bluuebunny/crossref_metadata_2025 huggingface dataset:
Single-step Photo fabrication of Kinoforms in use of Azobenzene-containing Polymer Films
Authors: Yasuda Shin , Minabe Jiro , Kawano Katsunori , Maruyama Tatsuya , Yamada Hidenori
Published: April 2011

We propose a new method of optically fabricating kinoforms using polyester containing cyanoazobenzene units in the side chain. This method utilizes the surface relief structures induced optically on the azopolymer films. Using a gray-tone amplitude mask with black and white lines as a spatial light modulator, we constructed the surface relief structures on the azopolymer films with an argon-ion laser beam (488nm). The relief depths constructed were deep enough to provide a wide range of visible light with a phase difference of 2π. In addition, irradiation on the azopolymer film with a spatially modulated light that had multilevel intensities inscribed the multilevel relief structure reflecting the intensity modulation. This property is applicable to the fabrication of diffractive optical elements, especially kinoforms, because the multilevel relief structure provides an incident light with phase modulation. We designed a phase pattern for a kinoform by computation and expressed it as a gray-tone amplitude mask. Irradiation on the film through the gray-tone mask with the pump beam inscribed a multilevel relief structure that diffracted an incident light to produce a desired image. The desired image appeared without the effect of the internal refractive index modulation of the film. We, therefore, confirmed a possibility of fabricating a kinoform with a multilevel relief structure on the azopolymer film. Since our fabrication method for kinoforms requires only exposure, it has a significant advantage over other techniques that require additional processes such as developing and etching.
The Effect of Interfacial Chemistry on Metal Ion Penetration into Polymeric Films
Authors: Mallikarjunan Anupama , Juneja Jasbir , Yang Guangrong , Murarka Shyam P. , Lu Toh-Ming
Published: April 2011

In order to boost the performance of next-generation silicon integrated circuits, polymers with lower dielectric constant compared to silicon dioxide are required as interlayer dielectrics (ILDs). Ion penetration from surrounding interconnect metal (typically copper or aluminum) or from barrier materials (e.g., tantalum or tantalum nitride) under thermal and electrical stresses can lead to premature failure of the polymers. Hence, ion penetration was studied in hybrid organosiloxane polymer (HOSP) using bias-temperature stressing. Metal/polymer interface chemistry, particularly the presence of interfacial oxygen, was found to play a key role in aiding metal ionization, and subsequent mobile ion penetration into dielectrics.
Correlation of Substituent Parameter Values to Electronic Properties of Molecules
Authors: Carroll Natalie , Matsunaga Nikita , Sohlberg Karl
Published: April 2011

There are a vast number of organic compounds that could be considered for use in molecular electronics. Because of this, the need for efficient and economical screening tools has emerged. We have demonstrated that the substituent parameter values (σ), commonly found in advanced organic chemistry textbooks, correlate very strongly with features of the charge migration process. This result supports the use of the σ values as a low cost time saving tool in the selection of compounds for use in molecular electronic devices.
First Applications of Electron Energy-Loss Spectroscopy with High Energy Resolution
Authors: Kothleitner Gerald , Mitterbauer Christoph , Grogger Werner , Zandbergen Henny , Tiemeijer Peter , Freitag Bert , Barfels Melanie , Hofer Ferdinand
Published: April 2011

A new transmission electron microscope equipped with a monochromator and a high resolution energy-filter was used for the first time to fully exploit the chemical bonding information contained in the near edge fine structures (ELNES) of electron energy-loss spectra. The instrument is capable of acquiring spectra with an energy resolution in the range of 0.1 eV, thus opening up the way for improved ELNES information. ELNES spectra of TiO2 and CoO have been recorded and are compared with data obtained with a conventional microscope and with x-ray absorption spectroscopy. In case of the L2,3 edges of the transition metals the new instrument revealed previously unobservable fine structure details, but for the O K edges the improved energy resolution does not result in more detailed structural features than observable in common microscopes. Furthermore, the potential of the new microscope to obtain chemical bonding information at the nanometer scale is discussed.
Mechanical properties of stratum corneum studied by nano-indentation
Authors: Yuan Yonghui , Verma Ritu
Published: April 2011

Stratum corneum acts as a barrier to protect our body, as well as a pathway for conducting skin sensations. Understanding the mechanical properties such as elasticity, yield stress, of stratum corneum is important to improve and develop new products in the personal care industry. In this work, structural properties of stratum corneum are studied by atomic force microscopy (AFM) imaging to reveal surface structure of stratum corneum. To study mechanical properties, AFM force measurements and nano-indentation techniques were used to characterize elastic properties of dry and wet stratum corneum. Nano-DMA measurements were also conducted to characterize visco-elastic properties of the same material.
Magnetic Domain Structures in CoNiFe Thin Films and Lines
Authors: Pérez Lucas , Abril Oscar de , Aroca Claudio , Sánchez Pedro , López Eloísa , Sánchez-Trujillo M.C.
Published: April 2011

Thin films and arrays of lines of magnetic CoNiFe alloy have been produced by electrodeposition. A magnetic field was applied during the electrodeposition process in order to induce a magnetic anisotropy in the sample. The dependence of the magnetic properties and the magnetic domain structures on the thickness of the films is reported. In addition to this, the magnetic properties and the domain structure of a thin film and an array of lines, with the same thickness and deposited in the same conditions, have been compared. An increase in the coercivity of the array of lines has been shown.
Magnetic Force Microscopy Imaging of Current Paths
Authors: Yongsunthon R. , Stanishevsky A. , Rous P. J. , Williams E. D.
Published: April 2011

We demonstrate Magnetic Force Microscopy (MFM) imaging, at room temperature in air, of a 0.25mA DC current path in a 140nm-wide gold nanowire. The nanowire was created by focused ion beam milling of a 12μm wide Cr/Au line of 20nm/110nm Cr/Au thickness. Iterative fitting of the MFM data to an idealized model of the structure yielded a nanowire resistivity a factor of 3.5 higher than that of a control Cr/Au region which was unaffected by the ion beam processing. MFM imaging of an ion-implant patterned line shows current deflection around the implant region.
Dislocation-mediated Mechanisms of Mass Transport around Nanoindentations in Fcc Metals
Authors: Fuente Oscar Rodríguez de la , Carrasco Esther , González Miguel A. , Rojo Juan M.
Published: April 2011

We present evidence for the operation on reconstructed Au(001) of a novel mechanism, involving dislocation motion, which is much more efficient than surface diffusion to redistribute mass around nanoindentations. Cross-slip of individual dislocations generated around the indentation point, with a screw component perpendicular to the surface, is shown to be responsible for the generation of multiple-storied, crystallographically-oriented terraces around the nanoindentation points. We also show that standard dislocation theory can be used to quantitatively describe the characteristics of the dislocations involved in the different processes around the nanoindentation.
Local Dynamics of Poly(ethylene oxide) Confined in 1nm Slits
Authors: Kuppa V. , Manias E.
Published: April 2011

Molecular Dynamics simulations are used to explore the short-time dynamics of nanoscopically confined poly(ethylene oxide). Both bulk and confined systems have been studied using an atomistically detailed force field so as to comparatively illustrate their differences and complement experimental results. Our aim is to elucidate the origins of the counter intuitive distribution of relaxation times for C-H bond reorientation for PEO in severe confinements, as experimentally observed in solid state 2H NMR studies. In contrast with the respective bulk PEO system, where a transition from distinct solid to liquid like dynamics is seen with increasing temperature, for the confined chains there is a coexistence of fast and slow segmental dynamics over a wide temperature range. Our studies have revealed that factors such as local density inhomogeneities, proximity of Li+, and translational motion, synergistically contribute to the generation of fast PEO segmental dynamics in 1nm confinements.
The Element Depth Profiles in Ultrathin Silicon Oxynitride Films
Authors: Asanov Igor P. , Choi Jinhak , Chung Youngsu , Choi Jaemin , Lee Jaecheol
Published: April 2011

Distribution of nitrogen in the thin silicon oxynitride films (less than 5 nm) obtained by plasma nitridation of SiO2 has been studied by non-destructive angular dependent XPS. For obtaining information about the element distribution in-depth the regularization technique has been applied. It is shown that the depth of nitrogen penetration increases with decreasing the SiO2 film thickness. In this case the maximum of the nitrogen distribution is enhanced and shifted to the Si-SiO2 interface. The results are compared with depth-profiling obtained by sputtering and wet chemical etching. The dependence of the binding energies on the film thickness has been studied. The influence of different factors on the chemical shift in the ultrathin films has been analyzed.
Advanced 13C Nuclear Magnetic Resonance Investigation of Metal-Ligand Interactions in Monolayer-Protected Gold Nanoparticles: NMR Shifts and Relaxations
Authors: Zelakiewicz Brian S. , Tong YuYe
Published: April 2011

While self-assembled monolayer (SAM) systems have been intensively investigated since the seminal work of Nuzzo and others in the later 1980s, the detailed nature of the interactions between thiol and gold in terms of surface bonding and ligand motion, a central theme crucial for any further advancements in the field of SAMs, is still elusive and subject to controversy. Nuclear magnetic resonance (NMR) spectroscopy, a canonical technique of chemistry and physics, has the unique ability of providing insightful chemical bonding and ligand motional information. Recent advances in wet chemistry in terms of synthesizing alkanethiol-protected, very stable and almost monodispersed, gold nanoparticles, due to Schriffin and co-workers, enable this feature of NMR to be harnessed in the study of thiol-metal bonding and ligand motions on gold surfaces. Here, we report a detailed 13C NMR shift and relaxation investigation of monolayer-protected gold nanoparticles as a function of metal particle size, by using selectively 13C1-labelled octanethiol. Several interesting results are obtained for the first time: as the gold particle size increases from ca. 1.5 to 4.0 nm, the 13C1 NMR shift moves down-field from ca. 39 to 50 ppm (with respect to TMS), the spin-lattice relaxation rate 1/T1 decreases, and the spin-spin relaxation rate 1/T2 increases. For a given particle size, the 1/T2 varies across the heterogeneously broadened line shape, being higher at the lower field, while there is no clear trend shown in 1/T1. All these results suggest that while particle tumbling may be the dominant spin-lattice relaxation mechanism, the physical properties of the metal core, i.e., more metallic vs. less metallic, are most probably the dominant factors influencing the 13C1 NMR shift and spin-spin relaxation. Now new doors are opened up for more detailed NMR investigations of metal-ligand interactions in SAM systems.
Structural and Elemental Characterization of Fe/Co Nanoparticles Produced through Organometallic Synthesis
Authors: Fejes P. L. , Dumestre F. , Amiens C. , Renaud P. , Chaudret B. , Zurcher P.
Published: April 2011

We report on the structure of and elemental distributions within various magnetic nano-particles synthesized using organometallic precursors. The characterization was carried out using high-resolution transmission electron microscopy (HRTEM), and electron energy loss spectroscopy (EELS), with spectral imaging to investigate elemental distributions within the particles. The crystallinity and oxidation of Fe, Co and Fe-Co particles are discussed. We observe heavy oxidation of Fe particles, while Co particles show, at most, only a thin surface layer of oxide. When Fe and Co are combined to form Fe-Co particles, they are seen to be inhomogeneous, consisting of an Fe core, surrounded by a Co-rich shell.
Tensile Deformation and Fatigue Crack Growth in Bulk Nanocrystalline Al-7.5Mg
Authors: Pao P.S. , Jones H.N. , Gill S.J. , Feng C. R.
Published: April 2011

The fatigue crack growth kinetics and tensile deformation of bulk nanocrystalline Al-7.5Mg were investigated. Nanocrystalline particulates were first prepared by mechanically ball milling spray atomized Al-7.5Mg powders in liquid nitrogen. These particulates were then degassed, consolidated by hot isostatic pressing, and extruded into rods. Bulk nanocrystalline Al-7.5Mg has significantly higher fatigue crack growth rates and lower fatigue crack growth thresholds than those of ingot-processed 7050-T7451. The fatigue crack growth thresholds exhibit only a weak stress ratio dependency and can be identified as having a Class I behavior when using the fatigue classification proposed by Vasudevan and Sadananda. In 3.5% NaCl solution, fatigue crack growth rates of bulk nanocrystalline Al-7.5Mg are as much as three times higher than those obtained in air. Tensile fracture of bulk nanocrystalline Al-7.5Mg is preceded by the formation of a localized shear band. In contrast to the low dislocation density in the as-extruded material, the gage section and the shear band region both exhibited a high dislocation density and dislocation cell structure.
Bimodal Microstructure and Mechanical Properties of Cryomilled Nanocrystalline Al-7.5Mg
Authors: Lee Zonghoon , Witkin David B. , Lavernia Enrique J. , Nutt Steven R.
Published: April 2011

The microstructure and mechanical properties consisting of tensile behavior and hardness of bulk nanocrystalline Al-7.5Mg alloy were investigated. Grain refinement was achieved by cryomilling of atomized Al-7.5Mg powders, and then nanocrystalline powders blended with 15% and 30% coarse-grained Al-7.5Mg powders were consolidated by hot isostatic pressing (HIP) followed by extrusion to produce bulk nanocrystalline Al-7.5Mg alloys. Bimodal structures, which enhance ductility and toughness of nanocrystalline metals, were produced that consisted of nanocrystalline grains and elongated coarse-grain bands. Examination of indentation revealed unusual deformation mechanisms and interactions between the coarse-grain bands and nanocrystalline regions. The ductile coarse-grain bands underwent extensive plastic deformation near indentation, while nanocrystalline regions exhibited limited deformation.
Hybrid nylon-6/silica nanocomposites with improved mechanical properties
Authors: García Monserrat , van Zyl Werner E. , Verweij Henk
Published: April 2011

The study involves the development of new strategies to form technically interesting hybrid nanocomposites with improved mechanical properties. In particular, a new ‘dissolution’ preparative route was developed which incorporates silica nanoparticles (<30 nm) into a nylon-6 matrix. The procedure relies on the judicious choice of organic solvent and pH control. The synthesis involves the dissolution of nylon-6 in formic acid followed by silica particle addition (as an acidified, monodisperse sol) with stirring. Viscous solutions were prepared under cleanroom conditions and casted as thin films which are dried and vacuum treated at ∼60°C. TEM images revealed that the silica particles i.) retained their original shape and size (10–30 nm), ii.) are mono-dispersed and iii.) mainly non-agglomerated. The degree of crystallinity of the composites was determined with XRD as a function of percentage filler added. The nylon-6 phase is semi-crystalline while the silica phase is amorphous. Initial mechanical tests on the composites were conducted and showed with 1wt% silica addition, the E modulus was increased to ∼2600 MPa. The increase in mechanical properties may be a result of the nanosize filler particles which has good synergy with the nylon matrix. Friction and wear properties were also investigated on a pin on disk tribometer by running a flat pin of steel against the composite disc.
Synthesis of Novel Vanadium Oxide Nanotubes and Nanofibers
Authors: Lutta Samuel T. , Dong Hong , Zavalij Peter Y. , Stanley Whittingham M.
Published: April 2011

We are exploring the synthesis and properties of structured vanadium oxides mainly nanotubes and nanorods. Nanotubes initially formed with surfactant templates have been readily exchanged with simple cations without change of the basal-plane structure. These compounds contain d-like vanadium oxide layers with the vanadium in VO6 octahedra. This structure is particularly suitable for redox reactions. In this paper we report on synthesis of vanadium oxide, (NH4)xV2O5-d·nH2O rods using organic polymer as template. This compound has been synthesized by sol-gel reaction and subsequent hydrothermal treatment. TGA, SEM, XRD and FTIR were used to characterize this compound. Thermal analysis of this compound shows that the fibrous morphology is maintained when it is heated in nitrogen and oxygen above 300 °C. However, in both cases the size of the fibers decreases. Performance of this compound as cathode material in secondary electrolyte has been investigated using LiPF6 as electrolyte. A capacity of 140 mAh/g was obtained which remained fairly constant with up to at least 10 cycles. We also investigated electrochemical behavior of thermal products.
An Approach to Nanoglasses through Anodic Oxidation of Sputtered Aluminum on Glass Surface
Authors: Inoue Satoru , Chu Song-Zhu , Wada Kenji
Published: April 2011

The new processes for the preparation of nanoglasses have been developed through anodic oxidation. The aluminum thin film sputtered on the ITO thin film on the glass surface was decomposed into alumina by anodic oxidation technique. The alumina layer possessed nanometer size pore array standing on the glass surface. The sizes of the pore was widened by acid etching from 10∼20nm to a few hundred nm. The glass substrate having the alumina nanostructures on the surface could transmit the UV and visible light at the wavelength range of 200 ∼ 800nm. The TiO2 sol was impregnated into the pores of alumina layer and the sample was heated at ∼ 400 °C for 2 hr, converted into TiO2 nanotubes of anatase phase. The acid etching could remove the alumina skeletons, leaving the TiO2 nanotube array on the glass surface. These glasses were transparent to the light in UV-visible region. The electro deposition technique was applied to the introduction of Ni metal into pores, giving Ni nanorod array on the glass surface. The glass samples possessing TiO2 nanotube array showed very good catalytic function on the decomposition of acetaldehyde gas under the irradiation of UV light. The effect of the dimensions of the Ni nanorods on the magnetization was investigated.
Microstructures and Mechanical Properties of Nanostructured Copper-304 Stainless Steel Multilayers Synthesized by Magnetron Sputtering
Authors: Zhang X. , Misra A. , Wang H. , Kung H. , Embury J. D. , Hoagland R. G. , Nastasi M.
Published: April 2011

Nanostructured Cu/304 stainless steel (SS) multilayers were prepared by magnetron sputtering at room temperature. 304SS has a face-centered cubic (fcc) structure in bulk. However, in the Cu/304SS multilayers, the SS layers exhibited fcc structure for layer thickness of less than or equal to 5 nm. For 304SS layer thickness larger than 5nm, bcc 304SS grains were observed to grow on top of the initial ≈ 5 nm of fcc SS. The maximum hardness of Cu/304SS multilayers was ≈ 5.5 GPa (factor of two enhancement compared to rule of mixtures hardness) achieved at a layer thickness of 5nm, with a decrease in hardness with decreasing layer thickness below 5 nm. The hardness of fcc/fcc Cu/304SS multilayers (layer thickness ≤ 5 nm) is compared with Cu/Ni, another fcc/fcc system, to gain insight on how the mismatch in physical properties such as lattice parameters and shear moduli of the constituent layers affect the peak hardness achieved in these nanoscale systems.
Characterization of Mechanical Deformation of Nanoscale Volumes
Authors: Perrey Christopher R. , Mook William M. , Barry Carter C. , Gerberich William W.
Published: April 2011

The mechanical properties of nanoscale volumes and their associated defect structure are key to many future applications in nanoengineered products. In this study, techniques of mechanical testing and microscopy have been applied to better understand the mechanical behavior of nanoscale volumes. Nanoindentation has been used to investigate important mechanical material parameters such as the elastic modulus and hardness for single nanoparticles. New sample preparation methods must be developed to allow the necessary TEM characterization of the inherent and induced defect structure of these nanoparticles. Issues of chemical homogeneity, crystallinity, and defect characteristics at the nanoscale are being addressed in this study. This integration of investigative methods will lead to a greater understanding of the mechanical behavior of nanostructured materials and insights into the nature of defects in materials at the nanoscale.
Interface Conduction between Conductive ReO3 Thin Film and NdBa2Cu3O6 Thin Film
Authors: Ohkubo Manabu , Fukai Kumiko , Matsuo Kohji , Iwata Nobuyuki , Yamamoto Hiroshi
Published: April 2011

The Re oxide films were deposited on quartz glasses by RF reactive sputtering from a Re metal target. The lowest resistivity was observed in the film in-situ annealed at 200°C in Ar atmosphere and showed the order of 10-4 Ω cm of which the value was still about 10 times as large as that of a single crystal ReO3. The temperature dependence of the resistivity revealed a metallic behavior. A superconductivity did not take place in the bilayered film of ReO3 / NdBa2Cu3O6. In the interface region the resistivity minimum probably caused by the Kondo effect was observed in the neighborhood of 120K.
The Growth of Bamboo-Structured Carbon Tubes Using a Copper Catalyst
Authors: Farmer B.L. , Holmes D.M. , Vandeperre L.J. , Stearn R.J. , Clegg W.J.
Published: April 2011

Catalytic decomposition of methane has been used to grow bamboo-structured carbon tubes at temperatures ranging from 1233 K to 1291 K. No tube growth was observed at temperatures less than 1233 K, whilst above 1291 K pyrocarbon was the dominant product. It is shown that the average size of the copper catalyst particles was influenced by the reaction temperature, with the reciprocal of the maximum size of the copper particle decreasing linearly with temperature. This is consistent with the idea that the melting point can be reduced by surface energy effects. Observations show that under the conditions here the catalyst particle penetrates into the carbon fibre and a mechanism is proposed for development of the bamboo structure based upon the energy changes that take place.
Rheological Behaviour and Model of Metal - Polymer - Ceramic Composite
Authors: Kireitseu Maksim V.
Published: April 2011

In the present paper rheological behaviour of composite coating consisting of Aluminum Oxide -Polymer – Chrome Carbide was examined by using rheological models for principal Hertzian contact of a sphere and a plate. The crystallography and morphologic texture was characterized and the fracture resistance was measured using fracture-mechanics. A rheological model of the composite coating has been proposed and confirmed by in situ experiments. Several requirements to rheological models were formulated regarding an adequate strain-deformation state of the composite coating. Load rating revealed ultimate strain-deformation rates. Analysis of the models and experimental results revealed better understanding of composite failure and degradation mechanics.
A Semiconductor Nano-Patterning Approach Using AFM-Scratching Through Oxide Thin Layers
Authors: Santinacci L. , Djenizian T. , Schmuki P.
Published: April 2011

AFM-scratching was performed through thin oxide layer which was either a native oxide layer (1.5 – 2 nm thick) or a thermal oxide layer (10 nm thick). Due to their insulating properties, the SiO2 films act as masks for the metal electrochemical deposition. In the scratched openings copper deposition can take place selectively and thus nano-scale metal lines could be successfully plated onto the p-type silicon substrates. Using particularly, if sufficiently thick thermal oxide has advantages over the native oxide, it allows a H-termination of the Si within the grooves (HF treatment) without eliminating the oxide layer on the rest of the surface.
Atomistically Informed Continuum Model of Polymer-Based Nanocomposites
Authors: Picu Catalin R. , Sarvestani Alireza , Ozmusul Murat S.
Published: April 2011

A model polymeric material filled with spherical nanoparticles is considered in this work. Monte Carlo simulations are performed to determine the polymer chain conformations in the vicinity of the curved interface with the filler. Several discrete models of increasing complexity are considered: the athermal system with excluded volume interactions only, the system in which entropic and energetic interactions take place while the filler is a purely repulsive sphere, and the system in which both filler-polymer and polymer-polymer energetic interactions are accounted for. The total density, chain end density, chain segment preferential orientation and chain size and shape variation with the distance from the filler wall are determined. The structure is graded, with the thickness of the transition region being dependent on the property and scale considered. Hence, the polymer in the vicinity of the filler is represented in the continuum sense by a material with graded properties whose elasticity is determined based on the local structure. Homogenization theory is the used to obtain the overall composite moduli. The filler size effect on the composite elasticity is evaluated.
Micromolding of Pb and Zn with Surface Engineered LiGA Mold Inserts
Authors: Cao D. M. , Guidry D. J. , Meng W. J. , Kelly K. W.
Published: April 2011

Molding of Pb and Zn metal plates with LiGA (Lithographie, Galvanoformung, Abformung) fabricated Ni micro-scale mold inserts was carried out with as fabricated Ni inserts and Ni inserts conformally coated with Ti-containing hydrocarbon (Ti-C:H) coatings. The molding performance was characterized using scanning electron microscopy (SEM) and energy-dispersive spectroscopy (EDS), in terms of the generated features on the metal plates as well as the inserts condition after molding. The present results demonstrate that, in cases where significant metal/insert chemical interactions exist, surface modification of the mold insert is necessary to obtain satisfactory performance. Furthermore, conformal deposition of suitable engineered ceramic coatings onto Ni micro-scale mold inserts is effective for high temperature micromolding of reactive metals.
Planar Extrinsic Biasing Of Thin Film Shape-Memory MEMS Actuators.
Authors: Grummon D. S. , Gotthardt R. , LaGrange T.
Published: April 2011

Although slow and dissipative, sputtered thin-film shape-memory alloys like equiatomic titanium-nickel can exert a large ohmically-excited force·displacement product when deployed in photolithographically micromachined actuators. They give energy densities far exceeding those typically produced by competing microactuator materials [1], and their size can probably be scaled down to the nanometer range (where the benefits of high surface to volume ratio are best exploited for speed and efficiency). But a large, energetic, and resettable actuation stroke is possible only if some agency has imparted a non-trivial initial plastic strain, of between one and five percent, to the martensite phase. Is not always obvious how this strain is to be achieved when discrete mechanical manipulation of the active element is difficult. Furthermore, for cyclic actuation, a resetting-force that periodically re-deforms the martensite during the cooling interval must arise naturally from mechanical elements in the design. Here, several methods responding these requirements are discussed in relation to various kinematic themes.
Surface Oxide Effects on Static Fatigue of Polysilicon MEMS
Authors: Kahn H. , Ballarini R. , Heuer A.H.
Published: April 2011

Static fatigue – crack growth causing delayed failure under constant stress and involving stress corrosion cracking – was investigated in polysilicon MEMS using two different surface-micromachined devices. One exploited residual tensile stresses to create stress concentrations at micromachined notches, and the other involved a single-edge notched beam specimen integrated with an electrostatic comb-drive microactuator. Tests with both devices revealed that polysilicon is not susceptible to static fatigue in humid environments. However, when a relatively thick (45 to 140 nm) surface oxide was thermally grown on the microactuator devices, the specimens demonstrated delayed fracture in a humid ambient, presumably due to static fatigue of the surface SiO2. The stress intensities at the resulting cracks in the SiO2were then sufficient to cause catastrophic crack propagation through the polysilicon specimens. The implications of our data on the issue of fatigue in polysilicon is discussed.
Pulsed Laser Annealing of Silicon-Germanium Films
Authors: Sedky Sherif , Schroeder Jeremy , Sands Timothy , Howe Roger , King Tsu-Jae
Published: April 2011

In this work, we investigate the possibility of using pulsed laser annealing to locally tailor the physical properties of Si1-xGex (18% < × < 90%) prepared by low pressure chemical vapor deposition (LPCVD) at 400°C. Films which were amorphous as deposited showed, after laser annealing, strong {111} texture and a columnar grain microstructure and an average resistivity of 0.7 mΩ.cm. AFM showed that the first few laser pulses result in a noticeable reduction in surface roughness, which is proportional to the pulse energy. However, a large number of successive pulses dramatically increases the surface roughness.
Residual Stress Control to Optimize Pzt Mems Performance
Authors: Kennedy M.S. , Bahr D.F. , Richards C.D. , Richards R.F.
Published: April 2011

Flexing piezoelectric membranes can be used to convert mechanical energy to electrical energy. The overall deflection of individual membranes is impacted by the residual stress in the system. Membranes comprised of silicon dioxide, Ti/Pt, lead- zirconate- titanate (PZT), and TiW/Au layers deposited on a micromachined boron doped silicon wafer were examined for both morphology and residual stress. By characterizing the membrane residual stress induced during processing with x-ray diffraction, wafer curvature, and bulge testing and identifying methods to reduce stress, the membrane performance and reliability can be optimized. For Zr:Ti ratios of 52:48, the residual stress in the PZT was 350 MPa tensile, with an overall effective stress in the composite membrane of 150 MPa. A reduction of stress was accomplished by changing the PZT chemistry to 40:60 Zr:Ti in the PZT to obtain a stress in the PZT of 160 MPa tensile and an overall effective membrane stress of 100 MPa. The crystallization of the 52:48 PZT film at 700 °C causes a 28% reduction in the thickness of the film.
Investigation of Polymer Micro-Actuators Based on Electrostrictive Poly(vinylidene fluoride-trifluoroethylene) Copolymers
Authors: Xu Tian-bing , Xia Feng , Cheng Z.-Y. , Zhang Q. M.
Published: April 2011

Micromachined actuators based on the electrostrictive P(VDF-TrFE) copolymer, which possesses a high strain (∼5%) and high elastic energy density (∼ 1 J/cm3), have been designed and fabricated. The performance of the devices have been characterized and modeled in terms of the properties of the copolymer and dimensions of the devices. The experimental results on the device responses under high AC fields (electrostrictive mode), weak AC fields in DC field biased state, and frequency dependence, are very close to the modeling results. Due to the large field induced strain and high frequency capability of the electrostrictive P(VDF-TrFE), the device possesses the capability of operation at non-resonance mode with high displacement and force output, and hence, the device is capable to be used over a broad frequency range. For example, for a device of 1 mm lateral dimension, the displacement output can reach more than 50 μm and the ratio of the displacement/applied voltage is more than 20 nm/Vrms. Furthermore, over more than 3 frequency decades (up to 100 kHz), the dispersion of the displacement is less than 20%. The observed performance of the devices indicates that this class of the electrostrictive P(VDF-TrFE) based micro-actuators is attractive for micropumps and valves.
Microscale Measurement of Stresses in a Silicon Flexure Using Raman Spectroscopy
Authors: Srikar V. T. , Swan A. K. , Goldberg B.B. , Ünlü M. S. , Spearing S. M.
Published: April 2011

We report the use of Raman spectroscopy to characterize the bending stresses in a deep reactive-ion etched, single-crystal, silicon flexure of length 2950 μm, width 480 μm, thickness 150 μm, and fillet radius 65 μm, subjected to a tip displacement of 69.5 μm. The spectral resolution of the measurement was 0.02 cm-1, which corresponds to a stress resolution of ∼10 MPa, and the spatial resolution was ∼1 μm. Line scans were performed across the thickness, at several locations along the length, of the flexure. The changes in the Raman shift were converted to stress values, assuming a uniaxial stress state, without the use of any fitting parameters. A comparison of the measured values with the predictions of analytical and numerical models indicates agreement to within 25–35 MPa (or ∼15%) at locations sufficiently distant from the root. At the root itself, the complex nature of the stress distribution precludes unambiguous stress determination using spectroscopic measurements.
Modeling Analysis of Free-Spreading Sublimation Growth of SiC Crystals
Authors: Bogdanov M. V. , Demina S. E. , Karpov S. Yu , Kulik A. V. , Ofengeim D. Kh , Ramm M. S. , Mokhov E. N. , Roenkov A. D. , Vodakov Yu. A. , Makarov Yu. A. , Helava H.
Published: April 2011

Recently, an advanced technique for growing free-spreading SiC bulk crystals by sublimation has been demonstrated. This method was used to grow 6H- and 4H-SiC boules free of polycrystalline deposits on the crystal periphery, up to 35 mm in diameter with the micropipe density less than 20 cm-2 and the dislocation density about 102-103 cm-2. In this paper, we report on the numerical modeling of free-spreading crystal growth. We consider the global heat transfer in an inductively heated growth system, species transport in the growth cell and in the powder charge, and thermoelastic stress, focusing on the crystallization front dynamics, poly-SiC deposition, and powder source evolution. Special attention was given to the validation of the simulations. The computed thermal field and evolution of the powder and crystal shape were found to agree qualitatively with observations.
Thermal Plasma Physical Vapor Deposition of Nanostructured SiC Coatings
Authors: Wang Xinhua , Eguchi Keisuke , Yamamoto Atsushi , Yoshida Toyonobu
Published: April 2011

Nanostructured and thick SiC coatings have been successfully deposited on Si and graphite substrates by thermal plasma physical vapor deposition (TPPVD) using ultrafine SiC powder as a starting material. The control of processing parameters such as substrate temperature, composition of plasma gases, permits to the deposition of SiC coatings with a variety of microstructures and with various morphologies from dense to columnar. The maximum deposition rate reached 200 nm/s. Seebeck coefficient up to −480 μV/K was obtained for the non-doped coatings with stoichiometric composition. Nitrogen doping to the coatings made it possible to decrease the electrical resistivity from 10-2∼10-3 to 10-4∼10-5 Ωm and showing the maximum power factor of 1.0×10-3 Wm-1K-2 at 973 K.
Memory Switching in Ion Bombarded Amorphous Silicon Carbide Thin Film Devices
Authors: Gateru R. G. , Shannon J. M. , Silva S. R. P.
Published: April 2011

Metal-semiconductor-metal (MSM) memory devices have been made in hydrogenated amorphous silicon carbide (a-SiCx:H). Switching in silicon-rich amorphous silicon alloys is believed to be related to the concentration of defects in the semiconductor material. We have used ion bombardment to introduce a controlled number of damage centres into amorphous silicon carbide. Both analog and digital switching behaviours are reported.
Thermal Chemical Vapor Deposition of Silicon Carbide Films as Protective Coatings for Microfluidic Structures
Authors: Gallis Spyros , Futschik Ulrike , Castracane James , Kaloyeros Alain E. , Efstathiadis Harry , Sherwood Walter , Hayes Susan , Fountzoulas Costas G.
Published: April 2011

Amorphous silicon carbide (SiC) films were deposited on silicon substrates by thermal chemical vapor deposition (TCVD) technique, at substrate temperatures ranging from 620 °C - 850 °C. A novel, single-source halide free precursor, SP-4000, belonging to the family of polysilenemethylenes (PSM) (nominal structure [-SiH2-CH2-]n, n = 2–8 including branched and cyclic isomers) was used as source. Argon was used, as both the precursor carrier gas and the dilution gas. Other reactants, such as hydrogen or hydrocarbons, were not used. The deposition yielded films with Si/C ratio of 1±0.2. The highest achieved growth rate was 83 nm/min.

The modulus of elasticity and the nanohardness of the SiC films were measured with the aid of a nanoindenter at various depths, which did not exceed 25% of the film thickness. The average nanohardness at indentation depths of approximately 10% of the film thickness was measured up to 13 ± 4 GPa. The results of the nanoindentation will be discussed in conjunction with the microstructural analysis of the films.

In addition, the development of a viable TCVD SiC process presents significant opportunities in the nano/micro systems field. In particular, the ability to custom tailor the surfaces of microfluidic structures allows for the development of valves, pumps and channels for use in corrosive or high temperature environments. Initial results from the deposition of SiC films on prototype microfluidic components will be presented.
Spatially Resolved Photoluminescence and Thermally Stimulated Luminescence in Semi-Insulating SiC Wafers
Authors: Suleimanov Yu. M. , Lulu S. , Tarasov I. , Ostapenko S. , Saddow S. E. , Torchinska T. V. , Heydemann V. D. , Roth M. D. , Kordina O. , MacMillan M. F.
Published: April 2011

We report on non-contact and non-destructive spatially resolved characterization of traps and luminescence centers in vanadium-free semi-insulating 6H-SiC. Two optical techniques were employed: photoluminescence (PL) mapping and thermally stimulated luminescence (TSL) imaging on SiC wafers. PL and TSL topography reveal inhomogeneity at the periphery regions of the wafers. Low-temperature PL spectra show broad bands with the maxima at 1.75eV and 1.2eV, including a sharp zero-phonon line at 1.344eV. The TSL glow curves at T>80K show different peaks in the visible and infrared bands. The luminescence spectrum of the 105K TSL peak replicates 1.75eV band, while the 120K peak corresponds to the 1.2eV band. Additionally, the high temperature TSL peak at 210K shows an excellent match with 1.344eV zero phonon line. The trap energies of different peaks are calculated. We discuss a model of complex defects composed of closely spaced electron (hole) trap and UD3 defect.
Accurate Lattice Constant and Mismatch Measurements of SiC Heterostructures by X-Ray Multiple-Order Reflections
Authors: Huang XianRong , Dudley Michael , Neudeck Philip G. , Anthony Powell J.
Published: April 2011

High-resolution X-ray diffraction (HRXRD) combined with other diffraction techniques is applied to characterize 3C SiC epilayers hoteroepitaxially grown on atomically flat mesas on 4H and 6H SiC substrates. Small-beam rocking curve scan and reciprocal mapping show extremely high crystalline perfection and homogeneity of the ideally grown 3C-SiC epilayers. Accurate lattice measurements based on X-ray multiple-order reflections reveal that: 1) no misorientation between the (0001) lattice planes across the 4H/3C or 6H/3C interface is detected, confirming the 2D nucleation mechanism of the 3C epilayer from a flat coherent interface; 2) in-plane substrate/epilayer lattice mismatch always exists, but the 3C epilayers do not correspond to a completely relaxed cubic structure, indicating that the epilayers are partially strained; 3) lattice mismatch varies for different regions, implying a complicated strain relaxation mechanism of 3C epilayers on various mesas.
Photo-Chemical Pattern Etching of Silicon-Carbide by Using Excimer Laser and Hydrogen Peroxide Solution
Authors: Sasaki D. , Murahara M.
Published: April 2011

A circuit pattern etching of a Silicon-carbide (SiC) surface was conducted with KrF excimer laser irradiation in the presence of HF and H2O2 mixed solutions. SiC have excellent properties of a high hardness, high melting point, wide band gap, high resistance to radiation and chemical stability. This material has come to attract attention as an integrated circuit material for high resistance to environment. However, the material is very difficult in minute processing by the photo-lithography because of its chemical stability. Thus, we developed the new etching method in which a SiC surface was photo-oxidized with H2O or H2O2 by using excimer laser irradiation and was etched by HF water solution. In this experiment, the mixed solution was poured into the thin gap between an Al2O3 glass and the SiC surface with capillary phenomenon. A patterned excimer laser light was, then, irradiated on the SiC surface. The H2O or H2O2 in the reaction solution was photo-dissociated, and the photo-dissociated active oxygen reacted with the SiC. CO2 and SiO2 were formed only on the part exposed by the pattered light forcibly, and an oxidized layer was formed. In this chemical reaction, the CO2 evaporated, and the SiO2 remained on the sample surface. The SiO2 layer was then dissolved by the HF water solution. Thus, etching was conducted by the repetition of the forced oxidization of the SiC and the dissolving of the oxidized layer. In this experiment, the most effective conditions were 20% of H2O2 water solution, 15% HF water solution and 256mJ/cm2 of KrF excimer laser. The etching depth was 80 Å at the laser shot number of 10000. It significantly improved compared with that of using an ArF excimer laser (256mJ/cm2, 193nm), 50 Å.
Strained SiC: Ge Layers in 4H SiC formed by Ge Implantation
Authors: Dashiell M. W. , Xuan G. , Zhang Xin , Ansorge E. , Kolodzey J.
Published: April 2011

The ion implantation of germanium into 4H-SiC at 1000 °C resulted in crystalline SiC:Ge layers that are coherently strained to the (0001) oriented 4H-SiC substrates. Germanium implantation energies of 140 keV and 50 keV were chosen to form approximately 100nm thick step-like SiC:Ge layers with Ge atomic fractions ranging from 0.0007 to 0.006. High-resolution x-ray diffraction (HRXRD) and reciprocal space mapping reveal a high-quality, compressively strained SiC:Ge layer. High-temperature annealing resulted in partial relaxation of the macroscopic layer strain, however the SiC:Ge layer remained strained with a coherent interface for annealing up to at least 1650°C. Because Ge is a group-IV atom like Si and C, its incorporation into the lattice is expected to act as an isoelectronic impurity, rather than a charged donor or acceptor. Thus, high-quality, SiC:Ge layers have the potential for bandgap and strain engineered electronics such as SiC-based high electron mobility transistors (HEMTs) for RF-power electronics. Currently there is no established heterojunction pair in SiC material technology for fabricating HEMTs and other heterojunction devices.
Towards Ferroelectric Field Effect Transistors in 4H-Silicon Carbide
Authors: Koo S.-M. , Khartsev S. I. , Zetterling C.-M. , Grishin A. M. , Östling M.
Published: April 2011

We report on the integration of ferroelectric Pb(Zr,Ti)O3 (PZT) thin films on 4H-silicon carbide and their electrical properties. The structures of metal-ferroelectric-(insulator)-semiconductor MF(I)S and metal-ferroelectric-metal-insulator-semiconductor MFMIS have been fabricated and characterized. The MFMIS structures of Au/PZT/Pt/Ti/SiO2/SiC have shown fully saturated P-E hysteresis loops with remnant polarization Pr =14.2μC/cm2 and coercive field Ec = 58.9 kV/cm. The MFIS structures exhibited stable capacitance-voltage C-V loops with low conductance (<0.1 mS/cm2, tan d ∼ 0.0007 at 12 V, 400kHz) and memory window as wide as 10 V, when a 5 nm-thick Al2O3 was used as a high bandgap (Eg ∼ 9eV) barrier buffer layer between PZT (Eg ∼ 3.5eV) and SiC (Eg ∼ 3.2eV). Both structures on n- and p- SiC have shown electrical properties promising for the application to the gate stacks for the SiC field-effect transistors (FETs) and the design and process issues on different types of the metal-ferroelectric-silicon carbide field-effect transistors (FETs) have also been proposed.
Development of a High Lateral Resolution Electron Beam Induced Current Technique for Electrical Characterization of InGaN-Based Quantum Well Light Emitting Diodes
Authors: Bunker Kristin L. , Gonzalez Juan Carlos , Batchelor Dale , Stark Terrence J. , Russell Phillip E.
Published: April 2011

Electron Beam Induced Current (EBIC) is a Scanning Electron Microscope (SEM)-based technique that can provide information on the electrical properties of semiconductor materials and devices. This work focuses on the design and implemenation of an EBIC system in a dedicated Scanning Transmission Electron Microscope (STEM). The STEM-EBIC technique was used in the characterization of an Indium Gallium Nitride (InGaN) quantum well Light Emitting Diode (LED). The conventional “H-bar” Transmission Electron Microscopy (TEM) sample preparation method using Focused Ion Beam Micromachining (FIBM) was adapted to create an electron-transparent membrane approximately 300 nm thick on the sample while preserving the electrical activity of the device. A STEM-EBIC sample holder with two insulated electrical feedthroughs making contact to the thinned LED was designed and custom made for these experiments. The simultaneous collection of Z-contrast images, EBIC images, and In and Al elemental images allowed for the determination of the p-n junction location, AlGaN and GaN barrier layers, and the thin InGaN quantum well layer within the device. The relative position of the p-n junction with respect to the thin InGaN quantum well was found to be (19 ± 3) nm from the center of the InGaN quantum well.
Simultaneous TEM and Cathodoluminescence Imaging of Non Uniformity in In0.1Ga0.9N Quantum Wells
Authors: Boyall Nicholas M. , Durose Ken , Watson Ian M.
Published: April 2011

Monochromatic cathodoluminescence (CL) imaging of metal-organic vapour phase epitaxy (MOVPE) grown In0.1Ga0.9N single quantum wells (QW) has been performed in a scanning transmission electron microscope (STEM). Spatially resolved fluctuations in the CL emission wavelength and intensity of the QW luminescence were recorded. The presence of regions with luminescent features asymmetrically distributed either side of the QW peak emission was inferred. These fluctuations may be attributed to, by for example, variations of ±0.01 in the In fraction of the In0.1Ga0.9N alloy, to changes of up to 0.6nm in the QW thickness. However these factors do not explain the gross fluctuations in QW emission intensity observed in TEM-CL on the scale of ∼1μm.