bluuebunny/crossref_metadata_2025 huggingface dataset:
Oxygen-Partial-Pressure Dependence of SiC Oxidation Rate Studied by In Situ Spectroscopic Ellipsometry
Authors: Yamamoto Takeshi , Hijikata Yasuto , Yaguchi Hiroyuki , Yoshida Sadafumi
Published: March 2009

Real time observations of SiC (000–1) C-face and (0001) Si-face oxidation were
performed using an in-situ ellipsometer over the oxygen-partial-pressure range from 0.1 to 1.0 atm.
We analyzed the relations between oxide growth rate and oxide thickness by applying an empirical
relation proposed by Massoud et al. We found the occurrence of oxidation enhancement in the thin
oxide regime also for Si-face as well as for C-face. We have discussed the oxygen-partial-pressure
dependence of the oxidation rate constants between SiC C- and Si face, comparing with that of Si.
Anomalously High Channel Mobility in SiC-MOSFETs with Al2O3/SiOx/SiC Gate Structure
Authors: Hino Shiro , Hatayama Tomohiro , Kato Jun , Miura Naruhisa , Oomori Tatsuo , Tokumitsu Eisuke
Published: March 2009

4H-SiC MOSFETs with Al2O3/SiC and Al2O3/SiOx/SiC gate structures have been
fabricated and characterized. Al2O3 was deposited by metal-organic chemical vapor deposition
(MOCVD) and the SiOx layer was formed by dry-O2 oxidation. Insertion of 1.2 nm-thickness-SiOx
layer drastically improves the channel mobility of Al2O3/SiC-MOSFET and anomalously high field
effect mobility (μFE) of 284 cm2/Vs was obtained. The μFE of Al2O3/SiOx/SiC-MOSFET with various
SiOx thickness was investigated, and it was found that insertion of a thin SiOx layer (< 2 nm) followed
by the low temperature deposition of Al2O3 results in Al2O3/SiOx/SiC-MOSFET with such a high
channel mobility.
High Channel Mobility of MOSFET Fabricated on 4H-SiC (11-20) Face Using Wet Annealing
Authors: Endo Takeshi , Okuno Eiichi , Sakakibara Toshio , Onda Shoichi
Published: March 2009

We studied the annealing process to improve the field-effect channel mobility (μFE) on the
4H-SiC (11-20) face. We found that wet annealing, in which a wet atmosphere was maintained during
the cooling-down period to 600°C after wet oxidation, was effective. The interface states (Dit) near
the conduction band edge decreased and the μFE increased up to 244 cm2/Vs. Furthermore, the origin
of this high channel mobility was investigated using secondary ion mass spectroscopy (SIMS)
measurement and thermal desorption spectroscopy (TDS) analysis. It was indicated that the hydrogen
density at the MOS interface was increased by the wet annealing and the hydrogen was desorbed
mainly at temperatures between 800 °C and 900 °C. These hydrogen desorption temperatures also
corresponded to the temperatures of the μFE reduction by argon annealing after the wet annealing.
These results indicated that this high channel mobility was achieved by hydrogen passivation during
the wet annealing at temperatures between 800 °C and 900 °C.
High Channel Mobility of 4H-SiC MOSFET Fabricated on Macro-Stepped Surface
Authors: Masuda Takeyoshi , Harada Shin , Tsuno Takashi , Namikawa Yasuo , Kimoto Tsunenobu
Published: March 2009

Improvement of the channel mobility is needed in 4H-SiC MOSFETs for the maximum
utilization of the material potential for novel power devices. We have attempted to obtain smoother
MOS interfaces as one of the ways to reduce the interface states which lead to decrease of the channel
mobility. We formed a terrace on the macro-stepped surface by annealing in Si melt and found that it
was atomically flat. We fabricated a lateral MOSFET on the macro-stepped surface and obtained a
high MOS channel mobility of 102 cm2/Vs.
Reduction of Interface Traps and Enhancement of Channel Mobility in n-Channel 6H-SiC MOSFETs by Irradiation with Gamma-Rays
Authors: Hishiki Shigeomi , Reshanov Sergey A. , Ohshima Takeshi , Itoh Hisayoshi , Pensl Gerhard
Published: March 2009

N-channel MOSFETs are irradiated with gamma-rays (g-rays) up to 3.16 MGy(SiO2) at
room temperature. Above 1 MGy, the effective channel mobility increases with increasing absorbed
dose. A similar increase is observed for the Hall mobility in the inversion layer. In addition, the
Hall-effect measurements indicate a reduction of the interface trap density.
Atomistic Scale Modeling of Factors Affecting the Channel Mobility in 4H-SiC MOSFETs
Authors: Chatterjee Aveek , Bhat Asha , Matocha Kevin
Published: March 2009

We have identified the crystal planes of 4H-SiC, interfacing with gate oxide, which will
lead to minimum defect density and lowest interface corrugations. The atomic surface density, surface
energy, and surface roughness of various crystal planes of 4H-SiC have been computationally
characterized using Molecular Dynamics simulations. We have also investigated the screening
distances of defects in SiO2 and SiC using a multiscale approach.
The Inefficiency of H2-Passivation as a Criterion for the Origin of SiC/SiO2 Deep Interface States - a Theoretical Study
Authors: Knaup Jan M. , Deák Peter , Frauenheim Thomas
Published: March 2009

Recently, Wang et. al. formulated a criterion for identifying the source of deep interface
sates at the SiC/SiO2 interface, based on the known inefficiency of H2 passivation. We apply this
criterion to a variety of excess carbon defects at the interface, which we have predicted to be
energetically feasible. We find that, also with respect to this criterion, the simple C split interstitials
are the most likely cause of the deep interface states among the examined defects.
Effect of Post-Oxidation Annealing on High-Temperature Grown SiO2/4H-SiC Interface
Authors: Moon Jeong Hyun , Cheong Kuan Yew , Song Ho Keun , Yim Jeong Hyuk , Oh Myeong Sook , Lee Jong Ho , Bahng Wook , Kim Nam Kyun , Kim Hyeong Joon
Published: March 2009

We have investigated the electrical and physical properties of high-temperature (1300,
1400 oC) grown dry oxide with or without post oxidation annealing (POA) in nitric oxide (NO) gas. A
significant reduction in interface-trap density (Dit) has been observed in 1300 oC-grown dry oxide
with or without NO POA if compared with the Dit of 1400 oC-grown dry oxide. The reason for this has
been explained in this paper.
Post Metallization Annealing Characterization of Interface Properties of High-κ Dielectrics Stack on Silicon Carbide
Authors: Weng Ming Hung , Mahapatra Rajat , Wright Nicolas G. , Horsfall Alton B.
Published: March 2009

The interface properties of TiO2/SiO2/SiC metal-insulator-semiconductor (MIS) capacitors
were investigated by C-V and G-V measurements over a range of frequencies between 10 kHz and 1
MHz from room temperature up to 500°C. Ledges from multiple traps were observed during high
frequency (1 MHz) sweeps from inversion to accumulation during measurements at elevated
temperatures. The high measuring temperature resulted in the annealing of the sample, where the
existence of trap ledges was observed to be temperature dependent. For n-type substrate negative Qf
causes the shift of the C-V curve to more negative gate bias with respect to the ideal C-V curve. These
fixed oxide charge is substantially reduced after post metallization annealing (PMA). We report the
flat band voltage, detail in reducing fixed oxide charge and temperature dependence of density of
interface traps before and after annealing of TiO2 high-κ gate dielectric stacks on a 4H-SiC based
device.
Impact of the Wafer Quality on the Reliability of MOS Structure on the C-Face of 4H-SiC
Authors: Hatakeyama Tetsuo , Suzuki Takuma , Senzaki Junji , Fukuda Kenji , Matsuhata Hirofumi , Shinohe Takashi , Arai Kazuo
Published: March 2009

We report on the reliability of the gate oxide on C-face of 4H-SiC. Constant current stress
TDDB measurement shows that QBD of the gate oxide of f200 [μm] on C-face is as much as 18 [C/
cm2], which is much larger than the typical value (0.1[C/ cm2]) of that on Si-face of 4H-SiC. The
lifetimes of the gate oxide under the electric field of 3[MV/cm] are roughly evaluated from the
leakage characteristics and obtained QBD. The estimated lifetimes of the gate oxide of f600 [μm] are
about 900 years. TDDB measurements of MOSs on two wafers, which have different dislocation
densities, show that reliability of gate oxide on C-face is insensitive to the dislocation density.
Meanwhile, reliability of the gate oxide is sensitive to the surface defect density: it is significantly
degraded on the wafer, which has 2000 surface defects in a whole 2-inch wafer.
Gate-Area Dependence of SiC Thermal Oxides Reliability
Authors: Senzaki Junji , Shimozato Atsushi , Okamoto Mitsuo , Kojima Kazutoshi , Fukuda Kenji , Okumura Hajime , Arai Kazuo
Published: March 2009

Reliability of thermal oxides grown on n-type 4H-SiC substrates using an area-scaling
rule has been investigated, and an influence of dislocation defects on the TDDB characteristics was
examined. Using the area-scaling rule, tBD distributions of thermal oxides with different gate-area
were converged to one distribution under the same breakdown factor. Finally, the reliability
prediction method of thermal oxides on 4H-SiC eliminating the effect of dislocation defects has
been established.
Negative Field Reliability of ONO Gate Dielectric on 4H-SiC
Authors: Tanimoto Satoshi , Suzuki Tatsuhiro , Yamagami Shigeharu , Tanaka Hideaki , Hayashi Tetsuya , Hirose Yukie , Hoshi Masakatsu
Published: March 2009

It was experimentally shown that an ONO gate dielectric carefully formed on 4H-SiC has
extremely high reliability even under a negative electric field at least up to a junction temperature of
300°C, making it promising for power MOS and CMOS applications. Medium charge to failure of
–30 C/cm2 was achieved for fully processed polycrystalline Si gate MONOS capacitors with an
equivalent SiO2 thickness of teq = 44 nm and a 200-μm diameter. The medium time to failure of these
capacitors projected for –3 MV/cm exceeds 86 and 6.3 thousand years at room temperature and 300°C,
respectively. A parasitic memory action did not appear even when Eox of -6.6 MV/cm was applied for
5000 seconds.
Impact of Nitridation on Negative and Positive Charge Buildup in SiC Gate Oxides
Authors: Rozen John , Dhar Sarit , Wang San Wu , Afanas'ev Valeri V. , Pantelides Sokrates T. , Williams John R. , Feldman Leonard C.
Published: March 2009

We report on the effect of nitridation on the negative and positive charge buildup in SiC
gate oxides during carrier injection. We observe that the incorporation of nitrogen at the SiO2/SiC
interface can enhance the reliability of the interface by suppressing the generation of interface states
upon electron injection but that it can also degrade the oxide by creating additional hole traps. We
relate these phenomena to the passivation of atomic-level defects by nitrogen.
Characteristics of Sol-Gel Derived SiO2 Thick Film on 4H-SiC
Authors: Tan Jo Lene , Cheong Kuan Yew , Rusli Rusli
Published: March 2009

Physical and electrical properties of sol-gel derived SiO2 thick film (100-130 nm)
deposited on n-type 4H-SiC have been investigated. The oxide was annealed in argon gas ambient
for 30 minutes at 650, 750, 850, and 950°C, in order to optimize the oxide properties. Results
indicated that the oxide is denser with a significant reduction in percentage of porosity as the
annealing temperature increases, except for sample annealed at 950°C. The oxide annealed at
850°C was having values of refractive index and dielectric constant close to the values reported in
thermally grown SiO2 and it has demonstrated the lowest leakage current density and total interface
trap density. Viscous shear flow effect has been proposed as the main contributor for the reduction
of physical properties when the oxide was annealed at 950°C.
New Chemical Planarization of SiC and GaN Using an Fe Plate in H2O2 Solution
Authors: Murata Junji , Kubota Akihisa , Yagi Keita , Sano Yasuhisa , Hara Hideyuki , Arima Kenta , Okamoto Takeshi , Mimura Hidekazu , Yamauchi Kazuto
Published: March 2009

A novel chemical planarization method was developed for silicon carbide (SiC) and
gallium nitride (GaN). This method uses catalytically generated hydroxyl radicals (OH*) to oxidize
the wafer surface. OH* are generated by the reductive decomposition of hydrogen peroxide (H2O2)
on the surface of the iron reference plate. An extremely flat surface without pits or scratches was
obtained. Atomic force microscopy (AFM) revealed that the planarized surface had an atomic
step-terrace structure, in which the step height corresponded to a single bilayer of 4H-SiC and GaN.
Low electron energy diffraction (LEED) and cathodeluminescence spectroscopy showed that there
was no crystallographic damage on the planarized surface.
Challenges of 4H-SiC MOSFETs on the C(000-1) Face toward the Achievement of Ultra Low On-Resistance
Authors: Fukuda Kenji , Harada Shinsuke , Senzaki Junji , Okamoto Mitsuo , Tanaka Yasunori , Kinoshita Akimasa , Kosugi Ryouji , Kojima Kazu , Kato Makoto , Shimozato Atsushi , Suzuki Kenji , Hayashi Yusuke , Takao Kazuto , Kato Tomohisa , Nishizawa Shin Ichi , Yatsuo Tsutomu , Okumura Hajime , Ohashi Hiromichi , Arai Kazuo
Published: March 2009

The C(000-1) face of 4H-SiC has a lot of advantages for the power device fabrication
such as the highest oxidation ratio and a smooth surface. However, the DMOS type power
MOSFETs on the C(000-1) face have not been realized because of the difficulty of epitaxial growth
and of high quality MOS interface formation. We have systematically investigated the device
fabrication techniques for power MOSFETs on the C(000-1) face, and succeeded with the IEMOS
which have blocking voltage of 660V and an on-resistance of 1.8mΩcm2 and excellent dynamic
characteristics.
Normally-Off 1400V/30A 4H-SiC DACFET and its Application to DC-DC Converter
Authors: Kitabatake Makoto , Tagome M. , Kazama S. , Yamashita K. , Hashimoto K. , Takahashi Kunimasa , Kusumoto O. , Utsunomiya Kazuya , Hayashi Masashi , Uchida M. , Ikegami R. , Kudo C. , Hashimoto S.
Published: March 2009

Large (3.6 x 3.6 mm2) chips of the SiC DACFET were fabricated and mounted in
TO220 packages. The drain-source avalanche breakdown voltage without any gate bias
(Vgs=0V) is measured to be >1400V. The SiC DACFET keeps the normally-off characteristics
even at 150°C. Ron and specific Ron of the SiC DACFET is measured to be 62mΩ and 6.7
mΩcm2 at RT while those at 150°C change to 107 mΩ and 11.6 mΩcm2. The 400V / 3 kW
DC-DC switched-mode power-conversion circuit with 100kHz switching was fabricated using
the SiC DACFET and the SiC SBD. The turn-off switching loss reduces dramatically using
the SiC-DACFET down to 77μJ/pulse which is less than 1/10 of that using the Si-IGBT.
Applications-Based Design of SiC Technology
Authors: Wright Nicolas G. , Johnson C. Mark , Horsfall Alton B. , Buttay Cyril , Vassilevski Konstantin , Loh W.S. , Skuriat R. , Agyakwa P.
Published: March 2009

The adoption of SiC devices as a viable technology depends crucially on maximising the potential
advantages of the material. This is best achieved by the adoption of co-design techniques in which
the optimisation of the SiC device is performed in parallel to that of the package and the overall
application. This paper considers suitable techniques for this co-design and describes new
approaches to the development of SiC technology for practical applications.
1200-V JBS Diodes with Low Threshold Voltage and Low Leakage Current
Authors: Yamamoto Takeo , Kojima Jun , Endo Takeshi , Okuno Eiichi , Sakakibara Toshio , Onda Shoichi
Published: March 2009

4H-SiC SBDs have been developed by many researchers and commercialized for power
application devices in recent years. At present time, the issues of an SiC-SBD are lower on-state
current and a relatively larger-leakage current at the reverse bias than Si-PN diodes. A JBS (Junction
Barrier Schottky) diode was proposed as a structure to realize a lower leakage current.
We simulated the electrical characteristics of JBS diodes, where the Schottky electrode was made
of molybdenum in order to optimize its performance. We fabricated JBS diodes based on the
simulation with a diameter of 3.9mm (11.9 mm2). The JBS diode has a lower threshold voltage of
0.45 V, a large forward current of 40 A at Vf = 2.5V and a high breakdown voltage of 1660 V.
Furthermore, the leakage current at 1200 V was remarkably low (Ir = 20 nA).
Breakdown Behavior of 900-V 4H-SiC Schottky Barrier Diodes Terminated with Boron-Implanted pn-Junction
Authors: Ivanov Pavel A. , Grekhov Igor V.
Published: March 2009

High-voltage (900 V) 4H-SiC Schottky-barrier diodes (SBD) terminated with guard pnjunction
were fabricated and investigated. The guard pn-junction was formed by room temperature
boron implantation followed by high temperature annealing. Owing to the transient enhanced boron
diffusion during anneal, the depth of guard pn-junction is about 1.7 μm, that is approximately 1 μm
deeper than the expected average range of 11B ions in 4H-SiC. The maximum reverse voltage of
4H-SiC SBD produced has been found to be limited by the avalanche breakdown in cylindrical
portion of planar pn-junction. The value of the breakdown voltage of 910 V is close to theoretical
one calculated for the dopant density = 2.5×1015 cm-3, n-base thickness d = 12.5 μm and junction
curvature rj = 1.7 μm. Dynamic (pulse) reverse current-voltage characteristics were measured in the
breakdown regime. It was found that dynamic breakdown voltage increases with shortening the
pulse duration. Due to homogeneous avalanche breakdown at the edge of the quard pn-junction and
high differential resistance in the breakdown regime, the diodes under test are able to withstand,
with no degradation, pulse reverse voltage at least 1600 V.
Characterization of Schottky Diodes on 4H-SiC with Various Off-Axis Angles Grown by Sublimation Epitaxy
Authors: Nakamura Mitsutaka , Hashino Yoshikazu , Furusho Tomoaki , Kinoshita Hiroyuki , Shiomi Hiromu , Yoshimoto Masahiro
Published: March 2009

The effects of basal-plane defects on the performance of 4H-SiC Schottky diodes using a
Ni electrode are demonstrated. Systematic characterization was performed using 4H-SiC epitaxial
layers grown by sublimation epitaxy on substrates with various off-axis angles. As the off-axis
angle increases, the ideality factor of the current-voltage characteristics increases, and the Schottky
barrier height decreases, corresponding to an increase in the number of basal-plane defects. The
reverse-bias current degrades for high off-axis samples. These results indicate that basal-plane
defects degrade the device performance. Schottky diodes that possesses good characteristics were
obtained for samples with low off-axis angles (2o- and 4o-off samples).
Device Simulation Model for Transient Analysis of SiC-SBD
Authors: Tomita Masaaki , Maeyama Yusuke , Sato M. , Fukuda Y. , Honma F. , Ono J. , Shimizu Masaaki , Iwakuro Hiroaki
Published: March 2009

We report that it seems to be necessary to select Bologna University mobility model for
accurate transient phenomenon analysis of SiC-SBD under the condition of forward surge current
because the maximum of the temperature inside SiC-SBD arises up to above 425 K. Other mobility
models seem to be mostly inadequate because they are corresponding to the experimental condition
under the temperature below 425 K.
Positron Beam Study of Co Doped ZnO Films Prepared by PLD
Authors: Ren Hong Feng , Weng Hui Min , Ye Bang Jiao , Han Rong Dian , Li Hui , Gao Chuan Bo
Published: March 2009

Slow positron beam are used to study defect structures in Co doped and undoped ZnO films prepared by Pulsed Laser Deposition (PLD) at 400°C, 600°C, 700°C on c-plane sapphire. Comparing with ZnO samples, Co doped ZnO samples have larger positron effective diffusion length (Leff), which change in different tendencies depending on the growth temperature. Crystal structures of the samples are investigated by X-ray diffraction (XRD) and wurtzite ZnO could be observed in Co doped samples.
Positron Implantation and Transmission Experiments on Free-Standing Nanometric Polymer Films
Authors: Palacio Carlos A. , De Baerdemaeker Jérémie , Segers Danny , Mostafa Khaled M. , Van Thourhout Dries , Dauwe Charles
Published: March 2009

Positron transmission experiments were performed on free-standing poly(methyl-methacrylate) (PMMA) and polystyrene (PS) films of nanometric thicknesses made by spin coating. The power_law equation z1/2(E) )=(α/ρ)En was determined from the measurements of the S-parameter as a function of the positron implantation energy. These transmission experiments indicate that n = 1.90(±0.08) and α = 1.33(±0.10) μg cm-2 which deviates from the values found by Algers et al. (n = 1.71(±0.05) and α = 2.8(±0.2) μg cm-2) and the commonly used parameters (n = 1.6 and α = 4.0 μg cm-2).
Positron Lifetime Spectroscopy on Controlled Pore Glass Porosimetry and Pore Size Distribution
Authors: Thränert Stefan , Enke D. , Dlubek G. , Krause-Rehberg Reinhard
Published: March 2009

Positron annihilation lifetime spectroscopy (PALS) is used to study a series of controlled pore glasses (CPG). The lifetime spectra were decomposed into four components using the routine LifeTime, version 9.0 (LT9). The largest lifetime τ4, which is attributed to the annihilation of ortho-positronium (o-Ps) localized at mesopores, varied at 300 K between 21 and 131 ns. The size of mesopores (mean free path), D, was determined by N2 adsorption and Hg intrusion techniques to vary between 1.8 and 56 nm. It is shown that the Tao-Eldrup model extended to cylinders of infinite length and diameter d = D describes well the experiment for an overlap parameter δ fitted to be δ = 0.193 nm. The spectra were also analyzed allowing a distribution of o-Ps lifetimes. A method is developed to calculate the pore size distribution n(d) from the τ4 distribution. This method is of particular interest since PALS is very sensitive to pores being too small to be exactly analyzed by conventional porosimetry.
Free Volumes in Polymer Nanocomposites
Authors: Chen Hong Min , Lee L. James , Yang Jin Tao , Gu Xiao Hong , Jean Yan Ching
Published: March 2009

We have employed positron annihilation lifetime spectroscopy to measure the free volumes in nanocomposites of polystyrene with addition of carbon nanofiber (CNF) and carbon dioxide as a function of composition and of temperature. We found that the glass transition temperature (Tg) increases as a function of CNF compositions but significantly decreases as the exposure of CO2. We also investigate the combination effect of CNF and CO2 and found that the CO2 significantly weakens the bonding between PS and CNF interfaces. The Tg changes are compared with DSC.
Positron Study of Carbon Black Parameters: Structure and Surface Area
Authors: Wang J. , Jobando V.O. , Quarles C.A.
Published: March 2009

Carbon black (CB) is essentially carbon in the form of extremely fine particle aggregates (100-200nm) having an amorphous molecular structure. Oil absorption or compressed dibutyl phthalate (CDBP) and iodine adsorption or nitrogen surface area (N2SA) are parameters commonly used to describe CB morphology or structure and the surface area of CB available for reaction with rubber. We have used both positron lifetime and Doppler broadening spectroscopy to study these two parameters for a variety of rubber CB composite samples. The o-Ps pickoff lifetime depends only on the type of rubber and is independent of CDBP and N2SA. However, the o-Ps lifetime intensity, I3, and the S parameter decrease with both CDBP and N2SA.
Study of the Defect Formation of Helium in Nanocrystalline Titanium Films
Authors: Long J.J. , Deng Ai Hong , Zhou Y.L. , Hou Q. , Yu X.X. , Yu J. , Cheng X. , Zhang Y.J. , Shi L.Q.
Published: March 2009

In this paper, helium-charged nanocrystalline Ti films with different bias voltages were deposited by the He-Ar magnetron co-sputtering method. XRD was used to investigate the microstructure of the He-Ti film. Meanwhile, in order to find out the factors of affecting the growth and size of helium clusters, kinetic Monte Carlo (KMC) simulation was carried out to study the growth of helium cluster, based on the simulation of helium behavior in titanium using molecular dynamics.
Development of Positron Microbeam in AIST
Authors: Oshima Nagayasu , Suzuki Ryoichi , Ohdaira Toshiyuki , Kinomura Atsushi , Narumi T. , Uedono Akira , Fujinami M.
Published: March 2009

To improve the spatial resolution of positron annihilation spectroscopy (PAS), a system to produce an intense positron microbeam was developed in AIST. A slow positron beam, which was produced by an electron linear accelerator, was focused by a lens onto a remoderator to enhance its brightness. The brightness-enhanced beam with an intensity of ≈1 × 106 e+/s was extracted from the remoderator and focused onto the sample by a lens. The beam size at the sample was 25 μm, which is more than two and half orders of magnitude smaller than that in the magnetic transport system (≈10 mm). Hence, the spatial resolution of PAS with an AIST positron microbeam can be drastically improved relative to PAS using conventional methods.
Optimization of Positron Lifetime Spectrometer Using Monte-Carlo Simulation of the Detectors
Authors: Crivelli P. , Gendotti Ulisse , Rubbia A. , Liszkay L. , Perez P.
Published: March 2009

In this paper, we present the Monte-Carlo simulation that we developed and used to design and to interpret the data of a new kind of lifetime spectrometer especially constructed for the determination of the ortho-positronium (o-Ps) re-emission yield from thin mesoporous silica films. The main issue was to have the detection efficiency independent of the o-Ps re-emission energy. This was done in order to avoid a bias of the results related to the positron implantation energy. Furthermore, the simulation is used to calculate the detection efficiencies for annihilation events yielding 2 and 3 gamma photons allowing a precise evaluation of the absolute yield of o-Ps produced in the samples. Calculations were performed using the GEANT4 package. New classes were written to describe the different decay types related to the Ps formation in matter. Moreover, the propagation and interaction of the o-Ps reemitted in a vacuum cavity were also included in the simulation.
Ortho-Positronium Reemission Yield and Energy in Surfactant-Templated Mesoporous Silica Films
Authors: Lizkay Laszlo , Corbel C. , Perez P. , Desgardin P. , Barthe Marie France , Ohdaira Toshiyuki , Suzuki Ryoichi , Crivelli P. , Gendotti Ulisse , Rubbia A. , Etienne M. , Walcarius A.
Published: March 2009

Positron annihilation gamma energy distribution, lifetime spectroscopy and time-of-flight method were used to study surfactant-templated mesoporous silica films deposited on glass. The lifetime depth profiling was correlated to Doppler broadening and 3γ annihilation fraction measurements to determine the annihilation characteristics inside the films. A set of consistent fingerprints for positronium annihilation, o-Ps reemission into vacuum, and pore size was directly determined. The lifetime measurements were performed in reflection mode with a specially designed lifetime spectrometer mounted on a slow positron beam system. The intensity of the 142 ns vacuum lifetime component was recorded as a function of the energy of the positron beam. In a film with high porosity a reemission efficiency of as high as 40 % was found at low positron energy. Positron lifetime in samples capped by a thin silica layer was used to determine the pore size. The energy of the reemitted o-Ps fraction was measured by a time-of-flight detector, mounted on the same system, allowing determination of both o-Ps re-emission efficiency and energy in the same sample. We demonstrate the potential of the simultaneous use of different positron annihilation techniques in the study of thin porous films.
A Phenomenological Description of the PALS Response in Glass - Forming Systems
Authors: Bartoš Josef
Published: March 2009

A phenomenological description of the ortho-positronium (o-Ps) response from positron annihilation spectroscopy (PALS) and the dynamics from viscosity studies on two typical glass-forming compounds within the framework of the two-order parameter (TOP) model is presented. The dynamical data are accounted for by the modified Vogel – Fulcher – Tamman - Hesse (M-VFTH) equation. Subsequently, the quasi-sigmoidal course of the o-Ps lifetime, τ3, with or without the high-temperature plateau region as a function of the temperature over a wide temperature range can be described by an effective free volume version of the TOP model. This simultaneous description suggests a close relationship between the PALS response and the dynamics of supercooled liquids and seems to support the liquid - like and solid - like domain physical picture of all the three physical states of the disordered phase of the condensed systems.
Effect of Oxygen on the Free Volume Property of Poly (Ether-Urethane) Irradiated by Neutron
Authors: Chen Zhe , Huang W. , Yu Wen , Fang Peng Fei , Wang Shao Jie , Xiong J. , Xu Y.S.
Published: March 2009

The free volume property and intermolecular interaction (especially hydrogen bonding) of poly (ether-urethane) (PEU) irradiated by neutron under different atmosphere has been studied by positron annihilation lifetime spectroscopy (PALS) and Fourier transform infrared (FTIR). The results suggested that the hydrogen-bonding interactions and free volume property in PEU depended strongly on the neutron irradiation dose.
Studying Polyamide Water Separation Film Using Slow Positron Beam
Authors: Zhang Ren Wu , Bell Patrick , Proirie Justin R. , Johnson Paul M. , Everhart Lindsay A. , Jean Yan Ching , Hu Chien Chieh
Published: March 2009

Different polyamide water separation films were prepared by interfacial polymerization by using different concentrations of Ethylenediamine (EDA)/H2O and some Trimesoylchloride (TMC)/Toluene on the modified Polyacronitrile (mPAN) substrates. By applying a slow positron beam, depth profiles of relative free volume hole sizes for different films were obtained. It was found that the hole size at the skin polyamide layer was almost identical and much smaller than that in the mPAN substrate layer. The results indicate that the thickness of the polyamide layer is the major factor in controlling the performance of a membrane during water separation.
Investigation of Free Volume in Epoxy Resins Studied by PALS
Authors: Wang Jun Jun , Wang Bo , Zhou Wei , Gong Jing , Gong Zhen Li , Yue Shao Jie
Published: March 2009

The influences of curing agents and the water absorption on the microstructure have been studied by positron annihilation lifetime spectroscopy (PALS) and gravimetric measurement for epoxy resins DER331 (E51). We found that the o-Ps lifetime 3τ dramatically decreases with the immersion time from 0h to 6h, and then reaches a saturate level in higher water absorption, while the o-Ps intensity almost remains a constant for all samples. This fact indicated that the water was first filled into free volume holes at low water content. The observation of the constant of I3 suggested that the free volume concentration was not affected by the water sorption. Experimental results indicated that both chemical reaction between the positronium and chlorines and electronegative chlorines attracting positrons can reduce the positronium formation.
Ab Initio Calculation of Electronic Structure and Magnetic Properties of Rare Earth Nitride Using LDA+U Approach: EuN and GaEuN
Authors: Kanoun-Bouayed N. , Goumri Said Souraya , Merad A.E. , Kanoun M.B.
Published: March 2009

Electronic and magnetic properties of the rare earth nitride EuN and Ga1-xEuxN (x = 0.0625) are studied with the full potential (linearized) augmented plane wave method plus local orbitals method. In this work we start our investigations by studying EuN using LDA and LDA+U. We will show the impact of LDA+U on the electronic properties. For Ga1-xEuxN we will present only the results related to the LDA+U method. It's found from the calculation of density of states (DOS) that the Eu-4f orbitals spin-polarize the host system and they are predominant in this diluted magnetic semi-conductor. The magnetic description is achieved by the calculation of spin densities difference contours and the magnetic moment.
Electrodeposition of CoNiFe Alloys on n-Type Silicon
Authors: Fortas G. , Sam S. , Fekih Z. , Gabouze N.
Published: March 2009

Co, CoNi and CoFeNi layers were formed on n-type silicon by electrodeposition method from sulfate solutions. The obtained films were characterized by Cyclic Voltammetry (CV), Scanning Electron Microscopy (SEM) and Energy Dispersive Spectrometry (EDS). The results show that the morphology and the stoechiometry of CoNi and CoNiFe deposits depend on several parameters (bath composition, applied potential…). The addition of sodium acetate as complexion agent in the bath leads to the formation of highly compacted and smooth films with a good adherence to the substrate.
Problems with Synthesis of Chalcopyrite CuIn1-xBxSe2
Authors: Olejníček J. , Darveau S.A. , Exstrom C.L. , Soukup Rodney J. , Ianno Ned J. , Kamler C.A. , Huguenin-Love James
Published: March 2009

Thin films of CuIn1-xBxSe2 (CIBS) as absorption layer in single-junction solar cells can potentially grant a higher band gap in comparison with other studied chalcopyrite materials like CuIn1-xGaxSe2 (CIGS) and CuIn1-xAlxSe2 (CIAS). The higher band gap near optimum value ~ 1.4 eV can help to achieve higher efficiency (today 19.5% for CuIn0.74Ga0.26Se2). In this paper are described first results of experiments with effort to produce CIBS films by selenization of CuInB precursor alloy in Se vapors. Resulting material was analyzed by Raman spectroscopy, X-ray diffraction, and Auger electron spectroscopy. Measurements show that formation of CIBS layer is complicated by forming of pure CuInSe2 layer with unwanted Cu2-xSe phases and by accumulation boron near to the substrate.
Improvement of Tribological Behaviour of Biomedical Nanocrystalline Titanium by Magnetron Sputtered DLC/SiC Double Layer Films
Authors: Xu Xiao Jing , Wang H. , Cheng Xiao Nong
Published: March 2009

The nano-indentation response, the film-substrate adhesion behaviors and the friction and wear properties of the DLC/SiC (diamond-like carbon/silicon carbon) double layer thin films (SiC films as interlayer) deposited on nanocrystalline titanium substrate using magnetron sputtering technique at room temperature were investigated. The results show that the DLC films exhibited a low nano-hardness (7.4 GPa) and Young's modulus (62.2 GPa) but a high hardness-to-modulus ratio (0.119). The films-substrate system displayed a good interface adhesion and a good friction/wear properties with the friction coefficient of about 0.1, the special wear rate in the magnitude order of 10−6 mm3 m−1 N−1 together with little film cracking and interface delaminating even at considerably high contact load, when sliding against Si3N4 (silicon nitride) ball using ball-on-disc wear tester under Kokubo simulation body fluid (SBF) at room temperature. The high wear-resistance is in accordance with the high ductility of the films, the good modulus match in the films-substrate system, and the high hardness-to-modulus ratio of the films. The nano-indentation response, the film-substrate adhesion behaviors and the tribological properties are in accordance and can be ascribed to the high activity of the nanocrystalline Ti substrate
Human Platelet Extracts Stimulate the Terminative Differentiation of Growth-Plate Chondrocytes in Rabbit
Authors: Yu Li , Tang Ming Qiao , Yan Wei Qun
Published: March 2009

Objective：To observe the effect of human platelet extracts on proliferation and differentiation of rabbit growth-plate chondrocytes in monolayer and fabrication of tissue engineering cartilage in vitro. Method: To determine the effects of platelet extracts at different concentrations on proliferation and differentiation of rabbit growth-plate chondrocytes using 3H-TdR、PNP and HE staining. Results: Platelet extracts had very strong stimulative effects on proliferation and differentiation of chondrocytes, especially the hypertropization (termination) of chondrocytes.
High-Cycle Fatigue Mechanisms of a NiTi Shape Memory Alloy under Different Mean Strains
Authors: Luo J.F. , Mao S.C. , Han X.D. , Chen G. , Zhang Z. , Wu M.H.
Published: March 2009

The high-cycle fatigue mechanisms of a NiTi shape memory alloy (SMA) under three different mean strains were investigated. Cold-rolled NiTi SMA specimens were heat treated at 600°C for 30min was selected to perform the fatigue test. Three samples were conducted cyclic deformation up to 2×105 cycles with three mean strains that subjected at full austenite, total stress-induced martensite (SIM) and austenite-martensite coexist status with the same strain amplitude of 0.25%. The cyclic stress-strain (CSS) curves show different cyclic softening and hardening at different mean strains. The S-S curves also reveal that cyclic deformation strain mainly occurred in martensite phase although austenite and martensite (A-M) coexisted. The transmission electron microscopy (TEM) investigation shows that slip dislocations with habit plane and basal plane dislocations were induced during the cycling, and these microstructure evolutions contribute to the cyclic softening and hardening.
Investigation of TiO2 Nanotube Electrodes: Fabrication, Annealing and Electrochemical Properties
Authors: Zhang Yun Huai , Fan Xiao Yan
Published: March 2009

Highly-ordered titania nanotube electrodes were fabricated by electrochemical anodization of pure titanium foil in potassium fluoride electrolyte. The nanotube electrodes were then annealed at different temperatures (300°C，500°C and 600°C) in air for 3 hours. The morphology and crystallinity of nanotube arrays were studied by SEM and XRD. The electrochemical properties of titania nanotube electrodes before and after annealed under different temperatures were investigated by means of cyclic voltammetry with 10mM K3[Fe(CN)6] as an electrolyte at a sweep rate of 0.1V/s.A pair of oxidation/reduction peaks was observed during the test. The results show that the higher annealing temperature, the larger oxidation/reduction peak separation. Photocurrent response was also measured in 0.01M Na2SO4 under the UV-Vis illumination.
Elemental Release from Ni-Cr Dental Alloy in Artificial Saliva and Saline Solution
Authors: Liu Jin Song , Wang Qi , Lv Chuan , Sun Jia Ning , Chen Zhi Qing , Gao Ning
Published: March 2009

The aims of this study were to quantify the elements released from a Ni-Cr dental alloy in artificial saliva and saline solution and to test whether immersion time and different immersion media are factors influencing elemental release from a nickel-based dental alloy. Standard sized Ni-Cr alloy castings were put into different immersion media (saline solution or artificial saliva) randomly. Inductively coupled plasma atomic emission spectroscopy (ICP-AES) was used to test the elemental release of the alloy at 1, 3, 7, 30 and 82 days. The surfaces of alloy were observed by scanning electron microscope (SEM). It has been found that except Ni in the artificial saliva, all the other elements remained unchanged statistically in the first week after initial release. The accumulative elemental release showed Cr in both media and Ni in the artificial saliva increased statistically in 30-day period and Ni, Cr, Be, Al, Co increased significantly in 82 days, while Mo in both media and Co in artificial saliva were not yet detected. The total mass of elements released in saline solution was greater than that in artificial saliva. Conclusion: With the immersion time increasing，more kinds of elements were released and more amount of elements released was detected in solutions. The alloy was prone to corrosion in saline solution than in artificial Saliva.
Corrosion Behavior of Magnesium Alloy AX53 in Simulated Body Fluids
Authors: Wang Jun , Zeng Rong Chang , Chen Jun , Chen Rongshi
Published: March 2009

Magnesium alloys have attracted scientists’ attention as potential implant materials, due to their excellent biocompatibility and good mechanical compatibility. Potentiodynamic electrochemical technique was applied to investigate the corrosion behavior of magnesium alloy AX53 (Mg-4.76Al-3.17Ca) in Hank's solutions, 0.9 wt% NaCl+0.7 g/L NaHCO3 solutions and 0.9 wt% NaCl solutions at room temperature. Corrosion morphologies of the alloys were observed by means of scanning electron microscope, and the chemical compositions were examined through x-ray diffraction. The results demonstrated that free corrosion potential (Ecorr) of AX53 in 0.9 wt % NaCl solution rose rapidly at initial stage, and then stabilized, whereas Ecorr of this alloy increased continuously in the other two solutions. Corrosion rates in Hank’s solutions were lower than in the other solutions. Intergranular corrosion occurred in these solutions.
Stimuli-Responsive Materials Applied as Carriers of Immobilized Enzymes
Authors: Zhang Yu , Xu Jing Liang , Yuan Zhen Hong
Published: March 2009

Enzymes, immobilized on pH/temperature/ion-responsive carriers, relieve poor contact and could be conveniently recycled as well. Enzymes were immobilized on pH-responsive carriers often by covalent method, which was better than non-covalent method (adsorption). The immobilized enzymes showed slight steric hindrance for enzymatic reaction, but always lose much activity during recycle process. The Km values were often increased significantly via immobilization on temperature/ion responsive carriers, while the immobilized enzymes expressed superior reusability. Both covalent and non-covalent methods were fit for enzymes to be immobilized on temperature-responsive carriers. Non-covalent method (entrapment) was preferential choose for enzymes to be immobilized on ion-responsive carriers. Many drawbacks, such as large activity loss and slow respondence during stimulus occurrence, seriously restrained the effect of the immobilized enzymes. It was supposed to open up special stimuli-responsive materials for enzymes immobilization, and choose proper immobilization methods, correspondingly.
Application of Inorganic Clay in Preparation of Coated Water-Transmitting Fiber
Authors: ZHANG Zengzhi , Gu Na , Wang Bo Tao , Zhang Ji Fei
Published: March 2009

Water Storage and Controlled-release Film (WSCF) material is a kind of composite film which can form a “small reservoir” in the soil to meet the need of plant growth when packed with water and embedded in soil around tree roots. Coated water-transmitting fiber is a kind of functional fiber which has effect of transmitting water in WSCF material. Different coated water-transmitting fibers were prepared by treating natural fiber using colloidal composite materials made of polyvinyl alcohol and inorganic clay such as Common clay, Kaolin or Bentonite. Furthermore, the water-transmitting capacity and surface morphology of coated water-transmitting fibers were studied by thermal multi-analyzer, instrument for quick moisture measure and SEM. The results show that coated water-transmitting fiber with continuous and compact surface has better water-transmitting capacity than those with uneven surface and the addition amount of clay also can affect the water-transmitting capacity of coated fiber. Additionally, coated water-transmitting fibers can regulate water transferring according to the variation of temperature or soil humidity.
Selective Deposition of Titanium Dioxide Thin Film on Glass Monolayers by Impregnating Method
Authors: Hu Yao Bo , Pan Fu Sheng , Wang Jing Feng
Published: March 2009

Titanium dioxide (TiO2) thin film was fabricated on the surface of glass monolayers at room temperature, using KH-550 as self-assembled monolayers (SAMs). The TiO2 gel precursor was characterized with differential scanning calorimetry – thermogravimetry (DSC-TG), and the TiO2 powder was analyzed with X-ray diffraction (XRD). The TiO2 thin film was tested with X-ray fluorescence spectroscopy (XRF). With the application of atomic force microscope (AFM) the surface topography of siloxane layer and TiO2 film were studied. Their hydrophilicities were measured. The transmittance of TiO2 film was detected by using dual beam ultraviolet - visible spectrophotometer. The results show that the TiO2 thin film is in monolayer with nanometer level, the deposition is the anatase structure. TiO2 is deposited on the surface instead of channel or gap of siloxane, the hydrophilicities of TiO2 monolayer film are perfect, and TiO2 monolayer film has a good transmissivity in the visible light area.
Surface Modification of Super-Fine Magnesium Hydroxide Powder and it’s Flame-Retardant Treatment of Flexible PVC
Authors: Du Gao Xiang , Ding Hao , Wang Bai Kun , Xue Qiang
Published: March 2009

Surface modification is very important to industrial application of the magnesium hydroxide (MDH) powder, which is used as a kind of environment-friendly flame-retardant. In this paper, a kind of MDH powder surface-modified with silicane coupling agent and stearic acid is synthesized, and its potential usage in the flame-retardant treatment of flexible PVC is studied. The influence of the surface treatment to the dispersion of the powder in PVC, the flame-retardant and other physical properties of the MDH flame-retardant treated flexible PVC are discussed in detail. The surface modification mechanism of MDH is studied by the FTIR analysis, and then the surface modification model is established. Results show that molecules between the surface of the particle and these two modifiers form stable chemical bonds, and this kind of surface modification can improve the MDH’s dispersion and the compatibility of the flexible PVC. When the flame-retardant flexible PVC is produced according to the mass composition of PVC/DOP/MDH=100:50:80 and a few other additives, its oxygen index is 31.5, the elongation at break is 240%, the tensile strength is 13.0MPa, the hypothermia tendering is +30/-0, the volume resistivity at 20°C is 3.2×1011Ω•m. These index are just correspondent with requires of the halogen-free fire-retardant flexible PVC.
Development of Alkali Activated Slag Cement Based Ecomaterial and its Environmental Coordination Evaluation
Authors: Chen Ke , Yang Chang Hui , Wu Fang , Ye Jian Xiong , Pan Qun , Yu Ze Dong
Published: March 2009

The slag is used as solid dispersing component with addition of a little amount of alkali component, a clinker free, alkali activated slag cement based ecomaterial (AASCBE) has been developed. The experiment results showed that the alkali activated slag cement based ecomaterial has excellent mechanical performances and durability, i.e., low energy consumption in manufacture, low environmental pollution, increased utilization of solid waste, enhanced efficiency of solid waste utilization, the heat from waste tyre or municipal domestic waste burning can be used for the material production, the CO2 can be recycled as a resource for the material curing and making the regeneration and recirculation possible.
LCA study of this material shows that the complex environmental index of the alkali activated slag cement based ecomaterial is 2.9337×10-12 year/ton, which takes only 19.8% of that for Portland cement or 25.9% of that for slag cement, such material has certain environmental compensation function, therefore it is a new ecomaterial with excellent environmental coordination.
Effect of Electromagnetic Stirring on Tin Bronze Plate Blank
Authors: Li Hua Qing , Xiang Chao Jian , Chen Zhong Ping , Wang Ming Pu
Published: March 2009

In the present work, the effect of electromagnetic field on the microstructure and the alloying agent distribution was investigated. Tin element was shown to have the tendency to be inversely segregated on the surface of tin bronze. The microstructures of the continuous cast tin bronze plates are coarse and inhomogeneous. The factory test parameters were determined according the simulated data. The flow behavior of the mercury to be stirred as well as the relations between the microstructure of plate blanks and the current parameters were analyzed. With an appropriate electromagnetic stirring, the inverse segregation of tin for C51900 alloy plant blank was improved by 80%, and the microstructure was refined from about 10mm to 1~3mm in grain size.