bluuebunny/crossref_metadata_2025 huggingface dataset:
The profile of the Greek ‘XXL’ family
Authors: Christoforidis Athanasios , Batzios Spyros , Sidiropoulos Haralampos , Provatidou Maria , Cassimos Dimitris
Published: May 2011

Objective

To identify Greek families in which all members were overweight or obese (XXL families) and to describe their profile with regard to their socio-economic status and their eating behaviours and practices.

Design

A prospective cohort study.

Setting

The metropolitan area of Kavala.

Subjects

We recruited children aged 11 and 12 years from twelve primary schools, and their parents, from volunteers. Auxologic measurements of the children included height and weight. A structured questionnaire pertaining to information on the socio-economic status of the family, anthropometric values and educational status of parents, dietary habits and the availability of various food products and beverages at home, as well as dietary intake, physical activity, time spent sleeping and time spent watching television, was filled in by one of the parents of each child. A total of 331 families finally participated.

Results

In sixty-one families (18·43 %) both parents and child were either overweight or obese (XXL family), and in seven of these families all members were obese. Only twenty-eight families (8·46 %) had all members with a normal BMI. The XXL family was associated with lower educational status of both parents, whereas a higher percentage of XXL families resided in rural areas and had lower income. Skipping breakfast and spending more than 3 h in front of a screen every day were more frequently observed in XXL families. With regard to the availability of various food products and beverages at home, no significant differences were observed between XXL families and the rest of the studied families.

Conclusions

Greek XXL families have lower educational status and lower annual income.
Diagnostik und Therapie der interstitiellen Zystitis
Authors: Meyer  , Gregorin  , Schmid
Published: May 2011

Die interstitielle Zystitis, erstmals 1887 als entzündliche Erkrankung der Harnblasenwand beschrieben, gilt heute als eine häufige Erkrankung mit hoher Dunkelziffer. Grund für die Unterdiagnose sind vielfach zu strikte Ausschlusskriterien. Die Erkrankung lässt sich bereits durch sorgfältige Anamneseerhebung und klinische Untersuchung im Frühstadium erkennen und mittels multimodaler Therapieansätze erfolgversprechend behandeln. Neben der symptomorientierten oralen Therapie stellen lokale Instillationen von Bestandteilen der schützenden Glykosaminoglykan-Schicht, deren gestörte Integrität als Schlüsselrolle in der Pathogenese der interstitiellen Zystitis gilt, den häufigsten Therapieansatz dar.
Safe Osteocutaneous Radial Forearm Flap Harvest with Prophylactic Internal Fixation
Authors: Shnayder Yelizaveta , Tsue Terance T. , Toby E. Bruce , Werle Andreas H. , Girod Douglas A.
Published: May 2011

We studied the efficacy of prophylactic plate fixation technique and a modified harvest of the osteocutaneous radial forearm free flap (OCRFFF) to minimize the incidence of postoperative donor radius pathological fracture. We retrospectively studied of the first 70 consecutive patients undergoing OCRFFF harvest by the University of Kansas Head and Neck Microvascular Reconstruction Team. Mean follow-up was 13 months. One of two patients undergoing OCRFFF harvest without prophylactic fixation developed a pathological radius fracture. The 68 subsequent OCRFFF patients underwent prophylactic fixation of the donor radius, and none developed a symptomatic radius fracture. Five of 68 patients did have a radiographically visible fracture requiring no intervention. The plate fixation technique was further modified to exclude monocortical screws in the radius bone donor defect (subsequent 39 patients), without any further fractures detected. One patient required forearm hardware removal for an attritional extensor tendon tear. The described modified OCRFFF harvest and prophylactic plate fixation technique may eliminate postoperative pathological fracture of the donor radius. Donor morbidity is similar to that of the fasciocutaneous radial forearm free flap , affording safe use of OCRFFF in head and neck reconstruction.
SOx on ceria from adsorbed SO2
Authors: Lu Zhansheng , Müller Carsten , Yang Zongxian , Hermansson Kersti , Kullgren Jolla
Published: May 2011

Results from first-principles calculations present a rather clear picture of the interaction of SO2 with unreduced and partially reduced (111) and (110) surfaces of ceria. The Ce3+/Ce4+ redox couple, together with many oxidation states of S, give rise to a multitude of SOx species, with oxidation states from +III to +VI. SO2 adsorbs either as a molecule or attaches via its S-atom to one or two surface oxygens to form sulfite (SO32−) and sulfate (SO42−) species, forming new S–O bonds but never any S–Ce bonds. Molecular adsorption is found on the (111) surface. SO32− structures are found on both the (111) and (110) surfaces of both stoichiometric and partially reduced ceria. SO42− structures are observed on the (110) surface together with the formation of two reduced Ce3+ surface cations. SO2 can also partially heal the ceria oxygen vacancies by weakening a S–O bond, when significant electron transfer from the surface (Ce4f) into the lowest unoccupied molecular orbital of the SO2 adsorbate takes place and oxidizes the surface Ce3+ cations. Furthermore, we propose a mechanism that could lead to monodentate sulfate formation at the (111) surface.
Effect of filament aspect ratio on the dielectric response of multiwalled carbon nanotube composites
Authors: Kerr C. J. , Huang Y. Y. , Marshall J. E. , Terentjev E. M.
Published: May 2011

Subpercolated composites consisting of highly polar fillers in an insulating matrix have long been predicted to exhibit a large dielectric constant. In this study, we examine the feasibility of experimentally reproducing such an effect based on a multiwalled carbon nanotubes (MWNTs)-polydimethylsiloxane (PDMS) composite system. MWNTs of different diameters were subjected to high-power ultrasound. The sonication-induced scission of nanotubes shows saturation at a final length dependent on the tube diameter, in agreement with a theoretical model. Sonication allows us to produce MWNTs with a prescribed mean aspect ratio between 10 and 55. Composites were formed from these MWNTs with PDMS elastomer at a fixed 1 wt% doping level, using a common solution-processing method. Results from AC impedance spectroscopy indicate that the tube length minimally affects the dielectric response of these composites when the doping level is below the percolation threshold.
External coupled-cluster perturbation theory: Description and application to weakly interaction dimers. Corrections to the random phase approximation
Authors: Lotrich V. , Bartlett Rodney J.
Published: May 2011

The formalism for developing perturbation theory by using an arbitrary fixed (external) set of amplitudes as an initial approximation is presented in a compact form: external coupled-cluster perturbation theory (xCCPT). Nonperturbative approaches also fit into the formalism. As an illustration, the weakly interacting dimers Ne2 and Ar2 have been studied in the various ring-coupled-cluster doubles (CCD) approximations; ring, direct-ring, antisymmetrized ring, and antisymmetrized direct ring, and a second-order correction in the xCCPT approach is added. The direct approaches include the summation of just Coulomb terms with the intention of selectively summing the largest terms in the perturbation first. “Coulomb attenuation” is effected by taking the random phase approximation to define such amplitudes, whose results are then improved upon using perturbation theory. Interaction energies at the ring-CCD level are poor but the xCCPT correction employed predicts binding energies which are only a few percent from the coupled-cluster single double (triple) values for the direct ring-CCD variants. Using the MP2 amplitudes which neglect exchange, the initial Coulomb-only term, leads to very accurate Ne2 and Ar2 potentials. However, to accurately compute the Na2 potential required a different initial wavefunction, and hence perturbation. The potential energy surfaces of Ne2 and Ar2 are much too shallow using linear coupled-cluster doubles. Using xCCPT(2) with these amplitudes as the initial wavefunction led to slightly worse results. These observations suggest that an optimal external set of amplitudes exists which minimizes perturbational effects and hence improve the predictability of methods.
Field emission in air and space-charge-limited currents from iridium-iridium oxide tips with gaps below 100 nm
Authors: Brimley Scott , Miller Mark S. , Hagmann Mark J.
Published: May 2011

Field emission diodes made with Ir/IrO2 tips separated by gaps below 100 nm and operating in air gave currents of up to 1 μA just above 10 V and largely survived potentials up to 200 V. The current-voltage characteristics included signatures of Fowler–Nordheim emission and both coherent and incoherent space-charge limited emission, where both behaviors implied molecular-scale effective emission areas. The significant, nanoampere currents that flowed at biases below the expected bulk work functions corroborate the 0.1 eV work functions from Fowler–Nordheim analysis, and are attributed to molecular scale oxide structures and adsorbates shifting the surface Fermi level. Electron transit time analysis indicates that on average only one electron crossed the gap at a time, implying that the space-charge effects are due to self-interactions.
Enhanced light output power of GaN-based light-emitting diodes by nano-rough indium tin oxide film using ZnO nanoparticles
Authors: Deul Ryu Beo , Uthirakumar Periyayya , Hye Kang Ji , Jun Kwon Bong , Chandramohan S. , Kyu Kim Hyun , Yun Kim Hee , Hyoung Ryu Jae , Gu Kim Hyung , Hong Chang-Hee
Published: May 2011

We demonstrate the performance improvement of GaN-based light-emitting diodes (LEDs) using zinc oxide (ZnO) nanoparticles inserted between the p-GaN and the indium tin oxide (ITO) layers. Upon deposition of an ITO film over the dispersed ZnO nanoparticles, the ITO surface tends to attain a nano-rough morphology due to the presence of ZnO nanoparticles. The light output power of the fabricated LEDs with ZnO nanoparticles is 39% higher than that of conventional LEDs at an injection current of 20 mA. This is attributed to the improved light extraction favored by the light scattering tendency of ZnO nanoparticles and the nano-roughened ITO film. In addition, the intermediate refractive index (n ∼2) of ZnO materials between those of the p-GaN (n ∼2.5) and the ITO (n ∼1.9) results in a broader critical angle and a reduction of total internal reflection.
Numerical analysis of laser-driven reservoir dynamics for shockless loading
Authors: Li Mu , Zhang Hongping , Sun Chengwei , Zhao Jianheng , Yuan Hong
Published: May 2011

Laser-driven plasma loader for shockless compression provides a new approach to study the rapid compression response of materials not attainable in conventional shock experiments. In this method, the strain rate is varied from ∼106/s to ∼108/s, significantly higher than other shockless compression methods. Thus, this loading process is attractive in the research of solid material dynamics and astrophysics. The objective of the current study is to demonstrate the dynamic properties of the jet from the rear surface of the reservoir, and how important parameters such as peak load, rise time, shockless compression depth, and stagnating melt depth in the sample vary with laser intensity, laser pulse length, reservoir thickness, vacuum gap size, and even the sample material. Numerical simulations based on the space-time conservation element and solution element method, together with the bulk ablation model, were used. The dynamics of the reservoir depend on the laser intensity, pulse length, equation of state, as well as the molecular structure of the reservoir. The critical pressure condition at which the reservoir will unload, similar to a gas or weak plasma, is 40–80 GPa before expansion. The momentum distribution bulges downward near the front of the plasma jet, which is an important characteristic that determines shockless compression. The total energy density is the most important parameter, and has great influence on the jet characteristics, and consequently on the shockless compression characteristics. If the reservoir is of a single material irradiated at a given laser condition, the relation of peak load and shockless compression depth is in conflict, and the highest loads correspond to the smallest thickness of sample. The temperature of jet front runs up several electron volts after impacting on the sample, and the heat transfer between the stagnating plasma and the sample is sufficiently significant to induce the melting of the sample surface. However, this diffusion heat wave propagates much more slowly than the stress wave, and has minimal effect on the shockless compression progress at a deeper position.
Matrix Korteweg-de Vries and modified Korteweg-de Vries hierarchies: Noncommutative soliton solutions
Authors: Carillo Sandra , Schiebold Cornelia
Published: May 2011

The present work continues work on KdV-type hierarchies presented by S. Carillo and C. Schiebold [“Noncommutative Korteweg-de Vries and modified Korteweg-de Vries hierarchies via recursion methods,” J. Math. Phys. 50, 073510 (2009)]10.1063/1.3155080. General solution formulas for the KdV and mKdV hierarchies are derived by means of Banach space techniques both in the scalar and matrix case. A detailed analysis is given of solitons, breathers, their countable superpositions as well as of multisoliton solutions for the matrix hierarchies.
Two dimensional laser induced fluorescence spectroscopy: A powerful technique for elucidating rovibronic structure in electronic transitions of polyatomic molecules
Authors: Gascooke Jason R. , Alexander Ula N. , Lawrance Warren D.
Published: May 2011

We demonstrate the power of high resolution, two dimensional laser induced fluorescence (2D-LIF) spectroscopy for observing rovibronic transitions of polyatomic molecules. The technique involves scanning a tunable laser over absorption features in the electronic spectrum while monitoring a segment, in our case 100 cm−1 wide, of the dispersed fluorescence spectrum. 2D-LIF images separate features that overlap in the usual laser induced fluorescence spectrum. The technique is illustrated by application to the S1–S0 transition in fluorobenzene. Images of room temperature samples show that overlap of rotational contours by sequence band structure is minimized with 2D-LIF allowing a much larger range of rotational transitions to be observed and high precision rotational constants to be extracted. A significant advantage of 2D-LIF imaging is that the rotational contours separate into their constituent branches and these can be targeted to determine the three rotational constants individually. The rotational constants determined are an order of magnitude more precise than those extracted from the analysis of the rotational contour and we find the previously determined values to be in error by as much as 5% [G. H. Kirby, Mol. Phys. 19, 289 (1970)10.1080/00268977000101291]. Comparison with earlier ab initio calculations of the S0 and S1 geometries [I. Pugliesi, N. M. Tonge, and M. C. R. Cockett, J. Chem. Phys. 129, 104303 (2008)10.1063/1.2970092] reveals that the CCSD/6–311G** and RI-CC2/def2-TZVPP levels of theory predict the rotational constants, and hence geometries, with comparable accuracy. Two ground state Fermi resonances were identified by the distinctive patterns that such resonances produce in the images. 2D-LIF imaging is demonstrated to be a sensitive method capable of detecting weak spectral features, particularly those that are otherwise hidden beneath stronger bands. The sensitivity is demonstrated by observation of the three isotopomers of fluorobenzene-d1 in natural abundance in an image taken for a supersonically cooled sample. The ability to separate some of the 13C isotopomers in natural abundance is also demonstrated. The equipment required to perform 2D-LIF imaging with sufficient resolution to resolve the rotational features of large polyatomics is available from commercial suppliers.
Acousto-spinodal decomposition of compressible polymer solutions: Early stage analysis
Authors: Rasouli Ghoncheh , Rey Alejandro D.
Published: May 2011

The structure and dynamics of early stage kinetics of pressure-induced phase separation of compressible polymer solutions via spinodal decomposition is analyzed using a linear Euler–Cahn–Hilliard model and the modified Sanchez Lacombe equation of state. The integrated density wave and Cahn–Hilliard equations combine the kinetic and structural characteristics of spinodal decomposition with density waves arising from pressure-induced couplings. When mass transfer rate is slower that acoustic waves, concentration gradients generate density waves that cycle back into the spinodal decomposition dynamics, resulting in oscillatory demixing. The wave attenuation increases with increasing mass transfer rates eventually leading to nonoscillatory spinodal demixing. The novel aspects of acousto-spinodal decomposition arise from the coexistence of stable oscillatory density dynamics and the unstable monotonic concentration dynamics. Scaling laws for structure and dynamics indicate deviations from incompressible behavior, with a significant slowing down of demixing due to couplings with density waves. Partial structure factors for density and density-concentration reflect the oscillatory nature of acousto-spinodal modes at lower wave vectors, while the single maximum at a constant wave vector reflects the presence of a dominant mode in the linear regime. The computed total structure factor is in qualitative agreement with experimental data for a similar polymer solution.
The two-dimensional cobalt oxide (9 × 2) phase on Pd(100)
Authors: Gragnaniello L. , Barcaro G. , Sementa L. , Allegretti F. , Parteder G. , Surnev S. , Steurer W. , Fortunelli A. , Netzer F. P.
Published: May 2011

The two-dimensional (2D) Co oxide monolayer phase with (9 × 2) structure on Pd(100) has been investigated experimentally by scanning tunneling microscopy (STM) and theoretically by density functional theory (DFT). The high-resolution STM images reveal a complex pattern which on the basis of DFT calculations is interpreted in terms of a coincidence lattice, consisting of a CoO(111)-type bilayer with significant symmetry relaxation and height modulations to reduce the polarity in the overlayer. The most stable structure displays an unusual zig-zag type of antiferromagnetic ordering. The (9 × 2) Co oxide monolayer is energetically almost degenerate with the c(4 × 2) monolayer phase, which is derived from a single CoO(100)-type layer with a Co3O4 vacancy structure. Under specific preparation conditions, the (9 × 2) and c(4 × 2) structures can be observed in coexistence on the Pd(100) surface and the two phases are separated by a smooth interfacial boundary line, which has been analyzed at the atomic level by STM and DFT. The here described 2D Co oxide nanolayer systems are characterized by a delicate interplay of chemical, electronic, and interfacial strain interactions and the associated complexities in the theoretical description are emphasized and discussed.
Model for laminar and turbulent flows of viscous and nonlinear viscous non-Newtonian fluids
Authors: Litvinov W. G.
Published: May 2011

We develop a model that describes laminar and turbulent flows of viscous and nonlinear viscous fluids. A basis for the model is a characteristic, which we call a local Reynolds number, and which is calculated at each point of the domain of flow. In the subdomain wherein the local Reynolds number does not exceed some value, the flow is laminar; otherwise it is turbulent, i.e., the model identifies the areas of laminar and turbulent flows. The model predicts the existence of a laminar boundary layer at turbulent flows. It enables us to describe special features of turbulent flows such as a drastic increase in the resistance to flow and the variation of the velocity profile with the increase of the Reynolds number, and so on. The model is mathematically grounded. We prove the existence of global solutions to stationary and nonstationary flow problems with the nonhomogeneous Dirichlet and mixed boundary conditions, where velocities and surface forces are given on different parts of the boundary. Numerical methods for solving stationary and nonstationary flow problems are investigated.
Direct observation of basal-plane to threading-edge dislocation conversion in 4H-SiC epitaxy
Authors: Chung Suk , Wheeler Virginia , Myers-Ward Rachael , Eddy Charles R. , Gaskill D. Kurt , Wu Ping , Picard Yoosuf N. , Skowronski Marek
Published: May 2011

The propagation behavior of basal plane dislocations from off-oriented 4H-SiC substrates into homoepitaxial layers has been investigated using transmission electron microscopy (TEM), secondary electron microscopy (SEM), and chemical etching. Cross-sectional TEM shows that basal plane dislocations in the substrate are dissociated into pairs of partial dislocations separated by a stacking fault with a width of about 40 nm. Near the substrate/epilayer interface, where most of the basal plane dislocations convert to threading edge dislocations, the two partials constrict before converting. Threading edge segments are inclined by about 20° from the c-axis toward the down-step direction. It is concluded that the critical and limiting step of the dislocation conversion process is constriction of the dissociated partials. Growth surface morphology at the emergence point of the basal plane dislocation was imaged using SEM and is thought to play an important role in the constriction.
A metrology perspective on the dark injection transient current method for charge mobility determination in organic semiconductors
Authors: Esward T. , Knox S. , Jones H. , Brewer P. , Murphy C. , Wright L. , Williams J.
Published: May 2011

Charge mobility is a key parameter for understanding the performance of organic semiconductor devices and materials. A range of techniques is available that can measure charge mobility with varying accuracy and precision. In this paper we analyze the dark injection transient current (DITC) method from a metrology perspective. We carried out a systematic study of the sensitivity of single carrier analogues of organic light-emitting diodes (OLEDs) to small changes in electrical input and environmental conditions. We observed that the experimental results depend strongly on the previous history of the device under test, with both long term and short term effects in evidence. Our findings demonstrate the need for caution in interpreting the results of single experiments to determine the charge mobility of OLEDs and the difficulty of associating uncertainty statements with the results of charge mobility measurements.
Degradation mechanism beyond device self-heating in high power light-emitting diodes
Authors: Yung K. C. , Liem H. , Choy H. S. , Lun W. K.
Published: May 2011

A unique degradation property of high power InGaN/GaN multiple quantum well (MQW) white light-emitting diodes (LEDs) was identified. The LEDs were stressed under different forward-currents. The various ageing characteristics were analyzed for both the electrical response and electro-luminescence (EL) spectra. The Raman spectroscopy allowed noninvasive probing of LED junction temperature profiles which correlated well with the EL characteristics, showing a junction temperature drop during degradation at certain current levels. In addition to the common observations: (1) a broadening of the light intensity-current (L-I) characteristic in the nonlinear regime, and (2) a shift of the current-voltage (I-V) dependence to higher current levels, the EL spectra showed different temperature responses of the two blue emission peaks, 440 and 463 nm. The former was temperature sensitive and thus related to shallow defect levels, while the latter was thermally stable and deeper defect states were involved in the degradation process. This unique selection rule resulted in the enhancement of the blue emission peak at 463 nm after degrading the LEDs. This study suggests that LED device heating is not directly linked to the degradation process.
Magnetic coercivity of focused ion beam irradiated lines in a Pt/Co(1.4 nm)/Pt film
Authors: Jaworowicz J. , Zablotskii V. , Jamet J.-P. , Ferré J. , Vernier N. , Chauleau J.-Y. , Kisielewski M. , Sveklo I. , Maziewski A. , Gierak J. , Bourhis E.
Published: May 2011

Regular sets of ultranarrow lines have been patterned on a Pt/Co(1.4 nm)/Pt ultrathin magnetic film by focusing a Ga+ ion beam (FIB) at different fluences. Ga+ ion irradiation is known to soften magnetic properties in such films. Even at low Ga+ ion fluence, and as proved by atomic force microscopy, the transverse perturbed region in the lines is much wider than calculated by Stopping and Range of Ions in Matter (SRIM) simulations, demonstrating that a swelling effect superimposes to more localized irradiation damages. Field-induced magnetization reversal and static or dynamic coercivity of these FIB lines separated by nonirradiated ferromagnetic tracks have been investigated by polar MOKE microscopy. The nucleation of small reversed domains is much easier in FIB lines irradiated at high fluence, and a remnant domain structure can be stabilized in that case. The coercive field of the FIB irradiated lines is calculated using a modified one-dimensional-droplet model.
Near-infrared–ultraviolet absorption cross sections for Ge nanocrystals in SiO2 thin films: Effects of shape and layer structure
Authors: Uhrenfeldt Christian , Chevallier Jacques , Larsen Arne Nylandsted , Nielsen Brian Bech
Published: May 2011

Measured absolute optical absorption cross sections of 2–6 nm Ge nanocrystals embedded in SiO2 in the near-infrared–ultraviolet spectral range are reported. Thin layers of Ge sandwiched between SiO2 layers were prepared in a multilayered configuration, which upon heat treatment at 800 °C led to multilayers of Ge nanocrystals with a narrow size distribution. Four samples with different nanocrystal average sizes were prepared by this technique. In addition, samples containing Ge nanocrystals randomly distributed in SiO2 films were also prepared in order to clarify the effects of the multilayer configuration on the optical properties. The size distribution and density of the nanocrystals were obtained from transmission electron microscopy investigations and Rutherford backscattering spectrometry measurements. In combination with this structural information the nanocrystal absorption cross sections were obtained from optical transmission measurements, which were corrected for thin film interference effects by a self-consistent procedure. The measurements clearly show that the nanocrystal absorption per atom in the 1.5–5 eV spectral range is smaller than in bulk Ge atoms regardless of the nanocrystal size and that the absorption cross sections per atom for the nanocrystals are largely independent of the nanocrystal size. Moreover, we find that the absorption cross sections for small concentrations of Ge nanocrystals embedded in SiO2 are quantitatively well described by the Mie theory using bulk values for the dielectric function of Ge in the spectral range investigated. Hence quantum confinement effects have only minor if any influence on the dominant features of the absorption spectra for spherical Ge nanocrystals embedded in SiO2. For Ge nanocrystals ordered in multilayers we find that the experimental absorption cross section for the larger and more close packed nanocrystals exceeds that for similar concentrations of nanocrystals randomly distributed in the films, whereas this effect is not observed for multilayered samples with smaller and less densely packed nanocrystals. The combined results show that for all the Ge nanocrystals studied the nanocrystal shape and the matrix in which the nanocrystals are embedded, as well as the nanocrystal configuration play an important role in the optical response of the Ge nanocrystals and that these effects dominate the effects of quantum confinement in the absorption from spherical Ge nanocrystals embedded in SiO2.
Laser plasma plume structure and dynamics in the ambient air: The early stage of expansion
Authors: Cirisan M. , Jouvard J. M. , Lavisse L. , Hallo L. , Oltra R.
Published: May 2011

Laser ablation plasma plume expanding into the ambient atmosphere may be an efficient way to produce nanoparticles. From that reason it would be interesting to study the properties of these laser induced plasmas formed under conditions that are known to be favorable for nanoparticles production. In general, plume behavior can be described as a two-stage process: a “violent” plume expansion due to the absorption of the laser beam energy (during the laser pulse) followed by a fast adiabatic expansion in the ambient gas (after the end of the laser pulse). Plasma plume may last a few microseconds and may have densities 10−6 times lower than the solid densities at temperatures close to the ambient temperature. Expansion of the plasma plume induced by the impact of a nanosecond laser beam (λ = 1064 nm) on the surface of metallic samples in the open air has been investigated by means of fast photography. Spatio-temporal evolution of the plume at the early stage of its expansion (first 330 ns) has been recorded. Structure and dynamics of the plasma plume have been investigated and compared to numerical simulations obtained with a hydro-code, as well as some scaling laws. In addition, measurements using different sample materials (Al, Fe, and Ti) have been performed in order to analyze the influence of target material on plume expansion.
Quantum phase dynamics in an LC shunted Josephson junction
Authors: Kaiser Ch. , Bauch T. , Lombardi F. , Siegel M.
Published: May 2011

We have studied both theoretically and experimentally how an LC series circuit connected in parallel to a Josephson junction influences the Josephson dynamics. The presence of the shell circuit introduces two energy scales, which in specific cases, can strongly differ from the plasma frequency of the isolated junction. Josephson junctions were manufactured using the Nb/Al-AlOx/Nb fabrication technology with various on-chip LC shunt circuits. Spectroscopic measurements in the quantum limit show excellent agreement with theory taking into account the shunt inductance and capacitance in the resistively and capacitively shunted junction model. The results clearly show that the dynamics of the system are two-dimensional, resulting in two resonant modes of the system. These findings have important implications for the design and operation of Josephson junction based quantum bits.
Enhancement of piezoelectric response in (100)/(001) oriented tetragonal Pb(Zr, Ti)O3 films by controlling tetragonality and volume fraction of the (001) orientation
Authors: Nakajima Mitsumasa , Okamoto Syoji , Nakaki Hiroshi , Yamada Tomoaki , Funakubo Hiroshi
Published: May 2011

(100)/(001)-oriented 2 μm-thick Pb(Ti, Zr)O3, films with the Zr/(Zr + Ti) ratio of 0.39 and 0.50 were prepared by metalorganic chemical vapor deposition. The volume fraction of (001)-oriented domain, Vc, was controlled by selecting the kinds of substrates with different thermal expansion coefficient. The effective piezoelectric constant increased up to 310 pm/V with decreasing the Vc and tetragonality (lattice parameter ratio of c axis to a axis) determined by the decrease of the Zr/(Zr + Ti) ratio. Observed large piezoelectric response was considered to be mainly contributed by the extrinsic effect, such as the 90o domain switching. These experimental inputs suggest the new concept for enhancement of the piezoelectric properties.
A non-filamentary model for unipolar switching transition metal oxide resistance random access memories
Authors: Xue Kan-Hao , Paz de Araujo Carlos A. , Celinska Jolanta , McWilliams Christopher
Published: May 2011

A model for resistance random access memory (RRAM) is proposed. The RRAM under research utilizes certain transition metal oxide (TMO) such as NiO which shows unipolar switching behavior. The existence of metal/insulator states is not explained by filaments but attributed to different Hubbard U values, which stems from an electron correlation effect. Current-voltage formulae are given both on the metal and insulator sides by putting the appropriate solutions of Hubbard model into the mesoscopic Meir-Wingreen transport equation. The RESET phenomenon is explained by a sufficient separation of Fermi levels in the electrodes and hence a Mott transition can be triggered in the anodic region due to a lack of electrons. The SET behavior originates from a tunneling current which removes the insulating region near the anode. Several experimental evidences are also presented to support this model. The model also serves as the theoretical prototype of Correlated Electron Random Access Memory (CeRAM) which is defined to be a TMO RRAM whose working mechanism is based on the strong electron correlation effects.
Material and process optimization of correlated electron random access memories
Authors: Celinska Jolanta , McWilliams Christopher , Paz de Araujo Carlos , Xue Kan-Hao
Published: May 2011

A method of making transition metal oxide materials that result in resistive switching properties stable over time and temperature is described. We have developed an ultra low temperature (≤450°C) process for carbonyl ligand modified NiO thin films based on the chemical solution deposition (CSD) for correlated electron random access memory (CeRAM) applications. CeRAMs form the general class of devices that use the electron-electron interaction as the primary mode of operation. These devices are fabricated in the conductive state (born-ON), thus, they do not require electroforming to enter the variable resistance state. Several process parameters such as film stoichiometry, thickness, annealing temperature and ambient have been investigated to optimize CeRAMs properties. We present the coordination number ‘fine tuning’ in NiO ultra thin films via carbonyl ligand doping that regulate the number of oxygen vacancies and the surface excess of metal ions. CeRAMs contrary to just standard NiO based resistive memories use the pure Mott-like charge transfer insulator in which an abrupt metal to insulator transition is the dominant mechanism without the aid of charge trapping vacancies. In our films the effect of the oxygen vacancies are canceled due to the stabilizing effect of the carbonyl based extrinsic ligand. In this paper, detailed process sequence and the extrinsic ligand doping scheme is described in some length. It is shown that complexes formed by the introduction of the extrinsic ligand promote Ni2+ ions to enter the disproportionation reaction Ni2+ + Ni2+→Ni1+ + Ni3+ which is considered to be responsible for the memory mechanism.
Influence of Ti substitution on the electrical properties of metal-ferroelectric (BiFeO3)-insulator (HfO2)-silicon structures for nonvolatile memory applications
Authors: Pi-Chun Juan Trevor , Liu Yu-Wei
Published: May 2011

Metal-ferroelectric (Ti-substituted BiFeO3)-insulator (HfO2)-semiconductor structures have been fabricated via the cosputtering technique. Ti4+ substitution at the Fe site was investigated through x-ray photoelectron spectra and x-ray diffraction patterns at postannealing temperatures of 500 to 700 °C. The capacitance-voltage memory windows as functions of the insulator film thickness and the dc power for Ti were measured and compared. A memory window of 3.1 V was obtained at a sweep voltage of 8 V under O2-rich conditions. The leakage current and the charge injection effect, especially gate injection, can be greatly improved by Ti substitution. The effects of the postannealing temperature and the substitution amount on the leakage current can be well explained by the defect reaction model.
Strong growth orientation dependence of strain relaxation in epitaxial (Ba,Sr)TiO3 films and the resulting dielectric properties
Authors: Yamada Tomoaki , Kamo Takafumi , Funakubo Hiroshi , Su Dong , Iijima Takashi
Published: May 2011

The growth orientation dependence of strain relaxation and the dielectric properties were investigated for (001)- and (111)-epitaxial (Ba,Sr)TiO3 films. The films were deposited on SrRuO3/SrTiO3 and SrTiO3 substrates using rf magnetron sputtering. The residual strain was found to be remarkably different between the two orientations, although these lattice mismatches are identical; the strain relaxation of the (001)-epitaxial films is significantly slower than that of the (111)-epitaxial films and is promoted only when the growth rate is very low (≤5 nm/h). The observed orientation dependence is discussed with the surface energy for both growth orientations, which influences the growth mode of the films. Due to the large contrast of the strain in the (001)- and (111)-epitaxial films, the paraelectric to ferroelectric phase transition temperature of the (001)-epitaxial films is much higher than that of unstrained bulks, while the (111)-epitaxial films show a phase transition temperature corresponding to that of unstrained bulks regardless of the growth rates.
Improvement of barium strontium titanate solidly mounted resonator quality factor by reduction in electrode surface roughness
Authors: Saddik George N. , Son Junwoo , Stemmer Susanne , York Robert A.
Published: May 2011

Two barium strontium titanate solidly mounted resonators with different bottom electrode surface roughnesses were fabricated and tested. The surface roughness of the bottom electrode was reduced by changing the deposition method of the SiO2 layer in the acoustic Bragg reflector in the solidly mounted resonator. The surface roughness was reduced from 2.81 nm RMS to 1.45 nm RMS. This reduction in the surface roughness contributed to a significant increase in the quality factor of the resonator. The quality factor for the device with a smooth platinum bottom electrode was 110 to 87 over a bias range of 5 to 40 V, and for the device with a rough platinum bottom electrode it was 1 to 31 over the same bias range. The effective electromechanical coupling coefficient was 4% at 40 V and 3.4% at 40 V for the smooth and rough platinum bottom electrodes, respectively.
Correlation between nanoscale and nanosecond resolved ferroelectric domain dynamics and local mechanical compliance
Authors: Polomoff N. A. , Rakin A. , Lee S. , Palumbo V. , Yu P. , Chu Y. H. , Ramesh R. , Huey B. D.
Published: May 2011

The local dynamics of ferroelectric domain polarization are uniquely investigated with sub-20-nm resolved maps of switching times, growth velocities, and growth directions. This is achieved by analyzing movies of hundreds of consecutive high speed piezo force microscopy images, which record domain switching dynamics through repeatedly alternating between high speed domain imaging and the application of 20-nanosecond voltage pulses. Recurrent switching patterns are revealed, and domain wall velocities for nascent domains are uniquely reported to be up to four times faster than for mature domains with radii greater than approximately 100 nm. Switching times, speeds, and directions are also shown to correlate with local mechanical compliance, with domains preferentially nucleating and growing in compliant sample regions while clearly shunting around locations with higher stiffness. This deterministic switching behavior strongly supports a defect-mediated energy landscape which controls polarization reversal, and that can therefore be predicted, modeled, and even manipulated through composition, processing, and geometry. Such results have important implications for the practical performance of ferroelectric devices by enabling guided optimization of switching times and feature densities, while the methods employed provide a new means to investigate and correlate dynamic functionality with mechanical properties at the nanoscale.
Device characterization of correlated electron random access memories
Authors: McWilliams Christopher R. , Celinska Jolanta , Paz de Araujo Carlos A. , Xue Kan-Hao
Published: May 2011

The switching properties and characterization of correlated electron random Access Memories (CeRAMs) are described herein. High temperature retention, cycle dispersion and optimization, cycle Fatigue, and switching parameter optimization have been investigated. CeRAM’s display initially conductive or “born-ON” behavior without the need for the high electroforming voltages usually required for other transition metal oxide based resistive memories. Nonvolatile data retention at elevated temperatures up to 573 K (300 °C) in addition to a wide operating range from 4 to 423 K for CeRAM has been confirmed. CeRAMs also show exceptional read endurance with no evidence of fatigue out to 1012 cycles. Desirable scaling characteristics for high density memory application have also been shown for CeRAMs due to a widening of the read window and consistent write window as devices are scaled down.
Ultracompact beam splitters based on plasmonic nanoslits
Authors: Zhou Chuanhong , Kohli Punit
Published: May 2011

An ultracompact plasmonic beam splitter is theoretically and numerically investigated. The splitter consists of a V-shaped nanoslit in metal films. Two groups of nanoscale metallic grooves inside the slit (A) and at the small slit opening (B) are investigated. We show that there are two energy channels guiding light out by the splitter: the optical and the plasmonic channels. Groove A is used to couple incident light into the plasmonic channel. Groove B functions as a plasmonic scatter. We demonstrate that the energy transfer through plasmonic path is dominant in the beam splitter. We find that more than four times the energy is transferred by the plasmonic channel using structures A and B. We show that the plasmonic waves scattered by B can be converted into light waves. These light waves redistribute the transmitted energy through interference with the field transmitted from the nanoslit. Therefore, different beam splitting effects are achieved by simply changing the interference conditions between the scattered waves and the transmitted waves. The impact of the width and height of groove B are also investigated. It is found that the plasmonic scattering of B is changed into light scattering with increase of the width and the height of B. These devices have potential applications in optical sampling, signal processing, and integrated optical circuits.
Electrical type conversion of p-type HgCdTe induced by nanoimprinting
Authors: Martyniuk M. , Sewell R. H. , Westerhout R. , Umana-Membreno G. A. , Musca C. A. , Dell J. M. , Antoszewski J. , Faraone L. , Macintyre D. S. , Thoms S. , Ironside C. N.
Published: May 2011

A nanoimprinting method was used to generate square imprints and arrays of imprints ranging in lateral dimension from 1 μm to 50 μm in p-type HgCdTe. Laser Beam Induced Current (LBIC) characterization shows electrical type conversion around each imprint and imprint array. The LBIC signal intensity surface maps of imprinted regions and their dependence with measurement temperature correspond well with surface maps of n-on-p HgCdTe photodiodes formed by conventional techniques.
Thermal annealing effects on photoluminescence properties of carbon-doped silicon-rich oxide thin films implanted with erbium
Authors: Nikas Vasileios , Gallis Spyros , Huang Mengbing , Kaloyeros Alain E.
Published: May 2011

Results are presented from the photoluminescence properties of C-doped Si-rich thin film oxides implanted with Er, as investigated for various postdeposition implantation and subsequent annealing and passivation conditions. In particular, it was found that the near-infrared Er luminescence intensity can be increased by up to a factor of ∼4 after a postdeposition anneal at temperatures of 300–1100 °C. The postdeposition annealing also resulted in an enhancement of the green-red (500–600 nm) PL band associated with the film matrix. Post-Er implantation passivation in an oxygen atmosphere resulted in a gradual reduction in intensity for both the Er and matrix PLs, and led eventually to a complete quenching of both PLs at the highest passivation temperature (900 °C). In contrast, hydrogen passivation increased the matrix PL intensity by a factor up to ∼2, but was found to have negligible effects on Er PL intensity over a wide range of passivation temperatures. Analysis of Er and matrix-related PL characteristics suggests that the matrix luminescence centers are most likely the sensitizers responsible for energy transfer to Er in C-doped silicon oxides. In this context, a discussion is presented of potential types of matrix-related luminescence centers present in such materials, along with the possible mechanisms leading to differences in Er excitation and deexcitation between the C-doped Si-rich oxide films analyzed herein and commonly reported Si-rich oxide materials containing Si nanocrystals.
Discretized modeling of electrically driven viscoelastic jets in the initial stage of electrospinning
Authors: Carroll Colman P. , Joo Yong Lak
Published: May 2011

The focus of this work is the modeling and simulation of the initial “stable jet” phase seen during the electrospinning process. The basis of the modeling is the bead-spring approach first proposed by Reneker et al. [J. Appl. Phys. 87, p. 4531 (2000)], who used this methodology to predominantly simulate the bending instability in electrospinning. In a previous work [Carroll et al., Phys. Fluids 18, 053102 (2006)], it was seen that a continuum model was able to accurately simulate the development of the jet in the stable jet region. Based on a comparison between these two approaches, a more detailed conservation of charge relationship, surface tension forces in the jet axial direction and the presence of a Newtonian viscous solvent are added into the bead-spring model. The jet profile predictions given by the modified model are in greatly improved agreement with experimental data from the electrospinning of various fluids including poorly electrically conducting PIB Boger fluids and highly conducting PEO/water solutions. The accurate bead-spring model predictions constitute a promising springboard for the further study of the emergence and propagation of the bending instability in electrospinning.
Analytical single-mode model for subwavelength metallic Bragg waveguides
Authors: Zhong Xiao-Lan , Li Zhi-Yuan , Wang Chen , Zhou Yun-Song
Published: May 2011

We develop a theoretical formalism that incorporates the method of moment with the analytical eigenmode expansion to investigate the dispersion relation of light transport in subwavelength metallic Bragg waveguide (WG) with each unit cell composed of a wide and a narrow segment of metallic gap. The approach fully accounts for the light scattering at the interface between two consecutive discontinuous segments. A simple single-mode analytical model is derived for both the fundamental even and odd guided modes. The model shows that the band structure of light transport in the structure resembles that of an ordinary dielectric one-dimensional photonic crystal with appropriate physical and geometric parameters that can be analytically derived. Numerical simulations by the finite-difference time-domain method on the optical transmission spectra and band diagrams for these metallic Bragg WGs agree well with the analytical results of band diagrams. In addition, the analytical model can handle structures working in both the microwave and infrared regimes. This indicates that the simple analytical model is effective and efficient in handling various light transport problems for subwavelength metallic Bragg WGs.