bluuebunny/crossref_metadata_2025 huggingface dataset:
Lipoxins and novel 15‐epi‐lipoxin analogs display potent anti‐inflammatory actions after oral administration
Authors: Bannenberg Gerard , Moussignac Rose‐Laure , Gronert Karsten , Devchand Pallavi R , Schmidt Birgitta A , Guilford William J , Bauman John G , Subramanyam Babu , Daniel Perez H , Parkinson John F , Serhan Charles N
Published: September 2004

Lipoxins (LX) and aspirin‐triggered 15‐epi‐lipoxins (ATL) exert potent anti‐inflammatory actions. In the present study, we determined the anti‐inflammatory efficacy of endogenous LXA4 and LXB4, the stable ATL analog ATLa2, and a series of novel 3‐oxa‐ATL analogs (ZK‐996, ZK‐990, ZK‐994, and ZK‐142) after intravenous, oral, and topical administration in mice.

LXA4, LXB4, ATLa2, and ZK‐994 were orally active, exhibiting potent systemic inhibition of zymosan A‐induced peritonitis at very low doses (50 ng kg−1–50 μg kg−1).

Intravenous ZK‐994 and ZK‐142 (500 μg kg−1) potently attenuated hind limb ischemia/reperfusion‐induced lung injury, with 32±12 and 53±5% inhibition (P<0.05), respectively, of neutrophil accumulation in lungs. The same dose of ATLa2 had no significant protective action.

Topical application of ATLa2, ZK‐994, and ZK‐142 (∼20 μg cm−2) prevented vascular leakage and neutrophil infiltration in LTB4/PGE2‐stimulated ear skin inflammation. While ATLa2 and ZK‐142 displayed approximately equal anti‐inflammatory efficacy in this model, ZK‐994 displayed a slower onset of action.

In summary, native LXA4 and LXB4, and analogs ATLa2, ZK‐142, and ZK‐994 retain broad anti‐inflammatory effects after intravenous, oral, and topical administration. The 3‐oxa‐ATL analogs, which have enhanced metabolic and chemical stability and a superior pharmacokinetic profile, provide new opportunities to explore the actions and therapeutic potential for LX and ATL.

British Journal of Pharmacology (2004) 143, 43–52. doi:10.1038/sj.bjp.0705912
Nonlinear optical properties of tungstate fluorophosphate glasses
Authors: Falcão-Filho E. L. , de Araújo Cid B. , Bosco C. A. C. , Acioli L. H. , Poirier G. , Messaddeq Y. , Boudebs G. , Poulain M.
Published: September 2004

The optical nonlinearity of tungstate fluorophosphate glasses, synthesized in the NaPO3-BaF2-WO3 system, was investigated through experiments based on the third-order susceptibility, χ(3). Nonlinear (NL) refraction and NL absorption measurements in the picosecond regime were performed using the Z-scan technique at 532 nm. NL refractive index, n2∝Re χ(3), ranging from 0.4×10−14 cm2/W to 0.6×10−14 cm2/W were determined. The two-photon absorption coefficient, α2∝Im χ(3), for excitation at 532 nm, vary from 0.3 to 0.5 cm/GW. Light induced birefringence experiments performed in the femtosecond regime indicate that the response time of the nonlinearity at 800 nm is faster than 100 fs. The experiments show that χ(3) is enhanced when the WO3 concentration increases and this behavior is attributed to the hyperpolarizabilities associated to W–O bonds.
Deterministic and finite temperature micromagnetics of nanoscale structures: A simulation study
Authors: Roy Pierre E. , Svedlindh Peter
Published: September 2004

Zero and finite temperature micromagnetic studies have been performed for two nanoscale structures of different geometries by means of numerical integration of the deterministic and stochastic Landau-Lifshitz-Gilbert equations of motion. The results indicate that not only do thermal fluctuations cause a decrease of the coercivity and the time scales involved in switching, but they can also alter the magnetization reversal path. In the case of thermally induced changes in the switching path it is found that with sufficient thermal energy the particle can form other states prior to switching than in the deterministic model. This leads to the identification of two switching regimes in the structures considered, whereby switching from one of the states significantly decreases the coercivity. Furthermore, a study of the time scales involved and the transient magnetic configurations appearing during fast switching was performed.
Chirally oriented heteroepitaxial thin films grown by pulsed laser deposition: Pt(621) on SrTiO3(621)
Authors: Francis Andrew J. , Salvador Paul A.
Published: September 2004

Pulsed laser deposition has been used to grow Pt(621) thin films having a chiral orientation on SrTiO3(621) substrates. Films were deposited over a range of conditions, then characterized for their crystallinity and epitaxy using x-ray diffraction and for their surface morphologies using atomic force microscopy (AFM). Films deposited at 600°C grew epitaxially, but with an island growth mode. Pt deposited at 250°C displayed smooth surfaces but did not grow epitaxially. A three-step process wherein films were seeded at 600°C, deposited at 250°C, and postannealed was shown to result in excellent epitaxial growth and flat surface morphologies. Films grown using the three-step process exhibited excellent epitaxy, having the orientation relationship (621)Pt‖(621)SrTiO3:[01¯2]Pt‖[01¯2]SrTiO3. When postannealed at 800°C, they exhibited flat surfaces (rms≈20Å) having long terraces separated by steps running along the expected [01¯2] direction of the SrTiO3(621) substrate. Films postannealed at 600°C were flatter (rms≈10Å) with no evident step directionality. The SrTiO3(621) substrates were observed to be extremely flat (rms≈2Å) and to have morphologically featureless surfaces, as expected for a (621) surface. The good crystalline quality of the SrTiO3 substrate surface is considered to drive the growth of the chirally oriented heteroepitaxial Pt films. Similarities and differences between Pt growth on chiral surfaces and on low-index achiral surfaces are discussed.
Electrical characteristics of AlxGa1−xN Schottky diodes prepared by a two-step surface treatment
Authors: Motayed Abhishek , Sharma Ashok , Jones Kenneth A. , Derenge Michael A. , Iliadis Agis A. , Mohammad S. Noor
Published: September 2004

Near-ideal Schottky barrier contacts to n-type Al0.22Ga0.78N have been developed by a two-step surface treatment technique. Plasma etching of the AlxGa1−xN surface prior to Schottky metal deposition, combined with sequential chemical treatment of the etched surface, holds promise for developing high quality low-leakage Schottky contacts for low noise applications and for recessed gate high electron mobility transistors. In this work, the effect of postetch chemical treatment of the n-type Al0.22Ga0.78N surface on the performance of the Ni∕Au based Schottky contact has been investigated. Three different types of chemical treatment: viz, reactive ion etching, reactive ion etching plus dipping in hot aqua regia, and reactive ion etching plus dipping in hot KOH, are studied. Detailed current-voltage studies of three different surface treated diodes and a comparison with as-deposited diodes reveal significant improvement in the diode characteristics. The latter surface treatment yields Ni∕Au Schottky diodes with very low reverse leakage currents, breakdown voltages greater than 44V, and an ideality factor as low as 1.14.
Local interface composition and native stacking fault density in ZnSe∕GaAs(001) heterostructures
Authors: Colli A. , Carlino E. , Pelucchi E. , Grillo V. , Franciosi A.
Published: September 2004

We performed a comparative investigation of interface structure and composition in pseudomorphic ZnSe∕GaAs(001) heterostructures grown using interface fabrication procedures that produce epilayers with minimum stacking fault densities (below 104cm−2). We detected in all cases a 1nm thick intermixed region at the interface that is depleted of As and is comprised of a (Zn,Ga)As alloy with zincblende structure. No ZnAs formation was found in any of the interfaces examined. Our results imply that Ga-Se reactions at the ZnSe∕GaAs interface do not necessarily lead to nucleation of high densities of stacking faults and that ZnAs formation plays no role in the observed reduction of the native defect density.
Dynamics of energy transfer and frequency upconversion in Tm3+ doped fluoroindate glass
Authors: Jerez Vladimir A. , de Araújo Cid B. , Messaddeq Y.
Published: September 2004

Blue and ultraviolet upconversion (UC) emissions at 455 and 363nm were observed from Tm3+ doped fluoroindate glasses pumped at 650nm. The time behavior of the UC signals was studied for different Tm3+ concentrations. The measurements revealed the origin of the UC process as well as allowed to quantify the interaction between Tm3+ ions. The results indicate that a two-step one-photon absorption process is responsible for the UC emissions, and dipole-dipole interaction provides the main contribution for energy transfer (ET) among active ions. The critical distance between Tm3+ ions at which the ET rate is equal to the decay rate of noninteracting Tm3+ ions was determined.
Effect of substrate-induced strain on the structural, electrical, and optical properties of polycrystalline ZnO thin films
Authors: Ghosh R. , Basak D. , Fujihara S.
Published: September 2004

The effect of substrate-induced strain in polycrystalline ZnO thin films on different substrate, e.g., GaN epilayer, sapphire (0001), quartz glass, Si(111)∕SiO2, and glass deposited by sol-gel process, has been investigated by x-ray diffraction, scanning electron microscope, electrical resistivity, and photoluminescence measurements. A strong dependence of orientation, crystallite size, and electrical resistivity upon the substrate-induced strain along the c axis has been found. The results of structural and morphological studies indicate that relatively larger tensile strain exists in ZnO deposited on sapphire and glass, while a smaller compressive strain appears in film deposited on GaN and the strain is relaxed in larger crystallite size. The electrical resistivity of the films increases exponentially with increasing strain. The excitonic peak positions are found to shift slightly towards lower energy side with increasing strain. The analysis shows that GaN being a closely lattice-matched substrate produces ZnO films of better crystallinity with a lower resistivity.
Layer morphology and Al implant profiles after annealing of supersaturated, single-crystalline, amorphous, and nanocrystalline SiC
Authors: Heera V. , Mücklich A. , Dubois C. , Voelskow M. , Skorupa W.
Published: September 2004

Al supersaturated SiC layers (5×1020Alcm−3) were produced by multienergy, high-dose ion implantation into 6H- and 4H-SiC. Several implantation schemes with varying implantation sequence and temperature were investigated. In dependence on the implantation conditions damaged single-crystalline, amorphous, or nanocrystalline layers were formed. The layer morphology and Al distribution in the as-implanted state as well as structural changes and related Al redistribution after high-temperature annealing (1500–1700°C) were characterized by cross-sectional transmission electron microscopy, Rutherford backscattering spectrometry in combination with ion channeling, atomic force microscopy, and secondary-ion mass spectrometry. Remarkable Al redistribution effects have been found after annealing of Al supersaturated SiC. During high-temperature annealing Al atoms in excess to the solid solubility (2×1020Alcm−3) tend to precipitate in single-crystalline SiC whereas they diffuse out in amorphous or nanocrystalline SiC. Redistribution of Al with concentration below the solid solubility is governed by transient enhanced diffusion which can be controlled by the annealing scheme. Amorphization of SiC is advantageous in the case of Al doping to levels higher than the solid solubility because it prevents Al precipitation during annealing and helps to form boxlike Al profiles with smooth plateau and abrupt edge.
Mechanism of silicon etching in the presence of CF2, F, and Ar+
Authors: Humbird David , Graves David B.
Published: September 2004

Molecular dynamics simulations of CF2, F, and Ar+ impacting silicon surfaces reveal the spontaneous formation of segregated layers of Si-C and SiFx, formed due to Ar+ ion impact and ion-induced mixing. The mechanisms of steady-state etching under these conditions involve a leading front of SiFx that fluorinates the Si substrate, followed by a region or zone of Si-C. The SiFx and Si-C layers move through the substrate Si during steady-state etching. Si is generally etched from the surface of the Si-C layer by an ion impact. Carbon reaction with Si in the Si-C zone raises the total atomic density in the Si-C layer to nearly three times the value observed in undisturbed Si and reduces the Si etch rate by limiting ion mixing. Etching stops completely if the Si-C layer becomes so impervious that ions cannot reach the SiFx front. The importance of the depth profile of ion energy deposition in sustaining etching is very clearly observed in the simulations.
Current-driven switching of exchange biased spin-valve giant magnetoresistive nanopillars using a conducting nanoprobe
Authors: Hayakawa J. , Ito K. , Fujimori M. , Heike S. , Hashizume T. , Steen J. , Brugger J. , Ohno H.
Published: September 2004

An array of exchange biased spin-valve giant-magnetoresistance nanopillars was fabricated and the current I dependence of the resistance R was investigated using an electrically conducting atomic-force microscope (AFM) probe contact at room temperature. We observed current induced switching in a MnIr∕CoFe∕Cu∕CoFe∕NiFe nanopillar using the AFM probe contact. Current-driven switching using nanoprobe contact is a powerful method for developing nonvolatile and rewritable magnetic memory with high density.
Hyperchaos of arbitrary order generated by a single feedback circuit, and the emergence of chaotic walks
Authors: Thomas René , Basios Vasileios , Eiswirth Markus , Kruel Thomas , Rössler Otto E.
Published: September 2004

It is shown that hyperchaos of order m (i.e., with m positive Lyapunov exponents) can be generated by a single feedback circuit in n=2m+1 variables. This feedback circuit is constructed such that, dividing phase space into hypercubes, it changes sign wherever the trajectory passes from one hypercube into an adjacent one. Letting the negative diagonal elements in the Jacobian tend to zero, the dynamics becomes conservative. Instead of chaotic attractors, unbounded chaotic walks are then generated. Here we report chaotic walks emerging from a continuous system rather than the well known chaotic walks present in “Lorentz gas” and “couple map lattices.”
Structure and optical properties of cored wurtzite (Zn,Mg)O heteroepitaxial nanowires
Authors: Heo Y. W. , Abernathy C. , Pruessner K. , Sigmund W. , Norton D. P. , Overberg M. , Ren F. , Chisholm M. F.
Published: September 2004

The synthesis, structure, and optical properties of one-dimensional heteroepitaxial cored (Zn,Mg)O semiconductor nanowires grown by a catalyst-driven molecular beam epitaxy technique are discussed. The structures form spontaneously in a Zn, Mg and O2∕O3 flux, consisting of a single crystal, Zn-rich Zn1−xMgxO(x<0.02) core encased by an epitaxial Zn1−yMgyO(y⪢0.02) sheath. High resolution Z-contrast scanning transmission electron microscopy shows core diameters as small as 4nm. The cored structure forms spontaneously under constant flux due to a bimodal growth mechanism in which the core forms via bulk like vapor-liquid-solid growth, while the outer sheath grows as a heteroepitaxial layer. Temperature-dependent photoluminescence shows a slight blueshift in the near band edge peak, which is attributed to a few percent Mg doping in the nanoscale ZnO core. The catalyst-driven molecular beam epitaxy technique provides for site-specific nanorod growth on arbitrary substrates.
Modeling of temperature sensor built on thin silicon on insulator using advanced carrier-mobility model
Authors: Wu Z. H. , Lai P. T.
Published: September 2004

Based on the minority-carrier exclusion theory, an analytical model is developed to explain the operating principle of temperature sensors fabricated on thin silicon film. The model also takes into account the effects of temperature and carrier concentrations on carrier mobilities. Device simulation is used to verify the proposed model in terms of the carrier-concentration distribution in the minority-exclusion region, exclusion length, and the temperature dependence of the sensor resistance. Results show that the model is applicable for a sensor operating over a wide temperature range, provided that its bias current is not too high.
Moisture-driven crack growth in blanket low dielectric constant and ultralow dielectric constant films
Authors: Liniger E. G. , Simonyi E. E.
Published: September 2004

Moisture-driven crack growth was measured as a function of film thickness for a variety of low dielectric constant and ultralow dielectric constant films and a comparison of the crack driving force was made. By plotting the crack velocity versus the crack driving force, a series of universal curves was produced which showed that fracture resistance scales with the dielectric constant.
Time-resolved photoluminescence and capacitance–voltage analysis of the neutral vacancy defect in silicon implanted SiO2 on silicon substrate
Authors: Lin Gong-Ru , Lin Chun-Jung , Yu Kuo-Chen
Published: September 2004

The nanosecond photoluminescence (PL) dynamics of neutral oxygen vacancy (NOV) defects at 410–460nm, and less pronounced nanocrystallite Si precursor (E′δ) defects at 520nm in multi-energy silicon-ion-implanted SiO2 (SiO2:Si+) are investigated. The density of NOV defects in as-implanted SiO2:Si+ of 8×1016cm−3 (or 2.5×1016cm−3 calculated from time-resolved PL) is determined by using capacitance-voltage measurement. After annealing at 1100°C for 3h, the NOV defects are completely activated with a concentration of 4.8×1017cm−3 and a corresponding absorption cross section of 9×10−17cm2. The time-resolved PL lifetime of NOV defects in SiO2:Si+ is significantly shortened from 26to3.6ns and these defects are fully activated after annealing for 3h. Longer annealing time greatly attenuates the blue-green PL intensity and eliminates the NOV defects, whereas the PL intensity and concentration of E′δ defects with lifetime of 20–50ns increases by a factor of 2.
Influence of crystal defects on the piezoresistive properties of 3C–SiC
Authors: Eickhoff M. , Stutzmann M.
Published: September 2004

We present a model for the quantitative assessment of the influence of crystal defects on the piezoresistive properties of n-type cubic silicon carbide. In an extended carrier trapping model, the strain dependent transport at potential barriers formed by electrons in defect states at internal boundaries is calculated. Based on experimental results of electronic and structural characterization, the piezoresistive properties of nanocrystalline silicon carbide are derived. The magnitude of the piezoresistive gauge factor as well as its dependence on temperature, carrier density, and crystal orientation shows excellent agreement with the experimental findings. Taking the depth profile of the defect density into account, the same model is used to explain the depth dependence of the piezoresistive gauge factors in single crystalline cubic silicon carbide layers.
Effect of outermost layers on resonant cavity enhanced devices
Authors: Chung Il-Sug , Lee Yong Tak , Kim Jae-Eun , Park Hae Yong
Published: September 2004

Both the reflectivity and the reflection delay of a quarter wave mirror (QWM) can be controlled by choosing the outermost layer of the QWM appropriately. For a GaAs∕Al0.75Ga0.25As QWM, depositing a Si layer as the incoming outermost layer decreases the reflectivity to the same degree as removing 19.6 layers, and increases the reflection delay by 12.0 times. Likewise, when using a TiO2 layer, the reflectivity decreases to a level similar to the removal of 16.1 layers while the reflection delay is 7.9 times longer. Therefore, an efficient method to fabricate resonant cavity enhanced photodetectors for bidirectional optical interconnects is proposed. This method needs no subsequent etching process while giving a quantum efficiency of approximately 90% using currently available deposition techniques. Furthermore, the tunable wavelength and bandwidth ranges of microelectromechanical system tunable filters can be controlled separately by the outermost layer, thereby allowing filters with different bandwidths to be fabricated on the same wafer.
Hollow and solid spherical magnetostrictive particulate composites
Authors: Nersessian Nersesse , Or Siu Wing , Carman Gregory P. , Choe Wonyoung , Radousky Harry B.
Published: September 2004

Nickel microspheres were produced by the spark erosion technique under both liquid nitrogen and water conditions. Density measurements and Scanning electron microscope analysis revealed that a significant portion of the Ni particles produced under the liquid nitrogen conditions are hollow spheres with a density of 6.67(4)g∕cm3 while the particles produced in water are primarily solid spheres with a density of 8.40(1)g∕cm3, close to the bulk nickel value of 8.90g∕cm3. Nickel∕polymer composites incorporating the hollow and solid nickel microspheres were manufactured with volume fractions of 25% and 36%, respectively. The hollow and solid nickel composites exhibited saturation magnetostrictions of −24 and −28ppm, respectively. In addition, small quantities of Terfenol-D (Tb0.3Dy0.7Fe2) were spark eroded under liquid argon conditions with ∼10% by volume of the spark eroded particles being solid microspheres. Calculations indicate that aligned composites that incorporate these Terfenol-D microspheres could reach a strain value of 2000ppm.
Sexithiophene films on clean and oxidized Si(111) surfaces: Growth and electronic structure
Authors: Ivanco J. , Krenn J. R. , Ramsey M. G. , Netzer F. P. , Haber T. , Resel R. , Haase A. , Stadlober B. , Jakopic G.
Published: September 2004

The growth and the electronic properties of sexithiophene thin films on silicon surfaces have been studied by angle resolved ultraviolet photoelectron spectroscopy while morphology and crystalline order have been assessed by atomic force microscopy and x-ray diffraction. The influence of the surface modification of the substrate as well as of the growth temperature and the growth rate were investigated in ultrahigh vacuum through controlled multistep growth sequences ranging from (sub)monolayer coverage up to thick films. Depending on the preparation, two electronically distinct sexithiophene (6T) films could be produced, as revealed by their ionization potentials which differed by ∼0.7eV. The evolution of the electronic energy levels with film thickness is considered in terms of the concepts of interface dipole and band bending, with the latter being argued to be inappropriate. Irrespective of substrate or growth conditions the thick 6T films were found to all have the same work function of ∼0.4eV, which is related to near vertically oriented molecules on the films surface. Against general expectations 6T grown at a low rate on the reactive Si(111) substrate and those grown at high rates on the oxide surface produces films that are more uniform and crystalline than those grown at low rates on the passive oxidized Si surfaces. The latter promotes the formation of small three-dimensional crystallites and a much poorer morphology for planar devices.
Interface instabilities and electronic properties of ZrO2 on silicon (100)
Authors: Fulton C. C. , Cook T. E. , Lucovsky G. , Nemanich R. J.
Published: September 2004

The interface stability of Zr-based high-k dielectrics with an oxide buffer layer was explored with x-ray (hυ=1254eV) and ultraviolet (hυ=21.2eV) photoemission spectroscopy. Zirconium oxide films were grown and characterized in situ in a stepwise sequence to explore their chemical stability and electronic properties as a function of film thickness and processing conditions. The buffer layers serve to lower the interface state density and to address the high temperature instabilities of ZrO2 in direct contact with Si. This research addresses three issues: (1) the development of the band offsets and electronic structure during the low temperature (T<300°C) growth processes, (2) variations in the band structure as effected by process conditions and annealing (T<700°C), and (3) the interface stability of Zr oxide films at high temperatures (T>700°C). Annealing the as-grown films to 600°C results in an ∼2eV shift of the ZrO2-Si band alignment, giving a band offset that is, favorable to devices, in agreement with predictions and in agreement with other experiments. We propose that the as-grown films contain excess oxygen resulting in a charge transfer from the Si substrate to the internal (ZrO2-SiO2) interface and that annealing to 600°C is sufficient to drive off this oxygen. Further annealing to 900°C, in the presence of excess Si at the surface, results in decomposition of the oxide to form ZrSi2.
Polarized Raman spectroscopy of multilayer Ge∕Si(001) quantum dot heterostructures
Authors: Baranov A. V. , Fedorov A. V. , Perova T. S. , Moore R. A. , Solosin S. , Yam V. , Bouchier D. , Thanh V. Le
Published: September 2004

Polarized Raman spectroscopy in backscattering geometry has been applied here for the investigation of Ge∕Si(001) quantum dot multilayer structures (with the number of layers ranging from 1 to 21) grown by the Stranski-Krastanov technique. The characteristic Raman spectra of the dots have been obtained by taking the difference between the Raman spectra of the dot sample and the reference Si substrate, taken under the same excitation/scattering conditions. We found that the Raman spectra of Ge∕Si dots obtained in such a manner are strongly polarized, in particular, for the Ge-Ge (at ∼295cm−1) and Si-Ge (at ∼413cm−1) vibrational modes. The dependence of peak intensity and peak position of the Ge-Ge and Ge Raman bands versus the number of dot layers has been analyzed. It was found that studied quantum dot (QD) systems possess prominent anisotropic intermixing. This results in the Si content in the dots being high and this increases with the number of QD layers. At the same time, the increase of the number of layers was followed by a reduction in the compressive stress within the dots.
Ion ranges and irradiation-induced defects in multiwalled carbon nanotubes
Authors: Pomoell J. A. V. , Krasheninnikov A. V. , Nordlund K. , Keinonen J.
Published: September 2004

Recent experiments on ion irradiation of carbon nanotubes have revealed a wealth of intriguing phenomena. However, in spite of the experimental progress, the production of irradiation-induced defects in multiwalled nanotubes (MWNTs) and their properties are not yet well understood. By employing molecular dynamics with analytical potentials we simulate irradiation of MWNTs with various noble-gas ions and calculate the ion ranges as a function of ion energy. We also use the conventional binary collision stochastic approach to estimate the ranges and compare the results obtained through the two methods. We further characterize the irradiation-induced defects which appear in MWNTs under both single ion impacts and high-dose bombardment. We finally study if, similarly to carbon onions, irradiation can give rise to transformations of nanotubes to nanodiamond rods and demonstrate that such transformations do not occur in MWNTs due to their tubular structure.
Magnetically soft, high moment grain-refined Fe films: Application to magnetic tunnel junctions
Authors: Georgieva M. T. , Telling N. D. , Grundy P. J. , Faunce C. A. , Jones G. A.
Published: September 2004

The effect of N-doping on the microstructure and magnetic properties of thin Fe layers has been employed to construct all Fe-electrode magnetic tunnel junctions that displayed the tunneling magnetoresistance (TMR) effect. Using low nitrogen doses, a reduction in coercivity was achieved due to grain refinement, without a concurrent decrease in the saturation magnetization of the Fe films caused by the formation of crystalline iron nitride phases. It was demonstrated that this N-induced grain refinement can be applied beneficially to control the switching field of the “free” layer in magnetic trilayer structures. In general the ability to control magnetic softness without reducing saturation magnetization will prove important for incorporating high spin-polarized materials into spin valves and TMR devices.
Examining nanoparticle assemblies using high spatial resolution x-ray microtomography
Authors: Jenneson P. M. , Luggar R. D. , Morton E. J. , Gundogdu O. , Tüzün U.
Published: September 2004

An experimental system has been designed to examine the assembly of nanoparticles in a variety of process engineering applications. These applications include the harvesting from solutions of nanoparticles into green parts, and the subsequent sintering into finished components. The system is based on an x-ray microtomography with a spatial resolution down to 5μm. The theoretical limitations in x-ray imaging are considered to allow experimental optimization. A standard nondestructive evaluation type apparatus with a small focal-spot x-ray tube, high-resolution complementary metal oxide semiconductor flat-panel pixellated detector, and a mechanical rotational stage is used to image the static systems. Dynamic sintering processes are imaged using the same x-ray source and detector but a custom rotational stage which is contained in an environmental chamber where the temperature, atmospheric pressure, and compaction force can be controlled. Three-dimensional tomographic data sets are presented here for samples from the pharmaceutical, nutraceutical, biotechnology, and nanoparticle handling industries and show the microscopic features and defects which can be resolved with the system.
Comparison of oxide breakdown progression in ultra-thin oxide silicon-on-insulator and bulk metal-oxide-semiconductor field effect transistors
Authors: Chen M. C. , Ku S. H. , Chan C. T. , Wang Tahui
Published: September 2004

Enhanced oxide breakdown progression in ultra-thin oxide silicon-on-insulator p-type metal-oxide-semiconductor field-effect transistors is observed, as compared to bulk devices. The enhanced progression is attributed to the increase of hole stress current resulting from breakdown induced channel carrier heating in a floating-body configuration. Numerical analysis of hole tunneling current and hot carrier luminescence measurement are performed to support our proposed theory. This phenomenon is particularly significant to the reliability of devices with ultra-thin oxides and low operation gate voltage.
Stochastic Coulomb interactions in space charge limited electron emission
Authors: Nijkerk M. D. , Kruit P.
Published: September 2004

Emission models that form the basis of self-consistent field computations make use of the approximation that emitted electrons form a smooth space charge jelly. In reality, electrons are discrete particles that are subject to statistical Coulomb interactions. A Monte Carlo simulation tool is used to evaluate the influence of discrete space charge effects on self-consistent calculations of cathode-ray tube optics. We find that interactions in the space charge cloud affect the electron trajectories such that the velocity distribution is Maxwellian, regardless of the current density. Interactions near the emitter effectively conserve the Maxwellian distribution. The surprising result is that the width of the distribution of transversal velocities does not change. The distribution of longitudinal velocities does broaden, as expected from existing theories.
Instability induced tunneling and repeatable charge injection to SiO2 surfaces by electrostatic force microscopy
Authors: Klein L. J. , Williams C. C.
Published: September 2004

The dynamic response and stability of a voltage biased oscillating cantilever in the proximity of an insulating sample surface is investigated. As the tip approaches the sample surface, the cantilever can jump between two different oscillation modes. The jump is detected as an abrupt increase in the amplitude. This abrupt increase in amplitude can bring the tip into tunneling range of the sample surface and electrons can tunnel between the metallic tip and insulator surface. The electron tunneling decreases the electrostatic force and force gradient sensed by the cantilever. These changes reduce the oscillation amplitude, causing the cantilever to return to the original oscillation mode. The tunneling of tens of electrons from a metallic tip to a SiO2 surface is detected by measuring the electrostatic force between the tip and the sample. Manipulation of a small number of electrons can be achieved by changing the polarity of the voltage applied, allowing the injection and extraction of electrons to and from an insulator surface.
Laser trapping and patterning of protein microcrystals: Toward highly integrated protein microarrays
Authors: Hosokawa Yoichiroh , Matsumura Satoshi , Masuhara Hiroshi , Ikeda Keiko , Shimo-oka Ai , Mori Hajime
Published: September 2004

Some insect virus infections occlude into a crystalline matrix consisting of a protein named polyhedrin. The shape of the matrix is a cubic polyhedron of the size of a few micrometers. Recently it was shown that these polyhedra could immobilize various functional proteins within them. Therefore, the polyhedron is interesting as an element in a protein chip. In this work, individual polyhedra were arrayed and bonded under a microscope by focused laser beams, with the aim of fabricating a highly integrated protein chip. The polyhedron was trapped and transferred to a suitable position on a polymer substrate by optical trapping with a 1064nmNd3+:YAG (YAG, yttrium aluminum garnet) laser. To bond the polyhedron on the substrate, the polymer surface was mechanically and chemically modified by multiphoton absorption of a 120fs, 800nm femtosecond Ti: sapphire laser, which results in strong adhesion of the polyhedron to the substrate. The arraying and bonding of polyhedra were successful, to a precision of about 1μm, with this procedure. The biological activity of polyhedra after these laser irradiations was confirmed by the fluorescence of green fluorescent protein occluded in the polyhedrin matrix.
Effect of oxygen precipitates and induced dislocations on oxidation-induced stacking faults in nitrogen-doped Czochralski silicon
Authors: Wang Hongjie , Yang Deren , Yu Xuegong , Ma Xiangyang , Tian Daxi , Shen Yijun , Li Liben , Que Duanlin
Published: September 2004

The effect of oxygen precipitates and induced dislocations on oxidation-induced stacking faults (OSFs) in nitrogen-doped Czochralski (NCZ) silicon has been investigated. Both CZ and NCZ wafers were annealed at 800°C and 1000°C for 225h with or without a post-treatment at 1200°C for 8h, and then were totally oxidized at 1150°C. It was found that after oxidization, few OSFs generated in the NCZ silicon subjected to the annealing at 800 and 1000°C, while larger numbers of OSFs in the CZ silicon. However, if the post-treatment at 1200°C was employed prior to oxidization, OSFs density in the NCZ silicon was almost similar to that in the CZ silicon. It is considered that the high density of oxygen precipitates and induced dislocations formed in NCZ silicon can absorb the self-interstitial silicon atoms so that the generation of OSFs is inhibited. After the postannealing, most dislocations shrank and dissolved with the dissolution of oxygen precipitates in the NCZ silicon so as to induce the same amount of OSFs as that in the CZ silicon.
High-quality as-grown MgB2 thin-film fabrication at a low temperature using an in-plane-lattice near-matched epitaxial-buffer layer
Authors: Sakata O. , Kimura S. , Takata M. , Yata S. , Kato T. , Yamanaka K. , Yamada Y. , Matsushita A. , Kubo S.
Published: September 2004

An as-grown MgB2 crystalline thin film was fabricated at a low temperature of 270°C on an in-plane-lattice near-matched TiZr buffer layer grown on a sapphire Al2O3 (0001) surface. The critical temperature and the superconductivity critical current density of MgB2∕TiZr∕Al2O3 were found to be high compared with those of MgB2∕Al2O3. The film was characterized by using synchrotron x-ray diffraction. The epitaxial relationship in the plane was MgB2[011¯0]∕∕TiZr[011¯0]∕∕ sapphire [112¯0]. In-plane-lattice spacings, d∕∕MgB2, d∕∕TiZr, and d∕∕sapphire obtained were 0.268, 0.258, and 0.239nm for the MgB2(011¯0), TiZr(011¯0), and sapphire (112¯0) planes, respectively.
Natural computation measured as a reduction of complexity
Authors: Stoop R. , Stoop N.
Published: September 2004

We argue that the deeper nature of computation is to reduce the statistical obstruction against prediction. From this, we derive an explicit measure of computation for general, artificial as well as natural, systems (electronic circuits, neurons, mechanical devices, etc.). The applicability and usefulness of this concept is demonstated using well-studied families of dynamical systems, as well as experimental time series from cortical neurons.
Electric-field-induced conductance transition in 8-hydroxyquinoline aluminum (Alq3)
Authors: Mahapatro Ajit Kumar , Agrawal Ruchi , Ghosh Subhasis
Published: September 2004

We report an electric-field-induced conductance transition from an insulating state to a conducting state in a thin layer of Alq3 sandwiched between two metal electrodes. Field-induced switching behavior with a high on-off ratio of ∼105 is observed in the devices, in which the cathode electrode is Al and the anode electrode is varied including Al, Au, and indium tin oxide. The switching behavior is absent in devices in which both electrodes have a high work function, indicating that efficient electron injection has an important role in the electric-field-induced switching behavior of Alq3-based single-layer devices.
Flux pinning and magnetic relaxation in melt-processed YBa2Cu3O7−δ doped with Li
Authors: Shlyk L. , Krabbes G. , Fuchs G. , Nenkov K. , Schüpp B.
Published: September 2004

Melt-processed samples of YBa2Cu3O7−δ (YBCO) doped with Li additions substituting at Cu(2) plane sites were used to study the effects of doping on the superconducting temperature, critical current density, irreversibility field, upper critical field, coherence length, and magnetic relaxation as a function of temperature and magnetic field. The intrinsic superconducting properties were found only slightly influenced by Li additions at some optimal concentration (0.6at.%). At this Li concentration the volume pinning force of doped material is about five times that of undoped YBCO in intermediate magnetic fields at 77K. No significant change of the maximum volume pinning force with oxygen defects after long-time oxygenation experiment (∼450h) has been observed. The normalized pinning force of the sample optimally doped with Li obeys the same scaling law as a function of magnetic field and temperature before and after additional heat treatment, indicative of a single type of pinning centers. The time dependence of the magnetization in the standard and in the Li-doped sample has been analyzed in the framework of collective pinning theory. The magnetic relaxation measurements combined with the B-T phase diagram data provide evidence of an elastic-plastic transition. The pinning parameters estimated show a considerable enhancement of the critical current density in the optimally doped sample, but only an insignificant change in the effective activation energy, pointing to a weak pinning of pointlike pinning centers, created by Li additions.
Quantitative impedance measurement using atomic force microscopy
Authors: O’Hayre Ryan , Feng Gang , Nix William D. , Prinz Fritz B.
Published: September 2004

Obtaining quantitative electrical information with scanning probe microscopy techniques poses a significant challenge since the nature of the probe/sample contact is frequently unkown. For example, obtaining quantitative kinetic data from the recently developed atomic force microscopy (AFM) impedance technique requires normalization by the probe/sample contact area. In this paper, a methodology is proposed that enables the extraction of quantitative information from the AFM impedance technique. This methodology applies results from nanoindentation experiments and contact mechanics theory to characterize AFM probe contacts. Using these results, probe/sample contact forces (which can be accurately measured in the AFM) may be converted into probe/sample contact area estimates. These contact area estimates, when included in model of the probe/sample contact, enable the extraction of quantitative data. This methodology is applied to the recently developed AFM impedance measurement technique, enabling a quantitative study of the oxygen reduction reaction (ORR) at nanometer length scales. Using the AFM impedance system, kinetic data for the (ORR) at nanoscale Platinum/Nafion contacts is extracted. The kinetic data obtained from the AFM impedance technique match previous bulk measurements—affirming the technique’s quantitative potential.
Sensing using differential surface plasmon ellipsometry
Authors: Hooper I. R. , Sambles J. R.
Published: September 2004

In this work a differential ellipsometric method utilizing surface plasmons (SPs) for monitoring refractive index changes, which could be used in chemical and biological sensors, is presented. The method is based upon determining the azimuth of elliptically polarized light reflected from a Kretschmann SP system, resulting from linearly polarized light containing both p and s components incident upon it. The sensitivity of this azimuth to the refractive index of a dielectric on the nonprism side of the metal film is demonstrated both experimentally and theoretically. The smallest refractive index change which is resolvable is of the order of 10−7 refractive index units, although it is believed that this could be improved upon were it not for experimental constraints due to atmospheric changes and vibrations. The method requires the Kretschmann configuration to be oriented at a fixed angle, and the SP to be excited at a fixed wavelength. With no moving parts this method would be particularly robust from an application point of view.
Breath figures: Self-organizing masks for the fabrication of photonic crystals and dichroic filters
Authors: Haupt M. , Miller S. , Sauer R. , Thonke K. , Mourran A. , Moeller M.
Published: September 2004

Controlled condensation of water vapor on a nonpolar liquid polymer film leads to the formation of submicrometer arrays of water droplets. Dissolution of a small amount of a polymer surfactant in the volatile liquid prevents the drops from coalescing and stabilizes their hexagonal arrangement. When subsequently the solvent and the water evaporate a solid polymer film patterned with hexagonally ordered holes remains—similar in shape to a honeycomb pattern. The hole size and the polydispersity are controlled by the solvent type, the flow rate of the condensing vapor, and the polymer concentration. The pattern is used as a lithographic mask to structure semiconductor surfaces. To this end, metal is deposited on the prestructured surface and subsequently lifted off to create two complementary structures: an array of metal disks on the semiconductor and a metal network. The lateral periodicity of the patterns can be varied between 300nm and several micrometers covering macroscopic areas (∼1cm2). Employing the metallic disk pattern as a mask in a plasma dry-etching process we have fabricated two-dimensional photonic crystals with small lattice constants in silicon. We have also used the complementary metal net for the production of metallic dichroic filters. The thin metal net acts as an optical short-pass in the infrared region of the spectrum due to its small lateral structure dimensions. The optical transmission of the dichroic filters is measured and simulated by a model calculation.
Radio frequency induced ionized collisional flow model for application at atmospheric pressures
Authors: Roy Subrata , Gaitonde Datta
Published: September 2004

We present the development and application of a versatile finite-element method to discretize direct current and radio frequency (rf) induced plasma-sheath dynamics, using multifluid equations. For the former, argon gas is assumed, and the solution is verified by comparison with a theoretical model obtained from the literature. For rf discharges, partially ionized helium gas is considered between two electrodes coated in a dielectric material. The computed solutions for charge densities, the ion velocity and the neutral gas density and crossflow distributions show expected trends. Specifically, ion and electron number densities at the peak discharge current are compared with published numerical results. The derived electric field is utilized with a simple phenomenological model applicable to the transverse velocity in a one-dimensional situation to predict the anticipated hump in the near wall profile. The next step of extending the model, through future work, to two dimensions and for polyphase supply as implemented in realistic configurations is greatly facilitated by the generality of the chosen finite-element method.
Structure of GaSb layers grown on (111) GaAs surfaces
Authors: Babkevich A. Yu. , Cowley R. A. , Mason N. J. , Shields P. A. , Stadelman T. , Brown S. , Mannix D. , Paul D.
Published: September 2004

The structure of GaSb layers with thicknesses of 70Å, 160Å, and 1260Å grown on GaAs (111) substrates by metal-organic vapor phase epitaxy has been studied by high-resolution x-ray diffraction. The lattice mismatch between the layer and the substrate is large and most of the misfit strain is taken up by a regular network of dislocations localized at the interface between the GaSb and the GaAs. The spacing between the dislocations is about 49Å along the [1¯1¯2] direction. We observe that the layers have both the ABC… and ACB… face-centered-cubic (fcc) domains with a domain size of about 1500Å. The presence of approximately the same volume of both the domains in the overall layer suggests that the particular domain is chosen largely randomly and independent of the orientation of the substrate. In contrast, the results show that the structure of the GaAs substrate was a single fcc domain. The widths of the off-axis Bragg reflections along the [111] direction for the thinnest sample was within error the same as those for the (hhh) Bragg reflections showing that each fcc domain penetrated through the entire layer.
Nonlocal photopolymerization effect in the formation of reflective holographic polymer-dispersed liquid crystals
Authors: Qi Jun , Li Liuliu , De Sarkar Mousumi , Crawford Gregory P.
Published: September 2004

The optical performance of reflective holographic polymer-dispersed liquid crystals (H-PDLCs) is investigated as a function of sample thickness and laser exposure intensity, and, the data are analyzed in terms of a nonlocal photopolymerization model. The intensity of laser exposure is proven to have a strong influence on the reflection efficiency of H-PDLCs. We have found that the experimental results cannot be completely interpreted by the previous local diffusion model. Combined with transfer matrix analysis, a modified diffusion model with a nonlocal photopolymerization term is proposed herein, which qualitatively describes our experimental observations. The experimental data demonstrates our assertion that the nonlocal effect is strongly correlated to the exposure conditions. Under the low exposure condition, the diffusion effect is screened by this nonlocal effect, and effectively a small diffusion constant is observed. Under the high exposure condition, the nonlocal effect can be suppressed and the modified diffusion model can be deduced to the original local diffusion model. Also, within the framework of this nonlocal model, overexposure can be properly explained.