bluuebunny/crossref_metadata_2025 huggingface dataset:
Evaluation of the influence of GaN and AlN as pseudosubstrates on the crystalline quality of InN layers
Authors: Lozano J. G. , Morales F. M. , García R. , Lebedev V. , Cimalla V. , Ambacher O. , González D.
Published: March 2007

A study of the impact of different pseudosubstrates as AlN, GaN or AlN/GaN on the crystalline quality of InN layers by transmission electron microscopy is reported. The temperature of the substrate was found to play an important role: for higher temperatures, low quality InN layers are obtained, poorly supported on the buffers and consequently almost free of dislocations; whereas for lower temperatures, higher qualities, with smooth surfaces and continuous interfaces are observed. In these cases, high resolution electron microscopy showed that the high lattice mismatch existing between the pseudosubstrate and the InN epilayer is mainly accommodated by a network of geometrical misfit dislocations at the heterointerface. Additionally, low densities of threading dislocations, also decaying exponentially with the increasing thickness were observed. The introduction of a GaN buffer layer on top of AlN promotes the reduction in one order of magnitude the density of threading dislocations in the epilayer, partially due to the reduction of dislocations propagating from the pseudosubstrate. However, other relevant factors as the domains coalescence or the generation of secondary misfit dislocation must be taken into account. (© 2007 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)
Controlling of hydrogen and oxygen atoms in CdTe by means of far‐infrared spectroscopy using synchrotron radiation
Authors: Cebulski J. , Sheregii E. M. , Polit J. , Marcelli A. , Robouch B. , Castelli Gudi M. , Piccinini M. , Kisiel A.
Published: March 2007

The work presents far‐and middle‐infrared reflectivity spectra collected with synchrotron radiation on specially prepared CdTe‐monocrystals in the temperature region of 30‐300 K. The investigated samples were of three different types characterized by the three different levels of hydrogenation – strong, middle and the low ones. In order to interpret the experimental data, the imaginary part of the dielectric function was evaluated by means of Kramers‐Kronig transformation. To determine quantitatively the influence of hydrogen atoms on the phonon and vibrational spectra of hydrogenated CdTe crystals we used the special statistical model proposed in this paper. This model takes into account the tetrahedron as the basic structural unit and distinguishes the contribution of the hydrogen bearing tetrahedra from the contribution of the hydrogen free ones to the crystal phonon spectra. (© 2007 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)
On the energy band structure of the GaInP/GaAs heterojunction bipolar transistor
Authors: Mimila‐Arroyo J.
Published: March 2007

The GaInP/GaAs heterojunction bipolar transistor energy band gap close to the junction is determined through the behavior of its collector and base currents and current gain as a function of the temperature. It results that the emitter‐base junction is a gradual one with the emitter bandgap, at the place where the carrier injection takes place, being wider than that of the GaAs by just ∼13 meV. It is also shown that for T > 200 K the diffusion contribution to the base current is due to injected holes into the emitter, imposing a strong limitation on the device current gain. Besides, such bandgap difference between the emitter and the base makes the device current gain to decrease as the temperature increases. In view of these results technological modifications are discussed to improve the transistor performance. (© 2007 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)
Evolution of the cathodoluminescence spectral shape and intensity of GaN quantum dots under 10 keV electron beam irradiation
Authors: Sieber B.
Published: March 2007

In‐situ degradation experiments are performed by means of plan‐view spectral cathodoluminescence experiments on GaN quantum dots. The influence of the electron beam current density J in the range of 1 to 5.5 A/cm2 is specially studied. Whatever is the J value, the CL peak red‐shifts between 11 and 6 meV and its intensity decreases. Morevoer, a modification of the CL shape is observed which depends on the J value. The results are interpreted in terms of interdiffusion and strain relaxation. (© 2007 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)
Influence of laser shock waves on As implanted HgCdTe
Authors: Yakovyna V. , Berchenko N. , Kuzma M. , Vlasov A.
Published: March 2007

The principal purpose of our research is to show that low‐temperature treatment of materials can be successfully used instead of annealing. Laser shock waves (LSW) were chosen as an alternative to form p‐n junctions in HgCdTe after arsenic ions were implanted. Electrical characteristics of As implanted HgCdTe bulk crystals were studied to determine the effect of LSW generated by nanosecond laser irradiation pulses. The samples were of n ‐type conductivity immediately after the implantation. Then LSW processing was performed under increasingly growing laser beam power density and shock wave pressure. The experiment demonstrated that a threshold shock wave pressure should be reached to ensure the p ‐to‐n conductivity conversion in the surface layer of samples. On the whole the results provide evidence that LSW combined with ion implantation can be used to form p ‐n junctions in HgCdTe. (© 2007 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)
Microstructural study of ferromagnetic Fe‐implanted 6H‐SiC
Authors: Declémy A. , Drouet M. , Eymery J. P. , Dupeyrat C. , Ott F. , Viret M.
Published: March 2007

Association of multi‐energy ion implantation with magnetic and structural analysis methods, particularly X‐ray diffraction reciprocal space maps (XRD RSM), is shown to be able to give new original information about the microstructure of Fe‐implanted SiC, a good candidate for diluted magnetic semiconductors (DMS) applications. (© 2007 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)
Fabrication of GaN/ZnO bilayers on sapphire by pulsed laser ablation‐deposition
Authors: Muto Hachizo , Nakamura T. , Wang R. , Kusumori T. , Morita K.
Published: March 2007

GaN/ZnO and ZnO/GaN bilayers have been fabricated on Al2O3‐c by pulsed laser ablation‐deposition, since such heteroepitaxial multilayers may be helpful for developing devices and lowering the device cost. Their crystallographic qualities are studied by RHEED and XRD as functions of the deposition conditions; temperature (Th), ambient pressure of oxygen and ammonia, and pulse frequency by fixing the fluence of the Nd:YAG fourth harmonic laser (1.0 J/cm2/pulse). Both epitaxial bilayers with (0001) orientation could be fabricated at optimal conditions. GaN layer can grow on ZnO at lower Th (900‐1000 °C) than on Al2O3 (950‐1100 °C) and gives rise to a better epitaxial bilayer than ZnO/GaN bilayer. (© 2007 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)
Optical effect of diamond‐like carbon film coating of long‐period optical fiber gratings
Authors: Smietana M. , Szmidt J. , Korwin‐Pawlowski M. L. , Bock W. J.
Published: March 2007

The paper presents diamond‐like carbon (DLC) film as a coating for long‐period grating (LPG) optical fiber structure. The spectral response of a DLC‐coated LPG structure is strictly dependent on Radio Frequency Plasma Chemical Vapour Deposition (RF PCVD) process parameters. The paper discusses the influence of DLC deposition time and self‐bias voltage to shift of the LPG resonance peak and explores the possibility of using the structure as a refractometric sensor. (© 2007 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)
Low temperature liquid phase epitaxy with Sn‐based solvent
Authors: Abdo F. , Fave A. , Lemiti M. , Pisch A. , Bernard C.
Published: March 2007

Silicon thin film is an attractive option for solar cell applications because of their low cost potential. Liquid Phase Epitaxy (LPE) is an interesting technique because it allows growth of single crystal Si film even at low temperature (<800 °C). Main difficulties are the low solubility of silicon in usual solvent and the presence of a native silicon oxide. In this study, we developed a technique using two successive different Sn‐based melts, one to remove native oxide, second one to grow the active layer under argon or hydrogen flow. This technique leads to smooth and homogeneous Si layer presenting a p/p+ structure. Solar cells were fabricated using standard technology. The photo‐generated current density is in the 16‐19 mA/cm2range after of Si3N4coating deposition. To improve active layer thickness and to enlarge the Si solubility, we proposed to use metallic alloys as Si‐Sn‐Cu‐Al. (© 2007 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)
Diffused p‐n GaAs junctions with nano/microrelief active interface
Authors: Borkovskaya O. Yu. , Dmitruk N. L. , Horváth Zs. J. , Mamontova I. B. , Sukach A. V.
Published: March 2007

The technology of a submicron p+‐GaAs layer formation on nano/microtextured n ‐GaAs substrate by a low‐temperature (550 °C) diffusion of Zn is elaborated aimed at ensuring both improved optical and good electronic properties of a textured p‐n junction for the photodiode and solar cells (SC) application. The optical, photoelectric and electrical characteristics of the obtained photodiode structures were studied as a function of the surface microrelief morphology of dendritic or quasigrating type, preliminary processing and the process diffusion duration. Different diffusion conditions were shown to be optimal to obtain maximal improving SC efficiency for structure with different microrelief morphology. (© 2007 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)
Impact of growth conditions on the spatial non‐uniformities of composition in InGaP epitaxial layers
Authors: Gregušová D. , Kučera M. , Hasenöhrl S. , Vávra I. , Štrichovanec P. , Martaus J. , Novák J.
Published: March 2007

Composition uniformity of InGaP thick epitaxial layers grown on InGaP/GaP graded buffer structure was studied by stepwise wet chemical etching and low temperature photoluminescence. We compared properties of two epitaxial layers grown by MOCVD technique on different graded buffers. Influence of strain and growth condition on the properties of both epitaxial layer was studied and related to the buffer design. (© 2007 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)
Barium titanate thin films plasma etch rate as a function of the applied RF power and Ar/CF4 mixture gas mixing ratio
Authors: Werbowy A. , Firek P. , Chojnowski J. , Olszyna A. , Szmidt J. , Kwietniewski N.
Published: March 2007

BaTiO3 (BT) nanocrystalline thin films were plasma etched in the course of several experiments which varied in RF power as well as CF4/(CF4 + Ar) gas‐mixing ratio. The maximum etch rate of approximately 30 nm/min was observed for the maximum power (300 W) and pure Ar plasma atmosphere, which indicates that the process is controlled by the physical mechanism of Ar ion bombardment, while the increasing content of chemically active plasma component (CF4) in the gas mixture slows down barium titanate etch rate. (© 2007 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)
Photoluminescence, cathodo‐luminescence and micro‐Raman spectroscopy of as‐grown stacking faults in 4H‐SiC
Authors: Juillaguet S. , Albrecht M. , Lewandowska R. , Camassel J. , Chassagne T.
Published: March 2007

We report the results of combined investigations of as‐grown stacking faults found in a‐thick, undoped, 4H‐SiC epitaxial layer grown by CVD. We have use successively, low temperature photoluminescence (LTPL), room temperature cathodo‐luminescence (RT‐CL), micro‐Raman (µ‐R) and low temperature cathodo‐luminescence (LT‐CL) spectroscopy. From LTPL we find that the defects behave like thin, 2‐dimensional, quantum wells made of 4 bilayers of the 3C polytype embedded in the 4H‐SiC matrix. From RT‐CL, we show that the faults have a triangular shape with a large extension in the basal plane and a maximum emission wavelength centered at about 480 nm at 300 K. This makes them intermediate between the usual (semi‐infinite) QWs and the pure (1‐dimensional) quantum dots. To confirm the 3C character of the SFs, we used µR. Finally, using LT‐CL we scanned across one single (isolated) triangular defect and found that the maximum signal wavelength shifts, depending on the exciting spot position over the defect. To the best of our knowledge, this constitutes the first experimental evidence of a screening of the built‐in electric field when increasing the carrier concentration in the well. (© 2007 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)
Electronic properties of c‐BN thick film layers obtained on silicon and ceramics substrates
Authors: Firek P. , Jakubowska M. , Werbowy A. , Zwierkowska E. , Szmidt J.
Published: March 2007

A novel thick film has been produced using paste based on single crystal cubic boron nitride powders. The major paste component are particles of cubic boron nitride of different grain shape and size obtained by different methods. Another component is inorganic glass based on bismuth oxide with high wetting characteristics for binding together the particles of c‐BN and ensure good adhesion of the layer to the substrate. Structures were crated with c‐BN films acting as an insulator which enabled electrical characterization by means of current‐voltage measurements. Observed variation in specimen characteristics resulted primarily from different content of the secondary phase (glass) as well as different types of used c‐BN powders. The results of the experimental work has enabled a preliminary analysis of the room temperature conduction mechanisms in structures with c‐BN based thick film layers. (© 2007 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)
Electrical properties of short period InAs/GaSb superlattice
Authors: Christol P. , Konczewicz L. , Cuminal Y. , Aït‐Kaci H. , Rodriguez J. B. , Joullié A.
Published: March 2007

Electrical properties in the temperature range between 80 K and 300 K of type‐II short period InAs/GaSb superlattice (SL) photodiode are reported. Resistivity and Hall measurements have been carried out on a 300 periods unintentionally doped SL grown on semi‐insulating GaAs substrate while capacitance‐voltage and current‐voltage measurements have been performed on the same SL structure elaborated on n‐type GaSb substrate. Whatever the electrical investigations, the behaviour of the InAs/GaSb SL versus temperature exhibited a reproducible change in type of conductivity. The SL is n‐type at high temperatures range with n(300 K) = 6 × 1016 cm–3 whereas it is p‐type at low temperatures with p(100 K) = 2 × 1016 cm–3. This versatile change in type of conductivity is attributed to the presence of inserted InSb layer at the InAs‐GaSb interface. (© 2007 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)
Structural and optical characterization of pure ZnO films synthesised by thermal annealing on GaSb single crystals
Authors: Martínez O. , Plaza J. L. , Mass J. , Capote B. , Diéguez E. , Jiménez J.
Published: March 2007

ZnO films have been grown on GaSb substrates by metallic Zn thermal evaporation and oxidation by annealing in atmospheric conditions. The evaporation times ranged from 20 up to 80 seconds. The oxidation process was carried out at temperatures from 410 °C to 600 °C. The morphology of the surface as well as the luminescence properties have been studied as a function of the growth conditions. The samples were characterized by means of SEM, micro‐Photoluminescence and Cathodoluminescence spectroscopies. The samples present good luminescence emission; the spectra show an intense UV emission with a low intense band in the visible. SbOx phases seem to be formed for some specific growth conditions. (© 2007 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)
Surface passivation of GaInAsSb photodiodes with thioacetamide
Authors: Salesse A. , Joullié A. , Calas P. , Nieto J. , Chevrier F. , Cuminal Y. , Ferblantier G. , Christol P.
Published: March 2007

AlGaAsSb/GaInAsSb heterojunction mesa photodiodes having 2.2 µm cutoff wavelength, grown by MBE on (p) GaSb substrates, have been passivated using thioacetamide CH4CSNH2 and ammonium sulphide (NH4)2S. Superior characteristics were obtained from devices processed with thioacetamide in acid medium (pH = 2.4). At room temperature the surface leakage currents were suppressed, and the photodiodes showed R0A product as high as 16 Ωcm2 and detectivity D* (2 µm, 0 V) ∼ 1010 cm Hz1/2 W–1. A model explaining sulfuration mechanisms with thioacetamide and (NH4)2S is proposed. (© 2007 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)
Characterization of corrugated MQW heterostructure prepared on patterned (001) GaAs substrate by MOVPE
Authors: Štrichovanec P. , Kúdela R. , Vávra I. , Kováč J. , Šoltýs J. , Novák J.
Published: March 2007

We have studied Si‐doped n‐type quantum well infrared photodetectors (QWIPs) using an Al0.28Ga0.72As/GaAs MQW heterostructure grown on patterned (001) GaAs substrate. Two patterning techniques were applied to reveal stripe patterns. Wet etching with a H3PO4‐based solution using [1‐10]‐oriented stripe mask was used to reveal ridges confined by {111}A quasi‐facets. We also prepared various mesa ridges with sidewall angle varied from 30 to 45 degree, using an additional sacrificial heterostructure based on a GaAs/AlAs system. The patterned substrates were MOVPE‐overgrown to prepare nonplanar Si‐doped AlGaAs/GaAs n‐QWIP. Properties of non‐planar multiple quantum well (MQW) heterostructures were investigated by cros‐sectional transmition electron microscopy (TEM) and low temperature photoluminescence (PL). QWIP with non‐planar MQW heterostructure exhibited wide absorption spectra peaked at ∼8‐9 μm wavelength without additional gratings or corrugations. A relatively large asymmetry was observed in dark I‐V characteristics at 77 K. (© 2007 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)
Sulphur passivation of GaSb, InGaAsSb and AlGaAsSb surfaces
Authors: Papis E. , Piotrowska A. , Kamińska E. , Gołaszewska K. , Kruszka R. , Piotrowski T. T. , Rzodkiewicz W. , Szade J. , Winiarski A. , Wawro A.
Published: March 2007

The effects of electrochemical treatment in either 21%(NH4)2S‐H2O or 16%Na2S‐C3H7OH solutions on the surface properties of GaSb, In0.23Ga77As0.18Sb0.82 and Al0.34Ga0.66As0.025Sb0.975 have been investigated by complementary use of Variable Angle Spectroscopic Ellipsometry (VASE) and X‐ray Photoelectron Spectroscopy (XPS). We have shown that electrochemical sulphuration enables to produce 94–350 nm thick insulating overcoats with good surface morphology. The main components of the passivating layers are Ga2S3 and Sb2S5when formed on GaSb, while additional components of In2S3, admixture of Al2O3 and appearance of Al‐As bond were observed on InGaAsSb and AlGaAsSb, respectively. The main feature distinguishing the effect of electrochemical treatment in Na2S–C3H7OH when comparing to those in (NH4)2S‐H2O is that passivating layers contain additional components of Na2SO3 and/or Na2SO4. (© 2007 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)
Doping effect on the optical properties of ZnO nanostructures
Authors: Stoehr M. , Juillaguet S. , Kyaw T. M. , Wen J. G.
Published: March 2007

High quality undoped and Ga2O3 or In2O3 doped ZnO nanostructures are grown by chemical vapor transport and condensation. The doping effect on the optical properties is investigated by photoluminescence. At room temperature, photoluminescence on Ga2O3 doped ZnO nanostructures reveals an enhancement of the ultraviolet near band edge emission at 390 nm, while the intensity of the deep level emission at 530 nm weakens. At 5 K, an intense neutral‐donor‐bound exciton (D0X) line dominates the undoped and doped ZnO photoluminescence spectra. The presence of well resolved two‐electron satellite lines allow to determine the type of donors. At 5 K, the results indicate that ZnO nanostructures grown with 10% of Ga2O3 display an excellent optical quality, proved by an intense D0X line, a high intensity ratio between the D0X line and the deep level emission as well as the presence of numerous phonon replicas of the main lines. (© 2007 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)
Combined (200) DF‐TEM and X‐ray diffraction investigations of interfaces in MOVPE grown InGaP/GaAs heterojunctions
Authors: Frigeri C. , Pelosi C. , Germini F. , Attolini G. , Bosi M.
Published: March 2007

The presence of interlayers at the inverted GaAs‐on‐InGaP interfaces in MOVPE grown InxGa1–xP/GaAs heterojunctions has been evidenced by (200) dark field (DF) transmission electron microscopy and high resolution X‐ray diffraction. A relatively large negative strain is associated with the interlayers. Analysis of the kinematical DF contrast has allowed to establish which kind of InxGa1–xAs1–yPy compound the interlayer can be made of and the possible ranges for the compositions x and y. The localization of the interlayer at the bottom of the GaAs layer and inside it would suggest that its formation can be due to the incorporation into GaAs of P atoms remained in the reactor after PH3 was switched off and In carry‐over. (© 2007 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)
Investigation of CdS/InP heterojunction prepared by chemical bath deposition
Authors: Rakovics V. , Horváth Zs. J. , Horváth Zs. E. , Bársony I. , Frigeri C. , Besagni T.
Published: March 2007

CdS thin films have been deposited on InP and glass substrates using the chemical bath deposition technique. Baths containing CdSO4, thiourea, and NH3 were used. The temperature of the deposition process was 65 °C and the duration of deposition varied between 20 and 160 minutes. The properties of the CdS/InP heterojuntion were investigated by TEM, EDS and X‐ray diffraction. TEM pictures, EDS and X‐ray rocking curves indicate the formation of a β‐In2S3 transition layer at the InP‐CdS interface, wich may reduce the lattice mismatch between InP and CdS. (© 2007 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)
Drain current DLTS of normally‐off AlGaN/GaN HEMTs
Authors: Mizutani T. , Kawano A. , Kishimoto S. , Maeazawa K.
Published: March 2007

It has been demonstrated that the drain current DLTS is effective in characterizing the transient behavior of the normally‐off AlGaN/GaN HEMTs in which the conventional capacitance DLTS cannot be applied because the carriers in the channel are depleted in the normal bias condition. In the measurement, two bulk/interface‐related negative peaks and one surface‐state‐related positive peak were observed. Drain voltage dependence was also discussed. (© 2007 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)
Polycrystalline GaN layer recrystallization by metal‐induced method during the baking process
Authors: Jagoda A. , Stańczyk B. , Dobrzański L. , Diduszko R.
Published: March 2007

Radio frequency reactive sputtering was used to produce gallium nitride films on thermally oxidized silicon substrates at room temperature. Metallic Ga (purity 6N) was used as the target, N2 and Ar were utilized as sputtering gases. Amorphous GaN was obtained by metal‐induced crystallization with a Ni assistance. The nickel particles were scattered onto the surface by rf sputtering and their density was 2 × 1014 atoms/cm2 or 4 × 1014 atoms/cm2, which corresponds to 0.02 nm and 0.04 nm thick layer. These values are less than a monolayer thickness, so they are not continuous. Samples were annealed at 700 °C for 3 h and at 900 °C for 5 min in a RTP furnace. The 2.5 μm GaN layers grown on the Ni‐coated SiO2 surface recrystalized during annealing forming crystals of (002) orientation. The catalytic regrowth mechanism of GaN is discussed on the basis of experimental results. (© 2007 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)
Comparison of the p‐to‐n conversion caused by ion beam milling or anodic oxidation/annealing in Hg1–xCdxTe and Pb1–xSnxTe
Authors: Berchenko N. , Izhnin I. , Yudenkov V. , Pociask M.
Published: March 2007

The comparative analysis of how an n‐layer is formed in differently doped Hg1–xCdxTe and Pb1–xSnxTe is made for two techniques: ion beam milling and anodic oxidation followed by annealing. The initial and step‐by‐step chemical etching characterization of samples was made through measuring the Hall coefficient. It was found that ion beam milling forms an n‐layer in all Hg1–xCdxTe and Pb1–xSnxTe samples. In contrast, anodic oxidation followed by annealing causes the formation of an n‐layer in Hg‐vacancy doped Hg1–xCdxTe only. A common mechanism of the n‐layer formation in these materials is the enrichment of a surface with a metal (Hg or Pb) that results in metal in‐diffusing by interstitials. Thermodynamic calculations are made to predict the conditions necessary to form the n‐layer after oxidation. (© 2007 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)
Recent improvements of SiC micro‐resonators
Authors: Godignon P. , Placidi M.
Published: March 2007

The cover picture of this issue of physica status solidi (c) has been taken from the article [1].
Epitaxial TiC/SiC multilayers
Authors: Eklund P. , Högberg H. , Hultman L.
Published: March 2007

Epitaxial TiC/SiC multilayers were grown by magnetron sputtering at a substrate temperature of 550 °C, where SiC is normally amorphous. The epitaxial TiC template induced growth of cubic SiC up to a thickness of ∼2 nm. Thicker SiC layers result in a direct transition to growth of the metastable amorphous SiC followed by renucleation of nanocrystalline TiC layers.

magnified image

X‐ray diffraction pole‐figure plot of an epitaxial TiC/SiC multilayer.

(© 2007 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)
Gel‐Phase 13C NMR Spectroscopy of Selected Solid Phase Systems
Authors: Braunshier Christian , Hametner Christian
Published: March 2007

Studies on the applicability of conventional liquid‐state NMR spectroscopy for the analysis of solid‐phase organic reactions directly on the resin will be described. For a systematic investigation small and easily assignable molecules substituted with a chain of varying length were synthesized. In a subsequent step these so‐called sensor molecules were attached to commercially available resins. After swelling experiments, 13C NMR spectra of the solid phase systems in gel form were recorded using Composite Pulse Decoupling (CPD) and Attached Proton Test (APT) techniques. The quality of the resulting spectra was analyzed using the half‐height linewidths of the signals as the most important criterion. Based on these data, the parameters to obtain high quality spectra were determined.
Novel characterization of the folding of proteins
Authors: Liu Liwei , Wang Tianming
Published: March 2007

In this paper, we consider a characterization of the folding of 3D model proteins. In this characterization, we describe the different kinds of 3‐step path conformation, then construct an augmented Hasse matrix which reflects some properties of the protein folding. This method can characterize the folding degree of 3D model proteins and evaluate the similarity/diversity of these five model proteins. © 2007 Wiley Periodicals, Inc. Int J Quantum Chem, 2007
Reaction‐path dynamics and theoretical rate constants for the reaction CH4 + O3 → HOOO + CH3
Authors: Yang Jing , Shu Li Qian , Zhang Shaowen
Published: March 2007

We present a direct ab initio dynamics study of thermal rate constants of the hydrogen abstraction reaction of CH4 + O3 → HOOO +CH3. The geometries of all the stationary points are optimized at MPW1K/6‐31+G(d,p), MPWB1K/6‐31+G(d,p), and BHandHLYP/6‐31+G(d,p) levels of theory. The energies are refined at a multi‐high‐level method. The extended Arrhenius expression fitted from the CVT/SCT and μVT/Eckart rate constants of ozonolysis of methane in the temperature range 200–2500 K are kCVT/SCT(T) = 5.96 × 10−29T4.49e(−17321.3/T) and kμVT/Eckart(T) = 7.92 × 10−29T4.46e(−17301.7/T), respectively. © 2007 Wiley Periodicals, Inc. Int J Quantum Chem, 2007
Efficient schema matching algorithm based on pre‐checking
Authors: Kubo Kengo , Yamada Keizo , Hirata Kouichi , Harao Masateru
Published: March 2007

Matching, which is an operation that applies a substitution to one representation to make it identical to another representation, is indispensable for knowledge processing. In this paper, we formulate generalized knowledge, which is referred to as a schema, as a second‐order logical formula and discuss schema matching, which is a matching of that schema and a first‐order logical formula. First, we formulate the schema matching algorithm based on the imitation, projection, and unification operations of the second‐order matching algorithm. Generally, there is an exponential number of matching substitutions (or simply matchers) for schema matching. However, from a knowledge processing viewpoint, obtaining the optimum matcher is more important than obtaining all matchers. Therefore, in this paper, we introduce pre‐checking for checking the applicability of projection in advance to efficiently extract matchers that preserve the syntax information of the schema and design a complete schema matching algorithm. Finally, we implement this algorithm and use experimental results to show that efficiency is improved. © 2007 Wiley Periodicals, Inc. Syst Comp Jpn, 38(4): 84–92, 2007; Published online in Wiley InterScience (www.interscience.wiley.com). DOI 10.1002/scj.10273
Proposal of a hierarchical heuristic algorithm for node assignment in bidirectional Manhattan street networks
Authors: Yonezu Masataka , Funabiki Nobuo , Kitani Tomoya , Yokohira Tokumi , Nakanishi Toru , Higashino Teruo
Published: March 2007

In wavelength division multiplexing (WDM) technology, high‐speed large‐capacity communication is realized by transmitting multiple optical signals with different wavelengths in parallel on an optical fiber. In WDM technology, the logical topology of the network can generally be modified by changing the wavelength assignment to the transmitters and receivers. Thus it is important to develop an algorithm that derives the wavelength assignment that maximizes the transmission efficiency of the network. This paper considers a bidirectional Manhattan street network which has a regular topology, and proposes a hierarchical two‐stage heuristic algorithm. In the first stage, the initial solution is derived by hierarchical region division and node assignment to the regions. In the second stage, the solution is improved by simulated annealing (SA). The proposed algorithm is evaluated by simulations of random instances and instances for which optimal solutions are already known. The effectiveness of the proposed algorithm is demonstrated through comparisons to the existing one. © 2007 Wiley Periodicals, Inc. Syst Comp Jpn, 38(4): 74–83, 2007; Published online in Wiley InterScience (www.interscience.wiley.com). DOI 10.1002/scj.10534
A proposal of improved lip contour extraction method using deformable template matching and its application to dental treatment
Authors: Yokogawa Yujin , Funabiki Nobuo , Higashino Teruo , Oda Masashi , Mori Yoshihide
Published: March 2007

Studies of facial parts have been conducted in recent years in various fields of medical science and psychology, including studies of the lip contour and location. In fact, in the treatment of cleft lip patients in oral surgery, it is desirable to extract the precise lip contour and to identify its location on the face in order to plan the plastic surgery procedure and to follow up the site after surgery. Aiming at applications to dental treatment, in this study we attempt to extend the lip contour extraction procedure based on the deformable template to the case of a template with left– right asymmetry. An algorithm is also proposed for adjusting the hue and value thresholds in order to improve extraction accuracy and reduce the burden on the user. The proposal is evaluated using sample images of normal subjects and cleft lip patients. It is shown that the shape and location of the lip can be extracted precisely and automatically by the proposed method. In connection with application to dental clinics, we present an example of a quantitative evaluation of the lip shape by using the parameters extracted by the proposed method. © 2007 Wiley Periodicals, Inc. Syst Comp Jpn, 38(5): 80– 89, 2007; Published online in Wiley InterScience (www.interscience.wiley.com). DOI 10.1002/scj.10668
The architecture and performance of topic‐driven P2P resource discovery system
Authors: Nakatsuji Makoto , Kawahara Minoru , Kawano Hiroyuki
Published: March 2007

Many network applications over peer‐to‐peer networks, such as Gnutella, have been developed drastically. However, by using distributed systems with simple search functions, it is difficult to discover suitable information resources and to guarantee practical response time. Furthermore, we are faced with several problems of search performance which are caused by the bandwidth of networks and the instability of peer‐to‐peer network topology. In order to realize good network performance and advanced functions with content‐based search, we introduce the index methods with the characteristic of each file. We propose the topic‐oriented search mechanism, which selects optimal search hosts, based on heuristic functions with several parameters in each host. We evaluated the performance of our proposed methods on a simulation of a prototype system and confirmed that our system achieves a suitable search performance with capability of responding to changes in network topology. © 2007 Wiley Periodicals, Inc. Syst Comp Jpn, 38(5): 69– 79, 2007; Published online in Wiley InterScience (www.interscience.wiley.com). DOI 10.1002/scj.20190
Performance evaluation of L2 over MPLS
Authors: Katsuno Satoshi , Yamazaki Katsuyuki , Asami Tohru , Esaki Hiroshi
Published: March 2007

This is a study of Layer 2 virtual private wire service over MPLS (L2 over MPLS). On existing network technologies, ATM has strict requirements for network performance. The performance of an installation of L2 over MPLS on an actual router as an ATM network was evaluated for ATM virtual private wire service over MPLS with consideration of the effect on network performance of the encapsulation of MPLS packets in ATM cells. With the results of theoretical study and performance testing, the network performance of L2 over MPLS was considered from perspectives of its specifications, installation, and operation, and the possibility of its use as an ATM virtual private wire service is demonstrated. © 2007 Wiley Periodicals, Inc. Syst Comp Jpn, 38(5): 59– 68, 2007; Published online in Wiley InterScience (www.interscience.wiley.com). DOI 10.1002/scj.20279
Learning a dynamic policy by using policy gradient: application to biped walking
Authors: Matsubara Takamitsu , Morimoto Jun , Nakanishi Jun , Sato Masa‐Aki , Doya Kenji
Published: March 2007

This paper discusses a method in which periodic motion, such as biped walking, is acquired by the framework of reinforced learning. For an object with multiple degrees of freedom, it is in general difficult to acquire the policy by reinforced learning. There must be a framework of learning which is matched to the motion task under consideration. From this viewpoint, this paper proposes “dynamic policy,” that is, a policy with internal state and dynamics. Its learning procedure is then considered. When periodic motion such as biped walking is to be acquired by learning, dynamical entrainment to the control object can be utilized if the policy has internal dynamics. Furthermore, by providing a policy with internal state, the controller is made robust to time delay and noise in the sensor inputs. The use of the policy gradient is discussed as a method of learning the policy without explicitly considering its internal state. As an example, dynamic policy is applied to a three‐link biped walking robot model. The dynamic policy in this example is realized by a feedback controller based on a neural oscillator and sensor inputs. By using the policy gradient, appropriate rules for sensor feedback to the neural oscillator are learned by trial and error. It is shown by simulation that a dynamic policy realizing biped walking is acquired. The method is further applied to a five‐link biped walking robot in order to investigate the possibility of extension to a system with multiple degrees of freedom. © 2007 Wiley Periodicals, Inc. Syst Comp Jpn, 38(4): 25–38, 2007; Published online in Wiley InterScience (www.interscience.wiley.com). DOI 10.1002/scj.20441
Construction of a metadata space for a specific field of knowledge from an index of a document
Authors: Nakanishi Takafumi , Kishimoto Sadaya , Sakurai Tetsuya , Kitagawa Takashi
Published: March 2007

In this paper, we propose a method for generating a metadata space of associations between words from an index of a book dealing with a specific field of interest. In order to implement a search mechanism using a mathematical model of meaning that deals with a specific field of interest, it is necessary to generate a search space called a metadata space dealing with the field of interest. In the past, the metadata space has been generated by using a terminology dictionary and a highly specialized knowledge base. Also, it is difficult to generate the metadata space if there is no terminology dictionary that deals with the field of interest. The proposed method does not require a terminology dictionary, and it allows the generation of the metadata space without a highly specialized knowledge base. Further, by applying this metadata space generation method to a mathematical model of meaning, a search mechanism based on the associations between words in the search target data, such as documents and media data, in the specific field of interest can be implemented. In this paper, taking examples from the IT field, the effectiveness of the method is verified by comparing the use of a metadata space generated from a terminology dictionary and the use of a metadata space generated from an index to search graphic media data. © 2007 Wiley Periodicals, Inc. Syst Comp Jpn, 38(5): 30– 42, 2007; Published online in Wiley InterScience (www.interscience.wiley.com). DOI 10.1002/scj.20524
Omnidirectional 3D reconstruction using rotating camera with mirrors
Authors: Jiang Wei , Sugimoto Shigeki , Okutomi Masatoshi
Published: March 2007

Technology for capturing omnidirectional (360°) three‐dimensional information in a real environment has applications in many areas, such as security with surveillance cameras, or the implementation of a complex sense of reality. In this paper, the authors propose an imaging device constructed of one camera and two flat mirrors and a technique for omnidirectional three‐dimensional reconstruction using spatiotemporal volume. The proposed technique uses an imaging device with mirrors, whereby a large baseline length can be implemented without the use of multiple cameras and measurement precision can be improved beyond that of conventional methods using a single camera. Also, when capturing depth, a multibaseline algorithm using SSSD (Sum of SSD) is used to extract the trajectory for a spatiotemporal volume corresponding to the left and right mirror fields. Thereby, incorrect correspondences due to image noise or repeated pattern are reduced. Moreover, the influence of occlusion can also be reduced by separately evaluating the trajectory extraction results for the left and right mirror fields and selecting the good side. Experiments were performed using synthetic images and real images, an improvement in estimation precision with the imaging device was demonstrated, as well as the effectiveness of the proposed algorithm. © 2007 Wiley Periodicals, Inc. Syst Comp Jpn, 38(4): 12–24, 2007; Published online in Wiley InterScience (www.interscience.wiley.com). DOI 10.1002/scj.20606
Low‐delay multiview video coding for free‐viewpoint video communication
Authors: Kimata Hideaki , Kitahara Masaki , Kamikura Kazuto , Yashima Yoshiyuki , Fujii Toshiaki , Tanimoto Masayuki
Published: March 2007

We have proposed free‐viewpoint video communications, in which a viewer can change the viewpoint and viewing angle when receiving and watching video content. A free‐viewpoint video consists of several views, whose viewpoints are different. To freely and instantaneously change the viewpoint and view angle, a random access capability to decode the requested view with little delay is necessary. In this paper, a multiview video coding method to achieve high coding efficiency with low‐delay random access functionality is proposed. In the proposed method, the GOP is the basic unit of a view, and selective reference picture memory management is applied to multiple GOPs to improve coding efficiency. In addition, the coding method of disparity vectors, which utilizes the camera arrangement, is proposed. © 2007 Wiley Periodicals, Inc. Syst Comp Jpn, 38(5): 14– 29, 2007; Published online in Wiley InterScience (www.interscience.wiley.com). DOI 10.1002/scj.20683
Development of an XML‐document compaction method to improve data‐processing performance
Authors: Yoshida Shigeru , Nakashima Satoshi , Odagiri Junichi , Itoh Shuichi
Published: March 2007

XML (Extensible Markup Language) is the global standardized form for representing digital data. It is flexible and extensible, but on the other hand uses vast amounts of main memory for data processing, thus representing a burden. In order to resolve this problem when processing data in large XML documents, in this paper the authors propose the “CSV compaction for XML” method to improve data processing performance by using a format conversion for an XML document with a record structure. In this method, redundant elements are packed in CSV (Comma Separated Values) format from the perspective of accessing the XML document prior to data processing. The results of evaluating this method confirmed that memory usage and deployment time were improved in proportion to the percentage of elements that could be packed and eliminated using the CSV format. This method is a reversible conversion for an XML document. Since the authors created software to execute the method as XSL (Extensible Stylesheet Language) Transformation, it can be executed using various programming languages. In this method, specifications that designate elements to be packed in CSV format in a record are needed, and creating them is troublesome. Thus, the authors created a support tool to create the specifications simply using a GUI (Graphical User Interface). As a result of these developments, complex documents with a hierarchical structure and documents with a large number of elements can be readily handled in this method. © 2007 Wiley Periodicals, Inc. Syst Comp Jpn, 38(5): 1– 13, 2007; Published online in Wiley InterScience (www.interscience.wiley.com). DOI 10.1002/scj.20736
Study on Physicochemical Characteristics of Waxy and High‐amylose Wheat Starches in Comparison with Normal Wheat Starch
Authors: Hung Pham Van , Maeda Tomoko , Morita Naofumi
Published: March 2007

Waxy and high‐amylose wheats are genetically modified cultivars produced firstly in Japan. The physicochemical properties of waxy and high‐amylose wheat starches were investigated and compared to those of normal bread‐wheat starch. The waxy wheat starch (˜ 1% of amylose) showed higher gelatinization temperature, transition enthalpy and crystallinity of granules than the normal and high‐amylose wheat starches. The paste of waxy wheat starch had higher peak viscosity and swelling power, lower pasting temperature and final viscosity, which are favorable for producing Japanese white‐salted noodles (Udon) of high‐quality. In contrast, the high‐amylose wheat starch had higher amylose content (37.5%), blue value and wavelength of maximal iodine absorption but lower gelatinization temperature and crystallinity than the normal wheat starch. The paste of high‐amylose wheat starch had lower peak viscosity, breakdown and final viscosity than that of the normal wheat starch. These properties of the high‐amylose wheat starch contributed to improve textural properties of noodles which were similar to durum wheat noodles.
Software reliability — what is it?
Authors: Dyer M.
Published: March 2007

Software has become a household necessity in today's world but little has been done to measure its reliability for the consumer. Since software failure has a different basis than hardware failure, existing reliability theory cannot be applied directly: a new software unique theory needs to be defined. Current software practice relies on software quality measures to describe software reliability but recent work has identified both theory and practice for appropriate software reliability analysis. This paper discusses: the need for software reliability analysis in order to more accurately describe system reliability, the shortcomings of current practice, and both the direction of new work in, and the future roles for, software reliability analysis.
An exercise in weakest preconditions
Authors: Whitty Robin
Published: March 2007

Weakest preconditions are used to formulate the requirements for a 2‐state memory cell and it is proved that the flip‐flop device meets these requirements. This is an exercise in the use of the weakest preconditions which is more realistic than the usual examples of non‐looping arithmetic algorithms.
Herstellung von Präzisionsschichten mittels Ionenstrahlsputtern
Authors: Gawlitza Peter , Braun Stefan , Leson Andreas , Lipfert Sebastian , Nestler Matthias
Published: March 2007

Die Ionenstrahlsputterbeschichtung zeichnet sich gegenüber alternativen Vakuum‐Beschichtungstechniken wie Verdampfung oder Magnetronsputtern durch höhere kinetische Energien der schichtbildenden Teilchen aus. Damit lassen sich dichte, glatte und defektfreie Schichten im Allgemeinen sehr unkompliziert herstellen.

Neueste Ionenquellenentwicklungen hin zu mehr Prozessstabilität und ‐reproduzierbarkeit, aber auch zu größeren Geometrien machen den Einsatz der Technik für die Abscheidung von Nanometer‐Multischichtsystemen höchster Präzisionsanforderung attraktiv. Die gezielte und weitgehend voneinander unabhängige Einstellbarkeit von Ionenenergien, Sputter‐ und Reaktivgaspartialdrücken und Beschichtungsraten lässt maßgeschneidertes Schichtwachstum verschiedenster Materialien zu.

Die Ionenstrahlsputter‐Beschichtungsanlage “IonSys 1600” wurde gemeinsam vom Fraunhofer IWS Dresden und der Fa. Roth & Rau AG (Hohenstein‐Ernstthal) speziell für großflächige Präzisions‐Multischichten entwickelt und ergänzt seit diesem Jahr die Beschichtungstechnik des IWS. Substrate bis 200 mm (rund) bzw. 500 mm (rechteckig) können beschichtet werden, wobei komplexe Schichtstapel aus bis zu sechs verschiedenen Materialien aufgebaut werden können. Durch ein spezielles Blenden‐ und Substratbewegungssystem können 1‐ und 2‐dimensionale laterale Schichtdickengradienten mit Solldickenabweichungen < 0,1 % über der gesamten Substratfläche aufgebracht werden.

Anhand von Beispielen aus verschiedenen Anwendungsgebieten von Multischichten wird gezeigt, wie das Ionenstrahlsputtern mit seinen speziellen Eigenschaften für Materialsysteme mit schwierigem Wachstumsverhalten oder für Beschichtungen mit hohen Anforderungen hinsichtlich Reinheit, chemischer Zusammensetzung oder Struktur vorteilhaft eingesetzt werden kann.
Kohlenstoff‐Nanoröhren – Phönix aus der Asche
Authors: Vohrer U. , Zschoerper N.
Published: March 2007

Kohlenstoff‐Nanoröhren (Carbon Nanotubes; CNT) gelten als das Material des 21. Jahrhunderts. Obwohl bereits 1952 TEM‐Aufnahmen in einer russischen Publikation abgebildet waren, wird die Entdeckung der Nanoröhren durch S. Iijima, in der Asche eines Bogenentladungsexperimentes zur Herstellung von Fullerenen, üblicherweise auf das Jahr 1991 datiert. Aufgrund ihrer außergewöhnlichen Eigenschaften wurden bereits kurz nach ihrer Entdeckung und der Verbesserung der Herstellungsverfahren Anwendungen und Produkte postuliert, die nahezu jede Branche revolutionieren sollten. Tatsächlich sind inzwischen einige Produkte am Markt. Dennoch sind für eine branchenübergreifende Verwendung noch viel offene Fragen zu klären. Während die Herstellung, insbesondere der sogenannten mehrwandigen Kohlenstoff Nanoröhren (multi wall carbon nanotubes; MWNT) inzwischen in industriellem Maßstab durchgeführt wird, gibt es noch u. a. aufgrund der inerten, hydrophoben Eigenschaften, Schwierigkeiten in der Verarbeitung. Hier ist eine chemische Funktionalisierung, z. B. mittels Niederdruckplasmen, notwendig, um die Löslichkeit und Dispergierfähigkeit zu verbessern. Außerdem wird viel Zeit und Geld verwendet für eine frühzeitige Risikoabschätzung und toxikologische Bewertung begleitend zur Produktentwicklung.