Demonstration and Analysis of Materials Processing by Ablation Plasma Ion Implantation (APII)

NASA Astrophysics Data System (ADS)

Qi, B.; Gilgenbach, R. M.; Lau, Y. Y.; Jones, M. C.; Lian, J.; Wang, L. M.; Doll, G. L.; Lazarides, A.

2001-10-01

Experiments have demonstrated laser-ablated Fe ion implantation into Si substrates. Baseline laser deposited films (0 kV) showed an amorphous Fe-Si film overlying the Si substrate with a top layer of nanocrystalline Fe. APII films exhibited an additional Fe ion-induced damage layer, extending 7.6 nm below the Si surface. The overlying Fe-Si layer and Fe top layer were amorphized by fast ions. Results were confirmed by XPS vs Ar ion etching time for depth profile of the deposited films. XPS showed primarily Fe (top layer), transitioning to roughly equal Fe/Si , then mostly Si with lower Fe (implanted region). These data clearly prove Fe ion implantation into Si, verifying the feasibility of APII as an ion acceleration and implantation process [1]. SRIM simulations predict about 20 percent deeper Fe ion penetration than data, due to:(a) Subsequent ions must pass through the Fe film deposited by earlier ions, and (b) the bias voltage has a slow rise and fall time. Theoretical research has developed the scaling laws for APII [2]. Recently, a model has successfully explained the shortening of the decay time in the high voltage pulse with the laser ablation plasma. This reduces the theoretical RC time constant, which agrees with the experimental data. * Research supported by National Science Foundation Grant CTS-9907106 [1] Appl. Phys. Lett. 78, 3785 (2001) [2] Appl. Phys. Lett. 78, 706 (2001)),

Mn-doped Ge self-assembled quantum dots via dewetting of thin films

NASA Astrophysics Data System (ADS)

Aouassa, Mansour; Jadli, Imen; Bandyopadhyay, Anup; Kim, Sung Kyu; Karaman, Ibrahim; Lee, Jeong Yong

2017-03-01

In this study, we demonstrate an original elaboration route for producing a Mn-doped Ge self-assembled quantum dots on SiO2 thin layer for MOS structure. These magnetic quantum dots are elaborated using dewetting phenomenon at solid state by Ultra-High Vacuum (UHV) annealing at high temperature of an amorphous Ge:Mn (Mn: 40%) nanolayer deposed at very low temperature by high-precision Solid Source Molecular Beam Epitaxy on SiO2 thin film. The size of quantum dots is controlled with nanometer scale precision by varying the nominal thickness of amorphous film initially deposed. The magnetic properties of the quantum-dots layer have been investigated by superconducting quantum interference device (SQUID) magnetometry. Atomic force microscopy (AFM), x-ray energy dispersive spectroscopy (XEDS) and transmission electron microscopy (TEM) were used to examine the nanostructure of these materials. Obtained results indicate that GeMn QDs are crystalline, monodisperse and exhibit a ferromagnetic behavior with a Curie temperature (TC) above room temperature. They could be integrated into spintronic technology.

Fabrication and ferromagnetism of Si-SiGe/MnGe core-shell nanopillars.

PubMed

Wang, Liming; Liu, Tao; Wang, Shuguang; Zhong, Zhenyang; Jia, Quanjie; Jiang, Zuimin

2016-10-07

Si-Si0.5Ge0.5/Mn0.08Ge0.92 core-shell nanopillar samples were fabricated on ordered Si nanopillar patterned substrates by molecular beam epitaxy at low temperatures. The magnetic properties of the samples are found to depend heavily on the growth temperature of the MnGe layer. The sample grown at a moderate temperature of 300 °C has the highest Curie temperature of 240 K as well as the strongest ferromagnetic signals. On the basis of the microstructural results, the ferromagnetic properties of the samples are believed to come from the intrinsic Mn-doped amorphous or crystalline Ge ferromagnetic phase rather than any intermetallic ferromagnetic compounds of Mn and Ge. After being annealed at a temperature of 500 °C, all the samples exhibit the same Curie temperature of 220 K, which is in sharp contrast to the different Curie temperature for the as-grown samples, and the ferromagnetism for the annealed samples comes from Mn5GeSi2 compounds which are formed during the annealing.

Phase transformations in ion-irradiated silicides

NASA Technical Reports Server (NTRS)

Hewett, C. A.; Lau, S. S.; Suni, I.; Hung, L. S.

1985-01-01

The present investigation has three objectives. The first is concerned with the phase transformation of CoSi2 under ion implantation and the subsequent crystallization characteristics during annealing, taking into account epitaxial and nonepitaxial recrystallization behavior. The second objective is related to a study of the general trend of implantation-induced damage and crystallization behavior for a number of commonly used silicides. The last objective involves a comparison of the recrystallization behavior of cosputtered refractory silicides with that of the ion-implanted silicides. It was found that epitaxial regrowth of ion-irradiated CoSi2 occurred for samples with an epitaxial seed left at the Si/CoSi2 interface. A structural investigation of CoSi2 involving transmission electron microscopy (TEM) showed that after high-dose implantation CoSi2 is amorphous.

Nanoindentation of silicon implanted with hydrogen: effect of implantation dose on silicon’s mechanical properties and nanoindentation-induced phase transformation

NASA Astrophysics Data System (ADS)

Jelenković, Emil V.; To, Suet; Goncharova, Lyudmila V.; Wong, Sing Fai

2017-07-01

Implantation of hydrogen in single-crystal silicon (c-Si) is known to affect its machining. However, very little is reported on the material and mechanical properties of hydrogen-implanted silicon (Si). In this article, near-surface regions (~0-500 nm) of lightly doped (1 0 0) Si were modified by varying the hydrogen concentration using ion implantation. The maximum hydrogen concentration was varied from ~4  ×  1020 to ~3.2  ×  1021 cm-3. The implanted Si was investigated by nanoindentation. From the dynamic nanoindentation test, it was found that in hydrogen-implanted Si hardness is increased significantly, while the elastic modulus is reduced. The nanoindentation-induced Si phase transformation was studied under different load/unload rates and loads. Raman spectroscopy revealed that the hydrogen implantation tends to suppress Si-XII and Si-III phases and facilitates amorphous Si formation during the unloading stage of nanoindentation. Both the mechanical properties and phase transformations were qualitatively related not only to the hydrogen concentration, but also to the implantation-generated defects and strain.

Effect of magnetic field annealing on soft magnetic properties of Co71Fe2Si14-xB9+xMn4 amorphous alloys with low permeability

NASA Astrophysics Data System (ADS)

Fan, Xingdu; Li, Meng; Zhang, Tao; Yuan, Chenchen; Shen, Baolong

2018-05-01

The effect of transverse magnetic field annealing (TFA) on soft magnetic properties of Co71Fe2Si14-xB9+xMn4 amorphous alloys was investigated with the aim of reducing effective permeability (μe). It was revealed that the increasing B content improved thermal stability, increased saturation magnetic flux density (Bs) of as-quenched alloys, while the samples exhibited a slightly larger coercivity (Hc) when the atom percentages of Si and B were similar. Permeability decreased dramatically after TFA. The decrease of permeability mainly depended on annealing temperature and magnetic field intensity. Besides, flat hysteresis loops were obtained after TFA, Lorentz micrograph observation revealed the TFA sample exhibited denser magnetic domain walls, which confirmed it was more difficult to be saturated. The Co71Fe2Si9B14Mn4 alloy was successful prepared with low μe of 3020, low Hc of 1.7 A/m and high resistance to DC bias 6 times that of as-quenched alloy at the DC field of 300 A/m.

Synthesis of graphene and graphene nanostructures by ion implantation and pulsed laser annealing

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

Wang, Xiaotie; Rudawski, Nicholas G.; Appleton, Bill R.

2016-07-14

In this paper, we report a systematic study that shows how the numerous processing parameters associated with ion implantation (II) and pulsed laser annealing (PLA) can be manipulated to control the quantity and quality of graphene (G), few-layer graphene (FLG), and other carbon nanostructures selectively synthesized in crystalline SiC (c-SiC). Controlled implantations of Si{sup −} plus C{sup −} and Au{sup +} ions in c-SiC showed that both the thickness of the amorphous layer formed by ion damage and the doping effect of the implanted Au enhance the formation of G and FLG during PLA. The relative contributions of the amorphousmore » and doping effects were studied separately, and thermal simulation calculations were used to estimate surface temperatures and to help understand the phase changes occurring during PLA. In addition to the amorphous layer thickness and catalytic doping effects, other enhancement effects were found to depend on other ion species, the annealing environment, PLA fluence and number of pulses, and even laser frequency. Optimum II and PLA conditions are identified and possible mechanisms for selective synthesis of G, FLG, and carbon nanostructures are discussed.« less

Lattice sites of ion-implanted Mn, Fe and Ni in 6H-SiC

NASA Astrophysics Data System (ADS)

Costa, A. R. G.; Wahl, U.; Correia, J. G.; David-Bosne, E.; Amorim, L. M.; Augustyns, V.; Silva, D. J.; da Silva, M. R.; Pereira, L. M. C.

2018-01-01

Using radioactive isotopes produced at the CERN-ISOLDE facility, the lattice location of the implanted transition metal (TM) ions 56Mn, 59Fe and 65Ni in n-type single-crystalline hexagonal 6H-SiC was studied by means of the emission channeling technique. TM probes on carbon coordinated tetrahedral interstitial sites (T C) and on substitutional silicon sites (S Si,h+k ) were identified. We tested for but found no indication that the TM distribution on S Si sites deviates from the statistical mixture of 1/3 hexagonal and 2/3 cubic sites present in the 6H crystal. The TM atoms partially disappear from T C positions during annealing at temperatures between 500 °C and 700 °C which is accompanied by an increase on S Si and random sites. From the temperature associated with these site changes, interstitial migration energies of 1.7-2.7 eV for Mn and Ni, and 2.3-3.2 eV for Fe were estimated. TM lattice locations are compared to previous results obtained in 3C-SiC using the same technique.

Reflectivity modification of polymethylmethacrylate by silicon ion implantation

NASA Astrophysics Data System (ADS)

Hadjichristov, Georgi B.; Ivanov, Victor; Faulques, Eric

2008-05-01

The effect of silicon ion implantation on the optical reflection of bulk polymethylmethacrylate (PMMA) was examined in the visible and near UV. A low-energy (30 and 50 keV) Si + beam at fluences in the range from 10 13 to 10 17 cm -2 was used for ion implantation of PMMA. The results show that a significant enhancement of the reflectivity from Si +-implanted PMMA occurs at appropriate implantation energy and fluence. The structural modifications of PMMA by the silicon ion implantation were characterized by means of photoluminescence and Raman spectroscopy. Formation of hydrogenated amorphous carbon (HAC) layer beneath the surface of the samples was established and the corresponding HAC domain size was estimated.

High-dose MeV electron irradiation of Si-SiO2 structures implanted with high doses Si+

NASA Astrophysics Data System (ADS)

Kaschieva, S.; Angelov, Ch; Dmitriev, S. N.

2018-03-01

The influence was studied of 22-MeV electron irradiation on Si-SiO2 structures implanted with high-fluence Si+ ions. Our earlier works demonstrated that Si redistribution is observed in Si+-ion-implanted Si-SiO2 structures (after MeV electron irradiation) only in the case when ion implantation is carried out with a higher fluence (1016 cm-2). We focused our attention on the interaction of high-dose MeV electron irradiation (6.0×1016 cm-2) with n-Si-SiO2 structures implanted with Si+ ions (fluence 5.4×1016 cm-2 of the same order magnitude). The redistribution of both oxygen and silicon atoms in the implanted Si-SiO2 samples after MeV electron irradiation was studied by Rutherford back-scattering (RBS) spectroscopy in combination with a channeling technique (RBS/C). Our results demonstrated that the redistribution of oxygen and silicon atoms in the implanted samples reaches saturation after these high doses of MeV electron irradiation. The transformation of amorphous SiO2 surface into crystalline Si nanostructures (after MeV electron irradiation) was evidenced by atomic force microscopy (AFM). Silicon nanocrystals are formed on the SiO2 surface after MeV electron irradiation. The shape and number of the Si nanocrystals on the SiO2 surface depend on the MeV electron irradiation, while their size increases with the dose. The mean Si nanocrystals height is 16-20 nm after irradiation with MeV electrons at the dose of 6.0×1016 cm-2.

Solid-state synthesis of uniform Li2MnSiO4/C/graphene composites and their performance in lithium-ion batteries

NASA Astrophysics Data System (ADS)

Gong, Huaxu; Zhu, Yongchun; Wang, Linlin; Wei, Denghu; Liang, Jianwen; Qian, Yitai

2014-01-01

Uniform nanospherical Li2MnSiO4/C/graphene composites have been obtained by polyethylene glycol-600 (PEG-600) assisted solid-state reaction using spherical SiO2 as precursor, and heat treatment with the mixed carbon sources (glucose, cellulose acetate and graphene oxide). The transmission electron microscope (TEM) images show that Li2MnSiO4 nanospheres with size of 50 nm are embedded in the three-dimensional (3D) nest-like carbon network. Electrochemical measurements reveal that the composites exhibit first discharge capacity of 215.3 mAh g-1 under 0.05 C, together with a stable discharge capacity of 175 mAh g-1 after 40 cycles. The 3D carbon network and the carbon layer (amorphous carbon and graphene) are favorable for improving the electrochemical performance.

Implanted neural network potentials: Application to Li-Si alloys

NASA Astrophysics Data System (ADS)

Onat, Berk; Cubuk, Ekin D.; Malone, Brad D.; Kaxiras, Efthimios

2018-03-01

Modeling the behavior of materials composed of elements with different bonding and electronic structure character for large spatial and temporal scales and over a large compositional range is a challenging problem. Cases in point are amorphous alloys of Si, a prototypical covalent material, and Li, a prototypical metal, which are being considered as anodes for high-energy-density batteries. To address this challenge, we develop a methodology based on neural networks that extends the conventional training approach to incorporate pre-trained parts that capture the character of different components, into the overall network; we refer to this model as the "implanted neural network" method. We show that this approach works well for the Si-Li amorphous alloys for a wide range of compositions, giving good results for key quantities like the diffusion coefficients. The method is readily generalizable to more complicated situations that involve two or more different elements.

Perpendicularly magnetized (001)-textured D0{sub 22} MnGa films grown on an (Mg{sub 0.2}Ti{sub 0.8})O buffer with thermally oxidized Si substrates

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

Lee, Hwachol; Sukegawa, Hiroaki, E-mail: sukegawa.hiroaki@nims.go.jp; Liu, Jun

2015-10-28

We report the growth of (001)-textured polycrystalline D0{sub 22} MnGa films with perpendicular magnetic anisotropy (PMA) on thermally oxidized Si substrates using an (Mg{sub 0.2}Ti{sub 0.8})O (MTO) buffer layer. The ordered D0{sub 22} MnGa film grown at the optimum substrate temperature of 530 °C on the MTO buffer layer shows PMA with magnetization of 80 kA/m, PMA energy density of 0.28 MJ/m{sup 3}, and coercivity of 2.3 T. The scanning transmission electron microscope analysis confirms the formation of a highly (001)-textured structure and the elementally sharp interfaces between the MTO layer and the MnGa layer. The achieved D0{sub 22} MnGa PMA films on anmore » amorphous substrate will provide the possible pathway of integration of a Mn-based PMA film into Si-based substrates.« less

Ferromagnetic laser-welded Fe78Si13B9 and Co71.5Fe2.5SigMn2Mo1B14ils amorphous foils

NASA Astrophysics Data System (ADS)

Pawlak, Ryszard

1997-10-01

In the paper the results of attempts at laser welding of amorphous ferromagnetic foils on the iron and cobalt base have been presented. The usefulness of this technology for making small magnetic circuits of metallic glass has been demonstrated. The action of laser radiation leading to rendering the structure amorphous and the infraction of a laser beam with an amorphous material have been discussed. Finally, the results of pulsed welding of a pack of amorphous foils and some properties of the welds formed have been discussed.

Dynamics of Defects and Dopants in Complex Systems: Si and Oxide Surfaces and Interfaces

NASA Astrophysics Data System (ADS)

Kirichenko, Taras; Yu, Decai; Banarjee, Sanjay; Hwang, Gyeong

2004-10-01

Fabrication of forthcoming nanometer scale electronic devices faces many difficulties including formation of extremely shallow and highly doped junctions. At present, ultra-low-energy ion implantation followed by high-temperature thermal annealing is most widely used to fabricate such ultra-shallow junctions. In the process, a great challenge lies in achieving precise control of redistribution and electrical activation of dopant impurities. Native defects (such as vacancies and interstitials) generated during implantation are known to be mainly responsible for the TED and also influence significantly the electrical activation/deactivation. Defect-dopant dynamics is rather well understood in crystalline Si and SiO2. However, little is known about their diffusion and annihilation (or precipitation) at the surfaces and interfaces, despite its growing importance in determining junction profiles as device dimensions get smaller. In this talk, we will present our density functional theory calculation results on the atomic and electronic structure and dynamical behavior of native defects and dopant-defect complexes in disordered/strained Si and oxide systems, such as i) clean and absorbent-modified Si(100) surface and subsurface layers, ii) amorphous-crystalline Si interfaces and iii) amorphous SiO2/Si interfaces. The fundamental understanding and data is essential in developing a comprehensive kinetic model for junction formation, which would contribute greatly in improving current process technologies.

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.

Modification of the Near Surface Region Metastable Phases and Ion Induced Reactions

DTIC Science & Technology

1984-02-03

cell Si Dave Lilienfeld - amorphous Si layer thickness Au diffusion in metallic glasses Dave Lilienfeld & - low temperature Cu diffusion in Si Tim...Sullivan Fritz Stafford - defect characterization in implanted & annealed silicon-on-sapphire Peter Zielinski - Composition of CuZr metallic glass...ribbons 5. Prof. Johnson Dave Kuhn - measurement of Pd layer thickness Alexandra Elve - hydrogen profiles in metals Lauren Heitner - hydrogen diffusion in

Ultra-fast vapour-liquid-solid synthesis of Si nanowires using ion-beam implanted gallium as catalyst.

PubMed

Hetzel, Martin; Lugstein, Alois; Zeiner, Clemens; Wójcik, Tomasz; Pongratz, Peter; Bertagnolli, Emmerich

2011-09-30

The feasibility of gallium as a catalyst for vapour-liquid-solid (VLS) nanowire (NW) growth deriving from an implantation process in silicon by a focused ion beam (FIB) is investigated. Si(100) substrates are subjected to FIB implantation of gallium ions with various ion fluence rates. NW growth is performed in a hot wall chemical vapour deposition (CVD) reactor at temperatures between 400 and 500 °C with 2% SiH(4)/He as precursor gas. This process results in ultra-fast growth of (112)- and (110)-oriented Si-NWs with a length of several tens of micrometres. Further investigation by transmission electron microscopy indicates the presence of a NW core-shell structure: while the NW core yields crystalline structuring, the shell consists entirely of amorphous material.

Self-Diffusion in Amorphous Silicon by Local Bond Rearrangements

NASA Astrophysics Data System (ADS)

Kirschbaum, J.; Teuber, T.; Donner, A.; Radek, M.; Bougeard, D.; Böttger, R.; Hansen, J. Lundsgaard; Larsen, A. Nylandsted; Posselt, M.; Bracht, H.

2018-06-01

Experiments on self-diffusion in amorphous silicon (Si) were performed at temperatures between 460 to 600 ° C . The amorphous structure was prepared by Si ion implantation of single crystalline Si isotope multilayers epitaxially grown on a silicon-on-insulator wafer. The Si isotope profiles before and after annealing were determined by means of secondary ion mass spectrometry. Isothermal diffusion experiments reveal that structural relaxation does not cause any significant intermixing of the isotope interfaces whereas self-diffusion is significant before the structure recrystallizes. The temperature dependence of self-diffusion is described by an Arrhenius law with an activation enthalpy Q =(2.70 ±0.11 ) eV and preexponential factor D0=(5.5-3.7+11.1)×10-2 cm2 s-1 . Remarkably, Q equals the activation enthalpy of hydrogen diffusion in amorphous Si, the migration of bond defects determining boron diffusion, and the activation enthalpy of solid phase epitaxial recrystallization reported in the literature. This close agreement provides strong evidence that self-diffusion is mediated by local bond rearrangements rather than by the migration of extended defects as suggested by Strauß et al. (Phys. Rev. Lett. 116, 025901 (2016), 10.1103/PhysRevLett.116.025901).

Scanning electron microscopy of the surfaces of ion implanted SiC

NASA Astrophysics Data System (ADS)

Malherbe, Johan B.; van der Berg, N. G.; Kuhudzai, R. J.; Hlatshwayo, T. T.; Thabethe, T. T.; Odutemowo, O. S.; Theron, C. C.; Friedland, E.; Botha, A. J.; Wendler, E.

2015-07-01

This paper gives a brief review of radiation damage caused by particle (ions and neutrons) bombardment in SiC at different temperatures, and its annealing, with an expanded discussion on the effects occurring on the surface. The surface effects were observed using SEM (scanning electron microscopy) with an in-lens detector and EBSD (electron backscatter diffraction). Two substrates were used, viz. single crystalline 6H-SiC wafers and polycrystalline SiC, where the majority of the crystallites were 3C-SiC. The surface modification of the SiC samples by 360 keV ion bombardment was studied at temperatures below (i.e. room temperature), just at (i.e. 350 °C), or above (i.e. 600 °C) the critical temperature for amorphization of SiC. For bombardment at a temperature at about the critical temperature an extra step, viz. post-bombardment annealing, was needed to ascertain the microstructure of bombarded layer. Another aspect investigated was the effect of annealing of samples with an ion bombardment-induced amorphous layer on a 6H-SiC substrate. SEM could detect that this layer started to crystalize at 900 °C. The resulting topography exhibited a dependence on the ion species. EBSD showed that the crystallites forming in the amorphized layer were 3C-SiC and not 6H-SiC as the substrate. The investigations also pointed out the behaviour of the epitaxial regrowth of the amorphous layer from the 6H-SiC interface.

Iodine assisted retainment of implanted silver in 6H-SiC at high temperatures

NASA Astrophysics Data System (ADS)

Hlatshwayo, T. T.; van der Berg, N. G.; Msimanga, M.; Malherbe, J. B.; Kuhudzai, R. J.

2014-09-01

The effect of high temperature thermal annealing on the retainment and diffusion behaviour of iodine (I) and silver (Ag) both individually and co-implanted into 6H-SiC has been investigated using RBS, RBS-C and heavy ion ERDA (Elastic Recoil Detection Analysis). Iodine and silver ions at 360 keV were both individually and co-implanted into 6H-SiC at room temperature to fluences of the order of 1 × 1016 cm-2. RBS analyses of the as-implanted samples indicated that implantation of Ag and of I and co-implantation of 131I and 109Ag at room temperature resulted in complete amorphization of 6H-SiC from the surface to a depth of about 290 nm for the co-implanted samples. Annealing at 1500 °C for 30 h (also with samples annealed at 1700 °C for 5 h) caused diffusion accompanied by some loss of both species at the surface with some iodine remaining in the iodine implanted samples. In the Ag implanted samples, the RBS spectra showed that all the Ag disappeared. SEM images showed different recrystallization behaviour for all three sets of samples, with larger faceted crystals appearing in the SiC samples containing iodine. Heavy Ion ERDA analyses showed that both 109Ag and 131I remained in the co-implanted SiC samples after annealing at 1500 °C for 30 h. Therefore, iodine assisted in the retainment of silver in SiC even at high temperature.

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.

Structural and Magnetic Properties of Sputter-Deposited Polycrystalline Ni-Mn-Ga Ferromagnetic Shape-Memory Thin Films

NASA Astrophysics Data System (ADS)

Vinodh Kumar, S.; Seenithurai, S.; Manivel Raja, M.; Mahendran, M.

2015-10-01

Polycrystalline Ni-Mn-Ga ferromagnetic shape-memory thin films have been deposited on Si (100) substrates using a direct-current magnetron sputtering technique. The microstructure and the temperature dependence of magnetic properties of the films have been investigated by x-ray diffraction, scanning electron microscopy, and thermomagnetic measurements. As-deposited Ni50.2Mn30.6Ga19.2 film showed quasi-amorphous structure with paramagnetic nature at room temperature. When annealed at 873 K, the quasi-amorphous film attained crystallinity and possessed L21 cubic ordering with high magnetic transition temperature. Saturation magnetization and coercivity values for the annealed film were found to be 220 emu/cm3 and 70 Oe, respectively, indicating soft ferromagnetic character with low magnetocrystalline anisotropy. The magnetic transitions of the film deposited at 100 W were above room temperature, making this a potential candidate for use in microelectromechanical system devices.

Growth of rutile TiO2 nanorods in Ti and Cu ion sequentially implanted SiO2 and the involved mechanisms

NASA Astrophysics Data System (ADS)

Mu, Xiaoyu; Liu, Xiaoyu; Wang, Xiaohu; Dai, Haitao; Liu, Changlong

2018-01-01

TiO2 in nanoscale exhibits unique physicochemical and optoelectronic properties and has attracted much more interest of the researchers. In this work, TiO2 nanostructures are synthesized in amorphous SiO2 slices by implanting Ti ions, or sequentially implanting Ti and Cu ions combined with annealing at high temperature. The morphology, structure, spatial distribution and optical properties of the formed nanostructures have been investigated in detail. Our results clearly show that the thermal growth of TiO2 nanostructures in SiO2 substrate is significantly enhanced by presence of post Cu ion implantation, which depends strongly on the applied Cu ion fluence, as well as the annealing atmosphere. Due to the formation of Cu2O in the substrate, rutile TiO2 nanorods of large size have been well fabricated in the Ti and Cu sequentially implanted SiO2 after annealing in N2 atmosphere, in which Cu2O plays a role as a catalyst. Moreover, the sample with well-fabricated TiO2 nanorods exhibits a narrowed band gap, an enhanced optical absorption in visible region, and catalase-/peroxidase-like catalytic characteristics. Our findings provide an effective route to fabricate functional TiO2 nanorods in SiO2 via ion implantation.

Effect of Al and Mg Contents on Wettability and Reactivity of Molten Zn-Al-Mg Alloys on Steel Sheets Covered with MnO and SiO2 Layers

NASA Astrophysics Data System (ADS)

Huh, Joo-Youl; Hwang, Min-Je; Shim, Seung-Woo; Kim, Tae-Chul; Kim, Jong-Sang

2018-05-01

The reactive wetting behaviors of molten Zn-Al-Mg alloys on MnO- and amorphous (a-) SiO2-covered steel sheets were investigated by the sessile drop method, as a function of the Al and Mg contents in the alloys. The sessile drop tests were carried out at 460 °C and the variation in the contact angles (θc) of alloys containing 0.2-2.5 wt% Al and 0-3.0 wt% Mg was monitored for 20 s. For all the alloys, the MnO-covered steel substrate exhibited reactive wetting whereas the a-SiO2-covered steel exhibited nonreactive, nonwetting (θc > 90°) behavior. The MnO layer was rapidly removed by Al and Mg contained in the alloys. The wetting of the MnO-covered steel sheet significantly improved upon increasing the Mg content but decreased upon increasing the Al content, indicating that the surface tension of the alloy droplet is the main factor controlling its wettability. Although the reactions of Al and Mg in molten alloys with the a-SiO2 layer were found to be sluggish, the wettability of Zn-Al-Mg alloys on the a-SiO2 layer improved upon increasing the Al and Mg contents. These results suggest that the wetting of advanced high-strength steel sheets, the surface oxide layer of which consists of a mixture of MnO and SiO2, with Zn-Al-Mg alloys could be most effectively improved by increasing the Mg content of the alloys.

Maskless nano-implant of 20 keV Ga+ in bulk Si(1 0 0) substrates

NASA Astrophysics Data System (ADS)

Milazzo, R. G.; D'Arrigo, G.; Mio, A. M.; Rimini, E.; Spinella, C.; Peto, L.; Nadzeyka, A.; Bauerdick, S.

2014-12-01

Multidirectional SPEG (Solid Phase Epitaxial Growth) of silicon has been investigated in micro and nanoamorphous structures generated on a crystalline substrate by a nano-sized ion beam, Gaussian shaped and with a standard deviation of about 5 nm. The 20 keV Ga+ ions were implanted at a fluence of 5 × 1014 ions cm-2 in a bulk Si(1 0 0) single crystal. Two structures were used for the implants: circular regions of 100 nm and 1 μm diameters respectively and straight lines 10 nm in width and few microns in length along (1 0 0) or (1 1 0) directions. The lateral spread of ions has been taken into account in the damage estimation. Transmission Electron Microscopy indicates that the structures are made of an amorphous core surrounded by a defective and filamentary shell. The recovery of the damaged outer regions promptly occurs during the early stages of the thermal treatment at 500-600 °C for all the structures. By prolonging annealing time, re-crystallization of the amorphous cores is achieved too by the movement of the underneath crystal-amorphous interface. The re-growth is almost defects free when the contribution of the crystalline seed below the structures is present, defective and twin mediated if it misses as in the thinnest regions of the specimen.

Formation of Ge nanoparticles in SiO xN y by ion implantation and thermal annealing

DOE PAGES

Mirzaei, Sahar; Kremer, F.; Sprouster, D. J.; ...

2015-10-20

Germanium nanoparticles embedded within dielectric matrices hold much promise for applications in optoelectronic and electronic devices. Here we investigate the formation of Ge nanoparticles in amorphous SiO 1.67N 0.14 as a function of implanted atom concentration and thermal annealing temperature. Using x-ray absorption spectroscopy and other complementary techniques, we show Ge nanoparticles exhibit significant finite-size effects such that the coordination number decreases and structural disorder increases as the nanoparticle size decreases. While the composition of SiO 1.67N 0.14 is close to that of SiO 2, we demonstrate that the addition of this small fraction of N yields a much reducedmore » nanoparticle size relative to those formed in SiO 2 under comparable implantation and annealing conditions. We attribute this difference to an increase in an atomic density and a much reduced diffusivity of Ge in the oxynitride matrix. Finally, these results demonstrate the potential for tailoring Ge nanoparticle sizes and structural properties in the SiO xN y matrices by controlling the oxynitride stoichiometry.« less

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

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

Damage growth in Si during self-ion irradiation: A study of ion effects over an extended energy range

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

Holland, O.W.; El-Ghor, M.K.; White, C.W.

1989-01-01

Damage nucleation/growth in single-crystal Si during ion irradiation is discussed. For MeV ions, the rate of growth as well as the damage morphology are shown to vary widely along the track of the ion. This is attributed to a change in the dominant, defect-related reactions as the ion penetrates the crystal. The nature of these reactions were elucidated by studying the interaction of MeV ions with different types of defects. The defects were introduced into the Si crystal prior to high-energy irradiation by self-ion implantation at a medium energy (100 keV). Varied damage morphologies were produced by implanting different ionmore » fluences. Electron microscopy and ion-channeling measurements, in conjunction with annealing studies, were used to characterize the damage. Subtle changes in the predamage morphology are shown to result in markedly different responses to the high-energy irradiation, ranging from complete annealing of the damage to rapid growth. These divergent responses occur over a narrow range of dose (2--3 /times/ 10/sup 14/ cm/sup /minus/2/) of the medium-energy ions; this range also marks a transition in the growth behavior of the damage during the predamage implantation. A model is proposed which accounts for these observations and provides insight into ion-induced growth of amorphous layers in Si and the role of the amorphous/crystalline interface in this process. 15 refs, 9 figs.« less

Selective Oxidation of a 0.1C-6Mn-2Si Third Generation Advanced High-Strength Steel During Dew-Point Controlled Annealing

NASA Astrophysics Data System (ADS)

Pourmajidian, Maedeh; McDermid, Joseph R.

2018-03-01

The present study investigates the selective oxidation of a 0.1C-6Mn-2Si medium-Mn advanced high-strength steel during austenization annealing heat treatments as a function of process atmosphere oxygen partial pressure and annealing time. It was determined that the surface oxide growth kinetics followed a parabolic rate law with the minimum rate belonging to the lowest oxygen partial pressure atmosphere at a dew point of 223 K (- 50 °C). The chemistry of the surface and subsurface oxides was studied using STEM + EELS on the sample cross sections, and it was found that the surface oxides formed under the 223 K (- 50 °C) dew-point atmosphere consisted of a layered configuration of SiO2, MnSiO3, and MnO, while in the case of the higher pO2 process atmospheres, only MnO was detected at the surface. Consistent with the Wagner calculations, it was shown that the transition to internal oxidation for Mn occurred under the 243 K (- 30 °C) and 278 K (+ 5 °C) dew-point atmospheres. However, the predictions of the external to internal oxidation for Si using the Wagner model did not correlate well with the experimental findings nor did the predictions of the Mataigne et al. model for multi-element alloys. Investigations of the internal oxide network at the grain boundaries revealed a multilayer oxide structure composed of amorphous SiO2 and crystalline MnSiO3, respectively, at the oxide core and outer shell. A mechanism for the formation of the oxide morphologies observed, based on kinetic and thermodynamic factors, was proposed. It is expected that only the fine and nodule-like MnO oxides formed on the surface of the samples annealed under the 278 K (+ 5 °C) dew-point process atmosphere for 60 and 120 seconds are sufficiently thin and of the desired dispersed morphology to promote reactive wetting by the molten galvanizing bath.

Tunnel oxide passivated contacts formed by ion implantation for applications in silicon solar cells

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

Reichel, Christian, E-mail: christian.reichel@ise.fraunhofer.de; National Renewable Energy Laboratory; Feldmann, Frank

Passivated contacts (poly-Si/SiO{sub x}/c-Si) doped by shallow ion implantation are an appealing technology for high efficiency silicon solar cells, especially for interdigitated back contact (IBC) solar cells where a masked ion implantation facilitates their fabrication. This paper presents a study on tunnel oxide passivated contacts formed by low-energy ion implantation into amorphous silicon (a-Si) layers and examines the influence of the ion species (P, B, or BF{sub 2}), the ion implantation dose (5 × 10{sup 14 }cm{sup −2} to 1 × 10{sup 16 }cm{sup −2}), and the subsequent high-temperature anneal (800 °C or 900 °C) on the passivation quality and junction characteristics using double-sided contacted silicon solar cells.more » Excellent passivation quality is achieved for n-type passivated contacts by P implantations into either intrinsic (undoped) or in-situ B-doped a-Si layers with implied open-circuit voltages (iV{sub oc}) of 725 and 720 mV, respectively. For p-type passivated contacts, BF{sub 2} implantations into intrinsic a-Si yield well passivated contacts and allow for iV{sub oc} of 690 mV, whereas implanted B gives poor passivation with iV{sub oc} of only 640 mV. While solar cells featuring in-situ B-doped selective hole contacts and selective electron contacts with P implanted into intrinsic a-Si layers achieved V{sub oc} of 690 mV and fill factor (FF) of 79.1%, selective hole contacts realized by BF{sub 2} implantation into intrinsic a-Si suffer from drastically reduced FF which is caused by a non-Ohmic Schottky contact. Finally, implanting P into in-situ B-doped a-Si layers for the purpose of overcompensation (counterdoping) allowed for solar cells with V{sub oc} of 680 mV and FF of 80.4%, providing a simplified and promising fabrication process for IBC solar cells featuring passivated contacts.« less

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

Tsuo, Y.S.; Smith, E.B.; Deb, S.K.

A Kaufman ion beam source was used to implant hydrogen atoms into glow-discharge-deposited amorphous silicon materials in which the hydrogen content had been driven out by heating. We found that the hydrogen atoms introduced by this low-energy (less than 700 eV) ion implantation method bonded predominantly as SiH. An air mass one, photo-to-dark-conductivity ratio as high as 5.6 x 10/sup 5/ has been obtained with hydrogen-implanted materials. No light-induced reduction of the photo- and dark conductivities has been observed in these materials after 20 h of AMl illumnination.

Nickel silicide formation in silicon implanted nickel

NASA Astrophysics Data System (ADS)

Rao, Z.; Williams, J. S.; Pogany, A. P.; Sood, D. K.; Collins, G. A.

1995-04-01

Nickel silicide formation during the annealing of very high dose (≥4.5×1017 ions/cm2) Si implanted Ni has been investigated, using ion beam analytical techniques, electron microscopy, and x-ray diffraction analysis. An initial amorphous Si-Ni alloy, formed as a result of high dose ion implantation, first crystallized to Ni2Si upon annealing in the temperature region of 200-300 °C. This was followed by the formation of Ni5Si2 in the temperature region of 300-400 °C and then by Ni3Si at 400-600 °C. The Ni3Si layer was found to have an epitaxial relationship with the substrate Ni, which was determined as Ni3Si<100>∥Ni<100> and Ni3Si<110>∥Ni<110> for Ni(100) samples. The minimum channeling yield in the 2 MeV He Rutherford backscattering and channeling spectra of this epitaxial layer improved with higher annealing temperatures up to 600 °C, and reached a best value measured at about 8%. However, the epitaxial Ni3Si dissolved after long time annealing at 600 °C or annealing at higher temperatures to liberate soluble Si into the Ni substrate. The epitaxy is attributed to the excellent lattice match between the Ni3Si and the Ni. The annealing behavior follows the predictions of the Ni-Si phase diagram for this nickel-rich binary system.

Biomineral microstructures in ferromanganese nodules: evidence of the biological and abiogenous origin

NASA Astrophysics Data System (ADS)

Lysyuk, G. N.

2011-10-01

Manganese oxides, which are widespread and of great practical importance, are formed and transformed by the active role of microorganisms. Manganese aggregates occur as both crystallized varieties and disordered fine-grained phases with significant ore grade and up to 50-60 vol % of X-ray amorphous components. X-ray amorphous nanosizedMn oxides in Fe-Mn nodules from the Pacific Ocean floor were examined from the standpoint of their biogenic origin. SEM examination showed abundant mineralized biofilms on the studied samples. The chemical composition of bacterial mass is as follows (wt %): 28.34 MnO, 17.14 Fe2O3, 7.11 SiO2, 2.41 CaO, 17.90 TiO2, 1.74Na2O,1.73 A12O3,1.30 MgO, 1.25P2O5,1.25 SO3,0.68 CoO, 0.54 CuO, 0.53 NiO, and 0.50 K2O. The chemical composition of fossilized cyanobacterial mats within the interlayer space of nodules is as follows (wt %): 48.35 MnO, 6.23 Fe2O3, 8.76 MgO, 5.05 A12O3, 4.45 SiO2, 3.63 NiO, 2.30 Na2O, 2.19 CuO, 1.31 CaO, and 0.68 K2O is direct evidence for participation of bacteria in Mn oxide formation. This phase consists of mineralized glycocalix consisting of nanosized flakes of todorokite. Native metals (Cu, Fe, and Zn) as inclusions 10-20 μm in size were identified in ferromanganese nodules as well. The formation of native metals can be explained by their crystallization at highly reducing conditions maintained by organic matter.

Reduction in number of crystal defects in a p+Si diffusion layer by germanium and boron cryogenic implantation combined with sub-melt laser spike annealing

NASA Astrophysics Data System (ADS)

Murakoshi, Atsushi; Harada, Tsubasa; Miyano, Kiyotaka; Harakawa, Hideaki; Aoyama, Tomonori; Yamashita, Hirofumi; Kohyama, Yusuke

2017-09-01

To reduce the number of crystal defects in a p+Si diffusion layer by a low-thermal-budget annealing process, we have examined crystal recovery in the amorphous layer formed by the cryogenic implantation of germanium and boron combined with sub-melt laser spike annealing (LSA). The cryogenic implantation at -150 °C is very effective in suppressing vacancy clustering, which is advantageous for rapid crystal recovery during annealing. The crystallinity after LSA is shown to be very high and comparable to that after rapid thermal annealing (RTA) owing to the cryogenic implantation, although LSA is a low-thermal-budget annealing process that can suppress boron diffusion effectively. It is also shown that in the p+Si diffusion layer, there is high contact resistance due to the incomplete formation of a metal silicide contact, which originates from insufficient outdiffusion of surface contaminants such as fluorine. To widely utilize the marked reduction in the number of crystal defects, sufficient removal of surface contaminants will be required in the low-thermal-budget process.

High-Temperature Annealing Induced He Bubble Evolution in Low Energy He Ion Implanted 6H-SiC

NASA Astrophysics Data System (ADS)

Liu, Yu-Zhu; Li, Bing-Sheng; Zhang, Li

2017-05-01

Bubble evolution in low energy and high dose He-implanted 6H-SiC upon thermal annealing is studied. The < 0001> -oriented 6H-SiC wafers are implanted with 15 keV helium ions at a dose of 1× 1017 cm-2 at room temperature. The samples with post-implantation are annealed at temperatures of 1073, 1173, 1273, and 1473 K for 30 min. He bubbles in the wafers are examined via cross-sectional transmission electron microscopy (XTEM) analysis. The results present that nanoscale bubbles are almost homogeneously distributed in the damaged layer of the as-implanted sample, and no significant change is observed in the He-implanted sample after 1073 K annealing. Upon 1193 K annealing, almost full recrystallization of He-implantation-induced amorphization in 6H-SiC is observed. In addition, the diameters of He bubbles increase obviously. With continually increasing temperatures to 1273 K and 1473 K, the diameters of He bubbles increase and the number density of lattice defects decreases. The growth of He bubbles after high temperature annealing abides by the Ostwald ripening mechanism. The mean diameter of He bubbles located at depths of 120-135 nm as a function of annealing temperature is fitted in terms of a thermal activated process which yields an activation energy of 1.914+0.236 eV. Supported by the National Natural Science Foundation of China under Grant No 11475229.

Effects of thermal annealing on the structural and optical properties of carbon-implanted SiO2.

PubMed

Poudel, P R; Paramo, J A; Poudel, P P; Diercks, D R; Strzhemechny, Y M; Rout, B; McDaniel, F D

2012-03-01

Amorphous carbon (a-C) nanoclusters were synthesized by the implantation of carbon ions (C-) into thermally grown silicon dioxide film (-500 nm thick) on a Si (100) wafer and processed by high temperature thermal annealing. The carbon ions were implanted with an energy of 70 keV at a fluence of 5 x 10(17) atoms/cm2. The implanted samples were annealed at 1100 degrees C for different time periods in a gas mixture of 96% Ar+4% H2. Raman spectroscopy, X-ray photoelectron spectroscopy (XPS) and High Resolution Transmission Electron Microscopy (HRTEM) were used to study the structural properties of both the as-implanted and annealed samples. HRTEM reveals the formation of nanostructures in the annealed samples. The Raman spectroscopy also confirms the formation of carbon nano-clusters in the samples annealed for 10 min, 30 min, 60 min and 90 min. No Raman features originating from the carbon-clusters are observed for the sample annealed further to 120 min, indicating a complete loss of implanted carbon from the SiO2 layer. The loss of the implanted carbon in the 120 min annealed sample from the SiO2 layer was also observed in the XPS depth profile measurements. Room temperature photoluminescence (PL) spectroscopy revealed visible emissions from the samples pointing to carbon ion induced defects as the origin of a broad 2.0-2.4 eV band, and the intrinsic defects in SiO2 as the possible origin of the -2.9 eV bands. In low temperature photoluminescence spectra, two sharp and intense photoluminescence lines at -3.31 eV and -3.34 eV appear for the samples annealed for 90 min and 120 min, whereas no such bands are observed in the samples annealed for 10 min, 30 min, and 60 min. The Si nano-clusters forming at the Si-SiO2 interface could be the origin of these intense peaks.

The Use of Atomic-Force Microscopy for Studying the Crystallization Process of Amorphous Alloys

NASA Astrophysics Data System (ADS)

Elmanov, G. N.; Ivanitskaya, E. A.; Dzhumaev, P. S.; Skrytniy, V. I.

The crystallization process of amorphous alloys is accompanied by the volume changes as a result of structural phase transitions. This leads to changes in the surface topography, which was studied by atomic force microscopy (AFM). The changes of the surface topography, structure and phase composition during multistage crystallization process of the metallic glasses with composition Ni71,5Cr6,8Fe2,7B11,9Si7,1 and Ni63,4Cr7,4Fe4,3Mn0,8B15,6Si8,5 (AWS BNi2) has been investigated. The obtained results on changing of the surface topography in crystallization process are in good agreement with the data of X-ray diffraction analysis (XRD). The nature of redistribution of some alloy components in the crystallization process has been suggested.

Magnetization Processes in Ribbons of Soft Magnetic Amorphous Alloys

NASA Astrophysics Data System (ADS)

Skulkina, N. A.; Ivanov, O. A.; Mazeeva, A. K.; Kuznetsov, P. A.; Stepanova, E. A.; Blinova, O. V.; Mikhalitsyna, E. A.

2018-02-01

Using iron-based (Fe-B-Si-C; Fe-Ni-Si-B) and cobalt-based (Co-Fe-Ni-Cr-Mn-Si-B) soft magnetic alloys as examples, we have studied the dependences of the remanence measured using minor hysteresis loops on the maximum induction. The different degrees of stabilization of the 180° and 90° domain walls allows these dependences to be used to analyze the magnetization processes that occur in the rapidly quenched soft magnetic alloys. It has been established from the B r( B m) dependences that, in the ribbons of soft magnetic amorphous alloys, the processes of the rotation of the magnetization oriented perpendicular to the ribbon plane start before the end of the processes of the displacement of the walls of domains with planar magnetization. After the end of the magnetization rotation processes, the magnetization processes can be interpreted as the displacement of the domain walls with a planar magnetization accompanied by a decrease in their number and a transition to a bistable state.

Pulsed laser annealing of high-dose Ag+-ion implanted Si layer

NASA Astrophysics Data System (ADS)

Batalov, R. I.; Nuzhdin, V. I.; Valeev, V. F.; Vorobev, V. V.; Osin, Yu N.; Ivlev, G. D.; Stepanov, A. L.

2018-01-01

The formation of a crystalline composite Ag:Si material with Ag nanoparticles by low-energy (E  =  30 keV) high-dose (D  =  1.5  ×  1017 ion cm-2) Ag+ implantation into a monocrystalline c-Si substrate followed by nanosecond pulsed laser annealing (PLA) is demonstrated. Compared to traditional thermal annealing, PLA allows us to perform local heating of the sample both for its depth and area, and eliminate implantation-induced defects more efficiently, due to rapid liquid-phase recrystallization. Moreover, dopant diffusion during a nanosecond laser pulse is mainly limited by the molten region, where the dopant diffusion coefficient is several orders of magnitude higher than in the solid state. During PLA by a ruby laser (λ  =  0.694 µm), the optical probing of the irradiated zone at λ  =  1.064 µm with registration of time-dependent reflectivity R(t) was carried out. By scanning electron microscopy, it was established that Ag+ implantation leads to the creation of a thin amorphous Ag:Si layer of porous structure, containing Ag nanoparticles with sizes of 10-30 nm. PLA with energy density W  =  1.2-1.8 J cm-2 results in the melting of the implanted layer (d ~ 60 nm) and the topmost layers of the c-Si substrate (d  <  400 nm), followed by the rapid recrystallization of the Si matrix containing Ag nanoparticles with dominate sizes of 5-15 nm and some fraction of larger particles of 40-60 nm. Energy dispersive x-ray (EDX) spectroscopy did not show a noticeable change of Ag atomic concentration in the implanted layer after PLA. Spectral dependence R(λ) of Ag:Si layers showed the partial recovery of c-Si bands with maxima at 275 and 365 nm with simultaneous weakening of plasmon band for Ag nanoparticles in Si at 835 nm.

Threshold switching in SiGeAsTeN chalcogenide glass prepared by As ion implantation into sputtered SiGeTeN film

NASA Astrophysics Data System (ADS)

Liu, Guangyu; Wu, Liangcai; Song, Zhitang; Liu, Yan; Li, Tao; Zhang, Sifan; Song, Sannian; Feng, Songlin

2017-12-01

A memory cell composed of a selector device and a storage device is the basic unit of phase change memory. The threshold switching effect, main principle of selectors, is a universal phenomenon in chalcogenide glasses. In this work, we put forward a safe and controllable method to prepare a SiGeAsTeN chalcogenide film by implanting As ions into sputtered SiGeTeN films. For the SiGeAsTeN material, the phase structure maintains the amorphous state, even at high temperature, indicating that no phase transition occurs for this chalcogenide-based material. The electrical test results show that the SiGeAsTeN-based devices exhibit good threshold switching characteristics and the switching voltage decreases with the increasing As content. The decrease in valence alternation pairs, reducing trap state density, may be the physical mechanism for lower switch-on voltage, which makes the SiGeAsTeN material more applicable in selector devices through component optimization.

Facile Synthesis of Highly Efficient Amorphous Mn-MIL-100 Catalysts: Formation Mechanism and Structure Changes during Application in CO Oxidation.

PubMed

Zhang, Xiaodong; Li, Hongxin; Lv, Xutian; Xu, Jingcheng; Wang, Yuxin; He, Chi; Liu, Ning; Yang, Yiqiong; Wang, Yin

2018-06-21

A comprehensive study was carried out on amorphous metal-organic frameworks Mn-MIL-100 as efficient catalysts for CO oxidation. This study focused on explaining the crystalline-amorphous-crystalline transformations during thermolysis of Mn-MIL-100 and studying the structure changes during the CO oxidation reaction. A possible formation mechanism of amorphous Mn-MIL-100 was proposed. Amorphous Mn-MIL-100 obtained by calcination at 250 °C (a-Mn-250) showed a smaller specific surface area (4 m 2  g -1 ) but high catalytic activity. Furthermore, the structure of amorphous Mn-MIL-100 was labile during the reaction. When a-Mn-250 was treated with reaction atmosphere at high temperature (giving used-a-Mn-250-S), the amorphous catalysts transformed into Mn 2 O 3 . Meanwhile, the BET surface area (164 m 2  g -1 ) and catalytic performance both sharply increased. In addition, used-a-Mn-250-S catalyst transformed from Mn 2 O 3 into Mn 3 O 4 , and this resulted in a slight decrease of catalytic activity in the presence of 1 vol % water vapor in the feed stream. A schematic mechanism of the structure changes during the reaction process was proposed. The success of the synthesis relies on the increase in BET surface area by using CO as retreatment atmosphere, and the enhanced catalytic activity was attributed to the unique structure, a large quantity of surface active oxygen species, oxygen vacancies, and good low-temperature reduction behavior. © 2018 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim.

Carbon and metal-carbon implantations into tool steels for improved tribological performance

NASA Astrophysics Data System (ADS)

Hirvonen, J.-P.; Harskamp, F.; Torri, P.; Willers, H.; Fusari, A.; Gibson, N.; Haupt, J.

1997-05-01

The high-fluence implantation of carbon and dual implantations of metal-metalloid pairs into steels with different microstructures are briefly reviewed. A previously unexamined system, the implantation of Si and C into two kinds of tool steels, M3 and D2, have been studied in terms of microstructure and tribological performance. In both cases ion implantation transfers a surface into an amorphous layer. However, the tribological behavior of these two materials differs remarkably: in the case of ion-implanted M3 a reduction of wear in a steel pin is observed even at high pin loads, whereas in the case of ion-implanted D2 the beneficial effects of ion implantation were limited to the lowest pin load. The importance of an initial phase at the onset of sliding is emphasized and a number of peculiarities observed in ion-implanted M3 steel are discussed.

Xenon-ion-induced and thermal mixing of Co/Si bilayers and their interplay

NASA Astrophysics Data System (ADS)

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

2011-05-01

Studies on ion-irradiated transition-metal/silicon bilayers demonstrate that interface mixing and silicide phase formation depend sensitively on the ion and film parameters, including the structure of the metal/Si interface. Thin Co layers e-gun evaporated to a thickness of 50 nm on Si(1 0 0) wafers were bombarded at room temperature with 400-keV Xe + ions at fluences of up to 3 × 10 16 cm -2. We used either crystalline or pre-amorphized Si wafers the latter ones prepared by 1.0-keV Ar-ion implantation. The as-deposited or Xe-ion-irradiated samples were then isochronally annealed at temperatures up to 700 °C. Changes of the bilayer structures induced by ion irradiation and/or annealing were investigated with RBS, XRD and HRTEM. The mixing rate for the Co/c-Si couples, Δ σ2/ Φ = 3.0(4) nm 4, is higher than the value expected for ballistic mixing and about half the value typical for spike mixing. Mixing of pre-amorphized Si is much weaker relative to crystalline Si wafers, contrary to previous results obtained for Fe/Si bilayers. Annealing of irradiated samples produces very similar interdiffusion and phase formation patterns above 400 °C as in the non-irradiated Co/Si bilayers: the phase evolution follows the sequence Co 2Si → CoSi → CoSi 2.

Adsorption of Amorphous Silica Nanoparticles onto Hydroxyapatite Surfaces Differentially Alters Surfaces Properties and Adhesion of Human Osteoblast Cells

PubMed Central

Kalia, Priya; Brooks, Roger A.; Kinrade, Stephen D.; Morgan, David J.; Brown, Andrew P.; Rushton, Neil; Jugdaohsingh, Ravin

2016-01-01

Silicon (Si) is suggested to be an important/essential nutrient for bone and connective tissue health. Silicon-substituted hydroxyapatite (Si-HA) has silicate ions incorporated into its lattice structure and was developed to improve attachment to bone and increase new bone formation. Here we investigated the direct adsorption of silicate species onto an HA coated surface as a cost effective method of incorporating silicon on to HA surfaces for improved implant osseointegration, and determined changes in surface characteristics and osteoblast cell adhesion. Plasma-sprayed HA-coated stainless steel discs were incubated in silica dispersions of different concentrations (0–42 mM Si), at neutral pH for 12 h. Adsorbed Si was confirmed by XPS analysis and quantified by ICP-OES analysis following release from the HA surface. Changes in surface characteristics were determined by AFM and measurement of surface wettability. Osteoblast cell adhesion was determined by vinculin plaque staining. Maximum Si adsorption to the HA coated disc occurred after incubation in the 6 mM silica dispersion and decreased progressively with higher silica concentrations, while no adsorption was observed with dispersions below 6 mM Si. Comparison of the Si dispersions that produced the highest and lowest Si adsorption to the HA surface, by TEM-based analysis, revealed an abundance of small amorphous nanosilica species (NSP) of ~1.5 nm in diameter in the 6 mM Si dispersion, with much fewer and larger NSP in the 42 mM Si dispersions. 29Si-NMR confirmed that the NSPs in the 6 mM silica dispersion were polymeric and similar in composition to the larger NSPs in the 42 mM Si dispersion, suggesting that the latter were aggregates of the former. Amorphous NSP adsorbed from the 6 mM dispersion on to a HA-coated disc surface increased the surface’s water contact angle by 53°, whereas that adsorbed from the 42 mM dispersion decreased the contact angle by 18°, indicating increased and decreased hydrophobicity, respectively. AFM showed an increase in surface roughness of the 6 mM Si treated surface, which correlated well with an increase in number of vinculin plaques. These findings suggest that NSP of the right size (relative to charge) adsorb readily to the HA surface, changing the surface characteristics and, thus, improving osteoblast cell adhesion. This treatment provides a simple way to modify plasma-coated HA surfaces that may enable improved osseointegration of bone implants. PMID:26863624

Study of shallow junction formation by boron-containing cluster ion implantation of silicon and two-stage annealing

NASA Astrophysics Data System (ADS)

Lu, Xin-Ming

Shallow junction formation made by low energy ion implantation and rapid thermal annealing is facing a major challenge for ULSI (ultra large scale integration) as the line width decreases down to the sub micrometer region. The issues include low beam current, the channeling effect in low energy ion implantation and TED (transient enhanced diffusion) during annealing after ion implantation. In this work, boron containing small cluster ions, such as GeB, SiB and SiB2, was generated by using the SNICS (source of negative ion by cesium sputtering) ion source to implant into Si substrates to form shallow junctions. The use of boron containing cluster ions effectively reduces the boron energy while keeping the energy of the cluster ion beam at a high level. At the same time, it reduces the channeling effect due to amorphization by co-implanted heavy atoms like Ge and Si. Cluster ions have been used to produce 0.65--2keV boron for low energy ion implantation. Two stage annealing, which is a combination of low temperature (550°C) preannealing and high temperature annealing (1000°C), was carried out to anneal the Si sample implanted by GeB, SiBn clusters. The key concept of two-step annealing, that is, the separation of crystal regrowth, point defects removal with dopant activation from dopant diffusion, is discussed in detail. The advantages of the two stage annealing include better lattice structure, better dopant activation and retarded boron diffusion. The junction depth of the two stage annealed GeB sample was only half that of the one-step annealed sample, indicating that TED was suppressed by two stage annealing. Junction depths as small as 30 nm have been achieved by two stage annealing of sample implanted with 5 x 10-4/cm2 of 5 keV GeB at 1000°C for 1 second. The samples were evaluated by SIMS (secondary ion mass spectrometry) profiling, TEM (transmission electron microscopy) and RBS (Rutherford Backscattering Spectrometry)/channeling. Cluster ion implantation in combination with two-step annealing is effective in fabricating ultra-shallow junctions.

In situ spectroscopic study of the plastic deformation of amorphous silicon under non-hydrostatic conditions induced by indentation

PubMed Central

Gerbig, Y.B; Michaels, C.A.; Bradby, J.E.; Haberl, B.; Cook, R.F.

2016-01-01

Indentation-induced plastic deformation of amorphous silicon (a-Si) thin films was studied by in situ Raman imaging of the deformed contact region of an indented sample, employing a Raman spectroscopy-enhanced instrumented indentation technique. Quantitative analyses of the generated in situ Raman maps provide unique, new insight into the phase behavior of as-implanted a-Si. In particular, the occurrence and evolving spatial distribution of changes in the a-Si structure caused by processes, such as polyamorphization and crystallization, induced by indentation loading were measured. The experimental results are linked with previously published work on the plastic deformation of a-Si under hydrostatic compression and shear deformation to establish a sequence for the development of deformation of a-Si under indentation loading. The sequence involves three distinct deformation mechanisms of a-Si: (1) reversible deformation, (2) increase in coordination defects (onset of plastic deformation), and (3) phase transformation. Estimated conditions for the occurrence of these mechanisms are given with respect to relevant intrinsic and extrinsic parameters, such as indentation stress, volumetric strain, and bond angle distribution (a measure for the structural order of the amorphous network). The induced volumetric strains are accommodated solely by reversible deformation of the tetrahedral network when exposed to small indentation stresses. At greater indentation stresses, the increased volumetric strains in the tetrahedral network lead to the formation of predominately five-fold coordination defects, which seems to mark the onset of irreversible or plastic deformation of the a-Si thin film. Further increase in the indentation stress appears to initiate the formation of six-fold coordinated atomic arrangements. These six-fold coordinated arrangements may maintain their amorphous tetrahedral structure with a high density of coordination defects or nucleate as a new crystalline β-tin phase within the a-Si network. PMID:26924926

Investigation of amorphization energies for heavy ion implants into silicon carbide at depths far beyond the projected ranges

NASA Astrophysics Data System (ADS)

Friedland, E.

2017-01-01

At ion energies with inelastic stopping powers less than a few keV/nm, radiation damage is thought to be due to atomic displacements by elastic collisions only. However, it is well known that inelastic processes and non-linear effects due to defect interaction within collision cascades can significantly increase or decrease damage efficiencies. The importance of these processes changes significantly along the ion trajectory and becomes negligible at some distance beyond the projected range, where damage is mainly caused by slowly moving secondary recoils. Hence, in this region amorphization energies should become independent of the ion type and only reflect the properties of the target lattice. To investigate this, damage profiles were obtained from α-particle channeling spectra of 6H-SiC wafers implanted at room temperature with ions in the mass range 84 ⩽ M ⩽ 133, employing the computer code DICADA. An average amorphization dose of (0.7 ± 0.2) dpa and critical damage energy of (17 ± 6) eV/atom are obtained from TRIM simulations at the experimentally observed boundary positions of the amorphous zones.

Magnetic and electrical properties of several Mn-based amorphous alloys

NASA Astrophysics Data System (ADS)

Obi, Y.; Morita, H.; Fujimori, H.

1987-03-01

Magnetic and electrical properties of amorphous Mn-Y, Mn-Zr, and Mn-Nb alloys have been investigated. All these alloys have a temperature-dependent susceptibility which is well fitted by a Curie-Weiss law. This implies the existence of localized magnetic moments associated with the Mn atoms. In addition, amorphous Mn-Y alloys exhibit spin-glass characteristics at low temperature. The experimental results of the electrical resistivity show that the temperature coefficient of resistivity (TCR) of both Mn-Y and Mn-Zr are negative, while Mn-Nb has a positive TCR. On the other hand, the resistivity-temperature curves of Mn-Zr and Mn-Nb have nearly the same tendency but are different from that of Mn-Y.

3D silicon shapes through bulk nano structuration by focused ion beam implantation and wet etching

NASA Astrophysics Data System (ADS)

Salhi, Billel; Troadec, David; Boukherroub, Rabah

2017-05-01

The work presented in this paper concerns the synthesis of silicon (Si) 2D and 3D nanostructures using the delayed effect, caused by implanted Ga ions, on the dissolution of Si in aqueous solutions of tetramethylammonium hydroxide (TMAH). The crystalline silicon substrates (100) are first cleaned and then hydrogenated by immersion in an aqueous solution of hydrofluoric acid. The ion implantation is then carried out by a focused ion beam by varying the dose and the exposure time. Chemical etching in aqueous solutions of TMAH at 80 °C leads to the selective dissolution of the Si planes not exposed to the ions. The preliminary results obtained in the laboratory made it possible to optimize the experimental conditions for the synthesis of 2D and 3D nanoobjects of controlled shape and size. Analysis by transmission electron microscopy and energy dispersive x-ray showed the amorphous nature of the nanostructures obtained and the presence of 5%-20% Ga in these nanoobjects. The first experiments of recrystallization by rapid thermal annealing allowed to reconstitute the crystal structure of these nanoobjects.

3D silicon shapes through bulk nano structuration by focused ion beam implantation and wet etching.

PubMed

Salhi, Billel; Troadec, David; Boukherroub, Rabah

2017-05-19

The work presented in this paper concerns the synthesis of silicon (Si) 2D and 3D nanostructures using the delayed effect, caused by implanted Ga ions, on the dissolution of Si in aqueous solutions of tetramethylammonium hydroxide (TMAH). The crystalline silicon substrates (100) are first cleaned and then hydrogenated by immersion in an aqueous solution of hydrofluoric acid. The ion implantation is then carried out by a focused ion beam by varying the dose and the exposure time. Chemical etching in aqueous solutions of TMAH at 80 °C leads to the selective dissolution of the Si planes not exposed to the ions. The preliminary results obtained in the laboratory made it possible to optimize the experimental conditions for the synthesis of 2D and 3D nanoobjects of controlled shape and size. Analysis by transmission electron microscopy and energy dispersive x-ray showed the amorphous nature of the nanostructures obtained and the presence of 5%-20% Ga in these nanoobjects. The first experiments of recrystallization by rapid thermal annealing allowed to reconstitute the crystal structure of these nanoobjects.

Expansion and melting of Xe nanocrystals in Si

NASA Astrophysics Data System (ADS)

Faraci, Giuseppe; Pennisi, Agata R.; Zontone, Federico; Li, Boquan; Petrov, Ivan

2006-12-01

Xe agglomerates confined in a Si matrix by ion implantation were synthesized with different size depending on the implantation process and/or the thermal treatment. At low temperature Xe nanocrystals are formed, whose expansion and melting were studied in the range 15- 300K . Previous high resolution x-ray diffraction spectra were corroborated with complementary techniques such as two-dimensional imaging plate patterns and transmission electron microscopy. We detected fcc Xe nanocrystals whose properties were size dependent. The experiments showed that in annealed samples epitaxial condensation of small Xe clusters, on the cavities of the Si matrix, gave in fact expanded and oriented Xe, suggesting a possible preferential growth of Xe(311) planes oriented orthogonally to the Si[02-2] direction. On the contrary, small Xe clusters in an amorphous Si matrix have a fcc lattice contracted as a consequence of surface tension. Furthermore, a solid-to-liquid phase transition size dependent was found. Expansion of fcc Xe lattice was accurately determined as a function of the temperature. Overpressurized nanocrystals and/or binary size distributions were disproved.

Design of Amorphous Manganese Oxide@Multiwalled Carbon Nanotube Fiber for Robust Solid-State Supercapacitor.

PubMed

Shi, Peipei; Li, Li; Hua, Li; Qian, Qianqian; Wang, Pengfei; Zhou, Jinyuan; Sun, Gengzhi; Huang, Wei

2017-01-24

Solid-state fiber-based supercapacitors have been considered promising energy storage devices for wearable electronics due to their lightweight and amenability to be woven into textiles. Efforts have been made to fabricate a high performance fiber electrode by depositing pseudocapacitive materials on the outer surface of carbonaceous fiber, for example, crystalline manganese oxide/multiwalled carbon nanotubes (MnO 2 /MWCNTs). However, a key challenge remaining is to achieve high specific capacitance and energy density without compromising the high rate capability and cycling stability. In addition, amorphous MnO 2 is actually preferred due to its disordered structure and has been proven to exhibit superior electrochemical performance over the crystalline one. Herein, by incorporating amorphous MnO 2 onto a well-aligned MWCNT sheet followed by twisting, we design an amorphous MnO 2 @MWCNT fiber, in which amorphous MnO 2 nanoparticles are distributed in MWCNT fiber uniformly. The proposed structure gives the amorphous MnO 2 @MWCNT fiber good mechanical reliability, high electrical conductivity, and fast ion-diffusion. Solid-state supercapacitor based on amorphous MnO 2 @MWCNT fibers exhibits improved energy density, superior rate capability, exceptional cycling stability, and excellent flexibility. This study provides a strategy to design a high performance fiber electrode with microstructure control for wearable energy storage devices.

Structural and chemical alteration of crystalline olivine under low energy He+ irradiation

NASA Astrophysics Data System (ADS)

Demyk, K.; Carrez, Ph.; Leroux, H.; Cordier, P.; Jones, A. P.; Borg, J.; Quirico, E.; Raynal, P. I.; d'Hendecourt, L.

2001-03-01

We present the results of irradiation experiments on crystalline olivine with He+ ions at energies of 4 and 10 keV and fluences varying from 5 1016 to 1018 ions/cm2. The aim of these experiments is to simulate ion implantation into interstellar grains in shocks in the ISM. Irradiated samples were analysed by transmission electron microscopy (TEM). The irradiation causes the amorphization of the olivine, at all He+ fluences considered. The thickness of the amorphized region is 40 +/- 15 nm and 90 +/- 10 nm for the 4 keV and 10 keV experiments, respectively. The amorphization of the olivine occurs in conjunction with an increase in the porosity of the material due to the formation of bubbles. In addition, the amorphized layer is deficient in oxygen and magnesium. We find that the O/Si and Mg/Si ratios decrease as the He+ fluence increases. These experiments show that the irradiation of dust in supernova shocks can efficiently alter the dust structure and composition. Our result are consistent with the lack of crystalline silicates in the interstellar medium and also with the compositional evolution observed from olivine-type silicates around evolved stars to pyroxene-type silicates around protostars.

Enhanced Cycleability of Amorphous MnO₂ by Covering on α-MnO₂ Needles in an Electrochemical Capacitor.

PubMed

Liu, Quanbing; Ji, Shan; Yang, Juan; Wang, Hui; Pollet, Bruno G; Wang, Rongfang

2017-08-24

An allomorph MnO₂@MnO₂ core-shell nanostructure was developed via a two-step aqueous reaction method. The data analysis of Scanning Electron Microscopy, Transmission Electron Microscopy, X-Ray Diffraction and N₂ adsorption-desorption isotherms experiments indicated that this unique architecture consisted of a porous layer of amorphous-MnO₂ nano-sheets which were well grown onto the surface of α-MnO₂ nano-needles. Cyclic voltammetry experiments revealed that the double-layer charging and Faradaic pseudo -capacity of the MnO₂@MnO₂ capacitor electrode contributed to a specific capacitance of 150.3 F·g -1 at a current density of 0.1 A·g -1 . Long cycle life experiments on the as-prepared MnO₂@MnO₂ sample showed nearly a 99.3% retention after 5000 cycles at a current density of 2 A·g -1 . This retention value was found to be significantly higher than those reported for amorphous MnO₂-based capacitor electrodes. It was also found that the remarkable cycleability of the MnO₂@MnO₂ was due to the supporting role of α-MnO₂ nano-needle core and the outer amorphous MnO₂ layer.

Manganese modified structural and optical properties of zinc soda lime silica glasses.

PubMed

Samsudin, Nur Farhana; Matori, Khamirul Amin; Wahab, Zaidan Abdul; Fen, Yap Wing; Liew, Josephine Ying Chi; Lim, Way Foong; Mohd Zaid, Mohd Hafiz; Omar, Nur Alia Sheh

2016-03-20

A series of MnO-doped zinc soda lime silica glass systems was prepared by a conventional melt and quenching technique. In this study, the x-ray diffraction analysis was applied to confirm the amorphous nature of the glasses. Fourier transform infrared spectroscopy shows the glass network consists of MnO₄, SiO₄, and ZnO₄ units as basic structural units. The glass samples under field emission scanning electron microscopy observation demonstrated irregularity in shape and size with glassy phase-like structure. The optical absorption studies revealed that the optical bandgap (E_opt) values decrease with an increase of MnO content. Through the results of various measurements, the doping of MnO in the glass matrix had effects on the performance of the glasses and significantly improved the properties of the glass sample as a potential host for phosphor material.

Synthesis of crystalline and amorphous, particle-agglomerated 3-D nanostructures of Al and Si oxides by femtosecond laser and the prediction of these particle sizes

NASA Astrophysics Data System (ADS)

Sivayoganathan, Mugunthan; Tan, Bo; Venkatakrishnan, Krishnan

2012-11-01

We report a single step technique of synthesizing particle-agglomerated, amorphous 3-D nanostructures of Al and Si oxides on powder-fused aluminosilicate ceramic plates and a simple novel method of wafer-foil ablation to fabricate crystalline nanostructures of Al and Si oxides at ambient conditions. We also propose a particle size prediction mechanism to regulate the size of vapor-condensed agglomerated nanoparticles in these structures. Size characterization studies performed on the agglomerated nanoparticles of fabricated 3-D structures showed that the size distributions vary with the fluence-to-threshold ratio. The variation in laser parameters leads to varying plume temperature, pressure, amount of supersaturation, nucleation rate, and the growth rate of particles in the plume. The novel wafer-foil ablation technique could promote the possibilities of fabricating oxide nanostructures with varying Al/Si ratio, and the crystallinity of these structures enhances possible applications. The fabricated nanostructures of Al and Si oxides could have great potentials to be used in the fabrication of low power-consuming complementary metal-oxide-semiconductor circuits and in Mn catalysts to enhance the efficiency of oxidation on ethylbenzene to acetophenone in the super-critical carbon dioxide.

Synthesis of crystalline and amorphous, particle-agglomerated 3-D nanostructures of Al and Si oxides by femtosecond laser and the prediction of these particle sizes.

PubMed

Sivayoganathan, Mugunthan; Tan, Bo; Venkatakrishnan, Krishnan

2012-11-09

We report a single step technique of synthesizing particle-agglomerated, amorphous 3-D nanostructures of Al and Si oxides on powder-fused aluminosilicate ceramic plates and a simple novel method of wafer-foil ablation to fabricate crystalline nanostructures of Al and Si oxides at ambient conditions. We also propose a particle size prediction mechanism to regulate the size of vapor-condensed agglomerated nanoparticles in these structures. Size characterization studies performed on the agglomerated nanoparticles of fabricated 3-D structures showed that the size distributions vary with the fluence-to-threshold ratio. The variation in laser parameters leads to varying plume temperature, pressure, amount of supersaturation, nucleation rate, and the growth rate of particles in the plume. The novel wafer-foil ablation technique could promote the possibilities of fabricating oxide nanostructures with varying Al/Si ratio, and the crystallinity of these structures enhances possible applications. The fabricated nanostructures of Al and Si oxides could have great potentials to be used in the fabrication of low power-consuming complementary metal-oxide-semiconductor circuits and in Mn catalysts to enhance the efficiency of oxidation on ethylbenzene to acetophenone in the super-critical carbon dioxide.

Synthesis of crystalline and amorphous, particle-agglomerated 3-D nanostructures of Al and Si oxides by femtosecond laser and the prediction of these particle sizes

PubMed Central

2012-01-01

We report a single step technique of synthesizing particle-agglomerated, amorphous 3-D nanostructures of Al and Si oxides on powder-fused aluminosilicate ceramic plates and a simple novel method of wafer-foil ablation to fabricate crystalline nanostructures of Al and Si oxides at ambient conditions. We also propose a particle size prediction mechanism to regulate the size of vapor-condensed agglomerated nanoparticles in these structures. Size characterization studies performed on the agglomerated nanoparticles of fabricated 3-D structures showed that the size distributions vary with the fluence-to-threshold ratio. The variation in laser parameters leads to varying plume temperature, pressure, amount of supersaturation, nucleation rate, and the growth rate of particles in the plume. The novel wafer-foil ablation technique could promote the possibilities of fabricating oxide nanostructures with varying Al/Si ratio, and the crystallinity of these structures enhances possible applications. The fabricated nanostructures of Al and Si oxides could have great potentials to be used in the fabrication of low power-consuming complementary metal-oxide-semiconductor circuits and in Mn catalysts to enhance the efficiency of oxidation on ethylbenzene to acetophenone in the super-critical carbon dioxide. PMID:23140103

Surface damage on polycrystalline β-SiC by xenon ion irradiation at high fluence

NASA Astrophysics Data System (ADS)

Baillet, J.; Gavarini, S.; Millard-Pinard, N.; Garnier, V.; Peaucelle, C.; Jaurand, X.; Duranti, A.; Bernard, C.; Rapegno, R.; Cardinal, S.; Escobar Sawa, L.; De Echave, T.; Lanfant, B.; Leconte, Y.

2018-05-01

Polycrystalline β-silicon carbide (β-SiC) pellets were prepared by Spark Plasma Sintering (SPS). These were implanted at room temperature with 800 keV xenon at ion fluences of 5.1015 and 1.1017 cm-2. Microstructural modifications were studied by electronic microscopy (TEM and SEM) and xenon profiles were determined by Rutherford Backscattering Spectroscopy (RBS). A complete amorphization of the implanted area associated with a significant oxidation is observed for the highest fluence. Large xenon bubbles formed in the oxide phase are responsible of surface swelling. No significant gas release has been measured up to 1017 at.cm-2. A model is proposed to explain the different steps of the oxidation process and xenon bubbles formation as a function of ion fluence.

Ion-Beam-Induced Atomic Mixing in Ge, Si, and SiGe, Studied by Means of Isotope Multilayer Structures

PubMed Central

Radek, Manuel; Liedke, Bartosz; Schmidt, Bernd; Voelskow, Matthias; Bischoff, Lothar; Lundsgaard Hansen, John; Nylandsted Larsen, Arne; Bougeard, Dominique; Böttger, Roman; Prucnal, Slawomir; Posselt, Matthias; Bracht, Hartmut

2017-01-01

Crystalline and preamorphized isotope multilayers are utilized to investigate the dependence of ion beam mixing in silicon (Si), germanium (Ge), and silicon germanium (SiGe) on the atomic structure of the sample, temperature, ion flux, and electrical doping by the implanted ions. The magnitude of mixing is determined by secondary ion mass spectrometry. Rutherford backscattering spectrometry in channeling geometry, Raman spectroscopy, and transmission electron microscopy provide information about the structural state after ion irradiation. Different temperature regimes with characteristic mixing properties are identified. A disparity in atomic mixing of Si and Ge becomes evident while SiGe shows an intermediate behavior. Overall, atomic mixing increases with temperature, and it is stronger in the amorphous than in the crystalline state. Ion-beam-induced mixing in Ge shows no dependence on doping by the implanted ions. In contrast, a doping effect is found in Si at higher temperature. Molecular dynamics simulations clearly show that ion beam mixing in Ge is mainly determined by the thermal spike mechanism. In the case of Si thermal spike, mixing prevails at low temperature whereas ion beam-induced enhanced self-diffusion dominates the atomic mixing at high temperature. The latter process is attributed to highly mobile Si di-interstitials formed under irradiation and during damage annealing. PMID:28773172

Ion-Beam-Induced Atomic Mixing in Ge, Si, and SiGe, Studied by Means of Isotope Multilayer Structures.

PubMed

Radek, Manuel; Liedke, Bartosz; Schmidt, Bernd; Voelskow, Matthias; Bischoff, Lothar; Hansen, John Lundsgaard; Larsen, Arne Nylandsted; Bougeard, Dominique; Böttger, Roman; Prucnal, Slawomir; Posselt, Matthias; Bracht, Hartmut

2017-07-17

Crystalline and preamorphized isotope multilayers are utilized to investigate the dependence of ion beam mixing in silicon (Si), germanium (Ge), and silicon germanium (SiGe) on the atomic structure of the sample, temperature, ion flux, and electrical doping by the implanted ions. The magnitude of mixing is determined by secondary ion mass spectrometry. Rutherford backscattering spectrometry in channeling geometry, Raman spectroscopy, and transmission electron microscopy provide information about the structural state after ion irradiation. Different temperature regimes with characteristic mixing properties are identified. A disparity in atomic mixing of Si and Ge becomes evident while SiGe shows an intermediate behavior. Overall, atomic mixing increases with temperature, and it is stronger in the amorphous than in the crystalline state. Ion-beam-induced mixing in Ge shows no dependence on doping by the implanted ions. In contrast, a doping effect is found in Si at higher temperature. Molecular dynamics simulations clearly show that ion beam mixing in Ge is mainly determined by the thermal spike mechanism. In the case of Si thermal spike, mixing prevails at low temperature whereas ion beam-induced enhanced self-diffusion dominates the atomic mixing at high temperature. The latter process is attributed to highly mobile Si di-interstitials formed under irradiation and during damage annealing.

Improvement on electrical conductivity and electron field emission properties of Au-ion implanted ultrananocrystalline diamond films by using Au-Si eutectic substrates

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

Sankaran, K. J.; Institute for Materials Research; Sundaravel, B.

2015-08-28

In the present work, Au-Si eutectic layer was used to enhance the electrical conductivity/electron field emission (EFE) properties of Au-ion implanted ultrananocrystalline diamond (Au-UNCD) films grown on Si substrates. The electrical conductivity was improved to a value of 230 (Ω cm){sup −1}, and the EFE properties was enhanced reporting a low turn-on field of 2.1 V/μm with high EFE current density of 5.3 mA/cm{sup 2} (at an applied field of 4.9 V/μm) for the Au-UNCD films. The formation of SiC phase circumvents the formation of amorphous carbon prior to the nucleation of diamond on Si substrates. Consequently, the electron transport efficiency of themore » UNCD-to-Si interface increases, thereby improving the conductivity as well as the EFE properties. Moreover, the salient feature of these processes is that the sputtering deposition of Au-coating for preparing the Au-Si interlayer, the microwave plasma enhanced chemical vapor deposition process for growing the UNCD films, and the Au-ion implantation process for inducing the nanographitic phases are standard thin film preparation techniques, which are simple, robust, and easily scalable. The availability of these highly conducting UNCD films with superior EFE characteristics may open up a pathway for the development of high-definition flat panel displays and plasma devices.« less

Observation of silicon self-diffusion enhanced by the strain originated from end-of-range defects using isotope multilayers

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

Isoda, Taiga; Uematsu, Masashi; Itoh, Kohei M., E-mail: kitoh@appi.keio.ac.jp

2015-09-21

Si self-diffusion in the presence of end-of-range (EOR) defects is investigated using {sup nat}Si/{sup 28}Si isotope multilayers. The isotope multilayers were amorphized by Ge ion implantation, and then annealed at 800–950 °C. The behavior of Si self-interstitials is investigated through the {sup 30}Si self-diffusion. The experimental {sup 30}Si profiles show further enhancement of Si self-diffusion at the EOR defect region, in addition to the transient enhanced diffusion via excess Si self-interstitials by EOR defects. To explain this additional enhanced diffusion, we propose a model which takes into account enhanced diffusion by tensile strain originated from EOR defects. The calculation results basedmore » on this model have well reproduced the experimental {sup 30}Si profiles.« less

Robustness up to 400°C of the passivation of c-Si by p-type a-Si:H thanks to ion implantation

NASA Astrophysics Data System (ADS)

Defresne, A.; Plantevin, O.; Roca i Cabarrocas, Pere

2016-12-01

Heterojunction solar cells based on crystalline silicon (c-Si) passivated by hydrogenated amorphous silicon (a-Si:H) thin films are one of the most promising architectures for high energy conversion efficiency. Indeed, a-Si:H thin films can passivate both p-type and n-type wafers and can be deposited at low temperature (<200°C) using PECVD. However, such passivation layers, in particular p-type a-Si:H, show a dramatic degradation in passivation quality above 200°C. Yet, annealing at 300 - 400°C the TCO layer and metallic contacts is highly desirable to reduce the contact resistance as well as the TCO optical absorption. In this work, we show that as expected, ion implantation (5 - 30 keV) introduces defects at the c-Si/a-Si:H interface which strongly degrade the effective lifetime, down to a few micro-seconds. However, the passivation quality can be restored and lifetime values can be improved up to 2 ms over the initial value with annealing. We show here that effective lifetimes above 1 ms can be maintained up to 380°C, opening up the possibility for higher process temperatures in silicon heterojunction device fabrication.

Enhanced Cycleability of Amorphous MnO2 by Covering on α-MnO2 Needles in an Electrochemical Capacitor

PubMed Central

Liu, Quanbing; Yang, Juan; Wang, Hui; Pollet, Bruno G.; Wang, Rongfang

2017-01-01

An allomorph MnO2@MnO2 core-shell nanostructure was developed via a two-step aqueous reaction method. The data analysis of Scanning Electron Microscopy, Transmission Electron Microscopy, X-Ray Diffraction and N2 adsorption-desorption isotherms experiments indicated that this unique architecture consisted of a porous layer of amorphous-MnO2 nano-sheets which were well grown onto the surface of α-MnO2 nano-needles. Cyclic voltammetry experiments revealed that the double-layer charging and Faradaic pseudo-capacity of the MnO2@MnO2 capacitor electrode contributed to a specific capacitance of 150.3 F·g−1 at a current density of 0.1 A·g−1. Long cycle life experiments on the as-prepared MnO2@MnO2 sample showed nearly a 99.3% retention after 5000 cycles at a current density of 2 A·g−1. This retention value was found to be significantly higher than those reported for amorphous MnO2-based capacitor electrodes. It was also found that the remarkable cycleability of the MnO2@MnO2 was due to the supporting role of α-MnO2 nano-needle core and the outer amorphous MnO2 layer. PMID:28837099

Low frequency sonochemical synthesis of nanoporous amorphous manganese dioxide (MnO2) and adsorption of remazol reactive dye

NASA Astrophysics Data System (ADS)

Hasan, Siti Zubaidah; Yusop, Muhammad Rahimi; Othman, Mohamed Rozali

2015-09-01

Nanoporous amorphous-MnO2 was synthesized by sonochemical process (sonication) on the solid manganese (II) acetate tetrahydrate (Mn(CH3COO)2.4H2O) in 0.1 M KMnO4. The product was characterized by X-ray diffraction (XRD), morphology of the material was scanned by Field Emission Scanning Electron Microscopy (FE-SEM) and absorptions of MnO2 bonding was characterized by Fourier Transform Infra-Red Spectrometer (FT-IR). Remazol reactive dye or Red 3BS, was used in the adsorption study using nanoporous amorphous-MnO2. In batch experiment, 10 ppm of Remazol reactive dye was used and experiment was carried out at room temperature. Adsorption of Remazol dye on 0.2g synthesized nanoporous amorphous-MnO2 showed 99 - 100% decolorization.

Nucleation and growth of electrodeposited Mn oxide rods for supercapacitor electrodes

NASA Astrophysics Data System (ADS)

Clark, Michael; Ivey, Douglas G.

2015-09-01

The nucleation and growth of electrodeposited Mn oxide rods has been investigated by preparing deposits on Au coated Si at varying deposition times between 0.5 s and 10 min. The deposits were investigated using high resolution scanning and transmission electron microscopy. A model for the nucleation and growth of Mn oxide rods has been proposed. Nucleation begins as thin sheets along Au grain boundaries and triple points. As these nucleation sites are consumed, nucleation spreads across the grains. Nucleation of sheets in close proximity causes agglomeration and the formation of rounded particles. Some of these rounded particles then accelerate in growth, initially in all directions and then primarily in the direction normal to the sample surface. Accelerated growth normal to the sample surface leads to the formation of rods. As rods grow, the growth of other particles accelerates and they become rods themselves. Eventually the entire sample surface is covered with rods 15-20 μm long and about 2 μm wide. The sheet-like morphology of the deposits is retained at all stages of deposition. Electron diffraction analysis of 3 s and 6 s deposits shows that the sheets are initially amorphous and then begin to crystallize into a cubic spinel Mn3O4 crystal structure. High resolution imaging of the 6 s sample shows small crystalline regions (˜5 nm in size) within an amorphous matrix.

Water-soluble thin film transistors and circuits based on amorphous indium-gallium-zinc oxide.

PubMed

Jin, Sung Hun; Kang, Seung-Kyun; Cho, In-Tak; Han, Sang Youn; Chung, Ha Uk; Lee, Dong Joon; Shin, Jongmin; Baek, Geun Woo; Kim, Tae-il; Lee, Jong-Ho; Rogers, John A

2015-04-22

This paper presents device designs, circuit demonstrations, and dissolution kinetics for amorphous indium-gallium-zinc oxide (a-IGZO) thin film transistors (TFTs) comprised completely of water-soluble materials, including SiNx, SiOx, molybdenum, and poly(vinyl alcohol) (PVA). Collections of these types of physically transient a-IGZO TFTs and 5-stage ring oscillators (ROs), constructed with them, show field effect mobilities (∼10 cm2/Vs), on/off ratios (∼2×10(6)), subthreshold slopes (∼220 mV/dec), Ohmic contact properties, and oscillation frequency of 5.67 kHz at supply voltages of 19 V, all comparable to otherwise similar devices constructed in conventional ways with standard, nontransient materials. Studies of dissolution kinetics for a-IGZO films in deionized water, bovine serum, and phosphate buffer saline solution provide data of relevance for the potential use of these materials and this technology in temporary biomedical implants.

Low frequency sonochemical synthesis of nanoporous amorphous manganese dioxide (MnO{sub 2}) and adsorption of remazol reactive dye

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

Hasan, Siti Zubaidah; Yusop, Muhammad Rahimi; Othman, Mohamed Rozali, E-mail: rozali@ukm.edu.my

2015-09-25

Nanoporous amorphous-MnO{sub 2} was synthesized by sonochemical process (sonication) on the solid manganese (II) acetate tetrahydrate (Mn(CH{sub 3}COO){sub 2}.4H{sub 2}O) in 0.1 M KMnO{sub 4}. The product was characterized by X-ray diffraction (XRD), morphology of the material was scanned by Field Emission Scanning Electron Microscopy (FE-SEM) and absorptions of MnO{sub 2} bonding was characterized by Fourier Transform Infra-Red Spectrometer (FT-IR). Remazol reactive dye or Red 3BS, was used in the adsorption study using nanoporous amorphous-MnO{sub 2}. In batch experiment, 10 ppm of Remazol reactive dye was used and experiment was carried out at room temperature. Adsorption of Remazol dye onmore » 0.2g synthesized nanoporous amorphous-MnO{sub 2} showed 99 – 100% decolorization.« less

He-irradiation effects on glass-ceramics for joining of SiC-based materials

NASA Astrophysics Data System (ADS)

Gozzelino, L.; Casalegno, V.; Ghigo, G.; Moskalewicz, T.; Czyrska-Filemonowicz, A.; Ferraris, M.

2016-04-01

CaO-Al2O3 (CA) and SiO2-Al2O3-Y2O3 (SAY) glass-ceramics are promising candidates for SiC/SiC indirect joints. In view of their use in locations where high radiation level is expected (i.e. fusion plants) it is important to investigate how radiation-induced damage can modify the material microstructure. To this aim, pellets of both types were irradiated with 5.5 MeV 4He+ ions at an average temperature of 75 °C up to a fluence of almost 2.3·1018 cm-2. This produces a displacement defect density that increases with depth and reaches a value of about 40 displacements per atom in the ion implantation region, where the He-gas reaches a concentration of several thousands of atomic parts per million. X-ray diffractometry and scanning electron microscopy showed no change in the microstructure and in the morphology of the pellet surface. Moreover, a transmission electron microscopy investigation on cross-section lamellas revealed the occurrence of structural defects and agglomerates of He-bubbles in the implantation region for the CA sample and a more homogeneous He-bubble distribution in the SAY pellet, even outside the implantation layer. In addition, no amorphization was found in both samples, even in correspondence to the He implantation zone. The radiation damage induced only occasional micro-cracks, mainly located at grain boundaries (CA) or within the grains (SAY).

Excess oxygen limited diffusion and precipitation of iron in amorphous silicon dioxide

NASA Astrophysics Data System (ADS)

Leveneur, J.; Langlois, M.; Kennedy, J.; Metson, James B.

2017-10-01

In micro- and nano- electronic device fabrication, and particularly 3D designs, the diffusion of a metal into sublayers during annealing needs to be minimized as it is usually detrimental to device performance. Diffusion also causes the formation and growth of nanoprecipitates in solid matrices. In this paper, the diffusion behavior of low energy, low fluence, ion implanted iron into a thermally grown silicon oxide layer on silicon is investigated. Different ion beam analysis and imaging techniques were used. Magnetization measurements were also undertaken to provide evidence of nanocrystalline ordering. While standard vacuum furnace annealing and electron beam annealing lead to fast diffusion of the implanted species towards the Si/SiO2 interface, we show that furnace annealing in an oxygen rich atmosphere prevents the diffusion of iron that, in turn, limits the growth of the nanoparticles. The diffusion and particle growth is also greatly reduced when oxygen atoms are implanted in the SiO2 prior to Fe implantation, effectively acting as a diffusion barrier. The excess oxygen is hypothesized to trap Fe atoms and reduce their mean free path during the diffusion. Monte-Carlo simulations of the diffusion process which consider the random walk of Fe, Fick's diffusion of O atoms, Fe precipitation, and desorption of the SiO2 layer under the electron beam annealing were performed. Simulation results for the three preparation conditions are found in good agreement with the experimental data.

Optical, mechanical and surface properties of amorphous carbonaceous thin films obtained by plasma enhanced chemical vapor deposition and plasma immersion ion implantation and deposition

NASA Astrophysics Data System (ADS)

Turri, Rafael G.; Santos, Ricardo M.; Rangel, Elidiane C.; da Cruz, Nilson C.; Bortoleto, José R. R.; Dias da Silva, José H.; Antonio, César Augusto; Durrant, Steven F.

2013-09-01

Diverse amorphous hydrogenated carbon-based films (a-C:H, a-C:H:F, a-C:H:N, a-C:H:Cl and a-C:H:Si:O) were obtained by radiofrequency plasma enhanced chemical vapor deposition (PECVD) and plasma immersion ion implantation and deposition (PIIID). The same precursors were used in the production of each pair of each type of film, such as a-C:H, using both PECVD and PIIID. Optical properties, namely the refractive index, n, absorption coefficient, α, and optical gap, ETauc, of these films were obtained via transmission spectra in the ultraviolet-visible near-infrared range (wavelengths from 300 to 3300 nm). Film hardness, elastic modulus and stiffness were obtained as a function of depth using nano-indentation. Surface energy values were calculated from liquid drop contact angle data. Film roughness and morphology were assessed using atomic force microscopy (AFM). The PIIID films were usually thinner and possessed higher refractive indices than the PECVD films. Determined refractive indices are consistent with literature values for similar types of films. Values of ETauc were increased in the PIIID films compared to the PECVD films. An exception was the a-C:H:Si:O films, for which that obtained by PIIID was thicker and exhibited a decreased ETauc. The mechanical properties - hardness, elastic modulus and stiffness - of films produced by PECVD and PIIID generally present small differences. An interesting effect is the increase in the hardness of a-C:H:Cl films from 1.0 to 3.0 GPa when ion implantation is employed. Surface energy correlates well with surface roughness. The implanted films are usually smoother than those obtained by PECVD.

Area laser crystallized LTPS TFTs with implanted contacts for active matrix OLED displays

NASA Astrophysics Data System (ADS)

Persidis, Efstathios; Baur, Holger; Pieralisi, Fabio; Schalberger, Patrick; Fruehauf, Norbert

2008-03-01

We have developed a four mask low temperature poly-Si (LTPS) TFT process for p- and n-channel devices. Our PECVD deposited amorphous silicon is recrystallized to polycrystalline silicon with single area excimer laser crystallization while formation of drain and source is carried out with self aligned ion beam implantation. We have investigated implantation parameters, suitability of various metallizations as well as laser activation and annealing procedures. To prove the potential capability of our devices, which are suitable for conventional and inverted OLEDs alike, we have produced several functional active matrix backplanes implementing different pixel circuits. Our active matrix backplane process has been customized to drive small molecules as well as polymers, regardless if top or bottom emitting.

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

Girsova, S. L., E-mail: girs@ispms.tsc.ru; Poletika, T. M., E-mail: poletm@ispms.tsc.ru; Meisner, S. N., E-mail: msn@ispms.tsc.ru

The study was carried on for the single NiTi crystals subjected to the Si-ion beam implantation. Using the transmission electron microscopy technique (TEM), the surface layer structure [111]{sub B2} was examined for the treated material. The modified near-surface sublayers were found to have different composition. Thus the uppermost sublayer contained mostly oxides; the lower-lying modified sublayer material was in an amorphous state and the thin underlying sublayer had a defect structure.

Extremely hard amorphous-crystalline hybrid steel surface produced by deformation induced cementite amorphization

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

Guo, Wei; Meng, Yifei; Zhang, Xie

Amorphous and nanograined (NG) steels are two categories of strong steels. However, over the past decade, their application has been hindered by their limited plasticity, the addition of expensive alloying elements, and processing challenges associated with producing bulk materials. Here in this work, we report that the surface of a carburized Fe-Mn-Si martensitic steel with extremely low elemental alloying additions can be economically fabricated into an amorphous-nanocrystalline hybrid structure. Atom probe tomography and nanobeam diffraction of a hard turned steel surface together with molecular dynamics (MD) simulations reveal that the original cementite surface structure experiences a size-dependent amorphization and phasemore » transformation during heavy plastic deformation. MD simulations further show that the martensite-cementite interface serves as a nucleation site for cementite amorphization, and that cementite can become disordered if further strained when the cementite particles are relatively small. These graded structures exhibit a surface hardness of ~16.2 GPa, which exceeds the value of ~8.8 GPa for the original nanocrystalline martensitic steel and most nanocrystalline steels reported before. Finally, this practical and cost-efficient approach for producing a hard surface with retained bulk ductility and toughness can provide expanded opportunities for producing an amorphous-crystalline hybrid structure in steels and other alloy systems.« less

Extremely hard amorphous-crystalline hybrid steel surface produced by deformation induced cementite amorphization

DOE PAGES

Guo, Wei; Meng, Yifei; Zhang, Xie; ...

2018-04-11

Amorphous and nanograined (NG) steels are two categories of strong steels. However, over the past decade, their application has been hindered by their limited plasticity, the addition of expensive alloying elements, and processing challenges associated with producing bulk materials. Here in this work, we report that the surface of a carburized Fe-Mn-Si martensitic steel with extremely low elemental alloying additions can be economically fabricated into an amorphous-nanocrystalline hybrid structure. Atom probe tomography and nanobeam diffraction of a hard turned steel surface together with molecular dynamics (MD) simulations reveal that the original cementite surface structure experiences a size-dependent amorphization and phasemore » transformation during heavy plastic deformation. MD simulations further show that the martensite-cementite interface serves as a nucleation site for cementite amorphization, and that cementite can become disordered if further strained when the cementite particles are relatively small. These graded structures exhibit a surface hardness of ~16.2 GPa, which exceeds the value of ~8.8 GPa for the original nanocrystalline martensitic steel and most nanocrystalline steels reported before. Finally, this practical and cost-efficient approach for producing a hard surface with retained bulk ductility and toughness can provide expanded opportunities for producing an amorphous-crystalline hybrid structure in steels and other alloy systems.« less

Phase composition and in vitro bioactivity of porous implants made of bioactive glass S53P4.

PubMed

Fagerlund, S; Massera, J; Moritz, N; Hupa, L; Hupa, M

2012-07-01

This work studied the influence of sintering temperature on the phase composition, compression strength and in vitro properties of implants made of bioactive glass S53P4. The implants were sintered within the temperature range 600-1000°C. Over the whole temperature range studied, consolidation took place mainly via viscous flow sintering, even though there was partial surface crystallization. The mechanical strength of the implants was low but increased with the sintering temperature, from 0.7 MPa at 635°C to 10 MPa at 1000°C. Changes in the composition of simulated body fluid (SBF), the immersion solution, were evaluated by pH measurements and ion analysis using inductively coupled plasma optical emission spectrometry. The development of a calcium phosphate layer on the implant surfaces was verified using scanning electron microscopy-electron-dispersive X-ray analysis. When immersed in SBF, a calcium phosphate layer formed on all the samples, but the structure of this layer was affected by the surface crystalline phases. Hydroxyapatite formed more readily on amorphous and partially crystalline implants containing both primary Na(2)O·CaO·2SiO(2) and secondary Na(2)Ca(4)(PO(4))(2)SiO(4) crystals than on implants containing only primary crystals. Copyright © 2012 Acta Materialia Inc. Published by Elsevier Ltd. All rights reserved.

A hierarchical nanostructure consisting of amorphous MnO 2, Mn 3O 4 nanocrystallites, and single-crystalline MnOOH nanowires for supercapacitors

NASA Astrophysics Data System (ADS)

Hu, Chi-Chang; Hung, Ching-Yun; Chang, Kuo-Hsin; Yang, Yi-Lin

In this communication, a porous hierarchical nanostructure consisting of amorphous MnO 2 (a-MnO 2), Mn 3O 4 nanocrystals, and single-crystalline MnOOH nanowires is designed for the supercapacitor application, which is prepared by a simple two-step electrochemical deposition process. Because of the gradual co-transformation of Mn 3O 4 nanocrystals and a-MnO 2 nanorods into an amorphous manganese oxide, the cycle stability of a-MnO 2 is obviously enhanced by adding Mn 3O 4. This unique ternary oxide nanocomposite with 100-cycle CV activation exhibits excellent capacitive performances, i.e., excellent reversibility, high specific capacitances (470 F g -1 in CaCl 2), high power property, and outstanding cycle stability. The highly porous microstructures of this composite before and after the 10,000-cycle CV test are examined by means of scanning electron microscopy (SEM) and transmission electron microscopy (TEM).

Alternating current magnetic susceptibility and heat dissipation by Mn1-xZnxFe2O4 nanoparticles for hyperthermia treatment

NASA Astrophysics Data System (ADS)

Kondo, T.; Mori, K.; Hachisu, M.; Yamazaki, T.; Okamoto, D.; Watanabe, M.; Gonda, K.; Tada, H.; Hamada, Y.; Takano, M.; Ohuchi, N.; Ichiyanagi, Y.

2015-05-01

Mn-Zn ferrite, Mn1-xZnxFe2O4 nanoparticles encapsulated in amorphous SiO2 were prepared using our original wet chemical method. X-ray diffraction patterns confirmed that the diameters of these particles were within 7-30 nm. Magnetization measurements for various sample compositions revealed that the saturation magnetization (Ms) of 7 nm particles was maximum for the x = 0.2 sample. AC magnetic susceptibility measurements were performed for Mn0.8Zn0.2Fe2O4 (x = 0.2) samples with 13-30 nm particles. The peak of the imaginary part of the magnetic susceptibility χ″ shifted to higher temperatures as the particle size increased. An AC field was found to cause the increase in temperature, with the 18 nm particles exhibiting the highest temperature increase, as expected. In addition, in vitro experiments were carried out to study the hyperthermia effects of Mn1-xZnxFe2O4 (x = 0.2, 18 nm) particles on human cancer cells.

Palladium silicide formation under the influence of nitrogen and oxygen impurities

NASA Technical Reports Server (NTRS)

Ho, K. T.; Lien, C.-D.; Nicolet, M.-A.

1985-01-01

The effect of impurities on the growth of the Pd2Si layer upon thermal annealing of a Pd film on 100 line-type and amorphous Si substrates is investigated. Nitrogen and oxygen impurities are introduced into either Pd or Si which are subsequently annealed to form Pd2Si. The complementary techniques of Rutherford backscattering spectrometry, and N-15(p, alpha)C-12 or O-18(p, alpha)N-15 nuclear reaction, are used to investigate the behavior of nitrogen or oxygen and the alterations each creates during silicide formation. Both nitrogen and oxygen retard the silicide growth rate if initially present in Si. When they are initially in Pd, there is no significant retardation; instead, an interesting snow-plowing effect of N or O by the reaction interface of Pd2Si is observed. By using N implanted into Si as a marker, Pd and Si appear to trade roles as the moving species when the silicide front reaches the nitrogen-rich region.

Atomistic Texture of Amorphous Manganese Oxides for Electrochemical Water Splitting Revealed by Ab Initio Calculations Combined with X-ray Spectroscopy.

PubMed

Mattioli, Giuseppe; Zaharieva, Ivelina; Dau, Holger; Guidoni, Leonardo

2015-08-19

Amorphous transition-metal (hydr)oxides are considered as the most promising catalysts that promote the oxidation of water to molecular oxygen, protons, and "energized" electrons, and, in turn, as fundamental parts of "artificial leaves" that can be exploited for large scale generation of chemical fuels (e.g., hydrogen) directly from sunlight. We present here a joint theoretical-experimental investigation of electrodeposited amorphous manganese oxides with different catalytic activities toward water oxidation (MnCats). Combining the information content of X-ray absorption fine structure (XAFS) measurements with the predictive power of ab initio calculations based on density functional theory, we have been able to identify the essential structural and electronic properties of MnCats. We have elucidated (i) the localization and structural connection of Mn(II), Mn(III), and Mn(IV) ions in such amorphous oxides and (ii) the distribution of protons at the MnCat/water interface. Our calculations result in realistic 3D models of the MnCat atomistic texture, formed by the interconnection of small planar Mn-oxo sheets cross-linked through different kinds of defective Mn atoms, isolated or arranged in closed cubane-like units. Essential for the catalytic activity is the presence of undercoordinated Mn(III)O5 units located at the boundary of the amorphous network, where they are ready to act as hole traps that trigger the oxidation of neighboring water molecules when the catalyst is exposed to an external positive potential. The present validation of a sound 3D model of MnCat improves the accuracy of XAFS fits and opens the way for the development of mechanistic schemes of its functioning beyond a speculative level.

Dy–Mn–Si as a representative of family of ‘Dy–Transition Metal–Si’ systems: Its isothermal sections, empirical rProd. Type: FTPules and new rare-earth manganese silicides

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

Morozkin, A.V., E-mail: morozkin@general.chem.msu.ru; Knotko, A.V.; Yapaskurt, V.O.

2013-10-15

X-ray and microprobe analyses were employed for the investigation of Dy–Mn–Si system at 870/1070/1170 K. The Dy–Mn–Si system, contains the known DyMn{sub 2}Si{sub 2}, DyMnSi and Dy{sub 2}Mn{sub 3}Si{sub 5} compounds and DyMn{sub 4}Si{sub 2}, Dy{sub 2}MnSi{sub 2} and Dy{sub 3}Mn{sub 2}Si{sub 3} were new compounds identified first time and their structure are of the type TmCu{sub 4}Sb{sub 2}, Sc{sub 2}CoSi{sub 2} and Hf{sub 3}Ni{sub 2}Si{sub 3} respectively. The quasi-binary solid solutions were detected at 870/1070/1170 K: the ThMn{sub 12}-type Dy{sub 8}Mn{sub 87}Si{sub 5}, Th{sub 6}Mn{sub 23}-type Dy{sub 23}Mn{sub 72}Si{sub 5}, MgCu{sub 2}-type Dy{sub 33}Mn{sub 58}Si{sub 9} and AlB{sub 2}-typemore » Dy{sub 38}Mn{sub 2}Si{sub 58}. The other binary compounds of the Dy–Mn–Si system do not show any visible solubility. New phases R{sub 2}MnSi{sub 2} and R{sub 3}Mn{sub 2}Si{sub 3} (R=Gd, Tb, Ho–Tm) were found out and their structure of the type Sc{sub 2}CoSi{sub 2} and Hf{sub 3}Ni{sub 2}Si{sub 3} respectively. The specific features of ‘Dy–Transition Metal–Si’ systems were discussed. - Graphical abstract: The isothermal section of Dy–Mn–Si contains the known DyMn{sub 2}Si{sub 2}, DyMnSi, Dy{sub 2}Mn{sub 3}Si{sub 5} and new TmCu{sub 4}Sb{sub 2}-type DyMn{sub 4}Si{sub 2}, Sc{sub 2}CoSi{sub 2}-type Dy{sub 2}MnSi{sub 2} and Hf{sub 3}Ni{sub 2}Si{sub 3}-type Dy{sub 3}Mn{sub 2}Si{sub 3} ternary compounds. The ternary solid solution based on the binary compounds of the Dy–Mn and Dy–Si systems: the ThMn{sub 12}-type Dy{sub 8}Mn{sub 87}Si{sub 5}, Th{sub 6}Mn{sub 23}-type Dy{sub 23}Mn{sub 72}Si{sub 5}, MgCu{sub 2}-type Dy{sub 33}Mn{sub 58}Si{sub 9} and AlB{sub 2}-type Dy{sub 38}Mn{sub 2}Si{sub 58}. The other binary compounds of the Dy–Mn–Si system do not show any visible solubility. New Sc{sub 2}CoSi{sub 2}-type R{sub 2}MnSi{sub 2} and Hf{sub 3}Ni{sub 2}Si{sub 3}-type R{sub 3}Mn{sub 2}Si{sub 3} phases were discovered for R=Gd, Tb, Ho–Tm. Display Omitted - Highlights: • The Dy–Mn–Si section contains three known and three new ternary compounds (phases). • New phase the TmCu{sub 4}Sb{sub 2}-type DyMn{sub 4}Si{sub 2} compound. • New Sc{sub 2}CoSi{sub 2}-type R{sub 2}MnSi{sub 2} and Hf{sub 3}Ni{sub 2}Si{sub 3}-type R{sub 3}Mn{sub 2}Si{sub 3} were detected for R=Gd–Tm. • Dy–Mn–Si supplements the ‘Dy–3d metal–Si’ series and leads to the ‘RT{sub m}X{sub n}’ row's rule.« less

Complementary study of the internal porous silicon layers formed under high-dose implantation of helium ions

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

Lomov, A. A., E-mail: lomov@ftian.ru; Myakon’kikh, A. V.; Chesnokov, Yu. M.

The surface layers of Si(001) substrates subjected to plasma-immersion implantation of helium ions with an energy of 2–5 keV and a dose of 5 × 10{sup 17} cm{sup –2} have been investigated using high-resolution X-ray reflectivity, Rutherford backscattering, and transmission electron microscopy. The electron density depth profile in the surface layer formed by helium ions is obtained, and its elemental and phase compositions are determined. This layer is found to have a complex structure and consist of an upper amorphous sublayer and a layer with a porosity of 30–35% beneath. It is shown that the porous layer has the sharpestmore » boundaries at a lower energy of implantable ions.« less

Amorphous surface layers in Ti-implanted Fe

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

Knapp, J.A.; Follstaedt, D.M.; Picraux, S.T.

1979-01-01

Implanting Ti into high-purity Fe results in an amorphous surface layer which is composed of not only Fe and Ti, but also C. Implantations were carried out at room temperature over the energy range 90 to 190 keV and fluence range 1 to 2 x 10/sup 16/ at/cm/sup 2/. The Ti-implanted Fe system has been characterized using transmission electron microscopy (TEM), ion backscattering and channeling analysis, and (d,p) nuclear reaction analysis. The amorphous layer was observed to form at the surface and grow inward with increasing Ti fluence. For an implant of 1 x 10/sup 17/ Ti/cm/sup 2/ at 180more » keV the layer thickness was 150 A, while the measured range of the implanted Ti was approx. 550 A. This difference is due to the incorporation of C into the amorphous alloy by C being deposited on the surface during implantation and subsequently diffusing into the solid. Our results indicate that C is an essential constituent of the amorphous phase for Ti concentrations less than or equal to 10 at. %. For the 1 x 10/sup 17/ Ti/cm/sup 2/ implant, the concentration of C in the amorphous phase was approx. 25 at. %, while that of Ti was only approx. 3 at. %. A higher fluence implant of 2 x 10/sup 17/ Ti/cm/sup 2/ produced an amorphous layer with a lower C concentration of approx. 10 at. % and a Ti concentration of approx. 20 at. %.« less

Structural evolution in Ar+ implanted Si-rich silicon oxide

NASA Astrophysics Data System (ADS)

Brusa, R. S.; Karwasz, G. P.; Mariotto, G.; Zecca, A.; Ferragut, R.; Folegati, P.; Dupasquier, A.; Ottaviani, G.; Tonini, R.

2003-12-01

Silicon-rich silicon oxide films were deposited by plasma-enhanced chemical vapor deposition. Energy was released into the film by ion bombardment, with the aim of promoting formation of Si nanoclusters and reordering the oxide matrix. The effect of the initial stoichiometry, as well as the evolution of the oxide films due to the ion bombardment and to subsequent thermal treatments, has been studied by depth-resolved positron annihilation Doppler spectroscopy, Raman scattering and Fourier transform infrared spectroscopy. As-deposited films were found to contain an open volume fraction in the form of subnanometric cavities that are positively correlated with oxygen deficiency. No Si aggregates were observed. The ion bombardment was found to promote the formation of amorphous Si nanoclusters, together with a reduction of the open volume in the matrix and a substantial release of hydrogen. It also leaves electrically active sites in the oxide and produces gas-filled vacancy defects in the substrate, with the concentrations depending on the implantation temperature. Thermal treatment at 500 °C removes charge defects in the oxide, but vacancy defects are not completely annealed even at 1100 °C. In one case, heating at 1100 °C produced cavities of about 0.6 nm in the oxide. Transformation of Si nanoclusters into nanocrystals is observed to occur from 800 °C.

Corrosion resistance and cytocompatibility of biodegradable surgical magnesium alloy coated with hydrogenated amorphous silicon.

PubMed

Xin, Yunchang; Jiang, Jiang; Huo, Kaifu; Tang, Guoyi; Tian, Xiubo; Chu, Paul K

2009-06-01

The fast degradation rates in the physiological environment constitute the main limitation for the applications of surgical magnesium alloys as biodegradable hard-tissue implants. In this work, a stable and dense hydrogenated amorphous silicon coating (a-Si:H) with desirable bioactivity is deposited on AZ91 magnesium alloy using magnetron sputtering deposition. Raman spectroscopy and Fourier transform infrared spectroscopy reveal that the coating is mainly composed of hydrogenated amorphous silicon. The hardness of the coated alloy is enhanced significantly and the coating is quite hydrophilic as well. Potentiodynamic polarization results show that the corrosion resistance of the coated alloy is enhanced dramatically. In addition, the deterioration process of the coating in simulated body fluids is systematically investigated by open circuit potential evolution and electrochemical impedance spectroscopy. The cytocompatibility of the coated Mg is evaluated for the first time using hFOB1.19 cells and favorable biocompatibility is observed. 2008 Wiley Periodicals, Inc.

In situ observation of shear-driven amorphization in silicon crystals.

PubMed

He, Yang; Zhong, Li; Fan, Feifei; Wang, Chongmin; Zhu, Ting; Mao, Scott X

2016-10-01

Amorphous materials are used for both structural and functional applications. An amorphous solid usually forms under driven conditions such as melt quenching, irradiation, shock loading or severe mechanical deformation. Such extreme conditions impose significant challenges on the direct observation of the amorphization process. Various experimental techniques have been used to detect how the amorphous phases form, including synchrotron X-ray diffraction, transmission electron microscopy (TEM) and Raman spectroscopy, but a dynamic, atomistic characterization has remained elusive. Here, by using in situ high-resolution TEM (HRTEM), we show the dynamic amorphization process in silicon nanocrystals during mechanical straining on the atomic scale. We find that shear-driven amorphization occurs in a dominant shear band starting with the diamond-cubic (dc) to diamond-hexagonal (dh) phase transition and then proceeds by dislocation nucleation and accumulation in the newly formed dh-Si phase. This process leads to the formation of an amorphous Si (a-Si) band, embedded with dh-Si nanodomains. The amorphization of dc-Si via an intermediate dh-Si phase is a previously unknown pathway of solid-state amorphization.

Amorphous manganese-calcium oxides as a possible evolutionary origin for the CaMn₄ cluster in photosystem II.

PubMed

Najafpour, Mohammad Mahdi

2011-06-01

In this paper a few calcium-manganese oxides and calcium-manganese minerals are studied as catalysts for water oxidation. The natural mineral marokite is also studied as a catalyst for water oxidation for the first time. Marokite is made up of edge-sharing Mn(3+) in a distorted octahedral environment and eight-coordinate Ca(2+) centered polyhedral layers. The structure is similar to recent models of the oxygen evolving complex in photosystem II. Thus, the oxygen evolving complex in photosystem II does not have an unusual structure and could be synthesized hydrothermally. Also in this paper, oxygen evolution is studied with marokite (CaMn₂O₄), pyrolusite (MnO₂) and compared with hollandite (Ba(0.2)Ca(0.15)K(0.3)Mn(6.9)Al(0.2)Si(0.3)O(16)), hausmannite (Mn₃O₄), Mn₂O₃.H₂O, Ca Mn₃O₆.H₂O, CaMn₄O₈.H₂O, CaMn₂O₄.H₂O and synthetic marokite (CaMn₂O₄). I propose that the origin of the oxygen evolving complex in photosystem II resulted from absorption of calcium and manganese ions that were precipitated together in the archean oceans by protocyanobacteria because of changing pH from ~5 to ~8-10. As reported in this paper, amorphous calcium-manganese oxides with different ratios of manganese and calcium are effective catalysts for water oxidation. The bond types and lengths of the calcium and manganese ions in the calcium-manganese oxides are directly comparable to those in the OEC. This primitive structure of these amorphous calcium-manganese compounds could be changed and modified by environmental groups (amino acids) to form the oxygen evolving complex in photosystem II.

Ion implantation in group III-nitride semiconductors: a tool for doping and defect studies

NASA Astrophysics Data System (ADS)

Zolper, J. C.

1997-06-01

Ion implantation is a flexible process technology for introducing an array of doping or compensating impurities into semiconductors. As the crystal quality of the group III-nitride materials continues to improve, ion implantation is playing an enabling role in exploring new dopant species and device structures. In this paper we review the recent developments in ion implantation processing of these materials with a particular emphasis on how this technology has brought new understanding to this materials system. In particular, the use of ion implantation to characterize impurity luminescence, doping, and compensation in III-nitride materials is reviewed. In addition, we address the nature of implantation induced damage in GaN which demonstrates a very strong resistance to amorphization while at the same time forming damage that is not easily removed by thermal annealing. Finally, we review the coupling of implantation with high temperature rapid thermal annealing to better understand the thermal stability of these materials and the redistribution properties of the common dopant (Si, O, Be, Mg, Ca, and Zn).

Kinetic Investigations of SiMn Slags From Different Mn Sources

NASA Astrophysics Data System (ADS)

Kim, Pyunghwa Peace; Tangstad, Merete

2018-06-01

The kinetics of MnO and SiO2 reduction were investigated for Silicomanganese (SiMn) slags using a Thermogravimetric analysis (TGA) between 1773 K and 1923 K (1500 °C and 1650 °C) under CO atmospheric pressure. The charge materials were based on Assmang ore and HC FeMn Slag. Rate models for MnO and SiO2 reduction were applied to describe the metal-producing rates, as shown by the following equations: r_{MnO} = k_{MnO} × A × ( {a_{MnO} - {a_{Mn} }/{K_{T }}} ) r_{{{SiO}2 }} = k_{SiO2} × A × ( {a_{{{SiO}2 }} - {a_{Si} }/{K_{T }}} ). The results show that the choice of raw materials in the charge considerably affected the reduction rate of MnO and SiO2. The highest reduction rate was found to be from charges using HC FeMn slag. The difference in the driving forces was insignificant among the SiMn slags, and the similar slag viscosities could not explain the different reduction rates. Instead, the difference is attributed to small amounts of sulfur and the amount of iron in the charge. In addition, the rate models were applicable to describe the reduction of MnO and SiO2 in SiMn slags.

Amorphization of nanocrystalline 3C-SiC irradiated with Si+ ions

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

Jiang, Weilin; Wang, H.; Zhang, Yanwen

2010-01-01

Irradiation induced amorphization in nanocrystalline and single crystal 3C-SiC has been studied using 1 MeV Si+ ions under identical irradiation conditions at room temperature and 400 K. The disordering behavior has been characterized using in-situ ion channeling and ex-situ x-ray diffraction methods. The results show that, compared to single crystal 3C-SiC, full amorphization of small 3C-SiC grains (~3.8 nm in size) at room temperature occurs at a slightly lower dose. Grain size decreases with increasing dose until a fully amorphized state is attained. The amorphization dose increases at 400 K relative to room temperature. However, at 400 K, the dosemore » for amorphization for 2.0 nm grains is about a factor of 4 and 8 smaller than for 3.0 nm grains and bulk single crystal 3C-SiC, respectively. The behavior is attributed to the dominance of defect-stimulated interfacial amorphization.« less

Pressure-induced transformations in amorphous silicon: A computational study

NASA Astrophysics Data System (ADS)

Garcez, K. M. S.; Antonelli, A.

2014-02-01

We study the transformations between amorphous phases of Si through molecular simulations using the environment dependent interatomic potential (EDIP) for Si. Our results show that upon pressure, the material undergoes a transformation from the low density amorphous (LDA) Si to the high density amorphous (HDA) Si. This transformation can be reversed by decompressing the material. This process, however, exhibits clear hysteresis, suggesting that the transformation LDA ↔ HDA is first-order like. The HDA phase is predominantly five-fold coordinated, whereas the LDA phase is the normal tetrahedrally bonded amorphous Si. The HDA phase at 400 K and 20 GPa was submitted to an isobaric annealing up to 800 K, resulting in a denser amorphous phase, which is structurally distinct from the HDA phase. Our results also show that the atomic volume and structure of this new amorphous phase are identical to those of the glass obtained by an isobaric quenching of the liquid in equilibrium at 2000 K and 20 GPa down to 400 K. The similarities between our results and those for amorphous ices suggest that this new phase is the very high density amorphous Si.

Metalliferous sediments from Eolo Seamount (Tyrrhenian Sea): Hydrothermal deposition and re-deposition in a zone of oxygen depletion

USGS Publications Warehouse

Dekov, V.M.; Kamenov, George D.; Savelli, C.; Stummeyer, Jens; Thiry, M.; Shanks, Wayne C.; Willingham, A.L.; Boycheva, T.B.; Rochette, P.; Kuzmann, E.; Fortin, D.; Vertes, A.

2009-01-01

A sediment core taken from the south-east slope of the Eolo Seamount is composed of alternating red-brown and light-brown to bluish-grey layers with signs of re-deposition in the middle-upper section. The red-brown layers are Fe-rich metalliferous sediments formed as a result of low-temperature (??? 77????C) hydrothermal discharge, whereas the bluish-grey layers most probably originated from background sedimentation of Al-rich detrital material. The metalliferous layers are composed mainly of Si-rich goethite containing some Al. Co-precipitation of hydrothermally released SiO44- and Fe2+ as amorphous or poorly crystalline Fe-Si-oxyhydroxides explains the high Si concentration in goethite. The elevated Al content of the goethite is fairly unusual, but reflects the extremely high background Al content of the Tyrrhenian seawater due to the high eolian terrigenous flux from the Sahara desert. The Sr and Nd isotope data suggest that the Eolo metalliferous sediments are the product of a 3-component mixture: hydrothermal fluid, seawater, and detrital material (Saharan dust and Aeolian Arc material). The enrichment in Fe, P, As, Mo, Cd, Be, Sb, W, Y, V, depletion in REE and transition elements (Cu, Co, Ni, Zn) and the REE distribution patterns support the low-temperature hydrothermal deposition of the metalliferous layers. The hydrothermal field is located in a seawater layer of relative O2 depletion, which led to a significant fractionation of the hydrothermally emitted Fe and Mn. Fe-oxyhydroxides precipitated immediately around the vents whereas Mn stayed in solution longer and the Mn-oxides precipitated higher up on the seamount slope in seawater with relatively higher O2 levels. High seismic activity led to sediment re-deposition and slumping of the Mn-rich layers down slope and mixing with the Fe-rich layers. ?? 2009 Elsevier B.V. All rights reserved.

Sedimentary mechanisms of a modern banded iron formation on Milos Island, Greece

NASA Astrophysics Data System (ADS)

Fru, Ernest Chi; Kilias, Stephanos; Ivarsson, Magnus; Rattray, Jayne E.; Gkika, Katerina; McDonald, Iain; He, Qian; Broman, Curt

2018-05-01

An early Quaternary shallow submarine hydrothermal iron formation (IF) in the Cape Vani sedimentary basin (CVSB) on Milos Island, Greece, displays banded rhythmicity similar to Precambrian banded iron formation (BIF). Field-wide stratigraphic and biogeochemical reconstructions show two temporal and spatially isolated iron deposits in the CVSB with distinct sedimentological character. Petrographic screening suggests the presence of a photoferrotrophic-like microfossil-rich IF (MFIF), accumulated on a basement consisting of andesites in a ˜ 150 m wide basin in the SW margin of the basin. A banded nonfossiliferous IF (NFIF) sits on top of the Mn-rich sandstones at the transition to the renowned Mn-rich formation, capping the NFIF unit. Geochemical data relate the origin of the NFIF to periodic submarine volcanism and water column oxidation of released Fe(II) in conditions predominated by anoxia, similar to the MFIF. Raman spectroscopy pairs hematite-rich grains in the NFIF with relics of a carbonaceous material carrying an average δ13Corg signature of ˜ -25‰. A similar δ13Corg signature in the MFIF could not be directly coupled to hematite by mineralogy. The NFIF, which postdates large-scale Mn deposition in the CVSB, is composed primarily of amorphous Si (opal-SiO2 ṡ nH2O) while crystalline quartz (SiO2) predominates the MFIF. An intricate interaction between tectonic processes, changing redox, biological activity, and abiotic Si precipitation are proposed to have collectively formed the unmetamorphosed BIF-type deposits in a shallow submarine volcanic center. Despite the differences in Precambrian ocean-atmosphere chemistry and the present geologic time, these formation mechanisms coincide with those believed to have formed Algoma-type BIFs proximal to active seafloor volcanic centers.

Characterization of carbon ion implantation induced graded microstructure and phase transformation in stainless steel

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

Feng, Kai; Wang, Yibo; Li, Zhuguo, E-mail: lizg@sjtu.edu.cn

Austenitic stainless steel 316L is ion implanted by carbon with implantation fluences of 1.2 × 10{sup 17} ions-cm{sup −} {sup 2}, 2.4 × 10{sup 17} ions-cm{sup −} {sup 2}, and 4.8 × 10{sup 17} ions-cm{sup −} {sup 2}. The ion implantation induced graded microstructure and phase transformation in stainless steel is investigated by X-ray diffraction, X-ray photoelectron spectroscopy and high resolution transmission electron microscopy. The corrosion resistance is evaluated by potentiodynamic test. It is found that the initial phase is austenite with a small amount of ferrite. After low fluence carbon ion implantation, an amorphous layer and ferrite phase enrichedmore » region underneath are formed. Nanophase particles precipitate from the amorphous layer due to energy minimization and irradiation at larger ion implantation fluence. The morphology of the precipitated nanophase particles changes from circular to dumbbell-like with increasing implantation fluence. The corrosion resistance of stainless steel is enhanced by the formation of amorphous layer and graphitic solid state carbon after carbon ion implantation. - Highlights: • Carbon implantation leads to phase transformation from austenite to ferrite. • The passive film on SS316L becomes thinner after carbon ion implantation. • An amorphous layer is formed by carbon ion implantation. • Nanophase precipitate from amorphous layer at higher ion implantation fluence. • Corrosion resistance of SS316L is improved by carbon implantation.« less

Amorphous hierarchical porous GeO(x) as high-capacity anodes for Li ion batteries with very long cycling life.

PubMed

Wang, Xiao-Liang; Han, Wei-Qiang; Chen, Haiyan; Bai, Jianming; Tyson, Trevor A; Yu, Xi-Qian; Wang, Xiao-Jian; Yang, Xiao-Qing

2011-12-28

Many researchers have focused in recent years on resolving the crucial problem of capacity fading in Li ion batteries when carbon anodes are replaced by other group-IV elements (Si, Ge, Sn) with much higher capacities. Some progress was achieved by using different nanostructures (mainly carbon coatings), with which the cycle numbers reached 100-200. However, obtaining longer stability via a simple process remains challenging. Here we demonstrate that a nanostructure of amorphous hierarchical porous GeO(x) whose primary particles are ~3.7 nm diameter has a very stable capacity of ~1250 mA h g(-1) for 600 cycles. Furthermore, we show that a full cell coupled with a Li(NiCoMn)(1/3)O(2) cathode exhibits high performance. © 2011 American Chemical Society

Silicon decreases both uptake and root-to-shoot translocation of manganese in rice

PubMed Central

Che, Jing; Yamaji, Naoki; Shao, Ji Feng; Ma, Jian Feng; Shen, Ren Fang

2016-01-01

Silicon (Si) is known to alleviate manganese (Mn) toxicity in a number of plant species; however, the mechanisms responsible for this effect are poorly understood. Here, we investigated the interaction between Si and Mn in rice (Oryza sativa) by using a mutant defective in Si uptake. Silicon alleviated Mn toxicity in the wild-type (WT) rice, but not in the mutant exposed to high Mn. The Mn concentration in the shoots was decreased, but that in the roots was increased by Si in the WT. In contrast, the Mn concentration in the roots and shoots was unaffected by Si in the mutant. Furthermore, Si supply resulted in an increased Mn in the root cell sap, decreased Mn in the xylem sap in the WT, but these effects of Si were not observed in the mutant. A short-term labelling experiment with 54Mn showed that the uptake of Mn was similar between plants with and without Si and between WT and the mutant. However, Si decreased root-to-shoot translocation of Mn in the WT, but not in the mutant. The expression of a Mn transporter gene for uptake, OsNramp5, was unaffected by a short exposure (<1 d) to Si, but down-regulated by relatively long-term exposure to Si in WT. In contrast, the expression of OsNramp5 was unaffected by Si in the mutant. These results indicated that Si-decreased Mn accumulation results from both Si-decreased root-to-shoot translocation of Mn, probably by the formation of Mn-Si complex in root cells, and uptake by down-regulating Mn transporter gene. PMID:26733690

Origin and chemical composition of the amorphous material from the intergrain pores of self-assembled cubic ZnS:Mn nanocrystals

NASA Astrophysics Data System (ADS)

Stefan, Mariana; Vlaicu, Ioana Dorina; Nistor, Leona Cristina; Ghica, Daniela; Nistor, Sergiu Vasile

2017-12-01

We have shown in previous investigations that the low temperature collective magnetism observed in mesoporous cubic ZnS:Mn nanocrystalline powders prepared by colloidal synthesis, with nominal doping concentrations above 0.2 at.%, is due to the formation of Mn2+ clusters with distributed antiferromagnetic coupling localized in an amorphous phase found between the cubic ZnS:Mn nanocrystals. Here we investigate the composition, origin and thermal annealing behavior of this amorphous phase in such a mesoporous ZnS:Mn sample doped with 5 at.% Mn nominal concentration. Correlated analytical transmission electron microscopy, multifrequency electron paramagnetic resonance and Fourier transform infrared spectroscopy data show that the amorphous nanomaterial consists of unreacted precursor hydrated zinc and manganese acetates trapped inside the pores and on the surface of the cubic ZnS nanocrystals. The decomposition of the acetates under isochronal annealing up to 270 °C, where the mesoporous structure is still preserved, lead to changes in the nature and strength of the magnetic interactions between the aggregated Mn2+ ions. These results strongly suggest the possibility to modulate the magnetic properties of such transition metal ions doped II-VI mesoporous structures by varying the synthesis conditions and/or by post-synthesis thermochemical treatments.

Surface Damage Mechanism of Monocrystalline Si Under Mechanical Loading

NASA Astrophysics Data System (ADS)

Zhao, Qingliang; Zhang, Quanli; To, Suet; Guo, Bing

2017-03-01

Single-point diamond scratching and nanoindentation on monocrystalline silicon wafer were performed to investigate the surface damage mechanism of Si under the contact loading. The results showed that three typical stages of material removal appeared during dynamic scratching, and a chemical reaction of Si with the diamond indenter and oxygen occurred under the high temperature. In addition, the Raman spectra of the various points in the scratching groove indicated that the Si-I to β-Sn structure (Si-II) and the following β-Sn structure (Si-II) to amorphous Si transformation appeared under the rapid loading/unloading condition of the diamond grit, and the volume change induced by the phase transformation resulted in a critical depth (ductile-brittle transition) of cut (˜60 nm ± 15 nm) much lower than the theoretical calculated results (˜387 nm). Moreover, it also led to abnormal load-displacement curves in the nanoindentation tests, resulting in the appearance of elbow and pop-out effects (˜270 nm at 20 s, 50 mN), which were highly dependent on the loading/unloading conditions. In summary, phase transformation of Si promoted surface deformation and fracture under both static and dynamic mechanical loading.

XPS and EELS characterization of Mn2SiO4, MnSiO3 and MnAl2O4

NASA Astrophysics Data System (ADS)

Grosvenor, A. P.; Bellhouse, E. M.; Korinek, A.; Bugnet, M.; McDermid, J. R.

2016-08-01

X-ray Photoelectron Spectroscopy (XPS) and Electron Energy Loss Spectroscopy (EELS) are strong candidate techniques for characterizing steel surfaces and substrate-coating interfaces when investigating the selective oxidation and reactive wetting of advanced high strength steels (AHSS) during the continuous galvanizing process. However, unambiguous identification of ternary oxides such as Mn2SiO4, MnSiO3, and MnAl2O4 by XPS or EELS, which can play a significant role in substrate reactive wetting, is difficult due to the lack of fully characterized standards in the literature. To resolve this issue, samples of Mn2SiO4, MnSiO3 and MnAl2O4 were synthesized and characterized by XPS and EELS. The unique features of the XPS and EELS spectra for the Mn2SiO4, MnSiO3 and MnAl2O4 standards were successfully derived, thereby allowing investigators to fully differentiate and identify these oxides at the surface and subsurface of Mn, Si and Al alloyed AHSS using these techniques.

L'etude de l'InP et du GaP suite a l'implantation ionique de Mn et a un recuit thermique

NASA Astrophysics Data System (ADS)

Bucsa, Ioan Gigel

Cette these est dediee a l'etude des materiaux InMnP et GaMnP fabriques par implantation ionique et recuit thermique. Plus precisement nous avons investigue la possibilite de former par implantation ionique des materiaux homogenes (alliages) de InMnP et GaMnP contenant de 1 a 5 % atomiques de Mn qui seraient en etat ferromagnetique, pour des possibles applications dans la spintronique. Dans un premier chapitre introductif nous donnons les motivations de cette recherche et faisons une revue de la litterature sur ce sujet. Le deuxieme chapitre decrit les principes de l'implantation ionique, qui est la technique utilisee pour la fabrication des echantillons. Les effets de l'energie, fluence et direction du faisceau ionique sur le profil d'implantation et la formation des dommages seront mis en evidence. Aussi dans ce chapitre nous allons trouver des informations sur les substrats utilises pour l'implantation. Les techniques experimentales utilisees pour la caracterisation structurale, chimique et magnetique des echantillons, ainsi que leurs limitations sont presentees dans le troisieme chapitre. Quelques principes theoriques du magnetisme necessaires pour la comprehension des mesures magnetiques se retrouvent dans le chapitre 4. Le cinquieme chapitre est dedie a l'etude de la morphologie et des proprietes magnetiques des substrats utilises pour implantation et le sixieme chapitre, a l'etude des echantillons implantes au Mn sans avoir subi un recuit thermique. Notamment nous allons voir dans ce chapitre que l'implantation de Mn a plus que 1016 ions/cm 2 amorphise la partie implantee du materiau et le Mn implante se dispose en profondeur sur un profil gaussien. De point de vue magnetique les atomes implantes se trouvent dans un etat paramagnetique entre 5 et 300 K ayant le spin 5/2. Dans le chapitre 7 nous presentons les proprietes des echantillons recuits a basses temperatures. Nous allons voir que dans ces echantillons la couche implantee est polycristalline et les atomes de Mn sont toujours dans un etat paramagnetique. Dans les chapitres 8 et 9, qui sont les plus volumineux, nous presentons les resultats des mesures sur les echantillons recuits a hautes temperatures: il s'agit d'InP et du GaP implantes au Mn, dans le chapitre 8 et d'InP co-implante au Mn et au P, dans le chapitre 9. D'abord, dans le chapitre 8 nous allons voir que le recuit a hautes temperatures mene a une recristallisation epitaxiale du InMnP et du GaMnP; aussi la majorite des atomes de Mn se deplacent vers la surface a cause d'un effet de segregation. Dans les regions de la surface, concentres en Mn, les mesures XRD et TEM identifient la formation de MnP et d'In cristallin. Les mesures magnetiques identifient aussi la presence de MnP ferromagnetique. De plus dans ces mesures on trouve qu'environ 60 % du Mn implante est en etat paramagnetique avec la valeur du spin reduite par rapport a celle trouvee dans les echantillons non-recuits. Dans les echantillons InP co-implantes au Mn et au P la recristallisation est seulement partielle mais l'effet de segregation du Mn a la surface est beaucoup reduit. Dans ce cas plus que 50 % du Mn forme des particules MnP et le restant est en etat paramagnetique au spin 5/2, dilue dans la matrice de l'InP. Finalement dans le dernier chapitre, 10, nous presentons les conclusions principales auxquels nous sommes arrives et discutons les resultats et leurs implications. Mots cles: implantation ionique, InP, GaP, amorphisation, MnP, segregation, co-implantation, couche polycristalline, paramagnetisme, ferromagnetisme.

Amorphization of nanocrystalline 3C-SiC irradiated with Si+ ions

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

Jiang, Weilin; Wang, Haiyan; Kim, Ickchan

2010-11-23

Irradiation induced amorphization in nanocrystalline and single crystal 3C-SiC has been studied using 1 MeV Si+ ions under the identical irradiation conditions at room temperature and 400 K. The disordering behavior has been characterized using in-situ ion channeling and ex-situ x-ray diffraction methods. The results show that, compared to single crystal 3C-SiC, full amorphization of small 3C-SiC grains (~3.8 nm in size) occurs at a slightly lower dose at room temperature. For grains with sizes of 3.0 - 3.8 nm, the amorphization dose is lower at room temperature than 400 K. A significantly lower dose for amorphization of smaller grainsmore » (2.0 nm in size) is observed at 400 K. The behavior has been interpreted based on the competition between the interface and interior amorphization.« less

Diffusion Behavior of Mn and Si Between Liquid Oxide Inclusions and Solid Iron-Based Alloy at 1473 K

NASA Astrophysics Data System (ADS)

Kim, Sun-Joong; Tago, Hanae; Kim, Kyung-Ho; Kitamura, Shin-ya; Shibata, Hiroyuki

2018-06-01

In order to clarify the changes in the composition of oxide inclusions in steel, the effect of the metal and oxide composition on the reaction between solid Fe-based alloys and liquid multi-component oxides was investigated using the diffusion couple method at 1473 K. The measured concentration gradients of Mn and Si in the metal indicated that Mn diffused into the metal from the oxide, while the diffusion of Si occurred in the opposite direction. In addition, the MnO content in the oxide decreased with heat treatment time, while the SiO2 content increased. The compositional changes in both phases indicated that the Mn content in the metal near the interface increased with heat treatment with decreasing MnO content in the oxide. Assuming local equilibrium at the interface, the calculated [Mn]2/[Si] ratio at the interface in equilibrium with the oxide increased with increases in the MnO/SiO2 ratio in the oxide. The difference in the [Mn]2/[Si] ratios between the interface and the metal matrix increased, which caused the diffusion of Mn and Si between the multi-component oxide and metal. By measuring the diffusion lengths of Mn and Si in the metal, the chemical diffusion coefficients of Mn and Si were obtained to calculate the composition changes in Mn and Si in the metal. The calculated changes in Mn and Si in the metal agreed with the experimental results.

Silicon-ion-implanted PMMA with nanostructured ultrathin layers for plastic electronics

NASA Astrophysics Data System (ADS)

Hadjichristov, G. B.; Ivanov, Tz E.; Marinov, Y. G.

2014-12-01

Being of interest for plastic electronics, ion-beam produced nanostructure, namely silicon ion (Si+) implanted polymethyl-methacrylate (PMMA) with ultrathin nanostructured dielectric (NSD) top layer and nanocomposite (NC) buried layer, is examined by electric measurements. In the proposed field-effect organic nanomaterial structure produced within the PMMA network by ion implantation with low energy (50 keV) Si+ at the fluence of 3.2 × 1016 cm-2 the gate NSD is ion-nanotracks-modified low-conductive surface layer, and the channel NC consists of carbon nanoclusters. In the studied ion-modified PMMA field-effect configuration, the gate NSD and the buried NC are formed as planar layers both with a thickness of about 80 nm. The NC channel of nano-clustered amorphous carbon (that is an organic semiconductor) provides a huge increase in the electrical conduction of the material in the subsurface region, but also modulates the electric field distribution in the drift region. The field effect via the gate NSD is analyzed. The most important performance parameters, such as the charge carrier field-effect mobility and amplification of this particular type of PMMA- based transconductance device with NC n-type channel and gate NSD top layer, are determined.

Composition dependence of solid-phase epitaxy in silicon-germanium alloys: Experiment and theory

NASA Astrophysics Data System (ADS)

Haynes, T. E.; Antonell, M. J.; Lee, C. Archie; Jones, K. S.

1995-03-01

The rates of solid-phase epitaxy (SPE) in unstrained Si1-xGex alloys have been measured by time-resolved reflectivity for eight different alloy compositions, including both Si-rich and Ge-rich layers. Amorphous layers 300-400 nm thick were first formed in 8-μm-thick, relaxed, epitaxial Si1-xGex layers (0.02<=x<=0.87) by ion implantation of Si+. For each composition, the measured SPE rates spanned approximately two orders of magnitude. The alloy SPE rates are shown to be related to the regrowth rates of the two pure elements by a simple equation expressed in terms of the composition parameter x and having no adjustable parameters. The form of this equation implies that crystallization occurs by a serial attachment process at the amorphous-crystal interface and that the rate of attachment of each individual atom is determined by the identities of its four nearest neighbors. Such a process is consistent with the dangling-bond model proposed by Spaepen and Turnbull [in Laser-Solid Interactions and Laser Processing, edited by S. D. Ferris, H. J. Leamy, and J. M. Poate, AIP Conf. Proc. No. 50 (AIP, New York, 1979)] if the SPE rate is limited by the migration rate of dangling bonds rather than by their formation rate. Based on this analysis, an interpretation is proposed for the anomalously large activation energies that have been measured for SPE in some Si-rich compositions.

Magnetotransport properties of microstructured AlCu2Mn Heusler alloy thin films in the amorphous and crystalline phase

NASA Astrophysics Data System (ADS)

Barzola-Quiquia, José; Stiller, Markus; Esquinazi, Pablo D.; Quispe-Marcatoma, Justiniano; Häussler, Peter

2018-06-01

We have studied the resistance, magnetoresistance and Hall effect of AlCu2Mn Heusler alloy thin films prepared by flash evaporation on substrates cooled at 4He liquid temperature. The as-prepared samples were amorphous and were annealed stepwise to induce the transformation to the crystalline phase. The amorphous phase is metastable up to above room temperature and the transition to the crystalline phase was observed by means of resistance measurements. Using transmission electron microscopy, we have determined the structure factor S (K) and the pair correlation function g (r) , both results indicate that amorphous AlCu2Mn is an electronic stabilized phase. The X-ray diffraction of the crystallized film shows peaks corresponding to the well ordered L21 phase. The resistance shows a negative temperature coefficient in both phases. The magnetoresistance (MR) is negative in both phases, yet larger in the crystalline state compared to the amorphous one. The magnetic properties were studied further by anomalous Hall effect measurements, which were present in both phases. In the amorphous state, the anomalous Hall effect disappears at temperatures below 175 K and is present up to above room temperature in the case of crystalline AlCu2Mn.

Tuning the Magnetic and Electronic Properties of Iron(x )Silicon(1-x) Thin Films for Spintronics

NASA Astrophysics Data System (ADS)

Karel, Julie Elizabeth

This dissertation investigated the magnetic and electronic properties of a potentially better alternative: off-stoichimetry, bcc-like FexSi 1-x thin films (0.43800 K) and theoretically predicted high spin polarization (100%). However, little work has been done on off-stoichiometry FexSi1-x thin films (0.43

Atom-Level Understanding of the Sodiation Process in Silicon Anode Material.

PubMed

Jung, Sung Chul; Jung, Dae Soo; Choi, Jang Wook; Han, Young-Kyu

2014-04-03

Despite the exceptionally large capacities in Li ion batteries, Si has been considered inappropriate for applications in Na ion batteries. We report an atomic-level study on the applicability of a Si anode in Na ion batteries using ab initio molecular dynamics simulations. While crystalline Si is not suitable for alloying with Na atoms, amorphous Si can accommodate 0.76 Na atoms per Si atom, corresponding to a specific capacity of 725 mA h g(-1). Bader charge analyses reveal that the sodiation of an amorphous Si electrode continues until before the local Na-rich clusters containing neutral Na atoms are formed. The amorphous Na0.76Si phase undergoes a volume expansion of 114% and shows a Na diffusivity of 7 × 10(-10) cm(2) s(-1) at room temperature. Overall, the amorphous Si phase turns out quite attractive in performance compared to other alloy-type anode materials. This work suggests that amorphous Si might be a competitive candidate for Na ion battery anodes.

Scanning transmission electron microscopy (STEM) study on surface modified CVD diamond/Si(111) film post implanted Fe-B and NiFe-B related to GMR properties

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

Purwanto, Setyo, E-mail: setyo-p@batan.go.id, E-mail: purwantosetyo@yahoo.com; Dimyati, A., E-mail: arbi-dimyati@hotmail.com; Iskandar, R.

Nanostructure investigation on the post implantation by Fe-B and NiFe-B on CVD diamond/Si(111) film have been studied by means of STEM related to their GMR phenomena. Two samples were investigated carefully, firstly sample is post NiFe-B at E=70keV and dose= 10{sup 15} ions/cm{sup 2} (denoted as A-E3D1). Secondly, is post FeB at E=20 keV and dose= 10{sup 15} ions/cm{sup 2} (denoted as B-E1D1). Based on FPP measurement at room temperature (RT) and H{sub applied} = 8 kOe, A-E3D1 sample has MR ratio almost 80% and MR ratio in B-E1D1 sample is 45%. Based on STEM-EDX investigation, there are two aspectsmore » of how MR ratio of A-E3D1 more higher than those of B-E1D1. Firstly, surface nanostructure on the top of A-E3D1 film is more grazing than on the top of B-E1D1. Analysis with Scanning Transmission Electron Microscope (STEM) equipped with Electron Energy Loss Spectroscopy (EELS) the growth of amorphous carbon layer on top of the implanted diamond film with thickness around 100 nm and only 20 nm on the no implanted sample have observed. Boron atoms were found inside the carbon amorphous layer distributed homogenously. Secondly, oxygen content at the interface between diamond film and silicon substrate in sample A-E3D1 was lower than those in B-E1D1 sample. This condition gives the resistance value in A-E3D1 lower than value in B-E1D1. This result is close to the Raman Spectroscopy data measurement which obviously suggests changes on the Raman spectrum due to implantation related to Oxygen excitation from B-E1D1 sample.« less

Reduction of thermal conductivity in MnSi{sub 1.7} multi-layered thin films with artificially inserted Si interfaces

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

Kurosaki, Y., E-mail: yosuke.kurosaki.uy@hitachi.com; Yabuuchi, S.; Nishide, A.

We report a lowered lattice thermal conductivity in nm-scale MnSi{sub 1.7}/Si multilayers which were fabricated by controlling thermal diffusions of Mn and Si atoms. The thickness of the constituent layers is 1.5–5.0 nm, which is comparable to the phonon mean free path of both MnSi{sub 1.7} and Si. By applying the above nanostructures, we reduced the lattice thermal conductivity down to half that of bulk MnSi{sub 1.7}/Si composite materials. The obtained value of 1.0 W/K m is the experimentally observed minimum in MnSi{sub 1.7}-based materials without any heavy element doping and close to the minimum thermal conductivity. We attribute the reduced latticemore » thermal conductivity to phonon scattering at the MnSi{sub 1.7}/Si interfaces in the multilayers.« less

Fabrication of nanometer single crystal metallic CoSi2 structures on Si

NASA Technical Reports Server (NTRS)

Nieh, Kai-Wei (Inventor); Lin, True-Lon (Inventor); Fathauer, Robert W. (Inventor)

1991-01-01

Amorphous Co:Si (1:2 ratio) films are electron gun-evaporated on clean Si(111), such as in a molecular beam epitaxy system. These layers are then crystallized selectively with a focused electron beam to form very small crystalline Co/Si2 regions in an amorphous matrix. Finally, the amorphous regions are etched away selectively using plasma or chemical techniques.

Promising Ta-Ti-Zr-Si metallic glass coating without cytotoxic elements for bio-implant applications

NASA Astrophysics Data System (ADS)

Lai, J. J.; Lin, Y. S.; Chang, C. H.; Wei, T. Y.; Huang, J. C.; Liao, Z. X.; Lin, C. H.; Chen, C. H.

2018-01-01

Tantalum (Ta) is considered as one of the most promising metal due to its high corrosion resistance, excellent biocompatibility and cell adhesion/in-growth capabilities. Although there are some researches exploring the biomedical aspects of Ta and Ta based alloys, systematic characterizations of newly developed Ta-based metallic glasses in bio-implant applications is still lacking. This study employs sputtering approach to produced thin-film Ti-based metallic glasses due to the high melting temperature of Ta (3020 °C). Two fully amorphous Ta-based metallic glasses composed of Ta57Ti17Zr15Si11 and Ta75Ti10Zr8Si7 are produced and experimentally characterized in terms of their mechanical properties, bio-corrosion properties, surface hydrophilic characteristics, and in-vitro cell viability and cells attachment tests. Compare to conventional pure Ti and Ta metals, the developed Ta-based metallic glasses exhibit higher hardness and lower modulus which are better match to the mechanical properties of bone. MTS assay results show that Ta-based metallic glasses show comparable cell viability and cell attachment rate compared to that of pure Ti and Ta surface in a 72 h in-vitro test.

Cryogenic ion implantation near amorphization threshold dose for halo/extension junction improvement in sub-30 nm device technologies

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

Park, Hugh; Todorov, Stan; Colombeau, Benjamin

2012-11-06

We report on junction advantages of cryogenic ion implantation with medium current implanters. We propose a methodical approach on maximizing cryogenic effects on junction characteristics near the amorphization threshold doses that are typically used for halo implants for sub-30 nm technologies. BF{sub 2}{sup +} implant at a dose of 8 Multiplication-Sign 10{sup 13}cm{sup -2} does not amorphize silicon at room temperature. When implanted at -100 Degree-Sign C, it forms a 30 - 35 nm thick amorphous layer. The cryogenic BF{sub 2}{sup +} implant significantly reduces the depth of the boron distribution, both as-implanted and after anneals, which improves short channelmore » rolloff characteristics. It also creates a shallower n{sup +}-p junction by steepening profiles of arsenic that is subsequently implanted in the surface region. We demonstrate effects of implant sequences, germanium preamorphization, indium and carbon co-implants for extension/halo process integration. When applied to sequences such as Ge+As+C+In+BF{sub 2}{sup +}, the cryogenic implants at -100 Degree-Sign C enable removal of Ge preamorphization, and form more active n{sup +}-p junctions and steeper B and In halo profiles than sequences at room temperature.« less

Growth of amorphous and epitaxial ZnSiP 2–Si alloys on Si

DOE PAGES

Martinez, Aaron D.; Miller, Elisa M.; Norman, Andrew G.; ...

2018-01-30

ZnSiP 2is a wide band gap material lattice matched with Si, with potential for Si-based optoelectronics. Here, amorphous ZnSiP 2–Si alloys are grown with tunable composition. Films with Si-rich compositions can be crystallized into epitaxial films.

Direct-patterned optical waveguides on amorphous silicon films

DOEpatents

Vernon, Steve; Bond, Tiziana C.; Bond, Steven W.; Pocha, Michael D.; Hau-Riege, Stefan

2005-08-02

An optical waveguide structure is formed by embedding a core material within a medium of lower refractive index, i.e. the cladding. The optical index of refraction of amorphous silicon (a-Si) and polycrystalline silicon (p-Si), in the wavelength range between about 1.2 and about 1.6 micrometers, differ by up to about 20%, with the amorphous phase having the larger index. Spatially selective laser crystallization of amorphous silicon provides a mechanism for controlling the spatial variation of the refractive index and for surrounding the amorphous regions with crystalline material. In cases where an amorphous silicon film is interposed between layers of low refractive index, for example, a structure comprised of a SiO.sub.2 substrate, a Si film and an SiO.sub.2 film, the formation of guided wave structures is particularly simple.

Atomistic simulation of damage accumulation and amorphization in Ge

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

Gomez-Selles, Jose L., E-mail: joseluis.gomezselles@imdea.org; Martin-Bragado, Ignacio; Claverie, Alain

2015-02-07

Damage accumulation and amorphization mechanisms by means of ion implantation in Ge are studied using Kinetic Monte Carlo and Binary Collision Approximation techniques. Such mechanisms are investigated through different stages of damage accumulation taking place in the implantation process: from point defect generation and cluster formation up to full amorphization of Ge layers. We propose a damage concentration amorphization threshold for Ge of ∼1.3 × 10{sup 22} cm{sup −3} which is independent on the implantation conditions. Recombination energy barriers depending on amorphous pocket sizes are provided. This leads to an explanation of the reported distinct behavior of the damage generated by different ions.more » We have also observed that the dissolution of clusters plays an important role for relatively high temperatures and fluences. The model is able to explain and predict different damage generation regimes, amount of generated damage, and extension of amorphous layers in Ge for different ions and implantation conditions.« less

Study of the amorphization of surface silicon layers implanted by low-energy helium ions

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

Lomov, A. A., E-mail: lomov@ftian.ru; Myakon’kikh, A. V.; Oreshko, A. P.

2016-03-15

The structural changes in surface layers of Si(001) substrates subjected to plasma-immersion implantation by (2–5)-keV helium ions to a dose of D = 6 × 10{sup 15}–5 × 10{sup 17} cm{sup –2} have been studied by highresolution X-ray diffraction, Rutherford backscattering, and spectral ellipsometry. It is found that the joint application of these methods makes it possible to determine the density depth distribution ρ(z) in an implanted layer, its phase state, and elemental composition. Treatment of silicon substrates in helium plasma to doses of 6 × 10{sup 16} cm{sup –2} leads to the formation of a 20- to 30-nm-thick amorphizedmore » surface layer with a density close to the silicon density. An increase in the helium dose causes the formation of an internal porous layer.« less

Amorphous Mn oxide-ordered mesoporous carbon hybrids as a high performance electrode material for supercapacitors.

PubMed

Nam, Inho; Kim, Nam Dong; Kim, Gil-Pyo; Park, Junsu; Yi, Jongheop

2012-07-01

A supercapacitor has the advantages of both the conventional capacitors and the rechargeable batteries. Mn oxide is generally recognized one of the potential materials that can be used for a supercapacitor, but its low conductivity is a limiting factor for electrode materials. In this study, a hybrid of amorphous Mn oxide (AMO) and ordered mesoporous carbon (OMC) was prepared and characterized using X-ray diffraction, transmission electron microscopy, N2/77 K sorption techniques, and electrochemical analyses. The findings indicate that the electrochemical activities of Mn oxide were facilitated when it was in the hybrid state because OMC acted as a pathway for both the electrolyte ions and the electrons due to the characteristics of the ordered mesoporous structure. The ordered mesoporous structure of OMC was well maintained even after hybridization with amorphous Mn oxide. The electrochemical-activity tests revealed that the AMO/OMC hybrid had a higher specific capacitance and conductivity than pure Mn oxide. In the case where the Mn/C weight ratio was 0.75, the composite showed a high capacitance of 153 F/g, which was much higher than that for pure Mn oxide, due to the structural effects of OMC.

Chemistry, mineralogy, and grain properties at Namib and High dunes, Bagnold dune field, Gale crater, Mars: A synthesis of Curiosity rover observations.

PubMed

Ehlmann, B L; Edgett, K S; Sutter, B; Achilles, C N; Litvak, M L; Lapotre, M G A; Sullivan, R; Fraeman, A A; Arvidson, R E; Blake, D F; Bridges, N T; Conrad, P G; Cousin, A; Downs, R T; Gabriel, T S J; Gellert, R; Hamilton, V E; Hardgrove, C; Johnson, J R; Kuhn, S; Mahaffy, P R; Maurice, S; McHenry, M; Meslin, P-Y; Ming, D W; Minitti, M E; Morookian, J M; Morris, R V; O'Connell-Cooper, C D; Pinet, P C; Rowland, S K; Schröder, S; Siebach, K L; Stein, N T; Thompson, L M; Vaniman, D T; Vasavada, A R; Wellington, D F; Wiens, R C; Yen, A S

2017-12-01

The Mars Science Laboratory Curiosity rover performed coordinated measurements to examine the textures and compositions of aeolian sands in the active Bagnold dune field. The Bagnold sands are rounded to subrounded, very fine to medium sized (~45-500 μm) with ≥6 distinct grain colors. In contrast to sands examined by Curiosity in a dust-covered, inactive bedform called Rocknest and soils at other landing sites, Bagnold sands are darker, less red, better sorted, have fewer silt-sized or smaller grains, and show no evidence for cohesion. Nevertheless, Bagnold mineralogy and Rocknest mineralogy are similar with plagioclase, olivine, and pyroxenes in similar proportions comprising >90% of crystalline phases, along with a substantial amorphous component (35% ± 15%). Yet Bagnold and Rocknest bulk chemistry differ. Bagnold sands are Si enriched relative to other soils at Gale crater, and H 2 O, S, and Cl are lower relative to all previously measured Martian soils and most Gale crater rocks. Mg, Ni, Fe, and Mn are enriched in the coarse-sieved fraction of Bagnold sands, corroborated by visible/near-infrared spectra that suggest enrichment of olivine. Collectively, patterns in major element chemistry and volatile release data indicate two distinctive volatile reservoirs in Martian soils: (1) amorphous components in the sand-sized fraction (represented by Bagnold) that are Si-enriched, hydroxylated alteration products and/or H 2 O- or OH-bearing impact or volcanic glasses and (2) amorphous components in the fine fraction (<40 μm; represented by Rocknest and other bright soils) that are Fe, S, and Cl enriched with low Si and adsorbed and structural H 2 O.

Chemistry, Mineralogy, and Grain Properties at Namib and High Dunes, Bagnold Dune Field, Gale Crater, Mars: A Synthesis of Curiosity Rover Observations: Bagnold Dune Sands Composition

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

Ehlmann, B. L.; Edgett, K. S.; Sutter, B.

The Mars Science Laboratory Curiosity rover performed coordinated measurements to examine the textures and compositions of aeolian sands in the active Bagnold dune field. The Bagnold sands are rounded to subrounded, very fine- to medium- sized (~45-500 µm) with ≥6 distinct grain colors. In contrast to sands examined by Curiosity in a dust-covered, inactive bedform called Rocknest and soils at other landing sites, Bagnold sands are darker, less red, better sorted, have fewer silt-sized or smaller grains, and show no evidence for cohesion. Nonetheless, Bagnold mineralogy and Rocknest mineralogy are similar with plagioclase, olivine, and pyroxenes in similar proportions comprisingmore » >90% of crystalline phases, along with a substantial amorphous component (35% ± 15%). Yet, Bagnold and Rocknest bulk chemistry differ. Bagnold sands are Si-enriched relative to other soils at Gale crater, and H 2O, S, and Cl are lower relative to all previously measured martian soils and most Gale crater rocks. Mg, Ni, Fe, and Mn are enriched in the coarse-sieved fraction of Bagnold sands, corroborated by VNIR spectra that suggest enrichment of olivine. Together, patterns in major element chemistry and volatile release data indicate two distinctive volatile reservoirs in martian soils: (1) amorphous components in the sand-sized fraction (represented by Bagnold) that are Si-enriched, hydroxylated alteration products and/or impact or volcanic glasses; and (2) amorphous components in the fine fraction (<40 µm; represented by Rocknest and other bright soils) that are Fe-, S-, and Cl-enriched with low Si and adsorbed and structural H 2O.« less

Chemistry, mineralogy, and grain properties at Namib and High dunes, Bagnold dune field, Gale crater, Mars: A synthesis of Curiosity rover observations

NASA Astrophysics Data System (ADS)

Ehlmann, B. L.; Edgett, K. S.; Sutter, B.; Achilles, C. N.; Litvak, M. L.; Lapotre, M. G. A.; Sullivan, R.; Fraeman, A. A.; Arvidson, R. E.; Blake, D. F.; Bridges, N. T.; Conrad, P. G.; Cousin, A.; Downs, R. T.; Gabriel, T. S. J.; Gellert, R.; Hamilton, V. E.; Hardgrove, C.; Johnson, J. R.; Kuhn, S.; Mahaffy, P. R.; Maurice, S.; McHenry, M.; Meslin, P.-Y.; Ming, D. W.; Minitti, M. E.; Morookian, J. M.; Morris, R. V.; O'Connell-Cooper, C. D.; Pinet, P. C.; Rowland, S. K.; Schröder, S.; Siebach, K. L.; Stein, N. T.; Thompson, L. M.; Vaniman, D. T.; Vasavada, A. R.; Wellington, D. F.; Wiens, R. C.; Yen, A. S.

2017-12-01

The Mars Science Laboratory Curiosity rover performed coordinated measurements to examine the textures and compositions of aeolian sands in the active Bagnold dune field. The Bagnold sands are rounded to subrounded, very fine to medium sized ( 45-500 μm) with ≥6 distinct grain colors. In contrast to sands examined by Curiosity in a dust-covered, inactive bedform called Rocknest and soils at other landing sites, Bagnold sands are darker, less red, better sorted, have fewer silt-sized or smaller grains, and show no evidence for cohesion. Nevertheless, Bagnold mineralogy and Rocknest mineralogy are similar with plagioclase, olivine, and pyroxenes in similar proportions comprising >90% of crystalline phases, along with a substantial amorphous component (35% ± 15%). Yet Bagnold and Rocknest bulk chemistry differ. Bagnold sands are Si enriched relative to other soils at Gale crater, and H2O, S, and Cl are lower relative to all previously measured Martian soils and most Gale crater rocks. Mg, Ni, Fe, and Mn are enriched in the coarse-sieved fraction of Bagnold sands, corroborated by visible/near-infrared spectra that suggest enrichment of olivine. Collectively, patterns in major element chemistry and volatile release data indicate two distinctive volatile reservoirs in Martian soils: (1) amorphous components in the sand-sized fraction (represented by Bagnold) that are Si-enriched, hydroxylated alteration products and/or H2O- or OH-bearing impact or volcanic glasses and (2) amorphous components in the fine fraction (<40 μm represented by Rocknest and other bright soils) that are Fe, S, and Cl enriched with low Si and adsorbed and structural H2O.

Chemistry, Mineralogy, and Grain Properties at Namib and High Dunes, Bagnold Dune Field, Gale Crater, Mars: A Synthesis of Curiosity Rover Observations: Bagnold Dune Sands Composition

DOE PAGES

Ehlmann, B. L.; Edgett, K. S.; Sutter, B.; ...

2017-06-12

The Mars Science Laboratory Curiosity rover performed coordinated measurements to examine the textures and compositions of aeolian sands in the active Bagnold dune field. The Bagnold sands are rounded to subrounded, very fine- to medium- sized (~45-500 µm) with ≥6 distinct grain colors. In contrast to sands examined by Curiosity in a dust-covered, inactive bedform called Rocknest and soils at other landing sites, Bagnold sands are darker, less red, better sorted, have fewer silt-sized or smaller grains, and show no evidence for cohesion. Nonetheless, Bagnold mineralogy and Rocknest mineralogy are similar with plagioclase, olivine, and pyroxenes in similar proportions comprisingmore » >90% of crystalline phases, along with a substantial amorphous component (35% ± 15%). Yet, Bagnold and Rocknest bulk chemistry differ. Bagnold sands are Si-enriched relative to other soils at Gale crater, and H 2O, S, and Cl are lower relative to all previously measured martian soils and most Gale crater rocks. Mg, Ni, Fe, and Mn are enriched in the coarse-sieved fraction of Bagnold sands, corroborated by VNIR spectra that suggest enrichment of olivine. Together, patterns in major element chemistry and volatile release data indicate two distinctive volatile reservoirs in martian soils: (1) amorphous components in the sand-sized fraction (represented by Bagnold) that are Si-enriched, hydroxylated alteration products and/or impact or volcanic glasses; and (2) amorphous components in the fine fraction (<40 µm; represented by Rocknest and other bright soils) that are Fe-, S-, and Cl-enriched with low Si and adsorbed and structural H 2O.« less

Dose dependence of radiation damage in nano-structured amorphous SiOC/crystalline Fe composite

DOE PAGES

Su, Qing; Price, Lloyd; Shao, Lin; ...

2015-10-29

Here, through examination of radiation tolerance properties of amorphous silicon oxycarbide (SiOC) and crystalline Fe composite to averaged damage levels, from approximately 8 to 30 displacements per atom (dpa), we demonstrated that the Fe/SiOC interface and the Fe/amorphous Fe xSi yO z interface act as efficient defect sinks and promote the recombination of vacancies and interstitials. For thick Fe/SiOC multilayers, a clear Fe/SiOC interface remained and no irradiation-induced mixing was observed even after 32 dpa. For thin Fe/SiOC multilayers, an amorphous Fe xSi yO z intermixed layer was observed to form at 8 dpa, but no further layer growth wasmore » observed for higher dpa levels.« less

Synthesis and structural stability of Cr-doped Li2MnSiO4/C cathode materials by solid-state method

NASA Astrophysics Data System (ADS)

Cheng, Hong-Mei; Zhao, Shi-Xi; Wu, Xia; Zhao, Jian-Wei; Wei, Lei; Nan, Ce-Wen

2018-03-01

The crystal structure of the Li2MnSiO4 cathode material would collapse during the charge and discharge process because of that the Mn-O coordination polyhedron changed from [MnO4] into [MnO6] in the process of Mn+2 to Mn+4, but the Cr element could remain [CrO4] crystal ligand from Cr+2 to Cr+4, so Cr element substitution was used to improve the structural stability of the Li2MnSiO4 cathode material. In this work, Li2Mn1-xCrxSiO4/C nanocomposites were synthesized by solid-state method. XRD, SEM and TEM observations show that the as-prepared Li2Mn1-xCrxSiO4/C materials presents an orthorhombic crystal structure (S.G. Pmn21), the particle size of Li2Mn1-xCrxSiO4/C powder ranges from 50 to 100 nm. The XRD and XPS results indicate that Cr+2 is successfully doped into Li2MnSiO4 lattice and has well compatibility with Li2MnSiO4. The electrochemical results display that Li2Mn92.5%Cr7.5%SiO4/C exhibits significantly enhanced cycle stability and discharge capability. The initial discharge capacity of the Li2Mn92.5%Cr7.5%SiO4/C sample is 255 mAh g-1, and the discharge capacity was still about 60 mAh g-1 after 50 cycles. Furthermore, the XRD patterns, TEM images and Raman analysis reveal that the Cr doping enhances the structural stability of Li2Mn1-xCrxSiO4/C and improves the electrochemical activity of the cathode. Thus, the Li2Mn92.5%Cr7.5%SiO4/C have shown potential applications for lithium ion batteries.

Interface formation of epitaxial MgO/Co2MnSi(001) structures: Elemental segregation and oxygen migration

NASA Astrophysics Data System (ADS)

McFadden, Anthony; Wilson, Nathaniel; Brown-Heft, Tobias; Pennachio, Daniel; Pendharkar, Mihir; Logan, John A.; Palmstrøm, Chris J.

2017-12-01

The interface formation in epitaxial MgO /Co2MnSi (001) films was studied using in-situ X-ray photoelectron spectroscopy (XPS). MgO was deposited on single crystal Co2MnSi (001) layers using e-beam evaporation: a technique which is expected to oxidize the Co2MnSi layer somewhat due to the rise in oxygen partial pressure during MgO deposition while leaving the deposited MgO oxygen deficient. Not unexpectedly, we find that e-beam evaporation of MgO raises the oxygen background in the deposition chamber to a level that readily oxidizes the Co2MnSi surface, with oxygen bonding preferentially to Mn and Si over Co. Interestingly, this oxidation causes an elemental segregation, with Mn-Si effectively moving toward the surface, resulting in an MgO /Co2MnSi interface with a composition significantly differing from the original surface of the unoxidized Co2MnSi film. As MgO is deposited on the oxidized Co2MnSi , the Mn-oxides are reduced, while the Si oxide remains, and is only somewhat reduced after additional annealing in ultrahigh vacuum. Annealing after the MgO is grown on Co2MnSi causes oxygen to move away from the oxidized Co2MnSi interface toward the surface and into the MgO. This observation is consistent with an increase in the tunneling magnetoresistance ratio with post-growth annealing measured in fabricated magnetic tunnel junctions (MTJs). The findings are discussed in light of fabrication of MgO/Heusler based MTJs, where the exponential decay of tunneling probability with contact separation exemplifies the importance of the ferromagnet/tunnel barrier interface.

Influence of Ga vacancies, Mn and O impurities on the ferromagnetic properties of GaN micro- and nanostructures

NASA Astrophysics Data System (ADS)

Guzmán, G.; Escudero, R.; Silva, R.; Herrera, M.

2018-04-01

We present a study of the influence of gallium vacancy (VGa) point defects on the ferromagnetic properties of GaN:Mn and GaN:Mn,O micro- and nanostructures. Results demonstrate that the generation of these point defects enhances the ferromagnetic signal of GaN:Mn microstructures, while incorporation of oxygen as an impurity inhibits this property. XPS measurements revealed that Mn impurities in ferromagnetic GaN:Mn samples mainly exhibit a valence state of 2+. Cathodoluminescence (CL) spectra from Mn-doped GaN samples displayed emissions centered at about 1.97 eV, attributed to transitions between the 4T1-6A1 states of the Mn2+ d orbitals, and emissions centered at 2.45 and 2.9 eV, associated with the presence of VGa. CL measurements also revealed a blue shift of the GaN band-edge emission generated by the expansion of the wurtzite lattice due to Mn incorporation, which was confirmed by XRD measurements. These latter measurements also revealed an amorphization of GaN:Mn due to the incorporation of oxygen as impurities. The GaN:Mn samples were synthesized by thermal evaporation of GaN and MnCO3 powders onto Ni0.8Cr0.2/Si(100) in a horizontal furnace operated at low vacuum. The residual air inside the system was used as a source of oxygen during the synthesis of Mn and O co-doped GaN nanostructures. Mn and O impurities were incorporated into the nanostructures at different concentrations by varying the growth temperature. Energy Dispersive Spectroscopy, XRD, and XPS measurements confirmed that the obtained samples predominantly consisted of GaN.

Synthesis and Microstructural Characterization of Manganese Oxide Electrodes for Application as Electrochemical Supercapacitors

NASA Astrophysics Data System (ADS)

Babakhani, Banafsheh

The aim of this thesis work was to synthesize Mn-based oxide electrodes with high surface area structures by anodic electrodeposition for application as electrochemical capacitors. Rod-like structures provide large surface areas leading to high specific capacitances. Since templated electrosynthesis of rods is not easy to use in practical applications, it is more desirable to form rod-like structures without using any templates. In this work, Mn oxide electrodes with rod-like structures (˜1.5 µm in diameter) were synthesized from a solution of 0.01 M Mn acetate under galvanostatic control without any templates, on Au coated Si substrates. The electrochemical properties of the synthesized nanocrystalline electrodes were investigated to determine the effect of morphology, chemistry and crystal structure on the corresponding electrochemical behavior of Mn oxide electrodes. Mn oxides prepared at different current densities showed a defective antifluoritetype crystal structure. The rod-like Mn oxide electrodes synthesized at low current densities (5 mAcm.2) exhibited a high specific capacitance due to their large surface areas. Also, specific capacity retention after 250 cycles in an aqueous solution of 0.5 M Na2SO4 at 100 mVs -1 was about 78% of the initial capacity (203 Fg-1 ). To improve the electrochemical capacitive behavior of Mn oxide electrodes, a sequential approach and a one-step method were adopted to synthesize Mn oxide/PEDOT electrodes through anodic deposition on Au coated Si substrates from aqueous solutions. In the former case, free standing Mn oxide rods (about 10 µm long and less than 1.5 µm in diameter) were first synthesized, then coated by electro-polymerization of a conducting polymer (PEDOT) giving coaxial rods. The one-step, co-electrodeposition method produced agglomerated Mn oxide/PEDOT particles. The electrochemical behavior of the deposits depended on the morphology and crystal structure of the fabricated electrodes, which were affected by the composition and pH of the electrolyte, temperature, current density and polymer deposition time. Mn oxide/PEDOT coaxial core/shell rods consisted of MnO2 with an antifluorite-type structure coated with amorphous PEDOT. The Mn oxide/PEDOT coaxial core/shell electrodes prepared by the sequential method showed significantly better specific capacity and redox performance properties relative to both uncoated Mn oxide rods and co- electrodeposited Mn oxide/PEDOT electrodes. The best specific capacitance for Mn oxide/PEDOT rods produced sequentially was ˜295 F g-1 with ˜92% retention after 250 cycles in 0.5 M Na2SO4 at 100 mV s-1. To further improve the electrochemical capacitive behavior of Mn oxide electrodes, Co-doped and Fe-doped Mn oxide electrodes with a rod-like morphology and antifluorite-type crystal structure were synthesized by anodic electrodeposition, on Au coated Si substrates, from dilute solutions of Mn acetate and Co sulphate and Mn acetate and Fe chloride. Also, Mn-Co oxide/PEDOT coaxial core/shell rods were synthesized by applying a shell of PEDOT on Mn-Co oxide electrodes. Mn-Co oxide/PEDOT electrodes consisted of MnO2, with partial Co 2+ and Co3+ ion substitution for Mn4+, and amorphous PEDOT. Mn-Fe oxide electrodes consisted of MnO2, with partial Fe2+ and Fe3+ ion substitution for Mn4+. Electrochemical analysis showed that the capacitance values for all deposits increased with increasing scan rate to 100 mVs -1, and then decreased after 100 mVs-1. The Mn-Co oxide/PEDOT electrodes showed improved specific capacity and electrochemical cyclability relative to uncoated Mn-Co oxides and Mn-Fe oxides. Mn-Co oxide/PEDOT electrodes with rod-like structures had high capacitances (up to 310 Fg -1) at a scan rate of 100 mVs-1 and maintained their capacitance after 500 cycles in 0.5 M Na2SO4 (91% retention). Capacitance reduction for the deposits was mainly due to the loss of Mn ions by dissolution in the electrolyte solution. To better understand the nucleation and growth mechanisms of Mn oxide electrodes, the effects of supersaturation ratio on the morphology and crystal structure of electrodeposited Mn oxide were studied. By changing deposition parameters, including deposition current density, electrolyte composition, pH and temperature, a series of nanocrystalline Mn oxide electrodes with various morphologies (continuous coatings, rod-like structures, aggregated rods and thin sheets) and an antifluorite-type crystal structure was obtained. Mn oxide thin sheets showed instantaneous nucleation and single crystalline growth; rods had a mix of instantaneous/progressive nucleation and polycrystalline growth and continuous coatings formed by progressive nucleation and polycrystalline growth. Electrochemical analysis revealed the best capacitance behaviour obtained for Mn oxide thin sheets followed by Mn oxide rods, with dimensions on the microscale, and then continuous coatings. The highest specific capacitance (˜230 Fg-1) and capacitance retention rates (˜88%) were obtained for Mn oxide thin sheets after 250 cycles in 0.5 M Na2 SO4 at 20 mVs-1.

Mechanisms of aluminium-induced crystallization and layer exchange upon low-temperature annealing of amorphous Si/polycrystalline Al bilayers.

PubMed

Wang, J Y; Wang, Z M; Jeurgens, L P H; Mittemeijer, E J

2009-06-01

Aluminium-induced crystallization (ALIC) of amorphous Si and subsequent layer exchange (ALILE) occur in amorphous-Si/polycrystalline-Al bilayers (a-Si/c-Al) upon annealing at temperatures as low as 165 degrees C and were studied by X-ray diffraction and Auger electron spectroscopic depth profiling. It follows that: (i) nucleation of Si crystallization is initiated at Al grain boundaries and not at the a-Si/c-Al interface; (ii) low-temperature annealing results in a large Si grain size in the continuous c-Si layer produced by ALILE. Thermodynamic model calculations show that: (i) Si can "wet" the Al grain boundaries due to the favourable a-Si/c-Al interface energy (as compared to the Al grain-boundary energy); (ii) the wetting-induced a-Si layer at the Al grain boundary can maintain its amorphous state only up to a critical thickness, beyond which nucleation of Si crystallization takes place; and (iii) a tiny driving force controls the kinetics of the layer exchange.

Effects of the addition of Co, Ni or Cr on the decolorization properties of Fe-Si-B amorphous alloys

NASA Astrophysics Data System (ADS)

Zhang, Changqin; Zhu, Zhengwang; Zhang, Haifeng

2017-11-01

Fe-based amorphous alloys show great potential in degrading azo dyes and other organic pollutants, and are widely investigated as a kind of environmental-friendly materials for wastewater remediation. In this paper, the effects of Co, Ni or Cr addition on the decolorization properties of Fe-Si-B amorphous alloys were studied, and the mechanism of their different effects was analyzed. Co addition could lower the activation energy of Fe-Si-B amorphous alloys in decolorizing azo dyes, and had no weakening effect on the decolorization capability of Fe-Si-B amorphous alloys. Ni addition led to partial crystallization of Fe-Si-B amorphous alloys, and the decolorization mechanism at low temperatures changed from chemical degradation to physical adsorption. Cr addition could enhance the corrosion resistance of Fe-Si-B amorphous alloys, but the amorphous alloys completely lost the decolorization capability no matter at lower or higher temperatures. The results of X-ray photoelectron spectroscopy (XPS) and scanning electron microscopy (SEM) indicated that the addition of Co, Ni or Cr could generate different surface structures that had significant influences on the decolorization process. Our work demonstrated that the effiecient decolorization of azo dyes by Fe-based alloys could be realized only when amorphous nature and incompact surface structure were simultaneously achieved for the alloys.

Lithium implantation at low temperature in silicon for sharp buried amorphous layer formation and defect engineering

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

Oliviero, E.; David, M. L.; Beaufort, M. F.

The crystalline-to-amorphous transformation induced by lithium ion implantation at low temperature has been investigated. The resulting damage structure and its thermal evolution have been studied by a combination of Rutherford backscattering spectroscopy channelling (RBS/C) and cross sectional transmission electron microscopy (XTEM). Lithium low-fluence implantation at liquid nitrogen temperature is shown to produce a three layers structure: an amorphous layer surrounded by two highly damaged layers. A thermal treatment at 400 Degree-Sign C leads to the formation of a sharp amorphous/crystalline interfacial transition and defect annihilation of the front heavily damaged layer. After 600 Degree-Sign C annealing, complete recrystallization takes placemore » and no extended defects are left. Anomalous recrystallization rate is observed with different motion velocities of the a/c interfaces and is ascribed to lithium acting as a surfactant. Moreover, the sharp buried amorphous layer is shown to be an efficient sink for interstitials impeding interstitial supersaturation and {l_brace}311{r_brace} defect formation in case of subsequent neon implantation. This study shows that lithium implantation at liquid nitrogen temperature can be suitable to form a sharp buried amorphous layer with a well-defined crystalline front layer, thus having potential applications for defects engineering in the improvement of post-implantation layers quality and for shallow junction formation.« less

Amorphous-Metal-Film Diffusion Barriers

NASA Technical Reports Server (NTRS)

Nicolet, M. A.

1987-01-01

Incorporation of N into Ni/W films reduces reactivity with Si substrate. Paper describes reactions between Si substrates and deposited amorphous Ni/W or Ni/N/W films. Thermal stability of amorphous Ni/W films as diffusion barriers in Si markedly improved by introduction of N into Ni/W films during deposition.

Alternating current magnetic susceptibility and heat dissipation by Mn{sub 1−x}Zn{sub x}Fe{sub 2}O{sub 4} nanoparticles for hyperthermia treatment

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

Kondo, T.; Mori, K.; Hachisu, M.

2015-05-07

Mn-Zn ferrite, Mn{sub 1−x}Zn{sub x}Fe{sub 2}O{sub 4} nanoparticles encapsulated in amorphous SiO{sub 2} were prepared using our original wet chemical method. X-ray diffraction patterns confirmed that the diameters of these particles were within 7–30 nm. Magnetization measurements for various sample compositions revealed that the saturation magnetization (M{sub s}) of 7 nm particles was maximum for the x = 0.2 sample. AC magnetic susceptibility measurements were performed for Mn{sub 0.8}Zn{sub 0.2}Fe{sub 2}O{sub 4} (x = 0.2) samples with 13–30 nm particles. The peak of the imaginary part of the magnetic susceptibility χ″ shifted to higher temperatures as the particle size increased. An AC field was found to causemore » the increase in temperature, with the 18 nm particles exhibiting the highest temperature increase, as expected. In addition, in vitro experiments were carried out to study the hyperthermia effects of Mn{sub 1−x}Zn{sub x}Fe{sub 2}O{sub 4} (x = 0.2, 18 nm) particles on human cancer cells.« less

Amorphization resistance of nano-engineered SiC under heavy ion irradiation

NASA Astrophysics Data System (ADS)

Imada, Kenta; Ishimaru, Manabu; Xue, Haizhou; Zhang, Yanwen; Shannon, Steven C.; Weber, William J.

2016-09-01

Silicon carbide (SiC) with a high-density of planar defects (hereafter, 'nano-engineered SiC') and epitaxially-grown single-crystalline 3C-SiC were simultaneously irradiated with Au ions at room temperature, in order to compare their relative resistance to radiation-induced amorphization. It was found that the local threshold dose for amorphization is comparable for both samples under 2 MeV Au ion irradiation; whereas, nano-engineered SiC exhibits slightly greater radiation tolerance than single crystalline SiC under 10 MeV Au irradiation. Under 10 MeV Au ion irradiation, the dose for amorphization increased by about a factor of two in both nano-engineered and single crystal SiC due to the local increase in electronic energy loss that enhanced dynamic recovery.

Effects of Mn Ion Implantation on XPS Spectroscopy of GaN Thin Films

NASA Astrophysics Data System (ADS)

Majid, Abdul; Ahmad, Naeem; Rizwan, Muhammad; Khan, Salah Ud-Din; Ali, Fekri Abdulraqeb Ahmed; Zhu, Jianjun

2018-02-01

Gallium nitride (GaN) thin film was deposited onto a sapphire substrate and then implanted with 250 keV Mn ions at two different doses of 2 × 1016 ions/cm2 and 5 × 1016 ions/cm2. The as-grown and post-implantation-thermally-annealed samples were studied in detail using x-ray photoelectron spectroscopy (XPS). The XPS peaks of Ga 3 d, Ga 2 p, N 1 s, Mn 2 p and C 1 s were recorded in addition to a full survey of the samples. The doublet peaks of Ga 2 p for pure GaN were observed blue-shifted when compared with elemental Ga, and appeared further shifted to higher energies for the implanted samples. These observations point to changes in the bonds and the chemical environment of the host as a result of ion implantation. The results revealed broadening of the N 1 s peak after implantation, which is interpreted in terms of the presence of N-Mn bonds in addition to N-Ga bonds. The XPS spectra of Mn 2 p recorded for ion-implanted samples indicated splitting of Mn 2 p 1/2 and Mn 2 p 3/2 peaks higher than that for metallic Mn, which helps rule out the possibility of clustering and points to substitutional doping of Mn. These observations provide a framework that sheds light on the local environment of the material for understanding the mechanism of magnetic exchange interactions in Mn:GaN based diluted magnetic semiconductors.

Measurement of Damage Profiles from Solar Wind Implantation

NASA Technical Reports Server (NTRS)

McNamara, K. M.; Synowicki, R. A.; Tiwald, T. E.

2007-01-01

NASA's Genesis Mission launched from Cape Canaveral in August of 2001 with the goal of collecting solar wind in ultra-pure materials. The samples were returned to Earth more than three years later for subsequent analysis. Although the solar wind is comprised primarily of protons, it also contains ionized species representing the entire periodic table. The Genesis mission took advantage of the natural momentum of these ionized species to implant themselves in specialized collectors including single crystal Si and SiC. The collectors trapped the solar wind species of interest and sustained significant damage to the surface crystal structure as a result of the ion bombardment. In this work, spectroscopic ellipsometry has been used to evaluate the extent of this damage in Si and SiC samples. These results and models are compared for artificially implanted samples and pristine non-flight material. In addition, the flown samples had accumulated a thin film of molecular contamination as a result of outgassing in flight, and we demonstrate that this layer can be differentiated from the material damage. In addition to collecting bulk solar wind samples (continuous exposure), the Genesis mission actually returned silicon exposed to four different solar wind regimes: bulk, high speed, low speed, and coronal mass ejections. Each of these solar wind regimes varies in energy, but may vary in composition as well. While determining the composition is a primary goal of the mission, we are also interested in the variation in depth and extent of the damage layer as a function of solar wind regime. Here, we examine flight Si from the bulk solar wind regime and compare the results to both pristine and artificially implanted Si. Finally, there were four samples which were mounted in an electrostatic "concentrator" designed to reject a large fraction (>85%) of incoming protons while enhancing the concentration of ions mass 4-28 amu by a factor of at least 20. Two of these samples were single crystal 6H silicon carbide. (The others were polycrystalline CVD diamond and amorphous carbon that were not examined in the work.) The ion damaged SiC samples from the concentrator were studied in comparison to the flight Si from the bulk array to understand differences in the extent of the damage.

New Methods of Simulation of Mn(II) EPR Spectra: Single Crystals, Polycrystalline and Amorphous (Biological) Materials

NASA Astrophysics Data System (ADS)

Misra, Sushil K.

Biological systems exhibit properties of amorphous materials. The Mn(II) ion in amorphous materials is characterized by distributions of spin-Hamiltonian parameters around mean values. It has a certain advantage over other ions, being one of the most abundant elements on the earth. The extent to which living organisms utilize manganese varies from one organism to the other. There is a fairly high concentration of the Mn(II) ion in green plants, which use it in the O2 evolution reaction of photosynthesis (Sauer, 1980). Structure-reactivity relationships in Mn(II)-O2 complexes are given in a review article by Coleman and Taylor (1980). Manganese is a trace requirement in animal nutrition; highly elevated levels of manganese in the diet can be toxic, probably because of an interference with iron homeostasis (Underwood, 1971). On the other hand, animals raised with a dietary deficiency of manganese exhibit severe abnormalities in connective tissue; these problems have been attributed to the obligatory role of Mn(II) in mucopolysaccharide metabolism (Leach, 1971). Mn(II) has been detected unequivocally in living organisms.

MnO2/carbon nanowalls composite electrode for supercapacitor application

NASA Astrophysics Data System (ADS)

Hassan, Sameh; Suzuki, Masaaki; Mori, Shinsuke; El-Moneim, Ahmed Abd

2014-03-01

Amorphous MnO2/carbon nanowalls composite films are developed for the supercapacitor applications. Synthesis of carbon nanowalls template is performed by plasma-enhanced chemical vapor deposition in a CO/H2 microwave discharge system. A well dispersion of amorphous MnO2 domains throughout carbon nanowalls template is obtained by potentiostatic anodic deposition technique. Carbon nanowalls enable to improve the capacitive behavior and rate capability of MnO2, a specific capacitance of 851 F g-1 at a current density of 1 mA cm-2 and charge transfer resistance of 1.02 Ω are obtained. MnO2/carbon nanowalls composite film exhibits energy density of 118 wh kg-1, power density of 783 wh kg-1, and capacitance retention of 92% after long cycle life of 2000 cycles by charging and discharging at 3 mA cm-2. The high density of atomic scale graphitic edges and large surface area of carbon nanowalls in conjunction with the presence of amorphous MnO2 domains facilitate rapid electron and ion transport and hence offering the potential of the improved capacitive behavior.

In situ TEM observation of preferential amorphization in single crystal Si nanowire

NASA Astrophysics Data System (ADS)

Su, Jiangbin; Zhu, Xianfang

2018-06-01

The nanoinstability of a single crystal Si nanowire under electron beam irradiation was in situ investigated at room temperature by the transmission electron microscopy technique. It was observed that the Si nanowire amorphized preferentially from the surface towards the center, with the increasing of the electron dose. In contrast, in the center of the Si nanowire the amorphization seemed much more difficult, being accompanied by the rotation of crystal grains and the compression of d-spacing. Such a preferential amorphization, which is athermally induced by the electron beam irradiation, can be well accounted for by our proposed concepts of the nanocurvature effect and the energetic beam-induced athermal activation effect, while the classical knock-on mechanism and the electron beam heating effect seem inadequate to explain these processes. Furthermore, the findings revealed the difference of amorphization between a Si nanowire and a Si film under electron beam irradiation. Also, the findings have important implications for the nanoinstability and nanoprocessing of future Si nanowire-based devices.

In situ TEM observation of preferential amorphization in single crystal Si nanowire.

PubMed

Su, Jiangbin; Zhu, Xianfang

2018-06-08

The nanoinstability of a single crystal Si nanowire under electron beam irradiation was in situ investigated at room temperature by the transmission electron microscopy technique. It was observed that the Si nanowire amorphized preferentially from the surface towards the center, with the increasing of the electron dose. In contrast, in the center of the Si nanowire the amorphization seemed much more difficult, being accompanied by the rotation of crystal grains and the compression of d-spacing. Such a preferential amorphization, which is athermally induced by the electron beam irradiation, can be well accounted for by our proposed concepts of the nanocurvature effect and the energetic beam-induced athermal activation effect, while the classical knock-on mechanism and the electron beam heating effect seem inadequate to explain these processes. Furthermore, the findings revealed the difference of amorphization between a Si nanowire and a Si film under electron beam irradiation. Also, the findings have important implications for the nanoinstability and nanoprocessing of future Si nanowire-based devices.

Fast Li-Ion Transport in Amorphous Li 2Si 2O 5: An Ab Initio Molecular Dynamics Simulation

DOE PAGES

Lei, Xueling; Wang, Jie; Huang, Kevin

2016-05-03

The present study reports an ab-initio molecular dynamics (AIMD) simulation of ionic diffusion in the amorphous Li 2Si 2O 5 in a temperature range of 573–823 K. The results show that the amorphous Li 2Si 2O 5 is primarily a Li + conductor with negligible O 2- and Si 4+ contributions. The obtained activation energy of 0.47 eV for Li + diffusion is higher than Na + in the analogue amorphous Na 2Si 2O 5, but close to other types of Li + conductors. The predicted Li + conductivity is on the order of 10 -2 S·cm -1 at 623–823more » K. Our simulations also reveal that Li + in the amorphous Li 2Si 2O 5 diffuses via a hopping mechanism between the nearest sites in the channels formed by two adjacent SiO 4 layers.« less

Wettability of MnxSiyOz by Liquid Zn-Al Alloys

NASA Astrophysics Data System (ADS)

Kim, Yunkyum; Shin, Minsoo; Tang, Chengying; Lee, Joonho

2010-08-01

The wettability of MnxSiyOz by liquid Zn-Al alloys was investigated to obtain basic information on the coating properties of high-strength steels with surface oxides in the hot-dip galvanizing process. In this study, the contact angles of liquid Zn-Al alloys (Al concentrations were 0.12 and 0.23 wt pct) on four different MnxSiyOz oxides, namely MnO, MnSiO3, Mn2SiO4, and SiO2, were measured with the dispensed drop method. The contact angle did not change across time. With an increasing Al concentration, the contact angle was slightly decreased for MnO and Mn2SiO4, but there was no change for MnSiO3 and SiO2. With an increasing SiO2 content, the contact angle gradually increased by 54 wt pct to form MnSiO3, and for pure SiO2 substrate, the contact angle decreased again. Consequently, the MnSiO3 substrate showed the worst wettability among the four tested oxide substrates.

Dependence of short and intermediate-range order on preparation in experimental and modeled pure a-Si

DOE PAGES

Holmstrom, Eero; Haberl, Bianca; Pakarinen, Olli H.; ...

2016-02-20

Variability in the short-to-intermediate range order of pure amorphous silicon prepared by different experimental and computational techniques is probed by measuring mass density, atomic coordination, bond-angle deviation, and dihedral angle deviation. It is found that there is significant variability in order parameters at these length scales in this archetypal covalently bonded, monoatomic system. This diversity strongly reflects preparation technique and thermal history in both experimental and simulated systems. Experiment and simulation do not fully quantitatively agree, partly due to differences in the way parameters are accessed. However, qualitative agreement in the trends is identified. Relaxed forms of amorphous silicon closelymore » resemble continuous random networks generated by a hybrid method of bond-switching Monte Carlo and molecular dynamics simulation. As-prepared ion implanted amorphous silicon can be adequately modeled using a structure generated from amorphization via ion bombardement using energetic recoils. Preparation methods which narrowly avoid crystallization such as experimental pressure-induced amorphization or simulated melt-quenching result in inhomogeneous structures that contain regions with significant variations in atomic ordering. Ad hoc simulated structures containing small (1 nm) diamond cubic crystal inclusions were found to possess relatively high bond-angle deviations and low dihedral angle deviations, a trend that could not be reconciled with any experimental material.« less

Electron-beam induced amorphization of stishovite: Silicon-coordination change observed using Si K-edge extended electron energy-loss fine structure

NASA Astrophysics Data System (ADS)

van Aken, P. A.; Sharp, T. G.; Seifert, F.

The analysis of the extended energy-loss fine structure (EXELFS) of the Si K-edge for sixfold-coordinated Si in synthetic stishovite and fourfold-coordinated Si in natural α-quartz is reported by using electron energy-loss spectroscopy (EELS) in combination with transmission electron microscopy (TEM). The stishovite Si K-edge EXELFS spectra were measured as a time-dependent series to document irradiation-induced amorphization. The amorphization was also investigated through the change in Si K- and O K-edge energy-loss near edge structure (ELNES). For α-quartz, in contrast to stishovite, electron irradiation-induced vitrification, verified by selected area electron diffraction (SAED), produced no detectable changes of the EXELFS. The Si K-edge EXELFS were analysed with the classical extended X-ray absorption fine structure (EXAFS) treatment and compared to ab initio curve-waved multiple-scattering (MS) calculations of EXAFS spectra for stishovite and α-quartz. Highly accurate information on the local atomic environment of the silicon atoms during the irradiation-induced amorphization of stishovite is obtained from the EXELFS structure parameters (Si-O bond distances, coordination numbers and Debye-Waller factors). The mean Si-O bond distance R and mean Si coordination number N changes from R=0.1775 nm and N=6 for stishovite through a disordered intermediate state (R 0.172 nm and N 5) to R 0.167 nm and N 4.5 for a nearly amorphous state similar to α-quartz (R=0.1609 nm and N=4). During the amorphization process, the Debye-Waller factor (DWF) passes through a maximum value of as it changes from for sixfold to for fourfold coordination of Si. This increase in Debye-Waller factor indicates an increase in mean-square relative displacement (MSRD) between the central silicon atom and its oxygen neighbours that is consistent with the presence of an intermediate structural state with fivefold coordination of Si. The distribution of coordination states can be estimated by modelling the amorphization as a decay process. Using the EXELFS data for amorphization, a new method is developed to derive the relative amounts of Si coordinations in high-pressure minerals with mixed coordination. For the radiation-induced amorphization process of stishovite the formation of a transitory structure with Si largely in fivefold coordination is deduced.

Mn@Si14+: a singlet fullerene-like endohedrally doped silicon cluster.

PubMed

Ngan, Vu Thi; Pierloot, Kristine; Nguyen, Minh Tho

2013-04-21

The electronic structure of Mn@Si14(+) is determined using DFT and CASPT2/CASSCF(14,15) computations with large basis sets. The endohedrally Mn-doped Si cationic cluster has a D3h fullerene-like structure featuring a closed-shell singlet ground state with a singlet-triplet gap of ~1 eV. A strong stabilizing interaction occurs between the 3d(Mn) and the 2D-shell(Si14) orbitals, and a large amount of charge is transferred from the Si14 cage to the Mn dopant. The 3d(Mn) orbitals are filled by encapsulation, and the magnetic moment of Mn is completely quenched. Full occupation of [2S, 2P, 2D] shell orbitals by 18 delocalized electrons confers the doped Mn@Si14(+) cluster a spherically aromatic character.

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

Molecular dynamics simulations of damage production by thermal spikes in Ge

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

Lopez, Pedro; Pelaz, Lourdes; Santos, Ivan

2012-02-01

Molecular dynamics simulation techniques are used to analyze damage production in Ge by the thermal spike process and to compare the results to those obtained for Si. As simulation results are sensitive to the choice of the inter-atomic potential, several potentials are compared in terms of material properties relevant for damage generation, and the most suitable potentials for this kind of analysis are identified. A simplified simulation scheme is used to characterize, in a controlled way, the damage generation through the local melting of regions in which energy is deposited. Our results show the outstanding role of thermal spikes inmore » Ge, since the lower melting temperature and thermal conductivity of Ge make this process much more efficient in terms of damage generation than in Si. The study is extended to the modeling of full implant cascades, in which both collision events and thermal spikes coexist. Our simulations reveal the existence of bigger damaged or amorphous regions in Ge than in Si, which may be formed by the melting and successive quenching induced by thermal spikes. In the particular case of heavy ion implantation, defect structures in Ge are not only bigger, but they also present a larger net content in vacancies than in Si, which may act as precursors for the growth of voids and the subsequent formation of honeycomb-like structures.« less

Role of pre-existing point defects on primary damage production and amorphization in silicon carbide (β-SiC)

NASA Astrophysics Data System (ADS)

Sahoo, Deepak Ranjan; Szlufarska, Izabela; Morgan, Dane; Swaminathan, Narasimhan

2018-01-01

Molecular dynamics simulations of displacement cascades were conducted to study the effect of point defects on the primary damage production in β-SiC. Although all types of point defects and Frenkel pairs were considered, Si interstitials and Si Frenkel pairs were unstable and hence excluded from the cascade studies. Si (C) vacancies had the maximum influence, enhancing C (Si) antisites and suppressing C interstitial production, when compared to the sample without any defects. The intracascade recombination mechanisms, in the presence of pre-existing defects, is explored by examining the evolution of point defects during the cascade. To ascertain the role of the unstable Si defects on amorphization, simulations involving explicit displacements of Si atoms were conducted. The dose to amorphization with only Si displacements was much lower than what was observed with only C displacements. The release of elastic energy accumulated due to Si defects, is found to be the amorphizing mechanism.

Characterization of PEEK, PET and PI implanted with Mn ions and sub-sequently annealed

NASA Astrophysics Data System (ADS)

Mackova, A.; Malinsky, P.; Miksova, R.; Pupikova, H.; Khaibullin, R. I.; Slepicka, P.; Gombitová, A.; Kovacik, L.; Svorcik, V.; Matousek, J.

2014-04-01

Polyimide (PI), polyetheretherketone (PEEK) and polyethylene terephthalate (PET) foils were implanted with 80 keV Mn+ ions at room temperature at fluencies of 1.0 × 1015-1.0 × 1016 cm-2. Mn depth profiles determined by RBS were compared to SRIM 2012 and TRIDYN simulations. The processes taking place in implanted polymers under the annealing procedure were followed. The measured projected ranges RP differ slightly from the SRIM and TRIDYN simulation and the depth profiles are significantly broader (up to 2.4 times) than those simulated by SRIM, while TRIDYN simulations were in a reasonable agreement up to the fluence 0.5 × 1016 in PEEK. Oxygen and hydrogen escape from the implanted layer was examined using RBS and ERDA techniques. PET, PEEK and PI polymers exhibit oxygen depletion up to about 40% of its content in virgin polymers. The compositional changes induced by implantation to particular ion fluence are similar for all polymers examined. After annealing no significant changes of Mn depth distribution was observed even the further oxygen and hydrogen desorption from modified layers appeared. The surface morphology of implanted polymers was characterized using AFM. The most significant change in the surface roughness was observed on PEEK. Implanted Mn atoms tend to dissipate in the polymer matrix, but the Mn nanoparticles are too small to be observed on TEM micrographs. The electrical, optical and structural properties of the implanted and sub-sequently annealed polymers were investigated by sheet resistance measurement and UV-Vis spectroscopy. With increasing ion fluence, the sheet resistance decreases and UV-Vis absorbance increases simultaneously with the decline of optical band gap Eg. The most pronounced change in the resistance was found on PEEK. XPS spectroscopy shows that Mn appears as a mixture of Mn oxides. Mn metal component is not present. All results were discussed in comparison with implantation experiment using the various ion species (Ni, Co) and energies used in our former experiments. Interesting differences were found in Mn concentration distribution, Mn nano-particle creation and structural changes comparing to Ni, Co ions implantation into the same polymers.

Amorphization resistance of nano-engineered SiC under heavy ion irradiation

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

Imada, Kenta; Ishimaru, Manabu; Xue, Haizhou

Silicon carbide (SiC) with a high-density of planar defects (hereafter, ‘nano-engineered SiC’) and epitaxially-grown single-crystalline 3C-SiC were simultaneously irradiated with Au ions at room temperature, in order to compare their relative resistance to radiation-induced amorphization. Furthermore, it was found that the local threshold dose for amorphization is comparable for both samples under 2 MeV Au ion irradiation; whereas, nano-engineered SiC exhibits slightly greater radiation tolerance than single crystalline SiC under 10 MeV Au irradiation. Under 10 MeV Au ion irradiation, the dose for amorphization increased by about a factor of two in both nano-engineered and single crystal SiC due tomore » the local increase in electronic energy loss that enhanced dynamic recovery.« less

Amorphization resistance of nano-engineered SiC under heavy ion irradiation

DOE PAGES

Imada, Kenta; Ishimaru, Manabu; Xue, Haizhou; ...

2016-06-19

Silicon carbide (SiC) with a high-density of planar defects (hereafter, ‘nano-engineered SiC’) and epitaxially-grown single-crystalline 3C-SiC were simultaneously irradiated with Au ions at room temperature, in order to compare their relative resistance to radiation-induced amorphization. Furthermore, it was found that the local threshold dose for amorphization is comparable for both samples under 2 MeV Au ion irradiation; whereas, nano-engineered SiC exhibits slightly greater radiation tolerance than single crystalline SiC under 10 MeV Au irradiation. Under 10 MeV Au ion irradiation, the dose for amorphization increased by about a factor of two in both nano-engineered and single crystal SiC due tomore » the local increase in electronic energy loss that enhanced dynamic recovery.« less

Uniform surface modification of diatomaceous earth with amorphous manganese oxide and its adsorption characteristics for lead ions

NASA Astrophysics Data System (ADS)

Li, Song; Li, Duanyang; Su, Fei; Ren, Yuping; Qin, Gaowu

2014-10-01

A novel method to produce composite sorbent material compromising porous diatomaceous earth (DE) and surface functionalized amorphous MnO2 is reported. Via a simple in situ redox reaction over the carbonized DE powders, a uniform layer of amorphous MnO2 was anchored onto the DE surface. The hybrid adsorbent was characterized by X-ray diffraction, scanning electron microscopy, and infrared spectroscopy. The batch method has been employed to investigate the effects of surface coating on adsorption performance of DE. According to the equilibrium studies, the adsorption capacity of DE for adsorbing lead ions after MnO2 modification increased more than six times. And the adsorption of Pb2+ on the MnO2 surface is based on ion-exchange mechanism. The developed strategy presents a novel opportunity to prepare composite adsorbent materials by integrating nanocrystals with porous matrix.

The role of tree uprooting dynamics on the dynamics of Fe (Mn, Al and Si) forms in different forest soils

NASA Astrophysics Data System (ADS)

Tejnecký, V.; Samonil, P.; Boruvka, L.; Nikodem, A.; Drabek, O.; Valtera, M.

2013-12-01

Tree uprooting dynamics plays an important role in the development of forest ecosystems. This process causes bioturbation of soils and creates new microenvironments which consist of pits and mounds. These microtopographical forms could persist for some thousands of years. Pits and mounds undergo different pedogenesis in comparison to adjacent undisturbed soils. The stage of pedogenesis can be assessed according to the results of fractionation of Fe and also partially Mn, Al and Si. The main aim of this contribution is to assess the fractionation of Fe, Mn, Al and Si for three different soil regions. Soil samples were collected at three localities occurred along hypothetical gradient of soil weathering and leaching processes: The first was a (spruce)-fir-beech natural forest in the Razula region. The second location is the same type of natural forest in Zofin; however it has contrasting lithology. Both these natural forests are located in the Czech Republic (CZ). The third forest was a northern hardwood forest in Upper Peninsula, Michigan, USA. The prevailing soil types - Haplic Cambisols have formed on flysch parent materials in the Razula reserve; Entic Podzols have developed on granite residuum at the Zofin reserve, and Albic Podzols occurred in outwash parent materials at the Michigan sites (Šamonil et al., in press). In total 790 soil samples were analysed. These samples were collected from 5 depths (0-10, 15, 30, 50 and 100 cm) within the pit, mound and control, currently undisturbed position. For each sample, content of Fe (and Mn, Al, Si) forms: exchangeable, crystalline, and amorphous together with organically complexed Fe were determined. We generally observed an increased content of Fe soil forms in the pits of studied treethrows. The content of Fe forms increased along depth gradient at the disturbed sites. However, exchangeable Fe was most abundant in the 0-10cm layer which corresponds to the A horizon. Naturally, if present, the E horizon exhibited the lowest content of exchangeable Fe forms. The content of crystalline Fe forms also increased with the age of the windthrow. Differences in the amounts of Fe, Mn, Al and Si forms were observed between all studied localities. Research was supported by the Czech Science Foundation (project No. P504/11/2135). Šamonil P., Schaetzl R. J., Valtera M., Goliáš V., Baldrian P., Vašíčková I., Adam D., Janík D., Hort L. (in press). Crossdating of disturbances by tree uprooting: Can treethrow microtopography persist for 6,000 years? Forest Ecology and Management.

Transverse mode control in proton-implanted and oxide-confined VCSELs via patterned dielectric anti-phase filters

NASA Astrophysics Data System (ADS)

Kesler, Benjamin; O'Brien, Thomas; Dallesasse, John M.

2017-02-01

A novel method for controlling the transverse lasing modes in both proton implanted and oxide-confined vertical- cavity surface-emitting lasers (VCSELs) with a multi-layer, patterned, dielectric anti-phase (DAP) filter is pre- sented. Using a simple photolithographic liftoff process, dielectric layers are deposited and patterned on individual VCSELs to modify (increase or decrease) the mirror reflectivity across the emission aperture via anti-phase reflections, creating spatially-dependent threshold material gain. The shape of the dielectric pattern can be tailored to overlap with specific transverse VCSEL modes or subsets of transverse modes to either facilitate or inhibit lasing by decreasing or increasing, respectively, the threshold modal gain. A silicon dioxide (SiO2) and titanium dioxide (TiO2) anti-phase filter is used to achieve a single-fundamental-mode, continuous-wave output power greater than 4.0 mW in an oxide-confined VCSEL at a lasing wavelength of 850 nm. A filter consisting of SiO2 and TiO2 is used to facilitate injection-current-insensitive fundamental mode and lower order mode lasing in proton implanted VCSELs at a lasing wavelength of 850 nm. Higher refractive index dielectric materials such as amorphous silicon (a-Si) can be used to increase the effectiveness of the anti-phase filter on proton implanted devices by reducing the threshold modal gain of any spatially overlapping modes. This additive, non-destructive method allows for mode selection at any lasing wavelength and for any VCSEL layer structure without the need for semiconductor etching or epitaxial regrowth. It also offers the capability of designing a filter based upon available optical coating materials.

Structure and Properties of SiO x Films Prepared by Chemical Etching of Amorphous Alloy Ribbons

NASA Astrophysics Data System (ADS)

Fedorov, V. A.; Berezner, A. D.; Beskrovnyi, A. I.; Fursova, T. N.; Pavlikov, A. V.; Bazhenov, A. V.

2018-04-01

The structure and the physical properties of amorphous SiO x films prepared by chemical etching of an iron-based amorphous ribbon alloy have been studied. The neutron diffraction and also the atomicforce and electron microscopy show that the prepared visually transparent films have amorphous structure, exhibit dielectric properties, and their morphology is similar to that of opals. The samples have been studied by differential scanning calorimetry, Raman and IR spectroscopy before and after their heat treatment. It is found that annealing of the films in air at a temperature of 1273 K leads to a change in their chemical compositions: an amorphous SiO2 compound with inclusions of SiO2 nanocrystals (crystobalite) forms.

Mechanism of selenite removal by a mixed adsorbent based on Fe-Mn hydrous oxides studied using X-ray absorption spectroscopy.

PubMed

Chubar, Natalia; Gerda, Vasyl; Szlachta, Małgorzata

2014-11-18

Selenium cycling in the environment is greatly controlled by various minerals, including Mn and Fe hydrous oxides. At the same time, such hydrous oxides are the main inorganic ion exchangers suitable (on the basis of their chemical nature) to sorb (toxic) anions, separating them from water solutions. The mechanism of selenite adsorption by the new mixed adsorbent composed of a few (amorphous and crystalline) phases [maghemite, MnCO3, and X-ray amorphous Fe(III) and Mn(III) hydrous oxides] was studied by extended X-ray absorption fine structure (EXAFS) spectroscopy [supported by Fourier transform infrared (FTIR) and X-ray diffraction (XRD) data]. The complexity of the porous adsorbent, especially the presence of the amorphous phases of Fe(III) and Mn(III) hydrous oxides, is the main reason for its high selenite removal performance demonstrated by batch and column adsorption studies shown in the previous work. Selenite was bound to the material via inner-sphere complexation (via oxygen) to the adsorption sites of the amorphous Fe(III) and Mn(III) oxides. This anion was attracted via bidentate binuclear corner-sharing coordination between SeO3(2-) trigonal pyramids and both FeO6 and MnO6 octahedra; however, the adsorption sites of Fe(III) hydrous oxides played a leading role in selenite removal. The contribution of the adsorption sites of Mn(III) oxide increased as the pH decreased from 8 to 6. Because most minerals have a complex structure (they are seldom based on individual substances) of various crystallinity, this work is equally relevant to environmental science and environmental technology because it shows how various solid phases control cycling of chemical elements in the environment.

Grain boundary resistance to amorphization of nanocrystalline silicon carbide

PubMed Central

Chen, Dong; Gao, Fei; Liu, Bo

2015-01-01

Under the C displacement condition, we have used molecular dynamics simulation to examine the effects of grain boundaries (GBs) on the amorphization of nanocrystalline silicon carbide (nc-SiC) by point defect accumulation. The results show that the interstitials are preferentially absorbed and accumulated at GBs that provide the sinks for defect annihilation at low doses, but also driving force to initiate amorphization in the nc-SiC at higher doses. The majority of surviving defects are C interstitials, as either C-Si or C-C dumbbells. The concentration of defect clusters increases with increasing dose, and their distributions are mainly observed along the GBs. Especially these small clusters can subsequently coalesce and form amorphous domains at the GBs during the accumulation of carbon defects. A comparison between displacement amorphized nc-SiC and melt-quenched single crystal SiC shows the similar topological features. At a dose of 0.55 displacements per atom (dpa), the pair correlation function lacks long range order, demonstrating that the nc-SiC is fully amorphilized. PMID:26558694

Grain boundary resistance to amorphization of nanocrystalline silicon carbide.

PubMed

Chen, Dong; Gao, Fei; Liu, Bo

2015-11-12

Under the C displacement condition, we have used molecular dynamics simulation to examine the effects of grain boundaries (GBs) on the amorphization of nanocrystalline silicon carbide (nc-SiC) by point defect accumulation. The results show that the interstitials are preferentially absorbed and accumulated at GBs that provide the sinks for defect annihilation at low doses, but also driving force to initiate amorphization in the nc-SiC at higher doses. The majority of surviving defects are C interstitials, as either C-Si or C-C dumbbells. The concentration of defect clusters increases with increasing dose, and their distributions are mainly observed along the GBs. Especially these small clusters can subsequently coalesce and form amorphous domains at the GBs during the accumulation of carbon defects. A comparison between displacement amorphized nc-SiC and melt-quenched single crystal SiC shows the similar topological features. At a dose of 0.55 displacements per atom (dpa), the pair correlation function lacks long range order, demonstrating that the nc-SiC is fully amorphilized.

Electron-irradiation-induced crystallization at metallic amorphous/silicon oxide interfaces caused by electronic excitation

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

Nagase, Takeshi, E-mail: t-nagase@uhvem.osaka-u.ac.jp; Division of Materials and Manufacturing Science, Graduate School of Engineering, Osaka University, 2-1, Yamada-Oka, Suita, Osaka 565-0871; Yamashita, Ryo

2016-04-28

Irradiation-induced crystallization of an amorphous phase was stimulated at a Pd-Si amorphous/silicon oxide (a(Pd-Si)/SiO{sub x}) interface at 298 K by electron irradiation at acceleration voltages ranging between 25 kV and 200 kV. Under irradiation, a Pd-Si amorphous phase was initially formed at the crystalline face-centered cubic palladium/silicon oxide (Pd/SiO{sub x}) interface, followed by the formation of a Pd{sub 2}Si intermetallic compound through irradiation-induced crystallization. The irradiation-induced crystallization can be considered to be stimulated not by defect introduction through the electron knock-on effects and electron-beam heating, but by the electronic excitation mechanism. The observed irradiation-induced structural change at the a(Pd-Si)/SiO{sub x} and Pd/SiO{sub x}more » interfaces indicates multiple structural modifications at the metal/silicon oxide interfaces through electronic excitation induced by the electron-beam processes.« less

Reduction Behavior of Assmang and Comilog ore in the SiMn Process

NASA Astrophysics Data System (ADS)

Kim, Pyunghwa Peace; Holtan, Joakim; Tangstad, Merete

The reduction behavior of raw materials from Assmang and Comilog based charges were experimentally investigated with CO gas up to 1600 °C. Quartz, HC FeMn slag or limestone were added to Assmang or Comilog according to the SiMn production charge, and mass loss results were obtained by using a TGA furnace. The results showed that particle size, type of manganese ore and mixture have close relationship to the reduction behavior of raw materials during MnO and SiO2 reduction. The influence of particle size to mass loss was apparent when Assmang or Comilog was mixed with only coke (FeMn) while it became insignificant when quartz and HC FeMn slag (SiMn) were added. This implied that quartz and HC FeMn slag had favored the incipient slag formation regardless of particle size. This explained the similar mass loss tendencies of SiMn charge samples between 1200-1500 °C, contrary to FeMn charge samples where different particle sizes showed significant difference in mass loss. Also, while FeMn charge samples showed progressive mass loss, SiMn charge samples showed diminutive mass loss until 1500 °C. However, rapid mass losses were observed with SiMn charge samples in this study above 1500 °C, and they have occurred at different temperatures. This implied rapid reduction of MnO and SiO2 and the type of ore and addition of HC FeMn slag have significant influence determining these temperatures. The temperatures observed for the rapid mass loss were approximately 1503 °C (Quartz and HC FeMn slag addition in Assmang), 1543 °C (Quartz addition in Assmang) and 1580-1587 °C (Quartz and limestone addition in Comilog), respectively. These temperatures also showed indications of possible SiMn production at process temperatures lower than 1550 °C.

Arrays of suspended silicon nanowires defined by ion beam implantation: mechanical coupling and combination with CMOS technology.

PubMed

Llobet, J; Rius, G; Chuquitarqui, A; Borrisé, X; Koops, R; van Veghel, M; Perez-Murano, F

2018-04-02

We present the fabrication, operation, and CMOS integration of arrays of suspended silicon nanowires (SiNWs). The functional structures are obtained by a top-down fabrication approach consisting in a resistless process based on focused ion beam irradiation, causing local gallium implantation and silicon amorphization, plus selective silicon etching by tetramethylammonium hydroxide, and a thermal annealing process in a boron rich atmosphere. The last step enables the electrical functionality of the irradiated material. Doubly clamped silicon beams are fabricated by this method. The electrical readout of their mechanical response can be addressed by a frequency down-mixing detection technique thanks to an enhanced piezoresistive transduction mechanism. Three specific aspects are discussed: (i) the engineering of mechanically coupled SiNWs, by making use of the nanometer scale overhang that it is inherently-generated with this fabrication process, (ii) the statistical distribution of patterned lateral dimensions when fabricating large arrays of identical devices, and (iii) the compatibility of the patterning methodology with CMOS circuits. Our results suggest that the application of this method to the integration of large arrays of suspended SiNWs with CMOS circuitry is interesting in view of applications such as advanced radio frequency band pass filters and ultra-high-sensitivity mass sensors.

Arrays of suspended silicon nanowires defined by ion beam implantation: mechanical coupling and combination with CMOS technology

NASA Astrophysics Data System (ADS)

Llobet, J.; Rius, G.; Chuquitarqui, A.; Borrisé, X.; Koops, R.; van Veghel, M.; Perez-Murano, F.

2018-04-01

We present the fabrication, operation, and CMOS integration of arrays of suspended silicon nanowires (SiNWs). The functional structures are obtained by a top-down fabrication approach consisting in a resistless process based on focused ion beam irradiation, causing local gallium implantation and silicon amorphization, plus selective silicon etching by tetramethylammonium hydroxide, and a thermal annealing process in a boron rich atmosphere. The last step enables the electrical functionality of the irradiated material. Doubly clamped silicon beams are fabricated by this method. The electrical readout of their mechanical response can be addressed by a frequency down-mixing detection technique thanks to an enhanced piezoresistive transduction mechanism. Three specific aspects are discussed: (i) the engineering of mechanically coupled SiNWs, by making use of the nanometer scale overhang that it is inherently-generated with this fabrication process, (ii) the statistical distribution of patterned lateral dimensions when fabricating large arrays of identical devices, and (iii) the compatibility of the patterning methodology with CMOS circuits. Our results suggest that the application of this method to the integration of large arrays of suspended SiNWs with CMOS circuitry is interesting in view of applications such as advanced radio frequency band pass filters and ultra-high-sensitivity mass sensors.

UV Light-Driven Photodegradation of Methylene Blue by Using Mn0.5Zn0.5Fe2O4/SiO2 Nanocomposites

NASA Astrophysics Data System (ADS)

Indrayana, I. P. T.; Julian, T.; Suharyadi, E.

2018-04-01

The photodegradation activity of nanocomposites for 20 ppm methylene blue solution has been investigated in this work. Nanocomposites Mn0.5Zn0.5Fe2O4/SiO2 have been synthesized using coprecipitation method. The X-ray diffraction (XRD) pattern confirmed the formation of three phases in sample Mn0.5Zn0.5Fe2O4/SiO2 i.e., Mn0.5Zn0.5Fe2O4, Zn(OH)2, and SiO2. The appearance of SiO2 phase showed that the encapsulation process has been carried out. The calculated particles size of Mn0.5Zn0.5Fe2O4/SiO2 is greater than Mn0.5Zn0.5Fe2O4. Bonding analysis via vibrational spectra for Mn0.5Zn0.5Fe2O4/SiO2 confirmed the formation of bonds Me-O-Si stretching (2854.65 cm-1) and Si-O-Si asymmetric stretching (1026.13 cm-1). The optical gap energy of Mn0.5Zn0.5Fe2O4/SiO2 was smaller (2.70 eV) than Mn0.5Zn0.5Fe2O4 (3.04 eV) due to smaller lattice dislocation and microstrain that affect their electronic structure. The Mn0.5Zn0.5Fe2O4/SiO2 showed high photodegradation ability due to smaller optical gap energy and the appearance of SiO2 ligand that can easily attract dye molecules. The Mn0.5Zn0.5Fe2O4/SiO2 also showed high degradation activity even without UV light radiation. The result showed that photodegradation reaction doesn’t follow pseudo-first order kinetics.

Bimetal catalysts

DOEpatents

Ng, K. Y. Simon; Salley, Steve O.; Wang, Huali

2017-10-03

A catalyst comprises a carbide or nitride of a metal and a promoter element. The metal is selected from the group consisting of Mo, W, Co, Fe, Rh or Mn, and the promoter element is selected from the group consisting of Ni, Co, Al, Si, S or P, provided that the metal and the promoter element are different. The catalyst also comprises a mesoporous support having a surface area of at least about 170 m.sup.2 g.sup.-1, wherein the carbide or nitride of the metal and the promoter element is supported by the mesoporous support, and is in a non-sulfided form and in an amorphous form.

The aluminosilicate fraction of North Pacific manganese nodules

USGS Publications Warehouse

Bischoff, J.L.; Piper, D.Z.; Leong, K.

1981-01-01

Nine nodules collected from throughout the deep North Pacific were analyzed for their mineralogy and major-element composition before and after leaching with Chester-Hughes solution. Data indicate that the mineral phillipsite accounts for the major part (> 75%) of the aluminosilicate fraction of all nodules. It is suggested that formation of phillipsite takes place on growing nodule surfaces coupled with the oxidation of absorbed manganous ion. All the nodules could be described as ternary mixtures of amorphous iron fraction (Fe-Ti-P), manganese oxide fraction (Mn-Mg Cu-Ni), and phillipsite fraction (Al-Si-K-Na), these fractions accounting for 96% of the variability of the chemical composition. ?? 1981.

Preparation and Characterization of ZnO Nanoparticles Supported on Amorphous SiO2

PubMed Central

Chen, Ying; Ding, Hao; Sun, Sijia

2017-01-01

In order to reduce the primary particle size of zinc oxide (ZnO) and eliminate the agglomeration phenomenon to form a monodisperse state, Zn2+ was loaded on the surface of amorphous silica (SiO2) by the hydrogen bond association between hydroxyl groups in the hydrothermal process. After calcining the precursors, dehydration condensation among hydroxyl groups occurred and ZnO nanoparticles supported on amorphous SiO2 (ZnO–SiO2) were prepared. Furthermore, the SEM and TEM observations showed that ZnO nanoparticles with a particle size of 3–8 nm were uniformly and dispersedly loaded on the surface of amorphous SiO2. Compared with pure ZnO, ZnO–SiO2 showed a much better antibacterial performance in the minimum inhibitory concentration (MIC) test and the antibacterial properties of the paint adding ZnO–SiO2 composite. PMID:28796157

Constructing first-principles phase diagrams of amorphous LixSi using machine-learning-assisted sampling with an evolutionary algorithm

NASA Astrophysics Data System (ADS)

Artrith, Nongnuch; Urban, Alexander; Ceder, Gerbrand

2018-06-01

The atomistic modeling of amorphous materials requires structure sizes and sampling statistics that are challenging to achieve with first-principles methods. Here, we propose a methodology to speed up the sampling of amorphous and disordered materials using a combination of a genetic algorithm and a specialized machine-learning potential based on artificial neural networks (ANNs). We show for the example of the amorphous LiSi alloy that around 1000 first-principles calculations are sufficient for the ANN-potential assisted sampling of low-energy atomic configurations in the entire amorphous LixSi phase space. The obtained phase diagram is validated by comparison with the results from an extensive sampling of LixSi configurations using molecular dynamics simulations and a general ANN potential trained to ˜45 000 first-principles calculations. This demonstrates the utility of the approach for the first-principles modeling of amorphous materials.

Synthesis of Amorphous Powders of Ni-Si and Co-Si Alloys by Mechanical Alloying

NASA Astrophysics Data System (ADS)

Omuro, Keisuke; Miura, Harumatsu

1991-05-01

Amorphous powders of the Ni-Si and Co-Si alloys are synthesized by mechanical alloying (MA) from crystalline elemental powders using a high energy ball mill. The alloying and amorphization process is examined by X-ray diffraction, differential scanning calorimetry (DSC), and scanning electron microscopy. For the Ni-Si alloy, it is confirmed that the crystallization temperature of the MA powder, measured by DSC, is in good agreement with that of the powder sample prepared by mechanical grinding from the cast alloy ingot products of the same composition.

Si amorphization by focused ion beam milling: Point defect model with dynamic BCA simulation and experimental validation.

PubMed

Huang, J; Loeffler, M; Muehle, U; Moeller, W; Mulders, J J L; Kwakman, L F Tz; Van Dorp, W F; Zschech, E

2018-01-01

A Ga focused ion beam (FIB) is often used in transmission electron microscopy (TEM) analysis sample preparation. In case of a crystalline Si sample, an amorphous near-surface layer is formed by the FIB process. In order to optimize the FIB recipe by minimizing the amorphization, it is important to predict the amorphous layer thickness from simulation. Molecular Dynamics (MD) simulation has been used to describe the amorphization, however, it is limited by computational power for a realistic FIB process simulation. On the other hand, Binary Collision Approximation (BCA) simulation is able and has been used to simulate ion-solid interaction process at a realistic scale. In this study, a Point Defect Density approach is introduced to a dynamic BCA simulation, considering dynamic ion-solid interactions. We used this method to predict the c-Si amorphization caused by FIB milling on Si. To validate the method, dedicated TEM studies are performed. It shows that the amorphous layer thickness predicted by the numerical simulation is consistent with the experimental data. In summary, the thickness of the near-surface Si amorphization layer caused by FIB milling can be well predicted using the Point Defect Density approach within the dynamic BCA model. Copyright © 2017 Elsevier B.V. All rights reserved.

Ion-sculpting of nanopores in amorphous metals, semiconductors, and insulators

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

George, H. Bola; Madi, Charbel S.; Aziz, Michael J.

2010-06-28

We report the closure of nanopores to single-digit nanometer dimensions by ion sculpting in a range of amorphous materials including insulators (SiO{sub 2} and SiN), semiconductors (a-Si), and metallic glasses (Pd{sub 80}Si{sub 20})--the building blocks of a single-digit nanometer electronic device. Ion irradiation of nanopores in crystalline materials (Pt and Ag) does not cause nanopore closure. Ion irradiation of c-Si pores below 100 deg. C and above 600 deg. C, straddling the amorphous-crystalline dynamic transition temperature, yields closure at the lower temperature but no mass transport at the higher temperature. Ion beam nanosculpting appears to be restricted to materials thatmore » either are or become amorphous during ion irradiation.« less

Exploring the origins of the Dzyaloshinskii-Moriya interaction in MnSi

DOE PAGES

Dhital, C.; DeBeer-Schmitt, L.; Zhang, Q.; ...

2017-12-19

By using magnetization and small-angle neutron scattering (SANS) measurements, we have investigated the magnetic behavior of the Mn 1-xIr xSi system to explore the effect of increased carrier density and spin-orbit interaction on the magnetic properties of MnSi. We determine estimates of the spin wave stiffness and the Dzyalloshinski-Moriya (DM) interaction strength and compare with Mn 1-xCo xSi and Mn 1-xFe xSi. Despite the large differences in atomic mass and size of the substituted elements, Mn 1-xCo xSi and Mn 1-xIr xSi show nearly identical variations in their magnetic properties with substitution. We find a systematic dependence of the transitionmore » temperature, the ordered moment, the helix period, and the DM interaction strength with electron count for Mn 1-xIr xSi, Mn 1-xCo xSi, and Mn 1-xFe xSi, indicating that the magnetic behavior is primarily dependent upon the additional carrier density, rather than on the mass or size of the substituting species. This indicates that the variation in magnetic properties, including the DM interaction strength, is primarily controlled by the electronic structure, as Co and Ir are isovalent. Our work suggests that although the rigid band model of electronic structure, along with Moriya’s model of weak itinerant magnetism, describes this system surprisingly well, phenomenological models for the DM interaction strength are not adequate to describe this system.« less

Effects of Mn addition on microstructure and hardness of Al-12.6Si alloy

NASA Astrophysics Data System (ADS)

Biswas, Prosanta; Patra, Surajit; Mondal, Manas Kumar

2018-03-01

In this work, eutectic Al-12.6Si alloy with and without manganese (Mn) have been developed through gravity casting route. The effect of Mn concentration (0.0 wt.%, 1 wt%, 2 wt% and 3 wt%) on microstructural morphology and hardness property of the alloy has been investigated. The eutectic Al-12.6 Si alloy exhibits the presence of combine plate, needle and rod-like eutectic silicon phase with very sharp corners and coarser primary silicon particles within the α-Al phase. In addition of 1wt.% of Mn in the eutectic Al-12.6Si alloy, sharp corners of the primary Si and needle-like eutectic Si are became blunt and particles size is reduced. Further, increase in Mn concentration (2.0 wt.%) in the Al-12.6Si alloy, irregular plate shape Al6(Mn,Fe) intermetallics are formed inside the α-Al phase, but the primary and eutectic phase morphology is similar to the eutectic Al-12.6Si alloy. The volume fraction of Al6(Mn,Fe) increases and Al6(Mn,Fe) particles appear as like chain structure in the alloy with 3 wt.% Mn. An increase in Mn concentration in the Al-12.6Si alloys result in the increase in bulk hardness of the alloy as an effects of microstructure modification as well as the presence of harder Al6(Mn,Fe) phase in the developed alloy.

The parameter influence of ion irradiation on the distribution profile of the defect in silicon films

NASA Astrophysics Data System (ADS)

Shemukhin, A. A.; Balaskshin, Yu. V.; Evseev, A. P.; Chernysh, V. S.

2017-09-01

As silicon is an important element in semiconductor devices, the process of defect formation under ion irradiation in it is studied well enough. Modern electronic components are made on silicon lattices (films) that are 100-300 nm thick (Chernysh et al., 1980; Shemukhin et al., 2012; Ieshkin et al., 2015). However, there are still features to be observed in the process of defect formation in silicon. In our work we investigate the effect of fluence and target temperature on the defect formation in films and bulk silicon samples. To investigate defect formation in the silicon films and bulk silicon samples we present experimental data on Si+ implantation with an energy of 200 keV, fluences range from 5 * 1014 to 5 * 1015 ion/cm2 for a fixed flux 1 μA/cm2 and the substrate temperatures from 150 to 350 K The sample crystallinity was investigated by using the Rutherford backscattering technique (RBS) in channeling and random modes. It is shown that in contrast to bulk silicon for which amorphization is observed at 5 × 1016 ion/cm2, the silicon films on sapphire amorphize at lower critical fluences (1015 ion/cm2). So the amorphization critical fluences depend on the target temperature. In addition it is shown that under similar implantation parameters, the disordering of silicon films under the action of the ion beam is stronger than the bulk silicon.

Surface modification by carbon ion implantation for the application of ni-based amorphous alloys as bipolar plate in proton exchange membrane fuel cells

NASA Astrophysics Data System (ADS)

Kim, Min-Uk; Kim, Do-Hyang; Han, Seung-hee; Fleury, Eric; Seok, Hyun-Kwang; Cha, Pil-Ryung; Kim, Yu-Chan

2011-04-01

Ni-based amorphous alloys with surface modification by carbon ion implantation are proposed as an alternative bipolar plate material for polymer electrolyte membrane fuel cells (PEMFCs). Both Ni60Nb20Ti10Zr10 alloys with and without carbon ion implantation have corrosion resistance as good as graphite as well as much lower contact resistance than 316L stainless steel in the PEMFC environment. The formation of conductive surface carbide due to carbon ion implantation results in a decrease in the contact resistance to a level comparable to that of graphite. This combination of excellent properties indicates that carbon ion implanted Ni-based amorphous alloys can be potential candidate materials for bipolar plates in PEMFCs.

Critical Evaluations and Thermodynamic Optimizations of the MnO-Mn2O3-SiO2 and FeO-Fe2O3-MnO-Mn2O3-SiO2 Systems

NASA Astrophysics Data System (ADS)

Kang, Youn-Bae; Jung, In-Ho

2017-06-01

A critical evaluation and thermodynamic modeling for thermodynamic properties of all oxide phases and phase diagrams in the Fe-Mn-Si-O system (MnO-Mn2O3-SiO2 and FeO-Fe2O3-MnO-Mn2O3-SiO2 systems) are presented. Optimized Gibbs energy parameters for the thermodynamic models of the oxide phases were obtained which reproduce all available and reliable experimental data within error limits from 298 K (25°C) to above the liquidus temperatures at all compositions covering from known oxide phases, and oxygen partial pressure from metal saturation to 0.21 bar. The optimized thermodynamic properties and phase diagrams are believed to be the best estimates presently available. Slag (molten oxide) was modeled using the modified quasichemical model in the pair approximation. Olivine (Fe2SiO4-Mn2SiO4) was modeled using two-sublattice model in the framework of the compound energy formalism (CEF), while rhodonite (MnSiO3-FeSiO3) and braunite (Mn7SiO_{12} with excess Mn2O3) were modeled as simple Henrian solutions. It is shown that the already developed models and databases of two spinel phases (cubic- and tetragonal-(Fe, Mn)3O4) using CEF [Kang and Jung, J. Phys. Chem. Solids (2016), vol. 98, pp. 237-246] can successfully be integrated into a larger thermodynamic database to be used in practically important higher order system such as silicate. The database of the model parameters can be used along with a software for Gibbs energy minimization in order to calculate any type of phase diagram section and thermodynamic properties.

Characterization of crystal structure features of a SIMOX substrate

NASA Astrophysics Data System (ADS)

Eidelman, K. B.; Shcherbachev, K. D.; Tabachkova, N. Yu.; Podgornii, D. A.; Mordkovich, V. N.

2015-12-01

The SIMOX commercial sample (Ibis corp.) was investigated by a high-resolution X-ray diffraction (HRXRD), a high-resolution transmission electron microscopy (HRTEM) and an Auger electron spectroscopy (AES) to determine its actual parameters (the thickness of the top Si and a continuous buried oxide layer (BOX), the crystalline quality of the top Si layer). Under used implantation conditions, the thickness of the top Si and BOX layers was 200 nm and 400 nm correspondingly. XRD intensity distribution near Si(0 0 4) reciprocal lattice point was investigated. According to the oscillation period of the diffraction reflection curve defined thickness of the overtop silicon layer (220 ± 2) nm. HRTEM determined the thickness of the oxide layer (360 nm) and revealed the presence of Si islands with a thickness of 30-40 nm and a length from 30 to 100 nm in the BOX layer nearby "BOX-Si substrate" interface. The Si islands are faceted by (1 1 1) and (0 0 1) faces. No defects were revealed in these islands. The signal from Si, which corresponds to the particles in an amorphous BOX matrix, was revealed by AES in the depth profiles. Amount of Si single crystal phase at the depth, where the particles are deposited, is about 10-20%.

Spectroellipsometric detection of silicon substrate damage caused by radiofrequency sputtering of niobium oxide

NASA Astrophysics Data System (ADS)

Lohner, Tivadar; Serényi, Miklós; Szilágyi, Edit; Zolnai, Zsolt; Czigány, Zsolt; Khánh, Nguyen Quoc; Petrik, Péter; Fried, Miklós

2017-11-01

Substrate surface damage induced by deposition of metal atoms by radiofrequency (rf) sputtering or ion beam sputtering onto single-crystalline silicon (c-Si) surface has been characterized earlier by electrical measurements. The question arises whether it is possible to characterize surface damage using spectroscopic ellipsometry (SE). In our experiments niobium oxide layers were deposited by rf sputtering on c-Si substrates in gas mixture of oxygen and argon. Multiple angle of incidence spectroscopic ellipsometry measurements were performed, a four-layer optical model (surface roughness layer, niobium oxide layer, native silicon oxide layer and ion implantation-amorphized silicon [i-a-Si] layer on a c-Si substrate) was created in order to evaluate the spectra. The evaluations yielded thicknesses of several nm for the i-a-Si layer. Better agreement could be achieved between the measured and the generated spectra by inserting a mixed layer (with components of c-Si and i-a-Si applying the effective medium approximation) between the silicon oxide layer and the c-Si substrate. High depth resolution Rutherford backscattering (RBS) measurements were performed to investigate the interface disorder between the deposited niobium oxide layer and the c-Si substrate. Atomic resolution cross-sectional transmission electron microscopy investigation was applied to visualize the details of the damaged subsurface region of the substrate.

Electronic transport properties of nanostructured MnSi-films

NASA Astrophysics Data System (ADS)

Schroeter, D.; Steinki, N.; Scarioni, A. Fernández; Schumacher, H. W.; Süllow, S.; Menzel, D.

2018-05-01

MnSi, which crystallizes in the cubic B20 structure, shows intriguing magnetic properties involving the existence of skyrmions in the magnetic phase diagram. Bulk MnSi has been intensively investigated and thoroughly characterized, in contrast to MnSi thin film, which exhibits widely varying properties in particular with respect to electronic transport. In this situation, we have set out to reinvestigate the transport properties in MnSi thin films by means of studying nanostructure samples. In particular, Hall geometry nanostructures were produced to determine the intrinsic transport properties.

Surface-enhanced Raman scattering of amorphous silica gel adsorbed on gold substrates for optical fiber sensors

NASA Astrophysics Data System (ADS)

Degioanni, S.; Jurdyc, A. M.; Cheap, A.; Champagnon, B.; Bessueille, F.; Coulm, J.; Bois, L.; Vouagner, D.

2015-10-01

Two kinds of gold substrates are used to produce surface-enhanced Raman scattering (SERS) of amorphous silica obtained via the sol-gel route using tetraethoxysilane Si(OC2H5)4 (TEOS) solution. The first substrate consists of a gold nanometric film elaborated on a glass slide by sputter deposition, controlling the desired gold thickness and sputtering current intensity. The second substrate consists of an array of micrometer-sized gold inverted pyramidal pits able to confine surface plasmon (SP) enhancing electric field, which results in a distribution of electromagnetic energy inside the cavities. These substrates are optically characterized to observe SPR with, respectively, extinction and reflectance spectrometries. Once coated with thin layers of amorphous silica (SiO2) gel, these samples show Raman amplification of amorphous SiO2 bands. This enhancement can occur in SERS sensors using amorphous SiO2 gel as shells, spacers, protective coatings, or waveguides, and represents particularly a potential interest in the field of Raman distributed sensors, which use the amorphous SiO2 core of optical fibers as a transducer to make temperature measurements.

Low Thermal Conductivity of Bulk Amorphous Si1- x Ge x Containing Nano-Sized Crystalline Particles Synthesized by Ball-Milling Process

NASA Astrophysics Data System (ADS)

Muthusamy, Omprakash; Nishino, Shunsuke; Ghodke, Swapnil; Inukai, Manabu; Sobota, Robert; Adachi, Masahiro; Kiyama, Makato; Yamamoto, Yoshiyuki; Takeuchi, Tsunehiro; Santhanakrishnan, Harish; Ikeda, Hiroya; Hayakawa, Yasuhiro

2018-06-01

Amorphous Si0.65Ge0.35 powder containing a small amount of nano-sized crystalline particles was synthesized by means of the mechanical alloying process. Hot pressing for 24 h under the pressure of 400 MPa at 823 K, which is below the crystallization temperature, allowed us to obtain bulk amorphous Si-Ge alloy containing a small amount of nanocrystals. The thermal conductivity of the prepared bulk amorphous Si-Ge alloy was extremely low, showing a magnitude of less than 1.35 Wm-1 K-1 over the entire temperature range from 300 K to 700 K. The sound velocity of longitudinal and transverse waves for the bulk amorphous Si0.65Ge0.35 were measured, and the resulting values were 5841 m/s and 2840 m/s, respectively. The estimated mean free path of phonons was kept at the very small value of ˜ 4.2 nm, which was mainly due to the strong scattering limit of phonons in association with the amorphous structure.

Metal-oxide thin-film transistor-based pH sensor with a silver nanowire top gate electrode

NASA Astrophysics Data System (ADS)

Yoo, Tae-Hee; Sang, Byoung-In; Wang, Byung-Yong; Lim, Dae-Soon; Kang, Hyun Wook; Choi, Won Kook; Lee, Young Tack; Oh, Young-Jei; Hwang, Do Kyung

2016-04-01

Amorphous InGaZnO (IGZO) metal-oxide-semiconductor thin-film transistors (TFTs) are one of the most promising technologies to replace amorphous and polycrystalline Si TFTs. Recently, TFT-based sensing platforms have been gaining significant interests. Here, we report on IGZO transistor-based pH sensors in aqueous medium. In order to achieve stable operation in aqueous environment and enhance sensitivity, we used Al2O3 grown by using atomic layer deposition (ALD) and a porous Ag nanowire (NW) mesh as the top gate dielectric and electrode layers, respectively. Such devices with a Ag NW mesh at the top gate electrode rapidly respond to the pH of solutions by shifting the turn-on voltage. Furthermore, the output voltage signals induced by the voltage shifts can be directly extracted by implantation of a resistive load inverter.

MnO2 nanorods/SiO2 sphere coated on single-wall carbon nanotubes as supercapacitor electrode for high energy storage applications

NASA Astrophysics Data System (ADS)

Iro, Zaharaddeen S.; Subramani, C.; Kesavan, T.; Dash, S. S.; Sasidharan, M.; Sundramoorthy, Ashok K.

2017-12-01

A composite of MnO2/SiO2 sphere was coated on single-wall carbon nanotubes (MnO2/SiO2/SWCNT) using one-pot hydrothermal synthesis method. KMnO4 was used as an oxidizing agent for mild functionalization of single-wall carbon nanotubes (SWCNT), and also as a precursor of MnO2. A comparative study in the presence of SiO2 and SWCNT was carried out using bare MnO2 as a reference. After addition of SiO2, the composite obtained showed an increase in both the specific capacitance and cycle life which can be associated with spherical shape of SiO2 which offered reduction sites for MnO2. With the addition of SWCNT less than 5%, the composite further showed an increase in capacitance and cycle life, this is because of the good conductive nature, excellent mechanical property and chemical stability of SWCNT. The electrochemical behaviour was studied using cyclic voltammetry and galvanostatic charge/discharge method in 1 M Na2SO4 electrolyte. The specific capacitance of MnO2, MnO2/SiO2 and MnO2/SiO2/SWCNT composite is 73.6 F g-1, 108.7 F g-1 and 136 F g-1 at a current density of 1 A g-1, respectively. The MnO2/SiO2/SWCNT energy density was 68 Wh kg-1 with power density of 444.4 W kg-1. The MnO2/SiO2/SWCNT composite retained 88% of its specific capacitance after 500 cycles. We envisage that this hybrid material could be applied for preparation of supercapacitor electrode.

Synthesis of microsphere silicon carbide/nanoneedle manganese oxide composites and their electrochemical properties as supercapacitors

NASA Astrophysics Data System (ADS)

Kim, Myeongjin; Yoo, Youngjae; Kim, Jooheon

2014-11-01

Synthesis of microsphere silicon carbide/nanoneedle MnO2 (SiC/N-MnO2) composites for use as high-performance materials in supercapacitors is reported herein. The synthesis procedure involves the initial treatment of silicon carbide (SiC) with hydrogen peroxide to obtain oxygen-containing functional groups to provide anchoring sites for connection of SiC and the MnO2 nanoneedles (N-MnO2). MnO2 nanoneedles are subsequently formed on the SiC surface. The morphology and microstructure of the as-prepared composites are characterized via X-ray diffractometry, field-emission scanning electron microscopy, thermogravimetric analysis, and X-ray photoelectron spectroscopy. The characterizations indicate that MnO2 nanoneedles are homogeneously formed on the SiC surface in the composite. The capacitive properties of the as-prepared SiC/N-MnO2 electrodes are evaluated using cyclic voltammetry, galvanostatic charge/discharge testing, and electrochemical impedance spectroscopy in a three-electrode experimental setup using a 1-M Na2SO4 aqueous solution as the electrolyte. The SiC/N-MnO2(5) electrode, for which the MnO2/SiC feed ratio is 5:1, displays a specific capacitance as high as 273.2 F g-1 at 10 mV s-1.

Enhanced electrochemical properties of F-doped Li2MnSiO4/C for lithium ion batteries

NASA Astrophysics Data System (ADS)

Wang, Chao; Xu, Youlong; Sun, Xiaofei; Zhang, Baofeng; Chen, Yanjun; He, Shengnan

2018-02-01

The Li2MnSiO4 as a novel cathode material for lithium ion batteries, performs high specific capacity, high thermal stability, low cost and etc. However, it suffers from relatively low electronic conductivity and lithium ion diffusion rate. Herein, we successfully introduce fluorine to Li2MnSiO4 (Li2MnSiO4-xFx, x = 0.00, 0.01, 0.03 and 0.05) to overcome these obstacles. The results show that F doping not only enlarges the lattice parameters but also decreases the particle size, synergistically improving the lithium ion diffusion of Li2MnSiO4. Moreover, F doping increase electronic conductivity of Li2MnSiO4/C by inhibiting the formation of C-O bonds in the carbon layers. Meanwhile, F doping improves the crystallinity and stabilizes the crystal structure of Li2MnSiO4. Finally, the Li2MnSiO3.97F0.03/C with the best electrochemical performances delivers the initial specific discharge capacity of 279 mA h g-1 at 25mA g-1 current density from 1.5 V to 4.8 V. Also, it maintains a higher capacity (201 mA h g-1) than F-free Li2MnSiO4 (145 mA h g-1) after 50 cycles.

Nanostructured manganese oxides as highly active water oxidation catalysts: a boost from manganese precursor chemistry.

PubMed

Menezes, Prashanth W; Indra, Arindam; Littlewood, Patrick; Schwarze, Michael; Göbel, Caren; Schomäcker, Reinhard; Driess, Matthias

2014-08-01

We present a facile synthesis of bioinspired manganese oxides for chemical and photocatalytic water oxidation, starting from a reliable and versatile manganese(II) oxalate single-source precursor (SSP) accessible through an inverse micellar molecular approach. Strikingly, thermal decomposition of the latter precursor in various environments (air, nitrogen, and vacuum) led to the three different mineral phases of bixbyite (Mn2 O3 ), hausmannite (Mn3 O4 ), and manganosite (MnO). Initial chemical water oxidation experiments using ceric ammonium nitrate (CAN) gave the maximum catalytic activity for Mn2 O3 and MnO whereas Mn3 O4 had a limited activity. The substantial increase in the catalytic activity of MnO in chemical water oxidation was demonstrated by the fact that a phase transformation occurs at the surface from nanocrystalline MnO into an amorphous MnOx (1

A study of the formation of amorphous calcium phosphate and hydroxyapatite on melt quenched Bioglass using surface sensitive shallow angle X-ray diffraction.

PubMed

Martin, R A; Twyman, H; Qiu, D; Knowles, J C; Newport, R J

2009-04-01

Melt quenched silicate glasses containing calcium, phosphorous and alkali metals have the ability to promote bone regeneration and to fuse to living bone. These glasses, including 45S5 Bioglass((R)) [(CaO)(26.9)(Na(2)O)(24.4)(SiO(2))(46.1)(P(2)O(5))(2.6)], are routinely used as clinical implants. Consequently there have been numerous studies on the structure of these glasses using conventional diffraction techniques. These studies have provided important information on the atomic structure of Bioglass((R)) but are of course intrinsically limited in the sense that they probe the bulk material and cannot be as sensitive to thin layers of near-surface dissolution/growth. The present study therefore uses surface sensitive shallow angle X-ray diffraction to study the formation of amorphous calcium phosphate and hydroxyapatite on Bioglass((R)) samples, pre-reacted in simulated body fluid (SBF). Unreacted Bioglass((R)) is dominated by a broad amorphous feature around 2.2 A(-1) which is characteristic of sodium calcium silicate glass. After reacting Bioglass((R)) in SBF a second broad amorphous feature evolves ~1.6 A(-1) which is attributed to amorphous calcium phosphate. This feature is evident for samples after only 4 h reacting in SBF and by 8 h the amorphous feature becomes comparable in magnitude to the background signal of the bulk Bioglass((R)). Bragg peaks characteristic of hydroxyapatite form after 1-3 days of reacting in SBF.

Excellent Brightness with Shortening Lifetime of Textured Zn2SiO4:Mn2+ Phosphor Films on Quartz Glass

NASA Astrophysics Data System (ADS)

Park, Jehong; Park, Kwangwon; Lee, Jaebum; Kim, Jongsu; Kim, Seongsin Margaret; Kung, Patrick

2010-04-01

Green-emissive textured Zn2SiO4:Mn2+ phosphor films were fabricated by the thermal diffusion of ZnO:Mn on quartz glass. The Zn2SiO4:Mn2+ phosphor films became textured along several hexagonal directions and their chemical composition was continuously graded at the interface. The decay time of Mn2+ was as short as 4.4 ms, and the optical transition probability of the films defined as the inverse of decay time showed a strong correlation with film texture degree as a function of annealing temperature. The brightest Zn2SiO4:Mn2+ film showed a photoluminescent brightness as high as 65% compared with a commercial Zn2SiO4:Mn2+ phosphor powder screen and a maximum absolute transparency of 70%. These excellent optical properties are explained by the combination of the unique textured structure and continuous grading of the Zn2SiO4:Mn2+ chemical composition at the interface.

Absorption Amelioration of Amorphous Si Film by Introducing Metal Silicide Nanoparticles.

PubMed

Sun, Hui; Wu, Hsuan-Chung; Chen, Sheng-Chi; Ma Lee, Che-Wei; Wang, Xin

2017-12-01

Amorphous Si (a-Si) films with metal silicide are expected to enhance the absorption ability of pure a-Si films. In this present study, NiSi (20 nm)/Si (40 nm) and AlSi (20 nm)/Si (40 nm) bilayer thin films are deposited through radio frequency (RF) sputtering at room temperature. The influence of the film's composition and the annealing temperature on the film's optical absorption is investigated. The results show that all the NiSi/Si films and AlSi/Si films possess higher absorption ability compared to a pure a-Si film (60 nm). After annealing from 400 to 600 °C under vacuum for 1 h, the Si layer remains amorphous in both NiSi/Si films and AlSi/Si films, while the NiSi layer crystallizes into NiSi 2 phase, whereas Al atoms diffuse through the whole film during the annealing process. Consequently, with increasing the annealing temperature, the optical absorption of NiSi/Si films increases, while that of AlSi/Si films obviously degrades.

Enhanced photovoltaic property by forming p-i-n structures containing Si quantum dots/SiC multilayers

PubMed Central

2014-01-01

Si quantum dots (Si QDs)/SiC multilayers were fabricated by annealing hydrogenated amorphous Si/SiC multilayers prepared in a plasma-enhanced chemical vapor deposition system. The thickness of amorphous Si layer was designed to be 4 nm, and the thickness of amorphous SiC layer was kept at 2 nm. Transmission electron microscopy observation revealed the formation of Si QDs after 900°C annealing. The optical properties of the Si QDs/SiC multilayers were studied, and the optical band gap deduced from the optical absorption coefficient result is 1.48 eV. Moreover, the p-i-n structure with n-a-Si/i-(Si QDs/SiC multilayers)/p-Si was fabricated, and the carrier transportation mechanism was investigated. The p-i-n structure was used in a solar cell device. The cell had the open circuit voltage of 532 mV and the power conversion efficiency (PCE) of 6.28%. PACS 81.07.Ta; 78.67.Pt; 88.40.jj PMID:25489285

Field-Induced Crystalline-to-Amorphous Phase Transformation on the Si Nano-Apex and the Achieving of Highly Reliable Si Nano-Cathodes

PubMed Central

Huang, Yifeng; Deng, Zexiang; Wang, Weiliang; Liang, Chaolun; She, Juncong; Deng, Shaozhi; Xu, Ningsheng

2015-01-01

Nano-scale vacuum channel transistors possess merits of higher cutoff frequency and greater gain power as compared with the conventional solid-state transistors. The improvement in cathode reliability is one of the major challenges to obtain high performance vacuum channel transistors. We report the experimental findings and the physical insight into the field induced crystalline-to-amorphous phase transformation on the surface of the Si nano-cathode. The crystalline Si tip apex deformed to amorphous structure at a low macroscopic field (0.6~1.65 V/nm) with an ultra-low emission current (1~10 pA). First-principle calculation suggests that the strong electrostatic force exerting on the electrons in the surface lattices would take the account for the field-induced atomic migration that result in an amorphization. The arsenic-dopant in the Si surface lattice would increase the inner stress as well as the electron density, leading to a lower amorphization field. Highly reliable Si nano-cathodes were obtained by employing diamond like carbon coating to enhance the electron emission and thus decrease the surface charge accumulation. The findings are crucial for developing highly reliable Si-based nano-scale vacuum channel transistors and have the significance for future Si nano-electronic devices with narrow separation. PMID:25994377

Ferrofluids based on Co-Fe-Si-B amorphous nanoparticles

NASA Astrophysics Data System (ADS)

Wang, Tianqi; Bian, Xiufang; Yang, Chuncheng; Zhao, Shuchun; Yu, Mengchun

2017-03-01

Magnetic Co-Fe-Si-B amorphous nanoparticles were successfully synthesized by chemical reduction method. ICP, XRD, DSC, and TEM were used to investigate the composition, structure and morphology of Co-Fe-Si-B samples. The results show that the Co-Fe-Si-B samples are amorphous, which consist of nearly spherical nanoparticles with an average particle size about 23 nm. VSM results manifest that the saturation magnetization (Ms) of Co-Fe-Si-B samples ranges from 46.37 to 62.89 emu/g. Two kinds of ferrofluids (FFs) were prepared by dispersing Co-Fe-Si-B amorphous nanoparticles and CoFe2O4 nanoparticles in kerosene and silicone oil, respectively. The magnetic properties, stability and viscosity of the FFs were investigated. The FFs with Co-Fe-Si-B samples have a higher Ms and lower coercivity (Hc) than FFs with CoFe2O4 sample. Under magnetic field, the silicone oil-based FFs exhibit high stability. The viscosity of FFs under different applied magnetic fields was measured by a rotational viscometer, indicating that FFs with Co-Fe-Si-B particles present relative strong response to an external magnetic field. The metal-boride amorphous alloy nanoparticles have potential applications in the preparation of magnetic fluids with good stability and good magnetoviscous properties.

Thermal decomposition of silane to form hydrogenated amorphous Si

DOEpatents

Strongin, M.; Ghosh, A.K.; Wiesmann, H.J.; Rock, E.B.; Lutz, H.A. III

Hydrogenated amorphous silicon is produced by thermally decomposing silane (SiH/sub 4/) or other gases comprising H and Si, at elevated temperatures of about 1700 to 2300/sup 0/C, in a vacuum of about 10/sup -8/ to 10/sup -4/ torr. A gaseous mixture is formed of atomic hydrogen and atomic silicon. The gaseous mixture is deposited onto a substrate to form hydrogenated amorphous silicon.

Elemental Gains/Losses Associated with Alteration Fractures in an Eolian Sandstone, Gale Crater, Mars

NASA Technical Reports Server (NTRS)

Ming, D. W.; Yen, A. S.; Gellert, R.; Sutter, B.; Berger, J. A.; Thompson, L. M.; Schmidt, M. E.; Morris, R. V.; Treiman, A. H.

2016-01-01

The Mars Science Laboratory rover Curiosity has traversed up section through approximately 100 m of sedimentary rocks deposited in fluvial, deltaic, lacustrine, and eolian environments (Bradbury group and overlying Mount Sharp group). The Stimson formation unconformably overlies a lacustrine mudstone at the base of the Mount Sharp group and has been interpreted to be a cross-bedded sandstone of lithified eolian dunes. Unaltered Stimson sandstone has a basaltic composition similar to the average Mars crustal composition, but is more variable and ranges to lower K and higher Al. Fluids passing through alteration "halos" adjacent to fractures have altered the chemistry and mineralogy of the sandstone. Elemental mass gains and losses in the alteration halos were quantified using immobile element concentrations, i.e., Ti (taus). Alteration halos have elemental gains in Si, Ca, S, and P and large losses in Al, Fe, Mn, Mg, Na, K, Ni, and Zn. Mineralogy of the altered Stimson is dominated by Ca-sulfates, Si-rich X-ray amorphous materials along with plagioclase feldspar, magnetite, and pyroxenes. The igneous phases were less abundant in the altered sandstone with a lower pyroxene/plagioclase feldspar. Large elemental losses suggest acidic fluids initially removed these elements (Al mobile under acid conditions). Enrichments in Si, Ca, and S suggest secondary fluids (possibly alkaline) passed through these fractures leaving behind X-ray amorphous Si and Ca-sulfates. The mechanism for the large elemental gains in P is unclear. The geochemistry and mineralogy of the altered sandstone suggests a complicated diagenetic history with multiple episodes of aqueous alteration under a variety of environmental conditions (e.g., acidic, alkaline).

Application of DFT-Derived Relationships Between Chemical Environment and 29Si Nuclear Magnetic Resonance Spectroscopy to Determine Structure in Silicon Oxycarbide Ceramics

NASA Astrophysics Data System (ADS)

Nimmo, John Paul, II

Silicon oxycarbide (SiCO) is an amorphous ceramic material widely used in industrial applications, for its useful electronic and biologically-compatible properties. SiCO is resistant to crystallization, remaining amorphous even above temperatures at which amorphous SiO2 would crystallize. Though silica (SiO2) and silicon carbide (SiC) are almost immiscible, it is useful to consider the material as a phase composition of these along with carbon, according to the formula below. The first two terms in braces can be considered as being the "SiCO glass" into which a third term representing excess or "free" carbon is incorporated as graphite-like nano-flakes and bands.

Folate conjugated Mn{sub 3}O{sub 4}@SiO{sub 2} nanoparticles for targeted magnetic resonance imaging in vivo

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

Yang, Xinyi; Zhou, Zhiguo, E-mail: zgzhou@shnu.edu.cn; Wang, Li

2014-09-15

Graphical abstract: The Mn{sub 3}O{sub 4}@SiO{sub 2}(PEG)–FA has been used as a T{sub 1}-MRI probe for in vivo. - Highlights: • The PEG and FA modified Mn{sub 3}O{sub 4}@SiO{sub 2} nanoparticles (Mn{sub 3}O{sub 4}@SiO{sub 2}–FA) were prepared. • Mn{sub 3}O{sub 4}@SiO{sub 2}–FA exhibited the good colloidal stability in the simulated biological medium. • Mn{sub 3}O{sub 4}@SiO{sub 2}–FA showed the targeting ability to HeLa cells overexpressed the FA receptor. • The T{sub 1}-weighted magnetic resonance (MR) imaging demonstrated the targeting ability of Mn{sub 3}O{sub 4}@SiO{sub 2}–FA in vivo tumor. - Abstract: The monodisperse silica-coated manganese oxide nanoparticles (Mn{sub 3}O{sub 4}@SiO{sub 2}more » NPs) were synthesized via the high temperature pyrolysis approach and were aminated through silanization. The amine-functionalized Mn{sub 3}O{sub 4} NPs enabled the covalent conjugation of hydrophilic methoxypoly(ethylene glycol) (PEG) and the targeting ligand of folate (FA) onto their surface. The formed PEG and FA modified Mn{sub 3}O{sub 4} NPs (Mn{sub 3}O{sub 4}@SiO{sub 2}(PEG)–FA) exhibited the good colloidal stability in the simulated biological medium and the targeting ability to HeLa cells overexpressed the FA receptor. The T{sub 1}-weighted magnetic resonance (MR) imaging and inductively coupled plasma atomic emission spectroscopy (ICP-AES) analysis of Mn{sub 3}O{sub 4}@SiO{sub 2}(PEG)–FA NPs further demonstrated their targeting ability in tumor.« less

Hot-spot durability testing of amorphous cells and modules

NASA Technical Reports Server (NTRS)

Gonzalez, Charles; Jetter, Elizabeth

1985-01-01

This paper discusses the results of a study to determine the hot-spot susceptibility of amorphous-silicon (a-Si) cells and modules, and to provide guidelines for reducing that susceptibility. Amorphous-Si cells are shown to have hot-spot susceptibility levels similar to crystalline-silicon (C-Si) cells. This premise leads to the fact that the same general guidelines must apply to protecting a-Si cells from hot-spot stressing that apply to C-Si cells. Recommendations are made on ways of reducing a-Si module hot-spot susceptibility including the traditional method of using bypass diodes and a new method unique to thin-film cells, limiting the string current by limiting cell area.

Irradiation-induced microchemical changes in highly irradiated 316 stainless steel

NASA Astrophysics Data System (ADS)

Fujii, K.; Fukuya, K.

2016-02-01

Cold-worked 316 stainless steel specimens irradiated to 74 dpa in a pressurized water reactor (PWR) were analyzed by atom probe tomography (APT) to extend knowledge of solute clusters and segregation at higher doses. The analyses confirmed that those clusters mainly enriched in Ni-Si or Ni-Si-Mn were formed at high number density. The clusters were divided into three types based on their size and Mn content; small Ni-Si clusters (3-4 nm in diameter), and large Ni-Si and Ni-Si-Mn clusters (8-10 nm in diameter). The total cluster number density was 7.7 × 1023 m-3. The fraction of large clusters was almost 1/10 of the total density. The average composition (in at%) for small clusters was: Fe, 54; Cr, 12; Mn, 1; Ni, 22; Si, 11; Mo, 1, and for large clusters it was: Fe, 44; Cr, 9; Mn, 2; Ni, 29; Si, 14; Mo,1. It was likely that some of the Ni-Si clusters correspond to γ‧ phase precipitates while the Ni-Si-Mn clusters were precursors of G phase precipitates. The APT analyses at grain boundaries confirmed enrichment of Ni, Si, P and Cu and depletion of Fe, Cr, Mo and Mn. The segregation behavior was consistent with previous knowledge of radiation induced segregation.

Synthesis and electrochemical characterizations of spinel LiMn1.94MO4 (M = Mn0.06, Mg0.06, Si0.06, (Mg0.03Si0.03)) compounds as cathode materials for lithium-ion batteries

NASA Astrophysics Data System (ADS)

Zhao, Hongyuan; Liu, Xingquan; Cheng, Cai; Li, Qiang; Zhang, Zheng; Wu, Yue; Chen, Bing; Xiong, Weiqiang

2015-05-01

The spinel LiMn1.94MO4 (M = Mn0.06, Mg0.06, Si0.06, (Mg0.03Si0.03)) compounds are successfully synthesized by citric acid-assisted sol-gel method. The crystal structures and morphologies of synthesized compounds are characterized by X-ray diffraction (XRD), scanning electron microscopy (SEM) and transmission electron microscopy (TEM), respectively. All the compounds possess the cubic spinel structure of LiMn2O4 with space group of Fd-3m. The electrochemical properties of synthesized compounds are investigated by galvanostatic charge-discharge test, cyclic voltammetry (CV) and electrochemical impedance spectroscopy (EIS). The results show that the Si-doping can increase the discharge capacity of LiMn2O4 due to the more expanded and regular MnO6 octahedra. In particular, for the LiMn1.94Mg0.03Si0.03O4 compound, the addition of Si4+ ions can make up for the shortage of Mg-doping in term of the discharge capacity. As a result, the Mg2+ and Si4+ co-doping has the effect of synergistic enhancement, which can make full use of the respective advantages of Mg-doping and Si-doping. The optimal LiMn1.94Mg0.03Si0.03O4 can deliver the initial discharge capacity of 128.3 mAh g-1 with good capacity retention of 92.8% after 100 cycles at 0.5 C in the voltage range of 3.20-4.35 V. Compared with the undoped LiMn2O4, the co-doped compound also presents superior rate performance, especially the capacity recovery performance.

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

Dhital, C.; DeBeer-Schmitt, L.; Zhang, Q.

By using magnetization and small-angle neutron scattering (SANS) measurements, we have investigated the magnetic behavior of the Mn 1-xIr xSi system to explore the effect of increased carrier density and spin-orbit interaction on the magnetic properties of MnSi. We determine estimates of the spin wave stiffness and the Dzyalloshinski-Moriya (DM) interaction strength and compare with Mn 1-xCo xSi and Mn 1-xFe xSi. Despite the large differences in atomic mass and size of the substituted elements, Mn 1-xCo xSi and Mn 1-xIr xSi show nearly identical variations in their magnetic properties with substitution. We find a systematic dependence of the transitionmore » temperature, the ordered moment, the helix period, and the DM interaction strength with electron count for Mn 1-xIr xSi, Mn 1-xCo xSi, and Mn 1-xFe xSi, indicating that the magnetic behavior is primarily dependent upon the additional carrier density, rather than on the mass or size of the substituting species. This indicates that the variation in magnetic properties, including the DM interaction strength, is primarily controlled by the electronic structure, as Co and Ir are isovalent. Our work suggests that although the rigid band model of electronic structure, along with Moriya’s model of weak itinerant magnetism, describes this system surprisingly well, phenomenological models for the DM interaction strength are not adequate to describe this system.« less

Formation of Al15Mn3Si2 Phase During Solidification of a Novel Al-12%Si-4%Cu-1.2%Mn Heat-Resistant Alloy and Its Thermal Stability

NASA Astrophysics Data System (ADS)

Suo, Xiaojing; Liao, Hengcheng; Hu, Yiyun; Dixit, Uday S.; Petrov, Pavel

2018-02-01

The formation of Al15Mn3Si2 phase in Al-12Si-4Cu-1.2Mn (wt.%) alloy during solidification was investigated by adopting CALPHAD method and microstructural observation by optical microscopy, SEM-EDS, TEM-EDS/SAD and XRD analysis; SEM fixed-point observation method was applied to evaluate its thermal stability. As-cast microstructural observation consistently demonstrates the solidification sequence of the studied alloy predicted by phase diagram calculation. Based on the phase diagram calculation, SEM-EDS, TEM-EDS/SAD and XRD analysis, as well as evidences on Al-Si-Mn-Fe compounds from the literature, the primary and eutectic Mn-rich phases with different morphologies in the studied alloy are identified to be Al15Mn3Si2 that has a body-centered cubic (BCC) structure with a lattice constant of a = 1.352 nm. SEM fixed-point observation and XRD analysis indicate that Al15Mn3Si2 phase has more excellent thermal stability at high temperature than that of CuAl2 phase and can serve as the major strengthening phase in heat-resistant aluminum alloy that has to face a high-temperature working environment. Results of tension test show that addition of Mn can improve the strength of Al-Si-Cu alloy, especially at elevated temperature.

Red Mn4+-Doped Fluoride Phosphors: Why Purity Matters.

PubMed

Verstraete, Reinert; Sijbom, Heleen F; Joos, Jonas J; Korthout, Katleen; Poelman, Dirk; Detavernier, Christophe; Smet, Philippe F

2018-06-06

Traditional light sources, e.g., incandescent and fluorescent lamps, are currently being replaced by white light-emitting diodes (wLEDs) because of their improved efficiency, prolonged lifetime, and environmental friendliness. Much effort has recently been spent to the development of Mn 4+ -doped fluoride phosphors that can enhance the color gamut in displays and improve the color rendering index, luminous efficacy of the radiation, and correlated color temperature of wLEDs used for lighting. Purity, stability, and degradation of fluoride phosphors are, however, rarely discussed. Nevertheless, the typical wet chemical synthesis routes (involving hydrogen fluoride (HF)) and the large variety of possible Mn valence states often lead to impurities that drastically influence the performance and stability of these phosphors. In this article, the origins and consequences of impurities formed during synthesis and aging of K 2 SiF 6 :Mn 4+ are revealed. Both crystalline impurities such as KHF 2 and ionic impurities such as Mn 3+ are found to affect the phosphor performance. While Mn 3+ mainly influences the optical absorption behavior, KHF 2 can affect both the optical performance and chemical stability of the phosphor. Moisture leads to decomposition of KHF 2 , forming HF and amorphous hydrated potassium fluoride. As a consequence of hydrate formation, significant amounts of water can be absorbed in impure phosphor powders containing KHF 2 , facilitating the hydrolysis of [MnF 6 ] 2- complexes and affecting the optical absorption of the phosphors. Strategies are discussed to identify impurities and to achieve pure and stable phosphors with internal quantum efficiencies of more than 90%.

A high-performance ternary Si composite anode material with crystal graphite core and amorphous carbon shell

NASA Astrophysics Data System (ADS)

Sui, Dong; Xie, Yuqing; Zhao, Weimin; Zhang, Hongtao; Zhou, Ying; Qin, Xiting; Ma, Yanfeng; Yang, Yong; Chen, Yongsheng

2018-04-01

Si is a promising anode material for lithium-ion batteries, but suffers from sophisticated engineering structures and complex fabrication processes that pose challenges for commercial application. Herein, a ternary Si/graphite/pyrolytic carbon (SiGC) anode material with a structure of crystal core and amorphous shell using low-cost raw materials is developed. In this ternary SiGC composite, Si component exists as nanoparticles and is spread on the surface of the core graphite flakes while the sucrose-derived pyrolytic carbon further covers the graphite/Si components as the amorphous shell. With this structure, Si together with the graphite contributes to the high specific capacity of this Si ternary material. Also the graphite serves as the supporting and conducting matrix and the amorphous shell carbon could accommodate the volume change effect of Si, reinforces the integrity of the composite architecture, and prevents the graphite and Si from direct exposing to the electrolyte. The optimized ternary SiGC composite displays high reversible specific capacity of 818 mAh g-1 at 0.1 A g-1, initial Coulombic efficiency (CE) over 80%, and excellent cycling stability at 0.5 A g-1 with 83.6% capacity retention (∼610 mAh g-1) after 300 cycles.

Pressure-induced silica quartz amorphization studied by iterative stochastic surface walking reaction sampling.

PubMed

Zhang, Xiao-Jie; Shang, Cheng; Liu, Zhi-Pan

2017-02-08

The crystal to amorphous transformation is a common phenomenon in Nature and has important impacts on material properties. Our current knowledge on such complex solid transformation processes is, however, limited because of their slow kinetics and the lack of long-range ordering in amorphous structures. To reveal the kinetics in the amorphization of solids, this work, by developing iterative reaction sampling based on the stochastic surface walking global optimization method, investigates the well-known crystal to amorphous transformation of silica (SiO 2 ) under external pressures, the mechanism of which has long been debated for its non-equilibrium, pressure-sensitive kinetics and complex product components. Here we report for the first time the global potential energy surface (PES) and the lowest energy pathways for α-quartz amorphization from first principles. We show that the pressurization at 15 GPa, the reaction condition, can lift the quartz phase energetically close to the amorphous zone, which thermodynamically initializes the amorphization. More importantly, the large flexibility of Si cation coordination (including four, five and six coordination) results in many kinetically competing routes to more stable dense forms, including the known MI, stishovite, newly-identified MII and TI phases. All these pathways have high barriers due to the local Si-O bond breaking and are mediated by amorphous structures with five-fold Si. This causes simultaneous crystal-to-crystal and crystal-to-amorphous transitions. The high barrier and the reconstructive nature of the phase transition are the key kinetics origin for silica amorphization under pressures.

Core-shell structured MnSiO3 supported with CNTs as a high capacity anode for lithium-ion batteries.

PubMed

Feng, Jing; Li, Qin; Wang, Huijun; Zhang, Min; Yang, Xia; Yuan, Ruo; Chai, Yaqin

2018-04-17

Metal silicates are good candidates for use in lithium ion batteries (LIBs), however, their electrochemical performance is hindered by their poor electrical conductivity and volume expansion during Li+ insertion/desertion. In this work, one-dimensional core-shell structured MnSiO3 supported with carbon nanotubes (CNTs) (referred to as CNT@MnSiO3) with good conductivity and electrochemical performance has been successfully synthesized using a solvothermal process under moderate conditions. In contrast to traditional composites of CNTs and nanoparticles, the CNT@MnSiO3 composite in this work is made up of CNTs with a layer of MnSiO3 on the surface. The one-dimensional CNT@MnSiO3 nanotubes provide a useful channel for transferring Li+ ions during the discharge/charge process, which accelerates the Li+ diffusion speed. The CNTs inside the structure not only enhance the conductivity of the composite, but also prevent volume expansion. A high reversible capacity (920 mA h g-1 at 500 mA g-1 over 650 cycles) and good rate performance were obtained for CNT@MnSiO3, showing that this strategy of synthesizing coaxial CNT@MnSiO3 nanotubes offers a promising method for preparing other silicates for LIBs or other applications.

Amorphization driven by defect-induced mechanical instability.

PubMed

Jiang, Chao; Zheng, Ming-Jie; Morgan, Dane; Szlufarska, Izabela

2013-10-11

Using ab initio molecular dynamics simulations, we perform a comparative study of the defect accumulation process in silicon carbide (SiC) and zirconium carbide (ZrC). Interestingly, we find that the fcc Si sublattice in SiC spontaneously and gradually collapses following the continuous introduction of C Frenkel pairs (FPs). Above a critical amorphization dose of ~0.33 displacements per atom (dpa), the pair correlation function exhibits no long-range order. In contrast, the fcc Zr sublattice in ZrC remains structurally stable against C sublattice displacements up to the highest dose of 1.0 dpa considered. Consequently, ZrC cannot be amorphized by the accumulation of C FPs. We propose defect-induced mechanical instability as the key mechanism driving the amorphization of SiC under electron irradiation.

Sulfide and Oxide Heterostructures For the SrTiO3 Thin Film Growth on Si and Their Structural and Interfacial Stabilities

NASA Astrophysics Data System (ADS)

Yoo, Young‑Zo; Song, Jeong‑Hwan; Konishi, Yoshinori; Kawasaki, Masashi; Koinuma, Hideomi; Chikyow, Toyohiro

2006-03-01

Epitaxial SrTiO3 (STO) thin films with high electrical properties were grown on Si using ZnS single- and SrS/MnS hetero-buffer layers. STO films on both ZnS-buffered and SrS/MnS-buffered Si showed two growth orientations, (100) and (110). The temperature dependence of the growth orientation for STO films was different for the ZnS single-buffer layer in comparison with the SrS/MnS heterobuffer layers. (100) growth of STO films on SrS/MnS-buffered Si became dominant at high temperatures about 700 °C, while (100) growth of STO films on ZnS-buffered Si became dominant at a relatively low growth temperature of 550 °C. STO(100) films on ZnS-buffered and SrS/MnS-buffered Si showed lattice and domain matches for epitaxial relationships with [001]ZnS\\parallel[011]STO and SrS[001]\\parallel[011]STO, respectively via 45° in-plane rotation of STO films relative to both ZnS and SrS layers. The ZnS buffer layer contained many stacking faults because of the mismatch between ZnS and Si, however, those defects were terminated at the ZnS/STO interface. In contrast, the MnS buffer was very stable against stacking defect formation. Transmission electron microscopy measurements revealed the presence of a disordered region at the ZnS/Si and MnS/Si interfaces. Auger electron spectroscopy and transmission electron microscopy results showed that a good MnS/Si interface at the initial growth stage degraded to a SiS2-x-rich phase during MnS deposition and again into a SiO2-x-rich phase during STO deposition at the high growth temperature of 700 °C. It was also observed that STO on SrS/MnS-buffered Si showed a markedly high dielectric constant compared with that of STO on ZnS-buffered Si.

Synthesis of Radioisotope Mn-56@SiO2, Sm-153@SiO2, and Dy-165@SiO2 Hybrid Nanoparticles for Use as Radiotracer.

PubMed

Seo, Sang-Ei; Kang, Yun Ok; Jung, Sung-Hee; Choi, Seong-Ho

2015-09-01

Radioisotope hybrid nanoparticles (NPs) of Mn-56@SiO2, Sm-153@SiO2, and Dy-165@SiO2 were synthesized by neutron irradiation of Mn-55@SiO2, Sm-150@SiO2, and Dy-163@SiO2 NPs respectively using the HANARO research reactor. The Mn-55@SiO2, Sm-150@SiO2, and Dy-163@SiO2 NPs were synthesized by calcination in air flow at 500 degrees C for 8 h of the hybrid NPs that has been prepared by the sol-gel reaction of tetraethyl silicate in the presence of the complex precursors. Mn-55, Sm-150, and Dy-163 were selected for use as radiotracers were selected because these elements can be easily gamma-activated by neutrons (activation limits: 1 picogram (Dy), 1-10 picogram (Mn), 10-100 picogram (Sm)). The successful synthesis of the radioisotope hybrid NPs was confirmed by Transmission Electron Microscopy (TEM), Energy Dispersive X-ray Spectrometry (EDS), Scanning Electron Microscopy (SEM), and Gamma Spectroscopy analysis. The synthesized the radioisotope hybrid NPs could be used as radiotracers in the scientific, environmental, engineering, and industrial fields.

Amorphous and nanocrystalline luminescent Si and Ge obtained via a solid-state chemical metathesis synthesis route

NASA Astrophysics Data System (ADS)

McMillan, Paul F.; Gryko, Jan; Bull, Craig; Arledge, Richard; Kenyon, Anthony J.; Cressey, Barbara A.

2005-03-01

A new solid-state metathesis synthesis route was applied to obtain bulk samples of amorphous or microcrystalline Si and Ge. The method involves reaction of Zintl phases such as NaSi or NaGe, with ammonium or metal (e.g., CuCl, CoBr 2) halides. The driving force for the solid-state reaction is provided by the formation of alkali halides and the transition metals or metal silicides, or gaseous ammonia and hydrogen. The semiconductors were purified by washing to remove other solid products. The amorphous semiconductors were obtained in bulk form from reactions carried out at 200-300 °C. Syntheses at higher temperatures gave rise to microcrystalline semiconductors, or to micro-/nanocrystalline particles contained within the amorphous material. Similar crystalline/amorphous composites were obtained after heat treatment of bulk amorphous materials.

Effect of Heat-Treatment Temperature on the Interfacial Reaction Between Oxide Inclusions and Si-Mn Killed Steel

NASA Astrophysics Data System (ADS)

Zhang, Xueliang; Yang, Shufeng; Liu, Chengsong; Li, Jingshe; Hao, Weixing

2018-06-01

The effect of heat-treatment temperature on the interfacial reaction between MnO-SiO2-FeO oxide and Fe-Mn-Si alloy was investigated by the diffusion couple method in the temperature range of 1173-1573 K. The reaction at the interface between the alloy and oxide was not obvious during treatment at 1173 K, but, with increasing heat-treatment temperature, the interfacial reaction was strengthened and the proportion of the MnO·SiO2 phase in the oxide increased. The width of the particle-precipitation zone in the alloy increased with increasing temperature from 1173 K to 1473 K but decreased at 1573 K owing to coarsening of the precipitated particles. In addition, Mn2+ and Si4+ in the oxide significantly diffused into the alloy at 1573 K, resulting in an obvious increase of the Mn and Si contents in the alloy near the interface.

Study on ion implantation conditions in fabricating compressively strained Si/relaxed Si1-xCx heterostructures using the defect control by ion implantation technique

NASA Astrophysics Data System (ADS)

Arisawa, You; Sawano, Kentarou; Usami, Noritaka

2017-06-01

The influence of ion implantation energies on compressively strained Si/relaxed Si1-xCx heterostructures formed on Ar ion implanted Si substrates was investigated. It was found that relaxation ratio can be enhanced over 100% at relatively low implantation energies, and compressive strain in the topmost Si layer is maximized at 45 keV due to large lattice mismatch. Cross-sectional transmission electron microscope images revealed that defects are localized around the hetero-interface between the Si1-xCx layer and the Ar+-implanted Si substrate when the implantation energy is 45 keV, which decreases the amount of defects in the topmost Si layer and the upper part of the Si1-xCx buffer layer.

A delta-doped amorphous silicon thin-film transistor with high mobility and stability

NASA Astrophysics Data System (ADS)

Kim, Pyunghun; Lee, Kyung Min; Lee, Eui-Wan; Jo, Younjung; Kim, Do-Hyung; Kim, Hong-jae; Yang, Key Young; Son, Hyunji; Choi, Hyun Chul

2012-12-01

Ultrathin doped layers, known as delta-doped layers, were introduced within the intrinsic amorphous silicon (a-Si) active layer to fabricate hydrogenated amorphous silicon (a-Si:H) thin-film transistors (TFTs) with enhanced field-effect mobility. The performance of the delta-doped a-Si:H TFTs depended on the phosphine (PH3) flow rate and the distance from the n+ a-Si to the deltadoping layer. The delta-doped a-Si:H TFTs fabricated using a commercial manufacturing process exhibited an enhanced field-effect mobility of approximately ˜0.23 cm2/Vs (compared to a conventional a-Si:H TFT with 0.15 cm2/Vs) and a desirable stability under a bias-temperature stress test.

The role of hydrogenated amorphous silicon oxide buffer layer on improving the performance of hydrogenated amorphous silicon germanium single-junction solar cells

NASA Astrophysics Data System (ADS)

Sritharathikhun, Jaran; Inthisang, Sorapong; Krajangsang, Taweewat; Krudtad, Patipan; Jaroensathainchok, Suttinan; Hongsingtong, Aswin; Limmanee, Amornrat; Sriprapha, Kobsak

2016-12-01

Hydrogenated amorphous silicon oxide (a-Si1-xOx:H) film was used as a buffer layer at the p-layer (μc-Si1-xOx:H)/i-layer (a-Si1-xGex:H) interface for a narrow band gap hydrogenated amorphous silicon germanium (a-Si1-xGex:H) single-junction solar cell. The a-Si1-xOx:H film was deposited by plasma enhanced chemical vapor deposition (PECVD) at 40 MHz in a same processing chamber as depositing the p-type layer. An optimization of the thickness of the a-Si1-xOx:H buffer layer and the CO2/SiH4 ratio was performed in the fabrication of the a-Si1-xGex:H single junction solar cells. By using the wide band gap a-Si1-xOx:H buffer layer with optimum thickness and CO2/SiH4 ratio, the solar cells showed an improvement in the open-circuit voltage (Voc), fill factor (FF), and short circuit current density (Jsc), compared with the solar cells fabricated using the conventional a-Si:H buffer layer. The experimental results indicated the excellent potential of the wide-gap a-Si1-xOx:H buffer layers for narrow band gap a-Si1-xGex:H single junction solar cells.

Manganese Recovery by Silicothermic Reduction of MnO in BaO-MnO-MgO-CaF2 (-SiO2) Slags

NASA Astrophysics Data System (ADS)

Heo, Jung Ho; Park, Joo Hyun

2018-04-01

The effects of reducing agent, CaF2 content, and reaction temperature upon the silicothermic reduction of MnO in the BaO-MnO-MgO-CaF2 (-SiO2) slags were investigated. Mn recovery was proportional to Si activity in the molten alloy. Moreover, 90 pct yield of Mn recovery was obtained under 5 mass pct CaF2 content and 1873 K (1600 °C) reaction temperature. Increasing CaF2 content above 5 pct yielded little or no further increase in Mn recovery, because it was accompanied by increased slag viscosity owing to the precipitation of high melting point compounds such as Ba2SiO4.

The enhancement of anomalous Hall effect by inserting MgO layer in perpendicular anisotropic Pd/Co2MnSi/MgO/Pd films

NASA Astrophysics Data System (ADS)

Fu, H. R.; Ma, L.; Tian, N.; You, C. Y.; Wang, K.

2018-05-01

A systematic study of anomalous Hall effect (AHE) was performed in perpendicular magnetic anisotropic Pd/Co2MnSi(tCMS)/MgO/Pd films. The AHE was significantly intensified by inserting MgO layer, which can be ascribed to the enhancement of spin-orbit coupling and interfacial scattering contribution. Moreover, it was found that the Co and Mn ions were reduced at the interface of Co2MnSi/MgO with annealing process. The stable amount of Mn-O bonding was observed at the Co2MnSi/MgO interface after annealing, implying that the proper Mn-O bonding could be favorable for achieving large AHE.

Fabrication of luminescent porous silicon with stain etches and evidence that luminescence originates in amorphous layers

NASA Technical Reports Server (NTRS)

Fathauer, R. W.; George, T.; Ksendzov, A.; Lin, T. L.; Pike, W. T.; Vasquez, R. P.; Wu, Z.-C.

1992-01-01

Simple immersion of Si in stain etches of HF:HNO3:H2O or NaNO2 in aqueous HF was used to produce films exhibiting luminescence in the visible similar to that of anodically-etched porous Si. All of the luminescent samples consist of amorphous porous Si in at least the near surface region. No evidence was found for small crystalline regions within these amorphous layers.

Influence of the chemical composition of rapidly quenched amorphous alloys (Ni, Fe, Cr)-B-Si on its crystallization process

NASA Astrophysics Data System (ADS)

Elmanov, G.; Dzhumaev, P.; Ivanitskaya, E.; Skrytnyi, V.; Ruslanov, A.

2016-04-01

This paper presents results of research of the structure and phase transformations during the multistage crystallization of the metallic glasses with the compositions Ni71,5Cr6,8Fe2,7B11,9Si7,1 and Ni63,4Cr7,4Fe4,3Mn0,8B15,6Si8,5 labeled as AWS BNi-2 according to American Welding Society. Differential scanning calorimetry (DSC), X-ray diffraction analysis (XRD), scanning electron microscopy (SEM) and energy-dispersive X-ray microanalysis (EDX) were used as experimental research methods. The influence of the alloys chemical composition (boron, manganese and iron) on the temperatures and the exothermic heat effects of phase transformations, as well as on the phase composition of alloys at three stages of crystallization was analyzed. We present a thermodynamic explanation of the observed heat effects. It has been shown that manganese has the main influence on the phase transformations temperatures and heat effects in these two alloys. It is also assumed that at the final crystallization stage simultaneously with the formation of phases Ni3B and β1-Ni3Si should occur the nucleation of borides of CrB type with high Cr and low Si content.

Surface plasmon effects in the absorption enhancements of amorphous silicon solar cells with periodical metal nanowall and nanopillar structures.

PubMed

Lin, Hung-Yu; Kuo, Yang; Liao, Cheng-Yuan; Yang, C C; Kiang, Yean-Woei

2012-01-02

The authors numerically investigate the absorption enhancement of an amorphous Si solar cell, in which a periodical one-dimensional nanowall or two-dimensional nanopillar structure of the Ag back-reflector is fabricated such that a dome-shaped grating geometry is formed after Si deposition and indium-tin-oxide coating. In this investigation, the effects of surface plasmon (SP) interaction in such a metal nanostructure are of major concern. Absorption enhancement in most of the solar spectral range of significant amorphous Si absorption (320-800 nm) is observed in a grating solar cell. In the short-wavelength range of high amorphous Si absorption, the weakly wavelength-dependent absorption enhancement is mainly caused by the broadband anti-reflection effect, which is produced through the surface nano-grating structures. In the long-wavelength range of diminishing amorphous Si absorption, the highly wavelength-sensitive absorption enhancement is mainly caused by Fabry-Perot resonance and SP interaction. The SP interaction includes the contributions of surface plasmon polariton and localized surface plasmon.

Manganese Silylene Hydride Complexes: Synthesis and Reactivity with Ethylene to Afford Silene Hydride Complexes.

PubMed

Price, Jeffrey S; Emslie, David J H; Britten, James F

2017-05-22

Reaction of the ethylene hydride complex trans-[(dmpe) 2 MnH(C 2 H 4 )] (1) with Et 2 SiH 2 at 20 °C afforded the silylene hydride [(dmpe) 2 MnH(=SiEt 2 )] (2 a) as the trans-isomer. By contrast, reaction of 1 with Ph 2 SiH 2 at 60 °C afforded [(dmpe) 2 MnH(=SiPh 2 )] (2 b) as a mixture of the cis (major) and trans (minor) isomers, featuring a Mn-H-Si interaction in the former. The reaction to form 2 b also yielded [(dmpe) 2 MnH 2 (SiHPh 2 )] (3 b); [(dmpe) 2 MnH 2 (SiHR 2 )] (R=Et (3 a) and Ph (3 b)) were accessed cleanly by reaction of 2 a and 2 b with H 2 , and the analogous reactions with D 2 afforded [(dmpe) 2 MnD 2 (SiHR 2 )] exclusively. Both 2 a and 2 b engaged in unique reactivity with ethylene, generating the silene hydride complexes cis-[(dmpe) 2 MnH(R 2 Si=CHMe)] (R=Et (4 a), Ph (4 b)). Compounds trans-2 a, cis-2 b, 3 b, and 4 b were crystallographically characterized, and bonding in 2 a, 2 b, 4 a, and 4 b was probed computationally. © 2017 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim.

Phase transformation and magnetic properties of MnAl powders prepared by elemental-doping and salt-assisted ball milling

NASA Astrophysics Data System (ADS)

Qian, Hui-Dong; Si, Ping-Zhan; Choi, Chul-Jin; Park, Jihoon; Cho, Kyung Mox

2018-05-01

The effects of elemental doping of Si and Fe on the ɛ→τ phase transformation and the magnetic properties of MnAl were studied. The magnetic powders of Si- and Fe-doped MnAl were prepared by using induction melting followed by water-quenching, annealing, and salt-assisted ball-milling. The Fe-doped MnAl powders are mainly composed of the L10-structured τ-phase, while the Si-doped MnAl are composed of τ-phase and a small fraction of γ2- and β-phases. A unique thin leaves-like morphology with thickness of several tens of nanometers and diameter size up to 500 nm were observed in the Si-doped MnAl powders. The Fe-doped MnAl powders show irregular shape with much larger dimensions in the range from several to 10 μm. The morphology difference of the samples was ascribed to the variation of the mechanical properties affected by different doping elements. The phase transformation temperatures of the ɛ-phase of the samples were measured. The doping of Fe decreases the onset temperature of the massive phase transformation in MnAl, while the Si-doping increases the massive phase transformation temperature. Both Fe and Si increase the Curie temperature of MnAl. A substantially enhanced coercivity up to 0.45 T and 0.42 T were observed in the ball-milled MnAl powders doped with Si and Fe, respectively.

Size-dependent characterization of embedded Ge nanocrystals: Structural and thermal properties

NASA Astrophysics Data System (ADS)

Araujo, L. L.; Giulian, R.; Sprouster, D. J.; Schnohr, C. S.; Llewellyn, D. J.; Kluth, P.; Cookson, D. J.; Foran, G. J.; Ridgway, M. C.

2008-09-01

A combination of conventional and synchrotron-based techniques has been used to characterize the size-dependent structural and thermal properties of Ge nanocrystals (NCs) embedded in a silica (a-SiO2) matrix. Ge NC size distributions with four different diameters ranging from 4.0 to 9.0 nm were produced by ion implantation and thermal annealing as characterized with small-angle x-ray scattering and transmission electron microscopy. The NCs were well represented by the superposition of bulklike crystalline and amorphous environments, suggesting the formation of an amorphous layer separating the crystalline NC core and the a-SiO2 matrix. The amorphous fraction was quantified with x-ray-absorption near-edge spectroscopy and increased as the NC diameter decreased, consistent with the increase in surface-to-volume ratio. The structural parameters of the first three nearest-neighbor shells were determined with extended x-ray-absorption fine-structure (EXAFS) spectroscopy and evolved linearly with inverse NC diameter. Specifically, increases in total disorder, interatomic distance, and the asymmetry in the distribution of distances were observed as the NC size decreased, demonstrating that finite-size effects govern the structural properties of embedded Ge NCs. Temperature-dependent EXAFS measurements in the range of 15-300 K were employed to probe the mean vibrational frequency and the variation of the interatomic distance distribution (mean value, variance, and asymmetry) with temperature for all NC distributions. A clear trend of increased stiffness (higher vibrational frequency) and decreased thermal expansion with decreasing NC size was evident, confirming the close relationship between the variation of structural and thermal/vibrational properties with size for embedded Ge NCs. The increase in surface-to-volume ratio and the presence of an amorphous Ge layer separating the matrix and crystalline NC core are identified as the main factors responsible for the observed behavior, with the surrounding a-SiO2 matrix also contributing to a lesser extent. Such results are compared to previous reports and discussed in terms of the influence of the surface-to-volume ratio in objects of nanometer dimensions.

Thin-film Rechargeable Lithium Batteries

DOE R&D Accomplishments Database

Dudney, N. J.; Bates, J. B.; Lubben, D.

1995-06-01

Thin film rechargeable lithium batteries using ceramic electrolyte and cathode materials have been fabricated by physical deposition techniques. The lithium phosphorous oxynitride electrolyte has exceptional electrochemical stability and a good lithium conductivity. The lithium insertion reaction of several different intercalation materials, amorphous V{sub 2}O{sub 5}, amorphous LiMn{sub 2}O{sub 4}, and crystalline LiMn{sub 2}O{sub 4} films, have been investigated using the completed cathode/electrolyte/lithium thin film battery.

Diffuse flow hydrothermal manganese mineralization along the active Mariana and southern Izu-Bonin arc system, western Pacific

USGS Publications Warehouse

Hein, J.R.; Schulz, M.S.; Dunham, R.E.; Stern, R.J.; Bloomer, S.H.

2008-01-01

Abundant ferromanganese oxides were collected along 1200 km of the active Izu-Bonin-Mariana arc system. Chemical compositions and mineralogy show that samples were collected from two deposit types: Fe-Mn crusts of mixed hydrogenetic/hydrothermal origin and hydrothermal Mn oxide deposits; this paper addresses only the second type. Mn oxides cement volcaniclastic and biogenic sandstone and breccia layers (Mn sandstone) and form discrete dense stratabound layers along bedding planes and within beds (stratabound Mn). The Mn oxide was deposited within coarse-grained sediments from diffuse flow systems where precipitation occurred below the seafloor. Deposits were exposed at the seabed by faulting, mass wasting, and erosion. Scanning electron microscopy and microprobe analyses indicate the presence of both amorphous and crystalline 10 ?? and 7 ?? manganate minerals, the fundamental chemical difference being high water contents in the amorphous Mn oxides. Alternation of amorphous and crystalline laminae occurs in many samples, which likely resulted from initial rapid precipitation of amorphous Mn oxides from waxing pulses of hydrothermal fluids followed by precipitation of slow forming crystallites during waning stages. The chemical composition is characteristic of a hydrothermal origin including strong fractionation between Fe (mean 0.9 wt %) and Mn (mean 48 wt %) for the stratabound Mn, generally low trace metal contents, and very low rare earth element and platinum group element contents. However, Mo, Cd, Zn, Cu, Ni, and Co occur in high concentrations in some samples and may be good indicator elements for proximity to the heat source or to massive sulfide deposits. For the Mn sandstones, Fe (mean-8.4%) and Mn (12.4%) are not significantly fractionated because of high Fe contents in the volcaniclastic material. However, the proportion of hydrothermal Fe (nondetrital Fe) to total Fe is remarkably constant (49-58%) for all the sample groups, regardless of the degree of Mn mineralization. Factor analyses indicate various mixtures of two dominant components: hydrothermal Mn oxide for the stratabound Mn and detrital aluminosilicate for the Mn-cemented sandstone; and two minor components, hydrothermal Fe oxyhydroxide and biocarbonate/biosilica. Our conceptual model shows that Mn mineralization was produced by hydrothermal convection cells within arc volcanoes and sedimentary prisms that occur along, the flanks and within calderas. The main source of hydrothermal fluid was seawater that penetrated through fractures, faults, and permeable volcanic edifices. The fluids were heated by magma, enriched in metals by leaching of basement rocks and sediments, and mixed with magmatic fluids and gases. Dikes and sills may have been another source of heat that drove small-scale circulation within sedimentary prisms. Copyright 2008 by the American Geophysical Union.

Diffuse flow hydrothermal manganese mineralization along the active Mariana and southern Izu-Bonin arc system, western Pacific

NASA Astrophysics Data System (ADS)

Hein, James R.; Schulz, Marjorie S.; Dunham, Rachel E.; Stern, Robert J.; Bloomer, Sherman H.

2008-08-01

Abundant ferromanganese oxides were collected along 1200 km of the active Izu-Bonin-Mariana arc system. Chemical compositions and mineralogy show that samples were collected from two deposit types: Fe-Mn crusts of mixed hydrogenetic/hydrothermal origin and hydrothermal Mn oxide deposits; this paper addresses only the second type. Mn oxides cement volcaniclastic and biogenic sandstone and breccia layers (Mn sandstone) and form discrete dense stratabound layers along bedding planes and within beds (stratabound Mn). The Mn oxide was deposited within coarse-grained sediments from diffuse flow systems where precipitation occurred below the seafloor. Deposits were exposed at the seabed by faulting, mass wasting, and erosion. Scanning electron microscopy and microprobe analyses indicate the presence of both amorphous and crystalline 10 Å and 7 Å manganate minerals, the fundamental chemical difference being high water contents in the amorphous Mn oxides. Alternation of amorphous and crystalline laminae occurs in many samples, which likely resulted from initial rapid precipitation of amorphous Mn oxides from waxing pulses of hydrothermal fluids followed by precipitation of slow forming crystallites during waning stages. The chemical composition is characteristic of a hydrothermal origin including strong fractionation between Fe (mean 0.9 wt %) and Mn (mean 48 wt %) for the stratabound Mn, generally low trace metal contents, and very low rare earth element and platinum group element contents. However, Mo, Cd, Zn, Cu, Ni, and Co occur in high concentrations in some samples and may be good indicator elements for proximity to the heat source or to massive sulfide deposits. For the Mn sandstones, Fe (mean 8.4%) and Mn (12.4%) are not significantly fractionated because of high Fe contents in the volcaniclastic material. However, the proportion of hydrothermal Fe (nondetrital Fe) to total Fe is remarkably constant (49-58%) for all the sample groups, regardless of the degree of Mn mineralization. Factor analyses indicate various mixtures of two dominant components: hydrothermal Mn oxide for the stratabound Mn and detrital aluminosilicate for the Mn-cemented sandstone; and two minor components, hydrothermal Fe oxyhydroxide and biocarbonate/biosilica. Our conceptual model shows that Mn mineralization was produced by hydrothermal convection cells within arc volcanoes and sedimentary prisms that occur along the flanks and within calderas. The main source of hydrothermal fluid was seawater that penetrated through fractures, faults, and permeable volcanic edifices. The fluids were heated by magma, enriched in metals by leaching of basement rocks and sediments, and mixed with magmatic fluids and gases. Dikes and sills may have been another source of heat that drove small-scale circulation within sedimentary prisms.

On the Mass Fractal Character of Si-Based Structural Networks in Amorphous Polymer Derived Ceramics

PubMed Central

Sen, Sabyasachi; Widgeon, Scarlett

2015-01-01

The intermediate-range packing of SiNxC4−x (0 ≤ x ≤ 4) tetrahedra in polysilycarbodiimide and polysilazane-derived amorphous SiCN ceramics is investigated using 29Si spin-lattice relaxation nuclear magnetic resonance (SLR NMR) spectroscopy. The SiCN network in the polysilylcarbodiimide-derived ceramic consists predominantly of SiN4 tetrahedra that are characterized by a 3-dimensional spatial distribution signifying compact packing of such units to form amorphous Si3N4 clusters. On the other hand, the SiCN network of the polysilazane-derived ceramic is characterized by mixed bonded SiNxC4−x tetrahedra that are inefficiently packed with a mass fractal dimension of Df ~2.5 that is significantly lower than the embedding Euclidean dimension (D = 3). This result unequivocally confirms the hypothesis that the presence of dissimilar atoms, namely, 4-coordinated C and 3-coordinated N, in the nearest neighbor environment of Si along with some exclusion in connectivity between SiCxN4−x tetrahedra with widely different N:C ratios and the absence of bonding between C and N result in steric hindrance to an efficient packing of these structural units. It is noted that similar inefficiencies in packing are observed in polymer-derived amorphous SiOC ceramics as well as in proteins and binary hard sphere systems. PMID:28347016

Amorphous and nanocrystalline luminescent Si and Ge obtained via a solid-state chemical metathesis synthesis route

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

McMillan, Paul F.; Gryko, Jan; Bull, Craig

A new solid-state metathesis synthesis route was applied to obtain bulk samples of amorphous or microcrystalline Si and Ge. The method involves reaction of Zintl phases such as NaSi or NaGe, with ammonium or metal (e.g., CuCl, CoBr{sub 2}) halides. The driving force for the solid-state reaction is provided by the formation of alkali halides and the transition metals or metal silicides, or gaseous ammonia and hydrogen. The semiconductors were purified by washing to remove other solid products. The amorphous semiconductors were obtained in bulk form from reactions carried out at 200-300{sup o}C. Syntheses at higher temperatures gave rise tomore » microcrystalline semiconductors, or to micro-/nanocrystalline particles contained within the amorphous material. Similar crystalline/amorphous composites were obtained after heat treatment of bulk amorphous materials.« less

Minor-Cu doped soft magnetic Fe-based FeCoBCSiCu amorphous alloys with high saturation magnetization

NASA Astrophysics Data System (ADS)

Li, Yanhui; Wang, Zhenmin; Zhang, Wei

2018-05-01

The effects of Cu alloying on the amorphous-forming ability (AFA) and magnetic properties of the P-free Fe81Co5B11C2Si1 amorphous alloy were investigated. Addition of ≤ 1.0 at.% Cu enhances the AFA of the base alloy without significant deterioration of the soft magnetic properties. The Fe80.5Co5B11C2Si1Cu0.5 alloy with the largest critical thickness for amorphous formation of ˜35 μm possesses a high saturation magnetization (Bs) of ˜1.78 T, low coercivity of ˜14.6 A/m, and good bending ductility upon annealing in a wide temperature range of 513-553 K with maintaining the amorphous state. The fabrication of the new high-Fe-content Fe-Co-B-C-Si-Cu amorphous alloys by minor doping of Cu gives a guideline to developing high Bs amorphous alloys with excellent AFA.

High temperature magnetism and microstructure of ferromagnetic alloy Si1-x Mn x

NASA Astrophysics Data System (ADS)

Aronzon, B. A.; Davydov, A. B.; Vasiliev, A. L.; Perov, N. S.; Novodvorsky, O. A.; Parshina, L. S.; Presniakov, M. Yu; Lahderanta, E.

2017-02-01

The results of a detailed study of magnetic properties and of the microstructure of SiMn films with a small deviation from stoichiometry are presented. The aim was to reveal the origin of the high temperature ferromagnetic ordering in such compounds. Unlike SiMn single crystals with the Curie temperature ~30 K, considered Si1-x Mn x compounds with x  =  0.5  +Δx and Δx in the range of 0.01-0.02 demonstrate a ferromagnetic state above room temperature. Such a ferromagnetic state can be explained by the existence of highly defective B20 SiMn nanocrystallites. These defects are Si vacancies, which are suggested to possess magnetic moments. The nanocrystallites interact with each other through paramagnons (magnetic fluctuations) inside a weakly magnetic manganese silicide matrix giving rise to a long range ferromagnetic percolation cluster. The studied structures with a higher value of Δx  ≈  0.05 contained three different magnetic phases: (a)—the low temperature ferromagnetic phase related to SiMn; (b)—the above mentioned high temperature phase with Curie temperature in the range of 200-300 K depending on the growth history and (c)—superparamagnetic phase formed by separated noninteracting SiMn nanocrystallites.

Thermal decomposition of silane to form hydrogenated amorphous Si film

DOEpatents

Strongin, Myron; Ghosh, Arup K.; Wiesmann, Harold J.; Rock, Edward B.; Lutz, III, Harry A.

1980-01-01

This invention relates to hydrogenated amorphous silicon produced by thermally decomposing silano (SiH.sub.4) or other gases comprising H and Si, at elevated temperatures of about 1700.degree.-2300.degree. C., and preferably in a vacuum of about 10.sup.-8 to 10.sup.-4 torr, to form a gaseous mixture of atomic hydrogen and atomic silicon, and depositing said gaseous mixture onto a substrate outside said source of thermal decomposition to form hydrogenated amorphous silicon.

Kinetic Monte Carlo (kMC) simulation of carbon co-implant on pre-amorphization process.

PubMed

Park, Soonyeol; Cho, Bumgoo; Yang, Seungsu; Won, Taeyoung

2010-05-01

We report our kinetic Monte Carlo (kMC) study of the effect of carbon co-implant on the pre-amorphization implant (PAL) process. We employed BCA (Binary Collision Approximation) approach for the acquisition of the initial as-implant dopant profile and kMC method for the simulation of diffusion process during the annealing process. The simulation results implied that carbon co-implant suppresses the boron diffusion due to the recombination with interstitials. Also, we could compare the boron diffusion with carbon diffusion by calculating carbon reaction with interstitial. And we can find that boron diffusion is affected from the carbon co-implant energy by enhancing the trapping of interstitial between boron and interstitial.

Synchronized Re-Entrant Flux Reversal of Multiple FeSiB Amorphous Wires Having the Larger Output

NASA Astrophysics Data System (ADS)

Takajo, Minoru; Yamasaki, Jiro

Technique to synchronize the re-entrant flux reversal of the multiple magnetostrictive Fe77.5Si7.5B15 amorphous wires was developed using a flux keeper of amorphous ribbons contacted to the wire ends. It is comprehended that the characteristics of the re-entrant flux takes place respectively at almost the same time in the three Fe-Si-B amorphous wires with a diameter of 65, 95μm. This phenomenon can be explained by considering the strong magnetic coupling of wires and amorphous ribbon by stray field from the each wire ends. As a result, the magnitude of the induced voltage in the sense coil is increased in proportion to the multiplication of the number of the wires.

EPR and Structural Characterization of Water-Soluble Mn2+-Doped Si Nanoparticles

PubMed Central

2016-01-01

Water-soluble poly(allylamine) Mn2+-doped Si (SiMn) nanoparticles (NPs) were prepared and show promise for biologically related applications. The nanoparticles show both strong photoluminescence and good magnetic resonance contrast imaging. The morphology and average diameter were obtained through transmission electron microscopy (TEM) and high-resolution transmission electron microscopy (HRTEM); spherical crystalline Si NPs with an average diameter of 4.2 ± 0.7 nm were observed. The doping maximum obtained through this process was an average concentration of 0.4 ± 0.3% Mn per mole of Si. The water-soluble SiMn NPs showed a strong photoluminescence with a quantum yield up to 13%. The SiMn NPs had significant T1 contrast with an r1 relaxivity of 11.1 ± 1.5 mM–1 s–1 and r2 relaxivity of 32.7 ± 4.7 mM–1 s–1 where the concentration is in mM of Mn2+. Dextran-coated poly(allylamine) SiMn NPs produced NPs with T1 and T2 contrast with a r1 relaxivity of 27.1 ± 2.8 mM–1 s–1 and r2 relaxivity of 1078.5 ± 1.9 mM–1 s–1. X-band electron paramagnetic resonance spectra are fit with a two-site model demonstrating that there are two types of Mn2+ in these NP’s. The fits yield hyperfine splittings (A) of 265 and 238 MHz with significant zero field splitting (D and E terms). This is consistent with Mn in sites of symmetry lower than tetrahedral due to the small size of the NP’s. PMID:28154618

Laboratory study on the adsorption of Mn(2+) on suspended and deposited amorphous Al(OH)(3) in drinking water distribution systems.

PubMed

Wang, Wendong; Zhang, Xiaoni; Wang, Hongping; Wang, Xiaochang; Zhou, Lichuan; Liu, Rui; Liang, Yuting

2012-09-01

Manganese (II) is commonly present in drinking water. This paper mainly focuses on the adsorption of manganese on suspended and deposited amorphous Al(OH)(3) solids. The effects of water flow rate and water quality parameters, including solution pH and the concentrations of Mn(2+), humic acid, and co-existing cations on adsorption were investigated. It was found that chemical adsorption mainly took place in drinking water with pHs above 7.5; suspended Al(OH)(3) showed strong adsorption capacity for Mn(2+). When the total Mn(2+) input was 3 mg/L, 1.0 g solid could accumulate approximately 24.0 mg of Mn(2+) at 15 °C. In drinking water with pHs below 7.5, because of H(+) inhibition, active reaction sites on amorphous Al(OH)(3) surface were much less. The adsorption of Mn(2+) on Al(OH)(3) changed gradually from chemical coordination to physical adsorption. In drinking water with high concentrations of Ca(2+), Mg(2+), Fe(3+), and HA, the removal of Mn(2+) was enhanced due to the effects of co-precipitation and adsorption. In solution with 1.0 mg/L HA, the residual concentration of Mn(2+) was below 0.005 mg/L, much lower than the limit value required by the Chinese Standard for Drinking Water Quality. Unlike suspended Al(OH)(3), deposited Al(OH)(3) had a much lower adsorption capacity of 0.85 mg/g, and the variation in flow rate and major water quality parameters had little effect on it. Improved managements of water age, pipe flushing and mechanical cleaning were suggested to control residual Mn(2+). Copyright © 2012 Elsevier Ltd. All rights reserved.

Chemistry, mineralogy, and grain properties at Namib and High dunes, Bagnold dune field, Gale crater, Mars: A synthesis of Curiosity rover observations

PubMed Central

Edgett, K. S.; Sutter, B.; Achilles, C. N.; Litvak, M. L.; Lapotre, M. G. A.; Sullivan, R.; Fraeman, A. A.; Arvidson, R. E.; Blake, D. F.; Bridges, N. T.; Conrad, P. G.; Cousin, A.; Downs, R. T.; Gabriel, T. S. J.; Gellert, R.; Hamilton, V. E.; Hardgrove, C.; Johnson, J. R.; Kuhn, S.; Mahaffy, P. R.; Maurice, S.; McHenry, M.; Meslin, P.‐Y.; Ming, D. W.; Minitti, M. E.; Morookian, J. M.; Morris, R. V.; O'Connell‐Cooper, C. D.; Pinet, P. C.; Rowland, S. K.; Schröder, S.; Siebach, K. L.; Stein, N. T.; Thompson, L. M.; Vaniman, D. T.; Vasavada, A. R.; Wellington, D. F.; Wiens, R. C.; Yen, A. S.

2017-01-01

Abstract The Mars Science Laboratory Curiosity rover performed coordinated measurements to examine the textures and compositions of aeolian sands in the active Bagnold dune field. The Bagnold sands are rounded to subrounded, very fine to medium sized (~45–500 μm) with ≥6 distinct grain colors. In contrast to sands examined by Curiosity in a dust‐covered, inactive bedform called Rocknest and soils at other landing sites, Bagnold sands are darker, less red, better sorted, have fewer silt‐sized or smaller grains, and show no evidence for cohesion. Nevertheless, Bagnold mineralogy and Rocknest mineralogy are similar with plagioclase, olivine, and pyroxenes in similar proportions comprising >90% of crystalline phases, along with a substantial amorphous component (35% ± 15%). Yet Bagnold and Rocknest bulk chemistry differ. Bagnold sands are Si enriched relative to other soils at Gale crater, and H2O, S, and Cl are lower relative to all previously measured Martian soils and most Gale crater rocks. Mg, Ni, Fe, and Mn are enriched in the coarse‐sieved fraction of Bagnold sands, corroborated by visible/near‐infrared spectra that suggest enrichment of olivine. Collectively, patterns in major element chemistry and volatile release data indicate two distinctive volatile reservoirs in Martian soils: (1) amorphous components in the sand‐sized fraction (represented by Bagnold) that are Si‐enriched, hydroxylated alteration products and/or H2O‐ or OH‐bearing impact or volcanic glasses and (2) amorphous components in the fine fraction (<40 μm; represented by Rocknest and other bright soils) that are Fe, S, and Cl enriched with low Si and adsorbed and structural H2O. PMID:29497589

Silencing tumor necrosis factor-alpha in vitro from small interfering RNA-decorated titanium nanotube array can facilitate osteogenic differentiation of mesenchymal stem cells.

PubMed

Wang, Zhenlin; Hu, Zhiqiang; Zhang, Dawei; Zhuo, Mengchuan; Cheng, Jiwei; Xu, Xingping; Xing, Yongming; Fan, Jie

2016-01-01

Titanium implants are known for their bone bonding ability. However, the osseointegration may be severely disturbed in the inflammation environment. In order to enhance osseointegration of the implant in an inflamed environment, the small interfering RNA (siRNA) targeting tumor necrosis factor alpha (TNF-α) was used to functionalize titanium surface for gene silencing. The chitosan-tripolyphosphate-hyaluronate complexes were used to formulate nanoparticles (NPs) with siRNA, which were adsorbed directly by the anodized titanium surface. The surface characterization was analyzed by scanning electron microscope, atomic force microscopy, as well as contact angle measurement. The fluorescence microscope was used to monitor the degradation of the layer. The coculture system was established with mesenchymal stem cells (MSCs) grown directly on functionalized titanium surface and RAW264.7 cells (preactivated by lipopolysaccharide) grown upside in a transwell chamber. The transfection and knockdown efficiency of TNF-α in RAW264.7 cells were determined by fluorescence microscope, quantitative polymerase chain reaction, and enzyme-linked immunosorbent assay. The cytoskeleton and osteogenic differentiation of MSCs were also analyzed. Regular vertical aligned nanotubes (~100 nm diameter and ~300 nm length) were generated after anodization of polished titanium. After loading with NPs, the nanotubes were filled and covered by a layer of amorphous particles. The surface topography changed and wettability decreased after covering with NPs. As expected, a burst degradation of the film was observed, which could provide sufficient NPs in the released supernatant and result in transfection and knockdown effects in RAW264.7 cells. The cytoskeleton arrangement of MSCs was elongated and the osteogenic differentiation was also significantly improved on NPs loading surface. In conclusion, the siRNA decorated titanium implant could simultaneously suppress inflammation and improve osteogenesis, which may be suitable for peri-implant bone formation under inflammatory conditions.

Group III impurities Si interstitials interaction caused by ion irradiation

NASA Astrophysics Data System (ADS)

Romano, L.; Piro, A. M.; De Bastiani, R.; Grimaldi, M. G.; Rimini, E.

2006-01-01

The off-lattice displacement of substitutional impurities (B, Ga) in Si caused by irradiation with energetic light ion beams has been investigated. Samples have been prepared by solid phase epitaxy (SPE) of pre-amorphized Si subsequently implanted with B and Ga at a concentration of about 1 × 1020 at/cm3 confined in a 300 nm thick surface region. The off-lattice displacement of the impurities was induced at room temperature (RT) by irradiation with high energy (>600 keV) light ion beams (H, He) and detected by the channelling technique along different axes, using the 11B(p,α)8Be reaction and standard RBS, for B and Ga, respectively. The normalized channelling yield χ of the impurity signal increases with the ion fluence, indicating a progressive off-lattice displacement of the dopant during irradiation, until it saturates at χF < 1 suggesting a non-random displacement of the dopant. Although the precise value of χF depends on the channelling direction and dopant species, the off-lattice displacement rate, deduced from the χ versus interstitial fluence curve, only depends on the excess of Si self-interstitials (SiI) generated by the irradiating beam through a parameter σ that can be interpreted as an effective cross-section for the impurity-SiI interaction.

New soft magnetic amorphous cobalt based alloys with high hysteresis loop linearity

NASA Astrophysics Data System (ADS)

Nosenko, V. K.; Maslov, V. V.; Kochkubey, A. P.; Kirilchuk, V. V.

2008-02-01

The new amorphous Co56÷59(Fe,Ni,Mn)21÷24(Si0.2B0.8)20-based metal alloys (AMA) with high saturation induction (BS>=1T) were developed. Toroidal tape wound magnetic cores made from these AMA after heat-magnetic treatment (HMT) in a reversal field are characterized by high hysteresis loop linearity, minimum effective magnetic permeability and its high field stability in combination with low coercivity Hc (1-3 A/m, 1 kHz). For the most prospecting alloy compositions the value of effective magnetic permeability decreases compared to known alloys up to 550 - 670 units and remains constant in the wide magnetic field range 1100 - 1300 A/m. Maximum remagnetization loop linearity is achieved after optimum HMT in high Ni containing AMAs, which are characterized by the record low squareness ratio values Ks=0.002-0.02 and Hc=1.0 A/m. Magnetic cores made from the new amorphous alloys can be used both in filter chokes of switch-mode power supply units and in matching mini-transformers of telecommunication systems; at that, high efficiency and accuracy of signal transmission including high frequency pulses are ensured under conditions of long-term influence of dc magnetic bias.

Channeling implantation of high energy carbon ions in a diamond crystal: Determination of the induced crystal amorphization

NASA Astrophysics Data System (ADS)

Erich, M.; Kokkoris, M.; Fazinić, S.; Petrović, S.

2018-02-01

This work reports on the induced diamond crystal amorphization by 4 MeV carbon ions implanted in the 〈1 0 0〉 oriented crystal and its determination by application of RBS/C and EBS/C techniques. The spectra from the implanted samples were recorded for 1.2, 1.5, 1.75 and 1.9 MeV protons. For the two latter ones the strong resonance of the nuclear elastic scattering 12C(p,p0)12C at 1.737 MeV was explored. The backscattering channeling spectra were successfully fitted and the ion beam induced crystal amorphization depth profile was determined using a phenomenological approach, which is based on the properly defined Gompertz type dechanneling functions for protons in the 〈1 0 0〉 diamond crystal channels and the introduction of the concept of ion beam amorphization, which is implemented through our newly developed computer code CSIM.

Fabrication of an Fe80.5Si7.5B6Nb5Cu Amorphous-Nanocrystalline Powder Core with Outstanding Soft Magnetic Properties

NASA Astrophysics Data System (ADS)

Zhang, Zongyang; Liu, Xiansong; Feng, Shuangjiu; Rehman, Khalid Mehmood Ur

2018-03-01

In this study, the melt spinning method was used to develop Fe80.5Si7.5B6Nb5Cu amorphous ribbons in the first step. Then, the Fe80.5Si7.5B6Nb5Cu amorphous-nanocrystalline core with a compact microstructure was obtained by multiple processes. The main properties of the magnetic powder core, such as micromorphology, thermal behavior, permeability, power loss and quality factor, have been analyzed. The obtained results show that an Fe80.5Si7.5B6Nb5Cu amorphous-nanocrystalline duplex core has high permeability (54.8-57), is relatively stable at different frequencies and magnetic fields, and the maximum power loss is only 313 W/kg; furthermore, it has a good quality factor.

Microstructure and degradation behavior of forged Fe-Mn-Si alloys

NASA Astrophysics Data System (ADS)

Xu, Zhigang; Hodgson, Michael A.; Cao, Peng

2015-03-01

This work presents a comparative study of a series of Fe-Mn-Si alloys proposed as degradable biomaterials for medical applications. Five Fe-28wt.%Mn-xSi (where x = 0 to 8 wt.%) alloys were fabricated by an arc-melting method. All the as-cast alloys were subsequently subjected to homogenization treatment and hot forging. The microstructure and phase constituents were investigated. It is found that the grain size of the as-forged alloys ranged approximately from 30 to 50 μm. The as-forged Fe-Mn-Si alloys containing Si from 2 to 6 wt.% was comprised of duplex martensitic ɛ and austenitic γ phases; however, the Si-free and 8 wt.% Si alloys only consisted of a single γ phase. After 30 days of static immersion test in a simulated body fluid (SBF) medium, it is found that pitting and general corrosion occur on the sample surfaces. Potentiodynamic analysis reveals that the degradation rate of the Fe-Mn-Si alloys increased gradually with Si content up to 6 wt.%, beyond which the degradation slows down.

Dust input in the formation of rock varnish from the Dry Valleys (Antarctica)

NASA Astrophysics Data System (ADS)

Zerboni, A.; Guglielmin, M.

2017-12-01

Rock varnish is a glossy, yellowish to dark brown coating that covers geomorphically stable, aerially exposed rock surfaces and landforms in warm and cold arid lands. In warm deserts, rock varnish consists of clay minerals, Mn-Fe oxides/hydroxides, and Si+alkalis dust; it occasionally containis sulphates, phosphates, and organic remains. In Antarctica, rock varnish developed on a variety of bedrocks and has been described being mostly formed of Si, Al, Fe, and sulphates, suggesting a double process in its formation, including biomineralization alternated to dust accretion. We investigated rock coatings developed on sandstones outcropping in the Dry Valleys of Antarctica and most of the samples highlithed an extremely complex varnish structure, alternating tihn layer of different chemical compostion. Optical microscope evidenced the occurrence of highly birefringent minerals, occasionally thinly laminated and consisitng of Si and Al-rich minerals (clays). These are interlayered by few micron-thick dark lenses and continous layers. The latter are well evident under the scanning electron microscope and chemical analysis confirmed that they consist of different kinds of sulphates; jarosite is the most represented species, but gypsum crystals were also found. Fe-rich hypocoatings and intergranula crusts were also detected, sometimes preserving the shape of the hyphae they have replaced. Moreover, small weathering pits on sandstone surface display the occurrence of an amorphous, dark Mn/Fe-rich rock varnish. The formation of rock varnish in the Dry Valleys is a complex process, which required the accretion of airborne dust of variable composition and subsequent recrystallization of some constituent, possibly promoted by microorganisms. In particualr, the formation of sulphates seems to preserve the memory of S-rich dust produced by volcanic eruptions. On the contrary, the formation of Mn-rich varnish should be in relation with the occurrence of higher environmental humidity within weathering pits. Rock varnish in the Dry Valleys represents a potential tool to reconstruct past water availability and changes in the aeolian fallout.

Mesoporous Amorphous Silicon: A Simple Synthesis of a High-Rate and Long-Life Anode Material for Lithium-Ion Batteries.

PubMed

Lin, Liangdong; Xu, Xuena; Chu, Chenxiao; Majeed, Muhammad K; Yang, Jian

2016-11-02

Amorphous Si (a-Si) shows potential advantages over crystalline Si (c-Si) in lithium-ion batteries, owing to its high lithiation potential and good tolerance to intrinsic strain/stress. Herein, porous a-Si has been synthesized by a simple process, without the uses of dangerous or expensive reagents, sophisticated equipment, and strong acids that potential cause environment risks. These porous a-Si particles exhibit excellent electrochemical performances, owing to their porous structure, amorphous nature, and surface modification. They deliver a capacity of 1025 mAh g -1 at 3 A g -1 after 700 cycles. Moreover, the reversible capacity after electrochemical activation, is quite stable throughout the cycling, resulting in a capacity retention about around 88 %. The direct comparison between a-Si and c-Si anodes clearly supports the advantages of a-Si in lithium-ion batteries. © 2016 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim.

Heusler Alloyed Electrodes Integrated in Magnetic Tunnel-Junctions

NASA Astrophysics Data System (ADS)

Hütten, Andreas; Kämmerer, Sven; Schmalhorst, Jan; Reiss, Günter

As a consequence of the growing theoretically predictions of 100% spin polarized half- and full-Heusler compounds over the past 6 years, Heusler alloys are among the most promising materials class for future magnetoelectronic and spintronic applications. We have integrated Co2MnSi as a representative of the full-Heusler compound family as one magnetic electrode into technological relevant magnetic tunnel junctions. The resulting tunnel magnetoresistance at 20 K was determined to be 95% corresponding to a Co2MnSi spin polarization of 66% in combination with an AlOx barrier thickness of 1.8 nm. For magnetic tunnel junctions prepared with an initially larger Al layer prior to oxidation the tunnel magnetoresistance at 20 K increases to about 108% associated with a Co2MnSi spin polarization of 72% clearly proving that Co2MnSi is already superior to 3d-based magnetic elements or their alloys. The corresponding room temperature values of the tunnel magnetoresistance are 33% and 41%, respectively. Structural and magnetic properties of the Co2MnSi AlOx - barrier interface have been studied with X-ray diffraction, electron and X-ray absorption spectroscopy and X-ray magnetic circular dichroism and it is shown that the ferromagnetic order of Mn and Co spins at this interface is only induced in optimally annealed Co2MnSi layer. The underlying atomic ordering mechanism responsible for achieving about its theoretical magnetic moment could be assigned to the elimination of Co-Si antisite defects whereas the reduction of Co-Mn antisite defects results in large tunnel magnetoresistance. The presence of a step like tunnel barrier which is already created during plasma oxidation while preparing the AlOx tunnel barrier has been identified as the current limitation to achieve larger tunnel magnetoresistance and hence larger spin polarization and is a direct consequence of the oxygen affinity of the Co2MnSi - Heusler elements Mn and Si.

Silicon crystallization in nanodot arrays organized by block copolymer lithography

NASA Astrophysics Data System (ADS)

Perego, Michele; Andreozzi, Andrea; Seguini, Gabriele; Schamm-Chardon, Sylvie; Castro, Celia; BenAssayag, Gerard

2014-12-01

Asymmetric polystyrene- b-polymethylmethacrylate (PS- b-PMMA) block copolymers are used to fabricate nanoporous PS templates with different pore diameter depending on the specific substrate neutralization protocol. The resulting polymeric templates are used as masks for the subsequent deposition of a thin ( h = 5 nm) amorphous Si layer by electron beam evaporation. After removal of the polymeric film and of the silicon excess, well-defined hexagonally packed amorphous Si nanodots are formed on the substrate. Their average diameter ( d < 20 nm), density (1.2 × 1011 cm-2), and lateral distribution closely mimic the original nanoporous template. Upon capping with SiO2 and high temperature annealing (1050 °C, N2), each amorphous Si nanodot rearranges in agglomerates of Si nanocrystals ( d < 4 nm). The average diameter and shape of these Si nanocrystals strongly depend on the size of the initial Si nanodot.

Silicon and Manganese Partition Between Slag and Metal Phases and Their Activities Pertinent to Ferromanganese and Silicomanganese Production

NASA Astrophysics Data System (ADS)

Cengizler, Hakan; Eric, R. Hurman

Equilibrium between MnO-CaO-MgO-SiO2-Al2O3 slags and carbon saturated Mn-Si-Fe-C alloys was investigated under CO at 1500oC. Manganese and silicon activities were obtained by using the present data and the previously determined MnO and SiO2 activities of the slag. Quadratic multi-coefficient regression equations were developed for activity coefficients of manganese and silicon. The conclusions of this work are:(i)increase in the basicity and the CaO/Al2O3 ratios decreases the Mn distribution ratio,(ii)increase in the silica concentration and the MgO/CaO ratio increases the Mn distribution ratio, iii)carbon and manganese as well as carbon and silicon of the metal phase are inversely proportional,(iv)as Mn/Fe and Mn/Si ratio increases in the metal the carbon solubility increases,(v)decrease in the basicity increases the silicon content of the metal and (vi)increase in the silica content of the slag increases the silicon content of the metal and this effect is more pronounced at the higher Mn/Fe and Mn/Si ratios.

Final Report: Hot Carrier Collection in Thin Film Silicon with Tailored Nanocrystalline/Amorphous Structure

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

Collins, Reuben T.

This project developed, characterized, and perfected a new type of highly tunable nanocrystalline silicon (nc-Si:H) incorporating quantum confined silicon nanoparticles (SiNPs). A dual zone deposition process and system were developed and demonstrated. The depositions of SiNPs, the amorphous phase, and co-deposited material were characterized and optimized. Material design and interpretation of results were guided by new theoretical tools that examined both the electronic structure and carrier dynamics of this hybrid material. Heterojunction and p-i-n solar cells were demonstrated and characterized. Photo-thin-film-transistors allowed mobility to be studied as a function SiNP density in the films. Rapid (hot) transfer of carriers frommore » the amorphous matrix to the quantum confined SiNPs was observed and connected to reduced photo-degradation. The results carry quantum confined Si dots from a novelty to materials that can be harnessed for PV and optoelectronic applications. The growth process is broadly extendable with alternative amorphous matrices, novel layered structures, and alternative NPs easily accessible. The hot carrier effects hold the potential for third generation photovoltaics.« less

Facile preparation of magnetic mesoporous MnFe2O4@SiO2-CTAB composites for Cr(VI) adsorption and reduction.

PubMed

Li, Na; Fu, Fenglian; Lu, Jianwei; Ding, Zecong; Tang, Bing; Pang, Jiabin

2017-01-01

Chromium-contaminated water is regarded as one of the biggest threats to human health. In this study, a novel magnetic mesoporous MnFe 2 O 4 @SiO 2 -CTAB composite was prepared by a facile one-step modification method and applied to remove Cr(VI). X-ray diffraction, scanning electron microscopy, transmission electron microscopy, specific surface area, and vibrating sample magnetometer were used to characterize MnFe 2 O 4 @SiO 2 -CTAB composites. The morphology analysis showed that the composites displayed a core-shell structure. The outer shell was mesoporous silica with CTAB and the core was MnFe 2 O 4 nanoparticles, which ensured the easy separation by an external magnetic field. The performance of MnFe 2 O 4 @SiO 2 -CTAB composites in Cr(VI) removal was far better than that of bare MnFe 2 O 4 nanoparticles. There were two reasons for the effective removal of Cr(VI) by MnFe 2 O 4 @SiO 2 -CTAB composites: (1) mesoporous silica shell with abundant CTA + significantly enhanced the Cr(VI) adsorption capacity of the composites; (2) a portion of Cr(VI) was reduced to less toxic Cr(III) by MnFe 2 O 4 , followed by Cr(III) immobilized on MnFe 2 O 4 @SiO 2 -CTAB composites, which had been demonstrated by X-ray photoelectron spectroscopy results. The adsorption of Cr(VI) onto MnFe 2 O 4 @SiO 2 -CTAB followed the Freundlich isotherm model and pseudo-second-order model. Tests on the regeneration and reuse of the composites were performed. The removal efficiency of Cr(VI) still retained 92.4% in the sixth cycle. MnFe 2 O 4 @SiO 2 -CTAB composites exhibited a great potential for the removal of Cr(VI) from water. Copyright © 2016 Elsevier Ltd. All rights reserved.

Synthesis of K2SiF6:Mn4+ phosphor for LED lamp

NASA Astrophysics Data System (ADS)

Takarkhede, M. G.; Patil, R. R.; Moharil, S. V.; Joshi, C. P.; Talewar, Rupesh

2018-05-01

Now a days red emitting Mn4+ activated dialkali fluorosilicate phosphors have found applications in solid state lighting and displays. In this paper we describe development of K2SiF6 phosphor doped with Mn synthesized by simple method using Si metal powder with addition of oxidizing agent KMnO4. The photoluminescence spectra of K2SiF6:Mn show that emission is in the red region. In addition to this we studied LED spectra by coating the LED with phosphor mixed in different proportions with epoxy.

Immunotoxicity evaluation of novel bioactive composites in male mice as promising orthopaedic implants

PubMed Central

El-Bassyouni, Gehan T.; Eshak, Mariam G.; Barakat, Ibrahim A.H.

2017-01-01

Objective In orthopaedics, novel bioactive composites are largely needed to improve the synthetic achievement of the implants. In this work, semiconducting metal oxides such as SiO2, TiO2, and ZrO2 particles (Ps) were used individually and in different ratios to obtain different biphasic composites. The immunotoxicity of these composites was tested to inspect the potential toxicity prior to their use in further medical applications. Materials and methods In vitro mineralisation ability was inspected by soaking the composites in simulated body fluid (SBF). Additionally, in vivo experiments were performed consuming male mice using ISSR-PCR, micronucleus (MN) test, comet assay, glutathione peroxidase activity, and determination of albumin, globulin, lymphocyte population, ALT, and AST levels. Several groups of adult male albino mice were treated with 100, 200, and 400 mg/kg body weight of SiO2, TiO2, and ZrO2-Ps in pure or mixed forms. Results Our findings revealed that treatment of mice with low and medium doses of SiO2, TiO2, and ZrO2-Ps in pure or mixed form revealed values relatively similar to the control group. However, using 400 mg/kg especially from TiO2-Ps in genuine form or mixed with SiO2 showed proliferation in the toxicity rates compared with the high dose of SiO2 and ZrO2-Ps. Conclusions The results suggest that TiO2 composite induced in vivo toxicity, oxidative DNA damage, bargain of the antioxidant enzymes, and variations in the levels of albumin, globulin, lymphocyte population, ALT, and AST in a dose-dependent manner. However, SiO2, and ZrO2 composites revealed a lower toxicity in mice compared with that of TiO2. PMID:28680331

First-principles study of spin-transfer torque in Co{sub 2}MnSi/Al/Co{sub 2}MnSi spin-valve

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

Tang, Ling, E-mail: lingtang@zjut.edu.cn; Yang, Zejin, E-mail: zejinyang@zjut.edu.cn

The spin-transfer torque (STT) in Co{sub 2}MnSi(CMS)/Al/Co{sub 2}MnSi spin-valve system with and without interfacial disorder is studied by a first-principles noncollinear wave-function-matching method. It is shown that in the case of clean interface the angular dependence of STT for CoCo/Al (the asymmetry parameter Λ≈4.5) is more skewed than that for MnSi/Al (Λ≈2.9), which suggests the clean CoCo/Al architecture is much more efficient for the application on radio frequency oscillation. We also find that even with interfacial disorder the spin-valve of half-metallic CMS still has a relatively large parameter Λ compared to that of conventional ferromagnet. In addition, for clean interfacemore » the in-plane torkance of MnSi/Al is about twice as large as that of CoCo/Al. However, as long as the degree of interfacial disorder is sufficiently large, the CoCo/Al and MnSi/Al will show approximately the same magnitude of in-plane torkance. Furthermore, our results demonstrate that CMS/Al/CMS system has very high efficiency of STT to switch the magnetic layer of spin-valve.« less

Ferroelectric Properties of Mn-implanted CdTe

NASA Astrophysics Data System (ADS)

Fu, D. J.; Lee, J. C.; Lee, W. C.; Choi, S. W.; Lee, S. J.; Kang, T. W.

2005-06-01

We report a study of ferroelectricity in CdTe:Mn, which were prepared by implantation of CdTe wafers with 200-keV Mn ions to a dose of 5×1016 cm-2 and subsequently treated by rapid thermal annealing. An insulating layer was created by the implantation in the surface region of the samples. Ferroelectric characterization of the implanted sample revealed a clear hysteresis in its polarization-voltage curves. The remnant polarization of CdTe:Mn amounts to 0.64 μC/cm2 at 400 Hz. The polarization decreases with increasing temperature in a continuous and diffusive manner. Capacitance measurement demonstrated a maximum capacitance at 140°C, and fitting of the data with Curie-Weiss law shows the occurrence of a second-order type phase transition.

Amorphization of hard crystalline materials by electrosprayed nanodroplet impact

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

Gamero-Castaño, Manuel, E-mail: mgameroc@uci.edu; Torrents, Anna; Borrajo-Pelaez, Rafael

2014-11-07

A beam of electrosprayed nanodroplets impacting on single-crystal silicon amorphizes a thin surface layer of a thickness comparable to the diameter of the drops. The phase transition occurs at projectile velocities exceeding a threshold, and is caused by the quenching of material melted by the impacts. This article demonstrates that the amorphization of silicon is a general phenomenon, as nanodroplets impacting at sufficient velocity also amorphize other covalently bonded crystals. In particular, we bombard single-crystal wafers of Si, Ge, GaAs, GaP, InAs, and SiC in a range of projectile velocities, and characterize the samples via electron backscatter diffraction and transmissionmore » electron microscopy to determine the aggregation state under the surface. InAs requires the lowest projectile velocity to develop an amorphous layer, followed by Ge, Si, GaAs, and GaP. SiC is the only semiconductor that remains fully crystalline, likely due to the relatively low velocities of the beamlets used in this study. The resiliency of each crystal to amorphization correlates well with the specific energy needed to melt it except for Ge, which requires projectile velocities higher than expected.« less

The U.S. and Japanese amorphous silicon technology programs A comparison

NASA Technical Reports Server (NTRS)

Shimada, K.

1984-01-01

The U.S. Department of Energy/Solar Energy Research Institute Amorphous Silicon (a-Si) Solar Cell Program performs R&D on thin-film hydrogenated amorphous silicon for eventual development of stable amorphous silicon cells with 12 percent efficiency by 1988. The Amorphous Silicon Solar Cell Program in Japan is sponsored by the Sunshine Project to develop an alternate energy technology. While the objectives of both programs are to eventually develop a-Si photovoltaic modules and arrays that would produce electricity to compete with utility electricity cost, the U.S. program approach is research oriented and the Japanese is development oriented.

Direct measurement of free-energy barrier to nucleation of crystallites in amorphous silicon thin films

NASA Technical Reports Server (NTRS)

Shi, Frank G.

1994-01-01

A method is introduced to measure the free-energy barrier W(sup *), the activation energy, and activation entropy to nucleation of crystallites in amorphous solids, independent of the energy barrier to growth. The method allows one to determine the temperature dependence of W(sup *), and the effect of the preparation conditions of the initial amorphous phase, the dopants, and the crystallization methds on W(sup *). The method is applied to determine the free-energy barrier to nucleation of crystallites in amorphous silicon (a-Si) thin films. For thermally induced nucleation in a-Si thin films with annealing temperatures in the range of from 824 to 983 K, the free-energy barrier W(sup *) to nucleation of silicon crystals is about 2.0 - 2.1 eV regardless of the preparation conditions of the films. The observation supports the idea that a-Si transforms into an intermediate amorphous state through the structural relaxation prior to the onset of nucleation of crystallites in a-Si. The observation also indicates that the activation entropy may be an insignificant part of the free-energy barrier for the nucleation of crystallites in a-Si. Compared with the free-energy barrier to nucleation of crystallites in undoped a-Si films, a significant reduction is observed in the free-energy barrier to nucleation in Cu-doped a-Si films. For a-Si under irradiation of Xe(2+) at 10(exp 5) eV, the free-energy barrier to ion-induced nucleation of crystallites is shown to be about half of the value associated with thermal-induced nucleation of crystallites in a-Si under the otherwise same conditions, which is much more significant than previously expected. The present method has a general kinetic basis; it thus should be equally applicable to nucleation of crystallites in any amorphous elemental semiconductors and semiconductor alloys, metallic and polymeric glasses, and to nucleation of crystallites in melts and solutions.

Magneto-mechanical modeling study of CO-based amorphous micro- and nanowires for acoustic sensing medical applications

NASA Astrophysics Data System (ADS)

Atitoaie, Alexandru; Stancu, Alexandru; Ovari, Tibor-Adrian; Lupu, Nicoleta; Chiriac, Horia

2016-04-01

Magnetic nanowires are potential candidates for substituting, within enhanced cochlear implants, the role played by hair cilia from the inner ear, which are responsible for the transduction of acoustic vibrations into electric signals. The sound waves pressure that is bending the magnetic wires induces stresses that are leading to changes in magnetic properties, such as magnetization and permeability. These changes can be detected by a GMR sensor placed below the nanowire array or, in the case of different designs, by a pick-up coil wrapped around the fixed-end of the wires. For the latter case, we are studying the stress distributions caused by bending deformations using the COMSOL finite element software package. We are also proposing a theoretical method for the evaluation of magnetic permeability variation vs. induced stress dependence. The study is performed on CoFeSiB amorphous micro- and nanowires subjected to mechanical perturbations similar to the ones produced by sound pressure waves.

Effect of Doping on the Properties of Hydrogenated Amorphous Silicon Irradiated with Femtosecond Laser Pulses

NASA Astrophysics Data System (ADS)

Denisova, K. N.; Il'in, A. S.; Martyshov, M. N.; Vorontsov, A. S.

2018-04-01

A comparative analysis of the effect of femtosecond laser irradiation on the structure and conductivity of undoped and boron-doped hydrogenated amorphous silicon ( a-Si: H) is performed. It is demonstrated that the process of nanocrystal formation in the amorphous matrix under femtosecond laser irradiation is initiated at lower laser energy densities in undoped a-Si: H samples. The differences in conductivity between undoped and doped a-Si: H samples vanish almost completely after irradiation with an energy density of 150-160 mJ/cm2.

Si-FeSi2/C nanocomposite anode materials produced by two-stage high-energy mechanical milling

NASA Astrophysics Data System (ADS)

Yang, Yun Mo; Loka, Chadrasekhar; Kim, Dong Phil; Joo, Sin Yong; Moon, Sung Whan; Choi, Yi Sik; Park, Jung Han; Lee, Kee-Sun

2017-05-01

High capacity retention Silicon-based nanocomposite anode materials have been extensively explored for use in lithium-ion rechargeable batteries. Here we report the preparation of Si-FeSi2/C nanocomposite through scalable a two-stage high-energy mechanical milling process, in which nano-scale Si-FeSi2 powders are besieged by the carbon (graphite/amorphous phase) layer; and investigation of their structure, morphology and electrochemical performance. Raman analysis revealed that the carbon layer structure comprised of graphitic and amorphous phase rather than a single amorphous phase. Anodes fabricated with the Si-FeSi2/C showed excellent electrochemical behavior such as a first discharge capacity of 1082 mAh g-1 and a high capacity retention until the 30th cycle. A remarkable coulombic efficiency of 99.5% was achieved within a few cycles. Differential capacity plots of the Si-FeSi2/C anodes revealed a stable lithium reaction with Si for lithiation/delithiation. The enhanced electrochemical properties of the Si-FeSi2/C nanocomposite are mainly attributed to the nano-size Si and stable solid electrolyte interface formation and highly conductive path driven by the carbon layer.

Giant magnetic coercivity in CaCu{sub 5}-type SmNi{sub 3}TSi (T=Mn–Cu) solid solutions

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

Yao, Jinlei; Yan, Xu; Morozkin, A.V., E-mail: morozkin@tech.chem.msu.ru

The effects of transition metal substitution for Ni on the magnetic properties of the CaCu{sub 5}-type SmNi{sub 3}TSi (T=Mn, Fe, Co, Cu) solid solutions have been investigated. SmNi{sub 3}MnSi, SmNi{sub 3}FeSi, SmNi{sub 3}CoSi and SmNi{sub 3}CuSi show ferromagnetic ordering at 125 K, 190 K, 46 K and 12 K and field induced transitions at 65 K, 110 K, 30 K and 6 K, respectively. The magnetocaloric effects of SmNi{sub 3}TSi (T=Mn, Fe, Co, Cu) were calculated in terms of isothermal magnetic entropy change (ΔS{sub m}). The magnetic entropy ΔS{sub m} reaches value of −1.1 J/kg K at 130 K formore » SmNi{sub 3}MnSi, −0.4 J/kg K at 180 K for SmNi{sub 3}FeSi, −0.37 J/kg K at 45 K for SmNi{sub 3}CoSi and −0.5 J/kg K at 12 K for SmNi{sub 3}CuSi in field change of 0–50 kOe around the ferromagnetic ordering temperature. They show positive ΔS{sub m} of +2.4 J/kg K at 30 K for SmNi{sub 3}MnSi, −2.6 J/kg K at 65 K for SmNi{sub 3}FeSi, +0.73 J/kg K at 15 K for SmNi{sub 3}CoSi and −0.5 J/kg K at 6 K for SmNi{sub 3}CuSi in field change of 0–50 kOe around the metamagnetic-like transition temperature. Below the field induced transition temperature, SmNi{sub 3}TSi (T=Mn, Fe, Co, Cu) exhibits giant magnetic coercivity of 80 kOe at 20 K for SmNi{sub 3}MnSi, 87 kOe at 40 K for SmNi{sub 3}FeSi, 27 kOe at 20 K for SmNi{sub 3}CoSi and 54 kOe at 5 K for SmNi{sub 3}CuSi. - Graphical abstract: CaCu{sub 5}-type SmNi{sub 3}MnSi, SmNi{sub 3}FeSi, SmNi{sub 3}CoSi and SmNi{sub 3}CuSi show ferromagnetic ordering at 125 K, 190 K, 46 K and 12 K and field induced transitions at 65 K, 110 K, 30 K and 6 K, respectively. The magnetic entropy ΔS{sub m} reaches value of −1.1 J/kg K at 130 K for SmNi{sub 3}MnSi, −0.4 J/kg K at 180 K for SmNi{sub 3}FeSi, −0.37 J/kg K at 45 K for SmNi{sub 3}CoSi and −0.5 J/kg K at 12 K for SmNi{sub 3}CuSi in field change of 0–50 kOe around the ferromagnetic ordering temperature. They show positive ΔS{sub m} of +2.4 J/kg K at 30 K for SmNi{sub 3}MnSi, −2.6 J/kg K at 65 K for SmNi{sub 3}FeSi, +0.73 J/kg K at 15 K for SmNi{sub 3}CoSi and −0.5 J/kg K at 6 K for SmNi{sub 3}CuSi in field change of 0–50 kOe around the metamagnetic-like transition temperature. Below the field induced transition temperature, SmNi{sub 3}TSi (T=Mn, Fe, Co, Cu) exhibits giant magnetic coercivity of 80 kOe at 20 K for SmNi{sub 3}MnSi, 87 kOe at 40 K for SmNi{sub 3}FeSi, 27 kOe at 20 K for SmNi{sub 3}CoSi and 54 kOe at 5 K for SmNi{sub 3}CuSi. - Highlights: • CaCu{sub 5}-type SmNi{sub 3}{Mn, Fe, Co, Cu}Si exhibit the Curie points at 12–190 K. • SmNi{sub 3}{Mn, Fe, Co, Cu}Si show field induced transition at 6–110 K. • SmNi{sub 3}MnSi shows huge magnetic hysteresis with coercive field of 80 kOe at 20 K. • SmNi{sub 3}FeSi shows huge magnetic hysteresis with coercive field of 87 kOe at 40 K. • SmNi{sub 3}CuSi shows giant coercive field of 54 kOe at 5 K.« less

MnTiO3-driven low-temperature oxidative coupling of methane over TiO2-doped Mn2O3-Na2WO4/SiO2 catalyst

PubMed Central

Wang, Pengwei; Zhao, Guofeng; Wang, Yu; Lu, Yong

2017-01-01

Oxidative coupling of methane (OCM) is a promising method for the direct conversion of methane to ethene and ethane (C2 products). Among the catalysts reported previously, Mn2O3-Na2WO4/SiO2 showed the highest conversion and selectivity, but only at 800° to 900°C, which represents a substantial challenge for commercialization. We report a TiO2-doped Mn2O3-Na2WO4/SiO2 catalyst by using Ti-MWW zeolite as TiO2 dopant as well as SiO2 support, enabling OCM with 26% conversion and 76% C2-C3 selectivity at 720°C because of MnTiO3 formation. MnTiO3 triggers the low-temperature Mn2+↔Mn3+ cycle for O2 activation while working synergistically with Na2WO4 to selectively convert methane to C2-C3. We also prepared a practical Mn2O3-TiO2-Na2WO4/SiO2 catalyst in a ball mill. This catalyst can be transformed in situ into MnTiO3-Na2WO4/SiO2, yielding 22% conversion and 62% selectivity at 650°C. Our results will stimulate attempts to understand more fully the chemistry of MnTiO3-governed low-temperature activity, which might lead to commercial exploitation of a low-temperature OCM process. PMID:28630917

Au5+ ion implantation induced structural phase transitions probed through structural, microstructural and phonon properties in BiFeO3 ceramics, using synergistic ion beam energy

NASA Astrophysics Data System (ADS)

Dey, Ranajit; Bajpai, P. K.

2018-04-01

Implanted Au5+-ion-induced modification in structural and phonon properties of phase pure BiFeO3 (BFO) ceramics prepared by sol-gel method was investigated. These BFO samples were implanted by 15.8 MeV ions of Au5+ at various ion fluence ranging from 1 × 1014 to 5 × 1015 ions/cm2. Effect of Au5+ ions' implantation is explained in terms of structural phase transition coupled with amorphization/recrystallization due to ion implantation probed through XRD, SEM, EDX and Raman spectroscopy. XRD patterns show broad diffuse contributions due to amorphization in implanted samples. SEM images show grains collapsing and mounds' formation over the surface due to mass transport. The peaks of the Raman spectra were broadened and also the peak intensities were decreased for the samples irradiated with 15.8 MeV Au5+ ions at a fluence of 5 × 1015 ion/cm2. The percentage increase/decrease in amorphization and recrystallization has been estimated from Raman and XRD data, which support the synergistic effects being operative due to comparable nuclear and electronic energy losses at 15.8 MeV Au5+ ion implantation. Effect of thermal treatment on implanted samples is also probed and discussed.

Large reversible magnetostrictive effect of MnCoSi-based compounds prepared by high-magnetic-field solidification

NASA Astrophysics Data System (ADS)

Hu, Q. B.; Hu, Y.; Zhang, S.; Tang, W.; He, X. J.; Li, Z.; Cao, Q. Q.; Wang, D. H.; Du, Y. W.

2018-01-01

The MnCoSi compound is a potential magnetostriction material since the magnetic field can drive a metamagnetic transition from an antiferromagnetic phase to a high magnetization phase in it, which accompanies a large lattice distortion. However, a large driving magnetic field, magnetic hysteresis, and poor mechanical properties seriously hinder its application for magnetostriction. By substituting Fe for Mn and introducing vacancies of the Mn element, textured and dense Mn0.97Fe0.03CoSi and Mn0.88CoSi compounds are prepared through a high-magnetic-field solidification approach. As a result, large room-temperature and reversible magnetostriction effects are observed in these compounds at a low magnetic field. The origin of this large magnetostriction effect and potential applications are discussed.

Pink manganian phengite in a high P/ T meta-conglomerate from northern Syros (Cyclades, Greece)

NASA Astrophysics Data System (ADS)

Altherr, Rainer; Soder, Christian; Panienka, Sandra; Peters, Daniel; Meyer, Hans-Peter

2013-11-01

A new occurrence of Mn-rich rocks was discovered within the high-pressure/low-temperature metamorphic rocks on the Palos peninsula of Syros (Greece). Near the summit of Mount Príonas, a meta-conglomerate consists of calcite (~63 wt%), pink manganian phengite, blue-purple manganian aegirine-jadeite, microcline, albite and quartz. In addition, it contains abundant braunite-rich aggregates (up to ~1.5 cm in diameter) that include hollandite [(Ba0.98-1.02K<0.01Na<0.02Ca<0.03) (Mn{1.02-1.52/3+}Fe{0.38-0.88/3+}Ti0.29-0.92Mn{5.11-5.76/4+})O16], barite and manganian hematite. Due to metamorphic recrystallization and deformation, the contacts between clasts and matrix are blurred and most clasts have lost their identity. In back-scattered electron images, many aegirine-jadeite grains appear patchy and show variable jadeite contents (Jd10-67). These pyroxenes occur in contact with either quartz or albite. Manganian phengite (3.41-3.49 Si per 11 oxygen anions) is of the 3T type and contains 1.4-2.2 wt% of Mn2O3. At the known P- T conditions of high-pressure metamorphism on Syros (~1.4 GPa/ 470 °C), the mineral sub-assemblage braunite + quartz + calcite (former aragonite) suggests high oxygen fugacities relative to the HM buffer (+7 ≤ ΔfO2 ≤ + 17) and relatively high CO2 fugacities. The exact origin of the conglomerate is not known, but it is assumed that the Fe-Mn-rich and the calcite-rich particles originated from different sources. Braunite has rather low contents of Cu (~0.19 wt%) and the concentrations of Co, Ni and Zn are less than 0.09 wt%. Hollandite shows even lower concentrations of these elements. Furthermore, the bulk-rock compositions of two samples are characterized by low contents of Cu, Co and Ni, suggesting a hydrothermal origin of the manganese ore. Most likely, these Fe-Mn-Si oxyhydroxide deposits consisted of ferrihydrite, todorokite, birnessite, amorphous silica (opal-A) and nontronite. Al/(Al + Fe + Mn) ratios of 0.355 and 0.600 suggest the presence of an aluminosilicate detrital component.

Universal aspects of sonolubrication in amorphous and crystalline materials

NASA Astrophysics Data System (ADS)

Pfahl, V.; Ma, C.; Arnold, W.; Samwer, K.

2018-01-01

We studied sonolubricity, a phenomenon reducing the friction between two sliding surfaces by ultrasound. Friction force measurements were performed using an atomic force microscope (AFM) when the tip-surface contact was excited to out-of-plane oscillations by a transducer attached to the rear of the sample or by oscillating the AFM cantilever by the built-in piezoelectric element in the cantilever holder. Experiments were carried out near or at the first cantilever contact-resonance. We studied friction on crystalline and amorphous Pd77.5Cu6Si16.5 ribbons, on a silicon wafer at room temperature, and on a La0.6Sr0.4MnO3 (LSMO) thin film at different temperatures. Measurements were carried out varying the cantilever amplitude, the ultrasonic frequency, and the normal static load. The effect of sonolubrication is explained by the non-linear force-distance curve between the sample and the tip due to the local interaction potential. The reduction of friction in LSMO as a function temperature is due to the direct coupling of the tip's stress-field to the electrons.

Tin induced a-Si crystallization in thin films of Si-Sn alloys

NASA Astrophysics Data System (ADS)

Neimash, V.; Poroshin, V.; Shepeliavyi, P.; Yukhymchuk, V.; Melnyk, V.; Kuzmich, A.; Makara, V.; Goushcha, A. O.

2013-12-01

Effects of tin doping on crystallization of amorphous silicon were studied using Raman scattering, Auger spectroscopy, scanning electron microscopy, and X-ray fluorescence techniques. Formation of silicon nanocrystals (2-4 nm in size) in the amorphous matrix of Si1-xSnx, obtained by physical vapor deposition of the components in vacuum, was observed at temperatures around 300 °C. The aggregate volume of nanocrystals in the deposited film of Si1-xSnx exceeded 60% of the total film volume and correlated well with the tin content. Formation of structures with ˜80% partial volume of the nanocrystalline phase was also demonstrated. Tin-induced crystallization of amorphous silicon occurred only around the clusters of metallic tin, which suggested the crystallization mechanism involving an interfacial molten Si:Sn layer.

Signature of a highly spin polarized resonance state at Co2MnSi(0 0 1)/Ag(0 0 1) interfaces

NASA Astrophysics Data System (ADS)

Lidig, Christian; Minár, Jan; Braun, Jürgen; Ebert, Hubert; Gloskovskii, Andrei; Kronenberg, Alexander; Kläui, Mathias; Jourdan, Martin

2018-04-01

We investigated interfaces of halfmetallic Co2MnSi(1 0 0) Heusler thin films with Ag(1 0 0), Cr(1 0 0), Cu and Al layers relevant for spin valves by high energy x-ray photoemission spectroscopy (HAXPES). Experiments on Co2MnSi samples with an Ag(1 0 0) interface showed a characteristic spectral shoulder feature close to the Fermi edge, which is strongly diminished or suppressed at Co2MnSi (1 0 0) interfaces with the other metallic layers. This feature is found to be directly related to the Co2MnSi(1 0 0) layer, as reflected by control experiments with reference non-magnetic films, i.e. without the Heusler layer. By comparison with HAXPES calculations, the shoulder feature is identified as originating from an interface state related to a highly spin polarized surface resonance of Co2MnSi (1 0 0).

Secondary Al-Si-Mg High-pressure Die Casting Alloys with Enhanced Ductility

NASA Astrophysics Data System (ADS)

Bösch, Dominik; Pogatscher, Stefan; Hummel, Marc; Fragner, Werner; Uggowitzer, Peter J.; Göken, Mathias; Höppel, Heinz Werner

2015-03-01

Al-Si-Mg-based secondary cast alloys are attractive candidates for thin-walled high-pressure die castings for applications in the transport industry. The present study investigates the effect of manganese additions at high cooling rates on microstructure, mechanical properties, and on the dominating fracture mechanisms of alloy AlSi10Mg with an elevated iron concentration. Systematic variations of the Mn content from 0.20 to 0.85 wt pct at a constant Fe content of 0.55 wt pct illustrate the key changes in type, phase fraction, and shape of the Fe-containing intermetallic phases, and the corresponding influence on the alloy's ductility. For high-pressure die casting (HPDC), an optimal range of the Mn content between 0.40 and 0.60 wt pct, equivalent to a Mn/Fe ratio of approximately 1, has been identified. At these Mn and Fe contents, the high cooling rates obtained in HPDC result in the formation of fine and homogeneously distributed α-Al15(Fe,Mn)3Si2 phase, and crack initiation is transferred from AlFeSi intermetallics to eutectic silicon. The study interprets the microstructure-property relationship in the light of thermodynamic calculations which reveal a significant increase in undercooling of the α-Al15(Fe,Mn)3Si2 phase with increased Mn content. It concludes that the interdependence of the well-defined Mn/Fe ratio and the high cooling rate in HPDC can generate superior ductility in secondary AlSi10Mg cast alloys.

Spinodal decomposition in amorphous metal-silicate thin films: Phase diagram analysis and interface effects on kinetics

NASA Astrophysics Data System (ADS)

Kim, H.; McIntyre, P. C.

2002-11-01

Among several metal silicate candidates for high permittivity gate dielectric applications, the mixing thermodynamics of the ZrO2-SiO2 system were analyzed, based on previously published experimental phase diagrams. The driving force for spinodal decomposition was investigated in an amorphous silicate that was treated as a supercooled liquid solution. A subregular model was used for the excess free energy of mixing of the liquid, and measured invariant points were adopted for the calculations. The resulting simulated ZrO2-SiO2 phase diagram matched the experimental results reasonably well and indicated that a driving force exists for amorphous Zr-silicate compositions between approx40 mol % and approx90 mol % SiO2 to decompose into a ZrO2-rich phase (approx20 mol % SiO2) and SiO2-rich phase (>98 mol % SiO2) through diffusional phase separation at a temperature of 900 degC. These predictions are consistent with recent experimental reports of phase separation in amorphous Zr-silicate thin films. Other metal-silicate systems were also investigated and composition ranges for phase separation in amorphous Hf, La, and Y silicates were identified from the published bulk phase diagrams. The kinetics of one-dimensional spinodal decomposition normal to the plane of the film were simulated for an initially homogeneous Zr-silicate dielectric layer. We examined the effects that local stresses and the capillary driving force for component segregation to the interface have on the rate of spinodal decomposition in amorphous metal-silicate thin films.

Electroluminescence and transport properties in amorphous silicon nanostructures

NASA Astrophysics Data System (ADS)

Irrera, Alessia; Iacona, Fabio; Crupi, Isodiana; Presti, Calogero D.; Franzò, Giorgia; Bongiorno, Corrado; Sanfilippo, Delfo; Di Stefano, Gianfranco; Piana, Angelo; Fallica, Pier Giorgio; Canino, Andrea; Priolo, Francesco

2006-03-01

We report the results of a detailed study on the structural, electrical and optical properties of light emitting devices based on amorphous Si nanostructures. Amorphous nanostructures may constitute an interesting system for the monolithic integration of optical and electrical functions in Si ULSI technology. In fact, they exhibit an intense room temperature electroluminescence (EL), with the advantage of being formed at a temperature of 900 °C, while at least 1100 °C is needed for the formation of Si nanocrystals. Optical and electrical properties of amorphous Si nanocluster devices have been studied in the temperature range between 30 and 300 K. The EL is seen to have a bell-shaped trend as a function of temperature with a maximum at around 60 K. The efficiency of these devices is comparable to that found in devices based on Si nanocrystals, although amorphous nanostructures exhibit peculiar working conditions (very high current densities and low applied voltages). Time resolved EL measurements demonstrate the presence of a short lifetime, only partially due to the occurrence of non-radiative phenomena, since the very small amorphous clusters formed at 900 °C are characterized by a short radiative lifetime. By forcing a current through the device a phenomenon of charge trapping in the Si nanostructures has been observed. Trapped charges affect luminescence through an Auger-type non-radiative recombination of excitons. Indeed, it is shown that unbalanced injection of carriers (electrons versus holes) is one of the main processes limiting luminescence efficiency. These data will be reported and the advantages and limitations of this approach will be discussed.

Bacterial nanometric amorphous Fe-based oxide: a potential lithium-ion battery anode material.

PubMed

Hashimoto, Hideki; Kobayashi, Genki; Sakuma, Ryo; Fujii, Tatsuo; Hayashi, Naoaki; Suzuki, Tomoko; Kanno, Ryoji; Takano, Mikio; Takada, Jun

2014-04-23

Amorphous Fe(3+)-based oxide nanoparticles produced by Leptothrix ochracea, aquatic bacteria living worldwide, show a potential as an Fe(3+)/Fe(0) conversion anode material for lithium-ion batteries. The presence of minor components, Si and P, in the original nanoparticles leads to a specific electrode architecture with Fe-based electrochemical centers embedded in a Si, P-based amorphous matrix.

Investigating the stability of cathode materials for rechargeable lithium ion batteries

NASA Astrophysics Data System (ADS)

Huang, Yiqing

Lithium ion batteries are widely used in portable electronic devices and electric vehicles. However, safety is one of the most important issues for the Li-ion batteries' use. Some cathode materials, such as LiCoO 2, are thermally unstable in the charged state. Upon decomposition these cathode materials release O2, which could react with organic electrolyte, leading to a thermal runaway. Thus understanding the stability of the cathode materials is critical to the safety of lithium ion batteries. Olivine-type LiMnPO4 is a promising cathode material for lithium ion batteries because of its high energy density. We have revealed the critical role of carbon in the stability and thermal behaviour of olivine MnPO 4 obtained by chemical delithiation of LiMnPO4. (Li)MnPO 4 samples with various particle sizes and carbon contents were studied. Carbon-free LiMnPO4 obtained by solid state synthesis in O 2 becomes amorphous upon delithiation. Small amounts of carbon (0.3 wt.%) help to stabilize the olivine structure, so that completely delithiated crystalline olivine MnPO4 can be obtained. Larger amount of carbon (2 wt.%) prevents full delithiation. Heating in air, O2, or N 2 results in structural disorder (< 300 °C), formation of an intermediate sarcopside Mn3(PO4)2 phase (350 -- 450 °C), and complete decomposition to Mn2P2O 7 on extended heating at 400 °C. Carbon protects MnPO4 from reacting with environmental water, which is detrimental to its structural stability. We not only studied the crystalline olivine MnPO4, but also investigated the amorphous products obtained from carbon-free LiMnPO 4. We have revealed the Mn dissolution phenomenon during chemical delithiation of LiMnPO4, which causes the amorphization of olivine MnPO 4. Properties of crystalline-MnPO4 obtained from carbon-coated LiMnPO4 and of amorphous product resulting from the delithiation of pure LiMnPO4 were studied and compared. The P-rich amorphous phases in the latter are considered to be MnHP2O7 and MnH2P2O7 from XAS and XPS analysis. Safety of batteries not only depends on the stability of the active materials, but also the interactions between the active materials and electrolyte. Thus we study the stability between the cathode materials and the electrolyte. The thermal stability of electrochemically delithiated Li0.1N 0.8C0.15Al0.05O2 (NCA), FePO4 (FP), Mn0.8Fe0.2PO4 (MFP), hydrothermally synthesized VOPO4, LiVOPO4 and electrochemically lithiated Li2VOPO4 is investigated by differential scanning calorimetry (DSC) and thermogravimetric analysis, coupled with mass spectrometry (TGA-MS). The thermal stability is found in the order: NCA< VOPO4< MFP< FP=LiVOPO4=Li2VOPO4. Sealed capsule high pressure experiments show a phase transformation of VOPO4 → HVOPO4 → H2VOPO4 when VOPO4 reacts with electrolyte (1 M LiPF6 in EC: DMC=1:1) between 200 and 300 °C. Finally, we characterize the lithium storage and release mechanism of V2O5 aerogels by x-ray photoelectron spectroscopy (XPS). We study the influence of n--butyllithium (n--BuLi) treatments on the electrochemical performance of the aerogel. In addition to fully reversible V reduction and oxidation due to the intercalation reaction, we observe the formation of LiOH species that are only partially reversible. This is attributed to reaction with the interlayer water and is considered responsible for the gradual capacity fade. The n--BuLi treated aerogels display a higher capacity than those without and our XPS analysis reveals an additional reversible formation of Li2O.

Radiation damage in a-SiO 2 exposed to intense positron pulses

NASA Astrophysics Data System (ADS)

Cassidy, D. B.; Mills, A. P.

2007-08-01

In addition to its numerous technological applications amorphous silica (a-SiO 2) is also well suited to the creation and study of exotic atoms such as positronium (Ps) and muonium. In particular, a dense Ps gas may be created by implanting an intense positron pulse into a porous a-SiO 2 sample. However, such positron pulses can constitute a significant dose of radiation, which may damage the sample. We have observed a reduction in the amount of Ps formed in a thin film of porous a-SiO 2 following irradiation by intense positron pulses, indicating the creation of paramagnetic centers. The data show that the primary effect of the irradiation is the inhibition of Ps formation, with no significant change in the subsequent Ps lifetime, from which we deduce that damage centers are created primarily in the bulk material and not on the internal surfaces of the pores, where they would be accessible to the long-lived Ps. We find that the damage is reversible, and that the system may be returned to its original state by heating to 700 K. The implications of these results for experiments with dense Ps in porous materials are discussed.

Tin-Doped Inorganic Amorphous Films for Use as Transparent Monolithic Phosphors.

PubMed

Masai, Hirokazu; Miyata, Hiroki; Yamada, Yasuhiro; Okumura, Shun; Yanagida, Takayuki; Kanemitsu, Yoshihiko

2015-06-10

Although inorganic crystalline phosphors can exhibit high quantum efficiency, their use in phosphor films has been limited by a reliance on organic binders that have poor durability when exposed to high-power and/or high excitation energy light sources. To address this problem, Sn(2+)-doped transparent phosphate films measuring several micrometers in thickness have been successfully prepared through heat treatment and a subsequent single dip-coating process. The resulting monolithic inorganic amorphous film exhibited an internal quantum efficiency of over 60% and can potentially utilize transmitted light. Analysis of the film's emissivity revealed that its color can be tuned by changing the amount of Mn and Sn added to influence the energy transfer from Sn(2+) to Mn(2+). It is therefore concluded that amorphous films containing such emission centers can provide a novel and viable alternative to conventional amorphous films containing crystalline phosphors in light-emitting devices.

Tin-Doped Inorganic Amorphous Films for Use as Transparent Monolithic Phosphors

PubMed Central

Masai, Hirokazu; Miyata, Hiroki; Yamada, Yasuhiro; Okumura, Shun; Yanagida, Takayuki; Kanemitsu, Yoshihiko

2015-01-01

Although inorganic crystalline phosphors can exhibit high quantum efficiency, their use in phosphor films has been limited by a reliance on organic binders that have poor durability when exposed to high-power and/or high excitation energy light sources. To address this problem, Sn2+ -doped transparent phosphate films measuring several micrometers in thickness have been successfully prepared through heat treatment and a subsequent single dip-coating process. The resulting monolithic inorganic amorphous film exhibited an internal quantum efficiency of over 60% and can potentially utilize transmitted light. Analysis of the film’s emissivity revealed that its color can be tuned by changing the amount of Mn and Sn added to influence the energy transfer from Sn2+ to Mn2+. It is therefore concluded that amorphous films containing such emission centers can provide a novel and viable alternative to conventional amorphous films containing crystalline phosphors in light-emitting devices. PMID:26061744

Localization of vibrational modes leads to reduced thermal conductivity of amorphous heterostructures

NASA Astrophysics Data System (ADS)

Giri, Ashutosh; Donovan, Brian F.; Hopkins, Patrick E.

2018-05-01

We investigate the vibrational heat transfer mechanisms in amorphous Stillinger-Weber silicon and germanium-based alloys and heterostructures via equilibrium and nonequilibrium molecular dynamics simulations along with lattice dynamics calculations. We find that similar to crystalline alloys, amorphous alloys demonstrate large size effects in thermal conductivity, while layering the constituent materials into superlattice structures leads to length-independent thermal conductivities. The thermal conductivity of an amorphous SixGe1 -x alloy reduces by as much as ˜53 % compared to the thermal conductivity of amorphous silicon; compared to the larger reduction in crystalline phases due to alloying, we show that compositional disorder rather than structural disorder has a larger impact on the thermal conductivity reduction. Our thermal conductivity predictions for a-Si/a-Ge superlattices suggest that the alloy limit in amorphous SiGe-based structures can be surpassed with interface densities above ˜0.35 nm-1 . We attribute the larger reduction in thermal conductivity of layered Si/Ge heterostructures to greater localization of modes at and around the cutoff frequency of the softer layer as demonstrated via lattice dynamics calculations and diffusivities of individual eigenmodes calculated according to the Allen-Feldman theory [P. B. Allen and J. L. Feldman, Phys. Rev. B 48, 12581 (1993), 10.1103/PhysRevB.48.12581] for our amorphous SiGe-based alloys and superlattice structures.

High spin-polarization in ultrathin Co2MnSi/CoPd multilayers

NASA Astrophysics Data System (ADS)

Galanakis, I.

2015-03-01

Half-metallic Co2MnSi finds a broad spectrum of applications in spintronic devices either in the form of thin films or as spacer in multilayers. Using state-of-the-art ab-initio electronic structure calculations we exploit the electronic and magnetic properties of ultrathin Co2MnSi/CoPd multilayers. We show that these heterostructures combine high values of spin-polarization at the Co2MnSi spacer with the perpendicular magnetic anisotropy of binary compounds such as CoPd. Thus they could find application in spintronic/magnetoelectronic devices.

Solid-phase crystallization of amorphous Si films on glass and Si wafer

NASA Astrophysics Data System (ADS)

Lee, Dong Nyung

2011-11-01

When amorphous silicon films deposited on glass by physical or chemical vapor deposition are annealed, they undergo crystallization by nucleation and growth. The growth rate of Si crystallites is the highest in their <111> directions along or nearly along the film surface. The directed crystallization is likely to develop the <110>//ND or <111>//ND oriented Si crystallites. As the annealing temperature increases, the equiaxed crystallization increases, which in turn increases the random orientation. When amorphous Si is under a stress of the order of 0.1 GPa at about 540 °C, the tensile stress increases the growth rate of Si grains, whereas the compressive stress decreases the growth rate. However, the crystal growth rate increases with the increasing hydrostatic pressure, when the pressure is of the order of GPa at 530-540 °C. These phenomena have been discussed based on the directed crystallization model advanced before, which has been further elaborated.

First-principles investigation of band offsets and dielectric properties of Silicon-Silicon Nitride interfaces

NASA Astrophysics Data System (ADS)

Pham, Tuan Anh; Li, Tianshu; Gygi, Francois; Galli, Giulia

2011-03-01

Silicon Nitride (Si3N4) is a possible candidate material to replace or be alloyed with SiO2 to form high-K dielectric films on Si substrates, so as to help prevent leakage currents in modern CMOS transistors. Building on our previous work on dielectric properties of crystalline and amorphous Si3N4 slabs, we present an analysis of the band offsets and dielectric properties of crystalline-Si/amorphous Si3N4 interfaces based on first principles calculations. We discuss shortcomings of the conventional bulk-plus line up approach in band offset calculations for systems with an amorphous component, and we present the results of band offsets obtained from calculations of local density of states. Finally, we describe the role of bonding configurations in determining band edges and dielectric constants at the interface. We acknowledge financial support from Intel Corporation.

Mechanical stresses and amorphization of ion-implanted diamond

NASA Astrophysics Data System (ADS)

Khmelnitsky, R. A.; Dravin, V. A.; Tal, A. A.; Latushko, M. I.; Khomich, A. A.; Khomich, A. V.; Trushin, A. S.; Alekseev, A. A.; Terentiev, S. A.

2013-06-01

Scanning white light interferometry and Raman spectroscopy were used to investigate the mechanical stresses and structural changes in ion-implanted natural diamonds with different impurity content. The uniform distribution of radiation defects in implanted area was obtained by the regime of multiple-energy implantation of keV He+ ions. A modification of Bosia's et al. (Nucl. Instrum. Meth. B 268 (2010) 2991) method for determining the internal stresses and the density variation in an ion-implanted diamond layer was proposed that suggests measuring, in addition to the surface swelling of a diamond plate, the radius of curvature of the plate. It is shown that, under multiple-energy implantation of He+, mechanical stresses in the implanted layer may be as high as 12 GPa. It is shown that radiation damage reaches saturation for the implantation fluence characteristic of amorphization of diamond but is appreciably lower than the graphitization threshold.

The kinetic friction of ZnO nanowires on amorphous SiO2 and SiN substrates

NASA Astrophysics Data System (ADS)

Roy, Aditi; Xie, Hongtao; Wang, Shiliang; Huang, Han

2016-12-01

ZnO nanowires were bent on amorphous SiO2 and SiN substrates in an ambient atmosphere using optical nanomanipulation. The kinetic friction between the nanowires and substrate was determined from the bent shape of the nanowires. The kinetic friction force per unit area, i.e. frictional shear stress, for the ZnO/SiO2 and ZnO/SiN nanowire/substrate systems being measured were 1.05 ± 0.28 and 2.08 ± 0.33 MPa, respectively. The surface roughness and the Hamaker constant of SiO2 and SiN substrates had significant effect on the frictional stresses.

Antiferromagnetism in semiconducting SrMn2Sb2 and BaMn2Sb2 single crystals

NASA Astrophysics Data System (ADS)

Sangeetha, N. S.; Smetana, V.; Mudring, A.-V.; Johnston, D. C.

2018-01-01

Crystals of SrMn2Sb2 and BaMn2Sb2 were grown using Sn flux and characterized by powder and single-crystal x-ray diffraction, respectively, and by single-crystal electrical resistivity ρ , heat capacity Cp, and magnetic susceptibility χ measurements versus temperature T , and magnetization versus field M (H ) isotherm measurements. SrMn2Sb2 adopts the trigonal CaAl2Si2 -type structure, whereas BaMn2Sb2 crystallizes in the tetragonal ThCr2Si2 -type structure. The ρ (T ) data indicate semiconducting behaviors for both compounds with activation energies of ≳0.35 eV for SrMn2Sb2 and 0.16 eV for BaMn2Sb2 . The χ (T ) and Cp(T ) data reveal antiferromagnetic (AFM) ordering at TN = 110 K for SrMn2Sb2 and 450 K for BaMn2Sb2 . The anisotropic χ (T ≤TN) data also show that the ordered moments in SrMn2Sb2 are aligned in the hexagonal a b plane, whereas the ordered moments in BaMn2Sb2 are aligned collinearly along the tetragonal c axis. The a b -plane M (H ) data for SrMn2Sb2 exhibit a continuous metamagnetic transition at low fields 0

H+-induced irradiation damage resistance in Fe- and Ni-based metallic glass

NASA Astrophysics Data System (ADS)

Zhang, Hongran; Mei, Xianxiu; Zhang, Xiaonan; Li, Xiaona; Wang, Yingmin; Sun, Jianrong; Wang, Younian

2016-05-01

In this study, use of 40-keV H+ ion for irradiating metallic glass Fe80Si7.43B12.57 and Ni62Ta38 as well as metallic tungsten (W) at fluences of 1 × 1018 and 3 × 1018 ions/cm2, respectively, was investigated. At the fluence of 1 × 1018 ions/cm2, a crystalline layer appeared in metallic glass Fe80Si7.43B12.57, with α-Fe as the major crystalline phase, coupled with a little Fe2B, Fe3B, and metastable β-Mn-type phase. Fe80Si7.43B12.57 exhibited good soft magnetic properties after irradiation. At the fluence of 3 × 1018 ions/cm2, Ni62Ta38 was found to be amorphous-based, with a little μ-NiTa and Ni3Ta phases. No significant irradiation damage phenomenon appeared in metallic glasses Fe80Si7.43B12.57 and Ni62Ta38. Blistering, flaking, and other damage occurred on the surface of metallic W, and the root-mean-square (RMS) roughness increased with the increase of fluence. Metallic glass Ni62Ta38 exhibited better resistance to H+ irradiation than Fe80Si7.43B12.57, both of which were superior to the metallic W.

Mechanism of MnS Precipitation on Al2O3-SiO2 Inclusions in Non-oriented Silicon Steel

NASA Astrophysics Data System (ADS)

Li, Fangjie; Li, Huigai; Huang, Di; Zheng, Shaobo; You, Jinglin

2018-05-01

This study investigates the mechanism of MnS precipitation on Al2O3-SiO2 inclusions during the solidification of non-oriented silicon steel, especially the influence of the phase structures and sizes of the oxides on the MnS precipitation, by scanning electron microscopy and transmission electron microscopy coupled with energy dispersive spectrometry. The investigation results show that MnS tends to nucleate on submicron-sized Al2O3-SiO2 inclusions formed by interdendritic segregation and that it covers the oxides completely. In addition, MnS can precipitate on micron-sized oxides and its precipitation behavior is governed by the phase structure of the oxides. The MnS embryo formed in a MnO-containing oxide can act as a substrate for MnS precipitation, thus permitting further growth via diffusion of solute atoms from the matrix. MnS also precipitates in a MnO-free oxide by the heterogeneous nucleation mechanism. Furthermore, MnS is less prone to precipitation in the Al2O3-rich regions of the Al2O3-SiO2 inclusions; this can be explained by the high lattice disregistry between MnS and Al2O3.

Optoelectronic transport properties in amorphous/crystalline silicon solar cell heterojunctions measured by frequency-domain photocarrier radiometry: multi-parameter measurement reliability and precision studies.

PubMed

Zhang, Y; Melnikov, A; Mandelis, A; Halliop, B; Kherani, N P; Zhu, R

2015-03-01

A theoretical one-dimensional two-layer linear photocarrier radiometry (PCR) model including the presence of effective interface carrier traps was used to evaluate the transport parameters of p-type hydrogenated amorphous silicon (a-Si:H) and n-type crystalline silicon (c-Si) passivated by an intrinsic hydrogenated amorphous silicon (i-layer) nanolayer. Several crystalline Si heterojunction structures were examined to investigate the influence of the i-layer thickness and the doping concentration of the a-Si:H layer. The experimental data of a series of heterojunction structures with intrinsic thin layers were fitted to PCR theory to gain insight into the transport properties of these devices. The quantitative multi-parameter results were studied with regard to measurement reliability (uniqueness) and precision using two independent computational best-fit programs. The considerable influence on the transport properties of the entire structure of two key parameters that can limit the performance of amorphous thin film solar cells, namely, the doping concentration of the a-Si:H layer and the i-layer thickness was demonstrated. It was shown that PCR can be applied to the non-destructive characterization of a-Si:H/c-Si heterojunction solar cells yielding reliable measurements of the key parameters.

Optoelectronic transport properties in amorphous/crystalline silicon solar cell heterojunctions measured by frequency-domain photocarrier radiometry: Multi-parameter measurement reliability and precision studies

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

Zhang, Y.; Institute of Electronic Engineering and Optoelectronic Technology, Nanjing University of Science and Technology, Nanjing, Jiangsu 210094; Melnikov, A.

2015-03-15

A theoretical one-dimensional two-layer linear photocarrier radiometry (PCR) model including the presence of effective interface carrier traps was used to evaluate the transport parameters of p-type hydrogenated amorphous silicon (a-Si:H) and n-type crystalline silicon (c-Si) passivated by an intrinsic hydrogenated amorphous silicon (i-layer) nanolayer. Several crystalline Si heterojunction structures were examined to investigate the influence of the i-layer thickness and the doping concentration of the a-Si:H layer. The experimental data of a series of heterojunction structures with intrinsic thin layers were fitted to PCR theory to gain insight into the transport properties of these devices. The quantitative multi-parameter results weremore » studied with regard to measurement reliability (uniqueness) and precision using two independent computational best-fit programs. The considerable influence on the transport properties of the entire structure of two key parameters that can limit the performance of amorphous thin film solar cells, namely, the doping concentration of the a-Si:H layer and the i-layer thickness was demonstrated. It was shown that PCR can be applied to the non-destructive characterization of a-Si:H/c-Si heterojunction solar cells yielding reliable measurements of the key parameters.« less

Hydrothermal-reduction synthesis of manganese oxide nanomaterials for electrochemical supercapacitors.

PubMed

Zhang, Xiong; Chen, Yao; Yu, Peng; Ma, Yanwei

2010-11-01

In the present work, amorphous manganese oxide nanomaterials have been synthesized by a common hydrothermal method based on the redox reaction between MnO4(-) and Fe(2+) under an acidic condition. The synthesized MnO2 samples were characterized by X-ray diffraction (XRD), X-ray photoelectron spectroscopy (XPS), field emission scanning electron microscopy (FESEM), transmission electron microscopy (TEM), high-resolution transmission electron microscopy (HRTEM), and electrochemical studies. XRD results showed that amorphous manganese oxide phase was obtained. XPS quantitative analysis revealed that the atomic ratio of Mn to Fe was 3.5 in the MnO2 samples. TEM images showed the porous structure of the samples. Electrochemical properties of the MnO2 electrodes were studied using cyclic voltammetry and galvanostatic charge-discharge cycling in 1 M Na2SO4 aqueous electrolyte, which showed excellent pseudocapacitance properties. A specific capacitance of 192 Fg(-1) at a current density of 0.5 Ag(-1) was obtained at the potential window from -0.1 to 0.9 V (vs. SCE).

Effect of Copper on Corrosion of Forged AlSi1MgMn Automotive Suspension Components

NASA Astrophysics Data System (ADS)

Koktas, Serhan; Gokcil, Emre; Akdi, Seracettin; Birol, Yucel

2017-09-01

Recently, modifications in the alloy composition and the manufacturing process cycle were proposed to achieve a more uniform structure with no evidence of coarse grains across the section of the AlSi1MgMn alloys. Cu was added to the AlSi1MgMn alloy to improve its age hardening capacity without a separate solution heat treatment. However, Cu addition degrades the corrosion resistance of this alloy due to the formation of Al-Cu precipitates along the grain boundaries that are cathodic with respect to the aluminum matrix and thus encourage intergranular corrosion. The present work was undertaken to identify the impact of Cu addition on the corrosion properties of AlSi1MgMn alloys with different Cu contents. A series of AlSi1MgMn alloys with 0.06-0.89 wt.% Cu were tested in order to identify an optimum level of Cu addition.

Encapsulation of superparamagnetic Fe 3 O 4 @SiO 2 core/shell nanoparticles in MnO 2 microflowers with high surface areas

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

Sun, Yu-Gang; Truong, Tu T.; Liu, Yu-Zi

2015-02-01

Microflowers made of interconnected MnO2 nanosheets have been successfully synthesized in a microwave reactor through a hydrothermal reduction of KMnO4 with aqueous HCl at elevated temperatures in the presence of superparamagnetic Fe3O4@SiO2 core-shell nanoparticles. Due to the chemical compatibility between SiO2 and MnO2, the heterogeneous reaction leads to the spontaneous encapsulation of the Fe3O4@SiO2 core-shell nanoparticles in the MnO2 microflowers. The resulting hybrid particles exhibit multiple properties including high surface area associated with the MnO2 nanosheets and superparamagnetism originated from the Fe3O4@SiO2 core-shell nanoparticles, which are beneficial for applications requiring both high surface area and magnetic separation. (C) 2014 Yu-Gangmore » Sun.« less

Realization of magnetostructural coupling by modifying structural transitions in MnNiSi-CoNiGe system with a wide Curie-temperature window.

PubMed

Liu, Jun; Gong, Yuanyuan; Xu, Guizhou; Peng, Guo; Shah, Ishfaq Ahmad; Ul Hassan, Najam; Xu, Feng

2016-03-16

The magnetostructural coupling between structural and magnetic transitions leads to magneto-multifunctionalities of phase-transition alloys. Due to the increasing demands of multifunctional applications, to search for the new materials with tunable magnetostructural transformations in a large operating temperature range is important. In this work, we demonstrate that by chemically alloying MnNiSi with CoNiGe, the structural transformation temperature of MnNiSi (1200 K) is remarkably decreased by almost 1000 K. A tunable magnetostructural transformation between the paramagnetic hexagonal and ferromagnetic orthorhombic phase over a wide temperature window from 425 to 125 K is realized in (MnNiSi)1-x(CoNiGe)x system. The magnetic-field-induced magnetostructural transformation is accompanied by the high-performance magnetocaloric effect, proving that MnNiSi-CoNiGe system is a promising candidate for magnetic cooling refrigerant.

Antiferromagnetism in semiconducting SrMn 2 Sb 2 and BaMn 2 Sb 2 single crystals

DOE PAGES

Sangeetha, N. S.; Smetana, V.; Mudring, A. -V.; ...

2018-01-03

Here, crystals of SrMn 2Sb 2 and BaMn 2Sb 2 were grown using Sn flux and characterized by powder and single-crystal x-ray diffraction, respectively, and by single-crystal electrical resistivity ρ, heat capacity C p, and magnetic susceptibility χ measurements versus temperature T, and magnetization versus field M(H) isotherm measurements. SrMn 2Sb 2 adopts the trigonal CaAl 2Si 2-type structure, whereas BaMn 2Sb 2 crystallizes in the tetragonal ThCr 2Si 2-type structure. The ρ(T) data indicate semiconducting behaviors for both compounds with activation energies of ≳0.35 eV for SrMn 2Sb 2 and 0.16 eV for BaMn 2Sb 2. The χ(T) andmore » C p(T) data reveal antiferromagnetic (AFM) ordering at T N = 110 K for SrMn 2Sb 2 and 450 K for BaMn 2Sb 2. The anisotropic χ(T≤T N) data also show that the ordered moments in SrMn 2Sb 2 are aligned in the hexagonal ab plane, whereas the ordered moments in BaMn 2Sb 2 are aligned collinearly along the tetragonal c axis. The ab-plane M(H) data for SrMn 2Sb 2 exhibit a continuous metamagnetic transition at low fields 02Sb 2 exhibits no metamagnetic transitions up to 5.5 T. The χ(T) and C p(T) data for both SrMn 2Sb 2 and BaMn 2Sb 2 indicate strong dynamic short-range AFM correlations above their respective T N up to at least 900 K within a local-moment picture, corresponding to quasi-two-dimensional magnetic behavior. The present results and a survey of the literature for Mn pnictides with the CaAl 2Si 2 and ThCr 2Si 2 crystal structures show that the T N values for the CaAl 2Si 2-type compounds are much smaller than those for the ThCr 2Si 2-type materials.« less

Enhanced Azo-Dyes Degradation Performance of Fe-Si-B-P Nanoporous Architecture

PubMed Central

Weng, Nan; Wang, Feng; Qin, Fengxiang; Tang, Wanying; Dan, Zhenhua

2017-01-01

Nanoporous structures were fabricated from Fe76Si9B10P5 amorphous alloy annealed at 773 K by dealloying in 0.05 M H2SO4 solution, as a result of preferential dissolution of α-Fe grains in form of the micro-coupling cells between α-Fe and cathodic residual phases. Nanoporous Fe-Si-B-P powders exhibit much better degradation performance to methyl orange and direct blue azo dyes compared with gas-atomized Fe76Si9B10P5 amorphous powders and commercial Fe powders. The degradation reaction rate constants of nanoporous powders are almost one order higher than those of the amorphous counterpart powders and Fe powders, accompanying with lower activation energies of 19.5 and 26.8 kJ mol−1 for the degradation reactions of methyl orange and direct blue azo dyes, respectively. The large surface area of the nanoporous structure, and the existence of metalloids as well as residual amorphous phase with high catalytic activity are responsible for the enhanced azo-dyes degradation performance of the nanoporous Fe-Si-B-P powders. PMID:28846622

Suppression of nanoindentation-induced phase transformation in crystalline silicon implanted with hydrogen

NASA Astrophysics Data System (ADS)

Jelenković, Emil V.; To, Suet

2017-09-01

In this paper the effect of hydrogen implantation in silicon on nanoindentation-induced phase transformation is investigated. Hydrogen ions were implanted in silicon through 300 nm thick oxide with double energy implantation (75 and 40 keV). For both energies implantation dose was 4 × 1016 cm-2. Some samples were thermally annealed at 400 °C. The micro-Raman spectroscopy was applied on nanoindentation imprints and the obtained results were related to the pop out/elbow appearances in nanoindentatioin unloading-displacement curves. The Raman spectroscopy revealed a suppression of Si-XII and Si-III phases and formation of a-Si in the indents of hydrogen implanted Si. The high-resolution x-ray diffraction measurements were taken to support the analysis of silicon phase formation during nanoindentation. Implantation induced strain, high hydrogen concentration, and platelets generation were found to be the factors that control suppression of c-Si phases Si-XII and Si-III, as well as a-Si phase enhancement during nanoindentation. [Figure not available: see fulltext.

Microstructure, hardness and modulus of carbon-ion-irradiated new SiC fiber (601-4)

NASA Astrophysics Data System (ADS)

Huang, Qing; Lei, Guanhong; Liu, Renduo; Li, Jianjian; Yan, Long; Li, Cheng; Liu, Weihua; Wang, Mouhua

2018-05-01

Two types of SiC fibers, one is low-oxygen and carbon-rich fiber denoted by 601-4 and the other is low-oxygen and near-stoichiometric Tyranno SA, were irradiated with 450 keV C+ ions at room temperature. The Raman spectra indicate that irradiation induced distortion and amorphization of SiC crystallites in fibers. TEM characterization of Tyranno SA suggests that SiC crystallites undergo a continued fragmentation into smaller crystalline islands and a continued increase of surrounding amorphous structure. The SiC nano-crystallites (<15 nm) in 601-4 fiber are more likely to be amorphized than larger crystallites (∼200 nm) in Tyranno SA. The hardness and modulus of 601-4 continuously decreases with increasing fluence, while that of Tyranno SA first increases and then decreases.

Thermal conductivity measurement of amorphous dielectric multilayers for phase-change memory power reduction

NASA Astrophysics Data System (ADS)

Fong, S. W.; Sood, A.; Chen, L.; Kumari, N.; Asheghi, M.; Goodson, K. E.; Gibson, G. A.; Wong, H.-S. P.

2016-07-01

In this work, we investigate the temperature-dependent thermal conductivities of few nanometer thick alternating stacks of amorphous dielectrics, specifically SiO2/Al2O3 and SiO2/Si3N4. Experiments using steady-state Joule-heating and electrical thermometry, while using a micro-miniature refrigerator over a wide temperature range (100-500 K), show that amorphous thin-film multilayer SiO2/Si3N4 and SiO2/Al2O3 exhibit through-plane room temperature effective thermal conductivities of about 1.14 and 0.48 W/(m × K), respectively. In the case of SiO2/Al2O3, the reduced conductivity is attributed to lowered film density (7.03 → 5.44 × 1028 m-3 for SiO2 and 10.2 → 8.27 × 1028 m-3 for Al2O3) caused by atomic layer deposition of thin-films as well as a small, finite, and repeating thermal boundary resistance (TBR) of 1.5 m2 K/GW between dielectric layers. Molecular dynamics simulations reveal that vibrational mismatch between amorphous oxide layers is small, and that the TBR between layers is largely due to imperfect interfaces. Finally, the impact of using this multilayer dielectric in a dash-type phase-change memory device is studied using finite-element simulations.

Amorphous silicon-carbon nanospheres synthesized by chemical vapor deposition using cheap methyltrichlorosilane as improved anode materials for Li-ion batteries.

PubMed

Zhang, Zailei; Zhang, Meiju; Wang, Yanhong; Tan, Qiangqiang; Lv, Xiao; Zhong, Ziyi; Li, Hong; Su, Fabing

2013-06-21

We report the preparation and characterization of amorphous silicon-carbon (Si-C) nanospheres as anode materials in Li-ion batteries. These nanospheres were synthesized by a chemical vapor deposition at 900 °C using methyltrichlorosilane (CH3SiCl3) as both the Si and C precursor, which is a cheap byproduct in the organosilane industry. The samples were characterized by X-ray diffraction, transmission electron microscopy, scanning electron microscopy, nitrogen adsorption, thermal gravimetric analysis, Raman spectroscopy, and X-ray photoelectron spectroscopy. It was found that the synthesized Si-C nanospheres composed of amorphous C (about 60 wt%) and Si (about 40 wt%) had a diameter of 400-600 nm and a surface area of 43.8 m(2) g(-1). Their charge capacities were 483.6, 331.7, 298.6, 180.6, and 344.2 mA h g(-1) at 50, 200, 500, 1000, and 50 mA g(-1) after 50 cycles, higher than that of the commercial graphite anode. The Si-C amorphous structure could absorb a large volume change of Si during Li insertion and extraction reactions and hinder the cracking or crumbling of the electrode, thus resulting in the improved reversible capacity and cycling stability. The work opens a new way to fabricate low cost Si-C anode materials for Li-ion batteries.

Surface and corrosion characteristics of carbon plasma implanted and deposited nickel-titanium alloy

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

Poon, R.W.Y.; Liu, X.Y.; Chung, C.Y.

2005-05-01

Nickel-titanium shape memory alloys (NiTi) are potentially useful in orthopedic implants on account of their super-elastic and shape memory properties. However, the materials are prone to surface corrosion and the most common problem is out-diffusion of harmful Ni ions from the substrate into body tissues and fluids. In order to improve the corrosion resistance and related surface properties, we used the technique of plasma immersion ion implantation and deposition to deposit an amorphous hydrogenated carbon coating onto NiTi and implant carbon into NiTi. Both the deposited amorphous carbon film and carbon plasma implanted samples exhibit much improved corrosion resistances andmore » surface mechanical properties and possible mechanisms are suggested.« less

Theoretical investigation on radiation tolerance of {{\\boldsymbol{M}}}_{{\\boldsymbol{n}}+1}{{\\boldsymbol{AX}}}_{{\\boldsymbol{n}}} phases

NASA Astrophysics Data System (ADS)

Yin, Ke-Di; Zhang, Xi-Tong; Huang, Qing; Xue, Jian-Ming

2017-06-01

Ternary {M}n+1{{AX}}n phases with layered hexagonal structures, as candidate materials used for next-generation nuclear reactors, have shown great potential in tolerating radiation damage due to their unique combination of ceramic and metallic properties. However, {M}n+1{{AX}}n materials behave differently in amorphization when exposed to energetic neutron and ion irradiations in experiment. We first analyze the irradiation tolerances of different {M}n+1{{AX}}n (MAX) phases in terms of electronic structure, including the density of states (DOS) and charge density map. Then a new method based on the Bader analysis with the first-principle calculation is used to estimate the stabilities of MAX phases under irradiation. Our calculations show that the substitution of Cr/V/Ta/Nb by Ti and Si/Ge/Ga by Al can increase the ionicities of the bonds, thus strengthening the radiation tolerance. It is also shown that there is no obvious difference in radiation tolerance between {M}n+1A{{{C}}}n and {M}n+1A{{{N}}}n due to the similar charge transfer values of C and N atoms. In addition, the improved radiation tolerance from Ti3AlC2 to Ti2AlC (Ti3AlC2 and Ti2AlC have the same chemical elements), can be understood in terms of the increased Al/TiC layer ratio. Criteria based on the quantified charge transfer can be further used to explore other {M}n+1{{AX}}n phases with respect to their radiation tolerance, playing a critical role in choosing appropriate MAX phases before they are subjected to irradiation in experimental test for future nuclear reactors. Project supported by the National Natural Science Foundation of China (Grant Nos. 91226202 and 91426304).

Electric measurements of PV heterojunction structures a-SiC/c-Si

NASA Astrophysics Data System (ADS)

Perný, Milan; Šály, Vladimír; Janíček, František; Mikolášek, Miroslav; Váry, Michal; Huran, Jozef

2018-01-01

Due to the particular advantages of amorphous silicon or its alloys with carbon in comparison to conventional crystalline materials makes such a material still interesting for study. The amorphous silicon carbide may be used in a number of micro-mechanical and micro-electronics applications and also for photovoltaic energy conversion devices. Boron doped thin layers of amorphous silicon carbide, presented in this paper, were prepared due to the optimization process for preparation of heterojunction solar cell structure. DC and AC measurement and subsequent evaluation were carried out in order to comprehensively assess the electrical transport processes in the prepared a-SiC/c-Si structures. We have investigated the influence of methane content in deposition gas mixture and different electrode configuration.

Structures, phase stabilities, and electrical potentials of Li-Si battery anode materials

NASA Astrophysics Data System (ADS)

Tipton, William W.; Bealing, Clive R.; Mathew, Kiran; Hennig, Richard G.

2013-05-01

The Li-Si materials system holds promise for use as an anode in Li-ion battery applications. For this system, we determine the charge capacity, voltage profiles, and energy storage density solely by ab initio methods without any experimental input. We determine the energetics of the stable and metastable Li-Si phases likely to form during the charging and discharging of a battery. Ab initio molecular dynamics simulations are used to model the structure of amorphous Li-Si as a function of composition, and a genetic algorithm coupled to density-functional theory searches the Li-Si binary phase diagram for small-cell, metastable crystal structures. Calculations of the phonon densities of states using density-functional perturbation theory for selected structures determine the importance of vibrational, including zero-point, contributions to the free energies. The energetics and local structural motifs of these metastable Li-Si phases closely resemble those of the amorphous phases, making these small unit cell crystal phases good approximants of the amorphous phase for use in further studies. The charge capacity is estimated, and the electrical potential profiles and the energy density of Li-Si anodes are predicted. We find, in good agreement with experimental measurements, that the formation of amorphous Li-Si only slightly increases the anode potential. Additionally, the genetic algorithm identifies a previously unreported member of the Li-Si binary phase diagram with composition Li5Si2 which is stable at 0 K with respect to previously known phases. We discuss its relationship to the partially occupied Li7Si3 phase.

Si-Mn/reduced graphene oxide nanocomposite anodes with enhanced capacity and stability for lithium-ion batteries.

PubMed

Park, A Reum; Kim, Jung Sub; Kim, Kwang Su; Zhang, Kan; Park, Juhyun; Park, Jong Hyeok; Lee, Joong Kee; Yoo, Pil J

2014-02-12

Although Si is a promising high-capacity anode material for Li-ion batteries (LIB), it suffers from capacity fading due to excessively large volumetric changes upon Li insertion. Nanocarbon materials have been used to enhance the cyclic stability of LIB anodes, but they have an inherently low specific capacity. To address these issues, we present a novel ternary nanocomposite of Si, Mn, and reduced graphene oxide (rGO) for LIB anodes, in which the Si-Mn alloy offers high capacity characteristics and embedded rGO nanosheets confer structural stability. Si-Mn/rGO ternary nanocomposites were synthesized by mechanical complexation and subsequent thermal reduction of mixtures of Si nanoparticles, MnO2 nanorods, and rGO nanosheets. Resulting ternary nanocomposite anodes displayed a specific capacity of 600 mAh/g with ∼90% capacity retention after 50 cycles at a current density of 100 mA/g. The enhanced performance is attributed to facilitated Li-ion reactions with the MnSi alloy phase and the formation of a structurally reinforced electroconductive matrix of rGO nanosheets. The ternary nanocomposite design paradigm presented in this study can be exploited for the development of high-capacity and long-life anode materials for versatile LIB applications.

Estimation of the Temperature-Dependent Nitrogen Solubility in Stainless Fe-Cr-Mn-Ni-Si-C Steel Melts During Processing

NASA Astrophysics Data System (ADS)

Wendler, Marco; Hauser, Michael; Sandig, Eckhard Frank; Volkova, Olena

2018-04-01

The influence of chemical composition, temperature, and pressure on the nitrogen solubility of various high alloy stainless steel grades, namely Fe-14Cr-(0.17-7.77)Mn-6Ni-0.5Si-0.03C [wt pct], Fe-15Cr-3Mn-4Ni-0.5Si-0.1C [wt pct], and Fe-19Cr-3Mn-4Ni-0.5Si-0.15C [wt pct], was studied in the melt. The temperature-dependent N-solubility was determined using an empirical approach proposed by Wada and Pehlke. The thus calculated N-concentrations overestimate the actual N-solubility of all the studied Fe-Cr-Mn-Ni-Si-C steel melts at a given temperature and pressure. Consequently, the calculation model has to be modified by Si and C because both elements are not recognized in the original equation. The addition of the 1st and 2nd order interaction parameters for Si and C to the model by Wada and Pehlke allows a precise estimation of the temperature-dependent nitrogen solubility in the liquid steel bath, and fits very well with the measured nitrogen concentrations during processing of the steels. Moreover, the N-solubility enhancing effect of Cr- and Mn-additions has been demonstrated.

Amorphous metallizations for high-temperature semiconductor device applications

NASA Technical Reports Server (NTRS)

Wiley, J. D.; Perepezko, J. H.; Nordman, J. E.; Kang-Jin, G.

1981-01-01

The initial results of work on a class of semiconductor metallizations which appear to hold promise as primary metallizations and diffusion barriers for high temperature device applications are presented. These metallizations consist of sputter-deposited films of high T sub g amorphous-metal alloys which (primarily because of the absence of grain boundaries) exhibit exceptionally good corrosion-resistance and low diffusion coefficients. Amorphous films of the alloys Ni-Nb, Ni-Mo, W-Si, and Mo-Si were deposited on Si, GaAs, GaP, and various insulating substrates. The films adhere extremely well to the substrates and remain amorphous during thermal cycling to at least 500 C. Rutherford backscattering and Auger electron spectroscopy measurements indicate atomic diffussivities in the 10 to the -19th power sq cm/S range at 450 C.

Nanoscale solely amorphous layer in silicon wafers induced by a newly developed diamond wheel

PubMed Central

Zhang, Zhenyu; Guo, Liangchao; Cui, Junfeng; Wang, Bo; Kang, Renke; Guo, Dongming

2016-01-01

Nanoscale solely amorphous layer is achieved in silicon (Si) wafers, using a developed diamond wheel with ceria, which is confirmed by high resolution transmission electron microscopy (HRTEM). This is different from previous reports of ultraprecision grinding, nanoindentation and nanoscratch, in which an amorphous layer at the top, followed by a crystalline damaged layer beneath. The thicknesses of amorphous layer are 43 and 48 nm at infeed rates of 8 and 15 μm/min, respectively, which is verified using HRTEM. Diamond-cubic Si-I phase is verified in Si wafers using selected area electron diffraction patterns, indicating the absence of high pressure phases. Ceria plays an important role in the diamond wheel for achieving ultrasmooth and bright surfaces using ultraprecision grinding. PMID:27734934

Magnetic and structural properties of ferromagnetic Fe 5PB 2 and Fe 5SiB 2 and effects of Co and Mn substitutions

DOE PAGES

McGuire, Michael A.; Parker, David S.

2015-10-22

Crystallographic and magnetic properties of Fe 5PB 2, Fe 4CoPB 2, Fe 4MnPB 2, Fe 5SiB 2, Fe 4CoSiB 2, and Fe 4MnSiB 2 are reported. All adopt the tetragonal Cr 5B 3 structure-type and are ferromagnetic at room temperature with easy axis of magnetization along the c-axis. The spin reorientation in Fe 5SiB 2 is observed as an anomaly in the magnetization near 170 K, and is suppressed by substitution of Co or Mn for Fe. The silicides are found to generally have larger magnetic moments than the phosphides, but the data suggests smaller magnetic anisotropy in the silicides.more » Cobalt substitution reduces the Curie temperatures by more than 100 K and ordered magnetic moments by 16-20%, while manganese substitution has a much smaller effect. This suggests Mn moments align ferromagnetically with the Fe and that Co does not have an ordered moment in these structures. Anisotropic thermal expansion is observed in Fe 5PB 2 and Fe 5SiB 2, with negative thermal expansion seen along the c-axis of Fe 5SiB 2. First principles calculations of the magnetic properties of Fe 5SiB 2 and Fe 4MnSiB 2 are reported. The results, including the magnetic moment and anisotropy, and are in good agreement with experiment.« less

Electrochemical performance of carbon-coated lithium manganese silicate for asymmetric hybrid supercapacitors

NASA Astrophysics Data System (ADS)

Karthikeyan, K.; Aravindan, V.; Lee, S. B.; Jang, I. C.; Lim, H. H.; Park, G. J.; Yoshio, M.; Lee, Y. S.

Nanoscale carbon-coated Li 2MnSiO 4 powder is prepared using a conventional solid-state method and can be used as the negative electrode in a Li 2MnSiO 4/activated carbon (AC) hybrid supercapacitor. Carbon-coated Li 2MnSiO 4 material presents a well-developed orthorhombic crystal structure with a P mn2 1 space group, although there is a small impurity of MnO. The maximum specific capacitance of the Li 2MnSiO 4/AC hybrid supercapacitor is 43.2 F g -1 at 1 mA cm -2 current density. The cell delivers a specific energy as high as 54 Wh kg -1 at a specific power of 150 W kg -1 and also exhibits an excellent cycle performance with more than 99% columbic efficiency and the maintenance of 85% of its initial capacitance after 1000 cycles.

Optimization of single keV ion implantation for the construction of single P-donor devices

NASA Astrophysics Data System (ADS)

Yang, Changyi; Jamieson, David N.; Hopf, Toby; Andresen, Soren E.; Hearne, Sean M.; Hudson, Fay E.; Pakes, Christopher I.; Mitic, Mladen; Gauja, Eric; Tamanyan, Grigori; Dzurak, Andrew S.; Prawer, Steven; Clark, Robert G.

2005-02-01

We report recent progress in single keV ion implantation and online detection for the controlled implantation of single donors in silicon. When integrated with silicon nanofabrication technology this forms the "top down" strategy for the construction of prototype solid state quantum computer devices based on phosphorus donors in silicon. We have developed a method of single ion implantation and online registration that employs detector electrodes adjacent to the area into which the donors are to be implanted. The implantation sites are positioned with nanometer accuracy using an electron beam lithography patterned PMMA mask. Control of the implantation depth of 20 nm is achieved by tuning the phosphorus ion energy to 14 keV. The counting of single ion implantation in each site is achieved by the detection of e-/h+ pairs produced by the implanted phosphorus ion in the substrate. The system is calibrated by use of Mn K-line x-rays (5.9 and 6.4 keV) and we find the ionization energy of the 14 keV phosphorus ions in silicon to be about 3.5-4.0 keV for implants through a 5 nm SiO2 surface layer. This paper describes the development of an improved PIN detector structure that provides more reliable performance of the earlier MOS structure. With the new structure, the energy noise threshold has been minimized to 1 keV or less. Unambiguous detection/counting of single keV ion implantation events were achieved with a confidence level greater than 98% with a reliable and reproducible fabrication process.

Novel Amorphous Fe-Zr-Si(Cu) Boron-free Alloys

NASA Astrophysics Data System (ADS)

Kopcewicz, M.; Grabias, A.; Latuch, J.; Kowalczyk, M.

2010-07-01

Novel amorphous Fe80(ZrxSi20-x-y)Cuy boron-free alloys, in which boron was completely replaced by silicon as a glass forming element, have been prepared in the form of ribbons by a melt quenching technique. The X-ray diffraction and Mössbauer spectroscopy measurements revealed that the as-quenched ribbons with the composition of x = 6-10 at. % and y = 0, 1 at. % are predominantly amorphous. DSC measurements allowed the estimation of the crystallization temperatures of the amorphous alloys. The soft magnetic properties have been studied by the specialized rf-Mössbauer technique in which the spectra were recorded during an exposure of the samples to the rf field of 0 to 20 Oe at 61.8 MHz. Since the rf-collapse effect observed is very sensitive to the local anisotropy fields it was possible to evaluate the soft magnetic properties of amorphous alloys studied. The rf-Mössbauer studies were accompanied by the conventional measurements of the quasi-static hysteresis loops from which the magnetization and coercive fields were estimated. It was found that amorphous Fe-Zr-Si(Cu) alloys are magnetically very soft, comparable with those of the conventional amorphous B-containing Fe-based alloys.

Optical properties of amorphous Ba0.7Sr0.3TiO3 thin films obtained by metal organic decomposition technique

NASA Astrophysics Data System (ADS)

Qiu, Fei; Xu, Zhimou

2009-08-01

In this study, the amorphous Ba0.7Sr0.3TiO3 (BST0.7) thin films were grown onto fused quartz and silicon substrates at low temperature by using a metal organic decomposition (MOD)-spin-coating procedure. The optical transmittance spectrum of amorphous BST0.7 thin films on fused quartz substrates has been recorded in the wavelength range 190~900 nm. The films were highly transparent for wavelengths longer than 330 nm; the transmission drops rapidly at 330 nm, and the cutoff wavelength occurs at about 260 nm. In addition, we also report the amorphous BST0.7 thin film groove-buried type waveguides with 90° bent structure fabricated on Si substrates with 1.65 μm thick SiO2 thermal oxide layer. The design, fabrication and optical losses of amorphous BST0.7 optical waveguides were presented. The amorphous BST0.7 thin films were grown onto the SiO2/Si substrates by using a metal organic decomposition (MOD)-spin-coating procedure. The optical propagation losses were about 12.8 and 9.4 dB/cm respectively for the 5 and 10 μm wide waveguides at the wavelength of 632.8 nm. The 90° bent structures with a small curvature of micrometers were designed on the basis of a double corner mirror structure. The bend losses were about 1.2 and 0.9 dB respectively for 5 and 10 μm wide waveguides at the wavelength of 632.8 nm. It is expected for amorphous BST0.7 thin films to be used not only in the passive optical interconnection in monolithic OEICs but also in active waveguide devices on the Si chip.

Fracture behavior of neutron-irradiated high-manganese austenitic steels

NASA Astrophysics Data System (ADS)

Yoshida, H.; Miyata, K.; Narui, M.; Kayano, H.

1991-03-01

The instrumented Charpy impact test was applied to study the fracture behavior of high-manganese austenitic steels before and after neutron irradiations. Quarter-size specimens of a commercial high-manganese steel (18% Mn-5% Ni-16% Cr), three reference steels (21% Mn-1% Ni-9% Cr, 20% Mn-1% Ni-11% Cr, 15% Mn-1% Ni-13% Cr) and two model steels (17% Mn-4.5% Si-6.5% Cr, 22% Mn-4.5% Si-6.5% Cr-0.2% N) were used for the impact tests at temperatures between 77 and 523 K. The load-deflection curves showed typical features corresponding to characteristics of the fracture properties. The temperature dependences of fracture energy and failure deflection obtained from the curves clearly demonstrate only small effects up to 2 × 10 23 n/m 2 ( E > 0.1 MeV) and brittleness at room temperature in 17% Mn-Si-Cr steel at 1.6 × 10 25 n/m 2 ( E > 0.1 MeV), while ductility still remains in 22%Mn-Si-Cr steel.

Achieving High Luminescent Performance K2SiF6:Mn4+ Phosphor by Co-precipitation Process with Controlling the Reaction Temperature

NASA Astrophysics Data System (ADS)

Tran, Tat-Dat; Nguyen, Duy-Hung; Pham, Thanh-Huy; Nguyen, Duy-Cuong; Duong, Thanh-Tung

2018-05-01

K2SiF6:Mn4+ (KSF:Mn) phosphor was synthesized by the one-step co-precipitation process, at different temperatures. It was found that the reaction temperature played a key role in photoluminescence performance of the product. When the reaction temperature decreased from 0°C to - 20°C, the doping concentration, Mn/Si ratio, increased from 2% to 10%. However, further decrement of temperature (to - 30°C) reduced the Mn/Si ratio to 7%. The photo-luminescence (PL) intensity was maximized at the highest Mn/Si (10%), which corresponds to a reaction temperature of - 20°C. The KSF:Mn phosphor showed excellent luminescent properties at a wide range of temperatures (from room temperature to 470 K), especially after being dispersed in a polymer matrix. When combined with a commercial white light emitting diode (WLED), KSF:Mn significantly improved luminescent properties, such as color rendering index (CRI), correlated color temperature (CCT) and luminous efficiency. In particular, CRI increased from 67.3 to 87.4, while the CCT decreased from 7800 K to 3204 K. The luminous efficiency increased from 82.0 lm/W to 95.3 lm/W. The results indicated that the high quality KSF:Mn red phosphor could be achieved by a simple one-step co-precipitation method with a fine control of reaction temperature.

Integration of an Axcelis Optima HD Single Wafer High Current Implanter for p- and n-S/D Implants in an Existing Batch Implanter Production Line

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

Schmeide, Matthias; Kontratenko, Serguei; Krimbacher, Bernhard

2008-11-03

This paper is focused on the integration and qualification of an Axcelis Optima HD single wafer high current spot beam implanter in an existing 200 mm production line with different types of Axcelis batch implanters for high current applications. Both the design of the beamline and the beam shape are comparable between single wafer and batch high current spot beam implanters. In contrast to the single wafer high current ribbon beam implanter, energy contamination is not a concern for the considered spot beam tool because the drift mode can be used down to energies in the 2 keV region. Themore » most important difference between single wafer and batch high current implanters is the significantly higher dose rate and, therefore, the higher damage rate for the single wafer tool due to the different scanning architecture. The results of the integration of high dose implantations, mainly for p- and n-S/D formation, for DRAM 110 nm without pre-amorphization implantation (PAI), CMOS Logic from around 250 nm down to 90 nm without and with PAI, are presented and discussed. Dopant concentration profile analysis using SIMS was performed for different technologies and implantation conditions. The impurity activation was measured using sheet resistance and in some cases spreading resistance technique was applied. The amorphous layer thickness was measured using TEM. Finally, device data are presented in combination with dose, energy and beam current variations. The results have shown that the integration of implantation processes into crystalline structure without PAI is more complex and time consuming than implantations into amorphous layer where the damage difference due to the different dose rates is negligible.« less

Synthesis of PANi-SiO2 Nanocomposite with In-Situ Polymerization Method: Nanoparticle Silica (NPS) Amorphous and Crystalline Phase

NASA Astrophysics Data System (ADS)

Munasir; Luvita, N. R. D.; Kusumawati, D. H.; Putri, N. P.; Triwikantoro; Supardi, Z. A. I.

2018-03-01

Silica which is synthesized from natural materials such as Bancar Tuban’s sand composited with Polyaniline (PANi), where the silica used are silica has an amorphous phase and cristobalite phase. In this research, the composite method used is in- situ polymerization, which is silica entered during the fabrication of PANi, then automatically silica will be substitute into the chain bonding of PANi. The aim of this research is to find out the results of a composite process using in-situ methods as well as differences in the morphology of PANi/a- SiO2 and PANi/c-SiO2. For the characterization of samples tested in the form of FTIR to determine the functional groups of the composite and SEM to determine the morphology of the sample. From the test results of FTIR are known composite possibility has occurred because there are several functional groups belonging to silica also functional groups belonging polyaniline, functional group that’s happened in wave numbers were almost identical between PANi/a-SiO2 and PANi/c-SiO2, but there are little differences were seen in the form of a graph generated from the peak and intensity that occurred charts for PANi/c-SiO2 has peak more pointed or sharp compared to PANi/a-SiO2 because that bond of crystal is strong, stiff and has a larger particle size than the amorphous composite. Then from the data of SEM seen clearly their morphological differences between PANi/a-SiO2 and PANi/c-SiO2 where polyaniline is composited with amorphous silica will have a fault that is not uniform or irregular different from PANi/c -SiO2 has a regular fault and this is corresponding with the nature of the typical structure of amorphous and crystalline.

The New Mode of Energy Transferring between Mn2+ and Eu2+ in Nitride Based Phosphor SrAlSi4N7 with Tunable Light and Excellent Thermal Stability.

PubMed

Ding, Jianyan; Seto, Takatoshi; Wang, Yichao; Cao, Yaxin; Li, Hua; Wang, YuHua

2018-06-19

In this work, energy transfers reciprocally between Mn2+ and Eu2+ ions in nitride SrAlSi4N7 have been found and investigated in detailed. In contrast to Mn2+ and Eu2+ activated oxide based phosphors, the red light centering at 608 nm is ascribed to 4f-5d transitions of Eu2+ ions and Mn2+ activated SrAlSi4N7 emits a cyan light peaked at 500 nm. Additionally, the special broad excitation band of SrAlSi4N7: Mn2+ centering at 362 nm has been covered by that of Eu2+ ions ranging from 300 to 550 nm. The overlap of energy level of Mn2+ and Eu2+ ions creates the condition for the energy transferring reciprocally between Eu2+ and Mn2+ ions. A series of SrAlSi4N7: 0.002Mn2+, xEu2+ (0 ≤x≤ 005) with tunable emission light have been synthesized and the decay curves of samples prove the happening of the energy transfer between Mn2+ and Eu2+ ions reciprocally. This mode of energy transfer not only prevents the loss of energy, but also improves the thermal stability and the intensity of SrAlSi4N7: Mn2+, Eu2+ at 150 °C is still beyond 92 % of the initial intensity. The results provide a new mode of energy transfer, which is expected to improve the drawback existing in energy transfer. © 2018 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim.

Tempering of Mn and Mn-Si-V dual-phase steels

NASA Astrophysics Data System (ADS)

Speich, G. R.; Schwoeble, A. J.; Huffman, G. P.

1983-06-01

Changes in the yield behavior, strength, and ductility of a Mn and a Mn-Si-V d11Al-phase (ferrite-martensite) steel were investigated after tempering one hour at 200 to 600 °C. The change in yield behavior was complex in both steels with the yield strength first increasing and then decreasing as the tempering temperature was increased. This complex behavior is attributed to a combination of factors including carbon segregation to dislocations, a return of discontinuous yielding, and the relief of resid11Al stresses. In contrast, the tensile strength decreased continuously as the tempering temperature was increased in a manner that could be predicted from the change in hardness of the martensite phase using a simple composite strengthening model. The initial tensile ductility (total elongation) of the Mn-Si-V steel was much greater than that of the Mn steel. However, upon tempering up to 400 °C, the ductility of the Mn-Si-V decreased whereas that of the Mn steel increased. As a result, both steels had similar ductilities after tempering at 400 °C or higher temperatures. These results are attributed to the larger amounts of retained austenite in the Mn-Si-V steel (9 pct) compared to the Mn steel (3 pct) and its contribution to tensile ductility by transforming to martensite during plastic straining. Upon tempering at 400 °C, the retained austenite decomposes to bainite and its contribution to tensile ductility is eliminated.

High-yield synthesis of a unique Mn(iii) siloxide complex through KMnO4 oxidation of a Mn(ii) precursor.

PubMed

Lorenz, Volker; Ehle, Sophie; Liebing, Phil; Engelhardt, Felix; Hashemi-Haeri, Haleh; Oehler, Florian; Hinderberger, Dariush; Busse, Sabine; Urbaschok, Jens; Edelmann, Frank T

2017-12-19

A unique trivalent manganese siloxide complex, blue-violet Mn III Li 2 Cl[(Ph 2 SiO) 2 O] 2 (THF) 4 ·2THF (3) has been prepared by a straightforward two-step synthetic protocol. Lithiation of (Ph 2 SiOH) 2 O (1) followed by reaction with MnCl 2 (THF) 2 gave the structurally remarkable Mn(ii) precursor Mn II Li 4 Cl 2 [(Ph 2 SiO) 2 O] 2 (THF) 5 ·2THF (2). Surprisingly, the final oxidation step could be achieved using KMnO 4 in THF to provide the Mn(iii) species 3 in high yield (91%). Both title compounds were structurally characterized by single-crystal X-ray diffraction.

Amorphous TiO2 Shells: A Vital Elastic Buffering Layer on Silicon Nanoparticles for High-Performance and Safe Lithium Storage.

PubMed

Yang, Jianping; Wang, Yunxiao; Li, Wei; Wang, Lianjun; Fan, Yuchi; Jiang, Wan; Luo, Wei; Wang, Yang; Kong, Biao; Selomulya, Cordelia; Liu, Hua Kun; Dou, Shi Xue; Zhao, Dongyuan

2017-12-01

Smart surface coatings of silicon (Si) nanoparticles are shown to be good examples for dramatically improving the cyclability of lithium-ion batteries. Most coating materials, however, face significant challenges, including a low initial Coulombic efficiency, tedious processing, and safety assessment. In this study, a facile sol-gel strategy is demonstrated to synthesize commercial Si nanoparticles encapsulated by amorphous titanium oxide (TiO 2 ), with core-shell structures, which show greatly superior electrochemical performance and high-safety lithium storage. The amorphous TiO 2 shell (≈3 nm) shows elastic behavior during lithium discharging and charging processes, maintaining high structural integrity. Interestingly, it is found that the amorphous TiO 2 shells offer superior buffering properties compared to crystalline TiO 2 layers for unprecedented cycling stability. Moreover, accelerating rate calorimetry testing reveals that the TiO 2 -encapsulated Si nanoparticles are safer than conventional carbon-coated Si-based anodes. © 2017 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim.

Porous MnO2 prepared by sol-gel method for electrochemical supercapacitor

NASA Astrophysics Data System (ADS)

Bazzi, K.; Kumar, A.; Jayakumar, O. D.; Nazri, G. A.; Naik, V. M.; Naik, R.

2015-03-01

MnO2 has attracted great attention as material for electrochemical pseudocapacitor due to its high theoretical specific faradic capacitance (~ 1370 F .g-1) , environmental friendliness and wide potential window in both aqueous and nonaqueous electrolytes. However, the MnO2 has a low surface area which depresses its electrochemical performance. The amorphous α-MnO2 composite was synthesized by sol gel method in the presence of the tri-block copolymer P123. Our aim is to investigate the role of P123 on the electrochemical performance of MnO2. The samples with and without P123 were prepared and characterized by x-ray diffraction (XRD), SEM, TEM and Brunauer-Emmett-Teller (BET) method. The electrochemical performances of the amorphous MnO2 composites as the electrode materials for supercapacitors were evaluated by cyclic voltammetry and AC impedance measurements in a 1M Na2SO4 solution. The results show that the sample prepared without P123 exhibited a relatively low specific capacitance of 28F .g-1, whereas the porous MnO2 prepared with P123 exhibited 117 F .g-1at 5 mV/s. The results of crystalline MnO2 composites will also be presented. The authors acknowledge the support from the Richard J. Barber Foundation for Interdisciplinary Research.

Influence of off-stoichiometry on magnetoresistance characteristics of Co2MnSi/Ag-based current-perpendicular-to-plane spin valves

NASA Astrophysics Data System (ADS)

Inoue, Masaki; Hu, Bing; Moges, Kidist; Inubushi, Kazuumi; Nakada, Katsuyuki; Yamamoto, Masafumi; Uemura, Tetsuya

2017-08-01

The influence of off-stoichiometry of Co2MnSi (CMS) spin sources on giant magnetoresistance characteristics was investigated for CMS/Ag-based current-perpendicular-to-plane spin valves prepared with various Mn compositions α in Co2MnαSi0.82 electrodes. The magnetoresistance ratio of the prepared CMS/Co50Fe50 (CoFe) (1.1 nm)/Ag/CoFe (1.1)/CMS spin valves systematically increased with α from 11.4% for Mn-deficient α = 0.62 to 20.7% for Mn-rich α = 1.45 at 290 K. This result suggests that increasing α from a Mn-deficient to Mn-rich value increases the spin polarization by suppressing CoMn antisites harmful to the half-metallicity. Thus, our results demonstrate that appropriately controlling the film composition toward a Mn-rich one is highly effective for enhancing the half-metallicity of CMS in CMS-based spin valves, as it is in CMS-based magnetic tunnel junctions.

Surface topographical and structural analysis of Ag+-implanted polymethylmethacrylate

NASA Astrophysics Data System (ADS)

Arif, Shafaq; Rafique, M. Shahid; Saleemi, Farhat; Naab, Fabian; Toader, Ovidiu; Sagheer, Riffat; Bashir, Shazia; Zia, Rehana; Siraj, Khurram; Iqbal, Saman

2016-08-01

Specimens of polymethylmethacrylate (PMMA) were implanted with 400-keV Ag+ ions at different ion fluences ranging from 1 × 1014 to 5 × 1015 ions/cm2 using a 400-kV NEC ion implanter. The surface topographical features of the implanted PMMA were investigated by a confocal microscope. Modifications in the structural properties of the implanted specimens were analyzed in comparison with pristine PMMA by X-ray diffraction (XRD) and Raman spectroscopy. UV-Visible spectroscopy was applied to determine the effects of ion implantation on optical transmittance of the implanted PMMA. The confocal microscopic images revealed the formation of hillock-like microstructures along the ion track on the implanted PMMA surface. The increase in ion fluence led to more nucleation of hillocks. The XRD pattern confirmed the amorphous nature of pristine and implanted PMMA, while the Raman studies justified the transformation of Ag+-implanted PMMA into amorphous carbon at the ion fluence of ⩾5 × 1014 ions/cm2. Moreover, the decrease in optical transmittance of PMMA is associated with the formation of hillocks and ion-induced structural modifications after implantation.

Synthesis, thermal stability and the effects of ion irradiation in amorphous Si-O-C alloys

NASA Astrophysics Data System (ADS)

Colón Santana, Juan A.; Mora, Elena Echeverría; Price, Lloyd; Balerio, Robert; Shao, Lin; Nastasi, Michael

2015-05-01

Amorphous films of Si-O-C alloys were synthesized via sputtering deposition at room temperature. These alloys were characterized using grazing incidence diffraction, both as a function of temperature and irradiation dose. It was found that the material retained its amorphous structure, both at high temperatures (up to 1200 °C) and ion irradiation doses up to 1.0 dpa. The depth profile from photoemission spectroscopy provided evidence of the oxidation state of these alloys and their atomic composition. The studies suggest that Si-O-C alloys might belong to a group of radiation tolerant materials suitable for applications in reactor-like harsh environments.

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

Singh, Mukhtiyar; Saini, Hardev S.; Thakur, Jyoti

Heusler alloys based thin-films often exhibit a degree of atomic disorder which leads to the lowering of spin polarization in spintronic devices. We present ab-initio calculations of atomic disorder effects on spin polarization and half-metallicity of Mn{sub 2}CoSi inverse Heusler alloy. The five types of disorder in Mn{sub 2}CoSi have been proposed and investigated in detail. The A2{sub a}-type and B2-type disorders destroy the half-metallicity whereas it sustains for all disorders concentrations in DO{sub 3a}- and A2{sub b}-type disorder and for smallest disorder concentration studied in DO{sub 3b}-type disorder. Lower formation energy/atom for A2{sub b}-type disorder than other four disordersmore » in Mn{sub 2}CoSi advocates the stability of this disorder. The total magnetic moment shows a strong dependence on the disorder and the change in chemical environment. The 100% spin polarization even in the presence of disorders explicitly supports that these disorders shall not hinder the use of Mn{sub 2}CoSi inverse Heusler alloy in device applications. - Graphical abstract: Minority-spin gap (E{sub g↓}) and HM gap (E{sub sf}) as a function of concentrations of various possible disorder in Mn{sub 2}CoSi inverse Heusler alloy. The squares with solid line (black color)/dotted line (blue color)/dashed line (red color) reperesents E{sub g↓} for DO{sub 3a}-/DO{sub 3b}-/A2{sub b}-type disorder in Mn{sub 2}CoSi and the spheres with solid line (black color)/dottedline (blue color)/dashed line (red color) represents E{sub sf} for DO{sub 3a}-/DO{sub 3b}-/A2{sub b}-type disorder in Mn{sub 2}CoSi. - Highlights: • The DO{sub 3}- and A2-type disorders do not affect the half-metallicity in Mn{sub 2}CoSi. • The B2-type disorder solely destroys half-metallicity in Mn{sub 2}CoSi. • The A2-type disorder most probable to occur out of all three types. • The total spin magnetic moment strongly depends on the disorder concentrations.« less

Electron microscopy study of Ni induced crystallization in amorphous Si thin films

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

Radnóczi, G. Z.; Battistig, G.; Pécz, B., E-mail: pecz.bela@ttk.mta.hu

2015-02-17

The crystallization of amorphous silicon is studied by transmission electron microscopy. The effect of Ni on the crystallization is studied in a wide temperature range heating thinned samples in-situ inside the microscope. Two cases of limited Ni source and unlimited Ni source are studied and compared. NiSi{sub 2} phase started to form at a temperature as low as 250°C in the limited Ni source case. In-situ observation gives a clear view on the crystallization of silicon through small NiSi{sub 2} grain formation. The same phase is observed at the crystallization front in the unlimited Ni source case, where a secondmore » region is also observed with large grains of Ni{sub 3}Si{sub 2}. Low temperature experiments show, that long annealing of amorphous silicon at 410 °C already results in large crystallized Si regions due to the Ni induced crystallization.« less

Silylated functionalized silicon-based composite as anode with excellent cyclic performance for lithium-ion battery

NASA Astrophysics Data System (ADS)

Li, Xiao; Tian, Xiaodong; Yang, Tao; Wang, Wei; Song, Yan; Guo, Quangui; Liu, Zhanjun

2018-05-01

Inferior cycling stability and rate performance respectively caused by rigorous volume change and poor electrical conductivity were the main challenge of state-of-the-art Silicon-based electrode. In this work, silylated functionalized exfoliated graphite oxide (EGO)/silicon@amorphous carbon (3-APTS-EGO/Si@C) was synthesized by adopting silane as intermediate to connect Si particles with EGO sheets followed by introduction of amorphous carbon. The result suggested that 3-Aminopropyltriethoxysilan connected the EGO sheets and Si nanoparticles via covalent bonds. Owing to the strong covalent interaction and the synergistic effect between the silicon, EGO sheets and amorphous carbon, 3-APTS-EGO/Si@C composite possessed a high capacity of 774 mAh g-1 even after 450 cycles at 0.4 A g-1 with the retention capacity of 97%. This work also provided an effective strategy to improve the long cycling life performance of Si-based electrode.

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

Sangeetha, N. S.; Smetana, V.; Mudring, A. -V.

Here, crystals of SrMn 2Sb 2 and BaMn 2Sb 2 were grown using Sn flux and characterized by powder and single-crystal x-ray diffraction, respectively, and by single-crystal electrical resistivity ρ, heat capacity C p, and magnetic susceptibility χ measurements versus temperature T, and magnetization versus field M(H) isotherm measurements. SrMn 2Sb 2 adopts the trigonal CaAl 2Si 2-type structure, whereas BaMn 2Sb 2 crystallizes in the tetragonal ThCr 2Si 2-type structure. The ρ(T) data indicate semiconducting behaviors for both compounds with activation energies of ≳0.35 eV for SrMn 2Sb 2 and 0.16 eV for BaMn 2Sb 2. The χ(T) andmore » C p(T) data reveal antiferromagnetic (AFM) ordering at T N = 110 K for SrMn 2Sb 2 and 450 K for BaMn 2Sb 2. The anisotropic χ(T≤T N) data also show that the ordered moments in SrMn 2Sb 2 are aligned in the hexagonal ab plane, whereas the ordered moments in BaMn 2Sb 2 are aligned collinearly along the tetragonal c axis. The ab-plane M(H) data for SrMn 2Sb 2 exhibit a continuous metamagnetic transition at low fields 02Sb 2 exhibits no metamagnetic transitions up to 5.5 T. The χ(T) and C p(T) data for both SrMn 2Sb 2 and BaMn 2Sb 2 indicate strong dynamic short-range AFM correlations above their respective T N up to at least 900 K within a local-moment picture, corresponding to quasi-two-dimensional magnetic behavior. The present results and a survey of the literature for Mn pnictides with the CaAl 2Si 2 and ThCr 2Si 2 crystal structures show that the T N values for the CaAl 2Si 2-type compounds are much smaller than those for the ThCr 2Si 2-type materials.« less

Sacroiliac joint stability: Finite element analysis of implant number, orientation, and superior implant length.

PubMed

Lindsey, Derek P; Kiapour, Ali; Yerby, Scott A; Goel, Vijay K

2018-03-18

To analyze how various implants placement variables affect sacroiliac (SI) joint range of motion. An experimentally validated finite element model of the lumbar spine and pelvis was used to simulate a fusion of the SI joint using various placement configurations of triangular implants (iFuse Implant System ® ). Placement configurations were varied by changing implant orientation, superior implant length, and number of implants. The range of motion of the SI joint was calculated using a constant moment of 10 N-m with a follower load of 400 N. The changes in motion were compared between the treatment groups to assess how the different variables affected the overall motion of the SI joint. Transarticular placement of 3 implants with superior implants that end in the middle of the sacrum resulted in the greatest reduction in range of motion (flexion/extension = 73%, lateral bending = 42%, axial rotation = 72%). The range of motions of the SI joints were reduced with use of transarticular orientation (9%-18%) when compared with an inline orientation. The use of a superior implant that ended mid-sacrum resulted in median reductions of (8%-14%) when compared with a superior implant that ended in the middle of the ala. Reducing the number of implants, resulted in increased SI joint range of motions for the 1 and 2 implant models of 29%-133% and 2%-39%, respectively, when compared with the 3 implant model. Using a validated finite element model we demonstrated that placement of 3 implants across the SI joint using a transarticular orientation with superior implant reaching the sacral midline resulted in the most stable construct. Additional clinical studies may be required to confirm these results.

Sacroiliac joint stability: Finite element analysis of implant number, orientation, and superior implant length

PubMed Central

Lindsey, Derek P; Kiapour, Ali; Yerby, Scott A; Goel, Vijay K

2018-01-01

AIM To analyze how various implants placement variables affect sacroiliac (SI) joint range of motion. METHODS An experimentally validated finite element model of the lumbar spine and pelvis was used to simulate a fusion of the SI joint using various placement configurations of triangular implants (iFuse Implant System®). Placement configurations were varied by changing implant orientation, superior implant length, and number of implants. The range of motion of the SI joint was calculated using a constant moment of 10 N-m with a follower load of 400 N. The changes in motion were compared between the treatment groups to assess how the different variables affected the overall motion of the SI joint. RESULTS Transarticular placement of 3 implants with superior implants that end in the middle of the sacrum resulted in the greatest reduction in range of motion (flexion/extension = 73%, lateral bending = 42%, axial rotation = 72%). The range of motions of the SI joints were reduced with use of transarticular orientation (9%-18%) when compared with an inline orientation. The use of a superior implant that ended mid-sacrum resulted in median reductions of (8%-14%) when compared with a superior implant that ended in the middle of the ala. Reducing the number of implants, resulted in increased SI joint range of motions for the 1 and 2 implant models of 29%-133% and 2%-39%, respectively, when compared with the 3 implant model. CONCLUSION Using a validated finite element model we demonstrated that placement of 3 implants across the SI joint using a transarticular orientation with superior implant reaching the sacral midline resulted in the most stable construct. Additional clinical studies may be required to confirm these results. PMID:29564210

Indentation creep behaviors of amorphous Cu-based composite alloys

NASA Astrophysics Data System (ADS)

Song, Defeng; Ma, Xiangdong; Qian, Linfang

2018-04-01

This work reports the indentation creep behaviors of two Si2Zr3/amorphous Cu-based composite alloys utilizing nanoindentation technique. By analysis with Kelvin model, the retardation spectra of alloys at different positions, detached and attached regions to the intermetallics, were deduced. For the indentation of detached regions to Si2Zr3 intermetallics in both alloys, very similarity in creep displacement can be observed and retardation spectra show a distinct disparity in the second retardation peak. For the indentation of detached regions, the second retardation spectra also display distinct disparity. At both positions, the retardation spectra suggest that Si elements may lead to the relatively dense structure in the amorphous matrix and to form excessive Si2Zr3 intermetallics which may deteriorate the plastic deformation of current Cu-based composite alloys.

Synthesis and characterization of bulk metallic glasses prepared by laser direct deposition

NASA Astrophysics Data System (ADS)

Ye, Xiaoyang

Fe-based and Zr-based metallic glasses have attracted extensive interest for structural applications due to their excellent glass forming ability, superior mechanical properties, unique thermal and corrosion properties. In this study, the feasibility of synthesizing metallic glasses with good ductility by laser direct deposition is explored. Both in-situ synthesis with elemental powder mixture and ex-situ synthesis with prealloyed powder are discussed. Microstructure and properties of laser direct deposited metallic glass composites are analyzed. Synthesis of Fe-Cr-Mo-W-Mn-C-Si-B metallic glass composite with a large fraction of amorphous phase was accomplished using laser direct deposition. X-ray diffraction (XRD) and transmission electron microscopy investigations revealed the existence of amorphous structure. Microstructure analyses by optical microscopy and scanning electron microscopy (SEM) indicated the periodically repeated microstructures of amorphous and crystalline phases. Partially crystallized structure brought by laser reheating and remelting during subsequent laser scans aggregated in the overlapping area between each scan. XRD analysis showed that the crystalline particle embedded in the amorphous matrix was Cr 1.07Fe18.93 phase. No significant microstructural differences were found from the first to the last layer. Microhardness of the amorphous phase (HV0.2 1591) showed a much higher value than that of the crystalline phase (HV0.2 947). Macrohardness of the top layer had a value close to the microhardness of the amorphous region. Wear resistance property of deposited layers showed a significant improvement with the increased fraction of amorphous phase. Zr65Al10Ni10Cu15 amorphous composites with a large fraction of amorphous phase were in-situ synthesized by laser direct deposition. X-ray diffraction confirmed the existence of both amorphous and crystalline phases. Laser parameters were optimized in order to increase the fraction of amorphous phase. The microstructure analysis by scanning electron microscopy revealed the deposited structure was composed of periodically repeated amorphous and crystalline phases. Overlapping regions with nanoparticles aggregated were crystallized by laser reheating and remelting processes during subsequent laser scans. Vickers microhardness of the amorphous region showed around 35% higher than that of crystalline region. Average hardness obtained by a Rockwell macrohardness tester was very close to the microhardness of the amorphous region. The compression test showed that the fracture strain of Zr65Al10Ni10Cu15 amorphous composites was enhanced from less than 2% to as high as 5.7%, compared with fully amorphous metallic glass. Differential scanning calorimetry test results further revealed the amorphous structure and glass transition temperature Tg was observed to be around 655K. In 3 mol/L NaCl solution, laser direct deposited amorphous composites exhibited distinctly improved corrosion resistance, compared with fully-crystallized samples.

Modeling of amorphous SiCxO6/5 by classical molecular dynamics and first principles calculations.

PubMed

Liao, Ningbo; Zhang, Miao; Zhou, Hongming; Xue, Wei

2017-02-14

Polymer-derived silicon oxycarbide (SiCO) presents excellent performance for high temperature and lithium-ion battery applications. Current experiments have provided some information on nano-structure of SiCO, while it is very challenging for experiments to take further insight into the molecular structure and its relationship with properties of materials. In this work, molecular dynamics (MD) based on empirical potential and first principle calculation were combined to investigate amorphous SiC x O 6/5 ceramics. The amorphous structures of SiCO containing silicon-centered mix bond tetrahedrons and free carbon were successfully reproduced. The calculated radial distribution, angular distribution and Young's modulus were validated by current experimental data, and more details on molecular structure were discussed. The change in the slope of Young's modulus is related to the glass transition temperature of the material. The proposed modeling approach can be used to predict the properties of SiCO with different compositions.

Modeling of amorphous SiCxO6/5 by classical molecular dynamics and first principles calculations

NASA Astrophysics Data System (ADS)

Liao, Ningbo; Zhang, Miao; Zhou, Hongming; Xue, Wei

2017-02-01

Polymer-derived silicon oxycarbide (SiCO) presents excellent performance for high temperature and lithium-ion battery applications. Current experiments have provided some information on nano-structure of SiCO, while it is very challenging for experiments to take further insight into the molecular structure and its relationship with properties of materials. In this work, molecular dynamics (MD) based on empirical potential and first principle calculation were combined to investigate amorphous SiCxO6/5 ceramics. The amorphous structures of SiCO containing silicon-centered mix bond tetrahedrons and free carbon were successfully reproduced. The calculated radial distribution, angular distribution and Young’s modulus were validated by current experimental data, and more details on molecular structure were discussed. The change in the slope of Young’s modulus is related to the glass transition temperature of the material. The proposed modeling approach can be used to predict the properties of SiCO with different compositions.

Microstructure and magnetic behavior of Mn doped GeTe chalcogenide semiconductors based phase change materials

NASA Astrophysics Data System (ADS)

Adam, Adam Abdalla Elbashir; Cheng, Xiaomin; Abuelhassan, Hassan H.; Miao, Xiang Shui

2017-06-01

Phase-change materials (PCMs) are the most promising candidates to be used as an active media in the universal data storage and spintronic devices, due to their large differences in physical properties of the amorphous-crystalline phase transition behavior. In the present study, the microstructure, magnetic and electrical behaviors of Ge0.94Mn0.06Te thin film were investigated. The crystallographic structure of Ge0.94Mn0.06Te thin film was studied sing X-ray diffractometer (XRD) and High Resolution Transmission Electron Microscope (HR-TEM). The XRD pattern showed that the crystallization structure of the film was rhombohedral phase for GeTe with a preference (202) orientation. The HR-TEM image of the crystalline Ge0.94Mn0.06Te thin film demonstrated that, there were two large crystallites and small amorphous areas. The magnetization as a function of the magnetic field analyses of both amorphous and crystalline states showed the ferromagnetic hysteretic behaviors. Then, the hole carriers concentration of the film was measured and it found to be greater than 1021 cm-3 at room temperature. Moreover, the anomalous of Hall Effect (AHE) was clearly observed for the measuring temperatures 5, 10 and 50 K. The results demonstrated that the magnitude of AHE decreased when the temperature was increasing.

Synergistic Effects of Iodine and Silver Ions Co-Implanted in 6H-SiC

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

Kuhudzai, Remeredzai J.; Malherbe, Johan; Hlatshwayo, T. T.

2015-10-23

Motivated by the aim of understanding the release of fission products through the SiC coating of fuel kernels in modern high temperature nuclear reactors, a fundamental investigation is conducted to understand the synergistic effects of implanted silver (Ag) and iodine (I) in 6H-SiC. The implantation of the individual species, as well as the co-implantation of 360 keV ions of I and Ag at room temperature in 6H-SiC and their subsequent annealing behavior has been investigated by Secondary Ion Mass Spectrometry (SIMS), Atom Probe Tomography (APT) and X-ray Photoelectron Spectroscopy (XPS). SIMS and APT measurements indicated the presence of Ag inmore » the co-implanted samples after annealing at 1500 ºC for 30 hours in sharp contrast to the samples implanted with Ag only. In samples implanted with Ag only, complete loss of the implanted Ag was observed. However, for I only implanted samples, some iodine was retained. APT of annealed co-implanted 6H-SiC showed clear spatial association of Ag and I clusters in SiC, which can be attributed to the observed I assisted retention of Ag after annealing. Such detailed studies will be necessary to identify the fundamental mechanism of fission products migration through SiC coatings.« less

Improving the photoresponse spectra of BaSi2 layers by capping with hydrogenated amorphous Si layers prepared by radio-frequency hydrogen plasma

NASA Astrophysics Data System (ADS)

Xu, Zhihao; Gotoh, Kazuhiro; Deng, Tianguo; Sato, Takuma; Takabe, Ryota; Toko, Kaoru; Usami, Noritaka; Suemasu, Takashi

2018-05-01

We studied the surface passivation effect of hydrogenated amorphous silicon (a-Si:H) layers on BaSi2 films. a-Si:H was formed by an electron-beam evaporation of Si, and a supply of atomic hydrogen using radio-frequency plasma. Surface passivation effect was first investigated on a conventional n-Si(111) substrate by capping with 20 nm-thick a-Si:H layers, and next on a 0.5 μm-thick BaSi2 film on Si(111) by molecular beam epitaxy. The internal quantum efficiency distinctly increased by 4 times in a wide wavelength range for sample capped in situ with a 3 nm-thick a-Si:H layer compared to those capped with a pure a-Si layer.

Structure analysis of aluminium silicon manganese nitride precipitates formed in grain-oriented electrical steels

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

Bernier, Nicolas, E-mail: n.bernier@yahoo.fr; Xhoffer, Chris; Van De Putte, Tom, E-mail: tom.vandeputte@arcelormittal.com

We report a detailed structural and chemical characterisation of aluminium silicon manganese nitrides that act as grain growth inhibitors in industrially processed grain-oriented (GO) electrical steels. The compounds are characterised using energy dispersive X-ray spectrometry (EDX) and energy filtered transmission electron microscopy (EFTEM), while their crystal structures are analysed using X-ray diffraction (XRD) and TEM in electron diffraction (ED), dark-field, high-resolution and automated crystallographic orientation mapping (ACOM) modes. The chemical bonding character is determined using electron energy loss spectroscopy (EELS). Despite the wide variation in composition, all the precipitates exhibit a hexagonal close-packed (h.c.p.) crystal structure and lattice parameters ofmore » aluminium nitride. The EDX measurement of ∼ 900 stoichiometrically different precipitates indicates intermediate structures between pure aluminium nitride and pure silicon manganese nitride, with a constant Si/Mn atomic ratio of ∼ 4. It is demonstrated that aluminium and silicon are interchangeably precipitated with the same local arrangement, while both Mn{sup 2+} and Mn{sup 3+} are incorporated in the h.c.p. silicon nitride interstitial sites. The oxidation of the silicon manganese nitrides most likely originates from the incorporation of oxygen during the decarburisation annealing process, thus creating extended planar defects such as stacking faults and inversion domain boundaries. The chemical composition of the inhibitors may be written as (AlN){sub x}(SiMn{sub 0.25}N{sub y}O{sub z}){sub 1−x} with x ranging from 0 to 1. - Highlights: • We study the structure of (Al,Si,Mn)N inhibitors in grain oriented electrical steels. • Inhibitors have the hexagonal close-packed symmetry with lattice parameters of AlN. • Inhibitors are intermediate structures between pure AlN and (Si,Mn)N with Si/Mn ∼ 4. • Al and Si share the same local arrangement; Mn is incorporated in both Mn{sup 2+} and Mn{sup 3+}. • Oxygen incorporation is invoked to account for the thermal stability of (Al,Si,Mn)N.« less

Hydrogenated amorphous silicon formation by flux control and hydrogen effects on the growth mechanism

NASA Astrophysics Data System (ADS)

Toyoda, H.; Sugai, H.; Kato, K.; Yoshida, A.; Okuda, T.

1986-06-01

The composition of particle flux to deposit hydrogenated amorphous silicon films in a glow discharge is controlled by a combined electrostatic-magnetic deflection technique. As a result, the films are formed firstly without hydrogen ion flux, secondly by neutral flux only, and thirdly by all species fluxes. Comparison of these films reveals the significant role of hydrogen in the surface reactions. Hydrogen breaks the Si-Si bond, decreases the sticking probability of the Si atom, and replaces the SiH bond by a SiH2 bond to increase the hydrogen content of the films.

Synthesis of magnetically recyclable MnFe2O4@SiO2@Ag nanocatalyst: Its high catalytic performances for azo dyes and nitro compounds reduction

NASA Astrophysics Data System (ADS)

Kurtan, U.; Amir, Md.; Yıldız, A.; Baykal, A.

2016-07-01

In this study, magnetically recycable MnFe2O4@SiO2@Ag nanocatalyst (MnFe2O4@SiO2@Ag MRCs) has been synthesized through co-precipition and chemical reduction method. XRD analysis confirmed the synthesis of single phase nanoproduct with crystallite size of 10 nm. VSM measurements showed the superparamagnetic property of the product. Catalytic studies showed that MnFe2O4@SiO2@Ag MRC could catalyze the reduction of the various azo compounds like methyl orange (MO), methylene blue (MB), eosin Y (EY), and rhodamine B (RhB) and also aromatic nitro compounds such as 4-nitrophenol (4-NP), 4-nitroaniline (4-NA) and 2-nitroaniline (2-NA). Moreover, the magnetic nanocatalyst showed an excellent reusability properties that remained unchanged after several cycles. Therefore, MnFe2O4@SiO2@Ag is the potential candidate for the application of organic pollutants for wastewater treatment.

Impact of a long term fire retardant (Fire Trol 931) on the leaching of Na, Al, Fe, Mn, Cu and Si from a Mediterranean forest soil: a short-term, lab-scale study.

PubMed

Koufopoulou, Sofia; Michalopoulos, Charalampos; Tzamtzis, Nikolaos; Pappa, Athina

2014-06-01

Long term fire retardant (LTR) application for forest fire prevention purposes as well as wildland fires can result in chemical leaching from forest soils. Large quantities of sodium (Na), aluminium (Al), iron (Fe), manganese (Mn), copper (Cu) and silicon (Si) in leachates, mainly due to ammonium (one of the major LTR components) soil deposition, could affect the groundwater quality. The leaching of Na, Al, Fe, Mn, Cu and Si due to nitrogen based LTR application (Fire Trol 931) was studied at laboratory scale. The concentrations of Na(+), Al(3+), Fe(3+)/Fe(2+), Mn(2+), Cu(2+) and Si(4+) were measured in the resulting leachates from pots with forest soil and pine trees alone and in combination with fire. The leaching of Na, Fe and Si from treated pots was significantly greater than that from control pots. The leaching of Al, Mn and Cu was extremely low.

Very low temperature materials and self-alignment technology for amorphous hydrated silicon thin film transistors fabricated on transparent large area plastic substrates

NASA Astrophysics Data System (ADS)

Yang, Chien-Sheng

The purpose of this research has been to (1) explore materials prepared using plasma enhanced chemical vapor deposition (PECVD) at 110sp°C for amorphous silicon thin film transistors (TFT's) fabricated on low temperature compatible, large area flexible polyethylene terephthalate (PET) substrates, and (2) develop full self-alignment technology using selective area n+ PECVD for source/drain contacts of amorphous silicon TFT's. For item (1), silicon nitride films, as gate dielectrics of TFT's, were deposited using SiHsb4+NHsb3, SiHsb4+NHsb3+Nsb2, SiHsb4+NHsb3+He, or SiHsb4+NHsb3+Hsb2 gases. Good quality silicon nitride films can be deposited using a SiHsb4+NHsb3 gas with high NHsb3/SiHsb4 ratios, or using a SiHsb4+NHsb3+Nsb2 gas with moderate NHsb3/SiHsb4 ratios. A chemical model was proposed to explain the Nsb2 dilution effect. This model includes calculations of (a) the electron energy distribution function in a plasma, (b) rate constants of electron impact dissociation, and (3) the (NHsbx) / (SiHsby) ratio in a plasma. The Nsb2 dilution was shown to have a effect of shifting the electron energy distribution into high energy, thus enhancing the (NHsbx) / (SiHsbyrbrack ratio in a plasma and promoting the deposition of N-rich silicon nitride films, which leads to decreased trap state density and a shift in trap state density to deeper in the gap. Amorphous silicon were formed successfully at 110sp°C on large area glass and plastic(PET) substrates. Linear mobilities are 0.33 and 0.12 cmsp2/Vs for TFT's on glass and plastic substrates, respectively. ON/OFF current ratios exceed 10sp7 for TFT's on glass and 10sp6 for TFT's on PET. For item (2), a novel full self-alignment process was developed for amorphous silicon TFT's. This process includes (1) back-exposure using the bottom gate metal as the mask, and (2) selective area n+ micro-crystalline silicon PECVD for source/drain contacts of amorphous silicon TFT's. TFT's fabricated using the full self-alignment process showed linear mobilities ranging from 0.5 to 1.0 cmsp2/Vs.

The optical properties of Sr3SiAl10O20 and Sr3SiAl10O20:Mn4+

NASA Astrophysics Data System (ADS)

Jansen, Thomas; Jüstel, Thomas

2017-11-01

Mn4+-activated luminescent materials have attracted significant attention recently. In particular, alkaline earth aluminates, such as Sr4Al14O25:Mn4+ and CaAl12O19:Mn4+, emit light in the red region, which can be exploited in phosphor-converted LEDs. We applied a sol-gel precursor followed by a ceramic method to synthesize highly crystalline Mn4+-doped Sr3SiAl10O20. The compound Sr3SiAl10O20:Mn4+ exhibits deep red photoluminescence that peaks at 663 nm, which can be assigned to the 2Eg → 4A2g intraconfigurational transition of Mn4+ ([Ar]3d.3 configuration) within the [MnO6]8- octahedra on the aluminum site in the Sr3SiAl10O20 (Space group C12/m1) host structure. The photoluminescence properties, such as the temperature dependence of the luminescence intensity and luminescence lifetime, are presented. Furthermore, the luminescence intensity as function of the activator concentration was investigated. Additionally, the band structure of the undoped host material was treated with Density Functional Theory (DFT). The theoretical results were evaluated experimentally with diffuse UV reflectance spectroscopy. Finally, the crystal field and Racah parameters were extracted to compare with those reported in the literature.

Thin film solar cells with Si nanocrystallites embedded in amorphous intrinsic layers by hot-wire chemical vapor deposition.

PubMed

Park, Seungil; Parida, Bhaskar; Kim, Keunjoo

2013-05-01

We investigated the thin film growths of hydrogenated silicon by hot-wire chemical vapor deposition with different flow rates of SiH4 and H2 mixture ambient and fabricated thin film solar cells by implementing the intrinsic layers to SiC/Si heterojunction p-i-n structures. The film samples showed the different infrared absorption spectra of 2,000 and 2,100 cm(-1), which are corresponding to the chemical bonds of SiH and SiH2, respectively. The a-Si:H sample with the relatively high silane concentration provides the absorption peak of SiH bond, but the microc-Si:H sample with the relatively low silane concentration provides the absorption peak of SiH2 bond as well as SiH bond. Furthermore, the microc-Si:H sample showed the Raman spectral shift of 520 cm(-1) for crystalline phase Si bonds as well as the 480 cm(-1) for the amorphous phase Si bonds. These bonding structures are very consistent with the further analysis of the long-wavelength photoconduction tail and the formation of nanocrystalline Si structures. The microc-Si:H thin film solar cell has the photovoltaic behavior of open circuit voltage similar to crystalline silicon thin film solar cell, indicating that microc-Si:H thin film with the mixed phase of amorphous and nanocrystalline structures show the carrier transportation through the channel of nanocrystallites.

Reduced interface spin polarization by antiferromagnetically coupled Mn segregated to the C o2MnSi /GaAs (001) interface

NASA Astrophysics Data System (ADS)

Rath, Ashutosh; Sivakumar, Chockalingam; Sun, C.; Patel, Sahil J.; Jeong, Jong Seok; Feng, J.; Stecklein, G.; Crowell, Paul A.; Palmstrøm, Chris J.; Butler, William H.; Voyles, Paul M.

2018-01-01

We have investigated the interfacial structure and its correlation with the calculated spin polarization in C o2MnSi /GaAs(001) lateral spin valves. C o2MnSi (CMS) films were grown on As-terminated c(4 ×4 ) GaAs(100) by molecular beam epitaxy using different first atomic layers: MnSi, Co, and Mn. Atomically resolved Z -contrast scanning transmission electron microscopy (STEM) imaging and electron energy loss spectroscopy (EELS) were used to develop atomic structural models of the CMS/GaAs interfaces that were used as inputs for first-principles calculations to understand the magnetic and electronic properties of the interface. First-principles structures were relaxed and then validated by comparing experimental and simulated high-resolution STEM images. STEM-EELS results show that all three films have similar six atomic layer thick, Mn- and As-rich multilayer interfaces. However, the Co-initiated interface contains a M n2As -like layer, which is antiferromagnetic, and which is not present in the other two interfaces. Density functional theory calculations show a higher degree of interface spin polarization in the Mn- and MnSi-initiated cases, compared to the Co-initiated case, although none of the interfaces are half-metallic. The loss of half-metallicity is attributed, at least in part, to the segregation of Mn at the interface, which leads to the formation of interface states. The implications for the performance of lateral spin valves based on these interfaces are discussed briefly.

Properties of homoepitaxial 4H-SiC and characteristics of Ti/4H-SiC Schottky barrier diodes

NASA Astrophysics Data System (ADS)

Chen, G.; Li, Z. Y.; Bai, S.; Han, P.

2008-02-01

This paper describes the properties of the homoepitaxial 4H-SiC layer, the fabrication and electrical parameters of Ti/4H-SiC Schottky barrier diode (SBD). The 4H-SiC epitaxial layers, grown on the commercially available 8°off-oriented Si-face(0001) single-crystal 4H-SiC wafers, have been performed at 1550~1600°C by using the step controlled epitaxy with low pressure chemical vapor deposition. X-ray diffraction measurement result indicates the single crystal nature of the epilayer, and Raman spectrum shows the typical 4H-SiC feature peaks. When the off-oriented angle of substrate is 8°, the epitaxial growth perfectly replicates the substrate's polytype. High quality 4H-SiC epilayer has been generated on the 4H-SiC substrate. Ti/4H-SiC SBDs with blocking voltage 1kV have been made on an undoped epilayer with 12um in thick and 3×10 15cm -3 in carrier density. The ideality factor n=1.16 and the effective barrier height φ e=0.9V of the Ti/4H-SiC SBDs are measured with method of forward density-voltage (J-V). The diode rectification ratio of forward to reverse (defined at +/-1V) is over 10 7 at room temperature. By using B + implantation, an amorphous layer as the edge termination is formed. The SBDs have on-state current density of 200A/cm2 at a forward voltage drop of about 2V. The specific on-resistance for the rectifier is found to be as 6.6mΩ•cm2.

Propagation losses in undoped and n-doped polycrystalline silicon wire waveguides.

PubMed

Zhu, Shiyang; Fang, Q; Yu, M B; Lo, G Q; Kwong, D L

2009-11-09

Polycrystalline silicon (polySi) wire waveguides with width ranging from 200 to 500 nm are fabricated by solid-phase crystallization (SPC) of deposited amorphous silicon (a-Si) on SiO(2) at a maximum temperature of 1000 degrees C. The propagation loss at 1550 nm decreases from 13.0 to 9.8 dB/cm with the waveguide width shrinking from 500 to 300 nm while the 200-nm-wide waveguides exhibit quite large loss (>70 dB/cm) mainly due to the relatively rough sidewall of waveguides induced by the polySi dry etch. By modifying the process sequence, i.e., first patterning the a-Si layer into waveguides by dry etch and then SPC, the sidewall roughness is significantly improved but the polySi crystallinity is degraded, leading to 13.9 dB/cm loss in the 200-nm-wide waveguides while larger losses in the wider waveguides. Phosphorus implantation causes an additional loss in the polySi waveguides. The doping-induced optical loss increases relatively slowly with the phosphorus concentration increasing up to 1 x 10(18) cm(-3), whereas the 5 x 10(18) cm(-3) doped waveguides exhibit large loss due to the dominant free carrier absorption. For all undoped polySi waveguides, further 1-2 dB/cm loss reduction is obtained by a standard forming gas (10%H(2) + 90%N(2)) annealing owing to the hydrogen passivation of Si dangling bonds present in polySi waveguides, achieving the lowest loss of 7.9 dB/cm in the 300-nm-wide polySi waveguides. However, for the phosphorus doped polySi waveguides, the propagation loss is slightly increased by the forming gas annealing.

Synthesis of a Novel Polyethoxysilsesquiazane and Thermal Conversion into Ternary Silicon Oxynitride Ceramics with Enhanced Thermal Stability.

PubMed

Iwase, Yoshiaki; Horie, Yoji; Daiko, Yusuke; Honda, Sawao; Iwamoto, Yuji

2017-12-05

A novel polyethoxysilsesquiazane ([EtOSi(NH) 1.5 ] n , EtOSZ) was synthesized by ammonolysis at -78 °C of ethoxytrichlorosilane (EtOSiCl₃), which was isolated by distillation as a reaction product of SiCl₄ and EtOH. Attenuated total reflection-infra red (ATR-IR), 13 C-, and 29 Si-nuclear magnetic resonance (NMR) spectroscopic analyses of the ammonolysis product resulted in the detection of Si-NH-Si linkage and EtO group. The simultaneous thermogravimetric and mass spectrometry analyses of the EtOSZ under helium revealed cleavage of oxygen-carbon bond of the EtO group to evolve ethylene as a main gaseous species formed in-situ, which lead to the formation at 800 °C of quaternary amorphous Si-C-N with an extremely low carbon content (1.1 wt %) when compared to the theoretical EtOSZ (25.1 wt %). Subsequent heat treatment up to 1400 °C in N₂ lead to the formation of X-ray amorphous ternary Si-O-N. Further heating to 1600 °C in N₂ promoted crystallization and phase partitioning to afford Si₂N₂O nanocrystallites identified by the XRD and TEM analyses. The thermal stability up to 1400 °C of the amorphous state achieved for the ternary Si-O-N was further studied by chemical composition analysis, as well as X-ray photoelectron spectroscopy (XPS) and 29 Si-NMR spectroscopic analyses, and the results were discussed aiming to develop a novel polymeric precursor for ternary amorphous Si-O-N ceramics with an enhanced thermal stability.

Shift in room-temperature photoluminescence of low-fluence Si+-implanted SiO2 films subjected to rapid thermal annealing.

PubMed

Fu, Ming-Yue; Tsai, Jen-Hwan; Yang, Cheng-Fu; Liao, Chih-Hsiung

2008-12-01

We experimentally demonstrate the effect of the rapid thermal annealing (RTA) in nitrogen flow on photoluminescence (PL) of SiO 2 films implanted by different doses of Si + ions. Room-temperature PL from 400-nm-thick SiO 2 films implanted to a dose of 3×10 16 cm -2 shifted from 2.1 to 1.7 eV upon increasing RTA temperature (950-1150 °C) and duration (5-20 s). The reported approach of implanting silicon into SiO 2 films followed by RTA may be effective for tuning Si-based photonic devices.

Shift in room-temperature photoluminescence of low-fluence Si+-implanted SiO2 films subjected to rapid thermal annealing

PubMed Central

Fu, Ming-Yue; Tsai, Jen-Hwan; Yang, Cheng-Fu; Liao, Chih-Hsiung

2008-01-01

We experimentally demonstrate the effect of the rapid thermal annealing (RTA) in nitrogen flow on photoluminescence (PL) of SiO2 films implanted by different doses of Si+ ions. Room-temperature PL from 400-nm-thick SiO2 films implanted to a dose of 3×1016 cm−2 shifted from 2.1 to 1.7 eV upon increasing RTA temperature (950–1150 °C) and duration (5–20 s). The reported approach of implanting silicon into SiO2 films followed by RTA may be effective for tuning Si-based photonic devices. PMID:27878029

Improved retention of phosphorus donors in germanium using a non-amorphizing fluorine co-implantation technique

NASA Astrophysics Data System (ADS)

Monmeyran, Corentin; Crowe, Iain F.; Gwilliam, Russell M.; Heidelberger, Christopher; Napolitani, Enrico; Pastor, David; Gandhi, Hemi H.; Mazur, Eric; Michel, Jürgen; Agarwal, Anuradha M.; Kimerling, Lionel C.

2018-04-01

Co-doping with fluorine is a potentially promising method for defect passivation to increase the donor electrical activation in highly doped n-type germanium. However, regular high dose donor-fluorine co-implants, followed by conventional thermal treatment of the germanium, typically result in a dramatic loss of the fluorine, as a result of the extremely large diffusivity at elevated temperatures, partly mediated by the solid phase epitaxial regrowth. To circumvent this problem, we propose and experimentally demonstrate two non-amorphizing co-implantation methods; one involving consecutive, low dose fluorine implants, intertwined with rapid thermal annealing and the second, involving heating of the target wafer during implantation. Our study confirms that the fluorine solubility in germanium is defect-mediated and we reveal the extent to which both of these strategies can be effective in retaining large fractions of both the implanted fluorine and, critically, phosphorus donors.

Functional associations between the metabolome and manganese tolerance in Vigna unguiculata

PubMed Central

Führs, Hendrik; Specht, André; Erban, Alexander; Kopka, Joachim; Horst, Walter J.

2012-01-01

Genotypic- and silicon (Si)-mediated differences in manganese (Mn) tolerance of cowpea (Vigna unguiculata) arise from a combination of symplastic and apoplastic traits. A detailed metabolomic inspection could help to identify functional associations between genotype- and Si-mediated Mn tolerance and metabolism. Two cowpea genotypes differing in Mn tolerance (TVu 91, Mn sensitive; TVu 1987, Mn tolerant) were subjected to differential Mn and Si treatments. Gas chromatography–mass spectrometry (GC-MS)-based metabolite profiling of leaf material was performed. Detailed evaluation of the response of metabolites was combined with gene expression and physiological analyses. After 2 d of 50 μM Mn supply TVu 91 expressed toxicity symptoms first in the form of brown spots on the second oldest trifoliate leaves. Silicon treatment suppressed symptom development in TVu 91. Despite higher concentrations of Mn in leaves of TVu 1987 compared with TVu 91, the tolerant genotype did not show symptoms. From sample cluster formation as identified by independent component analysis (ICA) of metabolite profiles it is concluded that genotypic differences accounted for the highest impact on variation in metabolite pools, followed by Mn and Si treatments in one of two experiments. Analysis of individual metabolites corroborated a comparable minor role for Mn and Si treatments in the modulation of individual metabolites. Mapping individual metabolites differing significantly between genotypes onto biosynthetic pathways and gene expression studies on the corresponding pathways suggest that genotypic Mn tolerance is a consequence of differences (i) in the apoplastic binding capacity; (ii) in the capability to maintain a high antioxidative state; and (iii) in the activity of shikimate and phenylpropanoid metabolism. PMID:21934118

Stress effects on the initial lithiation of crystalline silicon nanowires: Reactive molecular dynamics simulations using ReaxFF

DOE PAGES

Ostadhossein, Alireza; Cubuk, Ekin D.; Tritsaris, Georgios A.; ...

2014-12-18

Silicon (Si) has been recognized as a promising anode material for the next-generation high-capacity lithium (Li)-ion batteries because of its high theoretical energy density. Recent in situ transmission electron microscopy (TEM) revealed that the electrochemical lithiation of crystalline Si nanowires (c-SiNWs) proceeds by the migration of the interface between the lithiated Si (LixSi) shell and the pristine unlithiated core, accompanied by solid-state amorphization. The underlying atomic mechanisms of Li insertion into c-Si remain poorly understood. In this research, we perform molecular dynamics (MD) simulations using the reactive force field (ReaxFF) to characterize the lithiation process of c-SiNWs. Our calculations showmore » that ReaxFF can accurately reproduce the energy barriers of Li migration from DFT calculations in both crystalline (c-Si) and amorphous Si (a-Si). The ReaxFF-based MD simulations reveal that Li insertion into interlayer spacing between two adjacent (111) planes results in the peeling-off of the (111) facets and subsequent amorphization, in agreement with experimental observations. We find that breaking of the Si–Si bonds between (111)-bilayers requires a rather high local Li concentration, which explains the atomically sharp amorphous–crystalline interface (ACI). Our stress analysis shows that lithiation induces compressive stress at the ACI layer, causing retardation or even the stagnation of the reaction front, also in good agreement with TEM observations. Lithiation at high temperatures (e.g. 1200 K) shows that Li insertion into c-SiNW results in an amorphous to crystalline phase transformation at Li : Si composition of ~4.2:1. In conclusion, our modeling results provide a comprehensive picture of the effects of reaction and diffusion-induced stress on the interfacial dynamics and mechanical degradation of SiNW anodes under chemo-mechanical lithiation.« less

Growth and Electronic Structure of Heusler Compounds for Use in Electron Spin Based Devices

NASA Astrophysics Data System (ADS)

Patel, Sahil Jaykumar

Spintronic devices, where information is carried by the quantum spin state of the electron instead of purely its charge, have gained considerable interest for their use in future computing technologies. For optimal performance, a pure spin current, where all electrons have aligned spins, must be generated and transmitted across many interfaces and through many types of materials. While conventional spin sources have historically been elemental ferromagnets, like Fe or Co, these materials pro duce only partially spin polarized currents. To increase the spin polarization of the current, materials like half-metallic ferromagnets, where there is a gap in the minority spin density of states around the Fermi level, or topological insulators, where the current transport is dominated by spin-locked surface states, show promise. A class of materials called Heusler compounds, with electronic structures that range from normal metals, to half metallic ferromagnets, semiconductors, superconductors and even topological insulators, interfaces well with existing device technologies, and through the use of molecular beam epitaxy (MBE) high quality heterostructures and films can be grown. This dissertation examines the electronic structure of surfaces and interfaces of both topological insulator (PtLuSb-- and PtLuBi--) and half-metallic ferromagnet (Co2MnSi-- and Co2FeSi--) III-V semiconductor heterostructures. PtLuSb and PtLuBi growth by MBE was demonstrated on Alx In1--xSb (001) ternaries. PtLuSb (001) surfaces were observed to reconstruct with either (1x3) or c(2x2) unit cells depending on Sb overpressure and substrate temperature. viii The electronic structure of these films was studied by scanning tunneling microscopy/spectroscopy (STM/STS) and photoemission spectroscopy. STS measurements as well as angle resolved photoemission spectropscopy (ARPES) suggest that PtLuSb has a zero-gap or semimetallic band structure. Additionally, the observation of linearly dispersing surface states, with an approximate crossing point 240meV above the Fermi level, suggests that PtLuSb (001) films are topologically non-trivial. PtLuBi films also display a Fermi level position approximately 500meV below the valence band maximum. Co2MnSi and Co2FeSi were also grown by MBE on GaAs (001) for use as spin injectors into GaAs lateral spin valve devices. By the growth of the quaternary alloy Co2FexMn1-- xSi and varying x, electron doping of the full Heusler compound was demonstrated by observation of a crossover from a majority spin polarization of Co2MnSi to a minority spin polarization in Co2FeSi. Co2MnSi films were studied as a function of the nucleation sequence, using either Co-- or MnSi-- initiated films on c(4x4) GaAs. Studies using x-ray photoemission spectroscopy (XPS), STM/STS, and transmission electron microscopy (TEM) suggest that the bulk of the Co2MnSi films and the interfacial structure between Co 2MnSi and GaAs is not modified by the nucleation sequence, but a change in spin transport characteristics suggests a modification of semiconductor band structure at the Co2MnSi/GaAs interface due to diffusion of Mn leading to compensation of the Schottky barrier contact. Diffusion of Mn into the GaAs was confirmed by secondary ion mass spectrometry (SIMS) measurements. The proposed mechanism for the modified spin transport characteristics for MnSi initiated films is that additional diffusion of Mn into the GaAs, widens the Schottky barrier contact region. These studies suggest that the ideal initiation sequence for Co2MnSi/GaAs (001) lateral spin valve devices is achieved by deposition of Co first.

Evaluation of distribution and manganese availability in soils under soybean cultivation

NASA Astrophysics Data System (ADS)

Mendes Coutinho, Edson Luiz; de Cássia Gomes São João, Andréia; Mendes Coutinho Neto, André; Corá, José Eduardo; Fernandes, Carolina

2013-04-01

Manganese (Mn) deficiency in soybean became a problem in Brazil, mainly, due to soil low fertility use or soil high pH due to incorrect lime use. However, the manganese deficiency have not been thoroughly investigated. The effect of Mn soil application on Mn distribution among exchangeable, organic matter, amorphous Fe and Al oxides, crystalline Fe and Al oxides, and residual fractions were studied on a Typic Quartzipsament (RQ), a clayey Typic Haplustox (LVA) and a sandy clay loam Typic Haplustox (LV), in a greenhouse experiment carried out in Jaboticabal (SP) - Brazil (21°14'05'' S and 48°17'09'' W). A complete randomized design with three replications of treatments in a 3 x 6 factorial arrangement (three soils and six manganese rates) was used. Five soybean plants were grown during 34 days in pots with 2.5 kg of soil. The Mn contents in these fractions were correlated with those extracted by DTPA and by Mehlich-1 extractants and with soybean shoot Mn contents. Mn rates (0, 5, 10, 20, 40 and 60 mg kg-1) were applied using manganese sulphate (MnSO4). In the Oxisols, most of the Mn was associated with the Fe and Al oxides (amorphous and crystalline) and residual fractions. In the sandy soil (RQ), higher contents were found in exchangeable and residual fractions. Exchangeable fraction was the most important Mn supplier to soybean plants. Multiple regression analysis showed that Mn extracted by DTPA and Mehlich-1 were associated with soil exchangeable fraction.

Low temperature production of large-grain polycrystalline semiconductors

DOEpatents

Naseem, Hameed A [Fayetteville, AR; Albarghouti, Marwan [Loudonville, NY

2007-04-10

An oxide or nitride layer is provided on an amorphous semiconductor layer prior to performing metal-induced crystallization of the semiconductor layer. The oxide or nitride layer facilitates conversion of the amorphous material into large grain polycrystalline material. Hence, a native silicon dioxide layer provided on hydrogenated amorphous silicon (a-Si:H), followed by deposited Al permits induced crystallization at temperatures far below the solid phase crystallization temperature of a-Si. Solar cells and thin film transistors can be prepared using this method.

Microstructural properties and evolution of nanoclusters in liquid Si during a rapid cooling process

NASA Astrophysics Data System (ADS)

Gao, T.; Hu, X.; Li, Y.; Tian, Z.; Xie, Q.; Chen, Q.; Liang, Y.; Luo, X.; Ren, L.; Luo, J.

2017-11-01

The formation of amorphous structures in Si during the rapid quenching process was studied based on molecular dynamics simulation by using the Stillinger-Weber potential. The evolution characteristics of nanoclusters during the solidification were analyzed by several structural analysis methods. The amorphous Si has been formed with many tetrahedral clusters and few nanoclusters. During the solidification, tetrahedral polyhedrons affect the local structures by their different positions and connection modes. The main kinds of polyhedrons randomly linked with one another to form an amorphous network structures in the system. The structural evolution of crystal nanocluster demonstrates that the nanocluster has difficulty to growth because of the high cooling rate of 1012 K/s.

Transport properties of Sb doped Si nanowires

NASA Astrophysics Data System (ADS)

Nukala, Prathyusha; Sapkota, Gopal; Gali, Pradeep; Usha, Philipose

2011-10-01

n-type Si nanowires were synthesized at ambient pressure using SiCl4 as Si source and Sb source as the dopant. Sb doping of 3-4 wt % was achieved through a post growth diffusion technique. The nanowires were found to have an amorphous oxide shell that developed post-growth; the thickness of the shell is estimated to be about 3-4 nm. The composition of the amorphous shell covering the crystalline Si core was determined by Raman spectroscopy, with evidence that the shell was an amorphous oxide layer. Optical characterization of the as-grown nanowires showed green emission, attributed to the presence of the oxide shell covering the Si nanowire core. Etching of the oxide shell was found to decrease the intensity of this green emission. A single undoped Si nanowire contacted in an FET type configuration was found to be p-type with channel mobility of 20 cm^2V-1S-1. Sb doped Si nanowires exhibited n-type behavior, compensating for the holes in the undoped nanowire. The doped nanowires had carrier mobility and concentration of 160 cm^2V-1S-1 and 9.6 x 10^18cm-3 respectively.

Lifetime of excitons localized in Si nanocrystals in amorphous silicon

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

Gusev, O. B.; Belolipetskiy, A. V., E-mail: alexey.belolipetskiy@mail.ioffe.ru; Yassievich, I. N.

2016-05-15

The introduction of nanocrystals plays an important role in improving the stability of the amorphous silicon films and increasing the carrier mobility. Here we report results of the study on the photoluminescence and its dynamics in the films of amorphous hydrogenated silicon containing less than 10% of silicon nanocrystals. The comparing of the obtained experimental results with the calculated probability of the resonant tunneling of the excitons localized in silicon nanocrystals is presented. Thus, it has been estimated that the short lifetime of excitons localized in Si nanocrystal is controlled by the resonant tunneling to the nearest tail state ofmore » the amorphous matrix.« less

Effects of dew point on selective oxidation of TRIP steels containing Si, Mn, and B

NASA Astrophysics Data System (ADS)

Lee, Suk-Kyu; Kim, Jong-Sang; Choi, Jin-Won; Kang, Namhyun; Cho, Kyung-Mox

2011-04-01

The selective oxidation of Si, Mn, and B on TRIP steel surfaces is a widely known phenomenon that occurs during heat treatment. However, the relationship between oxide formation and the annealing factors is not completely understood. This study examines the effect of the annealing conditions (dew point and annealing temperature) on oxide formation. A low dew point of -40 °C leads to the formation of Si-based oxides on the surface. A high dew point of -20 °C changes the oxide type to Mn-based oxides because the formation of Si oxides on the surface is suppressed by internal oxidation. Mn-based oxides exhibit superior wettability due to aluminothermic reduction during galvanizing.

First-principles calculation of the effects of tetragonal distortions on the Gilbert damping parameter of Co2MnSi

NASA Astrophysics Data System (ADS)

Pradines, B.; Arras, R.; Calmels, L.

2017-05-01

We present an ab initio study of the influence of the tetragonal distortion, on the static and dynamic (Gilbert damping parameter) magnetic properties of a Co2MnSi crystal. This tetragonal distortion can for instance be due to strain, when Co2MnSi is grown on a substrate with a small lattice mismatch. Using fully relativistic Korringa-Kohn-Rostoker (KKR) calculations, in conjunction with the coherent potential approximation (CPA) to describe atomic disorder and the linear response formalism to compute the Gilbert damping parameter, we show that a tetragonal distortion can substantially change the properties of Co2MnSi, in a way which depends on the kind of atomic disorder.

Cyclic and isothermal oxidation behavior at 1100 and 1200 C of Ni-20Cr, Ni-20Cr-3Mn, Ni-20Cr-3Si, and Ni-40Cr alloys

NASA Technical Reports Server (NTRS)

Lowell, C. E.

1973-01-01

Alloys of Ni-20Cr, Ni-20Cr-3Mn, Ni-20Cr-3Si, and Ni-40Cr were cyclically oxidized at 1100 and 1200 C for up to 100 hours. Oxidation behavior was judged by sample thickness and weight change, metallography, diffraction, and microprobe analysis. The least attacked were Ni-40Cr and Ni-20Cr-3Si. The alloy Ni-20Cr-3Mn was much less attacked than Ni-20Cr, but more than the other alloys. The formation of Cr2O3 accounted for the increased resistance of Ni-Cr and Ni-20Cr-3Si, and the formation of MnCr2O4 accounts for the improvement in Ni-20Cr-3mn over Ni-20Cr.

Transition from Irradiation-Induced Amorphization to Crystallization in Nanocrystalline Silicon Carbide

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

Jiang, Weilin; Jiao, Liang; Wang, Haiyan

2011-12-01

Response to irradiation of nanocrystalline 3C-SiC is studied using 2 MeV Au+ ions near the critical temperature for amorphization and is compared to the behavior of its monocrystalline counterpart under the identical irradiation conditions. The irradiated samples have been characterized using in-situ ion channeling, ex-situ x-ray diffraction, and helium ion microscopy. Compared to monocrystalline 3C-SiC, a faster amorphization process in the nanocrystalline material (average grain size = 3.3 nm) is observed at 500 K. However, the nanograin grows with increasing ion fluence at 550 K and the grain size tends to saturate at high fluences. The striking contrast demonstrates amore » sharp transition from irradiation-induced interface-driven amorphization at 500 K to crystallization at 550 K. The results could show potential impacts of nanocrystalline SiC on nuclear fuel cladding and structural components of next-generation nuclear energy systems.« less

Magnetic ordering in intermetallic La1-xTbxMn2Si2 compounds

NASA Astrophysics Data System (ADS)

Korotin, Dm. M.; Streltsov, S. V.; Gerasimov, E. G.; Mushnikov, N. V.; Zhidkov, I. S.; Kukharenko, A. I.; Finkelstein, L. D.; Cholakh, S. O.; Kurmaev, E. Z.

2018-05-01

The magnetic structures and magnetic phase transitions in intermetallic layered La1-xTbxMn2Si2 compounds (the ThCr2Si2-type structure) are investigated using the first-principles method and XPS measurements. The experimentally observed transition from ferromagnetic (FM) to antiferromagnetic (AFM) ordering of Mn sublattice with increase of terbium concentration is successfully reproduced in calculations for collinear magnetic moments model. The FM →AFM change of interplane magnetic ordering at small x is irrelevant to the number of f-electrons of the rare-earth ion. In contrast it was shown to be related to the Mn-Mn in-plane distance. Calculated Tb critical concentration for this transition x ≈ 0.14 corresponds to the Mn-Mn in-plane distance 0.289 nm, very close to the experimentally observed transition distance 0.287 nm. The crystal cell compression due to substitution increases an overlap between Mndxz,yz and the rare-earth ion d orbitals. Resulting hybridized states manifest themselves as an additional peak in the density of states. We suggest that a corresponding interlayer Mn-R-Mn superexchange interaction stabilizes AFM magnetic ordering in these compounds with Tb doping level x > 0.2 . The results of DFT calculations are in agreement with X-ray photoemission spectra for La1-xTbxMn2Si2 .

Quantitative Phase Analysis of Plasma-Treated High-Silica Materials

NASA Astrophysics Data System (ADS)

Kosmachev, P. V.; Abzaev, Yu. A.; Vlasov, V. A.

2018-06-01

The paper presents the X-ray diffraction (XRD) analysis of the crystal structure of SiO2 in two modifications, namely quartzite and quartz sand before and after plasma treatment. Plasma treatment enables the raw material to melt and evaporate after which the material quenches and condenses to form nanoparticles. The Rietveld refinement method is used to identify the lattice parameters of SiO2 phases. It is found that after plasma treatment SiO2 oxides are in the amorphous state, which are modeled within the microcanonical ensemble. Experiments show that amorphous phases are stable, and model X-ray reflection intensities approximate the experimental XRD patterns with fine precision. Within the modeling, full information is obtained for SiO2 crystalline and amorphous phases, which includes atom arrangement, structural parameters, atomic population of silicon and oxygen atoms in lattice sites.

Microstructure, soft magnetic properties and applications of amorphous Fe-Co-Si-B-Mo-P alloy

NASA Astrophysics Data System (ADS)

Hasiak, Mariusz; Miglierini, Marcel; Łukiewski, Mirosław; Łaszcz, Amadeusz; Bujdoš, Marek

2018-05-01

DC thermomagnetic properties of Fe51Co12Si16B8Mo5P8 amorphous alloy in the as-quenched and after annealing below crystallization temperature are investigated. They are related to deviations in the microstructure as revealed by Mössbauer spectrometry. Study of AC magnetic properties, i.e. hysteresis loops, relative permeability and core losses versus maximum induction was aimed at obtaining optimal initial parameters for simulation process of a resonant transformer for a rail power supply converter. The results obtained from numerical analyses including core losses, winding losses, core mass, and dimensions were compared with the same parameters calculated for Fe-Si alloy and ferrite. Moreover, Steinmetz coefficients were also calculated for the as-quenched Fe51Co12Si16B8Mo5P8 amorphous alloy.

Freestanding ultrathin single-crystalline SiC substrate by MeV H ion-slicing

NASA Astrophysics Data System (ADS)

Jia, Qi; Huang, Kai; You, Tiangui; Yi, Ailun; Lin, Jiajie; Zhang, Shibin; Zhou, Min; Zhang, Bin; Zhang, Bo; Yu, Wenjie; Ou, Xin; Wang, Xi

2018-05-01

SiC is a widely used wide-bandgap semiconductor, and the freestanding ultrathin single-crystalline SiC substrate provides the material platform for advanced devices. Here, we demonstrate the fabrication of a freestanding ultrathin single-crystalline SiC substrate with a thickness of 22 μm by ion slicing using 1.6 MeV H ion implantation. The ion-slicing process performed in the MeV energy range was compared to the conventional case using low-energy H ion implantation in the keV energy range. The blistering behavior of the implanted SiC surface layer depends on both the implantation temperature and the annealing temperature. Due to the different straggling parameter for two implant energies, the distribution of implantation-induced damage is significantly different. The impact of implantation temperature on the high-energy and low-energy slicing was opposite, and the ion-slicing SiC in the MeV range initiates at a much higher temperature.

Examining metallic glass formation in LaCe:Nb by ion implantation

DOE PAGES

Sisson, Richard; Reinhart, Cameron; Bridgman, Paul; ...

2017-01-01

In order to combine niobium (Nb) with lanthanum (La) and cerium (Ce), Nb ions were deposited within a thin film of these two elements. According to the Hume-Rothery rules, these elements cannot be combined into a traditional crystalline metallic solid. The creation of an amorphous metallic glass consisting of Nb, La, and Ce is then investigated. Amorphous metallic glasses are traditionally made using fast cooling of a solution of molten metals. In this paper, we show the results of an experiment carried out to form a metallic glass by implanting 9 MeV Nb 3+ atoms into a thin film ofmore » La and Ce. Prior to implantation, the ion volume distribution is calculated by Monte Carlo simulation using the SRIM tool suite. As a result, using multiple methods of electron microscopy and material characterization, small quantities of amorphous metallic glass are indeed identified.« less

Tribocorrosion Failure Mechanism of TiN/SiOx Duplex Coating Deposited on AISI304 Stainless Steel.

PubMed

Chen, Qiang; Xie, Zhiwen; Chen, Tian; Gong, Feng

2016-11-26

TiN/SiO x duplex coatings were synthesized on AISI304 stainless steel by plasma immersion ion implantation and deposition (PIIID) followed by radio frequency magnetron sputtering (RFMS). The microstructure and tribocorrosion failure behaviors of the duplex coatings were investigated by X-ray diffraction, X-ray photoelectron spectroscopy, scanning electron microscopy, atomic force microscopy, reciprocating-sliding tribometer, and electrochemical tests. The as-deposited duplex coating had a two-layered columnar growth structure consisting of face-centered cubic TiN and amorphous SiO x . Sliding tests showed that the TiN interlayer had good adhesion with the substrate, but the SiO x layer suffered from severe delamination failure. Friction force induced a number of micro-cracks in the coating, which provided channels for the diffusion of NaCl solution. The tribocorrosion test showed that the duplex coating exhibited a lower wear-performance in NaCl solution than in ambient atmosphere. Multi-scale chloride ion corrosion occurred simultaneously and substantially degraded the bonding strength of the columnar crystals or neighboring layers. Force-corrosion synergy damage eventually led to multi-degradation failure of the duplex coating. The presented results provide a comprehensive understanding of the tribocorrosion failure mechanism in coatings with duplex architecture.

X-ray photoelectron study of Si+ ion implanted polymers

NASA Astrophysics Data System (ADS)

Tsvetkova, T.; Balabanov, S.; Bischoff, L.; Krastev, V.; Stefanov, P.; Avramova, I.

2010-11-01

X-ray photoelectron spectroscopy was used to characterize different polymer materials implanted with low energy Si+ ions (E=30 keV, D= 1.1017 cm-2). Two kinds of polymers were studied - ultra-high-molecular-weight poly-ethylene (UHMWPE), and poly-methyl-methacrylate (PMMA). The non-implanted polymer materials show the expected variety of chemical bonds: carbon-carbon, carbon being three- and fourfold coordinated, and carbon-oxygen in the case of PMMA samples. The X-ray photoelectron and Raman spectra show that Si+ ion implantation leads to the introduction of additional disorder in the polymer material. The X-ray photoelectron spectra of the implanted polymers show that, in addition to already mentioned bonds, silicon creates new bonds with the host elements - Si-C and Si-O, together with additional Si dangling bonds as revealed by the valence band study of the implanted polymer materials.

The effects of ion implantation on the tribology of perfluoropolyether-lubricated 440C stainless steel couples

NASA Technical Reports Server (NTRS)

Shogrin, Bradley; Jones, William R., Jr.; Wilbur, Paul J.; Pilar, Herrera-Fierro; Williamson, Don L.

1995-01-01

The lubricating lifetime of thin films of a perfluoropolyether (PFPE) based on hexafluoropropene oxide in the presence of ion implanted 440C stainless steel is presented. Stainless steel discs, either unimplanted or implanted with N2, C, Ti, Ti + N2, or Ti + C had a thin film of PFPE (60-400 A) applied to them reproducibly (+/- 20 percent) and uniformly (+/- 15 percent) using a device developed for this study. The lifetimes of these films were quantified by measuring the number of sliding-wear cycles required to induce an increase in the friction coefficient from an initial value characteristic of the lubricated wear couple to a final, or failure value, characteristic of an unlubricated, unimplanted couple. The tests were performed in a dry nitrogen atmosphere (less than 1 percent RH) at room temperature using a 3 N normal load with a relative sliding speed of 0.05 m/s. The lubricated lifetime of the 440C couple was increased by an order of magnitude by implanting the disc with Ti. Ranked from most to least effective, the implanted species were: Ti; Ti+C; unimplanted; N2; C approximately equals Ti+N2. The mechanism postulated to explain these results involves the formation of a passivating or reactive layer which inhibits or facilitates the production of active sites. The corresponding surface microstructures induced by ion implantation, obtained using x-ray diffraction and conversion electron Mossbauer spectroscopy, ranked from most to least effective in enhancing lubricant lifetime were: amorphous Fe-Cr-Ti; amorphous Fe-Cr-Ti-C + TiC; unimplanted; epsilon-(Fe,Cr)(sub x)N, x = 2 or 3; amorphous Fe-Cr-C approximately equals amorphous Fe-Cr-Ti-N.

Integral bypass diodes in an amorphous silicon alloy photovoltaic module

NASA Technical Reports Server (NTRS)

Hanak, J. J.; Flaisher, H.

1991-01-01

Thin-film, tandem-junction, amorphous silicon (a-Si) photovoltaic modules were constructed in which a part of the a-Si alloy cell material is used to form bypass protection diodes. This integral design circumvents the need for incorporating external, conventional diodes, thus simplifying the manufacturing process and reducing module weight.

The mixing mechanism during lithiation of Si negative electrode in Li-ion batteries: an ab initio molecular dynamics study.

PubMed

Johari, Priya; Qi, Yue; Shenoy, Vivek B

2011-12-14

In order to realize Si as a negative electrode material in commercial Li-ion batteries, it is important to understand the mixing mechanism of Li and Si, and stress evolution during lithiation in Si negative electrode of Li-ion batteries. Available experiments mainly provide the diffusivity of Li in Si as an averaged property, neglecting information regarding diffusivity of Si. However, if Si can diffuse as fast as Li, the stress generated during Li diffusion can be reduced. We, therefore, studied the diffusivity of Li as well as Si atoms in the Si-anode of Li-ion battery using an ab initio molecular dynamics-based methodology. The electrochemical insertion of Li into crystalline Si prompts a crystalline-to-amorphous phase transition. We considered this situation and thus examined the diffusion kinetics of Li and Si atoms in both crystalline and amorphous Si. We find that Li diffuses faster in amorphous Si as compared to crystalline Si, while Si remains relatively immobile in both cases and generates stresses during lithiation. To further understand the mixing mechanism and to relate the structure with electrochemical mixing, we analyzed the evolution of the structure during lithiation and studied the mechanism of breaking of Si-Si network by Li. We find that Li atoms break the Si rings and chains and create ephemeral structures such as stars and boomerangs, which eventually transform to Si-Si dumbbells and isolated Si atoms in the LiSi phase. Our results are found to be in agreement with the available experimental data and provide insights into the mixing mechanism of Li and Si in Si negative electrode of Li-ion batteries.

Nanoscale density variations induced by high energy heavy ions in amorphous silicon nitride and silicon dioxide

NASA Astrophysics Data System (ADS)

Mota-Santiago, P.; Vazquez, H.; Bierschenk, T.; Kremer, F.; Nadzri, A.; Schauries, D.; Djurabekova, F.; Nordlund, K.; Trautmann, C.; Mudie, S.; Ridgway, M. C.; Kluth, P.

2018-04-01

The cylindrical nanoscale density variations resulting from the interaction of 185 MeV and 2.2 GeV Au ions with 1.0 μm thick amorphous SiN x :H and SiO x :H layers are determined using small angle x-ray scattering measurements. The resulting density profiles resembles an under-dense core surrounded by an over-dense shell with a smooth transition between the two regions, consistent with molecular-dynamics simulations. For amorphous SiN x :H, the density variations show a radius of 4.2 nm with a relative density change three times larger than the value determined for amorphous SiO x :H, with a radius of 5.5 nm. Complementary infrared spectroscopy measurements exhibit a damage cross-section comparable to the core dimensions. The morphology of the density variations results from freezing in the local viscous flow arising from the non-uniform temperature profile in the radial direction of the ion path. The concomitant drop in viscosity mediated by the thermal conductivity appears to be the main driving force rather than the presence of a density anomaly.

The composition of secondary amorphous phases under different environmental conditions

NASA Astrophysics Data System (ADS)

Smith, R.; Rampe, E. B.; Horgan, B. H. N.; Dehouck, E.; Morris, R. V.

2017-12-01

X-ray diffraction (XRD) patterns measured by the CheMin instrument on the Mars Science Laboratory Curiosity rover demonstrate that amorphous phases are major components ( 15-60 wt%) of all rock and soil samples in Gale Crater. The nature of these phases is not well understood and could be any combination of primary (e.g., glass) and secondary (e.g., silica, ferrihydrite) phases. Secondary amorphous phases are frequently found as weathering products in soils on Earth, but these materials remain poorly characterized. Here we study a diverse suite of terrestrial samples including: sediments from recently de-glaciated volcanoes (Oregon), modern volcanic soils (Hawaii), and volcanic paleosols (Oregon) in order to determine how formation environment, climate, and diagenesis affect the abundance and composition of amorphous phases. We combine bulk XRD mineralogy with bulk chemical compositions (XRF) to calculate the abundance and bulk composition of the amorphous materials in our samples. We then utilize scanning transmission electron microscopy (STEM) and energy dispersive x-ray spectroscopy (EDS) to study the composition of individual amorphous phases at the micrometer scale. XRD analyses of 8 samples thus far indicate that the abundance of amorphous phases are: modern soils (20-80 %) > paleosols (15-40 %) > glacial samples (15-30 %). Initial calculations suggest that the amorphous components consist primarily of SiO2, Al2O3, TiO2, FeO and Fe2O3, with minor amounts of other oxides (e.g., MgO, CaO, Na2O). Compared to their respective crystalline counterparts, calculations indicate bulk amorphous components enriched in SiO2 for the glacial sample, and depleted in SiO2 for the modern soil and paleosol samples. STEM analyses reveal that the amorphous components consist of a number of different phases. Of the two samples analyzed using STEM thus far, the secondary amorphous phases have compositions with varying ratios of SiO2, Al2O3, TiO2, and Fe-oxides, consistent with mass balance calculation results, but inconsistent with well-known amorphous phase compositions (e.g., allophane, ferrihydrite). These results show that a number of secondary amorphous phases can form within a single soil environment. Continued analysis can help determine whether compositional trends can be linked to environmental factors.

Anti-site-induced diverse diluted magnetism in LiMgPdSb-type CoMnTiSi alloy

NASA Astrophysics Data System (ADS)

Lin, T. T.; Dai, X. F.; Guo, R. K.; Cheng, Z. X.; Wang, L. Y.; Wang, X. T.; Liu, G. D.

2017-02-01

The effect of three kinds of anti-site disorder to electronic structure and magnetic properties of the LiMgPdSb-type CoMnTiSi alloy are investigated. It was found the Mn-Ti anti-site disorder can induce the diluted magnetism in CoMnTiSi matrix. The magnetic structure has an oscillation between the ferromagnetic and antiferromagnetic states with the different degree of Mn-Ti anti-site disorder. Two novel characteristics: the diluted antiferromagnetic half-metallicity and the diluted zero-gap half-metallity are found in the different degree range of the Mn-Ti anti-site disorder. The Co-Mn and Co-Ti anti-site disorder have little effect on the magnetic properties. The width of energy gap and the intensity of DOS at the Fermi level can be adjusted by the degree of Co-Mn or Co-Ti anti-site disorder. The independent control to the carrier concentration and magnetization can be realized by introducing the different anti-site disorder.

A Step toward High-Energy Silicon-Based Thin Film Lithium Ion Batteries.

PubMed

Reyes Jiménez, Antonia; Klöpsch, Richard; Wagner, Ralf; Rodehorst, Uta C; Kolek, Martin; Nölle, Roman; Winter, Martin; Placke, Tobias

2017-05-23

The next generation of lithium ion batteries (LIBs) with increased energy density for large-scale applications, such as electric mobility, and also for small electronic devices, such as microbatteries and on-chip batteries, requires advanced electrode active materials with enhanced specific and volumetric capacities. In this regard, silicon as anode material has attracted much attention due to its high specific capacity. However, the enormous volume changes during lithiation/delithiation are still a main obstacle avoiding the broad commercial use of Si-based electrodes. In this work, Si-based thin film electrodes, prepared by magnetron sputtering, are studied. Herein, we present a sophisticated surface design and electrode structure modification by amorphous carbon layers to increase the mechanical integrity and, thus, the electrochemical performance. Therefore, the influence of amorphous C thin film layers, either deposited on top (C/Si) or incorporated between the amorphous Si thin film layers (Si/C/Si), was characterized according to their physical and electrochemical properties. The thin film electrodes were thoroughly studied by means of electrochemical impedance spectroscopy, Raman spectroscopy, X-ray photoelectron spectroscopy, and atomic force microscopy. We can show that the silicon thin film electrodes with an amorphous C layer showed a remarkably improved electrochemical performance in terms of capacity retention and Coulombic efficiency. The C layer is able to mitigate the mechanical stress during lithiation of the Si thin film by buffering the volume changes and to reduce the loss of active lithium during solid electrolyte interphase formation and cycling.

Interactions between DPPC as a component of lung surfactant and amorphous silica nanoparticles investigated by HILIC-ESI-MS.

PubMed

Silina, Yuliya E; Welck, Jennifer; Kraegeloh, Annette; Koch, Marcus; Fink-Straube, Claudia

2016-09-01

This paper reports a rapid HILIC-ESI-MS assay to quantify dipalmitoylphosphatidylcholine (DPPC) as component of lung surfactant for nanosafety studies. The technique was used to investigate the concentration-dependent sorption of DPPC to two-sizes of amorphous SiO2 nanoparticles (SiO2-NPs) in a MeOH:H2O (50/50v/v) mixture and in cell culture medium. In MeOH:H2O (50/50v/v), the sorption of DPPC was positively correlated with the nanoparticles concentration. A substantial affinity of small amorphous SiO2-NPs (25nm) to DPPC standard solution compared to bigger SiO2-NPs (75nm) was not confirmed for biological specimens. After dispersion of SiO2-NPs in DPPC containing cell culture medium, the capacity of the SiO2-NPs to bind DPPC was reduced in comparison to a mixture of MeOH:H2O (50/50v/v) regardless from the nanoparticles size. Furthermore, HILIC-ESI-MS revealed that A549 cells internalized DPPC during growth in serum containing medium complemented with DPPC. This finding was in a good agreement with the potential of alveolar type II cells to recycle surfactant components. Binding of lipids present in the cell culture medium to amorphous SiO2-NPs was supported by means of HILIC-ESI-MS, TEM and ICP-MS independently. Copyright © 2016 Elsevier B.V. All rights reserved.

Oxidation Protection of Porous Reaction-Bonded Silicon Nitride

NASA Technical Reports Server (NTRS)

Fox, D. S.

1994-01-01

Oxidation kinetics of both as-fabricated and coated reaction-bonded silicon nitride (RBSN) were studied at 900 and 1000 C with thermogravimetry. Uncoated RBSN exhibited internal oxidation and parabolic kinetics. An amorphous Si-C-O coating provided the greatest degree of protection to oxygen, with a small linear weight loss observed. Linear weight gains were measured on samples with an amorphous Si-N-C coating. Chemically vapor deposited (CVD) Si3N4 coated RBSN exhibited parabolic kinetics, and the coating cracked severely. A continuous-SiC-fiber-reinforced RBSN composite was also coated with the Si-C-O material, but no substantial oxidation protection was observed.

Effect of Co Addition on the Microstructure, Martensitic Transformation and Shape Memory Behavior of Fe-Mn-Si Alloys

NASA Astrophysics Data System (ADS)

Maji, Bikas C.; Krishnan, Madangopal; Sujata, M.; Gouthama; Ray, Ranjit K.

2013-01-01

The effect of Co addition has been studied in Fe-30Mn-6Si- xCo ( x = 0 to 9 wt pct) shape memory alloys in terms of their microstructure, martensitic transformation and shape recovery. Microstructural investigations reveal that in Fe-Mn-Si-Co alloys, the microstructure remains single-phase austenite (γ) up to 5 pct Co and beyond that becomes two-phase comprising γ and off-stoichiometric (Fe,Co)5Mn3Si2 intermetallic π-phases. The forward γ-ɛ martensite transformation start temperature ( M S) decreases with the addition of Co up to 5 pct, and alloys containing more than 5 pct Co, show slightly higher M S possibly on account of two-phase microstructure. Unlike M S, the ɛ-γ reverse transformation start temperature ( A S) has been found to remain almost unaltered by Co addition. In general, addition of Co to Fe-Mn-Si alloys deteriorates shape recovery due to decreasing resistance to plastic yielding concomitant with the formation of stress induced ɛ martensite. However, there is an improvement in shape recovery beyond 5 pct Co addition, possibly due to the strengthening effect arising from the presence of (Fe,Co)5Mn3Si2 precipitates within the two-phase microstructure and due to higher amount of stress induced ɛ martensite.

Comparative study of helimagnets MnSi and Cu2OSeO3 at high pressures

NASA Astrophysics Data System (ADS)

Stishov, Sergei; Sidorov, Vladimir; Petrova, Alla; Berdonosov, Peter; Dolgikh, Valery

2014-03-01

The heat capacity of helical magnets Cu2OSeO3 and MnSi has been investigated at high pressures by the ac-calorimetric technique. Despite the differing nature of their magnetic moments, Cu2OSeO3 and MnSi demonstrate a surprising similarity in behavior of their magnetic and thermodynamic properties at the phase transition. Two characteristic features of the heat capacity at the phase transitions of both substances (peak and shoulder) behave also in a similar way at high pressures if analyzed as a function of temperature. This probably implies that the longitudinal spin fluctuations typical of weak itinerant magnets like MnSi contribute little to the phase transition. The shoulders of the heat capacity curves shrink with decreasing temperature suggesting that they arise from classical fluctuations. In case of MnSi the sharp peak and shoulder at the heat capacity disappear simultaneously probably signifying the existence of a tricritical point and confirming the fluctuation nature of the first order phase transition in MnSi as well as in Cu2OSeO3. This work was supported by the Russian Foundation for Basic Research (grant 12-02-00376-a, 12-03-92604), Program of the Physics Department of RAS on Strongly Correlated Electron Systems and Program of the Presidium of RAS on Strongly Compressed Matter.

Structural simplicity as a restraint on the structure of amorphous silicon

NASA Astrophysics Data System (ADS)

Cliffe, Matthew J.; Bartók, Albert P.; Kerber, Rachel N.; Grey, Clare P.; Csányi, Gábor; Goodwin, Andrew L.

2017-06-01

Understanding the structural origins of the properties of amorphous materials remains one of the most important challenges in structural science. In this study, we demonstrate that local "structural simplicity", embodied by the degree to which atomic environments within a material are similar to each other, is a powerful concept for rationalizing the structure of amorphous silicon (a -Si) a canonical amorphous material. We show, by restraining a reverse Monte Carlo refinement against pair distribution function (PDF) data to be simpler, that the simplest model consistent with the PDF is a continuous random network (CRN). A further effect of producing a simple model of a -Si is the generation of a (pseudo)gap in the electronic density of states, suggesting that structural homogeneity drives electronic homogeneity. That this method produces models of a -Si that approach the state-of-the-art without the need for chemically specific restraints (beyond the assumption of homogeneity) suggests that simplicity-based refinement approaches may allow experiment-driven structural modeling techniques to be developed for the wide variety of amorphous semiconductors with strong local order.

Electron irradiation induced amorphous SiO2 formation at metal oxide/Si interface at room temperature; electron beam writing on interfaces.

PubMed

Gurbán, S; Petrik, P; Serényi, M; Sulyok, A; Menyhárd, M; Baradács, E; Parditka, B; Cserháti, C; Langer, G A; Erdélyi, Z

2018-02-01

Al 2 O 3 (5 nm)/Si (bulk) sample was subjected to irradiation of 5 keV electrons at room temperature, in a vacuum chamber (pressure 1 × 10 -9 mbar) and formation of amorphous SiO 2 around the interface was observed. The oxygen for the silicon dioxide growth was provided by the electron bombardment induced bond breaking in Al 2 O 3 and the subsequent production of neutral and/or charged oxygen. The amorphous SiO 2 rich layer has grown into the Al 2 O 3 layer showing that oxygen as well as silicon transport occurred during irradiation at room temperature. We propose that both transports are mediated by local electric field and charged and/or uncharged defects created by the electron irradiation. The direct modification of metal oxide/silicon interface by electron-beam irradiation is a promising method of accomplishing direct write electron-beam lithography at buried interfaces.

Intrinsic charge trapping in amorphous oxide films: status and challenges

NASA Astrophysics Data System (ADS)

Strand, Jack; Kaviani, Moloud; Gao, David; El-Sayed, Al-Moatasem; Afanas’ev, Valeri V.; Shluger, Alexander L.

2018-06-01

We review the current understanding of intrinsic electron and hole trapping in insulating amorphous oxide films on semiconductor and metal substrates. The experimental and theoretical evidences are provided for the existence of intrinsic deep electron and hole trap states stemming from the disorder of amorphous metal oxide networks. We start from presenting the results for amorphous (a) HfO2, chosen due to the availability of highest purity amorphous films, which is vital for studying their intrinsic electronic properties. Exhaustive photo-depopulation spectroscopy measurements and theoretical calculations using density functional theory shed light on the atomic nature of electronic gap states responsible for deep electron trapping observed in a-HfO2. We review theoretical methods used for creating models of amorphous structures and electronic structure calculations of amorphous oxides and outline some of the challenges in modeling defects in amorphous materials. We then discuss theoretical models of electron polarons and bi-polarons in a-HfO2 and demonstrate that these intrinsic states originate from low-coordinated ions and elongated metal-oxygen bonds in the amorphous oxide network. Similarly, holes can be captured at under-coordinated O sites. We then discuss electron and hole trapping in other amorphous oxides, such as a-SiO2, a-Al2O3, a-TiO2. We propose that the presence of low-coordinated ions in amorphous oxides with electron states of significant p and d character near the conduction band minimum can lead to electron trapping and that deep hole trapping should be common to all amorphous oxides. Finally, we demonstrate that bi-electron trapping in a-HfO2 and a-SiO2 weakens Hf(Si)–O bonds and significantly reduces barriers for forming Frenkel defects, neutral O vacancies and O2‑ ions in these materials. These results should be useful for better understanding of electronic properties and structural evolution of thin amorphous films under carrier injection conditions.

Engineering helimagnetism in MnSi thin films

NASA Astrophysics Data System (ADS)

Zhang, S. L.; Chalasani, R.; Baker, A. A.; Steinke, N.-J.; Figueroa, A. I.; Kohn, A.; van der Laan, G.; Hesjedal, T.

2016-01-01

Magnetic skyrmion materials have the great advantage of a robust topological magnetic structure, which makes them stable against the superparamagnetic effect and therefore a candidate for the next-generation of spintronic memory devices. Bulk MnSi, with an ordering temperature of 29.5 K, is a typical skyrmion system with a propagation vector periodicity of ˜18 nm. One crucial prerequisite for any kind of application, however, is the observation and precise control of skyrmions in thin films at room-temperature. Strain in epitaxial MnSi thin films is known to raise the transition temperature to 43 K. Here we show, using magnetometry and x-ray spectroscopy, that the transition temperature can be raised further through proximity coupling to a ferromagnetic layer. Similarly, the external field required to stabilize the helimagnetic phase is lowered. Transmission electron microscopy with element-sensitive detection is used to explore the structural origin of ferromagnetism in these Mn-doped substrates. Our work suggests that an artificial pinning layer, not limited to the MnSi/Si system, may enable room temperature, zero-field skyrmion thin-film systems, thereby opening the door to device applications.

A new photoluminescence emission peak of ZnO SiO2 nanocomposites and its energy transfer to Eu3+ ions

NASA Astrophysics Data System (ADS)

Hong, Jian-He; Cong, Chang-Jie; Zhang, Zhi-Guo; Zhang, Ke-Li

2007-07-01

This work reports a new photoluminescence (PL) emission peak at about 402 nm from amorphous ZnO nanoparticles in a silica matrix, and the energy transfer from it to Eu3+ ions. The amorphous ZnO SiO2 nanocomposites were prepared by the sol gel method, which is verified by X-ray diffraction (XRD) profiles and FT IR spectra. The luminescence emission spectra are fitted by four Gauss profiles, two of which at longer wavelength are due to the defects of the material and the others to amorphous ZnO nanoparticles and the Zn O Si interface state. With the reduction of Zn/Si ratio and diethanolamine, the relative intensities of visible emission decrease. The weak visible emission is due to the reduction of defects after calcined at high temperature. The new energy state at the Zn O Si interface results in strong emission at about 402 nm. When Eu3+ ions are co-doped, weak energy transfer from ZnO SiO2 nanocomposites to Eu3+ emission are observed in the excitation spectra.

Interdiffusion in nanometer-scale multilayers investigated by in situ low-angle x-ray diffraction

NASA Astrophysics Data System (ADS)

Wang, Wei-Hua; Bai, Hai Yang; Zhang, Ming; Zhao, J. H.; Zhang, X. Y.; Wang, W. K.

1999-04-01

An in situ low-angle x-ray diffraction technique is used to investigate interdiffusion phenomena in various metal-metal and metal-amorphous Si nanometer-scale compositionally modulated multilayers (ML's). The temperature-dependent interdiffusivities are obtained by accurately monitoring the decay of the first-order modulation peak as a function of annealing time. Activation enthalpies and preexponential factors for the interdiffusion in the Fe-Ti, Ag-Bi, Fe-Mo, Mo-Si, Ni-Si, Nb-Si, and Ag-Si ML's are determined. Activation enthalpies and preexponential factors for the interdiffusion in the ML's are very small compared with that in amorphous alloys and crystalline solids. The relation between the atomic-size difference and interdiffusion in the ML's are investigated. The observed interdiffusion characteristics are compared with that in amorphous alloys and crystalline α-Zr, α-Ti, and Si. The experimental results suggest that a collective atomic-jumping mechanism govern the interdiffusion in the ML's, the collective proposal involving 8-15 atoms moving between extended nonequilibrium defects by thermal activation. The role of the interdiffusion in the solid-state reaction in the ML's is also discussed.

Improved Battery Performance of Nanocrystalline Si Anodes Utilized by Radio Frequency (RF) Sputtered Multifunctional Amorphous Si Coating Layers.

PubMed

Ahn, In-Kyoung; Lee, Young-Joo; Na, Sekwon; Lee, So-Yeon; Nam, Dae-Hyun; Lee, Ji-Hoon; Joo, Young-Chang

2018-01-24

Despite the high theoretical specific capacity of Si, commercial Li-ion batteries (LIBs) based on Si are still not feasible because of unsatisfactory cycling stability. Herein, amorphous Si (a-Si)-coated nanocrystalline Si (nc-Si) formed by versatile radio frequency (RF) sputtering systems is proposed as a promising anode material for LIBs. Compared to uncoated nc-Si (retention of 0.6% and Coulombic efficiency (CE) of 79.7%), the a-Si-coated nc-Si (nc-Si@a-Si) anodes show greatly improved cycling retention (C 50th /C first ) of ∼50% and a first CE of 86.6%. From the ex situ investigation with electrochemical impedance spectroscopy (EIS) and cracked morphology during cycling, the a-Si layer was found to be highly effective at protecting the surface of the nc-Si from the formation of solid-state electrolyte interphases (SEI) and to dissipate the mechanical stress upon de/lithiation due to the high fracture toughness.

Time-of-flight secondary ion mass spectrometry studies of cluster ion analysis for semiconductors and diffusion of manganese in gallium arsenide at low temperatures

NASA Astrophysics Data System (ADS)

Goacher, Robyn Elizabeth

Secondary Ion Mass Spectrometry (SIMS) is an established method for the quantitative analysis of dopants in semiconductors. The quasi-parallel mass acquisition of Time-of-Flight SIMS, along with the development of polyatomic primary ions, have rapidly increased the use of SIMS for analysis of organic and biological specimens. However, the advantages and disadvantages of using cluster primary ions for quantitative analysis of inorganic materials are not clear. The research described in this dissertation investigates the consequences of using polyatomic primary ions for the analysis of inorganic compounds in ToF-SIMS. Furthermore, the diffusion of Mn in GaAs, which is important in Spintronic material applications such as spin injection, is also studied by quantitative ToF-SIMS depth profiling. In the first portion of this work, it was discovered that primary ion bombardment of pre-sputtered compound semiconductors GaAs and InP for the purpose of spectral analysis resulted in the formation of cluster secondary ions, as well as atomic secondary ions (Chapter 2). In particular, bombardment using a cluster primary ion such as Bi3q + or C60q+ resulted in higher yields of high-mass cluster secondary ions. These cluster secondary ions did not have bulk stoichiometry, "non-stoichiometric", in contrast to the paradigm of stoichiometric cluster ions generated from salts. This is attributed to the covalent bonding of the compound semiconductors, as well as to preferential sputtering. The utility of high-mass cluster secondary ions in depth profiling is also discussed. Relative sensitivity factors (RSFs) calculated for ion-implanted Fe and Mn samples in GaAs also exhibit differences based on whether monatomic or polyatomic primary ions are utilized (Chapter 3). These RSFs are important for the quantitative conversion of intensity to concentration. When Bi 32+ primary ions are used for analysis instead of Bi + primary ions, there is a significantly higher proportion of Mn and Fe ions present in the spectra, as referenced to the matrix species. The magnitude of this effect differs depending on the sputtering ion, Cs or C60. The use of C60cluster primary ions for depth profiling of GaAs is also investigated (Chapter 4). In particular, for quantitative depth profiling, parameters such as depth resolution, ion and sputter yields, and relative sensitivity factors are pertinent to profiling thin layered structures quantitatively and quickly. C60 sputtering is compared to Cs sputtering in all of these aspects. It is found that 10 keV C60+ is advantageous for the analysis of metals (such as Au contacts on Si) but that previously reported roughness problems prohibit successful analysis in Si. For Al delta layers and quantum wells in GaAs, C60 q+ sputtering induced very little roughness in the sample, and resulted in high ion yields and excellent signal-to-noise as compared to Cs+ sputtering. However, the depth resolution of C60 is at best equivalent to 1 keV Cs+ and does not extend into the sub 2-nm range. Furthermore, C60 sputtering results in significant carbon implantation. In the second portion of this work, quantitative ToF-SIMS depth profiling was used to evaluate the diffusion of Mn into GaAs. Samples were prepared by Molecular Beam Epitaxy in the department of Physics. Mn diffusion from MnAs was investigated first, and Mn diffusion from layered epitaxial structures of GaAs / Ga1-xMnxAs / GaAs was investigated second. Diffusion experiments were conducted by annealing portions of the samples in sealed glass ampoules at low temperatures (200-400°C). Different sputtering rates were measured for MnAs and GaAs and the measured depth profiles were corrected for these effects. RSFs measured for Mn ion-implanted standards were used to calibrate the intensity scale. For diffusion from MnAs, thin MnAs layers resulted in no measurable changes except in the surface transient. For thick MnAs layers, it was determined that substantial loss of As occurred at 400°C, resulting in severe sample roughening, which inhibited proper SIMS analysis. Results for the diffusion of Mn out of a thick buried layer of Ga1-xMnxAs show that annealing induces diffusion of Mn species from the Ga1-xMnxAs layer into the neighboring GaAs with an activation energy of 0.69+/-0.09 eV. This results in doping of the GaAs layer, which is detrimental to spin injection for Spintronics devices.

Effect of Mn and AlTiB Addition and Heattreatment on the Microstructures and Mechanical Properties of Al-Si-Fe-Cu-Zr Alloy.

PubMed

Yoo, Hyo-Sang; Kim, Yong-Ho; Lee, Seong-Hee; Son, Hyeon-Taek

2018-09-01

The microstructure and mechanical properties of as-extruded Al-0.1 wt%Si-0.2 wt%Fe- 0.4 wt%Cu-0.04 wt%Zr-xMn-xAlTiB (x = 1.0 wt%) alloys under various annealing processes were investigated and compared. After the as-cast billets were kept at 400 °C for 1 hr, hot extrusion was carried out with a reduction ratio of 38:1. In the case of the as-extruded Al-Si-Fe-Cu-Zr alloy at annealed at 620 °C, large equiaxed grain was observed. When the Mn content is 1.0 wt%, the phase exhibits a skeleton morphology, the phase formation in which Mn participated. Also, the volume fraction of the intermetallic compounds increased with Mn and AlTiB addition. For the Al-0.1Si-0.2Fe-0.4Cu-0.04Zr alloy with Mn and AlTiB addition from 1.0 wt%, the ultimate tensile strength increased from 100.47 to 119.41 to 110.49 MPa. The tensile strength of the as-extruded alloys improved with the addition of Mn and AlTiB due to the formation of Mn and AlTiB-containing intermetallic compounds.

Understanding the behavior of buried Bi nanostructures from first principles

NASA Astrophysics Data System (ADS)

Sims, Hunter; Pantelides, Sokrates; Song, Jiaming; Hudak, Bethany; Lupini, Andrew; Snijders, Paul

Bismuth dopants in silicon provide several advantages over other n-type options such as phosphorus for usage as quantum bits (qubits). Self-assembled Bi nanolines on Si (100) surfaces may provide a means of introducing these dopants with greater control over placement and with less damage to the host system than is possible using ion implantation. However, these structures have thus far only been observed in vacuum, limiting their usefulness for application. We examine Bi nanolines overgrown with amorphous Si using density functional theory, comparing our findings with observations from scanning tunneling microscopy (STM) and atomic-resolution scanning transmission electron microscopy (STEM) in order to better understand the way in which the Si surface is influenced by both the Bi ad-dimers and the capping layer. We compare the thermodynamic stability of the generally accepted haiku defect core to the modified core that we observe and offer insight from total energy calculations into how the overgrowth process affects the nanolines. Supported by Department of Energy Grant DE-FG02- 09ER46554 (VU) and by the Laboratory Directed Research and Development Program of Oak Ridge National Laboratory, managed by UT-Battelle, LLC, for the U. S. Department of Energy (ORNL).

Identification of vacancy-oxygen complexes in oxygen-implanted silicon probed with slow positrons

NASA Astrophysics Data System (ADS)

Fujinami, M.; Miyagoe, T.; Sawada, T.; Suzuki, R.; Ohdaira, T.; Akahane, T.

2004-04-01

Defects and their annealing behavior for low (2×1015/cm2) and high (1.7×1018/cm2) doses of 180 keV oxygen-implanted silicon have been investigated by the coincidence Doppler broadening (CDB) and lifetime measurements in variable-energy positron annihilation spectroscopy. In the low-dose sample, divacancies are induced throughout the entire implantation region. In the vacancy-oxygen coexisting region (300-500 nm depths), by raising the annealing temperature to 600 °C, vacancy-oxygen VxOy complexes with one vacant site are formed and, simultaneously, the migration of oxygen begins to takes place. In the vacancy-rich region (-200 nm depths), the evolution of simple vacancy clusters to V4 is mainly observed below 600 °C. From CDB and lifetime measurements, it has been proven that after annealing at 800 °C, the VxOy complexes are formed throughout the implanted region and they contain four vacant sites and a high ratio of y to x. On the other hand, high-dose implantation at 550 °C produces the VxOy complexes with a lifetime of a 430 ps in the near-surface region (less than 200 nm deep) and annealing at 1100 °C leads to the highest ratio of y to x. These complexes cannot be annealed out even by annealing at 1350 °C, and their structure is found to be very similar to that for the electron-irradiated amorphous SiO2.

Iron-Based Amorphous Metals: High-Performance Corrosion-Resistant Material Development

NASA Astrophysics Data System (ADS)

Farmer, Joseph; Choi, Jor-Shan; Saw, Cheng; Haslam, Jeffrey; Day, Dan; Hailey, Phillip; Lian, Tiangan; Rebak, Raul; Perepezko, John; Payer, Joe; Branagan, Daniel; Beardsley, Brad; D'Amato, Andy; Aprigliano, Lou

2009-06-01

An overview of the High-Performance Corrosion-Resistant Materials (HPCRM) Program, which was cosponsored by the Defense Advanced Research Projects Agency (DARPA) Defense Sciences Office (DSO) and the U.S. Department of Energy (DOE) Office of Civilian and Radioactive Waste Management (OCRWM), is discussed. Programmatic investigations have included a broad range of topics: alloy design and composition, materials synthesis, thermal stability, corrosion resistance, environmental cracking, mechanical properties, damage tolerance, radiation effects, and important potential applications. Amorphous alloys identified as SAM2X5 (Fe49.7Cr17.7Mn1.9Mo7.4W1.6B15.2C3.8Si2.4) and SAM1651 (Fe48Mo14Cr15Y2C15B6) have been produced as meltspun ribbons (MSRs), dropcast ingots, and thermal-spray coatings. Chromium (Cr), molybdenum (Mo), and tungsten (W) additions provided corrosion resistance, while boron (B) enabled glass formation. Earlier electrochemical studies of MSRs and ingots of these amorphous alloys demonstrated outstanding passive film stability. More recently, thermal-spray coatings of these amorphous alloys have been made and subjected to long-term salt-fog and immersion tests; good corrosion resistance has been observed during salt-fog testing. Corrosion rates were measured in situ with linear polarization, while the open-circuit corrosion potentials (OCPs) were simultaneously monitored; reasonably good performance was observed. The sensitivity of these measurements to electrolyte composition and temperature was determined. The high boron content of this particular amorphous metal makes this amorphous alloy an effective neutron absorber and suitable for criticality-control applications. In general, the corrosion resistance of such iron-based amorphous metals is maintained at operating temperatures up to the glass transition temperature. These materials are much harder than conventional stainless steel and Ni-based materials, and are proving to have excellent wear properties, sufficient to warrant their use in earth excavation, drilling, and tunnel-boring applications. Large areas have been successfully coated with these materials, with thicknesses of approximately 1 cm. The observed corrosion resistance may enable applications of importance in industries such as oil and gas production, refining, nuclear power generation, shipping, etc.

Effect of Si on Fe-rich intermetallic formation and mechanical properties of heat-treated Al–Cu–Mn–Fe alloys

NASA Astrophysics Data System (ADS)

Zhao, Yuliang; Zhang, Weiwen; Yang, Chao; Zhang, Datong; Wang, Zhi

2018-04-01

The effect of Si on Fe-rich intermetallics formation and mechanical properties of heat-treated squeeze cast Al-5.0Cu-0.6Mn-0.7Fe alloy was investigated. Our results show that increasing Si content promotes the formation of Al15(FeMn)3(SiCu)2 (${\\alpha}$-Fe), and varying the morphology of T (Al20Cu3Mn2) where the size decreases and the amount increases. The major reason is that Si promotes heterogeneous nucleation of the intermetallics leading to finer precipitates. Si addition significantly enhances ultimate tensile strength and yield strength of the alloys. The strengthening effect is mainly owing to the dispersoid strengthening by increasing volume fraction of T phase and less harmful ${\\alpha}$-Fe with a compact structure, which make the cracks more difficult to initiate and propagation during tensile test. The squeeze cast Al-5.0Cu-0.6Mn-0.7Fe alloy with 1.1% Si shows significantly improved mechanical properties than the alloy without Si addition, which has tensile strength of 386 MPa, yield strength of 280 MPa and elongation of 8.6%.

Characterization of modified SiC@SiO2 nanocables/MnO2 and their potential application as hybrid electrodes for supercapacitors.

PubMed

Zhang, Yujie; Chen, Junhong; Fan, Huili; Chou, Kuo-Chih; Hou, Xinmei

2015-12-14

In this research, we demonstrate a simple route for preparing SiC@SiO2 core-shell nanocables and furthermore obtain SiC@SiO2 nanocables/MnO2 as hybrid electrodes for supercapacitors using various modified methods. The modified procedure consists of mild modifications using sodium hydroxide as well as UV light irradiation and deposition of MnO2. The morphology and microstructural characteristics of the composites are investigated using XRD, XPS, FE-SEM with EDS and TEM. The results indicate that the surfaces of modified SiC@SiO2 nanocables are uniformly coated with a MnO2 thin layer. The electrochemical behaviors of the hybrid electrodes are systematically measured in a three-electrode system using cyclic voltammetry, galvanostatic charge/discharge and electrochemical impedance spectroscopy. The resultant electrode presents a superb charge storage characteristic with a large specific capacitance of 276.3 F g(-1) at the current density of 0.2 A g(-1). Moreover, the hybrid electrode also displays a long cycle life with a good capacitance retention (∼92.0%) after 1000 CV cycles, exhibiting a promising potential for supercapacitors.

Degradable and porous Fe-Mn-C alloy for biomaterials candidate

NASA Astrophysics Data System (ADS)

Pratesa, Yudha; Harjanto, Sri; Larasati, Almira; Suharno, Bambang; Ariati, Myrna

2018-02-01

Nowadays, degradable implants attract attention to be developed because it can improve the quality of life of patients. The degradable implant is expected to degrade easily in the body until the bone healing process already achieved. However, there is limited material that could be used as a degradable implant, polymer, magnesium, and iron. In the previous study, Fe-Mn-C alloys had succesfully produced austenitic phase. However, the weakness of the alloy is degradation rate of materials was considered below the expectation. This study aimed to produce porous Fe-Mn-C materials to improve degradation rate and reduce the density of alloy without losing it non-magnetic properties. Potassium carbonate (K2CO3) were chosen as filler material to produce foam structure by sintering and dissolution process. Multisteps sintering process under argon gas environment was performed to generate austenite phase. The product showed an increment of the degradation rate of the foamed Fe-Mn-C alloy compared with the solid Fe-Mn-C alloy without losing the Austenitic Structure

Asymmetric supercapacitors based on functional electrospun carbon nanofiber/manganese oxide electrodes with high power density and energy density

NASA Astrophysics Data System (ADS)

Lin, Sheng-Chi; Lu, Yi-Ting; Chien, Yu-An; Wang, Jeng-An; You, Ting-Hsuan; Wang, Yu-Sheng; Lin, Chih-Wen; Ma, Chen-Chi M.; Hu, Chi-Chang

2017-09-01

Carbon nanofibers modified with carboxyl groups (CNF-COOH) possessing good wettability and high porosity are homogeneously deposited with amorphous manganese dioxide (amorphous MnO2) by potentiodynamic deposition for asymmetric super-capacitors (ASCs). The potential-cycling in 1 M H2SO4 successfully enhances the hydrophilicity of carbonized polymer nanofibers and facilitates the access of electrolytes within the CNF-COOH matrix. This modification favors the deposition of amorphous MnO2 and improves its electrochemical utilization. In this composite, MnO2 homogeneously dispersed onto CNF-COOH provides desirable pseudocapacitance and the CNF-COOH network works as the electron conductor. The composite of CNF-COOH@MnO2-20 shows a high specific capacitance of 415 F g-1 at 5 mV s-1. The capacitance retention of this composite is 94% in a 10,000-cycle test. An ASC cell consisting of this composite and activated carbon as positive and negative electrodes can be reversibly charged/discharged to a cell voltage of 2.0 V in 1 M Na2SO4 and 4 mM NaHCO3 with specific energy and power of 36.7 Wh kg-1 and 354.9 W kg-1, respectively. This ASC also shows excellent cell capacitance retention (8% decay) in the 2V, 10,000-cycle stability test, revealing superior performance.

Nano-SiC region formation in (100) Si-on-insulator substrate: Optimization of hot-C+-ion implantation process to improve photoluminescence intensity

NASA Astrophysics Data System (ADS)

Mizuno, Tomohisa; Omata, Yuhsuke; Kanazawa, Rikito; Iguchi, Yusuke; Nakada, Shinji; Aoki, Takashi; Sasaki, Tomokazu

2018-04-01

We experimentally studied the optimization of the hot-C+-ion implantation process for forming nano-SiC (silicon carbide) regions in a (100) Si-on-insulator substrate at various hot-C+-ion implantation temperatures and C+ ion doses to improve photoluminescence (PL) intensity for future Si-based photonic devices. We successfully optimized the process by hot-C+-ion implantation at a temperature of about 700 °C and a C+ ion dose of approximately 4 × 1016 cm-2 to realize a high intensity of PL emitted from an approximately 1.5-nm-thick C atom segregation layer near the surface-oxide/Si interface. Moreover, atom probe tomography showed that implanted C atoms cluster in the Si layer and near the oxide/Si interface; thus, the C content locally condenses even in the C atom segregation layer, which leads to SiC formation. Corrector-spherical aberration transmission electron microscopy also showed that both 4H-SiC and 3C-SiC nanoareas near both the surface-oxide/Si and buried-oxide/Si interfaces partially grow into the oxide layer, and the observed PL photons are mainly emitted from the surface SiC nano areas.

Preparation, mechanical strengths, and thermal

NASA Astrophysics Data System (ADS)

Inoue, A.; Furukawa, S.; Hagiwara, M.; Masumoto, T.

1987-05-01

Ni-based amorphous wires with good bending ductility have been prepared for Ni75Si8B17 and Ni78P12B10 alloys containing 1 to 2 at. pct Al or Zr by melt spinning in rotating water. The enhancement of the wire-formation tendency by the addition of Al has been clarified to be due to the increase in the stability of the melt jet through the formation of a thin A12O3 film on the outer surface. The maximum wire diameter is about 190 to 200 μm for the Ni-Si (or P)-B-Al alloys and increases to about 250 μm for the Ni-Si-B-Al-Cr alloys containing 4 to 6 at. pct Cr. The tensile fracture strength and fracture elongation are 2730 MPa and 2.9 pct for (Ni0.75Si0.08B0.17 99Al1) wire and 2170 MPa and 2.4 pct for (Ni0.78P0.12B0.1)99Al1 wire. These wires exhibit a fatigue limit under dynamic bending strain in air with a relative humidity of 65 pct; this limit is 0.50 pct for a Ni-Si-B-Al wire, which is higher by 0.15 pct than that of a Fe75Si10B15 amorphous wire. Furthermore, the Ni-base wires do not fracture during a 180-deg bending even for a sample annealed at temperatures just below the crystallization temperature, in sharp contrast to high embrittlement tendency for Fe-base amorphous alloys. Thus, the Ni-based amorphous wires have been shown to be an attractive material similar to Fe- and Co-based amorphous wires because of its high static and dynamic strength, high ductility, high stability to thermal embrittlement, and good corrosion resistance.

Amorphous Ge quantum dots embedded in crystalline Si: ab initio results.

PubMed

Laubscher, M; Küfner, S; Kroll, P; Bechstedt, F

2015-10-14

We study amorphous Ge quantum dots embedded in a crystalline Si matrix through structure modeling and simulation using ab initio density functional theory including spin-orbit interaction and quasiparticle effects. Three models are generated by replacing a spherical region within diamond Si by Ge atoms and creating a disordered bond network with appropriate density inside the Ge quantum dot. After total-energy optimisations of the atomic geometry we compute the electronic and optical properties. We find three major effects: (i) the resulting nanostructures adopt a type-I heterostructure character; (ii) the lowest optical transitions occur only within the Ge quantum dots, and do not involve or cross the Ge-Si interface. (iii) for larger amorphous Ge quantum dots, with diameters of about 2.0 and 2.7 nm, absorption peaks appear in the mid-infrared spectral region. These are promising candidates for intense luminescence at photon energies below the gap energy of bulk Ge.

Gold atoms and dimers on amorphous SiO(2): calculation of optical properties and cavity ringdown spectroscopy measurements.

PubMed

Del Vitto, Annalisa; Pacchioni, Gianfranco; Lim, Kok Hwa; Rösch, Notker; Antonietti, Jean-Marie; Michalski, Marcin; Heiz, Ulrich; Jones, Harold

2005-10-27

We report on the optical absorption spectra of gold atoms and dimers deposited on amorphous silica in size-selected fashion. Experimental spectra were obtained by cavity ringdown spectroscopy. Issues on soft-landing, fragmentation, and thermal diffusion are discussed on the basis of the experimental results. In parallel, cluster and periodic supercell density functional theory (DFT) calculations were performed to model atoms and dimers trapped on various defect sites of amorphous silica. Optically allowed electronic transitions were calculated, and comparisons with the experimental spectra show that silicon dangling bonds [[triple bond]Si(.-)], nonbridging oxygen [[triple bond]Si-O(.-)], and the silanolate group [[triple bond]Si-O(-)] act as trapping centers for the gold particles. The results are not only important for understanding the chemical bonding of atoms and clusters on oxide surfaces, but they will also be of fundamental interest for photochemical studies of size-selected clusters on surfaces.

Comparative Wide Temperature Core Loss Characteristics of Two Candidate Ferrites for the NASA/TRW 1500 W PEBB Converter

NASA Technical Reports Server (NTRS)

Niedra, Janis M.

1999-01-01

High frequency core loss and magnetization properties of commercial type MN8CX and PC40, high resistivity, MnZn based, power ferrites are presented over the temperature range of -l50 C to 150 C, at selected values of peak flux density (B (sub p)). Most of the data is at 100 kHz, with some data extended to 200 and 300 kHz for the MN8CX. Plots of the specific Core loss against temperature exhibit the minimal characteristic of such ferrites. These plots show that the MN8CX is optimized for minimum loss at about 25 C, whereas the PC40 is optimized at about 80 C. At the points of minimum loss and for the same B (sub p), the MN8CX has roughly half the losses of the PC40 at the lower flux densities. This loss ratio continues down to cryogenic temperatures. However, above about 80 C the losses are practically equal. The lowest 100 kHz loss recorded, 50 mW/cm3 for the MNGCX at a B (sub p) of 0.1T, equals that of a very low loss, Co based, transverse magnetically annealed, amorphous ribbon material. Except possibly at lower B (sub p) or much higher frequencies, these ferrites are not competitive for low losses over a wide temperature range with certain specialty amorphous materials. Permeability is computed from a linear model, plots against temperature are presented and again compared to the specialty amorphous materials.

Ab-initio study of electronic structure and magnetic properties of half-metallic Fe{sub 2}Mn{sub 1−x}V{sub x}Si{sub 0.5}Al{sub 0.5} alloys

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

Go, Anna, E-mail: annago@alpha.uwb.edu.pl

2014-11-15

Ab-initio electronic structure calculations are carried out for quinternary Fe{sub 2}Mn{sub 1−x}V{sub x}Si{sub 0.5}Al{sub 0.5} alloys. When x=0 the alloy is half-metallic ferromagnet, with magnetic moment following the Slater–Pauling rule. Replacement of Mn by V, changes its electronic and magnetic structure. V-doped alloys exhibit half-metallic behavior for x≤0.25. However, even for higher V concentrations, electronic spin polarization is still very high, what makes the alloys interesting for spintronic applications. - Graphical abstract: Densities of states of Fe{sub 2}MnSi{sub 0.5}Al{sub 0.5} and magnetic moments of Fe{sub 2}Mn{sub 1−x}V{sub x}Si{sub 0.5}Al{sub 0.5}. - Highlights: • Fe{sub 2}MnSi{sub 0.5}Al{sub 0.5} is a half-metallicmore » ferromagnet with a minority band gap of 0.49 eV. • Half-metallic band gap is very stable against the change of the lattice parameter. • Half-metallic band gap is obtained for Fe{sub 2}Mn{sub 1−x}V{sub x}Si{sub 0.5}Al{sub 0.5} for x≤0.25. • Electronic spin polarization is very high and equal to at least 95% for x≤0.625. • The main carrier of magnetism of the compound is manganese.« less

Spontaneous crystalline-to-amorphous phase transformation of organic or medicinal compounds in the presence of porous media, part 1: thermodynamics of spontaneous amorphization.

PubMed

Qian, Ken K; Bogner, Robin H

2011-07-01

Spontaneous crystalline-to-amorphous phase transformation of organic or medicinal molecules in the presence of mesoporous materials has been observed, for which pathway was suggested to be via the vapor phase, that is, sublimation of the crystalline molecules followed by adsorption on the porous media. The objective of this paper is to rigorously evaluate this amorphization pathway and to study the thermodynamics of spontaneous amorphization. Mesoporous silicon dioxide (SiO(2)) was used as a model system. Physical mixtures of SiO(2) and crystalline compounds were prepared and stored at 0% relative humidity (RH) and 40 °C. Loss of crystallinity of the model compounds was confirmed using powder X-ray diffraction and polarized light microscopy. Adsorption chamber was set up, in which naphthalene and SiO(2) were stored, without physical contact, under reduced pressure at 0% RH and 40 °C. Data confirmed that the rate and extent of sublimation and adsorption of naphthalene were significant for amorphization to occur on a pharmaceutically relevant timescale. Furthermore, a thermodynamic model has been developed to explain spontaneous amorphization. This unique phase transformation phenomenon can be a simple and effective method to improve the aqueous solubility and bioavailability of poorly soluble drug molecules. Copyright © 2011 Wiley-Liss, Inc. and the American Pharmacists Association

75 FR 65453 - Certain Hot-Rolled Flat-Rolled Carbon Quality Steel Flat Products From Brazil: Notice of...

Federal Register 2010, 2011, 2012, 2013, 2014

2010-10-25

... which meets the following chemical, physical and mechanical specifications: C Mn P S Si Cr Cu Ni 0.10-0... specifications: C Mn P S Si Cr Cu Ni Mo 0.10-0.16% 0.70-0.90% 0.025% Max 0.006% Max 0.30-0.50% 0.50-0.70% 0.25... following chemical, physical and mechanical specifications: C Mn P S Si Cr Cu Ni V (wt.) Cb 0.10-0.14% 1.30...

75 FR 64254 - Certain Hot-Rolled Flat-Rolled Carbon Quality Steel Products From Brazil; Final Results of...

Federal Register 2010, 2011, 2012, 2013, 2014

2010-10-19

... which meets the following chemical, physical and mechanical specifications: C Mn P S Si Cr Cu Ni 0.10-0... specifications: C Mn P S Si Cr Cu Ni Mo 0.10-0.16% 0.70-0.90% 0.025% Max 0.006% Max 0.30-0.50% 0.50-0.70% 0.25... following chemical, physical and mechanical specifications: C Mn P S Si Cr Cu Ni V(wt.) Cb 0.10-0.14% 1.30-1...

75 FR 43931 - Certain Hot-Rolled Flat-Rolled Carbon-Quality Steel Products from Brazil: Preliminary Results of...

Federal Register 2010, 2011, 2012, 2013, 2014

2010-07-27

... following chemical, physical and mechanical specifications: C Mn P S Si Cr Cu Ni 0.10-0.14% 0.90% Max... mechanical specifications: C Mn P S Si Cr Cu Ni Mo 0.10-0.16% 0.70-0.90%........ 0.025% Max........ 0.006... mechanical specifications: C Mn P S Si Cr Cu Ni V(wt.) Cb 0.10-0.14% 1.30-1.80%...... 0.025% Max...... 0.005...

Crystallization and Martensitic Transformation Behavior of Ti-Ni-Si Alloy Ribbons Prepared via Melt Spinning.

PubMed

Park, Ju-Wan; Kim, Yeon-Wook; Nam, Tae-Hyun

2018-09-01

Ti-(50-x)Ni-xSi (at%) (x = 0.5, 1.0, 3.0, 5.0) alloy ribbons were prepared via melt spinning and their crystallization procedure and transformation behavior were investigated using differential scanning calorimtry, X-ray diffraction, and transmission electron microscopy. Ti-Ni-Si alloy ribbons with Si content less than 1.0 at% were crystalline, whereas those with Si content more than 3.0 at% were amorphous. Crystallization occurred in the sequence of amorphous →B2 → B2 → Ti5Si4 + TiNi3 → B2 + Ti5Si4 + TiNi3 + TiSi in the Ti-47.0Ni-3.0Si alloy and amorphous →R → R + Ti5Si4 + TiNi3 → R + Ti5Si4 + TiNi3 + TiSi in the Ti-45.0Ni-5.0Si alloy. The activation energy for crystallization was 189 ±8.6 kJ/mol for the Ti-47Ni-3Si alloy and 212±8.6 kJ/mol for the Ti-45Ni-5Si alloy. One-stage B2-R transformation behavior was observed in Ti-49.5Ni-0.5Si, Ti-49.0Ni-1.0Si, and Ti-47.0Ni- 3.0Si alloy ribbons after heating to various temperatures in the range of 873 K to 1073 K. In the Ti-45.0Ni-5.0Si alloy, one-stage B2-R transformation occurred after heating to 893 K, two-stage B2-R-B19' occurred after heating to 973 K, and two-stage B2-R-B19' occurred on cooling and one-stage B19'-B2 occurred on heating, after heating to 1073 K.

Correlated topographic and structural modification on Si surface during multi-shot femtosecond laser exposures: Si nanopolymorphs as potential local structural nanomarkers

NASA Astrophysics Data System (ADS)

Ionin, A. A.; Kudryashov, S. I.; Levchenko, A. O.; Nguyen, L. V.; Saraeva, I. N.; Rudenko, A. A.; Ageev, E. I.; Potorochin, D. V.; Veiko, V. P.; Borisov, E. V.; Pankin, D. V.; Kirilenko, D. A.; Brunkov, P. N.

2017-09-01

High-pressure Si-XII and Si-III nanocrystalline polymorphs, as well as amorphous Si phase, appear consequently during multi-shot femtosecond-laser exposure of crystalline Si wafer surface above its spallation threshold along with permanently developing quasi-regular surface texture (ripples, microcones), residual hydrostatic stresses and subsurface damage, which are characterized by scanning and transmission electron microscopy, as well as by Raman micro-spectroscopy. The consequent yields of these structural Si phases indicate not only their spatially different appearance, but also potentially enable to track nanoscale, transient laser-induced high-pressure, high-temperature physical processes - local variation of ablation mechanism and rate, pressurization/pressure release, melting/resolidification, amorphization, annealing - versus cumulative laser exposure and the related development of the surface topography.

Synthesis and characterization of a novel polyborosilazane for SiBNC ceramic

NASA Astrophysics Data System (ADS)

Zhang, C. Y.; Liu, Y.; Han, K. Q.; Chang, X. F.; Yu, M. H.

2018-05-01

A novel polyborosilazane (PBSZ) for preparing SiBNC ceramics was successfully synthesized via co-condensation approach using tetrachlorosilan (SiCl4), trichloride (BCl3) and propylamine (C3H7NH2) as starting materials. After pyrolysis of these precursors, amorphous SiBNC ceramics were obtained. The chemical composition, structure and thermal stability of the synthesized PBSZ precursor and SiBNC ceramics were analyzed by using FT-IR, NMR, TGA and XRD methods. The results indicated that the PBSZ contained the major framework of –Si-N-B- and six-membered boron-nitrogen rings. The PBSZ precursor had an approximately ceramic yield of 63 wt% prolyzed at 900°C in nitrogen atmosphere. The SiBNC ceramics shows excellent oxidation resistance and maintained amorphous up to 1600°C.

Electronic structure and the origin of the Dzyaloshinskii-Moriya interaction in MnSi

DOE PAGES

Satpathy, S.; Shanavas, K. V.

2016-05-02

Here, the metallic helimagnet MnSi has been found to exhibit skyrmionic spin textures when subjected to magnetic fields at low temperatures. The Dzyaloshinskii-Moriya (DM) interaction plays a key role in stabilizing the skyrmion state. With the help of first-principles calculations, crystal field theory and a tight-binding model we study the electronic structure and the origin of the DM interaction in the B20 phase of MnSi. The strength ofmore » $$\\vec{D}$$ parameter is determined by the magnitude of the spin-orbit interaction and the degree of orbital mixing, induced by the symmetry-breaking distortions in the B20 phase. We find that, strong coupling between Mn-$d$ and Si-$p$ states lead to a mixed valence ground state $$|d^{7-x}p^{2+x}\\rangle$$ configuration. The experimental magnetic moment of $$0.4~\\mu_B$$ is consistent with the Coulomb-corrected DFT+$U$ calculations, which redistributes electrons between the majority and minority spin channels. We derive the magnetic interaction parameters $J$ and $$\\vec{D}$$ for Mn-Si-Mn superexchange paths using Moriya's theory assuming the interaction to be mediated by $$e_g$$ electrons near the Fermi level. Finally, using parameters from our calculations, we get reasonable agreement with the observations.« less

Tunable white light of a Ce3+,Tb3+,Mn2+ triply doped Na2Ca3Si2O8 phosphor for high colour-rendering white LED applications: tunable luminescence and energy transfer.

PubMed

Lü, Wei; Xu, Huawei; Huo, Jiansheng; Shao, Baiqi; Feng, Yang; Zhao, Shuang; You, Hongpeng

2017-07-18

A tunable white light emitting Na 2 Ca 3 Si 2 O 8 :Ce 3+ ,Tb 3+ ,Mn 2+ phosphor with a high color rendering index (CRI) has been prepared. Under UV excitation, Na 2 Ca 3 Si 2 O 8 :Ce 3+ phosphors present blue luminescence and exhibit a broad excitation ranging from 250 to 400 nm. When codoping Tb 3+ /Mn 2+ ions into Na 2 Ca 3 Si 2 O 8 , energy transfer from Ce 3+ to Tb 3+ and Ce 3+ to Mn 2+ ions is observed from the spectral overlap between Ce 3+ emission and Tb 3+ /Mn 2+ excitation spectra. The energy-transfer efficiencies and corresponding mechanisms are discussed in detail. The mechanism of energy transfer from Ce 3+ to Tb 3+ is demonstrated to be a dipole-quadrupole mechanism by the Inokuti-Hirayama model. The wavelength-tunable white light can be realized by coupling the emission bands centered at 440, 550 and 590 nm ascribed to the contribution from Ce 3+ , Tb 3+ and Mn 2+ , respectively. The commission on illumination value of color tunable emission can be tuned by controlling the content of Ce 3+ , Tb 3+ and Mn 2+ . Temperature-dependent luminescence spectra proved the good thermal stability of the as-prepared phosphor. White LEDs with CRI = 93.5 are finally fabricated using a 365 nm UV chip and the as-prepared Na 2 Ca 3 Si 2 O 8 :Ce 3+ ,Tb 3+ ,Mn 2+ phosphor. All the results suggest that Na 2 Ca 3 Si 2 O 8 :Ce 3+ ,Tb 3+ ,Mn 2+ can act as potential color-tunable and single-phase white emission phosphors for possible applications in UV based white LEDs.

Role of sodium ions in the vitrification process: glass matrix modification, slag structure depolymerization, and influence of metal immobilization.

PubMed

Kuo, Yi-Ming

2014-07-01

This study investigates the role of Na ions, a common flux, in the vitrification process. Artificial glass systems composed of Al2O3, CaO, and SiO2 with various Na concentrations were melted at 1450 degrees C. The specimens were cooled by air cooling and water quenching and the metal mobility was evaluated using a sequential extraction procedure. The X-ray diffraction analysis and scanning electron microscopy observations showed that Na ions governed the air-cooled slag's structure. Na ions initially depolymerized CaSiO3-linked chains into CaSiO3 chains, and further cut them into shorter and nonuniform ones, making the slag structure amorphous. With even more Na ions, CaSiO3 chains were divided into single SiO4 tetrahedrons and formed Na-related crystals (Na2Ca3Si2O8 and NaAlSiO4). The phase distributions of Al, Cr, Cu Mn, and Ni showed that Na has a positive effect on the immobilization of heavy metals at suitable concentrations, but a negative effect when in excess amounts. Implications: Vitrification has been widely used to treat hazardous materials. The Na-bearing additives were often used as a flux to improve the melting process. This study described the role of Na played in the vitrification process. The Na ions acted as glass modifier and depolymerize the chain structure of slag. With adequate addition amount of Na ions, the immobilization of heavy metals was improved. The results provided much information about the crystalline phase variation, metal mobility, and surface characteristics while Na serves as a flux.

Processing method for forming dislocation-free SOI and other materials for semiconductor use

DOEpatents

Holland, Orin Wayne; Thomas, Darrell Keith; Zhou, Dashun

1997-01-01

A method for preparing a silicon-on-insulator material having a relatively defect-free Si overlayer involves the implanting of oxygen ions within a silicon body and the interruption of the oxygen-implanting step to implant Si ions within the silicon body. The implanting of the oxygen ions develops an oxide layer beneath the surface of the silicon body, and the Si ions introduced by the Si ion-implanting step relieves strain which is developed in the Si overlayer during the implanting step without the need for any intervening annealing step. By relieving the strain in this manner, the likelihood of the formation of strain-induced defects in the Si overlayer is reduced. In addition, the method can be carried out at lower processing temperatures than have heretofore been used with SIMOX processes of the prior art. The principles of the invention can also be used to relieve negative strain which has been induced in a silicon body of relatively ordered lattice structure.

Facile synthesis of amorphous FeOOH/MnO2 composites as screen-printed electrode materials for all-printed solid-state flexible supercapacitors

NASA Astrophysics Data System (ADS)

Lu, Qiang; Liu, Li; Yang, Shuanglei; Liu, Jun; Tian, Qingyong; Yao, Weijing; Xue, Qingwen; Li, Mengxiao; Wu, Wei

2017-09-01

More convenience and intelligence life lead by flexible/wearable electronics requires innovation and hommization of power sources. Here, amorphous FeOOH/MnO2 composite as screen-printed electrode materials for supercapacitors (SCs) is synthesized by a facile method, and solid-state flexible SCs with aesthetic design are fabricated by fully screen-printed process on different substrates, including PET, paper and textile. The amorphous FeOOH/MnO2 composite shows a high specific capacitance and a good rate capability (350.2 F g-1 at a current density of 0.5 A g-1 and 159.5 F g-1 at 20 A g-1). It also possesses 95.6% capacitance retention even after 10 000 cycles. Moreover, the all-printed solid-state flexible SC device exhibits a high area specific capacitance of 5.7 mF cm-2 and 80% capacitance retention even after 2000 cycles. It also shows high mechanical flexibility. Simultaneously, these printed SCs on different substrates in series are capable to light up a 1.9 V yellow light emitting diode (LED), even after bending and stretching.

Amorphization and reduction of thermal conductivity in porous silicon by irradiation with swift heavy ions

NASA Astrophysics Data System (ADS)

Newby, Pascal J.; Canut, Bruno; Bluet, Jean-Marie; Gomès, Séverine; Isaiev, Mykola; Burbelo, Roman; Termentzidis, Konstantinos; Chantrenne, Patrice; Fréchette, Luc G.; Lysenko, Vladimir

2013-07-01

In this article, we demonstrate that the thermal conductivity of nanostructured porous silicon is reduced by amorphization and also that this amorphous phase in porous silicon can be created by swift (high-energy) heavy ion irradiation. Porous silicon samples with 41%-75% porosity are irradiated with 110 MeV uranium ions at six different fluences. Structural characterisation by micro-Raman spectroscopy and SEM imaging show that swift heavy ion irradiation causes the creation of an amorphous phase in porous Si but without suppressing its porous structure. We demonstrate that the amorphization of porous silicon is caused by electronic-regime interactions, which is the first time such an effect is obtained in crystalline silicon with single-ion species. Furthermore, the impact on the thermal conductivity of porous silicon is studied by micro-Raman spectroscopy and scanning thermal microscopy. The creation of an amorphous phase in porous silicon leads to a reduction of its thermal conductivity, up to a factor of 3 compared to the non-irradiated sample. Therefore, this technique could be used to enhance the thermal insulation properties of porous Si. Finally, we show that this treatment can be combined with pre-oxidation at 300 °C, which is known to lower the thermal conductivity of porous Si, in order to obtain an even greater reduction.

Ab initio investigation of competing antiferromagnetic structures in low Si-content FeMn(PSi) alloy

NASA Astrophysics Data System (ADS)

Li, Guijiang; Eriksson, Olle; Johansson, Börje; Vitos, Levente

2016-06-01

The antiferromagnetic structures of a low Si-content FeMn(PSi) alloy were investigated by first principles calculations. One possible antiferromagnetic structure in supercell along the c-axis was revealed in FeMnP0.75Si0.25 alloy. It was found that atomic disorder occupation between Fe atom on 3f and Mn atoms on 3g sites is responsible for the formation of antiferromagnetic structures. Furthermore the magnetic competition and the coupling between possible AFM supercells along the c and a-axis can promote a non-collinear antiferromagnetic structure. These theoretical investigations help to deeply understand the magnetic order in FeMn(PSi) alloys and benefit to explore the potential magnetocaloric materials in Fe2P-type alloys.

Stability of half-metallic behavior with lattice variation for Fe2MnZ (Z = Si, Ge, Sn) Heusler alloy

NASA Astrophysics Data System (ADS)

Jain, Vivek Kumar; Lakshmi, N.; Jain, Rakesh

2018-05-01

The electronic structure and magnetic properties with variation of lattice constant for Fe2MnZ (Z = Si, Ge, Sn) Heusler alloys have been studied. Optimized lattice constant are found to be 5.59, 5.69, 6.00 Å for Z= Si, Ge and Sn respectively. Total magnetic moments of the alloys are ˜3 µB as predicted by the Slater Pauling rule and is maintained over a wide range of lattice variation for all three alloys. Half metallic ferromagnetic nature with 100% spin polarization is observed for Fe2MnSi for a lattice range from 5.40-5.70 Å. Fe2MnGe and Fe2MnSn show ferromagnetic and metallic natures with more than 90% spin polarization over a wide range of lattice constant. Due to the stability of half metallic character of these alloys with respect to variation in the lattice parameters, they are promising robust materials suitable for spintronics device applications.

Magnetic properties of Sm2(Fe0.95M0.05)17Nx (M=Cr and Mn) anisotropic coarse powders with high coercivity

NASA Astrophysics Data System (ADS)

Ito, Mikio; Majima, Kazuhiko; Shimuta, Toru; Katsuyama, Shigeru; Nagai, Hiroshi

2002-09-01

Sm2(Fe0.95Cr0.05)17Nx and Sm2(Fe0.95Mn0.05)17Nx coarse powders 10-70 mum in size were synthesized by crushing mother alloy ingots into 32-74 mum in particle size and subsequent nitrogenation at 748 K in a flowing mixed gas of 60 vol % H2+40 vol % NH3. The effects of Cr or Mn substitution for Fe on the nitrogenation rate, magnetic properties, and microstructure of the Sm2Fe17Nx hard magnetic material were investigated. Cr and Mn substitution was quite effective for accelerating nitrogenation. When the powders were nitrogenated beyond x=3, amorphous phase formation was observed as the x value increased. The magnetic properties of the nitrogenated powders were significantly improved by Cr and Mn substitution, and these powders also possessed a satisfactory magnetic anisotropy. The maximum coercivity in this study, 0.59 MA/m, was obtained for the Sm2(Fe0.95Mn0.05)17N5.0 powder in spite of its large particle size. The high coercivity of the coarse powders was caused by a cell-like microstructure composed of fine 2-17 crystalline grains 20-30 nm in size surrounded by an amorphous phase.

Conciliatory Inductive Model Explaining the Origin of Changes in the η(2)-SiH Bond Length Caused by Presence of Strongly Electronegative Atoms X (X = F, Cl) in Cp(OC)2Mn[η(2)-H(SiH3-nXn)] (n = 0-3) Complexes.

PubMed

Jabłoński, Mirosław

2016-06-23

Using three theoretical methods, QTAIM, IQA, and NCI, we analyze an influence of halogen atoms X (X = F, Cl) substituted at various positions in the -SiH3-nXn group on the charge density distribution within the η(2)-SiH bond and on the SiH bond energies in Cp(OC)2Mn[η(2)-H(SiH3-nXn)] complexes and isolated HSiH3-nXn molecules. It is shown that shortening of the η(2)-SiH bond in Cp(OC)2Mn[η(2)-H(SiH3-nXn)] complexes should be considered as a normal inductive result of halogenation. This η(2)-SiH bond's compression may, however, be overcome by a predominant elongation resulting from a contingent presence of a halogen atom at position trans to the η(2)-SiH bond. This trans effect is particularly large for bulky and highly polarizable chlorine. Moreover, peculiar properties of the trans chlorine atom are manifested in several ways. To explain the origin of all the observed changes in both the length and the electron charge distribution of the η(2)-SiH bond in investigated Cp(OC)2Mn[η(2)-H(SiH3-nXn)] complexes a new model, called the Conciliatory Inductive Model, is being proposed.

Stabilization of Wide Band-Gap p-Type Wurtzite MnTe Thin Films on Amorphous Substrates

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

Zakutayev, Andriy A; Siol, Sebastian; Han, Yanbing

An important challenge in the development of optoelectronic devices for energy conversion applications is the search for suitable p-type contact materials. For example, p-type MnTe would be a promising alternative back contact to due to their chemical compatibility, but at normal conditions it has too narrow band gap due to octahedrally coordinated nickeline (NC) structure. The tetrahedrally coordinated wurtzite (WZ) polymorph of MnTe has not been reported, but it is especially interesting due to its predicted wider band gap, and because of better structural compatibility with CdTe and related II-VI semiconductor materials. Here, we report on the stabilization of WZ-MnTemore » thin films on amorphous indium zinc oxide (a-IZO) substrates relevant to photovoltaic applications. Optical spectroscopy of the WZ-MnTe films shows a wide direct band gap of Eg = 2.7 eV, while PES measurements reveal weak p-type doping with the Fermi level 0.6 eV above the valence band maximum. The results of electron microscopy and photoelectron spectroscopy (PES) measurements indicate that the WZ-MnTe is stabilized due to interdiffusion at the interface with IZO. The results of this work introduce a substrate stabilized WZ-MnTe polymorph as a potential p-type contact material candidate for future applications in CdTe devices for solar energy conversion and other optoelectronic technologies.« less

Synthesis and characterization of carbon coated LiCo1/3Ni1/3Mn1/3O2 and bio-mass derived graphene like porous carbon electrodes for aqueous Li-ion hybrid supercapacitor

NASA Astrophysics Data System (ADS)

Ramkumar, B.; Yuvaraj, S.; Surendran, S.; Pandi, K.; Ramasamy, Hari Vignesh; Lee, Y. S.; Kalai Selvan, R.

2018-01-01

For the fabrication of aqueous Li-ion hybrid supercapacitor, carbon coated LiCo1/3Ni1/3Mn1/3O2 (or LiCo1/3Ni1/3Mn1/3O2@C composite) is synthesized by polymeric precursor method with subsequent thermal decomposition procedures for carbon coating. Graphene like porous carbon is obtained by chemical activation from the biomass of Agave Americana. The XRD analysis reveals that LiCo1/3Ni1/3Mn1/3O2 is having a hexagonal layered structure and activated carbon exists in both amorphous and graphitic nature. The TEM image infers that LiCo1/3Ni1/3Mn1/3O2 particles having the non-uniform shape with sub-micron size and the LiCo1/3Ni1/3Mn1/3O2 particles are embedded into amorphous carbon cloud in the composite. The activated carbon shows the specific surface area of 1219 m2 g-1. Finally, the fabricated aqueous LiCo1/3Ni1/3Mn1/3O2@C‖AC hybrid supercapacitor delivers the specific capacitance of 56 F g-1 with good capacity retention even after 5000 cycles.

High resolution amorphous silicon radiation detectors

DOEpatents

Street, R.A.; Kaplan, S.N.; Perez-Mendez, V.

1992-05-26

A radiation detector employing amorphous Si:H cells in an array with each detector cell having at least three contiguous layers (n-type, intrinsic, p-type), positioned between two electrodes to which a bias voltage is applied. An energy conversion layer atop the silicon cells intercepts incident radiation and converts radiation energy to light energy of a wavelength to which the silicon cells are responsive. A read-out device, positioned proximate to each detector element in an array allows each such element to be interrogated independently to determine whether radiation has been detected in that cell. The energy conversion material may be a layer of luminescent material having a columnar structure. In one embodiment a column of luminescent material detects the passage therethrough of radiation to be detected and directs a light beam signal to an adjacent a-Si:H film so that detection may be confined to one or more such cells in the array. One or both electrodes may have a comb structure, and the teeth of each electrode comb may be interdigitated for capacitance reduction. The amorphous Si:H film may be replaced by an amorphous Si:Ge:H film in which up to 40 percent of the amorphous material is Ge. Two dimensional arrays may be used in X-ray imaging, CT scanning, crystallography, high energy physics beam tracking, nuclear medicine cameras and autoradiography. 18 figs.

High resolution amorphous silicon radiation detectors

DOEpatents

Street, Robert A.; Kaplan, Selig N.; Perez-Mendez, Victor

1992-01-01

A radiation detector employing amorphous Si:H cells in an array with each detector cell having at least three contiguous layers (n type, intrinsic, p type), positioned between two electrodes to which a bias voltage is applied. An energy conversion layer atop the silicon cells intercepts incident radiation and converts radiation energy to light energy of a wavelength to which the silicon cells are responsive. A read-out device, positioned proximate to each detector element in an array allows each such element to be interrogated independently to determine whether radiation has been detected in that cell. The energy conversion material may be a layer of luminescent material having a columnar structure. In one embodiment a column of luminescent material detects the passage therethrough of radiation to be detected and directs a light beam signal to an adjacent a-Si:H film so that detection may be confined to one or more such cells in the array. One or both electrodes may have a comb structure, and the teeth of each electrode comb may be interdigitated for capacitance reduction. The amorphous Si:H film may be replaced by an amorphous Si:Ge:H film in which up to 40 percent of the amorphous material is Ge. Two dimensional arrays may be used in X-ray imaging, CT scanning, crystallography, high energy physics beam tracking, nuclear medicine cameras and autoradiography.

Effects of MgO and SiO2 on Plasma-Sprayed Hydroxyapatite Coating: An in Vivo Study in Rat Distal Femoral Defects.

PubMed

Ke, Dongxu; Robertson, Samuel F; Dernell, William S; Bandyopadhyay, Amit; Bose, Susmita

2017-08-09

Plasma-sprayed hydroxyapatite (HA)-coated titanium implants have been widely used in orthopedic applications due to their inheritance of an excellent mechanical property from titanium and great osteoconductivity from HA. However, the lack of osteoinductivity limits their further applications. In this study, 1 wt % MgO and 0.5 wt % SiO 2 were mixed with HA for making plasma-sprayed coatings on titanium implants. Plasma-sprayed HA- and MgO/SiO 2 -HA-coated titanium implants showed adhesive bond strengths of 25.73 ± 1.92 and 23.44 ± 2.89 MPa, respectively. The presence of MgO and SiO 2 significantly increased the osteogenesis, osseointegration, and bone mineralization of HA-coated titanium implants by the evaluation of their histomorphology after 6, 10, and 14 weeks of implantation in rat distal femoral defects. Implant pushout tests also showed a shear modulus of 149.83 ± 3.69 MPa for MgO/SiO 2 -HA-coated implants after 14 weeks of implantation, compared to 52.68 ± 10.41 MPa for uncoated implants and 83.92 ± 3.68 MPa for pure HA-coated implants; These are differences in the shear modulus of 96% and 56.4%, respectively. This study assesses for the first time the quality of the bone-implant interface of induction plasma-sprayed MgO and SiO 2 binary-doped HA coatings on load-bearing implants compared to bare titanium and pure HA coatings in a quantitative manner. Relating the osseointegration and interface shear modulus to the quality of implant fixation is critical to the advancement and implementation of HA-coated orthopedic implants.

Radiation-induced amorphization of Ce-doped Mg2Y8(SiO4)6O2 silicate apatite

NASA Astrophysics Data System (ADS)

Zhou, Jianren; Yao, Tiankai; Lian, Jie; Shen, Yiqiang; Dong, Zhili; Lu, Fengyuan

2016-07-01

Ce-doped Mg2Y8(SiO4)6O2 silicate apatite (Ce = 0.05 and 0.5) were irradiated with 1 MeV Kr2+ ion beam irradiation at different temperatures and their radiation response and the cation composition dependence of the radiation-induced amorphization were studied by in situ TEM. The two Ce-doped Mg2Y8(SiO4)6O2 silicate apatites are sensitive to ion beam induced amorphization with a low critical dose (0.096 dpa) at room temperature, and exhibits significantly different radiation tolerance at elevated temperatures. Ce concentration at the apatite AI site plays a critical role in determining the radiation response of this silicate apatite, in which the Ce3+ rich Mg2Y7.5Ce0.5(SiO4)6O2 displays lower amorphization susceptibility than Mg2Y7.95Ce0.05(SiO4)6O2 with a lower Ce3+ occupancy at the AI sites. The critical temperature (Tc) and activation energy (Ea) change from 667.5 ± 33 K and 0.162 eV of Mg2Y7.5Ce0.5(SiO4)6O2 to 963.6 ± 64 K and 0.206 eV of Mg2Y7.95Ce0.05(SiO4)6O2. We demonstrate that the radiation tolerance can be controlled by varying the chemical composition, and enhanced radiation tolerance is achieved by increasing the Ce concentration at the AI site.

High-Strength Ultra-Fine-Grained Hypereutectic Al-Si-Fe-X (X = Cr, Mn) Alloys Prepared by Short-Term Mechanical Alloying and Spark Plasma Sintering

PubMed Central

Průša, Filip; Bláhová, Markéta; Vojtěch, Dalibor; Kučera, Vojtěch; Bernatiková, Adriana; Kubatík, Tomáš František; Michalcová, Alena

2016-01-01

In this work, Al-20Si-10Fe-6Cr and Al-20Si-10Fe-6Mn (wt %) alloys were prepared by a combination of short-term mechanical alloying and spark plasma sintering. The microstructure was composed of homogeneously dispersed intermetallic particles forming composite-like structures. X-ray diffraction analysis and TEM + EDS analysis determined that the α-Al along with α-Al15(Fe,Cr)3Si2 or α-Al15(Fe,Mn)3Si2 phases were present, with dimensions below 130 nm. The highest hardness of 380 ± 7 HV5 was observed for the Al-20Si-10Fe-6Mn alloy, exceeding the hardness of the reference as-cast Al-12Si-1Cu-1 Mg-1Ni alloy (121 ± 2 HV5) by nearly a factor of three. Both of the prepared alloys showed exceptional thermal stability with the hardness remaining almost the same even after 100 h of annealing at 400 °C. Additionally, the compressive strengths of the Al-20Si-10Fe-6Cr and Al-20Si-10Fe-6Mn alloys reached 869 MPa and 887 MPa, respectively, and had virtually the same values of 870 MPa and 865 MPa, respectively, even after 100 h of annealing. More importantly, the alloys showed an increase in ductility at 400 °C, reaching several tens of percent. Thus, both of the investigated alloys showed better mechanical properties, including superior hardness, compressive strength and thermal stability, as compared to the reference Al-10Si-1Cu-1Mg-1Ni alloy, which softened remarkably, reducing its hardness by almost 50% to 63 ± 8 HV5. PMID:28774094

Formation of iron disilicide on amorphous silicon

NASA Astrophysics Data System (ADS)

Erlesand, U.; Östling, M.; Bodén, K.

1991-11-01

Thin films of iron disilicide, β-FeSi 2 were formed on both amorphous silicon and on crystalline silicon. The β-phase is reported to be semiconducting with a direct band-gap of about 0.85-0.89 eV. This phase is known to form via a nucleation-controlled growth process on crystalline silicon and as a consequence a rather rough silicon/silicide interface is usually formed. In order to improve the interface a bilayer structure of amorphous silicon and iron was sequentially deposited on Czochralski <111> silicon in an e-gun evaporation system. Secondary ion mass spectrometry profiling (SIMS) and scanning electron micrographs revealed an improvement of the interface sharpness. Rutherford backscattering spectrometry (RBS) and X-ray diffractiometry showed β-FeSi 2 formation already at 525°C. It was also observed that the silicide growth was diffusion-controlled, similar to what has been reported for example in the formation of NiSi 2 for the reaction of nickel on amorphous silicon. The kinetics of the FeSi 2 formation in the temperature range 525-625°C was studied by RBS and the activation energy was found to be 1.5 ± 0.1 eV.

New Approaches to the Computer Simulation of Amorphous Alloys: A Review.

PubMed

Valladares, Ariel A; Díaz-Celaya, Juan A; Galván-Colín, Jonathan; Mejía-Mendoza, Luis M; Reyes-Retana, José A; Valladares, Renela M; Valladares, Alexander; Alvarez-Ramirez, Fernando; Qu, Dongdong; Shen, Jun

2011-04-13

In this work we review our new methods to computer generate amorphous atomic topologies of several binary alloys: SiH, SiN, CN; binary systems based on group IV elements like SiC; the GeSe 2 chalcogenide; aluminum-based systems: AlN and AlSi, and the CuZr amorphous alloy. We use an ab initio approach based on density functionals and computationally thermally-randomized periodically-continued cells with at least 108 atoms. The computational thermal process to generate the amorphous alloys is the undermelt-quench approach, or one of its variants, that consists in linearly heating the samples to just below their melting (or liquidus) temperatures, and then linearly cooling them afterwards. These processes are carried out from initial crystalline conditions using short and long time steps. We find that a step four-times the default time step is adequate for most of the simulations. Radial distribution functions (partial and total) are calculated and compared whenever possible with experimental results, and the agreement is very good. For some materials we report studies of the effect of the topological disorder on their electronic and vibrational densities of states and on their optical properties.

New Approaches to the Computer Simulation of Amorphous Alloys: A Review

PubMed Central

Valladares, Ariel A.; Díaz-Celaya, Juan A.; Galván-Colín, Jonathan; Mejía-Mendoza, Luis M.; Reyes-Retana, José A.; Valladares, Renela M.; Valladares, Alexander; Alvarez-Ramirez, Fernando; Qu, Dongdong; Shen, Jun

2011-01-01

In this work we review our new methods to computer generate amorphous atomic topologies of several binary alloys: SiH, SiN, CN; binary systems based on group IV elements like SiC; the GeSe2 chalcogenide; aluminum-based systems: AlN and AlSi, and the CuZr amorphous alloy. We use an ab initio approach based on density functionals and computationally thermally-randomized periodically-continued cells with at least 108 atoms. The computational thermal process to generate the amorphous alloys is the undermelt-quench approach, or one of its variants, that consists in linearly heating the samples to just below their melting (or liquidus) temperatures, and then linearly cooling them afterwards. These processes are carried out from initial crystalline conditions using short and long time steps. We find that a step four-times the default time step is adequate for most of the simulations. Radial distribution functions (partial and total) are calculated and compared whenever possible with experimental results, and the agreement is very good. For some materials we report studies of the effect of the topological disorder on their electronic and vibrational densities of states and on their optical properties. PMID:28879948

Molecular dynamics study of interfacial thermal transport between silicene and substrates.

PubMed

Zhang, Jingchao; Hong, Yang; Tong, Zhen; Xiao, Zhihuai; Bao, Hua; Yue, Yanan

2015-10-07

In this work, the interfacial thermal transport across silicene and various substrates, i.e., crystalline silicon (c-Si), amorphous silicon (a-Si), crystalline silica (c-SiO2) and amorphous silica (a-SiO2) are explored by classical molecular dynamics (MD) simulations. A transient pulsed heating technique is applied in this work to characterize the interfacial thermal resistance in all hybrid systems. It is reported that the interfacial thermal resistances between silicene and all substrates decrease nearly 40% with temperature from 100 K to 400 K, which is due to the enhanced phonon couplings from the anharmonicity effect. Analysis of phonon power spectra of all systems is performed to interpret simulation results. Contradictory to the traditional thought that amorphous structures tend to have poor thermal transport capabilities due to the disordered atomic configurations, it is calculated that amorphous silicon and silica substrates facilitate the interfacial thermal transport compared with their crystalline structures. Besides, the coupling effect from substrates can improve the interface thermal transport up to 43.5% for coupling strengths χ from 1.0 to 2.0. Our results provide fundamental knowledge and rational guidelines for the design and development of the next-generation silicene-based nanoelectronics and thermal interface materials.

Development of Formulations for a-SiC and Manganese CMP and Post-CMP Cleaning of Cobalt

NASA Astrophysics Data System (ADS)

Lagudu, Uma Rames Krishna

We have investigated the chemical mechanical polishing (CMP) of amorphous SiC (a-SiC) and Mn and Post CMP cleaning of cobalt for various device applications. During the manufacture of copper interconnects using the damascene process the polishing of copper is followed by the polishing of the barrier material (Co, Mn, Ru and their alloys) and its post CMP cleaning. This is followed by the a-SiC hard mask CMP. Silicon carbide thin films, though of widespread use in microelectronic engineering, are difficult to process by CMP because of their hardness and chemical inertness. The earlier part of the SiC work discusses the development of slurries based on silica abrasives that resulted in high a-SiC removal rates (RRs). The ionic strength of the silica dispersion was found to play a significant role in enhancing material removal rate, while also providing very good post-polish surface-smoothness. For example, the addition of 50 mM potassium nitrate to a pH 8 aqueous slurry consisting of 10 wt % of silica abrasives and 1.47 M hydrogen peroxide increased the RR from about 150 nm/h to about 2100 nm/h. The role of ionic strength in obtaining such high RRs was investigated using surface zeta-potentials measurements and X-ray photoelectron spectroscopy (XPS). Evidently, hydrogen peroxide promoted the oxidation of Si and C to form weakly adhered species that were subsequently removed by the abrasive action of the silica particles. The effect of potassium nitrate in increasing material removal is attributed to the reduction in the electrostatic repulsion between the abrasive particles and the SiC surface because of screening of surface charges by the added electrolyte. We also show that transition metal compounds when used as additives to silica dispersions enhance a-SiC removal rates (RRs). Silica slurries containing potassium permanganate gave RRs as high as 2000 nm/h at pH 4. Addition of copper sulfate to this slurry further enhanced the RRs to ˜3500 nm/h at pH 6. Furthermore, addition of a low concentration of 250 ppm Brij-35 to this slurry suppressed the RRs of silicon dioxide to zero, while retaining the RRs of a-SiC at ˜2700 nm/h , a combination of RRs that is appropriate for hard mask polishing. The second part of this thesis focuses on the polishing of manganese which was proposed as a "self-forming" barrier material to prevent copper diffusion in advanced generation (22 nm and smaller) Si devices. A major challenge associated with such a self-forming Mn barrier for Cu interconnects in sub-22nm devices is galvanic corrosion that can occur at the Cu-Mn interface during chemical mechanical planarization. In the present work, it was shown that an aqueous solution of sucrose, BTA and potassium periodate reduces the corrosion potential gap between Cu and Mn to ˜ 0.01 V at pH 10 while also lowering the galvanic currents significantly and hence can be an excellent candidate for a polishing slurry. We discuss the role of these reagents and the inhibiting film that can be formed at the interface of the bimetallic system in this solution. Preliminary polishing results for Cu and Mn using a silica-based slurry formulated with this solution are also presented. The third part involves the development of compositions for Post CMP cleaning of cobalt barriers in advanced generation (22 nm and smaller). The thickness of the cobalt films was found to impact the corrosion behavior of the films. Thinner films of cobalt were found be more prone to galvanic corrosion in the presence of copper. The corrosion currents were low for both Cu and Co in all the solutions tested but the galvanic currents varied significantly. It was found that while BTA was not able to suppress the galvanic corrosion between Cu and Co (2000 A) at pH 8, either 60 mM of 3 Amino 1,2,4 triazole or 30 mM of 3 Amino 5 methyl thio 1,2,4 triazole were able to suppress the galvanic corrosion between Cu and Co (2000 A) to < 0.3 micro amperes per square cm at pH 8. These compositions however were not able to suppress the galvanic corrosion of Co (20 A) films. Changing the pH to 10 did not improve the results. Furthermore, addition of several complexing agents and other corrosion inhibitors also did not lower the Ecorr of Co (20 A) and Cu. Further experiments are being conducted to identify compositions to protect Co and Cu from corrosion. (Abstract shortened by UMI.).

Modeling of grain-oriented Si-steel and amorphous alloy iron core under ferroresonance using Jiles-Atherton hysteresis method

NASA Astrophysics Data System (ADS)

Sima, Wenxia; Zou, Mi; Yang, Ming; Yang, Qing; Peng, Daixiao

2018-05-01

Amorphous alloy is increasingly widely used in the iron core of power transformer due to its excellent low loss performance. However, its potential harm to the power system is not fully studied during the electromagnetic transients of the transformer. This study develops a simulation model to analyze the effect of transformer iron core materials on ferroresonance. The model is based on the transformer π equivalent circuit. The flux linkage-current (ψ-i) Jiles-Atherton reactor is developed in an Electromagnetic Transients Program-Alternative Transients Program and is used to represent the magnetizing branches of the transformer model. Two ferroresonance cases are studied to compare the performance of grain-oriented Si-steel and amorphous alloy cores. The ferroresonance overvoltage and overcurrent are discussed under different system parameters. Results show that amorphous alloy transformer generates higher voltage and current than those of grain-oriented Si-steel transformer and significantly harms the power system safety.

Electron-rich driven electrochemical solid-state amorphization in Li-Si alloys.

PubMed

Wang, Zhiguo; Gu, Meng; Zhou, Yungang; Zu, Xiaotao; Connell, Justin G; Xiao, Jie; Perea, Daniel; Lauhon, Lincoln J; Bang, Junhyeok; Zhang, Shengbai; Wang, Chongmin; Gao, Fei

2013-09-11

The physical and chemical behaviors of materials used in energy storage devices, such as lithium-ion batteries (LIBs), are mainly controlled by an electrochemical process, which normally involves insertion/extraction of ions into/from a host lattice with a concurrent flow of electrons to compensate charge balance. The fundamental physics and chemistry governing the behavior of materials in response to the ions insertion/extraction is not known. Herein, a combination of in situ lithiation experiments and large-scale ab initio molecular dynamics simulations are performed to explore the mechanisms of the electrochemically driven solid-state amorphization in Li-Si systems. We find that local electron-rich condition governs the electrochemically driven solid-state amorphization of Li-Si alloys. This discovery provides the fundamental explanation of why lithium insertion in semiconductor and insulators leads to amorphization, whereas in metals, it leads to a crystalline alloy. The present work correlates electrochemically driven reactions with ion insertion, electron transfer, lattice stability, and phase equilibrium.

Electron-Rich Driven Electrochemical Solid-State Amorphization in Li-Si Alloys

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

Wang, Zhiguo; Gu, Meng; Zhou, Yungang

2013-08-14

The physical and chemical behaviors of materials used in energy storage devices, such as lithium-ion batteries (LIBs), are mainly controlled by an electrochemical process, which normally involves insertion/extraction of ions into/from a host lattice with a concurrent flow of electrons to compensate charge balance. The fundamental physics and chemistry governing the behavior of materials in response to the ions insertion/extraction is not known. Herein, a combination of in situ lithiation experiments and large-scale ab initio molecular dynamics simulations are performed to explore the mechanisms of the electrochemically driven solid-state amorphization in Li-Si systems. We find that local electron-rich condition governsmore » the electrochemically driven solid-state amorphization of Li-Si alloys. This discovery provides the fundamental explanation of why lithium insertion in semiconductor and insulators leads to amorphization, whereas in metals, it leads to a crystalline alloy. The present work correlates electrochemically driven reactions with ion insertion, electron transfer, lattice stability and phase equilibrium.« less

Formation of the Fe-Containing Intermetallic Compounds during Solidification of Al-5Mg-2Si-0.7Mn-1.1Fe Alloy

NASA Astrophysics Data System (ADS)

Que, Zhongping; Wang, Yun; Fan, Zhongyun

2018-06-01

Iron (Fe) is the most common and the most detrimental impurity element in Al alloys due to the formation of Fe-containing intermetallic compounds (IMCs), which are harmful to mechanical performance of the Al-alloy components. In this paper we investigate the formation of Fe-containing IMCs during solidification of an Al-5Mg-2Si-0.7Mn-1.1Fe alloy under varied solidification conditions. We found that the primary Fe-containing intermetallic compound (P-IMC) in the alloy is the BCC α-Al15(Fe,Mn)3Si2 phase and has a polyhedral morphology with {1 1 0} surface termination. The formation of the P-IMCs can be easily suppressed by increasing the melt superheat and/or cooling rate, suggesting that the nucleation of the α-Al15(Fe,Mn)3Si2 phase is difficult. In addition, we found that the IMCs with a Chinese script morphology is initiated on the {1 0 0} surfaces of the P-IMCs during the binary eutectic reaction with the α-Al phase. Both the binary and ternary eutectic IMCs are also identified as the BCC α-Al15(Fe,Mn)3Si2 phase. Furthermore, we found that the Fe content increases and the Mn content decreases in the Fe-containing intermetallic compounds with the decrease of the formation temperature, although the sum of the Fe and Mn contents in all of the IMCs is constant.

Mechanism of γ-irradiation induced phase transformations in nanocrystalline Mn{sub 0.5}Zn{sub 0.5}Fe{sub 2}O{sub 4} ceramics

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

Jagadeesha Angadi, V.; Anupama, A.V.; Choudhary, Harish K.

The structural, infrared absorption and magnetic property transformations in nanocrystalline Mn{sub 0.5}Zn{sub 0.5}Fe{sub 2}O{sub 4} samples irradiated with different doses (0, 15, 25 and 50 kGy) of γ-irradiation were investigated in this work and a mechanism of phase transformation/decomposition is provided based on the metastable nature of the Mn-atoms in the spinel lattice. The nano-powder sample was prepared by solution combustion route and the pellets of the sample were exposed to γ-radiation. Up to a dose of 25 kGy of γ-radiation, the sample retained the single phase cubic spinel (Fd-3m) structure, but the disorder in the sample increased. On irradiatingmore » the sample with 50 kGy γ-radiation, the spinel phase decomposed into new stable phases such as α-Fe{sub 2}O{sub 3} and ZnFe{sub 2}O{sub 4} phases along with amorphous MnO phase, leading to a change in the surface morphology of the sample. Along with the structural transformations the magnetic properties deteriorated due to breakage of the ferrimagnetic order with higher doses of γ-irradiation. Our results are important for the understanding of the stability, durability and performance of the Mn-Zn ferrite based devices used in space applications. - Graphical abstract: The nanocrystalline Mn{sub 0.5}Zn{sub 0.5}Fe{sub 2}O{sub 4} ceramic sample transforms to crystalline α-Fe{sub 2}O{sub 3} and ZnFe{sub 2}O{sub 4} phases (and amorphous MnO phase) at a γ-irradiation dose of 50 kGy, as MnO goes out of the spinel lattice. The high energy γ-irradiation causes structural damage to the nanomaterials leading to change in morphology of the sample as seen in the SEM images. - Highlights: • Mn atoms are more unstable in the Mn-Zn ferrite spinel lattice than Zn-atoms. • Displacement of Mn atoms by γ-radiation from the lattice renders phase transformation. • In Mn{sub 0.5}Zn{sub 0.5}Fe{sub 2}O{sub 4}, Mn-ferrite cell transforms to crystalline α-Fe{sub 2}O{sub 3} and amorphous MnO. • The stable ZnFe{sub 2}O{sub 4} phase retains its structure even after 50 KGy γ-irradiation. • The γ-irradiation degrades the magnetic properties of Mn{sub 0.5}Zn{sub 0.5}Fe{sub 2}O{sub 4} ceramics.« less

High-energy X-ray powder diffraction and atomic-pair distribution-function studies of charged/discharged structures in carbon-hybridized Li2MnSiO4 nanoparticles as a cathode material for lithium-ion batteries

NASA Astrophysics Data System (ADS)

Moriya, Maki; Miyahara, Masahiko; Hokazono, Mana; Sasaki, Hirokazu; Nemoto, Atsushi; Katayama, Shingo; Akimoto, Yuji; Hirano, Shin-ichi; Ren, Yang

2014-10-01

The stable cycling performance with a high discharge capacity of ∼190 mAh g-1 in a carbon-hybridized Li2MnSiO4 nanostructured powder has prompted an experimental investigation of the charged/discharged structures using synchrotron-based and laboratory-based X-rays and atomic-pair distribution-function (PDF) analyses. A novel method of in-situ spray pyrolysis of a precursor solution with glucose as a carbon source enabled the successful synthesis of the carbon-hybridized Li2MnSiO4 nanoparticles. The XRD patters of the discharged (lithiated) samples exhibit a long-range ordered structure characteristic of the (β) Li2MnSiO4 crystalline phase (space group Pmn21) which dissipates in the charged (delithiated) samples. However, upon discharging the long-range ordered structure recovers in each cycle. The disordered structure, according to the PDF analysis, is mainly due to local distortions of the MnO4 tetrahedra which show a mean Mn-O nearest neighbor distance shorter than that of the long-range ordered phase. These results corroborate the notion of the smaller Mn3+/Mn4+ ionic radii in the Li extracted phase versus the larger Mn2+ ionic radius in Li inserted phase. Thus Li extraction/insertion drives the fluctuation between the disordered and the long-range ordered structures.

Synthesis and characterization of P-doped amorphous and nanocrystalline Si

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

Wang, Jialing; Ganguly, Shreyashi; Sen, Sabyasachi

Intentional impurity doping lies at the heart of the silicon technology. The dopants provide electrons or holes as necessary carriers of the electron current and can significantly modify the electric, optical and magnetic properties of the semiconductors. P-doped amorphous Si (a-Si) was prepared by a solid state and solution metathesis reaction of a P-doped Zintl phase precursor, NaSi 0.99P 0.01, with an excess of NH 4X (X = Br, I). After the salt byproduct was removed from the solid state reaction, the a-Si material was annealed at 600 °C under vacuum for 2 h, resulting in P-doped nanocrystalline Si (nc-Si)more » material embedded in a-Si matrix. The product from the solution reaction also shows a combination of nc-Si embedded in a-Si; however, it was fully converted to nc-Si after annealing under argon at 650 °C for 30 min. Powder X-ray diffraction (XRD) and high resolution transmission electron microscopy (HRTEM) show the amorphous nature of the P-doped Si material before the annealing and the nanocrystallinity after the annealing. Fourier Transform Infrared (FTIR) spectroscopy shows that the P-doped Si material surface is partially capped by H and O or with solvent. Finally, electron microprobe wavelength dispersive spectroscopy (WDS) as well as energy dispersive spectroscopy (EDS) confirm the presence of P in the Si material. 29Si and 31P solid state magic-angle-spinning nuclear magnetic resonance (MAS NMR) spectroscopy data provide the evidence of P doping into the Si structure with the P concentration of approximately 0.07 at.%.« less

Effective surface modification of MnFe2O4@SiO2@PMIDA magnetic nanoparticles for rapid and high-density antibody immobilization

NASA Astrophysics Data System (ADS)

Rashid, Zahra; Soleimani, Masoud; Ghahremanzadeh, Ramin; Vossoughi, Manouchehr; Esmaeili, Elaheh

2017-12-01

The present study is aimed at the synthesis of MnFe2O4@SiO2@PMIDA in terms of highly efficient sensing platform for anti-prostate specific membrane antigen (PSMA) immobilization. Superparamagnetic manganese ferrite nanoparticles were synthesized following co-precipitation method and then SiO2 shell was coated on the magnetic core with tetraethyl orthosilicate (TEOS) through a silanization reaction to prevent oxidation, agglomeration and, increase the density of OH groups on the surface of MnFe2O4. Subsequently, MnFe2O4@SiO2@PMIDA obtained as a result of the reaction between N-(phosphonomethyl)iminodiacetic acid (PMIDA) and MnFe2O4@SiO2. The reactive carboxyl groups on the surface of magnetic nanoparticles can efficiently conjugate to a monoclonal antibody, specific to PSMA, which was confirmed by enzyme-linked immune sorbent assay (ELISA). Thus, this kind of functionalized magnetic nanoparticles is promising to be utilized in the improvement of ELISA-based biosensors and also will be effective in a variety of biomedical applications such as cell separation, diagnosis, and monitoring of human diseases.

Biodegradable FeMnSi Sputter-Coated Macroporous Polypropylene Membranes for the Sustained Release of Drugs

PubMed Central

Fornell, Jordina; Soriano, Jorge; Guerrero, Miguel; Sirvent, Juan de Dios; Ferran-Marqués, Marta; Ibáñez, Elena; Barrios, Leonardo; Baró, Maria Dolors; Suriñach, Santiago; Nogués, Carme; Sort, Jordi; Pellicer, Eva

2017-01-01

Pure Fe and FeMnSi thin films were sputtered on macroporous polypropylene (PP) membranes with the aim to obtain biocompatible, biodegradable and, eventually, magnetically-steerable platforms. Room-temperature ferromagnetic response was observed in both Fe- and FeMnSi-coated membranes. Good cell viability was observed in both cases by means of cytotoxicity studies, though the FeMnSi-coated membranes showed higher biodegradability than the Fe-coated ones. Various strategies to functionalize the porous platforms with transferrin-Alexa Fluor 488 (Tf-AF488) molecules were tested to determine an optimal balance between the functionalization yield and the cargo release. The distribution of Tf-AF488 within the FeMnSi-coated PP membranes, as well as its release and uptake by cells, was studied by confocal laser scanning microscopy. A homogeneous distribution of the drug within the membrane skeleton and its sustained release was achieved after three consecutive impregnations followed by the addition of a layer made of gelatin and maltodextrin, which prevented exceedingly fast release. The here-prepared organic-inorganic macroporous membranes could find applications as fixed or magnetically-steerable drug delivery platforms. PMID:28672792

Electrically Active Defects In Solar Cells Based On Amorphous Silicon/Crystalline Silicon Heterojunction After Irradiation By Heavy Xe Ions

NASA Astrophysics Data System (ADS)

Harmatha, Ladislav; Mikolášek, Miroslav; Stuchlíková, L'ubica; Kósa, Arpád; Žiška, Milan; Hrubčín, Ladislav; Skuratov, Vladimir A.

2015-11-01

The contribution is focused on the diagnostics of structures with a heterojunction between amorphous and crystalline silicon prepared by HIT (Heterojunction with an Intrinsic Thin layer) technology. The samples were irradiated by Xe ions with energy 167 MeV and doses from 5 × 108 cm-2 to 5 × 1010 cm-2. Radiation defects induced in the bulk of Si and at the hydrogenated amorphous silicon and crystalline silicon (a-Si:H/c-Si) interface were identified by Deep Level Transient Spectroscopy (DLTS). Radiation induced A-centre traps, boron vacancy traps and different types of divacancies with a high value of activation energy were observed. With an increased fluence of heavy ions the nature and density of the radiation induced defects was changed.

H and H2 NMR properties in amorphous hydrogenated silicon (a-Si:H)

NASA Astrophysics Data System (ADS)

Lee, Sook

1986-07-01

It is shown that the basic NMR properties of ortho-H2 molecules with a rotational angular momentum J and a spin angular momentum I under the influence of a completely asymmetric crystalline field in an amorphous matrix can be described by an effective nuclear spin Hamiltonian which contains only the nuclear spin angular momentum operators (Ii), but is independent of the molecular rotational angular momentum operators (Ji). By directly applying the existing magnetic-resonance theories to this effective nuclear spin Hamiltonian, a simple description is presented for various static and dynamic NMR properties of the ortho-H2 NMR centers in amorphous hydrogenated silicon (a-Si:H), thereby resolving many difficulties and uncertainties encountered in understanding and explaining the H and H2 NMR observations in a-Si:H.

Ab initio study of Fe{sub 2}MnZ (Al, Si, Ge) Heusler alloy using GGA approximation

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

Jain, Vivek Kumar, E-mail: vivek.jain129@gmail.com; Jain, Vishal, E-mail: vivek.jain129@gmail.com; Lakshmi, N., E-mail: vivek.jain129@gmail.com

Density functional theory based on FP-LAPW method used to investigate the electronic structure of Fe{sub 2}MnZ, shows that the total spin magnetic moment shows a trend consistent with the Slater–Pauling curve. The Fe and Mn magnetic moment depend on choice of Z element although the magnetic moment of Z element is negative and less than 0.1 μ{sub B}. Spin polarization calculations evidence 100% spin polarization for Fe{sub 2}MnSi. Fe{sub 2}MnAl and Fe{sub 2}MnGe show metallic behavior with 93%, 98% spin polarization.

Heteroepitaxial Growth of Ferromagnetic MnSb(0001) Films on Ge/Si(111) Virtual Substrates.

PubMed

Burrows, Christopher W; Dobbie, Andrew; Myronov, Maksym; Hase, Thomas P A; Wilkins, Stuart B; Walker, Marc; Mudd, James J; Maskery, Ian; Lees, Martin R; McConville, Christopher F; Leadley, David R; Bell, Gavin R

2013-11-06

Molecular beam epitaxial growth of ferromagnetic MnSb(0001) has been achieved on high quality, fully relaxed Ge(111)/Si(111) virtual substrates grown by reduced pressure chemical vapor deposition. The epilayers were characterized using reflection high energy electron diffraction, synchrotron hard X-ray diffraction, X-ray photoemission spectroscopy, and magnetometry. The surface reconstructions, magnetic properties, crystalline quality, and strain relaxation behavior of the MnSb films are similar to those of MnSb grown on GaAs(111). In contrast to GaAs substrates, segregation of substrate atoms through the MnSb film does not occur, and alternative polymorphs of MnSb are absent.

Anomalous Hall conductivity and electronic structures of Si-substituted Mn2CoAl epitaxial films

NASA Astrophysics Data System (ADS)

Arima, K.; Kuroda, F.; Yamada, S.; Fukushima, T.; Oguchi, T.; Hamaya, K.

2018-02-01

We study anomalous Hall conductivity (σAHC) and electronic band structures of Si-substituted Mn2CoAl (Mn2CoAl1 -xSix ). First-principles calculations reveal that the electronic band structure is like a spin-gapless system even after substituting a quaternary element of Si for Al up to x =0.2 in Mn2CoAl1 -xSix . This means that the Si substitution enables the Fermi-level shift without largely changing the electronic structures in Mn2CoAl . By using molecular beam epitaxy techniques, Mn2CoAl1 -xSix epitaxial films can be grown, leading to the systematic control of x (0 ⩽x ⩽0.3 ). In addition to the electrical conductivity, the values of σAHC for the Mn2CoAl1 -xSix films are similar to those in Mn2CoAl films shown in previous reports. We note that a very small σAHC of ˜1.1 S/cm is obtained for x = 0.225, and the sign of σAHC is changed from positive to negative at around x = 0.25. We discuss the origin of the sign reversal of σAHC as a consequence of the Fermi-level shift in Mn2CoAl . Considering the presence of the structural disorder in the Mn2CoAl1 -xSix films, we can conclude that the small value and sign reversal of σAHC are not related to the characteristics of spin-gapless semiconductors.

Anisotropic electrical conduction and reduction in dangling-bond density for polycrystalline Si films prepared by catalytic chemical vapor deposition

NASA Astrophysics Data System (ADS)

Niikura, Chisato; Masuda, Atsushi; Matsumura, Hideki

1999-07-01

Polycrystalline Si (poly-Si) films with high crystalline fraction and low dangling-bond density were prepared by catalytic chemical vapor deposition (Cat-CVD), often called hot-wire CVD. Directional anisotropy in electrical conduction, probably due to structural anisotropy, was observed for Cat-CVD poly-Si films. A novel method to separately characterize both crystalline and amorphous phases in poly-Si films using anisotropic electrical conduction was proposed. On the basis of results obtained by the proposed method and electron spin resonance measurements, reduction in dangling-bond density for Cat-CVD poly-Si films was achieved using the condition to make the quality of the included amorphous phase high. The properties of Cat-CVD poly-Si films are found to be promising in solar-cell applications.

Hierarchical Mn2O3 Microspheres In-Situ Coated with Carbon for Supercapacitors with Highly Enhanced Performances

PubMed Central

Gong, Feilong; Lu, Shuang; Peng, Lifang; Zhou, Jing; Kong, Jinming; Jia, Dianzeng; Li, Feng

2017-01-01

Porous Mn2O3 microspheres have been synthesized and in-situ coated with amorphous carbon to form hierarchical C@Mn2O3 microspheres by first producing MnCO3 microspheres in solvothermal reactions, and then annealing at 500 °C. The self-assembly growth of MnCO3 microspheres can generate hollow structures inside each of the particles, which can act as micro-reservoirs to store biomass-glycerol for generating amorphous carbon onto the surfaces of Mn2O3 nanorods consisting of microspheres. The C@Mn2O3 microspheres, prepared at 500 °C, exhibit highly enhanced pseudocapacitive performances when compared to the particles after annealed at 400 °C and 600 °C. Specifically, the C@Mn2O3 microspheres prepared at 500 °C show high specific capacitances of 383.87 F g−1 at current density of 0.5 A g−1, and excellent cycling stability of 90.47% of its initial value after cycling for 5000 times. The asymmetric supercapacitors assembled with C@Mn2O3 microspheres after annealed at 500 °C and activated carbon (AC) show an energy density of up to 77.8 Wh kg−1 at power density of 500.00 W kg−1, and a maximum power density of 20.14 kW kg−1 at energy density of 46.8 Wh kg−1. We can attribute the enhanced electrochemical performances of the materials to their three-dimensional (3D) hierarchical structure in-situ coated with carbon. PMID:29168756

The Sands of the Bagnold Dunes, Mars and Volatiles in Mars Soils

NASA Astrophysics Data System (ADS)

Ehlmann, B. L.; Edgett, K. S.; Sutter, B.; Achilles, C.; Litvak, M. L.; Lapotre, M. G. A.; Sullivan, R. J., Jr.; Fraeman, A. A.; Arvidson, R. E.; Blake, D. F.; Bridges, N. T.; Conrad, P. G.; Cousin, A.; Downs, R. T.; Gabriel, T. S. J.; Gellert, R.; Hamilton, V. E.; Hardgrove, C. J.; Johnson, J. R.; Kuhn, S.; Mahaffy, P. R.; Maurice, S.; Meslin, P. Y.; McHenry, M.; Ming, D. W.; Minitti, M. E.; Morookian, J.; Morris, R. V.; O'Connell-Cooper, C.; Pinet, P. C.; Rowland, S. K.; Schröder, S.; Siebach, K. L.; Stein, N.; Thompson, L. M.; Vaniman, D.; Vasavada, A. R.; Wellington, D. F.; Wiens, R. C.; Yen, A.

2017-12-01

The Mars Science Laboratory Curiosity rover performed coordinated measurements to examine the textures and compositions of aeolian sands in an active portion of the Bagnold dune field. The composition and grain size information were reviewed in Ehlmann et al. [2017, JGR-Planets and papers referenced therein]. The Bagnold sands are rounded to subrounded, very fine to medium sized ( 45-500 μm) with ≥6 distinct grain colors. In contrast to sands examined by Curiosity in a dust-covered, inactive bedform called Rocknest and soils at other landing sites, Bagnold sands are darker, less red, better sorted, have fewer silt-sized or smaller grains, and show no evidence for cohesion. Nevertheless, Bagnold mineralogy and Rocknest mineralogy are similar with plagioclase, olivine, and pyroxenes in similar proportions comprising >90% of crystalline phases, along with a substantial amorphous component (35% ± 15%) [Achilles et al., 2017]. Like Rocknest, release of CO2 and NO is higher than Gale rocks, implying enrichment in the carrier phases of these volatiles [Sutter et al., 2017]. Yet Bagnold and Rocknest bulk chemistries differ. Bagnold sands are Si-enriched relative to other soils at Gale crater [Cousin et al., 2017; O'Connell-Cooper et al., 2017], and H2O, S, and Cl are lower relative to all previously measured Martian soils and most Gale crater rocks. Mg, Ni, Fe, and Mn are enriched in the coarse-sieved fraction of Bagnold sands [Cousin et al., 2017; O'Connell-Cooper et al., 2017], corroborated by visible/near-infrared spectra that suggest enrichment of olivine [Johnson et al., 2017]. Collectively, patterns in major element chemistry and volatile release data indicate two distinctive volatile reservoirs in Martian soils: (1) amorphous components in the sand-sized fraction (represented by Bagnold) that are Si-enriched, hydroxylated alteration products and/or impact or volcanic glasses and (2) amorphous components in the fine fraction (<40 μm; represented by Rocknest and other bright soils) that are Fe, S, and Cl enriched with low Si and adsorbed and structural H2O. This has implications for the origins of the volatiles and their potential extractability. Future isotopic measurements of later-acquired sand samples may help elucidate the origins and timing of the volatiles sequestration in Martian sands and soils.

77 FR 32513 - Hot-Rolled Flat-Rolled Carbon-Quality Steel Products From the Russian Federation; Preliminary...

Federal Register 2010, 2011, 2012, 2013, 2014

2012-06-01

..., physical and mechanical specifications: C Mn P S Si Cr Cu Ni 0.10-0.14% 0.90% Max 0.025% Max 0.005% Max 0... meets the following chemical, physical and mechanical specifications: C Mn P S Si Cr Cu Ni 0.10-0.16% 0... specifications: C Mn P S Si Cr Cu Ni 0.10-0.14% 1.30-1.80% 0.025% Max 0.005% Max 0.30-0.50% 0.50-0.70% 0.20-0.40...

Structural analysis of ion-implanted chemical-vapor-deposited diamond by transmission electron microscope

NASA Astrophysics Data System (ADS)

Jiang, N.; Deguchi, M.; Wang, C. L.; Won, J. H.; Jeon, H. M.; Mori, Y.; Hatta, A.; Kitabatake, M.; Ito, T.; Hirao, T.; Sasaki, T.; Hiraki, A.

1997-04-01

A transmission electron microscope (TEM) study of ion-implanted chemical-vapor-deposited (CVD) diamond is presented. CVD diamond used for transmission electron microscope observation was directly deposited onto Mo TEM grids. As-deposited specimens were irradiated by C (100 keV) ions at room temperature with a wide range of implantation doses (10 12-10 17/cm 2). Transmission electron diffraction (TED) patterns indicate that there exists a critical dose ( Dc) for the onset of amorphization of CVD diamond as a result of ion induced damage and the value of critical dose is confirmed to be about 3 × 10 15/cm 2. The ion-induced transformation process is clearly revealed by high resolution electron microscope (HREM) images. For a higher dose implantation (7 × 10 15/cm 2) a large amount of diamond phase is transformed into amorphous carbon and many tiny misoriented diamond blocks are found to be left in the amorphous solid. The average size of these misoriented diamond blocks is only about 1-2 nm. Further bombardment (10 17/cm 2) almost kills all of the diamond phase within the irradiated volume and moreover leads to local formation of micropolycrystalline graphite.

In situ spectroscopic study of the plastic deformation of amorphous silicon under nonhydrostatic conditions induced by indentation

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

Gerbig, Yvonne B.; Michaels, C. A.; Bradby, Jodie E.

Indentation-induced plastic deformation of amorphous silicon (a-Si) thin films was studied by in situ Raman imaging of the deformed contact region of an indented sample, employing a Raman spectroscopy-enhanced instrumented indentation technique (IIT). The occurrence and evolving spatial distribution of changes in the a-Si structure caused by processes, such as polyamorphization and crystallization, induced by indentation loading were observed. Furthermore, the obtained experimental results are linked with previously published work on the plastic deformation of a-Si under hydrostatic compression and shear deformation to establish a model for the deformation behavior of a-Si under indentation loading.

In situ spectroscopic study of the plastic deformation of amorphous silicon under nonhydrostatic conditions induced by indentation

DOE PAGES

Gerbig, Yvonne B.; Michaels, C. A.; Bradby, Jodie E.; ...

2015-12-17

Indentation-induced plastic deformation of amorphous silicon (a-Si) thin films was studied by in situ Raman imaging of the deformed contact region of an indented sample, employing a Raman spectroscopy-enhanced instrumented indentation technique (IIT). The occurrence and evolving spatial distribution of changes in the a-Si structure caused by processes, such as polyamorphization and crystallization, induced by indentation loading were observed. Furthermore, the obtained experimental results are linked with previously published work on the plastic deformation of a-Si under hydrostatic compression and shear deformation to establish a model for the deformation behavior of a-Si under indentation loading.

Magnetism from Fe2O3 nanoparticles embedded in amorphous SiO2 matrix

NASA Astrophysics Data System (ADS)

Sendil Kumar, A.; Bhatnagar, Anil K.

2018-02-01

Fe2O3 nanoparticles are embedded in amorphous SiO2 matrix by coprecipitation method with varying concentrations. Conditions are optimized to get almost monodispersed Fe2O3 nanoparticles with high chemical stability. Microstructure of synthesized nanoparticles is well characterized and found that Fe2O3 is in nanocrystalline form and embedded uniformly in amorphous SiO2 matrix. Enhanced surface reactivity is found for nanoparticles which influences physical properties of the SiO2 supported Fe2O3 system due to adsorption. In oxide nanoparticles, significant number of defect sites at the surface is expected but when supported medium such as SiO2 it reduces this defect concentration. Field- and temperature-dependent magnetisation studies on these samples show superparamagnetic behaviour. Superparamagnetic behaviour is seen in all the concentration systems but the coercivity observed in the lower concentration systems is found to be anomalous compared to that of higher concentrations. The observed magnetic behaviour comes from either unsaturated bond existing due to the absence of anions at the surface of nanoparticles or reconstruction of atomic orbitals taking place at interface of Fe2O3-SiO2 system.

In vitro and in vivo genotoxicity investigations of differently sized amorphous SiO2 nanomaterials.

PubMed

Maser, Elena; Schulz, Markus; Sauer, Ursula G; Wiemann, Martin; Ma-Hock, Lan; Wohlleben, Wendel; Hartwig, Andrea; Landsiedel, Robert

2015-12-01

In vitro and in vivo genotoxic effects of differently sized amorphous SiO2 nanomaterials were investigated. In the alkaline Comet assay (with V79 cells), non-cytotoxic concentrations of 300 and 100-300μg/mL 15nm-SiO2 and 55nm-SiO2, respectively, relevant (at least 2-fold relative to the negative control) DNA damage. In the Alkaline unwinding assay (with V79 cells), only 15nm-SiO2 significantly increased DNA strand breaks (and only at 100μg/mL), whereas neither nanomaterial (up to 300μg/mL) increased Fpg (Formamidopyrimidine DNA glycosylase)-sensitive sites reflecting oxidative DNA base modifications. In the Comet assay using rat precision-cut lung slices, 15nm-SiO2 and 55nm-SiO2 induced significant DNA damage at ≥100μg/mL. In the Alkaline unwinding assay (with A549 cells), 30nm-SiO2 and 55nm-SiO2 (with larger primary particle size (PPS)) induced significant increases in DNA strand breaks at ≥50μg/mL, whereas 9nm-SiO2 and 15nm-SiO2 (with smaller PPS) induced significant DNA damage at higher concentrations. These two amorphous SiO2 also increased Fpg-sensitive sites (significant at 100μg/mL). In vivo, within 3 days after single intratracheal instillation of 360μg, neither 15nm-SiO2 nor 55nm-SiO2 caused genotoxic effects in the rat lung or in the bone marrow. However, pulmonary inflammation was observed in both test groups with findings being more pronounced upon treatment with 15nm-SiO2 than with 55nm-SiO2. Taken together, the study shows that colloidal amorphous SiO2 with different particle sizes may induce genotoxic effects in lung cells in vitro at comparatively high concentrations. However, the same materials elicited no genotoxic effects in the rat lung even though pronounced pulmonary inflammation evolved. This may be explained by the fact that a considerably lower dose reached the target cells in vivo than in vitro. Additionally, the different time points of investigation may provide more time for DNA damage repair after instillation. Copyright © 2015 The Authors. Published by Elsevier B.V. All rights reserved.

Unique light-induced degradation in yellow-emitting K₂SiF₆:Mn²⁺ phosphor

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

Oyama, Takuya; Adachi, Sadao, E-mail: adachi@el.gunma-u.ac.jp

2014-10-07

Photo-induced luminescence intensity degradation in yellow-emitting K₂SiF₆:Mn²⁺ phosphor is studied using x-ray diffraction measurement, photoluminescence (PL) analysis, PL excitation (PLE) spectroscopy, PL decay analysis, and electron spin resonance (ESR) measurement. The yellow-emitting K₂SiF₆:Mn²⁺ phosphor exhibits remarkable degradation in the PL intensity under Xe lamp exposure. Coherent laser irradiation also induces degradation and its degree is in the order of He–Cd (λ = 325 nm) > Ar⁺ (488 nm) > He–Ne laser (632.8 nm). The degradation mechanism is proposed to be due to change in the valence state of manganese ions from Mn²⁺ to Mn³⁺ by the photooxidation (Mn²⁺ → Mn³⁺)more » or disproportionation reaction (2Mn²⁺ → Mn⁺ + Mn³⁺). The ESR measurement confirms the decreased Mn²⁺ spin density in the sample exposed with Xe lamp. The PLE spectrum suggests that the excitation of Mn³⁺ ions occurs through energy transfer upon absorption of exciting radiation by the Mn²⁺ ions. Thermal annealing of the degraded samples at ≥200 °C causes a blueshift in the PL emission band with an appearance of the Mn⁴⁺-related sharp red emission lines.« less

Reaction of amorphous/crystalline SiOC/Fe interfaces by thermal annealing

DOE PAGES

Su, Qing; Zhernenkov, Mikhail; Ding, Hepeng; ...

2017-06-12

The development of revolutionary new alloys and composites is crucial to meeting materials requirements for next generation nuclear reactors. The newly developed amorphous silicon oxycarbide (SiOC) and crystalline Fe composite system has shown radiation tolerance over a wide range of temperatures. To advance understanding of this new composite, we investigate the structure and thermal stability of the interface between amorphous SiOC and crystalline Fe by combining various experimental techniques and simulation methods. We show that the SiOC/Fe interface is thermally stable up to at least 400 °C. When the annealing temperature reaches 600 °C, an intermixed region forms at thismore » interface. This region appears to be a crystalline phase that forms an incoherent interface with the Fe layer. Density functional theory (DFT) Molecular dynamics (MD) is performed on the homogeneous SiFeOC phase to study the early stages of 2 formation of the intermixed layer. Both experimental and simulation results suggest this phase has the fayalite crystal structure. As a result, the physical processes involved in the formation of the intermixed region are discussed.« less

Temperature-Dependent Helium Ion-Beam Mixing in an Amorphous SiOC/Crystalline Fe Composite

DOE PAGES

Su, Qing; Price, Lloyd; Shao, Lin; ...

2016-10-31

Temperature dependent He-irradiation-induced ion-beam mixing between amorphous silicon oxycarbide (SiOC) and crystalline Fe was examined with a transmission electron microscope (TEM) and via Rutherford backscattering spectrometry (RBS). The Fe marker layer (7.2 ± 0.8 nm) was placed in between two amorphous SiOC layers (200 nm). The amount of ion-beam mixing after 298, 473, 673, 873, and 1073 K irradiation was investigated. Both TEM and RBS results showed no ion-beam mixing between Fe and SiOC after 473 and 673 K irradiation and a very trivial amount of ion-beam mixing (~2 nm) after 298 K irradiation. At irradiation temperatures higher than 873more » K, the Fe marker layer broke down and RBS could no longer be used to quantitatively examine the amount of ion mixing. The results indicate that the Fe/SiOC nanocomposite is thermally stable and tends to demix in the temperature range from 473 to 673 K. For application of this composite structure at temperatures of 873 K or higher, layer stability is a key consideration.« less

3D hierarchical assembly of ultrathin MnO2 nanoflakes on silicon nanowires for high performance micro-supercapacitors in Li- doped ionic liquid

PubMed Central

Dubal, Deepak P.; Aradilla, David; Bidan, Gérard; Gentile, Pascal; Schubert, Thomas J.S.; Wimberg, Jan; Sadki, Saïd; Gomez-Romero, Pedro

2015-01-01

Building of hierarchical core-shell hetero-structures is currently the subject of intensive research in the electrochemical field owing to its potential for making improved electrodes for high-performance micro-supercapacitors. Here we report a novel architecture design of hierarchical MnO2@silicon nanowires (MnO2@SiNWs) hetero-structures directly supported onto silicon wafer coupled with Li-ion doped 1-Methyl-1-propylpyrrolidinium bis(trifluromethylsulfonyl)imide (PMPyrrBTA) ionic liquids as electrolyte for micro-supercapacitors. A unique 3D mesoporous MnO2@SiNWs in Li-ion doped IL electrolyte can be cycled reversibly across a voltage of 2.2 V and exhibits a high areal capacitance of 13 mFcm−2. The high conductivity of the SiNWs arrays combined with the large surface area of ultrathin MnO2 nanoflakes are responsible for the remarkable performance of these MnO2@SiNWs hetero-structures which exhibit high energy density and excellent cycling stability. This combination of hybrid electrode and hybrid electrolyte opens up a novel avenue to design electrode materials for high-performance micro-supercapacitors. PMID:25985388

White long-lasting phosphorescence generation in a CaAl2Si2O8 : Eu2+, Mn2+, Dy3+ system through persistent energy transfer

NASA Astrophysics Data System (ADS)

Zhang, Jinsu; Chen, Baojiu; Sun, Jiashi; Li, Xiangping; Cheng, Lihong; Zhong, Haiyang

2012-08-01

Based on the persistent energy transfer principle, Mn2+ was introduced into a CaAl2Si2O8 : Eu2+/Dy3+ phosphor to achieve white long-lasting emissions. Eu2+, Mn2+ and Dy3+ tri-doped CaAl2Si2O8 phosphors with various Mn2+ concentrations were prepared via a solid-state reaction, and the crystal structure of the phosphors was identified by the x-ray diffraction technique. The luminescent properties of the Eu2+, Mn2+ and Dy3+ tri-doped CaAl2Si2O8 phosphors were studied. The energy transfer behaviour from Eu2+ to Mn2+ was analysed within the framework of Dexter theory. The physical mechanism of energy transfer was assigned to the electric dipole-quadrupole interaction. It was also demonstrated that the colour coordinates of the phosphors can be tuned from the blue region to the white region in the colour space. Furthermore, the afterglow decay and thermoluminescence curves were measured, indicating excellent phosphorescence properties of the current phosphors.

Fabrication of Si-As-Te ternary amorphous semiconductor in the microgravity environment (M-13)

NASA Technical Reports Server (NTRS)

Hamakawa, Yoshihiro

1993-01-01

Ternary chalcogenide Si-As-Te system is an interesting semiconductor from the aspect of both basic physics and technological applications. Since a Si-As-Te system consists of a IV-III-II hedral bonding network, it has a very large glass forming region with a wide physical constant controllability. For example, its energy gap can be controlled in a range from 0.6 eV to 2.5 eV, which corresponds to the classical semiconductor Ge (0.66 eV), Si (1.10 eV), GaAs (1.43 eV), and GaP (2.25 eV). This fact indicates that it would be a suitable system to investigate the compositional dependence of the atomic and electronic properties in the random network of solids. In spite of these significant advantages in the Si-As-Te amorphous system, a big barrier impending the wide utilization of this material is the huge difficulty encountered in the material preparation which results from large differences in the weight density, melting point, and vapor pressure of individual elements used for the alloying composition. The objective of the FMPT/M13 experiment is to fabricate homogeneous multi-component amorphous semiconductors in the microgravity environment of space, and to make a series of comparative characterizations of the amorphous structures and their basic physical constants on the materials prepared both in space and in normal terrestrial gravity.

Magnesium and Manganese Silicides For Efficient And Low Cost Thermo-Electric Power Generation

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

Trivedi, Sudhir B.; Kutcher, Susan W.; Rosemeier, Cory A.

2013-12-02

Thermoelectric Power Generation (TEPG) is the most efficient and commercially deployable power generation technology for harvesting wasted heat from such things as automobile exhausts, industrial furnaces, and incinerators, and converting it into usable electrical power. We investigated the materials magnesium silicide (Mg2Si) and manganese silicide (MnSi) for TEG. MgSi2 and MnSi are environmentally friendly, have constituent elements that are abundant in the earth's crust, non-toxic, lighter and cheaper. In Phase I, we successfully produced Mg2Si and MnSi material with good TE properties. We developed a novel technique to synthesize Mg2Si with good crystalline quality, which is normally very difficult duemore » to high Mg vapor pressure and its corrosive nature. We produced n-type Mg2Si and p-type MnSi nanocomposite pellets using FAST. Measurements of resistivity and voltage under a temperature gradient indicated a Seebeck coefficient of roughly 120 V/K on average per leg, which is quite respectable. Results indicated however, that issues related to bonding resulted in high resistivity contacts. Determining a bonding process and bonding material that can provide ohmic contact from room temperature to the operating temperature is an essential part of successful device fabrication. Work continues in the development of a process for reproducibly obtaining low resistance electrical contacts.« less

The reduction of critical H implantation dose for ion cut by incorporating B-doped SiGe/Si superlattice into Si substrate

NASA Astrophysics Data System (ADS)

Xue, Zhongying; Chen, Da; Jia, Pengfei; Wei, Xing; Di, Zengfeng; Zhang, Miao

2016-11-01

An approach to achieve Si or SiGe film exfoliation with as low as 3 × 1016/cm2 H implantation dose was investigated. Two intrinsic Si0.75Ge0.25/Si samples, merged with B-doped Si0.75Ge0.25 layer and B-doped Si0.75Ge0.25/Si superlattice (SL) layer respectively, were used to study the formation of crack after 3 × 1016/cm2 H implantation and annealing. For the sample into which B doped Si0.75Ge0.25 layer is incorporated, only few discrete cracks are observed along both sides of the B doped Si0.75Ge0.25 layer; on the contrary, a continuous (100) oriented crack is formed in the B-doped Si0.75Ge0.25/Si SL layer, which means ion cut can be achieved using this material with 3 × 1016/cm2 H implantation. As the SIMS profiles confirm that hydrogen tends to be trapped at B-doped SiGe/Si interface, the formation of continuous crack in SL layer can be ascribed to the more efficient hydrogen trapping by the multiple B-doped SiGe/Si interfaces.

Effect of Ion Flux (Dose Rate) in Source-Drain Extension Ion Implantation for 10-nm Node FinFET and Beyond on 300/450mm Platforms

NASA Astrophysics Data System (ADS)

Shen, Ming-Yi

The improvement of wafer equipment productivity has been a continuous effort of the semiconductor industry. Higher productivity implies lower product price, which economically drives more demand from the market. This is desired by the semiconductor manufacturing industry. By raising the ion beam current of the ion implanter for 300/450mm platforms, it is possible to increase the throughput of the ion implanter. The resulting dose rate can be comparable to the performance of conventional ion implanters or higher, depending on beam current and beam size. Thus, effects caused by higher dose rate must be investigated further. One of the major applications of ion implantation (I/I) is source-drain extension (SDE) I/I for the silicon FinFET device. This study investigated the dose rate effects on the material properties and device performance of the 10-nm node silicon FinFET. In order to gain better understanding of the dose rate effects, the dose rate study is based on Synopsys Technology CAD (TCAD) process and device simulations that are calibrated and validated using available structural silicon fin samples. We have successfully shown that the kinetic monte carlo (KMC) I/I simulation can precisely model both the silicon amorphization and the arsenic distribution in the fin by comparing the KMC simulation results with TEM images. The results of the KMC I/I simulation show that at high dose rate more activated arsenic dopants were in the source-drain extension (SDE) region. This finding matches with the increased silicon amorphization caused by the high dose-rate I/I, given that the arsenic atoms could be more easily activated by the solid phase epitaxial regrowth process. This increased silicon amorphization led to not only higher arsenic activation near the spacer edge, but also less arsenic atoms straggling into the channel. Hence, it is possible to improve the throughput of the ion implanter when the dopants are implanted at high dose rate if the same doping level with a lower wafer dose can be achieved. In addition, the leakage current might also be reduced due to less undesired dopants in the channel. However, the twin defects from the problematic Si{111} recrystallization is well-known to cause excessive leakage current to the FinFET. This drawback can offset the benefits of the high dose rate I/I mentioned above. This work produced the first attempt at simulating the electrical impact of twin defects on advanced-node (10 nm) FinFET device performance. It was found that the high dose-rate I/I causes more twin defects in the silicon fin, and the physical locations of these defects were close to the channel. The defects undesirably induced trap-assisted band-to-band tunneling near the drain, which increased the leakage current. This issue could be mitigated by using asymmetrical gate overlap/underlap design or thicker spacer for SDE I/I so that the twin defects are not located in the depletion region near the drain.

Spin transport and spin accumulation signals in Si studied in tunnel junctions with a Fe/Mg ferromagnetic multilayer and an amorphous SiOxNy tunnel barrier

NASA Astrophysics Data System (ADS)

Nakane, Ryosho; Hada, Takato; Sato, Shoichi; Tanaka, Masaaki

2018-04-01

We studied the spin accumulation signals in phosphorus-doped n+-Si (8 × 1019 cm-3) by measuring the spin transport in three-terminal vertical devices with Fe(3 nm)/Mg(0 and 1 nm)/SiOxNy(1 nm)/n+-Si(001) tunnel junctions, where the amorphous SiOxNy layer was formed by oxnitridation of the Si substrate with radio frequency plasma. Obvious spin accumulation signals were observed at 4-300 K in the spin extraction geometry when the thickness of the Mg insertion layer was 1 nm. We found that by inserting a thin (1 nm) Mg layer, intermixing of Fe and SiOxNy is suppressed, leading to the appearance of the spin accumulation signals, and this result is consistent with the dead layer model recently proposed by our group [S. Sato et al., Appl. Phys. Lett. 107, 032407 (2015)]. We obtained relatively high spin polarization (PS) of electrons tunneling through the junction and long spin lifetime (τS): PS = 16% and τS = 5.6 ns at 4 K and PS = 7.5% and τS = 2.7 ns at 300 K. Tunnel junctions with an amorphous SiOxNy tunnel barrier are very promising for Si-based spintronic devices, since they can be formed by the method compatible with the silicon complementary metal-oxide-semiconductor technology.

Dimensional isotropy of 6H and 3C SiC under neutron irradiation

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

Snead, Lance L.; Katoh, Yutai; Koyanagi, Takaaki

2016-01-16

This investigation experimentally determines the as-irradiated crystal axes dimensional change of the common polytypes of SiC considered for nuclear application. Single crystal α-SiC (6H), β-SiC (3C), CVD β-SiC, and single crystal Si have been neutron irradiated near 60 °C from 2 × 10 23 to 2 × 10 26 n/m 2 (E > 0.1 MeV), or about 0.02–20 dpa, in order to study the effect of irradiation on bulk swelling and strain along independent crystalline axes. Single crystal, powder diffractometry and density measurement have been carried out. For all neutron doses where the samples remained crystalline all SiC materials demonstratedmore » equivalent swelling behavior. Moreover the 6H–SiC expanded isotropically. The magnitude of the swelling followed a ~0.77 power law against dose consistent with a microstructure evolution driven by single interstitial (carbon) mobility. Extraordinarily large ~7.8% volume expansion in SiC was observed prior to amorphization. Above ~0.9 × 10 25 n/m 2 (E > 0.1 MeV) all SiC materials became amorphous with an identical swelling: a 11.7% volume expansion, lowering the density to 2.84 g/cm 3. As a result, the as-amorphized density was the same at the 2 × 10 25 and 2 × 10 26 n/m 2 (E > 0.1 MeV) dose levels.« less

Power Generation Potential and Cost of a Roof Top Solar PV System in Kathmandu, Nepal

NASA Astrophysics Data System (ADS)

Sanjel, N.; Zhand, A.

2017-12-01

The paper presents a comparative study of the 3 most used solar PV module technologies in Nepal, which are Si-mono-crystalline, Si-poly-crystalline and Si-amorphous. The aim of the paper is to present and discuss the recorded Global Solar Radiation, received in the Kathmandu valley by three different, Si-mono-crystalline, Si-poly-crystalline and Si-amorphous calibrated solar cell pyranometers and to propose the best-suited solar PV module technology for roof top solar PV systems inside the Kathmandu valley. Data recorded over the course of seven months, thus covering most of the seasonal meteorological conditions determining Kathmandu valley's global solar radiation reception are presented. The results indicate that the Si-amorphous pyranometer captured 1.56% more global solar radiation than the Si-mono-crystalline and 18.4% more than Si-poly-crystalline pyranometer over the course of seven months. Among the three pyranometer technologies the maximum and minimum cell temperature was measured by the Si-mono-crystalline pyranometer. Following the technical data and discussion, an economical analysis, using the versatile software tool PVSYST V5.01is used to calculate the life cycle costs of a 1kW roof top solar PV RAPS system, with battery storage, and a 1kW roof top solar PV grid connected system with no energy storage facility, through simulations, using average recorded global solar radiation data for the KTM valley and investigated market values for each solar PV module and peripheral equipment costs.

High-Temperature Corrosion Behavior of SiBCN Fibers for Aerospace Applications.

PubMed

Ji, Xiaoyu; Wang, Shanshan; Shao, Changwei; Wang, Hao

2018-06-13

Amorphous SiBCN fibers possessing superior stability against oxidation have become a desirable candidate for high-temperature aerospace applications. Currently, investigations on the high-temperature corrosion behavior of these fibers for the application in high-heat engines are insufficient. Here, our polymer-derived SiBCN fibers were corroded at 1400 °C in air and simulated combustion environments. The fibers' structural evolution after corrosion in two different conditions and the potential mechanisms are investigated. It shows that the as-prepared SiBCN fibers mainly consist of amorphous networks of SiN 3 C, SiN 4 , B-N hexatomic rings, free carbon clusters, and BN 2 C units. High-resolution transmission electron microscopy cross-section observations combined with energy-dispersive spectrometry/electron energy-loss spectroscopy analysis exhibit a trilayer structure with no detectable cracks for fibers after corrosion, including the outermost SiO 2 layer, the h-BN grain-contained interlayer, and the uncorroded fiber core. A high percentage of water vapor contained in the simulated combustion environment triggers the formation of abundant α-cristobalite nanoparticles dispersing in the amorphous SiO 2 phase, which are absent in fibers corroded in air. The formation of h-BN grains in the interlayer could be ascribed to the sacrificial effects of free carbon clusters, Si-C, and Si-N units reacting with oxygen diffusing inward, which protects h-BN grains formed by networks of B-N hexatomic rings in original SiBCN fibers. These results improve our understanding of the corrosion process of SiBCN fibers in a high-temperature oxygen- and water-rich atmosphere.

An investigation of hydrogenized amorphous Si structures with Doppler broadening positron annihilation techniques

NASA Astrophysics Data System (ADS)

Petkov, M. P.; Marek, T.; Asoka-Kumar, P.; Lynn, K. G.; Crandall, R. S.; Mahan, A. H.

1998-07-01

In this letter, we examine the feasibility of applying positron annihilation spectroscopy to the study of hydrogenized amorphous silicon (a-Si:H)-based structures produced by chemical vapor deposition techniques. The positron probe, sensitive to open volume formations, is used to characterize neutral and negatively charged silicon dangling bonds, typical for undoped and n-doped a-Si:H, respectively. Using depth profiling along the growth direction a difference was observed in the electronic environment of these defects, which enables their identification in a p-i-n device.

Acoustic emission study of the plastic deformation of quenched and partitioned 35CrMnSiA steel

NASA Astrophysics Data System (ADS)

Li, Yang; Xiao, Gui-yong; Chen, Lu-bin; Lu, Yu-peng

2014-12-01

Acoustic emission (AE) monitored tensile tests were performed on 35CrMnSiA steel subjected to different heat treatments. The results showed that quenching and partitioning (Q-P) heat treatments enhanced the combined mechanical properties of high strength and high ductility for commercial 35CrMnSiA steel, as compared with traditional heat treatments such as quenching and tempering (Q-T) and austempering (AT). AE signals with high amplitude and high energy were produced during the tensile deformation of 35CrMnSiA steel with retained austenite (RA) in the microstructure (obtained via Q-P and AT heat treatments) due to an austenite-to-martensite phase transformation. Moreover, additional AE signals would not appear again and the mechanical properties would degenerate to a lower level once RA degenerated by tempering for the Q-P treated steel.

Experimental Study on Dynamic Mechanical Properties of 30CrMnSiNi2A Steel.

NASA Astrophysics Data System (ADS)

Huang, Fenglei; Yao, Wei; Wu, Haijun; Zhang, Liansheng

2009-06-01

Under dynamic conditions, the strain-rate dependence of material response and high levels of hydrostatic pressure cause the material behavior to be significantly different from what is observed under quasi-static condition. The curves of stress and strain of 30CrMnSiNi2A steel in different strain rates are obtained with SHPB experiments. Metallographic analyses show that 30CrMnSiNi2A steel is sensitive to strain rate, and dynamic compression leads to shear failure with the angle 45^o as the small carbide which precipitates around grain boundary changes the properties of 30CrMnSiNi2A steel. From the SHPB experiments and quasi-static results, the incomplete Johnson-Cook model has been obtained: σ=[1587+382.5(ɛ^p)^0.245][1+0.017ɛ^*], which can offer parameters for theory application and numerical simulation.

Synthesis of Li2MnSiO4-graphene composite and its electrochemical performances as a cathode material for lithium ion batteries.

PubMed

Kim, Jeonghyun; Song, Taeseup; Park, Hyunjung; Yuh, Junhan; Paik, Ungyu

2014-10-01

The Li2MnSiO4 is a promising candidate as a cathode for lithium ion batteries due to its large theoretical capacity of 330 mA h g(-1) and high thermal stability. However, the problems related to low electronic conductivity and large irreversible capacity at the first cycle limits its practical use as a Li-ion cathode material. We have developed a carbon coated Li2MnSiO4-graphene composite electrode to overcome these problems. Our designed electrode exhibits high reversible capacity of 301 mA h g(-1), with a high initial coulombic efficiency, and a discharge capacity at current rate of 0.5 C, that is double value of carbon coated Li2MnSiO4-carbon black composite electrode. These significant improvements are attributed to fast electron transport along the graphene sheet.

Spontaneous crystalline-to-amorphous phase transformation of organic or medicinal compounds in the presence of porous media, part 2: amorphization capacity and mechanisms of interaction.

PubMed

Qian, Ken K; Suib, Steven L; Bogner, Robin H

2011-11-01

Amorphization of crystalline compounds using mesoporous media is a promising technique to improve the solubility and dissolution rate of poorly soluble compounds. The objective of this paper is to determine the capacity of amorphization and understand the mechanisms of phase transformation. Commercial grades of mesoporous silicon dioxide (SiO(2)) samples (5- to 30-nm mean pore diameters) with either constant surface area or constant pore volume were used. The amorphization capacity of naphthalene was not proportional to either the surface area or the pore volume measured using adsorption chambers. Instead, the amorphization capacity correlated with surface curvature, that is, the smaller the pore diameter and the higher the surface curvature, the greater the amorphization capacity. The change in surface chemistry due to a highly curved surface may be responsible for the enhanced amorphization capacity as well. The amorphization of crystalline compounds was facilitated through capillary condensation, with the decrease in pore volume as the direct experimental evidence. The amorphization capacity was also enhanced by the dipole-dipole or dipole-induced dipole interaction, promoted by the hydroxyl groups on the surface of SiO(2). The enthalpy of vapor-solid condensation of crystalline compounds was a useful indicator to predict the rank order of amorphization capacity. Copyright © 2011 Wiley-Liss, Inc.

Antiferromagnetism in pressure-amorphized Fe2SiO4

USGS Publications Warehouse

Kruger, M.B.; Jeanloz, R.; Pasternak, M.P.; Taylor, R.D.; Snyder, B.S.; Stacy, A.M.; Bohlen, S.R.

1992-01-01

Amorphous Fe2SiO4 synthesized at elevated pressures exhibits a Ne??el transition at a temperature identical to that observed in the crystalline form, TN = 65 (??2) kelvin at zero pressure. This behavior contrasts sharply with observations on other disordered systems, such as spin glasses, which characteristically exhibit strong "frustration" of the spins and consequent marked suppression of the Ne??el transition.

Near surface silicide formation after off-normal Fe-implantation of Si(001) surfaces

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

Khanbabaee, B., E-mail: khanbabaee@physik.uni-siegen.de; Pietsch, U.; Lützenkirchen-Hecht, D.

We report on formation of non-crystalline Fe-silicides of various stoichiometries below the amorphized surface of crystalline Si(001) after irradiation with 5 keV Fe{sup +} ions under off-normal incidence. We examined samples prepared with ion fluences of 0.1 × 10{sup 17} and 5 × 10{sup 17} ions cm{sup −2} exhibiting a flat and patterned surface morphology, respectively. Whereas the iron silicides are found across the whole surface of the flat sample, they are concentrated at the top of ridges at the rippled surface. A depth resolved analysis of the chemical states of Si and Fe atoms in the near surface region was performed by combining X-raymore » photoelectron spectroscopy and X-ray absorption spectroscopy (XAS) using synchrotron radiation. The chemical shift and the line shape of the Si 2p core levels and valence bands were measured and associated with the formation of silicide bonds of different stoichiometric composition changing from an Fe-rich silicides (Fe{sub 3}Si) close to the surface into a Si-rich silicide (FeSi{sub 2}) towards the inner interface to the Si(001) substrate. This finding is supported by XAS analysis at the Fe K-edge which shows changes of the chemical environment and the near order atomic coordination of the Fe atoms in the region close to surface. Because a similar Fe depth profile has been found for samples co-sputtered with Fe during Kr{sup +} ion irradiation, our results suggest the importance of chemically bonded Fe in the surface region for the process of ripple formation.« less

The Effect of SiC Polytypes on the Heat Distribution Efficiency of a Phase Change Memory.

NASA Astrophysics Data System (ADS)

Aziz, M. S.; Mohammed, Z.; Alip, R. I.

2018-03-01

The amorphous to crystalline transition of germanium-antimony-tellurium (GST) using three types of silicon carbide’s structure as a heating element was investigated. Simulation was done using COMSOL Multiphysic 5.0 software with separate heater structure. Silicon carbide (SiC) has three types of structure; 3C-SiC, 4H-SiC and 6H-SiC. These structures have a different thermal conductivity. The temperature of GST and phase transition of GST can be obtained from the simulation. The temperature of GST when using 3C-SiC, 4H-SiC and 6H-SiC are 467K, 466K and 460K, respectively. The phase transition of GST from amorphous to crystalline state for three type of SiC’s structure can be determined in this simulation. Based on the result, the thermal conductivity of SiC can affecting the temperature of GST and changed of phase change memory (PCM).

Nanotubes within transition metal silicate hollow spheres: Facile preparation and superior lithium storage performances

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

Zhang, Fan; An, Yongling; Zhai, Wei

2015-10-15

Highlights: • The hollow Co{sub 2}SiO{sub 4}, MnSiO{sub 3} and CuSiO{sub 3} were successfully prepared by a facile hydrothermal method using SiO{sub 2} nanosphere. • The hollow Co{sub 2}SiO{sub 4}, MnSiO{sub 3} and CuSiO{sub 3} were tested as anode materials for lithium batteries. • The hollow Co{sub 2}SiO{sub 4}, MnSiO{sub 3} and CuSiO{sub 3} delivered superior electrochemical performance. • The lithium storage mechanism is probe via cyclic voltammetry and XPS. - Abstract: A series of transition metal silicate hollow spheres, including cobalt silicate (Co{sub 2}SiO{sub 4}), manganese silicate (MnSiO{sub 3}) and copper silicate (CuSiO{sub 3}.2H{sub 2}O, CuSiO{sub 3} as abbreviationmore » in the text) were prepared via a simple and economic hydrothermal method by using silica spheres as chemical template. Time-dependent experiments confirmed that the resultants formed a novel type of hierarchical structure, hollow spheres assembled by numerous one-dimensional (1D) nanotubes building blocks. For the first time, the transition metal silicate hollow spheres were characterized as novel anode materials of Li-ion battery, which presented superior lithium storage capacities, cycle performance and rate performance. The 1D nanotubes assembly and hollow interior endow this kind of material facilitate fast lithium ion and electron transport and accommodate the big volume change during the conversion reactions. Our study shows that low-cost transition metal silicate with rationally designed nanostructures can be promising anode materials for high capacity lithium-ion battery.« less

Amorphous silicon ionizing particle detectors

DOEpatents

Street, Robert A.; Mendez, Victor P.; Kaplan, Selig N.

1988-01-01

Amorphous silicon ionizing particle detectors having a hydrogenated amorphous silicon (a--Si:H) thin film deposited via plasma assisted chemical vapor deposition techniques are utilized to detect the presence, position and counting of high energy ionizing particles, such as electrons, x-rays, alpha particles, beta particles and gamma radiation.

Annealing properties of open volumes in HfSiOx and HfAlOx gate dielectrics studied using monoenergetic positron beams

NASA Astrophysics Data System (ADS)

Uedono, A.; Ikeuchi, K.; Yamabe, K.; Ohdaira, T.; Muramatsu, M.; Suzuki, R.; Hamid, A. S.; Chikyow, T.; Torii, K.; Yamada, K.

2005-07-01

Thin Hf0.6Si0.4Ox and Hf0.3Al0.7Ox films fabricated by metal-organic chemical-vapor deposition and atomic-layer-deposition techniques were characterized using monoenergetic positron beams. Measurements of the Doppler broadening spectra of annihilation radiation and the lifetime spectra of positions indicated that positrons annihilated from the trapped state by open volumes that exist intrinsically in amorphous structures of the films. For HfSiOx, the mean size of the open volumes and their size distribution decreased with increasing postdeposition annealing (PDA) temperature. For HfAlOx, although the overall behavior of the open volumes in response to annealing was similar to that for HfSiOx, PDA caused a separation of the mean size of the open volumes. When this separation occurred, the value of the line-shape parameter S increased, suggesting an oxygen deficiency in the amorphous matrix. This fragmentation of the amorphous matrix can be suppressed by decreasing the annealing time.

Influences of ultra-thin Ti seed layers on the dewetting phenomenon of Au films deposited on Si oxide substrates

NASA Astrophysics Data System (ADS)

Kamiko, Masao; Kim, So-Mang; Jeong, Young-Seok; Ha, Jae-Ho; Koo, Sang-Mo; Ha, Jae-Geun

2018-05-01

The influences of a Ti seed layer (1 nm) on the dewetting phenomenon of Au films (5 nm) grown onto amorphous SiO2 substrates have been studied and compared. Atomic force microscopy results indicated that the introduction of Ti between the substrate and Au promoted the dewetting phenomenon. X-ray diffraction measurements suggested that the initial deposition of Ti promoted crystallinity of Au. A series of Auger electron spectroscopy and X-ray photoelectron spectroscopy results revealed that Ti transformed to a Ti oxide layer by reduction of the amorphous SiO2 substrate surface, and that the Ti seed layer remained on the substrate, without going through the dewetting process during annealing. We concluded that the enhancement of Au dewetting and the improvement in crystallinity of Au by the insertion of Ti could be attributed to the fact that Au location was changed from the surface of the amorphous SiO2 substrate to that of the Ti oxide layer.

Amorphization and reduction of thermal conductivity in porous silicon by irradiation with swift heavy ions

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

Newby, Pascal J.; Institut Interdisciplinaire d'Innovation Technologique; Canut, Bruno

2013-07-07

In this article, we demonstrate that the thermal conductivity of nanostructured porous silicon is reduced by amorphization and also that this amorphous phase in porous silicon can be created by swift (high-energy) heavy ion irradiation. Porous silicon samples with 41%-75% porosity are irradiated with 110 MeV uranium ions at six different fluences. Structural characterisation by micro-Raman spectroscopy and SEM imaging show that swift heavy ion irradiation causes the creation of an amorphous phase in porous Si but without suppressing its porous structure. We demonstrate that the amorphization of porous silicon is caused by electronic-regime interactions, which is the first timemore » such an effect is obtained in crystalline silicon with single-ion species. Furthermore, the impact on the thermal conductivity of porous silicon is studied by micro-Raman spectroscopy and scanning thermal microscopy. The creation of an amorphous phase in porous silicon leads to a reduction of its thermal conductivity, up to a factor of 3 compared to the non-irradiated sample. Therefore, this technique could be used to enhance the thermal insulation properties of porous Si. Finally, we show that this treatment can be combined with pre-oxidation at 300 Degree-Sign C, which is known to lower the thermal conductivity of porous Si, in order to obtain an even greater reduction.« less

Manganese molybdate nanoflakes on silicon microchannel plates as novel nano energetic material

PubMed Central

Zhang, Chi; Wu, Dajun; Shi, Liming; Zhu, Yiping; Xiong, Dayuan; Xu, Shaohui; Huang, Rong; Qi, Ruijuan; Zhang, Wenchao; Chu, Paul K.

2017-01-01

Nano energetic materials have attracted great attention recently owing to their potential applications for both civilian and military purposes. By introducing silicon microchannel plates (Si-MCPs) three-dimensional (3D)-ordered structures, monocrystalline MnMoO4 with a size of tens of micrometres and polycrystalline MnMoO4 nanoflakes are produced on the surface and sidewall of nickel-coated Si-MCP, respectively. The MnMoO4 crystals ripen controllably forming polycrystalline nanoflakes with lattice fringes of 0.542 nm corresponding to the (1¯11) plane on the sidewall. And these MnMoO4 nanoflakes show apparent thermite performance which is rarely reported and represents MnMoO4 becoming a new category of energetic materials after nanocrystallization. Additionally, the nanocrystallization mechanism is interpreted by ionic diffusion caused by 3D structure. The results indicate that the Si-MCP is a promising substrate for nanocrystallization of energetic materials such as MnMoO4. PMID:29308255

Manganese molybdate nanoflakes on silicon microchannel plates as novel nano energetic material.

PubMed

Zhang, Chi; Wu, Dajun; Shi, Liming; Zhu, Yiping; Xiong, Dayuan; Xu, Shaohui; Huang, Rong; Qi, Ruijuan; Zhang, Wenchao; Wang, Lianwei; Chu, Paul K

2017-12-01

Nano energetic materials have attracted great attention recently owing to their potential applications for both civilian and military purposes. By introducing silicon microchannel plates (Si-MCPs) three-dimensional (3D)-ordered structures, monocrystalline MnMoO 4 with a size of tens of micrometres and polycrystalline MnMoO 4 nanoflakes are produced on the surface and sidewall of nickel-coated Si-MCP, respectively. The MnMoO 4 crystals ripen controllably forming polycrystalline nanoflakes with lattice fringes of 0.542 nm corresponding to the [Formula: see text] plane on the sidewall. And these MnMoO 4 nanoflakes show apparent thermite performance which is rarely reported and represents MnMoO 4 becoming a new category of energetic materials after nanocrystallization. Additionally, the nanocrystallization mechanism is interpreted by ionic diffusion caused by 3D structure. The results indicate that the Si-MCP is a promising substrate for nanocrystallization of energetic materials such as MnMoO 4 .

FTIR study of silicon carbide amorphization by heavy ion irradiations

NASA Astrophysics Data System (ADS)

Costantini, Jean-Marc; Miro, Sandrine; Pluchery, Olivier

2017-03-01

We have measured at room temperature (RT) the Fourier-transform infra-red (FTIR) absorption spectra of ion-irradiated thin epitaxial films of cubic silicon carbide (3C-SiC) with 1.1 µm thickness on a 500 µm thick (1 0 0) silicon wafer substrate. Irradiations were carried out at RT with 2.3 MeV 28Si+ ions and 3.0 MeV 84Kr+ ions for various fluences in order to induce amorphization of the SiC film. Ion projected ranges were adjusted to be slightly larger than the film thickness so that the whole SiC layers were homogeneously damaged. FTIR spectra of virgin and irradiated samples were recorded for various incidence angles from normal incidence to Brewster’s angle. We show that the amorphization process in ion-irradiated 3C-SiC films can be monitored non-destructively by FTIR absorption spectroscopy without any major interference of the substrate. The compared evolutions of TO and LO peaks upon ion irradiation yield valuable information on the damage process. Complementary test experiments were also performed on virgin silicon nitride (Si3N4) self-standing films for similar conditions. Asymmetrical shapes were found for TO peaks of SiC, whereas Gaussian profiles are found for LO peaks. Skewed Gaussian profiles, with a standard deviation depending on wave number, were used to fit asymmetrical peaks for both materials. A new methodology for following the amorphization process is proposed on the basis of the evolution of fitted IR absorption peak parameters with ion fluence. Results are discussed with respect to Rutherford backscattering spectrometry channeling and Raman spectroscopy analysis.

Heat capacities and thermodynamic properties of braunite (Mn7 SiO12) and rhodonite (MnSiO3)

USGS Publications Warehouse

Robie, R.A.; Huebner, J.S.; Hemingway, B.S.

1995-01-01

The heat capacities, C0P, of synthetic rhodonite and braunite have been measured by adiabatic calorimetry from 6 to ~350 K. The heat capacity of braunite was also measured to ~900 K by differential scanning calorimetry. Brunite exhibits a ??-peak in C0P in the temperature region 93.4-94.2 K. Rhodonite did not show the expected peak in C0P characteristic of the co-operative ordering of the Mn2+ spins at temperatures above 6 K. A revised petrogenetic grid for the system Mn-Si-O-C at 2000 bars is presented and is consistent with both thermochemical values and occurrence of natural assemblages. -from Authors