bluuebunny/crossref_metadata_2025 huggingface dataset:
Reliability of Dielectric Barrier Films in Copper Damascene Applications
Authors: Lee Albert S. , Lakshmanan Annamalai , Rajagopalan Nagarajan , Cui Zhenjiang , Le Maggie , Xia Li Qun , Kim Bok Heon , M'Saad Hichem
Published: April 2011

The film properties of two PECVD deposited dielectric copper barrier films have been optimized to improve BEOL device reliability in terms of electromigration. Two critical aspects that affect electromigration are the dielectric barrier film hermeticity and adhesion to copper. We use a method to quantify the barrier film hermeticity and have optimized the hermeticity of the BLOκ™ low-κ dielectric barrier film to be similar to that of silicon nitride. By using FT-IR we find that the film porosity has a much stronger effect than the film stoichiometry on hermeticity. In addition, the interfaces between Damascene Nitride™ with copper, as well as BLOκ with copper have been engineered to improve the interfacial adhesion energy to >10 J/m2 for both Damascene Nitride and BLOκ.
Effect of mass transport along interfaces and grain boundaries on copper interconnect degradation
Authors: Zschech Ehrenfried , Meyer Moritz A. , Langer Eckhard
Published: April 2011

In-situSEM electromigration studies were performed at fully embedded via/line interconnect structures to visualize the time-dependent void evolution in inlaid copper interconnects. Void formation, growth and movement, and consequently interconnect degradation, depend on both interface bonding and copper microstructure. Two phases are distinguished for the electromigration-induced interconnect degradation process: In the first phase, agglomerations of vacancies and voids are formed at interfaces and grain boundaries, and voids move along weak interfaces. In the second phase of the degradation process, they merge into a larger void which subsequently grows into the via and eventually causes the interconnect failure. Void movement along the copper line and void growth in the via are discontinuous processes, whereas their step-like behavior is caused by the copper microstructure. Directed mass transport along inner surfaces depends strongly on the crystallographic orientation of the copper grains. Electromigration lifetime can be drastically increased by changing the copper/capping layer interface. Both an additional CoWP coating and a local copper alloying with aluminum increase the bonding strength of the top interface of the copper interconnect line, and consequently, electromigration-induced mass transport and degradation processes are reduced significantly.
Statistical Analysis of Electromigration Lifetimes and Void Evolution for Cu Interconnects
Authors: Hauschildt M. , Gall M. , Thrasher S. , Justison P. , Michaelson L. , Hernandez R. , Kawasaki H. , Ho P. S.
Published: April 2011

Electromigration (EM) failure statistics and the origin of the lognormal deviation (σ) for Cu interconnects have been investigated by analyzing the lifetime statistics and void size distributions at various stages during EM testing. Experiments were performed on 0.18 μm wide Cu interconnects with tests terminated after specific amounts of resistance increases, or after a specified test time. Void size distributions of resistance-based, as well as time-based EM tests were obtained using focused ion beam (FIB) microscopy. The lifetime and void size distributions were found to follow lognormal distribution functions. The σ values of EM lifetime and time-based void size distributions decrease with higher percentages of resistance increase, reaching an asymptotic value of σ ∼ 0.14. In contrast, σ values of resistance-based void size distributions are significantly smaller and do not show an obvious dependence on time. The statistics of resistance-based void size distributions can mainly be accounted for by geometrical variations of the void shape, while the statistics of time-based void size distributions requires consideration of kinetic aspects of the EM process. The σ values of EM lifetime distributions at long times can be simulated based on measured void size distributions, taking into account geometrical and experimental factors of EM. In contrast, for short times the statistics of initial void formation and the kinetics of interfacial mass transport have to be considered.
An original flexible structure for Organic Photovoltaic Devices
Authors: Sanna Ornella , Cossu Mario , Pilia Tomas , Bonfiglio Annalisa
Published: April 2011

A simple idea is proposed for the realization of organic photovoltaic devices on flexible substrates. According to this, a poly(ethylene terephtalate) layer (Mylar), transparent, a few micrometers thick and completely flexible, works as mechanical support. It is an insulating material, which has good mechanical and dielectric properties and, most important, it is completely transparent to ultraviolet light. For this reason it could be suitable for being used as transparent supporting layer for large area photovoltaic devices. Furthermore, its mechanical properties allow to employ it in a roll-to-roll lamination procedure that could give rise to low cost extended films carrying solar cells on the surface.
Electrical Hysteresis of PEDOT/PSS-Metal Contact Devices
Authors: Liu Zhengchun , Su Yi , Varahramyan Kody
Published: April 2011

PEDOT/PSS is an air-stable and solution-processable semiconductor polymer with great potential for electronic applications. In this research, we investigated the PEDOT/PSS-metal contacts using Al-PEDOT/PSS-Au as a test device. Abnormal electrical hysteresis phenomena were observed in both the current-voltage and capacitance-voltage characteristics of the device. A model in terms of metal-polymer interfacial MIS structure and ion motion in the polymer is proposed for explanation of the ‘hysteresis’ phenomena.
Electron-Transporting Thiophene-Based Semiconductors Exhibiting Very High Field Effect Mobilities
Authors: Facchetti Antonio , Yoon Myung-Han , Marks Tobin J.
Published: April 2011

Organic semiconductors exhibiting complementary n-type carrier mobility are the key components for the development of the field of “plastic electronics”. We present here a novel series of oligothiophenes designed to improve performance and stability under electron- transporting conditions. Furthermore, the key structural features of these compounds allows additional modifications of the n-type conducting core to achieve material solubility and processability. Thin film transistor (TFT) devices were fabricated employing both vacuum- and solution-deposited semiconducting layers. Field-effect transistor measurements indicate that all the members of this new series are n-type semiconductors with mobilities and Ion:Ioff ratios approaching 1 cm2/(Vs) and 107, respectively. This family represents a key milestone in the design, understanding, and development of the next generation of highly efficient n-type OTFT components.
Temperature Dependent Carrier Transport in Single-Crystalline Si TFTs inside a Location-Controlled Grain
Authors: Rana V. , Ishihara R. , Hiroshima Y. , Abe D. , Inoue S. , Shimoda T. , Metselaar J.W. , Beenakker C. I.M
Published: April 2011

Temperature dependant I-V characteristics were measured on single-crystalline Si (c-Si) TFTs fabricated inside a location-controlled grain by [.proportional]-Czochralski process using an excimer-laser. At ON-state, temperature the activation energy (Ea) of the drain current drops to a negative value. The field effect mobility ([.proportional]FE) also decreases with temperature with a power of -1.86, which indicates that, the carriers transport are governed by acoustic phonon scattering. At OFF state with a small gate bias, leakage current is dominated by thermal generation, however the Ea was 0.9eV, i.e., near the band gap value of Si. This suggests that the carrier generation centers are not located at the mid-gap states. These distinctive results from a typical poly-Si TFTs are systematically investigated for c-Si TFTs having ECR- PECVD and LPCVD SiO2 gate insulator.
Organic field-effect transistors with bending radius down to 1 mm
Authors: Sekitani Tsuyoshi , Kawaguchi Hiroshi , Sakurai Takayasu , Someya Takao
Published: April 2011

We have investigated the allowed bending radius of high-quality pentacene field-effect transistors (OFETs) manufactured on a plastic substrate of a polyethylenenaphthalate (PEN) film with a polyimide gate dielectric layer. It is found that the reduction of mobility due to the application of an expansive stress with a radius of curvature (R) smaller than about 1 mm, was only 20 %. Furthermore, the mobility increase by 7 % to 0.28 cm2/Vs on a compressive stress with R=4.6 mm. We also studied the recovery performance after stressing OFETs. No significant change and residual effect in performance has been found after the removal of the compressive bending the device down to a radius of 4.6 mm (1.4 ± 0.1 % in strain). In the analysis of the mechanical flexibility, we demonstrated that our OFETs electrical properties were fairly stable during the application of an expansive and compressive stress down to several mm in bending radius.
Flexible PLED displays and related technologies
Authors: Nisato G. , Mutsaers C. , Buijk H. , Duineveld P. , Janssen E. , Goede J. de , Bouten P. , Zuidema H.
Published: April 2011

Flexible, free shape displays are the enabling technology for new robust, lightweight, extremely thin, portable electronic devices. Polymer Light Emitting Diodes (PLED) are especially suited for these applications, due to their fast response time, low voltage, high luminous efficiency and viewing angle performance. On the other hand, PLED displays are extremely sensitive to moisture and oxygen. Substrate materials provided with high performance hermetic and conducting layers are therefore an essential component for manufacturing these flexible devices. Polymer based substrates provide the necessary mechanical flexibility; they also require several thin, brittle, functional inorganic layers such diffusion barriers and transparent electrodes. The structural integrity, dimensional stability and thermal properties of the substrate stack are crucial to insure device functionality and reliability. For polymer-based substrate several effects lead to dimensional variation of the substrates, such as solvent uptake, physical ageing of the polymer base, thermal expansion and stress induced deformations. These effects must be taken into account to successfully perform classic photolithographic steps.

Ink-jet printing is a critical enabling technology for flexible PLED displays, providing a customizable means to dispense solution-based polymers onto a flexible substrate, allowing for multi-color devices. On the other hand, IJP must meet several challenges, especially to comply with industrial applications. For example, accurate landing position of the droplets to form homogeneous hole-transport and electroluminescent layers as well as good wetting characteristic of the substrates must be obtained with reliable high throughput techniques.
Mechanical Performance of Thin Films in Flexible Displays
Authors: Lewis Jay , Grego Sonia , Vick Erik , Chalamala Babu , Temple Dorota
Published: April 2011

The use of brittle materials in flexible displays requires the understanding of the mechanical limitations of the materials and the various display architectures. We discuss various approaches to mechanical bend tests for components of flexible displays and describe a new test method based on a three-axis motion. We discuss the mechanical limitations of indium tin oxide (ITO) as a transparent conductor, and present results for a more mechanically robust multilayer transparent conductor made of an ITO-metal-ITO (IMI) stack. The IMI structures showed dramatically improved mechanical properties when subjected to bending both as a function of radius of curvature as well as number of cycles to a fixed radius. Organic light emitting devices fabricated on IMI anodes showed improved performance compared with those made on ITO anodes at current densities greater than 1 mA/cm2 due to the improved conductivity of the anode. We discuss the difficulties in analysis of the mechanical failure of transparent thin film permeation barriers. We present a novel approach for etching barrier-coated polymer substrates such that film cracking is readily visible. We report on the bend test results for sputter- deposited SiOxNy films.
Technique for Monitoring the Etching Rate of Alumina
Authors: Deb B. , Altay A. , Gilliss S. R. , Munoz N.E. , Carter C. B.
Published: April 2011

The effect of chemical and thermal treatments on the grains and grain boundaries of polycrystalline μ-Al2O3has been examined using a combination of microscopy techniques. Commercially available alumina samples (Lucalox™) were chemically etched in phosphoric acid at 200°C in increments of 15 min. Thermal treatments were carried out at 1650°C before chemical treatments. Using maps obtained by visible-light microscopy (VLM) as a guide, the same regions were re-examined using atomic force microscopy (AFM) after subsequent treatments. Variations in the dissolution rates of different grains and grain boundaries could then be studied using AFM. The geometry of the grain-boundary grooves was compared after thermal and chemical treatments. Electron backscattered diffraction (EBSD) patterns recorded in the scanning electron microscope (SEM) were used to obtain crystallographic orientations of the grains which enabled variations in dissolution rates between grains to be correlated to orientation.
Grain Boundary Engineering of Copper Shaped-Charge Liners
Authors: Blobaum Kerri J.M. , Stölken James S. , Kumar Mukul
Published: April 2011

Grain boundary engineering technology has been successfully transferred from rolling and forging to back-extrusion, and back- extruded copper shaped-charge liners with engineered microstructures have been produced. The grain-boundary engineered SCLs have special boundary fractions of 0.60 and 0.66, compared to 0.48 in a conventionally processed SCL. It is hoped that these engineered SCLs will perform better through a combination of a delayed onset of plastic instability and an improved resistance to void nucleation and coalescence.

Previous work demonstrates that SCL performance is affected by microstructure, and there is significant evidence which shows that microstructure influences both the fracture and constitutive responses of a material. For SCLs, constitutive properties which affect both the strength and stability of a material are important to performance. In the work described here, the focus is on improving stability properties such as strain-hardening rate and strain-rate sensitivity through grain boundary engineering.

Initial mechanical tests of grain boundary engineered copper indicate that its yield strength is nearly the same as conventionally processed material, even though the engineered sample has a larger grain size. Yield strength certainly affects the strength of an SCL, but its effect on stability, in terms of delaying the onset of plastic instability in a jet, is still under investigation. Although we can measure constitutive properties such as yield strength and strain to failure in the laboratory, the true effects of grain boundary engineering on SCL performance can only be measured in actual tests of the liners. Therefore, conventionally processed and grain boundary engineered SCLs will be fielded in real shaped-charges.
Modeling and Simulation of the Percolation Problem in High-Tc Superconductors: Role of Crystallographic Constraints on Grain Boundary Connectivity
Authors: Frary Megan , Schuh Christopher A.
Published: April 2011

Superconductivity in high-Tc materials is often modeled as a percolation problem in which grain boundaries are classified as strong or weak-links for current transmission based on their disorientation angle. Using Monte Carlo simulations, we have explored the topology and percolation thresholds for grain boundary networks in orthorhombic and tetragonal polycrystals where the grain boundary disorientations are assigned in a crystallographically consistent manner. We find that the networks are highly nonrandom, and that the percolation thresholds differ from those found with standard percolation theory. For biaxially textured materials, we have also developed an analytical model that illustrates the role of local crystallographic constraint on the observed nonrandom behavior.
The Er3+ and Yb3+-related emission from Er, Yb co-implanted Al0.70Ga0.30As/GaAs substrates prepared MOCVD method
Authors: Arai Tomoyuki , Uekusa Shin-ichiro
Published: April 2011

Ytterbium (Yb) ions were co-implanted into Al0.70Ga0.30As:Er substrates at room temperature. The photoluminescence (PL) and PL lifetime were characterized. Co-implanted Yb3+ enhanced PL intensity of Er3+-related emission. Er3+-related main peak (1538.2 nm), in addition to Yb3+ dose, was enhanced approximately twice. The energy transfers from 2F5/2 (the first excited state) → 2F7/2 (the grand excited state) of Yb3+ to 4I11/2 (the second excited state) → 4I15/2 (the grand excited state) and 4I15/2 → (the first excited state) 4I15/2 of Er3+ was observed.
First-principles Calculation of Electron Mobilities in Ultrathin SOI MOSFETs
Authors: Evans Matthew H. , Zhang Xiaoguang , Joannopoulos John D. , Pantelides Sokrates T.
Published: April 2011

Ultrathin silicon-on-insulator (UTSOI) technology1 has emerged as a key candidate for sub-100nm gate length CMOS devices. Recent experiments have characterized MOSFETs with silicon channels as thin as 1nm (four atomic layers of silicon),2,3 and found them to be well-behaved electrically. Quantum effects are important to the electron transport in such devices, and the penetration of the electron wavefunction into the gate oxide introduces new scattering mechanisms. We introduce here a novel method for first-principles calculation of electron mobilities in ultrathin SOI channels, including surface roughness and defect scattering. The electronic structure and scattering potentials are calculated with Density Functional Theory in the Local Density Approximation (DFT-LDA), and the mobility is calculated through Green's functions. The method requires little computational effort beyond that of the DFT-LDA calculations, and allows the calculation of temperature- and carrier concentration-dependent mobilities. Since the silicon-oxide interface is treated at the atomic-scale, the mobility contributions of different defects (e.g. suboxide bonds, oxide protrusions) and impurities (e.g. nitrogen, hydrogen) can be calculated separately, giving a precise physical picture of channel electron transport.
High Quality MPCVD Epitaxial Diamond Film for Power Device Application
Authors: Yang Jie , Huang Weixiao , Chow T. P. , Butler James E.
Published: April 2011

As a wide bandgap (5.47 eV) semiconductor material, single crystal diamond has high electron mobility (reportedly between 2000 and 4400 cm2V-1s-1), high electron saturation velocity (2×107 cms-1), high breakdown voltage (>107 Vcm-1), and high thermal conductivity (>21 Wcm-1K-1). Diamond-based semiconductor devices offer the potential of operation at high voltages, power levels, temperatures and under extreme radiation conditions. In this work, we present our effort to grow high quality homo-epitaxial diamond films on (100)-single crystal diamond substrates by microwave plasma chemical vapor deposition (MPCVD). The growth rate can vary from 0.01 to 100 micrometers per hour, depending on growth conditions, doping, and quality; and using a “lift-off” process, free-standing homo-epi films with remarkably low p-type doping (1×1014–1×1017 cm-3) and exceptionally low compensation ∼ 1×1013 cm-3 have been made. Vertical and lateral structure high voltage diamond Schottky rectifiers have been built for frequency dependent capacitance-voltage (C-V), and current-voltage (I-V) measurements. A breakdown voltage of 8 kV at 100 μm distance and 12.4 kV at 300 μm distance is recorded for lateral structure devices without Ohmic contact (back to back Schottky contacts), while an un-optimized vertical device with an back-side Ohmic contact has demonstrated a forward voltage drop of 7 V at 18 A/cm2 in a device that can only block 600 V. New test results show 3.7 kV blocking voltage vertical devices on 20 μm freestanding MPCVD diamond film. This data shows that the quality of diamond film extremely affect the electrical properties of the built devices.
Metal-oxide Semiconductor Field-effect Transistors using Single ZnO Nanowire
Authors: Heo Young-Woo , Kang B. S. , Tien L. C. , Kwon Y. , La Roche J. R. , Gila B. P. , Ren F. , Pearton S. J. , Norton D. P.
Published: April 2011

Single ZnO nanowire metal-oxide semiconductor field effect transistors (MOSFETs) were fabricated using nanowires grown by site selective Molecular Beam Epitaxy. When measured in the dark at 25°C, the depletion-mode transistors exhibit good saturation behavior, a threshold voltage of ∼-3V and a maximum transconductance of order 0.3 mS/mm. Under ultra-violet (366nm) illumination, the drain-source current increase by approximately a factor of 5 and the maximum transconductance is ∼ 5 mS/mm. The channel mobility is estimated to be ∼3 cm2 /V.s, which is comparable to that reported for thin film ZnO enhancement mode MOSFETs and the on/off ratio was ∼25 in the dark and ∼125 under UV illumination.
Beam Induced Lateral Epitaxy of GaAs on a GaAs/Si Template
Authors: Naritsuka Shigeya , Saitoh Koji , Kondo Toshiyuki , Maruyama Takahiro
Published: April 2011

Beam induced lateral epitaxy (BILE) on truncated ridges was applied to the heteroepitaxial growth of GaAs on a Si substrate. A GaAs buffer layer was formed on the Si substrate, and then this GaAs/Si template was used as a substrate for the BILE process. As a result, overgrown regions of GaAs of widths as large as 6.5 μm were grown laterally from the sides of the truncated ridges. The growth regions had a flat, smooth top surface consisting of a (111) facet. Although stacking faults from the GaAs/Si template remained in the growth region, which are unfavorable for device applications, the lateral grown region has no dislocations. Thus, the BILE method is useful for reducing dislocations in heteroepitaxy.
Sublimation growth of AlN bulk crystals by seeded and spontaneous nucleation methods
Authors: Balakrishnan Krishnan , Banno Masao , Nakano Kiyotaka , Narita Go , Tsuchiya Noritaka , Imura Masataka , Iwaya Motoaki , Kamiyama Satoshi , Shimono Kenji , Noro Tadashi , Takagi Takashi , Amano Hiroshi , Akasaki Isamu
Published: April 2011

Single crystals of AlN have been grown by seeded (on SiC substrates) and unseeded (spontaneous nucleation) sublimation techniques. Tantalum carbide coated graphite crucibles were used. Temperature gradient and source-substrate distance have been found to be the most influencing parameters of crystal growth. AlN crystals of maximum dimension 12 mm (length) × 10 mm (width) × 300 μm (thickness) were grown on 6H-SiC substrates and the best (0002) oriented crystal showed an XRD omega rocking curve FWHM of 4.81 arcmin. AlN nucleated as independent hexagonal islands and coalesced as growth progressed on. Growth rate of AlN grown on C-face SiC has been found to be higher than that on Si-face SiC. Tantalum carbide coated crucibles have been found to be better suited for AlN growth as the impurity incorporation in to the crystals due to crucible was very less. Spontaneously nucleated crystals exhibited an incompleted pyramid-like structure with (1010) and (1100) as their prominent faces.
Extended X-ray Absorption Fine Structure Studies of InGaN Epilayers
Authors: Katchkanov V. , O'Donnell K.P. , Mosselmans J.F.W. , Hernandez S. , Martin R.W. , Nanishi Y. , Kurouchi M. , Watson I. , Van der Stricht W. , Calleja E.
Published: April 2011

The local structure around In atoms in InGaN epilayers grown by Molecular Beam Epitaxy (MBE) and by Metal-Organic Chemical Vapour Deposition (MOCVD) was studied by means of Extended X-ray Absorption Fine Structure (EXAFS). The averaged In fraction of MOCVD grown samples ranged from 10% to 40% as estimated by Electron Probe Microanalysis (EPMA). The In fraction of MBE grown samples spanned the range from 13% to 96%. The In–N bond length was found to vary slightly with composition, both for MBE and MOCVD grown samples. Moreover, for the same In content, the In-N bond lengths in MOCVD samples were longer than those in MBE grown samples. In contrast, the In-In radial separations in MOCVD and MBE samples were found to be indistinguishable for the same In molar fraction. The In-Ga bond length was observed to deviate fromaveragecation-cation distance predicted by Vegard's law for MBE grown samples which indicates alloy compositional fluctuations.
Reduction of Threading Dislocations in GaN grown on ‘c’ plane sapphire by MOVPE
Authors: Datta R. , Kappers M. J. , Barnard J. S. , Humphreys C. J.
Published: April 2011

The reduction of threading dislocations (TDs) in GaN is very important as TDs act as non-radiative recombination centres and generally reduce the luminescence efficiency of GaN-based optoelectronic devices, particularly UV emitting devices. In order to reduce the density of TDs, we have used an in-situ ELO technique by depositing a non-uniform SiNx mask (as revealed by STEM-EDX) using simultaneous flow of silane and ammonia gas, either on a sapphire substrate or on a GaN pseudo-substrate. The effect of several growth parameters, such as V/III ratio, duration of Si/N treatment, pressure and temperature, on the morphology, structural quality and reduction mechanisms of TDs in GaN have been investigated and the effects of the first two parameters are reported here. To start the epilayer growth with a low V/III ratio gives rise to predominantly 3D growth, forming islands with multiple inclined facets and a vanishing top (0001) facet. A high V/III ratio enhances the lateral growth, and islands with inclined {-2112} facets together with wide flat top (0001) facets are formed. The duration of the Si/N treatment and the low V/III ratio growth regime are optimised in order to reduce the TD density down to 8×107 cm−2, as measured from plan-view TEM images. It is observed that TDs bend through 90° at inclined side facets. The role of atomic ledges moving across inclined facets which are responsible for bending the line direction of the TDs is briefly discussed.
Spintronics in Nitrides
Authors: Dietl Tomasz
Published: April 2011

The report of progress in studies of magnetism in the group III nitrides doped with transition metals and rare earth elements is described taking into account conclusions stemming from the recent advances in understanding of Ga1−xMnxAs, GaAs:MnAs, and related systems. The actual position of magnetic impurities in the host lattice as well as a possible role of structural, atomic, and electronic phase separation is described. The question whether the hole introduced by the Mn impurities is localized tightly on the Mn d-levels or rather on the hybridized p-d bonding states is addressed. The nature of spin-spin interactions and magnetic phases, as provided by theoretical and experimental findings, is outlined, and possible origins of high and low temperature ferromagnetism observed in these systems is discussed. Finally, the suitability of nitrides for single spin manipulation is analyzed considering linear in k spin splitting.
Improved Optoelectronic Characteristics of Nanocrystalline Porous Silicon by High-Pressure Water Vapor Annealing
Authors: Gelloz Bernard , Kojima Akira , Koshida Nobuyoshi
Published: April 2011

A high-pressure H2O vapor annealing technique has been applied to nanocrystalline porous silicon (PS). The effects on the photoluminescence (PL) are reported here for PS samples of different initial porosities, in different conditions of the annealing pressure. A drastic enhancement of the PL intensity has been achieved, while both the emission band and the peak wavelength remain almost unchanged. The best results have been obtained with an initial PS porosity of about 68 %. The resulting layers consist of Si nanocrystals embedded into an SiO2tissue. The high external quantum efficiency obtained in treated PS (23%) may be attributed mainly to a very high surface passivation by high quality oxide and an enhancement in the localization of photoexcited carriers.
Structural Modifications of nc-Si/SiO2 Superlattices by Localized Photo-induced Heating
Authors: Kamenev B. V. , Grebel H. , Tsybeskov L. , Timoshenko V. Yu.
Published: April 2011

Structural modifications in nanocrystalline silicon-silicon dioxide (nc-Si/SiO2) superlattices (SL) under high intensity laser irradiation have been studied experimentally and theoretically. The melting threshold in nc-Si/SiO2 SLs was found in the range of 5–8 kW/cm2 for cw excitation by 514 nm line of Ar+ laser and ∼11–15 mJ/cm2 for pulsed irradiation by 248 nm, π∼20 ns KrF laser. The irradiation of the samples above the melting threshold induces the irreversible modification of nc-Si layers, which is controlled by the thickness of the separating SiO2 layers, and increases the PL intensity increases by more than 300%.
Enhancing the Sound Pressure of Thermally Induced Ultrasonic Emitter Based on Nanocrystalline Porous Silicon
Authors: Tsubaki Kenji , Komoda Takuya , Koshida Nobuyoshi
Published: April 2011

It is shown that the acoustic pulse output of nanocrystalline porous silicon (nc-PS) ultrasonic emitter can be enhanced by appropriate control of both the driving mode and the nc-PS structure. The device is composed of a patterned heater electrode, an nc-PS layer, and a single-crystalline silicon (c-Si) substrate. As the sound pressure is proportional to input power in principle, the nc-PS device can generate a high acoustic power under the mode of temporal burst electrical input. The most important limiting factor for maximum electrical input power is a mechanical stress at the electrode/nc-PS interface induced by a rapid interfacial temperature raise rather than a simple electro-migration inside the thin metal film. In fact the maximum sound pressure is enhanced with increasing the hardness and Young's modulus of the nc-PS layer. The present result provides useful information for further progress of the nc-PS acoustic device.
Size Control and Phonon Confinement of Silicon Nanowires Synthesized by Laser Ablation
Authors: Fukata N. , Oshima T. , Tsurui T. , Ito S. , Murakami K.
Published: April 2011

Size control of silicon nanowires (SiNWs) synthesized by laser ablation of a Si target with nickel (Ni) as catalysts were investigated. The diameter of SiNWs decreased with decreasing synthesis temperature and content of Ni catalyst. Gradual down shift and asymmetric broadening of Si optical phonon peak depending on the diameter of SiNWs were observed for continuously, thermally oxidized SiNWs and SiNWs with smaller diameters formed at lower temperature. This can be interpreted by the phonon confinement effect. On the other hand, further thermal oxidation produced an upshift of the optical phonon peak. This is considered to be due to compressive stress since this stress was relieved by removing the surface oxide layers formed around the SiNW cores, resulting in a downshift of the optical phonon peak.
Synthesis and Characterization of Nanocrystalline Diamond and Its Biomedical Application
Authors: Xu Zhenqing , Kumar Arun , Kumar Ashok , Sikder Arun
Published: April 2011

Diamond is known as the material that has excellent mechanical, electrical and chemical properties. Diamond is also an ideal interface that is compatible with microelectronics process and biological environments to work as a biosensor platform with excellent selectivity and stability. In our study, nanocrystalline diamond (NCD) films were grown on Si substrates by the microwave plasma enhanced chemical vapor deposition (MPECVD) method. Parameters such as gas composition, temperature and pressure are investigated to get the best film quality. Scanning electron microscopy (SEM) and Raman spectroscopy were used to characterize the NCD films. Then the NCD films were treated by hydrogen plasma in the CVD chamber to obtain the hydrogen terminated surface. This hydrogenated NCD film is ready for bio-modification and can work as the platform of the biosensors. Fourier Transform Infrared Spectroscopy (FTIR) and X-ray Photoelectron Spectroscopy (XPS) were employed to confirm the surface hydrogenation.
Adhesion Improvement of CVD Diamond Coatings on WC-Co Substrates for Machining Applications
Authors: Xu Zhenqing , Kumar Ashok , Lev Leonid , Lukitsch Michael , Sikder Arun
Published: April 2011

In order to improve the performance of WC-Co cutting tools, high quality microcrystalline diamond coatings were produced using microwave plasma enhanced chemical vapor deposition (MPECVD) method. The adhesion of the diamond film deposited on the substrate has been considered to play an important role in the performance of the cutting tools in machining applications. A thin layer of Cr was coated on the WC-Co substrate before the diamond deposition; 75 μm diamond powders were sandblasted on the surface at 40 Psi to increase the nucleation density. Diamond film has been successfully deposited on the substrate at temperature around 750°C with 1.5 % CH4 in Hydrogen plasma. Scanning electron microscopy (SEM) has been used to study the surface morphology and Raman spectroscopy has been performed to characterize the quality of the diamond films and measure the residual stress. The adhesion of the diamond film has been evaluated by Rockwell indentation test. The results indicated that film grown on the Cr interlayer with diamond powder sandblasting has much better adhesion strength.
200. mm Silicon Wafer-to-Wafer Bonding with Thin Ti Layer under BEOL-Compatible Process Conditions
Authors: Yu J. , McMahon J. J. , Lu J.-Q. , Gutmann R. J.
Published: April 2011

Wafer level monolithic three-dimensional (3D) integration is an emerging technology to realize enhanced performance and functionality with reduced form-factor and manufacturing cost. The cornerstone for this 3D processing technology is full-wafer bonding under back-end-of-the-line (BEOL) compatible process conditions. For the first time to our knowledge, we demonstrate nearly void-free 200 mm wafer-to-wafer bonding with an ultra-thin Ti adhesive coating, annealed at BEOL-compatible temperature (400 °C) in vacuum with external pressure applied. Mechanical integrity test showed that bonded wafer pair survived after a stringent three-step thinning process (grinding/polishing/wet-etching) with complete removal of top Si wafer, while allowing optical inspection of bonding interface. Mechanisms contributing to the strong bonding at Ti/Si interface are briefly discussed.
Development of Biodegradable Polyphosphazene- Nanohydroxyapatite Composite Nanofibers Via Electrospinning
Authors: Bhattacharyya Subhabrata , Nair Lakshmi S. , Singh Anurima , Krogman Nick R. , Bender Jared , Greish Yaser E. , Brown Paul W. , Allcock Harry R. , Laurencin Cato T.
Published: April 2011

Biodegradable polymeric nanofibers are of great interest as scaffolds for tissue engineering and drug delivery due to their extremely high surface area, high aspect ratio and similarity in structure to the extracellular matrix (ECM). Polyphosphazenes due to their synthetic flexibility, wide range of physico-chemical properties, non-toxic and neutral degradation products and excellent biocompatibility are suitable candidates for biomedical applications. The objective of the present study was to develop and evaluate composite nanofibers of a biodegradable polyphosphazene, poly[bis(ethyl alanato)phosphazene] (PNEA) and nanocrystals of hydroxyapatite (nHAp) via electrospinning. A suspension of nHAp in dimethyl formamide (DMF) sonicated with PNEA solution in tetrahydrofuran (THF) was used to develop composite nanofiber matrices via electrospinning at ambient conditions. In the present study the theoretical loading of nHAp was varied from 50%-90% (w/w) to PNEA. The nHAp content (actual loading of nHAp) of the composite nanofibers was determined by gravimetric estimation. The composite nanofibers were characterized by transmission electron microscopy (TEM), gravimetry and energy dispersive X-ray mapping. This study demonstrated the feasibility of developing novel composite nanofibers of biodegradable polyphosphazenes with more than 50% (w/w) loading of nHAp on and within the nanofibers.
Floating Zone Growth of Bulk Single Crystals of Complex Oxides
Authors: Guptasarma Prasenjit , Williamsen Mark S. , Ray Shishir K.
Published: April 2011

In this MRS Proceedings paper, we present a review of the floating zone growth process, and describe growth techniques as relevant to four selected families of current or continued interest in the area of condensed matter physics of highly correlated electron systems: Cuprate oxides (Bi2Sr2CaCu2Oy), Ruthenate oxides (Sr2RuO4), Manganite oxides (La1-xSrxMnO3, La2–2xSr1+2xMn2O7, (RE) MnO3 (RE=Rare Earth)) and Ferrite oxides (BiFeO3). We also discuss our experiences with factors that tend to contribute to poor crystal growth, as relevant to experiments to probe correlated-electron physics in such crystals.
Fabrication of Anatase TiO2 Thin Film Using Pulsed DC Magnetron Sputtering
Authors: Al-Homoudi Ibrahim A. , Zhang Linfeng , McCullen Erik F. , Huang Changhe , Rimai L. , Baird R.J. , Simon Ng K.Y. , Naik R. , Auner G.W. , Newaz G.
Published: April 2011

TiO2 thin films (500 – 1000 nm in thickness) were deposited using pulsed DC magnetron reactive sputtering, on glass substrates. The depositions used a Ti source in an Ar+O2 gas mixture with different parameters of power (350 - 500W), substrate temperature (no additional heat - 400°C), growth pressure (3.0 - 5.0 mTorr) and oxygen gas flow rate (6.0 - 8.0 sccm). The x-ray diffractions (XRD) show amorphous and/or anatase phases depending on the deposition conditions. The films were found to be amorphous at lower substrate temperature and at lower powers. The sample with 4 mTorr, 400W of power, a substrate temperature of 250 C with 7.0 sccm of oxygen flow has the best crystalline quality. The temperature dependent electrical conductivity measurement in air for the above films shows an exponential increase in conductivity with temperature.
Crystallochemistry of Thortveitite-Like and Thortveitite-Type Compounds
Authors: Juarez-Arellano E. A. , Campa-Molina J. , Ulloa-Godínez S. , Bucio L. , Orozco E.
Published: April 2011

In this article we present the main features and structural relationships between thortveitite-type and thortveitite-like germanates compounds. We describe in detail the crystal structures, how they are built and the difference between them. Bond-valence and polyhedra distortion analysis are made and crystal structure stability ranges are given.
Effect of Mn Doping on the Structural and Ferroelectric properties of SrBi2Ta2O9
Authors: Sookawee T. , Pdungsap L. , Winotai P. , Suryanarayanan R. , Naik V.M. , Naik R.
Published: April 2011

SrBi2Ta2O9 (SBT) samples have been prepared by sol-gel technique with varying amount of excess Bi added to the starting composition. The excess Bi profoundly affects the dielectric and ferroelectric properties. The dielectric constant (ε) and remnant polarization increases from 80 and 1.4 μ C/cm2 for SBT with 1 mole % of excess Bi to 120 and 6.5 μ C/cm2 for SBT with 20 mole % of excess Bi. The Raman spectra, scanning electron microscopy images and the x-ray diffraction analysis show an improvement in structural quality of the samples with addition of excess Bi to the starting composition. The effect of Mn doping has also been studied by preparing SrBi2Ta2-x Mnx O9 (SBT-Mn) with x = 0 – 0.1. In the case of SBT-Mn samples, the XRD spectra revealed an unknown phase when x > 0.025. However, Raman spectra reveal the retention of Bi layer structure for all Mn compositions, with possibly small distortions. With Mn addition, ε increased to ∼ 140 for x < 0.005, but decreased to ≤ 120 when x > 0.015. The value of ε is independent of frequency from 60 to 85 kHz for all compositions of Mn. The effect of Mn addition resulted in a strong decrease in the area of the hysteresis loops.
The Contribution To Bond Valences By Lone Electron Pairs
Authors: Wang Xiqu , Liebau Friedrich
Published: April 2011

Bond valence sums (BVS) calculated for lone-pair cations are found increasingly higher than their formal valences as the retraction of the lone electron pair (LEP) from the nucleus is more pronounced. The increase in BVS is interpreted as a continuous increase of an effective valence of an atom that is a measure of its actual ability to bind other atoms without changing its formal valence. How the LEP of a lone-pair cation affects the effective valence of other atoms in a structure is studied by bond valence calculations for specific structures. For structures rich in alkali cations, it is found that the high effective valence of the lone-pair cations tends to be balanced by low effective valence of alkali cations. The LEP transfers bonding power or effective valence from the alkali cations to the lone-pair cations by joining the coordination sphere of the alkali cations.
Study of the percolative nature of thermoelectric power and resistivity in Pr0.66R0.04Sr0.3MnO3 (R = Tb, Y, Ho and Er) manganites.
Authors: Rama N. , Sankaranarayanan V. , Rao M.S.R.
Published: April 2011

We have studied the resistivity and thermoelectric power of Pr0.66R0.04Sr0.3MnO3 where R = Tb, Y, Ho and Er and have analyzed it within a percolative framework. Both resistivity and thermoelectric power quantities were found to show a strong dependence on the disorder (<σ>2) with the high temperature activation energy in both increasing as <σ>2 is increased, implying that as the disorder increases, carriers get more localized. The percolative nature of the thermopower was analyzed assuming that the lattice has coexisting metallic (Smet) and insulating (Sins) components above and below the Curie temperature (TC) which are independent of each other. Hence total S(T) = pSmet(T) + (1-p)Sins with the volume metallic fraction p=1/(1+exp(-Uo(1-T/TC)/kBT) [1]. A similar analysis was done using the resistivity data. It was seen that the TC from both thermopower and resistivity fits were nearly the same indicating that they have a common origin. This analysis clearly proves that the metal insulator transition in manganites is percolative in nature and that the transport properties show a strong percolation tendency.
Phase Change Mechanisms in Pulsed Laser-Matter Interaction
Authors: Xu Xianfan
Published: April 2011

Laser micro-machining is finding many applications in materials processing and manufacturing. Various laser techniques are being used to fabricate micro-electronics, optics, and medical components. This paper will mainly deal with the fundamental issues involved in laser-matter interaction. Our studies are focused on laser induced thermal and thermomechanical phenomena and phase change mechanisms that determine the materials removal process during laser micro-machining. It is shown that during nanosecond laser machining, explosive phase change could occur, during which the liquid is superheated to close to the thermodynamic critical point, followed by an explosive, homogeneous phase transformation. On the other hand, it is observed in the experiment that the time needed for nucleation during laser induced phase explosion is on the order of one nanosecond. Thus, when a laser with a pulsewidth of the order of picosecond or less is used, it is likely that the material can be heated above the critical point, and another type of phase change, spinodal decomposition is possible. Molecular dynamics studies showed that with the use of a femtosecond laser pulse, it is possible to superheat the material to above the critical point, and spinodal decomposition is the dominant mechanism for materials removal.
Processing and Characterization of Short Glass Fiber/ABS/Polyamide-6 Composites
Authors: Ozkoc Guralp , Bayram Goknur , Bayramli Erdal
Published: April 2011

The main objective of this study is to determine the effects of short glass fiber (SGF) content and extrusion conditions such as screw speed and barrel temperature, on the mechanical properties and morphologies of structural composites produced by compounding SGFs with poly (acrylonitrile-butadiene-styrene) (ABS). It was also aimed to determine the effects of adhesion at the fiber/matrix interface, which was promoted by incorporation of polyamide-6 (PA6) to the ABS/SGF composite. Results showed that increasing screw speed during extrusion decreased the average fiber length; therefore mechanical properties of the composites affected negatively. The increasing extrusion temperature decreased the fiber length degradation and higher tensile strength and modulus values were obtained. The use of PA6 in composites increased the interfacial adhesion, which was supported by SEM microphotographs; therefore, improved mechanical properties were obtained.
Análise da resposta em regime transitório e permanente de algoritmos para filtragem digital utilizados em relés numéricos: velocidade de convergência, overshoot e sensibilidade em relação a constante de tempo
Authors: Machado Tatiane Martins , Cardoso Jr Ghendy , Stefanello Nilvania , Morais Adriano Peres de , Mariotto Lenois
Published: April 2011

Este trabalho visa avaliar o desempenho de algoritmos de filtragem digital para relés numéricos em termos da capacidade de rejeição da componente DC, resposta transitória, exatidão, freqüência de amostragem e imunidade a ruídos. Além dos filtros clássicos de Fourier de ciclo completo e Cosseno também, são consideradas duas Transformadas Discretas de Fourier (TDF) modificadas. Os sinais de corrente utilizados nos testes foram gerados por equações matemáticas e por simulações computacionais em um sistema teste. Os resultados mostram que na maioria dos casos os filtros de Fourier modificados apresentam o melhor desempenho. Esses algoritmos exigem um maior esforço computacional, devido ao número de operações matemáticas envolvidas. No entanto, esse fato não causou aumento considerável no tempo de simulação.
Cálculo de la concurrencia para el modelo de Heisenberg
Authors: Castellanos R , Franco R , Silva-Valencia J
Published: April 2011

La concurrencia es una cantidad que nos permite medir el grado de entreveramiento que presenta un sistema cuántico y se puede calcular a partir de la matriz densidad reducida. En este artículo mostramos explicitamente como calcular la concurrencia para una cadena finita de espines s =1/2 descrita por el modelo de Heisenberg anistrópico. Nosotros mostramos que para cadenas finitas la concurrencia tiene un máximo en el punto crítico Δ = 1, la cual es una de las principales características en el límite termodinámico. Se mostró que es posible obtener información sobre las transiciones de fase del modelo calculando la concurrencia para cadenas de por lo menos 12 sitios
Constante de Boltzmann
Authors: Lopes Wilson
Published: April 2011

Estabeleceu-se, neste trabalho, uma equação barométrica para relacionar as grandezas físicas da baixa atmosfera terrestre: pressão, altitude e temperatura, com a razão entre a constante de Boltzmann e a massa média das moléculas dos gases constituintes. Para uma altitude geopotencial não superior a 33 km e considerando-se a massa média da molécula 4,809 x 10-26 kg, obteve-se um valor médio para a constante de Boltzmann de 1,373 x 10-23 J/K