bluuebunny/crossref_metadata_2025_split huggingface dataset:
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

ABSTRACTA 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

ABSTRACTWe 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

ABSTRACTRecently, 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

ABSTRACTA 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

ABSTRACTNanometer-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

ABSTRACTIn 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

ABSTRACTThe 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

ABSTRACT1.6 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

ABSTRACTCopper-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

ABSTRACTThe 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

ABSTRACTEach 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

ABSTRACTIncorporating 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

AbstractA 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.
Thickness Dependence of Leakage Current Behavior in Epitaxial (Ba,Sr)TiO3 Thin Films
Authors: Ahn Kun Ho , Kim Sang Sub , Baik Sunggi 
Published: April 2011

AbstractThickness dependence of leakage current behaviors was investigated in epitaxial (Ba0.5Sr0.5)TiO3 thin films with different thicknesses of 55 - 225 nm prepared on Pt(001)/MgO(001) substrates by a radio-frequency magnetron sputtering technique. Below a certain critical film thickness (≤ 55 nm), the Schottky emission is a ruling leakage conduction mechanism over a wide electric field range. In contrast, in thicker films (> 55 nm), the Schottky emission still operates at low electric fields, however at high electric fields the Fowler-Nordheim (F-N) tunneling dominates. The transition film thickness appears to be associated with overlapping of the depletion layers formed at the top and bottom electrode interfaces.
Synthesis and Ferroelectric Properties of Sr- and Nb-codoped Bi4−xSrxTi3−xNbxO12 Thin Films by Sol-Gel Method
Authors: Matsuda Hirofumi , Iijima Takashi , Uchida Hiroshi , Okada Isao , Watanabe Takayuki , Funakubo Hiroshi 
Published: April 2011

AbstractFerroelectric Bi4Ti3O12 (BIT) thin films were modified by the substitution of Sr2+ ions for Bi3+ ions and of Nb5+ for Ti4+ (codoping) by spin-coating and decomposition of chemical solutions of metal-alkoxide materials (the nominal compositions of Bi4−xSrxTi3−xNbxO12 where x=0.0, 0.5, 1.0, 1.5). Single-phase thin films were crystallized above 550°C with BIT-type structure. The ferroelectric properties were found, though, with the values of Pr=10 μC/cm2 Ec=100 kV/cm, εr=300, and tanδ<5 % for Bi3.5Sr0.5Ti2.5Nb0.5O12 (x=0.5) annealed at 650 °C. Perhaps due to the lowering of the Curie temperature with increasing x, the maximum value of δr increased.
Simulation of the Variability in Next-Generation Microelectronic Capacitors with Polycrystalline Dielectrics
Authors: Cousins Jesse L. , Kotecki David E. 
Published: April 2011

AbstractMonte Carlo simulations of capacitors with polycrystalline (Bax, Sr1−x)TiO3 (BST) dielectrics were performed. The variation in capacitors due to the polycrystalline microstructure of the dielectric was investigated, as well as the effects of varying the distribution of crystal sizes. When a lognormal probability density function (pdf) was used to approximate the crystal area pdf and the average number of crystals per capacitor was near 100, it was found that the minimum capacitance value was nearly independent of the standard deviation of crystal area distribution. Both the mean and maximum capacitance values were found to increase as the width of the standard deviation increased.
High Temperature Dielectric Properties of Sol-Gel Derived Thick PZT thin Films with Different Zr/Ti Atom Ratios
Authors: Cheng Jinrong , Zhu Wenyi , Li Nan , Cross L.Eric 
Published: April 2011

AbstractPZT thin films of different thicknesses and Zr/Ti ratios of 60/40, 52/48 and 45/55 were coated onto platinized silicon substrates by using 2 methoxyethanol (2-MOE) based sol-gel spinon technique and crystallized with a rapid thermal annealing (RTA) process. XRD analysis revealed that thin PZT films exhibit random texture, while the thicker ones exhibit (100) texture, which was independent of composition. Dielectric constants and dissipation factors of PZT thin films were measured at elevated temperatures and as a function of frequency. For films with a thickness of ∼ 4 μm, the Curie points are at 350, 375 and 422°C for Zr/Ti ratios of 60/40, 52/48 and 45/55, respectively. All these films exhibit a high remnant polarization. A remnant polarization of 35 μC/cm2 had been achieved for the 60/40 films. No enhancement of the dielectric constant was observed in films with a composition close to MPB. The higher dielectric constant observed in films with the highest Zr content was explained by the concept of domain engineering.
Structure and Morphology of Epitaxially Intergrown (100)- and (116)-Oriented SrBi2Ta2O9 Ferroelectric Thin Films on SrLaGaO4(110) Substrates
Authors: Lee H. N. , Zakharov D. N. , Reiche P. , Uecker R. , Hesse D. 
Published: April 2011

AbstractSrBi2Ta2O9 (SBT) epitaxial thin films having a mix of (100) and (116) orientations have been grown on SrLaGaO4(110) by pulsed laser deposition. X-ray diffraction θ2 θ and pole figure scans, and cross-sectional transmission electron microscopy (TEM) analyses revealed the presence of two epitaxial orientations, SBT(100) ∥ SLG(110); SBT[001] ∥ SLG[001] and SBT(116) ∥ SLG(110); SBT [110] ∥ SLG[001]. By calculating the integrated intensity of certain x-ray diffraction peaks, it was established that the crystallinity and the in-plane orientation of the (100) and (116) orientation are best at a substrate temperature of 775 °C and 788 °C, respectively, and that the volume fraction of the (100) orientation at about 770 °C reached about 60%. By scanning force microscopy and cross-sectional TEM investigations we found that the a-axisoriented grains are rounded and protrude out due to the rapid growth along the [110] direction, leading to a distinct difference of the surface morphology between (100)- and (116)-oriented grains.
Lead telluride-based far-infrared photodetectors – a promising alternative to doped Si and Ge
Authors: Dolzhenko Dmitriy , Ivanchik Ivan , Khokhlov Dmitriy 
Published: April 2011

AbstractDoping of the lead telluride and related alloys with the group III impurities results in appearance of unique physical features of the material, such as persistent photoresponse, enhanced responsive quantum efficiency (up to 100 photoelectrons/incident photon), radiation hardness and many others. We review physical principles of operation of the photodetecting devices based on the group III-doped IV-VI including possibilities of fast quenching of the persistent photoresponse, construction of a focal-plane array, new readout technique, and others. Comparison of performance of the state of the art Ge(Ga) and Si(Sb) photodetectors with their lead telluride-based analogs shows that the responsivity of PbSnTe(In) photodetectors is by several orders of magnitude higher. High photoresponse is detected at the wavelength 116 micrometers in PbSnTe(In), and it is possible that the photoconductivity spectrum covers all the submillimeter wavelength range.
Hole concentration vs. Mn fraction in a diluted (Ga,Mn)As ferromagnetic semiconductor
Authors: Santos Raimundo R. dos , Oliveira L. E. , Castro J. d'Albuquerque e 
Published: April 2011

AbstractThe dependence of the hole density on that of Mn sites in Ga1−xMnxAs is studied within a mean-field approach to the hole-mediated ferromagnetism in III-V Mn-based semiconductor compounds. We parametrize the hole concentration, p, as a function of the fraction of Mn sites, x, in terms of the product m* (Jpd)2 (where m* is the hole effective mass and Jpd is the Kondo-like hole/local-moment coupling), and the critical temperature Tc. By fitting m* (Jpd)2 to experimental data for Tc(x), we establish the dependence of p on x, which is interpreted in terms of a reentrant metal-insulator transition taking place in the hole gas.
Thin Films of Antimony-Tin Oxide as Counter-Electrodes for Proton Working Electrochromic Devices
Authors: Naghavi N. , Marcel C. , Dupont L. , Rougier A. , Tarascon J-M. 
Published: April 2011

AbstractWe report here on thin films proton-working electrochromic devices based on the wellknown tungsten oxide as the coloring electrode, and Antimony Tin Oxide (ATO) as the ionstorage counter-electrode. We show that films deposited by Pulsed Laser Deposition (PLD) technique have an apparent Sb solubility up to 70 at %, and exhibit unusual electrochromic properties. Through potentiostatic tests we'll demonstrate that depending on the composition which influences film morphology, the Sn-Sb-O films could either present a faradic or a capacitive-like behavior, associated to a color or a neutral switching over a wide range of potentials, respectively. The structural properties of ATO films are characterized by X-ray diffraction and transmission electron microscopy (TEM). Electrochromic behavior is studied by means of cyclic voltamperometry coupled with ex situ optical transmittance measurements in the visible range. The maximum proton-storage capacity is observed for ATO films containing 40–50 at % Sb, while being quasi-neutral when switching over a wide range of potentials. These compositions are finally retained for the assembly of our WO3/proton-electrolyte/ATO devices, whose performances are reported.