bluuebunny/crossref_metadata_2025 huggingface dataset:
Preparation and properties of molecular‐weight‐controlled polyimides derived from 1,4‐bis(4′‐amino‐2′‐trifluoromethylphenoxy)benzene and 4,4′‐oxydiphthalic anhydride
Authors: Wang K. , Yang S. Y. , Fan L. , Zhan M. Sh. , Liu J. G.
Published: February 2006

A series of molecular‐weight‐controlled fluorinated aromatic polyimides were synthesized through the polycondensation of a fluorinated aromatic diamine, 1,4‐bis(4′‐amino‐2′‐trifluoromethylphenoxy)benzene, with 4,4′‐oxydiphthalic anhydride in the presence of phthalic anhydride as the molecular‐weight‐controlling and end‐capping agent. Experimental results demonstrated that the resulting polyimides could melt at temperatures of 250–300 °C to give high flowing molten fluids, which were suitable for melt molding to give strong and flexible polyimide sheets. Moreover, the aromatic polyimides also showed good solubility both in polar aprotic solvents and in common solvents. Polyimide solutions with solid concentrations higher than 25 wt % could be prepared with relatively low viscosity and were stable in storage at the ambient temperature. High‐quality polyimide films could be prepared via the casting of the polyimide solutions onto glass plates, followed by baking at a relatively low temperature. The molten behaviors and organosolubility of the molecular‐weight‐controlled aromatic polyimides depended significantly on the polymer molecular weights. Both the melt‐molded polyimide sheets and the solution‐cast polymer films exhibited outstanding combined mechanical and thermal properties. © 2006 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 44: 1997–2006, 2006
Comparative studies on miscibility and phase behavior of linear and star poly(2‐methyl‐2‐oxazoline) blends with poly(vinylidene fluoride)
Authors: Shen Jia , Zheng Sixun
Published: February 2006

The comparative studies on the miscibility and phase behavior between the blends of linear and star‐shaped poly(2‐methyl‐2‐oxazoline) with poly(vinylidene fluoride) (PVDF) were carried out in this work. The linear poly(2‐methyl‐2‐oxazoline) was synthesized by the ring opening polymerization of 2‐methyl‐2‐oxazoline in the presence of methylp‐toluenesulfonate (MeOTs) whereas the star‐shaped poly(2‐methyl‐2‐oxazoline) was synthesized with octa(3‐iodopropyl) polyhedral oligomeric silsesquioxane [(IC3H6)8Si8O12, OipPOSS] as an octafunctional initiator. The polymers with different topological structures were characterized by means of Fourier transform infrared spectroscopy and nuclear magnetic resonance spectroscopy. It is found that the star‐shaped poly(2‐methyl‐2‐oxazoline) was miscible with poly(vinylidene fluoride) (PVDF), which was evidenced by single glass‐transition temperature behavior and the equilibrium melting‐point depression. Nonetheless, the blends of linear poly(2‐methyl‐2‐oxazoline) with PVDF were phase‐separated. The difference in miscibility was ascribed to the topological effect of PMOx macromolecules on the miscibility. © 2006 Wiley Periodicals, Inc. J Polym Sci Part B: Polym Phys 44: 942–952, 2006
Modeling the amorphous phase of comb‐like polymers
Authors: Curcó David , Alemán Carlos
Published: February 2006

In this work, we apply a methodology recently developed by us to perform atomistic simulations of the amorphous phase of poly(α‐octadecyl β‐aspartate) and poly‐ (octadecyl acrylate). The simulation method, which is denoted SuSi/CB, combines the strength of an algorithm specially designed to generate atomistic models of dense amorphous polymers and the Configurational Bias Monte Carlo procedure. Modeling results reveal that poly(octadecyl acrylate) presents a tendency to adopt backbone helical conformations, while no trace of helicity was detected in the amorphous phase poly(α‐octadecyl β‐aspartate). Regarding the side chain organization, the paraffinic pool formed by the octadecyl side chains is slightly greater for the poly(acrylate) than for the poly(β‐aspartate). According to these features, it can be concluded that the small chemical differences between the two investigated polymers are enough to provide some distinctive structural features. © 2006 Wiley Periodicals, Inc. J Polym Sci Part B: Polym Phys 44: 953–966, 2006
Computer Simulations for Processing Plasmas
Authors: Bogaerts Annemie , De Bleecker Kathleen , Georgieva Violeta , Kolev Ivan , Madani Myriam , Neyts Erik
Published: February 2006

Summary: In this paper, some of our modeling efforts for processing plasmas are presented. We make use of fluid models or particle‐in‐cell–Monte Carlo (PIC‐MC) simulations for the plasma behavior, depending on the application. Fluid models are most suitable to describe the detailed plasma chemistry, like the formation and growth of nanoparticles in so‐called dusty plasmas, and for dielectric barrier discharges (DBDs) at atmospheric pressure. PIC‐MC simulations are the best choice to describe magnetron discharges, operating at low pressure, and for dealing with the plasma dynamics in single‐ and dual‐frequency rf discharges. Finally, we also apply molecular dynamics (MD) simulations for plasma‐surface interaction, more specifically for the plasma deposition of diamond‐like carbon (DLC) films.

Calculated potential distribution and electron density profile in the magnetron discharge.

image

Calculated potential distribution and electron density profile in the magnetron discharge.
Detection of Biological Molecules from Hard Biological Tissue Using Ion‐Beam‐Induced Desorption and Femtosecond Laser Ablation
Authors: Daskalova Albena , Husinsky Wolfgang
Published: February 2006

Summary: In the last 10–15 years laser ablation became very popular for the analysis of solid samples. The study of laser‐matter interaction processes on different time scales – nano, pico, femto, and their application in different fields developed a thorough knowledge of the fundamental laws involved in this process. The intention in the current research was to determine the general features of different ablation processes (ns, fs) and ion beam desorption process. The aim was to perform a complete set of measurements of different target materials by means of mass spectrometry studies. More specifically, the mass spectra of ablated and sputtered particles from organic matter were studied. Time of flight mass spectrometer was used for detection. An investigation of the mechanism of laser ablation of biological tissue is a complicated problem due to the complexity of the examined organic material. In our experiments the main aim was to obtain optimal signal detection without the onset of considerable fragmentation. Comparison will be made between the mass spectra from biological samples obtained with laser ablation, and those obtained under bombardment with 9 keV‐accelerated Xe+ ions. As a general tendency in nanosecond ablation and in SIMS experiments the detection of higher mass molecular species is negligible in correspondence to femtosecond laser ablation mass spectra. This can be due to the process of heating that develops under ion bombardment. This work demonstrates the sensitivity of the TOF technique and the potential of using this method for exploring the dynamics of the laser ablation and ion beam desorption processes.

An example of 20 µm holes drilled into vascular transplant‐grafts by 30 fs pulses.

image

An example of 20 µm holes drilled into vascular transplant‐grafts by 30 fs pulses.
Cross Sections and Rate Constants for Charge Transfer into Excited States
Authors: Temelkov Krassimir A. , Vuchkov Nikolay K. , Sabotinov Nikola V.
Published: February 2006

Summary: Cross sections and rate constants for charge transfer into excited states in thermal energy collisions are calculated for a gas discharge in He/Cu, Ne/Cu, He/Ag, Ne/Ag, He/Al, Ne/Al, He/Au, He/Hg, He/Cd, and He/Zn mixtures. To our knowledge, the polarizability of the above‐mentioned metal atoms, which determines the ion‐atom interaction and, therefore, the cross section, is calculated for the first time. A cross section for the Ne+Cu impact couple is experimentally obtained.

Schematic diagram of the experimental setup.

image

Schematic diagram of the experimental setup.
Application of Pseudobinary Alloys (Al2O3)x(TiO2)1 − x as High‐k Dielectrics on Silicon
Authors: Vitanov Petko , Harizanova Antoaneta , Ivanova Tatyana , Alexieva Zvetanka , Ivanova Katya , Agostinelli Guido
Published: February 2006

Summary: An interesting opportunity arises when two or more oxides are used as alloys in an attempt to combine the desirable properties of several materials. These systems are predominantly non‐stoichiometric, and in the case of two oxides, they are called pseudobinary alloys. Varying the ratio of the two oxides, thin films with certain preset characteristics can be obtained—refractive index, energy band gap, dielectric constants etc. Our investigations were focussed on spin‐coated (Al2O3)x(TiO2)1 − x films. The electrical properties of (Al2O3)x(TiO2)1 − x were studied forming MIS structures. For accurate determinations of the dielectric constant various measurement methods were used: classical C‐V, impedance spectroscopy and CV map B instrument. The effect of adding Al2O3 to TiO2 is to produce an amorphous dielectric film, which is thermodynamically stable on Si.

C‐V curves at 1 MHz of MIS structures with PBA (Al2O3)x(TiO2)1 − x and ALD Al2O3 film.

image

C‐V curves at 1 MHz of MIS structures with PBA (Al2O3)x(TiO2)1 − x and ALD Al2O3 film.
Investigation of p‐Type MOS Structure Irradiated with 23 MeV Electrons
Authors: Kaschieva Sonia , Halova Elena , Vlaikova Emilia , Alexandrova Sashka , Valcheva Evgenia , Dmitriev Sergey
Published: February 2006

Summary: p‐type silicon MOS structures were irradiated with 23 MeV electrons in vacuum for different durations. Capacitance‐voltage (C/V), current‐voltage (I/V) and conductance‐voltage (G/V) methods were used to investigate the changes in the electrical characteristic of the MOS structures after electron irradiation. Our results show that high‐energy electron irradiation generates positive charges in the oxide and at the SiSiO2 interface, which are frequency dependent. After electron irradiation, two kinds of interface traps are determined. The traps energy position evaluated by these three independent methods is very close to Ev + 0.16 eV and Ev + 0.36 eV. As these results are in a very good agreement with our earlier results, obtained by TSC and DLTS methods, the observed traps can be attributed to the boron‐ (V/B) and oxygen (V/O) vacancies complexes.

I/V characteristics of a reference and of a MOS structures, the latter being irradiated by 23 MeV electrons.

image

I/V characteristics of a reference and of a MOS structures, the latter being irradiated by 23 MeV electrons.
RBS Investigation of Ion Implanted SiSiO2 Structures Irradiated with 20 MeV Electrons
Authors: Kaschieva Sonia B. , Angelov Christo V. , Dmitriev Sergey N. , Tsutsumanova Gichka I.
Published: February 2006

Summary: The influence of high‐energy electron irradiation on the redistribution of silicon and oxygen atoms in implanted SiSiO2 structures has been investigated by Rutherford backscattering spectroscopy (RBS). Two groups of SiSiO2 samples implanted with different doses of silicon ions (1 × 1012 cm−2 and 1 × 1016 cm−2) are used. The ion energy of 15 keV is chosen to produce maximum radiation defects at the SiSiO2 interface. The structures are then irradiated with 20 MeV electrons for different durations (from 60 s up to 120 min). After electron irradiation, the redistribution of the oxygen and silicon atoms in the samples implanted with 1 × 1012 cm−2 Si+ ions is negligible: significant redistribution of these atoms is found only in SiSiO2 samples implanted a with dose of 1016 cm−2. These results demonstrate that the structural changes at the silicon surface of implanted SiSiO2 samples, which take place after electron irradiation, depend more strongly on the implantation dose than on the electron dose irradiation.

RBS spectra of SiSiO2 samples implanted with silicon ions and subsequently electron irradiated.

image

RBS spectra of SiSiO2 samples implanted with silicon ions and subsequently electron irradiated.
Raman Scattering Characterization of Ion‐Beam Synthesized Mg2Si, 1
Authors: Atanassov Alexander , Zlateva Genoveva , Baleva Mitra , Goranova Ekaterina , Amov Blagoj , Angelov Christo , Mikli Valdek
Published: February 2006

Summary: The unpolarized Raman scattering spectra of ion beam synthesized Mg2Si phase, embedded in (100) Si matrix are studied. We used two different doses for the Mg ions, 4 × 1017 cm−2 and 8 × 1017 cm−2, each of them with two different energies 40 keV and 60 keV, which were implanted into (100) Si substrates. After implantation, the samples were subjected to rapid thermal annealing for different durations. The samples' surfaces were studied by scanning electron microscopy (SEM). On the basis of the Raman spectra behavior, conclusions were drawn about the influence of the technological parameters on the formation of the Mg2Si phase.

SEM microphotographs of samples produced with an ion dose of 8 × 1017 cm−2, an ion energy of 40 keV, and annealed for 60 s.

image

SEM microphotographs of samples produced with an ion dose of 8 × 1017 cm−2, an ion energy of 40 keV, and annealed for 60 s.
Influence of the Implantation Dose and of the Annealing Duration on the Raman Spectra of Ion‐Beam Synthesized β‐FeSi2 Layers
Authors: Marinova Maya , Zlateva Genoveva , Baleva Mitra
Published: February 2006

Summary: The samples under investigation are prepared by ion‐beam synthesis, followed by rapid thermal annealing. Fe ions with two different doses, each of them with two different energies, are implanted into Si substrates. The two step implantation with the iron doses used ensure the formation of unburied polycrystalline continuous β‐FeSi2 layers with a thickness of about 50 nm in the case of the lowest implantation dose, and of about 100 nm in the case of the higher one. We observed the same Raman modes, which are predicted theoretically and detected experimentally by other authors as well. The influence of the Fe ion dose and of the annealing time on the Raman spectra behavior is characterized.

Raman spectra of a sample obtained by implantation with 5 × 1016 cm−2 dose of iron ions, and annealed at 900 °C for 60 s.

image

Raman spectra of a sample obtained by implantation with 5 × 1016 cm−2 dose of iron ions, and annealed at 900 °C for 60 s.
Electron Energy Distribution Function Measurements in an Inductively Driven Tandem Plasma Source
Authors: Tsankov Tsanko , Kiss'ovski Zhivko , Djermanova Nina , Kolev Stanimir
Published: February 2006

Summary: Electron energy distribution functions (EEDF) are obtained from probe measurement data along the axis of the metallic chamber of an inductively driven tandem plasma source. The numerical procedure for calculating the second derivative of the probe current combines Savitzky‐Golay smoothing filter and the three‐point differentiator with a varying step. The EEDF is obtained through the Druyvesteyn formula from the calculated second derivative. The shape of the EEDFs in argon gas at low pressures is investigated for the case of a tandem plasma source. Experimental EEDFs are compared with Maxwellian distributions, and deviations in the tail are observed at higher pressures, which are explained in terms of the ratio between the electron‐electron collision frequency and the excitation frequency. Axial variations of the slope and of the area below the EEDF curve result in electron temperature and concentration decrease along the axis.

Electron energy distribution function (EEDF) measured for gas pressure of 26 mTorr, at an axial position of 12 cm.

image

Electron energy distribution function (EEDF) measured for gas pressure of 26 mTorr, at an axial position of 12 cm.
Spatial Distribution of the Wave Field of Filamented High‐Frequency Discharges
Authors: Lishev Stiliyan , Schlüter Hans , Shivarova Antonia , Tarnev Khristo
Published: February 2006

Summary: This study is on high pressure surface wave‐sustained discharges at the stage of their contraction into filaments: gas discharge channels positioned in the off‐center region of the cross section of the discharge and extended along its length. Based on results for the dispersion behavior and the space distribution of the wave field, obtained by a 2D numerical code developed for describing surface wave properties in plasma with an arbitrary distribution of density, the structure of the modes sustaining the discharge was identified. It is reminiscent of the superposition of an azimuthally‐symmetric and azimuthally‐asymmetric field configurations. The results obtained form the basis for modelling the plasma behavior in the discharge.

Space distribution of the amplitude of the Ez field component of a surface wave sustaining a dipole filamentary structure.

image

Space distribution of the amplitude of the Ez field component of a surface wave sustaining a dipole filamentary structure.
Fabrication and Study of Periodically Structured Y2O3 Waveguides
Authors: Dikovska Anna Og. , Tonchev Svetlen H. , Vasilev Cvetelin , Atanasov Petar A.
Published: February 2006

Summary: Periodically structured waveguides have several advantages over their unstructured‐planar film counterparts such as lower threshold for laser generation, due to the lateral confinement of both the pump and the laser modes, higher coupling efficiency, and easy operation. The structural and optical qualities of the waveguides, on the one hand, and the diffraction efficiency of the periodic structure, on the other, are the key parameters that must be controlled in order to obtain planar waveguides suitable for laser application. In the present work, thin Er, Yb‐doped Y2O3 films were grown on a periodically structured glass substrate by laser ablation. The waveguide structure has a period of 560 nm. The smooth surface, good adhesion, and possibility to repeat the substrate structure make the deposition method suitable for preparation of structured waveguides. The waveguide thickness non‐uniformity introduced by the laser deposition method was estimated to be about 4.6%. It does not affect the waveguide propagation.

AFM image of the surface after deposition of the waveguide.

image

AFM image of the surface after deposition of the waveguide.
Laser Heterodyne Measurement of Photothermal Displacement for Material Surface Characterization
Authors: Pencheva Vasilka , Penchev Stoyan , Naboko Vasilii , Donchev Todor , Kolev Svetoslav , Kutzarova Tania
Published: February 2006

Summary: Double‐heterodyne photodisplacement technique (PDT), based on the detection of the thermal expansion of a sample under irradiation by laser light has been employed to improve the resolution of photothermal displacement measurements up to orders of sub‐picometers. We have developed an ultra‐sensitive system to measure photothermal displacement of metallic and non‐metallic materials, such as silicon, due to the illumination by an ordinary laser diode. Non‐destructive characteristics of the scheme are well suited for conditions that restrict access to the sample to be measured. Careful consideration is given to eliminate the noise sources, so as to achieve the level of sensitivity that needed to detect the structural inhomogeneity of materials. Good agreement between experimental results and theoretical predictions is demonstrated.

Laser double‐heterodyne detection of the photo‐thermal expansion of metallic and non‐metallic materials illuminated by a laser diode.

image

Laser double‐heterodyne detection of the photo‐thermal expansion of metallic and non‐metallic materials illuminated by a laser diode.
Electrical and Optical Characteristics of Ta2O5 Thin Films Deposited by Electron‐Beam Vapor Deposition
Authors: Todorova Zhana , Donkov Nikolay , Ristić Zoran , Bundaleski Nenad , Petrović Suzana , Petkov Mario
Published: February 2006

Summary: Ta2O5 is a material with good perspectives for many applications in modern electronics and information technologies. Several deposition techniques of thin Ta2O5 films have been suggested. Reliable information is still needed, however, on structural, electrical and optical parameters of the films, and their dependence on the deposition technique. We have deposited Ta2O5 thin films by electron‐beam evaporation of Ta2O5 powder onto Si, tantalum and glass substrates. The resistivity of the films with various thicknesses was measured by four‐point probe method before and after annealing in an oxygen atmosphere. The reflectance in the IR region depending on the substrate and film thickness was shown.

IR characteristics of the 320 nm thick films deposited on glass substrates after annealing.

image

IR characteristics of the 320 nm thick films deposited on glass substrates after annealing.
Detection of NH3 by Quartz Crystal Microbalance Coated with Ta2O5
Authors: Georgieva Velichka , Spassov Lozan , Donkov Nikolay , Petkov Plamen , Atanassov Mitko
Published: February 2006

Summary: This paper reports a study of the sorption properties of thin Ta2O5 films to NH3 vapors. The films are deposited using electron beam evaporation. In order to determine the sorption ability of Ta2O5 to NH3, a quartz crystal microbalance (QCM) with a thin Ta2O5 film is investigated. The Ta2O5 film is used as a receptor for the NH3 gas. The AT‐cut, 14 MHz quartz resonators allow conversion of the additional mass loading that occurs as a result of sorption into a frequency shift. The experiments are carried out by measuring the resonant frequency shift of the QCM to vapors from an aqueous solution of NH3 with different concentrations from 10 to 10 000 ppm. The obtained experimental results indicate that the variations of the resonant frequency are a function of the ammonia concentration and the thickness of the Ta2O5 layer. The process of sorption is found to be reversible. The reported investigation shows that a QCM covered with a thin Ta2O5 layer is sensitive to ammonia vapors at room temperature and is able to detect NH3 concentrations in the investigated range (10–10 000 ppm).

Relative change of QCM frequency versus ammonia concentration

image

Relative change of QCM frequency versus ammonia concentration
Determination of Nitrogen Atoms Loss Probabilities on Copper, Aluminium, Alumina, Brass and Nylon Surfaces
Authors: Sarrette Jean‐Philippe , Rouffet Benoît , Ricard André
Published: February 2006

Summary: Materials exposure to a flowing post discharge jet can induce a significant rise of materials temperature. This increase is related to the recombination of the atomic species produced in the discharge at the surface of the exposed materials, which is a highly exothermic process. At pressures below 10 Torr, this process is the main loss term for the atoms far away from the discharge. Nevertheless, a very small number of reliable data concerning atomic recombination probabilities, γ, is available in the literature. In this work, such data are obtained for the recombination of the nitrogen atoms on five materials (copper, aluminium, alumina, brass and Nylon) by the adjustment between measured surface temperatures and calculated values obtained by a 3D modelling of the post discharge reactor, which includes the enthalpy deposition at the walls. Results show a general decrease of the γ‐values with increasing pressure, as already mentioned by other authors. The sensitivity of the method is also studied.

Evolution with pressure of the N‐atom recombination probability γN for aluminium, copper, brass, alumina and Nylon.

image

Evolution with pressure of the N‐atom recombination probability γN for aluminium, copper, brass, alumina and Nylon.
PIC – MCC Numerical Simulation of a DC Planar Magnetron
Authors: Kolev Ivan , Bogaerts Annemie
Published: February 2006

Summary: A 2d3v numerical model of a DC sputter magnetron is presented. The model is fully self‐consistent and kinetic. Based on the Particle‐in‐Cell/Monte Carlo Collisions technique it includes modules for the gas heating and the diffusion transport of the sputtered atoms. An external electric circuit is incorporated to achieve the calculation of the cathode voltage in a self‐consistent manner, as well as the simulation of the constant current regime. The model is applied to a laboratory magnetron operated in argon.

Calculated distribution of the electric potential, V, at p = 10 mTorr. The white line corresponds to V = 0 V.

image

Calculated distribution of the electric potential, V, at p = 10 mTorr. The white line corresponds to V = 0 V.
Spectroscopic Ellipsometry as a Tool for Damage Profiling in Very Shallow Implanted Silicon
Authors: Karmakov Iordan , Konova Anka , Chakarov Ivan
Published: February 2006

Summary: Ion implantation is still one of the key steps in Si integrated circuit technology. Spectroscopic Ellipsometry (SE) detects the defects created in the implanted Si. The successful application of SE for damage profiling depends on the quality of the algorithm used for evaluating the damage profile from SE data. In this work, we present retrieved SE damage depth profiles by our previously published algorithm in the as‐implanted Si with very low energies Ge+ ions‐ from 2 keV to 20 keV and 1 keV B+ ions (1 × 1015 cm−2). The comparisons of the SE retrieved damage depth profiles with experimental atomic concentration depth profiles, or simulated by the state‐of‐the‐art computer ATHENA code of Silvaco TCAD suits were made. The functional relation was obtained by proper fitting of measured by SE a/c depths, and the depths named “ends of damage” with the experimental or simulated ions concentration depth profiles. For reasons not understood, the damage profile of 5 keV Ge+ in c‐Si is smoother in shape beyond the a/c depth, with a longer tail.

The damage profiles measured by SE for 5 keV Ge+ in c‐Si with two different doses: curve 1 ‐ for 6 × 1013 cm−2 and curve 2 ‐ for 1 × 1015 cm−2. Curve 3 ‐ presents the damage profile simulated by ATHENA for Ge+ ions with 5 keV; 1 × 1015 cm−2.

image

The damage profiles measured by SE for 5 keV Ge+ in c‐Si with two different doses: curve 1 ‐ for 6 × 1013 cm−2 and curve 2 ‐ for 1 × 1015 cm−2. Curve 3 ‐ presents the damage profile simulated by ATHENA for Ge+ ions with 5 keV; 1 × 1015 cm−2.
EHD Ponderomotive Forces and Aerodynamic Flow Control Using Plasma Actuators
Authors: Pinheiro Mario J.
Published: February 2006

Summary: We present a self‐consistent two‐dimensional fluid model of the temporal and spatial development of the one atmosphere uniform glow discharge plasma (OAUGDP®). Continuity equations for electrically charged species N, N, O, O, and electrons are solved coupled to the Poisson equation, subject to appropriate boundary conditions. An algorithm proposed by Patankar was used (S. V. Patankar, “Numerical Heat Transfer and Fluid Flow”, Taylor Francis, New York 1980). The transport parameters and rate coefficients for electrons at atmospheric pressure are obtained by solving the homogeneous Boltzmann equation for electrons under the hydrodynamic assumption. Operational variables are obtained as a function of time: electric current; surface charge accumulated on the dielectric surface; the memory voltage and the gas voltage controlling the discharge. The spatial distribution of the electric field, the populations of charged species, the resulting ponderomotive forces, and the gas speed are also obtained.

Schematic representation of electrode geometry of an energized OAUGD® plasma panel.

image

Schematic representation of electrode geometry of an energized OAUGD® plasma panel.
Growth and Modification of Organosilicon Films in PECVD and Remote Afterglow Reactors
Authors: Supiot Philippe , Vivien Céline , Granier Agnès , Bousquet Angélique , Mackova Anna , Escaich David , Clergereaux Richard , Raynaud Patrice , Stryhal Zdenek , Pavlik Jaroslav
Published: February 2006

Summary: Five hundred nanometer thick organosilicon coatings are prepared on Si substrates in parallel by the plasma‐assisted polymerisation of hexamethyldisiloxane (HMDSO) in an RF‐inductively coupled plasma (RFICP) and distributed electron cyclotron resonance plasma (DECRP) at low pressure (0.27 Pa) and of tetramethyldisiloxane (TMDSO) premixed with oxygen in an N2 microwave induced remote afterglow (MIRA) at 560 Pa. The structure of these different films is analyzed by different techniques, such as Fourier‐transform infrared spectroscopy, Rutherford backscattering spectrometry, atomic force microscopy, ellipsometry, and contact angle measurements. Results of the film composition (at least 30% carbon content), optical properties, and morphology indicate a low cross‐linking degree accompanied by short chain length for RFICP and DECRP films, in contrast to a high‐molecular‐weight structure observed for the MIRA film. Carbon removal is achieved within the same plasma reactors by further oxygen‐containing plasma treatment performed in the RF‐ICP (3.33 Pa), DECRP (0.27 Pa, −200 V biased substrate), and MIRA (N2/O2 (98.7:1.3, 560 Pa)) reactors. The same measurements are carried out on the treated samples in order to detect the main changes in film composition, optical properties, and morphology. The evolution of surface energy is also studied. The results are discussed according to film structure and process specificity.

O/Si and C/Si elemental ratios calculated from RBS analysis for an as‐deposited RF‐inductively coupled plasma coating (RFICP) and films post‐treated by N2/O2 microwave induced remote afterglow (MIRA), O2 RFICP and O2 distributed electron cyclotron resonance plasma (DECRP, biased sample) processes.

image

O/Si and C/Si elemental ratios calculated from RBS analysis for an as‐deposited RF‐inductively coupled plasma coating (RFICP) and films post‐treated by N2/O2 microwave induced remote afterglow (MIRA), O2 RFICP and O2 distributed electron cyclotron resonance plasma (DECRP, biased sample) processes.
Raman Scattering Characterization of Ion‐Beam Synthesized Mg2Si, 2
Authors: Zlateva Genoveva , Atanassov Alexander , Baleva Mitra , Nicolova Lora
Published: February 2006

Summary: The polarized Raman spectra of ion‐beam synthesized Mg2Si, embedded in (001) and (111) Si substrates were studied. The relative intensities of the F2g mode measured in several exact scattering configurations are compared with those calculated under the condition for minimum mismatch between the Si and Mg2Si lattices. A conclusion for the orientational growth of the Mg2Si phase in Si is drawn.

The matching of the (111) Si and (111) Mg2Si planes.

image

The matching of the (111) Si and (111) Mg2Si planes.
Osmolyte‐induced protein folding free energy changes
Authors: Wu Peng , Bolen D.W.
Published: February 2006

Upon addition of protecting osmolyte to an aqueous solution of an intrinsically unstructured protein, spectral observables are often seen to change in a sigmoid fashion as a function of increasing osmolyte concentration. Commonly, such data are analyzed using the linear extrapolation model (LEM), a method that defines a scale from 0%–100% folded species at each osmolyte concentration by means of extending pre‐ and post‐folding baselines into the transition region. Defining the 0%–100% folding scale correctly for each osmolyte is an important part of the analysis, leading to evaluation of the fraction of folded protein existing in the absence of osmolytes. In this study, we used reduced and carboxyamidated RNase T1 (RCAM‐T1) as an intrinsically unstructured protein, and determined the thermodynamic stability of RCAM‐T1 induced by naturally occurring osmolytes. Because the folded fraction of the protein population determined by experiments of thermal and urea‐induced denaturation is nonzero in the absence of osmolytes at 15°C, the commonly used LEM can lead to false values of ΔG for protein folding due to the arbitrary assumption that the protein is 100% unfolded in the presence of buffer alone. To correct this problem, titration of the protein solution with urea and extrapolating back to zero urea concentration gives the spectral value for 100% denatured protein. With fluorescence as the observable we redefine F/F0 to F/F = 1.0 and require that the denatured‐state baseline have this value as its intercept. By so doing, the 0%–100% scale‐corrected ΔG values of RCAM‐T1 folding in the presence of various osmolytes are then found to be identical, with small error, demonstrating that ΔG is independent of the osmolytes used. Such a finding is an important step in validating this quantity derived from the LEM as having the properties expected of an authentic thermodynamic parameter. The rank order of osmolyte efficacies in stabilizing RCAM‐T1 is sarcosine > sucrose > sorbitol > proline > betaine > glycerol. Proteins 2006. © 2006 Wiley‐Liss, Inc.
Two‐stage support vector regression approach for predicting accessible surface areas of amino acids
Authors: Nguyen Minh N. , Rajapakse Jagath C.
Published: February 2006

We address the problem of predicting solvent accessible surface area (ASA) of amino acid residues in protein sequences, without classifying them into buried and exposed types. A two‐stage support vector regression (SVR) approach is proposed to predict real values of ASA from the position‐specific scoring matrices generated from PSI‐BLAST profiles. By adding SVR as the second stage to capture the influences on the ASA value of a residue by those of its neighbors, the two‐stage SVR approach achieves improvements of mean absolute errors up to 3.3%, and correlation coefficients of 0.66, 0.68, and 0.67 on the Manesh dataset of 215 proteins, the Barton dataset of 502 nonhomologous proteins, and the Carugo dataset of 338 proteins, respectively, which are better than the scores published earlier on these datasets. A Web server for protein ASA prediction by using a two‐stage SVR method has been developed and is available (http://birc.ntu.edu.sg/∼pas0186457/asa.html). Proteins 2006. © 2006 Wiley‐Liss, Inc.
Predicting protease types by hybridizing gene ontology and pseudo amino acid composition
Authors: Zhou Guo‐Ping , Cai Yu‐Dong
Published: February 2006

Proteases play a vitally important role in regulating most physiological processes. Different types of proteases perform different functions with different biological processes. Therefore, it is highly desired to develop a fast and reliable means to identify the types of proteases according to their sequences, or even just identify whether they are proteases or nonproteases. The avalanche of protein sequences generated in the postgenomic era has made such a challenge become even more critical and urgent. By hybridizing the gene ontology approach and pseudo amino acid composition approach, a powerful predictor called GO‐PseAA predictor was introduced to address the problems. To avoid redundancy and bias, demonstrations were performed on a dataset where none of proteins has ≥ 25% sequence identity to any other. The overall success rates thus obtained by the jackknife cross‐validation test in identifying protease and nonprotease was 91.82%, and that in identifying the protease type was 85.49% among the following five types: (1) aspartic, (2) cysteine, (3) metallo, (4) serine, and (5) threonine. The high jackknife success rates yielded for such a stringent dataset indicate the GO‐PseAA predictor is very powerful and might become a useful tool in bioinformatics and proteomics. Proteins 2006. © 2006 Wiley‐Liss, Inc.
Comment on: “Energy landscape of a small peptide revealed by dihedral angle principal component analysis”
Authors: Hinsen Konrad
Published: February 2006

The dihedral angle principal component analysis method published recently by Mu, Nguyen, and Stock, is shown to produce distortions of the free energy landscape due to the neglect of constraints in the coordinates. It is further shown that these distortions can create artificial minima and energy barriers. The rugged energy landscape that the authors find for a small peptide chain might thus be an artifact of their method. Proteins 2006. © 2006 Wiley‐Liss, Inc.
Compton profile study of tin
Authors: Ahuja B. L. , Khera S. , Mathur S. , Heda N. L.
Published: February 2006

In this paper we report the Compton profile of β‐tin, measured at an intermediate resolution, using 661.65‐keV γ‐radiation from a 137Cs source. We have also computed the Compton profiles for α‐ and β‐tin using the CRYSTAL03 code. The Compton profiles within the framework of linear combination of atomic orbitals (LCAO) using Hartree–Fock (HF), density functional (DF) and pseudopotential‐HF schemes embodied in the CRYSTAL03 code have been reported for both phases. Good accordance of the experiment for β‐tin with the corresponding theoretical profiles has been observed for the LCAO‐HF and DF schemes. A real‐space analysis of the experimental Compton profile shows the metal‐like behavior of β‐tin. (© 2006 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)
Hydrostatic‐pressure effects on the correlated electron–hole transition energies in GaAs–Ga1–xAlxAs semiconductor quantum wells
Authors: Raigoza N. , Duque C. A. , Reyes‐Gómez E. , Oliveira L. E.
Published: February 2006

The effects of hydrostatic pressure on the correlated e–h transition energies in single GaAs–Ga1–xAlxAs quantum wells are calculated via a variational procedure, in the framework of the effective‐mass and non‐degenerate parabolic‐band approximations. The valence‐band anisotropy is included in our theoretical model by using different hole masses in different spatial directions. Both heavy‐ and light‐hole exciton energies are obtained, and correlated e–h transition energies are found in good agreement with available experimental measurements. (© 2006 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)
Raman spectroscopy of open‐ended Single Wall Carbon Nanotubes under pressure: effect of the pressure transmitting medium
Authors: Merlen A. , Toulemonde P. , Bendiab N. , Aouizerat A. , Sauvajol J. L. , Montagnac G. , Cardon H. , Petit P. , San Miguel A.
Published: February 2006

We performed high pressure Raman experiments on purified open‐ended single wall carbon nanotubes using different pressure transmitting media (paraffin oil, argon and 4:1 methanol ethanol mixture) and two excitating wavelength (514.5 nm and 632.8 nm). We state that the behavior of the Raman spectrum under pressure is significantly dependent on the pressure transmitting medium. This result points out the relevance of the interactions between the medium and the nanotubes, at the origin of the disagreement between the phase transition sequences reported in literature. The comparaison of tangential modes profiles clearly shows that 4:1 methanol ethanol induces few strain on nanotubes in the opposite of what is observed for argon and paraffin oil pressure transmitting media. These observations are discussed in terms of intercalation and stress due to non hydrostatic conditions. (© 2006 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)
Effect of electric current on the Jahn–Teller distortion modes in La0.67–yPryCa0.33MnO3
Authors: Ma Y. Q. , Yang J. , Zhao B. C. , Du J. J. , Sun Y. P.
Published: February 2006

The sensitivity of transport and the lattice to a direct current has been investigated by means of in situ measurements of resistivity ϱ and Young's modulus E along with magnetic measurements in La0.67–yPryCa0.33MnO3 (y = 0, 0.15, 0.25, and 0.30) compounds. Increasing the Pr doping level enhances the softening of the magnitude of E with the appearance of a minimum in the curve of the temperature dependence of the modulus, E(T). The direct current depresses the resistivity and shifts the E(T) minimum to lower temperatures dramatically for the compounds with y ≥ 0.25, which exhibit a distinct magnetic hysteresis loop. The resistivity drop caused by the larger current may result from the depression of the Q3‐type distortion mode of Mn3+O6 octahedra by the current, which may favor the lower resistivity. (© 2006 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)
(II,Mn)VI nanostructures in mesoporous silica hosts – from powder samples to thin films
Authors: Chen L. , Klar P. J. , Heimbrodt W. , Kurz T. , Krug von Nidda H.‐A. , Loidl A. , Kouzema A. V. , Fröba M.
Published: February 2006

The diluted magnetic semiconductor Cd1–x Mnx S with x up to 0.2 was synthesized within the pores of mesoporous thin film (MTF) silica host structures by a wet impregnation technique from an aqueous solution of the respective metal acetates, followed by drying steps and a conversion to sulfides by thermal H2S treatment. The presence of Cd1–x Mnx S nanoparticles inside the pores was confirmed by Raman spectroscopy. Photoluminescence excitation (PLE) measurements clearly reveal quantum confinement of the electronic states of the nanostructured Cd1–x Mnx S. Electron‐paramagnetic resonance (EPR) measurements on low x samples are used to prove that Mn is incorporated on cation site of the II–VI host and to demonstrate that the magnetic properties of Cd1–x Mnx S nanostructures are strongly affected by the reduction of the lateral dimensions. The quality of the Cd1–x Mnx S nanostructures synthesized in MTF silica hosts is comparable to that of Cd1–x Mnx S nanostructures inside MCM‐41 mesoporous silica powder. (© 2006 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)
Observation of Zn vacancies in ZnO grown by chemical vapor transport
Authors: Tuomisto F. , Saarinen† K. , Grasza K. , Mycielski A.
Published: February 2006

We have used positron annihilation spectroscopy to study the vacancy defects in ZnO crystals grown by both the conventional and contactless chemical vapor transport (CVT and CCVT). Our results show that Zn vacancies or Zn vacancy related defects are present in as‐grown ZnO, irrespective of the growth method. Zn vacancies are observed in CVT‐grown undoped ZnO and (Zn,Mn)O. The Zn vacancies present in undoped CCVT‐ZnO are the dominant negatively charged point defect in the material. Doping the material with As introduces also Zn vacancy‐related defect complexes with larger open volume. (© 2006 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)
Optical probing of spin‐dependent interactions in II–VI semiconductor structures
Authors: Gaj J. A. , Cibert J. , Ferrand D. , Golnik A. , Goryca M. , Karczewski G. , Kossacki P. , Kossut J. , Kowalik K. , Krebs O. , Kudelski A. , Kutrowski M. , Lemaitre A. , Maślana W. , Nawrocki M. , Pacuski W. , Płochocka P. , Senellart P. , Tatarenko S. , Voisin P. , Wojtowicz T.
Published: February 2006

We present a selection of optical experiments, providing information on several spin‐dependent interactions in II–VI semiconductor structures. Exciton–exciton and exciton–carrier interactions were studied by time‐resolved picosecond pump–probe measurements. Several examples of recent studies involving ion‐carrier exchange interaction in quantum wells and layers are discussed, concerning the quest for room temperature ferromagnetic semiconductors, spin temperature of Mn ions in (Cd,Mn)Te quantum wells, and spin relaxation in such wells under pulsed magnetic field. Finally, anisotropic electron–hole exchange in semiconductor quantum dots is discussed in the context of efforts to obtain generation of entangled photon pairs in a biexciton–exciton cascade in a semiconductor quantum dot. (© 2006 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)
Nanosecond spin memory of electrons in CdTe/CdMgTe quantum wells
Authors: Astakhov G. V. , Kiessling T. , Yakovlev D. R. , Zhukov E. A. , Bayer M. , Ossau W. , Zakharchenya B. P. , Karczewski G. , Wojtowicz T. , Kossut J.
Published: February 2006

We report on spin memory relaxation time τ s of free electrons in CdTe‐based quantum wells which is found to be in the nanosecond range. In these studies two different techniques have been exploited: (i) the Hanle effect under cw excitation and (ii) the time‐resolved pump‐&‐probe Kerr rotation measured under excitation by 1.8‐ps optical pulses. These independent techniques give very close results τ s ns and τ s = 14 ns, respectively. To our knowledge this is by two orders of magnitude longer than the electron spin relaxation times reported for CdTe‐based quantum wells so far. (© 2006 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)
III–V/II–VI heterovalent double quantum wells
Authors: Toropov A. A. , Sedova I. V. , Sorokin S. V. , Terent'ev Ya. V. , Ivchenko E. L. , Lykov D. N. , Ivanov S. V. , Bergman J. P. , Monemar B.
Published: February 2006

We report on design, fabrication by molecular beam epitaxy, and photoluminescence (PL) studies of III–V/II–VI heterovalent structures containing a GaAs/AlGaAs/ZnSe/ZnCdMnSe double quantum well (QW). The studies of temperature‐dependent and time‐resolved PL have provided an insight into the nature of the exciton localization potential induced by the heterovalent interface. It is found that under the resonant conditions the observed emission mostly originates from the recombination of excitons confined in type II quantum‐dot‐like structures, where the holes are localised within the GaAs QW due to the well width fluctuations and the electrons are localized in the plane of the ZnCdMnSe QW due to the fluctuations of the conduction band offset at the heterovalent interface, induced by random variation of the interface microscopic structure. (© 2006 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)
Identification of isoenzymes using matrix‐assisted laser desorption/ionization time‐of‐flight mass spectrometry
Authors: Hardouin Julie , Hubert‐Roux Marie , Delmas Agnès F. , Lange Catherine
Published: February 2006

The identification of isoforms is one of the great challenges in proteomics due to the large number of identical amino acids preventing their separations by two‐dimensional electrophoresis. Matrix‐assisted laser desorption/ionization time‐of‐flight mass spectrometry (MALDI‐TOFMS) has become a rapid and sensitive tool in proteomics, notably with the new instrumental improvements. In this study, we used several acquisition modes of MALDI‐TOFMS to identify isoforms of porcine glutathiones S‐transferase. The use of multiple proteases coupled to the different acquisition modes of MALDI‐TOFMS (linear, reflectron, post‐source decay (PSD) and in‐source decay, positive and negative modes) allowed the identification of two sequences. Moreover, a third sequence is pointed out from a PSD study of a tryptic ion revealing the modification of the amino acid tyrosine 146 to phenylalanine. Copyright © 2006 John Wiley & Sons, Ltd.
Complementary structural information of positive‐ and negative‐ion MSn spectra of glycopeptides with neutral and sialylated N‐glycans
Authors: Deguchi Kisaburo , Ito Hiroki , Takegawa Yasuhiro , Shinji Nagai , Nakagawa Hiroaki , Nishimura Shin‐Ichiro
Published: February 2006

Positive‐ and negative‐ion MSn spectra of chicken egg yolk glycopeptides binding a neutral and a sialylated N‐glycan were acquired by using electrospray ionization linear ion trap time‐of‐flight mass spectrometry (ESI‐LIT‐TOFMS) and collision‐induced dissociation (CID) with helium as collision gas. Several characteristic differences were observed between the positive‐ and negative‐ion CID MSn (n = 2, 3) spectra. In the positive‐ion MS2 spectra, the peptide moiety was presumably stable, but the neutral N‐glycan moiety caused several B‐type fragmentations and the sialylated N‐glycan almost lost sialic acid(s). In contrast, in the negative‐ion MS2 spectra, the peptide moiety caused several side‐chain and N‐glycan residue (e.g., N‐acetylglucosamine (GlcNAc) residue) fragmentations in addition to backbone cleavages, but the N‐glycan moieties were relatively stable. The positive‐ion MS3 spectra derived from the protonated peptide ion containing a GlcNAc residue (203.1 Da) provided enough information to determine the peptide amino‐acid sequence including the glycosylation site, while the negative‐ion MS3 spectra derived from the deprotonated peptide containing a 0,2X1‐type cross‐ring cleavage (83.1 Da) complicated the peptide sequence analysis due to side‐chain and 0,2X1 residue related fragmentations. However, for the structural information of the N‐glycan moiety of the glycopeptides, the negative‐ion CID MS3 spectra derived from the deprotonated 2,4A6‐type cross‐ring cleavage ion (neutral N‐glycan) or the doubly deprotonated B6‐type fragment ion (sialylated N‐glycan) are more informative than are those of the corresponding positive‐ion CID MS3 spectra. Thus, the positive‐ion mode of CID is useful for the analyses of peptide amino‐acid sequences including the glycosylation site. The negative‐ion mode of CID is especially useful for sialylated N‐glycan structural analysis. Therefore, in the structural analysis of N‐glycopeptides, their roles are complementary. Copyright © 2006 John Wiley & Sons, Ltd.