
Published: April 2011

An analytical model is developed to derive diffusion coefficients from the element profiles of the most mobile glass elements. Congruent dissolution is considered as a transient phenomenon and neglected. In the model, altered glass consists of two sublayers: a gel layer at the solution side, and a diffusion layer at the pristine glass side. In both layers, mobile glass elements diffuse towards the solution, while hydrogen/water diffuses towards the pristine glass.

Fitting the element profiles of boron, sodium and lithium leads to diffusion coefficients in the diffusion layer, which at 90°C are typically of the order of 10-22m2/s to 10-21m2/s. At 40°C, these diffusion coefficients are typically a factor ten lower. The diffusion coefficients in the gel are by less than a factor two hundred larger than those in the diffusion layer.

The diffusion coefficients derived from the profiles in this way are used to predict the dissolution behavior. These predictions, for which a constant value (representing congruent dissolution) is added to the predicted diffusive release, agree reasonably well with the measured dissolution data. Those results support the idea that diffusion determines the long term release of glass matrix elements in synthetic interstitial clay water. Flux conservation at the interface between the gel and the diffusion layer is not consistent with a constant (as a function of time) width of the diffusion layer. Some experimental evidence supports that this width increases with time.
SON68 Glass Dissolution Kinetics at High Reaction Progress: Experimental Evidence of the Residual Rate
Authors: Gin S. , Frugier P.
Published: April 2011

SON68 borosilicate glass dissolution involves several parallel mechanisms: interdiffusion, hydrolysis of the silicate network, recondensation of dissolved species leading to the formation of an amorphous gel layer and precipitation of secondary crystalline phases. In a highly confined medium corresponding to geological disposal conditions, the gel formed during SON68 glass alteration quickly becomes protective and the hydrolysis rate drops by about 4 orders of magnitude compared with the initial dissolution rate. This study focuses on the state of reaction progress corresponding to apparent saturation of the solution. At 90°C in static mode, new experimental data show that the decreasing rate due to the protective gel formation is followed by a quasi-constant residual rate. Several hypotheses are discussed. We first demonstrate that silica dissociation related to a slowly rising pH is not a valid explanation. This hypothesis proposed 15 years ago was consistent with a rate controlled by affinity (equilibrium between the glass and solution). The hypothetical precipitation of secondary crystalline phases that consume elements from the protective gel layer is then considered in the light of data obtained with a simplified 8-oxide glass, but this mechanism is not sufficient to account for residual rate of the SON68 glass. Other hypotheses based on the gel evolution (dissolution, evolution of the porous texture) are also proposed. The proposed mechanisms imply the persistence of a protective gel with a constant thickness. Finally, this paper shows that the residual rate could be a decisive phenomenon affecting the long term behavior of glass in disposal conditions.
Layered Manufacturing: Challenges and Opportunities
Authors: Cooper Khershed P.
Published: April 2011

Layered Manufacturing (LM) refers to computer-aided manufacturing processes in which parts are made in sequential layers relatively quickly. Parts that are produced by LM can be formed from a wide range of materials such as photosensitive polymers, metals and ceramics in sizes from a centimeter to a few meters with sub-millimeter feature resolutions. LM has found use in diverse areas including biomedical engineering, pharmaceuticals, aerospace, defense, electronics and design engineering. The promise of LM is the capability to make customized complex-shaped functional parts without specialized tooling and without assembly. LM is still a few years away from fully realizing its promise but its potential for manufacturing remains high. A few of the fundamental challenges in materials processing confronting the community are improving the quality of the surface finish, eliminating residual stress, controlling local composition and microstructure, achieving fine feature size and dimensional tolerance and accelerating processing speed. Until these challenges are met, the applicability of LM and its commercialization will be restricted. Sustained scientific activity in LM has advanced over the past decade into many different areas of manufacturing and has enabled exploration of novel processes and development of hybrid processes. The research community of today has the opportunity to shape the future direction of science research to realize the full potential of LM.
Alumina-Doped Silica Gradient-Index (GRIN) Lenses by Slurry-Based Three-Dimensional Printing (S-3DP™)
Authors: Wang Hong-Ren , Cima Michael J. , Sachs Emanuel M.
Published: April 2011

The traditional Slurry-based Three-dimensional Printing (S-3DP™) process has been used to fabricate complex structure materials by printing organic binders in selected positions on each printing layer. This process is modified to fabricate functional graded materials, such as gradient index (GRIN) lenses, by depositing different concentrations of dopant at different positions. The modified S-3DP™ process offers advantages over conventional GRIN lens processes, including reduced processing time, improved compositional flexibility, and increased index profile dimensionality. Two different approximately parabolic dopant concentration profiles, which have maximum alumina concentrations of 1.63 mol% and 2.50 mol%, are printed into silica powder beds using S-3DP™. The samples with maximum alumina concentration of 1.63 mol% have been sintered into optical transparency at 1650 0C for 30 minutes in a vacuum furnace (5×10-6 torr) while an additional dehydration process before sintering was required for the samples with maximum alumina concentration of 2.50 mol%. The magnifying effects of GRIN lenses with profiles of 1.63 mol% and 2.50 mol% alumina were observed, yielding effective focal lengths of 10 cm and 6.1 cm, respectively. Light diffraction, which results from the locally inhomogeneous dopant distribution and reduces the optical quality of GRIN lenses, was also observed.
Tunneling Current-Distance Characteristic of Scanning Vibrating Probe / 1-Alkanethiol Self-Assembled Monolayer (SAM) / Au (111) Structure
Authors: Yasutake Yuhsuke , Azuma Yasuo , Nagano Kouhei , Majima Yutaka
Published: April 2011

We report measurements of the tunneling current – distance (I-d) dependence above alkanethiol self-assembled monolayers (SAMs) on Au (111) substrates with high probe voltage. From the semilogarithmic I-d plots of hexanethiol and octanethiol SAMs, a kink in the tunneling current slopes is clearly observed, which shows the point where the STM tip contacts the end of the SAMs. The conductance decay constants of the vacuum layer and the alkanethiol SAMs are estimated from the tunneling current slopes. We also discuss the contact conductance of alkanethiol SAMs.
Measurement of Work of Adhesion on Wafers for Direct Bonding
Authors: Turner Kevin T. , Mark Spearing S.
Published: April 2011

The displacement loaded double cantilever beam (DCB), often referred to as the blade-insertion test or crack-opening method by the wafer bonding community, has become a common method for evaluating the work of adhesion of bonded wafer pairs. The test, while easy to perform, often yields results with large scatter and questionable accuracy. The mechanics of the specimen are investigated in detail in the current work. Expressions that demonstrate how wafer bow may lead to residual stresses that result in large errors in the calculated work of adhesion are developed. A three-dimensional finite element model is used to show that due to the circular wafer geometry and silicon anisotropy there is a large variation of the strain energy release rate across a straight crack front. The model is used to predict the actual crack front shape and shows good agreement with experiments. The results of the finite element simulations are compared to the traditional expression used for data reduction and implications of the model highlighted.
Optimization of Poly-SiGe Deposition Processes for Modular MEMS Integration
Authors: Lin Blake C.-Y. , King Tsu-Jae , Howe Roger T.
Published: April 2011

This paper describes a bi-layer deposition technique to reduce the strain gradient of polycrystalline silicon-germanium (poly-SiGe) thin films without the use of any post-deposition annealing. By adjusting deposition conditions such as temperature, pressure, and/or flow rates of reactants, poly-SiGe films with required low average stresses can be obtained. Using the bi-layer technique, a strain gradient of 1.1×10-5 μm-1 (equivalent to 88 mm radius-of-curvature) has been achieved in 3.9 μm-thick poly-SiGe. This strain gradient would cause only 0.055 μm tip deflection for a 100 μm-long cantilever. The thermal budget was ∼10 hours at 425 °C, and no post-deposition annealing was required. The bi-layer film also exhibits low compressive average stress (-36 MPa) and low resistivity (0.55 mΩ-cm).
3D Small Angle X-Ray Scattering (SAXS) on deformed PVDF Foils
Authors: Maier Guenther , Wallner Gernot , Fratzl Peter
Published: April 2011

3D Small Angle X-ray scattering (3D – SAXS) was applied to study the microstructure and the deformation mechanism in PVDF – foils (polyvinyhdene fluoride). SAXS is a powerful tool to investigate structural changes in deformed polymers to reveal morphology at the nanometer scale. When PVDF is strained the structure changes from spherohtic isotropie to a highly anisotropie fiber bundle structure, which requires a full three-dimensional analysis of the SAXS signal.
Study of high aspect ratio etching in silicon by a mixture of SF6/O2 using a 2-D model based on a Monte Carlo approach.
Authors: Marcos G. , Rhallabi A. , Ranson P.
Published: April 2011

The subject of this paper is to describe and comment on results from an etching model based on Monte Carlo method. It calculates the temporal profile evolution of the silicon substrate under an SF6/O2 plasma chemistry and a cryogenic process. This work was conducted in correlation with an experimental set-up to ensure the validity of the final results. Some in-situ measurements obtained in the gas phase allowed estimation of the incident kinetic parameters such as main ion and neutral fluxes. Collisionless sheath model is connected to the surface model to determine energetic and angular ion distribution functions. The study focuses on final properties of deep and thin trenches used in new power components. The development of a simulation tool appears as an useful mean to understand the role of certain parameters not easily controlled by the etching machine. In this article, results concerning the topography and defects usually met during such an etching process are shown and discussed.
Resist Poisoning-Free Advanced PECVD-Based Anti-Reflective Coating (ARC) for 90nm Technology and Beyond
Authors: Ahn Sang H. , Rathi Sudha , Liu Jean , Botelho Heraldo , Yeh Wendy , Seamons Martin , Witty Derek , M'Saad Hichem
Published: April 2011

A nitrogen-free (N-free) dielectric anti-reflective coating (DARC®) was cost-effectively developed in a plasma-enhanced chemical vapor deposition (PECVD) reactor to eliminate the 193nm resist poisoning interaction caused when N2O is used as a precursor [1]. Although it was found that even a N-free ARC could poison sensitive 193nm resists with –OH radicals [2], which either exist inherently in the ARC or result from H2O absorption by the ARC surface, the current investigation has revealed that it was possible to minimize resist poisoning. Our investigation showed that compressive film stress directly correlates to H2O resistance. Therefore, it was possible to greatly improve the ARC resistance to H2O absorption by creating and maintaining a process regime that makes the ARC film dense. The dense ARC film demonstrated promising lithography performance with minimal resist poisoning as well as excellent shelf life and O2-ashing resistance. This paper explores the N-free DARC material, its development, lithographic integration results and implementation in a production environment to eliminate 193nm resist poisoning.
Structure Evolution and Corresponding Electrical Properties in Weakly Bound Co-C60 Mixture
Authors: Sakai Seiji , Naramoto Hiroshi , Xu Yonghua , Priyanto Tri Hardi , Lavrentiev Vasily , Narumi Kazumasa
Published: April 2011

Mixture films of Co and C60 with various compositions were fabricated by co-evaporation under UHV condition. As for the saturation composition with C60-based phase, Co5C60 is deduced from the systematic Raman analysis. It is reasonably interpreted that the C60-based phase can be realized by less than one electron transfer per a Co atom into C60 and the contribution of a covalent bonding which induces a differently coordinated structure of the C60 molecules from the fcc-C60. The electrical conduction features are dependent on the Co content. In the C60-based phase up to Co5C60, the conduction mechanism seems to be described by the band concept modified with the disorder, followed by the hopping conduction through the precipitated Co clusters or particles and then, by the metallic one with increasing Co content.