bluuebunny/crossref_metadata_2025 huggingface dataset:
Microstructural and Thermal Properties of Nanocrystalline Silica Xerogel Powders Converted from Sago Waste Ash Material
Authors: Aripin Haji , Mitsudo Seitaro , Sudiana Inyoman Nyoman , Prima Endangsusilowati S. , Sako Katsuhide , Fujii Yutaka , Saito Teruo , Idehara Toshitaka , Sano Saboru , Purwasasmita Bambang Sunendar , Hernawan H. , Sabchevski Sliven
Published: March 2013

In the present investigation, nanocrystalline silica xerogel (NSX) powders were produced from an amorphous silica xerogel (ASX) extracted from sago waste ash. The NSX powders have been calcined at 1200oC, milled and then annealed at temperatures ranging from a room temperature to 1200oC. Their properties (and most notably the size of the particles) have been characterized on the basis of the experimental data obtained using thermal analysis (DSC/TGA), X-ray diffraction (XRD), Infrared and Raman spectroscopy. For the crystalline silica xerogel powders the results show a narrow distribution of the particle sizes centered around an average value of 636  67 nm. The DSC analysis of NSX indicates that in the temperature range from a room temperature to 300oC five distinct stages of the crystallization process take place, which are delimited by the transition temperature of 38oC, 92oC, 129oC, 168oC, and 246oC, respectively. Above 300oC, the crystalline phase is similar to an amorphous silica xerogel (ASX), i.e. cristoballite-like and tridymite-like crystalline silica phases confirmed by the XRD analysis. It has been observed that the characteristic band of cristoballite is strongly dependent on the thermal history and the NSX transforms into a stable form at a temperature of 1200oC. Both the Raman and the FTIR spectra elucidate the bonding system of the constituent atoms and groups (such as Si, O and OH) and throw light on their underlying structure. The obtained results are important for optimization of the parameters of the technological processes for production of nanocrystalline silica glass ceramics used as a host matrix for luminescence materials, each of which requires a specific porosity and structure.
Pattern Transfer of 23-Nm-Diameter Block Copolymer Self-Assembled Nanodots Using CF4 Etching with Carbon Hard Mask (CHM) as Mask
Authors: Huda Miftakhul , Liu Jing , bin Mohamad Zulfakri , Yin You , Hosaka Sumio
Published: March 2013

The self-assembly of block copolymer (BCP) has demonstrated as promising alternative technology to overcome the limitation of conventional lithography owing to its ability in forming nanostructure with size 3-100 nm. In this study, we investigated a technique to transfer self-assembled nanodots of Poly(styrene-b-dimethyl siloxane) (PS-PDMS) BCP to Si. The pattern transfer of PS-PDMS nanodots with the pitch of 33 nm and the diameter of 23 nm using CF4 etching with Carbon Hard Mask (CHM) as Mask is demonstrated. Si nanopillar with height of 51 nm was fabricated. This result improves the potential use of PS-PDMS BCP self-assembly technique for fabrication nano-electronic devices, such as quantum dot solar cell and ultrahigh density of magnetic recording.
Dye-Sensitized Solar Cells (DSSC) from Black Rice and its Performance Improvement by Depositing Interconnected Copper (Copper Bridge) into the Space between TiO2 Nanoparticles
Authors: Saehana Sahrul , Yuliza Elfi , Arifin Pepen , Khairurrijal Khairurrijal , Abdullah Mikrajuddin
Published: March 2013

Dye-sensitized solar cell (DSSC) which employed natural dye from black rice has been successfully fabricated and improved its performance by depositing interconnected copper (copper bridge) on the space between TiO2. The copper bridge has significant role in minimizing recombination of electron-hole which occurred in TiO2 surface by trapping electron and facilitating to anode. The presence of interconnected copper nanoparticle in the space between TiO2 nanoparticle was confirmed by Scanning Electron Microscopy (SEM) and X-Ray Diffractometer (XRD). The current-voltage (I-V) characterization of DSSC solar cells by using Keithley 617 was also performed to investigate performance of solar cells under sun illumination in varying intensities. It is found that performance of copper coated DSSC solar cells (efficiency 0.35% and fill factor 0.35) is higher than DSSC without copper coating (efficiency 0.17% and fill factor 0.35). This result is consistent with impedance spectroscopy analyzing where the internal resistance of copper coated DSSC solar cells is lower than DSSC without coated. It is concluded that performance of DSSC increasing with decreasing of internal resistance. Our finding is higher than other researcher reports in Ref. [13] and [14] with similar structure and kind of natural dye. In addition, this paper also reports the use of polymer electrolyte which employing polyvinyl acetate (PVA) containing lithium ion to maintain long-term stability of device.
Effect of Electrochemical Reaction Enviroment on the Surface Morphology and Photoluminescence of Porous Silicon
Authors: Syari’ati Ali , Suendo Veinardi
Published: March 2013

Porous silicon (p-Si) is a well-known silicon based material that can emit visible light at room temperature. The radiative recombination that originated from quantum confinement effect shows photoluminescence (PL) in red, while the defect on silicon oxide at the surface of p-Si shows in blue-green region. Porous silicon can be synthesized through two methods; wet-etching and electrochemical anodization using hydrofluoric acid as the main electrolyte. The electrochemical anodization is more favorable due to faster etching rate at the surface than the conventional wet-etching method. The objective of this research is to show that both of porous silicons can be synthesized using the same main electrolyte but by varying the reaction environment during anodization/etching process. Here, we shows the wet-etching method that enhanced by polarization concentration will produce porous silicon with silicon oxide defects by means blue-green emission, while direct electrochemical anodization will produce samples that emit red PL signal. The effect of introducing KOH into the electrolyte was also studied in the case of enhanced-wet-etching method. Surface morphology of porous silicon and their photoluminescence were observed by Scanning Electron Microscope and PL spectroscopy, respectively.
XPS and NEXAFS Investigation of Electronic Energy Structure of Ti-Ni and TiNi-Cu Alloys
Authors: Senkovskiy Boris , Usachov Dmitry , Chikina Alla , Ulyanov Pavel , Shelyakov Alexander , Adamchuk Vera K.
Published: March 2013

The electronic energy structure of Ti-Ni and TiNi-Cu alloys has been studied experimentally by XPS and NEXAFS and theoretically by the full-potential local-orbital minimum-basis code. The study has revealed formation in the valence band of the Ti50Ni50 alloy of a common d-band through hybridization of the d-states of Ti with those of Ni, which is localized within a narrow binding-energy interval. This brings about an intra-atomic redistribution of Ti electron density in the Ti50Ni50 alloy compared to the pure metal: decrease of the occupancy of the Ti d-shell is countered by an increase in the number of Ti p-electrons. The occupancy of the Ti d-shell in the TiNi-Cu alloys, where Ni atoms are partially substituted by Cu, and in the Ti-Ni alloys with an excess of the Ni is more than in the equiatomic Ti50Ni50 alloy. The occupancy of the Ni and Cu d-shells in the Ti-Ni and TiNi-Cu alloys is independent of the atomic composition. The Ti d-shell sensitivity to variation of the nearest atomic environment is apparently due to their relatively itinerant behavior in the studied alloys. The results obtained suggest that the increase of the stiffness of an interatomic bond in the TiNi-Cu alloys with increasing Cu content and in the Ti-Ni alloys with increasing Ni content is possibly associated with the filling of Ti bonding d-states.
The Self-Accommodation and Rearrangement of Martensite Multi-Variants under Cyclic Stress: Phase-Field Simulation
Authors: Cui Yan Guang , Wan Jian Feng , Man J. , Guo Z.H. , Zhang J.H. , Rong Y.H.
Published: March 2013

A twin boundary model was established to describe the multi-variant interface in the martensitic materials. The modified semi-implicit Fourier-spectral method was proposed to solve the 3-D phase-field equation. Self-accommodation plays an important role in the micro-structural evolution during the loading and unloading. The external compressive stress can cause the rearrangement of martensites from three variants to one variant. After releasing the loading, another variant can nucleate and grow in one variant at the twin boundary. Cyclic stress may lead to the redistribution of martensite variants besides the rearrangement.
Phase Stability at Martensitic Transformation in Zr-Based Shape Memory Intermetallics
Authors: Firstov Georgiy , Timoshevski Andrei , Koval Yuri , Yablonovski Sergey , Van Humbeeck Jan
Published: March 2013

This article is dedicated to the estimation of the relative stability for B2, B19`, B33 and Cm phase in ZrCu-ZrNi-ZrCo intermetallic compound row through the ab-initio electronic structure calculations and subsequent crystal structure Rietveld refinement. The information about electronic and crystal structure of phases in Zr-based intermetallics will allow selecting for this high temperature shape memory alloy such alloying elements that will significantly improve shape memory behavior through definite structural changes.
CuZr Based Shape Memory Alloys: Effect of Cr and Co on the Martensitic Transformation
Authors: Biffi Carlo Alberto , Figini Albisetti Alessandro , Tuissi Ausonio
Published: March 2013

In the present work an investigation on CuZr based shape memory alloys was proposed. In particular, this study has been addressed the effect of the addition of Cr and Co on the martensitic transformation behaviour. The characterization was performed using DSC in terms of evolution of characteristic temperatures. The analysis of the proposed alloys was completed with the evaluation of the microhardness and the microstructure, observed by means of a scanning electron. Moreover, X-rays diffraction analysis was also carried out to check the crystal structures in the different alloys. It was shown how the addition of Co can improve thermal stability and the thermal hysteresis of the martensitic transformation by the first thermal cycles, even if the characteristic temperatures were significantly decreased.
Unexpected Constrained Twin Hierarchy in Equiatomic Ru-Based High Temperature Shape Memory Alloy Martensite
Authors: Vermaut Philippe , Manzoni Anna , Denquin Anne , Prima Frédéric , Portier Richard
Published: March 2013

Among the different systems for high temperature shape memory alloys (SMA’s), equiatomic RuNb and RuTa alloys demonstrate both shape memory effect (SME) and MT temperatures above 800°C. Equiatomic compounds undergo two successive martensitic transformations, β (B2) → β’ (tetragonal) → β’’ (monoclinic), whereas out of stoechiometry alloys exhibit a single transition from cubic to tetragonal. In the case of two successive martensitic transformations, we expect to have a finer microstructure of the second martensite because it is supposed to develop inside the smallest twin elements of the former one. In equiatomic Ru-based alloys, if the first martensitic transformation is “normal”, the second one gives different unexpected microstructures with, for instance, twins with a thickness which is larger than the smallest spacing between twin variants of the first martensite. In fact, the reason for this unexpected hierarchy of the twins size is that the second martensitic transformation takes place in special conditions: geometrically, elastically and crystallographically constrained.
The Microstructural Design and Control of Ultrahigh Strength-Ductility Martensitic Steels Based on a Novel Quenching-Partitioning-Tempering Process
Authors: Rong Yong Hua , Zhang Ke , Dai Jia Wei , Yu Hai Liang
Published: March 2013

Since Hsu in our group proposed a novel quenching-partitioning-tempering (Q-P-T) process in 2007, Q-P-T steels with ultrahigh strength and ultrahigh strength-ductility are greatly developed. In this paper a novel Q–P–T process based on design of microstructure is first introduced, including the comparison of Q-P-T process with a novel quenching-partitioning (Q&P) and traditional quenching and tempering (Q&T) process. The mechanical properties of Q-P-T steels at room temperature and elevated temperatures are then exhibited, including nanolath martensitic steel with the tensile strength of over 2000MPa and ultrahigh strength-ductility steel with the product of strength and elongation of over 30000MPa%. The mechanisms of ductility enhancement by retained austenite are finally summarized, including a new effect proposed by us, named DARA (dislocation absorption by retained austenite) effect after TRIP (transformation induced plasticity) effect and BMP (blocking microcrack propagation) effect proposed by other investigators 50 years ago.
Influence of Mechanical Alloying on the Behavior of Fe-Mn-Si-Cr-Ni Shape Memory Alloys Made by Powder Metallurgy
Authors: Pricop Bogdan , Söyler Umut , Özkal Burak , Lohan Nicoleta Monica , Paraschiv Adrian Liviu , Suru Marius Gabriel , Bujoreanu Leandru Gheorghe
Published: March 2013

Fe-14 Mn-6 Si-9 Cr-5 Ni (mass. %) shape memory alloys (SMAs) were produced from raw powders employed both in initial commercial state and in a mixture state of equal fractions of commercial and mechanically alloyed (MA’d) particles. After blending, pressing and sintering, powder compacts were hot rolled (HR’d) and solution treated (ST’d) before being machined into plane-parallel lamellas. Specimens with special geometry were pre-strained on a tensile testing machine. By means of X-ray diffraction (XRD) and scanning electron microscopy (SEM) the presence of ε hexagonal close packed and α’ body center cubic stress induced martensites was revealed and their thermally induced reversion to γ face center cubic austenite was evaluated by modulated differential scanning calorimetry (MDSC). The results enabled the study of the influence of MA, HR, ST and pre-straining on phase structure and associated on shape memory effect (SME). The lamellas were hot formed into rings, which were trained in bending. Diameter reduction of trained enlarged rings, on heating, was monitored by cinematographic analysis.
Effect of Flux Constituents and Basicity Index on Mechanical Properties and Microstructural Evolution of Submerged Arc Welded High Strength Low Alloy Steel
Authors: Jindal Sandeep , Chhibber Rahul , Mehta N.P.
Published: March 2013

The application of high strength low alloy (HSLA) steels has been limited by unavailability of suitable joining and filler metals in submerged arc welding (SAW) processes. The present work aims at the design and development of flux for Submerged Arc Welding of HSLA steel. In the work L8 array of Taguchi Design is used to formulate eight types of fluxes to vary basicity index (BI) from 1.26 to 2.81 and to study the effect of flux constituents and basicity index on tensile strength, microhardness and microstructure of the weld metal. Empirical models for ultimate tensile strength and microhardness at the centre of weld versus flux constituents and basicity index have been developed. From the experiments it is found that ultimate tensile strength increase with increase of basicity index with minimum at 1.26 increases upto 2.33 and then further decreases whereas opposite in case of microhardness which is highest at 1.26 and minimum at 1.9. Increase of CaO in the flux increases ultimate tensile strength but microhardness remains unaffected whereas increase of SiO2 decreases ultimate tensile strength but microhardness remains constant. Microhardness decreases critically with increase of CaF2.
In Situ Optical Microscope Examinations of the ε↔γ Transformations in FeMn(Cr) Austenitic Steels during Thermal Cycling
Authors: Benke Marton , Mertinger Valéria , Tranta Ferenc
Published: March 2013

A group of austenitic steels exhibit high deformability and strength due to TRansformation Induced Plasticity (TRIP) and/or TWinning Induced Plasticity (TWIP). The phase transformations of the TRIP and TWIP steels have been examined in details in many FeMnX alloy systems (X: Ni, Al, Si). However, less attention was given to the FeMn(Cr) alloys. The γ ↔ ε transformations in the austenitic FeMn(Cr) alloys have been examined during heat cycling by in situ optical microscopy and DSC measurements.
Pseudo Elastic Cyclic Deformation of Ti-Ni Alloy under Various Temperatures
Authors: Kaputkin Dmitry E. , Morozova Tatiana V. , Esina Elena V.
Published: March 2013

Scheme of pseudo elastic cyclic deformation of Ti49,4Ni50,6 wire (Ms=0±2oC) in 18-70оС temperature range included loading up to 4,3% elongation and unloading. It was shown that the parameters of the strain/stress patterns are strongly resulting from numbers of preliminary deformation cycles. Preliminary deformation cycling in the range of 3-4 percent provides stabilization after 10-15 cycles of the whole complex of mechanical properties including 30-50% increase of the stress during unloading, which is necessary to finish of the reverse martensitic transformation. Following cycling stabilizes all mechanical characteristics excluding one. An increase of numbers of preliminary deformation cycles (up to 50) results in monotonous decrease of the energy, which disappears during one cycle.
In Situ Structural Characterization of Laser Welded NiTi Shape Memory Alloys
Authors: Braz Fernandes Francisco Manuel , Mahesh Karimbi Koosappa , Crăciunescu Corneliu Marius , Oliveira João Pedro , Schell Norbert , Miranda Rosa Maria , Quintino Luisa , Ocaña José Luis
Published: March 2013

The demand of emerging joining techniques for shape memory alloys (SMA) has become of great importance, as their functional properties, namely shape memory effect (SME) and superelasticity (SE) present unique solutions for state-of-the-art applications. Literature shows that significant efforts have been conducted on laser welding of these alloys, although very limited results concerning mechanical properties are repeatedly achieved. A better understanding of the mechanical behaviour of these welded joints may be got through a detailed analysis of the structural characteristics of the material from the base metal to the weld bead. Such studies have been carried out on a series of Ni-rich Ni-Ti SMA laser welded plates using synchrotron radiation.
Study of Martensitic Transformation in Tini Intermetallic by the Methods of Low Frequency Internal Friction
Authors: Markova Galina Viktorovna , Shuytcev Alexander V. , Kasimtcev Anatoliy V.
Published: March 2013

The present article is dedicated to the study of thermoelastic martensitic transformation in the TiNi equiatomic composition by low-frequency internal friction. Considered the influence of oscillation frequency, strain amplitude and heating rate on the internal friction peak of the martensitic nature.
Structural Changes in Co-Based F-SMA
Authors: Kopeček Jaromír , Kopecký Vít , Landa Michal , Heczko Oleg
Published: March 2013

The Co38Ni33Al29 alloy as a potential ferromagnetic shape memory alloy was investigated. The method of preparation of the unidirectional solidified single-crystals from cast material is described. The high-temperature annealing and subsequent quenching was found to be necessary condition for the shape memory behavior. The martensitic transformation temperatures of annealed samples were about 200 K determined from magnetic measurement while as-cast sample did not exhibit any sharp transformation. All martensitic structures observed at room temperature by microscopic methods are thus stress induced. These results agree with pseudoelastic behavior observed in annealed and quenched samples.
Theoretical Study of Magnetic Properties and Multiple Twin Boundary Motion in Heusler Ni-Mn-X Shape Memory Alloys Using First Principles and Monte Carlo Method
Authors: Kostromitin K.I. , Buchelnikov Vasiliy D. , Sokolovskiy Vladimir V. , Kamantsev Alexander P. , Koledov Victor , Shavrov Vladimir G. , Entel P.
Published: March 2013

In this paper we firstly propose and study a microscopic model of multiple twin boundary motion using the first principles and Monte Carlo simulations in Heusler Ni-Mn-X (for example, X = Ga) alloys on real tetragonal lattice. The two variants of the low temperature martensite which divided by twin boundary are considered. The Heisenberg model for magnetic subsystem and Blume-Emery-Griffiths (BEG) one for structural subsystem with magnetostructural interaction between these subsystems are used. The influence of external magnetic field and anisotropy on the twin boundary motion is studied. It is shown that proposed model gives the picture of twin boundary motion as in experiments.
Reversible Martensitic Transformation Produced by Severe Plastic Deformation of Metastable Austenitic Steel
Authors: Litovchenko Igor , Tyumentsev Alexander , Korznikov Alexander V.
Published: March 2013

The peculiarities of martensitic transformations and formation of nanostructured states in metastable austenitic steel (Fe-18Cr-8Ni-Ti) after severe plastic deformation by high pressure torsion are investigated. It is shown that during severe plastic deformation with increased strain rate not only direct (γ→α΄) but also reverse (α΄→γ) martensitic transformations occur, which is revealed by the changes in the volume content of α΄ - martensite during deformation. The fragments thought to be formed by direct and reverse martensitic transformations and those of dynamic recrystallization of austenite are observed.
Optimization of Superelastic Properties in Titanium-Niobium Alloys Using Short-Time Thermal Treatments
Authors: Prima Frédéric , Sun Fan , El May Wafa , Gloriant T. , Laheurte Pascal , Jordan Laurence , Vermaut Philippe , Portier Richard , Hao Yu Lin
Published: March 2013

The short-time thermal treatment strategy has been proved to be very efficient in improving the mechanical properties of various titanium based alloys. The mechanical properties of alloys such as Ti-Nb, Ti-Nb-Zr and Ti-Nb-Zr-Sn based alloys, are extremely sensitive to the β phase stability, microstructure and phase constitution. The concept of the short-time treatment is designed to control precisely the material structure (phase precipitation, etc…) without extensive modification of the distribution of alloying elements. This results in reliable optimizations regarding the balance between elastic modulus, pseudo- (super-) elasticity and strength. Currently, the structural evolution mechanisms involved in the STAT are under systematic investigations in the aim of achieving accurate control of the microstructures and optimized balance of mechanical properties.
Effect of Nitrogen Addition on Tempering and Strain Aging Processes of Thermomechanically Strengthened Structural Steels
Authors: Kaputkina Lyudmila M. , Prokoshkina Vera , Khadeev Grigory
Published: March 2013

Mechanical behavior of structural nitrogen-containing steels with various structures and compositions, including the same steels with different summary C+N content and C/N ratio were studied using pressing tests in a wide temperature range, tensile tests, impact bending tests, hardness measurements and shock-wave loading resistance. The tempering and aging under load processes after quenching or thermomechanical treatment with various regimes have been investigated using optical and electron microscopies, X-ray diffraction analysis, calorimetric and dilatometric analyses. Hot strain resistance of the austenite is determined essentially by the steel composition, while the final structure and mechanical properties of hot-deformed austenite are determine mainly by hot deformation conditions. The higher the nitrogen content and C/N ratio, the higher hot strain resistance was and earlier the softening processes start, especially recrystallization process. The nitrogen microalloying of low-alloyed structural steels changes kinetics of the martensite tempering. Application of the high temperature thermomechanical treatment or combined thermomechanical strengthening with following tempering under load allows the use of these steels in a high-strength state after low-temperature tempering.
TiPt HTSMA Produced by Spark Plasma Sintering of Elemental Powders
Authors: Chikosha Silethelwe , Chikwanda Hilda Kundai
Published: March 2013

Titanium-platinum (Ti50Pt50) alloy has been identified as a potential candidate for high temperature shape memory alloy (HTSMA) applications such as actuators in jet engines. This work evaluates powder metallurgy as an alternative processing route with the added benefit that near net shaped components can be formed. Spark plasma sintering (SPS) of blended elemental titanium and platinum powders was carried out. The sintering conditions used were: temperatures ranging from 1200 to 1400 °C and sintering times ranging from 10 to 30 minutes. SEM with EDS, XRD and DSC were carried out to study the results. Results showed that SPS only achieved high density, but not homogenisation of the alloys. All sintering conditions resulted in formation of the martensitic TiPt phase of interest, together with some or all of the following phases: Ti, Ti3Pt, Ti4Pt3, Ti3Pt5 and Pt. Post sintering annealing treatments were carried out to homoginise the alloys at 1300 °C for times ranging from 5 to 15 hours. With sufficient annealing times a two phase microstructure was produced with TiPt as the majority matrix phase and Ti3Pt5 as the precipitate phase.
In Situ Tensile Deformation of TRIP Steel / Mg-PSZ Composites
Authors: Weidner Anja , Berek Harry , Segel Christian , Aneziris Christos G. , Biermann Horst
Published: March 2013

Composite material on the basis of a TRIP (transformation induced plasticity) steel with zirconia particles as reinforcement was produced by powder metallurgical technology and conventional sinter process. The goal of such type of material is to obtain exceptional mechanical properties like high deformation energy absorption due to the combination of martensitic phase transformations both in steel and ceramic. The steel matrix was made of the commercial steel AISI 304, which shows a deformation-induced martensitic phase transformation from the austenitic phase (fcc) into the α’-martensite (bcc). The zirconia particles were partially stabilized with MgO and show a stress-assisted martensitic phase transformation from the tetragonal to the monocline phase. Flat specimens were tensile deformed in-situ in a scanning electron microscope in order to follow the damage behaviour of the material. Some zirconia particles were characterized before and after tensile testing both by backscattered electron contrast as well as by electron backscatter diffraction (EBSD) in combination with energy dispersive X-ray spectroscopy (EDS).
Tension - Compression Asymmetry in Co49Ni21Ga30 High-Temperature Shape Memory Alloy Single Crystals
Authors: Niendorf Thomas , Dadda Jayaram , Lackmann Jan , Monroe James A. , Karaman Ibrahim , Panchenko Elena , Karaca Haluk E. , Maier Hans J.
Published: March 2013

This paper reports on the tension-compression asymmetry of [001]-oriented Co49Ni21Ga30 single crystals at elevated temperatures. Maximum strains of -4.8 % and 8.6 % in compression and tension, respectively, were found. A linear Clausius-Clapeyron relationship was observed for both stress-states where the smaller slope in tension resulted in a significant increase of the phase transformation temperatures with stress, which reached 180 °C under a constant stress level of 150 MPa. In addition, the material demonstrated a large pseudoelastic temperature range of about 300 °C under both stress state conditions. The results in this study unequivocally indicate the potential of these alloys for applications where elevated temperatures and stress levels prevail.
In Situ X-Ray Study of Phase Transformations in Ti-Nb-Based SMA under Variable Stress-Temperature Conditions: Preliminary Results
Authors: Dubinskiy Sergey , Brailovski Vladimir , Prokoshkin Sergey , Inaekyan Karine
Published: March 2013

The technique and preliminary results of in situ X-ray diffraction analysis of the martensitic transformation in the newly developed Ti-Nb-Zr SMA for biomedical application are presented. To perform the in situ analysis, an original tensile stage, powered by a Ti-Ni SMA actuator and fit within the “TTK450” thermal chamber of a “PANalytical X’Pert Pro” diffractometer is designed, manufactured and validated. The tensile stage working principle and analysis methodology are described in detail. Preliminary results obtained during in-situ X-ray analysis of the phase transformations in Ti-Nb-Zr SMA are also presented.
Distribution of Residual Elastic Microstress in Rolled Ti-Ni Single Crystals
Authors: Perlovich Yuriy , Isaenkova Margarita , Fesenko Vladimir , Dementyeva Tatyana
Published: March 2013

Typical modes of the microstress distribution were found by X-ray study of Ti-Ni rolled single crystals using the X-ray method of Generalized Pole Figures. The method consists in successive measurements of the peak position 2θ for the same X-ray line of B2 phase by all possible positions of the sample in the course of diffractometric study of its texture. In the case of one-component rolling texture maxima in pole figure break into halves with opposite signs of elastic deformation, whereas by two-component rolling textures the one-sign elastic strain dominates within different maxima.
High Temperature SiC Sensor with an Isolated Package
Authors: Draghici Florin , Brezeanu Gheorghe , Rusu Ion , Bernea Florin , Godignon Philippe
Published: March 2013

This paper presents an improved version and new results on a temperature sensor based on SiC Schottky Barrier Diode (SBD). SiC SBD structures of different areas were packaged in a metallic-glass case. The encapsulated sensor was electrically measured at several temperatures. A good linearity of the forward voltage measured at a constant current versus temperature dependence was obtained in the temperature range of 150-400°C where the sensor is meant to operate. Optical investigation, correlated with electrical measurements, prove the reliability of the sensor structure and of the package solutions at temperatures up to 400°C.
Superfast Drift Step Recovery Diodes (DSRDs) and Vacuum Field Emission Diodes Based on 4H-SiC
Authors: Afanasyev Alexey V. , Ivanov Boris V. , Ilyin Vladimir A. , Kardo-Sysoev Alexey F. , Kuznetsova Maria A. , Luchinin Victor V.
Published: March 2013

This paper presents the results of research and development of two types diode structures based on wide bandgap 4H-SiC: drift step recovery diodes (DSRDs) and field emission diodes (FED). Diodes’ structure and manufacturing methods are reviewed. Diode’s characteristics were obtained (static current-voltage characteristics and capacitor-voltage characteristic, switching properties’ characteristics for DSRDs). Field emission 4H-SiC structures illustrated high (≥102 А/сm2) current densities at electric field intensity of approximately 10V/um. 4H-SiC DSRDs in the generator structure with a single oscillating contour allowed to form sub nanosecond impulses at a load 50 Ohm and 1,5-2kV amplitude for a single diode (current density at V=2kV J= 4•103 А/сm2),what is significantly higher than similar DSRD’s parameters obtained for silicon.
Properties of Graphene Side Gate Transistors
Authors: Hähnlein Bernd , Händel Benjamin , Schwierz Frank , Pezoldt Joerg
Published: March 2013

Epitaxial graphene grown on semiinsulating silicon carbide was used to fabricate side gate graphene transistors. The transconductance of the side gate transistors is comparable to top gate designs. The transconductance decreases with increasing gate width independently on the gate to channel distance in agreement with the transconductance reduction in top gate transistor configu¬rations with increasing channel length. The transconductance of the side gate transistors decreases with increasing channel width due to a decreased specific gate capacitance.
AlGaN Solid Solution Grown on 3C-SiC(111)/Si(111) Pseudosubstrates
Authors: Tonisch Katja , Benzig Robert , Ecke Gernot , Pezoldt Joerg
Published: March 2013

The growth of AlGaN solid solutions on 3C-SiC(111)/Si(111) is demonstrated. The residual stress of the grown layer was investigated by high resolution X-ray diffraction (HRXRD) and infrared ellipsometry. Analysis of the HRXRD data showed that the observed lattice distortion was caused partially by hydrostatic pressure and partially by biaxial tension. The residual stress depends on the layer composition and weakly on the growth temperature.
Complementary JFET Logic for Low-Power Applications in Extreme Environments
Authors: Habib H. , Wright N.G. , Horsfall A.B.
Published: March 2013

The static and dynamic characteristics of Complementary JFET (CJFET) logic inverter are studied across a range of temperatures and supply voltages to assess potential improvements in performance of digital logic functions for operation in extreme environments. The logic inverter is truly the core of all digital designs. The design and analysis of inverter enables the design of more complex structures, such as NAND, NOR and XOR gates. These complex structures in turn form the building blocks for modules, such as adders, multipliers and microprocessors. At 500 deg C and operating at a supply voltage of 1 V, the CJFET inverter have noise margin comparable to that of room temperature silicon and silicon on insulator CMOS inverters. Furthermore, the static power dissipation by CJFET inverter at 500 deg C is 20.6 nW which is six orders of magnitude lower than that by current SiC technologies, making CJFET technology ideal for achieving complex logic functions, far greater than a few-transistors ICs, in the nearer term.
High-Speed Drive Circuit with Separate Source Terminal for 600 V / 40 A Normally-off SiC-JFET
Authors: Ishikawa Katsumi , Katoh Kaoru , Hatanaka Ayumu , Ogawa Kazutoshi , Shimizu Haruka , Yokoyama Natsuki
Published: March 2013

When using JFETs with a threshold voltage lower than 2 V in a power supply system or inverter system, a high-speed drive circuit capable of precisely controlling the gate current and a mounting method are important to reduce the switching loss. In this paper, a drive circuit of a normally-off SiC-JFET with a separate source terminal is proposed and the effects are evaluated. By dividing the common source inductance and applying the speed-up capacitor, the turn-on time and turn-on energy losses can be decreased by 40% and 60%, respectively. A speed-up capacitor larger than 100 nF greatly decreases the rising time (tr) and turn-on energy losses. By applying the developed normally-off SiC-JFETs and proposed gate driver to PFC circuits and DC/DC circuits, a highly efficient power supply will be achieved.
Vertical Channel Silicon Carbide JFETs Based Operational Amplifiers
Authors: Maralani Ayden , Mazzola M.S. , Pisano A.P.
Published: March 2013

Superior performance of the Silicon Carbide (SiC) semiconductor in high temperature and harsh environment is widely known. However, utilizing the Vertical Channel 4H–SiC JFET (SiC VJFET) for analog circuit design exhibits significant design challenges, even at room temperature. The fundamental challenges are low intrinsic gain, the limitation of the Gate to Source Voltage Range (GSVR), and restrictions on utilizing Channel Length (CL) as a design parameter due to fabrication complexity. These challenges must be successfully overcome at room temperature, before moving forward with high temperature design. After addressing these issues, two operational amplifiers (opamps) with two distinct design topologies are designed and fabricated. The first design (opamp-1) emphasizes on the gain and Common Mode Rejection Ratio (CMRR) performances [1]. The second design (opamp-2) presents a novel opamp [2] with universal applications where the reliability and unity gain frequency performances are also improved. In this paper, the performance parameters of these two opamps along with their design topologies are reported and compared.
Silicon Nitride as Top Gate Dielectric for Epitaxial Graphene
Authors: Wehrfritz Peter , Fromm Felix , Malzer Stefan , Seyller Thomas
Published: March 2013

Silicon nitride (SiN) was deposited by plasma enhanced chemical vapor deposition (PECVD) as a top gate dielectric on epitaxial graphene on 6H-SiC(0001). We compare x-ray photoelectron spectroscopy (XPS), Raman spectroscopy, and transport measurements which were performed before and after the SiN deposition. We demonstrate that closed layers of SiN are formed without the need for surface activation and that the plasma process leads only to a minor degradation of the graphene. The SiN layer induces strong n-type doping. For a limited gate voltage range, a small hysteresis of 0.2 V is observed in top-gated field effect devices.
Effect of Surface Polarity on the Conversion of Threading Dislocations in Solution Growth
Authors: Yamamoto Yuji , Harada Shunta , Seki Kazuaki , Horio Atsushi , Mitsuhashi Takato , Ujihara Toru
Published: March 2013

We investigated the dislocation behaviors during the solution growth on Si-face and C-face off-axis 4H-SiC seed crystals by using synchrotron X-ray topography. On Si-face, almost all threading screw dislocations (TSDs) and threading edge dislocations (TEDs) are converted into Frank-type defects and basal plane dislocations (BPDs), respectively. On the other hand, on C-face, TSDs were hardly converted. Some of TEDs were converted to BPDs and BPD-TED reconversion was often occurred. Therefore, to reduce density of threading dislocations in the grown crystal, it is better to use Si-face off-axis seed crystal.
Surface Evolution of 4H-SiC(0001) during In Situ Surface Preparation and its Influence on Graphene Properties
Authors: Hassan Jawad , Meyer Axel , Cakmakyapan Semih , Kazar Ozgur , Ingo Flege Jan , Falta Jens , Ozbay Ekmel , Janzén Erik
Published: March 2013

The evolution of SiC surface morphology during graphene growth process has been studied through the comparison of substrate surface step structure after in-situ etching and graphene growth in vacuum. Influence of in-situ substrate surface preparation on the properties of graphene was studied through the comparison of graphene layers on etched and un-etched substrates grown under same conditions.
On-Axis Homoepitaxial Growth of 4H-SiC PiN Structure for High Power Applications
Authors: Hassan Jawad , Booker Ian D. , Lilja Louise , Hallén Anders , Fagerlind Martin , Bergman Peder , Janzén Erik
Published: March 2013

We demonstrate on-axis homoepitaxial growth of 4H-SiC(0001) PiN structure on 3-inch wafers with 100% 4H polytype in the epilayer excluding the edges. The layers were grown with a thickness of 105 µm and controlled n-type doping of 4 x 1014 cm-3.The epilayers were completely free of basal plane dislocations, in-grown stacking faults and other epitaxial defects, as required for 10 kV high power bipolar devices. Some part of the wafer had a lifetime enhancement procedure to increase lifetime to above 2 s using carbon implantation. An additional step of epilayer polishing was adapted to reduce surface roughness and implantation damage.
Study of the Nucleation of p-Doped SiC in Selective Epitaxial Growth Using VLS Transport
Authors: Carole Davy , Vo Ha Arthur , Thomas Anthony , Lazar Mihai , Thierry-Jebali Nicolas , Tournier Dominique , Cauwet François , Soulière Véronique , Brylinski Christian , Brosselard Pierre , Planson D. , Ferro Gabriel
Published: March 2013

This work deals with the study of the Selective Epitaxial Growth (SEG) of SiC using Vapour-Liquid-Solid (VLS) transport at temperature ≤ 1100°C. Focus was made on the nucleation step by observing the evolution of the growth as a function of growth duration with variable Si-content of the Al-Si liquid phase. Addition of propane during the initial heating ramping-up not only avoids liquid de-wetting but also allows good starting of the epitaxial growth. Additionally, it was observed that, by increasing the silicon content in the liquid, the morphology of the grown SiC is improved, and no parasitic Al4C3 inclusions are formed. Limiting the growth rate is found to be essential for getting controlled smooth growth process.
Low Resistivity, Thick Heavily Al-Doped 4H-SiC Epilayers Grown by Hot-Wall Chemical Vapor Deposition
Authors: Ji Shi Yang , Kojima Kazutoshi , Ishida Yuuki , Tsuchida Hidekazu , Yoshida Sadafumi , Okumura Hajime
Published: March 2013

By using hot-wall CVD method, thick heavily Al-doped 4H-SiC epilayers (~90 μm) were grown on 3-inches 4H-SiC wafers. Around the solubility limit, the incorporation behaviors of Al into 4H-SiC were investigated by varying the growth conditions. Among the samples having smooth surfaces, the maximum Al dopants concentration of 3.5×1020 cm-3 and the minimum resistivity of 16.5 mΩcm were achieved. The results of Hall-effect measurement demonstrate that, along with the increase of Al doping level, the activation ratio of Al dopants gradually increases from several percent up to 100% where the Al dopants concentration is 1.5×1020 cm-3.
Step-Flow Growth of Fluorescent 4H-SiC Layers on 4 Degree Off-Axis Substrates
Authors: Schimmel Saskia , Kaiser Michl , Hens Philip , Jakubavicius Valdas , Liljedahl Rickard , Sun Jian Wu , Yakimova Rositza , Ou Yi Yu , Ou Hai Yan , Linnarsson Margareta K. , Wellmann Peter J. , Syväjärvi Mikael
Published: March 2013

Homoepitaxial layers of fluorescent 4H-SiC were grown on 4 degree off-axis substrates by sublimation epitaxy. Luminescence in the green spectral range was obtained by co-doping with nitrogen and boron utilizing donor-acceptor pair luminescence. This concept opens possibilities to explore green light emitting diodes using a new materials platform.
Morphological and Optical Stability in Growth of Fluorescent SiC on Low Off-Axis Substrates
Authors: Jokubavicius Valdas , Kaiser Michl , Hens Philip , Wellmann Peter J. , Liljedahl Rickard , Yakimova Rositza , Syväjärvi Mikael
Published: March 2013

Fluorescent silicon carbide was grown using the fast sublimation growth process on low off-axis 6H-SiC substrates. In this case, the morphology of the epilayer and the incorporation of dopants are influenced by the Si/C ratio. Differently converted tantalum foils were introduced into the growth cell in order to change vapor phase stochiometry during the growth. Fluorescent SiC grown using fresh and fully converted tantalum foils contained morphological instabilities leading to lower room temperature photoluminescence intensity while an improved morphology and optical stability was achieved with partly converted tantalum foil. This work reflects the importance of considering the use of Ta foil in sublimation epitaxy regarding the morphological and optical stability in fluorescent silicon carbide.
Vapor-Phase Catalyst Delivery Method for Growing SiC Nanowires
Authors: Thirumalai Rooban Venkatesh K.G. , Krishnan Bharat , Davydov Albert , Merrett Joseph Neil , Koshka Yaroslav
Published: March 2013

A method was developed for growing SiC nanowires without depositing a metal catalyst on the targeted surfaces prior to the CVD growth. The proposed method utilizes in-situ vapor-phase catalyst delivery via sublimation of the catalyst from a metal source placed in the hot zone of the CVD reactor, followed by condensation of the catalyst-rich vapor on the bare substrate surface to form the catalyst nanoparticles. The vapor-phase catalyst delivery and the resulting nanowire density was found to be influenced by both the gas flow rate and the catalyst diffusion through the boundary layer above the catalyst source. The origin of undesirable bushes of nanowires and the role of the C/Si ratio were established.
10 × 100 mm 4H-SiC Epitaxial Growth by Warm-Wall Planetary Reactor
Authors: Dong Lin , Sun Guo Sheng , Yu Jun , Yan Guo Guo , Zhao Wan Shun , Wang Lei , Zhang Xin He , Li Xi Guang , Wang Zhan Guo
Published: March 2013

We present our recent results on of 10 × 100 mm 4H-SiC epitaxy by a warm-wall planetary reactor at a growth rate of 10 μm/h. The epilayers grown by this high-throughput reactor show specular surfaces and good uniformities of thickness and doping. The intra-wafer and wafer-to-wafer thickness uniformities are 2.0% and 0.5%, respectively, while intra-wafer and wafer-to-wafer doping uniformities are 14.0% and 3.4%, respectively. The obtained surface RMS roughness is 0.2 nm. These results suggest that this 10 × 100 mm warm-wall planetary reactor provides very promising prospect on the mass production of 4H-SiC epilayers, which will further promote the development of SiC-based electronic devices.
Monte Carlo Study of the Hetero-Polytypical Growth of Cubic on Hexagonal Silicon Carbide Polytypes
Authors: Camarda Massimo , La Magna Antonino , La Via Francesco
Published: March 2013

We use three dimensional kinetic Monte Carlo simulations on super-lattices to study the hetero-polytypical growth of cubic silicon carbide polytype (3C-SiC) on misoriented hexagonal (4H and 6H) substrates finding that the growth on misoriented (4°-10° degree off) 6H substrates, with step bunched surfaces, can strongly improve the quality of the cubic epitaxial film promoting 3C single domain growths
Elaboration of Core Si/Shell SiC Nanowires
Authors: Ollivier Maelig , Latu-Romain Laurence , Mantoux Arnaud , Martin Mickaël , Baron Thierry , Soulière Véronique , Ferro Gabriel , Bano Edwige
Published: March 2013

Silicon nanowires obtained by a top-down approach have been carburized at high temperature and atmospheric pressure with two different gaseous precursors: CH4 and C3H8. These processes reveal core silicon / shell 3C-SiC nanowires. After being characterized by SEM, FIB-SEM and TEM microscopies, the 3C-SiC layer has been used as seed layer for the growth of epitaxial 3C-SiC on the nanowires. Preferential growth of 3C-SiC on the sidewalls of nanowires has been observed. Thanks to the biocompatibility of SiC compared to Si, this layer could act as a protective shell for biosensors based on Si nanowires transistor.
Photoluminescence of 8H-SiC
Authors: Henry Anne , Ivanov Ivan G. , Janzén Erik , Hatayama Tomoaki , Yano Hiroshi , Fuyuki Takashi
Published: March 2013

8H-SiC epilayers grown on small 8H-SiC Lely platelets are investigated optically using photoluminescence spectroscopy. At low temperature the near band gap emission detected in the 2.78 to 2.67 eV range contains sharp lines associated to nitrogen-bound-exciton recombination. Three different no-phonon lines are detected accompanied by their phonon replicas. Free-exciton replicas are also observed which allows the determination of the excitonic band gap. The binding energy of the bound excitons can thus be determined and the ionization energies of the three nitrogen levels in 8H-SiC are estimated and found to be rather shallow compared to the values for other hexagonal polytypes. Additional bound-exciton lines are observed when the experimental photoluminescence temperature is increased.
P-6H-SiC Conductivity Compensation after Irradiation of 8MeV Protons
Authors: Lebedev Alexander A. , Kozlovski Vitalii V. , Belov Sergey V. , Bogdanova Elena V. , Oganesyan Gagik A.
Published: March 2013

Carrier removal rate (Vd) in p-6H-SiC in its irradiation with 8 MeV protons has been studied. p-6H-SiC samples were produced by sublimation in a vacuum. Vd was determined by analysis of capacitance-voltage characteristics and from results of Hall effect measurements. It was found that full compensation of samples with initial value of Na-Nd 1.5 x1018 cm-3 occurs at an irradiation dose of ~1.1 1016 cm-2. In this case, the carrier removal rate was ~130 cm-1
Comparative Analysis of Defect Formation in Silicon Carbide under Electron and Proton Irradiation
Authors: Ivanov Alexander M. , Lebedev Alexander A. , Kozlovski Vitalii V.
Published: March 2013

The irradiation with 0.9 MeV electrons and with 8 MeV and 15 MeV protons were performed for studying radiation defects. Proton scattering in a silicon carbide film has been numerically simulated. Distribution histograms of the energy imparted to recoil atoms are obtained. Two energy ranges are considered when analyzing the histograms. In the first range of “low” energies, individual Frenkel pairs with closely spaced components are created. In the second range, recoil atoms have energies sufficient for generating a cascade of displacements. This gives rise to microscopic regions with high density of vacancies and vacancy complexes of various kinds.