bluuebunny/crossref_metadata_2025 huggingface dataset:
Dielectric Relaxation Spectroscopic Measurements on a Novel Electroactive Polyimide
Authors: Jawad Saadi Abdul , Alnajjar Abdalla , Bader Mamoun M.
Published: April 2011

AC electrical behavior of a novel aromatic electro-optic polyimide was investigated in the temperature range 25 °C to 300 °C and a frequency range from 1 Hz to 106 Hz. Three electrical quantities: impedance, permittivity and electric modulus are reported. The dependence of imaginary and real components of these quantities on temperature and frequency are discussed. The experimental results show that the polymer has high thermal stability below 200 °C, where the resistivity, dielectric constant and permittivity are nearly temperature-independent indicating highly rigid structure. Above this temperature, however, a well-defined broad peak corresponding to a relaxation process was observed for which the activation energy was calculated to be 8.5 Kcal/mole. This relaxation is associated with a restricted local rotational motion of the side chain chromophore.
Ferroelectric and Piezoelectric Properties of Blends of Poly(Vinylidene Fluoride Trifluoroethylene) and a Graft Elastomer
Authors: Su J. , Ounaies Z. , Harrison J. S.
Published: April 2011

A piezoelectric polymeric blend system has been developed. The system contains two components: ferroelectric poly(vinylidene fluoride-trifluoroethylene) and graft elastomer. The remanent polarization, Pr, and the piezoelectric strain coefficient, d31, of the blends have been studied as a function of relative composition of the two components, temperature and frequency. Both blended copolymer and graft unit in the elastomer contribute to the total crystallinity of the blend-system, and hence to the remanent polarization and piezoelectricity. The piezoelectric strain coefficient, d31, of the blend systems shows dependence on both the remanent polarization and the mechanical stiffness, which in turn are determined by the fraction of the two components in the blends. This mechanism makes it possible for the piezoelectric strain response of the blend to be tailored by adjusting the relative composition. Although Pr of the copolymer is higher than that of the blends, the blend films containing 75 wt.% copolymer exhibit a higher d31 at room temperature, possibly due to their lower modulus. The blend films containing 50 wt.% copolymer exhibit a constant value of d31, from room temperature to 70°C.
Superplasticity of Liquid-Phase Sintered β-SiC
Authors: Nagano T. , Kaneko K. , Zhan G.D. , Mitomo M.
Published: April 2011

Abstrtact

The compression and the tension tests of liquid-phase sintered β-SiC fabricated by hot-pressing using ultra fine powders were performed at 1973 K ∼ 2048 K in N2 atmosphere. Amorphous phases were observed at the grain boundaries and at multi-grain junctions in the assintered material. Strain hardening was observed under all experimental conditions. Stress exponents in the compression test were from 1.7 to 2.1 in the temperature ranging from 1973 K to 2023 K. A maximum tensile elongation of 170 % was achieved at the initial strain rate of 2 Χ 10−5 s−1 at 2048 K.
Effects of Crystallographic Texture on Internal Stress Superplasticity Induced by Anisotropic Thermal Expansion
Authors: Kitazono K. , Hirasaka R. , Sato E. , Kuribayashi K. , Motegi T.
Published: April 2011

Polycrystalline materials having crystallographic anisotropy show internal stress superplasticity under thermal cycling conditions. The deformation mechanism is analyzed using a theoretical model based on continuum micromechanics including the effects of crystallographic texture. The model is experimentally verified through the thermal cycling creep tests using polycrystalline zinc having two kinds of fiber-texture, and agrees well with the experimental results.
The Microstructure and Superplastic Behavior of Clean Mechanically Alloyed Titanium–Titanium Boride Alloys
Authors: Brown A.P. , Brydson R , Hammond C. , Wisbey A. , Godfrey T.M.T.
Published: April 2011

The superplastic forming (SPF) of titanium alloys is an established technology. A reduction in grain size from that of the typical sheet materials would lead to enhanced SPF properties and hence a reduction in production cycle times. This study describes the microstructural development and superplastic behaviour of fine-grained Ti-6%Al-4%V alloys. Ball-milling Ti-6%Al-4%V powder produces a nanocrystalline material; however on consolidation by hot isostatic pressing rapid grain growth occurs. Addition of boron powder during milling leads to boride precipitates in the matrix of the consolidated alloy. The precipitates are dispersed inhomogeneously, resulting in localized grain refinement. Superplastic testing revealed cavitation formation but in comparison to conventional sheet material, large elongations were achieved at relatively high strain rates.
Grain Refinement of Aluminum using Equal-Channel Angular Pressing
Authors: Horita Z. , Furukawa M. , Nemoto M. , Langdon T.G.
Published: April 2011

Using the technique of equal-channel angular (ECA) pressing, it is possible to reduce the grain size of polycrystalline materials to the submicrometer level. Thus, this processing technique has the potential for producing materials which may exhibit superplasticity. This paper describes various factors affecting the development and evolution of the microstructure produced by ECA pressing. Optimization of such factors is then presented for the advent of superplasticity.
Texture Evolution During Low-Temperature Superplasticity in 5083 and 5052 Al-Mg Alloys
Authors: Su S.W. , Hsiao I.C. , Huang J.C.
Published: April 2011

Absyract:

Low temperature superplasticity (LTSP) at 250°C and 1×10−3 s−1 was observed in the 5083 Al-Mg base alloy after thermomechanical treatments (TMT). With increasing TMT rolling strain, the high angle grain boundary fraction increased, more favorable for the further operation of grain boundary sliding and LTSP. The strong texture components and bimodal misorientation distributions present after TMT were not affected by static annealing at 250 °C but evolved gradually into a random orientation distribution during LTSP straining from 30% to 100%. When the LTSP elongation was greater than 150%, the macro-deformation anisotropy R ratio would finally reach a stable level. It seems that the LTSP performance was controlled by a large fraction of high angle boundaries, but not by the special coincidence site lattice boundaries.
High Hf Content NITIHF Shape Memory Films
Authors: Zhang Chen , Thoma Paul E. , Zee Ralph
Published: April 2011

Polycrystalline NiTiHf films with around 9at% Hf have been successfully deposited from a single NiTiHf target using a DC magnetron sputtering system. Free standing films were obtained by depositing the films on single crystal silicon substrates. Thickness of the films was controlled between 10-12µm. In this investigation, the effects of deposition temperature on the crystallinity and transformation temperatures of the films were studied. Substrate temperature during deposition was varied between 300°C and 700°C at 100°C intervals. The influence of heat treatment temperature on the properties of the films was also investigated. The heat treatment temperature was between 300°C and 800°C at 100° C intervals. Transformation temperatures of these films were determined by differential scanning calorimetry (DSC). The crystallinity was determined using x-ray diffractometry. It was found that all the as-deposited films were crystalline even when the substrate temperature was as low as 300°C. Both martensite and austenite transformation temperatures increase with increasing substrate temperature and increasing heat treatment temperature.
Investigation of Wear of Microelectromechanical Contacts
Authors: Gally Brian J. , Abnet C. Cameron , Brown Stuart
Published: April 2011

A test system has been assembled to examine factors controlling the reliability of microdevice switching. The system consists of a spherically tipped sputter-coated post driven by a piezoresistive actuator into a sputter-coated micromechanical membrane. Contact forces are calculated based upon the measured deflection of the micromechanical membrane, which is induced by post actuation. Membrane deflection is measured using white light interferometry. The known geometry of the membrane and probe tip permits the estimation of contact area and, hence, contact pressure. Preliminary testing of sputtered gold contacts resulted in localized melting, material transport to the membrane and failure of contact surfaces at relatively low contact pressures and current densities. Further testing will examine the factors governing the reliability of microdevice contacts, such as material properties, contact pressure and current density.
Study of PZT Film Stress in Multilayer Structures for MEMS Devices
Authors: Zakar E. , Dubey M. , Polcawich R. , Piekarski B. , Piekarz R. , Conrad J. , Widuta R.
Published: April 2011

Residual stress in the multilayer Si/Dielectric/Pt/PZT/Pt stack was measured as a function of annealing conditions, sol-gel derived PZT (Lead Zirconate Titanate -52/48) thickness, SiO2and/or Si3N4dielectric films thickness. Residual stress in the Si3N4layer varied from -201 to +1275 MPa and from -430 to + 511 MPa in the Si02layer. Furnace annealing of the bottom Pt film reduced the stress over rapid thermal annealing (RTA). Stress due to PZT films was the controlling factor for the final stress of the stack. Upon increasing PZT thickness, stress became less tensile for Si3N4dielectric and more tensile for Si02. The deposition of the top Pt on PZT followed by RTA at 300°C in nitrogen had a minimal effect on the final stress of the stack. The average tensile stress for the Si/Si02/Pt/PZT/Pt and Si/Si3N4/Pt/PZT/Pt stacks was 140 ± 25 and 476±235 MPa respectively.
Roughness Characterization of Si(110) Etched in TMAH by Atomic Force Microscopy
Authors: Moktadir Z. , Sato K. , Matsumuro A. , Kayukawa K. , Shikida M.
Published: April 2011

We have investigated the roughness of a silicon (110)-oriented surface after being etched with 20% TMAH (Tetra-methyl Ammonium Hydroxide). We have used an Atomic Force Microscope to determine the roughness exponent α using three different methods: fractal, power spectrum density and scaling analysis. The value of the parameter α was identified to be close to 1/2. This value is different from the KPZ value, which is 0.4 in 2+1 dimension
New Materials and New Processes for MEMS Applications
Authors: Schweitz J.-Å. , Larsson K. , Thornell G. , Björkman H. , Nikolajeff F.
Published: April 2011

The field of “non-silicon MEMS” is today rapidly expanding. The reasons are numerous: silicon has a limited functionality in many MEMS applications; the toolbox for micromaching of non-silicon materials is steadily growing in size and versatility; the price level of a variety of other advanced materials for MEMS has become more competitive etc. This development is here illustrated by a number of examples from a wide variety of materials classes, methods for synthesis and microprocessing, and fields of application. Among these examples are high-aspect ratio processing of different materials by ion track technology (MITE) and deep ion projection lithography (DIPL); laser microprocessing and free-space 3D laser writing; high-precision 3D diamond replicas from microstructured silicon masters; and microreplication in polymeric materials for microoptics and microsystems technology.
New Approaches to Chemical Bath Deposition of Chalcogenides
Authors: O’brien Paul , Heinrich Markus R. , Otway David J. , Robbe Odile , Bayer Alexander , Boyle David S.
Published: April 2011

We have been studying new approaches to conventional Chemical Bath Deposition (CBD) of chalcogenide containing materials, using continuous circulation and replenishment of CBD solution over a heated substrate. Crystalline thin films produced by this method offer potential for use in solar cell devices or other optoelectronic applications. Films of CdS, ZnS and the ternary material CdxZn1−xS have been deposited on TO-glass substrates. In this paper we demonstrate our approach for the deposition of CdS films. These have been characterized by XPS, SEM, XRD and UV/vis spectroscopy and shown to be good quality. The films have been used to fabricate Au/CdTe/CdS/TO-glass solar cells of efficiency 10.1% under AMl.5 illumination.
Fabrication of Crack-Free La0.2Sr0.8CoO3−x Membranes on Asymmetric and Porous Ceramic Supports—Effects of a Metallic Covering
Authors: Cao Z-D. , Hong L. , Chen X.
Published: April 2011

Crack-free La0.2Sr0.8CoO3−x (LSCO) membranes have been fabricated on porous ceramic supports such as MgO and CeO2 through dip coating and sintering. To avoid cracks in a LSCO membrane during sintering, a silver coating on top of the LSCO powder-packed layer that is formed via dip coating was found successful. The cracks would be otherwise unavoidable due to the shrinkage mismatch between the membrane and the support during sintering. The silver can be readily removed from the sintered LSCO membrane chemically without causing damages in the membrane.
Group IVB Oxides as High Permittivity Gate Insulators
Authors: Campbell S. A. , He B. , Smith R. , Ma T. , Hoilien N. , Taylor C. , Gladfelter W. L.
Published: April 2011

Increasing MOSFET performance requires scaling, the systematic reduction in device dimensions. Tunneling leakage, however, provides an absolute scaling limit for SiO2of about 1.5 nm. Power limitations and device reliability are likely to pose softer limits slightly above 2 nm. We have investigated the use of high permittivity materials such as TiO2, ZrO2, and their silicates as potential replacements for SiO2. We have synthesized titanium nitrate (Ti(NO3)4or TN), zirconium nitrate (Zr(NO3)4or ZrN), and hafnium nitrate (Hf(NO3)4or HfN) as hydrogen and carbon free deposition precursors. Several problems arise in the use of these films including the formation of an amorphous low permittivity interfacial layer. For TiO2this layer is formed by silicon up diffusion. Surface nitridation retards the formation of the interfacial layer. We discuss the effects of both thermal and remote plasma surface nitridation treatments on the properties of the film stack. ZrO2and HfO2appear to form a thermal layer of silicon oxide between the high permittivity film and the silicon and have excess oxygen in the bulk of the film.
Chemical Synthesis of Pure and Doped LaGaO3 Powders of Oxide Fuel Cells by Amorphous Citrate/EG Method
Authors: Tas A.C. , Schluckwerder H. , Majewski P. , Aldinger F.
Published: April 2011

Powders of LaGaO3, La0.9Sr0.1GaO2.95 and La0.8Sr0.2Ga0.83Mg0.17O2.815 were prepared by the amorphous citrate/EG method. The calcination behavior of the precursor powders of the above phases were studied in the temperature range of 200°-1400°C, in an air atmosphere. Characterization of the samples were performed by XRD, TG/DTA, FTLR, SEM, ICP-AES, and carbon and nitrogen analyses.
A Study of the Oxygen Surface Exchange Coefficient on La0.5Sr0.5CoO3−δ Thin Films
Authors: Chen X. , Wang S. , Yang Y.L. , Smith L. , Wu N.J. , Jacobson A.J. , Ignatiev A.
Published: April 2011

La0.5Sr0.5CoO3−δ (LSCO) can be used as a cathode material for low temperature solid oxide fuel cell applications. LSCO epitaxial thin films have been deposited on LaAlO3 substrates by pulsed laser deposition (PLD). The transient behavior of the thin film conductivity with the pressure changes was recorded as a function of temperature and partial oxygen pressure. The surface exchange coefficient k of the LSCO thin film was obtained from analysis of the electrical conductivity relaxation data. The measured surface exchange coefficient increases with temperature and with final pressure but is not sensitive to the initial pressure. After prolonged annealing at 900°C, the k value was found to have greatly increased. The mechanism of the dependence of the measured k on pressure is discussed.
Low Temperature Chemical Vapor Deposition of Titanium Nitride Thin Films With Hydrazine and Tetrakis-(dimethylamide)Titanium
Authors: Amato-Wierda Carmela , Norton Edward T. , Wierda Derk A.
Published: April 2011

Hydrazine and tetrakis-(dimethylamido)titanium have been used as precursors for the low temperature chemical vapor deposition of TiN thin films between 50°C and 200°C at growth rates between 5 to 35 nm/min. At hydrazine to TDMAT ratios of 50:1 and 100:1 the resulting films show an increase in the Ti:N ratio with increasing deposition temperature. They contain 2% carbon, and varying amounts of oxygen up to 36% as a result of diffusion after air exposure. The low temperature growth is improved when hydrazine-ammonia mixtures containing as little as 1.9% hydrazine are used. Their Ti:N ratio is almost 1:1 and they contain no carbon or oxygen according to RBS. The TiN films grown from pure hydrazine or the hydrazine-ammonia mixture have some crystallinity according to x-ray diffraction and their resistivity is on the order of 104µω cm. The low temperature growth is attributed to the weak N–N bond in hydrazine and its strong reducing ability. In these films, the Ti:N ratio is approximately 1:1.
Electronic Bandgap and Refractive Index Dispersion of Single Crystalline Epitaxial ZnGeN2
Authors: Zhu L.D. , Norris P.E. , Bouthillette L.O.
Published: April 2011

The electronic band gap of single crystalline ZnGeN2 epitaxial layer grown on sapphire substrate by metal organic chemical vapor deposition has been measured by optical transmission and room temperature photoluminescence. The band gap energy is 2.99eV at room temperature, and the band gap is a direct transition type. The interference oscillations of the transmission spectra together with rutile prism coupling measurements have been used to determine the r fractive index and the dispersion characteristics of the single crystal ZnGeN2 below the band gap energy. The rutile prism coupling measurement displays the wave guide modes of the film at 6 2.8nm wavelength of the He-Ne laser, enabling determination of the film thickness and refractive index precisely at the wavelength. The refractive index of ZnGeN2 crystal is 2.35 at 6328Å wavelength. The measured refractive index dispersion curve can be fitted with the first-order Sellmeier equation n2(λ) = A + λ2/(λ2-B), using fitting parameters A=4.3 1, B=0.076.
Impurity-Induced Defect States in Pb1−xGexTe Alloys Doped With Gallium
Authors: Skipetrov E.P. , Zvereva E.A. , Belousov V.V. , Skipetrova L.A.
Published: April 2011

Galvanomagnetic properties of n-Pb1−xGexTe(O.04≤x≤O.08) single crystals have been investigated in the shielded from external background illumination chamber and under controlled illumination from infrared heat source. Low temperature activation range of the impurity conductivity on the dark curves of ρ(l/T) was revealed and attributed to the appearance of gallium-induced deep level EGa in the gap of the alloys. It was shown that the alloys possess high infrared photosensitivity at temperatures below Tc=50%60 K, and effect of the persistent photoconductivity at helium temperatures was revealed.
Anisotropy of Optical and Electron Transport Properties of Atomic Ordering in CdGeAs2
Authors: Bairamov B. H. , Fernelius N. , Irmer G. , Monecke J. , Polushina I. K. , Pandey R. , Rud' V.Yu. , Rud Yu. V. , Schunemann P.G. , Ohmer M.C.
Published: April 2011

Inelastic light scattering by optical phonons and the temperature dependent electrical conductivity, Hall constant and photosensitivity were studied in oriented CdGeAs2 crystals grown by ultra-low gradient freeze technique from near-stoichiometric melts. Observation of the clear polarization dependence of the inelastic light scattering spectra by optical phonons combined with the absence of any dependence of the intensity and frequency shift of the observed lines with mapping measurements in 300 μm steps indicated the high optical quality and homogeneity of these single crystals. It is shown that surface-barrier structures using these single crystals may be used as wide-band detectors for natural light, as well as selective photoanalyzers for linearly polarized radiation.
Thermal Admittance Studies of Electron-Irradiated CdGeAs2
Authors: Smith S.R. , Evwaraye A.O. , Ohmer M.C. , Drevinsky P. J. , Bliss D. F.
Published: April 2011

Brudnyi, et al., and Zwieback, et al., have shown that introducing damage by irradiation with MeV electrons can alter the electrical and optical properties of undoped p-type CdGeAs2(CGA) crystals. Brudnyi's studies of the electrical transport properties of isochronally annealed samples demonstrated type conversion and identified at least two new centers, one a stable donor. Zwieback used multi-MeV electrons to introduce compensating donors, thereby, significantly improving the optical transparency of CGA crystals. However, at the present little is known about these centers. Therefore, we have studied these centers by observing the properties of electron-irradiated specimens using Thermal Admittance Spectroscopy (TAS) and correlated the results of these measurements with capacitance-voltage measurements and Hall effect measurements. Measurements before an after irradiation are compared. The as-grown native acceptor concentrations in our samples varied from a low in the mid 1016 cm−3to nearly 1019 cm−3. Significant changes in the electrically active states in the band gap were seen as a result of a single irradiation with 2 MeV electrons to a total dose of 5 × 105cm−2. The samples appear to respond more strongly than Brudnyi's samples. The thermal activation energies have been determined using TAS and they will be reported.
Photoluminescence Measurements in Interband Transition in Fast Neutron Irradiated In0.07Ga0.93As/A10.4Ga0.6 As Multiple Quantum Wells
Authors: Manasreh M. O. , Subramanian S.
Published: April 2011

Interband transitions in n-type InGaAs/AlGaAs multiple quantum wells were studied using a photoluminescence (PL) technique after the samples were irradiated with fast neutrons. It was observed that the PL intensity of the interband transition is reduced as the irradiation dose is increased. In Addition, the peak position energy of the interband transition was increased and then decreased as a function of irradiation dose. The results are explained in terms of electrons trapping, many-body effects, and irradiation-induced damages at the interfaces as well as in the well and barrier regions.
High-Temperature W Diode Lasers Emitting at 3.3µm
Authors: Olafsen L. J. , Bewley W. W. , Vurgaftman I. , Felix C. L. , Aifer E. H. , Stokes D. W. , Meyer J. R. , Lee H. , Menna R. J. , Martinelli R. U. , Garbuzov D. Z. , Maiorov M. , Connolly J. C. , Sugg A. R. , Olsen G. H.
Published: April 2011

W lasers based on type-II antimonides were recently operated nearly to room temperature under the conditions of cw optical pumping. However, the development of electrically pumped mid-infrared lasers has not yet reached the same level of performance. This is largely related to the more challenging task of simultaneously optimizing the doping/transport and gain/optical properties of the devices. Here we report a demonstration of type-II mid-IR diode lasers employing W active quantum wells. Laser structures with 5 or 10 active periods sandwiched between broadened-waveguide separate confinement regions and quaternary optical cladding layers were processed into 100-µm-wide stripes, cleaved into 1-mm-long cavities, and mounted junction side down. For 0.5-1 µs pulses at a repetition rate of 200 Hz, lasing was obtained up to a maximum operating temperature of 310 K, where the emission wavelength was 3.27 µm. The threshold current densities were 110 A/cm2and 25 kA/cm2 at 78 and 310 K, respectively. The characteristic temperature, To, was 48 K for temperatures between 100 and 280 K. Operation in cw mode was obtained to 195 K, with threshold current densities of 63 A/cm2and 1.4 kA/cm2at 78 and 195 K, respectively, with To = 38 K between 78 and 195 K. Significant further improvements in the operating characteristics are expected once the optimization of the designs and fabrication procedures is complete.
Self-interstitials have never been observed in crystalline Si. How about amorphous Si?
Authors: Roorda Sjoerd
Published: April 2011

In the early days of point defect studies in electron irradiated crystalline silicon, it was surmised that the Si self-interstitial is highly mobile even at 4 K and escapes direct detection. The existence of self-interstitials has of course been confirmed through the diffusion behaviour of a range of impurities and the direct observation of larger interstitial-type clusters. Against this background, the direct observation of self-interstitials in amorphous Si would seem next to impossible. Yet just such an observation may have been made recently, through a comparison of the high-resolution radial distribution function of pure amorphous Si before and after thermal anneal and that of crystalline Si.
Doping of amorphous and microcrystalline silicon films by hot-wire CVD and RFPECVD at low substrate temperatures on plastic substrates
Authors: Alpuim P. , Chu V. , Conde J.P.
Published: April 2011

Deposition of n and p-type amorphous (a-Si:H) and microcrystalline (µc-Si:H) silicon thin films on polyethylene terephthalate (PET) at substrate temperatures (Tsub) of 100°C and 25°C (RT) prepared by hot-wire (HW) chemical vapor deposition and radio-frequency (RF) plasma-enhanced chemical vapor deposition is studied as a function of hydrogen dilution. Doping is achieved by addition of phosphine (ntype) and diborane (p-type) to the gas phase reactive mixture. At Tsub=100°C, n-type a-Si:H is obtained by HW with dark conductivity σd10−4 ω−1cm−1 and by RF with σd~10−3 ω−1cm−1. P-type a-Si:H is obtained by HW with σd=8×10−7 ω−1cm−1 and by RF with σd=6×10−7 ω−1cm−1. Decreasing the temperature of deposition to 25°C decreases the sd of RF n-type amorphous samples to 5×10−5 ω−1cm−1 but the σd of p-type samples remains unchanged. RT HW a-Si:H films show a decrease of sd both for ntype film (σd=4×10−6 ω−1cm−1) and p-type film (σd=1.2×10−7 ω−1cm−1). N-type µc-Si:H was obtained by HW with σd=7×10−2 ω−1cm−1 and by RF with σd>10−2 ω−1cm−1 at 100°C. Using the same Tsub, p-type µc-Si:H was deposited by HW and by RF with σd~0.5 ω−1cm−1. At RT, only p-type µc-Si:H films could be prepared using HW (σd~1 ω−1cm−1) and RF (σd=4×10−3 ω−1cm−1). The structural properties of the films were studied using Raman spectroscopy. The structural and transport properties were correlated.
Electroreflectance Study of Light-Emitting Porous Silicon
Authors: Toyama Toshihiko , Shimode Akihito , Okamoto Hiroaki
Published: April 2011

Electroreflectance spectroscopy measurements have been performed on light-emitting porous Si (LEPSi). The transmission electron microscope measurements reveal that LEPSi includes Si nanocrystals with a mean crystal size of 1–2 nm. The ER features are observed at a transition energy of 3.4 eV in all of the samples, giving that LEPSi still keeps the threedimensional (3D) electronic structure. Changes in the transition energies are not found for LEPSi with the different mean crystal sizes. Furthermore, we directly observed interband transitions of quantized states due to quantum-confined electron-hole (e-h) pairs in LEPSi as two or three extra ER features being located between 1.2 and 3.1 eV which are never observed in bulk crystalline Si. Employing a simple effective mass approximation model, we have evaluated the reduced mass, the kinetic energies and the Coulomb attraction energies of the quantumconfined e-h pairs. We also found that the energy distance between the transition energies at the ground state and the photoluminescence (PL) peak energies basically corresponds to the Coulomb attraction energies. Finally, we propose a new luminescent model based on interband transitions involving the quantum-confined dense e-h plasma.
Temperature Dependent Transport in Microcrystalline PIN Diodes
Authors: Brammer T. , Stiebig H. , Lambertz A. , Reetz W. , Wagner H.
Published: April 2011

The optoelectronic behavior of diodes deposited by plasma enhanced chemical vapor deposition was investigated for a series of different silane concentrations in the gas phase. The purpose of this work was to correlate device characteristics with inherent properties of microcrystalline silicon by experiments and numerical simulations. Dark diode characteristics and, therefore, the open circuit voltage behavior of this series were dominated by the bulk properties of the i-layer (equilibrium carrier concentration) as shown by numerical modeling. Measurement of the solar cell output parameters as a function of the temperature showed that the fill factor of solar cells with small silane concentrations is dominated by the dark diode characteristics. This is in contrast to the temperature dependent fill factor of solar cells with large silane concentration which is limited by the extraction efficiency of the photogenerated carriers. Interface effects dominated the temperature dependent blue response. The gain in blue response increased with temperature and silane concentration by up to 200 % which revealed transport limiting material properties in the vicinity of the p/i-interface. This behavior was attributed to the nucleation region.
Microstructural Control Of Thin Film Si Using Low Energy, High Flux Ions In Reactive Magnetron Sputter Deposition
Authors: Gerbi Jennifer E. , Abelson John R.
Published: April 2011

Using plasma growth sources with concurrent particle bombardment, silicon thin films can be deposited with various phases and microstructures. DC Reactive Magnetron Sputtering (RMS), in particular, can produce amorphous, mixed-phase, nanocrystalline, polycrystalline, porous columnar, and epitaxial Si films. In particular, a large flux of low energy, heavy ions strongly affects the phase and microstructure, and therefore the resulting film qualities. Lowpressure (1.6 mTorr) RMS is particularly suited for this type of plasma manipulation: we bias the substrate to produce the ion energy of choice, and use an external magnetic field to control the ion/neutral flux ratio, therefore decoupling the parameters of bombardment energy and flux. In this work, we study the influence of slow (<40eV), heavy (Ar+), ions in RMS deposition on the formation kinetics and microstructures of microcrystalline, mixed-phase, and poly crystalline Si films. The analytical methods are ellipsometry, Raman scattering, and AFM. We will show how ion bombardment influences the direct nucleation of extremely smooth polycrystalline Si on glass at temperatures below 400°C, enhances the crystallinity of this polycrystalline Si in the bulk, and produces nanocrystalline Si with tailored grain sizes at temperatures below 200°C.
Comparison of Structural Properties and Solar Cell Performance of a-Si:H Films Prepared at Various Deposition Rates using 13.56 and 70 MHz PECVD Methods
Authors: Jones S.J. , Williamson D.L. , Liu T. , Deng X. , Izu M.
Published: April 2011

The advantage of using very high frequencies for preparation of a-Si:H materials at high rates (above 5 Å/s) for intrinsic layers (i-layer) of solar cells has been well documented. In an effort to identify film properties which may be related to this superior device performance, a study of the structural, optical and electrical properties of films made at various deposition rates between 1 and 15 Å/s using rf frequencies of 13.56 and 70 MHz has been made. The films were characterized using a number of techniques including small-angle x-ray scattering, infrared absorption spectroscopy, and scanning electron microscopy. For the films made using the 70 MHz frequency, the amount of nanovoids with sizes of < 100Å increases systematically as the deposition rates increases beyond 5 Å/s. Accompanying the increase in void fraction in the films are increases in the hydrogen content and the amount of 2070 cm-1 mode in the infrared absorption spectra. In addition to an increase in the amount of nanovoids in the films as the deposition rate exceeds 5 Å/s, the films made using the 13.56 MHz and high deposition rates have large amounts of SAXS related to scattering features with sizes > 200 Å. This scattering is associated with large bulk density fluctuations and/or enhanced surface roughness. None of the films in the study displayed signs of having columnar-like microstructures. The nanovoids are not related to changes in the solar cells with increasing i-layer deposition rate for both fabrication processes, perhaps due to the relatively small volume fractions of less than 0.2% and/or good void-surface passivation. However, the larger-scale structures detected in the films made using the 13.56 MHz technique could cause poorer performance in cells prepared at high growth rates.
Millimetre and Submillimetre Wave Components for Future Diagnostic Instrumentation
Authors: Mann Chris
Published: April 2011

Contrary to common belief the technology associated with components and systems for operation in the millimetre and submillimetre or Terahertz (THz) region of the electromagnetic spectrum is mature. However, it has largely been developed for use in the fields of radio astronomy and remote sensing, two areas where size and cost have not been the driving issues. This is changing, both fields now have ambitious plans to put large complex systems into space in experiments such as NASA'a EOS MLS and ESA'a FIRST amongst others. Also, ground based systems such as ALMA are planned where the total number of receivers exceeds 1000. For such instruments cost and size now becomes important. Taking these factors into account for the last decade or so there has been a concerted drive towards smaller and cheaper instrumentation. Initially, the use of quasi-optical systems was implemented in place of waveguide mainly because of its prohibitive manufacturing cost. Quas-ioptical systems are still being developed but waveguide has recently seen a revival due to the use of new micromachining techniques for its fabrication. Planar or integrated circuitry mounted in waveguide has now demonstrated state of the art performance to 2.5THz. Combining these factors means that for the first time the cost of manufacturing high performance RF electronics in the THz region has finally become affordable thereby making it available to new areas of research, material science is one of many. This paper describes how new devices and systems may be implemented to realise the basic building blocks of such instrumentation, namely, detectors and sources.
The Effects of Width Transitions on the Reliability of Interconnects
Authors: Hau-Riege C. S. , Thompson C.V. , Marieb T.N.
Published: April 2011

Experimental and modeling studies of Al-based interconnects with narrow-to-wide transitions show that the width transition is a site of atomic flux divergence due to the discontinuity in diffusivities between the narrow and wide segments, which have different microstructures. Lifetimes have been experimentally determined for populations of lines with width transitions, which have varying line-width ratios and varying locations of the width transitions with respect to the line end. The electromigration failure rate is increased as the width-transition is moved closer to the electron-source via. Correlation of the effects width transitions on lifetimes allows determination of the critical stress range for void -nucleation failure, which was found to be 600 ± 108 MPa.
Photo-Induced Growth of Low Dielectric Constant Porous Silica Film at Room Temperature
Authors: Zhang Jun-Ying , Boyd Ian W.
Published: April 2011

We report low temperature (25-200°C) photo-assisted sol-gel processing for the formation of porous silicon dioxide films on Si (100) substrates using 172 nm radiation from an excimer lamp. The effects of substrate temperature and irriadation time on the properties of the films formed have been studied using ellipsometry, Fourier transform infrared spectroscopy (FTIR), and electrical measurements. The FTIR spectra revealed the presence of a Si-O-Si stretching vibration peak at 1070 cm-1 after UV irradiation at 200°C. This is similar to that recorded for oxides grown by thermally oxidation of silicon at temperatures between 600-1000°C. Capacitance measurements indicated that the dielectric constant values of the films, found to be between 1.7-3.3, strongly depended on the substrate temperature during irradiation. Dielectric constant values as low as 1.7 were readily achievable at room temperature. These results show that the photochemical induced effects initiated by the UV radiation enable both reduced processing times and reduced processing temperatures to be used.
Microstructural Analysis of Copper Interconnections Using Picosecond Ultrasonics
Authors: Harper James M.E. , Malhotra Sandra G. , Cabral Cyril , Lavoie Christian , Hao Hsin-Yi , Homsi Wadih , Maris Humphrey J.
Published: April 2011

We demonstrate that picosecond ultrasonics provides detailed information on the structure and properties of patterned arrays of copper fine lines used in silicon chip interconnections. In this method, the sample surface is momentarily heated several °C using a pump laser beam, and the transient change in the optical reflectivity is measured by a probe laser beam. Measurements of the optical reflectivity are made on time scales ranging from picoseconds to nanoseconds, revealing information on electronic, acoustic and thermal properties. We have applied this method to samples consisting of copper line arrays of 0.4 µm linewidth, 0.65 µm pitch and 0.35 µm depth in SiO2 on silicon wafers. For comparison, we examined the picosecond ultrasonic response of 200 nm-thick blanket copper thin films. The patterned Cu lines are found to have long-term oscillations at frequencies of 4.39 and 8.29 GHz with lifetimes at least 10 times longer than the oscillations in the blanket Cu film. A two-dimensional mechanical analysis was developed which uses as input parameters the dimensions and sound velocities of the materials in the sample, and finds the normal mode frequencies and displacements. The main vibrational modes are identified and described for the patterned lines, and the simulations confirm that the lowest frequency modes have very small damping coefficients. Also, the time-dependent signal is shown to reveal details of interface layers and integrity of the copper/liner interface.
Volatile Liquid Precursors for the Chemical Vapor Deposition (CVD) of Thin Films Containing Tungsten
Authors: Gordon Roy G. , Barry Seán , Broomhall-Dillard Randy N. R. , Wagner Valerie A. , Wang Ying
Published: April 2011

A new CVD process is described for depositing conformal layers containing tungsten, tungsten nitride or tungsten oxide. A film of tungsten metal is deposited by vaporizing liquid tungsten(0) pentacarbonyl 1-methylbutylisonitrile and passing the vapors over a surface heated to 400 to 500 °C. This process can be used to form gate electrodes compatible with ultrathin dielectric layers. Tungsten nitride films are deposited by combining ammonia gas with this tungsten-containing vapor and using substrates at temperatures of 250 to 400 °C. Tungsten nitride can act as a barrier to diffusion of copper in microelectronic circuits. Tungsten oxide films are deposited by adding oxygen gas to the tungsten-containing vapor and using substrates at temperatures of 200 to 300 °C. These tungsten oxide films can be used as part of electrochromic windows, mirrors or displays. Physical properties of several related liquid tungsten compounds are described. These low-viscosity liquids are stable to air and water. These new compounds have a number of advantages over tungsten-containing CVD precursors used previously.
A Comparative Study of Ti/Low-k HSQ (Hydrogen Silsesquioxane) and Ti/TEOS (Tetraethylorthosilicate) Structures at Elevated Temperatures
Authors: Zeng Yuxiao , Chen Linghui , Alford T. L.
Published: April 2011

For the benefit of reducing capacitance in multilevel interconnect technology, low-k dielectric HSQ (hydrogen silsesquioxane) has been used as a gapfill material in Al-metallization- based non-etchback embedded scheme. The vias are consequently fabricated through the HSQ layer followed by W plug deposition. In order to reduce the extent of via poisoning and achieve good W/Al contact, thin Ti/TiN stack films are typically deposited before via plug deposition. In this case, HSQ makes direct contact with the Ti layer. The reliability of the Ti/HSQ structures at elevated temperatures has been systematically studied in this work by using a variety of techniques. These results are also compared with those from Ti/TEOS (Tetraethylorthosilicate) structure, where TEOS is a conventional intra-metal dielectric. When the temperature is below 550 °C, a significant number of oxygen atoms are observed to diffuse into the titanium layer. The primary source of oxygen is believed to come from the HSQ film. When the temperature is above 550 °C, HSQ starts to react with Ti. At 700 °C, a TiO/Ti5Si3/HSQ stack structure forms. The Ti/HSQ system exhibits a higher reactivity than that of the Ti/TEOS system.
High Density Plasma Silicon Carbide as a Barrier/Etch Stop Film for Copper Damascene Interconnects
Authors: M'Saad Hichem , Cho Seon-Mee , Vellaikal Manoj , Li Zhuang
Published: April 2011

A low κ dielectric barrier/etch stop has been developed for use in copper damascene application. The film is deposited using methane, silane and argon as precursors in a HDP-CVD reactor. The film has a dielectric constant of 4.2 which is lower than the dielectric constant of conventional SiC or plasma silicon nitride (>7). Film characterization including physical, electrical, adhesion to ILD films, etch selectivity, and copper diffusion barrier properties show that this film is a better barrier than silicon nitride for low κ copper damascene interconnects. This film consists of a refractive index in the range of 1.7 to 1.8, a compressive stress of 1.0-1.5×109 dynes/cm2, and a leakage current of 5.0×10−10 A/cm2 at 1 MV/cm. When integrated in-situ with HDP-FSG, an effective dielectric constant of 3.5 can be achieved.
High-Jc YBCO Conductors Fabricated By Magnetron Deposition
Authors: Savvides N. , Gnanarajan S. , Herrmann J. , Thorley A. , Katsaros A. , Molodyk A.
Published: April 2011

Superconducting YBCO/YSZ/Hastelloy tapes or coated conductors were fabricated by combining ion beam assisted deposition (ILBAD) and magnetron sputtering techniques. The degree of biaxial alignment of the YSZ buffer layers and the epitaxial YBCO films was determined from x-ray pole figures and ø-scans. The best YSZ buffer layers had FWHFM δø= 7°- 10°. The corresponding YBCO tapes achieved a similar degree of biaxial alignment and high critical current density, Jc(77K,0T) = (0.9 – l.25)×106 A cm−2.
Kinetic Monte Carlo Simulation of Dynamic Phenomena in thin Film Growth
Authors: Gallivan M. A. , Murray R. M. , Goodwin D. G.
Published: April 2011

In this paper we describe the response of a Kinetic Monte Carlo model to time-varying growth conditions. We vary temperature and partial pressure sinusoidally and identify behavior typical of low-dimensional nonlinear systems. In particular, the frequency content of the roughness response is sensitive to the presence of steps in the surface.
Localized Excimer Laser Energy Modulation in the Crystallization Of Poly-Si Film On Stepped Substrate
Authors: Park Kee-Chan , Jung Sang-Hoon , Nam Woo-Jin , Han Min-Koo
Published: April 2011

Anew excimer laser recrystallization method of a-Si film to increase the grain size of poly-Si film has been proposed. Excimer laser energy was locally modulated by being irradiated on stepped substrate with 500 nm deep trench on which a-Si film was deposited. Fairly large poly-Si grains (over 1 µm) were obtained due to lateral thermal gradient which resulted from the laser energy difference on the vertical wall and on the horizontal bottom plane of the trench without altering laser energy density elaborately.
From the Solid-Fluid Interfacial Structure to Genuine Morphology of Crystals
Authors: Liu X.Y.
Published: April 2011

Crystals reveal a large variety of shapes, depending on the chemical composition and the structure of crystals, and the growth conditions. To predict precisely the growth morphology of crystals remains a challenging issue for both academia and industry. In this paper, the principles for predicting the growth morphology of crystals based on the best available theories are highlighted and demonstrated.
Modeling of Interface Scattering Effects during Light Emission from Thin Film Phosphors for Field Emission Displays
Authors: Cho K. G. , Singh R. K. , Chen Z. , Kumar D. , Holloway P. H.
Published: April 2011

It has been experimentally shown that the light trapping due to internal reflection from a smooth surface is reduced as the surface becomes progressively rougher. Although this phenomenon is qualitatively understood well, there has been a lack of detailed analysis of the scattering phenomenon which affects the light emission from thin film phosphors (TFPs). Factors which affect the light emission from the TFPs include electron beam-solid interaction (EBSI), film thickness, microstructure, surface recombination rate, surface roughness, and substrate (thus the interface formed). In many cases, they cannot be varied independently and thus making it difficult to interpret the results quantitatively. Furthermore, as the surface roughness is smaller or same as the wavelength of the emitted light, classical theories based on rectilinear propagation of the light cannot be used without gross simplification. A new theoretical model has been developed by incorporating diffraction scattering at the various interfaces and the factors mentioned above. The model provides an integrated solution to explain the cathodoluminescence (CL) properties of TFPs for field emission displays (FEDs).
Stability in Electrical Properties of Ultra Thin Tin Oxide Films
Authors: Matsui Yuji , Yamamoto Yuichi , Takeda Satoshi
Published: April 2011

Tin Oxide films of less than 30nm in thickness were developed as transparent conductive electrodes. The films were deposited onto glass substrates by APCVD. Fluorine was used as a doping component. Stability to heat treatments in air at more than 500• was studied. Carrier concentration decreased and Hall mobility increased by the heat treatments. It was found relations between carrier concentration and mobility exhibited an exponential relation in extremely low fluorine concentration films. The exponent of the relation was close to −1.5. Resistivity decreased for the films, while it increased for films with high fluorine concentration. It was also found migration of sodium from the substrates into the films increased with increase of fluorine concentration in the films. Results suggest the sodium migration would affect grain growth and electrical properties of the films.
Nitride Phosphors for Low Voltage Cathodoluminescence Devices
Authors: Kanie Hisashi , Kawano Takahiro , Sugimoto Kose , Kawai Ryoji
Published: April 2011

Undoped and Zn doped InGaN microcrystals were synthesized by a two-step method. The InGaN microcrystals have a wurtzite structure and brownish body color. The InGaN samples prepared at 900°C did not contain a metal In phase. The InGaN:Zn microcrystals showed blue photoluminescence (PL) at 77K different from that of GaN:Zn. Reflectivity and photoluminescence excitation (PLE) measurement showed that the fundamental absorption edge of the InGaN:Zn phosphors is 3.47 eV, which implies that the In content in the InGaN:Zn phosphors is less than 0.2%. GaN:Zn and InGaN:Zn showed a Zn related PLE peak at 3.34 eV. InGaN and InGaN:Zn showed an In related PLE peak at 3.14 eV. When the InGaN:Zn samples were selectively excited at 3.15 eV, an In-related emission band centered at 2.2 eV emerged. The InGaN:Zn phosphors mounted on vacuum fluorescent displays (VFDs) showed room-temperature blue cathodoluminescence (CL) and the CL peak shifted slightly toward the low energy compared to that of the GaN:Zn phosphors because of the superimposed In related band. The InGaN:Zn phosphors had a luminance of 50 cd/m2 and a luminance efficiency of 0.03 lm/W at an anode voltage of 50 V.