bluuebunny/crossref_metadata_2025 huggingface dataset:
Characterization of SodC, a Periplasmic Superoxide Dismutase from
Burkholderia cenocepacia
Authors: Keith Karen E. , Valvano Miguel A.
Published: February 2007

Burkholderia cenocepacia
is a gram-negative, non-spore-forming bacillus and a member of the
Burkholderia cepacia
complex.
B. cenocepacia
can survive intracellularly in phagocytic cells and can produce at least one superoxide dismutase (SOD). The inability of O
2
−
to cross the cytoplasmic membrane, coupled with the periplasmic location of Cu,ZnSODs, suggests that periplasmic SODs protect bacteria from superoxide that has an exogenous origin (for example, when cells are faced with reactive oxygen intermediates generated by host cells in response to infection). In this study, we identified the
sodC
gene encoding a Cu,ZnSOD in
B. cenocepacia
and demonstrated that a
sodC
null mutant was not sensitive to a H
2
O
2
, 3-morpholinosydnonimine, or paraquat challenge but was killed by exogenous superoxide generated by the xanthine/xanthine oxidase method. The
sodC
mutant also exhibited a growth defect in liquid medium compared to the parental strain, which could be complemented in
trans
. The mutant was killed more rapidly than the parental strain was killed in murine macrophage-like cell line RAW 264.7, but killing was eliminated when macrophages were treated with an NADPH oxidase inhibitor. We also confirmed that SodC is periplasmic and identified the metal cofactor.
B. cenocepacia
SodC was resistant to inhibition by H
2
O
2
and was unusually resistant to KCN for a Cu,ZnSOD. Together, these observations establish that
B. cenocepacia
produces a periplasmic Cu,ZnSOD that protects this bacterium from exogenously generated O
2
−
and contributes to intracellular survival of this bacterium in macrophages.
TELEPARALLEL ENERGY–MOMENTUM DISTRIBUTION OF LEWIS–PAPAPETROU SPACETIMES
Authors: SHARIF M. , JAMIL AMIR M.
Published: February 2007

In this paper, we find the energy–momentum distribution of stationary axisymmetric spacetimes in the context of teleparallel theory by using Möller prescription. The metric under consideration is the generalization of the Weyl metrics called the Lewis–Papapetrou metric. The class of stationary axisymmetric solutions of the Einstein field equations has been studied by Galtsov to include the gravitational effect of an external source. Such spacetimes are also astrophysically important as they describe the exterior of a body in equilibrium. The energy density turns out to be nonvanishing and well-defined and the momentum becomes constant except along θ-direction. It is interesting to mention that the results reduce to the already available results for the Weyl metrics when we take ω = 0.
PHASE STRUCTURE OF QED3 AT FINITE CHEMICAL POTENTIAL AND TEMPERATURE
Authors: HE MIN , FENG HONG-TAO , SUN WEI-MIN , ZONG HONG-SHI
Published: February 2007

We study the dynamical chiral symmetry breaking (DCSB) of three-dimensional quantum electrodynamics (QED3) at finite chemical potential and temperature in the framework of Dyson–Schwinger approach. Based on the rainbow approximation and assumption that the wave-function renormalization factor equals to one, the dynamically generated mass function is derived and then the corresponding phase diagram in the (T, μ) plane is obtained.
CHAOTIC MOTION IN MULTI-BLACK HOLE SPACETIMES AND HOLOGRAPHIC SCREENS
Authors: HANAN WILLIAM , RADU EUGEN
Published: February 2007

We investigate the geodesic motion in D-dimensional Majumdar–Papapetrou multi-black hole spacetimes and find that the qualitative features of the D = 4 case are shared by the higher dimensional configurations. The motion of timelike and null particles is chaotic, the phase space being divided into basins of attraction which are separated by a fractal boundary, with a fractal dimension dB. The mapping of the geodesic trajectories on a screen placed in the asymptotic region is also investigated. We find that the fractal properties of the phase space induces a fractal structure on the holographic screen, with a fractal dimension dB - 1.
WRITER STYLE ADAPTATION IN ONLINE HANDWRITING RECOGNIZERS BY A FUZZY MECHANISM APPROACH: THE ADAPT METHOD
Authors: MOUCHÈRE HAROLD , ANQUETIL ERIC , RAGOT NICOLAS
Published: February 2007

This study presents an automatic online adaptation mechanism to the handwriting style of a writer for the recognition of isolated handwritten characters. The classifier we use here is based on a Fuzzy Inference System (FIS) similar to those we have designed for handwriting recognition. In this FIS each premise rule is composed of a fuzzy prototype which represents intrinsic properties of a class. Furthermore, the conclusion part of rules associates a score to the prototype for each class. The adaptation mechanism affects both the conclusions of the rules and the fuzzy prototypes by recentering and reshaping them thanks to a new approach called ADAPT inspired by the Learning Vector Quantization. Thus the FIS is automatically fitted to the handwriting style of the writer that currently uses the system. Our adaptation mechanism is compared with well known adaptation techniques. The tests were based on eight different writers and the results illustrate the benefits of the method in terms of error rate reduction (86% in average). This allows such kind of simple classifiers to achieve up to 98.4% of recognition accuracy on the 26 Latin letters in a writer dependent context.
MIXED DISCRIMINANT TRAINING OF HYBRID ANN/HMM SYSTEMS FOR ONLINE HANDWRITTEN WORD RECOGNITION
Authors: CAILLAULT EMILIE , VIARD-GAUDIN CHRISTIAN
Published: February 2007

Online handwritten word recognition systems usually rely on Hidden Markov Models (HMMs), which are effective under many circumstances, but suffer some major limitations in real world applications. Artificial neural networks (ANN) appear to be a promising alternative, however they failed to model sequence data such as online handwriting due to their variable lengths. As a consequence, by combining HMMs and ANN, we can expect to take advantage of the robustness and flexibility of the HMMs generative models and of the discriminative power of the ANN. Training such a hybrid system is not straightforward, this is why so few attempts are encountered in literature. We compare several different training schemes: maximum likelihood (ML) and maximum mutual information (MMI) criteria in the framework of online handwriting recognition with a global optimization approach defined at the word level. A new generic criterion mixing generative model and discriminant trainings is proposed, it allows to train a multistate TDNN-HMM system directly at the word level. This architecture is based on an analytical approach with an implicit segmentation. To control the implicit segmentation and to initialize correctly the system without bootstrapping with another recognition system, we have defined a process that constraints the segmentation path and a measure called Average Segmentation Rate (ASR). Recognition experiments on the online IRONOFF database demonstrated the interest of the generic training criterion and the control of the implicit segmentation.
EVOLUTIONARY PROTOTYPING FOR HANDWRITING RECOGNITION
Authors: CORDELLA L. P. , DE STEFANO C. , FONTANELLA F.
Published: February 2007

A new prototyping method based on the evolutionary computation paradigm and on the concept of Vector Quantization is proposed. It uses a specifically devised evolutionary algorithm for evolving a set of prototype feature vectors and does not require any a priori knowledge about either the actual number of prototypes or the statistical properties of the input data. Experiments performed by using both synthetic data and handwritten digits randomly extracted from the NIST database have confirmed the effectiveness of the approach.
40 YEARS OF THE DYNAMICAL PROTON-NEUTRON PAIRING SYMMETRIES
Authors: SZPIKOWSKI STANISŁAW
Published: February 2007

In the years 1964-66 several physicists from several groups were searching quite independently for new symmetries related to the proton-neutron pairing interaction. They exploited the so-called quasi-spin method introduced earlier to apply to the system of electrons and then to identical nucleons (only protons or only neutrons). In what follows, a short introduction to the quasi-spin method is presented and then its application to the pairing interaction of neutrons (protons) is given. With the help of the quasi-spin method, the orthogonal symmetry groups SO(5) and SO(8) are shown to deal with proton-neutron pairing interaction in j - j and L - S coupling schemes, respectively. Comments about chronology of published papers related to the symmetry of pairing interaction written by inventors of the new symmetries are also made.
ON THE AVERAGE PAIRING ENERGY IN NUCLEI
Authors: NERLO-POMORSKA BOŻENA , POMORSKI KRZYSZTOF
Published: February 2007

The macroscopic-microscopic method is applied to calculate the nuclear energies, especially the microscopic shell and pairing corrections. The single-particle levels are obtained with the Yukawa folded mean-field potential. The macroscopic energy is evaluated using the Lublin-Strasbourg Drop model. The shell corrections are obtained using the Strutinsky method with smoothing in nucleon number space. The average nuclear pairing energy is also determined by folding the BCS sums in nucleon number space. The average pairing energy dependence on the nuclear elongation is investigated.
PARTICLE NUMBER RESTORATION: ITS IMPLEMENTATION AND IMPACT IN NUCLEAR STRUCTURE CALCULATIONS
Authors: ROBLEDO LUIS M.
Published: February 2007

In this paper we summarize the technical aspects associated to the restoration of the particle number symmetry broken by the mean field HFB method. Special attention is paid to how to deal with density dependent forces which are so popular nowadays for large scale nuclear structure calculations. A few remarks on the difficulties encountered will be made and its implications discussed.
PROBING THE EFFECTIVE NUCLEON-NUCLEON INTERACTION AT BAND TERMINATION
Authors: SATUŁA W.
Published: February 2007

Low-energy nuclear structure is not sensitive enough to resolve the fine details of the nucleon-nucleon (NN) interaction. The insensitivity of the low-energy (infrared) physics to the details of the short-range strong interaction allows for a consistent, free of high-energy (ultraviolet) divergences, formulation of a local theory at the level of the local energy density functional (LEDF) including on the same footing, particle-hole and particle-particle channels. A major difficulty is related to the parameterization of the nuclear LEDF and its density dependence. It is argued that the structural simplicity of terminating or isomeric states offers an invaluable source of information that can be used for fine-tuning of the NN interaction in general and the nuclear LEDF parameters in particular. Practical applications of terminating states at the level of LEDF and nuclear shell-model are discussed.
TERMINATING STATES AS A UNIQUE LABORATORY FOR TESTING NUCLEAR ENERGY DENSITY FUNCTIONAL
Authors: ZALEWSKI M. , SATUŁA W.
Published: February 2007

Systematic calculations of favored signature maximum-spin Imax and unfavored signature Imax - 1 terminating states for [Formula: see text] and [Formula: see text] configurations (n denotes number of valence particles) in A~44 mass region are presented. Following the result of Zduńczuk et al., Phys. Rev. C58 (2005) 024305 the calculations are performed using Skyrme energy density functional with empirical Landau parameters and slightly reduced spin-orbit strength. The aim is to identify and phenomenologically restore rotational symmetry broken by the Skyrme-Hartree-Fock solutions. In particular, it is shown that correlation energy due to symmetry restoration is absolutely crucial in order to reproduce energy splitting E(Imax) - E(Imax - 1) in [Formula: see text] configurations but is relatively less important for [Formula: see text] configurations.
TEST OF APPROXIMATION USED IN DESCRIPTION OF NON-AXIAL HEXADECAPOLE SHAPES OF HEAVIEST NUCLEI
Authors: SOBICZEWSKI A. , SHVEDOV L. , KOWAL M.
Published: February 2007

Approximation of description of non-axial hexadecapole deformations of heaviest nuclei, used for a long time in the past, is tested. A large, 5-dimensional deformation space is used for that. The analysis is done within a macro-micro approach. Two superheavy nuclei (262 Sg and 284114), for which non-axial hexadecapole deformations are important, are considered. It is shown that the approximation is not good. The reason for its inadequacy is given.
ROLE OF HIGHER-MULTIPOLARITY DEFORMATIONS IN THE POTENTIAL ENERGY OF HEAVIEST NUCLEI
Authors: KOWAL M. , SOBICZEWSKI A.
Published: February 2007

Potential energy of the superheavy nucleus 284114 is analyzed in a 6-dimensional deformation space. This space includes two quadrupole, three hexadecapole and one multipolarity-6 deformation parameter. The energy is minimized simultaneously in all 6 degrees of freedom. The analysis is done within a macroscopic-microscopic approach. As in the studies of other superheavy nuclei, the result is found to be very individual for a given nucleus. A more general feature is a small effect of one (γ4) of the hexadecapole deformation parameters on the energy of the nucleus.
MICROSCOPIC DETERMINATIONS OF FISSION BARRIERS (MEAN-FIELD AND BEYOND)
Authors: DOBROWOLSKI A. , GOUTTE H. , BERGER J.-F.
Published: February 2007

With a help of the selfconsistent Hartree-Fock-Bogoliubov (HFB) approach with the D1S effective Gogny interaction and the Generator Coordinate Method (GCM) we incorporate the transverse collective vibrations to the one-dimensional model of the fission-barrier penetrability based on the traditional WKB method. The average fission barrier corresponding to the least-energy path in the two-dimensional potential energy landscape as function of quadrupole and octupole degrees of freedom is modified by the influence of the transverse collective vibrations along the nuclear path to fission. The set of transverse vibrational states built in the fission valley corresponding to a successively increasing nuclear elongation produces the new energy barrier which is compared with the least-energy barrier. These collective states are given as the eigensolutions of the GCM purely vibrational Hamiltonian. In addition, the influence of the collective inertia on the fission properties is displayed, and it turns out to be the decisive condition for the possible transitions between different fission valleys.
SADDLE-POINT MASSES OF EVEN-EVEN ACTINIDE NUCLEI
Authors: BARTEL JOHANN , DOBROWOLSKI ARTUR , POMORSKI KRZYSZTOF
Published: February 2007

In the framework of the macroscopic-microscopic approach the Yukawa folding procedure is used together with the Lublin-Strasbourg Drop liquid-drop type energy to describe atomic nuclei in the actinide region. The nuclear deformation is described by a 4-dimensional shape parametrisation similar to the well-known Funny-Hills expression. It is demonstrated that left-right asymmetry and non-axiality are present at the first and second saddle and should be included in the theoretical description. The importance of a different deformation of the proton and the neutron distribution also appears in the present analysis.
PREDICTIONS OF NUCLEAR MASSES IN DIFFERENT MODELS
Authors: NERLO–POMORSKA BOŻENA , POMORSKI KRZYSZTOF , ZWIERZCHOWSKA MONIKA
Published: February 2007

The modern version of the liquid-drop model is compared to the macroscopic Thomas-Fermi (TF) energy and the macroscopic part of the binding energy evaluated within the Hartree-Fock-Bogoliubov theory with the Gogny force and the relativistic mean field theory. The limits of nuclear stability predicted by these models are discussed.
ROLE OF MASS ASYMMETRY IN FUSION OF SUPER-HEAVY NUCLEI
Authors: SIWEK-WILCZYŃSKA K. , SKWIRA-CHALOT I. , WILCZYŃSKI J.
Published: February 2007

By using well tested standard statistical model for calculating survival probabilities of super-heavy compound nuclei, Psurv, and reliably predicted capture cross sections σcap, "empirical" values of the fusion hindrance Pfus = σsyn/(σcap · Psurv) have been determined from the formation cross sections σsyn for production of super-heavy nuclei of 102 ≤ Z ≤ 113 measured at GSI Darmstadt and RIKEN. So determined fusion hindrance can be well reproduced with a simple model based on the Smoluchowski diffusion equation applied to describe thermal shape fluctuations of the fusing system. An applicability of this model for a wider class of fusing systems could be verified on data from an interesting experiment on the synthesis of isotopes of Hs (Z = 108) in the 136 Xe + 136 Xe reaction, scheduled to be carried out in Dubna this year. Synthesis cross sections for 269-271 Hs isotopes, strongly reduced by the fusion hindrance effect in this symmetric fusion reaction, are predicted.
DYNAMICS OF MASSIVE SYSTEMS AND SYNTHESIS OF SUPERHEAVY ELEMENTS
Authors: ABE YASUHISA , MARCHIX ANTHONY , SHEN CAIWAN , YILMAZ BULENT , KOSENKO GRIGORI , BOILLEY DAVID , GIRAUD BERTRAND G.
Published: February 2007

For the synthesis of superheavy elements, it is indispensable to divide the fusion process into two steps : Overcoming the Coulomb barrier and passing over the conditional saddle or the ridgeline. To facilitate the understanding of the mechanism which explains the fusion hindrance, we first employ an analytic model with an inverted parabola for the saddle. Then, results by realistic calculations are given for the cold fusion. Ambiguities of the model are also discussed for future investigations. Since the model is general, it is applied to incident channels with neutron-rich projectiles and/or targets. These are necessary for synthesis of nucleides in so-called superheavy island around Z =114 and N =184.
STRUCTURE OF BARRIER DISTRIBUTIONS: PROBING THE ROLE OF NEUTRON-TRANSFER CHANNELS
Authors: PIASECKI E. , ŚWIDERSKI Ł. , RUSEK K. , KISIELIŃSKI M. , JASTRZEBSKI J. , KORDYASZ A. , KOWALCZYK M. , MUTTERER M. , KROGULSKI T. , PIASECKI K. , RUSSOTTO P. , STEFANINI A. M. , ROWLEY N.
Published: February 2007

In view of its large deformation, which should give rise to strong barrier structures, the 20 Ne projectile has been used to study the influence of neutron-transfer channels on the distribution of barrier heights. A previous experiment with a combination of projectiles 20,22 Ne suggested that the role of α-particle transfer channels is small. By an appropriate choice of targets (90 Zr and 92 Zr ), having very similar intrinsic structures (excited states and deformation parameters) but giving rise to different Q-values for neutron transfers, we highlight the role of these channels.
QUANTUM FLUCTUATIONS AND STABILITY OF TETRAHEDRAL DEFORMATIONS IN ATOMIC NUCLEI
Authors: ZBERECKI K. , MAGIERSKI P. , HEENEN P.-H. , SCHUNCK N.
Published: February 2007

The possible existence of stable axial octupole and tetrahedral deformations is investigated in 80 Zr and 98 Zr . HFBCS calculations with parity projection have been performed for various parametrizations of the Skyrme energy functional. The correlation and excitation energies of negative parity states associated with shape fluctuations have been obtained using the generator coordinate method (GCM). The results indicate that in these nuclei both the axial octupole and tetrahedral deformations are of dynamic character and possess similar characteristics. Various Skyrme forces give consistent results as a function of these two octupole degrees of freedom both at the mean-field level as well as for configuration mixing calculations.
OPTIMIZED DESCRIPTION OF NUCLEAR SHAPES AND SYMMETRIES
Authors: GÓŹDŹ ANDRZEJ , DUDEK JERZY
Published: February 2007

We propose a group-theory-based method of analysis of the multipole type (αλμ) deformation spaces for the large scale calculations within nuclear mean-field applications. It allows to find ahead of time which sub-sets of the deformation space, although formally different, in fact represent the same information (the same nuclear shapes expressed by an alternative combination of the deformation parameters). The approach presented allows to save important amounts of the computing time in the large-scale mean-field calculations, both in constrained Hartree-Fock (where αλμ is replaced by the constraint equation [Formula: see text]), and in the Strutinsky type approaches.
AN EXACT MICROSCOPIC MULTIPHONON APPROACH TO NUCLEAR COLLECTIVE EXCITATIONS
Authors: ANDREOZZI F. , LO IUDICE N. , PORRINO A. , KNAPP F. , KVASIL J.
Published: February 2007

The method outlined here consists of constructing a set of equations of motion within a subspace spanned by states which are tensor products of n Tamm Dancoff phonons. Recursive relations allow to solve these equations iteratively, starting from the particle-hole vacuum, and, thereby, to generate a basis of microscopic multiphonon states. In such a basis, the Hamiltonian takes on a simple form and can be easily diagonalized. For illustrative purposes, we apply the method to 16 O .
THE ASSOCIATED Σ PRODUCTION AND THE NUCLEAR INTERACTION OF Σ HYPERONS
Authors: DABROWSKI J. , ROŻYNEK J.
Published: February 2007

The recently measured kaon spectrum from (π-, K+) reaction on 28 Si target in the region of Σ production is analyzed in impulse approximation for different strengths of the Σ single particle nuclear potential UΣ = VΣ + iWΣ. The comparison with the measured kaon spectrum leads to the conclusion that the potential VΣ inside the nuclear core is strongly repulsive. A comparison with other estimates of the strength of VΣ is presented.
GENERALIZING T-CONORMS TO FACE SATURATION IN MAMDANI FUZZY INFERENCE SYSTEMS
Authors: NERI MARIO ARRIGONI , CHERUBINI ALESSANDRA
Published: February 2007

Fuzzy aggregation is the way in which different contributions to the same fuzzy fact are merged together to obtain a possibility distribution representative of the acquired knowledge. The choice of the aggregation function is a fundamental step in the definition of inference framework. In most cases aggregation has some monotonicity property and this can lead to saturation problems in complex frameworks, particularly in stateful rational agents. In this paper, we propose an extension to the fuzzy aggregation to handle these cases and apply fuzzy reasoning to complex KBs. We especially focus on Mamdani inference framework, where aggregation is implemented by a triangular conorm.
A Perspective on Next-Generation Silicon Devices
Authors: Takuo Sugano Takuo Sugano
Published: February 2007

The minimum size of metal oxide semiconductor field-effect transistors assessed in terms of their circuit performance, the possibility of quantum-mechanical engineering of the electronic properties of silicon through the modification of the energy band with mechanical stress, Brillouin zone folding, and artificially built-in nanometer-scale potential as well as through the utilization of low dimensional electrons, and single electronics as a quantum limit of nano-power electronics are reviewed. Furthermore, effects of the statistical fluctuation of device edge definition in fabrication and dopant distribution on the minimum size of silicon devices are discussed and the importance of dopant location control is emphasized.
Optoelectronic Devices and Material Technologies for Photo-Electronic Integrated Systems
Authors: Izuo Hayashi Izuo Hayashi
Published: February 2007

The future direction of optoelectronic technologies is discussed while emphasizing what is needed to establish collaboration between photons and electrons in a single system. Drastic improvements, and even new functions, will be obtained with systems that combine the best features of both electronics and photonics. Optical interconnections in computers are just the first indication of “photo-electronic integrated systems” and the optical interconnection in microprocessors described in this article will constitute the basis of the Photo-electronic Integrated System. Technologies for integration of micro-optoelectronic devices with microelectronic integrated circuits will be the key for the Photo-Electronic Integrated System. A variety of “optical systems” should become feasible upon introduction of electronic circuits in many parts of such systems, where logical operations are required. Conversely, introduction of optical circuits into “electronic systems” will result in great revolution of system functions.
A Novel Contactless and Nondestructive Measurement Method of Surface Recombination Velocity on Silicon Surfaces by Photoluminescence
Authors: Saitoh Toshiya , Nishimoto Youichiro , Sawada Takayuki , Hasegawa Hideki
Published: February 2007

A novel photoluminescence (PL)-based measurement method for the surface recombination velocity, S, is presented. It consists of detailed measurement of the band-edge photoluminescence efficiency as a function of the excitation intensity, and its subsequent analysis by computer. The measurement principle and the computer analysis procedure are presented, as well as detailed discussion on the underlying recombination physics. As a demonstration, the new method is applied to various unpassivated and passivated Si wafers, giving the values of S under 1 sun condition of 3000 cm/s-50000 cm/s. It is also pointed out that the value of S is considerably reduced by concentrated sunlight. By this method, the value of S under device operation conditions as well as N
ss distribution can be determined in a contactless and nondestructive fashion.
Area-Selective Aluminum Patterning Using Atomic Hydrogen Resist
Authors: Tsubouchi Kazuo , Kazuya Masu Kazuya Masu , Keiichi Sasaki Keiichi Sasaki
Published: February 2007

We have proposed atomic-scale lithographic technology using atomic hydrogen resist. The key features of the atomic hydrogen resist process are (1) patterning of monolayer-thick terminated H on a Si surface by electron beam exposure and (2) selective growth of Al on remaining terminated H by low-pressure chemical vapor deposition using (CH3)2AlH and H2. In the electron-beam-exposed area, the terminated H on Si is removed and the Si surface is activated. Then the activated Si surface is oxidized in nanometer thickness in a clean-room air environment. The Al is selectively deposited on the remaining terminated-H region. A clear Al pattern has been successfully formed by the atomic hydrogen resist process.
The Initial Stages of the Thermal Oxidation of Si(001)2×1 Surface Studied by Scanning Tunneling Microscopy
Authors: Udagawa Masaharu , Sumita Masaaki Niwa
Published: February 2007

The initial stages of the thermal oxidation of Si(001)2×1 surface were studied by scanning tunneling microscopy. The O2 exposure at 600°C produced Si islands and initial oxides. The oxides appeared as “dark sites”, “sequence of dots”, and “dots with dark surroundings”. Among the oxides, most of the “dark sites” were removed by successive heating at 600°C, while the “sequence of dots” and the “dots with dark surroundings” remained. All the oxides were removed by successive heating at 800°C. The thermal oxidation of Si(001)2×1 surface is discussed in terms of these sites.
Scanning Force/Tunneling Microscopy as a Novel Technique for the Study of Nanometer-Scale Dielectric Breakdown of Silicon Oxide Layer
Authors: Fukano Yoshinobu , Sugawara Yasuhiro , Yamanishi Yoshiki , Oasa Takahiko , Seizo Morita Seizo Morita
Published: February 2007

Scanning force/tunneling microscopy (AFM/STM) was proposed as a novel technique to investigate local dielectric breakdown voltage for the silicon oxide layer. It was manifested that this novel technique could simultaneously measure surface topography and distribution of dielectric breakdown voltage with nanometer-scale resolution. We confirmed that the dielectric breakdown voltage measured with the AFM/STM increased monotonously with the increase in oxide thickness. In addition to the above results, we observed that the oxide layer with visible defect had a lower dielectric breakdown voltage.
Preoxide-Controlled Oxidation for Very Thin Oxide Films
Authors: Makihara Koji , Teramoto Akinobu , Nakamura Kou , Kwon Myoung Youn , morita mizuho , Ohmi Tadahiro
Published: February 2007

Very thin oxide films with high insulating performance and high reliability are formed by controlling preoxide growth with an ultraclean oxidation method during heating of the wafer to thermal oxidation temperature. The current level through the preoxide-controlled ultraclean oxide is lower than that through the oxide incorporating a thicker preoxide, and the preoxide-controlled ultraclean oxide has high reliability with respect to hot electron injection.
Investigation on Defects in Czochralski Silicon with High-Sensitive Laser/Microwave Photoconductance Technique
Authors: Katayama Ken-ichi , Agarwal Aditya , Zbigniew J. Radzimski Zbigniew J. Radzimski , Fumio Shimura Fumio Shimura
Published: February 2007

High sensitivity of a noncontact laser/microwave photoconductance (LM-PC) technique for defects in heat-treated Czochralski (CZ) silicon crystals was confirmed in comparison with other diagnostic techniques such as Fourier transform infrared spectroscopy (FT-IR) and deep-level transient spectroscopy (DLTS). The energy levels of recombination centers (E
T) in samples subjected to a three-step intrinsic gettering (IG) thermal process were obtained with LM-PC although no significant oxygen reduction in the samples was observed with FT-IR. The defect density detection limits of LM-PC and DLTS for samples after the three-step IG process are estimated to be ≤1×107 cm-3 and ∼1×1010 cm-3, respectively. Moreover, the dependence of effective minority-carrier recombination lifetime on defect density was found to be influenced greatly by carbon concentration through the enhancement effect on oxygen precipitation.
Proximity Gettering of Heavy Metals by High-Energy Ion Implantation
Authors: Kuroi Takashi , Kawasaki Youji , Komori Shigeki , Fukumoto Kouji , Inuishi Masahide , Tsukamoto Katsuhiro , Shinyashiki Hiroshi , Shingyoji Takayuki
Published: February 2007

We studied the proximity gettering of heavy metals by secondary defects, using high-energy, high-dose ion implantation by means of intentional contamination of samples with copper and iron. It was demonstrated that the secondary defects induced by high-energy boron or silicon implantation can act as gettering sites of heavy metals and reduce the junction leakage current. Proximity gettering by silicon implantation is found to be more effective than that by boron implantation. Moreover it is found to be difficult to getter iron atoms in comparison with copper atoms.
Lateral Solid Phase Epitaxy of Amorphous Si Films under Ultrahigh Pressure
Authors: Ishiwara Hiroshi , Wakabayashi Hitoshi , Miyazaki Keizo , Sawaoka Kazuichi Fukao
Published: February 2007

The effect of hydrostatic pressure on the lateral solid phase epitaxy (L-SPE) of amorphous Si (a-Si) films has been investigated. It has been found from the annealing experiment under ultrahigh pressure up to 2 GPa (20 kbar) that both the L-SPE growth rate and the nucleation rate of polycrystalline grains are increased with increase in pressure, when uncoated a-Si films are used. It has also been found that the nucleation rate is decreased and a greater L-SPE length can be achieved when a-Si films are coated with SiO2 films prior to L-SPE.
Controlling the Solid-Phase Nucleation of Amorphous Si by Means of a Substrate Step Structure and Local Phosphorus Doping
Authors: Moniwa Masahiro , Kusukawa Kikuo , Makoto Ohkura Makoto Ohkura , Eiji Takeda Eiji Takeda
Published: February 2007

We propose a solid-phase crystallization technique that controls the location of crystal grain formation on SiO2 substrates. This enables the formation of electronic devices in a single grain. To determine the condition of the technique, the nucleation characteristics of amorphous Si with P- and B-doping are investigated. Also, the characteristics with and without step structures on the substrate surface are reported and discussed. The various nucleation behaviors can be interpreted in terms of the critical size of the nucleus and of the rate of crystal growth.
Amorphization Processes and Structural Relaxation in Ion Implanted Si
Authors: Motooka Teruaki , Kobayashi Fumihiko , Hiroyama Yuichi , Tokuyama Takashi , Wei Long , Tanigawa Shoichiro
Published: February 2007

Amorphization processes in Si+, P+, Ge+, and As+ ion implanted Si as well as structural relaxation of amorphous Si (a-Si) during low-temperature (200-450°C) annealing have been investigated using Raman spectroscopy and depth-resolved positron annihilation spectroscopy. Based on the analysis of bond angle deviation Δθ derived from the a-Si Raman TO peak width and line-shape parameter, the S prameter, obtained by the positron annihilation measurements, we have proposed that (1) amorphization is controlled by ion-beam-induced divacancy concentration; and (2) there exist microvoids in the a-Si layers and during isothermal annealing, both of Δθ and the S parameter do not decrease monotonically but show an increase after the initial decrease due to dissociation of the microvoids.
Processing Uniformity Improvement by Magnetic Field Distribution Control in Electron Cyclotron Resonance Plasma Chamber
Authors: Nishimura Hiroshi , Mikiho Kiuchi Mikiho Kiuchi , Seitaro Matsuo Seitaro Matsuo
Published: February 2007

A novel electron cyclotron resonance (ECR) processing apparatus has been developed to improve processing uniformity by adjusting the plasma refractive index determined by the magnetic field distribution in the ECR plasma chamber. With SiO2 deposition, an excellent uniformity of ±1% for six-inch wafers and ±2% for eight-inch wafers has been obtained. The conditions required for specimen processing, such as perpendicular ion incidence, can be selected independently of uniformity because uniformity is controlled only at the plasma generation region. This method can also be applied to other ECR techniques, such as ECR ion-stream etching.
Molecular Scale E-Beam Resist Development Simulation for Pattern Fluctuation Analysis
Authors: Scheckler Edward W. , Shoji Shukuri Shoji Shukuri , Eiji Takeda Eiji Takeda
Published: February 2007

To better understand nanometer scale pattern fluctuation in lithography, we present a new model for electron-beam exposed (poly)methyl-methacrylate resist development, which considers the molecular scale material structure. The polymer chains in the resist are represented as spheres with a radius proportional to the square root of the chain length. Monte Carlo electron scattering simulation in the resist gives the local absorbed energy, which in turn sets the local molecular weight distribution. The development model uses the Poisson probability for removing each surface polymer chain in a small time step. The Poisson removal rate is derived using a mass equivalence with macroscopic etch rate models. The simulations predict the macroscopic shape of patterned resisi features as well as microscopic surface roughness and nanometer scale line-edge variation. Observations with atomic force microscopy confirm the simulation results, including 10 nm edge variation and rough developed surfaces at exposures doses near the transition from low etch rate to high etch rate.
Fabrication and Bonding Strength of Bonded Silicon-Quartz Wafers
Authors: Abe Takao , Sunagawa Ken , Uchiyama Atsuo , Yoshizawa Katsuo , Nakazato Yasuyuki
Published: February 2007

A multiply repeated process of thinning of silicon layer and annealing of the bonded silicon-quartz interface is proposed for tight bonding between a silicon wafer and a quartz wafer which have different thermal expansion coefficients. Silicon layers on quartz with a thickness of 2 µm±0.5 µm were debonded by a high temperature annealing over 650 C, whereas in the case of thinner silicon layers with a thickness under 0.5 µm tensile strengths over 80 MPa (800 kgf/cm2) were obtained in the temperature range from 700 C to 1100 C.
Quarter-Micron Interconnection Technologies for 256-Mbit Dynamic Random Access Memories
Authors: Kikkawa Takamaro , Kikuta Kuniko , Tsunenari Kinji , Ohto Koichi , Aoki Hidemitsu , Drynan John M. , Naoki Kasai Naoki Kasai , Takemitsu Kunio Takemitsu Kunio
Published: February 2007

Quarter-micron interconnection technologies for 256-Mbit dynamic random access memories (DRAMs) are reviewed. Since the density of memory capacity is increased, both decreasing feature size and increasing sophistication of cell structures are required, resulting in three-dimensional structures. This trend leads us to the introduction of new interconnection technologies which have good coverage, low resistivity and high reliability, because the three-dimensional device structure requires high aspect-ratio contact hole plugs and narrow-pitch metal lines on different surface levels. The state of the art and current problems are discussed for quarter-micron contact-hole filling and quarter-micron interconnection lines.
Structural and Electrical Properties of Ta2O5 Grown by the Plasma-Enhanced Liquid Source CVD Using Penta Ethoxy Tantalum Source
Authors: Murawala Prakash A. , Sawai Mikio , Tatsuta Toshiaki , Tsuji Osamu , Fujita Shizuo , Fujita Shigeo
Published: February 2007

We report on structural and electrical properties of tantalum penta oxide (Ta2O5) material with a high dielectric constant grown from a penta ethoxy tantalum [Ta(OC2H5)5] liquid source by the plasma-enhanced liquid source chemical vapor deposition (PE-LS-CVD) technique. We have investigated several basic plasma deposition conditions. Structural properties investigated by θ-2θ X-ray measurements showed the amorphous nature of the films, and Auger electron spectrosopy (AES) and secondary ion mass spectroscopy (SIMS) indicated growth of Ta2O5 films having proper stoichiometry (Ta/O=0.4). Optical transmission spectroscopy showed that the band gap (E
g) of Ta2O5 is 5.28 eV. Electrical measurements performed on Au/Ta2O5/n, p-Si metal oxide semiconductor (MOS) structure exhibited very well defined capacitance-voltage (C-V) characteristics with flat band voltage as low as -0.1 eV, low leakage current, high breakdown voltage and high dielectric constant (25-38). As a hitherto unreported step in Ta2O5 processing we also performed rapid thermal (RTA) annealing at 700°C and 900°C for 5 min which resulted in much improved electrical properties. All results suggest growth of high-quality Ta2O5 films from a carbon-based Ta liquid source, due to an effect of plasma-enhanced deposition process.
Electron Emission into Vacuum from Lead-Zirconate-Titanate Ferroelectric Ceramics Induced by Polarization Reversal
Authors: Asano Jun-ichi , Masanori Okuyama Masanori Okuyama , Yoshihiro Hamakawa Yoshihiro Hamakawa
Published: February 2007

Electron emission from the surface of the ferroelectric PZT plate induced by polarization reversal has been observed in vacuum by applying a very high field. This electron emission has been obtained even in low vacuum of less than 10-1 Torr. It is possible to increase or decrease the amount of the emitted charge by applying a voltage to the additional grid. A maximum emission current of about 9 A/cm2 has been obtained at the grid voltage of 135 V. This electron emission can be applied to an electron emitter in vacuum electronic devices such as microtriodes and flat panel displays.
The Impact of Titanium Silicide on the Contact Resistance for Shallow Junction Formed by Out-Diffusion of Arsenic from Polysilicon
Authors: Yang Wen Luh , Lei Tan Fu , Cheng Tung Huang Cheng Tung Huang , Chung Len Lee Chung Len Lee
Published: February 2007

A novel technology of Ti-polycided shallow junctions formed by out-diffusion of As+ from polysilicon was proposed and investigated. Junction depth as shallow as 0.1 µm and leakage current density as small as 0.4 nA/cm2 can be easily obtained by this process. Contact resistance measurements show that the presence of a deliberately grown interfacial oxide leads to a significant increase in the contact resistance and small values of the specific contact resistivity (4∼7×10-7 Ω-cm2) can be obtained if Ti thicknesses are larger than half of polysilicon thicknesses. This is due to the polysilicon layer had been consumed completely and the interfacial oxide would be broken under the silicidation process. This implies that the contact resistance is mainly determined by the polysilicon/mono-silicon interface property and it is necessary to eliminate the interfacial oxide for a good contact system.
Characterization of GeSi/Si Heteroepitaxial Layered Structures by Convergent Beam Electron Diffraction
Authors: Shao G. , Yang Z. , Weiss B. L.
Published: February 2007

Both normal and off-axis convergent beam electron diffraction patterns (CBEDPs) have been applied to the characterization of GeSi epitaxial layer on Si substrate. The results show that CBED is an accurate method for the determination of the change in lattice parameters across the GeSi/Si interface. A CBED shadow imaging (CBSIM) technique has been introduced to detect, map and measure small crystal strains with an accuracy approaching that attainable using X-ray diffraction, but with far better spatial resolution. This allows the strain variation across the interface to be accurately determined. With the combination of normal CBEDPs, off-axis CBEDPs and CBSIMs, CBED has good feasibility for the strain characterization of layered structures.
Optical Properties of Porous Silicon and Small Silicon Clusters: Search for the Origin of Visible Photoluminescence of Porous Silicon
Authors: Kanemitsu Yoshihiko , Suzuki Katsunori , Uto Hiroshi , Masumoto Yasuaki , Higuchi Koichi , Kyushin Soichiro , Matsumoto Hideyuki
Published: February 2007

We have studied and compared the optical properties of both porous Si and the chemically synthesized small Si clusters. In planar and cubic Si clusters, broad photoluminescence (PL) spectra were observed at the visible region. The characteristics of broad visible PL and PL excitation spectra of porous Si were similar to those of small Si clusters.
Hydrogen Termination and Optical Properties of Porous Silicon: Photochemical Etching Effect
Authors: Kanemitsu Yoshihiko , Matsumoto Takahiro , Futagi Toshiro , Mimura Hidenori
Published: February 2007

We have studied photoluminescence (PL) from porous Si depending on the hydrogen termination on Si nanocrystallites. The hydrogen concentration in the samples was controlled by photochemical etching after the electrochemical anodization. The PL spectra, the PL excitation spectra and the picosecond PL decay rate were sensitive to the photochemical etching process. Spectroscopic analysis suggests that the photocarriers are generated in the inside of the Si crystallites and the radiative recombination occurs at the near-surface region of the Si crystallites.
Quantum-Size Effect from Photoluminescence of Low-Temperature-Oxidized Porous Si
Authors: Nakajima Anri , Nara Yasuo , Sugita Yoshihiro , Toru Itakura Toru Itakura , Noriaki Nakayama Noriaki Nakayama
Published: February 2007

We examined the change in photoluminescence spectra of porous Si after several repetitions of chemical oxidation and reduction. We observed the shift to higher frequencies of the photoluminescence peak as the repetition times increased. We also observed the shift to higher frequencies of the photoluminescence when the porous Si was oxidized using synchrotron radiation (SR) followed by chemical reduction. Raman measurements were used to estimate the microcrystalline size of the porous Si. These Raman results indicate that the photoluminescence peak shifts to higher frequencies are closely related to quantum-size effect.
Low-Temperature Metal-Oxide-Semiconductor Field-Effect Transistor Operation by Temperature Scaling Theory
Authors: Yokoyama Michio , Hidaka Tetsuya , Yi You-Wen , Kazuya Masu Kazuya Masu , Kazuo Tsubouchi Kazuo Tsubouchi
Published: February 2007

We have demonstrated 77 K operation of deep-submicron metal-oxide-semiconductor field-effect transistors (MOSFET's) based on the temperature scaling concept. The measured subthreshold swing and the threshold voltage for the 77 K devices designed using the temperature scaling theory are both found to be scaled down to 1/4(≃77 K/300 K) as compared with those for 300 K devices. The threshold voltage shifts and the subthreshold swing shifts due to short-channel effects are also found to be scaled down by a factor of 1/4. Furthermore, it is demonstrated that a 0.18 µm 77 K MOSFET designed using the temperature-dimension combination scaling theory has the scaled characteristics of subthreshold swing and threshold voltage with no degradation due to short-channel effects. The temperature-dimension combination scaling theory provides a design guideline for 77 K deep-submicron MOSFET's.
Hot-Hole-Induced Interface State Generation in p-Channel MOSFETs with Thin Gate Oxide
Authors: Khosru Quazi Deen Mohd , Yasuda Naoki , Kenji Taniguchi Kenji Taniguchi , Chihiro Hamaguchi Chihiro Hamaguchi
Published: February 2007

Interface state generation in p-channel metal oxide semiconductor field effect transistors (MOSFETs) due to uniform hot-hole injection into the thin gate oxide and postinjection behavior of the generated interface states are investigated. The absence of a significant oxide electric field dependence of interface state generation supports the existence of a single generation mechanism. The experimental results suggest a mechanism associated with the interaction of neutral hydrogen for interface state generation. The number of generated interface states is linearly proportional to the number of trapped holes regardless of oxide thickness, which indicates active involvement of hole trapping in the formation of interface states. In contrast to the reports describing time-delayed formation of interface states during relaxation, we observed spontaneous postinjection annihilation of the generated interface states which was also linearly related to the number of detrapped holes. The experimental results suggest the presence of a reversible atomic structure at the Si/SiO2 interface with respect to trapping and subsequent detrapping of holes. The annealing efficiency of the generated interface states depends on the postinjection oxide field polarity.
Low-Voltage High-Gain 0.2 µm N-Channel Metal Oxide Semiconductor Field Effect Transistors by Channel Counter Doping with Arsenic
Authors: Nagai Ryo , Kazunori Umeda Kazunori Umeda , Eiji Takeda Eiji Takeda
Published: February 2007

A counter-doped n-channel metal oxide semiconductor field effect transistor (NMOSFET) whose threshold voltage is controlled by channel counter doping with arsenic is proposed in order to realize a sub-half-micron device with low threshold voltage. It is found that threshold voltage adjustment is possible without losing good short-channel characteristics. The counter-doped NMOSEET is applicable to 0.2 µm devices with a threshold voltage of 0.2 V. Electron mobility of this transistor is found to be 30% higher than that of conventional devices. Smaller gate current also reduces hot carrier-induced threshold voltage shift.
Fabrication of a Si1-xGex Channel Metal-Oxide-Semiconductor Field-Effect Transistor (MOSFET) Containing High Ge Fraction Layer by Low-Pressure Chemical Vapor Deposition
Authors: Goto Kinya , Murota Junichi , Maeda Takahiro , SchÜtz Reiner , Aizawa Kiyohito , Kircher Roland , Kuniyoshi Yokoo Kuniyoshi Yokoo , Shoichi Ono Shoichi Ono
Published: February 2007

A method for growing the high-quality strained epitaxial heterostructure of Si/Si1-x
Ge
x
/Si by low-pressure chemical vapor deposition (CVD) and the fabrication of Si1-x
Ge
x
-channel metal-oxide-semiconductor field-effect transistors (MOSFET's) with a high Ge fraction layer have been investigated. It is found that lowering of the deposition temperature of the Si1-x
Ge
x
and Si capping layers is necessary with increasing Ge fraction in order to prevent island growth of the layers. With the use of the optimized fabrication process, Si/Si1-x
Ge
x
/Si heterostructures with flat surfaces and interfaces were realized, and a high-performance Si0.5Ge0.5-channel MOSFET has been achieved with a large mobility enhancement of about 70% at 300 K and over 150% at 77 K compared with that of a MOSFET without a Si1-x
Ge
x
channel.