bluuebunny/crossref_metadata_2025 huggingface dataset:
Multiple Imputation for Missing Data in Life Cycle Inventory
Authors: Liu Yu , Gong Xian Zheng , Wang Zhi Hong , Liu Wei , Nie Zuo-Ren
Published: March 2009

The major environmental loads of mineral separation process in China iron production (with missing data) are analyzed. And the inner relationship between these loads data is qualified and the missing data are imputed using a statistic method called multiple imputation (MI), aimed to improve the quality of LCA datasets and allow industry to easily conduct a highly reliable LCA. By using computer simulation, MI replaces each missing value with a set of plausible values which represent the uncertainty of the missing data. The multiply imputed datasets are then analyzed by the standard procedures for completing data and combining the results from these analyses. The result proves that MI Method is an effective and reasonable method to solve the problem of missing data and therefore can ensure the validity and reliability of LCA.
The Controlling Factors in the Content of Cr6+ in Green Strontium Ferrite
Authors: Chen Nan Chun , Ao Han Mei , Zhan Zhi Liang
Published: March 2009

In order to reach the standard of the RoHS that the content of Cr6+ lower than 200ppm in ferrite, this reserch focused on the factors that influence on the content of Cr6+ during the preparation of Strontium Ferrite. The results show that the content of Cr6+ in Strontium Ferrit can be controlled among 91~117 ppm, and the optimum condition is as follows: the quality ratio of raw materials/graphite=10:1.25, the rate of the N2 flow 0.1~0.15 L/min, sintered temperature 950~1020°C, residence time 25~35min at the corresponding temperature point, granularity of the mixed system lower than 0.1~0.3mm.
Preparation and Characterization of TiO2 Nanowires on Aluminum Substrate
Authors: Wang Hui , Dai Dan , Zhang Xin , Wu Xue Dong
Published: March 2009

Combined with sol-gel method, ultrasonic impregnation approach was employed to prepare TiO2/ Al2O3 surface composite on aluminum. The results showed that with the effect of ultrasonic, the TiO2 colloid fabricated by sol-gel method can enter the inner of the ordered AAO film to form anatase TiO2 nano wires after being heated at 500°C for 2h. The diameters and lengths of TiO2 nano wires were controlled by the diameter and thickness of AAO film. Close to the bottom of aluminum substrate, the TiO2 nano wires became nano pipes, plates and particles.
Thermoelectric Properties P-Type Si-20 at % Ge by Addition of TiN Nanoparticles
Authors: Wang Zhong , Chen Hui , Chu Ying , Cheng Yan , Zhu Lei , Jian Xu Yu , Yu Hai Jun
Published: March 2009

SiGe alloy composite material including TiN nanoparticle were prepared. The TiN nanoparticles as the inert scattering center were fabricated by Nitrogen plasma-metal reaction. The sintered samples were characterized by electrical resistivity and seebeck coefficient measurement. Adding nanophase inclusion into the SiGe alloy matrix, the Seebeck coefficient increased, the electrical conductivity decreased and the electrical power factor only slightly reduced.
Research on Technology of Blast Furnace Energy Saving and Optimization of Operation Principle
Authors: Yang Shuang Ping , Sun J.
Published: March 2009

By study the development situation of blast furnace smelting in china and the blast furnace operation system and technology, combined with production conditions of JISC BF, based on a large number of the production data, the comparison analysis test on JISC BF operation system and technology was did. Through continuously optimization and practice, the relatively suitable operation system and technology of JISC BF at present was explored, which could reduce the coke ratio into furnace while increasing the coal injection ratio and making great economic effect.
Deposition and Characterization of GaN Films on ITO Glass Substrates by PECVD
Authors: Yuan Jin She , Yu Guo Hao , Yang Chang Min , Wang Ming Yue
Published: March 2009

The GaN film deposited on ITO glass substrate by PECVD was characterized using XPS, SEM and reflectance spectra. XPS analysis indicated that the chemical status of the film surface was predominated in mixture phase of GaN and Ga2O3. It was observed that Tthe film annealed at 400°C exhibited platelet-shaped and hexagonal structure and c-plane textured morphology from SEM images. The reflectance spectra show that the absorption cutoff wavelength of the sample annealed at 400 °C was broadened to 1100nm roughly. From the results, Iit is concluded that the GaN film grown on ITO glass substrate by PECVD will be a promising full spectra material.
Preparation and Properties of Alginate Salt Fibers: An Inherent Flame-Retardant, Biodegradable Fiber
Authors: Kong Qing Shan , Ji Quan , Yu Jian , Xia Yan Zhi
Published: March 2009

Alginate calcium fibers were prepared through wet spinning with good tensile strength which can be used for cloth materials. The morphology, mechanical property and combustion property of alginate calcium fibers were investigated. Blending yarns and textile of alginate calcium fibers and combed cotton was fabricated with good hand feeling and strength. Alginate salt fiber was prepared with wet spinning machine designed according to viscose fiber spinning machine. The diameter of alginate calcium fibers was about 10-15µm in diameter with smooth surface. The tensile strength of alginate salt fiber was larger than 4.8 cN in the dry state. The value of Limited Oxygen Index (LOI) of alginate calcium fibers was 34%. The average heat release rates (HRR) of the alginate fiber is about 21 kW/m2 which was much lower than that of most synthetic and natural fibers analysized with Cone. Alginate calcium fibers is an inherent flame-retardant fiber.
Investigation on Lithiation Mechanism of Interphase Ni3Sn4 Alloy Used as Anode Material for Lithium-Ion Batteries
Authors: Hou Xian Hua , Hu She Jun , Yu Hong Wen , Zhao Ling Zhi , Ru Qiang , Tan Chun Lin , Li Wei Shan
Published: March 2009

Sn-based anode materials have poor cycling performance due to mechanical fatigue caused by volume expansion during lithium insertion and extraction processes. In this work, the mechanism of lithium insertion/extraction in the Ni3Sn4 alloy electrode is investigated using the first-principle plane-wave pseudopotential and experimnetal method. The calculated results indicate that the Ni3Sn4 alloy phase has relatively minor expansion ratio and fluctuating electrochemical potential, which the tendency is consistent with the experimental result. On the other hand, the Sn-Ni alloy thin films with different tin content are prepared by electrodepostion on copper as an anode for lithium-ion batteries. The structural and electrochemical characteristics of Sn-Ni alloy are examined using X-ray diffraction (XRD) and repeated constant current charge/discharge (CC). The results show Tthheat Ni3Sn4 alloy phase has best cyclic stability during the lithium insertion and extraction processes.
Using Demercurated Lighting Phosphor and MSWI Scrubber Residues to Prepare High Performance Plastic Concrete
Authors: Huang Wu Jang , Chu Wei , Hsieh Ling Hui , Chen Jian Guo
Published: March 2009

This study aimed to prepare a high performance plastic concrete made of epoxy resin and Portland type-I cement mixed with at least one inorganic solid waste of demercurated lighting phosphor powder or municipal solid waste incineration scrubber residue. The ratio between liquid epoxy resin and cement was 1:2; the scrubber residue and demercurated phosphor powder were added as modifiers for cement component in order to improve the strength and thermal properties of synthesized plastic concrete. The results indicate that, the addition of scrubber residue causes a decrease in both strength and thermal properties; whereas, the demercurated phosphor powder can replace 100% of the contents of cement without any significantly change in either strength or thermal properties. Atomic force microscopy and Raman spectroscopy were used to characterize the chemical structure of cured concrete and the results indicate that the surface softness increases with an increase in the mixed percentage of epoxy resin.
Investigation of Nano/Microcrystalline Diamond Composite Films for Thermal Applications
Authors: Guan Yu Lan , Dai Wen Qi , Wang Lin Jun , Huang Jian , Lai Jian Ming , Tang Ke , Xia Yi Ben
Published: March 2009

A newly developed nano/microcrystalline diamond composite film for thermal applications was prepared in this investigation. A microcrystalline diamond (MCD) film was deposited onto silicon substrate by hot filament chemical vapor deposition (HFCVD) method, and then a nanocrystalline diamond (NCD) film was grown onto this MCD film to obtain a NCD/MCD composite film. The root-mean-square (RMS) value of surface roughness for the composite film estimated from the atomic force microscope image was 42.7nm. Compared with 85.9nm for the MCD film. And it was also found that the thermal diffusivity increased from 32.61mm2/s to 37.63mm2/s by further growing a NCD film. Results indicated that the deposition of NCD film reduced the rough surface of the MCD film with grain sizes of the order of microns, and thus increased the efficiency of diamond films as thermal spreading device. It was found that the NCD/MCD composite film had a smoother surface and a higher thermal diffusivity compared with MCD film.
Nano Effects of Helium Plasma Treatment Nano SiO2 Coating Kevlar Filaments
Authors: Zou Jing , Zhang Ying Chen , Wu Hong Yan , Qiu Y.P.
Published: March 2009

The strain rate sensitivity of helium plasma treated Nano Silicon Dioxide particles sol-gel coating Kevlar filaments (HPTNSDPKEVLAR) and concurrent micro-structural evolution. The results of SEM observation and contact angle analysis showed that the treated Kevlar filament had a rougher surface and lower contact angles than the untreated one. According to the FTIR results, the change of wettability was attributable to the amount of polar functional groups on the fiber surface introduced by the treatments. Moreover, the changes of physico-mechanical properties by HPTNSDPKEVLAR were analyzed by using tensile test at different strain rates range from ranging from 0.01 s-1 to 0.6 s-1. It was found that the materials were strain rate sensitive, and both the tensile strength and failure strain increased with increasing strain rate. The dependence of yield stress by HPTNSDPKEVLAR with strain rate followed Eyring’s equation, and may be characterized by implying the similarity in the onset of plastic deformation.
Nano Effects of Helium-Plasma Treatment Nano-SiO2 Coating Vectran
Authors: Zhang Ying Chen , Huang J.N. , Wu Hong Yan , Qiu Y.P.
Published: March 2009

The plasticity treatment of APPJ on microstructure and tensile deformation of Nano SiO2 coating Vectran in the dynamic states was investigated by specialized tensile testing at room temperature. With the addition of low-temperature Helium plasma treatment, Young's modulus and yield stress changed. It was found that micro structural parameter such as the activation volume was important to describe the Nano SiO2 coating Vectran and inter-phase strength between filaments and coating. The results of different APPJ treatments on the Nano SiO2 coating Vectran showed the change of the rate sensitivity of the filaments. The flow stress dependence of the strain rate sensitivity indicated that dynamical recover processes associated with the dislocation-dislocation interactions, which develop in the APPJ treatment Nano SiO2 coating Vectran and Vectran after small amount of deformation, leaded to strain localizations and early failure. Results revealed that APPJ treatment Nano SiO2 coating Vectran and the inter-phase would enhance the ductility of Vecetran at room temperature.
Nano Effects of Oxygen-Plasma Treatment Nano-SiO2 Sol-Gel Coating T-300 Carbon Fiber
Authors: Zhu Hai Yan , Zhang Ying Chen , Wu Hong Yan , Qiu Y.P.
Published: March 2009

The purpose of the present work was to investigate the effects of oxygen-plasma treatment on tensile deformation of nano-SiO2 sol-gel coating T-300 carbon fiber (HONS3C) were studied and a new concept for the nano-structural interphase between fiber surface and nano-coating provided in the paper. The tensile test results showed that besides the enhanced ductility of T-300 carbon fibers by nano-SiO2 sol-gel coating the T-300 carbon fibers treated by oxygen-plasma, the activation volumes of T-300 carbon fibers untreated and treated with oxygen-plasma ranging from 681.9628 to 32342(nm)3 by following Eyring’s equation were important descriptors for the properties of the nano-structural interphase between fiber surface and nano-coating, From the results of SEM and FTIR, it was observed that the uniform dispersion of the nano-SiO2 coating of the T-300 carbon fibers treated by oxygen-plasma not only formed a protective layer to cover the fibers, but also introduced the activated functional groups on the fiber surfaces.
Choice of Bubble Radius in Floatation Refining of Magnesium Alloy
Authors: Su Zhong Hua , Xie Wei Dong , Peng Xiao Dong , Yang Yan , Wei Qun Yi
Published: March 2009

The species and shapes of impurities in magnesium alloy melt were studied. Floatation Refining method of Magnesium Alloys melt and eduction dynamics analysis were used to judge the floatation condition of gas bubble with MgO impurity. Models of floatation eduction were established to study the dynamics relationship of weight, drag and buoyancy. The relation curve between refining gas bubble radius and floating up rate was established. The choice method of gas bubble radius was provided and a practical process scheme proposed for floatation refining of magnesium alloys melt.
Effect of Solid Solution Time on the Microstructure and Mechanical Properties of AZ81-4Gd Magnesium Alloy
Authors: Guo Quan Ying , Mao Ping Li , Liu Zheng , Sun Jing , Wang Chang Yi , Wang Feng , Lin Li
Published: March 2009

The effect of solid solution treatment at temperature of 415oC and different holding time prior aging at 168oC for 16 hours on the mechanical properties and microstructure of AZ81-4Gd magnesium alloy were analyzed by X-ray and SEM. The results demonstrated that with increasing the solid solution time the primary β-Mg17Al12 phase dissolve in the matrix eventually. While the holding time increases to 20 hrs, the primary β-Mg17Al12 phase was completely vanished, but Al2Gd phase kept unchanged with increasing the holding time. In the mean while, the volume fraction of the β-Mg17Al12 phase precipitated during aging increased at first with increasing the holding time then decreased. Moreover, subgrains and twins began to form within the α grain matrix when the solid solution time increased to 12hrs, and the subgains parallele with each other or in the shape of oval. Increasing the solid solution time to 20 hrs the microstructure change dramatically and consist of very fine recrystallized α grains. Futher increasing the holding time the recrystallized grain size increased accordingly. The mechanical properties testing results showed that when the solid solution time increased to 24 hrs the ultimate tensile strength of AZ81-4Gd magnesium alloy was 270 MPa and the elongation was 11.6% respectively.
Comparison of Microstructure and Mechanical Properties between ZM21 and ZME210 with Different Hot Extrusion Ratios
Authors: Peng Jian , Song Cheng Meng , Zhao Ya Zhong , Pan Fu Sheng
Published: March 2009

The mechanical properties and microstructure of the as-extruded ZM21 magnesium alloy and its modified alloy ZME210 with addition of 0.35wt% cerium were investigated with different extrusion ratios from 14 to 182 by using mechanical property test, microscopic structure quantitative analysis, SEM observation and energy spectrum analysis. The results showed that both ZM21 and ZME210 had an extrusion ratio limit for grain refining, and the grains were found to be finer with higher extrusion ratio when the ratio was not higher than the limit value. The extrusion ratio limit for the best effect for grain refining of ZME210 is lower than that of ZM21. It was found that the Ce can refine the grains effectively after hot extrusion with different extrusion ratios. The effects of Ce on the microstructure and mechanical properties were analyzed.
Mechanical Properties and Microstructures of Mg-Al-Zn Alloys with High Aluminum Contents
Authors: Li Xing Gang , Zhang Kui , Li Yong Jun , Zhao Xin , Mi Xu Jun
Published: March 2009

The effect of Al contents on the properties and structures of AZ80, AZ91，AZ131 and AZ151 magnesium alloys has been studied. The experiments of homogenization treatment, hot extrusion, and annealing treatment are carried out in order to study the effects of these processes to the properties and structure of AZ80, AZ91, AZ131 and AZ151 magnesium alloys. The parameters of homogenization treatment (420°C×24h, 420°C×36h) determined by DSC and metallurgical photo are sufficient which ensure the eutectic phase melt into magnesium matrix greatly. The strength of extruded bars shortly after homogenization treatment increase (Rp0.2 from 232 to 310MPa), but elongation decrease (A from 12 to 2.5%) with Al contents. The differences and causes of structure and mechanical properties of extruded bar after the process of aging are analyzed in detail by tensile experiments, hardness measurement, and optical observation.
Microstructure and Mechanical Properties of an Mg-Zn-Zr Alloy Modified by Rare Earth of Erbium
Authors: Zhang Jing , Zhang Xu Feng , Pan Fu Sheng , Liu Chuan Pu , He Qu Bo
Published: March 2009

The microstructures, mechanical properties, and formability of an Mg-1.5Zn-0.1Zr alloy with rare earth element of Erbium addition have been examined by using optical microscopy, scanning electron microscopy/energy dispersive X-ray spectroscopy, and thermal mechanical testing. The results showed that Erbium combined with Mg and impurity elements forming small particles dispersed on the matrix. Therm-mechanical simulation in the temperature range from 250°C to 400°C and strain rate from 0.1 to 1.0 indicated that the flow stress decreases with the increase of the temperature and the decrease of the strain rate. Sheet samples were prepared through ingot casting, hot rolling, cold rolling, and intermediate annealing. Remarkable grain size refinement was realized through recrystallization during the rolling process. Good combination of strength and ductility was achieved by applying intermediate annealing before the very last cold rolling. Further improvement of ductility and formability could be obtained by conducting proper heat treatment on the finishing cold-rolled sheets.
Research on the Rolling of AZ31 Strip Prepared by Twin Roll Casting
Authors: Wang Jian , Jiang Bin , Ding Pei Dao , Huang Guang Jie , Pan Fu Sheng
Published: March 2009

The AZ31 thin sheet (minimum thickness less than 1mm) was obtained by rolling the cast strip which was prepared by vertical twin roll casting in this paper. Since the absolute deformation during rolling was smaller,due to the small thickness of the strip of 3mm, the rolling of cast strip was different from the conventional rolling process. It was found that homogenizing time at 400°C for the cast strip was 4h and reduction per pass should be 8-10% for producing thinner (1-1.5mm) rolled AZ31 sheet at 350°C. Mechanical properties of the sheet were equivalent to conventional rolling sheet’s.
Friction and Wear Properties of Magnetron Sputtered DLC/SiC Films on Magnesium Alloy
Authors: Xu Xiao Jing , Xia Deng Fu
Published: March 2009

The nano-indentation response and the friction/wear properties of DLC/SiC (diamond-like carbon/silicon carbon) double layer thin films deposited on Mg alloy (AZ91D) substrate using magnetron sputtering technique at room temperature were investigated. The results show that the DLC films displayed low nano-hardness (3.05 GPa), low Young's modulus (24.67 GPa) but high hardness-to-modulus ratio (0.124). The films-substrate system exhibited a good friction and wear properties with the mean friction coefficient of about 0.175, the special wear rate in the magnitude order of 10−6 mm3 m−1 N−1 together with little film-cracking and interface-delaminating, when sliding against Si3N4 (silicon nitride) ball using ball-on-disc wear tester under dry frictional condition. The high wear-resistance is in accordance with high ductility of the films, good modulus match in the films-substrate system, and high hardness-to-modulus ratio of the films. The underlying factors are discussed and are believed to be due to the substrate is Mg, a metal with high activity.
Structures of Zinc-Manganese Phosphate Film and Organic Coating on Magnesium Alloys
Authors: Lan Wei , Sun Jian Chun , Zhou An Ruo , Zhang Ding Fei
Published: March 2009

The solution mainly containing Zn2+, Mn2+, Ni2+ and H2PO4- was used to prepare phosphate film on AZ31 magnesium alloys. The process was adjusted to the following parameters, PH value 3～4, temperature 25～40°C, treatment time 3～10 min. Surface characteristics and microstructure of the phosphate film were also investigated by SEM and XRD. The film can fit for organic coatings prepared with electrophoresis and painting.It is found that the coatings adhered well to the phosphate film, and the anti-corrosion abilities were improved. The coating has no change in 3% NaCl solution for 360h and in neutral salt fog for 168h, respectively.
The Anticorrosive Properties of Sol-Gel Coating on AZ31 Magnesium Alloy
Authors: Hu Yao Bo , Pan Fu Sheng , Wang Jing Feng , Peng Jian
Published: March 2009

Titanium dioxide (TiO2) and silicon dioxide (SiO2) coating deposition were respectively performed by the dip coating technique on magnesium AZ31 alloy with extrusion surface finishes. The anticorrosive effect of different sol-gel coating was compared by measuring the weight loss when the samples were immerged in atmosphere, acetic acid aqueous solution with pH 5.0, distilled water with pH 6.4, aqueous 5% sodium chloride solution with pH 7.0. Morphological and structural characteristics of the coatings were analyzed by scanning electron microscopy (SEM), and semi quantitative analyses of the composition were performed by energy dispersive X-ray analysis (EDX) line scans. The results show that the anticorrosion properties of magnesium alloy with SiO2 or TiO2 are magnificently impactful in atmosphere. The anticorrosion effect of TiO2 coating is much preferable in a relatively strong acid environment.
Turning of Basal Plane Dislocations during Epitaxial Growth on 4° Off-Axis 4H-SiC
Authors: Myers-Ward Rachael L. , VanMil Brenda L. , Stahlbush Robert E. , Katz S.L. , McCrate J.M. , Kitt S.A. , Eddy Charles R. , Gaskill D. Kurt
Published: March 2009

Epitaxial layers were grown on 4° off-axis 4H-SiC substrates by hot-wall chemical vapor deposition. The reduced off-cut angle resulted in lower basal plane dislocation (BPD) densities. The dependence of BPD reduction on growth conditions was investigated using ultraviolet photoluminescence (UVPL) imaging. With this method, it was found that the dislocations were converting to threading edge dislocations throughout the thickness of the film. A high (≥ 97%) conversion efficiency was found for all films grown with this orientation. A conversion of 100% was achieved for several films without pre-growth treatments or growth interrupts.
PL Imaging Study of In-Grown Stacking Faults in 4H-SiC Epitaxial Layer
Authors: Hattori Ryo , Shimizu R. , Chiba I. , Hamano K. , Oomori Tatsuo
Published: March 2009

Two types of in-grown stacking faults in 4H-SiC epitaxial layers (SFs) were investigated using a new photoluminescence (PL) topographic imaging system, macro/micro PL mapping system, TEM and molten KOH etch pit observation. Shockley type SFs (SSFs) of 3C and 8H inclusion were identified as two different types of triangular PL emission patterns with corner angle of 60° and 30° spreading to the <11-20> down step direction. The peak wavelengths are 423nm and 465nm, respectively. The 60° triangular SSFs are 3C inclusion related with threading edge dislocations. The 30° triangular SSFs are 8H inclusions related with basal plane dislocations. Such SFs are caused by dislocation- related disturbance of the step flow growth resulting in insertion of new cubic sites in between the 4H hexagonal turns. The substrate surface roughness at the early stage of the epitaxial growth and the growth rate may correlate with the might be deeply related in the SFs formation of SFmight be deeply related in the SFs.
On-Axis Homoepitaxy on Full 2” 4H-SiC Wafer for High Power Applications
Authors: ul Hassan Jawad , Bergman Peder , Henry Anne , Brosselard Pierre , Godignon Philippe , Janzén Erik
Published: March 2009

Homoepitaxial growth has been performed on Si-face nominally on-axis 4H-SiC substrates. Special attention was paid to the surface preparation before starting the growth. Si-face polished surfaces were studied after etching under C-rich, Si-rich and under pure hydrogen ambient conditions. In-situ surface preparation, starting growth parameters and growth temperature are found to play a vital role to maintain the polytype stability in the epilayer. High quality epilayers with 100% 4H-SiC were obtained on full 2” wafer. Complete PiN structure was grown and more than 70% of the diodes showed a stable behavior and the forward voltage drift was less than 0.1 V. Also, a comparison of the electroluminescence images of diodes before and after heavy injection of 125 A/cm2 for 30 min did not show any sign of stacking fault formation in the device active region.
Silicon Carbide Crystalline Films Synthesis out of Organosilicon Monomers Vapors in Reactor with Cold Walls
Authors: Sinelnikov Boris M. , Tarala Vitaly A. , Mitchenko Ivan S.
Published: March 2009

The possibility of silicon carbide films production out of organosilicon chlorine-containing monomers is under analysis in this research. Silicon carbide films samples were produced by chemical deposition method out of gas phase in reactor with “cold walls”, in the conditions of low pressure. The influence of monomer type, substrate temperature on crystalline SiC films composition is also under consideration. The results of infrared spectroscopy, Raman scattering spectrometry and x-ray phase analysis are presented.
Effects of Temperature and Heating Rate on the Precipitation of 3C-SiC Islands on 4H-SiC(0001) from a Liquid Phase
Authors: Kim-Hak Olivier , Ferro Gabriel , Dazord Jacques , Chaudouët Patrick , Chaussende Didier
Published: March 2009

Like on 6H-SiC substrates, 3C-SiC islands precipitation was found to be the initial stage of the VLS growth of 3C-SiC layers on 4H-SiC surfaces. This precipitation happens between 1100 and 1200°C with a heating rate of 2.8°C.s-1, without addition of propane. The islands size increases in a similar manner whether the final temperature increases (for a given heating rate) or the heating rate decreases (for a given final temperature). This enlargement can give rise to a complete cubic layer for the highest temperatures or the slowest heating rates. It is suggested that the carbon atoms involved in the enlargement process (after the nucleation) come from the graphite crucible.
Structural and Electronic Properties of Epitaxial Graphene on SiC (0001)
Authors: Riedl Christian , Starke Ulrich
Published: March 2009

The structural and electronic properties of epitaxial graphene on SiC(0001) are investigated by low energy electron diffraction (LEED) and angle resolved ultraviolet photoelectron spectroscopy (ARUPS). Fingerprints in the spot intensity spectra in LEED allow for the exact determination of the number of layers for the first three graphene layers after being correlated with the electronic bandstructure obtained from ARUPS using He II excitation. Our analysis includes the consideration of samples with different doping levels. A possible influence of the polytype 4H- or 6H-SiC is discussed. LEED by itself turns out to be an easy and practical method for the thickness analysis of epitaxial graphene on SiC(0001).
In Situ Observation of Polytype Switches during SiC PVT Bulk Growth by High Energy X-Ray Diffraction
Authors: Wellmann Peter J. , Konias Katja , Hens Philip , Hock Rainer , Magerl Andreas
Published: March 2009

This work reports on the in-situ observation of a polytype switch during physical vapor transport (PVT) growth of bulk SiC crystals by x-ray diffraction. A standard PVT reactor for 2” and 3” bulk growth was set up in a high-energy x-ray diffraction lab. Due to the high penetration depth of the high-energy x-ray beam no modification of the PVT reactor was necessary in order to measure Laue diffraction patterns of the growing crystal with good signal to noise ratio. We report for the first time upon the in-situ observation of polytype switching during SiC bulk PVT growth.
Study of the Electrical Characteristics of the CNT/SiC Interface
Authors: Castellino Micaela , Bianco Stefano , Perrone Denis , Musso Simone , Giorcelli Mauro , Maccioni Gabriele , Ferrero Sergio , Scaltrito Luciano , Tagliaferro Alberto
Published: March 2009

Vertically aligned multiwall carbon nanotubes were directly grown by means of thermal Chemical Vapor Deposition onto epitaxial and bulk double side polished 4H-SiC substrates. Their structure and morphology have been examined through Field Emission Scanning Electron Microscopy and Raman spectroscopy. The results have been compared with CNTs carpets grown in the same conditions on Si substrates. Preliminary analysis of their electrical properties has been performed using the four-point probe technique in order to evaluate their resistivity.
Characterization of Screw Dislocations in a 4H-Silicon Carbide Diode Using X-Ray Microbeam Three-Dimensional Topography
Authors: Tanuma Ryohei , Tamori Tae , Yonezawa Yoshiyuki , Yamaguchi Hirotaka , Matsuhata Hirofumi , Fukuda Kenji , Arai Kazuo
Published: March 2009

This paper describes the study of non-hollow-core elementary screw dislocations (SDs) in silicon carbide (SiC) diodes using X-ray microbeam three-dimensional topography. Strain analysis shows that typical screw dislocations having a symmetric strain field tend to cause microplasma breakdown, whereas deformed SDs do not. The symmetry break in SDs will relax the focussing of strain and lessen the formation of defects, thereby leading to the desirable non-leak property.
Photoluminescence-Topography of the p-Type Doped SiC Wafers for Determination of Doping Inhomogeneity
Authors: Oehlschläger Felix , Juillaguet Sandrine , Peyre Hervé , Camassel Jean , Wellmann Peter J.
Published: March 2009

Photoluminescence(PL)-topography is a powerful method to determine the charge carrier concentration of SiC-wafers. The following work describes the development of a PL-topography method for the determination of charge carrier distribution in p-type SiC and shows the correlation of PL-Intensity and charge carrier concentration. With this setup it is possible to characterize wafers up to a size of 2” at room- and low temperature in a non-destructive way.
Polytype and Crystal Quality of SiC Crystals Grown on 3C-SiC by Seeded Solution Method
Authors: Seki Kazuaki , Tanaka Ryo , Ujihara Toru , Takeda Yoshikazu
Published: March 2009

We investigated the effects of the solution growth process on the polytype and crystal quality of the crystals grown on (111) 3C-SiC seed crystals. In spite of the use of 3C-SiC seed crystals, the polytype of the grown crystal changed from 3C-SiC to 6H-SiC, because the stacking errors easily occur due to the similarity of the (111) face of 3C-SiC and the (0001) face of 6H-SiC. Moreover, the grown 6H-SiC crystal affected the crystal quality of the seed crystal, i.e., high-density stacking faults were induced in the seed crystal after the growth process.
Temperature Dependence of Hole Impact Ionization Coefficient in 4H-SiC Photodiodes
Authors: Loh W.S. , David John P.R. , Ng B.K. , Soloviev Stanislav I. , Sandvik Peter M. , Ng J.S. , Johnson C. Mark
Published: March 2009

Hole initiated multiplication characteristics of 4H-SiC Separate Absorption and Multiplication Avalanche Photodiodes (SAM-APDs) with a n- multiplication layer of 2.7 µm were obtained using 325nm excitation at temperatures ranging from 300 to 450K. The breakdown voltages increased by 200mV/K over the investigated temperature range, which indicates a positive temperature coefficient. Local ionization coefficients, including the extracted temperature dependencies, were derived in the form of the Chynoweth expression and were used to predict the hole multiplication characteristics at different temperatures. Good agreement was obtained between the measured and the modeled multiplication using these ionization coefficients. The impact ionization coefficients decreased with increasing temperature, corresponding to an increase in breakdown voltage. This result agrees well with the multiplication characteristics and can be attributed to phonon scattering enhanced carrier cooling which has suppressed the ionization process at high temperatures. Hence, a much higher electric field is required to achieve the same ionization rates.
Deep Levels Generated by Ion-Implantation in n- and p-Type 4H-SiC
Authors: Kawahara Koutarou , Alfieri Giovanni , Kimoto Tsunenobu
Published: March 2009

The authors have investigated deep levels in the whole energy range of bandgap of 4H-SiC, which are generated by N+, P+, Al+ implantation, by deep level transient spectroscopy (DLTS). Ne+-implanted samples have been also prepared to investigate the pure implantation damage. In the n-type as-grown material, Z1/2 (Ec – 0.63 eV) and EH6/7 (Ec – 1.6 eV) are dominant deep levels. When the implant dose is low, seven peaks (IN1, IN3 ~ IN6, IN8, IN9) have emerged by implantation and annealing at 1000oC in the DLTS spectra from all n-type samples. After high-temperature annealing at 1700oC, however, most DLTS peaks disappeared, and two peaks, Z1/2 and EH6/7 survive. In the p-type as-grown material, D center (Ev + 0.40 eV) and HK4 (Ev + 1.4 eV) are dominant. When the implant dose is low, two peaks (IP1, IP3) have emerged by implantation and annealing at 1000oC, and four traps IP2, IP4 (Ev + 0.72 eV), IP7 (Ev + 1.3 eV), and IP8 (Ev + 1.4 eV) are dominant after annealing at 1700oC.
The Influence of Growth Conditions on the Annealing of Irradiation Induced EH6,7 Defects in 4H-SiC
Authors: Pintilie Ioana , Løvlie Lars S. , Irmscher K. , Wagner Günter , Svensson Bengt Gunnar , Thomas Bernd
Published: March 2009

Nitrogen doped 4H-SiC epitaxial layers grown by hot-wall chemical vapor deposition were investigated by deep level transient spectroscopy after irradiation with 6 MeV electrons or 1.6 MeV protons. The influence of silane and propane flows used during the epilayers growth on the behaviour of radiation induced EH6,7 levels is studied. Samples grown under different conditions were investigated: 1 sample grown in steps of different C/Si ratio obtained by changing the propane flow only; 1 sample grown in steps of different C/Si ratio obtained by changing the silane flow only; 2 samples grown with a C/Si ratio of 1.5 but with different flows of propane and silane. These investigations revealed that the low thermal stability of EH6,7 (the defects anneal out at temperatures as low as 750K) is due to the magnitude of silane flow used during the growth irrespective of the C/Si ratio. A possible structure of the EH6,7 defect is discussed.
Nanoimaging in SiC and Related Materials: Beyond Surface Morphology to Charge Transport and Physical Parameters Mapping
Authors: Raineri Vito , Giannazzo Filippo , Roccaforte Fabrizio
Published: March 2009

We describe the potential use of scanning probe microscopy (SPM) to image at nanoscale the charge transport in conductive layers, through dielectrics and barriers and in general for mapping of physical properties in wide band gap materials, processing and devices. Measurements through conductive layers are described discussing the limits and potentialities. Carrier profiling by SPM is presented and critically discussed as a complex method, crossing information from several techniques, to extract more insights related to carrier distribution.
Interface States and Barrier Heights on Metal/4H-SiC Interfaces
Authors: Khanna Shaweta , Noor Arti , Tyagi Man Singh , Neeleshwar Sonnathi
Published: March 2009

Available data on Schottky barrier heights on silicon and carbon rich faces of 4H-SiC have been carefully analyzed to investigate the mechanism of barrier formation on these surfaces. As in case of 3C and 6H-SiC, the barrier heights depend strongly upon method of surface preparation with a considerable scatter in the barrier height for a given metal-semiconductor system. However, for each metal the barrier height depends on the metal work function and strong pinning of the Fermi level has not been observed. The slopes of the linear relation between the barrier heights and metal work functions varies over a wide range from 0.2 to about 0.75 indicating that the density of interface states depends strongly on the method of surface preparation. By a careful examination of the data on barrier heights we could identify a set of nearly ideal interfaces in which the barrier heights vary linearly with metal work function approaching almost to the Schottky limit. The density of interface states for these interfaces is estimated to lie between 4.671012 to 2.631012 states/ cm2 eV on the silicon rich surface and about three times higher on the carbon rich faces. We also observed that on these ideal interfaces the density of interface states was almost independent of metal indicating that the metal induced gap states (MIGS) play no role in determining the barrier heights in metal-4H-SiC Schottky barriers.
Crystalline Quality and Surface Morphology of 3C-SiC Films on Si Evaluated by Electron Channeling Contrast Imaging
Authors: Picard Yoosuf N. , Locke Christopher , Frewin Christopher L. , Twigg Mark E. , Saddow Stephen E.
Published: March 2009

Electron channeling contrast imaging (ECCI) has been utilized to evaluate the surface morphology and crystalline quality of 3C-SiC films grown by chemical vapor deposition (CVD) on (100) and (111) Si substrates. ECCI in this study was performed using an electron backscatter diffraction (EBSD) system equipped with forescatter diode detectors and mounted inside a commercial scanning electron microscope (SEM). This nondestructive method permits direct dislocation imaging through local fluctuations in forescattered electron yield attributable to lattice strain. Coordinated ECCI, SEM, and EBSD analysis of film surfaces allowed correlations between film orientation, surface morphology, and dislocation behavior. Evidence of lateral dislocations parallel to <110> directions and atomic step pinning by dislocations was observed.
Investigation of Si/4H-SiC Hetero-Junction Growth and Electrical Properties
Authors: Guy Owen James , Pérez-Tomás Amador , Jennings Michael R. , Lodzinski Michal , Castaing A. , Mawby Philip  Andrew , Covington James A. , Wilks S.P. , Hammond R. , Connolly D. , Jones S. , Hopkins J. , Wilby T. , Rimmer N. , Baker K. , Conway S. , Evans S.
Published: March 2009

This paper describes the growth and characterisation of Si/SiC heterojunction structures. Heterojunction structures are of interest for low on-resistance diodes and as potential solutions to fabricating SiC MOS devices with lower interface state densities. The formation of the Si/SiC heterojunction using Chemical Vapour Deposition (CVD), Molecular Beam Epitaxy (MBE), Electron Beam Evaporation under UHV conditions (EBE-UHV) and Layer Transfer (LT) are reported. The physical nature of Si/SiC structures has been investigated using scanning electron microscopy (SEM). Results of electrical characterisation of the Si/SiC heterojunctions, are also reported. Finally, thermal oxidation of a Si / SiC heterojunction structures has been performed. The C(V) characteristics of the resulting oxides are compared to conventional thermal oxides on SiC.
Nitrogen Doping of 3C-SiC Single Crystals Grown by CF-PVT
Authors: Eid Jessica , Galben-Sandulache Irina G. , Zoulis Georgios , Robert Teddy , Chaussende Didier , Juillaguet Sandrine , Tiberj Antoine , Camassel Jean
Published: March 2009

We present a structural and optical investigation of nitrogen-doped single crystals of cubic silicon carbide prepared by the continuous feed - physical vapour transport method. Self-nucleated crystals were produced which exhibited well faceted square and triangular shapes. KOH etching was used to characterize the structural defects, like stacking faults and dislocations. The effect of changing the nitrogen flow rate on the different crystalline orientations was investigated by Raman spectroscopy and low temperature photoluminescence techniques.
Electrical Characterization of Al Implanted 4H-SiC Layers by Four Point Probe and Scanning Capacitance Microscopy
Authors: Giannazzo Filippo , Rambach Martin , Salinas Dario , Roccaforte Fabrizio , Raineri Vito
Published: March 2009

We studied the evolution of the electrical activation with annealing temperature and time in 4H-SiC implanted with Al ions at room temperature (RT). An accurate comparison between the electrical activation data obtained by FPP and SCM was carried out. The dependence of the electrically active profiles on annealing time was studied during isothermal (Tann=1600 °C) annealings for times ranging from 0 (spike anneal) to 30 min. By performing isochronal (t=30 min) processes at temperatures from 1550 to 1650 °C, the effect of the annealing temperature on the net doping concentration profiles was studied. Moreover, the activation energy (6.30.3 eV) associated to the process was extracted from the Arrhenius plot of the net active dose. Finally, the effect of the different thermal budgets on the roughening of the Al implanted 4H-SiC surface was also investigated in details by atomic force microscopy.
Microstructural Study of Fe-Implanted SiC: Comparison of Different Post-Implantation Treatments
Authors: Declémy Alain , Dupeyrat Cyril , Thomé Lionel , Debelle Aurelien
Published: March 2009

Silicon carbide (SiC) could be a good candidate for Diluted Magnetic Semiconductor (DMS). In this paper we report on preliminary results on the microstructure of Fe-implanted 6H-SiC subsequently submitted to Rapid Thermal Annealing (RTA), laser processing in the solid phase and swift heavy ion irradiation and analyzed by means of X-ray diffraction (XRD) and Rutherford backscattering and channeling (RBS/C).
SIMS Investigation of Gex(4H-SiC)1-x Solid Solutions Synthesized by Ge-Ion Implantation up to x=0.2
Authors: Peyre Hervé , Pezoldt Joerg , Voelskow M. , Skorupa Wolfgang , Camassel Jean
Published: March 2009

A detailed investigation of the Ge concentration in implanted samples has been carried out by SIMS and the effects affecting the depth distribution and measurement results have been determined. It is found that the MCs+ SIMS technique is best suited to investigate Gex(4H-SiC)1-x solid solutions up to x=0.2, while the O2+ SIMS configuration is limited to x=0.1. The Ge concentrations obtained by SIMS are very close to the nominal values. On the opposite, performing a comparison with previous RBS data, we find that the RBS values are systematically underestimated by ~30%. Finally, at very high dose, we find that some of the implanted species are lost by recoil and sputtering effects.
Model Calculation of SiC Oxide Growth Rate Based on the Silicon and Carbon Emission Model
Authors: Hijikata Yasuto , Yaguchi Hiroyuki , Yoshida Sadafumi
Published: March 2009

We proposed a kinetic model for SiC oxidation, named ‘silicon and carbon (Si-C) emission model’, taking into account the emission of Si and C atoms from the SiC–oxide interface, which suppresses the oxidation rate at the interface. Based on the model, we calculated oxide growth rates for SiC (0001) Si- and (000–1) C-face and found that the calculated values exhibit good fits to the measured ones in the entire oxide thickness range for both faces. We also calculated depth profiles of Si and C interstitials and oxidants, and discussed the oxidation mechanism of SiC as well as the difference in the oxidation process of Si-face and C-face.
Advances in Liquid Phase Conversion of (100) and (111) Oriented Si Wafers into Self-Standing 3C-SiC
Authors: Zielinski Marcin , Portail Marc , Chassagne Thierry , Juillaguet Sandrine , Peyre Hervé , Leycuras André , Camassel Jean
Published: March 2009

We report on recent advances in liquid phase epitaxial (LPE) conversion of a bulk Si wafer into self standing 3C-SiC. This includes the role of the stress control within the (100) oriented “crucibles”, the elaboration of crack-free (111) “crucibles” and the successful conversion of (100) and (111) oriented Si wafer. To date up to 100µm thick 3C-SiC(100) as well as 30µm thick crack-free 3C-SiC (111) materials have been obtained. The growth rate ranges from 20 to 100µm/h and locally can even reach ~1mm/h. In this work we focus on the structural, morphological and optical properties of the LPE-grown material.
Analysis of the Electron Traps at the 4H-SiC/SiO2 Interface of a Gate Oxide Obtained by Wet Oxidation of a Nitrogen Pre-Implanted Layer
Authors: Pintilie Ioana , Moscatelli Francesco , Nipoti Roberta , Poggi Antonella , Solmi Sandro , Svensson Bengt Gunnar
Published: March 2009

This work is focusing on the effect of a high concentration of nitrogen (N) introduced by ion implantation at the SiO2/4H-SiC interface in MOS capacitors. The N implanted sample (Ninterface ~1x1019cm-3) is compared with a non-implanted one (Ninterface ~1x1016cm-3) by means of the electron interface trap density (Dit). The Dit is determined via High-Low frequency C-V method and Thermal Dielectric Relaxation Current (TDRC) technique. It is shown that the TDRC method, mainly used so far for determination of near interface oxide charges, can be exploited to gain information about the Dit too. The determined value of Dit in the N-implanted sample is nearly one order of magnitude lower than that in the sample without N implantation. Good agreement between the TDRC results and those obtained from High-Low frequency C-V measurements is obtained. Furthermore, the TDRC method shows a high accuracy and resolution of Dit evaluation in the region close to the majority carrier band edge and gives information about the traps located into the oxide.
Effect of Post Deposition Annealing on the Characteristics of Sol-Gel Derived HfO2 on 4H-SiC
Authors: Hoong Chee Chung , Cheong Kuan Yew
Published: March 2009

The effects of post deposition annealing in forming gas (5 % H2 in 95 % N2) ambient at different temperatures (850, 950, and 1050 oC) on metal-oxide-semiconductor characteristics of sol-gel derived HfO2 gate on n-type 4H-SiC have been investigated. After 30 min of the annealing, an accumulation of positive effective oxide charge (Qeff) has been observed in all samples. The total interface trap density and Qeff of the oxides annealed at 850 and 950 oC are comparable but an increment and reduction of the respective densities have been recorded when the oxide was annealed at 1050 oC. A reduction of near interface trap density has been revealed as the annealing temperature has been increased. These observation was closely related to the increment of leakage current density as the annealing temperature increased.
High-Temperature Reliable Ni2Si-Based Contacts on SiC Connected to Si-Doped Al Interconnect via Ta/TaN Barrier
Authors: Tanimoto Satoshi , Oohashi Hiromichi
Published: March 2009

One major problem when operating SiC power devices at a junction temperature of more than 200°C is the pronounced degradation of the Ni2Si-based ohmic contacts caused by interaction with the Al interconnect. In this paper, measures against such trouble and their effectiveness are discussed. Two measures highly compatible with Si device technology have been devised and experimentally implemented: (1) insertion of a Ta/TaN barrier metal between the Al interconnect and the Ni2Si contacts; (2) use of 1 wt% Si-doped Al as the interconnect. A failure lifetime of more than 12000 hours has been attained in a temperature range up to 385°C.