bluuebunny/crossref_metadata_2025 huggingface dataset:
Theoretical spectroscopy of the calcium dimer in the AΣu+1, cΠu3, and aΣu+3 manifolds: An ab initio nonadiabatic treatment
Authors: Bussery-Honvault Béatrice , Launay Jean-Michel , Korona Tatiana , Moszynski Robert
Published: September 2006

Nonadiabatic theory of molecular spectra of diatomic molecules is presented. It is shown that in the fully nonadiabatic framework, the rovibrational wave functions describing the nuclear motions in diatomic molecules can be obtained from a system of coupled differential equations. The rovibrational wave functions corresponding to various electronic states are coupled through the relativistic spin-orbit coupling interaction and through different radial and angular coupling terms, while the transition intensities can be written in terms of the ground state rovibrational wave function and bound rovibrational wave functions of all excited electronic states that are electric dipole connected with the ground state. This theory was applied in the nearly exact nonadiabatic calculations of energy levels, line positions, and intensities of the calcium dimer in the AΣu+1(1S1+1D1), cΠu3(1P3+1S1), and aΣu+3(1P3+1S1) manifolds of states. The excited state potentials were computed using a combination of the linear response theory within the coupled-cluster singles and doubles framework for the core-core and core-valence electronic correlations and of the full configuration interaction for the valence-valence correlation, and corrected for the one-electron relativistic terms resulting from the first-order many-electron Breit theory. The electric transition dipole moment governing the AΣu+1←XΣg+1 transitions was obtained as the first residue of the frequency-dependent polarization propagator computed with the coupled-cluster method restricted to single and double excitations, while the spin-orbit and nonadiabatic coupling matrix elements were computed with the multireference configuration interaction wave functions restricted to single and double excitations. Our theoretical results explain semiquantitatively all the features of the observed Ca2 spectrum in the AΣu+1(1S1+1D1), cΠu3(1P3+1S1), and aΣu+3(1P3+1S1) manifolds of states.
Hydrogen-induced crystallization of amorphous silicon thin films. I. Simulation and analysis of film postgrowth treatment with H2 plasmas
Authors: Sriraman Saravanapriyan , Valipa Mayur S. , Aydil Eray S. , Maroudas Dimitrios
Published: September 2006

We present a detailed atomic-scale analysis of the postdeposition treatment of hydrogenated amorphous silicon (a-Si:H) thin films with H2 plasmas. The exposure of a-Si:H films to H atoms from a H2 plasma was studied through molecular-dynamics (MD) simulations of repeated impingement of H atoms with incident energies ranging from 0.04to5.0eV. Structural and chemical characterizations of the H-exposed a-Si:H films was carried out through a detailed analysis of the evolution of the films’ Si–Si pair correlation function, Si–Si–Si–Si dihedral angle distribution, structural order parameter, Si–H bond length distributions, as well as film surface composition. The structural evolution of the a-Si:H films upon exposure to H atoms showed that the films crystallize to form nanocrystalline silicon at temperatures over the range of 500–773K, i.e., much lower than those required for crystallization due to thermal annealing. The MD simulations revealed that during H exposure of a-Si:H the reactions that occur include surface H adsorption, surface H abstraction, etching of surface silicon hydrides, dangling-bond-mediated dissociation of surface hydrides, surface H sputtering/desorption, diffusion of H into the a-Si:H film, and insertion of H into strained Si–Si bonds.
Hydrogen-induced crystallization of amorphous Si thin films. II. Mechanisms and energetics of hydrogen insertion into Si–Si bonds
Authors: Valipa Mayur S. , Sriraman Saravanapriyan , Aydil Eray S. , Maroudas Dimitrios
Published: September 2006

We report a detailed study of the mechanisms and energetics of hydrogen (H) insertion into strained Si–Si bonds during H-induced crystallization of hydrogenated amorphous Si (a-Si:H) thin films. Our analysis is based on molecular-dynamics (MD) simulations of exposure of a-Si:H films to H atoms from a H2 plasma through repeated impingement of H atoms. Hydrogen atoms insert into Si–Si bonds as they diffuse through the a-Si:H film. Detailed analyses of the evolution of Si–Si and Si–H bond lengths from the MD trajectories show that diffusing H atoms bond to one of the Si atoms of the strained Si–Si bond prior to insertion; upon insertion, a bridging configuration is formed with the H atom bonded to both Si atoms, which remain bonded to each other. After the H atom leaves the bridging configuration, the Si–Si bond is either further strained, or broken, or relaxed, restoring the Si–Si bond length closer to the equilibrium bond length in crystalline Si. In some cases, during its diffusion in the a-Si:H film, the H atom occupies a bond-center position between two Si atoms that are not bonded to each other; after the H diffuses away from this bond-center position, a Si–Si bond is formed between these previously nonbonded Si atoms. The activation energy barrier for the H insertion reaction depends linearly on both the initial strain in the corresponding Si–Si bond and a strain factor that takes into account the additional stretching of the Si–Si bond in the transition-state configuration. The role of the H insertion reactions in the structural relaxation of the a-Si:H network that results in disorder-to-order transitions is discussed.
Single-crystal, polarized, Raman scattering study of the molecular and lattice vibrations for the energetic material cyclotrimethylene trinitramine
Authors: Haycraft James J. , Stevens Lewis L. , Eckhardt Craig J.
Published: September 2006

The single-crystal, polarized, Raman spectra for cyclotrimethylene trinitramine (RDX) have been studied at room temperature and pressure over the region of 5–3400cm−1. While the observed Raman bands agree well with a previous Raman study, this work provides a consistent interpretation of the Raman spectra by assignment of fundamental modes, overtones, and combination bands. A total of 56 internal vibrations were observed, 36 of which were labeled as fundamental molecular vibrations. In addition, all 24 lattice optical phonons are identified. All six possible polarizations were probed to obtain the Ag, B1g, B2g, and B3g symmetry modes for both the lattice and molecular modes. Finally, the importance of these phonons for coupling with “doorway” Raman-active modes of RDX is discussed in relation to proposed mechanisms for detonation initiation.
Spatially resolved distribution of dislocations and crystallographic tilts in GaN layers grown on Si(111) substrates by maskless cantilever epitaxy
Authors: Barabash R. I. , Roder C. , Ice G. E. , Einfeldt S. , Budai J. D. , Barabash O. M. , Figge S. , Hommel D.
Published: September 2006

The spatial distribution of strain, misfit and threading dislocations, and crystallographic orientation in uncoalesced GaN layers grown on Si(111) substrates by maskless cantilever epitaxy was studied by polychromatic x-ray microdiffraction, high resolution monochromatic x-ray diffraction, and scanning electron microscopy. Tilt boundaries formed at the column/wing interface depending on the growth conditions. A higher lateral to vertical growth ratio suppressed sidewall deposition and was found to produce larger lattice tilts in the GaN films. Two kinds of crystallographic tilts are observed in the films. The measurements revealed that the free-hanging wings are tilted upward at room temperature in the direction perpendicular to the stripes. Finite element simulations of the thermally induced part of the wing tilt are presented. Moreover, a misorientation between the GaN(0001) and the Si(111) planes is observed in the parallel to the stripe direction. Its origin is discussed with respect to the strain of the epitaxial GaN on a miscut Si(111) surface and misfit dislocations formed at the interface.
X-ray diffraction measurements in shock compressed magnesium doped LiF crystals
Authors: Jensen B. J. , Gupta Y. M.
Published: September 2006

X-ray diffraction measurements, utilizing multiple and single diffraction methods, were used to examine lattice compression of magnesium doped (approximately 100ppm) LiF single crystals shocked along the [100] direction. Unlike ultrapure LiF crystals, examined in previous x-ray diffraction studies, magnesium doped crystals display large elastic wave amplitudes under shock wave compression. Analysis of multiple diffraction data from the (200) and (202) planes and single diffraction data from the (200) planes showed that the crystal lattice for doped crystals was compressed isotropically in the peak state, similar to that observed for ultrapure crystals. This agreement demonstrates that the large elastic wave amplitude and subsequent stress relaxation observed in wave propagation measurements for the doped LiF crystals are a transient phenomenon and do not appear to affect the lattice compression in the final state. Implications of this finding are discussed.
Phase field modeling of excimer laser crystallization of thin silicon films on amorphous substrates
Authors: Shih C. J. , Fang C. H. , Lu C. C. , Wang M. H. , Lee M. H. , Lan C. W.
Published: September 2006

Excimer laser crystallization processing of thin silicon films on amorphous silicon oxide substrates was simulated by means of phase field modeling. The quantitative phase field model was derived from the Gibbs-Thompson equation coupled with energy conservation. Because the adaptive mesh scheme was adopted, the present calculations could accommodate both two-dimensional superlateral growth (SLG) phenomena and the realistic interface thickness (in the order of 10−10m). The vertical growth of fine-grained nucleation structures was simulated using one-dimensional calculations, and the results are consistent with those obtained in previous experiments. Two cases of SLG were also simulated, and the evolution of the interface and thermal fields was determined. Based on our simulation results, we conclude that SLG crystallization does not achieve steady growth because of the extremely fast heat dissipation from the substrate. To obtain very uniform electric characteristics for device fabrication, the layout design and the device position should take the SLG laser mask into consideration.
The effect of potential fluctuations on the optical properties of InGaAs∕InGaAlAs single and coupled double quantum wells
Authors: Poças L. C. , Duarte J. L. , Lopes E. M. , Dias I. F. L. , Laureto E. , César D. F. , Harmand J. C.
Published: September 2006

A study was conducted on potential fluctuations using the photoluminescence (PL) technique with temperature and excitation intensity variations, in a sample containing InGaAs∕InGaAlAs coupled double quantum wells, with spikes of InGaAlAs of different thicknesses, and a single quantum well as the control. With the inclusion of a spike at the center of the well, an increase in the magnitude of the potential fluctuation occurs, in relation to the control well, due to an increase in the contribution from both the interface roughness and the compositional disorders to the potential fluctuations. The enhancement of the effects of the potential fluctuations, such as the PL linewidth and the blueshift of the PL peak energy with the temperature, as the spike thickness increases, was attributed to the increase in the contribution from the alloy composition fluctuation to the potential fluctuation, caused by an increase in the interaction of the wave function with the central and lateral barriers. This study also discusses the strong influence of the excitation intensity on the variation of the emission energy with temperature.
Roughness evolution during a-C:H film growth in methane plasmas
Authors: Kim In-Young , Hong Suk-Ho , Consoli Angelo , Benedikt Jan , von Keudell Achim
Published: September 2006

The roughness evolution during plasma deposition of amorphous hydrogenated carbon (a-C:H) films is investigated. Films were deposited from an inductively coupled methane plasma using a wide range of process parameters. Plasma deposition is uniquely described by the dissipated energy per source gas molecule Emean. Depending on Emean, a specific set of radicals contributes to film growth causing a characteristic roughness development. The film roughness is measured using atomic force microscopy and spectroscopic ellipsometry and is expressed using the static and dynamic scaling coefficients α and β, respectively. For low Emean<20eV, α∼0.65 and β∼0.19 indicating film deposition via a growth precursor with a large surface diffusion length. For Emean>20eV, α∼0.9 and β∼0.25 indicating film deposition via a growth precursor with a small surface diffusion length.
Microstructure and magnetic properties of SmCo5 thin films deposited on Cu and Pt underlayers
Authors: Takahashi Y. K. , Ohkubo T. , Hono K.
Published: September 2006

The microstructure of the SmCo5 thin films sputter deposited on Cu underlayers was investigated to explain the high coercivity Hc. Energy filtered elemental map and energy dispersive x-ray spectroscopy line analysis showed that Cu diffused into the SmCo5 layer to form a Sm(Co,Cu)5 solid solution. Composition fluctuations with a scale length of 40nm were found within the Sm(Co,Cu)5 layer, which would cause the local changes in the magnetocrystalline anisotropy. The high coercivity that was observed in the continuous Sm(Co,Cu)5 layer may be attributed to the pinning force for the magnetic domain wall motion due to the fluctuation of the magnetocrystalline anisotropy. The structure and magnetic properties of the SmCo5 thin film deposited on a Pt underlayer were also examined for comparison.
CH radical production from 248nm photolysis or discharge-jet dissociation of CHBr3 probed by cavity ring-down absorption spectroscopy
Authors: Romanzin C. , Boyé-Péronne S. , Gauyacq D. , Bénilan Y. , Gazeau M.-C. , Douin S.
Published: September 2006

The A-X bands of the CH radical, produced in a 248nm two-photon photolysis or in a supersonic jet discharge of CHBr3, have been observed via cavity ring-down absorption spectroscopy. Bromoform is a well-known photolytic source of CH radicals, though no quantitative measurement of the CH production efficiency has yet been reported. The aim of the present work is to quantify the CH production from both photolysis and discharge of CHBr3. In the case of photolysis, the range of pressure and laser fluences was carefully chosen to avoid postphotolysis reactions with the highly reactive CH radical. The CH production efficiency at 248nm has been measured to be Φ=N(CH)∕N(CHBr3)=(5.0±2.5)10−4 for a photolysis laser fluence of 44mJcm−2 per pulse corresponding to a two-photon process only. In addition, the internal energy distribution of CH(XΠ2) has been obtained, and thermalized population distributions have been simulated, leading to an average vibrational temperature Tvib=1800±50K and a rotational temperature Trot=300±20K. An alternative technique for producing the CH radical has been tested using discharge-induced dissociation of CHBr3 in a supersonic expansion. The CH product was analyzed using the same cavity ring-down spectroscopy setup. The production of CH by discharge appears to be as efficient as the photolysis technique and leads to rotationally relaxed radicals.
Particulate structure of FePt thin films enhanced by Au and Ag alloying
Authors: You C. Y. , Takahashi Y. K. , Hono K.
Published: September 2006

The additions of Au and Ag to FePt thin film change the film structure from an interconnected network to a completely isolated island structure. In particular, the Ag addition led to an isolated particulate structure smaller than 100nm, which increased the coercivity from 5.4to20.5kOe. Energy filtered elemental mapping did not show evidence for the precipitation or segregation of Au and Ag.
Channel waveguides of LiNbO3 crystals fabricated by low-dose oxygen ion implantation
Authors: Wang Xue-Lin , Chen Feng , Wang Lei , Jiao Yang
Published: September 2006

The planar and channel waveguides in z-cut LiNbO3 crystals have been fabricated by multienergy (2.2+1.8+1.6MeV) oxygen ion implantation to a total dose of 6×1014ions∕cm2 at room temperature, followed by a thermal anneal at 260°C for 30min in dry oxygen atmosphere. The image and optical intensity distribution of the light in the waveguides were obtained by an end-fire coupling method. The guiding modes of the planar waveguides were measured by the prism-coupling method at 633nm. The Rutherford backscattering/channeling technique was used to investigate the damage induced by oxygen ions after annealing treatment; the minimum yield of the spectra was 4.5%.
Texture evolution of Terfenol-D by solidification in a magnetic field
Authors: Deng Peiran , Li Jianguo , Xu Zhenming
Published: September 2006

The orientation of crystals of the giant magnetostrictive compound Terfenol-D solidified in a static magnetic field has been investigated. When the melt with size ϕ16×18mm2 solidifies slowly in a static magnetic field of 140mT, texture of the samples appears and the easy magnetization axis of the polycrystal tends to align towards the magnetic field gradually. ⟨111⟩ texture of Tb0.3Dy0.7Fe1.9 alloy is dominant in the sample solidified at a cooling rate of about 0.8°C∕min. These experimental results show that on the condition of slow cooling in the presence of a static magnetic field, free crystal nuclei of these materials in high temperature melt are easily be induced and aligned with their easy magnetic axes along the field at the beginning of the solidification.
Limits of localized heating by electromagnetically excited nanoparticles
Authors: Keblinski Pawel , Cahill David G. , Bodapati Arun , Sullivan Charles R. , Taton T. Andrew
Published: September 2006

Based on an analysis of the diffusive heat flow equation, we determine limits on the localization of heating of soft materials and biological tissues by electromagnetically excited nanoparticles. For heating by rf magnetic fields or heating by typical continuous wave lasers, the local temperature rise adjacent to magnetic or metallic nanoparticles is negligible. However, heat dissipation for a large number of nanoparticles dispersed in a macroscopic region of a material or tissue produces a global temperature rise that is orders of magnitude larger than the temperature rise adjacent to a single nanoparticle. One approach for producing a significant local temperature rise on nanometer length scales is heating by high-power pulsed or modulated lasers with low duty cycle.
Structural and magnetic studies in ferrihydrite nanoparticles formed within organic-inorganic hybrid matrices
Authors: Silva N. J. O. , Amaral V. S. , Carlos L. D. , Rodríguez-González B. , Liz-Marzán L. M. , Millan A. , Palacio F. , de Zea Bermudez V.
Published: September 2006

We report detailed transmission electron microscopy, high resolution transmission electron microscopy (HRTEM), and scanning transmission electron microscopy∕energy dispersive x-ray spectroscopy (STEM∕EDS) studies on ferrihydrite nanoparticles in an organic-inorganic matrix. The Fourier transform of HRTEM images indicates the existence of six-line ferrihydrite. Combined STEM and EDS studies give further confirmation of the presence of iron in the observed particles and its absence in the matrix. The derived mean particle size and size distribution is 4.7±0.2nm with a lognormal deviation of s=0.4±0.1. These values were used for analysis of magnetic measurements, yielding the determination of the anisotropy constant Keff=4×105erg∕cm3 and the power relation between the number of iron ions per particle and the number of uncompensated ones p≈1∕3. This value indicates that the uncompensated spins are mainly randomly distributed at the surface. According to this model, a shell thickness of about one ferrihydrite unit cell is estimated.
A model for the elastic moduli of three-dimensional fiber networks and nanocomposites
Authors: Chatterjee Avik P.
Published: September 2006

A model is developed for the tensile and shear elastic moduli of three-dimensional fiber networks. The semiempirical Halpin-Tsai [J. C. Halpin and J. L. Kardos, J. Appl. Phys. 43, 2235 (1972)] equations for fiber-reinforced materials are combined with results from percolation theory and the present treatment of elastic fiber networks. A unified description of the moduli of nanocomposites containing elongated filler particles over a range of volume fractions spanning the filler percolation threshold is provided. Estimates are developed for the strains at the elastic limits under tensile and shear deformation, and model calculations are presented for the dependences of composite moduli and yield strains on particle aspect ratios and volume fractions.
Spatial distribution of polarization and space charge in barium strontium titanate ceramics
Authors: Farhat N. , Holé S. , Ditchi T. , Lewiner J. , Button T. W. , Su B.
Published: September 2006

Ferroelectric films of BaSrTiO3 (BST) are identified as a potential alternative to silicon dioxide in the silicon-based microelectronics industry owing to their very high dielectric constant. In this paper the distribution of space charge and polarization in BST ceramics is studied at room temperature with the laser induced pressure pulse method. Under voltage, dipoles orient rapidly but are subjected to the material nonuniformities. At longer time the ceramic becomes uniformly poled, indicating a transformation of the material. The remnant polarization remains uniform and stable for at least two days once the sample shorted. Long stress cycles and annealing have shown similar effects on the electrical behavior owing to similar microregion rearrangements.
Domain growth as manifestation of a Coulomb instability of bound charge
Authors: Molotskii Michel I. , Shvebelman Maria M.
Published: September 2006

Repulsion of bound charges near a domain apex results in Coulomb forces elongating the domain. This allows for consideration of the domain growth as manifestation of a Coulomb instability of the bound charge. The character of the instability depends on the type of the external field. A domain that grows in a homogeneous field never reaches equilibrium. As the domain elongates, the value of the bound charge continually increases; the elongating force and the forward growth velocity slowly increase and become practically saturated. The domain elongation has a character of a pinpoint Coulomb explosion. In a nonhomogeneous field of an atomic force microscope (AFM) the Coulomb explosion does not occur since the Coulomb instability is compensated at finite domain length by surface tension forces and by forces due to the field of the AFM. It is shown that the domain breakdown phenomenon, which is the deep penetration of the domain apex into the region with zero AFM field, may be considered as extreme manifestation of a Coulomb instability of the bound charge.
Dynamic response of two strain-hardened aluminum alloys
Authors: Boteler J. M. , Dandekar D. P.
Published: September 2006

Despite their common usage in armor applications such as lightweight armored vehicles, the dynamic material response of 5083-H131 and 5083-H32 strain-hardened aluminum alloys has not been previously reported in the open literature. Measurement of the dynamic material properties, including the shock Hugoniot equation of state (EOS), provides hydrocode modelers with critical information required for accurate modeling of material response to intense loading. In the work reported here we investigate the Hugoniot EOS and Hugoniot elastic limit over the stress range of 1.5–8.0GPa. All experiments were performed on the Army Research Laboratory 102mm bore single-stage light gas gun. Impact conditions were uniaxial and planar to within 1mrad of tilt. Both direct-impact- and shock-transmission-type experiments were performed using velocity interferometry diagnostics to record particle velocity histories with 0.5ns temporal resolution. The shock Hugoniot for 5083-H131 is extrapolated to 50GPa and compared to the previous high pressure results of Hauver and Melani (1973) [Ballistic Research Laboratory December Technical Report No. BRL 2345, 1973] and to prior shock studies of 5083-O aluminum alloy.
Laser-induced dendritic microstructures on the surface of Ag+-doped glass
Authors: Nahal A. , Mostafavi-Amjad J. , Ghods A. , Khajehpour M. R. H. , Reihani S. N. S. , Kolahchi M. R.
Published: September 2006

Fractal dendritic silver microstructures are observed on the surface of the Ag+-doped glasses as a result of a photothermal interaction with a focused multiline cw high-power (Pmax=8 W) Ag+ laser beam. It is found that evolution of the structures depends on the exposure time and also on the concentration of the silver ions in the sample. The fractal dimension of the generated dendritic microstructures increases with the exposure time. Instability of the contact line of the molten silver flow toward the periphery of the interaction area is discussed as a result of the temperature gradient, due to the Gaussian intensity distribution across the laser beam.
Structural and magnetic properties of V∕Cofcc and Cohcp∕V bilayers grown on MgO(100): A comparative study
Authors: Calleja J. F. , Huttel Y. , Contreras M. C. , Navarro E. , Presa B. , Matarranz R. , Cebollada A.
Published: September 2006

A detailed study of the structure and magnetic properties of V∕Co versus Co∕V bilayers grown on MgO(001) substrates with cubic and hexagonal Co crystal structures is presented. Co is found to adopt fcc structure when grown on MgO(001), while it adopts hcp structure when grown on V(001). The different magnetocrystalline anisotropy associated with each structure gives rise to different magnetic properties for the otherwise equivalent symmetric Co–V bilayers.
High-K dielectrics for the gate stack
Authors: Locquet Jean-Pierre , Marchiori Chiara , Sousa Maryline , Fompeyrine Jean , Seo Jin Won
Published: September 2006

This article gives an overview of recent developments in the search for the next-generation dielectric for the complementary metal-oxide semiconductor gate stack. After introducing the main quantities of interest, the paper concentrates on a figure of merit that connects two main properties of the gate stack, namely, the leakage current and the capacitance. This is done for single layers as well as for bilayers consisting of interfacial SiOx and a high-K dielectric. In the case of the bilayers, the impact of the interfacial layer SiOx is enormous, reducing the leakage current by an order of magnitude per monolayer. This extreme dependance makes a good correlation between the leakage and the structural parameters nearly impossible. This is illustrated using numerical examples designed to help the reader evaluate the orders of magnitude involved. The origin of the interfacial layer is traced back by means of thermodynamic considerations. As the estimates put forward in the literature do not correspond to the results observed, a detailed review is made, and additional mechanisms are suggested. By using reasonable values for the Gibbs free energy of an interfacial solid silicon oxide phase it is demonstrated how the reaction equilibria shift. Such an interface phase may fundamentally change the stability criteria of oxides on Si. Furthermore, it can also provide a major source of electronic defects that will affect the device performance. Finally, a second figure of merit is introduced that connects the capacitance with a strongly reduced carrier mobility, which might also be related to the same electronic defects.
Several features of emission spectra of Pr+3 ions incorporated into Li2B4O7 glass matrices
Authors: Majchrowski A. , Kityk I. V. , Mandowska E. , Mandowski A. , Ebothé Jean , Lukasiewicz T.
Published: September 2006

Influence of lithium tetraborate (Li2B4O7, TBL) glass matrix on the luminescent properties of the Pr+3 ions emission was investigated. It was demonstrated that the decrease of matrix long-range ordering leads to substantial widening of corresponding peaks in the emission spectra in comparison with crystalline Ca4GdO(BO3)3 matrices. During the decrease of temperature from 292 down to 82K a distinct low-energy spectral shift of the principal red luminescent band from 607to610nm is observed, which is a consequence of a coexistence of several structural borate fragments. Simulations of incorporation the Pr3+ ions into the TBL glasslike matrix were carried out using the Langevin molecular dynamics simulations and quantum chemical simulations. Possibility of partial substitution of boron ions by Pr3+ ions is demonstrated. The contribution of the electron-phonon subsystems to the spectral broadening of the corresponding emission red lines was evaluated. It was shown that the main contribution to the emission bands gives harmonic electron-phonon interactions contrary to the generally adopted model assuming prevailing role of anharmonic electron-phonon interactions.
Effect of xenon bombardment on ruthenium-coated grazing incidence collector mirror lifetime for extreme ultraviolet lithography
Authors: Nieto Martin , Allain Jean-Paul , Titov Vladimir , Hendricks Matthew R. , Hassanein Ahmed , Rokusek Daniel , Chrobak Christopher , Tarrio Charles , Barad Yaniv , Grantham Steven , Lucatorto Thomas B. , Rice Brian
Published: September 2006

The effect of energetic xenon ion bombardment on the extreme ultraviolet (EUV) reflectivity performance of mirrors is of vital importance for the performance of discharge- and laser-produced plasma extreme ultraviolet lithography sources. To study these effects, we measured absolute and relative reflectivities at the National Institute of Standards and Technology and the Interaction of Materials with Particles and Components Testing facility to quantify the effects of singly ionized Xe ion bombardment on the reflectivity of Ru EUV collector mirrors. Results show that unity sputtering is reached at Xe+ energies near 400–500eV. The Xe+-induced sputter yield decreases an order of magnitude with only a 60% decrease in energy. Incident angle-dependent data of Xe+ bombardment show that the sputter yield is weakly dependent on angle at energies near 1keV. Dynamic measurements of in situ EUV reflectivity during Xe+ irradiation show that the oxygen state of the reflecting mirror has a significant effect on reflectivity performance. For example, 13.5nm light reflecting from an oxygen-rich mirror results in over a 40% loss in reflectivity. These studies also found that the surface roughness increased only at the atomic scale (subnanometer scale) when exposed to energetic Xe+ and thus did not contribute to EUV reflectivity losses except for cases of very high fluences (>1016cm−2).
Ion and gas temperatures of 0.46MHz inductive plasma discharges
Authors: Tuszewski M.
Published: September 2006

The ion and gas temperatures of inductively coupled plasma discharges, operated with low nitrogen gas pressures, are studied with optical emission spectroscopy. The nonresolved gas and ion rotational temperatures are estimated by comparing the measured and calculated spectra of selected transitions with a least-square procedure. The measured gas and ion temperatures increase weakly with gas pressure, and somewhat stronger with rf power. The ion temperatures (∼0.1eV) consistently exceed the corresponding gas temperatures by factors of 2–2.5, in contrast with past results. This may be due in part to ion heating by the low-frequency rf fields.
Nonlithographic nanopatterning through anodic aluminum oxide template and selective growth of highly ordered GaN nanostructures
Authors: Wang Y. D. , Zang K. Y. , Chua S. J.
Published: September 2006

Ordered GaN nanostructures, i.e., nanopore and nanodot arrays, have been demonstrated by combining a nonlithographic nanopatterning technique and nanoscale selective epitaxial growth. Hexagonal-close-packed nanopore arrays were fabricated in GaN surfaces and SiO2 surfaces on GaN films by inductively coupled plasma etching using anodic aluminum oxide templates as etching masks. Selective area growth through nanopores in SiO2 by metal organic chemical vapor deposition results in ordered GaN nanodot arrays with an average dot diameter and height of 60 and 100nm, respectively. The diameter and density of the GaN nanopore arrays and nanodot arrays are controlled by that of the anodic aluminum oxide template, which can be tuned in a wide range by controlling the anodization conditions. Applying anodic aluminum oxide as an etching mask provides an effective nonlithographic and free of foreign catalysts method to fabricate ordered and dense nitride nanostructures for either bottom-up or top-down technique in the application of high efficiency nitride light emitting diodes.
Optical emission in magnetically confined laser-induced breakdown spectroscopy
Authors: Shen X. K. , Lu Y. F. , Gebre T. , Ling H. , Han Y. X.
Published: September 2006

Magnetically confined laser-induced breakdown spectroscopy was investigated by studying the optical emission from laser-induced plasma plumes expanding across an external transverse magnetic field. KrF excimer laser pulses with a pulse duration of 23ns and a wavelength of 248nm were used to produce plasmas from Al, Cu, and Co targets. Various optical emission lines obtained from Al and Cu targets show an obvious enhancement in the intensity of optical emission when a magnetic field of ∼0.8T is applied, while the optical emission lines from Co targets show a decrease in the optical emission intensity. The enhancement factors of optical emission lines were measured to be around 2 for the Al and Mn (impurity) lines from Al targets, and 6–8 for Cu lines from Cu targets. Temporal evolution of the optical emission lines from the Al samples shows a maximum enhancement in emission intensity at time delays of 8–20μs after the incident laser pulse, while from the Cu targets it shows a continuous enhancement at time delays of 3–20μs after the pulse. The enhancement in the optical emission from the Al and Cu plasmas was presumably due to the increase in the effective plasma density as a result of magnetic confinement. The decrease in the emission intensity from the Co plasmas was suggested to be due to the decrease of effective plasma density as a result of the magnetic force.
Polymer memory device based on conjugated polymer and gold nanoparticles
Authors: Prakash Ankita , Ouyang Jianyong , Lin Jen-Lien , Yang Yang
Published: September 2006

Electrical bistability is demonstrated in a polymer memory device with an active layer consisting of conjugated poly(3-hexylthiophene) and gold nanoparticles capped with 1-dodecanethiol sandwiched between two metal electrodes. The device was fabricated through a simple solution processing technique and exhibited a remarkable electrical bistable behavior. Above a threshold voltage the pristine device, which was in a low conductivity state, exhibited an increase in conductivity by more than three orders of magnitude. The device could be returned to the low conductivity state by applying a voltage in the reverse direction. The electronic transition is attributed to an electric-field-induced charge transfer between the two components in the system. The conduction mechanism changed from a charge-injection-controlled current in the low conductivity state to a charge-transport-controlled current in the high conductivity state. In the high conductivity state the conduction was dominated by a field-enhanced thermal excitation of trapped charges at room temperature, while it is dominated by charge tunneling at low temperatures. The device exhibited excellent stability in both the conductivity states and could be cycled between the two states for numerous times. The device exhibits tremendous potential for its application as fast, stable, low-cost, high storage density nonvolatile electronic memory.
Magnetic properties of MnGa2Se4 in the temperature range of 2–300K
Authors: Morocoima M. , Quintero M. , Quintero E. , González J. , Tovar R. , Bocaranda P. , Ruiz J. , Marchán N. , Caldera D. , Calderon E. , Woolley J. C. , Lamarche G. , Lamarche A.-M. , Broto J. M. , Rakoto H. , D’Onofrio L. , Cadenas R.
Published: September 2006

Measurements of low field static magnetic susceptibility and of magnetization with pulsed magnetic fields up to 32T have been made as a function of temperature on polycrystalline samples of the compound MnGa2Se4 which has a tetragonal structure. The resulting data have been used to give information on the magnetic spin-flop and magnetic saturation transitions. It has been found that MnGa2Se4 has a zero-field Néel temperature TN of 8.1K and shows a triple point at (7.8K, 2.2T). Details of the magnetic B-T phase diagrams were determined for the phases and the results compared with the predictions of theoretical uniaxial models. The susceptibility χ(T) curves for B=3 and 5T show magnetothermal effects below 4.5K.
Convergence properties of critical dimension measurements by spectroscopic ellipsometry on gratings made of various materials
Authors: Antos Roman , Pistora Jaromir , Mistrik Jan , Yamaguchi Tomuo , Yamaguchi Shinji , Horie Masahiro , Visnovsky Stefan , Otani Yoshichika
Published: September 2006

Spectroscopic ellipsometry (SE) in the visible/near-UV spectral range is applied to monitor optical critical dimensions of quartz, Si, and Ta gratings, namely, the depth, linewidth, and period. To analyze the SE measurements, the rigorous coupled-wave theory is applied, whose implementation is described in detail, referred to as the Airy-like internal reflection series with the Fourier factorization rules taken into account. It is demonstrated that the Airy-like series implementation of the coupled-wave theory with the factorization rules provides fast convergence of both the simulated SE parameters and the extracted dimensions. The convergence properties are analyzed with respect to the maximum Fourier harmonics retained inside the periodic media and also with respect to the fineness of slicing imperfect Ta wires with paraboloidally curved edges.
Lateral size effects on domain structure in epitaxial PbTiO3 thin films
Authors: Lee Kilho , Yi Hyunjung , Park Wang-Hyun , Kim Yong Kwan , Baik Sunggi
Published: September 2006

Lateral size effects of ferroelastic domain structures in epitaxial PbTiO3 thin films were investigated systematically with a viewpoint of misfit strain relaxation mechanism. The epitaxial PbTiO3 thin films were patterned into discrete islands and the effects of lateral dimension were analyzed by reciprocal space mapping using synchrotron x-ray diffraction as well as finite element simulation. As the lateral two-dimensional planar size decreases in the PbTiO3 patterns on MgO(001), some of the a domains turned into c domains due to the relaxed tensile strain. In the PbTiO3 patterns on Pt(001)∕MgO(001), on the other hand, the formation of 90° domains is enhanced by the reduction in compressive misfit strain. As the pattern size decreases further to 100nm, the untilted a domains arise due to the almost completely relaxed misfit strains. Equilibrium domain structures in the epitaxial thin films and discrete islands are also analyzed by the finite element simulation and found to be consistent with the experimental observation. These results manifest that the domain structure and evolution of the epitaxial thin films could be engineered by the control of misfit strain and its relaxation.
Theory for equilibrium 180° stripe domains in PbTiO3 films
Authors: Stephenson G. B. , Elder K. R.
Published: September 2006

A thermodynamic theory is developed for equilibrium 180° stripe domains in ferroelectric thin films on insulating substrates. Such stripe domains form to minimize the energy of the depolarizing field, and lead to a suppression of TC in thin films. Expressions including depolarizing field and domain wall energy are developed and applied to coherently strained PbTiO3 films on SrTiO3 substrates, with an upper boundary condition of either a dielectric (SrTiO3), a conductor, or vacuum. An elastic solution appropriate for epitaxially strained stripe domains and 180° domain walls is presented. We minimize the full nonlinear free energy using a numerical technique to obtain equilibrium polarization and field distributions, and determine the equilibrium stripe period as a function of temperature and film thickness for each upper boundary condition. While the stripe periods found agree reasonably well with the existing analytical solution using a linearized free energy, the suppression of TC as film thickness decreases is as much as a factor of 10 smaller than that given by the linear solution.
Integration of lead zirconium titanate thin films for high density ferroelectric random access memory
Authors: Kim Kinam , Lee Sungyung
Published: September 2006

Interests are being focused on types of nonvolatile memories such as ferroelectric random access memory (FRAM), phase change random access memory, or magnetoresistance random access memory due to their distinct memory properties such as excellent write performance which conventional nonvolatile memories do not possess. Among these types of nonvolatile memories, FRAM whose cell structure and operation are almost identical to dynamic random access memory (DRAM) can ideally realize cell size and speed of DRAM. Thus FRAM is the most appropriate candidate for future universal memory where all memory functions are performed with a single chip solution. Due to the poor ferroelectric properties of downscaled ultrathin lead zirconium titanate (PZT) capacitors as well as technical issues such as hydrogen and plasma related degradation arising from embedding ferroelectric metal-insulator-metal capacitors into conventional complementary metal oxide semiconductor processes, current FRAM still falls far below its ideally attainable cell size and performance. In this paper, based upon PZT capacitor, current mass-productive one pass transistor and one storage capacitor (1T1C), capacitor over bit line (COB) cell technologies are introduced upon which cell size of 0.937μm2 at 250nm minimum feature size technology node has been realized. And then, most recent 1T1C, COB cell technologies are discussed from which cell size of 0.27μm2 at 150nm minimum feature size technology node has been realized, and finally future three dimensional capacitor technologies for the FRAM with cell size of less than 0.08μm2 beyond 100nm minimum feature size technology node are suggested.
Scaling of structure and electrical properties in ultrathin epitaxial ferroelectric heterostructures
Authors: Nagarajan V. , Junquera J. , He J. Q. , Jia C. L. , Waser R. , Lee K. , Kim Y. K. , Baik S. , Zhao T. , Ramesh R. , Ghosez Ph. , Rabe K. M.
Published: September 2006

Scaling of the structural order parameter, polarization, and electrical properties was investigated in model ultrathin epitaxial SrRuO3∕PbZr0.2Ti0.8O3∕SrRuO3∕SrTiO3 heterostructures. High-resolution transmission electron microscopy images revealed the interfaces to be sharp and fully coherent. Synchrotron x-ray studies show that a high tetragonality (c∕a∼1.058) is maintained down to 50Å thick films, suggesting indirectly that ferroelectricity is fully preserved at such small thicknesses. However, measurement of the switchable polarization (ΔP) using a pulsed probe setup and the out-of-plane piezoelectric response (d33) revealed a systematic drop from ∼140μC∕cm2 and 60pm∕V for a 150Å thick film to 11μC∕cm2 and 7pm∕V for a 50Å thick film. This apparent contradiction between the structural measurements and the measured switchable polarization is explained by an increasing presence of a strong depolarization field, which creates a pinned 180° polydomain state for the thinnest films. Existence of a polydomain state is demonstrated by piezoresponse force microscopy images of the ultrathin films. These results suggest that the limit for a ferroelectric memory device may be much larger than the fundamental limit for ferroelectricity.
Dielectric properties of BaTiO3∕SrTiO3 ferroelectric thin film artificial lattice
Authors: Lee Jaichan , Kim Leejun , Kim Juho , Jung Donggeun , Waghmare Umesh V.
Published: September 2006

Dielectric behavior on BaTiO3∕SrTiO3 artificial lattices has been investigated along with quantum mechanical simulation (first principles calculation). From the oxide artificial lattice approach, strain manipulation was performed to obtain a wide range of lattice deformation in the consisting BaTiO3 and SrTiO3 layers, which leads to two important consequences. First, we obtained enhanced dielectric constant and extremely large nonlinearity in the artificial lattices with very short stacking periods. Second, it is found that there exists a maximum dielectric constant in each BaTiO3 lattice and SrTiO3 lattice at a certain degree of lattice deformation. The first principles study successfully explains the dielectric behavior of strained BaTiO3 and SrTiO3 lattices, the existence of the maximum dielectric constant. The first principles study on BaTiO3∕SrTiO3 artificial lattices with very short stacking periods also reveals that the artificial lattice undergoes phase transition between the tetragonal and monoclinic phases with a misfit lattice strain and exhibits an anomalous dielectric behavior at the phase boundary. Optical phonon behavior of the BaTiO3∕SrTiO3 artificial lattice resembles that of strained SrTiO3 lattice and optical phonon softening primarily derives the anomaly of the dielectric tensor at the phase boundary. The lattice deformation is a primary influencing factor to phonon and dielectric behaviors rather than interface layer effect in BaTiO3∕SrTiO3 artificial lattice with very short stacking periods.
Liquid phase immunoassay utilizing magnetic marker and high Tc superconducting quantum interference device
Authors: Enpuku K. , Soejima K. , Nishimoto T. , Tokumitsu H. , Kuma H. , Hamasaki N. , Yoshinaga K.
Published: September 2006

We have developed a liquid phase immunoassay system utilizing a magnetic marker and a superconducting quantum interference device (SQUID). In this system, the magnetic marker was used to detect the biological material called antigen. The magnetic marker was designed so as to generate a remanence, and the remanence field of the markers that bound to the antigens was measured with the SQUID. The measurement was performed in a solution that contained both the bound and free (or unbound) markers, i.e., without using the so-called bound/free (BF) separation process. The Brownian rotation of the free markers in the solution was used to distinguish the bound markers from the free ones. Using the system, we conducted the detection of biological material called IgE without BF separation. At present, we could detect the IgE down to 7pg (or 39amol).
Properties of GaP(001) surfaces chemically treated in NH4OH solution
Authors: Morota Hiroaki , Adachi Sadao
Published: September 2006

Chemically cleaned GaP(001) surfaces in 25% NH4OH solution have been studied using spectroscopic ellipsometry (SE), ex situ atomic force microscopy (AFM), x-ray photoelectron spectroscopy (XPS), and wettability measurement techniques. The SE data clearly indicate that the solution causes removal of the native oxide film immediately upon immersing the sample. The SE data also indicate that when the native oxide film is completely etch removed, the resulting surface is still roughened. The estimated roughness thickness is ∼1.2nm, in excellent agreement with the AFM rms value (∼1.2nm). The XPS spectra confirm the removal of the native oxide from the GaP surface. The XPS data also suggest a thin oxide overlayer, ∼0.3nm thick, on the etch-cleaned GaP surface. The wettability measurements indicate that the as-degreased surface is hydrophobic, while the NH4OH-cleaned surface is hydrophilic. This result is in direct contrast to those obtained from acid cleaned surfaces, which are usually hydrophobic. The origin of hydrophilicity may be singular and associated hydroxyl groups bonded on the GaP surface.