bluuebunny/crossref_metadata_2025 huggingface dataset:
Si/SiGe Nanostructures Fabricated by Atomic Force Microscopy Oxidation
Authors: Bo Xiang-Zheng , Rokhinson Leonid P. , Yin Haizhou , Tsui D. C. , Sturm J. C.
Published: April 2011

In this work, local AFM oxidation technique in a controlled humidity environment has been used to create small features in strained SiGe alloys. When directly oxidizing SiGe alloys, minimum line widths of 20nm were achieved by adjusting parameters such as the bias voltage on the microscope tip and the tip writing speed. It was found that when bias voltage increases, and/or when the tip writing speed decreases, the oxidation height of silicon-germanium increases. In contrast to conventional thermal oxidation, the oxide height on SiGe alloys is slightly less than that on Si. Finally, this method was used to successfully cut conducting SiGe quantum well lines with high resolution.
Silicon Single-Electron Transistors and Single-Electron CCD
Authors: Takahashi Yasuo , Fujiwara Akira , Ono Yukinori , Inokawa Hiroshi
Published: April 2011

We have developed two types of devices for silicon-single-electronics; a single-electron transistor (SET) and a single-electron charge coupled device (CCD). Both devices were fabricated on SOI (silicon on insulator) wafers. For the SET fabrication, we used a novel method called pattern-dependent oxidation (PADOX), which exploits special phenomena that occur during thermal oxidation of a small silicon structure. The Si structures are converted into small Si SETs by consequence of stress-induced bandgap narrowing and quantum size effects. Since the size of the resultant Si island is about 10 nm, the SETs operate at relatively high temperatures. We have already developed several kinds of application of Si SETs by utilizing the special features of SETs. In addition, we have developed a single-electron CCD that enables us to manipulate a single electron without tunnel capacitors. The device utilizes small Si-wire MOSFETs connected in series, and an elementary charge can be transferred like in a CCD.
Interfacial Diffusion Studies of Hf and Zr into Si from Thermally Annealed Hf and Zr Silicates
Authors: Quevedo-Lopez M. A. , El-Bouanani M. , Gnade B. E. , Colombo L. , Bevan M. , Douglas M. , Visokay M. , Wallace R. M.
Published: April 2011

Hf and Zr incorporation from thermally annealed high-κ gate dielectric thin films (4-5 nm) candidates HfSixOy and ZrSixOy into Si are presented. The dielectric films were subjected either to rapid thermal annealing (RTA) or standard furnace annealing in an N2 atmosphere. After annealing, the films were removed by chemical etching prior to depth profiling using both time of flight secondary ion mass spectroscopy (ToF-SIMS), and Heavy Ion Rutherford Backscattering Spectrometry (HI-RBS) combined with UV-ozone oxidation/etching cycles. As-deposited and annealed films were studied using monochromatic X-ray Photoelectron Spectroscopy (XPS), and high resolution TEM. A Zr incorporation depth after annealing of up to 20 nm into the Si substrate was observed. Depth profiling shows that, although most of the remnant Zr after annealing/etching is located at or near the surface of the Si substrate, incorporation into the substrate is also present. No significant Hf diffusion into Si was observed for either RTP or furnace-annealed films
Diffusion Characteristics of Cu in TiN Thin Films
Authors: Gupta Abhishek , Wang Hiyan , Kvit Alex V. , Duscher Gerd , Narayan Jay
Published: April 2011

We have investigated the diffusion characteristics of Cu in nanocrystalline, polycrystalline and single crystal TiN thin films, which are being used as a diffusion barrier for sub-quarter-micron metallization. These films were synthesized on Si (100) substrate by first ablating TiN and then ablating Cu targets using Pulse Laser Deposition technique. The three different microstructures of TiN were achieved by growing the films at different substrate temperatures, where higher temperatures (650 °C) leads to epitaxy. Then a uniform thin layer of Cu was deposited on TiN/Si substrate at room temperature for all the three depositions above. These structures were characterized using X-Ray diffraction technique and high-resolution transmission electron microscopy. Each sample is then annealed at 500 °C for 30min to study the diffusion barrier characteristics as a function of microstructure of TiN. Study of diffusion profile and Cu concentration measurement were performed using Scanning Transmission Electron Microscopy-Z contrast Imaging (0.12nm resolution), Electron Energy Loss Spectroscopy and Secondary Ion Mass Spectroscopy. From the results obtained the effect of microstructure of TiN thin films on the diffusion characteristics of Cu after annealing was analyzed. Four points probe resistivity measurements were made to establish structure property correlations.
Strength Analysis of a Micro-Rocket Combustion Chamber
Authors: Noonan Erin E. , Protz Christopher S. , Peles Yoav P. , Mark S.
Published: April 2011

This paper presents the fabrication, testing and analysis of the MIT micro-rocket combustion chamber structure. The structure is a rocket chamber with a closed throat and pressure feeds. It is fabricated with the same processes as the full micro-rocket builds. Mechanical test results are correlated with inspection of failed devices for flaws and with finite element modeling of the test condition. This analysis provides recommendations for modifications to improve the strength of the micro-rocket chamber. These recommendations are discussed in the context of the current status of the micro-rocket.
Frictional Properties of Self-Assembled Alkylsilane Chains on Silica
Authors: Chandross M. , Park B. , Stevens M. , Grest G.S.
Published: April 2011

We present the results of molecular dynamics simulations of pairs of alkylsilane monolayers on silica surfaces under shear. In particular, we investigate the effects of shear velocity on the friction for chains of 6, 8, 12, and 18 carbon atoms covalently bonded to a crystalline surface. Our studies are performed at loads close to 0.2 and 2 GPa for relative velocities of 0.2, 2.0, and 20.0 m/s. We find that for perfect (defect-free) monolayers, the effects of chain length and velocity are weak, indicating that the experimentally measured dependence of friction on these properties is primarily due to defects in the monolayer. We have investigated possible finite size effects by varying our system dimensions from 43 Å ×50 Å Å to 174 Å × 201 Å. We find that increasing the surface area by a factor of N reduces the noise in the shear stress by a factor of , and has a comparable effect to averaging the smaller system data over bins of points. This indicates that finite size effects are negligible in our simulations.
Process Development of Silicon-Silicon Carbide Hybrid Micro-Engine Structures
Authors: Choi Dongwon , Shinavski Robert J. , Steffier Wayne S. , Hoyt Skip , Spearing S.Mark
Published: April 2011

A MEMS-based gas turbine engine is being developed for use as a button-sized portable power generator or micro-aircraft propulsion source. Power densities expected for the micro- engine require high combustor exit temperatures (1300-1700K) and very high rotor peripheral speeds (300-600m/s). These harsh operating conditions induce high stress levels in the engine structure, and thus require refractory materials with high strength. Silicon carbide has been chosen as the most promising material for use in the near future due to its high strength and chemical inertness at elevated temperatures. However, techniques for microfabricating single- crystal silicon carbide to the level of high precision needed for the micro-engine are not currently available. To circumvent this limitation and to take advantage of the well-established precise silicon microfabrication technologies, silicon-silicon carbide (SiC) hybrid turbine structures are being developed using chemical vapor deposition of poly-SiC on silicon wafers and wafer bonding processes. Residual stress control of SiC coatings is of critical importance to all the silicon-silicon carbide hybrid structure fabrication steps since a high level of residual stresses causes wafer cracking during the planarization, as well as excessive wafer bow, which is detrimental to the subsequent planarization and bonding processes. The origins of the residual stresses in CVD SiC layers have been studied. SiC layers (as thick as 30µm) with low residual stresses (on the order of several tens of MPa) have been produced by controlling CVD process parameters such as temperature and gas ratio. Wafer-level SiC planarization has been accomplished by mechanical polishing using diamond grit and bonding processes are currently under development using interlayer materials such as silicon dioxide or poly-silicon. These process development efforts will be reviewed in the context of the overall micro-engine development program.
Diffusion Mechanism of Cations and Anions in Cation-Exchange Process for Fabrication of High-Tc Superconducting HgBa2CaCu2O6+δ?Films
Authors: Xie Y. Y. , Wu J. Z. , Aytug T. , Christen D. K.
Published: April 2011

We have investigated the diffusion mechanism of Hg and Tl cations in cation-exchange process that has been used successfully for fabrication of Hg-based high-Tc superconducting films. Scanning electron microscopy/energy dispersive spectroscopy (SEM/EDS) was employed to map the distribution of Tl and Hg cations in films quenched at different stages of the cation exchange process. SEM/EDS mappings showed that the nonuniform distribution of Hg is visible in micrometer size on the surface of samples quenched after short-time (∼10min) Hg-annealing, but this nonuniformity disappears for longer-time (∼45 min) Hg-annealing samples. This change could be ascribed to different stages in Hg diffusion -- the former is the early stage when Hg is concentrated in the channels and the latter Hg-cations have already diffuse to grains. Our experimental results hence suggest that Hg-cations channel through defects in the films then diffuse into grains along a-b planes and vise versa for Tl-cations. The diffusion mechanism of anions (oxygen) in post annealing has also been discussed. Fluorine-doped Hg-1212 films were post annealed in flowing oxygen at 300 °C for several hours. Magnetic measurement has shown these samples are comprised pure overdoped Hg-1212 phase with smooth and sharp transition below 120 K, but resistivity vs. temperature measurement shows a kink at ∼123 K. This implies that the optimally doped Hg-1212 phase with higher Tc might be surrounded by overdoped Hg-1212 phase and their contribution to magnetization is minimized, thus the possible diffusion mechanism for anions is also through grain boundaries at a much larger time scale compared to the cations.
Influence of Lateral Critical Current Density Distributions on AC Transport Losses for Ag-Sheathed (Bi, Pb)-2223 Multifilamentary Tapes with Different Filament Arrangements
Authors: Inada Ryoji , Sakamoto Shusaku , Zhang Pingxiang , Oota Akio , Fujimoto Hiroyuki
Published: April 2011

The influence of lateral critical current density (Jc) distributions on AC transport losses in self-fields at 77 K have been investigated on the Ag-sheathed (Bi, Pb)-2223 multifilamentary tapes with different filament arrangements. The trapped magnetic field distributions in a remanent state on the tape surface measured by a scanning Hall sensor depend on the filament arrangements and gradually deviate from the calculation results of magnetic profile without any Jc variations in their cross sections. The transport loss values are strongly influenced from the filament arrangements in each tape, although the main contribution to the losses comes by the hysteresis loss in the superconductor. These results are explained by the calculation results of the shape of field-free core and flux-penetration-regions, varying with filament arrangements and local Jc distributions along a width direction.
Search for New Thermoelectric Materials through Exploratory Solid State Chemistry. The Quaternary Phases A1+xM3−2xBi7+xSe14, A1−xM3−xBi11+xSe20, A1−xM4−xBi11+xSe21 and A1−xM5−xBi11+xSe22 (A = K, Rb, Cs, M = Sn, Pb) and the Homologous Series Am[M6Se8]m[M5+nSe9+n]
Authors: Mrotzek Antje , Hogan Tim , Kanatzidis Mercouri G.
Published: April 2011

The compound types A1+xM3-2xBi7+xSe14, A1−xM3−xBi11+xSe20, A1−xM4−xBi11+xSe21 and A1−xM5−xBi11+xSe22 (A = K, Rb, Cs; M = Sn, Pb) form from reactions involving A2Se, Bi2Se3, M and Se. The single crystal structures reveal that they are all structurally related so that they all belong to the homologous series Am[M6Se8]m[M5+nSe9+n] (M = di- and trivalent metal), whose characteristics are three-dimensional anionic frameworks with tunnels filled with alkali ions. The building units that make up these structures are derived from different sections of the NaCl lattice. In these structures, the Bi and Sn (Pb) atoms are extensively disordered over the metal sites of the chalcogenide network, giving rise to very low thermal conductivity. These phases are all narrow gap semiconductors with 0.25 < Eg< 0.60 eV and many possess physico-chemical and charge transport properties suitable for thermoelectric investigations.
The Hall Carrier Mobility of AgBiTe2-Ag2Te Composite
Authors: Sakakibara T. , Takigawa Y. , Kurosawa K.
Published: April 2011

We prepared a series of (AgBiTe2)1−x(Ag2Te)x(0≤×≤1) composite materials by melt and cool down [1]. The Hall coefficient and the electrical conductivity were measured by the standard van der Pauw technique over the temperature range from 93K to 283K from which the Hall carrier mobility was calculated. Ag2Te had the highest mobility while the mobility of AgBiTe2was the lowest of all samples at 283K. However the mobility of the (AgBiTe2)0.125(Ag2Te)0.875composite material was higher than the motility of Ag2Te below 243K. It seems that a small second phase dispersed in the matrix phase is effective against the increased mobility.
Sb3Zn4, a promising new thermoelectric material. Elaboration and caracterisation
Authors: Izard V. , Record M.C. , Haines J. , Tedenac J.C.
Published: April 2011

Sb-Zn alloys have interesting thermoelectric properties. Sb3Zn4 is a high performance ptype thermoelectric material appearing as a promising substitute for PbTe due to a higher factor of merit, ZT=1.3 at 673K [1] with the advantage of being Pb free. The preparation of the Sb3Zn4 compound is, however, not without problems. Even if some authors reported measurements on a single-phased material or single crystals [1,2], others described it as multi-phased alloy giving confused explanations for this result based on the existence of metastabilities due to strong interactions in the liquid phase [3,4].

Hence, the knowledge of a very trustful phase diagram of the Sb-Zn sytem is indispensable. As the previous published data on this system were discordant, we have reinvestigated it and from our results we have elaborated and characterised the thermoelectric compound Sb3Zn4.
Determining the Limit of Hardness in Ternary Carbide thin Films
Authors: Krzanowski James E. , Endrino Jose L. , Koutzaki Sirma H.
Published: April 2011

In this study we examine the structure and mechanical properties of ternary carbide films, with the objective of understanding the role that residual stress, density, grain size, texture and crystallinity play in determining film hardness. The main variables we used to alter film structure are the nominal film compositions and substrate bias voltage. The systems examined here are Ti-Hf-C and Hf-Si-C, and are compared to previous work on Ti-Si-C. The Hf-Si-C films show hardness levels above that of HfC alone. Residual stress measurements show a compressive stress to be present, with the exception of the -25V sample where the stress was tensile. However, compositional analysis of the biased samples by XPS reveals that Si content in the films is reduced by the application of substrate bias. Consistent with this, the films with higher bias have larger grain sizes and better crystallinity. For the Ti-Hf-C films, the results for hardness vs. bias are consistent with known stress and densification effects of the bias, and values are consistent with rule-of-mixtures expectations.
Changes in Surface Mechanical Properties Through Electrochemical Modifications
Authors: McCann Martha M. , Corcoran Sean G.
Published: April 2011

The mechanical response of materials can be dramatically altered by the presence of absorbed species on the surface. An electrochemical environment enables discrete control of the surface, keeping it clean (comparable to ultra-high vacuum) and inducing stable stress states. Applying a potential to the surface alters surface charge, which changes the surface free energy. Oxides are easily added or removed. Utilizing the phenomenon of underpotential deposition (UPD), one monolayer of metal can be added to a surface. The degree of lattice mismatch between the metal and the deposited monolayer will also vary the stress state of the surface. The changes in the mechanical properties of these highly controlled surfaces are measured by in-situ nanoindentation at various potentials. Nanoindentation of single crystals with very low dislocation densities allows careful observation of dislocation behavior with applied load. This enables the identification of dislocation mechanisms by quantifying the changes in mechanical properties under specific environments. Au has been extensively studied in electrochemistry literature; it is well behaved and well characterized. It is a model system that has demonstrated variation in mechanical properties in different electrochemical states. Lessons learned on Gold have also been applied to Zn and Ni systems.
Functionally Graded CVD Mullite Coatings
Authors: Basu Soumendra N. , Sarin Vinod K.
Published: April 2011

Functionally graded mullite (3Al2O3.2SiO2) coatings were deposited on SiC substrates by Chemical Vapor Deposition (CVD) using the AlCl3-SiCl4-CO2-H2 system. It was found that due to preferential adsorption, coatings on SiC started off being Si-rich, while coatings on alumina substrates started out being Al-rich. In either case, if the coating composition was not close to stoichiometric mullite, the microstructure consisted ofg-Al2O3 nanocrystallites imbedded in a vitreous SiO2-rich matrix (nanocrystalline microstructure). On grading the composition, mullite grains nucleated when the composition of the growing nanocrystalline coatings reached a narrow surface composition range of Al/Si molar ratio of 2.9-3.4. Once nucleated, columnar mullite grains could be graded to highly nonstoichiometric Al-rich compositions. However, if the nucleated mullite grains were graded to be Si-rich, the mullite structure could not be sustained, and the coating reverted back to the nanocrystalline microstructure. This phenomenon is explained on the basis of the linkage of coordination polyhedra in the atomic structure of mullite.
Relationships between the structural, chemical, and mechanical properties of Si-aC:H thin films
Authors: Evans Ryan D. , Doll Gary L. , Morrison Philip W. , Bentley James , More Karren L. , Glass Jeffrey T.
Published: April 2011

Silicon-incorporated amorphous hydrocarbon (Si-aC:H) films with varying Si contents were deposited onto a Ti interlayer on Si and steel substrates by reactive sputtering in an unbalanced magnetron sputtering system. The objective of this study was to measure and relate the structural, chemical, and mechanical properties of these Si-aC:H films. Transmission electron microscopy revealed that the Si-aC:H phase is amorphous and TiC exists at the Si-aC:H/Ti phase boundary for all compositions. Mechanical properties such as hardness, indentation modulus, and intrinsic stress decreased with increasing Si and H content in the films, for Si/C ≥ 0.04. XPS measurements suggested that this is most likely due to the decreasing presence of a C-C sp3 interlinked network, accompanied by an increase in C-H and Si-H bonds. This conclusion was supported by radial distribution functions obtained using extended electron energy-loss fine structure analysis (EXELFS).
The Structures of Copper-Doped Carbon Aerogels Prepared by an Ion Exchange Method
Authors: Yoshizawa Noriko , Fu Ruowen , Dresselhaus Mildred S. , Dresselhaus Gene , Satcher Joe , Baumann Ted
Published: April 2011

Abstract -- The copper-doped carbon aerogels were fabricated by ion exchange method. Their structures were investigated by surface area detection, TEM, SEM and XPS. The experimental results showed that the copper-doped carbon aerogels produced have low mass density, a high density of nano-pores and high surface areas. Many copper nano-particles were produced after carbonization of copper-doped carbon aerogels. Before carbonization, part of the copper atoms were reduced into low valence compounds, such as Cu2O.
Nanoscale Electrochemical Deposition of Metals on FIB Sensitized p-Type Silicon
Authors: Spiegel Adrian , Döbeli M. , Schmuki Patrik
Published: April 2011

Sub-micrometer copper nanostructures were deposited on p-type silicon (p-Si) by means of a selective electrochemical reaction. Ga+-ions from a focused ion beam (FIB) were used to 'write' damage patterns on p-Si; in a subsequent electrochemical reaction Cu was deposited selectively at these defect sites. So far we have been able to obtain Cu structures with a lateral resolution of 300nm, which is also the limit of the FIB currently used.

The process may offer advantages over traditional lithographic methods for producing nanometer sized metal structure on Si as no masking steps are required. Also, structures with a lateral resolution in the sub- 100nm region seem possible; so far the process has only been limited by the FIB's lateral resolution.
Effects of Mask Materials on Near Field Optical Nanolithography
Authors: McNab Sharee J. , Blaikie Richard J.
Published: April 2011

Simulations have been performed to study the effects of different masking materials (Cr, Au, W and Si) on near field optical contact lithography. For near field amplitude masks it is found that Cr is an excellent material at blue/UV wavelengths, due to its small skin depth. Au is too transmissive to be considered. W has a small skin depth like Cr, although its dielectric behaviour at blue/UV wavelengths leads to image reversal phenomena that may be undesirable. Image reversal is even more pronounced for Si. For Evanescent Interferometric Lithography (EIL) - a technique that relies on surface-plasmon-induced resonant enhancement of the evanescent fields beneath a grating - Cr and W are again superior to Au, and significant intensity enhancements are predicted beyond the grating cutoff. For Si the resonant enhancements can be very large and narrow band, which may be of great advantage. For example, near field exposure intensity approximately 100 times the incident intensity is predicted for a 270 nm period silicon grating illuminated at a wavelength less than 10 percent higher than cutoff.
Design, Synthesis and Electrospinning of a Novel Fluorescent Polymer for Optical Sensor Applications
Authors: Lee Soo-Hyoung , Ku Bon-Cheol , Wang X. , Samuelson L.A. , Kumar J.
Published: April 2011

This work describes the synthesis and electrospinning of new fluorescent polymers and their use for the fabrication of optical chemical sensors. A new fluorescent monomer was first synthesized by coupling reactions between methacryloyl chloride and a pyrene derivative, 1-pyrene butanol. Fluorescent polymers containing pyrene molecules were then obtained by the copolymerization of this monomer with methylmethacrylate using 2,2'-azobisisobutyronitrile as the initiator. These polymers show distinct and well-defined fluorescence that is characteristic of the pyrene chromophores. Electrospinning was used to process these polymers into high surface area nanofibrous membranes for optical sensing. The resulting membranes show a high sensitivity to 2,4-dinitro toluene based on the fluorescence quenching of the pyrene chromophores. Fluorescence intensities decreased with increasing concentration of the 2,4-dinitro toluene. The quenching behavior follows Stern-Volmer bimolecular quenching kinetics. The synthesis, characterization, electrospinning fabrication, and sensing capability of these polymers will be discussed.
Reductive photopatterning of phenylene-vinylene-based polymers
Authors: Kavc T. , Langer G. , Kern W. , Ruplitsch A. , Mahler K. , Stelzer F. , Hayn G. , Saf R. , List E.J.W. , Zojer E. , Ahmed M. T. , Pogantsch A. , Iskra K.F. , Neger T. , Hörhold H.-H. , Tillmann H. , Kranzelbinder G. , Toussaere E. , Jakopic G.
Published: April 2011

Photochemical methods were developed to obtain a variation of the refractive index in aromatic polymer surfaces and a change in the photoluminescence characteristics of phenylenevinylene-based polymers. Films of aromatic polymers, among them polystyrene (PS), poly(2-vinylnaphthalene) (PVN) and derivatives of poly(p-phenylene-vinylene) (PPV) were UV irradiated in the presence of gaseous hydrazine (N2H4). The photoreaction led to a strong reduction of the refractive index of the polymers due to a hydrogenation of the aromatic units. In the case of PPV, we observed reductive photobleaching. This new technique was employed to produce photogenerated patterns in PPV. The results are compared to oxidative bleaching.
Singlet and Triplet Energy Transfer in Phosphorescent Dye Doped Polymer Light Emitting Devices
Authors: Noh Yong-Young , Lee Chang-Lyoul , Lee Hae Won , Cho Hyun-Nam , Kim Jang-Joo
Published: April 2011

Effect of host polymers on energy transfer in phosphorescent dye doped polymer light emitting devices has been investigated. Poly (N-vinylcarbazol) [PVK] and poly (9,9'-di-n-hexyl-2,7-fluorene-alt-1,4(2,5dinhexyloxy) phenylene) [PFHP] were examined as the host materials for the phosphorescent dyes fac tris(2-phenypyridine) irdium(III) [Ir(ppy)3] and 2,3,7,8,12,13,17,18-octaethyl-21H,23H-porphyrin platinum(II) [PtOEP]. The host and guest materials have the large spectrum overlap between the emission of the hosts and absorption of the guests. When the guests were doped in PVK, the singlet-singlet and triplet-triplet energy transfer took place efficiently. On the contrary, the energy transfer did not take place from φ-conjugated polymer PFHP to the guests, even though common requirements for Förster and Dexter energy transfer were fulfilled. Host aggregation in PFHP based phosphorescent dye doped light emitting devices can play an undesired role obstructing efficient energy transfer.
Optoelectronic Junction Devices Based on Organic/Inorganic Hetero-paired Semiconductors
Authors: Schroeder R. , Ullrich B.
Published: April 2011

The use of hybrid devices consisting of organic and inorganic semiconductors provides many advantages for optoelectronic applications, such as combining the high charge carrier mobilities in inorganic polycrystalline thin films and high photosensitivity, intense photoluminescence, and ease of deposition of conjugated molecules. In this paper, thin film hybrid structures based on organic conjugated molecules and II-VI inorganic semiconductors were fabricated using spin-coating, evaporation and pulsed-laser deposition (PLD), respectively. A promising hetero-pairing is CdS and DQP, a diisoquinoline perrylene derivate, with the potential to form sensitive photodiodes and effective solar cells. Varying the deposition techniques alters the quality of the interface between CdS and DQP and results in different efficiencies of charge collection and recombination in the device.
Rational Design of Organic Electro-Optic Materials
Authors: Jen Alex , Neilsen Robert , Robinson Bruce , Steier William H. , Dalton Larry
Published: April 2011

A number of material properties must be optimized before organic electro-optic materials can be used for practical device applications. These include electro-optic activity, optical transparency, and stability including both thermal and photochemical stability. Exploiting an improved understanding of the structure/function relationships, we have recently prepared materials exhibiting electro-optic coefficients of greater than 50 pm/V and optical loss values of less than 0.7 dB/cm at the telecommunication wavelengths of 1.3 and 1.55 microns. When oxygen is excluded to a reasonable extent, long-term photostability to optical power levels of 20 mW has been observed. Photostability is further improved by addition of scavengers and by lattice hardening. Long-term (greater than 1000 hours) thermal stability of poling-induced electro-optic activity is also observed at elevated temperatures (greater than 80°C) when appropriate lattice hardening is used. The successful improvement of organic electro-optic materials rests upon (1) attention to the design of chromophore structure including design to inhibit unwanted intermolecular electrostatic interactions and to improve chromophore instability and (2) attention to processing conditions including those involved in spin casting, electric field poling, and lattice hardening. A particularly attractive new direction has been the exploitation of dendrimer structures and particularly of multi-chromophore containing dendrimer structures. This approach has permitted the simultaneous improvement of all material properties. Development of new materials has facilitated the fabrication of a number of prototype devices and most recently has permitted investigation of the incorporation of electro-optic materials into photonic bandgap and microresonator structures. The latter are relevant to active wavelength division multiplexing (WDM). Significant quality factors (greater than 10,000) have been realized for such devices permitting wavelength discrimination at telecommunication wavelengths of 0.01 nm.
Low-loss Polymer Optical Waveguides with High Thermal Stability
Authors: Kang Jae-Wook , Kim Jae-Pil , Lee Won-Young , Kim Joon-Sung , Lee Jae-Suk , Kim Jang-Joo
Published: April 2011

We synthesized novel cross-linkable fluorinated copoly(arylene ether sulfide)s for optical waveguide applications, which have high thermal stability, high optical transparency in the infrared communication region, and much smaller birefringence than other thermally stable fluorinated polyimides. The refractive index of the material can be easily controlled from 1.515 to 1.587 by changing the copolymer composition in the materials. The birefringence of the cured polymers were 0.0031∼0.0039 at the wavelength of 1.55 μm. This is much lower than those of fluorinated polyimides for optical waveguides. The refractive index of fluorinated poly(arylene ether sulfide) (FPAESI) after being stored at 100 °C for 1000 hr remains almost constant demonstrating the thermal stability. The propagation loss of the channel waveguides fabricated using reactive ion etching was less than 0.4 dB/cm at the wavelength of 1.55 μm.
XRD, SEM and TEM Study of the Gd-Doped Zirconolites
Authors: Stefanovsky Sergey V. , Troole Albert Y. , Lapina Maria I. , Nikonov Boris S. , Sivtsov Anatoliy V. , Yudintsev Sergey V.
Published: April 2011

Ceramic samples with formulations Ca1-xGdxZrTi2-xAlxO7(0 ≤ x ≤1) were prepared by cold pressing in pellets at 200 MPa followed by their sintering at either 1400 or 1500 °C for 5 hours. All the samples produced were single phase with rare grains of cubic zirconia based solid solution in the samples with high Gd and Al contents (x = 0.9 and 1.0). The samples produced at 1500 °C were more homogeneous and less porous than the samples sintered at 1400 °C. From SEM/EDS data average compositions of zirconolite in the samples are very close to specified formulation (within experimental error), for example, the zirconolite formula in the ceramic with x = 1 was found to be Gd1.04Zr1.02Ti1.07Al0.85O7. XRD and TEM patterns showed monoclinic (2M) structure for zirconolites, which transforms to higher symmetry modification within 0 ≤ x ≤ 0.5 compositional range. Zirconolite with high Gd content x →1 forms two varieties with trigonal and orthorhombic structure.
Performance Assessment of Low-Level Waste Disposal Facilities Using Coupled Unsaturated Flow and Reactive Transport Simulators
Authors: Bacon Diana H. , McGrail B. Peter , Freedman Vicky L. , Ventura Giancarlo , Risoluti Piero , Krupk Kenneth M.
Published: April 2011

Recent advances in the development of reactive chemical transport simulators have made it possible to use these tools in performance assessments (PAs) for nuclear waste disposal. Reactive transport codes were used to evaluate the impacts of design modifications on the performance of two shallow subsurface disposal systems for low-level radioactive waste. The first disposal system, located at the Hanford site in Richland, Washington, is for disposal of lowlevel waste glass. Glass waste blocks will be disposed in subsurface trenches, surrounded by backfill material. Using different waste package sizes and layering had a small impact on technetium release rates to the vadose zone. The second disposal system involves a hypothetical repository for low-level waste in Italy. A model of uranium release from a grout waste form was developed using the STORM reactive transport code. Uranium is predicted to be relatively insoluble for several hundred years under the high-pH environment of the cement pore water. The effect of using different filler materials between the waste packages on uranium flux to the vadose zone proved to have a negligible impact on release rates.
Evaluating Cladding Creep during Dry Storage and Repository Emplacement
Authors: Siegmann Eric , Macheret Pierre
Published: April 2011

Creep strain has been identified as the dominant failure mode for commercial spent nuclear fuel cladding during dry storage, including the vacuum drying phase. It could also be important during the early period of repository closure. A statistical analysis of creep failure during these three phases was performed. Statistical analysis is an important tool for predicting fuel behavior and the distributions can be modified for specific applications. A burnup distribution (rod average = 44 MWd/kgU, range = 2 to 75 MWd/kgU) was assumed and a distribution of rod properties, including stress was developed. The Murty creep correlation was selected after comparing six different correlations with results from five different experiments. It was then modified to better predict irradiated cladding creep data. Creep failure criteria is a Complementary Cumulative Distribution Function (CCDF) based on 52 failure tests. The fuel rods are exposed to three consecutive temperature histories that are typical of what is to be expected: 24 hours of vacuum drying, 20 years dry storage, and 1000 years of repository thermal history. Each phase has a peak temperature, treated as an independent variable, and temperature history taken from the literature. Uncertainties in the temperatures and strain rate are included. The radial temperature distribution across the waste package is also modeled. For the first phase, vacuum drying, rod failures start to occur at about 550°C and exceed 1% failure at 600°C. With a peak vacuum drying temperature of 430°C, rods begin to fail during dry storage when the peak temperature reaches 400°C and approached a 1% failure level at 450°C. With representative peak temperatures of 430°C for drying and 350°C for dry storage, rod failures start to occur during repository closure at a peak cladding temperature of 390°C. They reached 1% at about 430°C. In the current repository design, the cladding temperatures are below 210°C and rod failures from creep are not expected
FTIR Characterization Of PZT Nano Fibers Synthesized from Metallo-organic Compounds Using Electrospinning
Authors: Wang Yu , Santiago-Avilés Jorge J.
Published: April 2011

We have synthesized Pb(Zr0.54Ti0.48)O3 fibers with diameter ranging from 500 nm to several microns using electrospinning and metallo-organics decomposition (MOD) techniques. By a refinement of our electrospinning technique, i.e. by increasing the viscosity of the precursor solution, and by adding a filter to the tip of the syringe, the diameter of synthesized PZT fibers has been reduced to the neighborhood of a hundred nanometers. The complex thermal decomposition was characterized using Fourier-transform infrared (FTIR) spectroscopy and x-ray diffraction (XRD). It was found that alcohol evaporated during electrospinning and that the organic groups had pyrolized before the intermediate pyrochlore phase was formed. There is a good correspondence between XRD and FTIR spectra. It was also found that a thin film of platinum coated on silicon substrate surface not only seems to have catalyzed the phase transformation to PZT but also favored the formation of 110 texture in the synthesized PZT fibers.
Initial Development of a Portable Acoustic Array on a Large-Scale E-Textile Substrate
Authors: Luthy K. A. , Mattos L. S. , Braly J. C. , Grant E. , Muth J. F. , Dhawan A. , Natarajan K. , Ghosh T. , Seyam A.
Published: April 2011

Electronic textiles offer possibilities for producing large-area sensors circuits on conformal substrates. To demonstrate this concept, a 5×4 element acoustic array was produced on a 3m × 1m fabric substrate. In the course of fabricating the acoustic array a variety of production issues were identified that impacted the performance of the prototype when experimental tests were carried out with this prototype acoustic array. Fabric-based acoustic array design and production, along with design issues related to scaling an acoustic array to handle larger numbers of microphones on large-area fabrics, are the focus of this paper.
Resonant photoluminescence and excitation spectroscopy of CdSe/ZnSe and CdTe/ZnTe self-assembled quantum dots
Authors: Nguyen T. A. , Mackowski S. , Rho H. , Jackson H. E. , Smith L. M. , Wrobel J. , Fronc K. , Kossut J. , Karczewski G. , Dobrowolska M. , Furdyna J.
Published: April 2011

We show that two major carrier excitation mechanisms are present in II-VI self-assembled quantum dots. The first one is related to direct excited state – ground state transition. It manifests itself by the presence of sharp and intense lines in the excitation spectrum measured from single quantum dots. Apart from these lines, we also observe up to four much broader excitation lines. The energy spacing between these lines indicates that they are associated with absorption related to longitudinal optical phonons. By analyzing resonantly excited photoluminescence spectra, we are able to separate the contributions from these two mechanisms. In the case of CdTe dots, the excited state – ground state relaxation is important for all dots in ensemble, while phonon-assisted processes are dominant for the dots with smaller lateral size.
Charge Retention in Single Silicon Nanocrystal Layers
Authors: Krishnan Rishikesh , Krauss Todd D. , Fauchet Philippe M.
Published: April 2011

Silicon (Si) nanocrystals formed by controlled thermal crystallization of amorphous silicon dioxide (a-SiO2)/amorphous silicon (a-Si)/amorphous silicon dioxide (a-SiO2) layers hold considerable promise for application in non-volatile memory products and optoelectronic devices. The size of the nanocrystals is fixed by the thickness of the Si layer and strong quantum confinement is provided in the vertical (growth) direction by the insulating a-SiO2 layers. However, the extent of quantum confinement in the lateral dimensions remains to be established. Electron energy loss spectroscopy (EELS) measurements performed within a scanning transmission electron microscope (STEM) indicate that the nanocrystals are laterally isolated by approximately 2nm of a-SiO2. The confinement potential provided by this barrier is insufficient to localize carriers within a nanocrystal for prolonged durations and can permit quantum mechanical tunneling via wave function overlap between adjacent nanocrystals. Charge leakage kinetics within a sheet of Si nanocrystals was studied using electric force microscopy. Approximately 750 electrons were injected within a 100nm radius circular patch with an atomic force microscope cantilever. The entire charge dissipated from this area in 70min via lateral conduction routes. With a goal of localizing the injected charge and enhancing its retention time, the samples were subjected to relatively low temperature dry oxidation at 750°C. After 20 min of oxidation, retention times above 400 minutes were observed.
Formation of SiGe Nanoparticles by Dry and Steam Thermal Oxidation of Thin Polycrystalline Layers
Authors: Ortiz M. I. , Ballesteros C. , Rodríguez A. , Sangrador J. , Rodríguez T. , Avella M. , Martín P. , Jiménez J.
Published: April 2011

Nanoparticles embedded in a dielectric medium have been formed by dry and steam thermal oxidation at specific temperatures and process times of polycrystalline Si0.7Ge0.3 layers deposited on thermally oxidized Si substrates. We present a study of the influence of the oxidation process parameters: oxidation atmosphere, temperature and time on: a) the composition of the grown oxide, b) the Ge segregation, c) the formation of nanoparticles, their composition and size, and d) the properties of the cathodoluminescence emission of the oxidized films. Oxidation in a dry O2 atmosphere results in a full Ge segregation. The formation of Ge islands embedded in an oxide matrix is demonstrated. Ge segregation is slower in steam thermal oxidation than in dry O2. In this case Ge-rich SiGe particles are formed. In both processes, an important increase in the cathodoluminescence emission associated with the presence of Ge rich nanoparticles is obtained.
Effect of Surface Treatments in Nanocrystalline Silicon
Authors: Mandal N. P. , Dey S. , Agarwal S. C.
Published: April 2011

Exposure to ammonia (NH3) increases the dark current (DC) in porous silicon (PS), but evaporated selenium (Se) deposited on PS decreases DC. Photoluminescence (PL) measurement shows that there are two types of centers. PL in one region of PS (Peak ∼ 800nm) initially increases with the NH3 exposure and then decreases. But the PL from another region of PS has a peak at ∼ 780nm and it decreases continuously with the NH3 exposure. Dipping PS in water and drying in air shifts the PL peak at 800 nm to 744 nm. Atomic Force Microscopy (AFM) shows that the as prepared sample has wires of diameters 2.4nm, 3.4nm, 4.6nm and bigger. However, in the AFM images of the water treated sample the wires of diameters 3.4nm and 4.6nm are absent. The PL results are explained using the AFM data and the John-Singh model of quantum confinement.
Comparative Study Of The Growth Curves Of B. subtilis, K. pneumoniae, C. xerosis And E. coli Bacteria In Medium Containing Nanometric Silicon Particles
Authors: Pérez Lilyanna , Flores Marjorie , Avalos J. , San Miguel L. , Resto O. , Fonseca L.
Published: April 2011

In this research nanometric particles from luminescent (625nm) porous silicon film were synthesized. This particles were later inoculated in bacterial strains of B. subtilis (BSi) and K. pneumoniae (KSi). A comparison of the behavior of their growth curve and the ones reported for C. xerosis (XSi) and E. coli (ESi) in presence of silicon nanoparticles is presented. The growth curve of BSi, as well as the KSi, present changes compared to their standard curves. The BSi growth curve grows below the standard curve after the fifth hour, while in the KSi this happens after the eighth hour. Based on our preliminary findings we can speculate that at this point in time a critical population is present, and this may give rise to the possible incorporation of the silicon particles by the bacteria, or a possible pleomorphism inhibits reproduction. The stationary region, in both cases, takes place sooner than in the standard curve. No significant oscillations are observed in any case, which differs form the XSi curve, were oscillations of intervals of almost 1 hour were reported. In addition, these curves have a different behavior when compared to the ESi growth curve, in which no significant differences between the standard and the particle containing sample were reported.
Evidence of Ti-related Inclusions in an Al Alloy Interconnecting Layer for Nanometer 256MBit DRAM Semiconductor Devices Characterized by TEM, STEM, EELS Elemental Mapping, and XEDS Linescan
Authors: Zhao Wei , Graca Steve
Published: April 2011

With the introduction of high aspect ratio and steep geometries in deep-subquarter-micron dynamic random access memory (DRAM) device, it becomes more and more critical to understand the formation of undesired intermetallic Ti-Al phases in Al-metallization and thus better-control the profile of interconnectors. In this article, Ti-related inclusions in Metal 1 (M1) interconnecting layer (an AlCu-0.5% alloy) originated from the bottom Ti liner were characterized with an Analytical TEM. Samples were cleaved from nanometer 256Mbit dynamic random access memory DRAM devices. The TEM employed is a JEOL 2010F with a field emission gun (FEG) and running at 200KV acceleration voltage. Correlations among transmission electron microscopy (TEM), scanning transmission electron microscopy (STEM), electron energy loss spectroscopy (EELS) elemental mapping, and x-ray energy dispersive spectroscopy (XEDS) elemental linescan were established. The results here not only provide important feedbacks to semiconductor product integration and optimization, but also demonstrate the full-functionality of the start-of-the-art analytical TEM in investigations of nanometer semiconductor devices.
Moisture effects of crack initiation in nanocrystalline silicon: a hybrid density-functional/molecular-dynamics study
Authors: Ogata Shuji , Belkada Rachid , Shimojo Fuyuki , Nakano Aiichiro
Published: April 2011

A hybrid quantum-mechanical/molecular-dynamics simulation is performed for a cracked-Si model under tension with multiple H2O molecules around the crack-front, to investigate possible effects of the environmental molecules on fracture initiation in Si. Electronic structures near the crack-front are calculated quantum-mechanically on the basis of the density-functional theory. The quantum-mechanical atoms are embedded in a system of classical atoms. The hybrid simulation results show significant effects of stress intensity factor on the reaction processed of the H2O molecules at the crack front.
Sol-gel synthesis and characterization of CuO–based nanosystems
Authors: Armelao Lidia , Barreca Davide , Bertapelle Manuel , Bottaro Gregorio , Sada Cinzia , Tondello Eugenio
Published: April 2011

This paper is focused on the sol-gel synthesis and characterization of CuO-based nanosystems both in the form of supported films and as guest nanoclusters embedded in a silica matrix. In both cases copper acetate (Cu(CH3COO)2· H2O) was used as Cu source and, for the CuO :SiO2nanocomposite systems, tetraethoxysilane (Si(OC2H5)4, TEOS) was adopted as silica precursor. Films were obtained by a dip-coating procedure and subsequently treated in air between 100 and 900°C. The system evolution on thermal annealing was studied by X-ray photoelectron spectroscopy (XPS), Glancing-Incidence X-ray diffraction (GIXRD) and optical absorption. Irrespective of the processing conditions, the formation oftenorite(CuO) crystallites with nanometric dimension was observed. In the nanocomposite samples, copper was homogeneously distributed in the host matrix and stable CuO nanoclusters (φ ≈ 15 nm) were obtained.
Techniques and Applications for Non-Planar Lithography
Authors: Rogers John A.
Published: April 2011

Certain classes of three dimensional nanostructures can be fabricated by contact printing patterns onto curved or non-flat surfaces. This paper reviews some of our work that demonstrates this approach by using microcontact printing to form a range of three dimensional structures with feature sizes as small as 1–2 microns and it demonstrates their use in a variety of functional devices. We also describe a nanotransfer printing technique with operational characteristics that are similar to those of microcontact printing but which enables nanometer resolution. High resolution replica molding techniques provide a method for producing copies of some of these printed structures.