bluuebunny/crossref_metadata_2025 huggingface dataset:
Grain Boundary Migration in Alumina
Authors: Farrer Jeffrey K. , Ravishankar N. , Michael Joseph R. , Carter C. Barry
Published: April 2011

The sintering process of ceramics involves grain-boundary migration (GBM) that is accompanied by mass transport across an interface. In this study, electron backscatter diffraction (EBSD) has been used to examine grain-boundary migration in alumina bicrystals with liquid films at the interface. EBSD patterns, taken near the sintered interface, have been used to study the effects of crystallography on GBM and to study the orientation relationships within the migrated regions of the crystal. Results indicate that the direction of migration is not always the same as that predicted by the current theories on GBM. It was also found that there may be small-angle misorientations in the migrated regions.
The Effect Of Extended Superdislocation / Domain Boundary Interactions in Ordered Intermetallic Compounds
Authors: Rong Tie-Sheng , Aindow Mark , Jones Ian P.
Published: April 2011

It has been known for many years that the presence of a distribution of domain boundaries in crystals with ordered superlattice structures can affect both the separation of glissile superpartial dislocations and the yield stress. Based on the details of the interactions between the domain boundaries and glissile extended superdislocations, we incorporate the effects of the thin band of perfect crystal that arises whencoupled superpartial dislocations straddle a domain boundary, and the additional domain boundary area createdonce the whole superdislocation has passed through. If these effects are included then, in an ordered phase containing many domains, we would expect the equilibrium separation of the coupled superpartial dislocations to vary more significantly with domain size than is predicted by previous models. These effects also change the way in which yield stress is predicted to vary with domain size. This variation gives a much better match to published experimental data than existing models.
Misfit Accommodation Mechanisms at Moving Reaction Fronts During the Initial Growth Stage of La2Zr2O7-based Pyrochlore on (001)YSZ
Authors: Lu C.J. , Senz S. , Hesse D.
Published: April 2011

La2Zr2O7-based pyrochlore (LZO) islands were grown on (001)-oriented Y2O3-stabilized ZrO2 (YSZ) single crystal surfaces by the reaction between the crystals and a La2O3 vapour. The islands are epitaxial with a small tilt. On a flat substrate surface each pyramidal island consists of four domains which are slightly tilted around different <110> axes with respect to the YSZ lattice. On a YSZ surface with pits of high density, more interestingly, each larger island formed at a pit has a central hole and contains two to four <100>-tilted stripe domains in addition to the four regular <110>-tilted domains. A square network of interfacial edge dislocations having Bur- gers vectors as/2 [101] (as being the lattice parameter of YSZ) was observed in the regular domains at the LZO/YSZ reaction front of positive lattice mismatch (+5%). In stripe domains two sets of orthogonal misfit dislocations are present with different Burgers vectors of type b = as/2 [101] andas/2 [010]. The perpendicular components of the Burgers vectors give rise to the observed tilts of the LZO lattices. Possible models are proposed to explain the generation of dislocation half-loops, the preferred nucleation of the islands near YSZ surface pits as well as their growth kinetics and the formation of stripe domains.
Atomic Force and Electron Microscopy Studies of Tin Dioxide Films Prepared from Solutions with High Fluorine Content
Authors: Acosta Dwight R. , Castanedo Rebeca , Estrada Walter , Avila-Godoy Rosario
Published: April 2011

Atomic force microscopy and electron microscopy were used to study surface and structural properties in SnO2:F thin films deposited by spray pyrolysis on glass at a constant substrate temperature. The influence of high levels of fluorine in the starting solution on the surface topology and morphology of thin films and correlations with electrical properties are presented in this work.
Classical Interatomic Potential for Nb-Alumina Interfaces
Authors: Albe K. , Benedek R. , Seidman D. N. , Averback R.S.
Published: April 2011

A modified-embedded-atom-method (MEAM) potential is derived for the ternary system Al-O-Nb in order to simulate the model oxide-metal interface sapphire-niobium. In the present work, MEAM parameters for Al and O given by Baskes were adopted, and the parameters for Nb are adjusted to match experimental data for pure Nb and calculated properties for Nb oxides and aluminides. The properties for niobium oxides and aluminides were obtained from local- density-functional-theory (LDFT) calculations. The resultant potential was tested in simulations for the Nb(111)/α -alumina(0001) interface. MEAM predictions of the work of separation and the interlayer relaxations for two interface terminations are in excellent agreement with LDFT calculations. The MEAM potential therefore appears suitable for large-scale computer simulation of oxide-metal interface properties.
MOCVD of Ir and IrO2 Thin Films for PZT Capacitors
Authors: Shimizu M. , Kita K. , Fujisawa H. , Niu H.
Published: April 2011

Ir films were prepared on SiO2/Si at 275-500°C by M°CVD (Metalorganic Chemical Vapor Deposition) using a new Ir precursor, Ir(EtCp)(cod) (iridium(ethylcyclopentadienyl) (1,5-cyclo°Ctadiene): Ir(C2H5C5H4)(1,5-C8H12). Ir films prepared at 275-300°C showed highly reflecting surfaces with Rrms roughness (root-mean-square roughness) of 1.4-10nm. At 500°C, Ir and IrO2 mixture-oriented films were grown. Ir films deposited at 300°C on patterned SiO2/Si substrates with aspect ratios of 0.3-2.0 showed good step coverage of 70-85%. Auger analysis revealed that Ir film had no incorporation of carbon and oxygen, and that Ir films performed well as a diffusion barrier in PZT/Ir/SiO2/Si structure.
A Dielectric Bolometer Behavior of BST Thin Film Prepared by Metal-Organic-Decomposition with Excellent Reproducibility in Thermal Cycling Test
Authors: Noda Minoru , Zhu Hong , Xu Huaping , Mukaigawa Tomonori , Hashimoto Kazuhiko , Okuyama Masanori
Published: April 2011

We have proposed a new type of simple detector pixel circuit and device structure for application of dielectric bolometer mode (DB) of infrared (IR) image sensor. The DB mode has merits such as uncooled room temperature operation, chopperless, low power dissipation, and high-sensitivity. A stable Ba1划xSrxTiO3 (BST) thin film has been successfully developed as a dielectric bolometer material for IR detector by Metal-Organic-Decomposition (MOD) method. The film was prepared on both Pt/Ti/SiO2/Si-bulk and Pt/Ti/NSG/Si3N4/SiO2 membrane structures, where an IR light is detected at the membrane as a change in dielectric constant (ε). So, the important issue for realizing a reliable IR sensor with high-sensitivity has been achieved to have a good thermal stability in ε against change in the detector temperature. XRD patterns and D-E hysteresis curves were measured and revealed that the BST film has a good perovskite structure and shows an adequate ferroelectric loops, especially for final annealing temperature higher than 700 °C. Temperature Coefficient of Dielectric constant (TCD), which decides the IR sensitivity, of the MOD made BST film is about 1 %/K. The reproducibility in ε, namely IR detector capacitance, was found to be very good in temperature ranging from about 10 to 80 °C within a relative change of 2 %. Finally, the stabilities in both the temperature dependence of ε and the output level have been obtained with a fairly large IR detectivity, where voltage sensitivity(Rv) and specific detectivity(D*) were about 1.2 kV/W and 2.9e8 cmHz 1/2/W, respectively.
Experimental and Theoretical Investigation into the Dielectric Behaviour of Ferroelectric Thin Film Superlattices
Authors: Gregg J. M. , O'Neill D. , Catalan G. , Bowman R. M.
Published: April 2011

Pulsed laser deposition has been used to fabricate thin-film capacitor structures in which the dielectric layer is composed of a superlattice of Ba0.8Sr0.2TiO3 and Ba0.2Sr0.8TiO3. The properties of the capacitors were investigated as a function of superlattice periodicity. The dielectric constant was significantly enhanced, and temperature migration of the peak in dielectric constant as a function of frequency was observed, at stacking periodicities of a few unit cells. However, such ‘relaxor-like’ features were found to be associated with high dielectric loss. Analysis of the imaginary permittivity as a function of frequency showed that fine-scale superlattices conform to Maxwell-Wagner behaviour, indicating that the observed features may be an artefact of increased carrier mobility. Modelling showed that both dielectric enhancement and frequency relaxation could readily be reproduced by Maxwell-Wagner formalism.
Nanoscale Properties of SrBi2Ta2O9 Thin Films
Authors: Gruverman A. , Isobe C. , Tanaka M.
Published: April 2011

Piezoresponse scanning force microscopy (PFM) was applied to study the nanoscale mechanism of retention loss in SrBi2Ta2O9 (SBT) thin films. Experiments were conducted by performing local polarization reversal within an individual grain with subsequent imaging of a resulting domain structure at different time intervals. The retention behavior of the films was studied as a function of switching conditions and electrode material. SFM was also used for nanoscale mapping of leakage current sites and investigation of electrical conduction mechanism at these sites. For the first time, the development of dielectric breakdown in SBT films was directly observed at nanoscale.
Surface Reaction Mechanisms in the Chemical Vapor Deposition of (Ba,Sr)TiO3 Films
Authors: Yamamuka M. , Kawahara T. , Tarutani M. , Horikawa T. , Oomori T. , Shibano T.
Published: April 2011

Surface reaction mechanisms in the chemical vapor deposition of (Ba,Sr)TiO3 [BST] films were studied by investigating the effects of O2 gas and source supply ratios on the characteristics of atomic incorporation rates. The atomic incorporation rates of Ba, Sr, and Ti increased with increasing incident flux of each source material, and then the values of the atomic incorporation rates became saturated. The saturated values increased monotonously with increasing O2 gas flow rate, in a range where atomic incorporation reactions might be controlled by the kinetics on the film surface (kinetically limited). Accordingly, O2 gas may effect the behavior of film precursors on BST film growth surfaces. From this, we assumed a CVD model, where the precursors are transported onto the film surface and adsorbed on adsorptive sites, and where the O2 gas has an effect on the formation of the adsorptive sites. With this model, atomic incorporation rates and overall sticking coefficients for the CVD of BST films were numerically simulated, and were in good agreement with experimental results for several O2 flow rates and source supply ratios.
Composite BST/MgO thin films for microwave tunable devices
Authors: Rivkin T. V. , Perkins J. D. , Parilla P. A. , Ginley D. S. , Carlson C. M. , Sengupta L. C. , Chiu L. , Zhang X. , Zhu Y. , Sengupta S.
Published: April 2011

Composite thin films of 60 wt% Ba0.6Sr0.4TiO3 and 40 wt% MgO were produced by Pulsed Laser Deposition. The biaxial texture of the BST component on the MgO substrate has been established with XRD. All as-deposited films had an enlarged BST out-of-plane lattice parameter. A more relaxed lattice constant as well as higher degree of texture has been obtained in the films deposited at higher temperature and lower deposition rate. Post-deposition annealing in flowing oxygen results in a further relaxation and alignment of the BST lattice. The as-deposited films were not tunable at room temperature. The greatest dielectric tuning was achieved in films annealed at 1200 °C. The observed difference in tunability for the films annealed at different temperatures may result from a spatial redistribution of BST material on the substrate surface during annealing.
Effect of Laser Energy and Laser Pulses on the Microstructure, Composition and Properties of Barium Strontium Titanate Thin Films Synthesized by Pulsed Laser Deposition
Authors: Fountzoulas Costas G. , Demaree J. D. , Mcknight Steven H.
Published: April 2011

Barium strontium titanate (BSTO) films were synthesized by the pulsed laser deposition technique (PLD) on silicon substrates at room temperature. The thin films were synthesized at ambient temperature and 30 mT oxygen partial pressure, with 300, 400 and 500 mJ/cm2 laser fluence at 5, 10 and 20 pulses per second on silicon wafer substrates. All films were subsequently post-annealed at 750°C in a continuous oxygen stream. The microstructure, crystallinity and lattice constant of the BSTO films were studied with the aid of atomic force microscopy (FEM) and Glancing Angle X-ray Diffraction analysis (GAXRD). The hardness and modulus of elasticity of the films were studied with the aid of a nanohardness indenter. The film stoichiometry was determined with the aid of Rutherford Backscattering Spectrometry (RBS). The results of this research will be combined with the results of our previous work [1, 2] on the effect of substrate temperature and oxygen partial pressure on the microstructure and properties of the BSTO films in order to construct a structural zone model (SZM) of the BSTO films synthesized by PLD.
Adjustment of Membrane Stress Using Aluminum Oxide and Silicon Dioxide Multi Layer Structure
Authors: Kubo Ryuichi , Yoshino Yukio , Inoue Kazuhiro , Makino Takahiro , Arai Seiichi
Published: April 2011

Relaxation of internal stress for micro-electromechanical systems (MEMS) using SiO2 / Al2O3 / SiO2 membrane has been studied. The aluminum oxide thin films were formed by electron beam evaporation at room temperature. No peaks were observed in the X-ray diffraction pattern of the films. The ratio of Al and O in aluminum oxide was stoichiometric compared with Al2O3 target material. The internal stress was tensile at about 300-400 MPa. Bottom SiO2 thin film was formed by thermal oxidation and the top one by RF magnetron sputtering method. The internal stress of thermally oxidized SiO2 film was compressive at about 440 MPa, while that of the films deposited by sputtering, was compressive at about 100 MPa. The ratio of Si and O in each SiO2 thin films remained stoichiometric. The total stress of the membrane was controlled by optimizing the thickness of each film for relaxing the total stress of the membrane. The total stress of the membrane became almost zero under optimum conditions of SiO2 and Al2O3 films.
Processing of Thick Dielectric Films for Power MEMS: Stress and Fracture
Authors: Chen Kuo-Shen , Zhang Xin , Spearing S. Mark
Published: April 2011

This paper presents residual stress characterization and fracture analysis of thick silane based PECVD oxide films. The motivation for this work is to elucidate the factors contributing to residual stress, deformation and fracture of oxide films so as to refine the fabrication process for power MEMS. It is shown that residual stress in oxide films strongly depended on thermal processing history. Dissolved gases were found to play an important role in governing intrinsic stress. The tendency to form cracks is a strong function of film thickness and annealing temperature. Mixed mode fracture mechanics was applied to predict critical cracking temperature, and there is a fairly good match between theoretical predictions and experimental observations.
Influence of γ- Irradiation on the Phase Structure of Yba 2Cu 3O7-x
Authors: Khidirov I. , Baktibaev K. , Gafurov U.
Published: April 2011

The influence of γ - irradiation on the structure of both superconducting and non-superconducting non-stoichiometric ceramics YBa 2 Cu 3 O 7−x by the neutron diffraction method has been investigated.

The results caused due to the γ-irradiation of a powder sample YBa2Cu3O6.98 in evacuated ampoule crystalline lattice distortion can manifest themselves when content of O atoms decreases up to (7-x ) 6,64. The O atoms move away from O(1) and O(4) position mainly during this process. The Meissner effect does not appear. The lattice parameters are changed in an irradiated non -stoichoimetric sample mainly due to arising radiation defects.
Crystal Growth of Bi2Sr2CaCu2Ox Superconductor by Zone Melting Technique
Authors: Iwamoto T. , Watauchi S. , Tanaka I.
Published: April 2011

We attempted to grow single crystals of Bi2Sr2CaCu2Ox (Bi-2212) by Traveling Solvent Zone Melting (TSZM) technique using a gold crucible to stabilize the molten zone as well as to control the composition of Bi-2212 single crystals. As the results of crystal growth, chemical composition of the grown crystals was determined to be Bi: Sr: Ca: Cu = 1.97(4): 1.75(7): 0.88(3): 2.0, which was close to that of feeds. TSZM growth may be effective on the control of composition of Bi-2212 crystals. Superconducting properties of the grown crystal of Bi-2212 were TcTconset=85 K andΔTc=10 K.
Elementary approach to self-assembly in random copolymers
Authors: Chitanvis Shirish M.
Published: April 2011

We have mapped the physics of a system of random copolymers onto a time-dependent density functional-type field theory using techniques of functional integration. Time in the theory is merely a label for the location of a given monomer along the extent of a flexible chain. We derive heuristically within this approach a non-local constraint which prevents segments on chains in the system from straying too far from each other, and leads to self-assembly. The structure factor is then computed in a straightforward fashion. The dependence of various calculated quantities on the average chain length are compared with experiments. The profile and size of spherulitic mesoscale domains is also computed.
Fabrication and Characterisation of Calcium Phosphate - Liposome Composites as an Implant Coating
Authors: Pongsaanutin Tarinee , Czernuszka Jan T.
Published: April 2011

Calcium phosphate in the form of apatite has been successfully precipitated on the surface of liposomes. Liposome vesicles were prepared by sonication of phosphatidylcholine and this was introduced into an aqueous solution of calcium and phosphate ions supersaturated with respect to hydroxyapatite. Calcium phosphate was shown to precipitate solely on the outer layer surface of the liposome vesicles. These composite assemblies were then deposited onto a stainless steel cathode substrate using an electrophoretic method at physiological temperatures.

Scanning electron microscopy (SEM), transmission electron microscopy (TEM), powder xray diffraction (PXRD) and Fourier transform infrared spectroscopy (FTIR) were used to analyse the morphology, structure and chemical composition of the composite coating. The results from PXRD and FTIR show a mixture of amorphous and poor crystalline hydroxyapatite (HAp). This was verified by electron diffraction. Dark field images confirmed that the precipitated HAp deposited solely at the outer surface of the liposomes. SEM micrographs demonstrated a thin uniform coating at the microstructure level. These results suggest that these calcium phosphateliposome composites can be formed. They have tremendous potential for use as drug delivery devices in aiding the treatments of bone disorders.
Effects of Block Lengths and Initial Water Content on the Swelling and Degradative Characteristics of an Injectable Poly(propylene Fumarate-Co-Ethylene Glycol) Block Copolymer Hydrogel
Authors: Shung Albert K. , Mikos Antonios G.
Published: April 2011

The overall goal of this project is to develop an in-situ polymerizable, biodegradable material for use in cardiovascular applications that minimizes non-specific cell adhesion and contains functional moieties for the attachment of peptides to induce specific cell attachment. A novel block copolymer has been developed incorporating poly(propylene fumarate) (PPF) and poly(ethylene glycol) which satisfies these criteria. PPF is a new biodegradable polymer currently being investigated for orthopedic and cardiovascular applications while PEG is a hydrophilic polymer that has been extensively studied for biomedical applications. The copolymer is chemically crosslinked with PEG diacrylate using an ammonium persulfate-ascorbic acid redox initiator system to form the hydrogel. The PEG and PPF block lengths can be varied to modulate the properties of the hydrogel formed. In this study, the following three parameters were studied, (1) PPF block length, (2) PEG block length, and (3) initial water content, were varied to examine their effects on swelling, degradation and elastic modulus. A factorial experimental design was implemented to assess which of these three parameters had the greatest impact on swelling, degradation and elastic modulus. Swelling was found to be most affected by the initial water content followed by PEG block length and PPF block length. The swelling of the hydrogels ranged from 48% water uptake with low initial water content to up to 77% water uptake with the high initial water content. After three weeks, degradation of the hydrogels ranged from 4-13% mass fraction lost. Elastic modulus was determined by tensile testing of the various hydrogel formulations and ranged from 0.4 to 7.7 MPa.
Stress and Microstructure Evolution during the Deposition and Crystallization of DCMagnetron Sputter Deposited Amorphous ITO
Authors: Yeom Hyo-Young , Lanier Courtney , Chason Eric , Paine David C.
Published: April 2011

The deposition of ITO onto glass substrates at room temperature results in a metastable amorphous phase that undergoes crystallization at remarkably low homologous temperatures (T/Tm<0.2). We have evaluated ITO film stress in the as-deposited condition and during crystallization of 200 nm thick films isothermally heated at 250°C. To explore the effect of stoichiometry on the amorphous structure, ITO films were deposited under low, optimum, and high (0, 0.1, and 2 vol %, respectively) oxygen partial pressures. In this report we have correlated changes in stress with changes in the electron transport characteristics (hall mobility and carrier density) and film microstructure.
Transparent P-type Conducting LaCuOS Layered Oxysulfide
Authors: Ueda Kazushige , Inoue Shin-ichiro , Hirose Sakyo , Kawazoe Hiroshi , Hosono Hideo
Published: April 2011

Materials design for transparent p-type conducting oxides was extended to oxysulfide system. LaCuOS was selected as a candidate for a transparent p-type semiconductor. It was found that the electrical conductivity of LaCuOS was p-type and controllable from semiconducting to semi-metallic states by substituting Sr2+ for La3+. LaCuOS films showed high transparency in the visible region, and the bandgap estimated was approximately 3.1 eV. Moreover, it was revealed that LaCuOS showed sharp excitonic absorption and emission at the bandgap edge, which is advantageous for optical applications. A layered oxysulfide, LaCuOS, was proposed to be a promising material for optoelectronic devices.
Optical and Structural Properties of Zinc-oxide Thin Film Deposited by Pulsed Laser Deposition
Authors: Ohshima Tamiko , Thareja Raj K. , Yamagata Yukihiko , Ikegami Tomoaki , Ebihara Kenji
Published: April 2011

We report optical and structural properties of ZnO films deposited by pulsed laser deposition technique on silicon (100) n-type, quartz, sapphire, and corning glass substrates. We have studied the influence of the deposition parameters, such as substrate temperature, oxygen pressure, and laser fluence on the properties of the grown films. Dependence of nanocrystallites on temperature of substrate and ambient gas pressure is investigated. ZnO plasma created at varying fluence of KrF laser (248 nm) on the target was investigated using optical emission spectroscopy and 2-d images of the expanding plumes at various pressures of the ambient gas. X-ray diffraction, atomic force microscopy, electron probe micro-analyzer, and spectro-photometry were used to characterize as grown films.
A New Kinetic Model for The Nucleation and Growth of Self-Interstitial Clusters in Silicon
Authors: Ortiz Christophe J. , Mathiot Daniel
Published: April 2011

A model for nucleation and growth of {311} defects is proposed on the basis of thermodynamic and kinetic considerations. Simulated results are discussed and compared to experimental results found in the literature. According to our model it is found that formation energies of self-interstitial clusters depends on the local interstitial supersaturation. Physical parameters extracted from experimental results by inverse modeling are in good agreement with recent values published in the literature.
Characterization and Control of Copper CMP with Optoacoustic Metrology
Authors: Gostein Michael , Lefevre Paul , Maznev Alex A. , Joffe Michael
Published: April 2011

We discuss applications of optoacoustic film thickness metrology for characterization of copper chemical-mechanical polishing (CMP). We highlight areas where the use of optoacoustics for CMP characterization provides data complementary to that obtained by other techniques because of its ability to directly measure film thickness with high spatial resolution in a rapid, non-destructive manner. Examples considered include determination of planarization length, measurement of film thickness at intermediate stages of polish, and measurement of arrays of metal lines.
CMP related/CMP revealed short- and long-range integration interactions in copper dual damascene technology
Authors: Gotkis Yehiel , Kistler Rodney
Published: April 2011

More than 4 years have passed since IBM made the official announcement approving copper dual damascene (Cu2D) technology, which drew the rest of the semiconductor world into the Cu2D race. And the technology appeared to be a hard nut to crack. Nowadays, after more than three years of extensive R&D work, the EOL yields are still low, and a lot of process integration work has to be done to make it mass production ready.
Environmentally-benign cleaning for giga DRAM using electrolyzed water
Authors: Ryoo Kunkul , Kang Byeongdoo
Published: April 2011

A present semiconductor cleaning technology is based upon RCA cleaning technology which consumes vast amounts of chemicals and ultra pure water(UPW) and is the high temperature process. Therefore, this technology gives rise to the many environmental issues, and some alternatives such as functional water cleaning are being studied. The electrolyzed water was generated by an electrolysis system which consists of anode, cathode, and middle chambers. Oxidative water and reductive water were obtained in anode and cathode chambers, respectively. In case of NH4Clelectrolyte, the oxidation-reduction potential and pH for anode water(AW) and cathode water(CW) were measured to be +1050mV and 4.8, and -750mV and 10.0, respectively. AW and CW were deteriorated after electrolyzed, but maintained their characteristics for more than 40 minutes sufficiently enough for cleaning. Their deterioration was correlated with CO2 concentration changes dissolved from air. It was known that AW was effective for Cu removal, while CW was more effective for Fe removal. The particle distributions after various particle removal processes maintained the same pattern. In this work, RCA consumed about 9 chemicals, while EW did only 400ml HCl electrolyte or 600ml NH4Cl electrolyte. It was hence concluded that EW cleaning technology would be very effective for eliminating environment, safety, and health(ESH) issues in the next generation semiconductor manufacturing.
Epitaxial growth and interface roughness of PdMn/Fe bilayer structures grown by ion-beam sputtering
Authors: Cheng Ning , Ahn J.P. , Grogger Werner , Krishnan Kannan
Published: April 2011

Different orientations of PdMn films and different stacking orders of PdMn and Fe on MgO(001) were studied. At low temperatures (T< 280°C) dominated by the kinetics of growth, a-axis orientated [PdMn(100)/Fe(001)/MgO(001)] was stabilized whilst c-axis [PdMn(001)/Fe(001)/MgO(001)] were obtained at higher temperatures (T> 300°C). The inverted structures, Fe(001)/PdMn(001)/MgO(001) and Fe(001)/PdMn(100)/MgO(001), were obtained epitaxially for the first time. The magnetic exchange coupling (He) of these PdMn/Fe bilayers show a wide range in values: ∼ 10 Oe for annealed a-axis samples, ∼ 33 Oe for c-axis normal samples and ∼ 68 Oe for c-axis inverted samples. The interface roughness of these samples was characterized by energy-filtered transmission electron microscopy (EFTEM). The orientation relationships were confirmed by x-ray diffraction and TEM. The possible origins for the He difference in a-axis and c-axis growth samples and the normal and inverted samples are discussed.
Properties of InGaN/GaN Quantum Wells Grown by Metalorganic Chemical Vapor Deposition
Authors: Cheong M. G. , Kim K. S. , Kim C. S. , Choi R. J. , Yoon H. S. , Yu S. W. , Hong Y. K. , Hong C.-H. , Suh E.-K. , Lee H. J.
Published: April 2011

Optical and structural properties of InGaN/GaN quantum wells having growth interruption were investigated using high-resolution x-ray diffraction, photoluminescence and transmission microscopy. InxGa1−xN/GaN (x>0.25) six pair quantum wells used in this study were grown on c- plane sapphire by metalorganic chemical vapor deposition. The growth interruption was carried out by closing the group-III metal organic sources before and after growth of InGaN quantum well layers. With increasing the interruption time, the quantum dot-like region and well thickness decreases due to indium re-evaporation or thermal etching effect. As a result, PL peak position is blue-shifted and intensity is reduced. The size and number of V-defect did not vary with interruption time. The interruption time is not directly related with formation of the defect. The V-defect in quantum wells originates at threading dislocations and inversion domain boundaries due to higher misfit strain.
Temperature and Coverage Dependence of the Surface Roughness for the Growth of Cu on Cu(001): An X-ray Scattering Study
Authors: Botez Cristian E. , Elliott William C. , Miceli Paul F. , Stephens Peter W.
Published: April 2011

Synchrotron X-ray scattering was used to study the temperature and coverage dependence of the root-mean-square (rms) surface roughness, σ, during the homoepitaxial growth on Cu(001). At temperatures between 370 and 160K, the rms roughness was found to increase as a power law, σ =Θβ, with the coverage Θ. The roughness exponent, β, amounts to ∼1/2 for T≤200K, and it monotonically decreases with increasing T, reaching β∼1/3 at T=370K. The mean-square roughness measured at a constant coverage of 15ML, σ2 15 ML, also depends on the temperature of the substrate: between 370 and 200K, σ2 15 ML becomes progressively larger at lower temperatures, but at 110K a reentrant smoother growth is observed.
Dynamics of the Euler Buckling Instability
Authors: Golubovic Leonardo
Published: April 2011

We review recent systematic investigations of the dynamics of the classical Euler buckling of compressed solid membranes and thin sheets. We relate the membrane buckling dynamics to phase ordering phenomena. Evolving membranes develop wavelike patterns whose wavelength grows, via coarsening, as a power of time. We find that evolving membranes are similar to interfaces of thin films in molecular-beam epitaxy growth with slope selection: They are characterized by the presence of mounds whose typical size grows as a power of time. The morphologies of the evolving membranes are characterized by the presence of a network of growing ridges where the elastic energy is mostly concentrated. We used this fact to develop a scaling theory of the buckling dynamics that gives analytic estimates of the coarsening exponents. Our findings show that the membrane buckling dynamics is characterized by a distinct scaling behavior not found in other coarsening phenomena.
Heteroepitaxial Growth and Phase Transition Properties of Vanadium Dioxide Thin Films on Different Orientations of Sapphire Substrates
Authors: Wu Z.P. , Naramoto H.
Published: April 2011

Vanadium dioxide thin films have been deposited on sapphire substrates with different orientations by pulsed laser ablation. The samples are analyzed by x-ray diffraction and pole figures to determine epitaxial relationship. The crystal quality is evaluated by RBS/Channeling techniques. The results has shown that the growth of VO2 is of strong substrate dependence, the film on (0001) sapphire substrate exhibits better crystal quality than that on (1120) and (0112) sapphire substrates. The epitaxy can be divided into two processes, the first is surface symmetry determined oriented growth, and the second is in-plane oriented growth dominated by the minimization of in-plane lattice mismatch. More over, different substrates result in different defect microstructures, 120o twin is observed in VO2 film on (0001) substrate while 180o on (1120) and no twin on (0112), which also reflects the surface symmetries of the substrates.
Direct and Real-Time Observation of Sub-Micron Domain Dynamics in Magnetically Biased Strontium Ferrite Permanent Magnets by Room Temperature Scanning Micro-Hall Probe Microscopy
Authors: Sandhu Adarsh , Iida Naoji , Masuda Hiroshi , Oral Ahmet , Bending Simon J.
Published: April 2011

A room temperature scanning micro-Hall probe microscope (RT-SHPM) was used for imaging stray magnetic field fluctuations at the surfaces of strontium ferrite permanent magnets (SFM) in the presence of external bias fields. The RT-SHPM enables the extremely fast, non-invasive, and quantitative measurement of localized surface magnetic fields on the sub-micron-scale. A 0.8 × 0.8 μm2 GaAs/AlGaAs micro-Hall probe (300K Hall coefficient =0.3ω/G; field sensitivity=0.04 G/√Hz ) with an integrated STM tip for precise vertical positioning was used as a magnetic field sensor. External bias fields (Hex) of up to 2700 Oe were applied parallel to the easy and hard axes of thermally demagnetized SFMs. Sample areas of up to 50×50 μm were imaged at a height of 0.3 μm above the SFM surface for each Hex, with scan speeds of approximately one frame/second (128×128 pixels) enabling quasi-real time imaging in synchronization with bias field changes. RT-SHPM images of surfaces normal to the easy axis of demagnetized samples at Hex=0, clearly showed the presence of 8-15 μm sized domains and stray magnetic field fluctuations of ±200G; images of surfaces normal to the hard axis showed 20 μm sized domains with magnetic field fluctuations of ±100G. Pronounced domain movement and rotation was observed for surfaces normal to the easy axis at bias fields above 700 Oe applied along the easy axis. A good correlation was found between domain movement and vibrating sample magnetometer hysteresis measurements. The RT-SHPM system was demonstrated to be a valuable tool for the direct and non-invasive study of micro-magnetic phenomena in ferromagnetic materials.
Encapsulated Molecules in Carbon Nanotubes: Structure and Properties
Authors: Russo Richard , Smith Brian W. , Satishkumar B.C. , Luzzi David E. , Dorn Harry C.
Published: April 2011

We encapsulate a number of fullerenes inside single-walled carbon nanotubes (SWNTs) including La2@C80 and ErxSc3–xN@C80(x=0–3). The structural properties of these nanoscopic hybrid materials are described using high resolution transmission electron microscopy and electron diffraction. It is found that the encapsulated fullerenes self-assemble into long, one-dimensional chains. The thermal stability of these supramolecular assemblies are studied and large variations are found. The behavior is nominally consistent with the mass of the encapsulated metallofullerenes.
Chemical Bonding of Polymer on Carbon Nanotube
Authors: Wei Chengyu , Cho Kyeongjae , Srivastava Deepak
Published: April 2011

Recently, carbon nanotubes are considered as nanoscale fibers, which can strengthen polymer composite materials. Nanotube-polymer composite materials can be used for micron scale devices with designed mechanical properties and smart polymer coating to protect materials under extreme physical conditions such as microsatellites. To explore these possibilities it is important to develop a detailed atomic scale understanding of the mechanical coupling between polymer matrix and embedded nanotubes. In this work we study the chemical bonding between polymer molecules and carbon nanotubes (CNTs) using molecular dynamics. Study shows that the bonding between polyethylene and a CNT is energetically favorable. Chemical bonds can be formed at multiple sites, which make the mechanical load transfer from the polymer chain to the tube more favorable. We will discuss about the resulting mechanical coupling between the CNTs and polymer matrix to develop efficient nano-composite materials.
Hall-Petch Relationship in Nano-RuAl Prepared by Mechanical Alloying
Authors: Liu K. W. , Mücklich F. , Birringer R.
Published: April 2011

A transition from a normal Hall-Petch relationship to an abnormal one is observed at a grain size of approximately 18.5 nm for nano-RuAl. Several models each representing a controlling factor have been employed to rationalize the transition mechanism. The grain sizes corresponding to the dislocation pile-ups lower bound [2] in grain interior are much smaller than the observed transition grain size and no apparent transition grain size has been derived from the grain size dependence of unit cell volume change [5]. While the grain sizes corresponding to the transition of strain rate according to Coble creep [1] and to the significant triple junction volume fraction [3, 4] (1 %) are well consistent with the observed transition grain size. The overall results indicate that the transition of H-P relationship is dominated by the weakening effect of grain boundaries and triple junctions.
Nanometer-sized Bismuth Crystallites Synthesized from a High-temperature Reducing System
Authors: Fang Jiye , Stokes Kevin L. , Zhou Weilie L. , Murray C. B. , O'Connor Charles J.
Published: April 2011

Nanometer-sized bismuth has successfully been prepared using a high-temperature organic reducing system by presence of proper capping/stabilizing agents. Self-assembly of bismuth was, at the first time, obtained using size-selected nanoparticles (15nm in size). Various synthetic conditions, which may significantly affect the formation of self-assembled nanocrystalline bismuth, have been optimized and discussed in this paper. The as-prepared nanocrystallites exist in a single rhombohedral phase with high crystallinity, and oxidation problem has been efficiently overcome within limited period by employing this method.
Novel Model for the Optical Function: Application to Hexagonal Gan
Authors: Chan Y. , Djurišić Aleksandra B. , Li E. Herbert
Published: April 2011

In this work we propose an analytical expression for the complex dielectric function that includes both discrete and continuum exciton effects. The model is based on the work of Elliott and the proposed model has been applied to modeling the experimental data for the hexagonal GaN. We have obtained good agreement with the experimental data. The model assumes Lorentzian broadening in order to obtain dielectric function equations in analytically closed form. We show that Lorentzian broadened dielectric function decays more slowly than the experimental data for hexagonal GaN at the low energy side. This indicates that the broadening of the absorption edge in GaN is not purely Lorentzian. The agreement with the experimental data can be improved using adjustable broadening modification.
The Calculation of Transmission Coefficients at Heterogeneous Semiconductor Interfaces: A Case Study Based on the n-InP | poly(pyrrole) Interface
Authors: Daniels-Hafer Carrie , Jang Meehae , Jones Frank E. , Boettcher Shannon W. , Danner Rob , Lonergan Mark C.
Published: April 2011

The n-InP | poly(pyrrole) interface is used as a case study to discuss the calculation of the transmission coefficient, describing the probability of majority carrier transfer, at a non-ideal semiconductor interface exhibiting anomalous behavior assumed to be due to a spatial distribution of barrier heights. The most notable anomaly is a weaker dependence of current on voltage than predicted by thermionic emission (i.e. quality or ideality factor greater than unity). Central to this discussion is the calculation of the equilibrium exchange current density Jo and barrier height Φb in light of a heterogeneous and potentially voltage-dependent barrier distribution. Various approaches to the measurement of Φb and Jovalid for semiconductor interfaces characterized by a uniform, voltage- and temperature-independent barrier are discussed when applied to a heterogeneous interface. In particular, the use of a capacitance-voltage measured barrier is demonstrated to result in an overestimation of κ whereas the use of a Richardson plot barrier is demonstrated to result in an underestimation. Depending on method, errors in excess of five orders-of-magnitude are observed for the n-InP | poly(pyrrole) interface under conditions where it exhibits only mildly anomalous behavior (ideality factor ≍ 1.2). The greatest confidence in the transmission coefficients occurs when the ideality factor is unity and the capacitance-voltage barrier agrees with the Richardson Plot barrier.
Defects in 4H-SiC Induced by High Energy Helium Implantation
Authors: Beaufort Marie F. , Oliviero Erwan , David Marie L. , Declémy Alain , Blanchard Christian , Ntsoenzok Esidor , Barbot Jean F.
Published: April 2011

1.6 MeV He+ ions were implanted at room temperature into (0001) 4H-SiC at a dose of 1×1017 cm−2 and then annealed at 1500°C for 30 min. Small bubbles are readily observed in the as-implanted sample but also an amorphous layer. After a 1500°C annealing, recrystallization of the amorphous state occurs and large bubbles or cavities are observed. However their shape strongly depends of their location inside the buried layer. The recrystallization consists of polytypisme, 4H-SiC growth along the c-direction from the substrate, columnar 4H-SiC and epitaxial growth of 3C-SiC.
Copper ohmic contacts to n-type SiC formed with pulsed excimer laser irradiation
Authors: Abe K. , Sumitomo M. , Eryu O. , Nakashima K.
Published: April 2011

Copper-based ohmic contacts to n-type 6H-SiC have been investigated. In this study, ohmic contacts have been fabricated with pulsed excimer laser irradiation to Cu-deposited substrates at room temperature. It is shown that current-voltage characteristics depend on the laser energy density. Contacts formed by the laser irradiation at the energy density above 1.2 J/cm2 have shown the ohmic behavior. Cu atoms have slightly diffused into SiC by the laser irradiation at 1.4 J/cm2. As a result, a thin ohmic contact layer has been obtained by the laser processing. AES and XRD study have revealed that a Cu-SiC alloy containing Cu silicide (Cu3Si) is formed by the laser irradiation.
Fundamental Study on Adhesion of Epoxy Underfill Materials with Passivation Layer in Flip-chip Packaging
Authors: Luo Shijian , Wong C. P.
Published: April 2011

The influence of aging in an environment with a high temperature and a high humidity on the adhesion performance of underfill material (epoxy cured with acid anhydride) to the passivation layer in flip chip packaging is discussed. Adhesion of underfill to different passivation materials degrades after aging in a high temperature and high humidity environment. The extent of this degradation is dependent on the hydrophilicity of the passivation material. Hydrophilic passivation such as silicon oxide (SiO2) and silicon nitride (Si3N4) shows much more severe adhesion degradation than hydrophobic passivation such as benzocyclobutene (BCB) and polyimide (PI). The mobility of absorbed water and of polymer chains is studied with solid state nuclear magnetic resonance (NMR) spectroscopy. Higher mobility of absorbed water and of polymer chains in rubbery state polymers contributes to faster adhesion degradation during high temperature and high humidity aging. The adhesion stability of hydrophilic passivation can be successfully improved by use of a silane coupling agent that introduces stable chemical bond at interface. A flow micro-calorimeter was used to study the absorption of silane coupling agent onto glass surface. The difference in adhesion retention improvement between aminosilane and epoxysilane is discussed.
Cultivating Graduate Students: Techniques to Inspire Effective Research
Authors: Braun David , Vanasupa Linda , London Blair , Kingsbury Kevin , Smith Heather
Published: April 2011

Each year, U.S. institutions grant well over 10,000 bachelor's degrees in science and engineering. However, only a small fraction of those students pursue graduate study. Many who do often experience great difficulty partly due to a lack of preparation for research: the nature of research is inherently foreign to those who are accustomed to studying course material and demonstrating their mastery of it by passing an exam. Carefully involving undergraduates in research can be an effective means for inspiring students to pursue graduate study. We have found that one can create a positive research experience for the student by implementing simple techniques. In this presentation, we present these practical techniques which include: Defining a manageable undergraduate research project; marketing the project to undergraduates; enabling effective record keeping in laboratory notebooks; focussing and directing research through efficient experimental designs. Along with these techniques, we will present examples—taken mainly from our Polymer Electronics Laboratory. We will also present the inherent pitfalls associated with these techniques.
The Materials World Modules Program: Incorporating Technology in Pre-College Education
Authors: Hsu Matthew , Dewald Renee , Turner Ken
Published: April 2011

Incorporating technology in pre-college education is an important goal. There is a clear mandate from the national education standards movement to address the issues of scientific and technologically literate citizenship. The Materials World Modules (MWM) Program uses a unique approach based upon design and inquiry to unite the abstract, quantitative methods of scientific inquiry with the concrete methods of technological design to help students develop and integrate these complementary skills. By experiencing MWM, students learn science by doing science. Using the MWM modules, students will be doing what scientists and engineers do: integrating the design process of propose, build, test and evaluate with the inquiry process of question, predict, experiment, reflect, and communicate. This kind of active application of learning leads to mastery of scientific concepts and greater retention.
Micro-machined Pyroelectric Infrared Detector Based on Sol-gel Derived Pb(Zr0.3Ti0.7)O3/PbTiO3 Multilayer Thin Films
Authors: Sun Ling Ling , Liu Wei Guo , Tan Ooi Kiang , Zhu Wei Guang
Published: April 2011

A sol-gel derived Pb(Zr0.3Ti0.7)O3/PbTiO3 (PZT/PT) multilayer thin film structure has been studied for the application of infrared detection. Compared to the pure Pb(Zr0.3Ti0.7)O3 (PZT) thin film deposited by the same process, the multilayer thin film shows a lower dielectric constant and similar pyroelectric coefficient and dielectric loss. The detectivity figures of merit for the PZT/PT and PT thin films are 20.3×10−6 Pa-1/2 and 18.7×10−6 Pa−1/2, and values of voltage response figures of merit are 0.038 m2/C and 0.028 m2/C, respectively. The results show that the multilayer PZT/PT film is a better choice for pyroelectric infrared detection. Pyroelectric infrared detectors have been successfully developed based on the multilayer PZT/PT thin film. A silicon bulk-machined thermal isolation structure has been applied to reduce thermal loss from the sensing thin film to the Si substrate. To evaluate the detector performance and to aid in the thermal structure design, finite element analysis (FEA) of the detector in terms of heat transfer has been carried out by using a software package “ANSYS”. The detector response has been characterized by a modified Chynoweth system. At 7 Hz, the dynamic pyroelectric voltage responsivity is measured to be 108 V/W (in rms) with the sensing element size of 240×360 μm2. The measured results are consistent with the simulated results.