bluuebunny/crossref_metadata_2025 huggingface dataset:
Study on Mechanical Properties and Toughening Mechanism of MWCNTs/Ti(C, N) Cermets-Based Composites
Authors: Liu Shuo Qi , Liu Wei Liang
Published: March 2013

MWCNTs/Ti(C, N) cermets-based composites were prepared by vacuum hot-pressing sintering method. The mechanical properties of samples were examined. XRD and SEM were used to investigate the crystal structure of the composites and microstructure of fractures surface, respectively. The toughening mechanism of composites was discussed particularly. The experimental results showed that the optimum comprehensive mechanical properties of samples were obtained by adding 1wt% MWCNTs in the composites. The bending strength, Vickers hardness and fracture toughness of the composites were 1275.14MPa, 22.75GPa and 10.60MPa•m1/2, respectively, which were improved by 16.89%, 17.15% and 25.59%, respectively, compared to the Ti(C, N)-based cermets without MWCNTs. Bridging and pulling out of MWCNTs, crack deflection, residual stress toughening and micro-voids toughening were attributed to the toughening mechanism of the composites.
Comparisons of Microstructures and Hardness Distribution between Clinocardium Californiense and Veined Rapa Whelk Shells
Authors: Ji Hong Mei , Jiang Yun , Yang Wen , Zhang Guang Ping , Li Xiao Wu
Published: March 2013

Abstract. Microstructures, phase compositions and microhardness distribution of two kinds of natural biological materials called Burnt-end Ark and Veined rapa whelk shells were studied and discussed for comparisons. It was found that the both shells present a hierarchical structure comprising three layers in thickness, i.e., inner, middle and outer layers. The inner and middle layers of the two kinds of shells exhibit cross-lamellar structures with somewhat of differences in the morphology and dimension. The outer layer presents a porous blocky structure for Burnt-end Ark shell and a layered structure for Veined rapa whelk shell. The X-ray diffraction (XRD) analyses show that all the layers of Burnt-end Ark shell as well as the inner and middle layers of Veined rapa whelk consist of crystalline aragonite CaCO3, while the out layer of Veined rapa whelk consists of crystalline calcite CaCO3. The microhardness measurements on the cross sections perpendicular to the growth lines of the shells demonstrate that the hardness of the both shells decreases gradually from the inner layer to the outer layer, strongly depending upon their microstructures.
Synthesis of Dispersed Y2O3 Nanopowder from Yttrium Stearate
Authors: Li Jin Sheng , Sun Xu Dong , Liu Shao Hong , Huo Di , Li Xiao Dong , Li Ji Guang , Zhu Qi , Zhang Mu
Published: March 2013

Fine yttrium stearate powder was produced at a relatively low temperature using yttrium nitrate hexahydrate, ammonia and stearic acid as the raw materials. Dispersed Y2O3 nanopowder was synthesized by calcining the yttrium stearate. The formation mechanism of the precursor and the Y2O3 nanopowder was studied by means of XRD, TG-DTA, FT-IR, BET, FE-SEM and HR-TEM. Pure and dispersed Y2O3 nanopowder with an average particle size of 30 nm was produced by calcining the precursor at 600 °C. The particle size increases to about 60 nm with the increase of the calcination temperature to 1000 °C. In the preparation of Y2O3 from yttrium stearate, no water medium is involved, thus capillarity force and bridging of adjacent particles by hydrogen bonds can be avoided, resulting in good dispersion of the particles. The dispersed Y2O3 nanopowder prepared in this work has potential application in phosphors and transparent ceramic materials.
The Influence of Steel Cover Thickness on Ballistic Performance of Confined TiC-TiB2 Ceramic Tiles against the Impact of Long-Rod Tungsten Alloy Penetrator of 1.4 km · s-1
Authors: Pan Chuan Zeng , Zhao Zhong Min , Zhang Long , Zhang Jing
Published: March 2013

By conducting DOP test to evaluate the ballistic performance of confined TiC-TiB2 ceramic tiles against long-rod tungsten alloy penetrators under the impact of 1.4 km · s-1, the influences of steel cover thickness on ballistic performance of TiC-TiB2 ceramic tilSubscript textes laterally confined by heat shrinkage of medium-carbon-steel sleeves were investigated. The results of ballistic testing showed that the steel covers with the thickness of 1.5 mm and 3.5 mm failed to axially confined the ceramic tiles with the mass efficiency smaller than 2.0. Since the steel covers in thickness larger than 10 mm had a sufficient stiffness to support their axially confinement on the ceramic tiles and ensure the ceramic tiles with high integrity to ballistic impact by inhibiting the comminuted ceramic to sputter out, not only resulting in the limited room-making of the penetrators in the ceramic tiles for their penetration, but also more importantly yielding the intensified erosion of commuted ceramic to the penetrators, finally, the improved ballistic performance of the ceramic tiles was achieved with the mass efficiency larger than 2.5.
Cyclic Contact Fatigue of Dental Porcelain
Authors: Chen Hui Juan , Liu Yi Hong , Wang Yong , Qiu Yan , Bao Yi Wang
Published: March 2013

The residual strength of dental porcelain discs were test after cycling fatigue compressive load in this study. Moreover, the effects of stress intensity and cycle frequency to the damage of porcelain were explored. The porcelain specimens were bonded to the epoxy resin blocks, with 12.5mm height. The cycling fatigue contact loads were subjected on the porcelain surfaces of the bi-layer composites with silicon nitride spheres of radius 2.5mm. The crosshead speed was 6mm/min. The top load value was varied from 10N-20N in every load cycles. The cycling number was from 50-300. After cycling test, the residual strength of all porcelain samples was measured by bi-axial bending test. Fractured pieces of the specimens were collected and examined with optical microscope and SEM. On the fracture surfaces of porcelain discs after bi-axial bending test, Hertz cone cracks were presented due to cycling fatigue load. The result showed that the residual strength of dental porcelain had negative correlation with the fatigue load values and cycles. When the fatigue load cycles were lower than 100, the residual strength of porcelain presented no significant different under 10 or 20N fatigue load. In contrary, when the fatigue load cycles were over 100, the residual strength of porcelain was much lower under 20N fatigue load than 10N fatigue load. Based on the limited results of this study, the conclusion could be drawn that the residual strength of porcelain under fatigue compressive stress was main determined by load cycles in the range of small load values. The porcelain could be destroyed after very few cycles if the load is up to a critical value.
The Chemical Plating Copper of the SiC Particles and Thermal Expansion Behavior of the SiCp/Cu Composites
Authors: Hu Ming , Zhang Yun Long , Liu You Jin , Gao Jing
Published: March 2013

In this paper, the chemical copper plating technology was utilized to modify the SiC particles and the SiCp/Cu composites were fabricated by the pressure-less sintering technology. The effect of pretreatment solution on the coating quality of the SiC particles was discussed in details. The pure copper and copper- coated SiC particles or SiC particles without coated copper were used to fabricate the SiCp/Cu composites. At the same time, the microstructures and thermal expansion coefficients of the SiCp/Cu composites were studied. The results showed that the uniform and continuous Cu coating on the SiC particles can be obtained after chemical copper plating, and the copper-coated SiC particles can distributed continuously in the matrix of the SiCp/Cu composites. The chemical copper plating technology could improve the wettability between SiC particles and copper matrix obviously. The addition of the SiC particle could reduce the CTE of the SiCp/Cu composites.
Corrosion Behavior of ZrO2-Mo Composite in Na2SO4 Solution
Authors: Nian Hong Qiang , Xia Jin Feng , Feng Tao , Jiang Dan Yu
Published: March 2013

Due to the excellent mechanical properties, ZrO2 was widely used as structural material in multi-industry, such as chemistry, power, biology, metallurgy and so on. The complex working environments require better properties. Besides, thermal shock resistance and corrosion resistance are the most important properties that we need to concern. In this work, ZrO2-Mo composites were synthesis with pressureless sintering method under vacuum environment. The corrosion behavior of ZrO2-Mo in 1 mol/L Na2SO4 solution was investigated. The corrosion experiment was performed in 80°C hot solution for 5, 10, 15 and 20 hours, respectively. The results showed that the composites had good corrosion resisitance in hot Na2SO4 solution. The microstructures were also studied to reveal the corrision behavire of the composite.
Study on Extraction of Alumina from Sericite Phyllite
Authors: Zhao Hong Wei , Liu Kai Qi , Li Zhuang , Huang Zhao Hui
Published: March 2013

Alumina from sericite phyllite was extracted by the way of limestone self-pulverization sintering technique. The key technical processes, including self-pulverization sintering, clinker leaching reaction and the carbonation decomposition, were investigated systematically. The results showed that the main phases of pulverized clinker consisted of γ-C2S and C12A7, and the self-pulverization rate was 95% . The dissolution rate of Al2O3 clinker could reach 86.7% when the concentration of Na2CO3 solution was 7% and the solid-liquid ratio was 1:3. The Al(OH)3 prepared at 80°C carbonation temperature and pH=10.5 was relatively pure, with hexagonal plate-like crystals. The α-alumina could be acquired by calcination at 1200°C with the content of 99.71% Al2O3 and 0.02% Na2O. This work provided optimal technological parameters for effectively extracting alumina from the sericite and other inexpensive non-bauxite mineral resources with A/S ratio lower than 1.
A Comparative Study on Relative Translucency of Four Dental All-Ceramic Core Materials
Authors: Shi Guang , Xu Juan , Liang Li Min , Yi Yuan Fu , Shao Long Quan , Wen Ning , Gu Bin , Liu Yi Han , Lu Rong Jian , Deng Bin
Published: March 2013

The aim of this study were to compare the relative translucency of four dental all-ceramic core materialsIPS e.max Press,Zenostar,Lava Zirconia and Upcera Zirconia.All core materials were fabricated into samples at the diameter of 10mm and the thickness of 0.50.02mm.The relative translucency of samples were determined with color difference meter and analysed with SPSS 13.0 software.It was showed that the relative translucency of 4 all-ceramic core materials were statistically different.There was a decreasing order of their relative translucency,IPS e.max PressLava Zirconia ZenostarUpcera Zirconia.IPS e.max Press has the hightest translucency,and it was advisably used to restore anterior tooth.Upcera Zirconia was the most opaque of 4 all-ceramic core materials,and it was suitable for post tooth.
Early Age Property Study of Phosphate Cement by Electrical Conductivity Measurement
Authors: Ding Zhu , Wang Xiao Dong , Dong Bi Qin , Li Zong Jin , Xing Feng
Published: March 2013

The properties and electrical conductivity at early age of magnesium phosphate cement (MPC) was studied. Electrical resistivity or conductivity had been used for explaining the microstructure development of cement materials. In the current study, an electrodeless resistivity meter (ERM) was used to study the early property of MPC, which was mixed with and without fly ash respectively. The hardening process was investigated by the conductivity variation, incorporating with strength development and temperature rise during the initial reaction. The products and microstructure morphology of MPC paste were analysed by XRD and SEM. Results showed the mechanical property of MPC can be improved by fly ash. Fly ash lowers the maximum temperature rise during initial reaction of MPC with water. The electrical conductivity results divids the hardening process of MPC into three stages: acceleration, deceleration and stabilization. Conductivity measurement is an excellent method to explain the hardening process of MPC.
The Research on Jadeite-Jade Lavender Based on CIE DE2000
Authors: Wang Shuang , Wang Hong , Guo Ying , Zhao Jia Hui
Published: March 2013

The aim of this paper is to research human visual differentiation of lavender jadeite-jade classification through color difference.The result of E*2000 matches human eyes best. Based on that, using Color i5 for measuring Color parameters of jade samples and analyzing the differences of the color appearance among L*2000, C*2000 and H*2000.Taking consideration that variation range of purple is wide in color science, although L*2000 contributes most to E*2000(r=0.854), it is extremely not rigorous if we ignore the influence of H*2000 or C*2000. L*2000 less than H*2000 and C*2000 for all the lavender of jadeite parameters affecting the appearance.
Determination and Evaluation of Dead Time for X-Ray Fluorescence Spectrometer
Authors: Yan Ran , Liu Yu Bing , Dai Ping
Published: March 2013

When an X-ray photon which is generated by the sample enters into the detector, pulses can be produced and recorded. The detector is unable to respond to another photon that enters at the same time when a photon is being detected. The time that the detector takes to respond to a photon is regarded as dead time. For the x-ray fluorescence detector, the recorded count is less than the real count impulse due to dead time. Hence, to correct x-ray intensity of samples whose element content is vastly different, determination of dead time is necessary. In this paper, a new and complete way to determine dead time is proposed, which can be summarized as “intensity pair method”. Three “intensity pairs” were used for determining dead time, which were “intensity pair” of collimators (S2 and S4), “intensity pair” of spectral lines (Kα and Kβ) and “intensity pair” of beads with different flux-sample ratio (higher SH and lower SL analyte content in the beads). It comes to a conclusion that dead time obtained from “intensity pair” of beads is the most practical method for correcting X-ray fluorescence intensity. As for routine analysis, the dead time of proportional counter can be accurate to 1×10-9s, which can make intensity correction error less than 0.1%.
Preparation and Characterization of Gd2Zr2O7 Nanoparticles via the Citric Acid Chelating Agent Method
Authors: Ma Lei , Ma Wei Min , Sun Xu Dong
Published: March 2013

Gd2Zr2O7 nanocrystals with cubic structure were prepared via the citric acid chelating agent method using zirconium oxychloride and gadolinium oxide as starting materials. The samples was characterized using thermal gravimetric-differential thermal analysis, X-ray diffraction technique, Fourier transform infrared methods, transmission electron microscopy technique, and laser particle size analyzer instrument. The effect of the heat treatment temperature on the Gd2Zr2O7 nanocrystal grain size was also analyzed. The results show that citric acid and ethylene glycol underwent esterification, and the metal ions were wrapped in an organic network, resulting in molecular-level dispersion. A single Gd2Zr2O7 phase was formed at 600 °C, and the crystal size of the nanocrystals increased with increasing thermal treatment temperature. Gd2Zr2O7 with an excellent defective fluorite structure, which belongs to the space group, was prepared after treatment at 900 °C for 2 h. The Gd2Zr2O7 crystallites consist of 50 nm to 60 nm spherical particles with agglomerated structures. In addition, the d111 and d222 interplanar distances were 0.310 and 0.152 nm, respectively, which were measured from high resolution transmission electron microscopy images.
Insulating Properties of Package for Ultrahigh-Voltage, High-Temperature Devices
Authors: Hayashi Toshihiko , Izumi Toru , Hemmi Tetsuro , Asano Katsunori
Published: March 2013

Insulating properties of package for ultrahigh-voltage, high-temperature devices have been investigated. While all the packages have enough insulating strength at room temperature, deterioration of the insulating property at high temperature has been found with some packages. The authors have found that this deterioration is attributed to degrade the insulation property of AlN ceramics for DBC substrate at high temperature and that there is a various degree in the deterioration.
Electromagnetic Interference in Silicon Carbide DC-DC Converters
Authors: Mostaghimi Omid , Stevens Rupert C. , Wright Nicholas G. , Horsfall Alton B.
Published: March 2013

A comparison of radiated noise for Silicon and Silicon Carbide converters is presented. SiC JBS diodes were used in this evaluation to enable fast switching times, whilst minimizing the transistor junction temperature. Radiated electromagnetic-interference measurements showed the highest noise signature for the SiC JFET and lowest for the SiC MOSFET. The negative gate voltage requirement of the SiC MOSFET introduces up to 6 dBµV increase in radiated noise, due to the induced current in the high frequency resonant stray loop in the negative power plane of the gate drive. The SiC JFET and MOSFET have shown overall converter efficiencies of 96% and 95.5% respectively. This efficiency shows only a weak frequency dependence, in contrast to the CoolMOS/SiC JBS diode combination which demonstrated an efficiency drop from 95% to 92.5% when increasing the frequency from 100kHz to 250kHz.
High Temperature Digital and Analogue Integrated Circuits in Silicon Carbide
Authors: Young R.A.R. , Clark David T. , Cormack Jennifer D. , Murphy A.E. , Smith Dave A. , Thompson Robin. F. , Ramsay Ewan P. , Finney S.
Published: March 2013

Silicon Carbide devices are capable of operating as a semiconductor at high temperatures and this capability is being exploited today in discrete power components, bringing system advantages such as reduced cooling requirements [1]. Therefore there is an emerging need for control ICs mounted on the same modules and being capable of operating at the same temperatures. In addition, several application areas are pushing electronics to higher temperatures, particularly sensors and interface devices required for aero engines and in deep hydrocarbon and geothermal drilling. This paper discusses a developing CMOS manufacturing process using a 4H SiC substrate, which has been used to fabricate a range of simple logic and analogue circuits and is intended for power control and mixed signal sensor interface applications [2]. Test circuits have been found to operate at up to 400°C. The introduction of a floating capacitor structure to the process allows the use of switched capacitor techniques in mixed signal circuits operating over an extended temperature range.
A Simplified Model for SiC Power Diode Modules for Implementation in Spice Based Simulators
Authors: Chimento Filippo , Nawaz Muhammad , Mora Niccoló , Tomarchio Salvatore
Published: March 2013

A simplified model for SiC Power diodes has been developed and implemented in Spice simulator in order to get the advantages of a modular and hierarchical structure that can be easily used for modeling of power semiconductor modules. The proposed approach is based on the lumped charge technique. One of the main targets for the proposed model is the implementation of a modeling structure starting from the evaluation and simplification of the semiconductor equations. The paper will show the implementation of the model along with an experimental evaluation of the proposed method.
Impact of Substrate Steps and of Monolayer-Bilayer Junctions on the Electronic Transport in Epitaxial Graphene on 4H-SiC (0001)
Authors: Giannazzo Filippo , Deretzis Ioannis , La Magna Antonino , Di Franco Salvatore , Piluso Nicolò , Fiorenza Patrick , Roccaforte Fabrizio , Schmid Patrick , Lerch Wilfried , Yakimova Rositza
Published: March 2013

Two dimensional maps of the electronic conductance in epitaxial graphene (EG) grown on SiC were obtained by conductive atomic force microscopy (CAFM). The correlation between morphological and electrical maps revealed the local conductance degradation in EG over the SiC substrate steps or at the junction between monolayer (1L) and bilayer (2L) graphene regions. The effect of steps strongly depends on the charge transfer phenomena between the step sidewall and graphene, whereas the resistance increase at 1L/2L junction is a purely quantum mechanical effect, due to the weak coupling between 1L and 2L electron wavefunctions.
X-Ray Diffraction and Raman Spectroscopy Study of Strain in Graphene Films Grown on 6H-SiC(0001) Using Propane-Hydrogen-Argon CVD
Authors: Michon Adrien , Largeau Ludovic , Tiberj Antoine , Huntzinger Jean Roch , Mauguin Olivia , Vézian Stephane , Lefebvre Denis , Cheynis Fabien , Leroy Frédéric , Müller Pierre , Chassagne Thierry , Zielinski Marcin , Portail Marc
Published: March 2013

We have grown graphene films on 6H-SiC(0001) using propane CVD and evidenced the strong impact of the hydrogen/argon mixture used as the carrier gas on the graphene/SiC interface and on the orientation of graphene layers. By studying a set of samples grown with different hydrogen/argon mixture using Raman spectroscopy and grazing incidence X-ray diffraction, we evidence the links between graphene/SiC interface and strain in graphene.
Raman Spectroscopy and XPS Analysis of Epitaxial Graphene Grown on 4H-SiC (0001) Substrate under an Argon Pressure of 900 mbar Environment
Authors: Wang Dang Chao , Zhang Yu Ming , Zhang Yi Men , Guo Hui , Wang Yue Hu
Published: March 2013

This paper investigated a feasible process of growing epitaxial graphene on 4H hexagonal poly-type of silicon carbide Si-faced polar surface (0001) under an argon pressure of 900 mbar conditions. Using Raman Spectroscopy, Scanning Electron Microscopy and X-ray Photoelectron Spectroscopy, epitaxial graphene grown at temperature 1600°C is confirmed to take shape weakly on 4H-SiC (0001) with an average domain size of several tens of nanometers, and this can be seen as the characteristic of initial formation of epitaxial graphene on substrate.
A DC Comparison Study between H-Intercalated and Native Epi-Graphenes on SiC Substrates
Authors: Winters Michael , Thorsell Mattias , ul Hassan Jawad , Rorsman Niklas , Janzén Erik , Zirath Herbert
Published: March 2013

Abstract. The aim of this study is to compare DC characteristics of ‘as-grown’ and hydrogen (H)-intercalated epitaxial graphenes on SiC substrates [1,2]. Epitaxial graphene is grown on SiC at 1400-1600C, and H-intercalation is performed via in-situ introduction of Hydrogen during the graphitization process [6]. The fabrication processing steps used to define test structures are identical for the two materials. Results on the DC behaviour and uniformity issues with respect to both materials are reported. As-grown material behaves as a linear resistance, while H-intercalated demonstrates a non-linear characteristic. Hysteresis effects and time dependent behaviors are also observed in both materials. Extensive Hall measurements are performed on both materials with the aim of providing a qualitative understanding of material uniformity in both epi-graphenes.
High Temperature Stability of Oxygen Functionalized Epitaxial Graphene/Metal Contact Interfaces
Authors: Nagareddy V. Karthik , Hernández Sandra C. , Wheeler Virginia D. , Nyakiti Luke O. , Myers-Ward Rachael L. , Eddy Charles R. , Goss Jonathan P. , Wright Nicolas G. , Walton Scott G. , Gaskill D. Kurt , Horsfall Alton B.
Published: March 2013

The electrical characteristics of oxygen functionalized epitaxial graphene and Ti/Au metal contact interfaces were systematically investigated as a function of temperature. As the temperature was increased from 300 K to 673 K, the contact resistance and the sheet resistance decreased by 75% and 33%, respectively. The resistance of oxygen functionalized graphene vs temperature exhibited Arrhenius type behavior with activation energy of 38 meV. The results showed no hysteresis effects in resistance measurements over the temperatures studied here, suggesting the contact interfaces remain stable at high temperatures.
Thickness Uniformity and Electron Doping in Epitaxial Graphene on SiC
Authors: Eriksson Jens , Puglisi Donatella , Vasiliauskas Remigijus , Lloyd Spetz Anita , Yakimova Rositza
Published: March 2013

Large variations have been observed in the uniformity and carrier concentration of epitaxial graphene grown on SiC by sublimation for samples grown under identical conditions and on nominally on-axis hexagonal SiC (0001) substrates. We have previously shown that these issues are both related to the morphology of the graphene-SiC surface after sublimation growth. Here we present a study on how the substrate polytype, substrate surface morphology and surface restructuring during sublimation growth affect the uniformity and carrier concentration in epitaxial graphene on SiC. These issues were investigated employing surface morphology mapping by atomic force microscopy coupled with local surface potential mapping using Scanning Kelvin probe microscopy.
Step Instability in Sublimation Epitaxy on Low Off-Axis 6H-SiC
Authors: Ariyawong Kanaparin , Jokubavicius Valdas , Liljedahl Rickard , Syväjärvi Mikael
Published: March 2013

The growth of homoepitaxial layers on off-oriented 6H-SiC substrates proceeds via step flow growth. Such epilayers can exhibit irregularities like step bunching, splicing or crossover of steps. The effects of the substrate off-orientation and growth temperature show an influence on formation of surface irregularities. The mean features seem to be given by the growth mode competition of two-dimensional growth to the step-flow growth.
3C-SiC Heteroepitaxy on Hexagonal SiC Substrates
Authors: Henry Anne , Li Xun , Jacobson Henrik , Andersson Sven , Boulle Alexandre , Chaussende Didier , Janzén Erik
Published: March 2013

The growth of 3C-SiC on hexagonal polytype is addressed and a brief review is given for various growth techniques. The Chemical Vapor Deposition is shown as a suitable technique to grow single domain 3C epilayers on 4H-SiC substrate and a 12.5 µm thick layer is demonstrated; even thicker layers have been obtained. Various characterization techniques including optical microscopy, X-ray techniques and photoluminescence are compared for the evaluation of the crystal quality and purity of the layers.
Application of 3-D X-Ray Computed Tomography for the In Situ Visualization of the SiC Crystal Growth Interface during PVT Bulk Growth
Authors: Neubauer Georg , Salamon Michael , Roider Florian , Uhlmann Norman , Wellmann Peter J.
Published: March 2013

In this paper, we present for the first time an in-situ 3-D reconstruction of the SiC crystal growth interface using X-ray computed tomography (CT). We show that the shape of the growth interface can be determined with high precision at growth temperatures above 2100 °C in a conventional 3” PVT (physical vapor transport) growth system.
Growth of 4H-SiC in Current-Controlled Liquid Phase Epitaxy
Authors: Mitani Takeshi , Okamura Masayuki , Takahashi Tetsuo , Komatsu Naoyoshi , Kato Tomohisa , Okumura Hajime
Published: March 2013

4H-SiC crystallization from Si-C solution in electric current-controlled liquid phase epitaxy was investigated. The dependence of growth speed on a DC current shows that dissolution/growth is controlled by the electric current without altering temperature gradient in the furnace. Application of an electric current leads to reduction of growth speed with negative polarity and enhancement of growth speed with positive polarity. The variation of the growth speed with a DC current density has been explained by the combination of the effects of electromigration of C solute and Joule heating.
Investigation of Solution Growth of SiC by Temperature Difference Method Using Fe-Si Solvent
Authors: Yoshikawa Takeshi , Kawanishi Sakiko , Morita Kazuki , Tanaka Toshihiro
Published: March 2013

This paper describes the solution growth of SiC by a temperature difference method using an Fe-Si solvent. Crystal growth of SiC from an Fe-40 mol%Si solvent onto a seed wafer of 6H-SiC or 4H-SiC was carried out at 1623 – 1723 K under induction heating. Homo-epitaxial growth on both 6H-SiC and 4H-SiC was identified by Raman spectroscopy, and the SiC growth rate was found to be 90 – 260 μm/h. Experiments were also conducted under resistance heating at 1623 K using conditions which suppressed natural convection. Convective mass transfer in the solution was found to be important for rapid growth of SiC.
Exploring SiC Growth Limitation of Vapor-Liquid-Solid Mechanism when Using Two Different Carbon Precursors
Authors: Alassaad Kassem , Cauwet François , Carole Davy , Soulière Véronique , Ferro Gabriel
Published: March 2013

Abstract. In this paper, conditions for obtaining high growth rate during epitaxial growth of SiC by vapor-liquid-solid mechanism are investigated. The alloys studied were Ge-Si, Al-Si and Al-Ge-Si with various compositions. Temperature was varied between 1100 and 1300°C and the carbon precursor was either propane or methane. The variation of layers thickness was studied at low and high precursor partial pressure. It was found that growth rates obtained with both methane and propane are rather similar at low precursor partial pressures. However, when using Ge based melts, the use of high propane flux leads to the formation of a SiC crust on top of the liquid, which limits the growth by VLS. But when methane is used, even at extremely high flux (up to 100 sccm), no crust could be detected on top of the liquid while the deposit thickness was still rather small (between 1.12 μm and 1.30 μm). When using Al-Si alloys, no crust was also observed under 100 sccm methane but the thickness was as high as 11.5 µm after 30 min growth. It is proposed that the upper limitation of VLS growth rate depends mainly on C solubility of the liquid phase.
Polytype Inclusions in Cubic Silicon Carbide
Authors: Vasiliauskas Remigijus , Malinovskis Paulius , Mekys Algirdas , Syväjärvi Mikael , Storasta Jurgis , Yakimova Rositza
Published: March 2013

The 3C-SiC layers on nominally on-axis 6H-SiC substrates were grown using sublimation epitaxy. More than 90% coverage by 3C-SiC is typically achieved at growth temperature of 1775°C. The main reason for the polytype inclusions to appear is local supersaturation non-uniformities over the sample surface which appear due to the temperature gradient and spiral growth nature of 6H-SiC. On the 6H-SiC spirals with small steps supersaturation is smaller and 3C-SiC nucleation and growth is diminished. Due to surface free energy and surface diffusion differences, polytype inclusions appear differently when 3C-SiC is grown on the Si- and C-faces. The 6H-SiC inclusions as well as twin boundaries act as neutral scattering centers and lower charge carrier mobility.
Determination of the Electrical Capture Process of the EH6-Center in n-Type 4H-SiC
Authors: Weber Jonas , Beljakowa Svetlana , Weber Heiko B. , Pensl Gerhard , Zippelius Bernd , Kimoto Tsunenobu , Krieger M.
Published: March 2013

Deep Level Transient Spectroscopy (DLTS) investigations at different temperatures and with various filling pulse lengths were performed on n-type 4H-SiC epitaxial layers using Iridium Schottky contacts to determine the electrical capture process of the EH6-center. The temperature dependence of the electrical capture cross section σ ~ T-2.0 suggests a cascade capture process, which is not thermally activated. Together with earlier work by Zippelius et al. [4] this proves the acceptor-type of the EH6-center.
Photoluminescence Spectroscopy of Neutron-Irradiated Cubic SiC Crystals
Authors: Bratus Victor , Melnyk Roman , Kolomys Oleksandr , Shanina Bela , Strelchuk Victor
Published: March 2013

Photoluminescence (PL) spectroscopy has been used to characterize neutron-irradiated cubic silicon carbide crystals. The effects of thermal annealing (600-1100OC) on the PL bands have been studied. Several PL bands consisting of a sharp line and its phonon replicas have been observed in the 9-80 K temperature range. Certain of them like the D1 spectrum doublet with 1.975 eV and 1.977 eV zero-phonon lines (ZPL) at 9 K and the L2 spectrum with ZPL at 1.121 eV were reported previously for ion-implanted and electron irradiated 3C-SiC crystals, respectively. Besides, some new bands with ZPL at 2.027, 1.594, 0.989 and 0.844 eV and a broad band at 1.360 eV have been found. A correlation of PL and EPR spectra intensities of these neutron-irradiated and annealed cubic SiC crystals is briefly discussed.
Deep-Level-Transient Spectroscopy Characterization of Mobility-Limiting Traps in SiO2/SiC Interfaces on C-Face 4H-SiC
Authors: Hatakeyama Tetsuo , Shimizu T. , Suzuki T. , Nakabayashi Y. , Okumura Hajime , Kimoto K.
Published: March 2013

Constant-capacitance deep-level-transient spectroscopy (CCDLTS) characterization of traps (or states) in SiO2/SiC interfaces on the C-face was carried out to clarify the cause of low-channel mobility of SiC MOSFETs. CCDLTS measurements showed that the interface-state density (Dit) near the conduction band of SiO2/SiC interfaces fabricated using N2O oxidation was much higher than that of SiO2/SiC interfaces fabricated using wet oxidation. The high density of interface states near the conduction band is likely to be the main cause of the low mobility of MOSFETs fabricated using N2O oxidation.
Absence of Back Stress Effect in the PVT Growth of 6H Silicon Carbide
Authors: Seiss Martin , Ouisse Thierry , Chaussende Didier
Published: March 2013

The growth process of silicon carbide crystals by physical vapor transport (PVT) on Si-face (0001) on-axis 6H-SiC substrates was analyzed. The growth rate was observed to be almost inversely proportional to the deposition pressure (R ∝ p-1) meaning that the growth rate is not limited by the number of growth spirals but by the vapor phase transport of the depositing species from the source to the sample surface. Analysis of the spiral step width shows an inverse square root dependence on the growth rate (y0 ∝ R-½). This experimental result is in accordance with the Burton, Cabrera and Frank theory and hence it can be concluded that there is no back-stress effect present.
Improvement of Interface State and Channel Mobility Using 4H-SiC (0-33-8) Face
Authors: Hiyoshi Toru , Masuda Takeyoshi , Wada Keiji , Harada Shin , Namikawa Yasuo
Published: March 2013

In this paper, we characterized MOS devices fabricated on 4H-SiC (0-33-8) face. The interface state density of SiO2/4H-SiC(0-33-8) was significantly low compared to that of SiO2/4H-SiC(0001). The field-effect channel mobility obtained from lateral MOSFET (LMOSFET) was 80 cm2/Vs, in spite of a high p-well concentration of 5x1017 cm-3 (implantation). The double implanted MOSFET (DMOSFET) fabricated on 4H-SiC(0-33-8) showed a specific on-resistance of 4.0 mΩcm2 with a blocking voltage of 890 V.
Modeling of the Mass Transport during Homo-Epitaxial Growth of Silicon Carbide by Fast Sublimation Epitaxy
Authors: Hupfer Thomas , Hens Philip , Kaiser Michl , Jokubavicius Valdas , Syväjärvi Mikael , Wellmann Peter J.
Published: March 2013

Ballistic and diffusive growth regimes in the Fast Sublimation Growth Process of silicon carbide can be determined using suggested theoretical model for the mean free path calculations. The influences of temperature and inert gas pressure on the mass transport for the growth of epitaxial layers were analyzed theoretically and experimentally.
Correlation of Interface Characteristics to Electron Mobility in Channel-Implanted 4H-SiC Mosfets
Authors: Strenger Christian , Uhnevionak Viktoryia , Burenkov Alex , Bauer Anton J. , Mortet Vincent , Bedel-Pereira Elena , Cristiano Fuccio , Krieger M. , Ryssel Heiner
Published: March 2013

To study mobility limiting mechanisms in (0001) 4H-SiC, lateral n-channel MOSFETs in p-implanted wells on n-type epitaxial layers were manufactured and additionally selectively shallow implanted with different nitrogen (N) doses in the channel region. The mobility was found to be limited by Columbic scattering at low electric fields. Further surface roughness scattering was con-sidered as a possible mobility degradation mechanism at high electric fields. First investigations of the SiC surface by atomic force microscopy (AFM) in the channel region after implantation, anneal-ing, and gate oxide removal revealed a rather rough topology. This could lead to fluctuations in the surface potential at the SiC/SiO2 interface, thus accounting in part for surface roughness scattering.
Characterization of POCl3-Annealed 4H-Sic Mosfets by Charge Pumping Technique
Authors: Osawa Ai , Yano Hiroshi , Hatayama Tomoaki , Fuyuki Takashi
Published: March 2013

4H-SiC MOSFETs were characterized using charge pumping (CP) technique to monitor interface state density (Dit) not only in the upper half of the bandgap (Eg) but also in the lower half of Eg. Comparison between POCl3- and NO-annealed MOSFETs was made using CP technique to reveal the different interface properties. The CP measurements of MOSFETs revealed that POCl3 annealing can reduce Dit near Ec, whereas it increases donor-like Dit in the lower half of Eg.
Recombination and Excess Currents in 4H-SiC Structure with Low-Doped n-Region
Authors: Strel'chuk Anatoly M. , Kalinina Evgenia V.
Published: March 2013

Presented in this paper are the results of a study of forward and reverse current-voltage characteristics of the 4H-SiC pn structures produced by implantation of Al+ ions in low-doped ((5-7)∙1014cm-3) n-type conductivity epitaxial layer. A forward current was identified which is consistent with the model of recombination in the space charge region of a pn junction via a deep level: J=Joexp(qU/nkT), where Jo=Jo*exp[-Ea/(kT)] (or J= Jo*exp[(qU-2Ea)/nkT)]) with the ideality factor n=2. Parameters of this current are as follows: Jo(293 K) ~ 8∙10-25 A/cm2, Ea 1.73-1.75 eV (2Ea3.46-3.5 eV), Jo*~7∙105 A/cm2. A comparison of the experimental and model-based values of Ea, with allowance for all clearly defined temperature dependences, both strong and weak, of the model of recombination in the space charge region shows that the effective lifetime increases and effective trapping cross section σeff of the recombination level decreases with increasing temperature: σeff ~ T-2÷σeff ~ T-2.5 or σeff ~exp(ΔE /kT) where ΔE=80-100 meV. Reverse current practically in whole temperature range is excess current, only at high temperatures (~800 K) reverse current became close to generation current in space charge region. Special interest are the excess currents as a result of the application of a reverse or forward voltage at high temperature. The barrier type excess currents is characteristic of SiC.
3C-, 4H- and 6H-SiC Bulks Studied by Silicon K-Edge X-Ray Absorption
Authors: Zeng Wei , Feng Zhe Chuan , Zheng Rui Sheng , Jang Ling Yun , Liu Chee Wei
Published: March 2013

High-resolution synchrotron radiation X-ray absorption of Si K-edge have been employed to investigate 6H-, 4H- and 3C-SiC. Detailed analyses of the extended x-ray absorption fine structure are taken by using the IFEFFIT program, and significant results on the atomic bonding are obtained from these comparative studies. The x-ray absorption near-edge structures of the Si K-edge are investigated, and the electronic structure of 3C-, 4H- and 6H-SiC are studied. In order to investigate the angular dependence, the x-ray absorption near-edge spectra were operated at 55o and 90o of the angle between the surface and the X-ray direction.
Comparison of Etch Pit Shapes on Off-Oriented 4H-SiC Using Different Halogen Gases
Authors: Hatayama Tomoaki , Tamura Tetsuya , Yano Hiroshi , Fuyuki Takashi
Published: March 2013

An etch pit shape of off-angled 4H-SiC Si-face formed by different halogen gases such as chlorine trifluoride (ClF3) and a mixed gas (O2+Cl2) of oxygen and chlorine in nitrogen (N2) ambience has been studied. One kind of etch pit with the crooked hexagon was formed at etching temperature under 500oC. The angle of etch pit measured by the cross-sectional atomic force microscope image was about 10o from the [11-20] view. A dislocation type of the etch pit was discussed in comparison with the etch pit shape and an X-ray topography image.
Complex Study of SiC Epitaxial Films
Authors: Geyfman E.M. , Chibirkin V.V. , Kamentsev G.Yu. , Gartsev N.A. , Davydova N.M. , Surin B.P.
Published: March 2013

4H-SiC epitaxial films grown on 4H-SiC in CVD reactor VP508GFR are investigated using FTIR, X-Ray diffraction, C-V measurements, stylus profiler and DIC optical microscopy.
Electrical Properties of MOS Structures on 4H-SiC (11-20) Face
Authors: Senzaki Junji , Shimozato Atsushi , Kajima Kozutoshi , Aryoshi Keiko , Kojima Takahito , Harada Shinsuke , Tanaka Yasunori , Himi Hiroaki , Okumura Hajime
Published: March 2013

Threshold voltage (VTH) instability, channel mobility and oxide reliability have been investigated for meta-oxide-semiconductor (MOS) structures on 4H-SiC (11-20) face using various gate oxidation procedures. Channel mobility of n-channel MOSFET with a gate oxide by pyrogenic oxidation is higher than that by dilute-DRY oxidation followed by a nitrous oxide (N2O) post-oxidation annealing (POA). On the other hand, oxide reliability for the pyrogenic oxides is poor compared with the dilute-DRY/N2O oxides. A Hydrogen POA is effective in an improvement of channel mobility for both oxides, but causes a harmful effect on VTH stability. Temperature dependence of VTH instability indicates that MOS structure grown by dilute-DRY followed by N2O POA is suitable for a practical use of SiC MOS power devices.
Study of Surface Defects in 4H-SiC Schottky Diodes Using a Scanning Kelvin Probe
Authors: Mizsei J. , Korolkov O. , Toompuu J. , Mikli V. , Rang T.
Published: March 2013

Abstract. In the present paper we attempt to study and explain the increased leakage currents in Schottky diodes with an integrated p-n-structure. By a scanning Kelvin probe method (vibrating capacitor) were obtained the local variations of surface contact potential difference (CPD) for the chips with large and small leakage currents. It is shown that samples with higher leakage currents have smaller surface potential barrier. The SEM investigations revealed that a critical role in increasing leakage currents play the dislocations penetrating from the substrate into the epitaxial layer.
Effect of Interfacial Localization of Phosphorus on Electrical Properties and Reliability of 4H-SiC MOS Devices
Authors: Akagi Tsuyoshi , Yano Hiroshi , Hatayama Tomoaki , Fuyuki Takashi
Published: March 2013

Metal-oxide-semiconductor (MOS) capacitors with phosphorus localized near the SiO2/SiC interface were fabricated on 4H-SiC by direct POCl3 treatment followed by SiO2 deposition. Post-deposition annealing (PDA) temperature affected MOS device properties and phosphorus distribution in the oxide. The sample with PDA at 800 °C showed narrow phosphorus-doped oxide region, resulting in low interface state density near the conduction band edge and small flatband voltage shift after FN injection. The interfacial localization of phosphorus improved both interface properties and reliability of 4H-SiC MOS devices.
The Influence of Post-Oxidation Annealing Process in O2 and N2O on the Quality of Al/SiO2/n-Type 4H-SiC MOS Interface
Authors: Król Krystian , Kalisz Malgorzata , Sochacki Mariusz , Szmidt Jan
Published: March 2013

The effect of the n-type 4H-SiC (0001) oxidation in wet O2 at temperature of 1175 °C followed by low temperature annealing in N2O at temperature of 800°C for 2 or 4 hours followed by high temperature annealing in nitrogen ambient on nitrogen distribution in silicon dioxide was investigated. It was shown that the oxidation and annealing have a strong impact on the behavior of electrical parameters of MOS capacitors using the oxides as gate dielectric what is probably an effect of nitrogen incorporation. The explanation of the observed electrical properties is included.
Efficient Characterization of Threshold Voltage Instabilities in SiC nMOSFETs Using the Concept of Capture-Emission-Time Maps
Authors: Pobegen Gregor , Grasser Tibor
Published: March 2013

We utilize the recently suggested capture-emission-time (CET) maps for the first time for SiC technologies. CET maps are a very powerful characterization technique which allow the elegant and comprehensive analysis of oxide/interface traps at or near the semiconductor-dielectric interface and were originally developed to characterize degradation of Si based MOSFETs. For as-processed SiC MOSFETs we present first results of the SiC-SiO2 interface using CET maps. We suggest that oxide traps are mainly responsible for the instability in SiC MOSFETs. Furthermore we state that the large time constants and the temperature activation of the traps in SiC MOSFETs can be consistently explained when accounting for multi-phonon processes for the microscopic charge exchange. A recently suggested model including such microscopic transitions is applied to SiC MOSFETs and shown to reproduce our experimental data with high accuracy for a large temperature range.
Optimization of Copper Top-Side Metallization for High Performance SiC-Devices
Authors: Behrens Tim , Suenner Thomas , Geinitz Eckart , Schletz Andreas , Frey Lothar
Published: March 2013

While aluminum-based metallization schemes on Si have been optimized for the last decades, only few investigations have been done on copper metallization with SiC-devices. Thus, in this work the mechanical as well as the electrical interactions of this metallization system have been analyzed and optimized for SiC-devices in high reliability applications. For optimizing the adhesion of the copper metallization stack on SiC devices, different metallization schemes consisting of adhesion promoters (Ti, Cr, Al, Ta, WTi), diffusion barriers (TiN, Ta, WTi), and the final copper layer have been tested by peel-tests. For investigating the electrical interactions TLM measurements as well as leakage-current measurements have been done on copper metalized SiC samples.
Basic Experiment on Atmospheric-Pressure Plasma Etching with Slit Aperture for High-Efficiency Dicing of SiC Wafer
Authors: Sano Yasuhisa , Nishikawa Hiroaki , Aida Kohei , Tangpatjaroen Chaiyapat , Yamamura Kazuya , Matsuyama Satoshi , Yamauchi Kazuto
Published: March 2013

Silicon carbide (SiC) is a promising semiconductor material for high-temperature, high-frequency, high-power, and energy-saving applications. However, because the hardness and chemical stability of SiC are high, few conventional machining methods can handle this material efficiently. We previously developed a plasma chemical vaporization machining (PCVM) technique, which is an atmospheric-pressure plasma etching process, and investigated its application to the processing of SiC substrates. In this paper, we propose a novel style of PCVM technique for dicing, using slit apertures to confine the plasma. From experiments by means of an apparatus with a one-slit aperture formed by two masks, it was found that the kerf loss was almost proportional to the slit width, and that the etching depth increased with RF power. Furthermore, from experiments on a SiC wafer, we obtained a 130-μm etching depth and 300-μm kerf loss for an 11-min processing time and 200-μm slit width.
Model Calculations of SiC Oxide Growth Rates at Sub-Atmospheric Pressures Using the Si and C Emission Model
Authors: Hijikata Yasuto , Yagi Shuhei , Yaguchi Hiroyuki , Yoshida Sadafumi
Published: March 2013

We found that the ‘Si and C emission model’ that we proposed as an oxidation model of SiC could not reproduce the initial oxide growth rates of SiC at sub-atmospheric pressures. The comparison between calculated and observed growth rates suggests that the oxide growth on the oxide surface is enhanced in the initial oxidation stage and thus our oxidation model is inaccurate in the description on the surface oxidation. Accordingly, we reconsidered the parameters on surface oxidation and, as a result, found that a much enlarged oxygen concentration on the oxide surface is necessary for solving the discrepancy between calculated and observed growth rates.