Correlation between thermal annealing temperature and Joule-heating based insulator-metal transition in VO2 nanobeams

NASA Astrophysics Data System (ADS)

Rathi, Servin; Park, Jin-Hyung; Lee, In-yeal; Jin Kim, Min; Min Baik, Jeong; Kim, Gil-Ho

2013-11-01

Rapid thermal annealing of VO2 nanobeams in an ambient argon environment has been carried out at various temperatures after device fabrication. Our analysis revealed that increasing the annealing temperature from 200 °C to 400 °C results in the reduction of both ohmic and nanobeam resistances with an appreciable decrease in joule-heating based transition voltage and transition temperature, while samples annealed at 500 °C exhibited a conducting rutile-phase like characteristics at room temperature. In addition, these variation trends were explored using a physical model and the results were found to be in agreement with the observed results, thus verifying the model.

Annealing effect on structural and optical properties of chemical bath deposited MnS thin film

DOE Office of Scientific and Technical Information (OSTI.GOV)

Ulutas, Cemal, E-mail: cemalulutas@hakkari.edu.tr; Gumus, Cebrail

2016-03-25

MnS thin film was prepared by the chemical bath deposition (CBD) method on commercial microscope glass substrate deposited at 30 °C. The as-deposited film was given thermal annealing treatment in air atmosphere at various temperatures (150, 300 and 450 °C) for 1 h. The MnS thin film was characterized by using X-ray diffraction (XRD), UV-vis spectrophotometer and Hall effect measurement system. The effect of annealing temperature on the structural, electrical and optical properties such as optical constants of refractive index (n) and energy band gap (E{sub g}) of the film was determined. XRD measurements reveal that the film is crystallized inmore » the wurtzite phase and changed to tetragonal Mn{sub 3}O{sub 4} phase after being annealed at 300 °C. The energy band gap of film decreased from 3.69 eV to 3.21 eV based on the annealing temperature.« less

Effects of Laves phase particles on recovery and recrystallization behaviors of Nb-containing FeCrAl alloys

DOE PAGES

Sun, Zhiqian; Edmondson, Philip D.; Yamamoto, Yukinori

2017-11-15

The microstructures and mechanical properties of deformed and annealed Nb-containing FeCrAl alloys were investigated. Fine dispersion of Fe 2Nb-type Laves phase particles was observed in the bcc-Fe matrix after applying a thermomechanical treatment, especially along grain/subgrain boundaries, which effectively stabilized the recovered and recrystallized microstructures compared with the Nb-free FeCrAl alloy. The stability of recovered areas increased with Nb content up to 1 wt%. The recrystallized grain structure in Nb-containing FeCrAl alloys consisted of elongated grains along the rolling direction with a weak texture when annealed below 1100 °C. An abnormal relationship between recrystallized grain size and annealing temperature wasmore » found. Microstructural inhomogeneity in the deformed and annealed states was explained based on the Taylor factor. Annealed Nb-containing FeCrAl alloys showed a good combination of strength and ductility, which is desirable for their application as fuel cladding in light-water reactors.« less

Effect of solvent and subsequent thermal annealing on the performance of phenylenevinylene copolymer: PCBM solar cells.

PubMed

Sharma, G D; Suresh, P; Sharma, S S; Vijay, Y K; Mikroyannidis, John A

2010-02-01

The morphology of the photoactive layer used in the bulk heterojunction photovoltaic devices is crucial for efficient charge generation and their collection at the electrodes. We investigated the solvent vapor annealing and thermal annealing effect of an alternating phenylenevinylene copolymer P:PCBM blend on its morphology and optical properties. The UV-visible absorption spectroscopy shows that both solvent and thermal annealing can result in self-assembling of copolymer P to form an ordered structure, leading to enhanced absorption in the red region and hole transport enhancement. By combining the solvent and thermal annealing of the devices, the power conversion efficiency is improved. This feature was attributed to the fact that the PCBM molecules begin to diffuse into aggregates and together with the ordered copolymer P phase form bicontinuous pathways in the entire layer for efficient charge separation and transport. Furthermore, the measured photocurrent also suggests that the space charges no longer limit the values of the short circuit current (J(sc)) and fill factor (FF) for solvent-treated and thermally annealed devices. These results indicate that the higher J(sc) and PCE for the solvent-treated and thermally annealed devices can be attributed to the phase separation of active layers, which leads to a balanced carrier mobility. The overall PCE of the device based on the combination of solvent annealing and thermal annealing is about 3.7 %.

Orientation and faulted structure of γ'-phases in lanthanum-alloyed Ni-Al-Cr superalloy

NASA Astrophysics Data System (ADS)

Nikonenko, Elena; Shergaeva, Lyubov'; Popova, Natalya; Koneva, Nina; Qin, Rongshan; Gromov, Victor; Fedorischeva, Marina

2017-12-01

The paper presents the transmission and the scanning electron microscope investigations of thin foils of Ni-Al-Cr-based superalloy, which is obtained by the directional crystallization technique. This superalloy contains γ'- and γ- phases. Additionally, lanthanum is introduced in the superalloy in 0.015, 0.10 and 0.30 wt % concentrations. The superalloy specimens are then subjected to 1273 K annealing during 10 and 25 h. It is shown that γ'-phase is major. In the superalloy, lanthanides La2Ni3 and Al2La are detected along with carbide La2C3 particles located on dislocations of the major phase. The amount of phases in the superalloy depends on its thermal treatment and lanthanum concentration. The investigations include the effect of annealing on scalar density of dislocations in γ'-phase. It is demonstrated that lanthanum alloying modifies the preferred orientation of γ'-phase. Annealing of lanthanum-alloyed superalloy causes the orientation dispersion. In γ'-phase, the correlation is observed between the degree of heterogeneity of solid solution and scalar dislocation density. It is shown that this heterogeneity results in the formation of high-density dislocations in γ'- phase.

Structure and phase composition of ultrafine-grained TiNb alloy after high-temperature annealings

NASA Astrophysics Data System (ADS)

Eroshenko, Anna Yu.; Glukhov, Ivan A.; Mairambekova, Aikol; Tolmachev, Alexey I.; Sharkeev, Yurii P.

2017-12-01

The paper presents the experimental data observed in the microstructure and phase composition of ultrafine-grained Ti-40 mass % Nb (Ti40Nb) alloy after high-temperature annealings. The ultrafine-grained Ti40Nb alloy is produced by severe plastic deformation (SPD). This method includes multiple abc-pressing and multi-pass rolling followed by further pre-recrystallizing annealing which, in its turn, enhances the formation of ultrafine-grained structures with mean size of 0.28 µm involving stable β- and α-phase and metastable nanosized ω-phase in the alloy. It is shown that annealing at 500°C preserves the ultrafine-grained structure and phase composition. In cases of annealing at 800°C the ultrafine-grained state transforms into the coarse-grained state. The stable β-phase and the nanosized metastable ω-phase have been identified in the coarse-grained structure.

Solvent annealing induced phase separation and dewetting in PMMA∕SAN blend film: film thickness and solvent dependence.

PubMed

You, Jichun; Zhang, Shuangshuang; Huang, Gang; Shi, Tongfei; Li, Yongjin

2013-06-28

The competition between "dewetting" and "phase separation" behaviors in polymer blend films attracts significant attention in the last decade. The simultaneous phase separation and dewetting in PMMA∕SAN [poly(methyl methacrylate) and poly(styrene-ran-acrylonitrile)] blend ultrathin films upon solvent annealing have been observed for the first time in our previous work. In this work, film thickness and annealing solvent dependence of phase behaviors in this system has been investigated using atomic force microscopy and grazing incidence small-angle X-ray scattering (GISAXS). On one hand, both vertical phase separation and dewetting take place upon selective solvent vapor annealing, leading to the formation of droplet∕mimic-film structures with various sizes (depending on original film thickness). On the other hand, the whole blend film dewets the substrate and produces dispersed droplets on the silicon oxide upon common solvent annealing. GISAXS results demonstrate the phase separation in the big dewetted droplets resulted from the thicker film (39.8 nm). In contrast, no period structure is detected in small droplets from the thinner film (5.1 nm and 9.7 nm). This investigation indicates that dewetting and phase separation in PMMA∕SAN blend film upon solvent annealing depend crucially on the film thickness and the atmosphere during annealing.

Photoelectrochemical (PEC) studies on Cu2SnS3 (CTS) thin films deposited by chemical bath deposition method.

PubMed

Shelke, H D; Lokhande, A C; Kim, J H; Lokhande, C D

2017-11-15

Cu 2 SnS 3 (CTS) thin films have been successfully deposited on a cost-effective stainless steel substrate by simple and inexpensive chemical bath deposition (CBD) method. The films are deliberated in provisos of their structural, morphological, optical and photoelectrochemical (PEC) properties before and after annealing treatment, using various physico-chemical techniques. The XRD studies showed the formation of triclinic phase of CTS films with nanocrystalline structure. Also, the crystallinity is enhanced with annealing and the secondary phase of Cu 2 S observed. Raman analysis confirmed the formation of CTS compound with secondary Cu 2 S phase. The SEM images also discovered mostly tiny spherical grains and significant progress in the size of grains after annealing. The films possess direct transitions with band gap energies of 1.35eV and 1.31eV before and after annealing, respectively. The improved photoconversion efficiency of CTS thin film based PEC cell is explained with the help of theoretical modeling of energy band diagram and correspondent circuit model of the impedance spectra. Copyright © 2017 Elsevier Inc. All rights reserved.

Iron-platinum multilayer thin film reactions to form L1(0) iron-platinum and exchange spring magnets

NASA Astrophysics Data System (ADS)

Yao, Bo

FePt films with the L10 phase have potential applications for magnetic recording and permanent magnets due to its high magnetocrystalline anisotropy energy density. Heat treatment of [Fe/Pt] n multilayer films is one approach to form the L10 FePt phase through a solid state reaction. This thesis has studied the diffusion and reaction of [Fe/Pt]n multilayer films to form the L10 FePt phase and has used this understanding to construct exchange spring magnets. The process-structure-property relations of [Fe/Pt] n multilayer films were systematically examined. The transmission electron microscopy (TEM) study of the annealed multilayers indicates that the Pt layer grows at the expense of Fe during annealing, forming a disordered fcc FePt phase by the interdiffusion of Fe into Pt. This thickening of the fcc Pt layer can be attributed to the higher solubilities of Fe into fcc Pt, as compared to the converse. For the range of film thickness studied, a continuous L10 FePt product layer that then thickens with further annealing is not found. Instead, the initial L10 FePt grains are distributed mainly on the grain boundaries within the fcc FePt layer and at the Fe/Pt interfaces and further transformation of the sample to the ordered L10 FePt phase proceeds coupled with the growth of the initial L10 FePt grains. A comprehensive study of annealed [Fe/Pt]n films is provided concerning the phase fraction, grain size, nucleation/grain density, interdiffusivity, long-range order parameter, and texture, as well as magnetic properties. A method based on hollow cone dark field TEM is introduced to measure the volume fraction, grain size, and density of ordered L10 FePt phase grains in the annealed films, and low-angle X-ray diffraction is used to measure the effective Fe-Pt interdiffusivity. The process-structure-properties relations of two groups of samples with varying substrate temperature and periodicity are reported. The results demonstrate that the processing parameters (substrate temperature, periodicity) have a strong influence on the structure (effective interdiffusivity, L1 0 phase volume fraction, grain size, and density) and magnetic properties. The correlation of these parameters suggests that the annealed [Fe/Pt]n multilayer films have limited nuclei, and the subsequent growth of L10 phase is very important to the extent of ordered phase formed. A correlation between the grain size of fcc FePt phase, grain size of the L10 FePt phase, the L10 FePt phase fraction, and magnetic properties strongly suggests that the phase transformation of fcc →L10 is highly dependent on the grain size of the parent fcc FePt phase. A selective phase growth model is proposed to explain the phenomena observed. An investigation of the influence of total film thickness on the phase formation of the L10 FePt phase in [Fe/Pt] n multilayer films and a comparison of this to that of FePt co-deposited alloy films is also conducted. A general trend of greater L1 0 phase formation in thicker films was observed in both types of films. It was further found that the thickness dependence of the structure and of the magnetic properties in [Fe/Pt]n multilayer films is much stronger than that in FePt alloy films. This is related to the greater chemical energy contained in [Fe/Pt]n films than FePt alloy films, which is helpful for the L10 FePt phase growth. However, the initial nucleation temperature of [Fe/Pt]n multilayers and co-deposited alloy films was found to be similar. An investigation of L10 FePt-based exchange spring magnets is presented based on our understanding of the L10 formation in [Fe/Pt] n multilayer films. It is known that exchange coupling is an interfacial magnetic interaction and it was experimentally shown that this interaction is limited to within several nanometers of the interface. A higher degree of order of the hard phase is shown to increase the length scale slightly. Two approaches can be used to construct the magnets. For samples with composition close to stoichiometric L10 FePt, the achievement of higher energy product is limited by the average saturation magnetization, and therefore, a lower annealing temperature is beneficial to increase the energy product, allowing a larger fraction of disordered phase. For samples with higher Fe concentration, the (BH)max is limited by the low coercivity of annealed sample, and a higher annealing temperature is beneficial to increase the energy product.

Cesium lead iodide solar cells controlled by annealing temperature.

PubMed

Kim, Yu Geun; Kim, Tae-Yoon; Oh, Jeong Hyeon; Choi, Kyoung Soon; Kim, Youn-Jea; Kim, Soo Young

2017-02-22

An inorganic lead halide perovskite film, CsPbI 3 , used as an absorber in perovskite solar cells (PSCs) was optimized by controlling the annealing temperature and the layer thickness. The CsPbI 3 layer was synthesized by one-step coating of CsI mixed with PbI 2 and a HI additive in N,N-dimethylformamide. The annealing temperature of the CsPbI 3 film was varied from 80 to 120 °C for different durations and the thickness was controlled by changing the spin-coating rpm. After annealing the CsPbI 3 layer at 100 °C under dark conditions for 10 min, a black phase of CsPbI 3 was formed and the band gap was 1.69 eV. Most of the yellow spots disappeared, the surface coverage was almost 100%, and the rms roughness was minimized to 3.03 nm after annealing at 100 °C. The power conversion efficiency (PCE) of the CsPbI 3 based PSC annealed at 100 °C was 4.88%. This high PCE value is attributed to the low yellow phase ratio, high surface coverage, low rms roughness, lower charge transport resistance, and lower charge accumulation. The loss ratio of the PCE of the CH 3 NH 3 PbI x Cl 3-x and CsPbI 3 based PSCs after keeping in air was 47 and 26%, respectively, indicating that the stability of the CsPbI 3 based PSC is better than that of the CH 3 NH 3 PbI x Cl 3-x based PSC. From these results, it is evident that CsPbI 3 is a potential candidate for solar cell applications.

Chemical characterization of surface precipitates in La0.7Sr0.3Co0.2Fe0.8O3-δ as cathode material for solid oxide fuel cells

DOE Office of Scientific and Technical Information (OSTI.GOV)

Yu, Yang; Nikiforov, Alexey Y.; Kaspar, Tiffany C.

2016-11-01

In this study, a strontium doped lanthanum cobalt ferrite thin film with 30% Sr on A-site, denoted as La0.7Sr0.3Co0.2Fe0.8O3-δ or LSCF-7328, was investigated before and after annealing at 800 °C under CO2 containing atmosphere for 9 hours. The formation of secondary phases on surface of post-annealed LSCF-7328 has been observed using atomic force microscope (AFM) and scanning electron microscope (SEM). The extent of Sr segregation at the film surface was observed using the synchrotron-based total reflection X-ray fluorescence (TXRF) technique. The bonding environment of the secondary phases formed on the surface was investigated by synchrotron-based hard X-ray photoelectron spectroscopy (HAXPES).more » Transmission electron microscope (TEM) and related spectroscopy techniques were used for microstructural and quantitative elemental analyses of the secondary phases on surface. These studies revealed that the secondary phases on surface consisted of SrO covered with a capping layer of SrCO3. The formation of Co-rich phases has also been observed on the surface of post-annealed LSCF-7328.« less

Radio frequency surface resistance of Tl-Ba-Ca-Cu-O films on metal and single-crystal substrates

NASA Astrophysics Data System (ADS)

Arendt, P. N.; Reeves, G. A.; Elliott, N. E.; Cooke, D. W.; Gray, E. R.; Houlton, R. J.; Brown, D. R.

1990-01-01

Films of Tl-Ba-Ca-Cu were dc magnetron sputtered from a single multielement target. The films were deposited onto substrates of: (1) magnesium oxide, (2) a silver based alloy (Consil 995), (3) a nickel based alloy (Haynes 230), and (4) buffer layers of barium fluoride or copper oxide on Consil. To form superconducting phases, post-deposition anneals were made on these films using an alumina crucible with an over pressure of thallium and flowing oxygen. After annealing, the film phases were determined using x-ray diffraction. The film surface resistances (Rs) were measured at 22 GHz in a TE011 cavity.

Phase and structural transformations in VVER-440 RPV base metal after long-term operation and recovery annealing

NASA Astrophysics Data System (ADS)

Kuleshova, E. A.; Gurovich, B. A.; Maltsev, D. A.; Frolov, A. S.; Bukina, Z. V.; Fedotova, S. V.; Saltykov, M. A.; Krikun, E. V.; Erak, D. Yu; Zhurko, D. A.; Safonov, D. V.; Zhuchkov, G. M.

2018-04-01

This study was carried out to evaluate the possibility of 1st generation VVER-440 reactors lifetime extension by recovery re-annealing with the respect to base metal (BM). Comprehensive studies of the structure and properties of BM templates (samples cut from the inner surface of the shells in beltline region) of operating VVER-440 reactor (after primary standard recovery annealing 475 °C/150 h and subsequent long-term re-irradiation within reactor pressure vessel (RPV)) were conducted. These templates were also subjected to laboratory re-annealing 475 °C/150 h. TEM, SEM and APT studies of BM after laboratory re-annealing revealed significant recovery of radiation-induced hardening elements (Cu-rich precipitates and dislocation loops). Simultaneously a process of strong phosphorus accumulation at grain boundaries occurs since annealing temperature corresponds to the maximum reversible temper brittleness development. The latter is not observed for VVER-440 weld metal (WM). Comparative assessment of the properties return level for the beltline BM templates after recovery re-annealing 475 °C/150 h showed that it does not reach the one typical for beltline WM after the same annealing.

Annealing effects on the structural and magnetic properties of off-stoichiometric Fe-Mn-Ga ferromagnetic shape memory alloys

DOE PAGES

Chen, Yan; Bei, Hongbin; Dela Cruz, Clarina R; ...

2016-05-07

Annealing plays an important role in modifying structures and properties of ferromagnetic shape memory alloys (FSMAs). The annealing effect on the structures and magnetic properties of off-stoichiometric Fe 45Mn 26Ga 29 FSMA has been investigated at different elevated temperatures. Rietveld refinements of neutron diffraction patterns display that the formation of the γ phase in Fe 45Mn 26Ga 29 annealed at 1073 K increases the martensitic transformation temperature and reduces the thermal hysteresis in comparison to the homogenized sample. The phase segregation of a Fe-rich cubic phase and a Ga-rich cubic phase occurs at the annealing temperature of 773 K. Themore » atomic occupancies of the alloys are determined thanks to the neutron's capability of differentiating transition metals. The annealing effects at different temperatures introduce a different magnetic characteristic that is associated with distinctive structural changes in the crystal.« less

Prevention of nanoparticle coalescence under high-temperature annealing.

PubMed

Mizuno, Mikihisa; Sasaki, Yuichi; Yu, Andrew C C; Inoue, Makoto

2004-12-21

An effective method of employing 3-aminopropyldimethylethoxysilane linker molecules to stabilize 4.4 nm FePt nanoparticle monolayer films on a SiO2 substrate as well as to prevent coalescence of the particles under 800 degrees C annealing is reported. As-deposited FePt nanoparticle films in chemically disordered face-centered-cubic phase transform to mostly chemically ordered L1 0 structure after annealing, while the nanoparticles are free from serious coalescence. The method may fulfill the pressing need to prevent nanoparticle coalescence under high-temperature annealing for the development of FePt nanoparticle based products, such as ultrahigh-density magnetic recording media and novel memory devices.

Growth and characterization of sol-gel derived CuGaO2 semiconductor thin films for UV photodetector application

NASA Astrophysics Data System (ADS)

Tsay, Chien-Yie; Chen, Ching-Lien

2017-06-01

In this study, a p-type wide-bandgap oxide semiconductor CuGaO2 thin film was grown on quartz substrate by sol-gel method. The authors report the influence of annealing temperature on the phase transformation, structural features, and electrical properties of sol-gel derived Cu-Ga-O thin films. At relatively low annealing temperatures (≤900 °C), the films are a mixture of CuGa2O4, CuGaO2, and CuO phases. At relatively high annealing temperatures (≥925 °C), the majority phase in the films is delafossite CuGaO2. All as-prepared Cu-Ga-O thin films exhibited p-type conductivity, as confirmed by Hall measurements. The mean electrical resistivity of the Cu-Ga-O films decreased from 3.54×104 Ω-cm to 1.35×102 Ω-cm and then increased slightly to 3.51×102 Ω-cm when the annealing temperature was increased from 850 °C to 950 °C. We found that annealing the Cu-based oxide thin films at 925 °C produced nearly phase-pure CuGaO2 thin films with good densification. Such thin films exhibited the best electrical properties: a mean electrical resistivity of 1.35×102 Ω-cm, and a mean hole concentration of 1.60×1016 cm-3. In addition, we also fabricated and characterized MSM-type CuGaO2 UV photodetectors on quartz substrates.

Microstructure based simulations for prediction of flow curves and selection of process parameters for inter-critical annealing in DP steel

NASA Astrophysics Data System (ADS)

Deepu, M. J.; Farivar, H.; Prahl, U.; Phanikumar, G.

2017-04-01

Dual phase steels are versatile advanced high strength steels that are being used for sheet metal applications in automotive industry. It also has the potential for application in bulk components like gear. The inter-critical annealing in dual phase steels is one of the crucial steps that determine the mechanical properties of the material. Selection of the process parameters for inter-critical annealing, in particular, the inter-critical annealing temperature and time is important as it plays a major role in determining the volume fractions of ferrite and martensite, which in turn determines the mechanical properties. Selection of these process parameters to obtain a particular required mechanical property requires large number of experimental trials. Simulation of microstructure evolution and virtual compression/tensile testing can help in reducing the number of such experimental trials. In the present work, phase field modeling implemented in the commercial software Micress® is used to predict the microstructure evolution during inter-critical annealing. Virtual compression tests are performed on the simulated microstructure using finite element method implemented in the commercial software, to obtain the effective flow curve of the macroscopic material. The flow curves obtained by simulation are experimentally validated with physical simulation in Gleeble® and compared with that obtained using linear rule of mixture. The methodology could be used in determining the inter-critical annealing process parameters required for achieving a particular flow curve.

Nanoalloying and phase transformations during thermal treatment of physical mixtures of Pd and Cu nanoparticles

PubMed Central

Mukundan, Vineetha; Yin, Jun; Joseph, Pharrah; Luo, Jin; Shan, Shiyao; Zakharov, Dmitri N; Zhong, Chuan-Jian; Malis, Oana

2014-01-01

Nanoscale alloying and phase transformations in physical mixtures of Pd and Cu ultrafine nanoparticles are investigated in real time with in situ synchrotron-based x-ray diffraction complemented by ex situ high-resolution transmission electron microscopy. The combination of metal–support interaction and reactive/non-reactive environment was found to determine the thermal evolution and ultimate structure of this binary system. At 300 °C, the nanoparticles supported on silica and carbon black intermix to form a chemically ordered CsCl-type (B2) alloy phase. The B2 phase transforms into a disordered fcc alloy at higher temperature (> 450 °C). The alloy nanoparticles supported on silica and carbon black are homogeneous in volume, but evidence was found of Pd surface enrichment. In sharp contrast, when supported on alumina, the two metals segregated at 300 °C to produce almost pure fcc Cu and Pd phases. Upon further annealing of the mixture on alumina above 600 °C, the two metals interdiffused, forming two distinct disordered alloys of compositions 30% and 90% Pd. The annealing atmosphere also plays a major role in the structural evolution of these bimetallic nanoparticles. The nanoparticles annealed in forming gas are larger than the nanoparticles annealing in helium due to reduction of the surface oxides that promotes coalescence and sintering. PMID:27877663

ZBLAN Fiber Phase B Study

NASA Technical Reports Server (NTRS)

Workman, Gary L.; Smith, Guy A.

1997-01-01

A Phase B feasibility study will be performed for the study of the effects of microgravity on the preform processing and fiber pulling of ZBLAN optical glass. Continuing from the positive results achieved in the fiber annealing experiments in 20 second intervals at 0.001 g on the KC-135 and the 5 minute experiments on the SPAR rocket, experiments will continue to work towards design of a fiber sting to initiate fiber pulling operations in space. Anticipated results include less homogeneous nucleation than ground-based annealed fibers. Infrared Fiber Systems and Galileo are the participating industrial investigators.

Effect of annealing temperature on the properties of copper oxide films prepared by dip coating technique

NASA Astrophysics Data System (ADS)

Raship, N. A.; Sahdan, M. Z.; Adriyanto, F.; Nurfazliana, M. F.; Bakri, A. S.

2017-01-01

Copper oxide films were grown on silicon substrates by sol-gel dip coating method. In order to study the effects of annealing temperature on the properties of copper oxide films, the temperature was varied from 200 °C to 450 °C. In the process of dip coating, the substrate is withdrawn from the precursor solution with uniform velocity to obtain a uniform coating before undergoing an annealing process to make the copper oxide film polycrystalline. The physical properties of the copper oxide films were measured by an X-ray diffraction (XRD), a field emission scanning electron microscope (FESEM), an atomic force microscopy (AFM) and a four point probe instrument. From the XRD results, we found that pure cuprite (Cu2O) phase can be obtained by annealing the films annealed at 200 °C. Films annealed at 300 °C had a combination phase which consists of tenorite (CuO) and cuprite (Cu2O) phase while pure tenorite (CuO) phase can be obtained at 450 °C annealing temperature. The surface microstructure showed that the grains size is increased whereas the surface roughness is increased and then decreases by increasing in annealing temperature. The films showed that the resistivity decreased with increasing annealing temperature. Consequently, it was observed that annealing temperature has strong effects on the structural, morphological and electrical properties of copper oxide films.

Free Energy Minimization by Simulated Annealing with Applications to Lithospheric Slabs and Mantle Plumes

NASA Astrophysics Data System (ADS)

Bina, C. R.

An optimization algorithm based upon the method of simulated annealing is of utility in calculating equilibrium phase assemblages as functions of pressure, temperature, and chemical composi tion. Operating by analogy to the statistical mechanics of the chemical system, it is applicable both to problems of strict chemical equilibrium and to problems involving metastability. The method reproduces known phase diagrams and illustrates the expected thermal deflection of phase transitions in thermal models of subducting lithospheric slabs and buoyant mantle plumes. It reveals temperature-induced changes in phase transition sharpness and the stability of Fe-rich γ phase within an α+γ field in cold slab thermal models, and it suggests that transitions such as the possible breakdown of silicate perovskite to mixed oxides can amplify velocity anomalies.

Structural characterization of multimetallic nanoparticles

NASA Astrophysics Data System (ADS)

Mukundan, Vineetha

Bimetallic and trimetallic alloy nanoparticles have enhanced catalytic activities due to their unique structural properties. Using in situ time-resolved synchrotron based x-ray diffraction, we investigated the structural properties of nanoscale catalysts undergoing various heat treatments. Thermal treatment brings about changes in particle size, morphology, dispersion of metals on support, alloying, surface electronic properties, etc. First, the mechanisms of coalescence and grain growth in PtNiCo nanoparticles supported on planar silica on silicon were examined in detail in the temperature range 400-900°C. The sintering process in PtNiCo nanoparticles was found to be accompanied by lattice contraction and L10 chemical ordering. The mass transport involved in sintering is attributed to grain boundary diffusion and its corresponding activation energy is estimated from the data analysis. Nanoscale alloying and phase transformations in physical mixtures of Pd and Cu ultrafine nanoparticles were also investigated in real time with in situ synchrotron based x-ray diffraction complemented by ex situ high-resolution transmission electron microscopy. PdCu nanoparticles are interesting because they are found to be more efficient as catalysts in ethanol oxidation reaction (EOR) than monometallic Pd catalysts. The combination of metal support interaction and reactive/non-reactive environment was found to determine the thermal evolution and ultimate structure of this binary system. The composition of the as prepared Pd:Cu mixture in this study was 34% Pd and 66% Cu. At 300°C, the nanoparticles supported on silica and carbon black intermix to form a chemically ordered CsCl-type (B2) alloy phase. The B2 phase transforms into a disordered fcc alloy at higher temperature (>450°C). The alloy nanoparticles supported on silica and carbon black are homogeneous in volume, but evidence was found of Pd surface enrichment. In sharp contrast, when supported on alumina, the two metals segregated at 300°C to produce almost pure fcc Cu and Pd phases. Upon further annealing of the mixture on alumina above 600°C, the two metals interdiffused, forming two distinct disordered alloys of compositions 30% and 90% Pd. The annealing atmosphere also plays a major role in the structural evolution of these bimetallic nanoparticles. The nanoparticles annealed in forming gas are larger than the nanoparticles annealed in helium due to reduction of the surface oxides that promotes coalescence and sintering. The nanoscale composition and structure of alloy catalysts affect heterogeneous catalysis. We also studied Pd:Cu nanoparticle mixtures of different compositions. In Pd:Cu of composition ratio 1:1, ordered B2 phase is formed during annealing at 450C. During the ramped annealing from 450°C to 750°C, the B2 phase transforms into two different alloys, one alloy rich in copper and the other rich in Pd. This structural evolution is different from that of Pd-Cu system in bulk. In the 3:1 composition, the B2 phase dominates in the isothermal anneal at 450C but a disordered alloy fcc phase is also formed. On annealing to 750°C, the disordered fcc phase grows at the expense of the B2 phase. These findings have important applications for the thermal activation of Pd-Cu nanocatalysts for EOR reactions.

Effect of thermal annealing on the phase evolution of silver tungstate in Ag/WO₃ films.

PubMed

Bose, R Jolly; Sreedharan, R Sreeja; Krishnan, R Resmi; Reddy, V R; Gupta, Mukul; Ganesan, V; Sudheer, S K; Pillai, V P Mahadevan

2015-06-15

Silver/tungsten oxide multi-layer films are deposited over quartz substrates by RF magnetron sputtering technique and the films are annealed at temperatures 200, 400 and 600°C. The effect of thermal annealing on the phase evolution of silver tungstate phase in Ag/WO3 films is studied extensively using techniques like X-ray diffraction, micro-Raman analysis, atomic force microscopy and photoluminescence studies. The XRD pattern of the as-deposited film shows only the peaks of cubic phase of silver. The film annealed at 200°C shows the presence of XRD peaks corresponding to orthorhombic phase of Ag2WO4 and peaks corresponding to cubic phase of silver with reduced intensity. It is found that, as annealing temperature increases, the volume fraction of Ag decreases and that of Ag2WO4 phase increases and becomes highest at a temperature of 400°C. When the temperature increases beyond 400°C, the volume fraction of Ag2WO4 decreases, due to its decomposition into silver and oxygen deficient phase Ag2W4O13. The micro-Raman spectra of the annealed films show the characteristic bands of tungstate phase which is in agreement with XRD analysis. The surface morphology of the films studied by atomic force microscopy reveals that the particle size and r.m.s roughness are highest for the sample annealed at 400°C. In the photoluminescence study, the films with silver tungstate phase show an emission peak in blue region centered around the wavelength 441 nm (excitation wavelength 256 nm). Copyright © 2015 Elsevier B.V. All rights reserved.

Effect of Annealing Treatments on the Microstructure, Mechanical Properties and Corrosion Behavior of Direct Metal Laser Sintered Ti-6Al-4V

NASA Astrophysics Data System (ADS)

Xu, Yangzi; Lu, Yuan; Sundberg, Kristin L.; Liang, Jianyu; Sisson, Richard D.

2017-05-01

An experimental investigation on the effects of post-annealing treatments on the microstructure, mechanical properties and corrosion behavior of direct metal laser sintered Ti-6Al-4V alloys has been conducted. The microstructure and phase evolution as affected by annealing treatment temperature were examined through scanning electron microscopy and x-ray diffraction. The tensile properties and Vickers hardness were measured and compared to the commercial Grade 5 Ti-6Al-4V alloy. Corrosion behavior of the parts was analyzed electrochemically in simulated body fluid at 37 °C. It was found out that the as-printed parts mainly composed of non-equilibrium α' phase. Annealing treatment allowed the transformation from α' to α phase and the development of β phase. The tensile test results indicated that post-annealing treatment could improve the ductility and decrease the strength. The as-printed Ti-6Al-4V part exhibits inferior corrosion resistance compared to the commercial alloy, and post-annealing treatment can reduce its susceptibility to corrosion by reducing the two-phase interface area.

Alpha phase precipitation from phase-separated beta phase in a model Ti-Mo-Al alloy studied by direct coupling of transmission electron microscopy and atom probe tomography

DOE Office of Scientific and Technical Information (OSTI.GOV)

Devaraj, Arun; Nag, Soumya; Banerjee, Rajarshi

2013-10-19

The benefit of direct coupling of APT with TEM dark field imaging to investigate early stages of phase transformation in multicomponent alloys is demonstrated by analyzing alpha phase precipitated in a model Ti-10 at% Mo-10 at% Al alloy during annealing at 400oC. Through such a direct coupling approach a thermodynamically unexpected solute partitioning trend between beta matrix and alpha precipitate is observed in the early stages of precipitation, which is explained based on possible nucleation of alpha phase in the Ti rich (Mo and Al depleted regions) created as a result of phase separation in beta matrix. On further highermore » temperature annealing at 600oC for 1 hour, the alpha precipitates were shown to grow and get enriched in Al and further depleted in Mo reaching the thermodynamic equilibrium.« less

Non-Conventional Techniques for the Study of Phase Transitions in NiTi-Based Alloys

NASA Astrophysics Data System (ADS)

Nespoli, Adelaide; Villa, Elena; Passaretti, Francesca; Albertini, Franca; Cabassi, Riccardo; Pasquale, Massimo; Sasso, Carlo Paolo; Coïsson, Marco

2014-07-01

Differential scanning calorimetry and electrical resistance measurements are the two most common techniques for the study of the phase transition path and temperatures of shape memory alloys (SMA) in stress-free condition. Besides, it is well known that internal friction measurements are also useful for this purpose. There are indeed some further techniques which are seldom used for the basic characterization of SMA transition: dilatometric analysis, magnetic measurements, and Seebeck coefficient study. In this work, we discuss the attitude of these techniques for the study of NiTi-based phase transition. Measurements were conducted on several fully annealed Ni50- x Ti50Cu x samples ranging from 3 to 10 at.% in Cu content, fully annealed at 850 °C for 1 h in vacuum and quenched in water at room temperature. Results show that all these techniques are sensitive to phase transition, and they provide significant information about the existence of intermediate phases.

Two- and multi-step annealing of cereal starches in relation to gelatinization.

PubMed

Shi, Yong-Cheng

2008-02-13

Two- and multi-step annealing experiments were designed to determine how much gelatinization temperature of waxy rice, waxy barley, and wheat starches could be increased without causing a decrease in gelatinization enthalpy or a decline in X-ray crystallinity. A mixture of starch and excess water was heated in a differential scanning calorimeter (DSC) pan to a specific temperature and maintained there for 0.5-48 h. The experimental approach was first to anneal a starch at a low temperature so that the gelatinization temperature of the starch was increased without causing a decrease in gelatinization enthalpy. The annealing temperature was then raised, but still was kept below the onset gelatinization temperature of the previously annealed starch. When a second- or third-step annealing temperature was high enough, it caused a decrease in crystallinity, even though the holding temperature remained below the onset gelatinization temperature of the previously annealed starch. These results support that gelatinization is a nonequilibrium process and that dissociation of double helices is driven by the swelling of amorphous regions. Small-scale starch slurry annealing was also performed and confirmed the annealing results conducted in DSC pans. A three-phase model of a starch granule, a mobile amorphous phase, a rigid amorphous phase, and a crystalline phase, was used to interpret the annealing results. Annealing seems to be an interplay between a more efficient packing of crystallites in starch granules and swelling of plasticized amorphous regions. There is always a temperature ceiling that can be used to anneal a starch without causing a decrease in crystallinity. That temperature ceiling is starch-specific, dependent on the structure of a starch, and is lower than the original onset gelatinization of a starch.

Rapid shear alignment of sub-10 nm cylinder-forming block copolymer films based on thermal expansion mismatch

NASA Astrophysics Data System (ADS)

Nicaise, Samuel M.; Gadelrab, Karim R.; G, Amir Tavakkoli K.; Ross, Caroline A.; Alexander-Katz, Alfredo; Berggren, Karl K.

2018-01-01

Directed self-assembly of block copolymers (BCPs) provided by shear-stress can produce aligned sub-10 nm structures over large areas for applications in integrated circuits, next-generation data storage, and plasmonic structures. In this work, we present a fast, versatile BCP shear-alignment process based on coefficient of thermal expansion mismatch of the BCP film, a rigid top coat and a substrate. Monolayer and bilayer cylindrical microdomains of poly(styrene-b-dimethylsiloxane) aligned preferentially in-plane and orthogonal to naturally-forming or engineered cracks in the top coat film, allowing for orientation control over 1 cm2 substrates. Annealing temperatures, up to 275 °C, provided low-defect alignment up to 2 mm away from cracks for rapid (<1 min) annealing times. Finite-element simulations of the stress as a function of annealing time, annealing temperature, and distance from cracks showed that shear stress during the cooling phase of the thermal annealing was critical for the observed microdomain alignment.

Microstructure evolution and large magnetocaloric effect of La0.8Ce0.2(Fe0.95Co0.05)11.8Si1.2 alloy prepared by strip-casting and annealing

NASA Astrophysics Data System (ADS)

Zhong, X. C.; Feng, X. L.; Huang, J. H.; Zhang, H.; Huang, Y. L.; Liu, Z. W.; Jiao, D. L.

2018-04-01

The microstructure and magnetocaloric effect of the La0.8Ce0.2(Fe0.95Co0.05)11.8Si1.2 strip-cast flakes annealed between 1273K and 1423K for different time have been investigated. For the flakes annealed for 2h from 1273K to 1423K, the shape and distribution of α-Fe, La-rich and NaZn13-type 1:13 phases are quite sensitive to the annealing temperature. Especially, at a high annealing temperature of 1423K, the 1:13 phase began to decompose into macroscopic α-Fe conglomerations and La-rich dendrites. With the increase of annealing time from 0 to 12h at 1323K, the amount of 1:13 phase increased significantly and reached ˜93.50 wt.% at 12h. However, an overlong annealing time also led to 1:13 phase decomposition and influenced the magnetic performance. For the flakes annealed at 1323K for 12h, large magnetic entropy change value of 18.12Jkg-1K-1 at 5T has been obtained. The present results indicate that strip casting method can potentially be used in mass production of high performance magnetocaloric materials.

Structure Evolution of Graphene Oxide during Thermally Driven Phase Transformation: Is the Oxygen Content Really Preserved?

PubMed Central

Sun, Pengzhan; Wang, Yanlei; Liu, He; Wang, Kunlin; Wu, Dehai; Xu, Zhiping; Zhu, Hongwei

2014-01-01

A mild annealing procedure was recently proposed for the scalable enhancement of graphene oxide (GO) properties with the oxygen content preserved, which was demonstrated to be attributed to the thermally driven phase separation. In this work, the structure evolution of GO with mild annealing is closely investigated. It reveals that in addition to phase separation, the transformation of oxygen functionalities also occurs, which leads to the slight reduction of GO membranes and furthers the enhancement of GO properties. These results are further supported by the density functional theory based calculations. The results also show that the amount of chemically bonded oxygen atoms on graphene decreases gradually and we propose that the strongly physisorbed oxygen species constrained in the holes and vacancies on GO lattice might be responsible for the preserved oxygen content during the mild annealing procedure. The present experimental results and calculations indicate that both the diffusion and transformation of oxygen functional groups might play important roles in the scalable enhancement of GO properties. PMID:25372142

Effect of annealing on structure, morphology and optoelectronic properties of nanocrystalline CuO thin films

NASA Astrophysics Data System (ADS)

Jundale, D. M.; Pawar, S. G.; Patil, S. L.; Chougule, M. A.; Godse, P. R.; Patil, V. B.

2011-10-01

The nanocrystalline CuO thin films were prepared on glass substrates by the sol-gel method. The structural, morphological, electrical and optical properties of CuO thin films, submitted to an annealing treatment in the 400-700 °C ranges are studied by X-ray diffraction (XRD), Scanning Electron Microscopy (SEM), Four Probe Technique and UV-visible spectroscopic. XRD measurements show that all the films are crystallized in the monoclinic phase and present a random orientation. Four prominent peaks, corresponding to the (110) phase (2θ≈32.70°), (002) phase (2θ≈35.70°), (111) phase (2θ≈38.76°) and (202) phase (2θ≈49.06°) appear on the diffractograms. The crystallite size increases with increasing annealing temperature. These modifications influence the microstructure, electrical and optical properties. The optical band gap energy decreases with increasing annealing temperature. These mean that the optical quality of CuO films is improved by annealing.

Effect of annealing on structural and luminescence properties of Eu3+ doped NaYF4 phosphor

NASA Astrophysics Data System (ADS)

Pathak, Trilok K.; Kumar, Ashwini; Swart, H. C.; Kroon, R. E.

2018-04-01

Eu3+ doped NaYF4 phosphors have been synthesized by the combustion method. The effect of annealing on the structural, morphological and luminescence properties has been investigated. X-ray diffraction analysis revealed that the Eu3+ doped NaYF4 phosphors consisted of mixed phases: α-phase and β-phase which were affected by the annealing of the phosphor. The surface morphology showed a significant change with annealing in the Eu3+ doped NaYF4 phosphors. The elemental mapping and energy dispersive X-ray spectroscopy spectra proved the formation of the desired materials. The photoluminescence spectra illustrated the optical properties of Eu3+ in the as-prepared and annealed Eu3+ doped NaYF4 phosphors. The intensity of the peaks 5D0 → 7F2 and 5D0 → 7F1 varied in as-prepared and annealed samples. The lifetime of the Eu3+ luminescence at 615 nm was also weakly affected by the Eu3+ doping and annealing temperature.

Effect of solution annealing temperature on precipitation in 2205 duplex stainless steel

DOE Office of Scientific and Technical Information (OSTI.GOV)

Kashiwar, A., E-mail: akashiwar@gmail.com; Vennela, N. Phani, E-mail: phanivennela@gmail.com; Kamath, S.L., E-mail: kamath@iitb.ac.in

2012-12-15

In the present study, effect of solution annealing temperature (1050 Degree-Sign C and 1100 Degree-Sign C) and isothermal ageing (700 Degree-Sign C: 15 min to 6 h) on the microstructural changes in 2205 duplex stainless steel has been investigated systematically. Scanning electron microscopy and X-ray diffraction were adopted to follow the microstructural evolution, while an energy dispersive spectrometer attached to scanning electron microscope was used to obtain localised chemical information of various phases. The ferritic matrix of the two phase 2205 duplex stainless steel ({approx} 45% ferrite and {approx} 55% austenite) undergoes a series of metallurgical transformations during ageing-formation ofmore » secondary austenite ({gamma}{sub 2}) and precipitation of Cr and Mo rich intermetallic (chi-{chi} and sigma-{sigma}) phases. For solution annealing at 1050 Degree-Sign C, significant amount of carbides were observed in the ferrite grains after 1 h of ageing at 700 Degree-Sign C. {chi} Phase precipitated after the precipitation of carbides-preferentially at the ferrite-ferrite and also at the ferrite-austenite boundaries. {sigma} Phase was not observed in significant quantity even after 6 h of ageing. The sequence of precipitation in samples solution annealed at 1050 Degree-Sign C was found to be carbides {yields} {chi} {yields} {sigma}. On the contrary, for samples solution annealed at 1100 Degree-Sign C, the precipitation of {chi} phase was negligible. {chi} Phase precipitated before {sigma} phase, preferentially along the ferrite-ferrite grain boundaries and was later consumed in the {sigma} phase precipitation. The {sigma} phase precipitated via the eutectoid transformation of ferrite to yield secondary austenite {gamma}{sub 2} and {sigma} phase in the ferrite and along the ferrite-austenite grain boundaries. An increase in the volume fraction of {gamma}{sub 2} and {sigma} phase with simultaneous decrease in the ferrite was evidenced with ageing. - Highlights: Black-Right-Pointing-Pointer Effect of solution annealing temperature on microstructural evolution is studied. Black-Right-Pointing-Pointer {chi} Phase precipitated preferentially in the samples solution annealed at 1050 Degree-Sign C. Black-Right-Pointing-Pointer {sigma} Phase precipitated preferentially in the samples solution annealed at 1100 Degree-Sign C. Black-Right-Pointing-Pointer For SA at 1050 Degree-Sign C, the sequence of precipitation was carbides {yields} {chi} phase {yields} {sigma} phase. Black-Right-Pointing-Pointer For SA at 1100 Degree-Sign C, {sigma} phase precipitated via the eutectoid reaction: ferrite (F) {yields} {sigma} + {gamma}{sub 2}.« less

Aqueous Solution-Phase Selenized CuIn(S,Se)2 Thin Film Solar Cells Annealed under Inert Atmosphere.

PubMed

Oh, Yunjung; Yang, Wooseok; Kim, Jimin; Woo, Kyoohee; Moon, Jooho

2015-10-14

A nonvacuum solution-based approach can potentially be used to realize low cost, roll-to-roll fabrication of chalcopyrite CuIn(S,Se)2 (CISSe) thin film solar cells. However, most solution-based fabrication methods involve highly toxic solvents and inevitably require sulfurization and/or postselenization with hazardous H2S/H2Se gases. Herein, we introduce novel aqueous-based Cu-In-S and Se inks that contain an amine additive for producing a high-quality absorber layer. CISSe films were fabricated by simple deposition of Cu-In-S ink and Se ink followed by annealing under an inert atmosphere. Compositional and phase analyses confirmed that our simple aqueous ink-based method facilitated in-site selenization of the CIS layer. In addition, we investigated the molecular structures of our aqueous inks to determine how crystalline chalcopyrite absorber layers developed without sulfurization and/or postselenization. CISSe thin film solar cells annealed at 550 °C exhibited an efficiency of 4.55% under AM 1.5 illumination. The low-cost, nonvacuum method to deposit chalcopyrite absorber layers described here allows for safe and simple processing of thin film solar cells.

Growth and study of first order metal insulator transition in VO2 films

NASA Astrophysics Data System (ADS)

Rathore, Ajay K.; Kumar, Satish; Kumar, Dhirendra; Sathe, V. G.

2015-06-01

VO2 films have been grown on Si substrate using pulse laser deposition technique. The as-deposited film prepared by V2O3 target is found to possess signatures of V2O5 phase. Up on annealing at 780°C the film transforms to VO2 phase. The annealed film is found to be highly oriented along (011) and single phase in nature. The high temperature Raman spectroscopic measurements on the annealed film showed first order transition from monoclinic insulating phase to conductive tetragonal rutile phase around 65°C.

The effect of low temperature thermal annealing on the magnetic properties of Heusler Ni-Mn-Sn melt-spun ribbons

NASA Astrophysics Data System (ADS)

Llamazares, J. L. Sánchez; Quintana-Nedelcos, A.; Ríos-Jara, D.; Sánchez-Valdes, C. F.; García-Fernández, T.; García, C.

2016-03-01

We report the effect of low temperature vacuum annealing (823 K; 550 °C) on the elemental chemical composition, structural phase transition temperatures, phase structure, and magnetic properties of Ni50.6Mn36.3Sn13.1 as-solidified ribbons. Their elemental chemical composition, highly oriented columnar-like microstructure and single-phase character (L21-type crystal structure for austenite) remain unchanged after this low temperature annealing. Annealed ribbons show a reduction of interatomic distances which lead to a small change in the characteristic phase transition temperatures ( 3-6 K) but to a significant rise of 73 and 63% in the saturation magnetization of the martensite and austenite phases, respectively, that can be strictly ascribed to the strengthening of ferromagnetic interactions due to the change in interatomic distances.

Exponential Speedup of Quantum Annealing by Inhomogeneous Driving of the Transverse Field

NASA Astrophysics Data System (ADS)

Susa, Yuki; Yamashiro, Yu; Yamamoto, Masayuki; Nishimori, Hidetoshi

2018-02-01

We show, for quantum annealing, that a certain type of inhomogeneous driving of the transverse field erases first-order quantum phase transitions in the p-body interacting mean-field-type model with and without longitudinal random field. Since a first-order phase transition poses a serious difficulty for quantum annealing (adiabatic quantum computing) due to the exponentially small energy gap, the removal of first-order transitions means an exponential speedup of the annealing process. The present method may serve as a simple protocol for the performance enhancement of quantum annealing, complementary to non-stoquastic Hamiltonians.

Thermal stability of atomic layer deposited WCxNy electrodes for metal oxide semiconductor devices

NASA Astrophysics Data System (ADS)

Zonensain, Oren; Fadida, Sivan; Fisher, Ilanit; Gao, Juwen; Danek, Michal; Eizenberg, Moshe

2018-01-01

This study is a thorough investigation of the chemical, structural, and electrical stability of W based organo-metallic films, grown by atomic layer deposition, for future use as gate electrodes in advanced metal oxide semiconductor structures. In an earlier work, we have shown that high effective work-function (4.7 eV) was produced by nitrogen enriched films (WCxNy) dominated by W-N chemical bonding, and low effective work-function (4.2 eV) was produced by hydrogen plasma resulting in WCx films dominated by W-C chemical bonding. In the current work, we observe, using x-ray diffraction analysis, phase transformation of the tungsten carbide and tungsten nitride phases after 900 °C annealing to the cubic tungsten phase. Nitrogen diffusion is also observed and is analyzed with time-of-flight secondary ion mass spectroscopy. After this 900 °C anneal, WCxNy effective work function tunability is lost and effective work-function values of 4.7-4.8 eV are measured, similar to stable effective work function values measured for PVD TiN up to 900 °C anneal. All the observed changes after annealing are discussed and correlated to the observed change in the effective work function.

Temperature dependent surface and spectral modifications of nano V2O5 films

NASA Astrophysics Data System (ADS)

Manthrammel, M. Aslam; Fatehmulla, A.; Al-Dhafiri, A. M.; Alshammari, A. S.; Khan, Aslam

2017-03-01

Nanocrystalline V2O5 films have been deposited on glass substrates at 300°C substrate temperature using thermal evaporation technique and were subjected to thermal annealing at different temperatures 350, 400, and 550°C. X-ray diffraction (XRD) spectra exhibit sharper and broader characteristic peaks respectively indicating the rearrangement of nanocrystallite phases with annealing temperatures. Other phases of vanadium oxides started emerging with the rise in annealing temperature and the sample converted completely to VO2 (B) phase at 550°C annealing. FESEM images showed an increase in crystallite size with 350 and 400°C annealing temperatures followed by a decrease in crystallite size for the sample annealed at 550°C. Transmission spectra showed an initial redshift of the fundamental band edge with 350 and 400°C while a blue shift for the sample annealed at 550°C, which was in agreement with XRD and SEM results. The films exhibited smart window properties as well as nanorod growth at specific annealing temperatures. Apart from showing the PL and defect related peaks, PL studies also supported the observations made in the transmission spectra.

Effect of Annealing Temperature on the Mechanical and Corrosion Behavior of a Newly Developed Novel Lean Duplex Stainless Steel.

PubMed

Guo, Yanjun; Hu, Jincheng; Li, Jin; Jiang, Laizhu; Liu, Tianwei; Wu, Yanping

2014-09-12

The effect of annealing temperature (1000-1150 °C) on the microstructure evolution, mechanical properties, and pitting corrosion behavior of a newly developed novel lean duplex stainless steel with 20.53Cr-3.45Mn-2.08Ni-0.17N-0.31Mo was studied by means of optical metallographic microscopy (OMM), scanning electron microscopy (SEM), magnetic force microscopy (MFM), scanning Kelvin probe force microscopy (SKPFM), energy dispersive X-ray spectroscopy (EDS), uniaxial tensile tests (UTT), and potentiostatic critical pitting temperature (CPT). The results showed that tensile and yield strength, as well as the pitting corrosion resistance, could be degraded with annealing temperature increasing from 1000 up to 1150 °C. Meanwhile, the elongation at break reached the maximum of 52.7% after annealing at 1050 °C due to the effect of martensite transformation induced plasticity (TRIP). The localized pitting attack preferentially occurred at ferrite phase, indicating that the ferrite phase had inferior pitting corrosion resistance as compared to the austenite phase. With increasing annealing temperature, the pitting resistance equivalent number (PREN) of ferrite phase dropped, while that of the austenite phase rose. Additionally, it was found that ferrite possessed a lower Volta potential than austenite phase. Moreover, the Volta potential difference between ferrite and austenite increased with the annealing temperature, which was well consistent with the difference of PREN.

Effect of Annealing Temperature on the Mechanical and Corrosion Behavior of a Newly Developed Novel Lean Duplex Stainless Steel

PubMed Central

Guo, Yanjun; Hu, Jincheng; Li, Jin; Jiang, Laizhu; Liu, Tianwei; Wu, Yanping

2014-01-01

The effect of annealing temperature (1000–1150 °C) on the microstructure evolution, mechanical properties, and pitting corrosion behavior of a newly developed novel lean duplex stainless steel with 20.53Cr-3.45Mn-2.08Ni-0.17N-0.31Mo was studied by means of optical metallographic microscopy (OMM), scanning electron microscopy (SEM), magnetic force microscopy (MFM), scanning Kelvin probe force microscopy (SKPFM), energy dispersive X-ray spectroscopy (EDS), uniaxial tensile tests (UTT), and potentiostatic critical pitting temperature (CPT). The results showed that tensile and yield strength, as well as the pitting corrosion resistance, could be degraded with annealing temperature increasing from 1000 up to 1150 °C. Meanwhile, the elongation at break reached the maximum of 52.7% after annealing at 1050 °C due to the effect of martensite transformation induced plasticity (TRIP). The localized pitting attack preferentially occurred at ferrite phase, indicating that the ferrite phase had inferior pitting corrosion resistance as compared to the austenite phase. With increasing annealing temperature, the pitting resistance equivalent number (PREN) of ferrite phase dropped, while that of the austenite phase rose. Additionally, it was found that ferrite possessed a lower Volta potential than austenite phase. Moreover, the Volta potential difference between ferrite and austenite increased with the annealing temperature, which was well consistent with the difference of PREN. PMID:28788201

Single-source-precursor synthesis of hafnium-containing ultrahigh-temperature ceramic nanocomposites (UHTC-NCs).

PubMed

Yuan, Jia; Hapis, Stefania; Breitzke, Hergen; Xu, Yeping; Fasel, Claudia; Kleebe, Hans-Joachim; Buntkowsky, Gerd; Riedel, Ralf; Ionescu, Emanuel

2014-10-06

Amorphous SiHfBCN ceramics were prepared from a commercial polysilazane (HTT 1800, AZ-EM), which was modified upon reactions with Hf(NEt2)4 and BH3·SMe2, and subsequently cross-linked and pyrolyzed. The prepared materials were investigated with respect to their chemical and phase composition, by means of spectroscopy techniques (Fourier transform infrared (FTIR), Raman, magic-angle spinning nuclear magnetic resonance (MAS NMR)), as well as X-ray diffraction (XRD) and transmission electron microscopy (TEM). Annealing experiments of the SiHfBCN samples in an inert gas atmosphere (Ar, N2) at temperatures in the range of 1300-1700 °C showed the conversion of the amorphous materials into nanostructured UHTC-NCs. Depending on the annealing atmosphere, HfC/HfB2/SiC (annealing in argon) and HfN/Si3N4/SiBCN (annealing in nitrogen) nanocomposites were obtained. The results emphasize that the conversion of the single-phase SiHfBCN into UHTC-NCs is thermodynamically controlled, thus allowing for a knowledge-based preparative path toward nanostructured ultrahigh-temperature stable materials with adjusted compositions.

Thermal phase separation of ZrSiO4 thin films and frequency- dependent electrical characteristics of the Al/ZrSiO4/p-Si/Al MOS capacitors

NASA Astrophysics Data System (ADS)

Lok, R.; Kaya, S.; Yilmaz, E.

2018-05-01

In this work, the thermal phase separation and annealing optimization of ZrSiO4 thin films have been carried out. Following annealing optimization, the frequency-dependent electrical characteristics of the Al/ZrSiO4/p-Si/Al MOS capacitors were investigated in detail. The chemical evolution of the films under various annealing temperatures was determined by Fourier transform infrared spectroscopy (FTIR) measurements. The phase separation was determined by x-ray diffraction (XRD) measurements. The electrical parameters were determined via the capacitance–voltage (C–V), conductance–voltage (G/ω) and leakage-current–voltage (Ig–Vg ). The results demonstrate that zirconium silicate formations are present at 1000 °C annealing with the SiO2 interfacial layer. The film was in amorphous form after annealing at 250 °C. The tetragonal phases of ZrO2 were obtained after annealing at 500 °C. When the temperature approaches 750 °C, transitions from the tetragonal phase to the monoclinic phase were observed. The obtained XRD peaks after 1000 °C annealing matched the crystalline peaks of ZrSiO4. This means that the crystalline zirconium dioxide in the structure has been converted into a crystalline silicate phase. The interface states increased to 5.71 × 1010 and the number of border traps decreased to 7.18 × 1010 cm‑2 with the increasing temperature. These results indicate that an excellent ZrSiO4/Si interface has been fabricated. The order of the leakage current varied from 10‑9 Acm‑2 to 10‑6 Acm‑2. The MOS capacitor fabricated with the films annealed at 1000 °C shows better behavior in terms of its structural, chemical and electrical properties. Hence, detailed frequency-dependent electrical characteristics were performed for the ZrSiO4 thin film annealed at 1000 °C. Very slight capacitance variations were observed under the frequency variations. This shows that the density of frequency-dependent charges is very low at the ZrSiO4/Si interface. The barrier height of the device varies slightly from 0.776 eV to 0.827 eV under frequency dispersion. Briefly, it is concluded that the devices annealed at 1000 °C exhibit promising electrical characteristics.

Phase diagram and electronic indication of high-temperature superconductivity at 65 K in single-layer FeSe films.

PubMed

He, Shaolong; He, Junfeng; Zhang, Wenhao; Zhao, Lin; Liu, Defa; Liu, Xu; Mou, Daixiang; Ou, Yun-Bo; Wang, Qing-Yan; Li, Zhi; Wang, Lili; Peng, Yingying; Liu, Yan; Chen, Chaoyu; Yu, Li; Liu, Guodong; Dong, Xiaoli; Zhang, Jun; Chen, Chuangtian; Xu, Zuyan; Chen, Xi; Ma, Xucun; Xue, Qikun; Zhou, X J

2013-07-01

The recent discovery of possible high-temperature superconductivity in single-layer FeSe films has generated significant experimental and theoretical interest. In both the cuprate and the iron-based high-temperature superconductors, superconductivity is induced by doping charge carriers into the parent compound to suppress the antiferromagnetic state. It is therefore important to establish whether the superconductivity observed in the single-layer sheets of FeSe--the essential building blocks of the Fe-based superconductors--is realized by undergoing a similar transition. Here we report the phase diagram for an FeSe monolayer grown on a SrTiO3 substrate, by tuning the charge carrier concentration over a wide range through an extensive annealing procedure. We identify two distinct phases that compete during the annealing process: the electronic structure of the phase at low doping (N phase) bears a clear resemblance to the antiferromagnetic parent compound of the Fe-based superconductors, whereas the superconducting phase (S phase) emerges with the increase in doping and the suppression of the N phase. By optimizing the carrier concentration, we observe strong indications of superconductivity with a transition temperature of 65±5 K. The wide tunability of the system across different phases makes the FeSe monolayer ideal for investigating not only the physics of superconductivity, but also for studying novel quantum phenomena more generally.

Microstructure and Magnetic Properties of Optimally Annealed Ni43Mn41Co5Sn11Heusler Alloy

NASA Astrophysics Data System (ADS)

Elwindari, Nastiti; Kurniawan, Budhy; Kurniawan, Candra; Manaf, Azwar

2017-05-01

In this work, synthesis and characterization of a polycrystalline Ni43Mn41Co5Sn11 (NMCS) alloy are reported. Alloy preparation was conducted by melting the constituent components of the designated alloy under an inert Argon (Ar) atmosphere in a vacuum mini arc-melting furnace. Microstructure observation to the as-cast and annealed ingots showing dendritic structure in the as-cast sample. Series of annealing treatment to the sample at 1173 K have changed dendrites progressively in the homogeneous structure after 24 hours annealing time. The annealed sample consisted of a NiMnCoSn main phase with 99.3 % volume fraction. Hence, the 24 hours annealed ingot is a single phase alloy. The curie temperature of the annealed NMCS alloys was found in the range 348∼351 K. Loop hysteresis evaluation of the annealed ingots showed that ingot which annealed for 12 hours showed the largest magnetization value of 57.96 emu/g.

Glass-derived superconducting ceramics with zero resistance at 107 K in the Bi(1.5)Pb(0.5)Sr2Ca2Cu3O(x) system

NASA Technical Reports Server (NTRS)

Bansal, Narottam P.; Farrell, D. E.

1989-01-01

A melt of composition Bi(1.5)Pb(0.5)Sr2Ca2Cu3O(x) was fast quenched to form a glass. This was subsequently air annealed and the influence of annealing time and temperature on the formation of various crystalline phases was investigated. X-ray powder diffraction indicate that none of the resulting samples were single phase. However, for an annealing temperature of 840 C, the volume fraction of the high Tc phase (isostructural with Bi2Sr2Ca2Cu3O10) increased with annealing time. A specimen annealed at this temperature for 243 h followed by slow cooling showed a sharp transition and Tc (R = 0) = 107.2 K.

Non-stoquastic Hamiltonians in quantum annealing via geometric phases

NASA Astrophysics Data System (ADS)

Vinci, Walter; Lidar, Daniel A.

2017-09-01

We argue that a complete description of quantum annealing implemented with continuous variables must take into account the non-adiabatic Aharonov-Anandan geometric phase that arises when the system Hamiltonian changes during the anneal. We show that this geometric effect leads to the appearance of non-stoquasticity in the effective quantum Ising Hamiltonians that are typically used to describe quantum annealing with flux qubits. We explicitly demonstrate the effect of this geometric non-stoquasticity when quantum annealing is performed with a system of one and two coupled flux qubits. The realization of non-stoquastic Hamiltonians has important implications from a computational complexity perspective, since it is believed that in many cases quantum annealing with stoquastic Hamiltonians can be efficiently simulated via classical algorithms such as Quantum Monte Carlo. It is well known that the direct implementation of non-stoquastic Hamiltonians with flux qubits is particularly challenging. Our results suggest an alternative path for the implementation of non-stoquasticity via geometric phases that can be exploited for computational purposes.

Annealing effects on electrical behavior of gold nanoparticle film: Conversion of ohmic to non-ohmic conductivity

NASA Astrophysics Data System (ADS)

Ebrahimpour, Zeinab; Mansour, Nastaran

2017-02-01

This paper reports on the electrical behavior of self-assembled gold nanoparticle films before and after high-temperature annealing in ambient environment. These films are made by depositing gold nanoparticles from a colloidal solution on glass substrates using centrifuge deposition technique. The current-voltage (I-V) characteristics of these films exhibits ohmic and non-ohmic properties for un-annealed and annealed films respectively. As the annealing time duration increases, the onset of non-ohmic behavior occurs at higher voltages. To understand the underlying mechanisms for the observed electrical conduction behavior in these films and how electrical conduction is effected by film morphology and structural properties before and after annealing, systematic comparative studies based on scanning electron microscopy (SEM), UV-vis absorption spectroscopy and X-ray photoelectron spectroscopy (XPS) have been performed. The morphology of the films shows that the assembled gold nanoparticles are distributed on the substrate in a random way before annealing. After 2 h annealing gold nanoparticles exhibit a higher filling fraction when examined by SEM, which means that they coalesce, upon annealing, with respect to un-annealed films. The UV-vis absorption spectra of the films show that there is a red-shift and broadening in the absorption band for the annealed films. The observed phenomenon is related to the plasmon near-field coupling effect and suggests that the nanoparticle ensembles interspacing has decreased. The structural and crystallinity of the films exhibit amorphous structure before annealing and pure crystalline phases with a preferential growth direction along the (111) plane after annealing. The XPS analysis further suggests the existence of the stable thin oxide layer in the phase of Au2O3 in the annealed films. The I-V characteristics have been described by Simmons' model for tunnel transport through metal-insulator-metal (MIM) junctions. The Fowler-Nordheim (F-N) plots show the transition of the in-plane charge transport mechanism from direct tunneling to field emission in annealed films. Our results suggest that, the formation of a thin layer of Au2O3 , the proximity of the nanoparticles as well as their higher filling fraction are important parameters related with the tunneling process enhancement. The observed non-ohmic conductivity property can make these self-assembled gold nanoparticle films very useful structures in different applications such as sensing, resistors and other nanoelectronic applications.

Formation of the 110-K superconducting phase in Pb-doped Bi-Sr-Ca-Cu-O thin films

DOE Office of Scientific and Technical Information (OSTI.GOV)

Kula, W.; Sobolewski, R.; Gorecka, J.

1991-09-15

Investigation of the 110-K Bi{sub 2}Sr{sub 2}Ca{sub 2}Cu{sub 3}O{sub {ital x}} phase formation in superconducting thin films of Bi-based cuprates is reported. The films were dc magnetron sputtered from single Bi(Pb)-Sr-Ca-Cu-O targets of various stoichiometries, and subsequently annealed in air at high temperatures. The influence of the initial Pb content, annealing conditions, as well as the substrate material on the growth of the 110-K phase was investigated. We found that the films, fully superconducting above 100 K could be reproducibly fabricated on various dielectric substrates from Pb-rich targets by optimizing annealing conditions for each initial Pb/Bi ratio. Heavy Pb dopingmore » considerably accelerated formation of the 110-K phase, reducing the film annealing time to less than 1 h. Films containing, according to the x-ray measurement, more than 90% of the 110-K phase were obtained on MgO substrates, after sputtering from the Bi{sub 2}Pb{sub 2.5}Sr{sub 2}Ca{sub 2.15}Cu{sub 3.3}O{sub {ital x}} target and annealing in air for 1 h at 870 {degree}C. The films were {ital c}-axis oriented, with 4.5-K-wide superconducting transition, and zero resistivity at 106 K. Their critical current density was 2 {times} 10{sup 2} A/cm{sup 2} at 90 K, and above 10{sup 4} A/cm{sup 2} below 60 K. The growth of the 110-K phase on epitaxial substrates, such as CaNdAlO{sub 4} and SrTiO{sub 3}, was considerably deteriorated, and the presence of the 80- and 10-K phases was detected. Nevertheless, the best films deposited on these substrates were fully superconducting at 104 K and exhibited critical current densities above 2 {times} 10{sup 5} A/cm{sup 2} below 60 K{minus}one order of magnitude greater than the films deposited on MgO.« less

Tunability of morphological properties of Nd-doped TiO2 thin films

NASA Astrophysics Data System (ADS)

Rehan, Imran; Sultana, Sabiha; Khan, Nauman; Qamar, Zahid; Rehan, Kamran

2016-11-01

In this work, an endeavor is made toward structural assessment and morphological variation of titanium dioxide (TiO2) thin films when doped with neodymium (Nd). The electron beam deposition technique was employed to fabricate Nd-based TiO2 thin films on n-Type Si substrates. Nd concentration was varied from 0.0 to 2.0 atomic percent (at.%) under identical growth environments. The films were deposited in an oxygen-deficient environment to cause the growth of rutile phases. Energy dispersive x-ray spectroscopy confirmed the presence and variation of Nd dopant in TiO2. X-ray diffraction analysis showed the transformation of amorphous structures of the as-grown samples to anatase polycrystalline after annealing at 500 °C, while atomic force microscopy exposed linearity in grain density in as-grown samples with doping until 1 at.%. Raman spectrums of as-grown and annealed samples revealed the growth of the anatase phase in the annealed samples. Based on these results it can be proposed that Nd doping has pronounced effects on the structural characteristics of TiO2 thin films.

Large ferroelectric polarization of TiN/Hf0.5Zr0.5O2/TiN capacitors due to stress-induced crystallization at low thermal budget

NASA Astrophysics Data System (ADS)

Kim, Si Joon; Narayan, Dushyant; Lee, Jae-Gil; Mohan, Jaidah; Lee, Joy S.; Lee, Jaebeom; Kim, Harrison S.; Byun, Young-Chul; Lucero, Antonio T.; Young, Chadwin D.; Summerfelt, Scott R.; San, Tamer; Colombo, Luigi; Kim, Jiyoung

2017-12-01

We report on atomic layer deposited Hf0.5Zr0.5O2 (HZO)-based capacitors which exhibit excellent ferroelectric (FE) characteristics featuring a large switching polarization (45 μC/cm2) and a low FE saturation voltage (˜1.5 V) as extracted from pulse write/read measurements. The large FE polarization in HZO is achieved by the formation of a non-centrosymmetric orthorhombic phase, which is enabled by the TiN top electrode (TE) having a thickness of at least 90 nm. The TiN films are deposited at room temperature and annealed at 400 °C in an inert environment for at least 1 min in a rapid thermal annealing system. The room-temperature deposited TiN TE acts as a tensile stressor on the HZO film during the annealing process. The stress-inducing TiN TE is shown to inhibit the formation of the monoclinic phase during HZO crystallization, forming an orthorhombic phase that generates a large FE polarization, even at low process temperatures.

Combustion-Assisted Photonic Annealing of Printable Graphene Inks via Exothermic Binders.

PubMed

Secor, Ethan B; Gao, Theodore Z; Dos Santos, Manuel H; Wallace, Shay G; Putz, Karl W; Hersam, Mark C

2017-09-06

High-throughput and low-temperature processing of high-performance nanomaterial inks is an important technical challenge for large-area, flexible printed electronics. In this report, we demonstrate nitrocellulose as an exothermic binder for photonic annealing of conductive graphene inks, leveraging the rapid decomposition kinetics and built-in energy of nitrocellulose to enable versatile process integration. This strategy results in superlative electrical properties that are comparable to extended thermal annealing at 350 °C, using a pulsed light process that is compatible with thermally sensitive substrates. The resulting porous microstructure and broad liquid-phase patterning compatibility are exploited for printed graphene microsupercapacitors on paper-based substrates.

High-Efficiency Small Molecule-Based Bulk-Heterojunction Solar Cells Enhanced by Additive Annealing.

PubMed

Li, Lisheng; Xiao, Liangang; Qin, Hongmei; Gao, Ke; Peng, Junbiao; Cao, Yong; Liu, Feng; Russell, Thomas P; Peng, Xiaobin

2015-09-30

Solvent additive processing is important in optimizing an active layer's morphology and thus improving the performance of organic solar cells (OSCs). In this study, we find that how 1,8-diiodooctane (DIO) additive is removed plays a critical role in determining the film morphology of the bulk heterojunction OSCs in inverted structure based on a porphyrin small molecule. Different from the cases reported for polymer-based OSCs in conventional structures, the inverted OSCs upon the quick removal of the additive either by quick vacuuming or methanol washing exhibit poorer performance. In contrast, the devices after keeping the active layers in ambient pressure with additive dwelling for about 1 h (namely, additive annealing) show an enhanced power conversion efficiency up to 7.78% with a large short circuit current of 19.25 mA/cm(2), which are among the best in small molecule-based solar cells. The detailed morphology analyses using UV-vis absorption spectroscopy, grazing incidence X-ray diffraction, resonant soft X-ray scattering, and atomic force microscopy demonstrate that the active layer shows smaller-sized phase separation but improved structure order upon additive annealing. On the contrary, the quick removal of the additive either by quick vacuuming or methanol washing keeps the active layers in an earlier stage of large scaled phase separation.

Quantum annealing with parametrically driven nonlinear oscillators

NASA Astrophysics Data System (ADS)

Puri, Shruti

While progress has been made towards building Ising machines to solve hard combinatorial optimization problems, quantum speedups have so far been elusive. Furthermore, protecting annealers against decoherence and achieving long-range connectivity remain important outstanding challenges. With the hope of overcoming these challenges, I introduce a new paradigm for quantum annealing that relies on continuous variable states. Unlike the more conventional approach based on two-level systems, in this approach, quantum information is encoded in two coherent states that are stabilized by parametrically driving a nonlinear resonator. I will show that a fully connected Ising problem can be mapped onto a network of such resonators, and outline an annealing protocol based on adiabatic quantum computing. During the protocol, the resonators in the network evolve from vacuum to coherent states representing the ground state configuration of the encoded problem. In short, the system evolves between two classical states following non-classical dynamics. As will be supported by numerical results, this new annealing paradigm leads to superior noise resilience. Finally, I will discuss a realistic circuit QED realization of an all-to-all connected network of parametrically driven nonlinear resonators. The continuous variable nature of the states in the large Hilbert space of the resonator provides new opportunities for exploring quantum phase transitions and non-stoquastic dynamics during the annealing schedule.

Quasi-equilibrium size distribution of subcritical nuclei in amorphous phase change AgIn-Sb2Te

NASA Astrophysics Data System (ADS)

Darmawikarta, Kristof; Lee, Bong-Sub; Shelby, Robert M.; Raoux, Simone; Bishop, Stephen G.; Abelson, John R.

2013-07-01

We investigate the effect of low temperature annealing or of extended storage at room temperature on the subsequent nucleation behavior of amorphous AgIn-incorporated Sb2Te (AIST), a material for phase change memories. Time-resolved reflectivity measurements during pulsed laser crystallization reveal the rates of solid-phase transformation, while fluctuation transmission electron microscopy detects the nanoscale order in the amorphous phase prior to crystallization. The nanoscale order is postulated to consist of subcritical nuclei that coarsen upon annealing at temperatures ranging from 25 °C (for months) or 100 °C (for hours). Samples that have been annealed remain fully amorphous as evaluated by conventional diffraction experiments. Shorter nucleation times are consistently associated with the observation of increased nanoscale order. The effect of annealing is observed to saturate: there is no further reduction in nucleation time or increase in nanoscale order for annealing at 100 °C beyond three hours. This result supports the general prediction of classical nucleation theory that the size distribution of subcritical nuclei increases from the as-deposited state to a quasi-equilibrium.

Formation of low resistivity titanium silicide gates in semiconductor integrated circuits

DOEpatents

Ishida, Emi [Sunnyvale, CA

1999-08-10

A method of forming a titanium silicide (69) includes the steps of forming a transistor having a source region (58), a drain region (60) and a gate structure (56) and forming a titanium layer (66) over the transistor. A first anneal is performed with a laser anneal at an energy level that causes the titanium layer (66) to react with the gate structure (56) to form a high resistivity titanium silicide phase (68) having substantially small grain sizes. The unreacted portions of the titanium layer (66) are removed and a second anneal is performed, thereby causing the high resistivity titanium silicide phase (68) to convert to a low resistivity titanium silicide phase (69). The small grain sizes obtained by the first anneal allow low resistivity titanium silicide phase (69) to be achieved at device geometries less than about 0.25 micron.

FAST TRACK COMMUNICATION: Directional annealing-induced texture in melt-spun (Sm12Co88)99Nb1 alloy

NASA Astrophysics Data System (ADS)

Jayaraman, T. V.; Rogge, P.; Shield, J. E.

2010-07-01

Developing texture in nanocrystalline permanent magnet alloys is of significant importance. Directional annealing is shown to produce texture in the permanent magnet alloy (Sm12Co88)99Nb1. Melt spinning produced isotropic grain structures of the hard magnetic metastable SmCo7 phase, with grain sizes of ~300 nm. Conventional annealing of melt-spun (Sm12Co88)99Nb1 alloy produced Sm2Co17 phase with random crystallographic orientation. Directional annealing of melt-spun (Sm12Co88)99Nb1 alloy, with appropriate combinations of annealing temperature and translational velocity, produced Sm2Co17 phase with (0 0 0 6) in-plane texture, as determined by x-ray diffraction analysis and magnetic measurements. The magnetization results show out-of-plane remanence higher than the in-plane remanence resulting in the degree of 'magnetic' texture in the order of 25-40%. Coercivity values above 2 kOe were maintained. The texture development via directional annealing while minimizing exposure to elevated temperatures provides a new route to anisotropic high-energy permanent magnets.

On simulated annealing phase transitions in phylogeny reconstruction.

PubMed

Strobl, Maximilian A R; Barker, Daniel

2016-08-01

Phylogeny reconstruction with global criteria is NP-complete or NP-hard, hence in general requires a heuristic search. We investigate the powerful, physically inspired, general-purpose heuristic simulated annealing, applied to phylogeny reconstruction. Simulated annealing mimics the physical process of annealing, where a liquid is gently cooled to form a crystal. During the search, periods of elevated specific heat occur, analogous to physical phase transitions. These simulated annealing phase transitions play a crucial role in the outcome of the search. Nevertheless, they have received comparably little attention, for phylogeny or other optimisation problems. We analyse simulated annealing phase transitions during searches for the optimal phylogenetic tree for 34 real-world multiple alignments. In the same way in which melting temperatures differ between materials, we observe distinct specific heat profiles for each input file. We propose this reflects differences in the search landscape and can serve as a measure for problem difficulty and for suitability of the algorithm's parameters. We discuss application in algorithmic optimisation and as a diagnostic to assess parameterisation before computationally costly, large phylogeny reconstructions are launched. Whilst the focus here lies on phylogeny reconstruction under maximum parsimony, it is plausible that our results are more widely applicable to optimisation procedures in science and industry. Copyright © 2016 The Authors. Published by Elsevier Inc. All rights reserved.

Suppressing the cellular breakdown in silicon supersaturated with titanium

NASA Astrophysics Data System (ADS)

Liu, Fang; Prucnal, S.; Hübner, R.; Yuan, Ye; Skorupa, W.; Helm, M.; Zhou, Shengqiang

2016-06-01

Hyper doping Si with up to 6 at.% Ti in solid solution was performed by ion implantation followed by pulsed laser annealing and flash lamp annealing. In both cases, the implanted Si layer can be well recrystallized by liquid phase epitaxy and solid phase epitaxy, respectively. Cross-sectional transmission electron microscopy of Ti-implanted Si after liquid phase epitaxy shows the so-called growth interface breakdown or cellular breakdown owing to the occurrence of constitutional supercooling in the melt. The appearance of cellular breakdown prevents further recrystallization. However, the out-diffusion and cellular breakdown can be effectively suppressed by solid phase epitaxy during flash lamp annealing due to the high velocity of amorphous-crystalline interface and the low diffusion velocity for Ti in the solid phase.

In-situ crystallization of GeTe\\GaSb phase change memory stacked films

DOE Office of Scientific and Technical Information (OSTI.GOV)

Velea, A., E-mail: alin.velea@psi.ch; National Institute of Materials Physics, RO-077125 Magurele, Ilfov; Borca, C. N.

2014-12-21

Single and double layer phase change memory structures based on GeTe and GaSb thin films were deposited by pulsed laser deposition (PLD). Their crystallization behavior was studied using in-situ synchrotron techniques. Electrical resistance vs. temperature investigations, using the four points probe method, showed transition temperatures of 138 °C and 198 °C for GeTe and GaSb single films, respectively. It was found that after GeTe crystallization in the stacked films, Ga atoms from the GaSb layer diffused in the vacancies of the GeTe crystalline structure. Therefore, the crystallization temperature of the Sb-rich GaSb layer is decreased by more than 30 °C. Furthermore, at 210 °C,more » the antimony excess from GaSb films crystallizes as a secondary phase. At higher annealing temperatures, the crystalline Sb phase increased on the expense of GaSb crystalline phase which was reduced. Extended X-ray absorption fine structure (EXAFS) measurements at the Ga and Ge K-edges revealed changes in their local atomic environments as a function of the annealing temperature. Simulations unveil a tetrahedral configuration in the amorphous state and octahedral configuration in the crystalline state for Ge atoms, while Ga is four-fold coordinated in both as-deposited and annealed samples.« less

Re-creation of single phase, and improvement of magnetic property of CoFe2O4 nanoparticles versus heat treatment

NASA Astrophysics Data System (ADS)

Tran, N.; Kim, D. H.; Phan, T. L.; Dang, N. T.; Bach, T. N.; Manh, D. H.; Lee, B. W.

2018-03-01

Our studies on the crystal characterization and magnetic property of CoFe2O4 nanoparticles (NPs) point out their instability in a specific temperature range. While as-prepared NPs exhibit single phase in a cubic spinel structure, annealing at temperatures T=673-1273 K leads to the development of an impurity phase of Fe2O3. Interestingly, annealing at higher temperatures re-creates the single phase of NPs. This strongly influences their magnetic property. The magnetic inhomogeneity and/or multiple phase exist in as-prepared NPs and in those annealed below 1273 K, better magnetic property is found in the samples with annealing temperature (Tan) higher than 1273 K. Ferromagnetic-paramagnetic phase transition temperatures of these samples are located around 815-850 K, and are less dependent on Tan. At room temperature, their saturation magnetization is located in the range of 41-55 emu/g, while the coercivity can be changed from 600 to 3200 Oe. These results are related to microstructures, structural phases, and exchange interactions between Fe and Co ions situated in the A and B sites of the spinel structure, which are modified by heat treatment.

DOE Office of Scientific and Technical Information (OSTI.GOV)

Righettoni, Marco; Pratsinis, Sotiris E., E-mail: sotiris.pratsinis@ptl.mavt.ethz.ch

Highlights: • Flame-made WO{sub 3} nanoparticles with closely controlled crystal and grain size. • Dynamic phase transition of annealing of pure and Si-doped WO{sub 3} by in situ XRD. • Irreversible evolution of WO{sub 3} crystallinity by heating/cooling during its annealing. • Si-doping alters the WO{sub 3} crystallinity dynamics and stabilizes nanosized WO{sub 3}. • Flame-made nano-WO{sub 3} can sense NO at the ppb level. - Abstract: Tungsten trioxide is a semiconductor with distinct applications in gas sensors, catalysis, batteries and pigments. As such the transition between its different crystal structures during its annealing are of interest, especially for sensormore » applications. Here, WO{sub 3} nanoparticles with closely controlled crystal and grain size (9–15 nm) and phase composition are made by flame spray pyrolysis and the formation of different WO{sub 3} phases during annealing is investigated. Most notably, the dynamic phase transition and crystal size evolution of WO{sub 3} during heating and cooling is monitored by in situ X-ray diffraction revealing how metastable WO{sub 3} phases can be captured stably. The effect of Si-doping is studied since it is used in practise to control crystal growth and phase transition during metal oxide synthesis and processing. Finally the influence of annealing on the WO{sub 3} sensing performance of NO, a lung inflammation tracer in the human breath, is explored at the ppb-level.« less

Hot plate annealing at a low temperature of a thin ferroelectric P(VDF-TrFE) film with an improved crystalline structure for sensors and actuators.

PubMed

Mahdi, Rahman Ismael; Gan, W C; Abd Majid, W H

2014-10-14

Ferroelectric poly(vinylidene fluoride-trifluoroethylene) (P(VDF-TrFE)) copolymer 70/30 thin films are prepared by spin coating. The crystalline structure of these films is investigated by varying the annealing temperature from the ferroelectric phase to the paraelectric phase. A hot plate was used to produce a direct and an efficient annealing effect on the thin film. The dielectric, ferroelectric and pyroelectric properties of the P(VDF-TrFE) thin films are measured as a function of different annealing temperatures (80 to 140 °C). It was found that an annealing temperature of 100 °C (slightly above the Curie temperature, Tc) has induced a highly crystalline β phase with a rod-like crystal structure, as examined by X-ray. Such a crystal structure yields a high remanent polarization, Pr = 94 mC/m2, and pyroelectric constant, p = 24 μC/m2K. A higher annealing temperature exhibits an elongated needle-like crystal domain, resulting in a decrease in the crystalline structure and the functional electrical properties. This study revealed that highly crystalline P(VDF-TrFE) thin films could be induced at 100 °C by annealing the thin film with a simple and cheap method.

Thermal stability and magnetic properties of MgFe2O4@ZnO nanoparticles

NASA Astrophysics Data System (ADS)

Mallesh, S.; Prabu, D.; Srinivas, V.

2017-05-01

Magnesium ferrite, MgFe2O4, (MgFO) nanoparticles (NPs) have been synthesized through sol-gel process. Subsequently, as prepared particles were coated with Zinc-oxide (ZnO) layer(s) through ultrasonication process. Thermal stability, structure and magnetic properties of as-prepared (AP) and annealed samples in the temperature range of 350 °C-1200 °C have been investigated. Structural data suggests that AP MgFO NPs and samples annealed below 500 °C in air exhibit stable ferrite phase. However, α-Fe2O3 and a small fraction of MgO secondary phases appear along with ferrite phase on annealing in the temperatures range 500 °C- 1000 °C. This results in significant changes in magnetic moment for AP NPs 0.77 μB increases to 0.92 μB for 1200 °C air annealed sample. The magnetic properties decreased at intermediate temperatures due to the presence of secondary phases. On the other hand, pure ferrite phase could be stabilized with an optimum amount of ZnO coated MgFO NPs for samples annealed in the temperature range 500 °C-1000 °C with improvement in magnetic behavior compared to that of MgFO samples.

Neutron and hard X-ray diffraction studies of the isothermal transformation kinetics in the research reactor fuel candidate U–8 wt%Mo

PubMed Central

Säubert, Steffen; Jungwirth, Rainer; Zweifel, Tobias; Hofmann, Michael; Hoelzel, Markus; Petry, Winfried

2016-01-01

Exposing uranium–molybdenum alloys (UMo) retained in the γ phase to elevated temperatures leads to transformation reactions during which the γ-UMo phase decomposes into the thermal equilibrium phases, i.e. U2Mo and α-U. Since α-U is not suitable for a nuclear fuel exposed to high burn-up, it is necessary to retain the γ-UMo phase during the production process of the fuel elements for modern high-performance research reactors. The present work deals with the isothermal transformation kinetics in U–8 wt%Mo alloys for temperatures between 673 and 798 K and annealing durations of up to 48 h. Annealed samples were examined at room temperature using either X-ray or neutron diffraction to determine the phase composition after thermal treatment, and in situ annealing studies disclosed the onset of phase decomposition. While for temperatures of 698 and 673 K the start of decomposition is delayed, for higher temperatures the first signs of transformation are already observable within 3 h of annealing. The typical C-shaped curves in a time–temperature–transformation (TTT) diagram for both the start and the end of phase decomposition could be determined in the observed temperature regime. Therefore, a revised TTT diagram for U–8 wt%Mo between 673 and 798 K and annealing durations of up to 48 h is proposed. PMID:27275139

Effect of annealing temperature on the microstructure and optical-electrical properties of Cu-Al-O thin films

NASA Astrophysics Data System (ADS)

Zhang, Y. J.; Liu, Z. T.; Zang, D. Y.; Che, X. S.; Feng, L. P.; Bai, X. X.

2013-12-01

We have successfully prepared Cu-Al-O thin films on silicon (100) and quartz substrates by radio frequency (RF) magnetron sputtering method. The as-deposited Cu-Al-O film is amorphous in nature and post-annealing treatment in argon ambience results in crystallization of the films and the formation of CuAlO2. The annealing temperature plays an important role in the surface morphology, phase constitution and preferred growth orientation of CuAlO2 phase, thus affecting the properties of the film. The film annealed at 900 °C is mainly composed of CuAlO2 phase and shows smooth surface morphology with well-defined grain boundaries, thus exhibiting the optimum optical-electrical properties with electrical resistivity being 79.7 Ω·cm at room temperature and optical transmittance being 80% in visible region. The direct optical band gaps of the films are found in the range of 3.3-3.8 eV depending on the annealing temperature.

Crystallization induced ordering of hard magnetic L1{sub 0} phase in melt-spun FeNi-based ribbons

DOE Office of Scientific and Technical Information (OSTI.GOV)

Sato, Kazuhisa, E-mail: sato@uhvem.osaka-u.ac.jp; Sharma, Parmanand; Zhang, Yan

2016-05-15

The microstructure of newly developed hard magnetic Fe{sub 42}Ni{sub 41.3}Si{sub x}B{sub 12-x}P{sub 4}Cu{sub 0.7} (x = 2 to 8 at%) nanocrystalline alloy ribbons has been studied by transmission electron microscopy (TEM) and electron diffraction. A high-density polycrystalline grains, ∼30 nm in size, were formed in a ribbon after annealing at 673 K for 288 hours. Elemental mapping of the annealed specimen revealed the coexistence of three regions, Fe-rich, Ni-rich, and nearly equiatomic Fe-Ni, with areal fractions of 37%, 40%, and 23 %, respectively. The equiatomic L1{sub 0}-type ordered phase of FeNi was detected in between the Fe and Ni-rich phases.more » The presence of superlattice reflections in nanobeam electron diffraction patterns confirmed the formation of the hard magnetic L1{sub 0} phase beyond any doubt. The L1{sub 0} phase of FeNi was detected in alloys annealed in the temperature range of 673 to 813 K. The present results suggest that the order-disorder transition temperature of L1{sub 0} FeNi is higher than the previously reported value (593 K). The high diffusion rates of the constituent elements induced by the crystallization of an amorphous phase at relatively low temperature (∼673 K) are responsible for the development of atomic ordering in FeNi.« less

Fuel additives and heat treatment effects on nanocrystalline zinc ferrite phase composition

NASA Astrophysics Data System (ADS)

Hu, Ping; Pan, De-an; Wang, Xin-feng; Tian, Jian-jun; Wang, Jian; Zhang, Shen-gen; Volinsky, Alex A.

2011-03-01

Nanocrystalline ZnFe 2O 4 powder was prepared by the auto-combustion method using citric acid, acetic acid, carbamide and acrylic acid as fuel additives. Pure spinel zinc ferrite with the crystallite size of about 15 nm can be obtained by using acrylic acid as fuel additive. Samples prepared using other fuel additives contain ZnO impurities. In order to eliminate ZnO impurities, the sample prepared with citric acid as fuel additive was annealed at different temperatures up to 1000 °C in air and in argon. Annealed powders have pure ZnFe 2O 4 phase when annealing temperature is higher than 650 °C in air. Sample annealed at 650 °C in air is paramagnetic. However, annealed powders become a mixture of Fe 3O 4 and FeO after annealing at 1000 °C in argon atmosphere due to Zn volatility and the reduction reaction.

Influence of low-temperature annealing time on the evolution of the structure and mechanical properties of a titanium Ti-Al-V alloy in the submicrocrystalline state

NASA Astrophysics Data System (ADS)

Ratochka, I. V.; Lykova, O. N.; Naidenkin, E. V.

2015-03-01

The effect of annealing at 673 K for 6-24 h on the structural and phase state and mechanical properties of the titanium alloy of a Ti-Al-V system that was previously subjected to severe plastic deformation by uniform compression deformation, has been studied. It has been established that these annealings lead to a nonmontonic dependence of the mechanical properties of the alloy on the annealing time. It has been shown that the annealing of the Ti-Al-V alloy in a submicrocrystalline state is accompanied by simultaneous hardening processes, i.e., the formation of fine particles during phase transformations and the formation of new nanosized grains, and softening processes, i.e., recovery processes and the growth grains to micron sizes. The prevalence of a given process during annealing determines the deterioration or improvement of the alloy's mechanical properties.

The annealing temperature dependences of microstructures and magnetic properties in electro-chemical deposited CoNiFe thin films

DOE Office of Scientific and Technical Information (OSTI.GOV)

Suharyadi, Edi, E-mail: esuharyadi@ugm.ac.id; Riyanto, Agus; Abraha, Kamsul

2016-04-19

CoNiFe thin films with various compositions had been successfully fabricated using electro-chemical deposition method. The crystal structure of Co{sub 65}Ni{sub 15}Fe{sub 20}, Co{sub 62}Ni{sub 15}Fe{sub 23}, and Co{sub 55}Ni{sub 15}Fe{sub 30} thin films was fcc, bcc-fcc mix, and bcc, respectively. The difference crystal structure results the difference in magnetic properties. The saturation magnetic flux density (Bs) of Co{sub 65}Ni{sub 15}Fe{sub 20}, Co{sub 62}Ni{sub 15}Fe{sub 23}, and Co{sub 55}Ni{sub 15}Fe{sub 30} thin films was 1.89 T, 1.93 T, and 2.05 T, respectively. An optimal annealing temperature was determined for controlling the microstructure and magnetic properties of CoNiFe thin films. Depending onmore » annealing temperature, the ratio of bcc and fcc structure varied without changing the film composition. By annealing at temperature of T ≥ 350°C, the intensity ratio of X-ray diffraction peaks for bcc(110) to fcc(111) increased. The increase of phase ratio of bcc(110) to fcc(111) caused the increase of Bs, from 1.89 T to 1.95 T. Coercivity (Hc) also increased after annealing, from 2.6 Oe to 18.6 Oe for fcc phase thin films, from 2.0 Oe to 12.0 Oe for fcc-bcc mix phase thin films, and 7.8 Oe to 8 Oe for bcc phase thin films. The changing crystal structures during annealing process indicated that the thermal treatment at high temperature cause the changing crystallinity and atomic displacement. The TEM bright-field images with corresponding selected-area electron diffraction (SAED) patterns showed that there are strongly effects of thermal annealing on the size of fcc and bcc phase crystalline grain as described by size of individual spot and discontinuous rings. The size of crystalline grains increased by thermal annealing. The evolution of bcc and fcc structures of CoNiFe during annealing is though to be responsible for the change of magnetic properties.« less

Effects of annealing heat treatment on the corrosion resistance of Zn/Mg/Zn multilayer coatings

NASA Astrophysics Data System (ADS)

Bae, KiTae; La, JoungHyun; Lee, InGyu; Lee, SangYul; Nam, KyungHoon

2017-05-01

Zn coatings alloyed with magnesium offer superior corrosion resistance compared to pure Zn or other Zn-based alloy coatings. In this study, Zn/Mg/Zn multilayer coatings with various Mg layer thicknesses were synthesized using an unbalanced magnetron sputtering process and were annealed to form Zn-Mg intermetallic phases. The effects of the annealing heat treatment on the corrosion resistance of the Zn/Mg/Zn multilayer coatings were evaluated using electrochemical measurements. The extensive diffusion of magnesium species into the upper and lower zinc layer from the magnesium layer in the middle of the coating was observed after the heat treatment. This phenomenon caused (a) the porous microstructure to transition into a dense structure and (b) the formation of a MgZn2 intermetallic phase. The results of the electrochemical measurements demonstrated that the heat treated Zn/Mg/Zn multilayer coatings possessed higher levels of corrosion resistance than the non-heat treated coatings. A Zn/Mg/Zn multilayer coating with MgZn2 and (Zn) phases showed the best corrosion resistance among the heat treated coatings, which could be attributed to the reduced galvanic corrosion effects due to a small potential gradient between the MgZn2 and zinc.

High frequency permeability of Fe-Cu-Nb-Si-B nanocrystalline flakes with the distribution of shape anisotropy fields

NASA Astrophysics Data System (ADS)

Luo, Xing; Wu, Yanhui; Han, Mangui; Deng, Longjiang

2018-04-01

Fe-Cu-Nb-Si-B flakes with multiphase nanostructures have been obtained by annealing the amorphous ribbon and subsequently ball milled for 30 h. The crystal structures have been examined by X-ray diffraction pattern and Mössbauer spectrum. The results show that the particles annealed at 900 °C are made up of amorphous ferromagnetic phase, α-Fe3Si ferromagnetic phase and Fe2B phase, and the average hyperfine magnetic field (HBhf) of particles is 24.02 T. Meanwhile, the relationships between the structure and the high frequency permeability have been studied. Compared with particles annealed at 600 °C, particles annealed at 900 °C exhibit higher saturation magnetization, which is evidenced by the larger HBhf. Also, three magnetic loss peaks in a permeability spectrum have been observed for the particles annealed at 900 °C. The natural resonance frequencies are calculated, which are in good agreement with the experimental resonance peaks. The origin of the multiple magnetic loss peaks can be explained from the perspective of the distribution of shape anisotropy fields which is caused by multiple phase structure.

The structure, bond strength and apatite-inducing ability of micro-arc oxidized tantalum and their response to annealing

NASA Astrophysics Data System (ADS)

Wang, Cuicui; Wang, Feng; Han, Yong

2016-01-01

In this study, the tantalum oxide coatings were formed on pure tantalum (Ta) by micro-arc oxidation (MAO) in electrolytic solutions of calcium acetate and β-glycerophosphate disodium, and the effect of the applied voltage on the microstructure and bond strength of the MAO coatings was systematically investigated. The effect of annealing treatment on the microstructure, bond strength and apatite-inducing ability of the MAO coatings formed at 350 and 450 V was also studied. The study revealed that during the preparation of tantalum oxide coatings on Ta substrate by MAO, the applied voltage considerably affected the phase components, morphologies and bond strength of the coatings, but had little effect on surface chemical species. After annealing treatment, newly formed CaTa4O11 phase mainly contributed to the much more stronger apatite-inducing ability of the annealed tantalum oxide coatings than those that were not annealed. The better apatite-inducing ability of the MAO coatings formed at 450 V compared to those formed at 350 V was attributed to the less amorphous phase and more crystalline phase as well as more Ca and P contained in the MAO coatings with increasing the applied voltage.

Effect of annealing temperature on thermochromic properties of vanadium dioxide thin films deposited by organic sol-gel method

NASA Astrophysics Data System (ADS)

Wu, Jing; Huang, Wanxia; Shi, Qiwu; Cai, Jinghan; Zhao, Dong; Zhang, Yubo; Yan, Jiazhen

2013-03-01

This paper described the synthesis of vanadium dioxide (VO2) thin films on mica substrates with different annealing temperatures by an organic sol-gel method. We performed X-ray diffraction, scanning electron microscope and optical transmission measurements to investigate the effect of the annealing temperature on the crystalline structure, morphology, and phase transition properties of these films. The results showed that a polycrystalline structure with high crystallinity and compact surface at the annealing temperature of 500 °C. The film exhibited a V6O13 phase and a flat surface with small grain size at 440 °C. By contrast, the VnO2n-1 appeared when the annealing temperature at 540 °C, and the film surface split into segregation of spherical grain and aggregates of continuously dendritic particles. Accordingly, the optimal annealing temperature was 500 °C using the organic sol-gel method. And it turned out that the films mainly contained VO2 (M) phase at room temperature with high content of V4+ valence. Particularly, the films showed different changes in the infrared transmittance and hysteresis width during the phase transition. The largest transformation of the infrared transmittance before and after MIT was 73%, while the narrowest temperature hysteresis width was 8 °C at 500 °C.

Tunable ferromagnetic resonance behavior in Co2FeSi film by post-annealing

NASA Astrophysics Data System (ADS)

Xu, Zhan; Zhang, Zhi; Hu, Fang; Li, Xia; Liu, Peng; Liu, Er; Xu, Feng

2018-05-01

Co2FeSi film is potential in the spintronics applications, due to its low damping factor, which is reflected in the ferromagnetic resonance behavior. In this work, we demonstrate that the ferromagnetic resonance behavior in Co2FeSi film can be well engineered by post-annealing. After 450 °C post-annealing for 1 hour, the Gilbert damping factor decreases drastically from 0.039 at as-deposited state to 0.006, and the inhomogeneity contribution of ferromagnetic resonance linewidth decreases to 60.5 Oe. These decreases are ascribed to the crystallization of film from amorphous state to an ordered B2 phase. Higher annealing temperature, however, leads to the formation of the A2 phase with higher atomic disorder, instead of B2 phase, and brings about the increase of Gilbert damping.

Color tunable light-emitting diodes based on p+-Si/p-CuAlO2/n-ZnO nanorod array heterojunctions

NASA Astrophysics Data System (ADS)

Ling, Bo; Zhao, Jun Liang; Sun, Xiao Wei; Tan, Swee Tiam; Kyaw, Aung Ko Ko; Divayana, Yoga; Dong, Zhi Li

2010-07-01

Wide-range color tuning from red to blue was achieved in phosphor-free p+-Si/p-CuAlO2/n-ZnO nanorod light-emitting diodes at room temperature. CuAlO2 films were deposited on p+-Si substrates by sputtering followed by annealing. ZnO nanorods were further grown on the annealed p+-Si/p-CuAlO2 substrates by vapor phase transport. The color of the p-CuAlO2/n-ZnO nanorod array heterojunction electroluminescence depended on the annealing temperature of the CuAlO2 film. With the increase of the annealing temperature from 900 to 1050 °C, the emission showed a blueshift under the same forward bias. The origin of the blueshift is related to the amount of Cu concentration diffused into ZnO.

Obtaining phase-pure CZTS thin films by annealing vacuum evaporated CuS/SnS/ZnS stack

NASA Astrophysics Data System (ADS)

Sánchez, T. G.; Mathew, X.; Mathews, N. R.

2016-07-01

Cu2ZnSnS4 (CZTS) thin films were obtained by the sequential thermal evaporation of metal binary sulfides in the order CuS/SnS/ZnS, followed by annealing in Ar/S atmosphere. The as-grown films were annealed at different temperatures ranging between 350 and 600 °C, for 10 min. Based on the preliminary results, the temperatures 550 °C and 600 °C were selected for further optimization and a second batch of films were annealed for different time durations (10 min, 30 min and 60 min) at these temperatures in order to identify the conditions to obtain phase-pure CZTS films. The structural properties and chemical compositions at each temperature were investigated in order to optimize the phase purity and film stoichiometry. We have identified adequate and reproducible conditions to obtain the elemental ratio Cu/(Zn+Sn) and Zn/Sn close to 0.78 and 1.19 respectively, which is in the range of material composition required for promising solar cells. In addition the optimized material showed excellent optical and electrical properties to be used as a photovoltaic absorber layer. The optical band gap was found to be about 1.52 eV, and the carrier concentration, hall mobility, and resistivity were in the range of 8.372×1015 cm-3, 3.103 cm2/Vs and 340.3 Ω-cm respectively. Three traps with activation energies 4.39, 8.1, and 34 meV were detected.

Study of Sigma Phase in Duplex SAF 2507

NASA Astrophysics Data System (ADS)

Fellicia, D. M.; Sutarsis; Kurniawan, B. A.; Wulanari, D.; Purniawan, A.; Wibisono, A. T.

2017-05-01

Super duplex stainless steel is one of the stainless steel which has a combination between high strength properties and excellent corrosion resistance. However, the resistance can decrease by precipitation of sigma phase which is formed at high temperature, for example after welding processes. A series of experiments has been performed to study the effect of solution annealing to existence of sigma phase on super duplex SAF 2507. Variations of solution-annealing temperatures were 1000 °C, 1065 °C and 1125 °C with holding time of 15 and 30 minutes for each temperature. Effect of solution annealing process was characterized by using XRD, SEM, and Optical Microscopy. The result showed precipitation of sigma phase completely dissolved at 1065 °C and 1125 °C because it reformed to austenite. After it was heated at 1065 °C, chromium carbide appeared in ferrite site and grain boundary. The amount of chromium carbide increased with the increasing of solution annealing temperature.

Influence of growth flux solvent on anneal-tuning of ground states in CaFe2As2

NASA Astrophysics Data System (ADS)

Roncaioli, Connor; Drye, Tyler; Saha, Shanta R.; Paglione, Johnpierre

2018-04-01

The effects of anneal-tuning of single-crystalline samples of CaFe2As2 synthesized via a molten Sn-flux method are investigated using x-ray diffraction, chemical composition, electrical transport, and magnetic susceptibility measurements in order to understand the role of growth conditions on the resultant phase diagram. Previous studies of CaFe2As2 crystals synthesized using a self-flux (FeAs) method revealed an ability to tune the structural and magnetic properties of this system by control of post-synthesis annealing conditions, resulting in an ambient pressure phase diagram that spans from tetragonal/orthorhombic antiferromagnetism to the collapsed tetragonal phase of this system. In this work, we compare previous results to those obtained on crystals synthesized via Sn flux, finding similar tunability in both self- and Sn-flux cases, but less sensitivity to annealing temperatures in the latter case, resulting in a temperature-shifted phase diagram.

Phase formation kinetics, hardness and magnetocaloric effect of sub-rapidly solidified LaFe11.6Si1.4 plates during isothermal annealing

NASA Astrophysics Data System (ADS)

Dai, Yuting; Xu, Zhishuai; Luo, Zhiping; Han, Ke; Zhai, Qijie; Zheng, Hongxing

2018-05-01

High-temperature phase transition behavior and intrinsic brittleness of NaZn13-type τ1 phase in La-Fe-Si magnetocaloric materials are two key problems from the viewpoint of materials production and practical applications. In the present work, the Johnson-Mehl-Avrami-Kolmogorov (JMAK) equation was introduced to quantitatively characterize the formation kinetics of τ1 phase in sub-rapidly solidified LaFe11.6Si1.4 plates during the isothermal annealing process. Avrami index was estimated to be 0.43 (∼0.5), which suggests that the formation of τ1 phase is in a diffusion-controlled one-dimensional growth mode. Meanwhile, it is found that the Vickers hardness as a function of annealing time for sub-rapidly solidified plates also agrees well with the JMAK equation. The Vickers hardness of τ1 phase was estimated to be about 754. Under a magnetic field change of 30 kOe, the maximum magnetic entropy change was about 22.31 J/(kg·K) for plates annealed at 1323 K for 48 h, and the effective magnetic refrigeration capacity reached 191 J/kg.

Investigation of (Ti-Zr-Hf-V-Nb)N Multicomponent Nanostructured Coatings before and after Thermal Annealing by Nuclear Physics Methods of Analysis

NASA Astrophysics Data System (ADS)

Pogrebnjak, A. D.; Beresnev, V. M.; Bondar', A. V.; Kaverin, M. V.; Ponomarev, A. G.

2013-10-01

(Ti-Zr-Hf-V-Nb)N multicomponent nanostructured coatings with thickness of 1.0-1.4 μm synthesized by the method of cathode arc-vapor deposition at temperatures of 250-300°С are investigated by various mutually complementary methods of elemental structural analysis using slow positron beams (SPB), proton microbeam based particle-induced x-ray emission (μ-PIXE), energy-dispersive x-ray spectroscopy (EDS) and scanning electron microscopy (SEM) analyses based on electron micro- and nanobeams, x-ray diffraction (XRD) method of phase structural analysis, and the "a-sin2φ" method of measuring a stressed-strained state (x-ray tensometry). The elemental composition, microstructure, residual stress in nanograins, profiles of defect and atom distributions with depth and over the coating surface in 3D-representation are studied for these coatings, and their phase composition, severely strained state, and composition of coatings before and after annealing at Tann = 600°С for annealing time τ = 30 min are investigated. It is demonstrated that the oxidation resistance of the examined coatings can be significantly increased by high-temperature annealing that leads to the formation of elastic severely strained compression state of the coating. Redistribution of elements and defects, their segregation near the interface boundaries and around grains and subgrains in the process of thermostimulated diffusion, and termination of spinodal segregation without considerable change of the average nanograin size are revealed.

Nanoscale doping of compound semiconductors by solid phase dopant diffusion

DOE Office of Scientific and Technical Information (OSTI.GOV)

Ahn, Jaehyun, E-mail: jaehyun.ahn@utexas.edu; Koh, Donghyi; Roy, Anupam

2016-03-21

Achieving damage-free, uniform, abrupt, ultra-shallow junctions while simultaneously controlling the doping concentration on the nanoscale is an ongoing challenge to the scaling down of electronic device dimensions. Here, we demonstrate a simple method of effectively doping ΙΙΙ-V compound semiconductors, specifically InGaAs, by a solid phase doping source. This method is based on the in-diffusion of oxygen and/or silicon from a deposited non-stoichiometric silicon dioxide (SiO{sub x}) film on InGaAs, which then acts as donors upon activation by annealing. The dopant profile and concentration can be controlled by the deposited film thickness and thermal annealing parameters, giving active carrier concentration ofmore » 1.4 × 10{sup 18 }cm{sup −3}. Our results also indicate that conventional silicon based processes must be carefully reviewed for compound semiconductor device fabrication to prevent unintended doping.« less

Mechanical properties, microstructure and thermal stability of a nanocrystalline CoCrFeMnNi high-entropy alloy after severe plastic deformation

DOE PAGES

Schuh, B.; Mendez-Martin, F.; Völker, B.; ...

2015-06-24

An equiatomic CoCrFeMnNi high-entropy alloy (HEA), produced by arc melting and drop casting, was subjected to severe plastic deformation (SPD) using high-pressure torsion. This process induced substantial grain refinement in the coarse-grained casting leading to a grain size of approximately 50 nm. As a result, strength increased significantly to 1950 MPa, and hardness to similar to 520 MV. Analyses using transmission electron microscopy (TEM) and 3-dimensional atom probe tomography (3D-APT) showed that, after SPD, the alloy remained a true single-phase solid solution down to the atomic scale. Subsequent investigations characterized the evolution of mechanical properties and microstructure of this nanocrystallinemore » HEA upon annealing. Isochronal (for 1 h) and isothermal heat treatments were performed followed by microhardness and tensile tests. The isochronal anneals led to a marked hardness increase with a maximum hardness of similar to 630 HV at about 450 degrees C before softening set in at higher temperatures. The isothermal anneals, performed at this peak hardness temperature, revealed an additional hardness rise to a maximum of about 910 MV after 100 h. To clarify this unexpected annealing response, comprehensive microstructural analyses were performed using TEM and 3D-APT. New nano-scale phases were observed to form in the originally single-phase HEA. After times as short as 5 min at 450 degrees C, a NiMn phase and Cr-rich phase formed. With increasing annealing time, their volume fractions increased and a third phase, FeCo, also formed. It appears that the surfeit of grain boundaries in the nanocrystalline HEA offer many fast diffusion pathways and nucleation sites to facilitate this phase decomposition. The hardness increase, especially for the longer annealing times, can be attributed to these nano-scaled phases embedded in the HEA matrix. The present results give new valuable insights into the phase stability of single-phase high-entropy alloys as well as the mechanisms controlling the mechanical properties of nanostructured multiphase composites. (C) 2015 Acta Materialia Inc. Published by Elsevier Ltd.« less

The effect of annealing on structure and hardness of (Fe-Cr)-50 at.% Al coatings synthesized by mechanical alloying

NASA Astrophysics Data System (ADS)

Ciswandi, Aryanto, Didik; Irmaniar, Tjahjono, Arif; Sudiro, Toto

2018-05-01

In this research, the deposition of (Fe-Cr)-50at.% Al coatings on low carbon steel was carried out by a mechanical alloying (MA) technique. The MA was performed in a shaker mill for 4 hours. Two types of Fe-Cr powders as starting material were used, high purity Fe-Cr powders: (Fe-12.5Cr)-50Al and (Fe-25Cr)-50Al, and Fe-Cr lump powder: (50FeCr)-50Al (in at.%). The coated samples were then annealed in a vacuum furnace at 700°C for 1h. The characterizations of coating structure before and after annealing were studied by XRD and SEM-EDX, while the coating hardness was measured by micro-Vickers hardness tester. Before annealing, all of coating composition were composed mainly of (Fe,Cr)Al phase. After annealing, the FeAl and Fe0.99Cr0.02Al0.99 intermetallic phases was formed in the (Fe-12.5Cr)-50Al and (Fe-25Cr)-50Al coatings. In addition, Fe2CrAlwas also found in the (Fe-25Cr)-50Al coating. Whilethe AlCr2 intermetallic phase was detected as the main phase of (50FeCr)-50Al coating. The cross-sectional microstructure showed that the (Fe-12.5Cr)-50Al and (Fe-25Cr)-50Al coatings have a smoother structure compared to (50FeCr)-50Al coating. The annealing led to intermetallic phase formation and an increasing coating hardness.

Image reconstruction through thin scattering media by simulated annealing algorithm

NASA Astrophysics Data System (ADS)

Fang, Longjie; Zuo, Haoyi; Pang, Lin; Yang, Zuogang; Zhang, Xicheng; Zhu, Jianhua

2018-07-01

An idea for reconstructing the image of an object behind thin scattering media is proposed by phase modulation. The optimized phase mask is achieved by modulating the scattered light using simulated annealing algorithm. The correlation coefficient is exploited as a fitness function to evaluate the quality of reconstructed image. The reconstructed images optimized from simulated annealing algorithm and genetic algorithm are compared in detail. The experimental results show that our proposed method has better definition and higher speed than genetic algorithm.

Development of a Refractory High Entropy Superalloy (Postprint)

DTIC Science & Technology

2016-03-17

pp. 159–183. 37. Nishimori, H .; Onuki , A. Pattern formation in phase-separating alloys with cubic symmetry. Phys. Rev. B 1990, 42, 980. [CrossRef] 38...207 MPa for 2 h , and then annealed at 1400 ˝C for 24 h in continuously flowing high-purity argon. During HIPing and annealing, the alloy was covered...after annealing at 1400 °C for 24 h . Second-phase precipitates (which are dark) are present at grain boundaries. (a) (b) Figure 4. High magnification

Resistance of a directionally solidified gamma/gamma prime-delta eutectic alloy to recrystallization. [Ni-base alloy

NASA Technical Reports Server (NTRS)

Tewari, S. N.; Scheuermann, C. M.; Andrews, C. W.

1976-01-01

A lamellar nickel-base directionally-solidified eutectic gamma/gamma prime-delta alloy has potential as an advanced gas turbine blade material. The microstructural stability of this alloy was investigated. Specimens were plastically deformed by uniform compression or Brinell indentation, then annealed between 750 and 1120 C. Microstructural changes observed after annealing included gamma prime coarsening, pinch-off and spheroidization of delta lamellae, and appearance of an unidentified blocky phase in surface layers. All but the first of these was localized in severely deformed regions, suggesting that microstructural instability may not be a serious problem in the use of this alloy.

Silicide formation process of Er films with Ta and TaN capping layers.

PubMed

Choi, Juyun; Choi, Seongheum; Kim, Jungwoo; Na, Sekwon; Lee, Hoo-Jeong; Lee, Seok-Hee; Kim, Hyoungsub

2013-12-11

The phase development and defect formation during the silicidation reaction of sputter-deposited Er films on Si with ∼20-nm-thick Ta and TaN capping layers were examined. TaN capping effectively prevented the oxygen incorporation from the annealing atmosphere, which resulted in complete conversion to the ErSi2-x phase. However, significant oxygen penetration through the Ta capping layer inhibited the ErSi2-x formation, and incurred the growth of several Er-Si-O phases, even consuming the ErSi2-x layer formed earlier. Both samples produced a number of small recessed defects at an early silicidation stage. However, large rectangular or square-shaped surface defects, which were either pitlike or pyramidal depending on the capping layer identity, were developed as the annealing temperature increased. The origin of different defect generation mechanisms was suggested based on the capping layer-dependent silicidation kinetics.

Hydrothermal synthesis of vanadium pentoxide nanowires

DOE Office of Scientific and Technical Information (OSTI.GOV)

Kumar, J. Santhosh; Thangadurai, P., E-mail: thangaduraip.nst@pondiuni.edu.in, E-mail: thangadurai.p@gmail.com

2016-05-23

Nanowires of V{sub 2}O{sub 5} were prepared via hydrothermal route using NH{sub 4}VO{sub 3} as precursor in the presence of sulfuric acid at 120°C for 24 h. This synthesis process is free of any templates and reducing agents. Thermal analysis showed a phase change at 350°C and the samples were annealed at 500°C. The XRD analysis showed the monoclinic phase for the as-prepared and orthorhombic phase of V{sub 2}O{sub 5} when annealed at 500°C. Characteristic Raman peaks also expressed the same structural features. Microstructure analysis by SEM showed the nanowire structure of V{sub 2}O{sub 5} with thickness in the range ofmore » 20–50 nm and length in micrometers. The possible mechanisms of formation of the nanowires were schematically explained based on the layered structure of V{sub 2}O{sub 5}.« less

Microstructural modifications induced by accelerated aging and lipid absorption in remelted and annealed UHMWPEs for total hip arthroplasty

PubMed Central

Puppulin, Leonardo; Zhu, Wenliang; Sugano, Nobuhiko

2014-01-01

Three types of commercially available ultra-high molecular weight polyethylene (UHMWPE) acetabular cups currently used in total hip arthroplasty have been studied by means of Raman micro-spectroscopy to unfold the microstructural modification induced by the oxidative degradation after accelerated aging with and without lipid absorption. The three investigated materials were produced by three different manufacturing procedures, as follows: irradiation followed by remelting, one-step irradiation followed by annealing, 3-step irradiation and annealing. Clear microstructural differences were observed in terms of phase contents (i.e. amorphous, crystalline and intermediate phase fraction). The three-step annealed material showed the highest crystallinity fraction in the bulk, while the remelted polyethylene is clearly characterized by the lowest content of crystalline phase and the highest content of amorphous phase. After accelerated aging either with or without lipids, the amount of amorphous phase decreased in all the samples as a consequence of the oxidation-induced recrystallization. The most remarkable variations of phase contents were detected in the remelted and in the single-step annealed materials. The presence of lipids triggered oxidative degradation especially in the remelted polyethylene. Such experimental evidence might be explained by the highest amount of amorphous phase in which lipids can be absorbed prior to accelerated aging. The results of these spectroscopic characterizations help to rationalize the complex effect of different irradiation and post-irradiation treatments on the UHMWPE microstructure and gives useful information on how significantly any single step of the manufacturing procedures might affect the oxidative degradation of the polymer. PMID:25179830

Nanoindentation testing as a powerful screening tool for assessing phase stability of nanocrystalline high-entropy alloys

DOE PAGES

Maier-Kiener, Verena; Schuh, Benjamin; George, Easo P.; ...

2016-11-19

The equiatomic high-entropy alloy (HEA), CrMnFeCoNi, has recently been shown to be microstructurally unstable, resulting in a multi-phase microstructure after intermediate-temperature annealing treatments. The decomposition occurs rapidly in the nanocrystalline (NC) state and after longer annealing times in coarse-grained states. To characterize the mechanical properties of differently annealed NC states containing multiple phases, nanoindentation was used in this paper. The results revealed besides drastic changes in hardness, also for the first time significant changes in the Young's modulus and strain rate sensitivity. Finally, nanoindentation of NC HEAs is, therefore, a useful complementary screening tool with high potential as a highmore » throughput approach to detect phase decomposition, which can also be used to qualitatively predict the long-term stability of single-phase HEAs.« less

Vanadium Dioxide Nanoparticle-based Thermochromic Smart Coating: High Luminous Transmittance, Excellent Solar Regulation Efficiency, and Near Room Temperature Phase Transition.

PubMed

Zhu, Jingting; Zhou, Yijie; Wang, Bingbing; Zheng, Jianyun; Ji, Shidong; Yao, Heliang; Luo, Hongjie; Jin, Ping

2015-12-23

An annealing-assisted preparation method of well-crystallized VxW1-xO2(M)@SiO2 core-shell nanoparticles for VO2-based thermochromic smart coatings (VTSC) is presented. The additional annealing process reduces the defect density of the initial hydrothermally prepared VxW1-xO2(M) nanoparticles and enhances their crystallinity so that the thermochromic film based on VxW1-xO2(M)@SiO2 nanoparticles can exhibit outstanding thermochromic performance with balanced solar regulation efficiency (ΔTsol) of 17.3%, luminous transmittance (Tlum) up to 52.2%, and critical phase transition temperature (Tc) around 40.4 °C, which is very promising for practical application. Furthermore, it makes great progress in reducing Tc of VTSC to near room temperature (25.2 °C) and simutaneously maintaining excellent optical properties (ΔTsol = 14.7% and Tlum = 50.6%). Such thermochromic performance is good enough to make VTSC applicable to practical architecture.

Structure, microstructure and microhardness of rapidly solidified Smy(FexNi1-x)4Sb12 (x = 0.45, 0.50, 0.70, 1) thermoelectric compounds

NASA Astrophysics Data System (ADS)

Artini, C.; Castellero, A.; Baricco, M.; Buscaglia, M. T.; Carlini, R.

2018-05-01

Skutterudites are interesting compounds for thermoelectric applications. The main drawback in the synthesis of skutterudites by solidification of the melt is the occurrence of two peritectic reactions requiring long annealing times to form a single phase. Aim of this work is to investigate an alternative route for synthesis, based on rapid solidification by planar flow casting. The effect of cooling rate on phases formation and composition, as well as on structure, microstructure and mechanical properties of the filled Smy(FexNi1-x)4Sb12 (x = 0.45, 0.50, 0.70, 1) skutterudites was studied. Conversely to slowly cooled ingots, rapidly quenched ribbons show skutterudite as the main phase, suggesting that deep undercooling of the liquid prevents the nucleation of high temperature phases, such as (Fe,Ni)Sb and (Fe,Ni)Sb2. In as-quenched samples, a slightly out of equilibrium Sm content is revealed, which does not alter the position of the p/n boundary; nevertheless, it exerts an influence on crystallographic properties, such as the cell parameter and the shape of the Sb4 rings in the structure. As-quenched ribbons show a fine microstructure of the skutterudite phase (grain size of 2-20 μm), which only moderately coarsens after annealing at 873 K for 4 days. Vickers microhardness values (350-400 HV) of the skutterudite phase in as-quenched ribbons are affected by the presence of softer phases (i.e. Sb), which are homogeneously and finely dispersed within the sample. The skutterudite hardens after annealing as a consequence of a moderate grain growth, which limits the matrix effect due to the presence of additional phases.

Controlling the microstructure and associated magnetic properties of Ni 0.2Mn 3.2Ga 0.6 melt-spun ribbons by annealing

DOE Office of Scientific and Technical Information (OSTI.GOV)

Khan, Mahmud; Alshammari, Ohud; Balasubramanian, Balamurugan

2017-03-01

Here we report on the structural and magnetic properties of Ni 0.2Mn 3.2Ga 0.6 melt-spun ribbons. The as-spun ribbons were found to exhibit mixed cubic phases that transform to non-cubic structure upon annealing. Additionally, an amorphous phase was found to co-exist in all ribbons. The SEM images show that minor grain formation occurs on the as-spun ribbons. However, the formation of extensive nano-grains was observed on the surfaces of the annealed ribbons. While the as-spun ribbons exhibit predominantly paramagnetic behavior, the ribbons annealed under various thermal conditions were found to be ferromagnetic with a Curie temperature of about 380 K.more » The ribbons annealed at 450 °C for 30 minutes exhibit a large coercive field of about 2500 Oe. The experimental results show that the microstructure and associated magnetic properties of the ribbons can be controlled by annealing techniques. The coercive fields and the shape of the magnetic hysteresis loops vary significantly with annealing conditions. As a result, exchange bias effects have also been observed in the annealed ribbons.« less

Microstructure and magnetic behavior of Cu-Co-Si ternary alloy synthesized by mechanical alloying and isothermal annealing

NASA Astrophysics Data System (ADS)

Chabri, Sumit; Bera, S.; Mondal, B. N.; Basumallick, A.; Chattopadhyay, P. P.

2017-03-01

Microstructure and magnetic behavior of nanocrystalline 50Cu-40Co-10Si (at%) alloy prepared by mechanical alloying and subsequent isothermal annealing in the temperature range of 450-650 °C have been studied. Phase evolution during mechanical alloying and isothermal annealing is characterized by X-ray diffraction (XRD), differential thermal analyzer (DTA), high resolution transmission electron microscopy (HRTEM) and magnetic measurement. Addition of Si has been found to facilitate the metastable alloying of Co in Cu resulting into the formation of single phase solid solution having average grain size of 9 nm after ball milling for 50 h duration. Annealing of the ball milled alloy improves the magnetic properties significantly and best combination of magnetic properties has been obtained after annealing at 550 °C for 1 h duration.

The effects of different heat treatment annealing on structural properties of LaFe11.5Si1.5 compound

NASA Astrophysics Data System (ADS)

Norizan, Yang Nurhidayah Asnida; Din, Muhammad Faiz Md; Zamri, Wan Fathul Hakim W.; Hashim, Fakroul Ridzuan; Jusoh, Mohd Taufik; Rahman, Mohd Rashid Abdul

2018-02-01

The cubic NaZn13-type LaFe13-xSix based compounds have been studied systematically and has become one of the most interesting systems for exploring large MCE. Its magnetic properties are strongly doping dependent and provides many of advantage compare to other as magnetic materials for magnetic refrigerator application. In other to produce high quality of cubic NaZn13-type structure, the structural properties of LaFe11.5Si1.5 compounds annealed at different temperature have been investigated. The LaFe11.5Si1.5 compounds was prepared by arc melting and annealed at two different heat treatment which are 1323 K for 14 days and 1523 K for 4 hour. The powder X-ray diffraction (XRD) shows that a short time and high temperature annealing process has benefits for the formation of the NaZn13-type phase compared to a long time and low temperature annealing process. This is shown by the weight fraction of cubic NaZn13- type structure increases from 80% for low temperature annealing to 83% for high temperature annealing. At the same time, high temperature annealing increase the main structure and decrease the impurity (α-Fe and LaFeSi). Furthermore, it can be clearly seen in the Rietveld refinement results that the lattice parameter is increase at the high temperature annealing because of more cubic NaZn13 is formed at higher temperature.

Phase Transformations of an Fe-0.85 C-17.9 Mn-7.1 Al Austenitic Steel After Quenching and Annealing

NASA Astrophysics Data System (ADS)

Cheng, Wei-Chun

2014-09-01

Low-density Mn-Al steels could potentially be substitutes for commercial Ni-Cr stainless steels. However, the development of the Mn-Al stainless steels requires knowledge of the phase transformations that occur during the steel making processes. Phase transformations of an Fe-0.85 C-17.9 Mn-7.1 Al (wt.%) austenitic steel, which include spinodal decomposition, precipitation transformations, and cellular transformations, have been studied after quenching and annealing. The results show that spinodal decomposition occurs prior to the precipitation transformation in the steel after quenching and annealing at temperatures below 1023 K and that coherent fine particles of L12-type carbide precipitate homogeneously in the austenite. The cellular transformation occurs during the transformation of high-temperature austenite into lamellae of austenite, ferrite, and kappa carbide at temperatures below 1048 K. During annealing at temperatures below 923 K, the austenite decomposes into lamellar austenite, ferrite, κ-carbide, and M23C6 carbide grains for another cellular transformation. Last, when annealing at temperatures below 873 K, lamellae of ferrite and κ-carbide appear in the austenite.

Exploring first-order phase transitions with population annealing

NASA Astrophysics Data System (ADS)

Barash, Lev Yu.; Weigel, Martin; Shchur, Lev N.; Janke, Wolfhard

2017-03-01

Population annealing is a hybrid of sequential and Markov chain Monte Carlo methods geared towards the efficient parallel simulation of systems with complex free-energy landscapes. Systems with first-order phase transitions are among the problems in computational physics that are difficult to tackle with standard methods such as local-update simulations in the canonical ensemble, for example with the Metropolis algorithm. It is hence interesting to see whether such transitions can be more easily studied using population annealing. We report here our preliminary observations from population annealing runs for the two-dimensional Potts model with q > 4, where it undergoes a first-order transition.

Selective Growth of Low Stored Energy Grains During δ Sub-solvus Annealing in the Inconel 718 Nickel-Based Superalloy

NASA Astrophysics Data System (ADS)

Agnoli, Andrea; Bernacki, Marc; Logé, Roland; Franchet, Jean-Michel; Laigo, Johanne; Bozzolo, Nathalie

2015-09-01

The microstructure stability during δ sub-solvus annealing in Inconel 718 was investigated, focusing on the conditions that may lead to the development of very large grains (about 100 μm) in a recrystallized fine grained matrix (4 to 5 μm) despite the presence of second-phase particles. Microstructure evolution was analyzed by EBSD (grain size, intragranular misorientation) and SEM ( δ phase particles). Results confirm that, in the absence of stored energy, the grain structure is controlled by the δ phase particles, as predicted by the Smith-Zener equation. If the initial microstructure is strained ( ɛ < 0.1) before annealing, then low stored energy grains grow to a large extent, despite the Zener pinning forces exerted by the second-phase particles on the grain boundaries. Those selectively growing grains could be those of the initial microstructure that were the least deformed, or they could result from a nucleation process. The balance of three forces acting on boundary migration controls the growth process: if the sum of capillarity and stored energy driving forces exceeds the Zener pinning force, then selective grain growth occurs. Such phenomenon could be simulated, using a level set approach in a finite element context, by taking into account the three forces acting on boundary migration and by considering a realistic strain energy distribution (estimated from EBSD measurements).

The Effect of Cu:Ag Atomic Ratio on the Properties of Sputtered Cu–Ag Alloy Thin Films

PubMed Central

Hsieh, Janghsing; Hung, Shunyang

2016-01-01

Cu–Ag thin films with various atomic ratios were prepared using a co-sputtering technique, followed by rapid thermal annealing at various temperatures. The films’ structural, mechanical, and electrical properties were then characterized using X-ray diffractometry (XRD), atomic force microscopy (AFM), FESEM, nano-indentation, and TEM as functions of compositions and annealing conditions. In the as-deposited condition, the structure of these films transformed from a one-phase to a dual-phase state, and the resistivity shows a twin-peak pattern, which can be explained in part by Nordheim’s Rule and the miscibility gap of Cu–Ag alloy. After being annealed, the films’ resistivity followed the mixture rule in general, mainly due to the formation of a dual-phase structure containing Ag-rich and Cu-rich phases. The surface morphology and structure also varied as compositions and annealing conditions changed. The recrystallization of these films varied depending on Ag–Cu compositions. The annealed films composed of 40 at % to 60 at % Cu had higher hardness and lower roughness than those with other compositions. Particularly, the Cu50Ag50 film had the highest hardness after being annealed. From the dissolution testing, it was found that the Cu-ion concentration was about 40 times higher than that of Ag. The galvanic effect and over-saturated state could be the cause of the accelerated Cu dissolution and the reduced dissolution of the Ag. PMID:28774033

Excimer laser annealing of NiTi shape memory alloy thin film

NASA Astrophysics Data System (ADS)

Xie, Qiong; Huang, Weimin; Hong, Ming Hui; Song, Wendong; Chong, Tow Chong

2003-02-01

NiTi Shape Memory Alloy (SMA) is with great potential for actuation in microsystems. It is particularly suitable for medical applications due to its excellent biocompatibility. In MEMS, local annealing of SMA is required in the process of fabrication. In this paper, local annealing of Ni52Ti48 SMA with excimer laser is proposed for the first time. The Ni52Ti48 thin film in a thickness of 5 μm was deposited on Si (100) wafer by sputtering at room temperature. After that, the thin film was annealed by excimer laser (248nm KrF laser) for the first time. Field-Emission Scanning Electron Microscopy (FESEM) and Atomic Force Microscopy (AFM) were used to characterize the surface profile of the deposited film after laser annealing. The phase transformation was measured by Differential Scanning Calorimeter (DSC) test. It is concluded that NiTi film sputtering on Si(100) substrate at room temperature possesses phase transformation after local laser annealing but with cracks.

A protected annealing strategy to enhanced light emission and photostability of YAG:Ce nanoparticle-based films

NASA Astrophysics Data System (ADS)

Revaux, Amelie; Dantelle, Geraldine; George, Nathan; Seshadri, Ram; Gacoin, Thierry; Boilot, Jean-Pierre

2011-05-01

A significant obstacle in the development of YAG:Ce nanoparticles as light converters in white LEDs and as biological labels is associated with the difficulty of finding preparative conditions that allow simultaneous control of structure, particle size and size distribution, while maintaining the optical properties of bulk samples. Preparation conditions frequently involve high-temperature treatments of precursors (up to 1400 °C), which result in increased particle size and aggregation, and lead to oxidation of Ce(iii) to Ce(iv). We report here a process that we term protected annealing, that allows the thermal treatment of preformed precursor particles at temperatures up to 1000 °C while preserving their small size and state of dispersion. In a first step, pristine nanoparticles are prepared by a glycothermal reaction, leading to a mixture of YAG and boehmite crystalline phases. The preformed nanoparticles are then dispersed in a porous silica. Annealing of the composite material at 1000 °C is followed by dissolution of the amorphous silica by hydrofluoric acid to recover the annealed particles as a colloidal dispersion. This simple process allows completion of YAG crystallization while preserving their small size. The redox state of Ce ions can be controlled through the annealing atmosphere. The obtained particles of YAG:Ce (60 +/- 10 nm in size) can be dispersed as nearly transparent aqueous suspensions, with a luminescence quantum yield of 60%. Transparent YAG:Ce nanoparticle-based films of micron thickness can be deposited on glass substrates using aerosol spraying. Films formed from particles prepared by the protected annealing strategy display significantly improved photostability over particles that have not been subject to such annealing.A significant obstacle in the development of YAG:Ce nanoparticles as light converters in white LEDs and as biological labels is associated with the difficulty of finding preparative conditions that allow simultaneous control of structure, particle size and size distribution, while maintaining the optical properties of bulk samples. Preparation conditions frequently involve high-temperature treatments of precursors (up to 1400 °C), which result in increased particle size and aggregation, and lead to oxidation of Ce(iii) to Ce(iv). We report here a process that we term protected annealing, that allows the thermal treatment of preformed precursor particles at temperatures up to 1000 °C while preserving their small size and state of dispersion. In a first step, pristine nanoparticles are prepared by a glycothermal reaction, leading to a mixture of YAG and boehmite crystalline phases. The preformed nanoparticles are then dispersed in a porous silica. Annealing of the composite material at 1000 °C is followed by dissolution of the amorphous silica by hydrofluoric acid to recover the annealed particles as a colloidal dispersion. This simple process allows completion of YAG crystallization while preserving their small size. The redox state of Ce ions can be controlled through the annealing atmosphere. The obtained particles of YAG:Ce (60 +/- 10 nm in size) can be dispersed as nearly transparent aqueous suspensions, with a luminescence quantum yield of 60%. Transparent YAG:Ce nanoparticle-based films of micron thickness can be deposited on glass substrates using aerosol spraying. Films formed from particles prepared by the protected annealing strategy display significantly improved photostability over particles that have not been subject to such annealing. Electronic supplementary information (ESI) available: Thermogravimetric analysis curve, picture of a YAG:Ce3+ thin film. See DOI: 10.1039/c0nr01000f

Y-TZP zirconia regeneration firing: Microstructural and crystallographic changes after grinding.

PubMed

Ryan, Daniel Patrick Obelenis; Fais, Laiza Maria Grassi; Antonio, Selma Gutierrez; Hatanaka, Gabriel Rodrigues; Candido, Lucas Miguel; Pinelli, Ligia Antunes Pereira

2017-07-26

This study evaluated microstructural and crystallographic phase changes after grinding (G) and regeneration firing/anneling (R) of Y-TZP ceramics. Thirty five bars (Lava TM and Ice Zirkon) were divided: Y-TZP pre-sintered, control (C), regeneration firing (R), dry grinding (DG), dry grinding+regeneration firing (DGR), wet grinding (WG) and wet grinding+regeneration firing (WGR). Grinding was conducted using a diamond bur and annealing at 1,000°C. The microstructure was analyzed by SEM and the crystalline phases by X-ray diffraction (XRD). XRD showed that pre-sintered specimens contained tetragonal and monoclinic phases, while groups C and R showed tetragonal, cubic and monoclinic phases. After grinding, the cubic phase was eliminated in all groups. Annealing (DGR and WGR) resulted in only tetragonal phase. SEM showed semi-circular cracks after grinding and homogenization of particles after annealing. After grinding, surfaces show tetragonal and monoclinic phases and R can be assumed to be necessary prior to porcelain layering when grinding is performed.

Phase transformation from cubic ZnS to hexagonal ZnO by thermal annealing

NASA Astrophysics Data System (ADS)

Mahmood, K.; Asghar, M.; Amin, N.; Ali, Adnan

2015-03-01

We have investigated the mechanism of phase transformation from ZnS to hexagonal ZnO by high-temperature thermal annealing. The ZnS thin films were grown on Si (001) substrate by thermal evaporation system using ZnS powder as source material. The grown films were annealed at different temperatures and characterized by X-ray diffraction (XRD), photoluminescence (PL), four-point probe, scanning electron microscope (SEM) and energy dispersive X-ray diffraction (EDX). The results demonstrated that as-deposited ZnS film has mixed phases but high-temperature annealing leads to transition from ZnS to ZnO. The observed result can be explained as a two-step process: (1) high-energy O atoms replaced S atoms in lattice during annealing process, and (2) S atoms diffused into substrate and/or diffused out of the sample. The dissociation energy of ZnS calculated from the Arrhenius plot of 1000/T versus log (resistivity) was found to be 3.1 eV. PL spectra of as-grown sample exhibits a characteristic green emission at 2.4 eV of ZnS but annealed samples consist of band-to-band and defect emission of ZnO at 3.29 eV and 2.5 eV respectively. SEM and EDX measurements were additionally performed to strengthen the argument.

Stepwise kinetic equilibrium models of quantitative polymerase chain reaction.

PubMed

Cobbs, Gary

2012-08-16

Numerous models for use in interpreting quantitative PCR (qPCR) data are present in recent literature. The most commonly used models assume the amplification in qPCR is exponential and fit an exponential model with a constant rate of increase to a select part of the curve. Kinetic theory may be used to model the annealing phase and does not assume constant efficiency of amplification. Mechanistic models describing the annealing phase with kinetic theory offer the most potential for accurate interpretation of qPCR data. Even so, they have not been thoroughly investigated and are rarely used for interpretation of qPCR data. New results for kinetic modeling of qPCR are presented. Two models are presented in which the efficiency of amplification is based on equilibrium solutions for the annealing phase of the qPCR process. Model 1 assumes annealing of complementary targets strands and annealing of target and primers are both reversible reactions and reach a dynamic equilibrium. Model 2 assumes all annealing reactions are nonreversible and equilibrium is static. Both models include the effect of primer concentration during the annealing phase. Analytic formulae are given for the equilibrium values of all single and double stranded molecules at the end of the annealing step. The equilibrium values are then used in a stepwise method to describe the whole qPCR process. Rate constants of kinetic models are the same for solutions that are identical except for possibly having different initial target concentrations. Analysis of qPCR curves from such solutions are thus analyzed by simultaneous non-linear curve fitting with the same rate constant values applying to all curves and each curve having a unique value for initial target concentration. The models were fit to two data sets for which the true initial target concentrations are known. Both models give better fit to observed qPCR data than other kinetic models present in the literature. They also give better estimates of initial target concentration. Model 1 was found to be slightly more robust than model 2 giving better estimates of initial target concentration when estimation of parameters was done for qPCR curves with very different initial target concentration. Both models may be used to estimate the initial absolute concentration of target sequence when a standard curve is not available. It is argued that the kinetic approach to modeling and interpreting quantitative PCR data has the potential to give more precise estimates of the true initial target concentrations than other methods currently used for analysis of qPCR data. The two models presented here give a unified model of the qPCR process in that they explain the shape of the qPCR curve for a wide variety of initial target concentrations.

Benefits of Intercritical Annealing in Quenching and Partitioning Steel

NASA Astrophysics Data System (ADS)

Wang, X.; Liu, L.; Liu, R. D.; Huang, M. X.

2018-03-01

Compared to the quenching and partitioning (Q&P) steel produced by full austenization annealing, the Q&P steel produced by the intercritical annealing shows a similar ultimate tensile stress but a larger tensile ductility. This property is attributable to the higher volume fraction and the better mechanical stability of the retained austenite after the intercritical annealing. Moreover, intercritical annealing produces more ferrite and fewer martensite phases in the microstructure, making an additional contribution to a higher work hardening rate and therefore a better tensile ductility.

Thermal Annealing to Modulate the Shape Memory Behavior of a Biobased and Biocompatible Triblock Copolymer Scaffold in the Human Body Temperature Range.

PubMed

Merlettini, Andrea; Gigli, Matteo; Ramella, Martina; Gualandi, Chiara; Soccio, Michelina; Boccafoschi, Francesca; Munari, Andrea; Lotti, Nadia; Focarete, Maria Letizia

2017-08-14

A biodegradable and biocompatible electrospun scaffold with shape memory behavior in the physiological temperature range is here presented. It was obtained starting from a specifically designed, biobased PLLA-based triblock copolymer, where the central block is poly(propylene azelate-co-propylene sebacate) (P(PAz60PSeb40)) random copolymer. Shape memory properties are determined by the contemporary presence of the low melting crystals of the P(PAz60PSeb40) block, acting as switching segment, and of the high melting crystal phase of PLLA blocks, acting as physical network. It is demonstrated that a straightforward annealing process applied to the crystal phase of the switching element gives the possibility to tune the shape recovery temperature from about 25 to 50 °C, without the need of varying the copolymer's chemical structure. The thermal annealing approach here presented can be thus considered a powerful strategy for "ad hoc" programming the same material for applications requiring different recovery temperatures. Fibroblast culture experiments demonstrated scaffold biocompatibility.

Selective Template Wetting Routes to Hierarchical Polymer Films: Polymer Nanotubes from Phase-Separated Films via Solvent Annealing.

PubMed

Ko, Hao-Wen; Cheng, Ming-Hsiang; Chi, Mu-Huan; Chang, Chun-Wei; Chen, Jiun-Tai

2016-03-01

We demonstrate a novel wetting method to prepare hierarchical polymer films with polymer nanotubes on selective regions. This strategy is based on the selective wetting abilities of polymer chains, annealed in different solvent vapors, into the nanopores of porous templates. Phase-separated films of polystyrene (PS) and poly(methyl methacrylate) (PMMA), two commonly used polymers, are prepared as a model system. After anodic aluminum oxide (AAO) templates are placed on the films, the samples are annealed in vapors of acetic acid, in which the PMMA chains are swollen and wet the nanopores of the AAO templates selectively. As a result, hierarchical polymer films containing PMMA nanotubes can be obtained after the AAO templates are removed. The distribution of the PMMA nanotubes of the hierarchical polymer films can also be controlled by changing the compositions of the polymer blends. This work not only presents a novel method to fabricate hierarchical polymer films with polymer nanotubes on selective regions, but also gives a deeper understanding in the selective wetting ability of polymer chains in solvent vapors.

Vapor Synthesis and Thermal Modification of Supportless Platinum–Ruthenium Nanotubes and Application as Methanol Electrooxidation Catalysts

DOE PAGES

Atkinson III, Robert W.; Unocic, Raymond R.; Unocic, Kinga A.; ...

2015-04-23

Metallic, mixed-phase, and alloyed bimetallic Pt-Ru nanotubes were synthesized by a novel route based on the sublimation of metal acetylacetonate precursors and their subsequent vapor deposition within anodic alumina templates. Nanotube architectures were tuned by thermal annealing treatments. As-synthesized nanotubes are composed of nanoparticulate, metallic platinum and hydrous ruthenium oxide whose respective thicknesses depend on the sample chemical composition. The Pt-decorated, hydrous Ru oxide nanotubes may be thermally annealed to promote a series of chemical and physical changes to the nanotube structures including alloy formation, crystallite growth and morphological evolution. Annealed Pt-Ru alloy nanotubes and their as-synthesized analogs demonstrate relativelymore » high specific activities for the oxidation of methanol. As-synthesized, mixed-phase Pt-Ru nanotubes (0.39 mA/cm2) and metallic alloyed Pt64Ru36NTs (0.33 mA/cm2) have considerably higher area-normalized activities than PtRu black (0.22 mA/cm2) at 0.65 V vs. RHE.« less

Studies of defects in Bi2Fe4O9 using Mössbauer spectroscopy

NASA Astrophysics Data System (ADS)

Panda, Alaka; Govindaraj, R.; Vinod, K.; Amarendra, G.

2018-05-01

Effect of oxygen vacancies on the stability and magnetic properties of Bi2Fe4O9 has been addressed in a detailed manner using Mössbauer spectroscopy along with magnetization studies. This is studied mainly based on the variations in Mössbauer hyperfine parameters due to the changes in the local structure and magnetic properties at 57Fe atoms in Bi2Fe4O9 which are observed to be significantly influenced due to vacuum annealing. Oxygen vacancies concomitantly result in the formation of iron associated antiferromagnetic phase preferably at the boundaries of the grains of Bi2Fe4O9. Growth of these phases is observed to be strongly dependent upon subsequent air annealing treatments of this system.

Thermal decomposition of solid phase nitromethane under various heating rates and target temperatures based on ab initio molecular dynamics simulations.

PubMed

Xu, Kai; Wei, Dong-Qing; Chen, Xiang-Rong; Ji, Guang-Fu

2014-10-01

The Car-Parrinello molecular dynamics simulation was applied to study the thermal decomposition of solid phase nitromethane under gradual heating and fast annealing conditions. In gradual heating simulations, we found that, rather than C-N bond cleavage, intermolecular proton transfer is more likely to be the first reaction in the decomposition process. At high temperature, the first reaction in fast annealing simulation is intermolecular proton transfer leading to CH3NOOH and CH2NO2, whereas the initial chemical event at low temperature tends to be a unimolecular C-N bond cleavage, producing CH3 and NO2 fragments. It is the first time to date that the direct rupture of a C-N bond has been reported as the first reaction in solid phase nitromethane. In addition, the fast annealing simulations on a supercell at different temperatures are conducted to validate the effect of simulation cell size on initial reaction mechanisms. The results are in qualitative agreement with the simulations on a unit cell. By analyzing the time evolution of some molecules, we also found that the time of first water molecule formation is clearly sensitive to heating rates and target temperatures when the first reaction is an intermolecular proton transfer.

Tuning phase transition temperature of VO2 thin films by annealing atmosphere

NASA Astrophysics Data System (ADS)

Liu, Xingxing; Wang, Shao-Wei; Chen, Feiliang; Yu, Liming; Chen, Xiaoshuang

2015-07-01

A simple new way to tune the optical phase transition temperature of VO2 films was proposed by only controlling the pressure of oxygen during the annealing process. Vanadium films were deposited on glass by a large-scale magnetron sputtering coating system and then annealed in appropriate oxygen atmosphere to form the VO2 films. The infrared transmission change (at 2400 nm) is as high as 58% for the VO2 thin film on the glass substrate, which is very good for tuning infrared radiation and energy saving as smart windows. The phase transition temperature of the films can be easily tuned from an intrinsic temperature to 44.7 °C and 40.2 °C on glass and sapphire by annealing oxygen pressure, respectively. The mechanism is: V3+ ions form in the film when under anaerobic conditions, which can interrupt the V4+ chain and reduce the phase transition temperature. The existence of V3+ ions has been observed by x-ray photoelectron spectroscopy (XPS) experiments as proof.

Electron backscatter diffraction study of deformation and recrystallization textures of individual phases in a cross-rolled duplex steel

DOE Office of Scientific and Technical Information (OSTI.GOV)

Zaid, Md; Bhattacharjee, P.P., E-mail: pinakib@iith.ac.in

2014-10-15

The evolution of microstructure and texture during cross-rolling and annealing was investigated by electron backscatter diffraction in a ferritic–austenitic duplex stainless steel. For this purpose an alloy with nearly equal volume fraction of the two phases was deformed by multi-pass cross-rolling process up to 90% reduction in thickness. The rolling and transverse directions were mutually interchanged in each pass by rotating the sample by 90° around the normal direction. In order to avoid deformation induced phase transformation and dynamic strain aging, the rolling was carried out at an optimized temperature of 898 K (625 °C) at the warm-deformation range. Themore » microstructure after cross warm-rolling revealed a lamellar structure with alternate arrangement of the bands of two phases. Strong brass and rotated brass components were observed in austenite in the steel after processing by cross warm-rolling. The ferrite in the cross warm-rolling processed steel showed remarkably strong RD-fiber (RD//< 011 >) component (001)< 011 >. The development of texture in the two phases after processing by cross warm-rolling could be explained by the stability of the texture components. During isothermal annealing of the 90% cross warm-rolling processed material the lamellar morphology was retained before collapse of the lamellar structure to the mutual interpenetration of the phase bands. Ferrite showed recovery resulting in annealing texture similar to the deformation texture. In contrast, the austenite showed primary recrystallization without preferential orientation selection leading to the retention of deformation texture. The evolution of deformation and annealing texture in the two phases of the steel was independent of one another. - Highlights: • Effect of cross warm-rolling on texture formation is studied in duplex steel. • Brass texture in austenite and (001)<110 > in ferrite are developed. • Ferrite shows recovery during annealing retaining the (001)<110 > component. • Austenite shows recrystallization during annealing retaining the deformation texture. • The deformation of recrystallization of two phases is independent of one other.« less

Optical properties of dip coated titanium-di-oxide (TiO2) thin films annealed at different temperatures

NASA Astrophysics Data System (ADS)

Biswas, Sayari; Kar, Asit Kumar

2018-02-01

Titanium dioxide (TiO2) thin films were synthesized by hydrothermal assisted sol-gel dip coating method on quartz substrate. The sol was prepared by hydrothermal method at 90 °C. Dip coating method was used to deposit the thin films. Later films were annealed at four different temperatures -600 °C, 800 °C, 1000 °C and 1200 °C. XRD study showed samples annealed at 600 °C are almost amorphous. At 800 °C, film turns into anatase phase and with further increment of annealing temperature they turn into rutile phase. Transmission spectra of thin films show sharp rise in the violet-ultraviolet transition region and a maximum transmittance of ˜60% was observed in the visible region for the sample annealed at the lowest temperature. Band gap of the prepared films varies from 2.9 eV to 3.5 eV.

Role of annealing temperatures on structure polymorphism, linear and nonlinear optical properties of nanostructure lead dioxide thin films

NASA Astrophysics Data System (ADS)

Zeyada, H. M.; Makhlouf, M. M.

2016-04-01

The powder of as synthesized lead dioxide (PbO2) has polycrystalline structure β-PbO2 phase of tetragonal crystal system. It becomes nanocrystallites α-PbO2 phase with orthorhombic crystal system upon thermal deposition to form thin films. Annealing temperatures increase nanocrystallites size from 28 to 46 nm. The optical properties of α-PbO2 phase were calculated from absolute values of transmittance and reflectance at nearly normal incidence of light by spectrophotometer measurements. The refractive and extinction indices were determined and showed a response to annealing temperatures. The absorption coefficient of α-PbO2 films is >106 cm-1 in UV region of spectra. Analysis of the absorption coefficient spectra near optical edge showed indirect allowed transition. Annealing temperature decreases the value of indirect energy gap for α-PbO2 films. The dispersion parameters such as single oscillator energy, dispersion energy, dielectric constant at high frequency and lattice dielectric constant were calculated and its variations with annealing temperatures are reported. The nonlinear refractive index (n2), third-order nonlinear susceptibility (χ(3)) and nonlinear absorption coefficient (βc) were determined. It was found that χ(3), n2 and β increase with increasing photon energy and decrease with increasing annealing temperature. The pristine film of α-PbO2 has higher values of nonlinear optical constants than for annealed films; therefore it is suitable for applications in manufacturing nonlinear optical devices.

The effect of anti-phase domain size on the ductility of a rapidly solidified Ni3Al-Cr alloy

NASA Technical Reports Server (NTRS)

Carro, G.; Bertero, G. A.; Wittig, J. E.; Flanagan, W. F.

1989-01-01

Tensile tests on splat-quenched Ni3Al-Cr alloys showed a sharp decrease in ductility with long-time annealing. The growth of the initially very-fine-size anti-phase domains showed a tenuous correlation with ductility up to a critical size, where ductility was lost. The grain size was relatively unaffected by these annealing treatments, but the grain-boundary curvature decreased, implying less toughness. An important observation was that, for the longest annealing time, a chromium-rich precipitate formed, which the data indicate could be a boride. Miniaturized tensile tests were performed on samples which were all obtained from the same splat-quenched foil, and the various domain sizes were controlled by subsequent annealing treatments.

Spin reorientations in Tb-Fe films grown on polyimide substrates

NASA Astrophysics Data System (ADS)

Maneesh, K. Sai; Arout Chelvane, J.; Talapatra, A.; Basumatary, Himalay; Mohanty, J.; Kamat, S. V.

2018-02-01

This paper reports the effect of film thickness and rapid thermal annealing on the spin reorientations in Tb-Fe films grown on flexible polyimide substrates. Magnetization studies indicated that the spins reorient from in-plane to out-of-plane direction with increase in film thicknesses. This was confirmed by magnetic force microscopy studies which showed weak featureless contrast for films deposited with lower thickness and a strong out-of-plane contrast for films grown with higher thicknesses. On subsequent rapid thermal annealing all the Tb-Fe films exhibited in-plane magnetic anisotropy. The results were explained based on competition between uniaxial and shape anisotropies, nature of residual stresses as well as nucleation of crystalline Fe phase in an amorphous Tb-Fe matrix on rapid thermal annealing.

Magnetic and structural properties of rapidly quenched Nd-Fe-Co-Ge-B alloys

NASA Astrophysics Data System (ADS)

Beitollahi, A.; Gholamipour, R.; Marghusian, V. K.; Andreev, S. V.; Bogatkin, A. N.; Duragin, S. S.; Kozlov, A. N.; Kudrevatykh, N. V.; Bogdanov, S. G.; Pirogov, A. N.

2006-12-01

We have studied the structure and magnetic properties of some rapidly quenched and subsequently annealed alloys prepared by centrifugal method with a composition (in wt %) Nd(29.5), Co(6), B(1.1), Ge (x), Fe(balance) with x=0.0, 0.2, 0.4, 0.6, 0.8, 1.0 (wt %) for Ge. Based on X-ray diffraction (XRD), elastic neutron diffraction, and small-angle neutron scattering (SANS), the formation of partially crystallized main hard magnetic 2:14:1 (Φ) phase in the amorphous matrix was detected for all as-spun samples. The size of the clusters formed for the sample with 1 wt % Ge determined based on SANS profiles was about 10 nm. It was shown that the addition of Ge shifts the maximum crystallization peak of the main 2:14:1 phase to higher temperatures. The variation of the magnitudes of different magnetic parameters such as i H c and M s versus Ge concentration for as-spun samples can be possibly related to the different rate of crystallization of the 2:14:1 phase formed. Further, for the samples doped with 0.8 and 1.0 wt % Ge and annealed at 760°C for 5 min the formation of some extra phases such as Nd5Ge3, NdFe2, NdB4, as well as α-Fe was detected by XRD. The magnetic measurements carried out using a vibrating-sample magnetometer (VSM) for these samples also supported the XRD data obtained. While the highest values of coercivity i H c = 772 kA/m were obtained for the annealed samples without Ge, the highest value of σr = 69 emu/g was also obtained for the samples substituted with 0.8 wt % Ge without an appreciable reduction in i H c.

Accumulative Roll Bonding and Post-Deformation Annealing of Cu-Al-Mn Shape Memory Alloy

NASA Astrophysics Data System (ADS)

Moghaddam, Ahmad Ostovari; Ketabchi, Mostafa; Afrasiabi, Yaser

2014-12-01

Accumulative roll bonding is a severe plastic deformation process used for Cu-Al-Mn shape memory alloy. The main purpose of this study is to investigate the possibility of grain refinement of Cu-9.5Al-8.2Mn (in wt.%) shape memory alloy using accumulative roll bonding and post-deformation annealing. The alloy was successfully subjected to 5 passes of accumulative roll bonding at 600 °C. The microstructure, properties as well as post-deformation annealing of this alloy were investigated by optical microscopy, scanning electron microscopy, x-ray diffraction, differential scanning calorimeter, and bend and tensile testing. The results showed that after 5 passes of ARB at 600 °C, specimens possessed α + β microstructure with the refined grains, but martensite phases and consequently shape memory effect completely disappeared. Post-deformation annealing was carried out at 700 °C, and the martensite phase with the smallest grain size (less than 40 μm) was obtained after 150 s of annealing at 700 °C. It was found that after 5 passes of ARB and post-deformation annealing, the stability of SME during thermal cycling improved. Also, tensile properties of alloys significantly improved after post-deformation annealing.

Phase change studies in Se85In15-xZnx chalcogenide thin films

NASA Astrophysics Data System (ADS)

Srivastava, Archana; Tiwari, S. N.; Alvi, M. A.; Khan, Shamshad A.

2018-03-01

This research work describes the phase change studies in Se85In15-xZnx thin films at various annealing temperatures. Glassy samples of Se85In15-xZnx were synthesized by the melt quenching method and thin films of thickness 400 nm were prepared by the vacuum evaporation technique on a glass/Si wafer substrate. The glass transition temperature (Tg) and the on-set crystallization temperature (Tc) of the prepared alloys were evaluated by non-isothermal differential scanning calorimetry studies. Thin films were annealed at three temperatures 330 K, 340 K, and 350 K (which are in between Tg and Tc of the synthesized samples) in a vacuum furnace for 2 h. High resolution X-ray diffraction studies demonstrate that the as-prepared films are amorphous in nature whereas the annealed films are of crystalline/polycrystalline in nature. Field emission scanning electron microscopy studies of thin films (as-deposited and crystallized) confirm the phase transformation in Se85In15-xZnx thin films. Optical band gaps were calculated from the Tauc's extrapolation procedure and were found to be enhanced with the Zn concentration and decrease with the increasing annealing temperature. Various optical parameters were evaluated for as-prepared and annealed Se85In15-xZnx thin films. The changes in optical parameters with annealing temperature were described on the basis of structural relaxation as well as changes in defect states and density of localized states during amorphous to crystalline phase transformation in Se85In15-xZnx thin films.

The induction of nanographitic phase on Fe coated diamond films for the enhancement in electron field emission properties

NASA Astrophysics Data System (ADS)

Panda, Kalpataru; Sundaravel, B.; Panigrahi, B. K.; Chen, H.-C.; Huang, P.-C.; Shih, W.-C.; Lo, S.-C.; Lin, L.-J.; Lee, C.-Y.; Lin, I.-N.

2013-03-01

A thin layer of iron coating and subsequent post-annealing (Fe-coating/post-annealing) is seen to significantly enhance the electron field emission (EFE) properties of ultrananocrystalline diamond (UNCD) films. The best EFE properties, with a turn on field (E0) of 1.98 V/μm and current density (Je) of 705 μA/cm2 at 7.5 V/μm, are obtained for the films, which were Fe-coated/post-annealed at 900 °C in H2 atmosphere. The mechanism behind the enhanced EFE properties of Fe coated/post-annealed UNCD films are explained by the microstructural analysis which shows formation of nanographitic phase surrounding the Fe (or Fe3C) nanoparticles. The role of the nanographitic phase in improving the emission sites of Fe coated/post-annealed UNCD films is clearly revealed by the current imaging tunneling spectroscopy (CITS) images. The CITS images clearly show significant increase in emission sites in Fe-coated/post-annealed UNCD films than the as-deposited one. Enhanced emission sites are mostly seen around the boundaries of the Fe (or Fe3C) nanoparticles which were formed due to the Fe-coating/post-annealing processes. Moreover, the Fe-coating/post-annealing processes enhance the EFE properties of UNCD films more than that on the microcrystalline diamond films. The authentic factor, resulting in such a phenomenon, is attributed to the unique granular structure of the UNCD films. The nano-sized and uniformly distributed grains of UNCD films, resulted in markedly smaller and densely populated Fe-clusters, which, in turn, induced more finer and higher populated nano-graphite clusters.

U-Pb isotopic systematics of shock-loaded and annealed baddeleyite: Implications for crystallization ages of Martian meteorite shergottites

NASA Astrophysics Data System (ADS)

Niihara, Takafumi; Kaiden, Hiroshi; Misawa, Keiji; Sekine, Toshimori; Mikouchi, Takashi

2012-08-01

Shock-recovery and annealing experiments on basalt-baddeleyite mixtures were undertaken to evaluate shock effects on U-Pb isotopic systematics of baddeleyite. Shock pressures up to 57 GPa caused fracturing of constituent phases, mosaicism of olivine, maskelynitization of plagioclase, and melting, but the phase transition from monoclinic baddeleyite structure to high-pressure/temperature polymorphs of ZrO2 was not confirmed. The U-Pb isotopic systems of the shock-loaded baddeleyite did not show a large-scale isotopic disturbance. The samples shock-recovered from 47 GPa were then employed for annealing experiments at 1000 or 1300 °C, indicating that the basalt-baddeleyite mixture was almost totally melted except olivine and baddeleyite. Fine-grained euhedral zircon crystallized from the melt was observed around the relict baddeleyite in the sample annealed at 1300 °C for 1 h. The U-Pb isotopic systems of baddeleyite showed isotopic disturbances: many data points for the samples annealed at 1000 °C plotted above the concordia. Both radiogenic lead loss/uranium gain and radiogenic lead gain/uranium loss were observed in the baddeleyite annealed at 1300 °C. Complete radiogenic lead loss due to shock metamorphism and subsequent annealing was not observed in the shock-loaded/annealed baddeleyites studied here. These results confirm that the U-Pb isotopic systematics of baddeleyite are durable for shock metamorphism. Since shergottites still preserve Fe-Mg and/or Ca zonings in major constituent phases (i.e. pyroxene and olivine), the shock effects observed in Martian baddeleyites seem to be less intense compared to that under the present experimental conditions. An implication is that the U-Pb systems of baddeleyite in shergottites will provide crystallization ages of Martian magmatic rocks.

Local configurations and atomic intermixing in as-quenched and annealed Fe1-xCrx and Fe1-xMox ribbons

NASA Astrophysics Data System (ADS)

Stanciu, A. E.; Greculeasa, S. G.; Bartha, C.; Schinteie, G.; Palade, P.; Kuncser, A.; Leca, A.; Filoti, G.; Birsan, A.; Crisan, O.; Kuncser, V.

2018-04-01

Local atomic configuration, phase composition and atomic intermixing in Fe-rich Fe1-xCrx and Fe1-xMox ribbons (x = 0.05, 0.10, 0.15), of potential interest for high-temperature applications and nuclear devices, are investigated in this study in relation to specific processing and annealing routes. The Fe-based thin ribbons have been prepared by induction melting, followed by melt spinning and further annealed in He at temperatures up to 1250 °C. The complex structural, compositional and atomic configuration characterisation has been performed by means of X-ray diffraction (XRD), transmission Mössbauer spectroscopy and differential scanning calorimetry (TG-DSC). The XRD analysis indicates the formation of the desired solid solutions with body-centred cubic (bcc) structure in the as-quenched state. The Mössbauer spectroscopy results have been analysed in terms of the two-shell model. The distribution of Cr/Mo atoms in the first two coordination spheres is not homogeneous, especially after annealing, as supported by the short-range order parameters. In addition, high-temperature annealing treatments give rise to oxidation of Fe (to haematite, maghemite and magnetite) at the surface of the ribbons. Fe1-xCrx alloys are structurally more stable than the Mo counterpart under annealing at 700 °C. Annealing at 1250 °C in He enhances drastically the Cr clustering around Fe nuclei.

Enhancement of thermoelectric power factor of Sr2CoMoO6 double perovskite by annealing in reducing atmosphere

NASA Astrophysics Data System (ADS)

Tanwar, Khagesh; Saxena, Mandvi; Maiti, Tanmoy

2017-10-01

In general, n-type thermoelectric materials are rather difficult to design. This study particularly pivoted on designing potential environmentally benign oxides based n-type thermoelectric material. We synthesized Sr2CoMoO6 (SCMO) polycrystalline ceramics via the solid-state synthesis route. XRD, SEM, and thermoelectric measurements were carried out for phase constitution, microstructure analysis, and to determine its potential for thermoelectric applications. As-sintered SCMO sample showed an insulator like behavior till 640 °C after which it exhibited an n-type non-degenerate semiconductor behavior followed by a p-n type conduction switching. To stabilize a high temperature n-type behavior, annealing of SCMO in reducing atmosphere (H2) at 1000 °C was carried out. After annealing, the SCMO demonstrated an n-type semiconductor behavior throughout the temperature range of measurement. The electrical conductivity (σ) and the power factor (S2σ) were found to be increased manifold in the annealed SCMO double perovskite.

Optical Constants of Crystallized TiO2 Coatings Prepared by Sol-Gel Process

PubMed Central

Wang, Xiaodong; Wu, Guangming; Zhou, Bin; Shen, Jun

2013-01-01

Titanium oxide coatings have been deposited by the sol-gel dip-coating method. Crystallization of titanium oxide coatings was then achieved through thermal annealing at temperatures above 400 °C. The structural properties and surface morphology of the crystallized coatings were studied by micro-Raman spectroscopy and atomic force microscopy, respectively. Characterization technique, based on least-square fitting to the measured reflectance and transmittance spectra, is used to determine the refractive indices of the crystallized TiO2 coatings. The stability of the synthesized sol was also investigated by dynamic light scattering particle size analyzer. The influence of the thermal annealing on the optical properties was then discussed. The increase in refractive index with high temperature thermal annealing process was observed, obtaining refractive index values from 1.98 to 2.57 at He-Ne laser wavelength of 633 nm. The Raman spectroscopy and atomic force microscopy studies indicate that the index variation is due to the changes in crystalline phase, density, and morphology during thermal annealing. PMID:28811410

Optical Constants of Crystallized TiO₂ Coatings Prepared by Sol-Gel Process.

PubMed

Wang, Xiaodong; Wu, Guangming; Zhou, Bin; Shen, Jun

2013-07-12

Titanium oxide coatings have been deposited by the sol-gel dip-coating method. Crystallization of titanium oxide coatings was then achieved through thermal annealing at temperatures above 400 °C. The structural properties and surface morphology of the crystallized coatings were studied by micro-Raman spectroscopy and atomic force microscopy, respectively. Characterization technique, based on least-square fitting to the measured reflectance and transmittance spectra, is used to determine the refractive indices of the crystallized TiO₂ coatings. The stability of the synthesized sol was also investigated by dynamic light scattering particle size analyzer. The influence of the thermal annealing on the optical properties was then discussed. The increase in refractive index with high temperature thermal annealing process was observed, obtaining refractive index values from 1.98 to 2.57 at He-Ne laser wavelength of 633 nm. The Raman spectroscopy and atomic force microscopy studies indicate that the index variation is due to the changes in crystalline phase, density, and morphology during thermal annealing.

Thermal stability of Pt-Ti bilayer films annealing in vacuum and ambient atmosphere

NASA Astrophysics Data System (ADS)

Weng, Sizhe; Qiao, Li; Wang, Peng

2018-06-01

The thermal stability of platinum/titanium bilayer film dominates the performance when the film electrodes operate under extreme conditions, such as high temperature. In this study, a platinum/titanium bilayer film deposited by magnetron sputtering was used as a model system to study the influence of annealing in vacuum and ambient atmosphere on structural and electrical resistivity changes. The results show that in both cases blow 773 K annealing the metal platinum is the dominant phase, the alloying and the diffusion happen only at the interface of Pt and Ti. Two different structural evolutions set in when the temperature above 873 K, in vacuum an alloying process promotes with increasing of annealing temperature and metal Pt phase transforms to TiPt8 and finally to TiPt3 compounds, which leads to the increase of electrical resistivity. In ambient atmosphere annealing, when titanium diffused out to the surface of film, the oxidation reaction between titanium and oxygen suppresses the alloying process between platinum and titanium, in this case the metal Pt phase remains in the film and starts to agglomerate, defects such as grain boundary and voids in film reduced due to the recrystallization, results in the reduction of electrical resistivity.

Mathematical model for the growth of phases in binary multiphase systems upon isothermic annealing

NASA Astrophysics Data System (ADS)

Molokhina, L. A.; Rogalin, V. E.; Filin, S. A.; Kaplunov, I. A.

2017-09-01

A phenomenological mathematical model of the formation and growth of phases in a binary multiphase system with allowance for factors influencing the process of diffusion in a binary system is presented. It is shown that phases can grow for a certain time at different ratios between diffusion parameters according to a parabolic law that depends on the duration of isothermic annealing. They then slow their growth after successor phases appear at their interface with one component and can completely disappear from a diffusion layer or begin to grow again, but only at a rate slower than during their initial formation. The dependence of the thickness of each phase layer in a multiphase diffusion zone on the duration of isothermic annealing and the ratio between the diffusion parameters in neighboring phases is obtained. It is established that a certain ratio between the phase growth and rates of dissolution with allowance for the coefficients of diffusion in each phase and the periods of incubation can result in the complete disappearance of one phase as early as the onset of the growth of phase nuclei and be interpreted as a process of reaction diffusion.

A protected annealing strategy to enhanced light emission and photostability of YAG:Ce nanoparticle-based films.

PubMed

Revaux, Amelie; Dantelle, Geraldine; George, Nathan; Seshadri, Ram; Gacoin, Thierry; Boilot, Jean-Pierre

2011-05-01

A significant obstacle in the development of YAG:Ce nanoparticles as light converters in white LEDs and as biological labels is associated with the difficulty of finding preparative conditions that allow simultaneous control of structure, particle size and size distribution, while maintaining the optical properties of bulk samples. Preparation conditions frequently involve high-temperature treatments of precursors (up to 1400 °C), which result in increased particle size and aggregation, and lead to oxidation of Ce(iii) to Ce(iv). We report here a process that we term protected annealing, that allows the thermal treatment of preformed precursor particles at temperatures up to 1000 °C while preserving their small size and state of dispersion. In a first step, pristine nanoparticles are prepared by a glycothermal reaction, leading to a mixture of YAG and boehmite crystalline phases. The preformed nanoparticles are then dispersed in a porous silica. Annealing of the composite material at 1000 °C is followed by dissolution of the amorphous silica by hydrofluoric acid to recover the annealed particles as a colloidal dispersion. This simple process allows completion of YAG crystallization while preserving their small size. The redox state of Ce ions can be controlled through the annealing atmosphere. The obtained particles of YAG:Ce (60 ± 10 nm in size) can be dispersed as nearly transparent aqueous suspensions, with a luminescence quantum yield of 60%. Transparent YAG:Ce nanoparticle-based films of micron thickness can be deposited on glass substrates using aerosol spraying. Films formed from particles prepared by the protected annealing strategy display significantly improved photostability over particles that have not been subject to such annealing. © The Royal Society of Chemistry 2011

78 FR 75371 - Diffusion-Annealed, Nickel-Plated Flat-Rolled Steel Products From Japan; Scheduling of the Final...

Federal Register 2010, 2011, 2012, 2013, 2014

2013-12-11

...-Plated Flat-Rolled Steel Products From Japan; Scheduling of the Final Phase of an Antidumping... imports from Japan of diffusion-annealed, nickel- plated flat-rolled steel products, provided for... diffusion-annealed, nickel- plated flat-rolled steel products from Japan are being sold in the United States...

High-fluence Ga-implanted silicon-The effect of annealing and cover layers

NASA Astrophysics Data System (ADS)

Fiedler, J.; Heera, V.; Hübner, R.; Voelskow, M.; Germer, S.; Schmidt, B.; Skorupa, W.

2014-07-01

The influence of SiO2 and SiNx cover layers on the dopant distribution as well as microstructure of high fluence Ga implanted Si after thermal processing is investigated. The annealing temperature determines the layer microstructure and the cover layers influence the obtained Ga profile. Rapid thermal annealing at temperatures up to 750 °C leads to a polycrystalline layer structure containing amorphous Ga-rich precipitates. Already after a short 20 ms flash lamp annealing, a Ga-rich interface layer is observed for implantation through the cover layers. This effect can partly be suppressed by annealing temperatures of at least 900 °C. However, in this case, Ga accumulates in larger, cone-like precipitates without disturbing the surrounding Si lattice parameters. Such a Ga-rich crystalline Si phase does not exist in the equilibrium phase diagram according to which the Ga solubility in Si is less than 0.1 at. %. The Ga-rich areas are capped with SiOx grown during annealing which only can be avoided by the usage of SiNx cover layers.

Effects of anodizing conditions and annealing temperature on the morphology and crystalline structure of anodic oxide layers grown on iron

NASA Astrophysics Data System (ADS)

Pawlik, Anna; Hnida, Katarzyna; Socha, Robert P.; Wiercigroch, Ewelina; Małek, Kamilla; Sulka, Grzegorz D.

2017-12-01

Anodic iron oxide layers were formed by anodization of the iron foil in an ethylene glycol-based electrolyte containing 0.2 M NH4F and 0.5 M H2O at 40 V for 1 h. The anodizing conditions such as electrolyte composition and applied potential were optimized. In order to examine the influence of electrolyte stirring and applied magnetic field, the anodic samples were prepared under the dynamic and static conditions in the presence or absence of magnetic field. It was shown that ordered iron oxide nanopore arrays could be obtained at lower anodizing temperatures (10 and 20 °C) at the static conditions without the magnetic field or at the dynamic conditions with the applied magnetic field. Since the as-prepared anodic layers are amorphous in nature, the samples were annealed in air at different temperatures (200-500 °C) for a fixed duration of time (1 h). The morphology and crystal phases developed after anodization and subsequent annealing were characterized using field-emission scanning electron microscopy (FE-SEM), X-ray diffraction (XRD), X-ray photoelectron spectroscopy (XPS), and Raman spectroscopy. The results proved that the annealing process transforms the amorphous layer into magnetite and hematite phases. In addition, the heat treatment results in a substantial decrease in the fluorine content and increase in the oxygen content.

Phase transition of AISI type 304L stainless steel induced by severe plastic deformation via cryo-rolling

NASA Astrophysics Data System (ADS)

Shit, Gopinath; Bhaskar, Pragna; Ningshen, S.; Dasgupta, A.; Mudali, U. Kamachi; Bhaduri, A. Kumar

2017-05-01

The phase transition induced by Severe Plastic Deformation (SPD) was confirmed in metastable AISI type 304L austenitic stainless steel (SS). SPD via cryo-rolling in liquid nitrogen (L-N2) temperature is the adopted route for correlating the phase transition and corrosion resistance. The thickness of the annealed AISI type 304L SS at 1050°C sheet was reduced step by step from 15% to 50% of its initial thickness. The phase changes and phase transformation are qualitatively analyzed by X-Ray Diffraction (XRD) method. During the process, the XRD of each Cryo-Rolled and annealed sample was analyzed and different phases and phase transitions are measured. The investigated AISI type 304L SS by SPD reveals a microstructure of γ-austenite; α'-marternsite and ɛ-martensite formation depending on the percentage of cryo-rolling. The Vickers hardness (HV) of the samples is also measured. The corrosion rate of the annealed sheet and cryo rolled sample was estimated in boiling nitric acid as per ASTM A-262 practice-C test.

Effect of annealing on physical characteristics of the vacuum evaporated mixed phase Sn x S y thin films

NASA Astrophysics Data System (ADS)

Banotra, A.; Padha, N.

2017-11-01

The mixed phase Sn x S y films of the thickness of 200 nm were obtained by annealing in an indigenously designed furnace at 473 K, 523 K, 573 K and 623 K for 1 h at each temperature. Prior to annealing, the precursor ‘Sn’ and ‘S’ materials were mixed up in a ball milling setup and thermally evaporated at the vacuum pressure ~2  ×  10-6 mbar on corning glass substrate. The increase in the annealing temperature influenced the reaction kinetics of ‘Sn’ and ‘S’ materials and led to the formation of SnS phase at 473 K. The SnS phase existed from 473 K to 573 K and transformed to Sn2S3 at temperatures between 573 K and 623 K. Besides this, the SnS2 phase co-existed in all undertaken temperatures where intensity of its most prominent peak increased with increase in annealing temperature. The transmittance (%) values of the undertaken films increased with increase in the annealing temperature in the wavelengths varying from 400 nm (visible) to 1600 nm (NIR). The absorption coefficient (α) values decreased with increase in annealing temperature from 1  ×  105 to 4  ×  104 cm-1 in the visible region and attained saturation values (~2  ×  104 cm-1) in the NIR region. The films possessed direct bandgap (E g) with values increasing from 1.90 eV to 2.82 eV with increase in the annealing temperature from 473 K to 623 K it also possessed indirect bandgaps with E g values varying from 0.82 eV to 1.52 eV with increase in annealing temperature in the same temperature range. The 473 K annealed samples provided irregular shaped SnS grains indicated by bright crystallites which reached to their stable position with enhanced crystallinity at the annealing temperatures of 523 K and 573 K. The SnS grains, however, reduced to lesser number at 623 K due to growth of Sn2S3 crystallites at the expense of SnS. The ‘S’ rich SnS phase (SnS2) crystallites were seen represented by darker crystallites appeared at 523 K, 573 K and 623 K. The current-voltage (I-V) study of the FTO/Film/Ag structure confirmed the schottky diode formation between Ag and film interface. There are variations in the I-V behaviour of diodes which resulted in random changes in the values of ‘ideality factor’ and ‘barrier heights’. The changes in diode parameters may be due to variation in the interface states, surface defects and barrier inhomogenities occurring due to compositional changes in Sn x S y films.

New Inverse-Heusler Materials with Potential Spintronics Applications

NASA Astrophysics Data System (ADS)

Bakkar, Said Adnan

Spintronics or spin-electronics attempt to utilize the electronic spin degree of freedom to make advanced materials and devices for the future. Heusler materials are considered very promising for spintronics applications as many highly spin-polarized materials potentially exist in this family. To accelerate materials discovery and development, The Materials Genome Initiative (https://www.mgi.gov/) was undertaken in 2011 to promote theory-driven search of new materials. In this thesis work, we outline our effort to develop several new materials that are predicted to be 100% spin-polarized (half-metallic) and thermodynamically stable by theory. In particular, two Mn-based Heusler families were investigated: Mn2CoZ (Z= Ga, Sb, Ge) and Mn2FeZ (Z=Si,Ge), where the latter is potentially a new Heusler family. These materials were synthesized using the arc-melting technique and their crystal structure was investigated using the X-ray diffraction (XRD) method before and after appropriate annealing of the samples. Preliminary magnetometry measurements are also reported. We first developed a heat-treatment procedure that could be applied to all the Mn-based compounds mentioned above. Mn2CoGa was successfully stabilized in the cubic inverse-Heusler phase with a=5.869 A and magnetic moment of 2.007 muB/fu. This is in good agreement with prior literature reports [1]. However, cubic phases of Mn2CoSb and Mn2CoGe could not be stabilized within the annealing temperature range that is accessible in our lab. We successfully synthesized a cubic Mn2FeSi phase using an annealing procedure similar to Mn2CoGa. The measured cubic lattice parameter of Mn2FeSi was 5.682 A. This is the first experimental report of this material to the best of our knowledge. Detailed analysis of relative intensities of different X-ray peaks revealed that the structure is most likely in an inverse Heusler phase, in agreement with theory. However, a substantial atomic-level disorder was also uncovered from XRD analysis that requires further investigation to understand its effect on its magnetism and half-metallicity. Mn2FeGe showed the existence of non-cubic phases that substantially weakened at high annealing temperatures.

Solid-state synthesis, structural and magnetic properties of CoPd films

NASA Astrophysics Data System (ADS)

Myagkov, V. G.; Bykova, L. E.; Zhigalov, V. S.; Tambasov, I. A.; Bondarenko, G. N.; Matsynin, A. A.; Rybakova, A. N.

2015-05-01

The results of the investigation of the structural and magnetic properties of CoPd films with equiatomic composition have been presented. The films have been synthesized by vacuum annealing of polycrystalline Pd/Co and epitaxial Pd/α-Co(110) and Pd/β-Co(001) bilayer samples. It has been shown that, for all samples, the annealing to 400°C does not lead to the mixing of layers and the formation of compounds. A further increase in the annealing temperature results in the formation of a disordered CoPd phase at the Pd/Co interface, which is fully completed after annealing at 650°C. The epitaxial relationships between the disordered CoPd phase and the MgO(001) substrate are determined as follows: CoPd(110)<

Influences of annealing temperature on sprayed CuFeO2 thin films

NASA Astrophysics Data System (ADS)

Abdelwahab, H. M.; Ratep, A.; Abo Elsoud, A. M.; Boshta, M.; Osman, M. B. S.

2018-06-01

Delafossite CuFeO2 thin films were successfully prepared onto quartz substrates using simple spray pyrolysis technique. Post annealing under nitrogen atmosphere for 2 h was necessary to form delafossite CuFeO2 phase. The effect of alteration in annealing temperature (TA) 800, 850 and 900 °C was study on structural, morphology and optical properties. The XRD results for thin film annealed at TA = 850 °C show single phase CuFeO2 with rhombohedral crystal system and R 3 bar m space group with preferred orientation along (0 1 2). The prepared copper iron oxide thin films have an optical transmission ranged ∼40% in the visible region. The optical direct optical band gap of the prepared thin films was ranged ∼2.9 eV.

Influence of Annealing on Microstructure and Mechanical Properties of Refractory CoCrMoNbTi0.4 High-Entropy Alloy

NASA Astrophysics Data System (ADS)

Zhang, Mina; Zhou, Xianglin; Zhu, Wuzhi; Li, Jinghao

2018-04-01

A novel refractory CoCrMoNbTi0.4 high-entropy alloy (HEA) was prepared via vacuum arc melting. After annealing treatment at different temperatures, the microstructure evolution, phase stability, and mechanical properties of the alloy were investigated. The alloy was composed of two primary body-centered cubic structures (BCC1 and BCC2) and a small amount of (Co, Cr)2Nb-type Laves phase under different annealing conditions. The microhardness and compressive strength of the heat-treated alloy was significantly enhanced by the solid-solution strengthening of the BCC phase matrix and newborn Laves phase. Especially, the alloy annealed at 1473 K (1200 °C) achieved the maximum hardness and compressive strength values of 959 ± 2 HV0.5 and 1790 MPa, respectively, owing to the enhanced volume fraction of the dispersed Laves phase. In particular, the HEAs exhibited promising high-temperature mechanical performance, when heated to an elevated temperature of 1473 K (1200 °C), with a compressive fracture strength higher than 580 MPa without fracture at a strain of more than 20 pct. This study suggests that the present refractory HEAs have immense potential for engineering applications as a new class of high-temperature structural materials.

Synthesis and Characterization of Some Alkaline-Earth-Oxide Nanoparticles

NASA Astrophysics Data System (ADS)

Singh, Jitendra Pal; Lim, Weon Cheol; Won, Sung Ok; Song, Jonghan; Chae, Keun Hwa

2018-04-01

The present work reports the synthesis of MgO and CaO nanoparticles by using the sol-gel autocombustion method. The annealing of the precursor at 1200 °C was observed to lead the formation of MgO nanoparticles having average crystallite size of 31 nm. Annealing the precursor at same temperature produced materials having a CaO phase with a minor impure phase of calcium carbonate ( 3%). The crystallite size corresponding to the CaO phase was 38 nm. A change of thermal history in the precursor was observed not to result in an improvement of the CaO phase. The change of thermal history in the precursor gave rise to mixed phases of CaCO3 and Ca(OH)2 rather than the phase of CaO. Further, annealing at 1200 °C for 12 h resulted in the formation of the CaO phase along with almost 1 - 5% of calcium hydroxide as an impurity phase. X-ray absorption spectroscopic measurements carried out on these materials revealed that the local electronic/atomic structure of these oxides was not only affected by the impurity phases but also influenced by the carbaneous impurities attached to the crystallites.

Stabilization of the high coercivity {epsilon}-Fe{sub 2}O{sub 3} phase in the CeO{sub 2}-Fe{sub 2}O{sub 3}/SiO{sub 2} nanocomposites

DOE Office of Scientific and Technical Information (OSTI.GOV)

Mantlikova, A., E-mail: mantlikova@fzu.cz; Poltierova Vejpravova, J.; Bittova, B.

2012-07-15

We have investigated the processes leading to the formation of the Fe{sub 2}O{sub 3} and CeO{sub 2} nanoparticles in the SiO{sub 2} matrix in order to stabilize the {epsilon}-Fe{sub 2}O{sub 3} as the major phase. The samples with two different concentrations of the Fe were prepared by sol-gel method, subsequently annealed at different temperatures up to 1100 Degree-Sign C, and characterized by the Moessbauer spectroscopy, Transmission Electron Microscopy (TEM), Powder X-ray Diffraction (PXRD), Energy Dispersive X-ray analysis (EDX) and magnetic measurements. The evolution of the different Fe{sub 2}O{sub 3} phases under various conditions of preparation was investigated, starting with themore » preferential appearance of the {gamma}-Fe{sub 2}O{sub 3} phase for the sample with low Fe concentration and low annealing temperature and stabilization of the major {epsilon}-Fe{sub 2}O{sub 3} phase for high Fe concentration and high annealing temperature, coexisting with the most stable {alpha}-Fe{sub 2}O{sub 3} phase. A continuous increase of the particle size of the CeO{sub 2} nanocrystals with increasing annealing temperature was also observed. - Graphical abstract: The graphical abstract displays the most important results of our work. The significant change of the phase composition due to the variation of preparation conditions is demonstrated. As a result, significant change of the magnetic properties from superparamagnetic {gamma}-Fe{sub 2}O{sub 3} phase with negligible coercivity to the high coercivity {epsilon}-Fe{sub 2}O{sub 3} phase has been observed. Highlights: Black-Right-Pointing-Pointer Research of the stabilization of the high coercivity {epsilon}-Fe{sub 2}O{sub 3} in CeO{sub 2}-Fe{sub 2}O{sub 3}/SiO{sub 2}. Black-Right-Pointing-Pointer Samples with two different concentrations of Fe and three annealing temperatures. Black-Right-Pointing-Pointer Phase transition {gamma}{yields}{epsilon}{yields}({beta}){yields}{alpha} with increasing annealing temperature and particle size. Black-Right-Pointing-Pointer Elimination of the superparamagnetic phases in samples with higher content of Fe. Black-Right-Pointing-Pointer Best conditions for high coercivity {epsilon}-Fe{sub 2}O{sub 3}-higher Fe content and T{sub A}=1100 Degree-Sign C.« less

Grain growth in U–7Mo alloy: A combined first-principles and phase field study

DOE Office of Scientific and Technical Information (OSTI.GOV)

Mei, Zhi-Gang; Liang, Linyun; Kim, Yeon Soo

2016-05-01

Grain size is an important factor in controlling the swelling behavior in irradiated U-Mo dispersion fuels. Increasing the grain size in UeMo fuel particles by heat treatment is believed to delay the fuel swelling at high fission density. In this work, a multiscale simulation approach combining first-principles calculation and phase field modeling is used to investigate the grain growth behavior in U-7Mo alloy. The density functional theory based first-principles calculations were used to predict the material properties of U-7Mo alloy. The obtained grain boundary energies were then adopted as an input parameter for mesoscale phase field simulations. The effects ofmore » annealing temperature, annealing time and initial grain structures of fuel particles on the grain growth in U-7Mo alloy were examined. The predicted grain growth rate compares well with the empirical correlation derived from experiments. (C) 2016 Elsevier B.V. All rights reserved.« less

STM study of the Ga thin films grown on Si(111) surface

NASA Astrophysics Data System (ADS)

Tao, Min-Long; Tu, Yu-Bing; Sun, Kai; Ye, Juan; Hao, Shao-Jie; Xiao, Hua-Fang; Wang, Ya-Li; Xie, Zheng-Bo; Wang, Jun-Zhong

2017-09-01

Structural evolution of Ga thin films grown on the Si(111)-√{ 3 } × √{ 3 } -Ga template have been investigated with a low-temperature scanning tunneling microscopy (STM). The first Ga layer exhibits a stripe structure along the base vectors of Si(111) lattices. Individual Ga dimers have been directly visualized from the high-resolution STM images of the first Ga layer. The second Ga layer reveals a pseudo 1×1 structure with respect to the Si(111). A new 5×5 phase has been found in the second Ga layer when annealing the sample to 120 ℃. Further annealing to 150 ℃ leads to the formation of 6.3×6.3 phase, which is more stable than the 5×5 phase. The existences of a variety of superstructures of Ga films demonstrates the delicate balance between the interactions of Si(111)-Ga and Ga-Ga. These results shed important light on the epitaxial growth mechanism of Ga films on semiconductor surfaces.

DOE Office of Scientific and Technical Information (OSTI.GOV)

Gries, K. I.; Vogel, S.; Straubinger, R.

The self-assembled formation of ordered, vertically stacked rocksalt/wurtzite Mg{sub x}Zn{sub 1−x}O heterostructures by planar phase separation is shown. These heterostructures form quasi “natural” two-dimensional hetero-interfaces between the different phases upon annealing of MgO-oversaturated wurtzite Mg{sub x}Zn{sub 1−x}O layers grown by plasma-assisted molecular beam epitaxy on c-plane sapphire substrates. The optical absorption spectra show a red shift simultaneous with the appearance of a cubic phase upon annealing at temperatures between 900 °C and 1000 °C. Transmission electron microscopy reveals that these effects are caused by phase separation leading to the formation of a vertically ordered rock salt/wurtzite heterostructures. To explain these observations, wemore » suggest a phase separation epitaxy model that considers this process being initiated by the formation of a cubic (Mg,Zn)Al{sub 2}O{sub 4} spinel layer at the interface to the sapphire substrate, acting as a planar seed for the epitaxial precipitation of rock salt Mg{sub x}Zn{sub 1−x}O. The equilibrium fraction x of magnesium in the resulting wurtzite (rock salt) layers is approximately 0.15 (0.85), independent of the MgO content of the as-grown layer and determined by the annealing temperature. This model is confirmed by photoluminescence analysis of the resulting layer systems after different annealing temperatures. In addition, we show that the thermal annealing process results in a significant reduction in the density of edge- and screw-type dislocations, providing the possibility to fabricate high quality templates for quasi-homoepitaxial growth.« less

Phase transformation in SiOx/SiO₂ multilayers for optoelectronics and microelectronics applications.

PubMed

Roussel, M; Talbot, E; Pratibha Nalini, R; Gourbilleau, F; Pareige, P

2013-09-01

Due to the quantum confinement, silicon nanoclusters (Si-ncs) embedded in a dielectric matrix are of prime interest for new optoelectronics and microelectronics applications. In this context, SiO(x)/SiO₂ multilayers have been prepared by magnetron sputtering and subsequently annealed to induce phase separation and Si clusters growth. The aim of this paper is to study phase separation processes and formation of nanoclusters in SiO(x)/SiO₂ multilayers by atom probe tomography. Influences of the silicon supersaturation, annealing temperature and SiO(x) and SiO₂ layer thicknesses on the final microstructure have been investigated. It is shown that supersaturation directly determines phase separation regime between nucleation/classical growth and spinodal decomposition. Annealing temperature controls size of the particles and interface with the surrounding matrix. Layer thicknesses directly control Si-nc shapes from spherical to spinodal-like structures. Copyright © 2012 Elsevier B.V. All rights reserved.

Phase Transformation Behavior of Medium Manganese Steels with 3 Wt Pct Aluminum and 3 Wt Pct Silicon During Intercritical Annealing

NASA Astrophysics Data System (ADS)

Sun, Binhan; Fazeli, Fateh; Scott, Colin; Yue, Stephen

2016-10-01

Medium manganese steels alloyed with sufficient aluminum and silicon amounts contain high fractions of retained austenite adjustable to various transformation-induced plasticity/twinning-induced plasticity effects, in addition to a reduced density suitable for lightweight vehicle body-in-white assemblies. Two hot rolled medium manganese steels containing 3 wt pct aluminum and 3 wt pct silicon were subjected to different annealing treatments in the present study. The evolution of the microstructure in terms of austenite transformation upon reheating and the subsequent austenite decomposition during quenching was investigated. Manganese content of the steels prevailed the microstructural response. The microstructure of the leaner alloy with 7 wt pct Mn (7Mn) was substantially influenced by the annealing temperature, including the variation of phase constituents, the morphology and composition of intercritical austenite, the Ms temperature and the retained austenite fraction. In contrast, the richer variant 10 wt pct Mn steel (10Mn) exhibited a substantially stable ferrite-austenite duplex phase microstructure containing a fixed amount of retained austenite which was found to be independent of the variations of intercritical annealing temperature. Austenite formation from hot band ferrite-pearlite/bainite mixtures was very rapid during annealing at 1273 K (1000 °C), regardless of Mn contents. Austenite growth was believed to be controlled at early stages by carbon diffusion following pearlite/bainite dissolution. The redistribution of Mn in ferrite and particularly in austenite at later stages was too subtle to result in a measureable change in austenite fraction. Further, the hot band microstructure of both steels contained a large fraction of coarse-grained δ-ferrite, which remained almost unchanged during intercritical annealing. A recently developed thermodynamic database was evaluated using the experimental data. The new database achieved a better agreement with the experimental results for the 7Mn steel compared with the existing commercial TCFE database; however, some discrepancy in the predicted phase fractions and compositions still existed. The phase transformation behavior of the two steels during annealing and its implication on the design of high aluminum-silicon medium manganese steels were discussed in detail.

Schottky barrier parameters and structural properties of rapidly annealed Zr Schottky electrode on p-type GaN

NASA Astrophysics Data System (ADS)

Rajagopal Reddy, V.; Asha, B.; Choi, Chel-Jong

2017-06-01

The Schottky barrier junction parameters and structural properties of Zr/p-GaN Schottky diode are explored at various annealing temperatures. Experimental analysis showed that the barrier height (BH) of the Zr/p-GaN Schottky diode increases with annealing at 400 °C (0.92 eV (I-V)/1.09 eV (C-V)) compared to the as-deposited one (0.83 eV (I-V)/0.93 eV (C-V)). However, the BH decreases after annealing at 500 °C. Also, at different annealing temperatures, the series resistance and BH are assessed by Cheung's functions and their values compared. Further, the interface state density (N SS) of the diode decreases after annealing at 400 °C and then somewhat rises upon annealing at 500 °C. Analysis reveals that the maximum BH is obtained at 400 °C, and thus the optimum annealing temperature is 400 °C for the diode. The XPS and XRD analysis revealed that the increase in BH may be attributed to the creation of Zr-N phases with increasing annealing up to 400 °C. The BH reduces for the diode annealed at 500 °C, which may be due to the formation of Ga-Zr phases at the junction. The AFM measurements reveal that the overall surface roughness of the Zr film is quite smooth during rapid annealing process. Project supported by the R&D Program for Industrial Core Technology (No. 10045216) and the Transfer Machine Specialized Lighting Core Technology Development Professional Manpower Training Project (No. N0001363) Funded by the Ministry of Trade, Industry and Energy (MOTIE), Republic of Korea.

Structural and Mössbauer characterization of the ball milled Fe x(Cr 2O 3) 1- x system

NASA Astrophysics Data System (ADS)

Biondo, Valdecir; de Medeiros, Suzana Nóbrega; Paesano, Andrea, Jr.; Ghivelder, Luis; Hallouche, Bachir; da Cunha, João Batista Marimon

2009-08-01

The Fe x(Cr 2O 3) 1- x system, with 0.10 ≤ X ≤ 0.80, was mechanically processed for 24 h in a high-energy ball-mill. In order to examine the possible formation of iron-chromium oxides and alloys, the milled samples were, later, thermally annealed in inert (argon) and reducing (hydrogen) atmospheres. The as-milled and annealed products were characterized by X-ray diffraction, Mössbauer spectroscopy, transmission electron microscopy and magnetization. The as-milled samples showed the formation of an Fe 1+ YCr 2- YO 4- δ nanostructured and disordered spinel phase, the α 1-Fe(Cr) and α 2-Cr(Fe) solid solutions and the presence of non-exhausted precursors. For the samples annealed in inert atmosphere, the chromite (FeCr 2O 4) formation and the recrystallization of the precursors were verified. The hydrogen treated samples revealed the reduction of the spinel phase, with the phase separation of the chromia phase and retention of the Fe-Cr solid solutions. All the samples, either as-milled or annealed, presented the magnetization versus applied field curves typical for superparamagnetic systems.

Effect of Cold Deformation and Annealing on the Microstructure and Tensile Properties of a HfNbTaTiZr Refractory High Entropy Alloy

NASA Astrophysics Data System (ADS)

Senkov, O. N.; Pilchak, A. L.; Semiatin, S. L.

2018-07-01

The microstructure and tensile properties of HfNbTaTiZr after cold working and annealing were investigated. Cold work was introduced by axial compression followed by rolling resulting in a total thickness reduction of 89 pct without any evidence of cracking. The cold-worked material retained a single-phase microstructure and had a room temperature tensile yield stress σ 0.2 = 1438 MPa, peak true stress σ p = 1495 MPa, and true fracture strain ɛ f = 5 pct. Annealing at 800 °C for up to 256 hours resulted in the precipitation of Nb and Ta rich particles with a BCC crystal structure inside a Hf-and-Zr-enriched BCC matrix. The second phase particles nucleated heterogeneously inside deformation bands and slip lines and coarsened during annealing. Analysis of the coarsening behavior suggested that kinetics were controlled by the diffusion of Nb and Ta. In the two-phase material, σ 0.2 and σ p decreased from 1159 to 1071 MPa and from 1174 to 1074 MPa, respectively, with an increase in particle diameter from 0.18 to 0.72 μm, while ɛ f remained between 5 and 8 pct. Full recrystallization and normal grain growth, with the activation energy of 238 kJ/mol and activation volume of 5.3 to 9.6 m3/mol, occurred during annealing above 1000 °C. After heat treatment at this temperature, the alloy was characterized by a single-phase BCC structure with σ 0.2 = 1110 to 1115 MPa, σ p = 1160 to 1195 MPa, and ɛ f = 12 to 19 pct with the maximum values attained after annealing for 1 hour.

Effect of Cold Deformation and Annealing on the Microstructure and Tensile Properties of a HfNbTaTiZr Refractory High Entropy Alloy

NASA Astrophysics Data System (ADS)

Senkov, O. N.; Pilchak, A. L.; Semiatin, S. L.

2018-05-01

The microstructure and tensile properties of HfNbTaTiZr after cold working and annealing were investigated. Cold work was introduced by axial compression followed by rolling resulting in a total thickness reduction of 89 pct without any evidence of cracking. The cold-worked material retained a single-phase microstructure and had a room temperature tensile yield stress σ 0.2 = 1438 MPa, peak true stress σ p = 1495 MPa, and true fracture strain ɛ f = 5 pct. Annealing at 800 °C for up to 256 hours resulted in the precipitation of Nb and Ta rich particles with a BCC crystal structure inside a Hf-and-Zr-enriched BCC matrix. The second phase particles nucleated heterogeneously inside deformation bands and slip lines and coarsened during annealing. Analysis of the coarsening behavior suggested that kinetics were controlled by the diffusion of Nb and Ta. In the two-phase material, σ 0.2 and σ p decreased from 1159 to 1071 MPa and from 1174 to 1074 MPa, respectively, with an increase in particle diameter from 0.18 to 0.72 μm, while ɛ f remained between 5 and 8 pct. Full recrystallization and normal grain growth, with the activation energy of 238 kJ/mol and activation volume of 5.3 to 9.6 m3/mol, occurred during annealing above 1000 °C. After heat treatment at this temperature, the alloy was characterized by a single-phase BCC structure with σ 0.2 = 1110 to 1115 MPa, σ p = 1160 to 1195 MPa, and ɛ f = 12 to 19 pct with the maximum values attained after annealing for 1 hour.

The Influence of Fe2O3 Addition on the Tio2 Structure and Photoactivity Properties

NASA Astrophysics Data System (ADS)

Wahyuningsih, S.; Ramelan, A. H.; Prasetyawati, L.; Saputri, L. N. M. Z.; Ichsan, S.; Kristiawan, Y. R.

2018-03-01

The influence of Fe2O3 addition on the TiO2 structure and photoactivity properties have been studied. The addition of Fe2O3 on the TiO2 done by TiO2-Fe2O3 synthesized with variation of annealing temperature. The result showed that peak of anatase TiO2 at 2θ = 25.35° and Fe2O3 at 2θ = 54.20°. The XRD of TiO2 show annealing temperature at 400°C is anatase phase and the composite with annealing at temperature 150°C, 300°C, 400°C and 500°C is crystalline anatase phase, due to the addition of Fe2O3. Photodegradation of Rhodamin B with TiO2 at 400°C annealing temperature showed optimum degradation 36.2 %, and the composite with annealing at 400°C showed optimum degradation 44.3% for 300 minutes irradiation.

Low-temperature growth of aligned ZnO nanorods: effect of annealing gases on the structural and optical properties.

PubMed

Umar, Ahmad; Hahn, Yoon-Bong; Al-Hajry, A; Abaker, M

2014-06-01

Aligned ZnO nanorods were grown on ZnO/Si substrate via simple aqueous solution process at low-temperature of - 65 degrees C by using zinc nitrate and hexamethylenetetramine (HMTA). The detailed morphological and structural properties measured by FESEM, XRD, EDS and TEM confirmed that the as-grown nanorods are vertically aligned, well-crystalline possessing wurtzite hexagonal phase and grown along the [0001] direction. The room-temperature photoluminescence spectrum of the grown nanorods exhibited a strong and broad green emission and small ultraviolet emission. The as-prepared ZnO nanorods were post-annealed in nitrogen (N2) and oxygen (O2) environments and further characterized in terms of their morphological, structural and optical properties. After annealing the nanorods exhibit well-crystallinity and wurtzite hexagonal phase. Moreover, by annealing the PL spectra show the enhancement in the UV emission and suppression in the green emission. The presented results demonstrate that simply by post-annealing process, the optical properties of ZnO nanostructures can be controlled.

Metastable tantalum oxide formation during the devitrification of amorphous tantalum thin films

DOE PAGES

Donaldson, Olivia K.; Hattar, Khalid; Trelewicz, Jason R.

2016-07-04

Microstructural evolution during the devitrification of amorphous tantalum thin films synthesized via pulsed laser deposition was investigated using in situ transmission electron microscopy (TEM) combined with ex situ isothermal annealing, bright-field imaging, and electron-diffraction analysis. The phases formed during crystallization and their stability were characterized as a function of the chamber pressure during deposition, devitrification temperature, and annealing time. A range of metastable nanocrystalline tantalum oxides were identified following devitrification including multiple orthorhombic oxide phases, which often were present with, or evolved to, the tetragonal TaO 2 phase. While the appearance of these phases indicated the films were evolving tomore » the stable form of tantalum oxide—monoclinic tantalum pentoxide—it was likely not achieved for the conditions considered due to an insufficient amount of oxygen present in the films following deposition. Nevertheless, the collective in situ and ex situ TEM analysis applied to thin film samples enabled the isolation of a number of metastable tantalum oxides. As a result, new insights were gained into the transformation sequence and stability of these nanocrystalline phases, which presents opportunities for the development of advanced tantalum oxide-based dielectric materials for novel memristor designs.« less

Thermal annealing induced multiple phase in V/V2O5 alternating multilayer structure

NASA Astrophysics Data System (ADS)

Ilahi, B.; Abdel-Rahman, M.; Zaaboub, Z.; Zia, M. F.; Alduraibi, M.; Maaref, H.

2016-09-01

In this paper, we report on microstructural, optical and electrical properties of alternating multilayer of vanadium pentoxide (V2O5), 25 nm, and vanadium (V), 5 nm, thin films deposited at room temperature by radio frequency (RF) and DC magnetron sputtering, respectively. Raman and photoluminescence (PL) spectroscopy have been employed to investigate the effects of thermal annealing for 20, 30 and 40 min at 400∘C in Nitrogen (N2) atmosphere on the multiple phase formation and its impact on the film resistance and temperature coefficient of resistance (TCR). We demonstrate that the oxygen free annealing environment allows the formation of multiple phases including V2O5, V6O13 and VO2 through oxygen diffusion and consequent deficiency in V2O5 layer.

Crystal structure and high-temperature properties of the Ruddlesden–Popper phases Sr{sub 3−x}Y{sub x}(Fe{sub 1.25}Ni{sub 0.75})O{sub 7−δ} (0≤x≤0.75)

DOE Office of Scientific and Technical Information (OSTI.GOV)

Samain, Louise; Amshoff, Philipp; Biendicho, Jordi J.

2015-07-15

Ruddlesden–Popper n=2 member phases Sr{sub 3−x}Y{sub x}Fe{sub 1.25}Ni{sub 0.75}O{sub 7−δ}, 0≤x≤0.75, have been investigated by X-ray and neutron powder diffraction, thermogravimetry and Mössbauer spectroscopy. Both samples as-prepared at 1300 °C under N{sub 2}(g) flow and samples subsequently air-annealed at 900 °C were studied. The as-prepared x=0.75 phase is highly oxygen deficient with δ=1, the O1 atom site being vacant, and the Fe{sup 3+}/Ni{sup 2+} ions having a square pyramidal coordination. For as-prepared phases with lower x values, the Mössbauer spectral data are in good agreement with the presence of both 5- and 4-coordinated Fe{sup 3+} ions, implying in addition amore » partial occupancy of the O3 atom sites that form the basal plane of the square pyramid. The air-annealed x=0.75 sample has a δ value of 0.61(1) and the structure has Fe/Ni ions in both square pyramids and octahedra. Mössbauer spectroscopy shows the phase to contain only Fe{sup 3+}, implying that all Ni is present as Ni{sup 3+}. Air-annealed phases with lower x values are found to contain both Fe{sup 3+} and Fe{sup 4+}. For both the as-prepared and the air-annealed samples, the Y{sup 3+} cations are found to be mainly located in the perovskite block. The high-temperature thermal expansion of as-prepared and air-annealed x=0.75 phases were investigated by high-temperature X-ray diffraction and dilatometry and the linear thermal expansion coefficient determined to be 14.4 ppm K{sup −1}. Electrical conductivity measurements showed that the air-annealed samples have higher conductivity than the as-prepared ones. - Highlights: • Ruddlesden–Popper, n=2, Sr{sub 3−x}Y{sub x}Fe{sub 1.25}Ni{sub 0.75}O{sub 7−δ}, 0≤x≤0.75, have been synthesised. • The crystal structures of the phases have been determined. • Sr{sub 2.25}Y{sub 0.75}Fe{sub 1.25}Ni{sub 0.75}O{sub 6}, made in N{sub 2}(g) has Fe{sup 3+}/Ni{sup 2+} in square pyramides. • Sr{sub 2.25}Y{sub 0.75}Fe{sub 1.25}Ni{sub 0.75}O{sub 6.4}, made in air has Fe{sup 3+}/Ni{sup 3+} in square pyramides and octahedra. • Air annealed samples have higher electrical conductivity than N{sub 2}(g) annealed.« less

Simulation of local ion transport in lamellar block copolymer electrolytes based on electron micrographs

DOE PAGES

Chintapalli, Mahati; Higa, Kenneth; Chen, X. Chelsea; ...

2016-12-19

A method is presented in this paper to relate local morphology and ionic conductivity in a solid, lamellar block copolymer electrolyte for lithium batteries, by simulating conductivity through transmission electron micrographs. The electrolyte consists of polystyrene-block-poly(ethylene oxide) mixed with lithium bis(trifluoromethanesulfonyl) imide salt (SEO/LiTFSI), where the polystyrene phase is structural phase and the poly(ethylene oxide)/LiTFSI phase is ionically conductive. The electric potential distribution is simulated in binarized micrographs by solving the Laplace equation with constant potential boundary conditions. A morphology factor, f, is reported for each image by calculating the effective conductivity relative to a homogenous conductor. Images from twomore » samples are examined, one annealed with large lamellar grains and one unannealed with small grains. The average value off is 0.45 ± 0.04 for the annealed sample, and 0.37 ± 0.03 for the unannealed sample, both close to the value predicted by effective medium theory, 1/2. Simulated conductivities are compared to published experimental conductivities. The value of f Unannealed/f Annealed is 0.82 for simulations and 6.2 for experiments. Simulation results correspond well to predictions by effective medium theory but do not explain the experimental measurements. Finally, observation of nanoscale morphology over length scales greater than the size of the micrographs (~1 μm) may be required to explain the experimental results.« less

Simulation of local ion transport in lamellar block copolymer electrolytes based on electron micrographs

DOE Office of Scientific and Technical Information (OSTI.GOV)

Chintapalli, Mahati; Higa, Kenneth; Chen, X. Chelsea

A method is presented in this paper to relate local morphology and ionic conductivity in a solid, lamellar block copolymer electrolyte for lithium batteries, by simulating conductivity through transmission electron micrographs. The electrolyte consists of polystyrene-block-poly(ethylene oxide) mixed with lithium bis(trifluoromethanesulfonyl) imide salt (SEO/LiTFSI), where the polystyrene phase is structural phase and the poly(ethylene oxide)/LiTFSI phase is ionically conductive. The electric potential distribution is simulated in binarized micrographs by solving the Laplace equation with constant potential boundary conditions. A morphology factor, f, is reported for each image by calculating the effective conductivity relative to a homogenous conductor. Images from twomore » samples are examined, one annealed with large lamellar grains and one unannealed with small grains. The average value off is 0.45 ± 0.04 for the annealed sample, and 0.37 ± 0.03 for the unannealed sample, both close to the value predicted by effective medium theory, 1/2. Simulated conductivities are compared to published experimental conductivities. The value of f Unannealed/f Annealed is 0.82 for simulations and 6.2 for experiments. Simulation results correspond well to predictions by effective medium theory but do not explain the experimental measurements. Finally, observation of nanoscale morphology over length scales greater than the size of the micrographs (~1 μm) may be required to explain the experimental results.« less

Magnetism-Structure Correlations during the epsilon ->tau Transformation in Rapidly-Solidified MnAl Nanostructured Alloys

DOE Office of Scientific and Technical Information (OSTI.GOV)

Jimenez-Villacorta, F; Marion, JL; Oldham, JT

2014-01-21

Magnetic and structural aspects of the annealing-induced transformation of rapidly-solidified Mn55Al45 ribbons from the as-quenched metastable antiferromagnetic (AF) epsilon-phase to the target ferromagnetic (FM) L1(0) tau-phase are investigated. The as-solidified material exhibits a majority hexagonal epsilon-MnAl phase revealing a large exchange bias shift below a magnetic blocking temperature T-B similar to 95 K (H-ex similar to 13 kOe at 10 K), ascribed to the presence of compositional fluctuations in this antiferromagnetic phase. Heat treatment at a relatively low annealing temperature T-anneal approximate to 568 K (295 degrees C) promotes the nucleation of the metastable L1(0) tau-MnAl phase at the expensemore » of the parent epsilon-phase, donating an increasingly hard ferromagnetic character. The onset of the epsilon ->tau transformation occurs at a temperature that is similar to 100 K lower than that reported in the literature, highlighting the benefits of applying rapid solidification for synthesis of the rapidly-solidified parent alloy.« less

Effect of silver on the phase transition and wettability of titanium oxide films

PubMed Central

Mosquera, Adolfo A.; Albella, Jose M.; Navarro, Violeta; Bhattacharyya, Debabrata; Endrino, Jose L.

2016-01-01

The effect of silver on the phase transition and microstructure of titanium oxide films grown by pulsed cathodic arc had been investigated by XRD, SEM and Raman spectroscopy. Following successive thermal annealing up to 1000 °C, microstructural analysis of annealed Ag-TiO2 films reveals that the incorporation of Ag nanoparticles strongly affects the transition temperature from the initial metastable amorphous phase to anatase and stable rutile phase. An increase of silver content into TiO2 matrix inhibits the amorphous to anatase phase transition, raising its temperature boundary and, simultaneously reduces the transition temperature to promote rutile structure at lower value of 600 °C. The results are interpreted in terms of the steric effects produced by agglomeration of Ag atoms into larger clusters following annealing which hinders diffusion of Ti and O ions for anatase formation and constrains the volume available for the anatase lattice, thus disrupting its structure to form rutile phase. The effect of silver on the optical and wetting properties of TiO2 was evaluated to demonstrate its improved photocatalytic performance. PMID:27571937

Evolution of the Structural-Phase State of a Ti-Al- V-Mo Alloy During Severe Plastic Deformation and SubSequent Annealing

NASA Astrophysics Data System (ADS)

Grabovetskaya, G. P.; Ratochka, I. V.; Mishin, I. P.; Zabudchenko, O. V.; Lykova, O. N.

2016-05-01

The effect of the initial phase composition of a Ti-Al-V-Mo alloy (VT16 according to Russian classification) on the evolution of its structural-phase state during the formation of ultrafine-grained structure and subsequent annealing is investigated by methods of optical and transmission electron microscopy and x-ray diffraction analysis. The structure is produced by cyclic pressing with a change of the deformation axis in each cycle combined with a gradual decrease of the pressing temperature from 1073 to 723 K. As this takes place, α″ → α + β and β → α phase transitions are found to develop in the test alloy. The phase state of the ultrafinegrained material thus produced depends for the most part on its elemental composition and severe plastic deformation regime. Annealing below the recrystallization temperature is shown to give rise to a β→α phase transition and alloying element redistribution. The foregoing processes allow for retaining a high level of the strength properties of the alloy.

Synthesis of Hollow Nanotubes of Zn2SiO4 or SiO2: Mechanistic Understanding and Uranium Adsorption Behavior.

PubMed

Tripathi, Shalini; Bose, Roopa; Roy, Ahin; Nair, Sajitha; Ravishankar, N

2015-12-09

We report a facile synthesis of Zn2SiO4 nanotubes using a two-step process consisting of a wet-chemical synthesis of core-shell ZnO@SiO2 nanorods followed by thermal annealing. While annealing in air leads to the formation of hollow Zn2SiO4, annealing under reducing atmosphere leads to the formation of SiO2 nanotubes. We rationalize the formation of the silicate phase at temperatures much lower than the temperatures reported in the literature based on the porous nature of the silica shell on the ZnO nanorods. We present results from in situ transmission electron microscopy experiments to clearly show void nucleation at the interface between ZnO and the silica shell and the growth of the silicate phase by the Kirkendall effect. The porous nature of the silica shell is also responsible for the etching of the ZnO leading to the formation of silica nanotubes under reducing conditions. Both the hollow silica and silicate nanotubes exhibit good uranium sorption at different ranges of pH making them possible candidates for nuclear waste management.

[Effect of annealing temperature on the crystallization and spectroscopic response of a small-molecule semiconductor doped in polymer film].

PubMed

Yin, Ming; Zhang, Xin-Ping; Liu, Hong-Mei

2012-11-01

The crystallization properties of the perylene (EPPTC) molecules doped in the solid film of the derivative of polyfluorene (F8BT) at different annealing temperatures, as well as the consequently induced spectroscopic response of the exciplex emission in the heterojunction structures, were studied in the present paper. Experimental results showed that the phase separation between the small and the polymer molecules in the blend film is enhanced with increasing the annealing temperature, which leads to the crystallization of the EPPTC molecules due to the strong pi-pi stacking. The size of the crystal phase increases with increasing the annealing temperature. However, this process weakens the mechanisms of the heterojunction configuration, thus, the total interfacial area between the small and the polymer molecules and the amount of exciplex are reduced significantly in the blend film. Meanwhile, the energy transfer from the polymer to the small molecules is also reduced. As a result, the emission from the exciplex becomes weaker with increasing the annealing temperature, whereas the stronger emission from the polymer molecules and from the crystal phase of the small molecules can be observed. These experimental results are very important for understanding and tailoring the organic heterojunction structures. Furthermore, this provides photophysics for improving the performance of photovoltaic or solar cell devices.

Annealing effect on the structural, morphological and electrical properties of TiO2/ZnO bilayer thin films

NASA Astrophysics Data System (ADS)

Khan, M. I.; Imran, S.; Shahnawaz; Saleem, Muhammad; Ur Rehman, Saif

2018-03-01

The effect of annealing temperature on the structural, morphological and electrical properties of TiO2/ZnO (TZ) thin films has been observed. Bilayer thin films of TiO2/ZnO are deposited on FTO glass substrate by spray pyrolysis method. After deposition, these films are annealed at 573 K, 723 K and 873 K. XRD shows that TiO2 is present in anatase phase only and ZnO is present in hexagonal phase. No other phases of TiO2 and ZnO are present. Also, there is no evidence of other compounds like Zn-Ti etc. It also shows that the average grain size of TiO2/ZnO films is increased by increasing annealing temperature. AFM (Atomic force microscope) showed that the average roughness of TiO2/ZnO films is decreased at temperature 573-723 K and then increased at 873 K. The calculated average sheet resistivity of thin films annealed at 573 K, 723 K and 873 K is 152.28 × 102, 75.29 × 102 and 63.34 × 102 ohm-m respectively. This decrease in sheet resistivity might be due to the increment of electron concentration with increasing thickness and the temperature of thin films.

Electrochemically induced annealing of stainless-steel surfaces.

PubMed

Burstein, G T; Hutchings, I M; Sasaki, K

2000-10-19

Modification of the surface properties of metals without affecting their bulk properties is of technological interest in demanding applications where surface stability and hardness are important. When austenitic stainless steel is heavily plastically deformed by grinding or rolling, a martensitic phase transformation occurs that causes significant changes in the bulk and surface mechanical properties of the alloy. This martensitic phase can also be generated in stainless-steel surfaces by cathodic charging, as a consequence of lattice strain generated by absorbed hydrogen. Heat treatment of the steel to temperatures of several hundred degrees can result in loss of the martensitic structure, but this alters the bulk properties of the alloy. Here we show that martensitic structures in stainless steel can be removed by appropriate electrochemical treatment in aqueous solutions at much lower temperature than conventional annealing treatments. This electrochemically induced annealing process allows the hardness of cold-worked stainless steels to be maintained, while eliminating the brittle martensitic phase from the surface. Using this approach, we are able to anneal the surface and near-surface regions of specimens that contain rolling-induced martensite throughout their bulk, as well as those containing surface martensite induced by grinding. Although the origin of the electrochemical annealing process still needs further clarification, we expect that this treatment will lead to further development in enhancing the surface properties of metals.

Evolution of secondary-phase precipitates during annealing of the 12Kh18N9T steel irradiated with neutrons to a dose of 5 DPA

NASA Astrophysics Data System (ADS)

Tsai, K. V.; Maksimkin, O. P.; Turubarova, L. G.

2007-03-01

The formation and evolution of thermally-induced secondary precipitates in an austenitic stainless steel 12Kh18N9T irradiated in the core of a laboratory reactor VVR-K to a dose of 5 dpa and subjected to post-radiation isochronous annealings for 1 h in a temperature range from 450 to 1050°C have been studied using transmission electron microscopy (TEM) and microhardness measurements. It has been shown that the formation of stitch (secondary) titanium carbides and M 23C6 carbides at grain and twin boundaries after annealing at 1050°C is preceded by a complex evolution of fineparticles of secondary phases (titanium carbides and nitrides) precipitated at dislocation loops and dislocations during annealing at temperatures above 750°C.

Rare earth indates (RE: La-Yb): influence of the synthesis route and heat treatment on the crystal structure.

PubMed

Shukla, Rakesh; Grover, Vinita; Srinivasu, Kancharlapalli; Paul, Barnita; Roy, Anushree; Gupta, Ruma; Tyagi, Avesh Kumar

2018-05-15

Rare earth indates are an interesting class of compounds with rich crystallography. The present study explores the crystallographic phases observed in REInO3 (RE: La-Yb) systems and their dependence on synthesis routes and annealing temperature. All REInO3 compositions were synthesized by a solid state route as well as gel-combustion synthesis (GC) followed by annealing at different temperatures. The systems were well characterized by powder XRD studies and were analysed by Rietveld refinement for the structural parameters. The cell parameters were observed to decrease in accordance with the trend in ionic radii on proceeding from lighter to heavier rare earth ions. Interestingly, the synthesis route and the annealing temperature had a profound bearing on the phase relationships observed in the REInO3 series. The solid state synthesized samples depicted an orthorhombic phase (Pbnm) field for LaInO3 to SmInO3, followed by a hexagonal-type phase (P63cm) for GdInO3 to DyInO3. However, the phase field distribution was greatly influenced upon employing gel-combustion (GC) wherein both single-phasic hexagonal and orthorhombic phase fields were found to shrink. Annealing the GC-synthesized compositions to still higher temperatures (1250 °C) further evolved the phase boundaries. An important outcome of the study is observance of polymorphism in SmInO3 which crystallized in the hexagonal phase when synthesized by GC and orthorhombic phase by solid state synthesis. This reveals the all-important role played by synthesis conditions. The existence and energetics of the two polymorphs have been elucidated and discussed with the aid of theoretical studies.

Thermal annealing studies of GeTe-Sb2Te3 alloys with multiple interfaces

NASA Astrophysics Data System (ADS)

Bragaglia, Valeria; Mio, Antonio M.; Calarco, Raffaella

2017-08-01

A high degree of vacancy ordering is obtained by annealing amorphous GeTe-Sb2Te3 (GST) alloys deposited on a crystalline substrate, which acts as a template for the crystallization. Under annealing the material evolves from amorphous to disordered rocksalt, to ordered rocksalt with vacancies arranged into (111) oriented layers, and finally converts into the stable trigonal phase. The role of the interface in respect to the formation of an ordered crystalline phase is studied by comparing the transformation stages of crystalline GST with and without a capping layer. The capping layer offers another crystallization interface, which harms the overall crystalline quality.

Impact of interlayer processing conditions on the performance of GaN light-emitting diode with specific NiOx/graphene electrode.

PubMed

Chandramohan, S; Kang, Ji Hye; Ryu, Beo Deul; Yang, Jong Han; Kim, Seongjun; Kim, Hynsoo; Park, Jong Bae; Kim, Taek Yong; Cho, Byung Jin; Suh, Eun-Kyung; Hong, Chang-Hee

2013-02-01

This paper reports on the evaluation of the impact of introducing interlayers and postmetallization annealing on the graphene/p-GaN ohmic contact formation and performance of associated devices. Current-voltage characteristics of the graphene/p-GaN contacts with ultrathin Au, Ni, and NiO(x) interlayers were studied using transmission line model with circular contact geometry. Direct graphene/p-GaN interface was identified to be highly rectifying and postmetallization annealing improved the contact characteristics as a result of improved adhesion between the graphene and the p-GaN. Ohmic contact formation was realized when interlayer is introduced between the graphene and p-GaN followed by postmetallization annealing. Temperature-dependent I-V measurements revealed that the current transport was modified from thermionic field emission for the direct graphene/p-GaN contact to tunneling for the graphene/metal/p-GaN contacts. The tunneling mechanism results from the interfacial reactions that occur between the metal and p-GaN during the postmetallization annealing. InGaN/GaN light-emitting diodes with NiO(x)/graphene current spreading electrode offered a forward voltage of 3.16 V comparable to that of its Ni/Au counterpart, but ended up with relatively low light output power. X-ray photoelectron spectroscopy provided evidence for the occurrence of phase transformation in the graphene-encased NiO(x) during the postmetallization annealing. The observed low light output is therefore correlated to the phase change induced transmittance loss in the NiO(x)/graphene electrode. These findings provide new insights into the behavior of different interlayers under processing conditions that will be useful for the future development of opto-electronic devices with graphene-based electrodes.

High-fluence Ga-implanted silicon—The effect of annealing and cover layers

DOE Office of Scientific and Technical Information (OSTI.GOV)

Fiedler, J., E-mail: jan.fiedler@hzdr.de; Heera, V.; Hübner, R.

2014-07-14

The influence of SiO{sub 2} and SiN{sub x} cover layers on the dopant distribution as well as microstructure of high fluence Ga implanted Si after thermal processing is investigated. The annealing temperature determines the layer microstructure and the cover layers influence the obtained Ga profile. Rapid thermal annealing at temperatures up to 750 °C leads to a polycrystalline layer structure containing amorphous Ga-rich precipitates. Already after a short 20 ms flash lamp annealing, a Ga-rich interface layer is observed for implantation through the cover layers. This effect can partly be suppressed by annealing temperatures of at least 900 °C. However, in this case,more » Ga accumulates in larger, cone-like precipitates without disturbing the surrounding Si lattice parameters. Such a Ga-rich crystalline Si phase does not exist in the equilibrium phase diagram according to which the Ga solubility in Si is less than 0.1 at. %. The Ga-rich areas are capped with SiO{sub x} grown during annealing which only can be avoided by the usage of SiN{sub x} cover layers.« less

Development of microstructure and mechanical properties during annealing of a cold-swaged Co-Cr-Mo alloy rod.

PubMed

Mori, Manami; Sato, Nanae; Yamanaka, Kenta; Yoshida, Kazuo; Kuramoto, Koji; Chiba, Akihiko

2016-12-01

In this study, we investigated the evolution of the microstructure and mechanical properties during annealing of a cold-swaged Ni-free Co-Cr-Mo alloy for biomedical applications. A Co-28Cr-6Mo-0.14N-0.05C (mass%) alloy rod was processed by cold swaging, with a reduction in area of 27.7%, and then annealed at 1173-1423K for various periods up to 6h. The duplex microstructure of the cold-swaged rod consisted of a face-centered cubic γ-matrix and hexagonal closed-packed ε-martensite developed during cold swaging. This structure transformed nearly completely to the γ-phase after annealing and many annealing twin boundaries were observed as a result of the heat treatment. A small amount of the ε-phase was identified in specimens annealed at 1173K. Growth of the γ-grains occurred with increasing annealing time at temperatures ≥1273K. Interestingly, the grain sizes remained almost unchanged at 1173K and a very fine grain size of approximately 8μm was obtained. The precipitation that occurred during annealing was attributed to the limited grain coarsening during heat treatment. Consequently, the specimens treated at this temperature showed the highest tensile strength and lowest ductility among the specimens prepared. An elongation-to-failure value larger than 30% is sufficient for the proposed applications. The other specimens treated at higher temperatures possessed similar tensile properties and did not show any significant variations with different annealing times. Optimization of the present rod manufacturing process, including cold swaging and interval annealing heat treatment, is discussed. Copyright © 2016 Elsevier Ltd. All rights reserved.

Enhanced Crystalline Phase Purity of CH3NH3PbI3-xClx Film for High-Efficiency Hysteresis-Free Perovskite Solar Cells.

PubMed

Yang, Yingguo; Feng, Shanglei; Xu, Weidong; Li, Meng; Li, Li; Zhang, Xingmin; Ji, Gengwu; Zhang, Xiaonan; Wang, Zhaokui; Xiong, Yimin; Cao, Liang; Sun, Baoquan; Gao, Xingyu

2017-07-12

Despite rapid successful developments toward promising perovskite solar cells (PSCs) efficiency, they often suffer significant hysteresis effects. Using synchrotron-based grazing incidence X-ray diffraction (GIXRD) with different probing depths by varying the incident angle, we found that the perovskite films consist of dual phases with a parent phase dominant in the interior and a child phase with a smaller (110) interplanar space (d (110) ) after rapid thermal annealing (RTA), which is a widely used post treatment to improve the crystallization of solution-processed perovskite films for high-performance planar PSCs. In particular, the child phase composition gradually increases with decreasing depth till it becomes the majority on the surface, which might be one of the key factors related to hysteresis in fabricated PSCs. We further improve the crystalline phase purity of the solution-processed CH 3 NH 3 PbI 3-x Cl x perovskite film (referred as g-perovskite) by using a facile gradient thermal annealing (GTA), which shows a uniformly distributed phase structure in pinhole-free morphology with less undercoordinated Pb and I ions determined by synchrotron-based GIXRD, grazing incidence small-angle X-ray scattering, scanning electron microscopy, and X-ray photoelectron spectroscopy. Regardless of device structures (conventional and inverted types), the planar heterojunction PSCs employing CH 3 NH 3 PbI 3-x Cl x g-perovskite films exhibit negligible hysteresis with a champion power conversion efficiency of 17.04% for TiO 2 -based conventional planar PSCs and 14.83% for poly(3,4-ethylenedioxythiophene:poly(styrenesulfonate) (PEDOT:PSS)-based inverted planar PSCs. Our results indicate that the crystalline phase purity in CH 3 NH 3 PbI 3-x Cl x perovskite film, especially in the surface region, plays a crucial role in determining the hysteresis effect and device performance.

Low Temperature Phase Transformations in Copper-Quenched Ti-44.5Al-8Nb-2.5V Alloy

PubMed Central

Cao, Shouzhen; Xiao, Shulong; Chen, Yuyong; Xu, Lijuan; Wang, Xiaopeng; Han, Jianchao

2017-01-01

In this study, an easily controlled transformation similar to the β + α → β + α + γ and the analysis of metastable phases in a β solidifying Ti-44.5Al-8Nb-2.5V alloy were investigated. Therefore, a liquid alloy copper-quenching followed by annealing at an application temperature (850 °C) has been carried out. Following quenching, a microstructure composed of several supersaturated phases—the basket-weave β0 (βbv) phase, the plate-like α2 (αp) phase and the stripe-like γ (γs) phase—was obtained. In the annealing processes, phase transformations in the prior βbv and αp phases domain corresponded nicely to the β + α → β + α + γ transformation during solidification. Also, in the annealed γs phase, the kinetics of the phase transformations involving the metastable L12 phase was firstly detected by transmission electron microscopy (TEM). The L12 phase had a lattice structure similar to the γ phase, whereas the composition of the phase was similar to the α2 phase. The formation of the γ pre-twin phase with an anti-phase boundary (APB) was detected in the γs phase of the matrix. The orientation relationships between the γs and precipitated: γ (γp) phase are <101]γs//<114]γp, (101¯)γs//(1¯10)γp and (01¯0)γs//(221¯)γp. PMID:28772561

Preparation of mesoporous carbon nitride structure by the dealloying of Ni/a-CN nanocomposite films

NASA Astrophysics Data System (ADS)

Zhou, Han; Shen, Yongqing; Huang, Jie; Liao, Bin; Wu, Xianying; Zhang, Xu

2018-05-01

The preparation of mesoporous carbon nitride (p-CN) structure by the selective dealloying process of Ni/a-CN nanocomposite films is investigated. The composition and structure of the Ni/a-CN nanocomposite films and porous carbon nitride (p-CN) films are determined by scan electron microscopy (SEM), transmission electron microscopy (TEM), X-ray diffraction (XRD), X-ray photoelectron spectroscopy (XPS) and Raman spectroscopy. Phase separated structure including nickel carbide phase and the surrounding amorphous carbon nitride (a-CN) matrix are detected for the as-deposited films. Though the bulk diffusion is introduced in the film during the annealing process, the grain sizes for the post-annealed films are around 10 nm and change little comparing with the ones of the as-deposited films, which is associated with the thermostability of the CN surrounding in the film. The p-CN skeleton with its pore size around 12.5 nm is formed by etching the post-annealed films, indicative of the stability of the phase separated structure during the annealing process.

In situ growth of sol-gel-derived nano-VO2 film and its phase transition characteristics

NASA Astrophysics Data System (ADS)

Shi, Qiwu; Huang, Wanxia; Lu, Tiecheng; Yue, Fang; Xiao, Yang; Hu, Yanyan

2014-10-01

We reported the growth of VO2 film deposited by an inorganic sol-gel method, followed by post-annealing. An in situ evolution of the grain size in the films with different annealing temperatures (300, 500, and 700 °C for 90 min), annealing times (500 °C for 20, 40, 60, and 90 min), and film thicknesses (30, 150 and 320 nm) was observed. The results indicated that the grain size distribution in the sol-gel-derived VO2 films was mediated by the density of nucleation center, which was varied in the films with different extents of thermal deformation during the annealing. By increasing the film thickness from 30 to 320 nm, a compact nanostructure with uniform distribution of grain size could be formed. It suggested that the in situ-evolved nanostructure in the thicker VO2 film will lead to lower threshold temperature and enhanced transition intensity in the phase transition. The effect of nanoscale grain size on the lower phase transition temperature in the VO2 film was discussed.

Silicide phases formation in Co/c-Si and Co/a-Si systems during thermal annealing

NASA Astrophysics Data System (ADS)

Novaković, M.; Popović, M.; Zhang, K.; Lieb, K. P.; Bibić, N.

2014-03-01

The effect of the interface in cobalt-silicon bilayers on the silicide phase formation and microstructure has been investigated. Thin cobalt films were deposited by electron beam evaporation to a thickness of 50 nm on crystalline silicon (c-Si) or silicon with pre-amorphized surface (a-Si). After deposition one set of samples was annealed for 2 h at 200, 300, 400, 500, 600 and 700 °C. Another set of samples was irradiated with 400 keV Xe+ ions and then annealed at the same temperatures. Phase transitions were investigated with Rutherford backscattering spectroscopy, X-ray diffraction and cross-sectional transmission electron microscopy. No silicide formation was observed up to 400 °C, for both non-irradiated and ion-irradiated samples. When increasing the annealing temperature, the non-irradiated and irradiated Co/c-Si samples showed a similar behaviour: at 500 °C, CoSi appeared as the dominant silicide, followed by the formation of CoSi2 at 600 and 700 °C. In the case of non-irradiated Co/a-Si samples, no silicide formation occurred up to 700 °C, while irradiated samples with pre-amorphized substrate (Co/a-Si) showed a phase sequence similar to that in the Co/c-Si system. The observed phase transitions are found to be consistent with predictions of the effective heat of formation model.

Miscibility of amorphous ZrO2-Al2O3 binary alloy

NASA Astrophysics Data System (ADS)

Zhao, C.; Richard, O.; Bender, H.; Caymax, M.; De Gendt, S.; Heyns, M.; Young, E.; Roebben, G.; Van Der Biest, O.; Haukka, S.

2002-04-01

Miscibility is a key factor for maintaining the homogeneity of the amorphous structure in a ZrO2-Al2O3 binary alloy high-k dielectric layer. In the present work, a ZrO2/Al2O3 laminate thin layer has been prepared by atomic layer chemical vapor deposition on a Si (100) wafer. This layer, with artificially induced inhomogeneity (lamination), enables one to study the change in homogeneity of the amorphous phase in the ZrO2/Al2O3 system during annealing. High temperature grazing incidence x-ray diffraction (HT-XRD) was used to investigate the change in intensity of the constructive interference peak of the x-ray beams which are reflected from the interfaces of ZrO2/Al2O3 laminae. The HT-XRD spectra show that the intensity of the peak decreases with an increase in the anneal temperature, and at 800 °C, the peak disappears. The same samples were annealed by a rapid thermal process (RTP) at temperatures between 700 and 1000 °C for 60 s. Room temperature XRD of the RTP annealed samples shows a similar decrease in peak intensity. Transmission electronic microscope images confirm that the laminate structure is destroyed by RTP anneals and, just below the crystallization onset temperature, a homogeneous amorphous ZrAlxOy phase forms. The results demonstrate that the two artificially separated phases, ZrO2 and Al2O3 laminae, tend to mix into a homogeneous amorphous phase before crystallization. This observation indicates that the thermal stability of ZrO2-Al2O3 amorphous phase is suitable for high-k applications.

Interfacial Microstructure and Its Influence on Resistivity of Thin Layers Copper Cladding Steel Wires

NASA Astrophysics Data System (ADS)

Li, Hongjuan; Ding, Zhimin; Zhao, Ruirong

2018-04-01

The interfacial microstructure and resistivity of cold-drawn and annealed thin layers copper cladding steel (CCS) wires have been systematically investigated by the methods of scanning electron microscopy (SEM), transmission electron microscopy (TEM), energy dispersive spectroscopy (EDS), and resistivity testing. The results showed that the Cu and Fe atoms near interface diffused into each other matrixes. The Fe atoms diffused into Cu matrixes and formed a solid solution. The mechanism of solid solution is of substitution type. When the quantity of Fe atoms exceeds the maximum solubility, the supersaturated solid solution would form Fe clusters and decompose into base Cu and α-Fe precipitated phases under certain conditions. A few of α-Fe precipitates was observed in the copper near Cu/Fe interfaces of cold-drawn CCS wires, with 1-5 nm in size. A number of α-Fe precipitates of 1-20 nm in size can be detected in copper near Cu/Fe interfaces of CCS wires annealed at 850°C. When annealing temperature was less than 750°C, the resistivity of CCS wires annealed was lower than that of cold-drawn CCS wires. However, when annealing temperature was above 750°C, the resistivity of CCS wires was greater than that of cold-drawn CCS wires and increased with rising the annealing temperature. The relationship between nanoscale α-Fe precipitation and resistivity of CCS wires has been well discussed.

Composition and annealing effects on superconductivity in sintered and arc-melted Fe1+εTe0.5Se0.5

NASA Astrophysics Data System (ADS)

Foreman, M. M.; Ponti, G.; Mozaffari, S.; Markert, J. T.

2018-03-01

We present the results of x-ray diffraction, electrical resistivity, and ac magnetic susceptibility measurements on specimens of the “11”-structure superconductor Fe1+εTe0.50Se0.50 (0 ≤ ε ≤ 0.15). Samples were initially either sintered in sealed quartz tubes or melted in a zirconium-gettered arc furnace. Sintered samples were fired two to three times at temperatures of 425°C, 600°C, or 675°C, while arc-melted samples were studied both asmelted and after annealing at 650°C. X-ray diffraction data show a predominant PbO-type tetragonal phase, with a secondary hexagonal NiAs-type phase; for sintered specimens annealed at 600°C, the secondary phase decreases as ε increases over the range 0 ≤ ε ≤ 0.10, with the composition Fe1.10Te0.5Se0.5 exhibiting x-ray phase purity. A higher annealing temperature of 675°C provided such tetragonal phase purity at the composition Fe1.05Te0.5Se0.5. The resistive superconducting transition temperature Tc was nearly independent of the iron concentration 1+ε, suggesting a single superconducting phase, while the magnetic screening fraction varied greatly with concentration and conditions, peaking at ɛ = 0.07, indicating that the amount of superconducting phase is strongly dependent on conditions. We propose that the behaviour can also be viewed in terms of an electron-doped, chalcogen-deficient stoichiometry.

Vacancy-Induced Ferromagnetism in SnO2 Nanocrystals: A Positron Annihilation Study

NASA Astrophysics Data System (ADS)

Chen, Zhi-Yuan; Chen, Zhi-Quan; Pan, Rui-Kun; Wang, Shao-Jie

2013-02-01

SnO2 nanopowders were pressed into pellets and annealed in air from 100 to 1400°C. Both XRD and Raman spectroscopy confirm that all annealed samples were single phase with a tetragonal rutile structure. Annealing induces an increase in the SnO2 grain size from 30 to 83 nm. Positron annihilation measurements reveal vacancy defects in the grain boundary region, and the interfacial defects remain stable after annealing below 400°C, then they are gradually recovered with increasing annealing temperature up to 1200°C. Room temperature ferromagnetism was observed for SnO2 nanocrystals annealed below 1200°C, and the magnetization decreases continuously with increasing annealing temperature. However, the ferromagnetism disappears at 1200°C annealing. This shows good coincidence with the recovery of interfacial defects in the nanocrystals, suggesting that the ferromagnetism is probably induced by vacancy defects in the interface region.

Iterative simulated quenching for designing irregular-spot-array generators.

PubMed

Gillet, J N; Sheng, Y

2000-07-10

We propose a novel, to our knowledge, algorithm of iterative simulated quenching with temperature rescaling for designing diffractive optical elements, based on an analogy between simulated annealing and statistical thermodynamics. The temperature is iteratively rescaled at the end of each quenching process according to ensemble statistics to bring the system back from a frozen imperfect state with a local minimum of energy to a dynamic state in a Boltzmann heat bath in thermal equilibrium at the rescaled temperature. The new algorithm achieves much lower cost function and reconstruction error and higher diffraction efficiency than conventional simulated annealing with a fast exponential cooling schedule and is easy to program. The algorithm is used to design binary-phase generators of large irregular spot arrays. The diffractive phase elements have trapezoidal apertures of varying heights, which fit ideal arbitrary-shaped apertures better than do trapezoidal apertures of fixed heights.

Quantum vertex model for reversible classical computing.

PubMed

Chamon, C; Mucciolo, E R; Ruckenstein, A E; Yang, Z-C

2017-05-12

Mappings of classical computation onto statistical mechanics models have led to remarkable successes in addressing some complex computational problems. However, such mappings display thermodynamic phase transitions that may prevent reaching solution even for easy problems known to be solvable in polynomial time. Here we map universal reversible classical computations onto a planar vertex model that exhibits no bulk classical thermodynamic phase transition, independent of the computational circuit. Within our approach the solution of the computation is encoded in the ground state of the vertex model and its complexity is reflected in the dynamics of the relaxation of the system to its ground state. We use thermal annealing with and without 'learning' to explore typical computational problems. We also construct a mapping of the vertex model into the Chimera architecture of the D-Wave machine, initiating an approach to reversible classical computation based on state-of-the-art implementations of quantum annealing.

Quantum vertex model for reversible classical computing

NASA Astrophysics Data System (ADS)

Chamon, C.; Mucciolo, E. R.; Ruckenstein, A. E.; Yang, Z.-C.

2017-05-01

Mappings of classical computation onto statistical mechanics models have led to remarkable successes in addressing some complex computational problems. However, such mappings display thermodynamic phase transitions that may prevent reaching solution even for easy problems known to be solvable in polynomial time. Here we map universal reversible classical computations onto a planar vertex model that exhibits no bulk classical thermodynamic phase transition, independent of the computational circuit. Within our approach the solution of the computation is encoded in the ground state of the vertex model and its complexity is reflected in the dynamics of the relaxation of the system to its ground state. We use thermal annealing with and without `learning' to explore typical computational problems. We also construct a mapping of the vertex model into the Chimera architecture of the D-Wave machine, initiating an approach to reversible classical computation based on state-of-the-art implementations of quantum annealing.

Influence of Step Annealing Temperature on the Microstructure and Pitting Corrosion Resistance of SDSS UNS S32760 Welds

NASA Astrophysics Data System (ADS)

Yousefieh, M.; Shamanian, M.; Saatchi, A.

2011-12-01

In the present work, the influence of step annealing heat treatment on the microstructure and pitting corrosion resistance of super duplex stainless steel UNS S32760 welds have been investigated. The pitting corrosion resistance in chloride solution was evaluated by potentiostatic measurements. The results showed that step annealing treatments in the temperature ranging from 550 to 1000 °C resulted in a precipitation of sigma phase and Cr2N along the ferrite/austenite and ferrite/ferrite boundaries. At this temperature range, the metastable pits mainly nucleated around the precipitates formed in the grain boundary and ferrite phase. Above 1050 °C, the microstructure contains only austenite and ferrite phases. At this condition, the critical pitting temperature of samples successfully arrived to the highest value obtained in this study.

Precision Laser Annealing of Focal Plane Arrays

DOE Office of Scientific and Technical Information (OSTI.GOV)

Bender, Daniel A.; DeRose, Christopher; Starbuck, Andrew Lea

2015-09-01

We present results from laser annealing experiments in Si using a passively Q-switched Nd:YAG microlaser. Exposure with laser at fluence values above the damage threshold of commercially available photodiodes results in electrical damage (as measured by an increase in photodiode dark current). We show that increasing the laser fluence to values in excess of the damage threshold can result in annealing of a damage site and a reduction in detector dark current by as much as 100x in some cases. A still further increase in fluence results in irreparable damage. Thus we demonstrate the presence of a laser annealing windowmore » over which performance of damaged detectors can be at least partially reconstituted. Moreover dark current reduction is observed over the entire operating range of the diode indicating that device performance has been improved for all values of reverse bias voltage. Additionally, we will present results of laser annealing in Si waveguides. By exposing a small (<10 um) length of a Si waveguide to an annealing laser pulse, the longitudinal phase of light acquired in propagating through the waveguide can be modified with high precision, <15 milliradian per laser pulse. Phase tuning by 180 degrees is exhibited with multiple exposures to one arm of a Mach-Zehnder interferometer at fluence values below the morphological damage threshold of an etched Si waveguide. No reduction in optical transmission at 1550 nm was found after 220 annealing laser shots. Modeling results for laser annealing in Si are also presented.« less

Resistance of a gamma/gamma prime - delta directionally solidified eutectic alloy to recrystallization

NASA Technical Reports Server (NTRS)

Tewari, S. N.; Scheuermann, C. M.; Andrews, C. W.

1975-01-01

The lamellar directionally solidified nickel-base eutectic alloy gamma/gamma prime-delta has potential as an advanced turbine blade material. The microstructural stability of this alloy was investigated. Specimens were plastically deformed by uniform compression or Brinell indentation, then annealed between 705 and 1120 C. Microstructural changes observed after annealing included gamma prime coarsening, pinch-off and spheroidization of delta lamellae, and the appearance of an unidentified blocky phase in surface layers. All but the first of these was localized in severely deformed regions, suggesting that microstructural instability is not a serious problem in the use of this alloy.

Effects of Intercritical Annealing Temperature on Mechanical Properties of Fe-7.9Mn-0.14Si-0.05Al-0.07C Steel

PubMed Central

Zhao, Xianming; Shen, Yongfeng; Qiu, Lina; Liu, Yandong; Sun, Xin; Zuo, Liang

2014-01-01

A medium Mn steel has been designed to achieve an excellent combination of strength and ductility based on the TRIP (Transformation Induced Plasticity) concept for automotive applications. Following six passes of hot rolling at 850 °C, the Fe-7.9Mn-0.14Si-0.05Al-0.07C (wt.%) steel was warm-rolled at 630 °C for seven passes and subsequently air cooled to room temperature. The sample was subsequently intercritically annealed at various temperatures for 30 min to promote the reverse transformation of martensite into austenite. The obtained results show that the highest volume fraction of austenite is 39% for the sample annealed at 600 °C. This specimen exhibits a yield stress of 910 MPa and a high ultimate tensile stress of 1600 MPa, with an elongation-to-failure of 0.29 at a strain rate of 1 × 10−3/s. The enhanced work-hardening ability of the investigated steel is closely related to martensitic transformation and the interaction of dislocations. Especially, the alternate arrangement of acicular ferrite (soft phase) and ultrafine austenite lamellae (50–200 nm, strong and ductile phase) is the key factor contributing to the excellent combination of strength and ductility. On the other hand, the as-warm-rolled sample also exhibits the excellent combination of strength and ductility, with elongation-to-failure much higher than those annealed at temperatures above 630 °C. PMID:28788282

Effects of Intercritical Annealing Temperature on Mechanical Properties of Fe-7.9Mn-0.14Si-0.05Al-0.07C Steel.

PubMed

Zhao, Xianming; Shen, Yongfeng; Qiu, Lina; Liu, Yandong; Sun, Xin; Zuo, Liang

2014-12-09

A medium Mn steel has been designed to achieve an excellent combination of strength and ductility based on the TRIP (Transformation Induced Plasticity) concept for automotive applications. Following six passes of hot rolling at 850 °C, the Fe-7.9Mn-0.14Si-0.05Al-0.07C (wt.%) steel was warm-rolled at 630 °C for seven passes and subsequently air cooled to room temperature. The sample was subsequently intercritically annealed at various temperatures for 30 min to promote the reverse transformation of martensite into austenite. The obtained results show that the highest volume fraction of austenite is 39% for the sample annealed at 600 °C. This specimen exhibits a yield stress of 910 MPa and a high ultimate tensile stress of 1600 MPa, with an elongation-to-failure of 0.29 at a strain rate of 1 × 10 -3 /s. The enhanced work-hardening ability of the investigated steel is closely related to martensitic transformation and the interaction of dislocations. Especially, the alternate arrangement of acicular ferrite (soft phase) and ultrafine austenite lamellae (50-200 nm, strong and ductile phase) is the key factor contributing to the excellent combination of strength and ductility. On the other hand, the as-warm-rolled sample also exhibits the excellent combination of strength and ductility, with elongation-to-failure much higher than those annealed at temperatures above 630 °C.

Interfacial characterization and electrical properties of Ni–GaSb contacts

DOE Office of Scientific and Technical Information (OSTI.GOV)

Lin, Kun-Lin, E-mail: kllin@narlabs.org.tw; Chen, Szu-Hung, E-mail: shchen168@narlabs.org.tw

2014-10-06

The microstructural characterization of Ni–GaSb junctions in samples annealed at 300 °C, 350 °C, and 400 °C in a N{sub 2} atmosphere was elucidated using transmission electron microscopy in conjunction with energy-dispersive spectrometry, nanobeam electron diffraction, and grazing-incident X-ray diffraction. Only the NiSb(Ga) phase is formed at the interface of Ni/GaSb when the annealing temperature is below 350 °C. However, three phases—NiSb, Ni{sub 2}Ga{sub 3}, and NiSb(Ga)—are formed simultaneously at the interface between Ni/GaSb when the annealing temperature is increased to 400 °C, which causes a significant increase in the sheet resistance of the Ni–GaSb alloy. These results indicate that the annealing temperature of themore » Ni/GaSb structure should be maintained below 350 °C for the formation of low-resistance metal Ni/GaSb contacts in GaSb-based p-type metal-oxide-semiconductor field-effect transistors.« less

Temperature-dependent interface characteristic of silicon wafer bonding based on an amorphous germanium layer deposited by DC-magnetron sputtering

NASA Astrophysics Data System (ADS)

Ke, Shaoying; Lin, Shaoming; Ye, Yujie; Mao, Danfeng; Huang, Wei; Xu, Jianfang; Li, Cheng; Chen, Songyan

2018-03-01

We report a near-bubble-free low-temperature silicon (Si) wafer bonding with a thin amorphous Ge (a-Ge) intermediate layer. The DC-magnetron-sputtered a-Ge film on Si is demonstrated to be extremely flat (RMS = 0.28 nm) and hydrophilic (contact angle = 3°). The effect of the post-annealing temperature on the surface morphology and crystallinity of a-Ge film at the bonded interface is systematically identified. The relationship among the bubble density, annealing temperature, and crystallinity of a-Ge film is also clearly clarified. The crystallization of a-Ge film firstly appears at the bubble region. More interesting feature is that the crystallization starts from the center of the bubbles and sprawls to the bubble edge gradually. The H2 by-product is finally absorbed by intermediate Ge layer with crystalline phase after post annealing. Moreover, the whole a-Ge film out of the bubble totally crystallizes when the annealing time increases. This Ge integration at the bubble region leads to the decrease of the bubble density, which in turn increases the bonding strength.

Effect of annealing on structural, optical and electrical properties of SILAR synthesized CuO thin film

NASA Astrophysics Data System (ADS)

Das, M. R.; Mukherjee, A.; Mitra, P.

2017-05-01

Nano crystalline CuO thin films were synthesize on glass substrate using SILAR technique. The structural, optical and electrical properties of the films were carried out for as deposited as well as for films post annealed in the temperature range 300 - 500° C. The X-ray diffraction pattern shows all the films are polycrystalline in nature with monoclinic phase. The crystallite size increase and lattice strain decreases with increase of annealing temperature indicating high quality of the films for annealed films. The value of band gap decreases with increases of annealing temperature of the film. The effect of annealing temperature on ionic conductivity and activation energy to electrical conduction process are discussed.

Ultrafast Self-Assembly of Sub-10 nm Block Copolymer Nanostructures by Solvent-Free High-Temperature Laser Annealing.

PubMed

Jiang, Jing; Jacobs, Alan G; Wenning, Brandon; Liedel, Clemens; Thompson, Michael O; Ober, Christopher K

2017-09-20

Laser spike annealing was applied to PS-b-PDMS diblock copolymers to induce short-time (millisecond time scale), high-temperature (300 to 700 °C) microphase segregation and directed self-assembly of sub-10 nm features. Conditions were identified that enabled uniform microphase separation in the time frame of tens of milliseconds. Microphase ordering improved with increased temperature and annealing time, whereas phase separation contrast was lost for very short annealing times at high temperature. PMMA brush underlayers aided ordering under otherwise identical laser annealing conditions. Good long-range order for sub-10 nm cylinder morphology was achieved using graphoepitaxy coupled with a 20 ms dwell laser spike anneal above 440 °C.

Effect of Ag doping and annealing on thermoelectric properties of PbTe

DOE Office of Scientific and Technical Information (OSTI.GOV)

Bala, Manju, E-mail: Manjubala474@gmail.com; Tripathi, T. S.; Avasthi, D. K.

2015-06-24

The present study reveals that annealing Ag doped PbTe thin films enhance thermoelectric properties. Phase formation was identified by using X-ray diffraction measurement. Annealing increases the crystallinity of both undoped and Ag doped PbTe. Electrical resistivity and thermoelectric power measurements are done using four probe and bridge method respectively. The increase in thermoelectric power of Ag doped PbTe is 29 % in comparison to undoped PbTe and it further increases to 34 % after annealing at 250{sup o} C for 1 hour whereas thermoelectric power increases by 14 % on annealing undoped PbTe thin films at same temperature.

Substrate-induced phase of a [1]benzothieno[3,2-b]benzothiophene derivative and phase evolution by aging and solvent vapor annealing.

PubMed

Jones, Andrew O F; Geerts, Yves H; Karpinska, Jolanta; Kennedy, Alan R; Resel, Roland; Röthel, Christian; Ruzié, Christian; Werzer, Oliver; Sferrazza, Michele

2015-01-28

Substrate-induced phases (SIPs) are polymorphic phases that are found in thin films of a material and are different from the single crystal or "bulk" structure of a material. In this work, we investigate the presence of a SIP in the family of [1]benzothieno[3,2-b]benzothiophene (BTBT) organic semiconductors and the effect of aging and solvent vapor annealing on the film structure. Through extensive X-ray structural investigations of spin coated films, we find a SIP with a significantly different structure to that found in single crystals of the same material forms; the SIP has a herringbone motif while single crystals display layered π-π stacking. Over time, the structure of the film is found to slowly convert to the single crystal structure. Solvent vapor annealing initiates the same structural evolution process but at a greatly increased rate, and near complete conversion can be achieved in a short period of time. As properties such as charge transport capability are determined by the molecular structure, this work highlights the importance of understanding and controlling the structure of organic semiconductor films and presents a simple method to control the film structure by solvent vapor annealing.

Sm5(Fe,Ti)17 melt-spun ribbons with high coercivity

NASA Astrophysics Data System (ADS)

Saito, Tetsuji; Horita, Toru

2018-05-01

It has previously been reported that annealing of amorphous Sm5Fe17 melt-spun ribbon resulted in the formation of the Sm5Fe17 phase and the resultant Sm5Fe17 melt-spun ribbon exhibited a high coercivity. However, the annealing condition of the amorphous Sm5Fe17 melt-spun ribbon was somewhat critical and it was not easy to obtain Sm5Fe17 grains with high coercivity. In the present study, it was found that the small substitution of Ti for Fe in the Sm5Fe17 melt-spun ribbon stabilized the Sm5Fe17 phase. Annealed Sm5Fe16.7Ti0.3 melt-spun ribbon consisted of small and homogeneous Sm5(Fe,Ti)17 grains and exhibited a higher coercivity than the annealed Sm5Fe17 melt-spun ribbon.

Interface observation in Au/Ni/p-GaN studied by HREM and energy-filtering TEM.

PubMed

Lim, Sung-Hwan; Ra, Tae-Yeub; Kim, Won-Yong

2003-01-01

The contact resistance of Au/Ni/p-GaN ohmic contacts for different annealing conditions was measured. This was then correlated with microstructure, including phase distribution, observed by high-resolution electron microscopy combined with energy-filtering imaging. A contact resistance of 2.22 x 10(-4) ohms cm2 for Au/Ni contacts to p-GaN after annealing at 500 degrees C for 5 min in air ambient was obtained. NiO layers were identified at the interface and upper area of annealed Ni/Au/p-GaN for air ambient. In addition, an Au layer was found at the interface of p-GaN due to a reversal reaction during annealing. Identification of the observed phases is discussed, along with possible formation mechanisms for the ohmic contacts in the Au/Ni/p-GaN system.

Structure and magnetic properties of the Nd9.5Fe84.5B6 alloy subjected to severe plastic deformation and annealing

NASA Astrophysics Data System (ADS)

Menushenkov, V. P.; Shchetinin, I. V.; Chernykh, S. V.; Savchenko, A. G.; Gorshenkov, M. V.; Zhukov, D. G.

2017-10-01

The effect of severe plastic deformation (SPD) by torsion and subsequent annealing on the structure and magnetic properties of the cast Nd9.5Fe84.5B6 alloy is studied. SPD by torsion is shown to lead to partial amorphization of the Nd2Fe14B phase and the precipitation of α-Fe; subsequent annealing results in the crystallization of the amorphous phase and the formation of a nanocomposite Nd2Fe14B/α-Fe structure. After SPD by torsion at 20 revolutions and annealing at 873 K, the (101) texture is formed; in this case, the coercive force is H c = 360 kA/m and the maximum energy product is ( BH) max = 166 kJ/m3. The residual magnetization and the squareness ratio of the hysteretic loop of the textured alloy decrease as the ambient temperature decreases.

Performance enhancement of hybrid solar cells through chemical vapor annealing.

PubMed

Wu, Yue; Zhang, Genqiang

2010-05-12

Improvement in power conversion efficiency has been observed in cadmium selenide nanorods/poly(3-hexylthiophene) hybrid solar cells through benzene-1,3-dithiol chemical vapor annealing. Phosphor NMR studies of the nanorods and TEM/AFM characterizations of the morphology of the blended film showed that the ligand exchange reaction and related phase separation happening during the chemical vapor annealing are responsible for the performance enhancement.

The effects of annealing on the microstructure and mechanical properties of Fe 28Ni 18Mn 33Al 21

DOE Office of Scientific and Technical Information (OSTI.GOV)

Meng, Fanling; Qiu, Jingwen; Baker, Ian

In this paper, As-cast Fe 28Ni 18Mn 33Al 21, which consists of aligned, 50 nm, (Ni, Al)-rich B2, and (Fe, Mn)-rich f.c.c. phases, was annealed at a variety of temperatures up to 1423 K and the microstructure and mechanical properties were examined. It was shown that the as-cast microstructure arises from a eutectoid transformation at ~1300 K. Annealing at temperatures ≤1073 K produces β-Mn-structured precipitates and hardness values up to 816 HV, while annealing at temperatures >1073 K leads to dramatic coarsening of the two-phase B2/f.c.c. microstructure (up to 5.5 µm after 50 h at 1273 K), but does notmore » lead to β-Mn precipitation. Interestingly, annealing at temperatures >1073 K delays the onset of β-Mn precipitation during subsequent anneals at lower temperatures. Coarsening the B2/f.c.c. lamellar structure by annealing at higher temperatures softens it and leads to increases in ductility from fracture before yield to ~8 % elongation. Finally, the presence of β-Mn precipitates makes the very fine, brittle B2/f.c.c. microstructures even more brittle, but significant ductility (8.4 % elongation) is possible even with β-Mn precipitates present if the B2/f.c.c. matrix is coarse and, hence, more ductile.« less

Surface modification of cellulose acetate membrane using thermal annealing to enhance produced water treatment

DOE Office of Scientific and Technical Information (OSTI.GOV)

Kusworo, T. D., E-mail: tdkusworo@che.undip.ac.id; Aryanti, N., E-mail: nita.aryanti@gmail.com; Firdaus, M. M. H.

2015-12-29

This study is performed primarily to investigate the effect of surface modification of cellulose acetate using thermal annealing on the enhancement of membrane performance for produced water treatment. In this study, Cellulose Acetate membranes were casted using dry/wet phase inversion technique. The effect of additive and post-treatment using thermal annealing on the membrane surface were examined for produced water treatment. Therma annealing was subjected to membrane surface at 60 and 70 °C for 5, 10 and 15 second, respectively. Membrane characterizations were done using membrane flux and rejection with produced water as a feed, Scanning Electron Microscopy (SEM) and Fouriermore » Transform Infra Red (FTIR) analysis. Experimental results showed that asymmetric cellulose acetate membrane can be made by dry/wet phase inversion technique. The results from the Scanning Electron Microscopy (FESEM) analysis was also confirmed that polyethylene glycol as additivie in dope solution and thermal annealing was affected the morphology and membrane performance for produced water treatment, respectively. Scanning electron microscopy micrographs showed that the selective layer and the substructure of membrane became denser and more compact after the thermal annealing processes. Therefore, membrane rejection was significantly increased while the flux was slighty decreased, respectively. The best membrane performance is obtained on the composition of 18 wt % cellulose acetate, poly ethylene glycol 5 wt% with thermal annealing at 70° C for 15 second.« less

The effects of annealing on the microstructure and mechanical properties of Fe 28Ni 18Mn 33Al 21

DOE PAGES

Meng, Fanling; Qiu, Jingwen; Baker, Ian; ...

2015-08-20

In this paper, As-cast Fe 28Ni 18Mn 33Al 21, which consists of aligned, 50 nm, (Ni, Al)-rich B2, and (Fe, Mn)-rich f.c.c. phases, was annealed at a variety of temperatures up to 1423 K and the microstructure and mechanical properties were examined. It was shown that the as-cast microstructure arises from a eutectoid transformation at ~1300 K. Annealing at temperatures ≤1073 K produces β-Mn-structured precipitates and hardness values up to 816 HV, while annealing at temperatures >1073 K leads to dramatic coarsening of the two-phase B2/f.c.c. microstructure (up to 5.5 µm after 50 h at 1273 K), but does notmore » lead to β-Mn precipitation. Interestingly, annealing at temperatures >1073 K delays the onset of β-Mn precipitation during subsequent anneals at lower temperatures. Coarsening the B2/f.c.c. lamellar structure by annealing at higher temperatures softens it and leads to increases in ductility from fracture before yield to ~8 % elongation. Finally, the presence of β-Mn precipitates makes the very fine, brittle B2/f.c.c. microstructures even more brittle, but significant ductility (8.4 % elongation) is possible even with β-Mn precipitates present if the B2/f.c.c. matrix is coarse and, hence, more ductile.« less

Effect of Annealing Temperature on Microstructure and Mechanical Properties of Hot-Dip Galvanizing DP600 Steel

NASA Astrophysics Data System (ADS)

Hai-yan, Sun; Zhi-li, Liu; Yang, Xu; Jian-qiang, Shi; Lian-xuan, Wang

Hot-dip galvanizing dual phase steel DP600 steel grade with low Si was produced by steel plant and experiments by simulating galvanizing thermal history. The microstructure was observed and analyzed by scanning electron microscopy (SEM) and transmission electron microscopy (TEM). The effect of different annealing temperatures on the microstructure and mechanical properties of dual-phase steel was also discussed. The experimental results show that the dual-phase steel possesses excellent strength and elongation that match EN10346 600MPa standards. The microstructure is ferrite and martensite. TEM micrograph shows that white ferrite with black martensite islands inlay with a diameter of around 1um and the content of 14 18%. The volume will expand and phase changing take the form of shear transformation when ferrite converted to martensite. So there are high density dislocations in ferrite crystalline grain near martensite. The martensite content growing will be obvious along with annealing temperature going up. But the tendency will be weak when temperature high.

Hydrogen-induced morphotropic phase transformation of single-crystalline vanadium dioxide nanobeams.

PubMed

Hong, Woong-Ki; Park, Jong Bae; Yoon, Jongwon; Kim, Bong-Joong; Sohn, Jung Inn; Lee, Young Boo; Bae, Tae-Sung; Chang, Sung-Jin; Huh, Yun Suk; Son, Byoungchul; Stach, Eric A; Lee, Takhee; Welland, Mark E

2013-04-10

We report a morphotropic phase transformation in vanadium dioxide (VO2) nanobeams annealed in a high-pressure hydrogen gas, which leads to the stabilization of metallic phases. Structural analyses show that the annealed VO2 nanobeams are hexagonal-close-packed structures with roughened surfaces at room temperature, unlike as-grown VO2 nanobeams with the monoclinic structure and with clean surfaces. Quantitative chemical examination reveals that the hydrogen significantly reduces oxygen in the nanobeams with characteristic nonlinear reduction kinetics which depend on the annealing time. Surprisingly, the work function and the electrical resistance of the reduced nanobeams follow a similar trend to the compositional variation due mainly to the oxygen-deficiency-related defects formed at the roughened surfaces. The electronic transport characteristics indicate that the reduced nanobeams are metallic over a large range of temperatures (room temperature to 383 K). Our results demonstrate the interplay between oxygen deficiency and structural/electronic phase transitions, with implications for engineering electronic properties in vanadium oxide systems.

Structural transformation study of TiO2 nanoparticles annealing at different temperatures and the photodegradation process of eosin-Y

NASA Astrophysics Data System (ADS)

Pandi, P.; Gopinathan, C.

2018-04-01

Hydrothermal method was used to prepare TiO2 nanoparticles with annealing temperature at 500 °C-700 °C. The mixture of anatase-rutile phase was investigated by powerful tool of X-ray diffraction (XRD). The structural parameters of anatase and rutile mixture phaseTiO2 nanoparticles were calculated from the Rietveld refinement. The transformation rate of rutile was increased linearly with an annealing temperature of 500 °C-700 °C. The spherical morphology of the anatase and rutile mixed phase were obtained by scanning electron microscope and transmission electron microscope. The spherical particle of the anatase and rutile TiO2 shows with great aggregation with different size and within the range of few tens nm. The EDAX study revealed the presence of titanium and oxygen. The best photocatalytic activity was identified as the 87.04% of anatase and 12.96% of rutile mixer phase of TiO2. Various factors could be involved for a better photocatalytic activity.

DOE Office of Scientific and Technical Information (OSTI.GOV)

Kasemer, Matthew; Quey, Romain; Dawson, Paul

Discussed is a computational study of the influence of the microstructure’s geometric morphology on the yield strength and ductility of Ti-6Al-4V. Uniaxial tension tests were conducted on physical specimens to determine the macroscopic yield strength and ductility of two microstructural variations (mill annealed and β annealed) to establish comparisons of macroscopic properties. A multi-experimental approach was utilized to gather two dimensional and three dimensional data, which were used to inform the construction of representative β annealed polycrystals. A highly parallelized crystal plasticity finite element framework was employed to model the deformation response of the generated polycrystals subjected to uniaxial tension.more » To gauge the macroscopic response’s sensitivity to the morphology of the geometry, the key geometrical features - namely the number of high temperature β phase grains, α phase colonies, and size of remnant secondary β phase lamellae - were altered systematically in a suite of simulations. Both single phase and dual phase aggregates were studied. Presented are the calculated yield strengths and ductilities, and the resulting trends as functions of geometric parameters are examined in light of the heterogeneity in deformation at the crystal scale.« less

Characterization of alloy 718 subjected to different thermomechanical treatments

DOE Office of Scientific and Technical Information (OSTI.GOV)

Silva, Chinthaka; Song, Miao; Leonard, Keith

2017-03-11

Chemical phase and microstructural investigations of alloy 718 solution-annealed and age-hardened were performed in this study. We focused on the effects of solution annealing temperature, aging temperature and holding time, and the amount of intermediate cold work on the alloy. We also studied the formation of secondary phases such as γ’-phase, γ”-phase, and δ-phase, grain sizes, and any deformations of the microstructure with respect to the processed conditions. Statistics such as size and number densities of these precipitates with respect to the processing conditions were evaluated and a discussion on optimum conditions in obtaining finer and higher density of γ’-more » and γ”-phase precipitates is also presented.« less

Thermal annealing and transient electronic excitations induced interfacial and magnetic effects on Pt/Co/Pt trilayer

NASA Astrophysics Data System (ADS)

Sehdev, Neeru; Medwal, Rohit; Malik, Rakesh; Kandasami, Asokan; Kanjilal, Dinakar; Annapoorni, S.

2018-04-01

Present study investigates the importance of thermal annealing and transient electronic excitations (using 100 MeV oxygen ions) in assisting the interfacial atomic diffusion, alloy composition, and magnetic switching field distributions in Pt/Co/Pt stacked trilayer. X-ray diffraction analysis reveals that thermal annealing results in the formation of the face centered tetragonal L1°CoPt phase. The Rutherford back scattering spectra shows a trilayer structure for as-deposited and as-irradiated films. Interlayer mixing on the thermally annealed films further improves by electronic excitations produced by high energy ion irradiation. Magnetically hard face centered tetragonal CoPt alloy retains its hard phase after ion irradiation and reveals an enhancement in the structural ordering and magnetic stability. Enhancement in the homogeneity of alloy composition and its correlation with the magnetic switching field is evident from this study. A detailed investigation of the contributing parameters shows that the magnetic switching behaviour varies with the type of thermal annealing, transient electronic excitations of ion beams and combination of these processes.

Effect of high temperature annealing on the thermoelectric properties of GaP doped SiGe

NASA Technical Reports Server (NTRS)

Vandersande, Jan W.; Wood, Charles; Draper, Susan

1987-01-01

Silicon-germanium alloys doped with GaP are used for thermoelectric energy conversion in the temperature range 300-1000 C. The conversion efficiency depends on Z = S-squared/rho lambda, a material's parameter (the figure of merit), where S is the Seebeck coefficient, rho is the electrical resistivity and lambda is the thermal conductivity. The annealing of several samples in the temperature range of 1100-1300 C resulted in the power factor P (= S-squared/rho) increasing with increased annealing temperature. This increase in P was due to a decrease in rho which was not completely offset by a drop in S-squared suggesting that other changes besides that in the carrier concentration took place. SEM and EDX analysis of the samples indicated the formation of a Ga-P-Ge rich phase as a result of the annealing. It is speculated that this phase is associated with the improved properties. Several reasons which could account for the improvement in the power factor of annealed GaP doped SiGe are given.

The role of annealing temperature and bio template (egg white) on the structural, morphological and magnetic properties of manganese substituted MFe2O4 (M=Zn, Cu, Ni, Co) nanoparticles

NASA Astrophysics Data System (ADS)

Ranjith Kumar, E.; Jayaprakash, R.; Kumar, Sanjay

2014-02-01

Manganese substituted ferrites (ZnFe2O4, CuFe2O4, NiFe2O4 and CoFe2O4) have been prepared in the bio template medium by using a simple evaporation method. The annealing temperature plays an important position on changing particle size and morphology of the mixed ferrite nanoparticles were found out by X-ray diffraction, transmission electron microscopy and scanning electron microscopy methods. The role of manganese substitution in the mixed ferrite nanoparticles were also analyzed for different annealing temperature. The substitution of Mn also creates a vital change in magnetic properties which is studied by using vibrating sample magnetometer (VSM). These spinel ferrites are decomposed to α-Fe2O3 after annealing above 550 °C in air. However, α-Fe2O3 phase was slowly vanished after ferrites annealing above 900 °C. The effect of this secondary phase on the structural change and magnetic properties of the mixed ferrite nanoparticles is discussed.

Minimizing the Discrepancy between Simulated and Historical Failures in Turbine Engines: A Simulation-Based Optimization Method (Postprint)

DTIC Science & Technology

2015-01-01

Procedure. The simulated annealing (SA) algorithm is a well-known local search metaheuristic used to address discrete, continuous, and multiobjective...design of experiments (DOE) to tune the parameters of the optimiza- tion algorithm . Section 5 shows the results of the case study. Finally, concluding... metaheuristic . The proposed method is broken down into two phases. Phase I consists of a Monte Carlo simulation to obtain the simulated percentage of failure

Visualization of phase evolution in model organic photovoltaic structures via energy-filtered transmission electron microscopy.

PubMed

Herzing, Andrew A; Ro, Hyun Wook; Soles, Christopher L; DeLongchamp, Dean M

2013-09-24

The morphology of the active layer in an organic photovoltaic bulk-heterojunction device is controlled by the extent and nature of phase separation during processing. We have studied the effects of fullerene crystallinity during heat treatment in model structures consisting of a layer of poly(3-hexylthiophene) (P3HT) sandwiched between two layers of [6,6]-phenyl-C61-butyric acid methyl ester (PCBM). Utilizing a combination of focused ion-beam milling and energy-filtered transmission electron microscopy, we monitored the local changes in phase distribution as a function of annealing time at 140 °C. In both cases, dissolution of PCBM within the surrounding P3HT was directly visualized and quantitatively described. In the absence of crystalline PCBM, the overall phase distribution remained stable after intermediate annealing times up to 60 s, whereas microscale PCBM aggregates were observed after annealing for 300 s. Aggregate growth proceeded vertically from the substrate interface via uptake of PCBM from the surrounding region, resulting in a large PCBM-depleted region in their vicinity. When precrystallized PCBM was present, amorphous PCBM was observed to segregate from the intermediate P3HT layer and ripen the crystalline PCBM underneath, owing to the far lower solubility of crystalline PCBM within P3HT. This process occurred rapidly, with segregation already evident after annealing for 10 s and with uptake of nearly all of the amorphous PCBM by the crystalline layer after 60 s. No microscale aggregates were observed in the precrystallized system, even after annealing for 300 s.

A novel technique based on a plasma focus device for nano-porous gallium nitride formation on P-type silicon

NASA Astrophysics Data System (ADS)

Sharifi Malvajerdi, S.; Salar Elahi, A.; Habibi, M.

2017-04-01

A new deposition formation was observed with a Mather-type Plasma Focus Device (MPFD). MPFD was unitized to fabricate porous Gallium Nitride (GaN) on p-type Silicon (Si) substrate with a (100) crystal orientation for the first time in a deposition process. GaN was deposited on Si with 4 and 7 shots. The samples were subjected to a 3 phase annealing procedure. First, the semiconductors were annealed in the PFD with nitrogen plasma shots after their deposition. Second, a thermal chemical vapor deposition annealed the samples for 1 h at 1050 °C by nitrogen gas at a pressure of 1 Pa. Finally, an electric furnace annealed the samples for 1 h at 1150 °C with continuous flow of nitrogen. Porous GaN structures were observed by Field emission scanning electron microscopy and atomic force microscopy. Furthermore, X-Ray diffraction analysis was carried out to determine the crystallinity of GaN after the samples were annealed. Energy-Dispersive X-Ray Spectroscopy indicated the amount of gallium, nitrogen, and oxygen due to the self-oxidation of the samples. Photoluminescence spectroscopy revealed emissions at 2.94 eV and 3.39 eV, which shows that hexagonal wurtzite crystal structures were formed.

Formation Mechanism of CuAlO2 Prepared by Rapid Thermal Annealing of Al2O3/Cu2O/Sapphire Sandwich Structure

NASA Astrophysics Data System (ADS)

Shih, C. H.; Tseng, B. H.

Single-phase CuAlO2 films were successfully prepared by thin-film reaction of an Al2O3/Cu2O/sapphire sandwich structure. We found that the processing parameters, such as heating rate, holding temperature and annealing ambient, were all crucial to form CuAlO2 without second phases. Thermal annealing in pure oxygen ambient with a lower temperature ramp rate might result in the formation of CuAl2O4 in addition to CuAlO2, since part of Cu2O was oxidized to form CuO and caused the change in reaction path, i.e. CuO + Al2O3 → CuAl2O4. Typical annealing conditions successful to prepare single-phase CuAlO2 would be to heat the sample with a temperature rampt rate higher than 7.3 °C/sec and hold the temperature at 1100 °C in air ambient. The formation mechanism of CuAlO2 has also been studied by interrupting the reaction after a short period of annealing. TEM observations showed that the top Al2O3 layer with amorphous structure reacted immediately with Cu2O to form CuAlO2 in the early stage and then the remaining Cu2O reacted with the sapphire substrate.

Electron microscopy of a Gd-Ba-Cu-O superconductor

NASA Technical Reports Server (NTRS)

Ramesh, R.; Thomas, G.; Meng, R. L.; Hor, P. H.; Chu, C. W.

1989-01-01

An electron microscopy study has been carried out to characterize the microstructure of a sintered Gd-Ba-Cu-O superconductor alloy. The GdBa2Cu3O(7-x) phase in the oxygen annealed sample is orthorhombic, while in the vacuum annealed sample it is tetragonal. It is shown that the details of the fine structure in the 001-line zone axis convergent beam patterns can be used to distinguish between the orthorhombic form and the tetragonal form. In addition to this matrix phase, an amorphous phase is frequently observed at the triple grain junctions. Gd-rich inclusions have been observed inside the matrix phase.

Thermodynamic analysis and purifying an amorphous phase of frozen crystallization centers

NASA Astrophysics Data System (ADS)

Lysov, V. I.; Tsaregradskaya, T. L.; Turkov, O. V.; Saenko, G. V.

2017-12-01

The possibility of dissolving frozen crystallization centers in amorphous alloys of the Fe-B system is considered by means of thermodynamic calculations. This can in turn improve the thermal stability of an amorphous alloy. The effect isothermal annealing has on the thermal stability of multicomponent amorphous alloys based on iron is investigated via the highly sensitive dilatometric technique, measurements of microsolidity, and electron microscopic investigations. The annealing temperature is determined empirically on the basis of the theses of the thermodynamic theory of the high temperature stability of multicomponent amorphous alloys, according to which there exists a range of temperatures that is characterized by a negative difference between the chemical potentials of phases in a heterogeneous amorphous matrix-frozen crystallization centers system. The thermodynamic condition of the possible dissolution of frozen crystallization centers is thus met. It is shown that introducing regimes of thermal processing allows us to expand the ranges of the thermal stability of iron-based amorphous alloys by 20-40 K through purifying an amorphous matrix of frozen crystallization centers. This conclusion is proved via electron microscopic investigations.

The mechanical properties and microstructures of vanadium bearing high strength dual phase steels processed with continuous galvanizing line simulations

NASA Astrophysics Data System (ADS)

Gong, Yu

For galvanized or galvannealed steels to be commercially successful, they must exhibit several attributes: (i) easy and inexpensive processing in the hot mill, cold mill and on the coating line, (ii) high strength with good formability and spot weldability, and (iii) good corrosion resistance. At the beginning of this thesis, compositions with a common base but containing various additions of V or Nb with or without high N were designed and subjected to Gleeble simulations of different galvanizing(GI), galvannealing(GA) and supercooling processing. The results revealed the phase balance was strongly influenced by the different microalloying additions, while the strengths of each phase were somewhat less affected. Our research revealed that the amount of austenite formed during intercritical annealing can be strongly influenced by the annealing temperature and the pre-annealing conditions of the hot band (coiling temperature) and cold band (% cold reduction). In the late part of this thesis, the base composition was a low carbon steel which would exhibit good spot weldability. To this steel were added two levels of Cr and Mo for strengthening the ferrite and increasing the hardenability of intercritically formed austenite. Also, these steels were produced with and without the addition of vanadium in an effort to further increase the strength. Since earlier studies revealed a relationship between the nature of the starting cold rolled microstructure and the response to CGL processing, the variables of hot band coiling temperature and level of cold reduction prior to annealing were also studied. Finally, in an effort to increase strength and ductility of both the final sheet (general formability) and the sheared edges of cold punched holes (local formability), a new thermal path was developed that replaced the conventional GI ferrite-martensite microstructure with a new ferrite-martensite-tempered martensite and retained austenite microstructure. The new microstructure exhibited a somewhat lower strength but much high general and local formabilities. In this thesis, both the physical and mechanical metallurgy of these steels and processes will be discussed. This research has shown that simple compositions and processes can result in DP steels with so-called Generation III properties.

Effect of prior deformation on microstructural development and Laves phase precipitation in high-chromium stainless steel.

PubMed

Hsiao, Z-W; Chen, D; Kuo, J-C; Lin, D-Y

2017-04-01

This study investigated the influence of deformation on precipitation behaviour and microstructure change during annealing. Here, the prior deformation of high-chromium stainless steel was tensile deformation of 3%, 6% and 10%, and the specimens were then annealed at 700˚C for 10 h. The specimens were subsequently analyzed using backscattered electron image and electron backscattering diffraction measurements with SEM. Compared with the deformation microstructure, the grains revealed no preferred orientation. The precipitates of TiN and NbC were formed homogenously in the grain interior and at grain boundaries after annealing. Fine Laves phase precipitates were observed in grains and along subgrain boundaries as the deformation increased. Furthermore, the volume fraction of Laves phase increased, but the average particle diameter of precipitate was reduced as the deformation increased. © 2017 The Authors Journal of Microscopy © 2017 Royal Microscopical Society.

DOE Office of Scientific and Technical Information (OSTI.GOV)

Makino, Nobuaki; Toshiba Corporation, 33 Shin-Isogo-Cho, Isogo-ku, Yokohama 235-0017; Shigeta, Yukichi

The stabilization of the amorphous structure in amorphous silicon film by adding Ge atoms was studied using Raman spectroscopy. Amorphous Si{sub 1−x}Ge{sub x} (x = 0.0, 0.03, 0.14, and 0.27) films were deposited on glass substrates from electron beam evaporation sources and annealed in N{sub 2} atmosphere. The change in the amorphous states and the phase transition from amorphous to crystalline were characterized using the TO, LO, and LA phonons in the Raman spectra. The temperature of the transition from the amorphous phase to the crystalline phase was higher for the a-Si{sub 1−x}Ge{sub x} (x = 0.03, 0.14) films, and the crystallization was hindered.more » The reason why the addition of a suitable quantity of Ge atoms into the three-dimensional amorphous silicon network stabilizes its amorphous structure is discussed based on the changes in the Raman signals of the TO, LO, and LA phonons during annealing. The characteristic bond length of the Ge atoms allows them to stabilize the random network of the amorphous Si composed of quasi-tetrahedral Si units, and obstruct its rearrangement.« less

Kinetics of Polymer-Fullerene Phase Separation during Solvent Annealing Studied by Table-Top X-ray Scattering.

PubMed

Vegso, Karol; Siffalovic, Peter; Jergel, Matej; Nadazdy, Peter; Nadazdy, Vojtech; Majkova, Eva

2017-03-08

Solvent annealing is an efficient way of phase separation in polymer-fullerene blends to optimize bulk heterojunction morphology of active layer in polymer solar cells. To track the process in real time across all relevant stages of solvent evaporation, laboratory-based in situ small- and wide-angle X-ray scattering measurements were applied simultaneously to a model P3HT:PCBM blend dissolved in dichlorobenzene. The PCBM molecule agglomeration starts at ∼7 wt % concentration of solid content of the blend in solvent. Although PCBM agglomeration is slowed-down at ∼10 wt % of solid content, the rate constant of phase separation is not changed, suggesting agglomeration and reordering of P3HT molecular chains. Having the longest duration, this stage most affects BHJ morphology. Phase separation is accelerated rapidly at concentration of ∼25 wt %, having the same rate constant as the growth of P3HT crystals. P3HT crystallization is driving force for phase separation at final stages before a complete solvent evaporation, having no visible temporal overlap with PCBM agglomeration. For the first time, such a study was done in laboratory demonstrating potential of the latest generation table-top high-brilliance X-ray source as a viable alternative before more sophisticated X-ray scattering experiments at synchrotron facilities are performed.

Optical and Structural Properties of Ion-implanted InGaZnO Thin Films Studied with Spectroscopic Ellipsometry and Transmission Electron Microscopy

NASA Astrophysics Data System (ADS)

Park, Jun Woo; Jeong, Pil Seong; Choi, Suk-Ho; Lee, Hosun; Kong, Bo Hyun; Koun Cho, Hyung

2009-11-01

Amorphous InGaZnO (IGZO) thin films were grown using RF sputtering deposition at room temperature and their corresponding dielectric functions were measured. In order to reduce defects and increase carrier concentrations, we examined the effect of forming gas annealing and ion implantation. The band gap energy increased with increasing forming gas annealing temperature. We implanted the IGZO thin films with F- ions in order to decrease oxygen vacancies. For comparison, we also implanted InO- ions. Transmission electron microscopy showed that the amorphous phase undergoes transformation to a nanocrystalline phase due to annealing. We also observed InGaZnO4 nanocrystals having an In-(Ga/Zn) superlattice structure. As the annealing temperature increased, the optical gap energy increased due to crystallization. After annealing, we observed an oxygen-vacancy-related 1.9 eV peak for both unimplanted and InO-implanted samples. However, F- ion implantation substantially reduced the amplitude of the 1.9 eV peak, which disappeared completely at a F fluence of 5×1015 cm-2. We observed other defect-related peaks at 3.6 and 4.2 eV after annealing, which also disappeared after F implantation.

Microstructural Evolution of Dy2O3-TiO2 Powder Mixtures during Ball Milling and Post-Milled Annealing

PubMed Central

Huang, Jinhua; Ran, Guang; Lin, Jianxin; Shen, Qiang; Lei, Penghui; Wang, Xina; Li, Ning

2016-01-01

The microstructural evolution of Dy2O3-TiO2 powder mixtures during ball milling and post-milled annealing was investigated using XRD, SEM, TEM, and DSC. At high ball-milling rotation speeds, the mixtures were fined, homogenized, nanocrystallized, and later completely amorphized, and the transformation of Dy2O3 from the cubic to the monoclinic crystal structure was observed. The amorphous transformation resulted from monoclinic Dy2O3, not from cubic Dy2O3. However, at low ball-milling rotation speeds, the mixtures were only fined and homogenized. An intermediate phase with a similar crystal structure to that of cubic Dy2TiO5 was detected in the amorphous mixtures annealed from 800 to 1000 °C, which was a metastable phase that transformed to orthorhombic Dy2TiO5 when the annealing temperature was above 1050 °C. However, at the same annealing temperatures, pyrochlore Dy2Ti2O7 initially formed and subsequently reacted with the remaining Dy2O3 to form orthorhombic Dy2TiO5 in the homogenous mixtures. The evolutionary mechanism of powder mixtures during ball milling and subsequent annealing was analyzed. PMID:28772375

Investigation of the annealing temperature effect on structural, morphology, dielectric and magnetic properties of BiFeO3 nanoparticles

NASA Astrophysics Data System (ADS)

Ranjbar, M.; Ghazi, M. E.; Izadifard, M.

2018-06-01

In this paper we have investigated the annealing temperature effect on the structure, morphology, dielectric and magnetic properties of sol-gel synthesized multiferroic BiFeO3 nanoparticles. X-ray diffraction spectroscopy revealed that all the samples have rhombohedrally distorted perovskite structure and the most pure BFO phase is obtained on the sample annealed at 800 °C. Field emission scanning electron microscopy (FESEM) revealed that increasing annealing temperature would increase the particle size. Decrease in dielectric constant was also observed by increasing annealing temperature. Vibrating sample method (VSM) analysis confirmed that samples annealed at 500-700 °C with particle size below the BFO's spiral spin structure length, have well saturated M-H curve and show ferromagnetic behavior.

Phase Transformation Induced Self-Healing Behavior of Al-Ag Alloy.

PubMed

Michalcová, Alena; Marek, Ivo; Knaislová, Anna; Sofer, Zdeněk; Vojtěch, Dalibor

2018-01-27

Self-healing alloys are promising materials that can decrease the consequences of accidents. To detect crack formation in a material is simple task that can be performed by e.g., sonic or ultrasound detection, but it is not always possible to immediately replace the damaged parts. In this situation, it is very advantageous to have the chance to heal the crack during operation, which can be done e.g., by annealing. In this paper, self-healing behavior was proven by TEM (Transmission electron microscope) observation of crack healing after annealing. The crack was observed in the rapidly solidified Al-30Ag alloy with non-equilibrium phase composition formed by a minor amount of Ag₂Al and a supersaturated solid solution of Ag in an fcc-Al matrix (fcc = face centered cubic). After annealing at 450 °C, equilibrium phase composition was obtained by forming a higher amount of Ag₂Al. This phase transformation did not allow the crack to be healed. Subsequent annealing at 550 °C caused recrystallization to a supersaturated solid solution of Ag in fcc-Al, followed by a return to the mixture of fcc-Al and Ag₂Al by cooling, and this process was accompanied by the closing of the crack. This observation proved the self-healing possibilities of the Ag₂Al phase. Practical application of this self-healing behavior could be achieved through the dispersion of fine Ag₂Al particles in a structural material, which will enrich the material with self-healing properties.

DOE Office of Scientific and Technical Information (OSTI.GOV)

Luňáček, J., E-mail: jiri.lunacek@vsb.cz

The present paper is devoted to detailed study of the magnetically separable sorbents based on a cerium dioxide/iron oxide composite annealed at temperatures T{sub a} = 773 K, 873 K, and 973 K. The X-ray diffraction and high resolution transmission electron microscopy are used to determine the phase composition and microstructure morphology. Mössbauer spectroscopy at room (300 K) and low (5 K) temperatures has contributed to more exact identification of iron oxides and their transformations Fe{sub 3}O{sub 4} → γ-Fe{sub 2}O{sub 3} (ε-Fe{sub 2}O{sub 3}) → α-Fe{sub 2}O{sub 3} in dependence on calcination temperature. Different iron oxide phase compositions andmore » grain size distributions influence the magnetic characteristics determined from the room- and low-temperature hysteresis loop measurements. The results are supported by zero-field-cooled and field-cooled magnetization measurements allowing a quantitative estimation of the grain size distribution and its effect on the iron oxide transformations. - Highlights: •Magnetically separable sorbents based on a CeO{sub 2}/Fe{sub 2}O{sub 3} composite were investigated. •Microstructure of sorbents was determined by XRD, TEM and Mössbauer spectroscopy. •Magnetic properties were studied by hysteresis loops at room- and low-temperatures. •Phase transitions of iron oxides with increasing annealing temperature are observed.« less

Simultaneous ultra-long data retention and low power based on Ge10Sb90/SiO2 multilayer thin films

NASA Astrophysics Data System (ADS)

You, Haipeng; Hu, Yifeng; Zhu, Xiaoqin; Zou, Hua; Song, Sannian; Song, Zhitang

2018-02-01

In this article, Ge10Sb90/SiO2 multilayer thin films were prepared to improve thermal stability and data retention for phase change memory. Compared with Ge10Sb90 monolayer thin film, Ge10Sb90 (1 nm)/SiO2 (9 nm) multilayer thin film had higher crystallization temperature and resistance contrast between amorphous and crystalline states. Annealed Ge10Sb90 (1 nm)/SiO2 (9 nm) had uniform grain with the size of 15.71 nm. After annealing, the root-mean-square surface roughness for Ge10Sb90 (1 nm)/SiO2 (9 nm) thin film increased slightly from 0.45 to 0.53 nm. The amorphization time for Ge10Sb90 (1 nm)/SiO2 (9 nm) thin film (2.29 ns) is shorter than Ge2Sb2Te5 (3.56 ns). The threshold voltage of a cell based on Ge10Sb90 (1 nm)/SiO2 (9 nm) (3.57 V) was smaller than GST (4.18 V). The results indicated that Ge10Sb90/SiO2 was a promising phase change thin film with high thermal ability and low power consumption for phase change memory application.

Crystallographic study of Si and ZrN coated U-Mo atomised particles and of their interaction with al under thermal annealing

NASA Astrophysics Data System (ADS)

Zweifel, T.; Palancher, H.; Leenaers, A.; Bonnin, A.; Honkimaki, V.; Tucoulou, R.; Van Den Berghe, S.; Jungwirth, R.; Charollais, F.; Petry, W.

2013-11-01

A new type of high density fuel is needed for the conversion of research and test reactors from high to lower enriched uranium. The most promising one is a dispersion of atomized uranium-molybdenum (U-Mo) particles in an Al matrix. However, during in-pile irradiation the growth of an interaction layer between the U-Mo and the Al matrix strongly limits the fuel's performance. To improve the in-pile behaviour, the U-Mo particles can be coated with protective layers. The SELENIUM (Surface Engineering of Low ENrIched Uranium-Molybdenum) fuel development project consists of the production, irradiation and post-irradiation examination of 2 flat, full-size dispersion fuel plates containing respectively Si and ZrN coated U-Mo atomized powder dispersed in a pure Al matrix. In this paper X-ray diffraction analyses of the Si and ZrN layers after deposition, fuel plate manufacturing and thermal annealing are reported. It was found for the U-Mo particles coated with ZrN (thickness 1 μm), that the layer is crystalline, and exhibits lower density than the theoretical one. Fuel plate manufacturing does not strongly influence these crystallographic features. For the U-Mo particles coated with Si (thickness 0.6 μm), the measurements of the as received material suggest an amorphous state of the deposited layer. Fuel plate manufacturing strongly modifies its composition: Si reacts with the U-Mo particles and the Al matrix to grow U(Al, Si)3 and U3Si5 phases. Finally both coatings have shown excellent performances under thermal treatment by limiting drastically the U-Mo/Al interdiffusion. U(Al,Si)3 with two lattice parameters (4.16 Å and 4.21 Å), A distorted U3Si5 phase. Note that these phases were not present in the U-Mo(Si) powders. These phases are usually found in the Silicon rich diffusion layer (SiRDL) obtained in dispersed fuels (as-manufactured U-Mo/Al(Si) fuel plates [12,3] or annealed UMo(Si)/Al fuel rods [40]) as well as in diffusion couples (U-Mo/Al(Si7) [37-39] or U-Mo/Si [41]). This analysis is furthermore in full agreement with the SEM/EDX characterisations which have highlighted the growth of a SiRDL in these U-Mo(Si)/Al_P fuel plates [30]. However it must be stressed that the amount of these U(Al,Si)3 and U3Si5 crystalline phases (about 0.3 wt%) is lower than the one obtained for fuel plates containing 4-6 wt% Si in the matrix [12]. It equals to the SiRDL amount measured in the IRIS4_2.1%Si fuel plate. Using these HE-XRD measurements, the Si concentration in SiRDLs is evaluated to 51 at%. This value is somewhat higher than when measured by EDX: it has been estimated to 40 at% in [30]. U2Mo and α"-U phase for compacts annealed at 340 °C, U2Mo and α'-U phase for compacts annealed at 450 °C [43], gamma;-U-Mo and α'-U for compacts annealed at 550 °C. These results obtained on compacts are in good agreement with previous works performed on U-8Mo ingots (see Fig. 9A) -even if some differences in the α-U phase structure must be mentioned - and in very close agreement with recent studies on thermally annealed U-Mo/Al fuel plates. Indeed destabilisation products found in this work are identical to those identified after fuel plate annealing at 550 °C [25] and 450 °C [43]. Moreover this work helps establishing that destabilisation products are U2Mo and α"-U at lower temperatures (below 450 °C). This was first demonstrated on fuel plates annealed at 425 °C for more than 50 h [43] and this is confirmed here with the analysis of the compacts annealed at 340 °C during 130 days. Note finally that whatever the presence of a coating, destabilisation ratios are very close in compacts annealed in the same conditions (see Fig. 9B) and that destabilisation ratios show the expected increase between 2 and 4 h annealing at 550 °C. The non-annealed U-Mo(Si)/Al compact has been lost during fabrication.

Effects of sintering temperature on the pyrochlore phase in PZT nanotubes and their transformation to the perovskite phase by coating with PbO multilayers.

PubMed

Han, Jin Kyu; Choi, Yong Chan; Jeon, Do Hyen; Lee, Min Ku; Bu, Sang Don

2014-11-01

We report the phase evolution of Pb(Zr0.52Ti0.48)O3 nanotubes (PZT-NTs), from the pyrochlore to perovskite phase, with an outer diameter of about 420 nm and a wall thickness of about 10 nm. The PZT-NTs were fabricated in pores of porous anodic alumina membrane (PAM) using a spin coating of PZT sol-gel solution and subsequent annealing at 500-700 degrees C in oxygen gas. The pyrochlore phase was found to be formed at 500 degrees C, and also found not to be transformed into the perovskite phase, even though annealing was performed at higher temperatures to 700 degrees C. Elementary distribution analysis of PZT-NTs embedded in PAM reveal that Pb diffusion from nanotubes into pore walls of PAM is one of the main reasons. By employing firstly an additional PbO coating on the pyrochlore nanotubes and then subsequent annealing at 700 degrees C, we have successfully achieved an almost pure perovskite phase in nanotubes. These results suggest that PbO acts as a Pb-compensation agent in the Pb- deficient PZT-NTs. Moreover, our method can be used in the synthesis of all metal-oxide materials, including volatile elements.

Tm-doped TiO2 and Tm2Ti2O7 pyrochlore nanoparticles: enhancing the photocatalytic activity of rutile with a pyrochlore phase.

PubMed

De Los Santos, Desiré M; Navas, Javier; Aguilar, Teresa; Sánchez-Coronilla, Antonio; Fernández-Lorenzo, Concha; Alcántara, Rodrigo; Piñero, Jose Carlos; Blanco, Ginesa; Martín-Calleja, Joaquín

2015-01-01

Tm-doped TiO2 nanoparticles were synthesized using a water-controlled hydrolysis reaction. Analysis was performed in order to determine the influence of the dopant concentration and annealing temperature on the phase, crystallinity, and electronic and optical properties of the resulting material. Various characterization techniques were utilized such as X-ray diffraction, Raman spectroscopy, X-ray photoelectron spectroscopy and UV-vis spectroscopy. For the samples annealed at 773 and 973 K, anatase phase TiO2 was obtained, predominantly internally doped with Tm(3+). ICP-AES showed that a doping concentration of up to 5.8 atom % was obtained without reducing the crystallinity of the samples. The presence of Tm(3+) was confirmed by X-ray photoelectron spectroscopy and UV-vis spectroscopy: the incorporation of Tm(3+) was confirmed by the generation of new absorption bands that could be assigned to Tm(3+) transitions. Furthermore, when the samples were annealed at 1173 K, a pyrochlore phase (Tm2Ti2O7) mixed with TiO2 was obtained with a predominant rutile phase. The photodegradation of methylene blue showed that this pyrochlore phase enhanced the photocatalytic activity of the rutile phase.

Influence of N2 annealing on TiO2 tubes structure and its photocatalytic activity

NASA Astrophysics Data System (ADS)

Chen, Xiaoxiang; Pan, Zhanchang; Yu, Ke; Xiao, Jun; Wu, Shoukun; Li, Jinghong; Chen, Chun; Lin, Yingsheng; Hu, Guanghui; Xu, Yanbin

2018-02-01

In this work, the TiO2 tubes (TBs) were prepared by solvothermal method. The morphology and phase structure of TiO2 TBs is significantly affected by N2 annealing temperature. XRD was used to characterize the phase structure of the as-prepared samples. The morphology and surface areas were characterized by SEM and N2 adsorption-desorption, which show that the tubes were assembled with about 100-nm nanosheets and small ball particles under 400 and 600 °C N2 annealing; when temperature reached 800 °C, the surface of tubes appeared a lot of collapse and many large holes. In addition, the surface areas of 400 °C TiO2, 600 °C TiO2, and 800 °C TiO2 TBs were significantly affected by N2 annealing. Most importantly, the UV-vis and electrochemical tests demonstrate 600 °C TiO2 TBs exhibit higher absorption intensity and photocurrent; thus, it possess on better photocatalytic activity. Therefore, the photocatalytic performance for TiO2 TBs is significantly co-affected by surface area and mix-phase. [Figure not available: see fulltext.

Ti{sub 2}AlN thin films synthesized by annealing of (Ti+Al)/AlN multilayers

DOE Office of Scientific and Technical Information (OSTI.GOV)

Cabioch, Thierry, E-mail: Thierry.cabioch@univ-poitiers.fr; Alkazaz, Malaz; Beaufort, Marie-France

2016-08-15

Highlights: • Epitaxial thin films of the MAX phase Ti{sub 2}AlN are obtained by thermal annealing. • A new metastable (Ti,Al,N) solid solution with the structure of α-T is evidenced. • The formation of the MAX phase occurs at low temperature (600 °C). - Abstract: Single-phase Ti{sub 2}AlN thin films were obtained by annealing in vacuum of (Ti + Al)/AlN multilayers deposited at room temperature by magnetron sputtering onto single-crystalline (0001) 4H-SiC and (0001) Al{sub 2}O{sub 3} substrates. In-situ X-ray diffraction experiments combined with ex-situ cross-sectional transmission electron microscopy observations reveal that interdiffusion processes occur in the multilayer at amore » temperature of ∼400 °C leading to the formation of a (Ti, Al, N) solid solution, having the hexagonal structure of α-Ti, whereas the formation of Ti{sub 2}AlN occurs at 550–600 °C. Highly oriented (0002) Ti{sub 2}AlN thin films can be obtained after an annealing at 750 °C.« less

Influence of Annealing on Microstructure and Mechanical Properties of a Nanocrystalline CrCoNi Medium-Entropy Alloy

PubMed Central

Schuh, Benjamin; Völker, Bernhard; Todt, Juraj; Kormout, Karoline S.; Schell, Norbert; Hohenwarter, Anton

2018-01-01

An equiatomic CrCoNi medium-entropy alloy was subjected to high-pressure torsion. This process led to a refinement of the microstructure to a grain size of about 50 nm, combined with a strong increase in the materials hardness. Subsequently, the thermodynamic stability of the medium entropy alloy was evaluated by isothermal and isochronal heat treatments. Annealed samples were investigated by scanning and transmission electron microscopy as well as X-ray diffraction, and were subjected to tensile tests to establish microstructure-property relationships. Furthermore, a comparison of mechanical properties with a grade 316L stainless steel was performed in order to evaluate if the CrCoNi alloy is competitive with commercially available structural materials in the nanocrystalline state. A minority phase embedded in the face-centered cubic matrix of the CrCoNi alloy could be observed in multiple annealed states, as well as the as-received and high-pressure torsion processed material. For 200 h of annealing at 500 °C, it was determined that the minority phase has a hexagonal-closed-packed crystal structure. A possible explanation for the formation of the phase is a preferential segregation of Co to stacking faults. PMID:29695142

Impedance of (CoFeZr)0,559(PbZrTiO3)0,441 nanocomposite annealed in a tubular furnace

NASA Astrophysics Data System (ADS)

Boiko, Oleksandr

2016-12-01

The objective of the present research has been to determine the influence of annealing in tubular furnace on capacity of (CoFeZr)0,559(PbZrTiO3)0,441 nanocomposite produced by ion beam sputtering using combined argon and oxygen beam. The phase angle of the nanocomposite directly after preparing demonstrates negative values, which indicates the capacitive type of electrical conductivity of the material. The rapid increase of conductivity when frequency increases indicates hopping conductance in the material. The additional polarization of the nanocomposite occurs with its extinction in the area of high frequencies. The electrons relaxation time has been defined as of ca τ = 1,25×10-4 s. Annealing of nanocomposite sample x = 55.9 at.% at temperature Ta = 548 K causes phase angle obtains positive values in high frequency area, which indicates the change of conduction type from capacitive to inductive. The voltage resonance phenomenon occurs in the material. Annealing in temperature of Ta = 648 K causes changes of the nanomaterials capacity. The additional oxidization of CoFeZr metallic phase nanograins which provides to the potential barrier formation around potential wells (CoFeZr nanoparticles).

The Effect of Heat Treatment on the Crystallography and Mineral Magnetism of Pyrrhotite

NASA Astrophysics Data System (ADS)

Hobart, K.; Feinberg, J. M.; Jones, D. S.

2017-12-01

Pyrrhotite (Fe1-xS, 0 ≤ x ≤ 0.125) is the second most common sulfide mineral after pyrite in the Earth's crust, and its properties are of interest to a wide variety of scientific disciplines, including electrical engineering, physical chemistry, planetary geology and meteoritics, and economic geology. The physical properties of pyrrhotite are highly dependent on slight variations in composition and the ordering of iron vacancies, resulting in a number of possible phases between the endmember compositions of FeS and Fe7S8­­. A common complication in studies on pyrrhotite is that different phases are frequently intergrown, making it difficult to isolate a natural single phase. This has led many researchers to rely on synthesis techniques, which produce a specific structure by using precise iron/sulfur ratios, heating protocols, and controlled cooling. One of the most common synthesis treatments used to create 4C pyrrhotite is an extended heating and annealing process, which is believed to allow the reordering of vacancies to a more thermodynamically stable, ordered state with elevated saturation magnetization. The process was first studied in detail by Schwarz and Vaughan (1972) who produced synthetic pyrrhotite at varying Fe/S ratios with annealing at either 700, 300, or 144°C. The most common method for producing 4C pyrrhotite is heating at 500°C for 24 hours under a vacuum followed by annealing at 250°C for 50 hours. While this technique has been broadly applied in diverse disciplines, there is debate about whether it produces ferrimagnetic, monoclinic 4C pyrrhotite or a different metastable disordered phase. We examined this process using a combination of rock magnetic, X-ray diffraction, and electron imaging techniques to study the effect of heating and annealing on a natural sample of pyrrhotite. Due to the lack of a Besnus transition in the annealed material, our data suggest that the increased magnetization we found following annealing, rather than being an increase in 4C ferrimagnetic pyrrhotite, was the preservation of a ferrimagnetic metastable phase which represents an intermediate to the original intergrown phases. Further work will examine the differences between heat treatments on synthetic and natural pyrrhotites.

Microstructure and Mechanical Properties of V-Nb Microalloyed Ultrafine-Grained Dual-Phase Steels Processed Through Severe Cold Rolling and Intercritical Annealing

NASA Astrophysics Data System (ADS)

Papa Rao, M.; Subramanya Sarma, V.; Sankaran, S.

2017-03-01

Ultrafine-grained (UFG) dual-phase (DP) steel was produced by severe cold rolling (true strain of 2.4) and intercritical annealing of a low carbon V-Nb microalloyed steel in a temperature range of 1003 K to 1033 K (730 °C to 760 °C) for 2 minutes, and water quenching. The microstructure of UFG DP steels consisted of polygonal ferrite matrix with homogeneously distributed martensite islands (both of size <1 µm) and a small fraction of the inter lath films of retained austenite. The UFG DP steel produced through intercritical annealing at 1013 K (740 °C) has good combination of strength (1295 MPa) and ductility (uniform elongation, 13 pct). The nanoscale V- and Nb-based carbides/carbonitrides and spheroidized cementite particles have played a crucial role in achieving UFG DP microstructure and in improving the strength and work hardening. Analysis of work hardening behavior of the UFG DP steels through modified Crussard-Jaoul analysis showed a continuously varying work hardening rate response which could be approximated by 2 or 3 linear regimes. The transmission electron microscopy analysis on post tensile-tested samples indicated that these regimes are possibly related to the work hardening of ferrite, lath, and twin martensite, respectively.

Identification and characterization of the intermediate phase in hybrid organic-inorganic MAPbI3 perovskite.

PubMed

Guo, Xin; McCleese, Christopher; Kolodziej, Charles; Samia, Anna C S; Zhao, Yixin; Burda, Clemens

2016-03-07

Perovskite films were prepared using single step solution deposition at different annealing temperatures and annealing times. The crystal structure, phases and grain size were investigated with XRD, XPS and SEM/EDX. The prepared films show a typical orientation of tetragonal perovskite phase and a gradual transition at room temperature from the yellow intermediate phase to the black perovskite phase. Films with high purity were obtained by sintering at 100 °C. In addition, the chemical composition and crystal structure of intermediate phase were investigated in detail. FTIR, UV-vis and NMR spectra revealed the occurance of DMF complexes. Interestingly, the intermediate phase could be transformed to the black perovskite phase upon X-ray irradiation. In addition, the recovery of the aged perovskite films from a yellow intermediate phase back to the black perovskite was shown to be viable via heating and X-ray irradiation.

Design, construction, and testing a purpose-built climate-controlled solvent vapor annealing chamber for guided self-assembly of block polymer thin films

NASA Astrophysics Data System (ADS)

Gnabasik, Ryan; Haase, Rustin; Baruth, Andrew

2014-03-01

Despite its efficacy to produce well-ordered, periodic nanostructures, the intricate role multiple parameters play in solvent vapor annealing has not been fully established. In solvent vapor annealing a thin polymer film is exposed to the vapors of a solvent(s) thus forming a swollen and mobile layer to direct the self-assembly process at the nanoscale. Recent developments in both theory and experiment have directly identified critical parameters, but controlling them in any systematic way has proven non-trivial. These identified parameters include vapor pressure, solvent concentration in the film, and, critically, the solvent evaporation rate. To explore their role, a purpose-built solvent vapor annealing chamber was designed and constructed. The all-metal chamber is inert to solvent exposure and pneumatically actuated valves allow for precision timing in the introduction and withdrawal of solvent vapor. Furthermore, the mass flow controlled inlet, chamber pressure gauges, in situ spectral reflectance-based thickness monitoring, and high precision micrometer relief valve, give real-time monitoring and control during the annealing and evaporation phases. Using atomic force microscopy to image the annealed films, we are able to map out the parameter space for a series of polystyrene- b-polylactide (Mn = 75 kg/mol and fPLA = 0.28) block polymer thin films with an intrinsic cylindrical morphology and identify their role in directed assembly. Funded by Creighton University Summer Research Grant.

Tuning Phase Composition of TiO2 by Sn(4+) Doping for Efficient Photocatalytic Hydrogen Generation.

PubMed

Wang, Fenglong; Ho, Jie Hui; Jiang, Yijiao; Amal, Rose

2015-11-04

The anatase-rutile mixed-phase photocatalysts have attracted extensive research interest because of the superior activity compared to their single phase counterparts. In this study, doping of Sn(4+) ions into the lattice of TiO2 facilitates the phase transformation from anatase to rutile at a lower temperature while maintaining the same crystal sizes compared to the conventional annealling approach. The mass ratios between anatase and rutile phases can be easily manipulated by varying the Sn-dopant content. Characterization results reveal that the Sn(4+) ions entered into the lattice of TiO2 by substituting some of the Ti(4+) ions and distributed evenly in the matrix of TiO2. The substitution induced the distortion of the lattice structure, which realized the phase transformation from anatase to rutile at a lower temperature and the close-contact phase junctions were consequently formed between anatase and rutile, accounting for the efficient charge separations. The mixed-phase catalysts prepared by doping Sn(4+) ions into the TiO2 exhibit superior activity for photocatalytic hydrogen generation in the presence of Au nanoparticles, relatively to their counterparts prepared by the conventional annealling at higher temperatures. The band allignment between anatase and rutile phases is established based on the valence band X-ray photoelectron spectra and diffuse reflectance spectra to understand the spatial charge separation process at the heterojunction between the two phases. The study provides a new route for the synthesis of mixed-phase TiO2 catalysts for photocatalytic applications and advances the understanding on the enhanced photocatalytic properties of anatase-rutile mixtures.

DOE Office of Scientific and Technical Information (OSTI.GOV)

Jana, S.; Devaraj, A.; Kovarik, L.

Transformation kinetics of metastable body-centered cubic γ-UMo phase in U-10 wt.percent Mo alloy during annealing at sub-eutectoid temperatures of 500C and 400C has been determined as a function of time using detailed microstructural characterization by scanning electron microscopy, X-ray diffraction analysis, scanning transmission electron microscopy, and atom probe tomography. Based on the results, we found that the phase transformation is initiated by cellular transformation at both the temperatures, which results in formation of a lamellar microstructure along prior γ-UMo grain boundaries.

Synthesis and characterization of Fe-Ti-Sb intermetallic compounds: Discovery of a new Slater-Pauling phase

NASA Astrophysics Data System (ADS)

Naghibolashrafi, N.; Keshavarz, S.; Hegde, Vinay I.; Gupta, A.; Butler, W. H.; Romero, J.; Munira, K.; LeClair, P.; Mazumdar, D.; Ma, J.; Ghosh, A. W.; Wolverton, C.

2016-03-01

Compounds of Fe, Ti, and Sb were prepared using arc melting and vacuum annealing. Fe2TiSb , expected to be a full Heusler compound crystallizing in the L 21 structure, was shown by XRD and SEM analyses to be composed of weakly magnetic grains of nominal composition Fe1.5TiSb with iron-rich precipitates in the grain boundaries. FeTiSb, a composition consistent with the formation of a half-Heusler compound, also decomposed into Fe1.5TiSb grains with Ti-Sb rich precipitates and was weakly magnetic. The dominant Fe1.5TiSb phase appears to crystallize in a defective L 21 -like structure with iron vacancies. Based on this finding, a first-principles DFT-based binary cluster expansion of Fe and vacancies on the Fe sublattice of the L 21 structure was performed. Using the cluster expansion, we computationally scanned >103 configurations and predict a novel, stable, nonmagnetic semiconductor phase to be the zero-temperature ground state. This new structure is an ordered arrangement of Fe and vacancies, belonging to the space group R 3 m , with composition Fe1.5TiSb , i.e., between the full- and half-Heusler compositions. This phase can be visualized as alternate layers of L 21 phase Fe2TiSb and C 1b phase FeTiSb, with layering along the [111] direction of the original cubic phases. Our experimental results on annealed samples support this predicted ground-state composition, but further work is required to confirm that the R 3 m structure is the ground state.

Fe-dominated samarskite - a new member of the samarskite 'group'?

NASA Astrophysics Data System (ADS)

Nicolescu, S.; Davis, F. E.; Cornell, D.; Eckert, J., Jr.; Bojar, H.; Walter, F.; Luzik, E.

2013-12-01

Davis and Nicolescu (2011) alluded to the fact that Fe-dominated samarskite from the pegmatite at the Spinelli prospect in Glastonbury, CT is a potential new member of the samarskite mineral 'group'. Further work on untreated material from the same occurrence confirms Fe dominance at the A site, and based on 29 microprobe and four LA-ICP-MS analyses the following empirical formula is obtained: (Fe3+0.384[Y0.239Dy0.026Gd0.018Sm0.012Nd0.007Er0.006Tb0.005Yb0.005Ho0.003Ce0.003Pr0.001Tm0.001]Σ0.326U0.090Mn0.052Th0.047Ti0.033Ca0.009Pb0.006Mg0.003Al0.003Si0.001Sc0.001)0.956(Nb0.814Ta0.149Sn0.026W0.019)1.007O4. The corresponding simplified formula is (Fe3+,Y,U,REE)(Nb,Ta)O4. Due to its UO2 and ThO2 content (9.12 and 4.67 wt. %, respectively) and age of ~ 260 Ma, Spinelli prospect samarskite is completely metamict. Literature data (Simmons et al., 2006 and references therein) suggest that annealing metamict samarskite in a slightly reducing atmosphere of 95 % Ar - 5 % H2 for 12 hrs. at 1100° C will result in recrystallized samarskite. Repeated experiments conducted on powdered Spinelli prospect material under these conditions, at gas flow rates of 100 cm3/min. and 200 cm3/min., resulted in sintered material composed of an ill-defined mixture of fergusonite, columbite, possible samarskite and an unidentified phase. Moreover, in each of the 1100° C annealing experiments a black radioactive sublimate was deposited at the cold end of the annealing apparatus, suggesting significant changes in the chemistry of the annealed material. Annealing the powdered metamict phase for 21 hrs. at 650° C (Tomašić et al., 2004) in a 95 % Ar - 5 % H2 atmosphere at a flow rate of 100 cm3/min. resulted in a mineral phase yielding broad X-ray diffraction peaks, especially at elevated diffraction angles. Because of the broad diffraction peaks and one ambiguous peak impossible to index, attempts to calculate the unit cell parameters of the annealed phase were unsuccessful for either monoclinic or orthorhombic symmetry. Hence, the unambiguous structural characterization of the mineral phase failed. Fe-dominated samarskite does not seem to be restricted to the Spinelli prospect pegmatite. Of the 19 samarskite specimens discussed by Warner and Ewing (1993), 13 are Fe-dominated. Efforts to fully characterize the Spinelli prospect Fe-rich samarskite mineral phase are continuing. REFERENCES Davis & Nicolescu, 2011, Bull. Peabody Museum of Nat. History, 52(1), 135-152 Simmons et al., 2006, Can. Min., 44(5), 1119-1125 Tomašić et al., 2004, N. Jb. Miner. Mh., 2004(4), 163-175 Waren & Ewing, 1993, Am. Min., 78(3-4), 419-424

Synthesis of stable TiO2 nanotubes: effect of hydrothermal treatment, acid washing and annealing temperature.

PubMed

López Zavala, Miguel Ángel; Lozano Morales, Samuel Alejandro; Ávila-Santos, Manuel

2017-11-01

Effect of hydrothermal treatment, acid washing and annealing temperature on the structure and morphology of TiO 2 nanotubes during the formation process was assessed. X-ray diffraction, scanning electron microscopy (SEM), transmission electron microscopy (TEM) and energy dispersive X-ray spectroscopy analysis were conducted to describe the formation and characterization of the structure and morphology of nanotubes. Hydrothermal treatment of TiO 2 precursor nanoparticles and acid washing are fundamental to form and define the nanotubes structure. Hydrothermal treatment causes a change in the crystallinity of the precursor nanoparticles from anatase phase to a monoclinic phase, which characterizes the TiO 2 nanosheets structure. The acid washing promotes the formation of high purity nanotubes due to Na + is exchanged from the titanate structure to the hydrochloric acid (HCl) solution. The annealing temperature affects the dimensions, structure and the morphology of the nanotubes. Annealing temperatures in the range of 400 °C and 600 °C are optimum to maintain a highly stable tubular morphology of nanotubes. Additionally, nanotubes conserve the physicochemical properties of the precursor Degussa P25 nanoparticles. Temperatures greater than 600 °C alter the morphology of nanotubes from tubular to an irregular structure of nanoparticles, which are bigger than those of the precursor material, i.e., the crystallinity turn from anatase phase to rutile phase inducing the collapse of the nanotubes.

Structure and magnetic properties of Alnico ribbons

NASA Astrophysics Data System (ADS)

Zhang, Ce; Li, Ying; Han, Xu-Hao; Du, Shuai-long; Sun, Ji-bing; Zhang, Ying

2018-04-01

Al-Ni-Co alloy has been widely applied in various industrial fields due to its excellent thermal and magnetic stability. In this paper, new Al-Ni-Co ribbons are prepared by simple processes combining melt-spinning with annealing, and their phase transition, microstructure and magnetic properties are studied. The results show that after as-spun ribbons are annealed, the grain size of ribbons increases from 1.1 ± 0.3 μm to 4.8 ± 0.8 μm, but still much smaller than that of the bulk Al-Ni-Co alloy manufactured by traditional technologies. In addition, some rod-like Al70Co20Ni10-type, Al9Co2-type and Fe2Nb-type phases are precipitated at grain boundaries; simultaneously, the distinct spinodal decomposition microstructure with periodic ingredient variation is thoroughly formed in all grains by the reaction of α → α1 + α2. Furthermore, the α1 and α2 distribute alternately like a maze, the Fe-Co-rich α1 phase holds 35.9-47.3 vol%, while the Al-Ni-rich α2 phase occupies the rest. Finally, the coercivity of annealed ribbons can reach to 485.3 ± 76.6 Oe. If the annealed ribbons are further aged at 560 °C, their Hc even increases to 738.1 ± 81.0 Oe. The coercivity mechanism is discussed by the combination of microstructure and domain structure.

Synthesis of embedded titanium dioxide nanoparticles by oxygen ion implantation in titanium films

NASA Astrophysics Data System (ADS)

Rukade, Deepti. A.; Desai, C. A.; Kulkarni, Nilesh; Tribedi, L. C.; Bhattacharyya, Varsha

2013-02-01

Thin films of titanium of 100nm thickness are deposited on fused silica substrates. These films are implanted by oxygen ions with implantation energy of 60keV obtained from ECR based highly charged ion accelerator. The implanted films are later annealed in a tube furnace to establish nanophase formation. The post implanted annealed films are characterized by UV-Visible Spectroscopy and Glancing Angle X-ray Diffraction technique (GAXRD). The phase formed and particle size is determined by GAXRD. Nanoparticle formation is confirmed by the UV-VIS spectroscopic analysis that shows quantum size effects in the form of a blue shift in the band-gap energy of titanium-oxide.

Temperature dependent structural and magnetic study of Co-sputtered Fe-Al thin film

NASA Astrophysics Data System (ADS)

Vyas, Anupam; Brajpuriya, Ranjeet

2017-05-01

The authors have deposited co-sputtered Fe-Al thin film on a glass substrate. It is the first ever reporting of Fe and Al co-sputtering in an Argon atmosphere under vacuum conditions. The sample was annealed at 200°C, 300°C, 400°C, so as to allow different phase formation in it. To study the structural and magnetic properties of the samples the GIXRD, XRR and MOKE measurements were done. After annealing at 400°C we observed disordered FeAl formation and which after further converted to more ordered phase which is also confirmed from reflectivity measurements. The magnetic measurement shows the magnetic nature of the sample even after annealing at 400°C/5hr.

DOE Office of Scientific and Technical Information (OSTI.GOV)

Simoes, A.Z., E-mail: alezipo@yahoo.com; Riccardi, C.S.; Dos Santos, M.L.

Bismuth ferrite thin films were deposited on Pt/Ti/SiO{sub 2}/Si substrates by a soft chemical method and spin-coating technique. The effect of annealing atmosphere (air, N{sub 2} and O{sub 2}) on the structure and electrical properties of the films are reported. X-ray diffraction analysis reveals that the film annealed in air atmosphere is a single-phase perovskite structure. The films annealed in air showed better crystallinity and the presence of a single BFO phase leading to lower leakage current density and superior ferroelectric hysteresis loops at room temperature. In this way, we reveal that BFO film crystallized in air atmosphere by themore » soft chemical method can be useful for practical applications, including nonvolatile digital memories, spintronics and data-storage media.« less

Special Features of Induction Annealing of Friction Stir Welded Joints of Medium-Alloy Steels

NASA Astrophysics Data System (ADS)

Priymak, E. Yu.; Stepanchukova, A. V.; Bashirova, E. V.; Fot, A. P.; Firsova, N. V.

2018-01-01

Welded joints of medium-alloy steels XJY750 and 40KhN2MA are studied in the initial condition and after different variants of annealing. Special features of the phase transformations occurring in the welded steels are determined. Optimum modes of annealing are recommended for the studied welded joints of drill pipes, which provide a high level of mechanical properties including the case of impact loading.

Effects of Intercritical Annealing Temperature on Mechanical Properties of Fe-7.9Mn-0.14Si-0.05Al-0.07C Steel

DOE PAGES

Zhao, Xianming; Shen, Yongfeng; Qiu, Lina; ...

2014-12-09

A medium Mn steel has been designed to achieve an excellent combination of strength and ductility based on the TRIP (Transformation Induced Plasticity) concept for automotive applications. Following six passes of hot rolling at 850 °C, the Fe-7.9Mn-0.14Si-0.05Al-0.07C (wt.%) steel was warm-rolled at 630 °C for seven passes and subsequently air cooled to room temperature. The sample was subsequently intercritically annealed at various temperatures for 30 min to promote the reverse transformation of martensite into austenite. The obtained results show that the highest volume fraction of austenite is 39% for the sample annealed at 600 °C. This specimen exhibits amore » yield stress of 910 MPa and a high ultimate tensile stress of 1600 MPa, with an elongation-to-failure of 0.29 at a strain rate of 1 × 10⁻³/s. The enhanced work-hardening ability of the investigated steel is closely related to martensitic transformation and the interaction of dislocations. Especially, the alternate arrangement of acicular ferrite (soft phase) and ultrafine austenite lamellae (50–200 nm, strong and ductile phase) is the key factor contributing to the excellent combination of strength and ductility. On the other hand, the as-warm-rolled sample also exhibits the excellent combination of strength and ductility, with elongation-to-failure much higher than those annealed at temperatures above 630 °C.« less

Synthesis and characterization of delafossite thin films by reactive RF magnetron sputtering

NASA Astrophysics Data System (ADS)

Asmat Uceda, Martin Antonio

This work presents a comparative study on optical and electrical properties of CuAlO2 thin films on sapphire (0001) substrates deposited with two different growth conditions using reactive RF-magnetron sputtering technique from metallic Cu and Al targets. CuAlO2 is a very promising material for transparent electronic applications, it is intended that comparison of results obtained from both approaches, could lead to optimization and control of the physical properties of this material, namely its electrical conductivity and optical transmittance. All samples were heat treated at 1100°C using rapid thermal annealing with varying time and rate of cooling. The effect of sputtering conditions and different annealing time on phase formation and evolution is studied with X-ray diffraction (XRD) and scanning electron microscopy (SEM). It is found that for most of the samples CuAlO2 phase is formed after 60 min of annealing time, but secondary phases were also present that depend on the deposition conditions. However, pure CuAlO2 phase was obtained for annealed CuO on sapphire films with annealing time of 60 min. The optical properties obtained from UV-Visible spectroscopic measurement reveals indirect and direct optical band gaps for CuAlO2 films and were found to be 2.58 and 3.72 eV respectively. The films show a transmittance of about 60% in the visible range. Hall effect measurements indicate p-type conductivity. Van der Pauw technique was used to measure resistivity of the samples. The highest electrical conductivity and charge carrier concentration obtained were of 1.01x10-1S.cm -1 and 3.63 x1018 cm-3 respectively.

The phase state at high temperatures in the MOX-SiO 2 system

NASA Astrophysics Data System (ADS)

Nakamichi, S.; Kato, M.; Sunaoshi, T.; Uchida, T.; Morimoto, K.; Kashimura, M.; Kihara, Y.

2009-06-01

Influence of impurity Si on microstructure in a plutonium and uranium mixed oxide (MOX), which is used for fast breeder reactor fuel, was investigated, and phase state in 25% SiO 2 - (U 0.7Pu 0.3)O 2 was observed as a function of oxygen chemical potential. Compounds composed of Pu and Si with other elements were observed at grain boundaries of the MOX parent phase in the specimens after annealing. These compounds were not observed in the grain interior and the MOX phase was not affected significantly by impurity Si. It was found that the compounds tended to form more observably with decreasing O/M ratio and with increasing annealing temperatures.

Effect of Mg(2+) doping on beta-alpha phase transition in tricalcium phosphate (TCP) bioceramics.

PubMed

Frasnelli, Matteo; Sglavo, Vincenzo M

2016-03-01

The beta to alpha transition in tricalcium phosphate (TCP) bioceramics containing different amount of magnesium was studied in the present work. Mg-doped TCP powder was obtained by solid-state reaction starting from pure calcium carbonate, ammonium phosphate dibasic and magnesium oxide powders. The β to α transformation temperature was identified by dilatometric and thermo-differential analyses. Small pellets produced by uniaxial pressing samples were employed to study the influence of Mg(2+) on the transition kinetic, after sintering at 1550°C and subsequent slow or fast cooling down to room temperature. The evolution of β- and α-TCP crystalline phases during each thermal treatment was determined by X-ray powder diffraction analysis combined with Rietveld method-based software An annealing treatment, suitable to reconvert metastable α phase to the more clinically suitable β phase, was also investigated. It is shown that the presence of magnesium within the TCP lattice strongly influences the kinetic of the β⇆α phase transition, promoting the spontaneous α→β reconversion even upon fast cooling, or slowing down the β→α transition during heating. Similarly, it allows the α→β transformation in TCP sintered components by optimized annealing treatment at 850°C. This work concerns the effect of Mg(2+) doping on the β→α phase reconstructive transition in tricalcium phosphate (TCP), one of the most important bio-resorbable materials for bone tissue regeneration. The transition occurs upon the sintering process and is has been shown to be strongly irreversible upon cooling, leading to technological issues such as poor mechanical properties and excessive solubility due to the presence of metastable α-phase. This paper points out the kinetic contribution of Mg(2+) on the spontaneous α→β reconversion also upon fast cooling (i.e. quenching). Moreover, an annealing treatment has been shown to be beneficial to remove the retained α-phase in sintered TCP components, the presence of Mg promoting the reconversion process. Copyright © 2016 Acta Materialia Inc. Published by Elsevier Ltd. All rights reserved.

Effect of heat treatment on the structure and hardness of high-entropy alloys CoCrFeNiMnV x ( x = 0.25, 0.5, 0.75, 1)

NASA Astrophysics Data System (ADS)

Shaysultanov, D. G.; Stepanov, N. D.; Salishchev, G. A.; Tikhonovsky, M. A.

2017-06-01

High-entropy alloys CoCrFeNiMnVKharkov Institute of Physics and Technology, ul. Akademicheskaya 1, Kharkov 61108 (Kharkov Institute of Physics and Technology, ul. Akademicheskaya 1, Kharkov 61108 = 0.25, 0.5, 0.75, 1) were prepared by vacuum arc melting. The structure and microhardness of the alloys have been studied in the cast state and after annealing at temperatures of 700-1100°C. It has been found that the alloys consist of the fcc (γ) solid solution and intermetallic sigma (σ) phase. The volume fraction of the σ phase increases with increasing vanadium content. As a result of annealing, phase transformations occur, including the precipitation of σ particles from the γ phase and, vice versa, the precipitation of γ particles from the σ phase. It has been shown that the change in the volume fraction of the σ phase upon annealing occurs due to the changes in the total content of σ-forming elements, chromium and vanadium, in accordance with the lever rule. With increasing temperature, the volume fraction of the σ phase varies nonmonotonically; first, it increases, then it decreases. The microhardness of the alloys correlates well with the change in the volume fraction of the σ phase. The mechanisms of the phase transformations and quantitative relationships between chemical and phase compositions of the alloys and their hardness are discussed.

Crystallization Kinetics in Fluorochloroziroconate Glass-Ceramics

NASA Astrophysics Data System (ADS)

Alvarez, Carlos J.

Annealing fluorochlorozirconate (FCZ) glasses nucleates BaCl2 nanocrystals in the glass matrix, resulting in a nanocomposite glass-ceramic that has optical properties suitable for use as a medical X-ray imaging plate. Understanding the way in which the BaCl¬2 nanocrystal nucleation, growth and phase transformation processes proceed is critical to controlling the optical behavior. However, there is a very limited amount of information about the formation, morphology, and distribution of the nanocrystalline particles in FCZ glass-ceramics. In this thesis, the correlation between the microstructure and the crystallization kinetics of FCZ glass-ceramics, are studied in detail. In situ X-ray diffraction and transmission electron microscopy annealing experiments are used to analyze the crystal structure, size and distribution of BaCl 2 nanocrystals in FCZ glass-ceramics as a function of annealing rate and temperature. Microstructural analysis of the early stages on nucleation identified the formation of both BaCl2 and BaF2 nanocrystals. Annealing FCZ glass-ceramics above 280°C can cause the formation of additional glass matrix phase crystals, their microstructure and the annealing parameters required for their growth are identified. As the crystalline phases grow directly from the glass, small variations in processing of the glass can have a profound influence on the crystallization process. The information obtained from these experiments improves the understanding of the nucleation, growth and phase transformation process of the BaCl¬2 nanocrystals and additional crystalline phases that form in FCZ glass-ceramics, and may help expedite the implementation of FCZ glass-ceramics as next-generation X-ray detectors. Lastly, as these glass-ceramics may one day be commercialized, an investigation into their degradation in different environmental conditions was also performed. The effects of direct contact with water or prolonged exposure to humid environments on the microstructure and the optical properties for FCZ glasses and glass-ceramics was explored.

The effect of annealing on structural and optical properties of α-Fe2O3/CdS/α-Fe2O3 multilayer heterostructures

NASA Astrophysics Data System (ADS)

Saleem, M.; Durrani, S. M. A.; Saheb, N.; Al-Kuhaili, M. F.; Bakhtiari, I. A.

2014-11-01

Multilayered thin film heterostructures of α-Fe2O3/CdS/α-Fe2O3 were prepared through physical vapor deposition. Each α-Fe2O3 layer was deposited by e-beam evaporation of iron in an oxygen atmosphere. The CdS layer was deposited by thermal evaporation in a vacuum. The effect of post annealing of multilayered thin films in air in the temperature range 250 °C to 450 °C was investigated. Structural characterization indicated the growth of the α-Fe2O3 phase with a polycrystalline structure without any CdS crystalline phase. As-deposited multilayer heterostructures were amorphous and transformed into polycrystalline upon annealing. The surface modification of the films during annealing was revealed by scanning electron microscopy. Spectrophotometric measurements were used to determine the optical properties, including the transmittance, absorbance, and band gap. All the films had both direct as well as indirect band gaps.

Nano crystalline Bi2(VO5) phases in lithium bismuth borate glasses containing mixed vanadium-nickel oxides

NASA Astrophysics Data System (ADS)

Yadav, Arti; Khasa, S.; Dahiya, M. S.; Agarwal, A.

2016-05-01

Glass composition 7V2O5.23Li2O.20Bi2O3.50B2O3 and x(2NiO.V2O5).(30-x)Li2O.20Bi2O3.50B2O3, x=0, 2, 5, 7 and 10, were produced by conventional melt quenching technique. The quenched amorphous glass samples were annealed at temperatures 400°C and 500°C for 6 hours. The Bi2(VO5) crystallite were grown in all prepared glass matrix. Tn vanadium lithium bismuth borate glass (annealed), the some phrase of V2O5-crystal were observed along with the nano crystalline Bi2(VO5) phase. The sharp peaks in FTTR spectra of all annealed compositions were also compatible with the XRD diffraction peaks of the system under investigation. Average crystalline size (D) of the Bi2(VO5) nano-crystallite was ~30nm for samples annealed at 400°C and ~42nm for samples annealed at 500°C. Lattice parameter and the lattice strain for all the samples was also calculated corresponding to the (113) plane of Bi2(VO5) crystallite.

Electrical Characteristics and Preparation of (Ba0.5Sr0.5)TiO3 Films by Spray Pyrolysis and Rapid Thermal Annealing

NASA Astrophysics Data System (ADS)

Koo, Horng-Show; Chen, Mi; Ku, Hong-Kou; Kawai, Tomoji

2007-04-01

Functional films of (Ba0.5Sr0.5)TiO3 on Pt (1000 Å)/Ti (100 Å)/SiO2 (2000 Å)/Si substrates are prepared by spray pyrolysis and subsequently rapid thermal annealing. Barium nitrate, strontium nitrate and titanium isopropoxide are used as starting materials with ethylene glycol as solvent. For (Ba0.5Sr0.5)TiO3 functional thin film, thermal characteristics of the precursor powder scratched from as-sprayed films show a remarkable peak around 300-400 °C and 57.7% weight loss up to 1000 °C. The as-sprayed precursor film with coffee-like color and amorphous-like phase is transformed into the resultant film with white, crystalline perovskite phase and characteristic peaks (110) and (100). The resultant films show correspondent increases of dielectric constant, leakage current and dissipation factor with increasing annealing temperatures. The dielectric constant is 264 and tangent loss is 0.21 in the resultant films annealed at 750 °C for 5 min while leakage current density is 1.5× 10-6 A/cm2 in the film annealed at 550 °C for 5 min.

Influence of Al Addition Upon the Microstructure and Mechanical Property of Dual-Phase 9Cr-ODS Steels

NASA Astrophysics Data System (ADS)

Zhou, Xiaosheng; Ma, Zongqing; Yu, Liming; Huang, Yuan; Li, Huijun; Liu, Yongchang

2018-06-01

With Al addition, dual-phase oxide dispersion strengthened (ODS) steels consisting of martensite and ferrite are fabricated by spark plasma sintering. It is found that Al addition has a negligible effect on martensite lath size, while the amount and size of ferrite grains are related to the Al content. M23C6 (M = Fe, Cr) carbides have been identified within the ferrite grains or along ferrite boundaries. With increasing Al concentration, more fine Y-Al-O oxide nanoparticles are formed. Upon annealing treatment, homogeneous and refined distribution of ferrite grains is obtained, which may involve the particle-stimulated nucleation of recrystallization caused by the large sized M23C6. As Al is increased from 0.05 to 0.1 wt%, the tensile strength of the annealed steel is decreased, as well as its ductility. For the annealed 9Cr-ODS steel containing 0.1 wt% Al, in tensile loading the large sized M23C6 along ferrite boundaries would facilitate the cracking along boundaries between the hard annealed ferrite and soft annealed martensite, producing the mixed fracture of dimple and intergranular fracture.

Process for preparing superconducting film having substantially uniform phase development

DOEpatents

Bharacharya, Raghuthan; Parilla, Philip A.; Blaugher, Richard D.

1995-01-01

A process for preparing a superconducting film, such as a thallium-barium-calcium-copper oxide superconducting film, having substantially uniform phase development. The process comprises providing an electrodeposition bath having one or more soluble salts of one or more respective potentially superconducting metals in respective amounts adequate to yield a superconducting film upon subsequent appropriate treatment. Should all of the metals required for producing a superconducting film not be made available in the bath, such metals can be a part of the ambient during a subsequent annealing process. A soluble silver salt in an amount between about 0.1% and about 4.0% by weight of the provided other salts is also provided to the bath, and the bath is electrically energized to thereby form a plated film. The film is annealed in ambient conditions suitable to cause formation of a superconductor film. Doping with silver reduces the temperature at which the liquid phase appears during the annealing step, initiates a liquid phase throughout the entire volume of deposited material, and influences the nucleation and growth of the deposited material.

Process for preparing superconducting film having substantially uniform phase development

DOEpatents

Bharacharya, R.; Parilla, P.A.; Blaugher, R.D.

1995-12-19

A process is disclosed for preparing a superconducting film, such as a thallium-barium-calcium-copper oxide superconducting film, having substantially uniform phase development. The process comprises providing an electrodeposition bath having one or more soluble salts of one or more respective potentially superconducting metals in respective amounts adequate to yield a superconducting film upon subsequent appropriate treatment. Should all of the metals required for producing a superconducting film not be made available in the bath, such metals can be a part of the ambient during a subsequent annealing process. A soluble silver salt in an amount between about 0.1% and about 4.0% by weight of the provided other salts is also provided to the bath, and the bath is electrically energized to thereby form a plated film. The film is annealed in ambient conditions suitable to cause formation of a superconductor film. Doping with silver reduces the temperature at which the liquid phase appears during the annealing step, initiates a liquid phase throughout the entire volume of deposited material, and influences the nucleation and growth of the deposited material. 3 figs.

Nanotwinning and structural phase transition in CdS quantum dots

NASA Astrophysics Data System (ADS)

Kumar, Pragati; Saxena, Nupur; Chandra, Ramesh; Gupta, Vinay; Agarwal, Avinash; Kanjilal, Dinakar

2012-10-01

Nanotwin structures are observed in high-resolution transmission electron microscopy studies of cubic phase CdS quantum dots in powder form by chemical co-precipitation method. The deposition of thin films of nanocrystalline CdS is carried out on silicon, glass, and TEM grids keeping the substrates at room temperature (RT) and 200°C by pulsed laser ablation. These films are then subjected to thermal annealing at different temperatures. Glancing angle X-ray diffraction results confirm structural phase transitions after thermal annealing of films deposited at RT and 200°C. The variation of average particle size and ratio of intensities in Raman peaks I 2LO/ I 1LO with annealing temperature are studied. It is found that electron-phonon interaction is a function of temperature and particle size and is independent of the structure. Besides Raman modes LO, 2LO and 3LO of CdS at approximately 302, 603, and 903 cm-1 respectively, two extra Raman modes at approximately 390 and 690 cm-1 are studied for the first time. The green and orange emissions observed in photoluminescence are correlated with phase transition.

Nanotwinning and structural phase transition in CdS quantum dots.

PubMed

Kumar, Pragati; Saxena, Nupur; Chandra, Ramesh; Gupta, Vinay; Agarwal, Avinash; Kanjilal, Dinakar

2012-10-23

Nanotwin structures are observed in high-resolution transmission electron microscopy studies of cubic phase CdS quantum dots in powder form by chemical co-precipitation method. The deposition of thin films of nanocrystalline CdS is carried out on silicon, glass, and TEM grids keeping the substrates at room temperature (RT) and 200°C by pulsed laser ablation. These films are then subjected to thermal annealing at different temperatures. Glancing angle X-ray diffraction results confirm structural phase transitions after thermal annealing of films deposited at RT and 200°C. The variation of average particle size and ratio of intensities in Raman peaks I2LO/I1LO with annealing temperature are studied. It is found that electron-phonon interaction is a function of temperature and particle size and is independent of the structure. Besides Raman modes LO, 2LO and 3LO of CdS at approximately 302, 603, and 903 cm-1 respectively, two extra Raman modes at approximately 390 and 690 cm-1 are studied for the first time. The green and orange emissions observed in photoluminescence are correlated with phase transition.

X-ray diffraction, Raman, and photoacoustic studies of ZnTe nanocrystals

NASA Astrophysics Data System (ADS)

Ersching, K.; Campos, C. E. M.; de Lima, J. C.; Grandi, T. A.; Souza, S. M.; da Silva, D. L.; Pizani, P. S.

2009-06-01

Nanocrystalline ZnTe was prepared by mechanical alloying. X-ray diffraction (XRD), energy dispersive spectroscopy, Raman spectroscopy, and photoacoustic absorption spectroscopy techniques were used to study the structural, chemical, optical, and thermal properties of the as-milled powder. An annealing of the mechanical alloyed sample at 590 °C for 6 h was done to investigate the optical properties in a defect-free sample (close to bulk form). The main crystalline phase formed was the zinc-blende ZnTe, but residual trigonal tellurium and hexagonal ZnO phases were also observed for both as-milled and annealed samples. The structural parameters, phase fractions, average crystallite sizes, and microstrains of all crystalline phases were obtained from Rietveld analyses of the X-ray patterns. Raman results corroborate the XRD results, showing the longitudinal optical phonons of ZnTe (even at third order) and those modes of trigonal Te. Nonradiative surface recombination and thermal bending heat transfer mechanisms were proposed from photoacoustic analysis. An increase in effective thermal diffusivity coefficient was observed after annealing and the carrier diffusion coefficient, the surface recombination velocity, and the recombination time parameters remained the same.

Characterization of Novel Thin-Films and Structures for Integrated Circuit and Photovoltaic Applications

NASA Astrophysics Data System (ADS)

Zhao, Zhao

Thin films have been widely used in various applications. This research focuses on the characterization of novel thin films in the integrated circuits and photovoltaic techniques. The ion implanted layer in silicon can be treated as ion implanted thin film, which plays an essential role in the integrated circuits fabrication. Novel rapid annealing methods, i.e. microwave annealing and laser annealing, are conducted to activate ion dopants and repair the damages, and then are compared with the conventional rapid thermal annealing (RTA). In terms of As+ and P+ implanted Si, the electrical and structural characterization confirms that the microwave and laser annealing can achieve more efficient dopant activation and recrystallization than conventional RTA. The efficient dopant activation in microwave annealing is attributed to ion hopping under microwave field, while the liquid phase growth in laser annealing provides its efficient dopant activation. The characterization of dopants diffusion shows no visible diffusion after microwave annealing, some extent of end range of diffusion after RTA, and significant dopant diffusion after laser annealing. For photovoltaic applications, an indium-free novel three-layer thin-film structure (transparent composited electrode (TCE)) is demonstrated as a promising transparent conductive electrode for solar cells. The characterization of TCE mainly focuses on its optical and electrical properties. Transfer matrix method for optical transmittance calculation is validated and proved to be a desirable method for predicting transmittance of TCE containing continuous metal layer, and can estimate the trend of transmittance as the layer thickness changes. TiO2/Ag/TiO2 (TAgT) electrode for organic solar cells (OSCs) is then designed using numerical simulation and shows much higher Haacke figure of merit than indium tin oxide (ITO). In addition, TAgT based OSC shows better performance than ITO based OSC when compatible hole transfer layer is employed. The electrical and structural characterization of hole transfer layers (HTLs) in OSCs reveals MoO3 is the compatible HTL for TAgT anode. In the end, the reactive ink printed Ag film for solar cell contact application is studied by characterizing its electromigration lifetime. A percolative model is proposed and validated for predicting the resistivity and lifetime of printed Ag thin films containing porous structure.

Effects of High-Temperature Annealing in Air on Hi-Nicalon Fiber-Reinforced Celsian Matrix Composites

NASA Technical Reports Server (NTRS)

Bansal, Narottam P.

2008-01-01

BN/SiC-coated Hi-Nicalon fiber-reinforced celsian matrix composites (CMC) were annealed for 100 h in air at various temperatures to 1200 C, followed by flexural strength measurements at room temperature. Values of yield stress and strain, ultimate strength, and composite modulus remain almost unchanged for samples annealed up to 1100 C. A thin porous layer formed on the surface of the 1100 C annealed sample and its density decreased from 3.09 to 2.90 g/cu cm. The specimen annealed at 1200 C gained 0.43 wt%, was severely deformed, and was covered with a porous layer of thick shiny glaze which could be easily peeled off. Some gas bubbles were also present on the surface. This surface layer consisted of elongated crystals of monoclinic celsian and some amorphous phase(s). The fibers in this surface ply of the CMC had broken into small pieces. The fiber-matrix interface strength was characterized through fiber push-in technique. Values of debond stress, alpha(sub d), and frictional sliding stress, tau(sub f), for the as-fabricated CMC were 0.31+/-0.14 GPa and 10.4+/-3.1 MPa, respectively. These values compared with 0.53+/-0.47 GPa and 8.33+/-1.72 MPa for the fibers in the interior of the 1200 C annealed sample, indicating hardly any change in fiber-matrix interface strength. The effects of thermal aging on microstructure were investigated using scanning electron microscopy. Only the surface ply of the 1200 C annealed specimens had degraded from oxidation whereas the bulk interior part of the CMC was unaffected. A mechanism is proposed explaining the various steps involved during the degradation of the CMC on annealing in air at 1200 C.

Annealing group III-V compound doped silicon-germanium alloy for improved thermo-electric conversion efficiency

NASA Technical Reports Server (NTRS)

Vandersande, Jan W. (Inventor); Wood, Charles (Inventor); Draper, Susan L. (Inventor)

1989-01-01

The thermoelectric conversion efficiency of a GaP doped SiGe alloy is improved about 30 percent by annealing the alloy at a temperature above the melting point of the alloy, preferably stepwise from 1200 C to 1275 C in air to form large grains having a size over 50 microns and to form a GeGaP rich phase and a silicon rich phase containing SiP and SiO2 particles.

Twin-induced phase transition from β-Ga2O3 to α-Ga2O3 in Ga2O3 thin films

NASA Astrophysics Data System (ADS)

Choi, Byeongdae; Allabergenov, Bunyod; Lyu, Hong-Kun; Lee, Seong Eui

2018-06-01

We deposited a 300-nm-thick Ga2O3 thin film on an amorphous SiO2/Si substrate via pulsed laser deposition. X-ray diffraction patterns revealed the formation of β-Ga2O3 phase at a substrate temperature of 700 °C. X-ray photoelectron spectra indicated that the degree of oxidation increased after annealing at 700 °C. Further annealings at higher temperatures led to a transition of the β-Ga2O3 phase to the α-Ga2O3 phase; this transition was caused by the twin structure formed during the crystallinity improvement process. In addition, we discuss the mechanism of the transition from the β phase to the α phase in the β-Ga2O3 thin films.

Synthesis of a single phase of high-entropy Laves intermetallics in the Ti-Zr-V-Cr-Ni equiatomic alloy

NASA Astrophysics Data System (ADS)

Yadav, T. P.; Mukhopadhyay, Semanti; Mishra, S. S.; Mukhopadhyay, N. K.; Srivastava, O. N.

2017-12-01

The high-entropy Ti-Zr-V-Cr-Ni (20 at% each) alloy consisting of all five hydride-forming elements was successfully synthesised by the conventional melting and casting as well as by the melt-spinning technique. The as-cast alloy consists entirely of the micron size hexagonal Laves Phase of C14 type; whereas, the melt-spun ribbon exhibits the evolution of nanocrystalline Laves phase. There was no evidence of any amorphous or any other metastable phases in the present processing condition. This is the first report of synthesising a single phase of high-entropy complex intermetallic compound in the equiatomic quinary alloy system. The detailed characterisation by X-ray diffraction, scanning and transmission electron microscopy and energy-dispersive X-ray spectroscopy confirmed the existence of a single-phase multi-component hexagonal C14-type Laves phase in all the as-cast, melt-spun and annealed alloys. The lattice parameter a = 5.08 Å and c = 8.41 Å was determined from the annealed material (annealing at 1173 K). The thermodynamic calculations following the Miedema's approach support the stability of the high-entropy multi-component Laves phase compared to that of the solid solution or glassy phases. The high hardness value (8.92 GPa at 25 g load) has been observed in nanocrystalline high-entropy alloy ribbon without any cracking. It implies that high-yield strength ( 3.00 GPa) and the reasonable fracture toughness can be achieved in this high-entropy material.

Structural effects due to the incorporation of Ar atoms in the lattice of ZrO 2 thin films prepared by ion beam assisted deposition

NASA Astrophysics Data System (ADS)

Holgado, J. P.; Escobar Galindo, R.; van Veen, A.; Schut, H.; de Hosson, J. Th. M.; González-Elipe, A. R.

2002-09-01

Two sets of ZrO 2 thin films have been prepared at room temperature by ion beam induced chemical vapour deposition and subsequently annealed up to 1323 K. The two sets of samples have been prepared by using either O 2+ or mixtures of (O 2++Ar +) ions for the decomposition of a volatile metallorganic precursor of zirconium. The structure and microstructure of these two sets of samples have been determined by means of X-ray diffraction, Fourier transform infrared spectroscopy and positron beam analysis (PBA). The samples were very compact and dense and had a very low-surface roughness. After annealing in air at T⩾573 K both sets of films were transparent and showed similar refraction indexes. For the (O 2++Ar +)-ZrO 2 thin films it is shown by X-ray photoelectron spectroscopy and Rutherford back scattering that a certain amount of incorporated Ar (5-6 at.%) remains incorporated within the oxide lattice. No changes were detected in the amount of incorporated Ar even after annealing at T=773 K. For higher annealing temperatures ( T>1073 K), the amount of Ar starts to decrease, and at T=1223 K only residual amounts of Ar (<0.4%) remain within the lattice. It has been found that as far as Ar atoms remain incorporated within the ZrO 2 network, the (O 2+-Ar +)-ZrO 2 films present a cubic/tetragonal phase. When the amount of "embedded" Ar decreases, the crystalline phase reverts to monoclinic, the majority phase observed for the (O 2+)-ZrO 2 films after any annealing treatments. The microstructure of the films after different annealing treatments has been investigated by PBA. The presence of Ar ions and the initial amorphous state of the layers were detected by this technique. An increase of the open volume was observed after annealing up to 773 K in both sets of samples. For higher annealing temperatures the samples showed a progressive crystallisation resulting in a decrease of the open volume. During this sintering the samples without embedded Ar present a higher concentration of open volume defects. After the release of Ar occurs ( T⩾1223 K) both samples approach to a similar defect free state. The incorporation of Ar within the ZrO 2 thin film structure, is proposed as the main factor contributing to the stabilisation of the cubic/tetragonal phase of ZrO 2 at room temperature.

Antiferroelectricity in lanthanum doped zirconia without metallic capping layers and post-deposition/-metallization anneals

NASA Astrophysics Data System (ADS)

Wang, Zheng; Gaskell, Anthony Arthur; Dopita, Milan; Kriegner, Dominik; Tasneem, Nujhat; Mack, Jerry; Mukherjee, Niloy; Karim, Zia; Khan, Asif Islam

2018-05-01

We report the effects of lanthanum doping/alloying on antiferroelectric (AFE) properties of ZrO2. Starting with pure ZrO2, an increase in La doping leads to the narrowing of the AFE double hysteresis loops and an increase in the critical voltage/electric field for AFE → ferroelectric transition. At higher La contents, the polarization-voltage characteristics of doped/alloyed ZrO2 resemble that of a non-linear dielectric without any discernible AFE-type hysteresis. X-ray diffraction based analysis indicates that the increased La content while preserving the non-polar, parent AFE, tetragonal P42/nmc phase leads to a decrease in tetragonality and the (nano-)crystallite size and an increase in the unit cell volume. Furthermore, antiferroelectric behavior is obtained in the as-deposited thin films without requiring any capping metallic layers and post-deposition/-metallization anneals due to which our specific atomic layer deposition system configuration crystallizes and stabilizes the AFE tetragonal phase during growth.

Band edge tailoring of InGaAs/AlAsSb coupled double quantum wells for a monolithically integrated all-optical switch.

PubMed

Feng, Jijun; Akimoto, Ryoichi; Gozu, Shin-ichiro; Mozume, Teruo; Hasama, Toshifumi; Ishikawa, Hiroshi

2013-07-01

We demonstrate a compact all-optical Michelson interferometer (MI) gating switch with monolithic integration of two different bandgap energies. Based on the ion-induced intermixing in InGaAs/AlAsSb coupled double quantum wells, the blueshift of the band edge can be tailored. Through phosphorus ion implantation with a dose of 5 × 10(14) cm(-2) and subsequent annealing at 720 °C for 60 s, an implanted sample can acquire a high transmittance compared with the as-grown one. Meanwhile, the cross-phase modulation (XPM) efficiency of a non-implanted sample undergoing the same annealing process decreases little. An implanted part for signal propagation and a non-implanted section for XPM are thus monolithically integrated for an MI switch by an area-selective manner. Full switching of a π-rad nonlinear phase shift is achieved with pump pulse energy of 5.6 pJ at a 10-GHz repetition rate.

Towards the Better: Intrinsic Property Amelioration in Bulk Metallic Glasses

NASA Astrophysics Data System (ADS)

Sarac, Baran; Zhang, Long; Kosiba, Konrad; Pauly, Simon; Stoica, Mihai; Eckert, Jürgen

2016-06-01

Tailoring the intrinsic length-scale effects in bulk metallic glasses (BMGs) via post-heat treatment necessitates a systematic analyzing strategy. Although various achievements were made in the past years to structurally enhance the properties of different BMG alloys, the influence of short-term sub-glass transition annealing on the relaxation kinetics is still not fully covered. Here, we aim for unraveling the connection between the physical, (thermo)mechanical and structural changes as a function of selected pre-annealing temperatures and time scales with an in-house developed Cu46Zr44Al8Hf2 based BMG alloy. The controlled formation of nanocrystals below 50 nm with homogenous distribution inside the matrix phase via thermal treatment increase the material’s resistance to strain softening by almost an order of magnitude. The present work determines the design aspects of metallic glasses with enhanced mechanical properties via nanostructural modifications, while postulating a counter-argument to the intrinsic property degradation accounted for long-term annealing.

Effect of Cr-N codoping on structural phase transition, Raman modes, and optical properties of TiO2 nanoparticles

NASA Astrophysics Data System (ADS)

Hassnain Jaffari, G.; Tahir, Adnan; Ali, Naveed Zafar; Ali, Awais; Qurashi, Umar S.

2018-04-01

Noncompensated cation-anion codoping in TiO2 nanoparticles has been achieved by a chemical synthesis route. Significant reduction in the optical bandgap and enhancement in the absorption of visible light have been observed. Structural phase transformation has been tracked in detail as a function of doping and heat treatment temperature. Anatase to rutile phase transition temperature for doped samples was higher in comparison to the pure TiO2 nanoparticles. Nitrogen and chromium addition increases the phase transformation barrier, where the effect of the former dopant is of more significance. The Raman results showed an increase in the oxygen content with higher post annealing temperatures. With Cr incorporation, the peak associated with the Eg mode has been found to shift towards a higher wave number, while with nitrogen incorporation, the shift was towards a lower wave number. A decrease in reflectance with N co-doping for all samples, irrespective of phase and annealing temperatures, has been observed. In compositions with nitrogen of the same content, bandgap reduction was higher in the rutile phase in comparison to the anatase phase. In general, overall results revealed that with a higher loading fraction of ammonia, the N content increases, while Cr addition prevents nitrogen loss even up to high post annealing temperatures, i.e., 850 °C.

Optical properties of spin-on deposited low temperature titanium oxide thin films

NASA Astrophysics Data System (ADS)

Rantala, J. T.; Kärkkäinen, A. H. O.

2003-06-01

This letter presents a method to fabricate high quality, high refractive index titanium oxide thin films by applying liquid phase spin-on deposition combined with low temperature annealing. The synthesis of the liquid form titanium oxide material is carried out using a sol-gel synthesis technique. The material can be annealed at low temperature (150 C°) to achieve relatively high refractive index of 1.94 at 632.8 nm wavelength, whereas annealing at 350 C° results in index of 2.03 at 632.8 nm. Film depositions are demonstrated on silicon substrates with 0.5% uniformity in thickness. Refractive indices and extinction coefficients are characterized over a broad wavelength range to demonstrate the optical performance of this novel aqueous phase spin-on deposited hybrid titanium oxide material.

Repair behavior of He+-irradiated W-Y2O3 composites after different temperature-isochronal annealing experiments

NASA Astrophysics Data System (ADS)

Yao, Gang; Tan, Xiao-Yue; Luo, Lai-Ma; Zan, Xiang; Liu, Jia-Qin; Xu, Qiu; Zhu, Xifao-Yong; Wu, Yu-Cheng

2018-01-01

W-2%Y2O3 composites were prepared by wet chemical and powder metallurgy. Commercial roll tungsten was selected as a comparative sample in the He+ irradiation experiment. The experiment was conducted under He+ beam energy of 50 eV, irradiation dose of approximately 9.9 × 1024 ions/m2, and temperature of 1503-1553 K. The samples were annealed at 1173, 1373, and 1573 K for 1 h. The irradiation surface was observed in situ. The W-2%Y2O3 composites and pure tungsten displayed different grain orientation damage morphologies. In addition, the fuzzy structure was more likely to converge densely at the phase interface. Annealing repairs material surface irradiation damage, whereas the phase interface acts as a He+ migration channel.

Dependence of growth of the phases of multiphase binary systems on the diffusion parameters

NASA Astrophysics Data System (ADS)

Molokhina, L. A.; Rogalin, V. E.; Filin, S. A.; Kaplunov, I. A.

2017-12-01

A mathematical model of the diffusion interaction of a binary system with several phases on the equilibrium phase diagram is presented. The theoretical and calculated dependences of the layer thickness of each phase in the multiphase diffusion zone on the isothermal annealing time and the ratio of the diffusion parameters in the neighboring phases with an unlimited supply of both components were constructed. The phase formation and growth in the diffusion zone during "reactive" diffusion corresponds to the equilibrium state diagram for two components, and the order of their appearance in the diffusion zone depends only on the ratio of the diffusion parameters in the phases themselves and on the duration of the incubation periods. The dependence of phase appearance on the incubation periods, annealing time, and difference in the movement rates of the components across the interface boundaries was obtained. An example of the application of the model for processing the experimental data on phase growth in a two-component three-phase system was given.

Quantum annealing with all-to-all connected nonlinear oscillators

PubMed Central

Puri, Shruti; Andersen, Christian Kraglund; Grimsmo, Arne L.; Blais, Alexandre

2017-01-01

Quantum annealing aims at solving combinatorial optimization problems mapped to Ising interactions between quantum spins. Here, with the objective of developing a noise-resilient annealer, we propose a paradigm for quantum annealing with a scalable network of two-photon-driven Kerr-nonlinear resonators. Each resonator encodes an Ising spin in a robust degenerate subspace formed by two coherent states of opposite phases. A fully connected optimization problem is mapped to local fields driving the resonators, which are connected with only local four-body interactions. We describe an adiabatic annealing protocol in this system and analyse its performance in the presence of photon loss. Numerical simulations indicate substantial resilience to this noise channel, leading to a high success probability for quantum annealing. Finally, we propose a realistic circuit QED implementation of this promising platform for implementing a large-scale quantum Ising machine. PMID:28593952

Rapid, cool sintering of wet processed yttria-stabilized zirconia ceramic electrolyte thin films.

PubMed

Park, Jun-Sik; Kim, Dug-Joong; Chung, Wan-Ho; Lim, Yonghyun; Kim, Hak-Sung; Kim, Young-Beom

2017-09-29

Here we report a photonic annealing process for yttria-stabilized zirconia films, which are one of the most well-known solid-state electrolytes for solid oxide fuel cells (SOFCs). Precursor films were coated using a wet-chemical method with a simple metal-organic precursor solution and directly annealed at standard pressure and temperature by two cycles of xenon flash lamp irradiation. The residual organics were almost completely decomposed in the first pre-annealing step, and the fluorite crystalline phases and good ionic conductivity were developed during the second annealing step. These films showed properties comparable to those of thermally annealed films. This process is much faster than conventional annealing processes (e.g. halogen furnaces); a few seconds compared to tens of hours, respectively. The significance of this work includes the treatment of solid-state electrolyte oxides for SOFCs and the demonstration of the feasibility of other oxide components for solid-state energy devices.

Synthesis and characterization of nickel oxide particulate annealed at different temperatures

NASA Astrophysics Data System (ADS)

Sharma, Khem Raj; Thakur, Shilpa; Negi, N. S.

2018-04-01

Nickel oxide has been synthesized by solution combustion technique. The nickel oxide ceramic was annealed at 600°C and 1000°C for 2 hours. Structural, electrical, dielectric and magnetic properties were analyzed which are strongly dependent upon the synthesis method. Structural properties were examined by X-ray diffractometer (XRD), which confirmed the purity and cubic phase of nickel oxide. XRD data reveals the increase in crystallite size and decrease in full width half maximum (FWHM) as the annealing temperature increases. Electrical conductivity is found to increase from 10-6 to 10-5 (Ω-1cm-1) after annealing. Dielectric constant is observed to increase from 26 to 175 when the annealing temperature is increased from 600°C to 1000°C. Low value of coercive field is found which shows weak ferromagnetic behavior of NiO. It is observed that all the properties of NiO particulate improve with increasing annealing temperature.

Novel thermal annealing methodology for permanent tuning polymer optical fiber Bragg gratings to longer wavelengths.

PubMed

Pospori, A; Marques, C A F; Sagias, G; Lamela-Rivera, H; Webb, D J

2018-01-22

The Bragg wavelength of a polymer optical fiber Bragg grating can be permanently shifted by utilizing the thermal annealing method. In all the reported fiber annealing cases, the authors were able to tune the Bragg wavelength only to shorter wavelengths, since the polymer fiber shrinks in length during the annealing process. This article demonstrates a novel thermal annealing methodology for permanently tuning polymer optical fiber Bragg gratings to any desirable spectral position, including longer wavelengths. Stretching the polymer optical fiber during the annealing process, the period of Bragg grating, which is directly related with the Bragg wavelength, can become permanently longer. The methodology presented in this article can be used to multiplex polymer optical fiber Bragg gratings at any desirable spectral position utilizing only one phase-mask for their photo-inscription, reducing thus their fabrication cost in an industrial setting.

Annealed scaling for a charged polymer in dimensions two and higher

NASA Astrophysics Data System (ADS)

Berger, Q.; den Hollander, F.; Poisat, J.

2018-02-01

This paper considers an undirected polymer chain on {Z}d , d ≥slant 2 , with i.i.d. random charges attached to its constituent monomers. Each self-intersection of the polymer chain contributes an energy to the interaction Hamiltonian that is equal to the product of the charges of the two monomers that meet. The joint probability distribution for the polymer chain and the charges is given by the Gibbs distribution associated with the interaction Hamiltonian. The object of interest is the annealed free energy per monomer in the limit as the length n of the polymer chain tends to infinity. We show that there is a critical curve in the parameter plane spanned by the charge bias and the inverse temperature separating an extended phase from a collapsed phase. We derive the scaling of the critical curve for small and for large charge bias and the scaling of the annealed free energy for small inverse temperature. We argue that in the collapsed phase the polymer chain is subdiffusive, namely, on scale \

Role of the nanocrystallinity on the chemical ordering of Co(x)Pt(100-x) nanocrystals synthesized by wet chemistry.

PubMed

Kameche, Farid; Ngo, Anh-Tu; Salzemann, Caroline; Cordeiro, Marco; Sutter, Eli; Petit, Christophe

2015-11-14

Co(x)Pt(100-x) nanoalloys have been synthesized by two different chemical processes either at high or at low temperature. Their physical properties and the order/disorder phase transition induced by annealing have been investigated depending on the route of synthesis. It is demonstrated that the chemical synthesis at high temperature allows stabilization of the fcc structure of the native nanoalloys while the soft chemical approach yields mainly poly or non crystalline structure. As a result the approach of the order/disorder phase transition is strongly modified as observed by high-resolution transmission electron microscopy (HR-TEM) studies performed during in situ annealing of the different nanoalloys. The control of the nanocrystallinity leads to significant decrease in the chemical ordering temperature as the ordered structure is observed at temperatures as low as 420 °C. This in turn preserves the individual nanocrystals and prevents their coalescence usually observed during the annealing necessary for the transition to an ordered phase.

Selective oxidation of dual phase steel after annealing at different dew points

NASA Astrophysics Data System (ADS)

Lins, Vanessa de Freitas Cunha; Madeira, Laureanny; Vilela, Jose Mario Carneiro; Andrade, Margareth Spangler; Buono, Vicente Tadeu Lopes; Guimarães, Juliana Porto; Alvarenga, Evandro de Azevedo

2011-04-01

Hot galvanized steels have been extensively used in the automotive industry. Selective oxidation on the steel surface affects the wettability of zinc on steel and the grain orientation of inhibition layer (Fe-Al-Zn alloy) and reduces the iron diffusion to the zinc layer. The aim of this work is to identify and quantify selective oxidation on the surface of a dual phase steel, and an experimental steel with a lower content of manganese, annealed at different dew points. The techniques employed were atomic force microscopy, X-ray photoelectron spectroscopy, and glow discharge optical emission spectroscopy. External selective oxidation was observed for phosphorus on steel surface annealed at 0 °C dp, and for manganese, silicon, and aluminum at a lower dew point. The concentration of manganese was higher on the dual phase steel surface than on the surface of the experimental steel. The concentration of molybdenum on the surface of both steels increased as the depth increased.

Ultra-low temperature (≤300 °C) growth of Ge-rich SiGe by solid-liquid-coexisting annealing of a-GeSn/c-Si structures

DOE Office of Scientific and Technical Information (OSTI.GOV)

Sadoh, Taizoh, E-mail: sadoh@ed.kyushu-u.ac.jp; Chikita, Hironori; Miyao, Masanobu

2015-09-07

Ultra-low temperature (≤300 °C) growth of Ge-rich SiGe on Si substrates is strongly desired to realize advanced electronic and optical devices, which can be merged onto Si large-scale integrated circuits (LSI). To achieve this, annealing characteristics of a-GeSn/c-Si structures are investigated under wide ranges of the initial Sn concentrations (0%–26%) and annealing conditions (300–1000 °C, 1 s–48 h). Epitaxial growth triggered by SiGe mixing is observed after annealing, where the annealing temperatures necessary for epitaxial growth significantly decrease with increasing initial Sn concentration and/or annealing time. As a result, Ge-rich (∼80%) SiGe layers with Sn concentrations of ∼2% are realized by ultra-low temperature annealingmore » (300 °C, 48 h) for a sample with the initial Sn concentration of 26%. The annealing temperature (300 °C) is in the solid-liquid coexisting temperature region of the phase diagram for Ge-Sn system. From detailed analysis of crystallization characteristics and composition profiles in grown layers, it is suggested that SiGe mixing is generated by a liquid-phase reaction even at ultra-low temperatures far below the melting temperature of a-GeSn. This ultra-low-temperature growth technique of Ge-rich SiGe on Si substrates is expected to be useful to realize next-generation LSI, where various multi-functional devices are integrated on Si substrates.« less

Advanced phase change composite by thermally annealed defect-free graphene for thermal energy storage.

PubMed

Xin, Guoqing; Sun, Hongtao; Scott, Spencer Michael; Yao, Tiankai; Lu, Fengyuan; Shao, Dali; Hu, Tao; Wang, Gongkai; Ran, Guang; Lian, Jie

2014-09-10

Organic phase change materials (PCMs) have been utilized as latent heat energy storage and release media for effective thermal management. A major challenge exists for organic PCMs in which their low thermal conductivity leads to a slow transient temperature response and reduced heat transfer efficiency. In this work, 2D thermally annealed defect-free graphene sheets (GSs) can be obtained upon high temperature annealing in removing defects and oxygen functional groups. As a result of greatly reduced phonon scattering centers for thermal transport, the incorporation of ultralight weight and defect free graphene applied as nanoscale additives into a phase change composite (PCC) drastically improve thermal conductivity and meanwhile minimize the reduction of heat of fusion. A high thermal conductivity of the defect-free graphene-PCC can be achieved up to 3.55 W/(m K) at a 10 wt % graphene loading. This represents an enhancement of over 600% as compared to pristine graphene-PCC without annealing at a comparable loading, and a 16-fold enhancement than the pure PCM (1-octadecanol). The defect-free graphene-PCC displays rapid temperature response and superior heat transfer capability as compared to the pristine graphene-PCC or pure PCM, enabling transformational thermal energy storage and management.

Enhancing the Compatibility of Poly (1,4-butylene adipate) and Phenoxy Resin in Blends

PubMed Central

Yang, Cheng-Fu; Wang, Hsiang-Ching; Su, Chean-Cheng

2017-01-01

This work concerns the enhancement in the compatibility of blends of poly (1,4-butylene adipate) (PBA) with poly (hydroxy ether of bisphenol-A) (phenoxy) via alcoholytic exchange. Results on the thermal behavior and morphology show that the blended PBA/phenoxy system exhibits a homogeneous phase and a composition-dependent glass transition temperature (Tg). The interaction parameter (χ12) of PBA/phenoxy blends was calculated using the melting point depression method and was found to be −0.336. However, the compatibilization of PBA/phenoxy blends can be enhanced by chemical exchange reactions between PBA and phenoxy upon annealing. Annealed PBA/phenoxy blends were found to have a homogeneous phase with a higher Tg than that of the blended samples, and a smooth surface topography that could be improved by annealing at high temperature. The results of this investigation demonstrate that promotional phase compatibilization in the PBA/phenoxy blend can only be obtained upon thermal annealing, thus causing transreactions to occur between the dangling –OH of the phenoxy and the ester functional groups in PBA. Extensive transreactions cause alcoholytic exchange between the PBA and phenoxy to form a network, thus reducing the mobility of the polymer chain. Finally, the crystallinity of PBA decreased as the degree of transreaction in the blends increased. PMID:28773050

Specific heat of Nb{sub 3}Sn: The case for a single gap

DOE Office of Scientific and Technical Information (OSTI.GOV)

Jo, Y. J., E-mail: jophy@knu.ac.kr; Zhou, Jian; Sung, Zu Hawn

2014-10-01

The important influence of multiple gaps in the superconductivity of MgB{sub 2} and Fe-based compounds, especially because of the possibility that manipulation of a second gap can significantly raise the upper critical field H{sub c2}, has refocused attention on Nb{sub 3}Sn because anomalies in both specific heat and point-contact tunneling studies have led to the proposal that Nb{sub 3}Sn is also a two-gap superconductor. Here, we search for evidence of the second gap in a careful study of the influence of the homogenization temperature on the sample uniformity. We show that it is very difficult to fabricate samples that aremore » both homogeneous and stoichiometric. We find so-called “second-gap” anomalies disappear only after high temperature and long-term annealing. Such a well-annealed sample shows only a strong, electron-phonon-coupled, single-gap behavior. In contrast, samples reacted and annealed at lower temperatures, as in the earlier two-gap studies, show small chemical composition variations of the A15 phase. We propose that the second gap sightings are actually due to variation of T{sub c} within very difficult-to-fully homogenize samples. A curiosity of the A15 Nb{sub 3}Sn phase is that almost any mixture of Nb and Sn tries to form a stoichiometric A15 composition, but the residue of course contains off-stoichiometric A15, Nb, and other phases when the Nb:Sn ratio departs from the true 3:1 stoichiometry.« less

Magnetic properties of Mn0.1Mg0.2TM0.7Fe2O4 (TM = Zn, Co, or Ni) prepared by hydrothermal processes: The effects of crystal size and chemical composition

NASA Astrophysics Data System (ADS)

Nhlapo, T. A.; Msomi, J. Z.; Moyo, T.

2018-02-01

Nano-crystalline Zn-, Co-, and Ni-substituted Mn-Mg ferrites were prepared by hydrothermal process and annealed at 1100 °C. Annealing conditions are critical on the crystalline phase. TEM and XRD data reveal particle sizes between 8 nm and 15 nm for the as-prepared fine powders, which increase to about 73 nm after sintering at 1100 °C. Mӧssbauer spectra show well resolved magnetic splitting in bulk samples. The as-prepared fine powders show weak hyperfine splitting and broad central doublets associated with fine particles. Magnetization data reveal a high coercive field at about 300 K of about 945 Oe in the Co-based nanosized oxide, which reduces to about 360 Oe after thermal annealing at 1100 °C. The magnetization curves of Zn- and Ni-based samples show much lower coercive fields indicative of superparamagnetic nanoparticles. The crystallite size and chemical composition have significant effects on the properties of Mn0.1Mg0.2(Zn,Co,Ni)0.7Fe2O4 investigated.

Improving superconductivity in BaFe2As2-based crystals by cobalt clustering and electronic uniformity.

PubMed

Li, L; Zheng, Q; Zou, Q; Rajput, S; Ijaduola, A O; Wu, Z; Wang, X P; Cao, H B; Somnath, S; Jesse, S; Chi, M; Gai, Z; Parker, D; Sefat, A S

2017-04-19

Quantum materials such as antiferromagnets or superconductors are complex in that chemical, electronic, and spin phenomena at atomic scales can manifest in their collective properties. Although there are some clues for designing such materials, they remain mainly unpredictable. In this work, we find that enhancement of transition temperatures in BaFe 2 As 2 -based crystals are caused by removing local-lattice strain and electronic-structure disorder by thermal annealing. While annealing improves Néel-ordering temperature in BaFe 2 As 2 crystal (T N  = 132 K to 136 K) by improving in-plane electronic defects and reducing overall a-lattice parameter, it increases superconducting-ordering temperature in optimally cobalt-doped BaFe 2 As 2 crystal (T c  = 23 to 25 K) by precipitating-out the cobalt dopants and giving larger overall a-lattice parameter. While annealing improves local chemical and electronic uniformity resulting in higher T N in the parent, it promotes nanoscale phase separation in the superconductor resulting in lower disparity and strong superconducting band gaps in the dominant crystal regions, which lead to both higher overall T c and critical-current-density, J c .

Improving superconductivity in BaFe 2As 2-based crystals by cobalt clustering and electronic uniformity

DOE PAGES

Li, L.; Zheng, Q.; Zou, Q.; ...

2017-04-19

Quantum materials such as antiferromagnets or superconductors are complex in that chemical, electronic, and spin phenomena at atomic scales can manifest in their collective properties. Although there are some clues for designing such materials, they remain mainly unpredictable. In this work, we find that enhancement of transition temperatures in BaFe 2As 2-based crystals are caused by removing local-lattice strain and electronic-structure disorder by thermal annealing. While annealing improves Neel-ordering temperature in BaFe 2As 2 crystal (T N=132K to 136K) by improving in-plane electronic defects and reducing overall a-lattice parameter, it increases superconducting-ordering temperature in optimally cobalt-doped BaFe 2As 2 crystalmore » (T c=23 to 25K) by precipitating-out the cobalt dopants and giving larger overall a-lattice parameter. And while annealing improves local chemical and electronic uniformity resulting in higher T N in the parent, it also promotes nanoscale phase separation in the superconductor resulting in lower disparity and strong superconducting band gaps in the dominant crystal regions, which lead to both higher overall T c and critical-current-density, J c« less

Improving superconductivity in BaFe 2As 2-based crystals by cobalt clustering and electronic uniformity

DOE Office of Scientific and Technical Information (OSTI.GOV)

Li, L.; Zheng, Q.; Zou, Q.

Quantum materials such as antiferromagnets or superconductors are complex in that chemical, electronic, and spin phenomena at atomic scales can manifest in their collective properties. Although there are some clues for designing such materials, they remain mainly unpredictable. In this work, we find that enhancement of transition temperatures in BaFe 2As 2-based crystals are caused by removing local-lattice strain and electronic-structure disorder by thermal annealing. While annealing improves Neel-ordering temperature in BaFe 2As 2 crystal (T N=132K to 136K) by improving in-plane electronic defects and reducing overall a-lattice parameter, it increases superconducting-ordering temperature in optimally cobalt-doped BaFe 2As 2 crystalmore » (T c=23 to 25K) by precipitating-out the cobalt dopants and giving larger overall a-lattice parameter. And while annealing improves local chemical and electronic uniformity resulting in higher T N in the parent, it also promotes nanoscale phase separation in the superconductor resulting in lower disparity and strong superconducting band gaps in the dominant crystal regions, which lead to both higher overall T c and critical-current-density, J c« less

Simultaneous high crystallinity and sub-bandgap optical absorptance in hyperdoped black silicon using nanosecond laser annealing

DOE Office of Scientific and Technical Information (OSTI.GOV)

Franta, Benjamin, E-mail: bafranta@gmail.com; Pastor, David; Gandhi, Hemi H.

2015-12-14

Hyperdoped black silicon fabricated with femtosecond laser irradiation has attracted interest for applications in infrared photodetectors and intermediate band photovoltaics due to its sub-bandgap optical absorptance and light-trapping surface. However, hyperdoped black silicon typically has an amorphous and polyphasic polycrystalline surface that can interfere with carrier transport, electrical rectification, and intermediate band formation. Past studies have used thermal annealing to obtain high crystallinity in hyperdoped black silicon, but thermal annealing causes a deactivation of the sub-bandgap optical absorptance. In this study, nanosecond laser annealing is used to obtain high crystallinity and remove pressure-induced phases in hyperdoped black silicon while maintainingmore » high sub-bandgap optical absorptance and a light-trapping surface morphology. Furthermore, it is shown that nanosecond laser annealing reactivates the sub-bandgap optical absorptance of hyperdoped black silicon after deactivation by thermal annealing. Thermal annealing and nanosecond laser annealing can be combined in sequence to fabricate hyperdoped black silicon that simultaneously shows high crystallinity, high above-bandgap and sub-bandgap absorptance, and a rectifying electrical homojunction. Such nanosecond laser annealing could potentially be applied to non-equilibrium material systems beyond hyperdoped black silicon.« less

Enhanced thermoelectric properties of phase-separating bismuth selenium telluride thin films via a two-step method

DOE Office of Scientific and Technical Information (OSTI.GOV)

Takashiri, Masayuki, E-mail: takashiri@tokai-u.jp; Kurita, Kensuke; Hagino, Harutoshi

2015-08-14

A two-step method that combines homogeneous electron beam (EB) irradiation and thermal annealing has been developed to enhance the thermoelectric properties of nanocrystalline bismuth selenium telluride thin films. The thin films, prepared using a flash evaporation method, were treated with EB irradiation in a N{sub 2} atmosphere at room temperature and an acceleration voltage of 0.17 MeV. Thermal annealing was performed under Ar/H{sub 2} (5%) at 300 °C for 60 min. X-ray diffraction was used to determine that compositional phase separation between bismuth telluride and bismuth selenium telluride developed in the thin films exposed to higher EB doses and thermal annealing. We proposemore » that the phase separation was induced by fluctuations in the distribution of selenium atoms after EB irradiation, followed by the migration of selenium atoms to more stable sites during thermal annealing. As a result, thin film crystallinity improved and mobility was significantly enhanced. This indicates that the phase separation resulting from the two-step method enhanced, rather than disturbed, the electron transport. Both the electrical conductivity and the Seebeck coefficient were improved following the two-step method. Consequently, the power factor of thin films that underwent the two-step method was enhanced to 20 times (from 0.96 to 21.0 μW/(cm K{sup 2}) that of the thin films treated with EB irradiation alone.« less

Experimental and Numerical Simulations of Phase Transformations Occurring During Continuous Annealing of DP Steel Strips

NASA Astrophysics Data System (ADS)

Wrożyna, Andrzej; Pernach, Monika; Kuziak, Roman; Pietrzyk, Maciej

2016-04-01

Due to their exceptional strength properties combined with good workability the Advanced High-Strength Steels (AHSS) are commonly used in automotive industry. Manufacturing of these steels is a complex process which requires precise control of technological parameters during thermo-mechanical treatment. Design of these processes can be significantly improved by the numerical models of phase transformations. Evaluation of predictive capabilities of models, as far as their applicability in simulation of thermal cycles thermal cycles for AHSS is considered, was the objective of the paper. Two models were considered. The former was upgrade of the JMAK equation while the latter was an upgrade of the Leblond model. The models can be applied to any AHSS though the examples quoted in the paper refer to the Dual Phase (DP) steel. Three series of experimental simulations were performed. The first included various thermal cycles going beyond limitations of the continuous annealing lines. The objective was to validate models behavior in more complex cooling conditions. The second set of tests included experimental simulations of the thermal cycle characteristic for the continuous annealing lines. Capability of the models to describe properly phase transformations in this process was evaluated. The third set included data from the industrial continuous annealing line. Validation and verification of models confirmed their good predictive capabilities. Since it does not require application of the additivity rule, the upgrade of the Leblond model was selected as the better one for simulation of industrial processes in AHSS production.

Relation between quantum fluctuations and the performance enhancement of quantum annealing in a nonstoquastic Hamiltonian

NASA Astrophysics Data System (ADS)

Susa, Yuki; Jadebeck, Johann F.; Nishimori, Hidetoshi

2017-04-01

We study the relation between quantum fluctuations and the significant enhancement of the performance of quantum annealing in a mean-field Hamiltonian. First-order quantum phase transitions were shown to be reduced to second order by antiferromagnetic transverse interactions in a mean-field-type many-body-interacting Ising spin system in a transverse field, which means an exponential speedup of quantum annealing by adiabatic quantum computation. We investigate if and how quantum effects manifest themselves around these first- and second-order phase transitions to understand if the antiferromagnetic transverse interactions appended to the conventional transverse-field Ising model induce notable quantum effects. By measuring the proximity of the semiclassical spin-coherent state to the true ground state as well as the magnitude of the concurrence representing entanglement, we conclude that significant quantum fluctuations exist around second-order transitions, whereas quantum effects are much less prominent at first-order transitions. Although the location of the transition point can be predicted by the classical picture, system properties near the transition need quantum-mechanical descriptions for a second-order transition but not necessarily for first order. It is also found that quantum fluctuations are large within the ferromagnetic phase after a second-order transition from the paramagnetic phase. These results suggest that the antiferromagnetic transverse interactions induce marked quantum effects, and this fact would be related to closely to the significant enhancement of the performance of quantum annealing.

Effects of microstructures on the performance of rare-earth-free MnBi magnetic materials and magnets

NASA Astrophysics Data System (ADS)

Nguyen, Vuong Van; Nguyen, Truong Xuan

2018-03-01

Since the solidification of MnBi alloys is peritectic, their microstructures always consist of the starting phases of Mn and Bi and the productive phase MnBi. The high performance of MnBi bulk magnets requires appropriate routes of preparing MnBi powders of high spontaneous magnetization Ms and large coercivity iHc as well a route of producing bulk magnets thereof. In these routes, the microstructures of arc-melted alloys, annealed alloys and magnets strongly related to the quality of powders and the performance of magnets. The paper proves that: i) The microstructure of fine Mn-inclusions embedded in the matrix of Bi is preferred for arc-melted alloys to realize the rapid evolution of the ferromagnetic phase inside them during their sequent annealing process; ii) The time-controlled annealing process plays a key role in controlling the microstructure with the main ferromagnetic phase matrix, in which the rest of Mn and the Bi accumulations are embedded; iii) The cold (in-liquid-nitrogen) ball milling annealed alloys is required for preparing a high quality powders with the preferred sub-micrometer microstructure without a Bi-decomposition; iv) The short-time warm compaction is crucial to fabricate dense, highly textured bulk magnets with the micrometer microstructure. The realization and control of these preferred microstructures figured in these routes enhance the chance of preparing MnBi bulk magnets with the energy product (BH)max larger than 8 MGOe.

Phase Formation and Superconductivity of Fe-TUBE Encapsulated and Vacuum-Annealed MgB2

NASA Astrophysics Data System (ADS)

Singh, K. P.; Awana, V. P. S.; Shahabuddin, Md.; Husain, M.; Saxena, R. B.; Nigam, Rashmi; Ansari, M. A.; Gupta, Anurag; Narayan, Himanshu; Halder, S. K.; Kishan, H.

We report optimization of the synthesis parameters viz. heating temperature (TH), and hold time (thold) for vacuum-annealed (10-5 Torr) and LN2 (liquid nitrogen) quenched MgB2 compound. These are single-phase compounds crystallizing in the hexagonal structure (space group P6/mmm) at room temperature. Our XRD results indicated that for phase-pure MgB2, the TH for 10-5 Torr annealed and LN2-quenched samples is 750°C. The right stoichiometry i.e., MgB2 of the compound corresponding to 10-5 Torr and TH of 750°C is found for the hold time (thold) of 2.30 hours. With varying thold from 1-4 hours at fixed TH (750°C) and vacuum (10-5 Torr), the c-lattice parameter decreases first and later increases with thold (hours) before a near saturation, while the a-lattice parameter first increases and later decreases beyond a thold of 2.30 hours. The c/a ratio versus thold plot showed an inverted bell-shaped curve, touching the lowest value of 1.141, which is the reported value for perfect stoichiometry of MgB2. The optimized stoichimetric MgB2 compound exhibited superconductivity at 39.2 K with a transition width of 0.6 K. In conclusion, the synthesis parameters for phase pure stoichimetric vacuum-annealed MgB2 compound are optimized and are compared with widely-reported Ta tube encapsulated samples.

Effect of complexing agent on the photoelectrochemical properties of bath deposited CdS thin films

NASA Astrophysics Data System (ADS)

Patil, S. B.; Singh, A. K.

2010-02-01

In the present paper photoelectrochemical (PEC) performance of bath deposited CdS thin films based on complexing agents i.e. ammonia and triethanolamine (TEA) has been discussed. Effect of annealing has also been analyzed. The as-deposited and annealed (at 523 K for 1 h in air) films were characterized by X-ray diffraction (XRD), ultraviolet-visible (UV-vis) absorption spectroscopy, SEM, electrochemical impedance spectroscopy (EIS), and PEC properties. XRD studies revealed that the films were nanocrystalline in nature with mixed hexagonal and cubic phases. TEA complex resulted in better crystallinity. Further improvement in the crystallinity of the films was observed after air annealing. The marigold flower-like structure, in addition to flakes morphology, was observed with TEA complex, whereas for ammonia complex only flakes morphology was observed. The UV-vis absorption studies revealed that the optical absorption edge for the films with ammonia and TEA complex was around 475 nm and 500 nm, respectively. Annealing of the films resulted in red shift in the UV-vis absorption. The PEC cell performance of CdS films was found to be strongly affected by crystallinity and morphology of the films resulted due to complexing agent and annealing. The air annealed film deposited using TEA complex showed maximum short circuit current density ( Jsc) and open circuit voltage ( Voc) i.e. 99 μA/cm 2 and 376 mV respectively, under 10 mW/cm 2 of illumination. The films deposited using TEA complex showed good stability under PEC cell conditions.

Fluid-Enhanced Annealing in the Subcontinental Lithospheric Mantle Beneath the Westernmost Margin of the Carpathian-Pannonian Extensional Basin System

NASA Astrophysics Data System (ADS)

Aradi, L. E.; Hidas, K.; Kovács, I. J.; Tommasi, A.; Klébesz, R.; Garrido, C. J.; Szabó, C.

2017-12-01

Mantle xenoliths from the Styrian Basin Volcanic Field (Western Pannonian Basin, Austria) are mostly coarse granular amphibole-bearing spinel lherzolites with microstructures attesting for extensive annealing. Olivine and pyroxene CPO (crystal-preferred orientation) preserve nevertheless the record of coeval deformation during a preannealing tectonic event. Olivine shows transitional CPO symmetry from [010]-fiber to orthogonal type. In most samples with [010]-fiber olivine CPO symmetry, the [001] axes of the pyroxenes are also dispersed in the foliation plane. This CPO patterns are consistent with lithospheric deformation accommodated by dislocation creep in a transpressional tectonic regime. The lithospheric mantle deformed most probably during the transpressional phase after the Penninic slab breakoff in the Eastern Alps. The calculated seismic properties of the xenoliths indicate that a significant portion of shear wave splitting delay times in the Styrian Basin (0.5 s out of approximately 1.3 s) may originate in a highly annealed subcontinental lithospheric mantle. Hydroxyl content in olivine is correlated to the degree of annealing, with higher concentrations in the more annealed textures. Based on the correlation between microstructures and hydroxyl content in olivine, we propose that annealing was triggered by percolation of hydrous fluids/melts in the shallow subcontinental lithospheric mantle. A possible source of these fluids/melts is the dehydration of the subducted Penninic slab beneath the Styrian Basin. The studied xenoliths did not record the latest large-scale geodynamic events in the region—the Miocene extension then tectonic inversion of the Pannonian Basin.

Examination of the effect of the annealing cation on higher order structures containing guanine or isoguanine repeats

PubMed Central

Pierce, Sarah E.; Wang, Junmei; Jayawickramarajah, Janarthanan; Hamilton, Andrew D.; Brodbelt, Jennifer S.

2010-01-01

Isoguanine (2-oxo-6-amino-guanine), a natural but non-standard base, exhibits unique self-association properties compared to its isomer, guanine, and results in formation of different higher order DNA structures. In this work, the higher order structures formed by oligonucleotides containing guanine repeats or isoguanine repeats after annealing in solutions containing various cations are evaluated by electrospray ionization mass spectrometry (ESI-MS) and circular dichroism (CD) spectroscopy. The guanine-containing strand (G9) consistently formed quadruplexes upon annealing, whereas the isoguanine strand (Ig9) formed both pentaplexes and quadruplexes depending on the annealing cation. Quadruplex formation with G9 showed some dependence on the identity of the cation present during annealing with high relative quadruplex formation detected with six of ten cations. Analogous annealing experiments with Ig9 resulted in complex formation with all ten cations, and the majority of the resulting complexes were pentaplexes. CD results indicated most of the original complexes survived the desalting process necessary for ESI-MS analysis. In addition, several complexes, especially the pentaplexes, were found to be capable of cation exchange with ammonium ions. Ab initio calculations were conducted for isoguanine tetrads and pentads coordinated with all ten cations to predict the most energetically stable structures of the complexes in the gas phase. The observed preference of forming quadruplexes versus pentaplexes as a function of the coordinated cation can be interpreted by the calculated reaction energies of both the tetrads and pentads in combination with the distortion energies of tetrads. PMID:19746468

The Effects of Strain-Annealing on Tuning Permeability and Lowering Losses in Fe-Ni-Based Metal Amorphous Nanocomposites

DOE PAGES

Aronhime, Natan; DeGeorge, Vincent; Keylin, Vladimir; ...

2017-07-25

Here, Fe-Ni-based metal amorphous nanocomposites with a range of compositions (Fe 100–xNi x) 80Nb 4Si 2B 14 (30 ≤ x ≤ 70) are investigated for motor and transformer applications, where it is beneficial to have tunable permeability. It is shown that strain annealing offers an effective method for tuning permeability in these alloys. For an Fe-rich alloy, permeability increased from 4000 to 16,000 with a positive magnetostriction. In a Ni-rich alloy, permeability decreased from 290 to 40 with a negative magnetostriction. Significant elongations (above 60%) are observed during strain annealing at high stress. Crystallization products have been determined in allmore » alloys heated to 480°C. γ-FeNi is formed in all alloys, while (Fe 30Ni 70) 80Nb 4Si 2B 14 also undergoes secondary crystallization at temperatures of approximately 480°C to form a phase with the Cr 23C 6-type structure and a likely composition of Fe 21Nb 2B 6. Toroidal losses have been measured for (Fe 70Ni 30) 80Nb 4Si y B 16–y (0 ≤ y ≤ 3) at various annealing temperatures. At an induction of 1 T and frequency of 400 Hz and 1 kHz, the toroidal losses obtained are W 1.0T, 400 Hz = 0.9 W/kg and W 1.0T, 1 kHz = 2.3 W/kg, respectively. These losses are lower than losses recently reported for state of the art 3.0% and 6.5% silicon steels, a Metglas Fe-based amorphous alloy, and some Fe-based nanocomposites.« less

The Effects of Strain-Annealing on Tuning Permeability and Lowering Losses in Fe-Ni-Based Metal Amorphous Nanocomposites

NASA Astrophysics Data System (ADS)

Aronhime, Natan; DeGeorge, Vincent; Keylin, Vladimir; Ohodnicki, Paul; McHenry, Michael E.

2017-11-01

Fe-Ni-based metal amorphous nanocomposites with a range of compositions (Fe100- x Ni x )80Nb4Si2B14 (30 ≤ x ≤ 70) are investigated for motor and transformer applications, where it is beneficial to have tunable permeability. It is shown that strain annealing offers an effective method for tuning permeability in these alloys. For an Fe-rich alloy, permeability increased from 4000 to 16,000 with a positive magnetostriction. In a Ni-rich alloy, permeability decreased from 290 to 40 with a negative magnetostriction. Significant elongations (above 60%) are observed during strain annealing at high stress. Crystallization products have been determined in all alloys heated to 480°C. γ-FeNi is formed in all alloys, while (Fe30Ni70)80Nb4Si2B14 also undergoes secondary crystallization at temperatures of approximately 480°C to form a phase with the Cr23C6-type structure and a likely composition of Fe21Nb2B6. Toroidal losses have been measured for (Fe70Ni30)80Nb4Si y B16- y (0 ≤ y ≤ 3) at various annealing temperatures. At an induction of 1 T and frequency of 400 Hz and 1 kHz, the toroidal losses obtained are W1.0T, 400 Hz = 0.9 W/kg and W1.0T, 1 kHz = 2.3 W/kg, respectively. These losses are lower than losses recently reported for state of the art 3.0% and 6.5% silicon steels, a Metglas Fe-based amorphous alloy, and some Fe-based nanocomposites.

The Effects of Strain-Annealing on Tuning Permeability and Lowering Losses in Fe-Ni-Based Metal Amorphous Nanocomposites

DOE Office of Scientific and Technical Information (OSTI.GOV)

Aronhime, Natan; DeGeorge, Vincent; Keylin, Vladimir

Here, Fe-Ni-based metal amorphous nanocomposites with a range of compositions (Fe 100–xNi x) 80Nb 4Si 2B 14 (30 ≤ x ≤ 70) are investigated for motor and transformer applications, where it is beneficial to have tunable permeability. It is shown that strain annealing offers an effective method for tuning permeability in these alloys. For an Fe-rich alloy, permeability increased from 4000 to 16,000 with a positive magnetostriction. In a Ni-rich alloy, permeability decreased from 290 to 40 with a negative magnetostriction. Significant elongations (above 60%) are observed during strain annealing at high stress. Crystallization products have been determined in allmore » alloys heated to 480°C. γ-FeNi is formed in all alloys, while (Fe 30Ni 70) 80Nb 4Si 2B 14 also undergoes secondary crystallization at temperatures of approximately 480°C to form a phase with the Cr 23C 6-type structure and a likely composition of Fe 21Nb 2B 6. Toroidal losses have been measured for (Fe 70Ni 30) 80Nb 4Si y B 16–y (0 ≤ y ≤ 3) at various annealing temperatures. At an induction of 1 T and frequency of 400 Hz and 1 kHz, the toroidal losses obtained are W 1.0T, 400 Hz = 0.9 W/kg and W 1.0T, 1 kHz = 2.3 W/kg, respectively. These losses are lower than losses recently reported for state of the art 3.0% and 6.5% silicon steels, a Metglas Fe-based amorphous alloy, and some Fe-based nanocomposites.« less

Dependence of annealing temperature on microstructure and photoelectrical properties of vanadium oxide thin films prepared by DC reactive sputtering

NASA Astrophysics Data System (ADS)

Li, Yan; Zhang, Dongping; Wang, Bo; Liang, Guangxing; Zheng, Zhuanghao; Luo, Jingting; Cai, Xingmin; Fan, Ping

2013-12-01

Vanadium oxide thin films were prepared by DC reactive sputtering method, and the samples were annealed in Ar atmosphere under different temperature for 2 hours. The microstructure, optical and electrical properties of the as-grown and treated samples were characterized by XRD, spectrophotometer, and four-probe technique, respectively. XRD results investigated that the main content of the annealed sample are VO2 and V2O5. With annealing temperature increasing, the intensity of the VO2 phase diffraction peak strengthened. The electrical properties reveal that the annealed samples exhibit semiconductor-to-metal transition characteristic at about 40°C. Comparison of transmission spectra of the samples at room temperature and 100°C, a drastic drop in IR region is found.

Development of advanced high strength tantalum base alloys. Phase 3: Influence of metallurgical condition on the mechanical properties of ASTAR-811C sheet

NASA Technical Reports Server (NTRS)

Ammon, R. L.; Buckman, R. W., Jr.; Harrod, D. L.

1972-01-01

Metallurgical condition was shown to have a significant effect on the creep properties of ASTAR-811C (Ta-8W-1Re-0.7Hf-0.025C) sheet. Cold worked material exhibited creep rates 30 times higher than solution annealed material and 10 times greater than for recrystallized material. Both grain size and the carbide morphology changes as the final annealing temperature was raised from 3000 F to 3600 F. However, the lowest creep rates were achieved for material which retained the high temperature form of the Ta2C precipitate. Samples with GTA weldments had essentially identical properties as recrystallized base metal. Cooling rates from 3600 F of 5, 50, and 800 F deg/min. had little effect on the 2000 and 2400 F creep behavior of ASTAR-811C.

Effect of Cl2 plasma treatment and annealing on vanadium based metal contacts to Si-doped Al0.75Ga0.25N

NASA Astrophysics Data System (ADS)

Lapeyrade, Mickael; Alamé, Sabine; Glaab, Johannes; Mogilatenko, Anna; Unger, Ralph-Stephan; Kuhn, Christian; Wernicke, Tim; Vogt, Patrick; Knauer, Arne; Zeimer, Ute; Einfeldt, Sven; Weyers, Markus; Kneissl, Michael

2017-09-01

In order to understand the electrical properties of V/Al/Ni/Au metal contacts to Si-doped Al0.75Ga0.25N layers, X-ray photoelectron spectroscopy analysis was performed on differently treated AlGaN:Si surfaces before metal deposition, and transmission electron microscopy was used to study the semiconductor-metal interface after contact annealing at 900 °C. Cl2 plasma etching of AlGaN increases the aluminum/nitrogen ratio at the surface, and Al oxide or oxynitride is always formed by any surface treatment applied after etching. After contact annealing, a complex interface structure including amorphous AlOx and different metal phases such as Al-Au-Ni, V-Al, and V2N were found. The electrical properties of the contacts were determined by thermionic emission and/or thermionic field emission in the low voltage regime. Nearly ohmic contacts on AlGaN surfaces exposed to a Cl2 plasma were only obtained by annealing the sample at a temperature of 815 °C under N2/NH3 prior to metallization. By this treatment, the oxygen contamination on the surface could be minimized, resulting in a larger semiconductor area to be in direct contact with metal phases such as Al-rich Al-Au-Ni or V-Al and leading to a contact resistivity of 2.5 × 10-2 Ω cm2. This treatment can be used to significantly reduce the operating voltage of current deep ultraviolet light emitting diodes which will increase their wall plug efficiency and lower the thermal stress during their operation.

Structure refinement for tantalum nitrides nanocrystals with various morphologies

DOE Office of Scientific and Technical Information (OSTI.GOV)

Liu, Lianyun; School of Science, Beijing Jiaotong University, 3 Shang Yuan Cun, Haidian District, Beijing 100044; Huang, Kai

2012-07-15

Graphical abstract: Tantalum nitrides nanocrystals with various phases and morphologies for the first time have been synthesized through homogenous sodium reduction under low temperature with the subsequent annealing process under high vacuum. Highlights: ► The spherical TaN, cuboidal TaN{sub 0.83} and TaN{sub 0.5} nanocrystals have been synthesized through homogenous sodium reduction under low temperature with the subsequent annealing process under high vacuum. ► The crystal structures of different tantalum nitrides were determined by Rietveld refinement on the X-ray diffraction data and the examinations of electron microcopies. ► The specific surface area of the tantalum nitrides powders was around 10 m{supmore » 2} g{sup −1}. ► Tantalum nitrides powders could be suitable for capacitor with high specific capacitance. -- Abstract: Tantalum nitrides (TaN{sub x}) nanocrystals with different phase and morphology have been synthesized through homogenous sodium reduction under low temperature with the subsequent annealing process under high vacuum. The crystal structures of tantalum nitrides were determined by Rietveld refinement based on the X-ray diffraction data. The morphologies of various tantalum nitrides nanocrystals in high quality were analyzed through the electron microcopies examinations. The spherical TaN nanoparticles, cuboidal TaN{sub 0.83} and TaN{sub 0.5} nanocrystals have been selectively prepared at different annealing temperatures. In addition, the specific surface areas of the tantalum nitrides nanocrystals measured by BET method were around 9.87–11.64 m{sup 2} g{sup −1}, indicating that such nano-sized tantalum nitrides could be suitable for capacitor with high specific capacitance.« less

Comparison between phase field simulations and experimental data from intragranular bubble growth in UO{sub 2}

DOE Office of Scientific and Technical Information (OSTI.GOV)

Tonks, M. R.; Biner, S. B.; Mille, P. C.

2013-07-01

In this work, we used the phase field method to simulate the post-irradiation annealing of UO{sub 2} described in the experimental work by Kashibe et al., 1993 [1]. The simulations were carried out in 2D and 3D using the MARMOT FEM-based phase-field modeling framework. The 2-D results compared fairly well with the experiments, in spite of the assumptions made in the model. The 3-D results compare even more favorably to experiments, indicating that diffusion in all three directions must be considered to accurate represent the bubble growth. (authors)

Simultaneous Strength-Ductility Enhancement of a Nano-Lamellar AlCoCrFeNi2.1 Eutectic High Entropy Alloy by Cryo-Rolling and Annealing.

PubMed

Bhattacharjee, T; Wani, I S; Sheikh, S; Clark, I T; Okawa, T; Guo, S; Bhattacharjee, P P; Tsuji, N

2018-02-19

Nano-lamellar (L1 2  + B2) AlCoCrFeNi 2.1 eutectic high entropy alloy (EHEA) was processed by cryo-rolling and annealing. The EHEA developed a novel hierarchical microstructure featured by fine lamellar regions consisting of FCC lamellae filled with ultrafine FCC grains (average size ~200-250 nm) and B2 lamellae, and coarse non-lamellar regions consisting of ultrafine FCC (average size ~200-250 nm), few coarse recrystallized FCC grains and rather coarse unrecrystallized B2 phase (~2.5 µm). This complex and hierarchical microstructure originated from differences in strain-partitioning amongst the constituent phases, affecting the driving force for recrystallization. The hierarchical microstructure of the cryo-rolled and annealed material resulted in simultaneous enhancement in strength (Yield Strength/YS: 1437 ± 26 MPa, Ultimate Tensile Strength/UTS: 1562 ± 33 MPa) and ductility (elongation to failure/e f  ~ 14 ± 1%) as compared to the as-cast as well as cold-rolled and annealed materials. The present study for the first time demonstrated that cryo-deformation and annealing could be a novel microstructural design strategy for overcoming strength-ductility trade off in multiphase high entropy alloys.

Self-organized morphological evolution and dewetting in solvent vapor annealing of spin coated polymer blend nanostructures.

PubMed

Roy, Sudeshna; Sharma, Ashutosh

2015-07-01

Dewetting pathways, kinetics and morphologies of thin films of phase separating polymer blends are governed by the relative mobilities of the two components. We characterize the morphological transformations of the nanostructures of a PS/PMMA blend by annealing in toluene and chloroform vapors. Toluene leads to faster reorganization of PS, whereas chloroform engenders the opposite effect. Spin coating produces a very rough PMMA rich layer that completely wets the substrate and forms a plethora of slender columns protruding through the continuous PS rich layer on top. The nanostructures were stable under long thermal annealing but in the vapor annealing, phase separation and dewetting occurred readily to form the equilibrium structures of dewetted droplets of PS on top of PMMA which also climbed around the PS droplets to form rims. Toluene and chloroform annealing required around 50 h and 1 h respectively to attain the equilibrium. Substantial differences are observed in the intermediate morphologies (heights of nanostructures, roughness and size). PMMA columns remained embedded in the dewetted PS droplets, whereas a high mobility of PMMA in chloroform allowed its rapid evacuation during dewetting to produce an intermediate swiss-cheese like morphology of PS domains. Copyright © 2015 Elsevier Inc. All rights reserved.

Effect of Sintering on Mechanical and Physical Properties of Plasma-Sprayed Thermal Barrier Coatings

NASA Technical Reports Server (NTRS)

Choi, Sung R.; Zhu, Dong-Ming; Miller, Robert A.

2004-01-01

The effect of sintering on mechanical and physical properties of free-standing plasma-sprayed ZrO2-8 wt% Y2O3 thermal barrier coatings (TBCs) was determined by annealing them at 1316 C in air. Mechanical and physical properties of the TBCs, including strength, modes I and II fracture toughness, elastic modulus, Poisson s response, density, microhardness, fractography, and phase stability, were determined at ambient temperature as a function of annealing time ranging from 0 to 500 h. All mechanical and physical properties, except for the amount of monoclinic phase, increased significantly in 5 to 100 h and then reached a plateau above 100 h. Annealing resulted in healing of microcracks and pores and in grain growth, accompanying densification of the TBC s body due to the sintering effect. However, an inevitable adverse effect also occurred such that the desired lower thermal conductivity and good expansivity, which makes the TBCs unique in thermal barrier applications, were degraded upon annealing. A model was proposed to assess and quantify all the property variables in response to annealing in a normalized scheme. Directionality of as-sprayed TBCs appeared to have an insignificant effect on their properties, as determined via fracture toughness, microhardness, and elastic modulus measurements.

Electrical properties of radio-frequency sputtered HfO2 thin films for advanced CMOS technology

NASA Astrophysics Data System (ADS)

Sarkar, Pranab Kumar; Roy, Asim

2015-08-01

The Hafnium oxide (HfO2) high-k thin films have been deposited by radio frequency (rf) sputtering technique on p-type Si (100) substrate. The thickness, composition and phases of films in relation to annealing temperatures have been investigated by using cross sectional FE-SEM (Field Emission Scanning Electron Microscope) and grazing incidence x-ray diffraction (GI-XRD), respectively. GI-XRD analysis revealed that at annealing temperatures of 350°C, films phases change to crystalline from amorphous. The capacitance-voltage (C-V) and current-voltage (I-V) characteristics of the annealed HfO2 film have been studied employing Al/HfO2/p-Si metal-oxide-semiconductor (MOS) structures. The electrical properties such as dielectric constant, interface trap density and leakage current density have been also extracted from C-V and I-V Measurements. The value of dielectric constant, interface trap density and leakage current density of annealed HfO2 film is obtained as 23,7.57×1011eV-1 cm-2 and 2.7×10-5 Acm-2, respectively. In this work we also reported the influence of post deposition annealing onto the trapping properties of hafnium oxide and optimized conditions under which no charge trapping is observed into the dielectric stack.

The local structure and ferromagnetism in Fe-implanted SrTiO3 single crystals

NASA Astrophysics Data System (ADS)

Lobacheva, O.; Chavarha, M.; Yiu, Y. M.; Sham, T. K.; Goncharova, L. V.

2014-07-01

We report a connection between the local structure of low-level Fe impurities and vacancies as the cause of ferromagnetic behavior observed in strontium titanate single crystals (STO), which were implanted with Fe and Si ions at different doses then annealed in oxygen. The effects of Fe doping and post-implantation annealing of STO were studied by X-ray Absorption Near Edge Structure (XANES) spectroscopy and Superconducting Quantum Interference Device magnetometry. XANES spectra for Fe and Ti K- and L-edge reveal the changes in the local environment of Fe and Ti following the implantation and annealing steps. The annealing in oxygen atmosphere partially healed implantation damages and changed the oxidation state of the implanted iron from metallic Fe0 to Fe2+/Fe3+ oxide. The STO single crystals were weak ferromagnets prior to implantation. The maximum saturation moment was obtained after our highest implantation dose of 2 × 1016 Fe atom/cm2, which could be correlated with the metallic Fe0 phases in addition to the presence of O/Ti vacancies. After recrystallization annealing, the ferromagnetic response disappears. Iron oxide phases with Fe2+ and Fe3+ corresponding to this regime were identified and confirmed by calculations using Real Space Multiple Scattering program (FEFF9).

Microstructure, electrical properties, and thermal stability of Au-based ohmic contacts to p-GaN

DOE Office of Scientific and Technical Information (OSTI.GOV)

Smith, L.L.; Davis, R.F.; Kim, M.J.

1997-09-01

The work described in this paper is part of a systematic study of ohmic contact strategies for GaN-based semiconductors. Au contacts exhibited ohmic behavior on p-GaN when annealed at high temperature. The specific contact resistivity ({rho}{sub c}) calculated from TLM measurements on Au/p-GaN contacts was 53{Omega}{center_dot}cm{sup 2} after annealing at 800{degree}C. Multilayer Au/Mg/Au/p-GaN contacts exhibited linear, ohmic current-voltage (I-V) behavior in the as-deposited condition with {rho}{sub c}=214{Omega}{center_dot}cm{sup 2}. The specific contact resistivity of the multilayer contact increased significantly after rapid thermal annealing (RTA) through 725{degree}C. Cross-sectional microstructural characterization of the Au/p-GaN contact system via high-resolution electron microscopy (HREM) revealed thatmore » interfacial secondary phase formation occurred during high-temperature treatments, which coincided with the improvement of contact performance. In the as-deposited multilayer Au/Mg/Au/p-GaN contact, the initial 32 nm Au layer was found to be continuous. However, Mg metal was found in direct contact with the GaN in many places in the sample after annealing at 725{degree}C for 15 s. The resultant increase in contact resistance is believed to be due to the barrier effect increased by the presence of the low work function Mg metal. {copyright} {ital 1997 Materials Research Society.}« less

Microstructural and magnetic property evolution with different heat-treatment conditions in an alnico alloy

DOE PAGES

Zhou, Lin; Tang, Wei; Ke, Liqin; ...

2017-05-08

Further property enhancement of alnico, an attractive near-term, non-rare-earth permanent magnet alloy system, primarily composed of Al, Ni, Co, and Fe, relies on improved morphology control and size refinement of its complex spinodally decomposed nanostructure that forms during heat-treatment. Using a combination of transmission electron microscopy and atom probe tomography techniques, this study evaluates the magnetic properties and microstructures of an isotropic 32.4Fe-38.1Co-12.9Ni-7.3Al-6.4Ti-3.0Cu (wt.%) alloy in terms of processing parameters such as annealing temperature, annealing time, application of an external magnetic field, as well as low-temperature “draw” annealing. Optimal spinodal morphology and spacing is formed within a narrow temperature andmore » time range (~840 °C and 10 min) during thermal-magnetic annealing (MA). The ideal morphology is a mosaic structure consisting of periodically arrayed ~40 nm diameter (Fe-Co)-rich rods (α 1 phase) embedded in an (Al-Ni)-rich (α 2 phase) matrix. A Cu-enriched phase with a size of ~3–5 nm is located at the corners of two adjacent {110} facets of the α 1 phase. The MA process significantly increased remanence (B r) (~40–70%) of the alloy due to biased elongation of the α 1 phase along the <100> crystallographic direction, which is closest in orientation to the applied magnetic field. As a result, the optimum magnetic properties of the alloy with an intrinsic coercivity (H cj) of 1845 Oe and a maximum energy product (BH max) of 5.9 MGOe were attributed to the uniformity of the mosaic structure.« less

Development of sputtered CuSbS2 thin films grown by sequential deposition of binary sulfides

NASA Astrophysics Data System (ADS)

Medina-Montes, M. I.; Vieyra-Brito, O.; Mathews, N. R.; Mathew, X.

2018-05-01

In this work, CuSbS2 thin films were developed by annealing binary precursors deposited sequentially by rf magnetron sputtering. The recrystallization process was optimized and the films were extensively characterized using a number of tools such as XRD, Raman, SEM, energy dispersive x-ray spectroscopy, atomic force microscopy, Hall, UV–vis spectroscopy, Ellipsometry, Seebeck, and photoresponse. The influence of annealing temperature on the structure, morphology, elemental composition, optical and electrical properties are reported. Annealing below 350 °C resulted in famatinite (Cu3SbS4) and chalcostibite (CuSbS2) ternaries as well as binary phases. Phase-pure chalcostibite was obtained in the range of 350 °C–375 °C. At 400 °C, although CuSbS2 was predominant, tetrahedrite phase (Cu12Sb4S13) appeared as an additional phase. The elemental composition of the films was slightly sulfur deficient, and the atomic percentages of Cu, Sb and S showed a dependence on annealing temperature. The material properties of the phase-pure CuSbS2 thin films are: optical band gap in the range of 1.5–1.62 eV, absorption coefficient close to 105 cm‑1, atomic ratios of Cu/Sb ∼1 and (Cu + Sb)/S ∼1.2, crystal size 18.3–24.5 nm and grain size 50–300 nm. The films were photo-sensitive, showed p-type semiconductor behavior. Electrical resistivity, carrier density and hole mobility were 94–459 Ω cm, 1.6–7.0 × 1015 cm‑3 and 8.4–9.5 cm2 V‑1 s respectively.

Pair distribution function analysis of sulfide glassy electrolytes for all-solid-state batteries: Understanding the improvement of ionic conductivity under annealing condition.

PubMed

Shiotani, Shinya; Ohara, Koji; Tsukasaki, Hirofumi; Mori, Shigeo; Kanno, Ryoji

2017-08-01

In general, the ionic conductivity of sulfide glasses decreases with their crystallization, although it increases for a few sulphide glasses owing to the crystallization of a highly conductive new phase (e.g., Li 7 P 3 S 11 : 70Li 2 S-30P 2 S 5 ). We found that the ionic conductivity of 75Li 2 S-25P 2 S 5 sulfide glass, which consists of glassy and crystalline phases, is improved by optimizing the conditions of the heat treatment, i.e., annealing. A different mechanism of high ionic conductivity from the conventional mechanism is expected in the glassy phase. Here, we report the glassy structure of 75Li 2 S-25P 2 S 5 immediately before the crystallization by using the differential pair distribution function (d-PDF) analysis of high-energy X-ray diffraction. Even though the ionic conductivity increases during the optimum annealing, the d-PDF analysis indicated that the glassy structure undergoes no structural change in the sulfide glass-ceramic electrolyte at a crystallinity of 33.1%. We observed the formation of a nanocrystalline phase in the X-ray and electron diffraction patterns before the crystallization, which means that Bragg peaks were deformed. Thus, the ionic conductivity in the mixture of glassy and crystalline phases is improved by the coexistence of the nanocrystalline phase.

Effect of annealing temperature on VO2(M)/ITO film nanomaterials for thermochromic smart windows application and study its contact angle

NASA Astrophysics Data System (ADS)

Shaban, Mohamed; Rabia, Mohamed; Ezzat, Sara; Mansour, Naglaa; Saeed, Ebtisam; Sayyah, Said M.

2018-01-01

Metastable phase VO2(B) film coated ITO glass was prepared using cyclic potentiometric device utilizing VOSO4 and H2SO4 solution. The optimum conditions for the deposition of the nanostructured VO2(B) film were determined using cathodic peak current density (Ipc) values. Ipc values increase with increasing both VOSO4 and H2SO4 concentrations and then decrease with further increasing the concentrations. Also, monoclinic phase VO2(M)/ITO film was prepared from VO2(B)/ITO film under the effect of annealing temperatures from 550°C to 750°C. Different analyses have been carried out to confirm the chemical, morphological, and crystal structure of the nanostructured VO2(M)/ITO film. From the XRD analysis, the crystallinity increases with the increasing of annealing temperature from 550°C to 750°C. The optical transmittance spectrum was ˜97% for the film annealed at 650°C. Also, the critical thermochromic temperature (Tc) of the optimized film was ˜47.5°C that measured using cooling and heating modes. Finally, the wettability of the VO2(M)/ITO film at different annealing temperature (550°C to 750°C) was studied, in which the contact angle increases from 81 deg to 92 deg with increasing annealing temperatures from 550°C to 750°C, respectively.

Nanotwinning and structural phase transition in CdS quantum dots

PubMed Central

2012-01-01

Nanotwin structures are observed in high-resolution transmission electron microscopy studies of cubic phase CdS quantum dots in powder form by chemical co-precipitation method. The deposition of thin films of nanocrystalline CdS is carried out on silicon, glass, and TEM grids keeping the substrates at room temperature (RT) and 200°C by pulsed laser ablation. These films are then subjected to thermal annealing at different temperatures. Glancing angle X-ray diffraction results confirm structural phase transitions after thermal annealing of films deposited at RT and 200°C. The variation of average particle size and ratio of intensities in Raman peaks I2LO/I1LO with annealing temperature are studied. It is found that electron-phonon interaction is a function of temperature and particle size and is independent of the structure. Besides Raman modes LO, 2LO and 3LO of CdS at approximately 302, 603, and 903 cm−1 respectively, two extra Raman modes at approximately 390 and 690 cm−1 are studied for the first time. The green and orange emissions observed in photoluminescence are correlated with phase transition. PMID:23092351

DOE Office of Scientific and Technical Information (OSTI.GOV)

Sundaramurthi, Prakash; Patapoff, Thomas W.; Suryanarayanan, Raj

To study the crystallization of trehalose in frozen solutions and to understand the phase transitions during the entire freeze-drying cycle. Aqueous trehalose solution was cooled to -40 C in a custom-designed sample holder. The frozen solution was warmed to -18 C and annealed, and then dried in the sample chamber of the diffractometer. XRD patterns were continuously collected during cooling, annealing and drying. After cooling, hexagonal ice was the only crystalline phase observed. However, upon annealing, crystallization of trehalose dihydrate was evident. Seeding the frozen solution accelerated the solute crystallization. Thus, phase separation of the lyoprotectant was observed in frozenmore » solutions. During drying, dehydration of trehalose dihydrate yielded a substantially amorphous anhydrous trehalose. Crystallization of trehalose, as trehalose dihydrate, was observed in frozen solutions. The dehydration of the crystalline trehalose dihydrate to substantially amorphous anhydrate occurred during drying. Therefore, analyzing the final lyophile will not reveal crystallization of the lyoprotectant during freeze-drying. The lyoprotectant crystallization can only become evident by continuous monitoring of the system during the entire freeze-drying cycle. In light of the phase separation of trehalose in frozen solutions, its ability to serve as a lyoprotectant warrants further investigation.« less

Surface morphology and structure of Ge layer on Si(111) after solid phase epitaxy

NASA Astrophysics Data System (ADS)

Yoshida, Ryoma; Tosaka, Aki; Shigeta, Yukichi

2018-05-01

The surface morphology change of a Ge layer on a Si(111) surface formed by solid phase epitaxy has been investigated with a scanning tunneling microscope (STM). The Ge film was deposited at room temperature and annealed at 400 °C or 600 °C. The STM images of the sample surface after annealing at 400 °C show a flat wetting layer (WL) with small three-dimensional islands on the WL. After annealing at 600 °C, the STM images show a surface roughening with large islands. From the relation between the average height of the roughness and the deposited layer thickness, it is confirmed that the diffusion of Ge atoms becomes very active at 600 °C. The Si crystal at the interface is reconstructed and the intermixing occurs over 600 °C. However, the intermixing is fairly restricted in the solid phase epitaxy growth at 400 °C. The surface morphology changes with the crystallization at 400 °C are discussed by the shape of the islands formed on the WL surface. It is shown that the diffusion of the Ge atoms in the amorphous phase is active even at 400 °C.

Microstructure characterization and phase transformation kinetic study of ball-milled m-ZrO 2-30 mol% a-TiO 2 mixture by Rietveld method

NASA Astrophysics Data System (ADS)

Pradhan, S. K.; Dutta, H.

2005-05-01

High-energy ball milling of monoclinic ZrO 2-30 mol% anatase TiO 2 mixture at different durations results in the formation of m-ZrO 2-a-TiO 2 solid solution from which the nucleation of nanocrystalline cubic (c) ZrO 2 polymorphic phase sets in. Post-annealing of 12 h ball-milled sample at different elevated temperatures for 1 h results in almost complete formation of c-ZrO 2 phase. Microstructure of the unmilled, all the ball milled and annealed samples has been characterized by Rietveld's X-ray powder structure refinement method. Particle size, rms lattice strain, change in lattice parameters and phase content of individual phases have been estimated from Rietveld analysis, and are utilized to interpret the results. In course of milling, (1 1 1) of cubic lattice became parallel to ( 1bar 1 1) plane of monoclinic lattice due to the orientation effect and cubic phase may have been formed on the (0 0 1) of the m-ZrO 2-a-TiO 2 solid solution lattice. A comparative study of microstructure and phase transformation kinetics of ZrO 2-10, 20 and 30 mol% a-TiO 2 ball-milled and post-annealed samples reveals that rate of phase transformation m→c-ZrO 2 increases with increasing a-TiO 2 concentration and ∼30 mol% of nanocrystalline c-ZrO 2 phase can be obtained within 4 h of milling time in the presence of 30 mol% of a-TiO 2. The post-annealing treatment at 773, 873 and 973 K for 1 h duration each reveals that rate of c-ZrO 2 formation with increasing temperature is retarded with increasing a-TiO 2 concentration but the amount of c-ZrO 2 becomes almost equal (∼95 mol%) at 973 K. It suggests that almost fully stabilized nanocrystalline c-ZrO 2 can be formed by adding a tetravalent solute to m-ZrO 2.

Effect of pressure-assisted thermal annealing on the optical properties of ZnO thin films.

PubMed

Berger, Danielle; Kubaski, Evaldo Toniolo; Sequinel, Thiago; da Silva, Renata Martins; Tebcherani, Sergio Mazurek; Varela, José Arana

2013-01-01

ZnO thin films were prepared by the polymeric precursor method. The films were deposited on silicon substrates using the spin-coating technique, and were annealed at 330 °C for 32 h under pressure-assisted thermal annealing and under ambient pressure. Their structural and optical properties were characterized, and the phases formed were identified by X-ray diffraction. No secondary phase was detected. The ZnO thin films were also characterized by field-emission scanning electron microscopy, Fourier transform infrared spectroscopy, photoluminescence and ultraviolet emission intensity measurements. The effect of pressure on these thin films modifies the active defects that cause the recombination of deep level states located inside the band gap that emit yellow-green (575 nm) and orange (645 nm) photoluminescence. Copyright © 2012 John Wiley & Sons, Ltd.

Magnetic proximity effect and shell-ferromagnetism in metastable Ni50Mn45Ga5

NASA Astrophysics Data System (ADS)

Krenke, Thorsten; ćakır, Aslı; Scheibel, Franziska; Acet, Mehmet; Farle, Michael

2016-12-01

The present study on magnetic and structural properties of Ni50Mn45Ga5 confirms that structural metastability is an inherent property of Ni50Mn50-xXx Heusler alloys with X as In, Ga, and Sn. The ternary alloy transforms during temper-annealing into a dual-phase composite alloy. The two phases are identified to be cubic L21, Ni50Mn25Ga25, and tetragonal L10 Ni50Mn50. Depending on the annealing temperature, the magnetic-proximity effect giving rise to shell-ferromagnetism has been observed when annealing is carried out under an external magnetic field. The upper and lower remanence values MR+ and MR- have the same sign even at high temperatures. Such alloys can be promising candidates for heat- and magnetic-field-resistant magnetic recording media.

Cryptomelane-type manganese oxide (KMn8O16) nanorods cathode materials synthesized by a rheological phase for lithium ion batteries

NASA Astrophysics Data System (ADS)

Zheng, Hao; Wang, Ting; Zhao, Rongfei; Chen, Jinsong; Li, Lin

2018-01-01

Cryotolerance-type manganese oxide (KMn8O16) nanorods were prepared for the first time by a rheological phase reaction method. The KMn8O16 samples were characterized by X-ray diffraction, scanning electron microscopy, the effects of different annealed temperatures on the morphologies and electrochemical properties of the final products were systematically investigated. The result that the annealed samples exhibit the superior electrochemical performances compared to the unannealed sample. The KMn8O16 nanorods annealed at 400 °C show the highest reversible discharge capacity (147.9 mAh/g even after 80 cycles) at current density of 50 mA/g and the best cycling stability. These results indicate that the KMn8O16 nanorods could be a promising cathode material for lithium ion batteries.

Formation of soft magnetic high entropy amorphous alloys composites containing in situ solid solution phase

NASA Astrophysics Data System (ADS)

Wei, Ran; Sun, Huan; Chen, Chen; Tao, Juan; Li, Fushan

2018-03-01

Fe-Co-Ni-Si-B high entropy amorphous alloys composites (HEAACs), which containing high entropy solid solution phase in amorphous matrix, show good soft magnetic properties and bending ductility even in optimal annealed state, were successfully developed by melt spinning method. The crystallization phase of the HEAACs is solid solution phase with body centered cubic (BCC) structure instead of brittle intermetallic phase. In addition, the BCC phase can transformed into face centered cubic (FCC) phase with temperature rise. Accordingly, Fe-Co-Ni-Si-B high entropy alloys (HEAs) with FCC structure and a small amount of BCC phase was prepared by copper mold casting method. The HEAs exhibit high yield strength (about 1200 MPa) and good plastic strain (about 18%). Meanwhile, soft magnetic characteristics of the HEAs are largely reserved from HEAACs. This work provides a new strategy to overcome the annealing induced brittleness of amorphous alloys and design new advanced materials with excellent comprehensive properties.

Microstructural Evolution During Cold Rolling and Subsequent Annealing in Low-Carbon Steel with Different Initial Microstructures

NASA Astrophysics Data System (ADS)

Ogawa, Toshio; Dannoshita, Hiroyuki; Maruoka, Kuniaki; Ushioda, Kohsaku

2017-08-01

Microstructural evolution during cold rolling and subsequent annealing of low-carbon steel with different initial microstructures was investigated from the perspective of the competitive phenomenon between recrystallization of ferrite and reverse phase transformation from ferrite to austenite. Three kinds of hot-rolled sheet specimens were prepared. Specimen P consisted of ferrite and pearlite, specimen B consisted of bainite, and specimen M consisted of martensite. The progress of recovery and recrystallization of ferrite during annealing was more rapid in specimen M than that in specimens P and B. In particular, the recrystallized ferrite grains in specimen M were fine and equiaxed. The progress of ferrite-to-austenite phase transformation during intercritical annealing was more rapid in specimen M than in specimens P and B. In all specimens, the austenite nucleation sites were mainly at high-angle grain boundaries, such as those between recrystallized ferrite grains. The austenite distribution was the most uniform in specimen M. Thus, we concluded that fine equiaxed recrystallized ferrite grains were formed in specimen M, leading to a uniform distribution of austenite.

Electroplated L1{sub 0} CoPt thick-film permanent magnets

DOE Office of Scientific and Technical Information (OSTI.GOV)

Oniku, Ololade D., E-mail: ololadeoniku@ufl.edu; Qi, Bin; Arnold, David P.

2014-05-07

The fabrication and magnetic characterization of 15-μm-thick electroplated L1{sub 0} CoPt hard magnets with good magnetic properties is reported in this paper. Experimental study of the dependence of the magnets' properties on annealing temperature reveals that an intrinsic coercivity H{sub ci} = ∼800 kA/m (10 kOe), squareness >0.8, and energy product of >150 kJ/m{sup 3} are obtained for photolithographically patterned structures (250 μm × 2 mm stripes; 15 μm thickness) electroplated on silicon substrates and annealed in hydrogen forming gas at 700 °C. Scanning electron microscopy is used to inspect the morphology of both the as-deposited and annealed magnetic layers, and X-ray Diffractometer analysis on the magnets annealed at 700 °Cmore » confirm a phase transformation to an ordered L1{sub 0} CoPt structure, with a minor phase of hcp Co. These thick films are intended for microsystems/MEMS applications.« less

Effect of heat treatment on surface hydrophilicity-retaining ability of titanium dioxide nanotubes

NASA Astrophysics Data System (ADS)

Sun, Yu; Sun, Shupei; Liao, Xiaoming; Wen, Jiang; Yin, Guangfu; Pu, Ximing; Yao, Yadong; Huang, Zhongbing

2018-05-01

The aim of this study is to investigate the effect of different annealing temperature and atmosphere on the surface wettability retaining properties of titania nanotubes (TNs) fabricated by anodization. The TNs morphology, crystal phase composition and surface elemental composition and water contact angle (WCA) were investigated by scanning electron microscopy, X-ray diffraction, X-ray photoelectron spectroscopy and contact angle instrument, respectively. After the samples annealed at 200 °C, 450 °C, 850 °C have been stored in air for 28 days, the WCAs increase to 31.7°, 21.1° and 110.5°, respectively. The results indicate that crystal phase composition of TNs plays an important role in surface wettability. Compared with the WCA (21.1°) of the samples annealed in air after 28 days, the WCA of samples annealed in oxygen-deficient atmosphere is lower, suggesting the contribution of oxygen vacancy in the enhanced hydrophilicity-retaining ability. Our study demonstrates that the surface hydrophilicity-retaining ability of TNs is related to the ordered nanotubular structure, crystal structure, the amount of surface hydroxyl group and oxygen vacancy defects.

Microstructure and Shape Memory Behavior of Ti-Nb Shape Memory Alloy Thin Film

NASA Astrophysics Data System (ADS)

Meng, X. L.; Sun, B.; Sun, J. Y.; Gao, Z. Y.; Cai, W.; Zhao, L. C.

2017-09-01

Ti-Nb shape memory alloy (SMA) thin film is a promising candidate applied as microactuator in biomedical field. In this study, the microstructure and shape memory behavior of Ti-Nb SMA thin films in different heat treatment conditions have been investigated. Fine ω phases embedded in the β phase matrix suppress the martensitic transformation of the films. As a result, the as-deposited and most of the annealed films consist of the β and α″ dual phases. The annealed Ti-Nb thin film shows excellent superelasticity effect when deformed above the reverse martensitic transformation temperature, that is 3.5% total recovery strain can be obtained when 4% pre-strain is loaded.

Sol-gel synthesis of nanosized titanium dioxide at various pH of the initial solution

NASA Astrophysics Data System (ADS)

Dorosheva, I. B.; Valeeva, A. A.; Rempel, A. A.

2017-09-01

Titanium dioxide (TiO2) was synthesized by sol-gel method at different values of pH = 3, 7, 8, 9, or 10. X-ray phase analysis has shown that in an acid rout an anatase phase was crystallized, and in an alkaline rout an amorphous phase of TiO2 was achieved. After annealing for 4 hours at 350 °C, all samples was transformed in the anatase phase. The particle size in the different samples varies from 7 to 49 nm depending on the pH. The diffuse reflection spectra revealed a high value of the band gap in the range from 3.2 to 3.7 eV and its narrowing after annealing to the range from 3.2 to 3.5 eV.

Dense and high-stability Ti2AlN MAX phase coatings prepared by the combined cathodic arc/sputter technique

NASA Astrophysics Data System (ADS)

Wang, Zhenyu; Liu, Jingzhou; Wang, Li; Li, Xiaowei; Ke, Peiling; Wang, Aiying

2017-02-01

Ti2AlN belongs to a family of ternary nano-laminate alloys known as the MAX phases, which exhibit a unique combination of metallic and ceramic properties. In the present work, the dense and high-stability Ti2AlN coating has been successfully prepared through the combined cathodic arc/sputter deposition, followed by heat post-treatment. It was found that the as-deposited Ti-Al-N coating behaved a multilayer structure, where (Ti, N)-rich layer and Al-rich layer grew alternately, with a mixed phase constitution of TiN and TiAlx. After annealing at 800 °C under vacuum condition for 1.5 h, although the multilayer structure still was found, part of multilayer interfaces became indistinct and disappeared. In particular, the thickness of the Al-rich layer decreased in contrast to that of as-deposited coating due to the inner diffusion of the Al element. Moreover, the Ti2AlN MAX phase emerged as the major phase in the annealed coatings and its formation mechanism was also discussed in this study. The vacuum thermal analysis indicated that the formed Ti2AlN MAX phase exhibited a high-stability, which was mainly benefited from the large thickness and the dense structure. This advanced technique based on the combined cathodic arc/sputter method could be extended to deposit other MAX phase coatings with tailored high performance like good thermal stability, high corrosion and oxidation resistance etc. for the next protective coating materials.

Improvement of the thermal stability of Nb:TiO2-x samples for uncooled infrared detectors

NASA Astrophysics Data System (ADS)

Reddy, Y. Ashok Kumar; Kang, In-Ku; Shin, Young Bong; Lee, Hee Chul

2018-01-01

In order to reduce the sun-burn effect in a sample of the bolometric material Nb:TiO2-x , oxygen annealing was carried out. This effect can be examined by comparing thermal stability test results between the as-deposited and oxygen-atmosphere-annealed samples under high-temperature exposure conditions. Structural studies confirm the presence of amorphous and rutile phases in the as-deposited and annealed samples, respectively. Composition studies reveal the offset of oxygen vacancies in the Nb:TiO2-x samples through oxygen-atmosphere annealing. The oxygen atoms were diffused and seemed to occupy the vacant sites in the annealed samples. As a result, the annealed samples show better thermal stability performance than the as-deposited samples. The universal bolometric parameter (β) values were slightly decreased in the oxygen-annealed Nb:TiO2-x samples. Although bolometric performance was slightly decreased in the oxygen-annealed samples, high thermal stability would be the most essential factor in the case of special applications, such as the military and space industries. Finally, these results will be very useful for reducing the sun-burn effect in infrared detectors.

Changes in microstructure and physical properties of skutterudites after severe plastic deformation.

PubMed

Rogl, Gerda; Grytsiv, Andriy; Bursik, Jiri; Horky, Jelena; Anbalagan, Ramakrishnan; Bauer, Ernst; Mallik, Ramesh Chandra; Rogl, Peter; Zehetbauer, Michael

2015-02-07

The best p-type skutterudites with ZT > 1.1 so far are didymium (DD) filled, Fe/Co substituted, Sb-based skutterudites. DD0.68Fe3CoSb12 was prepared using an annealing-reacting-melting-quenching technique followed by ball milling and hot pressing. After severe plastic deformation via high-pressure torsion (HPT), no phase changes but particular structural variations were achieved, leading to modified transport properties with higher ZT values. Although after measurement-induced heating some of the HPT induced defects were annealed out, a still attractive ZT-value was preserved. In this paper we focus on explanations for these changes via TEM investigations, Raman spectroscopy and texture measurements. The grain sizes and dislocation densities, evaluated from TEM images, showed that (i) the majority of cracks generated during high-pressure torsion are healed during annealing, leaving only small pores, that (ii) the grains have grown, and that (iii) the dislocation density is decreased. While Raman spectra indicate that after HPT processing and annealing the vibration modes related to the shorter Sb-Sb bonds in the Sb4 rings are more affected than those related to the longer Sb-Sb bonds, almost no visible changes were observed in the pole intensity and/or orientation.

Influence of annealing temperature on Raman and photoluminescence spectra of electron beam evaporated TiO₂ thin films.

PubMed

Vishwas, M; Narasimha Rao, K; Chakradhar, R P S

2012-12-01

Titanium dioxide (TiO(2)) thin films were deposited on fused quartz substrates by electron beam evaporation method at room temperature. The films were annealed at different temperatures in ambient air. The surface morphology/roughness at different annealing temperatures were analyzed by atomic force microscopy (AFM). The crystallinity of the film has improved with the increase of annealing temperature. The effect of annealing temperature on optical, photoluminescence and Raman spectra of TiO(2) films were investigated. The refractive index of TiO(2) films were studied by envelope method and reflectance spectra and it is observed that the refractive index of the films was high. The photoluminescence intensity corresponding to green emission was enhanced with increase of annealing temperature. The peaks in Raman spectra depicts that the TiO(2) film is of anatase phase after annealing at 300°C and higher. The films show high refractive index, good optical quality and photoluminescence characteristics suggest that possible usage in opto-electronic and optical coating applications. Copyright © 2012 Elsevier B.V. All rights reserved.

Understanding the effect of annealing temperature on crystalline structure, morphology, and photocatalytic activity of silver-loaded TiO2 nanotubes

NASA Astrophysics Data System (ADS)

Viet, Pham Van; Phuong Trang, Duong Dao; Phat, Bui Dai; Hieu, Le Van; Thi, Cao Minh

2018-05-01

In this study, we classified the effect of the annealing temperature on silver-loaded TiO2 nanotubes (Ag/TNTs). X-ray diffraction results demonstrate that TNTs have a tendency of phase transformation owing to silver nanoparticles (Ag NPs). The Brunauer-Emmett-Teller method indicates that Ag/TNTs is a mesopore material and the surface area of Ag/TNTs decreases when the annealing temperature increases. This research concluded that the TNT structure begins to break at high annealing temperatures (>400 °C) and is completely broken at 500 °C. The average diameter of the Ag NPs in Ag/TNTs increases linearly with the annealing temperature. In addition, this study clearly explained the oxidation state transformation of Ag in Ag/TNTs under the impact of the annealing temperature, therein, the Ag0 state is transferred completely to Ag+ at 400 °C, and some Ag+ is oxidized to form Ag2+. The Ag/TNTs and Ag/TNTs annealed at 300 °C provided the good methylene blue photodegradation ability for 150 min under sunlight condition.

Annealed Au-assisted epitaxial growth of si nanowires: control of alignment and density.

PubMed

Park, Yi-Seul; Jung, Da Hee; Kim, Hyun Ji; Lee, Jin Seok

2015-04-14

The epitaxial growth of 1D nanostructures is of particular interest for future nanoelectronic devices such as vertical field-effect transistors because it directly influences transistor densities and 3D logic or memory architectures. Silicon nanowires (SiNWs) are a particularly important 1D nanomaterial because they possess excellent electronic and optical properties. What is more, the scalable fabrication of vertically aligned SiNW arrays presents an opportunity for improved device applications if suitable properties can be achieved through controlling the alignment and density of SiNWs, yet this is something that has not been reported in the case of SiNWs synthesized from Au films. This work therefore explores the controllable synthesis of vertically aligned SiNWs through the introduction of an annealing process prior to growth via a Au-catalyzed vapor-liquid-solid mechanism. The epitaxial growth of SiNWs was demonstrated to be achievable using SiCl4 as the Si precursor in chemical vapor deposition, whereas the alignment and density of the SiNWs could be controlled by manipulating the annealing time during the formation of Au nanoparticles (AuNPs) from Au films. During the annealing process, gold silicide was observed to form on the interface of the liquid-phase AuNPs, depending on the size of the AuNPs and the annealing time. This work therefore makes a valuable contribution to improving nanowire-based engineering by controlling its alignment and density as well as providing greater insight into the epitaxial growth of 1D nanostructures.

Effect of Annealing Temperature on Flowerlike Cu3BiS3 Thin Films Grown by Chemical Bath Deposition

NASA Astrophysics Data System (ADS)

Deshmukh, S. G.; Patel, S. J.; Patel, K. K.; Panchal, A. K.; Kheraj, Vipul

2017-10-01

For widespread application of thin-film photovoltaic solar cells, synthesis of inexpensive absorber material is essential. In this work, deposition of ternary Cu3BiS3 absorber material, which contains abundant and environmentally benign elements, was carried out on glass substrate. Flowerlike Cu3BiS3 thin films with nanoflakes as building block were formed on glass substrate by chemical bath deposition. These films were annealed at 573 K and 673 K in sulfur ambient for structural improvement. Their structure was characterized using Raman spectroscopy, as well as their surface morphological and optical properties. The x-ray diffraction profile of as-deposited Cu3BiS3 thin film revealed amorphous structure, which transformed to orthorhombic phase after annealing. The Raman spectrum exhibited a characteristic peak at 290 cm-1. Scanning electron microscopy of as-deposited Cu3BiS3 film confirmed formation of nanoflowers with diameter of around 1052 nm. Wettability testing of as-deposited Cu3BiS3 thin film demonstrated hydrophobic nature, which became hydrophilic after annealing. The measured ultraviolet-visible (UV-Vis) absorption spectra of the Cu3BiS3 thin films gave an absorption coefficient of 105 cm-1 and direct optical bandgap of about 1.42 eV after annealing treatment. Based on all these results, such Cu3BiS3 material may have potential applications in the photovoltaic field as an absorber layer.

Complex structures of different CaFe2As2 samples

PubMed Central

Saparov, Bayrammurad; Cantoni, Claudia; Pan, Minghu; Hogan, Thomas C.; II, William Ratcliff; Wilson, Stephen D.; Fritsch, Katharina; Gaulin, Bruce D.; Sefat, Athena S.

2014-01-01

The interplay between magnetism and crystal structures in three CaFe2As2 samples is studied. For the nonmagnetic quenched crystals, different crystalline domains with varying lattice parameters are found, and three phases (orthorhombic, tetragonal, and collapsed tetragonal) coexist between TS = 95 K and 45 K. Annealing of the quenched crystals at 350°C leads to a strain relief through a large (~1.3%) expansion of the c-parameter and a small (~0.2%) contraction of the a-parameter, and to local ~0.2 Å displacements at the atomic-level. This annealing procedure results in the most homogeneous crystals for which the antiferromagnetic and orthorhombic phase transitions occur at TN/TS = 168(1) K. In the 700°C-annealed crystal, an intermediate strain regime takes place, with tetragonal and orthorhombic structural phases coexisting between 80 to 120 K. The origin of such strong shifts in the transition temperatures are tied to structural parameters. Importantly, with annealing, an increase in the Fe-As length leads to more localized Fe electrons and higher local magnetic moments on Fe ions. Synergistic contribution of other structural parameters, including a decrease in the Fe-Fe distance, and a dramatic increase of the c-parameter, which enhances the Fermi surface nesting in CaFe2As2, are also discussed. PMID:24844399

Microstructure Analysis on 6061 Aluminum Alloy after Casting and Diffuses Annealing Process

NASA Astrophysics Data System (ADS)

Wang, H. Q.; Sun, W. L.; Xing, Y. Q.

One factory using semi-continuous casting process produce the ф200×6000 mm 6061 aluminium alloy barstock, and then rotary forged for car wheels. 6061 distorting aluminium alloy is an forged aluminum alloy, and mainly containing Mg, Si, Cu and other alloying elements. The main strengthening phase is Mg2Si, and also has few phase of (FeMn) 3Si2Al15. In order to eliminate the segregation and separation which present in the crystal boundary, and make the distortion to be uniform, and does not present ear and fracture defects after the forging. So the 6061 distorting aluminium alloy adopt the diffusion annealing heat treatment before the forging process.According to the current conditions, we use the diffusion annealing which have the different heating temperature and different holding time.The best process we can obtain from the test which can improve the production efficiency and reduce the material waste, improve the mechanical properties, and eliminate the overheated film on the surface.Then,we using OM,SEM and EDS to analyse the microstructure and the chemical composition of compound between the surface and centre. The result shows that the amount of segregation were different in the surface and in the center, and the different diffusion annealing can cause the phase change in the surface and the center.

Recoil hysteresis of Sm -Co/Fe exchange-spring bilayers

NASA Astrophysics Data System (ADS)

Kang, K.; Lewis, L. H.; Jiang, J. S.; Bader, S. D.

2005-12-01

The exchange-spring behavior found in Sm-Co (20nm)/Fe epitaxial bilayer films was investigated by analyzing major hysteresis and recoil curves as a function of anneal conditions. The hard layer consists of nanocrystalline intermetallic Sm-Co hexagonal phases (majority phase Sm2Co7 with SmCo3 and SmCo5). Recoil curves, obtained from the successive removal to remanence and reapplication of an increasingly negative field from the major demagnetization curve, reveal the reversible and irreversible components of the magnetization. The Sm-Co thickness was fixed at 20nm while the Fe thicknesses of 10 and 20nm were studied, with ex situ annealing carried out in evacuated, sealed silica tubes at different temperatures. The peak in the recoil curve area is associated with the coercivity of the hard phase. The development of the soft component magnetization is revealed by the departure of the recoil area from zero with application of a reverse field. These two features together confirm that annealing stabilizes the 10nm Fe bilayer sample against local magnetic reversal while it weakens the 20nm bilayer sample. Furthermore, in both its as-deposited and annealed states the Sm -Co/Fe bilayer of 10nm Fe thickness always displays a higher exchange field and smaller recoil loop areas than the bilayer of 20nm Fe thickness, consistent with a stronger exchange response and more reversible magnetization in the former.

Controlling Spatial Confinement Effects in La0.3Pr0.4Ca0.3MnO3 Microbridges via Post Ar and Air Annealing

NASA Astrophysics Data System (ADS)

Jeon, Jaechun; Jung, Jan; Chow, Kim H.

2017-08-01

We report the effects of post Ar and air annealing of La0.3Pr0.4Ca0.3MnO3 microbridges which do not initially show spatial confinement effects. The removal or addition of oxygen via the post annealing changes the sizes and distribution of the metallic and insulating phase domains within these films and can create spatial confinement effects such as percolation induced resistance jumps and tunneling magnetoresistance.

Evolution of magnetic properties and microstructure of Hf2Co11B alloys

DOE PAGES

McGuire, Michael A.; Rios, Orlando

2015-02-05

Amorphous Hf 2Co 11B alloys produced by melt-spinning have been crystallized by annealing at 500-800 °C, and the products have been investigated using magnetization measurements, x-ray diffraction, and scanning electron microscopy. The results reveal the evolution of the phase fractions, microstructure, and magnetic properties with both annealing temperature and time. Crystallization of the phase denoted HfCo 7, which is associated with the development of coercivity, occurs slowly at 500 °C. Annealing at intermediate temperatures produces mixed phase samples containing some of the HfCo 7 phase with the highest values of remanent magnetization and coercivity. The equilibrium structure at 800 °Cmore » contains HfCo3B 2, Hf 6Co 23 and Co, and displays soft ferromagnetism. Maximum values for the remanent magnetization, intrinsic coercivity, and magnetic energy product among the samples are approximately 5.2 kG, 2.0 kOe, and 3.1 MGOe, respectively, which indicates that the significantly higher values observed in crystalline, melt-spun Hf 2Co 11B ribbons are a consequence of the non-equilibrium solidification during the melt-spinning process. Application of high magnetic fields during annealing is observed to strongly affect the microstructural evolution, which may provide access to higher performance materials in Zr/Hf-Co hard ferromagnets. The crystal structure of HfCo 7 and the related Zr analogues is unknown, and without knowledge of atomic positions powder diffraction cannot distinguish among proposed unit cells and symmetries found in the literature.« less

Magnetic properties and microstructure of gas atomized MRE2(Fe, Co)14B powder with ZrC addition (MRE=Nd + Y + Dy)

DOE Office of Scientific and Technical Information (OSTI.GOV)

Tang, W.; Wu, Y. Q.; Dennis, K.

2009-05-12

Gas atomization powder with Zr substitutions for the MRE and ZrC additions were systematically studied. The results show that the partial substitutions of Zr and the ZrC additions effectively improved glass formability in the alloys. Scanning electron microscopy (SEM) revealed that the as-atomized powder with a particle size of less than 32 {micro}m is predominately uniform equiaxed grains with an average grain size of 1.5 {micro}m. X-ray diffraction and differential thermal analysis measurements detected very tiny amounts of amorphous phase. After annealing at 700 C for 15 min, the SEM grain microstructure exhibits a minor change, but magnetic properties aremore » substantially improved. M versus T measurements reveal that the phase composition evolved from 2:14:1 plus a small amount of 2:17 phases to a single 2:14:1 phase during the annealing process. The sieve analysis of the powders showed a particle size distribution with 90 wt % of the powder less than 45 {micro}m. The magnetic properties of the annealed powder varied with particle size. (BH){sub max} first increases with increasing particle size from 5 {micro}m, reaches the peak value in the size range of 20-25 {micro}m, and then decreases with increasing particle size. For the 20-25 {micro}m powder sample annealed at 700 C for 15 min, the (BH){sub max} of 9.6 MG Oe at room temperature and 5.6 MG Oe at 200 C were obtained, respectively.« less

Isotropic rare earth based hard magnets through non-equilibrium processing

NASA Astrophysics Data System (ADS)

Sultana, Dilara

The aim of this thesis was to understand better the relationship of hard magnetic properties to the microstructure and use this knowledge to design a better magnet. The first project was focused on the development of isotropic Pr 9Fe85B6 ribbons with enhanced remanence, high coercivity and high (BH)max. The optimization was achieved by adjusting the composition, controlling the microstructure and processing parameters. The crystal structure in all the samples studied was found to consist of a fine mixture of hard phase 2:14:1 and soft alpha-Fe phase. In all the samples the optimum (BH)max obtained was in the optimally quenched ribbons. Annealing did improve the magnetic properties but did not exceed the highest (BH)max value obtained in the optimally quenched ribbons. Small additions of Tb and Co were found to improve the magnetic properties. The properties were optimized by first adjusting the wheel speed and then the ejection temperature of melt. A maximum (BH)max 21 MGOe and a remanence of 117 emu/g were obtained in the ribbons spun at 18 m/s and ejected at a temperature of 1360°C with a average grain size of 20 nm. This investigation suggests that a proper combination of composition and processing parameters is essential for the optimum (BH)max value for the Pr-Fe-B magnets. The second project was focused on the development of a single phase nanocrystalline Sm2(Co, Fe)17 magnets. The magnetic properties such as coercivity and energy product were optimized via the design of composition, control of melt-spinning parameters and heat treatment. The effect of non magnetic elements like Si, B, addition on the Sm(Co, Fe, M)z alloys were investigated. The effect of C addition on the Smx(Co 1-yMy)100-x-zCz series alloys where, M= Fe or Fe+Mn , X=10-15, Y= 0-0.375, Z= 0-6 were studied thoroughly. It is observed that the crystal structure of Sm(Co0.75Fe0.25) 7, Sm(Co0.65Fe0.25Si0.1)7 and Sm(Co0.65Fe0.25Si0.05B0.05 )8 alloy ribbons spun at low wheel speed shows the presence of 1:5 and 2:17 phase and the metastable 1:7 phase for high wheel speed. It is observed that C suppressed the formation of the stable 2:17 structure in favor of the disordered 1:7 phase. Addition of Si and B, C leads to the development of equiaxed finer grains. C may have act as grain growth inhibitor in the Sm-(Co-Fe)- C ribbons Microstructure refinement with the precipitation of RCoC2 carbides was observed in the C added ribbons. The carbon addition enhances the overall magnetic properties. The 3rd project was focused on the investigation of giant intrinsic magnetic hardness in Sm(Co0.45,Fe0.15,Cu0.4) 5 alloys and determine its dependence on grain / particle size. Melt-spinning and high energy ball milling was used to prepare sample with different grain size (6-500 nm). A single phase 1:5 structure was observed in both the ribbons and milled powders of the Sm(Co0.45,Fe0.15,Cu0.4 )5 alloy. The maximum coercivity obtained was 21 kOe for ribbons spun at 50 m/s (70 nm) and 15 kOe for the powders milled for 15 min (15 nm). Low temperature annealing of ribbons with large grain size > 500 nm for 133 h increases the coercivity to 44 kOe similar like bulk. The effect of low temperature annealing of ribbons with the coarse grain structure (> 70 nm) was the increasing of coercivity, it also increased the Curie temperature of 1: 5 phase and resistivity. The effect of low temperature annealing on the coercivity of high energy milled powders with a smaller grain size (< 70 nm) was different from the ribbons. The maximum coercivity of 21 kOe was obtained for 3h milled powders annealed at 400°C for 1 h. However, after longer annealing the coercivity decreases and this is different behavior from bulk. The effect of annealing on the homogenized crushed powders (>140nm) was more like bulk, even after annealing for 50 h at 400°C coercivity obtained was 38.48 kOe and increasing. (Abstract shortened by UMI.)

Comparison Between Different Processing Schedules for the Development of Ultrafine-Grained Dual-Phase Steel

NASA Astrophysics Data System (ADS)

Karmakar, Anish; Sivaprasad, S.; Nath, S. K.; Misra, R. D. K.; Chakrabarti, Debalay

2014-05-01

A comparative study was carried out on the development of ultrafine-grained dual-phase (DP) (ferrite-martensite) structures in a low-carbon microalloyed steel processed using two thermomechanical processing routes, (i) intercritical deformation and (ii) warm-deformation and intercritical annealing. The samples were deformed using Gleeble3500® simulator, maintaining a constant total strain ( ɛ = 1) and strain rate ( = 1/s). Evolution of microstructure and micro-texture was investigated by SEM, TEM, and EBSD. Ultrafine-grained DP structures could be formed by careful selection of deformation temperature, T def (for intercritical deformation) or annealing temperature, T anneal (for warm-deformation and annealing). Overall, the ferrite grain sizes ranged from 1.5 to 4.0 μm, and the sizes and fractions of the uniformly distributed fine-martensitic islands ranged from 1.5 to 3.0 μm and 15 to 45 pct, respectively. Dynamic strain-induced austenite-to-ferrite transformation followed by continuous (dynamic) recrystallization of the ferrite dictated the grain refinement during intercritical deformation, while, continuous (static) recrystallization by pronounced recovery dictated the grain refinement during the warm-deformation and the annealing. Regarding intercritical deformation, the samples cooled to T def indicated finer grain size compared with the samples heated to T def, which are explained in terms of the effects of strain partitioning on the ferrite and the heating during deformation. Alpha-fiber components dominated the texture in all the samples, and the fraction of high-angle boundaries (with >15 deg misorientation) increased with the increasing T def or T anneal, depending on the processing schedule. Fine carbide particles, microalloyed precipitates and austenitic islands played important roles in defining the mechanism of grain refinement that involved retarding conventional ferrite recrystallization and ferrite grain growth. With regard to the intercritical deformation, warm-deformation followed by annealing is a simpler process to control in the rolling mill; however, the need for high-power rolling mill and controlled annealing facility imposes industrial challenges.

An atom probe perspective on phase separation and precipitation in duplex stainless steels

NASA Astrophysics Data System (ADS)

Guo, Wei; Garfinkel, David A.; Tucker, Julie D.; Haley, Daniel; Young, George A.; Poplawsky, Jonathan D.

2016-06-01

Three-dimensional chemical imaging of Fe-Cr alloys showing Fe-rich (α)/Cr-rich (α‧) phase separation is reported using atom probe tomography techniques. The extent of phase separation, i.e., amplitude and wavelength, has been quantitatively assessed using the Langer-Bar-on-Miller, proximity histogram, and autocorrelation function methods for two separate Fe-Cr alloys, designated 2101 and 2205. Although the 2101 alloy possesses a larger wavelength and amplitude after annealing at 427 °C for 100-10 000 h, it exhibits a lower hardness than the 2205 alloy. In addition to this phase separation, ultra-fine Ni-Mn-Si-Cu-rich G-phase precipitates form at the α/α‧ interfaces in both alloys. For the 2101 alloy, Cu clusters act to form a nucleus, around which a Ni-Mn-Si shell develops during the precipitation process. For the 2205 alloy, the Ni and Cu atoms enrich simultaneously and no core-shell chemical distribution was found. This segregation phenomenon may arise from the exact Ni/Cu ratio inside the ferrite. After annealing for 10 000 h, the number density of the G-phase within the 2205 alloy was found to be roughly one order of magnitude higher than in the 2101 alloy. The G-phase precipitates have an additional deleterious effect on the thermal embrittlement, as evaluated by the Ashby-Orowan equation, which explains the discrepancy between the hardness and the rate of phase separation with respect to annealing time (Gladman T 1999 Mater. Sci. Tech. Ser. 15 30-36). ).

An atom probe perspective on phase separation and precipitation in duplex stainless steels

DOE PAGES

Garfinkel, David A.; Tucker, Julie D.; Haley, Daniel A.; ...

2016-05-16

Here, three-dimensional chemical imaging of Fe–Cr alloys showing Fe-rich (α)/Cr-rich (α') phase separation is reported using atom probe tomography techniques. The extent of phase separation, i.e., amplitude and wavelength, has been quantitatively assessed using the Langer-Bar-on-Miller, proximity histogram, and autocorrelation function methods for two separate Fe–Cr alloys, designated 2101 and 2205. Although the 2101 alloy possesses a larger wavelength and amplitude after annealing at 427 °C for 100–10 000 h, it exhibits a lower hardness than the 2205 alloy. In addition to this phase separation, ultra-fine Ni–Mn–Si–Cu-rich G-phase precipitates form at the α/α' interfaces in both alloys. For the 2101more » alloy, Cu clusters act to form a nucleus, around which a Ni–Mn–Si shell develops during the precipitation process. For the 2205 alloy, the Ni and Cu atoms enrich simultaneously and no core–shell chemical distribution was found. This segregation phenomenon may arise from the exact Ni/Cu ratio inside the ferrite. After annealing for 10 000 h, the number density of the G-phase within the 2205 alloy was found to be roughly one order of magnitude higher than in the 2101 alloy. The G-phase precipitates have an additional deleterious effect on the thermal embrittlement, as evaluated by the Ashby–Orowan equation, which explains the discrepancy between the hardness and the rate of phase separation with respect to annealing time (Gladman T 1999 Mater. Sci. Tech. Ser. 15 30–36).« less

Phase equilibrium and preparation, crystallization and viscous sintering of glass in the alumina-silica-lanthanum phosphate system

NASA Astrophysics Data System (ADS)

He, Feng

The phase equilibrium, viscosity of melt-quenched glasses, and processing of sol-gel glasses of the alumina-silica-lanthanum phosphate system were studied. These investigations were directed towards serving the objective of synthesizing nano-structured ceramic-matrix-composites via controlled crystallization of glass precursors. The thermal stability, phase equilibrium, and liquidus temperatures of the alumina- and mullite-lanthanum phosphate systems are determined. An iridium wire heater was constructed to anneal samples up to 2200°C. Phosphorus evaporation losses were significant at high temperatures, especially over 1800°C. The tentative phase diagrams of the two quasi-binary systems were presented. The viscosity of the melt-quenched mullite-lanthanum phosphate glasses was measured by three different methods, including viscous sintering of glass powder compacts, neck formation between two Frenkel glass beads, and thermal analysis of the glass transition. Improved methodologies were developed for applying the interpretative mathematical models to the results of the sintered powder and thermal analytical experiments. Good agreement was found between all three methods for both absolute values and temperature dependence. A sol-gel process was developed as a low temperature route to producing glasses. A unique, single phase mullite gel capable of low temperature (575°C) mullitization was made from tetraethoxysilane and aluminum isopropoxide at room temperature in three days. Low temperature crystallization was attributed to the avoidance of phase segregation during gel formation and annealing. This was greatly enhanced by a combination of low temperature preheating in the amorphous state, a high heating rate during crystallization and low water content. The Al2O3 content in mullite (61-68 mol%) depended on the highest annealing temperature. Two mullite-lanthanum phosphate gels were made based upon modifying the chemical procedures used for the homogeneous single phase and heterogeneous diphasic mullite gels from same starting chemicals. Amorphous powders were obtained after optimized calcinations. Their different crystallization routes and sintering behavior were investigated and correlated with the different homogeneities of precursor gels. Structurally stable open, porous ceramics (up to 80% porosity) were produced from the single-phase gel derived powder, where gases exsolved during calcination caused foaming coincident with sintering. Translucent, dense glass ceramic was made from the calcined diphasic gel by hot-pressing.

Tunable dielectric properties of TiO2 thin film based MOS systems for application in microelectronics

NASA Astrophysics Data System (ADS)

Gyanan; Mondal, Sandip; Kumar, Arvind

2016-12-01

Post-deposition annealing (PDA) is an inherent part of a sol-gel fabrication process to achieve the optimum device performance, especially in CMOS applications. Annealing removes the oxygen vacancies and improves the structural order of the dielectric films. The process also reduces the interface related defects and improves the interfacial properties. Here, we applied a sol-gel spin-coating technique to prepare high-k TiO2 films on the p-Si substrate. These films were fired at 400 °C for the duration of 20, 40, 60 and 80 min to know the effects of annealing time on the device characteristics. The current-voltage (I-V) and capacitance-voltage (C-V) characteristics of annealed TiO2 films were examined in Al/TiO2/p-Si device configuration at room temperature. The 60 min annealed film gives the optimum performance and contained 69.5% anatase and 39.5% rutile phase with refractive index 2.40 at 550 nm. The C-V and I-V characteristic showed a significant dependence on annealing time such as variation in dielectric constant and leakage current. This allows us to tune the various electrical properties of MOS systems. The accumulation capacitance (Cox), dielectric constant (κ) and the equivalent oxide thickness (EOT) of the film fired for 60 min were found to be 458 pF, 33, and 4.25 nm, respectively with a low leakage current density (3.13 × 10-7 A/cm2) fired for 80 min at -1 V. The current conduction mechanisms at high bias voltage were dominated by trap-charge limited current (TCLC), while at small voltages, space charge limited current (SCLC) was more prominent.

Effects of heat treatment on U-Mo fuel foils with a zirconium diffusion barrier

NASA Astrophysics Data System (ADS)

Jue, Jan-Fong; Trowbridge, Tammy L.; Breckenridge, Cynthia R.; Moore, Glenn A.; Meyer, Mitchell K.; Keiser, Dennis D.

2015-05-01

A monolith fuel design based on U-Mo alloy has been selected as the fuel type for conversion of the United States' high performance research reactors (HPRRs) from highly enriched uranium (HEU) to low-enriched uranium (LEU). In this fuel design, a thin layer of zirconium is used to eliminate the direct interaction between the U-Mo fuel meat and the aluminum-alloy cladding during irradiation. The co-rolling process used to bond the Zr barrier layer to the U-Mo foil during fabrication alters the microstructure of both the U-10Mo fuel meat and the U-Mo/Zr interface. This work studied the effects of post-rolling annealing treatment on the microstructure of the co-rolled U-Mo fuel meat and the U-Mo/Zr interaction layer. Microscopic characterization shows that the grain size of U-Mo fuel meat increases with the annealing temperature, as expected. The grain sizes were ∼9, ∼13, and ∼20 μm for annealing temperature of 650, 750, and 850 °C, respectively. No abnormal grain growth was observed. The U-Mo/Zr interaction-layer thickness increased with the annealing temperature with an Arrhenius constant for growth of 184 kJ/mole, consistent with a previous diffusion-couple study. The interaction layer thickness was 3.2 ± 0.5 μm, 11.1 ± 2.1 μm, 27.1 ± 0.9 μm for annealing temperature of 650, 750, to 850 °C, respectively. The homogeneity of Mo improves with post rolling annealing temperature and with U-Mo coupon homogenization. The phases in the Zr/U-Mo interaction layer produced by co-rolling, however, differ from those reported in the previous diffusion couple studies.

Effects of heat treatment on U–Mo fuel foils with a zirconium diffusion barrier

DOE Office of Scientific and Technical Information (OSTI.GOV)

Jue, Jan-Fong; Trowbridge, Tammy L.; Breckenridge, Cynthia R.

A monolith fuel design based on U–Mo alloy has been selected as the fuel type for conversion of the United States’ high performance research reactors (HPRRs) from highly enriched uranium (HEU) to low-enriched uranium (LEU). In this fuel design, a thin layer of zirconium is used to eliminate the direct interaction between the U–Mo fuel meat and the aluminum-alloy cladding during irradiation. The co-rolling process used to bond the Zr barrier layer to the U–Mo foil during fabrication alters the microstructure of both the U–10Mo fuel meat and the U–Mo/Zr interface. This work studied the effects of post-rolling annealing treatmentmore » on the microstructure of the co-rolled U–Mo fuel meat and the U–Mo/Zr interaction layer. Microscopic characterization shows that the grain size of U–Mo fuel meat increases with the annealing temperature, as expected. The grain sizes were ~9, ~13, and ~20 μm for annealing temperature of 650, 750, and 850 °C, respectively. No abnormal grain growth was observed. The U–Mo/Zr interaction-layer thickness increased with the annealing temperature with an Arrhenius constant for growth of 184 kJ/mole, consistent with a previous diffusion-couple study. The interaction layer thickness was 3.2 ± 0.5 μm, 11.1 ± 2.1 μm, 27.1 ± 0.9 μm for annealing temperature of 650, 750, to 850 °C, respectively. The homogeneity of Mo improves with post rolling annealing temperature and with U–Mo coupon homogenization. The phases in the Zr/U–Mo interaction layer produced by co-rolling, however, differ from those reported in the previous diffusion couple studies.« less

Effects of annealing on the structure and magnetic properties of Fe80B20 magnetostrictive fibers.

PubMed

Zhu, Qianke; Zhang, Shuling; Geng, Guihong; Li, Qiushu; Zhang, Kewei; Zhang, Lin

2016-07-04

Fe80B20 amorphous alloys exhibit excellent soft magnetic properties, high abrasive resistance and outstanding corrosion resistance. In this work, Fe80B20 amorphous micro-fibers with HC of 3.33 Oe were firstly fabricated and the effects of annealing temperature on the structure and magnetic properties of the fibers were investigated. In this study, Fe80B20 amorphous fibers were prepared by the single roller melt-spinning method. The structures of as-spun and annealed fibers were investigated by X-ray diffractometer (XRD) (PANalytical X,Pert Power) using Cu Kα radiation. The morphology of the fibers was observed by scanning electron microscopy (SEM) (HITACHI-S4800). Differential scanning calorimetry (DSC) measurements of the fibers were performed on Mettler Toledo TGA/DSC1 device under N2 protection. Vibrating sample magnetometer (VSM, Versalab) was used to examine the magnetic properties of the fibers. The resonance behavior of the fibers was characterized by an impedance analyzer (Agilent 4294A) with a home-made copper coil. The X-ray diffusion (XRD) patterns show that the fibers remain amorphous structure until the annealing temperature reaches 500°C. The differential scanning calorimetry (DSC) results show that the crystallization temperature of the fibers is 449°C. The crystallization activation energy is calculated to be 221 kJ/mol using Kissinger formula. The scanning electron microscopy (SEM) images show that a few dendrites appear at the fiber surface after annealing. The result indicates that the coercivity HC (//) and HC (⊥) slightly increases with increasing annealing temperature until 400°C, and then dramatically increases with further increasing annealing temperature which is due to significant increase in magneto-crystalline anisotropy and magneto-elastic anisotropy. The Q value firstly increases slightly when the annealing temperature rises from room temperature (RT) to 300°C, then decreases until 400°C. Eventually, the value of Q increases to ~2000 at annealing temperature of 500°C. In this study, Fe80B20 amorphous fibers with the diameter of 60 μm were prepared by the single roller melt-spinning method and annealed at 200°C, 300°C, 400°C, and 500°C, respectively. XRD results indicate that the fiber structure remains amorphous when the annealing temperature is below 400°C. α-Fe phase and Fe3B phase appear when the annealing temperature rises to 500°C, which is above the crystallization temperature of 449°C. The recrystallization activation energy is calculated to be 221 kJ/mol. The coercivity increases with increasing annealing temperature, which attributes to the increase of total anisotropy. All the as-spun and annealed fibers exhibit good resonance behavior for magnetostrictive sensors.

High temperature Ir segregation in Ir-B ceramics: Effect of oxygen presence on stability of IrB 2 and other Ir-B phases

DOE PAGES

Xie, Zhilin; Terracciano, Anthony C.; Cullen, David A.; ...

2015-05-13

The formation of IrB 2, IrB 1.35, IrB 1.1 and IrB monoboride phases in the Ir–B ceramic nanopowder was confirmed during mechanochemical reaction between metallic Ir and elemental B powders. The Ir–B phases were analysed after 90 h of high energy ball milling and after annealing of the powder for 72 h at 1050°C in vacuo. The iridium monoboride (IrB) orthorhombic phase was synthesised experimentally for the first time and identified by powder X-ray diffraction. Additionally, the ReB 2 type IrB 2 hexagonal phase was also produced for the first time and identified by high resolution transmission electron microscope. Irmore » segregation along disordered domains of the boron lattice was found to occur during high temperature annealing. Furthermore, these nanodomains may have useful catalytic properties.« less

Effect of Heat Treatment on Microstructure and Magnetostrictive Property of Melt-Spun Fe85Ga15 Ribbons

NASA Astrophysics Data System (ADS)

Liu, Hao; Wang, Haiou; Cao, Mengxiong; Tan, Weishi; Shi, Yangguang; Chen, Yu; Huang, Yuying

2013-09-01

In order to study the microstructure of Fe-Ga alloy, Fe85Ga15 ribbons prepared with different wheel velocity were studied by high resolution X-ray diffraction (HRXRD) and extend X-ray absorption fine structure (EXAFS). HRXRD patterns showed that only disordered A2 phase was observed in as-cast Fe85Ga15 alloy. A modified-DO3 phase was detected in all of the melt spun samples. The HRXRD associated with EXAFS results indicated that Ga atoms were located as second-nearest neighbor along [100] orientation. A little DO3 phase was found in ribbons annealed at 1000°C under 0.06 MPa Ar atmosphere. The result of magnetostriction measurement revealed that in the ribbon prepared with higher wheel velocity, more modified-DO3 phase will enhance the magnetostriction. DO3 phase in the annealed sample will deteriorate the magnetostrictive properties of Fe-Ga ribbons.

Anneal-Hardening Behavior of Cr-Fe-C Alloy Deposits Prepared in a Cr3+-Based Bath with Fe2+ Ions

PubMed Central

Huang, Ching An; Chen, Jhih You; Wang, Hai

2017-01-01

Cr-Fe-C alloy deposits were successfully prepared on high-carbon tool steel in a Cr3+-based electroplating bath containing Fe2+ ions and suitable complex agents. A Cr-based alloy deposit was obtained with an electroplating current density higher than 25 Adm−2, and a Fe-based alloy deposit was obtained using a current density of 20 Adm−2. Following electroplating, these alloy deposited specimens were annealed via rapid thermal annealing (RTA) at 500 °C for different periods up to 30 s. The experimental results show that Cr- and Fe-based alloy deposits could be significantly hardened after RTA at 500 °C for a few seconds. The maximum hardness was that of the Cr-Fe-C alloy deposit annealed at 500 °C for 10 s. The maximum hardness of 1205 Hv was detected from the annealed Cr-based alloy deposit prepared with 30 ASD. The hardening mechanism of annealed Cr- and Fe-based alloy deposits is attributed to the precipitation of C-related membranes. The hardness values of the annealed Cr- and Fe-based alloy deposits increase with the increasing degree of crystallization of the C-related membranes. PMID:29206206

Role of nanocrystallinity on the chemical ordering of Co xPt 100-x nanocrystals synthesized by wet chemistry

DOE PAGES

Cordeiro, Marco; Kameche, Farid; Ngo, Anh -Tu; ...

2015-03-17

Co xPt 100–x nanoalloys have been synthesized by two different chemical processes either at high or at low temperature. Their physical properties and the order/disorder phase transition induced by annealing have been investigated depending on the route of synthesis. It is demonstrated that the chemical synthesis at high temperature allows stabilization of the fcc structure of the native nanoalloys while the soft chemical approach yields mainly poly or non crystalline structure. As a result the approach of the order/disorder phase transition is strongly modified as observed by high-resolution transmission electron microscopy (HR-TEM) studies performed during in situ annealing of themore » different nanoalloys. The control of the nanocrystallinity leads to significant decrease in the chemical ordering temperature as the ordered structure is observed at temperatures as low as 420 °C. Furthermore, this in turn preserves the individual nanocrystals and prevents their coalescence usually observed during the annealing necessary for the transition to an ordered phase.« less

The DNA repair endonuclease XPG interacts directly and functionally with the WRN helicase defective in Werner syndrome

DOE Office of Scientific and Technical Information (OSTI.GOV)

Trego, Kelly S.; Chernikova, Sophia B.; Davalos, Albert R.

XPG is a structure-specific endonuclease required for nucleotide excision repair (NER). XPG incision defects result in the cancer-prone syndrome xeroderma pigmentosum, whereas truncating mutations of XPG cause the severe postnatal progeroid developmental disorder Cockayne syndrome. We show that XPG interacts directly with WRN protein, which is defective in the premature aging disorder Werner syndrome, and that the two proteins undergo similar sub-nuclear redistribution in S-phase and co-localize in nuclear foci. The co-localization was observed in mid- to late-S-phase, when WRN moves from nucleoli to nuclear foci that have been shown to contain protein markers of both stalled replication forks andmore » telomeric proteins. We mapped the interaction between XPG and WRN to the C-terminal domains of each and show that interaction with the C-terminal domain of XPG strongly stimulates WRN helicase activity. WRN also possesses a competing DNA single-strand annealing activity that, combined with unwinding, has been shown to coordinate regression of model replication forks to form Holliday junction/chicken foot intermediate structures. We tested whether XPG stimulated WRN annealing activity and found that XPG itself has intrinsic strand annealing activity that requires the unstructured R- and C-terminal domains, but not the conserved catalytic core or endonuclease activity. Annealing by XPG is cooperative, rather than additive, with WRN annealing. Taken together, our results suggest a novel function for XPG in S-phase that is at least in part carried out coordinately with WRN, and which may contribute to the severity of the phenotypes that occur upon loss of XPG.« less

Evolution of structural and magnetic properties of amorphous CoFeB film with thermal annealing

DOE Office of Scientific and Technical Information (OSTI.GOV)

Gupta, Ranjeeta; Gupta, Ajay; Gupta, Mukul

2013-08-14

Evolution of structural and magnetic properties of amorphous Co{sub 68}Fe{sub 14}B{sub 18} thin film with thermal annealing has been studied. Initially, the film exhibits a structural relaxation as evidenced by annihilation of excess free volume and an increase in topological short range order. Annealing at 473 K results in precipitation of primary phase followed by formation of boride phase at a still higher temperature of 598 K. Iron preferentially precipitates out in the primary phase, resulting in the formation of bcc Co{sub 58}Fe{sub 41}. This suggests an affinity of Co towards B. Such affinity between Co and B is evidencedmore » even in the as-deposited film, using hard x-ray photoelectron spectroscopy (HAXPES) measurements. As-deposited film exhibits an in-plane uniaxial magnetic anisotropy which disappears at a temperature well beyond crystallization temperature, suggesting that the origin of anisotropy is mainly a chemical short range order in the system. Variation in the coercivity with thermal annealing can be understood in terms of random anisotropy model. Precise measurement of Fe self-diffusion using neutron reflectivity shows that diffusion length associated with annihilation of excess free volume in the film is about 0.5 nm. This agrees with the length scale of structural fluctuations in amorphous alloys. Secondary ion mass spectrometry measurements show that thermal annealing results in depletion of B in the region of the interface with the substrate, with associated faster Fe diffusion in this region. This faster diffusion of Fe may be a possible cause of preferential crystallization of the film in the interfacial region as seen in some earlier studies.« less

Study of retained austenite and nano-scale precipitation and their effects on properties of a low alloyed multi-phase steel by the two-step intercritical treatment

DOE Office of Scientific and Technical Information (OSTI.GOV)

Xie, Z.J.; Han, G., E-mail: hangang@mater.ustb.edu.cn; Zhou, W.H.

2016-03-15

Microstructure evolution and properties were studied in a low carbon low alloyed hot-rolled bainitic steel by annealing and annealing plus tempering. Microstructure of the hot-rolled steel consists of lath bainite and martensite. By annealing at 720 °C for 30 min and water quenching, multi-phase microstructure consisting of intercritical ferrite, tempered bainite/martensite, retained austenite and fresh martensite was obtained. With increasing annealing temperature to 760 °C, microstructure of the steel consisted of intercritical ferrite, fresh martensite without retained austenite. After the second step of tempering at 680 °C for samples annealed both at 720 °C and 760 °C, ~ 8–9% volumemore » fraction of retained austenite was obtained in the multi-phase microstructure. Moreover, fine precipitates of VC with size smaller than 10 nm and copper precipitates with size of ~ 10–50 nm were obtained after tempering. Results from scanning transmission electron microscopy (STEM) give evidence to support that the partitioning of Mn, Ni and Cu is of significance for retained austenite stabilization. Due to the combined contribution of multiphase microstructure, the transformation-induced-plasticity effect of retained austenite and strengthening effect of nanometer-sized precipitates, yield strength greater than 800 MPa, yield to tensile ratio of 0.9, uniform elongation of ~ 9% and good low temperature impact toughness of 147 J at − 40 °C were achieved. - Highlights: • Stable retained austenite was produced in a low alloyed steel. • Partition of Mn, Ni and Cu was confirmed by STEM for austenite stabilization. • Nano-sized VC and Cu precipitates were achieved by second tempering. • High strength–high toughness with low Y/T ratio was obtained.« less

Thermal stability and reduction of iron oxide nanowires at moderate temperatures.

PubMed

Paolone, Annalisa; Angelucci, Marco; Panero, Stefania; Betti, Maria Grazia; Mariani, Carlo

2014-01-01

The thermal stability of iron oxide nanowires, which were obtained with a hard template method and are promising elements of Li-ion based batteries, has been investigated by means of thermogravimetry, infrared and photoemission spectroscopy measurements. The chemical state of the nanowires is typical of the Fe2O3 phase and the stoichiometry changes towards a Fe3O4 phase by annealing above 440 K. The shape and morphology of the nanowires is not modified by moderate thermal treatment, as imaged by scanning electron microscopy. This complementary spectroscopy-microscopy study allows to assess the temperature limits of these Fe2O3 nanowires during operation, malfunctioning or abuse in advanced Li-ion based batteries.

Combined Effect of Heating Rate and Microalloying Elements on Recrystallization During Annealing of Dual-Phase Steels

NASA Astrophysics Data System (ADS)

Bellavoine, Marion; Dumont, Myriam; Drillet, Josée; Hébert, Véronique; Maugis, Philippe

2018-05-01

Adjusting ferrite recrystallization kinetics during annealing is a way to control the final microstructure and thus the mechanical properties of advanced cold-rolled high-strength steels. Two strategies are commonly used for this purpose: adjusting heating rates and/or adding microalloying elements. The present work investigates the effect of heating rate and microalloying elements Ti, Nb, and Mo on recrystallization kinetics during annealing in various cold-rolled Dual-Phase steel grades. The use of combined experimental and modeling approaches allows a deeper understanding of the separate influence of heating rate and the addition of microalloying elements. The comparative effect of Ti, Nb, and Mo as solute elements and as precipitates on ferrite recrystallization is also clarified. It is shown that solute drag has the largest delaying effect on recrystallization in the present case and that the order of solute drag effectiveness of microalloying elements is Nb > Mo > Ti.

Microstructure and Dielectric Properties of LPCVD/CVI-SiBCN Ceramics Annealed at Different Temperatures

PubMed Central

Li, Jianping; Zhao, Mingxi; Liu, Yongsheng; Chai, Nan; Ye, Fang; Qin, Hailong; Cheng, Laifei; Zhang, Litong

2017-01-01

SiBCN ceramics were introduced into porous Si3N4 ceramics via a low-pressure chemical vapor deposition and infiltration (LPCVD/CVI) technique, and then the composite ceramics were heat-treated from 1400 °C to 1700 °C in a N2 atmosphere. The effects of annealing temperatures on microstructure, phase evolution, dielectric properties of SiBCN ceramics were investigated. The results revealed that α-Si3N4 and free carbon were separated below 1700 °C, and then SiC grains formed in the SiBCN ceramic matrix after annealing at 1700 °C through a phase-reaction between free carbon and α-Si3N4. The average dielectric loss of composites increased from 0 to 0.03 due to the formation of dispersive SiC grains and the increase of grain boundaries. PMID:28773015

Combined Effect of Heating Rate and Microalloying Elements on Recrystallization During Annealing of Dual-Phase Steels

NASA Astrophysics Data System (ADS)

Bellavoine, Marion; Dumont, Myriam; Drillet, Josée; Hébert, Véronique; Maugis, Philippe

2018-07-01

Adjusting ferrite recrystallization kinetics during annealing is a way to control the final microstructure and thus the mechanical properties of advanced cold-rolled high-strength steels. Two strategies are commonly used for this purpose: adjusting heating rates and/or adding microalloying elements. The present work investigates the effect of heating rate and microalloying elements Ti, Nb, and Mo on recrystallization kinetics during annealing in various cold-rolled Dual-Phase steel grades. The use of combined experimental and modeling approaches allows a deeper understanding of the separate influence of heating rate and the addition of microalloying elements. The comparative effect of Ti, Nb, and Mo as solute elements and as precipitates on ferrite recrystallization is also clarified. It is shown that solute drag has the largest delaying effect on recrystallization in the present case and that the order of solute drag effectiveness of microalloying elements is Nb > Mo > Ti.

Fabrication of VO2 thin film by rapid thermal annealing in oxygen atmosphere and its metal—insulator phase transition properties

NASA Astrophysics Data System (ADS)

Liang, Ji-Ran; Wu, Mai-Jun; Hu, Ming; Liu, Jian; Zhu, Nai-Wei; Xia, Xiao-Xu; Chen, Hong-Da

2014-07-01

Vanadium dioxide thin films have been fabricated through sputtering vanadium thin films and rapid thermal annealing in oxygen. The microstructure and the metal—insulator transition properties of the vanadium dioxide thin films were investigated by X-ray diffraction, X-ray photoelectron spectroscopy, and a spectrometer. It is found that the preferred orientation of the vanadium dioxide changes from (1¯11) to (011) with increasing thickness of the vanadium thin film after rapid thermal annealing. The vanadium dioxide thin films exhibit an obvious metal—insulator transition with increasing temperature, and the phase transition temperature decreases as the film thickness increases. The transition shows hysteretic behaviors, and the hysteresis width decreases as the film thickness increases due to the higher concentration carriers resulted from the uncompleted lattice. The fabrication of vanadium dioxide thin films with higher concentration carriers will facilitate the nature study of the metal—insulator transition.

Behaviour of implanted arsenic during rapid thermal annealing of Ti on Si

NASA Astrophysics Data System (ADS)

Ponpon, J. P.; Saulnier, A.; Stuck, R.

1987-11-01

The reaction during rapid thermal annealing of the Ti-Si couple with arsenic implanted either into titanium or into silicon has been investigated from the point of view of suicide formation kinetics and impurity redistribution. In contrast with similar experiments on other refractory metals, tungsten for example, the reaction is not blocked by the presence of arsenic but a temperature and dose dependent impurity effect leading to a lowering of the growth rate of the disilicide phase is observed. This has been attributed to arsenic segregation in the grain boundaries of the growing suicide which reduces the transport of silicon via easy diffusion paths towards the unreacted metal or a metal rich suicide phase. Arsenic, when present in the metal, has been found to produce the same effects as oxygen at the early beginning of the annealing. However, after the reaction has started the respective behaviour and influence of arsenic and oxygen become completely different.

Coherent diffractive imaging of solid state reactions in zinc oxide crystals

NASA Astrophysics Data System (ADS)

Leake, Steven J.; Harder, Ross; Robinson, Ian K.

2011-11-01

We investigated the doping of zinc oxide (ZnO) microcrystals with iron and nickel via in situ coherent x-ray diffractive imaging (CXDI) in vacuum. Evaporated thin metal films were deposited onto the ZnO microcrystals. A single crystal was selected and tracked through annealing cycles. A solid state reaction was observed in both iron and nickel experiments using CXDI. A combination of the shrink wrap and guided hybrid-input-output phasing methods were applied to retrieve the electron density. The resolution was 33 nm (half order) determined via the phase retrieval transfer function. The resulting images are nevertheless sensitive to sub-angstrom displacements. The exterior of the microcrystal was found to degrade dramatically. The annealing of ZnO microcrystals coated with metal thin films proved an unsuitable doping method. In addition the observed defect structure of one crystal was attributed to the presence of an array of defects and was found to change upon annealing.

Microstructural and Phase Composition Differences Across the Interfaces in Al/Ti/Al Explosively Welded Clads

NASA Astrophysics Data System (ADS)

Fronczek, Dagmara Malgorzata; Chulist, Robert; Litynska-Dobrzynska, Lidia; Lopez, Gabriel Alejandro; Wierzbicka-Miernik, Anna; Schell, Norbert; Szulc, Zygmunt; Wojewoda-Budka, Joanna

2017-09-01

The microstructure and phase composition of Al/Ti/Al interfaces with respect to their localization were investigated. An aluminum-flyer plate exhibited finer grains located close to the upper interface than those present within the aluminum-base plate. The same tendency, but with a higher number of twins, was observed for titanium. Good quality bonding with a wavy shape and four intermetallic phases, namely, TiAl3, TiAl, TiAl2, and Ti3Al, was only obtained at the interface closer to the explosive material. The other interface was planar with three intermetallic compounds, excluding the metastable TiAl2 phase. As a result of a 100-hour annealing at 903 K (630 °C), an Al/TiAl3/Ti/TiAl3/Al sandwich was manufactured, formed with single crystalline Al layers. A substantial difference between the intermetallic layer thicknesses was measured, with 235.3 and 167.4 µm obtained for the layers corresponding to the upper and lower interfaces, respectively. An examination by transmission electron microscopy of a thin foil taken from the interface area after a 1-hour annealing at 825 K (552 °C) showed a mixture of randomly located TiAl3 grains within the aluminum. Finally, the hardness results were correlated with the microstructural changes across the samples.

Microstructure, magnetic and magnetocaloric properties in Ni42.9Co6.9Mn38.3Sn11.9 alloy ribbons

NASA Astrophysics Data System (ADS)

Ma, S. C.; Ge, Q.; Yang, S.; Liu, K.; Han, X. Q.; Yu, K.; Song, Y.; Zhang, Z. S.; Jiang, Q. Z.; Chen, C. C.; Liu, R. H.; Zhong, Z. C.

2018-05-01

The microstructure, magnetic and magnetocaloric properties are investigated in the melt-spun and annealed Ni42.9Co6.9Mn38.3Sn11.9 ribbons. The columnar grains grow perpendicular to ribbon surfaces. After annealing, the grain size increases greatly. Meanwhile, the parent phase is suppressed and therefore L10 martensite predominates, indicating obvious shift of martensitic transformation to high temperature. More interestingly, the martensite variants are distinctly observed on the fractured cross-section of annealed ribbons, not just on the free surface in general. The significant enhancement of magnetic entropy change and effective refrigerant capacities with relatively smaller thermal hysteresis make annealed ribbons potential candidate in magnetic refrigeration around room temperature.

Influence of vacuum annealing on the properties of Cu2SnS3 thin films using low cost ultrasonic spray pyrolysis

NASA Astrophysics Data System (ADS)

Rahaman, Sabina; Sunil, M. Anantha; Shaik, Habibuddin; Ghosh, Kaustab

2018-05-01

Deposition of Cu2SnS3 (CTS) thin films is successfully carried out on soda lime glass substrate using low cost ultrasonic spray pyrolysis technique. Vacuum annealing of CTS films is carried out at different temperatures 350°C, 400°C and 450°C. The present work is to study the effect of annealing temperature on the crystal structure, surface morphology and optical properties of CTS thin films. Structural studies confirm the formation of CTS phase. Raman analysis is carried out to study presence of defects with annealing temperature. Optical studies confirm that film prepared at 450°C temperature is suitable as absorber material for photovoltaic applications.

Nanostructured Crystals of Fluorite Phases Sr1 - x R x F2 + x and Their Ordering: 12. Influence of Structural Ordering on the Fluorine-Ion Conductivity of Sr0.667 R 0.333F2.333 Alloys ( R = Tb or Tm) at Their Annealing

NASA Astrophysics Data System (ADS)

Sorokin, N. I.; Karimov, D. N.; Sul'yanova, E. A.; Sobolev, B. P.

2018-01-01

The ionic conductivity of Sr0.667 R 0.333F2.333 alloys (rational Sr2 RF7 compositions) in SrF2- RF3 systems ( R = Tb or Tm), prepared by spontaneous crystallization, has been investigated for the "as-grown" state and after annealing in CF4 at 900 ± 20°C for 96 h. As-grown samples of both compositions, prepared by fast (200°C/min) melt crystallization, exhibit partial (nonequilibrium) ordering, which increases from Tb to Tm. Annealing of Sr0.667 R 0.333F2.333 alloys yields strong ordering (equilibrium for the annealing temperatures) of the fluorite structure (CaF2 type, sp. gr. Fm3̅ m, Z = 4) at the formation of t-Sr2 RF7 tetragonal compound (sp. gr. I4/ m, Z = 30). It is established that ordering of the alloy fluorite structure reduces the fluorine-ion conductivity. After the annealing, the conductivity of Sr0.667R0.333F2.333 alloys with the initial (nonequilibrium) ordering stage of t-Sr2 RF7 phases with almost complete (equilibrium) ordering decreases by a factor of 3-4.5.

Effects of Al content and annealing on the phases formation, lattice parameters, and magnetization of A l x F e 2 B 2 ( x = 1.0 , 1.1 , 1.2 ) alloys

DOE Office of Scientific and Technical Information (OSTI.GOV)

Levin, E. M.; Jensen, B. A.; Barua, R.

AlFe 2B 2 is a ferromagnet with the Curie temperature around 300 K and has the potential to be an outstanding rare-earth free candidate for magnetocaloric applications. However, samples prepared from the melt contain additional phases which affect the functional response of the AlFe 2B 2 phase. Here, we report on the effects of Al content in samples with the initial (nominal) composition of Al xFe 2B 2 where x=1.0, 1.1, and 1.2 prepared by arc-melting followed by suction casting and annealing. The as-cast Al xFe 2B 2 alloys contain AlFe 2B 2 as well as additional phases including themore » primary solidifying FeB and Al 13Fe 4 compounds which are ferromagnetic and paramagnetic, respectively, at 300 K. The presence of these phases makes it difficult to extract the intrinsic magnetic properties of AlFe 2B 2 phase. Annealing of Al xFe 2B 2 alloys at 1040°C for 3 days allows for reaction of the FeB with Al 13Fe 4 to form the AlFe 2B 2 phase, significantly reduces the amount of additional phases, and results in nearly pure AlFe 2B2 phase as confirmed with XRD, magnetization, scanning electron microscopy, and electronic transport. The values of the magnetization, effective magnetic moment per Fe atom, specific heat capacity, electrical resistivity and Seebeck coefficient for the AlFe 2B 2 compound have been established.« less

Microstructure, microstructural stability and mechanical properties of sand-cast Mg–4Al–4RE alloy

DOE Office of Scientific and Technical Information (OSTI.GOV)

Rzychoń, Tomasz, E-mail: tomasz.rzychon@polsl.pl; Kiełbus, Andrzej; Lityńska-Dobrzyńska, Lidia

2013-09-15

This paper presents a methodology for assessing the phase composition and the results of structural stability tests of the sand-cast Mg–4Al–4RE alloy after annealing it at 175 and 250 °C for 3000 h. The microstructure was analyzed with optical, scanning electron, and transmission electron microscopy. The phase composition was determined with X-ray diffraction. The structure of the Mg–4Al–4RE (AE44) alloy is composed of large grains of α-Mg solid solution, needle-shaped precipitates of the Al{sub 11}RE{sub 3}phase, polyhedral precipitates of the Al{sub 2}RE phase and Al{sub 10}RE{sub 2}Mn{sub 7} phase. After annealing at 175 °C for 3000 h, no changes inmore » the alloy structure are observed, whereas after annealing at 250 °C the precipitates of the Al{sub 11}RE{sub 3} phase are found to be in the initial stages of spheroidization. The coarse-grained structure and unfavorable morphology of the intermetallic phases in the sand-cast AE44 alloy, which are caused by low solidification rates, result in low creep resistance up to 200 °C and low mechanical properties at ambient temperature and at 175 °C. - Highlights: • Complement the knowledge about the microstructure of Mg-Al-RE alloys. • Clarify the mechanism of formation of Mg17Al12 phase above 180 °C. • Applying a chemical dissolution of the α-Mg in order to phase identification. • Applying a statistical test to assess the spheroidization of precipitates. • Quantitative description of microstructure of Mg-Al-RE alloys.« less

Effects of Al content and annealing on the phases formation, lattice parameters, and magnetization of A lxF e2B2 (x =1.0 ,1.1 ,1.2 ) alloys

NASA Astrophysics Data System (ADS)

Levin, E. M.; Jensen, B. A.; Barua, R.; Lejeune, B.; Howard, A.; McCallum, R. W.; Kramer, M. J.; Lewis, L. H.

2018-03-01

AlF e2B2 is a ferromagnet with the Curie temperature around 300 K and has the potential to be an outstanding rare-earth free candidate for magnetocaloric applications. However, samples prepared from the melt contain additional phases which affect the functional response of the AlF e2B2 phase. We report on the effects of Al content in samples with the initial (nominal) composition of A lxF e2B2 , where x =1.0 , 1.1, and 1.2 prepared by arc-melting followed by suction casting and annealing. The as-cast A lxF e2B2 alloys contain AlF e2B2 as well as additional phases, including the primary solidifying FeB and A l13F e4 compounds, which are ferromagnetic and paramagnetic, respectively, at 300 K. The presence of these phases makes it difficult to extract the intrinsic magnetic properties of AlF e2B2 phase. Annealing of A lxF e2B2 alloys at 1040 °C for 3 days allows for reaction of the FeB with A l13F e4 to form the AlF e2B2 phase, significantly reduces the amount of additional phases, and results in nearly pure AlF e2B2 phase as confirmed with XRD, magnetization, scanning electron microscopy, and electronic transport. The values of the magnetization, effective magnetic moment per Fe atom, specific heat capacity, electrical resistivity, and Seebeck coefficient for the AlF e2B2 compound have been established.

Effects of Al content and annealing on the phases formation, lattice parameters, and magnetization of A l x F e 2 B 2 ( x = 1.0 , 1.1 , 1.2 ) alloys

DOE PAGES

Levin, E. M.; Jensen, B. A.; Barua, R.; ...

2018-03-26

AlFe 2B 2 is a ferromagnet with the Curie temperature around 300 K and has the potential to be an outstanding rare-earth free candidate for magnetocaloric applications. However, samples prepared from the melt contain additional phases which affect the functional response of the AlFe 2B 2 phase. Here, we report on the effects of Al content in samples with the initial (nominal) composition of Al xFe 2B 2 where x=1.0, 1.1, and 1.2 prepared by arc-melting followed by suction casting and annealing. The as-cast Al xFe 2B 2 alloys contain AlFe 2B 2 as well as additional phases including themore » primary solidifying FeB and Al 13Fe 4 compounds which are ferromagnetic and paramagnetic, respectively, at 300 K. The presence of these phases makes it difficult to extract the intrinsic magnetic properties of AlFe 2B 2 phase. Annealing of Al xFe 2B 2 alloys at 1040°C for 3 days allows for reaction of the FeB with Al 13Fe 4 to form the AlFe 2B 2 phase, significantly reduces the amount of additional phases, and results in nearly pure AlFe 2B2 phase as confirmed with XRD, magnetization, scanning electron microscopy, and electronic transport. The values of the magnetization, effective magnetic moment per Fe atom, specific heat capacity, electrical resistivity and Seebeck coefficient for the AlFe 2B 2 compound have been established.« less

Composition and crystal structure of N doped TiO2 film deposited at different O2 flow rate by direct current sputtering.

PubMed

Ding, Wanyu; Ju, Dongying; Chai, Weiping

2011-06-01

N doped Ti02 films were deposited by direct current pulse magnetron sputtering system at room temperature. The influence of 02 flow rate on the crystal structure of deposited films was studied by Stylus profilometer, X-ray photoelectron spectroscopy, and X-ray diffractometer. The results indicate that the 02 flow rate strongly controls the growth behavior and crystal structure of N doped Ti02 film. It is found that N element mainly exists as substitutional doped state and the chemical stiochiometry is near to TiO1.68±0.06N0.11±0.01 for all film samples. N doped Ti02 film deposited with 2 sccm (standard-state cubic centimeter per minute) 02 flow rate is amorphous structure with high growth rate, which contains both anatase phase and rutile phase crystal nucleuses. In this case, the film displays the mix-phase of anatase and rutile after annealing treatment. While N doped Ti02 film deposited with 12 cm(3)/min 02 flow rate displays anatase phase before and after annealing treatment. And it should be noticed that no TiN phase appears for all samples before and after annealing treatment. Copyright © 2011 The Research Centre for Eco-Environmental Sciences, Chinese Academy of Sciences. Published by Elsevier B.V. All rights reserved.

Analysis of Radiation Effects in Silicon using Kinetic Monte Carlo Methods

DOE PAGES

Hehr, Brian Douglas

2014-11-25

The transient degradation of semiconductor device performance under irradiation has long been an issue of concern. Neutron irradiation can instigate the formation of quasi-stable defect structures, thereby introducing new energy levels into the bandgap that alter carrier lifetimes and give rise to such phenomena as gain degradation in bipolar junction transistors. Normally, the initial defect formation phase is followed by a recovery phase in which defect-defect or defect-dopant interactions modify the characteristics of the damaged structure. A kinetic Monte Carlo (KMC) code has been developed to model both thermal and carrier injection annealing of initial defect structures in semiconductor materials.more » The code is employed to investigate annealing in electron-irradiated, p-type silicon as well as the recovery of base current in silicon transistors bombarded with neutrons at the Los Alamos Neutron Science Center (LANSCE) “Blue Room” facility. Our results reveal that KMC calculations agree well with these experiments once adjustments are made, within the appropriate uncertainty bounds, to some of the sensitive defect parameters.« less

Graphene Oxide Annealing Procedures for Graphene-Based Supercapacitors

DTIC Science & Technology

2015-09-01

Annealing Procedures for Graphene-Based Supercapacitors by Louis B Levine and Matthew H Ervin Sensors and Electron Devices Directorate, ARL...SUBTITLE Graphene Oxide Annealing Procedures for Graphene-Based Supercapacitors 5a. CONTRACT NUMBER 5b. GRANT NUMBER 5c. PROGRAM ELEMENT NUMBER 6

Room Temperature Thin Film Ba(x)Sr(1-x)TiO3 Ku-Band Coupled MicrostripPhase Shifters: Effects of Film Thickness, Doping, Annealing and Substrate Choice

NASA Technical Reports Server (NTRS)

VanKeuls, F. W.; Mueller, C. H.; Miranda, F. A.; Romanofsky, R. R.; Canedy, C. L.; Aggarwal, S.; Venkatesan, T.; Ramesh, R.; Horwitz, S.; Chang, W.

1999-01-01

We report on measurements taken on over twenty Ku-band coupled microstrip phase shifters (CMPS) using thin ferroelectric films of Ba(x)Sr(1-x)TiO3. This CMPS design is a recent innovation designed to take advantage of the high tunability and tolerate the high dielectric constant of ferroelectric films at Ku- and K-band frequencies. These devices are envisioned as a component in low-cost steerable beam phased area antennas, Comparisons are made between devices with differing film thickness, annealed vs unannealed, Mn-doped vs. undoped, and also substrates of LaAlO3 and MgO. A comparison between the CMPS structure and a CPW phase shifter was also made oil the same ferroelectric film.

Characterization of Laves phase in Crofer 22 H stainless steel.

PubMed

Hsiao, Zheng-Wen; Kuhn, Bernd; Chen, Delphic; Singheiser, Lorenz; Kuo, Jui-Chao; Lin, Dong-Yih

2015-07-01

This study investigated the effect of annealing temperature on the precipitation behavior of Crofer(®) 22 H at 600°C, 700°C, and 800°C. The grain size distribution, precipitate phase identification, and microstructure were analyzed using electron backscatter diffraction (EBSD) and energy dispersive X-ray spectroscopy (EDS). The morphology of Laves phase (Fe,Cr,Si)(2)(Nb,W) precipitates having the Cr(2)Nb structure changed from strip-like to needle-shaped as the annealing temperature was increased. The precipitates of the Laves phase also shifted from the grain boundaries to the grain interiors when the temperature was increased. However, the average grain size (150 μm) of the ferritic matrix did not significantly change at 600°C, 700°C, and 800°C for 10 h. Copyright © 2015 Elsevier Ltd. All rights reserved.

Crystallographic and magnetic structure of HAVAR under high-pressure using diamond anvil cell (DAC)

NASA Astrophysics Data System (ADS)

Halevy, Itzhak; Haroush, Shlomo; Eisen, Yosef; Silberman, Ido; Moreno, Dany; Hen, Amir; Winterrose, Mike L.; Ghose, Sanjit; Chen, Zhiqiang

2010-04-01

Annealed (H1) and cold-rolled (H2) HAVAR has been studied using high-pressure synchrotron X-ray diffraction. A structural phase transformation was discovered at ˜13 GPa at ambient temperature, transforming from m - 3 m (S.G. 225) to P 63/m m c (S.G. 194) symmetry. The transition was not reversible on pressure release. The low-pressure cubic phase was found to be more compressible than the high-pressure hexagonal phase. Conventional Mössbauer and NFS shows that the HAVAR is not magnetic at room temperature and no splitting is observed. The SQUID indicates a huge difference in the temperature dependence of the magnetic susceptibility between the cold Rolled HAVAR compared to the annealed HAVAR.

Interdiffusion and Intrinsic Diffusion in the Mg-Al System

DOE Office of Scientific and Technical Information (OSTI.GOV)

Brennan, Sarah; Bermudez, Katrina; Sohn, Yong Ho

2012-01-01

Solid-to-solid diffusion couples were assembled and annealed to examine the diffusion between pure Mg (99.96%) and Al (99.999%). Diffusion anneals were carried out at 300 , 350 , and 400 C for 720, 360, and 240 hours, respectively. Optical and scanning electron microscopes were utilized to identify the formation of the intermetallic phases, -Al12Mg17 and -Al3Mg2 and absence of the -phase in the diffusion couples. Thicknesses of the -Al12Mg17 and -Al3Mg2 phases were measured and the parabolic growth constants were calculated to determine the activation energies for the growth, 165 and 86 KJ/mole, respectively. Concentration profiles were determined with electronmore » microprobe analysis using pure elemental standards. Composition-dependent interdiffusion coefficients in Mg-solid solution, -Al12Mg17 and - Al3Mg2 and Al-solid solutions were calculated based on the Boltzmann-Matano analysis. Average effective interdiffusion coefficients for each phase were also calculated, and the magnitude was the highest for the -Al3Mg2 phase, followed by -Al12Mg17, Al-solid solution and Mg-solid solution. Intrinsic diffusion coefficients based on Huemann s analysis (e.g., marker plane) were determined for the ~38 at.% Mg in the -Al3Mg2 phase. Activation energies and the pre-exponential factors for the inter- and intrinsic diffusion coefficients were calculated for the temperature range examined. The -Al3Mg2 phase was found to have the lowest activation energies for growth and interdiffusion among all four phases studied. At the marker location in the -Al3Mg2 phase, the intrinsic diffusion of Al was found to be faster than that of Mg. Extrapolations of the impurity diffusion coefficients in the terminal solid solutions were made and compared to the available self- and impurity diffusion data from literature. Thermodynamic factor, tracer diffusion coefficients and atomic mobilities at the marker plane composition were approximated using available literature values of Mg activity in the -Al3Mg2 phase.« less

Effects of processing conditions and ambient environment on the microstructure and fracture strength of copper/niobium/copper interlayer joints for alumina

DOE Office of Scientific and Technical Information (OSTI.GOV)

Marks, Robert Alan

1999-12-01

Partial transient liquid phase (PTLP) bonding is a technique which can be used to join ceramics with metals and is used to form niobium-based joints for alumina. The principal advantage to PTLP bonding is that it enables refractory joints to be fabricated at temperatures below those typically required by solid state diffusion bonding. A thorough review of the important parameters (chemical compatibility, thermal expansion match, sufficient wettability of the liquid phase on the solid phases) in choosing a joining material for ceramics by the PTLP method is provided. As in conventional PTLP joining, the current study uses thin (=3 μm)more » copper layers sandwiched between the alumina (bulk) and niobium (127 μm). However, unlike the case of copper/nickel/copper obium is limited. Consequently, the copper is not entirely dissolved in the process, resulting in a two phase (copper-rich and niobium-rich phases) microstructure. Different processing conditions (temperature and applied load) result in different morphologies of the copper-rich and niobium-rich phases at the interface. These different microstructures exhibit distinct strength characteristics. Extended annealing of as-processed joints can influence the strengths differently depending on the ambient partial oxygen pressure at the annealing temperature. The focus of this work is to correlate processing conditions, microstructure, and resulting joint strength. Under optimum processing conditions (1400°C, 2.2 MPa), joints with strengths in excess of 200 MPa at 1200°C are fabricated.« less

Phase transformations in a Cu−Cr alloy induced by high pressure torsion

DOE Office of Scientific and Technical Information (OSTI.GOV)

Korneva, Anna, E-mail: a.korniewa@imim.pl; Straumal, Boris; Institut für Nanotechnologie, Karlsruher Institut für Technologie, Hermann-von-Helmholtz-Platz 1, 76344 Eggenstein-Leopoldshafen

2016-04-15

Phase transformations induced by high pressure torsion (HPT) at room temperature in two samples of the Cu-0.86 at.% Cr alloy, pre-annealed at 550 °C and 1000 °C, were studied in order to obtain two different initial states for the HPT procedure. Observation of microstructure of the samples before HPT revealed that the sample annealed at 550 °C contained two types of Cr precipitates in the Cu matrix: large particles (size about 500 nm) and small ones (size about 70 nm). The sample annealed at 1000 °C showed only a little fraction of Cr precipitates (size about 2 μm). The subsequentmore » HPT process resulted in the partial dissolution of Cr precipitates in the first sample and dissolution of Cr precipitates with simultaneous decomposition of the supersaturated solid solution in another. However, the resulting microstructure of the samples after HPT was very similar from the standpoint of grain size, phase composition, texture analysis and hardness measurements. - Highlights: • Cu−Cr alloy with two different initial states was deformed by HPT. • Phase transformations in the deformed materials were studied. • SEM, TEM and X-ray diffraction techniques were used for microstructure analysis. • HPT leads to formation the same microstructure independent of the initial state.« less

Estimates of point defect production in α-quartz using molecular dynamics simulations

NASA Astrophysics Data System (ADS)

Cowen, Benjamin J.; El-Genk, Mohamed S.

2017-07-01

Molecular dynamics (MD) simulations are performed to investigate the production of point defects in α-quartz by oxygen and silicon primary knock-on atoms (PKAs) of 0.25-2 keV. The Wigner-Seitz (WS) defect analysis is used to identify the produced vacancies, interstitials, and antisites, and the coordination defect analysis is used to identify the under and over-coordinated oxygen and silicon atoms. The defects at the end of the ballistic phase and the residual defects, after annealing, increase with increased PKA energy, and are statistically the same for the oxygen and silicon PKAs. The WS defect analysis results show that the numbers of the oxygen vacancies and interstitials (VO, Oi) at the end of the ballistic phase is the highest, followed closely by those of the silicon vacancies and interstitials (VSi, Sii). The number of the residual oxygen and silicon vacancies and interstitials are statistically the same. In addition, the under-coordinated OI and SiIII, which are the primary defects during the ballistic phase, have high annealing efficiencies (>89%). The over-coordinated defects of OIII and SiV, which are not nearly as abundant in the ballistic phase, have much lower annealing efficiencies (<63%) that decrease with increased PKA energy.

Magnetic softening and nanocrystallization in amorphous Co-rich alloys

NASA Astrophysics Data System (ADS)

Buttino, G.; Cecchetti, A.; Poppi, M.

1997-02-01

In this work we have analyzed the changes of the magnetic properties in the Co-based Metglas 2714A (made by Allied Chem. Corp., USA) caused by isothermal heat treatments in the range of temperature from room temperature to conventional crystallization temperature Tcr = 550°C. The nominal composition of the amorphous alloy is Co 66Fe 4Ni 1B 14Si 15. The analysis is made on toroidal samples prepared by winding lengths of amorphous ribbon of about 20 cm. The magnetic properties undergo variations depending on the treatment temperature, except for the saturation magnetization which remains unchanged. For heat treatments of about half an hour around 500°C, superior soft magnetic properties are obtained. Particularly, the initial permeability reaches values up to ten times the value of permeability in the as-received sample. Analysis by the transmission electron microscopy of the sample annealed around 500°C reveals the formation of a nanocrystalline phase, with average grain size of 2 nm, embedded in a residual amorphous matrix. The occurrence of permeability increases in concomitance with the formation of the nanocrystalline phase is ascribed to a drastic reduction in the local magnetocrystalline anisotropy randomly averaged out by the exchange interactions, similar to the case of the annealed Fe-based alloys containing Cu.

Influence of intermediate annealing on abnormal Goss grain growth in the rolled columnar-grained Fe-Ga-Al alloys

NASA Astrophysics Data System (ADS)

Liu, Yangyang; Li, Jiheng; Gao, Xuexu

2017-08-01

Magnetostrictive Fe82Ga4.5Al13.5 sheets with 0.1 at% NbC were prepared from directional solidified alloys with <0 0 1> preferred orientation. The slabs were hot rolled at 650 °C and warm rolled at 500 °C. Then some warm-rolled sheets were annealed intermediately at 850 °C for 5 min but the others not. After that, all the sheets were cold rolled to a final thickness of ∼0.3 mm. The microstructures, the textures and the distributions of second phase particles in the primary recrystallized samples were investigated. With intermediate annealing, the inhomogeneous microstructure was improved remarkably and strong Goss ({1 1 0}<0 0 1>) and γ-fiber (<1 1 1>//normal direction [ND]) textures were produced in the primary recrystallized samples. But, an evident disadvantage in size and quantity was observed for Goss grains in the primary recrystallized sample without intermediate annealing. After a final annealing, the final textures and magnetostrictions of samples with and without intermediate annealing were characterized. For samples without intermediate annealing, abnormal growth of {1 1 3} grains occurred and deteriorated the magnetostriction. In contrast, abnormal Goss grain growth occurred completely in samples with intermediate annealing and led to saturation magnetostriction as high as 156 ppm.

A multiscale coupled finite-element and phase-field framework to modeling stressed grain growth in polycrystalline thin films

DOE Office of Scientific and Technical Information (OSTI.GOV)

Jamshidian, M., E-mail: jamshidian@cc.iut.ac.ir; Institute of Structural Mechanics, Bauhaus-University Weimar, Marienstrasse 15, 99423 Weimar; Thamburaja, P., E-mail: prakash.thamburaja@gmail.com

A previously-developed finite-deformation- and crystal-elasticity-based constitutive theory for stressed grain growth in cubic polycrystalline bodies has been augmented to include a description of excess surface energy and grain-growth stagnation mechanisms through the use of surface effect state variables in a thermodynamically-consistent manner. The constitutive theory was also implemented into a multiscale coupled finite-element and phase-field computational framework. With the material parameters in the constitutive theory suitably calibrated, our three-dimensional numerical simulations show that the constitutive model is able to accurately predict the experimentally-determined evolution of crystallographic texture and grain size statistics in polycrystalline copper thin films deposited on polyimide substratemore » and annealed at high-homologous temperatures. In particular, our numerical analyses show that the broad texture transition observed in the annealing experiments of polycrystalline thin films is caused by grain growth stagnation mechanisms. - Graphical abstract: - Highlights: • Developing a theory for stressed grain growth in polycrystalline thin films. • Implementation into a multiscale coupled finite-element and phase-field framework. • Quantitative reproduction of the experimental grain growth data by simulations. • Revealing the cause of texture transition to be due to the stagnation mechanisms.« less

Finding Maximum Cliques on the D-Wave Quantum Annealer

DOE PAGES

Chapuis, Guillaume; Djidjev, Hristo; Hahn, Georg; ...

2018-05-03

This work assesses the performance of the D-Wave 2X (DW) quantum annealer for finding a maximum clique in a graph, one of the most fundamental and important NP-hard problems. Because the size of the largest graphs DW can directly solve is quite small (usually around 45 vertices), we also consider decomposition algorithms intended for larger graphs and analyze their performance. For smaller graphs that fit DW, we provide formulations of the maximum clique problem as a quadratic unconstrained binary optimization (QUBO) problem, which is one of the two input types (together with the Ising model) acceptable by the machine, andmore » compare several quantum implementations to current classical algorithms such as simulated annealing, Gurobi, and third-party clique finding heuristics. We further estimate the contributions of the quantum phase of the quantum annealer and the classical post-processing phase typically used to enhance each solution returned by DW. We demonstrate that on random graphs that fit DW, no quantum speedup can be observed compared with the classical algorithms. On the other hand, for instances specifically designed to fit well the DW qubit interconnection network, we observe substantial speed-ups in computing time over classical approaches.« less

High-temperature investigation on morphology, phase and size of iron/iron-oxide core–shell nanoclusters for radiation nanodetector

NASA Astrophysics Data System (ADS)

Khanal, Lokendra Raj; Williams, Thomas; Qiang, You

2018-06-01

Iron/iron-oxide (Fe–Fe3O4) core–shell nanoclusters (NCs) synthesized by a cluster deposition technique were subjected to a study of their high temperature structural and morphological behavior. Annealing effects have been investigated up to 800 °C in vacuum, oxygen and argon environments. The ~18 nm average size of the as-prepared NCs increases slowly in temperatures up to 500 °C in all three environments. The size increases abruptly in the argon environment but slowly in vacuum and oxygen when annealed at 800 °C. The x-ray diffraction (XRD) studies have shown that the iron core remains in the core–shell NCs only when they were annealed in the vacuum. A dramatic change in the surface morphology, an island like structure and/or a network like pattern, was observed at the elevated temperature. The as-prepared and annealed samples were analyzed using XRD, scanning electron microscopy and imageJ software for a close inspection of the temperature aroused properties. This work presents the temperature induced size growth mechanism, oxidation kinetics and phase transformation of the NCs accompanied by cluster aggregation, particle coalescence, and diffusion.

Finding Maximum Cliques on the D-Wave Quantum Annealer

DOE Office of Scientific and Technical Information (OSTI.GOV)

Chapuis, Guillaume; Djidjev, Hristo; Hahn, Georg

This work assesses the performance of the D-Wave 2X (DW) quantum annealer for finding a maximum clique in a graph, one of the most fundamental and important NP-hard problems. Because the size of the largest graphs DW can directly solve is quite small (usually around 45 vertices), we also consider decomposition algorithms intended for larger graphs and analyze their performance. For smaller graphs that fit DW, we provide formulations of the maximum clique problem as a quadratic unconstrained binary optimization (QUBO) problem, which is one of the two input types (together with the Ising model) acceptable by the machine, andmore » compare several quantum implementations to current classical algorithms such as simulated annealing, Gurobi, and third-party clique finding heuristics. We further estimate the contributions of the quantum phase of the quantum annealer and the classical post-processing phase typically used to enhance each solution returned by DW. We demonstrate that on random graphs that fit DW, no quantum speedup can be observed compared with the classical algorithms. On the other hand, for instances specifically designed to fit well the DW qubit interconnection network, we observe substantial speed-ups in computing time over classical approaches.« less

Possible ergodic-nonergodic regions in the quantum Sherrington-Kirkpatrick spin glass model and quantum annealing

NASA Astrophysics Data System (ADS)

Mukherjee, Sudip; Rajak, Atanu; Chakrabarti, Bikas K.

2018-02-01

We explore the behavior of the order parameter distribution of the quantum Sherrington-Kirkpatrick model in the spin glass phase using Monte Carlo technique for the effective Suzuki-Trotter Hamiltonian at finite temperatures and that at zero temperature obtained using the exact diagonalization method. Our numerical results indicate the existence of a low- but finite-temperature quantum-fluctuation-dominated ergodic region along with the classical fluctuation-dominated high-temperature nonergodic region in the spin glass phase of the model. In the ergodic region, the order parameter distribution gets narrower around the most probable value of the order parameter as the system size increases. In the other region, the Parisi order distribution function has nonvanishing value everywhere in the thermodynamic limit, indicating nonergodicity. We also show that the average annealing time for convergence (to a low-energy level of the model, within a small error range) becomes system size independent for annealing down through the (quantum-fluctuation-dominated) ergodic region. It becomes strongly system size dependent for annealing through the nonergodic region. Possible finite-size scaling-type behavior for the extent of the ergodic region is also addressed.

Magnetic analysis of a melt-spun Fe-dilute Cu60Ag35Fe5 alloy

NASA Astrophysics Data System (ADS)

Kondo, Shin-ichiro; Kaneko, Kazuhiro; Morimura, Takao; Nakashima, Hiromichi; Kobayashi, Shin-Taro; Michioka, Chishiro; Yoshimura, Kazuyoshi

2015-04-01

The magnetic properties of a melt-spun Fe-dilute Cu60Ag35Fe5 alloy are examined by X-ray diffraction, magnetic measurements, and transmission electron microscopy (TEM). The X-ray diffraction patterns show that the as-spun and annealed (773 K×36 ks) samples contain Cu and Ag phases and no Fe phases; thus, most Fe atoms are dispersed as clusters. Magnetic measurements indicate that the as-spun and annealed samples exhibit superparamagnetic behavior at 300 K, whereas ferromagnetic and superparamagnetic behaviors coexist at 4.2 K. The magnetic moments of small clusters at 300 K are determined by the nonlinear least squares method as 5148 and 4671 μB for as-spun and annealed samples, respectively, whereas those at 300 K are experimentally determined as 3500 and 3200 μB. This decrease in magnetic moments may imply the formation of anti-ferromagnetic coupling by annealing. TEM observation of the melt-spun sample suggests that there are three regions with different compositions: Cu-rich, Ag-rich, and Fe-rich with no precipitation in the matrix. In addition, these regions have obscure interfaces. The magnetic clusters are attributed to the Fe-rich regions.

HEAT TREATED U-Mo ALLOY

DOEpatents

McGeary, R.K.; Justusson, W.M.

1960-02-23

A reactor fuel element comprising a gamma-phase alloy consisting of 11 to 16 wt.% of molyhdenum and the balance uranium, annealed between 350 and 525 deg C and quenched to preserve the gamma phase, is reported.

Formation of TiO2 nanorings due to rapid thermal annealing of swift heavy ion irradiated films.

PubMed

Thakurdesai, Madhavi; Sulania, I; Narsale, A M; Kanjilal, D; Bhattacharyya, Varsha

2008-09-01

Amorphous thin films of TiO2 deposited by Pulsed Laser Deposition (PLD) method are irradiated by Swift Heavy Ion (SHI) beam. The irradiated films are subsequently annealed by Rapid Thermal Annealing (RTA) method. Atomic Force Microscopy (AFM) study reveals formation of nano-rings on the surface after RTA processing. Phase change is identified by Glancing Angle X-ray Diffraction (GAXRD) and Raman spectroscopy. Optical characterisation is carried out by UV-VIS absorption spectroscopy. Though no shift of absorption edge is observed after irradiation, RTA processing does show redshift.

Bandwidth-narrowed Bragg gratings inscribed in double-cladding fiber by femtosecond laser.

PubMed

Shi, Jiawei; Li, Yuhua; Liu, Shuhui; Wang, Haiyan; Liu, Ningliang; Lu, Peixiang

2011-01-31

Bragg gratings with the bandwidth(FWHM) narrowed up to 79 pm were inscribed in double-cladding fiber with femtosecond radiation and a phase mask followed by an annealing treatment. With the annealing temperature below a critical value, the bandwidth of Bragg gratings induced by Type I-IR and Type II-IR index change was narrowed without the reduction of reflectivity. The bandwidth narrowing is due to the profile transformation of the refractive index modulation caused by the annealing treatment. This mechanism was verified by comparing bandwidth narrowing processes of FBGs written with different power densities.

Effects of process variables in decarburization annealing of Fe-3%Si-0.3%C steel sheet on textures and magnetic properties

NASA Astrophysics Data System (ADS)

Park, Se Min; Koo, Yang Mo; Shim, Byoung Yul; Lee, Dong Nyung

2017-01-01

In Fe-3%Si-0.3%C steel sheet, a relatively strong <100>//ND texture can evolve in the surface layer through the α→γ→α phase transformation in relatively low vacuum (4 Pa) for an annealing time of 10 min and at a cooling rate of 20 K/s. Oxidation of the steel sheet surface prevents the evolution of the <100>//ND texture. However, vacuum-annealing under a vacuum pressure of 1.3×10-3 Pa causes decarburization of the steel sheet, which suppresses oxidation of the steel sheet surface, and subsequent annealing in wet hydrogen of 363 K in dew points causes a columnar grain structure with the <100>//ND texture. After the two-step-annealing (the vacuum annealing under a vacuum pressure of 1.3×10-3 Pa and subsequent decarburizing annealing in wet hydrogen of 363 K in dew points), the decarburized steel sheet exhibits good soft magnetic properties in NO with 3%Si, W15/50 (core loss at 1.5T and 50 Hz) = 2.47 W/kg and B50 (magnetic flux density at 5000 A/m) = 1.71 T.

Fast annealing DSA materials designed for sub-5 nm resolution

NASA Astrophysics Data System (ADS)

Deng, Hai; Li, Xuemiao; Peng, Yu; Zhou, Jianuo

2018-03-01

In recent years, high-χ block copolymers (BCPs) have been reported to achieve sub-5 nm resolution. These BCPs always require long annealing time at high annealing temperature, which may limit their implementation into semiconductor process. Since hot baking time in conventional semiconductor process is normally less than 3 minutes, how to shorter the thermal annealing time at lower temperature becomes a new topic for the sub-5 nm high-χ BCPs. In this manuscript, various fluoro-containing BCPs are synthesized by living anionic polymerization or atom transfer radical polymerization. The best BCP formed thermal equilibrium sub-5 nm nano domains after mere 1 min annealing at temperature lower than 100 °C, which is the fastest thermal annealing process reported so far. BCPs with various morphology and domain size are obtained by precise control of both the length and the molar ratio of the two blocks. The resulted smallest half-pitch of the BCPs are less than 5 nm in lamella and hexagonal morphologies. Linear and starshaped BCPs containing PMMA and fluoro-block are also synthesized, which also shows best phase separation into ca. 6 nm half-pitch, however, the annealing time is 1 hour at 180 °C.

Effect of annealing temperatures on the morphology and structural properties of PVDF/MgO nanocomposites thin films

NASA Astrophysics Data System (ADS)

Rozana, M. D.; Arshad, A. N.; Wahid, M. H. M.; Habibah, Z.; Sarip, M. N.; Rusop, M.

2018-05-01

This study investigates the effect of annealing on the topography, morphology and crystal phases of poly(vinylideneflouride)/Magnesium Oxide (MgO) nanocomposites thin films via AFM, FESEM and ATR-FTIR. The nanocomposites thin films were annealed at temperatures ranging from 70°C to 170°C. The annealed PVDF/MgO nanocomposites thin films were then cooled at room temperature before removal from the oven. This is to restructure the crystal lattice and to reduce imperfection for the PVDF/MgO nanocomposites thin films. PVDF/MgO nanocomposites thin films with annealing temperatures of 70°C, 90°C and 110°C showed uniform distribution of MgO nanoparticles, relatively low average surface roughness and no visible of defects. High application of annealing temperature on PVDF/MgO nanocomposites thin films caused tear-like defects on the thin films surface as observed by FESEM. The PVDF/MgO nanocomposites thin films annealed at 70°C was found to be a favourable film to be utilized in this study due to its enhanced β-crystalites of PVDF as evident in ATR-FTIR spectra.

Interfacial engineering of solution-processed Ni nanochain-SiO x (x< 2) cermets towards thermodynamically stable, anti-oxidation solar selective absorbers

DOE Office of Scientific and Technical Information (OSTI.GOV)

Yu, Xiaobai; Wang, Xiaoxin; Zhang, Qinglin

Here, cermet solar thermal selective absorber coatings are an important component of high-efficiency concentrated solar power (CSP) receivers. The oxidation of the metal nanoparticles in cermet solar absorbers is a great challenge for vacuum-free operation. Recently, we have demonstrated that oxidation is kinetically retarded in solution processed, high-optical-performance Ni nanochain-SiO x cermet system compared to conventional Ni-Al 2O 3 system when annealed in air at 450–600 °C for several hours. However, for long-term, high-temperature applications in CSP systems, thermodynamically stable antioxidation behavior is highly desirable, which requires new mechanisms beyond kinetically reducing the oxidation rate. Towards this goal, in thismore » paper, we demonstrate that pre-operation annealing of Ni nanochain-SiO x cermets at 900 °C in N 2 forms the thermodynamically stable orthorhombic phase of NiSi at the Ni/SiO x interfaces, leading to self-terminated oxidation at 550 °C in air due to this interfacial engineering. In contrast, pre-operation annealing at a lower temperature of 750 °C in N 2 (as conducted in our previous work) cannot achieve interfacial NiSi formation directly, and further annealing in air at 450–600 °C for >4 h only leads to the formation of the less stable (metastable) hexagonal phase of NiSi. Therefore, the high-temperature pre-operation annealing is critical to form the desirable orthorhombic phase of NiSi at Ni/SiO x interfaces towards thermodynamically stable antioxidation behavior. Remarkably, with this improved interfacial engineering, the oxidation of 80-nm-diameter Ni nanochain-SiO x saturates after annealing at 550 °C in air for 12 h. Additional annealing at 550 °C in air for as long as 20 h (i.e., 32 h air annealing at >550 °C in total) has almost no further impact on the structural or optical properties of the coatings, the latter being very sensitive to any interfacial changes due to the localized surface plasmon resonances of the metal nanostructures. This phenomenon holds true for Ni nanoparticle diameter down to 40 nm in Ni-SiO x system, where the optical response remains stable for 53 h at 550 °C in air. The oxidation vs. time curve also shows saturation behavior deviating from the kinetic Deal-Grove oxidation model. These results strongly suggest a promising approach to thermodynamically stable, anti-oxidation Ni/SiO x cermet absorbers via interfacial engineering.« less

In situ TEM and synchrotron characterization of U–10Mo thin specimen annealed at the fast reactor temperature regime

DOE Office of Scientific and Technical Information (OSTI.GOV)

Yun, Di, E-mail: diyun1979@xjtu.edu.cn; Xi'an Jiao Tong University, 28 Xian Ning West Road, Xi'an 710049; Mo, Kun

2015-12-15

U–Mo metallic alloys have been extensively used for the Reduced Enrichment for Research and Test Reactors (RERTR) program, which is now known as the Office of Material Management and Minimization under the Conversion Program. This fuel form has also recently been proposed as fast reactor metallic fuels in the recent DOE Ultra-high Burnup Fast Reactor project. In order to better understand the behavior of U–10Mo fuels within the fast reactor temperature regime, a series of annealing and characterization experiments have been performed. Annealing experiments were performed in situ at the Intermediate Voltage Electron Microscope (IVEM-Tandem) facility at Argonne National Laboratorymore » (ANL). An electro-polished U–10Mo alloy fuel specimen was annealed in situ up to 700 °C. At an elevated temperature of about 540 °C, the U–10Mo specimen underwent a relatively slow microstructure transition. Nano-sized grains were observed to emerge near the surface. At the end temperature of 700 °C, the near-surface microstructure had evolved to a nano-crystalline state. In order to clarify the nature of the observed microstructure, Laue diffraction and powder diffraction experiments were carried out at beam line 34-ID of the Advanced Photon Source (APS) at ANL. Phases present in the as-annealed specimen were identified with both Laue diffraction and powder diffraction techniques. The U–10Mo was found to recrystallize due to thermally-induced recrystallization driven by a high density of pre-existing dislocations. A separate in situ annealing experiment was carried out with a Focused Ion Beam processed (FIB) specimen. A similar microstructure transition occurred at a lower temperature of about 460 °C with a much faster transition rate compared to the electro-polished specimen. - Highlights: • TEM annealing experiments were performed in situ at the IVEM facility up to fast reactor temperature. • At 540 °C, the U-10Mo specimen underwent a slow microstructure transition where nano-sized grains were observed to emerge. • UO{sub 2} phase exists at the thin area of the as-annealed specimen whereas U-10Mo γ phase dominated at the thicker part. • Bcc γ U-10Mo recrystallized to become nano-meter sized crystallites near the specimen surface. • A separateannealing experiment was conducted with a FIB processed specimen where similar transition occurred at a lower temperature of 460 °C with a faster rate.« less

Interfacial engineering of solution-processed Ni nanochain-SiO x (x< 2) cermets towards thermodynamically stable, anti-oxidation solar selective absorbers

DOE PAGES

Yu, Xiaobai; Wang, Xiaoxin; Zhang, Qinglin; ...

2016-04-01

Here, cermet solar thermal selective absorber coatings are an important component of high-efficiency concentrated solar power (CSP) receivers. The oxidation of the metal nanoparticles in cermet solar absorbers is a great challenge for vacuum-free operation. Recently, we have demonstrated that oxidation is kinetically retarded in solution processed, high-optical-performance Ni nanochain-SiO x cermet system compared to conventional Ni-Al 2O 3 system when annealed in air at 450–600 °C for several hours. However, for long-term, high-temperature applications in CSP systems, thermodynamically stable antioxidation behavior is highly desirable, which requires new mechanisms beyond kinetically reducing the oxidation rate. Towards this goal, in thismore » paper, we demonstrate that pre-operation annealing of Ni nanochain-SiO x cermets at 900 °C in N 2 forms the thermodynamically stable orthorhombic phase of NiSi at the Ni/SiO x interfaces, leading to self-terminated oxidation at 550 °C in air due to this interfacial engineering. In contrast, pre-operation annealing at a lower temperature of 750 °C in N 2 (as conducted in our previous work) cannot achieve interfacial NiSi formation directly, and further annealing in air at 450–600 °C for >4 h only leads to the formation of the less stable (metastable) hexagonal phase of NiSi. Therefore, the high-temperature pre-operation annealing is critical to form the desirable orthorhombic phase of NiSi at Ni/SiO x interfaces towards thermodynamically stable antioxidation behavior. Remarkably, with this improved interfacial engineering, the oxidation of 80-nm-diameter Ni nanochain-SiO x saturates after annealing at 550 °C in air for 12 h. Additional annealing at 550 °C in air for as long as 20 h (i.e., 32 h air annealing at >550 °C in total) has almost no further impact on the structural or optical properties of the coatings, the latter being very sensitive to any interfacial changes due to the localized surface plasmon resonances of the metal nanostructures. This phenomenon holds true for Ni nanoparticle diameter down to 40 nm in Ni-SiO x system, where the optical response remains stable for 53 h at 550 °C in air. The oxidation vs. time curve also shows saturation behavior deviating from the kinetic Deal-Grove oxidation model. These results strongly suggest a promising approach to thermodynamically stable, anti-oxidation Ni/SiO x cermet absorbers via interfacial engineering.« less

Study the effect of mechanical alloying parameters on synthesis of Cr{sub 2}Nb–Al{sub 2}O{sub 3} nanocomposite

DOE Office of Scientific and Technical Information (OSTI.GOV)

Shayesteh, Payam, E-mail: shayesteh.payam@gmail.com; Mirdamadi, Shamseddin; Razavi, Hossein

2014-01-01

Graphical abstract: - Highlights: • Cr{sub 2}Nb–Al{sub 2}O{sub 3} nanocomposite synthesized through MA. • Effect of BPR, rotating speed, milling time and PCA concentration investigated. • After annealing at 1100 °C crystalline phase were appeared. • Williamson–Hall analysis was used in order to study the grain size of nano composite. - Abstract: In this study, Cr{sub 2}Nb–20 vol.% Al{sub 2}O{sub 3} nanocomposite was prepared successfully by mechanochemical reaction between Al, Nb and Cr{sub 2}O{sub 3} powders. Amorphization of powder occurred during mechanical alloying because of high energy collisions between powders and steel balls in milling container which transfer high degreemore » of energy to powders. Therefore, annealing was needed to form crystalline phases. The influence of different mechanical alloying parameters such as BPR, rotating speed, milling time and PCA concentration on synthesis of composite material were investigated. After mechanical alloying, the powder was encapsulated in quartz and then annealed at 1100 °C for 3 h. After annealing, 3 different phases were appeared (Cr{sub 2}Nb (cubic), Cr{sub 2}Nb (hexagonal) and α-Al{sub 2}O{sub 3}). The structural changes of powder particles during mechanical alloying were studied by X-ray diffractometry (XRD), atomic force microscopy (AFM), scanning electron microscopy (SEM) and transmission electron microscopy (TEM)« less

Self-organized TiO2 nanotube arrays in the photocatalytic degradation of methylene blue under UV light irradiation

NASA Astrophysics Data System (ADS)

Chung, Eun Hyuk; Baek, Seong Rim; Yu, Seong Mi; Kim, Jong Pil; Hong, Tae Eun; Kim, Hyun Gyu; Bae, Jong-Seong; Jeong, Euh Duck; Khan, F. Nawaz; Jung, Ok-sang

2015-04-01

Nanostructured titanium dioxide (NTiO2) is known to possess efficient photocatalytic activity and to have diverse applications in many fields due to its chemical stability, high surface area/volume ratio, high transmittance, and high refractive index in the visible and the near-ultraviolet regions. These facts prompted us to develop TiO2 nanotube (TiO2 NT) arrays through electrochemical anodic oxidation involving different electrolytes comprised of phosphoric acid — hydrofluoric acid aqueous systems by varying the voltage and the time. The annealing temperature of the nanotubes, TiO2 NTs, were varied to modify the surface morphology and were characterized by using X-ray diffraction and scanning electron microscopy. Scanning electron microscopy and X-ray diffraction results showed that the samples had uniform morphologies and good crystalline structures of the anatase phase at lower annealing temperatures and of the rutile phase at higher annealing temperatures. A secondary-ion mass-spectrometry analysis was used to investigate the surface atoms and to conduct a depth profile analysis of the TiO2 NTs. The efficiency of the photocatalytic activity of the TiO2 NT arrays in degrading methylene blue (MB) was investigated under UV-Vis light irradiation. The maximum photocatalytic activity was achieved for the samples with lower annealing temperatures due to their being in the anatase phase and having a higher surface area and a smaller crystal size, which play important roles in the degradation of organic pollutants.

Phase Engineering of Perovskite Materials for High-Efficiency Solar Cells: Rapid Conversion of CH3NH3PbI3 to Phase-Pure CH3NH3PbCl3 via Hydrochloric Acid Vapor Annealing Post-Treatment.

PubMed

Zhou, Weiran; Zhou, Pengcheng; Lei, Xunyong; Fang, Zhimin; Zhang, Mengmeng; Liu, Qing; Chen, Tao; Zeng, Hualing; Ding, Liming; Zhu, Jun; Dai, Songyuan; Yang, Shangfeng

2018-01-17

Organometal halide CH 3 NH 3 PbI 3 (MAPbI 3 ) has been commonly used as the light absorber layer of perovskite solar cells (PSCs), and, especially, another halide element chlorine (Cl) has been often incorporated to assist the crystallization of perovskite film. However, in most cases, a predominant MAPbI 3 phase with trace of Cl - is obtained ultimately and the role of Cl involvement remains unclear. Herein, we develop a low-cost and facile method, named hydrochloric acid vapor annealing (HAVA) post-treatment, and realize a rapid conversion of MAPbI 3 to phase-pure MAPbCl 3 , demonstrating a new concept of phase engineering of perovskite materials toward efficiency enhancement of PSCs for the first time. The average grain size of perovskite film after HAVA post-treatment increases remarkably through an Ostwald ripening process, leading to a denser and smoother perovskite film with reduced trap states and enhanced crystallinity. More importantly, the generation of MAPbCl 3 secondary phase via phase engineering is beneficial for improving the carrier mobility with a more balanced carrier transport rate and enlarging the band gap of perovskite film along with optimized energy level alignment. As a result, under the optimized HAVA post-treatment time (2 min), we achieved a significant enhancement of the power conversion efficiency (PCE) of the MAPbI 3 -based planar heterojunction-PSC device from 14.02 to 17.40% (the highest PCE reaches 18.45%) with greatly suppressed hysteresis of the current-voltage response.

Cu(In,Ga)Se2 thin films annealed using a continuous wave Nd:YAG laser (λ0 = 532 nm): Effects of laser-annealing time

NASA Astrophysics Data System (ADS)

Yoo, Myoung Han; Ko, Pil Ju; Kim, Nam-Hoon; Lee, Hyun-Yong

2017-12-01

Preparation of Cu(In,Ga)Se2 (CIGS) thin films has continued to face problems related to the selenization of sputtered Cu-In-Ga precursors when using H2Se vapor in that the materials are highly toxic and the facilities extremely costly. Another obstacle facing the production of CIGS thin films has been the required annealing temperature, as it relates to the decomposition temperature of a typical flexible polymer substrate. A novel laser-annealing process for CIGS thin films, which does not involve the selenization process and which can be performed at a lower temperature, has been proposed. Following sputtering with a Cu0.9In0.7Ga0.3Se2 target, the laser-annealing of the CIGS thin film was performed using a continuous 532-nm Nd:YAG laser with an annealing time of 200 - 1000 s at a laser optical power of 2.75 W. CIGS chalcopyrite (112), (220/204), and (312/116) phases, with some weak diffraction peaks corresponding to the Cu-Se- or the In-Se-related phases, were successfully obtained for all the CIGS thin films that had been laser-annealed at 2.75 W. The lattice parameters, the d-spacing, the tetragonal distortion parameter, and the strain led to the crystallinity being worse and grain size being smaller at 600 s while better crystallinity was obtained at 200 and 800 s, which was closely related to the deviations from molecularity and stoichiometry, which were greatest at 600 s while the values exhibited near-stoichiometric compositions at 200 and 800 s. The band gaps of the laser-annealed CIGS thin films were within a range of 1.765 - 1.977 eV and depended on the internal stress. The mean absorbance of the laser-annealed CIGS thin films was within a range of 1.598 - 1.900, suggesting that approximately 97.47 - 98.74% of the incident photons in the visible spectral region were absorbed by this 400-nm film. The conductivity types exhibited the same deviations (Δ m > 0 and Δ s < 0) in all the laser-annealed CIGS thin films. After laser-annealing, the resistivity fell abruptly to a range of 3.551 × 10 -2 - 1.022 × 10 -1 Ω·cm. The carrier concentration was on the order of 1019 - 1021 cm -3, and the carrier mobility was 5.7 × 10 -2 - 5.7 × 100 cm2/V·s.

In situ Observation of Phase Transformation in MnAl(C) Magnetic Materials

PubMed Central

Si, Ping-Zhan; Qian, Hui-Dong; Choi, Chul-Jin; Park, Jihoon; Han, Sangho; Ge, Hong-Liang; Shinde, Kiran P.

2017-01-01

The phase transformation in two modes, including both displacive and massive growth of τ-phase from ε-MnAl(C), was observed by in situ transmission electron microscopy. The exact temperature range for different phase transformation modes was determined by magnetic measurements. The displacive growth of ε→τ in Mn54Al46 (or Mn54Al46C2.44) occurs at temperatures below 650 K (or 766 K), above which both modes coexist. One-third or less of the ε-phase can be transformed into τ-phase via displacive mode while the remaining two-thirds or more via massive mode. In bulk τ-phase, most τ-nanocrystals formed via displacive mode are distributed in the matrix of large τ-grains that formed via massive mode. The typical massive growth rate of the τ-phase is 8–60 nm/s, while the displacive growth rate is low. A more complete understanding of the ε→τ phase transformations in the MnAl-based magnets was provided in this work, based on which the annealing process for ε→τ was optimized and thus high purity τ-phase with high saturation magnetization was obtained. PMID:28858231

Formability of Annealed Ni-Ti Shape Memory Alloy Sheet

NASA Astrophysics Data System (ADS)

Fann, K. J.; Su, J. Y.; Chang, C. H.

2018-03-01

Ni-Ti shape memory alloy has two specific properties, superelasiticity and shape memory effect, and thus is widely applied in diverse industries. To extend its application, this study attempts to investigate the strength and cold formability of its sheet blank, which is annealed at various temperatures, by hardness test and by Erichsen-like cupping test. As a result, the higher the annealing temperature, the lower the hardness, the lower the maximum punch load as the sheet blank fractured, and the lower the Erichsen-like index or the lower the formability. In general, the Ni-Ti sheet after annealing has an Erichsen-like index between 8 mm and 9 mm. This study has also confirmed via DSC that the Ni-Ti shape memory alloy possesses the austenitic phase and shows the superelasticity at room temperature.

Short communication on Kinetics of grain growth and particle pinning in U-10 wt.% Mo

NASA Astrophysics Data System (ADS)

Frazier, William E.; Hu, Shenyang; Overman, Nicole; Lavender, Curt; Joshi, Vineet V.

2018-01-01

The alloy U-10 wt% Mo was annealed at temperatures ranging from 700 °C to 900 °C for periods lasting up to 24 h. Annealed microstructures were examined using Electron Backscattered Diffraction (EBSD) to obtain average grain sizes and grain size distributions. From the temporal evolution of the average grain size, the activation energy of grain growth was determined to be 172.4 ± 0.961 kJ/mol. Grain growth over the annealing period stagnated after a period of 1-4 h. This stagnation is apparently caused by the pinning effect of second-phase particles in the materials. Back-scattered electron imaging (BSE) was used to confirm that these particles do not appreciably coarsen or dissolve during annealing at the aforementioned temperatures.

Enhancement of optical transmittance and electrical resistivity of post-annealed ITO thin films RF sputtered on Si

NASA Astrophysics Data System (ADS)

Ali, Ahmad Hadi; Hassan, Zainuriah; Shuhaimi, Ahmad

2018-06-01

This paper reports on the enhancement of optical transmittance and electrical resistivity of indium tin oxide (ITO) transparent conductive oxides (TCO) deposited by radio frequency (RF) sputtering on Si substrate. Post-annealing was conducted on the samples at temperature ranges of 500-700 °C. From X-ray diffraction analysis (XRD), ITO (2 2 2) peak was observed after post-annealing indicating crystallization phase of the films. From UV-vis measurements, the ITO thin film shows highest transmittance of more than 90% at post-annealing temperature of 700 °C as compared to the as-deposited thin films. From atomic force microscope (AFM), the surface roughness becomes smoother after post-annealing as compared to the as-deposited. The lowest electrical resistivity for ITO sample is 6.68 × 10-4 Ω cm after post-annealed at 700 °C that are contributed by high carrier concentration and mobility. The improved structural and surface morphological characteristics helps in increasing the optical transmittance and reducing the electrical resistivity of the ITO thin films.

Influence of surfactant and annealing temperature on optical properties of sol-gel derived nano-crystalline TiO2 thin films.

PubMed

Vishwas, M; Sharma, Sudhir Kumar; Rao, K Narasimha; Mohan, S; Gowda, K V Arjuna; Chakradhar, R P S

2010-03-01

Titanium dioxide thin films have been synthesized by sol-gel spin coating technique on glass and silicon substrates with and without surfactant polyethylene glycol (PEG). XRD and SEM results confirm the presence of nano-crystalline (anatase) phase at an annealing temperature of 300 degrees C. The influence of surfactant and annealing temperature on optical properties of TiO(2) thin films has been studied. Optical constants and film thickness were estimated by Swanepoel's (envelope) method and by ellipsometric measurements in the visible spectral range. The optical transmittance and reflectance were found to decrease with an increase in PEG percentage. Refractive index of the films decreased and film thickness increased with the increase in percentage of surfactant. The refractive index of the un-doped TiO(2) films was estimated at different annealing temperatures and it has increased with the increasing annealing temperature. The optical band gap of pure TiO(2) films was estimated by Tauc's method at different annealing temperature. Copyright 2010 Elsevier B.V. All rights reserved.

Characteristics of OMVPE grown GaAsBi QW lasers and impact of post-growth thermal annealing

NASA Astrophysics Data System (ADS)

Kim, Honghyuk; Guan, Yingxin; Babcock, Susan E.; Kuech, Thomas F.; Mawst, Luke J.

2018-03-01

Laser diodes employing a strain-compensated GaAs1-xBix/GaAs1-yPy single quantum well (SQW) active region were grown by organometallic vapor phase epitaxy (OMVPE). High resolution x-ray diffraction, room temperature photoluminescence, and real-time optical reflectance measurements during the OMVPE growth were used to find the optimum process window for the growth of the active region material. Systematic post-growth in situ thermal anneals of various lengths were carried out in order to investigate the impacts of thermal annealing on the laser device performance characteristics. While the lowest threshold current density was achieved after the thermal annealing for 30 min at 630 °C, a gradual decrease in the external differential quantum efficiency was observed as the annealing time increases. It was observed that the temperature sensitivities of the threshold current density increase while those of lasing wavelength and slope efficiency remain nearly constant with increasing annealing time. Z-contrast scanning transmission electron microscopic) analysis revealed inhomogeneous Bi distribution within the QW active region.

Thermal engineering of FAPbI3 perovskite material via radiative thermal annealing and in situ XRD

PubMed Central

Pool, Vanessa L.; Dou, Benjia; Van Campen, Douglas G.; Klein-Stockert, Talysa R.; Barnes, Frank S.; Shaheen, Sean E.; Ahmad, Md I.; van Hest, Maikel F. A. M.; Toney, Michael F.

2017-01-01

Lead halide perovskites have emerged as successful optoelectronic materials with high photovoltaic power conversion efficiencies and low material cost. However, substantial challenges remain in the scalability, stability and fundamental understanding of the materials. Here we present the application of radiative thermal annealing, an easily scalable processing method for synthesizing formamidinium lead iodide (FAPbI3) perovskite solar absorbers. Devices fabricated from films formed via radiative thermal annealing have equivalent efficiencies to those annealed using a conventional hotplate. By coupling results from in situ X-ray diffraction using a radiative thermal annealing system with device performances, we mapped the processing phase space of FAPbI3 and corresponding device efficiencies. Our map of processing-structure-performance space suggests the commonly used FAPbI3 annealing time, 10 min at 170 °C, can be significantly reduced to 40 s at 170 °C without affecting the photovoltaic performance. The Johnson-Mehl-Avrami model was used to determine the activation energy for decomposition of FAPbI3 into PbI2. PMID:28094249

Effect of thermal annealing on the structure and magnetism of Fe-doped ZnO nanocrystals synthesized by solid state reaction

NASA Astrophysics Data System (ADS)

Wang, Dong; Chen, Z. Q.; Wang, D. D.; Gong, J.; Cao, C. Y.; Tang, Z.; Huang, L. R.

2010-11-01

High purity Fe 2O 3/ZnO nanocomposites were annealed in air at different temperatures between 100 and 1200 °C to get Fe-doped ZnO nanocrystals. The structure and grain size of the Fe 2O 3/ZnO nanocomposites were investigated by X-ray diffraction 2θ scans. Annealing induces an increase of the grain size from 25 to 195 nm and appearance of franklinite phase of ZnFe 2O 4. Positron annihilation measurements reveal large number of vacancy defects in the interface region of the Fe 2O 3/ZnO nanocomposites, and they are gradually recovered with increasing annealing temperature. After annealing at temperatures higher than 1000 °C, the number of vacancies decreases to the lower detection limit of positrons. Room temperature ferromagnetism can be observed in Fe-doped ZnO nanocrystals using physical properties measurement system. The ferromagnetism remains after annealing up to 1000 °C, suggesting that it is not related with the interfacial defects.

Enhanced magnetic refrigeration properties in Mn-rich Ni-Mn-Sn ribbons by optimal annealing

PubMed Central

Zhang, Yu; Zhang, Linlin; Zheng, Qiang; Zheng, Xinqi; Li, Ming; Du, Juan; Yan, Aru

2015-01-01

The influence of annealing time on temperature range of martensitic phase transition (ΔTA-M), thermal hysteresis (ΔThys), magnetic hysteresis loss (ΔMhys), magnetic entropy change (ΔSM) and relative refrigeration capacity (RC) of the Mn-rich Ni43Mn46Sn11 melt spun ribbons have been systematically studied. By optimal annealing, an extremely large ΔSM of 43.2 J.kg−1K−1 and a maximum RC of 221.0 J.kg−1 could be obtained respectively in a field change of 5 T. Both ΔTA-M and ΔThys decreases after annealing, while ΔMhys and ΔSM first dramatically increase to a maximum then degenerates as increase of annealing time. A large effective cooling capacity (RCeff) of 115.4 J.kg−1 was achieved in 60 min annealed ribbons, which increased 75% compared with that unannealed ribbons. The evolution of magnetic properties and magnetocaloric effect has been discussed and proved by atomic ordering degree, microstructure and composition analysis. PMID:26055884

Thermal engineering of FAPbI 3 perovskite material via radiative thermal annealing and in situ XRD

DOE PAGES

Pool, Vanessa L.; Dou, Benjia; Van Campen, Douglas G.; ...

2017-01-17

Lead halide perovskites have emerged as successful optoelectronic materials with high photovoltaic power conversion efficiencies and low material cost. However, substantial challenges remain in the scalability, stability and fundamental understanding of the materials. Here we present the application of radiative thermal annealing, an easily scalable processing method for synthesizing formamidinium lead iodide (FAPbI 3) perovskite solar absorbers. Devices fabricated from films formed via radiative thermal annealing have equivalent efficiencies to those annealed using a conventional hotplate. By coupling results from in situ X-ray diffraction using a radiative thermal annealing system with device performances, we mapped the processing phase space ofmore » FAPbI 3 and corresponding device efficiencies. Our map of processing-structure-performance space suggests the commonly used FAPbI 3 annealing time, 10 min at 170 degrees C, can be significantly reduced to 40 s at 170 degrees C without affecting the photovoltaic performance. Lastly, the Johnson-Mehl-Avrami model was used to determine the activation energy for decomposition of FAPbI 3 into PbI 2.« less

Hafnium oxide films for application as gate dielectrics

NASA Astrophysics Data System (ADS)

Hsu, Shuo-Lin

The deposition and characterization of HfO2 films for potential application as a high-kappa gate dielectric in MOS devices has been investigated. DC magnetron reactive sputtering was utilized to prepare the HfO2 films. Structural, chemical, and electrical analyses were performed to characterize the various physical, chemical and electrical properties of the sputtered HfO2 films. The sputtered HfO2 films were annealed to simulate the dopant activation process used in semiconductor processing, and to study the thermal stability of the high-kappa, films. The changes in the film properties due to the annealing are also discussed in this work. Glancing angle XRD was used to analyse the atomic scale structure of the films. The as deposited films exhibit an amorphous, regardless of the film thickness. During post-deposition annealing, the thicker films crystallized at lower temperature (< 600°C), and ultra-thin (5.8 nm) film crystallized at higher temperature (600--720°C). The crystalline phase which formed depended on the thickness of the films. The low temperature phase (monoclinic) formed in the 10--20 nm annealed films, and high temperature phase (tetragonal) formed in the ultra-thin annealed HfO2 film. TEM cross-section studies of as deposited samples show that an interfacial layer (< 1nm) exists between HfO2/Si for all film thicknesses. The interfacial layer grows thicker during heat treatment, and grows more rapidly when grain boundaries are present. XPS surface analysis shows the as deposited films are fully oxidized with an excess of oxygen. Interfacial chemistry analysis indicated that the interfacial layer is a silicon-rich silicate layer, which tends to transform to silica-like layer during heat treatment. I-V measurements show the leakage current density of the Al/as deposited-HfO 2/Si MOS diode is of the order of 10-3 A/cm 2, two orders of magnitude lower than that of a ZrO2 film with similar physical thickness. Carrier transport is dominated by Schottky emission at lower electric fields, and by Frenkel-Poole emission in the higher electric field region. After annealing, the leakage current density decreases significantly as the structure remains amorphous structure. It is suggested that this decrease is assorted with the densification and defect healing which accures when the porous as-deposited amorphous structure is annealed. The leakage current density increases of the HfO2 layer crystallizes on annealing, which is attributed to the presence of grain boundaries. C-V measurements of the as deposited film shows typical C-V characteristics, with negligible hystersis, a small flat band voltage shift, but great frequency dispersion. The relative permittivity of HfO2/interfacial layer stack obtained from the capacitance at accumulation is 15, which corresponds to an EOT (equivalent oxide thickness) = 1.66 nm. After annealing, the frequency dispersion is greatly enhanced, and the C-V curve is shifted toward the negative voltage. Reliability tests show that the HfO2 films which remain amorphous after annealing possess superior resistance to constant voltage stress and ambient aging. This study concluded that the sputtered HfO 2 films exhibit an amorphous as deposited. Postdeposition annealing alters the crystallinity, interfacial properties, and electrical characteristics. The HfO2 films which remain amorphous structure after annealing possess the best electrical properties.

Ultra-soft magnetic properties and correlated phase analysis by {sup 57}Fe Mössbauer spectroscopy of Fe{sub 74}Cu{sub 0.8}Nb{sub 2.7}Si{sub 15.5}B{sub 7} alloy

DOE Office of Scientific and Technical Information (OSTI.GOV)

Manjura Hoque, S.; Liba, S. I.; Akhter, Shireen

2016-02-15

A detailed study of magnetic softness has been performed on FINEMENT type of ribbons by investigating the BH loop with maximum applied field of 960 A/m. The ribbon with the composition of Fe{sub 74}Cu{sub 0.8}Nb{sub 2.7}Si{sub 15.5}B{sub 7} was synthesized by rapid solidification technique and the compositions volume fraction was controlled by changing the annealing condition. Detail phase analysis was performed through X-ray diffraction (XRD), Differential scanning calorimetry (DSC), Vibrating sample magnetometer (VSM) and Mössbauer spectroscopy in order to correlate the ultrasoft magnetic properties with the volume fraction of amorphous and α-Fe(Si) soft nano composites. Bright (BF) and dark fieldmore » (DF) image with selective area diffraction (SAD) patterns by the transmission electron microscopy (TEM) of the sample annealed for the optimized annealed condition at 853 K for 3 min reveals nanocrystals with an average size between 10-15 nm possessing the bcc structure which matches with the grain size revealed by the X-ray diffraction. Kinetics of crystallization of α-Fe(Si) phases has been determined by DSC curves. Extremely small coercivity of 30.9 A/m and core loss of 2.5 W/Kg for the sample annealed at 853 K for 3 min was found. Similar values for other crystalline conditions were determined by using BH loop tracer with a maximum applied field of around 960 A/m. Mössbauer spectroscopy was used to determine chemical shift, hyperfine field distribution (HFD), and peak width of different phases. The volume fractions of the relative amount of amorphous and crystalline phases are also determined by Mössbauer spectroscopy. High saturation magnetization along with ultrasoft magnetic properties exhibits very high potentials technological applications.« less

Ultra-soft magnetic properties and correlated phase analysis by 57Fe Mössbauer spectroscopy of Fe74Cu0.8Nb2.7Si15.5B7 alloy

NASA Astrophysics Data System (ADS)

Manjura Hoque, S.; Liba, S. I.; Anirban, A.; Choudhury, Shamima; Akhter, Shireen

2016-02-01

A detailed study of magnetic softness has been performed on FINEMENT type of ribbons by investigating the BH loop with maximum applied field of 960 A/m. The ribbon with the composition of Fe74Cu0.8Nb2.7Si15.5B7 was synthesized by rapid solidification technique and the compositions volume fraction was controlled by changing the annealing condition. Detail phase analysis was performed through X-ray diffraction (XRD), Differential scanning calorimetry (DSC), Vibrating sample magnetometer (VSM) and Mössbauer spectroscopy in order to correlate the ultrasoft magnetic properties with the volume fraction of amorphous and α-Fe(Si) soft nano composites. Bright (BF) and dark field (DF) image with selective area diffraction (SAD) patterns by the transmission electron microscopy (TEM) of the sample annealed for the optimized annealed condition at 853 K for 3 min reveals nanocrystals with an average size between 10-15 nm possessing the bcc structure which matches with the grain size revealed by the X-ray diffraction. Kinetics of crystallization of α-Fe(Si) phases has been determined by DSC curves. Extremely small coercivity of 30.9 A/m and core loss of 2.5 W/Kg for the sample annealed at 853 K for 3 min was found. Similar values for other crystalline conditions were determined by using BH loop tracer with a maximum applied field of around 960 A/m. Mössbauer spectroscopy was used to determine chemical shift, hyperfine field distribution (HFD), and peak width of different phases. The volume fractions of the relative amount of amorphous and crystalline phases are also determined by Mössbauer spectroscopy. High saturation magnetization along with ultrasoft magnetic properties exhibits very high potentials technological applications.

Zero-temperature quantum annealing bottlenecks in the spin-glass phase.

PubMed

Knysh, Sergey

2016-08-05

A promising approach to solving hard binary optimization problems is quantum adiabatic annealing in a transverse magnetic field. An instantaneous ground state-initially a symmetric superposition of all possible assignments of N qubits-is closely tracked as it becomes more and more localized near the global minimum of the classical energy. Regions where the energy gap to excited states is small (for instance at the phase transition) are the algorithm's bottlenecks. Here I show how for large problems the complexity becomes dominated by O(log N) bottlenecks inside the spin-glass phase, where the gap scales as a stretched exponential. For smaller N, only the gap at the critical point is relevant, where it scales polynomially, as long as the phase transition is second order. This phenomenon is demonstrated rigorously for the two-pattern Gaussian Hopfield model. Qualitative comparison with the Sherrington-Kirkpatrick model leads to similar conclusions.

Evolution of rapidly solidified NiAlCu(B) alloy microstructure.

PubMed

Czeppe, Tomasz; Ochin, Patrick

2006-10-01

This study concerned phase transformations observed after rapid solidification and annealing at 500, 700 and 800 degrees C in 56.3 Ni-39.9 Al-3.8 Cu-0.06 B (E1) and 59.8 Ni-36.0 Al-4.3 Cu-0.06 B (E2) alloys (composition in at.%). Injection casting led to a homogeneous structure of very small, one-phase grains (2-4 microm in size). In both alloys, the phase observed at room temperature was martensite of L1(0) structure. The process of the formation of the Ni(5)Al(3) phase by atomic reordering proceeded at 285-394 degrees C in the case of E1 alloy and 450-550 degrees C in the case of E2 alloy. Further decomposition into NiAl (beta) and Ni(3)Al (gamma') phases, the microstructure and crystallography of the phases depended on the path of transformations, proceeding in the investigated case through the transformation of martensite crystallographic variants. This preserved precise crystallographic orientation between the subsequent phases, very stable plate-like morphology and very small beta + gamma' grains after annealing at 800 degrees C.

Influence of sputtering power on structural and magnetic properties of as-deposited, annealed and ERTA Co2FeSi films: A comparative study

NASA Astrophysics Data System (ADS)

Saravanan, L.; Raja, M. Manivel; Prabhu, D.; Therese, H. A.

2018-02-01

We report the effect of sputtering power (200 W - 350 W) on the structural, topographical and magnetic properties of Co2FeSi (CFS) films deposited at ambient temperatures as compared to the films which were either annealed at 300 °C or were subjected to Electron beam Rapid Thermal Annealed (ERTA) treatment. The structural and morphological analyses reveal changes in their crystalline phases and particle sizes. All the as-deposited and annealed CFS films showed A2 phase crystal structure. Whereas the CFS film sputtered at 350 W followed by ERTA displayed the fully ordered L21 structure. The particles are spherical in shape and their sizes increased gradually with increase in the sputtering power of the as-deposited and annealed CFS films. However, ERTA CFS films had spherical as well as columnar (elongated) shaped grains and their grain sizes increased nonlinearly with sputtering power. M-H studies on as-deposited, annealed and ERTA CFS films show ferromagnetic responses. The comparatively stronger ferromagnetic response was observed for the ERTA samples with low saturation field which depends on the enrichment of fine crystallites in these films. This indicates that, apart from higher sputtering powers used for deposition of CFS films, ERTA process plays a significant role in the enhancement of their magnetic responses. 350 W ERTA film has the considerable saturation magnetization (∼816 emu/cc), coercivity (∼527 Oe) and a good squareness values at 100 K than at 300 K, which could originate from the spin wave excitation effect. Further, the optimized parameters to achieve a CFS film with good structural and magnetic properties are discussed from the perspective of spintronics.

A fabrication and characterictics of microbolometer detectors using VOx/ZnO/VOx multilayer thin film processing

NASA Astrophysics Data System (ADS)

Han, Myung-Soo; Kim, Dae Hyeon; Ko, Hang Ju; Shin, Jae Chul; Kim, Hyo Jin; Kim, Do Gun

2014-06-01

In this work, a novel fabrication method for VOx-ZnO multilayers with mixed phase of the VO2 and V2O3 through the diffusion of oxygen by annealing at low temperature is presented. A stable sandwich structure of a VOx/ZnO/VOx multilayer was deposited at room temperature, through the oxygen gas flow rate, by RF sputtering system, and the mixed phase was formed through oxygen diffusion by annealing at O2 atmosphere. The results show that the single phase like multilayer formed by this process has a high TCR of more than -2.5%/K and low resistance of about 100 kohm at room temperature. XRD results for the as-deposited VOx/ZnO/VOx multilayer.

Effects of annealing temperature on the structural, mechanical and electrical properties of flexible bismuth telluride thin films prepared by high-pressure RF magnetron sputtering

NASA Astrophysics Data System (ADS)

Singkaselit, Kamolmad; Sakulkalavek, Aparporn; Sakdanuphab, Rachsak

2017-09-01

In this work Bi x Te y thin films were deposited on polyimide substrate by a high-pressure RF magnetron sputtering technique. The deposited condition was maintained using a high pressure of 1.3  ×  10-2 mbar. The as-deposited films show Bi2Te3 structure with Te excess phase (Te-rich Bi2Te3). After that, as-deposited films were annealed in the vacuum chamber under the N2 flow at temperatures from 250 to 400 °C for one hour. The microstructure, cross-section, [Bi]:[Te] content, and the mechanical, electrical and thermoelectric properties of as-deposited and different annealed films were investigated. It was found that the annealing temperature enhanced the crystallinity and film density for the temperature range 250-300 °C. However, the crystal structure of Bi2Te3 almost changed to the BiTe structure after annealing the films above 350 °C, due to the re-evaporation of Te. Nano-indentation results and cross-section images indicated that the hardness of the films related to the film density. The maximum hardness of 2.30 GPa was observed by annealing the films at 300 °C. As a result of an improvement in crystallinity and phase changes, the highest power factor of 11.45  ×  10-4 W m-1K-2 at 300 °C with the carrier concentration and mobility of 6.15  ×  1020 cm-3 and 34.03 cm2 V-1 s-1, respectively, was achieved for the films annealed at 400 °C. Contribution at the 4th Southeast Asia Conference on Thermoelectrics 2016 (SACT 2016), 15-18 December 2016, Da Nang City, Vietnam.

Method for homogenizing alloys susceptible to the formation of carbide stringers and alloys prepared thereby

DOEpatents

Braski, David N.; Leitnaker, James M.

1980-01-01

A novel fabrication procedure prevents or eliminates the reprecipitation of segregated metal carbides such as stringers in Ti-modified Hastelloy N and stainless steels to provide a novel alloy having carbides uniformly dispersed throughout the matrix. The fabrication procedure is applicable to other alloys prone to the formation of carbide stringers. The process comprises first annealing the alloy at a temperature above the single phase temperature for sufficient time to completely dissolve carbides and then annealing the single phase alloy for an additional time to prevent the formation of carbide stringers upon subsequent aging or thermomechanical treatment.

Shape-memory properties in Ni-Ti sputter-deposited film

NASA Technical Reports Server (NTRS)

Busch, J. D.; Johnson, A. D.; Lee, C. H.; Stevenson, D. A.

1990-01-01

A Ni-Ti alloy, generically called nitinol, was prepared from sputtering targets of two different compositions on glass substrates using a dc magnetron source. The as-deposited films were amorphous in structure and did not exhibit a shape memory. The amorphous films were crystallized with a suitable annealing process, and the transformation properties were measured using differential scanning calorimetry. The annealed films demonstrated a strong shape-memory effect. Stress/strain measurements and physical manipulation were used to evaluate the shape recovery. These tests demonstrated sustained tensile stresses of up to 480 MPa in the high-temperature phase, and a characteristic plastic deformation in the low-temperature phase.

Synthesis and Characterization of TiO2/SiO2 Thin Film via Sol-Gel Method

NASA Astrophysics Data System (ADS)

Halin, D. S. C.; Abdullah, M. M. A. B.; Mahmed, N.; Malek, S. N. A. Abdul; Vizureanu, P.; Azhari, A. W.

2017-06-01

TiO2/SiO2 thin films were prepared by sol-gel spin coating method. Structural, surface morphology and optical properties were investigated for different annealing temperatures at 300°C, 400°C and 500°C. X-ray diffraction pattern show that brookite TiO2 crystalline phase with SiO2 phase presence at 300°C. At higher temperatures of 400-500°C, the only phase presence was brookite. The surface morphology of film was characterized by scanning electron microscopy (SEM). The films annealed at 300°C shows an agglomeration of small flaky with crack free. When the temperature of annealing increase to 400-500°C, the films with large flaky and large cracks film were formed which was due to surface tension between the film and the air during the drying process. The UV-Vis spectroscopy shows that the film exhibits a low transmittance around 30% which was due to the substrate is inhomogeneously covered by the films. In order to improve the coverage of the film on the substrate, it has to repeatable the spin coating to ensure the substrate is fully covered by the films.

Thermal Spray Deposition, Phase Stability and Mechanical Properties of La2Zr2O7/LaAlO3 Coatings

NASA Astrophysics Data System (ADS)

Lozano-Mandujano, D.; Poblano-Salas, C. A.; Ruiz-Luna, H.; Esparza-Esparza, B.; Giraldo-Betancur, A. L.; Alvarado-Orozco, J. M.; Trápaga-Martínez, L. G.; Muñoz-Saldaña, J.

2017-08-01

This paper deals with the deposition of La2Zr2O7 (LZO) and LaAlO3 (LAO) mixtures by air plasma spray (APS). The raw material for thermal spray, single phase LZO and LAO in a 70:30 mol.% ratio mixture was prepared from commercial metallic oxides by high-energy ball milling (HEBM) and high-temperature solid-state reaction. The HEBM synthesis route, followed by a spray-drying process, successfully produced spherical agglomerates with adequate size distribution and powder-flow properties for feeding an APS system. The as-sprayed coating consisted mainly of a crystalline LZO matrix and partially crystalline LAO, which resulted from the high cooling rate experienced by the molten particles as they impact the substrate. The coatings were annealed at 1100 °C to promote recrystallization of the LAO phase. The reduced elastic modulus and hardness, measured by nanoindentation, increased from 124.1 to 174.7 GPa and from 11.3 to 14.4 GPa, respectively, after the annealing treatment. These values are higher than those reported for YSZ coatings; however, the fracture toughness ( K IC) of the annealed coating was only 1.04 MPa m0.5.

Influence of carboxylic acid type on microstructure and magnetic properties of polymeric complex sol-gel driven NiFe2O4

NASA Astrophysics Data System (ADS)

Hessien, M. M.; Mostafa, Nasser Y.; Abd-Elkader, Omar H.

2016-01-01

Citric, oxalic and tartaric acids were used for synthesis of NiFe2O4 using polymeric complex precursor route. The dry precursor gels were calcined at various temperatures (400-1100 °C) for 2 h. All carboxylic acids produce iron-deficient NiFe2O4 with considerable amount of α-Fe2O3 at 400 °C. Increase in the annealing temperature caused reaction of α-Fe2O3 with iron-deficient ferrite phase. The amount of initially formed α-Fe2O3 is directly correlated with stability constant and inversely correlated with the decomposition temperature of Fe(III) carboxylate precursors. In case of tartaric acid precursor, single phase of the ferrite was obtained at 450 °C. However, in case of oxalic acid and citric acid precursors, single phase ferrite was obtained at 550 °C and 700 °C, respectively. The lattice parameters were increased with increasing annealing temperature and with decreasing the amount of α-Fe2O3. Maximum saturation magnetization (55 emu/g) was achieved using tartaric acid precursor annealed at 1100 °C.

Fabrication of Cu2SnS3 thin films by ethanol-ammonium solution process by doctor-blade technique

NASA Astrophysics Data System (ADS)

Wang, Yaguang; Li, Jianmin; Xue, Cong; Zhang, Yan; Jiang, Guoshun; Liu, Weifeng; Zhu, Changfei

2017-11-01

In the present study, a low-cost and simple method is applied to fabricate Cu2SnS3 (CTS) thin films. Namely CTS thin films are prepared by a doctor-blade method with a slurry dissolving the Cu2O and SnS powders obtained from CBD reaction solution into ethanol-ammonium solvents. Series of characterization methods including XRD, Raman spectra, SEM and UV-Vis analyses are introduced to investigate the phase structure, morphology and optical properties of CTS thin films. As a result, monoclinic CTS films have been obtained with the disappearance of binary phases CuS and SnS2 while increasing the annealing temperature and time, high quality monoclinic CTS thin films consisting of compact and large grains have been successfully prepared by this ethanol-ammonium method. Moreover, the secondary phase Cu2Sn3S7 is also observed during the annealing process. In addition, the post-annealed CTS film with a band-gap about 0.89 eV shows excellent absorbance between 400 and 1200 nm, which is proper for the bottom layer in multi-junction thin film solar cells.[Figure not available: see fulltext.

Nano crystalline Bi{sub 2}(VO{sub 5}) phases in lithium bismuth borate glasses containing mixed vanadium-nickel oxides

DOE Office of Scientific and Technical Information (OSTI.GOV)

Yadav, Arti, E-mail: artidabhur@gmail.com; Khasa, S.; Dahiya, M. S.

2016-05-23

Glass composition 7V{sub 2}O{sub 5}·23Li{sub 2}O·20Bi{sub 2}O{sub 3}·50B{sub 2}O{sub 3} and x(2NiO·V{sub 2}O{sub 5})·(30-x)Li{sub 2}O·20Bi{sub 2}O{sub 3}·50B{sub 2}O{sub 3}, x=0, 2, 5, 7 and 10, were produced by conventional melt quenching technique. The quenched amorphous glass samples were annealed at temperatures 400°C and 500°C for 6 hours. The Bi{sub 2}(VO{sub 5}) crystallite were grown in all prepared glass matrix. Tn vanadium lithium bismuth borate glass (annealed), the some phrase of V{sub 2}O{sub 5}-crystal were observed along with the nano crystalline Bi{sub 2}(VO{sub 5}) phase. The sharp peaks in FTTR spectra of all annealed compositions were also compatible with the XRDmore » diffraction peaks of the system under investigation. Average crystalline size (D) of the Bi{sub 2}(VO{sub 5}) nano-crystallite was ~30 nm for samples annealed at 400°C and ~42 nm for samples annealed at 500°C. Lattice parameter and the lattice strain for all the samples was also calculated corresponding to the (113) plane of Bi{sub 2}(VO{sub 5}) crystallite.« less

A Two-Stage Annealing Strategy for Crystallization Control of CH3 NH3 PbI3 Films toward Highly Reproducible Perovskite Solar Cells.

PubMed

Zhang, Jing; Liang, Wensheng; Yu, Wei; Yu, Shuwen; Wu, Yiliang; Guo, Xin; Liu, Shengzhong Frank; Li, Can

2018-05-28

The solvent-engineering method is widely used to fabricate top-performing perovskite solar cells, which, however, usually exhibit inferior reproducibility. Herein, a two-stage annealing (TSA) strategy is demonstrated for processing of perovskite films, namely, annealing the intermediate phase at 60 °C for the first stage then at 100 °C for the second stage. Compared to conventional direct annealing temperature (DHA) at 100 °C, using this strategy, MAPbI 3 films become more controllable, leading to superior film uniformity and device reproducibility with the champion device efficiency reaching 19.8%. More specifically, the coefficient of variation of efficiency for 49 cells is reduced to 5.9%, compared to 9.8% for that using DHA. The TSA process is carefully studied using Fourier transform infrared spectroscopy, X-ray diffraction, and UV-vis absorption spectroscopy. It is found that in comparison with DHA the formation of hydrogen bonding and crystallization of perovskite are much slower and can be better controlled when using TSA. The improvements in film uniformity and device reproducibility are attributed to: 1) controllable MAPbI 3 crystal growth stemming from the progressive formation of hydrogen bonding between methylammonium and halide; 2) suppression of intermediate phase film dewetting, which is believed to be due to its decreased mobility at the initial low-temperature annealing stage. © 2018 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim.

Recent progress of quantum annealing

DOE Office of Scientific and Technical Information (OSTI.GOV)

Suzuki, Sei

2015-03-10

We review the recent progress of quantum annealing. Quantum annealing was proposed as a method to solve generic optimization problems. Recently a Canadian company has drawn a great deal of attention, as it has commercialized a quantum computer based on quantum annealing. Although the performance of quantum annealing is not sufficiently understood, it is likely that quantum annealing will be a practical method both on a conventional computer and on a quantum computer.

Characterization of pulsed laser deposition grown V2O3 converted VO2

NASA Astrophysics Data System (ADS)

Majid, Suhail; Shukla, D. K.; Rahman, F.; Gautam, Kamini; Sathe, V. G.; Choudhary, R. J.; Phase, D. M.

2016-10-01

Controllable tuning of Metal-insulator transition in VxOy thin film has been a field of extensive research. However controlled synthesis of desired Vanadium oxide phase is a challenging task. We have successfully achieved VO2 phase on Silicon substrate after post deposition annealing treatment to the PLD grown as deposited V2O3 thin films. The annealed thin film was characterized by x-ray diffraction (XRD), resistivity, Raman spectroscopy, X-ray absorption spectroscopy (XAS) and X-ray photoelectron spectroscopy (XPS) measurements. XRD confirms the crystalline nature and growth of VO2 phase in thin film. The characteristic MIT was observed from resistivity measurements and transition temperature appeared at lower value around 336 K, compared to bulk VO2. The structural transition accompanied with MIT from lower temperature monoclinic phase to higher temperature Rutile phase became evident from temperature dependent Raman measurements. Chemical state of vanadium was examined using XAS and XPS measurements which confirm the presence of +4 oxidation state of vanadium in thin film.

Microstructure control of Al-Cu films for improved electromigration resistance

DOEpatents

Frear, D.R.; Michael, J.R.; Romig, A.D. Jr.

1994-04-05

A process for the forming of Al-Cu conductive thin films with reduced electromigration failures is useful, for example, in the metallization of integrated circuits. An improved formation process includes the heat treatment or annealing of the thin film conductor at a temperature within the range of from 200 C to 300 C for a time period between 10 minutes and 24 hours under a reducing atmosphere such as 15% H[sub 2] in N[sub 2] by volume. Al-Cu thin films annealed in the single phase region of a phase diagram, to temperatures between 200 C and 300 C have [theta]-phase Al[sub 2] Cu precipitates at the grain boundaries continuously become enriched in copper, due, it is theorized, to the formation of a thin coating of [theta]-phase precipitate at the grain boundary. Electromigration behavior of the aluminum is, thus, improved because the [theta]-phase precipitates with copper hinder aluminum diffusion along the grain boundaries. Electromigration, then, occurs mainly within the aluminum grains, a much slower process. 5 figures.

De-vitrification of nanoscale phase-separated amorphous thin films in the immiscible copper-niobium system

NASA Astrophysics Data System (ADS)

Puthucode, A.; Devaraj, A.; Nag, S.; Bose, S.; Ayyub, P.; Kaufman, M. J.; Banerjee, R.

2014-05-01

Copper and niobium are mutually immiscible in the solid state and exhibit a large positive enthalpy of mixing in the liquid state. Using vapour quenching via magnetron co-sputter deposition, far-from equilibrium amorphous Cu-Nb films have been deposited which exhibit a nanoscale phase separation. Annealing these amorphous films at low temperatures (~200 °C) initiates crystallization via the nucleation and growth of primary nanocrystals of a face-centred cubic Cu-rich phase separated by the amorphous matrix. Interestingly, subsequent annealing at a higher temperature (>300 °C) leads to the polymorphic nucleation and growth of large spherulitic grains of a body-centred cubic Nb-rich phase within the retained amorphous matrix of the partially crystallized film. This sequential two-stage crystallization process has been investigated in detail by combining transmission electron microscopy [TEM] (including high-resolution TEM) and atom probe tomography studies. These results provide new insights into the crystallization behaviour of such unusual far-from equilibrium phase-separated metallic glasses in immiscible systems.

Dynamical phase transitions in generalized Kuramoto model with distributed Sakaguchi phase

NASA Astrophysics Data System (ADS)

Banerjee, Amitava

2017-11-01

In this numerical work, we have systematically studied the dynamical phase transitions in the Kuramoto-Sakaguchi model of synchronizing phase oscillators controlled by disorder in the Sakaguchi phases. We derive the numerical steady state phase diagrams for quenched and annealed kinds of disorder in the Sakaguchi parameters, using the conventional order parameter and other such statistical quantities as strength of incoherence and discontinuity measures. We have also considered the correlation profile of the local order parameter fluctuations in the various phases identified. The phase diagrams for quenched disorder are qualitatively much different from those in the global coupling regime. The order of various transitions is confirmed by a study of the distribution of the order parameter and its fourth order Binder’s cumulant across the transition for an ensemble of initial distribution of phases. For the annealed type of disorder, in contrast to the case with quenched disorder, the system is almost insensitive to the amount of disorder. We also elucidate the role of chimeralike states in the synchronizing transition of the system, and study the effect of disorder on these states. Finally, we seek justification of our results from simulations guided by the Ott-Antonsen ansatz.

Effect of thermal annealing on the structural, optical and dielectrical properties of P3HT:PC{sub 70}BM nanocomposites

DOE Office of Scientific and Technical Information (OSTI.GOV)

Aloui, Walid, E-mail: alouiwalid26@yahoo.fr; Adhikari, Tham; Nunzi, Jean-Michel

2016-06-15

Highlights: • A typical structure of ITO/PEDOT: PSS/P3HT: PC{sub 70}BM/Al was fabricated. • Charge carrier diffusion and recombination have been calculated. • AFM and optical results show that thermal annealing promotes the phase separation. • The annealing process improves the transport of charges. - Abstract: The effect of thermal annealing on the optical, structural and the dielectric properties of P3HT:PC{sub 70}BM blended films were investigated. By means of atomic force microscopy, we observed the morphology evolution of the annealed P3HT:PC{sub 70}BM nanocomposites. Raman spectroscopy showed a substantial ordering in the polymer film after annealing. The absorption spectra of the annealedmore » P3HT:PC{sub 70}BM films were improved and red shifted than un-annealed samples. The results indicate that the P3HT in the nanocomposite becomes an ordered structure with annealing. The ordered P3HT facilitates the charge transport. From the photoluminescence measurements, the formation of polymer crystallites was observed upon annealing. Thus, the device efficiency reaches 2.2% after annealing at 150 °C. Impedance spectroscopy shows the classical complex plan curves; the low frequency is related to the effective lifetime of charge carriers and the high frequency corresponds to the diffusion time of these carriers. Global mobilities are in the range 3.8–4.6 × 10{sup −3} cm{sup 2} V{sup −1} s{sup −1}.« less

Electron backscatter and X-ray diffraction studies on the deformation and annealing textures of austenitic stainless steel 310S

DOE Office of Scientific and Technical Information (OSTI.GOV)

Nezakat, Majid, E-mail: majid.nezakat@usask.ca

We studied the texture evolution of thermo-mechanically processed austenitic stainless steel 310S. This alloy was cold rolled up to 90% reduction in thickness and subsequently annealed at 1050 °C. At the early stages of deformation, strain-induced martensite was formed from deformed austenite. By increasing the deformation level, slip mechanism was found to be insufficient to accommodate higher deformation strains. Our results demonstrated that twinning is the dominant deformation mechanism at higher deformation levels. Results also showed that cold rolling in unidirectional and cross rolling modes results in Goss/Brass and Brass dominant textures in deformed samples, respectively. Similar texture components aremore » observed after annealing. Thus, the annealing texture was greatly affected by texture of the deformed parent phase and martensite did not contribute as it showed an athermal reversion during annealing. Results also showed that when the fraction of martensite exceeds a critical point, its grain boundaries impeded the movement of austenite grain boundaries during annealing. As a result, recrystallization incubation time would increase. This caused an incomplete recrystallization of highly deformed samples, which led to a rational drop in the intensity of the texture components. - Highlights: •Thermo-mechanical processing through different cold rolling modes can induce different textures. •Martensite reversion is athermal during annealing. •Higher fraction of deformation-induced martensite can increase the annealing time required for complete recrystallization. •Annealing texture is mainly influenced by the deformation texture of austenite.« less

Evidence of room temperature ferromagnetism in argon/oxygen annealed TiO2 thin films deposited by electron beam evaporation technique

NASA Astrophysics Data System (ADS)

Mohanty, P.; Kabiraj, D.; Mandal, R. K.; Kulriya, P. K.; Sinha, A. S. K.; Rath, Chandana

2014-04-01

TiO2 thin films deposited by electron beam evaporation technique annealed in either O2 or Ar atmosphere showed ferromagnetism at room temperature. The pristine amorphous film demonstrates anatase phase after annealing under Ar/O2 atmosphere. While the pristine film shows a super-paramagnetic behavior, both O2 and Ar annealed films display hysteresis at 300 K. X-ray photo emission spectroscopy (XPS), Raman spectroscopy, Rutherford's backscattering spectroscopy (RBS), cross-sectional transmission electron microscopy (TEM) and energy dispersive X-ray spectroscopy (EDS) were used to refute the possible role of impurities/contaminants in magnetic properties of the films. The saturation magnetization of the O2 annealed film is found to be higher than the Ar annealed one. It is revealed from shifting of O 1s and Ti 2p core level spectra as well as from the enhancement of high binding energy component of O 1s spectra that the higher magnetic moment is associated with higher oxygen vacancies. In addition, O2 annealed film demonstrates better crystallinity, uniform deposition and smoother surface than that of the Ar annealed one from glancing angle X-ray diffraction (GAXRD) and atomic force microscopy (AFM). We conclude that although ferromagnetism is due to oxygen vacancies, the higher magnetization in O2 annealed film could be due to crystallinity, which has been observed earlier in Co doped TiO2 film deposited by pulsed laser deposition (Mohanty et al., 2012 [10]).

The influence of thermal annealing on the characteristics of Au/Ni Schottky contacts on n-type 4 H-SiC

NASA Astrophysics Data System (ADS)

Omotoso, E.; Auret, F. D.; Igumbor, E.; Tunhuma, S. M.; Danga, H. T.; Ngoepe, P. N. M.; Taleatu, B. A.; Meyer, W. E.

2018-05-01

The effects of isochronal annealing on the electrical, morphological and structural characteristics of Au/Ni/4 H-SiC Schottky barrier diodes (SBDs) have been studied. Current-voltage ( I- V), capacitance-voltage ( C- V), deep-level transient spectroscopy, scanning electron microscope (SEM) and X-ray diffraction measurements were employed to study the thermal effect on the characteristics of the SBDs. Prior to thermal annealing of Schottky contacts, the I- V measurements results confirmed the good rectification behaviour with ideality factor of 1.06, Schottky barrier height of 1.20 eV and series resistance of 7 Ω. The rectification properties after annealing was maintained up to an annealing temperature of 500 °C, but deviated slightly above 500 °C. The uncompensated ionized donor concentration decreased with annealing temperature, which could be attributed to out-diffusion of the 4 H-SiC into the Au/Ni contacts and decrease in bonding due to formation of nickel silicides. We observed the presence of four deep-level defects with energies 0.09, 0.11, 0.16 and 0.65 eV below the conduction band before and after the isochronal annealing up to 600 °C. The conclusion drawn was that annealing did not affect the number of deep-level defects present in Au/Ni/4 H-SiC contacts. The variations in electrical properties of the devices were attributed to the phase transformations and interfacial reactions that occurred after isochronal annealing.

Efficient optical activation of Eu3+ ions doped in ZnGa2O4 thin films: Correlation between crystalline phase and photoluminescence

NASA Astrophysics Data System (ADS)

Akazawa, Housei; Shinojima, Hiroyuki

2018-06-01

The physicochemical properties of Eu-doped zinc gallate (ZnGaxO1+1.5x:Eu) (1 < x < 6) thin films were investigated by means of photoluminescence (PL) triggered by band-to-band transitions of the host crystal at λ = 325 nm. Close correspondence between PL spectra and crystalline phases was verified by performing combinatorial measurements over four-inch substrates on which there was a spread of Ga/Zn composition ratios. The phase formation kinetics for deposition with H2O as an oxygen source gas followed by post annealing were similar to those of hydrothermal synthesis. ZnGa2O4 preferentially formed for a wide range of compositions between 1 < x < 4 and post annealing temperatures between 400 and 800 °C; intense emissions from Eu3+ ions were observed from the films. In contrast, the phase formation kinetics for deposition with O2 gas followed by post annealing were similar to those of solid-state reactions. Vacuum annealing above 500 °C caused preferential losses of Ga atoms and precipitation of Zn2Ga2O5 crystallites at x < 4, whereas ZnGa2O4 formed when a large amount of Ga (x > 6) was initially contained in the as-deposited state. The resulting PL spectra from Zn2Ga2O5 exhibited only a broad emission band from 450 to 700 nm, which was ascribed to defects in the poorly crystallized Zn:Ga = 1:1 phase. When the films deposited with O2 were post annealed in an O2 ambient, Zn atoms were lost, producing β-Ga2O3 as the primary phase accompanied with ZnGa2O4. The resulting Eu3+ emission was very weak, possibly because the Eu3+ ions attached to Ga2O3 domains were not emission-active and/or could not be efficiently excited due to wide bandgap (5 eV). When ZnGa2O4:Eu films were crystallized during deposition at elevated temperatures, weak emissions only from Eu3+ ions were observed. Taken together, these experimental results indicate that Eu3+ ions attached to ZnGa2O4 are highly emission-active; i.e., ZnGa2O4 is a particularly good host crystal with which to secure optical activation of doped Eu3+ ions.

Interface-induced superconductivity at ∼25 K at ambient pressure in undoped CaFe2As2 single crystals

PubMed Central

Zhao, Kui; Lv, Bing; Deng, Liangzi; Huyan, Shu-Yuan; Xue, Yu-Yi; Chu, Ching-Wu

2016-01-01

Superconductivity has been reversibly induced/suppressed in undoped CaFe2As2 (Ca122) single crystals through proper thermal treatments, with Tc at ∼25 K at ambient pressure and up to 30 K at 1.7 GPa. We found that Ca122 can be stabilized in two distinct tetragonal (T) phases at room temperature and ambient pressure: PI with a nonmagnetic collapsed tetragonal (cT) phase at low temperature and PII with an antiferromagnetic orthorhombic (O) phase at low temperature, depending on the low-temperature annealing condition. Neither phase at ambient pressure is superconducting down to 2 K. However, systematic annealing for different time periods at 350 °C on the as-synthesized crystals, which were obtained by quenching the crystal ingot from 850 °C, reveals the emergence of superconductivity over a narrow time window. Whereas the onset Tc is insensitive to the anneal time, the superconductive volume fraction evolves with the time in a dome-shaped fashion. Detailed X-ray diffraction profile analyses further reveal mesoscopically stacked layers of the PI and the PII phases. The deduced interface density correlates well with the superconducting volume measured. The transport anomalies of the T–cT transition, which is sensitive to lattice strain, and the T–O transition, which is associated with the spin-density-wave (SDW) transition, are gradually suppressed over the superconductive region, presumably due to the interface interactions between the nonmagnetic metallic cT phase and the antiferromagnetic O phase. The results provide the most direct evidence to date for interface-enhanced superconductivity in undoped Ca122, consistent with the recent theoretical prediction. PMID:27799564

Influence of thermal treatment on the formation of zirconia nanostructured powder by thermal decomposition of different precursors

NASA Astrophysics Data System (ADS)

Stoia, Marcela; Barvinschi, Paul; Barbu-Tudoran, Lucian; Negrea, Adina; Barvinschi, Floricica

2013-10-01

The paper presents some results concerning the preparation of zirconia powders starting from ZrOCl2·8H2O by using two synthesis methods: (a) precipitation with NH3, at 90 °C, and (b) thermal decomposition of carboxylate precursors, obtained in the reaction of zirconium nitrate and two different alcohols, 1,3-propanediol (PD) and poly(vinyl alcohol) (PVA), at 150 °C. The precursors obtained at different temperatures have been characterized by thermal analysis (TG, DTA) and FT-IR spectroscopy. DTA analysis evidenced very clearly the transition temperatures between zirconia crystalline phases. The precursors have been annealed at different temperatures in order to obtain zirconia powders and the as obtained powders have been characterized by means of X-Ray Diffraction (XRD), Fourier Transform Infrared Spectroscopy (FTIR), and Scanning Electron Microscopy (SEM). In case of precipitation method the presence of the tetragonal phase was observed at 400 °C, while the monoclinic phase appears at temperatures higher than 400 °C, becoming major crystalline phase starting with 700 °C. In case of the powders prepared by thermal decomposition of carboxylate precursors, the tetragonal phase was formed at temperatures below 700 °C, when the monoclinic phase begin to crystallize as secondary phase, in a higher proportion for the samples synthesized with 1,3-propanediol. All powders annealed at 1200 °C are pure monoclinic zirconia. SEM images have evidenced for the zirconia powders annealed at 1000 °C particles with diameters up to 150 nm, agglomerated in micrometer-sized aggregates, more individualized and homogenous than that obtained in the case of zirconia powder synthesized with poly(vinyl alcohol).

Analysis of Blockade in Charge Transport Across Polymeric Heterojunctions as a Function of Thermal Annealing: A Different Perspective

NASA Astrophysics Data System (ADS)

Rathi, Sonika; Chauhan, Gayatri; Gupta, Saral K.; Srivastava, Ritu; Singh, Amarjeet

2017-02-01

A blend of poly(3-hexylthiophene-2,5diyl) (P3HT) and [6,6]-phenyl C61 butyric acid methyl ester (PCBM) is popularly used as an active medium in polymeric solar devices. According to the most recent understanding, the blend is a three-phase system contrary to its earlier understanding of two-phase bicontinuous network. We have synthesized a P3HT-PCBM based layered heterostructure system by spin coating and thermal vacuum evaporations. Current density ( J) was measured as a function of applied electric field ( E) across the system bound between two metal electrodes. J- E relations were analyzed into the backdrop of space charge limited current model and Schottky model. The later was used to predict dc-dielectric constants from the linear slopes of ln ( J) versus E 1/2. The curves were not monotonously linear, but observe a knee-bend separating into two linear segments for each curve. Thermal annealing from 40°C to 80°C was used as an activation tool for driving changes in the internal morphology via inter-diffusion of polymers and current measurements were performed at room temperature after each annealing. At the last stage of annealing the two linear slopes were highly distinct. The presence of sharp knee-bend results in approximately 20 times jump in dielectric constant as a function of electric field. Such high jumps in dielectric constant illustrate the potential for switching applications and charge storage. The high dielectric constants can be understood in terms of space charge polarization due to isolated domains which hindrance to charge transport. The high dielectric constants were confirmed by another experiment of capacitance measurements of a different set of similar samples. A study of thermal evolution of internal morphology was also carried out using x-ray diffraction and scanning electron microscopy techniques to correlate the morphological changes with the transport properties.

Study of the resonant frequencies of silicon microcantilevers coated with vanadium dioxide films during the insulator-to-metal transition

NASA Astrophysics Data System (ADS)

Rúa, Armando; Fernández, Félix E.; Hines, Melissa A.; Sepúlveda, Nelson

2010-03-01

Vanadium dioxide (VO2) thin films were grown on silicon microcantilevers and companion test substrates by pulsed laser deposition followed by in situ annealing in an oxidizing atmosphere, with annealing times used to control crystallite sizes. Annealing times of 18 min produced VO2 films with average crystallite sizes of ˜10 nm or less, while those annealed for 35 min had crystallites of average size ˜90 nm, comparable to sample thickness. X-ray diffraction and x-ray photoelectron spectroscopy studies of the samples showed that films with crystallite sizes ˜40 nm or greater consisted of substoichiometric VO2 in its monoclinic phase, with preferential orientation with (011) planes parallel to the sample surface, while finer structured samples had a substantially similar composition, but showed no clear evidence of preferential orientation and were probably partially amorphous. Forced vibration experiments were performed with the cantilevers as they were thermally cycled through the VO2 insulator-to-metal transition (IMT). Very large reversible changes in the resonant frequencies of up to 5% (3.6 kHz) as well as hysteretic behavior were observed, which depend strongly on film crystallite size. The average value of Young's modulus for VO2 films with crystallite sizes of ˜90 nm was estimated from the mechanical resonance data at room temperature to be ˜120 GPa, but the large tensile stresses which develop between film and substrate through the IMT impede a similar determination for the VO2 tetragonal phase, since the commonly used relationships for cantilever frequencies derived from elasticity theory are not applicable for strongly curved composite beams. The results presented show that VO2 thin films can be useful in novel microscale and nanoscale electromechanical resonators in which effective stiffness can be tuned thermally or optically. This response can provide additional functionality to VO2—based devices which take advantage of other property changes through the IMT.

Combinatorial investigation of Fe–B thin-film nanocomposites

PubMed Central

Brunken, Hayo; Grochla, Dario; Savan, Alan; Kieschnick, Michael; Meijer, Jan D; Ludwig, Alfred

2011-01-01

Combinatorial magnetron sputter deposition from elemental targets was used to create Fe–B composition spread type thin film materials libraries on thermally oxidized 4-in. Si wafers. The materials libraries consisting of wedge-type multilayer thin films were annealed at 500 or 700 °C to transform the multilayers into multiphase alloys. The libraries were characterized by nuclear reaction analysis, Rutherford backscattering, nanoindentation, vibrating sample magnetometry, x-ray diffraction (XRD) and transmission electron microscopy (TEM). Young's modulus and hardness values were related to the annealing parameters, structure and composition of the films. The magnetic properties of the films were improved by annealing in a H2 atmosphere, showing a more than tenfold decrease in the coercive field values in comparison to those of the vacuum-annealed films. The hardness values increased from 8 to 18 GPa when the annealing temperature was increased from 500 to 700 °C. The appearance of Fe2B phases, as revealed by XRD and TEM, had a significant effect on the mechanical properties of the films. PMID:27877435

Effect of sintering on optical, structural and photoluminescence properties of ZnO thin films prepared by sol-gel process.

PubMed

Vishwas, M; Narasimha Rao, K; Arjuna Gowda, K V; Chakradhar, R P S

2010-09-15

Zinc oxide (ZnO) thin films have been deposited on glass substrates via sol-gel technique using zinc acetate dihydrate as precursor by spin coating of the sol at 2000 rpm. Effects of annealing temperature on optical, structural and photo luminescence properties of the deposited ZnO films have been investigated. The phase transition from amorphous to polycrystalline hexagonal wurtzite structure was observed at an annealing temperature of 400 degrees C. An average transmittance of 87% in the visible region has been obtained at room temperature. The optical transmittance has slightly increased with increase of annealing temperature. The band gap energy was estimated by Tauc's method and found to be 3.22 eV at room temperature. The optical band gap energy has decreased with increasing annealing temperature. The photoluminescence (PL) intensity increased with annealing temperature up to 200 degrees C and decreased at 300 degrees C. Copyright 2010 Elsevier B.V. All rights reserved.

Structural Characterization of Sputtered Silicon Thin Films after Rapid Thermal Annealing for Active-Matrix Organic Light Emitting Diode

NASA Astrophysics Data System (ADS)

de Dieu Mugiraneza, Jean; Miyahira, Tomoyuki; Sakamoto, Akinori; Chen, Yi; Okada, Tatsuya; Noguchi, Takashi; Itoh, Taketsugu

2010-12-01

The microcrystalline phase obtained by adopting a two-step rapid thermal annealing (RTA) process for rf-sputtered silicon films deposited on thermally durable glass was characterized. The optical properties, surface morphology, and internal stress of the annealed Si films are investigated. As the thermally durable glass substrate allows heating of the deposited films at high temperatures, micro-polycrystalline silicon (micro-poly-Si) films of uniform grain size with a smooth surface and a low internal stress could be obtained after annealing at 750 °C. The thermal stress in the Si films was 100 times lower than that found in the films deposited on conventional glass. Uniform grains with an average grain size of 30 nm were observed by transmission electron microscopy (TEM) in the films annealed at 800 °C. These micro-poly-Si films have potential application for fabrication of uniform and reliable thin film transistors (TFTs) for large scale active-matrix organic light emitting diode (AMOLED) displays.

Effects of high pressure nitrogen annealing on ferroelectric Hf0.5Zr0.5O2 films

NASA Astrophysics Data System (ADS)

Kim, Taeho; Park, Jinsung; Cheong, Byoung-Ho; Jeon, Sanghun

2018-02-01

The effect of high-pressure nitrogen annealing at up to 50 atmospheres (atm) on Hf0.5Zr0.5O2 films at relatively low temperatures (450 °C) is analyzed using polarization-electric field curves, bipolar switching endurance measurements, grazing angle incidence X-ray diffraction, and piezoelectric force microscopy. Hf0.5Zr0.5O2 films annealed at 450 °C/50 atm have excellent characteristics, including remanent polarizations greater than 20 μC/cm2, a switching speed of 200 ns, and reliability, measured by sustained performance after 1010 bipolar switching cycles. The enhanced device features are attributed to the transition to the orthorhombic-phase from the tetragonal-phase of Hf0.5Zr0.5O2 at high pressure, which is also consistent with the results of "wake-up" analysis, and the variations of the pure polarization curves, extracted from the total displacement field under pressure.

Structural and photoluminescence study of bulk SrZnO2

NASA Astrophysics Data System (ADS)

Manju, Jain, Megha; Kumar, Ravi; Kumar, Shalendra; Thakur, Anup; Vij, Ankush

2018-05-01

In present work, we report synthesis, X-ray diffraction study and photoluminescence of SrZnO2. The SrZnO2 phosphors were prepared through high energy ball milling process and subsequent annealing. The annealing at various temperatures helped in emergence of single phased SrZnO2 phosphors. The texture coefficient of prominent planes was found to be growing with annealing temperature. At an excitation wavelength of 325 nm, the photoluminescence spectrum is spanning from yellow to IR region. As SrZnO2 is wide band gap phosphor, so the observed emission is believed to be due to oxygen vacancies or cation interstitial defects.

Removal of Micrometer Size Morphological Defects and Enhancement of Ultraviolet Emission by Thermal Treatment of Ga-Doped ZnO Nanostructures

PubMed Central

Manzoor, Umair; Kim, Do K.; Islam, Mohammad; Bhatti, Arshad S.

2014-01-01

Mixed morphologies of Ga-doped Zinc Oxide (ZnO) nanostructures are synthesized by vapor transport method. Systematic scanning electron microscope (SEM) studies of different morphologies, after periodic heat treatments, gives direct evidence of sublimation. SEM micrographs give direct evidence that morphological defects of nanostructures can be removed by annealing. Ultra Violet (UV) and visible emission depends strongly on the annealing temperatures and luminescent efficiency of UV emission is enhanced significantly with each subsequent heat treatment. X-Ray diffraction (XRD) results suggest that crystal quality improved by annealing and phase separation may occur at high temperatures. PMID:24489725

Removal of micrometer size morphological defects and enhancement of ultraviolet emission by thermal treatment of Ga-doped ZnO nanostructures.

PubMed

Manzoor, Umair; Kim, Do K; Islam, Mohammad; Bhatti, Arshad S

2014-01-01

Mixed morphologies of Ga-doped Zinc Oxide (ZnO) nanostructures are synthesized by vapor transport method. Systematic scanning electron microscope (SEM) studies of different morphologies, after periodic heat treatments, gives direct evidence of sublimation. SEM micrographs give direct evidence that morphological defects of nanostructures can be removed by annealing. Ultra Violet (UV) and visible emission depends strongly on the annealing temperatures and luminescent efficiency of UV emission is enhanced significantly with each subsequent heat treatment. X-Ray diffraction (XRD) results suggest that crystal quality improved by annealing and phase separation may occur at high temperatures.

Thermal annealing evolution to physical properties of ZnS thin films as buffer layer for solar cell applications

NASA Astrophysics Data System (ADS)

Kaushalya; Patel, S. L.; Purohit, A.; Chander, S.; Dhaka, M. S.

2018-07-01

The conventional CdS window layer in solar cells is found to be hazardous for the environment due to toxic nature of the cadmium. Therefore, in order to seek an alternative, a study on effect of post-annealing treatment on physical properties of e-beam evaporated ZnS thin films has been carried out where films of thickness 150 nm were deposited on glass and indium tin oxide (ITO) substrates. The post annealing treatment was performed in air atmosphere within the temperature range from 100 °C to 500 °C. X-ray diffraction analysis reveals that the films on glass substrate are found to be amorphous at low temperature annealing (≤300 °C) while have α-ZnS hexagonal phase (wurtzite structure) at higher annealing. The patterns also show that the possibility of oxidation is increased significantly at temperature 500 °C which leads to decrease in direct band gap from 3.28 eV to 3.18 eV except films annealed at 300 °C (i.e. 3.39 eV). The maximum transmittance is found about 95% as a result of Doppler blue shift while electrical analysis indicated almost ohmic behavior between current and voltage and surface roughness is increased with post-annealing treatment.

The role of nickel addition and annealing temperature on ion storage performance of nanostructured nickel ferrite thin films

NASA Astrophysics Data System (ADS)

Bazhan, Z.; Ghodsi, F. E.; Mazloom, J.

2016-10-01

The sol-gel spin-coated nickel ferrite (NF), NiFe2O4, thin films were synthesised and the effect of annealing temperature and compositional ratio on different properties of samples were investigated. Electrochemical performance of the films was measured in the presence of KOH and LiClO4/PC electrolyte. Generally, addition of nickel increases the current density. The NF thin films with molar ratio of 0.5 and annealed at 400 °C have the highest charge density value and the highest capacitance in both electrolytes. Annealing temperature had significant effect on electrochemical properties of NF thin films and the diffusion coefficient enhanced by increasing the annealing temperature. X-ray diffraction patterns of prepared samples showed the rhombohedral structure, hematite phase (α-Fe2O3), of iron oxide sample and the presence of inverse spinel structure confirms the formation of NF. Field emission scanning electron microscopy images revealed that the morphology of films changes from larvae shape to granular structure by nickel incorporation and the grain size increased by raising the annealing temperature. The absorption edge of the hematite shift to higher wavelength by annealing and nickel incorporation and band gap narrowing has been occurred.

Electrical and structural properties of (Pd/Au) Schottky contact to as grown and rapid thermally annealed GaN grown by MBE

DOE Office of Scientific and Technical Information (OSTI.GOV)

Nirwal, Varun Singh, E-mail: varun.nirwal30@gmail.com; Singh, Joginder; Gautam, Khyati

2016-05-06

We studied effect of thermally annealed GaN surface on the electrical and structural properties of (Pd/Au) Schottky contact to Ga-polar GaN grown by molecular beam epitaxy on Si substrate. Current voltage (I-V) measurement was used to study electrical properties while X-ray diffraction (XRD) measurement was used to study structural properties. The Schottky barrier height calculated using I-V characteristics was 0.59 eV for (Pd/Au) Schottky contact on as grown GaN, which increased to 0.73 eV for the Schottky contact fabricated on 700 °C annealed GaN film. The reverse bias leakage current at -1 V was also significantly reduced from 6.42×10{sup −5} Amore » to 7.31×10{sup −7} A after annealing. The value of series resistance (Rs) was extracted from Cheung method and the value of R{sub s} decreased from 373 Ω to 172 Ω after annealing. XRD results revealed the formation of gallide phases at the interface of (Pd/Au) and GaN for annealed sample, which could be the reason for improvement in the electrical properties of Schottky contact after annealing.« less

Effect of annealing on optical properties and structure of the vanadium dioxide thin films

NASA Astrophysics Data System (ADS)

Zhu, Huiqun; Li, Yi; Li, Yuming; Huang, Yize; Tong, Guoxiang; Fang, Baoying; Zheng, Qiuxin; Li, Liu; Shen, Yujian

2012-10-01

VO2 thin films were prepared on soda-lime glass substrates by DC magnetron sputtering at room temperature using vanadium target and post annealing in air. X-ray diffraction and FTIR spectroscopy analyses showed that the films obtained at the optimized parameters have high VO2 (011) orientation. Both low temperature deposition and post annealing method were beneficial to grow the nano-films with pure VO2 phase-structure and composition. Metalinsulator transition properties of the VO2 films in terms of infrared transmittance, transmittance variation and film thickness were investigated under varying annealing temperature. Results showed that infrared transmittance variation and transition temperature of the nano-films were significantly improved and reduced respectively. Therefore, this study was able to develop practical low-cost preparation methods for high-performance intelligent energy-saving thin films.

Investigation of high temperature annealing effectiveness for recovery of radiation-induced structural changes and properties of 18Cr-10Ni-Ti austenitic stainless steels

NASA Astrophysics Data System (ADS)

Gurovich, B. A.; Kuleshova, E. A.; Frolov, A. S.; Maltsev, D. A.; Prikhodko, K. E.; Fedotova, S. V.; Margolin, B. Z.; Sorokin, A. A.

2015-10-01

A complex study of structural state and properties of 18Cr-10Ni-Ti austenitic stainless steel after irradiation in BOR-60 fast research reactor (in the temperature range 330-400 °С up to damaging doses of 145 dpa) and in VVER-1000 light water reactor (at temperature ∼320 °С and damaging doses ∼12-14 dpa) was performed. The possibility of recovery of structural-phase state and mechanical properties to the level almost corresponding to the initial state by the recovery annealing was studied. The principal possibility of the recovery annealing of pressurized water reactor internals that ensures almost complete recovery of its mechanical properties and microstructure was shown. The optimal mode of recovery annealing was established: 1000 °C during 120 h.

The Nanocrystalline State of Narrow Gap Semiconducting Chalcogenides

DTIC Science & Technology

2010-08-23

using a 1 nm scanning probe and the EDS microanalysis . For Annealing studies nanocrystal powder samples were placed in ceramic crucibles and annealed...nanocrystals are homogenous single phase EDS spectral images were collected in scanning transmission electron microcopy using a 1 nm electron probe...explorations with alio-valent elements (e.g. Sb3+, Ag+ doping in PbTe). • Perform chemical and physical characterization to demonstrate that nanocrystals are

Computational Thermodynamics Characterization of 7075, 7039, and 7020 Aluminum Alloys Using JMatPro

DTIC Science & Technology

2011-09-01

parameters of temperature and time may be selected to simulate effects on microstructure during annealing , solution treating, quenching, and tempering...nucleation may be taken into account by use of a wetting angle function. Activation energy may be taken into account for rapidly quenched alloys...the stable forms of precipitates that result from solutionizing, annealing or intermediate heat treatment, and phase formation during nonequilibrium

Molecular layer deposition of "vanadicone", a vanadium-based hybrid material, as an electrode for lithium-ion batteries.

PubMed

Van de Kerckhove, Kevin; Mattelaer, Felix; Dendooven, Jolien; Detavernier, Christophe

2017-04-05

Molecular layer deposition (MLD) of hybrid organic-inorganic thin films called "vanadicones" was investigated using tetrakisethylmethylaminovanadium (TEMAV) as the metal precursor and glycerol (GL) or ethylene glycol (EG) as the organic reactant. Linear and continued growth could only be achieved with GL as the organic reactant. The TEMAV/GL process displayed self-limiting reactions for both precursor and reactant pulses in the temperature range from 80 °C to 180 °C, with growth rates of 1.2 to 0.5 Å per cycle, respectively. Infrared spectroscopy (FTIR) and X-ray photoelectron spectroscopy (XPS) revealed the hybrid nature of the films. From X-ray reflectivity, the density was estimated at 2.6 g cm -3 . A series of 21 nm vanadicone films were subjected to annealing under oxidizing (air) or inert (He) atmospheres at 500 °C. During annealing in air, the film crystallized to the V 2 O 5 phase and all carbon was removed from the film. The films annealed in helium remained amorphous and retained most of their carbon content. Electrochemical measurements revealed lithium-ion activity during cyclic voltammetry in all treated films, while the as deposited film was inactive. In the 2.9 to 3.5 V vs. Li + /Li potential region, no improvement over the V 2 O 5 reference was observed. However, the helium annealed samples outperformed V 2 O 5 in terms of capacity, rate performance and cyclability when charged and discharged in the 1.0 to 3.5 V vs. Li + /Li region. This result enables the application of V x O y -based hybrid electrodes in a wider potential range without sacrificing the stability and performance.

DOE Office of Scientific and Technical Information (OSTI.GOV)

Marrakchi, G.; Barbier, D.; Guillot, G.

Electrical and deep level transient spectroscopy measurements on Schottky barriers were performed in order to characterize electrically active defects in n-type GaAs (Bridgman substrates or liquid-phase epitaxial layers) after pulsed electron beam annealing. Both surface damage and bulk defects were observed in the Bridgman substrates depending on the pulse energy density. No electron traps were detected in the liquid-phase epitaxial layers before and after annealing for an energy density of 0.4 J/cm/sup 2/. The existence of an interfacial insulating layer at the metal-semiconductor interface, associated with As out-diffusion during the pulsed electron irradiation, was revealed by the abnormally high valuesmore » of the Schottky barrier diffusion potential. Moreover, two new electron traps with activation energy of 0.35 and 0.43 eV, called EP1 and EP2, were introduced in the Bridgman substrates after pulsed electron beam annealing. The presence of these traps, related to the As evaporation, was tentatively attributed to the decrease of the EL2 electron trap signal after 0.4-J/cm/sup 2/ annealing. It is proposed that these new defects states are due to the decomposition of the As/sub Ga/-As/sub i/ complex recently considered as the most probable defect configuration for the dominant EL2 electron trap usually detected in as-grown GaAs substrates.« less

Study of paramagnetic defect centers in as-grown and annealed TiO2 anatase and rutile nanoparticles by a variable-temperature X-band and high-frequency (236 GHz) EPR.

PubMed

Misra, S K; Andronenko, S I; Tipikin, D; Freed, J H; Somani, V; Prakash, Om

2016-03-01

Detailed EPR investigations on as-grown and annealed TiO 2 nanoparticles in the anatase and rutile phases were carried out at X-band (9.6 GHz) at 77, 120-300 K and at 236 GHz at 292 K. The analysis of EPR data for as-grown and annealed anatase and rutile samples revealed the presence of several paramagnetic centers: Ti 3+ , O - , adsorbed oxygen (O 2 - ) and oxygen vacancies. On the other hand, in as-grown rutile samples, there were observed EPR lines due to adsorbed oxygen (O 2 - ) and the Fe 3+ ions in both Ti 4+ substitutional positions, with and without coupling to an oxygen vacancy in the near neighborhood. Anatase nanoparticles were completely converted to rutile phase when annealed at 1000° C, exhibiting EPR spectra similar to those exhibited by the as-grown rutile nanoparticles. The high-frequency (236 GHz) EPR data on anatase and rutile samples, recorded in the region about g = 2.0 exhibit resolved EPR lines, due to O - and O 2 - ions enabling determination of their g-values with higher precision, as well as observation of hyperfine sextets due to Mn 2+ and Mn 4+ ions in anatase.

Effect of hot-dip galvanizing processes on the microstructure and mechanical properties of 600-MPa hot-dip galvanized dual-phase steel

NASA Astrophysics Data System (ADS)

Kuang, Chun-fu; Zheng, Zhi-wang; Wang, Min-li; Xu, Quan; Zhang, Shen-gen

2017-12-01

A C-Mn dual-phase steel was soaked at 800°C for 90 s and then either rapidly cooled to 450°C and held for 30 s (process A) or rapidly cooled to 350°C and then reheated to 450°C (process B) to simulate the hot-dip galvanizing process. The influence of the hot-dip galvanizing process on the microstructure and mechanical properties of 600-MPa hot-dip galvanized dual-phase steel (DP600) was investigated using optical microscopy, scanning electron microscopy (SEM), transmission electron microscopy (TEM), and tensile tests. The results showed that, in the case of process A, the microstructure of DP600 was composed of ferrite, martensite, and a small amount of bainite. The granular bainite was formed in the hot-dip galvanizing stage, and martensite islands were formed in the final cooling stage after hot-dip galvanizing. By contrast, in the case of process B, the microstructure of the DP600 was composed of ferrite, martensite, bainite, and cementite. In addition, compared with the yield strength (YS) of the DP600 annealed by process A, that for the DP600 annealed by process B increased by approximately 50 MPa because of the tempering of the martensite formed during rapid cooling. The work-hardening coefficient ( n value) of the DP600 steel annealed by process B clearly decreased because the increase of the YS affected the computation result for the n value. However, the ultimate tensile strength (UTS) and elongation ( A 80) of the DP600 annealed by process B exhibited less variation compared with those of the DP600 annealed by process A. Therefore, DP600 with excellent comprehensive mechanical properties (YS = 362 MPa, UTS = 638 MPa, A 80 = 24.3%, n = 0.17) was obtained via process A.

Influence of Gas Atmosphere Dew Point on the Galvannealing of CMnSi TRIP Steel

NASA Astrophysics Data System (ADS)

Cho, Lawrence; Kim, Myung Soo; Kim, Young Ha; De Cooman, Bruno C.

2013-11-01

The Fe-Zn reaction occurring during the galvannealing of a Si-bearing transformation-induced plasticity (TRIP) steel was investigated by field-emission electron probe microanalysis and field-emission transmission electron microscopy. The galvannealing was simulated after hot dipping in a Zn bath containing 0.13 mass pct Al at 733 K (460 °C). The galvannealing temperature was in the range of 813 K to 843 K (540 °C to 570 °C). The kinetics and mechanism of the galvannealing reaction were strongly influenced by the gas atmosphere dew point (DP). After the galvannealing of a panel annealed in a N2+10 pct H2 gas atmosphere with low DPs [213 K and 243 K (-60 °C and -30 °C)], the coating layer consisted of δ (FeZn10) and η (Zn) phase crystals. The Mn-Si compound oxides formed during intercritical annealing were present mostly at the steel/coating interface after the galvannealing. Galvannealing of a panel annealed in higher DP [263 K and 273 K, and 278 K (-10 °C, 0 °C, and +5 °C)] gas atmospheres resulted in a coating layer consisting of δ and Г (Fe3Zn10) phase crystals, and a thin layer of Г 1 (Fe11Zn40) phase crystals at the steel/coating interface. The Mn-Si oxides were distributed homogeneously throughout the galvannealed (GA) coating layer. When the surface oxide layer thickness on panels annealed in a high DP gas atmosphere was reduced, the Fe content at the GA coating surface increased. Annealing in a higher DP gas atmosphere improved the coating quality of the GA panels because a thinner layer of oxides was formed. A high DP atmosphere can therefore significantly contribute to the suppression of Zn-alloy coating defects on CMnSi TRIP steel processed in hot dip galvanizing lines.

Coercivity and nanostructure of melt-spun Ti-Fe-Co-B-based alloys

DOE PAGES

Zhang, W. Y.; Skomski, R.; Kashyap, A.; ...

2016-02-18

Nanocrystalline Ti-Fe-Co-B-based alloys, prepared by melt spinning and subsequent annealing, have been characterized structurally and magnetically. X-ray diffraction and thermomagnetic measurements show that the ribbons consist of tetragonal Ti 3(Fe,Co) 5B 2, FeCo-rich bcc, and NiAl-rich L2 1 phases; Ti 3(Fe,Co) 5B 2, is a new substitutional alloy series whose end members Ti 3Co 5B 2 and Ti 3Fe 5B 2 have never been investigated magnetically and may not even exist, respectively. Two compositions are considered, namely Ti 11+xFe 37.5-0.5xCo 37.5–0.5xB 14 (x = 0, 4) and alnico-like Ti 11Fe 26Co 26Ni 10Al 11Cu 2B 14, the latter also containingmore » an L2 1-type alloy. The volume fraction of the Ti 3(Fe,Co) 5B 2 phase increases with x, which leads to a coercivity increase from 221 Oe for x = 0 to 452 Oe for x = 4. Since the grains are nearly equiaxed, there is little or no shape anisotropy, and the coercivity is largely due to the magnetocrystallineanisotropy of the tetragonal Ti 3(Fe,Co) 5B 2 phase. The alloy containing Ni,Al, and Cu exhibits a magnetization of 10.6 kG and a remanence ratio of 0.59. Lastly, our results indicate that magnetocrystallineanisotropy can be introduced in alnico-like magnets, adding to shape anisotropy that may be induced by field annealing.« less

Self-assembly of tin wires via phase transformation of heteroepitaxial germanium-tin on germanium substrate

DOE Office of Scientific and Technical Information (OSTI.GOV)

Wang, Wei; Li, Lingzi; Yeo, Yee-Chia, E-mail: yeo@ieee.org

This work demonstrates and describes for the first time an unusual strain-relaxation mechanism by the formation and self-assembly of well-ordered tin wires during the thermal annealing of epitaxial Ge{sub 0.83}Sn{sub 0.17}-on-Ge(001) substrate. Fully strained germanium-tin alloys (Ge{sub 0.83}Sn{sub 0.17}) were epitaxially grown on Ge(001) substrate by molecular beam epitaxy. The morphological and compositional evolution of Ge{sub 0.83}Sn{sub 0.17} during thermal annealing is studied by atomic force microscopy, X-ray diffraction, transmission electron microscopy. Under certain annealing conditions, the Ge{sub 0.83}Sn{sub 0.17} layer decomposes into two stable phases, and well-defined Sn wires that are preferentially oriented along two orthogonal 〈100〉 azimuths aremore » formed. The formation of the Sn wires is related to the annealing temperature and the Ge{sub 0.83}Sn{sub 0.17} thickness, and can be explained by the nucleation of a grain with Sn islands on the outer front, followed by grain boundary migration. The Sn wire formation process is found to be thermally activated, and an activation enthalpy (E{sub c}) of 0.41 eV is extracted. This thermally activated phase transformation, i.e., 2D epitaxial layer to 3D wires, occurs via a mechanism akin to “cellular precipitation.” This synthesis route of Sn wires opens new possibilities for creation of nanoscale patterns at high-throughput without the need for lithography.« less

The effects of phase transformation on the structure and mechanical properties of TiSiCN nanocomposite coatings deposited by PECVD method

NASA Astrophysics Data System (ADS)

Abedi, Mohammad; Abdollah-zadeh, Amir; Bestetti, Massimiliano; Vicenzo, Antonello; Serafini, Andrea; Movassagh-Alanagh, Farid

2018-06-01

In the present study, the effects of phase transformations on the structure and mechanical properties of TiSiCN coatings were investigated. TiSiCN nanocomposite coatings were deposited on AISI H13 hot-work tool steel by a pulsed direct current plasma-enhanced chemical vapor deposition process at 350 or 500 °C, using TiCl4 and SiCl4 as the precursors of Ti and Si, respectively, in a CH4/N2/H2/Ar plasma as the source of carbon and nitrogen and reducing environment. Some samples deposited at 350 °C were subsequently annealed at 500 °C under Ar atmosphere. Super hard self-lubricant TiSiCN coatings, having nanocomposite structure consisting of TiCN nanocrystals and amorphous carbon particles embedded in an amorphous SiCNx matrix, formed through spinodal decomposition in the specimens deposited or annealed at 500 °C. In addition, it was revealed that either uncomplete or relatively coarse phase segregation of titanium compounds was achieved during deposition at 350 °C and 500 °C, respectively. On the contrary, by deposition at 350 °C followed by annealing at 500 °C, a finer structure was obtained with a sensible improvement of the mechanical properties of coatings. Accordingly, the main finding of this work is that significant enhancement in key properties of TiSiCN coatings, such as hardness, adhesion and friction coefficient, can be obtained by deposition at low temperature and subsequent annealing at higher temperature, thanks to the formation of a fine grained nanocomposite structure.

Sparse approximation problem: how rapid simulated annealing succeeds and fails

NASA Astrophysics Data System (ADS)

Obuchi, Tomoyuki; Kabashima, Yoshiyuki

2016-03-01

Information processing techniques based on sparseness have been actively studied in several disciplines. Among them, a mathematical framework to approximately express a given dataset by a combination of a small number of basis vectors of an overcomplete basis is termed the sparse approximation. In this paper, we apply simulated annealing, a metaheuristic algorithm for general optimization problems, to sparse approximation in the situation where the given data have a planted sparse representation and noise is present. The result in the noiseless case shows that our simulated annealing works well in a reasonable parameter region: the planted solution is found fairly rapidly. This is true even in the case where a common relaxation of the sparse approximation problem, the G-relaxation, is ineffective. On the other hand, when the dimensionality of the data is close to the number of non-zero components, another metastable state emerges, and our algorithm fails to find the planted solution. This phenomenon is associated with a first-order phase transition. In the case of very strong noise, it is no longer meaningful to search for the planted solution. In this situation, our algorithm determines a solution with close-to-minimum distortion fairly quickly.

Kinetics modeling of precipitation with characteristic shape during post-implantation annealing

DOE Office of Scientific and Technical Information (OSTI.GOV)

Li, Kun-Dar, E-mail: kundar@mail.nutn.edu.tw; Chen, Kwanyu

2015-11-15

In this study, we investigated the precipitation with characteristic shape in the microstructure during post-implantation annealing via a theoretical modeling approach. The processes of precipitates formation and evolution during phase separation were based on a nucleation and growth mechanism of atomic diffusion. Different stages of the precipitation, including the nucleation, growth and coalescence, were distinctly revealed in the numerical simulations. In addition, the influences of ion dose, temperature and crystallographic symmetry on the processes of faceted precipitation were also demonstrated. To comprehend the kinetic mechanism, the simulation results were further analyzed quantitatively by the Kolmogorov-Johnson-Mehl-Avrami (KJMA) equation. The Avrami exponentsmore » obtained from the regression curves varied from 1.47 to 0.52 for different conditions. With the increase of ion dose and temperature, the nucleation and growth of precipitations were expedited in accordance with the shortened incubation time and the raised coefficient of growth rate. A miscellaneous shape of precipitates in various crystallographic symmetry systems could be simulated through this anisotropic model. From the analyses of the kinetics, more fundamental information about the nucleation and growth mechanism of faceted precipitation during post-implantation annealing was acquired for future application.« less

Role of Crystallization in the Morphology of Polymer: Non-fullerene Acceptor Bulk Heterojunctions

DOE PAGES

O’Hara, Kathryn A.; Ostrowski, David P.; Koldemir, Unsal; ...

2017-05-22

Many high efficiency organic photovoltaics use fullerene-based acceptors despite their high production cost, weak optical absorption in the visible range, and limited synthetic variability of electronic and optical properties. To circumvent this deficiency, non-fullerene small-molecule acceptors have been developed that have good synthetic flexibility, allowing for precise tuning of optoelectronic properties, leading to enhanced absorption of the solar spectrum and increased open-circuit voltages ( V OC). We examined the detailed morphology of bulk heterojunctions of poly(3-hexylthiophene) and the small-molecule acceptor HPI-BT to reveal structural changes that lead to improvements in the fill factor of solar cells upon thermal annealing. Themore » kinetics of the phase transformation process of HPI-BT during thermal annealing were investigated through in situ grazing incidence wide-angle X-ray scattering studies, atomic force microscopy, and transmission electron microscopy. The HPI-BT acceptor crystallizes during film formation to form micron-sized domains embedded within the film center and a donor rich capping layer at the cathode interface reducing efficient charge extraction. Thermal annealing changes the surface composition and improves charge extraction. In conclusion, this study reveals the need for complementary methods to investigate the morphology of BHJs.« less

Role of Crystallization in the Morphology of Polymer: Non-fullerene Acceptor Bulk Heterojunctions

DOE Office of Scientific and Technical Information (OSTI.GOV)

O’Hara, Kathryn A.; Ostrowski, David P.; Koldemir, Unsal

Many high efficiency organic photovoltaics use fullerene-based acceptors despite their high production cost, weak optical absorption in the visible range, and limited synthetic variability of electronic and optical properties. To circumvent this deficiency, non-fullerene small-molecule acceptors have been developed that have good synthetic flexibility, allowing for precise tuning of optoelectronic properties, leading to enhanced absorption of the solar spectrum and increased open-circuit voltages ( V OC). We examined the detailed morphology of bulk heterojunctions of poly(3-hexylthiophene) and the small-molecule acceptor HPI-BT to reveal structural changes that lead to improvements in the fill factor of solar cells upon thermal annealing. Themore » kinetics of the phase transformation process of HPI-BT during thermal annealing were investigated through in situ grazing incidence wide-angle X-ray scattering studies, atomic force microscopy, and transmission electron microscopy. The HPI-BT acceptor crystallizes during film formation to form micron-sized domains embedded within the film center and a donor rich capping layer at the cathode interface reducing efficient charge extraction. Thermal annealing changes the surface composition and improves charge extraction. In conclusion, this study reveals the need for complementary methods to investigate the morphology of BHJs.« less

Effects of thermal treatment on the Mg{sub x}Zn{sub 1−x}O films and fabrication of visible-blind and solar-blind ultraviolet photodetectors

DOE Office of Scientific and Technical Information (OSTI.GOV)

Tian, Chunguang; Jiang, Dayong, E-mail: dayongjiangcust@126.com; Tan, Zhendong

Highlights: • Single-phase wurtzite/cubic Mg{sub x}Zn{sub 1−x}O films were grown by RF magnetron sputtering technique. • We focus on the red-shift caused by annealing the Mg{sub x}Zn{sub 1−x}O films. • MSM-structured visible-blind and solar-blind UV photodetectors were fabricated. - Abstract: A series of single-phase Mg{sub x}Zn{sub 1−x}O films with different Mg contents were prepared on quartz substrates by RF magnetron sputtering technique using different MgZnO targets, and annealed under the atmospheric environment. The absorption edges of Mg{sub x}Zn{sub 1−x}O films can cover the whole near ultraviolet and even the whole solar-blind spectra range, and the solar-blind wurtzite/cubic Mg{sub x}Zn{sub 1−x}Omore » films have been realized successfully by the same method. In addition, the absorption edges of annealed films shift to a long wavelength, which is caused by the diffusion of Zn atoms gathering at the surface during the thermal treatment process. Finally, the truly solar-blind metal-semiconductor-metal structured photodetectors based on wurtzite Mg{sub 0.445}Zn{sub 0.555}O and cubic Mg{sub 0.728}Zn{sub 0.272}O films were fabricated. The corresponding peak responsivities are 17 mA/W at 275 nm and 0.53 mA/W at 250 nm under a 120 V bias, respectively.« less

Carbon-based nanomaterial synthesis using nanosecond electrical discharges in immiscible layered liquids: n-heptane and water

NASA Astrophysics Data System (ADS)

Hamdan, Ahmad; Cha, Min Suk

2018-06-01

Plasmas in- or in-contact with liquids have been extensively investigated due to their high potential for a wide range of applications including, but not limited to, water treatment, material synthesis and functionalization, bio-medical applications, and liquid fuel reformation. Recently, we successfully developed a discharge using two immiscible liquids, having very different electrical permittivities, which could significantly intensify the electric field intensity. Here, we establish nanosecond discharges at the interface n-heptane-water (with respective relative dielectric permittivities of 2 and 80) to enable the synthesis of carbon-based nanomaterials. A characterization of the as-synthesized material and the annealed (500 °C) material, using various techniques (Fourier-transform, infra-red, scanning and transmission electron microscopes, etc), shows that the as-synthesized material is a mixture of two carbon-based phases: a crystalline phase (graphite like) embedded into a phase of hydrogenated amorphous carbon. The existence of two-phases may be explained by the non-homogeneity of the discharge that induces various chemical reactions in the plasma channel.

The investigations of characteristics of Sb2Te as a base phase-change material

NASA Astrophysics Data System (ADS)

Liu, Guangyu; Wu, Liangcai; Zhu, Min; Song, Zhitang; Rao, Feng; Song, Sannian; Cheng, Yan

2017-09-01

Chalcogenide alloys are paid much attention in the study of nonvolatile phase-change memory (PCM). A comprehensive research is investigated on Sb2Te (ST), a base material, from properties to performances in this paper. For the characteristics of ST films, the sheet resistance is extremely stable during cooling process in resistance-temperature measurement and the thickness change of ST film is 5.7%. However, low 10-year data retention temperature (∼55 °C) and large crystal grain are the demerits for ST. In addition, the structure characteristics show stable hexagonal phase and large grain of several hundred nanometers at crystalline state after annealing. As for electrical properties, although the ST-based PCM devices are characterized by fast operation speed of ∼20 ns, only about 8 × 103 times of stable operation cycles can be obtained. After that, the endurance performance deteriorates gradually due to the growth of grains. About resistance drift, the drift coefficients are very small both in crystalline state and in amorphous state.

Probing the A1 to L1{sub 0} transformation in FeCuPt using the first order reversal curve method

DOE Office of Scientific and Technical Information (OSTI.GOV)

Gilbert, Dustin A.; Liu, Kai; Liao, Jung-Wei

2014-08-01

The A1-L1{sub 0} phase transformation has been investigated in (001) FeCuPt thin films prepared by atomic-scale multilayer sputtering and rapid thermal annealing (RTA). Traditional x-ray diffraction is not always applicable in generating a true order parameter, due to non-ideal crystallinity of the A1 phase. Using the first-order reversal curve (FORC) method, the A1 and L1{sub 0} phases are deconvoluted into two distinct features in the FORC distribution, whose relative intensities change with the RTA temperature. The L1{sub 0} ordering takes place via a nucleation-and-growth mode. A magnetization-based phase fraction is extracted, providing a quantitative measure of the L1{sub 0} phasemore » homogeneity.« less

Effect of grain-boundary crystallization on the high-temperature strength of silicon nitride

NASA Technical Reports Server (NTRS)

Pierce, L. A.; Mieskowski, D. M.; Sanders, W. A.

1986-01-01

Si3N4 specimens having the composition 88.7 wt pct Si3N4-4.9 wt pct SiO2-6.4 wt pct Y2O3 were sintered at 2140 C under 25 atm N2 for 1 h and then subjected to a 5 h anneal at 1500 C. Crystallization of an amorphous grain-boundary phase resulted in the formation of Y2Si2O7. The short-time 1370 C strength of this material was compared with that of material of the same composition having no annealing treatment. No change in strength was noted. This is attributed to the refractory nature of the yttrium-rich grain-boundary phase (apparently identical in both glassy and crystalline phases) and the subsequent domination of the failure process by common processing flaws.

Interfacial engineering of solution-processed Ni nanochain-SiO{sub x} (x < 2) cermets towards thermodynamically stable, anti-oxidation solar selective absorbers

DOE Office of Scientific and Technical Information (OSTI.GOV)

Yu, Xiaobai; Wang, Xiaoxin; Liu, Jifeng, E-mail: Jifeng.Liu@dartmouth.edu

Cermet solar thermal selective absorber coatings are an important component of high-efficiency concentrated solar power (CSP) receivers. The oxidation of the metal nanoparticles in cermet solar absorbers is a great challenge for vacuum-free operation. Recently, we have demonstrated that oxidation is kinetically retarded in solution processed, high-optical-performance Ni nanochain-SiO{sub x} cermet system compared to conventional Ni-Al{sub 2}O{sub 3} system when annealed in air at 450–600 °C for several hours. However, for long-term, high-temperature applications in CSP systems, thermodynamically stable antioxidation behavior is highly desirable, which requires new mechanisms beyond kinetically reducing the oxidation rate. Towards this goal, in this paper, wemore » demonstrate that pre-operation annealing of Ni nanochain-SiO{sub x} cermets at 900 °C in N{sub 2} forms the thermodynamically stable orthorhombic phase of NiSi at the Ni/SiO{sub x} interfaces, leading to self-terminated oxidation at 550 °C in air due to this interfacial engineering. In contrast, pre-operation annealing at a lower temperature of 750 °C in N{sub 2} (as conducted in our previous work) cannot achieve interfacial NiSi formation directly, and further annealing in air at 450–600 °C for >4 h only leads to the formation of the less stable (metastable) hexagonal phase of NiSi. Therefore, the high-temperature pre-operation annealing is critical to form the desirable orthorhombic phase of NiSi at Ni/SiO{sub x} interfaces towards thermodynamically stable antioxidation behavior. Remarkably, with this improved interfacial engineering, the oxidation of 80-nm-diameter Ni nanochain-SiO{sub x} saturates after annealing at 550 °C in air for 12 h. Additional annealing at 550 °C in air for as long as 20 h (i.e., 32 h air annealing at >550 °C in total) has almost no further impact on the structural or optical properties of the coatings, the latter being very sensitive to any interfacial changes due to the localized surface plasmon resonances of the metal nanostructures. This phenomenon holds true for Ni nanoparticle diameter down to 40 nm in Ni-SiO{sub x} system, where the optical response remains stable for 53 h at 550 °C in air. The oxidation vs. time curve also shows saturation behavior deviating from the kinetic Deal-Grove oxidation model. These results strongly suggest a promising approach to thermodynamically stable, anti-oxidation Ni/SiO{sub x} cermet absorbers via interfacial engineering.« less

Si-Sb-Te materials for phase change memory applications.

PubMed

Rao, Feng; Song, Zhitang; Ren, Kun; Zhou, Xilin; Cheng, Yan; Wu, Liangcai; Liu, Bo

2011-04-08

Si-Sb-Te materials including Te-rich Si₂Sb₂Te₆ and Si(x)Sb₂Te₃ with different Si contents have been systemically studied with the aim of finding the most suitable Si-Sb-Te composition for phase change random access memory (PCRAM) use. Si(x)Sb₂Te₃ shows better thermal stability than Ge₂Sb₂Te₅ or Si₂Sb₂Te₆ in that Si(x)Sb₂Te₃ does not have serious Te separation under high annealing temperature. As Si content increases, the data retention ability of Si(x)Sb₂Te₃ improves. The 10 years retention temperature for Si₃Sb₂Te₃ film is ~393 K, which meets the long-term data storage requirements of automotive electronics. In addition, Si richer Si(x)Sb₂Te₃ films also show improvement on thickness change upon annealing and adhesion on SiO₂ substrate compared to those of Ge₂Sb₂Te₅ or Si₂Sb₂Te₆ films. However, the electrical performance of PCRAM cells based on Si(x)Sb₂Te₃ films with x > 3.5 becomes worse in terms of stable and long-term operations. Si(x)Sb₂Te₃ materials with 3 < x < 3.5 are proved to be suitable for PCRAM use to ensure good overall performance.

Liquid phase epitaxy of binary III–V nanocrystals in thin Si layers triggered by ion implantation and flash lamp annealing

DOE Office of Scientific and Technical Information (OSTI.GOV)

Wutzler, Rene, E-mail: r.wutzler@hzdr.de; Rebohle, Lars; Prucnal, Slawomir

2015-05-07

The integration of III–V compound semiconductors in Si is a crucial step towards faster and smaller devices in future technologies. In this work, we investigate the formation process of III–V compound semiconductor nanocrystals, namely, GaAs, GaSb, and InP, by ion implantation and sub-second flash lamp annealing in a SiO{sub 2}/Si/SiO{sub 2} layer stack on Si grown by plasma-enhanced chemical vapor deposition. Raman spectroscopy, Rutherford Backscattering spectrometry, and transmission electron microscopy were performed to identify the structural and optical properties of these structures. Raman spectra of the nanocomposites show typical phonon modes of the compound semiconductors. The formation process of themore » III–V compounds is found to be based on liquid phase epitaxy, and the model is extended to the case of an amorphous matrix without an epitaxial template from a Si substrate. It is shown that the particular segregation and diffusion coefficients of the implanted group-III and group-V ions in molten Si significantly determine the final appearance of the nanostructure and thus their suitability for potential applications.« less

Quantum simulation of transverse Ising models with Rydberg atoms

NASA Astrophysics Data System (ADS)

Schauss, Peter

2018-04-01

Quantum Ising models are canonical models for the study of quantum phase transitions (Sachdev 1999 Quantum Phase Transitions (Cambridge: Cambridge University Press)) and are the underlying concept for many analogue quantum computing and quantum annealing ideas (Tanaka et al Quantum Spin Glasses, Annealing and Computation (Cambridge: Cambridge University Press)). Here we focus on the implementation of finite-range interacting Ising spin models, which are barely tractable numerically. Recent experiments with cold atoms have reached the interaction-dominated regime in quantum Ising magnets via optical coupling of trapped neutral atoms to Rydberg states. This approach allows for the tunability of all relevant terms in an Ising spin Hamiltonian with 1/{r}6 interactions in transverse and longitudinal fields. This review summarizes the recent progress of these implementations in Rydberg lattices with site-resolved detection. Strong correlations in quantum Ising models have been observed in several experiments, starting from a single excitation in the superatom regime up to the point of crystallization. The rapid progress in this field makes spin systems based on Rydberg atoms a promising platform for quantum simulation because of the unmatched flexibility and strength of interactions combined with high control and good isolation from the environment.

A Study on Characterization of Light-Induced Electroless Plated Ni Seed Layer and Silicide Formation for Solar Cell Application

NASA Astrophysics Data System (ADS)

Takaloo, Ashkan Vakilipour; Joo, Seung Ki; Es, Firat; Turan, Rasit; Lee, Doo Won

2018-03-01

Light-induced electroless plating (LIEP) is an easy and inexpensive method that has been widely used for seed layer deposition of Nickel/Copper (Ni/Cu)-based metallization in the solar cell. In this study, material characterization aspects of the Ni seed layer and Ni silicide formation at different bath conditions and annealing temperatures on the n-side of a silicon diode structure have been examined to achieve the optimum cell contacts. The effects of morphology and chemical composition of Ni film on its electrical conductivity were evaluated and described by a quantum mechanical model. It has been found that correlation exists between the theoretical and experimental conductivity of Ni film. Residual stress and phase transformation of Ni silicide as a function of annealing temperature were evaluated using Raman and XRD techniques. Finally, transmission line measurement (TLM) technique was employed to determine the contact resistance of Ni/Si stack after thermal treatment and to understand its correlation with the chemical-structural properties. Results indicated that low electrical resistive mono-silicide (NiSi) phase as low as 5 mΩ.cm2 was obtained.

Controlling the Photocorrosion of Zinc Sulfide Nanoparticles in Water by Doping with Chloride and Cobalt Ions.

PubMed

Weide, Philipp; Schulz, Katharina; Kaluza, Stefan; Rohe, Markus; Beranek, Radim; Muhler, Martin

2016-12-06

Photodegradation under UV light irradiation is a major drawback in photocatalytic applications of sulfide semiconductors. ZnS nanoparticles were doped with very low amounts of chloride or cobalt ions in the ppm range and codoped with chloride and cobalt ions during their synthesis by precipitation in aqueous solution followed by calcination. The high-temperature wurtzite phase annealed at 800 °C had a high susceptibility to UV irradiation in water, while the low-temperature zincblende phase annealed at 400 °C was found to be stable. Chlorine doping increased the rate of photocorrosion in water, whereas cobalt doping led to a stabilization of the ZnS nanoparticles. Based on photochemical and spectroscopic investigations applying UV/vis, X-ray photoelectron, and photoluminescence spectroscopy, the increased susceptibility of Cl-doped ZnS is ascribed to a higher number of surface point defects, whereas the stabilization by Co 2+ is caused by additional recombination pathways for the charge carriers in the bulk, thus avoiding photocorrosion processes at the surface. Additional doping of Cl-doped ZnS with cobalt ions was found to counteract the detrimental effect of the chloride ions efficiently.

NATpipe: an integrative pipeline for systematical discovery of natural antisense transcripts (NATs) and phase-distributed nat-siRNAs from de novo assembled transcriptomes

PubMed Central

Yu, Dongliang; Meng, Yijun; Zuo, Ziwei; Xue, Jie; Wang, Huizhong

2016-01-01

Nat-siRNAs (small interfering RNAs originated from natural antisense transcripts) are a class of functional small RNA (sRNA) species discovered in both plants and animals. These siRNAs are highly enriched within the annealed regions of the NAT (natural antisense transcript) pairs. To date, great research efforts have been taken for systematical identification of the NATs in various organisms. However, developing a freely available and easy-to-use program for NAT prediction is strongly demanded by researchers. Here, we proposed an integrative pipeline named NATpipe for systematical discovery of NATs from de novo assembled transcriptomes. By utilizing sRNA sequencing data, the pipeline also allowed users to search for phase-distributed nat-siRNAs within the perfectly annealed regions of the NAT pairs. Additionally, more reliable nat-siRNA loci could be identified based on degradome sequencing data. A case study on the non-model plant Dendrobium officinale was performed to illustrate the utility of NATpipe. Finally, we hope that NATpipe would be a useful tool for NAT prediction, nat-siRNA discovery, and related functional studies. NATpipe is available at www.bioinfolab.cn/NATpipe/NATpipe.zip. PMID:26858106