bluuebunny/crossref_metadata_2025 huggingface dataset:
Modification of Wetting Property of Polycarbonate by Means of Ion Beam Implantation and Storage in Different Gas Environments
Authors: Poirier A. , Ross G. G. , Bertrand P. , Wiertz V.
Published: April 2011

Abstracr

The wetting property of polymers is very important in different applications such as biomaterials, textiles, aerospace (fluid management and materials processing in microgravity), and thin film adhesion. Therefore, there is a strong interest in the development of a new technology for the modification at will of this property. The use of low energy ion beams allows the modification of the first surface atomic layers. Nitrogen ions of 500 eV/at. were used to bombard the surface of polycarbonate (PC) samples to a fluence of 5×1016 at/cm2. Five different environments (oxygen, nitrogen, argon, dry air and vacuum) were used to store the samples for some hours (1 to 24 hours) after the implantation. Aging studies of the contact angle (advancing and receding) have shown that the environment gas influences the long term value of the contact angle and helps to maintain the stability of the treated surfaces with the passage of time. XPS and ToF-SIMS have been used to study the chemical effects of both N2+ ion irradiation and storage gas surrounding the samples. The results show faster aging in the case of the samples stored in vacuum, a harmful effect of nitrogen gas on the treatment and the formation of new chemical species for all treatments.
Size Dependence of Bombardment Characteristics Produced by Cluster Ion Beams
Authors: Seki T. , Tanomura M. , Aoki T. , Matsuo J. , Yamada I.
Published: April 2011

Cluster ion beam processes provide new surface modification techniques, such as surface smoothing, high rate sputtering and very shallow implantation, because of the unique interactions between cluster and surface atoms. To understand interactions with cluster and surface, Scanning Tunneling Microscope (STM) observations have been done for single impact traces.

Highly Oriented Pyrolitic Graphite (HOPG) surfaces were bombarded by carbon cluster ions (Va≤300kV), and large ridges and craters have been observed as a result of single cluster ion impact. The impact site diameters are proportional to the cluster size up to 10 atoms, and increase drastically for cluster sizes above 10. This indicates that non-linear multiple collisions occur only when a local area is bombarded by more than 10 atoms at the same time.
Aluminum and Electron-Irradiation Induced Deep-Levels In N-Type And P-Type 6H-Sic
Authors: Gong Min , Beling C. D. , Fung S. , Brauer G. , Wirth H. , Skorupa W. , You Zhi-Pu
Published: April 2011

Two deep levels, located at Ev+0.26eV and Ec-0.44eV, in Al-implanted n-type samples and one at Ev+0.48eV in p-type samples have been observed by the deep level transient spectroscopy. The level of is identified as the shallower aluminum-acceptor. The 1.7 MeV electron-irradiation, used as a probe to distinguish the implantation induced deep-levels, induces at least six electron traps in the n-SiC and one hole-trap in the p-type material. The peak positions of these deep-levels in DLTS spectra are quite different from those induced by Al-implantation. This result suggests that various damages are formed after heavy ion (Al) and light particle (e) irradiation.
New Approach to “High-Temperature” Quantum Switch and Quantum Field Effect Transistor
Authors: Meilikhov E.Z. , Aronzon B.A. , Bakaushiin D.A. , Ryl'kov V.V. , Vedeneev A.S.
Published: April 2011

We report results of studying some natural properties of highly disordered mesoscopic systems which seem to be promising for elevating quantum device work temperatures up to 77-300 K. They are FET-type Si-MNOS (metal-nitride-oxide-semiconductor) structures with built-in charge concentrations being so high that the systems remain to be strongly disordered even at room temperature. Disorder of studied structures could be controlled by varying charged traps concentration at the SiO2-Si3N4 interface that induce strong potential fluctuations. Important feature of the structures is the possibility to vary the built-in charge over a wide range (up to 1013 CM−2) that results in varying the disorder range. The conductance of such a system is shown to be controlled by the single small quantum-sized region with a ballistic transport which is a saddle-point region of the fluctuation relief. Narrowness of that “bottle neck” (comparable with the electron wavelength) results in quantizing conductance of the structure, and if the disorder is high enough, the conductance for some gate voltages shows a real tendency to reach a plateau at the quantum value e2/h. What is important, that tendency occurs a∼t high temperatures (77-300 K).
Recombination Strength at Intra and Intergrain Defects in Crystalline Silicon Investigated by Low Temperature Lbic Scan Maps
Authors: Perichaud I. , Martinuzzi S.
Published: April 2011

Annealing of multicrystalline silicon wafers in argon at temperatures higher than 800°C increases the recombination strength of extended defects irreversibly, while external gettering techniques applied at the same temperatures reduce their recombination strength. It is observed that in the light beam induced current (LBIC) scan maps at 80 K the contrast of some extended defects in raw samples is enhanced and additional defects are detected. The same features of defects are revealed by the LBIC maps of raw samples at 80 K as well as at 300 K after annealing. In other words, the LBIC scan maps at low temperature detect “sleeping” defects, which do not recombine at 300 K, but which are activated by thermal treatments during processing steps. The results can be explained by the Shockley-Read-Hall statistic involving the presence of deep and shallow energy levels in the band gap associated with the impurity-defect interaction.
Controlled Surface Fermi-level on the SeS2-passivated n-GaAs (100)
Authors: xi Sun Jing , Himpsel F. J. , Kuech T. F.
Published: April 2011

Selenium disulfide surface treatment can unpin the surface Fermi-level on n-GaAs (100) surfaces, resulting in a reduction in the surface band bending. The long-term stability of the surface Fermi-level unpinning has been studied using photoreflectance spectroscopy under room ambient conditions. Our results show that the SeS2-treated n-GaAs (100) surface is stable up to four months with negligible shift in the surface Fermi-level being noted. The mechanism of the long-term stability is attributed to the layered surface structure formed on the SeS2-treated n- GaAs (100) surface. The chemical structure of the passivated surface was determined by synchrotron radiation photoemission spectroscopy. The outermost layer of sulfur and arsenicbased sulfides and selenides may protect the electronic passivating layer, which consists of gallium-based selenides, from interaction with the atmosphere.
Whole-field Displacement Measurement Techniques for Thermal Deformation Analyses of Electronic Packages
Authors: Han Bongtae
Published: April 2011

Features and recent developments of various photomechanics methods are reviewed for thermal deformation analyses of electronic packages. Applications to diverse problems are illustrated to demonstrate wide applicability of the methods. The whole-field displacement information, with various sensitivity and resolution scales, is ideally suited for the deformation study of a broad range of problems in deformation analyses of electronic packaging. The methods are mature and they can be practiced routinely. A more extensive range of applications are anticipated.
Dynamic Coercivity and Thermal Decay of Magnetic Media
Authors: Rubin Kurt , Goldberg Jason , Rosen Hal , Marinero Ernesto , Doemer Mary , Schabes Manfred
Published: April 2011

Thermally induced decay of longitudinally recorded magnetic transitions is measured on a spin-stand. The decay rate increases with increased linear density and decreases with increased media coercivity. A new spin-stand experimental technique has been developed which allows measurements of the time dependence of the media coercivity as a function of write times spanning short times characteristic of write times in drives to long times associated with VSM measurements. The ratio of long to short write time coercivity was larger for media which are thermally unstable.
Computer Simulations of Thermal Switching in Small-Grain Ferromagnets
Authors: Novotny M. A. , Brown G. , Rikvold P. A.
Published: April 2011

We present Monte Carlo and Langevin micromagnetic calculations to investigate thermal switching of single-domain ferromagnetic particles. For the Monte Carlo study we place particular emphasis on the probability that the magnetization does not switch by time t, Pnot(t). We find that Pnot(t) has different behaviors in different regimes of applied field, temperature, and system size, and we explain this in terms of different reversal mechanisms that dominate in the different regimes. In the micromagnetic study of an array of Ni pillars, we show that the reversal mode is an ‘outside-in’ mode starting at the perimeter of the array of pillars.
Application of Cathodic Arc Deposited Amorphous Hard Carbon Films to the Head/Disk Tribology
Authors: Anders Simone , Singh Bhatia C. , Fong Walton , Yu Lo Roger , Bogy David B.
Published: April 2011

Amorphous hard carbon films deposited by filtered cathodic arc deposition exhibit very high hardness and elastic modulus, high mass density, low coefficient of friction, and the films are very smooth. All these properties are beneficial to applications of these films for the head/disk interface tribology. The properties of cathodic arc deposited amorphous carbon films are summarized, and they are compared to sputter deposited, hydrogenated (CHx), and nitrogenated (CNx) carbon films which are the present choice for hard disk and slider coatings. New developments in cathodic arc coaters are discussed which are of interest to the disk drive industry. Experiments on the nanotribology, mass density and hardness, corrosion behavior, and tribochemical behavior of cathodic arc films are reported. A number of applications of cathodic arc deposited films to hard disk and slider coatings are described. It is shown that their tribological performance is considerably better compared to CHx and CNx films.
Near-Field Magneto-Optic Fiber Probe
Authors: Seigler M.A. , Lambeth D.N.
Published: April 2011

A novel near-field magneto-optic fiber probe (NF-MOFP) for readback of ultra high density magnetic recording, or high resolution imaging of magnetic domains is described. This NFMOFP consists of a partially metalized tapered fiber, as used in conventional near-field scanning optical microscopy (NSOM), with the subwavelength sized aperture coated with a reflective magneto-optic (MO) film. This device is then used in a manner similar to conventional NSOM. The properties of the MO film deposited on the fiber tip, the NFMOFP's response to applied fields, and images of magnetic domains taken with the device are described.
Effect of pH and Concentration on the Synthesis of Monodispersed Spherical Fine Zirconia Powders Using Gas–Liquid Phase Reaction
Authors: Kim Chang–Hyun , Ri Chang–Seop , Lee Dae–Hee , Choo Ho–Sung , Lee Byung–Kyo , Chung Jong–Jae , Kim Song–Dae
Published: April 2011

Ammonia gas was blown into the solution of zirconium ion to induce homogeneous precipitation of supersaturated zirconium ion at gas-liquid interface with increase in pH. The precipitates formed using interface of gas-liquid phase were decomposed into fine spherical zirconia powder of high purity. As Concentration increase, mean diameter of particles increases to 140, 180, 240, 290 and 630nm. At pH of 4.5, maximum yield of 98.7% was obtained. From the above pH of 4.5, yield has been kept constant. Above pH of 5.0, large aggregates of precipitate consisting of primary particles were formed, and this may have been caused due to the existence of isoelectric point. Below pH of 4.5, almost aggregate-free fine spherical powders with particle size of below 100nm were produced.
Clay Nanolayer Reinforcement of a Glassy Epoxy Polymer
Authors: Massam Jarrod , Pinnavaia Thomas J.
Published: April 2011

Glassy epoxy-clay nanocomposites (Tg ≈ 82 °C) have been prepared by the reaction of diglycidyl ether of bisphenol A and a polyoxyalkylene amine curing agent in the presence of organo cation exchanged smectite (montmorillonite) clays. Commercially available AMS and CWC montmorillonites purified on the industrial scale (Nanocor, Inc.) afforded nanocomposites with performance properties comparable to those obtained from montmorillonite purified by laboratory methods. We provide the first evidence for clay nanolayer reinforcement of a glassy epoxy matrix under compressive strain. Compression stress - strain experiments revealed substantial improvements in the modulus and yield strength when the clay nanolayers were exfoliated in the glassy matrix. However, no improvement in the modulus or yield strength was observed when the clay component was merely intercalated by the epoxy matrix, signifying that nanolayer exfoliation is an essential feature of reinforcement. Furthermore, the mechanical properties of epoxy-clay nanocomposites prepared with the C18H37NH3+ - exchanged forms of the AMS and CWC clays have been tested by dynamic mechanical analysis and thermal mechanical analysis. The nanocomposites exhibit improved dynamic storage modulus above and below the glass transition temperature, as well as lower coefficients of thermal expansivity compared to the pure polymer. In addition, the solvent resistant properties of the nanocomposites are substantially improved compared to the pristine polymer.
Gel mineralization as a Model for Bone Formation
Authors: Calvert Paul , Frechette Joelle , Souvignier Chad
Published: April 2011

Extrusion freeform fabrication is a 3-D layerwise writing technique for forming objects directly under the control of a CAD program. This method is one of a family of rapid prototyping methods which include stereolithography, selective laser sintering and fused deposition modeling. This system can be used to build shapes, layer by layer, from hydrogels of agarose, polyacrylamide or other cross-linked water-soluble acrylic polymers.

Mineralization can be induced in these gels by first building a part from an aqueous gel slurry containing calcium sulfate powder. This part is then immersed in a carbonate or phosphate solution which diffuses into the gel and precipitates calcite or calcium phosphates as the sulfate slowly dissolves. The resulting material contains 5-10 vol% mineral, 5 vol% agarose and 85-90 vol% water. On drying a bone-like composite is formed. If the original part is not a solid but a mesh of connected struts, the drying step results in a stronger part.
Radiation-Induced Desorption from the Nanopowder
Authors: Khasanov O.L. , Pokholkov Yu.P. , Bondarenko A.L. , Krivobokov V.P.
Published: April 2011

The mechanisms of radiation-induced desorption (RID) from the nanodispersed powder (NDP) surface under the impulse excitation of heavy-current electron beam (HCEB) were studied. Electron-induced desorption (EID); temperature-induced desorption (TID) as a result of radiation heating of the adsorbent; radiation-induced diffusion of the adsorbed atoms; re-adsorption were considered.

It was shown that radiation-induced desorption was observed during the first two pulses. The main mechanism of this process was electron-induced desorption (EID).
Investigation for the Selection of Foaming Agents to Produce Steel Foams
Authors: Yu C. J. , Eifert H. H. , Knuewer M. , Weber M. , Baumeister J.
Published: April 2011

During earlier investigations conducted at the Fraunhofer Institute for Applied Materials Research (IFAM), concentrating on the metal foaming technology using the powder metallurgy process, it was shown that some steel alloys are foamable with Fraunhofer's patented powder technology approach. To further investigate the foamability of steel alloys, suitable foaming agents need to be identified and characterized. This article reports the finding of two metallic compounds used for steel foaming. The foaming behaviors of the selected foaming agents in the steel powder compacts are also evaluated in terms of different alloying elements.
The Influence of Internal Pore Pressure During Roll Forming of Structurally Porous Metals
Authors: Elzey D. M. , Wadley H. N. G.
Published: April 2011

Structurally porous metal sandwich panels consisting of dense face sheets and porous cores of controlled relative density can be manufactured by trapping inert gas during hot isostatic pressing and modifying its distribution via subsequent thermo-mechanical forming. At high pressures, the internal gas is expected to influence the forming response. This paper describes a model for the roll forming of a porous metal panel and its use to explore the effects of internal pore pressure upon rolling response. It is shown that for gas pressures below about half the yield strength of the fully dense matrix material, there is essentially no influence on the forming response. Only in the case of very high initial pore pressures or at relative densities approaching full theoretical does a noticeable effect arise. In this case, a limiting upper density is attainable which depends on the specific rolling conditions and geometry.
In-Situ Boron-Doped Epitaxial Silicon Films Grown by UHVRTCVD: Applications in Channel Engineering & Ultra-Shallow Junction Formation
Authors: Ban I. , Öztürk M. C. , LEE K. L.
Published: April 2011

A low-thermal budget, in-situ boron doped silicon epitaxy process for channel engineering and ultra shallow junction formation is presented. Ultra-thin silicon films (100–500 Å) have been deposited in a single-wafer Ultra High Vacuum Rapid Thermal Vapor Deposition (UHV-RTCVD) reactor using disilane (Si2H6), diborane (B2H6), and chlorine (Cl2) at temperatures between 750- 800°C. Boron doping can be varied five orders of magnitude (1016 cm-3 1021 cm3) with very abrupt doping transitions (∼50–70 Å/decade). Short channel (Leff =0.12 /μm) lightly-doped nchannel MOSFETs have been successfully realized free of ion-implantation in the channel region. As another application, ultra-shallow, defect-free, abrupt junctions (<500 Å) through diffusion from selectively-deposited in-situ boron doped films have been demonstrated.
Issues in Emissivity of Silicon
Authors: Abedrabbo S. , Hensel J. C. , Gokce O. H. , Tong F. M. , Sopori B. , Fiory A. T. , Ravindra N. M.
Published: April 2011

The first qualitative results of the effects of backside surface roughness on the radiative properties of silicon as a function of temperature in the wavelength range of 1–20μm are presented in this study. These measurements have been made utilizing a spectral emissometer operating at near- and mid-IR spectral range. Surface roughness of the silicon wafer has been observed to lead to increased emissivities.
Real-Time X-Ray Scattering Study of Surface Dynamics on Au(111) During Ar+ Ion Irradiation
Authors: Murty M.V. Ramana , Curcic T. , Judy A. , Cooper B.H. , Woll A.R. , Brock J.D. , Kycia S. , Headrick R.L.
Published: April 2011

X-ray scattering is used to investigate the surface dynamics on Au(111) during Ar+ ion irradiation. During 500 eV Ar+ ion irradiation, we observe the three regimes of step retraction, quasi-layer-by-layer removal and three dimensional rough erosion, analagous to molecular beam epitaxy. The quasi-layer-by-layer sputtering regime has been studied to identify similarities and differences in surface evolution during ion irradiation and molecular beam epitaxy. X-ray measurements suggest that 500 eV Ar+ ion irradiation does not lead to stable adatom island formation. Also, in contrast to molecular beam epitaxy, adatom detachment and diffusion seems important in describing the surface kinetics during ion irradiation.
Lattice Statics Green's Function for Modeling of Dislocations in Crystals
Authors: Tewary V.K.
Published: April 2011

A lattice statics Green's function method is described for modeling an edge dislocation in a crystal lattice. The edge dislocation is created by introducing a half plane of vacancies as in Volterra's construction. The defect space is decomposed into a part that has translation symmetry and a localized end space. The Dyson's equation for the defect Green's function is solved by using a defect space Fourier transform method for the translational part and matrix partitioning for the localized part. Preliminary results for a simple cubic model are presented.
Self-Organization of Fullerene Clusters
Authors: Rotkin Slava V.
Published: April 2011

The paper introduces the plasmon-Frenkel-exciton model [1] for the fullerene solids and explains a possible reason for the formation of the van-der-Waals [2] C50 cluster complexes. The interaction of the cluster and the organic (non-polar) liquid solvent will be considered. The motivation of this interest is related also to the experiments on the photoclusterization in the water solution [4] and cluster formation in beams [5].
On the concept of Multiregion Crack Growth
Authors: Semjonov S. L. , Bubnov M. M.
Published: April 2011

The effect of the two-region crack growth model on the static and dynamic fatigue curves for strong and abraded fibers is studied. The additional requirements to static and dynamic fatigue experiments necessary for the correct determination of the fatigue parameters are discussed.
Characterization of InGaN/GaN-Based Multi-Quantum Well Distributed Feedback Lasers
Authors: Hofstetter Daniel , Thornton Robert L. , Romano Linda T. , Bour David P. , Kneissl Michael , Donaldson Rose M. , Dunnrowicz Clarence
Published: April 2011

We present a device fabrication technology and measurement results of both optically pumped and electrically injected InGaN/GaN-based distributed feedback (DFB) lasers operated at room temperature. For the optically pumped DFB laser, we demonstrate a complex coupling scheme for the first time, whereas the electrically injected device is based on normal index coupling. Threshold currents as low as 1. 1 A were observed in 500 μm long and 10 μm wide devices. The 3rd order grating providing feedback was defined holographically and dry-etched into the upper waveguiding layer by chemically-assisted ion beam etching. Even when operating these lasers considerably above threshold, a spectrally narrow emission (3.5 Å) at wavelengths around 400 nm was seen.
Ion Channeling Analysis of Gallium Nitride Implanted with Deuterium
Authors: Wampler W. R. , Myers S. M.
Published: April 2011

Ion channeling and transmission electron microscopy were used to examine the microstructure of GaN implanted with deuterium (D) at high (>1 at. %) and low (< 0.1 at. %) D concentrations. At high concentrations, bubbles and basal-plane stacking faults were observed. Ion channeling showed the D was disordered relative to the GaN lattice, consistent with precipitation of D2 into bubbles. At low D concentrations, bubbles and stacking faults are absent and ion channeling shows that a large fraction of the D occupies sites near the center of the c-axis channel.
Tem Study of Defects in Laterally Overgrown GaN Layers
Authors: Liliental-Weber Z. , Benamara M. , Swider W. , Washburn J. , Park J. , Grudowski P. A. , Eiting C. J. , Dupuis R. D.
Published: April 2011

Transmission electron microscopy was applied to study defects in laterally overgrown GaN layers, with initial growth on A12O3 substrates followed by further growth over SiO2 masks. Dislocations found in the overgrown areas show changes in line direction. Most dislocations propagate along c-planes. In the overgrown material planar defects (faulted loops) are present on c-planes and their presence is most probably related to segregation of excess point defects and impurities present in this material. They appear to be initiated by the fast lateral growth. Some dislocations with screw orientation become helical resulting from climb motion.

Formation of voids and also a high dislocation density was observed at the boundaries where two overgrowing fronts meet. Tilt and twist components were observed for these boundaries that were different for different overgrown strips grown in the same crystallographic direction suggesting that the GaN subgrain orientations on the two sides of a SiO2 mask are responsible for the final tilt and twist value.
Electronic Structure and Optical Properties of ZnGeN2
Authors: Limpijumnong Sukit , Rashkeev Sergey N. , Lambrecht Walter R. L.
Published: April 2011

The electronic band structure, structural and bonding, and some linear and nonlinear optical properties are calculated for a new ternary nitride compound ZnGeN2 using first-principles methods. Good agreement is obtained with crystallographic data and with absorption data on the band gap. The prospects for use as nonlinear optical material are discussed.
Effect of Oxygen ION Implantation in Gallium Nitride
Authors: Jiang W. , Weber W.J. , Thevuthasan S. , Exarhos G.J. , Bozlee B.J.
Published: April 2011

Epitaxial single crystal GaN films (2.0 μtm thick) were implanted 60° off the <0001> surface normal with 600 keV O+ ions at 190 or 210 K over a range of ion fluences from 4.8x 1017 to 5.0 × 1020 ions/m2. The implantation damage, as determined by in-situ Rutherford Backscattering Spectrometry in a <0001> channeling geometry (RBS/C), ranged from dilute defects up to the formation of a disorder saturation state that was not fully amorphous. The relative disorder on the Ga sublattice exhibited a sigmoidal dependence on ion fluence. Results show that GaN crystals are extremely resistant to the ion implantation damage as compared to other ceramic materials like SiC. An asymmetric shape in the angular scan curve around the <0001> axis, which might be associated with the Ga lattice distortion in the crystal structure, was observed for the as-irradiated material to the highest ion fluence (5.o× 1020 O+/m2) at 210 K. Comparisons of Ga disorder depth-profiles from the experiment and SRIM97 simulations suggest that the damage peaks shift to greater depths at the low irradiation temperature (210 K). Significant recovery of these defects was not observed in the isochronal annealing steps (20-min) up to 970 K.
Contact Resistance of InGaN/GaN Light Emitting Diodes Grown on the Production Model Multi-Wafer Movpe Reactor
Authors: Chuang R.W. , Zou A.Q. , Lee H.P. , Dong Z.J. , Xiong F.F. , Shih R. , Bremser M. , Juergensen H.
Published: April 2011

We report both the device fabrication and characterization of InGaN/GaN single quantum well LEDs grown on sapphire substrates using multi-wafer MOVPE reactor. To improve current spreading of the LEDs, a self-aligned process is developed to define LED mesa that is coated with a thin, semi-transparent Ni/Au (40 Å/40 Å) layer. A detailed study on the ohmic contact resistance of Ni/Cr/Au on p-GaN versus annealing temperatures is carried out on transmission line test structures. It was found that the annealing temperatures between 300 to 500°C yield the lowest specific contact resistance rc (0.016 Ω-cm2 at a current density of 66.7 mA/cm). Based on the extracted rc from the transmission line measurement, we estimate that the contact resistance of the p-type GaN accounts for ∼ 88% of the total series resistance of the LED.
Amplification Path Length Dependence Studies of Stimulated Emission from Optically Pumped InGaN/GaN Multiple Quantum Wells
Authors: Schmidt T.J. , Bidnyk S. , Cho Yong-Hoon , Fischer A.J. , Song J.J. , Keller S. , Mishra U.K. , DenBaars S.P.
Published: April 2011

Optically pumped stimulated emission (SE) from InGaN/GaN multiple quantum wells (MQWs) grown by metalorganic chemical vapor deposition has been systematically studied as a function of excitation length (Lexc). Two distinct SE peaks were observed from these structures: one that originates at 425 nm at 10 K (430 nm at 300 K) and another that originates at 434 nm at 10 K (438 nm at 300 K). The SE threshold for the high energy peak was observed to always be lower than that of the low energy peak, but the difference was found to decrease greatly with increasing Lexc. A detailed study of the emission intensity of these two SE peaks as a function of excitation density shows that the two peaks compete for gain in the MQW active region.
Piezoelectric Properties of GaN Self-Organized Quantum Dots
Authors: Daudin B. , Widmann F. , Simon J. , Feuillet G. , Rouvi&re J. L. , Pelekanos N. T. , Fishman G.
Published: April 2011

It is demonstrated that GaN quantum dots with the wurtzite structure grown by molecular beam epitaxy on AIN exhibit optical properties which, depending on the size of the dots, may be dominated by piezoelectric effects. In “large” quantum dots with an average height and diameter of 4.1 and 17 nm, respectively, the photoluminescence peak is centered at 2.95 eV, nearly 0.5 eV below the bulk GaN bandgap, which is assigned to a piezoelectric field of 5.5 MV/cm present in the dots. The decay time of the photoluminescence was also measured. A comparison is carried out with theoretical calculation of the radiative lifetime.
On the Triggering of Shear Faults During Brittle Compressive Failure: A New Mechanism
Authors: Schulson E. M. , Iliescu D. , Renshaw C. E.
Published: April 2011

Direct observations are presented of the micromechanical events that contribute to the localization of deformation within brittle compressive shear faults. The observations were made on ice and show that faults are composed of both wing cracks and splay cracks. The latter features initiate from one side of inclined parent cracks and create sets of slender microcolumns fixed on one end and free on the other. It is proposed that the fault-triggering mechanism is the breaking of near-surface microcolumns owing to frictional sliding across their free ends. A lower-bound estimate of the compressive strength of ice is found to be in order of magnitude agreement with experiment.
Creep Cavitation Enhanced by Glass Pocket Formation in a Tetragonal Zirconia Doped with 0.3 WT% Pure Silica
Authors: Morita K. , Hiraga K. , Sakka Y.
Published: April 2011

The relationship between intergranular microstructures and cavitation is examined in a yttria-stabilized tetragonal zirconia doped with 0.2-0.4 wt% SiO2 under constant stress loading in tension. An increase in the initial grain size for a constant SiO2-addition or an increase in SiO2-addition for a constant grain size enhances the precipitation of a glass phase at the multiple grain junctions during deformation. Simultaneously with the enhanced glass phase precipitation, intergranular cavitation is also enhanced. This is because the precipitated glass phase act as the site of cavity formation.
Plastic Dynamics and Brittle vs. Ductile Failure in Noncrystalline Solids
Authors: Falk M.L.
Published: April 2011

We simulate fracture in two amorphous solids with different inter-particle potentials. These small changes in potential result in significant changes in dissipation near the crack tip. While one might expect these effects to arise from a change in flow stress, measurements reveal this is not the case. To understand why, we consider the relationship between crack dynamics, rate-dependent plasticity, and molecular-level structures in the glassy solid. In particular we discuss the macro-scale continuum theory of dynamic brittle fracture in a viscoplastic solid developed by Freund and Hutchinson and the meso-scale theory of viscoplasticity proposed by Falk and Langer. We further consider a simplified model on the molecular scale as a first-step toward the construction of first-principles models of dynamic plasticity and the brittle ductile transition in noncrystalline materials.
Athermal Fracture of Covalent Bonds
Authors: Gilman J. J.
Published: April 2011

Most fracture is athermal. Either because it occurs at low temperatures; or because it occurs too fast for thermal activation to be effective. Thus it must be directly activated by applied stresses. This can occur via quantum tunneling when the chemical bonding of a solid resides in localized (covalent) bonds. Then applied stresses can cause the bonding electrons to become delocalized (anti-bonded) through quantum tunneling. That is, the bonds become broken. The process is related to the Zener tunneling process that is thought to be responsible for dielectric breakdown in semiconductors. Under a driving force, bonding electrons tunnel at constant energy from their bonding states into anti-bonding states through the forbidden gap in the bonding energy spectrum.
Experiments and Simulations of Directionally dependent Fracture along Copper/Sapphire Interfaces
Authors: Kysar Jeffrey W.
Published: April 2011

To test the hypothesis that the brittleness and ductility of crystalline materials are controlled by a competition between dislocation nucleation and cleavage failure at a crack tip, Riceet al.[1] designed a four-point bend copper/sapphire bicrystal which has two cracks that propagate along the interface in opposing directions. They predicted, on the basis of the Rice-Thomson model [2], that the specimen would exhibit a directionally dependent fracture behavior; that is, one crack would propagate more readily than the other. Beltz and Wang [3] carried out the experiments and reported that the specimen exhibits a directionally dependent fracture behavior in accordance with the predictions. In the present work, these experiments are repeated independently and it is shown thatthe orientation of the experimentally observed directionally dependent behavior is opposite that of the predicted orientation.Furthermore, we show that Beltz and Wang incorrectly measured the orientation of the directional dependence in their experimental results. A correct interpretation of their results is consistent with the present work.

Taking advantage of the transparent sapphire, the normal crack opening displacement (NCOD) profile of both cracks is measured with optical interferometry. The measurements show that, away from the very tip of the crack, the NCOD takes the form of a constant angle, irrespective of load level. The opening angle of the apparently brittle crack is smaller than that of the apparently ductile crack. Complementary measurements of the very tip of the crack with Atomic Force Microscopy show that the near-tip crack opening profiles of the brittle and ductile cracks differ significantly.

The specimen is analyzed with the Finite Element Method, taking into account the elastic and plastic properties of the single crystal constituents. Since the very essence of the observed phenomenon is one of crack growth, the two cracks are simulated as they grow quasistatically along the interface. The asymptotic deformation fields, characteristic of single crystals, of the growing interfacial cracks are identified. The stress and strain fields, as well as the NCOD, are calculated. We present a plausible explanation of the directional dependence of fracture on the basis of the continuum plastic fields surrounding the quasistatically growing cracks.
Atomistic Modeling of Grain Boundary Fracture in Diamond
Authors: Shenderova O.A. , Brenner D.W. , Omeltchenko A. , Su X. , Yang L.
Published: April 2011

Molecular dynamics simulations using a bond-order potential were carried out to investigate the behavior under load of several <001> and <011> symmetrical tilt grain boundaries in diamond. Cohesive energies, work for fracture, maximum stresses and strains as functions of the type of grain boundary were evaluated. It was found that special short-periodic GBs possess higher strength and resistance to a crack propagation than GBs in the nearby misorientation range. Crack behavior in polycrystalline diamond samples under an applied load was also simulated, and found to be predominantly transgranular.
Metallorganic Chemical Vapor Deposition of Ir Films With Iridium Acetylacetonate and Carbonyl Precursors
Authors: Sun Y.-M. , Endle J. , Smith K. , Ekerdt J. G. , Hance R. L. , Alluri P. , White J. M.
Published: April 2011

Iridium acetylacetonate, dicarbonylacetylacetonato iridium, and tetrakisiridium dodecacarbonyl (iridium carbonyl) have been evaluated for metallorganic chemical vapor deposition (CVD) of pure iridium films. Temperature programmed mass spectroscopy reveals that iridium tris-acetylacetonate and dicarbonylacetylactonato iridium have high thermal stability and sublime at 200 and 100 °C in vacuum, respectively. Iridium carbonyl decomposes upon sublimation at temperatures above 120 °C. Pure CVD Ir films were obtained using iridium carbonyl; however, carbon is incorporated into the iridium films with the iridium trisacetylacetonate and dicarbonylacetylactonato iridium precursors unless a reactive gas, such as oxygen is co-dosed. Co-dosed oxygen also increases the film deposition rate and significantly decreases the film growth temperatures. Particles were found on the films grown with iridium carbonyl between 280 to 400 °C, indicating that gas phase nucleation occurred during deposition.
Origin of Imprint in Ferroelectric CSD SrBi2Ta2O9 Thin Films
Authors: Grossmann M. , Lohse O. , Bolten D. , Waser R. , Hartner W. , Schindler G. , Nagel N. , Dehm C.
Published: April 2011

The imprint behavior of CSD processed SrBi2Ta2O9 (SBT) thin films has been investigated as a function of time, applied bias, illumination with band gap light and post anneal under different oxygen partial pressures. Applying a bias in the direction of the polarization enhances the tendency of the capacitor to exhibit a voltage shift as well as illuminating the poled capacitor with band gap light. Post anneal after top electrode deposition and patterning under slightly reducing atmospheres does not affect the imprint rate. From these experimental results, a model is presented which explains the imprint behavior of SBT films by transport of electronic charges from the electrodes into the film and subsequent trapping of these charges near the interface.
Optical Properties of Sol-Gel Derived PbTiO3 and PbZr1−xTiO3 Ferroelectric Thin Films
Authors: Meng Xiangjian , Huang Zhiming , Ye Hongjian , Cheng Jiangong , Yang Pingxiong , Chu Junhao
Published: April 2011

With sol-gel processing and rapid thermal annealing (RTA), crack-free PbTiO3 and PbZr1−xTixO3(x=0.2-0.8) ferroelectric thin films were prepared on Si(100) and Pt/Ti/SiO2/Si(100) substrates respectively. Results from x-ray diffraction (XRD) show that the films are single perovskite phase structure. Scanning electron microscopy (SEM) was used to determine the grain sizes of the thin films. Energy dispersive spectroscopy (EDS) of x rays was used to analyze the composition of the films. From infrared reflection spectroscopy in the wavelength region of 40-700 cm−1 at 300K, the vibrational mode frequencies in PbTiO3 thin films on silicon substrates were obtained at the wavenumbers of 79, 155, 206, 298, 344, 461, 520 and 621 cm−1. Among these phonon modes, the modes at 298 and 461 cm−1 have not been reported before. The infrared optical constants and the thickness of PZT thin films on Pt/Ti/SiO2/Si(100) substrates were directly measured in the wavelength region of 2-12μm by an automatic wavelength swept infrared spectroscopic ellipsometer. These constants include: refractive index (n), extinction coefficient (k), thickness of the films and absorption coefficient (α). Possible correlation among the processing, microstructure and optical properties of the thin films were discussed.
Dielectric Relaxation in a Deeply Supercooled Liquid Crystals Confined in Random Porous Media
Authors: Sinha G. P. , Aliev F. M.
Published: April 2011

Liquid crystals (LCs)—pentylcyanobiphenyl (5CB) and octylcyanobiphenyl (8CB)—were confined in random porous media with narrow pores of mean size equal to 100 Å and investigated by means of broad band dielectric spectroscopy in deeply supercooled state. In liquid crystalline phases, bulk 5CB and 8CB have two dielectrically active modes. The main mode with the relaxation time τ ∼ 10”8s is due to the rotation of molecules about their short axis, and the secondary mode is due to the tumbling motion of molecules with the relaxation time ツ ∼ 10”10s. Bulk 5CB and 8CB are nonglass formers and they crystallize at cooling. The confinement strongly influences the dynamical behavior of LCs and is resulted in qualitative changes in their properties. Deep supercooling of LCs in pores up to ∼ 150 degrees below the bulk crystallization temperature was observed. The relaxation rate of the process due to the molecular rotation in deeply supercooled state is slower than at the temperatures corresponding to nematic phase by many orders of magnitude. This slowing down is accompanied by anomalous broadening of the dielectric spectra.

Other new properties observed in confined LCs are two low frequency relaxation processes absent in bulk LCs. One of these processes is due to the molecular relaxation in the surface layers at liquid crystal-solid pore wall interface. The second process is probably a collective mode due to the relaxation of the surface induced polarization. The collective process due to surface polarization and the surface molecular mode show features typical for glass formers.
Plasma Grafit Polymerized Styrene as an Electron-beam Resist
Authors: Morita Shinzo , Ogawa Shinji , Suzuki Mikinori , Kashem Md. Abul
Published: April 2011

Plasma graft polymerized styrene was formed by a reactor with a parallel plate electrode system on a pulsed plasma polymerized styrene film in a monomer vapor, where the pulsed plasma polymerization was performed by a low frequency 100%pulse modulation of 13.56 MHz power source in styrene vapor. The pulse duration was varied in the range of 0.01∼1 sec and ON time/duty cycle ratio was 1/10 and 1/20. The processes were monitored by a quartz crystal microbalance. The initial stage of plasma polymerization and grafting are discussed in this paper. Also sub 100 nm lines and spaces pattern on the resist delineated by an electron-beam pattering machine was developed by hexane.
Plasma Sterilization: Spore Destruction by Microwave Plasmas
Authors: Lerouge S. , Fozza A. C. , Wertheimer M. R. , Marchand R. , Tabrizian M. , Yahia L'H
Published: April 2011

Low-pressure plasmas are now being used for sterilization at ambient temperature. In this work, we have studied the possible mechanism of spore destruction by plasma, and compare it with etching of synthetic polymers. Bacillus subtilis spores were inoculated at the bottom of special glass vials and subjected to different plasma gas compositions, all known to etch polymers. The mortality rate of spores was found to vary with gas composition, between less than a 2 log decrease in 8 minutes for a pure oxygen plasma, to a 6 log decrease with 02CF4 mixture. Examination by scanning electron microscopy (SEM) showed that spores were significantly etched after 30 minutes of plasma exposure, but not completely. We speculate about their etch resistance, compared with that of synthetic polymers, on the basis of their morphology and their complex coating structure.
Electrodeposited CIS-Based Solar Cell Materials
Authors: Raffaelle R.P. , Potdevin T. , Mantovani J.G. , Friedfeld R. , Gorse J. , Breen M. , Bailey S.G. , Fhepp A.F.
Published: April 2011

We have been investigating the synthesis of novel materials and device structures based on CuInSe2 or CIS system We are interested in developing CIS for use in thin film photoltaic solar cells used in space power systems. Non-stoichiometric native defects allow CIS to be selectively doped n or p type by controlling the Cu to In ratio. The Cu to In ratio of an electrodeposited CIS thin film is shown to be directly proportional to the deposition voltage. This behavior has allowed us to deposit different semiconductor-type films, pn junctions, and multilayer structures from the same aqueous solution. The affect of annealing in an Argon atmosphere and the addition of a wetting agent to our deposition solutions on the structural and electrical behavior of our films was measured. A dramatic improvement in the crystallinity, which was proportional to the annealing temperature was observed. The addition of a wetting agent to the solution was shown to improve the surface morphology and provide uniformity in the grain size. The electrical characterization of Schottky barriers on the CIS showed a decrease in several orders of magnitude of the carrier density with annealing. The ability to incorporate our CIS-based films in pn junction devices using CdS window layers was demonstrated by the rectifying current versus voltage behavior of these junctions.
Genetically Engineered Nanostructure Devices
Authors: Klimeck Gerhard , Salazar-Lazaro Carlos H. , Stoica Adrian , Cwik Thomas
Published: April 2011

Material variations on an atomic scale enable the quantum mechanical functionality of devices such as resonant tunneling diodes (RTDs), quantum well infrared photodetectors (QWIPs), quantum well lasers, and heterostructure field effect transistors (HFETs). The design and optimization of such heterostructure devices requires a detailed understanding of quantum mechanical electron transport. The Nanoelectronic Modeling Tool (NEMO) is a general-purpose quantum device design and analysis tool that addresses this problem. NEMO was combined with a parallelized genetic algorithm package (PGAPACK) to optimize structural and material parameters. The electron transport simulations presented here are based on a full band simulation, including effects of non-parabolic bands in the longitudinal and transverse directions relative to the electron transport and Hartree charge self-consistency. The first result of the genetic algorithm driven quantum transport calculation with convergence of a random structure population to experimental data is presented.
Materials for Thermal Control for Mars Surface Operations
Authors: Hickey Gregory S.
Published: April 2011

The thermal environment for Mars surface exploration provides unique challenges for materials for use in structure and thermal control. The Sojourner Mars Rover has a lightweight integrated structure/insulation that has been environmentally tested and qualified for the Pathfinder mission to Mars. The basic structure with insulation, called the Warm Electronics Box (WEB), accounts for only 10% of the total Rover mass. The WEB is a thermal isolating composite structure with co-cured thermal control surfaces and an ultra-lightweight hydrophobic solid silica aerogel which minimizes conduction and radiation. This design provides excellent thermal insulation at low gas pressures and meets the structural requirements for spacecraft launch loads and for a 60 g impact landing at Mars without damage to the insulation or structure. Since the Pathfinder mission, this basic design concept has been developed and improved for future Mars surface robotic missions.
Work Hardening Characteristics and Recovery of Gamma Base Titanium Aluminides
Authors: Appel F , Sparka U. , Müllauer J.
Published: April 2011

The work hardening behaviour of gamma base titanium aluminides was investigated by mechanical testing, electron microscope observations and recovery experiments. The main objectives of the paper are: (i) to ascertain the nature of work hardening at room temperature, (ii) to identify deformation induced glide obstacles which can be overcome with the aid of thermal activation, (iii) to assess the thermal stability of deformation induced defect structures.
Orientation Effect on the Stress Response by Strain-Rate Change at 400K in Ni3Al Single Crystals
Authors: Demura M. , Hirano T.
Published: April 2011

Cyclic strain-rate change tests were performed by using binary, stoichiometric Ni3Al single crystalline specimens with different tensile orientations at 400 K. In all the specimens, the flow stress was independent of strain rate in steady state and exhibited a temporary change by the strain-rate change. The characteristics of the temporary stress change, the initial stress change and transient time, were independent of orientation. Based on the multiplication-immobilization model, we concluded that the immobilization mechanism, the Kear-Wilsdorf locking mechanism, is independent of orientation in binary, stoichiometric Ni3Al.