bluuebunny/crossref_metadata_2025 huggingface dataset:
Novel Methods to Reduce Pattern Size and Pitch for Data Storage Using Electron Beam Writing
Authors: Lu Zhou , Cartwright A. N.
Published: April 2011

Pattern size and pitch are two major factors that directly affect the capacity of a data storage unit. Electron beam lithography, because it can be used for direct writing at the nanometer scale, is one of the potential candidates to fabricate ultra-fine and ultra-compact patterns for the next generation of data storage media.

In the paper, we present methods to reduce the pattern size and pitch written by electron beam on positive tone resist Poly(methylmethacrylate) (PMMA). The first method uses a writing dose which is much lower than the critical dose of the PMMA. However, in this technique, the distance between the adjacent writing spots (which are approximately Gaussian in spatial extent) is finely adjusted until the partially overlapping Gaussian functions form a contour with periodic dose peaks higher than the critical dose. This overlapping exposure results in a periodic exposure of the PMMA. Most importantly, this writing strategy, using the overlapping of low dose Gaussian beams, results in patterns with smaller size and pitch compared to the conventional methods that use a higher writing dose than the critical dose. To further improve the results, we use ultrasonic development in combination with cold development to greatly increase the resist contrast. The increased contrast results in smaller pattern sizes, and enables smaller pattern pitches, as well as improving pattern uniformity and reproducibility.

Finally, as a demonstration of the technique using a conventional beam voltage of 15kV, we achieve ultra-fine and high density patterns with ∼10nm linewidths and 50nm in pitch, which corresponds to a storage capacity near 200 billion bits/inch2. In comparison, standard techniques (using a dose slightly higher than the critical dose and normal development strategy), we can only obtain patterns with linewidths of about 20-30nm and pitch of about 100nm.
Impact of planarization sheet addition on full wafer printing uniformity
Authors: Leveder Tanguy , Landis Stefan , Davoust Laurent , Chaix Nicolas
Published: April 2011

Uniformity of nanoimprint lithography has been quantitatively studied through the ability to replicate regular lines arrays by wafer-to-wafer imprint. Two statistic coefficients have been defined in order to quantify the local uniformity and the ability to identically imprint two similar areas respectively. Those coefficients enable to compare different imprint profiles in terms of uniformity and to point out the efficiency of soft layers insertion into the imprint stack.
Development of 3-D Magnetic Nano-Arrays by Electrodeposition into Mesoporous Silica Films
Authors: Manning Jason , Campbell Roger , Bakker Martin Gerard , Li Xuefa , Lee Dong Ryeol , Wang Jin
Published: April 2011

The development of periodic nanostructures fabricated by self-assembly of surfactants and block co-polymers has opened up the possibility of generating periodic magnetic nanostructures of types not accessible by self-assembly of nano-particles. The fabrication of mesoporous silica thin films around self-assembled block co-polymers is well established. Common structures for such films are SBA-15 which consists of hexagonal arrays of cylindrical pores and SBA-16 which has face centered arrays of spherical voids. These pores are connected by 1-2 nm thick flaws in the continuous silica phase producing an effectively continuous porous phase. After removal of the block co-polymer template, electrodeposition into the mesoporous silica thin films produces arrays of 5-10 nm diameter nano-wires and nano-particles. We have demonstrated that such materials can be fabricated on a wide range of metal substrates. Characterization by Scanning Electron Microscopies shows that the mesoporous silica is well ordered over micron scale areas. Grazing Incidence Small Angle X-ray Scattering (GISAXS) studies shows diffraction spots, consistent with the entire film being well ordered. GISAXS also shows that the mesoporous silica films survive removal of the template and electrodeposition of nickel and cobalt into the mesoporous silica films. Such films are of interest for their magnetic properties, as the nanophase and scale can be independently varied. Further, the presence of nanowires inside an insulator suggests that these films might also be of interest as the current confining element for Confined Current Path-Current Perpendicular to Plane GMR sensors.
Nanoelectrode Lithography
Authors: Yokoo Atsushi , Namatsu Hideo , Oda Masatoshi
Published: April 2011

Nanoelectrode lithography is a pattern duplication method which combine template and electrochemical reaction. With the nanoelectrode lithography, electrochemical reaction occurs along with the conductive area of the template, and oxide pattern can be directly fabricated on a surface of semiconductor or metal layer. This "Resist-less patterning" method may have advantage for precise patterning in the future.
Ab Initio Investigation of a CoFeB/MgO/CoFeB Interface
Authors: Domingos Helder Sousa , Martins José Julio
Published: April 2011

We have carried out density functional calculations on a CoFeB/MgO/CoFeB interface with amorphous electrodes. The interface was shown to be stable with 4 mono-layers (ML) and to contain spin-polarized metal-oxigen bonds at the interface. The interfacial energy was estimated, to be used as a comparative measure of stability. In addition, the exchange-coupling indicated a favouring of the anti-paralell magnetization configuration with respect to the paralell for 4 ML.
Electron Holography of Ferromagnetic Nanoparticles Encapsulated in Three-Dimensional Arrays of Aligned Carbon Nanotubes
Authors: Koziol Krzysztof K. , Kasama Takeshi , Dunin-Borkowski Rafal E. , Barpanda Prabeer , Windle Alan H.
Published: April 2011

Closely-spaced ferromagnetic nanoparticles are of interest for applications that include data storage, magnetic imaging and drug delivery. Here, we use off-axis electron holography and micromagnetic simulations to study the magnetic properties of iron nanoparticles encapsulated in three-dimensional arrays of carbon nanotubes. The nanotubes constrain the shapes, sizes and separations of the nanoparticles, as well protecting them from oxidation. We record magnetic induction maps from individual particles that each contain a single magnetic domain. We also discuss the use of electron holography to assess magnetostatic interactions between adjacent particles.
Enhancement of Plasmon Propagation Length Using Metamaterials
Authors: Brandon David , Krokhin Arkadii , Neogi Arup
Published: April 2011

We propose using a strongly anisotropic dielectric as a substrate for a thin metallic film along the boundary of which surface plasmon excitations may propagate. We show that the propagation range of surface plasmons is increased if the substrate is a birefringent dielectric crystal with a properly oriented optical axis. The increase of the propagation range depends on the degree of anisotropy, and, consequently, it turns out to be small for substrates of natural optical crystals, where anisotropy is weak. However, in specially designed photonic crystals, the anisotropy may be very strong, thus leading to appreciable increase of the propagation range. A photonic-crystal substrate, being a medium with nonlinear dispersion, also affects the dispersion law of the surface plasmon. All these effects may be used in order to increase the efficiency of modern plasmonic and optoelectronic devices.
Screen Printed Frequency-Selective Surfaces on Rigid, Flexible and Elastic Substrates
Authors: Kistenmacher Thomas , Francomacaro Shaun , Brawley Ben , Awadallah Ra'id , Vichot Paul , Fitch Michael , Spicer Jane , Wickenden Dennis
Published: April 2011

A series of frequency-selective surface (FSS) arrays based on nested split-ring triangle resonators have been fabricated using screen printing. A silver-filled polymer thick film (PTF) paste was selected as the active medium for the FSS arrays as it has good compatibility with the various substrates employed and is in itself naturally flexible. Substrates included FR4 boards and polyimide (PI), polyethylene terephthalate (PET) and silicone sheeting. Compared to arrays fabricated from Cu-clad FR4 board, the screen-printed arrays are resonance shifted owing to the magnitude of the dielectric constant and thickness of the various substrates. In addition, the quality factors of the screen-printed arrays are reduced compared to those fabricated from the more conductive Cu resonators. Despite these limitations, screen-printed arrays have considerable potential as components for low-cost flexible and conformal microwave devices.
Ferroelectric and Magnetic Characterization of Ferroic Pb(Fe0.5Nb0.5)O3 Ceramics
Authors: Raymond Oscar , Font Reynaldo , Alvarez Guillermo , Portelles Jorge , Srinivasan Gopalan , Siqueiros Jesús M.
Published: April 2011

Single phase multifunctional materials such as Pb(Fe0.5 Nb0.5)O3 (PFN), where ferroelectric and magnetic order coexist, are very promising and have great interest from the academic and technological points of view. PFN ceramics have been prepared from different kinds of FeNbO4 precursors with either monoclinic or orthorhombic structures. Crystallographic, compositional and surface morphological studies and the temperature-frequency response carried out and reported in previous works are summarized. Ferroelectric hysteretic, magnetic and magnetoelectric behaviors were measured. The remanent polarization (Pr) and coercive field (EC) as functions of temperature and external electric fields (Eext) were determined. Measurements of magnetic susceptibility (χm) exhibited antiferromagnetic order and, above the Núel point near 122 °K, Curie–Weis behavior; whereas a weak ferromagnetic observed from electron paramagnetic resonance (EPR) is discussed. However, magnetoelectric effects were not observed. Ferroelectric and magnetic behaviors, as functions of the kind of precursor used in the preparation, are discussed and correlated with the previous dielectric characterization where microstructural and equivalent circuit models were established using the impedance spectroscopy technique.
Cross-Sectional Observation of Nano-Domain Dots Formed in Congruent Single-Crystal LiTaO3
Authors: Cho Yasuo , Daimon Yasuhiro
Published: April 2011

Cross-sectional shapes of reversal nano-domain dots formed in a congruent LiTaO3 single-crystal recording medium were studied by scanning nonlinear dielectric microscopy (SNDM). Images obtained by SNDM measurements confirm that reversal nano-domain dots penetrate through the entire sample. The domain wall thickness was evaluated by the cross-sectional measurement results. The variation of the domain wall thickness as a function of sample thickness and of depth position was evaluated. It was found that thinner samples have a tendency to have thinner domain walls, and it was confirmed that the domain wall thickness at the bottom of the sample was thinner than at the front surface of the sample. A discussion of the measured result is also provided.
Dielectric Properties of Cr2O3 Doped (Ba,Sr,Ca)TiO3 Ceramics for Tunable Microwave Devices
Authors: Qin Bing , Jin Dengren , Chen Jinrong , Meng Zhongyan
Published: April 2011

Cr2O3-doped (Ba0.55Sr0.4Ca0.05)TiO3 ceramics were fabricated by the mixed-oxide method. Their dielectric properties were investigated with the variation of Cr3+ doping concentrations (0∼2.0mol%). All the BSCT specimens owned dense and homogeneous structure. Doping of Cr3+ could reduce the Curie temperature and their dielectric constant peak values, and improve the thermal stabilities of their dielectric properties. Both the dielectric constant and dielectric loss of the BSCT ceramics were reduced by doping Cr ions when the dopant concentration was lower than 1.5mol%. 1.0mol% Cr-doped BSCT specimens are expected to be the candidate materials for microwave tunable devices, whose tunability, dielectric constant and loss were 16.1%, 2700 and 0.24% respectively.
The Reconstructive Crystal Structure and the Exchange Energy
Authors: Yazdani Ahmad , Osati Araghi Reza , Arya Farid
Published: April 2011

In order to describe the role of temperature variation on suppress of broad range of magnetic transition, the effect of annealing on different samples of a Gd-based intermetallic compound (i.e., Gd2Au) is investigated. The X-ray, AC and D.C susceptibility and electrical resistivity measurements for different annealed samples revealed that: (i) A great exchange dispersion is observed in A.C susceptibility (ii) This unstable exchange can be stabilized at certain annealing temperature, where the short rang unstable Ferromagnetic (F.M) breaks down or even changes to an Antiferromagnetic (AF.M) stable state. (iii) The DC susceptibility shows a spin-glass like transition temperature at TN= 61 K, above which the compound exhibits a completely paramagnetic (P.M) behavior and is field independent. (iv) the iso-termal magnetization does not follow the field induced transition (F.I.T) and behaves completely as a paramagnet which is independent of the field up to the highest available fields. The electrical resistivity measurement shows: a) A pronounced sharp bend at TN=61 K is manifested in ρ(T). b)some strong peak of X-ray pattern change into double adjacent lines in some intervals of low temperatures
Nanodomain Size Distribution in Relaxor Ferroelectrics Determined from Temperature Dependent Raman Scattering
Authors: Gupta Sanju
Published: April 2011

Relaxors (PZN, in particular) is an important class of self-assembled nanostructure composite ferroelectric oxides (or perovskite) materials. The interesting features associated with the nanoregions/nanodomains required to describe these relaxors give rise to the most relevant device related characteristics and peculiar physical properties in these materials. In addition, they possess astronomical property coefficients by themselves or when modified with lead titanate (PT) forming solid solution. In the past, we conducted temperature dependent Raman scattering studies on solid solution (1−x)PZN−xPT relaxors single crystals with varying composition; x = 0.02, 0.085, and 0.11. These studies were performed to obtain relevant information about lattice/phonon dynamics for matching the application criteria such as electromechanical actuators. We showed that the sharp structural phase transition occurs at or near 460 K which is a first-order transition by fitting two spectroscopic variables in Raman spectra for one of the representative bands occurring at 277 cm−1. Besides structural phase transition, polarization mechanism for the unpoled (x = 0.02) and poled (x = 0.05) specimens is also investigated to understand the polarization mechanism in relaxors using Raman spectroscopy. The difference in the case of poled specimen is accounted for by the influence of residual electric field. Poling also suggested an enhanced local ordering and the increase in the volume of the polar nano-regions. In the present report, we attempted to determine the nanopolar region size and distribution using the above mentioned temperature dependent Raman spectra. We discuss the most suitable mathematical form of nanodomain size distribution for such inhomogeneous material is log-normal and it is bimodal depending upon the temperature regime in addition to composition. These studies helped to determine the size distribution of nanoscopic embodiments in relaxor ferroelectrics using Raman spectroscopy as a function of temperature which is a dynamical phenomenon.
Study of SrTiO3 Gate Dielectrics
Authors: Liu C.Y. , Tseng Tseung-Yuen
Published: April 2011

Among various possible candidates of high-k gate dielectrics, SrTiO3 plays an important role because it has high dielectric constant and it can be epitaxially grown on silicon substrate. The fabrication process and properties of SrTiO3 gate dielectrics are reported. The effect of the addition of SiO2 on the microstructure and electrical properties of SrTiO3 gate dielectric is also presented. The minimization of the effect of interfacial layer between SrTiO3 and Si is the most important issue for obtaining high quality high-k gate dielectrics. The possible methods to improve the interfacial properties and the measurement techniques to characterize the interfacial layer are discussed.
Ferroelectric Gate FET Memory based on Conduction of SBT-SiON Interface
Authors: Okuyama Masanori , Minami Takaaki , Lee Bong-Yeon , Kanashima Takeshi
Published: April 2011

A new type of ferroelectric gate field-effect transistor (FET) using ferroelectric-insulator interface conduction has been proposed. Drain current flows along the interface between the ferroelectric and insulator layers and requires no semiconductor. This FET is fabricated by forming of source and drain electrodes on a SiON/Si substrate, dpositing SrBi2Ta2O9(SBT) film, forming topgate electrode, and forming bottom electrode. Drain current versus topgate voltage characteristics show a clockwise hysteresis loop similarly to the conventional metal-ferroelectric-insulator-semiconductor-FET(MFIS-FET). This FET shows that the On/Off ratio of the drain current is 104 to 105 and the Off state current of about 10−9 A.
Rational Design of Highly Filled Reactive Resins for Electronic Material Applications with Multiple Performance Constraints
Authors: Duffy Daniel J , Xiao Allison
Published: April 2011

Cyanate ester resin and its blends with epoxy resin demonstrate a lower viscosity build up when filled with thermally treated silica fillers than with untreated silica fillers. The reduced viscosity build up resulting from the use of the thermally treated materials results in faster capillary flow rates by a factor of 2 to 5 with respect to untreated silica particles. Surface properties of the filler materials are used to interpret the viscosity and flow rate data and guide design of filler surface properties. The flow rate performance improvement contributes to design of new capillary underfill materials for electronic materials applications.
Effect of crystallization on Adhesion Strength of External Electrode in LTCC
Authors: Ko Minji , Lyoo SooHyun , Choi Yongseok , Kim Hyungho , Choo Hosung , Cho Beomjoon , Park EunTae
Published: April 2011

A mixture system of MO-SiO2(M: Ca, Sr, Ba) glass and Al2O3crystalline powder has been investigated as a substrate material for low temperature co-fired ceramics (LTCC). This type of glass-ceramic mixture is known to be crystallized during the sintering process. We found that the adhesion strength of external electrode was strongly related with sintering condition. Crystallization behavior was monitored by means of powder X-ray diffraction (XRD). The microstructure of sintered body after electroless plating was examined by Scanning Electron Microscopy (SEM). It was observed that the degree of crystallization was strongly affected by sintering condition. We focused ourselves on elucidating the relationship between the degree of crystallization and the adhesion strength of external electrode that was made by means of electroless plating.
Process and Material Requirements for Successful Heterogonous Passive Component Integration in RF System
Authors: Beyne Eric , De Raedt Walter , Carchon Geert , Soussan Philippe
Published: April 2011

Applications using rf radios operating at frequencies above 1GHz are proliferating. The highest operating frequencies continue to increase and applications above 10GHz and up to 77GHz are already emerging. Systems become more complex and devices need to operate at several different frequency bands using different wireless standards. The rf-front end sections of these devices are characterized by a high diversity of components, in particular high precision passive components. In order to be produced cost-effectively, these elements need to be integrated along with the semiconductor devices. This paper describes the requirements for successful integration of rf-passive devices and proposes multilayer thin film technology as an effective rf-integration technology.
A Charge Feedback Controller for a Piezoelectric Voltage Amplifier/Driver
Authors: Noras Maciej , McAnn Peter , Kieres Jerzy
Published: April 2011

In this paper, authors examine the design and implementation of a new charge feedback control circuitry for a voltage amplifier used in driving of a piezoelectric actuator. Actuators driven in the usual voltage feedback regime display a nonlinear voltage-displacement relationship, known as hysteresis. Use of the new charge feedback control circuitry resulted in significant reduction (70%) of the hysteresis-related nonlinearity.
Integration of PZT on SOI Wafers: Increasing Piezoelectric Film Thickness for Providing a Wide Range of Ultrasonic MEMS Applications
Authors: Belgacem Brahim , Calame Florian , Muralt Paul
Published: April 2011

Piezoelectric micromachined ultrasonic transducers comprising a 10 μm thick Si device layer and a 1-4 μm thick piezoelectric PZT layer were investigated. The PZT films were deposited by a sol-gel technique. The transverse piezoelectric coefficient was measured as -14.9 C/m2. The electromechanical coupling increased with PZT thickness, as expected. The influence of both the shape and area of the top electrode on the device performance has been investigated. The electromechanical coupling coefficient (k) and quality factor (Q) have been measured in air and were fitted to an equivalent circuit model. The maximal k2 was obtained as 7.8%.
High Density Direct Bond Interconnect (DBI) Technology for Three Dimensional Integrated Circuit Applications
Authors: Enquist Paul
Published: April 2011

A novel direct wafer bonding technology capable of forming a very high density of electrical interconnections across the bond interface integral to the bond process is described. Results presented include an 8 um interconnection pitch, die-to-wafer and wafer-to-wafer bonding formats, temperature cycling reliability × 10 greater than the JEDEC requirement, connection yield ∼ 99.999, > 50% part yield on parts with ∼ 450,000 connections, and < 0.1 Ohm connection resistance at 1pA without requiring a voltage surge to induce current.
Modeling and Simulation of Parasitic Effects in Stacked Silicon
Authors: Elst Gunter
Published: April 2011

Devices and interconnect structures of new semiconductor and packaging technologies show parasitic physical effects with a growing influences of the system behavior. Therefore, the design technology has to be developed and adjusted to ensure high system performance and reliability of these very complex systems on chip and in a stack. The influences of parasitic effects on the circuit behavior have to be minimized within the design process.

Typical parasitic effects of the Vertical System Integration (VSI®) by stacked silicon are discussed in this paper. Effects like electro thermal coupling, electromagnetic interactions, and the sensitivity due to parameter variations and their influence to the system behavior are identified and modeled. Approaches for minimization of these influences by design modifications are presented.
3-D Integration Technology for High Performance Detector Arrays
Authors: Temple Dorota , Bower Christopher A. , Malta Dean , Robinson James E. , Coffman Phillip R. , Skokan Mark R. , Welch Terry B.
Published: April 2011

This paper describes a technology for three-dimensional (3-D) integration of multiple layers of silicon integrated circuits. The technology promises to dramatically enhance on-chip signal processing capabilities of a variety of detector devices hybridized with Si electronics. The focus of the paper is on high performance infrared focal plane arrays based on HgCdTe, which offer the ultimate in infrared sensitivity and find application in high performance military systems. Performance data from test FPA devices with integrated multilayer Si stacks are discussed in this paper.
Damascene-Patterned Metal-Adhesive (Cu-BCB) Redistribution Layers
Authors: Gutmann Ronald J. , McMahon J. Jay , Lu Jian-Qiang
Published: April 2011

A monolithic, wafer-level three-dimensional (3D) technology platform is described that is compatible with next-generation wafer level packaging (WLP) processes. The platform combines the advantages of both (1) high bonding strength and adaptability to IC wafer topography variations with spin-on dielectric adhesive bonding and (2) process integration and via-area advantages of metal-metal bonding. A copper-benzocyclobutene (Cu-BCB) process is described that incorporates single-level damascene-patterned Cu vias with partially-cured BCB as the bonding adhesive layer. A demonstration vehicle consisting of a two-wafer stack of 2-4 μm diameter vias has shown the bondability of both Cu-to-Cu and BCB-to-BCB. Planarization conditions to achieve BCB-BCB bonding with low-resistance Cu-Cu contacts have been examined, with wafer-scale planarization requirements compared to other 3D platforms. Concerns about stress induced at the tantalum (Ta) liner-to-BCB interface resulting in partial delamination are discussed. While across-wafer uniformity has not been demonstrated, the viability of this WLP-compatible 3D platform has been shown.
Vertical Integration: A Confederacy of Alignment, Bonding, and Materials Technologies
Authors: Farrens Shari
Published: April 2011

Vertical or 3D integration is taking hold in both the CMOS IC industry and the MEMS industry. The need for smaller devices, lower power, increased functionality, and lower cost are driving the market toward chip and wafer level stacking. Equipment suppliers have been faced with numerous challenges to meet the demands of these emerging bonding applications. This paper will discuss the confederacy of alignment, bonding and materials unions that can lead to successful outcomes in integrated manufacturing.

1. Alignment strategies for 3D integration: IR, BSA, and ISA as they pertain to specific bond methods

2. Pros and Cons of 3D Bonding Techniques (Direct bonds, metal, adhesive, and eutectic)

3. Error analysis in alignment of 3D structures
3D Process Integration – Wafer-to-Wafer and Chip-to-Wafer Bonding
Authors: Matthias Thorsten , Wimplinger Markus , Pargfrieder Stefan , Lindner Paul
Published: April 2011

Many feasibility and design studies during the last years have shown that devices based on 3D chip stacking and integration can significantly outperform traditional planar (2D) devices. Furthermore, as packaging of the devices is a major cost factor, the possibility to integrate multiple functional entities in one package offers a huge potential for cost reduction. On research level the technical feasibility has been proven for a variety of processes. Today's focus lies on innovative manufacturing technologies and process integration schemes, which meet both, the economic and the technical demands.

Stacking of individual chips (both chip-to-wafer and wafer-to-wafer) has the inherent advantage that different functional subsystems like logic and memory can be processed on separate wafers thereby reducing the complexity and the number of process steps greatly. The individual chips can be processed on heterogeneous materials, in different fabs and by different producers.

Wafer-level integration has the advantage of higher throughput, enhanced cleanliness and the flexibility that standard fab equipment can be used for further processing. 3D integration applying chip-to-wafer bonding focuses on the yield (“good known die”) and enables to stack dies of different size e.g. several small dies on one big base die. This allows e.g. the integration of a logic device from a 300mm Si wafer with RF devices from a 150mm GaAs wafer.

In this paper a higher emphasis lies on the key enabling manufacturing technologies and supported processes.
Novel Wafer Dicing and Chip Thinning Technologies Realizing High Chip Strength
Authors: Takyu Shinya , Kurosawa Tetsuya , Shimizu Noriko , Harada Susumu
Published: April 2011

As telecommunication equipment that supports high-level information networks is being made portable, the requirements for telecommunication equipment to be small and lightweight are becoming stricter. Thus, miniaturization of semiconductor devices is necessary, and wafer dicing and chip thinning technologies are important key technologies to achieve it. Wafers are thinned by mechanical in-feed grinding using a grindstone containing diamond particles, and wafers are divided by mechanical blade dicing using a diamond blade. However, mechanical processes using diamond grits leave damage such as chipping, saw mark or residual strain on chip surfaces; thus, chip strength decreases. At chip thicknesses of 50 to 200 μm, such damage has to be avoided.

In this study, the relationship between chip residual damage and chip strength is examined, and novel wafer dicing and thinning technologies that realize an average chip strength have increased from 253 MPa to 1903 MPa are described.
The Energetics of Hydrogen Adsorbed in Nanoporous Silicon. An ab initio Simulational Study
Authors: Valladares Ariel A. , Valladares Alexander , Valladares R. M. , Calles A. G.
Published: April 2011

Porous silicon may be an interesting alternative to store hydrogen. Unlike carbon, its bonding multiplicity is limited, and because of this, the probability of having more dangling bonds on the pore surface is larger than in carbon. Using nanoporous silicon periodic supercells with 216 atoms and 50 % porosity, constructed with a novel ab initio approach devised by us, the dangling bonds of the silicon atoms were first saturated with hydrogen, then relaxed and its total energy calculated. Next the same number of hydrogen atoms was placed within the pore in the pure silicon supercell, then the sample relaxed, and finally its total energy calculated, with and without hydrogens. From these results the average energy per hydrogen atom is obtained. We compare our results to SiH bond energies and to previous results for hydrogenated carbon; conclusions are drawn concerning the possibility of using porous silicon as a fuel tank for hydrogen.
Synthesis and Characterization of BaZr0.8Y0.2O3 Protonic Conductor for Intermediate Temperature Solid Oxide Fuel Cells (IT-SOFCs)
Authors: D'Epifanio Alessandra , Fabbri Emiliana , Di Bartolomeo Elisabetta , Licoccia Silvia , Traversa Enrico
Published: April 2011

Barium zirconate BaZr0.8Y0.2O3-δ, to be used as protonic conductor under hydrogen containing atmosphere in intermediate temperature (500-700°C) solid oxide fuel cells (IT-SOFCs) was prepared using a sol-gel technique to produce materials with controlled chemical structure and microstructural properties. Several synthetic procedures were investigated, dissolving the metal cations in two solvents (water and ethylene glycol) and using different molar ratios of citric acid with respect to the total metal content. A single phase was obtained at temperature as low as 1100°C. To verify the chemical stability, all the sintered oxides were exposed to CO2 and the phase composition of the resulting specimens was investigated using X-ray diffraction (XRD) and field emission scanning electron microscopy (FE-SEM). Fuel cell polarization curves on symmetric Pt/BZY20/Pt cells of different thickness were measured at intermediate temperatures (500-700°C).
Study on the Perovskite-type Oxide Cathodes in Proton-conducting SOFC
Authors: Yahiro Hidenori , Yamaura Hiroyuki , Asamoto Makiko
Published: April 2011

The cathode performances of perovskite-type oxide electrodes were investigated in the H2-O2 fuel cell with proton-conducting electrolyte. Among the perovskite-type oxides tested in the present study, La1-xSrxFeO3(LSFO) showed the best cathode performance. The cathode performances of LSFO depended on the Sr content and the heat-treatment temperature prior to electrochemical measurements. The cathode reactions of both LSFO and Pt electrodes are discussed briefly based on the cathode overpotentials measured as a function of oxygen partial pressure. Finally, the structure and the electrical conductivity of the proton-conducting ceramic film fabricated on LSFO electrode substrate are presented.
Interfacial Structure and Point Defects in Ceria/Zirconia Superlattices
Authors: Dyer Michael , El-Azab Anter , Gao Fei
Published: April 2011

We report the results of a molecular dynamics simulation study aiming to understand the interfacial structure in ceria/zirconia superlattices and the impact of the interfaces on the energies of oxygen vacancy formation and Gd ion substitution in ceria and zirconia layers of the superlattice structure. It is found that the semi-coherent interface is characterized by misfit dislocations, paired at approximately 3-4 nm, with stacking-fault-like region in between, which agrees with the TEM observations. It is also found that the vacancy formation energy and the Gd substitution energy vary as a function of distance from the interface in the individual layers, and that these energies depend on the layer thickness. In addition, the simulations showed that the defect energy variations across the thickness of the ceria and zirconia layers are consistent with the XPS data for composition profile in the superlattice structure. Finally, in the semi-coherent superlattice structure, the formation energy of oxygen vacancies and the Gd substitution energy are found to depend on the position of these defects relative to the interfacial dislocation core. In particular, the oxygen vacancy formation energy is found to be negative close to the dislocation core, indicating that vacancy concentration will increase in such regions allowing for high conduction parallel to the interface.
New Polybenzimidazole-Based Membranes for Fuel Cells
Authors: Quartarone Eliana , Carollo Arianna , Mustarelli Piercarlo , Magistris Aldo , Tomasi Corrado , Garlaschelli Luigi , Righetti Pier Paolo
Published: April 2011

One of current trends of the PEM research is the development of new membranes working at high temperature and low humidity.

Acid-doped polybenzimidazoles are particularly appealing because of high proton conductivity without humidification and promising fuel cells performances. PBI contains basic functional groups that can easily interact with strong acids, such as H3PO4, H2SO4, allowing proton migration along the anionic chains via a Grotthuss mechanism.

In this work phosphoric acid-doped membranes, synthesised from benzimidazole-based monomers with increased basicity and molecular weight, are described and discussed. The influence of the monomer structure on the transport properties and on the physico-chemical interactions between acid and polymer has been investigated by means of impedance spectroscopy and 31P solid-state NMR. Test of methanol crossover and diffusion have been performed to check the membrane suitability for DMFCs.
State of Water in Nafion 117 Proton Exchange Membranes Studied by Dielectric Relaxation Spectroscopy
Authors: Polizos Georgios , Lu Zijie , Macdonald Digby D , Manias Evangelos
Published: April 2011

Dynamics of water in Nafion 117 membranes, in the acid form, at two hydration levels and several temperatures were investigated by means of dielectric relaxation spectroscopy in both, low (10−2to 107Hz, 25 to −80 °C) and microwave (0.045-26 GHz, 35 °C) frequency regions by employing different experimental setups. Three states of water were identified: a) strongly bound to the sulfonic groups (in agreement with other investigations) forming the first hydration layer; b) loosely bound, surrounding the first layer and c) free water, having similar dynamics as in the bulk state.
New Strategies on SOFC
Authors: Ruiz-Morales Juan Carlos , Peña-Martínez Juan , Marrero-López David , Pérez-Coll Domingo , Canales-Vázquez Jesús , Irvine John T.S. , Núñez Pedro
Published: April 2011

Fuel Cells are highly promising energy conversion systems for the new energy scenario. Particularly, Solid Oxide Fuel Cells (SOFCs) have been extensively studied during the last few years as a result of the increasing interest in the development of more efficient, and environmentally friendly ways of energy generation, as well as a consequence of their fuel flexibility. This work shows some strategies to improve the efficiency of SOFCs through the use of new anode materials, a novel method of microstructural optimisation by means of polymeric templates, using composites or cermets-based materials or applying a new concept in SOFC, e.g. the Symmetrical SOFC (SFC).
Electrochemical Characterization of La2-xPrxNiO4+x for Application as Cathodes in Intermediate Temperature SOFCs
Authors: Kim Gun Tae , Jacobson Allan J
Published: April 2011

The electrochemical properties of perovskite-type materials, Ln2NiO4+δ (Ln = La, Pr) as cathodes on Ce0.9Gd0.1O3 (CGO) and YSZ electrolytes were studied from 400 to 700 °C under different oxygen partial pressures (pO2 = 0.01-1 atm) by using AC impedance spectroscopy. These oxide electrodes yielded lower area specific resistance (ASR) compared to manganite perovskites. Ln2NiO4+δ (Ln = La, Pr) on CGO showed similar electrochemical performance though La2NiO4 (LNO) has a smaller ASR than Pr2NiO4 (PNO). The polarization resistance of LNO on YSZ was 2 orders higher than that on CGO. The interfacial resistance between the electrode and electrolyte was much smaller for LNO on CGO than for LNO on YSZ.
Impedance Analysis of Electrochemical NOx Sensor Using a Au/Yttria-Stabilized Zirconia (YSZ)/Au cell
Authors: Woo Leta Y. , Martin L. Peter , Glass Robert S. , Gorte Raymond J.
Published: April 2011

An electrochemical cell employing a YSZ electrolyte and two Au electrodes was utilized as a model system for investigating the mechanisms responsible for impedancemetric NOx (NO and NO2) sensing. The cell consists of two dense Au electrodes on top of a porous/dense YSZ bilayer structure (with the additional porous layer present only under the Au electrodes). Both electrodes were co-located on the same side of the cell, resulting in an in-plane geometry for the current path. The porous YSZ appears to extend the triple phase boundary and allows for enhanced NOx sensing performance, although the exact role of the porous layer is not completely understood. Impedance data were obtained over the frequency range of 0.1 Hz to 1 MHz, and over a range of oxygen (2 to 18.9%) and NOx (10 to 100 ppm) concentrations, and temperatures (600 to 700 °C). Data were fit with an equivalent circuit, and the values of the circuit elements were obtained for different concentrations and temperatures. Changes in a single low-frequency arc were found to correlate with concentration changes, and to be temperature dependent. In the absence of NOx, the effect of O2 on the low-frequency resistance could be described by a power law, and the temperature dependence described by a single apparent activation energy at all O2 concentrations. When both O2 and NOx were present, however, the power law exponent varied as a function of both temperature and concentration, and the apparent activation energy also showed dual dependence. Adsorption mechanisms are discussed as possibilities for the rate-limiting steps.
Impedancemetric Technique for NOx Sensing Using a YSZ-Based Electrochemical Cell
Authors: Martin L. Peter , Woo Leta Y. , Glass Robert S.
Published: April 2011

An impedancemetric technique for NOx sensing using a yttria-stabilized zirconia (YSZ) electrochemical cell is reported. The cell consists of a dense YSZ substrate disk with two YSZ/metal-oxide electrodes deposited on the same side. The cell is completely exposed to the test gas (no air reference). The NOx and O2 response of the cell were evaluated during constant-frequency operation at frequencies in the range from 1 to 1000 Hz. At 10 Hz, the NOx response (as measured by phase angle shift) is shown to be linear with concentration over the range from 8-50 ppm, with comparable response to both NO and NO2. A method of operation is described which enables compensation for the O2 response at oxygen concentrations greater than approximately 4%. This mode of operation allows the sensor to provide sub-10 ppm detection of NOx irrespective of the O2 concentration. The sensor exhibits good stability during continuous operation for more than 150 hr. It was observed that the O2 response of the cell may be too slow to be of practical use, taking several minutes to equilibrate after changing the concentration by a few percent. However, data will be presented which demonstrate that this response is related to the metal oxide used for the electrode, and that more rapid response times can be achieved by modification of the electrode material.
Iron Phosphates as Cathodes of Lithium-Ion Batteries
Authors: Wang Shijun , Whittingham M. Stanley
Published: April 2011

This study focusses on optimizing the parameters of the hydrothermal synthesis to produce iron phosphates for lithium ion batteries, with an emphasis on pure LiFePO4 with the olivine structure and compounds containing a higher iron:phosphate ratio. Lithium iron phosphate (LiFePO4) is a promising cathode candidate for lithium ion batteries due to its high theoretical capacity, environmentally benign and the low cost of starting materials. Well crystallized LiFePO4 can be successfully synthesized at temperatures above 150 °C. The addition of a reducing agent, such as hydrazine, is essential to minimize the oxidation of ferrous (Fe2+) to ferric (Fe3+) in the final compound. The morphology of LiFePO4 is highly dependent on the pH of the initial solution. This study also investigated the lipscombite iron phosphates of formula Fe1.33PO4OH. This compound has a log-like structure formed by Fe-O octahedral chains. The chains are partially occupied by the Fe3+ sites, and these iron atoms and some of the vacancies can be substituted by other cations. Most of the protons can be ion-exchanged for lithium, and the electrochemical capacity is much increased.
High Performance of Lithium Iron Phosphates for HEV with Quality Control Made by Magnetometry
Authors: Julien Christian M , Mauger Alain , Zaghib Karim , Gendron François
Published: April 2011

Optimized LiFePO4 positive electrode for Li-ion batteries was obtained after severe control of the fundamental properties of material. The nanoscopic structure and magnetic properties of a series of carbon-coated LiFePO4 particles prepared under various conditions were analyzed with XRD, FTIR, Raman and SQUID magnetometry. We evaluate intrinsic and extrinsic properties. The existence of low content of nano-sized ferromagnetic particles was evidenced by magnetic measurements in samples grown from iron(II) oxalate; such ferromagnetic clusters do not exist in the optimised samples grown from FePO4(H2O)2. Other impurity phases such as Fe2P, Li3Fe2(PO4)3, FeP2O7 were also detected for particular conditions of preparation. The impact of the carbon coating on the electrochemical properties is reported. Li-ion cells show excellent cyclability after 200 cycles at 60 °C without iron dissolution.
Novel Nanoporous Carbon Derived from Coal Tar Pitch/polyethylene Glycol Diacid Blends as Electrodes for Ultracapacitors
Authors: Rajagopalan Ramakrishnan , Perez Keith , Foley Henry
Published: April 2011

Nanoporous carbon materials with high surface area (1500 – 2000 m2/g) and narrow pore size distribution ranging from 1 – 3 nm were synthesized using polyfurfuryl alcohol/polyethylene glycol diacid and coal tar pitch/polymer blends. Electrical double layer capacitance of synthesized carbon was measured using cyclic voltammetry. There is a strong correlation between the surface area of the carbon and the specific capacitance. Carbon that had surface area smaller than 1000 m2/g had specific capacitance less than 50 F/g while the carbons having surface area from 1000 – 1500 m2/g showed specific capacitances in the order of 200 -250 F/g. It was shown that the mesoporosity and macroporosity in the parent carbon are critical for both activation and as well as the specific capacitance of the material. The use of these carbons in EDLCs was also demonstrated by fabricating a two-electrode ultracapacitor.
Mesoporous Carbon Materials as Electrodes for Electrochemical Double-Layer Capacitor
Authors: Park Sea , Liang Chengdu , Sheng Dai , Dudney Nancy , DePaoli David
Published: April 2011

Nanostructured carbon materials with a regular array and narrow size distribution of mesopores have been synthesized at Oak Ridge National Laboratory via the self-assembly of block copolymers as soft templates. One promising application for these materials is as electrodes for electrochemical double-layer capacitors. To evaluate the performance, electrodes were prepared by coating the precursor onto fibrous carbon paper, followed by curing and pyrolysis at 850°C. The resulting mesoporous carbon has a surface area of 310 m2/g and an average pore size of 8.5 nm. Results from cyclic voltammetry and impedance spectroscopy experiments using a sulfuric acid electrolyte showed high specific capacitance values of up to 300 F/g. For comparison, a commercially available aerogel carbon coated paper was also examined.
Titania-German Nanocomposites for Quantum Dot Solar Cells
Authors: Goyal Amita , Hazra Sukti , Shah S. Ismat
Published: April 2011

Several new photovoltaic semiconductor materials and technologies have been developed due to the increasing need for renewable energy sources. Quantum dot (QD) based solar cell is potentially one of the best contenders. We have developed a thermodynamically stable nanocomposite (stable up to 900°C) titania-germanium (TiO2-Ge) which shows promise as the active layer for QD solar cells. In TiO2-Ge nanocomposites Ge nanodots are distributed in a TiO2 matrix. Due to the 3-D quantum confinement effect, tailoring of the optoelectronic properties is relatively easily done by simply varying the Ge nanodots size. Ge is particularly advantageous since its Bohr radius is relatively large, 25 nm. In this paper results of the variation of the optoelectronic properties of TiO2-Ge nanocomposites as a function of the nanostructure parameters are presented. TiO2-Ge nanocomposite thin films were synthesized using RF magnetron sputtering. The structural studies (by XRD, HRTEM) established the fact that the Ge concentration in the composite target governs the size of the Ge nanodots whereas RF sputtering power controls the density of Ge nanodots in the nanocomposite films. The optical spectroscopic studies showed that the variation of the size of Ge nanodots in the TiO2-Ge films shifts the absorption edge from ∼ 0.66 eV (infrared) to ∼ 2.3 eV (blue-green). Similarly, dark conductivity also varies in a wide range of 10−7 - 10−2 Scm−1 by altering the concentration as well as the structural phase (amorphous or crystalline) of Ge.
Plasma Synthesis of Highly Monodisperse Ge Nanocrystals and Self-Assembly of Dense Nanocrystal Layers
Authors: Gresback Ryan , Holman Zak , Kortshagen Uwe
Published: April 2011

Germanium nanocrystals have been synthesized using a low-pressure, nonthermal plasma approach. The nanocrystal size can be adjusted between 4-20 nm by varying the plasma parame-ters, and the size distribution is relatively narrow with standard deviations of 10-20% of the av-erage crystal size. Stable colloidal solutions of the germanium crystals have been prepared by grafting organic alkene ligands onto the nanocrystal surfaces. When drop-cast from solution onto TEM grids, the nanocrystals form densely packed films.