bluuebunny/crossref_metadata_2025 huggingface dataset:
Kinetic parameters of CO adsorbed on Pt(111) studied by in situ high resolution x-ray photoelectron spectroscopy
Authors: Kinne M. , Fuhrmann T. , Whelan C. M. , Zhu J. F. , Pantförder J. , Probst M. , Held G. , Denecke R. , Steinrück H.-P.
Published: December 2002

The kinetics of the adsorption system CO/Pt(111) has been studied by time-resolved high-resolution x-ray photoelectron spectroscopy using third generation synchrotron radiation at BESSY II. CO is dosed by a supersonic molecular beam device which allows for a high sample pressure (here up to 10−6 mbar) and a fast switching of the pressure. The site-specific occupation of CO adsorbed on on-top and bridge sites is determined quantitatively from C 1s spectra, which can be taken with a minimum collection time of 1.5 s per spectrum. Based on the observation of thermal equilibrium between the two sites, we perform a phenomenological analysis of the data, assuming a constant binding energy difference ΔE. From the on-top/bridge occupation ratio as a function of coverage obtained by uptake measurements we extract a value of ΔE=41 meV. With the same ansatz, ΔE is calculated from temperature-dependent measurements at a constant coverage. Finally, determination of the coverage during isothermal desorption is used to obtain the total binding energy of CO on Pt(111). Differences between our evaluation methods and literature reports are discussed.
Analysis of electron transfer between electron irradiated metallic ball and insulators in vacuum: A specific alternative to the mirror method
Authors: Guerret-Piécourt C. , Juvé D. , Tréheux D. , Burais N.
Published: December 2002

In order to improve the knowledge of dielectric properties of insulators, we have imagined an original method of characterization of the charge buildup. Electrons of an electron beam are implanted through a metallic ball directly in contact with the insulator in a scanning electron microscope. By calculating and modeling the capacitance and the electrostatic force between the ball and the insulator plane, it has been possible to determine the relationship between the injected charges in the metallic ball and its surface potential. The major role of the dielectric thickness has been evidenced when the insulator is placed on a grounded metallic plane. At high potential values, a dielectric breakdown of the medium surrounding the sphere occurs and electrical charges are transferred from the ball to the dielectric sample. This transfer has been evidenced and quantified in the case of sapphire and quartz. Analytical calculations and numerical simulations using the finite-element method have been performed for interpreting these experimental results.
Fermi-level pinning at the metal/p-type CuGaS2 interfaces
Authors: Sugiyama M. , Nakai R. , Nakanishi H. , Chichibu SF.
Published: December 2002

A Schottky contact to p-type CuGaS2 that showed an extremely high rectification ratio of approximately 500 was realized using a Cu electrode on a HF/HNO3-treated surface, as well as an excellent Au ohmic contact on a HF-etched surface. The effective Schottky barrier height of 0.9 eV was obtained from the current–voltage and capacitance–voltage characteristics. The value was smaller by 1.1 eV than that calculated from the values of the work function of Cu and electron affinity of CuGaS2. The results indicated a surface pinning of the Fermi level to certain acceptor-type gap states below the midgap.
Role of strain on the wavy growth onset in strain-balanced InGaAs-based multiquantum wells
Authors: Nasi L. , Ferrari C. , Lazzarini L. , Clarke G.
Published: December 2002

Different strain-balanced InGaAs/InGaAs multiquantum wells (MQWs) were grown on (001) InP by changing the In composition in the wells and in the barriers in order to extend the absorption edge beyond 2 μm for thermophotovoltaic applications. The increase of the elastic strain in the structures results in the formation of isolated highly defected regions having their origin from lateral layer thickness modulations. Experimental results are consistent with the existence of a critical elastic energy density for the development of MQW waviness. An empirical model to predict the maximum number of layers that can be grown without modulations as a function of the strain energy stored in the MQW period is presented.
Field emission from an electron-beam irradiated C60 film
Authors: Hara Toshiki , Onoe Jun , Takeuchi Kazuo
Published: December 2002

The field-emission characteristics of an electron-beam (EB) irradiated C60 film have been investigated. A C60 film on a stainless-steel substrate was irradiated by a 3 keV EB primarily for 10 h in an ultrahigh vacuum and subsequently for 10 h under a hydrogen atmosphere in order to induce a coalescence reaction between the adjacent C60 molecules and to introduce C–H bonds, which provide a good emission site, to the film surface. The coalescence reaction and C–H bond formation were confirmed by in situ Fourier-transform infrared spectroscopy. It was found that the field emission was enhanced for the 20 h irradiated C60 film. This enhancement was discussed in terms of the structural change in the C60 film.
Inorganic solution-processed hole-injecting and electron-blocking layers in polymer light-emitting diodes
Authors: Reynolds K. J. , Barker J. A. , Greenham N. C. , Friend R. H. , Frey G. L.
Published: December 2002

The use of the solution-processed layered transition metal dichalcogenide (LTMDC) MoS2 as a hole-injecting electrode in polymer light-emitting diodes (LEDs) is reported. MoS2 functions as a very high work function metal and, in combination with an electron-blocking layer in the form of MoO3, provides good LED performance. In this study we investigated model LED devices with a single semiconductor layer, namely, the electron transporting polymer poly-[2,7-(9,9′-di-n-octylfluorene)-3,6-benzothiadiazole]. LED operation was successfully modeled using experimentally determined work functions, carrier mobilities, and barrier properties. Good agreement between experiment and model allows us to demonstrate that the MoS2 and the MoO3 layers act as a high work function hole-injection layer (MoS2) and an electron extraction barrier layer (MoO3), respectively. They improve device performance by allowing the buildup of electron density at the oxide/emissive layer interface which generates a local field, enhancing hole injection and recombination. Furthermore, the model shows the importance of controlling the thickness of the blocking layer to optimize device performance. The wide variety of polymeric emitters available and the range of electronic properties displayed by the LTMDC family and their corresponding oxides, provides the potential to tailor device performance through the selection of suitable organic and inorganic components.
Theory of low-frequency magnetoelectric effects in ferromagnetic-ferroelectric layered composites
Authors: Bichurin M. I. , Petrov V. M. , Srinivasan G.
Published: December 2002

A theoretical model is presented for low-frequency magnetoelectric (ME) effects in bilayers of magnetostrictive and piezoelectric phases. An approach is proposed for the consideration of actual boundary conditions at the interface. An averaging method is used to estimate effective material parameters. The model predicts the strongest ME effect in cobalt ferrite-lead zirconate titanate (PZT) among ferrite based composites. The ME voltage coefficient for transverse field orientation is estimated to be 25–50% higher than for the longitudinal case. Comparison with data for multilayer samples reveals poor interface coupling in cobalt ferrite-PZT and ideal coupling in nickel ferrite-PZT.
Temperature dependence of the activation volume in high-temperature Sm(Co,Fe,Cu,Zr)z magnets
Authors: Panagiotopoulos I. , Gjoka M. , Niarchos D.
Published: December 2002

Magnetization relaxation and remanence measurements in the temperature range from 100 to 600 °C were performed in a Sm(Co0.75F0.12Cu0.10Zr0.03)7.6 alloy in order to estimate the activation volume V*. The coefficient of magnetic viscosity S is found to decrease with temperature up to 500 °C showing an increase in the width of the energy barrier distribution function. A drastic increase of the value of V* above the Curie point of the intergranular phase is attributed to a crossover from a pinning to a nucleation type of magnetic reversal.
Carrier transport in conducting polymers with field dependent trap occupancy
Authors: Kumar Vikram , Jain S. C. , Kapoor Ashok K. , Geens Wim , Aernauts Tom , Poortmans J. , Mertens R.
Published: December 2002

The space charge limited currents J in conducting organic materials often show J∼Vm (where m>2) dependence on voltage V. Two models have been used extensively to understand this behavior. In one model, the mobility μ is assumed to be dependent on electric field F. In the other model, an exponential distribution of traps is assumed and the mobility is taken to be independent of field. In this model the influence of the high electric fields present in organic polymers has not been taken into account. We present a model to calculate the J(V) characteristics for single carrier organic polymers taking into account the change in the occupancy of the traps due to the high electrical fields present in these materials. We show that the field dependent trap occupancy (FDTO) model can effectively explain the current–voltage characteristics reported by several different groups. If the FDTO model is used, it is not necessary to use the two different models mentioned above.
Recombination processes in unintentionally doped GaTe single crystals
Authors: Zubiaga A. , Garcı́a J. A. , Plazaola F. , Muñoz-Sanjosé V. , Martı́nez-Tomás M. C.
Published: December 2002

Emission spectra of GaTe single crystals in the range of 1.90–1.38 eV have been analyzed at different temperatures and excitation intensities by photoluminescence, photoluminescence excitation, and selective photoluminescence. A decrease in band gap energy with an increase in temperature was obtained from the redshift of the free exciton recombination peak. The energy of longitudinal optical phonons was found to be 14±1 meV. A value of 1.796±0.001 eV for the band gap at 10 K was determined, and the bound exciton energy was found to be 18±0.3 meV. The activation energy of the thermal quenching of the main recombination peaks and of the ones relating to the ionization energy of impurities and defects was analyzed. The results obtained show the existence of two acceptor levels with ionization energies of 110±5 and 150±5 meV, respectively, and one donor level with an ionization energy of 75±5 meV. The study of chemical composition by inductively coupled plasma-optical emission spectroscopy and x-ray energy dispersion spectroscopy shows the existence of Na, Li, and Si. Sodium and lithium impurities could be associated with acceptor levels at gallium substitutional sites, and silicon ones with a donor level at Ga sites, whose vacancies can also be involved in these electronic levels.
Electronic and optical properties of lead iodide
Authors: Ahuja R. , Arwin H. , Ferreira da Silva A. , Persson C. , Osorio-Guillén J. M. , Souza de Almeida J. , Moyses Araujo C. , Veje E. , Veissid N. , An C. Y. , Pepe I. , Johansson B.
Published: December 2002

The electronic properties and the optical absorption of lead iodide (PbI2) have been investigated experimentally by means of optical absorption and spectroscopic ellipsometry, and theoretically by a full-potential linear muffin-tin-orbital method. PbI2 has been recognized as a very promising detector material with a large technological applicability. Its band-gap energy as a function of temperature has also been measured by optical absorption. The temperature dependence has been fitted by two different relations, and a discussion of these fittings is given.
Raman scattering study of stoichiometric Si and Ge type II clathrates
Authors: Nolas G. S. , Kendziora C. A. , Gryko Jan , Dong Jianjun , Myles Charles W. , Poddar Abhijit , Sankey Otto F.
Published: December 2002

Raman-scattering spectra of the type II clathrates Cs8Na16Si136, Cs8Na16Ge136, and Si136 were studied employing different laser wavelengths. Most of the Raman-active vibrational modes of these compounds were identified. Polarization measurements were used to identify the symmetric modes. The lowest frequency Raman-active optic “rattle” mode corresponding to the vibrations of the Cs atoms inside the hexakaidecahedra is identified for both the Si and the Ge clathrate compounds. We compare the experimental data directly with theoretical calculations. These materials continue to attract attention for potential superconducting, optoelectronic, and thermoelectric applications.
Origin of antiphase domain boundaries and their effect on the dielectric constant of Ba0.5Sr0.5TiO3 films grown on MgO substrates
Authors: Li Hao , Zheng H. , Salamanca-Riba L. , Ramesh R. , Naumov I. , Rabe K.
Published: December 2002

Epitaxial Ba1−xSrxTiO3 (BST) with x=0.5 films were grown on MgO substrates using pulsed-laser deposition. We have observed a high density of antiphase domain boundaries (ADB) in these BST films. We attribute the formation of the ADBs to the different crystal symmetry of the film and the substrate. Adjacent domains have an in plane phase shift of 12[110], or 12[11̄0] thus creating a phase shift of the in plane lattice planes of 12[010] or 12[100] across the boundary. We have used first-principles calculations to obtain the effect of the ADBs on the dielectric constant of SrTiO3 and found that they lower the effective in plane dielectric constant in the direction normal to the ADB. Upon annealing, the density of ADBs decreases and the dielectric properties improve.
Role of group V exchange on the shape and size of InAs/InP self-assembled nanostructures
Authors: Gutiérrez H. R. , Cotta M. A. , Bortoleto J. R. R. , de Carvalho M. M. G.
Published: December 2002

We have studied the influence of Group V overpressure on the final shape and size of InAs nanostructures grown on (001) InP substrates. The mechanisms leading to postgrowth modifications in the InAs nanostructures are discussed. The simultaneous action of Group V overpressure and stress field—produced by the InAs nanostructures—can induce strong material transport. The direction of this material net current depends on the type of Group V element used for the overpressure flux. In situ reflection high-energy electron diffraction, atomic force microscopy, and transmission electron microscopy measurements were used to characterize the transitions in morphology. Our results show that morphological studies considering the grown surface that do not take into account postgrowth processes can be misleading to understand the growth mechanisms governing the self-assembling process.
Anhysteretic field-induced rhombhohedral to orthorhombic transformation in 〈110〉-oriented 0.7Pb(Mg1/3Nb2/3)O3–0.3PbTiO3 crystals
Authors: Viehland D. , Li J. F.
Published: December 2002

The electric-field induced polarization (P–E) and strain (ε–E) characteristics of 〈110〉c-oriented 0.7Pb(Mg1/3Nb2/3)O3–0.3PbTiO3 crystals have been investigated, under both unipolar and bipolar drive. A field-induced transformation was observed below saturation. Under unipolar drive, the P–E and ε–E loops were anhysteretic even at the transformation point, demonstrating complete reversibility between ferroelectric rhombohedral and orthorhombic phases. The results show that “polarization rotation” can occur between 〈111〉c and 〈110〉c, where the polarization is confined to the (100)c in a monoclinic Mb type symmetry.
Temperature dependence of avalanche multiplication in submicron Al0.6Ga0.4As diodes
Authors: Harrison C. N. , David J. P. R. , Hopkinson M. , Rees G. J.
Published: December 2002

Photomultiplication measured in Al0.6Ga0.4As p+–i–n+ diodes falls with temperature in a manner that becomes less marked with decreasing i-region width and increasing electric field. Simple arguments relate this result to the effects of the ionization dead space, which is expected to depend weakly on temperature, and to the reduced scattering in the high electric fields present in thin avalanching structures. The temperature dependence of the “enabled” ionization coefficient can be approximately accounted for by simply subtracting the ballistic dead space from the width of the avalanche region. The simple arguments suggest the effect is independent of materials system.
Resonant Raman scattering studies of Fano-type interference in boron doped diamond
Authors: Wang Y. G. , Lau S. P. , Tay B. K. , Zhang X. H.
Published: December 2002

The light scattering properties of boron doped diamond film have been investigated by Raman spectroscopy using ultraviolet (325 and 244 nm) and visible (514 nm) excitations. The relative intensity of electronic Raman scattering to phonon scattering decreases with the increase of the excitation energies, while the Fano-type interference between discrete phonon scattering and continuum electronic scattering becomes weak and phonon scattering peak shifts to higher Raman shift. The decoupling zone center phonon frequency is estimated based on the ultraviolet (UV) Raman scattering; the result indicates that boron induced phonon “softening” in diamond is smaller than that estimated based on the visible Raman spectra. The two broad peaks located at about 500 and 1200 cm−1 on the visible Raman spectrum cannot be detected when it is excited by the UV lasers.
Structure and magnetic properties of Pr2Fe14(C,B)-type ribbons with high coercivity
Authors: Zhang Wen-yong , Rong Chuang-bing , Zhang Jian , Shen Bao-gen , Du Hong-lin , Jiang Jian-sheng , Yang Ying-chang
Published: December 2002

The effect of the substitution of B for C on the structure and magnetic properties of the Pr15Fe77C8−xBx (x=0–8) ribbons has been investigated. Microstructure analysis shows that the grain size and size distribution of the ribbons with x⩾2 do not change with B substitution. It is found that B substitution significantly improves the hard magnetic properties of the samples. The coercivity, remanence, and energy product increase from 0.0002 and 0.19 T and 0.001 MGOe for x=0 to 2.19 and 0.76 T and 14.3 MGOe for x=8, respectively. Without heat treatment, Pr2Fe14C-type ribbons with high coercivity of greater than 2 T have been prepared by melt spinning. The introduction of B changes the phase components, and leads to a substantial difference in coercivity mechanisms of the B-poor ribbons (x=2) and B-rich (x=8) ribbons.
Influence of Ar and O2 atmospheres on the Li atom concentration in the plasma produced by laser ablation of LiNbO3
Authors: Gordillo-Vázquez F. J. , Afonso C. N.
Published: December 2002

An analytic kinetic model is elaborated to determine the spatial evolution of the concentration of ground and excited Li atoms (up to the 3 2D level) present in the plasma generated by pulsed laser ablation of a LiNbO3 crystal in gas atmospheres (at 1 Torr) of different nature, both reactive (O2) and inert (Ar). Whereas the Li atom population densities in the plasma produced in gas are, in general, higher than those found in vacuum, the concentration of ground Li atoms close to the substrate is similar in vacuum and Ar, though lower than in O2. It is suggested that the reabsorption of radiation by the plasma is more important within O2 than in Ar since the absorber (ground Li) concentration is higher in O2 environments. A very reasonable qualitative agreement is found when comparing the Li I-670.8 nm spectral line emission intensity predicted by the model with that obtained experimentally in Ar and O2 atmospheres.
High-efficiency SiO2:Ce3+ glass scintillators
Authors: Chiodini N. , Fasoli M. , Martini M. , Rosetta E. , Spinolo G. , Vedda A. , Nikl M. , Solovieva N. , Baraldi A. , Capelletti R.
Published: December 2002

We present the effect of a rapid thermal treatment (RTT) at high temperature (1800 °C) on the radio-luminescence properties of Ce-doped SiO2 glasses prepared by the sol–gel method and previously densified at 1050 °C. Cerium concentrations ranging from 0.05 up to 1 mol % were considered. We found that, for all concentrations, the RTT induces a strong increase of the Ce3+ radio-luminescence efficiency; the x-ray-induced luminescence intensity of the SiO2:0.1% Ce is about twice that of Bi3Ge4O12. The decay time of the scintillation response, evaluated as ≈50 ns, is not affected by RTT. Infrared absorption measurements indicate that the luminescence increase cannot be related to significant release of OH groups during RTT. The conversion of Ce4+ ions into Ce3+ ions can also be ruled out since an increase of about 20% of the intensity of the 4.8 eV optical absorption band related to Ce4+ was observed after RTT. The occurrence of dissolution of rare-earth aggregates is suggested.
Direct observation of phase separation in La0.45Sr0.55MnO3−δ
Authors: Li Run-Wei , Zhang Zhen-Rong , Li Qing-An , Sun Ji-Rong , Wang Guang-Jun , Cheng Zhao-Hua , Wang Zhi-Hong , Zhang Shao-Ying , Han Bao-Shan , Shen Bao-Gen
Published: December 2002

We provide evidence of phase separation in La0.45Sr0.55MnO3−δ using electron spin resonance, magnetic force microscopy (MFM), x-ray diffraction, and magnetic and transport measurements. The results reveal that ferromagnetic and antiferromagnetic phase coexist at low temperature and that ferromagnetic and paramagnetic phases coexist in the temperature range between the Néel and the Curie temperature. Moreover, the size and shape of ferromagnetic phase (the minority phase) in the sample were observed directly by MFM. From these results, we infer an electroneutral type phase separation, possibly resulting from a nonuniform distribution of oxygen vacancies, as opposed to charge segregation.
Role of amorphous grain boundaries in nanocomposite NdFeB permanent magnets
Authors: Li Shandong , Gu Benxi , Bi Hong , Tian Zongjun , Xie Guozhi , Zhu Yuejin , Du Youwei
Published: December 2002

Two typical Nd–Fe–B permanent magnetic alloys of B-enriched Nd4.5Fe77B18.5 and Fe-enriched Nd9Fe85B6Zr0.5 have been employed to study the effect of annealing on the microstructure and the magnetic properties, respectively. It has been found that the maximum remanence, remanence ratio, intrinsic coercivity, and energy product are 1.32 T, 0.86, 212 kA/m, and 130 kJ/m3, respectively, for the B-enriched alloy, while they are 1.15 T, 0.82, 496 kA/m, and 162 kJ/m3, respectively, for the Fe-enriched alloy. In these samples, x-ray diffraction, Mössbauer spectroscopy, and high-resolution transmission electron microscopy revealed the existence of an amorphous phase between grains. It is believed that enhancement of the remanence and remanence ratio in the magnets originates from the amorphous grain boundaries, which increase the exchange coupling between neighboring grains.
Ferroelectric polarization in stretched piezo- and pyroelectric poly(vinylidene fluoride-hexafluoropropylene) copolymer films
Authors: Wegener M. , Künstler W. , Richter K. , Gerhard-Multhaupt R.
Published: December 2002

After suitable preparation, films of poly(vinylidene fluoride-hexafluoropropylene) [P(VDF-HFP)] show strong piezo- and pyroelectric effects. We investigated the polarization buildup in stretched P(VDF-HFP) copolymer films, cast from a dimethylsulfoxide/acetone solution. The films were poled under varying or constant electric fields. We observed a hysteresis of the polarization as a function of the electric field during poling of the stretched P(VDF-HFP) copolymer films with varying electric fields. From the hysteresis curve, a polarization of 24 mC/m2, and a coercive field of 100 MV/m were determined. The polarization values are lower than those of PVDF films cast from solution and stretched under the same conditions. It seems that HFP comonomer leads to a decrease in the amount of switchable dipoles. Nevertheless, the P(VDF-HFP) copolymer is very attractive because of its high piezo- and pyroelectric coefficients as well as its better chemical and thermal stability and its predicted longer lifetime. A rather uniform polarization across the whole sample thickness was found in spatially resolved measurements of the piezo- and pyroelectric properties. For comparison with PVDF and for structural information, we also report and discuss infrared transmission as well as dielectric response.
Electronic structure of thallium filled skutterudites studied by x-ray absorption and Mössbauer spectroscopy
Authors: Long Gary J. , Mahieu Bernard , Sales Brian C. , Hermann Raphaël P. , Grandjean Fernande
Published: December 2002

Thallium LIII-edge x-ray absorption and iron-57 and tin-119 Mössbauer spectral measurements have been carried out to probe the electronic structure of the three sites in the filled skutterudite TlxCo4−yFeySb12 and TlxCo4Sb12−zSnz compounds with a range of x, y, and z values. The thallium LIII-edge x-ray absorption spectra are independent of x, y, and z and are well reproduced by full multiple scattering calculations with a cluster with a radius of 8.5 Å centered on thallium. The iron-57 Mössbauer spectra consist of two doublets and the major component is assigned to iron on the cobalt sublattice in view of its hyperfine parameters. The origin of the minor component is uncertain and is tentatively assigned to either iron with thallium vacancies as next nearest neighbors or to iron in the voids. The tin-119 Mössbauer spectral hyperfine parameters clearly indicate that tin substitutes for antimony in the skutterudite structure. Further, the tin electronic configuration is very similar to that of antimony and is insensitive to the thallium content.
Effect of nitrogen at SiO2/Si interface on reliability issues—negative-bias-temperature instability and Fowler–Nordheim-stress degradation
Authors: Kushida-Abdelghafar Keiko , Watanabe Kikuo , Ushio Jiro , Murakami Eiichi
Published: December 2002

Degradation process of a metal–oxide–semiconductor (MOS) structure with NO-nitrided SiO2 under negative-bias-temperature (NBT) and Fowler–Nordheim (FN) stresses has been investigated. The FN stress immunity improves with increasing nitrogen concentration at the SiO2/Si interface, while the incorporation of excess nitrogen (more than 3 at. %) at the SiO2/Si interface accelerates NBT instability (NBTI). This stronger immunity of NO-nitrided SiO2 under FN stress is due to the stronger Si–N bonds formed by NO nitridation at the interface. Without hydrogen annealing to form Si–H bonds, the MOS capacitors do not show NBTI. This indicates that the Si–N bonds are not broken under NBT stress and the main cause of the NBTI is the breaking of the Si–H bonds. The NO nitridation decreases the number of Si–H bonds and thus suppresses NBTI. However, nitrogen provides hole-trap centers. Hydrogen at the interface is dissociated and bonds to the hole-trapping nitrogen, so interface traps are left behind. An excess amount of nitrogen thus accelerates NBTI.
Spontaneous growth of an InAs nanowire lattice in an InAs/GaSb superlattice
Authors: Nosho B. Z. , Bennett B. R. , Whitman L. J. , Goldenberg M.
Published: December 2002

We describe a lattice of InAs nanowires that spontaneously organizes in three dimensions within an InAs/GaSb superlattice grown under high As4 flux. As characterized by x-ray diffraction and cross-sectional scanning tunneling microscopy, the periodic nanowires are ∼10 nm high, 120 nm wide, and many microns long along [110], with face-centered cubic-like vertical ordering within the superlattice. The unusual vertical ordering creates a lateral composition modulation with half the period of the nanowires. The structure appears to arise from the InAs misfit stress combined with specific InAs and GaSb growth kinetic effects.
Spontaneous localization in InAs/GaAs self-assembled quantum-dot molecules
Authors: Sheng Weidong , Leburton Jean-Pierre
Published: December 2002

Spontaneous localization of hole states is predicted at all separations in vertically stacked InAs/GaAs self-assembled quantum dots. Eight-band k⋅p theory shows that valence band mixing enhanced by the unique three-dimensional strain distribution, subjects holes to very different environment than electrons. As a result, low energy holes are confined to their respective dots without forming bonding or antibonding states. This localization plays the same role as a vertically applied electric field in coupled quantum systems, and substantially decreases the exciton binding energy, which may be an impediment to the formation of entangled states in quantum-dot molecules.
Interfacial properties of single-crystalline CeO2 high-k gate dielectrics directly grown on Si (111)
Authors: Nishikawa Yukie , Yamaguchi Takeshi , Yoshiki Masahiko , Satake Hideki , Fukushima Noburu
Published: December 2002

Interfacial properties of single-crystalline CeO2 high-k dielectrics directly grown on Si (111) were investigated by comparing metal–insulator–semiconductor field-effect transistors (MISFETs) without any interfacial layer [(w/o-IL); direct growth of CeO2 on Si] and those with an interfacial layer (w-IL). FET characteristics, such as the drain current and the S factor, for the w/o-IL MISFET were much worse than those for the w-IL MISFET. The in-gap states attributed to the oxygen defects were detected in the CeO2 directly grown on Si by x-ray photoelectron spectroscopy measurements. The large interface state density induced by the oxygen defects at the CeO2/Si interface may deteriorate the w/o-IL MISFET performances.
Comparative study on the broadening of exciton luminescence linewidth due to phonon in zinc-blende and wurtzite GaN epilayers
Authors: Xu S. J. , Zheng L. X. , Cheung S. H. , Xie M. H. , Tong S. Y. , Yang Hui
Published: December 2002

Linewidth broadening of exciton luminescence in wurtzite and zinc-blende GaN epilayers was investigated as a function of temperature with photoluminescence. A widely accepted theoretical model was used to fit the experimental data, so that the coupling parameters between exciton and acoustic and longitudinal optical phonons were obtained for both structures. It was found that the coupling constants of both exciton–acoustic optical phonon coupling and exciton–longitudinal optical phonon coupling for zinc-blende GaN are almost twice as much as the corresponding values of wurtzite GaN. These results show that the relatively strong exciton–phonon scattering seems to be characteristic to zinc-blende GaN film.
Effect of charge transport through silicon nitride on thin gate oxide reliability
Authors: Cacciato A. , Scarpa A. , Evseev S. , Diekema M.
Published: December 2002

It is shown that photoconduction is triggered in silicon nitride films when they are exposed to plasma. As a consequence of the increased conductivity, they can act as antennas, being able to collect charges from unstable plasmas and inject them into the gate oxide, thus causing charging damage. The importance of this phenomenon for deep submicron microelectronic manufacturing is discussed.
Fabrication of 70 nm channel length polymer organic thin-film transistors using nanoimprint lithography
Authors: Austin Michael D. , Chou Stephen Y.
Published: December 2002

We report on the fabrication of short-channel polymer organic thin-film transistors (OTFTs) using nanoimprint lithography. Currently, there is significant interest in OTFTs due to their potential application in inexpensive, large-area electronics. However, polymer carrier mobilities are typically poor, and thus to increase the OTFT drive current per unit area, there is a need for short-channel devices. We have fabricated working devices with channel lengths from 1 μm down to 70 nm with high yields. The performance of these devices was studied as the channel length was reduced. We find that drive current density increases as expected, while the on/off current ratio remains 104. However, at short-channel lengths, OTFTs no longer saturate due to space charge limiting current effects.
Influence of quasibound states on the carrier capture in quantum dots
Authors: Magnusdottir I. , Uskov A. V. , Ferreira R. , Bastard G. , Mørk J. , Tromborg B.
Published: December 2002

The interaction of carriers in quantum-dot quasibound states with longitudinal optical phonons is investigated. For a level separation between the quasibound state and a discrete quantum-dot state in the vicinity of the phonon energy, a strong electron–phonon coupling occurs. A mixed electron–phonon mode—polaron—is formed. The finite lifetime of the phonons is shown to give rise to another type of carrier capture into quantum dots.
Size effects on generation-recombination noise
Authors: Gomila G. , Reggiani L.
Published: December 2002

We carry out an analytical theory of generation-recombination noise for a two-level resistor model which goes beyond those presently available by including the effects of both space charge fluctuations and diffusion current. Finite size effects are found responsible for the saturation of the low frequency current spectral density at high enough applied voltages. The saturation behavior is controlled essentially by the correlations coming from the long range Coulomb interaction. It is suggested that the saturation of the current fluctuations for high voltage bias constitutes a general feature of generation-recombination noise.
Tbit/inch
2
ferroelectric data storage based on scanning nonlinear dielectric microscopy
Authors: Cho Yasuo , Fujimoto Kenjiro , Hiranaga Yoshiomi , Wagatsuma Yasuo , Onoe Atsushi , Terabe Kazuya , Kitamura Kenji
Published: December 2002

Nanosized inverted domain dots in ferroelectric materials have potential applications in ultrahigh-density rewritable data storage systems. Here, a data storage system based on scanning nonlinear dielectric microscopy and thin films of ferroelectric single-crystal lithium tantalite is presented. Through domain engineering, nanosized inverted domain dots have been successfully formed at a data density of 1.50 Tbit/in.2.
Nanometer-scale pores in low-k dielectric films probed by positron annihilation lifetime spectroscopy
Authors: Wang C. L. , Weber M. H. , Lynn K. G. , Rodbell K. P.
Published: December 2002

We measured positron annihilation lifetime spectra in mesoporous low dielectric constant (low-k) methyl-silsesquioxane (MSSQ) films versus porogen load Φ from Φ=0% to 50%. The ortho-positronium lifetime parameters were obtained using both the maximum entropy and discrete lifetime analyses. Open and closed porosity distributions and the average radius of closed pores were obtained. The total porosity and the fraction of open/closed porosities were evaluated. The total porosity increases linearly with porogen load, consistent with the porosity obtained from density measurements. Open porosity occurs from 20% porogen load upwards.
Crystal structure of κ-In2Se3
Authors: Jasinski J. , Swider W. , Washburn J. , Liliental-Weber Z. , Chaiken A. , Nauka K. , Gibson G. A. , Yang C. C.
Published: December 2002

Structural properties of single-phase films of κ-In2Se3 and γ-In2Se3 were investigated. Both films were polycrystalline but their microstructures differed considerably. The a-lattice parameter of κ-In2Se3 has been measured. A comparison between these two materials indicates that κ-In2Se3 has a significantly larger unit cell (Δc=2.5±0.2% and Δa=13.5±0.5%) and a structure more similar to the α-phase of In2Se3.
Kinetic of phase transformation of SrBi2Ta2O9 deposited by metalorganic decomposition on platinum electrodes
Authors: Moert M. , Mikolajick T. , Schindler G. , Nagel N. , Hartner W. , Dehm C. , Kohlstedt H. , Waser R.
Published: December 2002

SrBi 2 Ta 2 O 9 thin films were prepared by metalorganic decomposition on Pt/Ti/SiO2/Si substrates and subsequently crystallized at temperatures ranging from 600 to 700 °C for 40 to 225 min. Data of the Aurivillius surface coverage taken from atomic force microscopy measurements were used to model the kinetics of isothermal phase transformation from the fluorite to the Aurivillius phase. A two-dimensional growth mechanism at a decreasing nucleation rate can be deduced. By evaluating the temperature dependence of the growth rates, an activation energy for phase transformation of 318 kJ/mol is determined.
Engineering kinetic barriers in copper metallization
Authors: Huang Hanchen , Wei H. L. , Woo C. H. , Zhang X. X.
Published: December 2002

In metallization processes of integrated circuits, it is desirable to deposit the metal lines (aluminum or copper) fast and at low temperatures. However, the lines (films) usually consist of undesirable columns and voids, because of the absence of sufficient diffusion—a direct result of large kinetic barriers. Following the proposal and realization of the three-dimensional Ehrlich-Schwoebel (3D ES) barrier, we present here a method to engineer this kinetic barrier so as to improve quality of deposited copper films. We deposit copper films by magnetron sputtering, characterize the film structure and texture by using the scanning electron microscope and the x-ray diffraction, respectively. Taking indium as surfactant during copper deposition, we have achieved much better density and bottom coverage of copper filled trenches. The characterizations show that the improvement is the result of the 3D ES barrier reduction caused by indium addition. Engineering the 3D ES barrier therefore leads to improved film quality.
Variation of Raman feature on excitation wavelength in silicon nanowires
Authors: Zhang Shu-Lin , Ding Wei , Yan Yan , Qu Jiang , Li Bibo , Li Le-yu , Yue Kwok To , Yu Dapeng
Published: December 2002

A variation of Raman feature on excitation wavelength in silicon nanowires was observed. Based on the quantum size confinement effect, the resonant Raman scattering phenomenon and the existence of different sizes of Si grains in the samples, a plausible mechanism to interpret the novel feature was proposed and supported by experimental facts.
Surface passivation of n-type crystalline Si by plasma-enhanced-chemical-vapor-deposited amorphous SiCx:H and amorphous SiCxNy:H films
Authors: Martı́n I. , Vetter M. , Orpella A. , Voz C. , Puigdollers J. , Alcubilla R.
Published: December 2002

Excellent passivation of n-type crystalline silicon surface is demonstrated by means of intrinsic amorphous silicon carbide (a-SiCx:H) thin films. An optimum CH4/SiH4 ratio is determined, leading to an effective surface recombination velocity, Seff, lower than 54 cm s−1. By adding a constant flow of N2 to the precursor gases, the surface passivation is improved to Seff⩽16 cm s−1. From infrared spectroscopy measurements of these films, it can be deduced that the N2 flow increases the carbon content of the layers for a constant CH4/SiH4 ratio. The dependence of the effective lifetime, τeff, on the excess charge carrier density, Δn, is measured using the quasisteady-state photoconductance technique, and these curves are simulated through an electrical model based on an insulator/semiconductor structure.
Electroluminescence of mixed organic dyes via resonant energy transfer from polysilane molecules
Authors: Kamata Norihiko , Ishii Reiji , Tonsyo Shinji , Terunuma Daiyo
Published: December 2002

We have observed an electroluminescence (EL) of perylene (blue), coumarin 6 (green), 4-(dicyanomethylene)-2-methyl-6-(p-dimethylaminostyryl)-4H-pyran and/or zinc tetra-phenylporphyrin (red) via an efficient intermolecular energy transfer from poly (m-hexoxyphenyl)phenylsilane (PHPPS). The EL device has a single layer which was prepared simply by spin coating the mixed solution of PHPPS and energy-matched dye molecules. The EL spectrum can easily be tailored by intermixing appropriate dye molecules in the solution. We demonstrated a white EL from the mixture of PHPPS and these four dyes. The combination of a conducting polysilane and energy-matched dye molecules enabled us to open a field of Si-based EL devices through wet processes.
Measurement of acoustic wavelength in optical fiber via acousto-optic interaction
Authors: Dashti P. Z. , Li Q. , Lee H. P.
Published: December 2002

The wavelength of the lowest-order propagating flexural acoustic wave in a single-mode fiber is measured by creating an acoustic cavity with variable length. The amplitude of the acoustic standing wave is probed by means of acousto-optic coupling between the core and cladding modes in the optical fiber. By monitoring the periodic modulation of the core–mode transmittance versus the cavity length, the acoustic wavelength can be measured to a high degree of accuracy. Excellent agreement (<1%) between the measured values and theoretical calculations for three types of 125 μm diameter single-mode fibers is obtained in the frequency range from 1.2 to 3.5 MHz.
DNA-dependent Protein Kinase Activity Is Not Required for Immunoglobulin Class Switching
Authors: Bosma Gayle C. , Kim Jiyoon , Urich Teresa , Fath Donna M. , Cotticelli Maria G. , Ruetsch Norman R. , Radic Marko Z. , Bosma Melvin J.
Published: December 2002

Class switch recombination (CSR), similar to V(D)J recombination, is thought to involve DNA double strand breaks and repair by the nonhomologous end–joining pathway. A key component of this pathway is DNA-dependent protein kinase (DNA-PK), consisting of a catalytic subunit (DNA-PKcs) and a DNA-binding heterodimer (Ku70/80). To test whether DNA-PKcs activity is essential for CSR, we examined whether IgM+ B cells from scid mice with site-directed H and L chain transgenes were able to undergo CSR. Although B cells from these mice were shown to lack DNA-PKcs activity, they were able to switch from IgM to IgG or IgA with close to the same efficiency as B cells from control transgenic and nontransgenic scid/+ mice, heterozygous for the scid mutation. We conclude that CSR, unlike V(D)J recombination, can readily occur in the absence of DNA-PKcs activity. We suggest nonhomologous end joining may not be the (primary or only) mechanism used to repair DNA breaks during CSR.
Adhesion Molecule–dependent Mechanisms Regulate the Rate of Macrophage Clearance During the Resolution of Peritoneal Inflammation
Authors: Bellingan Geoffrey John , Xu Ping , Cooksley Helen , Cauldwell Helen , Shock Anthony , Bottoms Stephen , Haslett Christopher , Mutsaers Steven Eugene , Laurent Geoffrey John
Published: December 2002

Macrophage clearance is essential for the resolution of inflammation. Much is known about how monocytes enter the inflammatory site but little is known about how resultant macro-phages are cleared. We have previously demonstrated that macrophage clearance from resolving peritonitis occurs by emigration into draining lymphatics rather than local apoptosis. We now examine mechanisms for this process, in particular by evaluating the hypothesis that modulation of adhesion interactions between macrophages and cells lining the lymphatics regulates the rate of macrophage clearance. We demonstrate in vivo that macrophages adhere specifically to mesothelium overlying draining lymphatics and that their emigration rate is regulated by the state of macrophage activation. We observed that macrophage–mesothelial adhesion is Arg-Gly-Asp (RGD) sensitive and partially mediated by very late antigen (VLA)-4 and VLA-5 but not αv or β2 integrins. Moreover, macrophage clearance into lymphatics can be blocked in vivo by RGD peptides and VLA-4 and VLA-5 but not β2 blocking antibodies. This is the first evidence that macrophage emigration from the inflamed site is controlled and demonstrates that this is exerted through specific adhesion molecule regulation of macrophage–mesothelial interactions. It highlights the importance of adhesion molecules governing entry of cells into the lymphatic circulation, thus opening a new avenue for manipulating the resolution of inflammation.
Essential Role for the C5a Receptor in Regulating the Effector Phase of Synovial Infiltration and Joint Destruction in Experimental Arthritis
Authors: Grant Ethan P. , Picarella Dominic , Burwell Timothy , Delaney Tracy , Croci Alisa , Avitahl Nicole , Humbles Alison A. , Gutierrez-Ramos Jose-Carlos , Briskin Michael , Gerard Craig , Coyle Anthony J.
Published: December 2002

A characteristic feature of rheumatoid arthritis is the abundance of inflammatory cells in the diseased joint. Two major components of this infiltrate are neutrophils in the synovial fluid and macrophages in the synovial tissue. These cells produce cytokines including tumor necrosis factor α and other proinflammatory mediators that likely drive the disease through its effector phases. To investigate what mechanisms underlie the recruitment of these cells into the synovial fluid and tissue, we performed expression analyses of chemoattractant receptors in a related family that includes the anaphylatoxin receptors and the formyl-MetLeuPhe receptor. We then examined the effect of targeted disruption of two abundantly expressed chemoattractant receptors, the receptors for C3a and C5a, on arthritogenesis in a mouse model of disease. We report that genetic ablation of C5a receptor expression completely protects mice from arthritis.
HLA-E–dependent Presentation of Mtb-derived Antigen to Human CD8+ T Cells
Authors: Heinzel Amy S. , Grotzke Jeff E. , Lines Rebecca A. , Lewinsohn Deborah A. , McNabb Andria L. , Streblow Daniel N. , Braud Veronique M. , Grieser Heather J. , Belisle John T. , Lewinsohn David M.
Published: December 2002

Previous studies in mice and humans have suggested an important role for CD8+ T cells in host defense to Mtb. Recently, we have described human, Mtb-specific CD8+ cells that are neither HLA-A, B, or C nor group 1 CD1 restricted, and have found that these cells comprise the dominant CD8+ T cell response in latently infected individuals. In this report, three independent methods are used to demonstrate the ability of these cells to recognize Mtb-derived antigen in the context of the monomorphic HLA-E molecule. This is the first demonstration of the ability of HLA-E to present pathogen-derived antigen. Further definition of the HLA-E specific response may aid development of an effective vaccine against tuberculosis.
A Signal Peptide Derived from hsp60 Binds HLA-E and Interferes with CD94/NKG2A Recognition
Authors: Michaëlsson Jakob , Teixeira de Matos Cristina , Achour Adnane , Lanier Lewis L. , Kärre Klas , Söderström Kalle
Published: December 2002

Human histocompatibility leukocyte antigen (HLA)-E is a nonclassical major histocompatibility complex (MHC) class I molecule which presents a restricted set of nonameric peptides, derived mainly from the signal sequence of other MHC class I molecules. It interacts with CD94/NKG2 receptors expressed on the surface of natural killer (NK) cells and T cell subsets. Here we demonstrate that HLA-E also presents a peptide derived from the leader sequence of human heat shock protein 60 (hsp60). This peptide gains access to HLA-E intracellularly, resulting in up-regulated HLA-E/hsp60 signal peptide cell-surface levels on stressed cells. Notably, HLA-E molecules in complex with the hsp60 signal peptide are no longer recognized by CD94/NKG2A inhibitory receptors. Thus, during cellular stress an increased proportion of HLA-E molecules may bind the nonprotective hsp60 signal peptide, leading to a reduced capacity to inhibit a major NK cell population. Such stress induced peptide interference would gradually uncouple CD94/NKG2A inhibitory recognition and provide a mechanism for NK cells to detect stressed cells in a peptide-dependent manner.