bluuebunny/crossref_metadata_2025 huggingface dataset:
Characterization of Changes in Properties and Microstructure of Glassy Polymeric Carbon Following Au Ion Irradiation
Authors: Abunaemeh Malek Amir , Seif Mohamed , Yang Young , Wang Lumin , Chen Yanbin , Ojo Ibidapo , Muntele Claudiu , Ila Daryush
Published: August 2010

The TRISO fuel has been used in some of the Generation IV nuclear reactor designs [1,2]. It consists of a fuel kernel of UOx coated with several layers of materials with different functions. Pyrolytic carbon (PyC) is one of the materials in the layers. In this study we investigate the possibility of using Glassy Polymeric Carbon (GPC) as an alternative to PyC. In this work, we are comparing the changes in physical and microstructure properties of GPC after exposure to irradiation fluence of 5 MeV Au equivalent to a 1 displacement per atom (dpa) at samples prepared at 1000, 1500 and 2000°C. The GPC material is manufactured and tested at the Center for Irradiation Materials (CIM) at Alabama A&M University. Transmission electron microscopy (TEM), Rutherford backscattering spectroscopy (RBS), X-ray photoelectron spectroscopy (XPS) and Raman spectroscopy were used for the analysis.
Dynamics of LO phonons in InN studied by subpicosecond time-resolved Raman spectroscopy
Authors: Tsen Kong-Thon
Published: August 2010

The phonon dynamics of both the A1(LO) and the E1 (LO) phonons in InN has been studied by time-resolved Raman spectroscopy on a subpicosecond time scale. From the temperature-dependence of their lifetimes, we demonstrate that both phonons decay primarily into a large wavevector TO phonon and a large wavevector TA/LA phonon consistent with the accepted phonon dispersion relationship for wurtzite InN. Their lifetimes have been found to decrease from 2.2 ps, at the low electron-hole pair density of5x1017cm-3 to 0.25 ps, at the highest density of2x1019cm-3. Our experimental findings demonstrate that carrier-density dependence of LO phonon lifetime is a universal phenomenon in polar semiconductors.
Atomistic Simulations of the Mechanical Response of Copper/Polybutadiene Joints under Stress
Authors: Valega Mackenzie Fidel Orlando , Thijsse Barend J.
Published: August 2010

Metal/polymer system joints are widely encountered nowadays in microscopic structures such as displays and microchips. In several critical cases they undergo thermal and mechanical loading, with contact failure due to fracture as a possible consequence. Because of their variety in nature and composition metal/polymer joints have become major challenges for experimental, theoretical, and numerical studies. Here we report on results of molecular dynamics simulations carried out to study the mechanical response of a metal/polymer joint, in this case the Cu/polybutadiene model system. The behavior of Cu and the cross-linked polybutadiene are modeled, respectively, by the Embedded Atom Method (EAM) and the Universal Force Field (UFF). Loading is applied under compression. Different potentials are used to describe the interactions in the metal/polymer interface, which allows us to qualitatively analyze possible mechanisms of failure in these joints, below the metal melting point and above the polymer glass transition temperatures.
Deformation Behavior of Nanocrystalline Co-Cu Alloys
Authors: Yuasa Motohiro , Nakano Hiromi , Kajikawa Kota , Nakazawa Takumi , Mabuchi Mamoru
Published: August 2010

Three kinds of nanocrystalline Co-Cu alloys: a nanocrystalline Co-Cu alloy with nanoscale lamellar structure, a supersaturated solid solution Co-Cu alloy and a nanocrystalline two-phase Co-Cu alloy were processed by electrodeposition, and their mechanical properties were investigated at room temperature. These nanocrystalline Co-Cu alloys showed the high hardness and the low activation volume. The mechanical properties of the nanocrystalline Co-Cu alloys strongly depended on the grain boundary characteristics. Molecular dynamics simulations were performed in the two-phase nanocrystalline Co-Cu alloy to investigate the dislocation emission at the Co/Cu interface. The MD simulations showed that the stacking faults, which are generated by the intense geometrical strain at the Co/Cu interface, play an important role in the dislocation emission.
Anisotropic Strain and Training of Conducting Polymer Artificial Muscles under High Tensile Stresses
Authors: Kaneto Keiichi , Hashimoto Hikaru , Tominaga Kazuo , Sedai Tomokazu , Takashima Wataru
Published: August 2010

Electrochemomechanical deformations (ECMD) of conducting polymer, polyaniline, films are studied to investigate the creeping and the memory effects. During electrochemical cycling under high tensile stresses up to 5 MPa, the films showed a remarkable creeping, resulting in the one dimensional anisotropic deformation. However, the creeping was recovered by release of the tensile stress, restoring from the anisotropic deformation. It was also found that the strain of ECMD after applying high tensile stresses increased compared with that before applying the large tensile stress. The result indicates that the artificial muscles are strengthened in strain by the experience of large tensile loads, and discussed taking the rheology of electrochemical cycles, viz., electrostatic crosslinking of polymer chains by oxidation and release of crosslinking by reduction.
Crevice Corrosion and Cracking Behavior of Cold Rolled Type 304 Stainless Steel in Chloride Environment
Authors: Kajikawa Shunji , Isobe Yasuaki , Okido Masazumi
Published: August 2010

The salt damage such as the snow melting salts in winter or the sea salt particle flying in the coast region has significant effect on the corrosive environment of the automobile. Moreover, the corrosive environment of the automobile become more severe by the wet/dry cyclic condition, for example, a car gets wet with the splash water and dryness by the thermal loading while driving. On the other hand, the further application of the high strength stainless steel to the automobile parts is expected because it can contribute durability and lightening. Then, it is important to clarify the corrosion characteristic of this material under the salt damage environment.
In this study cold rolled type304 stainless steel pipe with shot peening were used to investigate the corrosion property of high strength type304 stainless steel for automotive applications in a salt damage environment. The hardness of the pipe was about HV450, and a clear difference was not admitted in the thickness direction. A crevice was created between the outside of the pipe and an O-ring, and the pipe was applied stress by press fitting of another part. The corrosion property of the sample was evaluated in an automotive field test in Okinawa. Cracking from a corrosion pit was observed in the crevice. The Electron Prove Micro Analysis（EPMA） indicated that pitting corrosion was caused by chloride (from sea salt) concentrated in the crevice. The crack occurred in the residual compressive stress layer created by shot peening. In this regard, it was confirmed by the XRD analysis that about 85% of the metallographic structure had been transformed into the martensite. And the observation of the metallographic structure by the Electron Back Scatter Diffraction（EBSD） clarified the crystal grain was greatly transformed by the strong processing. It means that the accumulation of strain occurred. These two factors are considered to raise the receptivity to the crack generation of this sample.
A crack generated at a corrosion pit was reproduced in a wet/dry cyclic corrosion test after one flash of artificial seawater. To investigate the crack generating mechanism, a corrosion pit was previously generated on the sample by cyclic corrosion test, after which a cathodic charge test in artificial sea water was done. Similar cracking from a corrosion pit was observed on the sample after this test. Therefore, the cracking is presumed to be Hydrogen Embrittlement-Stress Corrosion Cracking（HE-SCC）
A Comparative Study of Characteristics of Ferrogels Prepared using Coated and Uncoated Fe3O4Nanoparticles
Authors: Suthar Kamlesh J. , Ghantasala Muralidhar K. , Mancini Derrick C. , Ilavsky Jan
Published: August 2010

This paper presents the results of our analysis of ferrogels prepared using uncoated and polyvinylpyrrolidone (PVP)-coated magnetite (Fe3O4) nanoparticles. The N-isopropylacrylamide (NIPAM) based hydrogel is used with 15-25 nm Fe3O4nanoparticles different concentrations in the range 1.25 -14%. These samples were analyzed using ultra small angle x-ray scattering (USAXS), Transmission Electron Microscopy (TEM), and Direct-Current Superconducting Quantum Interference Devices (DC-SQUID) magnetometry. Samples prepared with polyvinylpyrrolidone (PVP) coated nanoparticles showed a better single particle distribution compared to uncoated samples. USAXS data indicated that the gels prepared using uncoated nanoparticles have a large two particle agglomerations. In both cases, the volume fraction of the particles in the gel is linearly proportional to the initial particle concentrations. The DC-SQUID magnetometry analysis indicated that the magnetic moment of the gel samples prepared with uncoated particles is ∼ 2emu/g compared to ∼1.5emu/g of those having coated particles.
Multiscale Nanoporous Structures for Sensing and Diagnostics
Authors: Prasad Shalini
Published: August 2010

Current trends in sensing and diagnostics is towards developing hybrid devices that incorporate nanomaterial for enhancing device performance. These devices and systems have a broad impact ranging from personalized medicine in health care, environmental sensing and building multifunctional sensors for military applications. The overarching objective of the research work is to develop a new class of portable, bio-analytical tools with improved functionality and performance capabilities by utilizing the electrical effects on cellular and sub cellular species in micro and nanoscale domains.

There are two key ideas underlying this research work. The first is to design and manufacture structures comprising of nanoscale-confined spaces integrated on to multi-scale architecture platforms. This model architecture has been engineered to harness the principle of macromolecular crowding for biomolecule binding and detection by monitoring perturbations in the electrical bi-layer in tailored nanoscale confined spaces. Enhanced performance metrics in biomolecule detection have been demonstrated in developing electrical immunoassays. We have demonstrated picogram/ml sensitivity in detection of specific cardiovascular disease biomarkers, cancer biomarkers from human serum samples with a dynamic range of response varying from pg/ml to g/ml and response time within 120 seconds.
The Impact of Material Nanotopography on Cell Functions and Filopodia Extension: Experiments and Modeling
Authors: Yang Lei , Li Qunyang , Chinthapenta Viswanath , Liang Amy , Sheldon Brian W , Webster Thomas J
Published: August 2010

Exploring the cell-material interface is an emerging area of great interest in biomaterial science. Specifically, creating nanostructured surface interfaces to improve biomaterial efficacy is one of these key focus topics. As an example, an increasing number of studies have demonstrated the positive role nanostructured surfaces can have towards promoting various cell functions. However, the relevant mechanism behind this improvement in biological interactions at the cell-implant interface is not well understood. For this reason, here, osteoblast (bone forming cells) and fibroblast (fibrous, soft tissue forming cells) functions (including adhesion and proliferation) on two carefully fabricated diamond films with dramatically different topographies were tested. The results revealed greater cell responses on nanocrystalline diamond (grain sizes <100nm) compared to submicron crystalline diamond (grain sizes 200˜1000nm). In order to understand this positive impact of diamond nanotopography on cell responses, fibronectin absorption and subsequent cell spreading were studied. More importantly, cell filopodia extensions were also studied through computational mechanical modeling. A deflection-diffusion model of cell filopodia extension was established and clearly suggested that increasing the lateral dimension or height of nanometer surface features could inhibit cell filopodia extension and decrease cell spreading. Both the experiments and modeling from this study indicated that a nanometer surface topography can enhance cell responses to promote implant efficacy.
Fluorescence Measurements and AFM Imaging of Bacteriorhodopsin Coupled with CdSe Quantum Dots for Optoelectronic Applications
Authors: Bouchonville Nicolas , Molinari Michael , Sukhanova Alyona , Troyon Michel , Nabiev Igor
Published: August 2010

A new nanohybrid material with a potential impact on energy transfer processes in biomolecules was developed by coupling colloidal fluorescent semiconductor CdSe/ZnS quantum dots (QDs) with a photochromic membrane protein, the bacteriorhodopsin (bR). The interactions between the nanocrystals and the proteins were studied by fluorescence spectroscopy and atomic force microscopy (AFM) measurements. A quenching in the photoluminescence (PL) of QDs emitting in the range of the bR absorption suggests a fluorescence resonance energy transfer effect from QDs (donors) to bR (acceptor). As the quenching evolution is different with the surface charges of the QDs, it suggests that the QDs interact with bR through electrostatic interactions. The AFM images of bR coupled with QDs capped with positive or negative surface groups confirm that the electrostatic interactions between QDs and bR play a dominant role in the way they are coupling together. The observed interactions between QDs and bR can provide the basis for the development of novel functional materials with unique photonic properties and having applications in the all-optical switching, photovoltaics and data storage.
On Mechanics of Connective Tissue: Assessing the Electrostatic Contribution to Corneal Stroma Elasticity
Authors: Hatami-Marbini Hamed , Pinsky Peter M.
Published: August 2010

The extracellular matrix plays a crucial role in defining the mechanical properties of connective tissues like cornea, heart, tendon, bone and cartilage among many others. The unique properties of these collagenous tissues arise because of both the hierarchal structure of collagens and the presence of negatively charged proteoglycans (PGs) which hold collagen fibers together. Here, in an effort to understand the mechanics of these structures, using the nonlinear Poison-Boltzmann (PB) equation, we study the electrostatic contribution to the elasticity of corneal stroma due to the presence of negatively charged PG glycosminoglycans (GAGs). Since collagens and GAGs have a regular hexagonal arrangement inside the corneal stroma, a triangular unit cell is chosen. The finite element method is used to solve the PB equation inside this domain and to obtain the electric potential and ionic distributions. Having the ion and potential distributions throughout the unit cell, the electrostatic free energy is computed and the tissue elasticity is calculated using the energy method. It is shown that as the ionic bath concentration increases; the electrostatic contribution to tissue elasticity is reduced.
Hierarchical Biomaterials Mechanics of Bone and Bone Substitutes
Authors: Hellmich Christian , Fritsch Andreas , Dormieux Luc
Published: August 2010

Biomimetics deals with the application of nature-made ‘design solutions’ to the realm of engineering. In the quest to understand mechanical implications of structural hierarchies found in biological materials, multiscale mechanics may hold the key to understand ‘building plans’ inherent to entire material classes, here bone and bone replacement materials. Analyzing a multitude of biophysical hierarchical and biomechanical experiments through homogenization theories for upscaling stiffness and strength properties, reveals the following design principles: The elementary component ‘collagen’ induces, right at the nanolevel, the mechanical anisotropy of bone materials, which is amplified by fibrillar collagen-based structures at the 100 nm-scale, and by pores in the micrometer-to-millimeter regime. Hydroxyapatite minerals are poorly organized, and provide stiffness and strength in a quasi-brittle manner. Water layers between hydroxyapatite crystals govern the inelastic behavior of the nano-composite, unless the ‘collagen reinforcement’ breaks. Bone replacement materials should mimic these ‘microstructural mechanics’-features as closely as possible.
Electrically Modulated Drug Delivery using Nanoporous Electrodes
Authors: Robinson David B. , Gittard Shaun D. , Wu C.-A. Max , Ha Cindy M. , Narayan Roger J.
Published: August 2010

Nanoporous electrodes, such as those made from carbon or gold, can capture and release ionic analytes at concentrations near 1 mole per liter of pore volume through capacitive charging or electrochemically reversible adsorption. In vitro studies suggest that this phenomenon can be the basis for a noninvasive, precise, and programmable drug delivery method. It would eliminate the need for bulk fluid delivery to target tissue and require only a thin electrical connection, minimizing pain and tissue disruption. We have designed effective gold electrode assemblies and observed the depletion and release phenomena using electrochemical methods and charged dyes.
Synthesis and Characterization of Poly(2,5-benzimidazole) (ABPBI) Grafted Carbon Nanotubes
Authors: Kang Ji-Ye , Eo Su-Mi , Tan Loon-Seng , Baek Jong-Beom
Published: August 2010

Single-walled carbon nanotube (SWCNT) and multi-walled carbon nanotube (MWCNT) were functionalized with 3,4-diaminobenzoic acid via “direct” Friedel-Crafts acylation reaction in PPA/P2O5 to afford ortho-diamino-functionalized SWCNT (DIF-SWCNT) and MWCNT (DIF-MWCNT). The resultant DIF-SWCNT and DIF-MWCNT showed improved solubility and dispersibility. To improve interfacial adhesion between CNT and polymer matrix, the grafting of ABPBI onto the surface of DIF-SWCNT (10 wt%) or DIF-MWCNT (10 wt%) was conducted by simple in-situ polymerization of AB monomer, 3,4-diaminobenzoic acid dihydrochloride, in PPA. The resultant ABPBI-g-MWCNT and ABPBI-g-SWCNT showed improved the mechanical and electrical properties.
Electrospun Composite Nanofibers for Sensor Applications
Authors: Han Li , Andrady Anthony , Guzan Kim , Ensor David S
Published: August 2010

Electrospun polymer nanofiber materials have attracted tremendous interest in sensor applications as their effective sensing surface area dramatically increases with decreasing fiber diameter. The highly tunable polymer composite chemistry and surface functionality of the nanofiber material provides a wide platform for exploring different applications, such as filtration media, sound isolation materials, and sensor components. This paper presents a nanofiber sensor platform device composed of electrospun polymer/carbon composite nanofibers combined with electrodes directly printed onto the surface of the electrospun fiber mat. This structure forms an integrated sensor system for detecting various chemical vapors including volatile organic compounds (VOCs) and oxidative gases. In this sensor, the composite polymer nanofibers form a chemo-resistor sensing material, and the conductivity of these composite sensing materials varies with chemical vapor exposure. The sensor performance exhibits very stable baselines with dramatically reduced noise levels compared to conventional interdigitated electrodes. Furthermore, the sensor response to different vapors shows a linear relationship between conductivity change and vapor concentration in the range of ppb – ppm for some analytes, including methanol, chloroform and ozone. The sensitivity and selectivity of these sensors to different vapor analytes will also be discussed.
Functional Controlled Release Systems Triggered by Photothermal Effect of Gold Nanorods
Authors: Yamashita Shuji , Fukushima Hiromitsu , Niidome Yasuro , Mori Takeshi , Katayama Yoshiki , Niidome Takuro
Published: August 2010

Gold nanorods, rod-shaped gold nanoparticles, have transverse and longitudinal surface plasmon (SP) bands at visible and near-infrared (IR) regions, respectively. Since the absorbed light energy is converted into heat, photothermal effect of gold nanorods can be triggered without damaging the tissues in the path of near-IR laser light. In this study, we tried to construct controlled release system of functional molecules from surface of gold nanorods mediated by the photothermal effect. First, we evaluated controlled release of poly(ethyleneglycol) (PEG) chains from PEG-modified gold nanorods (PEG-NR). Next, we employed double stranded oligonucleotide as a thermo-responsive dissociating group (DNA-NR). Finally, we evaluated photothermal release of PEG chains mediated retro-Diels-Alder reaction (PEG-DA-NR). For construction of controlled release system of functional molecules, these studies will provide important information about the photothermal reactions of surface molecules on the gold nanorods triggered by near-IR light irradiation.
UV-embossed textured back reflector structures for thin film silicon solar cells
Authors: Escarre Jordi , Söderström Karin , Cubero Oscar , Haug Franz-Josef , Ballif Christophe
Published: August 2010

In this work, we study the replication of nanotextures used in thin film silicon solar cells to enhance light trapping onto inexpensive substrates such as glass or polyethylene naphtalate (PEN). Morphological analysis was carried out to asses the quality of these replicas. Moreover, single and tandem a-Si:H solar cells were deposited on top of the master and replica structures to verify their suitability to be used as substrates for solar cells in n-i-p configuration. We find stabilized efficiencies around 8% which are similar for tandem cells on masters and PEN replicas.
The Study of Optical and Electrical Properties of a-SiC:H for Multi-junction Si Thin Film Solar Cell
Authors: Shim Jenny H. , Yoon W.K. , Hwang S.T. , Ahn S.W. , Lee H.M.
Published: August 2010

Studies have shown that wide bandgap material is required for high efficiency multi-junction solar cell applications. Here, we address proper deposition condition for high quality a-SiC:H films. In high power high pressure regime, we observed that the defect density get much lowered to the similar defect level of a-Si:H film with high H2 dilution. Single junction solar cells fabricated with the optimized condition show high open circuit voltage and low LID effect. The degradation after the LID test was only 13 % reduction of the efficiency indicating that a-SiC:H could be promising material for multi-junction solar cells.
Micro-Channel Plate Detectors Based on Hydrogenated Amorphous Silicon
Authors: Wyrsch Nicolas , Powolny François , Despeisse Matthieu , Dunand Sylvain , Jarron Pierre , Ballif Christophe
Published: August 2010

A new type of micro-channel plate detector based on hydrogenated amorphous silicon is proposed which overcomes the fabrication and performance issues of glass or bulk silicon ones. This new type of detectors consists in 80-100 μm thick layers of amorphous silicon which are micro-machined by deep reactive ion etching to form the channels. This paper focuses on the structure and fabrication process and presents first results obtained with test devices on electron detection which demonstrate amplification effects. Fabrication and performance issues are also discussed.
Optical Absorption in Co-Deposited Mixed-Phase Hydrogenated Amorphous/Nanocrystalline Silicon Thin Films
Authors: Wienkes Lee , Besaw Aaron , Anderson Curtis , Bobela David , Stradins Paul , Kortshagen Uwe , Kakalios James
Published: August 2010

The conductivity of amorphous/nanocrystalline hydrogenated silicon thin films (a/nc-Si:H) deposited in a dual chamber co-deposition system exhibits a non-monotonic dependence on the nanocrystal concentration. Optical absorption measurements derived from the constant photocurrent method (CPM) and preliminary electron spin resonance (ESR) data for similarly prepared materials are reported. The optical absorption spectra, in particular the subgap absorption, are found to be independent of nanocrystalline density for relatively small crystal fractions (< 4%). For films with a higher crystalline content, the absorption spectra indicate broader Urbach slopes and higher midgap absorption. The ESR spectra show an approximately constant defect density across all of the films. These data are interpreted in terms of a model involving electron donation from the nanocrystals into the amorphous material.
The Staebler-Wronski Effect: New Physical Approaches and Insights as a Route to Reveal its Origin
Authors: Smets Arno H.M. , Wronski Chris R. , Zeman Miro , van de Sanden M.
Published: August 2010

In the recent years more and more theoretical and experimental evidence have been found that the hydrogen bonded to silicon in dense hydrogenated amorphous silicon (a-Si:H) predominantly resides in hydrogenated divacancies. In this contribution we will philosophize about the option that the small fraction of divacancies, missing at least one of its bonded hydrogen, may correspond to some of the native and metastable defect states of a-Si:H. We will discuss that such defect entities are an interesting basis for new and alternative views on the origin of the SWE.
Accuracy of the Fatigue Lifetime of Polysilicon Predicted from its Strength Distribution
Authors: Vu Le Huy , Gaspar Joao , Paul Oliver , Kamiya Shoji
Published: August 2010

This paper discusses the accuracy of the distribution of the fatigue lifetime of polysilicon thin films predicted from their strength distribution. On the basis of the authors' previous studies, where the fatigue process determining the lifetime was formulated using the well-known fatigue crack extension Paris' law, prediction error ranges for polysilicon specimens with different levels of strength are determined. The errors of the predicted fatigue lifetime in the logarithmic scale, defined as △logN= |log10Nexp-log10Npred| whereNexpandNpredwere the experimental and predicted number of cycle, were found to be less than 1 in the range of the cumulative fracture probability F between 0.1 and 0.9. Therefore, based on the measured Paris' law parameters of polysilicon, the fatigue lifetimes of different polysilicon thin film structures can be predicted from their strength distributions with errors of roughly 10% in the logarithmic scale, which was average of percentages of △logNto log10Nof experimental data.
High Efficiency Hydrogenated Nanocrystalline Silicon Solar Cells Deposited at High Rates
Authors: Yue Guozhen , Sivec Laura , Yan Baojie , Yang Jeff , Guha Subhendu
Published: August 2010

We report recent progress on hydrogenated nanocrystalline silicon (nc-Si:H) solar cells prepared at different deposition rates. The nc-Si:H intrinsic layer was deposited, using a modified very high frequency (MVHF) glow discharge technique, on Ag/ZnO back reflectors (BRs). The nc-Si:H material quality, especially the evolution of the nanocrystallites, was optimized using hydrogen dilution profiling. First, an initial active-area efficiency of 10.2% was achieved in a nc-Si:H single-junction cell deposited at ~5 Å/s. Using the improved nc-Si:H cell, we obtained 14.5% initial and 13.5% stable active-area efficiencies in an a-Si:H/nc-Si:H/nc-Si:H triple-junction structure. Second, we achieved a stabilized total-area efficiency of 12.5% using the same triple-junction structure but with nc-Si:H deposited at ~10 Å/s; the efficiency was measured at the National Renewable Energy Laboratory (NREL). Third, we developed a recipe using a shorter deposition time and obtained initial 13.0% and stable 12.7% active-area efficiencies for the same triple-junction design.
Intrinsic Surface Defects on 4H SiC Substrates
Authors: Zvanut Mary Ellen , Thomas Sarah , Dashdorj Jamiyanaa
Published: August 2010

We have investigated a point defect, common to all SiC substrates, that is thought to be a broken carbon bond. Electron paramagnetic resonance spectroscopy performed in combination with three different etching methods using p-type, n-type, and semi-insulating substrates demonstrate that the center lies near the surface of a wafer. The results suggest that on the order of 1013 cm-2 defects are removed within the first micron of the surface of a wafer.
Single Shockley Faults Evolution Under UV Optical Pumping
Authors: Canino Andrea , Camarda Massimo , La Magna Antonino , La Via Francesco
Published: August 2010

Single Shockley faults (SSF) have been studied in 4H-SiC epitaxial layers by using a spatial resolved micro-photoluminescence technique. In particular the effect of the UV pumping laser has been investigated. Samples have been irradiated at different power densities in order to find a threshold for the growth of the SSF defects. A low power density (115 W/cm2) exposition at 325 nm does not affect the structural properties of the epitaxial layers. We observed a growth of this defect through the epitaxial layers when the power density is increased over the value of 115 W/cm2.
Afterglow Chemical Processing for Oxide Growth on Silicon Carbide
Authors: Hoff Andrew M , Short Eugene , Thomas Helen B , Oborina Elena I
Published: August 2010

The unique capabilities and characteristics provided by afterglow or remote plasma chemical oxide growth processing of silicon carbide are reviewed. Such processing provides for thermal growth of oxide films at temperatures far below those employed by conventional atmospheric processing methods. Overshadowing this growth capability is the ability to create chemistries, sequential procedures, and specific process environments to address material and defect issues in a manner not possible under conventional atmospheric conditions. The details and outcomes of multi-step afterglow oxidation processing of SiC will be discussed. An example sequence might include; 1) surface conditioning, 2) film growth at 850C and 1 Torr total pressure, and 3) reduced pressure unexcited media post-growth treatments. Surface conditioning impacts the thickness uniformity of the final oxide film and the oxidation rate. The film growth interval produces a nominal 500Å of oxide film in 90 minutes at 850C, a temperature that would not produce any significant oxide film at atmospheric pressure. And the post-growth processing improves the performance of the dielectric film. Using in-line corona-Kelvin metrology the electrical characteristics stemming from these processes have been determined. Electrical effective oxide thickness results were used to assess thickness uniformity and to estimate process rate constants for comparison to other process methods. Fowler-Nordheim, F-N, characteristics determined with the same metrology demonstrate that afterglow, AG, oxides require higher field levels to produce the same F-N current as thermal oxides and that AG films are less susceptible to stress fluence. Process extensions from these and other results are discussed and related to chemical, physical, and electrical film outcomes and potential pathways to improve control over dielectric SiC structures.
Reducing Time Dependent Line to Line Leakage Following Post CMP Clean
Authors: Canaperi Donald F , Papa Rao Satyavolu , Hurd Trace Q. , Medd Steven B , Levin T. M. , Penny Christopher J , Chen James H.-C. , Smalley Matthew D
Published: August 2010

A systematic approach was taken to identify methods to prevent post CMP corrosion of copper in 22nm interconnect structures. Line to line current leakage measurements (at various times post CMP) were used as a means to quantify the extent and time-dependence of copper corrosion. Interruption of the corrosion mechanism by the use of passivating agents in post-CMP clean chemistries is explored. A broad-based screening was conducted to identify aqueous formulations of passivating agents for protection of copper which do not have deleterious effects on line resistance and overall defectivity. A formulation was identified which was effective in preventing corrosion when applied during post CMP brush clean.
Retaining Ring Design Impact on CMP Process Stability and Optimization
Authors: Smith Joseph , Wargo Christopher , Kakireddy Raghava , Singh Rakesh , Galpin Andrew , Philipossian Ara , Wei Xiaomin , Bennedine Karim , Reversat Claude , Chabourel Alain
Published: August 2010

The focus of this work is wafer retaining rings and their impact on chemical mechanical planarization (CMP) process stability, yield, and overall cost of ownership (CoO). The study looks at various CMP retaining ring materials and processing methods. Tribological investigations as well as wafer processing are critical to understand the retaining ring and polishing pad environment. Interactions at the ring/pad interface have a major effect on the planarization and defectivity of a polished wafer. Shear and normal forces at this interface, as well as temperature and lubrication regimes, were monitored to establish an empirical model. All process conditions equal, the material properties of retaining rings govern the coefficient of friction (COF) in the ring and pad contact area. Present study demonstrates a lower COF to be an indicator of extended ring lifetime, decreasing WTWNU and removal rate (RR) variation. The study correlates the findings on wafer level data from high volume manufacturing fabs with empirical data generated using applications lab tribological equipment to understand the on-wafer performance as a function of retaining ring material. The study's further aim is to understand for specific applications, the material interactions on-wafer using various retaining ring materials. CMP process optimization can be attained with a better understanding of retaining ring design and material characteristics, as well as polishing head and slurry parameters.
Real-time Control System for Improved CMP Pad Profiles
Authors: Menk Gregory E , Dhandapani Sivakumar , Garretson Charles Chad , Chang Shou-Sung , Cocca Christopher , Fung Jason , Qian Jun , Tsai Stan
Published: August 2010

Chemical mechanical planarization (CMP) pads require conditioning to maintain the surfaces yielding optimal performance. However, conditioning not only regenerates the pad surface but also wears away the pad material and slurry transport grooves. Non-optimized conditioning may result in non-uniform pad profiles, limiting the productive lifetimes of pads. A new approach to conditioning uses closed-loop control (CLC) of conditioning sweep to enable uniform groove depth removal across the pad, throughout pad life. A sensor integrated into the conditioning arm enables the pad stack thickness to be monitored in situ and in real time. Feedback from the thickness sensor is used to modify pad conditioner dwell times across the pad surface, correcting for drifts in the pad profile that may arise as the pad and disk age. Pad profile CLC enables uniform reduction in groove depth with continued conditioning, providing longer consumables lifetimes and reduced operating costs.
Contact Pressure Distribution in the Chemical Mechanical Planarization of 450mm Wafers
Authors: Timoney Padraig , Ahearne Eamonn , Byrne Gerald
Published: August 2010

Optimisation of spatial uniformity of material removal in chemical mechanical planarization requires an understanding of the mechanics of the wafer carrier system. Finite element analyses have been carried out by researchers identifying relationships between von Mises stress distribution and material removal rate. However, in many of these wafer scale models, the derivation of the material properties of the polishing pad and sub pad is unclear and consequently a large variation in values used is observed. Models are generally validated with a procedure different to that simulated in the model and with different output variables. Few models have incorporated the industry standard method of pressurizing the backside of the wafer independently to the wafer carrier loading using a pressurized air chamber located directly behind the backside of the wafer. The anticipated introduction of 450mm diameter wafers has surprisingly not been accompanied by wafer scale models investigating the issues that will arise from the diameter and thickness scaling ratio of the wafer.

This paper presents a unique approach to finite element modeling of CMP incorporating realistic boundary conditions for the wafer carrier and platen assemblies. Model predictions of interfacial contact pressure for a 200mm wafer loaded by a lip seal type carrier head were validated by unique measurements of the contact pressure between the wafer and the pad using Fujifilm Prescale TM pressure measurement film and accompanying analysis software. The results demonstrated a close correlation between the model's prediction and the measured values. Results are presented for the upscaling of this validated model to 450mm wafer dimensions. The results indicate a doubling of the contact pressure maximum values compared to the 200mm wafer model. These results illustrate the extent of the challenge facing CMP tool vendors in increasing the level of control of the mechanical force distributed by the wafer carrier on 450mm wafers. The model can be used as a design tool to optimize machine and process parameters.
Fabrication of Organic Thin Films for Copper Diffusion Barrier Layers Using Molecular Layer Deposition
Authors: Bent Stacey , Loscutoff Paul William , Clendenning Scott
Published: August 2010

Device scaling predicts that copper barrier layers of under 3 nm in thickness will soon be needed in back-end processing for integrated circuits, motivating the development of new barrier layer materials. In this work, nanoscale organic thin films for use as possible copper diffusion barrier layers are deposited by molecular layer deposition (MLD) utilizing a series of self-limiting reactions of organic molecules. MLD can be used to tailor film properties to optimize desirable barrier properties, including density, copper surface adhesion, thermal stability, and low copper diffusion. Three systems are examined as copper diffusion barriers, a polyurea film deposited by the reaction of 1,4-phenylene diisocyanate (PDIC) and ethylenediamine (ED), a polyurea film with a sulfide-modified backbone, and a polythiourea films using a modified coupling chemistry. Following deposition of the MLD films, copper is sputter deposited. The copper diffusion barrier properties of the film are tested through adhesion and annealing tests, including 4-point bend testing and TEM imaging to examine the level of copper penetration. The promise and challenges of MLD-formed organic copper diffusion barriers will be discussed.
Potential of the Ultra-thin Layer Fabricated by Wet-process as a Pore-seal for Porous Low-k Films
Authors: Ono Shoko Sugiyama , Kohmura Kazuo , Tanaka Hirofumi , Nakayama Kentaro , Kagayama Akifumi , Tsuchiya Toshihiko , Nakaura Makoto , Matsuoka Osamu , Takaki Toshihiko , Maekawa Kou
Published: August 2010

We succeeded in fabricating ultra-thin (<3 nm-thick) layer on top of the surface of porous low-k. The roughness of the surface of porous low-k remains homogeneous even after covering by the thin layer. Furthermore, we found that such ultra-thin layer suppresses the diffusion of metal into porous low-k film. Concerning adhesion property, the abrasion between the thin layer and copper was not detected after annealing at 350 deg C in forming gas. TVS measurement suggested that pH control of solution is the key to reduce damages of porous low-k and mobile ions. We believe that such ultra-thin layer, which we propose here, has a potential as a pore seal layer for porous low-k films.
Nanoscale Ruthenium Coatings of MEMS Switches Contacts
Authors: Karabanov Sergey , Karabanov Andrey S. , Suvorov Dmitriy V. , Grappe Benoit , Coutier Caroline , Sibuet Henri , Sazhin Boris N. , Krutilin Anatoliy A.
Published: August 2010

The paper reports the tests results of ruthenium contacts coatings of magnetically controlled MEMS switches. During the tests the contact resistance was measured and the lifetime of MEMS switches was evaluated. After testing the analysis of the form and contact surface structure using SEM-method was carried out. The experiment results showed that the application of ruthenium nanolayers as the contact coating at slight increase of the contact resistance improves the lifetime of MEMS switches considerably.

Nowadays the increase of the lifetime of all MEMS switch types (RF MEMS relays, magnetically controlled on-off MEMS switches) is the most actual problem. The work resource and operating characteristics, first of all, contact resistance, of any switching unit, the basis of the construction of which is a dry contact, are determined by the contact coating properties. This is true for MEMS switches too.

The paper presents the results of the study of the operating characteristics of magnetically controlled MEMS switches with ruthenium and gold contact coatings of up to 100 nm thickness. During tests the following switching mode was used: switching voltage – 3 V, current - 10 μA. Each MEMS switch was subjected to 100 million cycles switching at the frequency of 100 Hz. After testing the contact surface investigation by SEM-method and electrical characteristics measurement was carried out. The paper presents SEM-images of the contacts surface and statistical date of electrical characteristics.

After 100 million switching cycles MEMS switches with nanoscale ruthenium coating have shown 100% operating capacity; 16% of switches with gold contacts turned out to be inoperative due to electrical contacts sticking.

The results of researches by SEM-method show that the contacts without nanoscale coating have the traces of strong erosion and melting; the contacts with nanoscale ruthenium coating practically did not change the form and flatness.

So, the test results indicate that nanoscale ruthenium coatings of the electrical contacts provide excellent resource for the switches operation of hundred millions and more cycles.
Material, Process and Geometry Effects on Through-Silicon Via Reliability and Isolation
Authors: Karmarkar Aditya P , Xu Xiaopeng , Ramaswami Sesh , Dukovic John , Sapre Kedar , Bhatnagar Ajay
Published: August 2010

Through-silicon via (TSV) structures with various material and geometry configurations are assessed to study their impact on reliability, isolation and performance. Oxide liner insulators show a larger performance impact as compared to low-k liners and the effect decreases with increasing liner insulator thickness. Higher density of the TSV array causes greater stress impact on carrier mobility and increases the parasitic capacitance. Additionally, low-k liner reduces the parasitic capacitance, but exhibits lower strength and adhesion, therefore degraded reliability. These results provide an important perspective of performance and reliability trade-offs necessary for a robust TSV design.
The Quantitative Study of Trapped Charges in Nano-Scale Ge Islands probed by EFM Measurement
Authors: Lin Zhen , Brunkov Pavel , Bassani Franck , Bremond Georges
Published: August 2010

In this work, an individual Ge island on top of silicon dioxide layer has been charged by a conductive EFM tip and quantitatively characterized at room temperature. Electrons or holes were successfully injected and were trapped homogenously in the isolated nano-scale Ge island. In order to quantitatively study these trapped charges, a truncated capacitor model was used to approximate the real capacitance between the tip and island surface. The analytical expression of the quantity of trapped charges in isolated Ge island as a function of the EFM phase signal was deduced. Applying a tip bias for -7V during 30 seconds leads to an injection about 800 electrons inside an individual Ge island.
Electrical Properties of TaOx Thin Films for ReRAM Prepared by Reactive RF Magnetron Sputtering Method
Authors: Fukuda Natsuki , Kurihara Hidenao , Horita Kazumasa , Yoshida Yoshiaki , Kokaze Yutaka , Nishioka Yutaka , Suu Koukou
Published: August 2010

Recently the Flash Memory is scaling limit, Thus the Memory of various types is now under study for the next generation large capacity nonvolatile memory. Resistance random access memory (ReRAM) is attracts much attention due to its advantage for integration in the next generation nonvolatile memory, because it is depend on scaling by lithography compared with the Flash Memory of capacity type. The material for ReRAM is classified roughly into binary oxides and perovskite oxides. Several binary oxides such as a TaOx have the advantage for low-temperature process and low-cost materials compared with perovskite oxides such as a (Pr,Ca)MnO3 (PCMO). In this study, TaOx film with the thickness of 10nm were prepared by reactive RF magnetron sputtering on 8inch-Pt/Si substrate using a Ta metal target in oxygen ambient. The sputtering system was the multi chamber type mass production tool. The TaOx thin film was amorphous phase as a result of measurement by X-ray diffraction meter. Ta top electrodes with 50 um diameters were deposited on the surface of TaOx layer by the DC sputtering method using a shadow mask. The “Forming” voltage of TaOx-ReRAM was 5.0V. After “Forming” process, the “Set” and “Reset” voltage were 3.0V and –3.0V respectively. It has good switching properties with large on/off resistance ratio above 1,000.
A Ferroelectric NAND Flash Memory for Low-power and Highly Reliable Enterprise SSDs and a Ferroelectric 6T-SRAM for 0.5V Low-power CPU and SoC
Authors: Miyaji Kousuke , Hatanaka Teruyoshi , Tanakamaru Shuhei , Yajima Ryoji , Noda Shinji , Takahashi Mitsue , Sakai Shigeki , Takeuchi Ken
Published: August 2010

This paper overview recent research results about ferroelectric FETs such as a Ferroelectric (Fe-) NAND flash memory for enterprise SSDs and a Ferroelectric 6T-SRAM for 0.5V operation low-power CPU and SoC.

In the last five years, as the data through internet increases, the power consumption at the data center doubled. To solve the power crisis SSD is expected to replace HDD. For such an enterprise SSD, the Fe-NAND flash memory is most suitable due to a low power consumption and a high reliability. The Fe-NAND is composed of Metal Ferroelectric Insulator Semiconductor transistors. The program/erase voltage decreases from 20V to 6V. In the Fe-NAND, the electric polarization in the ferroelectric layer flips with a lower electric field and theVthof a memory cell shifts. Due to a low program/erase voltage, a low power operation is achieved. In the Fe-NAND, a high write/erase endurance, 100Million cycle, four orders of magnitudes higher than the conventional NAND, is realized because there is no stress-induced leakage current.

The Fe-NAND flash memory with a non-volatile (NV) page buffer is also proposed. The data fragmentation of SSD in a random write is removed by introducing a batch write algorithm. As a result, the SSD performance can double. The NV-page buffer realizes a power outage immune highly reliable operation. In addition, a zeroVthmemory cell scheme is proposed to best optimize the reliability of the Fe-NAND. TheVthshift caused by the read disturb, program disturb and data retention decreases by 32%, 24% and 10%, respectively. A 1.2V operation adaptive charge pump circuit for the low voltage and low power Fe-NAND is introduced. By using Fe-FETs as diodes in the charge pump and optimizing theVthof Fe-FETs at each pump stage, the power efficiency and the output voltage increase by 143% and 25% without the circuit area and process step penalty.

Finally, a ferroelectric 6T-SRAM is proposed for the 0.5V operation low power CPU and SoC. During the read/hold, theVthof Fe-FETs automatically changes to increase the static noise margin by 60%. During the stand-by, theVthincreases to decrease the leakage current by 42%. As a result, the supply voltage by 0.11V, which decreases the active power by 32%.