bluuebunny/crossref_metadata_2025 huggingface dataset:
Real-time Observation of Nucleation and Evolution of InAs Quantum Dots on GaAs(001) During MBE
Authors: Kamiya Itaru , Matsuura Kohtaro , Higashinakagawa Tsuyoshi
Published: April 2011

Self-assembled (SA) quantum dots (QDs) have been widely studied due to the facileness in their preparation. Unlike other types of QDs that require complicated fabrication processes, SA QDs are prepared merely by depositing materials that have different bandgaps and lattice constants to the with respect to the substrate by epitaxial crystal growth techniques. InAs QDs on GaAs(001) grown by MBE or MOCVD have been a typical example, and their optoelectronic properties have been extensively investigated. For device applications, it is essential that their size and spatial distribution are controlled. However, since SA QDs are formed through random processes, it is not easy to achieve size and distribution uniformity without prior processing the substrate prior to crystal growth. A number of studies have been performed to understand the fundamental mechanisms of SA QD formation that would provide us with information to achieve such goal.
Here, we performed real-time observation of SA InAs QD growth on GaAs(001) by MBE. In contrast to most previous reports that employed growth interruption, by following the time transient of RHEED specular beam in detail, we obtained information about nucleation and evolution of the QDs, and have been able to distinguish processes that are dependent and independent of growth rate. In addition, the results reveal that surface migration of In/As atoms and their incorporation into QDs, with the aid of the wetting layer, can be observed. We will also provide a quantitative discussion on these processes.
Enhanced Control of Porous Thin Film Morphology via Ion Bombardment
Authors: Fleischauer Michael D. , Sorge Jason B. , Joseph Robert A. , Brett Michael J.
Published: April 2011

Ion bombardment was used during and after the deposition of controlled-porosity thin films produced using the Glancing Angle Deposition (GLAD) technique. Post-deposition ion bombardment was used to mill vertical-post morphology GLAD films, whose constituent columns varied in size due to competition effects. Smaller columns, although in the minority, can have a significant impact on the function of these films in a variety of optics applications, and can only be avoided by pre-selecting column location (i.e. seeding). Uniform milling eliminated smaller columns and left only remnants of the largest columns, which then acted as seeds during subsequent depositions. This simple, non-lithographic technique leads to more uniform column morphology. Column tilt angle can also be adjusted using ion bombardment. Methods to tune column tilt angle as a function of ion current using ion-assisted deposition are discussed, with an emphasis on improved square spiral photonic band gap crystal fabrication. Ion bombardment was found to increase the tilt angle of each spiral arm, moving the architecture closer to the theoretical optimum structure.
Laser-induced Dewetting Nanomorphologies in Single and Bilayer Metal Films
Authors: Krishna Hare , Favazza Christopher , Sureshkumar R. , Kalyanaraman R.
Published: April 2011

Spatially ordered patterns result under ns laser-induced dewetting of nanoscopic metallic films like Co and Ag on inert substrates like SiO2. In both cases, the observed ordering length scale is due to thin film hydrodynamic instability with spinodal-like character. However, the morphological pathway during dewetting is different for the two metals: occurring through development of bicontinuous structures in the case of Ag and by progression of cellular networks for Co. Dewetting in bilayer structures of Ag and Co on SiO2 show that the morphology evolution is dictated by the thicker of the two films in the bilayer structure. We applied linear stability analysis to predict the length scales in single and bilayer metal film. The experimental observations are in good agreement with theoretical predictions from the analysis. An important result was that the length scales for the bilayer film were significantly smaller than a single layer of the same thickness suggesting that further control of patterning length scales may be achieved through multilayer dewetting.
Control of Growth and Morphology of a Crystal Surface by Induced Spatio-Temporal Oscillations of Surface Temperature
Authors: Khenner Mikhail
Published: April 2011

This paper presents the model for pattern formation in the course of thermodynamically stable and unstable crystal growth from vapor phase, which is influenced by rapid spatio-temporal variations of substrate and film temperature. In the model, such variations result from the interference heating of a substrate by weak pulsed laser beams. In the thermodynamically stable case the surface relaxational dynamics is influenced by surface diffusion mass transport from hot to cold regions of a substrate; this leads to accumulation of mass in cold regions and depletion in hot regions. In the thermodynamically unstable case the underlying faceting (spinodal) instability coupled to diffusion mass fluxes from hot to cold regions leads to formation of pyramidal surface structures. The scale of stationary coarsened structure increases as the separation distance of the adjacent interference fringes decreases (relative to the intrinsic faceting wave length, which is determined by the balance between the corner regularization energies and the surface energy anisotropy). On the other hand, the coarsening rates decrease with decreasing the separation distance, at least at particular typical deposition strength. The deposition strength and the separation distance of the interference fringes determine the transient and stationary pattern shape. By effectively redistributing adatoms on a substrate through the enhanced, spatially inhomogeneous diffusion, the interference heating mechanism delays, for large separation distances, the onset of spatiotemporal chaos as the growth rate increases.
Laser Irradiation of Atomic Chains: A Show-Case Study Based on the Density Functional Theory
Authors: Mazzone Anna M. , Bianconi Marco
Published: April 2011

This study is motivated by recent applications of short laser pulses to the manipulation of atomic structures at the atomic scale and is based on the Density Functional Theory. The structures considered are linear monoatomic chains, formed by covalent and metallic atoms, and the calculations illustrate their evolution under laser irradiation. The calaculations show that the modification of the chain structure spans from a slight relaxation of the interatomic distances to fragmentation and illustrate the times and energies needed to induce those changes.
Surface Modification Energized by FIB: The Influence of Etch Rates & Aspect Ratio on Ripple Wavelengths
Authors: MoberlyChan Warren
Published: April 2011

Ion beams have been used to modify surface topography, producing nanometer-scale modulations (and even subnanometer ripples in this work) that have potential uses ranging from designing self-assembly structures, to controlling stiction of micromachined surfaces, to providing imprint templates for patterned media. Modern computer-controlled Focused Ion Beam tools enable alternating submicron patterned zones of such ion-eroded surfaces, as well as dramatically increasing the rate of ion beam processing. The DualBeam FIB/SEM also expedites process development while minimizing the use of materials that may be precious (Diamond) and/or produce hazardous byproducts (Beryllium). A FIB engineer can prototype a 3-by-3-by-3 matrix of variables in tens of minutes and consume as little as zeptoliters of material; whereas traditional ion beam processing would require tens of days and tens of precious wafers. Saturation wavelengths have been reported for ripples on materials such as single crystal silicon or diamond (∼200nm); however this work achieves wavelengths >400nm on natural diamond. Conversely, Be can provide a stable and ordered 2-dimensional array of <40nm periodicity. Also ripples <0.4nm are fabricated on carbon-base surfaces, and these quantized picostructures are measured by HR-TEM and electron diffraction. Rippling is a function of material, ion beam, and angle; but is also controlled by chemical environment, redeposition, and aspect ratio. Ideally a material has a constant yield (atoms sputtered off per incident ion); however, pragmatic FIB processes, coupled with the direct metrological feedback in a DualBeam tool, reveal etch rates do not remain constant for nanometer-scale processing. Control of rippling requires controlled metrology, and robust software tools are developed to enhance metrology. In situ monitoring of the influence of aspect ratio and redeposition at the micron scale correlates to the rippling fundamentals that occur at the nanometer scale and are controlled by the boundary conditions of FIB processing.
FIB Precise Prototyping and Simulation
Authors: Nellen Philipp M. , Callegari Victor , Hofmann Juergen , Platzgummer Elmar , Klein Christof
Published: April 2011

We present a closed approach towards direct microstructuring and high precision prototyping with focused ion beams (FIB). The approach uses the simulation of the involved physical effects and the modeling of geometry/topography during milling while the ion beam is steered over the surface. Experimental examples are given including the milling of single spots, trenches, rectangles, and Fresnel lenses. Good agreements between simulations and experiments were obtained. The developed procedures can also be applied to other FIB prototyping examples.
Development of Block Co-Polymers as Self-Assembling Templates for Patterned Media
Authors: Warke Vishal , Curry Michael L , Bakker Martin Gerard , Hong Kunlun , Mays Jimmy , Britt Phillip , Li Xuefa , Wang Jin
Published: April 2011

Block copolymers that self-organize are of interest as templates for patterned media, as they potentially provide a low cost fabrication route. Poly(styrene)-Poly(methylmethacrylate) block co-polymers (PS-b-PMMA) of appropriate block length and PS to PMMA ratio self-assemble into a 2-D hexagonal phase in which the PS majority phase is continuous and surrounds cylinders of the minority, PMMA phase. For application of this phase to patterned media it is necessary that the cylinders of the minority phase be oriented perpendicular to the substrate surface. This can be achieved by a number of methods, including appropriate choice of substrate and use of a random co-polymer underlayer. Appropriate substrates include H-terminated silicon, some carbon coatings and some ITO glasses. Use of an acetic acid wash causes the minority PMMA component can be induced to be rearranged, giving rise to pores perpendicular to the substrate. Electrodeposition of a metal into the pores produces a hardmask which can be used with ion-milling to transfer the block co-polymer pattern onto a magnetic thin film.
Template Fabrication Challenges for Patterned Media
Authors: Resnick Douglas , Schmid Gerard , Miller Mike , Doyle Gary , Jones Chris , LaBrake Dwayne
Published: April 2011

The Step and Flash Imprint Lithography (S-FILTM) process uses field-to-field drop dispensing of UV curable liquids for step and repeat patterning for applications where high-resolution mix-and-match overlay is desired. Several applications, including patterned media, photonic crystals and wire grid polarizers, are better served by a patterning process that prints the full wafer since alignment requirements are not so stringent. In this paper, a methodology for creating high resolution thin templates for full wafer (or disk) imprinting is described. The methods have been applied toward the imprinting of both patterned media and photonic crystal devices using a large area printing tool developed around the S-FIL process. Techniques for further enhancing the pattern density as well as a method for addressing feature image placement are described. Finally, a process for replicating a Master Template is discussed in detail.
Observation of Ge2Sb2Te5 thin film phase transition behavior according to the number of cycles using Transmission Electron Microscope and Scanning Probe Microscope
Authors: Kim Hyunjung , Choi Sikyung , Kang Sukhoon , Oh Kyuhwan , Kweon Soonyong
Published: April 2011

Recently, the development of information technology (IT) increases the demands of memory devices. Phase change random access memory (PRAM), based on the reversible phase change of the chalcogenide alloy, Ge2Sb2Te5, is widely regarded as a favourite candidate for the next generation memory. Because of PRAM has a simple cell structure with high scalability; it is non-volatile, has a relatively high read/write operation speed (Â50ns). The PRAM operation relies on the fact that chalcogenide-based materials can be reversible switched from an amorphous phase to a crystalline state by an external electrical current. It is important to study the electrical property with set/reset cycles, since film thickness shrinkage occurs with the phase transition.

In this work, we fabricated the 100nm amorphous Ge2Sb2Te5 thin film on TiN/Ti/Si substrate using dc-magnetron sputtering. The 50X50§2 isolated Ge2Sb2Te5 cell was lithographed by the lift-off pattern and wet etching. And TiN top electrode was deposited using pattern align process at room temperature after the SiO2 insulator CMP. Phase transition behavior with the set/reset cycle was observed using I-V measurement and transmission electron microscope (TEM) on isolated Ge2Sb2Te5 cell. The set/reset programming was operated using tungsten SPM tip which was fabricated using focused ion beam (FIB) lithography. I-V curve which was observed by the I-V probe clearly showed that the phase transition was occurred by applying the electric field through the I-V probe. The resistivity difference between amorphous and crystal state was more than 102. After the phase transition, it was also demonstrated with transmission electron microscope (TEM) analysis. For the preparation of TEM specimen of the amorphous and crystalline cell, focused ion beam (FIB) lithography was adopted.
Nonvolatile Two-Terminal Molecular Memory
Authors: Snodgrass Jason , Kennedy Glen , Mei Wai-Ning , Sabirianov Renat
Published: April 2011

We propose a nonvolatile two-terminal memory with two resistance states based on the molecular tunnel junctions. This tunnel junction is composed of one or few monolayers of polar molecules sandwiched between two electrodes made of materials with different screening length. As a prototype model system we study rare earth endohedral metallofullerene molecule with reversible dipole moment sandwiched by metal and semiconducting electrodes forming a double barrier junction. We use the Thomas-Fermi model to calculate the potential profile across the device. Calculated tunneling conductance through the proposed structure changes by order of magnitude upon the reversal of the dipole orientation (due to the applied voltage). This effect originates from the difference of potential profile seen by tunneling electrons for two opposite dipole orientations.
Sequential Stretching Lithography
Authors: Lin Haojing , Lima Ocelio V , Tan Li , Li Zheng , Li Jiangyu
Published: April 2011

We developed an embossing/imprinting based nanofabrication technique, dubbed Sequential Stretching Lithography (SSL). In this process, a master pattern is imprinted into an elastomer containing a film of uncured elastomer. The elastomer is cured and then elongated to increase feature density and reduce feature size. Replication of this substrate yields a new master that can be used in further reduction steps. One-dimensional grating features with a pitch size below 200 nm were fabricated from 750 nm-pitch grating lines. This process gives us a faithful pattern miniaturization in all aspects and, as a result, a much effective control on density and dimension regulation.
GMR in Excess of 10% at Room Temperature and Low Magnetic Fields in Electrodeposited Cu/Co Nano-multilayer Structures
Authors: Pandya Dinesh K. , Gupta Priyanka , Kashyap Subhash C. , Chaudhary Sujeet
Published: April 2011

Electrodeposition has emerged as a novel economically viable technique with large-scale production capabilities in modern day micro technologies. The current trends are to extend the potential of the electrodeposition to nano fabrication. We have successfully electrodeposited Cu/Co multilayers, exhibiting appreciably high GMR, on ITO as well as on Cu/Si substrates. Multilayer stacks with films in thickness range 1 – 10 nm were deposited. The Co layers have different mechanisms of growth on these substrates, thus resulting in different microstructure and topography of the electrodeposited films. This leads to different GMR behavior of the multilayers in both these cases. Room temperature GMR values of 15% at low fields are obtained on ITO substrate and higher values are possible on Cu/Si substrate.
Formation and Characterization of Striped Nano-Channel Structure on the Functional Oxide Thin Film
Authors: Kasahara Masayasu , Matsuda Akifumi , Akita Yasuyuki , Hara Wakana , Kobayashi Keisuke , Kobayashi Kazuyoshi , Suzuki Toshimasa , Yoshimoto Mamoru
Published: April 2011

The striped nano-channel structure (about 10nm in depth) was formed on the NiO film surface by thermal annealing of the film deposited on the sapphire(0001) substrate with periodic straight atomic steps. The interval of each nano-channel was about 100nm in average and well corresponding to the separation of atomic steps on the used sapphire(0001) substrate. Effects of annealing temperature and impurity doping into NiO upon the nanochannel formation were examined in order to control the depth. The depth of nano-channels formed on the alkali-metal(Li or Na) doped NiO films were found to be larger than that of nano-channels on the non-doped NiO films and enlarged with increasing annealing temperature in the range of 500∼900°C. Atomic-scale cross sectional structure of the nano-channel was characterized by transmission electron microscopy with focused on the film/substrate interface.
Structural and Morphological Characterization of Nanostructured Cobalt Ferrite Thin Films by Pulsed Laser Deposition
Authors: Kant K. Mohan , Ramachandra Rao M.S.
Published: April 2011

Cobalt ferrite (CoFe2O4) thin films were deposited on quartz and single crystalline MgO(001) substrates using pulsed laser deposition (PLD) technique. The orientation of the as-deposited films were investigated as a function of substrate temperature (TS) in the range 200°C – 750°C. Films grown on MgO at higher substrate temperature were found to be (001) oriented while the films grown at lower substrate temperature were polycrystalline in nature. Magnetic measurements reveal that films deposited at lower substrate temperature had lower magnetic moment compared to that of films grown with higher substrate temperature, indicating the correlation between magnetic order and crystallinity. This is attributed to the presence of ordered magnetic domains in the oriented films even though the microstructure remains the same.
The Heating Effects of Dextran Coated Iron Oxides
Authors: Zeng Qi , Baker Ian , Hoopes Jack
Published: April 2011

The structural and quasi-static magnetic behaviors and the temperature rises of three Dextran-coated maghemite nanoparticles subjected to alternating magnetic field (AMF) were investigated for potential use in magnetic hyperthermia treatments. In order to elucidate the effect of the hydrodynamic particle size on the specific absorption rate, the temperature rises for various hydrodynamic particle sizes were investigated in AMFs of various strengths and frequencies. Structural characterization was performed using a TEM and a SEM as well as by dynamic light scattering, and the quasi-static magnetic hysteresis loops were measured using a VSM. The heating behavior is discussed in relation to the magnetic behavior and particle size. While it was found that the heating mechanism for the ferromagnetic particles was mainly magnetic hysteresis losses, Brownian relaxation losses also contributed to the heating.
Microemulsion Synthesis of Nd0.5Ca0.5MnO3 and Nd0.5Sr0.5MnO3 Nanoparticles
Authors: Wang Z. Q. , Yin K. B. , Gao F. , Wang K. F. , Ren Z. F. , Liu J. -M.
Published: April 2011

Nd0.5Ca0.5MnO3 (NCMO) and Nd0.5Sr0.5MnO3 (NSMO) nanoparticles have been synthesized using microemulsion synthesis method, with hexamethylene alkyl, a mixture of OP and 1-hexanol, NaOH as oil phase, surfactant, and precipitating agent, respectively. The phase formation of NCMO and NSMO nanoparticles was examined. The final NCMO and NSMO nanoparticles have average particle size of 24 and 50 nm, respectively, and present high-quality crystallinity. Measurements of the magnetic properties suggest that the charge-order state favored for bulk NCMO phase collapses in NCMO nanoparticles. The spin freezing behavior for both NCMO and NSMO nanoparticles was identified.
Guiding And Confining Light In Nanoporous Cu4O3-C Composite Thin Films
Authors: Das Mahua , Shivashankar S. A.
Published: April 2011

Nanoporous Cu4O3 – C composite thin films with spherical and bicontinuous elongated pore structure have been grown on stainless steel substrates by metalorganic chemical vapour deposition technique using a single source tetranuclear metalorganic complex as precursor. The guiding and confinement of light in these quasi-periodic structures has been investigated by glancing incidence (75°) infrared spectroscopy at room temperature. The transmittance spectra of these films between wave number 10000 – 400 cm−1 reveal light confinement modes in photonic band gap between 6127-8839 cm−1 and propagation modes between 5094-400 cm−1.
Structural and Magnetic Properties of Nanogranular BaTiO3-CoFe2O4 Thin Films Deposited by Laser Ablation on Si/Pt Substrates
Authors: Barbosa José , Almeida Bernardo , Mendes Jorge A. , Rolo Anabela G. , Araújo João P. , Sousa João B.
Published: April 2011

Thin film nanogranular composites of cobalt ferrite (CoFe2O4) dispersed in a barium titanate (BaTiO3) matrix were deposited by laser ablation with different cobalt ferrite concentrations (x). The films were polycrystalline and composed by a mixture of tetragonal-BaTiO3and CoFe2O4with the cubic spinnel structure. A slight (111) barium titanate phase orientation and (311) CoFe2O4phase orientation was observed. As the concentration of the cobalt ferrite increased, the grain size of the BaTiO3phase decreased, from 91nm to 30nm, up to 50% CoFe2O4concentration, beyond which the BaTiO3grain size take values in the range 30-35nm. On the other hand the cobalt ferrite grain size did not show a clear trend with increasing cobalt ferrite concentration, fluctuating in the range 25nm to 30nm. The lattice parameter of the CoFe2O4phase increased with increasingx. However, it was always smaller than the bulk value indicating that, in the films, the cobalt ferrite was under compressive stress that was progressively relaxed with increasing CoFe2O4concentration. The magnetic measurements showed a decrease of coercive field with increasingx, which was attributed to the relaxation of the stress in the films and to the increase of particle agglomeration in bigger polycrystalline clusters with increasing cobalt ferrite concentration.
Microwave Responce from La- and Dy- doped BiFeO3 Thin Films
Authors: Petrov Peter Kr. , Palkar Vaijayanti R , Alford Neil McN , Tagantsev Alexander K , Prashanthi K , Chien Hsin-I , Axelsson Anna-Karin , Bhattacharya S
Published: April 2011

The dielectric response of La- and Dy- doped BiFeO3 thin films to electric- and magnetic fields was measured at microwave frequencies (up to 12GHz) in a temperature range from 25 °C to 300 °C. Interesting phenomena were observed. Significant oscillations in the C(f) characteristic which were unaffected by the electric field or by elevated temperature but which were dampened by a magnetic field. We also observed ‘N’-type I-V characteristics. A possible explanation for this mesoscopic response is the presence of structural features that cause resonance (e.g. grains, grain-boundaries, domains, domain walls etc), with a contribution strong enough to be averaged by the system. The exact origin of these features is unknown at present.
Control of Ferroelectric Phases by 4f Magnetic Moments in Multiferroic RMnO3 Crystals
Authors: Kuwahara Hideki , Noda K. , Akaki M. , Nakamura F. , Akahoshi D.
Published: April 2011

We have investigated the magnetoelectric (ME) properties of the orthorhombic RMnO3 (R=mixed rare earth ions) crystals with and without the 4f magnetic moments, while keeping an average ionic size of R. In the presence of the magnetic contribution from the R ions ((Eu,Ho)MnO3), we have observed the ferroelectric polarization along the c axis (Pc) in a zero field, which arises from the bc spiral structure stabilized by the anisotropic exchange interaction between the R and Mn sublattices like TbMnO3. The Pc phase can be transferred to Pa by application of fields of ∼1.5 T parallel to the b axis. The observed decrease of transition field compared with TbMnO3 suggests that the magnetic contribution and the local distortion of the R ions are key factors for governing the ME properties.
Structural and Optical Properties of PbTiO3 Grown on SrTiO3 Substrates by Peroxide MBE
Authors: Izyumskaya Natalia , Avrutin Vitaliy , Gu Xing , Ozgur Umit , Kang Tae Dong , Lee Hosun , Smith David John , Morkoc Hadis
Published: April 2011

Lead titanate (PbTiO3), a ferroelectric material with perovskite structure, has received a great deal of attention owing to a unique combination of its piezoelectric, pyroelectric, dielectric, electo- and acousto-optic properties [1–3]. PbTiO3 is a very attractive material for the use in a wide variety of fields, including ultrasonic sensors, infrared detectors, electro-optic modulators, and ferroelectric random access memories. To harness the intrinsic properties of PbTiO3 for device applications, however, high-quality epitaxial films are required. PbTiO3 thin films have been prepared by various methods such as chemical vapor deposition, rf magnetron sputtering, pulsed laser deposition, hydrothermal method, and sol-gel technique. Surprisingly, molecular beam epitaxy (MBE), with its precise control over composition, has not been widely applied, except of a few reports on MBE growth with the use of ozone as an oxidizing agent [4]. In the present work, high-quality single-crystal PbTiO3 layers were grown on (001) SrTiO3 substrates by MBE with the use of hydrogen peroxide as an oxidant [5]. Phase composition as well as structural and optical properties of the films were examined as a function of growth parameters by high-resolution x-ray diffractometry, spectroscopic ellipsometry, and photoluminescence. It was found that single-phase PbTiO3 films grew epitaxially at substrate temperatures above 600°C, whereas layers grown at lower temperature contained lead oxide inclusions. All the PbTiO3 layers were c-axis oriented with the epitaxial relationship PbTiO3(100)//SrTiO3(100) and PbTiO3[001]//SrTiO3[001]. No evidence of a-domains was found. Full width at half maximum of (001) rocking curves for 50–60 nm thick PbTiO3 layers are as low as 6–8 arcmin, indicating their good crystal quality. Pseudodielectric function of PbTiO3 was measured using variable angle spectroscopic ellipsometry at room temperature. Refractive index was found to be 2.605 at 633 nm (1.96 eV), which is consistent with the literature data. With the help of the standard critical point (SCP) lineshape analysis the band gap energy was calculated to be (3.778±0.005) eV.
Structural and Ferroelectric Properties of Bi4-xNixTi3O12 Thin Films by Sol-Gel Process
Authors: Melgarejo Ricardo , Tomar Maharaj S , Singhal Rahul , Katiyar Ram S
Published: April 2011

Nickel-substituted Bi4Ti3O12 (i.e., Bi4-xNixTi3O12) were synthesized by sol-gel process for different compositions. Thin films were deposited on Pt (i.e., Pt/TiO2/SiO2/Si) substrate by spin coating. Materials were characterized by x-ray diffraction and Raman spectroscopy. This study indicates that the material makes a solid solution for the compositions: x = 0.00, 0.05, 0.10, 0.15, 0.20, and 0.30, where a Ni ion replaces the Bi site. The prominent effect of Ni substitution was observed in low-frequency Raman modes. Sol-gel derived thin films of Bi4-xNixTi3O12 on a Pt substrate and post annealed at 700°C were tested for ferroelectric response which showed high remnant polarization (Pr = 22 μC/cm2 for x = 0.15). The leakage current (less then 10−7 A/cm2) at low field was observed in the film with composition x = 0.15 .The polarization of the BNiT (x = 0.15) film decreased to 83% of the initial value after 1×109 switching cycles These results indicate the potential application of Ni substituted bismuth titanate films in non-volatile ferroelectric memories.
Growth of High-Quality Pb(ZrxTi1-x)O3 Films by Peroxide MBE and Their Optical and Structural Characteristics
Authors: Izyumskaya Natalia , Avrutin Vitaliy , Gu Xing , Ozgur Umit , Xiao Bo , Kang Tae Dong , Lee Hosun , Morkoc Hadis
Published: April 2011

The growth of Pb(ZrxTi1-x)O3 (PZT) films by molecular beam epitaxy was demonstrated. Single-crystal, single-phase PZT films were grown on (001) SrTiO3 substrates at a growth temperature of 600°C. In situ monitoring of the growth process by reflection high-energy electron diffraction revealed two dimensional growth for the PZT constituent ternaries, namely, PbTiO3 and PbZrO3, and three-dimensional growth for PZT films of intermediate compositions. Layer-by-layer growth of PZT films, however, was achieved by using a PbTiO3 buffer layer between the SrTiO3 substrate and PZT films. Optical properties of the films of the end ternaries were investigated by spectroscopic ellipsometry. Refractive index at 633 nm was found to be 2.66 for PbTiO3 and 2.40 for PbZrO3. Band gap energies of PbTiO3 and PbZrO3 were determined as 3.81 and 3.86 eV, in good agreement with theoretically calculated values. The P-E hysteresis loop of a 70-nm-thick PZT film was well saturated and had a square shape. The remanent polarization and the coercive field were 83 μC/cm2 and 77 kV/cm, respectively, which are respectable.
Long Term Retention Characteristic of Small Inverted Dots Formed on Congruent Single-Crystal LiTaO3
Authors: Cho Yasuo , Odagawa Nozomi
Published: April 2011

To investigate the long-term retention characteristics of a ferroelectric-data-storage system, 80-nm-thick congruent LiTaO3 plates with inverted-domain dot arrays composed of 100-nm-φpdots were baked at 220, 250, 280 and 300°C. After heat treatment over a range of different time intervals, the dots shrank. From the change in the dot radius data, the activation energy (Ea) and frequency factor (α), parameters of the Arrhenius equation, were determined to be = 0.76 eV, = 2.21×105. From these parameter we can predict competitive retention characteristics compared with general memory devices. The phenomenon of dot shrinking can be explained from the energy transition of the system based on wall energy.
Characterization of Alumina Optical Waveguides Grown by Ion Beam Assisted Deposition for SPARROW Biosensors
Authors: Poloju Praneetha , Samudrala P. K. , Nightingale J. R. , Korakakis D. , Hornak L. A.
Published: April 2011

Dielectric optical films with minimal surface roughness are required for biosensing applications since the coupling characteristics often used in signal transduction are dependent on the quality of the waveguides. This paper describes the fabrication and characterization of alumina-based optical waveguides for biosensor device for biomolecular detection. Alumina (Aluminum Oxide) Al2O3waveguides were chosen for their moisture stability and refractive index. Planar alumina optical waveguides were deposited on Borofloat substrates by a vacuum evaporation process using an ion assisted electron beam deposition technique. The deposited films showed RMS roughness of 0.3nm – 0.5nm and a range of refractive indices varying from 1.62 to 1.654 as a function of varying ion beam parameters such as oxygen flow rates and drive currents. The propagation losses for the TE0(Transverse Electric) mode of the alumina films at 632.8nm wavelength were found to vary between 2dB/cm – 6dB/cm at a wavelength of 632.8nm for TE0polarization as a function of ion beam parameters. It is shown that these factors influence the optical film quality and hold the potential for achieving further waveguide performance improvement for biosensing applications.
Massive Spalling of Intermetallic Compound in Lead-Free Solder Joints
Authors: Yang Su-Chun , Ho Cheng-En , Chang Chien-Wei , Kao C Robert
Published: April 2011

Spalling of intermetallic compounds in a massive scale has been reported in the literature for several solder/substrate systems, including SnAgCu soldered on Ni substrate, SnZn on Cu, high-Pb PbSn on Cu, and high-Pb PbSn on Ni. In this work, a common mechanism based on thermodynamic arguments is proposed to explain this rather peculiar phenomenon that occurs across several systems. According to this mechanism, two necessary conditions must be met. This first is that the most reactive element must be present in a limited amount, and the second is that the soldering reaction must be very sensitive to the concentration of this element. With the growth of intermetallic, more and more of the most reactive elements are extracted out of the solder and incorporated into intermetallic. As the concentration of this element decreases, the local equilibrium phase at the interface changes. This changing of the equilibrium phases caused the non-equilibrium phase to spall.
A Novel PPF Technique--Sn-PPF: Effects of In-Situ Formation Cu-Sn-Ni Intermetallic Nano-Layer on Electronic Packaging Performances
Authors: Liu Lilin , Fu Ran , Liu Deming , Zhang Tongyi
Published: April 2011

A novel preplated leadframe (PPF), i.e. Sn-PPF, is developed by electrodepositing a 3∼4nm thick Sn layer between the Cu base leadframe and the Ni plating. The nano-thick intermetallic compound (IMC) layer forms automatically through interdiffusion and reaction between Cu, Ni and Sn. High resolution transmission electron microscopy (HRTEM) observation reveals crystallography relationship between the IMC and Cu base. A drastic reduction of Cu out-diffusion is confirmed by an EDX based oxidation test carried, indicating a significant enhancement in the protection of the leadframe against oxidation and corrosion attack. The Cu diffusion coefficients in the IMC layer were estimated to be about at 250°C and m2/s at 300°C. Results of the wire pull test, the solderability test and the bending test exhibit Sn-PPF's quality with a Ni layer less than 200nm satisfying industrial requirements.
Factors Affecting the Mechanical Properties of Cu/Electroless Ni-P/Sn-3.5Ag Solder Joints
Authors: Kumar Aditya , Chen Zhong , Wong C. C. , Mhaisalkar S. G. , Kripesh Vaidhyanathan
Published: April 2011

This work investigates the factors that affect the mechanical properties of Cu/electroless Ni-P/Sn-3.5Ag solder joints. For the investigation, solder joints were tensile tested after solid-state aging at different temperatures for various durations. Several factors, such as the growth of interfacial compounds (IFCs), Ni3Sn4 morphology, the accumulation of spalled Ni3Sn4 intermetallic particles at the solder/Ni3Sn4 interface, and the formation of Kirkendall voids at the Ni3P/Cu interface, are found to deteriorate the mechanical properties of the joints. Among all these factors, the formation of a layer of Kirkendall voids at the Ni3P/Cu interface, which is a result of Cu diffusion from the interface, causes the most severe decrease in tensile strength with a brittle fracture at the Ni3P/Cu interface. This layer of Kirkendall voids remains the main cause of brittle failure even after the transformation of the Ni3P layer into a Ni-Sn-P layer.
Time-Lapse Measurements of Creep in Au-Sn Die Bonds
Authors: Marinis Ryan , Klempner Adam , Hefti Peter , Pryputniewicz Ryszard , Marinis Thomas , Soucy Joseph
Published: April 2011

Gold-tin braze is the preferred material for attaching high-precision MEMS inertial sensors within hermetic ceramic packages. The bonds can be made at relatively low temperatures, are mechanically robust, and outgas at very low rates in vacuum sealed packages. There is one significant limitation to Au-Sn bonds, however. The thermal expansion coefficients of MEMS die and ceramic packages are not perfectly matched and temperature gradients occur when the assembly is cooled after brazing. As a result, there is considerable residual stress in the bonded assembly, which is accommodated to some extent by distortion of the sensor die. Over time, as these stresses relax, the distortion of the die changes, which causes the spacing between elements of the integral MEMS sensor to change as well. An important element of sensor-package design is insuring that stress relaxation effects do not cause the instrument to drift beyond its performance specification limits over a typical lifetime of 20 years.

Even though Au-Sn has been used for decades to attach silicon chips to ceramic substrates, there is little data available, particularly at low temperatures. An oven, with a specially designed window, allowed in-situ measurements to be made as a function of temperature, joint thickness and load stress. Additionally, a MEMS device brazed to a package with Au-Sn has been measured interferometrically over time to quantify die distortion in a packaged application.
Investigation of Ultralow Loss Interconnection Technique for LTCC based System-in-Package(SIP) Technology at 60GHz
Authors: Kim Dong-Young , Mun Jae Kyoung , Jun Dong-Suk , Kim Haechoen
Published: April 2011

The effects of wire and ribbon bond interconnection on the transmission characteristics at millimeter wave frequency range was presented. The insertion loss and return loss was closely related with the ratio of the signal line width to that of bonded wire or ribbon. The most promise condition for low loss interconnection was that the width of bonded wire or ribbon should be compatible to the width of signal lines. In the actual fabrication of LTCC amp module, the insertion loss of packaging is very small which means that the loss due to bonding is nearly negligible. However, the S11 and S22 degraded severely due to the difference of the types of transmission lines between chip and packaging module. A new transition structure was introduced in order to compensate this difference of transmission lines.
Silicon Through-hole Interconnection for 3D-SiP Using Room Temperature Bonding
Authors: Tanaka Naotaka , Yoshimura Yasuhiro , Naito Takahiro , Akazawa Takashi
Published: April 2011

In rapidly growing market sectors, such as mobile information devices, SiP technology, in which multiple LSI chips are stacked three-dimensionally, is attracting attention as a means of greatly reducing the mounting area of electronic components to improve system performance while reducing system size. Hitachi, Ltd. and Renesas Technology developed a new way to interconnect stacked chips using through-hole electrodes with a lower cost and shorter turn around time (TAT). Stacked chips are electrically interconnected by simply applying a compressive force at room temperature to a conventional chip with multiple gold stud bumps. Gold stud bumps on the upper chips are pressed into the through-hole electrodes on the lower chips by applying a compressive force, which causes plastic to flow into the gold bump. That is, the use of a gmechanical caulkingh technique makes possible electrical connections between stacked chips at room temperature. Compared with conventional through-hole electrode interconnection (more than 200°C), this new method drastically reduces the production cost and the environmental load. By using this technology, the package thickness can be 1.0 mm or less even in ten-chip layers, compared with two-chip layers using wire bonding, which are approximately 1.25-mm thick.
Active Si Interposer : Combination of Through-Si Vias and Redistribution
Authors: Hara Kazumi , Hashimoto Nobuaki , Ito Haruki , Yokoyama Yoshihiko , Imamura Tsuyoshi
Published: April 2011

Active Si Interposers (ASI), which are device chips with through Si vias (TSVs) and redistribution wirings, are the focus of this study. A feature of the module is that the redistribution layer includes a stress buffer layer so that stress can be alleviated when it is mounted on a motherboard. For the purpose of this study, it was decided to conduct the process from the backside of the wafer for efficiency of production. One feature of this process is that a device wafer was processed with a glass wafer supported throughout the TSVs' process in order to facilitate process of a thin wafer. However, the maximum temperature of each process was limited. We addressed this problem by the optimization of some of the equipment and the modification of the adhesive that attaches the device wafer to a glass wafer. Finally, a module that was a combination with the ASI and a certain device operated normally. In the last part of this study, the results of the evaluation that studied the impact on the devices of the TSVs' process are presented.
Grinding and Mixed Silicon Copper CMP of Stacked Patterned Wafers for 3D Integration
Authors: De Munck Koen , Vaes Jan , Bogaerts Lieve , De Moor Piet , Van Hoof Chris , Swinnen Bart
Published: April 2011

3D integration promises to reduce system form factor through direct stacking and interconnection of chips made using different technologies, into a single system. In our case, these interconnects consist of small and deep through wafer vias in the form of Cu nails. One of the enabling technologies to achieve 3D stacks, is thinning on carrier. It involves backside grinding and CMP of patterned wafers down to 20 micron, while temporarily glued to a carrier.

Success of grinding on carrier is found to strongly depend on temporary glue layer properties and bonding quality. Voids in between device wafer and carrier of various origins were observed to cause thin wafer delamination and catastrophic breakage when grinding down below 50 micron. By improvements in the bonding process, we eventually enabled uniform bonding, compatible with standard grinding and CMP techniques.

CMP both removes grinding-induced damage and exposes the Cu nails at the thin wafer backside. The developed CMP consists of 2 steps which are optimized to reduce Cu smearing and within-die uniformity. Both are found to correlate with the local Cu nail density variations.
Relations between Microstructure of Mg/Cu Super-laminates and Kinetics of Hydrogen Absorption/desorption
Authors: Tanaka Koji , Takeichi Nobuhiko , Tanaka Hideaki , Kuriyama Nobuhiro , Ueda Tamotsu T. , Tsukahara Makoto , Miyamura Hiroshi , Kikuchi Shiomi
Published: April 2011

Super-laminates have been attracting attention since co-authors Ueda et al. reported that Mg/Cu super-laminates showed reversible hydrogenation and dehydrogenation at 473K. The Mg/Cu super-laminates were prepared by a repetitive fold and roll method. Initial activation at 573 K led the super-laminates to absorb hydrogen at 473K. TEM observations of micro/nano-structures in the super-laminates were performed in order to clarify the process of hydrogenation and dehydrogenation at 473K, The as-rolled Mg/Cu super-laminates have laminated structures in size of sub-micrometer thickness composed of Mg and Cu layers with dense lattice defects. The super-laminates after initial activation keep laminated structure and have uniformly distributed pores with a sub-micrometer diameter. It is considered that these micro/nano-structures of Mg/Cu super-laminates lead to lower dehydrogenation temperature and better kinetics, which would contribute to achieve high performance hydrogen storage materials.
Microstructure of the MgH2 Synthesized by Hydriding Chemical Vapor Deposition
Authors: Saita Itoko , Akiyama Tomohiro
Published: April 2011

It is hardly achieved to prepare highly pure MgH2 by the conventional method of solid-gas reaction between solid magnesium and hydrogen; therefore, we proposed and succeeded to synthesize MgH2 by Hydriding Chemical Vapor Deposition (HCVD). Very interestingly, the HCVDed MgH2 was made of single crystals with fibrous figures; however, further detail of the HCVDed product had not been studied. Therefore the aim of this study was to examine the HCVDed MgH2 in hydrogen storage and to observe the microstructure of the HCVDed MgH2 after the hydrogen desorption and absorption.

As the results of Pressure-Composition-Isotherm (PCT) measurement, the HCVDed MgH2 reversibly absorbed and desorbed 7.6 mass% hydrogen, as much as the theoretical maximum hydrogen capacity of magnesium, without any activation treatment. The equilibrium pressure was slightly lower than the reported value. Before and after the PCT measurement, the HCVDed MgH2 did not showed noticeable difference in figure; however, MgHx, which was prepared dehydriding the HCVDed MgH2 in the PCT, showed significant difference in figure: It had zebra stripes in the SEM observation. This observation showed that the hydrogen storage and release went in the radious direction and the hydrogen diffusion was no more rate-limiting. The phase boundaries of Mg and MgH2 involving strain should affected on the plateau pressure in PCT.
Mixed Conductivity and Oxygen Permeability of (BaxSr1-x)0.98Fe1-yMyO3-&[delta] ( x = 0.1-0.3, y = 0.1-0.4 and M = Ga, Al )
Authors: Yong Kang Chun , Kusaba Hajime , Einaga Hisahiro , Teraoka Yasutake
Published: April 2011

Substitution effects of Ga and Al for Fe in (BaxSr1-x)0.98FeO3-δ were studied with respect to crystal structure, conductivity and oxygen permeability. The solubility limits of Ga and Al in (BaxSr1-x)0.98Fe1-yMyO3-δ (M=Ga, Al) were between 20 and 30 mol%. The substitution of Ga and Al caused decreases in electronic and oxide ionic conductivities (mixed conductivities) but the enhancement of the reduction tolerance. Sintered membranes of the Ga- and Al-substituted oxides showed oxygen permeability under the He/air oxygen partial pressure gradient and were stable under the condition of methane partial oxidation at 900 °C.
Processing and Characterization of Sc2O3-CeO2-ZrO2 Electrolyte Based Intermediate Temperature Solid Oxide Fuel Cells
Authors: Zevalkink Alexandra , Hunter Allen , Swanson Matthew , Johnson Christopher , Kapat Jayanta , Orlovskaya Nina
Published: April 2011

ScCeZrO2 ceramic powders produced by two different manufacturers have been used for the manufacturing of ScCeZrO2 electrolyte based solid oxide fuel cells. Thin, porous anode and cathode layers have been deposited on 150 μm thick, dense electrolyte tapes. Preliminary electrochemical testing of the cells has been performed.
Assembly of Decavanadate Polyanions by Collagen Helices: Synthesis of an Hybrid Inorganic-Bioorganic Mmaterial
Authors: Marchal Axel , Steunou Nathalie , Mosser Gervaise , Coradin Thibaud , Maquet Jocelyne , Livage Jacques
Published: April 2011

Vanadium oxide-collagen hybrid nanocomposites were prepared by adding a V2O5 sol to a dilute collagen solution. 51V MAS NMR spectroscopy shows that the inorganic phase is composed of the decavanadate [H2V10O28]4− polyanion and V2O5 ribbon-like particles. The broadening of the 51V signals and the absence of Bragg peaks in the XRD pattern suggest a strong disorder concerning the organization of the V2O5 particles and of the decavanadate species in the composites. Analogous hybrid nanocomposites were obtained with a solution that contains only the decavanadate species, showing that the cohesion in the hydrid material results mainly from electrostatic interactions between decavanadate [H2V10O28]4− polyanions and positively-charged collagen helices.